Modified ternary positive electrode material, preparation method and application thereof

Abstract

The application provides a modified ternary positive electrode material and a preparation method and application thereof, Nb is doped into the ternary positive electrode material as a ternary positive electrode material base, and a niobium fluoride coating layer and a polymethacrylate coating layer are sequentially coated on the surface of the ternary positive electrode material base doped with Nb, so that the purpose of further modifying the ternary positive electrode material is achieved. The ternary positive electrode material doped with Nb as the base is beneficial to reducing lattice distortion and inhibiting the occurrence of a material surface side reaction, and improving the rate performance and cycle stability of the material; the existence of the coating layers sequentially constructed can effectively block the direct contact between the positive electrode material and the solid-state electrolyte, inhibit the occurrence of an interface side reaction, improve the stability and kinetic performance of the battery under high voltage, and reduce energy loss. Under the synergistic effect among the above structures, the cycle performance, rate performance and safety of the modified ternary positive electrode material are improved, and the development of high-performance full solid-state lithium ion batteries is promoted.

Description

TECHNICAL FIELD

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

[0002] In recent years, with the explosive demand of new energy vehicle market, the demand of lithium battery also shows an explosive growth. However, the traditional liquid lithium battery has significant shortcomings in safety and cycle life, especially the risk of thermal runaway caused by high energy density battery in use process, and the volatilization and leakage of liquid electrolyte in the battery, which seriously restricts the popularization and promotion of liquid lithium battery in high-end application fields such as new energy vehicles.

[0003] In view of the above challenges, solid-state lithium battery gradually stands out because of its unique performance advantages, and becomes a new hotspot in battery industry research and development. Solid-state lithium battery uses solid electrolyte to replace liquid electrolyte, which fundamentally solves the stability and safety problems of liquid electrolyte. At the same time, solid electrolyte also shows higher ionic conductivity, better thermal stability and better mechanical properties, which can effectively improve the power density and energy density of the battery, prolong the cycle life of the battery, and realize the stable work of the battery under extreme conditions. Among them, sulfide electrolyte is considered as a strong competitor of the next generation of solid-state electrolyte because of its excellent properties such as high ionic conductivity, good thermal stability and mechanical properties, which attracts the attention of many researchers and enterprises.

[0004] However, the interface problem between sulfide electrolyte and positive electrode material has always plagued the performance improvement of solid-state battery. During the charging and discharging process of the battery, the element interdiffusion between the positive electrode material and the sulfide electrolyte, the formation of space charge layer and the interface electrochemical side reaction will all cause pressure to the structural stability of the positive electrode material, and then affect the overall performance of the battery. Especially in high nickel ternary (NCM) material, these problems are more prominent due to the increase of Ni content, resulting in the decline of cycle performance and energy density of the battery at high rate.

[0005] The traditional polycrystalline ternary positive electrode material is composed of submicron primary grains randomly oriented, which leads to complex Li + diffusion path, uneven distribution of Li concentration in the particle, thereby causing stress and strain concentration, and finally forming cracks at the grain boundary, which seriously affects the structural integrity of the material and the electrochemical performance of the battery. In the long-term redox process of the all-solid-state battery, the surface side reaction caused by the volume change of the positive electrode material, the material crack and the loss of contact with the electrolyte will all lead to the destruction of the battery structure and the sharp decline of the electrochemical performance.

[0006] In recent years, single-crystal ternary materials have shown great potential in solving the defects of traditional secondary particle materials due to their more complete structure, smaller surface area, and elimination of inter-particle grain boundaries. These characteristics of single-crystal materials can effectively suppress Li + Inhomogeneous diffusion at the grain boundaries, reducing stress and strain within the battery, thereby improving the cycle stability and rate performance of the battery.

[0007] Improving the cycle stability and rate performance of high-nickel ternary cathode materials, and improving the interface between the cathode material and the solid-state electrolyte, developing high-energy-density solid-state batteries, are problems that need to be solved in the development process of current solid-state batteries. Therefore, the present application is proposed. SUMMARY

[0008] The main purpose of the present application is to provide a modified ternary cathode material and its preparation method and application, to solve the problems of surface side reactions, interface problems and Ni 2+ dissolution in the use process of the ternary cathode material in the prior art, and to achieve the purpose of comprehensively improving the cycle performance, rate performance and safety of the cathode material in the solid-state battery, to meet the development needs of high-energy-density solid-state batteries.

