High-nickel ternary positive electrode material, preparation method thereof and electrochemical device

Abstract

The invention provides a high-nickel ternary positive electrode material, a preparation method thereof and an electrochemical device. The positive electrode material comprises a matrix and a composite coating layer coating the surface of the matrix, the matrix is a nickel-cobalt-manganese ternary material, the composite coating layer comprises a first coating layer, a second coating layer and a third coating layer which are sequentially arranged from inside to outside, the first coating layer comprises at least one of Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo and Sn elements, the second coating layer comprises perovskite type crystals, and the third coating layer comprises at least one of Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo and Sn elements. And the third coating layer comprises at least one of Al, B, Ti, W, Li, P, Sr, Er and Mo elements. According to the positive electrode material provided by the invention, through the synergistic effect of the specific chemical composition of the matrix and the composite coating layer, the content of residual alkali on the surface can be reduced, the dissolution of transition metal can be inhibited and the transmission kinetics of lithium ions on the interface can be improved while high specific capacity is maintained.

Description

A high-nickel ternary cathode material and its preparation method, and an electrochemical device thereof. Technical Field

[0001] This application relates to the field of new energy technology, and in particular to a high-nickel ternary cathode material and its preparation method and electrochemical device. Background Technology

[0002] With the increasing demands for energy density and cycle life of lithium-ion batteries from new energy vehicles, high-nickel ternary cathode materials have become a research hotspot due to their high energy density and good cycle performance.

[0003] However, existing high-nickel ternary cathode materials have a lot of residual alkaline impurities on their surface, which are prone to side reactions with the electrolyte, exacerbating structural damage and metal ion dissolution. Especially under high voltage, their structural stability and cycle stability face severe challenges. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above technical problems, this application provides a high-nickel ternary cathode material.

[0005] In addition, this application also provides a method for preparing the aforementioned high-nickel ternary cathode material and an electrochemical device using the cathode material.

[0006] In a first aspect, embodiments of this application provide a high-nickel ternary cathode material, comprising a substrate and a composite coating layer covering the surface of the substrate. The substrate is a nickel-cobalt-manganese ternary material. The composite coating layer comprises a first coating layer, a second coating layer, and a third coating layer arranged sequentially from the inside to the outside. The first coating layer comprises at least one of the elements Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn. The second coating layer comprises perovskite-type crystals. The third coating layer comprises at least one of the elements Al, B, Ti, W, Li, P, Sr, Er, and Mo.

[0007] Based on the first aspect, in some possible embodiments, the perovskite crystal has the general formula LiAO3 and / or Li3AO4, wherein the a element includes at least one of Nb and Ta. Based on the first aspect, in some possible embodiments, the mass ratio of the first coating layer to the total mass of the matrix is ​​0.01% to 5.00%:1; wherein the mass ratio of Zr, Sr, Al, Ti, and Nb elements in the first coating layer to the matrix is ​​further preferably 0.05% to 0.50%:1; and the weight ratio of Co element in the first coating layer to the matrix is ​​further preferably 0.60% to 3.00%:1. Based on the first aspect, in some possible embodiments, the mass ratio of the second coating layer to the total mass of the first material is 0.01% to 2.00%:1; wherein the total mass of the first material is the sum of the masses of the matrix and the first coating layer; and the mass ratio of the second coating layer to the first total mass is further preferably 0.03% to 0.30%.

[0008] Based on the first aspect, in some possible embodiments, the mass ratio of the third coating layer to the total mass of the second material is 0.01% to 2.00%:1. Wherein, the total mass of the second material is the sum of the total mass of the first material and the mass of the second coating layer. The mass ratio of the third coating layer to the total mass of the second material is further preferably 0.03% to 0.30%:1. Based on the first aspect, in some possible embodiments, the chemical formula of the matrix is ​​Li. 1+X Ni α Co β Mn γ M θ O2, wherein 0 ≤ X ≤ 0.1, 0.6 ≤ α < 1, 0 < β ≤ 0.4, 0 < γ ≤ 0.4, and β + γ ≤ 0.4, 0 ≤ θ ≤ 0.4; M is a doping element, which includes at least one of Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn. Preferably, the doping element is Zr, Sr, Al, Ti, or Nb.

[0009] Based on the first aspect, in some possible embodiments, the high-nickel ternary cathode material comprises single-crystal particles, wherein the median particle size Dv50 of the single-crystal particles is 1.0 μm to 15.0 μm, and Dv2 is 0.5 μm to 8.0 μm. The Dv50 of the single-crystal particles is further preferably 2.5 μm to 4.5 μm, and the Dv2 is further preferably 0.5 μm to 2.5 μm.

[0010] Secondly, this application provides a method for preparing a high-nickel ternary cathode material, comprising: mixing a lithium salt, an additive, and a nickel-cobalt-manganese hydroxide precursor and performing a first sintering to obtain the matrix; mixing the matrix with a first coating material and performing a second sintering to form a first coating layer on the surface of the matrix, obtaining a first material; wet mixing and drying the first material with a second coating material to form a second coating layer on the surface of the first coating layer, obtaining a second material, wherein the second coating material comprises perovskite crystals; and mixing the second material with a third coating material and performing a third sintering to form a third coating layer on the surface of the second coating layer, thereby obtaining the high-nickel ternary cathode material.

[0011] Based on the second aspect, in some possible embodiments, the general formula of the perovskite crystal includes LiAO3 and / or Li3AO4, and the element A includes at least one of Nb and Ti.

