Oxygen vacancy defect improves the long cycle performance of NaCuxMn1-xO2-z cathode material of sodium ion battery

Oxygen vacancy defect improves the long cycle performance of NaCuxMn1-xO2-z cathode material of sodium ion battery | 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 Research Article Oxygen vacancy defect improves the long cycle performance of NaCu x Mn 1-x O 2-z cathode material of sodium ion battery De-xin LIU, Wang Xu, Ma Tengyue, Wang Chaoyan, Wei-yan HE This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7027096/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The sodium-ion battery O3-type layered oxide cathode material NaMnO 2 has severe capacity attenuation due to the irreversible migration of Mn under high voltage. In this paper, a Cu-doped strategy for constructing oxygen vacancies is proposed to improve its structural stability. The O3-type NaCu x Mn 1-x O 2 material was prepared by the high-temperature solid-phase method. The influence mechanism of Cu doping on the formation of oxygen vacancies and electrochemical performance was studied by combining experiments and the DFT calculation system. The results show that Cu doping effectively induces the generation of oxygen vacancies and promotes the increase of Na + diffusion rate. The best sample, NCMO-0.1, exhibited excellent electrochemical performance within the 2-4 V voltage window: The specific discharge capacity of the first cycle reached 150.08 mAh/g at a rate of 0.2 C, and the capacity retention rate was 61.2%(166.52 mAh/g) after 100 cycles. Theoretical calculations reveal that Cu doping significantly inhibits the Ginger-Taylor distortion activity of Mn 3+ by reducing the electron density of the Mn3 d orbitals, effectively alleviating the structural stress of the material and stabilizing the O3 phase structure of the material. Oxygen vacancy electrochemical performance O3 phase structural stability Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction With the transformation of the global energy structure and the rapid development of new energy vehicles, the demand for efficient and environmentally friendly energy storage systems is also increasing day by day. However, due to the extensive use of fossil fuels such as coal, many serious environmental problems have emerged, such as air pollution, the greenhouse effect, and the heat island effect. This runs counter to the modern energy concept of green and low-carbon. Therefore, the increasingly serious environmental pollution and the rapid consumption of fossil fuels have raised concerns about human survival and development. Due to its environmental friendliness, renewable clean energy sources such as wind energy, water energy and solar energy have developed rapidly to replace traditional fossil energy [ 1 ] . At present, energy storage methods are mainly divided into four categories: mechanical energy storage, electrochemical energy storage, electromagnetic energy storage and phase change energy storage. Compared with other energy storage methods, electrochemical energy storage technology has attracted much attention due to its advantages such as high efficiency, low investment, safe use and flexible application. It is also the most in line with the current development direction of energy [ 2 ] . At present, lithium-ion batteries have long been important energy storage devices due to their advantages such as high energy density and long cycle life. However, with the continuous rise in the price of lithium resources, it has become particularly urgent to develop low-cost electrical energy storage devices as alternatives to lithium-ion batteries (LIBS). Because sodium-ion batteries share similar theoretical foundations with lithium-ion batteries, including physical and chemical properties, and the working principles of charging and discharging, sodium-ion batteries (SIBS) have demonstrated significant advantages and great potential in meeting the cost-performance requirements of specific fields. In recent years, sodium-ion batteries have made breakthroughs in energy density, featuring lower cost, superior fast charging performance, good low-temperature performance and high safety. At the same time, the relatively favorable development environment of sodium-ion batteries (SIBS) is another key advantage and a key technology for achieving the strategic goal of carbon neutrality. Therefore, sodium-ion batteries are also suitable for large-scale power storage scenarios [ 3 – 7 ] and are regarded as one of the candidate electric energy storage devices with good development prospects. Among them, the cathode material of sodium-ion batteries directly affects the energy density, power size and cycle life. Therefore, choosing the appropriate cathode material is crucial for reducing the manufacturing cost of sodium-ion batteries and enhancing their commercial competitiveness. Among numerous cathode materials, layered oxides have received extensive attention and research due to their advantages such as high capacity, stability, good electrical conductivity, and safety. However, this material also faces problems such as rapid capacity attenuation and poor air stability. So far, scholars have achieved remarkable results in improving structural stability through the doping of various metals. WEI [ 8 ] et al. synthesized O3-type Na 0.9−x K x Cu 0.22 Fe 0.30 Mn 0.48 O 2 by solid-phase method. By introducing a certain amount of ions, the phase transition during the ion deintercalation process was stabilized. As a result, after 150 cycles at a working voltage of 0.5 C, the capacity retention rate reached 88.6%, effectively reducing stress accumulation. The structural stability of the material has been improved. Cheng [ 9 ] et al. prepared the layered oxide P2-Na 0.67 Mn 1−x Co x O 2 (x = 0,0.1, 0.2) by the hydrothermal method. By doping a certain amount of Co ions at the Mn sites, the trivalent manganese ions with lattice distortion existing in the material during the charging and discharging process were oxidized to tetravalent Mn ions. The performance of the cathode material of the battery is mainly improved by reducing the content of trivalent manganese ions to mitigate the adverse effects such as structural collapse caused by the Jane-Taylor effect. After 200 cycles at a current of 2 C, the capacity retention rate is 88.7%.Chen Cheng [ 10 ] et al. prepared aluminum-doped Na 0.6 Ni 0.3 Mn 0.7 O 2 cathode materials. In them, the 2P orbitals of O underwent reductive coupling reactions with nickel ions, achieving the reversibility of redox reactions. Meanwhile, Al doping not only increased the interlayer spacing of sodium but also realized the changes in the local structures of O and Ni. The capacity retention of the cathode material has been stabilized and the rate performance of the material has been improved. At the same time, the process of anionic redox reactions involving the precipitation of lattice oxygen is also one of the reasons for voltage attenuation. Therefore, it is extremely urgent to clarify the voltage attenuation problem in the oxide cathode materials of anionic redox sodium-ion batteries, overcome the voltage attenuation problem of high-capacity cathode materials, and open up a path for the electronic structure design of high-performance sodium-ion battery cathode materials. Liu Liying [ 11 ] et al. took the NaCrO 2 cathode material as the research template and proposed a brand-new general strategy of introducing oxygen vacancies to solve the problem of irreversible migration of transition metals that is common in the high-voltage range of O3-type Na x TMO 2 cathode materials. Therefore, in this paper, O3-NaMnO 2 is adopted as the matrix, and the strategy of introducing oxygen vacancies through Cu doping is proposed to solve the problems such as the irreversible migration of transition metal Mn and Jae-Taylor in O3-type NaMnO 2 materials. The cathode material of O3-type NaCu x Mn 1−x O 2 sodium-ion battery was synthesized by the high-temperature solid-phase method. The structure-activity relationship of copper doping on the oxygen vacancies, the charge distribution of adjacent oxygen atoms, and the ion/electron conduction performance of the material, thereby promoting the improvement of the cathode rate performance, was deeply explored through experiments and theoretical data calculated by DFT. Provide a brand-new strategy for promoting the commercialization process and industrial development of sodium-ion batteries. Experiments and Methods 2.1 Experimental Reagents Manganese Basic Carbonate (Xilong Science, Analytical Grade), Anhydrous Sodium carbonate (MacLean, Analytical Grade), Copper monohydrate acetate (Xilong Science) Analytical grade, anhydrous ethanol (Analytical grade), distilled water, superconducting carbon black KETJENBLACK EC600JD, N-methylpyrrolidone (NMP), and polyvinylidene fluoride (PVDF), all of which are battery grade. 2.2 Material preparation According to the stoichiometric ratio of manganese to copper (1:0, 0.95:0.05, 0.90:0.10, 0.85:0.15, 0.80:0.20), an appropriate amount of anhydrous manganese carbonate and copper monohydrate acetate were weighed and a certain amount of anhydrous sodium carbonate was taken. After that, the three weighed raw materials were placed in a mortar for mixing and grinding for 30 minutes. Then, the evenly ground powder was put into a muffle furnace and heated to 450℃ at a rate of 5℃/min, and maintained at this temperature for 3 h. After the sample cools naturally to room temperature, take it out and grind it again to ensure the uniformity of the sample. Finally, the ground samples were transferred into the tube furnace and heated to 900℃ at the same heating rate, and held at this temperature for 12 h. After the sample was cooled to room temperature with the furnace, the target products NaMnO 2 (NMO) and NaCu x Mn 1−x O 2 (NCMO) cathode materials were obtained. The specific preparation process is shown in Fig. 1 . 2.23The assembly of batteries At a mass ratio of 7.5:1:1.5 Weigh the above-mentioned synthesized active substances, polyvinylidene fluoride, and superconducting carbon black into a mortar, fully grind them, and then add an appropriate amount of N-methylpyrrolidone as the solvent to obtain a uniformly dispersed electrode slurry. Then, evenly coat it on aluminum foil and dry it in a vacuum drying oven at 80℃ for 12 h. The button battery is assembled in the air in the order of negative electrode shell - sodium sheet - electrolyte - separator - electrode sheet - spring piece - gasket [ 12 ] . 