[0009] The present application provides a modified ternary cathode material, which comprises: a Nb-doped ternary cathode material substrate, a niobium fluoride coating layer and a polymethyl acrylate coating layer; and the niobium fluoride coating layer is coated on the surface of the Nb-doped ternary cathode material substrate, and the polymethyl acrylate coating layer is coated on the surface of the niobium fluoride coating layer.

[0010] Further, 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 cathode material substrate is (0.001-0.05):1; preferably, the weight ratio of the polymethyl acrylate coating layer to the Nb-doped ternary cathode material coated with niobium fluoride is (0.001-0.03):1.

[0011] Further, the particle size of the modified ternary cathode material is 1.6-1.8 μm; preferably, the polymethyl acrylate is one or more of polymethyl methacrylate, polymethyl acrylate and polymethyl propyl acrylate.

[0012] According to another aspect of the present application, there is also provided a preparation method of the modified ternary cathode material, comprising the following steps: mixing a ternary precursor material, a lithium source and a niobium source to obtain a first mixture; performing first calcination on the first mixture to obtain a Nb-doped ternary cathode material base; mixing the Nb-doped ternary cathode material base with niobium fluoride to obtain a second mixture; performing second calcination on the second mixture to perform first coating to obtain a modified ternary cathode material A; mixing the modified ternary cathode material A, polymethyl acrylate and an organic solvent to obtain a third mixture; separating and drying the third mixture, and then performing heat treatment to perform second coating to obtain the modified ternary cathode material.

[0013] Further, the first calcination comprises: first performing first-stage calcination at 500-650 DEG C, and then performing second-stage calcination at 750-820 DEG C; preferably, the time for the first-stage calcination is 4-7 h, and the time for the second-stage calcination is 10-18 h.

[0014] Further, the temperature for the second calcination is 500-650 DEG C, and the time for the second calcination is 3-8 h.

[0015] Further, the heat treatment process comprises: first increasing the temperature to the heat treatment temperature at a temperature increasing rate of 2-5 DEG C / min, and then performing heat treatment operation in a heat preservation mode; preferably, the heat treatment temperature is 100-130 DEG C, and the heat treatment time is 20-26 h; 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 di-niobium trioxide, di-niobium pentoxide and niobium oxalate; preferably, the first calcination, the second calcination and the heat treatment are performed in an oxygen atmosphere.

[0016] Further, the weight ratio of the polymethyl acrylate 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 DEG C, and the drying time is 1-4 h; 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 a third aspect of the present application, there is also provided a cathode tab, wherein the active material in the cathode tab comprises the modified ternary cathode material; or, the active material in the cathode tab comprises the modified ternary cathode material prepared by the preparation method.

[0018] According to a fourth aspect of the present application, there is also provided a lithium ion solid-state battery, comprising the cathode tab.

[0019] The application provides a modified ternary positive electrode material, which is obtained by doping Nb into a ternary positive electrode material as a ternary positive electrode material substrate, and sequentially coating a niobium fluoride coating layer and a polymethyl acrylate coating layer on the surface of the Nb-doped ternary positive electrode material substrate to further modify the ternary positive electrode material. The Nb-doped ternary positive electrode material is used as the substrate of the modified ternary positive electrode material, which can enhance the stability of the crystal structure of the modified ternary positive electrode material and reduce lattice distortion, and on the other hand, the doped niobium can form a compound with lithium on the surface of the material, which can help to inhibit the surface side reaction, improve the rate performance and cycle stability of the material, and thus improve the power density and service life of the battery.

[0020] The niobium fluoride coating layer and the polymethyl acrylate coating layer are sequentially constructed on the surface of the Nb-doped ternary positive electrode material substrate, so that NbF5 can perform in-situ gas-solid reaction with the residual alkali on the surface of the positive electrode material, and form a Li-Nb-O-F electrolyte coating layer on the surface of the ternary positive electrode material substrate. The coating layer has stability at high voltage, can effectively block the direct contact between the positive electrode material and the solid-state electrolyte, inhibit the occurrence of interface side reaction, improve the stability and kinetic performance of the battery at high voltage, reduce energy loss and improve the charge and discharge efficiency. The polymethyl acrylate coating layer can also inhibit the dissolution of Ni 2+ in the organic electrolyte, reduce the side reaction between the surface of the material and the electrolyte, and improve the cycle stability and safety of the battery. 2+ form a stable chemical bond with the Ni 2+ on the surface of the positive electrode material to prevent the dissolution of Ni

[0021] The modified ternary positive electrode material described in the application can effectively improve the interface stability and internal structure stability of the positive electrode material in the application of solid-state batteries, significantly improve the cycle performance, rate performance and safety performance of the battery, and provide a solid foundation for the development of high-performance and high-safety solid-state lithium batteries.

