Enhancement of the electrochemical performance of LiNi0.5Mn1.5O4 cathode materials for Li-ion battery by Mo-Fco-doping

Enhancement of the electrochemical performance of LiNi0.5Mn1.5O4 cathode materials for Li-ion battery by Mo-Fco-doping | 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 Enhancement of the electrochemical performance of LiNi 0.5 Mn 1.5 O 4 cathode materials for Li-ion battery by Mo-Fco-doping Yuling Weng, Hailang L. Zhang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3457578/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract The pristine LiNi 0.5 Mn 1.5 O 4 (LNMO) and Mo-F co-doped LiNi 0.5 Mn 1.5 O 4 spinel materials were prepared via a rheological phase method. The four samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). Compared with the pristine LNMO sample, Mo-F co-doped LNMO materials could increase the lattice parameters, reduce particle sizes, increase Mn 3+ contents, and significantly improve the electrochemical performances of LNMO. The doped material exhibited optimum electrochemical properties when the Mo and F doping amounts are 1% and 3% ,respectively, denoted as Mo/F-2. The discharge capacity retention of Mo/F-2 is 95.6%, which is higher than the pristine sample (87.7%) after 100 cycles at 1C and room temperature. Furthermore, the discharge-specific capacity of the Mo/F-2 sample reaches 113.4 mAh g − 1 at 5C, while the pristine sample reaches only 61.9 mAh g − 1 . After CV and EIS analysis, it was found that the Mo-F co-doped LNMO materials had better Li + diffusion kinetics than the pristine LNMO sample. Thus, Mo-F co-doping is considered an effective modification method for LNMO cathode material. Li-ion battery LiNi0.5Mn1.5O4 Mo6+ and F− co-doping disordered phase electrochemical performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Nowadays, energy shortage and environmental pollution problems are increasingly prominent, and the need to explore new environment friendly energy is imminent. In this context, people vigorously seek and develop sustainable and renewable energy, and reusable batteries have become the main trend of energy development. Among many energy storage devices, lithium-ion battery (LIB) stands out with its advantages of high energy density, long cycle life, high rate performance, and good safety, and is considered to be a new large-scale power source for electric vehicles (EV) and hybrid electric vehicles (HEV) [ 1 ]. In addition, the cost of positive electrode materials accounts for 30% of the entire battery cost [ 2 ], and the reduction of the cost of positive electrode materials directly determines the reduction of the battery cost, so the research and development of high energy density positive electrode materials are very important. Among the lithium-ion cathode materials, the cobalt-free cathode material LiNi 0.5 Mn 1.5 O 4 (LNMO) is one of the promising cathode materials due to its high voltage plateau (4.7V vs Li + /Li), superior specific theoretical capacity (147 mAh g − 1 ), high energy density (650 Whk g − 1 ), low cost and less environmental impact. It is now being actively considered for use in the manufacture of all-solid-state batteries such as 5 V lithium metal batteries [ 3 – 6 ]. It has been reported that LNMO has two space groups which are the Fd3m space group of Ni/Mn-disordered face-centered cubic and the P4 3 32 space group of Ni/Mn-ordered sample cubic [ 6 ]. When calcined below 700°C, the ordered structure could be synthesized, and when calcined at a higher temperature, the structure changes from ordered structure to disordered structure. The process of structural transformation is often accompanied by oxygen deficiency, the formation of Li x Ni 1−x O rock-salt type impurities, and the generation of Mn 3+ [ 7 – 8 ]. This structural transition is usually reversible. P4 3 32 space group can increase by using synthesis processes under oxygen or post-annealing in air below 700°C, and Mn 3+ can be oxidized to Mn 4+ [ 9 ]. The ordered P4 3 32 phase and the disordered Fd3m phase generally exist together in LNMO, and the electrochemical performance of LNMO composed of different phases is also different [ 10 ]. However, the Fd3m phase has higher ionic and electronic diffusion coefficients than the P4 3 32 phase which also leads to better electrochemical properties of the disordered structure, Therefore, the disordered phase lithium nickel-manganate is more inclined to be synthesized [ 11 – 13 ]. However, disordered structures are often accompanied by problems such as the formation of impurity phases and the dissolution of Mn 3+ [ 14 , 15 ], which affects its electrochemical performance. In addition, the higher voltage will aggravate the decomposition of electrolytes, side reactions between the electrolyte and battery active material, and the formation of thick SEI film, which results in difficulties in the intercalation and deintercalation of lithium-ions [ 16 ]. These issues limit the further application and commercialization of LNMO [ 17 ]. To solve these issues, it is well known that elemental doping is an effective modifying method to enhance the electrochemical performances of LNMO. According to researches, elemental doping mainly includes cation doping( Al 3+ [ 18 ], Nb 5+ [ 19 ], Ti 4+ [ 20 ], La 3+ [ 21 ], Sr 2+ [ 22 ], Si 4+ [ 23 ], etc.), anion doping (Cl − [ 24 ], F − [ 25 ], S 2− [ 26 ], etc.), and multi-ion doping (Cr-F [ 27 ], Y-Ti [ 28 ], etc.). The multi-ion doped cathode materials usually have superior electrochemical properties with the synergistic of different elements [ 29 ]. Zeng et al. found that the doping of Mo 6+ in to LNMO could favor Li + diffusion and increase electronic conductivity [ 30 ]. A very small amount of doping of Mo 6+ was shown to improve the electrochemical performance of LNMO, including its rate and cycling performance and the Mo-doped material showed superior electrochemical performance when the doping amount is 1%. The F − ion is usually substituted for O 2− to inhibit the dissolution of Mn 3+ , to inhibit the side reactions between the electrolyte and the active material, to reduce the resistance, and to prevent the corrosion of HF in the electrolyte [ 25 , 31 ]. So it is our hope and speculation that the Mo 6+ and F − co-doping could improve the electrochemical performance of LNMO in a great deal. In this work, we prepared a series of samples with varying F content but fixed Mo content (x = 0.01) to investigate the synergistic effect of Mo 6+ and F − on the electrochemical performance of LNMO. Experimental section Synthesis and characterization of materials The undoped and doped LiNi 0.5 Mn 1.5 O 4 samples were prepared by the rheological phase method. The materials were prepared according to the element molar ratio (Ni 0.5 Mn 1.5 ): Mo = 1: 0.01, and O: F = 4-x: x (x = 0, 0.01, 0.03, 0.05). According to the element molar ratio to weigh Ni(CH 3 COO) 2 ·4H 2 O (AR, 99%), Mn(CH 3 COO) 2 ·4H 2 O (Sinopharm Chemical Reagent Co., AR, 99%), CH 3 COOLi (Sinopharm Chemical Reagent Co., AR, 99%), NH 4 F (AR, 99%) by exceeding 5%, and (NH 4 ) 6 Mo 7 O 24 ·4H 2 O (Sinopharm Chemical Reagent Co., AR, 99%). Mixed and ground the above raw materials thoroughly. An appropriate amount of distilled water/ethanol solution was added to form the paste, and an appropriate amount of ammonia (inopharm Chemical Reagent Co.,AR, 99%) was added to form a brown paste. Dried at 120°C for 12 h, pre-calcined at 500°C for 6h in an air atmosphere, and further calcined at 850°C for 12 h. The undoped and doped LiNi 0.5 Mn 1.5 O 4 samples are referred to as Pristine, Mo/F-1, Mo/F-2, and Mo/F-3, respectively. The samples were characterized by X-ray diffraction (XRD, Bruker D8 Advance) with Cu Kα radiation at a scan rate of 4° min − 1 in the 2θ range of 10–90°. Fourier transform infrared spectrometer (FT-IR, Thermo Fisher iS50, USA) was used to distinguish between the ordered and disordered phases. Scanning electron microscopy (SEM, S-4800, Hitachi, Japan) and energy dispersive spectrometer (EDS) were used to characterize the morphologies and elemental distribution. The surface chemical states were tested by X-ray photoelectron spectroscopy (XPS, Thermo K-alpha). Electrochemical measurement The button cells (CR-2032) were assembled to study the electrochemical performances of cathode materials. The active material (80 wt%), acetylene black (12 wt%), and polyvinylidene fluoride (PVDF, 8 wt%) dissolved in NMP solvent were mixed by enough stirring to obtain a slurry which was coated on aluminum foil with a Doctor blade technique. Dried the slurry in a vacuum oven at 80°C for 12 hours. Then, the foil is punched into a round electrode with a diameter of 14 mm. The CR2032 coin cells were assembled in an argon-filled glove box (SUPER 1220/750, made in Shanghai, China), using lithium metal as the counter electrode, Celgard 2325 as the separator, and 1 M LiPF 6 in EC: DMC: EMC (v: v: v = 1:1:1) solution as the electrolyte. To evaluate the electrochemical performances of the prepared samples, The constant current charge-discharge cycle test was carried out by using the LAND battery test system (CT2001A, Wuhan in China) at 25°C. Cells were tested at different current densities (1C = 147 mAh g − 1 ) in the voltage range of 3.5–4.95 V. