Solid electrolyte modified positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a solid electrolyte modified positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: a) dissolving an inorganic oxide electrolyte intermediate product in a mixed solution of water and an organic matter containing functional groups, adjusting the pH value to 2-9, adding lithium fluoride, stirring, and then evaporating and drying to obtain a first gel product; b) performing puffing treatment on the first-time gel product obtained in the step a), adding the first-time gel product and a ternary positive electrode material into a solvent, performing ultrasonic dispersion, stirring, and performing evaporation drying to obtain a second-time gel product; and c) sintering the second gel product obtained in the step b) in an oxygen-free environment to obtain the solid electrolyte modified positive electrode material. According to the invention, through cooperation of liquid-phase coating and high-temperature solid-phase diffusion treatment, a sintered stone structure with high ionic conductivity and high stability is introduced to the surface of the ternary material, and the problem of cyclic cracking of the ternary positive electrode material can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and more particularly to a solid electrolyte modified positive electrode material and a preparation method and application thereof. Background Art

[0002] As the most portable energy storage medium available, chemical power sources have become a crucial component in the development and utilization of new energy sources. Compared to traditional chemical power sources, lithium-ion batteries offer advantages such as high energy density and power density, making them the current electrochemical energy storage technology of choice. Furthermore, the increasing adoption of new energy vehicles is placing higher demands on battery life and safety, making the development of high-capacity, highly stable, and safe lithium-ion batteries crucial.

[0003] As the main component of lithium-ion batteries, the positive electrode material provides a lithium source for the entire battery system, determines the battery's capacity and average operating voltage, as well as its cycle life and safety. Its performance determines the electrochemical performance of the entire battery system. Ternary high-nickel positive electrode layered oxides have the characteristics of high capacity density, high lithium insertion and extraction potential, and low price, making them one of the best materials for high-energy-density lithium battery positive electrodes. However, with the increase of Ni content, the structural stability of the material deteriorates, and the surface is prone to side reactions with the electrolyte. More seriously, it leads to increased expansion and contraction of the primary particles of the material during charging and discharging, causing cracks along the grain boundaries during long cycles. The appearance of cracks not only destroys the overall structure of the particles, but also brings more serious interface reaction problems. Cracks along the grain boundaries and the resulting interface problems are considered to be the main reasons for the performance degradation of high-nickel ternary materials. The existing modification methods are mainly coating and doping. These methods often only solve part of the problem. For example, coating mainly stabilizes the surface of the material, slows down the side reaction with the electrolyte and the structural phase change of the surface layer, but it cannot effectively solve the bulk structural phase change and crack problems; doping is mainly used to stabilize the bulk structure, but the decline in the performance of the positive electrode material usually originates from surface degradation first, and doping has a weak effect on crack suppression. Therefore, it is necessary to stabilize the surface of the material while suppressing cracks in order to give full play to the performance advantages of high-nickel ternary positive electrode materials. The generation of intergranular cracks can be directly suppressed through grain boundary modification engineering (primary particle surface coating), effectively avoiding the penetration of electrolyte into the interior of the particles. However, the surface coating of primary particles requires the use of complex processes and equipment (such as ALD), as well as the use of cobalt-containing modified materials, which cannot be achieved in large-scale production and application in terms of process and cost. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a solid electrolyte modified positive electrode material and its preparation method and application. The present invention introduces a new oxide solid electrolyte based on the organic carbon three-dimensional network structure and forms a positive electrode material with good thermal stability and ionic conductivity. Applying it to lithium batteries can effectively improve the performance of lithium-ion batteries.

[0005] The present invention provides a method for preparing a solid electrolyte modified positive electrode material, comprising the following steps:

[0006] a) dissolving the inorganic oxide electrolyte intermediate product in a mixture of water and a functional group-containing organic compound, adjusting the pH to 2 to 9, adding lithium fluoride and stirring, and then evaporating and drying to obtain a first gel product;

[0007] b) subjecting the first gel product obtained in step a) to expansion treatment, adding it and the ternary cathode material to a solvent for ultrasonic dispersion, stirring, evaporating, and drying to obtain a second gel product;

[0008] c) sintering the second gel product obtained in step b) in an oxygen-free environment to obtain a solid electrolyte-coated ternary cathode material.

[0009] Preferably, in step a),

[0010] The inorganic oxide electrolyte intermediate product has the structure of formula (I):

[0011] Aa 3-α-2β Ab (1+α) / 3 M2O 7-β Formula (I);

[0012] Wherein, Aa is an alkali metal, Ab is a lanthanide element, and M is a cationic metal; 0≤α≤1, 0<β≤1.

[0013] Preferably, the inorganic oxide electrolyte intermediate product is prepared according to the following method:

[0014] The alkali metal salt, lanthanum source and cationic metal compound are mixed by a sand mill, then placed in an oven for drying, and finally ground and sintered in an air atmosphere box furnace to obtain an inorganic oxide having a structure of formula (I).

[0015] Preferably, the alkali metal salt is selected from one or more of Li salts, Na salts, and K salts; the lanthanum source is selected from lanthanum nitrate and / or lanthanum oxide; and the cationic metal compound is selected from one or more of niobium pentoxide, tantalum pentoxide, titanium dioxide, zirconium dioxide, hafnium dioxide, and vanadium pentoxide.

[0016] The mixed grinding medium is selected from one or more of deionized water, ethanol, and N-methylpyrrolidone;

[0017] The mixed grinding balls are zirconia balls with a diameter of 0.3 mm to 0.7 mm;

[0018] The mixing and grinding speed is 500r / min to 2000r / min, and the grinding time is 2h to 12h;

[0019] The sintering temperature is 900° C. to 1200° C., and the sintering time is 4 hours to 10 hours.

[0020] Preferably, the organic matter containing functional groups in step a) is selected from one or more of starch, cellulose, chitosan, polyacrylic acid, and citric acid; the amount of the organic matter containing functional groups added is 10% to 30% of the mass of the inorganic oxide electrolyte intermediate product; and the amount of water added is 5 to 20 times the amount of the organic matter containing functional groups.

[0021] Preferably, the puffing process in step b) is specifically as follows:

[0022] The first gel product is placed in a high-pressure puffing device, and the puffing temperature is set to 150°C to 250°C, the pressure is set to 1MPa to 5MPa, and the processing time is set to 10min to 30min to obtain a puffed product;

[0023] The solvent is selected from one or more of NMP, DMF, ethanol, isopropanol and water; the amount of the solvent added is 2 to 4 times the total mass of the expanded product and the ternary positive electrode material; the ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, wherein 0.8≤x≤0.99, the median particle size D50 is 2μm to 15μm, and the added amount is 1 to 5 times the mass of the expanded product.

