Battery, positive electrode active material, method for producing same, and electric device

Abstract

The application relates to the technical field of lithium batteries, in particular to a lithium ion secondary battery, a positive electrode active material and an electric device, the lithium ion secondary battery comprising the positive electrode active material; the positive electrode active material comprises secondary particles, the secondary particles comprise primary particles, and the primary particles comprise radial primary particles; the secondary particles comprise radial secondary particles, and the number ratio of the radial primary particles to the total number of the primary particles in a single radial secondary particle is 60% to 100%. The specific capacity of the positive electrode active material is relatively high, the stress accumulation degree is relatively low in the cyclic charging and discharging process, the generated stress is easier to release, the particle strength is higher, so that the electrochemical performance of the lithium ion secondary battery is improved, and the cyclic performance is better.

Description

TECHNICAL FIELD

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

[0002] In recent years, lithium ion batteries have developed greatly. The lithium ion batteries can be widely applied to energy storage power systems such as water power, fire power, wind power and solar power stations, and multiple fields such as electric vehicles, electric tools, military equipment and aerospace.

[0003] When the lithium ion batteries are applied to the field of electric vehicles such as electric bicycles, electric motorcycles and electric vehicles, as the market requires higher endurance of electric vehicles, the nickel-cobalt-manganese ternary material as the positive electrode active material has the phenomenon of low cycle performance, which needs to be further improved. The above statements are only used to provide background technical information related to the present application, and do not necessarily constitute the prior art. SUMMARY

[0004] Therefore, the present application mainly solves the technical problem of low cycle performance of the battery using the nickel-cobalt-manganese ternary material as the positive electrode material, so as to provide a battery, a positive electrode active material, a preparation method thereof and an electric device, which can improve the cycle performance of the battery using the nickel-cobalt-manganese ternary material as the positive electrode material.

[0005] A first aspect of the present application provides a lithium ion secondary battery, comprising 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 lithium nickel cobalt manganese oxide, the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%; the positive electrode active material comprises secondary particles, the secondary particles comprise primary particles, the primary particles comprise radial primary particles, in a cross-sectional scanning electron microscope picture of the secondary particles, the radial primary particles are primary particles with a smallest included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°; the secondary particles comprise radial secondary particles, and the number ratio of the radial primary particles to the total number of the primary particles in a single radial secondary particle is 60% to 100%.

[0006] In the embodiment, the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%, and the number ratio of radial primary particles to the total number of primary particles in a single radial secondary particle is 60% to 100%. The radial primary particles with a large number ratio make the arrangement of primary particles in the secondary particle have a higher order degree, and the secondary particle tends to be isotropic. In the process of cyclic charging and discharging, the primary particles in the secondary particle expand and shrink along the (003) crystal plane. The radial primary particles in the radial secondary particle expand or shrink along the direction perpendicular or tending to be perpendicular to the radius, and the stress generation is limited, the mutual extrusion between the primary particles is reduced, the local stress concentration degree in the radial secondary particle is relatively small, and the generated stress is more easily released, thereby relieving the cracking problem of the radial secondary particle and the positive active material, and thus being beneficial to improving the cycle performance of the lithium ion secondary battery.

[0007] In an embodiment, the Young's modulus of the radial secondary particle is 2 GPa to 400 GPa. In the embodiment, the Young's modulus of the radial secondary particle is relatively high, and the stiffness of the radial secondary particle is relatively strong. In the cold pressing process of the preparation of the positive electrode sheet in the lithium ion secondary battery, the probability of cracking of the radial secondary particle can be reduced. In the cycle process of the lithium ion secondary battery, the probability of cracking of the radial secondary particle can also be reduced, and the probability of cracking of the positive active material can be reduced, thereby being beneficial to improving the electrochemical performance of the positive active material.

[0008] In an embodiment, the average particle size of the primary particle is 50 nm to 2 μm. In the embodiment, the average particle size of the primary particle is in the above range, so that the stress accumulation degree in the secondary particle is lower, and the generated stress is more easily released.

[0009] In an embodiment, the number ratio of radial primary particles to the total number of primary particles in a single radial secondary particle is 75% to 95%. When the number ratio of radial primary particles is in the above range, it is beneficial to further relieve stress accumulation in the process of cyclic charging and discharging, so that the stress generated in the particle is more easily released, thereby being beneficial to further improving the particle strength of the positive active material and relieving the particle cracking problem, and thus being beneficial to further improving the cycle performance of the lithium ion secondary battery.

[0010] In an embodiment, the Young's modulus of the radial secondary particle is 10 GPa to 200 GPa. When the Young's modulus of the radial secondary particle is in the above range, it is beneficial to further reduce the cracking of the positive active material particle in the cold pressing and cycle processes, thereby being beneficial to further improving the electrochemical performance of the positive active material.

[0011] In an embodiment, the average particle size of the primary particles is 100 nm to 500 nm. In the embodiment of the present application, the average particle size of the primary particles is in the above range, so that the degree of stress accumulation in the secondary particles is lower, and the generated stress is more easily released.

[0012] In an embodiment, in the positive electrode active material, the proportion of the number of radial secondary particles is 80% to 100% based on the total number of secondary particles. In the embodiment of the present application, the proportion of the number of radial secondary particles in the secondary particles is higher, the radial secondary particles have a major influence on the performance of the positive electrode active material, the radial secondary particles can alleviate the cracking problem of the secondary particles, the performance of the radial secondary particles is better, and the overall performance of the positive electrode active material can be effectively improved, the probability of cracking of the positive electrode active material in the cycle process is reduced, and the cycle performance of the lithium ion secondary battery is improved.

[0013] In an embodiment, in the positive electrode active material, the proportion of the number of radial secondary particles is 90% to 100% based on the total number of secondary particles. In the embodiment of the present application, the proportion of the number of radial secondary particles in the secondary particles is further increased, the cracking problem of the secondary particles can be further alleviated, the overall performance of the positive electrode active material can be further effectively improved, the probability of cracking of the positive electrode active material in the cycle process is reduced, and the cycle performance of the lithium ion secondary battery is improved.

[0014] In an embodiment, in the cross-sectional scanning electron microscope image of the secondary particles, the long axis size of the primary particles is 0.3 μm to 3 μm. In the embodiment of the present application, the long axis size of the primary particles is in the above range, the secondary particles are easy to release stress, the degree of stress accumulation of the secondary particles is reduced, the structural stability of the secondary particles is increased, and the Young's modulus of the secondary particles is increased.

[0015] In an embodiment, in the cross-sectional scanning electron microscope image of the secondary particles, the long axis size of the primary particles is 0.5 μm to 2 μm. In the embodiment of the present application, the long axis size of the primary particles is in the above range, the secondary particles are easy to release stress, the degree of stress accumulation of the secondary particles is reduced, the structural stability of the secondary particles is increased, and the Young's modulus of the secondary particles is increased.

[0016] In an embodiment, the volume average particle size Dv50 of the secondary particles is 6 μm to 15 μm. In the embodiment of the present application, the volume average particle size Dv50 of the positive electrode active material is in the above range, the specific surface area of the positive electrode active material is larger, the Young's modulus of the positive electrode active material is better, and the electrochemical performance of the positive electrode active material is better.

[0017] In an embodiment, the volume average particle size Dv50 of the secondary particles is 9 μm to 12 μm. In the embodiment of the present application, the volume average particle size Dv50 of the positive electrode active material is in the above range, and the positive electrode active material has better electrochemical performance.

[0018] In an embodiment, the specific surface area of the positive electrode active material is 0.2 m 2 / g to 1.0 m 2 / g. In the embodiment of the present application, the specific surface area of the positive electrode active material is in the above range, so that the positive electrode active material has better tap density, and the lithium ion secondary battery has better energy density.

[0019] In an embodiment, the specific surface area of the positive electrode active material is 0.3 m 2 / g to 0.7 m 2 / g. In the embodiment of the present application, the specific surface area of the positive electrode active material is in the above range, so that the positive electrode active material has better tap density, and the lithium ion secondary battery has better energy density.

[0020] In an embodiment, the cross-sectional porosity of the positive electrode active material is 2% to 8%. In the embodiment of the present application, the cross-sectional porosity of the positive electrode active material is in the above range, so that the positive electrode active material can release stress, alleviate the occurrence of cracking of the secondary particles of the positive electrode active material, and improve the electrochemical cycle performance of the lithium ion secondary battery.

[0021] In an embodiment, the cross-sectional porosity of the positive electrode active material is 3% to 6%. In the embodiment of the present application, the cross-sectional porosity of the positive electrode active material is in the above range, so that the positive electrode active material can release stress, alleviate the occurrence of cracking of the secondary particles of the positive electrode active material, and improve the electrochemical cycle performance of the lithium ion secondary battery.

[0022] In an embodiment, the cross-sectional average pore size of the positive electrode active material is 0.1 μm to 2 μm. In the embodiment of the present application, the cross-sectional average pore size of the positive electrode active material is in the above range, so that the positive electrode active material can well alleviate and release stress, and the positive electrode active material has better tap density, and the lithium ion secondary battery has better energy density.

[0023] In an embodiment, the content of nickel element in the radial secondary particles is equal from the center to the surface region, or the difference in the content of nickel element from the center to the surface region is less than or equal to 2%. In the embodiment of the present application, the content of nickel element in the radial secondary particles is uniform from the center region to the surface region, that is, the nickel element is uniformly distributed in the radial secondary particles, so that the positive electrode active material has better electrochemical performance.

[0024] In an embodiment, the content of manganese element in the radial secondary particles is equal from the center to the surface region, or the difference in the content of manganese element from the center to the surface region is less than or equal to 0.5%. In the embodiment, the content of manganese element in the radial secondary particles is uniform from the center region to the surface region, i.e., the manganese element is uniformly distributed in the radial secondary particles, so that the electrochemical performance of the positive electrode active material is better.

[0025] In an embodiment, the positive electrode active material comprises a material with a structural formula of Li a Ni b Co c Mn d M1 e O f , wherein the M1 element comprises one or more of Zr, Ti, Y, Sb, W, Mo, Ba, Ta, Nb, and Al, 0.9≤a≤1.2, 0.85≤b<1, 0.01≤c≤0.09, 0.01≤d≤0.05, 0.001≤e≤0.005, 1.6≤f≤2.4, and b+c+d+e=1. The positive electrode active material provided in the embodiment combines the advantages of nickel, cobalt, and manganese elements, and the doping element M1 helps to improve the bulk stability and electrical stability of the positive electrode active material, reduces the cation mixing problem caused by high nickel, and is beneficial to promote the growth of radial primary particles, thereby improving the electrochemical performance of the positive electrode active material.

