A method for repairing surface structure of high-nickel positive electrode material, high-nickel positive electrode material obtained by the method and lithium ion battery

Abstract

The application provides a method for repairing the surface structure of a high-nickel positive electrode material, a high-nickel positive electrode material obtained by the method and a lithium ion battery. The method comprises the following steps: 1) mixing the high-nickel positive electrode material, a first lithium source and a metal oxide, and then performing sintering to obtain a sintered product; and 2) mixing the sintered product with an acid solution and performing reaction, then evaporating to dryness, and performing sintering to obtain a high-nickel positive electrode material with a repaired surface structure. According to the method, the first lithium source and the metal oxide are combined with nickel oxide and residual lithium on the surface of the material, respectively, to remove part of the impurity phases on the surface of the material and form a protective layer on the surface of the material; then, a weak acid is used to further remove the impurities on the surface of the material and form a lithium ion conductor coating layer on the surface of the material, so that the discharge capacity and the initial efficiency of the battery are improved, and the cycle performance and the safety performance are also improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage, and relates to a method for repairing the surface structure of a positive electrode material, in particular to a method for repairing the surface structure of a high-nickel positive electrode material, a high-nickel positive electrode material obtained by the method, and a lithium ion battery. BACKGROUND

[0002] With the continuous development of the new energy industry, people's requirements for power batteries are also getting higher and higher, and the nickel content in ternary materials is also increasing. However, the battery failure caused by the problems of positive electrode material stability, electrolyte matching, and high temperature rise during high-current charging is also getting more and more attention. Therefore, single crystal materials have emerged as the times require. Not only do they enhance the stability of the positive electrode material, but they can also increase the voltage of the entire system to a new level, providing a solution for the demand for higher energy density. At present, the widely used single crystal positive electrode materials on the market are mainly medium and low nickel single crystal positive electrode materials, including NCM523 and NCM622. The surface of the medium and low nickel single crystal positive electrode material has very little residual lithium and impurity phases, and the general physical and chemical properties are relatively stable. However, the energy density of the medium and low nickel single crystal positive electrode material is low, which cannot meet the requirements of pure electric vehicles for long endurance. The energy density of high-nickel single crystal positive electrode materials is high, which can meet the requirements of electric vehicles for long endurance. However, NCM811 and single crystal positive electrode materials with higher nickel content are less used at present. The main reason is that the surface of the high-nickel single crystal positive electrode material has more residual lithium and other impurity phases, which seriously affects the physical and chemical properties of the high-nickel single crystal material. In order to meet the market demand for single crystal positive electrode materials with higher energy density, it is of great significance to repair the surface structure of high-nickel single crystal positive electrode materials to prepare high-nickel single crystal positive electrode materials with excellent performance.

[0003] CN108011098A discloses a ternary positive electrode material and a preparation method thereof. The method mixes ternary material precursors Ni x Co y Mn z (OH)2, LiOH, and MoO2 in a certain proportion, then pre-burns at a first specified temperature for a first specified time to obtain a pre-burned mixture, wherein x+y+z=1; removes the un-sintered powder in the pre-burned mixture, and calcines the remaining pre-burned mixture at a second specified temperature for a second specified time to obtain a Mo-doped ternary material after cooling; and calcines the Mo-doped ternary material, Li2CO3, and Al2O3 at a third specified temperature for a third specified time in a certain proportion to obtain a ternary positive electrode material after cooling.

[0004] CN110010877A discloses a surface-coated high-nickel ternary material and a preparation method and application thereof, which generates a binary coating layer composed of sodium silicate and transition metal oxide on the surface of the high-nickel ternary material. The method comprises the following steps: 1) preparing coating liquid A: preparing a sodium silicate aqueous solution with a mass percentage concentration of 3-10 wt%, and the molecular formula of the sodium silicate is Na2O·nSiO2, n=1-3; 2) preparing coating liquid B: preparing a transition metal compound solution with a mass percentage concentration of 10-30 wt%; 3) dispersing the high-nickel ternary material in the coating liquid A, and stirring to obtain a suspension, the process is completed at a temperature of 10-60℃ for 1-5 hours, and the stirring rate is 200-1000 rpm; 4) then, the coating liquid B is dropped into the suspension obtained in step 3) for 0.5-2 hours to obtain a mixed solution, and the mixing process is maintained at a temperature of 10-60℃, and the stirring rate is 200-800 rpm; 5) the mixed solution of step 4) is heated in a water bath at 70-100℃, evaporated to a residual solution amount of 15-50% of the starting amount, filtered while hot, and the filter cake is dried in a blast drying oven for 2-6 hours, and then fully ground to obtain a powder for standby; 6) the obtained powder is treated at high temperature in an air atmosphere, the cavity gas atmosphere is normal pressure air, the cavity gas flow rate is 100-400 mL / min, the reaction temperature is 300-400℃, the treatment time is 1-3 hours, then the temperature is raised, the reaction temperature is 600-800℃, the treatment time is 1-3 hours, and the product is cooled in the furnace, the color of the product is black, and the product is fully ground for standby.

