Ternary positive electrode material and preparation method thereof, positive electrode and battery

Abstract

The present application provides a ternary positive electrode material and its preparation method, positive electrode and battery, which are applied to the field of batteries. The ternary positive electrode material includes a self-supporting microcage structure, the material of the microcage structure is a high-nickel ternary material, the microcage structure has a cavity inside, and part of the cavity inside the microcage structure is filled with a conductive agent. The microcage structure has a cavity inside to accommodate the entry and exit of lithium ions. Through this structural design, the volume expansion or contraction of the high-nickel ternary material during the charge and discharge process can be effectively suppressed, the structural changes of the material can be reduced, the stability of the high-nickel ternary material can be improved, and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a ternary positive electrode material and a preparation method thereof, a positive electrode and a battery. Background Art

[0002] The rapid development of electric vehicles and energy storage technologies has placed higher demands on the energy density, cycle life, and safety performance of lithium-ion batteries. High-nickel ternary cathode materials, due to their high specific capacity, have become one of the key materials for improving battery energy density.

[0003] When using traditional high-nickel ternary positive electrode materials, lithium ions enter and leave the high-nickel ternary positive electrode materials during the charging and discharging process, causing their structure to expand and contract, which in turn causes the crystal structure of the high-nickel ternary positive electrode materials to break or distort. Each expansion and contraction will accelerate the degradation of the material, causing the battery capacity to decay and affecting the battery's cycle performance.

[0004] Therefore, how to improve the structural stability of high-nickel ternary positive electrode materials is an urgent problem to be solved. Summary of the Invention

[0005] The present application provides a ternary positive electrode material and its preparation method, a positive electrode and a battery, which are used to improve the structural expansion caused by the precipitation and dissolution of lithium ions in the high-nickel ternary material during the charging and discharging process, thereby improving the cycle performance of the battery.

[0006] In a first aspect, the present application provides a ternary positive electrode material, which includes a self-supporting microcage structure. The material of the microcage structure is a high-nickel ternary material. There is a cavity inside the microcage structure, and part of the cavity inside the microcage structure is filled with a conductive agent.

[0007] Furthermore, the microcage structure in the ternary cathode material is a single-layer structure.

[0008] Furthermore, the microcage structure in the ternary cathode material is a multilayer structure.

[0009] Furthermore, part of the cavity inside the microcage structure is filled with a conductive agent.

[0010] Furthermore, the volume of the conductive agent filled in the microcage structure accounts for less than 70% of the volume of the microcage structure.

[0011] Furthermore, the microcage structure is spherical, and the diameter of the microcage structure is 50-500 nm; and / or the thickness of the cage wall structure is 5-50 nm.

[0012] Furthermore, the surface of the microcage structure is coated with a heterojunction film of a fast ion conductor.

[0013] Furthermore, the thickness of the heterojunction film of the fast ion conductor is 5-15 nm.

[0014] Furthermore, the heterojunction film of the fast ion conductor includes Li3PO4 and LiNbO3, and the molar ratio of the Li3PO4 to the LiNbO3 is 1:1-4:1.

[0015] Furthermore, the conductive agent is one or more of carbon nanotubes, graphene, graphite, and carbon black.

[0016] Furthermore, the conductive agent is filled between adjacent microcage structures.

[0017] Furthermore, the chemical formula of the high nickel ternary material is LiNi x Co y Mn z O2, where 0.8≤x<1, 0<y<0.3, 0<z<0.3, and x + y + z = 1.

[0018] A second aspect of the present application provides a method for preparing a ternary positive electrode material, the method being used to prepare the ternary positive electrode material according to any one of the first aspects, the method comprising:

[0019] The polystyrene nanospheres are uniformly dispersed on the substrate to form a closely packed polystyrene nanosphere template;

[0020] Depositing a soluble salt solution onto the surface of the polystyrene nanosphere template to form a precursor coating layer, wherein the soluble salt solution includes nickel ions, cobalt ions, and manganese ions prepared according to a preset stoichiometric ratio;

[0021] Performing a lithiation reaction on the precursor coating layer and a lithium source to convert the precursor into a high-nickel ternary material;

[0022] removing the polystyrene nanosphere template by calcination or dissolution with an organic solvent to obtain a high-nickel ternary cathode material having a self-supporting microcage structure;

[0023] The conductive agent dispersion is impregnated into the pores of the microcage structure of the high-nickel ternary positive electrode material, and a conductive network is formed by high-temperature carbonization.

[0024] Furthermore, the preparation method further comprises:

[0025] A fast ion conductor is coated on the surface of the microcage structure by a sol-gel method to form a heterojunction film.

[0026] A third aspect of the present application provides a positive electrode, which includes the ternary positive electrode material as described in any one of the first aspects, or includes the ternary positive electrode material prepared by the preparation method described in any one of the second aspects.

