Modified ternary positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a modified ternary positive electrode material and a preparation method and application thereof, Nb is doped into the ternary positive electrode material to serve as a ternary positive electrode material substrate, and the surface of the ternary positive electrode material substrate doped with Nb is sequentially coated with a niobium fluoride coating layer and a polymethacrylate coating layer. Therefore, the purpose of further modifying the ternary positive electrode material is achieved. The Nb-doped ternary positive electrode material is used as a substrate, so that lattice distortion is reduced, side reactions on the surface of the material are inhibited, and the rate capability and the cycling stability of the material are improved; due to the existence of the sequentially constructed coating layers, the direct contact between the positive electrode material and the solid electrolyte can be effectively blocked, the generation of interface side reaction is inhibited, the stability and dynamic performance of the battery under high voltage are improved, and the energy loss is reduced. Under the synergistic effect of the structures, the cycle performance, the rate capability and the safety of the modified ternary positive electrode material are improved, and the development of a high-performance all-solid-state lithium ion battery is promoted.

Description

Technical Field

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

[0002] In recent years, with the surge in demand for new energy vehicles, the demand for lithium batteries has also exploded. However, traditional liquid lithium batteries have significant shortcomings in terms of safety and cycle life, especially the risk of thermal runaway that may be caused by high energy density batteries during use, as well as the volatilization and leakage of liquid electrolytes inside the battery, which seriously restrict the popularization and promotion of liquid lithium batteries in high-end application fields such as new energy vehicles.

[0003] In response to the above challenges, solid-state lithium batteries have gradually emerged due to their unique performance advantages and have become a new hot spot in the research and development of the battery industry. Solid-state lithium batteries use solid electrolytes instead of liquid electrolytes, which fundamentally solves the stability and safety issues of liquid electrolytes. At the same time, solid electrolytes also show higher ionic conductivity, better thermal stability and better mechanical properties, which can effectively improve the power density and energy density of the battery, extend the cycle life of the battery, and achieve stable operation of the battery under extreme conditions. Among them, sulfide electrolytes are regarded as strong competitors for the next generation of solid electrolytes due to their excellent properties, such as high ionic conductivity, good thermal stability and mechanical properties, and have attracted the attention of many researchers and companies.

[0004] However, the interface problem between the sulfide electrolyte and the cathode material has always plagued the performance improvement of solid-state batteries. During the battery charging and discharging process, the element interdiffusion between the cathode material and the sulfide electrolyte, the formation of the space charge layer, and the interfacial electrochemical side reactions will put pressure on the structural stability of the cathode material, thereby affecting the overall performance of the battery. Especially in high-nickel ternary (NCM) materials, these problems are more prominent due to the increase in Ni content, resulting in a decrease in the battery's cycle performance and energy density at high rates.

[0005] Traditional polycrystalline ternary cathode materials are composed of submicron primary grains randomly oriented and combined. This structure leads to Li + The diffusion path is complex and the Li concentration is unevenly distributed inside the particles, which causes the concentration of stress and strain, and eventually forms cracks at the grain boundaries, seriously affecting the structural integrity of the material and the electrochemical performance of the battery. During the long-term redox process of the all-solid-state battery, the surface side reactions caused by the volume change of the positive electrode material, material cracks, and contact loss with the electrolyte will lead to the destruction of the battery structure and a sharp decline in electrochemical performance.

[0006] In recent years, single-crystal ternary materials have shown great potential in solving the defects of traditional secondary granular materials due to their more complete structure, smaller surface area and elimination of grain boundaries between particles. These characteristics of single-crystal materials can effectively inhibit Li + The uneven diffusion at the grain boundaries reduces the stress and strain inside the battery, thereby improving the battery's cycle stability and rate performance.

[0007] Improving the cycle stability and rate performance of high-nickel ternary cathode materials, improving the interface between cathode materials and solid electrolytes, and developing high-energy-density solid-state batteries are urgent issues to be solved in the current development of solid-state batteries. To this end, the present invention is proposed. Summary of the invention

[0008] The main purpose of the present invention is to provide a modified ternary positive electrode material and its preparation method and application, so as to solve the surface side reaction problems, interface problems and Ni 2+ dissolution problems, etc., so as to achieve the goal of comprehensively improving the cycle performance, rate performance and safety of the positive electrode materials in solid-state batteries, so as to meet the development needs of high energy density solid-state batteries.

[0009] The present invention provides a modified ternary positive electrode material, which comprises: a Nb-doped ternary positive electrode material substrate, a niobium fluoride coating layer and a polymethacrylate coating layer; the niobium fluoride coating layer is coated on the surface of the Nb-doped ternary positive electrode material substrate, and the polymethacrylate coating layer is coated on the surface of the niobium fluoride coating layer.

[0010] Furthermore, in the modified ternary cathode material, the molecular formula of the Nb-doped ternary cathode material substrate is LiNi x Co y Mn (1-x-y) Nb m O2, wherein 0.01≤m≤0.03, 0.9≤x≤0.95, 0.05≤y≤0.1, and x+y<1; preferably, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is (0.001~0.05):1; preferably, the weight ratio of the polymethacrylate coating layer to the niobium fluoride-coated Nb-doped ternary positive electrode material is (0.001~0.03):1.