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were carried out at an electrochemical workstation (IM6, Zahner, Germany) within the voltage range of 3.5–5.1 V. CV tests were conducted at the scan rate of 0.1 mV s − 1 . EIS tests were performed in the frequency range of 0.01–100 kHz and amplitude of 5 mV. Result and discussion 3.1. Morphology and structural analysis Figure 1 a exhibits the XRD patterns of pristine LNMO and LiNi 0.4975 Mn 1.4925 Mo 0.01 O 4−x F x (x = 0.01, 0.03, 0.05) samples. The diffraction peaks of all samples match the patterns of standard PDF card No. 80-2162, and the sharp diffraction peaks indicate good crystallinity of the materials, which infers that the low dose of Mo-F co-doping will not change the basic structure of the material. The absence of the (220) diffraction peak indicates that the transition metal ions do not occupy position 8a [ 32 ]. Located at 2θ = 37.6° and 43.7° are the weak peaks of the Li x Ni 1−x O impurity phase. With the preparation of the Fd3m structure of the LNMO sample at a high synthesis temperature, the oxygen deficiency formed, and the nickel departed from the spinel phase to form the rock salt impurities. Such a reaction was proposed [ 8 ]: LiNi 0.5 Mn 1.5 O 4 ↔αLi x Ni 1−x O + βLiNi 0.5−x Mn 1.5+x + γO 2 . (1) The impurity phase can decrease the content of the active material and reduce the specific capacity of the material, but there is no obvious significant negative effect on the cycling performance of the product [ 33 , 34 ]. The Rietveld refinement profiles of pristine, Mo/F-1, Mo/F-2, and Mo/F-3 are shown in Fig. 1 b-e. The lattice parameters obtained from Rietveld refinement patterns for all samples are shown in Table 1 . Compared with the bare LNMO, the lattice parameters of the Mo-F doped samples have a little increase. This can be attributed to an increase in the interlayer distance as Mo 6+ is doped [ 35 ]. Furthermore, it also can be attributed to the increase in the content of Mn 3+ in the material due to the doping of F − and Mo 6+ . The larger ion radius (0.58 Å for low and 0.65 Å for high spin manganese) of Mn 3+ compared with Mn 4+ (0.53 Å) makes the lattice parameters of the material expand, which is more conducive to the transport of Li + [ 30 , 36 ]. Table 1 Lattice parameters of all samples Samples Lattice parameter Inter R wp /% α /Å V /Å 3 d (111) / Å Pristine 8.17823 546.988 4.7217 3.47 Mo/F-1 8.17852 547.047 4.7219 3.77 Mo/F-2 8.18216 547.778 4.7240 3.33 Mo/F-3 8.18707 548.765 4.7268 3.57 LNMO can be divided into ordered P4 3 32 and disordered Fd3m phases due to the different order of Ni/Mn cations in the spinel structure. Because the scattering factors of Ni and Mn are very similar, XRD is hard to identify the two space groups accurately[ 37 ]. FT-IR spectroscopy can be used to analyze the degree of ordering of samples. It is reported that the P4 3 32 space group of LNMO material has 8 infrared absorption bands, while the Fd-3m space group has only 5 bands between 400 cm − 1 and 700 cm − 1 [ 38 ]. As shown in Fig. 1 f, five infrared absorption peaks can be seen at 621, 581, 555, 505, and 469 cm − 1 . Among them, the absorption peaks at 621 cm − 1 and 555 cm − 1 were related to the vibration of Mn-O, while the absorption peaks at 581 cm − 1 and 505 cm − 1 were related to the vibration of Ni-O. The intensity ratio of Mn-O at 621 cm − 1 and Ni-O at 581 cm − 1 ( I (621) / I (581) ) can be used qualitatively to assess the percentage of ordering in spinel [ 39 ]. The intensity of 621 cm − 1 is higher than the peak intensity at 581 cm − 1 for all samples, indicating that all samples are predominantly disordered Fd3m phases. The I (621) / I (581) ratios of the pristine, Mo/F-1, Mo/F-2, and Mo/F-3 samples were 1.073, 1.175, 1.188, and 1.196, respectively, so the Mo-F co-doped samples show a higher degree of disorder than the pristine LNMO. Compared with the ordered P4 3 32 phase, the disordered Fd3m phase has better rate capability [ 40 ]. The morphologies of the four materials were characterized by SEM, as shown in Fig. 2 a-d. After the doping of Mo 6+ and F − , the LNMO morphology changed from a truncated octahedral morphology to a standard octahedral structure. The (111) facet is conducive to the formation of SEI films, which makes the (111) facet more stable than (100) and (110) facets, The doped LNMO materials with the dominant (111) surfaces exhibit a superior cycle life compared to pristine LNMO [ 41 ]. It can be easily seen from Fig. 2 a-d that compared to pristine LNMO, the doped LNMO samples have relatively smaller particle sizes. The smaller particle size will shorten the Li + diffusion path, which improves the rate capability of the material [ 30 ]. Among doped LNMO materials, the Mo/F-2 sample has a smooth surface, sharper crystal edges, and uniform particle size. When the doping content continues to increase, as shown in Fig. 2 d, small particles appear on the large particle surface, which will be detrimental to the electrochemical performance of the material. EDS scanning photographs of Mn, Ni, O, Mo, and F elements in the Mo/F-2 sample are shown in Fig. 2 e-j. The distribution of each element is uniform, indicating that the Mo 6+ and F − were successfully introduced into the LNMO structure. XPS was used to further analyze the elemental composition and chemical valence states of the samples. Figure 3 a-b shows the XPS spectrums of Mn 2p for pristine and Mo/F-2 LNMO samples, where the peaks of Mn 2p 1/2 and Mn 2p 3/2 are located at ~ 654 eV and ~ 642 eV, respectively. The Mn 2p 3/2 is divided into Mn 4+ and Mn 3+ , whose peaks are located at ~ 643eV and ~ 642 eV respectively. This indicates that Mn 3+ and Mn 4+ both exist on the surface of the two samples, which once again proves the existence of the disordered Fd3m phase in the samples. By calculating the ratio of Mn 3+ /Mn 4+ peak areas in the two samples, it is found that the content of Mn 3+ in the Mo/F-2 LNMO sample is significantly higher than in the pristine LNMO sample. It was shown that an appropriate amount of Mo-F co-doping could increase the Mn 3+ content in the LNMO material which is good for improving the rate capability of the LNMO material. Figure 3 c shows the XPS pattern of Mo 3d of the Mo/F-2 sample. The Mo 3d peak shape is symmetrical, and the peaks of Mo 3d 5/2 and Mo 3d 3/2 are located at 232.16 eV and 235.37 eV, respectively, corresponding to the binding energy of MoO 3 . The XPS spectrum of F 1s is shown in Fig. 3 d, and a peak at 684.39 eV can be observed. The results showed that Mo 6+ and F − existed on the crystal surface of Mo/F-2-doped materials. 3.2. Electrochemical test A series of electrochemical tests were performed on the four samples to explore the effect of Mo-F co-doping on the electrochemical properties of the LNMO material. Figure 4 a shows the initial charge-discharge profiles for all samples at 0.2 C. It can be seen from the profiles that all samples have a short plateau at around 4.0 V and a long plateau at around 4.7 V. The former is derived from the Mn 3+ /Mn 4+ redox couple, and the latter is derived from the Ni 2+ /Ni 4+ redox couple. All samples have a short stage at 4.0 V, proving that there were disordered Fd3m phases in all samples. The first charge-discharge coulombic efficiency of all samples is poor, which can attributed to the decomposition of the electrolyte at high voltage, the formation of a solid electrolyte interface (SEI) layer onto the spinel, and the formation of Mn 3 O 4 -like structure and the rocksalt-like structure [ 42 – 44 ]. The initial discharge capacity of the pristine LNMO sample is 129.5 mAh g − 1 , while the discharge capacities of the doped samples of Mo/F-1, Mo/F-2, and Mo/F-3 were 132.8 mAh g − 1 , 136.4 mAh g − 1 and 134.7 mAh g − 1 , respectively. The Mo-F co-doped LNMO materials have better initial charge-discharge features than pristine LNMO, and the Mo/F-2 sample has the highest initial discharge capacity. The discharge capacity of Mo/F-3 is lower than Mo/F-2. It can be attributed to increased Mn 3+ which can be seen from the platform at 4 V. The Mn dissolution increased, and more Mn 2+ was deposited on the anode, hindering the extraction of Li + and also consuming part of Li + , resulting in a decrease in material capacity [ 15 ]. Figure 4 b shows the discharge capacities of all samples at different current densities at 0.2 C, 0.5 C, 1 C, 2 C, and 5 C, and then again to 0.2 C. The rate capacities of all the doped LNMO samples are significantly better than the pristine LNMO sample. The Mo/F-2 sample exhibits the optimal rate capability for 136.2, 135.1, 130.9, 126.0, and 113.4 mAh g − 1 at 0.2 C, 0.5 C, 1 C, 2 C and 5 C, respectively. However, the discharge capacities of the pristine LNMO sample at the same current densities were 130.7, 126.1, 118.6, 106.1, and 61.9 mAh g − 1 . It indicates that the doping of Mo 6+ and F − can improve the rate capability of LNMO materials. The improvement of its rate capability can be attributed to the following reasons: (i) Mo-F co-doping increases the lattice parameters of the material which facilitates the Li + diffusion (ii) All the particle sizes of the doped materials are smaller than pristine LNMO sample, which shortens the Li + diffusion path and is beneficial to Li + diffusion. (iii) The higher binding energy of Mo-O compared to Ni-O makes the spinel frame structure more stable and is conducive to the extraction and insertion of Li + [ 30 ] (iv) F − can inhibit the dissolution of the electrolyte, reduce Mn dissolution, and suppress the polarization [ 31 ]. When the discharge capacity returns from 5C to 0.2C, the discharge capacity of all samples almost returns to the original value, indicating that all samples have good structural stability after a rapid lithium-ion insertion/extraction process [ 45 ]. Figure 4 c-d shows the rate cycle performance curves of the pristine LNMO sample and the Mo/F-2 LNMO sample at 0.2-5 C. At the lower rates, the curves of the two samples are similar, with high electrode potential, wide discharge plateau, and two discharge plateaus at 4 V and 4.7 V. As the discharge current increased, the electrode potential of the pristine sample decreased significantly, the discharge plateau narrowed, and the 4.0 V plateau gradually disappeared. In contrast, the change in the discharge platform and electrode potential of the Mo/F-2 sample was relatively small, which indicated that Mo-F co-doping inhibited electrochemical polarization and ohmic polarization at high rates. The results indicate that the appropriate amount of Mo-F co-doping is favorable to reduce the polarization which improves the rate capability of the LNMO. Figure 4 e shows the cyclic volts curve of the pristine and Mo/F-2 materials at 0.1 mV s − 1 with the scan voltage range of 3.5 to 5.1 V. The CV curves of pristine and Mo/F-2 samples are similar, with a peak around 4V, corresponding to the Mn 3+ /Mn 4+ redox couples, and one peak at about 4.7 V, corresponding to the Ni 2+ /Ni 4+ redox couples [ 46 ]. The larger the peak area at 4 V, the greater the Mn 3+ there are [ 45 ]. It can be seen from the graph that the Mn 3+ in the Mo/F-2 sample has increased compared with the pristine sample. The Ni 2+ /Ni 4+ anodic and cathodic peaks correspond to 4.911 V and 4.563 V, respectively, and the voltage difference (ΔE) is 0.348 V. The Ni 2+ /Ni 4+ anodic and cathodic peaks of the Mo/F-2 sample correspond to 4.879 V and 4.578 V, respectively, and the ΔE value is 0.301 V. Typically, the potential difference (ΔE) between the anode peak and the cathode peak reflects the electrochemical polarization [ 47 ]. The ΔE value of Mo/F-2 sample is smaller than the pristine sample, indicating faster lithium insertion/extraction kinetics in Mo/F-2 