[0022] In summary, the application optimizes the crystal structure by doping niobium elements, constructs a stable electrolyte coating layer, anchors the ester group to inhibit the dissolution of Ni 2+ , and modifies the surface and internal structure in a synergistic manner, realizes the modification of the ternary positive electrode material, effectively overcomes the interface problem between the high-nickel ternary positive electrode material and the solid-state electrolyte in the prior art, improves the cycle performance, rate performance and safety performance of the positive electrode material, and provides a key solution for the development of high-performance full-solid-state lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The drawings illustrate one illustrative embodiment of the application and, together with the description, serve to explain the application. In the drawings:

[0024] Figure 1 An SEM image of the Nb-doped ternary cathode material base material prepared according to Embodiment 1 of the application is shown;

[0025] Figure 2 An SEM image of the modified ternary cathode material prepared according to Embodiment 1 of the application is shown;

[0026] Figure 3 A TEM image of the modified ternary cathode material prepared according to Embodiment 1 of the application is shown. DETAILED DESCRIPTION

[0027] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] As described in the background section, the conventional polycrystalline ternary cathode material is composed of sub-micron primary grains randomly oriented, which results in Li + diffusion path being complex, Li concentration being unevenly distributed within the particles, thereby causing stress and strain to be concentrated, and finally forming cracks at the grain boundaries, which seriously affects the structural integrity of the material and the electrochemical performance of the battery. In the long-term redox process of the all-solid-state battery, the surface side reactions caused by the volume change of the cathode material, the material cracks, and the loss of contact with the electrolyte, all of which will lead to the destruction of the battery structure and the sharp decline in the electrochemical performance. How to improve the cycle stability and rate performance, reduce the interface side reactions with the electrolyte, and reduce the dissolution of Ni 2+ , is an important issue to be solved in the current solid-state battery research field.

[0029] To solve the above problems, the present application provides a modified ternary cathode material, which comprises: a Nb-doped ternary cathode material base, 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 cathode material base, 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 application comprises: a Nb-doped ternary positive electrode material base, 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 base, and the polymethacrylate coating layer is coated on the surface of the niobium fluoride coating layer. The application achieves the purpose of modifying the ternary positive electrode material by doping Nb as the ternary positive electrode material base in the ternary positive electrode material, and coating the niobium fluoride coating layer and the polymethacrylate coating layer on the surface of the Nb-doped ternary positive electrode material base in turn.

[0031] Firstly, the Nb-doped ternary positive electrode material is used as the base of the modified ternary positive electrode material, which can optimize the crystal structure of the modified ternary positive electrode material. By doping niobium elements in the ternary material, 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 and lithium on the surface of the material form a compound, and the two together help to inhibit the occurrence of side reactions on the surface of the material, thereby being beneficial to improving the rate performance and cycle stability of the material and improving the power density and life of the battery. In addition, by doping niobium, the conductivity of the modified ternary positive electrode material can be further improved.

[0032] Secondly, the niobium fluoride coating layer and the polymethacrylate coating layer are constructed on the surface of the Nb-doped ternary positive electrode material base in turn. The niobium fluoride coating layer can construct a stable electrolyte coating layer for the modified ternary positive electrode material, because NbF5 can react with the residual alkali on the surface of the positive electrode material in situ, and form a Li-Nb-O-F electrolyte coating layer on the surface of the ternary positive electrode material. This coating layer has stability at high voltage, can effectively block the direct contact between the positive electrode material and the solid-state electrolyte, inhibit the occurrence of interface side reactions, improve the stability and kinetics of the battery at high voltage, reduce energy loss and improve the charge and discharge efficiency. The polymethacrylate coating layer can also inhibit the dissolution of Ni 2+ dissolution: the ester group in the polymethacrylate coating layer can form a stable chemical bond with the Ni 2+ on the surface of the positive electrode material, prevent the dissolution of Ni 2+ in the organic electrolyte, reduce the 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 provided by the application can effectively improve the interface stability and internal structure stability of the high-nickel ternary positive electrode material in the application of solid-state batteries, significantly improve the cycle performance, rate performance and safety performance of the battery, and provide a solid foundation for the development of high-performance and high-safety solid-state lithium batteries.