[0024] Preferably, the oxygen-free environment in step c) is controlled by introducing nitrogen or argon at a flow rate of 50 mL / min to 100 mL / min;

[0025] The sintering process is specifically as follows:

[0026] The temperature is raised to 400°C to 600°C at a heating rate of 2°C / min to 5°C / min and kept warm for 1h to 4h, and then raised to 800°C to 1000°C at a heating rate of 5°C / min to 10°C / min and kept warm for 2h to 10h to obtain a solid electrolyte coated ternary positive electrode material.

[0027] The present application also provides a solid electrolyte modified positive electrode material, comprising:

[0028] Ternary cathode materials;

[0029] An inorganic oxide electrolyte coated on the surface of the ternary cathode material; the inorganic oxide electrolyte has a structure of formula (II):

[0030] Aa 3-α-β Ab (1+α) / 3 M2O 7-β X β; (Formula II);

[0031] Wherein, Aa is an alkali metal, Ab is a lanthanide element, M is a cationic metal, X is F; 0≤α≤1, 0<β≤1;

[0032] Carbon coated on the surface of the inorganic oxide electrolyte.

[0033] The present application also provides a positive electrode plate for a lithium-ion battery, comprising the solid electrolyte modified positive electrode material described in the above technical solution or the solid electrolyte modified positive electrode material prepared by the method described in the above technical solution.

[0034] The present application also provides a lithium-ion battery, comprising the positive electrode sheet for the lithium-ion battery described in the above technical solution.

[0035] The present invention provides a method for preparing a solid electrolyte modified positive electrode material, comprising the following steps: a) dissolving an inorganic oxide electrolyte intermediate in a mixture of water and an organic matter containing functional groups, adjusting the pH to 2-9, adding lithium fluoride and stirring, and then evaporating and drying to obtain a first gel product; b) subjecting the first gel product obtained in step a) to a puffing treatment, adding the mixture to a solvent with a ternary positive electrode material and ultrasonically dispersing the mixture, stirring the mixture, and then evaporating and drying the mixture to obtain a second gel product; c) sintering the second gel product obtained in step b) in an oxygen-free environment to obtain a solid electrolyte coated ternary positive electrode material. The present invention first uses an organic matter containing functional groups to form a first gel product with lithium fluoride and an inorganic oxide electrolyte intermediate, then releases the functional groups in the organic matter through a puffing treatment, and then performs a secondary gel chelation on the ternary positive electrode material. After sintering, an inorganic oxide electrolyte coating layer is formed on the surface of the ternary positive electrode material, and a carbon coating layer is formed on the surface of the inorganic oxide electrolyte coating layer. At the same time, a carbon network structure scaffold is formed between the particles of the ternary positive electrode material to improve the conductivity and structural stability of the positive electrode material. This application introduces a sintered stone structure with high ionic conductivity and strong stability on the surface of the ternary material through liquid phase coating and high-temperature solid phase diffusion treatment, which can effectively solve the crack problem of the ternary positive electrode material; the prepared product not only exhibits excellent ionic conductivity, outstanding structural stability and good chemical compatibility, but also has the extremely critical advantage of inhibiting volume expansion.

[0036] At the same time, when the ternary cathode material prepared by the present invention is used in lithium batteries, it can significantly increase the battery's energy density, significantly enhance the battery's cycle stability, optimize the battery's charge and discharge performance at different rates, and broaden the battery's operating temperature range. This application constructs a multi-layered, synergistic coating system, with each layer working together to play a role in multiple dimensions, from ion transport and structural support to chemical protection, and can meet the urgent demand for high-energy-density batteries in modern electronic devices and electric vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The XRD patterns of the intermediate phase and pyrochlore phase electrolyte in Example 1 of the present application are shown in FIG.

[0038] Figure 2 The XRD patterns of the positive electrode materials before and after coating treatment in Example 1 of the present application are as follows;

[0039] Figure 3 This is an SEM image of the positive electrode material after coating treatment obtained in Example 1 of the present application. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] The present application provides a method for preparing a solid electrolyte modified positive electrode material, comprising the following steps:

[0042] a) dissolving the inorganic oxide electrolyte intermediate product in a mixture of water and a functional group-containing organic compound, adjusting the pH to 2 to 9, adding lithium fluoride and stirring, and then evaporating and drying to obtain a first gel product;

[0043] b) subjecting the first gel product obtained in step a) to expansion treatment, adding it and the ternary cathode material to a solvent for ultrasonic dispersion, stirring, evaporating, and drying to obtain a second gel product;

[0044] c) sintering the second gel product obtained in step b) in an oxygen-free environment to obtain a solid electrolyte-coated ternary cathode material.

[0045] This application first uses organic matter containing functional groups to form a first gel product with lithium fluoride and an inorganic oxide electrolyte intermediate, then releases the functional groups in the organic matter through expansion treatment, and then performs secondary gel chelation on the ternary positive electrode material. After sintering, an inorganic oxide electrolyte coating layer is formed on the surface of the ternary positive electrode material, and a carbon coating layer is formed on the surface of the inorganic oxide electrolyte coating layer. At the same time, a carbon network structure support is formed between the particles of the ternary positive electrode material to improve the conductivity and structural stability of the positive electrode material.

[0046] The present invention first dissolves the inorganic oxide electrolyte intermediate product in a mixture of water and organic matter containing functional groups, adjusts the pH to 2-9, preferably 4-6, then adds lithium fluoride and stirs, and then evaporates and dries to obtain a first gel product.

[0047] In the present invention, the inorganic oxide electrolyte intermediate product is preferably a pyrochlore solid electrolyte intermediate product having a structure of formula (I):

[0048] Aa 3-α-2β Ab (1+α) / 3 M2O 7-β Formula (I);

[0049] Wherein, Aa is an alkali metal, Ab is a lanthanide element, and M is a cationic metal; 0≤α≤1, 0<β≤1.

[0050] Preferably, Aa is selected from Li, Na, or K, more preferably Li. Ab is a lanthanide element, including lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, etc., preferably lanthanum. M is a cationic metal, preferably selected from any one or more of Nb, Ta, Ti, Zr, Hf, and V, more preferably Nb. 0≤α≤1, illustratively, α can be 0, 0.2, 0.33, 0.4, 0.5, 0.6, 0.8, 1, etc.

[0051] This application uses a pyrochlore solid electrolyte intermediate product having the structure of formula (I) as a raw material to obtain a pyrochlore solid electrolyte-coated ternary positive electrode material, which has excellent ionic conductivity and low-temperature performance, a wide operating temperature range, and good compatibility with a variety of electrode materials at the interface. The fluorine element in it makes the collected material more stable in the chemical environment and can resist corrosion and redox reactions of chemical substances.