sample. The result is consistent with the above rate performance test results, indicating that an appropriate amount of Mo-F co-doping can help reduce polarization which improves the rate capability of the LNMO material. Figure 4 f shows the cycle performances of all samples after 100 cycles at 1 C and 25°C. After 100 cycles, the discharge capacities of Pristine LNMO, Mo/F-1, Mo/F-2, and Mo/F-3 samples change from 117.6, 122.3, 130.5, and 126.7 mAh g − 1 to 103.2, 111.6, 124.8, and 119.5 mAh g − 1 , with the capacity retention rates of 87.7%, 91.3%, 95.6%, and 94.3%, respectively. The capacity retention rates of the doped samples are all higher than the undoped sample and the Mo/F-2 sample had optimal cycle stability which indicates that a proper amount of Mo-F co-doping is beneficial to the cycle performance. The result can be attributed to that the Mo 6+ and F − can make the structure of LNMO more stable which inhibits the contraction and expansion of the unit cell during the cycle. Furthermore, the doping of F − can reduce the side reaction between the cathode material and the electrolyte, and inhibit the dissolution of Mn 3+ , so that improve the cycling performance of the material. The capacity retention rate of the Mo/F-3 sample is slightly lower than that of the Mo/F-2 sample because there are some small particles on the surface of the Mo/F-3 sample, which affects the cycling performance of the material. As shown in Fig. 5 a, EIS was used to further analyze the electrochemical kinetic properties of the undoped and doped samples after 3 cycles in the frequency range of 0.01 Hz ~ 100 kHz. The impedance spectrum comprises a semicircular section followed by a linear segment in each curve. The point where the curve first intersects with Z' denotes the solution impedance (R s ), encompassing the ohmic resistance found within the electrolyte, porous membrane, wire, and active material particles. The semicircular shape observed within the mid-to-high frequency range signifies charge transfer resistance (R ct ), which represents the charge transfer of Li + between the electrolyte and the electrode. The oblique line in the low-frequency region corresponds to the Warburg impedance related to the diffusion impedance of Li + in the electrode [ 48 ]. According to the equivalent circuit diagram of Fig. 5 c, the impedance values calculated using the Z-view software are presented in Table 2 . The R s of Pristine, Mo/F-1, Mo/F-2, and Mo/F-3 are 6.15, 5.91, 4.45, and 5.11 Ω, respectively, the R s values of all materials are similar. In contrast, the R ct values of the four samples are more different, its values are 96.82, 71.57, 37.84, and 47.51 Ω, respectively. The R ct values of the Mo-F co-doped samples were all smaller than those of the pristine LNMO sample. This is because the doping of Mo 6+ and F − increased the content of Mn 3+ which improved the conductivity of the material. Furthermore, F − can reduce the oxidative decomposition of the electrolyte and the corrosion of HF in the electrolyte, thereby, reducing the side reactions on the surface and impedance caused by the decomposition products [ 31 ]. Among them, Mo/F-2 has the smallest resistance and has the best electrochemical kinetics, while Mo/F-3 resistance has increased, which may be because excess F − interferes with the migration of Li + . The results indicated that the proper amount of Mo-F co-doping could reduce the charge transfer resistance and improve the electronic conductivity of the LNMO material. Table 2 Impedance and Li + diffusion coefficient of all samples after the 3rd cycles Samples R s (Ω) R ct (Ω) σ D Li+ (cm 2 s − 1 ) Pristine 6.15 96.82 103.93 1.1×10 − 13 Mo/F-1 5.91 71.57 76.81 2.01×10 − 13 Mo/F-2 4.45 37.84 39.98 7.44×10 − 13 Mo/F-3 5.11 47.51 62.55 3.04×10 − 13 The diffusion coefficient of Li + can be calculated from the slope of the impedance low-frequency area in Fig. 5 b, and the formulas are as follows [ 49 ]: $${\text{D}}_{{\text{Li}}^{\text{+}}}\text{=}\frac{{\text{R}}^{\text{2}}{\text{T}}^{\text{2}}}{\text{2}{\text{n}}^{\text{4}}{\text{F}}^{\text{4}}{\text{C}}_{\text{Li}}^{\text{2}}{{\text{A}}_{\text{c}}^{\text{2}}\sigma }^{\text{2}}}$$ 2 $${\text{Z}}^{{\prime }}\text{=}{\text{R}}_{\text{s}}\text{+}{\text{R}}_{\text{ct}}\text{+σ}{\text{ω}}^{\text{-0.5}}$$ 3 In Eq. ( 2 ), D Li+ , R, T, n, F, C Li , and A c represent the Li + diffusion coefficient, gas constant (8.314 J mol − 1 K − 1 ), the absolute temperature of the test environment, the number of transfer electrons, the Faraday constant, the molar concentration of Li + in the cathode material and the contact area between the electrode and the electrolyte, respectively. In Eq. ( 3 ), ω is the angular frequency and σ is the Warburg impedance scale factor fitted by ω −0.5 and Z′. The Li + diffusion coefficients of the four samples are shown in Table 2 . The D Li+ of Pristine, Mo/F-1, Mo/F-2, and Mo/F-3 are 1.1×10 − 13 , 3.04×10 − 13 , 7.44×10 − 13 and 2.01×10 − 13 cm 2 s − 1 , and the Li + diffusion coefficients of all doped samples were higher than the pristine sample and Mo/F-2 had the highest D Li+ . The result can be attributed to that the introduction of Mo 6+ and F − made the material structure more stable, expanded the unit cell parameters of the material, and shortened the Li + diffusion path, which increased the Li + diffusion coefficient. Conclusion In this work, the synergistic effect of Mo 6+ and F − on the electrochemical performance of LNMO was explored. Through various characterization and electrochemical tests, it is found that the introduction of Mo 6+ and F − is beneficial to stabilize the material structure, increase Mn 3+ content, reduce the polarization, reduce the charge transfer resistance, and improve the electronic conductivity and Li + diffusion coefficient of the LNMO cathode material, and so that improve the rate capability and cyclic stability of LNMO cathode material. The Mo/F-2 sample showed the optimal electrochemical performance, with a capacity retention rate of 95.6% after 100 cycles at 1 C and a discharge capacity of 113.4 mAh g − 1 at 5 C. In summary, Mo-F co-doping is an effective modification method for LNMO, which is of great significance for improving the electrochemical performance and commercial application of LNMO. Declarations Ethical Approval No human and/or animal studies have been include in this paper. Also no any other ethical problems are involved. Competing interests I declare that the authors have no competing interests, or other interests that might be perceived to influence the results and/or discussion reported in this paper. Authors' contributions All the three authors have contributed to the work in this paper. But the first author has contributed the most. This manuscript contains contributions of all authors, and all authors have approved of the final version of the manuscript. Funding No funding for this paper. 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Advanced Functional Materials 32:2112279. Patoux S, Daniel L, Bourbon C, Lignier H, Pagano C, Cras FL, Jouanneau, Martinet S (2009) High voltage spinel oxides for Li-ion batteries: From the material research to the application. Journal of Power Sources 189(1): 344–352. Xiao J, Chen XL, Sushko PV, Sushko ML, Kovarik L, Feng JJ, Deng ZQ, Zhang JM, Graff GL, Nie ZM, Choi DW, Liu J, Zhang JG, Whittingham MS (2012) High-Performance LiNi 0.5 Mn 1.5 O 4 Spinel Controlled by Mn 3+ Concentration and Site Disorder. Advanced Materials 24(16): 2109–2116. Amin R, Belharouk I (2017) Part I: Electronic and ionic transport properties of the ordered and disordered LiNi 0.5 Mn 1.5 O 4 spinel cathode. Journal of Power Sources 348: 311–317. Atanasov M, Barras J L, Benco L, Daul C (2000) Electronic structure, chemical bonding, and vibronic coupling in Mn-IV/Mn-III mixed valent Li x Mn 2 O 4 spinels and their effect on the dynamics of intercalated Li: A cluster study using DFT. Journal of the American Chemical Society 122(19): 4718–4728. Park OK, Cho Y, Lee S, Yoo HC, Song HK, Cho J (2011) Who will drive electric vehicles, olivine or spinel? Energy & Environmental Science 4(5):1621–1633. Zhan C, Wu TP, Lu J, Amine K (2018) Dissolution, migration, and deposition of transition metal ions in Li-ion batteries exemplified by Mn-based cathodes - a critical review. Energy & Environmental Science 11: 243–257. Song YM, Han JG, Park S, Lee KT, Choi NS (2014) A multifunctional phosphite-containing electrolyte for 5 V-class LiNi 0.5 Mn 1.5 O 4 cathodes with superior electrochemical performance. Journal of Materials Chemistry A 2(25): 9506–9513. Liang G, Peterson VK, See KW, Guo ZP, Pang WK (2020) Developing high-voltage spinel LiNi 0.5 Mn 1.5 O 4 cathodes for high-energy-density lithium-ion batteries: current achievements and future prospects. Journal of Materials Chemistry A 8:15373–15398 Piao JY, Sun YG, Duan SY, Yang XQ, Goodenough JB, Wan LJ (2018) Stabilizing Cathode Materials of Lithium-Ion Batteries by Controlling Interstitial Sites on the Surface. Chem: 4: 1685–1695. Mao J, Dai KH, Xuan MJ, Shao GS, Qiao RM, Yang WL, Battaglia VS, Liu G (2016) Effect of Chromium and Niobium Doping on the Morphology and Electrochemical Performance of High-Voltage Spinel LiNi 0.5 Mn 1.5 O 4 Cathode Material. ACS Applied Materials & Interfaces 8(14): 9116–9124. Zheng XT, Liu WJ, Qu QT, Zheng HH, Huang YH (2019) Bi-functions of titanium and lanthanum co-doping to enhance the electrochemical performance of spinel LiNi 0.5 Mn 1.5 O 4 cathode. Journal of Materiomics 5(2): 156–163. Cui XL, Shi XM, Li GX, Li SY, Xu XL, Li YL, Mao LP, Ye XS (2013) Electrochemical performance of LiNi 0.5 Mn 1.5 O 4 doped with la and its compatibility with new electrolyte system. Russian Journal of Electrochemistry DOI: 10.1134/S102319351310011X . Ji X, Dai XY, Wu FZ, Mai Y, Chen HJ, Gu YJ (2021) In situ Sr 2+ - doped spinel LiNi 0.5 Mn 1.5 O 4 cathode material for Li-ion batteries with high electrochemical performance and its impact on morphology. Ceramics International 47:32043–32052. Bini M, Boni P, Mustarelli P, Quinzeni I, Bruni G (2018) Silicon-doped LiNi 0.5 Mn 1.5 O 4 as a high-voltage cathode for Li-ion batteries. Solid State Ionics 320: 1–6. Kim WK, Han DW, Ryu WH, Lim SJ, Eom JY, Kwon HS (2014) Effects of Cl doping on the structural and electrochemical properties of high voltage LiNi 0.5 Mn 1.5 O 4 cathode materials for Li-ion batteries. Journal of Alloys and Compounds 592: 48–52. Luo Y, Li HY, Lu TL, Zhang TX, Mao SS, Liu Z, Wen W, Xie JY, Yan LQ (2017) Fluorine gradient-doped LiNi 0.5 Mn 1.5 O 4 spinel with improved high voltage stability for Li-ion batteries. Electrochimica Acta 238: 237–245. Kim DW, Zettsu N, Shiiba H, Santolino GS, Ishikwa R, Ikuhara Y, Teshima K (2020) Metastable oxysulfide surface formation on LiNi 0.5 Mn 1.5 O 4 single crystal particles by carbothermal reaction with sulfur-doped heterocarbon nanoparticles: new insight into their structural and electrochemical characteristics, and their potential applications. Journal of Materials Chemistry A 8(42): 22302–22314. Li J, Li SF, Xu SJ, Huang S, Zhu JX (2017) Synthesis and Electrochemical Properties of LiNi 0.5 Mn 1.5 O 4 Cathode Materials with Cr 3+ and F – Composite Doping for Lithium-Ion Batteries. Nanoscale Research Letters 12:414. Liu JJ, Yuan ML, Li Z, Xie S, Wang TX, Yan JQ, Peng J (2022) Improving the electrochemical performance of single crystal LiNi 0.5 Mn 1.5 O 4 cathode materials by Y-Ti doping and unannealing process. Ceramics International 48(24): 36490–36499. Wei AJ, Mu, J P, He R, Bai X, Li XH, Wang, YJ, Liu ZF, Wang SN(2021). Li + and Cl co-doped LiNi 0.5 Mn 1.5 O 4 cathode material with truncated octahedral shape and enhanced electrochemical performance for Li-ion batteries. Solid State Ionics, 371: 115753. Zeng FF, Zhang Y, Shao ZC (2023) Synthesis and electrochemical performance of Mo-doped LiNi 0.5 Mn 1.5 O 4 cathode material. Materials and Manufacturing Processes 38(2): 197–205. Kim DW, Shiiba H, Zettsu N, Yamada T, Kimijima T et al (2017) Full picture discovery for mixed-fluorine anion effects on high-voltage spinel lithium nickel manganese oxide cathodes. NPG Asia Materials 9: e398. Yi TF, Han X, Chen B, Zhu YR, Xie Y (2017) Porous sphere-like LiNi 0.5 Mn 1.5 O 4 - CeO 2 composite with high cycling stability as cathode material for lithium-ion battery. Journal of Alloys and Compounds 703: 103–113. Chen TC, Lin FC, Wu HM, Zhou DF, Song JL, Guo JB (2023)Zn-Y co-doped LiNi 0.5 Mn 1.5 O 4 cathode materials with high electrochemical performance. Journal of Alloys and Compounds 941:168825. Liu GQ, Wen L, Wang X, Ma BY (2011) Effect of the impurity Li x Ni 1–x O on the electrochemical properties of 5 V cathode material LiNi 0.5 Mn 1.5 O. Journal of Alloys and Compounds 509(38): 9377–9381. Chen MF, Chen P, Yang F, Song HY, Liao SJ (2016) Ni, Mo Co-doped Lithium Manganate with Significantly Enhanced Discharge Capacity and Cycling Stability. Electrochimica Acta 206: 356–365. Hagh NM, Amatucci GG (2014) Effect of cation and anion doping on microstructure and electrochemical properties of the LiMn 1.5 Ni 0.5 O 4 δ spinel. Journal of Power Sources 256: 457–469. Potapenko AV, Kirillov SA (2014) Lithium manganese spinel materials for high-rate electrochemical applications. Journal of Energy Chemistry 23(5): 543–558. Lin FC, Guo JB, Wang LY, Zhou Y, Wu HM, Zhou DF(2021) Synergistic effect of Mg and Y co-dopants on enhancement of electrochemical properties of LiNi 0.5 Mn 1.5 O 4 spinel. Electrochimica Acta 399: 139433. Kunduraci M, Amatucci GG (2006) Synthesis and Characterization of Nanostructured 4.7 V Li x Ni 0.5 Mn 1.5 O 4 Spinels for High-Power Lithium-Ion Batteries. Journal of the Electrochemical Society 153(7): A1345-A1352. Yang JG, Han XP, Zhang XL, Cheng FY, Chen J (2013) Spinel LiNi 0.5 Mn 1.5 O 4 cathode for rechargeable lithium-ion batteries: Nano vs micro, ordered phase (P4 3 32) vs disordered phase (Fd3m). Nano Research 6(9): 679–87. Liu RR, Deng X, Liu XR, Yan HJ, Cao AM, Wang D (2014) Facet dependent SEI formation on the LiNi 0.5 Mn 1.5 O 4 cathode identified by in situ single particle atomic force microscopy. Chemical Communications 50(99): 15756–15759. Miyashiro H, Seki S, Kobayashi Y, Ohno Y, Mita Y, Usami A (2005) All-solid-state lithium polymer secondary battery with LiNi 0.5 Mn 1.5 O 4 by mixing of Li 3 PO 4 Electrochemistry Communications 7(11): 1083–1086. Yi TF, Chen B, Zhu YR, Li XY, Zhu RS (2014) Enhanced rate performance of molybdenum-doped spinel LiNi0.5Mn1.5O4 cathode materials for lithium ion battery. Journal of Power Sources 247: 778–785. Lin MX, Ben LB, Sun Y, Wang H, Yang ZZ, Gu L, Yu XQ, Yang XQ, Zhao HF, Yu RC, Armand M, Huang XJ (2015) Insight into the Atomic Structure of High-Voltage Spinel LiNi 0.5 Mn 1.5 O 4 Cathode Material in the First Cycle. Chemistry of Materials 27(1): 292–303. Yan SP, Sun XL, Zhang Y, Fu SX, Lang YQ, Wang L, Liang GC (2022) From coating to doping: Effect of post-annealing temperature on the alumina coating of LiNi 0.5 Mn 1.5 O 4 cathode material. Journal of Solid State Chemistry 306: 122765. Yi TF, Xie Y, Zhu YR, Zhu RS, Ye MF (2012) High rate micron-sized niobium-doped LiNi 0.5 Mn 1.5 O 4 as ultra high power positive-electrode material for lithium-ion batteries. Journal of Power Sources 211: 59–65. Zhou DF, Lin FC, Song JL, Guo JB (2022) Exploring the action of rare-earth yttrium dopant on enhancing electrochemical performance of LiNi 0.5 Mn 1.5 O 4 material. Journal of Materials Science: Materials in Electronics 33(20): 16621–16637. Yang HP, Zhang HL, Zhao WT (2023) Improvement of electrochemical performance of LiNi 0.5 Co 0.2 Mn 0.3 O 2 by LaF 3 coating at high cut-off voltage. Ionics 29:1335–1345 Deng JC, Xu YL, Xiong LL, Li L, Sun XF, Zhang Y (2016) Improving the fast discharge performance of high-voltage LiNi 0.5 Mn 1.5 O 4 spinel by Cu 2+ , Al 3+ , Ti 4+ tri-doping. Journal of Alloys and Compounds 677: 18–26. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Major revision 30 Oct, 2023 Reviews received at journal 26 Oct, 2023 Reviewers agreed at journal 19 Oct, 2023 Reviewers invited by journal 19 Oct, 2023 Submission checks completed at journal 18 Oct, 2023 Editor assigned by journal 18 Oct, 2023 First submitted to journal 17 Oct, 2023 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-3457578","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":240964297,"identity":"b45b39b3-defe-41e8-8ab8-9a9d5cb824da","order_by":0,"name":"Yuling Weng","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Yuling","middleName":"","lastName":"Weng","suffix":""},{"id":240964298,"identity":"7061e328-f068-4421-8cae-b764e3c808b4","order_by":1,"name":"Hailang L. Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYDACCebGBx8qbOQYmIGchIoaYrQwNhvOOJNmDNby4MwxorS0SfO2HE5sALIZH7YwE9YhP7ux2XBmQ1r6huO8BxgSG9gY+Nu7E/BqYZxzsPHBxx02uRsO8yUwJO6QYZA4c3YDXi3MEolAW86k5c5s5jFgSDzDxmAgkYtfC5tEItAvbYfTJcFa2pgJa+GBakngZyZWiwTIYcBANuxn5ks4kHDmGA9Bv8jPSD4Iikp5Nv6zBx/+qKiR42/vxa8F2Y0MB8AkCYAkxaNgFIyCUTCSAABk2kkt2WBcCQAAAABJRU5ErkJggg==","orcid":"","institution":"","correspondingAuthor":true,"prefix":"","firstName":"Hailang","middleName":"L.","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2023-10-17 12:44:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3457578/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3457578/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":44932034,"identity":"c8e939aa-1749-4fdc-ab6e-a05993850965","added_by":"auto","created_at":"2023-10-19 16:21:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":435976,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD patterns of all samples. The Rietveld refinement profiles of (b) pristine (c) Mo/F-1 d Mo/F-2 (e) Mo/F-3. (f) FT-IR spectra of all samples.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3457578/v1/c2e8ae4818c0371fce1a19cd.png"},{"id":44932035,"identity":"c5d97b90-fd84-414d-a2bc-3be0c5e2d575","added_by":"auto","created_at":"2023-10-19 16:21:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1340038,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of (a) pristine, (b) Mo/F-1, (c) Mo/F-2, and (d) Mo/F-3 samples. (e-j) EDS Mapping photographs of Mo/F-2 sample.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3457578/v1/d859b077353693776358f75a.png"},{"id":44932032,"identity":"0ad8d187-200f-41d3-9c2f-e2900276924c","added_by":"auto","created_at":"2023-10-19 16:21:02","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":305665,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XPS spectrum of Mn 2p for pristine LNMO sample. (b-d) XPS spectrum of Mn 2p, Mo 3d, F 1s for Mo/F-2 sample.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3457578/v1/89b6a3be8556d631de496717.png"},{"id":44932033,"identity":"b8c496de-289b-4a37-b785-ca9bdfc98b21","added_by":"auto","created_at":"2023-10-19 16:21:02","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":373455,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The initial specific charge-discharge curve of all samples at 0.2 C. (b) Rate capability of all samples. (c-d) The specific discharge capacity for the pristine LNMO and Mo/F-2 samples Discharge curve of at 0.2-5.0 C (e) CV curves of LNMO and Mo/F-2 samples (f) Cycling performance at 1 C for all samples.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3457578/v1/e3621bf4ea90fe382b33ec36.png"},{"id":44932697,"identity":"8b193a29-209e-4275-823b-c091b992f92c","added_by":"auto","created_at":"2023-10-19 16:29:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":188478,"visible":true,"origin":"","legend":"\u003cp\u003e(a) EIS plot after 3 cycles of all samples; (b) Z′-ɷ\u003csup\u003e-0.5\u003c/sup\u003e relationship curve at low frequency of all materials after 3 cycles (c) Equivalent circuit model\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3457578/v1/dcd6985acc6ec7c8e94cced7.png"},{"id":44934298,"identity":"c52728ba-7f46-4db4-acaf-8a263238b4bc","added_by":"auto","created_at":"2023-10-19 16:37:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2679012,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3457578/v1/10de10a6-85ff-49b2-94f6-236f90c07650.