Composite positive electrode material capable of being used for solid-state battery and preparation method and application of composite positive electrode material

Abstract

The invention relates to the technical field of batteries, in particular to a composite positive electrode material capable of being used for a solid-state battery as well as a preparation method and application of the composite positive electrode material. The composite positive electrode material comprises a positive electrode base material and a coating layer arranged on the surface of the positive electrode base material, the coating layer comprises halide electrolyte and a modification group-N (CH3) 3R, R is-CnH2n + 1, and n is greater than or equal to 9. According to the composite positive electrode material disclosed by the invention, by arranging the halide electrolyte coating layer with the modified group-N (CH3) 3R, the moisture stability of the composite positive electrode material in air can be improved, the composite positive electrode material has excellent smoothness and proper apparent density, the porosity of a positive electrode can be reduced, and space charge layer and interface reaction between the positive electrode material and sulfide electrolyte can be reduced; and the energy density, the rate capability and the cycling stability of the sulfide solid-state lithium ion battery are improved.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a composite positive electrode material that can be used in solid-state batteries, and a preparation method and application thereof. Background Art

[0002] Solid-state lithium-ion batteries overcome the problems of leakage and combustion of liquid electrolytes in traditional lithium-ion batteries and have higher safety. Sulfide electrolytes are a type of solid electrolyte with sulfur as the main component and PS4 or MS4 (M is a metal element such as Sn, Ge, etc.) as the basic structural unit. Sulfide electrolytes are the mainstream electrolyte materials used in current solid-state lithium-ion batteries due to their high lithium-ion conductivity (3mS / cm~25mS / cm), low interface resistance and excellent mechanical ductility. Lithium-ion batteries whose main electrolyte material is sulfide electrolyte are sulfide solid-state lithium-ion batteries, which are the mainstream among solid-state lithium-ion batteries.

[0003] The positive electrode material determines the capacity, rate and cycle stability of solid-state lithium-ion batteries. Sulfide solid-state lithium-ion battery positive electrode must be mixed with sulfide electrolyte to conduct lithium ions, which will cause the following problems: 1) The mismatch between sulfide and uncoated positive electrode materials causes a space charge layer, which increases polarization and reduces battery capacity and rate performance; 2) The electrochemical window of sulfide electrolyte is narrow, and when it is used with uncoated positive electrode materials at high voltage (>4.2V vs Li + / Li), the sulfide electrolyte at the interface continues to decompose, destroying the cycle stability; 3) Due to the lack of sliding between the sulfide electrolyte and the positive electrode material particles, the rigid positive electrode material is easily cracked during the rolling process, and the active material that is difficult to slide makes the thickness consistency of the positive electrode rolling poor; more importantly, the lack of sliding leads to high porosity of the rolled positive electrode, poor particle contact, and low positive electrode compaction density, which increases the positive electrode impedance and reduces the energy density of the sulfide solid-state lithium-ion battery.

[0004] In order to overcome the space charge layer, interface reaction and contact problems between the above-mentioned positive electrode material and the sulfide electrolyte, the currently widely used method is to construct a stable coating layer on the surface of the positive electrode material to isolate the direct contact between the positive electrode material and the sulfide electrolyte and reduce the interface reaction. However, the room temperature ionic conductivity of the existing coating layer is low, which is not conducive to the rate performance. In addition, in order to control the thickness of the coating layer and ensure the uniformity of the coating, equipment and processes such as magnetron sputtering and atomic layer deposition (ALD) need to be introduced, which is difficult to mass produce.

[0005] In addition, the most fundamental application barrier of existing electrolyte coatings is the problem of moisture stability under high dew points. Conventional electrolyte coatings are easily damaged during the coating process and subsequent storage and transportation, which will lead to a significant decrease in the ionic conductivity of the coating, loss of high-voltage positive electrode stability and other effects, and further lead to the deactivation of the positive electrode material due to decomposition of the coating. If the dew point control temperature is reduced from -30°C to -45°C, the energy consumption of the dehumidifier will increase by more than 50%; in addition to energy consumption, if the packaging is damaged during storage and transportation, not only will the entire batch of materials be scrapped, but there is also a risk of HCl leakage. As a bulk chemical, the production of positive electrode materials is often a continuous production process of tons of samples. It is impractical to control the dew point to less than -45°C in the halide coating section and subsequent processing and transportation sections.

[0006] Therefore, how to improve the moisture stability of the positive electrode material in a high dew point environment, reduce the porosity of the positive electrode material during the positive electrode rolling process, and reduce the space charge layer and interfacial reaction between the positive electrode material and the sulfide electrolyte are crucial to improving the rate performance, cycle stability and energy density of sulfide solid-state lithium-ion batteries.

[0007] In view of this, the present invention is proposed. Summary of the Invention

[0008] One object of the present invention is to provide a composite cathode material to address the technical issues of existing cathode materials, such as poor moisture stability in high dew point environments and high porosity after positive electrode roll pressing. The composite cathode material of the present invention, coated with a halide electrolyte coating layer containing a modified group -N(CH3)3R, improves its water vapor stability in air, surface smoothness, and apparent density, reduces cathode porosity, and reduces the space charge layer and interfacial reactions between the cathode material and the sulfide electrolyte.

[0009] Another object of the present invention is to provide a method for preparing a composite positive electrode material, which is simple, easy to implement, environmentally friendly, and enables the composite positive electrode material to have a more excellent coating effect, thereby obtaining a composite positive electrode material with better electrochemical performance.

[0010] Another object of the present invention is to provide a positive electrode sheet.

[0011] Another object of the present invention is to provide a battery.

[0012] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0013] A composite positive electrode material comprises a positive electrode base material and a coating layer arranged on the surface of the positive electrode base material, wherein the coating layer comprises a halide electrolyte and a modification group -N(CH3)3R, wherein R is -C n H 2n+1 , n≥9.

[0014] In some implementations, n satisfies: 9≤n≤30.

[0015] In some embodiments, the R is a straight chain or contains at least one branch, and the branch is located at the ω-2 to ω-6 positions of the R.

[0016] In some embodiments, the R is a straight chain or contains at least one branch, and the branch is located at the ω-2 to ω-6 positions in the R, and the branch is selected from at least one of methyl, ethyl, propyl and isopropyl.

[0017] In some embodiments, the chemical formula of the halide electrolyte includes Li z Q q M d , wherein 2≤z≤3, 0.5≤q≤1, 3≤d≤6, Q includes at least one of In, Y, Zr, Sc and Er, and M is selected from halogen.

[0018] In some embodiments, the mass content of the modifying group -N(CH3)3R in the composite positive electrode material is 0.01% to 0.5%.

[0019] In some embodiments, the mass ratio of the halide electrolyte to the modifying group -N(CH3)3R is (10-600):1.

[0020] In some embodiments, the positive electrode matrix material includes LiNi 1-x1-y1 Co x1 Mn y1 O2, LiCoO2, LiNi 0.5 Mn 1.5 O4 and x2Li2MnO3·(1-x2)LiNi a Co b Mn c At least one of O2, wherein 0.02≤x1≤0.15, 0.01≤y1≤0.1, 0.05≤x2≤0.95, 0≤b≤0.5, a+b+c=1.

[0021] In some embodiments, a base layer is further provided on the surface of the positive electrode base material, the coating layer is located on the surface of the base layer, and the base layer contains a lithium compound.

[0022] In some embodiments, the surface of the positive electrode base material is further provided with a base layer, the coating layer is located on the surface of the base layer, and the base layer includes LiNbO3, LiAlO2, Li2SiO3, Li2ZrO3, Li3PO4, Li3BO3 and Li 1.3 Al 0.3Ti 1.7 At least one of (PO4)3.

