Positive electrode material and preparation method therefor, positive electrode sheet, battery, and electric device

Abstract

Provided are a positive electrode material, a method for preparing the positive electrode material, a positive electrode sheet, a battery, and an electric device. The positive electrode material comprises a core and a shell covering the core, the core and the shell both comprise primary particles, most of the primary particles in the core are distributed in the radial direction of the core, and the distribution of most of the primary particles in the shell is different from the radial distribution in the core. The particle strength of the positive electrode material is improved, thereby improving the cycle life, high-temperature storage performance and energy density of the battery.

Description

Positive electrode material and preparation method thereof, positive electrode sheet, battery and electrical device

[0001] This application is based on and claims priority to the Chinese patent application with application number 202410002213.1 and application date January 2, 2024. All contents of the application are hereby introduced as a whole into this application. Technical Field

[0002] The present application relates to the technical field of lithium batteries, and in particular to a positive electrode material, a method for preparing a positive electrode material, a positive electrode sheet, a battery, and an electrical device. Background Art

[0003] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their energy density, cycle performance, and rate performance. Summary of the Invention

[0004] This application is based on the above-mentioned issues and aims to provide a positive electrode material, a method for preparing the positive electrode material, a positive electrode sheet, a battery, and an electrical device. The positive electrode material of this application achieves a more uniform stress distribution caused by lattice contraction and expansion during charge and discharge, thereby improving the material's particle strength and thereby enhancing the battery's cycle life, high-temperature storage performance, and energy density.

[0005] To achieve the above-mentioned object, the first aspect of the present application provides a positive electrode material, comprising a core and a shell covering the core, wherein the core and the shell both comprise primary particles, wherein the majority of the primary particles in the core are distributed along the radial direction of the core, and the distribution of the majority of the primary particles in the shell is different from the radial distribution of the core;

[0006] The core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ;in,

[0007] The M1 of the core and the shell independently include one or two elements of Mn and Al,

[0008] The M2 of the core and the shell independently include one or more elements selected from the group consisting of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, and P.

[0009] a of the core and the shell are independently greater than 0.9 and less than 1.2,

[0010] x of the core and the shell are independently greater than or equal to 0.5 and less than 1,

[0011] The y of the core and the shell are independently greater than 0 and less than or equal to 0.2,

[0012] The 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.50,

[0013] b of the core and the shell are independently greater than 0 and less than or equal to 0.02,

[0014] The z of the core and the shell are independently greater than 1.8 and less than 2.2.

[0015] As a result, it is beneficial to improve the particle strength of the positive electrode material as a whole, thereby improving the cycle life, high-temperature storage performance and energy density of the battery.

[0016] In any embodiment, a of the core and the shell is independently 1; and / or,

[0017] x of the core and the shell are independently greater than or equal to 0.5 and less than or equal to 0.9; and / or,

[0018] y of the core and the shell are independently greater than or equal to 0.05 and less than or equal to 0.2; and / or,

[0019] 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.3; and / or,

[0020] z of the core and the shell is independently 2.

[0021] In any embodiment, M2 of the core includes one or more elements selected from the group consisting of Zr, Sr, Y, Na, K, W, Nb, Sb, La, Ti, and Mo; and M2 of the shell includes one or more elements selected from the group consisting of Zr, Sr, Sb, La, F, Cl, B, P, Ti, and Te.

[0022] During the cycle, the core is prone to cracking, and the shell mainly undergoes interfacial ion exchange with the electrolyte. By doping the core and shell with specific elements, it is beneficial to improve the strength of the core and the cycle life of the battery. It is also beneficial to increase the lithium ion migration rate, improve the battery's kinetic performance, and also help improve the structural stability and corrosion resistance of the positive electrode material.

[0023] In any embodiment, the aspect ratio of the primary particles of the core is greater than the aspect ratio of the primary particles of the shell.

[0024] In any embodiment, the aspect ratio of the primary particles of the inner core is greater than or equal to 1.5 and less than or equal to 8, and can be greater than or equal to 1.8 and less than or equal to 5.

[0025] Therefore, the aspect ratio of the primary particles of the core is greater than that of the primary particles of the shell, which is beneficial to improving the cycle performance, high-temperature storage performance and rate performance of the battery.

[0026] In any embodiment, x of the core is greater than x of the shell.

[0027] In any embodiment, the ratio of x of the core to x of the shell is greater than 1 and less than 2.

[0028] This is beneficial to improving the electrochemical activity of the positive electrode material; it is beneficial to reducing the difference in lithium concentration between the core and the shell during the charge and discharge process, so as to improve the cycle performance of the battery; it is beneficial to reducing the lattice deformation of the shell to protect the core structure, reduce the corrosion of the electrolyte on the core and the occurrence of side reactions, so as to improve the cycle performance, specific capacity and high-temperature storage performance of the battery.

[0029] In any embodiment, the ratio of the average diameter of the inner core to the average thickness of the shell is 1:1-100:1, optionally 1:1-20:1, and more optionally 3:1-10:1.

[0030] As a result, the cracking and shedding of the positive electrode material shell during the charge and discharge process are reduced, the corrosion of the electrolyte on the core is reduced, and the battery's cycle performance, high-temperature storage performance and energy density are improved.

[0031] In any embodiment, the positive electrode material further includes a first coating layer coating the shell and a second coating layer coating the first coating layer; wherein the first coating layer coats the shell in an island shape, and / or the second coating layer continuously coats the first coating layer.

[0032] As a result, the island-like coating of the first coating layer improves the bonding between the primary particles of the shell, thereby enhancing the structural strength of the positive electrode material. The provision of two coating layers helps to increase the migration rate of lithium ions within the positive electrode material and the ion exchange rate between the positive electrode material and the electrolyte, which helps to reduce side reactions between the positive electrode material and the electrolyte, thereby improving the cycle life of the battery.

[0033] In any embodiment, the first cladding layer and the second cladding layer independently include one or more elements of Sr, B, Al, Ti, Zr, Nb, W, F, La, Ce, C, and Co.

