Ternary positive electrode material, preparation method thereof and electrochemical device

Abstract

The invention discloses a ternary positive electrode material, a preparation method thereof and an electrochemical device, the ternary positive electrode material comprises a plurality of particles, each particle comprises a body part and a microstructure layer located on the surface of the body part, and the microstructure layer comprises a plurality of tooth parts and concave parts located between any two adjacent tooth parts. The tooth part extends from the end close to the body part to the end away from the body part in the radial direction. The ternary positive electrode material provided by the invention is provided with the tooth parts and the concave parts which are positioned on the surface of the body part, so that when the ternary positive electrode material is stacked, particles can be mutually meshed through the tooth parts, and the contact area between the particles is increased, so that the powder resistivity of the ternary positive electrode material is effectively reduced, and the service life of the ternary positive electrode material is prolonged. The electronic conductivity of the ternary positive electrode material is improved, and the cycle performance of the ternary positive electrode material is effectively improved on the premise that the capacity of the ternary positive electrode material is not sacrificed.

Description

Technical Field

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

[0002] As an important component of lithium-ion batteries, the performance of cathode materials directly affects the overall performance of the battery. Among them, ternary cathode materials have become a hot topic of current research due to their high theoretical capacity, good thermal stability and high overall performance.

[0003] However, the powder resistance of ternary cathode materials is too high, resulting in poor cycling performance. Existing technologies typically use a conductive coating to reduce the resistance of ternary cathode materials to improve cycling performance, but this approach can result in a decrease in the capacity of the ternary cathode materials. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, an embodiment of the present application provides a new type of ternary positive electrode material.

[0005] In addition, the embodiments of the present application also provide a method for preparing the aforementioned ternary positive electrode material and an electrochemical device using the ternary positive electrode material.

[0006] An embodiment of the present application provides a ternary positive electrode material, which includes a plurality of particles, wherein the particles include a main body and a microstructure layer located on the surface of the main body, the microstructure layer includes a plurality of teeth and a recess located between any two adjacent teeth, and the teeth extend radially from one end close to the main body to an end away from the main body.

[0007] In some possible embodiments, the average distribution density Q of the teeth in the ternary positive electrode material is 0.5 / μm~2.5 / μm, and the testing method of Q includes: obtaining a scanning electron microscope image of the cross-section of the ternary positive electrode material, identifying the number M of the teeth of multiple particles in the ternary positive electrode material and the particle size D of the particles, and calculating the distribution density q of the teeth in the particles, wherein q=M / πD, and the average distribution density Q is the average value of the distribution density q.

[0008] In some possible embodiments, the uniformity N of the distribution of the teeth on the surface of the ternary positive electrode material is 70%~100%, and a scanning electron microscope image of the cross-section of the particle of the ternary positive electrode material is obtained. The surface of the particle includes n equal-sized regions, n is an integer greater than or equal to 5, and N is the ratio of the number of teeth in any two regions on the surface of the particle.

[0009] In some possible embodiments, the ternary cathode material satisfies at least one of the following characteristics: (1) The angle of the teeth is 0°~90°; (2) The radial thickness of the tooth portion is 50 nm to 500 nm; (3) The number of teeth of the particles of the ternary positive electrode material is 15 to 160; (4) The median particle size D50 of the particles of the ternary positive electrode material is 10 μm to 20 μm; (5) The specific surface area of the particles of the ternary positive electrode material is 0.4 m 2 / g~0.9m 2 / g.

[0010] In some possible embodiments, the particles of the ternary positive electrode material further include a metal oxide coating layer, and the metal oxide coating layer is located on the surfaces of the teeth and the recesses.

[0011] An embodiment of the present application also provides a method for preparing a ternary positive electrode material, which includes the following steps: mixing a nickel-cobalt-manganese precursor, a lithium source and a doping material and sintering them once to obtain a base material; and acid-treating the base material with an acid solution to form a plurality of teeth and recesses between any two adjacent teeth on the surface of the base material, wherein the teeth and the recesses constitute a microstructure layer, thereby obtaining a ternary positive electrode material.

[0012] In some possible embodiments, the acid treatment time is 2h~24h; and / or The temperature of the acid treatment is 30°C to 80°C.

[0013] In some possible embodiments, the method for preparing the ternary cathode material satisfies at least one of the following characteristics: (1) The concentration of the acid solution is 0.1 mol / L to 3 mol / L; (2) The solid ratio of the matrix material to the acid solution is 100 g / L to 1000 g / L; (3) The acid solution includes an inorganic acid and an organic acid.

[0014] In some possible embodiments, the preparation method further includes: adding the ternary positive electrode material to water containing a metal coating material for washing and filtering to obtain a mixed material; and performing secondary sintering on the mixed material to form a metal oxide coating layer on the surface of the tooth portion and the recess.

[0015] In addition, an embodiment of the present application further provides an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is the aforementioned ternary positive electrode material.

[0016] Compared with the prior art, the ternary positive electrode material provided in the embodiment of the present application has a microstructure layer on the surface of the main body, and the microstructure layer has a large number of teeth and recesses located between two adjacent teeth. When the ternary positive electrode material is stacked, the particles can engage with each other through the teeth, thereby increasing the contact area between the particles, thereby effectively reducing the powder resistivity of the ternary positive electrode material and improving the electronic conductivity of the ternary positive electrode material. Without sacrificing the capacity of the ternary positive electrode material, the cycle performance of the ternary positive electrode material is effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of the ternary positive electrode material provided in one embodiment of the present application.

