A chromium-titanium bimetallic layered sulfide positive electrode material, a preparation method and application thereof

Abstract

The application provides a chromium-titanium bimetallic layered sulfide positive electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion battery materials. x Ti y S2, and x+y=1, belongs to a hexagonal O1 type structure, and a space group is Pm1. Micro-morphology analysis shows that the material is in a granular form, a particle size distribution is 2-15 mu m, a particle surface is in a layered structure feature, and each element is uniformly distributed on the particle surface and in a bulk phase. The capacity of the material is mainly derived from oxidation and reduction between titanium and sulfur, chromium has a stable structure frame effect, and does not participate in a charge compensation process. Electrochemical analysis shows that the LiCr 2 / 3 Ti 1 / 3 S2 positive electrode material has a reversible capacity of 223 mAh g ‑1 , and is close to a theoretical value of the system positive electrode material. In addition, the material shows excellent rate performance and cycle stability, and still maintains a capacity retention rate of 80% after 330 cycles.

Description

Technical Field

[0001] This invention relates to a layered sulfide cathode material, its preparation method, and its application in lithium-ion batteries, belonging to the technical field of lithium-ion battery cathode materials. Background Technology

[0002] In recent years, the urgent need for improved energy density in portable electronic devices, electric vehicles, and large-scale energy storage systems has continuously driven the design and development of novel lithium-ion battery (LIB) cathode materials. Although layered transition metal oxides (such as LiCoO2 and LiNi)... x Mn y Co z O2 (x+y+z=1) has dominated commercial cathode materials for decades, but its theoretical capacity remains limited by the traditional cation redox reaction mechanism. In contrast, anionic redox chemistry—that is, the direct participation of lattice oxygen or sulfur in a reversible charge compensation mechanism—has been proven to overcome the theoretical bottleneck of traditional cation-based reactions, thereby significantly improving the specific capacity of electrode materials. Among numerous candidate materials, layered sulfides are considered an ideal system for realizing anionic redox reactions due to their unique electronic structure. Early mechanistic studies have shown that typical LiTiS2 layered sulfide materials, under deep charge, exhibit high specific capacity. 3+ Over-oxidized to Ti 4+ This will lead to the depletion of electrons in the Ti 3d band. This electron transfer process induces local lattice distortion by reconstructing the local environment of the electronic structure, ultimately leading to irreversible phase transitions, transition metal migration, and the collapse of the layered structural framework.

[0003] According to the Mott-Hubbard theory, the inherent limitations of LiTiS2 can be overcome by reducing the d-p band gap between the ligand and the transition metal to modulate its electronic structure. This can be achieved using redox-active cations (such as Co). 2+ Fe 2+ V 3+ (etc.) partially replaces Ti 3+ This strategy can introduce new d-band electronic states, effectively reducing the d-p band gap and thus promoting charge transfer from ligands to metals. It can activate redox reactions involving both cations and anions, although cation redox reactions still dominate. The voltage variation trend of such doped systems remains predictable: it changes linearly with increasing doping concentration and exhibits a stable voltage plateau across different compositions. However, although Co… 2+ Fe 2+ and V 3+The ligand-metal band gap is reduced to some extent and the sulfur participates in charge compensation, but the inherent low redox potential still limits the ultimate energy density that the material can achieve. To achieve a higher redox potential, the transition metal d orbital energy level needs to be as close as possible to the S 3p orbital to minimize the band gap between the two. Among the 3d transition metals, chromium (Cr) is the only element that meets the above conditions - its 3d orbital overlaps with the S 3p orbital, and its sulfide exhibits excellent thermodynamic stability, making Cr substitution a promising optimization strategy. The density of states calculation further confirms that in Cr-doped LiTiS2, the Cr 3d electronic state and the S 3p band are highly overlapped in energy, significantly reducing the thermodynamic potential barrier that needs to be overcome for electron transfer from the ligand to the metal, thereby enabling the sulfur anion to undergo reversible redox reactions at a higher potential. SUMMARY

[0004] The present application aims to solve the technical problem that when the existing layered oxide positive electrode material is applied to a lithium ion battery, it is prone to lattice oxygen loss, structure instability collapse and slow reaction kinetics during the anion redox reaction. In view of the above limitations, the present application proposes a chromium-titanium bimetallic layered sulfide positive electrode material, in which chromium is an inert component and has the function of stabilizing the structure framework. The material has a reversible capacity as high as 223 mAh g -1 , and exhibits significantly enhanced comprehensive electrochemical performance.