[0034] As a result, the energy density, cycle life and storage life of the battery are improved.

[0035] In any embodiment, the Dv50 particle size of the positive electrode material is greater than or equal to 5 μm and less than or equal to 20 μm, and can be greater than 5 μm and less than or equal to 15 μm; and / or,

[0036] The Span of the positive electrode material is greater than or equal to 0.4 and less than or equal to 5, and can be greater than or equal to 0.5 and less than or equal to 2, wherein,

[0037] Span of the positive electrode material = (Dv90 particle size - Dv10 particle size) / Dv50 particle size; and / or,

[0038] The BET specific surface area of ​​the positive electrode material at liquid nitrogen temperature is 0.3-1.5 cm 2 / g, optional 0.36–0.89cm 2 / g; and / or,

[0039] The compaction density of the positive electrode material at 30 MPa is 3.2–3.5 g / cm 3 .

[0040] The Dv50 particle size of the positive electrode material is within the above range, which improves the compaction density and volume energy density of the positive electrode material, reduces the material cracking phenomenon during the cycle process, and thus improves the cycle life and high-temperature storage performance of the battery.

[0041] The Span value of the positive electrode material is within the above range, which increases the compaction density of the positive electrode material and thus increases the energy density of the battery.

[0042] The BET of the positive electrode material is within the above range, which increases the electrochemical active sites of the positive electrode material and inhibits the side reactions between the positive electrode material and the electrolyte, thereby improving the energy density and cycle performance of the battery.

[0043] In any embodiment, the free lithium content in the positive electrode material is less than 3000 ppm by mass.

[0044] The free lithium mass content of the positive electrode material is within the above range, which reduces the risk of gelation during the electrode processing, improves the processability, reduces the side reaction between the positive electrode material and the electrolyte, and reduces the gas production of the side reaction.

[0045] The second aspect of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0046] The first solution is added to the base or its solution for reaction, and the addition rate of the first solution is 12-29 L / h to obtain a precursor 1; wherein the first solution includes a nickel source, a cobalt source and a source of the M1 element;

[0047] Adding the second solution to the precursor 1 and the base or its solution to react, the addition rate of the second solution is 12-25 L / h, to obtain the precursor 2; wherein the second solution includes a nickel source, a cobalt source and a source of the M1 element;

[0048] The precursor 2, the lithium source, and the source of the M2 element are mixed and sintered to obtain a sintered product, which is the positive electrode material.

[0049] As a result, it is beneficial to improve the particle strength of the positive electrode material as a whole, thereby improving the cycle life, high-temperature storage performance and energy density of the battery.

[0050] In any embodiment, the positive electrode material includes a core and a shell covering the core, the core and the shell both include primary particles, wherein the majority of the primary particles in the core are distributed along the radial direction of the core, and the distribution of the majority of the primary particles in the shell is different from the radial distribution of the core; the core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ;in,

[0051] The M1 of the core and the shell independently include one or two elements of Mn and Al,

[0052] The M2 of the core and the shell independently include one or more elements selected from the group consisting of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, and P.

[0053] a of the core and the shell are independently greater than 0.9 and less than 1.2,

[0054] x of the core and the shell are independently greater than or equal to 0.5 and less than 1,

[0055] The y of the core and the shell are independently greater than 0 and less than or equal to 0.2,

[0056] The 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.50,

[0057] b of the core and the shell are independently greater than 0 and less than or equal to 0.02,

[0058] The z of the core and the shell are independently greater than 1.8 and less than 2.2.

[0059] In any embodiment, the method further comprises the steps of:

[0060] mixing the sintered product with a first coating raw material and sintering to obtain an intermediate product;

[0061] Mixing the intermediate product with a second coating raw material and sintering to obtain a positive electrode material including two coating layers;

[0062] The positive electrode material includes a core, a shell covering the core, a first coating layer covering the shell, and a second coating layer covering the first coating layer, wherein the core and the shell both include primary particles, wherein the majority of the primary particles in the core are distributed along the radial direction of the core, and the distribution of the majority of the primary particles in the shell is different from the radial distribution of the core; the core and the shell include Li a (Ni x Co y M1 (1-x-y ) 1-b M2 b O z The first coating layer and the second coating layer independently include one or more elements of Sr, B, Al, Ti, Zr, Nb, W, F, La, Ce, C, and Co, and may optionally include one or more elements of Sr, B, Al, Zr, Nb, W, F, La, Ce, C, and Co; wherein,

[0063] The M1 of the core and the shell independently include one or two elements of Mn and Al,

[0064] The M2 of the core and the shell independently include one or more elements selected from the group consisting of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, and P.

[0065] a of the core and the shell are independently greater than 0.9 and less than 1.2,

[0066] x of the core and the shell are independently greater than or equal to 0.5 and less than 1,

[0067] The y of the core and the shell are independently greater than 0 and less than or equal to 0.2,

[0068] The 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.50,

[0069] b of the core and the shell are independently greater than 0 and less than or equal to 0.02,

[0070] The z of the core and the shell are independently greater than 1.8 and less than 2.2.

[0071] In any embodiment, in the step of preparing the precursor 2, after the reaction, the reaction product is aged to obtain the precursor 2.

[0072] In any embodiment, in the step of preparing the precursor 2, the aging temperature is 30° C.-80° C., and / or the aging time is 5-24 h.

[0073] In any embodiment,

[0074] In the steps of preparing the precursor 1 and the precursor 2, the reaction temperature is independently 40° C. to 80° C.; and / or,

[0075] In the step of preparing the precursor 1 and the precursor 2, the reaction is carried out in an inert gas atmosphere; and / or,

[0076] In the step of preparing the precursor 1 and the precursor 2, the reaction is carried out at a pH value of 9-12; and / or,

[0077] In the step of preparing the precursor 2, after the reaction or aging, the reaction product is washed and dried, the drying temperature is 100° C.-180° C., and the drying time is 5-15 hours; and / or,

[0078] In the step of preparing the sintered product, the sintering temperature is 750° C.-950° C.; and / or,

[0079] In the step of preparing the sintered product, the sintering time is 10-30 hours; and / or,

[0080] In the step of preparing the sintered product, the sintering is performed in an atmosphere containing oxygen; and / or,

[0081] In the steps of preparing the intermediate product and the positive electrode material comprising two coating layers, the sintering temperature is independently 250° C.-700° C.; and / or,

[0082] In the steps of preparing the intermediate product and the positive electrode material comprising two coating layers, the sintering time is independently 5-20 hours; and / or,

[0083] In the steps of preparing the intermediate product and the positive electrode material including two coating layers, the sintering is performed in an atmosphere containing oxygen.

