Sulfide solid electrolyte and all-solid-state lithium battery

Abstract

The invention relates to the technical field of electrochemistry, and provides a sulfide solid electrolyte and an all-solid-state lithium battery, the chemical formula of the sulfide solid electrolyte is Li < 7-2x-y > PMxS < 6-x-y > OxCl < 0.7-y > Br < 0.3 y >, M is at least one of Ca, Mg and Cu, x is more than or equal to 0.01 and less than or equal to 0.3, y is more than or equal to 0.5 and less than or equal to 2, x / y is more than or equal to 0.008 and less than or equal to 0.24, the molar ratio of the element M to the element O is 1: 1, and the molar ratio of the element Cl to the element Br is 7: 3; the grain boundary impedance of the sulfide solid electrolyte at 25 DEG C is 20 Omega to 100 Omega. Through the arrangement, the sulfide solid electrolyte disclosed by the invention has relatively low grain boundary impedance while maintaining high ionic conductivity and good air stability. Furthermore, when the sulfide solid electrolyte is applied to the all-solid-state lithium battery, the electrochemical performance of the all-solid-state lithium battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a sulfide solid-state electrolyte and a full solid-state lithium battery. BACKGROUND

[0002] Under the background of the continuous development of full solid-state lithium battery technology, sulfide solid-state electrolytes have attracted widespread attention due to their high lithium ion conductivity and excellent processing performance. Among them, lithium phosphorus sulfur chloride sulfide electrolytes, as typical argyrodite structure materials, have been widely used in the research and development of high-performance solid-state batteries.

[0003] However, lithium phosphorus sulfur chloride sulfide electrolytes still have the problem of high grain boundary impedance, which limits their overall ion conductivity in practical devices. Although the lithium ion conductivity of such sulfide solid-state electrolyte materials is high, the grain boundary region formed between the particles often causes lithium ion migration to be blocked due to structural discontinuity, defect enrichment or secondary phase precipitation, etc., resulting in obvious interface impedance. The existing technology mainly focuses on indirectly improving the grain boundary environment through sintering temperature, compaction process or particle size optimization, but the research on directly regulating the material bulk to reduce the grain boundary impedance is still limited. In addition, lithium phosphorus sulfur chloride sulfide solid-state electrolytes are extremely easy to decompose in air and will generate harmful gases such as hydrogen sulfide after contacting with moisture or oxygen, accompanied by structural damage and significant decline in electrochemical performance. This air stability defect greatly limits the reliability of sulfide solid-state electrolytes in industrial production, storage and transportation, and practical applications.

[0004] Therefore, it is urgent to develop a new type of sulfide electrolyte material with low grain boundary impedance, high overall ion conductivity and good air stability, thereby improving the electrochemical performance of full solid-state lithium batteries. SUMMARY

[0005] The purpose of the present application is to provide a sulfide solid-state electrolyte and a full solid-state lithium battery to maintain the high ion conductivity and good air stability of the sulfide solid-state electrolyte while reducing its grain boundary impedance, thereby improving the electrochemical performance of the full solid-state lithium battery. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a sulfide solid-state electrolyte with a chemical formula of Li 7-2x-y PM x S 6-x- y O x Cl 0.7y Br 0.3y, M is at least one of Ca, Mg and Cu, 0.01≤x≤0.3, 0.5≤y≤2, 0.008≤x / y≤0.24, the molar ratio of M element to O element is 1:1, and the molar ratio of Cl element to Br element is 7:3; the grain boundary impedance of the sulfide solid electrolyte at 25 DEG C is 20Ω to 100Ω.

[0007] In an embodiment of the present application, 0.02≤x≤0.1, 1.25≤y≤1.75.

[0008] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-2x-y PCa x S 6-x- y O x Cl 0.7y Br 0.3y , 0.02≤x≤0.1, 1.25≤y≤1.5.

[0009] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-2x-y PMg x S 6-x- y O x Cl 0.7y Br 0.3y , 0.03≤x≤0.07, 1.25≤y≤1.5.

[0010] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-2x-y PCu x S 6-x- y O x Cl 0.7y Br 0.3y , 0.05≤x≤0.1, 1.5≤y≤1.75.

[0011] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 5.65 PCa 0.05 S 4.7 O 0.05 Cl 0.87 5Br 0.375 , Li 5.71 PCa 0.02 S 4.73 O 0.02 Cl 0.875 Br 0.375 , Li 5.55 PCa 0.1 S 4.65 O0.1 Cl 0.875 Br 0.375 、Li 5.4 PCa 0.0 5S 4.45 O 0.05 Cl 1.05 Br 0.45 、Li 5.65 PMg 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 、Li 5.4 PCu 0.05 S 4.45 O 0.05 Cl 1.05 Br 0.45 .

[0012] In an embodiment of the present application, the unit cell parameter of the sulfide solid electrolyte satisfies: a = b = c = 9.85 ~ 10 Å.

[0013] In an embodiment of the present application, the particle size of the sulfide solid electrolyte satisfies: 0.5 µm < D50 < 3 µm, 6.5 µm < D90 < 9 µm.

[0014] In an embodiment of the present application, the ionic conductivity of the sulfide solid electrolyte is > 5 mS / cm.

[0015] A second aspect of the present application provides a full solid-state lithium battery, comprising a positive electrode, a negative electrode and the sulfide solid electrolyte of the first aspect of the present application.