[0023] In some embodiments, the mass growth rate of the composite cathode material after being stored in a -30°C dew point environment for 6 hours is less than 0.17%.

[0024] In some embodiments, the composite cathode material has a bulk density of 0.54 to 0.75 g / cc.

[0025] In some embodiments, the battery corresponding to the composite positive electrode material has an initial charge and discharge efficiency greater than 82% under the conditions of 0.1C and 1.9V to 3.7V.

[0026] In some embodiments, the capacity retention rate of a battery corresponding to the composite positive electrode material after 50 cycles at 0.33C is greater than 88%.

[0027] The method for preparing the composite positive electrode material as described above comprises the following steps:

[0028] Get [N + (CH3)3R]Z - , a coating system formed by halide precursor materials and solvents.

[0029] The coating system is mixed with a positive electrode base material to obtain a mixed system.

[0030] The mixed system is subjected to heat treatment.

[0031] In some embodiments, the [N + (CH3)3R]Z - In the equation, R is -C n H 2n+1 , n≥9, Z includes BF4 - 、FSI - TFSI - and PF6 - At least one of .

[0032] In some embodiments, the halide precursor material includes lithium halide and Q halide, and Q includes at least one of In, Y, Zr, Sc, and Er.

[0033] In some embodiments, the solvent is selected from polar solvents, and the polar solvent includes at least one of water, ethylenediamine, acetonitrile, methanol, ethanol, acetone, tetrahydrofuran and isopropanol.

[0034] In some embodiments, the method for preparing the coating system specifically comprises: + (CH3)3R]Z - The dispersion and the halide precursor material solution are mixed.

[0035] In some embodiments, the [N + (CH3)3R]Z - The mass percentage of the positive electrode matrix material is 0.01% to 0.5%.

[0036] In some embodiments, the halide electrolyte formed by the halide precursor material accounts for 0.1% to 2% by mass of the positive electrode matrix material.

[0037] In some embodiments, the solid content in the mixed system is ≥50% by weight.

[0038] In some embodiments, the positive electrode base material is subjected to a base material coating treatment before being mixed with the coating system to form a base layer on the surface of the positive electrode base material.

[0039] In some embodiments, the heat treatment temperature is 150-500° C., and the heat treatment time is 4-10 hours.

[0040] In some embodiments, the heat treatment atmosphere is selected from at least one of air, oxygen, and nitrogen, and is preferably air from which carbon dioxide has been removed.

[0041] In some embodiments, the heat-treated material is subjected to post-processing, which includes cooling, screening, and demagnetization. In some embodiments, the material is removed after cooling to a temperature ≤ 95°C; and in some embodiments, the dew point of the post-processing environment is ≤ -20°C.

[0042] In some embodiments, the dew point of the environment during the preparation of the coating system and the mixing system is ≤-10°C.

[0043] A positive electrode sheet comprises a positive electrode current collector and a positive electrode layer located on at least one surface of the positive electrode current collector, wherein the positive electrode layer comprises the composite positive electrode material or the composite positive electrode material prepared by the method for preparing the composite positive electrode material.

[0044] In some embodiments, the mass content of the composite positive electrode material in the positive electrode layer is ≥70%.

[0045] In some embodiments, the positive electrode layer further comprises a sulfide solid electrolyte, a conductive agent, and a binder; the mass content of the sulfide solid electrolyte in the positive electrode layer is 20% to 25%.

[0046] In some embodiments, the particle size D50 of the sulfide electrolyte is 0.5-8 μm.

[0047] In some embodiments, the porosity of the positive electrode sheet after rolling is ≤25%.

[0048] A battery comprises the positive electrode sheet.

[0049] In some embodiments, the battery further comprises a negative electrode sheet and a sulfide electrolyte separator.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] (1) In the composite cathode material of the present invention, the bulky organic cation of the modified group -N(CH3)3R can wrap the halide electrolyte through steric hindrance, thereby reducing the polar solvent and metal ions (such as Y 3+ 、In 3+ ) contact, thereby inhibiting the hydrolysis reaction; the -N(CH3)3R modified coating has excellent hydrophobicity and smoothness. -N(CH3)3R combines with the halide ions of the halide through strong electrostatic interaction to form a uniform and dense modification layer on the halide electrolyte. Under the protection of the hydrophobic long-chain alkyl group, the composite positive electrode material can exist stably in an environment with a high moisture content, breaking through the barrier that traditional halide electrolyte-coated positive electrodes need to be prepared and applied in harsh dry environments. The non-polar properties of the long-chain alkyl R can significantly reduce the surface energy of the positive electrode material, reduce the adhesion between the positive electrode materials and between the positive electrode material and the sulfide electrolyte, and make the contact surface easier to slide, thereby increasing the bulk density of the positive electrode material, reducing the porosity of the electrode sheet, and increasing the energy density of the sulfide solid-state lithium-ion battery; the -N(CH3)3R-modified halide electrolyte coating has high ionic conductivity, low Young's modulus and oxidation resistance, which can effectively solve the space charge layer, interface reaction and contact problems between the positive electrode material and the sulfide electrolyte, thereby improving the capacity, rate performance and cycle stability of the sulfide solid-state lithium-ion battery.

[0052] (2) The preparation method of the composite positive electrode material of the present invention is simple and easy to implement by adding a long-chain alkyl quaternary ammonium salt [N + (CH3)3R]Z - , halide precursor material and solvent mixture, [N + (CH3)3R]Z - The positive charge N + (CH3)3R combines with the halide ions through strong electrostatic interaction. After heat treatment, N + (CH3)3R is uniformly and densely modified on the surface of the halide electrolyte, N + (CH3)3R and halide electrolyte form a coating layer coated on the surface of the positive electrode matrix material. The coating layer has high ionic conductivity, low Young's modulus and oxidation resistance, which can effectively improve the electrochemical properties of the positive electrode matrix material.

[0053] (3) The positive electrode sheet of the present invention has suitable porosity, high energy density, and excellent structural stability. The battery obtained from the positive electrode sheet (especially sulfide solid-state lithium-ion battery) has high capacity, high rate performance and high cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 Schematic diagram of the structure of the composite positive electrode material in Example 1 of the present invention;

[0056] Figure 2 This is a scanning electron microscope image of the composite positive electrode material in Example 1 of the present invention;

[0057] Figure 3 This is an energy spectrum analysis diagram of the composite positive electrode material in Example 1 of the present invention;

[0058] Figure 4 This is a charge and discharge curve diagram of a battery obtained from the composite positive electrode material of Example 1 of the present invention;

[0059] Figure 5 This is a graph showing the cycle retention rate of the composite positive electrode material in Example 1 of the present invention.

[0060] Reference numerals:

[0061] 1-positive electrode matrix material, 2-coating layer, 201-halide electrolyte, 202-modifying group. DETAILED DESCRIPTION

[0062] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0063] According to one aspect of the present invention, the present invention relates to a composite positive electrode material, comprising a positive electrode base material and a coating layer arranged on the surface of the positive electrode base material, wherein the coating layer comprises a halide electrolyte and a modifying group -N(CH3)3R, wherein R is -C n H 2n+1, n≥9, for example, 9, 10, 11, 12, 13, 14, 15, 16, 17, 20, 22, 25, 30, 32, etc.