[0011] Furthermore, the particle size of the modified ternary positive electrode material is 1.6 to 1.8 μm; preferably, the polymethacrylate is one or more of polymethyl methacrylate, polyethyl methacrylate and polypropyl methacrylate.

[0012] According to another aspect of the present invention, a preparation method of the above-mentioned modified ternary positive electrode material is also provided, and the preparation method comprises the following steps: mixing a ternary precursor material, a lithium source and a niobium source to obtain a first mixed material; subjecting the first mixed material to a first calcination to obtain a Nb-doped ternary positive electrode material substrate; mixing the Nb-doped ternary positive electrode material substrate with niobium fluoride to obtain a second mixed material; subjecting the second mixed material to a second calcination to a first coating to obtain a modified ternary positive electrode material A; mixing the modified ternary positive electrode material A, polymethacrylate and an organic solvent to obtain a third mixed material; separating and drying the third mixed material, and then subjecting the third mixed material to a heat treatment to a second coating to obtain a modified ternary positive electrode material.

[0013] Furthermore, the first calcination includes: firstly performing a first stage calcination at 500-650°C, and then performing a second stage calcination at 750-820°C; preferably, the first stage calcination time is 4-7 hours, and the second stage calcination time is 10-18 hours.

[0014] Furthermore, the temperature of the second calcination is 500-650° C., and the time of the second calcination is 3-8 hours.

[0015] Furthermore, the heat treatment process includes: first heating the temperature to the heat treatment temperature at a heating rate of 2 to 5°C / min, and then keeping the temperature for heat treatment; preferably, the heat treatment temperature is 100 to 130°C, and the heat treatment time is 20 to 26 hours; preferably, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxide, lithium oxalate, lithium acetate and lithium nitrate; preferably, the niobium source is one or more of niobium trioxide, niobium pentoxide and niobium oxalate; preferably, the first calcination, the second calcination and the heat treatment are carried out under an oxygen atmosphere.

[0016] Further, the weight ratio of polymethacrylate to organic solvent is 1:(50-70); preferably, the organic solvent is one or more of acetone or ethanol; preferably, the drying temperature is 70-90° C., and the drying time is 1-4 hours; preferably, the molecular formula of the ternary precursor material is Ni x Co y Mn (1-x-y) (OH)2, wherein 0.9≤x≤0.95, 0.05≤y≤0.1, and x+y<1.

[0017] According to the third aspect of the present invention, a positive electrode plate is also provided, wherein the active material in the positive electrode plate includes the modified ternary positive electrode material mentioned above; or, the active material in the positive electrode plate includes the modified ternary positive electrode material prepared by the above preparation method.

[0018] According to a fourth aspect of the present invention, a lithium-ion solid-state battery is also provided, and the lithium-ion solid-state battery includes the above-mentioned positive electrode plate.

[0019] The present invention provides a modified ternary positive electrode material, which achieves the purpose of further modifying the ternary positive electrode material by doping Nb into the ternary positive electrode material as a ternary positive electrode material substrate, and sequentially coating a niobium fluoride coating layer and a polymethacrylate coating layer on the surface of the ternary positive electrode material substrate doped with Nb. Using the Nb-doped ternary positive electrode material as the substrate of the modified ternary positive electrode material, on the one hand, enhances the stability of the crystal structure of the modified ternary positive electrode material and reduces lattice distortion; on the other hand, the doped niobium forms a compound with lithium on the surface of the material, which helps to inhibit surface side reactions, improve the rate performance and cycle stability of the material, and thus improve the power density and life of the battery.

[0020] On the surface of the Nb-doped ternary cathode material substrate, a niobium fluoride coating layer and a polymethacrylate coating layer are sequentially constructed, so that NbF5 can react with the residual alkali on the surface of the cathode material in situ to form a Li-Nb-OF electrolyte coating layer on the surface of the ternary cathode material substrate. This coating layer is stable under high voltage, can effectively block the direct contact between the cathode material and the solid electrolyte, inhibit the occurrence of interfacial side reactions, improve the stability and kinetic performance of the battery under high voltage, reduce energy loss and improve charge and discharge efficiency. The polymethacrylate coating layer can also inhibit Ni 2+ Dissolution: The ester groups in the polymethacrylate (PMMA) coating can react with the Ni 2+ Form a stable chemical bond to prevent Ni 2+ Dissolve in organic electrolyte to reduce side reactions between the material surface and the electrolyte, and improve the cycle stability and safety of the battery.

[0021] The modified ternary positive electrode material described in the present invention, under the synergistic effect of the Nb-doped ternary positive electrode material substrate and the sequentially constructed niobium fluoride coating layer and polymethacrylate coating layer, can effectively improve the interface stability and internal structure stability of the positive electrode material in solid-state battery applications, significantly improve the battery's cycle performance, rate performance and safety performance, and provide a solid foundation for the development of high-performance, high-safety solid-state lithium batteries.

