Positive electrode active material, preparation method, positive electrode plate, battery and electric equipment

Abstract

The invention relates to the technical field of batteries, in particular to a positive active material, a preparation method, a positive pole piece, a battery and electric equipment. The positive electrode active material comprises a single-crystal lithium nickel cobalt manganese oxide doped with an element M, the single-crystal lithium nickel cobalt manganese oxide has a first region close to the center and a second region close to the outer layer, and the ratio of the average molar content of the element M in unit volume of the second region to the average molar content of the element M in unit volume of the first region is (2-10): 1, the M element comprises one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al. Through element distribution, a stable doping layer can be constructed at the position, close to the surface, of the single-crystal lithium nickel cobalt manganese oxide particles, so that phase change of the positive electrode active material in the charging and discharging process of the battery is inhibited, the structural stability of the positive electrode active material is improved, the cycle life of the battery is prolonged, and the capacity retention rate of the battery is increased.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to positive electrode active materials, preparation methods, positive electrode sheets, batteries and electrical equipment. Background Art

[0002] With the development of modern technology, lithium-ion batteries are considered the green and environmentally friendly battery of choice due to their high energy density, long cycle life, and environmental friendliness. Lithium-ion batteries are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in electric vehicles, power tools, military equipment, and aerospace applications.

[0003] Ternary nickel-cobalt-manganese oxide (NiCoO) materials have attracted considerable attention as positive electrode active materials due to their high energy density, excellent cycling performance, high voltage platform, good thermal stability, and long cycle life. However, ternary NiCoO materials suffer from poor structural stability during cycling, resulting in reduced cycle life and reversible capacity of the battery. Summary of the Invention

[0004] In view of this, the main technical problem to be solved by this application is the problem of reduced structural stability of ternary nickel cobalt manganese oxide materials during the cycle process, thereby providing positive electrode active materials, preparation methods, positive electrode plates, batteries and electrical equipment, which can improve the structural stability of ternary nickel cobalt manganese oxide materials as positive electrode materials during the cycle process, thereby improving the cycle life and capacity retention rate of the battery.

[0005] In order to solve the above technical problems, the first technical solution adopted in the present application is: providing a positive electrode active material, the positive electrode active material includes a single crystal lithium nickel cobalt manganese oxide doped with the M element, the particle size of a single particle of the single crystal lithium nickel cobalt manganese oxide is d, the geometric center of the single particle is the center of the circle, the area with a radius of 0.2d is the first area, and the area with a thickness of 0.1d on the surface of the single particle toward the geometric center is the second area; the ratio of the average molar content of the M element per unit volume of the second area to the average molar content of the M element per unit volume of the first area is (2-10):1; the M element includes one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al. By doping a larger amount of M element in the second region of the single-crystalline lithium nickel cobalt manganese oxide particles, a stable doping layer can be constructed near the surface of the single-crystalline lithium nickel cobalt manganese oxide particles, thereby stabilizing the surface structure of the single-crystalline lithium nickel cobalt manganese oxide; the surface structure can inhibit the phase change of the positive electrode active material during the charging and discharging process of the battery, thereby reducing the cracks caused by stress during the phase change, inhibiting the side reaction between the positive electrode active material and the electrolyte, and improving the structural stability of the positive electrode active material; in the embodiment of the present application, by controlling the ratio of the average molar content of the M element per unit volume of the second region and the second region within the above range, the structural stability of the single-crystalline lithium nickel cobalt manganese oxide in the embodiment of the present application is better, which can improve the cycle life and capacity retention rate of the battery.

[0006] Furthermore, since the doping amount of M element in the first region of the single crystal lithium nickel cobalt manganese oxide particles is relatively small, the amount of doping material used can be reduced, thereby reducing costs during industrial mass production, while helping to maintain the gram capacity of the positive electrode active material.

[0007] In one embodiment, the ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region is (5-10):1. Through the above configuration, the doping amount of the M element in the first region of the single crystal lithium nickel cobalt manganese oxide particles can be further reduced, thereby further reducing the amount of dopant used and increasing the gram capacity of the positive electrode active material.

[0008] In one embodiment, the average molar content of the M element per unit volume decreases in a step-wise manner from the surface of a single particle to the geometric center. During the charge and discharge process of the battery, the surface structure of the single crystal lithium nickel cobalt manganese oxide, which is used as the positive electrode active material, will preferentially undergo a phase change. The M element presents the above distribution in the particles, which can construct a stable doping layer on the surface of the particles, which is beneficial to improving the stability of the surface structure and inhibiting the phase change of the positive electrode active material. At the same time, the M element inside the particles can also inhibit the phase change occurring inside, thereby improving the structural stability of the positive electrode active material. In the embodiment of the present application, by setting the M element to present the above distribution in the particles, the structural stability of the positive electrode active material can be improved, and at the same time, the doping amount of the M element can be reduced, thereby increasing the gram capacity of the positive electrode active material.

[0009] In one embodiment, the M element includes at least three elements: Zr, Al, and Y, or three elements: Zr, Al, and Nb. This configuration can combine the advantages of different M elements, thereby improving the structural stability of the positive electrode active material while expanding the active ion transmission channel.

[0010] In one embodiment, the structure of the single crystal lithium nickel cobalt manganese oxide doped with M element includes Li 1+x (Ni a Co b Mn c ) 1-d M d O 2-y A y , A comprises one or more of S, N, F, Cl, Br, and I, -0.05 ≤ x ≤ 0.5, 0.3 ≤ a ≤ 0.7, 0.02 ≤ b ≤ 0.15, a + b + c = 1, 0 < d ≤ 0.1, and 0 ≤ y < 0.2. The single-crystal lithium nickel cobalt manganese oxide of the above structural formula possesses the fundamental advantages of a ternary positive electrode active material while also exhibiting excellent structural stability.

[0011] In one embodiment, the positive electrode active material further includes a coating layer coated on the surface of the single-crystalline lithium nickel cobalt manganese oxide doped with the M element. The coating layer contains a Q element, which includes one or more of titanium, zirconium, aluminum, and tungsten. Providing the coating layer on the surface of the single-crystalline lithium nickel cobalt manganese oxide reduces direct contact between the electrolyte and the positive electrode active material, inhibits side reactions between the electrolyte and the positive electrode active material, improves the stability of the positive electrode active material, and suppresses the increase in the cyclic DC internal resistance.

[0012] In one embodiment, the mass ratio of the sum of the mass of the M element in the first region and the second region to the mass ratio of the Q element in the coating layer is 1:(0.25-1.4). Alternatively, the mass ratio of the sum of the mass of the M element in the first region and the second region to the mass ratio of the Q element in the coating layer is 1:(0.6-0.8). By controlling the content of the Q element in the coating layer, on the one hand, direct contact between the electrolyte and the positive electrode active material can be effectively blocked. On the other hand, by controlling the mass ratio of the M element to the Q element, the stability of the single crystal lithium nickel cobalt manganese oxide is enhanced, and the capacity of the positive electrode active material is improved.

[0013] In one embodiment, the average particle size of the primary particles of the single-crystalline lithium nickel cobalt manganese oxide doped with the element M is greater than or equal to 600 nm. Within this average particle size range, suitable space can be provided for gradient doping of the element M, while also ensuring that the specific surface area of ​​the single-crystalline lithium nickel cobalt manganese oxide is within an optimal range, and the structural stability of the single-crystalline lithium nickel cobalt manganese oxide is enhanced.

