A high-capacity lithium-rich layered sulfide cathode material, a preparation method and application in lithium ion batteries

Abstract

The application relates to a novel lithium ion battery layered sulfide positive electrode material, which has a general formula of Li 1.33‑0.33x V x Ti 0.67‑0.67x S2, and 0<=x<=0.5. The positive electrode material belongs to a hexagonal crystal structure of O3 type, and a corresponding space group is P63 / mmc. The micro-morphology of the positive electrode material is granular, the particle size is about 20-50 mu m, and each element is uniformly distributed on the particle surface and inside. In the positive electrode material, almost all the capacity comes from the redox reaction of sulfur, and the capacity contribution of vanadium can be ignored. Electrochemical test and solid-state nuclear magnetic characterization results show that the Li 1.27 V 0.2 Ti 0.53 S2 positive electrode material has a reversible capacity of up to 308 mAh g ‑1 , and realizes reversible deintercalation of all Li + in the system. Meanwhile, the material exhibits extremely excellent rate and cycle performance, has a capacity retention rate of 81.0% after 4300 cycles of long cycle, and has almost no voltage attenuation in the cycle process.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium-rich layered sulfide cathode material, a preparation method and application in lithium ion batteries, and belongs to the technical field of lithium ion battery cathode materials. BACKGROUND

[0002] Lithium ion batteries are considered as one of the most potential portable electrochemical energy storage devices due to their high capacity, high specific energy and long life. Lithium-rich layered cathode material is a new type of cathode material, among which the most representative is lithium-rich manganese-based cathode material (xLi2MnO3·(1–x)LiTMO2, TM=Ni, Mn, Co, etc.), which has a theoretical capacity of more than 350 mAh g -1 and a reversible capacity of 350 mAh g -1 , and is considered as one of the most promising lithium ion cathode materials. Its high capacity is not only due to the redox of transition metal, but also due to the unique anion redox mechanism. The redox mechanism involving lattice oxygen provides more capacity for lithium-rich layered cathode material, so as to realize the reversible deintercalation of more than one lithium ion. The redox of lattice oxygen at high potential is usually not fully reversible, that is, the oxygen ions in the oxidation state will partially convert into peroxide ions, superoxide ions or even molecular oxygen. This irreversible reaction will cause serious structural rearrangement and transition metal migration, leading to the collapse of layered structure and irreversible phase change. SUMMARY

[0003] The technical problem to be solved by the present application is that the existing lithium-rich layered oxide cathode material has problems such as loss of lattice oxygen, migration of transition metal and slow kinetics when applied to lithium ion battery cathode material. The present application provides a lithium-rich layered sulfide cathode material, which has higher specific capacity and better electrochemical performance.

[0004] A lithium-rich layered sulfide cathode material, whose general formula is Li 1.33-0.33x V x Ti 0.67-0.67x S2, and 0

[0005] 0.1

[0006] The energy density is 430-480 Wh kg -1 .

[0007] The preparation method of the lithium-rich layered sulfide cathode material, comprising the following steps:

[0008] Step 1, mixing Li2S powder, vanadium powder, titanium powder and sulfur powder, grinding, tablet processing;

[0009] Step 2, after constant temperature heat treatment, quenching, obtaining positive electrode material.

[0010] Heat treatment temperature 600-800℃, time 20-40h.

[0011] During heat treatment, the vacuum degree is kept at about 10 -4 -10 -6 mbar.

[0012] Application of the above-mentioned layered lithium-rich sulfide positive electrode material in lithium ion battery.

[0013] The lithium ion battery adopts lithium metal negative electrode, and has 85-90% capacity retention rate after 4300 cycles of charging and discharging.