[0016] Advantages of the present application:

[0017] The present application provides a sulfide solid electrolyte and a full solid-state lithium battery, the chemical formula of the sulfide solid electrolyte is Li 7-2x-y PM x S 6-x-y O x Cl 0.7y Br 0.3y, M is at least one of Ca, Mg and Cu, 0.01≤x≤0.3, 0.5≤y≤2, 0.008≤x / y≤0.24, the molar ratio of M element to O element is 1:1, and the molar ratio of Cl element to Br element is 7:3; the grain boundary impedance of the sulfide solid electrolyte at 25℃ is 20Ω to 100Ω. Through the above settings, the sulfide solid electrolyte of the present application realizes low grain boundary impedance while maintaining high ionic conductivity and good air stability. Further, the sulfide solid electrolyte of the present application applied to the all-solid-state lithium battery can improve the electrochemical performance of the all-solid-state lithium battery.

[0018] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other embodiments can also be obtained by those skilled in the art based on these drawings.

[0020] Figure 1 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.65 PCa 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 ) prepared for Example 1;

[0021] Figure 2 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.65 PMg 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 ) prepared for Example 10;

[0022] Figure 3 X-ray diffraction pattern of the sulfide solid electrolyte (Li 5.4 PCu 0.05 S 4.45 O 0.05 Cl 1.05 Br 0.45 ) prepared for Example 11. DETAILED DESCRIPTION

[0023] The technical solutions in the present application will be clearly and completely described below with reference to the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application shall fall within the scope of the present application.

[0024] The first aspect of the present application provides a sulfide solid electrolyte with a chemical formula of Li 7-2x-y PM x S 6-x- y O x Cl 0.7y Br 0.3y , M is at least one of Ca, Mg and Cu, 0.01≤x≤0.3, 0.5≤y≤2, 0.008≤x / y≤0.24, the molar ratio of M element to O element is 1:1, and the molar ratio of Cl element to Br element is 7:3; the grain boundary resistance of the sulfide solid electrolyte at 25°C is 20Ω to 100Ω. Preferably, 0.02≤x≤0.1, 1.25≤y≤1.75. For example, x can be 0.01, 0.02, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3 or a range formed by any two of them, y can be 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2 or a range formed by any two of them, the value of x / y can be 0.008, 0.01, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.20, 0.22, 0.24 or a range formed by any two of them, and the grain boundary resistance of the sulfide solid electrolyte provided by the present application at 25°C can be 20Ω, 25Ω, 30Ω, 35Ω, 40Ω, 45Ω, 50Ω, 55Ω, 60Ω, 65Ω, 70Ω, 75Ω, 80Ω, 85Ω, 90Ω, 95Ω, 100Ω or a range formed by any two of them.

[0025] The sulfide solid electrolyte of the present application, in the argyrodite LPSC solid electrolyte, Li + is doped with at least one of Ca 2+ , Mg 2+ and Cu 2+ , S 2- is doped with O 2- , the molar ratio of M element to O element is controlled to be 1:1, the molar ratio of Cl element to Br element is controlled to be 7:3, and 0.01≤x≤0.3, 0.5≤y≤2, 0.008≤x / y≤0.24 are controlled, so that the grain boundary resistance of the sulfide solid electrolyte is reduced while maintaining high ionic conductivity and good air stability. Specifically, Li +site-doped Ca 2+ , Mg 2+ , Cu 2+ can reduce the generation of lithium ion vacancies, reduce the number of high-reactivity defects, slow down the degradation rate of the material, and further enhance the interface chemical stability. At the same time, Ca 2+ (1.00 Å), Mg 2+ (0.76 Å), and Cu 2+ (0.73 Å) have larger radii than Li + (0.6 Å), which will cause local lattice expansion and distortion, widen the lithium ion migration channel, and directly improve the diffusion ability of lithium ions. O 2- substitutes S 2- , the oxide matrix exhibits higher chemical inertness and resistance to moisture / oxygen erosion, which significantly improves the air stability of the material. At the same time, the introduction of O 2- near the Li + site can inhibit the reaction of the interface with moisture or oxygen in the air, forming a passivation layer-like protective effect and significantly improving the chemical stability of the material in the air. At the same time, doping at least one of Ca + , Mg 2+ , and Cu 2+ at the Li 2+ site and O 2- at the S 2- site can also form a local alkaline environment inside, reduce the diffusion of H and the probability of acid degradation reaction, reduce the reactivity of the material in the air, and further improve the chemical stability of the material, so that it can still maintain a low conductivity decay in a relatively high humidity environment. In addition, the molar ratio of M elements to O elements is 1:1 to achieve charge balance and defect compensation within the crystal structure. This equimolar doping strategy not only suppresses material structure distortion, but also helps to form stable M-O local structure units and enhance the orderliness of the lattice. Further, Cl elements and Br elements are co-doped at a molar ratio of 7:3, which can form a local polarization regulation effect at the crystal boundary region. has a strong electronic enrichment effect, which can promote lithium ion migration at the grain boundary; and has a larger radius, which causes local strain after doping, which is beneficial to grain boundary passivation and polarization symmetry improvement. The fixed Cl:Br molar ratio maintains the integrity of the crystal structure while reducing the unevenness of charge accumulation at the grain boundary, further reducing the impedance caused by the space charge layer, achieving high ionic conductivity and good air stability while reducing the grain boundary impedance of the sulfide solid electrolyte, thereby improving the electrochemical performance of the all-solid-state lithium battery. Further, the values of x and y are within the scope of the present application, which controls the Li + site and S2- The doping amount of different elements can easily adjust the crystal structure and electronic structure of the material, thereby improving the air stability and ionic conductivity of the material. When x is less than the range of the present application, i.e., x < 0.01, the doping amount is too low to achieve the purpose of modification, and when x is greater than the range of the present application, i.e., x > 0.3, the doping amount is too high to destroy the lattice structure of the material itself, the lithium ion transmission channel is destroyed, and at the same time, there are impurities that cannot be doped into the lattice, which makes the material conductivity decrease rapidly; when y is less than the range of the present application, i.e., y < 0.5, the halogen content is too low, which makes the ionic conductivity of the material decrease significantly, and when y is greater than the range of the present application, i.e., y > 2, the halogen content is too high, which also destroys the lattice structure of the material, making the ionic conductivity of the material decrease significantly. Further, by limiting the ratio of x / y to be within the range of 0.008 to 0.24, the appropriate defects can be introduced to optimize the lithium ion migration channel while ensuring the stability of the lattice. If x / y deviates from this range, the crystal may be locally over-rich in M-O bonds or the defect density may be unbalanced, thereby inducing stress concentration at the grain boundary, resulting in an increase in grain boundary impedance.