[0034] In summary, the present application optimizes the crystal structure by doping with niobium elements, constructs a stable electrolyte coating layer, and anchors the ester group to inhibit the Ni 2+ The solubility, surface and internal synergistic modification realize the modification of the ternary positive electrode material, effectively overcome the interface problem between the high-nickel ternary positive electrode material and the solid-state electrolyte in the prior art, and improve the cycle performance, rate performance and safety of the positive electrode material, thereby providing a key solution for the development of high-performance full-solid-state lithium ion batteries.

[0035] In a preferred embodiment, the molecular formula of the Nb-doped ternary positive electrode material base in the modified ternary positive electrode material 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 in the Nb-doped ternary positive electrode material base to Li elements and Nb elements within the above range can make the niobium in the modified ternary positive electrode material better doped in the ternary positive electrode material base, fully play the role of the doped niobium elements, and be beneficial to further improving the rate performance and cycle stability of the material and improving the power density and service life of the battery. In addition, the content of the Ni element in the ternary positive electrode material base 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 base is (0.001-0.05):1, and 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 Nb-doped ternary positive electrode material coated with the niobium fluoride coating layer is (0.001-0.03):1, and 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 the application of the solid-state battery, and be beneficial to further improving the cycle performance, rate performance and safety performance of the battery.

[0036] In a preferred embodiment, the particle size of the modified ternary positive electrode material is 1.6-1.8 um. Controlling the particle size of the modified ternary positive electrode material in the above range is conducive to further improving the performance of the modified ternary positive electrode material. Preferably, the polymethyl acrylate is one or more of polymethyl methacrylate, polyethyl methacrylate and polypropyl methacrylate. The above specific types of polymethyl acrylate are relatively common ester polymers, and the modified ternary positive electrode material obtained by using the above polymethyl acrylate has good effect, and further preferably, the polymethyl acrylate is polymethyl methacrylate, and the overall effect is better when using polymethyl methacrylate as the coating layer of the modified ternary positive electrode material, which is conducive to further improving the overall performance of the lithium ion battery.

[0037] According to another aspect of the present application, a preparation method of the above modified ternary positive electrode material is also provided, which comprises the following steps: mixing a ternary precursor material, a lithium source and a niobium source to obtain a first mixture; performing first calcination on the first mixture to obtain a Nb-doped ternary positive electrode material base; mixing the Nb-doped ternary positive electrode material base with niobium fluoride to obtain a second mixture; performing second calcination on the second mixture to perform first coating to obtain a modified ternary positive electrode material A; mixing the modified ternary positive electrode material A, polymethyl acrylate and an organic solvent to obtain a third mixture; separating and drying the third mixture, and then performing heat treatment to perform second coating to obtain the modified ternary positive electrode material.

[0038] In the preparation of the modified ternary positive electrode material, the ternary precursor material, the lithium source and the niobium source are first mixed and subjected to first calcination to obtain a Nb-doped ternary positive electrode material base; then the obtained Nb-doped ternary positive electrode material base is mixed with niobium fluoride and subjected to second calcination to perform first coating, so that the niobium fluoride is coated on the Nb-doped ternary positive electrode material base to obtain a modified ternary positive electrode material A; further, the modified ternary positive electrode material A is uniformly mixed with polymethyl acrylate and an organic solvent, and then subjected to solid-liquid separation and drying, and then subjected to heat treatment to perform second coating to obtain the modified ternary positive electrode material. The high-temperature solid-phase sintering method is used for niobium element doping, and the solid-phase method and the liquid-phase method are used for two times of coating respectively. The preparation process is simple in operation, reduces the production cost, improves the production efficiency, and significantly improves the electrochemical performance of the material.

[0039] It should be further pointed out that in the preparation of the above modified ternary positive electrode material, due to the possible loss of lithium, an excess of lithium is often added during preparation to obtain a material corresponding to the molecular formula. Preferably, the amount of lithium added is 1.01-1.1 times the molar amount of the ternary precursor material, which is the best. In the examples of the present application, the amount of lithium added is 1.02 times the molar amount of the ternary precursor material.