[0052] In the present invention, the pyrochlore solid electrolyte intermediate product Aa 3-α-2β Ab (1+α) / 3 M2O 7-β It can be purchased from the market or prepared as follows:

[0053] The alkali metal salt, lanthanide metal source and cationic metal compound are mixed by a sand mill, then placed in an oven for drying, and finally ground and sintered in an air atmosphere box furnace to obtain the pyrochlore solid electrolyte intermediate product Aa 3-α-2β Ab (1+α) / 3 M2O 7-β .

[0054] In the present invention, the alkali metal salt is preferably selected from one or more of Li salts, Na salts, and K salts, more preferably Li salts; the lanthanide metal source is preferably selected from lanthanide metal salts or lanthanide metal oxides, preferably lanthanum nitrate and / or lanthanum oxide, more preferably lanthanum nitrate; the cationic metal compound is preferably selected from one or more of niobium pentoxide, tantalum pentoxide, titanium dioxide, zirconium dioxide, hafnium dioxide, and vanadium pentoxide, more preferably niobium pentoxide; the present invention has no special restrictions on the sources of the alkali metal salts, lanthanum salts, and cationic metal compounds, and commercially available products familiar to those skilled in the art can be used.

[0055] In the present invention, the mixed grinding medium is preferably selected from one or more of deionized water, anhydrous ethanol, and N-methylpyrrolidone (NMP), more preferably deionized water; the mixed grinding balls are preferably zirconia balls, and the grinding ball diameter is preferably 0.3 mm to 0.7 mm; the mixed grinding speed is preferably 500 r / min to 2000 r / min, more preferably 1000 r / min, and the grinding time is preferably 2 h to 12 h, more preferably 6 h.

[0056] In the present invention, the drying temperature is preferably 70° C. to 90° C., more preferably 80° C., and the drying time is preferably 10 h to 15 h, more preferably 12 h.

[0057] In the present invention, the sintering temperature is preferably 900° C. to 1200° C., more preferably 1000° C., and the sintering time is preferably 4 h to 10 h, more preferably 6 h.

[0058] The present invention first synthesizes the intermediate product Aa of pyrochlore type solid electrolyte by a simple solid phase method. 3-α-2β Ab (1+α) / 3 M2O 7-β The solid-phase method is relatively simple to operate, which is conducive to large-scale production, but it can also achieve the synthesis of intermediate products with specific crystal structure and chemical composition, laying the foundation for the subsequent coating process.

[0059] In the present invention, the organic matter containing functional groups is preferably selected from one or more of starch, cellulose, chitosan, polyacrylic acid, and citric acid, and is more preferably starch. The present invention has no special restrictions on the source of the organic matter containing functional groups, and commercially available products well known to those skilled in the art can be used.

[0060] In the present invention, the amount of the functional group-containing organic matter added is preferably 10% to 30% of the mass of the inorganic oxide electrolyte intermediate product; the amount of water added is preferably 5 to 20 times the amount of the organic matter rich in multiple functional groups.

[0061] The organic matter containing functional groups selected in the present invention is an organic polymer or small molecule organic matter containing hydroxyl, carboxyl, and amino functional groups; these organic matter are reacted with lithium fluoride and inorganic oxide electrolyte intermediates, especially Aa 3-α-2β Ab (1+α) / 3 M2O 7-β Mix thoroughly, use stirring, ultrasound and other means to promote the functional groups of organic matter to react with lithium fluoride, Aa 3-α-2β Ab (1+α) / 3 M2O 7-β They are tightly bound together through physical effects such as hydrogen bonds and ionic bonds, or chemical reactions such as esterification and complexation, initially forming a uniformly dispersed system, which is then gelled by controlling temperature, humidity and other conditions, and then dried to obtain a stable gel complex.

[0062] In the present invention, the dissolving method is stirring, and the stirring time is preferably 1 hour to 3 hours.

[0063] In the present invention, the pH is adjusted to 2-9 preferably using 20%-40% ammonia water; lithium fluoride is then added with stirring, and then evaporated and dried at 70°C-80°C to form and solidify the gel to obtain the first gel product.

[0064] The present invention introduces lithium fluoride, which will dissociate under high temperature environment to produce lithium ions (Li + ) and fluoride ions (F - ); At the same time, Aa 3-α-2β Ab (1+α) / 3 M2O 7-β Some ions in the Li will also become more active due to high temperature, and will be in a state where they are easy to migrate and react. + The radius is relatively small, and it can easily enter the lattice position occupied by Aa in the crystal structure; if there are some vacancies in the Aa position or it is not fully occupied by other ions, the introduced lithium ions can fill these positions to compensate for Aa and stabilize the structure of the compound; fluoride ions (F - ) will be the same as Aa 3-α-2β Ab (1+α) / 3M2O 7-β The metal cations in the electrolyte combine to form new chemical bonds, thereby changing the composition and structure of the compound and gradually forming a pyrochlore-type solid electrolyte with the structure of formula (II):

[0065] Aa 3-α-β Ab (1+α) / 3 M2O 7-β X β (Formula II);

[0066] Wherein, Aa is an alkali metal, Ab is a lanthanide element, M is a cationic metal, X is F; 0≤α≤1, 0<β≤1.

[0067] After obtaining the first gel product, the present invention expands the first gel product, adds it and the ternary positive electrode material into a solvent for ultrasonic dispersion, and then evaporates and dries it after stirring to obtain a second gel product.

[0068] In the present invention, the puffing process is preferably as follows:

[0069] The first gel product is placed in a high-pressure puffing device, and the puffing temperature is set to 150°C to 250°C, the pressure is set to 1MPa to 5MPa, and the processing time is set to 10min to 30min to obtain a puffed product;

[0070] More preferably:

[0071] The first gel product is placed in a high-pressure puffing machine, set at a puffing temperature of 180°C to 220°C, a pressure of 2MPa to 4MPa, and a processing time of 15 to 25 minutes to obtain an expanded product. Under these temperature, pressure, and time conditions, the water in the mixture can quickly vaporize, generating a suitable expansion force, forming a large number of interconnected pores within the material, and effectively promoting the molecular structure of the organic matter to change and release more functional groups.

[0072] The present invention takes a certain amount of solvent and pours it into a clean container, and adds the expanded product and the ternary positive electrode material according to the designed ratio. In the present invention, the solvent is preferably selected from one or more of NMP, DMF, ethanol, isopropanol, and water, and more preferably NMP; the amount of the solvent added is preferably 2 to 4 times the total mass of the expanded product and the ternary positive electrode material; the selected ternary positive electrode material is preferably LiNi x Co y Mn 1-x-y O2, wherein 0.8≤x≤0.99, more preferably LiNi 0.8 Co 0.1 Mn 0.1 O2, wherein the median particle size D50 is preferably 2 μm to 15 μm, more preferably 4 μm to 10 μm, and the added amount is preferably 1 to 5 times the mass of the expanded product. The present invention has no particular limitation on the sources of the solvent and ternary positive electrode material; commercially available products familiar to those skilled in the art can be used.

