A method for improving the thermal stability of sulfide solid electrolytes

Abstract

The present invention provides a method for improving the thermal stability of a sulfide solid electrolyte, which includes: (1) successively adding a crystalline sulfide solid electrolyte and a regulator raw material in two steps for grinding to obtain a mixed powder; (2) a heat treatment process, subjecting the obtained mixed powder to heat treatment in a flowing inert atmosphere to obtain a sulfide solid electrolyte with a target; wherein, the structure factor Δ of the element composition of the mixed powder satisfies Δ≥301.5±1, and Δ={N(Li)×312.5 + N(P)×346}×4, where N(Li) represents the atomic percentage of Li, and N(P) represents the atomic percentage of P. The method of the present invention can effectively improve the thermal stability of the sulfide solid electrolyte, and successfully obtain a sulfide solid electrolyte that is not easily decomposed, not easily sulfur-separated, and has good ionic conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, relates to solid electrolytes, and particularly relates to a method for improving the thermal stability of crystalline sulfide solid electrolytes, and further obtaining a crystalline sulfide solid electrolyte with high thermal stability. Background Art

[0002] With the rapid development of science and technology and human society, lithium-ion batteries are widely used in fields such as consumer electronics, medical electronics, electric vehicles, rail transit, mobile energy storage, smart grid, aerospace, and national defense due to their excellent performance. However, these fields have put forward higher requirements for the energy density, power density, and safety of batteries. Conventional lithium-ion batteries have reached the "bottleneck" of energy density. Scientists in China, the United States, Japan, etc. unanimously believe that the energy density of scalable lithium-ion batteries cannot exceed 350 W·h / Kg, and during the process of increasing their energy density, volatile and flammable organic liquid electrolytes are extremely likely to induce safety accidents.

[0003] Since the commercially available lithium-ion batteries currently use electrolytes containing flammable organic solvents, it is necessary to install safety devices to suppress the temperature rise during short circuits or improve the structure and materials for preventing short circuits. Solid-state batteries using non-volatile and non-flammable solid electrolytes to replace organic liquid electrolytes are one of the main solutions to solve the "bottleneck" problem of existing lithium-ion batteries, which can simplify the safety device and have excellent manufacturing cost or productivity. Among them, sulfide solid electrolytes with high ionic conductivity and their solid electrolytes are the main development directions.

[0004] Although these sulfide solid electrolytes are non-volatile and non-flammable, at high temperatures, the sulfide solid electrolytes are not completely thermally safe, and processes such as phase transformation, thermal decomposition, and component volatilization will occur, which will have a huge impact on the ionic conductivity of the material and seriously affect the performance of the material. More importantly, the heated sulfide solid electrolyte will still release flammable sulfur, and flammable and highly toxic gases such as hydrogen sulfide will be generated in the air, causing huge safety risks. However, there are very few research reports in this regard and few research results. Therefore, it is extremely urgent to develop a method for improving the thermal stability of sulfide solid electrolytes. While improving the thermal stability of sulfide solid electrolytes, it will have a huge impact on their ionic conductivity and electronic conductivity. Therefore, the need to develop a method for improving the thermal stability of sulfide solid electrolytes is very urgent. Through a fast, effective, and low-cost method, on the premise of reducing the ionic conductivity of sulfide solid electrolytes, the thermal stability of the material is greatly improved, so that it can be applied to high-electrochemical-performance and high-safety batteries that can operate well in high-temperature environments. Summary of the Invention

[0005] Through the analysis of "material - structure - performance" of sulfide solid electrolytes, the present invention summarizes that by optimizing the material composition, target sulfide solid electrolyte materials with good thermal stability are quickly designed and screened out, an effective method for preparing the target sulfide solid electrolyte materials is provided, and sulfide solid electrolytes that are not easily decomposed, not easily sulfur - precipitated, and have good ionic conductivity are successfully obtained. The structure of crystalline sulfide solid electrolytes is relatively stable, and it is difficult to realize the regulation of composition and structure because once the crystal structure is formed, it will be in the most stable energy state, and a huge amount of energy is required to break the chemical bonds in the crystal structure. However, after the crystalline sulfide solid electrolyte is ground, its size will decrease, the surface defect states will increase, showing higher reaction activity, and the whole is in a relatively high - energy state. This phenomenon is particularly obvious at smaller particle sizes, which may be closely related to the size effect of the material. In addition, grinding can expose more surface interfaces of the crystalline sulfide solid electrolyte, providing more active reaction sites. Heat treatment in a flowing inert atmosphere is beneficial to adjusting the Li - P - S composition ratio of the crystalline sulfide solid electrolyte.

[0006] The present invention first provides a method for improving the thermal stability of sulfide solid electrolytes, including the following steps:

[0007] (1) Crystalline sulfide solid electrolyte and regulator raw materials are successively added in two steps for grinding to obtain a mixed powder;

[0008] (2) A heat treatment process, in which the obtained mixed powder is heat - treated in a flowing inert atmosphere to obtain a target sulfide solid electrolyte;

[0009] Among them, the structure factor Δ of the element composition of the mixed powder satisfies Δ≥301.5±1, where Δ = {N(Li)×312.5 + N(P)×346}×4. In the formula, N(Li) represents the atomic percentage of Li, and N(P) represents the atomic percentage of P.

[0010] Preferably, the structure factor Δ of the element composition of the mixed powder is 301.5±1 - 1384±1, and the thermal decomposition temperature ≥300°C;

[0011] Furthermore, the element composition and structure factor Δ of the mixed powder satisfy one of the following ranges:

[0012] I. The region where the material structure factor Δ is 301.5±1 - 980±1, and the element composition is 0 < N(Li)≤0.75, 0 < N(P)≤0.25, 0.25≤N(S)≤0.75;

[0013] II. The range of the material structure factor Δ is 468.7 ± 1 to 887.7 ± 1, and the elemental composition is in the range where 0 < N(Li) ≤ 0.67, 0 < N(P) ≤ 0.375, 0.3125 ≤ N(S) ≤ 0.625, and 0.03 ≤ N(M) ≤ 0.2;

[0014] III. The range of the material structure factor Δ is 781 ± 1 to 1300 ± 1, and the elemental composition is in the lithium-rich range where 0.25 ≤ N(Li) ≤ 1, 0 < N(P) ≤ 0.375, 0 < N(S) ≤ 0.375, and 0 ≤ N(M) ≤ 0.2;

[0015] IV. The range of the material structure factor Δ is 814 ± 1 to 1384 ± 1, and the elemental composition is in the phosphorus-rich range where 0 < N(Li) ≤ 0.375, 0.25 ≤ N(P) ≤ 1, 0 < N(S) ≤ 0.375, and 0 ≤ N(M) ≤ 0.18;

[0016] Among them, N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of the doping element M. The sum of the elements is 100%.

