Investigating the effect of screen-printed structured graphite electrodes with low tortuosity for high-capacity and fast-charging lithium-ion batteries

Investigating the effect of screen-printed structured graphite electrodes with low tortuosity for high-capacity and fast-charging lithium-ion batteries | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Investigating the effect of screen-printed structured graphite electrodes with low tortuosity for high-capacity and fast-charging lithium-ion batteries Himanaga Rama Krishna Manoj Emani, Dinesh Maddipatla, Tony Hanson, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6348014/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Aug, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract A flexible screen-printed graphite electrode was fabricated as an anode for developing fast-charging lithium-ion batteries with low tortuosity. A homogenous anode ink was prepared by mixing graphite as the active material, carbon black (C45) as the conductive additive, and polyvinylidene fluoride (PVDF) as the binder in N-Methyl-2-pyrrolidone (NMP) solvent. The ink was deposited on a flexible copper foil via a stainless-steel screen consisting of an array of pores, that act as secondary pore networks (SPNs), using the screen-printing process. Lithium-ion battery half-cells were assembled using the printed graphite anode, lithium metal foil as the counter electrode, and 1.2M lithium hexafluorophosphate (LiPF 6 ) in ethyl carbonate: ethyl methyl carbonate (EC: EMC = 3:7) as the electrolyte. The effect of SPNs on the cell performance was investigated by performing formation, rate and cycling tests on the assembled cells, at different C-rates. It was observed that the cells consisting of SPNs with a pore size of 100 µm and edge-to-edge distance of 100 µm between the pores exhibited significantly higher specific capacities of 168 and 129 mAh/g when compared to reference cells without SPNs, which had capacities of 120 and 85 mAh/g, at high C-rates of 4C and 6C, respectively. The cells with SPNs also demonstrated excellent cycling performance with ~ 95% capacity retention after 100 cycles at 2C. Physical sciences/Chemistry/Electrochemistry/Batteries Physical sciences/Energy science and technology/Energy storage/Batteries Structured electrode Secondary pore network Fast charging lithium-ion battery Flexible electrode Screen-printing High capacity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction With the growth in demand for electric vehicles (EVs), fast charging ability has become a key parameter for today’s lithium-ion battery (LIB) technology [1,2]. LIBs consist of porous electrodes, a separator, and a liquid electrolyte. Typically, the electrodes (both anode and cathode) have been developed by mixing an active material, conductive additive, polymer binder, and solvent thoroughly until a homogenous slurry is obtained. Then, these slurries are coated onto current collectors (copper for anode, aluminum for cathode) and vacuum dried to evaporate the solvent [3,4]. Following this, the electrodes are calendered to a desired porosity to enhance particle contact and volumetric energy density of the cell before subjecting them to electrochemical testing [5]. During charging, lithium ions (Li + ) migrate from the cathode to the anode through the separator. Similarly, during discharge, the process is reversed with current being drawn from the terminals of the battery [6]. Graphite, lithium titanium oxide (LTO), and silicon (Si) are among the widely used anode materials. Similarly, lithium nickel manganese cobalt oxides (NMC), lithium iron phosphate (LFP), and lithium cobalt oxide (LCO) are widely used as cathode materials to achieve LIBs with superior electrochemical performance [7]. Even though there have been several research efforts and continuous advancements in the battery field, the accelerated degradation of capacity and power capability of batteries remains a major concern at high current rates, or fast charging rates such as 1C or higher [8]. Lithium plating, dendrite formation, and mechanical failure remain the major reasons for degradation at high current rates due to current-dependent overpotential [9]. Lithium plating/dendrite formation is a phenomenon that often occurs on the anode surface of LIBs, leading to the irreversible loss of lithium, resulting in electrolyte decomposition and rapid capacity fading, and in turn mechanical failure of the LIBs [9]. The root cause for the lithium plating and dendrite formation is attributed to the high tortuosity of the electrodes, resulting in twisted pathways that are narrow and distorted, thus making it difficult for Li + transportation and, in turn, affecting the fast-charging ability of LIBs during charge/discharge cycles. This also results in increased internal ionic resistance of the LIB [10]. Therefore, reducing the tortuosity of the electrodes can enhance Li + flow, along with electrolyte mass transfer, resulting in enhanced electrochemical performance of the LIB. In other words, low tortuosity in LIBs facilitates effective ion transportation within electrode structure, which in turn leads to enhanced rate capability, lower ionic resistance, more uniform ion distribution, reduced stress on electrodes, improved columbic efficiency, ensures better utilization of active material, and promotes safer fast charging cycling stability [11]. Several researchers have explored various strategies to reduce tortuosity in LIBs, such as electrode thickness optimizing electrode thickness [12], controlling particle size and shape [13], using nano materials [14], and aligning electrodes along the ion flow direction [15]. However, these methods often require precise control over material uniformity, involve complex fabrication process (such as electrospinning or advanced templating) [16] and are material specific limiting their compatibility with all electrode materials. Moreover, reducing electrode thickness can lead to low energy, density which is not ideal for batteries performance. Fabricating structured electrodes is an efficient way to overcome the limitations associated with LIBs in terms of tortuosity. Electrochemical simulations have shown that introducing secondary pore networks (SPNs) in the electrodes enhances the transportation of electrolyte and Li + , which will have a significant effect in improving the electrochemical properties of the LIB [17–19]. The implementation of structured electrodes can effectively mitigate the problem of lithium plating on the surface of the anode electrode [20–22]. Despite these advantages, LIBs with structured electrodes are not yet commercially available to the best of our knowledge. This is due to the limitations associated with the large-scale fabrication of structured electrodes. Several advanced manufacturing processes, such as laser patterning, freeze casting, aerosol jet printing, inkjet printing, gravure printing, and screen printing, can be implemented to fabricate structured electrodes [23–29]. Processes such as inkjet and aerosol jet printing result in electrodes with very low mass loadings, typically in the range of 0.1-1 mg/cm 2 , due to the low viscosity of the inks [24,25]. Similarly, in the freeze-casting process, SPNs can be introduced into the electrode using the cooling stage while drying at -50°C during the curing process. However, this process takes more than 48 hours, and the uniformity of the structured electrode is not reliable [26]. In other words, the consistency in obtaining the same pore sizes and distance between the pores in SPNs is challenging. In contrast, screen-printing emerges as a promising approach for the precisely fabricating structured electrodes with high mass loadings, which can be implemented in high-volume roll-to-roll (R2R) printing. Screen printing offers design flexibility and a simple, swift, and repeatable method for manufacturing electrode architectures with variable mass loadings [30]. In this work, a homogenous anode ink was prepared by mixing graphite, carbon black, and polyvinylidene fluoride (PVDF) in N-Methyl-2-pyrrolidone (NMP) solvent. Screen printing was implemented for depositing the ink on a flexible copper current collector. Novel SPN-based microstructures with different pore diameters and edge-to-edge (ETE) distances were introduced during screen printing into the graphite electrode. Later, half-cell LIBs were assembled using the screen-printed graphite electrodes with and without SPNs. Electrochemical tests were conducted by performing formation, rate, and cycling tests on the assembled coin cells. Battery data were analyzed to study the significance between electrodes with and without SPNs (structured and reference electrodes). 2. Experimental 2.1 Materials and ink preparation The anode ink was formulated using graphite as the active material (5 µm particle size), carbon black (C-45, 100–200 nm, MSE Supplies) as the conductive additive, PVDF (5130, Kureha) as the binder, and NMP as the solvent (Sigma Aldrich ® ). All the materials were used as received without any further modification. Figure S1 (a) (please see the supplementary information) represents the schematic of ink preparation. Initially, the graphite and carbon black were added to the PVDF binder (8% in NMP) in wt.% of 90:3:7, respectively. Then, the mixture was dispersed in NMP, and the resulting electrode slurry was transferred to a Thinky AR-100 planetary centrifugal mixer. Following this, the slurry was mixed at 2000 rpm until a homogenous and uniform ink slurry was obtained for screen printing. The prepared ink had 60% solid loading without any residuals, indicating homogeneity and suitability for printing. 2.2 Ink characterization Certain properties of an ink affect the print quality, such as surface tension, and contact angle with respect to the substrate employed. These properties provide a better understanding of the wetting properties of the ink and can be measured using an FTA200 goniometer. Figures S1 (b) and (c) show the surface tension and contact angle of the graphite ink, respectively (please see the supplementary information) . The surface tension of the graphite ink was measured to be ~ 6.2 dynes/cm using the pendant drop method (Fig. S1 (b)) [30]. The surface energy of copper foil (substrate) was also measured with de-ionized (DI) water and hexadecane as 76 dynes/cm based on the Owens-Wendt method. The surface tension value obtained was less than the surface energy of the substrate indicating that the ink was printable onto the substrate. Similarly, a contact angle of 62.4° was measured for the ink with respect to a 9 µm thick copper substrate (MSE Supplies) using the sessile drop method using an FTA200 goniometer [31]. Contact angles < 90° indicate good wetting characteristics of the ink on the copper substrate. Following this, the viscosity of the ink was measured with an Anton Paar ® MCR-302 rheometer using parallel-plate geometry. The ink slurry was placed between parallel plates at room temperature and viscosity was recorded by varying the shear rate from 1 s -1 up to 500 s -1 . Figure S2(a) shows the shear thinning behavior of the graphite ink with varied shear rates (please see the supplementary information) . Since the prepared ink had high solid loading, the initial viscosity of 230 Pa.s was recorded at a shear rate of 1 s -1 and it reduced to 0.7 Pa.s at 500 s -1 indicating shear-thinning behavior, which helps in seamless ink transfer onto the substrate through the stainless-steel screen mesh. Figure S2(b) (please see the supplementary information) represents the anode ink’s thixotropic behavior where the viscosity of the ink was reduced from ~ 231 Pa.s to ~ 0.7 Pa.s and recovered to ~ 226 Pa.s, as the shear rate was varied from 1 s -1 to 500 s -1 and back to 1 s -1 , respectively. This demonstrates that the ink is stable and suitable for continuous deposition on the copper substrate. 