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eEnhancement of the electrochemical performance of LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode materials for Li-ion battery by Mo-Fco-doping\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eNowadays, energy shortage and environmental pollution problems are increasingly prominent, and the need to explore new environment friendly energy is imminent. In this context, people vigorously seek and develop sustainable and renewable energy, and reusable batteries have become the main trend of energy development. Among many energy storage devices, lithium-ion battery (LIB) stands out with its advantages of high energy density, long cycle life, high rate performance, and good safety, and is considered to be a new large-scale power source for electric vehicles (EV) and hybrid electric vehicles (HEV) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In addition, the cost of positive electrode materials accounts for 30% of the entire battery cost [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], and the reduction of the cost of positive electrode materials directly determines the reduction of the battery cost, so the research and development of high energy density positive electrode materials are very important. Among the lithium-ion cathode materials, the cobalt-free cathode material LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (LNMO) is one of the promising cathode materials due to its high voltage plateau (4.7V vs Li\u003csup\u003e+\u003c/sup\u003e/Li), superior specific theoretical capacity (147 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), high energy density (650 Whk g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), low cost and less environmental impact. It is now being actively considered for use in the manufacture of all-solid-state batteries such as 5 V lithium metal batteries [\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt has been reported that LNMO has two space groups which are the Fd3m space group of Ni/Mn-disordered face-centered cubic and the P4\u003csub\u003e3\u003c/sub\u003e32 space group of Ni/Mn-ordered sample cubic [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. When calcined below 700\u0026deg;C, the ordered structure could be synthesized, and when calcined at a higher temperature, the structure changes from ordered structure to disordered structure. The process of structural transformation is often accompanied by oxygen deficiency, the formation of Li\u003csub\u003ex\u003c/sub\u003eNi\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO rock-salt type impurities, and the generation of Mn\u003csup\u003e3+\u003c/sup\u003e [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This structural transition is usually reversible. P4\u003csub\u003e3\u003c/sub\u003e32 space group can increase by using synthesis processes under oxygen or post-annealing in air below 700\u0026deg;C, and Mn\u003csup\u003e3+\u003c/sup\u003e can be oxidized to Mn\u003csup\u003e4+\u003c/sup\u003e [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe ordered P4\u003csub\u003e3\u003c/sub\u003e32 phase and the disordered Fd3m phase generally exist together in LNMO, and the electrochemical performance of LNMO composed of different phases is also different [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, the Fd3m phase has higher ionic and electronic diffusion coefficients than the P4\u003csub\u003e3\u003c/sub\u003e32 phase which also leads to better electrochemical properties of the disordered structure, Therefore, the disordered phase lithium nickel-manganate is more inclined to be synthesized [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. However, disordered structures are often accompanied by problems such as the formation of impurity phases and the dissolution of Mn\u003csup\u003e3+\u003c/sup\u003e [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], which affects its electrochemical performance. In addition, the higher voltage will aggravate the decomposition of electrolytes, side reactions between the electrolyte and battery active material, and the formation of thick SEI film, which results in difficulties in the intercalation and deintercalation of lithium-ions [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. These issues limit the further application and commercialization of LNMO [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo solve these issues, it is well known that elemental doping is an effective modifying method to enhance the electrochemical performances of LNMO. According to researches, elemental doping mainly includes cation doping( Al\u003csup\u003e3+\u003c/sup\u003e [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], Nb\u003csup\u003e5+\u003c/sup\u003e [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], Ti\u003csup\u003e4+\u003c/sup\u003e [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], La\u003csup\u003e3+\u003c/sup\u003e [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], Sr\u003csup\u003e2+\u003c/sup\u003e [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], Si\u003csup\u003e4+\u003c/sup\u003e [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], etc.), anion doping (Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], F\u003csup\u003e\u0026minus;\u003c/sup\u003e [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], S\u003csup\u003e2\u0026minus;\u003c/sup\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], etc.), and multi-ion doping (Cr-F [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], Y-Ti [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], etc.). The multi-ion doped cathode materials usually have superior electrochemical properties with the synergistic of different elements [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eZeng et al. found that the doping of Mo\u003csup\u003e6+\u003c/sup\u003e in to LNMO could favor Li\u003csup\u003e+\u003c/sup\u003e diffusion and increase electronic conductivity [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. A very small amount of doping of Mo\u003csup\u003e6+\u003c/sup\u003e was shown to improve the electrochemical performance of LNMO, including its rate and cycling performance and the Mo-doped material showed superior electrochemical performance when the doping amount is 1%. The F\u003csup\u003e\u0026minus;\u003c/sup\u003e ion is usually substituted for O\u003csup\u003e2\u0026minus;\u003c/sup\u003e to inhibit the dissolution of Mn\u003csup\u003e3+\u003c/sup\u003e, to inhibit the side reactions between the electrolyte and the active material, to reduce the resistance, and to prevent the corrosion of HF in the electrolyte [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. So it is our hope and speculation that the Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e co-doping could improve the electrochemical performance of LNMO in a great deal. In this work, we prepared a series of samples with varying F content but fixed Mo content (x\u0026thinsp;=\u0026thinsp;0.01) to investigate the synergistic effect of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e on the electrochemical performance of LNMO.\u003c/p\u003e"},{"header":"Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eSynthesis and characterization of materials\u003c/h2\u003e \u003cp\u003eThe undoped and doped LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e samples were prepared by the rheological phase method. The materials were prepared according to the element molar ratio (Ni\u003csub\u003e0.5\u003c/sub\u003e Mn\u003csub\u003e1.5\u003c/sub\u003e): Mo\u0026thinsp;=\u0026thinsp;1: 0.01, and O: F\u0026thinsp;=\u0026thinsp;4-x: x (x\u0026thinsp;=\u0026thinsp;0, 0.01, 0.03, 0.05). According to the element molar ratio to weigh Ni(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO (AR, 99%), Mn(CH\u003csub\u003e3\u003c/sub\u003eCOO)\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO (Sinopharm Chemical Reagent Co., AR, 99%), CH\u003csub\u003e3\u003c/sub\u003eCOOLi (Sinopharm Chemical Reagent Co., AR, 99%), NH\u003csub\u003e4\u003c/sub\u003eF (AR, 99%) by exceeding 5%, and (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e6\u003c/sub\u003eMo\u003csub\u003e7\u003c/sub\u003eO\u003csub\u003e24\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO (Sinopharm Chemical Reagent Co., AR, 99%). Mixed and ground the above raw materials thoroughly. An appropriate amount of distilled water/ethanol solution was added to form the paste, and an appropriate amount of ammonia (inopharm Chemical Reagent Co.,AR, 99%) was added to form a brown paste. Dried at 120\u0026deg;C for 12 h, pre-calcined at 500\u0026deg;C for 6h in an air atmosphere, and further calcined at 850\u0026deg;C for 12 h. The undoped and doped LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e samples are referred to as Pristine, Mo/F-1, Mo/F-2, and Mo/F-3, respectively.\u003c/p\u003e \u003cp\u003eThe samples were characterized by X-ray diffraction (XRD, Bruker D8 Advance) with Cu Kα radiation at a scan rate of 4\u0026deg; min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the 2θ range of 10\u0026ndash;90\u0026deg;. Fourier transform infrared spectrometer (FT-IR, Thermo Fisher iS50, USA) was used to distinguish between the ordered and disordered phases. Scanning electron microscopy (SEM, S-4800, Hitachi, Japan) and energy dispersive spectrometer (EDS) were used to characterize the morphologies and elemental distribution. The surface chemical states were tested by X-ray photoelectron spectroscopy (XPS, Thermo K-alpha).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eElectrochemical measurement\u003c/h2\u003e \u003cp\u003eThe button cells (CR-2032) were assembled to \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003estudy\u003c/span\u003e the electrochemical performances of cathode materials. The active material (80 wt%), acetylene black (12 wt%), and polyvinylidene fluoride (PVDF, 8 wt%) dissolved in NMP solvent were mixed by enough stirring to obtain a slurry which was coated on aluminum foil with a Doctor blade technique. Dried the slurry in a vacuum oven at 80\u0026deg;C for 12 hours. Then, the foil is punched into a round electrode with a diameter of 14 mm. The CR2032 coin cells were assembled in an argon-filled glove box (SUPER 1220/750, made in Shanghai, China), using lithium metal as the counter electrode, Celgard 2325 as the separator, and 1 M LiPF\u003csub\u003e6\u003c/sub\u003e in EC: DMC: EMC (v: v: v\u0026thinsp;=\u0026thinsp;1:1:1) solution as the electrolyte.\u003c/p\u003e \u003cp\u003eTo evaluate the electrochemical performances of the prepared samples, The constant current charge-discharge cycle test was carried out by using the LAND battery test system (CT2001A, Wuhan in China) at 25\u0026deg;C. Cells were tested at different current densities (1C\u0026thinsp;=\u0026thinsp;147 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) in the voltage range of 3.5\u0026ndash;4.95 V. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were carried out at an electrochemical workstation (IM6, Zahner, Germany) within the voltage range of 3.5\u0026ndash;5.1 V. CV tests were conducted at the scan rate of 0.1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. EIS tests were performed in the frequency range of 0.01\u0026ndash;100 kHz and amplitude of 5 mV.