[0064] In the composite cathode material of the present invention, the bulky organic cation of the modified group -N(CH3)3R can wrap the halide electrolyte through steric hindrance, thereby reducing the polar solvent and metal ions (such as Y 3+ 、In 3+ ) contact, thereby inhibiting hydrolysis reactions; the -N(CH3)3R-modified coating possesses unprecedented hydrophobicity and smoothness for halide electrolytes. -N(CH3)3R binds to the halide ions of the halide through strong electrostatic interactions, forming a uniform and dense coating on the halide electrolyte. Protected by the hydrophobic long-chain alkyl groups, the composite cathode material can exist stably in environments with high moisture content, breaking through the barrier that traditional halide electrolyte-coated cathodes must be prepared and applied in harsh dry environments. The non-polar properties of the long-chain alkyl R can significantly reduce the surface energy of the positive electrode material, reduce the adhesion between the positive electrode materials and between the positive electrode material and the sulfide electrolyte, make the contact surface easier to slide, thereby increasing the bulk density of the positive electrode material, reducing the porosity of the electrode sheet, and increasing the energy density of the sulfide solid-state lithium-ion battery; the -N(CH3)3R-modified halide electrolyte coating has high ionic conductivity, low Young's modulus and oxidation resistance, which can effectively solve the space charge layer, interface reaction and contact problems between the positive electrode material and the sulfide electrolyte, and improve the capacity, rate performance and cycle stability of the sulfide solid-state lithium-ion battery.

[0065] In some embodiments, n satisfies: 9≤n≤30. The number of carbon atoms n in the long-chain alkyl group R of the present invention is preferably 9 to 16, which is beneficial to balancing hydrophobicity and steric hindrance. If the value of n is too small, the hydrophobicity is insufficient. If the value of n is too large, it is not conducive to the diffusion of lithium ions.

[0066] In some embodiments, the R is a straight chain or contains at least one branch, that is, it can be a straight chain alkyl group or a branched alkyl group, and the branch is located at the ω-2 to ω-6 position in the R (the branch is connected to the second to sixth carbon atoms from the last position of the main chain). By adjusting the molecular arrangement density, the density of the coating layer is enhanced. In some embodiments, the branch is selected from at least one of methyl, ethyl, propyl and isopropyl groups. The branch can increase intermolecular steric hindrance and inhibit electrolyte penetration.

[0067] In some embodiments, the chemical formula of the halide electrolyte includes Li z Q q M d, wherein 2≤z≤3 (z is for example 2, 2.5, 3, etc.), 0.5≤q≤1 (q is for example 0.5, 0.6, 0.7, 0.8 or 1), 3≤d≤6 (3, 4, 5 or 6), Q comprises at least one of In, Y, Zr, Sc and Er, and M is selected from halogen. In some embodiments, the halide electrolyte comprises Li3InCl6, Li3YCl6, Li3YBr6, Li2ZrCl6, Li3ScCl6, Li3ErCl3, Li3YCl3Br3, Li 2.5 Zr 0.5 In 0.5 Cl6 and Li2Sc 1 / 3 In 1 / The halide electrolyte of the present invention can provide a three-dimensional lithium ion transmission channel and has a stable crystal structure.

[0068] In some embodiments, the mass content of the modifying group -N(CH3)3R in the composite positive electrode material is 0.01% to 0.5%, for example, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc., or any range value therebetween. The present invention is more conducive to ensuring the interface properties and electrical properties of the coating layer by adopting an appropriate proportion of the modifying group -N(CH3)3R, thereby better improving the electrochemical properties of the positive electrode matrix material.

[0069] In some embodiments, the mass ratio of the halide electrolyte and the modifying group -N(CH3)3R is (10-600):1, for example, 10:1, 100:1, 200:1, 300:1, 400:1, 500:1 or 600:1. The present invention optimizes the mass ratio of the halide electrolyte and the modifying group -N(CH3)3R, and the two work synergistically to improve the interface stability of the coating layer.

[0070] In some embodiments, the cathode matrix material of the present invention comprises LiNi 1-x1-y1 Co x1 Mn y1 O2, LiCoO2, LiNi 0.5 Mn 1.5 O4 and x2Li2MnO3·(1-x2)LiNi a Co b Mn cAt least one of O2, wherein 0.02≤x1≤0.15 (x1 is, for example, 0.02, 0.05, 0.1, 0.15, etc.), 0.01≤y1≤0.1 (y1 is, for example, 0.01, 0.02, 0.05, 0.08, 0.1, etc.), 0.05≤x2≤0.95 (x2 is, for example, 0.05, 0.1, 0.2, 0.5, 0.7, 0.8, 0.95, etc.), 0≤b≤0.5 (b is, for example, 0.1, 0.2, 0.3, 0.5, etc.), a+b+c=1. The positive electrode matrix material of the present invention may be one or more of the above. LiNi 1-x1- y1 Co x1 Mn y1 The coating of O2 can inhibit the reaction of residual alkali on the surface with the electrolyte and alleviate gas production. a Co b Mn c O2 coating through the coating layer can alleviate the structural collapse caused by oxygen evolution during the first charge and discharge.

[0071] In some embodiments, a substrate layer is further provided on the surface of the positive electrode substrate material, and the coating layer is located on the surface of the substrate layer. The substrate layer contains a lithium compound. The present invention is beneficial to enhancing the bonding force between the coating layer and the substrate material by providing a substrate layer between the positive electrode substrate material and the coating layer. In addition, the substrate layer can provide an additional lithium ion transmission path to reduce the interface impedance. In some embodiments, the substrate layer includes LiNbO3, LiAlO2, Li2SiO3, Li2ZrO3, Li3PO4, Li3BO3 and Li 1.3 Al 0.3 Ti 1.7 A combination of one or more of (PO4)3, such as a combination of LiAlO2 and Li2SiO3, a combination of Li2SiO3, Li2ZrO3 and Li3PO4, etc. The present invention prefers the above-mentioned base layer, which is more conducive to improving the electrochemical properties of the positive electrode material.

[0072] In some embodiments, the friction coefficient of the composite positive electrode material is 0.05 to 0.5, preferably 0.1 to 0.3. The friction coefficient involved in the present invention is the microscopic friction coefficient of the positive electrode material, which can be measured by atomic force microscopy (AFM): in the lateral force microscopy (LFM) mode, the probe is drawn across the surface of the material with a constant load (1 to 100 nN), and the local friction force is calculated by the probe deflection signal, and the friction coefficient is obtained after conversion. The composite positive electrode material of the present invention has a low friction coefficient, which can improve the fluidity of the material, facilitate the uniform coating of the electrode slurry prepared therefrom, and reduce particle agglomeration.

[0073] In some embodiments, the composite positive electrode material is a single crystal positive electrode material and / or a polycrystalline positive electrode material. Single crystal materials can reduce grain boundary cracks and inhibit particle breakage during circulation. Polycrystalline materials compensate for the high reactivity at the grain boundaries through the coating layer. In some embodiments, the particle size D50 of the composite positive electrode material is 1.8 to 9 μm, for example, 1.8 μm, 2 μm, 3 μm, 4 μm, 5 μm, 7 μm, 9 μm, etc., or any range value between the two. The composite positive electrode material of the present invention has a suitable D50 particle size, which is conducive to improving the ion diffusion rate and improving the electrochemical performance.

[0074] In some embodiments, the composite cathode material has a mass growth rate of less than 0.17% when stored in a -30°C dew point environment for 6 hours, such as 0.05%, 0.1%, 0.12%, 0.15%, 0.7%, etc. The coating layer of the present invention can impart excellent hydrophobicity to the composite cathode material, improving its stability in a high-moisture environment.

[0075] In some embodiments, the composite cathode material has an apparent density of 0.54 to 0.75 g / cc, such as 0.54 g / cc, 0.6 g / cc, 0.65 g / cc, 0.7 g / cc, 0.75 g / cc, etc. The composite cathode material of the present invention has an appropriate apparent density, thereby ensuring an appropriate porosity of the electrode sheet, while balancing lithium ion transport and active material loading.