[0073] In the present invention, the ultrasonic dispersion is preferably carried out using an ultrasonic disperser, and the time is preferably 10 min to 20 min to preliminarily disperse the components. The components are then transferred to a magnetic stirrer and stirred at a speed of preferably 300 r / min to 500 r / min at 30°C to 60°C for 2h to 4h to fully mix the positive electrode material and the expanded product. Finally, the mixture is evaporated and dried to obtain a second gel product.

[0074] The first gel product prepared by the present invention is subjected to heat, pressure change, moisture and chemical reaction, etc., so that the weak chemical bonds in the molecules of the organic matter are broken and the structure is destroyed during the expansion treatment, thereby releasing the functional groups. The released functional groups can undergo secondary gel chelation with the ternary positive electrode material, which helps to form a stable Aa on the surface of the ternary positive electrode material. 3-α-β Ab (1+α) / 3 M2O 7-β X β The coating layer enhances the coating effect; the expansion treatment causes structural changes such as tiny pores or channels inside the material: on the one hand, it is beneficial to the subsequent formation of Aa 3-α-β Ab (1+α) / 3 M2O 7-β X β The coating layer better adheres to and penetrates the surface of the ternary cathode material, enhancing the coating effect; on the other hand, these structural changes may help form a carbon network structure scaffold between the ternary cathode materials and improve the overall performance of the material.

[0075] After obtaining the second gel product, the present invention sintered the obtained second gel product in an oxygen-free environment to obtain a solid electrolyte-coated ternary positive electrode material.

[0076] The present invention transfers the secondary gel product to a high-temperature tubular furnace, introduces nitrogen or argon, replaces the air in the furnace, and ensures that the furnace is an oxygen-free nitrogen or argon environment.

[0077] In the present invention, the oxygen-free environment is preferably controlled by introducing nitrogen at a flow rate of 50 mL / min to 100 mL / min.

[0078] In the present invention, the sintering process is preferably as follows:

[0079] The temperature is raised to 400-600°C at a heating rate of 2-5°C / min and maintained for 1-4 hours. Then, the temperature is raised to 800-1000°C at a heating rate of 5-10°C / min and maintained for 2-10 hours to obtain a solid electrolyte-coated ternary cathode material. Under high temperature and nitrogen, organic and other carbonaceous substances gradually carbonize. The formed carbon connects the LLNOF and cathode material to form a network structure, and also coats the LLNOF surface, improving its conductivity. Ultimately, a network structure of solid electrolyte LLNOF, carbon, and cathode material is obtained.

[0080] The present invention introduces secondary gel to allow the functional groups released from the organic matter to chelate with the ternary positive electrode material, introducing the ternary positive electrode material into the interior of the composite structure, making it less affected by the external environment and improving the chemical stability of the material; at the same time, the secondary gel can fill the microscopic defects and gaps on the surface of the material, so that the coating layer and the surface of the ternary positive electrode material have a higher degree of fit, further enhancing the bonding force between the two, and also avoiding the situation where the local coating is too thick or too thin.

[0081] In addition, this scheme uses a high temperature inert environment to calcine the gel composite, and the organic matter undergoes pyrolysis reaction and gradually transforms at high temperature and forms a 3-α-β Ab (1+α) / 3 M2O 7-β X β A carbon coating layer is deposited and formed on the surface; at the same time, during high-temperature calcination, the carbon source undergoes pyrolysis and carbonization around the ternary positive electrode material, and gradually deposits and grows around the ternary positive electrode material and between the particles, forming a continuous carbon network structure, connecting the particles of the ternary positive electrode material to form a scaffold.

[0082] The present invention also provides a solid electrolyte modified positive electrode material, which is prepared using the preparation method described in the above technical solution, comprising:

[0083] Ternary cathode materials;

[0084] An inorganic oxide electrolyte coated on the surface of the ternary cathode material; the inorganic oxide electrolyte has a structure of formula (II):

[0085] Aa 3-α-β Ab (1+α) / 3 M2O 7-β X β (Formula II)

[0086] Wherein, Aa is an alkali metal, Ab is a lanthanide element, M is a cationic metal, X is F; 0≤α≤1, 0<β≤1;

[0087] Carbon coated on the surface of the inorganic oxide electrolyte. In the inorganic oxide electrolyte having the structure of formula (II), Aa, Ab, M, and α are as described above, 0<β≤1, for example, 0.1, 0.5, 1, etc., and there is no special limitation in this application.

[0088] The present invention also provides a positive electrode plate for a lithium-ion battery, comprising the solid electrolyte-coated ternary positive electrode material described in the above technical solution or the solid electrolyte-coated ternary positive electrode material prepared by the method described in the above technical solution. In some specific implementations, the positive electrode plate is prepared by coating a positive electrode slurry on a positive electrode current collector (preferably aluminum foil), drying, and slicing; the positive electrode slurry is prepared by mixing (dry mixing) a positive electrode material, a conductive agent, and a binder in a mass ratio of (80-85):(5-10):10, followed by solvent dispersion; and the positive electrode material is the solid electrolyte-coated ternary positive electrode material described in the above technical solution.

[0089] In the present invention, the conductive agent is preferably selected from carbon black, carbon nanotubes, or graphene; the binder is preferably selected from one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and hydroxypropyl methylcellulose; and the solvent is preferably NMP or anhydrous ethanol. The sources of the conductive agent, binder, and solvent are not particularly limited; commercially available products known to those skilled in the art may be used.

[0090] In addition, the present invention mixes the negative electrode active material (graphite), a conductive agent, a binder, a thickener and a solvent to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and then sliced ​​after drying to obtain a negative electrode sheet.

[0091] In the present invention, the binder is preferably selected from one or more of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and hydroxypropyl methylcellulose; the conductive agent is preferably selected from carbon black, carbon nanotubes, or graphene; the organic solvent is preferably NMP or anhydrous ethanol; the thickener is preferably polyvinyl alcohol (PVA) or carboxymethyl cellulose (CMC); all of which can be obtained from commercially available sources well known to those skilled in the art.

[0092] The present invention also provides a lithium-ion battery, comprising the positive electrode sheet for the lithium-ion battery described in the above technical solution.

[0093] The present invention stacks the positive electrode sheets, separators and negative electrode sheets obtained by the above technical solution in sequence, and then winds them into a core to obtain an electrode assembly. The wound electrode assembly is placed in a battery casing, and an electrolyte solution prepared by 1 mol / L LiPF6, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (the volume ratio of EC to MC is 1:2) is added, and after packaging, a secondary battery is obtained.

