Lithium-ion secondary battery, positive electrode active material, production method, and electric device

Abstract

The application relates to the technical field of secondary batteries, in particular to a lithium ion secondary battery, a positive electrode active material, a preparation method and an electric device. The positive electrode active material of the lithium ion secondary battery comprises a first part and a second part. In the positive electrode active material, the content of a nickel element in transition elements is greater than or equal to 0.85. In a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of secondary particles in the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of secondary particles in the second part is greater than or equal to 1 and less than 1.1. Based on the total area of the secondary particles of the positive electrode active material, the area proportion of the secondary particles in the first part is 60% to 90%, and the area proportion of the secondary particles in the second part is 10% to 40%. The secondary particles in different parts cooperate with each other, the extension degree of the positive electrode sheet is reduced, and therefore the volume energy density and stability of the lithium ion secondary battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion secondary battery, a positive electrode active material, a preparation method and an electric device. BACKGROUND

[0002] In recent years, lithium ion secondary batteries are widely used in wireless communication, transportation, aerospace and other aspects. High-nickel ternary positive electrode active materials are widely concerned due to their high energy density and high rate, but the stability of lithium ion secondary batteries is a problem to be solved at present. SUMMARY

[0003] Therefore, the technical problem to be solved by the present application is how to improve the stability of the lithium ion secondary battery.

[0004] To solve the above technical problems, the first aspect of the technical scheme adopted by the present application is to provide a lithium ion secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a first part and a second part, in the positive electrode active material, the content of nickel element in the transition element is greater than or equal to 0.85, in the scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles in the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles in the second part is greater than or equal to 1 and less than 1.1; based on the total area of the secondary particles of the positive electrode active material, the area proportion of the secondary particles in the first part is 60% to 90%, and the area proportion of the secondary particles in the second part is 10% to 40%.

[0005] In the technical scheme of the present application, the active particles in the positive electrode active material include the first part of the secondary particles with the ratio of the longest diameter to the shortest diameter greater than or equal to 1.1, and the second part of the secondary particles with the ratio of the longest diameter to the shortest diameter greater than or equal to 1 and less than 1.1, the first part of the secondary particles is more close to non-spherical than the second part of the secondary particles, the second part of the secondary particles is more close to spherical than the first part of the secondary particles, the first part of the secondary particles accounts for 60% to 90% of the total area of the secondary particles of the positive electrode active material, and the second part of the secondary particles accounts for 10% to 40% of the total area of the secondary particles of the positive electrode active material, when the sheet coating is completed and cold pressing is performed, the non-spherical secondary particles in the sheet can better relieve the stress in cooperation with the spherical secondary particles, reduce the deformation of the sheet, and reduce the degree of extension of the sheet, thereby improving the volume energy density of the cell. At the same time, when the cell is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the extrusion of each other when the particles expand, reduce the expansion of the sheet and relieve the particle crushing, thereby improving the stability of the lithium ion secondary battery.

[0006] In an embodiment, the area ratio of the secondary particles in the first part is 65% to 85%.

[0007] In the embodiments of the present application, by setting the area ratio of the secondary particles in the first part within the above range, when the coating of the pole piece is completed and cold pressing is performed, the non-spherical secondary particles in the pole piece can better relieve stress in cooperation with the spherical secondary particles, reduce the deformation of the pole piece, reduce the degree of extension of the pole piece, and the gap between the particles can be filled, thereby improving the volumetric energy density of the battery cell. At the same time, when the battery cell is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the extrusion of the particles on each other when the particles swell, reduce the swelling of the pole piece and relieve the crushing of the particles, thereby improving the stability of the lithium ion secondary battery.

[0008] In an embodiment, the area ratio of the secondary particles in the second part is 15% to 35%.

[0009] In the embodiments of the present application, by setting the area ratio of the secondary particles in the second part within the above range, the secondary particles in the first part can be better cooperated to improve the volumetric energy density of the battery cell and improve the stability of the lithium ion secondary battery.

[0010] In an embodiment, the tap density of the positive pole piece under a pressure of 5T is 3.2 g / cm 3 ~ 3.8 g / cm 3 .

[0011] In the embodiments of the present application, the tap density of the positive pole piece under a pressure of 5T is within the above range, the gap between the secondary particles in the first part and the secondary particles in the second part is smaller, so that the proportion of the two kinds of particles per unit volume in the positive pole piece is larger, and the volumetric energy density of the battery cell can be improved.

[0012] In an embodiment, the volume average particle size DV50 of the secondary particles of the positive active material is 8.5 μm to 12 μm.

[0013] In the embodiments of the present application, by setting the volume average particle size DV50 of the secondary particles of the positive active material within the above range, the electrochemical performance of the lithium ion secondary battery can be better.

[0014] In an embodiment, the longest diameter of the secondary particles in the first part ranges from 2.5 μm to 18.5 μm, and the shortest diameter ranges from 1 μm to 15.5 μm.

[0015] In the embodiments of the present application, by setting the longest diameter and the shortest diameter of the secondary particles in the first part within the above range, the electrochemical performance of the lithium ion secondary battery can be better.

[0016] In an embodiment, the longest diameter of the secondary particles of the second portion ranges from 5 μm to 15.5 μm, and the shortest diameter ranges from 4.5 μm to 15 μm.

[0017] In the embodiments of the present application, by having the longest diameter and the shortest diameter of the secondary particles of the first portion within the above ranges, the lithium ion secondary battery has better electrochemical performance.

[0018] In an embodiment, the secondary particles of the first portion and the second portion of the positive electrode active material each independently comprise a host material, and the host material has a structure of Li a Ni b Co c Mn d M (1-b-c-d) O n , wherein M comprises one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, 0.5≤a≤1.2, 0.85≤b≤0.99, 0<c≤0.1, 0<d≤0.05, b+c+d≤1, 1.9≤n≤2.2, and the positive electrode active material comprises lithium nickel cobalt manganese oxide, and the molar content of nickel in all transition metal elements is greater than or equal to 0.85.

[0019] In the embodiments of the present application, the secondary particles of the positive electrode active material comprise an active material having a structure of Li a Ni b Co c Mn d M (1-b-c-d) O n , wherein the content of nickel is at least 0.85 of the total content of transition metal elements, and the positive electrode active material further comprises transition metal Co and Mn, so that the lithium ion secondary battery has better electrochemical performance. In addition, the positive electrode active material can be doped with any one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, etc., to improve the stability of the lithium ion secondary battery.

[0020] In an embodiment, the host material comprises lithium nickel cobalt manganese oxide, and the molar content of nickel in all transition metal elements is greater than or equal to 0.85.

[0021] In the embodiments of the present application, the host material of the positive electrode active material comprises lithium nickel cobalt manganese oxide, and the molar content of nickel in all transition metal elements is greater than or equal to 0.85, so that the lithium ion secondary battery has better electrochemical performance.

[0022] In an embodiment, the secondary particles of the first portion and the second portion of the positive electrode active material each independently further comprise a first coating layer, the first coating layer comprising one or more of Co, Al, F, Ti, and the mass percentage of the first coating layer based on the mass of the first portion and the second portion of the positive electrode active material is 1.68% to 2.03%.

[0023] In the embodiments of the present application, the residual alkali produced during the preparation of the positive electrode active material is consumed in the process of coating the first coating layer. The residual alkali produces a large amount of gas at high pressure, and also intensifies the side reactions of the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium ion secondary battery. In addition, the function of coating the secondary particles of the first portion and the second portion of the positive electrode active material with a coating layer is that the coating layer can reduce the side reactions on the surface of the positive electrode active material, thereby improving the electrochemical performance of the lithium ion secondary battery.

[0024] In an embodiment, the secondary particles of the first portion and the second portion of the positive electrode active material each independently further comprise a second coating layer, the second coating layer comprising one or more of B, Al, Y, and the mass percentage of the second coating layer based on the mass of the positive electrode active material is 0.09% to 0.21%.

[0025] In the embodiments of the present application, the second coating layer comprising one or more of B, Al, Y is coated on the surface of the positive electrode active material to improve the structural stability of the secondary particles, and also to inhibit the side reactions on the surface of the secondary particles, thereby significantly improving the cycle stability and safety of the positive electrode active material.

[0026] In an embodiment, in the first portion and / or the second portion, the content of the nickel element in the transition elements is greater than or equal to 0.85.

[0027] In the embodiments of the present application, in the first portion and / or the second portion, the content of the nickel element in the transition elements is greater than or equal to 0.85, which can make the lithium ion secondary battery have better electrochemical performance.

[0028] In an embodiment, the primary particles of the first portion have an average particle size of 50 nm to 2 μm.

[0029] In the embodiments of the present application, the average particle size of the primary particles of the first portion is in the range of 50 nm to 2 μm, so that the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and the electrochemical performance of the lithium ion secondary battery is better.

[0030] In an embodiment, the primary particles of the first portion have an average particle size of 100 nm to 500 nm.

[0031] In the embodiments of the present application, the average particle size of the primary particles in the first part is in the range of 100 nm to 500 nm, so that the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and making the electrochemical performance of the lithium ion secondary battery better.

[0032] In an embodiment, the average particle size of the primary particles in the second part is 50 nm to 2 μm.

[0033] In the embodiments of the present application, the average particle size of the primary particles in the second part is in the range of 50 nm to 2 μm, so that the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and making the electrochemical performance of the lithium ion secondary battery better.

[0034] In an embodiment, the average particle size of the primary particles in the second part is 100 nm to 500 nm.