[0022] In summary, the present invention optimizes the crystal structure by doping with niobium, constructs a stable electrolyte coating layer, and suppresses Ni 2+ Dissolution and surface-internal synergistic modification have achieved the modification of ternary positive electrode materials, effectively overcoming the interface problems between high-nickel ternary positive electrode materials and solid electrolytes in existing technologies, improving the cycle performance, rate performance and safety of positive electrode materials, and providing a key solution for the development of high-performance all-solid-state lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 The SEM image of the Nb-doped ternary cathode material substrate material prepared according to Example 1 of the present invention is shown;

[0025] Figure 2 The SEM image of the modified ternary cathode material prepared according to Example 1 of the present invention is shown;

[0026] Figure 3 The TEM image of the modified ternary positive electrode material prepared according to Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] As mentioned in the background technology section, the traditional polycrystalline ternary cathode material is composed of submicron primary grains with random orientation. This structure leads to the + The diffusion path is complex and the Li concentration is unevenly distributed inside the particles, which causes the concentration of stress and strain, and eventually forms cracks at the grain boundaries, seriously affecting the structural integrity of the material and the electrochemical performance of the battery. During the long-term redox process of all-solid-state batteries, the surface side reactions caused by the volume change of the positive electrode material, material cracks, and contact loss with the electrolyte will lead to the destruction of the battery structure and a sharp decline in electrochemical performance. How to improve its cycle stability and rate performance, reduce the interface side reactions with the electrolyte, and reduce Ni 2+ The dissolution of solid-state batteries is an important issue that needs to be solved urgently in the current research field of solid-state batteries.

[0029] In order to solve the above problems, the present invention provides a modified ternary positive electrode material, which comprises: a Nb-doped ternary positive electrode material substrate, a niobium fluoride coating layer and a polymethacrylate coating layer; and the niobium fluoride coating layer is coated on the surface of the Nb-doped ternary positive electrode material substrate, and the polymethacrylate coating layer is coated on the surface of the niobium fluoride coating layer.

[0030] The modified ternary positive electrode material provided by the present invention comprises: a Nb-doped ternary positive electrode material substrate, a niobium fluoride coating layer and a polymethacrylate coating layer; and the niobium fluoride coating layer is coated on the surface of the Nb-doped ternary positive electrode material substrate, and the polymethacrylate coating layer is coated on the surface of the niobium fluoride coating layer. The present invention achieves the purpose of modifying the ternary positive electrode material by doping Nb into the ternary positive electrode material as the ternary positive electrode material substrate, and sequentially coating the niobium fluoride coating layer and the polymethacrylate coating layer on the surface of the Nb-doped ternary positive electrode material substrate.

[0031] First, using Nb-doped ternary cathode materials as the base of modified ternary cathode materials can optimize the crystal structure of modified ternary cathode materials. By doping niobium elements in ternary materials, on the one hand, the stability of the crystal structure is enhanced and the lattice distortion is reduced; on the other hand, the doped niobium forms a compound with the lithium on the surface of the material, and the combined action of the two helps to inhibit the occurrence of side reactions on the surface of the material, which is beneficial to improve the rate performance and cycle stability of the material, and improve the power density and life of the battery. In addition, doping niobium can further improve the conductivity of the modified ternary cathode material.

[0032] Secondly, a niobium fluoride coating layer and a polymethacrylate coating layer were constructed in sequence on the surface of the Nb-doped ternary positive electrode material substrate. The niobium fluoride coating layer can construct a stable electrolyte coating layer for the modified ternary positive electrode material. This is because: NbF5 can undergo an in-situ gas-solid reaction with the residual alkali on the surface of the positive electrode material to form a Li-Nb-OF electrolyte coating layer on the surface of the ternary positive electrode material. This coating layer is stable under high voltage, can effectively block the direct contact between the positive electrode material and the solid electrolyte, inhibit the occurrence of interfacial side reactions, improve the stability and kinetics of the battery under high voltage, reduce energy loss and improve charge and discharge efficiency. The polymethacrylate coating layer can also inhibit Ni 2+ Dissolution: The ester groups in the polymethacrylate coating can react with the Ni 2+ Form a stable chemical bond to prevent Ni 2+ Dissolve in organic electrolyte to reduce side reactions between the material surface and the electrolyte, and improve the cycle stability and safety of the battery.

[0033] The modified ternary positive electrode material described in the present invention, under the synergistic effect of the Nb-doped ternary positive electrode material substrate and the sequentially constructed niobium fluoride coating layer and polymethacrylate coating layer, can effectively improve the interface stability and internal structure stability of the high-nickel ternary positive electrode material in solid-state battery applications, significantly improve the battery's cycle performance, rate performance and safety performance, and provide a solid foundation for the development of high-performance, high-safety solid-state lithium batteries.