[0012] Based on the second aspect, in some possible embodiments, the mass ratio of element A to the first material is 0.01% to 2.00%:1, and the mass ratio of element A to the first material is further preferably 0.03% to 0.30%:1.

[0013] Based on the second aspect, in some possible embodiments, the wet mixing includes: mixing the first material, the solvent, and the second coating material, stirring for 2 to 15 minutes, followed by solid-liquid separation and drying the resulting solid to obtain the second material, wherein the mass ratio of the first material to the second coating material is 1:0.01% to 2.00%. The mass ratio of the first material to the second coating material is further preferably 1:0.03% to 0.30%. The mass ratio of the solvent to the first material is (0.5-2):1. Based on the second aspect, in some possible embodiments, the primary sintering includes sequentially performing a first-stage sintering and a second-stage sintering; the temperature of the first-stage sintering is 550°C to 750°C, and the time is 5 to 15 hours; the temperature of the second-stage sintering is 800°C to 900°C, and the time is 5 to 25 hours.

[0014] Based on the second aspect, in some possible embodiments, the temperature of the three sintering processes is 200°C to 400°C, and the time is 5 hours to 15 hours.

[0015] Based on the second aspect, in some possible embodiments, the general chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni. α Co β Mn γ M θO2; wherein, 0.6≤α<1, 0<β≤0.4, 0<γ≤0.4, and β+γ≤0.4, 0≤θ≤0.4; M is a doping element, which includes at least one of Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo and Sn.

[0016] Based on the second aspect, in some possible embodiments, the third coating material includes at least one of the elements Al, B, Ti, W, Li, P, Sr, Er, and Mo.

[0017] Thirdly, this application provides an electrochemical device, the electrochemical device including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material being the high-nickel ternary positive electrode material as described above, or a positive electrode material prepared by the preparation method of the high-nickel ternary positive electrode material as described above.

[0018] Compared to existing technologies, the high-nickel ternary cathode material provided in this application achieves a comprehensive improvement and balance in capacity, cycle life, rate performance, and low-temperature power performance by constructing a composite structure consisting of a matrix, a first coating layer, a second coating layer, and a third coating layer. First, the first coating layer containing the first element and the second coating layer, made of perovskite crystal, work together to effectively neutralize and reduce residual alkaline substances on the material surface, reducing side reactions with the electrolyte at the source, thereby inhibiting the dissolution of transition metal ions and improving the bulk structural stability of the high-nickel ternary cathode material under high voltage. Second, the intermediate coating layer, made of distorted perovskite crystal, not only has stable chemical properties but also provides a fast channel for lithium-ion transport. This characteristic, combined with the effects of the first and third coating layers, allows the material to maintain high specific capacity while improving its rate discharge capability and DC internal resistance (DCR) performance under low-temperature conditions. Furthermore, the third coating layer, containing the second element, further strengthens the interface protection. Therefore, this solution achieves a comprehensive improvement and balance in the capacity, cycle life, rate performance, and low-temperature power performance of high-nickel ternary materials, providing a reliable solution to meet the fast charging and high-power application requirements of high-energy-density batteries. Attached Figure Description

[0019] Figure 1 is a process flow diagram of the preparation of high-nickel ternary cathode material in one embodiment of this application.

[0020] Figure 2 is a scanning electron microscope (SEM) image of the surface of the high-nickel ternary cathode material prepared in Example 1 of this application.

[0021] Figure 3 is a scanning electron microscope (SEM) image of the surface of the high-nickel ternary cathode material prepared in Comparative Example 2 of this application.

[0022] Figure 4 is a bar chart comparing the residual alkali content of the cathode materials in Examples 1 to 4 of this application with those in Comparative Examples 1 to 4.

[0023] Figure 5 is a bar chart comparing the amount of nickel and manganese metal elements dissolved in the electrolyte of the cathode materials of Examples 1 to 4 and Comparative Examples 1 to 4 of this application.

[0024] Figure 6 shows the cycle performance curves of the cathode materials of Examples 1 to 4 and Comparative Examples 1 to 4 at 45°C and the DC internal resistance (DCR) test voltage drop curves at -15°C. Detailed Implementation

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this application pertain. The terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the embodiments of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0026] The following describes some embodiments of this application in detail. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0027] The present application will be further described below with reference to specific embodiments and comparative examples.

[0028] To address the issues of high residual alkali content and severe interfacial side reactions in existing high-nickel ternary cathode materials, the industry currently mainly improves interfacial stability through surface coating methods, such as high-temperature coating with metal oxides like Al2O3. While coating with metal oxides like Al2O3 can isolate electrolyte corrosion and reduce surface impedance to some extent, this coating layer itself is an electronic insulator, often inevitably leading to capacity loss in the active material and an increase in overall internal resistance. This makes it difficult to maintain high capacity while simultaneously improving overall electrochemical performance such as rate capability and low-temperature performance. To overcome this technical bottleneck, the inventors conceived of developing a novel coating layer with excellent ionic conductivity and multiple interface improvements through a redesign of materials and processes.

[0029] Therefore, this application provides a high-nickel ternary cathode material. It comprises a substrate and a composite coating layer covering the surface of the substrate. The substrate is a nickel-cobalt-manganese ternary material. The composite coating layer includes a first coating layer, a second coating layer, and a third coating layer arranged sequentially from the inside out. The first coating layer includes at least one element selected from Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn. The second coating layer comprises perovskite-type crystals. The third coating layer includes at least one element selected from Al, B, Ti, W, Li, P, Sr, Er, and Mo.