[0027] A fourth aspect of the present application provides a battery, comprising the ternary positive electrode material as described in any one of the first aspects, or comprising the ternary positive electrode material prepared by the preparation method as described in any one of the second aspects.

[0028] The present application provides a ternary positive electrode material and a preparation method thereof, a positive electrode and a battery, wherein the ternary positive electrode material includes a self-supporting microcage structure, the material of the microcage structure is a high-nickel ternary material, and there is a cavity inside the microcage structure. The microcage structure has an internal cavity that can accommodate the entry and exit of lithium ions. Through this structural design, the volume expansion or contraction of the high-nickel ternary material during the charge and discharge process can be effectively suppressed, the structural changes of the material can be reduced, the stability of the high-nickel ternary material can be improved, and the cycle performance of the battery can be improved. In addition, due to the special design of the microcage structure, the area of ​​direct contact between the solid electrolyte and the high-nickel ternary material can be reduced, and the interface compatibility between the high-nickel ternary material and the solid electrolyte can be improved, thereby avoiding performance degradation caused by interface reactions. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] High-nickel ternary cathode materials are a type of cathode material used in lithium-ion batteries. They contain three metallic elements: nickel (Ni), cobalt (Co), and manganese (Mn), with a high nickel content, typically exceeding 60%.

[0031] Nickel has a high specific capacity and can store more lithium ions, thus providing a higher energy density. Therefore, high-nickel ternary materials offer higher energy density than traditional materials and are particularly suitable for applications that require long-term operation and large-capacity energy storage, such as electric vehicles and large-scale energy storage systems. However, during the charge and discharge process, as lithium ions precipitate and dissolve on the surface of the high-nickel ternary cathode material, the material structure expands and contracts, which may cause the crystal structure of the high-nickel ternary cathode material to break or distort. Each expansion and contraction accelerates the degradation of the material, leading to capacity decay and affecting the battery's cycle performance.

[0032] In response to the above issues, this application prepares a high-nickel ternary material into a self-supporting microcage structure with an internal space that can accommodate the entry and exit of lithium ions. This structure can effectively suppress the volume expansion or contraction of the high-nickel ternary material during the charge and discharge process, reduce the structural changes of the material, improve the stability of the high-nickel ternary material, and thus enhance the cycle performance of the battery.

[0033] Based on this, the first aspect of the present application provides a ternary positive electrode material, which includes a self-supporting microcage structure. The material of the microcage structure is a high-nickel ternary material. There is a cavity inside the microcage structure, and part of the cavity inside the microcage structure is filled with a conductive agent.

[0034] Among them, the chemical formula of the high nickel ternary material is LiNi x Co y Mn z O2, where 0.8≤x<1, 0<y<0.3, 0<z<0.3, and x + y + z = 1.

[0035] The high-nickel ternary material of this embodiment adopts a self-supporting design of a microcage structure, which includes a cavity structure inside. The cavity structure can accommodate more lithium ions in and out during the charge and discharge process, reduce the volume expansion problem of the electrode material, and further enhance the stability of the material. Due to the special design of the microcage structure, the area of ​​direct contact between the solid electrolyte and the high-nickel ternary material can be reduced, and the interface compatibility can be improved, thereby avoiding performance degradation caused by interface reactions. Filling the conductive agent can improve the electron transmission capacity inside the microcage, reduce the internal resistance, and improve the charge and discharge rate of the material.

[0036] In some embodiments, the microcage structure is a circular microcage structure, or a nearly circular microcage structure.

[0037] In some embodiments, the microcage structure is a rectangular microcage structure, or a nearly rectangular microcage structure.

[0038] In some embodiments, the microcage structure in the ternary cathode material is a single-layer structure.

[0039] The single-layer structure means that there is only one layer of microcage structure in the ternary positive electrode material. Lithium ions can enter and exit the microcage structure of the high-nickel ternary material relatively freely. The lithium ion transmission path is short, and it can quickly respond to the entry and exit of ions during the charging and discharging process, thereby optimizing the ion transmission path.

[0040] In some embodiments, the microcage structure in the ternary cathode material is a multilayer structure.

[0041] "Multi-layered" microcage structures refer to stacked microcage structures. Specifically, the microcage structures may be 2, 3, 4, 5, or 10 layers. The sizes of the microcage structures in different layers may be the same or different. For example, a ternary cathode material may include two consecutively arranged microcage structures, which are stacked together. Another example may include a ternary cathode material including three consecutively arranged microcage structures, which are stacked together.

[0042] The multi-layer structure can effectively disperse the stress generated during the charging and discharging process, avoiding the problem of cracking or falling off caused by insufficient dispersed stress in a single-layer structure, but its lithium ion transmission path is longer than that of a single-layer structure.

[0043] In some embodiments, the volume of the conductive agent filled in the microcage structure accounts for 0%-70% of the volume of the microcage structure.