[0005] To achieve the above application purposes, the present application adopts the following technical solutions:

[0006] The present application provides a chromium-titanium bimetallic layered sulfide positive electrode material, whose chemical general formula is LiCr x Ti y S2, and x+y=1, the crystal structure is hexagonal O1 type, and the space group is P m1.

[0007] Further, the micro-morphology of the material is granular, the particle size is 2-15 μm, the particle surface is layered, and the Cr, Ti and S elements are uniformly distributed on the particle surface and in the bulk phase.

[0008] Further, the reversible capacity of the material is ≥146.4 mAh g -1 , and the capacity retention rate after 330 cycles is ≥52%.

[0009] Further, the chemical general formula of the material is LiCr 2 / 3 Ti 1 / 3 S2; the reversible capacity of the material is 223 mAh g -1 , and the capacity retention rate after 330 cycles is 80%.

[0010] The application further provides a preparation method of the chromium-titanium bimetallic layered sulfide positive electrode material, comprising the following steps:

[0011] Step 1: mixing Li2S, a chromium source, a titanium source and a sulfur source according to stoichiometric ratios, grinding thoroughly and then pressing into a sheet;

[0012] Step 2: treating at a constant temperature of 500-900 DEG C for 10-40 h under a vacuum degree of 10 -2 ~10 -5 mbar and an inert atmosphere, and then quenching to room temperature to obtain the chromium-titanium bimetallic layered sulfide positive electrode material.

[0013] Further, the chromium source in step 1 is Cr powder or Cr2S3, the titanium source is Ti powder or TiS2, and the sulfur source is S powder, Cr2S3 or TiS2.

[0014] The application further provides an application of the chromium-titanium bimetallic layered sulfide positive electrode material as a lithium ion battery positive electrode material. The capacity retention rate of the positive electrode material is greater than or equal to 80% after 330 cycles at 2C (1C=100 mA g -1 ).

[0015] The application has the following beneficial effects:

[0016] (1) Compared with a layered oxide positive electrode material, the sulfide positive electrode material forms a strong metal-ligand covalent bond with 3d transition metal ions, and realizes a highly reversible sulfur anion oxidation-reduction reaction, so that the sulfide positive electrode material has a more stable structure and a higher specific capacity, and overcomes problems such as oxygen loss and structure collapse in the anion oxidation-reduction reaction process.

[0017] (2) The layered positive electrode material can only realize a partially reversible anion oxidation-reduction reaction in the charging and discharging process, and the capacity and reversibility still have a large space for improvement. The new material LiCr 2 / 3 Ti 1 / 3 S2 of the application can exhibit a reversible capacity of up to 223 mAh g -1 , close to the theoretical capacity value. In the charging and discharging process, the LiCr 2 / 3 Ti 1 / 3 S2 participates in charge compensation, and the capacity contribution of sulfur is dominant. The chromium in the structure is an inert component and does not participate in charge compensation, and has the effect of stabilizing the structure framework. In addition, the positive electrode material still has an initial capacity retention rate of 80% after 330 long cycles, which is significantly improved compared with the traditional LiTiS2 positive electrode material. In-situ XRD test results show that the LiCr 2 / 3 Ti1 / 3 S2 cathode material always keeps stable layered structure during charge-discharge process, thus ensuring lithium ions to be smoothly inserted and extracted during charge-discharge process. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 LiCr 2 / 3 Ti 1 / 3 Powder XRD patterns of S2 and LiTiS2 samples.

[0019] Figure 2 LiCr 2 / 3 Ti 1 / 3 Micro-morphology characterization of S2 powder sample. a. SEM image at low magnification. b. SEM image at high magnification.

[0020] Figure 3 Micro-morphology characterization of LiTiS2 powder sample. a. SEM image at low magnification. b. SEM image at high magnification.

[0021] Figure 4 LiCr 2 / 3 Ti 1 / 3 High resolution TEM image of S2 powder sample; c-f. LiCr 2 / 3 Ti 1 / 3 SEM image of S2 powder sample and corresponding EDS maps of Cr, Ti and S.