[0005] However, the above-mentioned scheme has limited performance improvement for high-nickel ternary materials, and it is still difficult to meet market needs. SUMMARY

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a method for repairing the surface structure of a high-nickel positive electrode material, a high-nickel positive electrode material obtained by the method, and a lithium ion battery. The method provided by the present application not only improves the discharge capacity and initial efficiency of the battery, but also improves the cycle performance and safety performance.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a method for repairing the surface structure of a high-nickel positive electrode material, the method comprising the following steps:

[0009] (1) mixing a high-nickel positive electrode material, a first lithium source and a metal oxide, and then sintering to obtain a sintered product;

[0010] (2) mixing the sintered product of step (1) with an acid solution and reacting, and then evaporating to dryness, sintering to obtain a high-nickel positive electrode material with repaired surface structure.

[0011] The method provided by the application first removes part of impurity phases on the surface of the material and forms a protective layer on the surface of the material by respectively reacting a first lithium source and a metal oxide with nickel oxide (Ni x O) and residual lithium on the surface of the material, and then further removes impurities on the surface of the material and forms a lithium ion conductor coating layer on the surface of the material by using a weak acid, so as to improve the discharge capacity, the initial efficiency, the cycle performance and the safety performance of the battery.

[0012] In the application, the operation of evaporation drying is adopted in step (2), and the purpose is to remove water in the material without damaging the coating layer on the surface of the material.

[0013] The following is a preferred technical solution of the application, but is not a limitation on the technical solution provided by the application. Through the following preferred technical solution, the technical purpose and beneficial effects of the application can be better achieved and realized.

[0014] As a preferred technical solution of the application, the chemical formula of the high-nickel positive electrode material in step (1) is LiNi 1-x- y Co x Mn y O2, wherein 0

[0015] Preferably, the first lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium acetate or lithium nitrate, and preferably is lithium hydroxide. The lithium hydroxide can react with impurities such as Ni x O on the surface of the high-nickel positive electrode material to generate a layered lithium metal oxide during the sintering process.

[0016] Preferably, the metal oxide in step (1) includes any one or a combination of at least two of aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, cobalt oxide, molybdenum oxide or niobium oxide. The metal oxide can be combined with residual lithium salt on the surface of the high-nickel positive electrode material to form a lithium metal oxide.

[0017] As a preferred technical solution of the present invention, based on the mass of the high-nickel cathode material described in step (1), the amount of the first lithium source added is 500-2000 ppm. For example, 500 ppm, 750 ppm, 1000 ppm, 1250 ppm, 1500 ppm, 1750 ppm, or 2000 ppm, etc., but not limited to the listed values; other unlisted values ​​within this range are also applicable. In the present invention, if too much of the first lithium source is added, it will result in a high residual alkali on the material surface; if too little of the first lithium source is added, it will affect the degree of sufficient reaction with the metal oxide.

[0018] Preferably, based on the mass of the high-nickel cathode material described in step (1), the amount of metal oxide added is 500-2000 ppm, such as 500 ppm, 750 ppm, 1000 ppm, 1250 ppm, 1500 ppm, 1750 ppm, or 2000 ppm, but not limited to the listed values; other unlisted values ​​within this range are also applicable. In this invention, if too much metal oxide is added, it will result in an excessively thick surface coating, affecting the discharge capacity of the material; if too little metal oxide is added, it will affect the degree of reaction with residual lithium on the surface.

[0019] Preferably, the sintering temperature in step (1) is 500-800℃, such as 500℃, 600℃, 700℃ or 800℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the sintering time in step (1) is 5-10h, such as 5h, 6h, 7h, 8h, 9h or 10h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the sintering in step (1) is carried out in an atmosphere furnace.

[0022] Preferably, the sintering in step (1) is carried out in an oxygen atmosphere.

[0023] As a preferred technical solution of the present invention, the concentration of the acid solution in step (2) is 0.05-0.1 mol / L, such as 0.05 mol / L, 0.06 mol / L, 0.07 mol / L, 0.08 mol / L, 0.09 mol / L, or 0.1 mol / L, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Here, if the acid solution concentration is too high, it will lead to damage to the surface structure; if the acid solution concentration is too low, it will lead to insufficient reaction with the residual alkali on the surface.

[0024] Preferably, the acid in step (2) includes any one or a combination of at least two of H2MoO4, H2WO4, H3BO3, or H3PO4. Using the above-mentioned acids allows for the reaction with LiOH and Li2CO3 on the surface of the high-nickel cathode material, not only reducing the material's alkalinity and improving its processing performance, but also causing lithium-ion conductors such as Li2MoO3, Li2WO4, LiBO2, and Li3PO4 to adhere to the material surface, thus improving product performance.

[0025] Preferably, in step (2), the solid-liquid mass ratio of the sintered product to the acid solution is 1.0-1.5, such as 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] The reaction described in step (2) is accompanied by stirring.