[0014] Beneficial effects

[0015] Compared with lithium-rich layered oxide positive electrode material, lithium-rich sulfide positive electrode material can form strong metal-ligand covalent interaction with common 3d transition metal ions, and realize highly reversible anion redox reaction, so that lithium-rich sulfide positive electrode material has more stable structure and higher specific capacity, and overcomes the adverse problems related to anion redox reaction. Lithium-rich layered positive electrode material can only reversibly deintercalate 1 Li + during charging and discharging, and has not yet reached its theoretical capacity, so there is still a lot of room for improvement. The new material Li 1.27 V 0.2 Ti 0.53 S2 can exhibit a reversible capacity of up to 308mAh g -1 , realizing complete reversible deintercalation of all Li + in the system. Li 1.27 V 0.2 Ti 0.53 S2 mainly involves sulfur in the charge compensation process during charging and discharging, and the capacity contribution of vanadium can be ignored. In addition, the positive electrode material still has an initial capacity retention rate of 80.3% after 4300 cycles of long cycle, and almost no voltage decay during the cycle. These electrochemical properties are superior to most of the currently reported lithium-rich layered positive electrode materials. In-situ and non-in-situ XRD tests show that the material has no obvious phase change during charging and discharging, and is a solid solution behavior. At the same time, reversible deintercalation of lithium in lithium layer and lithium in transition metal layer during charging and discharging is also observed by solid-state nuclear magnetic resonance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 : A series of Li 1.33-0.33xV x Ti 0.67-0.67x XRD patterns of S2(0≤x≤0.5) samples.

[0017] Figure 2 : Li 1.27 V 0.2 Ti 0.53 Rietveld refined XRD patterns of S2 samples.

[0018] Figure 3 : Li 1.27 V 0.2 Ti 0.53 Micro-morphology characterization of S2 powder samples. a. SEM images at low magnification. b. SEM images at high magnification.

[0019] Figure 4 : Li 1.27 V 0.2 Ti 0.53 TEM characterization of S2 samples. a. HAADF-STEM image along

[010] direction, bright spots are transition metals (V, Ti) and sulfur atoms. Right side is the corresponding O3-type crystal model image, where blue, yellow and green spheres represent transition metal (V, Ti) atoms, sulfur atoms and lithium atoms, respectively. b. ABF-STEM image along

[010] direction, right side is the corresponding O3-type crystal model image. c-g. HAADF images and corresponding EDS maps of Ti, V and S.

[0020] Figure 5 : Li 1.33-0.33x V x Ti 0.67-0.67x Electrochemical performance characterization of S2(0≤x≤0.5). a-f. The first three cycle capacity-voltage curves of a series of compositions with different vanadium doping contents (0≤x≤0.5) were tested in the voltage range of 1.8-3.0 V at a current density of 20 mA g –1

[0021] Figure 6 : A series of Li 1.33-0.33x V x Ti 0.67-0.67x The theoretical capacity calculated by removing all lithium ions in S2(0≤x≤0.5) materials and the real specific capacity actually tested at a small current density of 20 mA g -1 . At x = 0.2, the real capacity and theoretical capacity of the corresponding composition are almost equal.

[0022] Figure 7 : A series of Li 1.33-0.33x V x Ti​0.67-0.67x S2 (0≤x≤0.5) is the rate performance of the cathode material. Where x=0.2 corresponds to the composition (Li). 1.27 V 0.2 Ti 0.53 S2) exhibits the best rate performance at 1000 mA g. -1 It can still maintain 217.5 mAh g at a current density. -1 The capacity.

[0023] Figure 8 During the charging and discharging process, Li 1.27 V 0.2 Ti 0.53 The non-in-situ S2p XPS spectrum of the S2 cathode. The left side shows the first charge-discharge curve and the different charge-discharge states selected for testing the XPS spectrum.

[0024] Figure 9 Li 1.27 V 0.2 Ti 0.53 XAS spectra of S2 cathode material in the pristine, charged, and discharged states. (a) Normalized Ti K-edge XANES spectrum. (b) k 3 Ti K-edge EXAFS spectra obtained by weighted Fourier transform.