[0094] The present invention applies coated ternary cathode materials to lithium-ion batteries, which can significantly improve the overall performance of the batteries, including but not limited to increasing energy density, enhancing cycle stability, optimizing rate performance, and widening the operating temperature range; this high-performance, multifunctional and highly adaptable application is expected to show broad application prospects in the fields of mobile electronic device energy storage power supplies, new energy vehicles, large-scale energy storage devices, etc.

[0095] The present invention provides a method for preparing a solid electrolyte modified positive electrode material, comprising the following steps: a) dissolving an inorganic oxide electrolyte intermediate in a mixture of water and an organic matter containing functional groups, adjusting the pH to 2-9, adding lithium fluoride and stirring, and then evaporating and drying to obtain a first gel product; b) subjecting the first gel product obtained in step a) to a puffing treatment, adding the mixture to a solvent with a ternary positive electrode material and ultrasonically dispersing the mixture, stirring the mixture, and then evaporating and drying the mixture to obtain a second gel product; c) sintering the second gel product obtained in step b) in an oxygen-free environment to obtain a solid electrolyte coated ternary positive electrode material. The present invention first uses an organic matter containing functional groups to form a first gel product with lithium fluoride and an inorganic oxide electrolyte intermediate, then releases the functional groups in the organic matter through a puffing treatment, and then performs a secondary gel chelation on the ternary positive electrode material. After sintering, an inorganic oxide electrolyte coating layer is formed on the surface of the ternary positive electrode material, and a carbon coating layer is formed on the surface of the inorganic oxide electrolyte coating layer. At the same time, a carbon network structure scaffold is formed between the particles of the ternary positive electrode material to improve the conductivity and structural stability of the positive electrode material. Specifically, this application introduces a sintered stone structure with high ionic conductivity and strong stability on the surface of the ternary material through liquid phase coating and high-temperature solid phase diffusion treatment, which can effectively solve the crack problem of the ternary positive electrode material; the prepared product not only exhibits excellent ionic conductivity, outstanding structural stability and good chemical compatibility, but also has the extremely critical advantage of inhibiting volume expansion.

[0096] At the same time, when the ternary cathode material prepared by the present invention is used in lithium batteries, it can significantly increase the battery's energy density, significantly enhance the battery's cycle stability, optimize the battery's charge and discharge performance at different rates, and broaden the battery's operating temperature range. This application constructs a multi-layered, synergistic coating system, with each layer working together to play a role in multiple dimensions, from ion transport and structural support to chemical protection, and can meet the urgent demand for high-energy-density batteries in modern electronic devices and electric vehicles.

[0097] In order to further illustrate the present invention, the following examples are provided for detailed description. The raw materials used in the following examples of the present invention are all commercially available.

[0098] Example 1

[0099] 1. Material preparation:

[0100] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0101] Weigh 13.79g LiNO3, 32.49g La(NO3)3, and 58.45g Nb2O5 into a sand mill containing 0.5mm diameter zirconium oxide, add deionized water, grind at a speed of 1000r / min for 6h, and then dry at 80℃ for 12h. After grinding the dried mixture, place it in an air atmosphere box furnace and sinter it at 1000℃ for 6h to obtain the pyrochlore solid electrolyte intermediate product Li 0.8 La 0.4 Nb2O6.

[0102] XRD diffraction analysis of the pyrochlore solid electrolyte intermediate product is performed, see Figure 1 , Figure 1 1 is the XRD pattern of the intermediate phase and pyrochlore phase electrolyte in Example 1 of the present application.

[0103] 2. Preparation of the first gel product:

[0104] Weigh 10g of starch, add 150g of water, and stir evenly. Dissolve 100g of the pyrochlore solid electrolyte intermediate product obtained above in the solution and stir for 2h. Use 28% ammonia water to adjust the pH value of the solution to 5. Weigh 6.49g of lithium fluoride and slowly add it to the mixed solution and stir. Finally, transfer the solution to an evaporating dish and evaporate and dry it at 75°C to form a gel and solidify it to obtain the first gel product.

[0105] 3. Extrusion treatment:

[0106] The first gel product was placed in a high-pressure puffing device, and the puffing temperature was set to 200° C., the pressure was set to 3 MPa, and the processing time was set to 20 minutes to obtain a puffed product.

[0107] 4. Preparation of secondary gel product:

[0108] Take 250g of NMP and pour it into a clean container. Then add 25g of the expanded product and 100g of the ternary positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 (D50 particle size: 5 μm) was added. The vessel was placed in an ultrasonic disperser and sonicated for 15 minutes. The mixture was then transferred to a magnetic stirrer and stirred at 400 rpm at 50°C for 3 hours. Finally, the mixture was evaporated and dried to obtain a secondary gel product.

[0109] 5. Preparation of coated ternary cathode materials:

[0110] The secondary gel product was transferred to a high-temperature tube furnace and nitrogen was introduced at a flow rate of 80 mL / min to replace the air in the furnace. The temperature was raised to 400°C at a rate of 3°C / min and kept at that temperature for 2 h. The temperature was then raised to 900°C at a rate of 5°C / min and kept at that temperature for 6 h to obtain Li 1.8 La 0.4 Nb2O6F coated ternary positive electrode material.

[0111] The obtained coated ternary cathode material was subjected to XRD diffraction analysis and electron microscope scanning, and the results are shown in Figure 2 and Figure 3 , Figure 2 The XRD patterns of the positive electrode materials before and after coating treatment in Example 1 of the present application are as follows; Figure 3 This is the SEM image of the positive electrode material after coating treatment obtained in Example 1 of the present application. Figure 3 It can be seen that the coated positive electrode material prepared in this application still maintains its original spherical shape as a whole. Compared with the conventional polycrystalline ternary positive electrode material, the polyhedral primary particle size contour and grain boundary can be clearly observed, and a layer of loose porous solid electrolyte material with irregular morphology is tightly attached to the surface.

[0112] 2. Preparation of positive and negative electrode materials:

[0113] 6. Preparation of positive electrode material sheet:

[0114] The prepared positive electrode material, carbon black conductive agent, and polyvinylidene fluoride (PVDF) binder were dry-mixed in a mass ratio of 85:5:10, and an appropriate amount of NMP organic solvent was added to prepare a positive electrode slurry. The positive electrode slurry was coated on the positive electrode current collector aluminum foil, dried in an 80°C oven, and then sliced ​​to obtain positive electrode material sheets.

[0115] 7. Preparation of negative electrode sheet:

[0116] The negative electrode active material graphite, carbon nanotube conductive agent, styrene-butadiene rubber (SBR) binder, carboxymethyl cellulose (CMC) thickener, and anhydrous ethanol solvent were mixed in a ratio of 89.6:5:2:3.4 to prepare the negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, dried in a vacuum drying oven at 60°C, and then sliced ​​to obtain the negative electrode sheet.