[0027] Preferably, the stirring speed is 500-2000 r / min, such as 500 r / min, 800 r / min, 1000 r / min, 1200 r / min, 1500 r / min, 1750 r / min or 2000 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the reaction time in step (2) is 30-60 min, such as 30 min, 40 min, 50 min or 60 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the temperature for evaporation in step (2) is 80-120°C, such as 80°C, 90°C, 100°C, 110°C or 120°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the evaporation process in step (2) is performed by heating in an oil bath or a water bath.

[0031] Preferably, the sintering temperature in step (2) is 200-500℃, such as 200℃, 300℃, 400℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the sintering time in step (2) is 3-10h, such as 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the heating rate of the sintering in step (2) is 1-3℃ / min, such as 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min or 3℃ / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the sintering in step (2) is carried out in an atmosphere furnace.

[0035] Preferably, the sintering in step (2) is carried out in an oxygen atmosphere and / or an air atmosphere.

[0036] Preferably, step (2) further includes crushing the sintered product.

[0037] As a preferred technical solution of the present invention, the high-nickel cathode material in step (1) is a high-nickel single-crystal cathode material. Single-crystal materials are used because high-nickel single-crystal materials have broad application prospects in the future power battery field, but the material has defects such as high residual alkali on the surface and low initial coulombic efficiency that need to be improved.

[0038] As a preferred embodiment of the present invention, the high-nickel single-crystal cathode material is prepared according to the following method:

[0039] (1') Synthesis of high-nickel precursors;

[0040] (1”) The second lithium source is mixed with the high-nickel precursor described in step (1’) and sintered to obtain the high-nickel single-crystal cathode material.

[0041] Preferably, the synthesis method described in step (1') is a coprecipitation method.

[0042] Preferably, the chemical formula of the high-nickel precursor in step (1') is Ni 1-x-y Co x Mn y (OH)2, where 0 < x ≤ 0.10, for example, x is 0.01, 0.02, 0.04, 0.06, 0.08 or 0.1, etc., and 0 ≤ y ≤ 0.15, for example, y is 0, 0.2, 0.4, 0.6, 0.8, 0.9, 1.0, 1.1, 1.3 or 1.5, etc.

[0043] Preferably, the median particle size of the high-nickel precursor in step (1') is 2.0-4.0 μm, such as 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm or 4.0 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable. Using the above-mentioned median particle size of the precursor is beneficial to the synthesis of single-crystal high-nickel cathode materials.

[0044] Preferably, in step (1"), the second lithium source includes any one or a combination of at least two of lithium hydroxide, lithium nitrate, or lithium carbonate.

[0045] Preferably, in step (1”), the molar ratio of the second lithium source to the high-nickel precursor is 1.05-1.10, such as 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1 or 1.10:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the sintering temperature in step (1) is 850-1000℃, such as 850℃, 870℃, 890℃, 910℃, 930℃, 950℃, 960℃, 975℃, 980℃, 990℃ or 1000℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Preferably, the sintering time in step (1”) is 8-12h, such as 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] As a further preferred embodiment of the preparation method described in this invention, the method includes the following steps:

[0049] (1') A high-nickel precursor was synthesized by co-precipitation method. The chemical formula of the high-nickel precursor is Ni. 1-x-y Co x Mn y (OH)2, wherein 0 < x ≤ 0.10, 0 ≤ y ≤ 0.15, and the median particle size of the high-nickel precursor is 2.0-4.0 μm;

[0050] (1”) The second lithium source and the high-nickel precursor described in step (1’) are mixed at a molar ratio of 1.05:1-1.10:1 and sintered at 850-1000℃ for 8-12 hours to obtain a high-nickel single-crystal cathode material. The chemical formula of the high-nickel single-crystal cathode material is LiNi. 1-x-y Co x Mn y O2, where 0 < x ≤ 0.10, 0 ≤ y ≤ 0.15;

[0051] (1) After mixing the high-nickel cathode material, the first lithium source and the metal oxide described in step (1), the mixture is sintered in an atmosphere furnace at 500-800°C for 5-10 hours to obtain the sintered product.

[0052] Based on the mass of the high-nickel cathode material, the amount of the first lithium source added is 500-2000 ppm, and the amount of the metal oxide added is 500-2000 ppm.

[0053] (2) The sintered product described in step (1) is mixed with an acid solution with a concentration of 0.05-0.1 mol / L and reacted under stirring at a speed of 500-2000 r / min for 30-60 min. Then, it is evaporated at 80-120℃ and sintered at 200-500℃ for 3-10 h in an atmosphere furnace at a heating rate of 1-3℃ / min. The product is then crushed to obtain a high-nickel cathode material with repaired surface structure.

[0054] The solid-liquid mass ratio of the sintered product to the acid solution is 1.0-1.5.

[0055] In a second aspect, the present invention provides a high-nickel cathode material with repaired surface structure obtained by the method described in the first aspect.