[0022] Figure 5 a. First three charge-discharge curves of LiTiS2 cathode, test current density is 0.1 C, voltage window is 1.1-3.7 V; b. First three charge-discharge curves of LiCr 2 / 3 Ti 1 / 3 S2 cathode, test current density is 0.1 C, voltage window is 1.1-3.7 V.

[0023] Figure 6 Capacity contribution of Ti and S in redox process extracted from charge-discharge curves of LiTiS2 and LiCr 2 / 3 Ti 1 / 3 S2.

[0024] Figure 7 a. Differential capacity (dQ / dV) curve of LiTiS2 cathode; b. Differential capacity (dQ / dV) curve of LiCr 2 / 3 Ti 1 / 3 S2 cathode.

[0025] Figure 8 LiCr 2 / 3 Ti 1 / 3Charge compensation mechanism of S2 during charge-discharge process. a. Ti 2p XPS spectrum; b. S2p XPS spectrum; c. Cr 2p XPS spectrum.

[0026] Figure 9 LiCr 2 / 3 Ti 1 / 3 Charge-discharge curves and in-situ XRD patterns of S2 cathode during the first cycle.

[0027] Figure 10 LiTiS2and LiCr 2 / 3 Ti 1 / 3 Rate capability and long cycle performance of S2. a. Rate capability plot obtained at current densities from 0.1 to 10.0 C. b. Long cycle performance plot obtained at a current density of 2.0 C. DETAILED DESCRIPTION

[0028] Example 1 LiCr 2 / 3 Ti 1 / 3 Preparation of S2 cathode material:

[0029] (1) Dosing and mixing

[0030] The raw materials were weighed according to the molar ratio of Li:Cr:Ti:S = 1.05:0.667:0.333:2.00:

[0031] Li2S (brand Aladdin, purity 95.0 %, excess 5 wt% to compensate for high-temperature volatilization) 0.508 g;

[0032] Cr powder (brand Aladdin, purity 99.5 %) 0.700 g;

[0033] Ti powder (brand Aladdin, purity 99.5 %) 0.322 g;

[0034] S powder (brand Aladdin, purity 99.0 %) 0.972 g.

[0035] The above raw materials were ground in a mortar to obtain a uniform precursor powder.

[0036] (2) Tabletting and packaging

[0037] ① The precursor powder was pressed into a 19 mm diameter tablet-shaped precursor with a mass of 0.8 g using a tabletting die.

[0038] ② The tablet-shaped precursor was sealed in a quartz tube, and the vacuum degree was maintained at 10 -5 mbar.

[0039] (3) High-temperature solid-state reaction and quenching

[0040] The sealing tube was placed in a tube furnace and heated to 500°C at a rate of 5°C / min, and held at that temperature for 40 hours. Immediately after the process, it was quenched in cold water to rapidly cool it to room temperature.

[0041] (4) Post-processing

[0042] The cooled sample was transferred to a glove box and thoroughly ground into powder, resulting in black LiCr. 2 / 3 Ti 1 / 3 S2 powder, stored for later use. Preparation of LiCr 2 / 3 Ti 1 / 3 S2 needs to avoid contact with air throughout the entire process.

[0043] Example 2 LiCr 1 / 2 Ti 1 / 2 Preparation of S2 cathode material:

[0044] (1) Ingredients and mixing

[0045] Weigh the raw materials according to the molar ratio of Li∶Cr∶Ti∶S=1.05∶0.50∶0.50∶2.00:

[0046] Li2S (brand name Aladdin, purity 95.0%, excess 5 wt% to compensate for high temperature volatilization) 1.049 g;

[0047] Cr powder (brand name: Aladdin, purity: 99.5%) 0.525 g;

[0048] Ti powder (brand name: Aladdin, purity: 99.5%) 0.484 g;

[0049] S powder (brand name: Aladdin, purity: 99.0%) 0.972 g.

[0050] The above raw materials were thoroughly ground in a mortar and pestle to obtain a uniform precursor powder.

[0051] (2) Tableting and Packaging

[0052] ① The precursor powder was pressed into a 19 mm diameter sheet precursor using a tableting mold, with a mass of 0.8 g.

[0053] ② Seal the sheet-like precursor in a quartz tube, maintaining a vacuum of 10. -3 mbar.

[0054] (3) High-temperature solid-state reaction and quenching

[0055] The sealing tube was placed in a tube furnace and heated to 700°C at a rate of 5°C / min, and held at that temperature for 25 hours. Immediately after the process, it was quenched in cold water to rapidly cool it to room temperature.