[0084] In any embodiment,

[0085] The Dv50 particle size of the precursor 1 is 4.3-17.3 μm; and / or,

[0086] The Dv50 particle size of the precursor 2 is 5-20 μm; and / or,

[0087] In the first solution and the second solution, the molar percentage of nickel in the total metal elements is independently greater than 0.5 and less than 1; and / or,

[0088] In the first solution and the second solution, the molar percentage of cobalt element to the total metal elements is independently greater than 0 and less than 0.2; and / or,

[0089] The molar ratio of the precursor 2 to the lithium element in the lithium source is 5:6-10:9; and / or,

[0090] The molar ratio of the lithium element in the lithium source to the M2 element in the source of the M2 element is a:b, wherein a is greater than 0.9 and less than 1.2, and b is greater than 0 and less than or equal to 0.02; and / or

[0091] The mass ratio of the first coating raw material to the sintered product is greater than 0 and less than or equal to 1%, and can be optionally greater than 0 and less than or equal to 0.5%; and / or,

[0092] The mass ratio of the second coating raw material to the intermediate product is greater than 0 and less than or equal to 1%, and can be optionally greater than 0 and less than or equal to 0.5%.

[0093] The third aspect of the present application provides a positive electrode plate, comprising the positive electrode material of the first aspect of the present application or the positive electrode material prepared by the method of the second aspect of the present application.

[0094] The fourth aspect of the present application provides a battery, comprising the positive electrode material of the first aspect of the present application, the positive electrode material prepared by the method of the second aspect of the present application, or the positive electrode sheet of the third aspect of the present application.

[0095] The fifth aspect of the present application provides an electrical device comprising the battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] FIG1 is a schematic structural diagram of the radial distribution of primary particles along the core of the present application.

[0097] FIG2 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0098] FIG. 3 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 2 .

[0099] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0100] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0101] FIG. 6 is an exploded view of the battery pack shown in FIG. 5 according to an embodiment of the present application.

[0102] FIG. 7 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0103] FIG8 is a schematic diagram of the distribution direction of the core primary particles and the shell primary particles of the positive electrode material of Example 1 of the present application.

[0104] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly; 81 primary particles of the core; 82 primary particles of the shell. DETAILED DESCRIPTION

[0105] Below, the embodiments of the negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, battery cell, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are 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.

[0106] " 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.

[0107] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0108] 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.

[0109] 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.

[0110] Unless otherwise specified, the Dv50 particle size in this application refers to the particle size when the cumulative value of volume distribution is 50%.

[0111] [Battery Cell]

[0112] A battery cell, also known as a rechargeable battery or storage battery, refers to a battery that can be recharged to activate the active material after discharge and continue to be used.

[0113] Typically, a battery cell consists of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions) are embedded and released back and forth between the positive and negative electrode sheets. The separator is set between the positive and negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte between the positive and negative electrode sheets mainly plays the role of conducting active ions.

[0114] [Cathode material]

[0115] One embodiment of the present application provides a positive electrode material, comprising a core and a shell covering the core, wherein the core and the shell both comprise primary particles, wherein the majority of the primary particles in the core are distributed radially of the core, and the distribution of the majority of the primary particles in the shell is different from the radial distribution of the core;

[0116] The core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ;in,

[0117] The M1 of the core and the shell independently include one or two elements of Mn and Al,

[0118] The M2 of the core and the shell independently include one or more elements selected from the group consisting of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, and P.

[0119] a of the core and the shell are independently greater than 0.9 and less than 1.2 (e.g., 0.95, 1, 1.05, 1.1, 1.15, 1.18, or a range consisting of any of the above values),

[0120] The x of the core and the shell are independently greater than or equal to 0.5 and less than 1 (for example, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or a range consisting of any of the above values),

[0121] The y of the core and the shell are independently greater than 0 and less than or equal to 0.2 (for example, 0.01, 0.02, 0.05, 0.07, 0.09, 0.1, 0.12, 0.14, 0.15, 0.17, 0.18, 0.2 or a range consisting of any of the above values),

[0122] The 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.50 (e.g., 0.1, 0.2, 0.3, 0.4, 0.45, 0.5 or a range consisting of any of the above values),

[0123] b of the core and the shell are independently greater than 0 and less than or equal to 0.02 (e.g., 0.001, 0.003, 0.005, 0.007, 0.008, 0.009, 0.01, 0.012, 0.015, 0.016, 0.018, 0.02, or a range consisting of any of the above values),

[0124] The z of the core and the shell are independently greater than 1.8 and less than 2.2 (eg, 1.85, 1.9, 1.95, 2, 2.1, 2.15, or a range consisting of any of the above values).

[0125] Traditional high-nickel polycrystalline ternary positive electrode materials are prone to cracking during the cycle process; under high voltage conditions, as the charge and discharge depth increases, the material cracking phenomenon becomes more serious; therefore, more unmodified active surfaces will be exposed, resulting in accelerated material cycle attenuation and even a "diving" phenomenon.