[0056] Preferably, the high-nickel cathode material is a high-nickel single-crystal cathode material.

[0057] Thirdly, the present invention provides a lithium-ion battery comprising a high-nickel cathode material as described in the second aspect.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] In the method provided by this invention, lithium hydroxide and a metal oxide are added, wherein the lithium hydroxide can react with the Ni on the surface of the high-nickel cathode material during the sintering process. x Impurities such as O react to form layered lithium metal oxides. These metal oxides can then react with residual lithium salts (LiOH and Li₂CO₃) on the surface of the high-nickel cathode material to form lithium metal oxides. After sintering, not only are impurity phases eliminated from the substrate surface, but a protective layer is also formed, protecting the substrate material and preventing corrosion during subsequent acid treatment. A specific concentration of acid solution is then added. The acid primarily reacts with residual LiOH and Li₂CO₃ on the material surface, reducing the material's alkalinity and improving its processing performance. The resulting lithium-ion conductors, such as Li₂MoO₃, Li₂WO₄, LiBO₂, and Li₃PO₄, adhere to the material surface. These lithium-ion conductors have a high lithium-ion diffusion coefficient, improving the material's coulombic efficiency and cycle performance. The high-nickel cathode material with its surface structure repaired using the method provided by this invention achieves an initial discharge capacity of 216 mAh / g, an initial coulombic efficiency of 91%, a discharge retention rate of 94.5% at 2.0C compared to 0.5C, and a capacity retention rate of 97% after 50 cycles. Attached Figure Description

[0060] Figure 1 SEM image of the precursor prepared in Example 1;

[0061] Figure 2 SEM image of the high-nickel single-crystal cathode material with repaired surface structure obtained in Example 1;

[0062] Figure 3 The image shows the XRD pattern of the high-nickel single-crystal cathode material with repaired surface structure obtained in Example 1.

[0063] Figure 4 SEM image of the high-nickel single-crystal cathode material with repaired surface structure obtained in Example 2;

[0064] Figure 5 The image shows the XRD pattern of the high-nickel single-crystal cathode material with repaired surface structure obtained in Example 2.

[0065] Figure 6 SEM image of the high-nickel single-crystal cathode material with repaired surface structure obtained in Example 3;

[0066] Figure 7 Here is a SEM image of the high-nickel single-crystal cathode material obtained in Comparative Example 1;

[0067] Figure 8 The image shows the SEM image of the high-nickel single-crystal cathode material obtained in Comparative Example 2. Detailed Implementation

[0068] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention will be further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0069] The following are typical but non-limiting embodiments of the present invention:

[0070] Example 1

[0071] This embodiment provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0072] (1) A mixed solution containing nickel sulfate, cobalt sulfate and manganese sulfate in a molar ratio of Ni, Co and Mn of 8.3:1.1:0.6 was reacted with an 8 mol / L sodium hydroxide solution and a 13.3 mol / L ammonia solution to obtain a nickel-cobalt-manganese hydroxide precursor with a D50 of 3.5 μm through a co-precipitation reaction.

[0073] (2) The precursor obtained in step (1) and lithium hydroxide are mixed evenly (the molar ratio of lithium hydroxide to precursor is 1.05:1), and sintered at 880℃ for 10 h to obtain a high-nickel single-crystal cathode material (chemical formula LiNi) as the substrate. 0.83 Co 0.11 Mn 0.06 O2);

[0074] (3) The high-nickel single-crystal cathode material obtained in step (2) as the matrix, 500 ppm lithium hydroxide, and 1000 ppm alumina are mixed evenly and sintered at 750°C for 5 h in an oxygen atmosphere to obtain the secondary sintered material.

[0075] (4) The secondary sintering material obtained in step (3) is added to a molybdenum acid solution with a concentration of 0.05 mol / L (the solid-liquid mass ratio of the secondary sintering material to the acid solution is 1.1), stirred at 1000 r / min for 30 min, then evaporated in an oil bath at 100℃, and placed in an atmosphere furnace to be heated to 450℃ for 5 h in an air atmosphere at a heating rate of 2℃ / min. The material is then crushed to obtain a high-nickel single crystal cathode material with repaired surface structure.

[0076] Scanning electron microscopy revealed that the cathode material consists of single-crystal particles with uniform distribution, a median particle size of 4.0 μm, and a specific surface area of ​​0.45 m². 2 / g, the compacted density of the powder is 3.0 g / cm³. 3 .

[0077] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0078] Figure 1 The image shows the SEM image of the precursor prepared in step (1) of this embodiment. It can be seen from the image that the precursor volumetric particle size D50 is basically around 3.5 μm and the particle size distribution is concentrated.

[0079] Figure 2 This is a SEM image of the high-nickel single-crystal cathode material with repaired surface structure obtained in this embodiment. As can be seen from the image, the material surface is uniformly coated with a nanoscale coating layer.