[0044] In this embodiment, space must be reserved within the microcage structure for lithium ion precipitation. Therefore, the conductive agent cannot completely fill the microcage structure. For example, the volume of the conductive agent can account for 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70% of the volume of the microcage structure, or a range consisting of any two of these values.

[0045] When the volume of the conductive agent accounts for 0% of the volume of the microcage structure, it means that the microcage structure is not filled with conductive agent. The microcage structure itself has sufficient conductivity and needs to retain as much space as possible for lithium ions to ensure efficient lithium ion migration.

[0046] The proportion of conductive filler should be adjusted according to the actual application requirements. Lower proportions (e.g., 0%-30%) are suitable for applications requiring a higher volume of lithium ion migration, while higher proportions (e.g., 40%-70%) are suitable for applications with higher conductivity requirements. However, care should be taken not to compromise the available space within the microcage for lithium ion precipitation. The volume of lithium ion precipitation can be calculated based on the battery's capacity and the amount of material required to participate in the lithium ion precipitation. Ensure that the space reserved within the microcage structure is larger than the volume of lithium ion precipitation.

[0047] In some embodiments, the microcage structure is spherical, and the inner diameter of the microcage structure is 50-500 nm. Exemplarily, the inner diameter of the microcage structure is 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or a range consisting of any two of the above values.

[0048] In some embodiments, the thickness of the cage wall structure is 5-50 nm. Exemplarily, the thickness of the microcage structure is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 50 nm, or a range consisting of any two of the above values.

[0049] In some embodiments, the surface of the microcage structure is coated with a heterojunction thin film of a fast ion conductor.

[0050] Heterojunction film refers to a thin film structure composed of two or more different fast ion conductor materials. The fast ion conductor heterojunction film can reduce the interfacial impedance between the ternary material and the electrolyte, improve the interface compatibility, and improve the charge and discharge efficiency of the battery by providing a more uniform and efficient conductive interface. A layer of fast ion conductor heterojunction film is coated on the surface of the microcage structure, which can effectively avoid direct contact between the high-nickel ternary material and the solid electrolyte, thereby avoiding incompatibility or reaction between the electrolyte and the positive electrode material. In addition, the coating of the fast ion conductor heterojunction film can further optimize the ionic conductivity, ensure that lithium ions can move efficiently and stably in the positive electrode material, and improve the safety of the battery.

[0051] Fast ion conductors can be selected from the following material combinations: Li3PO4 / LiNbO3, Li3BO4 / Li3PO4, Li2B4O7 / Li3PO4, Li3BO3 / LiNbO3, Li2B4O7 / LiNbO3, Li4Ti5O 12 / LiNbO3、Li 1.5 Al 0.5 Ti 1.5 (PO4)3 / Li3PO4, LiLaTiO3 / Li3PO4, Li7La3Zr2O 12 / LiNbO3, Li2O / TiO2, Li2S / P2S5, or a combination of the above materials.

[0052] In a specific implementation, the heterojunction film of the fast ion conductor includes Li3PO4 and LiNbO3, and the molar ratio of Li3PO4 to LiNbO3 is 1:1-4:1.

[0053] Lithium phosphate (Li3PO4) is a commonly used lithium-ion conductor with high chemical stability and a low ion migration barrier, making it suitable as an electrolyte material. LiNbO3's main advantage is its ability to form a relatively stable charge transfer path. Heterojunction films of Li3PO4 and LiNbO3 combine the advantages of both, providing a more efficient ion conduction path between the microcage structure and the electrolyte.

[0054] The interface structure formed by Li3PO4 and LiNbO3 materials can reduce interfacial impedance and reduce electrochemical reaction losses between the electrolyte and electrode materials. The combination of Li3PO4 and LiNbO3 can help increase the migration rate of lithium ions in the battery by forming an excellent conductive network, allowing the battery to more efficiently transport ions during the charge and discharge process.

[0055] For example, the molar ratio of Li3PO4 to LiNbO3 can be 1:1, 2:1, 3:1, 4:1, or a range consisting of any two of the above ratios.

[0056] In some embodiments, the thickness of the fast ion conductor heterojunction film is 5-15 nm, for example, 5 nm, 7 nm, 9 nm, 10 nm, 11 nm, 13 nm, 14 nm, 15 nm, or a range consisting of any two of the above values.

[0057] In some embodiments, the conductive agent filled in the microcage structure is one or more of carbon nanotubes, graphene, graphite, carbon black, carbon fiber, conductive polymer (polyaniline, polypyrrole, polythiophene), and metal nanomaterials.

[0058] In some embodiments, a conductive agent is also filled between adjacent microcage structures.

[0059] Conductive agents between microcages can improve interfacial connectivity and reduce interfacial impedance. Filling the spaces between microcages optimizes current conduction between adjacent microcages, improving overall battery or capacitor performance, particularly during charge and discharge, enabling more efficient charge transfer. The conductive agents between microcages can also help enhance physical contact and stability between the microcages, particularly during multiple charge and discharge cycles, preventing separation or damage between the microcages due to expansion and contraction or thermal stress, thereby improving the mechanical stability of the material.