[0026] In solid-state electrolyte materials, the grain boundary structure is one of the key factors affecting the lithium ion conduction performance. The grain boundary impedance usually comes from the defect enrichment, polarization accumulation and structure distortion at the interface between the grains, which has high locality and complexity. The size depends not only on the overall composition of the material, but also on the spatial distribution of elements at the grain boundary, the defect type at the grain boundary, the influence of doping on the stress field of the crystal, and other micro factors. The ionic conductivity reflects the migration ability of lithium ions in the whole material, which is the comprehensive performance value of the grain conductivity and the grain boundary conductivity. In contrast, the ionic conductivity reflects the average migration ability of lithium ions in the whole material, which is often regarded as a macroscopic comprehensive index. Although the ionic conductivity can indirectly reflect the overall conduction performance of the material, in the system with complex grain boundary structure and fine doping strategy, even if different materials show similar ionic conductivity, the structural differences in the grain boundary region may still lead to significantly different impedance behaviors. Therefore, the approximation of ionic conductivity does not mean that the grain boundary impedance is also at the same level.

[0027] When the ion conductivity levels are substantially equivalent, sulfide solid-state electrolytes have the advantage of lower grain boundary impedance, which is beneficial in that: (1) first, the reduction of grain boundary impedance helps to reduce the interface polarization and space charge layer effect, and improves the interface stability in the ion migration process, especially for full solid-state battery systems in high-rate charging and discharging environment. (2) Secondly, the lower grain boundary impedance can significantly reduce the interface attenuation rate of the material during long-term cycling, thereby improving the consistency and cycle life of the battery. (3) In practical application, the grain boundary impedance is one of the key factors limiting the compaction forming performance and electrode matching performance of the electrolyte. Lower grain boundary impedance means that the electrolyte can still maintain excellent overall ion channel connectivity under relatively low density or smaller particle size conditions, which is beneficial to large-scale preparation and process tolerance.

[0028] In summary, the solid-state electrolyte material obtained by the present application within the above-mentioned element ratio window has a stable unit cell structure, sufficient passivation of grain boundary defects, and continuous ion migration channels, and exhibits excellent electrochemical performance. At room temperature, the grain boundary impedance is within 100Ω, and the ion conductivity can reach 10-3S / cm or more. The above.

[0029] In an embodiment of the present application, the chemical formula of the sulfide solid-state electrolyte is Li 7-2x-y PCa x S 6-x- y O x Cl 0.7y Br 0.3y , 0.02≤x≤0.1, 1.25≤y≤1.5. For example, x can be 0.02, 0.05, 0.07, 0.1 or a range composed of any two of the above values, and y can be 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or a range composed of any two of the above values. For example, in the argyrodite LPSC solid-state electrolyte, Li + doped with Ca 2+ at the S 2- site, doped with O 2- , and the value range of x and y is within the above range, the air stability, ion conductivity and grain boundary impedance of the sulfide solid-state electrolyte can be further improved, and the electrochemical performance of the full solid-state lithium battery is further improved.

[0030] In an embodiment of the present application, the chemical formula of the sulfide solid-state electrolyte is Li 7-2x-y PMg x S 6-x- y O x Cl 0.7y Br 0.3y, 0.03≤x≤0.07, 1.25≤y≤1.5. For example, x can be 0.03, 0.05, 0.07 or a range between any two of them, and y can be 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or a range between any two of them. The Li + Site-doped Mg 2+ , S 2- Site-doped O 2- , and the value range of x and y is within the above range, the air stability, ionic conductivity of the sulfide solid electrolyte can be further improved, and the grain boundary resistance can be reduced, further improving the electrochemical performance of the all-solid-state lithium battery.