[0126] Although the mechanism is still unclear, the applicant unexpectedly discovered that: most of the primary particles in the core of the positive electrode material of the present application are distributed along the radial direction of the core, which is beneficial to improving the transmission and diffusion of lithium ions; most of the primary particles in the shell are not distributed along the radial direction of the core, which is beneficial to reducing the erosion of the electrolyte, and is also beneficial to reducing the material inhomogeneity and local stress concentration caused by the extraction and embedding of lithium ions during charging and discharging, and reducing the cracking and deactivation of the positive electrode material; overall, it is beneficial to improve the uneven stress distribution of the positive electrode material caused by lattice shrinkage and expansion during charging and discharging, so as to enhance the particle strength of the material, thereby enhancing the cycle life, high-temperature storage performance and energy density of the battery.

[0127] In this application, a primary particle has a major axis, which refers to the direction of the maximum length of the largest surface area of ​​the primary particle. Radial distribution has a definition well known in the art. Specifically, in some embodiments, radial distribution of primary particles along the core can refer to a configuration in which the major axis of the primary particles is arranged at an angle of approximately ±10° relative to a direction (R) toward the center of the core, as shown in Figure 1.

[0128] In the present application, whether the primary particles of the core or shell are distributed along the radial direction of the core can be tested by conventional methods in the field; for example, a surface scan of the primary particles of the positive electrode material is performed by a SEM-EDS combination instrument to determine the boundary line between the core and the shell, and a radial line is drawn along the core of the core in the scanning electron microscope image; a protractor is used to measure the angle θ between the primary particles of multiple cores / shells and the radial direction of the core, and the range of the angle θ between the primary particles of the core and the radial direction of the core is obtained, and whether the primary particles of the core are distributed along the radial direction of the core is judged according to the range of the angle θ.

[0129] In this application, "majority" means greater than 50% in quantity, which can be selected as greater than or equal to 60% in quantity, greater than or equal to 70% in quantity, greater than or equal to 80% in quantity, greater than or equal to 90% in quantity, greater than or equal to 95% in quantity, greater than or equal to 98% in quantity, greater than or equal to 99% in quantity, greater than or equal to 99.5% in quantity, and greater than or equal to 99.9% in quantity.

[0130] In this application, the “radial direction of the kernel” refers to the direction of the line connecting the core of the kernel and the edge of the kernel.

[0131] In some embodiments, a of the core and the shell are independently 1; and / or,

[0132] x of the core and the shell are independently greater than or equal to 0.5 and less than or equal to 0.9; and / or,

[0133] y of the core and the shell are independently greater than or equal to 0.05 and less than or equal to 0.2; and / or,

[0134] 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.3; and / or,

[0135] z of the core and the shell is independently 2; and / or,

[0136] M1 of the core and the shell is Mn; and / or,

[0137] The M2 of the core and the shell independently include one or more elements of Zr and Y.

[0138] In some embodiments, M2 of the inner core includes one or more elements selected from the group consisting of Zr, Sr, Y, Na, K, W, Nb, Sb, La, Ti, and Mo; and M2 of the outer shell includes one or more elements selected from the group consisting of Zr, Sr, Sb, La, F, Cl, B, P, Ti, and Te.

[0139] During the cycle, the core is prone to cracking, and the shell mainly undergoes interfacial ion exchange with the electrolyte. By doping the core and shell with specific elements, it is beneficial to improve the strength of the core and the cycle life of the battery. It is also beneficial to increase the lithium ion migration rate, improve the battery's kinetic performance, and also help improve the structural stability and corrosion resistance of the positive electrode material.

[0140] In some embodiments, the aspect ratio of the primary particles of the core is greater than the aspect ratio of the primary particles of the shell;

[0141] Optionally, the aspect ratio of the primary particles of the inner core is greater than or equal to 1.5 and less than or equal to 8, and can be greater than or equal to 1.8 and less than or equal to 5, for example, 1.5, 2, 3, 4, 5, 6, 7, 8 or a range consisting of any of the above values.

[0142] Therefore, the aspect ratio of the primary particles of the core is greater than that of the primary particles of the shell, which is beneficial to improving the cycle performance, high-temperature storage performance and rate performance of the battery.

[0143] In some embodiments, the x of the core is greater than the x of the shell; optionally, the ratio of the x of the core to the x of the shell is greater than 1 and less than 2, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 1.8, 1.9 or a range consisting of any of the above values.

[0144] This is beneficial to improving the electrochemical activity of the positive electrode material; it is beneficial to reducing the difference in lithium concentration between the core and the shell during the charge and discharge process, so as to improve the cycle performance of the battery; it is beneficial to reducing the lattice deformation of the shell to protect the core structure, reduce the corrosion of the electrolyte on the core and the occurrence of side reactions, so as to improve the cycle performance, specific capacity and high-temperature storage performance of the battery.

[0145] In some embodiments, the ratio of the average diameter of the inner core to the average thickness of the shell is 1:1-100:1, optionally 1:1-20:1, more optionally 3:1-10:1, for example, 1:1, 2:1, 3:1, 5:1, 7:1, 8:1, 10:1, 12:1, 15:1, 16:1, 17:1, 19:1, 20:1, 22:1, 25:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1 or a range consisting of any of the above values.

[0146] As a result, the cracking and shedding of the positive electrode material shell during the charge and discharge process are reduced, the corrosion of the electrolyte on the core is reduced, and the battery's cycle performance, high-temperature storage performance and energy density are improved.

[0147] In some embodiments, the positive electrode material further includes a first coating layer coating the shell and a second coating layer coating the first coating layer; wherein the first coating layer coats the shell in an island shape, and / or the second coating layer continuously coats the first coating layer.

[0148] As a result, the island-like coating of the first coating layer improves the bonding between the primary particles of the shell, thereby enhancing the structural strength of the positive electrode material. The provision of two coating layers helps to increase the migration rate of lithium ions within the positive electrode material and the ion exchange rate between the positive electrode material and the electrolyte, which helps to reduce side reactions between the positive electrode material and the electrolyte, thereby improving the cycle life of the battery.

[0149] In some embodiments, the first coating layer and the second coating layer independently include one or more elements of Sr, B, Al, Ti, Zr, Nb, W, F, La, Ce, C, and Co, and may optionally include one or more elements of B, Al, and Ti.

[0150] As a result, the energy density, cycle life and storage life of the battery are improved.