[0060] In addition, the filling of conductive agent helps to reduce the internal resistance of the material, especially when a conductive network is formed between adjacent microcages, which can significantly reduce the internal resistance of the battery.

[0061] A second aspect of the present application provides a method for preparing a ternary positive electrode material, the method being used to prepare any of the above-mentioned ternary positive electrode materials, the method comprising:

[0062] Step 1: Evenly disperse polystyrene nanospheres on a substrate to form a tightly packed polystyrene nanosphere template.

[0063] A polystyrene (PS) nanosphere template is a template that disperses PS nanospheres on a substrate to create a regularly arranged nanostructure. The PS nanospheres can be evenly dispersed on the substrate through self-assembly or spin coating, and then photolithography or other microfabrication methods can be used to form a single or multi-layered PS nanosphere structure.

[0064] In one implementation, a PS nanosphere template is prepared by spin coating, and the PS nanospheres are evenly distributed on the substrate surface. Specifically, polystyrene nanospheres of appropriate size are selected, which can be purchased commercially or synthesized by polymerization. The substrate is then surface treated, for example, using plasma treatment (such as oxygen plasma) to clean the substrate and enhance its hydrophilicity. The polystyrene nanospheres are dissolved in a suitable solvent (such as water or an organic solvent), and the solution is evenly coated on the substrate surface. A certain amount of the PS nanosphere solution is dropwise added to the substrate, and the substrate is then rotated at high speed. During the spin coating process, the PS nanospheres are evenly dispersed on the substrate surface due to centrifugal force, ultimately forming a single or multi-layer nanosphere array. Multiple layers of PS nanospheres are then stacked by repeated spin coating or alternating dipping. To improve the stability of the PS nanosphere template, the substrate can be lightly heat treated to help the PS nanospheres adhere better to the substrate surface.

[0065] In one implementation, the dispersion and arrangement of PS nanospheres on a substrate surface can be controlled through self-assembly. Specifically, the PS nanospheres are dispersed in a suitable solvent, and the substrate is surface-modified, such as with oxygen plasma treatment or silanization, to enhance its hydrophilicity or selectivity, allowing for uniform nanosphere adhesion. The PS nanosphere solution is then dropwise added to the substrate. Through solvent evaporation or diffusion, the PS nanospheres naturally self-assemble into an ordered structure on the substrate surface. By adjusting parameters such as solution concentration and evaporation rate, a more compact and ordered nanosphere array can be obtained.

[0066] In one implementation, polystyrene (PS) nanospheres are dispersed in water. A surfactant is added to the water to help disperse the PS nanospheres on the water surface and prevent them from aggregating. Surfactant molecules typically adhere to the surface of the nanospheres, stabilizing their presence on the water surface. A solution containing PS nanospheres is then dripped onto the water surface. On the water surface, the PS nanospheres naturally self-assemble into an ordered monolayer or multilayer structure through the surfactant's assistance. Due to the interaction between the nanospheres, they spontaneously organize into a tightly packed array. Once the PS nanospheres have self-assembled into an ordered array on the water surface, a substrate (such as a silicon wafer or glass) is immersed in water, whereupon the nanosphere array adheres to the substrate's surface. By slowly lifting the substrate, the PS nanosphere array is transferred from the water surface to the substrate surface. After transfer, the water is removed by drying, and the nanosphere array is firmly fixed to the substrate, forming a stable polystyrene template.

[0067] Step 2: depositing a soluble salt solution onto the surface of the polystyrene nanosphere template to form a precursor coating layer, wherein the soluble salt solution includes nickel ions, cobalt ions, and manganese ions prepared according to a preset stoichiometric ratio.

[0068] In this step, soluble salts of metals (such as nitrates and chlorides) such as nickel, cobalt, and manganese are prepared in stoichiometric proportions to form a mixed solution. This solution contains the required metal components for the ternary material. Chemical bath deposition or atomic layer deposition can be used to uniformly deposit the metal precursors on the surface of the PS nanospheres.

[0069] In one implementation, metal ions are deposited by chemical bath deposition. Specifically, a prepared precursor solution is soaked or sprayed onto the surface of the PS nanospheres, and a chemical reaction in the solution deposits the metal precursor on the template surface, forming a uniform metal coating.

[0070] In one implementation, metal ions are deposited by atomic layer deposition. Specifically, by precisely controlling the gas reaction, a precursor is deposited onto the template surface to form a thin and uniform metal film.

[0071] Step 3: Lithium-reacting the precursor coating layer with a lithium source to convert the precursor into a high-nickel ternary material. The chemical formula of the high-nickel ternary material is LiNi x Co y Mn z O2, 0.8≤x<1, 0<y<0.3, 0<z<0.3, and x + y +z = 1.