[0035] In the embodiments of the present application, the average particle size of the primary particles in the second part is in the range of 100 nm to 500 nm, so that the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and making the electrochemical performance of the lithium ion secondary battery better.

[0036] In a second aspect, the present application provides a positive electrode active material, which comprises a first part and a second part, wherein the content of nickel element in the transition elements is greater than or equal to 0.85, the ratio of the longest diameter to the shortest diameter of the secondary particles in the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles in the second part is greater than or equal to 1 and less than 1.1 in a scanning electron microscope picture with a magnification of 2K; based on the total area of the secondary particles of the positive electrode active material, the area ratio of the secondary particles in the first part is 60% to 90%, and the area ratio of the secondary particles in the second part is 10% to 40%.

[0037] In the technical scheme of the embodiment of the present application, the active particles in the positive active material include a first part of secondary particles with a ratio of the longest diameter to the shortest diameter greater than or equal to 1.1 and a second part of secondary particles with a ratio of the longest diameter to the shortest diameter greater than or equal to 1 and less than 1.1, the first part of secondary particles is closer to a non-spherical shape than the second part of secondary particles, the second part of secondary particles is closer to a spherical shape than the first part of secondary particles, the first part of secondary particles accounts for 60% to 90% of the total area of the secondary particles of the positive active material, and the second part of secondary particles accounts for 10% to 40% of the total area of the secondary particles of the positive active material. When the electrode sheet is cold-pressed after coating, the non-spherical secondary particles and the spherical secondary particles in the electrode sheet can better relieve stress, reduce electrode sheet deformation, and reduce the degree of electrode sheet extension, thereby improving the volumetric energy density of the battery cell. At the same time, when the battery cell is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the extrusion of the particles on each other when the particles expand, reduce the expansion of the electrode sheet, and relieve particle crushing, thereby improving the stability of the lithium ion secondary battery.

[0038] The present application provides a preparation method of a lithium ion secondary battery in a third aspect, comprising: providing a positive electrode sheet, a separator and a negative electrode sheet to make a lithium ion secondary battery; the positive electrode sheet comprises a positive active material, wherein the preparation method of the positive active material comprises: adding a precipitating agent and a complexing agent into a solution comprising a nickel source, a manganese source and a cobalt source to react, to obtain a positive active material precursor; and sintering the positive active material precursor with a lithium source to obtain the positive active material; in the positive active material, the content of nickel element in transition elements is greater than or equal to 0.85; or the preparation method of the positive active material comprises: mixing a first part of positive active material and a second part of positive active material to obtain the positive active material, wherein in a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the first part of secondary particles is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the second part of secondary particles is greater than or equal to 1 and less than 1.1, the area ratio of the first part of secondary particles is 60% to 90% based on the total area of the secondary particles of the positive active material, and the area ratio of the second part of secondary particles is 10% to 40%, and in the positive active material, the content of nickel element in all transition elements is greater than or equal to 0.85.

[0039] In the technical scheme of the embodiment of the application, the precipitator and the complexing agent are added to the solution containing the nickel source, the manganese source and the cobalt source, which is conducive to controlling the morphology of the positive electrode active material precursor particles, and further controlling the morphology of the secondary particles of the positive electrode active material, or the positive electrode active material is obtained by mixing the first part of the positive electrode active material with the above morphology and the second part of the positive electrode active material, by providing the above positive electrode active material, when the cold pressing of the electrode piece coating is completed, the non-spherical secondary particles in the electrode piece can better relieve the stress, reduce the deformation of the electrode piece, and reduce the degree of extension of the electrode piece, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the mutual extrusion of the particles when they expand, reduce the expansion of the electrode piece, and relieve the particle crushing, thereby improving the stability of the lithium ion secondary battery.

[0040] In an embodiment, the precipitator includes at least one of sodium carbonate, sodium hydroxide and potassium hydroxide.

[0041] In the technical scheme of the embodiment of the application, the precipitator can react with the nickel source, the manganese source and the cobalt source to generate the corresponding hydroxide or / and basic salt precipitate, and then the precipitate is sintered to obtain the positive electrode active material.

[0042] In an embodiment, the concentration of the precipitator is 2mol / L-8mol / L.

[0043] In the technical scheme of the embodiment of the application, the concentration of the precipitator is in the above range, which is conducive to controlling the morphology of the positive electrode active material precursor particles.

[0044] In an embodiment, the concentration of the precipitator is 4mol / L-6mol / L.

[0045] In the technical scheme of the embodiment of the application, the concentration of the precipitator is in the above range, which is conducive to controlling the morphology of the positive electrode active material precursor particles.

[0046] In an embodiment, the complexing agent includes at least one of ammonia, urea, citric acid and ethylenediaminetetraacetic acid (EDTA).

[0047] In the technical scheme of the embodiment of the application, at least one of ammonia, urea, citric acid and ethylenediaminetetraacetic acid (EDTA) as the complexing agent can effectively complex the metal ions such as Ni, Co and Mn in the liquid, which is conducive to controlling the composition of the positive electrode active material precursor.

[0048] In an embodiment, the concentration of the complexing agent is 0.25mol / L-0.6mol / L.

[0049] The concentration of the complexing agent is controlled in the range of 0.25 mol / L to 0.6 mol / L in the technical scheme of the embodiment, which not only slows down the disturbance of the addition of raw materials on the precipitation balance, controls the supersaturation of the precipitate in the solution, but also reduces the nucleation and growth speed, slowly grows the crystal, and facilitates the regulation of the particle size uniformity of the positive active material precursor.

[0050] In an embodiment, the concentration of the complexing agent is 0.3 mol / L to 0.6 mol / L.

[0051] The concentration of the complexing agent is controlled in the range of 0.3 mol / L to 0.6 mol / L in the technical scheme of the embodiment, which not only slows down the disturbance of the addition of raw materials on the precipitation balance, controls the supersaturation of the precipitate in the solution, but also reduces the nucleation and growth speed, slowly grows the crystal, and facilitates the regulation of the particle size uniformity of the positive active material precursor.

[0052] In an embodiment, in the step of adding the precipitant and the complexing agent into the solution of the nickel source, the manganese source and the cobalt source to react, the PH is 11.5 to 14.5, and the temperature is 50 to 75 DEG C.

[0053] The PH and the reaction temperature of the coprecipitation reaction process are controlled in the above range in the technical scheme of the embodiment, which is beneficial to the control of the morphology of the positive active material precursor.

[0054] In an embodiment, in the step of adding the precipitant and the complexing agent into the solution of the nickel source, the manganese source and the cobalt source to react, the PH is 12 to 14, and the temperature is 50 to 65 DEG C.

[0055] The PH and the reaction temperature of the coprecipitation reaction process are controlled in the above range in the technical scheme of the embodiment, which is beneficial to the control of the morphology of the positive active material precursor.

[0056] In an embodiment, in the step of sintering the positive active material precursor and the lithium source, the sintering temperature is 700 to 800 DEG C, and the sintering time is 7 to 14 h.

[0057] The sintering temperature and the sintering time are controlled in the above range in the technical scheme of the embodiment, which can make the lithium better diffuse into the crystal, the crystal can grow more uniformly, and thus the positive active material with better electrochemical performance is prepared.

[0058] In an embodiment, in the step of sintering the positive active material precursor and the lithium source, the sintering temperature is 710 to 780 DEG C, and the sintering time is 8 to 13 h.

[0059] In the technical scheme of the embodiment of the present application, the sintering temperature and the sintering time are controlled in the above range, so that lithium can be diffused into the crystal better, the crystal can grow more uniformly, and thus the positive electrode active material with better electrochemical performance can be prepared.

[0060] In an embodiment, the step of sintering the positive electrode active material precursor and the lithium source comprises sintering the positive electrode active material precursor, the lithium source and a source of element M, wherein M comprises one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr and Ti.

[0061] In the technical scheme of the embodiment of the present application, one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr and Ti is doped into the positive electrode active material, so that the crystal structure of the material can be improved, the distortion of the layered structure can be reduced, and thus the structural stability and the cycle life of the positive electrode active material can be improved.

[0062] In an embodiment, after the step of sintering the positive electrode active material precursor and the lithium source, a first coating element source is added for sintering, and the first coating element source comprises one or more of Co, Al, F and Ti.

[0063] In the embodiment of the present application, the residual alkali generated during the preparation of the positive electrode active material can be consumed in the process of coating the first coating layer. The residual alkali can generate a large amount of gas at high pressure, and can also intensify the side reaction of the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium ion secondary battery. In addition, the function of coating the secondary particles of the positive electrode active material with a coating layer is that the coating layer can reduce the side reaction of the positive electrode active material and the electrolyte, and thus the electrochemical performance of the lithium ion secondary battery can be improved.

[0064] In an embodiment, after the step of sintering the positive electrode active material precursor and the lithium source, a second coating element source is added for sintering, and the second coating element comprises one or more of B, Al and Y.

[0065] In the embodiment of the present application, the second coating layer containing one or more of B, Al and Y is coated on the surface of the positive electrode active material, so as to improve the structural stability of the secondary particles, and also to inhibit the side reaction on the surface of the secondary particles, and thus the cycle stability and the safety of the positive electrode active material can be significantly improved.

[0066] The fourth aspect of the present application provides a power utilization device comprising the lithium ion secondary battery of the first aspect or / and the positive electrode active material of the second aspect or / and the preparation method of the lithium ion secondary battery of the third aspect.