[0031] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 7-2x-y PCu x S 6-x- y O x Cl 0.7y Br 0.3y , 0.05≤x≤0.1, 1.5≤y≤1.75. For example, x can be 0.05, 0.07, 0.1 or a range between any two of them, and y can be 1.5, 1.65, 1.7, 1.75 or a range between any two of them. The Li + Site-doped Cu 2+ , S 2- Site-doped O 2- , and the value range of x and y is within the above range, the air stability, ionic conductivity of the sulfide solid electrolyte can be further improved, and the grain boundary resistance can be reduced, further improving the electrochemical performance of the all-solid-state lithium battery.

[0032] In an embodiment of the present application, the chemical formula of the sulfide solid electrolyte is Li 5.65 PCa 0.05 S 4.7 O 0.05 Cl 0.87 5Br 0.375 , Li 5.71 PCa 0.02 S 4.73 O 0.02 Cl 0.875 Br 0.375 , Li 5.55 PCa 0.1 S 4.65 O 0.1 Cl 0.875 Br 0.375 , Li 5.4 PCa0.0 5S 4.45 O 0.05 Cl 1.05 Br 0.45 , Li 5.65 PMg 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 , Li 5.4 PCu 0.05 S 4.45 O 0.05 Cl 1.05 Br 0.45 The above sulfide solid electrolyte is selected to have higher air stability and ionic conductivity and lower grain boundary impedance.

[0033] In an embodiment of the present application, the unit cell parameter of the sulfide solid electrolyte satisfies: a = b = c = 9.85 ~ 10 Å. It is found by Rietveld fitting calculation of X-ray diffraction patterns that, within the doping ratio range defined in the present application (0.01 ≤ x ≤ 0.3, 0.5 ≤ y ≤ 2, 0.008 ≤ x / y ≤ 0.24), the unit cell parameter a of the obtained material is stably maintained in the interval of 9.85 ~ 10.00 Å, showing a clear lattice expansion trend. This unit cell expansion is on the one hand a proof of the crystal structure reconstruction caused by M-O cooperative doping, and on the other hand is conducive to expanding the lithium ion migration channel and reducing the stress concentration of grain boundary defects, and is an important structural basis for realizing low grain boundary impedance.

[0034] In an embodiment of the present application, the particle size of the sulfide solid electrolyte satisfies: 0.5 µm < D50 < 3 µm, 6.5 µm < D90 < 9 µm. The particle size of the sulfide solid electrolyte of the present application is in the above range, so that the sulfide solid electrolyte has good processing performance.

[0035] In an embodiment of the present application, the ionic conductivity of the sulfide solid electrolyte is > 5 mS / cm. Preferably, the ionic conductivity of the sulfide solid electrolyte is > 5.5 mS / cm; more preferably, the ionic conductivity of the sulfide solid electrolyte is > 6 mS / cm; still more preferably, the ionic conductivity of the sulfide solid electrolyte is > 7 mS / cm. The sulfide solid electrolyte of the present application has a low grain boundary impedance, and at the same time also has a high ionic conductivity, and when applied in a full solid-state lithium battery, can improve the electrochemical performance of the full solid-state lithium battery.

[0036] The application does not particularly limit the preparation method of the sulfide solid-state electrolyte, and any method that can achieve the purpose of the application can be used, for example, the preparation method of the sulfide solid-state electrolyte can include: mixing raw materials and a solvent under inert atmosphere protection to obtain a suspension; performing vacuum distillation drying on the suspension to obtain a solid-state electrolyte precursor mixture; and sintering the solid-state electrolyte precursor mixture to obtain the sulfide solid-state electrolyte.

[0037] The application does not particularly limit the types of raw materials and solvents, and any material that can achieve the purpose of the application can be used, for example, the raw materials can be Li2S, P2S5, LiCl, LiBr and alkaline oxides (such as CaO, MgO, CuO), and the solvent can be n-hexane, benzene, toluene, cyclohexane, n-pentane, cyclopentane, and dimethyl carbonate. Since Ca 2+ , Mg 2+ , and Cu 2+ are divalent cations, replacing monovalent will introduce charge imbalance, so the amount of is appropriately reduced in the design of raw materials to maintain overall charge balance and crystal structure stability. For example, while keeping the P and S components unchanged, reducing and increasing the proportion of Ca source, Mg source or Cu source can guide Ca 2+ , Mg 2+ or Cu 2+ to preferentially enter the lithium site without destroying framework units.

[0038] The application does not particularly limit the amount of raw materials and solvents, and any amount that can achieve the purpose of the application can be used, for example, the mass ratio of the raw materials to the solvent is 1:1-3. The application does not particularly limit the method of vacuum distillation drying, and any method that can achieve the purpose of the application can be used, for example, the temperature of vacuum distillation drying is 40-60°C, and the vacuum degree is -0.09Mpa--0.10Mpa. The application does not particularly limit the sintering method, and any method that can achieve the purpose of the application can be used, for example, a tubular furnace programmed heating method is used, first heated at 150-300°C for 2-4 hours, and then heated at 500-600°C for 4-6 hours for sintering to obtain the sulfide solid-state electrolyte.

[0039] The second aspect of the application provides a full solid-state lithium battery, which includes a positive electrode, a negative electrode and the sulfide solid-state electrolyte of the first aspect of the application.