[0014] The average particle size of the primary particles is common knowledge in the art, has a commonly known meaning in the art, and can be measured by methods and instruments in the art.

[0015] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising: mixing single-crystalline lithium nickel cobalt manganese oxide and a compound containing an M element to obtain an intermediate product; sintering the intermediate product at a first temperature to obtain single-crystalline lithium nickel cobalt manganese oxide doped with the M element; the first temperature is 550°C-750°C, and the M element includes one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al. In the embodiment of the present application, a single-crystal lithium nickel cobalt manganese oxide doped with the M element is obtained through a sintering process; at the same time, since the first temperature during sintering is relatively low, the kinetics of the M element doping is weakened, so that the M element is gradient-doped, and the average molar content of the M element per unit volume decreases step-by-step from the surface to the geometric center of the single-crystal lithium nickel cobalt manganese oxide particle, so that a stable doping layer can be constructed near the surface of the single-crystal lithium nickel cobalt manganese oxide particle, thereby stabilizing the surface structure of the single-crystal lithium nickel cobalt manganese oxide; the surface structure can inhibit the phase change of the positive electrode active material during the charge and discharge process of the battery, thereby reducing cracks caused by stress during the phase change, inhibiting the side reaction of the positive electrode active material with the electrolyte, and improving the structural stability of the positive electrode active material, thereby improving the cycle life and capacity retention rate of the battery.

[0016] In one embodiment, the step of mixing a single crystal lithium nickel cobalt manganese oxide with a compound containing an element M to obtain an intermediate product comprises: mixing a nickel cobalt manganese precursor, a lithium source, and a compound containing an element M to obtain a mixture; sintering and crushing the mixture at a second temperature to obtain a primary intermediate product, wherein the second temperature is greater than the first temperature; and mixing the primary intermediate product with the compound containing an element M to obtain an intermediate product. In the embodiment of the present application, the M element is uniformly distributed in various regions of the single crystal lithium nickel cobalt manganese oxide by first sintering and crushing the mixture at the second temperature; then, by mixing the primary intermediate product with the element M at the first temperature and then performing a secondary sintering, and by controlling the first temperature to be less than the second temperature, the secondary sintering can cause the M element to be gradiently doped from the surface to the center of the single crystal lithium nickel cobalt manganese oxide particles, so that the amount of the M element doped in the obtained single crystal lithium nickel cobalt manganese oxide is optimal, which is beneficial to improving the efficiency of preparing the positive electrode active material and improving the structural stability of the positive electrode active material.

[0017] In one embodiment, the ratio of the second temperature to the first temperature is (1.21-1.42):1, optionally (1.25-1.3):1. Controlling the ratio of the second temperature to the first temperature facilitates controlling the amount of M element doping, and controlling the single-crystal lithium nickel cobalt manganese oxide to gradually reduce the content of the M element from the surface to the geometric center of a single particle, thereby facilitating controlling the ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region to be (2-10):1.

[0018] In one embodiment, the second temperature is 850° C.-1000° C.; or / and the sintering time at the second temperature is 5 h-15 h. Through the above configuration, uniform bulk doping of the M element in the single crystal lithium nickel cobalt manganese oxide can be achieved.

[0019] In one embodiment, the nickel-cobalt-manganese precursor comprises a structural formula of Ni a Co b Mn c (OH)2 material, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1. The nickel-cobalt-manganese precursor is the source of nickel, cobalt and manganese in the single crystal lithium nickel-cobalt-manganese oxide positive electrode active material.

[0020] In one embodiment, the lithium source comprises lithium carbonate and / or lithium hydroxide. The lithium source is the source of lithium in the single crystal lithium nickel cobalt manganese oxide positive electrode active material.

[0021] In one embodiment, after obtaining a single-crystalline lithium nickel cobalt manganese oxide doped with an M element, the method further includes: mixing the single-crystalline lithium nickel cobalt manganese oxide doped with an M element with a compound containing an element Q, and sintering the mixture to form a coating layer containing the element Q on the surface of the single-crystalline lithium nickel cobalt manganese oxide doped with an M element. The element Q includes one or more of titanium, zirconium, aluminum, and tungsten. Forming the coating layer containing the element Q on the surface of the single-crystalline lithium nickel cobalt manganese oxide doped with an M element by this method can reduce direct contact between the electrolyte and the positive electrode active material, inhibit side reactions between the electrolyte and the positive electrode active material, and improve the stability of the positive electrode active material.

[0022] In a third aspect, the present application provides a positive electrode sheet, comprising the positive electrode active material of the first aspect and / or the positive electrode active material prepared by the preparation method of the positive electrode active material of the second aspect. The positive electrode sheet has at least the advantages of the positive electrode active material of the first aspect or the same advantages as the positive electrode active material prepared by the preparation method of the second aspect.

[0023] A fourth aspect of the present application provides a battery comprising the positive electrode active material of the first aspect, or / and the positive electrode active material prepared by the method for preparing the positive electrode active material of the second aspect, or / and the positive electrode sheet of the third aspect. The battery according to the embodiments of the present application has at least the advantages of the positive electrode active material of the first aspect, or the same advantages as the positive electrode active material prepared by the preparation method of the second aspect, or the advantages of the positive electrode sheet of the third aspect.

[0024] The fifth aspect of the present application provides an electrical device comprising the battery of the fourth aspect. The battery of the embodiment of the present application has at least the same advantages as the battery of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of a vehicle according to one embodiment of the present application.

[0026] Figure 2 It is a schematic diagram of the exploded structure of a battery according to one embodiment of the present application.

[0027] Figure 3 It is a schematic diagram of the exploded structure of a battery cell according to one embodiment of the present application.

[0028] Figure 4 This is a scanning electron microscope image of the positive electrode active material of Example 1 of the present application and the Al element content measured by X-ray electron spectroscopy (EDS spectrum). DETAILED DESCRIPTION

[0029] Below, the embodiments of the battery cells, batteries, and electrical equipment of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0030] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0034] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0035] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0036] Unless otherwise specified, the unit of temperature in this application is Celsius (°C).

[0037] Lithium-ion batteries, a new type of green secondary battery, are widely used in electric vehicles, energy storage systems, and renewable energy. With the rapid development of lithium-ion batteries in my country, they are bound to achieve multiple improvements. From a technical perspective, "high efficiency," "long life," and "low cost" will be the core solutions and goals for the development of power battery technology.

[0038] Nickel-cobalt-manganese ternary cathode material (NCM) is one of the mainstream cathode materials in lithium-ion batteries. Through the synergistic effect of these elements, the ternary material combines the advantages of nickel (Ni), cobalt (Co), and manganese (Mn), significantly improving the specific capacity and stability of the electrode material while reducing production costs.

[0039] Because of Ni + He Li + The radii of the electrodes are similar, so cation mixing will occur during the charge and discharge process of the battery, which will lead to the structural phase change of the positive electrode material and the formation of an irreversible inert phase. The layered ternary material will be transformed into a spinel structure and an inactive NiO-type rock salt structure, which will increase the disorder of the crystal phase, generate local microstress, damage the grains, form a passivation film at the rupture site, and lead to the loss of active lithium, which will eventually lead to the deterioration of the contact effect between the electrode material and the conductive agent, and reduce the cycle life and reversible capacity of the battery.