[0056] (4) Post-processing

[0057] The cooled sample was transferred to a glove box and thoroughly ground into powder, resulting in black LiCr. 1 / 2 Ti 1 / 2 S2 powder, stored for later use. Preparation of LiCr 1 / 2 Ti 1 / 2 S2 needs to avoid contact with air throughout the entire process.

[0058] Example 3 LiCr 1 / 3 Ti 2 / 3 Preparation of S2 cathode material:

[0059] (1) Ingredients and mixing

[0060] Weigh the raw materials according to the molar ratio of Li∶Cr∶Ti∶S=1.05∶0.33∶0.67∶2.00:

[0061] Li2S (brand name Aladdin, purity 95.0%, excess 5 wt% to compensate for high temperature volatilization) 1.049 g;

[0062] Cr powder (brand name: Aladdin, purity: 99.5%) 0.350 g;

[0063] Ti powder (brand name: Aladdin, purity: 99.5%) 0.645 g;

[0064] S powder (brand name: Aladdin, purity: 99.0%) 0.972 g.

[0065] The above raw materials were thoroughly ground in a mortar and pestle to obtain a uniform precursor powder.

[0066] (2) Tableting and Packaging

[0067] ① The precursor powder was pressed into a 19 mm diameter sheet precursor using a tableting mold, with a mass of 0.8 g.

[0068] ② Seal the sheet-like precursor in a quartz tube, maintaining a vacuum of 10. -2 mbar.

[0069] (3) High-temperature solid-state reaction and quenching

[0070] The sealing tube was placed in a tube furnace and heated to 900°C at a rate of 5°C / min, and held at that temperature for 10 hours. Immediately after the process, it was quenched in cold water to rapidly cool it to room temperature.

[0071] (4) Post-processing

[0072] The cooled sample was transferred to a glove box and thoroughly ground into powder, resulting in black LiCr. 1 / 3 Ti 2 / 3 S2 powder, stored for later use. Preparation of LiCr 1 / 3 Ti 2 / 3 S2 needs to avoid contact with air throughout the entire process.

[0073] Performance characterization of the cathode materials prepared in Examples 1-3:

[0074] (1) Structural and morphological characterization

[0075] The following uses the LiCr prepared in Example 1 as an example. 2 / 3 Ti 1 / 3 S2 represents the structural and morphological characterization results of the material of the present invention, specifically the LiCr in Example 2. 1 / 2 Ti 1 / 2 S2, LiCr in Example 3 1 / 3 Ti 2 / 3 S2 achieves similar results with the same trend.

[0076] For the synthesized LiCr 2 / 3 Ti 1 / 3 S2 and LiTiS2 samples were characterized by powder XRD, with a 2θ range of 10–80°. The test results are as follows: Figure 1 As shown. Powder XRD patterns confirm that LiCr 2 / 3 Ti 1 / 3 Both the S2 and LiTiS2 samples exhibit typical O1-type layered structure characteristics, corresponding to the space group P. m1. Lithium ions occupy octahedral sites in the lithium layer, while chromium and titanium ions occupy octahedral sites in the transition metal layer. This result is consistent with standard PDF cards JCPDS#74-0593 (LiCrS2) and #28-0595 (LiTiS2). LiCr... 2 / 3 Ti 1 / 3 The (001) peak of sample S2 is located between LiTiS2 and LiCrS2, indicating that chromium ions were successfully doped into LiTiS2 and conform to Vegard's law. Scanning electron microscopy (SEM) images show that LiCr... 2 / 3Ti 1 / 3 The particle size distribution of sample S2 is relatively uniform, ranging from 2 to 15 μm, with minimal agglomeration. Figure 2In contrast, LiTiS2 particles exhibit irregular polygonal shapes, a wider size distribution (approximately 2–20 μm), and significant agglomeration. Furthermore, surface cracking and lamellar exfoliation observed on LiTiS2 suggest that stress accumulation may have occurred during the synthesis process. Figure 3 High-resolution transmission electron microscopy (HR-TEM) images ( Figure 4 It exhibits clear lattice fringes with a lattice spacing of 0.605 nm, corresponding to LiCr 2 / 3T i1 / 3 The (001) plane of S2 is consistent with the XRD pattern. Furthermore, energy-dispersive X-ray spectroscopy (EDS) was used to investigate the LiCr... 2 / 3T i1 / 3 The distribution of each element in the particles of sample S2. For example... Figure 4 As shown, EDS confirmed the uniform distribution of Cr, Ti, and S within the particles, indicating that chromium-doped LiCr 2 / 3 Ti 1 / 3 The S2 sample was successfully synthesized and exhibited good homogeneity.