[0030] This high-nickel ternary cathode material achieves multiple technical effects through the construction of a composite structure of "matrix / first coating layer / second coating layer / third coating layer": First, the first and second coating layers can effectively neutralize and reduce the residual alkalinity on the material surface, reducing side reactions with the electrolyte from the source, thereby inhibiting the dissolution of transition metal ions and improving the structural and chemical stability of the material; the introduction of the third coating layer can further protect the interface and improve the material capacity at the same time; second, the second coating layer is composed of distorted perovskite crystals with ABO3 or A3BO4 structure. This layer is not only chemically stable, but also provides a fast channel for lithium ion migration. This characteristic, together with the third coating layer, enables the material to maintain a high specific capacity while improving rate performance and DC internal resistance (DCR) performance under low temperature conditions. Therefore, this composite structure achieves a comprehensive balance between the high capacity, long cycle life, excellent rate performance, and good low-temperature power performance of high-nickel ternary materials, providing a key material solution for developing high-performance lithium-ion batteries suitable for fast charging and high-power applications.

[0031] In some embodiments, the general formula of the distorted perovskite crystal includes LiAO3 and / or Li3AO4, wherein the a element includes at least one of Nb and Ta. These two types of distorted perovskite crystals can form a uniform and stable coating layer on the material surface. This coating layer helps reduce the residual alkali content of the material and inhibits the dissolution of transition metal ions, thereby having a positive effect on improving the material's initial discharge capacity, rate performance, and DC internal resistance (DCR) performance under low-temperature conditions.

[0032] In some embodiments, the mass ratio of the first coating layer to the total mass of the substrate is 0.01% to 5.00%:1, which helps to ensure the formation of a complete and dense coating while avoiding the negative impact of an excessively thick coating layer on lithium-ion diffusion and the overall specific capacity of the material. This mass ratio can be exemplarily 0.10%:1, 0.50%:1, 1.20%:1, 2.00%:1, 5.00%:1, or any value within the range of any two of the above values.

[0033] In some embodiments, the elements in the first coating layer may further include at least one of Co, Zr, Sr, Al, Ti, and Nb, which are beneficial for maintaining the stability of the high-nickel ternary layered structure.

[0034] The weight ratio of Zr, Sr, Al, Ti, and Nb elements in the first coating layer to the matrix is ​​preferably 0.05% to 0.50%:1, and the weight ratio of Co element in the first coating layer to the matrix is ​​preferably 0.60% to 3.00%:1. Controlling the addition of each element within the above ranges facilitates the formation of a uniform, dense, and chemically stable first coating layer on the matrix surface, thereby more effectively reducing residual alkali on the material surface, improving interfacial stability, and providing a good foundation for the uniform loading of the subsequent second coating layer. The total mass of the first material is the sum of the masses of the matrix and the first coating layer, and the mass ratio of the second coating layer to the total mass of the first material is 0.01% to 2.00%:1. This approach helps to fully utilize the fast ion conductor function provided by its distorted perovskite structure, reduce interfacial charge transfer impedance, and maintain good processing performance during electrode fabrication. The weight ratio can be, for example, 0.10%:1, 0.30%:1, 1.00%:1, 2:1, or any value within the range of any two of the above values. More preferably, the weight ratio is between 0.03% and 0.30%. By controlling the weight ratio within the above range, it is beneficial to ensure the fast ion conductor function is fully utilized and interfacial impedance is effectively reduced, while avoiding excessively thick coating layers that could affect the overall energy density and electrode processing performance of the material, thereby comprehensively optimizing the power characteristics and process applicability of the material. The total mass of the second material is the sum of the total mass of the first material and the mass of the second coating layer. The mass ratio of the third coating layer to the total mass of the second material is 0.01% to 2.00%:1, which is beneficial for forming a suitable and stable protective layer on top of the second coating layer. This further strengthens interfacial protection and suppresses side reactions without excessively increasing interfacial impedance, thereby synergistically improving the cycling stability and capacity retention of the material. The mass ratio can be, for example, 0.01%:1, 0.03%:1, 0.05%:1, 0.10%:1, 0.30%:1, 1.00%:1, 2:1, or any value within the range of any two of the above values. Furthermore, the mass ratio of the third coating layer to the substrate is preferably 0.03% to 0.30%:1, which can further improve the interfacial structure density and chemical stability of the material, thereby more effectively reducing the loss of active lithium during cycling and synergistically improving the capacity retention and long-term cycle life of the material.

[0035] Furthermore, by jointly controlling the proportions of the three coating layers with the first and second materials, this application can synergistically adjust the balance between surface modification, interfacial conduction, and outer layer protection, thereby achieving the goal of reducing the alkali content on the material surface, improving power and low-temperature performance, while also taking into account the high specific capacity and cycle stability of the material, thus obtaining a high-nickel ternary cathode material with better overall performance.

[0036] In some embodiments, the general chemical formula of the matrix is ​​Li 1+X Ni α Co β Mn γ M θ O2, where 0≤X≤0.1, 0.6≤α<1, 0<β≤0.4, 0<γ≤0.4, and β+γ≤0.4, 0≤θ≤0.4; M is a doping element, which includes at least one of Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo and Sn.