[0076] In some embodiments, the composite cathode material can provide a battery with an initial charge and discharge efficiency greater than 82% at 0.1C and 1.9V to 3.7V, for example, 83%, 84%, 85%, 86%, 88%, 90%, or the like. The coating of the present invention can reduce irreversible phase transitions, improve the utilization of active materials, and provide the battery with high charge and discharge efficiency.

[0077] In some embodiments, the capacity retention rate of a battery corresponding to the composite cathode material after 50 cycles at 0.33C is greater than 88%, for example, 88%, 90%, 92%, 93%, 94%, 95%, or any range therebetween. The coating layer of the present invention can inhibit transition metal dissolution and CEI thickening, which is beneficial for maintaining the integrity of the electrode structure and slowing down capacity decay. The battery corresponding to the composite cathode material has a high capacity retention rate.

[0078] According to another invention of the present invention, the present invention also relates to a method for preparing the composite positive electrode material as described above, comprising the following steps:

[0079] Get [N + (CH3)3R]Z - , a coating system formed by halide precursor materials and solvents.

[0080] The coating system is mixed with the positive electrode base material to obtain a mixed system.

[0081] The mixed system is heat treated.

[0082] The preparation method of the composite positive electrode material of the present invention is simple and easy, and the long-chain alkyl quaternary ammonium salt [N + (CH3)3R]Z - , halide precursor material and solvent mixture, [N + (CH3)3R]Z - The positive charge N + (CH3)3R combines with the halide ions through strong electrostatic interaction. After heat treatment, N + (CH3)3R is uniformly and densely modified on the surface of the halide electrolyte, N + (CH3)3R and halide electrolyte form a coating layer coated on the surface of the positive electrode matrix material. The coating layer has high ionic conductivity, low Young's modulus and oxidation resistance, which can effectively improve the electrochemical properties of the positive electrode matrix material.

[0083] In some embodiments, the method for preparing the coating system specifically comprises: + (CH3)3R]Z - The dispersion liquid and the halide precursor material solution are mixed. Specifically, the halide precursor and the solvent are mixed to obtain the halide precursor material solution; [N + (CH3)3R]Z - Mixed with solvent, [N + (CH3)3R]Z - Dispersion; [N + (CH3)3R]Z - The dispersion liquid and the halide precursor material solution are stirred and mixed to obtain a coating system.

[0084] In some embodiments, the solvent is selected from polar solvents, and the polar solvents include at least one of water, ethylenediamine, acetonitrile, methanol, ethanol, acetone, tetrahydrofuran and isopropanol. The present invention uses polar solvents to better dissolve the halide precursor material and [N + (CH3)3R]Z - Better dispersion. [N + (CH3)3R]Z - The polar solvents in the dispersion and the halide precursor material solution may be the same or different.

[0085] In the present invention, the long-chain alkyl quaternary ammonium salt [N + (CH3)3R]Z -The invention has a hydrophobic long-chain alkyl end and a hydrophilic quaternary ammonium salt end, and has the function of a surfactant, which can reduce the surface tension of the solvent; when the aqueous solution of the long-chain alkyl quaternary ammonium salt is stirred, the typical characteristic of the surfactant, i.e., foaming, occurs; the inventors unexpectedly discovered that when the aqueous dispersion of the long-chain alkyl quaternary ammonium salt is added to the aqueous solution of the halide precursor and stirred, the foaming disappears and a clear and transparent solution is formed. The reasons may include: the long-chain alkyl quaternary ammonium salt [N + (CH3)3R]Z - Due to the easily dissociated anion Z - ,[N + (CH3)3R] cation and Z - After dissociation, it will spontaneously form a strong electrostatic binding with the halogen anions in the halide precursor aqueous solution and be dragged into the solution by the easily free halogen anions, thus forming a clear and transparent solution.

[0086] In some embodiments, the [N + (CH3)3R]Z - In the equation, R is -C n H 2n+1 , n≥9, preferably, n satisfies: 9≤n≤30, and R is a straight chain or contains at least one branch, that is, it can be a straight chain alkyl or a branched chain alkyl, and the branch is located at the ω-2 to ω-6 position in R (the branch is connected to the second to sixth carbon from the end of the main chain). Z includes BF4 - 、FSI - (bis(fluorosulfonyl)imide) anion), TFSI - (bis(trifluoromethanesulfonyl)imide anion) and PF6 - At least one of them. - and FSI - The negative charge of Z is more dispersed, and the long-chain alkyl quaternary ammonium salt is easy to dissociate. - Taken from TFSI - and FSI - At least one of .

[0087] In some embodiments, [N + (CH3)3R]Z - The preparation method is based on the synthesis reaction of quaternary ammonium salt and is obtained by anion exchange method, comprising: (1) a nucleophilic substitution reaction between alkyl bromide (RBr) and trimethylamine (N(CH3)3) to generate [N + (CH3)3R]Br - (2) Through LiZ (Z including BF4 - 、FSI - TFSI - or PF6 -) aqueous solution for anion exchange, LiBr precipitates due to its low solubility, and [N + (CH3)3R]Z - .

[0088] In some embodiments, [N + (CH3)3R]Z - The preparation method specifically comprises:

[0089] (a) Dissolve alkyl bromide (RBr) in anhydrous acetonitrile, slowly add trimethylamine solution dropwise, maintaining a molar ratio of 1:1.1, heat to 75-85°C and reflux, stirring for 20-25 hours. After cooling, remove the acetonitrile by vacuum distillation to obtain a viscous solid. Wash with cold ether to remove the remaining reactants to obtain [N + (CH3)3R]Br - .

[0090] (b) [N + (CH3)3R]Br - Dissolve in 90-110 mL of deionized water. - 、FSI - TFSI - or PF6 - ) was dissolved in 90-100 mL of deionized water and slowly added dropwise to the above [N + (CH3)3R]Br - The solution was cooled in an ice bath to control heat release. Stirred for 10-15 hours, filtered to remove the precipitate; dichloromethane was added to the filtrate to extract the product, and the solvent was removed by rotary evaporation to obtain [N + (CH3)3R]TFSI - .

[0091] In some embodiments, bis(trifluoromethanesulfonyl)imide undecyltrimethylammonium ([N + (CH3)3C 11 H 23 ]TFSI - ), specifically comprising:

[0092] (1) Undecyl bromide was dissolved in anhydrous acetonitrile, trimethylamine solution was slowly added dropwise, maintaining the molar ratio at 1:1.1, heated to 80°C and refluxed, and stirred for 24 hours. After cooling, acetonitrile was removed by vacuum distillation to obtain a viscous solid phase. The remaining reactants were washed with cold ether to obtain [N + (CH3)3C 11 H 23 ]Br - .

[0093] (2) [N + (CH3)3C11 H 23 ]Br - Dissolve in 100 mL of deionized water. Separately, dissolve LiTFSI in 100 mL of deionized water and slowly add dropwise to the quaternary ammonium salt solution. Cool in an ice bath to control heat release. Stir for 12 hours, filter to remove the precipitate; add dichloromethane to the filtrate to extract the product, and remove the solvent by rotary evaporation to obtain [N + (CH3)3C11H 23 ]TFSI - .

[0094] In some implementation manners, the [N + (CH3)3R]Br - , please refer to the above [N + (CH3)3C 11 H 23 ]TFSI - The method can be used to prepare the alkyl bromide by adjusting the type of alkyl bromide (RBr).