[0077] (2) Electrochemical characterization

[0078] The prepared LiCr 2 / 3 Ti 1 / 3 Half-cells were assembled using S2 and LiTiS2 cathode materials, and charge-discharge tests were conducted. The test conditions were: current density 0.1 C (1C = 100 mA g). -1 The voltage window is 1.1–3.7 V. The charge / discharge curves for the first three cycles are as follows: Figure 5 As shown. According to existing research, the capacity of pristine LiTiS2 mainly comes from the low-voltage region below 2.5 V, corresponding to Ti 3+ / Ti 4+ The redox reaction yielded a specific capacity of approximately 116.6 mAh g⁻¹. -1 The energy density is 234.4 Wh kg. -1 In contrast, Cr 3+ Partial replacement of Ti 3+ Subsequently, its capacity and energy density were both improved, among which LiCr 1 / 3 Ti 2 / 3 S2, LiCr 1 / 2 Ti 1 / 2 S2 and LiCr 2 / 3 Ti 1 / 3 The corresponding capacity of S2 is 146.4 mAh g. -1 187.4 mAh g -1 and 223.0 mAh g -1The corresponding energy density is 311.8 Wh kg. -1 407.3Wh kg -1 and 488.8 Wh kg -1 Furthermore, its average discharge voltage gradually increased from 2.10 V for LiTiS2 to [a higher value] for LiCr. 2 / 3 Ti 1 / 3 S2 at 2.19 V. The activation of the sulfur redox process can be attributed to LiCr. 2 / 3 Ti 1 / 3 The unique overlapping band structure of LiTiS2 not only provides additional capacity through the redox reaction of sulfur but also contributes to increasing the redox potential of the material. Notably, the high-voltage plateau remains significant and stable in subsequent cycles, indicating that the sulfur-involved redox reaction has good reversibility and structural stability. Furthermore, comparisons with LiTiS2 and LiCr... 2 / 3 T i1 / 3 The voltage distribution curve of S2 can be used to extract the contribution of the titanium and sulfur redox reactions to the capacity, such as... Figure 6 As shown. Cr is introduced into LiTiS2. 3+ Partial replacement of Ti 3+ Subsequently, the redox activity of sulfur was significantly activated, increasing the capacity contribution of the anion (S) from 38.3 mAh g⁻¹. -1 Increased to 114.4 mAh g -1 . Figure 7 The corresponding differential capacity (dQ / dV) plot derived from the charge-discharge curves is shown. Consistent with previous results, the dQ / dV curve of LiTiS2 shows a broadened oxidation peak centered around 2.35 V, corresponding to Ti 3+ / Ti 4+ The redox pair exhibits a small characteristic peak at approximately 2.75 V, which may be related to the initial oxidation process of sulfur. Similarly, LiC... r2 / 3 Ti 1 / 3 S2 also exhibits redox peak pairs similar to LiTiS2 below 2.5 V, which can be attributed to Ti. 3+ / Ti 4+ Redox reactions. Notably, two additional oxidation peaks appeared in the high-voltage range above 2.5 V, indicating electron transfer from the ligand to the metal during deep delithiation, accompanied by a gradual oxidation of sulfur. These experimental results confirm the LiCr... 2 / 3 Ti 1 / 3 The redox mechanism involving both cations and anions in S2 highlights the synergistic effect of chromium doping on improving capacity and optimizing voltage distribution.

[0079] (3) Research on charge compensation mechanism

[0080] The following uses the LiCr prepared in Example 1 as an example. 2 / 3 Ti 1 / 3 S2 represents the charge compensation mechanism of the material of the present invention, as shown in Example 2, LiCr. 1 / 2 Ti 1 / 2 S2, LiCr in Example 3 1 / 3 Ti 2 / 3 S2 achieves similar results with the same trend.