[0037] The high-nickel ternary cathode material comprises single-crystal particles, wherein the median particle size Dv50 of the single-crystal particles is 1.0 μm to 15.0 μm. This range is beneficial for balancing the tap density of the material with the lithium-ion solid-phase diffusion path length, thereby achieving both high energy density and good rate performance. The median particle size Dv50 of the single-crystal particles is further preferably 2.5 μm to 4.5 μm. Dv50 can be, for example, 1.0 μm, 2.0 μm, 2.5 μm, 3.5 μm, 4.5 μm, 8 μm, 15 μm, or any value within the range of any two of the above values.

[0038] The Dv2 of the single crystal particles is 0.5μm to 8.0μm. This range is beneficial for controlling the fine powder content in the material, ensuring the uniformity of the slurry and the flatness of the electrode coating in the subsequent coating process. Dv2 is further preferably 0.5μm to 2.5μm. Exemplary values ​​of Dv2 can be 0.5μm, 0.8μm, 1.0μm, 1.5μm, 4μm, 8μm, or any value within the range of any two of the above values.

[0039] Please refer to Figure 1. An embodiment of this application provides a method for preparing a high-nickel ternary cathode material, including the following steps: Step S1: Mix lithium salt, additives and nickel cobalt manganese hydroxide precursor and sinter once to obtain a matrix.

[0040] The general chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni α Co β Mn γ M θO2, where 0.6≤α<1, 0<β≤0.4, 0<γ≤0.4, and β+γ≤0.4, 0≤θ≤0.4, and M is a dopant element, which includes at least one of Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn. This general formula design helps ensure that the synthesized matrix material has the high capacity resulting from the high nickel content, while stabilizing the crystal structure with appropriate amounts of cobalt (β) and manganese (γ), thus providing an ideal host for subsequent coating modification. Doping with the above M elements is beneficial for introducing structurally stabilizing elements during the material synthesis process, strengthening the lattice, and reducing mechanical stress and phase transitions during cycling. Furthermore, the dopant element M can include Al, Zr, combinations of Al and Zr, combinations of Al, Ti, and B, combinations of Nb and Ta, etc. α can be, for example, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.88, 0.90, 0.92, 0.95, 0.99, or 1, or any value within the range of any two of the above values. β can be, for example, 0.1, 0.2, 0.3, or 0.4, or any value within the range of any two of the above values. γ can be, for example, 0.1, 0.2, 0.3, or 0.4, or any value within the range of any two of the above values. θ can be, for example, 0, 0.01, 0.02, 0.05, 0.10, or 0.20, or any value within the range of any two of the above values.

[0041] In order to obtain a matrix material with good crystallinity and low cation mixing, the first sintering in step S1 includes a first low-temperature sintering and a second high-temperature sintering performed sequentially.

[0042] The sintering temperature of the first stage is 550℃ to 750℃. For example, the sintering temperature of the first stage can be 550℃, 600℃, 650℃, 680℃, 700℃, 730℃, or any value within the range of any two of the above values. The sintering time of the first stage is 5h to 15h. For example, the time can be 5h, 6h, 8h, 10h, 12h, 14h, or 15h, or any value within the range of any two of the above values. The sintering temperature of the second stage is 800℃ to 900℃. For example, the sintering temperature of the second stage can be 800℃, 820℃, 850℃, 870℃, 880℃, 890℃, 900℃, or any value within the range of any two of the above values. The sintering time of the second stage is 5h to 25h. For example, the time can be 5h, 8h, 12h, 15h, 20h, 23h, 25h, or any value within the range of any two of the above values.

[0043] This application utilizes a segmented sintering process, first allowing the lithium salt and precursor to fully react and decompose organic matter at a lower temperature, and then completing lattice recombination and growth at a higher temperature. This process is beneficial for obtaining a matrix material with uniform particle size, complete primary particle development, and low residual lithium on the surface, laying the foundation for subsequent uniform coating.

[0044] Step S2: After crushing and sieving the matrix, it is mixed with the first coating material by dry mixing and then sintered a second time to form a first coating layer on the surface of the matrix, thus obtaining the first material.

[0045] The mixing speed can be from 400 rpm to 1400 rpm, and the mixing time can be from 2 min to 15 min. For example, the speed can be 400 rpm, 500 rpm, 800 rpm, 1000 rpm, 1200 rpm, or 1400 rpm, and the mixing time can be 2 min, 5 min, 8 min, 10 min, 12 min, or 15 min, or any value between any two values ​​within the corresponding parameter range.

[0046] The specific process of secondary sintering includes: secondary sintering at a temperature of 650°C to 750°C for 5 to 15 hours to form a first coating layer on the surface of the substrate.

[0047] This step facilitates the interaction between the elements in the first coating material and the substrate surface through high-temperature solid-phase reaction, effectively neutralizing residual lithium compounds on the surface, reducing the material's alkalinity, and forming a dense and firmly adhered initial coating interface, providing a good foundation for the uniform loading of the subsequent second coating layer.

[0048] The "first coating material" refers to an oxide or hydroxide formed from a first element. The first element is selected from at least one of Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn.

[0049] Examples of secondary sintering temperatures include 650°C, 660°C, 680°C, 700°C, 720°C, 740°C, 750°C, or any value within the range of any two of the above values.

[0050] Examples of secondary sintering times include 5h, 6h, 8h, 10h, 12h, 14h, 15h, or any value within the range of any two of the above values.