[0026] In an embodiment, 0.9≤b<1, and / or 0.002≤e≤0.004. In the embodiment, the molar content of nickel in the lithium nickel cobalt manganese oxide is greater than or equal to 0.9, which is beneficial to further improve the energy density of the positive electrode active material; and the doping element is in the above range, which can further improve the electrochemical performance of the lithium nickel cobalt manganese oxide.

[0027] In an embodiment, the positive electrode active material further comprises a coating layer, the coating layer is located on the surface of the material with a structural formula of Li a Ni b Co c Mn d M1 e O f , and the coating layer comprises Co element or / and B element. In the embodiment, Co can play a role in repairing the grain boundary, improving the Young's modulus of the secondary particles, enhancing the electrochemical stability of the surface of the secondary particles, and improving the cycle life; and B can refine the primary grains, improve the deintercalation ability of lithium ions on the surface, and improve the electrochemical performance of the lithium ion secondary battery.

[0028] The second aspect of the present application also provides a method for manufacturing a lithium ion secondary battery, comprising: providing a slurry containing a positive electrode active material, coating the slurry containing the positive electrode active material on a positive electrode current collector to form a positive electrode sheet, wherein the positive electrode active material comprises lithium nickel cobalt manganese oxide, the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%; the positive electrode active material comprises secondary particles, the secondary particles comprise primary particles, the primary particles comprise radial primary particles, in a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a minimum included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°; the secondary particles comprise radial secondary particles, and the number ratio of the radial primary particles to the total number of primary particles in a single radial secondary particle is 60% to 100%; and arranging a separator between the positive electrode sheet and a negative electrode sheet to form a lithium ion secondary battery.

[0029] In an embodiment of the present application, the radial primary particles with a large number ratio make the arrangement of the primary particles in the secondary particles more ordered, and the secondary particles tend to be isotropic. During the cyclic charging and discharging process, the primary particles in the secondary particles expand and contract along the (003) crystal plane. The radial primary particles in the radial secondary particles expand or contract along a direction perpendicular or tending to be perpendicular to the radius, and the stress generated is limited. The mutual extrusion between the primary particles is reduced, the local stress concentration in the radial secondary particles is relatively small, the generated stress is more easily released, the cracking problem of the radial secondary particles is alleviated, and thus the cracking problem of the positive electrode active material is alleviated, thereby being beneficial to improving the cycle performance of the lithium ion secondary battery.

[0030] In an embodiment, the method for preparing the positive electrode active material comprises: providing a solution containing a nickel source, a cobalt source and a manganese source, wherein the molar ratio of the nickel element is greater than or equal to 85% and less than 100% based on the total molar amount of the nickel element, the cobalt element and the manganese element; adding a complexing agent with a concentration of 8.5 mol / L to 10 mol / L and a precipitating agent with a concentration of 2.1 mol / L to 15 mol / L into the solution containing the nickel source, the cobalt source and the manganese source, controlling the pH range to be 8 to 10, and forming a nickel cobalt manganese hydroxide precursor under the condition of 30°C to 50°C, wherein the volume average particle size Dv50 of the nickel cobalt manganese hydroxide precursor is 6 μm to 11 μm; mixing the nickel cobalt manganese hydroxide precursor with a lithium source, and reacting at 720°C to 890°C for 11 to 15 hours to obtain the positive electrode active material.

[0031] In the embodiment, the positive electrode active material can inherit the morphology of the nickel-cobalt-manganese hydroxide precursor. In the process of preparing the nickel-cobalt-manganese hydroxide precursor by the coprecipitation reaction, the complexing agent has a relatively large concentration, the pH value is relatively small, and the balance of the coprecipitation reaction is more inclined to the growth of the precursor material. Therefore, the primary particles of the material have sufficient time to grow into long grains, and the primary particles in the radial direction in the obtained precursor tend to grow in the radial direction. The proportion of the primary particles in the radial direction in the positive electrode active material is increased.

[0032] In an embodiment, the nickel-cobalt-manganese hydroxide precursor is mixed with a lithium source, and reacted at 720-890°C for 11-15h to obtain the positive electrode active material. The method comprises: mixing the nickel-cobalt-manganese hydroxide precursor, the lithium source, and a metal doping source, and reacting at 720-890°C for 11-15h to form a first intermediate product; mixing the first intermediate product with a first coating source, and reacting at 600-700°C for 5-8h to form a second intermediate product, wherein the first coating source comprises a Co source; and mixing the second intermediate product with a second coating source, and reacting at 300-400°C for 5-7h to obtain the positive electrode active material, wherein the second coating source comprises a B source. Through the above arrangement, the positive electrode active material with good stability and electrochemical performance can be obtained.

[0033] The third aspect of the application also provides a positive electrode active material. The positive electrode active material comprises lithium nickel cobalt manganese oxide, and the molar content of nickel elements in all transition metal elements is greater than or equal to 85% and less than 100%. The positive electrode active material comprises secondary particles, and the secondary particles comprise primary particles. The primary particles comprise radial primary particles. In a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a smallest included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°. The secondary particles comprise radial secondary particles. The proportion of the number of the radial primary particles is 60%-100% based on the total number of the primary particles in a single radial secondary particle. In the embodiment, the radial primary particles with a large number proportion make the arrangement of the primary particles in the secondary particles more ordered, and the secondary particles tend to be isotropic. In the process of cyclic charging and discharging, the primary particles in the secondary particles expand and shrink along the (003) crystal plane. The radial primary particles in the radial secondary particles expand or shrink along a direction perpendicular or tending to be perpendicular to the radius. The stress generated is limited, the mutual extrusion between the primary particles is reduced, the degree of local stress concentration in the radial secondary particles is relatively small, the generated stress is more easily released, the cracking problem of the radial secondary particles is alleviated, and thus the cracking problem of the positive electrode active material is alleviated.

[0034] In an embodiment, the radial secondary particles have a Young's modulus of 2 GPa to 400 GPa. In the embodiments of the present application, the radial secondary particles have a high Young's modulus and a high rigidity. In the cold pressing process in the preparation of the positive electrode sheet of the lithium ion secondary battery, the probability of cracking of the radial secondary particles can be reduced. In the cycle process of the lithium ion secondary battery, the probability of cracking of the radial secondary particles can also be reduced, and the probability of cracking of the positive active material can be reduced, thereby improving the electrochemical performance of the positive active material.

[0035] The fourth aspect of the present application also provides a preparation method of the positive active material, comprising: providing a solution containing a nickel source, a cobalt source and a manganese source, wherein the mole percentage of nickel element is greater than or equal to 85% and less than 100% based on the total mole amount of nickel element, cobalt element and manganese element; adding a complexing agent with a concentration of 8.5 mol / L to 10 mol / L and a precipitating agent with a concentration of 2.1 mol / L to 15 mol / L into the solution containing the nickel source, the cobalt source and the manganese source, controlling the pH value in the range of 8 to 10, and forming a nickel-cobalt-manganese hydroxide precursor under the condition of 30°C to 50°C, wherein the volume average particle size Dv50 of the nickel-cobalt-manganese hydroxide precursor is 6 μm to 11 μm; mixing the nickel-cobalt-manganese hydroxide precursor with a lithium source, and reacting at 720°C to 890°C for 11 to 15 hours to obtain the positive active material. In the embodiments, the positive active material can inherit the morphology of the nickel-cobalt-manganese hydroxide precursor. In the process of preparing the nickel-cobalt-manganese hydroxide precursor by coprecipitation reaction, the complexing agent has a relatively large concentration, the pH value is relatively small, and the balance of the coprecipitation reaction is more inclined to the growth of the precursor material. Therefore, the primary particles of the material have sufficient time to grow into long grains, and the obtained precursor primary particles tend to grow radially. The proportion of the radial primary particles in the positive active material is increased.

[0036] In an embodiment, the positive active material is obtained by mixing the nickel-cobalt-manganese hydroxide precursor with a lithium source and reacting at 720°C to 890°C for 11 to 15 hours, comprising: mixing the nickel-cobalt-manganese hydroxide precursor, a lithium source and a metal doping source, reacting at 720°C to 890°C for 11 to 15 hours to form a first intermediate product; mixing the first intermediate product with a first coating source and reacting at 600°C to 700°C for 5 to 8 hours to form a second intermediate product, wherein the first coating source comprises a Co source; and mixing the second intermediate product with a second coating source and reacting at 300°C to 400°C for 5 to 7 hours to obtain the positive active material, wherein the second coating source comprises a B source. Through the above settings, the positive active material with good stability and electrochemical performance can be obtained.

[0037] The fifth aspect of the present application also provides a power consuming device comprising the lithium ion secondary battery of the first aspect of the present application and / or the lithium ion secondary battery obtained by the manufacturing method of the second aspect of the present application and / or the positive electrode active material of the third aspect of the present application and / or the positive electrode active material obtained by the manufacturing method of the fourth aspect of the present application. Since the power consuming device of the present application comprises the lithium ion secondary battery and / or the positive electrode active material provided by the present application, it has at least the same advantages as the lithium ion secondary battery.

[0038] The above description is only a summary of the technical solutions of the present application. In order to enable one skilled in the art to better understand the technical means of the present application, the content of the specification can be implemented, and in order to enable the above and other purposes, features and advantages of the present application to be more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a cross-sectional scanning electron microscope (SEM) photo of the secondary particle provided by embodiment 1 of the present application;

[0040] Figure 2 is a structural schematic diagram of a battery cell provided by some embodiments of the present application;

[0041] Figure 3 is a disassembled structural schematic diagram of a lithium ion secondary battery provided by some embodiments of the present application;

[0042] Figure 4 is a schematic diagram of a power consuming device of an embodiment of the present application;

[0043] Figure 5 is a cross-sectional scanning electron microscope (SEM) photo of the secondary particle provided by comparative example 1 of the present application. DETAILED DESCRIPTION

[0044] Hereinafter, the embodiments of the lithium ion secondary battery, the battery and the power consuming device of the present application are 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 to those skilled in the art, 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. In addition, the accompanying drawings and the following description are provided in order 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.

[0045] The ranges disclosed herein are meant to be inclusive of the endpoints and include the end values in the range. Ranges can be combined to form new ranges, e.g., a range of "60-120 and 80-110" is understood to include 60-110 and 80-120. Further, if a minimum range value is listed as 1 and a maximum range value is listed as 3, then the following ranges are all contemplated: 1-3, 1-2, 1-3, 2-3, 2-2, and 2-3. In this application, unless otherwise indicated, a numerical range "a-b" is intended to indicate any range encompassed by any integer between a and b, where a and b are both integers. For example, the numerical range "0-5" indicates that all integers between 0 and 5 are contemplated herein, and "0-5" is merely a shorthand for listing all of the integers between 0 and 5. 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.