[0081] To clarify LiCr 2 / 3 Ti 1 / 3 The redox mechanism of S2 during electrochemical cycling was investigated using surface etching X-ray photoelectron spectroscopy (XPS) to study its charge compensation mechanism under different charge and discharge states. Figure 8 XPS spectra of Cr 2p, Ti 2p, and S 2p were collected under different charge / discharge states. In the initial state, the valence states of Cr, Ti, and S were fitted as +3, +3, and -2, respectively. During electrochemical cycling, significant changes in the binding energies of Ti 2p and S 2p were observed, indicating that both participated in redox reactions. Figure 8 ab). Specifically, when charged to 2.9 V, Ti 2p 3 / 2 The binding energy shifted from 457.0 eV to 457.8 eV, confirming the Ti... 3+ Oxidized to Ti 4+ This oxidation state of Ti 4+ The signal remained almost unchanged during the subsequent charging process, indicating that Ti 4+ It cannot be further oxidized. It is worth noting that when discharged to 1.1 V, Ti... 4+ The XPS signal disappeared, while the Ti 3+ The reappearance of the feature indicates that Ti 4+ Completely reversible reduction to Ti 3+ For the S 2pXPS spectrum, the doublet at 160.5 and 161.5 eV is attributed to lattice sulfides (S... 2- The characteristic peaks at 162.2 and 163.5 eV correspond to the oxide species S. n- (n < 2). During the initial charging process (< 2.9 V), no significant shift was detected in the S 2p spectrum, indicating that sulfur did not participate in the charge compensation process in the lower voltage range. In the fully charged state, S... n- The characteristic peaks confirmed that the electrochemical oxidation of sulfur mainly occurred between 2.9 V and 3.7 V. During the subsequent discharge process (3.7 V to 2.3 V), S... n-Species are gradually being reduced to S 2- It is noteworthy that the S 2p spectrum did not change further within the discharge range from 2.3 V to 1.1 V, indicating that the sulfur reduction reaction was essentially completed above 2.3 V. Furthermore, the Cr 2p spectrum did not show any significant shift throughout the entire charge-discharge process. Figure 8 c), indicating that Cr 3+ It remained electrochemically inert and did not undergo further oxidation. This result confirms that Cr... 3+ In the sulfur redox process, it mainly plays a role in stabilizing the structure, rather than participating in the reaction as an active redox center.

[0082] (4) Structural changes during the cycle

[0083] The following uses the LiCr prepared in Example 1 as an example. 2 / 3 Ti 1 / 3 S2 represents the structural changes of the material during the cycling process of the present invention, as shown in Example 2, LiCr. 1 / 2 Ti 1 / 2 S2, LiCr in Example 3 1 / 3 Ti 2 / 3 S2 achieves similar results with the same trend.

[0084] To monitor LiCr in real time 2 / 3 Ti 1 / 3 S2 electrode in Li + The structural evolution during the insertion / extraction process was assessed using in-situ X-ray diffraction (XRD) to evaluate the structural reversibility. Figure 9 The in-situ XRD patterns collected during the first cycle are shown. According to crystallographic theory, the (001) diffraction peak reflects the changes in the layered structure along the c-axis, while the (101) diffraction peak is related to the metal-ligand bonds within the transition metal layer. Figure 9 As can be seen, the 2θ angle of the (001) diffraction peak remains essentially unchanged throughout the charge-discharge process, indicating that the lattice parameter c remains almost constant during charge-discharge. In the deep charge state, the (101) diffraction peak shows a slight shift, which can be attributed to local lattice distortion caused by the redox reaction of sulfur in the highly delithiated state. Furthermore, the attenuation of the intensity of the (001) and (101) diffraction peaks is related to the large amount of Li... + The structural disorder caused by lithium desorption is related to the decomposition of lithium, a phenomenon commonly seen in layered cathode materials, usually stemming from excessive lithium desorption leading to a decrease in the long-range order of the crystal structure. During discharge, XRD patterns show that the diffraction peaks gradually return to their initial positions, indicating that the material exhibits good long-range order in Li₂. + Re-embedding allows the restoration of its original crystal structure. The changes in unit cell parameters, fitted based on in-situ XRD data, are as follows: Figure 9As shown in bc, the cell parameters change only slightly, indicating that the material structure remains stable during lithium-ion insertion / extraction. These results demonstrate that the introduction of Cr effectively stabilizes the layered framework, making LiCr... 2 / 3 Ti 1 / 3 S2 cathode can achieve Li + The reversible insertion and extraction of these components is crucial for their stability during long-term electrochemical cycling.