[0051] Step S3: The first material, solvent, and second coating material are wet-mixed for 2-15 minutes and then dried to form a second coating layer on the surface of the first coating layer, resulting in a second material. The second coating material comprises perovskite crystals. The mass ratio of the first material to the second coating material is 1:0.01% to 2.00%. More preferably, the mass ratio is 1:0.03% to 0.30%. The mass ratio of the solvent to the first material is (0.5-2):1. The solvent is, exemplarily, water or an aqueous medium. This wet mixing facilitates the uniform and thorough coating of distorted perovskite crystals on the particle surface. The mass ratio of the first material to the second coating material can be, for example, 0.01%:1, 0.03%:1, 0.05%:1, 0.10%:1, 0.20%:1, 0.30%:1, 2%:1, or any value within the range of any two of the above values. In some embodiments, the perovskite crystal is a distorted perovskite crystal, specifically including the general formula LiAO3 and / or Li3AO4, and the element A includes at least one of Nb and Ti.

[0052] Step S4: Mix the second material with the third coating material, and then sinter them three times at a temperature of 200°C to 400°C for 5 to 15 hours to form a third coating layer on the surface of the second coating layer, thereby obtaining a high-nickel ternary cathode material.

[0053] This low-temperature sintering facilitates the formation of a stable third coating layer without excessively affecting the main structure of the material. The "third coating material" refers to an oxide or hydroxide formed from a second element; the second element is selected from at least one of Al, B, Ti, W, Li, P, Sr, Er, and Mo.

[0054] Compared with existing technologies, the high-nickel ternary cathode material and preparation method provided in this application have the following beneficial effects: 1. The high-nickel ternary cathode material provided in this application solves the comprehensive technical problems of high residual alkali on the surface of traditional high-nickel materials, severe interfacial side reactions, and capacity and internal resistance deterioration caused by a single coating layer (such as Al2O3) by constructing a composite coating structure consisting of a first coating layer, a second coating layer, and a third coating layer on the substrate surface. Specifically, the first coating layer can effectively neutralize and reduce surface alkaline impurities and stabilize the interface; the core second coating layer is composed of perovskite-type crystals with fast ion conductor characteristics, which provides stable chemical protection while improving the transport kinetics of lithium ions at the interface; the outermost third coating layer further enhances the overall interface stability and improves the material capacity. This gradient functional design enables the material to maintain high specific capacity while improving cycle life, rate performance, and DC internal resistance (DCR) performance under low temperature conditions, achieving an excellent balance between energy density and comprehensive electrochemical performance.

[0055] 2. The preparation method provided in this application, through precise process design of "segmented sintering to build the matrix" and "three-step sequential coating to build the composite layer," offers a reliable and efficient approach for the controllable preparation of the aforementioned high-performance products. This method first obtains an ideal matrix with high crystallinity, uniform primary particles, and low surface residual lithium through a multi-segment sintering process (e.g., low temperature followed by high temperature). Subsequently, a dense first coating layer is formed through dry mixing and high-temperature sintering. A second coating layer of perovskite crystals is uniformly and completely coated through wet mixing. Finally, a stable third coating layer is formed through low-temperature sintering. This process not only ensures that each functional layer can be formed and firmly bonded under optimal process conditions, but also has clear and highly controllable process parameters, which is beneficial for achieving consistency and repeatability in mass production, thereby stably preparing high-nickel ternary cathode materials with high capacity, long lifespan, and excellent power characteristics.

[0056] This application also provides a positive electrode sheet comprising the high-nickel ternary positive electrode material described in any of the foregoing embodiments. Compared to the prior art, this positive electrode sheet, due to the use of the aforementioned positive electrode material with low residual alkali, stable structure, and excellent interfacial transport kinetics, exhibits advantages such as good slurry dispersion, uniform coating, and high electrode bonding strength during preparation, and ultimately demonstrates good cycling and rate performance under high areal density and high compaction density.

[0057] This application also provides an electrochemical device comprising the aforementioned positive electrode, negative electrode, and an electrolyte layer between them. Because the positive electrode uses the aforementioned high-performance positive electrode material, it exhibits fewer interfacial side reactions, higher structural stability, and lower lithium-ion transport impedance. Therefore, it can effectively improve the battery's energy density, cycle life, fast charging capability, and low-temperature discharge performance, while also contributing to enhanced battery safety and reliability.

[0058] The following specific examples further illustrate the aforementioned battery cathode material, its preparation method, and its application.

[0059] Example 1 Step S1, Preparation of the matrix: Step S1.1, Raw material preparation and mixing: Using a high-nickel ternary precursor (chemical formula Ni 0.85 Co 0.05 Mn 0.10 The primary raw materials are zirconium (OH)₂ and lithium source (LiOHH₂O), with additional zirconium source (ZrO₂), aluminum source (Al(OH)₃), and titanium source (TiO₂) added as doping elements. The amounts of the three doping materials added are 0.18%, 0.05%, and 0.05% of the total mass of the high-nickel ternary precursor and lithium source, respectively. All materials are added to a high-speed mixer and mixed at a precursor-to-lithium salt molar ratio of 1:1.05 until homogeneous, yielding the first mixture.

[0060] Step S1.2, Multi-stage sintering: The first mixture obtained in step S1.1 is subjected to multi-stage sintering. First, the first stage sintering is carried out at 680°C in an oxygen atmosphere for 10 hours; then, the second stage sintering is carried out at 840°C in an oxygen atmosphere for 15 hours, thereby preparing the matrix material.

[0061] Step S1.3, Crushing and Sieving: The matrix material obtained after sintering in step S1.2 is crushed and passed through a 200-mesh sieve to obtain matrix powder with a median particle size D50 of 3.0 μm.