[0046] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0047] 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.

[0048] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, a method comprising 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.

[0049] 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.

[0050] 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).

[0051] During the charging and discharging process of lithium ion secondary batteries, the insertion and extraction of active lithium ions in the positive electrode material can cause the expansion and contraction of the crystal lattice, resulting in stress accumulation inside the material particles. This stress accumulation can lead to the formation of micro-cracks inside the material particles, which in turn affects the cycle stability and safety of the battery.

[0052] Based on this, the present application provides a lithium ion secondary battery, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet includes a positive electrode active material, the positive electrode active material includes lithium nickel cobalt manganese oxide, the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%. The positive electrode active material includes secondary particles, the secondary particles include primary particles, the primary particles include radial primary particles, in the cross-sectional scanning electron microscope picture of the secondary particles, the radial primary particles are the primary particles with a smallest included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°. The secondary particles include radial secondary particles, based on the total number of primary particles in a single radial secondary particle, the number ratio of radial primary particles is 60% to 100%.

[0053] Among them, the primary particle refers to a single fine grain, which is the most basic unit in the positive electrode active material. The secondary particle refers to a larger particle formed by the agglomeration of multiple primary particles.

[0054] The radial primary particle is a special type of primary particle, the smallest included angle between the long axis direction of the primary particle and the radial direction of the secondary particle is less than or equal to 20°, and the primary particle is a radial primary particle.

[0055] The radial secondary particle is a special type of secondary particle, the number of radial primary particles in the secondary particle accounts for 60% to 100% of the total number of primary particles in the secondary particle, and the secondary particle is a radial secondary particle.

[0056] Please refer to Figure 1 , Figure 1 The cross-sectional scanning electron microscope (SEM) photo of the secondary particles provided for Example 1 of the present application. Figure 1 The circular particles in the central part are secondary particles, the secondary particles contain a plurality of fine primary particles, Figure 1CD is the radius direction of the secondary particle, AB is the long axis direction of a radial primary particle, and the angle between AB and CD is less than 20°, Figure 1 In the secondary particle shown, the number of radial primary particles accounts for 86.7% of the total number of primary particles, and at this time the secondary particle is a radial secondary particle.

[0057] In the embodiments of the present application, the positive active material of the lithium ion battery includes lithium nickel cobalt manganese oxide. The lithium nickel cobalt manganese oxide gathers the respective advantages of nickel (Ni), cobalt (Co), and manganese (Mn) elements through the synergistic effect of the elements, maintains a high specific capacity and good stability of the electrode material, and reduces the preparation cost. The molar content of the nickel element in all transition metal elements is greater than or equal to 85% and less than 100%, which can effectively improve the specific capacity of the positive active material, thereby being conducive to improving the energy density of the lithium ion battery. The molar content of the nickel element can be 85%, 88%, 90%, 95%, 99%, or a range formed by any two of the above values, such as 85%-88%, 85%-90%, 90%-95%, 95%-99%, and the like.

[0058] In the embodiments of the present application, the positive active material includes secondary particles, the secondary particles include primary particles, the primary particles include radial primary particles, and the number of radial primary particles accounts for 60%-100% of the total number of primary particles in a single radial secondary particle. Alternatively, when the number of radial primary particles in the secondary particles accounts for 60%-100%, most of the primary particles in the secondary particles are radial primary particles, and at this time the secondary particles are radial secondary particles. The radial primary particles with a large number account have a higher degree of order in the arrangement of the primary particles in the secondary particles, and the secondary particles tend to be isotropic. In the process of cyclic charging and discharging, the primary particles in the secondary particles expand and contract along the (003) crystal plane. The radial primary particles in the radial secondary particles expand or contract along a direction perpendicular or tending to be perpendicular to the radius. The stress generated is limited, the mutual extrusion between the primary particles is reduced, the degree of local stress concentration in the radial secondary particles is relatively small, the generated stress is more easily released, the cracking problem of the radial secondary particles is alleviated, and thus the cracking problem of the positive active material is alleviated, thereby being conducive to improving the cycle performance of the lithium ion secondary battery.

[0059] In the embodiments of the present application, the positive active material includes secondary particles, the secondary particles include primary particles, the primary particles include radial primary particles, and the number of radial primary particles accounts for 60%-100% of the total number of primary particles in a single radial secondary particle. Alternatively, when the number of radial primary particles in the secondary particles accounts for 60%-100%, most of the primary particles in the secondary particles are radial primary particles, and at this time the secondary particles are radial secondary particles. The radial primary particles with a large number account have a higher degree of order in the arrangement of the primary particles in the secondary particles, and the secondary particles tend to be isotropic. In the process of cyclic charging and discharging, the primary particles in the secondary particles expand and contract along the (003) crystal plane. The radial primary particles in the radial secondary particles expand or contract along a direction perpendicular or tending to be perpendicular to the radius. The stress generated is limited, the mutual extrusion between the primary particles is reduced, the degree of local stress concentration in the radial secondary particles is relatively small, the generated stress is more easily released, the cracking problem of the radial secondary particles is alleviated, and thus the cracking problem of the positive active material is alleviated, thereby being conducive to improving the cycle performance of the lithium ion secondary battery.

[0060] The radial direction of the secondary particle is defined as the radial direction connecting the geometric center of the cross section of the secondary particle and the farthest point of the primary particle close to the geometric center of the cross section of the secondary particle, and the minimum angle is the angle between the radial direction and the long axis direction of the primary particle. Please refer to Figure 1 , Figure 1 A cross section scanning electron microscope (SEM) photo of the secondary particle provided for Embodiment 1 of the present application. Figure 1 An example of the minimum angle between the long axis direction AB of the primary particle and the radial direction CD of the secondary particle in the cross section scanning electron microscope photo of the secondary particle is shown in FIG. 1. Figure 1 When the minimum angle is less than or equal to 20°, the primary particles are substantially arranged in a radial pattern with the geometric center of the cross section of the secondary particle as the origin. The minimum angle can be 0°, 5°, 6.8°, 8°, 10°, 13°, 15°, 19°, 20°, etc., or a range defined by any two of the above values, such as 0°-5°, 6.8°-10°, 13°-15°, 19°-20°, etc.

[0061] In an embodiment, the radial secondary particle has a Young's modulus of 2-400 GPa.

[0062] The radial secondary particle has a Young's modulus of 2-400 GPa. It can be 2 GPa, 15 GPa, 20 GPa, 65 GPa, 80 GPa, 90 GPa, 100 GPa, 120 GPa, 160 GPa, 200 GPa, 300 GPa, 360 GPa, 400 GPa, etc., or a range defined by any two of the above values, such as 2-15 GPa, 20-65 GPa, 80-90 GPa, 100-120 GPa, 160-300 GPa, 360-400 GPa, etc. The Young's modulus is an index describing the stiffness and elasticity of a material in material mechanics, which is defined as the proportional coefficient of stress and strain in the elastic deformation stage. The larger the Young's modulus, the less likely the material is to deform.

[0063] The Young's modulus of the radial secondary particle is known in the art and has the meaning known in the art, which can be measured by methods and instruments in the art.

[0064] In the embodiment of the present application, the radial secondary particles have a high Young's modulus and high rigidity, which can reduce the probability of cracking of the radial secondary particles in the cold pressing process of the preparation of the positive electrode sheet of the lithium ion secondary battery, and can reduce the probability of cracking of the positive active material, thereby improving the electrochemical performance of the positive active material.

[0065] In an embodiment, the average particle size of the primary particles is 50 nm to 2 μm.

[0066] The average particle size of the primary particles is a common knowledge in the art and has a meaning known in the art, and can be measured by methods and instruments in the art. The average particle size of the primary particles is 50 nm to 2 μm, which can be 50 nm, 60 nm, 80 nm, 1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.85 μm, 2 μm, or a range between any two of the above values, for example, 50 nm to 60 nm, 80 nm to 1 μm, 1.2 μm to 1.6 μm, 1.85 μm to 2 μm, etc. In the embodiment of the present application, the average particle size of the primary particles is in the above range, so that the stress accumulation in the secondary particles is lower and the generated stress is more easily released.

[0067] In an embodiment, the number of the radial primary particles accounts for 75% to 95% based on the total number of the primary particles in a single radial secondary particle. It can be 75%, 76%, 80%, 85%, 90%, 95%, or a range between any two of the above values, for example, 75% to 76%, 80% to 85%, 90% to 95%, etc.

[0068] The number of the radial primary particles accounts for 75% to 95% in the above range, which is beneficial to further relieve stress accumulation and make the stress generated in the particles more easily released, thereby further improving the particle strength of the positive active material and relieving the particle cracking problem, and thus further improving the cycle performance of the lithium ion secondary battery.

[0069] In an embodiment, the Young's modulus of the radial secondary particles is 10 GPa to 200 GPa. It can be 10 GPa, 20 GPa, 50 GPa, 75 GPa, 100 GPa, 130 GPa, 150 GPa, 160 GPa, 200 GPa, or a range between any two of the above values, for example, 10 GPa to 50 GPa, 75 GPa to 130 GPa, 150 GPa to 160 GPa, 160 GPa to 200 GPa, etc.

[0070] The Young's modulus of the radial secondary particles in the above range is conducive to further reducing the cracking of the positive active material particles during cold pressing and cycling, thereby further improving the electrochemical performance of the positive active material.

[0071] In an embodiment, the Young's modulus of the radial secondary particles can also be 80 GPa to 400 GPa. It can be 80 GPa, 90 GPa, 100 GPa, 120 GPa, 160 GPa, 200 GPa, 300 GPa, 360 GPa, 400 GPa, etc., or a range composed of any two of the above values, for example, it can be 80 GPa to 90 GPa, 100 GPa to 120 GPa, 160 GPa to 300 GPa, 360 GPa to 400 GPa, etc.

[0072] In an embodiment, the Young's modulus of the radial secondary particles can also be 150 GPa to 350 GPa. It can be 150 GPa, 160 GPa, 200 GPa, 300 GPa, 350 GPa, etc., or a range composed of any two of the above values, for example, it can be 150 GPa to 160 GPa, 200 GPa to 300 GPa, 300 GPa to 350 GPa, etc.

[0073] In an embodiment, the average particle size of the primary particles is 100 nm to 500 nm. It can be 100 nm, 110 nm, 150 nm, 165 nm, 200 nm, 230 nm, 250 nm, 275 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc., or a range composed of any two of the above values, for example, it can be 100 nm to 150 nm, 165 nm to 200 nm, 230 nm to 250 nm, 275 nm to 350 nm, 400 nm to 500 nm, etc.