[0040] Based on the above technical problems, the first aspect of the present application provides a positive electrode active material, which includes a single crystal lithium nickel cobalt manganese oxide doped with the M element, the particle size of a single particle of the single crystal lithium nickel cobalt manganese oxide is d, the geometric center of the single particle is the center of the circle, the area with a radius of 0.2d is the first area, and the area with a thickness of 0.1d on the surface of the single particle toward the geometric center is the second area; the ratio of the average molar content of the M element per unit volume of the second area to the average molar content of the M element per unit volume of the first area is (2-10):1; the M element includes one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al.

[0041] A single crystal grows from a single nucleus, with a nearly complete internal lattice structure. During compaction and high-temperature cycling, single-crystal cathode active materials are less susceptible to breakage and exhibit more stable physical and chemical properties, making them suitable for use as a high-voltage material system. Compared to polycrystalline cathode active materials, they offer improved structural stability and high-temperature resistance, effectively mitigating microcrack formation and maintaining structural integrity.

[0042] The particle size of a single particle refers to the average value of the longest diameter and the shortest diameter of a single particle.

[0043] Furthermore, doping M elements in single-crystal lithium nickel cobalt manganese oxide can change the inherent volume and interface of single-crystal lithium nickel cobalt manganese oxide, inhibit cation mixing, thereby producing a more stable metal microstructure framework, alleviating irreversible phase transitions, and improving lattice stability; reducing side reactions between the positive electrode active material and the electrolyte, reducing active lithium loss, reducing capacity loss, improving high-temperature storage performance, and extending cycle life; reducing oxidation reactions on the electrode surface and the gases produced by the reaction, maintaining normal internal pressure of the battery, and improving high-temperature gas production performance. In addition, some M elements (Zr, Mg, Nb, Al, etc.) can expand the Li + transmission channel, improving Li + The diffusion rate in the positive electrode active material increases the initial coulombic efficiency of the battery and improves the battery's kinetic performance. When there are two or more types of M elements, the advantages of different M elements can be combined.

[0044] Regarding the doping amount of the M element, considering that the positive electrode active material often undergoes phase change preferentially in the outer layer structure, the average molar content of the M element in the second region of the outer layer of the single crystal lithium nickel cobalt manganese oxide particle is significantly higher than that in the first region of the inner layer. A stable doping layer can be constructed near the outer layer of the single crystal lithium nickel cobalt manganese oxide particle, thereby stabilizing the surface structure of the single crystal lithium nickel cobalt manganese oxide; this surface structure can inhibit the phase change of the positive electrode active material during the charging and discharging process of the battery, thereby reducing cracks caused by stress during the phase change, inhibiting the side reaction between the positive electrode active material and the electrolyte, and improving the structural stability of the positive electrode active material. In the embodiment of the present application, by controlling the ratio of the average molar content of the M element per unit volume of the second region and the first region within the above range, the structural stability of the single crystal lithium nickel cobalt manganese oxide in the embodiment of the present application is better, which can improve the cycle life and capacity retention rate of the battery. The ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region can be (2:1), (4:1), (6:1), (8:1), (10:1), etc., or a range consisting of any two of the above values, (2:1)-(4:1), (4:1)-(8:1), (8:1)-(10:1), etc.

[0045] Furthermore, because the single-crystal lithium nickel cobalt manganese oxide particles contain a relatively low content of the element M in the first region, while the element M enhances the stability of the positive electrode active material, it can also reduce the amount of dopant required, thereby lowering costs during industrial mass production. Furthermore, the lower the content of the element M, the more conducive it is to maintaining the specific capacity of the positive electrode active material.

[0046] In one embodiment, the ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region is (5-10:1). The ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region can be (5:1), (6:1), (7:1), (8:1), (10:1), etc., or a range consisting of any two of the above values, (5:1)-(6:1), (6:1)-(7:1), (8:1)-(10:1), etc. In this case, the ratio of the average molar content of the M element per unit volume of the second region to the first region is further increased, thereby further reducing the doping amount of the M element in the first region of the single crystal lithium nickel cobalt manganese oxide particle, thereby further reducing the amount of dopant used while maintaining the gram capacity of the positive electrode active material.

[0047] In one embodiment, the average molar content of the M element per unit volume decreases stepwise from the surface to the geometric center of the single particle.

[0048] In the above-described embodiment, the M element exhibits a gradient distribution within the single-crystal lithium nickel cobalt manganese oxide particles, with the M element content gradually decreasing from the particle surface to the geometric center; alternatively, the M element content gradually increases from the particle's geometric center to the surface. During the battery's charge and discharge processes, the surface structure of the single-crystal lithium nickel cobalt manganese oxide, acting as the positive electrode active material, preferentially undergoes phase transitions. The aforementioned distribution of the M element within the particles allows for the formation of a stable doping layer on the particle surface, improving the stability of the surface structure and inhibiting phase transitions in the positive electrode active material. Furthermore, the M element within the particles can inhibit internal phase transitions, thereby enhancing the structural stability of the positive electrode active material.

[0049] In one embodiment, the M element includes at least three elements: Zr, Al, and Y, or three elements: Zr, Al, and Nb. This configuration can combine the advantages of different M elements, thereby improving the structural stability of the positive electrode active material while expanding the active ion transmission channel.

[0050] In one embodiment, the structure of the single crystal lithium nickel cobalt manganese oxide doped with M element includes Li 1+x (Ni a Co b Mn c ) 1-d M d O 2-y A y , A contains one or more of S, N, F, Cl, Br and I, -0.05≤x≤0.5, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1, 0<d≤0.1, 0≤y<0.2.

[0051] Among them, Li 1+x Provides Li-ion batteries that travel back and forth between the positive and negative electrodes during reversible charge and discharge. + , and the Li consumed when the solid electrolyte interphase (SEI) film is formed on the negative electrode surface during the first charge and discharge process + The value of x can be -0.05, 0, 0.1, 0.2, 0.3, 0.4, 0.5, etc., or a range consisting of any two of the above values, -0.05≤x≤0, 0.1≤x≤0.2, 0.2≤x≤0.5, etc.

[0052] (Ni a Co b Mn c ) 1-d That is the ternary in the ternary material: Co 3+ Reduce the cation mixing occupancy, stabilize the layered structure of the material, reduce the impedance value, increase the conductivity, and improve the cycle and efficiency performance; Ni 2+Improve the volume energy density of the material, and because Li + and Ni 2+ The radius is similar, too much Ni 2+ Also because of Li + The dislocation phenomenon causes lithium-nickel mixing. The greater the nickel ion concentration in the lithium layer, the more difficult it is for lithium to be inserted and removed from the layered structure, resulting in poor electrochemical performance. 4+ This not only reduces material costs but also improves material safety and stability. However, excessively high Mn content can easily cause the spinel phase to form, destroying the layered structure, resulting in reduced capacity and cycle attenuation. The value of a can be 0.3, 0.4, 0.5, 0.6, 0.7, etc., or a range consisting of any two of the above values, such as 0.3≤a≤0.4, 0.4≤a≤0.6, 0.5≤a≤0.7, etc. The value of b can be 0.02, 0.03, 0.05, 0.08, 0.12, 0.15, etc., or a range consisting of any two of the above values, such as 0.02≤b≤0.03, 0.05≤b≤0.08, 0.05≤b≤0.15, etc. The value of c is determined by the values ​​of a and b, satisfying a+b+c=1.