[0017] Among them, the doping element M is at least one of non-metallic elements such as oxygen O, selenium Se, fluorine F, chlorine Cl, bromine Br, iodine I, or metal elements such as magnesium Mg, calcium Ca, strontium Sr, zinc Zn, scandium Sc, antimony Sb, silicon Si, germanium Ge, tin Sn, boron B, aluminum Al, gallium Ga, indium In, titanium Ti, zirconium Zr, vanadium V, niobium Nb, copper Cu, nickel Ni, manganese Mn, chromium Cr, silver Ag, lanthanum La, cerium Ce, terbium Tb, tellurium Te, lead Pb, arsenic As, bismuth Bi, etc.

[0018] Among them, in the grinding process: the interval time between two feedings is more than 0.5 h, preferably 0.5 - 5 h; the grinding process adopts mechanical grinding, dry grinding, the mixing grinding time is 20 - 100 h, and the grinding atmosphere is an inert atmosphere.

[0019] Among them, in the heat treatment process:

[0020] The heat treatment environment is a flowing inert atmosphere, the heat treatment temperature is 200 - 600 °C; the heat treatment time is 2 - 10 h; the heating rate is not more than 2 °C / min.

[0021] Among them, before the grinding process, it also includes the step of separately grinding each raw material constituting the crystalline sulfide solid electrolyte and the regulator to obtain a raw material precursor.

[0022] Among them, the crystalline sulfide solid electrolyte or the raw material of the regulator independently contains one or more of the following materials: Li source, P source, S source, simple substance or compound containing doping element M, and satisfies the following formula requirements: 0.2 ≤ N(Li) ≤ 0.55, 0 < N(P) ≤ 0.25, 0.37 ≤ N(S) ≤ 0.65, 0 ≤ N(M) ≤ 0.2, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, N(M) represents the atomic percentage of doping element M, and the sum of each element is 100%.

[0023] Among them, the optimized sulfide solid electrolyte will not show an exothermic peak below 450 °C; or, there will be a phase transition peak near 200 - 350 °C, but there will be no exothermic peak of phase decomposition.

[0024] Among them, in the X-ray diffraction of the optimized sulfide solid electrolyte, there is a strong diffraction main peak before 2θ = 33.5 ± 0.5 deg, and the presented crystalline main peak will not appear after 2θ = 33.5 ± 0.5 deg.

[0025] Among them, in the X-ray diffraction of the optimized sulfide solid electrolyte above 300 °C, a crystalline peak of crystalline phase A will appear near 2θ = 26.9 ± 0.5 deg; or a crystalline peak of crystalline phase B will appear near 2θ = 32.5 ± 0.5 deg.

[0026] The beneficial effects produced by the present invention are as follows: Based on the composition of traditional sulfide solid electrolytes, instead of using expensive and low-reserve rare elements, inexpensive and abundant conventional elements are used. Through the corresponding design of the correlation between the structure factor Δ and the thermal stability performance of the material, as the basis for optimizing the proportion of constituent elements, a selection method and a regional range of new materials different from traditional sulfide solid electrolytes are obtained. The materials within the selected region have high thermal stability, do not decompose and do not release sulfur at high temperatures, and show good ionic conductivity and higher safety. According to the regional range of the new materials of the sulfide solid electrolyte selected based on the structure factor Δ, the present invention provides a method for improving the thermal stability of the sulfide solid electrolyte, that is, according to the optimized element composition of the target sulfide solid electrolyte meeting the requirements of the structural factor Δ limit range, and the material synthesis and treatment are carried out in two steps: a grinding process and a heat treatment process, and finally the thermal stability of the sulfide solid electrolyte is successfully improved. Description of the Drawings

[0027] The technical solutions of the embodiments of the present invention will be further described in detail below through the drawings and embodiments.

[0028] Figures 1-4They are the distribution diagrams of different regional ranges divided according to the structure factor Δ in the ternary composition diagram of LiPS and their corresponding examples.

[0029] Figure 5 It is a schematic flow chart of the method for improving the thermal stability of the crystalline sulfide solid electrolyte of the present invention.

[0030] Figure 6 It is a schematic diagram of the mixture of the crystalline sulfide solid electrolyte and the regulator after the grinding process.

[0031] Figure 7 It is the XRD test pattern of the crystalline sulfide solid electrolyte with high thermal stability in Example 140.

[0032] Figure 8 It is the DSC test pattern of the crystalline sulfide solid electrolyte with high thermal stability in Example 140.

[0033] Figure 9 It is the XRD test pattern of the crystalline sulfide solid electrolyte with high thermal stability in Example 140 after being treated at a high temperature of 600 °C.

[0034] Figure 10 It is the test result of the AC impedance spectrum of the crystalline sulfide solid electrolyte with high thermal stability in Example 140.

[0035] Figure 11 It is the test result of the DC polarization of the crystalline sulfide solid electrolyte with high thermal stability in Example 140.

[0036] Figure 12 It is the XRD test pattern of the crystalline sulfide solid electrolyte with high thermal stability in Example 141.

[0037] Figure 13 It is the DSC test pattern of the crystalline sulfide solid electrolyte with high thermal stability in Example 141.

[0038] Figure 14 It is the XRD test pattern of the crystalline sulfide solid electrolyte with high thermal stability in Example 141 after being treated at a high temperature of 750 °C.

[0039] Figure 15 It is the morphology of the crystalline sulfide solid electrolyte with high thermal stability in Example 141. Specific embodiments

[0040] The present invention will be further described below with reference to the accompanying drawings and specific examples, but it should be understood that these examples are only for more detailed description and should not be construed as limiting the present invention in any form, that is, it is not intended to limit the protection scope of the present invention.

[0041] In the microstructure of the Li-P-S-M sulfide solid electrolyte, it can be considered to be composed of a corresponding number of [Li-S] bonds, [P-S] bonds, and chemical bonds of the doping element M, and these bonds form corresponding polyhedra and further form the macroscopic electrolyte material. The material decomposition process (physically measured decomposition temperature) is closely related to the essential structure of the material, that is, closely related to the number of corresponding polyhedra and the number of bonds that make up the electrolyte material.

[0042] Therefore, we define the structure factor δ of the sulfide solid electrolyte, which reflects the energy possessed by all the polyhedra in the sulfide solid electrolyte, or the sum of the energies of all chemical bonds (Equations 1 and 2).