[0067] The lithium ion secondary battery of the embodiment of the present application has at least the same advantages as the lithium ion secondary battery of the first aspect, or / and at least the same advantages as the positive electrode active material of the second aspect, or / and at least the same advantages as the lithium ion secondary battery produced by the production method of the lithium ion secondary battery of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 is a schematic view of a vehicle according to an embodiment of the present application;

[0069] Figure 2 is a schematic view of a secondary battery according to an embodiment of the present application;

[0070] Figure 3 is a schematic view of a battery cell according to an embodiment of the present application;

[0071] Figure 4 is a scanning electron microscope image of a positive electrode active material according to an embodiment of the present application. DETAILED DESCRIPTION

[0072] Hereinafter, embodiments of the battery cell, the battery, and the electric device according to the present application will be specifically disclosed with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0073] The ranges disclosed herein are intended to be "open" ranges, i.e., the end values are not included in the range. For example, if a range is listed as 60-120 and 80-110, it is intended that 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0075] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0076] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, a method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0077] Unless otherwise specified, "including" and "comprising" mentioned in the present application means open-ended, and can also be closed-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0078] If not specifically stated, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0079] High-nickel ternary positive electrode active materials are widely used in lithium ion secondary batteries due to their high energy density and high rate capability. To improve the volumetric energy density of lithium ion secondary batteries, high-nickel ternary positive electrode active materials are usually prepared into spherical shapes so that the compaction density of the positive electrode sheet can be improved when cold-pressed. However, after cold-pressing, although the compaction density of the positive electrode sheet is improved, the degree of ductility of the positive electrode sheet is high, which significantly reduces the volumetric energy density of the lithium ion secondary battery. In addition, during the cyclic charging and discharging of the lithium ion secondary battery, the high-nickel ternary positive electrode active material particles will expand and contract, which will cause the particles to break, increase the side reactions, and ultimately result in a low capacity and poor cycle performance of the lithium ion secondary battery.

[0080] Based on the above problems, the first aspect of the present application provides a lithium ion secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a first part and a second part, in the positive electrode active material, the content of nickel element in transition elements is greater than or equal to 0.85, in the scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1; based on the total area of the secondary particles of the positive electrode active material, the area proportion of the secondary particles of the first part is 60% to 90%, and the area proportion of the secondary particles of the second part is 10% to 40%.

[0081] In the positive electrode active material, the content of nickel element in transition elements can be 0.85, 0.88, 0.9, 0.95, 0.99, or a range composed of any two of the above values, for example, 0.85 to 0.9, 0.9 to 0.95, 0.95 to 0.99, etc.

[0082] The ratio of the longest diameter to the shortest diameter of the secondary particles of the first part can be 1.1, 1.2, 1.5, 2, or a range composed of any two of the above values, for example, 1.1 to 1.2, 1.2 to 1.5, 1.5 to 2, etc.

[0083] The ratio of the longest diameter to the shortest diameter of the secondary particles in the second part can be 1, 1.02, 1.05, 1.09, or the like, or a range formed by any two of the above values, for example, 1-1.05, 1.05-1.09, or the like.

[0084] The area ratio of the secondary particles in the first part can be 60%, 70%, 75%, 80%, 90%, or the like, or a range formed by any two of the above values, for example, 60%-70%, 70%-80%, 80%-90%, or the like.

[0085] The area ratio of the secondary particles in the second part can be 10%, 20%, 25%, 30%, 40%, or the like, or a range formed by any two of the above values, for example, 10%-25%, 25%-40%, or the like.

[0086] The secondary particles are formed by agglomeration of primary particles, and the primary particles are crystals grown from a crystal nucleus.

[0087] The active particles in the positive electrode active material include first part secondary particles with a ratio of the longest diameter to the shortest diameter greater than or equal to 1.1, and second part secondary particles with a ratio of the longest diameter to the shortest diameter greater than or equal to 1 and less than 1.1, the first part secondary particles are more close to non-spherical than the second part secondary particles, the second part secondary particles are more close to spherical than the first part secondary particles, the first part secondary particles account for 60%-90% of the total area of the secondary particles in the positive electrode active material, and the second part secondary particles account for 10%-40% of the total area of the secondary particles in the positive electrode active material, the first part secondary particles account for a larger proportion than the second part secondary particles in the positive electrode active material, the first part secondary particles and the second part secondary particles cooperate to form a "rivet" effect, so that the combination between the first part secondary particles and the second part secondary particles is more firm. When the electrode sheet is cold-pressed after coating, the non-spherical secondary particles and the spherical secondary particles in the electrode sheet cooperate to better relieve stress, reduce electrode sheet deformation, and reduce the degree of electrode sheet extension, thereby improving the volumetric energy density of the battery cell. Meanwhile, when the battery cell is cycled, the non-spherical secondary particles can effectively relieve stress changes caused by mutual extrusion of the particles during expansion, reduce electrode sheet expansion, and relieve particle crushing, thereby improving the stability of the lithium ion secondary battery. The total area of the secondary particles in the positive electrode active material refers to the sum of the areas of the secondary particles in the positive electrode active material in the field of view of a scanning electron microscope with a magnification of 2K.

[0088] In an embodiment, the area ratio of the first part secondary particles is 65%-85%.

[0089] By controlling the area ratio of the secondary particles of the first part to be within the above range, when the electrode coating is completed and cold pressing is performed, the non-spherical secondary particles in the electrode can better relieve stress in cooperation with the spherical secondary particles, and the gap between the particles can be filled, reducing the deformation of the electrode and the degree of extension of the electrode, thereby improving the volumetric energy density of the battery. At the same time, when the battery is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the extrusion of the particles on each other when the particles swell, reducing the swelling of the electrode and alleviating the crushing of the particles, thereby improving the stability of the lithium ion secondary battery.

[0090] In an embodiment, the area ratio of the secondary particles of the second part is 15% to 35%.

[0091] By controlling the area ratio of the secondary particles of the second part to be within the above range, the secondary particles of the first part can better cooperate to improve the volumetric energy density of the battery and improve the stability of the lithium ion secondary battery.

[0092] In an embodiment, the compaction density of the positive electrode sheet under a pressure of 5T is 3.2g / cm 3 ~3.8g / cm 3 .

[0093] In an embodiment, the compaction density of the positive electrode sheet under a pressure of 5T is 3.2g / cm 3 , 3.4g / cm 3 , 3.5g / cm 3 , 3.7g / cm 3 , 3.8g / cm 3 , etc., or a range composed of any two of the above values, for example, 3.2g / cm 3 ~3.4g / cm 3 , 3.4g / cm 3 ~3.7g / cm 3 , 3.7g / cm 3 ~3.8g / cm 3 , etc.

[0094] When the compaction density of the positive electrode sheet under a pressure of 5T is within the above range, the gap between the secondary particles of the first part and the secondary particles of the second part is smaller, so that the proportion of the two types of particles per unit volume in the positive electrode sheet is higher, which can improve the volumetric energy density of the battery.

[0095] In an embodiment, the volume average particle size DV50 of the secondary particles of the positive active material is 8.5μm to 12μm.

[0096] By controlling the volume average particle size DV50 of the secondary particles of the positive active material to be 8.5μm to 12μm, the electrochemical performance of the lithium ion secondary battery can be better.

[0097] Specifically, by controlling the volume average particle size DV50 of the secondary particles of the positive electrode active material to be 8.5 μm to 12 μm, the specific surface area of the secondary particles of the positive electrode active material is in a preferable range, so that the sites for lithium intercalation and deintercalation of the positive electrode active material are more, and the energy density of the lithium ion secondary battery is ensured to be higher.

[0098] The volume average particle size DV50 of the positive electrode active material can be 8.5 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 12 μm, or a range formed by any two of the above values, for example, 8.5 μm to 10.5 μm, 10.5 μm to 12 μm, etc.

[0099] In an embodiment, the longest diameter of the secondary particles of the first part is in a range of 2.5 μm to 18.5 μm, and the shortest diameter is in a range of 1 μm to 15.5 μm.

[0100] The longest diameter of the secondary particles of the first part can be 2.5 μm, 5 μm, 10 μm, 14.5 μm, 18.5 μm, or a range formed by any two of the above values, for example, 2.5 μm to 10 μm, 10 μm to 14.5 μm, 14.5 μm to 18.5 μm, etc.

[0101] The shortest diameter of the secondary particles of the first part can be 1 μm, 2.5 μm, 5 μm, 10 μm, 15.5 μm, or a range formed by any two of the above values, for example, 1 μm to 5 μm, 5 μm to 10 μm, 10 μm to 15.5 μm, etc.

[0102] By controlling the longest diameter and the shortest diameter of the secondary particles of the first part to be in the above ranges, the electrochemical performance of the lithium ion secondary battery can be better.

[0103] In an embodiment, the longest diameter of the secondary particles of the second part is in a range of 5 μm to 15.5 μm, and the shortest diameter is in a range of 4.5 μm to 15 μm.

[0104] The longest diameter of the secondary particles of the second part can be 5 μm, 8 μm, 12 μm, 15.5 μm, or a range formed by any two of the above values, for example, 5 μm to 8 μm, 8 μm to 15.5 μm, etc. The shortest diameter of the secondary particles of the second part can be 4.5 μm, 7 μm, 10 μm, 12 μm, 15 μm, or a range formed by any two of the above values, for example, 4.5 μm to 7 μm, 7 μm to 12 μm, 12 μm to 15 μm, etc.

