Al-Nb co-coated ternary positive electrode material and preparation method and application thereof

Abstract

The invention provides an Al-Nb co-coated ternary positive electrode material and a preparation method and application thereof, and belongs to the technical field of ternary lithium ion battery nickel cobalt lithium manganate positive electrode materials, the Al-Nb co-coated ternary positive electrode material comprises a ternary positive electrode material and a coating layer, the surface of the ternary positive electrode material is coated with the coating layer, the chemical formula of the ternary positive electrode material is LiNixCoyMn1-x-yO2, x is larger than or equal to 0.8 and smaller than 0.95, y is larger than 0, and y is larger than 0. 1-x-y is not equal to 0, the coating layer comprises Al2O3 and LiNbO3, and the mass ratio of Al2O3 to LiNbO3 is 1: (1-0.4). According to the invention, the Al2O3 coating layer can be used as a barrier, so that direct contact between the nickel-cobalt-manganese ternary positive electrode material and an electrolyte is effectively reduced, possible side reactions are inhibited, and transition metal ions in the nickel-cobalt-manganese ternary positive electrode material are prevented from being dispersed into the electrolyte; liNbO3 has relatively high Li < + > conductivity, and as a nickel-cobalt-manganese ternary positive electrode material coating layer, the LiNbO3 can effectively improve the transmission efficiency of lithium ions, improve the electrochemical performance of the positive electrode material, enhance the interface stability and improve the high temperature resistance at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium nickel cobalt manganese oxide cathode materials for ternary lithium ion batteries, and particularly relates to a ternary cathode material coated with Al-Nb and a preparation method and application thereof. Background Art

[0002] Currently, lithium ion batteries (LIBs) have become the most important energy conversion and storage technology due to their excellent specific capacity and energy density. Among them, LiNi x Co y Mn 1-x-y O 2 (NCM) is considered to be the most important and promising cathode material for LIBs. An increase in the Ni content in the NCM material will bring higher capacity. Therefore, researchers have been committed to increasing the Ni content in NCM, and the Ni ratio in related materials has reached as high as 90-95%. However, an increase in the Ni content means a decrease in the Co and Mn contents, resulting in a reduction in the structural stability of high-nickel ternary materials and deterioration of the cycling and rate performance. These problems currently hinder the development and application of high-nickel NCM.

[0003] Therefore, an important problem faced by the development of ternary lithium ion battery cathode materials is how to simultaneously have high capacity and excellent cycling performance. The interfacial side reaction between NCM and the electrolyte is considered to be one of the main reasons for the battery capacity decay during long-term cycling. Usually, a chemically thermally stable material is coated on the surface of NCM particles to prevent direct contact between the NCM particles and the electrolyte, so as to reduce the occurrence of side reactions. In addition, this coating method can enhance the interfacial stability, reduce volume changes, provide better electrochemical and thermal stability, and thus improve the rate performance and capacity retention rate of the material.

[0004] In current materials, Al 2 O 3 is considered to be the most common coating material because its preparation method is simple and the cost is low. The Al 2 O 3 coating layer can act as a barrier to effectively reduce the direct contact between the NCM cathode material and the electrolyte, inhibit possible side reactions, and reduce the dispersion of transition metal ions (such as Ni, Co, Mn, etc.) in the NCM cathode material into the electrolyte. Although the Al 2 O 3 coating layer can provide a good electron insulation layer, but at the same time, it is necessary to ensure that lithium ions can pass through. If the coating layer is too thick or the density is too high, it will hinder the conduction of lithium ions, thus affecting the electrochemical performance of the battery. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present application provides a ternary cathode material co-coated with Al-Nb, and a preparation method and application thereof, aiming to solve the problems of low structural stability, poor cycling and rate performance of high-nickel ternary materials; setting Al on the surface of high-nickel ternary materials 2 O 3 The coating layer will hinder the conduction of lithium ions and reduce the electrochemical performance of the battery.