[0117] 8. Preparation of secondary batteries:

[0118] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and then wound into a core to obtain an electrode assembly. The wound electrode assembly is placed in the battery casing, and an electrolyte solution composed of 1 mol / L LiPF6, ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (the volume ratio of EC to MC is 1:2) is added. After packaging, the secondary battery is finally produced.

[0119] Example 2

[0120] 1. Material preparation:

[0121] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0122] Weigh 17.24g LiNO3, 27.08g La(NO3)3, and 58.45g Nb2O5 into a sand mill containing 0.3mm diameter zirconium oxide, add anhydrous ethanol, grind at 500r / min for 12h, and then dry at 90℃ for 15h. After grinding the dried mixture, place it in an air atmosphere box furnace and sinter at 1000℃ for 6h to obtain the pyrochlore solid electrolyte intermediate product LiLa 0.33 Nb2O6.

[0123] 2. Preparation of the first gel product:

[0124] Weigh 30g of starch, add 150g of water, and stir evenly. Dissolve 100g of the pyrochlore solid electrolyte intermediate product obtained above in the solution and stir for 2h. Use 28% ammonia water to adjust the pH value of the solution to 2. Weigh 6.49g of lithium fluoride and slowly add it to the mixed solution and stir. Finally, transfer the solution to an evaporating dish and evaporate and dry it at 75°C to form a gel and solidify it to obtain the first gel product.

[0125] 3. Extrusion treatment:

[0126] The first gel product was placed in a high-pressure puffing device, and the puffing temperature was set to 150° C., the pressure was set to 5 MPa, and the processing time was set to 30 minutes to obtain a puffed product.

[0127] 4. Preparation of secondary gel product:

[0128] Take 480g of NMP and pour it into a clean container, add 20g of the expanded product and 100g of the ternary positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 (D50 particle size: 2 μm) was added. The vessel was placed in an ultrasonic disperser and sonicated for 20 minutes. The mixture was then transferred to a magnetic stirrer and stirred at 500 rpm at 60°C for 2 hours. Finally, the mixture was evaporated and dried to obtain a secondary gel product.

[0129] 5. Preparation of coated ternary cathode materials:

[0130] The secondary gel product was transferred to a high-temperature tube furnace and nitrogen was introduced at a flow rate of 100 mL / min to replace the air in the furnace. The temperature was raised to 600°C at a rate of 2°C / min and kept at that temperature for 4 h. The temperature was then raised to 1000°C at a rate of 10°C / min and kept at that temperature for 10 h to obtain Li2La 0.33 Nb2O6F coated ternary positive electrode material.

[0131] 2. Preparation of positive and negative electrode materials:

[0132] 6. Preparation of positive electrode material sheet:

[0133] The prepared positive electrode material, carbon black conductive agent, and polyvinylidene fluoride (PVDF) binder were dry-mixed in a mass ratio of 80:10:10, and an appropriate amount of NMP organic solvent was added to prepare a positive electrode slurry. The positive electrode slurry was coated on the positive electrode current collector aluminum foil, dried in an 80°C oven, and then sliced ​​to obtain positive electrode material sheets.

[0134] 7. Preparation of negative electrode sheet:

[0135] Same as step 7 of Example 1;

[0136] 8. Preparation of secondary batteries:

[0137] Same as step 8 in Example 1;

[0138] Example 3

[0139] 1. Material preparation:

[0140] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0141] Weigh 10.34g LiNO3, 37.91g La(NO3)3, and 58.45g Nb2O5 into a sand mill containing zirconia with a diameter of 0.7mm, add deionized water, grind at a speed of 2000r / min for 2h, and then dry at 70℃ for 10h. After grinding the dried mixture, place it in an air atmosphere box furnace and sinter it at 1000℃ for 6h to obtain the pyrochlore solid electrolyte intermediate product Li 0.6 La 0.47 Nb2O6.

[0142] 2. Preparation of the first gel product:

[0143] Weigh 10g of starch, add 200g of water, and stir evenly. Dissolve 50g of the pyrochlore solid electrolyte intermediate product obtained above in the solution and stir for 2h. Use 28% ammonia water to adjust the pH value of the solution to 9. Weigh 6.49g of lithium fluoride and slowly add it to the mixed solution and stir. Finally, transfer the solution to an evaporating dish and evaporate and dry it at 75°C to form a gel and solidify it to obtain the first gel product.

[0144] 3. Extrusion treatment:

[0145] The first gel product was placed in a high-pressure puffing device, and the puffing temperature was set to 250° C., the pressure was set to 1 MPa, and the processing time was set to 10 minutes to obtain a puffed product.

[0146] 4. Preparation of secondary gel product:

[0147] Take 120g of NMP and pour it into a clean container, add 20g of the expanded product and 20g of the ternary positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 (D50 particle size: 15 μm) was added. The vessel was placed in an ultrasonic disperser and sonicated for 10 minutes. The mixture was then transferred to a magnetic stirrer and stirred at 300 rpm at 30°C for 4 hours. Finally, the mixture was evaporated and dried to obtain a secondary gel product.

[0148] 5. Preparation of coated ternary cathode materials:

[0149] The secondary gel product was transferred to a high-temperature tube furnace and nitrogen was introduced at a flow rate of 50 mL / min to replace the air in the furnace. The temperature was raised to 500°C at a rate of 5°C / min and kept at that temperature for 1 hour. The temperature was then raised to 800°C at a rate of 10°C / min and kept at that temperature for 2 hours to obtain Li 1.6 La 0.47 Nb2O6F coated ternary positive electrode material.

[0150] 2. Preparation of positive and negative electrode materials:

[0151] Same as steps 6 to 8 of Example 1.

[0152] Example 4

[0153] 1. Material preparation:

[0154] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0155] The same as step 1 of Example 1, except that 6.90g LiNO3, 43.05g La(NO3)3, and 58.45g Nb2O5 raw materials were weighed respectively to obtain the pyrochlore solid electrolyte intermediate product Li 0.4 La 0.53 Nb2O6.

[0156] The remaining steps 2 to 5 are the same as in Example 1 to obtain Li 1.4 La 0.53 Nb2O6F coated ternary positive electrode material.

[0157] 2. Preparation of positive and negative electrode materials:

[0158] Same as steps 6 to 8 of Example 1.

[0159] Example 5

[0160] 1. Material preparation:

[0161] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0162] The same as step 1 of Example 1, except that 3.45g LiNO3, 48.74g La(NO3)3, and 58.45g Nb2O5 raw materials were weighed respectively to obtain the pyrochlore solid electrolyte intermediate product Li 0.2 La 0.6 Nb2O6.

[0163] The remaining steps 2 to 5 are the same as in Example 1 to obtain Li 1.2 La 0.6 Nb2O6F coated ternary positive electrode material.