2.3 Fabrication Screen printing was used to fabricate the graphite electrodes using an HMI MSP-485 semi-automatic screen-printer. Stainless-steel screens consisting of an array of pores with varying diameters of 1000 µm, 500 µm, and 100 µm and an ETE distance of 2000 µm between the pores were fabricated at Microscreen ® . The screen size was 12 x 12 inches with a mesh count, wire diameter, and mesh angle of 325, 20 µm, and 22.5 degrees, respectively. It was made of MS-22 emulsion (Grafic HSS from Saati Chemicals) which is NMP resistant with a thickness of 15 µm. Figure S3 (please see the supplementary information) illustrates the fabricated screens and screen designs showing their respective SPN pore diameter (in red), and the ETE distance between the SPNs (in pink). The scale for the artwork was set to 200 µm for all the images. The blue color area in the images represents the emulsion (MS-22) which prevents the ink deposition through the screen onto the substrate resulting in the creation of a void in its place on the substrate. Based on the initial battery data (provided in the results section), SPNs with a small pore size of 100 µm exhibited better battery performance. For further investigation of SPNs pore diameter of 100 µm was kept constant and the ETE distance between the pores was gradually reduced from 2000 µm to 400 µm, 300 µm, 200 µm, 150 µm, and 100 µm. Figure 1 (a) shows the schematic representation of the electrode fabrication using the screen-printing process. To fabricate the anode, the copper substrate with ~ 9 µm thickness was placed on the screen printer platen and was cleaned with isopropyl alcohol (IPA). This helps in removing any dust particles present on the copper substrate. The platen consists of vacuum pores which enable the copper substrate to be held firmly to the platen. Graphite ink was uniformly spread on the screen and a silicone squeegee was used for printing the ink onto copper substrate. After screen-printing the graphite ink onto the copper substrate, the printed electrode was cured in a VWR ® oven at 45°C for 4 hours to partially evaporate the NMP solvent. Then, the electrode was transferred to a vacuum oven from Across International ® and was cured at 80°C for 10 hours to ensure complete evaporation of NMP. Figures S4 and S5 (please see the supplementary information) show the fabricated screen-printed graphite electrodes along with their optical microscopic images. Uniform printing was observed for all the samples. The electrode representations along with their respective mass loadings are summarized in Table 1. Electrode A (solid block without SPNs) was used as a reference electrode for comparing the electrochemical performance of the fabricated anodes. Electrodes B, C, and D have SPNs with diameters of 1000 µm, 500 µm, and 100 µm, respectively. The ETE distance was 2000 µm (2 mm) for these electrodes. For electrodes E to I, the size of SPNs was kept constant at 100 µm and the ETE distance between the pores was gradually reduced to 400 µm (electrode E), 300 µm (electrode F), 200 µm, (electrode G), 150 µm (electrode H), 100 µm (electrode I). Figure 1 (b) represents the schematic for lithium-ion flow in conventional electrodes without SPNs. Due to the sluggish kinetics of Li + , it takes more time for the Li + to reach the current collector. This results in an increased tortuosity of the LIB, which can lead to capacity fading at fast charging rates. Novel SPNs introduced during fabrication help in reducing the electrode’s tortuosity as shown in Fig. 1 (c). In addition, these SPNs increase the transportation of liquid electrolyte through the electrode, which enhances the Li + accessibility via a shorter route (Fig. 1 (d)). The enhanced Li + accessibility, along with superior contact between the active material and the liquid electrolyte, is an essential condition for achieving fast-charging LIBs with higher capacities. Figure 1 (e) shows the scanning electron microscopy (SEM) cross-section image of pore in the electrode using a Jeol ® JSM-IT200. Figure 1 (f) represents the thickness of the electrode measured around 54.4 ± 4.0 µm. The different pore diameters and ETE distances will result in different mass loading for each sample since the number of pores in a unit area varies with respect to pore diameter and ETE distance. Therefore, the mass loadings of all the electrodes were adjusted in the range of 6–7 mg/cm 2 to have a fair comparison between the electrodes with and without SPNs. All the electrodes were calendered between cylindrical rolls and the porosity (ε) was controlled at approximately 35%. Porosity was calculated using Equation S1 as shown in supplementary data. The calendering process helps in improving the particle contact and in turn, the energy density of the battery. 2.4 Mechanical characterization Mechanical characterization was performed on the fabricated electrodes by subjecting them to cyclical bend tests using a Mark-10 ESM 301 motorized test stand. Electrodes A and I were chosen for the bend test considering no SPNs in electrode A, and the highest pore density in a unit area for electrode I. The Young’s modulus for the graphite and copper film was measured using an Instron 4301 tensile tester and the values are tabulated in Table S1 (please see supplementary information) . Initially, simulations were performed using COMSOL Multiphysics software to study the maximum stress distribution on the printed electrodes during the bend test. Figures S6 and S7(a) (please see the supplementary information) represent the COMSOL simulations of electrodes A & I, respectively for bending radius varying from 10 to 60 mm. The simulation results have shown that the VonMises stress (MPa) is maximum on the electrodes when the bending radius is lower (10 mm) and the stress gradually reduces with an increase in bending radius. At a 60 mm bent radius, a small stress distribution was observed. Bending radii of 10 mm and 20 mm produced higher stress due to their extreme bending angles in comparison with other bent radii. Figure S7(b) (please see the supplementary information) shows the plot of average stress with respect to different bending radii from 10 to 60 mm, obtained from COMSOL simulations. Electrode-I experienced a stress of approximately 9.7 MPa at a 10 mm bending radius in comparison with electrode-A which experienced 10.9 MPa. The results show that the printed electrode with SPNs (electrode-I) experienced slightly lower stress compared to electrode-A without SPNs. The experimental setup for performing the bend test using a three-point attachment is shown in Fig. S7(c) (please see the supplementary information) . The electrodes were cut into test samples of size 40 mm x 20 mm. Since the electrodes experienced the highest stress at 10 mm, as per the simulations, the same bending radius was chosen for 100 bending cycles at room temperature. Following this, the surface morphology of the graphite anode samples was analyzed using SEM for any micro-structured cracks induced due to the applied mechanical stress. Figure S8(a-d) (please see the supplementary information) shows the SEM images of the test samples before and after the bending test for electrodes A & I. No microcracks were observed on the graphite anode surface for electrodes A and I. This shows that the printed electrodes can withstand high stress without any damage. 2.5 XRD, and SEM analysis X-ray diffraction (XRD) analysis was performed on graphite anode powder from 10° to 90° with XRD from Rigaku Systems ® (Fig. 2 (a)). The intensity peak (002) observed at 26.5° represents the graphitic layers with no contaminations in the graphite anode powder [32]. Figure 2 (b-j) shows the SEM microstructural surface morphology of the screen-printed graphite electrodes A-I. A smooth surface morphology was observed for the electrodes where the voids represent the pore region that facilitates the interaction between the electrode material and electrolyte solution, resulting in high ionic mass transport. Uniform printing was observed for all the electrodes with different pore diameters and ETE distances. The shapes of 1000 µm and 500 µm SPNs, which had an ETE distance of 2 mm between pores, were circular and not significantly affected by ink spreading during the printing process. However, for smaller SPNs (100 µm) with a closer ETE distance (100 µm − 400 µm), the pore shape was not completely circular due to ink spreading. Maintaining pore structures closer to the designed specifications is a significant challenge, especially when pore diameters become smaller (< 200 µm) in screen printing considering the limitations in screen production where the currently available stainless-steel mesh opening is limited to ~ 53 µm with a wire diameter of ~ 20 µm which can create a pore close to ~ 100 µm [33]. Since the pore diameter of the SPNs is 100 µm, inks with very high viscosities should be used for printing to avoid the spreading of printed patterns especially when the ETE between the pores is small (100–400 µm). Considering the smaller mesh opening and wire diameter, it is challenging to print the smaller patterns accurately. Energy dispersive X-ray spectroscopy (EDS) analysis was performed for element mapping, where uniform distribution of graphite (an allotrope of carbon), and fluoride (binder) were detected (Fig. 2 (k-l)). 3. Cell assembly and test protocol The electrochemical performance of the flexible screen-printed graphite anode was obtained by punching 1.6 cm 2 disks and assembling a CR-2032 half-cell LIB with Li-metal foil acting as the counter electrode. EC: EMC (3:7) by weight dissolved in 1.2M lithium hexafluorophosphate (LiPF 6 ) was used as electrolyte and polypropylene/polyethylene/polypropylene (PP/PE/PP) was used as the separator. All the coin cells were assembled inside a glove box under Argon gas. Coin cells assembled using electrodes A-I are represented as cells A-I, respectively. Electrochemical testing of the cells, such as formation, rate, and cycling tests, was performed in the voltage range of 0.01 V to 1.5 V using a CT 3002AU (5V 50mA) battery tester from Landt instruments. A constant current rate of 0.1C was used for performing the formation tests. The protocol was designed to run three cycles of discharging and charging at 0.1C on all coin cells at room temperature. The current rate of 0.1C corresponds to the testing time of ten hours (1/0.1 = 10 hours). After the formation test, the cells were subjected to a rate test using constant current-constant voltage (CC-CV) protocol for the charging and discharging process. The cells were charged at a constant current of 0.33C to 1.5 V, with a voltage hold at 1.5 V until the charging time reached three hours or until the current is less than 0.05C. Similarly, the cells were discharged to 0.01 V at current densities of 0.1C, 0.5C, 1C, 2C, 4C, and 6C. Voltage hold was applied during discharging at each C-rate until the current was less than 0.05C or until the time reached ten hours, two hours, one hour, half-hour, one-fourth hour, and one-sixth hour at respective C-rates. All the cells were recovered back to 0.1C at the end of the rate test to examine the capacity retention. At each C-rate, the cells underwent three cycles of testing. A cycling test was conducted on the cells using CC-CV mode with a voltage range of 0.01 V to 1.5 V. A 2C rate was used for the discharge of the cells and a current density of 0.33C was used for the charging process. Voltage hold was applied during charging and discharging until the testing time reached 3 hours and half-hours, respectively or the current went lower than 0.05C. 4. Results and discussion Initially, coin-cells A to D were assembled using electrodes A to D, to study the effect of the pore size on the electrochemical performance. Figures S9(a-d) (please see the supplementary information) show the voltage profile of the formation test cycles. Cells A, B, C, and D exhibited initial discharge capacities of 351, 339, 345, and 349 mAh/g, respectively. All the tested cells exhibited similar discharge curves with a slope feature above 0.25 V and three voltage plateaus around 0.25 V, 0.15 V, and 0.05 V. These plateaus can be correlated to the lithiation characteristics of graphite. The charge capacities were in the range of 325–330 mAh/g for cells B, C, and D when compared to cell A which exhibited ~ 338 mAh/g capacity at the end of the formation test. Figure 3 (a-b) represents the charge capacities and irreversible capacity loss (ICL) values of cells A, B, C, and D during formation. The ICL was less than 1% for all the cells at the end of formation test. In addition, there was no significant difference in the capacity of the cells at the end of the formation test. This indicates that SPNs have minimal effect at very low C-rates such as 0.1C. After formation, cells were subjected to the rate test by applying the CC-CV protocol. Figure 3 c shows the rate test results for cells A-D at varied C-rates. Cell D demonstrated slightly better capacities especially at higher rates such as 2C, 4C, and 6C in comparison to cells A, B, and C. For example, cell D exhibited capacities of 227, 139, and 103 mAh/g when compared to cell A (reference electrode) which exhibited capacities of 210, 120, and 85 mAh/g at 2C, 4C, and 6C, respectively. All the cells demonstrated good capacity retention close to their initial capacities at 0.1C by the end of the rate test. The drop in the capacity at higher C-rates can be correlated to overpotential because of the limited Li + diffusion in electrodes. A cycling test was performed on the coin cells for 100 cycles at 2C to determine the long-term stability. Figure 3 (d) shows the cycling performance for cells A to D. An increase in the capacities of the coin cells was observed at the beginning of the cycling test. This increase can be correlated to the formation of a solid electrolyte interface (SEI) layer on the surface of the electrodes. This SEI layer is crucial for the long-term stability and performance of the battery. During the formation of this SEI layer, an initial rise in capacity might occur as it provides additional pathways for Li + transport and improves electrode-electrolyte interface kinetics. In addition, during initial cycles at a higher C-rate, the electrolyte may redistribute inside the cell, leading to