[0006] In the first aspect, an embodiment of the present application provides a ternary cathode material co-coated with Al-Nb, including a ternary cathode material and a coating layer, the coating layer is coated on the surface of the ternary cathode material, and the chemical formula of the ternary cathode material is LiNi x Co y Mn 1-x-y O 2 , where 0.8 ≤ x < 0.95, y > 0, and 1 - x - y ≠ 0, the coating layer includes Al 2 O 3 and LiNbO 3 , and the mass ratio of Al 2 O 3 to LiNbO 3 is 1:(1~0.4).

[0007] In some embodiments, by mass percentage, it includes 98%~99.4% of the ternary cathode material and 2%~0.6% of the coating layer.

[0008] In the second aspect, an embodiment of the present application provides a preparation method of a ternary cathode material co-coated with Al-Nb, including the following steps: S1. Disperse LiNbO 3 and aluminum isopropoxide in a solvent, stir and mix to obtain a mixed solution; the concentration of LiNbO 3 in the mixed solution is 0.1~0.33 g / L, and the concentration of aluminum isopropoxide is 0.4~1.33 g / L; S2. Add the LiNi x Co y Mn 1-x-y O 2 ternary cathode material into the mixed solution, heat and stir, and obtain a ternary cathode material coated with an Al(OH) 3 and LiNbO 3 coating layer after evaporating the solvent; S3. Sinter the ternary cathode material coated with the Al(OH) 3 and LiNbO 3 coating layer to obtain a ternary cathode material co-coated with Al-Nb.

[0009] In some embodiments, in step S1, the solvent is at least one of ethanol, methanol, and isopropyl alcohol, the stirring and mixing temperature is 50 °C, and the time is 2 h; In step S2, the heating and stirring temperature is 80 °C, and the time is 4 h.

[0010] In some embodiments, LiNi x Co y Mn 1-x-y O 2 The preparation method of the ternary cathode material includes the following steps: (1) Disperse the Ni source, Co source, and Mn source in deionized water to obtain a transition metal dispersion; (2) Mix the NaOH solution, ammonia water solution, and transition metal dispersion for a coprecipitation reaction, and then successively age, filter, dry, and grind to obtain Ni x Co y Mn 1-x-y (OH) 2 precursor; (3) Mix the Ni x Co y Mn 1-x-y (OH) 2 precursor with the Li source, then sinter, cool, and grind to obtain LiNi x Co y Mn 1-x-y O 2 ternary cathode material.

[0011] In some embodiments, during the coprecipitation reaction in step (2), the stirring rate is 500 rpm, the reaction temperature is 55 - 60 °C, and the pH is 11.3 - 11.8.

[0012] In some embodiments, in step (3), the molar ratio of Li in the Li source to the sum of Ni, Co, and Mn in the Ni x Co y Mn 1-x-y (OH) 2 precursor is 1:1.05; The Ni source is NiSO 4 ·6H 2 O and / or LiOH, the Co source is CoSO 4 ·7H 2 O, the Mn source is MnSO 4 ·H 2 O, and the Li source is Li 2 CO 3 .

[0013] In some embodiments, the sintering conditions in step S3 are as follows: in an oxygen atmosphere, the temperature is 450 °C, and it is calcined for 4 h; The sintering conditions in step (3) are as follows: in an oxygen atmosphere, the furnace temperature is raised from room temperature to 500 °C at a heating rate of 2 °C / min, and then it is kept warm for 6 h for pre-sintering. After the pre-sintering is completed, the temperature is continuously raised to 800 °C and kept warm for 13 h.

[0014] In a third aspect, an embodiment of the present application provides a positive electrode plate, which includes a ternary positive electrode material co-coated with Al-Nb.

[0015] In a fourth aspect, an embodiment of the present application provides a secondary battery, which includes a positive electrode plate.