[0151] In some embodiments, the Dv50 particle size of the positive electrode material is greater than or equal to 5 μm and less than or equal to 20 μm, and can be greater than 5 μm and less than or equal to 15 μm, for example, 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 17 μm, 18 μm, 20 μm or a range consisting of any of the above values; and / or,

[0152] The Span of the positive electrode material is greater than or equal to 0.4 and less than or equal to 5, and can be greater than or equal to 0.5 and less than or equal to 2, such as 0.4, 0.5, 0.7, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or a range consisting of any of the above values, wherein,

[0153] Span of the positive electrode material = (Dv90 particle size - Dv10 particle size) / Dv50 particle size; and / or,

[0154] The BET specific surface area of ​​the positive electrode material at liquid nitrogen temperature is 0.3-1.5 cm 2 / g, optional 0.36–0.89cm 2 / g, for example 0.3cm 2 / g, 0.5cm 2 / g, 0.7cm 2 / g, 0.8cm 2 / g, 0.9cm 2 / g, 1.0cm 2 / g, 1.1cm 2 / g, 1.2cm 2 / g, 1.3cm 2 / g, 1.4cm 2 / g, 1.5cm 2 / g or any range consisting of the above values; and / or,

[0155] The compaction density of the positive electrode material at 30 MPa is 3.2–3.5 g / cm 3 , for example 3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 , 3.5g / cm 3 Or any range consisting of the above values.

[0156] The Dv50 particle size of the positive electrode material is within the above range, which improves the compaction density and volume energy density of the positive electrode material, reduces the material cracking phenomenon during the cycle process, and thus improves the cycle life and high-temperature storage performance of the battery.

[0157] The Span value of the positive electrode material is within the above range, which increases the compaction density of the positive electrode material and thus increases the energy density of the battery.

[0158] The BET of the positive electrode material is within the above range, which increases the electrochemical active sites of the positive electrode material and inhibits the side reactions between the positive electrode material and the electrolyte, thereby improving the energy density and cycle performance of the battery.

[0159] In some embodiments, the free lithium content in the positive electrode material is less than 3000 ppm by mass.

[0160] The free lithium mass content of the positive electrode material is within the above range, which reduces the risk of gelation during the electrode processing, improves the processability, reduces the side reaction between the positive electrode material and the electrolyte, and reduces the gas production of the side reaction.

[0161] In the present application, the aspect ratio of the primary particles of the core / shell is tested by conventional methods in the field; for example, the primary particles of the positive electrode material are scanned by a SEM-EDS combination to determine the boundary between the core and the shell, and then the aspect ratios of multiple primary particles of the core and multiple primary particles of the shell are observed separately by scanning electron microscope images. The above test is repeated for multiple primary particles of the positive electrode material, and the average value is the aspect ratio of the primary particles of the core and the aspect ratio of the primary particles of the shell.

[0162] In this application, the volume distribution particle sizes Dv10, Dv50 and Dv90 are measured using conventional methods in the art; for example, the sample is completely dispersed and then measured using a laser particle size analyzer in accordance with GB / T19077-2016 / ISO 13320:2009.

[0163] In the present application, the average diameter of the core and the average thickness of the shell are tested by conventional methods in the field; for example, the primary particles of the positive electrode material are scanned by a SEM-EDS combination to determine the boundary line between the core and the shell, and the distance from the core of the core to the boundary line and the distance from the core of the core to the outermost edge of the shell are measured in the scanning electron microscope image. The measurements are randomly oriented multiple times, and then the above tests are repeated on multiple primary particles of the positive electrode material. Twice the average value of the distance from the core of the core to the boundary line is the average diameter of the core, and the average value of the difference between the distance from the core of the core to the outermost edge of the shell and the distance from the core of the core to the boundary line is the average thickness of the shell.

[0164] In this application, the BET specific surface area is tested using conventional methods in the art; for example, it is tested using a nitrogen adsorption specific surface area analysis test method and calculated using the BET method, wherein the nitrogen adsorption specific surface area analysis test can be performed using a specific surface and pore analyzer, and the test steps can refer to GB / T 19587-2004.

[0165] In the present application, the particle strength of the positive electrode material is tested using conventional methods in the art; for example, a microhardness tester is used to select secondary particles of the positive electrode material, and the particles are squeezed by moving a probe equipped with a pressure sensor to record the particle strength.

[0166] In the present application, the compaction density of the positive electrode material is tested using conventional methods in the field; for example, the positive electrode material is placed in the mold of a compaction density tester, and the tester automatically applies a certain pressure to the powder until the powder is compacted. According to the cross-sectional area of ​​the mold and the thickness of the powder at this time, the volume of the powder can be calculated. According to compaction density = mass / volume, the compaction density of the powder material can be measured.

[0167] [Method for preparing positive electrode material]

[0168] One embodiment of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0169] The first solution is added to the base or its solution for reaction, and the addition rate of the first solution is 12-29 L / h (for example, 12 L / h, 14 L / h, 16 L / h, 18 L / h, 20 L / h, 22 L / h, 24 L / h, 25 L / h, 26 L / h, 27 L / h, 28 L / h, 29 L / h or a range consisting of any of the above values) to obtain a precursor 1; wherein the first solution includes a nickel source, a cobalt source and a source of the M1 element;

[0170] The second solution is added to the precursor 1 and the base or its solution to react, and the addition rate of the second solution is 12-25 L / h (the addition rate of the second solution is 12-25 L / h, for example, 12 L / h, 14 L / h, 16 L / h, 18 L / h, 20 L / h, 22 L / h, 24 L / h, 25 L / h or a range consisting of any of the above values) to obtain a precursor 2; wherein the second solution includes a nickel source, a cobalt source and a source of the M1 element;

[0171] The precursor 2, the lithium source, and the source of the M2 element are mixed and sintered to obtain a sintered product, which is the positive electrode material.