improved wetting of the electrode surface and enhanced ion transport. This electrolyte redistribution can contribute to the initial rise in capacity as the cell reaches optimal electrochemical conditions. Capacities of approximately 125, 127, 135, and 148 mAh/g were recorded for cells A, B, C, and D at the end of the cycle test (i.e., 100th cycle), respectively. A similar trend, as the rate test, was observed during the cycling performance, where cell D demonstrated the highest capacity retention of ~ 68% when compared to a capacity retention of ~ 59% for cell A at the end of the 100th cycle. In addition, larger SPNs result in the reduction of the energy density of the batteries in comparison to smaller SPNs due to decreased active material contact, electrode integrity, and diffusion limitations (larger pores might have slower Li + diffusion than smaller pores due to more vacant region without any electrode material). Based on the formation, rate, and cycling tests of cells A to D, SPNs with pore diameters of 100 µm were considered for further optimization of structured electrodes to enhance the fast-charging capabilities of the LIBs. The ETE distance between the pores was gradually reduced from 2000 µm to 400 µm, 300 µm, 200 µm, 150 µm, and 100 µm (electrodes E-I). The pore size and ETE were limited to 100 µm due to the screen manufacturing limitations and reducing them further will result in the complete erosion of screen emulsion. Coin cells were assembled for electrodes E-I with varying ETE distances between the pores and electrochemical performance was investigated by conducting formation, rate, and cycling tests. No changes were made to the testing protocols. Figure S10(a-e) (please see the supplementary information) displays the voltage profiles of the formation test cycles for the assembled coin cells E to I. Similar discharge slopes were observed around 0.25 V, 0.15 V, and 0.05 V indicating the lithiation properties of graphite. At the end of the formation, discharge and charge capacities were approximately in the range of 335–345 mAh/g indicating very little capacity loss of less than 1% by the end of the third cycle. Figure 4(a-b) shows the formation capacity and ICL of cells E to I. Later the cells were subjected to a rate test using the CC-CV protocol. Figure 4(c-d) shows the rate performance of cells E to I, at various current rates. The cells displayed similar capacities at 0.1C, 0.5C, and 1C indicating minimal effect of SPNs at low C-rates. An increment in the capacities was observed at higher C-rates as the ETE distance between the pores was gradually reduced. Capacities of 225, 237, 245, 249, and 255 mAh/g were observed at 2C for cells E to I, respectively. At 4C, the cells E to I, exhibited capacities of 149, 158, 164, 164, and 168 mAh/g, respectively. Similarly, when the current rate was increased to 6C, capacities of 108, 116, 120, 122, and 129 mAh/g were measured for cells E to I, respectively. All the electrodes achieved capacities close to their initial capacities towards the end of the rate test. The results show that cell I exhibited remarkable rate capacities at high C-rates among all the tested cells (Fig. 4(d)). Cell I achieved capacity improvements of 21%, 40%, and 52% at higher C-rates such as 2C, 4C, and 6C, respectively, when compared to cell A (without SPNs). At 6C, cell I displayed an increase in capacity of approximately 1.5 times greater when compared to electrode-A. Figure S11 (please see the supplementary information) displays the voltage profile of the rate test for cells A and I from 0.01 V − 1.5 V. A larger potential gap was observed for cell-A with an increase in C-rates when compared to cell I. These rate test results indicate the superior performance of electrodes with smaller SPNs and closer ETE distance between the pores when compared to conventional bar-coated electrodes. Similar to the rate performance, cell I displayed superior stability when compared to other cells at the end of the cycling test. Figure 4(e-f) represents the cycling performance of cells E to I. Capacity retentions of approximately 83%, 88%, 91%, 91%, and 95% were measured for cells E to I, respectively, at the end of the cycling test. This retention corresponds to the final capacity of the battery when compared to its initial capacity at the beginning of the cycling test. An overall improvement of 48%, 69%, 76%, 82%, and 94% was observed in terms of specific capacity for cells E to I when compared to cell A at the end of the cycling test, and the capacity fading in cell A can be correlated with the sluggish kinetics of Li + transportation. Similarly, the remarkable stability for printed electrodes can be attributed to the electrode design with SPNs which resulted in enhanced transport of electrolyte through the electrode along with an increase in Li + diffusion during cycling especially at fast charging current rates. Introducing larger SPNs (1000 µm, 500 µm) results in the decline of the energy density of the battery. This is due to the considerably small size of Li + compared to the pore diameter. In addition to smaller SPNs, the ETE distance between the pores plays a significant role in fast charging capability. Closer ETE distance between the pores results in increased SPNs in a unit area. Thus, smaller SPNs with closer ETE distance between pores result in further enhancement of three-dimensional Li + transfer efficiency through the electrode in addition to the increased energy density of fast-charging LIBs. In other words, the smaller SPNs with closer ETE distance between the pores help in attaining stable, fast charging, high capacity and energy density LIBs by providing shorter diffusion paths, uniform ion distribution, and faster kinetics at high rates. Finally, after cycling tests, EIS measurements were performed on the coin cells to investigate the resistance offered by the electrode and SEI layer. Figure S12 (a-b) (please see the supplementary information) represents the EIS plots for a frequency range of 0.01 Hz to 100 kHz. Generally, the Nyquist plot consists of two semi-circles in the high and medium frequency regions and a diagonal line at low frequencies (Warburg impedance). The first semi-circle represents the Li + transfer that occurs in the SEI film formed on the graphite surface. The second semi-circle is related to charge transfer resistance caused due to Li + intercalation process in the battery. These resistances usually occur in the high-frequency range followed by Warburg impedance in the low-frequency region. In LIBs, the increase in resistance after cycling for graphite anode can be correlated to a poor electrical network between the active material and the conductive additive, in addition to internal stress that originates from continuous Li + diffusion in and out of the graphite anode, especially at high charging rates. From the EIS plots, it was observed that the cells made of electrodes A to D displayed impedance of approximately 130 Ω, 78 Ω, 67 Ω, and 21 Ω, respectively (Fig. S12(a)) (please see the supplementary information) . Cells H and I which exhibited superior cycling stability had R ct (resistance due to charge transfer) of approximately 17 Ω and 14 Ω, respectively (Fig. S12(b)) (please see the supplementary information) . Similarly, for cells E to G the measured impedance values were 34 Ω, 24 Ω, and 20 Ω, respectively (Fig. S12(b)) (please see the supplementary information) . These EIS results revealed that the cells assembled from electrodes with 100 µm SPN and closer ETE distance between pores had very little internal impedance of Li + transport indicating a low hindrance effect even after cycling for 100 cycles. Figure S12(c) represents the equivalent circuit model for fitting the impedance spectra (please see the supplementary information) . The results from EIS data indicated low resistance to Li + transport and charge transfer for printed structured electrodes with smaller SPN and closer ETE distance when compared to reference electrode. These results can also be correlated to superior cycling stability for cells E to I with structured electrodes. These results demonstrate the significance of implementing micro-structured SPNs that enhance the charge transfer kinetics inside the battery for achieving fast-charging LIBs with high capacity and cycling stability. 5. Lithium plating characterization After cycling, lithium plating characterization was performed on the electrodes with and without SPNs. Lithium plating usually occurs on an anode surface due to the accumulation of lithium ions at the electrode surface. It is a major concern in LIBs and results in rapid capacity loss of the battery along with safety concerns such as short-circuiting in the cell [34–35]. Considering the electrochemical performance during rate and cycling tests, electrode I (with SPNs) was chosen along with electrode A (without SPNs) for lithium plating analysis on the anode surface to validate the importance of introducing SPNs into the electrode. The cells from electrodes A and I were disassembled inside a glovebox under argon gas. The cells were rinsed with EMC and were dried overnight before transferring them to SEM for surface morphology analysis. The SEM surface morphology of electrode A displayed agglomerates of small white particles on the anode surface along with graphite particles as shown in Fig. 5 (a). Figure 5 (b-c) represents the SEM images at higher magnification clearly showing the white particles present on the anode surface with irregular shapes and sizes. The EDS analysis of cycled electrode A indicated that the white particles consist only of oxygen with the absence of carbon (C), fluorine (F), and phosphorus (P) elements (Fig. 5 (d-f)). The lack of elements C, F, and P eliminates the possibility of these white particles as oxidized lithium salt from liquid electrolyte or during the formation of the SEI layer [36]. Since the Li element cannot be detected, considering its low energy radiation properties and atomic mass, it is highly feasible that the detected oxygen element occurred due to plated lithium particles which were oxidized while transferring the electrode from the glovebox to SEM. To investigate more about lithium plating, open circuit voltage (OCV) and differential/derivative open circuit voltage (dOCV) analysis were performed on cells A and I as reported by Kong et al. [37]. Using the OCV analysis, undesired lithium plating that occurs during fast charging conditions can be detected as shown in Fig. S13(a) (please see the supplementary information) . Figure S13(b) (please see the supplementary information) shows the sample OCV (yellow) and dOCV (green) curves representing the lithium plating onset of chemical intercalation of lithium during the rest period. The initial lithium plateau corresponds to the mixed potential between lithiated graphite (Li x C 6 ) and plated lithium. As more intercalation of lithium plating occurs, the Li/Li x C 6 potential converts to pure Li x C 6 after consuming some amount of surface lithium. These decay features are more notable as a function of derivative voltage, (dOCV) which was initially presented by Schindler et al. [38]. This OCV analysis helps to determine the state-of-charge (SOC) of the LIB at which the plating onset becomes significant. This is a key parameter in determining the fast-charging capability of the LIB along with good cycling life. To the best of the authors’ knowledge, this OCV analysis has never been used to study the effect of SPNs in printed electrodes. Lithium plating onset test was performed on coin-cells A and I. Figure S14 (please see the supplementary information) shows the test protocol of plating onset at 2C between SOC of 10% and 95%, in increments of 5% (shown up to 50% SOC in the figure for better legibility). All the coin cells were charged to 1.5V at a C-rate of C/3. Then the cells were discharged at 2C without voltage hold and rested for 30 minutes and the data during the rest period (highlighted in red, Fig. S14) was used for plotting the OCV and dOCV curves. The same protocol was used to perform the lithium plating onset test at fast-charging C-rates of 4C and 6C. Please see supplementary information for detailed explanation of OCV analysis at 2C (Fig. S15 and S16), 4C (Fig. S17 and S.18), and 6C (Fig. S19 and S20) (please see supplementary information) . Coulombic efficiencies (CE) were also analyzed for cells A and I by using the ratios between discharge and charge capacities during lithium plating onset testing, following the methodology outlined by Konz et al. [37]. Figure 7 represents the summarized CEs for the electrodes at 2C, 4C, and 6C. The initial drops in CE in Fig. 7 (a-c) are highlighted in red which corresponds to the SOC where the lithium plating onset was first detected. At 2C, cell A experienced a drop from 99.8–98.1% in CE around 95% SOC while cell I maintained CE greater than 99.8% consistently throughout the test (Fig. 7 (a)). At 4C, cell A experienced initial plating onset around 60% SOC corresponding to a drop in CE from 99–97.5% (Fig. 7 (b)). The CE drop was more evident with an