[0018] Figure 2 Schematic diagram of the stacking of ternary positive electrode material particles provided in one embodiment of the present application.

[0019] Figure 3 This is a process flow chart of a method for preparing a ternary positive electrode material provided in one embodiment of the present application.

[0020] Figure 4 These are SEM images of the ternary positive electrode materials provided in Example 1 and Comparative Example 1 of the present application, wherein Figure a is the SEM image of the ternary positive electrode material of Example 1, and Figure b is the SEM image of the ternary positive electrode material of Comparative Example 1. DETAILED DESCRIPTION

[0021] The embodiments of the present application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0022] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of this application; the implementation methods of this application and the features in the implementation methods can be combined with each other unless there is a conflict; many specific details are set forth in the following description to facilitate a full understanding of this application, and the implementation methods described are only part of the implementation methods of this application, not all of the implementation methods.

[0023] The inventors have found that in order to improve the cycle performance of the ternary positive electrode, coating technology is currently commonly used. However, with the increasing complexity of the coating process and the gradual thickening of the coating layer, the powder resistance of the ternary positive electrode material increases significantly, the conductivity decreases, and the cycle performance of the ternary positive electrode material deteriorates. In order to improve the conductivity of the ternary positive electrode material, a method of coating the surface of the ternary material with an inorganic or organic conductive coating layer (such as carbon, graphene, carbon fiber, carbon nanotubes, and conductive metal nitrides, etc.) is used to improve the electronic conductivity of the ternary positive electrode material. However, the above-mentioned conductive substances do not have the activity of the positive electrode material, which will affect the capacity of the ternary positive electrode material.

[0024] To do this, see Figure 1 As shown, the embodiment of the present application provides a novel ternary cathode material, which includes a plurality of particles 100. The particles 100 include a main body 10 and a microstructure layer 20 located on the surface of the main body. The microstructure layer 20 includes a plurality of teeth 21 and a recess 22 located between any two adjacent teeth 21. The teeth 21 extend radially from one end close to the main body 10 to the other end away from the main body 10. The chemical formula of the ternary cathode material can be Li a Ni b Co c Mn d O2, among which, 0.90≤a≤1.20, 0.75≤b≤1.0, 0≤c≤0.2, 0≤d≤0.2, 0<b+c+d≤1.

[0025] See also Figure 2 As shown, since the ternary positive electrode material particles have multiple teeth on the surface of the main body, presenting a gear-like structure, when multiple ternary positive electrode material particles are stacked, the ternary positive electrode material particles can engage with each other through the teeth, increasing the contact area between the particles, forming more conductive pathways, which is conducive to electron jumping between particles and optimizing the electron conduction path, thereby effectively reducing the powder resistivity of the ternary positive electrode material and improving the electronic conductivity of the ternary positive electrode material, thereby effectively improving the cycle performance of the ternary positive electrode material without reducing the capacity of the ternary positive electrode material.

[0026] Please refer again Figure 1 As shown, a scanning electron microscope image of the cross section of the ternary positive electrode material is obtained ( Figure 1 (for schematic diagrams only) identify the number M of teeth of multiple particles in the ternary positive electrode material and the particle size D of the particles, and calculate the distribution density q of the teeth in each particle, where q=M / πD, and the average distribution density Q is the average value of the distribution density q.

[0027] Among them, the average distribution density Q is 0.5 / μm~2.5 / μm, indicating that the density of the tooth distribution in the ternary positive electrode material is appropriate, which is conducive to providing appropriate teeth and recesses, so that the particles of the ternary positive electrode material are fully meshed when stacked, further increasing the contact area between the particles, and improving the conductivity and cycle performance of the ternary positive electrode material. The value of Q can be 0.5 / μm, 0.6 / μm, 0.7 / μm, 0.8 / μm, 0.9 / μm, 1.0 / μm, 1.1 / μm, 1.2 / μm, 1.3 / μm, 1.4 / μm, 1.5 / μm, 1.6 / μm, 1.7 / μm, 1.8 / μm, 1.9 / μm, 2.0 / μm, 2.1 / μm, 2.2 / μm, 2.3 / μm, 2.4 / μm, 2.5 / μm or any value within the numerical range consisting of any two of the above values. The value of Q can further be 1.0 / μm to 2.0 / μm, which is beneficial to the contact between particles.

[0028] In some embodiments, the uniformity N of the distribution of teeth on the surface of the ternary positive electrode material can be 70% to 100%. The testing method can be: obtain a scanning electron microscope image of a cross-section of a particle of the ternary positive electrode material, wherein the surface of the ternary positive electrode material is divided into n equal-sized regions, where n is an integer greater than or equal to 5, and N is the ratio of the number of teeth in any two regions of the particle surface (when the number of teeth in the two regions is different, the ratio N is the ratio of the smaller to the larger number of teeth in the two regions, N<100%; when the number of teeth in the two regions is the same, the ratio N is 100%). N in the range of 70% to 100% indicates that the teeth are relatively uniformly distributed on the surface of the ternary positive electrode material, which is beneficial to improving the uniformity of electron transport, reducing the phenomenon of electron conduction overload in tooth-dense areas and weakened electron conduction in sparse areas, thereby further improving the cycling performance of the ternary positive electrode material. The uniformity N can illustratively be any value within a numerical range consisting of 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any two of the above values. The uniformity N can further be 85% to 100%. It can be understood that the closer N is to 100%, the more uniform the distribution of the teeth on the surface of the ternary positive electrode material particles.