[0053] M d The doped M element inhibits phase transitions in the cathode active material and improves structural stability. The value of d can be 0.01, 0.02, 0.05, 0.08, 0.1, or any range consisting of two of the above values, such as 0.01 ≤ d ≤ 0.02, 0.02 ≤ d ≤ 0.05, or 0.05 ≤ d ≤ 0.1. Note that the value of d must be greater than 0.

[0054] In one embodiment, the positive electrode active material further includes a coating layer, the coating layer being coated on the surface of the single-crystalline lithium nickel cobalt manganese oxide doped with the M element, the coating layer containing a Q element, the Q element including one or more of titanium, zirconium, aluminum, and tungsten. The Q element may be present in the coating layer in the form of an oxide, such as one or more of titanium oxide, zirconium oxide, aluminum oxide, and tungsten oxide. Providing the coating layer on the surface of the single-crystalline lithium nickel cobalt manganese oxide can reduce direct contact between the electrolyte and the positive electrode active material, inhibit side reactions between the electrolyte and the positive electrode active material, improve the stability of the positive electrode active material, and inhibit the increase in the cyclic DC internal resistance.

[0055] In one embodiment, the ratio of the total mass of the M element in the first and second regions to the mass of the Q element in the coating layer is 1:(0.25-1.4). By controlling the content of the Q element in the coating layer, on the one hand, direct contact between the electrolyte and the positive electrode active material can be effectively blocked; on the other hand, under the premise that the single crystal lithium nickel cobalt manganese oxide is doped with the M element, the M element can reduce cracks caused by stress generated by phase change in the positive electrode material, thereby reducing contact between the electrolyte and the positive electrode active material, making the single crystal lithium nickel cobalt manganese oxide more stable. Therefore, the mass of the Q element can be appropriately reduced, thereby improving the capacity of the positive electrode active material. The mass ratio of the sum of the masses of the M elements in the first region and the second region to the mass ratio of the Q element in the coating layer can be (1:0.25), (1:0.3), (1:0.5), (1:1.0), (1:1.4), etc., or a range consisting of any two of the above values, (1:0.25)-(1:0.3), (1:0.5)-(1:1.0), (1:0.5)-(1:1.4), etc.

[0056] Furthermore, the mass ratio of the sum of the mass of the M element in the first region and the second region to the mass ratio of the Q element in the coating layer is 1:(0.6-0.8). It can be (1:0.6), (1:0.65), (1:0.7), (1:0.75), (1:0.8), etc., or a range consisting of any two of the above values, (1:0.6)-(1:0.7), (1:0.65)-(1:0.7), (1:0.7)-(1:0.8), etc.

[0057] In one embodiment, the average particle size of the primary particles of the single-crystalline lithium nickel cobalt manganese oxide doped with the element M is greater than or equal to 600 nm. Within this particle size range, suitable space is provided for gradient doping of the element M, while also ensuring that the specific surface area of ​​the single-crystalline lithium nickel cobalt manganese oxide is within an optimal range, and the structural stability of the single-crystalline lithium nickel cobalt manganese oxide is enhanced. In this embodiment of the present application, the average particle size of the primary particles can be measured using scanning electron microscopy images.

[0058] Preferably, the average particle size of the primary particles of the single crystal lithium nickel cobalt manganese oxide doped with the M element can be 800nm-8000nm. The positive electrode active material with a small average particle size of the primary particles of the single crystal lithium nickel cobalt manganese oxide doped with the M element has a larger specific surface area, a larger contact area between the positive electrode active material and the electrolyte, and a shorter diffusion path of lithium ions, which is conducive to the deintercalation of lithium ions, so the battery has better rate performance. Therefore, within the above-mentioned volume average particle size range, it can not only provide suitable space for the gradient doping of the M element, but also make the battery performance better. The average particle size of the primary particles can be 800nm, 850nm, 1000nm, 1400nm, 4000nm, 8000nm, etc., or a range composed of any two of the above values, 800nm-1000nm, 850nm-1400nm, 4000nm-8000nm, etc.

[0059] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising: mixing single-crystalline lithium nickel cobalt manganese oxide and a compound containing an M element to obtain an intermediate product; sintering the intermediate product at a first temperature to obtain single-crystalline lithium nickel cobalt manganese oxide doped with the M element; the first temperature is 550°C-750°C, and the M element includes one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al.

[0060] The compound containing the element M may be zirconium oxide, strontium oxide, tungsten oxide, magnesium oxide, titanium oxide, tin oxide, yttrium oxide, niobium oxide, aluminum oxide, boron oxide, and the like.

[0061] In the sintering process, the sintering atmosphere is air or oxygen; the sintering time is 6 hours to 12 hours; and the sintering temperature is a first temperature of 550°C to 750°C. Changing the sintering temperature can adjust the doping depth of the M element. The higher the sintering temperature, the greater the doping depth of the M element. A single crystal lithium nickel cobalt manganese oxide doped with the M element is obtained through the sintering process. The sintering temperature can be 550°C, 600°C, 700°C, 750°C, etc., or a range formed by any two of the above values, for example, 550°C to 600°C, 600°C to 700°C, 700°C to 750°C, etc. The sintering time can be 6 hours, 7 hours, 10 hours, 12 hours, etc., or a range formed by any two of the above values, for example, 6 hours to 7 hours, 7 hours to 10 hours, 10 hours to 12 hours, etc.

[0062] In the embodiment of the present application, a single-crystal lithium nickel cobalt manganese oxide doped with the M element is obtained through a sintering process; at the same time, since the first temperature during sintering is relatively low, the kinetics of the M element doping is weakened, so the M element can only enter the surface position of the single-crystal lithium nickel cobalt manganese oxide particles, and from the surface to the geometric center of the single-crystal lithium nickel cobalt manganese oxide particles, the average molar content of the M element per unit volume decreases step-by-step, which is called gradient doping. It is possible to construct a stable doping layer near the surface of the single-crystal lithium nickel cobalt manganese oxide particles, thereby stabilizing the surface structure of the single-crystal lithium nickel cobalt manganese oxide; this surface structure can inhibit the phase change of the positive electrode active material during the charge and discharge process of the battery, thereby reducing cracks caused by stress during the phase change, inhibiting the side reaction of the positive electrode active material with the electrolyte, and improving the structural stability of the positive electrode active material, thereby improving the cycle life and capacity retention rate of the battery.

[0063] In one embodiment, the step of mixing single-crystal lithium nickel cobalt manganese oxide and a compound containing the element M to obtain an intermediate product includes: mixing a nickel cobalt manganese precursor, a lithium source and a compound containing the element M to obtain a mixture; sintering the mixture at a second temperature and crushing it to obtain a primary intermediate product, wherein the second temperature is greater than the first temperature; and mixing the primary intermediate product with the compound containing the element M to obtain an intermediate product.