[0025] Figure 10 Li 1.27 V 0.2 Ti 0.53 Non-in-situ XAS spectral characterization of the S2 cathode material. a. Different charge-discharge states selected during the first charge-discharge cycle for testing XANES spectra. b. Normalized V K-edge XANES spectra under different charge-discharge states. (c)k 3 V K-edge EXAFS spectrum with weighted Fourier transform.

[0026] Figure 11 Li 1.27 V 0.2 Ti 0.53 7Li MAS ssNMR spectra of S2 cathode material at pristine, 2.8V, 3.0V, 2.5V, and 1.8V discharge conditions.

[0027] Figure 12 Li 1.27 V 0.2 Ti 0.53 Long-cycle performance of the S2 electrode. a. At 1000 mAg -1 The capacity retention and corresponding coulombic efficiency were obtained by testing at a current density of 1000 mAg. -1The energy density and corresponding energy efficiency obtained from the test at the current density of 1.0 mA / cm2. DETAILED DESCRIPTION

[0028] Example 1

[0029] Li 1.33-0.33x V x Ti 0.67-0.67x S2, (0≤x≤0.5) materials were synthesized with Li 1.27 V 0.2 Ti 0.53 S2, for example, the samples were prepared by a modified solid-state synthesis method.

[0030] First, the stoichiometric ratio of Li2S powder, vanadium powder, titanium powder and sulfur powder were ground in a mortar and mixed uniformly, and then pressed into a 16 mm diameter sheet precursor using a tablet grinder. Then the precursor was sealed in a quartz tube, and the vacuum degree was maintained at about 10 -5 mbar. Then the sealed precursor was placed in a tube furnace and slowly heated to 750°C and annealed for 35 h. Immediately after annealing, quenching in cold water was performed to cool it to room temperature quickly. Finally, the cooled sample was transferred to a glove box, ground into powder and stored for use. Li 1.27 V 0.2 Ti 0.53 S2 needs to avoid contact with air throughout the process.

[0031] Structure and morphology characterization

[0032] First, a series of Li 1.33-0.33x V x Ti 0.67-0.67x S2(0≤x≤0.5) samples with different vanadium doping contents were synthesized and characterized by XRD. The test 2θ range was 10-80°, and the test was as shown in Figure 1 The XRD pattern of the undoped Li2TiS3(x=0) sample showed typical O3-type layered structure characteristics, with lithium ions occupying the octahedral sites of the lithium layer, and part of the lithium and titanium ions occupying the octahedral sites of the transition metal layer. It is noted that there is a superlattice peak around 18-20°, which is caused by the ordered structure of LiTi6 units in the transition metal layer. With the introduction of vanadium ions (0.1≤x≤0.4), it is observed that the position of the main peak only shifts slightly, and no impurity phase is generated. This indicates that vanadium has been successfully doped into the Li2TiS3 system. At the same time, it is noted that with the increase of vanadium content, the signal of the superstructure peak gradually weakens and disappears. This is because the introduction of vanadium ions disrupts the ordered structure of the transition metal layer. When the vanadium content increases to 0.4≤x≤0.5, it is observed that the (003) main peak splits, which indicates that increasing the vanadium content will generate a small amount of impurity phase.

[0033] Using GSAS II software to analyze Li 1.27 V 0.2 Ti 0.53 The XRD pattern of sample S2 was refined using Rietveld, and the results are as follows: Figure 2 As shown in Table 1. All peaks in the XRD pattern correspond to... In the space group, vanadium ions replace the positions of titanium ions in the transition metal layer. However, the positions of lithium, vanadium, and titanium ions between the transition metal layers are long-range disordered, hence no superstructure peaks appear in the XRD. The cell parameters obtained through refinement are... More detailed parameters are shown in Table 1. Furthermore, the proportions of each element were verified by ICP testing, and the results are shown in Table 2. Li 1.27 V 0.2 Ti 0.53 The Li, V, and Ti ratios in sample S2 are consistent with expectations, and the normalized chemical formula is Li. 1.27 V 0.2 Ti 0.53 S2.

[0034] Table 1 Li 127 V 02 Ti 053 XRD Rietveld refinement results for sample S2.

