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 base material and a composite coating layer located on the surface of the base material, the base material comprises a ternary positive electrode active material, the composite coating layer comprises a first coating layer, a second coating layer and a third coating layer which are sequentially stacked on the surface of the base material, the first coating layer contains Li3NbO3, the second coating layer contains a WO3-ZrO2 composite oxide, and the third coating layer contains AlF3. According to the ternary positive electrode material, a coating system with high ionic conductivity, structural stability and interface compatibility is formed, and the cycling stability, rate capability and high-temperature performance of the ternary positive electrode material are effectively improved.

Description

Technical Field

[0001] This application relates to the field of new energy technology, specifically to ternary cathode materials, their preparation methods, and electrochemical devices. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and energy storage, high-voltage ternary cathode materials (such as LiNi) have become increasingly important. 0.68 Co 0.08 Mn 0.24 O2 or LiNi 0.7 Co 0.1 Mn 0.2 O2 and other similar substances have become the mainstream choice due to their high energy density.

[0003] However, high-voltage ternary materials are prone to interfacial side reactions with electrolytes, which leads to an increase in interfacial impedance. Moreover, during cycling, the dissolution of transition metals in high-voltage ternary materials can easily cause capacity decay and a decrease in cycling performance. In addition, during charge and discharge, lattice distortion of high-voltage ternary materials can easily generate microcracks, and the particles are easily broken. 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 ternary cathode material.

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

[0006] In a first aspect, embodiments of this application provide a ternary cathode material, which includes a matrix material and a composite coating layer located on the surface of the matrix material. The matrix material contains a ternary cathode active material, and the composite coating layer includes a first coating layer, a second coating layer, and a third coating layer sequentially stacked on the surface of the matrix material. The first coating layer contains Li3NbO3, the second coating layer contains WO3-ZrO2 composite oxide, and the third coating layer contains AlF3.

[0007] In some possible embodiments, based on the ternary cathode material, the composite coating layer accounts for 1.5wt% to 3.0wt% by mass.

[0008] In some possible embodiments, based on the ternary cathode material, the composite coating layer satisfies at least one of the following conditions: (1) the mass percentage of the first coating layer is 0.5wt% to 1.0wt%; (2) the mass percentage of the second coating layer is 0.8wt% to 1.65wt%; (3) the mass percentage of the third coating layer is 0.2wt% to 0.5wt%.

[0009] In some possible embodiments, the thickness of the first coating layer is 2nm to 5nm.

[0010] In some possible embodiments, the molar ratio of WO3 to ZrO2 in the WO3-ZrO2 composite oxide in the second coating layer is (1~3):1.

[0011] In some possible embodiments, the thickness of the third coating layer is 1 nm to 3 nm.

[0012] In some possible embodiments, the matrix material satisfies at least one of the following conditions: (1) the median particle size Dv50 of the matrix material is 3.0 μm to 4.0 μm; (2) the specific surface area of ​​the matrix material is in the range of 0.5 m². 2 / g~1.2m 2 / g; (3) The chemical formula of the matrix material is LiNi x Co y Mn 1-x-y O2, where 0 <x<1,0<y<1。

[0013] Secondly, embodiments of this application also provide a method for preparing a ternary cathode material, the method comprising the following steps: mixing a precursor of the ternary cathode material and a lithium source and performing a first sintering to obtain a matrix material; placing the matrix material in an atomic layer deposition apparatus and introducing a first coating material containing Nb to perform an atomic layer deposition reaction, wherein the first coating material forms a first coating layer containing Li3NbO3 on the surface of the matrix material, thereby obtaining a first intermediate product; adding the first intermediate product to a coating solution containing W and Zr and stirring to form a gel; drying the gel and performing a second sintering, wherein W and Zr react on the surface of the first coating layer to form a WO3-ZrO2 composite oxide to form a second coating layer, thereby obtaining a second intermediate product; and placing the second intermediate product in a chemical vapor deposition apparatus and introducing a second coating material containing Al and a third coating material containing F to perform a chemical vapor deposition reaction, wherein the second coating material and the third coating material react on the surface of the second coating layer to form AlF3 to form a third coating layer, thereby obtaining the ternary cathode material.

[0014] In some possible embodiments, the preparation method satisfies at least one of the following conditions: (1) the first coating material contains Nb2(NO3)5 and H2O; (2) the coating solution contains (NH4). 10 W 12 O 41·5H2O, Zr(NO3)4·5H2O, ethanol and citric acid; (3) the second coating material contains C3H9Al and H2O, and the third coating material contains NH4F, wherein the molar ratio of C3H9Al and NH4F is 1:(2~6).

[0015] Thirdly, embodiments of this application also provide 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 aforementioned ternary positive electrode material.