[0029] In some embodiments, the number of teeth of the particles of the ternary positive electrode material can be 15 to 160, and the number of teeth of a single particle is in the range of 15 to 160, which is conducive to the meshing of the teeth between the particles and increases the contact area between the particles. The number of teeth of the particles of the ternary positive electrode material can be 15, 20, 25, 30, 35, 40, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160 or any value within the numerical range composed of any two of the above values. The number of teeth of the particles of the ternary positive electrode material can further be 20 to 100, and can further be 30 to 95. It can be understood that, in general, when the average distribution density Q is the same, the larger the particle size of the ternary positive electrode material, the more teeth of the particles of the ternary positive electrode material.

[0030] In some embodiments, the median particle size D50 of the particles of the ternary positive electrode material can be 10 μm to 20 μm. For polycrystalline ternary positive electrode materials, the median particle size D50 of the particles of the ternary positive electrode material can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any value within a numerical range consisting of any two of the above values. The median particle size D50 of the particles of the ternary positive electrode material can further be 10 μm to 15 μm.

[0031] In some embodiments, the angle of the teeth can be 0°~90°, and the angle of the teeth is the angle between the farthest end of each of the two adjacent teeth radially away from the main body and the center of the main body. The angle between the two adjacent teeth is 0°~90°, which is conducive to the meshing between the particles of the ternary positive electrode material, and further increases the contact area between the particles of the ternary positive electrode material, and reduces the stress of the teeth. The angle of the teeth can be 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90° or any value within the numerical range composed of any two of the above values. The angle of the teeth can further be 30°~60°.

[0032] In some embodiments, along the radial direction of the particle, the thickness of the tooth portion may account for 0.25% to 5% of the particle radius. Specifically, the thickness of the tooth portion may be 50 nm to 500 nm, which is beneficial to reducing the risk of fracture of the tooth portion while ensuring sufficient bite depth and balancing the mechanical properties and conductivity of the ternary positive electrode material. The radial thickness of the tooth portion may illustratively be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or any value within the numerical range consisting of any two of the above values. The radial thickness of the tooth portion may further be 100 nm to 400 nm.

[0033] In some embodiments, the specific surface area of the particles of the ternary cathode material can be 0.4 m 2 / g~0.9m 2 / g, the specific surface area of the ternary cathode material is low, which can reduce the side reaction between the ternary cathode material and the electrolyte. The specific surface area of the particles of the ternary cathode material can be 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g or any value within the numerical range consisting of any two of the above values. The specific surface area of the particles of the ternary positive electrode material can further be 0.4m 2 / g~0.6m 2 / g.

[0034] In some embodiments, the ternary positive electrode material is also doped with doped metal elements, which may include at least one of Ti, Zr, Al, W, Sb and Sr. Doping the above elements into the ternary positive electrode material can enhance the high temperature performance, structural stability and cycle performance of the ternary positive electrode material, thereby improving the electrochemical properties and service life of the ternary positive electrode material.

[0035] Furthermore, the mass percentage of the above-mentioned doping metal element in the ternary positive electrode material can be 0.01% to 1%. The appropriate doping amount is conducive to enhancing the effect of the doping metal element on improving the above-mentioned properties of the ternary positive electrode material. The mass percentage of the doping metal element in the ternary positive electrode material can be 0.01%, 0.03%, 0.05%, 0.08%, 1%, or any value within a numerical range consisting of any two of the above values. The mass percentage of the doping metal element in the ternary positive electrode material can further be 0.05% to 1%.

[0036] In some embodiments, a relatively thin metal oxide coating is formed on the surface of the particles of the ternary positive electrode material. The coating is evenly coated on the surface of the teeth and recesses, so that the ternary positive electrode material after the coating is formed still retains a microstructure layer similar to the original, having a gear-like structure, and the particles of the ternary positive electrode material can still interlock with each other. Coating the surface of the ternary positive electrode material with a relatively thin and uniform metal oxide coating can physically isolate the electrolyte, further reducing the occurrence of side reactions, and improving the chemical and thermal stability of the surface of the ternary positive electrode material. In particular, the metal oxide coating can improve the structural stability of the teeth located on the surface of the main body, thereby improving the cycling performance of the ternary positive electrode material.

[0037] The metal oxide coating layer contains a coating metal element, and the coating metal element may include at least one of zirconium, aluminum, magnesium, lanthanum and yttrium.

[0038] Specifically, the thickness of the metal oxide coating layer can be 0.1nm~10nm, which not only allows the coated ternary positive electrode material to retain the original microstructure layer, but also allows the particles to bite each other, and improves the conductivity, chemical stability and thermal stability of the surface of the ternary positive electrode material.