[0035]

[0036] Table 2 shows the Li values ​​obtained from ICP-AES results. 1.27 V 0.2 Ti 0.53 Stoichiometry of elements in sample S2.

[0037]

[0038] Li was also characterized using SEM. 1.27 V 0.2 Ti 0.53 Microstructure of sample S2, such as Figure 3 As shown. Li 1.27 V 0.2 Ti 0.53 Sample S2 exhibits a granular morphology, with particle sizes mainly ranging from 20 to 50 μm. Magnified particles reveal a distinct layered structure, a common morphological characteristic of layered cathode materials.

[0039] To further characterize Li 1.27 V 0.2 Ti 0.53The microcrystalline structure of the S2 sample was also observed directly using advanced aberration-corrected transmission electron microscopy (STEM) combined with high-angle annular dark-field (HAADF) and annular bright-field (ABF) imaging. 1.27 V 0.2 Ti 0.53 Atomic arrangement order in sample S2 ( Figure 4 (ab). HAADF-STEM is mainly used for imaging samples containing heavy elements, while ABF-STEM can be used for imaging light elements. Figure 4 The value of 'a' shows the Li observed along the

[010] direction. 1.27 V 0.2 Ti 0.53 The HAADF-STEM image of sample S2 shows bright spots representing the positions of heavy elements (transition metals and sulfur). The atomic arrangement in the image conforms to the stacking sequence of the O3 layered structure and perfectly matches the crystal model. Transition metal and lithium layers alternate, with an interlayer spacing of [missing information]. about. Figure 4 b is the ABF-STEM image of the corresponding region, with bright spots representing lithium ion sites. Furthermore, Li was investigated using energy-dispersive X-ray spectroscopy (EDS). 1.27 V 0.2 Ti 0.53 The distribution of each element in sample S2 within the sample particles, and the test results are as follows: Figure 4 As shown in cf., the Ti, V, and S in the particles are uniformly distributed, indicating that the preparation has good homogeneity.

[0040] Electrochemical characterization

[0041] To determine the optimal vanadium doping ratio, the prepared Li 1.33-0.33x V x Ti 0.67-0.67x Electrochemical tests were conducted on S2 (0≤x≤0.5) cathode material. The cathode material, conductive agent (acetylene black), and binder (PVDF) were uniformly mixed in a 7:2:1 ratio to form the cathode sheet, which was then assembled with a lithium metal anode to form a half-cell. The electrolyte used was a 1.0M LiPF6 solution dissolved in a 1:1:1 volume ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The voltage range tested was 1.8–3.0 V. A small current (20 mAg) was initially used. -1 Perform charge and discharge tests, such as Figure 5 As shown, consistent with expectations, the anionic redox activity of Li₂TiS₃ is very low; the sulfur redox plateau near 2.8V contributes only 80 mAh g⁻¹. -1 The reversible capacity is around 339 mAh, although its theoretical capacity is as high as 339 mAh g. -1 (Figure 5 a). After doping with a small amount of vanadium (x = 0.1), the reversible capacity reached 140 mAh g -1 , which indicates that vanadium doping can significantly activate the redox activity of sulfur Figure 5 b). When the doping content of vanadium ions increased to x = 0.2, the reversible capacity reached 308 mAh g -1 , which is almost close to the theoretical value of Li 1.27 V 0.2 Ti 0.53 S2cathode 313 mAh g -1 Figure 5 c). This indicates that both lithium ions in the transition metal layer and lithium ions in the lithium layer in Li 1.27 V 0.2 Ti 0.53 S2cathode can be reversibly deintercalated in small current tests. It is also noted that the subsequent cycle curves are basically coincident, with almost no capacity and voltage decay, indicating that Li 1.27 V 0.2 Ti 0.53 S2has good structural stability. When the content of vanadium continues to increase (0.3≤x≤0.5), the reversible capacity appears a slight decrease, which may be due to the increase of vanadium content is not conducive to the system to continue to maintain the O3-type layered structure, which is consistent with the trend of the main peak splitting observed in the XRD pattern Figure 1 and Figure 5 d-f). At the same time, the relative atomic mass of vanadium is 50.942, and the relative atomic mass of titanium is 47.867, so increasing the content of vanadium will also lead to a decrease in the theoretical capacity. Nevertheless, these materials still exhibit reversible capacities of up to 287 mAh g -1 (x = 0.3), 278 mAh g -1 (x = 0.4) and 242 mAh g -1 (x = 0.1), and no capacity and voltage decay in subsequent cycles.