[0172] As a result, most of the primary particles in the inner core are distributed radially along the inner core, which is beneficial to improving the transmission and diffusion of lithium ions; most of the primary particles in the shell are not distributed radially along the inner core, which is beneficial to reducing the erosion of the electrolyte, and is also beneficial to reducing the material inhomogeneity and local stress concentration caused by the release and insertion of lithium ions during the charge and discharge process, and reducing the cracking and deactivation of the positive electrode material; on the whole, it is beneficial to improve the uneven stress distribution of the positive electrode material caused by the lattice contraction and expansion during the charge and discharge process, so as to enhance the particle strength of the material, thereby enhancing the cycle life, high-temperature storage performance and energy density of the battery.

[0173] In some embodiments, the positive electrode material includes a core and a shell covering the core, the core and the shell both include primary particles, wherein the majority of the primary particles in the core are distributed along the radial direction of the core, and the distribution of the majority of the primary particles in the shell is different from the radial distribution of the core; the core and the shell independently include Li a (Ni x Co y M1 (1-x- y) ) 1-b M2 b O zwherein M1 of the core and the shell independently comprises one or two elements of Mn and Al, M2 of the core and the shell independently comprises one or more elements of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, and P, a of the core and the shell independently is greater than 0.9 and less than 1.2 (e.g., 0.95, 1, 1.05, 1.1, 1.15, 1.18, or a range consisting of any of the above values), x of the core and the shell independently is greater than or equal to 0.5 and less than 1 (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or a range consisting of any of the above values), y of the core and the shell independently is greater than 0 and less than or equal to 0.2 (e.g., 0.01, 0.02, 0.05, 0.07, 0.09, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.56, 0 0.1, 0.12, 0.14, 0.15, 0.17, 0.18, 0.2 or a range consisting of any of the above numerical values), 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.50 (for example, 0.1, 0.2, 0.3, 0.4, 0.5 or a range consisting of any of the above numerical values), b of the core and the shell are independently greater than 0 and less than or equal to 0.02 (for example, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009, 0.01, 0.012, 0.015, 0.016, 0.018, 0.019 or a range consisting of any of the above numerical values), and z of the core and the shell are independently greater than 1.8 and less than 2.2 (for example, 1.85, 1.9, 1.95, 2, 2.1, 2.15 or a range consisting of any of the above numerical values).

[0174] In some embodiments, the method further comprises the steps of:

[0175] mixing the sintered product with a first coating raw material and sintering to obtain an intermediate product;

[0176] Mixing the intermediate product with a second coating raw material and sintering to obtain a positive electrode material including two coating layers;

[0177] The positive electrode material includes a core, a shell covering the core, a first coating layer covering the shell, and a second coating layer covering the first coating layer, wherein the core and the shell both include primary particles, wherein the majority of the primary particles in the core are distributed along the radial direction of the core, and the distribution of the majority of the primary particles in the shell is different from the radial distribution of the core; the core and the shell include Li a (Ni x Co y M1 (1-x-y ) 1-b M2 b O z, the first coating layer and the second coating layer independently include one or more elements of Sr, B, Al, Ti, Zr, Nb, W, F, La, Ce, C, and Co, and can be optionally one or more elements of Sr, B, Al, Zr, Nb, W, F, La, Ce, C, and Co; wherein M1 of the core and the shell independently include one or two elements of Mn and Al, and M2 of the core and the shell independently include Ti, Na, K, Zr, Sr, Sb, One or more elements selected from the group consisting of Mo, W, Nb, Y, Te, La, B, F, Cl, and P; a of the core and the shell are independently greater than 0.9 and less than 1.2 (e.g., 0.95, 1, 1.05, 1.1, 1.15, 1.18, or a range consisting of any of the above values); x of the core and the shell are independently greater than or equal to 0.5 and less than 1 (e.g., 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or a range consisting of any of the above values); The y of the core and the shell are independently greater than 0 and less than or equal to 0.2 (for example, 0.01, 0.02, 0.05, 0.07, 0.09, 0.1, 0.12, 0.14, 0.15, 0.17, 0.18, 0.2 or a range consisting of any of the above values), the 1-xy of the core and the shell are independently greater than 0 and less than or equal to 0.50 (for example, 0.1, 0.2, 0.3, 0.4, 0.5 or a range consisting of any of the above values), the core and the shell are independently greater than 0 and less than or equal to 0.50 (for example, 0.1, 0.2, 0.3, 0.4, 0.5 or a range consisting of any of the above values), b is independently greater than 0 and less than or equal to 0.02 (for example, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009, 0.01, 0.012, 0.015, 0.016, 0.018, 0.019, or a range consisting of any of the above values), and z of the core and the shell are independently greater than 1.8 and less than 2.2 (for example, 1.85, 1.9, 1.95, 2, 2.1, 2.15, or a range consisting of any of the above values).

[0178] In some embodiments, in the step of preparing the precursor 2, after the reaction, the reaction product is aged to obtain the precursor 2.

[0179] In some embodiments, in the step of preparing the precursor 2, the aging temperature is 30°C-80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or a range consisting of any of the above values.

[0180] In some embodiments, in the step of preparing the precursor 2, the aging time is 5-24 hours, for example, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 17, 19, 20, 21, 22, 23, 24 hours or a range consisting of any of the above values.

[0181] In some embodiments, in the steps of preparing the precursor 1 and the precursor 2, the reaction temperature is independently 40°C-80°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C or a range consisting of any of the above values.

[0182] In some embodiments, the steps of preparing the precursor 1 and the precursor 2 are carried out in an inert gas atmosphere.

[0183] In some embodiments, in the steps of preparing the precursor 1 and the precursor 2, the reaction is carried out at a pH value of 9-12 (e.g., 9, 9.5, 10, 10.5, 11, 11.5, 12, or a range consisting of any of the above values).

[0184] In some embodiments, in the step of preparing the precursor 2, after the reaction or aging, the reaction product is washed and dried, and optionally the drying temperature is 100°C-180°C, for example, 100°C, 120°C, 140°C, 150°C, 170°C, 180°C or a range consisting of any of the above values, and optionally the drying time is 5-15h, for example, 5, 6, 7, 8, 9, 10, 11, 13, 15h or a range consisting of any of the above values.