[0039] Furthermore, the mass percentage of the coating metal element in the ternary positive electrode material can be 0.02% to 0.2%. The appropriate coating amount is conducive to the metal oxide coating layer effectively improving the above-mentioned properties of the ternary positive electrode material while not affecting the external structure of the ternary positive electrode material. The mass percentage of the coating metal element in the ternary positive electrode material can be 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, or any value within the range of values consisting of any two of the above values. The mass percentage of the coating metal element in the ternary positive electrode material can further be 0.1% to 0.2%.

[0040] Compared with the prior art, the ternary cathode material provided in the embodiments of the present application has the following beneficial effects: 1. A microstructure layer is provided on the surface of the main body. The microstructure layer has a large number of teeth and recesses between two adjacent teeth, which is beneficial to the bite between the particles of the ternary positive electrode material, thereby increasing the contact area of the ternary positive electrode material particles, reducing the resistivity, and improving the electronic conductivity of the ternary positive electrode material. Without reducing the capacity of the ternary positive electrode material, the cycle performance of the ternary positive electrode material is effectively improved.

[0041] 2. There is also a metal oxide coating layer on the surface of the ternary positive electrode material, which can not only further improve the conductivity of the ternary positive electrode material, but also improve the structural stability of the ternary positive electrode material, especially the teeth, thereby extending the cycle life of the ternary positive electrode material.

[0042] See also Figure 3 As shown, based on the same inventive concept, the embodiment of the present application also provides a method for preparing a ternary positive electrode material, which specifically includes the following steps: Step S1: Mixing a nickel-cobalt-manganese precursor and a lithium source and sintering them once to obtain a matrix material.

[0043] In some embodiments, the ratio of the molar number of lithium in the lithium source to the total molar number of transition metals in the nickel-cobalt-manganese precursor can be (0.9-1.1):1, and can be 0.9:1, 0.92:1, 0.95:1, 1.0:1, 1.1:1, or any value within a range of any two of the above values. The molar ratio can further be (0.95-1.05):1.

[0044] In some embodiments, the lithium source may include at least one of lithium hydroxide, lithium nitrate, lithium carbonate, and lithium oxide.

[0045] In some embodiments, a dopant material may be added to the mixture of the nickel-cobalt-manganese precursor and the lithium source to improve the electronic conductivity, ionic conductivity, structural stability, and high-temperature performance of the ternary cathode material. The dopant material includes an oxide of a doped metal element, wherein the doped metal element includes at least one of Ti, Zr, Al, W, Sb, and Sr.

[0046] In some embodiments, the mass percentage of the doped metal element in the matrix material can be 0.01% to 1%, which is beneficial to improving the improvement effect of the doped metal element on the above-mentioned properties of the ternary positive electrode material.

[0047] In some embodiments, the mixing method may include mixing with a high-speed mixer, stirring, or grinding, etc., which can effectively and thoroughly mix the nickel-cobalt-manganese precursor and the lithium source. It is understood that the mixing method includes but is not limited to the above method, and any method that can achieve mixing of the nickel-cobalt-manganese precursor and the lithium source is possible.

[0048] In some embodiments, the primary sintering temperature can be 700°C to 850°C, and the primary sintering time can be 10 hours to 30 hours. By controlling the primary sintering temperature and time, the crystal structure of the matrix material is optimized, which is beneficial for improving the rate performance and cycle performance of the ternary cathode material.

[0049] In some embodiments, the primary sintering atmosphere may be an oxygen-containing atmosphere, which is beneficial for promoting the oxidation reaction of the nickel-cobalt-manganese precursor and improving the electrochemical properties and stability of the matrix material. The primary sintering atmosphere may further be an atmosphere with an oxygen concentration of 90% or more. The oxygen concentration of the oxygen-containing atmosphere may illustratively be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or any value within a numerical range consisting of any two of the above values. The primary sintering atmosphere may further be a pure oxygen atmosphere.

[0050] In step S2, the base material is acid-treated with an acid solution to form a plurality of teeth and recesses between any two adjacent teeth on the surface of the base material. The teeth and recesses constitute a microstructure layer, thereby obtaining a ternary positive electrode material.

[0051] Specifically, the base material is immersed in an acid solution for acid treatment, and the acid solution etches the surface of the base material. After the acid treatment, it is washed with deionized water until it is neutral to obtain a ternary positive electrode material. Due to the orientation of the grains on the surface of the base material and the difference in activity of different crystal faces, the degree of corrosion on the surface of the base material is different, resulting in the formation of teeth and recesses on the surface of the base material, resulting in a concave-convex gear-like structure, and the teeth and recesses constitute a microstructure layer. The interior of the base material is not corroded, forming a main body, and the above-mentioned microstructure layer is located on the surface of the main body. Since the ternary positive electrode material has multiple teeth on the surface, the particles of the ternary positive electrode material can bite each other through the teeth, increasing the contact area between the particles, thereby effectively reducing the powder resistivity of the ternary positive electrode material and improving the electronic conductivity of the ternary positive electrode material, achieving an effective improvement in the cycle performance of the ternary positive electrode material without sacrificing the capacity of the ternary positive electrode material.

[0052] In some embodiments, the acid treatment time can be 2h to 24h. The above time is conducive to the acid solution to fully etch the matrix material, thereby improving the conductivity of the ternary positive electrode material; without causing excessive etching, which damages or seriously degrades the crystal structure of the ternary positive electrode material, thereby maintaining the good electrochemical performance and structural stability of the ternary positive electrode material. The acid treatment time can be illustratively 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, or any value within the numerical range composed of any two of the above values. The acid treatment time can further be 2h to 8h.