[0074] In the embodiments of the present application, the average particle size of the primary particles is in the above range, so that the stress accumulation in the secondary particles is lower, and the generated stress is easier to release.

[0075] In an embodiment, in the positive active material, the number of the radial secondary particles accounts for 80% to 100% based on the total number of the secondary particles. It can be 80%, 85%, 88%, 90%, 96%, 100%, etc., or a range composed of any two of the above values, for example, it can be 80% to 85%, 88% to 90%, 96% to 100%, etc.

[0076] In the embodiment of the present application, the number of radial secondary particles accounts for a large proportion in the secondary particles, the radial secondary particles mainly affect the performance of the positive active material, the radial secondary particles can alleviate the cracking problem of the secondary particles, the performance of the radial secondary particles is better, the overall performance of the positive active material can be effectively improved, the probability of cracking of the positive active material in the cycle process is reduced, and the cycle performance of the lithium ion secondary battery is improved.

[0077] In an embodiment, the number of radial secondary particles accounts for 90% to 100% in the total number of secondary particles in the positive active material. It can be 90%, 92%, 95%, 98%, 99.5%, 100%, or a range composed of any two of the above values, for example, 90% to 92%, 95% to 98%, 99.5% to 100%, etc.

[0078] In the embodiment of the present application, the number of radial secondary particles accounts for a further increased proportion in the secondary particles, the cracking problem of the secondary particles can be further alleviated, the overall performance of the positive active material can be further effectively improved, the probability of cracking of the positive active material in the cycle process is reduced, and the cycle performance of the lithium ion secondary battery is improved.

[0079] In an embodiment, the long axis size of the primary particles is 0.3 μm to 3 μm in the cross-sectional scanning electron microscope picture of the secondary particles. It can be 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 2 μm, 2.2 μm, 2.6 μm, 3 μm, etc., or a range composed of any two of the above values, for example, 0.3 μm to 1 μm, 1 μm to 2.2 μm, 2.2 μm to 3 μm, etc.

[0080] The first direction along the geometric center of the cross section of the primary particle has the maximum size, which is the long axis size of the primary particle. In the embodiment of the present application, the long axis size of the primary particle is in the above range, the secondary particle is easy to release stress, the stress accumulation degree of the secondary particle is reduced, the structural stability of the secondary particle is increased, and the Young's modulus of the secondary particle is increased.

[0081] In an embodiment, the long axis size of the primary particles is 0.5 μm to 2 μm in the cross-sectional scanning electron microscope picture of the secondary particles. It can be 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 2 μm, etc., or a range composed of any two of the above values, for example, 0.5 μm to 0.8 μm, 1 μm to 1.3 μm, 1.3 μm to 2 μm, etc.

[0082] In the embodiments of the present application, the long axis size of the primary particles is within the above range, the secondary particles easily release stress, so that the stress accumulation degree of the secondary particles is reduced, the structural stability of the secondary particles is increased, and the Young's modulus of the secondary particles is increased.

[0083] In an embodiment, the volume average particle size Dv50 of the secondary particles is 6 μm to 15 μm. It can be 6 μm, 9 μm, 10 μm, 13 μm, 15 μm, or a range formed by any two of the above values, for example, 6 μm to 10 μm, 10 μm to 13 μm, 13 μm to 15 μm, etc.

[0084] The volume average particle size Dv50 is a common knowledge in the art, has the meaning known in the art, and can be measured by the methods and instruments in the art.

[0085] In the embodiments of the present application, the volume average particle size Dv50 of the positive electrode active material is within the above range, the specific surface area of the positive electrode active material is larger, the Young's modulus of the positive electrode active material is better, and the electrochemical performance of the positive electrode active material is better.

[0086] In an embodiment, the volume average particle size Dv50 of the secondary particles is 9 μm to 12 μm. It can be 9 μm, 10 μm, 11 μm, 12 μm, or a range formed by any two of the above values, for example, 9 μm to 10 μm, 10 μm to 11 μm, 11 μm to 12 μm, etc.

[0087] In the embodiments of the present application, the volume average particle size Dv50 of the positive electrode active material is within the above range, and the electrochemical performance of the positive electrode active material is better.

[0088] In an embodiment, the specific surface area of the positive electrode active material is 0.2 m 2 / g to 1.0 m 2 / g. It can be 0.2 m 2 / g, 0.4 m 2 / g, 0.55 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, etc., or a range formed by any two of the above values, for example, it can be 0.2 m 2 / g to 0.4 m 2 / g, 0.55 m 2 / g to 0.8 m 2 / g, 0.8 m 2 / g to 1.0 m 2 / g, etc.

[0089] The specific surface area is a common knowledge in the art, has the meaning known in the art, and can be measured by the methods and instruments in the art.

[0090] In the embodiments of the present application, the specific surface area of the positive electrode active material is in the above range, so that the compaction density of the positive electrode active material is better, and the energy density of the lithium ion secondary battery is better.

[0091] In one embodiment, the specific surface area of the positive electrode active material is 0.3m 2 2 / g. It can be 0.3m 2 / g, 0.4m 2 / g, 0.55m 2 / g, 0.62m 2 / g, 0.7m 2 / g, etc., or a range composed of any two of the above values, for example, 0.3m 2 / g to 0.4m 2 / g, 0.55m 2 / g to 0.62m 2 / g, 0.62m 2 / g to 0.7m 2 / g, etc. In the embodiments of the present application, the specific surface area of the positive electrode active material is in the above range, so that the compaction density of the positive electrode active material is better, and the energy density of the lithium ion secondary battery is better.

[0092] In one embodiment, the cross-sectional porosity of the positive electrode active material is 2% to 8%. It can be 2%, 4%, 5%, 6%, 8%, etc., or a range composed of any two of the above values, for example, 2% to 4%, 4% to 6%, 6% to 8%, etc.

[0093] The cross-sectional porosity is a well-known concept in the art and has the meaning known in the art, and can be measured by methods and instruments in the art.

[0094] The cross-sectional porosity of the positive electrode active material refers to the proportion of space occupied by the voids between particles. In the positive electrode material of the lithium ion battery, the porosity has a significant impact on the performance of the battery. In the embodiments of the present application, the cross-sectional porosity of the positive electrode active material is in the above range, so that the positive electrode active material can release stress and alleviate the occurrence of cracking of the secondary particles of the positive electrode active material, and improve the electrochemical cycle performance of the lithium ion secondary battery.

[0095] In one embodiment, the cross-sectional porosity of the positive electrode active material is 3% to 6%. It can be 3%, 4%, 5%, 5.5%, 6%, etc., or a range composed of any two of the above values, for example, 3% to 4%, 4% to 6%, 5.5% to 6%, etc.

[0096] ​In the embodiments of the present application, the cross-sectional porosity of the positive electrode active material is in the above range, so that the positive electrode active material can release stress, alleviate the occurrence of secondary particle cracking of the positive electrode active material, and improve the electrochemical cycle performance of the lithium ion secondary battery.

[0097] In an embodiment, the cross-sectional average pore diameter of the positive electrode active material is 0.1 μm to 2 μm. It can be 0.1 μm, 0.8 μm, 1 μm, 1.3 μm, 2 μm, or a range value composed of any two of the above values, for example, 0.1 μm to 0.8 μm, 0.8 μm to 1.3 μm, 1.3 μm to 2 μm, etc.

[0098] The cross-sectional average pore diameter is a common knowledge in the art and has the meaning known in the art, and can be measured by methods and instruments in the art.

[0099] The cross-sectional average pore diameter refers to the average value of the hole diameter in the positive electrode active material. In the embodiments of the present application, the cross-sectional average pore diameter of the positive electrode active material is in the above range, so that the positive electrode active material can well alleviate stress and release stress, and the compaction density of the positive electrode active material is better, so that the energy density of the lithium ion secondary battery is better.

[0100] In an embodiment, the content of nickel element in the radial secondary particles is equal from the center to the surface region, or the difference in the content of nickel element from the center to the surface region is less than or equal to 2%. In the embodiments of the present application, the content of nickel element in the radial secondary particles is uniform from the center region to the surface region, that is, the nickel element is uniformly distributed in the radial secondary particles. The uniform distribution of nickel element can reduce material defects and uneven distribution of nickel element concentration in local regions, promote the smooth deintercalation of Li + and better capacity of the material; at the same time, the uniform distribution of nickel element alleviates the unevenness of lithium deintercalation of the material, reduces local differences, improves the cycle stability of the material, and makes the electrochemical performance of the positive electrode active material better. In other embodiments, the difference in the content of nickel element from the center to the surface region can also be less than or equal to 1.8%.

[0101] In the embodiments of the present application, the content of nickel element refers to the mass percentage of nickel element in all elements in the test region.

[0102] In an embodiment, the content of manganese element in the radial secondary particles is equal from the center to the surface region, or the difference in the content of manganese element from the center to the surface region is less than or equal to 0.5%. In the embodiments of the present application, the content of manganese element in the radial secondary particles is uniform from the center region to the surface region, that is, the manganese element is uniformly distributed in the radial secondary particles. The uniform distribution of manganese element can reduce material defects and uneven distribution of manganese element concentration in local regions, promote the smooth deintercalation of Li+ The deintercalation is carried out smoothly and the capacity of the material is better exerted; at the same time, the uniform distribution of the manganese element alleviates the non-uniformity of the deintercalation of lithium of the material, can reduce the local difference, and improves the cycle stability of the material, so that the electrochemical performance of the positive electrode active material is better. In other embodiments, the difference in the content of the manganese element from the center to the surface region can also be less than or equal to 0.4%. In other embodiments, the difference in the content of the manganese element from the center to the surface region can also be the same as the difference in the content of the nickel element from the center to the surface region.

[0103] In the embodiments of the present application, the content of the manganese element refers to the mass percentage of the manganese element in all elements in the test region.

[0104] In an embodiment, the positive electrode active material does not include a coating layer, and the content of the cobalt element of the radial secondary particles from the center to the surface region is equal, or the difference in the content of the cobalt element from the center to the surface region is less than or equal to 0.6%. In the embodiments of the present application, the content of the cobalt element in the radial secondary particles from the center region to the surface region is uniform, that is, the cobalt element is uniformly distributed in the radial secondary particles. The uniform distribution of the cobalt element can reduce the defects of the material and the non-uniform distribution of the concentration of the cobalt element in the local region, promote the deintercalation of lithium, and improve the cycle stability of the material, so that the electrochemical performance of the positive electrode active material is better. + The deintercalation is carried out smoothly and the capacity of the material is better exerted; at the same time, the uniform distribution of the cobalt element alleviates the non-uniformity of the deintercalation of lithium of the material, can reduce the local difference, and improves the cycle stability of the material, so that the electrochemical performance of the positive electrode active material is better. In other embodiments, the difference in the content of the cobalt element from the center to the surface region can also be less than or equal to 0.5%. In other embodiments, the difference in the content of the cobalt element from the center to the surface region can also be the same as the difference in the content of the nickel element from the center to the surface region or the difference in the content of the manganese element from the center to the surface region.