[0034] In summary, the present invention optimizes the crystal structure by doping with niobium, constructs a stable electrolyte coating layer, and suppresses Ni 2+ Dissolution and surface-internal synergistic modification have achieved the modification of ternary positive electrode materials, effectively overcoming the interface problems between high-nickel ternary positive electrode materials and solid electrolytes in existing technologies, improving the cycle performance, rate performance and safety of positive electrode materials, and providing a key solution for the development of high-performance all-solid-state lithium-ion batteries.

[0035] In a preferred embodiment, in the modified ternary cathode material, the molecular formula of the Nb-doped ternary cathode material substrate is LiNi x Co y Mn (1-x-y) Nb m O2, wherein 0.01≤m≤0.03, 0.9≤x≤0.95, 0.05≤y≤0.1, and x+y<1. Controlling the molar ratio of the nickel-cobalt-manganese material to the Li element and the Nb element in the Nb-doped ternary positive electrode material substrate within the above range can better dope the niobium in the modified ternary positive electrode material into the ternary positive electrode material substrate, giving full play to the role of the doped niobium element, which is beneficial to further improve the rate performance and cycle stability of the material, and improve the power density and life of the battery. In addition, the content of the Ni element in the ternary positive electrode material substrate is within a relatively high range, and the high-nickel ternary positive electrode material has a higher capacity. Modifying the high-nickel ternary positive electrode material has a better effect on improving the overall performance of the solid-state battery. Preferably, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is (0.001-0.05):1, specifically, for example, 0.005:1, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1 or any ratio between any two of the above ratios. Preferably, the weight ratio of the polymethacrylate coating layer to the niobium fluoride-coated Nb-doped ternary positive electrode material is (0.001-0.03):1, specifically, for example, 0.002:1, 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1 or any ratio between any two of the above ratios. Controlling the weight ratio of the niobium fluoride coating layer and the polymethacrylate coating layer within the above range can better improve the interface stability and internal structure stability of the ternary positive electrode material in solid-state battery applications, which is beneficial to further improve the battery's cycle performance, rate performance and safety performance.

[0036] In a preferred embodiment, the particle size of the modified ternary positive electrode material is 1.6 to 1.8 um. Controlling the particle size of the modified ternary positive electrode material within the above range is beneficial to further improve the performance of the modified ternary positive electrode material. Preferably, the polymethacrylate is one or more of polymethyl methacrylate, polyethyl methacrylate and polypropyl methacrylate. The above specific types of polymethacrylates are all relatively common ester polymers, and the modified ternary positive electrode materials obtained using the above polymethacrylates have good effects. Further preferably, the polymethacrylate is polymethyl methacrylate, and the use of polymethyl methacrylate as the coating layer of the modified ternary positive electrode material has better overall effects, which is beneficial to further improve the overall performance of lithium-ion batteries.

[0037] According to another aspect of the present invention, a preparation method of the above-mentioned modified ternary positive electrode material is also provided, and the preparation method comprises the following steps: mixing a ternary precursor material, a lithium source and a niobium source to obtain a first mixed material; subjecting the first mixed material to a first calcination to obtain a Nb-doped ternary positive electrode material substrate; mixing the Nb-doped ternary positive electrode material substrate with niobium fluoride to obtain a second mixed material; subjecting the second mixed material to a second calcination to a first coating to obtain a modified ternary positive electrode material A; mixing the modified ternary positive electrode material A, polymethacrylate and an organic solvent to obtain a third mixed material; separating and drying the third mixed material, and then subjecting the third mixed material to a heat treatment to a second coating to obtain a modified ternary positive electrode material.

[0038] When preparing the modified ternary positive electrode material, the present invention first mixes the ternary precursor material, the lithium source and the niobium source, and performs a first calcination to obtain a Nb-doped ternary positive electrode material substrate; then the obtained Nb-doped ternary positive electrode material substrate is mixed with niobium fluoride and then subjected to a second calcination for a first coating, and niobium fluoride is coated on the Nb-doped ternary positive electrode material substrate to obtain a modified ternary positive electrode material A; and then the modified ternary positive electrode material A is evenly mixed with polymethacrylate and an organic solvent, and then the solid-liquid separation and drying are performed, and then heat treatment is performed for a second coating to obtain a modified ternary positive electrode material. The niobium element is doped by a high-temperature solid-phase sintering method, and the coating is performed twice by a solid-phase method and a liquid-phase method respectively. The preparation process is simple to operate, reduces production costs, improves production efficiency, and significantly improves the electrochemical properties of the material.

[0039] It should be further explained here that in the process of preparing the modified ternary cathode material, due to the possible loss of lithium, etc., an excess of lithium is often added during the preparation to obtain a material of the corresponding molecular formula, and it is preferred to control the amount of lithium added to be 1.01 to 1.1 times the molar amount of the ternary precursor material for the best effect. In the embodiment of the present invention, the amount of lithium added is controlled to be 1.02 times the molar amount of the ternary precursor material.