[0016] Compared to existing technologies, the ternary cathode material provided in this application forms a three-layer composite coating. The first coating layer, located in the inner layer, contains Li3NbO3, which can serve as an ion-conducting layer to accelerate lithium-ion transport and improve the conductivity of the ternary cathode material. The second coating layer, located in the middle layer, contains WO3-ZrO2 composite oxide, which can serve as a structural stabilizing layer to suppress lattice distortion and transition metal dissolution in the matrix material, thus improving the structural stability of the ternary cathode material. The third coating layer, located in the outer layer, contains AlF3, which can serve as an interface buffer layer to reduce interface stress and thermal expansion, thereby improving the interface compatibility of the ternary cathode material. This ternary cathode material, with its composite coating, forms a coating system that combines high ion conductivity, structural stability, and interface compatibility, effectively improving the cycle stability, rate performance, and high-temperature performance of the ternary cathode material. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of a ternary cathode material provided in an embodiment of this application.

[0018] Figure 2 This is a process flow diagram of a method for preparing a ternary cathode material according to an embodiment of this application. Detailed Implementation

[0019] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, 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 this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0020] To address the problems of high interfacial impedance, poor cycle performance, and poor structural stability in ternary cathode materials, especially high-voltage ternary cathode materials, researchers have proposed various coating modification strategies, including metal oxide coating and carbon coating. However, these methods still have certain limitations in practical applications. For example, when using Al2O3 for coating, although Al2O3 can inhibit electrolyte corrosion, its lithium-ion conductivity is only 10. -14 The S / cm ratio significantly affects the rate performance of the material; moreover, the poor uniformity of traditional coatings leads to localized protection failure; in addition, the large difference in the coefficients of thermal expansion between the coating and the matrix material (e.g., the difference in the coefficients of thermal expansion between ZrO2 and NCM622 can reach 20%) easily induces interfacial stress cracking. Therefore, developing a ternary cathode material that can improve cycle performance, enhance structural stability, and reduce interfacial impedance remains a key focus and challenge in current research.

[0021] Please see Figure 1 As shown, this application provides a novel ternary cathode material 100. The ternary cathode material 100 includes a substrate material 10 and a composite coating layer 20 located on the surface of the substrate material 10. The substrate material 10 contains a ternary cathode active material. The composite coating layer 20 includes a first coating layer 21, a second coating layer 22, and a third coating layer 23 sequentially stacked on the surface of the substrate material 10. The first coating layer 21 contains Li3NbO3, the second coating layer 22 contains a WO3-ZrO2 composite oxide, and the third coating layer 23 contains AlF3. It is understood that... Figure 1 This is just one structural schematic diagram of a ternary cathode material. In practical applications, the morphology of ternary cathode materials is not limited to this.

[0022] The ternary cathode material forms a three-layer composite coating layer, with the inner, middle and outer layers being: the first coating layer containing Li3NbO3 is located on the inner side of the ternary cathode material, close to the substrate material. The fast ion conductor Li3NbO3 enhances the ion transport rate at the interface between the composite coating layer and the substrate material. The first coating layer can also serve as an ion conduction layer to accelerate lithium ion transport, thereby improving the conductivity of the ternary cathode material.

[0023] In some embodiments, the thickness of the first coating layer can be 2 nm to 5 nm. This relatively thin thickness provides sufficient protection for the substrate material while minimizing energy density reduction. This nanoscale coating layer requires a precise deposition method to form an ultrathin continuous layer. The thickness of the first coating layer can, exemplarily, be 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, or any value within the range of any two of the above values. The thickness of the first coating layer can further be 2 nm to 3 nm.

[0024] In some embodiments, based on the ternary cathode material, the mass percentage of the first coating layer can be 0.5wt% to 1.0wt%, which is beneficial for controlling the thickness of the first coating layer within the above range and achieving an effective coating effect. The mass percentage of the first coating layer can, for example, be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, or any value within the range of any two of the above values. The mass percentage of the first coating layer can further be 0.5wt% to 0.8wt%.

[0025] The second coating layer containing WO3-ZrO2 composite oxide is located between the first and third coating layers. WO3 has oxygen vacancy defects, good heat resistance, and high hardness, while ZrO2 has high chemical and thermal stability. The WO3-ZrO2 composite oxide formed by the complementary advantages of the two can serve as a structural stabilizing layer, suppressing lattice distortion and transition metal dissolution in the matrix material, reducing volume expansion and structural collapse of the ternary cathode material during charge and discharge, thereby improving the structural stability, cycle performance, and high-temperature performance of the ternary cathode material.