[0105] In the embodiments of the present application, the content of the cobalt element refers to the mass percentage of the cobalt element in all elements in the test region.

[0106] In an embodiment, the positive electrode active material includes a material with a structural formula of Li a Ni b Co c Mn d M1 e O f , wherein the M1 element includes one or more of Zr, Ti, Y, Sb, W, Mo, Ba, Ta, Nb, and Al, 0.9≤a≤1.2, 0.85≤b<1, 0.01≤c≤0.09, 0.01≤d≤0.05, 0.001≤e≤0.005, 1.6≤f≤2.4, and b+c+d+e=1.

[0107] The lithium (Li) element provides lithium ions, which move between the positive and negative electrodes during charging and discharging of the battery, and is the key to energy storage and release of the battery. The nickel (Ni) element helps to increase the energy density of the positive electrode active material. In the above embodiment, the nickel (Ni) element accounts for a high proportion of the other metal elements in addition to the lithium element, so that the positive electrode active material has a high energy density. The cobalt (Co) element helps to stabilize the material structure, reduce the impedance value, improve the electrical conductivity, and improve the cycle and efficiency performance. The manganese (Mn) element can reduce the cost of the material, and also can improve the safety and stability of the material.

[0108] The doping element M1 helps to improve the bulk stability and electrical stability of the positive electrode active material, reduces the problem of cationic disordering caused by high nickel, and at the same time is conducive to promoting the growth of radial primary particles, thereby improving the electrochemical performance of the positive electrode active material.

[0109] In an embodiment, 0.9≤b<1, and / or 0.002≤e≤0.004. In the embodiment of the present application, in the lithium nickel cobalt manganese oxide, the molar content of nickel in all transition metal elements is greater than or equal to 0.9, which is conducive to further improving the energy density of the positive electrode active material; and the doping element is in the above range, which can further improve the electrochemical performance of the lithium nickel cobalt manganese oxide.

[0110] In an embodiment, the positive electrode active material further comprises a coating layer, the coating layer is located on the surface of the material with the structural formula Li a Ni b Co c Mn d M1 e O f The coating layer comprises Co element or / and B element.

[0111] In the embodiment of the present application, by coating the substance containing Co element on the surface of the material with the structural formula Li a Ni b Co c Mn d M1 e O f The Co element can penetrate into the grain boundary of the primary particle, can play a role in repairing the grain boundary, can improve the Young's modulus of the secondary particle, can enhance the electrochemical stability of the surface of the secondary particle, and can improve the cycle life. The coating layer contains B element, B can refine the primary grain, improve the deintercalation ability of lithium ions on the surface, and improve the electrochemical performance of the lithium ion secondary battery.

[0112] The application also provides a method for manufacturing a lithium ion secondary battery, comprising: providing a slurry containing a positive electrode active material, coating the slurry containing the positive electrode active material on a positive electrode current collector to form a positive electrode sheet, wherein the positive electrode active material comprises lithium nickel cobalt manganese oxide, the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%; the positive electrode active material comprises secondary particles, the secondary particles comprise primary particles, the primary particles comprise radial primary particles, in a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a minimum included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°; the secondary particles comprise radial secondary particles, and the number ratio of the radial primary particles to the total number of primary particles in a single radial secondary particle is 60% to 100%; and a separator is arranged between the positive electrode sheet and a negative electrode sheet to form the lithium ion secondary battery.

[0113] In an embodiment of the application, the radial primary particles with a large number ratio make the arrangement of the primary particles in the secondary particles more ordered, and the secondary particles tend to be isotropic. In the process of cyclic charging and discharging, the primary particles in the secondary particles expand and shrink along the (003) crystal plane. The radial primary particles in the radial secondary particles expand or shrink along a direction perpendicular or tending to be perpendicular to the radius, and the stress generated is limited, the mutual extrusion between the primary particles is reduced, the local stress concentration in the radial secondary particles is relatively small, the generated stress is more easily released, the cracking problem of the radial secondary particles is alleviated, and thus the cracking problem of the positive electrode active material is alleviated, thereby being beneficial to improving the cycle performance of the lithium ion secondary battery.

[0114] In an embodiment, the method for preparing the positive electrode active material comprises: providing a solution containing a nickel source, a cobalt source and a manganese source, wherein the molar ratio of the nickel element is greater than or equal to 85% and less than 100% based on the total molar amount of the nickel element, the cobalt element and the manganese element; adding a complexing agent with a concentration of 8.5 mol / L to 10 mol / L and a precipitating agent with a concentration of 2.1 mol / L to 15 mol / L into the solution containing the nickel source, the cobalt source and the manganese source, controlling the pH range to be 8 to 10, and forming a nickel cobalt manganese hydroxide precursor under the condition of 30°C to 50°C, wherein the volume average particle size Dv50 of the nickel cobalt manganese hydroxide precursor is 6 μm to 11 μm; and mixing the nickel cobalt manganese hydroxide precursor with a lithium source, and reacting at 720°C to 890°C for 11 to 15 hours to obtain the positive electrode active material.

[0115] In an embodiment, the nickel source, the cobalt source and the manganese source are a metal salt solution of Ni, Co and Mn, and the metal salt comprises one or more of a sulfate, a nitrate, an oxalate and a chloride of Ni, Co and Mn.

[0116] In an embodiment, the precipitant includes one or more of sodium hydroxide, sodium carbonate, potassium carbonate, potassium hydroxide; the complexing agent includes one or more of ammonia, ammonium chloride, ammonium sulfate, urea, citric acid, EDTA.

[0117] In the embodiment, the positive electrode active material can inherit the morphology of the nickel-cobalt-manganese hydroxide precursor. In the process of preparing the nickel-cobalt-manganese hydroxide precursor by the coprecipitation reaction, the complexing agent has a relatively large concentration and a relatively small pH value, and the balance of the coprecipitation reaction is more inclined to the growth of the precursor material. Therefore, the primary particles of the material have sufficient time to grow into relatively long grains, and thus the primary particles of the obtained precursor tend to grow radially, and the proportion of the radial primary particles in the positive electrode active material is increased.

[0118] In an embodiment, the nickel-cobalt-manganese hydroxide precursor is mixed with a lithium source, and reacted at 720-890°C for 11-15h to obtain the positive electrode active material. In an embodiment, the nickel-cobalt-manganese hydroxide precursor, a lithium source, and a metal doping source are mixed, and reacted at 720-890°C for 11-15h to form a first intermediate product. The first intermediate product is mixed with a first coating source, and reacted at 600-700°C for 5-8h to form a second intermediate product. The first coating source includes a Co source. The second intermediate product is mixed with a second coating source, and reacted at 300-400°C for 5-7h to obtain the positive electrode active material. The second coating source includes a B source. Through the above arrangement, the positive electrode active material with good stability and electrochemical performance can be obtained.

[0119] In an embodiment, the lithium source includes one or two or more of LiOH·H2O, Li2CO3, Li2SO4, LiNO3, LiC2O4, and CH3COOLi. In an embodiment, the Co source includes one or more of CoO, Co(NO3)2, CoCO3, Co(OH)2, and CoOOH. In an embodiment, the B source includes one or more of B2O3, HBO2, LiBO2, and B(OH)3.

[0120] The application also provides a positive electrode active material. The positive electrode active material includes lithium nickel cobalt manganese oxide, and the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%. The positive electrode active material includes secondary particles, and the secondary particles include primary particles. The primary particles include radial primary particles, and in a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a smallest included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°. The secondary particles include radial secondary particles, and the proportion of the number of the radial primary particles is 60%-100% based on the total number of the primary particles in a single radial secondary particle.

[0121] In the embodiment, the radially oriented primary particles in the radially oriented secondary particles are prone to expand or contract along a direction perpendicular or tending to be perpendicular to the radius, and the stress generation is limited, the mutual extrusion between the primary particles is reduced, the local stress concentration degree in the radially oriented secondary particles is relatively small, and the generated stress is more easily released, thereby relieving the cracking problem of the radially oriented secondary particles and the cracking problem of the positive electrode active material.

[0122] The application further provides a preparation method of the positive electrode active material, including: providing a solution containing a nickel source, a cobalt source and a manganese source, wherein the mole percentage of the nickel element is greater than or equal to 85% and less than 100% based on the total mole amount of the nickel element, the cobalt element and the manganese element; adding a complexing agent with a concentration of 8.5 mol / L-10 mol / L and a precipitating agent with a concentration of 2.1 mol / L-15 mol / L into the solution containing the nickel source, the cobalt source and the manganese source, controlling the pH range to be 8-10, and forming a nickel-cobalt-manganese hydroxide precursor under the condition of 30°C-50°C, wherein the volume average particle size Dv50 of the nickel-cobalt-manganese hydroxide precursor is 6 μm-11 μm; mixing the nickel-cobalt-manganese hydroxide precursor with a lithium source, and reacting for 11-15 h under 720°C-890°C to obtain the positive electrode active material. In the embodiment, the positive electrode active material can inherit the morphology of the nickel-cobalt-manganese hydroxide precursor. During the preparation of the nickel-cobalt-manganese hydroxide precursor by the coprecipitation reaction, the complexing agent has a relatively large concentration, the pH value is relatively small, and the balance of the coprecipitation reaction is more inclined to the growth of the precursor material, so that the primary particles of the material have sufficient time to grow into relatively long grains, and therefore the primary particles of the obtained precursor tend to grow radially, and the proportion of the radially oriented primary particles in the positive electrode active material is increased.

[0123] In an embodiment, the positive electrode active material is obtained by mixing the nickel-cobalt-manganese hydroxide precursor with a lithium source and reacting for 11 h-15 h under 720°C-890°C, including: mixing the nickel-cobalt-manganese hydroxide precursor, a lithium source and a metal doping source, reacting for 11 h-15 h under 720°C-890°C to form a first intermediate product; mixing the first intermediate product with a first coating source and reacting for 5 h-8 h under 600°C-700°C to form a second intermediate product, wherein the first coating source includes a Co source; mixing the second intermediate product with a second coating source and reacting for 5 h-7 h under 300°C-400°C to obtain the positive electrode active material, wherein the second coating source includes a B source. Through the above settings, the positive electrode active material with good stability and electrochemical performance can be obtained.