[0062] Step S2, First Coating (High-Temperature Dry Coating): Step S2.1, Mixing: Add the matrix powder obtained in Step S1.3 to a high-speed mixer, and then add cobalt source (Co(OH)2), aluminum source (Al2O3), and titanium source (TiO2) as the first coating materials. The addition amounts of the three coating sources are 1.2%, 0.05%, and 0.05% of the mass of the matrix powder, respectively. Mix at 1400 rpm for 15 minutes to ensure uniform mixing.

[0063] Step S2.2, Sintering: Place the uniformly mixed material from step S2.1 into a kiln and sinter at 700℃ for 10 hours to obtain a primary coated sintered material with a first layer of coating on the surface.

[0064] Step S3, Second Coating (Wet Coating of Perovskite Layer): Step S3.1, Wet Mixing: The primary coating sinter obtained in Step S2.2 is mixed with water at a mass ratio of 1:1, and perovskite-type crystal LiNbO3 is added as a second coating source, wherein the amount of LiNbO3 added accounts for 0.05% of the mass of the primary coating sinter. Stir for 5 minutes to ensure that the coating source is uniformly dispersed in the liquid phase and adheres to the surface of the material.

[0065] Step S3.2, Drying: The material after wet mixing in step S3.1 is filtered by pressure to separate most of the moisture, and then dried at 150°C for 6 hours to obtain a dried second mixture.

[0066] Step S4, Third Coating (Low-Temperature Coating) and Finished Product Acquisition: Step S4.1, Mixing: Add the second mixture obtained after drying in Step S3.2 to a high-speed mixer, and then add boron source (H3BO3) and aluminum source (Al(OH)3) as the third coating source. The addition amounts of the two coating sources are 0.1% and 0.05% of the mass of the second mixture, respectively. Mix for 15 minutes to ensure uniform mixing.

[0067] Step S4.2, Low-temperature sintering: Place the uniformly mixed material from step S4.1 into a kiln and sinter at 320°C for 10 hours in an air atmosphere to form the third coating layer.

[0068] Step S4.3, Sieving and Finished Product: The material after low-temperature sintering in step S4.2 is sieved through a 400-mesh sieve to finally obtain a high-nickel ternary cathode material with a median particle size D50 of 3.0 μm, which is modified by coating with distorted perovskite-type crystals (LiNbO3).

[0069] Example 2: The difference between this example and Example 1 lies in the type of perovskite crystal used in the second coating (wet coating). Specifically, in step S3.1 (wet mixing) of this example, the niobium source used is Li3NbO4, and the amount added is 0.05% of the mass of the first coating sintered material, measured by the Nb element contained therein. The rest is the same as in Example 1 and will not be repeated here.

[0070] Example 3: The difference between this example and Example 1 lies in the type of perovskite crystal used in the second coating (wet coating). Specifically, in step S3.1 (wet mixing) of this example, the niobium source is replaced with the tantalum source Li3TaO4, and the amount added is 0.05% of the mass of the first coating sintered material, measured by the Ta element contained therein. The rest is the same as in Example 1 and will not be repeated here.

[0071] Example 4: The only difference between this example and Example 1 is the sintering process in step S1.2: the two-stage sintering is changed to a single-stage sintering. Specifically, the first mixture is sintered directly in an oxygen atmosphere at 840°C for 15 hours to prepare the matrix. The subsequent crushing and sieving (step S1.3) and all coating steps (S2, S3, S4) are the same as in Example 1.

[0072] Comparative Example 1: The difference between this comparative example and Example 1 is that after obtaining the first coated sintered material in step S2, step S3 (second coating, i.e., wet coating of the perovskite layer) is not performed. Instead, the material is directly subjected to step S4 (third coating). The remaining steps and conditions are consistent with those in Example 1.

[0073] Comparative Example 2: The only difference between this comparative example and Example 1 is the implementation method of step S3: wet coating (second mixing) is replaced with dry coating. Specifically, the primary coating sintering material and niobium source LiNbO3 (added at 0.05% of the material mass) are placed in a high-speed mixer and mixed in a dry manner for 15 minutes, then dried (same as step S3.2), followed by step S4. All other steps are the same as in Example 1.

[0074] Comparative Example 3: The difference between this comparative example and Example 1 is that step S2 (first coating) is omitted. That is, after completing the substrate preparation (step S1.3), the substrate is not coated for the first time, but steps S3 (second coating) and S4 (third coating) are performed directly on the substrate. All other parameters and conditions are the same as in Example 1.

[0075] Comparative Example 4: The only difference between this comparative example and Example 1 is step S4: no new coating source is added in the third sintering. Specifically, after obtaining the second mixed dried material in step S3, the mixing in step S4.1 is not performed (i.e., no boron source or aluminum source is added). Instead, this dried material is directly sintered at 320°C for 10 hours in air atmosphere, and then sieved (i.e., only the sintering and post-treatment in steps S4.2 and S4.3 are performed). The remaining steps are the same as in Example 1.

[0076] Test method: Particle size test: The test was conducted using a Malvern Master Size 3000 tester.

[0077] Surface morphology: Tested using field emission scanning electron microscopy.

[0078] Testing and evaluation: To evaluate the electrochemical performance and stability of the high-nickel ternary cathode materials prepared in the examples and comparative examples, the following test methods were used, and the test results are shown in Table 1 below.

[0079] Preparation of button cells: CR2025 button cell model, active material: conductive agent: binder ratio is 90:5:5.