[0040] In a preferred embodiment, the first calcination includes: firstly performing the first stage calcination at 500-650°C, and then performing the second stage calcination at 750-820°C; preferably, the time of the first stage calcination is 4-7h, and the time of the second stage calcination is 10-18h. When preparing the Nb-doped ternary positive electrode material substrate, the staged calcination can make the modified ternary positive electrode material have a better crystal structure, which is conducive to further improving the comprehensive performance of the modified ternary positive electrode material. In addition, the first and second stage calcinations at the above temperature can further reduce the residual impurities in the modified ternary positive electrode material, improve the electrochemical activity and stability of the material, and better avoid the volatilization of Li in the material caused by the excessively high calcination temperature, which affects the stoichiometric ratio and stability of the material. Preferably, the temperature of the second calcination is 500-650°C, and the time of the second calcination is 3-8h. Controlling the temperature and time of the second calcination within the above range can better coat the niobium fluoride coating layer, which is beneficial to better enable NbF5 to undergo an in-situ gas-solid reaction with the residual alkali on the surface of the ternary positive electrode material and form a Li-Nb-OF electrolyte coating layer on its surface, thereby further reducing the side reactions on the surface of the modified ternary positive electrode material and improving the stability of battery performance.

[0041] In a preferred embodiment, the heat treatment process includes: firstly heating the temperature to the heat treatment temperature at a heating rate of 2 to 5°C / min, and then maintaining the temperature for heat treatment operation; preferably, the heat treatment temperature is 100 to 130°C, and the heat treatment time is 20 to 26 hours. Controlling the heat treatment heating rate, heat treatment temperature and time in the process of forming the polymethacrylate coating layer within the above range can make the Ni at the interface between the polymethacrylate coating layer and the ternary material 2+ Better play a role and further improve the Ni in the modified ternary cathode material 2+Dissolution phenomenon. Preferably, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxide, lithium oxalate, lithium acetate and lithium nitrate; preferably, the niobium source is one or more of niobium trioxide, niobium pentoxide and niobium oxalate. Further preferably, the lithium source is lithium hydroxide; further preferably, the niobium source is niobium trioxide. Selecting lithium hydroxide as the lithium source makes it easier to decompose as a lithium source during the sintering process, which is beneficial to further reduce the alkalinity of the modified ternary positive electrode material and its sensitivity to humidity, thereby further improving the electrochemical properties of the modified ternary positive electrode material. Niobium pentoxide is selected as the niobium source because niobium pentoxide has better stability. Preferably, the first calcination, the second calcination and the heat treatment are carried out under an oxygen atmosphere. The calcination and heat treatment process is carried out in an oxygen atmosphere. First, oxygen, as an oxidant, can promote the oxidation reaction of the metal, making the sintering reaction more complete and thorough. Second, sintering in an oxygen atmosphere can reduce the calcination and heat treatment temperature and improve production efficiency. Third, oxygen can further improve the stability of the product's crystal structure, increase the material's specific surface area and discharge capacity, and thus improve the battery's energy density and cycle stability. At the same time, calcination and heat treatment processes in an oxygen atmosphere can also reduce equipment losses.

[0042] In a preferred embodiment, the weight ratio of polymethacrylate to organic solvent is 1:(50-70); preferably, the organic solvent is one or more of acetone or ethanol; preferably, the drying temperature is 70-90°C and the drying time is 1-4h. The organic solvent can help the uniform dispersion and coating process, and improve the coating efficiency and quality. Controlling the drying temperature and time within the above range can better form the polymethacrylate coating layer, while avoiding the degradation of material properties due to excessively high drying temperature. Preferably, the molecular formula of the ternary precursor material is Ni x Co y Mn (1-x-y) (OH)2, wherein 0.9≤x≤0.95, 0.05≤y≤0.1, and x+y<1.

[0043] According to the third aspect of the present invention, a positive electrode plate is also provided, wherein the active material in the positive electrode plate includes the above-mentioned modified ternary positive electrode material; or, the active material in the positive electrode plate includes the modified ternary positive electrode material prepared by the above-mentioned preparation method.

[0044] According to a fourth aspect of the present invention, a lithium-ion solid-state battery is also provided, the lithium-ion solid-state battery comprising the above-mentioned positive electrode sheet. The modified ternary positive electrode material proposed by the present invention is used as the main component of the active material in the positive electrode sheet, which can effectively improve the cycle performance, rate performance and safety of the modified lithium-ion solid-state battery, and provide a key solution for the development of high-performance all-solid-state lithium-ion batteries.

[0045] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0046] Example 1

[0047] The ternary precursor material Ni 0.93 Co 0.06 Mn 0.01 (OH)2, lithium source LiOH·H2O and niobium source Nb2O5 are mechanically ground and fully mixed to obtain a first mixed material, wherein the molar ratio of the ternary precursor material to the Li element and the Nb element is 1:1.02:0.02; the first mixed material is first calcined in a tube furnace under an oxygen atmosphere, and after cooling to room temperature, a Nb-doped ternary positive electrode material substrate can be obtained, wherein the first calcination process includes: first calcining at 500°C for 5 hours, and then calcining at 780°C for 14 hours. The molecular formula of the obtained Nb-doped ternary positive electrode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.02 O2, the Nb-doped ternary cathode material substrate obtained above was subjected to SEM testing, and the results were as follows Figure 1 As shown, the obtained substrate material has a good single crystal morphology and a smooth surface.