[0053] In some embodiments, the temperature of the acid treatment may be 30°C to 80°C, which is conducive to the smooth progress of the acid solution etching reaction of the substrate material. The temperature of the acid treatment may illustratively be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or any value within a numerical range consisting of any two of the above values. The temperature of the acid treatment may further be 30°C to 50°C.

[0054] In some embodiments, the acid solution concentration can be 0.1 mol / L to 3 mol / L, which can provide appropriate corrosive power, allowing the acid solution to effectively etch the surface of the substrate material while avoiding damage to the substrate material structure caused by excessive etching. This acid solution concentration can increase the etching depth, thereby affecting the thickness of the teeth, forming a ternary cathode material with multiple teeth of appropriate radial thickness, thereby improving the conductivity and cycling stability of the ternary cathode material.

[0055] In some embodiments, acid treatment can be performed under stirring conditions with a stirring frequency of 1 Hz to 10 Hz, which is conducive to the acid solution etching the matrix material to form evenly distributed and uniformly thick teeth, facilitating inter-particle engagement, thereby further improving the conductivity and cycle stability of the ternary positive electrode material.

[0056] In some embodiments, the solid-to-liquid ratio of the matrix material to the acid solution can be 100 g / L to 1000 g / L, which is conducive to the acid solution fully infiltrating the matrix material and performing moderate etching on the matrix material. The solid-to-liquid ratio of the matrix material to the acid solution can illustratively be 100 g / L, 200 g / L, 300 g / L, 400 g / L, 500 g / L, 600 g / L, 700 g / L, 800 g / L, 900 g / L, 1000 g / L, or any value within a numerical range consisting of any two of the above values. The solid-to-liquid ratio of the matrix material to the acid solution can illustratively be 300 g / L to 800 g / L.

[0057] In some embodiments, the acid solution may include at least one of an inorganic acid and an organic acid, both of which can effectively etch the surface of the substrate material. The inorganic acid may include at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and inorganic acids are relatively acidic. The organic acid may include at least one of citric acid, oxalic acid, succinic acid, malic acid, acetic acid, and maleic acid, and generally has low corrosiveness, can control the etching rate, and reduce damage to the internal structure of the material. It is understood that the acid solution may be a mixed solution of an organic acid and an inorganic acid. A reasonable combination of the inorganic acid and the organic acid can better control the efficiency and rate of etching, which is conducive to the formation of an ideal structure on the surface of the substrate material.

[0058] After the acid treatment, the preparation method may further include the following steps to coat the ternary positive electrode material: Step S3: adding the ternary positive electrode material to water containing the metal coating material, washing and filtering to obtain a mixed material.

[0059] Specifically, compared with dry coating, water washing and filtration can evenly coat the coated metal elements on the surface of the ternary positive electrode material without destroying the external structure of the ternary positive electrode material.

[0060] In some embodiments, the coating material may include a compound of a coating metal element, wherein the coating metal element includes at least one of zirconium, aluminum, magnesium, lanthanum, and yttrium. Coating the surface of the ternary cathode material with the coating metal element further improves the conductivity and structural stability of the ternary cathode material, and reduces side reactions with the electrolyte.

[0061] In some embodiments, the mass percentage of the coating metal element in the ternary positive electrode material can be 0.02% to 0.2%, which is beneficial for controlling the thickness of the coating layer so as to coat a thinner coating layer on the surface of the particle.

[0062] Specifically, the coating layer thickness can be 0.1nm~10nm, which not only allows the coated ternary positive electrode material to retain the original microstructure layer, but also allows the particles to bite each other, and improves the conductivity, chemical stability and thermal stability of the surface of the ternary positive electrode material.

[0063] Step S4: sintering the mixed material twice to form a metal oxide coating layer on the surface of the ternary positive electrode material.

[0064] Specifically, the mixed material is sintered twice to form a thin and uniform metal oxide coating layer on the surface of the ternary positive electrode material, which is beneficial to improving the conductivity of the ternary positive electrode material and the structural stability of the ternary positive electrode material (especially the teeth), thereby extending the cycle life of the ternary positive electrode material.

[0065] In some embodiments, the secondary sintering temperature can be 500°C to 700°C, and the secondary sintering time can be 5 hours to 15 hours. A lower sintering temperature of 500°C to 700°C is conducive to forming a high-quality, evenly distributed metal oxide coating layer without affecting the crystal structure of the ternary cathode material.

[0066] In some embodiments, the atmosphere of the secondary sintering can be an oxygen-containing atmosphere, which is conducive to the formation of the metal oxide coating layer structure. The atmosphere of the secondary sintering can further be an atmosphere with an oxygen concentration of 50% or more, and the oxygen concentration of the oxygen-containing atmosphere can illustratively be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 83%, 85%, 90%, 95%, 100% or any value within the numerical range composed of any two of the above values. The atmosphere of the secondary sintering can further be an oxygen-containing atmosphere with an oxygen concentration of 90% or more, and can further be a pure oxygen atmosphere.