[0016] Different from the prior art solutions, the beneficial effects of the present application include: 1. The present application uses Al 2 O 3 and LiNbO 3 together as the coating layer of the ternary positive electrode material. The Al 2 O 3 coating layer can serve as a barrier, effectively reducing the direct contact between the nickel-cobalt-manganese ternary positive electrode material and the electrolyte, inhibiting possible side reactions, and reducing the dispersion of transition metal ions (such as Ni, Co, Mn, etc.) in the nickel-cobalt-manganese ternary positive electrode material into the electrolyte; LiNbO 3 has a high Li + conductivity. As the coating layer of the nickel-cobalt-manganese ternary positive electrode material, it can effectively improve the lithium ion transmission efficiency, enhance the electrochemical performance of the positive electrode material, enhance the interface stability, and at the same time improve the high temperature resistance performance.

[0017] When Al 2 O 3 is used as the coating layer, when the coating layer is too thick or the density is too high, it will hinder the conduction of lithium ions, thereby affecting the electrochemical performance of the battery; the preparation process of the LiNbNO 3 coating layer is relatively complex, the raw material price is high, and the cost is large. Therefore, the above two coating layer materials are combined and co-coated on the surface of the high-nickel nickel-cobalt-manganese ternary positive electrode material, so that it has the advantages of Al 2 O 3 being cheap, durable and easy to deposit and the high Li 3 conductivity of LiNbNO + .

[0018] 2. The present application uses the co-precipitation method to synthesize the nickel-cobalt-manganese ternary precursor, and then synthesizes the positive electrode material by the high-temperature solid-phase method. Finally, Al 2 O 3 -LiNbO 3Coated on the surface of the cathode material to form a uniform and dense coating layer. The sol-gel method first disperses the raw materials in a solvent to form a solution with low viscosity, ensuring molecular-level uniformity in a very short time. When forming the gel, the reactants are uniformly mixed at the molecular level, which helps to form a uniform and dense coating layer on the surface of the nickel-cobalt-manganese ternary cathode material. At the same time, compared with the solid-phase reaction, the chemical reaction in the sol-gel method is easier to carry out and only requires a lower synthesis temperature, which helps to reduce the influence of thermal stress on the nickel-cobalt-manganese ternary cathode material and maintain its original structure and performance. In addition, using the sol-gel method as the coating method for the nickel-cobalt-manganese ternary cathode material also has the advantages of mild reaction conditions, strong adaptability and flexibility, controllable preparation process and simple equipment, and environmental friendliness and sustainability, and is suitable for industrial production.

[0019] The above description is only an overview of the technical solution of this application. In order to be able to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of this application more obvious and understandable, the specific embodiments of this application are specifically listed below. Brief Description of the Drawings

[0020] In order to more clearly illustrate the technical solution of this application, the drawings used in this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 SEM scanning images of the ternary cathode materials prepared in this application, where 1(a) is the NCM prepared in Comparative Example 1; 1(b) is the NCM-AlNb-0.3 prepared in Example 1; 1(c) is the NCM-AlNb-0.6 prepared in Example 2; 1(d) is the NCM-AlNb-1 prepared in Example 3.

[0022] Figure 2 Cycling performance test diagrams of the cathode materials prepared in Examples 1-3 and Comparative Example 1 of this application.

[0023] Figure 3 Rate performance test diagrams of the cathode materials prepared in Examples 1-3 and Comparative Example 1 of this application. Detailed Description of the Embodiments

[0024] The embodiments of the technical solution of this application will be described in detail below with reference to the drawings. The following embodiments are only used to illustrate the technical solution of this application more clearly, so they are only examples and cannot be used to limit the protection scope of this application.

[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 technical field to which this application belongs; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0026] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0027] Reference to "embodiment" herein means that a particular feature, structure or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase does not necessarily refer to the same embodiment at every occurrence in the specification, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0028] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this text generally represents an "or" relationship between the associated objects before and after.

[0029] In the description of the embodiments of this application, the term "a plurality" refers to more than two (including two). Similarly, "a plurality of groups" refers to more than two groups (including two groups), and "a plurality of sheets" refers to more than two sheets (including two sheets).