increase in SOC (CE of ~ 88% at 95% SOC). The initial drop in CE for cell I at 4C was observed from 98.9–96.9% around 85% SOC. It recorded a CE of approximately 95% at the end of the onset test. Similarly, at 6C, cell A exhibited a CE of 81.6% at the end of the test with an initial drop in the CE value from 99.3–98.3% around 50% SOC. Whereas, cell I exhibited a CE of 93.1% at 95% SOC with an initial drop in CE from 99.4–98.3% which was observed at 75% SOC (Fig. 7 (c)). The results indicate lower CE for cell A in comparison to cell I and this can be correlated to early detection of lithium plating onset on the anode surface which results in the reduction of CE as the SOC gradually increases. The printed electrodes with SPNs were able to suppress lithium plating for a longer duration, especially at 4C and 6C resulting in less reduction in CE when compared to electrodes without SPNS. These lithium plating results portray the significance of introducing SPNs into the electrode to effectively counter the lithium plating on the anode surface in addition to achieving high capacity, fast-charging, and stable LIBs, especially for EV applications. Although SPNs help with Li + and mass liquid electrolyte transportation, the pore size of SPNs and the ETE distance between the pores play a significant role in determining the battery’s performance and stability. From this work, it is evident that larger SPNs did not have a significant effect on improving the battery’s performance considering the size of Li + being much smaller than the diameter of SPNs. In addition, introducing larger SPNs into the electrode will also lead to a significant reduction in the energy density of the battery. Thus, by reducing the pore diameter of SPNs, we can increase the number of pores in a unit area which helps in assisting the mass transfer of liquid electrolyte. Similarly, reducing the ETE distance between the pores will enhance Li + diffusion. Even though the current work illustrates the significance of introducing SPNs into the electrode through rate, cycling, and lithium plating tests at the coin-cell level, further printing and electrochemical tests are required for these electrodes by assembling pouch cells using a Systec® roll-to-roll (R2R) cylindrical screen printer to demonstrate high-volume manufacturability. Figure S22 (please see the supplementary information) shows the schematic representations of transitioning from sheet-to-sheet (S2S) printing to R2R printing for fabricating electrodes for LIBs. Implementing R2R printing will further help in optimizing the printing conditions depending on the size and ETE distance of the SPNs since printing smaller SPNs with closer ETE distances could be challenging. NMC will be used as the cathode material for testing R2R screen-printed flexible electrodes to achieve high-capacity and fast-charging LIBs. Converting the fabrication technique from S2S to R2R will enhance the ease of implementation of SPNs in the electrodes on a commercial and industrial basis with little material wastage. 6. Conclusion In this work, a flexible graphite anode was fabricated by introducing novel SPNs using the screen-printing process to enhance the LIB’s performance. The cells assembled with micro-structured SPNs of smaller pore size and closer ETE distance demonstrated better rate and cycling performance in addition to displaying the ability to suppress lithium plating at fast charging current rates in comparison to the reference electrode. Rate test of the structured electrode consisting of 100 µm SPN with 100 µm and, 150 µm ETE distance had ~ 50% capacity improvement when compared to the reference electrode at a fast-charging C-rate of 6C. Superior cycling performance with capacity retention greater than 91% was also observed for cells with structured electrodes when compared to reference electrode which measured retention of 60% by the end of the 100th cycle. Lithium plating tests proved the significance of introducing SPNs to suppress plating and improve the stability of the batteries. Further investigation involves the fabrication of electrodes using a Systec® roll-to-roll cylindrical screen printer for multilayer pouch cell testing. Declarations Funding Acknowledgement: This material is based upon work supported by the U.S. Department of Energy’s Office on Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office, award number DE- EE0009111. Author Contribution M.Z., Q.W., and D.M. designed and supervised the research. H.R. K. M. E., T.H., and V. P. performed the experiments. H. R. K. M. E. and T. H. analyzed the data. H. R. K. M. E. and D. M. wrote the paper. D. M., G. W., B. N., W. 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Supplementary Files SupplementaryInformation.docx Cite Share Download PDF Status: Published Journal Publication published 06 Aug, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 22 Apr, 2025 Reviews received at journal 15 Apr, 2025 Reviews received at journal 15 Apr, 2025 Reviewers agreed at journal 11 Apr, 2025 Reviewers agreed at journal 10 Apr, 2025 Reviewers agreed at journal 08 Apr, 2025 Reviewers invited by journal 08 Apr, 2025 Editor assigned by journal 08 Apr, 2025 Editor invited by journal 07 Apr, 2025 Submission checks completed at journal 04 Apr, 2025 First submitted to journal 04 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6348014","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":440925205,"identity":"c3c020c3-3ee1-4ffb-b96e-9e37c18f92a8","order_by":0,"name":"Himanaga Rama Krishna Manoj Emani","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvElEQVRIiWNgGAWjYBACAwglIcfAwNjAzAAiidViTLIWhkSQSuK0mDMwH93wc4dF+oZrhxs/FzDYyG44QECLZQNb2s3eMxK5G24nNkvPYEgzJqjF4ACP2Q3eNoncbbcT25h5GA4nEqGF/9vNv20S6WYQLf+J0cLDdhtoSwJUywEitBxmM7st2yZhuB/kFx6DZOOZBLUcb352821bnbzk7PSHn3kq7GT7CGkBxwWSCYSUj4JRMApGwSggCgAAtYlDM4/G8n8AAAAASUVORK5CYII=","orcid":"","institution":"Western Michigan University","correspondingAuthor":true,"prefix":"","firstName":"Himanaga","middleName":"Rama Krishna Manoj","lastName":"Emani","suffix":""},{"id":440925209,"identity":"02166eb9-ba4b-4e36-a757-818a59d9d018","order_by":1,"name":"Dinesh Maddipatla","email":"","orcid":"","institution":"Western Michigan University","correspondingAuthor":false,"prefix":"","firstName":"Dinesh","middleName":"","lastName":"Maddipatla","suffix":""},{"id":440925210,"identity":"b714c82f-7677-4ba3-8af2-59bb249acf60","order_by":2,"name":"Tony Hanson","email":"","orcid":"","institution":"Western Michigan University","correspondingAuthor":false,"prefix":"","firstName":"Tony","middleName":"","lastName":"Hanson","suffix":""},{"id":440925212,"identity":"dc9538b1-7702-4374-9b41-3a967968765a","order_by":3,"name":"Valliammai Palaniappan","email":"","orcid":"","institution":"Western Michigan University","correspondingAuthor":false,"prefix":"","firstName":"Valliammai","middleName":"","lastName":"Palaniappan","suffix":""},{"id":440925213,"identity":"79cd1e0d-4506-4e5b-838d-88c2319ed1d1","order_by":4,"name":"Guanyi Wang","email":"","orcid":"","institution":"Western Michigan University","correspondingAuthor":false,"prefix":"","firstName":"Guanyi","middleName":"","lastName":"Wang","suffix":""},{"id":440925214,"identity":"71812878-5011-4b3d-9fff-e53202c5508f","order_by":5,"name":"Binu Baby Narakathu","email":"","orcid":"","institution":"SafeSense Technologies, LLC","correspondingAuthor":false,"prefix":"","firstName":"Binu","middleName":"Baby","lastName":"Narakathu","suffix":""},{"id":440925215,"identity":"19860e03-502e-4d9f-9bc0-7ff61ae3ef81","order_by":6,"name":"Wenquan Lu","email":"","orcid":"","institution":"Argonne National Laboratory","correspondingAuthor":false,"prefix":"","firstName":"Wenquan","middleName":"","lastName":"Lu","suffix":""},{"id":440925216,"identity":"25b836f8-0b1a-40f1-8760-4a548a0484cc","order_by":7,"name":"Qingliu Wu","email":"","orcid":"","institution":"Western Michigan University","correspondingAuthor":false,"prefix":"","firstName":"Qingliu","middleName":"","lastName":"Wu","suffix":""},{"id":440925217,"identity":"158cbbee-df22-413d-ac6d-c42235de61e5","order_by":8,"name":"Massood Atashbar","email":"","orcid":"","institution":"Western Michigan University","correspondingAuthor":false,"prefix":"","firstName":"Massood","middleName":"","lastName":"Atashbar","suffix":""}],"badges":[],"createdAt":"2025-03-31 22:53:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6348014/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6348014/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-12909-4","type":"published","date":"2025-08-06T15:57:01+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":80422721,"identity":"171d6505-b192-4f6c-8d0e-908e97b8ae55","added_by":"auto","created_at":"2025-04-11 19:44:26","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":720528,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Schematic of electrode fabrication using screen-printing; and illustrations of lithium-ion flow in (b) conventional electrode, (c) proposed electrode with SPNs, (d) free flow of lithium ions through the SPNs with low tortuosity, (e) cross-section SEM images showing the pore in the electrode, and (f) thickness measurement (54 ± 4.0 µm) of the electrode.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/62d3cad44ede7c24d4028808.jpg"},{"id":80422722,"identity":"4a4ee1f8-e314-488d-b0a5-111e8e0b765d","added_by":"auto","created_at":"2025-04-11 19:44:26","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2041847,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD analysis of graphite anode; SEM surface morphologies of (b) electrode-a, (c) electrode-b, (d) electrode-c, (e) electrode-d, (f)1electrode-e, (g) electrode-f, (h) electrode-g, (i) electrode-h, (j) electrode-i, (k,l) SEM image of graphite electrode at high magnification along with its EDS analysis. Note: Scale for (b) 20 µm, (c-j) 200 µm, and (k,l) 2 µm.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/0b9ea2c81e7b098c0a471be4.jpg"},{"id":80423488,"identity":"45fba942-648e-4b40-9724-1a26558084aa","added_by":"auto","created_at":"2025-04-11 20:00:26","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":521489,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical performance of cells A, B, C, and D representing (a) formation capacity at 0.1C for three cycles, (b) irreversible capacity loss (ICL) during formation as a function of cycle number, (c) rate performance at different C-rates, (d) cycling performance at 2C-rate for 100 cycles.\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/c13fa7666860b9728444d43e.jpg"},{"id":80423078,"identity":"73f7f988-5711-4f60-ad61-163add2c7e60","added_by":"auto","created_at":"2025-04-11 19:52:26","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":745990,"visible":true,"origin":"","legend":"\u003cp\u003eElectrochemical performance of cells E, F, G, H, and I representing (a) Formation capacity, (b) ICL, (c, d) Rate performance at different C-rates, (e, f) Cycling performance at 2C-rate for 100 cycles.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/e44eb1629cbc5f24f1b63fbb.jpg"},{"id":80422726,"identity":"041b0d7f-c1aa-4aac-b3fa-53e6cb85b343","added_by":"auto","created_at":"2025-04-11 19:44:26","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":342770,"visible":true,"origin":"","legend":"\u003cp\u003eSEM surface images of cycled cell-A at (a) low magnification, (b, c) high magnification, (d-f) EDS elemental mapping of cycled electrode A. Note: Scale for (a) 100 µm, (b) 1 µm and, (c-f) 2 µm.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/2014cb453cb00afca29da907.jpg"},{"id":80422729,"identity":"87f10c4e-be79-485c-a9cb-befc8875d9f7","added_by":"auto","created_at":"2025-04-11 19:44:26","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":455102,"visible":true,"origin":"","legend":"\u003cp\u003eSEM surface images of cycled cell I at (a) low magnification of ×43, (b, c) high magnification of ×650 and ×3000, (d-f) EDS elemental mapping of cycled electrode I. \u003cem\u003eNote\u003c/em\u003e: Scale for (a) 500 µm, (b) 20 µm and, (c-f) 5 µm.\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/b94bcbc809260ef91f72ba47.jpg"},{"id":80423087,"identity":"d79f94d5-cdbc-4adc-9c17-419dff137a25","added_by":"auto","created_at":"2025-04-11 19:52:27","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":299263,"visible":true,"origin":"","legend":"\u003cp\u003eCoulombic efficiencies (CE) of cells A and I during lithium plating onset test from 10% to 95% SOC at C-rates of (a) 2C, (b) 4C, and (c) 6C. The drop in values of CE was in trend with plating onset detected at different SOC. Initial drop in CE values were highlighted using red circles.\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/32eacc1ceae34bddbd326e46.jpg"},{"id":88814066,"identity":"abeeffb9-9559-4ed5-98d5-d40bf2ae2986","added_by":"auto","created_at":"2025-08-11 16:05:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5815173,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/d4dd7130-db3d-4d5d-8eed-dc1238d34353.pdf"},{"id":80422751,"identity":"38e5c77f-8d49-421e-8ea8-f3a81497533f","added_by":"auto","created_at":"2025-04-11 19:44:29","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":46597188,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6348014/v1/9385cd5a349b6b61a4c3d1bb.