[0026] In some embodiments, the molar ratio of WO3 to ZrO2 in the WO3-ZrO2 composite oxide can be (1~3):1. By controlling the molar ratio within the above range, it is beneficial for the second coating layer to form an ideal composite structure. Furthermore, through the complementary advantages in thermal stability and chemical stability, it provides better coating performance than a single oxide. The molar ratio of WO3 to ZrO2 in the second coating layer can, for example, be 1:1, 1.33:1, 1.5:1, 1.67:1, 2:1, 2.5:1, 2.67:1, 3:1, or any value within the range of any two of the above values. The molar ratio of WO3 to ZrO2 in the second coating layer can further be (1~2):1.

[0027] In some embodiments, the mass percentage of the second coating layer can be 0.8 wt% to 1.65 wt%, which can effectively improve the chemical and structural stability of the ternary cathode material while maintaining its energy density. The mass percentage of the second coating layer can, for example, be 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.65 wt%, or any value within the range of any two of the above values. The mass percentage of the second coating layer can further be 0.9 wt% to 1.3 wt%.

[0028] The third coating layer containing AlF3 is located on the outside of the ternary cathode material. AlF3 has a thermal expansion coefficient that is close to that of the ternary cathode material, as well as good stability and mechanical strength. It can also prevent the electrolyte from directly contacting the matrix material and causing side reactions, and can promote the formation of the SEI layer. Therefore, the third coating layer can serve as an interface buffer layer, reducing the interface stress and thermal expansion of the ternary cathode material, thereby stabilizing the structure of the ternary cathode material and improving the interfacial compatibility between the ternary cathode material and the electrolyte.

[0029] In some embodiments, the thickness of the third coating layer can be 1 nm to 3 nm. This relatively thin thickness can effectively protect the substrate material while reducing the decrease in energy density. The third coating layer is also a nanoscale coating layer, requiring a more precise deposition method to form an ultrathin continuous layer. The thickness of the third coating layer can, exemplarily, be 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, or any value within the range of any two of the above values. The thickness of the first coating layer can further be 2 nm to 3 nm.

[0030] In some embodiments, the mass percentage of the third coating layer can be 0.2wt% to 0.5wt%, which is beneficial for effectively buffering the mechanical and thermal stresses of the ternary cathode material and fully isolating the matrix material from the electrolyte. The mass percentage of the third coating layer can, for example, be 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, or any value within the range of any two of the above values. The mass percentage of the third coating layer can further be 0.3wt% to 0.5wt%.

[0031] The aforementioned inner, middle, and outer three-layer coating constitute the composite coating of the ternary cathode material, forming a coating system that combines high ionic conductivity, structural stability, and interfacial compatibility, effectively improving the cycle stability, rate performance, and high-temperature performance of the ternary cathode material.

[0032] Based on ternary cathode materials, the total mass percentage of the composite coating can be 1.5 wt% to 3.0 wt%. Adjusting the mass percentage of the composite coating within this range is beneficial for the ternary cathode material to achieve both improved electrochemical performance and high energy density. The mass percentage of the composite coating can, for example, be 1.5 wt%, 1.8 wt%, 2.0 wt%, 2.25 wt%, 2.5 wt%, 2.8 wt%, 3.0 wt%, or any value within the range of any two of the above values. The mass percentage of the composite coating can further be 2 wt% to 2.5 wt%.

[0033] The matrix material contains ternary cathode active materials, including but not limited to nickel-cobalt-manganese ternary cathode active materials or nickel-manganese-aluminum ternary cathode active materials.

[0034] In some embodiments, the median particle size Dv50 of the matrix material can be 3.0 μm to 4.0 μm, which is beneficial to improving the tap density of the ternary cathode material. The median particle size Dv50 of the matrix material can be, for example, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm or any value within the range formed by any two of the above values.

[0035] In some embodiments, the specific surface area of the matrix material ranges from 0.5 m 2 / g to 1.2 m 2 / g, which is beneficial to reducing the side reaction between the matrix material and the electrolyte and reducing the dissolution of transition metal ions; the smaller specific surface area is also beneficial to reducing the interfacial stress between the matrix material and the composite coating layer, cooperating with the interfacial buffering effect of the composite coating layer, and further improving the structural stability of the ternary cathode material. Exemplarily, the specific surface area of the matrix material can be 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g or any value within the range formed by any two of the above values. The specific surface area of the matrix material can further be 0.6 m 2 / g to 1.1 m 2 / g.

[0036] In some embodiments, the chemical formula of the matrix material can be LiNi x Co y Mn 1-x-y O2, where 0 < x < 1 and 0 < y < 1, which is beneficial to obtaining a matrix material that can operate stably at high voltages (4.3 V to 4.5 V) and has a high energy density, thereby improving the high-voltage stability and energy density of the ternary cathode material. The matrix material can be, for example, LiNi 0.68 Co<​​​​​​​​​​​Compared to existing technologies, the ternary cathode material provided in this application utilizes a synergistic composite coating technology with +3 and higher valence elements (Nb, W, Zr, and Al) to construct a three-layer composite coating system consisting of an "ion conduction layer, a structural stabilization layer, and an interface buffer layer," resulting in the following beneficial effects for the ternary cathode material: 1. Optimized ion transport: The fast ion conductor Li3NbO3 in the first coating layer can improve the lithium-ion conductivity at the cathode material interface and accelerate lithium-ion transport.