[0030] In the current material, Al 2 O 3 is considered the most common coating material because its preparation method is simple and the cost is low. The Al 2 O 3 coating layer can act as a barrier to effectively reduce the direct contact between the NCM cathode material and the electrolyte, inhibit possible side reactions, and reduce the dispersion of transition metal ions (such as Ni, Co, Mn, etc.) in the NCM cathode material into the electrolyte. Although the Al 2 O 3 coating layer can provide a good electron insulation layer, it is necessary to ensure that lithium ions can pass through at the same time. If the coating layer is too thick or the density is too high, it will hinder the conduction of lithium ions, thereby affecting the electrochemical performance of the battery.

[0031] To solve the technical problems that the high-nickel ternary material has low structural stability, poor cycling and rate performance, and that the Al 2 O 3 coating layer will hinder lithium-ion conduction and reduce the electrochemical performance of the battery, this application provides a ternary cathode material co-coated with Al-Nb, its preparation method and application. Among them, Al 2 O 3 and LiNbO 3 are jointly used as the coating layer of the ternary cathode material. The Al 2 O 3 coating layer can act as a barrier to effectively reduce the direct contact between the nickel-cobalt-manganese ternary cathode material and the electrolyte, inhibit possible side reactions, and reduce the dispersion of transition metal ions (such as Ni, Co, Mn, etc.) in the nickel-cobalt-manganese ternary cathode material into the electrolyte; LiNbO 3 has a high Li + conduction ability. As the coating layer of the nickel-cobalt-manganese ternary cathode material, it can effectively improve the lithium-ion transport efficiency, enhance the electrochemical performance of the cathode material, improve the interfacial stability, and at the same time improve the high-temperature resistance performance.

[0032] In the first aspect, the embodiment of this application provides a ternary cathode material co-coated with Al-Nb, including a ternary cathode material and a coating layer. The coating layer is coated on the surface of the ternary cathode material. The chemical formula of the ternary cathode material is LiNi x Co y Mn 1-x-y O 2 , where 0.8 ≤ x < 0.95, y > 0, and 1 - x - y ≠ 0. The coating layer includes Al 2 O 3 and LiNbO 3 . The mass ratio of Al 2 O 3 to LiNbO 3 is 1:(1~0.4).

[0033] In the technical solution of the embodiment of this application, a high-nickel ternary cathode material is used, which can improve the capacity of the lithium battery. However, the high-nickel ternary cathode material has low structural stability, and the cycling and rate performance deteriorate. This application uses Al 2 O 3 and LiNbO 3 to jointly coat the surface of the ternary cathode material. Al 2 O 3The coating layer can act as a barrier to effectively reduce the direct contact between the nickel-cobalt-manganese ternary cathode material and the electrolyte, inhibit possible side reactions, and reduce the dispersion of transition metal ions (such as Ni, Co, Mn, etc.) in the nickel-cobalt-manganese ternary cathode material into the electrolyte; LiNbO 3 has a high Li + conductivity. As the coating layer of the nickel-cobalt-manganese ternary cathode material, it can effectively improve the lithium-ion transport efficiency, enhance the electrochemical performance of the cathode material, strengthen the interface stability, and at the same time improve the high-temperature resistance performance.

[0034] In some embodiments, by mass percentage, it includes 98% - 99.4% of the ternary cathode material and 2% - 0.6% of the coating layer.

[0035] In a second aspect, an embodiment of the present application provides a method for preparing an Al-Nb co-coated ternary cathode material, including the following steps: S1. Disperse LiNbO 3 and aluminum isopropoxide in a solvent, stir and mix to obtain a mixed solution; the concentration of LiNbO 3 in the mixed solution is 0.1 - 0.33 g / L, and the concentration of aluminum isopropoxide is 0.4 - 1.33 g / L; S2. Add the LiNi x Co y Mn 1-x-y O 2 ternary cathode material into the mixed solution, heat and stir, and after evaporating the solvent, obtain the ternary cathode material coated with Al(OH) 3 and LiNbO 3 coating layer; S3. Sinter the ternary cathode material coated with Al(OH) 3 and LiNbO 3 coating layer to obtain the Al-Nb co-coated ternary cathode material.