[0042] The measured capacity and theoretical capacity of all components in Li 1.33-0.33x V x Ti 0.67-0.67x S2(0≤x≤0.5) materials are summarized, as shown in Figure 6 . Among them, the theoretical capacity corresponds to the maximum capacity calculated by removing all lithium ions in the components (including the lithium layer and the transition metal layer), and the measured capacity is obtained in the voltage range of 1.8-3.0 V at a current density of 20 mAg –1 . With the increase of the doping content of vanadium ions, the theoretical capacity decreases from 339 mAh g -1 ​(x = 0) gradually decreased to 273 mAh g -1 (x = 5), due to the increase of vanadium content, which leads to the increase of relative molecular mass of the component. The measured capacity presents a trend of increasing first and then decreasing with the increase of vanadium ion doping content, in which the component corresponding to x = 0.2 (Li 1.27 V 0.2 Ti 0.53 S2) reaches the maximum value and is almost equal to the theoretical value. This preliminarily indicates that the component corresponding to x = 0.2 is the best doping ratio.

[0043] Li 1.33-0.33x V x Ti 0.67-0.67x The rate performance of the Li2TiS3(0≤x≤0.5) cathode material was tested, and the current density was 20, 50, 100, 200, 500 and 1000 mAg -1 , and the test results are shown in Figure 7 . The initial capacity of the Li2TiS3 sample is low, only 78 mAh g -1 , and the capacity gradually decreases to 23 mAh g -1 as the current density increases to 1000 mAg -1 . With the gradual increase of vanadium component to x = 0.2, the rate performance is significantly improved. The specific capacity obtained under the test of current density of 20, 50, 100, 200, 500 and 1000 mAg -1 is 308, 289.3, 276.1, 262.6, 238.8 and 217.5 mAh g -1 , respectively, and the corresponding capacity retention rate is 100%, 94%, 90%, 85%, 78% and 71%. When the current returns to 20 mAg -1 , the capacity also completely recovers to the initial capacity level, showing excellent rate performance. Other components (0.3≤x≤0.5) also show rate performance, but the capacity decreases.