[0072] The PS template with the metal precursor deposited on it is mixed with a lithium source (such as lithium carbonate, lithium hydroxide, etc.). The lithium source reacts with the precursor at high temperature to form lithium nickel cobalt manganese oxide (LiNi xCo y Mn z O2), that is, high nickel ternary material.

[0073] The lithium source and the precursor undergo a thermal reaction at above 800°C to complete the conversion of the precursor into a high-nickel ternary material.

[0074] Step 4: Remove the polystyrene nanosphere template by calcination or organic solvent dissolution to obtain a high-nickel ternary positive electrode material with a self-supporting microcage structure.

[0075] In one implementation, the polystyrene nanosphere template is heated to a relatively high temperature (between 500°C and 700°C), and the PS nanospheres are burned at the high temperature, leaving behind an oxide with a microcage structure.

[0076] In one implementation, a solvent (such as dichloromethane) is used to dissolve the PS nanospheres, leaving behind a microcage structure of nickel cobalt manganese oxide.

[0077] By removing the PS template, a self-supporting microcage structure with a hollow interior is obtained, which provides a high specific surface area and good porosity.

[0078] Through the above steps, a high-nickel ternary all-solid-state cathode material with a self-supporting microcage structure can be prepared. The microcage structure has a hollow space inside. During charging, lithium ions can be precipitated inside the microcage structure, avoiding damage caused by structural expansion. The microcage structure can be filled with a conductive agent, and the space between the microcages can be filled with a conductive agent.

[0079] After the above step 4, in some embodiments, in order to improve the conductivity and stability of the ternary positive electrode material, the following step 5 is also required.

[0080] Step 5: Impregnate the conductive agent dispersion into the pores of the microcage structure of the high-nickel ternary positive electrode material, and form a conductive network through high-temperature carbonization.

[0081] Under an inert atmosphere (such as nitrogen or argon), a conductive agent dispersion is impregnated into the microcage structure. The conductive agent disperses between the microcages and within the microcages. The microcage structure, impregnated with the conductive agent, is heated to a high temperature (between 800°C and 1000°C) to carbonize the conductive agent within the microcage pores, forming a stable conductive network. This creates a highly efficient conductive network, enhancing the conductivity of the microcage structure and improving the overall performance of the battery or capacitor.

[0082] The conductive agent may be one or more of carbon nanotubes, graphene, graphite, and carbon black.

[0083] To control the volume of the conductive agent within the microcage structure, the total amount of dispersant can be controlled. The amount of dispersant directly determines the amount of conductive agent filling the microcage structure. By controlling the total amount of dispersant, the filling rate of the conductive agent within the microcage structure can be precisely controlled.

[0084] The total amount of dispersant filled can be controlled by any of the following methods:

[0085] 1. Controlling the dispersant concentration. The dispersant is a dissolving medium for the conductive agent and is typically a liquid (such as water, alcohol, or other solvent). During impregnation, the concentration of the conductive agent in the solution can be adjusted. A low concentration of the dispersant results in less conductive agent being incorporated into the microcage structure, while a high concentration may result in overfilling.

[0086] 2. Control of immersion time: In addition to controlling the amount of dispersed material, immersion time also affects the adsorption of the conductive agent. A shorter immersion time may result in insufficient filling of the microcage pores by the conductive agent, while a longer immersion time may result in an excess of conductive agent.

[0087] 3. Solution volume control: During the dispersion impregnation process, if too much solution is used, the conductive agent may penetrate the outside of the microcage or even overflow, affecting its volume share. By controlling the volume of the dispersion, the amount of conductive agent filling the microcage can be limited.

[0088] In addition to regulating the total amount of dispersant, the proportion of conductive agent filled inside the microcage structure can also be controlled by adjusting the particle size of the conductive agent. The pores on the wall of the microcage structure are of a certain size. Conductive agents with smaller particle sizes can better penetrate into the pores of the microcage, thereby filling the microcage structure. Larger particle sizes may not be able to be effectively filled due to pore limitations. Therefore, a variety of conductive materials are mixed in the filled conductive agent, and the particle sizes of the various conductive materials are different. The conductive agent with a smaller particle size is used to fill the microcage structure, and the conductive agent with a larger particle size can only be filled between two microcage structures, or cannot be filled. In this way, by controlling the amount of conductive agent with a smaller particle size filled, the volume of the conductive agent inside the microcage structure is controlled.

[0089] In some embodiments, the volume of the conductive agent filled in the microcage structure accounts for 0%-60% of the volume of the microcage structure.

[0090] Optionally, in order to further improve the interface compatibility between the solid electrolyte and the high-nickel ternary material and reduce the interface resistance, step 6 is further included after the above step 4 or step 5.

[0091] Step 6: coating the surface of the microcage structure with a fast ion conductor by a sol-gel method to form a heterojunction film.