\u003c/p\u003e \u003c/div\u003e"},{"header":"Result and discussion","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Morphology and structural analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea exhibits the XRD patterns of pristine LNMO and LiNi\u003csub\u003e0.4975\u003c/sub\u003eMn\u003csub\u003e1.4925\u003c/sub\u003eMo\u003csub\u003e0.01\u003c/sub\u003eO\u003csub\u003e4\u0026minus;x\u003c/sub\u003eF\u003csub\u003ex\u003c/sub\u003e (x\u0026thinsp;=\u0026thinsp;0.01, 0.03, 0.05) samples. The diffraction peaks of all samples match the patterns of standard PDF card No. 80-2162, and the sharp diffraction peaks indicate good crystallinity of the materials, which infers that the low dose of Mo-F co-doping will not change the basic structure of the material. The absence of the (220) diffraction peak indicates that the transition metal ions do not occupy position 8a [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Located at 2θ\u0026thinsp;=\u0026thinsp;37.6\u0026deg; and 43.7\u0026deg; are the weak peaks of the Li\u003csub\u003ex\u003c/sub\u003eNi\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO impurity phase. With the preparation of the Fd3m structure of the LNMO sample at a high synthesis temperature, the oxygen deficiency formed, and the nickel departed from the spinel phase to form the rock salt impurities. Such a reaction was proposed [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]:\u003c/p\u003e \u003cp\u003eLiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e \u0026harr;αLi\u003csub\u003ex\u003c/sub\u003eNi\u003csub\u003e1\u0026minus;x\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;βLiNi\u003csub\u003e0.5\u0026minus;x\u003c/sub\u003eMn\u003csub\u003e1.5+x\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;γO\u003csub\u003e2\u003c/sub\u003e. (1)\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe impurity phase can decrease the content of the active material and reduce the specific capacity of the material, but there is no obvious significant negative effect on the cycling performance of the product [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The Rietveld refinement profiles of pristine, Mo/F-1, Mo/F-2, and Mo/F-3 are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb-e. The lattice parameters obtained from Rietveld refinement patterns for all samples are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Compared with the bare LNMO, the lattice parameters of the Mo-F doped samples have a little increase. This can be attributed to an increase in the interlayer distance as Mo\u003csup\u003e6+\u003c/sup\u003e is doped [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Furthermore, it also can be attributed to the increase in the content of Mn\u003csup\u003e3+\u003c/sup\u003e in the material due to the doping of F\u003csup\u003e\u0026minus;\u003c/sup\u003e and Mo\u003csup\u003e6+\u003c/sup\u003e. The larger ion radius (0.58 \u0026Aring; for low and 0.65 \u0026Aring; for high spin manganese) of Mn\u003csup\u003e3+\u003c/sup\u003e compared with Mn\u003csup\u003e4+\u003c/sup\u003e (0.53 \u0026Aring;) makes the lattice parameters of the material expand, which is more conducive to the transport of Li\u003csup\u003e+\u003c/sup\u003e [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\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\u003eLattice parameters of all samples\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\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eLattice parameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eInter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003e\u003cem\u003ewp\u003c/em\u003e\u003c/sub\u003e/%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eα\u003c/em\u003e/\u0026Aring;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eV\u003c/em\u003e/\u0026Aring;\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e(111)\u003c/em\u003e\u003c/sub\u003e/ \u0026Aring;\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePristine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.17823\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e546.988\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.7217\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMo/F-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.17852\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e547.047\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.7219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.77\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMo/F-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.18216\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e547.778\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.7240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMo/F-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8.18707\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e548.765\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.7268\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.57\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\u003eLNMO can be divided into ordered P4\u003csub\u003e3\u003c/sub\u003e32 and disordered Fd3m phases due to the different order of Ni/Mn cations in the spinel structure. Because the scattering factors of Ni and Mn are very similar, XRD is hard to identify the two space groups accurately[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. FT-IR spectroscopy can be used to analyze the degree of ordering of samples. It is reported that the P4\u003csub\u003e3\u003c/sub\u003e32 space group of LNMO material has 8 infrared absorption bands, while the Fd-3m space group has only 5 bands between 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef, five infrared absorption peaks can be seen at 621, 581, 555, 505, and 469 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Among them, the absorption peaks at 621 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 555 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were related to the vibration of Mn-O, while the absorption peaks at 581 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 505 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003ewere\u003c/span\u003e related to the vibration of Ni-O. The intensity ratio of Mn-O at 621 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and Ni-O at 581 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e(621)\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003e(581)\u003c/sub\u003e) can be used qualitatively to assess the percentage of ordering in spinel [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The intensity of 621 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is higher than the peak intensity at 581 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for all samples, indicating that all samples are predominantly disordered Fd3m phases. The \u003cem\u003eI\u003c/em\u003e\u003csub\u003e(621)\u003c/sub\u003e/\u003cem\u003eI\u003c/em\u003e\u003csub\u003e(581)\u003c/sub\u003e ratios of the pristine, Mo/F-1, Mo/F-2, and Mo/F-3 samples were 1.073, 1.175, 1.188, and 1.196, respectively, so the Mo-F co-doped samples show a higher degree of disorder than the pristine LNMO. Compared with the ordered P4\u003csub\u003e3\u003c/sub\u003e32 phase, the disordered Fd3m phase has better rate capability [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe morphologies of the four materials were characterized by SEM, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-d. After the doping of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e, the LNMO morphology changed from a truncated octahedral morphology to a standard octahedral structure. The (111) facet is conducive to the formation of SEI films, which makes the (111) facet more stable than (100) and (110) facets, The doped LNMO materials with the dominant (111) surfaces exhibit a superior cycle life compared to pristine LNMO [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. It can be easily seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-d that compared to pristine LNMO, the doped LNMO samples have relatively smaller particle sizes. The smaller particle size will shorten the Li\u003csup\u003e+\u003c/sup\u003e diffusion path, which improves the rate capability of the material [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Among doped LNMO materials, the Mo/F-2 sample has a smooth surface, sharper crystal edges, and uniform particle size. When the doping content continues to increase, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, small particles appear on the large particle surface, which will be detrimental to the electrochemical performance of the material.\u003c/p\u003e \u003cp\u003eEDS scanning photographs of Mn, Ni, O, Mo, and F elements in the Mo/F-2 sample are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee-j. The distribution of each element is uniform, indicating that the Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e were successfully introduced into the LNMO structure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eXPS was used to further analyze the elemental composition and chemical valence states of the samples. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-b shows the XPS spectrums of Mn 2p for pristine and Mo/F-2 LNMO samples, where the peaks of Mn 2p\u003csub\u003e1/2\u003c/sub\u003e and Mn 2p\u003csub\u003e3/2\u003c/sub\u003e are located at ~\u0026thinsp;654 eV and ~\u0026thinsp;642 eV, respectively. The Mn 2p\u003csub\u003e3/2\u003c/sub\u003e is divided into Mn\u003csup\u003e4+\u003c/sup\u003e and Mn\u003csup\u003e3+\u003c/sup\u003e, whose peaks are located at ~\u0026thinsp;643eV and ~\u0026thinsp;642 eV respectively. This indicates that Mn\u003csup\u003e3+\u003c/sup\u003e and Mn\u003csup\u003e4+\u003c/sup\u003e both exist on the surface of the two samples, which once again proves the existence of the disordered Fd3m phase in the samples. By calculating the ratio of Mn\u003csup\u003e3+\u003c/sup\u003e/Mn\u003csup\u003e4+\u003c/sup\u003e peak areas in the two samples, it is found that the content of Mn\u003csup\u003e3+\u003c/sup\u003e in the Mo/F-2 LNMO sample is significantly higher than in the pristine LNMO sample. It was shown that an appropriate amount of Mo-F co-doping could increase the Mn\u003csup\u003e3+\u003c/sup\u003e content in the LNMO material which is good for improving the rate capability of the LNMO material. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the XPS pattern of Mo 3d of the Mo/F-2 sample. The Mo 3d peak shape is symmetrical, and the peaks of Mo 3d\u003csub\u003e5/2\u003c/sub\u003e and Mo 3d\u003csub\u003e3/2\u003c/sub\u003e are located at 232.16 eV and 235.37 eV, respectively, corresponding to the binding energy of MoO\u003csub\u003e3\u003c/sub\u003e. The XPS spectrum of F 1s is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, and a peak at 684.39 eV can be observed. The results showed that Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e existed on the crystal surface of Mo/F-2-doped materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Electrochemical test\u003c/h2\u003e \u003cp\u003eA series of electrochemical tests were performed on the four samples to explore the effect of Mo-F co-doping on the electrochemical properties of the LNMO material. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea shows the initial charge-discharge profiles for all samples at 0.2 C. It can be seen from the profiles that all samples have a short plateau at around 4.0 V and a long plateau at around 4.7 V. The former is derived from the Mn\u003csup\u003e3+\u003c/sup\u003e/Mn\u003csup\u003e4+\u003c/sup\u003e redox couple, and the latter is derived from the Ni\u003csup\u003e2+\u003c/sup\u003e/Ni\u003csup\u003e4+\u003c/sup\u003e redox couple. All samples have a short stage at 4.0 V, proving that there were disordered Fd3m phases in all samples. The first charge-discharge coulombic efficiency of all samples is poor, which can attributed to the decomposition of the electrolyte at high voltage, the formation of a solid electrolyte interface (SEI) layer onto the spinel, and the formation of Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-like structure and the rocksalt-like structure [\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The initial discharge capacity of the pristine LNMO sample is 129.5 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, while the discharge capacities of the doped samples of Mo/F-1, Mo/F-2, and Mo/F-3 were 132.8 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 136.4 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 134.7 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. The Mo-F co-doped LNMO materials have better initial charge-discharge features than pristine LNMO, and the Mo/F-2 sample has the highest initial discharge capacity. The discharge capacity of Mo/F-3 is lower than Mo/F-2. It can be attributed to increased Mn\u003csup\u003e3+\u003c/sup\u003e which can be seen from the platform at 4 V. The Mn dissolution increased, and more Mn\u003csup\u003e2+\u003c/sup\u003e was deposited on the anode, hindering the extraction of Li\u003csup\u003e+\u003c/sup\u003e and also consuming part of Li\u003csup\u003e+\u003c/sup\u003e, resulting in a decrease in material capacity [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows the discharge capacities of all samples at different current densities at 0.2 C, 0.5 C, 1 C, 2 C, and 5 C, and then again to 0.2 C. The rate capacities of all the doped LNMO samples are significantly better than the pristine LNMO sample. The Mo/F-2 sample exhibits the optimal rate capability for 136.2, 135.1, 130.9, 126.0, and 113.4 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.2 C, 0.5 C, 1 C, 2 C and 5 C, respectively. However, the discharge capacities of the pristine LNMO sample at the same current densities were 130.7, 126.1, 118.6, 106.1, and 61.9 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. It indicates that the doping of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e can improve the rate capability of LNMO materials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe improvement of its rate capability can be attributed to the following reasons: (i) Mo-F co-doping increases the lattice parameters of the material which facilitates the Li\u003csup\u003e+\u003c/sup\u003e diffusion (ii) All the particle sizes of the doped materials are smaller than pristine LNMO sample, which shortens the Li\u003csup\u003e+\u003c/sup\u003e diffusion path and is beneficial to Li\u003csup\u003e+\u003c/sup\u003e diffusion. (iii) The higher binding energy of Mo-O compared to Ni-O makes the spinel frame structure more stable and is conducive to the extraction and insertion of Li\u003csup\u003e+\u003c/sup\u003e [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] (iv) F\u003csup\u003e\u0026minus;\u003c/sup\u003e can inhibit the dissolution of the electrolyte, reduce Mn dissolution, and suppress the polarization [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. When the discharge capacity returns from 5C to 0.2C, the discharge capacity of all samples almost returns to the original value, indicating that all samples have good structural stability after a rapid lithium-ion insertion/extraction process [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec-d shows the rate cycle performance curves of the pristine LNMO sample and the Mo/F-2 LNMO sample at 0.2-5 C. At the lower rates, the curves of the two samples are similar, with high electrode potential, wide discharge plateau, and two discharge plateaus at 4 V and 4.7 V. As the discharge current increased, the electrode potential of the pristine sample decreased significantly, the discharge plateau narrowed, and the 4.0 V plateau gradually disappeared. In contrast, the change in the discharge platform and electrode potential of the Mo/F-2 sample was relatively small, which indicated that Mo-F co-doping inhibited electrochemical polarization and ohmic polarization at high rates. The results indicate that the appropriate amount of Mo-F co-doping is favorable to reduce the polarization which improves the rate capability of the LNMO.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee shows the cyclic volts curve of the pristine and Mo/F-2 materials at 0.1 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with the scan voltage range of 3.5 to 5.1 V. The CV curves of pristine and Mo/F-2 samples are similar, with a peak around 4V, corresponding to the Mn\u003csup\u003e3+\u003c/sup\u003e/Mn\u003csup\u003e4+\u003c/sup\u003e redox couples, and one peak at about 4.7 V, corresponding to the Ni\u003csup\u003e2+\u003c/sup\u003e/Ni\u003csup\u003e4+\u003c/sup\u003e redox couples [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The larger the peak area at 4 V, the greater the Mn\u003csup\u003e3+\u003c/sup\u003e there are [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. It can be seen from the graph that the Mn\u003csup\u003e3+\u003c/sup\u003e in the Mo/F-2 sample has increased compared with the pristine sample. The Ni\u003csup\u003e2+\u003c/sup\u003e/Ni\u003csup\u003e4+\u003c/sup\u003e anodic and cathodic peaks correspond to 4.911 V and 4.563 V, respectively, and the voltage difference (ΔE) is 0.348 V. The Ni\u003csup\u003e2+\u003c/sup\u003e/Ni\u003csup\u003e4+\u003c/sup\u003e anodic and cathodic peaks of the Mo/F-2 sample correspond to 4.879 V and 4.578 V, respectively, and the ΔE value is 0.301 V. Typically, the potential difference (ΔE) between the anode peak and the cathode peak reflects the electrochemical polarization [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The ΔE value of Mo/F-2 sample is smaller than the pristine sample, indicating faster lithium insertion/extraction kinetics in Mo/F-2 sample. The result is consistent with the above rate performance test results, indicating that an appropriate amount of Mo-F co-doping can help reduce polarization which improves the rate capability of the LNMO material.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef shows the cycle performances of all samples after 100 cycles at 1 C and 25\u0026deg;C. After 100 cycles, the discharge capacities of Pristine LNMO, Mo/F-1, Mo/F-2, and Mo/F-3 samples change from 117.6, 122.3, 130.5, and 126.7 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 103.2, 111.6, 124.8, and 119.5 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with the capacity retention rates of 87.7%, 91.3%, 95.6%, and 94.3%, respectively. The capacity retention rates of the doped samples are all higher than the undoped sample and the Mo/F-2 sample had optimal cycle stability which indicates that a proper amount of Mo-F co-doping is beneficial to the cycle performance. The result can be attributed to that the Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e can make the structure of LNMO more stable which inhibits the contraction and expansion of the unit cell during the cycle. Furthermore, the doping of F\u003csup\u003e\u0026minus;\u003c/sup\u003e can reduce the side reaction between the cathode material and the electrolyte, and inhibit the dissolution of Mn\u003csup\u003e3+\u003c/sup\u003e, so that improve the cycling performance of the material. The capacity retention rate of the Mo/F-3 sample is slightly lower than that of the Mo/F-2 sample because there are some small particles on the surface of the Mo/F-3 sample, which affects the cycling performance of the material.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, EIS was used to further analyze the electrochemical kinetic properties of the undoped and doped samples after 3 cycles in the frequency range of 0.01 Hz\u0026thinsp;~\u0026thinsp;100 kHz. The impedance spectrum comprises a semicircular section followed by a linear segment in each curve. The point where the curve first intersects with Z' denotes the solution impedance (R\u003csub\u003es\u003c/sub\u003e), encompassing the ohmic resistance found within the electrolyte, porous membrane, wire, and active material particles. The semicircular shape observed within the mid-to-high frequency range signifies charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e), which represents the charge transfer of Li\u003csup\u003e+\u003c/sup\u003e between the electrolyte and the electrode. The oblique line in the low-frequency region corresponds to the Warburg impedance related to the diffusion impedance of Li\u003csup\u003e+\u003c/sup\u003e in the electrode [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. According to the equivalent circuit diagram of Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, the impedance values calculated using the Z-view software are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The R\u003csub\u003es\u003c/sub\u003e of Pristine, Mo/F-1, Mo/F-2, and Mo/F-3 are 6.15, 5.91, 4.45, and 5.11 Ω, respectively, the R\u003csub\u003es\u003c/sub\u003e values of all materials are similar. In contrast, the R\u003csub\u003ect\u003c/sub\u003e values of the four samples are more different, its values are 96.82, 71.57, 37.84, and 47.51 Ω, respectively. The R\u003csub\u003ect\u003c/sub\u003e values of the Mo-F co-doped samples were all smaller than those of the pristine LNMO sample. This is because the doping of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e increased the content of Mn\u003csup\u003e3+\u003c/sup\u003e which improved the conductivity of the material. Furthermore, F\u003csup\u003e\u0026minus;\u003c/sup\u003e can reduce the oxidative decomposition of the electrolyte and the corrosion of HF in the electrolyte, thereby, reducing the side reactions on the surface and impedance caused by the decomposition products [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Among them, Mo/F-2 has the smallest resistance and has the best electrochemical kinetics, while Mo/F-3 resistance has increased, which may be because excess F\u003csup\u003e\u0026minus;\u003c/sup\u003e interferes with the migration of Li\u003csup\u003e+\u003c/sup\u003e. The results indicated that the proper amount of Mo-F co-doping could reduce the charge transfer resistance and improve the electronic conductivity of the LNMO material.