[0044] Research on charge compensation mechanism

[0045] According to the previous electrochemical characterization test, the redox platform is preliminarily determined to activate the redox reaction of sulfur in the Li 1.33-0.33x V x Ti 0.67- 0.67x S2(0≤x≤0.5) cathode material by the doped vanadium ion, and the trend of increasing first and then decreasing is presented with the increase of vanadium ion content. In order to explore the charge compensation mechanism in the material, the optimal doping ratio of Li 1.27 V 0.2 Ti0.53 The S2 cathode material was used as the research object for subsequent research. Through ex-situ XPS testing, the valence state changes of sulfur in the Li 1.27 V 0.2 Ti 0.53 S2 cathode material during charge and discharge processes were characterized, as Figure 8 shown. XPS technology is an important semi-quantitative elemental analysis technology and can be used to analyze the chemical state of elements. Five points were selected to test the ex-situ S2p XPS spectra of the Li 1.27 V 0.2 Ti 0.53 S2 cathode material, corresponding to different states on the left charge-discharge curve. The right side shows the fitting data of the S2p XPS spectra. For the original sample, the S2p XPS spectra could be fitted into a double peak at 161.5 eV (2p 3 / 2 ) and 162.5 eV (2p 1 / 2 ), which belongs to the chemical state of S 2- , consistent with the design and expectation. As the charging process proceeds, the XPS spectra show a trend of shifting to higher binding energy, and a second set of double peaks are fitted at 163.0 eV and 164.0 eV, corresponding to the S m- (1 < m < 2) chemical state. This indicates that sulfur is gradually oxidized during the charging process. At the fully charged state, the proportion of the S m- (1 < m < 2) chemical state reaches the maximum value. During the subsequent discharging process, the proportion of the S m- (1 < m < 2) chemical state gradually decreases again, which means that sulfur is gradually reduced. When the full discharge ends, the peak of the S m- (1 < m < 2) chemical state completely disappears, and only the peak of the S 2- chemical state remains, consistent with the initial state. The XPS spectra of S2p during the entire charge-discharge process show completely reversible changes, that is, the redox of sulfur has good reversibility. According to the analysis results of XPS, it has been verified that sulfur provides charge compensation during charge and discharge. According to the material design and the references consulted, the valence states of V, Ti, and S in the Li 1.27 V 0.2 Ti 0.53 S2 system are +3, +4, and -2 valence respectively. Among them, +4-valent Ti cannot be further oxidized because it has no d electrons in its outermost layer. While +3-valent V has a d 2 configuration, so V may participate in the oxidation reaction and be oxidized to +4 valence or even +5 valence. In order to explore whether the transition metals Ti and V also participate in the redox reaction, ex-situ XAS testing was carried out using synchrotron radiation light source ( Figure 9 and Figure 10 ). Figure 9 shows the Li 1.27 V 0.2 Ti0.53 XAS spectra of Ti element of S2 cathode material in original state, charged state and discharged state. From the XANES spectra, it can be seen that there is almost no shift of Ti K-edge absorption edge during the charging and discharging process. This indicates that Ti keeps the same valence state (+4 valence) during the charging and discharging process, i.e. Ti does not participate in charge compensation Figure 9 a) of FIG. 4. In addition, k 3 The Ti K-edge EXAFS spectra of weighted Fourier transform also indicate that the bond length of Ti-S bond almost does not change, i.e. the local chemical environment around Ti does not change significantly Figure 9 b) of FIG. 4. The above results fully prove that Ti does not participate in charge compensation during the charging and discharging process. For V, 7 points are selected to test XAS during the charging and discharging process in order to more accurately characterize the valence state change of V at different stages Figure 10 a) of FIG. 4. It should be noted that no obvious shift of V K-edge absorption edge in XANES spectrum is observed. Although there is a slight shift, the energy of the shift is very small, and the valence state change caused thereby is basically negligible. This abnormal behavior may be related to the electron transfer from ligand sulfur to metal vanadium, i.e. the electron is transferred from sulfur to vanadium and then to the external circuit, and the whole process does not cause the vanadium to gain or lose electrons, and the valence state remains unchanged.k 3 The V K-edge EXAFS spectra of weighted Fourier transform also indicate that the bond length of V-S bond is slightly shortened during the charging process, and completely returns to the initial bond length at the end of discharging, and this slight local environment change is very likely caused by the gain and loss of electrons of sulfur Figure 10 b) of FIG. 4. At the same time, the previous electrochemical test shows that there is only a single redox peak during the charging and discharging process, which is consistent with the test results of XAS, i.e. only sulfur participates in charge compensation during the whole process, and the valence state change of titanium and vanadium can be ignored. Based on the above results, it is considered that almost all the capacity is contributed by the redox reaction of sulfur, and vanadium and titanium themselves do not participate in charge compensation.