[0092] Depending on the desired fast ion conductor (e.g., Li₃PO₄ / LiNbO₃), the corresponding metal salt or metal-organic compound is selected as a precursor. For example, the precursors for Li₃PO₄ can be lithium dihydrogen phosphate (LiH₂PO₄) and lithium chloride (LiCl); the precursors for LiNbO₃ can be lithium chloride (LiCl) and niobium chloride (NbCl₅). The selected precursors are dissolved in a solvent (typically an alcohol such as isopropyl alcohol or ethanol) or water to prepare a sol. An appropriate amount of stabilizer (such as an alcohol surfactant or acidic solution) is added to maintain the stability of the sol and prevent precursor aggregation or precipitation. The sol concentration is adjusted based on the final film thickness and desired conductive properties. A low sol concentration may result in a thin film, while a high concentration may cause precipitation. The sol is evenly coated on the surface of the microcages. Common coating methods include dipping, spin coating, and drop coating. The coated microcages are dried at 50-100°C to remove the solvent and transform the sol from a liquid into a solid gel. During the drying process, the sol gradually transforms into a gel, forming a thin film. To stabilize the film and improve its conductivity, the dried gel is heat-treated (sintered) to help form a crystalline structure and remove organic residues. During sintering, the film further densifies, forming a heterojunction film with higher conductivity. The sintering temperature varies depending on the fast ion conductor material selected. For example, the sintering temperature for Li3PO3 / LiNbO3 can be selected between 700-1000°C.

[0093] Through the above step 6, a uniform heterojunction film can be effectively formed on the surface of the microcage structure, providing good conductivity and stability, and effectively isolating the high-nickel ternary material and the solid electrolyte.

[0094] In a third aspect, the present application provides a positive electrode comprising any of the ternary positive electrode materials described in the first aspect, or comprising a ternary positive electrode material prepared by any of the preparation methods described in the second aspect. Regarding the preparation of a positive electrode sheet, the ternary positive electrode material can be prepared on the surface of an aluminum foil current collector to obtain a positive electrode sheet. Alternatively, the prepared ternary positive electrode material can be transferred to the aluminum foil current collector to form a positive electrode sheet.

[0095] In a fourth aspect, the present application provides a battery comprising any of the ternary positive electrode materials described in the first aspect, or comprising a ternary positive electrode material prepared by any of the preparation methods described in the second aspect. In the preparation method of the positive electrode sheet, a positive electrode sheet comprising the positive electrode material, a solid electrolyte, and a negative electrode sheet comprising the negative electrode material are assembled into an all-solid-state lithium-ion battery.

[0096] The present invention is further described below through specific examples.

[0097] Example 1

[0098] 1. Template preparation: A PS nanosphere template with a diameter of 300 nm was prepared by the sol-gel method. The PS nanospheres were dispersed on a glass substrate and a uniform multilayer PS nanosphere template was formed by spin coating.

[0099] 2. Precursor deposition: nickel sulfate, cobalt sulfate and manganese sulfate are prepared according to LiNi 0.85 Co 0.1 Mn 0.05 The mixed solution was prepared with a stoichiometric ratio of O2, and the mixed solution was deposited on the surface of the PS nanosphere template at 80°C using the atomic layer deposition method. The deposition cycle was 50 cycles to form a precursor coating layer with a thickness of about 40 nanometers.

[0100] 3. Lithiation treatment: The template with the deposited precursor is mixed with lithium hydroxide in a molar ratio of 1:1.3, and calcined at 850°C for 8 hours in an oxygen atmosphere to convert the precursor into the high-nickel ternary material LiNi 0.85 Co 0.1 Mn 0.05 O2.

[0101] 4. Template removal: The lithiated sample was immersed in a toluene solution for 24 hours to remove the PS nanosphere template and obtain a self-supporting microcage structured high-nickel ternary all-solid-state cathode material.

[0102] Example 2

[0103] The difference from Example 1 is that a single-layer PS nanosphere template is prepared by spin coating.

[0104] Example 3

[0105] 1. Template preparation: PS nanospheres with a diameter of 200 nm were dispersed on a silicon wafer substrate and a densely packed monolayer PS nanosphere template was formed by centrifugation and self-assembly.

[0106] 2. Precursor deposition: Nickel nitrate, cobalt nitrate and manganese nitrate are prepared according to the LiNi 0.85 Co 0.1 Mn 0.05 The mixed solution was prepared in a stoichiometric ratio of O2, and the mixed solution was deposited on the surface of the PS nanosphere template at 50°C using a chemical bath deposition method for 2 hours to form a precursor coating layer with a thickness of about 30 nanometers.

[0107] 3. Lithiation treatment: The template with the deposited precursor is mixed with lithium carbonate in a molar ratio of 1:1.2, and calcined at 800°C for 10 hours in an oxygen atmosphere to convert the precursor into the high-nickel ternary material LiNi 0.85 Co 0.1 Mn 0.05O2.