[0064] The nickel-cobalt-manganese precursor may be nickel-cobalt-manganese hydroxide or nickel-cobalt-manganese oxide. Different nickel-cobalt-manganese hydroxides or nickel-cobalt-manganese oxides may be produced according to different composition ratios of nickel, cobalt and manganese elements.

[0065] In one embodiment, the nickel-cobalt-manganese precursor comprises a structural formula of Ni a Co b Mn c (OH)2 materials, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1. Nickel-cobalt-manganese precursors are the source of nickel, cobalt, and manganese in single-crystal lithium nickel-cobalt-manganese oxide positive electrode active materials. The value of a can be 0.3, 0.4, 0.5, 0.6, 0.7, or a range consisting of any two of the above values, 0.3≤a≤0.4, 0.4≤a≤0.6, 0.5≤a≤0.7, etc.; the value of b can be 0.02, 0.03, 0.05, 0.08, 0.12, 0.15, etc., or a range consisting of any two of the above values, 0.02≤b≤0.03, 0.05≤b≤0.08, 0.05≤b≤0.15, etc.; the value of c is determined by the values ​​of a and b, satisfying a+b+c=1.

[0066] The lithium source is the source of lithium in the single crystal lithium nickel cobalt manganese oxide positive electrode active material. In one embodiment, the lithium source includes lithium carbonate and / or lithium hydroxide. The lithium in the positive electrode active material provides the lithium that travels back and forth between the positive and negative electrodes during the reversible charge and discharge process. + , and the Li consumed when the SEI film is formed on the negative electrode surface during the first charge and discharge process + .

[0067] When a mixture containing a nickel-cobalt-manganese precursor, a lithium source and a compound containing the M element is sintered at a second temperature, the sintering atmosphere is air or oxygen; the second sintering temperature is greater than the first temperature, so the kinetics of M element doping is enhanced, and the M element can enter the interior of the single crystal lithium nickel-cobalt-manganese oxide particles. At the same time, the distribution of the M element inside the particles is close to uniform, which is called bulk doping.

[0068] By sintering and crushing the mixture at the second temperature, the M element can be distributed in various regions of the single crystal lithium nickel cobalt manganese oxide, further improving the structural stability of the positive electrode active material.

[0069] In one embodiment, the ratio of the second temperature to the first temperature is (1.2-1.65):1. Controlling the ratio of the second temperature to the first temperature facilitates controlling the amount of M element doping, and controlling the gradual decrease in the M element content of the single-crystal lithium nickel cobalt manganese oxide from the surface to the geometric center of a single particle, thereby facilitating controlling the ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region to be (2-10):1. The ratio of the second temperature to the first temperature can be (1.2:1), (1.25:1), (1.3:1), (1.65:1), etc., or a range consisting of any two of the foregoing values, such as (1.2:1)-(1.25:1), (1.2:1)-(1.3:1), (1.3:1)-(1.65:1), etc.

[0070] Furthermore, the ratio of the second temperature to the first temperature is (1.25-1.3): 1. The ratio of the second temperature to the first temperature can be (1.25:1), (1.28:1), (1.29:1), (1.3:1), etc., or a range consisting of any two of the above values, (1.25:1)-(1.28:1), (1.28:1)-(1.3:1), (1.29:1)-(1.3:1), etc.

[0071] In one embodiment, the second temperature is 850°C-1000°C; or / and the sintering time at the second temperature is 5h-15h. Through the above settings, uniform bulk doping of the M element in the single crystal lithium nickel cobalt manganese oxide can be achieved. Among them, the second temperature can be 850°C, 900°C, 950°C, 1000°C, etc., or a range formed by any two of the above values, for example, 850°C-900°C, 900°C-950°C, 900°C-1000°C, etc. The sintering time can be 5h, 8h, 11h, 15h, etc., or a range formed by any two of the above values, for example, 5h-8h, 8h-11h, 8h-15h, etc.

[0072] In one embodiment, after obtaining a single-crystalline lithium nickel cobalt manganese oxide doped with an M element, the method further includes: mixing the single-crystalline lithium nickel cobalt manganese oxide doped with an M element with a compound containing an element Q, and sintering the mixture to form a coating layer containing the element Q on the surface of the single-crystalline lithium nickel cobalt manganese oxide doped with an M element. The element Q includes one or more of titanium, zirconium, aluminum, and tungsten. Forming the coating layer containing the element Q on the surface of the single-crystalline lithium nickel cobalt manganese oxide doped with an M element by this method can reduce direct contact between the electrolyte and the positive electrode active material, inhibit side reactions between the electrolyte and the positive electrode active material, and improve the stability of the positive electrode active material.

[0073] In a third aspect, the present application provides a positive electrode sheet, comprising the positive electrode active material of the first aspect and / or the positive electrode active material prepared by the preparation method of the positive electrode active material of the second aspect. The positive electrode sheet has at least the advantages of the positive electrode active material of the first aspect or the advantages of the positive electrode active material prepared by the preparation method of the second aspect.

[0074] In a fourth aspect, the present application provides a battery comprising the positive electrode active material of the first aspect, or / and the positive electrode active material prepared by the method for preparing the positive electrode active material of the second aspect, or / and the positive electrode sheet of the third aspect. The battery according to an embodiment of the present application has at least the advantages of the positive electrode active material of the first aspect, or the advantages of the positive electrode active material prepared by the preparation method of the second aspect, or the advantages of the positive electrode sheet of the third aspect.

[0075] A fifth aspect of the present application provides an electrical device comprising the battery of the fourth aspect. The battery of the embodiment of the present application has at least the same advantages as the battery of the fourth aspect.

[0076] The battery disclosed in the embodiments of the present application can be used in electrical devices that use the battery as a power source or various energy storage systems that use the battery as an energy storage element. The electrical devices may be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like, and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, and the like.

[0077] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0078] Please refer to Figure 1 , Figure 1 A schematic structural diagram of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle. The new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000. The battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000. For example, the battery 100 may serve as an operating power source for the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to power the motor 300, for example, to meet the power requirements for starting, navigating and driving the vehicle 1000.

[0079] In some embodiments of the present application, the battery 100 can serve not only as an operating power source for the vehicle 1000, but also as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0080] Please refer to Figure 2 , Figure 2This is a schematic diagram of the exploded structure of a battery 100 provided in some embodiments of the present application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 is used to provide a storage space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 can include a first portion 11 and a second portion 12, which overlap each other and together define a storage space for the battery cell 20. The second portion 12 can be a hollow structure with one end open. The first portion 11 can be a plate-like structure, with the first portion 11 overlapping the open side of the second portion 12, so that the first portion 11 and the second portion 12 together define a storage space. The first portion 11 and the second portion 12 can also be hollow structures with one end open, with the open side of the first portion 11 overlapping the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a rectangular parallelepiped, etc.

[0081] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a hybrid connection. A hybrid connection refers to a combination of series and parallel connections among the multiple battery cells 20. The multiple battery cells 20 may be directly connected in series, in parallel, or in a hybrid connection, and then the entire battery cell 20 may be housed within the housing 10. Alternatively, the battery 100 may be constructed by first connecting multiple battery cells 20 in series, in parallel, or in a hybrid connection to form a battery module, which is then connected in series, in parallel, or in a hybrid connection to form a complete battery module, and then housed within the housing 10. The battery 100 may also include other structures, such as a busbar assembly for electrically connecting the multiple battery cells 20.