[0043] δ = E{Li x P y S z M m} = ∑{E[Li-S]} + ∑{E[P-S]} + ∑{E[M]} (1)

[0044] δ = E{Li x P y S z M m} = ∑{E[LiS 4} + ∑{E[PS 3 + ∑{E[PS 4 + ∑{E[P 2 S 7 + ∑{E[P 2 S 6} + ∑{E[M]} (2)

[0045] In Equations 1 and 2, E{Li x P y S z M m} represents the energy value possessed by Li x P y S z M m ; E[Li-S] represents the energy contained in the [Li-S] bond; E[P-S] represents the energy contained in the [P-S] bond; E[M] represents the energy contained in the chemical bonds formed by the doping element M; E[LiS 4 , E[PS 3 , E[PS 4 , E[P 2 S 7 , E[P 2 S 6represent the energies contained in [LiS4], [PS3], [P2S7], [PS4], and [P2S6] polyhedra respectively.

[0046] Since the purpose of introducing the doping element M is to increase the ionic conductivity and minimize the disruption of the overall ratio with less impact on the total energy of the material, the energy part E[M] can be ignored in subsequent calculations to simplify the model. Further, the number of [Li-S] and [P-S] bonds can be estimated through polyhedra, simplifying Equation 2 to:

[0047]

[0048] For comparison, a unit mole is used as a reference for normalization. We define the structure factor Δ of the normalized sulfide solid electrolyte. The structure factor Δ is obtained by normalizing δ in unit measurement, reflecting the energy possessed by all polyhedra in the sulfide solid electrolyte under unit measurement, or the total sum of the energies of all chemical bonds.

[0049]

[0050] In Equations 3 and 4, N[LiS4], N[PS3], N[P2S7], N[PS4], and N[P2S6] represent the numbers of [LiS4], [PS3], [P2S7], [PS4], and [P2S6] polyhedra respectively, and E[LiS 4 , E[PS 3 , E[PS 4 , E[P 2 S 7 , E[P 2 S 6 represent the energies contained in [LiS4], [PS3], [P2S7], [PS4], and [P2S6] polyhedra respectively. N Total refers to the total number of atoms in the unit cell and is used as a normalization coefficient for fair comparison between various systems with different unit cell sizes. To further simplify the calculation, the number of atoms of the doping element M can be ignored during the calculation, and N Total is denoted as the sum of the numbers of Li, S, and P atoms.

[0051] The amounts of N[LiS4], N[PS3], N[P2S7], N[PS4] and N[P2S6] can be represented by the number of central atoms therein. For example, N[LiS4] is closely related to the number of central atom Li, and N[PS3] is closely related to the number of central atom P. Based on the crystal structure of the sulfide electrolyte, it can be known that [P2S7], [PS3] and [P2S6] can all be equivalent to different connection modes of two [PS4], and can be equivalent to the structure of [PS4] in terms of quantity. Therefore, Equation 4 can be further simplified by multiplying the number of central atoms by the number of bonds included in the polyhedron derived from the central atom to obtain Equation 5. Equation 5 is conducive to quickly calculating the result without the aid of computer assistance, improving the practicability.

[0052] Δ = {N(Li) × E[Li-S] + N() × E[P-S]} × 4 (5)

[0053] Where N(Li) represents the atomic percentage of central atom Li, N(P) represents the atomic percentage of central atom P, E[Li-S] represents the energy contained in the [Li-S] bond, and E[P-S] represents the energy contained in the [P-S] bond.

[0054] E[Li-S] and E[P-S] can be obtained from the "Handbook of Chemistry and Physics". In this way, Equation 5 can be further simplified to Equation 6.

[0055] Δ = {N(Li) × 312.5 + N(P) × 346} × 4 (6)

[0056] Where N(Li) represents the atomic percentage of central atom Li, and N(P) represents the atomic percentage of central atom P.

[0057] Thus, we define the structure factor Δ (Equation 6) of the normalized sulfide solid electrolyte. The structure factor Δ represents the simplified calculation of the total energy of all Li-S bonds and all P-S bonds inside the sulfide solid electrolyte, reflecting the thermal stability performance in terms of the material structure. Since this structure factor Δ is a simplified result obtained by analyzing and summarizing the "material-structure-property" three dimensions of the sulfide solid electrolyte, and this result is uniquely related to the composition of Li-P-S-M, we expect that by optimizing the composition ratio of Li-P-S-M in the sulfide solid electrolyte, the thermal stability of the sulfide solid electrolyte can be effectively improved, enabling the sulfide solid electrolyte to stably exist at high temperatures without obvious thermal decomposition process and sulfur evolution process, and having good ionic conductivity.

[0058] Among them, in the Li-P-S-M sulfide solid electrolyte, the element M is at least one of non-metal elements such as oxygen O, selenium Se, fluorine F, chlorine Cl, bromine Br, iodine I, or metal elements such as magnesium Mg, calcium Ca, strontium Sr, zinc Zn, scandium Sc, antimony Sb, silicon Si, germanium Ge, tin Sn, boron B, aluminum Al, gallium Ga, indium In, titanium Ti, zirconium Zr, vanadium V, niobium Nb, copper Cu, nickel Ni, manganese Mn, chromium Cr, silver Ag, lanthanum La, cerium Ce, terbium Tb, tellurium Te, lead Pb, arsenic As, bismuth Bi, etc.

[0059] According to the derivation process of the above Equation 6, it can be seen that the above Equation 6 is also applicable to the Li-P-S sulfide solid electrolyte without the doping element M, which is equivalent to the M content being 0.

[0060] In order to verify the relationship between the structure factor Δ and the thermal stability, we selected a series of sulfide solid electrolyte materials with different compositions containing lithium Li, phosphorus P, sulfur S, and other elements M. The sulfide solid electrolytes with different atomic numbers are summarized in Table 1. Through ICP testing, the accurate Li and P atomic ratios of the sulfide solid electrolyte can be obtained, and then the structure factor Δ can be calculated. The sulfide solid electrolyte was also tested by electrochemical impedance spectroscopy (the testing instrument is ZahnerZennium Pro), and the ionic conductivity of the sulfide solid electrolyte is also summarized in Table 1. During the calculation of the structure factor Δ, when calculating the atomic percentages (N(P) and N(Li)), the total number of atoms (N Total ) does not include the atomic number of the doping element.

[0061] The sulfide solid electrolyte in Table 1 was placed in a muffle furnace for heat treatment, and then the heat-treated sulfide solid electrolyte was tested and analyzed by powder X-ray diffraction with CuKα rays to obtain the phase decomposition temperature of the sulfide solid electrolyte. The structure factor Δ and their thermal decomposition temperatures of the above-mentioned high-temperature-resistant sulfide solid electrolytes with different atomic ratios are summarized in Table 1.