[0095] In some embodiments, the halide precursor material includes lithium halide and Q halide, Q includes at least one of In, Y, Zr, Sc and Er. The lithium halide includes at least one of LiCl and LiBr. The Q halide includes at least one of InCl3, YCl3, ZrCl4, ScCl3 and ErCl3. The lithium halide and Q halide are prepared according to the chemical formula of the halide electrolyte Li z Q q M d Mixing was performed using an appropriate molar ratio.

[0096] In some embodiments, the positive electrode base material is subjected to a base material coating treatment before being mixed with the coating system to form a base layer on the surface of the positive electrode base material. The base material includes oxides and hydroxides corresponding to Nb, Al, Si, and Zr (for example, Nb2O5, Al2O3, Al(OH)3, SiO2, ZrO2, Zr(OH)4), and at least one of ammonium hydrogen phosphate, H3BO3, and aluminum oxide-titanium oxide-ammonium hydrogen phosphate. The present invention uses the above-mentioned base materials for coating to form a suitable base layer on the surface of the positive electrode base material, thereby enhancing the bonding force between the coating layer and the base material, and at the same time providing an additional lithium ion transmission path to reduce the interface impedance.

[0097] In some embodiments, the [N + (CH3)3R]Z -The mass percentage of the positive electrode matrix material is 0.01% to 0.5%, such as 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc. The present invention adopts an appropriate ratio of [N + (CH3)3R]Z - , which can ensure the interface performance and electrical properties of the coating layer, and thus help to improve the electrochemical properties of the positive electrode matrix material.

[0098] In some embodiments, the halide electrolyte formed by the halide precursor material accounts for 0.1% to 2% by mass of the positive electrode matrix material, such as 0.1%, 0.5%, 0.8%, 1%, 1.5% or 2%. The present invention improves the coating effect and the electrochemical performance of the coating layer by using a suitable proportion of halide electrolyte to better graft the modifying groups in a suitable proportion.

[0099] In some embodiments, the solid content of the mixed system is ≥50%, such as 50%, 60%, 70%, 80%, 85%, etc., preferably ≥80%. The appropriate solid content of the mixed system of the present invention is beneficial to ensuring the mixing effect, facilitating the coating, and forming a coating layer with better performance.

[0100] In some embodiments, the temperature of the heat treatment is 150 to 500°C, such as 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 500°C, etc., and the time of the heat treatment is 4 to 10h, such as 4h, 5h, 6h, 7h, 8h, 10h, etc. In some embodiments, the atmosphere of the heat treatment is selected from at least one of air, oxygen and nitrogen, preferably air with carbon dioxide removed. In some embodiments, the heating rate is 1 to 8°C / min, such as 1°C / min, 5°C / min, 8°C / min, etc. After the heat treatment, the solvent is removed, and a dense halide electrolyte coating is uniformly formed on the surface of the positive electrode material. Due to the reaction between the halogen ions and [N + (CH3)3R], the surface of the halide electrolyte is modified with a layer of uniformly distributed -N(CH3)3R; the present invention adopts appropriate heat treatment conditions, which are more conducive to the coating effect, so that the modified long-chain alkyl functional group R gives the coating layer better hydrophobic and smooth properties.

[0101] In some embodiments, the material after the heat treatment is post-processed, and the post-processing includes cooling, screening and demagnetization, and packaging after demagnetization. Preferably, the material is taken out after cooling to a temperature ≤95°C (for example, 30°C, 50°C, 60°C, 85°C, etc.); preferably, the dew point of the post-treatment environment is ≤-20°C, and preferably the dew point is ≤-30°C. Dew point refers to the temperature when air is cooled to a saturated state (relative humidity reaches 100%) under constant air pressure. When the water vapor in the air reaches this temperature, it will condense into liquid water (dew) or solid water (frost). The specific form depends on whether the dew point is above or below the freezing point. The lower the dew point, the lower the moisture content in the air.

[0102] In some embodiments, the dew point of the environment during the preparation of the coating system and the mixing system is ≤ -10° C., preferably ≤ -20° C. During the material preparation process, controlling the dew point of the environment plays a key role in product quality and process stability.

[0103] According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising a positive electrode current collector and a positive electrode layer located on at least one side surface thereof, wherein the positive electrode layer comprises the composite positive electrode material or the composite positive electrode material prepared by the preparation method of the composite positive electrode material.

[0104] The positive electrode sheet of the present invention has suitable porosity, high energy density and excellent structural stability.

[0105] In some embodiments, the mass content of the composite positive electrode material in the positive electrode layer is ≥ 70%, for example, 70%, 75%, 80%, 85%, etc. The appropriate mass content of the composite positive electrode material in the positive electrode layer is more conducive to ensuring the structural stability and electrochemical performance of the positive electrode layer.

[0106] In some embodiments, the positive electrode layer further comprises a sulfide solid electrolyte, a conductive agent, and a binder. The sulfide solid electrolyte comprises 20% to 25% by weight of the positive electrode layer, for example, 20%, 22%, 25%, etc. These components are coordinated to improve the electrochemical performance of the positive electrode layer.

[0107] In some embodiments, the sulfide electrolyte comprises Li7P3S 11 、Li3PS4、Li6PS5Cl、Li 10 GeP2S 12 、Li6PS5Br、Li 5.5 PS 4.5 Cl 1.5 He Li 5.3 PS 4.3 Cl 0.8 Br 0.7 One or more of, for example, Li7P3S11 and Li3PS4, such as Li6PS5Br, Li 5.5 PS 4.5 Cl 1.5 He Li 5.3 PS 4.3 Cl 0.8 Br 0.7 In some embodiments, the particle size D50 of the sulfide electrolyte is 0.5 to 8 μm, such as 0.5 μm, 1 μm, 2 μm, 5 μm or 8 μm. The present invention uses the sulfide electrolyte with the above-mentioned appropriate particle size to reduce interfacial impedance and improve transmission efficiency.

[0108] In some embodiments, the conductive agent is selected from one or more of vapor-grown carbon fiber (VGCF), Super-P, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, Ketjen black, and acetylene black, such as a combination of multi-walled carbon nanotubes and graphene, or a combination of graphene and Ketjen black. The use of the above conductive agents in the present invention is more conducive to improving the conductivity of the positive electrode layer.

[0109] In some embodiments, the binder is selected from one or more of polyvinyl alcohol, hydrogenated nitrile rubber, styrene-butadiene rubber, polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF), such as a combination of polyvinyl alcohol and hydrogenated nitrile rubber. The present invention uses the above-mentioned binder to ensure adhesion between the positive electrode layer and the positive electrode current collector.

[0110] In some embodiments, the positive electrode current collector is aluminum foil or carbon-coated aluminum foil.

[0111] In some embodiments, since the composite positive electrode material has excellent surface smoothness, the friction between the composite positive electrode materials and the composite positive electrode materials, and between the composite positive electrode materials and the sulfide electrolyte is small, and the porosity of the positive electrode sheet after rolling is ≤25%, for example, 18%, 20%, 22%, etc., preferably ≤20%.

[0112] In some embodiments, the preparation of the positive electrode sheet includes: fully mixing the positive electrode material, conductive carbon, sulfide electrolyte and binder in a certain proportion, and compounding them with the positive electrode current collector by a wet method or a dry method.

[0113] According to another aspect of the present invention, the present invention also relates to a battery comprising the positive electrode sheet.

[0114] The battery obtained from the composite positive electrode material of the present invention has excellent capacity, cycle performance and rate performance.

[0115] In some embodiments, the battery further comprises a negative electrode and a sulfide electrolyte separator. In some embodiments, the negative electrode is selected from at least one of lithium metal alloy, lithium indium alloy, lithium metal, graphite, and Si-C composite negative electrode. In some embodiments, the sulfide electrolyte of the sulfide electrolyte separator is Li7P3S 11 、Li3PS4、Li6PS5Cl、Li 10 GeP2S 12 、Li 10 SnP2S 12 、Li6PS5Br、Li 5.5 PS 4.5 Cl 1.5 、Li 5.3 PS 4.3 Cl 0.8 Br 0.7 One or more of.