[0080] 1. Initial charge and discharge performance test: The positive electrode material is made into a coin cell and charged and discharged at a constant current rate of 0.1C within a voltage range of 2.8V to 4.3V for 5 cycles. The discharge specific capacity of the 5th cycle is taken as the initial discharge capacity.

[0081] 2. Rate Performance Testing: The cathode material was fabricated into coin cells and tested within a voltage range of 2.8V to 4.3V. First, the baseline capacity was measured by charge-discharge at a rate of 0.1C. Subsequently, charge-discharge tests were performed sequentially at higher rates of 1C, 2C, and 3C, with 5 cycles at each rate. The retention rate of the material's discharge capacity at different high rates relative to the 0.1C baseline capacity was calculated.

[0082] 3. Low-temperature DC internal resistance (DCR) test: The positive electrode material is made into a coin cell. In a low-temperature environment of -15℃, the battery is adjusted to 20% state of charge (SOC). A short-term high-current pulse is applied, and the DC internal resistance (DCR) of the battery is calculated by measuring the voltage transient.

[0083] 4. Cycle stability test: The positive electrode material is made into a coin cell and continuously charged and discharged at a rate of 1C within a voltage range of 2.8V to 4.3V. The discharge capacity at the 50th and 100th cycles is recorded, and the capacity retention rate is calculated (based on the discharge capacity of the first cycle).

[0084] 5. Transition Metal Dissolution Test: A certain amount of cathode material was immersed in a specific electrolyte (lithium hexafluorophosphate (LiPF6) + EC (cyclic carbonate), DMC (dimethyl carbonate), DEC (ethylene glycol carbonate), and EMC (ethylene carbonate)) and kept at a simulated battery operating temperature for a certain period of time. Subsequently, the sample was treated with complexing agents such as EDTA to dissolve any metal ions that may dissolve. Finally, inductively coupled plasma (ICP) spectrometry was used to quantitatively analyze the content of transition metal elements such as nickel (Ni), cobalt (Co), and manganese (Mn) in the solution.

[0085] Table 1 Results Analysis: Figure 2 shows a scanning electron microscope (SEM) image of the surface of the material prepared in Example 1 (wet coating of LiNbO3), and Figure 3 shows a SEM image of the surface of the material prepared in Comparative Example 2 (dry coating of LiNbO3). The comparison shows that the coating layer on the surface of the material in Figure 2 exhibits a continuous and uniform morphology, while the coating material in Figure 3 shows agglomeration and uneven distribution. This indicates that the wet coating process is more conducive to forming a uniform coating layer. Therefore, the wet process promotes the full dispersion and adhesion of the coating material on the substrate surface through the liquid phase environment, thereby constructing a more complete interfacial protection structure. This provides a key morphological basis for obtaining better and more consistent electrochemical performance of the material. Furthermore, the uniformity of the coating layer directly affects the uniformity and stability of interfacial lithium-ion transport. Uneven coating may lead to uneven local charge distribution, thus affecting the overall performance.

[0086] Electrochemical performance data further confirms the impact of the aforementioned morphological differences on performance. Analysis of the data in Table 1 shows that, compared to Comparative Example 1 without this coating, the wet-process introduction of LiNbO3 or Li3NbO4 in Examples 1 and 2 resulted in a balanced improvement in both the initial discharge capacity and rate performance of the materials. This result can be attributed to the fact that the uniform and complete coating layer effectively reduces the direct contact area between the electrode material and the electrolyte, suppressing side reactions. Simultaneously, its inherent ionic conductivity or optimized interface structure further promotes more efficient lithium-ion insertion / extraction kinetics.

[0087] Example 3, which uses a wet coating process to coat Li3TaO4, also exhibits the same trend, further verifying the universality of the wet process in enhancing the performance of this type of coating material. However, compared to Example 1 and Comparative Example 2, which uses a dry coating process, the performance improvement effect of the dry process is relatively limited, which is directly related to the unevenness and low coverage of its coating layer. This indicates that a specific wet coating method is a key technical step in achieving the expected comprehensive performance improvement of this solution, rather than just the coating material itself. In addition, the rate capability decrease of Comparative Example 3 (lacking the high-temperature coating stage) indicates that the high-temperature coating layer plays an important role in forming a stable initial interface and optimizing the charge transfer process; the reversible capacity decrease of Comparative Example 5 (lacking the low-temperature coating stage) indicates that the low-temperature coating layer is crucial for further stabilizing the third coating layer interface and reducing the loss of active lithium. These comparative examples collectively highlight the synergistic and indispensable holistic nature of each step in the multi-stage sintering and three-step coating process designed in this invention.

[0088] The test results for material stability provide further evidence. A comparison of Figure 4 (alkali content) and Figure 5 (metal leaching) shows that the residual alkali content and nickel and manganese metal leaching amounts in Examples 1 to 4, which used wet coating, were lower than those in the control samples. The reduction in residual alkali content directly stems from the effective coverage and isolation of the material surface by the coating layer, reducing the reaction between residual lithium compounds on the surface and air or electrolyte. The reduction in transition metal leaching is closely related to the coating layer's inhibition of interfacial corrosion and crystal structure surface reconstruction in the electrolyte. This has a positive effect on improving the cycling stability and safety of the material under high voltage, as the reduction of the aforementioned side reactions directly alleviates gas generation, electrolyte consumption, and electrode structure degradation during cycling.