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Investigating the effect of screen-printed structured graphite electrodes with low tortuosity for high-capacity and fast-charging lithium-ion batteries","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the growth in demand for electric vehicles (EVs), fast charging ability has become a key parameter for today\u0026rsquo;s lithium-ion battery (LIB) technology [1,2]. LIBs consist of porous electrodes, a separator, and a liquid electrolyte. Typically, the electrodes (both anode and cathode) have been developed by mixing an active material, conductive additive, polymer binder, and solvent thoroughly until a homogenous slurry is obtained. Then, these slurries are coated onto current collectors (copper for anode, aluminum for cathode) and vacuum dried to evaporate the solvent [3,4]. Following this, the electrodes are calendered to a desired porosity to enhance particle contact and volumetric energy density of the cell before subjecting them to electrochemical testing [5]. During charging, lithium ions (Li\u003csup\u003e+\u003c/sup\u003e) migrate from the cathode to the anode through the separator. Similarly, during discharge, the process is reversed with current being drawn from the terminals of the battery [6]. Graphite, lithium titanium oxide (LTO), and silicon (Si) are among the widely used anode materials. Similarly, lithium nickel manganese cobalt oxides (NMC), lithium iron phosphate (LFP), and lithium cobalt oxide (LCO) are widely used as cathode materials to achieve LIBs with superior electrochemical performance [7].\u003c/p\u003e \u003cp\u003eEven though there have been several research efforts and continuous advancements in the battery field, the accelerated degradation of capacity and power capability of batteries remains a major concern at high current rates, or fast charging rates such as 1C or higher [8]. Lithium plating, dendrite formation, and mechanical failure remain the major reasons for degradation at high current rates due to current-dependent overpotential [9]. Lithium plating/dendrite formation is a phenomenon that often occurs on the anode surface of LIBs, leading to the irreversible loss of lithium, resulting in electrolyte decomposition and rapid capacity fading, and in turn mechanical failure of the LIBs [9]. The root cause for the lithium plating and dendrite formation is attributed to the high tortuosity of the electrodes, resulting in twisted pathways that are narrow and distorted, thus making it difficult for Li\u0026thinsp;+\u0026thinsp;transportation and, in turn, affecting the fast-charging ability of LIBs during charge/discharge cycles. This also results in increased internal ionic resistance of the LIB [10]. Therefore, reducing the tortuosity of the electrodes can enhance Li\u003csup\u003e+\u003c/sup\u003e flow, along with electrolyte mass transfer, resulting in enhanced electrochemical performance of the LIB. In other words, low tortuosity in LIBs facilitates effective ion transportation within electrode structure, which in turn leads to enhanced rate capability, lower ionic resistance, more uniform ion distribution, reduced stress on electrodes, improved columbic efficiency, ensures better utilization of active material, and promotes safer fast charging cycling stability [11].\u003c/p\u003e \u003cp\u003eSeveral researchers have explored various strategies to reduce tortuosity in LIBs, such as electrode thickness optimizing electrode thickness [12], controlling particle size and shape [13], using nano materials [14], and aligning electrodes along the ion flow direction [15]. However, these methods often require precise control over material uniformity, involve complex fabrication process (such as electrospinning or advanced templating) [16] and are material specific limiting their compatibility with all electrode materials. Moreover, reducing electrode thickness can lead to low energy, density which is not ideal for batteries performance.\u003c/p\u003e \u003cp\u003eFabricating structured electrodes is an efficient way to overcome the limitations associated with LIBs in terms of tortuosity. Electrochemical simulations have shown that introducing secondary pore networks (SPNs) in the electrodes enhances the transportation of electrolyte and Li\u003csup\u003e+\u003c/sup\u003e, which will have a significant effect in improving the electrochemical properties of the LIB [17\u0026ndash;19]. The implementation of structured electrodes can effectively mitigate the problem of lithium plating on the surface of the anode electrode [20\u0026ndash;22]. Despite these advantages, LIBs with structured electrodes are not yet commercially available to the best of our knowledge. This is due to the limitations associated with the large-scale fabrication of structured electrodes. Several advanced manufacturing processes, such as laser patterning, freeze casting, aerosol jet printing, inkjet printing, gravure printing, and screen printing, can be implemented to fabricate structured electrodes [23\u0026ndash;29]. Processes such as inkjet and aerosol jet printing result in electrodes with very low mass loadings, typically in the range of 0.1-1 mg/cm\u003csup\u003e2\u003c/sup\u003e, due to the low viscosity of the inks [24,25]. Similarly, in the freeze-casting process, SPNs can be introduced into the electrode using the cooling stage while drying at -50\u0026deg;C during the curing process. However, this process takes more than 48 hours, and the uniformity of the structured electrode is not reliable [26]. In other words, the consistency in obtaining the same pore sizes and distance between the pores in SPNs is challenging. In contrast, screen-printing emerges as a promising approach for the precisely fabricating structured electrodes with high mass loadings, which can be implemented in high-volume roll-to-roll (R2R) printing. Screen printing offers design flexibility and a simple, swift, and repeatable method for manufacturing electrode architectures with variable mass loadings [30].\u003c/p\u003e \u003cp\u003eIn this work, a homogenous anode ink was prepared by mixing graphite, carbon black, and polyvinylidene fluoride (PVDF) in N-Methyl-2-pyrrolidone (NMP) solvent. Screen printing was implemented for depositing the ink on a flexible copper current collector. Novel SPN-based microstructures with different pore diameters and edge-to-edge (ETE) distances were introduced during screen printing into the graphite electrode. Later, half-cell LIBs were assembled using the screen-printed graphite electrodes with and without SPNs. Electrochemical tests were conducted by performing formation, rate, and cycling tests on the assembled coin cells. Battery data were analyzed to study the significance between electrodes with and without SPNs (structured and reference electrodes).\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and ink preparation\u003c/h2\u003e \u003cp\u003eThe anode ink was formulated using graphite as the active material (5 \u0026micro;m particle size), carbon black (C-45, 100\u0026ndash;200 nm, MSE Supplies) as the conductive additive, PVDF (5130, Kureha) as the binder, and NMP as the solvent (Sigma Aldrich\u003csup\u003e\u0026reg;\u003c/sup\u003e). All the materials were used as received without any further modification. Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(a) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e represents the schematic of ink preparation. Initially, the graphite and carbon black were added to the PVDF binder (8% in NMP) in wt.% of 90:3:7, respectively. Then, the mixture was dispersed in NMP, and the resulting electrode slurry was transferred to a Thinky AR-100 planetary centrifugal mixer. Following this, the slurry was mixed at 2000 rpm until a homogenous and uniform ink slurry was obtained for screen printing. The prepared ink had 60% solid loading without any residuals, indicating homogeneity and suitability for printing.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Ink characterization\u003c/h2\u003e \u003cp\u003eCertain properties of an ink affect the print quality, such as surface tension, and contact angle with respect to the substrate employed. These properties provide a better understanding of the wetting properties of the ink and can be measured using an FTA200 goniometer. Figures \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(b) and (c) show the surface tension and contact angle of the graphite ink, respectively \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. The surface tension of the graphite ink was measured to be ~\u0026thinsp;6.2 dynes/cm using the pendant drop method (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e(b)) [30]. The surface energy of copper foil (substrate) was also measured with de-ionized (DI) water and hexadecane as 76 dynes/cm based on the Owens-Wendt method. The surface tension value obtained was less than the surface energy of the substrate indicating that the ink was printable onto the substrate. Similarly, a contact angle of 62.4\u0026deg; was measured for the ink with respect to a 9 \u0026micro;m thick copper substrate (MSE Supplies) using the sessile drop method using an FTA200 goniometer [31]. Contact angles\u0026thinsp;\u0026lt;\u0026thinsp;90\u0026deg; indicate good wetting characteristics of the ink on the copper substrate. Following this, the viscosity of the ink was measured with an Anton Paar \u003csup\u003e\u0026reg;\u003c/sup\u003e MCR-302 rheometer using parallel-plate geometry. The ink slurry was placed between parallel plates at room temperature and viscosity was recorded by varying the shear rate from 1 s\u003csup\u003e-1\u003c/sup\u003e up to 500 s\u003csup\u003e-1\u003c/sup\u003e. Figure S2(a) shows the shear thinning behavior of the graphite ink with varied shear rates \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. Since the prepared ink had high solid loading, the initial viscosity of 230 Pa.s was recorded at a shear rate of 1 s\u003csup\u003e-1\u003c/sup\u003e and it reduced to 0.7 Pa.s at 500 s\u003csup\u003e-1\u003c/sup\u003e indicating shear-thinning behavior, which helps in seamless ink transfer onto the substrate through the stainless-steel screen mesh. Figure S2(b) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e represents the anode ink\u0026rsquo;s thixotropic behavior where the viscosity of the ink was reduced from ~\u0026thinsp;231 Pa.s to ~\u0026thinsp;0.7 Pa.s and recovered to ~\u0026thinsp;226 Pa.s, as the shear rate was varied from 1 s\u003csup\u003e-1\u003c/sup\u003e to 500 s\u003csup\u003e-1\u003c/sup\u003e and back to 1 s\u003csup\u003e-1\u003c/sup\u003e, respectively. This demonstrates that the ink is stable and suitable for continuous deposition on the copper substrate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Fabrication\u003c/h2\u003e \u003cp\u003eScreen printing was used to fabricate the graphite electrodes using an HMI MSP-485 semi-automatic screen-printer. Stainless-steel screens consisting of an array of pores with varying diameters of 1000 \u0026micro;m, 500 \u0026micro;m, and 100 \u0026micro;m and an ETE distance of 2000 \u0026micro;m between the pores were fabricated at Microscreen\u003csup\u003e\u0026reg;\u003c/sup\u003e. The screen size was 12 x 12 inches with a mesh count, wire diameter, and mesh angle of 325, 20 \u0026micro;m, and 22.5 degrees, respectively. It was made of MS-22 emulsion (Grafic HSS from Saati Chemicals) which is NMP resistant with a thickness of 15 \u0026micro;m. Figure S3 \u003cem\u003e(please see the supplementary information)\u003c/em\u003e illustrates the fabricated screens and screen designs showing their respective SPN pore diameter (in red), and the ETE distance between the SPNs (in pink). The scale for the artwork was set to 200 \u0026micro;m for all the images. The blue color area in the images represents the emulsion (MS-22) which prevents the ink deposition through the screen onto the substrate resulting in the creation of a void in its place on the substrate. Based on the initial battery data (provided in the results section), SPNs with a small pore size of 100 \u0026micro;m exhibited better battery performance. For further investigation of SPNs pore diameter of 100 \u0026micro;m was kept constant and the ETE distance between the pores was gradually reduced from 2000 \u0026micro;m to 400 \u0026micro;m, 300 \u0026micro;m, 200 \u0026micro;m, 150 \u0026micro;m, and 100 \u0026micro;m.