[0080] Figure 3 The image shows the XRD pattern of the high-nickel single-crystal cathode material with repaired surface structure obtained in this embodiment. It can be seen from the image that the structure of the substrate has not changed due to the surface coating. At the same time, the diffraction peaks of lithium molybdate can be seen, indicating that there is indeed a lithium molybdate coating layer on the surface of the material.

[0081] Example 2

[0082] This embodiment provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0083] (1) The precursor obtained in step (1) of Example 1 and lithium hydroxide were mixed evenly (the molar ratio of lithium hydroxide to precursor was 1.05:1), and sintered at 880°C for 10 h to obtain a high-nickel single-crystal cathode material (chemical formula LiNi) as the substrate. 0.83 Co 0.11 Mn 0.06 O2);

[0084] (2) The high-nickel single-crystal cathode material obtained in step (1) as the matrix, 500 ppm lithium hydroxide, and 1000 ppm zirconium oxide are mixed evenly and sintered at 750°C for 8 hours in an oxygen atmosphere to obtain the secondary sintered material.

[0085] (3) The secondary sintering material obtained in step (2) is added to a tungstic acid solution with a concentration of 0.05 mol / L (the solid-liquid ratio of the secondary sintering material to the acid solution is 1.1), stirred at 1000 r / min for 30 min, then evaporated in an oil bath at 100℃, and placed in an atmosphere furnace to be heated to 500℃ for 5 h in an air atmosphere at a heating rate of 2℃ / min. The material is then crushed to obtain a high-nickel single crystal cathode material with repaired surface structure.

[0086] Scanning electron microscopy revealed that the cathode material consists of single-crystal particles with uniform distribution, a median particle size of 4.5 μm, and a specific surface area of ​​0.65 m². 2 / g, the compacted density of the powder is 3.1g / cm³. 3 .

[0087] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0088] Figure 4 This is a SEM image of the high-nickel single-crystal cathode material with repaired surface structure obtained in this embodiment. The image shows that there is a discontinuous coating layer on the surface of the material.

[0089] Figure 5 The image shows the XRD pattern of the high-nickel single-crystal cathode material with repaired surface structure obtained in this embodiment. It can be seen from the image that the matrix structure of the material has not changed, and there are lithium tungstate diffraction peaks of a certain intensity, indicating that a lithium tungstate coating layer has been successfully formed on the surface of the material.

[0090] Example 3

[0091] This embodiment provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0092] (1) The precursor obtained in step (1) of Example 1 and lithium hydroxide were mixed evenly (the molar ratio of lithium hydroxide to precursor was 1.05:1), and sintered at 880°C for 10 h to obtain a high-nickel single-crystal cathode material (chemical formula LiNi) as the substrate. 0.83 Co 0.11 Mn 0.06 O2);

[0093] (2) The high-nickel single-crystal cathode material obtained in step (1) as the matrix, 500 ppm lithium hydroxide, and 1000 ppm titanium oxide are mixed evenly and sintered at 750°C for 10 h in an oxygen atmosphere to obtain the secondary sintered material.

[0094] (3) The secondary sintering material obtained in step (2) is added to a boric acid solution with a concentration of 0.1 mol / L (the solid-liquid ratio of the secondary sintering material to the acid solution is 1.5), stirred at 1000 r / min for 30 min, then evaporated in an oil bath at 100℃, and placed in an atmosphere furnace to be heated to 500℃ for 5 h in an air atmosphere at a heating rate of 2℃ / min. The material is then crushed to obtain a high-nickel single crystal cathode material with repaired surface structure.

[0095] Scanning electron microscopy revealed that the cathode material consists of single-crystal particles with uniform distribution, a median particle size of 5.0 μm, and a specific surface area of ​​0.50 m². 2 / g, the compacted density of the powder is 2.9g / cm³. 3 .

[0096] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0097] Figure 6 This is a SEM image of the high-nickel single-crystal cathode material with repaired surface structure obtained in this embodiment. As can be seen from the image, a continuous and uniform coating layer is formed on the surface of the material.

[0098] Example 4

[0099] This embodiment provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0100] (1) The high-nickel single-crystal cathode material (chemical formula LiNi) obtained in Example 1 was used as the substrate. 8.3 Co 1.1 Mn 0.6 O2), 1000ppm lithium hydroxide and 500ppm titanium oxide are mixed evenly and sintered at 500°C for 10 hours in an oxygen atmosphere to obtain the secondary sintered material.

[0101] (2) The secondary sintering material obtained in step (1) is added to a molybdenum acid solution with a concentration of 0.07 mol / L (the solid-liquid mass ratio of the secondary sintering material to the acid solution is 1.1), stirred at 500 r / min for 45 min, then evaporated in an oil bath at 80℃, and placed in an atmosphere furnace to sinter at 200℃ for 10 h in an oxygen atmosphere at a heating rate of 1℃ / min. The material is then crushed to obtain a high-nickel single crystal cathode material with repaired surface structure.