[0089] The overall performance is reflected in the test results shown in Figure 6. In the cyclic test at 45°C, Examples 1 to 4 exhibited more stable capacity retention, which is directly related to the stable interface contributed by their lower residual alkali and metal dissolution, as well as the durable structural protection provided by the uniform coating. In the low-temperature test at -15°C, these examples showed smaller voltage drops, indicating that their DC internal resistance was optimized and their power characteristics were improved. This is due to the improved interfacial ionic conductivity that may be achieved by the uniform coating layer, as well as the lower charge transfer impedance resulting from the stable interface.

[0090] In summary, the analysis of surface morphology (Figures 2 and 3), electrochemical performance (Table 1), material stability (Figures 4 and 5), and comprehensive evaluation (Figure 6) demonstrates that this application, through a multi-stage sintering combined with a three-step coating process, particularly the wet introduction of a perovskite layer, constructs a uniform, stable, and functionally layered composite coating structure. This structure physically achieves effective coverage and protection of the substrate, chemically reduces surface activity and inhibits transition metal dissolution, and electrochemically optimizes interfacial ion transport kinetics. Therefore, it can synergistically improve the capacity, rate capability, cycle life, and low-temperature power performance of high-nickel ternary cathode materials while reducing residual alkali and stabilizing the interface.

[0091] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A high-nickel ternary cathode material, characterized in that, The device comprises a substrate and a composite coating layer covering the surface of the substrate. The substrate is a nickel-cobalt-manganese ternary material. The composite coating layer comprises a first coating layer, a second coating layer, and a third coating layer arranged sequentially from the inside to the outside. The first coating layer comprises at least one of the elements Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn. The second coating layer comprises perovskite crystals. The third coating layer comprises at least one of the elements Al, B, Ti, W, Li, P, Sr, Er, and Mo.

2. The high-nickel ternary cathode material according to claim 1, characterized in that, The general formula of the perovskite crystal includes LiAO3 and / or Li3AO4, wherein the element A includes at least one of Nb and Ta.

3. The high-nickel ternary cathode material according to claim 1, characterized in that, The mass ratio of the first coating layer to the total mass of the substrate is 0.01% to 5.00%:1; the mass ratio of the second coating layer to the total mass of the first material is 0.01% to 2.00%:1; the mass ratio of the third coating layer to the total mass of the second material is 0.01% to 2.00%:1; wherein, the total mass of the first material is the sum of the masses of the substrate and the first coating layer; the total mass of the second material is the sum of the total mass of the first material and the mass of the second coating layer.

4. The high-nickel ternary cathode material according to claim 1, characterized in that, The general chemical formula of the matrix is ​​Li. 1+ X Ni α Co β Mn γ M θ O2, wherein 0≤X≤0.1, 0.6≤α<1, 0<β≤0.4, 0<γ≤0.4, and β+γ≤0.4, 0≤θ≤0.4; M is a doping element, which includes at least one of Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo and Sn; and / or the high-nickel ternary cathode material includes single crystal particles, wherein the median particle size Dv50 of the single crystal particles is 1.0μm~8.0μm, and Dv2 is 0.2μm~4.0μm.

5. A method for preparing a high-nickel ternary cathode material, characterized in that, include: The matrix is ​​obtained by mixing lithium salt, additives and nickel cobalt manganese hydroxide precursor and sintering once. The substrate is mixed with a first coating material and sintered a second time to form a first coating layer on the surface of the substrate, resulting in a first material. The first coating material includes at least one of the elements Co, Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo, and Sn. The first material is then wet-mixed with a second coating material and dried to form a second coating layer on the surface of the first coating layer, resulting in a second material, wherein the second coating material includes perovskite crystals. The second material is then mixed with a third coating material and sintered a third time to form a third coating layer on the surface of the second coating layer, thereby obtaining the high-nickel ternary cathode material. The third coating material includes at least one of the elements Al, B, Ti, W, Li, P, Sr, Er, and Mo.

6. The method for preparing the high-nickel ternary cathode material according to claim 5, characterized in that, The general formula of the perovskite crystal includes LiAO3 and / or Li3AO4, and the element A includes at least one of Nb and Ti.

7. The method for preparing the high-nickel ternary cathode material according to claim 6, characterized in that, The mass ratio of element A to the first material is 0.01% to 2.00%.

8. The method for preparing the high-nickel ternary cathode material according to claim 5, characterized in that, The wet mixing process includes: mixing the first material, the solvent, and the second coating material, stirring for 2 min to 15 min, then performing solid-liquid separation and drying the resulting solid to obtain the second material, wherein the mass ratio of the first material to the second coating material is 1:0.01% to 2.00%.

9. The method for preparing the high-nickel ternary cathode material according to claim 5, characterized in that, The first sintering process includes a first stage sintering and a second stage sintering performed sequentially; the temperature of the first stage sintering is 550°C to 750°C, and the time is 5 hours to 15 hours; the temperature of the second stage sintering is 800°C to 900°C, and the time is 5 hours to 25 hours; and / or the temperature of the third sintering is 200°C to 400°C, and the time is 5 hours to 15 hours; and / or the chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni α Co β Mn γ M θ O2, wherein 0.6≤α<1, 0<β≤0.4, 0<γ≤0.4, and β+γ≤0.4, 0≤θ≤0.4, and M is a doping element, wherein the doping element includes at least one of Al, Zr, Sr, B, Nb, W, Ti, Ba, V, Ta, Ga, Ge, Se, Mo and Sn.

10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, the positive electrode material is a high-nickel ternary positive electrode material as described in any one of claims 1 to 4, or a positive electrode material prepared by the preparation method of the high-nickel ternary positive electrode material as described in any one of claims 5 to 9.

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