[0038] 2. Enhanced structural stability: The WO3-ZrO2 composite oxide in the second coating layer can suppress lattice distortion of the matrix material and dissolution of transition metals, thereby improving the structural stability of the ternary cathode material.

[0039] 3. Improved interface compatibility: Through the interface buffering effect of AlF3 in the third coating layer, the difference in interface stress and thermal expansion coefficient between the composite coating layer and the matrix material can be reduced, thereby improving the interface compatibility between the composite coating layer and the matrix material. It also isolates the matrix material from the electrolyte, thereby improving the interface compatibility between the ternary cathode material and the electrolyte.

[0040] 4. Synergistic effect: The three-layer coating of the inner, middle and outer layers works synergistically to improve the cycle stability, rate performance and high temperature performance of the ternary cathode material, and achieve a comprehensive improvement in the electrochemical performance of the ternary cathode material.

[0041] Based on the same inventive concept, please refer to Figure 2 As shown in the figure, this application provides a method for preparing a ternary cathode material, which specifically includes the following steps: Step S1: The precursor of the ternary cathode material and the lithium source are mixed and sintered once to obtain the matrix material.

[0042] Specifically, the precursor of the ternary cathode material and the lithium source are mixed at a ratio of (1.0~1.1):1 of the number of moles of lithium in the lithium source to the total number of moles of transition metal in the precursor. The mixture is then heated to 750~850℃ in an oxygen atmosphere at a rate of 3℃ / min~10℃ / min, held for 10h~16h, and cooled to obtain the matrix material.

[0043] In some embodiments, the precursor of the ternary cathode material can be a nickel-cobalt-manganese precursor. The preparation method of the nickel-cobalt-manganese precursor can adopt the co-precipitation method. Dissolve NiSO4·6H2O, CoSO4·7H3O, and MnSO4·H2O in deionized water according to the stoichiometric ratio to prepare a mixed solution with a total metal concentration of 1.5 mol / L. Then, use ammonia water (mass fraction of 25%) and NaOH (concentration of 1.0 mol / L) as co-precipitants, control the pH = 11.0 ± 0.2 and the temperature at 65 ± 5 °C in the reaction kettle, and react for 12 h to obtain the nickel-cobalt-manganese precursor. It can be understood that the preparation method of the precursor of the ternary cathode material includes but is not limited to the above method.

[0044] In some embodiments, the matrix material can also be washed with water and spray-dried. Among them, the inlet air temperature of the spray drying is 200 °C to 300 °C, and the outlet air temperature is 50 °C to 150 °C, effectively removing residual alkali and improving the morphology of the matrix material to obtain spherical matrix material particles.

[0045] In some embodiments, a sintering aid can also be added to the precursor of the ternary cathode material and the lithium source, which is beneficial to reducing the primary sintering temperature and improving the density and uniformity of the matrix material. The sintering aid can include MgO, and the addition amount of the sintering aid can be 0.05 wt% to 0.5 wt% of the total mass of the precursor of the ternary cathode material and the lithium source.

[0046] In some embodiments, the lithium source can include at least one of lithium hydroxide, lithium carbonate, and lithium oxalate, etc.

[0047] In some embodiments, the chemical formula of the matrix material can be LiNi x Co y Mn 1-x-y O2, where 0 < x < 1, 0 < y < 1, is a high-voltage material, which can improve the high-voltage performance and energy density of the ternary cathode material. Exemplarily, the chemical formula of the matrix material can be LiNi[[ID=​​​​​​​​​​​​​​​​Specifically, the ALD method is used to achieve molecular-level coating on the surface of the substrate material, depositing a continuous and uniform first coating layer. The ALD method can precisely control the thickness of the first coating layer, realize single-atom layer-by-layer deposition, and has high uniformity, good adhesion and stability, thereby further improving the conductivity of the first coating layer.

[0050] In some embodiments, the first coating material contains Nb2(NO3)5 and H2O. Nb2(NO3)5 reacts with residual Li on the surface of the matrix material to generate Li3NbO3, which can both reduce the residual alkali on the surface of the matrix material and form Li3NbO3 fast ion conductor, thereby accelerating lithium ion transport.