[0116] The composite cathode material of the present invention is particularly suitable for sulfide solid-state lithium-ion batteries and can improve their energy density. The long-chain alkyl-modified halide electrolyte coating layer has high ionic conductivity, low Young's modulus and oxidation resistance, which can effectively solve the space charge layer, interface reaction and contact problems between the composite cathode material and the sulfide electrolyte, and can improve the capacity, rate performance and cycle stability of the sulfide solid-state lithium-ion battery.

[0117] The following is further explained with reference to specific embodiments and comparative examples.

[0118] Example 1

[0119] A method for preparing a composite positive electrode material comprises the following steps:

[0120] (1) In an environment with a dew point of -20°C, weigh InCl3 and LiCl in a molar ratio of 1:3 and dissolve them in deionized water to obtain an aqueous solution of LiCl·InCl3. Weigh an appropriate amount of bis(trifluoromethanesulfonyl)imide undecyltrimethylammonium, i.e. [N + (CH3)3C 11 H 23 ]TFSI - , put into deionized water and stir to obtain [N + (CH3)3C 11 H 23 ]TFSI - The aqueous dispersion of LiCl·InCl3 and [N + (CH3)3C 11 H 23 ]TFSI - The aqueous dispersion is mixed and stirred to obtain a coating system.

[0121] (2) Weigh an appropriate amount of LiNi 0.90 Co 0.05 Mn 0.05 O2 material was added to the coating system and stirred at 500 rpm for 5 minutes to obtain a solid-liquid mixed system with a solid content of 90%. 0.90 Co 0.05 Mn 0.05 O2:Li3InCl3:[N + (CH3)3C 11 H 23 ]TFSI - The mass ratio is 100:1:0.05.

[0122] (3) The solid-liquid mixed system was heated to 200°C at a heating rate of 3°C / min in an air atmosphere free of carbon dioxide, kept at this temperature for 8 hours, and then annealed to obtain a composite positive electrode material.

[0123] The structural diagram of the composite cathode material is shown in Figure 1 As shown, it includes a positive electrode base material 1 and a coating layer 2 arranged on the surface of the positive electrode base material 1, and the coating layer 2 contains a halide electrolyte 201 and a modifying group 202.

[0124] Example 2

[0125] A method for preparing a composite positive electrode material comprises the following steps:

[0126] (1) In an environment with a dew point of -20°C, YCl3 and LiCl were weighed in a molar ratio of 1:3 and dissolved in deionized water to obtain an aqueous solution of LiCl·YCl3. An appropriate amount of bis(trifluoromethanesulfonyl)imide undecyltrimethylammonium, i.e. [N + (CH3)3C 11 H 23 ]TFSI - , put into deionized water and stir to obtain [N + (CH3)3C 11 H 23 ]TFSI - The aqueous dispersion of LiCl·YCl3 and [N + (CH3)3C 11 H 23 ]TFSI - The aqueous dispersion is mixed and stirred to obtain a coating system.

[0127] (2) Weigh an appropriate amount of LiNi 0.90 Co 0.05 Mn 0.05O2 material was added to the coating system and stirred at 500 rpm for 5 minutes to obtain a solid-liquid mixed system with a solid content of 90%. 0.90 Co 0.05 Mn 0.05 O2:Li3YCl3:[N + (CH3)3C 11 H 23 ]TFSI - The mass ratio is 100:1:0.05.

[0128] (3) The solid-liquid mixed system was heated to 250°C at a heating rate of 3°C / min in an air atmosphere free of carbon dioxide, kept at this temperature for 6 hours, and then annealed to obtain a composite positive electrode material.

[0129] Example 3

[0130] A method for preparing a composite positive electrode material comprises the following steps:

[0131] (1) In an environment with a dew point of -20°C, weigh InCl3 and LiCl in a molar ratio of 1:3 and dissolve them in deionized water to obtain an aqueous solution of LiCl·InCl3. Weigh an appropriate amount of hexadecyltrimethylammonium bis(trifluoromethanesulfonyl)imide, i.e. [N + (CH3)3C 16 H 33 ]TFSI - , put into deionized water and stir to obtain [N + (CH3)3C 16 H 33 ]TFSI - aqueous dispersion of LiCl·InCl3 and [N + (CH3)3C 16 H 33 ]TFSI - The aqueous dispersion is mixed and stirred to obtain a coating system.

[0132] (2) Weigh an appropriate amount of LiNi 0.8 Co 0.10 Mn 0.1 O2 material was added to the coating system and stirred at 600 rpm for 10 min to obtain a solid-liquid mixed system with a solid content of 95%. 0.8 Co 0.10 Mn 0.1 O2:Li3InCl3:[N + (CH3)3C 16 H 33 ]TFSI - The mass ratio is 100:1.5:0.04.

[0133] (3) The solid-liquid mixed system was heated to 200°C at a heating rate of 3°C / min under an oxygen atmosphere, kept at this temperature for 8 hours, and then annealed to obtain a composite positive electrode material.

[0134] Example 4

[0135] A method for preparing a composite positive electrode material comprises the following steps:

[0136] (1) In an environment with a dew point of -20°C, weigh InCl3 and LiCl in a molar ratio of 1:3 and dissolve them in deionized water to obtain an aqueous solution of LiCl·InCl3. Weigh an appropriate amount of bis(trifluoromethanesulfonyl)imide undecyltrimethylammonium, i.e. [N + (CH3)3C 11 H 23 ]TFSI - , put into deionized water and stir to obtain [N + (CH3)3C 11 H 23 ]TFSI - The aqueous dispersion of LiCl·InCl3 and [N + (CH3)3C 11 H 23 ]TFSI - The aqueous dispersion is mixed and stirred to obtain a coating system.

[0137] (2) Weigh an appropriate amount of LiNi 0.90 Co 0.05 Mn 0.05 O2 material, mixed with 2000ppm ZrO2, and calcined at 600℃ for 6h in oxygen atmosphere to obtain Li2ZrO3 coated LiNi 0.90 Co 0.05 Mn 0.05 O2 material.

[0138] (3) Li2ZrO3 coated LiNi 0.90 Co 0.05 Mn 0.05 O2 material was added to the coating system and stirred at 500 rpm for 5 min to obtain a solid-liquid mixed system with a solid content of 90%. 0.90 Co 0.05 Mn 0.05 O2:Li3InCl3:[N + (CH3)3C 11 H 23 ]TFSI - The mass ratio is 100:0.5:0.02.

[0139] (4) The solid-liquid mixed system was heated to 250°C at a heating rate of 3°C / min in an air atmosphere free of carbon dioxide, kept at this temperature for 6 hours, and then annealed to obtain a composite positive electrode material.

[0140] Example 5

[0141] A method for preparing a composite positive electrode material comprises the following steps:

[0142] (1) In an environment with a dew point of -20°C, InCl3, ScCl3, and LiCl were weighed in a molar ratio of 1:1:6 and dissolved in ethanol to obtain an aqueous solution of InCl3·ScCl3·LiCl; an appropriate amount of bis(trifluoromethanesulfonyl)imide undecyltrimethylammonium, i.e., [N + (CH3)3C 11 H 23 ]TFSI - , put into ethanol and stir to obtain [N + (CH3)3C 11 H 23 ]TFSI - ethanol dispersion; InCl3·ScCl3·LiCl ethanol solution and [N + (CH3)3C 11 H 23 ]TFSI - The ethanol dispersion was mixed and stirred to obtain a coating system.