[0105] By controlling the longest diameter and the shortest diameter of the secondary particles of the first part to be in the above ranges, the electrochemical performance of the lithium ion secondary battery can be better.

[0106] In an embodiment, the secondary particles of the first portion and the second portion of the positive active material each independently comprise a host material having a structure of Li a Ni b Co c Mn d M (1-b-c-d) O n , wherein M comprises one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, 0.5≤a≤1.2, 0.85≤b≤0.99, 0<c≤0.1, 0<d≤0.05, b+c+d≤1, 1.9≤n≤2.2.

[0107] The secondary particles of the positive active material comprise an active material having a structure of Li a Ni b Co c Mn d M (1-b-c-d) O n , wherein the content of nickel element is at least 0.85 of the total content of transition metal elements, and the positive active material further comprises transition metal Co element and Mn element, so that the lithium ion secondary battery has better electrochemical performance. In addition, the positive active material can be doped with any one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti, etc. to improve the stability of the lithium ion secondary battery.

[0108] Li a is used to provide Li + for intercalation and deintercalation on the positive electrode and the negative electrode during the cyclic charging and discharging process of the lithium ion secondary battery. The value of a can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc., or a range formed by any two of the above values, for example, 0.5≤a≤0.7, 0.7≤a≤0.9, 0.9≤a≤1.2, etc.

[0109] Ni b Co c Mn dThe ternary material is a ternary material. The presence of nickel ions increases the unit cell parameter, which helps to increase the specific capacity of the positive active material. Cobalt ions can inhibit the cation mixing problem in the material, improve the electronic conductivity of the material, and improve the cycle performance of the lithium ion secondary battery. However, too high a cobalt content will also lead to a decrease in actual capacity. Manganese ions can stabilize the material structure, increase the safety of the lithium ion secondary battery, and reduce the cost. However, too high a content of cobalt and manganese will reduce the specific capacity of the lithium ion secondary battery. The value of b can be 0.85, 0.87, 0.9, 0.93, 0.96, 0.99, etc., or a range composed of any two of the above values, for example, 0.85-0.9, 0.9-0.96, 0.96-0.99, etc. The value of c can be 0.02, 0.05, 0.07, 0.1, etc., or a range composed of any two of the above values, for example, 0.02-0.05, 0.05-0.1, etc. The value of d can be 0.02, 0.03, 0.04, 0.05, etc., or a range composed of any two of the above values, for example, 0.02-0.03, 0.03-0.04, 0.04-0.05, etc.

[0110] M (1-b-c-d) The doping element includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti. Doping the above metal elements in the positive active material can improve the ionic conductivity and structural stability, thereby improving the electrochemical performance of the positive active material.

[0111] The value of n can be 1.9, 2, 2.1, 2.2, etc., or a range composed of any two of the above values, for example, 1.9-2, 2-2.1, 2.1-2.2, etc.

[0112] In an embodiment, the host material includes lithium nickel cobalt manganese oxide, and the molar content of nickel elements in all transition metal elements is greater than or equal to 0.85.

[0113] The host material of the positive active material includes lithium nickel cobalt manganese oxide, and the molar content of nickel elements in all transition metal elements is greater than or equal to 0.85, so that the lithium ion secondary battery has better electrochemical performance.

[0114] Specifically, the nickel element in the lithium nickel cobalt manganese oxide has a high redox potential, by controlling the molar content of the nickel element in the lithium nickel cobalt manganese oxide in all transition metal elements to be greater than or equal to 0.85, the content of the nickel element is relatively high, so that the lithium ion secondary battery has a high energy density. The molar content of the nickel element in all transition metal elements can be 0.85, 0.88, 0.93, 0.96, 0.99, or a range formed by any two of the above values, for example, 0.85-0.93, 0.93-0.99.

[0115] In an embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently further comprise a first coating layer, the first coating layer comprises one or more of Co, Al, F, Ti, and the mass percentage of the first coating layer is 1.68%-2.03% based on the mass of the positive electrode active material.

[0116] The mass percentage of the first coating layer can be 1.68%, 1.75%, 1.85%, 1.95%, 2.03%, or a range formed by any two of the above values, for example, 1.68%-1.85%, 1.85%-1.95%, 1.95%-2.03%, etc.

[0117] The residual alkali generated during the preparation of the positive electrode active material is consumed in the process of coating the first coating layer. The residual alkali generates a large amount of gas at high pressure, and also intensifies the side reaction of the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium ion secondary battery. In addition, the function of coating a layer of coating layer on the secondary particles of the first part and the second part of the positive electrode active material is that the coating layer can reduce the side reaction on the surface of the positive electrode active material, thereby improving the electrochemical performance of the lithium ion secondary battery.

[0118] In an embodiment, the secondary particles of the first part and the second part of the positive electrode active material each independently further comprise a second coating layer, the second coating layer comprises one or more of B, Al, Y, and the mass percentage of the second coating layer is 0.09%-0.21% based on the mass of the positive electrode active material.

[0119] The mass percentage of the second coating layer can be 0.09%, 0.12%, 0.17%, 0.21%, or a range formed by any two of the above values, for example, 0.09%-0.17%, 0.17%-0.21%, etc.

[0120] Coating the second coating layer containing one or more of B, Al, and Y on the surface of the positive electrode active material can improve the structural stability of the secondary particles, and also inhibit the side reaction on the surface of the secondary particles, thereby improving the cycle stability and safety of the positive electrode active material.

[0121] In an embodiment, the content of the nickel element in the transition elements in the first part and / or the second part is greater than or equal to 0.85.

[0122] In some embodiments, the content of the nickel element in the transition elements in the first part and / or the second part can be 0.85, 0.88, 0.9, 0.95, 0.99, or a range between any two of the above values, for example, 0.85-0.9, 0.9-0.95, 0.95-0.99, etc.

[0123] The content of the nickel element in the transition elements in the first part and / or the second part is greater than or equal to 0.85, which can make the lithium ion secondary battery have better electrochemical performance.

[0124] In an embodiment, the average particle size of the primary particles in the first part is 50 nm-2 μm.

[0125] Controlling the average particle size of the primary particles in the first part to be in the range of 50 nm-2 μm makes the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and can make the lithium ion secondary battery have better electrochemical performance.

[0126] The average particle size of the primary particles in the first part can be 50 nm, 300 nm, 500 nm, 1 μm, 1.5 μm, 1.7 μm, 2 μm, or a range between any two of the above values, for example, 50 nm-1000 nm, 1000 nm-1500 nm, 1500 nm-2000 nm, etc.

[0127] In an embodiment, the average particle size of the primary particles in the first part is 100 nm-500 nm.

[0128] The average particle size of the primary particles in the first part is in the range of 100 nm-500 nm, which makes the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and can make the lithium ion secondary battery have better electrochemical performance.

[0129] The average particle size of the primary particles in the first part can be 100 nm, 200 nm, 300 nm, 350 nm, 500 nm, or a range between any two of the above values, for example, 100 nm-300 nm, 300 nm-500 nm, etc.

[0130] In an embodiment, the average particle size of the primary particles in the second part is 50 nm-2 μm.

[0131] The average particle size of the primary particles of the second part is controlled in the range of 50 nm to 2 μm, so that the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and the electrochemical performance of the lithium ion secondary battery is better.

[0132] The average particle size of the primary particles of the second part can be 50 nm, 300 nm, 500 nm, 1 μm, 1.5 μm, 1.7 μm, 2 μm, or a range formed by any two of the above values, such as 50 nm to 1000 nm, 1000 nm to 1500 nm, 1500 nm to 2000 nm, etc.

[0133] In an embodiment, the average particle size of the primary particles of the second part is 100 nm to 500 nm.

[0134] The average particle size of the primary particles of the second part is in the range of 100 nm to 500 nm, so that the primary particles have a shorter electron transport path, which helps to improve the electron transport efficiency, thereby improving the charge and discharge performance of the battery, and the electrochemical performance of the lithium ion secondary battery is better.

[0135] The average particle size of the primary particles of the second part can be 100 nm, 200 nm, 300 nm, 350 nm, 500 nm, etc., or a range formed by any two of the above values, such as 100 nm to 300 nm, 300 nm to 500 nm, etc.

[0136] In a second aspect, the present application provides a positive electrode active material, which comprises a first part and a second part, wherein the content of nickel element in the transition elements is greater than or equal to 0.85, the ratio of the longest diameter to the shortest diameter of the secondary particles of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the secondary particles of the second part is greater than or equal to 1 and less than 1.1 in a scanning electron microscope picture with a magnification of 2K; based on the total area of the secondary particles of the positive electrode active material, the area ratio of the secondary particles of the first part is 60% to 90%, and the area ratio of the secondary particles of the second part is 10% to 40%.

[0137] In the technical scheme of the embodiment of the present application, the active particles in the positive active material include a first part of secondary particles with a ratio of the longest diameter to the shortest diameter greater than or equal to 1.1 and a second part of secondary particles with a ratio of the longest diameter to the shortest diameter greater than or equal to 1 and less than 1.1, the first part of secondary particles is closer to a non-spherical shape than the second part of secondary particles, the second part of secondary particles is closer to a spherical shape than the first part of secondary particles, the first part of secondary particles accounts for 60% to 90% of the total area of the secondary particles of the positive active material, and the second part of secondary particles accounts for 10% to 40% of the total area of the secondary particles of the positive active material. When the electrode sheet is cold-pressed after coating, the non-spherical secondary particles and the spherical secondary particles in the electrode sheet can better relieve stress, reduce electrode sheet deformation, and reduce the degree of electrode sheet extension, thereby improving the volumetric energy density of the battery cell. At the same time, when the battery cell is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the extrusion of the particles on each other when the particles expand, reduce the expansion of the electrode sheet, and relieve particle crushing, thereby improving the stability of the lithium ion secondary battery.