\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\u003eImpedance and Li\u003csup\u003e+\u003c/sup\u003e diffusion coefficient of all samples after the 3rd cycles\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eR\u003c/em\u003e\u003csub\u003ect\u003c/sub\u003e (Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eσ\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eD\u003c/em\u003e\u003csub\u003eLi+\u003c/sub\u003e (cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\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\u003ePristine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e96.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e103.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMo/F-1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e71.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e76.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.01\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMo/F-2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e37.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e39.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.44\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMo/F-3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e47.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e62.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.04\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e\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\u003e \u003c/p\u003e \u003cp\u003eThe diffusion coefficient of Li\u003csup\u003e+\u003c/sup\u003e can be calculated from the slope of the impedance low-frequency area in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, and the formulas are as follows [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${\\text{D}}_{{\\text{Li}}^{\\text{+}}}\\text{=}\\frac{{\\text{R}}^{\\text{2}}{\\text{T}}^{\\text{2}}}{\\text{2}{\\text{n}}^{\\text{4}}{\\text{F}}^{\\text{4}}{\\text{C}}_{\\text{Li}}^{\\text{2}}{{\\text{A}}_{\\text{c}}^{\\text{2}}\\sigma }^{\\text{2}}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${\\text{Z}}^{{\\prime }}\\text{=}{\\text{R}}_{\\text{s}}\\text{+}{\\text{R}}_{\\text{ct}}\\text{+\u0026sigma;}{\\text{\u0026omega;}}^{\\text{-0.5}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eIn Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e2\u003c/span\u003e), D\u003csub\u003eLi+\u003c/sub\u003e, R, T, n, F, C\u003csub\u003eLi\u003c/sub\u003e, and A\u003csub\u003ec\u003c/sub\u003e represent the Li\u003csup\u003e+\u003c/sup\u003e diffusion coefficient, gas constant (8.314 J mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), the absolute temperature of the test environment, the number of transfer electrons, the Faraday constant, the molar concentration of Li\u003csup\u003e+\u003c/sup\u003e in the cathode material and the contact area between the electrode and the electrolyte, respectively. In Eq.\u0026nbsp;(\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e3\u003c/span\u003e), ω is the angular frequency and σ is the Warburg impedance scale factor fitted by ω\u003csup\u003e\u0026minus;0.5\u003c/sup\u003e and Z\u0026prime;. The Li\u003csup\u003e+\u003c/sup\u003e diffusion coefficients of the four samples are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The D\u003csub\u003eLi+\u003c/sub\u003e of Pristine, Mo/F-1, Mo/F-2, and Mo/F-3 are 1.1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e, 3.04\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e, 7.44\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e and 2.01\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;13\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the Li\u003csup\u003e+\u003c/sup\u003e diffusion coefficients of all doped samples were higher than the pristine sample and Mo/F-2 had the highest D\u003csub\u003eLi+\u003c/sub\u003e. The result can be attributed to that the introduction of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e made the material structure more stable, expanded the unit cell parameters of the material, and shortened the Li\u003csup\u003e+\u003c/sup\u003e diffusion path, which increased the Li\u003csup\u003e+\u003c/sup\u003e diffusion coefficient.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this work, the synergistic effect of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e on the electrochemical performance of LNMO was explored. Through various characterization and electrochemical tests, it is found that the introduction of Mo\u003csup\u003e6+\u003c/sup\u003e and F\u003csup\u003e\u0026minus;\u003c/sup\u003e is beneficial to stabilize the material structure, increase Mn\u003csup\u003e3+\u003c/sup\u003e content, reduce the polarization, reduce the charge transfer resistance, and improve the electronic conductivity and Li\u003csup\u003e+\u003c/sup\u003e diffusion coefficient of the LNMO cathode material, and so that improve the rate capability and cyclic stability of LNMO cathode material. The Mo/F-2 sample showed the optimal electrochemical performance, with a capacity retention rate of 95.6% after 100 cycles at 1 C and a discharge capacity of 113.4 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 5 C. In summary, Mo-F co-doping is an effective modification method for LNMO, which is of great significance for improving the electrochemical performance and commercial application of LNMO.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo human and/or animal studies have been include in this paper. Also no any other ethical problems are involved.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eI declare that the authors have no competing interests, or other interests that might be perceived to influence the results and/or discussion reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the three authors have contributed to the work in this paper. But the first author has contributed the most. This manuscript contains contributions of all authors, and all authors have approved of the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding for this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eQin X, Zhou MS, Zong B, Guo JL, Gong JJ, Wang L, Liang GC (2018) Urea-assisted hydrothermal synthesis of a hollow hierarchical LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e cathode material with tunable morphology characteristics. 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Journal of Alloys and Compounds 677: 18\u0026ndash;26.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Li-ion battery, LiNi0.5Mn1.5O4, Mo6+ and F− co-doping, disordered phase, electrochemical performance","lastPublishedDoi":"10.21203/rs.3.rs-3457578/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3457578/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe pristine LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (LNMO) and Mo-F co-doped LiNi\u003csub\u003e0.5\u003c/sub\u003eMn\u003csub\u003e1.5\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e spinel materials were prepared via a rheological phase method. The four samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). Compared with the pristine LNMO sample, Mo-F co-doped LNMO materials could increase the lattice parameters, reduce particle sizes, increase Mn\u003csup\u003e3+\u003c/sup\u003e contents, and significantly improve the electrochemical performances of LNMO. The doped material exhibited optimum electrochemical properties when the Mo and F doping amounts are 1% and 3% ,respectively, denoted as Mo/F-2. The discharge capacity retention of Mo/F-2 is 95.6%, which is higher than the pristine sample (87.7%) after 100 cycles at 1C and room temperature. Furthermore, the discharge-specific capacity of the Mo/F-2 sample reaches 113.4 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 5C, while the pristine sample reaches only 61.9 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. After CV and EIS analysis, it was found that the Mo-F co-doped LNMO materials had better Li\u003csup\u003e+\u003c/sup\u003e diffusion kinetics than the pristine LNMO sample. Thus, Mo-F co-doping is considered an effective modification method for LNMO cathode material.\u003c/p\u003e","manuscriptTitle":"Enhancement of the electrochemical performance of LiNi0.5Mn1.5O4 cathode materials for Li-ion battery by Mo-Fco-doping","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-10-19 16:20:58","doi":"10.21203/rs.3.rs-3457578/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-10-30T07:59:30+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-10-26T07:56:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"4430752b-e7fb-45dd-9258-d9816559e652","date":"2023-10-19T10:52:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-10-19T10:41:49+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-10-18T04:15:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-10-18T04:15:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2023-10-17T12:38:40+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5682de58-3727-4715-a85a-278fb43d89e2","owner":[],"postedDate":"October 19th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2023-12-26T11:29:56+00:00","versionOfRecord":[],"versionCreatedAt":"2023-10-19 16:20:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3457578","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3457578","identity":"rs-3457578","version":["v1"]},"buildId":"J0_U0BvcaRcwD8yVFaRlm","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}