[0036] In the technical solution of the embodiment of the present application, dispersing LiNbO 3 and aluminum isopropoxide in a solvent forms a solution with low viscosity, ensuring molecular-level uniformity in a very short time. During the heating and stirring process, when the solvent gradually evaporates to form a gel, LiNbO 3 and aluminum isopropoxide are uniformly mixed at the molecular level, which helps to form a uniform and dense coating layer on the surface of the nickel-cobalt-manganese ternary cathode material. At the same time, compared with the solid-phase reaction, the chemical reaction in the sol-gel method is easier to carry out and only requires a lower synthesis temperature, which helps to reduce the influence of thermal stress on the nickel-cobalt-manganese ternary cathode material and maintain its original structure and performance.

[0037] In some embodiments, in step S1, the solvent is at least one of ethanol, methanol, and isopropyl alcohol, the stirring and mixing temperature is 50 °C, and the time is 2 h; In step S2, the heating and stirring temperature is 80 °C, and the time is 4 h.

[0038] In some embodiments, LiNi x Co y Mn 1-x-y O 2 The preparation method of the ternary cathode material includes the following steps: (1) Disperse the Ni source, Co source, and Mn source in deionized water to obtain a transition metal dispersion; (2) Mix the NaOH solution, ammonia water solution, and the transition metal dispersion for coprecipitation reaction, and then successively age, filter, dry, and grind to obtain Ni x Co y Mn 1-x-y (OH) 2 precursor; (3) Mix the Ni x Co y Mn 1-x-y (OH) 2 precursor with the Li source, then sinter, cool, and grind to obtain LiNi x Co y Mn 1-x-y O 2 ternary cathode material.

[0039] In the technical solution of the embodiment of the present application, the present application uses the coprecipitation method to synthesize the nickel-cobalt-manganese ternary precursor, and then synthesizes the ternary cathode material by the high-temperature solid-phase method.

[0040] In some embodiments, during the coprecipitation reaction in step (2), the stirring rate is 500 rpm, the reaction temperature is 55-60 °C, and the pH is 11.3-11.8.

[0041] In some embodiments, in step (3), the molar ratio of Li in the Li source to the sum of Ni, Co, and Mn in the Ni x Co y Mn 1-x-y (OH) 2 precursor is 1:1.05; The Ni source is NiSO 4 ·6H 2 O and / or LiOH, the Co source is CoSO 4 ·7H 2 O, the Mn source is MnSO 4 ·H 2 O, and the Li source is Li 2CO 3 。

[0042] In some embodiments, the sintering conditions in step S3 are as follows: in an oxygen atmosphere, the temperature is 450 °C and the calcination is carried out for 4 h; The sintering conditions in step (3) are as follows: in an oxygen atmosphere, the furnace temperature is raised from room temperature to 500 °C at a heating rate of 2 °C / min, followed by holding for 6 h for pre-sintering. After the pre-sintering is completed, the temperature is continuously raised to 800 °C and held for 13 h.

[0043] Thirdly, the embodiments of the present application provide a positive electrode sheet, which includes a ternary positive electrode material coated with Al-Nb.

[0044] Fourthly, the embodiments of the present application provide a secondary battery, which includes a positive electrode sheet.

[0045] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and cannot be construed as a limitation to the present application. For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0046] I. Preparation method Example 1 S1. Preparation of nickel-cobalt-manganese ternary precursor Ni 0.8 Co 0.1 Mn 0.1 (OH) 2 : Weigh a certain amount of NiSO 4 ·6H 2 O, CoSO 4 ·7H 2 O and MnSO 4 ·H 2 O respectively using an electronic balance, add deionized water to dissolve them, so that the total concentration of transition metals Ni, Co and Mn in the solution is 2 mol / L, where the metal ion concentrations of Ni 2+ , Co 2 + and Mn 2+They are 1.6, 0.2, and 0.2 mol / L (8:1:1) respectively. At the same time, 4 mol / L NaOH solution and 0.6 mol / L ammonia water solution are prepared. The transition metal solution, NaOH solution, and ammonia water solution are added to the co-precipitation reactor at the same rate through a peristaltic pump, with a stirring rate of 500 rpm. During the reaction, a constant-temperature oil bath is used to control the reaction temperature at 55 - 60 °C, and the solution pH is controlled at 11.3 - 11.8. After reacting for 18 h, aging is continued for 6 h. After the aging is completed, stirring is stopped, and the reaction solution is suction-filtered through a Buchner funnel to separate the filtrate and the filter cake. The filter cake is washed with deionized water multiple times until the washing liquid is neutral. Subsequently, the filter cake is dried in a vacuum drying oven at 110 °C for 12 h, and after grinding, the Ni 0.8 Co 0.1 Mn 0.1 (OH) 2 precursor is obtained.