[0138] The present application provides a preparation method of a lithium ion secondary battery in a third aspect, comprising: providing a positive electrode sheet, a separator and a negative electrode sheet to make a lithium ion secondary battery; the positive electrode sheet comprises a positive active material, wherein the preparation method of the positive active material comprises: adding a precipitating agent and a complexing agent into a solution comprising a nickel source, a manganese source and a cobalt source to react, to obtain a positive active material precursor; and sintering the positive active material precursor with a lithium source to obtain the positive active material; in the positive active material, the content of nickel element in transition elements is greater than or equal to 0.85; or the preparation method of the positive active material comprises: mixing a first part of positive active material and a second part of positive active material to obtain the positive active material, wherein in a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of the first part of secondary particles is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of the second part of secondary particles is greater than or equal to 1 and less than 1.1, the area ratio of the first part of secondary particles is 60% to 90% based on the total area of the secondary particles of the positive active material, and the area ratio of the second part of secondary particles is 10% to 40%, and in the positive active material, the content of nickel element in all transition elements is greater than or equal to 0.85.

[0139] In the technical scheme of the embodiment of the present application, the precipitant and the complexing agent are added to the solution containing the nickel source, the manganese source and the cobalt source, which is conducive to controlling the morphology of the positive electrode active material precursor particles, and further conducive to controlling the morphology of the secondary particles of the positive electrode active material, or the positive electrode active material is obtained by mixing the first part of the positive electrode active material with the above morphology and the second part of the positive electrode active material, by providing the above positive electrode active material, when the cold pressing of the electrode piece coating is completed, the non-spherical secondary particles in the electrode piece can better relieve the stress by cooperating with the spherical secondary particles, reduce the deformation of the electrode piece, and reduce the degree of extension of the electrode piece, thereby improving the volume energy density of the battery cell. At the same time, when the battery cell is cycled, the non-spherical secondary particles can effectively relieve the stress change caused by the mutual extrusion of the particles when they expand, reduce the expansion of the electrode piece and relieve the particle breakage, thereby improving the stability of the lithium ion secondary battery.

[0140] The nickel source is selected from one or more of nickel carbonate, nickel hydroxide, nickel acetate, nickel sulfate, nickel chloride, nickel nitrate and nickel oxalate. The cobalt source is selected from one or more of cobalt carbonate, cobalt hydroxide, cobalt acetate, cobalt sulfate, cobalt chloride, cobalt nitrate and cobalt oxalate. The manganese source is selected from one or more of manganese dioxide, electrolytic manganese dioxide, trimanganese tetraoxide, etc.

[0141] In an embodiment, the precipitant includes at least one of sodium carbonate, sodium hydroxide and potassium hydroxide.

[0142] The precipitant can react with the nickel source, the manganese source and the cobalt source to generate a precipitate of the corresponding hydroxide or / and basic salt, and then the precipitate can be sintered to obtain the positive electrode active material precursor.

[0143] In an embodiment, the concentration of the precipitant is 2 mol / L to 8 mol / L.

[0144] The precipitant has a greater influence on the nucleation rate and growth rate of the crystal of the positive electrode active material precursor. By controlling the concentration of the precipitant within the above range, the positive electrode active material precursor has a suitable particle size range and morphology. The concentration of the precipitant can be 2 mol / L, 4 mol / L, 6 mol / L, 8 mol / L, etc., or a range composed of any two of the above values, such as 2 mol / L to 6 mol / L, 6 mol / L to 8 mol / L, etc.

[0145] In an embodiment, the concentration of the precipitant is 4 mol / L to 6 mol / L.

[0146] The precipitant has a great influence on the nucleation rate and growth rate of the crystal of the positive active material precursor. By controlling the concentration of the precipitant in the above range, the positive active material precursor has a suitable particle size range and morphology. The concentration of the precipitant can be 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, etc., or a range composed of any two of the above values, such as 4 mol / L to 5 mol / L, 5 mol / L to 6 mol / L, etc.

[0147] In an embodiment, the complexing agent includes at least one of ammonia, urea, citric acid, and ethylenediaminetetraacetic acid (EDTA).

[0148] At least one of ammonia, urea, citric acid, and ethylenediaminetetraacetic acid (EDTA) as a complexing agent can effectively complex metal ions such as Ni, Co, and Mn in the liquid, which helps to control the composition of the positive active material precursor.

[0149] In an embodiment, the concentration of the complexing agent is 0.25 mol / L to 0.6 mol / L.

[0150] Ammonia as a complexing agent can effectively complex metal ions such as Ni, Co, and Mn in the mixed liquid to complex free metal ions in the mixed liquid together, which helps to control the proportion of metal ions in the positive active material precursor.

[0151] Controlling the concentration of the complexing agent in the range of 0.25 mol / L to 0.6 mol / L not only slows down the disturbance of the addition of raw materials to the precipitation equilibrium and controls the supersaturation of the precipitate in the solution, but also reduces the nucleation and growth rate, allowing the crystal to grow slowly, which facilitates the regulation of the particle size uniformity of the positive active material precursor. The concentration of the complexing agent can be 0.25 mol / L, 0.35 mol / L, 0.45 mol / L, 0.6 mol / L, etc., or a range composed of any two of the above values, such as 0.25 mol / L to 0.45 mol / L, 0.45 mol / L to 0.6 mol / L, etc.

[0152] In an embodiment, the concentration of the complexing agent is 0.3 mol / L to 0.6 mol / L.

[0153] Controlling the concentration of the complexing agent in the range of 0.3 mol / L to 0.6 mol / L not only slows down the disturbance of the addition of raw materials to the precipitation equilibrium and controls the supersaturation of the precipitate in the solution, but also reduces the nucleation and growth rate, allowing the crystal to grow slowly, which facilitates the regulation of the particle size uniformity of the positive active material precursor.

[0154] In an embodiment, in the step of adding a precipitant and a complexing agent into the solution of the nickel source, the manganese source and the cobalt source to react, the pH is 11.5-14.5 and the temperature is 50-75°C.

[0155] Controlling the pH and the temperature in the process of the co-precipitation reaction in the above ranges is conducive to controlling the morphology of the positive electrode active material precursor.

[0156] Specifically, the pH can control the growth rate and the nucleation rate of the positive electrode active material particles. Controlling the pH in the process of the co-precipitation reaction in the range of pH=10-15 can slow the nucleation rate of the positive electrode active material precursor particles and accelerate the growth rate of the particles, which is conducive to subsequent control of the distribution of the secondary particle size of the positive electrode active material precursor and is also conducive to controlling the morphology of the positive electrode active material precursor. Controlling the temperature in the range of 50-70°C can accelerate the reaction speed without affecting the crystal growth and nucleation. The pH can be 11.5, 12, 13, 14, 14.5, or a range defined by any two of the above values, such as 11.5-12, 12-13, 13-14.5, etc. The temperature can be 50°C, 60°C, 65°C, 75°C, or a range defined by any two of the above values, such as 50-65°C, 65-75°C, etc.

[0157] In an embodiment, in the step of adding a precipitant and a complexing agent into the solution of the nickel source, the manganese source and the cobalt source to react, the pH is 12-14 and the temperature is 50-65°C.

[0158] Controlling the pH and the temperature in the process of the co-precipitation reaction in the above ranges is conducive to controlling the morphology of the positive electrode active material precursor.

[0159] In an embodiment, in the step of sintering the positive electrode active material precursor with a lithium source, the sintering temperature is 700-800°C and the sintering time is 7-14h.

[0160] The positive electrode active material precursor is sintered with a lithium source to obtain a positive electrode active material capable of embedding and embedding out active lithium in a transition metal oxide lattice. The sintering temperature is controlled in the range of 700-800℃, and the sintering time is controlled in the range of 7-14h, so that lithium can better diffuse into the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance. The sintering temperature can be 700℃, 720℃, 730℃, 740℃, 750℃, 760℃, 800℃, or a range formed by any of the above values, such as 700-730℃, 730-750℃, 750-800℃, etc. The sintering time can be 7h, 9h, 11h, 12h, 13h, 14h, or a range formed by any of the above values, such as 7-11h, 11-13h, 13-14h, etc.

[0161] In an embodiment, in the step of sintering the positive electrode active material precursor with a lithium source, the sintering temperature is 710-780℃, and the sintering time is 8-13h. Controlling the sintering temperature and the sintering time in the above ranges can make lithium better diffuse into the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance.

[0162] The positive electrode active material precursor is sintered with a lithium source to obtain a positive electrode active material capable of embedding and embedding out active lithium in a transition metal oxide lattice. The sintering temperature is controlled in the range of 710-780℃, and the sintering time is controlled in the range of 8-13h, so that lithium can better diffuse into the crystal, and the crystal can grow more uniformly, thereby preparing a positive electrode active material with better electrochemical performance. The sintering temperature can be 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 780℃, or a range formed by any of the above values, such as 700-730℃, 730-750℃, 750-780℃, etc. The sintering time can be 8h, 9h, 10h, 12h, 13h, or a range formed by any of the above values, such as 8-10h, 10-12h, 12-13h, etc.