[0124] The application also provides a power consuming device comprising the lithium ion secondary battery and / or the positive electrode active material described above. The power consuming device has the same or similar advantages as the lithium ion secondary battery and / or the positive electrode active material.

[0125] In addition, the lithium ion secondary battery, the battery cell and the power consuming device of the application are described below with appropriate reference to the accompanying drawings.

[0126] In the embodiment of the application, the battery cell refers to the smallest unit of a battery. The battery cell also comprises an electrolyte and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet and mainly functions to prevent short circuit of the positive electrode and the negative electrode and to allow ions to pass through. In the process of charging and discharging of the battery, active ions Li+ are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet.

[0127] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. The positive electrode film layer comprises the positive electrode active material described above in the embodiment of the application.

[0128] For example, the positive electrode current collector has two opposite surfaces in the thickness direction thereof. The positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0129] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can comprise 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, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0130] In some embodiments, the positive electrode film layer can optionally further comprise a binder. For example, the binder can comprise 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.

[0131] In some embodiments, the positive electrode film layer can optionally further comprise a conductive agent. For example, the conductive agent can comprise at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0132] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, 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 a positive electrode current collector, and then performing processes such as drying, cold pressing, and the like to obtain the positive electrode sheet.

[0133] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including the negative electrode active material of the above-mentioned embodiments.

[0134] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0135] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. 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.).

[0136] In some embodiments, the negative electrode 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).

[0137] In some embodiments, the negative electrode film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0138] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na), etc.

[0139] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode 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 a negative electrode current collector, and then performing processes such as drying, cold pressing, and the like to obtain the negative electrode sheet.

[0140] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements.

[0141] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0142] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0143] In some embodiments, the solvent may 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, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0144] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0145] In some embodiments, the lithium-ion secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0146] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0147] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into a cell assembly using a winding or stacking process.

[0148] In some implementations, such as Figure 2 As shown, the battery cell 10 may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned cell assembly 11 and electrolyte. The outer packaging includes an end cap 12, a housing 13, and other functional components.

[0149] The end cover 12 refers to a component that covers the opening of the shell 13 to isolate the internal environment of the battery cell 10 from the external environment. Without limitation, the shape of the end cover 12 can be adapted to the shape of the shell 13 to fit the shell 13. Optionally, the end cover 12 can be made of a material with certain hardness and strength, such as aluminum alloy, so that the end cover 12 is less likely to deform when subjected to extrusion collision, allowing the battery cell 10 to have higher structural strength and improved safety performance. The end cover 12 can be provided with functional components such as electrode terminals 12a. The electrode terminals 12a can be used to electrically connect with the cell assembly 11 for outputting or inputting the electrical energy of the battery cell 10. In some embodiments, the end cover 12 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 10 reaches a threshold value. The material of the end cover 12 can also 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 thereon. In some embodiments, an insulating member (not shown in the figure) can also be provided on the inner side of the end cover 12, which can be used to isolate the electrical connection components in the shell 13 from the end cover 12 to reduce the risk of short circuit. Exemplarily, the insulating member can be plastic, rubber, etc.

[0150] The shell 13 is a component for fitting the end cover 12 to form the internal environment of the battery cell 10, wherein the formed internal environment can be used to accommodate the cell assembly 11, the electrolyte and other components. The shell 13 and the end cover 12 can be independent components, and an opening can be provided on the shell 13, and the end cover 12 is made to cover the opening to form the internal environment of the battery cell 10. Without limitation, the end cover 12 and the shell 13 can also be integrated, specifically, the end cover 12 and the shell 13 can form a common connecting surface before other components enter the shell, and when it is necessary to seal the inside of the shell 13, the end cover 12 is made to cover the shell 13. The shell 13 can be various shapes and sizes, such as cuboid, cylinder, hexagonal prism, etc. Specifically, the shape of the shell 13 can be determined according to the specific shape and size of the cell assembly 11. The material of the shell 13 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 thereon.

[0151] The shell 13 can contain one or more cell assemblies 11. The parts of the positive and negative electrode sheets without active material each constitute a tab 11a. The positive and negative tabs can be located together at one end of the main body or at two ends of the main body respectively. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs 11a are connected to the electrode terminals to form a current loop.

[0152] Please refer to Figure 3 , Figure 3A schematic diagram of a lithium-ion secondary battery according to some embodiments of the present application is shown in FIG. 1. The lithium-ion secondary battery 100 includes a housing 20 and a battery cell 10, which is accommodated in the housing 20. The housing 20 is configured to provide a space for accommodating the battery cell 10, and can have various configurations. In some embodiments, the housing 20 can include a first part 21 and a second part 22, which are coupled to each other to define a space for accommodating the battery cell 10. The second part 22 can have a hollow structure with an open end, and the first part 21 can have a plate-like structure, which is coupled to the open end of the second part 22 to define the space for accommodating the battery cell 10. Alternatively, the first part 21 and the second part 22 can each have a hollow structure with an open end, and the open end of the first part 21 is coupled to the open end of the second part 22. Of course, the housing 20 formed by the first part 21 and the second part 22 can have various shapes, such as a cylindrical shape, a cuboid shape, etc.

[0153] In the lithium-ion secondary battery 100, the battery cell 10 can be a plurality of battery cells 10, which can be connected in series, in parallel, or in a mixed manner. The mixed manner means that the plurality of battery cells 10 are connected in series and in parallel. The plurality of battery cells 10 can be directly connected in series, in parallel, or in a mixed manner, and the plurality of battery cells 10 can be accommodated in the housing 20. Alternatively, the lithium-ion secondary battery 100 can include a plurality of battery modules, each of which includes a plurality of battery cells 10 connected in series, in parallel, or in a mixed manner, and the plurality of battery modules can be connected in series, in parallel, or in a mixed manner to form a whole, which is accommodated in the housing 20. The lithium-ion secondary battery 100 can further include other structures, such as a busbar for electrically connecting the plurality of battery cells 10.

[0154] The battery cell 10 can have a cylindrical shape, a flat shape, a cuboid shape, or other shapes.

[0155] In some embodiments, the lithium-ion secondary battery 100 can be assembled into a battery module, and the number of batteries included in the battery module can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0156] In addition, the application also provides a power-using device, which comprises at least one of the lithium ion secondary battery and / or the battery cell provided by the application. The lithium ion secondary battery or the battery pack can be used as a power supply of the power-using device, or can be used as an energy storage unit of the power-using device. The power-using device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0157] As the power-using device, the lithium ion secondary battery and / or the battery can be selected according to the use requirement thereof.

[0158] Figure 4 As shown in the figure, the power-using device is a vehicle such as a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle. A structure schematic diagram of the specifically provided vehicle 1000 is shown. The vehicle 1000 is internally provided with a lithium ion secondary battery 100, which can be arranged at the bottom, the head or the tail of the vehicle 1000. The lithium ion secondary battery 100 can be used for power supply of the vehicle 1000, for example, the lithium ion secondary battery 100 can be used as an operating power supply of the vehicle 1000. The vehicle 1000 can further comprise a controller 200 and a motor 300, and the controller 200 is used to control the lithium ion secondary battery 100 to supply power to the motor 300, for example, to meet the power requirement of the vehicle 1000 during starting, navigation and driving.

[0159] In some embodiments of the application, the lithium ion secondary battery 100 can not only be used as an operating power supply of the vehicle 1000, but also be used as a driving power supply of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0160] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0161] Embodiment 1

[0162] Preparation method of the positive electrode active material:

[0163] S1: a high-nickel ternary material substrate precursor is prepared by a coprecipitation reaction: a Ni, Co, and Mn sulfate solution with a concentration of 5 mol / L is prepared according to the molar ratio of Ni, Co, and Mn in the high-nickel ternary material substrate, which is 0.917:0.07:0.01; a NaOH solution with a concentration of 10 mol / L and an ammonia solution with a concentration of 15 mol / L are prepared; 20% of pure water by volume is added to a reaction kettle; the three solutions are pumped into the reaction kettle; the flow rates of the sulfate and the ammonia solution are kept constant (0.5 L / h) during the reaction; the stirring speed is set to 1000 r / min; the reaction is carried out at a constant temperature, and the temperature range is 50°C; a precipitant (sodium hydroxide) and a complexing agent (ammonia) are added to adjust the pH in the reaction kettle; the pH is kept constant during the reaction, and the pH is 9.5; after the reaction is completed, centrifugation, washing, filtration, and drying are performed to obtain the high-nickel ternary material substrate precursor; the volume average particle size Dv50 of the high-nickel ternary material substrate precursor is 11 μm.

[0164] S2: the high-nickel ternary material precursor prepared in step S1 is mixed with LiOH·H2O and ZrO2 powder with a molar ratio of 0.003 in a plowshare mixer, and first sintering is performed to obtain a first lithium nickel cobalt manganese oxide. The total metal molar ratio Li / Me of LiOH·H2O to the high-nickel ternary precursor substrate is 1.05, Me is the total molar of Ni, Co, and Mn elements; the first sintering temperature is 730°C; the first sintering time is 15 h; and the first sintering atmosphere is O2.

[0165] S3: the first lithium nickel cobalt manganese oxide obtained in step S2 is mixed with Co(OH)2, and second sintering is performed, wherein the addition amount of Co(OH)2 is 12000 ppm of the mass of Co element to the first lithium nickel cobalt manganese oxide; the second sintering temperature is 600°C; the second sintering time is 8 h; the second sintering atmosphere is O2; and the second lithium nickel cobalt manganese oxide, that is, the first lithium nickel cobalt manganese oxide coated with cobalt oxide, is obtained.

[0166] S4: the second lithium nickel cobalt manganese oxide obtained in step S3 is mixed with B2O3, and third sintering is performed; the addition amount of B2O3 is 800 ppm of the mass of B element to the second lithium nickel cobalt manganese oxide; the third sintering temperature is 300°C; the third sintering time is 6 h; the third sintering atmosphere is O2; and the third lithium nickel cobalt manganese oxide is obtained.

[0167] In the embodiments of the present application, the third lithium nickel cobalt manganese oxide is used as a positive electrode active material, Li 1.02 Ni 0.917 Co 0.07 Mn 0.01 Zr 0.003 O2, coated with cobalt oxide and boron oxide.

[0168] The preparation method of the positive electrode sheet comprises the following steps:

[0169] The positive electrode active material, the conductive carbon black (Super-P) and the polyvinylidene fluoride (PVDF) are mixed with N,N-dimethylpyrrolidone (NMP) at a weight ratio of 96.5:3:1.5, and the mixture is stirred uniformly to obtain a slurry of the positive electrode sheet. The slurry of the positive electrode sheet is uniformly coated on both sides of the aluminum foil. The sheet is cold-pressed and sliced to obtain the positive electrode sheet.