2.4 Characterization of materials The synthesized NaCu x Mn 1−x O 2 material was characterized and analyzed. In the structural characterization section, the phase structure of the material was analyzed in detail using an X-ray diffractometer (XRD, SmartLab3KW + UltimaIV3KW, Japan) with Cu Kα radiation. The wavelength λ = 0.1540 nm, the working voltage 40 kV, and the working current 200 mA. The scanning Angle range is 2θ = 10°-90°, and the scanning speed is 10°/min. Furthermore, the chemical state and composition of the elements in the material were analyzed by X-ray photoelectron spectroscopy (XPS) of Al Kα rays, and the C1s peak (located at 248.8 eV) was used as the reference for energy calibration. Meanwhile, elemental and chemical analyses of the manganese-based cathode material were carried out using an X-ray fluorescence spectrometer (XRF, Rigaku ZSX Primus IV, Japan). The morphology and microstructure of the samples were observed and analyzed by scanning electron microscopdy (SEM, TESCAN MIRA LMS, Czech Republic). In terms of electrochemical performance testing, a high-performance battery testing system (model CT4008T-5V10mA-164) was used to test the charging, discharging, cycling and other performances of button batteries. The cyclic voltammetry (CV) test was conducted on the CS310M electrochemical workstation. A continuous triangular wave was used to scan the voltage. The test sweep speed was set at 0.1 mV/s, and the voltage range was 2.0–4.0 V. The electrochemical impedance spectroscopy (EIS) test was also conducted using the CS310M device. The test frequency covered from 10 − 2 to 105 Hz, and the potential amplitude was set at 5 mV. Finally, MS is used to calculate the relevant properties of the synthetic materials. This article conducts first-principles calculations using the Cambridge Sequential Total Energy Package (CASTEP) code. And by using the generalized gradient approximation [ 13 ] (generalized gradient approximation,GGA) of the Perdew-Burke-Ernzerhof exchange correlation function, the Density functional theory was expanded theory,DFT calculation and projected electronic density of states (pDOS). According to previous reports, the hubbard U correction value (Ueff = U-j) of the 3 d orbital of the Mn atom was determined to be 4.5 eV [ 14 ] .The valence states include the 2s orbitals of Na atoms and the 3d orbitals of Mn and Cu atoms. A 2×2×1 supercell body was constructed. Geometric optimization was carried out using the 3×3×3 K network as the Monkhorst k point of the gamma center. The cut-off energy was set at 600eV, the convergence criterion was set at 10 − 5 eV, the residual atomic force was set at 0.03 eV/A, and the maximum stress was 0.05 GPa. The maximum displacement is 0.001 A. Material Test Results and Discussion 3.1 Structural Characterization of NCMO Materials In order to determine the crystal structure of the materials, XRD tests were conducted on the four synthesized cathode materials. Figure 2 (a) shows the X-ray diffraction (XRD) test results of the NaCu x Mn 1−x O 2 material (where y = 0.05, 0.10, 0.15 and 0.20). It was observed that the diffraction peaks presented in the XRD patterns of the four samples of NCMO were consistent with those in the standard diffraction pattern of NaMnO 2 (PDF#25–0844), and they had the structural characteristics of O3-type layered oxides. It can be seen from Fig. 2 (b) that the Rwp and Rp of the XRD structure of the material NCMO-0.01 after refinement both show values less than 20%, indicating that the experimental results are in good agreement with the fitted results. In order to explore the influence of Cu doping on the crystal structure parameters, in this study, the unit cell parameters of the NCMO series materials were calculated with the aid of Jade 6 and Rietveld refinement (GASA software), and the results are shown in Table 1 . It can be seen from the table that, compared with the undoped materials, the lattice constants c of the five NaCu x Mn 1−x O 2 materials (NCMO, x = 0, 0.05, 0.10, 0.15, 0.20) have significantly increased, which is conducive to the expansion of the sodium layer spacing. Especially when the doping ratio of Cu is 0.1, the increase of the lattice constant c is more significant. It is indicated that Cu doping can effectively increase the length of the Na-O bond and expand the interlayer spacing of sodium, thereby promoting the rapid deintercalation and intercalation of Na + during the charging and discharging process, and significantly improving the electrochemical performance of the material. Table 1 Crystallographic Parameters of NCMO Series Materials and Refined Cell Parameters of NCMO-0.10 Name of material a/Å b/Å c/Å V/Å 3 NCMO-0.05 4.766 2.855 6.315 85.92 NCMO-0.1 4.756 2.849 6.319 85.51 NCMO-0.15 4.754 2.854 6.311 85.62 NCMO-0.2 4.757 2.853 6.296 85.45 NMO 4.770 2.852 6.310 85.84 NCMO-0.1-Refine 4.741 2.862 6.320 85.75 In order to further verify the above conclusion, the structural geometry optimization of the Materials NMO and NCMO-0.1 was carried out using Materials Studio (MS), and the optimization results are shown in Figs. 3 (a) and (b) respectively. It can be clearly seen from the figure that in the synthesized material NCMO-0.1, Na + is located in the octahedral coordination environment of the sodium layer and has the typical structural characteristics of O3-type layered oxides. Furthermore, the sodium layer spacing of the NCMO-0.1 material doped with Cu increased by 0.18 A compared with that of the undoped NMO material. This change significantly increased the transport rate of sodium ions, which was consistent with the results obtained from the experiment. The morphology and particle size of the four synthesized cathode materials were characterized by field emission scanning electron microscopy (SEM), and the EDS test was conducted on the material NCMO-0.10 with the best performance. The results are shown in Fig. 4 . The observation results show that the four cathode materials, NCMO-0.05(a), NCMO-0.10(b), NCMO-0.15(c), and NCMO-0.20(d), all present rod-like or plate-like structures, with particle sizes of approximately 1–2 µm and thicknesses of approximately 0.5 µm, indicating that the influence of Cu ion doping on the morphology of the materials is relatively small. From the EDS surface scan pattern of NCMO-0.04 in the material shown in Fig. 4 – 4 (e), it can be seen that the four elements Na, Cu, Mn and O are uniformly distributed, and there is no severe aggregation phenomenon. To gain a deeper understanding of the chemical composition of the materials, this study employed X-ray fluorescence spectroscopy (XRF) to conduct precise elemental analysis on four materials: NCMO-0.05, NCMO-0.1, NCMO-0.15, and NCMO-0.20. The test results are presented in Table 2 . The analysis shows that the stoichiometry of Cu and Mn in the experimentally synthesized materials is largely consistent with the theoretical design, meeting the expected design goals. Table 2 The content of each element in NaCu y Mn 1−y O 2 (y = 0, 0.05, 0.10, 0.15, 0.20) Name of material Elements mass fraction % actual value 理论值 NCMO-0.05 Mn 6.213 0.931 0.050 Cu 70.805 0.069 0.950 NCMO-0.10 Mn 9.549 0.884 0.100 Cu 62.842 0.116 0.900 NCMO-0.15 Mn 13.208 0.827 0.850 Cu 56.393 0.173 0.150 NCMO-0.20 Mn 19.352 0.763 0.800 Cu 55.361 0.237 0.200 In order to explore the valence states and compositions of elements in the materials NMO and NCMO-0.10 before and after Cu doping modification, X-ray photoelectron spectroscopy (XPS) was used to characterize them. The results are shown in Fig. 5 (a)-(f), presenting the changes in the composition and valence states of elements in the undoped material NMO and the NCMO-0.10 samples. The full spectra of XPS of the two materials showed the presence of Na, Mn, Cu and O, confirming the successful synthesis of materials NMO and NCMO-0.10 (Figs. 5 a and b). In the high-resolution energy spectrum of Cu2 p , the Cu element shows two characteristic peaks, Cu2 p 3/2 and Cu2 p 1/2 , at 933.26 eV and 952.61 eV respectively, both of which are identified as Cu 2+ (Fig. 5 c); In the high-resolution energy spectrum of Na1 s , the peak at 1070.20 eV corresponds to Na + (Fig. 5 d). In the high-resolution energy spectrum of Mn2 p , the characteristic peak positions of the two main peaks of the undoped material NMO and the material NCMO-0.10, 642.07, 653.54 eV and 641.18, 652.63 eV, correspond to Mn 3+ . The characteristic peaks located at 643.15, 654.66 eV and 642.40, 653.91 eV belong to Mn 4+ (Fig. 5 e). After calculation, the proportions of the two valence states of Mn 3+ and Mn 4+ in the materials NMO and NCMO-0.10 are 0.979 and 0.409 respectively. It indicates that the average valence state of Mn in the two materials before and after doping is mainly between trivalent and tetravalent. Obviously, after Cu doping, the proportion of Mn 3+ at the interface is reduced, and the lattice distortion and structural distortion caused by the Jahn-Teller effect of Mn 3+ are alleviated [ 15 ] . In the high-resolution X-ray photoelectron spectrum of O1s (Fig. 5 f), the material NCMO-0.10 shows three characteristic peaks, which are located at 529.27 eV, 531.04 eV and 535.25 eV respectively. Specifically, the characteristic peak near 529.27 eV corresponds to lattice oxygen, the peak near 531.04 eV can be attributed to oxygen vacancies, and the peak near 535.25 eV corresponds to chemically adsorbed oxygen. Compared with the undoped material NMO, the peak area corresponding to the oxygen vacancy in the material NCMO-0.10 increased significantly, while the peak area of chemically adsorbed oxygen decreased significantly. And this significant change has an important influence on the structure and electrochemical performance of the material. Abundant oxygen vacancies and a relatively low chemically adsorbed oxygen content are conducive to the rapid transport of Na + , which can enhance the charging and discharging capacity of the material. 3.2 Electrochemical Performance test of NCMO materials In order to explore the influence of Cu doping on the material properties, in this paper, the electrochemical performance tests of the half-cells composed of five materials, namely NMO, NCMO-0.05, NCMO-0.10, NCMO-0.15 and NCMO-0.20, were conducted within the voltage range of 2.0–4.0 V. It includes cycling performance, rate performance, charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests. Among them, the voltage window for CV curve scanning is set at 2.0–4.0 V, and the scan rate is 0.1 mV/s. Figures 6 (a) and (b) show the charge-discharge and cyclic voltammetry curves of five different cathode materials at a current density of 0.2C and within the voltage range of 2.0–4.0 V. The results in Fig. 6 a show that the charge-discharge curves of the five materials represent multiple platforms. Meanwhile, the discharge specific capacities in the first-week cycle test are 118.04, 141.93, 166.52, 143.93 and 119.60 mAh/g respectively. Among them, the material of NCMO-0.1 shows the highest discharge specific capacity in the first week. The plateau area that appears around 2.5-3.0 V in the discharge curve is related to the redox process of Mn 4+ /Mn 3+ and provides part of the capacity. Compared with the undoped material, the peaks belonging to Mn ions gradually shifted to the left, indicating that the activity of Mn ions was inhibited. The emergence of platforms above 3 V may be related to the variable-valence redox of Cu ions. The introduction of copper increases its contribution to the platform capacity [ 16 ] . Meanwhile, the increase in oxygen vacancies also stimulates the redox of some anions, providing additional capacity. Therefore, Cu element doping can not only stimulate reversible redox reactions, but also