[0185] In some embodiments, in the step of preparing the sintered product, the sintering temperature is 750°C-950°C, for example, 750°C, 800°C, 850°C, 900°C, 950°C or a range consisting of any of the above values.

[0186] In some embodiments, in the step of preparing the sintered product, the sintering time is 10-30 hours, for example, 10, 15, 20, 25, 30 hours or a range consisting of any of the above values.

[0187] In some embodiments, in the step of preparing the sintered product, the sintering is performed in an atmosphere containing oxygen.

[0188] In some embodiments, in the steps of preparing the intermediate product and the positive electrode material comprising two coating layers, the sintering temperature is independently 250°C-700°C, for example, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C or a range consisting of any of the above values.

[0189] In some embodiments, in the steps of preparing the intermediate product and the positive electrode material comprising two coating layers, the sintering time is independently 5-20 hours, for example, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 17, 18, 19, 20 hours or a range consisting of any of the above values.

[0190] In some embodiments, in the steps of preparing the intermediate product and the positive electrode material including two coating layers, the sintering is performed in an atmosphere containing oxygen.

[0191] In some embodiments, the Dv50 particle size of the precursor 1 is 4.3-17.3 μm, for example, 4.3 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17.3 μm or a range consisting of any of the above values.

[0192] In some embodiments, the Dv50 particle size of the precursor 2 is 5-20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or a range consisting of any of the above values.

[0193] In some embodiments, in the first solution and the second solution, the molar percentage of nickel element to the total metal elements is independently greater than 0.5 and less than 1.

[0194] In some embodiments, in the first solution and the second solution, the molar percentage of cobalt element in the total metal elements is independently greater than 0 and less than 0.2, for example, 0.01, 0.05, 0.08, 0.1, 0.12, 0.14, 0.15, 0.18, 0.19 or a range consisting of any of the above values.

[0195] In some embodiments, the molar ratio of the precursor 2 to the lithium element in the lithium source is 5:6-10:9, for example, 5:6, 1:1.06, 1:1, 1.05:1, 10:9 or any range thereof.

[0196] In some embodiments, the molar ratio of the lithium element in the lithium source to the M2 element in the source of the M2 element is a:b, wherein a is greater than 0.9 and less than 1.2, for example, 0.95, 1, 1.05, 1.1, 1.15, 1.18 or a range consisting of any of the above values, and b is greater than 0 and less than or equal to 0.02, for example, 0.001, 0.003, 0.005, 0.007, 0.008, 0.009, 0.01, 0.012, 0.015, 0.016, 0.018, 0.02 or a range consisting of any of the above values.

[0197] In some embodiments, the mass ratio of the first coating raw material to the sintered product is greater than 0 and less than or equal to 1%, and can be optionally greater than 0 and less than or equal to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range consisting of any of the above values.

[0198] In some embodiments, the mass ratio of the second coating raw material to the intermediate product is greater than 0 and less than or equal to 1%, and can be optionally greater than 0 and less than or equal to 0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range consisting of any of the above values.

[0199] [Positive electrode]

[0200] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0201] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0202] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0203] 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.

[0204] 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.).

[0205] In some embodiments, the positive electrode material may further increase the positive electrode materials for batteries known in the art. As an example, the positive electrode material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0206] 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.

[0207] 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.

[0208] 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 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.

[0209] [Negative electrode]

[0210] 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.

[0211] 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.

[0212] 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.).

[0213] 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.

[0214] In some embodiments, the negative electrode film layer may further include a binder. For example, the 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).

[0215] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0216] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0217] 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.

[0218] [Electrolytes]

[0219] 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.

[0220] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0221] 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.

[0222] 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.

[0223] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0224] [Isolation film]

[0225] In some embodiments, the battery cell 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.

[0226] 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.

[0227] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0228] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0229] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0230] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG2 shows a battery cell 5 with a square structure as an example.

[0231] In some embodiments, referring to Figure 3, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0232] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0233] FIG4 illustrates an exemplary battery module 4. Referring to FIG4 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Alternatively, the arrangement may be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0234] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0235] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0236] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0237] In addition, the present application also provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0238] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0239] Figure 7 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells, a battery pack or battery module can be used.

[0240] [Example]

[0241] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0242] Example 1

[0243] (1) Preparation of positive electrode materials:

[0244] Dissolving nickel sulfate, cobalt sulfate, and manganese sulfate in deionized water at a molar ratio of 8:1:1 to obtain a first solution with a total concentration of 1 mol / L;

[0245] Dissolving nickel sulfate, cobalt sulfate, and manganese sulfate in deionized water at a molar ratio of 6:2:2 to obtain a second solution with a total concentration of 1 mol / L;

[0246] The concentration of ammonia water is 5g / L.

[0247] ① In a nitrogen atmosphere, the first solution and sodium hydroxide were introduced into a 500L reactor, the temperature of the reactor was controlled to be 60°C, the rotation speed was maintained at 200-300rpm, the flow rate of the first solution was 15-25L / h, and the pH value of the reaction system was maintained at 11. As the particle size grew, the flow rate of the first solution was gradually reduced, and ammonia water was introduced at the same time to maintain the ammonia concentration in the reactor at 5g / L to obtain a precursor 1 with a Dv50 particle size of 8μm, namely Ni 0.8 Co 0.1 Mn 0.1 (OH)2;

[0248] ② Keeping other conditions the same as step ①, the second solution was introduced, the flow rate was controlled at 12-16 L / h, and the growth was continued. Then, the mixture was aged at 60°C for 10 h, filtered, the residue was washed, and dried at 100°C for 15 h to obtain the precursor 2 with a Dv50 particle size of 10 μm, namely Ni 0.6 Co 0.2 Mn 0.2 (OH)2 coated Ni 0.8 Co 0.1 Mn 0.1 (OH)2;

[0249] ③ Precursor 2, LiOH·H2O, and ZrO2 were mixed in a mixer at a molar ratio of 0.99:1.00:0.01 and sintered at 800°C for 18 h in an oxygen atmosphere;

[0250] ④ The sintered product was mixed with alumina in a molar ratio of 1:0.01, and then sintered at 500°C in an oxygen atmosphere for 10 h to obtain a positive electrode material.