[0082] Each battery cell 20 may be a battery or a primary battery, and may also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular, or in other shapes.

[0083] Please refer to Figure 3 , Figure 3 The following is a schematic diagram of the decomposition structure of a battery cell 20 provided in some embodiments of the present application. A battery cell 20 is the smallest unit that makes up a battery. Figure 3 The battery cell 20 includes an end cover 21, a shell 22, a battery cell assembly 23 and other functional components.

[0084] The end cap 21 is a component that covers the opening of the housing 22 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the end cap 21 can be adapted to the shape of the housing 22 to match the housing 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as an aluminum alloy). This prevents the end cap 21 from deforming when subjected to compression or collision, giving the battery cell 20 greater structural strength and improved safety. The end cap 21 can be provided with functional components such as electrode terminals 21a. The electrode terminals 21a can be used to electrically connect to the battery cell assembly 23 to output or input electrical energy to the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for relieving internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The end cap 21 can also be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application are not particularly limited in this regard. In some embodiments, an insulating member may be provided inside the end cap 21 to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be made of plastic, rubber, or the like.

[0085] The housing 22 is a component that cooperates with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can be used to accommodate the battery cell assembly 23, electrolyte, and other components. The housing 22 and end cap 21 can be separate components. An opening can be provided in the housing 22, and the end cap 21 is placed over the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and housing 22 can be integrated. Specifically, the end cap 21 and housing 22 can form a common connection surface before other components are inserted into the housing. When the interior of the housing 22 needs to be enclosed, the end cap 21 is placed over the housing 22. The housing 22 can have a variety of shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined based on the specific shape and size of the battery cell assembly 23. The housing 22 can be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this embodiment of the present application does not impose any specific limitations on this.

[0086] The cell assembly 23 is a component in the battery cell 100 where electrochemical reactions occur. One or more cell assemblies 23 may be contained in the housing 22. The cell assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and a separator is usually provided between the positive and negative electrode sheets. The parts of the positive and negative electrode sheets with active materials constitute the main body of the cell assembly, and the parts of the positive and negative electrode sheets without active materials each constitute a tab 23a. The positive and negative electrode tabs may be located together at one end of the main body or respectively at both ends of the main body. During the charge and discharge process of the battery, the positive active material and the negative active material react with the electrolyte, and the tabs 23a connect the electrode terminals to form a current loop.

[0087] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0088] [Positive electrode]

[0089] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0090] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0091] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0093] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the second binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0095] [Negative electrode]

[0096] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0097] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0098] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0099] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0100] In some embodiments, the negative electrode film layer may further include a third binder. The third binder may 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).

[0101] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0103] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0104] [Isolation film]

[0105] In some embodiments, the battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0106] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven 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.

[0107] [Electrolytes]

[0108] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0109] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0110] 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 difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0111] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0112] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into a battery cell assembly through a winding process or a lamination process.

[0113] In some embodiments, the housing 22 may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like.

[0114] The present application has no particular limitation on the shape of the battery cell 20 , which may be cylindrical, square, or any other shape.

[0115] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0116] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0117] 1. Battery device production

[0118] Example 1

[0119] Preparation of positive electrode active materials

[0120] Step 1) nickel sulfate, manganese sulfate and cobalt sulfate were added to deionized water at a molar ratio of nickel element, cobalt element and manganese element of 55:15:30 to prepare a mixed solution, 0.4 mol / L ammonia water (as a complexing agent) and 1 mol / L sodium hydroxide aqueous solution were added, the pH of the mixed solution was adjusted to 11.3, and coprecipitated at 40°C and 600 rpm for 24 hours to obtain Ni0.55 Co 0.15 Mn 0.3 (OH)2 solid product, the solid product was washed with deionized water and dried to obtain Ni 0.55 Co 0.15 Mn 0.3 (OH)2 positive electrode active material precursor.

[0121] Step 2) Ni 0.55 Co 0.15 Mn 0.3 (OH)2 and lithium carbonate are mixed at a molar ratio of 1:1.06 between the total molar amount of nickel, cobalt and manganese elements and the lithium element, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are added, and mechanical mixing is performed using a high-speed mixer. After mixing, the mixture is sintered at 900°C for 10 hours in an air atmosphere. After the material is cooled, it is crushed and ground using a jet mill to obtain a primary intermediate product 1.

[0122] Step 3) Mechanically mixing the primary intermediate product 1 with 1000 ppm of Al2O3 and 700 ppm of Y2O3 to obtain an intermediate product 1, sintering the intermediate product 1 at 700°C for 7 hours in an air atmosphere, and cooling the material to obtain a single crystal lithium nickel cobalt manganese oxide 1 doped with the M element;

[0123] Step 4) The above-mentioned single-crystalline lithium nickel cobalt manganese oxide doped with the M element 1 is mechanically mixed with 1000 ppm of TiO2. After mixing, it is sintered at 535°C for 7 hours in an air atmosphere. After the material is cooled, a single-crystalline lithium nickel cobalt manganese oxide doped with the M element having a Ti coating layer on the surface is obtained, which is marked as positive electrode active material 1.

[0124]

Preparation of positive electrode sheet

[0125] The prepared positive electrode active material 1, conductive agent conductive carbon black, and binder polyvinylidene fluoride (PVDF) were fully mixed in a mass ratio of 98:1:1, and then solvent N-methylpyrrolidone (NMP) was added and stirred to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on aluminum foil and placed in a drying oven at 80°C for drying. After cold pressing and slitting, the positive electrode sheets were obtained.

[0126]

Preparation of negative electrode sheet

[0127] The negative electrode active material artificial graphite, the conductive agent conductive carbon black, the binder styrene-butadiene rubber and the thickener sodium carboxymethyl cellulose were fully mixed in a mass ratio of 95:1:2:2, and then deionized water was added for stirring and dispersion to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on a copper foil, placed in a drying oven at 80°C for drying, and cold pressed and cut to obtain a negative electrode sheet.

[0128] Preparation of electrolyte

[0129] In an argon atmosphere glove box, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3 / 7 to obtain a solvent, LiPF6 was added to the solvent at a mass percentage of 12.5% ​​and dissolved, and stirred to obtain an electrolyte.

[0130] [Diaphragm]

[0131] Polypropylene film is used as the isolation film.

[0132]

Battery preparation

[0133] The positive electrode sheet, separator and negative electrode sheet are stacked in this order so that the separator can isolate the positive and negative electrodes. Then they are wound into a square bare cell. The bare cell is placed in an aluminum-plastic film. After the processes of liquid injection, packaging, formation, exhaust and so on, a lithium-ion battery is obtained.

[0134] Example 2

[0135] The difference from Example 1 is that: there is no step 4) of preparing the positive electrode active material, the obtained positive electrode active material is marked as positive electrode active material 2, and the rest is the same as Example 1.

[0136] Example 3

[0137] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 1000 ppm of ZrO2 and 1000 ppm of Al2O3 to obtain primary intermediate product 3; in the preparation step 3) of the positive electrode active material, 1000 ppm of Al2O3 and 700 ppm of Y2O3 are replaced by 1000 ppm of Nb2O5 to obtain single crystal lithium nickel cobalt manganese oxide 2; in the preparation step 4), 1000 ppm of TiO2 is replaced by 1000 ppm of Sb2O5 and 2000 ppm of TiO2, and the obtained positive electrode active material is marked as positive electrode active material 3. The rest is the same as in Example 1.