[0040] The application does not particularly limit the positive electrode and the negative electrode in the all-solid-state lithium battery, and any positive electrode and negative electrode that can achieve the purpose of the application can be used. For example, the positive electrode includes a positive electrode active material, a sulfide solid electrolyte, and conductive carbon. The positive electrode active material can be ternary positive electrode NCM523, NCM622, NCM712, NCM811, NCM90, or can be lithium iron phosphate, lithium manganese iron phosphate LiMn x Fe 1-x PO4, LiCoO2 material, lithium-rich manganese-based material (aLi2MnO3•(1-a)LiMO2) (0≤a≤1, M is at least one of Ni, Co, or Mn), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) material, etc. The sulfide solid electrolyte is the electrolyte in the application, and the conductive carbon can be Super P, carbon black. The mass ratio of the positive electrode active material, the sulfide solid electrolyte, and the conductive carbon can be 60-80%:10-35%:3-10%. The negative electrode includes lithium-indium alloy, lithium metal, graphite, and silicon-carbon. Preferably, the all-solid-state lithium battery further includes a current collector arranged on the side of the positive electrode material. The current collector can be a carbon-coated aluminum foil or a pure aluminum foil.

[0041] The application does not particularly limit the preparation method of the all-solid-state lithium battery, and any preparation method that can achieve the purpose of the application can be used. For example, the preparation method of the all-solid-state lithium battery includes: mixing a positive electrode active material, a sulfide solid electrolyte, and conductive carbon to obtain a composite positive electrode powder; loading the sulfide solid electrolyte into a solid-state battery mold for first pressing to obtain an electrolyte layer; adding the composite positive electrode powder to one side of the electrolyte layer for second pressing to obtain a positive electrode; and adding a negative electrode material to the other side of the electrolyte layer for third pressing to obtain an all-solid-state lithium battery.

[0042] The sulfide solid electrolyte of the application has high ionic conductivity, high air stability, and low grain boundary resistance. Therefore, the all-solid-state lithium battery including the sulfide solid electrolyte of the application has excellent electrochemical performance.

[0043] Examples

[0044] Hereinafter, examples and comparative examples are given to more specifically describe the embodiments of the application. Various tests and evaluations are performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0045] Test methods and equipment:

[0046] Ionic conductivity test and grain boundary resistance test

[0047] In an argon-filled glove box, 100 mg of sulfide solid-state electrolyte powder was weighed and placed in a mold cell (Wuhan Chuangneng CN-01) with a 9 mm diameter stainless steel sheet at both ends. It was pressed into a sheet with a thickness of 1 mm at a pressure of 200 MPa. The mold cell was used for AC impedance spectroscopy testing.

[0048] In an argon-filled glove box, 110 mg of sulfide solid-state electrolyte powder was weighed and placed in a mold cell (Wuhan Chuangneng CN-01) with a 9 mm diameter stainless steel sheet at both ends. It was pressed into a sheet with a thickness of 1 mm at a pressure of 300 MPa. The mold cell was used for AC impedance spectroscopy testing.

[0049] At 25°C, the electrolyte impedance was measured by electrochemical impedance spectroscopy (EIS). The impedance was measured on an electrochemical workstation (ChenHua, CHI630E) by applying a direct current (DC) polarization voltage of 1 V. The amplitude was 50 mV, and the frequency range was 1 Hz to 10 MHz. The ionic conductivity of the electrolyte material was calculated according to the following ion conductivity formula, as follows:

[0050] Where σ is the ionic conductivity, with units of ; L is the thickness of the electrolyte sheet, with units of cm; R is the electrolyte impedance, with units of ; S is the effective contact area between the stainless steel sheet and the electrolyte powder, with units of cm 2 .

[0051] To further distinguish the contributions of the bulk and grain boundary, the Nyquist plot was fitted with an equivalent circuit. A series R b -CPE b (bulk) and R gb -CPE gb (grain boundary) unit was used, where R b -CPE b and R gb -CPE gb correspond to the bulk resistance and grain boundary resistance, respectively, and CPE is a constant phase element. The grain boundary impedance R gb was obtained by fitting the medium frequency region.

[0052] Air stability test

[0053] Air stability is mainly described by the retention rate of the ionic conductivity of the sulfide solid-state electrolyte under air exposure.

[0054] Ion conductivity retention test: The ion conductivity of the sulfide solid-state electrolyte was tested using the ion conductivity test method described above, and was recorded as the conductivity before exposure; then the sulfide solid-state electrolyte was directly exposed to air at a dew point temperature of -40°C, and the sulfide solid-state electrolyte was recovered at 12 hours, 24 hours, and 48 hours, respectively, and the ion conductivity was tested using the ion conductivity test method described above, and was recorded as the conductivity after exposure. The conductivity retention rate = conductivity after exposure / conductivity before exposure x 100%.

[0055] X-ray powder diffraction test

[0056] The crystal structure of the sample was analyzed by X-ray powder diffraction (XRD) technology. The experiment used a Bruker D8 Advance diffractometer equipped with Cu Kα radiation (λ = 1.5406 Å) as the light source. The test parameters were set as follows: tube voltage 40 kV, tube current 40 mA, scanning range 2θ = 5°-90°, scanning step 0.02°, scanning rate 5° / min. The sample was uniformly dispersed in the form of powder on a glass slide without diffraction background, and was treated by compaction to reduce the influence of inter-particle voids on the diffraction results.

[0057] The XRD data were processed and analyzed by Jade software. First, the raw data were imported into the software, and background subtraction and signal optimization were performed. The peak position was automatically identified by peak search function, and Gaussian function was selected for peak shape fitting. The parameters were adjusted to make the fitting curve consistent with the experimental data. After fitting, the software directly outputted the peak area I of the diffraction peak.