[0102] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0103] Example 5

[0104] This embodiment provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0105] (1) The high-nickel single-crystal cathode material (chemical formula LiNi) obtained in Example 1 was used as the substrate. 8.3 Co 1.1 Mn 0.6 O2), 2000ppm lithium hydroxide and 2000ppm titanium oxide are mixed evenly and sintered at 800℃ for 5 hours in an oxygen atmosphere to obtain the secondary sintered material.

[0106] (2) The secondary sintering material obtained in step (1) is added to a molybdenum acid solution with a concentration of 0.06 mol / L (the solid-liquid mass ratio of the secondary sintering material to the acid solution is 1.0), stirred at 2000 r / min for 60 min, then evaporated in an oil bath at 120℃, and placed in an atmosphere furnace to be heated to 480℃ for 3 h in an air atmosphere at a heating rate of 3℃ / min. The material is then crushed to obtain a high-nickel single crystal cathode material with repaired surface structure.

[0107] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0108] Example 6

[0109] The method for repairing the surface structure of high-nickel single-crystal cathode material in this embodiment is the same as in Example 1. The difference is that in step (1), the ratio of nickel sulfate, cobalt sulfate and manganese sulfate is such that the molar ratio of Ni, Co and Mn is 0.75:0.1:0.15, and the D50 of the precursor is controlled to be 2.0 μm; in step (2), the molar ratio of lithium hydroxide to the precursor is 1.08:1, the sintering temperature is 850℃, and the sintering time is 12h.

[0110] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0111] Example 7

[0112] The method for repairing the surface structure of high-nickel single-crystal cathode material in this embodiment is the same as in Example 1. The difference is that in step (1), the ratio of nickel sulfate, cobalt sulfate and manganese sulfate is such that the molar ratio of Ni, Co and Mn is 0.94:0.05:0.01, and the D50 of the precursor is controlled to be 4.0 μm; in step (2), the molar ratio of lithium hydroxide to the precursor is 1.10:1, the sintering temperature is 1000℃, and the sintering time is 8h.

[0113] The electrochemical performance test results of the high-nickel cathode material with repaired surface structure obtained in this embodiment are shown in Table 1.

[0114] Comparative Example 1

[0115] This comparative example provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0116] (1) The precursor obtained in step (1) of Example 1 and lithium hydroxide were mixed evenly (the molar ratio of lithium hydroxide to precursor was 1.05:1), and sintered at 880°C for 10 h to obtain a high-nickel single-crystal cathode material (chemical formula LiNi) as the substrate. 8.3 Co 1.1 Mn 0.6 O2);

[0117] (2) The high-nickel single-crystal cathode material obtained in step (1) as the matrix, 500ppm lithium hydroxide, and 1000ppm alumina are mixed evenly and sintered at 750°C for 5 hours in an oxygen atmosphere to obtain a secondary sintered material as the cathode material product.

[0118] Scanning electron microscopy revealed that the cathode material exhibited secondary particle morphology with uniform distribution, a median particle size of 4.0 μm, and a specific surface area of ​​0.36 m². 2 / g, the compacted density of the powder is 3.1g / cm³. 3 ;

[0119] The electrochemical performance test results of the high-nickel cathode material obtained in this comparative example are shown in Table 1.

[0120] Figure 7 The image shows the SEM image of the high-nickel single-crystal cathode material obtained in this comparative example. As can be seen from the image, there is an aluminum compound coating layer on the surface of the material.

[0121] Comparative Example 2

[0122] This comparative example provides a method for repairing the surface structure of a high-nickel single-crystal cathode material, the method comprising the following steps:

[0123] (1) The precursor obtained in step (1) of Example 1 and lithium hydroxide were mixed evenly (the molar ratio of lithium hydroxide to precursor was 1.05:1), and sintered at 880°C for 10 h to obtain a high-nickel single-crystal cathode material (chemical formula LiNi) as the substrate. 8.3 Co 1.1 Mn 0.6 O2);

[0124] (2) The high-nickel single-crystal cathode material obtained in step (1) as the matrix, 500ppm lithium hydroxide, and 1000ppm zirconium oxide are mixed evenly and sintered at 750°C for 5 hours in an oxygen atmosphere to obtain a secondary sintered material as the cathode material product.

[0125] Scanning electron microscopy revealed that the cathode material exhibited secondary particle morphology with uniform distribution, a median particle size of 4.5 μm, and a specific surface area of ​​0.48 m². 2 / g, the compacted density of the powder is 3.0 g / cm³. 3 ;

[0126] The electrochemical performance test results of the high-nickel cathode material obtained in this comparative example are shown in Table 1.

[0127] Figure 8 The image shows a SEM image of the high-nickel single-crystal cathode material obtained in this comparative example. The image shows that a zirconium compound coating layer exists on the surface of the material.

[0128] Comparative Example 3

[0129] The operation of this comparative example is the same as that of Example 1, except that the operation of step (4) is to put the secondary sintering material obtained in step (3) into an atmosphere furnace and heat it to 450°C for 5 hours in an air atmosphere at a heating rate of 2°C / min, and then crush it to obtain the processed high-nickel single crystal cathode material.