[0067] Compared with the prior art, the preparation method of the ternary cathode material provided in the embodiment of the present application has the following beneficial effects: 1. By etching the substrate with an acid solution, a microstructured layer consisting of teeth and recesses is formed on the surface of the unaffected bulk material, based on the orientation of the substrate's surface grains and the differences in activity between different crystal faces. This method, without requiring complex processes or procedures, effectively improves the cycling performance of the ternary cathode material without sacrificing its capacity.

[0068] 2. By further adjusting the acid treatment time, the acid solution is conducive to fully etching the matrix material, thereby improving the conductivity of the ternary positive electrode material and enabling the ternary positive electrode material to maintain good electrochemical properties and structural stability.

[0069] 3. A thin, high-quality, and evenly distributed metal oxide coating layer is formed on the surface of the ternary positive electrode material through water washing and secondary sintering, which is beneficial to improving the conductivity of the ternary positive electrode material and the structural stability of the ternary positive electrode material (especially the teeth).

[0070] 4. This preparation method is simple and efficient, which is conducive to the large-scale production of ternary positive electrode materials and has excellent commercial prospects.

[0071] An embodiment of the present application also provides an electrochemical device (such as a battery), which includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the positive electrode plate includes a positive electrode active material, and the positive electrode active material is the ternary positive electrode material as described above.

[0072] The electrochemical device prepared using the aforementioned ternary cathode material has the advantages of good cycle performance, high temperature performance and high energy density.

[0073] The above-mentioned ternary cathode material, preparation method thereof, and electrochemical device are further described below through specific examples.

[0074] Example 1 Step S1: Mix a nickel-cobalt-manganese precursor, lithium hydroxide as a lithium source, and zirconium oxide as a doping material and perform a single sintering in an oxygen atmosphere with an oxygen content of more than 90% to obtain a matrix material, wherein the molar ratio of Li to the transition metal in the nickel-cobalt-manganese precursor is 1.05:1, the mass percentage of the element Zr in the doping material in the matrix material is 0.2%, and the single sintering condition is sintering at 710°C for 15 hours.

[0075] Step S2: Add the matrix material to a 1 mol / L hydrochloric acid solution and stir at a rate of 5 Hz, and perform acid treatment at 40°C for 5 hours, wherein the solid ratio of the matrix material to the acid solution is 500 g / L, so as to form a plurality of teeth and recesses between any two adjacent teeth on the surface of the matrix material, the teeth and recesses constitute a microstructure layer, thereby obtaining a ternary positive electrode material.

[0076] Example 2 The difference between Example 2 and Example 1 is that in step S2, the acid treatment time is 2 hours. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and will not be described in detail here.

[0077] Example 3 The difference between Example 3 and Example 1 is that in step S2, the acid treatment time is 8 hours. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and will not be described in detail here.

[0078] Example 4 The difference between Example 4 and Example 1 is that in step S2, the concentration of the acid solution is 0.1 mol / L. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and will not be described in detail here.

[0079] Example 5 The difference between Example 5 and Example 1 is that in step S2, the concentration of the acid solution is 2 mol / L. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and will not be described in detail here.

[0080] Example 6 The difference between Example 6 and Example 1 is that in step S2, the acid solution is acetic acid. The preparation method of the remaining ternary cathode materials is basically the same as that of Example 1 and will not be described in detail here.

[0081] Example 7 The difference between Example 7 and Example 1 is that in step S2, the solid-liquid ratio of the matrix material to the acid solution is 100 g / L. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and will not be described in detail here.

[0082] Example 8 The difference between Example 8 and Example 1 is that in step S2, the solid-liquid ratio of the matrix material to the acid solution is 1000 g / L. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and will not be described in detail here.

[0083] Example 9 The difference between Example 9 and Example 1 is that after step S2, the method for preparing the ternary positive electrode material further includes: Step S3, adding the ternary positive electrode material to an aqueous solution containing a metal coating of sodium aluminate, washing and filtering, and drying to obtain a mixed material, wherein the mass percentage of the coated metal element in the coated material to the ternary positive electrode material is 0.08%.

[0084] Step S4: performing secondary sintering on the mixed material at 600° C. for 10 hours in an oxygen atmosphere to form a metal oxide coating layer on the surfaces of the teeth and the recesses.

[0085] The preparation methods of the remaining ternary positive electrode materials are basically the same as those in Example 1 and will not be described in detail here.

[0086] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that step S2 is not performed, and the obtained base material is a ternary positive electrode material. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 1 and is not described in detail here.

[0087] Comparative Example 2 The difference between Comparative Example 2 and Example 9 is that step S2 is not performed, and the resulting base material is a ternary positive electrode material. The preparation method of the remaining ternary positive electrode materials is basically the same as that of Example 9 and is not described in detail here.

[0088] 1. The following tests were performed on the ternary cathode materials obtained in Examples 1-9 and Comparative Examples 1-2. The test results are shown in Tables 1 and 2.

[0089] Test method: 1. Scanning Electron Microscope (SEM) Testing: The samples were polished using a Hitachi IM4000Plus ion cross-section polisher to obtain polished cross-section samples. A Hitachi SU8000 field emission scanning electron microscope (SEM) was then used. This instrument, with its high-resolution imaging capabilities, clearly observed the microscopic morphology and structural features of the cathode material. The acceleration voltage was 1.00 kV, and the magnification was 8000x.