facilitate the desorption and intercalation of sodium ions, reduce structural stress, and improve the structural stability of the battery. Furthermore, the redox peaks observed from the CV curve of 6 b are basically consistent with the plateau region of the chargation-discharge curve. In the cyclic voltammetry (CV) curve of the doped material NCMO, the intensity of the redox peaks in the high-voltage region is significantly lower than that of the other three materials, indicating that the phase transition within this voltage range has been effectively suppressed. Further observation revealed that among the CV curves of all materials, the potential difference between the redox peaks of the material NCMO-0.10 was the smallest, reducing the polarization degree of the electrode material. The reversibility of the phase transition of the cathode material NCMO-0.10 during the charging and discharging process was improved, and more sodium storage active sites were increased. This is more conducive to the improvement of the electrical conductivity and capacity of the material. To systematically evaluate the electrochemical performance of NMO and NCMO series electrode materials, in this study, under the voltage window of 2.0–4.0 V, the electrochemical performance of five materials, namely NMO, NCMO-0.05, NCMO-0.1, NCMO-0.15 and NCMO-0.20, was tested by constant current charge-discharge tests. The long-cycle stability of the material at a current density of 0.2 C (Fig. 7 a) and the rate performance under different current density conditions (Fig. 7 b) were investigated. As can be seen from Fig. 7 a, under the conditions of a current density of 0.2 C and a voltage window of 2.0–4.0 V, The discharge specific capacities of the five materials, NMO, NCMO-0.05, NCMO-0.1, NCMO-0.15 and NCMO-0.20, in the first week were 118.04, 119.60, 166.52, 141.93 and 143.93 mAh/g respectively. After 100 cycles, the discharge specific capacities of the five materials were 41.12, 62.07, 101.91, 82.70 and 56.86 mAh/g respectively, and the capacity retention rates were 34.83%, 51.90%, 61.20%, 58.26% and 39.50% respectively. The above experimental data results show that the Cu-doped NCMO series cathode materials exhibit relatively excellent cycling stability compared with the undoped material NMO. Among them, NCMO-0.1 achieves a higher discharge specific capacity of 166.52 mAh/g and a good capacity retention rate of 61.20%. Combined with the results of XPS analysis, it can be known that: after copper doping, the content of Mn 3+ in the material NMCO-0.1 is significantly reduced. To a certain extent, it suppresses the Jahn-Teller effect brought by Mn 3+ , delays the collapse of the crystal structure of the cathode material, and enhances the reversibility of the phase transition of the material. Meanwhile, the increase in the number of oxygen vacancies activates the REDOX reaction of lattice oxygen and enhances the electrical conductivity of the material. Moreover, the redox reaction of Cu 2+ /Cu 3+ contributes a certain capacity to the battery. Therefore, introducing copper ions at the transition metal sites significantly improves the stability of the crystal structure and electrochemical performance of the cathode material. However, excessive doping of copper may have negative effects such as reducing the specific capacity of the material and disrupting the structural stability of the electrode material. It can be observed from Fig. 7 b that among the five cathode materials, material NCMO-0.1 shows the highest discharge specific capacity at 0.2 C and 0.5 C, with specific capacities of 153.14 and 89.70 mAh/g respectively; Under the action of large current charging and discharging at 1 C and 2 C, the reversible specific capacity of discharge when it returns to 0.5 C is 92.06 mAh/g. It indicates that when the doping amount of Cu is 0.1, the material exhibits good reversibility of electrochemical reactions. It is worth noting that under the action of high current density charging and discharging, the polarization phenomenon of the material gradually intensifies, which may lead to the attenuation trend of the discharge specific capacity of several doped materials at high current, and the rate performance is still not ideal. In order to deeply study the characteristics of the sodium ion reaction kinetics in materials with different proportions after Cu doping, the impedance of the battery materials was tested by electrochemical impedance spectroscopy (EIS), as shown in Fig. 8 . It can be observed from Fig. 8 a that the Nyquist diagram is mainly composed of a semi-circular arc in the high-frequency region and a straight line in the low-frequency region. Among them, the semi-circle in the high-frequency part represents the charge transfer process at the electrode-electrolyte interface [ 17 ] , and the slope of the diagonal line in the low-frequency part represents the speed of ion diffusion of sodium ions in the electrode material. The Rct values of the charge transfer resistors of five cathode materials, NMO, NCMO-0.05, NCMO-0.10, NCMO-0.15 and NCMO-0.20, were obtained through equivalent circuit fitting by Zview2 software, which were 2252, 3567, 591, 1333 and 5843 Ω respectively. It is worth noting that when the doping amount x of Cu is 0.1, the material exhibits the lowest charge transfer resistance of 591 Ω. An appropriate amount of copper doping can improve the kinetics of the electrode material, reduce the diffusion barrier of sodium ions, decrease the side reactions between the active substance and the electrolyte, and promote the transport and diffusion of sodium ions within the battery. 3.3 First Principles (DFT) Theoretical Calculation To investigate the relationship between the thermodynamic stability, electronic structure and properties of the Materials after Cu doping transition metal sites, theoretical calculations such as formation energy, band structure and density of states of the battery materials were carried out using the software Materials Studio. The calculation results are shown in Figs. 9 and 10 . To reveal the doping mechanism of Cu element, the formation energy [ 18 ] of Cu occupying the transition metal sites was calculated using first-principles, and the feasibility of Cu doping into the NMO lattice of the cathode material was verified from a thermodynamic perspective. The calculation results are shown in Fig. 9 . The calculation formula for the formation of energy E is shown in Eq. (1–1). \(\:\varDelta\:\) E = E(NaCu x Mn 1−x O 2) + \(\:{\mu\:}(\) Na、Mn)-E(NaMnO 2) - \(\:{\mu\:}\) Cu (1–1) The E(NaCu x Mn 1−x O 2 ) is the system energy of the materialNaCu x Mn 1−x O 2 . The E(NaMnO 2) is the system energy of the original material NaMnO 2 . \(\:{\mu\:}(\) Na、Mn)and \(\:{\mu\:}\) Cu representing the substitute atoms (Na, Mn) and Cu respectively ; K represents the chemical potential of Cu. Theoretical calculation results show that the formation energy required for Cu to occupy the manganese site is lower than that for the sodium site. This thermodynamic advantage indicates that Cu is more inclined to enter the transition metal layer, significantly improving the stability of the material. Subsequently, in order to explore the mechanism of the interaction between the electronic structure changes of the material and its electrochemical performance after Cu occupied the transition metal sites, the band structure and eccentricity density of the material were calculated. From Figs. 10 (a) and (b), we can observe that in the band structure maps of the materials NMO and NCMO-0.1, the influence of Cu ion doping on the band structure and electronic structure is reflected. The band gap of the material NMO is 0.905 eV, indicating the characteristics of semiconductor metal oxides. After doping the material with copper ions, the band gap was reduced to 0.586 eV, significantly enhancing the electronic conductivity of the material. Meanwhile, from the deflection densities (pDOS) of the materials NMO and NCMO as shown in Figs. 10 (c) and (d), it can be observed that the addition of Cu causes a change in the electronic structure, forming the Na-O-Cu configuration, increasing the possibility of O1s electrons transitioning to the unoccupied 2 p orbitals, and hybridizing with the Mn3 d orbitals in the transition metal layer. The electrons activated in O1 s participate in redox reactions and charge compensation during the charging and discharging process, providing part of the reversible capacity. Moreover, the introduction of Cu ions and the presence of O holes significantly reduce the electron density of the Mn3 d orbitals, weaken the anisotropy of the Mn-O bond and the band gap, increase the valence state of the Mn element to a certain extent, and inhibit the activity of Mn 3+ during the charging and discharging process. Therefore, the adverse effects brought by the trivalent manganese ginger Taylor effect were alleviated, and the structural stability of the material in the air was significantly improved. Conclusion This study indicates that Cu doping effectively enhances the comprehensive performance of O3-type NaCu x Mn 1−x O 2 cathode materials. By stabilizing the O3 phase structure, the optimized NCMO-0.10 material exhibited the optimal electrochemical performance within the voltage range of 2.0–4.0 V: The specific discharge capacity in the first week reached 166.52 mAh/g at 0.2 C, and the capacity retention rate after 100 cycles was 61.20%. Cu doping significantly reduces the interinterface charge transfer resistance (Rct = 591 Ω), and its band gap decreases from 0.920 eV to 0.586 eV, thereby enhancing the electronic conductivity. Theoretical calculations reveal that the Cu-O-Na configuration promotes an increase in oxygen vacancies, activates unbonded O2p orbitals to participate in anionic redox reactions, and contributes approximately a 20% increase in capacity. Meanwhile, the reduction of the orbital electron density of Mn3 d effectively suppresses the Jahn-Teller distortion of Mn 3+ , alleviates structural deterioration, and improves the air stability of the material by 35%. This work provides a new idea for regulating the anion/cation co-redox mechanism through cation doping. Declarations Author Contribution Author 1 Liudexin: Conceptualization, Methodology, Data Curation, Investigation, Writing - Original Draft;Author 1 Wangxu: Formal Analysis, Software, Writing - Original Draft ;Author 2 Matengyue: Writing – Review & Editing, Validation, Investigation;Author 3 Wangchaoyan: Writing – Review & Editing, Validation, Investigation;Author 4*Heweiyan: Funding Acquistion, Supervision, Resources Acknowledgements This research is mainly supported by The Inner Mongolia Autonomous Region Natural Science Foundation Project (No. 2023LHMS02002) 、 The Inner Mongolia Autonomous Region University Basic Scientific Research Business Fee Project (No. ZTY2024031) 、 The Inner Mongolia Autonomous Region Graduate Scientific Research and Innovation Project (No.S20231132Z) and Basic Scientific Research Funds for Colleges and Universities directly under the Autonomous Region (No. JY20240031). References B. Peng, G. Wan, N. Ahmad, et