[0062] Judging from the experimental results, the structure factor Δ changes synchronously with the thermal decomposition temperature of the sulfide solid electrolyte. The structure factor Δ of the present invention is positively correlated with the thermal decomposition temperature (thermal stability) of the sulfide solid electrolyte and can be used as an important parameter to measure the thermal stability performance of the sulfide solid electrolyte.

[0063] Table 1 Summary table of ionic conductivity and structure factor Δ of sulfide solid electrolytes with different atomic ratios

[0064]

[0065]

[0066]

[0067]

[0068] According to the compositional proportional relationship of the Li-P-S sulfide solid electrolyte, we can establish a ternary composition diagram of LiPS. For the doping element M, since its content is very small, it can be regarded as the doping element replacing part of P and / or S in the ternary composition, and the energy fluctuation effect brought by the doping element M is also ignored in the calculation of the structure factor Δ. Therefore, the content of LiPS in the quaternary composition containing the doping element M is regarded as the same as that of LiPS in the ternary composition without considering the doping element M. Thus, the quaternary composition diagram containing the doping element M can be replaced by the LiPS ternary composition diagram without considering the doping element M.

[0069] In the LiPS ternary composition diagram, according to the magnitude of the structure factor Δ, we can select the elemental composition ranges in different regions so that the structure factor Δ of the material compositions within the selected regions meets the requirement of a sufficiently large range, so that the material compositions within the selected regions all meet a certain thermal decomposition temperature requirement, thereby providing a feasible basis for optimizing the thermal stability requirement of the sulfide solid electrolyte material design.

[0070] Specifically, the material ranges designed and selected based on the structure factor Δ include but are not limited to:

[0071] The region where the material structure factor Δ is 301.5 ± 1 to 980 ± 1, and the elemental composition is 0 < N(Li) ≤ 0.75, 0 < N(P) ≤ 0.25, 0.25 ≤ N(S) ≤ 0.75. The thermal decomposition temperature of the materials within this region is ≥ 300 °C. The representative example distributions within the region are shown as Examples 1 to 35 in Table 1. The region range and the example distribution are as Figure 1 shown.

[0072] The region where the material structure factor Δ is 468.7 ± 1 to 887.7 ± 1, and the elemental composition is 0 < N(Li) ≤ 0.67, 0 < N(P) ≤ 0.375, 0.3125 ≤ N(S) ≤ 0.625, 0.03 ≤ N(M) ≤ 0.2. The thermal decomposition temperature of the materials within this region is ≥ 300 °C. The representative example distributions within the region are shown as Examples 36 to 74 in Table 1. The region range and the example distribution are as Figure 2 shown.

[0073] The material structure factor Δ is in the range of 781±1 to 1300±1, and the elemental composition is in the lithium-rich region where 0.25≤N(Li)≤1, 0<N(P)≤0.375, 0<N(S)≤0.375, and 0≤N(M)≤0.2. The thermal decomposition temperature of the material within this region is ≥400°C. The representative examples within this region are shown as Examples 75 to 107 in Table 1. The region range and the distribution of examples are as Figure 3 shown.

[0074] The material structure factor Δ is in the range of 814±1 to 1384±1, and the elemental composition is in the phosphorus-rich region where 0<N(Li)≤0.375, 0.25≤N(P)≤1, 0<N(S)≤0.375, and 0≤N(M)≤0.18. The thermal decomposition temperature of the material within this region is ≥400°C. The representative examples within this region are shown as Examples 108 to 139 in Table 1. The region range and the distribution of examples are as Figure 4 shown.

[0075] To effectively obtain a sulfide solid electrolyte that meets the target range of the structure factor Δ, we provide the following method, which uses a "two-step process" of a grinding process and a heat treatment process. On the one hand, by achieving the target composition ratio of the sulfide solid electrolyte defined within the range of the structure factor Δ, the thermal stability performance index of the obtained sulfide solid electrolyte is improved. On the other hand, by stepwise feeding and grinding, the microstructure of the target composition is further optimized, which also promotes the improvement of thermal stability.

[0076] Specifically, in the grinding process, the crystalline sulfide solid electrolyte and the regulator raw material are successively fed in two steps for grinding to obtain a mixed powder; then it enters the heat treatment process, and the obtained mixed powder is heat-treated in a flowing inert atmosphere to obtain a sulfide solid electrolyte with the target. Figure 5 shows a schematic flow diagram of the method of the present invention.

[0077] In the above method, the structure factor Δ corresponding to the elemental composition of the mixed powder is ≥301.5±1, which can be 301.5±1 to 1384±1. The specific corresponding elemental composition can be the elemental composition within the above different region ranges, so that the thermal decomposition temperature of the obtained sulfide solid electrolyte material can meet the design requirement of not less than 300°C.

[0078] The raw materials of the crystalline sulfide solid electrolyte may include one or more of the following materials: Li source, P source, S source, simple substance or compound containing doping element M, such as lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), sulfur S, lithium chloride (LiCl), etc., and other lithium sources, phosphorus sources, and sulfur sources. In some embodiments, the chemical formula of the crystalline sulfide solid electrolyte is Li-M-P-S, and the atomic percentages of each atom satisfy the following requirements: 0.2 ≤ N(Li) ≤ 0.55, 0 < N(P) ≤ 0.25, 0.37 ≤ N(S) ≤ 0.65, 0 ≤ N(M) ≤ 0.2, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, and N(M) represents the atomic percentage of doping element M, and the sum of each element is 100%.

[0079] The raw materials of the regulator may also include one or more of the following materials: Li source, P source, S source, simple substance or compound containing doping element M, such as lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), sulfur S, lithium chloride (LiCl), etc., and other lithium sources, phosphorus sources, and sulfur sources. After determining the material composition of the sulfide solid electrolyte in the target range according to the structure factor Δ, the elemental composition of the mixed powder in the method process can be determined. Then, through the chemical composition of the selected raw materials of the crystalline sulfide solid electrolyte, the chemical composition of the raw materials of the regulator can be calculated, and further the ratio of each raw material in the regulator can be determined.

[0080] In the above method, the interval time between the two feedings in the grinding process is more than 0.5 h, and it can be 0.5 - 5 h. The feeding order is an important part of this invention patent. By controlling the feeding order, it can ensure that an appropriate amount of regulator is coated on the surface of the crystalline sulfide solid electrolyte, which is convenient for the next-step treatment. Figure 6 Shows a schematic diagram of the mixture of the crystalline sulfide solid electrolyte and the regulator after the grinding process.