[0090] 2. Particle Size Measurement: Particle size was measured using a Mastersizer 3000 laser diffraction technique. After 5 minutes of internal ultrasonic dispersion, the particle size distribution was measured. The particle size was determined by measuring the intensity of scattered light as the laser beam passed through the dispersed particle sample. This data was then used to analyze and calculate the particle size distribution, which formed the scattering spectrum. D50 is the median particle size, the particle size at which the cumulative particle size distribution percentage for a sample reaches 50%.

[0091] 3. Structural test of ternary cathode materials: (1) Test method for the number of teeth and the average distribution density Q of the teeth in the particles of the ternary positive electrode material: The sample was polished using a Hitachi IM4000Plus ion cross-section polisher to obtain a polished cross-section sample. Scanning electron microscopy was then performed with an acceleration voltage of 1.00 kV and a magnification of 8000 times. SEM images of ten or more polycrystalline particles of the ternary positive electrode material were randomly selected, and the number of teeth M and particle diameter D on the surface of each particle were counted. The distribution density of the teeth in the ternary positive electrode material particles was calculated according to q=M / πD, with Q being the average value of q. The average distribution density Q of the teeth in the ternary positive electrode material was obtained.

[0092] (2) Test of the uniformity of the distribution of teeth on the surface of the ternary positive electrode material: a cross-sectional scanning electron microscope image of the ternary positive electrode material is obtained with an acceleration voltage of 1.00 kV and a magnification of 8000 times. The surface of the ternary positive electrode material particle is divided into n regions of equal size, where n is an integer greater than or equal to 5, and N is the ratio of the number of teeth in any two regions on the surface of the ternary positive electrode material.

[0093] (3) Test of radial thickness of teeth: A cross-sectional scanning electron microscope image of the ternary cathode material was obtained with an acceleration voltage of 1.00 kV and a magnification of 8000 times. The radial thickness of five teeth distributed in different areas of the same particle surface in the scanning electron microscope image was measured using ImageJ software, and the average value was calculated.

[0094] 4. Specific surface area test of ternary cathode materials: Using the nitrogen adsorption-desorption method, at liquid nitrogen temperature, the equilibrium adsorption amount of nitrogen on the surface of an object is related to its specific surface area and other characteristics. Combined with the law of change of adsorption amount with relative pressure during the adsorption process, the specific surface area test can be performed.

[0095] 5. Ternary cathode material powder resistivity test: Take 1g powder sample and use Yuanneng Technology's PRCD1100 powder resistance tester with test pressures of 12MPa and 80MPa to test the powder resistivity.

[0096] 6. Electrical performance test conditions are as follows: The positive electrode material, glue (PVDF and NMP = 1:15), binder, and conductive agent were dried under high temperature and vacuum, then evenly dispersed in a ratio of active material: conductive agent: PVDF = 96.5:1.5:2. The mixture was then evenly coated onto 15µm thick aluminum foil, vacuum dried at 110°C, and rolled using a roller press. Finally, the positive electrode sheets were cut into circular pieces with a diameter of 14mm using a slicer. The battery separator was a PE membrane, the electrolyte was a 1 mol / L LiPF6 solution in a mixture of dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC), and the negative electrode was a metal lithium sheet. The battery assembly was completed in a sealed glove box filled with an inert dry atmosphere.

[0097] The button cell prepared above was subjected to a capacity test under the following test conditions: at 25°C, a voltage range of 3.0V to 4.3V, a charge and discharge rate of 0.1CV / 0.1CD, and the charge and discharge specific capacity and coulombic efficiency were measured.

[0098] The button cell prepared above was subjected to a cycle capability test under the following test conditions: at 45°C, a voltage range of 3.0-4.3V, a charge and discharge rate of 0.5CV / 1.0CD, and 20 cycles. The capacity retention rate after 20 cycles was measured.

[0099] The above results show: like Figure 4 As shown, Figure 4 Figure a is a scanning electron microscope image of the ternary cathode material particles in Example 1. In Example 1, convex and concave portions are formed on the surface of the particles by etching; Figure 4 Figure b is a scanning electron microscope image of the ternary cathode material particles in Comparative Example 1. There are essentially no teeth, and the particles cannot interlock. Combined with Tables 1 and 2, the ternary cathode material particles in Example 1 can interlock with each other through the teeth, increasing the contact area between the particles. This significantly reduces the powder resistivity of the ternary cathode material and increases its electronic conductivity, effectively improving the cycling performance of the ternary cathode material without sacrificing its capacity.

[0100] Compared with Comparative Example 1-2, the ternary positive electrode material particles in Example 1-9 have engageable protrusions, and the powder resistivity of the ternary positive electrode material in Example 1-9 is lower than that in Comparative Example 1-2, and the conductivity is improved; the capacity of the battery made of the ternary positive electrode material in Example 1-9 is basically the same as that of Comparative Example 1-2, but the cycle performance of the battery in Example 1-9 is significantly improved.

[0101] Among them, the acid treatment of Example 1 has the best etching effect. The average distribution density Q of the teeth in the obtained ternary positive electrode material particles is 1.37 / μm, and the uniformity N reaches 100%, indicating that the number of teeth is appropriate and evenly distributed, the number of teeth and recesses is equivalent, and the radial thickness of the teeth is 310nm, which is also within the appropriate range, which is conducive to achieving the best bite effect. The powder resistance of the ternary positive electrode material is the lowest and the cycle performance is good.