[0138] Example 4

[0139] The difference from Example 1 is that in step 3) of preparing the positive electrode active material, the primary intermediate product 1 is mechanically mixed with 1000 ppm of Al2O3 to obtain single-crystalline lithium nickel cobalt manganese oxide 4. The resulting positive electrode active material is labeled as positive electrode active material 4. All other aspects are the same as in Example 1.

[0140] Example 5

[0141] The difference from Example 1 is that in step 2) of preparing the positive electrode active material, 800 ppm of Y2O3 is replaced with 1500 ppm of Y2O3 to obtain a primary intermediate product 5; and in step 3) of preparing the positive electrode active material, the primary intermediate product 5 is mechanically mixed with 1000 ppm of Al2O3 to obtain an intermediate product 5. The resulting positive electrode active material is labeled as positive electrode active material 5. All other aspects are the same as in Example 1.

[0142] Example 6

[0143] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, the sintering temperature of 900° C. is replaced by 850° C. The obtained positive electrode active material is marked as positive electrode active material 6. The rest is the same as Example 1.

[0144] Example 7

[0145] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, the sintering temperature of 900°C is replaced by 852°C; in the preparation step 3) of the positive electrode active material, the sintering temperature of 700°C is replaced by 600°C. The obtained positive electrode active material is marked as positive electrode active material 7. The rest is the same as Example 1.

[0146] Example 8

[0147] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 800 ppm of ZrO2 to obtain a primary intermediate product 8; in the preparation step 3) of the positive electrode active material, the above-mentioned primary intermediate product 8 is mechanically mixed with 1000 ppm of Al2O3 and 1000 ppm of Y2O3 to obtain an intermediate product 8, and the sintering temperature of 700°C is replaced by 650°C; in the preparation step 4) of the positive electrode active material, 1000 ppm of TiO2 is replaced by 1500 ppm of TiO2, and the final positive electrode active material is marked as positive electrode active material 8. The rest is the same as Example 1.

[0148] Example 9

[0149] The difference from Example 1 is that: in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 600 ppm of ZrO2, and the sintering temperature of 900°C is replaced by 1000°C to obtain a primary intermediate product 9; in the preparation step 3) of the positive electrode active material, the above-mentioned primary intermediate product 9 is mechanically mixed with 1000 ppm of Al2O3 and 1000 ppm of Y2O3 to obtain an intermediate product 9, and the sintering temperature of 700°C is replaced by 750°C; in the preparation step 4) of the positive electrode active material, 1000 ppm of TiO2 is replaced by 1500 ppm of TiO2, and the final positive electrode active material is marked as positive electrode active material 9. The rest is the same as Example 1.

[0150] Example 10

[0151] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 1500 ppm of ZrO2 to obtain a primary intermediate product 10; the preparation step 3) of the positive electrode active material is cancelled; in the preparation step 4) of the positive electrode active material, 1000 ppm of TiO2 is replaced by 2100 ppm of TiO2, and the final positive electrode active material is marked as positive electrode active material 10. The rest is the same as Example 1.

[0152] Example 11

[0153] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 1500 ppm of ZrO2 and 500 ppm of Y2O3 to obtain a primary intermediate product 11; in the preparation step 3) of the positive electrode active material, the above intermediate product 11 is mechanically mixed with 750 ppm of Al2O3 to obtain an intermediate product 11; in the preparation step 4) of the positive electrode active material, 1000 ppm of TiO2 is replaced by 2000 ppm of TiO2, and the final positive electrode active material is marked as positive electrode active material 11. The rest is the same as Example 1.

[0154] Example 12

[0155] The differences from Example 1 are: in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 500 ppm of ZrO2 and 500 ppm of Y2O3; in the preparation step 3) of the positive electrode active material, 1000 ppm of Al2O3 and 700 ppm of Y2O3 are replaced by 1000 ppm of Al2O3 and 500 ppm of Y2O3; in the preparation step 4) of the positive electrode active material, 1000 ppm of TiO2 is replaced by 2500 ppm of TiO2. The final positive electrode active material is marked as positive electrode active material 12, and the rest is the same as Example 1.

[0156] Comparative Example 1

[0157] The difference from Example 1 is that in step 3) of preparing the positive electrode active material, 1000 ppm of Al2O3 and 700 ppm of Y2O3 are replaced with 30 ppm of Al2O3. The final positive electrode active material is marked as positive electrode active material 13. The rest is the same as Example 1.

[0158] Comparative Example 2

[0159] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, 1500 ppm of ZrO2 and 800 ppm of Y2O3 are replaced by 1500 ppm of ZrO2; in the preparation step 3) of the positive electrode active material, 1000 ppm of Al2O3 and 700 ppm of Y2O3 are replaced by 3000 ppm of Al2O3 and 3000 ppm of Y2O3. The final positive electrode active material is marked as positive electrode active material 14. The rest is the same as Example 1.

[0160] Comparative Example 3

[0161] The difference from Example 1 is that in the preparation step 2) of the positive electrode active material, the addition of 1500 ppm of ZrO2 and 800 ppm of Y2O3 and the mixing step are removed, and only sintering is performed; in the preparation step 3), 1000 ppm of Al2O3 and 700 ppm of Y2O3 and the mixing step are removed, and only sintering is performed. The obtained positive electrode active material is marked as positive electrode active material 15, and the rest is the same as Example 1.

[0162] 2. Performance Testing

[0163] The relevant parameter testing methods in the above embodiments and comparative examples are as follows:

[0164] 1) Average particle size test of primary particles

[0165] Software name: LIBMAS Lithium-ion Battery Material Microscopic Intelligent Analysis System

[0166] Automatically identify single crystal particles using AI, draw particle outlines, and obtain particle quantity, number, area, and maximum caliper diameter. Calculate averages and obtain distribution maps, and provide support for manual intervention.

[0167] Average primary particle size = sum of all measured particle sizes / sum of all measured particle numbers.

[0168] 2) Cathode active material morphology test

[0169] The positive electrode active material was tested using a ZEISS sigma 300 scanning electron microscope and then tested according to the standard JY / T010-1996 to observe the sample morphology and element distribution.

[0170] 3) Electrochemical performance test

[0171] 3.1) High temperature cycle performance test

[0172] Place the battery in a 60°C oven and let it sit for 2 hours. Once the battery temperature remains at 60°C, perform the charge and discharge test. Charge the battery at a constant current of 1C to 3.65V. Continue charging at a constant voltage until the charge current falls below 0.05C, then terminate the test. Pause for 5 minutes. Discharge the battery at a constant current of 1C to 2.8V. Pause for 5 minutes. This constitutes one charge and discharge cycle for the battery. Repeat this cycle until the battery capacity decays to 80% of its initial value. Record the number of cycles.

[0173] 3.2) High temperature gas production test

[0174] After fully charging the battery to 4.4V at 1C, place it in a 70°C incubator for 60 days. The initial volume and volume after 60 days of standing were measured using the water displacement method to determine the battery's volume expansion rate. Battery volume expansion rate (%) = (volume after 60 days of standing / initial volume - 1) × 100%.