[0143] (2) Weigh an appropriate amount of 0.3Li2MnO3·0.7LiNi 0.5 Co 0.04 Mn 0.46 O2 material was added to the coating system and stirred at 500 rpm for 5 minutes to obtain a solid-liquid mixed system with a solid content of 95%. 0.5 Co 0.04 Mn 0.46 O2:Li2Sc 1 / 3 In 1 / 3 Cl4:[N + (CH3)3C 11 H 23 ]TFSI - The mass ratio is 100:2:0.08.

[0144] (3) The solid-liquid mixed system was heated to 200°C at a heating rate of 3°C / min under an oxygen atmosphere, kept at this temperature for 8 hours, and then annealed to obtain a composite positive electrode material.

[0145] Example 6

[0146] A method for preparing a composite positive electrode material, which differs from Example 1 in that:

[0147] Long chain alkyl quaternary ammonium salt [N + (CH3)3R]Z - Undecyltrimethylammonium bis(trifluoromethanesulfonyl)imide and hexadecyltrimethylammonium bis(trifluoromethanesulfonyl)imide were used in a mass ratio of 3:1.

[0148] Example 7

[0149] A method for preparing a composite positive electrode material comprises the following steps:

[0150] (1) In an environment with a dew point of -20°C, weigh InCl3 and LiCl in a molar ratio of 1:3 and dissolve them in deionized water to obtain an aqueous solution of LiCl·InCl3. Weigh an appropriate amount of bis(trifluoromethanesulfonyl)imide triacontyltrimethylammonium, i.e. [N + (CH3)3C 30 H 61 ]TFSI - , put into deionized water and stir to obtain [N + (CH3)3C 30 H 61 ]TFSI - The aqueous dispersion of LiCl·InCl3 and [N + (CH3)3C 30 H 61 TFSI - The aqueous dispersion is mixed and stirred to obtain a coating system.

[0151] (2) Weigh an appropriate amount of LiNi 0.90 Co 0.05 Mn 0.05 O2 material was added to the coating system and stirred at 500 rpm for 5 minutes to obtain a solid-liquid mixed system with a solid content of 90%. 0.90 Co 0.05 Mn 0.05 O2:Li3InCl3:[N + (CH3)3C 30 H 61 ]TFSI - The mass ratio is 100:1:0.05.

[0152] (3) The solid-liquid mixed system was heated to 200°C at a heating rate of 3°C / min in an air atmosphere free of carbon dioxide, kept at this temperature for 8 hours, and then annealed to obtain a composite positive electrode material.

[0153] Comparative Example 1

[0154] A method for preparing a composite positive electrode material comprises the following steps:

[0155] (1) In an environment with a dew point of -20°C, InCl3 and LiCl were weighed in a molar ratio of 1:3 and dissolved in deionized water to obtain an aqueous solution of LiCl·InCl3.

[0156] (2) Weigh an appropriate amount of LiNi 0.90 Co 0.05 Mn 0.05 O2 material was added to the above-mentioned LiCl·InCl3 aqueous solution and stirred at 500 rpm for 5 min to obtain a solid-liquid mixed system with a solid content of 90%; LiNi 0.90 Co 0.05 Mn 0.05 The mass ratio of O2 and Li3InCl3 is 100:1.

[0157] (3) The solid-liquid mixed system was heated to 200°C at a heating rate of 3°C / min in an air atmosphere free of carbon dioxide, kept at this temperature for 8 hours, and then annealed to obtain a composite positive electrode material.

[0158] Comparative Example 2

[0159] A method for preparing a composite positive electrode material comprises the following steps:

[0160] (1) In an environment with a dew point of -20°C, weigh InCl3 and LiCl in a molar ratio of 1:3 and dissolve them in deionized water to obtain an aqueous solution of LiCl·InCl3; weigh an appropriate amount of amyltrimethylammonium bromide, i.e., [N + (CH3)3C5H 11 ]Br - , put into deionized water and stir to obtain [N + (CH3)3C5H 11 ]Br - aqueous dispersion of LiCl·InCl3 and [N + (CH3)3C5H 11 ]Br - The aqueous dispersion is mixed and stirred to obtain a coating system.

[0161] (2) Weigh an appropriate amount of LiNi 0.90 Co 0.05 Mn 0.05 O2 material was added to the coating system and stirred at 500 rpm for 5 minutes to obtain a solid-liquid mixed system with a solid content of 90%. 0.90 Co 0.05 Mn 0.05 O2:Li3InCl3:[N + (CH3)3C5H11 ]Br - The mass ratio is 100:1:0.05.

[0162] (3) The solid-liquid mixed system was heated to 200°C at a heating rate of 3°C / min in an air atmosphere free of carbon dioxide, kept at this temperature for 8 hours, and then annealed to obtain a composite positive electrode material.

[0163] Experimental Example 1

[0164] 1. Performance test of composite cathode materials

[0165] 1. Graph Analysis

[0166] The composite cathode material of Example 1 was subjected to scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis, and the results were as follows: Figure 2 and Figure 3 SEM characterization shows that evenly distributed long-chain alkyl-modified Li3InCl6 can be observed on the surface of the composite cathode material. EDS characterization shows that the halide In, Cl and alkyl C elements are evenly distributed.

[0167] 2. Storage quality change rate test of composite positive electrode materials

[0168] The composite cathode materials of each Example and Comparative Example were placed in an open environment at a dew point of -30°C for 6 hours, and their mass change rate was measured. The composite cathode materials of Comparative Example 1 were divided into two groups: one group underwent the aforementioned mass change rate test; and the other group was not placed in a -30°C dew point environment and did not undergo the mass change rate test.

[0169] 3. Bulk density test

[0170] The Scott volumetric method is used for measurement: the powder flows freely into the distribution box through the sieve, alternately passes through 4 glass plates with an inclination angle of 25°, and falls freely from a certain height through the funnel to fill the measuring cup. The result is calculated from the net weight of the powder and the volume of the measuring cup.

[0171] The performance test results of the composite cathode material are shown in Table 1.

[0172] Table 1 Performance test results of composite cathode materials

[0173]

[0174] As can be seen from Table 1, the mass growth rate of the composite positive electrode materials in each embodiment of the present invention after being exposed to a dew point environment of -30°C for 6 hours is less than 0.17%, indicating that the long-chain alkyl-modified halide coating is hydrophobic and can reduce the reaction with moisture at high dew points; the composite positive electrode material has a suitable bulk density (0.54-0.73 g / cc), which is conducive to the positive electrode sheet having a suitable porosity.

[0175] The composite cathode material of Comparative Example 1 exhibited a mass growth rate of 3.61% after 6 hours of exposure to a -30°C dew point. This is because the Li₃InCl₃ coating absorbs moisture from the air, causing the Li₃InCl₃ to decompose into InCl₃·mH₂O and LiCl·nH₂O. The composite cathode material of Comparative Example 1 exhibited a low bulk density.

[0176] The mass growth rate of the composite cathode material in Comparative Example 2 after being exposed to a dew point environment at -30°C for 6 hours is as high as 2.91%, indicating that the short-chain alkyl group cannot effectively make the coating layer hydrophobic and the bulk density of the composite cathode material is low.

[0177] 2. Battery performance test

[0178] Batteries were prepared from the composite cathode materials of the embodiments and comparative examples, specifically comprising:

[0179] The composite cathode material, Li6PS5Cl, VGCF and PTFE were weighed in a mass ratio of 75:23.8:1:0.2, and the four materials were fully mixed and coated on a carbon-coated aluminum foil current collector by dry roller pressing to prepare a cathode sheet with an area density of 20 mg / cm 2 The positive electrode sheet, Li6PS5Cl and lithium-indium alloy sheet were pressed at 200 MPa for 10 minutes and then assembled into a sulfide solid-state lithium-ion battery.