[0102] Specifically: Compared with Example 2, Example 1 extends the acid treatment time, increases the number of teeth, increases the radial thickness of the teeth, improves the bite effect, reduces the powder resistance, and further improves the cycle performance.

[0103] Compared with Example 3, Example 1 shortens the acid treatment time, reduces the corrosion of the acid solution on the teeth, has an appropriate number of teeth and radial thickness, has a better bite effect, reduces powder resistance, and further improves cycle performance.

[0104] Compared with Example 4 and Example 5, Example 1 adjusts the concentration of the acid solution to obtain the optimal number of teeth and radial thickness, resulting in better bite effect, reduced powder resistance, and further improved cycle performance.

[0105] Compared to Example 6 which uses a less acidic organic acid, Example 1 uses a more acidic hydrochloric acid solution, which improves the etching effect, the number of teeth and the radial thickness are appropriate, the bite effect is better, the powder resistance is reduced, and the cycle performance is further improved. Compared to Examples 7 and 8, Example 1 adjusts the solid-liquid ratio of the matrix material and the acid solution to obtain the optimal number of teeth and radial thickness, the bite effect is better, the powder resistance is reduced, and the cycle performance is further improved. Compared to Example 1, Example 9 adds a metal oxide coating layer. Although the powder resistance increases slightly, the coating further improves the cycle performance of the ternary positive electrode material. And compared to Comparative Example 2 which only has the same metal oxide coating layer but does not have a convex and concave structure, the powder resistivity in Example 9 is significantly reduced, and the cycle performance is improved.

[0106] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A ternary cathode material, characterized in that: The ternary positive electrode material includes a plurality of particles, each of the particles includes a main body and a microstructure layer located on the surface of the main body, the microstructure layer includes a plurality of teeth and a recess located between any two adjacent teeth, and the teeth extend radially from one end close to the main body to an end away from the main body.

2. The ternary cathode material according to claim 1, characterized in that The average distribution density Q of the teeth in the ternary positive electrode material is 0.5 / μm~2.5 / μm, and the testing method of Q includes: obtaining a scanning electron microscope image of the cross-section of the ternary positive electrode material, identifying the number M of the teeth of multiple particles in the ternary positive electrode material and the particle size D of the particles, and calculating the distribution density q of the teeth in the particles, wherein q=M / πD, and the average distribution density Q is the average value of the distribution density q.

3. The ternary cathode material according to claim 1, characterized in that The uniformity N of the distribution of the teeth on the surface of the ternary positive electrode material is 70%~100%. A scanning electron microscope image of the cross-section of the particle of the ternary positive electrode material is obtained. The surface of the particle includes n areas of equal size, n is an integer greater than or equal to 5, and N is the ratio of the number of teeth in any two areas on the surface of the particle.

4. The ternary cathode material according to claim 1, characterized in that The ternary cathode material satisfies at least one of the following characteristics: (1) The angle of the teeth is 0°~90°; (2) The radial thickness of the tooth portion is 50 nm to 500 nm; (3) The number of teeth of the particles of the ternary positive electrode material is 15 to 160; (4) The median particle size D50 of the particles of the ternary positive electrode material is 10 μm to 20 μm; (5) The specific surface area of the particles of the ternary positive electrode material is 0.4 m 2 / g~0.9m 2 / g.

5. The ternary cathode material according to claim 1, characterized in that The particles of the ternary positive electrode material further include a metal oxide coating layer, and the metal oxide coating layer is located on surfaces of the teeth and the recesses.

6. A method for preparing a ternary positive electrode material, characterized in that: include: Mixing a nickel-cobalt-manganese precursor, a lithium source and a doping material and performing a primary sintering to obtain a matrix material; as well as The base material is acid-treated with an acid solution to form a plurality of teeth and recesses between any two adjacent teeth on the surface of the base material, wherein the teeth and the recesses constitute a microstructure layer, thereby obtaining the ternary positive electrode material.

7. The method for preparing the ternary cathode material according to claim 6, characterized in that: The acid treatment time is 2h~24h; and / or The temperature of the acid treatment is 30°C to 80°C.

8. The method for preparing the ternary cathode material according to claim 6, wherein: The preparation method of the ternary cathode material satisfies at least one of the following characteristics: (1) The concentration of the acid solution is 0.1 mol / L to 3 mol / L; (2) The solid-liquid ratio of the matrix material to the acid solution is 100 g / L to 1000 g / L; (3) The acid solution includes an inorganic acid and / or an organic acid.

9. The method for preparing the ternary cathode material according to claim 6, wherein: The preparation method further comprises: Adding the ternary positive electrode material to water containing a metal-coated material, washing the material with water, and filtering the mixture to obtain a mixed material; and The mixed material is subjected to secondary sintering to form a metal oxide coating layer on the surfaces of the teeth and the recesses.

10. An electrochemical device, characterized in that The electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is a ternary positive electrode material as described in any one of claims 1 to 5 or a ternary positive electrode material prepared by the preparation method of the ternary positive electrode material as described in any one of claims 6 to 9.

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