[0058] Calculation of the ratio of impurity peak to main peak in XRD after 24 hours of exposure: The sulfide solid-state electrolyte was directly exposed to air at a dew point temperature of -40°C for 24 hours, and the sulfide solid-state electrolyte was recovered. The peak area of the impurity peak and the main peak was tested and the ratio of the two was calculated using the above method.

[0059] Cell parameter analysis: The XRD data were processed and analyzed by Jade software. First, the raw data were imported into the software, and background subtraction and signal optimization were performed, and then were exported in text format. The text file was imported into the refinement software FullProf, and an initial model was established according to the known crystal structure of the sample. The preliminary cell parameters and space group were inputted, and the instrument parameters such as zero point shift and sample displacement were adjusted, and the preliminary fitting was completed.

[0060] In the refinement process, the peak shape parameters (such as peak width, peak shape factor), background function, cell parameters (a, b, c, a, b, g) and atomic positions and occupancy are optimized step by step, and finally the convergence of the fitting is realized. The evaluation of the fitting results is based on the goodness of fit Chi2, and the fitting quality is judged by combining the residual spectrum. When the refinement result converges (Chi2<3), the cell parameters a, b, c can be obtained in the result text output by the software.

[0061] Test of particle size distribution

[0062] A Zeiss Sigma 300 scanning electron microscope (SEM) was used to observe the surface morphology and particle size distribution of the sulfide solid electrolyte. It was fixed on the sample stage, and the sample stage was placed in the vacuum chamber. The acceleration voltage, beam intensity and working distance of the SEM were adjusted to optimize the imaging effect, and the surface morphology information was obtained by the secondary electron detector. The particle size of the sulfide solid electrolyte in the SEM image was measured and counted using Image J software, and the particle size distribution was obtained.

[0063] Electrochemical performance test

[0064] The electrochemical performance test was mainly carried out by assembling a full solid-state battery with the sulfide solid electrolyte and a layered high-nickel NCM811 ternary positive electrode material.

[0065] Preparation of full solid-state battery: (1) Preparation of positive electrode material: the positive electrode active material NCM811, the sulfide solid electrolyte of the application and conductive carbon (Super P) were mixed in a mass ratio of 75:20:5, ground in a mortar for 30 minutes to obtain a composite positive electrode powder; (2) negative electrode material: lithium-indium alloy (lithium content of 30wt%); (3) sulfide solid electrolyte: the sulfide solid electrolyte of the application was used; (4) assembly of full solid-state battery: in an argon-filled glove box, first weigh 100mg of sulfide solid electrolyte into a solid-state battery mold with an inner diameter of 10mm, press to 300Mpa for 1 minute to obtain an electrolyte layer; add 10mg of composite positive electrode powder on one side of the electrolyte layer, cover with a 15µm aluminum foil, press to 100Mpa for 1 minute to obtain a positive electrode; then add 100µm of lithium-indium alloy negative electrode material on the other side, slightly press with 50Mpa, then assemble the mold to obtain an assembled full solid-state lithium ion battery. After verifying the airtightness, it was taken out of the glove box and transferred to a battery test system for electrochemical charge-discharge cycle test.

[0066] Charge-discharge test: the charge-discharge performance test of the battery adopts the LAND battery test system, and is carried out under the condition of constant temperature 25℃. The constant current charge-discharge test can directly reflect the electrochemical performance of the active material in the battery, and is an important means to evaluate the practical application potential of the material. In the test, the current density is based on the mass of the material, and the specific capacity corresponding to 1C is defined as , wherein 0.2C is . During the 0.2C rate cycle process, first, the battery is charged from 2.6V to the preset cut-off voltage (3.9V, 4.0V, 4.1V, 4.2V, 4.3V or 4.4V) at a constant current, and the highest voltage at which the battery can stably operate is selected as the cut-off voltage, and then discharged to 2.6V at a constant current of 0.2C, and the whole process is completed in a constant current mode. Record the capacity retention rate (initial efficiency) of the all-solid-state lithium ion battery in the first charge-discharge process at 0.2C, the capacity retention rate after 200 cycles in the charge-discharge cycle process at 0.2C, and the cycle number when the discharge capacity jumps (the discharge capacity jump in this application refers to the sudden and sharp decrease of the discharge capacity).

[0067] The specific capacity of the first charge-discharge process of the battery is used to calculate the first discharge efficiency (initial efficiency), and the calculation method is: initial efficiency = first discharge capacity / first charge capacity × 100%. This index can be used to evaluate the capacity loss caused by irreversible reactions (such as electrolyte decomposition or solid electrolyte interface film formation) in the first cycle.

[0068] The capacity retention rate after 200 cycles = the 200th discharge capacity / the first discharge capacity × 100%.

[0069] Example 1

[0070] In an Ar atmosphere, weigh the raw materials of Li2S, P2S5, LiCl, LiBr and alkaline oxide CaO with a molar ratio of 2.2:0.5:0.875:0.375:0.05, take 1 kg of raw materials and add 1 kg of n-hexane for mixing to obtain a suspension; the suspension is subjected to vacuum distillation drying under the condition of temperature 40℃ and vacuum degree-0.098Mpa to obtain a solid electrolyte precursor mixture; in an Ar atmosphere, the solid electrolyte precursor mixture obtained above is heated at 200℃ for 3 hours and then at 550℃ for 5 hours by using a tubular furnace programmed heating method to obtain a sulfide solid electrolyte (Li 5.65 PCa 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 ), and the X-ray diffraction pattern thereof is shown in Figure 1 .