[0170] The preparation method of the negative electrode sheet comprises the following steps:

[0171] In the embodiment of the present application, the negative electrode active material, the conductive agent, the thickening agent and the binder are mixed with deionized water to form a slurry of the negative electrode sheet. Specifically, in the embodiment of the present application, the negative electrode active material comprises a silicon-based material and a carbon-based material. The carbon-based material is artificial graphite, and the silicon-based material is nano-silicon. The conductive agent is conductive carbon black (Super-P) and carbon nanotubes. The thickening agent is sodium carboxymethyl cellulose (CMC-Na). The binder is styrene-butadiene rubber (SBR).

[0172] Specifically, in the embodiment of the present application, the artificial graphite, the conductive carbon black (Super-P), the carbon nanotubes, the sodium carboxymethyl cellulose (CMC-Na), the styrene-butadiene rubber (SBR) are mixed with deionized water at a weight ratio of 96.9:0.5:0.1:1:1.5, and the mixture is stirred uniformly to obtain a slurry of the coated negative electrode sheet. The viscosity can be adjusted by deionized water during the stirring process. Then, the slurry is coated on both sides of the negative current collector with a certain width, and the negative electrode sheet is obtained after cold-pressing and slicing. In the embodiment of the present application, the negative current collector is a 6μm thick copper foil, and the material and thickness of the negative current collector are not limited in the embodiment of the present application.

[0173] The preparation method of the lithium ion secondary battery comprises the following steps:

[0174] The positive electrode sheet, the separator and the negative electrode sheet are wound into a cell assembly, and the lithium ion secondary battery is obtained after the tab welding, the packaging of the aluminum shell, the injection of the electrolyte, the packaging formation and the air extraction. The width, the thickness and the height of the cell assembly are 148mm, 28mm and 98mm respectively, and the capacity is 60Ah. The injected electrolyte is a 1mol / L LiPF6 solution, and the solvent of the LiPF6 solution is ethylene carbonate (EC) and dimethyl carbonate (DMC). The volume ratio of the ethylene carbonate (EC) to the dimethyl carbonate (DMC) is 1:2. In the embodiment of the present application, the separator is a 7μm thick polyethylene (PE).

[0175] The lithium ion secondary battery obtained by the embodiment of the application comprises a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises lithium nickel cobalt manganese oxide, the molar content of nickel element in all transition metal elements is 91.7%, the positive electrode active material comprises secondary particles, the secondary particles comprise primary particles, and the average particle size of the primary particles is 600 nm. The primary particles comprise radial primary particles, in a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a smallest included angle between the long axis direction of the primary particles and the radial direction of the secondary particles less than or equal to 20°, and the secondary particles comprise radial secondary particles, the number ratio of the radial primary particles to the total number of primary particles in a single radial secondary particle is 86.7%, the Young's modulus of the radial secondary particles is 320 GPa, and the number ratio of the radial secondary particles is 98%.

[0176] Embodiment 2-8

[0177] Other differences from embodiment 1 are shown in Table 1 and Table 2, and other aspects are similar to embodiment 1.

[0178] Comparative example

[0179] Preparation method of positive electrode active material:

[0180] S1: A high-nickel ternary material substrate precursor is prepared by a coprecipitation reaction: a Ni, Co and Mn sulfate solution with a concentration of 5 mol / L is prepared according to the molar ratio of Ni, Co and Mn elements in the high-nickel ternary material substrate of 0.917:0.07:0.01, a NaOH solution with a concentration of 2 mol / L and an ammonia solution with a concentration of 2 mol / L are prepared at the same time, 20% of pure water by volume is added to the reaction kettle, and the above three solutions are pumped into the reaction kettle. The flow rates of the sulfate and ammonia solution are kept constant (0.5 L / h) during the reaction. The stirring speed is set to 1000 r / min, the reaction is carried out at a constant temperature, the temperature range is 50°C, the pH in the reaction kettle is adjusted by adding a precipitating agent (sodium hydroxide) and a complexing agent (ammonia), and the pH is kept constant during the reaction, and the pH is 11. After the reaction is completed, centrifugation, washing, filtration and drying are carried out to obtain the high-nickel ternary material substrate precursor, and the volume average particle size Dv50 of the high-nickel ternary material substrate precursor is 11 μm. When the complexing agent concentration is relatively small and the pH value is relatively large, the coprecipitation reaction is more inclined to the nucleation of the precursor material rather than the growth, and excessive nucleation leads to insufficient time for the primary particles of the material to grow into longer grains, so that the obtained precursor primary particles are randomly accumulated rather than radially grown.

[0181] S2: The high-nickel ternary material precursor prepared in step S1 is mixed with LiOH H2O and ZrO2 powder in a mole ratio of 0.003 in a plowshare mixer, and first sintering is performed to obtain a first lithium nickel cobalt manganese oxide. The mole ratio of LiOH H2O to the total metal in the high-nickel ternary precursor substrate is 1.05, Li / Me, where Me is the total mole of Ni, Co, and Mn elements. The first sintering temperature is 730°C, the first sintering time is 15 h, and the first sintering atmosphere is O2.

[0182] S3: The first lithium nickel cobalt manganese oxide obtained in step S2 is mixed with Co(OH)2, and second sintering is performed. The amount of Co(OH)2 added is 12000 ppm of the mass of Co element with respect to the first lithium nickel cobalt manganese oxide. The second sintering temperature is 600°C, the second sintering time is 8 h, the second sintering atmosphere is O2, and a second lithium nickel cobalt manganese oxide, i.e., a first lithium nickel cobalt manganese oxide coated with cobalt oxide on the surface, is obtained.

[0183] S4: The second lithium nickel cobalt manganese oxide obtained in step S3 is mixed with B2O3, and third sintering is performed. The amount of B2O3 added is 800 ppm of the mass of B element with respect to the second lithium nickel cobalt manganese oxide. The third sintering temperature is 300°C, the third sintering time is 6 h, the third sintering atmosphere is O2, and a third lithium nickel cobalt manganese oxide is obtained.

[0184] In Comparative Example 1, the third lithium nickel cobalt manganese oxide is used as a positive electrode active material, Li 1.02 Ni 0.917 Co 0.07 Mn 0.01 Zr 0.003 O2@CoO@B2O3, coated with cobalt oxide and boron oxide on the surface, Figure 5 The cross-sectional scanning electron microscope (SEM) photo of the secondary particles provided for Comparative Example 1 of the present application is shown in the figure, and the arrangement of the primary particles is relatively disordered.

[0185] The lithium ion secondary batteries of Examples 1-7 and Comparative Example 1 above are subjected to battery performance testing. The positive electrode active material is subjected to standard testing.

[0186] (1) In the radial secondary particles, the number ratio of the radial primary particles is:

[0187] The sample is prepared according to the ion milling scanning electron microscope (CP-EDS) sample preparation standard. The ion-thinned sample is observed under SEM, and a total of 50 secondary particles with a particle size of 6-15 μm are photographed. The number ratio of the radial primary particles in the 50 secondary particles is counted, and the average value of the radial primary particle ratio in the 50 secondary particles is taken.

[0188] (2) Young's modulus:

[0189] The Young's modulus of the secondary particles was determined using a Dimension Icon SPM (scanning probe electron microscope) of Bruker, and the determination method was as follows:

[0190] 1) The SPM test system was calibrated using a standard sample.

[0191] 2) Sample preparation: The positive electrode active material powder was dispersed with alcohol, placed in an ultrasonic oscillator, and dropped onto a silicon substrate using a pipette.

[0192] 3) Sample loading: The silicon substrate was attached to the metal sample holder of the instrument with double-sided tape, the magnetic sample disc was fixed on the sample stage at the appropriate position, the sample holder with the silicon substrate was adsorbed on the magnetic sample disc, and the sample surface was focused.

[0193] 4) Sample scanning: The sample surface was scanned in the Contact mode, the scanning range was set to 500 nm, the scanning rate was 0.977 Hz, the probe DNISP-HS was used, the scanning image was saved, and the force curve of the sample was obtained: the force-probe sample distance relationship (F-D curve). After the probe contacted the sample, the distance D between the probe and the sample corresponded to the deformation amount of the sample.

[0194] 5) Calculation of Young's modulus: The relationship between the force and the deformation amount of the sample in the F-D curve was fitted and calculated by the DMT (Derjaguin-Muller-Toporov) model to obtain the Young's modulus of the sample.

[0195] (3) Number ratio of radial secondary particles in secondary particles:

[0196] Randomly count 50 secondary particles, and test the number ratio of radial primary particles and the Young's modulus, and count the number of radial secondary particles. The number ratio of radial secondary particles in secondary particles was obtained by comparing the number of radial secondary particles with 50.

[0197] (4) Average particle size of primary particles:

[0198] The positive electrode active material was tested using a ZEISS sigma 300 scanning electron microscope, and then the sample morphology was observed according to the standard JY / T010-1996.

[0199] Software name: LIBMAS lithium-ion battery material microscopic intelligent analysis system. The scanning electron microscope image of the positive electrode active material is automatically AI-identified by the LIBMAS lithium-ion battery material microscopic intelligent analysis system, the particle contour, particle number, number, area, maximum caliper diameter, average, and manual intervention are drawn. The average particle size of primary particles = the sum of all measured particle sizes / the sum of all measured primary particle numbers.

[0200] (5) Measurement of the long axis length of primary particles:

[0201] Ion milling scanning electron microscopy (CP-EDS) test is performed on the secondary particles of the positive electrode active material, and the cross-sectional scanning electron microscope image of the secondary particles with a particle size of 6-15 μm is taken, and the long axis length of 50 primary particles is measured.

[0202] (6) Specific surface area test of positive electrode active material:

[0203] The sample to be tested is prepared into a uniform powder or particle, then placed in a vacuum and set to a specific treatment temperature to remove surface-adsorbed gas and moisture. The sample is placed in an adsorption instrument, the liquid nitrogen temperature is set to 77.35k, and the adsorption isotherm is measured by gradually increasing the pressure of nitrogen. According to the adsorption isotherm data, the slope and intercept of the adsorption isotherm are obtained by fitting using the BET equation. According to the parameters in the BET equation, the specific surface area of the sample is calculated.