[0040] In a preferred embodiment, the first calcination comprises: first stage calcination at 500-650℃, and second stage calcination at 750-820℃; preferably, the first stage calcination is performed for 4-7h, and the second stage calcination is performed for 10-18h. In the preparation of Nb-doped ternary positive electrode material base, the use of staged calcination can make the modified ternary positive electrode material have better crystal structure, thereby being conducive to further improving the comprehensive performance of the modified ternary positive electrode material. In addition, the first stage and second stage calcination at the above-mentioned temperatures can further reduce the residual impurities in the modified ternary positive electrode material, improve the electrochemical activity and stability of the material, and also better avoid the influence of Li volatilization in the material due to excessively high calcination temperature on the stoichiometric ratio and stability of the material. Preferably, the second calcination temperature is 500-650℃, and the second calcination time is 3-8h. Controlling the second calcination temperature and time within the above-mentioned range can make the niobium fluoride coating layer better coated, and be conducive to better enabling NbF5 to perform in-situ gas-solid reaction with the residual alkali on the surface of the ternary positive electrode material and form a Li-Nb-O-F electrolyte coating layer on the surface thereof, thereby further reducing the side reactions on the surface of the modified ternary positive electrode material and improving the stability of the battery performance.

[0041] In a preferred embodiment, the heat treatment process comprises: first increasing the temperature to the heat treatment temperature at a temperature increasing rate of 2-5℃ / min, and then heat treatment operation is performed under heat preservation; preferably, the heat treatment temperature is 100-130℃, and the heat treatment time is 20-26h. Controlling the heat treatment temperature increasing rate and the heat treatment temperature and time in the formation process of the polymethacrylate coating layer within the above-mentioned range can make the interface between the polymethacrylate coating layer and the ternary material better act, and further improve the Ni 2+ better act, and further improve the Ni 2+The solubility 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 di-niobium trioxide, di-niobium pentoxide, and niobium oxalate. Further preferably, the lithium source is lithium hydroxide; further preferably, the niobium source is di-niobium trioxide. The selection of lithium hydroxide as the lithium source is because lithium hydroxide is more likely to decompose in the process of sintering, thereby facilitating the further reduction of the alkalinity of the modified ternary cathode material and its sensitivity to humidity, thereby further improving the electrochemical performance of the modified ternary cathode material. The selection of di-niobium pentoxide as the niobium source is because di-niobium pentoxide has better stability. Preferably, the first calcination, the second calcination, and the heat treatment are carried out in an oxygen atmosphere. Carrying out the calcination and heat treatment processes in an oxygen atmosphere, firstly, oxygen as an oxidizing agent can promote the oxidation reaction of the metal, making the sintering reaction more complete and thorough; secondly, sintering in an oxygen atmosphere can reduce the calcination and heat treatment temperature, improve the production efficiency; thirdly, oxygen can further improve the stability of the crystal structure of the product, improve the specific surface area and discharge capacity of the material, and thereby improve the energy density and cycle stability performance of the battery. At the same time, carrying out the calcination and heat treatment processes in an oxygen atmosphere can also reduce the wear and tear of the equipment.

[0042] In a preferred embodiment, 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. The organic solvent can help with uniform dispersion and coating process, improving 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 decline in material performance caused by 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 a third aspect of the present application, a cathode sheet is also provided, wherein the active material in the cathode sheet comprises the modified ternary cathode material described above; or the active material in the cathode sheet comprises the modified ternary cathode material prepared by the preparation method described above.

[0044] According to a fourth aspect of the present application, a lithium ion solid-state battery is also provided, which comprises the cathode sheet described above. Using the modified ternary cathode material proposed by the present application as the main component of the active material in the cathode sheet can effectively improve the cycle performance, rate performance, and safety of the modified lithium ion solid-state battery, and provides a key solution for the development of high-performance all-solid-state lithium ion batteries.

[0045] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0046] Example 1

[0047] Ni, a ternary precursor material 0.93 Co 0.06 Mn 0.01 (OH)₂, lithium source LiOH·H₂O, and niobium source Nb₂O₅ are mechanically ground and thoroughly mixed to obtain a first mixture, wherein the molar ratio of the ternary precursor material to Li and Nb is 1:1.02:0.02. The first mixture is then subjected to a first calcination in a tube furnace under an oxygen atmosphere. After cooling to room temperature, an Nb-doped ternary cathode material substrate is obtained. The first calcination process includes: calcination at 500℃ for 5 hours, followed by calcination at 780℃ for 14 hours. The molecular formula of the obtained Nb-doped ternary cathode material substrate is LiNi. 0.93 Co 0.06 Mn 0.01 Nb 0.02 O2 was used to perform SEM testing on the Nb-doped ternary cathode material substrate obtained above. The results are as follows: Figure 1 As shown, the obtained substrate material exhibits a good single-crystal morphology and a smooth surface.