[0047] S2, Synthesis of the cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 : Lithium carbonate (Li 2 CO 3 ) is used as the lithium source. Weigh a certain amount of Li 2 CO 3 and the precursor obtained in S1 respectively. The molar ratio of the lithium source to the transition metals (Ni, Co, and Mn) is 1.05 ( : = 1.05, M = Ni + Co + Mn). After simply grinding the two, they are put into a mixer and mixed at a frequency of 1000 r / min for 10 min. After mixing evenly, they are put into a crucible and sintered in a tube furnace, with oxygen continuously introduced during the sintering process. First, the furnace temperature is raised from room temperature to 500 °C at a heating rate of 2 °C / min, then it is kept at this temperature for 6 h for pre-sintering. After the pre-sintering is completed, the temperature is continued to be raised to 800 °C and kept at this temperature for 13 h. Subsequently, after naturally cooling to room temperature, the material is taken out and ground into powder, and the lithium nickel cobalt manganese oxide cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 is obtained.

[0048] S3, Al 2 O 3 -LiNbO 3 coating First, 3 mg of lithium niobate (LiNbO 3 ) and 12 mg of aluminum isopropoxide are dissolved in 30 mL of ethanol, stirred and mixed at 50 °C for 2 h, and then 1 g of LiNi obtained in S2 is taken0.8 Co 0.1 Mn 0.1 O 2 (NCM811) was added to the mixture. Subsequently, the mixture was stirred at 80 °C for 4 hours to completely evaporate the solvent. During the stirring process, a thin layer of Al(OH) 3 and LiNbO 3 coating layer was formed to obtain a ternary cathode material co-coated with Al-Nb, where the mass percentages of Al 2 O 3 and LiNbO 3 were both 0.3 wt%.

[0049] S3, secondary sintering The evaporated material in S3 was collected and calcined in a box furnace at 450 °C for 4 hours in an oxygen atmosphere to obtain the NCM cathode material with an Al 2 O 3 -LiNbO 3 coating layer. Finally, the modified NCM cathode material was stored in an Ar atmosphere for standby.

[0050] The modified ternary cathode material co-coated with Al-Nb is designated as NCM-AlNb-x, where x represents the weight percentage of each of the Al 2 O 3 and LiNbO 3 coating layers. In this example, the weight ratio of Al 2 O 3 and LiNbO 3 was set to 1:1, that is, NCM-AlNb-0.3 indicates that 0.3 wt% of Al 2 O 3 and 0.3 wt% of LiNbO 3 were added.

[0051] Example 2 The difference between Example 2 and Example 1 is that the ternary cathode material co-coated with Al-Nb contains 0.6 wt% of Al 2 O 3 and 0.6 wt% of LiNbO 3 .

[0052] Example 3 The difference between Example 3 and Example 1 is that the ternary cathode material co-coated with Al-Nb contains 1 wt% of Al 2 O 3 and 1 wt% of LiNbO 3 .

[0053] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the lithium nickel cobalt manganese oxide cathode material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM) is not coated.

[0054] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that only 1 wt% of Al 2 O 3 .

[0055] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that only 1 wt% of LiNbO 3 .

[0056] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that the mass ratio of Al 2 O 3 and LiNbO 3 is 1:2.

[0057] Comparative Example 5 The difference between Comparative Example 4 and Example 2 is that the mass ratio of Al 2 O 3 and LiNbO 3 is 1:0.2.

[0058] II. Test Methods 1. The surface morphology of the material was characterized by scanning electron microscopy (SEM).