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a) shows the schematic representation of the electrode fabrication using the screen-printing process. To fabricate the anode, the copper substrate with ~\u0026thinsp;9 \u0026micro;m thickness was placed on the screen printer platen and was cleaned with isopropyl alcohol (IPA). This helps in removing any dust particles present on the copper substrate. The platen consists of vacuum pores which enable the copper substrate to be held firmly to the platen. Graphite ink was uniformly spread on the screen and a silicone squeegee was used for printing the ink onto copper substrate. After screen-printing the graphite ink onto the copper substrate, the printed electrode was cured in a VWR\u003csup\u003e\u0026reg;\u003c/sup\u003e oven at 45\u0026deg;C for 4 hours to partially evaporate the NMP solvent. Then, the electrode was transferred to a vacuum oven from Across International\u003csup\u003e\u0026reg;\u003c/sup\u003e and was cured at 80\u0026deg;C for 10 hours to ensure complete evaporation of NMP. Figures S4 and S5 \u003cem\u003e(please see the supplementary information)\u003c/em\u003e show the fabricated screen-printed graphite electrodes along with their optical microscopic images. Uniform printing was observed for all the samples. The electrode representations along with their respective mass loadings are summarized in Table\u0026nbsp;1. Electrode A (solid block without SPNs) was used as a reference electrode for comparing the electrochemical performance of the fabricated anodes. Electrodes B, C, and D have SPNs with diameters of 1000 \u0026micro;m, 500 \u0026micro;m, and 100 \u0026micro;m, respectively. The ETE distance was 2000 \u0026micro;m (2 mm) for these electrodes. For electrodes E to I, the size of SPNs was kept constant at 100 \u0026micro;m and the ETE distance between the pores was gradually reduced to 400 \u0026micro;m (electrode E), 300 \u0026micro;m (electrode F), 200 \u0026micro;m, (electrode G), 150 \u0026micro;m (electrode H), 100 \u0026micro;m (electrode I).\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b) represents the schematic for lithium-ion flow in conventional electrodes without SPNs. Due to the sluggish kinetics of Li\u003csup\u003e+\u003c/sup\u003e, it takes more time for the Li\u003csup\u003e+\u003c/sup\u003e to reach the current collector. This results in an increased tortuosity of the LIB, which can lead to capacity fading at fast charging rates. Novel SPNs introduced during fabrication help in reducing the electrode\u0026rsquo;s tortuosity as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c). In addition, these SPNs increase the transportation of liquid electrolyte through the electrode, which enhances the Li\u003csup\u003e+\u003c/sup\u003e accessibility via a shorter route (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d)). The enhanced Li\u003csup\u003e+\u003c/sup\u003e accessibility, along with superior contact between the active material and the liquid electrolyte, is an essential condition for achieving fast-charging LIBs with higher capacities. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(e) shows the scanning electron microscopy (SEM) cross-section image of pore in the electrode using a Jeol\u003csup\u003e\u0026reg;\u003c/sup\u003e JSM-IT200. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(f) represents the thickness of the electrode measured around 54.4 \u0026plusmn; 4.0 \u0026micro;m. The different pore diameters and ETE distances will result in different mass loading for each sample since the number of pores in a unit area varies with respect to pore diameter and ETE distance. Therefore, the mass loadings of all the electrodes were adjusted in the range of 6\u0026ndash;7 mg/cm\u003csup\u003e2\u003c/sup\u003e to have a fair comparison between the electrodes with and without SPNs. All the electrodes were calendered between cylindrical rolls and the porosity (ε) was controlled at approximately 35%. Porosity was calculated using Equation S1 as shown in supplementary data. The calendering process helps in improving the particle contact and in turn, the energy density of the battery.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Mechanical characterization\u003c/h2\u003e \u003cp\u003eMechanical characterization was performed on the fabricated electrodes by subjecting them to cyclical bend tests using a Mark-10 ESM 301 motorized test stand. Electrodes A and I were chosen for the bend test considering no SPNs in electrode A, and the highest pore density in a unit area for electrode I. The Young\u0026rsquo;s modulus for the graphite and copper film was measured using an Instron 4301 tensile tester and the values are tabulated in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e \u003cem\u003e(please see supplementary information)\u003c/em\u003e. Initially, simulations were performed using COMSOL Multiphysics software to study the maximum stress distribution on the printed electrodes during the bend test. Figures S6 and S7(a) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e represent the COMSOL simulations of electrodes A \u0026amp; I, respectively for bending radius varying from 10 to 60 mm. The simulation results have shown that the VonMises stress (MPa) is maximum on the electrodes when the bending radius is lower (10 mm) and the stress gradually reduces with an increase in bending radius. At a 60 mm bent radius, a small stress distribution was observed. Bending radii of 10 mm and 20 mm produced higher stress due to their extreme bending angles in comparison with other bent radii. Figure S7(b) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e shows the plot of average stress with respect to different bending radii from 10 to 60 mm, obtained from COMSOL simulations. Electrode-I experienced a stress of approximately 9.7 MPa at a 10 mm bending radius in comparison with electrode-A which experienced 10.9 MPa. The results show that the printed electrode with SPNs (electrode-I) experienced slightly lower stress compared to electrode-A without SPNs.\u003c/p\u003e \u003cp\u003eThe experimental setup for performing the bend test using a three-point attachment is shown in Fig. S7(c) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. The electrodes were cut into test samples of size 40 mm x 20 mm. Since the electrodes experienced the highest stress at 10 mm, as per the simulations, the same bending radius was chosen for 100 bending cycles at room temperature. Following this, the surface morphology of the graphite anode samples was analyzed using SEM for any micro-structured cracks induced due to the applied mechanical stress. Figure S8(a-d) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e shows the SEM images of the test samples before and after the bending test for electrodes A \u0026amp; I. No microcracks were observed on the graphite anode surface for electrodes A and I. This shows that the printed electrodes can withstand high stress without any damage.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 XRD, and SEM analysis\u003c/h2\u003e \u003cp\u003eX-ray diffraction (XRD) analysis was performed on graphite anode powder from 10\u0026deg; to 90\u0026deg; with XRD from Rigaku Systems\u003csup\u003e\u0026reg;\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a)). The intensity peak (002) observed at 26.5\u0026deg; represents the graphitic layers with no contaminations in the graphite anode powder [32]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b-j) shows the SEM microstructural surface morphology of the screen-printed graphite electrodes A-I. A smooth surface morphology was observed for the electrodes where the voids represent the pore region that facilitates the interaction between the electrode material and electrolyte solution, resulting in high ionic mass transport. Uniform printing was observed for all the electrodes with different pore diameters and ETE distances. The shapes of 1000 \u0026micro;m and 500 \u0026micro;m SPNs, which had an ETE distance of 2 mm between pores, were circular and not significantly affected by ink spreading during the printing process. However, for smaller SPNs (100 \u0026micro;m) with a closer ETE distance (100 \u0026micro;m \u0026minus;\u0026thinsp;400 \u0026micro;m), the pore shape was not completely circular due to ink spreading. Maintaining pore structures closer to the designed specifications is a significant challenge, especially when pore diameters become smaller (\u0026lt;\u0026thinsp;200 \u0026micro;m) in screen printing considering the limitations in screen production where the currently available stainless-steel mesh opening is limited to ~\u0026thinsp;53 \u0026micro;m with a wire diameter of ~\u0026thinsp;20 \u0026micro;m which can create a pore close to ~\u0026thinsp;100 \u0026micro;m [33]. Since the pore diameter of the SPNs is 100 \u0026micro;m, inks with very high viscosities should be used for printing to avoid the spreading of printed patterns especially when the ETE between the pores is small (100\u0026ndash;400 \u0026micro;m). Considering the smaller mesh opening and wire diameter, it is challenging to print the smaller patterns accurately. Energy dispersive X-ray spectroscopy (EDS) analysis was performed for element mapping, where uniform distribution of graphite (an allotrope of carbon), and fluoride (binder) were detected (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(k-l)).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Cell assembly and test protocol","content":"\u003cp\u003eThe electrochemical performance of the flexible screen-printed graphite anode was obtained by punching 1.6 cm\u003csup\u003e2\u003c/sup\u003e disks and assembling a CR-2032 half-cell LIB with Li-metal foil acting as the counter electrode. EC: EMC (3:7) by weight dissolved in 1.2M lithium hexafluorophosphate (LiPF\u003csub\u003e6\u003c/sub\u003e) was used as electrolyte and polypropylene/polyethylene/polypropylene (PP/PE/PP) was used as the separator. All the coin cells were assembled inside a glove box under Argon gas. Coin cells assembled using electrodes A-I are represented as cells A-I, respectively.\u003c/p\u003e \u003cp\u003eElectrochemical testing of the cells, such as formation, rate, and cycling tests, was performed in the voltage range of 0.01 V to 1.5 V using a CT 3002AU (5V 50mA) battery tester from Landt instruments. A constant current rate of 0.1C was used for performing the formation tests. The protocol was designed to run three cycles of discharging and charging at 0.1C on all coin cells at room temperature. The current rate of 0.1C corresponds to the testing time of ten hours (1/0.1\u0026thinsp;=\u0026thinsp;10 hours). After the formation test, the cells were subjected to a rate test using constant current-constant voltage (CC-CV) protocol for the charging and discharging process. The cells were charged at a constant current of 0.33C to 1.5 V, with a voltage hold at 1.5 V until the charging time reached three hours or until the current is less than 0.05C. Similarly, the cells were discharged to 0.01 V at current densities of 0.1C, 0.5C, 1C, 2C, 4C, and 6C. Voltage hold was applied during discharging at each C-rate until the current was less than 0.05C or until the time reached ten hours, two hours, one hour, half-hour, one-fourth hour, and one-sixth hour at respective C-rates. All the cells were recovered back to 0.1C at the end of the rate test to examine the capacity retention. At each C-rate, the cells underwent three cycles of testing.\u003c/p\u003e \u003cp\u003eA cycling test was conducted on the cells using CC-CV mode with a voltage range of 0.01 V to 1.5 V. A 2C rate was used for the discharge of the cells and a current density of 0.33C was used for the charging process. Voltage hold was applied during charging and discharging until the testing time reached 3 hours and half-hours, respectively or the current went lower than 0.05C.\u003c/p\u003e"},{"header":"4. Results and discussion","content":"\u003cp\u003eInitially, coin-cells A to D were assembled using electrodes A to D, to study the effect of the pore size on the electrochemical performance. Figures S9(a-d) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e show the voltage profile of the formation test cycles. Cells A, B, C, and D exhibited initial discharge capacities of 351, 339, 345, and 349 mAh/g, respectively. All the tested cells exhibited similar discharge curves with a slope feature above 0.25 V and three voltage plateaus around 0.25 V, 0.15 V, and 0.05 V. These plateaus can be correlated to the lithiation characteristics of graphite. The charge capacities were in the range of 325\u0026ndash;330 mAh/g for cells B, C, and D when compared to cell A which exhibited\u0026thinsp;~\u0026thinsp;338 mAh/g capacity at the end of the formation test. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a-b) represents the charge capacities and irreversible capacity loss (ICL) values of cells A, B, C, and D during formation. The ICL was less than 1% for all the cells at the end of formation test. In addition, there was no significant difference in the capacity of the cells at the end of the formation test. This indicates that SPNs have minimal effect at very low C-rates such as 0.1C.\u003c/p\u003e \u003cp\u003eAfter formation, cells were subjected to the rate test by applying the CC-CV protocol. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the rate test results for cells A-D at varied C-rates. Cell D demonstrated slightly better capacities especially at higher rates such as 2C, 4C, and 6C in comparison to cells A, B, and C. For example, cell D exhibited capacities of 227, 139, and 103 mAh/g when compared to cell A (reference electrode) which exhibited capacities of 210, 120, and 85 mAh/g at 2C, 4C, and 6C, respectively. All the cells demonstrated good capacity retention close to their initial capacities at 0.1C by the end of the rate test. The drop in the capacity at higher C-rates can be correlated to overpotential because of the limited Li\u003csup\u003e+\u003c/sup\u003e diffusion in electrodes.\u003c/p\u003e \u003cp\u003eA cycling test was performed on the coin cells for 100 cycles at 2C to determine the long-term stability. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d) shows the cycling performance for cells A to D. An increase in the capacities of the coin cells was observed at the beginning of the cycling test. This increase can be correlated to the formation of a solid electrolyte interface (SEI) layer on the surface of the electrodes. This SEI layer is crucial for the long-term stability and performance of the battery. During the formation of this SEI layer, an initial rise in capacity might occur as it provides additional pathways for Li\u003csup\u003e+\u003c/sup\u003e transport and improves electrode-electrolyte interface kinetics. In addition, during initial cycles at a higher C-rate, the electrolyte may redistribute inside the cell, leading to improved wetting of the electrode surface and enhanced ion transport. This electrolyte redistribution can contribute to the initial rise in capacity as the cell reaches optimal electrochemical conditions. Capacities of approximately 125, 127, 135, and 148 mAh/g were recorded for cells A, B, C, and D at the end of the cycle test (i.e., 100th cycle), respectively. A similar trend, as the rate test, was observed during the cycling performance, where cell D demonstrated the highest capacity retention of ~\u0026thinsp;68% when compared to a capacity retention of ~\u0026thinsp;59% for cell A at the end of the 100th cycle. In addition, larger SPNs result in the reduction of the energy density of the batteries in comparison to smaller SPNs due to decreased active material contact, electrode integrity, and diffusion limitations (larger pores might have slower Li\u003csup\u003e+\u003c/sup\u003e diffusion than smaller pores due to more vacant region without any electrode material).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the formation, rate, and cycling tests of cells A to D, SPNs with pore diameters of 100 \u0026micro;m were considered for further optimization of structured electrodes to enhance the fast-charging capabilities of the LIBs. The ETE distance between the pores was gradually reduced from 2000 \u0026micro;m to 400 \u0026micro;m, 300 \u0026micro;m, 200 \u0026micro;m, 150 \u0026micro;m, and 100 \u0026micro;m (electrodes E-I). The pore size and ETE were limited to 100 \u0026micro;m due to the screen manufacturing limitations and reducing them further will result in the complete erosion of screen emulsion. Coin cells were assembled for electrodes E-I with varying ETE distances between the pores and electrochemical performance was investigated by conducting formation, rate, and cycling tests. No changes were made to the testing protocols.\u003c/p\u003e \u003cp\u003eFigure S10(a-e) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e displays the voltage profiles of the formation test cycles for the assembled coin cells E to I. Similar discharge slopes were observed around 0.25 V, 0.15 V, and 0.05 V indicating the lithiation properties of graphite. At the end of the formation, discharge and charge capacities were approximately in the range of 335\u0026ndash;345 mAh/g indicating very little capacity loss of less than 1% by the end of the third cycle. Figure\u0026nbsp;4(a-b) shows the formation capacity and ICL of cells E to I.\u003c/p\u003e \u003cp\u003eLater the cells were subjected to a rate test using the CC-CV protocol. Figure\u0026nbsp;4(c-d) shows the rate performance of cells E to I, at various current rates. The cells displayed similar capacities at 0.1C, 0.5C, and 1C indicating minimal effect of SPNs at low C-rates. An increment in the capacities was observed at higher C-rates as the ETE distance between the pores was gradually reduced. Capacities of 225, 237, 245, 249, and 255 mAh/g were observed at 2C for cells E to I, respectively. At 4C, the cells E to I, exhibited capacities of 149, 158, 164, 164, and 168 mAh/g, respectively. Similarly, when the current rate was increased to 6C, capacities of 108, 116, 120, 122, and 129 mAh/g were measured for cells E to I, respectively. All the electrodes achieved capacities close to their initial capacities towards the end of the rate test. The results show that cell I exhibited remarkable rate capacities at high C-rates among all the tested cells (Fig.\u0026nbsp;4(d)). Cell I achieved capacity improvements of 21%, 40%, and 52% at higher C-rates such as 2C, 4C, and 6C, respectively, when compared to cell A (without SPNs). At 6C, cell I displayed an increase in capacity of approximately 1.5 times greater when compared to electrode-A. Figure S11 \u003cem\u003e(please see the supplementary information)\u003c/em\u003e displays the voltage profile of the rate test for cells A and I from 0.01 V \u0026minus;\u0026thinsp;1.5 V. A larger potential gap was observed for cell-A with an increase in C-rates when compared to cell I. These rate test results indicate the superior performance of electrodes with smaller SPNs and closer ETE distance between the pores when compared to conventional bar-coated electrodes.\u003c/p\u003e \u003cp\u003eSimilar to the rate performance, cell I displayed superior stability when compared to other cells at the end of the cycling test. Figure\u0026nbsp;4(e-f) represents the cycling performance of cells E to I. Capacity retentions of approximately 83%, 88%, 91%, 91%, and 95% were measured for cells E to I, respectively, at the end of the cycling test. This retention corresponds to the final capacity of the battery when compared to its initial capacity at the beginning of the cycling test. An overall improvement of 48%, 69%, 76%, 82%, and 94% was observed in terms of specific capacity for cells E to I when compared to cell A at the end of the cycling test, and the capacity fading in cell A can be correlated with the sluggish kinetics of Li\u003csup\u003e+\u003c/sup\u003e transportation. Similarly, the remarkable stability for printed electrodes can be attributed to the electrode design with SPNs which resulted in enhanced transport of electrolyte through the electrode along with an increase in Li\u003csup\u003e+\u003c/sup\u003e diffusion during cycling especially at fast charging current rates. Introducing larger SPNs (1000 \u0026micro;m, 500 \u0026micro;m) results in the decline of the energy density of the battery. This is due to the considerably small size of Li\u003csup\u003e+\u003c/sup\u003e compared to the pore diameter. In addition to smaller SPNs, the ETE distance between the pores plays a significant role in fast charging capability. Closer ETE distance between the pores results in increased SPNs in a unit area. Thus, smaller SPNs with closer ETE distance between pores result in further enhancement of three-dimensional Li\u003csup\u003e+\u003c/sup\u003e transfer efficiency through the electrode in addition to the increased energy density of fast-charging LIBs. In other words, the smaller SPNs with closer ETE distance between the pores help in attaining stable, fast charging, high capacity and energy density LIBs by providing shorter diffusion paths, uniform ion distribution, and faster kinetics at high rates.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFinally, after cycling tests, EIS measurements were performed on the coin cells to investigate the resistance offered by the electrode and SEI layer. Figure S12 (a-b) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e represents the EIS plots for a frequency range of 0.01 Hz to 100 kHz. Generally, the Nyquist plot consists of two semi-circles in the high and medium frequency regions and a diagonal line at low frequencies (Warburg impedance). The first semi-circle represents the Li\u003csup\u003e+\u003c/sup\u003e transfer that occurs in the SEI film formed on the graphite surface. The second semi-circle is related to charge transfer resistance caused due to Li\u003csup\u003e+\u003c/sup\u003e intercalation process in the battery. These resistances usually occur in the high-frequency range followed by Warburg impedance in the low-frequency region. In LIBs, the increase in resistance after cycling for graphite anode can be correlated to a poor electrical network between the active material and the conductive additive, in addition to internal stress that originates from continuous Li\u003csup\u003e+\u003c/sup\u003e diffusion in and out of the graphite anode, especially at high charging rates. From the EIS plots, it was observed that the cells made of electrodes A to D displayed impedance of approximately 130 Ω, 78 Ω, 67 Ω, and 21 Ω, respectively (Fig. S12(a)) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. Cells H and I which exhibited superior cycling stability had R\u003csub\u003ect\u003c/sub\u003e (resistance due to charge transfer) of approximately 17 Ω and 14 Ω, respectively (Fig. S12(b)) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. Similarly, for cells E to G the measured impedance values were 34 Ω, 24 Ω, and 20 Ω, respectively (Fig. S12(b)) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. These EIS results revealed that the cells assembled from electrodes with 100 \u0026micro;m SPN and closer ETE distance between pores had very little internal impedance of Li\u003csup\u003e+\u003c/sup\u003e transport indicating a low hindrance effect even after cycling for 100 cycles. Figure S12(c) represents the equivalent circuit model for fitting the impedance spectra \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. The results from EIS data indicated low resistance to Li\u003csup\u003e+\u003c/sup\u003e transport and charge transfer for printed structured electrodes with smaller SPN and closer ETE distance when compared to reference electrode. These results can also be correlated to superior cycling stability for cells E to I with structured electrodes. These results demonstrate the significance of implementing micro-structured SPNs that enhance the charge transfer kinetics inside the battery for achieving fast-charging LIBs with high capacity and cycling stability.\u003c/p\u003e"},{"header":"5. Lithium plating characterization","content":"\u003cp\u003eAfter cycling, lithium plating characterization was performed on the electrodes with and without SPNs. Lithium plating usually occurs on an anode surface due to the accumulation of lithium ions at the electrode surface. It is a major concern in LIBs and results in rapid capacity loss of the battery along with safety concerns such as short-circuiting in the cell [34\u0026ndash;35]. Considering the electrochemical performance during rate and cycling tests, electrode I (with SPNs) was chosen along with electrode A (without SPNs) for lithium plating analysis on the anode surface to validate the importance of introducing SPNs into the electrode. The cells from electrodes A and I were disassembled inside a glovebox under argon gas. The cells were rinsed with EMC and were dried overnight before transferring them to SEM for surface morphology analysis.\u003c/p\u003e \u003cp\u003eThe SEM surface morphology of electrode A displayed agglomerates of small white particles on the anode surface along with graphite particles as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e (b-c) represents the SEM images at higher magnification clearly showing the white particles present on the anode surface with irregular shapes and sizes. The EDS analysis of cycled electrode A indicated that the white particles consist only of oxygen with the absence of carbon (C), fluorine (F), and phosphorus (P) elements (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d-f)). The lack of elements C, F, and P eliminates the possibility of these white particles as oxidized lithium salt from liquid electrolyte or during the formation of the SEI layer [36]. Since the Li element cannot be detected, considering its low energy radiation properties and atomic mass, it is highly feasible that the detected oxygen element occurred due to plated lithium particles which were oxidized while transferring the electrode from the glovebox to SEM.