[0048] A second mixture was prepared by mixing and grinding a Nb-doped ternary cathode material substrate with niobium fluoride to obtain a second mixture. This second mixture was then subjected to a second calcination for a first coating, resulting in modified ternary cathode material A. The second calcination temperature was 550℃, and the calcination time was 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 was 0.03:1.

[0049] Modified ternary cathode material A, polyethyl methacrylate, and organic solvent acetone were mixed at a weight ratio of 0.15:10:50 and stirred at a speed of 3500 r / min to obtain a third mixture. After solid-liquid separation of the third mixture, the obtained solid part was vacuum dried at 85°C for 2 h, and then heat-treated in an oxygen atmosphere for a second coating. The heat treatment process included: first heating to 120°C at a heating rate of 2°C / min, then holding at that temperature for 25 h, and then crushing to obtain modified ternary cathode material with a particle size of 1.6-1.8 μm.

[0050] The modified ternary cathode material prepared above was subjected to SEM testing, and the results are as follows: Figure 2 As shown, by Figure 2It can be seen that the obtained modified ternary positive electrode material has obvious particle coating, and the coating is uniformly distributed, which indicates that the niobium fluoride coating and the polymethyl methacrylate are uniformly coated on the surface of the Nb-doped ternary positive electrode material base material; the modified ternary positive electrode material obtained by the above preparation is subjected to TEM test, and the results are shown in Figure 3 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 and the polymethyl methacrylate are uniformly coated on the surface of the Nb-doped ternary positive electrode material base material.

[0051] Example 2

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

[0053] The Nb-doped ternary positive electrode material base is mixed and ground with niobium fluoride to obtain a second mixed material; the second mixed material is subjected to second calcination to perform first coating to obtain a modified ternary positive electrode material A. The temperature of the second calcination is 650℃, and the time of the second calcination is 3h. In the obtained modified ternary positive electrode material A, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material base is 0.03:1;

[0054] The modified ternary positive electrode material A, polymethyl methacrylate and an organic solvent acetone are mixed at a weight ratio of 0.15:10:50, and are uniformly mixed at a stirring speed of 3500r / min to obtain a third mixed material; the third mixed material is subjected to solid-liquid separation, and the obtained solid part is vacuum dried at 70℃ for 4h, and then is subjected to heat treatment under an oxygen atmosphere to perform second coating, and the heat treatment process includes: first increasing the temperature to 100℃ at a temperature increasing rate of 2℃ / min, then keeping the temperature at 100℃ for 26h, and then crushing to obtain a modified ternary positive electrode material with a particle size of 1.6-1.8um.

[0055] Example 3​

[0056] The ternary precursor material Ni 0.93 Co 0.06 Mn 0.01 (OH)2, a lithium source LiOH·H2O and a niobium source Nb2O5 are mixed after mechanical grinding to obtain a first mixture, 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 mixture is subjected to first calcination in a tube furnace under an oxygen atmosphere, and after cooling to room temperature, a Nb-doped ternary positive electrode material base is obtained, wherein the first calcination process comprises: first calcination at 650℃ for 4h, and then calcination at 820℃ for 10h. The molecular formula of the obtained Nb-doped ternary positive electrode material base is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.02 O2;

[0057] The Nb-doped ternary positive electrode material base is mixed with niobium fluoride and ground uniformly to obtain a second mixture; the second mixture is subjected to second calcination to perform first coating to obtain a modified ternary positive electrode material A. The temperature of the second calcination is 500℃, and the time of the second calcination is 8h. In the obtained modified ternary positive electrode material A, the weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material base is 0.03:1;

[0058] The modified ternary positive electrode material A, polyethyl methacrylate and an organic solvent ethanol are mixed in a weight ratio of 0.15:10:50, and are uniformly mixed at a stirring speed of 3500r / min to obtain a third mixture; the third mixture is subjected to solid-liquid separation, the obtained solid part is vacuum dried at 90℃ for 1h, and then is subjected to heat treatment under an oxygen atmosphere to perform second coating, the heat treatment process comprises: first increasing the temperature to 130℃ at a temperature increasing rate of 5℃ / min, then maintaining the temperature for 20h, and then performing crushing treatment to obtain a modified ternary positive electrode material with a particle size of 1.6-1.8um.

[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 base 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 base is 0.02:1.

[0063] Example 6

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

[0065] Example 7

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

[0067] Example 8

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

[0069] Example 9

[0070] Example 9 differs from Example 1 in that the weight ratio of the polymethacrylate coating layer to the modified ternary positive electrode material A in the modified ternary positive electrode material is 0.001:1.