[0046] Reversible deintercalation mechanism of lithium ions

[0047] Based on the analysis of the previous electrochemical and XRD characterization tests, it is preliminarily verified that Li 1.27 V 0.2 Ti 0.53 All Li + in the lithium layer and the transition metal layer in the S2 cathode material can be reversibly deintercalated. In order to more accurately characterize the deintercalation of Li + during the charging and discharging process, the chemical shift of lithium at different charging and discharging states is characterized by 7 Li solid-state nuclear magnetic resonance (SSNMR) spectrum Figure 11). According to the capacity voltage curve of the first circle, five points were selected for 7 Li solid-state nuclear magnetic resonance tests were performed on the original sample, the sample charged to 2.8V, the sample charged to 3.0V, the sample discharged to 2.5V and the sample discharged to 1.8V. The peaks appearing near 70ppm and 0.5ppm in the original sample can generally be attributed to lithium in the lithium layer in the transition metal layer. After charging to 2.8V, it was found that the peak around 70ppm still existed, indicating that the Li in the lithium layer was preferentially removed during the delithiation process + , which is consistent with the description in the literature. Subsequently, after charging to 3.0V, it was found that the peak around 70ppm had basically disappeared, which meant that the lithium Li + in the transition metal layer also left at the end of charging. In the subsequent discharge process, it was observed that the peak around 70ppm gradually recovered to the original height, i.e. Li + re-embedded into the transition metal layer, and the structure returned to the initial state. Based on the results on the machine, it was proved that Li 1.27 V 0.2 Ti 0.53 S2positive electrode material has a high capacity, which is derived from all Li + in the lithium layer and the transition metal layer can be reversibly deintercalated.

[0048] In addition to capacity and rate performance, long cycle test is one of the important indicators for evaluating positive electrode materials. According to the above characterization, the optimal doping ratio (Li 1.27 V 0.2 Ti 0.53 S2) has been determined, and next the material will be characterized for long cycle performance under high current. The long cycle test is carried out in constant current charge and discharge mode, and the current is set to 1000mAg -1 , and the voltage interval is 1.8-3.0V. As shown in a of Figure 12 , the initial capacity of Li 1.27 V 0.2 Ti 0.53 S2tested under a current density of 1000mAg -1 is 205.0mAh g -1 , and the capacity after 1000 cycles is 181.5mAg -1 , with a capacity retention rate of 88.5%, which is better than most of the currently reported sulfide positive electrode materials. After 4300 cycles, the discharge capacity is still 166.1mAh g -1 , with a capacity retention rate of 81.0%. Throughout the cycle process, the coulombic efficiency is maintained near 100%, indicating that the delithiation of Li + has very good reversibility. In addition, the energy density and energy efficiency during the long cycle process were calculated according to the test results, as shown in Figure 12Li 1.27 V 0.2 Ti 0.53 The initial energy density of S2 was 470.2 Wh kg -1 , and still had 365.0 Wh kg -1 after cycling to 4300 cycles, and the energy efficiency remained above 86.3%.

Claims

1. A lithium-rich layered sulfide cathode material, characterized in that, The general formula is Li 1.33-0.33x V x Ti 0.67-0.67x S2, and 0 < x ≤ 0.5, belongs to hexagonal O3 type crystal structure, and the corresponding space group is .

2. The lithium-rich layered oxysulfide cathode material of claim 1, wherein, 0.1＜x≤0.4。 3. The lithium-rich layered oxysulfide cathode material of claim 1, wherein, The positive electrode material has an energy density of 430-480 Wh kg -1 .

4. The method of producing a lithium-rich layered sulfide cathode material according to claim 1, characterized in that, It comprises the following steps: step 1, mixing Li2S powder, vanadium powder, titanium powder and sulfur powder, and grinding, tabletting; step 2, after constant temperature heat treatment, quenching, obtaining the positive electrode material.

5. The preparation method according to claim 4, characterized in that, The heat treatment temperature is 600-800 DEG C, and the time is 20-40h.

6. The preparation method according to claim 4, characterized in that, During the heat treatment process, the vacuum degree is kept at 10 -4 -10 -6 mbar.

7. The application of the lithium-rich layered sulfide positive electrode material in claim 1 in lithium ion batteries.

8. Use according to claim 7, characterized in that, The lithium ion battery adopts a lithium metal negative electrode, and has an 85-90% capacity retention rate when charged and discharged 4300 times.

Images