[0051] For example, the specific operation of the ALD method may include: placing the substrate material in an ALD device, using Nb2(NO3)5 and H2O as the first coating materials, and depositing at 150℃~200℃ for 8~12 cycles to form a Li3NbO3 first coating layer with a thickness of 2nm~5nm. Other process parameters are set as follows: Nb2(NO3)5 pulse time 0.1s, N2 purging time 10s, H2O pulse time 0.05s, and N2 purging time 10s. It can be understood that the process parameters of the ALD method can be adjusted according to requirements such as the thickness and density of the first coating layer.

[0052] Step S3: The first intermediate product is added to a coating solution containing W and Zr elements and stirred to form a gel. The gel is dried and then sintered a second time. The W and Zr elements react on the surface of the first coating layer to form a WO3-ZrO2 composite oxide to form a second coating layer, thus obtaining the second intermediate product.

[0053] Specifically, using the sol-gel method, the first intermediate product is added to a coating solution containing W and Zr elements and stirred at 60℃~80℃ for 3h~6h to form a gel. Then, it is dried under vacuum at 80℃~100℃ for 10h~14h, followed by secondary sintering in air at 800℃~900℃ for 4h~8h. During this process, W and Zr elements react and deform on the surface of the first coating layer away from the substrate material, forming a WO3-ZrO2 composite oxide, thus forming a second coating layer on the surface of the first coating layer. The sol-gel method can reduce the agglomeration problem caused by traditional co-precipitation methods, improve the density of the second coating layer, and further enhance its structural stability. The sol-gel method can also achieve molecular-level mixing of W and Zr elements, uniformly coating the surface of the first coating layer, and even penetrating into the nanopores of the first coating layer to form a dense second coating layer.

[0054] In some embodiments, the coating solution contains (NH4). 10 W 12 O41 ·5H2O, Zr(NO3)4·5H2O, ethanol and citric acid, wherein (NH4) 10 W 12 O 41 ·5H2O and Zr(NO3)4·5H2O can be used as coating materials to form composite oxides during secondary sintering; citric acid can act as a ligand to react with metal ions W 6+ and Zr 4+ The metal salts undergo coordination reactions to form a gel. Ethanol can be used as a solvent to dissolve the metal salts, promote the sol-gel reaction, and regulate the viscosity of the gel, which is beneficial for the uniform distribution and deposition of metal oxides.

[0055] Furthermore, (NH4) 10 W 12 O 41 The concentration of ·5H2O can be 0.003mol / L~0.0075mol / L, the concentration of Zr(NO3)4·5H2O can be 0.01mol / L~0.05mol / L, and the molar ratio of citric acid to metal ions (W and Zr) can be 1:1 (1.1~1.5), which is conducive to the metal ions fully coordinating with citric acid to form a stable complex.

[0056] Step S4: The second intermediate product is placed in a chemical vapor deposition apparatus, and a second coating material containing Al and a third coating material containing F are introduced to carry out a chemical vapor deposition reaction. The second and third coating materials react on the surface of the second coating layer to form AlF3, thereby forming the third coating layer and obtaining the ternary cathode material.

[0057] Specifically, chemical vapor deposition (CVD) is used. The second intermediate product is placed in a CVD apparatus, and a second coating material containing Al is introduced. Deposition is performed at 150℃~300℃ for 8~12 cycles, forming an Al₂O₃ layer 1nm~3nm thick on the surface of the second intermediate product. Then, at 150℃~300℃, a third coating material containing F is introduced and reacted for 10min~60min. During this reaction, F reacts with Al₂O₃ to form AlF₃, thus obtaining a third coating layer on the surface of the second coating layer. The first, second, and third coating layers constitute a composite coating layer. It can be understood that the process parameters of the CVD method can be adjusted according to requirements such as the thickness and density of the third coating layer. The CVD method can precisely control the thickness of the third coating layer, achieving nanoscale coating and rapidly forming a dense outer barrier, thereby further improving the uniformity and density of the third coating layer.

[0058] In some embodiments, the second coating material contains C3H9Al and H2O, and the third coating material contains NH4F, wherein the molar ratio of C3H9Al to NH4F is 1:(2~6), which is beneficial for the reaction to generate AlF3 and reduces the waste of unreacted raw materials and the generation of impurities.

[0059] In some embodiments, before introducing the third coating material containing F, the second intermediate product with deposited Al2O3 can be transferred to a fluorination furnace for subsequent reactions to improve the safety of the preparation method.

[0060] Compared with the prior art, the preparation method of ternary cathode material provided in this application has the following beneficial effects: 1. The first coating layer is generated by atomic layer deposition technology, which can achieve molecular-level uniform coating, reduce the thickness error of the first coating layer, and improve the adhesion of the first coating layer. This is conducive to forming a continuous, uniform and thin first coating layer, improving the conductivity of the first coating layer and the bonding force between the first coating layer and the substrate material.