[0048] The Nb-doped ternary cathode material substrate and niobium fluoride are mixed and ground evenly to obtain a second mixed material; the second mixed material is subjected to a second calcination for a first coating to obtain a modified ternary cathode material A. The temperature of the second calcination is 550°C, and the time of the second calcination is 4 hours. In the obtained modified ternary cathode material A, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary cathode material substrate is 0.03:1;

[0049] The modified ternary positive electrode material A, polyethyl methacrylate and organic solvent acetone are mixed in a weight ratio of 0.15:10:50, and mixed evenly at a stirring speed of 3500r / mi to obtain a third mixed material; after the third mixed material is separated from the solid and liquid, the obtained solid part is vacuum dried at 85°C for 2h, and then heat-treated in an oxygen atmosphere for a second coating, and the heat treatment process includes: first heating to 120°C at a heating rate of 2°C / min, and then keeping warm at this temperature for 25h, and then crushing to obtain a modified ternary positive electrode material with a particle size of 1.6 to 1.8um.

[0050] The modified ternary cathode material prepared above was subjected to SEM test, and the results are as follows: Figure 2 As shown by Figure 2It can be seen that there is an obvious particle coating on the surface of the modified ternary cathode material, and the coating is evenly distributed, indicating that the niobium fluoride coating layer and polyethyl methacrylate are evenly coated on the surface of the Nb-doped ternary cathode material substrate. The modified ternary cathode material prepared above was subjected to TEM test, and the results are as follows: Figure 3 As shown, Figure 3 It can be seen that there is an obvious coating layer with a lighter shadow, which further proves that the niobium fluoride coating layer and polyethyl methacrylate are uniformly coated on the surface of the Nb-doped ternary positive electrode material substrate.

[0051] Example 2

[0052] The ternary precursor material Ni 0.93 Co 0.06 Mn 0.01 (OH)2, lithium source LiOH·H2O and niobium source Nb2O5 are mechanically ground and fully mixed to obtain a first mixed material, wherein the molar ratio of the ternary precursor material to the Li element and the Nb element is 1:1.02:0.02; the first mixed material is first calcined in a tube furnace under an oxygen atmosphere, and after cooling to room temperature, a Nb-doped ternary positive electrode material substrate can be obtained, wherein the first calcination process includes: first calcining at 500°C for 7h, and then calcining at 750°C for 18h. The molecular formula of the obtained Nb-doped ternary positive electrode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.02 O2;

[0053] The Nb-doped ternary cathode material substrate and niobium fluoride are mixed and ground evenly to obtain a second mixed material; the second mixed material is subjected to a second calcination for a first coating to obtain a modified ternary cathode material A. The temperature of the second calcination is 650°C, and the time of the second calcination is 3 hours. In the obtained modified ternary cathode material A, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary cathode material substrate is 0.03:1;

[0054] The modified ternary positive electrode material A, polyethyl methacrylate and organic solvent acetone are mixed in a weight ratio of 0.15:10:50, and mixed evenly at a stirring speed of 3500r / min to obtain a third mixed material; after the third mixed material is separated from the solid and liquid, the obtained solid part is vacuum dried at 70°C for 4h, and then heat-treated in an oxygen atmosphere for a second coating, and the heat treatment process includes: first heating to 100°C at a heating rate of 2°C / min, and then keeping warm at this temperature for 26h, and then crushing to obtain a modified ternary positive electrode material with a particle size of 1.6 to 1.8um.

[0055] Example 3

[0056] The ternary precursor material Ni 0.93 Co 0.06 Mn 0.01 (OH)2, lithium source LiOH·H2O and niobium source Nb2O5 are mechanically ground and fully mixed to obtain a first mixed material, wherein the molar ratio of the ternary precursor material to the Li element and the Nb element is 1:1.02:0.02; the first mixed material is first calcined in a tube furnace under an oxygen atmosphere, and after cooling to room temperature, a Nb-doped ternary positive electrode material substrate can be obtained, wherein the first calcination process includes: first calcining at 650°C for 4 hours, and then calcining at 820°C for 10 hours. The molecular formula of the obtained Nb-doped ternary positive electrode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.02 O2;

[0057] The Nb-doped ternary cathode material substrate and niobium fluoride are mixed and ground evenly to obtain a second mixed material; the second mixed material is subjected to a second calcination for a first coating to obtain a modified ternary cathode material A. The temperature of the second calcination is 500°C, and the time of the second calcination is 8 hours. In the obtained modified ternary cathode material A, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary cathode material substrate is 0.03:1;

[0058] The modified ternary positive electrode material A, polyethyl methacrylate and organic solvent ethanol are mixed in a weight ratio of 0.15:10:50, and mixed evenly at a stirring speed of 3500r / mi to obtain a third mixed material; after the third mixed material is separated from the solid and liquid, the obtained solid part is vacuum dried at 90°C for 1h, and then heat-treated in an oxygen atmosphere for a second coating, and the heat treatment process includes: first heating to 130°C at a heating rate of 5°C / min, and then keeping warm at this temperature for 20h, and then crushing to obtain a modified ternary positive electrode material with a particle size of 1.6 to 1.8um.