[0081] In the above method, the grinding process of the grinding process adopts the mechanical grinding method, preferably dry (without any solvent). And the mixing and grinding time is 20 - 100 h. If a solvent is mixed in the grinding and mixing process, it is very easy to cause the production of the solvent or the reaction between the solvent and the activated sulfide solid electrolyte, resulting in a decrease in ionic conductivity or other negative effects. The grinding atmosphere is an inert atmosphere, such as nitrogen, argon, helium, etc., and argon is preferred.

[0082] In the above method, the key environment of the heat treatment process is a flowing inert atmosphere, the heat treatment temperature is 200 - 600 °C, and the heat treatment time is 2 - 10 h. Through heat treatment at a certain temperature, the reaction between the activated sulfide solid electrolyte and the regulator can be effectively promoted, and the activity of the sulfide solid electrolyte can be reduced during the cooling process to form a stable sulfide solid electrolyte.

[0083] In the above method, the heating rate of the heat treatment process needs to be below 2 °C / min. Through a slow heating process, the physical and chemical reactions at different temperatures can be ensured to proceed fully.

[0084] In the above method, before the grinding process, it also includes the step of respectively grinding each raw material constituting the crystalline sulfide solid electrolyte and the regulator to obtain a raw material precursor. Each raw material precursor is well crushed through pre-grinding to form an active particle surface, which is beneficial to the further mixing of each raw material.

[0085] The following further introduces the preparation of the sulfide solid electrolyte in this case through detailed examples.

[0086] Example 140

[0087] A method for improving the thermal stability of a crystalline sulfide solid electrolyte provided by the present invention mainly solves the above problems through "two steps", namely the grinding process and the heat treatment process of the sulfide solid electrolyte, thereby greatly improving the thermal stability of the sulfide solid electrolyte.

[0088] This example uses Figure 5 the shown synthesis method to improve the thermal stability of the sulfide solid electrolyte. The main process is: (1) the grinding process, in which the crystalline sulfide solid electrolyte raw material is put into a container for mixing to obtain an activated powder. (2) The heat treatment process, in which the above-obtained activated powder is heat-treated in a flowing inert atmosphere to obtain a sulfide solid electrolyte with high thermal stability.

[0089] The preferred crystalline sulfide solid electrolyte in this example is a sulfide solid electrolyte containing lithium Li, phosphorus P, sulfur S, and chlorine Cl, and its chemical formula is Li6P1.2S5.4Cl1.2.

[0090] The preferred regulator in this example contains lithium Li, phosphorus P, and sulfur S. After the regulator is mixed with the crystalline sulfide solid electrolyte, the range of the atomic ratio of the components of the mixture satisfies: preferably N(Li) = 0.386, N(P) = 0.135, N(S) = 0.479. The raw material types are lithium sulfide (Li2S), diphosphorus pentasulfide (P2S5), sulfur S, and other lithium sources, phosphorus sources, and sulfur sources.

[0091] Grinding process: After weighing the corresponding raw materials in a glove box under an Ar atmosphere (dew point -70°C) according to the above composition, pour them into an agate mortar in sequence. Grind them evenly with force to obtain the raw material precursor. Then, put the obtained raw material precursors into 45 ml zirconia ball milling jars respectively, and further put in zirconia balls (φ10 mm, 20 - 30 pieces). Seal the ball milling jars completely (Ar atmosphere). Install the ball milling jars on a planetary ball mill and conduct mechanical grinding for 20 hours at a table rotation speed of 250 rpm. The feeding sequence is to first put in the crystalline sulfide solid electrolyte, and then put in the regulator, and the time interval between the two is about 3 h. In this way, the crystalline sulfide solid electrolyte will first be refined into micro-nano particles, and at the same time, more chemically active surface interfaces will be exposed, accelerating the reaction process. Through ball milling, a sulfide solid electrolyte with high chemical activity can be obtained, with uniform particle size and a near-spherical structure.

[0092] Heat treatment process: Uniformly disperse the above-activated sulfide solid electrolyte in a crucible container, place it in a flowing inert atmosphere, and conduct heat treatment through a resistance furnace. The heat treatment temperature is 360°C. The heat treatment time is 10 h. In the heat treatment process, the heating rate of the furnace body needs to be 2°C / min, and the selected furnace body is a resistance wire heating furnace. After the furnace body cools down, the optimized sulfide solid electrolyte can be obtained. Figure 7 The XRD test pattern of the sulfide solid electrolyte powder optimized by the method is shown.

[0093] ICP test: Grind the optimized sulfide solid electrolyte of the test sample into fine powder in a mortar, transfer it into a crucible, place it in an oven at 105°C for 1 hour, and then transfer it to a desiccator to cool. Weigh 0.1 g of the sample (accurate to 0.1 mg), put it into a 100 mL beaker, add 5 mL of the standard digestion solution, heat it on a hot plate (70°C) until the sample is completely dissolved, and cool it to room temperature. Transfer the sample solution into a 250 mL volumetric flask, make up the volume with ultrapure water, and mix well. Then take 5 mL of the volumetric sample solution and dilute it to 50 mL, that is, dilute it 10 times. Transfer the sample solution and the diluted solution into the test instrument Thermofisher iCAP 7200 for testing. The carrier gas is N2, the gas flow is 0.5 L / min, the nebulizer pressure is 0.19 Mpa, and the high-frequency power is 1150 W. Through the ICP test, the accurate Li and P atomic ratios of the optimized sulfide solid electrolyte can be obtained, which conform to the designed feeding composition of the elements. Furthermore, the structure factor Δ of the optimized sulfide solid electrolyte is calculated to be 668.6 (calculated by Δ = {N(Li) × 312.5 + N(P) × 346} × 4, where N(Li) represents the atomic percentage of Li and N(P) represents the atomic percentage of P).

[0094] DSC Test: To accurately obtain the thermal stability parameters of the optimized sulfide solid electrolyte, differential scanning calorimetry was used for accurate testing and evaluation in this embodiment. 5 mg of the optimized sulfide solid electrolyte to be tested was added to a stainless-steel container for DSC (differential scanning calorimeter) and sealed. The sealed container was placed in a DSC device (NETZSCH DSC 214) and measured. For the reference, 5 mg of Al2O3 was used, the heating rate was set at 5 °C / minute, and the termination temperature was set at 450 °C. According to the DSC results, the heat generation start temperature and the heat generation peak temperature were obtained. It should be noted that the heat generation start temperature refers to the temperature when the heat flow rises, and the heat generation peak temperature refers to the peak temperature (heat generation peak temperature) at the lowest (highest) point of the heat flow. Figure 8 The DSC test pattern of the optimized sulfide solid electrolyte is shown. It was found that a phase transition peak appeared at 230 °C for this sulfide solid electrolyte, but no exothermic peak of phase decomposition appeared.