[0061] 2. The second coating layer is generated by the sol-gel method, which can avoid the agglomeration problem of the traditional coprecipitation method, improve the density of the second coating layer, and improve the bonding force between the second coating layer and the first coating layer, thereby further improving the inhibitory effect of the second coating layer on the structural collapse of the matrix material and the dissolution of transition metal ions.

[0062] 3. Chemical vapor deposition (CVD) generates a third coating layer, which can achieve nanoscale uniform coating, improve the uniformity of the third coating layer, reduce surface defects, and quickly form a dense outer barrier. This further enhances the buffering effect of the third coating layer in reducing the interfacial stress and thermal expansion differences between the composite coating layer and the substrate material.

[0063] This application provides an electrochemical device (e.g., a battery) that includes a positive electrode plate, the positive electrode plate including a positive electrode material, wherein the positive electrode material is the aforementioned ternary positive electrode material.

[0064] Compared to existing technologies, the electrochemical device provided in this application embodiment is prepared using the aforementioned ternary cathode material and has good energy density, cycle stability, rate performance and high-temperature performance.

[0065] The following specific examples further illustrate the aforementioned ternary cathode material, its preparation method, and electrochemical device.

[0066] Example 1 Step S1: The precursor Ni of the ternary cathode material 0.68 Co 0.08 Mn 0.24(OH)₂ and lithium hydroxide were mixed, and 0.1 wt% MgO was added as a combustion aid. The molar ratio of lithium in the lithium hydroxide to the total molar ratio of transition metals in the nickel-cobalt-manganese precursor was 1.05:1. The mixture was then sintered at 850 °C for 12 h under an oxygen atmosphere at a heating rate of 5 °C / min to obtain the matrix material LiNi. 0.68 Co 0.08 Mn 0.24 O2.

[0067] Step S2: Place the substrate material in the ALD device, using Nb2(NO3)5 and H2O as the first coating materials, and deposit for 10 cycles at 200°C to form a 2nm thick Li3NbO3 first coating layer. Other process parameters are set as follows: Nb2(NO3)5 pulse time 0.1s, N2 purging time 10s, H2O pulse time 0.05s, and N2 purging time 10s.

[0068] Step S3: Add the first intermediate product to the coating solution and stir at 60°C for 4 hours to form a gel. The coating solution contains 0.005 mol / L of (NH4). 10 W 12 O 41 The mixture is prepared by mixing 5H2O, 0.03 mol / L Zr(NO3)4·5H2O, ethanol solvent, and citric acid. The molar ratio of W to Zr is 2:1, and the molar ratio of citric acid to metals (W and Zr) is 1:1.2. The mixture is then vacuum dried at 80℃ for 12 h, followed by secondary sintering at 850℃ in air for 6 h. This allows W and Zr to react on the surface of the first coating layer away from the substrate material to form a WO3-ZrO2 composite oxide, which forms the second coating layer, resulting in the second intermediate product.

[0069] Step S4: The second intermediate product is placed in a CVD device, and a second coating material containing C3H9Al and H2O is introduced. Deposition is carried out at 200°C for 10 cycles, and a 2nm thick Al2O3 layer is deposited on the surface of the second intermediate product. The second intermediate product with deposited Al2O3 is then transferred to a fluorination furnace at 200°C, and a third coating material containing NH4F vapor is introduced. The reaction is carried out for 30 minutes, and AlF3 is formed on the surface of the second coating layer to form the third coating layer, thus obtaining the ternary cathode material.

[0070] Example 2 Step S1: The precursor Ni of the ternary cathode material 0.68 Co 0.08 Mn 0.24(OH)₂ and lithium hydroxide were mixed, and 0.1 wt% MgO was added as a combustion aid. The molar ratio of lithium in the lithium hydroxide to the total molar ratio of transition metals in the nickel-cobalt-manganese precursor was 1.05:1. The mixture was then sintered at 850 °C for 12 h under an oxygen atmosphere at a heating rate of 5 °C / min to obtain the matrix material LiNi. 0.68 Co 0.08 Mn 0.24 O2.

[0071] Step S2: Place the substrate material in the ALD device, using Nb2(NO3)5 and H2O as the first coating materials, and deposit for 20 cycles at 200°C to form a 2.5 nm thick Li3NbO3 first coating layer. Other process parameters are set as follows: Nb2(NO3)5 pulse time 0.1 s, N2 purging time 10 s, H2O pulse time 0.05 s, and N2 purging time 10 s.

[0072] Step S3: Add the first intermediate product to the coating solution and stir at 60°C for 4 hours to form a gel. The coating solution contains 0.0075 mol / L of (NH4). 10 W 12 O 41 The mixture is prepared by mixing 5H2O, 0.03 mol / L Zr(NO3)4·5H2O, ethanol solvent, and citric acid. The molar ratio of W to Zr is 3:1, and the molar ratio of citric acid to metals (W and Zr) is 1:1.2. The mixture is then vacuum dried at 80℃ for 12 h, followed by secondary sintering at 850℃ in air for 6 h. This allows W and Zr to react on the surface of the first coating layer away from the substrate material to form a WO3-ZrO2 composite oxide, thus forming the second coating layer and yielding the second intermediate product.