[0059] Example 4

[0060] The difference between Example 4 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is 0.005:1.

[0061] Example 5

[0062] The difference between Example 5 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is 0.02:1.

[0063] Example 6

[0064] The difference between Example 6 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is 0.04:1.

[0065] Example 7

[0066] The difference between Example 7 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is 0.001:1.

[0067] Example 8

[0068] The difference between Example 8 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is 0.05:1.

[0069] Example 9

[0070] The difference between Example 9 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the polymethacrylate coating layer to the modified ternary positive electrode material A is 0.001:1.

[0071] Example 10

[0072] The difference between Example 10 and Example 1 is that in the modified ternary positive electrode material, the weight ratio of the polymethacrylate coating layer to the modified ternary positive electrode material A is 0.03:1.

[0073] Embodiment 11

[0074] The difference between Example 11 and Example 1 is that in the Nb-doped ternary cathode material substrate, the molar ratio of the ternary precursor material to the Li element and the Nb element is 1:1.02:0.01, and the molecular formula of the obtained Nb-doped ternary cathode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.01 O2.

[0075] Example 12

[0076] The difference between Example 12 and Example 1 is that in the Nb-doped ternary cathode material substrate, the molar ratio of the ternary precursor material to the Li element and the Nb element is 1:1.02:0.03, and the molecular formula of the obtained Nb-doped ternary cathode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.03 O2.

[0077] Example 13

[0078] The difference between Example 13 and Example 1 is that in the Nb-doped ternary cathode material substrate, the molar ratio of the ternary precursor material to the Li element and the Nb element is 1:1.02:0.005, and the molecular formula of the obtained Nb-doped ternary cathode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.005 O2; the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material substrate is 0.06:1; preferably, the ratio of the sum of the weight of the polymethacrylate coating layer to the Nb-doped ternary positive electrode material substrate and the niobium fluoride coating layer is 0.05:1.

[0079] Comparative Example 1

[0080] The ternary precursor material Ni 0.93 Co 0.06 Mn 0.01 (OH)2 and lithium source LiOH·H2O are mechanically ground and fully mixed to obtain a first mixed material, wherein the molar ratio of the ternary precursor material to the Li element is 1:1.02; the first mixed material is first calcined in a tube furnace under an oxygen atmosphere, and after cooling to room temperature, a ternary positive electrode material can be obtained, wherein the first calcination process includes: first calcining at 500°C for 5 hours, and then calcining at 780°C for 14 hours. The molecular formula of the obtained ternary positive electrode material is LiNi 0.93 Co 0.06 Mn 0.01 O2.

[0081] Comparative Example 2

[0082] The Nb-doped ternary positive electrode material substrate prepared in Example 1 was used as a modified ternary positive electrode material.

[0083] Comparative Example 3

[0084] The modified ternary positive electrode material A prepared in Example 1 was used as the modified ternary positive electrode material.

[0085] The modified ternary cathode material prepared in the above embodiment, the unmodified ternary cathode material in Comparative Example 1, and the corresponding modified ternary cathode materials in Comparative Example 2 and Comparative Example 3 were used to prepare all-solid-state batteries, and the corresponding all-solid-state batteries were tested for relevant performances, and the results are shown in Table 1. The assembly and testing methods of the all-solid-state batteries are as follows:

[0086] (1) Assembly of all-solid-state battery: Weigh 120 mg of LGPS (Li 10 GeP2S 12) solid electrolyte powder is placed in a battery mold, and the electrolyte powder is cold-pressed into a ceramic sheet (Φ=10 nm) under a pressure of 250 MPa. The corresponding ternary positive electrode materials and LGPS powder in the embodiment and comparative example are respectively ground and mixed in a mass ratio of 70:30 to form a composite positive electrode, which is evenly spread on one side of the electrolyte and maintained at a pressure of 380 MPa for 3 minutes. Finally, the lithium sheet and the indium sheet are attached to one side of the electrolyte sheet, and packaging is completed at 65 MPa to obtain an all-solid-state battery.

[0087] (2) Assembly and testing of all-solid-state batteries: Constant current charge and discharge tests are performed between 2.0 and 3.68 V.

[0088] Table 1

[0089]

[0090]

[0091] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0092] Examples 1 to 13 use the modified ternary cathode material proposed in the present invention as the active material in the cathode of the all-solid-state battery. According to the data in Table 1, the first charge and discharge efficiency and the capacity retention rate after 100 cycles of the corresponding all-solid-state battery are both above 90%, which is at a good level. In particular, the parameters in the preparation process of the modified ternary cathode material are controlled within the preferred range, and the first charge and discharge efficiency and the capacity retention rate after 100 cycles of the battery in the corresponding example are better.