[0059] 2. The prepared cathode material, conductive agent (Super P), and binder (PVDF) were mixed evenly in an organic solvent N-methyl-2-pyrrolidone (NMP) at a mass ratio of 8:1:1. The prepared slurry was coated on an aluminum foil with a coating thickness of 15 mm, and dried in a vacuum drying oven at 110 °C for 12 h to remove moisture and organic solvents. After drying, it was cut into a cathode sheet with a diameter of 12 mm, and the weight of the electrode sheet was weighed to calculate the active substance content. Subsequently, the cathode sheet was rolled, and the compaction density was 3 g / cm 3 . Lithium metal (diameter 14 mm) was used as the anode, and the electrolyte was a mixed solution of 1 M lithium hexafluorophosphate (LiPF 6 ) and ethylene carbonate (EC) plus ethyl methyl carbonate (EMC) (EC: EMC = 3:7 vol%). The CR2032 coin cell was assembled in a glove box under argon protection. After the assembled battery was left standing for 24 h, the electrochemical performance test was carried out.

[0060] III. Analysis of Test Results of Each Example and Comparative Example (1) The ternary cathode materials co-coated with Al-Nb prepared in Examples 1 to 3 and the ternary cathode material prepared in Comparative Example 1 were scanned by SEM as follows Figure 1 shown. It can be seen from the figure that the ternary cathode materials prepared in each example are spherical secondary particles with a particle size of about 10 mm, which are composed of small nanoscale primary particles. Compared with Comparative Example 1, all samples in Examples 1 to 3 showed very similar morphologies, indicating that the coating modification process does not affect the particle morphology or size of the ternary cathode material particles.

[0061] (2) The cathode materials prepared in Examples 1 to 3 and Comparative Example 1 were assembled into coin cells for electrochemical performance testing. The test results are shown in Figure 2 .

[0062] It can be seen from Figure 2 that the initial discharge capacity of the uncoated ternary cathode material in Comparative Example 1 is 180.6 mAh / g, the initial discharge capacity of the sample with 0.3 wt% Al-Nb addition in Example 1 is 183.0 mAh / g, the initial discharge capacity of the sample with 0.6 wt% addition in Example 2 is 188.4 mAh / g, and the initial discharge capacity of the sample with 1 wt% addition in Example 3 is 180.7 mAh / g. The capacity retention rates after 100 cycles are 78.77%, 78.83%, 83.2%, and 81.31% respectively. It can be seen that with the increase of the Al-Nb addition amount, the discharge capacity of the material increases and the capacity retention rate increases. The discharge capacity is the highest and the cycling performance is the best at the 0.6 wt% addition amount in Example 2. After that, when the addition amount continues to increase, the battery capacity decreases.

[0063] It can be seen from Figure 3 that the discharge capacity of the material decreases with the increase of the rate at different rates. The battery prepared from the ternary cathode material co-coated with Al-Nb with 0.6 wt% addition in Example 2 always maintains a relatively high discharge capacity and shows better performance at high rates, with better rate performance. Experiments prove that coating modification with an appropriate amount of Al-Nb coating agent can effectively improve the cycling and rate performance of high-nickel ternary cathode materials.

[0064] (3) The cathode materials prepared in Example 1 and Comparative Examples 2 to 5 were assembled into coin cells, and their initial discharge capacity, capacity retention rate after 100 cycles, and Li+ were tested. The test results are shown in Table 1 below.

[0065] Table 1 Electrochemical Performance Test Results of Cathode Materials Prepared in Example 1 and Comparative Examples 2 to 5

[0066] As can be seen from Table 1, adding Al to the coating layer 2 O 3 is beneficial to improving the cyclic capacity retention rate of the cathode material and enhancing the stability of the cathode material. Adding LiNbO to the coating layer 3 is beneficial to improving the first discharge capacity and Li + conduction ability; the comprehensive performance of Example 2 is stronger than that of Comparative Examples 2 to 5. Using the proportions of Al 2 O 3 and LiNbO 3 in this application to prepare the coating layer can achieve the best electrochemical performance.