[0073] Step S4: The second intermediate product is placed in a CVD device, and a second coating material containing C3H9Al and H2O is introduced. The material is deposited at 200°C for 20 cycles to form a 2.5 nm thick Al2O3 layer on the surface of the second intermediate product. The second intermediate product with deposited Al2O3 is then transferred to a fluorination furnace at 200°C, and a third coating material containing NH4F vapor is introduced. The reaction is carried out for 30 min to form AlF3 on the surface of the second coating layer, thus forming the third coating layer and obtaining the ternary cathode material.

[0074] Comparative Example 1 The difference from Example 1 is that step S3 is omitted. The other steps are basically the same as in Example 1; please refer to Example 1.

[0075] Comparative Example 2 The difference from Example 1 is that only step S1 is performed, resulting in an uncoated matrix material, LiNi. 0.68Co 0.08 Mn 0.24 O2 is the ternary cathode material. For specific steps in S1, please refer to Example 1.

[0076] The following tests were conducted on the ternary cathode materials obtained in Example 1 and Comparative Examples 1-2 and the batteries prepared from the ternary cathode materials.

[0077] Battery preparation: (1) Positive electrode sheet: The ternary positive electrode material, Super P (5wt%), and PVDF (5wt%) were stirred evenly in NMP and coated onto aluminum foil (area density 20mg / cm³). 2 (1) Dry in vacuum at 120℃ for 12h; (2) Battery assembly: Using lithium metal sheet as negative electrode, Celgard 2400 as separator, and 1mol / L LiPF6 (where EC:DEC=1:1) as electrolyte, assemble into 2032 type button cell in argon glove box.

[0078] (a) Initial discharge specific capacity: At room temperature of 25℃, the lithium-ion battery is charged at a constant current of 0.1C (C represents the current rate, 1C=2A) to 4.4V, and then charged at a constant voltage until the current drops to 0.05C, at which point charging stops, and the initial charge capacity is recorded; then it is discharged at 0.1C to the cutoff voltage of 2.8V, and the initial discharge capacity is recorded. The 0.1C specific capacity of the positive electrode material is calculated based on the initial discharge capacity, and the initial charge and discharge efficiency of the battery is calculated according to the following formula, i.e., the initial efficiency: Initial charge and discharge efficiency = (initial discharge capacity / initial charge capacity) * 100%.

[0079] (ii) High temperature cycling stability: The capacity retention rate after 500 cycles is tested when the working voltage range is 2.8V~4.4V, the temperature is 45℃, the charge and discharge rate is +1C / -1C, and the CV cutoff current is 0.01C.

[0080] (III) Rate Performance: At 25℃, a battery with a state of charge (SOC) of 0% (2.0V) is charged at 0.33C to 4.4V, and then discharged at 1C to 2.8V. The discharge capacity at this point is recorded as C1. Using the same battery and under the same test conditions, a battery with a SOC of 0% (2.0V) is charged at 0.33C to 100% (4.4V), and then discharged at 10C to 2.8V. The discharge capacity at this point is recorded as C2. The test index for discharge rate performance is capacity retention = C2 / C1 × 100%.

[0081] (iv) Mn dissolution amount: The test substance was dissolved by EDTA to obtain a solution, and the content of Mn transition metal element in the solution was tested by ICP (inductively coupled plasma) instrument.

[0082] (v) Interface impedance: The assembled battery was tested using an electrochemical impedance spectroscopy (EIS) instrument. The sample was placed in a 25°C constant temperature chamber for testing to measure the electrochemical impedance of the battery.

[0083] (vi) Interfacial stress: The coated ternary material is cut / processed into miniature tensile specimens, with no pretreatment damage to the composite coating layer and the matrix material. The specimens are held using a nano-tensile machine (such as Instron 5948), and a force is applied at a rate of 0.1-1 μm / s, with the load-displacement curve recorded in real time. Calculation results: When the interface peels off, the corresponding maximum load is Fmax, and the interface stress area is A (the contact area of ​​the interface in the specimen cross-section). Then, the interfacial stress σ = Fmax / A.

[0084] The relevant preparation processes and test results of Examples 1-2 and Comparative Examples 1-2 are shown in Tables 1 and 2.

[0085] The above results indicate that: The three-layer composite coating system in Examples 1-2 achieves a comprehensive improvement in the electrochemical performance of ternary cathode materials through the first coating layer containing Li3NbO3 to enhance ion conduction, the second coating layer containing WO3-ZrO2 to suppress structural collapse, and the third coating layer containing AlF3 to optimize interface compatibility.