[0095] XRD Diffraction Test: The sample was measured by XRD using a sealed test sample stage without contact with air. The 2θ position of the diffraction peak was determined by the centroid method using the XRD analysis program JADE. The test was carried out under conventional test conditions using a powder X-ray diffractometer of Purkinje General (other brands are also acceptable). Since there are differences in test parameters for different instruments, taking the setting parameters of the powder X-ray diffractometer of Purkinje General as an example, tube voltage: 36 kV; tube current: 20 mA; X-ray wavelength: Cu-Kα ray; detector: scintillation counter; measurement range: 2θ = 10 - 80 deg; step width, scanning speed: 0.02 deg, 1 deg / minute; during the process of analyzing the peak positions for confirming the existence of the crystal structure based on the measurement results, the XRD analysis program JADE was used, and a baseline was drawn by fitting with a cubic equation to obtain the peak positions. Figure 7 The XRD test pattern of the sulfide solid electrolyte in this embodiment is shown. The novel sulfide solid electrolyte was placed in a muffle furnace and heated to 600 °C, and then tested and analyzed by powder X-ray diffraction with CuKα ray. Figure 9 The XRD test pattern of the sulfide solid electrolyte after being treated at 600 °C at high temperature is shown. Combining Figure 7 and Figure 9As a result, it can be known that the XRD diffraction peaks of the sulfide solid electrolyte before heating show a strong main diffraction peak before 2θ = 34 deg, and the presented crystalline main peak does not appear after 2θ = 34 deg. Further, after heat treatment of the sulfide solid electrolyte, when the heat treatment temperature exceeds 600 °C, the XRD diffraction peaks of the sulfide solid electrolyte show a crystalline peak at 32.5, belonging to crystalline phase B, and the main phase is Li2PS3.

[0096] Ionic conductivity test: Electrochemical impedance spectroscopy was performed on the sulfide solid electrolyte using a Zahner Zennium Pro instrument to obtain the ionic conductivity of the interface layer. The sulfide solid electrolyte obtained in this example was pressed into a sheet (500 MPa) to obtain a sheet with a thickness of about 1.0 mm and a diameter of φ10 mm. At room temperature, the ionic conductivity was calculated by measuring the AC impedance using the two-terminal method. The measurement frequency range was 100 mHz to 8 MHz, and the amplitude was 5 mV. Figure 10 The AC impedance spectroscopy test results of the sulfide solid electrolyte are shown, and it can be measured that the ionic conductivity of the sulfide solid electrolyte is 1.07 mS / cm. The polarization voltage was adjusted to 500 mV, and the electronic conductivity of the sulfide solid electrolyte was obtained by performing a DC polarization test. Figure 11 The DC polarization test results of the sulfide solid electrolyte are shown, and the electronic conductivity of the sulfide solid electrolyte can be obtained as 0.28×10 -10 S / cm.

[0097] (Thermal decomposition experiment) The sulfide solid electrolyte was sealed in a quartz tube, and the quartz tube was placed in the central position of a muffle furnace. This part was heat-treated, and at the same time, the morphological changes of the sulfide solid electrolyte during heating were observed. By cooling one end of the quartz tube sealed with the sulfide solid electrolyte, the sulfur precipitation situation could be obtained to observe the sulfur evolution reaction of the sulfide solid electrolyte. Through the whole-process thermal decomposition experiment of the sulfide solid electrolyte, the results show that the sulfur evolution temperature of the sulfide solid electrolyte is 570 °C. Further, it shows that when the ambient temperature exceeds 570 °C, the sulfide solid electrolyte will undergo a sulfur evolution reaction process and partial decomposition will occur.

[0098] (Density test) The powder density of the novel sulfide solid electrolyte was measured using a true density meter, and its density was obtained as 1.98 g / cm3.

[0099] (Chromaticity Test) By performing a whiteness test on the novel sulfide solid electrolyte, the test instrument is a powder whiteness meter. Put the powder to be tested into the test chamber, place the sample to be measured at the reflection test port of the instrument, enter the measurement interface, press the measurement button briefly to start the measurement. The buzzer makes a "beep" sound, and at the same time, the LED indicator light flashes until the flashing stops, and the buzzer makes a "beep" sound again to complete the chromaticity measurement of the sulfide solid electrolyte. The brightness L* value in the L*a*b* chromaticity system is preferably 70.0.

[0100] Example 141

[0101] A method for improving the thermal stability of a crystalline sulfide solid electrolyte provided by the present invention mainly solves the above problems through "two steps", namely, a grinding process and a heat treatment process for the sulfide solid electrolyte, thereby greatly improving the thermal stability of the sulfide solid electrolyte.

[0102] This example uses Figure 2 the shown synthesis method to improve the thermal stability of the sulfide solid electrolyte. The main process is as follows: (1) Grinding process, in which the crystalline sulfide solid electrolyte raw material is put into a container for mixing to obtain activated powder. (2) Heat treatment process, in which the activated powder obtained above is heat-treated in a flowing inert atmosphere to obtain a sulfide solid electrolyte with high thermal stability.

[0103] The preferred crystalline sulfide solid electrolyte in this example is a sulfide solid electrolyte containing lithium (Li), phosphorus (P), germanium (Ge), and sulfur (S), and its chemical formula is Li10P2S11Ge0.5.

[0104] The preferred regulator in this example is a sulfide solid electrolyte containing lithium (Li), phosphorus (P), and sulfur (S). After the regulator is mixed with the crystalline sulfide solid electrolyte, the atomic ratio range of the mixture components satisfies: N(Li)=0.435, N(P)=0.215, N(S)=0.35. The raw material types are lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), sulfur (S), and other lithium sources, phosphorus sources, and sulfur sources.

[0105] Grinding process: After weighing the corresponding raw materials in a glove box under an Ar atmosphere (dew point -70 °C) according to the above composition, the powders were then separately poured into an agate mortar and ground evenly with force to obtain the raw material precursors. Next, the obtained raw material precursors were respectively put into a 100 ml zirconia grinding jar, and further zirconia balls (φ10 mm, 20 - 30 pieces) were added. The grinding jar was completely sealed (Ar atmosphere). The grinding jar was installed on a small vibration mill and subjected to vibration mechanical grinding at an amplitude of 8 mm, a vibration frequency of 1440 r / min, and a grinding time of 60 h. The feeding sequence was to first put in the crystalline sulfide solid electrolyte, and then put in the regulator, and the time interval between the two was about 2.5 h. In this way, the crystalline sulfide solid electrolyte would first be refined into micro-nano particles, and at the same time, more chemically active surface interfaces would be exposed, accelerating the reaction process. Through grinding, a sulfide solid electrolyte with high chemical activity could be obtained, with uniform particle size and a nearly spherical structure.