[0130] The electrochemical performance test results of the high-nickel cathode material obtained in this comparative example are shown in Table 1.

[0131] Comparative Example 4

[0132] The operation of this comparative example is the same as that of Example 1, except that lithium hydroxide is not added in step (3).

[0133] The electrochemical performance test results of the high-nickel cathode material obtained in this comparative example are shown in Table 1.

[0134] Comparative Example 5

[0135] The operation of this comparative example is the same as that of Example 1, except that in step (3), aluminum oxide is not added.

[0136] The electrochemical performance test results of the high-nickel cathode material obtained in this comparative example are shown in Table 1.

[0137] Comparative Example 6

[0138] The electrochemical performance of the high-nickel single-crystal cathode material obtained in step (2) of Example 1 was tested, and the results are shown in Table 1.

[0139] Performance testing methods

[0140] The positive electrode materials obtained in each embodiment and comparative example were used as positive electrode active materials to prepare lithium-ion batteries. The preparation method was as follows: the positive electrode active material, binder PVDF, and conductive agent SP were mixed in NMP at a ratio of 96:2:2 to form a slurry, and the solid content was controlled to be 70%. This slurry was then coated on aluminum foil as the positive electrode; lithium sheets were used as the negative electrode; and coin cells were prepared using a 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte and a Celgard 2400 separator. Electrochemical tests were performed on this type of battery.

[0141] The Blue Battery Testing System was used to test the initial discharge capacity and initial coulombic efficiency by performing 0.1C / 0.1C charge and discharge at 25℃ and within a voltage range of 3.0 to 4.3V.

[0142] Using the Blue Battery Testing System, under conditions of 25℃ and a voltage range of 3.0~4.3V, 0.5C charging, 0.5C / 1.0C / 2.0C rate discharging were performed, and the capacity retention rate at 2.0C / 0.5C was tested.

[0143] The capacity retention rate was tested after 50 cycles using the Blue Battery Testing System at 25℃ and a voltage range of 3.0 to 4.3V, with charging at 0.5C and discharging at 1.0C.

[0144] The test results are shown in the table below:

[0145] Table 1

[0146]

[0147]

[0148] Based on the above embodiments and comparative examples, it can be seen that the surface structure repair method of Examples 1-7 firstly removes some impurity phases on the material surface by reacting the first lithium source and metal oxide with nickel oxide and residual lithium on the material surface, respectively, and forms a protective layer on the material surface; then, the impurities on the material surface are further removed by using a weak acid, and a lithium-ion conductor coating layer is formed on the material surface, which not only improves the discharge capacity and first efficiency of the battery, but also improves the cycle performance and safety performance.

[0149] Comparative Examples 1 and 2 did not undergo the mixing reaction of the sintered product with the acid solution, evaporation, and subsequent sintering operations, resulting in higher residual lithium salts on the surface, which affected the material's processing performance, discharge capacity, and capacity retention.

[0150] Although Comparative Example 3 underwent subsequent sintering, it did not perform the previous operation of mixing the secondary sintering product with the acid solution, resulting in lower ionic conductivity and affecting the discharge capacity and cycle retention rate at high rates.

[0151] Comparative Example 4 did not include a first lithium source, resulting in a lower discharge capacity and poorer cycle and rate performance compared to Example 1.

[0152] Comparative Example 5 did not contain any metal oxides, resulting in a higher residual lithium content on the material surface, which affected processing performance and resulted in poor rate performance and cycle performance.

[0153] Comparative Example 6 did not perform surface structure repair on the high-nickel single-crystal cathode material, therefore its performance in all aspects is inferior to that of Examples 1-3.

[0154] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for repairing the surface structure of a high-nickel cathode material, characterized in that, The method includes the following steps: (1) After mixing high-nickel cathode material, first lithium source and metal oxide, sintering is performed to obtain sintered product; The high-nickel cathode material mentioned in step (1) is a high-nickel single-crystal cathode material; the chemical formula of the high-nickel cathode material is LiNi. 1-x-y Co x Mn y O2, where 0 < x ≤ 0.10, 0 ≤ y ≤ 0.15; the mass of the high-nickel cathode material in step (1) is the basis, and the amount of metal oxide added is 500-2000 ppm; (2) The sintering product described in step (1) is mixed with an acid solution and reacted, then evaporated to dryness and sintered to obtain a high-nickel cathode material with repaired surface structure. In step (2), the solid-liquid mass ratio of the sintered product to the acid solution is 1.0-1.5; The concentration of the acid solution in step (2) is 0.05-0.1 mol / L; the acid solution in step (2) is H2MoO4 or H2WO4.

2. The method according to claim 1, characterized in that, Step (1) The first lithium source includes any one or a combination of at least two of lithium hydroxide, lithium acetate or lithium nitrate.