[0071] Example 10

[0072] Example 10 differs from Example 1 in that the weight ratio of the polymethacrylate coating layer to the modified ternary positive electrode material A in the modified ternary positive electrode material is 0.03:1.

[0073] Example 11

[0074] Example 11 differs from Example 1 in that the mole ratio of the ternary precursor material to the Li element and the Nb element in the Nb-doped ternary positive electrode material substrate is 1:1.02:0.01, and the molecular formula of the obtained Nb-doped ternary positive electrode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.01 O2.

[0075] Example 12

[0076] Example 12 differs from Example 1 in that the mole ratio of the ternary precursor material to the Li element and the Nb element in the Nb-doped ternary positive electrode material substrate is 1:1.02:0.03, and the molecular formula of the obtained Nb-doped ternary positive electrode material substrate is LiNi 0.93 Co 0.06 Mn 0.01 Nb 0.03 O2.

[0077] Example 13

[0078] The difference between Example 13 and Example 1 is that the molar ratio of the ternary precursor material to Li element and the Nb element in the Nb-doped ternary positive electrode material base is 1:1.02:0.005, and the molecular formula of the obtained Nb-doped ternary positive electrode material base 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 base is 0.06:1; and preferably, the ratio of the polymethacrylate coating layer to the sum of the weights of the Nb-doped ternary positive electrode material base 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, a lithium source LiOH·H2O were mechanically ground and fully mixed to obtain a first mixture, wherein the molar ratio of the ternary precursor material to Li element is 1:1.02; the first mixture was subjected to first calcination in a tube furnace under an oxygen atmosphere, and after cooling to room temperature, a ternary positive electrode material was obtained, wherein the first calcination process comprises: first calcination at 500°C for 5h, and then calcination at 780°C for 14h. 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 base 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 a modified ternary positive electrode material.

[0085] The modified ternary positive electrode materials prepared in the above examples, and the unmodified ternary positive electrode material in Comparative Example 1, and the corresponding modified ternary positive electrode materials in Comparative Example 2 and Comparative Example 3 were used to prepare full solid-state batteries, and the corresponding full solid-state batteries were tested for relevant performance, and the results are shown in Table 1. Among them, the assembly and testing method of the full solid-state battery is as follows:

[0086] (1) Assembly of full solid-state battery: 120mg of LGPS (Li 10 GeP2S 12) The solid electrolyte powder is put into a battery mold, and the electrolyte powder is cold-pressed into a ceramic sheet (Φ = 10 nm) under a pressure of 250 MPa, the ternary positive electrode material and the LGPS powder in the examples and the comparative examples are respectively mixed according to a mass ratio of 70:30 to form a composite positive electrode, and are uniformly spread on one side of the electrolyte, and are kept under a pressure of 380 MPa for 3 min, finally, a lithium sheet and an indium sheet are attached to one side of the electrolyte sheet, and are packaged under a pressure of 65 MPa, to obtain a full solid-state battery.

[0087] (2) Assembly and testing of the full solid-state battery: constant current charge and discharge tests are carried out between 2.0 and 3.68 V.

[0088] Table 1

[0089]

[0090]

[0091] From the above description, it can be seen that the above-mentioned examples of the present application achieve the following technical effects:

[0092] Examples 1 to 13 are full solid-state batteries using the modified ternary positive electrode material proposed by the present application as the active material in the positive electrode of the full solid-state battery, and according to the data in Table 1, the first charge and discharge efficiency and the capacity retention rate after 100 cycles of the corresponding full solid-state battery are both above 90%, which is at a good level. In particular, by controlling the parameters in the preparation process of the modified ternary positive electrode material within the preferred range, 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 without 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, and the corresponding ternary positive electrode materials in the above comparative examples are used in full solid-state batteries, and the first charge and discharge efficiency and the capacity retention rate after 100 cycles of the full solid-state battery have a large gap with the corresponding data of the examples of the present application.

[0094] Therefore, the modified ternary positive electrode material provided by the present application, 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 the application of solid-state batteries, significantly improve the cycle performance, rate performance and safety performance of the battery, 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 full solid-state lithium ion batteries.

[0095] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A modified ternary cathode material, characterized in that, The modified ternary positive electrode material comprises: a Nb-doped ternary positive electrode material base, a niobium fluoride coating layer, and a polymethyl acrylate coating layer. The niobium fluoride coating layer is coated on the surface of the Nb-doped ternary positive electrode material base, and the polymethyl acrylate 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, The modified ternary cathode material, the molecular formula of the Nb-doped ternary cathode material base 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.