[0175] 3.3) High temperature storage performance test

[0176] At 25°C, the battery was charged to 4.4V at a constant current rate of 0.33C, then charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged to 2.8V at a constant current rate of 0.33C. The initial discharge capacity of the battery was obtained by testing. At 25°C, the battery was charged to 4.4V at a constant current rate of 0.33C, then charged at a constant voltage until the current was less than or equal to 0.05C, and then the fully charged battery was placed in a 60°C oven for storage for 60 days. The battery was taken out after 60 days of high-temperature storage, and naturally cooled to 25°C, and discharged to 2.8V at a constant current rate of 0.33C, then charged to 4.4V at a constant current rate of 0.33C, then charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged to 2.8V at a constant current rate of 0.33C. The discharge capacity of the battery after 60 days of high-temperature storage was obtained by testing.

[0177] Capacity retention rate (%) of the battery after 60 days of high-temperature storage = discharge capacity after 60 days of high-temperature storage / initial discharge capacity×100%.

[0178]

[0179] 3. Performance Test Results Analysis

[0180] See also Figure 4 , Figure 4 The scanning electron microscope image and the Al content measured by X-ray electron spectroscopy (EDS spectrum) of the positive electrode active material of Example 1 of the present application are shown in FIG. As can be seen from the figure, the molar content of the Al element corresponding to each site of the positive electrode active material particle from the surface to the geometric center direction is 1.52%, 1.05%, 0.61%, 0.18%, 0.1% and 0.01%, respectively, indicating that the molar content of the Al element in the positive electrode active material particle gradually decreases from 1.52% to 0.01% from the surface to the geometric center direction of the positive electrode active material particle, indicating that in the embodiment of the present application, the molar content of the Al element in the positive electrode active material particle decreases in a step-by-step manner from the surface to the geometric center direction of the positive electrode active material particle.

[0181] Table 1 shows the process and performance parameters of each embodiment and comparative example. In the positive electrode active material 13 obtained in comparative example 1, the ratio of the M element in the second region to the first region is less than that in the embodiments 1-12 of the present application; in the positive electrode active material 14 obtained in comparative example 2, the ratio of the M element in the second region to the first region is greater than that in the embodiments 1-12 of the present application; and in the positive electrode active material 15 obtained in comparative example 3, no M element is doped. Based on comparative examples 1-3, the high-temperature cycle life and capacity retention rate of Examples 1-12 of the present application are improved, while the high-temperature gas production performance is reduced. This shows that in Examples 1-12 of the present application, by doping the single-crystalline lithium nickel cobalt manganese oxide particles with the M element, the structural stability of the single-crystalline lithium nickel cobalt manganese oxide particles can be improved; and by controlling the ratio of the average molar content of the M element per unit volume in the second region to the first region within the range of (2-10):1, the structural stability of the single-crystalline lithium nickel cobalt manganese oxide in the embodiment of the present application is better, which can improve the high-temperature cycle life of the battery, the capacity retention rate of the battery for 60 days of high-temperature storage, and reduce the high-temperature gas production of the battery.

[0182] The above is only an implementation method of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the description and drawings of this application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material includes a single-crystal lithium nickel cobalt manganese oxide doped with an M element, wherein the particle size of a single particle of the single-crystal lithium nickel cobalt manganese oxide is d, the geometric center of the single particle is the center of a circle, the region with a radius of 0.2d is a first region, and the region with a thickness of 0.1d on the surface of the single particle toward the geometric center is a second region; the ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region is (2-10):1; the M element includes one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al.

2. The positive electrode active material according to claim 1, characterized in that The ratio of the average molar content of the M element per unit volume of the second region to the average molar content of the M element per unit volume of the first region is (5-10):

1.

3. The positive electrode active material according to claim 1, characterized in that From the surface of the single particle to the geometric center, the average molar content of the M element per unit volume decreases stepwise.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The M element includes at least three elements: Zr, Al, and Y or three elements: Zr, Al, and Nb.

5. The positive electrode active material according to claim 1, characterized in that The structural formula of the single crystal lithium nickel cobalt manganese oxide doped with M element includes Li 1+x (Ni a Co b Mn c ) 1-d M d O 2-y A y , A contains one or more of S, N, F, Cl, Br and I, -0.05≤x≤0.5, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1, 0<d≤0.1, 0≤y<0.

2.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The positive electrode active material further includes a coating layer, which is coated on the surface of the single crystal lithium nickel cobalt manganese oxide doped with the M element. The coating layer contains a Q element, and the Q element includes one or more of titanium, zirconium, aluminum and tungsten.

7. The positive electrode active material according to claim 6, characterized in that The mass ratio of the total mass of the M element in the first region and the second region to the mass of the Q element in the cladding layer is 1:(0.25-1.4).

8. The positive electrode active material according to claim 1, characterized in that The average particle size of the primary particles of the single-crystalline lithium nickel cobalt manganese oxide doped with the M element is greater than or equal to 600 nm.

9. A method for preparing the positive electrode active material according to any one of claims 1 to 8, characterized in that: mixing single crystal lithium nickel cobalt manganese oxide and a compound containing an M element to obtain an intermediate product; The intermediate product is sintered at a first temperature to obtain a single crystal lithium nickel cobalt manganese oxide doped with an M element; the first temperature is 550°C-750°C, and the M element includes one or more of Na, Zr, Sr, W, B, Ba, Ti, Mg, Sn, Y, Nb and Al.

10. The method according to claim 9, characterized in that The step of mixing the single crystal lithium nickel cobalt manganese oxide and the compound containing the M element to obtain the intermediate product comprises: Mixing a nickel-cobalt-manganese precursor, a lithium source, and a compound containing an M element to obtain a mixture; sintering the mixture at a second temperature, crushing it, and obtaining a primary intermediate product, wherein the second temperature is greater than the first temperature; The primary intermediate product is mixed with the compound containing the M element to obtain the intermediate product.

11. The method according to claim 10, characterized in that The second temperature is 850°C-1000°C; or / and The sintering time at the second temperature is 5 hours to 15 hours.

12. The method according to claim 10, characterized in that The nickel-cobalt-manganese precursor includes a structural formula of Ni a Co b Mn c (OH)2 material, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1; or / and, The lithium source includes lithium carbonate and / or lithium hydroxide.

13. The method according to any one of claims 9 to 12, characterized in that: After obtaining the single crystal lithium nickel cobalt manganese oxide doped with the M element, the method further comprises: The single crystal lithium nickel cobalt manganese oxide doped with the M element and a compound containing the Q element are mixed and sintered to form a coating layer containing the Q element on the surface of the single crystal lithium nickel cobalt manganese oxide doped with the M element, wherein the Q element includes one or more of titanium, zirconium, aluminum and tungsten.

14. A positive electrode plate, characterized in that: The positive electrode sheet comprises the positive electrode active material according to any one of claims 1 to 8 or / and a positive electrode active material prepared by the method for preparing a positive electrode active material according to any one of claims 9 to 13.

15. A battery, characterized in that: The positive electrode sheet comprises the positive electrode active material according to any one of claims 1 to 8 or / and the positive electrode active material prepared by the method for preparing the positive electrode active material according to any one of claims 9 to 13, or the positive electrode sheet according to claim 14.

16. An electrical device, characterized in that: Including the battery according to claim 15.

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