[0163] The lithium source is selected from one or more of LiOH·H2O, Li2CO3, Li2SO4, LiNO3, LiC2O4, and CH3COOLi.

[0164] In an embodiment, the step of sintering the positive electrode active material precursor with a lithium source is to sinter the positive electrode active material precursor, a lithium source, and an element M source, wherein M includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, and Ti elements.

[0165] Doping one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti and other metal elements into the positive electrode active material can improve the crystal structure of the material, reduce the distortion of the layered structure, and thus improve the structural stability and cycle life of the positive electrode active material.

[0166] In an embodiment, after the step of sintering the positive electrode active material precursor with the lithium source, further comprising: adding a first coating element source for sintering, the first coating element source comprising one or more of Co, Al, F, Ti.

[0167] The residual alkali produced during the preparation of the positive electrode active material is consumed during the coating of the first coating layer. The residual alkali produces a large amount of gas at high pressure, and also intensifies the side reactions of the positive electrode active material and the electrolyte. Therefore, the reduction of the residual alkali can improve the safety of the lithium ion secondary battery. In addition, the effect of coating the secondary particles of the positive electrode active material with a coating layer is that the coating layer can reduce the side reactions on the surface of the positive electrode active material, and thus can improve the electrochemical performance of the lithium ion secondary battery.

[0168] In the embodiments of the present application, the temperature during sintering with the first coating element is 400-650°C, and the sintering time is 5-11h.

[0169] By controlling the temperature and time during the coating of the first coating source within the above ranges, the thickness, uniformity and structure of the coating layer can be optimized, and thus the overall performance and stability of the lithium ion battery can be improved. The temperature during sintering with the first coating element can be 400°C, 440°C, 480°C, 520°C, 560°C, 600°C, 650°C, or a range formed by any of the above values, for example, 400-480°C, 480-560°C, 560-650°C, etc. The sintering time can be 5h, 7h, 9h, 10h, 11h, etc., or a range formed by any of the above values, for example, 5-7h, 7-10h, 10-11h, etc.

[0170] In an embodiment, after the step of sintering the positive electrode active material precursor with the lithium source, further comprising: adding a second coating element source for sintering, the second coating element comprising one or more of B, Al, Y.

[0171] Coating the surface of the positive electrode active material with a second coating layer comprising one or more of B, Al, Y can improve the structural stability of the secondary particles, and also inhibit the side reactions on the surface of the secondary particles, and thus can significantly improve the cycle stability and safety of the positive electrode active material.

[0172] In the embodiments of the present application, the temperature during sintering with the second coating element is 250-400°C, and the sintering time is 5-12h.

[0173] By controlling the temperature and time during the coating process of the second coating source within the aforementioned range, the thickness, uniformity, and structure of the coating layer can be optimized, thereby improving the overall performance and stability of the lithium-ion battery. Specifically, the sintering temperature during the addition of the second coating element can be 250℃, 280℃, 310℃, 350℃, 370℃, 400℃, or any range of the aforementioned values, such as 250℃~280℃, 280℃~350℃, 350℃~400℃, etc. The sintering time can be 5h, 7h, 9h, 10h, 12h, or any range of the aforementioned values, such as 5h~7h, 7h~10h, 10h~12h, etc.

[0174] This application provides a fourth aspect of an electrical device, including a lithium-ion secondary battery of the first aspect and / or a positive electrode active material of the second aspect and / or a method for preparing a lithium-ion secondary battery of the third aspect. The lithium-ion secondary battery of this application possesses at least the same advantages as the lithium-ion secondary battery of the first aspect, and / or at least the same advantages as the positive electrode active material of the second aspect, and / or at least the same advantages as the positive electrode sheet prepared by the method for preparing a lithium-ion secondary battery of the third aspect.

[0175] The batteries disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, and spacecraft. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; spacecraft can include airplanes, rockets, space shuttles, and spacecraft.

[0176] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0177] Please refer to Figure 1 , Figure 1A structural schematic diagram of a vehicle 1000 is provided for some embodiments of the present application. The vehicle 1000 can be a fuel automobile, a gas automobile, or a new energy automobile, which can be a pure electric vehicle, a hybrid electric vehicle, or a range extended vehicle, etc. The vehicle 1000 is internally provided with a secondary battery 100, which can be arranged at the bottom, head, or tail of the vehicle 1000. The secondary battery 100 can be used for power supply of the vehicle 1000, for example, the secondary battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further include a controller 200 and a motor 300, the controller 200 being used to control the secondary battery 100 to supply power to the motor 300, for example, for the working power demand of the vehicle 1000 during starting, navigation, and driving.

[0178] In some embodiments of the present application, the secondary battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0179] Please refer to Figure 2 , Figure 2 A disassembled structural schematic diagram of the battery 100 is provided for some embodiments of the present application. The secondary battery 100 includes a box body 10 and a battery cell 20, and the battery cell 20 is accommodated in the box body 10. Among them, the box body 10 is used to provide an accommodation space for the battery cell 20, and the box body 10 can adopt various structures. In some embodiments, the box body 10 can include a first part 11 and a second part 12, the first part 11 and the second part 12 are mutually covered, and the first part 11 and the second part 12 jointly define an accommodation space for accommodating the battery cell 20. The second part 12 can be a hollow structure with one end open, and the first part 11 can be a plate-shaped structure, the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define the accommodation space; the first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the box body 10 formed by the first part 11 and the second part 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0180] In the secondary battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the casing 10. Alternatively, the secondary battery 100 can also consist of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple secondary battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the casing 10. The secondary battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0181] Each battery cell 20 can be a battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0182] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of a battery cell 20 provided in some embodiments of this application. The battery cell 20 refers to the smallest unit that makes up a battery. Figure 3 The battery cell 20 includes an end cap 21, a housing 22, a cell assembly 23, and other functional components.

[0183] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, allowing battery cell 20 to have higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with cell assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0184] The shell 22 is a component for cooperating with the end cover 21 to form an internal environment of the battery cell 20, and the formed internal environment can be used to accommodate the electrode assembly 23, electrolyte, and other components. The shell 22 and the end cover 21 can be independent components, and an opening can be provided on the shell 22, and the end cover 21 is used to cover the opening to form the internal environment of the battery cell 20. Without limitation, the end cover 21 and the shell 22 can also be integrated, specifically, the end cover 21 and the shell 22 can form a common connecting surface before other components enter the shell, and when it is necessary to seal the internal environment of the shell 22, the end cover 21 is used to cover the shell 22. The shell 22 can be of various shapes and sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special limitations thereto.

[0185] The electrode assembly 23 is a component in which electrochemical reactions occur in the battery cell 20. One or more electrode assemblies 23 can be contained in the shell 22. The electrode assembly 23 is mainly formed by winding or stacking a positive electrode sheet and a negative electrode sheet, and a separator is usually provided between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet and the negative electrode sheet have a portion with active material constituting a main body of the electrode assembly, and a portion without active material of the positive electrode sheet and the negative electrode sheet respectively constitutes a tab 23a. The positive electrode tab and the negative electrode tab can be located at one end of the main body together or at two ends of the main body respectively. In the charging and discharging process of the battery, the positive active material and the negative active material react with the electrolyte, and the tab 23a connects the electrode terminal to form a current loop.

[0186] Generally, the secondary battery 100 includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. In the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is provided between the positive electrode sheet and the negative electrode sheet, and mainly plays a role in preventing short circuit between the positive electrode and the negative electrode, while allowing ions to pass through.

[0187] [Positive electrode sheet]

[0188] In some embodiments, the positive electrode sheet includes a positive electrode current collector, and a positive active material layer is provided on at least one surface of the positive electrode current collector.

[0189] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof, and the positive active material layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0190] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0191] In some embodiments, the positive active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0192] In some embodiments, the positive active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-described components for preparing the positive electrode sheet, such as the phosphate composite material and spinel-structured lithium manganese oxide, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive current collector, and subjecting the same to processes such as drying, cold pressing, etc., to obtain the positive electrode sheet.

[0194] [Negative electrode sheet]

[0195] The negative electrode sheet includes a negative current collector and a negative film layer disposed on at least one surface of the negative current collector, the negative film layer including a negative active material.

[0196] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is disposed on either one or both of the two opposite surfaces of the negative current collector.

[0197] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0198] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0199] In some embodiments, the negative film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0200] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0201] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) etc.

[0202] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-described components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative current collector, and then performing processes such as drying, cold pressing, etc. to obtain the negative electrode sheet.

[0203] [Separator]

[0204] In some embodiments, a separator film is further included in the battery. The type of the separator film is not particularly limited in the present application, and any known porous structure separator film having good chemical stability and mechanical stability can be selected.

[0205] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0206] [Electrolyte]

[0207] The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited in the present application, and can be selected according to the needs. For example, the electrolyte can be in a liquid state, a gel state, or a full solid state.

[0208] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0209] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0210] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0211] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be made into an electric cell assembly through a winding process or a stacking process.

[0212] In some embodiments, the shell 22 can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.

[0213] The shape of the battery cell 20 is not particularly limited in the present application, and can be cylindrical, square, or any other shape.

[0214] The beneficial effects of the present application are further illustrated below in conjunction with examples.