3. The modified ternary cathode material according to claim 2, characterized in that, The weight ratio of the niobium fluoride coating layer to the Nb-doped ternary positive electrode material base is (0.001-0.05):

1.

4. The modified ternary cathode material of claim 2, characterized in that, The weight ratio of the polymethyl acrylate coating layer to the Nb-doped ternary positive electrode material coated with the niobium fluoride is (0.001-0.03):

1. 5.The modified ternary cathode material of claim 1, characterized in that, The particle size of the modified ternary positive electrode material is 1.6-1.8 µm.

6. The modified ternary cathode material according to claim 5, characterized in that, The polymethyl acrylate is one or more of polymethyl methacrylate, polymethyl ethacrylate, and polymethyl propylacrylate.

7. A method for producing the modified ternary positive electrode material according to any one of claims 1 to 6, characterized by, The preparation method comprises the following steps: Mixing a ternary precursor material, a lithium source, and a niobium source to obtain a first mixture; performing first calcination on the first mixture to obtain a Nb-doped ternary positive electrode material base; Mixing the Nb-doped ternary positive electrode material base and niobium fluoride to obtain a second mixture; performing second calcination on the second mixture to perform first coating to obtain a modified ternary positive electrode material A; Mixing the modified ternary positive electrode material A, polymethyl acrylate, and an organic solvent to obtain a third mixture; separating and drying the third mixture, and then performing heat treatment to perform second coating to obtain the modified ternary positive electrode material.

8. The method of claim 7, wherein the modified ternary cathode material is prepared by the steps of: preparing a precursor material by mixing a lithium source, a transition metal source, and a carbon source; and calcining the precursor material in a non-oxidizing atmosphere. The first calcination comprises: first-stage calcination at 500-650 ℃, and second-stage calcination at 750-820 ℃.

9. The method of claim 8, wherein the modified ternary cathode material is prepared by the steps of: The first-stage calcination time is 4-7 h, and the second-stage calcination time is 10-18 h. ​ 10. The method of claim 7, wherein the modified ternary cathode material is prepared by the steps of: The second calcination temperature is 500-650 ℃, and the second calcination time is 3-8 h. ​ 11. The method of claim 7, wherein the modified ternary cathode material is prepared by the steps of: preparing a precursor material by mixing a lithium source, a transition metal source, and a carbon source; and calcining the precursor material in a non-oxidizing atmosphere. The heat treatment process comprises: first, increasing the temperature to the heat treatment temperature at a temperature increasing rate of 2-5 ℃ / min, and then, performing the heat treatment operation.

12. The method of claim 11, wherein the modified ternary cathode material is prepared by the steps of: The heat treatment temperature is 100-130 ℃, and the heat treatment time is 20-26 h. ​ 13. The method of claim 11, wherein the modified ternary cathode material is prepared by the steps of: The lithium source is one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, lithium oxide, lithium oxalate, lithium acetate, and lithium nitrate. ​ 14. The method of claim 11, wherein the modified ternary cathode material is prepared by the steps of: The niobium source is one or more of di-niobium trioxide, di-niobium pentoxide, and niobium oxalate. ​ 15. The method of claim 11, wherein the modified ternary cathode material is prepared by the steps of: preparing a precursor material; and adding a lithium source to the precursor material. The first calcination, the second calcination, and the heat treatment are performed in an oxygen atmosphere.

16. The method of claim 7, wherein the modified ternary cathode material is prepared by the steps of: The weight ratio of the polymethyl acrylate to the organic solvent is 1:(50-70). ​ 17. The method of claim 16, wherein the modified ternary cathode material is prepared by the steps of: The organic solvent is one or more of acetone or ethanol. ​ 18. The method of claim 16, wherein the modified ternary cathode material is prepared by the steps of: The drying temperature is 70-90 ℃, and the drying time is 1-4 h. ​ 19. The method of claim 16, wherein the modified ternary cathode material is prepared by the steps of: preparing a precursor material; and adding a lithium source to the precursor material. 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.

20. A positive electrode sheet characterized by comprising: The active material in the positive electrode tab comprises the modified ternary positive electrode material of any one of claims 1-6; or, the active material in the positive electrode tab comprises the modified ternary positive electrode material prepared by the preparation method of any one of claims 7-19.

21. A lithium-ion solid-state battery, characterized by, The lithium ion solid-state battery comprises the positive electrode tab of claim 20.

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