[0071] Example 2 to Example 9

[0072] Except for adjusting the molar ratio of the raw materials to obtain sulfide solid electrolytes with different chemical formulas in Table 1, the remaining steps are the same as those in Example 1.

[0073] Example 10

[0074] In addition to replacing the "alkaline oxide CaO" with "alkaline oxide MgO", the sulfide solid electrolyte (Li 5.6 5PMg 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 ), the remaining steps are the same as those in Example 1. Its X-ray diffraction pattern is as follows Figure 2 shown.

[0075] Example 11

[0076] In addition to replacing "alkaline oxide CaO" with "alkaline oxide CuO" and adjusting the molar ratio of the raw materials, the sulfide solid electrolyte (Li 5.4 PCu 0.05 S 4.45 O 0.05 Cl 1.05 Br 0.45 ), the remaining steps are the same as those in Example 1. Its X-ray diffraction pattern is as follows Figure 3 shown.

[0077] Example 12

[0078] The raw materials were replaced with "Li2S, P2S5, LiCl, LiBr, basic oxide CaO, basic oxide MgO in a molar ratio of 2.2: 0.5: 0.875: 0.375: 0.025: 0.025" to obtain a sulfide solid electrolyte (Li 5.65 PCa 0.02 5Mg 0.025 S 4.7 O 0.05 Cl 0.875 Br 0.375 ), the remaining steps are the same as those in Example 1.

[0079] Example 13

[0080] The sulfide solid electrolyte is the same as that in Example 1, and the positive electrode active material for the electrochemical performance test is Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, the negative electrode material is graphite, and the rest of the electrochemical performance test steps are the same as the above test method.

[0081] Example 14

[0082] The sulfide solid electrolyte is the same as that of Example 1, the positive active material for the electrochemical performance test is LiFe 0.5 Mn 0.5 PO4, the negative material is silicon carbon, and the remaining electrochemical performance test steps are the same as the above test method.

[0083] Comparative Examples 1 to 6

[0084] Except that the molar ratio of the raw materials is adjusted to obtain sulfide solid electrolytes of different chemical formulas in Table 1, the remaining steps are the same as those of Example 1.

[0085] Comparative Example 7

[0086] The raw materials are replaced with “raw materials of Li2S, P2S5, LiCl, LiBr and basic oxide CaO with a molar ratio of 2.2: 0.5: 0.625: 0.625: 0.05”, to obtain a sulfide solid electrolyte (Li 5.65 PCa 0.05 S 4.7 O 0.05 Cl 0.625 Br 0.625 ) except that the remaining steps are the same as those of Example 1.

[0087] Comparative Example 8

[0088] The raw materials are replaced with “raw materials of Li2S, P2S5, LiCl and LiBr with a molar ratio of 2.25: 0.5: 0.875: 0.375”, to obtain a sulfide solid electrolyte (Li 5.75 PS 4.75 Cl 0.875 Br 0.375 ) except that the remaining steps are the same as those of Example 1.

[0089] Comparative Example 9

[0090] The raw materials are replaced with “raw materials of Li2S, P2S5, LiCl, LiBr and CaS with a molar ratio of 2.2: 0.5: 0.875: 0.375: 0.05”, to obtain a sulfide solid electrolyte (Li 5.65 PCa 0.05 S 4.75 Cl 0.875 Br 0.375 ) except that the remaining steps are the same as those of Example 1.

[0091] Comparative Example 10

[0092] The remaining steps were the same as those of Comparative Example 9 except that the molar ratio of the raw materials was adjusted to obtain a sulfide solid electrolyte (Li 5.73 PCa 0.01 S 4.75 Cl 0.875 Br 0.375 ).

[0093] Comparative Example 11

[0094] The remaining steps were the same as those of Example 1 except that the raw materials were replaced with "raw materials of Li2S, P2S5, LiCl, LiBr, P2O5 in a molar ratio of 2.25: 0.48: 0.875: 0.375: 0.02" to obtain a sulfide solid electrolyte (Li 5.75 PS 4.65 O 0.1 Cl 0.875 Br 0.375 ).

[0095] Comparative Example 12

[0096] The remaining steps were the same as those of Comparative Example 11 except that the molar ratio of the raw materials was adjusted to obtain a sulfide solid electrolyte (Li 5.75 PS 4.73 O 0.02 Cl 0.875 Br 0.375 ).

[0097] Comparative Example 13

[0098] The remaining steps were the same as those of Example 1 except that the molar ratio of the raw materials was adjusted to obtain a sulfide solid electrolyte (Li 5.3 Ca 0.05 PS 4.35 O 0.05 Cl 1.4 Br 0.2 ).

[0099] Comparative Example 14

[0100] The remaining steps were the same as those of Example 10 except that the molar ratio of the raw materials was adjusted to obtain a sulfide solid electrolyte (Li 5.3 Mg 0.05 PS 4.35 O 0.05 Cl 1.4 Br 0.2 ).