[0180] At 25°C, the prepared battery was subjected to charge and discharge tests at a current density of 0.1C, with the charge and discharge range being 1.9V to 3.7V. The charge and discharge curve of the sulfide solid-state lithium-ion battery obtained from the composite positive electrode material in Example 1 in the first cycle is as follows: Figure 4 As shown in the figure, the cycle capacity retention rate is as follows Figure 5 The charge and discharge efficiency of the batteries obtained from the composite positive electrode materials in other embodiments and comparative examples during the initial charge and discharge process and the capacity retention rate after 50 cycles at 0.33C are shown in Table 2.

[0181] Table 2 Battery performance

[0182]

[0183]

[0184] As can be seen from Table 2, the positive electrode sheets obtained from the composite positive electrode materials in the various embodiments of the present invention have a relatively low porosity, not exceeding 22%, and the resulting batteries have the characteristics of high energy density, high discharge efficiency and high capacity retention. The energy density of a battery depends on the electrode characteristics of the battery. On the positive electrode side, a positive electrode material with a high bulk density corresponds to a positive electrode with a low porosity, reflecting that the thickness of the positive electrode sheet is low under the same positive electrode material loading; on the other hand, a positive electrode material with a high gram capacity reflects that the capacity of the positive electrode is high under the same positive electrode material loading; therefore, the solution provided by the present invention can effectively improve the gram capacity and bulk density of the positive electrode material, thereby improving the energy density of the solid-state lithium-ion battery.

[0185] The porosity of the positive electrode sheets obtained from the composite positive electrode materials in Comparative Examples 1 and 2 is relatively high. The energy density, charge-discharge efficiency, and capacity retention of the batteries obtained from the composite positive electrode materials in Comparative Examples 1 and 2 are significantly reduced.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite positive electrode material, characterized in that The invention comprises a positive electrode base material and a coating layer arranged on the surface of the positive electrode base material, wherein the coating layer comprises a halide electrolyte and a modification group -N(CH3)3R, wherein R is -C n H 2n+1 , n≥9.

2. The composite cathode material according to claim 1, characterized in that Contains at least one of the following features (1) to (6): (1) n satisfies: 9≤n≤30; (2) R is a straight chain or contains at least one branch, and the branch is located at the ω-2 to ω-6 positions of R; (3) R is a straight chain or contains at least one branch, and the branch is located at the ω-2 to ω-6 positions of R, and the branch is selected from at least one of methyl, ethyl, propyl and isopropyl; (4) The chemical formula of the halide electrolyte includes Li z Q q M d , wherein 2≤z≤3, 0.5≤q≤1, 3≤d≤6, Q comprises at least one of In, Y, Zr, Sc and Er, and M is selected from halogen; (5) The mass content of the modified group -N(CH3)3R in the composite positive electrode material is 0.01% to 0.5%; (6) The mass ratio of the halide electrolyte to the modifying group -N(CH3)3R is (10-600):

1.

3. The composite cathode material according to claim 1, characterized in that Contains at least one of the following features (1) to (3): (1) The positive electrode matrix material includes LiNi 1-x1-y1 Co x1 Mn y1 O2, LiCoO2, LiNi 0.5 Mn 1.5 O4 and x2Li2MnO3·(1-x2)LiNi a Co b Mn c At least one of O2, wherein 0.02≤x1≤0.15, 0.01≤y1≤0.1, 0.05≤x2≤0.95, 0≤b≤0.5, a+b+c=1; (2) A base layer is further provided on the surface of the positive electrode base material, the coating layer is located on the surface of the base layer, and the base layer contains a lithium compound; (3) The surface of the positive electrode base material is further provided with a base layer, the coating layer is located on the surface of the base layer, and the base layer includes LiNbO3, LiAlO2, Li2SiO3, Li2ZrO3, Li3PO4, Li3BO3 and Li 1.3 Al 0.3 Ti 1.7 At least one of (PO4)3.

4. The composite cathode material according to any one of claims 1 to 3, characterized in that Contains at least one of the following features (1) to (4): (1) The mass growth rate of the composite cathode material when stored in a -30°C dew point environment for 6 hours is less than 0.17%; (2) The bulk density of the composite cathode material is 0.54 to 0.75 g / cc; (3) The battery corresponding to the composite positive electrode material has an initial charge and discharge efficiency greater than 82% under the conditions of 0.1C, 1.9V to 3.7V; (4) The capacity retention rate of the battery corresponding to the composite positive electrode material after 50 cycles at 0.33C is greater than 88%.

5. The method for preparing a composite cathode material according to any one of claims 1 to 4, wherein: The following steps are involved: Get [N + (CH3)3R]Z - , a coating system formed by a halide precursor material and a solvent; mixing the coating system with a positive electrode base material to obtain a mixed system; The mixed system is subjected to heat treatment.

6. The method for preparing a composite cathode material according to claim 5, wherein: Contains at least one of the following features (1) to (6): (1) The [N + (CH3)3R]Z - In the equation, R is -C n H 2n+1 , n≥9, Z includes BF4 - 、FSI - TFSI - and PF6 - At least one of; (2) The halide precursor material includes lithium halide and Q halide, and Q includes at least one of In, Y, Zr, Sc and Er; (3) The solvent is selected from polar solvents, and the polar solvent includes at least one of water, ethylenediamine, acetonitrile, methanol, ethanol, acetone, tetrahydrofuran and isopropanol; (4) The preparation method of the coating system specifically comprises: + (CH3)3R]Z - The dispersion and the halide precursor material solution are mixed; (5) The [N + (CH3)3R]Z - The mass percentage of the positive electrode matrix material is 0.01% to 0.5%; (6) The halide electrolyte formed by the halide precursor material accounts for 0.1% to 2% by mass of the positive electrode matrix material.

7. The method for preparing a composite cathode material according to claim 5, wherein: Contains at least one of the following features (1) to (6): (1) The solid mass content of the mixed system is ≥50%; (2) The positive electrode base material is subjected to a base material coating treatment before being mixed with the coating system to form a base layer on the surface of the positive electrode base material; (3) The heat treatment temperature is 150 to 500° C., and the heat treatment time is 4 to 10 hours; (4) The atmosphere of the heat treatment is selected from at least one of air, oxygen and nitrogen, preferably air from which carbon dioxide has been removed; (5) performing post-processing on the heat-treated material, wherein the post-processing includes cooling, screening, and demagnetization; preferably, the material is taken out after being cooled to a temperature ≤ 95°C; preferably, the dew point of the post-processing environment is ≤ -20°C; (6) The environmental dew point of the coating system and the mixed system during the preparation process is ≤-10°C.

8. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode layer located on at least one surface thereof, wherein the positive electrode layer comprises the composite positive electrode material according to any one of claims 1 to 4 or a composite positive electrode material prepared by the method for preparing the composite positive electrode material according to any one of claims 5 to 7.

9. The positive electrode sheet according to claim 8, characterized in that: Contains at least one of the following features (1) to (3): (1) The mass content of the composite positive electrode material in the positive electrode layer is ≥70%; (2) The positive electrode layer further comprises a sulfide solid electrolyte, a conductive agent, and a binder; the mass content of the sulfide solid electrolyte in the positive electrode layer is 20% to 25%; (3) The porosity of the positive electrode sheet after rolling is ≤25%.

10. A battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to claim 8 or 9; Preferably, the battery further comprises a negative electrode sheet and a sulfide electrolyte separator.

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