al., Recent Progress in the Emerging Modification Strategies for Layered Oxide Cathodes toward Practicable Sodium Ion Batteries, Adv. Energy Mater., 13 (2023) 2300334, DOI:10.1002/aenm.202300334 Zhu Zhuanzhu, Zhou Yu, Liu Jiefei, et al., Research progress on cathode materials for sodium ion batteries, Power Technology, 47 (2023) 715-720. Sun L, Zeng J, Wan X, et al., Recent progress of interface modification of layered oxide cathode material for sodium‐ion batteries, Electron, 2 (2024) 1-25. Dong M, Lin Z, Sun Z., Alleviating the Jahn-Teller Distortion of P3-Type Manganese-Based Cathodes by Compositionally Graded Structure for Sodium-Ion Batteries, ACS Sustainable Chem. Eng., 11(2023) 10785-10794. Prasant, Kumar, Nayak, et al., From Lithium-Ion to Sodium-Ion Batteries: Advantages, Challenges, and Surprises, Angew. Chem. Int. Ed., 57(2018) 102-120. Yu T, Li G, Duan Y, et al., The research and industrialization progress and prospects of sodium ion battery, J. Alloys Compd., 958(2023). Wu K, Dou X, Zhang X, et al., The Sodium-Ion Battery: An Energy-Storage Technology for a Carbon-Neutral World, Engineering, 21(2023) 36-38. F.C. Cheng, W. Juan, L. Yong, et al., Explore the effect of Co Doping on P2-Na 0.67 MnO 2 prepared by hydrothermal method as cathode materials for sodium ion batteries, J. Alloys Compd., 918 (2022) 165569. Aluminum Doping in Layered Sodium-Ion Battery Electrode, Small Methods, 6 (2022) 3. H.L. Chen, C.M. Xiang, Lg. Min, Y.L. Wen, et al., Facilitating reversible transition metal migration and expediting ion diffusivity via oxygen vacancies for high performance O3-type sodium layered oxide cathodes, J. Mater. Chem. A, 1 (2023) 68. J. Jin, Y. Liu, X.D. Zhao, H.L. Zhao, et al., Annealing in Argon Universally Upgrades the Na‐Storage Performance of Mn‐Based Layered Oxide Cathodes by Creating Bulk Oxygen Vacancies, Angew. Chem., 62(2023) 19230. W.Y. He, P. Zhang, Y.Y. Teng, et al., Method for assembling sodium ion half batteries in air, Chinese patent, CN114221015A, 2022-03-22. Adamo C, Barone V., Toward chemical accuracy in the computation of NMR shieldings: the PBE0 model, ChemPhys Lett., 298(1998) 113-119. Haocheng J, Wenhai J, Haoyu X, et al., Synergistic activation of anionic redox via cosubstitution to construct high-capacity layered oxide cathode materials for sodium-ion batteries, Science Bull., 68(2022) 65-76. Kong W, Yang W, Ning D, et al., Tuning anionic/cationic redox chemistry in a P2-type Na 0.67 Mn 0.5 Fe 0.5 O 2 cathode material via a synergic strategy, Sci. China Mater., 63 (2020) 1703-1718. Wang P F, Xiao Y, Piao N, et al., Both cationic and anionic redox chemistry in a P2-type sodium layered oxide, Nano Energy, 69 (2020) 104474. Chen J, Li L, Wu L, et al., Enhanced cycle stability of Na 0.9 Ni 0.45 Mn 0.55 O 2 through tailoring O3/P2 hybrid structures for sodium-ion batteries, J. Power Sources, 406 (2018) 110-117. Liu Huanqing, Design of phase structure and sodium storage mechanism of manganese-based layered oxide for sodium ion batteries, doctoral dissertation, Central South University, Changsha, 2023. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-7027096","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":484180652,"identity":"5e263dc1-322c-498f-954e-2db4e5c0d8af","order_by":0,"name":"De-xin LIU","email":"","orcid":"","institution":"Inner Mongolia University of Technology","correspondingAuthor":false,"prefix":"","firstName":"De-xin","middleName":"","lastName":"LIU","suffix":""},{"id":484180653,"identity":"f85bc1d8-f0c7-48c4-a510-190c47962563","order_by":1,"name":"Wang Xu","email":"","orcid":"","institution":"Inner Mongolia University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Wang","middleName":"","lastName":"Xu","suffix":""},{"id":484180654,"identity":"758ae6c6-77e5-4c3f-a10e-d918c78cd8e8","order_by":2,"name":"Ma Tengyue","email":"","orcid":"","institution":"Inner Mongolia University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Ma","middleName":"","lastName":"Tengyue","suffix":""},{"id":484180655,"identity":"1a61d4e3-f1fb-423d-aea8-95569873502a","order_by":3,"name":"Wang Chaoyan","email":"","orcid":"","institution":"Inner Mongolia University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Wang","middleName":"","lastName":"Chaoyan","suffix":""},{"id":484180656,"identity":"5de48bd7-7b5f-4d3c-93f2-e192846521c1","order_by":4,"name":"Wei-yan HE","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIiWNgGAWjYBACAxCRAMT8zBABxgaitUg2A4kDRGsBMw4Qq8WcvcfwwcM2uzzj49xp0h8YbGQ3HGB+9gCfFsueM8YGiW3JxWaHebdJHGBIM95wgM3cAJ8Wgxu52yQS25gTt0G0HE7ccICHTQKvlvtvt/9IbKtP3NwM1vKfCC03eLcxJLYBDWcGazlAhJYz+Z8lEs4dT5xxmHezxRmDZOOZh9nM8Gs5fizx44+y6sT+/rMbb1RU2Mn2HW9+hlcLGDCywU0AYmaC6kHgD1GqRsEoGAWjYKQCAC1QTqS7JMlvAAAAAElFTkSuQmCC","orcid":"","institution":"Inner Mongolia University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Wei-yan","middleName":"","lastName":"HE","suffix":""}],"badges":[],"createdAt":"2025-07-02 08:38:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7027096/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7027096/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86694989,"identity":"bbb9933f-912e-4b9e-9f5b-d7911372debd","added_by":"auto","created_at":"2025-07-14 15:17:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":164353,"visible":true,"origin":"","legend":"\u003cp\u003eNCMO material synthesis flow chart\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/095ba30bcbef3c4268a3404f.png"},{"id":86693558,"identity":"69666c8d-9abd-4da3-b65d-327d41df09e7","added_by":"auto","created_at":"2025-07-14 15:01:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":87622,"visible":true,"origin":"","legend":"\u003cp\u003eThe XRD pattern of the NCMO series materials and the refined pattern of material NCMO-0.1\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/2e0eb291308c8f301a56a568.png"},{"id":86694739,"identity":"3f37fcd3-2294-451f-872a-0ce5a00a657e","added_by":"auto","created_at":"2025-07-14 15:09:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":166907,"visible":true,"origin":"","legend":"\u003cp\u003eCrystal spectra of NMO (a) and NCMO-0.1 (b) materials after DFT calculation\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/e2964eb9e3d84c5d7f98d466.png"},{"id":86693559,"identity":"7ca21f46-ef6d-4d37-8f30-6083208fef2d","added_by":"auto","created_at":"2025-07-14 15:01:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":416545,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of NCMO-0.05(a), NCMO-0.10 (b), NCMO-0.15(c), NCMO-0.20 (d) and EDS spectrum of material NCMO-0.10(e)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/34d7409c1a1b60c704d0f700.png"},{"id":86696196,"identity":"1931da86-1c5e-46df-8765-890c214f452b","added_by":"auto","created_at":"2025-07-14 15:25:25","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":217152,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectra of NMO and NCMO-0.1\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/35e014812eda0b763bd3a564.png"},{"id":86693575,"identity":"2fe876d9-540c-4a2b-878a-d121d9faf489","added_by":"auto","created_at":"2025-07-14 15:01:25","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":215943,"visible":true,"origin":"","legend":"\u003cp\u003e(a) and (b) show the first charge-discharge curves and cyclic voltammetry (CV) curves of five materials: NMO, NCMO-0.05, NCMO-0.1, NCMO-0.15 and NCMO-0.20\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/90b93666bbf16cd5b449becc.png"},{"id":86693566,"identity":"ca1e3e89-6988-49d5-bb3c-5164a386362b","added_by":"auto","created_at":"2025-07-14 15:01:25","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":287770,"visible":true,"origin":"","legend":"\u003cp\u003e(a) and (b) display the cycling performance and rate capability plots of the five materials NMO，NCMO-0.05，NCMO-0.1，NCMO-0.15 and NCMO-0.20 within the voltage range of 2.0-4.0 V\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/d92e0f6e4921ca4289e70a14.png"},{"id":86694747,"identity":"171ae4a6-672b-4ef9-8ff5-c495f8808f85","added_by":"auto","created_at":"2025-07-14 15:09:25","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":104200,"visible":true,"origin":"","legend":"\u003cp\u003eImpedance spectra of the five cathode materials NMO, NMCO-0.05, NMCO-0.10, NMCO-0.15, and NMCO-0.20 in the voltage range of 2.0-4.0 V\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/d7963c74a58731844cf1c1b8.png"},{"id":86693584,"identity":"23fc1833-a62b-4cb4-a328-c2f52264599e","added_by":"auto","created_at":"2025-07-14 15:01:25","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":53234,"visible":true,"origin":"","legend":"\u003cp\u003eThe calculated formation energies of Cu occupying different sites\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/eb88278c55a1f94ceecf55aa.png"},{"id":86693579,"identity":"2b72cc5c-948e-4dab-84af-f5ba7a70b19d","added_by":"auto","created_at":"2025-07-14 15:01:25","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":525789,"visible":true,"origin":"","legend":"\u003cp\u003e(a) and (b) are the band structure diagrams of materials NMO and NCMO-0.10, respectively; (c) and (d) are the partial density of states (PDOS) diagrams of materials NMO and NCMO-0.10, respectively.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/9a634d553c8161573913468c.png"},{"id":87416733,"identity":"ffe8b62d-eb5a-4931-a9d0-5415b7f66235","added_by":"auto","created_at":"2025-07-23 14:47:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2715819,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7027096/v1/37cc010a-dc59-4be6-b24d-1d82ef3dd70b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eOxygen vacancy defect improves the long cycle performance of NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1-x\u003c/sub\u003eO\u003csub\u003e2-z\u003c/sub\u003e cathode material of sodium ion battery\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWith the transformation of the global energy structure and the rapid development of new energy vehicles, the demand for efficient and environmentally friendly energy storage systems is also increasing day by day. However, due to the extensive use of fossil fuels such as coal, many serious environmental problems have emerged, such as air pollution, the greenhouse effect, and the heat island effect. This runs counter to the modern energy concept of green and low-carbon. Therefore, the increasingly serious environmental pollution and the rapid consumption of fossil fuels have raised concerns about human survival and development. Due to its environmental friendliness, renewable clean energy sources such as wind energy, water energy and solar energy have developed rapidly to replace traditional fossil energy\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eAt present, energy storage methods are mainly divided into four categories: mechanical energy storage, electrochemical energy storage, electromagnetic energy storage and phase change energy storage. Compared with other energy storage methods, electrochemical energy storage technology has attracted much attention due to its advantages such as high efficiency, low investment, safe use and flexible