[0164] 2. Preparation of positive and negative electrode materials:

[0165] Same as steps 6 to 8 of Example 1.

[0166] Example 6

[0167] 1. Material preparation:

[0168] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0169] The same as step 1 of Example 1, except that 0g LiNO3, 54.15g La(NO3)3, and 58.45g Nb2O5 raw materials were weighed respectively to obtain the pyrochlore solid electrolyte intermediate product La 0.67 Nb2O6.

[0170] The remaining steps 2 to 5 are the same as in Example 1 to obtain Li1La 0.67 Nb2O6F coated ternary positive electrode material.

[0171] 2. Preparation of positive and negative electrode materials:

[0172] Same as steps 6 to 8 of Example 1.

[0173] Example 7

[0174] 1. Material preparation:

[0175] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0176] The same as step 1 of Example 1, except that 39.65g LiNO3, 40.62g La(NO3)3, and 58.45g Nb2O5 raw materials were weighed respectively to obtain the pyrochlore solid electrolyte intermediate product Li 2.3 La 0.5 Nb2O 6.9 .

[0177] 2. Preparation of the first gel product:

[0178] The same as step 2 of Example 1, except that 0.65 g of lithium fluoride was weighed and added dropwise to the mixed solution.

[0179] The remaining steps 3 to 5 are the same as in Example 1 to obtain Li 2.4 La 0.5 Nb2O 6.9 F 0.1 Coated ternary positive electrode material.

[0180] 2. Preparation of positive and negative electrode materials:

[0181] Same as steps 6 to 8 of Example 1.

[0182] Example 8

[0183] 1. Material preparation:

[0184] 1. Preparation of pyrochlore solid electrolyte intermediates:

[0185] The same as step 1 of Example 1, except that 25.86g LiNO3, 40.62g La(NO3)3, and 58.45g Nb2O5 raw materials were weighed respectively to obtain the pyrochlore solid electrolyte intermediate product Li 1.5 La 0.5 Nb2O 6.5 .

[0186] 2. Preparation of the first gel product:

[0187] The same as step 2 of Example 1, except that 3.24 g of lithium fluoride was weighed and added dropwise to the mixed solution.

[0188] The remaining steps 3 to 5 are the same as in Example 1 to obtain Li2La 0.5 Nb2O 6.5 F 0.5 Coated ternary positive electrode material.

[0189] 2. Preparation of positive and negative electrode materials:

[0190] Same as steps 6 to 8 of Example 1.

[0191] Comparative Example 1

[0192] The difference from Example 1 was that the preparation and addition steps of the pyrochlore solid electrolyte intermediate were omitted. Instead, 10 g of starch was directly weighed, 150 g of water was added, and the mixture was stirred evenly. The pH of the solution was then adjusted to 5 using 28% aqueous ammonia. 6.49 g of lithium fluoride was then slowly added to the mixed solution with stirring. Finally, the solution was transferred to an evaporating dish and evaporated and dried at 75°C to form a gel and solidify it, yielding a primary gel product. Subsequent processing was performed in the same manner as in Example 1 to obtain a secondary battery.

[0193] Comparative Example 2

[0194] Compared with Example 1, the positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2 was used for treatment, and the electrode and secondary battery were directly prepared according to the same method and parameters as in Example 1.

[0195] Performance tests were performed on the positive electrode materials and secondary batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 2. The results are shown in Tables 1, 2, and 3. Table 1 shows the ionic conductivity test data of the positive electrode material, and Table 2 shows the volume expansion rate test data of the secondary battery after 1C rate cycling at room temperature; Table 3 shows the capacity retention rate test data of the battery cell after 1C rate cycling at room temperature.

[0196] Table 1 Ionic conductivity of the positive electrode materials provided in the examples and comparative examples

[0197] Group Ionic conductivity (S / cm) Example 1 <![CDATA[2.21×10 -5 ]]> Example 2 <![CDATA[1.92×10 -5 ]]> Example 3 <![CDATA[2.39×10 -5 ]]> Example 4 <![CDATA[3.87×10 -5 ]]> Example 5 <![CDATA[4.62×10 -5 ]]> Example 6 <![CDATA[1.33×10 -5 ]]> Example 7 <![CDATA[2.03×10 -5 ]]> Example 8 <![CDATA[1.77×10 -5 ]]> Comparative Example 1 <![CDATA[1.12×10 -5 ]]> Comparative Example 2 <![CDATA[1.33×10 -5 ]]>

[0198] Table 2 Volume expansion ratio of secondary batteries prepared in Examples and Comparative Examples

[0199] Group Volume expansion rate after 200 cycles (%) Example 1 2.3 Example 2 2.0 Example 3 1.7 Example 4 1.7 Example 5 1.9 Example 6 2.4 Example 7 2.1 Example 8 2.0 Comparative Example 1 2.9 Comparative Example 2 3.1

[0200] Table 3 Initial capacity and capacity retention rate of secondary batteries prepared in Examples and Comparative Examples

[0201] Group Initial capacity (Ah) Capacity retention rate after 200 cycles (%) Example 1 2.488 89.3 Example 2 2.489 88.5 Example 3 2.483 92.2 Example 4 2.487 92.4 Example 5 2.491 91.9 Example 6 2.488 90.8 Example 7 2.490 89.8 Example 8 2.490 86.7 Comparative Example 1 2.485 84.0 Comparative Example 2 2.492 82.1

[0202] It can be seen from Table 1 that the LLNOF-coated ternary cathode LiNi after expansion and high temperature treatment 0.8 Co 0.1 Mn 0.1 The ionic conductivity of O2 materials is significantly improved compared to the same cathode materials without coating or with only carbon coating, and can be increased to 4.62×10 -5 S / cm, which can significantly improve the lithium ion insertion and extraction rate during the charge and discharge process;

[0203] As can be seen from Table 2, when the ternary cathode material coated with LLNOF is used in battery cell cycling, the volume expansion effect caused by irreversible structural deterioration and side reaction gas production during charge and discharge can be significantly suppressed compared with the same cathode material without coating or treated with carbon only.

[0204] It can be seen from Table 3 that the ternary positive electrode material coated with LLNOF can significantly improve its cycle stability when used in battery cell cycles, and its residual capacity after long cycles is higher than that of the uncoated ternary positive electrode material.