[0106] Heat treatment process: The above-activated sulfide solid electrolyte was evenly dispersed in a crucible container, placed in a flowing inert atmosphere, and heat-treated in a resistance furnace at a heat treatment temperature of 460 °C. The heat treatment time was 10 h. In the heat treatment process, the heating rate of the furnace body needed to be 1 °C / min, and the selected furnace body was a resistance wire heating furnace. After the furnace body cooled down, the optimized sulfide solid electrolyte could be obtained. Figure 12 The XRD test pattern of the sulfide solid electrolyte powder after method optimization is shown.

[0107] ICP test: The optimized sulfide solid electrolyte of the test sample was put into a mortar and ground into a fine powder, transferred to a crucible, placed in an oven at 105 °C for 1 hour, and then transferred to a desiccator to cool. Weigh 0.1 g of the sample (accurate to 0.1 mg) and put it into a 100 mL beaker, add 5 mL of the standard digestion solution, heat it on a hot plate (70 °C) until the sample is completely dissolved, and cool it to room temperature. Transfer the sample solution to a 250 mL volumetric flask, make up the volume with ultrapure water, and mix well. Then take 5 mL of the volumetric sample solution and dilute it to 50 mL, that is, dilute it 10 times. The sample solution and the diluted solution were transferred into a test instrument Thermofisher iCAP 7200 for testing. The carrier gas was N2, the gas flow was 0.5 L / min, the nebulizer pressure was 0.19 Mpa, and the high-frequency power was 1150 W. Through the ICP test, the accurate Li and P atomic ratios of the optimized sulfide solid electrolyte could be obtained, which met the designed feeding composition of the elements, and then the structure factor Δ of the optimized sulfide solid electrolyte was calculated to be 841.3 (calculated by Δ = {N(Li) × 312.5 + N(P) × 346} × 4, where N(Li) represents the atomic percentage of Li and N(P) represents the atomic percentage of P).

[0108] DSC Test: To accurately obtain the thermal stability parameters of the optimized sulfide solid electrolyte, differential scanning calorimetry was used for accurate testing and evaluation in this embodiment. 5 mg of the optimized sulfide solid electrolyte to be tested was added to a stainless-steel container for DSC (differential scanning calorimeter) and sealed. The sealed container was placed in a DSC device (NETZSCH DSC 214) and measured. For the reference, 5 mg of Al2O3 was used, the heating rate was set at 5 °C / minute, and the termination temperature was set at 450 °C. According to the DSC results, the heat generation start temperature and the heat generation peak temperature were obtained. It should be noted that the heat generation start temperature refers to the temperature when the heat flow rises, and the heat generation peak temperature refers to the peak temperature (heat generation peak temperature) at the lowest (highest) point of the heat flow. Figure 13 The DSC test pattern of the optimized sulfide solid electrolyte is shown. It was found that there was no phase transition peak at 230 °C for this sulfide solid electrolyte, nor was there an exothermic peak of phase decomposition.

[0109] XRD Diffraction Test: The sample was measured by an XRD sealed test stage without contacting with air. The 2θ position of the diffraction peak was determined by the centroid method using the XRD analysis program JADE. The powder X-ray diffraction of Purkinje General (other brands are also available) was used for testing under conventional test conditions. Since there are differences in test parameters for different instruments, taking the setting parameters of the powder X-ray diffraction of Purkinje General as an example, the tube voltage: 36 kV; the tube current: 20 mA; the X-ray wavelength: Cu-Kα ray; the detector: scintillation counter; the measurement range: 2θ = 10 - 80 deg; the step width and scanning speed: 0.02 deg, 1 deg / minute; during the process of analyzing the peak position for confirming the existence of the crystal structure according to the measurement results, the XRD analysis program JADE was used to draw the baseline by fitting with a cubic equation, thereby obtaining the peak position. Figure 12 Shown is the XRD test pattern of the sulfide solid electrolyte in this embodiment. The novel sulfide solid electrolyte was placed in a muffle furnace for heat treatment, heated to 750 °C, and then tested and analyzed by powder X-ray diffraction with CuKα ray. Figure 14 The XRD test pattern of the sulfide solid electrolyte after being treated at a high temperature of 750 °C is shown. Combining Figure 12 and Figure 14As a result, it can be known that the XRD diffraction peaks of the sulfide solid electrolyte before heating show a strong main diffraction peak before 2θ = 34°, and the presented crystallization main peak does not appear after 2θ = 34°. Further, after heat treatment of the sulfide solid electrolyte, when the heat treatment temperature exceeds 750 °C, the XRD diffraction peaks of the sulfide solid electrolyte show a crystallization peak at 26.7, belonging to the crystalline phase A, and the main phase is Li2S.

[0110] SEM test: In a glove box under an Ar environment (dew point -70 °C), after grinding the sulfide solid electrolyte powder finely with an agate mortar, gently sprinkle it on the SEM test sample stage, then seal the sample stage with a vacuum transfer box, and place an Ar atmosphere inside to protect the sample. Transfer the electrode sample in the sealed vacuum transfer box to the SEM instrument cavity and start the SEM instrument. Fix the sample stage on the sample rod, push it into the exchange chamber, and evacuate; open the door between the exchange chamber and the vacuum chamber, and use the sample rod to push the sample stage into the vacuum chamber. After sample injection, click the On button in the control software to apply high voltage (acceleration voltage), and set the acceleration voltage to 10 kV. Search for the sample at low magnification and observe it at high magnification. Magnify the sample to find the area of interest. Perform focusing and astigmatism elimination operations on the image, adjust the brightness / contrast, and scan and store the photo after obtaining a clear field of view. Figure 15 The morphology of the crystalline sulfide solid electrolyte with high thermal stability after two-step processes is shown.

[0111] Thermal decomposition experiment: Seal the sulfide solid electrolyte in a quartz tube, place the quartz tube at the central position of a muffle furnace, heat-treat this part, and simultaneously observe the morphological changes of the sulfide solid electrolyte during heating. By cooling one end of the quartz tube sealed with the sulfide solid electrolyte, the sulfur precipitation situation can be obtained to observe the sulfur evolution reaction of the sulfide solid electrolyte. Through the whole-process thermal decomposition experiment on the new sulfide solid electrolyte, the results show that the sulfur evolution temperature of the sulfide solid electrolyte is 717 °C. Further, it shows that when the ambient temperature exceeds 717 °C, the sulfide solid electrolyte will undergo a sulfur evolution reaction process and partial decomposition will occur.