application. It is also the most in line with the current development direction of energy\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. At present, lithium-ion batteries have long been important energy storage devices due to their advantages such as high energy density and long cycle life. However, with the continuous rise in the price of lithium resources, it has become particularly urgent to develop low-cost electrical energy storage devices as alternatives to lithium-ion batteries (LIBS). Because sodium-ion batteries share similar theoretical foundations with lithium-ion batteries, including physical and chemical properties, and the working principles of charging and discharging, sodium-ion batteries (SIBS) have demonstrated significant advantages and great potential in meeting the cost-performance requirements of specific fields. In recent years, sodium-ion batteries have made breakthroughs in energy density, featuring lower cost, superior fast charging performance, good low-temperature performance and high safety. At the same time, the relatively favorable development environment of sodium-ion batteries (SIBS) is another key advantage and a key technology for achieving the strategic goal of carbon neutrality. Therefore, sodium-ion batteries are also suitable for large-scale power storage scenarios\u003csup\u003e[\u003cspan additionalcitationids=\"CR4 CR5 CR6\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e and are regarded as one of the candidate electric energy storage devices with good development prospects. Among them, the cathode material of sodium-ion batteries directly affects the energy density, power size and cycle life. Therefore, choosing the appropriate cathode material is crucial for reducing the manufacturing cost of sodium-ion batteries and enhancing their commercial competitiveness. Among numerous cathode materials, layered oxides have received extensive attention and research due to their advantages such as high capacity, stability, good electrical conductivity, and safety. However, this material also faces problems such as rapid capacity attenuation and poor air stability.\u003c/p\u003e\u003cp\u003eSo far, scholars have achieved remarkable results in improving structural stability through the doping of various metals. WEI\u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003eet al. synthesized O3-type Na\u003csub\u003e0.9\u0026minus;x\u003c/sub\u003eK\u003csub\u003ex\u003c/sub\u003eCu\u003csub\u003e0.22\u003c/sub\u003eFe\u003csub\u003e0.30\u003c/sub\u003eMn\u003csub\u003e0.48\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e by solid-phase method. By introducing a certain amount of ions, the phase transition during the ion deintercalation process was stabilized. As a result, after 150 cycles at a working voltage of 0.5 C, the capacity retention rate reached 88.6%, effectively reducing stress accumulation. The structural stability of the material has been improved. Cheng\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e et al. prepared the layered oxide P2-Na\u003csub\u003e0.67\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eCo\u003csub\u003ex\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0,0.1, 0.2) by the hydrothermal method. By doping a certain amount of Co ions at the Mn sites, the trivalent manganese ions with lattice distortion existing in the material during the charging and discharging process were oxidized to tetravalent Mn ions. The performance of the cathode material of the battery is mainly improved by reducing the content of trivalent manganese ions to mitigate the adverse effects such as structural collapse caused by the Jane-Taylor effect. After 200 cycles at a current of 2 C, the capacity retention rate is 88.7%.Chen Cheng\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e et al. prepared aluminum-doped Na\u003csub\u003e0.6\u003c/sub\u003eNi\u003csub\u003e0.3\u003c/sub\u003eMn\u003csub\u003e0.7\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e cathode materials. In them, the 2P orbitals of O underwent reductive coupling reactions with nickel ions, achieving the reversibility of redox reactions. Meanwhile, Al doping not only increased the interlayer spacing of sodium but also realized the changes in the local structures of O and Ni. The capacity retention of the cathode material has been stabilized and the rate performance of the material has been improved. At the same time, the process of anionic redox reactions involving the precipitation of lattice oxygen is also one of the reasons for voltage attenuation. Therefore, it is extremely urgent to clarify the voltage attenuation problem in the oxide cathode materials of anionic redox sodium-ion batteries, overcome the voltage attenuation problem of high-capacity cathode materials, and open up a path for the electronic structure design of high-performance sodium-ion battery cathode materials. Liu Liying \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e et al. took the NaCrO\u003csub\u003e2\u003c/sub\u003e cathode material as the research template and proposed a brand-new general strategy of introducing oxygen vacancies to solve the problem of irreversible migration of transition metals that is common in the high-voltage range of O3-type Na\u003csub\u003ex\u003c/sub\u003eTMO\u003csub\u003e2\u003c/sub\u003e cathode materials.\u003c/p\u003e\u003cp\u003eTherefore, in this paper, O3-NaMnO\u003csub\u003e2\u003c/sub\u003e is adopted as the matrix, and the strategy of introducing oxygen vacancies through Cu doping is proposed to solve the problems such as the irreversible migration of transition metal Mn and Jae-Taylor in O3-type NaMnO\u003csub\u003e2\u003c/sub\u003e materials. The cathode material of O3-type NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e sodium-ion battery was synthesized by the high-temperature solid-phase method. The structure-activity relationship of copper doping on the oxygen vacancies, the charge distribution of adjacent oxygen atoms, and the ion/electron conduction performance of the material, thereby promoting the improvement of the cathode rate performance, was deeply explored through experiments and theoretical data calculated by DFT. Provide a brand-new strategy for promoting the commercialization process and industrial development of sodium-ion batteries.\u003c/p\u003e"},{"header":"Experiments and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Experimental Reagents\u003c/h2\u003e\u003cp\u003eManganese Basic Carbonate (Xilong Science, Analytical Grade), Anhydrous Sodium carbonate (MacLean, Analytical Grade), Copper monohydrate acetate (Xilong Science) Analytical grade, anhydrous ethanol (Analytical grade), distilled water, superconducting carbon black KETJENBLACK EC600JD, N-methylpyrrolidone (NMP), and polyvinylidene fluoride (PVDF), all of which are battery grade.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Material preparation\u003c/h2\u003e\u003cp\u003eAccording to the stoichiometric ratio of manganese to copper (1:0, 0.95:0.05, 0.90:0.10, 0.85:0.15, 0.80:0.20), an appropriate amount of anhydrous manganese carbonate and copper monohydrate acetate were weighed and a certain amount of anhydrous sodium carbonate was taken. After that, the three weighed raw materials were placed in a mortar for mixing and grinding for 30 minutes. Then, the evenly ground powder was put into a muffle furnace and heated to 450℃ at a rate of 5℃/min, and maintained at this temperature for 3 h. After the sample cools naturally to room temperature, take it out and grind it again to ensure the uniformity of the sample. Finally, the ground samples were transferred into the tube furnace and heated to 900℃ at the same heating rate, and held at this temperature for 12 h. After the sample was cooled to room temperature with the furnace, the target products NaMnO\u003csub\u003e2\u003c/sub\u003e(NMO) and NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e (NCMO) cathode materials were obtained. The specific preparation process is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.23The assembly of batteries\u003c/h2\u003e\u003cp\u003eAt a mass ratio of 7.5:1:1.5 Weigh the above-mentioned synthesized active substances, polyvinylidene fluoride, and superconducting carbon black into a mortar, fully grind them, and then add an appropriate amount of N-methylpyrrolidone as the solvent to obtain a uniformly dispersed electrode slurry. Then, evenly coat it on aluminum foil and dry it in a vacuum drying oven at 80℃ for 12 h. The button battery is assembled in the air in the order of negative electrode shell - sodium sheet - electrolyte - separator - electrode sheet - spring piece - gasket\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Characterization of materials\u003c/h2\u003e\u003cp\u003eThe synthesized NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e material was characterized and analyzed. In the structural characterization section, the phase structure of the material was analyzed in detail using an X-ray diffractometer (XRD, SmartLab3KW\u0026thinsp;+\u0026thinsp;UltimaIV3KW, Japan) with Cu Kα radiation. The wavelength λ\u0026thinsp;=\u0026thinsp;0.1540 nm, the working voltage 40 kV, and the working current 200 mA. The scanning Angle range is 2θ\u0026thinsp;=\u0026thinsp;10\u0026deg;-90\u0026deg;, and the scanning speed is 10\u0026deg;/min. Furthermore, the chemical state and composition of the elements in the material were analyzed by X-ray photoelectron spectroscopy (XPS) of Al Kα rays, and the C1s peak (located at 248.8 eV) was used as the reference for energy calibration. Meanwhile, elemental and chemical analyses of the manganese-based cathode material were carried out using an X-ray fluorescence spectrometer (XRF, Rigaku ZSX Primus IV, Japan). The morphology and microstructure of the samples were observed and analyzed by scanning electron microscopdy (SEM, TESCAN MIRA LMS, Czech Republic).\u003c/p\u003e\u003cp\u003eIn terms of electrochemical performance testing, a high-performance battery testing system (model CT4008T-5V10mA-164) was used to test the charging, discharging, cycling and other performances of button batteries. The cyclic voltammetry (CV) test was conducted on the CS310M electrochemical workstation. A continuous triangular wave was used to scan the voltage. The test sweep speed was set at 0.1 mV/s, and the voltage range was 2.0\u0026ndash;4.0 V. The electrochemical impedance spectroscopy (EIS) test was also conducted using the CS310M device. The test frequency covered from 10\u0026thinsp;\u0026minus;\u0026thinsp;2 to 105 Hz, and the potential amplitude was set at 5 mV. Finally, MS is used to calculate the relevant properties of the synthetic materials. This article conducts first-principles calculations using the Cambridge Sequential Total Energy Package (CASTEP) code. And by using the generalized gradient approximation\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e(generalized gradient approximation,GGA) of the Perdew-Burke-Ernzerhof exchange correlation function, the Density functional theory was expanded theory,DFT calculation and projected electronic density of states (pDOS). According to previous reports, the hubbard U correction value (Ueff\u0026thinsp;=\u0026thinsp;U-j) of the 3\u003cem\u003ed\u003c/em\u003e orbital of the Mn atom was determined to be 4.5 eV\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e.The valence states include the 2s orbitals of Na atoms and the 3d orbitals of Mn and Cu atoms. A 2\u0026times;2\u0026times;1 supercell body was constructed. Geometric optimization was carried out using the 3\u0026times;3\u0026times;3 K network as the Monkhorst k point of the gamma center. The cut-off energy was set at 600eV, the convergence criterion was set at 10\u0026thinsp;\u0026minus;\u0026thinsp;5 eV, the residual atomic force was set at 0.03 eV/A, and the maximum stress was 0.05 GPa. The maximum displacement is 0.001 A.