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate more about lithium plating, open circuit voltage (OCV) and differential/derivative open circuit voltage (dOCV) analysis were performed on cells A and I as reported by Kong et al. [37]. Using the OCV analysis, undesired lithium plating that occurs during fast charging conditions can be detected as shown in Fig. S13(a) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e. Figure S13(b) \u003cem\u003e(please see the supplementary information)\u003c/em\u003e shows the sample OCV (yellow) and dOCV (green) curves representing the lithium plating onset of chemical intercalation of lithium during the rest period. The initial lithium plateau corresponds to the mixed potential between lithiated graphite (Li\u003csub\u003ex\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003e) and plated lithium. As more intercalation of lithium plating occurs, the Li/Li\u003csub\u003ex\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003e potential converts to pure Li\u003csub\u003ex\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003e after consuming some amount of surface lithium. These decay features are more notable as a function of derivative voltage, (dOCV) which was initially presented by Schindler et al. [38]. This OCV analysis helps to determine the state-of-charge (SOC) of the LIB at which the plating onset becomes significant. This is a key parameter in determining the fast-charging capability of the LIB along with good cycling life. To the best of the authors\u0026rsquo; knowledge, this OCV analysis has never been used to study the effect of SPNs in printed electrodes.\u003c/p\u003e \u003cp\u003eLithium plating onset test was performed on coin-cells A and I. Figure S14 \u003cem\u003e(please see the supplementary information)\u003c/em\u003e shows the test protocol of plating onset at 2C between SOC of 10% and 95%, in increments of 5% (shown up to 50% SOC in the figure for better legibility). All the coin cells were charged to 1.5V at a C-rate of C/3. Then the cells were discharged at 2C without voltage hold and rested for 30 minutes and the data during the rest period (highlighted in red, Fig. S14) was used for plotting the OCV and dOCV curves. The same protocol was used to perform the lithium plating onset test at fast-charging C-rates of 4C and 6C. Please see supplementary information for detailed explanation of OCV analysis at 2C (Fig. S15 and S16), 4C (Fig. S17 and S.18), and 6C (Fig. S19 and S20) \u003cem\u003e(please see supplementary information)\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eCoulombic efficiencies (CE) were also analyzed for cells A and I by using the ratios between discharge and charge capacities during lithium plating onset testing, following the methodology outlined by Konz et al. [37]. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e represents the summarized CEs for the electrodes at 2C, 4C, and 6C. The initial drops in CE in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a-c) are highlighted in red which corresponds to the SOC where the lithium plating onset was first detected. At 2C, cell A experienced a drop from 99.8\u0026ndash;98.1% in CE around 95% SOC while cell I maintained CE greater than 99.8% consistently throughout the test (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a)). At 4C, cell A experienced initial plating onset around 60% SOC corresponding to a drop in CE from 99\u0026ndash;97.5% (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b)). The CE drop was more evident with an increase in SOC (CE of ~\u0026thinsp;88% at 95% SOC). The initial drop in CE for cell I at 4C was observed from 98.9\u0026ndash;96.9% around 85% SOC. It recorded a CE of approximately 95% at the end of the onset test. Similarly, at 6C, cell A exhibited a CE of 81.6% at the end of the test with an initial drop in the CE value from 99.3\u0026ndash;98.3% around 50% SOC. Whereas, cell I exhibited a CE of 93.1% at 95% SOC with an initial drop in CE from 99.4\u0026ndash;98.3% which was observed at 75% SOC (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c)). The results indicate lower CE for cell A in comparison to cell I and this can be correlated to early detection of lithium plating onset on the anode surface which results in the reduction of CE as the SOC gradually increases. The printed electrodes with SPNs were able to suppress lithium plating for a longer duration, especially at 4C and 6C resulting in less reduction in CE when compared to electrodes without SPNS.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese lithium plating results portray the significance of introducing SPNs into the electrode to effectively counter the lithium plating on the anode surface in addition to achieving high capacity, fast-charging, and stable LIBs, especially for EV applications. Although SPNs help with Li\u003csup\u003e+\u003c/sup\u003e and mass liquid electrolyte transportation, the pore size of SPNs and the ETE distance between the pores play a significant role in determining the battery\u0026rsquo;s performance and stability. From this work, it is evident that larger SPNs did not have a significant effect on improving the battery\u0026rsquo;s performance considering the size of Li\u003csup\u003e+\u003c/sup\u003e being much smaller than the diameter of SPNs. In addition, introducing larger SPNs into the electrode will also lead to a significant reduction in the energy density of the battery. Thus, by reducing the pore diameter of SPNs, we can increase the number of pores in a unit area which helps in assisting the mass transfer of liquid electrolyte. Similarly, reducing the ETE distance between the pores will enhance Li\u003csup\u003e+\u003c/sup\u003e diffusion. Even though the current work illustrates the significance of introducing SPNs into the electrode through rate, cycling, and lithium plating tests at the coin-cell level, further printing and electrochemical tests are required for these electrodes by assembling pouch cells using a Systec\u0026reg; roll-to-roll (R2R) cylindrical screen printer to demonstrate high-volume manufacturability. Figure S22 \u003cem\u003e(please see the supplementary information)\u003c/em\u003e shows the schematic representations of transitioning from sheet-to-sheet (S2S) printing to R2R printing for fabricating electrodes for LIBs. Implementing R2R printing will further help in optimizing the printing conditions depending on the size and ETE distance of the SPNs since printing smaller SPNs with closer ETE distances could be challenging. NMC will be used as the cathode material for testing R2R screen-printed flexible electrodes to achieve high-capacity and fast-charging LIBs. Converting the fabrication technique from S2S to R2R will enhance the ease of implementation of SPNs in the electrodes on a commercial and industrial basis with little material wastage.\u003c/p\u003e"},{"header":"6. Conclusion","content":"\u003cp\u003eIn this work, a flexible graphite anode was fabricated by introducing novel SPNs using the screen-printing process to enhance the LIB\u0026rsquo;s performance. The cells assembled with micro-structured SPNs of smaller pore size and closer ETE distance demonstrated better rate and cycling performance in addition to displaying the ability to suppress lithium plating at fast charging current rates in comparison to the reference electrode. Rate test of the structured electrode consisting of 100 \u0026micro;m SPN with 100 \u0026micro;m and, 150 \u0026micro;m ETE distance had\u0026thinsp;~\u0026thinsp;50% capacity improvement when compared to the reference electrode at a fast-charging C-rate of 6C. Superior cycling performance with capacity retention greater than 91% was also observed for cells with structured electrodes when compared to reference electrode which measured retention of 60% by the end of the 100th cycle. Lithium plating tests proved the significance of introducing SPNs to suppress plating and improve the stability of the batteries. Further investigation involves the fabrication of electrodes using a Systec\u0026reg; roll-to-roll cylindrical screen printer for multilayer pouch cell testing.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding Acknowledgement:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis material is based upon work supported by the U.S. Department of Energy\u0026rsquo;s Office on Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office, award number DE- EE0009111.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.Z., Q.W., and D.M. designed and supervised the research. H.R. K. M. E., T.H., and V. P. performed the experiments. H. R. K. M. E. and T. H. analyzed the data. H. R. K. M. E. and D. M. wrote the paper. D. M., G. W., B. N., W. L., Q. W., and M.Z., contributed to valuable feedback of the manuscript. All the authors read and revised the manuscript\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data generated or analyzed during this study is provided within the manuscript or supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLi, S. et al. Fast charging anode materials for lithium-ion batteries: current status and perspectives. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e \u003cb\u003e32\u003c/b\u003e, 2200796. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/adfm.202200796\u003c/span\u003e\u003cspan address=\"10.1002/adfm.202200796\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (June 2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang, Q. et al. 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Power Sources\u003c/em\u003e. \u003cb\u003e304\u003c/b\u003e, 170\u0026ndash;180. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jpowsour.2015.11.044\u003c/span\u003e\u003cspan address=\"10.1016/j.jpowsour.2015.11.044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (February 2016).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Structured electrode, Secondary pore network, Fast charging lithium-ion battery, Flexible electrode, Screen-printing, High capacity","lastPublishedDoi":"10.21203/rs.3.rs-6348014/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6348014/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eA flexible screen-printed graphite electrode was fabricated as an anode for developing fast-charging lithium-ion batteries with low tortuosity. A homogenous anode ink was prepared by mixing graphite as the active material, carbon black (C45) as the conductive additive, and polyvinylidene fluoride (PVDF) as the binder in N-Methyl-2-pyrrolidone (NMP) solvent. The ink was deposited on a flexible copper foil via a stainless-steel screen consisting of an array of pores, that act as secondary pore networks (SPNs), using the screen-printing process. Lithium-ion battery half-cells were assembled using the printed graphite anode, lithium metal foil as the counter electrode, and 1.2M lithium hexafluorophosphate (LiPF\u003csub\u003e6\u003c/sub\u003e) in ethyl carbonate: ethyl methyl carbonate (EC: EMC\u0026thinsp;=\u0026thinsp;3:7) as the electrolyte. The effect of SPNs on the cell performance was investigated by performing formation, rate and cycling tests on the assembled cells, at different C-rates. It was observed that the cells consisting of SPNs with a pore size of 100 \u0026micro;m and edge-to-edge distance of 100 \u0026micro;m between the pores exhibited significantly higher specific capacities of 168 and 129 mAh/g when compared to reference cells without SPNs, which had capacities of 120 and 85 mAh/g, at high C-rates of 4C and 6C, respectively. The cells with SPNs also demonstrated excellent cycling performance with ~\u0026thinsp;95% capacity retention after 100 cycles at 2C.\u003c/p\u003e","manuscriptTitle":"Investigating the effect of screen-printed structured graphite electrodes with low tortuosity for high-capacity and fast-charging lithium-ion batteries","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-11 19:44:21","doi":"10.21203/rs.3.rs-6348014/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-22T04:59:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-15T18:08:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-15T15:07:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"263425939189988210656939647347397992213","date":"2025-04-11T07:18:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"137069842202061863240594644850338572385","date":"2025-04-10T04:41:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"297655558969597979879525997386520617862","date":"2025-04-08T06:16:18+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-08T06:09:11+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-08T05:49:43+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-04-07T09:54:14+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-04T06:36:58+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-04-04T06:35:50+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f8d41e22-13f7-490f-bed5-07246c85c4b2","owner":[],"postedDate":"April 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":46945484,"name":"Physical sciences/Chemistry/Electrochemistry/Batteries"},{"id":46945485,"name":"Physical sciences/Energy science and technology/Energy storage/Batteries"}],"tags":[],"updatedAt":"2025-08-11T15:59:06+00:00","versionOfRecord":{"articleIdentity":"rs-6348014","link":"https://doi.org/10.1038/s41598-025-12909-4","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-08-06 15:57:01","publishedOnDateReadable":"August 6th, 2025"},"versionCreatedAt":"2025-04-11 19:44:21","video":"","vorDoi":"10.1038/s41598-025-12909-4","vorDoiUrl":"https://doi.org/10.1038/s41598-025-12909-4","workflowStages":[]},"version":"v1","identity":"rs-6348014","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6348014","identity":"rs-6348014","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}