[0215] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail in combination with the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and in no way limits the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0216] Embodiment 1

[0217] Preparation of the positive electrode active material

[0218] Step (1): A mixed solution of 3 mol / L of Ni, Co and Mn sulfate salts was prepared according to the molar ratio of Ni, Co and Mn of 93:6:1, and the mixed solution, sodium carbonate and ammonia water were added to a reaction kettle, the concentration of ammonia water was 0.45 mol / L, the concentration of sodium carbonate was 4 mol / L, the pH in the reaction kettle was controlled to maintain at 12.4, and the temperature was controlled at 53℃, and the co-precipitation reaction was carried out, and after the reaction was completed, the positive electrode active material precursor (Ni 0.93 Co 0.06 Mn 0.01 (OH)2) was obtained after washing and drying.

[0219] Step (2): The above positive electrode active material precursor was mixed with LiOH according to a molar ratio of 1:1.05, then 1200 ppm of SrO and 800 ppm of ZrO2 were added, and then the mixed powder was added to a sintering furnace, and the temperature was maintained at 735℃ for 13h, and then the temperature was lowered to room temperature at a rate of 5℃ / min, and the main material of the positive electrode active material was obtained.

[0220] Step (3): The main material of the positive electrode active material obtained in step (2) was crushed and mixed with 12000 ppm of CoOOH and 500 ppm of Al2O3, and the mixed powder was added to a sintering furnace for sintering, the first sintering temperature was 620℃, the first sintering time was 7.5h, and then the temperature was lowered to room temperature at a rate of 5℃ / min.

[0221] Step (4): 300g of the powder obtained in step (3) was added to 300mL of deionized water and stirred for 5min, then filtered to obtain a solid powder, and then dried in a 60℃ air oven.

[0222] Step (5): The powder obtained in step (4) was added into a sintering furnace and mixed with 1200 ppm of H2B03, and the mixed powder was subjected to secondary sintering at a temperature of 350°C for 6 h, and then cooled to room temperature at a rate of 1.5°C / min, to obtain the positive electrode active material of Example 1.

[0223] [Preparation of the positive electrode sheet]

[0224] The positive electrode active material prepared above, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-methyl pyrrolidone (NMP) at a mass ratio of 98:0.5:1.5, and after being fully stirred and mixed uniformly, a positive electrode slurry was obtained. Then the positive electrode slurry was uniformly coated on both sides of a 60-μm aluminum foil, and was subjected to drying and cold pressing, to obtain a positive electrode sheet with a thickness of 120 μm.

[0225] [Preparation of the negative electrode sheet]

[0226] The artificial graphite, the hard carbon, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) were added into a deionized water solvent at a mass ratio of 90:5:2:2:1, and after being fully stirred and mixed uniformly, the mixture was coated on both sides of a copper foil, and was subjected to drying, cold pressing, and other processes, to obtain a negative electrode sheet.

[0227] [Preparation of the electrolyte]

[0228] In an argon atmosphere glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and sodium carboxymethyl cellulose (CMC) were mixed uniformly at a volume ratio of 1:1:1 to obtain a solvent, and LiPF6 was added and dissolved in the above solvent, and was stirred uniformly to obtain a 1 mol / L LiPF6 electrolyte.

[0229] [Separator]

[0230] A polyethylene with a thickness of 13 μm was used as the separator.

[0231] [Preparation of the battery]

[0232] The separator, the negative electrode sheet, and the positive electrode sheet were stacked in the order of "separator-negative electrode sheet-separator-positive electrode sheet", and were processed and molded, and were packaged with an aluminum plastic bag, and were injected with the 1 mol / L electrolyte, and were packaged and subjected to formation, to obtain a soft-pack lithium ion secondary battery. The length of the battery core assembly was 50 mm, the width was 42 mm, and the thickness was 0.4 mm.

[0233] Example 2

[0234] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the application are different from those of embodiment 1 in that the molar ratio of the nickel source, the manganese source and the cobalt source is 88:6:6, the concentration of the precipitant is 6 mol / L, the reaction temperature is 50 ℃, PH=11, and the complexing agent concentration is 0.25 mol / L. The sintering temperature of the precursor with the lithium source, SrO and ZrO2 is 700 ℃, and the sintering time is 7 h, wherein the addition amount of SrO is 1000 ppm. The first sintering temperature is 400 ℃, the first sintering time is 5 h, the second sintering temperature is 250 ℃, and the second sintering time is 5 h. The others are similar to those of embodiment 1, and are not described herein.

[0235] Embodiment 3

[0236] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the application are different from those of embodiment 1 in that the molar ratio of the nickel source, the manganese source and the cobalt source is 92:6:2, the concentration of the precipitant is 8 mol / L, the reaction temperature is 65 ℃, PH=12, the complexing agent concentration is 0.3 mol / L, the sintering temperature of the precursor with the lithium source, SrO and ZrO2 is 720 ℃, the sintering time is 10 h, wherein the addition amount of SrO is 1000 ppm, and the addition amount of ZrO2 is 1000 ppm. The first sintering temperature is 500 ℃, the first sintering time is 11 h, the second sintering temperature is 400 ℃, and the second sintering time is 8 h, and the addition amount of AI2O3 in the second sintering process is 600 ppm. The others are similar to those of embodiment 1, and are not described herein.

[0237] Embodiment 4

[0238] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the application are different from those of embodiment 1 in that the concentration of the precipitant is 2 mol / L, the reaction temperature is 75 ℃, PH=14, the complexing agent concentration is 0.6 mol / L, the sintering temperature of the precursor with the lithium source, SrO and ZrO2 is 740 ℃, and the sintering time is 14 h, wherein the addition amount of SrO is 1000 ppm, and the addition amount of ZrO2 is 1000 ppm. The first sintering temperature is 650 ℃, the second sintering time is 12 h, and the addition amount of AI2O3 in the second sintering process is 800 ppm. The others are similar to those of embodiment 1, and are not described herein.

[0239] Embodiment 5

[0240] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the application are different from those of embodiment 1 in that PH=14.5, the sintering temperature of the precursor with the lithium source, SrO and ZrO2 is 800, and steps (3)-(5) are cancelled. The others are similar to those of embodiment 1, and are not described herein.

[0241] Example 6

[0242] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the precipitant is sodium hydroxide, and the precursor is only mixed with SrO for sintering. The others are similar to those of Example 1, and are not described here again.

[0243] Example 7

[0244] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the concentration of the nickel source is 2.5 mol / L, the concentration of the manganese source is 2.5 mol / L, the concentration of the cobalt source is 2.5 mol / L, the molar ratio of the nickel source, the manganese source and the cobalt source is 92.5:6.5:1, the precipitant is potassium hydroxide, and the precursor is only mixed with ZrO2 for sintering. The others are similar to those of Example 1, and are not described here again.

[0245] Example 8

[0246] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the concentration of the nickel source is 3.5 mol / L, the concentration of the manganese source is 3.5 mol / L, the concentration of the cobalt source is 3.5 mol / L, the molar ratio of the nickel source, the manganese source and the cobalt source is 92.5:6.5:1, the complexing agent is citric acid, the precursor is only mixed with WO3 for sintering, and the addition amount of WO3 is 800 ppm. The others are similar to those of Example 1, and are not described here again.

[0247] Example 9

[0248] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that the precipitant is urea. In the second sintering process, 1200 ppm of AIF3 is added for coating of the second coating layer. The others are similar to those of Example 1, and are not described here again.

[0249] Example 10

[0250] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the present application are different from those of Example 1 in that after the first sintering of the precursor with 12000 ppm of CoOOH and 500 ppm of Mg2O3, the second sintering is performed with 1200 ppm of H2BO3 and 500 ppm of AIF3. The others are similar to those of Example 1, and are not described here again.

[0251] Comparative Example 1

[0252] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the application differ from those of embodiment 1 in that the concentration of the precipitant is 0.5 mol / L, the concentration of the complexing agent is 0.7 mol / L, the PH is 14.5, the reaction temperature is 49℃, the sintering temperature of the precursor and the lithium source is 710℃, and the sintering time is 15 h. The others are similar to those of embodiment 1, and are not described here again.

[0253] Comparative example 2

[0254] The lithium ion secondary battery and the preparation method of the lithium ion secondary battery of the embodiment of the application differ from those of embodiment 1 in that the concentration of the precipitant is 9 mol / L, the concentration of the complexing agent is 0.2 mol / L, the PH is 9.5, the reaction temperature is 71℃, the sintering temperature of the precursor and the lithium source is 715℃, and the sintering time is 13 h. The others are similar to those of embodiment 1, and are not described here again.

[0255] The test method of the related parameters in the above embodiments and comparative examples is as follows:

[0256] 1. Test of the compaction density of the powder

[0257] A certain amount of powder is placed in a compaction special mold, and then the mold is placed on a compaction density instrument, a pressure of 5T (ton) is set to compact the powder, and the thickness of the powder is read on the equipment after unloading, so that the compaction density can be calculated. The compaction density of the powder is tested by using a compaction density instrument with a model number of CARVER4350.

[0258] 2. Test of the particle size of primary particles

[0259] The particle size test adopts a SEM scanning electron microscope test method, the scanning electron microscope used for the SEM test has a model number of Philips XL30, and the test method is as follows: the sample is placed on a scanning electron microscope sample table for testing, the scanning range is 100 nm-2 μm, the particle size of the primary particles is marked on the scale, and the average particle size of the primary particles is equal to the sum of all measured particle sizes / the sum of all measured particle numbers.