[0204] (7) Cross-sectional porosity and cross-sectional average pore size test of positive electrode active material:

[0205] The sample powder is adhered to an aluminum foil using PVDF, and is placed under an argon ion beam thinner for cutting. The cut section is placed under a scanning electron microscope for observation, and a SEM image of the material cross-section is taken. The pore portion is identified and the area is calculated using graphics software, and then the porosity is calculated using the ratio of pore area to total area.

[0206] The pore size is directly measured using the SEM image, 50 pore sizes are measured, and the average value is obtained, i.e. the cross-sectional average pore size.

[0207] (8) Volume average particle size Dv50 test:

[0208] Device model: Malvern 2000 laser particle size analyzer, reference standard procedure: GB / T19077-2016 / ISO 13320:2009, specific test procedure: take the appropriate amount of sample to be tested (the sample concentration ensures that the light intensity is 8% to 12%), add 20 mL of deionized water, and simultaneously super 5 min (53 KHz / 120 W) to ensure that the sample is completely dispersed, and then determine the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0209] (9) Lithium ion secondary battery cycle capacity retention rate test:

[0210] The specific test conditions are: at 25°C, 1 / 3C mark (nominal capacity) constant current charging to the end voltage 4.4V, then constant voltage charging to 0.05C mark, standing for 5 min, then discharging to the discharge cut-off voltage 2.5V at 1 / 3C mark, obtaining the discharge energy E and capacity C, the obtained capacity is recorded as the initial capacity C0. Repeat the above steps for the same lithium ion secondary battery, and record the discharge capacity Cn of the battery after the nth cycle, then the battery capacity retention rate Pn = Cn / C0 x 100% after each cycle. In this test process, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2, …, the 100th cycle corresponds to n = 100, and the capacity retention rate after 100 cycles is tested.

[0211]

[0212]

[0213] According to the test results in Table 2, compared with the comparative examples with low radial primary particle number ratio, the positive electrode active materials of embodiments 1-8 provided by the application exhibit higher Young's modulus, and the corresponding lithium ion secondary batteries have higher cycle retention rates, because the positive electrode active materials provided by the application include a large number of radial primary particles, and therefore exhibit higher structural stability, thereby improving the cycle performance of the battery.

[0214] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A lithium-ion secondary battery, characterized by comprising: The positive electrode sheet, the negative electrode sheet, and an electrolyte; The positive electrode 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 85% and less than 100%; The positive electrode active material includes secondary particles, the secondary particles include primary particles, and the primary particles include radial primary particles, in a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a minimum angle between the long axis direction of the primary particles and the radial direction of the secondary particles being less than or equal to 20°; The secondary particles include radial secondary particles, and the proportion of the number of the radial primary particles to the total number of the primary particles in a single radial secondary particle is 60% to 100%.

2. The lithium-ion secondary battery according to claim 1, characterized by The Young's modulus of the radial secondary particles is 2 GPa to 400 GPa.

3. The lithium-ion secondary battery according to claim 1 or 2, characterized by The proportion of the number of the radial primary particles to the total number of the primary particles in a single radial secondary particle is 75% to 95%.

4. The lithium-ion secondary battery according to claim 1 or 2, characterized by The Young's modulus of the radial secondary particles is 10 GPa to 200 GPa.

5. The lithium-ion secondary battery according to any one of claims 1, characterized by The average particle size of the primary particles is 50 nm to 2 μm.

6. The lithium-ion secondary battery according to claim 1 or 2 or 5, characterized by, In the positive electrode active material, the proportion of the number of the radial secondary particles to the total number of the secondary particles is 80% to 100%.

7. The lithium-ion secondary battery according to claim 1 or 2 or 5, characterized by, In the cross-sectional scanning electron microscope image of the secondary particles, the long axis size of the primary particles is 0.3 μm to 3 μm.

8. The lithium-ion secondary battery according to claim 1, characterized by The volume average particle size Dv50 of the secondary particles is 6 μm to 15 μm; and / or, The specific surface area of the positive electrode active material is 0.2 m 2 / g ~ 1.0 m 2 / g; and / or, The cross-sectional porosity of the positive electrode active material is 2% to 8%; and / or, The cross-sectional average pore size of the positive electrode active material is 0.1 μm to 2 μm.

9. The lithium ion secondary battery according to claim 1, wherein The content of nickel elements of the radial secondary particles is equal from the center to the surface area, or the difference in the content of nickel elements from the center to the surface area is less than or equal to 2%; The content of manganese elements of the radial secondary particles is equal from the center to the surface area, or the difference in the content of manganese elements from the center to the surface area is less than or equal to 0.5%.

10. The lithium-ion secondary battery according to claim 1 or 2 or 5 or 8 or 9, characterized by, The positive electrode active material includes a material of structural formula Li a Ni b Co c Mn d M1 e O f wherein the M1 element includes one or more of Zr, Ti, Y, Sb, W, Mo, Ba, Ta, Nb, Al, 0.9≤a≤1.2, 0.85≤b<1, 0.01≤c≤0.09, 0.01≤d≤0.05, 0.001≤e≤0.005, 1.6≤f≤2.4, b+c+d+e=1.

11. The lithium-ion secondary battery according to claim 10, characterized by The positive electrode active material further includes a coating layer on a surface of the material of the structural formula Li a Ni b Co c Mn d M1 e O f The coating layer includes a Co element or / and a B element.

12. A method for manufacturing a lithium-ion secondary battery, characterized by comprising: The positive electrode sheet, the negative electrode sheet, and an electrolyte; The positive electrode 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 85% and less than 100%; The isolation film is arranged between the positive electrode tab and the negative electrode tab to form the lithium ion secondary battery.

13. The method of producing a lithium-ion secondary battery according to claim 12, characterized by, The preparation method of the positive electrode active material comprises: a solution containing a nickel source, a cobalt source and a manganese source is provided, wherein, based on the total molar amount of nickel element, cobalt element and manganese element, the molar proportion of the nickel element is greater than or equal to 85% and less than 100%; a complexing agent with a concentration of 8.5 mol / L to 10 mol / L and a precipitating agent with a concentration of 2.1 mol / L to 15 mol / L are added to the solution containing the nickel source, the cobalt source and the manganese source, the pH is controlled in the range of 8 to 10, and a nickel-cobalt-manganese hydroxide precursor is formed under the condition of 30°C to 50°C, the volume average particle size Dv50 of the nickel-cobalt-manganese hydroxide precursor being 6 μm to 11 μm; the nickel-cobalt-manganese hydroxide precursor is mixed with a lithium source, and reacted at 720°C to 890°C for 11 to 15 hours to obtain the positive electrode active material.

14. The method of producing a lithium-ion secondary battery according to claim 13, wherein the nickel-cobalt-manganese hydroxide precursor is mixed with a lithium source, and reacted at 720°C to 890°C for 11 to 15 hours to obtain the positive electrode active material. the nickel-cobalt-manganese hydroxide precursor, a lithium source and a metal doping source are mixed, and reacted at 720°C to 890°C for 11 to 15 hours to form a first intermediate product; the first intermediate product is mixed with a first coating source, and reacted at 600°C to 700°C for 5 to 8 hours to form a second intermediate product, the first coating source comprising a Co source; the second intermediate product is mixed with a second coating source, and reacted at 300°C to 400°C for 5 to 7 hours to obtain the positive electrode active material, the second coating source comprising a B source.

15. A positive electrode active material, characterized by, The positive electrode active material comprises lithium nickel cobalt manganese oxide, and the molar content of nickel element in all transition metal elements is greater than or equal to 85% and less than 100%. The positive electrode active material comprises secondary particles, the secondary particles comprise primary particles, and the primary particles comprise radial primary particles, in a cross-sectional scanning electron microscope image of the secondary particles, the radial primary particles are primary particles with a minimum included angle between the long axis direction of the primary particles and the radial direction of the secondary particles being less than or equal to 20°. The secondary particles comprise radial secondary particles, and the number proportion of the radial primary particles in the total number of the primary particles in a single radial secondary particle is 60% to 100%.

16. The positive electrode active material according to claim 15, characterized by The radial secondary particles have a Young's modulus of 2 GPa to 400 GPa.

17. A method for producing a positive electrode active material, characterized by, comprises: a solution containing a nickel source, a cobalt source and a manganese source is provided, wherein, based on the total molar amount of nickel element, cobalt element and manganese element, the molar proportion of the nickel element is greater than or equal to 85% and less than 100%; a complexing agent with a concentration of 8.5 mol / L to 10 mol / L and a precipitating agent with a concentration of 2.1 mol / L to 15 mol / L are added to the solution containing the nickel source, the cobalt source and the manganese source, the pH is controlled in the range of 8 to 10, and a nickel-cobalt-manganese hydroxide precursor is formed under the condition of 30°C to 50°C, the volume average particle size Dv50 of the nickel-cobalt-manganese hydroxide precursor being 6 μm to 11 μm; Mixing the nickel-cobalt-manganese hydroxide precursor with a lithium source, and reacting at 720 DEG C to 890 DEG C for 11 to 15 hours to obtain the positive electrode active material, the positive electrode active material comprising lithium nickel cobalt manganese oxide, the molar content of nickel element in all transition metal elements being greater than or equal to 85% and less than 100%; the positive electrode active material comprising secondary particles, the secondary particles comprising primary particles, the primary particles comprising radial primary particles, in the cross-sectional scanning electron microscope picture of the secondary particles, the radial primary particles being primary particles with the minimum included angle between the long axis direction of the primary particles and the radial direction of the secondary particles being less than or equal to 20 DEG ; the secondary particles comprising radial secondary particles, the number ratio of the radial primary particles to the total number of the primary particles in a single radial secondary particle being 60% to 100%.

18. The method of producing a positive electrode active material according to claim 17, characterized by, The mixing of the nickel-cobalt-manganese hydroxide precursor with a lithium source, and reacting at 720 DEG C to 890 DEG C for 11 to 15 hours to obtain the positive electrode active material comprises: Mixing the nickel-cobalt-manganese hydroxide precursor, a lithium source and a metal doping source, and reacting at 720 DEG C to 890 DEG C for 11 to 15 hours to form a first intermediate product; Mixing the first intermediate product with a first coating source, and reacting at 600 DEG C to 700 DEG C for 5 to 8 hours to form a second intermediate product, the first coating source comprising a Co source; Mixing the second intermediate product with a second coating source, and reacting at 300 DEG C to 400 DEG C for 5 to 7 hours to obtain the positive electrode active material, the second coating source comprising a B source.

19. An electrical device, comprising: The lithium ion secondary battery prepared by the manufacturing method of the lithium ion secondary battery according to any one of claims 1 to 11 and / or the manufacturing method of the positive electrode active material according to claim 15 or 16 and / or the manufacturing method of the positive electrode active material according to claim 17 or 18.

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