[0067] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that those skilled in the art can think of to the embodiments and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. An Al-Nb co-coated ternary positive electrode material, characterized in that: It comprises a ternary positive electrode material and a coating layer, wherein the coating layer is coated on the surface of the ternary positive electrode material, and the chemical formula of the ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, wherein 0.8≤x<0.95, y>0, and 1-xy≠0, the coating layer comprises Al2O3 and LiNbO3, and the mass ratio of Al2O3 to LiNbO3 is 1:(1~0.4).

2. The Al-Nb co-coated ternary positive electrode material according to claim 1, characterized in that: In terms of mass percentage, it includes 98%~99.4% of ternary positive electrode material and 2%~0.6% of coating layer.

3. A method for preparing the Al-Nb co-coated ternary positive electrode material as claimed in claim 1 or 2, characterized in that: The steps include: S1. Dispersing LiNbO3 and aluminum isopropoxide in a solvent, stirring and mixing, to obtain a mixed solution; wherein the concentration of LiNbO3 in the mixed solution is 0.1-0.33 g / L, and the concentration of aluminum isopropoxide is 0.4-1.33 g / L; S2, LiNi x Co y Mn 1-x-y O2 ternary positive electrode material is added to the mixed solution, heated and stirred, and the solvent is evaporated to obtain a ternary positive electrode material coated with Al(OH)3 and LiNbO3 coating layers; S3, sintering the ternary positive electrode material coated with the Al(OH)3 and LiNbO3 coating layers to obtain an Al-Nb co-coated ternary positive electrode material.

4. The method for preparing the Al-Nb co-coated ternary positive electrode material according to claim 3, characterized in that: In step S1, the solvent is at least one of ethanol, methanol and isopropanol, and the stirring mixing temperature is 50° C. and the time is 2 h; The heating and stirring temperature in step S2 is 80° C. and the time is 4 hours.

5. The method for preparing the Al-Nb co-coated ternary positive electrode material according to claim 3, characterized in that: The LiNi x Co y Mn 1-x-y The preparation method of O2 ternary positive electrode material comprises the following steps: (1) dispersing a Ni source, a Co source, and a Mn source in deionized water to obtain a transition metal dispersion; (2) mixing NaOH solution, ammonia solution and the transition metal dispersion to perform a coprecipitation reaction, and then aging, filtering, drying and grinding in sequence to obtain Ni x Co y Mn 1-x-y (OH)2 precursor; (3) The Ni x Co y Mn 1-x-y The (OH)2 precursor is mixed with a Li source, sintered, cooled, and ground to obtain LiNi x Co y Mn 1-x-y O2 ternary positive electrode material.

6. The method for preparing the Al-Nb co-coated ternary positive electrode material according to claim 5, characterized in that: During the co-precipitation reaction in step (2), the stirring rate is 500 rpm, the reaction temperature is 55-60° C., and the pH is 11.3-11.

8.

7. The method for preparing the Al-Nb co-coated ternary positive electrode material according to claim 5, characterized in that: In the step (3), the Li and Ni x Co y Mn 1-x-y The molar ratio of the sum of Ni, Co, and Mn in the (OH)2 precursor is 1:1.05; The Ni source is NiSO4·6H2O and / or LiOH, the Co source is CoSO4·7H2O, the Mn source is MnSO4·H2O, and the Li source is Li2CO3.

8. The method for preparing the Al-Nb co-coated ternary positive electrode material according to claim 5, characterized in that: The sintering conditions in step S3 are: calcining for 4 hours at a temperature of 450° C. in an oxygen atmosphere; The sintering conditions in step (3) are as follows: in an oxygen atmosphere, the temperature in the furnace is raised from room temperature to 500°C at a heating rate of 2°C / min, followed by pre-sintering for 6 hours, and after the pre-sintering is completed, the temperature is further raised to 800°C and maintained for 13 hours.

9. A positive electrode sheet, characterized in that: The invention comprises the Al-Nb co-coated ternary positive electrode material as described in claim 1 or 2.

10. A secondary battery, characterized in that: The invention comprises the positive electrode sheet as claimed in claim 9.

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