[0101] Comparative Example 15

[0102] The remaining steps were the same as those of Example 1 except that "alkali metal oxide CaO" was replaced with "ZnO" and the molar ratio of the raw materials was adjusted to obtain a sulfide solid electrolyte (Li 5.3 Zn0.05 PS 4.35 O 0.05 Cl 1.4 Br 0.2 The remaining steps are the same as Example 1 except for the above.

[0103] The preparation parameters and performance parameters of the sulfide solid electrolyte of each example and comparative example are shown in Tables 1 and 2, and the performance parameters of the all-solid-state battery prepared therefrom are shown in Tables 3 and 4.

[0104] Table 1 Preparation parameters of sulfide solid electrolyte

[0105] In Table 1, " / " indicates no relevant parameter.

[0106] Table 2 Performance parameters of sulfide solid electrolyte

[0107] Table 3 Performance parameters of all-solid-state battery

[0108] Table 4 Performance parameters of all-solid-state battery of different systems

[0109] As can be seen from Table 1, the unit cell parameters of the sulfide solid electrolyte of the present application satisfy a=b=c=9.85~10Å; the particle size of the sulfide solid electrolyte satisfies 0.5µm<D50<3µm, 6.5µm<D90<9µm; as can be seen from Table 2, the sulfide solid electrolyte of the present application has high ionic conductivity, good air stability and low grain boundary resistance, its ionic conductivity is greater than 5mS / cm, the conductivity retention rate is ≥82% after exposure to a dew point temperature of -40°C for 12 hours, the conductivity retention rate is ≥77% after exposure to a dew point temperature of -40°C for 24 hours, and the conductivity retention rate is ≥70% after exposure to a dew point temperature of -40°C for 48 hours. The ratio of the impurity peak to the main peak after exposure to a dew point temperature of -40°C for 24 hours is ≤0.18%, and its grain boundary resistance is within 100Ω. As can be seen from Table 3, the sulfide solid electrolyte of the present application is applied to all-solid-state lithium batteries to improve the first discharge efficiency, cycle performance and cut-off voltage of the all-solid-state lithium batteries. The first discharge efficiency is ≥80.4%, the capacity retention rate after 200 cycles at 0.2C is ≥95.1%, the number of cycles at 0.2C is ≥331 times, and the cut-off voltage is ≥4.2V. As can be seen from Table 4, the sulfide solid electrolyte of the present application is applied to all-solid-state lithium batteries of different systems, and the obtained all-solid-state lithium batteries have high first discharge efficiency, good cycle performance and high cut-off voltage. In summary, the sulfide solid electrolyte of the present application achieves the goal of reducing grain boundary impedance while maintaining high ionic conductivity and good air stability, thereby improving the electrochemical performance of all-solid-state lithium batteries.

[0110] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A sulfide solid electrolyte with the chemical formula Li 7-2x-y PM x S 6-x-y O x Cl 0.7y Br 0.3y , M is at least one of Ca, Mg and Cu, 0.01≤x≤0.3, 0.5≤y≤2, 0.008≤x / y≤0.24, the molar ratio of M element to O element is 1:1, and the molar ratio of Cl element to Br element is 7:3; The grain boundary resistance of the sulfide solid electrolyte at 25° C. is 20Ω to 100Ω.

2. The sulfide solid electrolyte according to claim 1, wherein 0.02≤x≤0.1, 1.25≤y≤1.

75.

3. The sulfide solid electrolyte according to claim 1, wherein The chemical formula of the sulfide solid electrolyte is Li 7-2x-y PCa x S 6-x-y O x Cl 0.7y Br 0.3y , 0.02≤x≤0.1, 1.25≤y≤1.

5.

4. The sulfide solid electrolyte according to claim 1, wherein The chemical formula of the sulfide solid electrolyte is Li 7-2x-y PMg x S 6-x-y O x Cl 0.7y Br 0.3y , 0.03≤x≤0.07, 1.25≤y≤1.

5.

5. The sulfide solid electrolyte according to claim 1, wherein The chemical formula of the sulfide solid electrolyte is Li 7-2x-y PCu x S 6-x-y O x Cl 0.7y Br 0.3y , 0.05≤x≤0.1, 1.5≤y≤1.

75.

6. The sulfide solid electrolyte according to claim 1, wherein The sulfide solid electrolyte is Li 5.65 PCa 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 、Li 5.71 PCa 0.02 S 4.73 O 0.02 Cl 0.875 Br 0.375 、Li 5.55 PCa 0.1 S 4.65 O 0.1 Cl 0.875 Br 0.375 、Li 5.4 PCa 0.05 S 4.45 O 0.05 Cl 1.05 Br 0.45 、Li 5.65 PMg 0.05 S 4.7 O 0.05 Cl 0.875 Br 0.375 、Li 5.4 PCu 0.05 S 4.4 5O 0.05 Cl 1.05 Br 0.45 .

7. The sulfide solid electrolyte according to claim 1, wherein The unit cell parameters of the sulfide solid electrolyte satisfy: a=b=c=9.85~10Å.

8. The sulfide solid electrolyte according to claim 1, wherein The particle size of the sulfide solid electrolyte satisfies the following requirements: 0.5µm<D50<3µm, 6.5µm<D90<9µm.

9. The sulfide solid electrolyte according to claim 1, wherein The ionic conductivity of the sulfide solid electrolyte is greater than 5 mS / cm.

10. An all-solid-state lithium battery comprising a positive electrode, a negative electrode, and the sulfide solid electrolyte according to any one of claims 1 to 9.

Images