[0093] The ternary positive electrode material in Comparative Example 1 is a ternary positive electrode material that has not undergone any modification treatment, the modified ternary positive electrode material in Comparative Example 2 is the Nb-doped ternary positive electrode material substrate prepared in Example 1, and the modified ternary positive electrode material in Comparative Example 3 is the modified ternary positive electrode material A prepared in Example 1. The corresponding ternary positive electrode materials in the above comparative examples are used in all-solid-state batteries. The initial charge and discharge efficiency and the capacity retention rate after 100 cycles of the all-solid-state batteries are significantly different from the corresponding data in the embodiments of the present invention.

[0094] It can be seen that the modified ternary positive electrode material provided by the present invention, under the synergistic effect of the Nb-doped ternary positive electrode material substrate and the sequentially constructed niobium fluoride coating layer and polymethacrylate coating layer, can effectively improve the interface stability and internal structure stability of the positive electrode material in solid-state battery applications, significantly improve the battery's cycle performance, rate performance and safety performance, provide a solid foundation for the development of high-performance and high-safety solid-state lithium batteries, and also provide a key solution for the development of high-performance all-solid-state lithium-ion batteries.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A modified ternary cathode material, characterized in that: The modified ternary positive electrode material comprises: a Nb-doped ternary positive electrode material substrate, a niobium fluoride coating layer and a polymethacrylate coating layer; The niobium fluoride coating layer is coated on the surface of the Nb-doped ternary positive electrode material substrate, and the polymethacrylate coating layer is coated on the surface of the niobium fluoride coating layer.

2. The modified ternary cathode material according to claim 1, characterized in that: In the modified ternary positive electrode material, the molecular formula of the Nb-doped ternary positive electrode material substrate is LiNi x Co y Mn (1-x-y) Nb m O2, where 0.01≤m≤0.03, 0.9≤x≤0.95, 0.05≤y≤0.1, and x+y<1; Preferably, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary cathode material substrate is (0.001-0.05):1; Preferably, the weight ratio of the polymethacrylate coating layer to the Nb-doped ternary positive electrode material coated with niobium fluoride is (0.001-0.03):

1.

3. The modified ternary cathode material according to claim 1, characterized in that: The particle size of the modified ternary positive electrode material is 1.6 to 1.8 μm; Preferably, the polymethacrylate is one or more of polymethyl methacrylate, polyethyl methacrylate and polypropyl methacrylate.

4. A method for preparing the modified ternary cathode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: Mixing a ternary precursor material, a lithium source and a niobium source to obtain a first mixed material; performing a first calcination on the first mixed material to obtain a Nb-doped ternary positive electrode material substrate; The Nb-doped ternary cathode material substrate is mixed with niobium fluoride to obtain a second mixed material; the second mixed material is subjected to a second calcination to perform a first coating to obtain a modified ternary cathode material A; The modified ternary positive electrode material A, polymethacrylate and an organic solvent are mixed to obtain a third mixed material; the third mixed material is separated and dried, and then subjected to a heat treatment for a second coating to obtain the modified ternary positive electrode material.

5. The method for preparing the modified ternary cathode material according to claim 4, characterized in that: The first calcination comprises: firstly performing a first stage calcination at 500-650°C, and then performing a second stage calcination at 750-820°C; Preferably, the first stage calcination time is 4 to 7 hours, and the second stage calcination time is 10 to 18 hours.

6. The method for preparing the modified ternary cathode material according to claim 4, characterized in that: The temperature of the second calcination is 500-650° C., and the time of the second calcination is 3-8 hours.

7. The method for preparing the modified ternary cathode material according to claim 4, characterized in that: The heat treatment process comprises: firstly heating the temperature to the heat treatment temperature at a heating rate of 2 to 5°C / min, and then maintaining the temperature to perform the heat treatment operation; Preferably, the temperature of the heat treatment is 100 to 130° C., and the time of the heat treatment is 20 to 26 hours; Preferably, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxide, lithium oxalate, lithium acetate and lithium nitrate; Preferably, the niobium source is one or more of niobium trioxide, niobium pentoxide and niobium oxalate; Preferably, the first calcination, the second calcination and the heat treatment are performed under an oxygen atmosphere.

8. The method for preparing the modified ternary cathode material according to any one of claims 4 to 7, characterized in that: The weight ratio of the polymethacrylate to the organic solvent is 1:(50-70); Preferably, the organic solvent is one or more of acetone or ethanol; Preferably, the drying temperature is 70-90°C, and the drying time is 1-4h; Preferably, the molecular formula of the ternary precursor material is Ni x Co y Mn (1-x-y) (OH)2, wherein 0.9≤x≤0.95, 0.05≤y≤0.1, and x+y<1.

9. A positive electrode sheet, characterized in that: The active material in the positive electrode plate includes the modified ternary positive electrode material described in any one of claims 1 to 3; or, the active material in the positive electrode plate includes the modified ternary positive electrode material prepared by the preparation method described in any one of claims 4 to 8.

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

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