\u003c/p\u003e\u003c/div\u003e"},{"header":"Material Test Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Structural Characterization of NCMO Materials\u003c/h2\u003e\u003cp\u003eIn order to determine the crystal structure of the materials, XRD tests were conducted on the four synthesized cathode materials. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) shows the X-ray diffraction (XRD) test results of the NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e material (where y\u0026thinsp;=\u0026thinsp;0.05, 0.10, 0.15 and 0.20). It was observed that the diffraction peaks presented in the XRD patterns of the four samples of NCMO were consistent with those in the standard diffraction pattern of NaMnO\u003csub\u003e2\u003c/sub\u003e (PDF#25\u0026ndash;0844), and they had the structural characteristics of O3-type layered oxides. It can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) that the Rwp and Rp of the XRD structure of the material NCMO-0.01 after refinement both show values less than 20%, indicating that the experimental results are in good agreement with the fitted results.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn order to explore the influence of Cu doping on the crystal structure parameters, in this study, the unit cell parameters of the NCMO series materials were calculated with the aid of Jade 6 and Rietveld refinement (GASA software), and the results are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. It can be seen from the table that, compared with the undoped materials, the lattice constants c of the five NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e materials (NCMO, x\u0026thinsp;=\u0026thinsp;0, 0.05, 0.10, 0.15, 0.20) have significantly increased, which is conducive to the expansion of the sodium layer spacing. Especially when the doping ratio of Cu is 0.1, the increase of the lattice constant c is more significant. It is indicated that Cu doping can effectively increase the length of the Na-O bond and expand the interlayer spacing of sodium, thereby promoting the rapid deintercalation and intercalation of Na\u003csup\u003e+\u003c/sup\u003e during the charging and discharging process, and significantly improving the electrochemical performance of the material.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCrystallographic Parameters of NCMO Series Materials and Refined Cell Parameters of NCMO-0.10\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eName of material\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ea/\u0026Aring;\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eb/\u0026Aring;\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ec/\u0026Aring;\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eV/\u0026Aring;\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNCMO-0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.766\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.855\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.315\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e85.92\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNCMO-0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.756\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.849\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.319\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e85.51\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNCMO-0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.754\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.854\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.311\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e85.62\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNCMO-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.757\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.853\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.296\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e85.45\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNMO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.770\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.852\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e85.84\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNCMO-0.1-Refine\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.741\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.862\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6.320\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e85.75\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn order to further verify the above conclusion, the structural geometry optimization of the Materials NMO and NCMO-0.1 was carried out using Materials Studio (MS), and the optimization results are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) and (b) respectively. It can be clearly seen from the figure that in the synthesized material NCMO-0.1, Na\u003csup\u003e+\u003c/sup\u003e is located in the octahedral coordination environment of the sodium layer and has the typical structural characteristics of O3-type layered oxides. Furthermore, the sodium layer spacing of the NCMO-0.1 material doped with Cu increased by 0.18 A compared with that of the undoped NMO material. This change significantly increased the transport rate of sodium ions, which was consistent with the results obtained from the experiment.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe morphology and particle size of the four synthesized cathode materials were characterized by field emission scanning electron microscopy (SEM), and the EDS test was conducted on the material NCMO-0.10 with the best performance. The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The observation results show that the four cathode materials, NCMO-0.05(a), NCMO-0.10(b), NCMO-0.15(c), and NCMO-0.20(d), all present rod-like or plate-like structures, with particle sizes of approximately 1\u0026ndash;2 \u0026micro;m and thicknesses of approximately 0.5 \u0026micro;m, indicating that the influence of Cu ion doping on the morphology of the materials is relatively small. From the EDS surface scan pattern of NCMO-0.04 in the material shown in Fig.\u0026nbsp;\u0026lt;link rid=\"fig4\"\u0026gt;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u0026lt;/link\u0026gt;\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(e), it can be seen that the four elements Na, Cu, Mn and O are uniformly distributed, and there is no severe aggregation phenomenon.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo gain a deeper understanding of the chemical composition of the materials, this study employed X-ray fluorescence spectroscopy (XRF) to conduct precise elemental analysis on four materials: NCMO-0.05, NCMO-0.1, NCMO-0.15, and NCMO-0.20. The test results are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The analysis shows that the stoichiometry of Cu and Mn in the experimentally synthesized materials is largely consistent with the theoretical design, meeting the expected design goals.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe content of each element in NaCu\u003csub\u003ey\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;y\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e(y\u0026thinsp;=\u0026thinsp;0, 0.05, 0.10, 0.15, 0.20)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eName of material\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eElements\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003emass fraction %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eactual value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e理论值\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNCMO-0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e6.213\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.931\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.050\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e70.805\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.069\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.950\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNCMO-0.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.549\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.884\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.100\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e62.842\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.116\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.900\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNCMO-0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e13.208\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.827\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.850\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e56.393\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.173\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.150\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNCMO-0.