[0205] In summary, the present invention provides a solid electrolyte coated ternary cathode material and its preparation method and application, which have the following beneficial effects:

[0206] (1) The present invention prepares a coated ternary cathode material, in which organic matter is used as a carrier to realize secondary gelation. Through the thermal decomposition and carbonization of the organic matter itself, a carbon coating layer and a carbon network structure are constructed on the surface of the pyrochlore solid electrolyte and between the particles of the ternary cathode material; the carbon coating layer significantly improves the electronic conductivity of the material, accelerates the electron transfer rate, and thus improves the charge and discharge performance of the battery; the carbon network structure acts like a supporting skeleton, enhancing the overall structural stability of the material, buffering the volume change of the ternary cathode material during the charge and discharge process, inhibiting the agglomeration and pulverization of the particles, and ultimately effectively extending the cycle life of the battery and improving its safety performance.

[0207] (2) The present invention prepares a coated ternary cathode material, wherein the organic matter rich in various functional groups is fully blended with the pyrochlore-type solid electrolyte intermediate product and lithium fluoride during the first gelation by means of a secondary gelation process; the second gelation is carried out by means of the functional groups released after the expansion treatment to chelate with the ternary cathode material, which not only enables the pyrochlore-type solid electrolyte to be uniformly coated on the surface of the ternary cathode material, but also optimizes the carbonization process of the organic matter, forms a uniform and dense carbon coating layer and a stable and efficient carbon network scaffold, and comprehensively improves the comprehensive performance of the material.

[0208] (3) The present invention prepares a coated ternary positive electrode material, which uses an expansion treatment to produce unique microstructural changes inside the material, forming a large number of tiny and interconnected pores and channels; these microstructural changes not only increase the specific surface area of ​​the material, which is beneficial to the subsequent chemical reactions, but also provide more paths for ion transport.

[0209] (4) The present invention prepares a coated ternary positive electrode material, in which a pyrochlore solid electrolyte is formed on the surface of the ternary positive electrode material through high-temperature calcination treatment. The pyrochlore solid electrolyte itself has excellent ionic conductivity, good low-temperature performance and a wide operating temperature range. Compared with other traditional coating materials, it can provide a more stable working environment for the ternary positive electrode material and improve the performance of the battery under different temperature conditions; and it has good compatibility with various electrode materials at the interface, which can effectively reduce the interface resistance and improve the overall performance of the battery.

[0210] (5) The present invention prepares a coated ternary positive electrode material. The presence of fluorine in the coating layer makes the solid electrolyte more stable in a chemical environment, and can resist the corrosion of chemical substances and redox reactions, further enhancing the stability and service life of the ternary positive electrode material.

[0211] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a solid electrolyte modified positive electrode material, characterized in that: The following steps are involved: a) dissolving the inorganic oxide electrolyte intermediate product in a mixture of water and a functional group-containing organic compound, adjusting the pH to 2 to 9, adding lithium fluoride and stirring, and then evaporating and drying to obtain a first gel product; b) subjecting the first gel product obtained in step a) to expansion treatment, adding it and the ternary cathode material to a solvent for ultrasonic dispersion, stirring, evaporating, and drying to obtain a second gel product; c) sintering the second gel product obtained in step b) in an oxygen-free environment to obtain a solid electrolyte-coated ternary cathode material.

2. The preparation method according to claim 1, characterized in that In step a), The inorganic oxide electrolyte intermediate product has the structure of formula (I): Aa 3-α-2β Ab (1+α) / 3 M2O 7-β Formula (I); Wherein, Aa is an alkali metal, Ab is a lanthanide element, and M is a cationic metal; 0≤α≤1, 0<β≤1.

3. The preparation method according to claim 2, characterized in that The inorganic oxide electrolyte intermediate product is prepared according to the following method: The alkali metal salt, lanthanide metal source and cationic metal compound are mixed by a sand mill, then placed in an oven for drying, and finally ground and sintered in an air atmosphere box furnace to obtain an inorganic oxide electrolyte intermediate product having a structure of formula (I).

4. The preparation method according to claim 3, characterized in that The alkali metal salt is selected from one or more of Li salts, Na salts, and K salts; the lanthanide metal source is selected from lanthanum nitrate and / or lanthanum oxide; and the cationic metal compound is selected from one or more of niobium pentoxide, tantalum pentoxide, titanium dioxide, zirconium dioxide, hafnium dioxide, and vanadium pentoxide; The mixed grinding medium is selected from one or more of deionized water, ethanol, and N-methylpyrrolidone; The mixed grinding balls are zirconia balls with a diameter of 0.3 mm to 0.7 mm; The mixing and grinding speed is 500r / min to 2000r / min, and the grinding time is 2h to 12h; The sintering temperature is 900° C. to 1200° C., and the sintering time is 4 hours to 10 hours.

5. The preparation method according to claim 1, characterized in that The organic matter containing functional groups in step a) is selected from one or more of starch, cellulose, chitosan, polyacrylic acid, and citric acid; the amount of the organic matter containing functional groups added is 10% to 30% of the mass of the inorganic oxide electrolyte intermediate product; and the amount of water added is 5 to 20 times the amount of the organic matter containing functional groups.

6. The preparation method according to claim 1, characterized in that The process of the puffing treatment in step b) is specifically as follows: The first gel product is placed in a high-pressure puffing device, and the puffing temperature is set to 150°C to 250°C, the pressure is set to 1MPa to 5MPa, and the processing time is set to 10min to 30min to obtain a puffed product; The solvent is selected from one or more of NMP, DMF, ethanol, isopropanol and water; the amount of the solvent added is 2 to 4 times the total mass of the expanded product and the ternary positive electrode material; the ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, wherein 0.8≤x≤0.99, the median particle size D50 is 2μm to 15μm, and the added amount is 1 to 5 times the mass of the expanded product.

7. The preparation method according to claim 1, characterized in that The oxygen-free environment in step c) is controlled by introducing nitrogen or argon at a flow rate of 50 mL / min to 100 mL / min; The sintering process is specifically as follows: The temperature is raised to 400°C to 600°C at a heating rate of 2°C / min to 5°C / min and kept warm for 1h to 4h, and then raised to 800°C to 1000°C at a heating rate of 5°C / min to 10°C / min and kept warm for 2h to 10h to obtain a solid electrolyte coated ternary positive electrode material.

8. A solid electrolyte modified cathode material, characterized in that: include: Ternary cathode materials; An inorganic oxide electrolyte coated on the surface of the ternary cathode material; the inorganic oxide electrolyte has a structure of formula (II): Aa 3-α-β Ab (1+α) / 3 M2O 7-β X β (Formula II); Wherein, Aa is an alkali metal, Ab is a lanthanide element, M is a cationic metal, X is F; 0≤α≤1, 0<β≤1; Carbon coated on the surface of the inorganic oxide electrolyte.

9. A positive electrode sheet for a lithium-ion battery, comprising the solid electrolyte modified positive electrode material according to claim 8 or the solid electrolyte modified positive electrode material prepared by the method according to any one of claims 1 to 7.

10. A lithium ion battery, characterized in that: The invention comprises the positive electrode sheet for lithium-ion battery according to claim 9.

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