[0085] (5) Rate and long-cycle electrochemical performance evaluation

[0086] Figure 10 a comparison of LiTiS2 and LiCr 2 / 3 Ti 1 / 3 The rate performance of S2 at different current densities from 0.1C to 10C. It can be seen that LiCr... 2 / 3 Ti 1 / 3 S2 exhibits a significantly higher discharge capacity than LiTiS2 at all discharge rates. Specifically, the discharge capacity of LiTiS2 at 0.1C is approximately 116.6 mAh g⁻¹. -1 At 10 C, it drops to 52.5 mAh g. -1 Only about 45% of its capacity is retained. In contrast, LiCr 2 / 3 Ti 1 / 3 The S2 exhibits excellent rate performance, with discharge capacities of 223.0, 216.8, 204.3, 190.6, 172.9, 145.2, and 117.5 mAhg at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 C, respectively. -1 This significant improvement in rate performance indicates that, after reducing the d–p band gap between the ligand and the transition metal through chromium doping, Li… + Diffusion kinetics and charge transfer processes were significantly improved. Furthermore, Figure 10 b demonstrates the long-cycle performance of the two materials at a current density of 2 C. LiTiS2 exhibits significant capacity decay, retaining only 40% of its initial capacity after 330 cycles. In Cr... 3+ Partial replacement of Ti 3+ Afterwards, the cycling performance was significantly improved, with LiCr showing improved performance after 330 cycles. 1 / 3 Ti 2 / 3 S2 and LiCr 1 / 2 Ti 1 / The capacity retention rates of 2S2 reached 52% and 71%, respectively. In particular, LiCr... 2 / 3 Ti 1 / 3 S2 maintained 142.7 mAh g after the same number of cycles. -1The discharge capacity was maintained at 80%, demonstrating a significant enhancement in structural stability. This is mainly attributed to the reduction in the d–p band gap caused by chromium doping, which promotes electron transfer between ligands and metals, thereby activating a sustained and efficient sulfur redox reaction.

Claims

1. A chromium-titanium bimetallic layered sulfide cathode material, characterized in that, Its general chemical formula is LiCr x Ti y S2, and x+y=1, has a hexagonal crystal system of type O1 and a space group of P. m1; The material is prepared by the following steps: Step 1: Mix Li2S, chromium source, titanium source and sulfur source in stoichiometric ratio, grind thoroughly and then press into sheets; Step 2: At a vacuum degree of 10 -2 ~10 -5 The material is subjected to constant temperature treatment at 500~900℃ for 10~40 h at mbar, followed by immediate quenching and cooling to room temperature to obtain a chromium-titanium bimetallic layered sulfide cathode material. In the material, Ti and S provide reversible redox capacity, while Cr has the function of stabilizing the structure and reducing the dp band gap, but does not participate in charge compensation.

2. The chromium-titanium bimetallic layered sulfide cathode material according to claim 1, characterized in that, The material has a granular morphology with a particle size of 2~15μm. The particle surface is layered, and Cr, Ti, and S elements are uniformly distributed on the particle surface and in the bulk phase.

3. The chromium-titanium bimetallic layered sulfide cathode material according to claim 1, characterized in that, The material has a reversible capacity ≥146.4 mAh g. -1 After 330 cycles, the capacity retention rate is ≥52%.

4. The chromium-titanium bimetallic layered sulfide cathode material according to claim 1, characterized in that, The chemical formula of the material is LiCr 2 / 3 Ti 1 / 3 S2; The reversible capacity of the material is 223 mAh g. -1 After 330 cycles, the capacity retention rate was 80%.

5. The chromium-titanium bimetallic layered sulfide cathode material according to claim 1, characterized in that, In step 1, the chromium source is Cr powder or Cr2S3, the titanium source is Ti powder or TiS2, and the sulfur source is S powder, Cr2S3, or TiS2.

6. The application of the chromium-titanium bimetallic layered sulfide cathode material according to any one of claims 1-5 as a cathode material for lithium-ion batteries.

7. The application according to claim 6, characterized in that, The cathode material retains ≥ 80% capacity after 330 cycles at 2C.

8. The application according to claim 6, characterized in that, In cathode materials, Ti and S provide reversible redox capacity, while Cr plays a role in stabilizing the structure and reducing the dp band gap, but does not participate in charge compensation.

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