[0112] Density test: By performing powder density test on the new sulfide solid electrolyte, the test instrument is a true density meter, and its density is obtained as 2.30 g / cm 3 。

[0113] Chromaticity test: The whiteness of the novel sulfide solid electrolyte was tested using a powder whiteness meter. The powder to be tested was placed in the test chamber, and the sample to be measured was placed at the reflection test port of the instrument. Enter the measurement interface, press the measurement button briefly to start the measurement. The buzzer emits a "beep" sound, and at the same time, the LED indicator flashes until the flashing stops. Then the buzzer emits a "beep" sound again to complete the chromaticity measurement of the sulfide solid electrolyte. The luminance L* value in the L*a*b* chromaticity system is preferably 65.0.

[0114] Through the method provided by the present invention, a method for improving the thermal stability of crystalline sulfide solid electrolytes was successfully obtained. The composition of the crystalline sulfide solid electrolyte and the regulator was optimized and designed through the structure factor Δ. Since the structure factor Δ changes synchronously with the thermal decomposition temperature of the sulfide solid electrolyte and shows a positive correlation, it can be used as an important parameter to measure the thermal stability performance of the sulfide solid electrolyte. By optimizing the composition ratio of the raw material mixture Li-P-S, the thermal stability of the crystalline sulfide solid electrolyte can be effectively improved, enabling the sulfide solid electrolyte to stably exist at high temperatures without obvious thermal decomposition and sulfur evolution processes, and having good ionic conductivity.

[0115] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the thermal stability of sulfide solid electrolytes, comprising the following steps: (1) The crystalline sulfide solid electrolyte and the raw materials of the regulator are successively added in two steps for grinding to obtain a mixed powder; the structure factor Δ of the element composition of the mixed powder is ≥301.

5. After determining the material composition of the sulfide solid electrolyte in the target range according to the structure factor Δ, the element composition of the mixed powder in the method process can be determined, and then through the chemical composition of the selected crystalline sulfide solid electrolyte raw material, the chemical composition of the regulator raw material can be calculated, and further the ratio of each raw material in the regulator can be determined; (2) Heat treatment process, the obtained mixed powder is heat-treated in a flowing inert atmosphere to obtain a sulfide solid electrolyte with the target; Wherein, The raw materials of the regulator include one or more of the following materials: Li source, P source, S source, simple substance or compound containing doped element M; Wherein, Δ = {N(Li)×312.5 + N(P)×346}×4, in the formula, N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, and the atomic percentage of doped element M is not considered in Δ.

2. The method for improving the thermal stability of sulfide solid electrolytes according to claim 1, characterized in that, The structure factor Δ of the element composition of the mixed powder is 301.5 to 1384, and the thermal decomposition temperature ≥300 °C.

3. The method for improving the thermal stability of sulfide solid electrolytes according to claim 1, characterized in that, The element composition and structure factor Δ of the mixed powder satisfy one of the following ranges: I. The material structure factor Δ is 301.5 to 980, and the element composition is in the range of 0 < N(Li) ≤ 0.75, 0 < N(P) ≤ 0.25, 0.25 ≤ N(S) ≤ 0.75; II. The material structure factor Δ is 468.7 to 887.7, and the element composition is in the range of 0 < N(Li) ≤ 0.64, 0 < N(P) ≤ 0.375, 0.3125 ≤ N(S) ≤ 0.625, 0.03 ≤ N(M) ≤ 0.2; III. The material structure factor Δ is 781 to 1300, and the element composition is in the lithium-rich range of 0.25 ≤ N(Li) ≤ 1, 0 < N(P) ≤ 0.375, 0 < N(S) ≤ 0.375, 0 ≤ N(M) ≤ 0.2; IV. The material structure factor Δ is 814 to 1384, and the element composition is in the phosphorus-rich range of 0 < N(Li) ≤ 0.375, 0.25 ≤ N(P) ≤ 1, 0 < N(S) ≤ 0.375, 0 ≤ N(M) ≤ 0.18; Wherein N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, N(M) represents the atomic percentage of doped element M, and the sum of each element is 100%.

4. The method for improving the thermal stability of sulfide solid electrolytes according to claim 1, characterized in that, Wherein, The doping element M is at least one of non-metallic elements such as oxygen O, selenium Se, fluorine F, chlorine Cl, bromine Br, iodine I, or metallic elements such as magnesium Mg, calcium Ca, strontium Sr, zinc Zn, scandium Sc, antimony Sb, silicon Si, germanium Ge, tin Sn, boron B, aluminum Al, gallium Ga, indium In, titanium Ti, zirconium Zr, vanadium V, niobium Nb, copper Cu, nickel Ni, manganese Mn, chromium Cr, silver Ag, lanthanum La, cerium Ce, terbium Tb, tellurium Te, lead Pb, arsenic As, bismuth Bi.

5. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 1, wherein, in the grinding process: the interval time between two-step feeding is more than 0.5 h; the grinding process adopts mechanical grinding, dry grinding, the mixing grinding time is 20 - 100 h, and the grinding atmosphere is an inert atmosphere.

6. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 5, wherein, in the grinding process, the interval time between two-step feeding is 0.5 - 5 h.

7. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 1, wherein, in the heat treatment process: the heat treatment environment is a flowing inert atmosphere, the heat treatment temperature is 200 - 600 °C; the heat treatment time is 2 - 10 h; the heating rate is not greater than 2 °C / min.

8. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 1, wherein, before the grinding process, it further includes the step of separately grinding each raw material constituting the crystalline sulfide solid electrolyte and the regulator to obtain raw material precursors.

9. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 1, wherein, the chemical formula of the crystalline sulfide solid electrolyte is Li-M-P-S, and the atomic percentages of each atom satisfy the following requirements: 0.2 ≤ N(Li) ≤ 0.55, 0 < N(P) ≤ 0.25, 0.37 ≤ N(S) ≤ 0.65, 0 ≤ N(M) ≤ 0.2, where N(Li) represents the atomic percentage of Li, N(P) represents the atomic percentage of P, N(S) represents the atomic percentage of S, N(M) represents the atomic percentage of the doping element M, and the sum of each element is 100%.

10. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 1, wherein, the optimized sulfide solid electrolyte will not show an exothermic peak below 450 °C; or, there will be a phase transition peak at 200 - 350 °C, but there will be no exothermic peak of phase decomposition.

11. The method for improving the thermal stability of a sulfide solid electrolyte according to claim 1, wherein, in the X-ray diffraction of the optimized sulfide solid electrolyte, there is a strong diffraction main peak before 2θ = 33.5, and the presented crystallization main peak will not appear after 2θ = 33.5; after heat treatment above 300 °C, a crystallization peak of crystalline phase A will appear near 2θ = 26.9; or a crystallization peak of crystalline phase B will appear near 2θ = 32.5.

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