[0108] 4. Template removal: The lithiated sample was calcined at 500°C for 2 hours to remove the PS nanosphere template and obtain a self-supporting microcage structured high-nickel ternary all-solid-state cathode material.

[0109] 5. Composite conductive network: In an inert atmosphere, impregnate the carbon nanotube / graphene dispersion into the microcage pores with a conductive agent impregnation amount of 2wt%, carbonize at 800℃, and calcine for 2 hours.

[0110] A self-supporting microcage structure high-nickel ternary all-solid-state positive electrode material is obtained by the above method, and the volume of the conductive agent impregnated into the microcage structure accounts for 30% of the volume of the microcage structure.

[0111] Example 4

[0112] The difference from Example 3 is that the volume of the conductive agent impregnated into the microcage structure accounts for 10% of the volume of the microcage structure.

[0113] Example 5

[0114] The difference from Example 3 is that the volume of the conductive agent impregnated into the microcage structure accounts for 50% of the volume of the microcage structure.

[0115] Example 6

[0116] The difference from Example 3 is that the volume of the conductive agent impregnated into the microcage structure accounts for 70% of the volume of the microcage structure.

[0117] Example 7

[0118] The difference from Example 3 is that after the composite conductive network is formed, a Li3PO4 / LiNbO3 fast ion conductor heterojunction film is coated on the surface of the microcage by a sol-gel method. The coated Li3PO4 / LiNbO3 (molar ratio 3:1) has a thickness of 10 nm.

[0119] Comparative Example 1

[0120] The high nickel ternary cathode material LiNi was prepared by traditional co-precipitation method. 0.85 Co 0.1 Mn 0.05O2, does not have a self-supporting microcage structure. Nickel chloride, cobalt chloride, and manganese chloride are dissolved in deionized water in a certain molar ratio (Ni:Co:Mn = 0.85:0.1:0.05) and stirred until completely dissolved to form a metal salt solution. In another container, lithium hydroxide (LiOH) is dissolved in deionized water to form a lithium hydroxide solution. The metal salt solution and lithium hydroxide solution are mixed and stirred continuously. Ammonia water is slowly added to the mixed solution to control the pH value between 8-11. Metal hydroxide precursors (Ni(OH)2, Co(OH)2, Mn(OH)2) are generated. The precipitate is filtered through filter paper to remove impurities in the solution, and then the precipitate is repeatedly washed with deionized water to remove ions dissolved in the precipitate, such as chloride ions, ammonia ions, etc., until the pH value of the washing solution is close to neutral. The dried precursor is calcined at high temperature in a tube furnace. Calcination in an oxygen atmosphere at a calcination temperature of 700°C forms an oxide structure (LiNi 0.85 Co 0.1 Mn 0.05 O2). Take out the cooled product and crush it into the required particle size using a grinder or ball mill.

[0121] Comparative Example 2

[0122] The difference from Example 3 is that the volume of the conductive agent impregnated into the microcage structure accounts for 85% of the volume of the microcage structure.

[0123] Comparative Example 3

[0124] The difference from Example 3 is that the volume of the conductive agent impregnated into the microcage structure accounts for 99% of the volume of the microcage structure.

[0125] Test Case

[0126] Charge and discharge test

[0127] The positive electrode material prepared above is assembled with a sulfide solid electrolyte and a silicon-based negative electrode material into an all-solid-state lithium-ion battery, and charge and discharge tests are carried out at room temperature. Use a battery tester to set the appropriate charge and discharge current and charge voltage range. Usually, the upper limit of battery charge is 4.2V and the lower limit of discharge is 2.5V. Charge at a certain current (such as 0.1C) until the battery voltage reaches the upper limit of 4.2V. After full charge, a discharge test is carried out until the battery voltage drops to the lower limit of 2.5V. During discharge, the tester records the discharge curve and current of the battery. Based on the discharge current and discharge time of the battery, the total capacity during the discharge process is calculated, and the specific capacity (mAh / g) between the discharge capacity and the mass of the click material is calculated.

[0128] Perform multiple charge and discharge cycles. The charge and discharge conditions (current, time, upper and lower voltage limits) should be consistent each time. After each charge and discharge cycle, record the discharge capacity and calculate the capacity retention rate.

[0129] Porosity test

[0130] First, prepare a sample of the electrode material to be tested. Measure the total volume of the sample using a density meter or a gas adsorption method (e.g., the BET method). Determine the sample's porosity using techniques such as gas adsorption / desorption or mercury permeation.

[0131] The first discharge specific capacity and capacity retention rate data of the above examples and comparative examples are detailed in Table 1.