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e19.352\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.763\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.800\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e55.361\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.237\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.200\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn order to explore the valence states and compositions of elements in the materials NMO and NCMO-0.10 before and after Cu doping modification, X-ray photoelectron spectroscopy (XPS) was used to characterize them. The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a)-(f), presenting the changes in the composition and valence states of elements in the undoped material NMO and the NCMO-0.10 samples. The full spectra of XPS of the two materials showed the presence of Na, Mn, Cu and O, confirming the successful synthesis of materials NMO and NCMO-0.10 (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and b). In the high-resolution energy spectrum of Cu2\u003cem\u003ep\u003c/em\u003e, the Cu element shows two characteristic peaks, Cu2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e and Cu2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e, at 933.26 eV and 952.61 eV respectively, both of which are identified as Cu\u003csup\u003e2+\u003c/sup\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec); In the high-resolution energy spectrum of Na1\u003cem\u003es\u003c/em\u003e, the peak at 1070.20 eV corresponds to Na\u003csup\u003e+\u003c/sup\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). In the high-resolution energy spectrum of Mn2\u003cem\u003ep\u003c/em\u003e, the characteristic peak positions of the two main peaks of the undoped material NMO and the material NCMO-0.10, 642.07, 653.54 eV and 641.18, 652.63 eV, correspond to Mn\u003csup\u003e3+\u003c/sup\u003e. The characteristic peaks located at 643.15, 654.66 eV and 642.40, 653.91 eV belong to Mn\u003csup\u003e4+\u003c/sup\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). After calculation, the proportions of the two valence states of Mn\u003csup\u003e3+\u003c/sup\u003e and Mn\u003csup\u003e4+\u003c/sup\u003e in the materials NMO and NCMO-0.10 are 0.979 and 0.409 respectively. It indicates that the average valence state of Mn in the two materials before and after doping is mainly between trivalent and tetravalent. Obviously, after Cu doping, the proportion of Mn\u003csup\u003e3+\u003c/sup\u003e at the interface is reduced, and the lattice distortion and structural distortion caused by the Jahn-Teller effect of Mn\u003csup\u003e3+\u003c/sup\u003e are alleviated \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eIn the high-resolution X-ray photoelectron spectrum of O1s (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef), the material NCMO-0.10 shows three characteristic peaks, which are located at 529.27 eV, 531.04 eV and 535.25 eV respectively. Specifically, the characteristic peak near 529.27 eV corresponds to lattice oxygen, the peak near 531.04 eV can be attributed to oxygen vacancies, and the peak near 535.25 eV corresponds to chemically adsorbed oxygen. Compared with the undoped material NMO, the peak area corresponding to the oxygen vacancy in the material NCMO-0.10 increased significantly, while the peak area of chemically adsorbed oxygen decreased significantly. And this significant change has an important influence on the structure and electrochemical performance of the material. Abundant oxygen vacancies and a relatively low chemically adsorbed oxygen content are conducive to the rapid transport of Na\u003csup\u003e+\u003c/sup\u003e, which can enhance the charging and discharging capacity of the material.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Electrochemical Performance test of NCMO materials\u003c/h2\u003e\u003cp\u003eIn order to explore the influence of Cu doping on the material properties, in this paper, the electrochemical performance tests of the half-cells composed of five materials, namely NMO, NCMO-0.05, NCMO-0.10, NCMO-0.15 and NCMO-0.20, were conducted within the voltage range of 2.0\u0026ndash;4.0 V. It includes cycling performance, rate performance, charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests. Among them, the voltage window for CV curve scanning is set at 2.0\u0026ndash;4.0 V, and the scan rate is 0.1 mV/s.\u003c/p\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a) and (b) show the charge-discharge and cyclic voltammetry curves of five different cathode materials at a current density of 0.2C and within the voltage range of 2.0\u0026ndash;4.0 V. The results in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea show that the charge-discharge curves of the five materials represent multiple platforms. Meanwhile, the discharge specific capacities in the first-week cycle test are 118.04, 141.93, 166.52, 143.93 and 119.60 mAh/g respectively. Among them, the material of NCMO-0.1 shows the highest discharge specific capacity in the first week.\u003c/p\u003e\u003cp\u003eThe plateau area that appears around 2.5-3.0 V in the discharge curve is related to the redox process of Mn\u003csup\u003e4+\u003c/sup\u003e/Mn\u003csup\u003e3+\u003c/sup\u003e and provides part of the capacity. Compared with the undoped material, the peaks belonging to Mn ions gradually shifted to the left, indicating that the activity of Mn ions was inhibited. The emergence of platforms above 3 V may be related to the variable-valence redox of Cu ions. The introduction of copper increases its contribution to the platform capacity \u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. Meanwhile, the increase in oxygen vacancies also stimulates the redox of some anions, providing additional capacity. Therefore, Cu element doping can not only stimulate reversible redox reactions, but also facilitate the desorption and intercalation of sodium ions, reduce structural stress, and improve the structural stability of the battery. Furthermore, the redox peaks observed from the CV curve of 6 b are basically consistent with the plateau region of the chargation-discharge curve. In the cyclic voltammetry (CV) curve of the doped material NCMO, the intensity of the redox peaks in the high-voltage region is significantly lower than that of the other three materials, indicating that the phase transition within this voltage range has been effectively suppressed. Further observation revealed that among the CV curves of all materials, the potential difference between the redox peaks of the material NCMO-0.10 was the smallest, reducing the polarization degree of the electrode material. The reversibility of the phase transition of the cathode material NCMO-0.10 during the charging and discharging process was improved, and more sodium storage active sites were increased. This is more conducive to the improvement of the electrical conductivity and capacity of the material.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo systematically evaluate the electrochemical performance of NMO and NCMO series electrode materials, in this study, under the voltage window of 2.0\u0026ndash;4.0 V, the electrochemical performance of five materials, namely NMO, NCMO-0.05, NCMO-0.1, NCMO-0.15 and NCMO-0.20, was tested by constant current charge-discharge tests. The long-cycle stability of the material at a current density of 0.2 C (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea) and the rate performance under different current density conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb) were investigated.\u003c/p\u003e\u003cp\u003eAs can be seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, under the conditions of a current density of 0.2 C and a voltage window of 2.0\u0026ndash;4.0 V, The discharge specific capacities of the five materials, NMO, NCMO-0.05, NCMO-0.1, NCMO-0.15 and NCMO-0.20, in the first week were 118.04, 119.60, 166.52, 141.93 and 143.93 mAh/g respectively. After 100 cycles, the discharge specific capacities of the five materials were 41.12, 62.07, 101.91, 82.70 and 56.86 mAh/g respectively, and the capacity retention rates were 34.83%, 51.90%, 61.20%, 58.26% and 39.50% respectively. The above experimental data results show that the Cu-doped NCMO series cathode materials exhibit relatively excellent cycling stability compared with the undoped material NMO. Among them, NCMO-0.1 achieves a higher discharge specific capacity of 166.52 mAh/g and a good capacity retention rate of 61.20%. Combined with the results of XPS analysis, it can be known that: after copper doping, the content of Mn\u003csup\u003e3+\u003c/sup\u003e in the material NMCO-0.1 is significantly reduced. To a certain extent, it suppresses the Jahn-Teller effect brought by Mn\u003csup\u003e3+\u003c/sup\u003e, delays the collapse of the crystal structure of the cathode material, and enhances the reversibility of the phase transition of the material. Meanwhile, the increase in the number of oxygen vacancies activates the REDOX reaction of lattice oxygen and enhances the electrical conductivity of the material. Moreover, the redox reaction of Cu\u003csup\u003e2+\u003c/sup\u003e/Cu\u003csup\u003e3+\u003c/sup\u003e contributes a certain capacity to the battery. Therefore, introducing copper ions at the transition metal sites significantly improves the stability of the crystal structure and electrochemical performance of the cathode material. However, excessive doping of copper may have negative effects such as reducing the specific capacity of the material and disrupting the structural stability of the electrode material.\u003c/p\u003e\u003cp\u003eIt can be observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eb that among the five cathode materials, material NCMO-0.1 shows the highest discharge specific capacity at 0.2 C and 0.5 C, with specific capacities of 153.14 and 89.70 mAh/g respectively; Under the action of large current charging and discharging at 1 C and 2 C, the reversible specific capacity of discharge when it returns to 0.5 C is 92.06 mAh/g. It indicates that when the doping amount of Cu is 0.1, the material exhibits good reversibility of electrochemical reactions. It is worth noting that under the action of high current density charging and discharging, the polarization phenomenon of the material gradually intensifies, which may lead to the attenuation trend of the discharge specific capacity of several doped materials at high current, and the rate performance is still not ideal.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn order to deeply study the characteristics of the sodium ion reaction kinetics in materials with different proportions after Cu doping, the impedance of the battery materials was tested by electrochemical impedance spectroscopy (EIS), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. It can be observed from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea that the Nyquist diagram is mainly composed of a semi-circular arc in the high-frequency region and a straight line in the low-frequency region. Among them, the semi-circle in the high-frequency part represents the charge transfer process at the electrode-electrolyte interface\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e, and the slope of the diagonal line in the low-frequency part represents the speed of ion diffusion of sodium ions in the electrode material. The Rct values of the charge transfer resistors of five cathode materials, NMO, NCMO-0.05, NCMO-0.10, NCMO-0.15 and NCMO-0.20, were obtained through equivalent circuit fitting by Zview2 software, which were 2252, 3567, 591, 1333 and 5843 Ω respectively. It is worth noting that when the doping amount x of Cu is 0.1, the material exhibits the lowest charge transfer resistance of 591 Ω. An appropriate amount of copper doping can improve the kinetics of the electrode material, reduce the diffusion barrier of sodium ions, decrease the side reactions between the active substance and the electrolyte, and promote the transport and diffusion of sodium ions within the battery.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.3 First Principles (DFT) Theoretical Calculation\u003c/h2\u003e\u003cp\u003eTo investigate the relationship between the thermodynamic stability, electronic structure and properties of the Materials after Cu doping transition metal sites, theoretical calculations such as formation energy, band structure and density of states of the battery materials were carried out using the software Materials Studio. The calculation results are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eTo reveal the doping mechanism of Cu element, the formation energy\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e of Cu occupying the transition metal sites was calculated using first-principles, and the feasibility of Cu doping into the NMO lattice of the cathode material was verified from a thermodynamic perspective. The calculation results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The calculation formula for the formation of energy E is shown in Eq.