[0086] The Li3NbO3 and AlF3 double-layer coating of Comparative Example 1 is superior to the uncoated Comparative Example 2 in terms of cycle stability and rate performance. However, compared with Example 1, due to the lack of the intermediate second coating layer, the structural stability of Comparative Example 1 is significantly reduced, the dissolution of transition metals is doubled, and the capacity retention rate after 500 cycles is also reduced by 5.2%. In addition, the initial discharge specific capacity and 10C discharge specific capacity are also lower than those of Example 1, and the interface impedance is increased by 20.3Ω compared with Example 1. This indicates that there is a synergistic effect among the three layers of coating. Without the second coating layer, even with double coating, the capacity, rate performance and conductivity of the ternary cathode material will decrease. Compared to Example 1, Comparative Example 2 suffers from severe interfacial side reactions between the ternary cathode material and the electrolyte due to the lack of effective coating, resulting in increased dissolution of transition metals and capacity decay. The poor structural stability of the ternary cathode material leads to a decrease in cycle performance, and the capacity, rate performance, cycle performance, and high-temperature performance of the ternary cathode material all decrease significantly.

[0087] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these 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 device includes a substrate material and a composite coating layer located on the surface of the substrate material. The substrate material contains a ternary cathode active material. The composite coating layer includes a first coating layer, a second coating layer, and a third coating layer sequentially stacked on the surface of the substrate material. The first coating layer contains Li3NbO3, the second coating layer contains WO3-ZrO2 composite oxide, and the third coating layer contains AlF3.

2. The ternary cathode material according to claim 1, characterized in that, Based on the ternary cathode material, the mass percentage of the composite coating layer is 1.5wt%~3.0wt%.

3. The ternary cathode material according to claim 2, characterized in that, Based on the ternary cathode material, the composite coating layer satisfies at least one of the following conditions: (1) The mass percentage of the first coating layer is 0.5wt%~1.0wt%; (2) The mass percentage of the second coating layer is 0.8wt%~1.65wt%; (3) The mass percentage of the third coating layer is 0.2wt%~0.5wt%.

4. The ternary cathode material according to claim 1, characterized in that, The thickness of the first coating layer is 2nm~5nm.

5. The ternary cathode material according to claim 1, characterized in that, In the WO3-ZrO2 composite oxide in the second coating layer, the molar ratio of WO3 to ZrO2 is (1~3):

1.

6. The ternary cathode material according to claim 1, characterized in that, The thickness of the third coating layer is 1 nm to 3 nm.

7. The ternary cathode material according to claim 1, characterized in that, The matrix material satisfies at least one of the following conditions: (1) The median particle size Dv50 of the matrix material is 3.0 μm to 4.0 μm; (2) The specific surface area of ​​the matrix material is in the range of 0.5m². 2 / g~1.2m 2 / g; (3) The chemical formula of the matrix material is LiNi x Co y Mn 1-x-y O2, where 0 <x<1,0<y<1。 8. A method for preparing a ternary cathode material, characterized in that, The preparation method includes: The precursor of the ternary cathode material and the lithium source are mixed and sintered once to obtain the matrix material. The substrate material is placed in an atomic layer deposition apparatus, and a first coating material containing Nb is introduced to perform an atomic layer deposition reaction. The first coating material forms a first coating layer containing Li3NbO3 on the surface of the substrate material, and a first intermediate product is obtained. The first intermediate product is added to a coating solution containing W and Zr elements and stirred to form a gel. The gel is dried and then sintered a second time. The W and Zr elements react on the surface of the first coating layer to form a WO3-ZrO2 composite oxide, thereby forming a second coating layer and obtaining a second intermediate product; and The second intermediate product is placed in a chemical vapor deposition apparatus, and a second coating material containing Al and a third coating material containing F are introduced to carry out a chemical vapor deposition reaction. The second coating material and the third coating material react on the surface of the second coating layer to form AlF3, thereby forming the third coating layer and obtaining the ternary cathode material.

9. The method for preparing the ternary cathode material according to claim 8, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The first coating material contains Nb2(NO3)5 and H2O; (2) The coating solution contains (NH4). 10 W 12 O 41 ·5H2O, Zr(NO3)4·5H2O, ethanol and citric acid; (3) The second coating material contains C3H9Al and H2O, and the third coating material contains NH4F, wherein the molar ratio of C3H9Al and NH4F is 1:(2~6).

10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode plate, the positive electrode plate includes a positive electrode material, the positive electrode material is a ternary positive electrode material as described in any one of claims 1 to 7 or is prepared by the method of preparing a ternary positive electrode material as described in any one of claims 8 to 9.

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