3. The method according to claim 1, characterized in that, The metal oxide in step (1) includes any one or a combination of at least two of aluminum oxide, titanium oxide, zirconium oxide, yttrium oxide, cobalt oxide, molybdenum oxide, or niobium oxide.

4. The method according to claim 1, characterized in that, Based on the mass of the high-nickel cathode material described in step (1), the amount of the first lithium source added is 500-2000 ppm.

5. The method according to claim 1, characterized in that, The sintering temperature in step (1) is 500-800℃.

6. The method according to claim 1, characterized in that, The sintering time in step (1) is 5-10 hours.

7. The method according to claim 1, characterized in that, The sintering described in step (1) is carried out in an atmosphere furnace.

8. The method according to claim 7, characterized in that, The sintering described in step (1) is carried out in an oxygen atmosphere.

9. The method according to claim 1, characterized in that, The reaction described in step (2) is accompanied by stirring.

10. The method according to claim 9, characterized in that, The stirring speed is 500-2000 r / min.

11. The method according to claim 1, characterized in that, The reaction time in step (2) is 30-60 min.

12. The method according to claim 1, characterized in that, The temperature for evaporation in step (2) is 80-120℃.

13. The method according to claim 1, characterized in that, The evaporation process described in step (2) involves heating the product in an oil bath or water bath.

14. The method according to claim 1, characterized in that, The sintering temperature in step (2) is 200-500℃.

15. The method according to claim 1, characterized in that, The sintering time in step (2) is 3-10 hours.

16. The method according to claim 1, characterized in that, The heating rate for sintering in step (2) is 1-3℃ / min.

17. The method according to claim 1, characterized in that, The sintering described in step (2) is carried out in an atmosphere furnace.

18. The method according to claim 17, characterized in that, The sintering described in step (2) is carried out in an oxygen atmosphere and / or an air atmosphere.

19. The method according to claim 1, characterized in that, Step (2) also includes crushing the sintered product.

20. The method according to claim 1, characterized in that, The high-nickel single-crystal cathode material is prepared according to the following method: (1') Synthesis of high-nickel precursors; (1”) The second lithium source is mixed with the high-nickel precursor described in step (1’) and sintered to obtain the high-nickel single-crystal cathode material.

21. The method according to claim 20, characterized in that, The synthesis method described in step (1') is a coprecipitation method.

22. The method according to claim 20, characterized in that, The chemical formula of the high-nickel precursor in step (1') is Ni 1-x-y Co x Mn y (OH)2, where 0 < x ≤ 0.10, 0 ≤ y ≤ 0.

15.

23. The method according to claim 20, characterized in that, The median particle size of the high-nickel precursor in step (1') is 2.0-4.0 μm.

24. The method according to claim 20, characterized in that, In step (1”), the second lithium source includes any one or a combination of at least two of lithium hydroxide, lithium nitrate or lithium carbonate.

25. The method according to claim 20, characterized in that, In step (1”), the molar ratio of the second lithium source to the high-nickel precursor is 1.05:1-1.10:

1.

26. The method according to claim 20, characterized in that, The sintering temperature in step (1) is 850-1000℃.

27. The method according to claim 20, characterized in that, The sintering time in step (1) is 8-12 hours.

28. The method according to claim 1, characterized in that, The method includes the following steps: (1') A high-nickel precursor was synthesized by co-precipitation method. The chemical formula of the high-nickel precursor is Ni. 1-x-y Co x Mn y (OH)2, wherein 0 < x ≤ 0.10, 0 ≤ y ≤ 0.15, and the median particle size of the high-nickel precursor is 2.0-4.0 μm; (1”) The second lithium source and the high-nickel precursor described in step (1’) are mixed at a molar ratio of 1.05:1-1.10:1 and sintered at 850-1000℃ for 8-12 hours to obtain a high-nickel single-crystal cathode material. The chemical formula of the high-nickel single-crystal cathode material is LiNi. 1-x- y Co x Mn y O2, where 0 < x ≤ 0.10, 0 ≤ y ≤ 0.15; (1) After mixing the high-nickel cathode material, the first lithium source and the metal oxide described in step (1), the mixture is sintered in an atmosphere furnace at 500-800°C for 5-10 hours to obtain the sintered product. Based on the mass of the high-nickel cathode material, the amount of the first lithium source added is 500-2000 ppm, and the amount of the metal oxide added is 500-2000 ppm. (2) The sintered product described in step (1) is mixed with an acid solution with a concentration of 0.05-0.1 mol / L and reacted under stirring at a speed of 500-2000 r / min for 30-60 min. Then, it is evaporated at 80-120℃ and sintered at 200-500℃ for 3-10 h in an atmosphere furnace at a heating rate of 1-3℃ / min. The product is then crushed to obtain a high-nickel cathode material with repaired surface structure. The solid-liquid mass ratio of the sintered product to the acid solution is 1.0-1.

5.

29. A high-nickel cathode material with repaired surface structure obtained by the method according to any one of claims 1-28.

30. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the high-nickel cathode material as described in claim 29.

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