[0260] 3. Test of the volume average particle size DV50

[0261] The device model number is MasterSizer 2000 laser particle size instrument, the reference standard process is GB / T19077-2016 / ISO 13320:2009, and the specific test process is as follows: an appropriate amount of the sample to be tested (the sample concentration is ensured to be 8%-12% obscuration) is taken, 20 ml of deionized water is added, and ultrasonic treatment is performed for 5 min (53KHz / 120W) to ensure that the sample is completely dispersed, and then the sample is measured according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0262] 4. Electrochemical performance testing

[0263] 4.1g capacity test

[0264] After assembling the above positive and negative electrode sheets into a soft-pack battery, let it stand for 120 minutes, then charge it to 4.25V at a constant current of 0.1C under a constant temperature environment of 25℃, then charge it to 0.05mA at a constant voltage of 4.25V until the current drops to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.8V at a constant current of 0.1C, thus obtaining the specific capacity C1.

[0265] 4.2 Cyclic Performance Test

[0266] The secondary battery was charged at a constant current of 0.33C to 4.25V under a constant temperature environment of 25℃, then charged at a constant voltage of 4.25V until the current dropped to 0.05mA, and then discharged at a constant current of 0.33C to 2.8V, yielding the initial discharge capacity D1. This charging and discharging process was repeated until the 100th cycle, yielding the discharge capacity D100 after 100 cycles. The capacity retention rate after 100 cycles = D100 / D1.

[0267] Capacity retention rate = discharge capacity after 100 cycles (D100) / discharge capacity in the first cycle (D1).

[0268] 4.3 Volumetric Energy Density Test

[0269] Referring to the 4.1 gram capacity test, the capacity Cp of the battery cell and the corresponding voltage plateau U1 of the battery cell are obtained by constant current charge and discharge test of the battery cell. The volume V1 of the battery cell is measured and the volumetric energy density of the battery cell is calculated.

[0270] The formula for calculating volumetric energy density is:

[0271] Vd=(Cp×U1) / V1

[0272] Table 1. Preparation process parameters of Examples 1-10 and Comparative Examples 1-2

[0273]

[0274] Table 2 Performance test results of Examples 1-10 and Comparative Examples 1-2

[0275]

[0276] like Figure 4 As shown, Figure 4 This is a scanning electron microscope image of the positive electrode active material according to one embodiment of this application. From... Figure 4 It is obvious from the middleFigure 4 The positive active material particles in the positive electrode active material particles have secondary particles with a second part close to spherical shape, and a first part of secondary particles that are quite different from the spherical particles, and the particles with smaller particle size fill in between the particles with larger particle size. The particles close to spherical shape and the non-spherical particles cooperate with each other, and when the electrode plate is subjected to pressure, the particles close to spherical shape and the non-spherical particles can cooperate with each other to achieve the purpose of better relieving pressure, reducing the deformation of the electrode plate, and reducing the degree of elongation of the electrode plate.

[0277] As shown in Table 1 and Table 2, Table 1 is the preparation parameters of Examples 1-10 and Comparative Examples 1-2, and Table 2 is the performance test results of Examples 1-10 and Comparative Examples 1-2. As shown in Table 1, in the preparation process of the precursor of Examples 1-10, the concentration of the precipitator, the concentration of the complexing agent, the PH, and the reaction temperature are in the range of 2mol / L-8mol / L, 0.25mol / L-0.6mol / L, 11.5-14.5, and 50℃-75℃, respectively, so that the area ratio of the first part of the secondary particles to the total secondary particles is in the range of 60%-90%, and the area ratio of the second part of the secondary particles to the total particles is in the range of 10%-40%. As can be seen from Table 2, Examples 1-10 have better gram capacity, capacity retention rate, and volume energy density. Among them, in Example 1, when the concentration of the precipitator is 4mol / L, the concentration of the complexing agent is 0.45mol / L, the PH is 12.4, and the co-precipitation reaction temperature is 53℃, the area ratio of the first part of the secondary particles (i.e. the non-spherical secondary particles) to the total secondary particles reaches 69%, and the gram capacity, capacity retention rate, and volume energy density of Example 1 are the best. When the sintering temperature, sintering time, and the amount of added coating elements of the first coating and second coating processes gradually increase, the electrochemical performance of the lithium ion secondary battery basically shows a trend of first increasing and then decreasing, and the cycle stability is better when the first sintering temperature is 620℃, the first sintering time is 7.5h, the second sintering temperature is 350℃, the second sintering time is 6h, and the addition amounts of CoOOH, AI2O3, and H2BO3 are 12000ppm, 500ppm, and 1200ppm, respectively.

[0278] Comparative Examples 1-2 compared with Examples 1-10, due to the unsuitable preparation parameters of the precursor, such as too small or too large concentration of the precipitator and the complexing agent, etc., the area ratio of the first part of the secondary particles to the total secondary particles in Comparative Example 1 is small, and the area ratio of the second part of the secondary particles to the total secondary particles in Comparative Example 2 is large, so that the first part of the secondary particles and the second part of the secondary particles cannot cooperate well, and finally lead to poor gram capacity, capacity retention rate, and volume energy density.

[0279] The above merely describes the embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation, or direct or indirect application in other related technical fields, which is made by using the content of the present application specification and drawings, is also included in the patent protection scope of the present application.

Claims

1. A lithium-ion secondary battery, characterized by comprising: The positive electrode sheet, the negative electrode sheet and the electrolyte; The positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a first part and a second part, the positive electrode active material comprises lithium nickel cobalt manganese oxide, the content of nickel element in all transition elements contained in the lithium nickel cobalt manganese oxide is greater than or equal to 0.85, in a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of each secondary particle of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of each secondary particle of the second part is greater than or equal to 1 and less than 1.1; the area percentage of the secondary particles of the first part is 60% to 90% based on the total area of the secondary particles of the positive electrode active material, and the area percentage of the secondary particles of the second part is 10% to 40%.

2. The lithium-ion secondary battery according to claim 1, characterized by The area percentage of the secondary particles of the first part is 65% to 85%.

3. The lithium-ion secondary battery according to claim 1 or 2, characterized by The area percentage of the secondary particles of the second part is 15% to 35%.

4. The lithium-ion secondary battery according to claim 1, characterized by The positive electrode tab has a compacted density of 3.2 g / cm 3 3.8 g / cm 3 .

5. The lithium-ion secondary battery according to claim 1 or 2 or 4, characterized by The secondary particles of the first and second portions of the positive electrode active material each independently include a host material having a structural formula of Li a Ni b Co c Mn d M (1-b-c-d) O n a material of M , wherein M includes one or more of Mg, Na, Zr, Y, Al, Ca, W, Nb, Ta, Sr, Ti elements, 0.5≤a≤1.2, 0.85≤b≤0.99, 0<c≤0.1, 0<d≤0.05, b+c+d≤1, 1.9≤n≤2.

2.

6. A positive electrode active material, characterized by, The positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises a first part and a second part, the positive electrode active material comprises lithium nickel cobalt manganese oxide, the content of nickel element in all transition elements contained in the lithium nickel cobalt manganese oxide is greater than or equal to 0.85, in a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of each secondary particle of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of each secondary particle of the second part is greater than or equal to 1 and less than 1.1; the area percentage of the secondary particles of the first part is 60% to 90% based on the total area of the secondary particles of the positive electrode active material, and the area percentage of the secondary particles of the second part is 10% to 40%.

7. A method for producing a lithium-ion secondary battery, characterized by, It comprises: A positive electrode sheet, a separator and a negative electrode sheet are provided to form a lithium ion secondary battery; The positive electrode sheet comprises a positive electrode active material, wherein The preparation method of the positive electrode active material comprises: A precipitating agent and a complexing agent are added to a solution comprising a nickel source, a manganese source and a cobalt source to react, to obtain a positive electrode active material precursor; The positive electrode active material precursor is sintered with a lithium source to obtain the positive electrode active material, the positive electrode active material comprises lithium nickel cobalt manganese oxide, the content of nickel element in all transition elements contained in the lithium nickel cobalt manganese oxide is greater than or equal to 0.85, the positive electrode active material comprises a first part and a second part, in a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of each secondary particle of the first part is greater than or equal to 1.1, and the ratio of the longest diameter to the shortest diameter of each secondary particle of the second part is greater than or equal to 1 and less than 1.1; the area percentage of the secondary particles of the first part is 60% to 90% based on the total area of the secondary particles of the positive electrode active material, and the area percentage of the secondary particles of the second part is 10% to 40%; or The preparation method of the positive electrode active material comprises: Mixing the first part of the positive electrode active material and the second part of the positive electrode active material, to obtain the positive electrode active material, wherein, in a scanning electron microscope picture with a magnification of 2K, the ratio of the longest diameter to the shortest diameter of each secondary particle of the first part is greater than or equal to 1.1, the ratio of the longest diameter to the shortest diameter of each secondary particle of the second part is greater than or equal to 1 and less than 1.1, the area percentage of the secondary particles of the first part is 60% to 90% based on the total area of the secondary particles of the positive electrode active material, the area percentage of the secondary particles of the second part is 10% to 40%, and the content of nickel in all transition elements in the positive electrode active material is greater than or equal to 0.

85.

8. The method of producing a lithium-ion secondary battery according to claim 7, characterized by, After the step of sintering the positive electrode active material precursor with the lithium source, further comprising: adding a first coating element source for sintering, the first coating element source comprising one or more of Co, Al, F, and Ti.

9. An electric device, characterized by The lithium ion secondary battery comprising the positive electrode active material according to any one of claims 1 to 5, and / or the lithium ion secondary battery prepared by the preparation method of the lithium ion secondary battery according to any one of claims 7 to 8.

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