[0132] Table 1 Charge and discharge test data

[0133]

[0134] According to the above data, the first discharge specific capacity of Example 1 reaches 190mAh / g, and after 100 cycles, the capacity retention rate is 82%. For the traditional high-nickel ternary material in Comparative Example 1, the first discharge specific capacity is 180mAh / g, and after 100 cycles, the capacity retention rate is 70%. Compared with the traditional high-nickel ternary material, the first discharge specific capacity of Example 1 is improved, and the capacity cycle retention rate is improved by 12%. Through the above comparison, it is proved that the design of the microcage structure can effectively suppress the volume expansion or contraction of the high-nickel ternary material during the charge and discharge process, reduce the structural changes of the material, improve the stability of the high-nickel ternary material, and thus improve the cycle performance of the battery.

[0135] By comparing Example 1 and Example 2, the data proves that the design of the single-layer microcage structure can improve the discharge specific capacity and capacity retention rate relative to the multi-layer structure.

[0136] By comparing Example 3 with Example 7, the data proves that adding a fast ion conductor heterojunction film can increase the stability of the high-nickel ternary material, thereby improving the cycle performance of the battery.

[0137] Through the data of Examples 2 to 6, as well as Comparative Examples 2 and 3, it is proved that after the proportion of the conductive agent inside the microcage structure exceeds 70%, the improvement effect decreases. Because the internal space is insufficient, lithium ions will be precipitated outside, causing volume changes, resulting in structural instability of the high-nickel ternary material, and reducing the capacity cycle retention rate.

[0138] In addition, the battery interface resistance of Example 7 is less than 30Ω·cm², no binder is used, the electrode porosity is greater than 40%, and the lithium ion transmission rate is increased by 50% compared with Example 2. At a rate of 0.1C, the first discharge specific capacity is as high as 230mAh / g. After 200 cycles, the capacity retention rate is 96%.

[0139] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein, and various modifications and variations may be made without departing from the scope of the present invention. The scope of the present invention is limited solely by the appended claims.

Claims

1. A ternary cathode material, characterized in that: The ternary positive electrode material includes a self-supporting microcage structure, the material of the microcage structure is a high-nickel ternary material, the microcage structure has a cavity inside, and part of the cavity inside the microcage structure is filled with a conductive agent; the diameter of the microcage structure is 50-500nm, and / or the cage wall thickness of the microcage structure is 5-50nm; The volume of the conductive agent filled in the microcage structure accounts for less than 70% of the volume of the microcage structure; The surface of the microcage structure is coated with a fast ion conductor heterojunction film; the fast ion conductor heterojunction film includes Li3PO4 and LiNbO3, and the molar ratio of the Li3PO4 to the LiNbO3 is 1:1-4:

1.

2. The ternary cathode material according to claim 1, characterized in that The microcage structure in the ternary positive electrode material is a single-layer structure.

3. The ternary cathode material according to claim 1, characterized in that The microcage structure in the ternary positive electrode material is a multilayer structure.

4. The ternary cathode material according to any one of claims 1 to 3, characterized in that: The microcage structure is spherical.

5. The ternary cathode material according to claim 1, characterized in that The thickness of the heterojunction film of the fast ion conductor is 5-15 nm.

6. The ternary cathode material according to any one of claims 1 to 3, characterized in that: The conductive agent is one or more of carbon nanotubes, graphene, graphite, and carbon black.

7. The ternary cathode material according to any one of claims 1 to 3, characterized in that: The conductive agent is filled between adjacent microcage structures.

8. The ternary cathode material according to any one of claims 1 to 3, characterized in that: The chemical formula of the high nickel ternary material is LiNi x Co y Mn z O2, where 0.8≤x<1, 0<y<0.3, 0<z<0.3, and x + y + z = 1.

9. A method for preparing a ternary cathode material, characterized in that: The preparation method is used to prepare the ternary positive electrode material according to any one of claims 1 to 8, and the preparation method comprises: The polystyrene nanospheres are uniformly dispersed on the substrate to form a closely packed polystyrene nanosphere template; Depositing a soluble salt solution onto the surface of the polystyrene nanosphere template to form a precursor coating layer, wherein the soluble salt solution includes nickel ions, cobalt ions, and manganese ions prepared according to a preset stoichiometric ratio; Performing a lithiation reaction on the precursor coating layer and a lithium source to convert the precursor into a high-nickel ternary material; removing the polystyrene nanosphere template by calcination or dissolution with an organic solvent to obtain a high-nickel ternary cathode material having a self-supporting microcage structure; The conductive agent dispersion is impregnated into the pores of the microcage structure of the high-nickel ternary positive electrode material, and a conductive network is formed by high-temperature carbonization.

10. The preparation method according to claim 9, characterized in that The preparation method further comprises: A fast ion conductor is coated on the surface of the microcage structure by a sol-gel method to form a heterojunction film.

11. A positive electrode, characterized in that The positive electrode comprises the ternary positive electrode material according to any one of claims 1 to 8, or comprises the ternary positive electrode material prepared by the preparation method according to claim 9 or 10.

12. A battery, characterized in that: The invention comprises the ternary positive electrode material according to any one of claims 1 to 8, or comprises the ternary positive electrode material prepared by the preparation method according to claim 9 or 10.

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