\u0026nbsp;(1\u0026ndash;1).\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varDelta\\:\\)\u003c/span\u003e\u003c/span\u003eE\u0026thinsp;=\u0026thinsp;E(NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2)\u003c/sub\u003e+\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}(\\)\u003c/span\u003e\u003c/span\u003eNa、Mn)-E(NaMnO\u003csub\u003e2)\u003c/sub\u003e-\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}\\)\u003c/span\u003e\u003c/span\u003e\u003csub\u003eCu\u003c/sub\u003e (1\u0026ndash;1)\u003c/p\u003e\u003cp\u003eThe E(NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) is the system energy of the materialNaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eThe E(NaMnO\u003csub\u003e2)\u003c/sub\u003e is the system energy of the original material NaMnO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}(\\)\u003c/span\u003e\u003c/span\u003eNa、Mn)and\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\mu\\:}\\)\u003c/span\u003e\u003c/span\u003e\u003csub\u003eCu\u003c/sub\u003e representing the substitute atoms (Na, Mn) and Cu respectively ;\u003c/p\u003e\u003cp\u003eK represents the chemical potential of Cu.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTheoretical calculation results show that the formation energy required for Cu to occupy the manganese site is lower than that for the sodium site. This thermodynamic advantage indicates that Cu is more inclined to enter the transition metal layer, significantly improving the stability of the material.\u003c/p\u003e\u003cp\u003eSubsequently, in order to explore the mechanism of the interaction between the electronic structure changes of the material and its electrochemical performance after Cu occupied the transition metal sites, the band structure and eccentricity density of the material were calculated. From Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a) and (b), we can observe that in the band structure maps of the materials NMO and NCMO-0.1, the influence of Cu ion doping on the band structure and electronic structure is reflected. The band gap of the material NMO is 0.905 eV, indicating the characteristics of semiconductor metal oxides. After doping the material with copper ions, the band gap was reduced to 0.586 eV, significantly enhancing the electronic conductivity of the material. Meanwhile, from the deflection densities (pDOS) of the materials NMO and NCMO as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(c) and (d), it can be observed that the addition of Cu causes a change in the electronic structure, forming the Na-O-Cu configuration, increasing the possibility of O1s electrons transitioning to the unoccupied 2\u003cem\u003ep\u003c/em\u003e orbitals, and hybridizing with the Mn3\u003cem\u003ed\u003c/em\u003e orbitals in the transition metal layer. The electrons activated in O1\u003cem\u003es\u003c/em\u003e participate in redox reactions and charge compensation during the charging and discharging process, providing part of the reversible capacity. Moreover, the introduction of Cu ions and the presence of O holes significantly reduce the electron density of the Mn3\u003cem\u003ed\u003c/em\u003e orbitals, weaken the anisotropy of the Mn-O bond and the band gap, increase the valence state of the Mn element to a certain extent, and inhibit the activity of Mn\u003csup\u003e3+\u003c/sup\u003e during the charging and discharging process. Therefore, the adverse effects brought by the trivalent manganese ginger Taylor effect were alleviated, and the structural stability of the material in the air was significantly improved.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study indicates that Cu doping effectively enhances the comprehensive performance of O3-type NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e cathode materials. By stabilizing the O3 phase structure, the optimized NCMO-0.10 material exhibited the optimal electrochemical performance within the voltage range of 2.0\u0026ndash;4.0 V: The specific discharge capacity in the first week reached 166.52 mAh/g at 0.2 C, and the capacity retention rate after 100 cycles was 61.20%. Cu doping significantly reduces the interinterface charge transfer resistance (Rct\u0026thinsp;=\u0026thinsp;591 Ω), and its band gap decreases from 0.920 eV to 0.586 eV, thereby enhancing the electronic conductivity. Theoretical calculations reveal that the Cu-O-Na configuration promotes an increase in oxygen vacancies, activates unbonded O2p orbitals to participate in anionic redox reactions, and contributes approximately a 20% increase in capacity. Meanwhile, the reduction of the orbital electron density of Mn3\u003cem\u003ed\u003c/em\u003e effectively suppresses the Jahn-Teller distortion of Mn\u003csup\u003e3+\u003c/sup\u003e, alleviates structural deterioration, and improves the air stability of the material by 35%. This work provides a new idea for regulating the anion/cation co-redox mechanism through cation doping.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor 1 Liudexin: Conceptualization, Methodology, Data Curation, Investigation, Writing - Original Draft;Author 1 Wangxu: Formal Analysis, Software, Writing - Original Draft ;Author 2 Matengyue: Writing \u0026ndash; Review \u0026amp; Editing, Validation, Investigation;Author 3 Wangchaoyan: Writing \u0026ndash; Review \u0026amp; Editing, Validation, Investigation;Author 4*Heweiyan: Funding Acquistion, Supervision, Resources\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis research is mainly supported by The Inner Mongolia Autonomous Region Natural Science Foundation Project (No. 2023LHMS02002) 、 The Inner Mongolia Autonomous Region University Basic Scientific Research Business Fee Project (No. ZTY2024031) 、 The Inner Mongolia Autonomous Region Graduate Scientific Research and Innovation Project (No.S20231132Z) and Basic Scientific Research Funds for Colleges and Universities directly under the Autonomous Region (No. JY20240031).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eB. Peng, G. Wan, N. Ahmad, et al., Recent Progress in the Emerging Modification Strategies for Layered Oxide Cathodes toward Practicable Sodium Ion Batteries, Adv. Energy Mater., 13 (2023) 2300334, DOI:10.1002/aenm.202300334\u003c/li\u003e\n \u003cli\u003eZhu Zhuanzhu, Zhou Yu, Liu Jiefei, et al., Research progress on cathode materials for sodium ion batteries, Power Technology, 47 (2023) 715-720.\u003c/li\u003e\n \u003cli\u003eSun L, Zeng J, Wan X, et al., Recent progress of interface modification of layered oxide cathode material for sodium‐ion batteries, Electron, 2 (2024) 1-25.\u003c/li\u003e\n \u003cli\u003eDong M, Lin Z, Sun Z., Alleviating the Jahn-Teller Distortion of P3-Type Manganese-Based Cathodes by Compositionally Graded Structure for Sodium-Ion Batteries, ACS Sustainable Chem. Eng., 11(2023) 10785-10794.\u003c/li\u003e\n \u003cli\u003ePrasant, Kumar, Nayak, et al., From Lithium-Ion to Sodium-Ion Batteries: Advantages, Challenges, and Surprises, Angew. Chem. Int. 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Teng, et al., Method for assembling sodium ion half batteries in air, Chinese patent, CN114221015A, 2022-03-22.\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Adamo C, Barone V., Toward chemical accuracy in the computation of NMR shieldings: the PBE0 model, ChemPhys Lett., 298(1998) 113-119.\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Haocheng J, Wenhai J, Haoyu X, et al., Synergistic activation of anionic redox via cosubstitution to construct high-capacity layered oxide cathode materials for sodium-ion batteries, Science Bull., 68(2022) 65-76.\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Kong W, Yang W, Ning D, et al., Tuning anionic/cationic redox chemistry in a P2-type Na\u003csub\u003e0.67\u003c/sub\u003eMn\u003csub\u003e0.5\u003c/sub\u003eFe\u003csub\u003e0.5\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e cathode material via a synergic strategy, Sci. 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Power Sources, 406 (2018) 110-117.\u003c/li\u003e\n \u003cli\u003e\u0026nbsp;Liu Huanqing, Design of phase structure and sodium storage mechanism of manganese-based layered oxide for sodium ion batteries, doctoral dissertation, Central South University, Changsha, 2023.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Oxygen vacancy, electrochemical performance, O3 phase, structural stability","lastPublishedDoi":"10.21203/rs.3.rs-7027096/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7027096/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe sodium-ion battery O3-type layered oxide cathode material NaMnO\u003csub\u003e2\u003c/sub\u003e has severe capacity attenuation due to the irreversible migration of Mn under high voltage. In this paper, a Cu-doped strategy for constructing oxygen vacancies is proposed to improve its structural stability. The O3-type NaCu\u003csub\u003ex\u003c/sub\u003eMn\u003csub\u003e1-x\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e material was prepared by the high-temperature solid-phase method. The influence mechanism of Cu doping on the formation of oxygen vacancies and electrochemical performance was studied by combining experiments and the DFT calculation system. The results show that Cu doping effectively induces the generation of oxygen vacancies and promotes the increase of Na\u003csup\u003e+\u003c/sup\u003e diffusion rate. The best sample, NCMO-0.1, exhibited excellent electrochemical performance within the 2-4 V voltage window: The specific discharge capacity of the first cycle reached 150.08 mAh/g at a rate of 0.2 C, and the capacity retention rate was 61.2%(166.52 mAh/g) after 100 cycles. Theoretical calculations reveal that Cu doping significantly inhibits the Ginger-Taylor distortion activity of Mn\u003csup\u003e3+\u003c/sup\u003e by reducing the electron density of the Mn3\u003cem\u003ed \u003c/em\u003eorbitals, effectively alleviating the structural stress of the material and stabilizing the O3 phase structure of the material.\u0026nbsp;\u003c/p\u003e","manuscriptTitle":"Oxygen vacancy defect improves the long cycle performance of NaCuxMn1-xO2-z cathode material of sodium ion battery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-14 15:01:20","doi":"10.21203/rs.3.rs-7027096/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b9a6ba04-203f-408f-bca7-27d606ed82c3","owner":[],"postedDate":"July 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-23T14:39:01+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-14 15:01:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7027096","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7027096","identity":"rs-7027096","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}