[0251] The distribution direction of the primary particles of the core and the primary particles of the shell in the positive electrode material can be observed using a scanning electron microscope. A schematic diagram of the distribution direction of the primary particles of the core 81 and the primary particles of the shell 82 is shown in FIG8 .

[0252] (2) Preparation of positive electrode sheet:

[0253] The positive electrode material, polyvinylidene fluoride and conductive carbon black were mixed in a mass ratio of 90:5:5, and then N-methylpyrrolidone (NMP) was added and stirred for 2 hours. Then, it was stirred in a homogenizer at 1000r / min until the mixture was uniformly mixed, and then evenly coated on the double-sided surface of a 13-micron thick aluminum foil current collector. After coating, it was dried in a drying oven at 100°C, cold pressed, and cut to obtain positive electrode sheets.

[0254] (3) Preparation of electrolyte:

[0255] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:2 to form a mixed solvent. Thoroughly dried lithium hexafluorophosphate was then dissolved in the mixed solvent in an argon atmosphere glove box and mixed thoroughly to obtain an electrolyte solution. The lithium salt concentration in the electrolyte solution was 1 mol / L.

[0256] (4) Preparation of negative electrode sheet:

[0257] The negative electrode active materials graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber and acetylene black were mixed in a mass ratio of 96:1:1:2, deionized water was added, and the mixture was stirred evenly in a blender. The slurry was then coated on both sides of an 8-micron-thick copper foil, dried in an oven at 100°C, cold pressed, and cut to obtain negative electrode sheets.

[0258] (5) Isolation film: Polypropylene film is used.

[0259] (6) Preparation of secondary batteries:

[0260] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the above-prepared electrolyte is added. After packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0261] The preparation methods and products of Examples 2-20 and Comparative Examples 1-3 are similar to those of Example 1. The different process parameters and product parameters are shown in Tables 1-3.

[0262] Materials and battery testing

[0263] (1) Chemical formula of core and shell and test of elements contained in coating layer:

[0264] The primary particles of the positive electrode material (particle size is Dv50 particle size ± 0.3 μm) are scanned by SEM-EDS to determine the boundary line between the core, shell and coating layer. Then, ten points are selected in the core, shell and coating layer using point scanning by SEM-EDS to take the average value, and then the chemical formula of the core and shell and the elements contained in the coating layer are determined.

[0265] (2) Test of the aspect ratio of the primary particles of the core, the aspect ratio of the primary particles of the shell, and the aspect ratio of the primary particles of the positive electrode material:

[0266] The primary particles of the positive electrode material (particle size is Dv50 particle size ± 0.3 μm) are scanned by a SEM-EDS combination instrument to determine the boundary line between the core and the shell. Then, the aspect ratios of 50 primary particles of the core and 50 primary particles of the shell are observed respectively by scanning electron microscope images. A total of 50 primary particles of the positive electrode material are taken to repeat the above test, and the average value is the aspect ratio of the primary particles of the core and the aspect ratio of the primary particles of the shell.

[0267] Take primary particles of the positive electrode material (particle size is Dv50 particle size ± 0.3 μm), observe the aspect ratio of the primary particles through scanning electron microscopy, take a total of 50 primary particles of the positive electrode material and repeat the above test, and take the average value as the aspect ratio of the primary particles of the positive electrode material.

[0268] (3) Test of the coating layer as island coating or continuous coating:

[0269] Electron probe X-ray microscopy (EPMA) is used to analyze the coating layer. If the display area of ​​the coating layer element is less than 1μm 2 And the distribution is discontinuous, the test result is island coating, otherwise it is layer coating.

[0270] (4) Volume distribution particle size Dv10, Dv50 and Dv90 test:

[0271] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009.

[0272] Detailed test process: Take an appropriate amount of washed sample (sample concentration ensures 8% to 12% shading), add 20mL of anhydrous ethanol, and ultrasonicate for 5 minutes (53KHz / 120W) to ensure that the sample is completely dispersed. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

[0273] (5) Test of average diameter of core and average thickness of shell:

[0274] The primary particles of the positive electrode material (particle size is Dv50 particle size ± 0.3 μm) are scanned by a SEM-EDS combination instrument to determine the boundary line between the core and the shell. The distance from the core to the boundary line and the distance from the core to the outermost edge of the shell are measured in the scanning electron microscope image. The random orientation measurement is repeated 50 times. Then, a total of 50 primary particles of the positive electrode material are taken to repeat the above test. Twice the average value of the distance from the core to the boundary line is the average diameter of the core, and the average value of the difference between the distance from the core to the outermost edge of the shell and the distance from the core to the boundary line is the average thickness of the shell.

[0275] (6) BET specific surface area test:

[0276] The nitrogen adsorption specific surface area analysis test method is used for testing and is calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri Star II surface area and pore analyzer from Micromeritics, USA. The test steps can refer to GB / T 19587-2004.

[0277] The detailed steps are as follows: dry the sample to be tested in a vacuum drying oven at 200°C for 2 hours; weigh 1g of the sample to be tested and place it in a test tube, fill the liquid nitrogen cup with liquid nitrogen, insert it into the test tube, use nitrogen as the adsorption gas, and use the specific surface and pore analyzer to map the adsorption and desorption curve with a relative pressure P / P0 of 0 to 0.99, where P is the equilibrium adsorption pressure and P0 is the saturated vapor pressure. The BET specific surface area of ​​the positive electrode active material is calculated by the BET method.

[0278] (7) Test of particle strength of positive electrode material:

[0279] A microhardness tester (Shimadzu DUH-211S) was used to select secondary particles of cathode materials with a Dv50 particle size of ±0.3 μm. The particles were squeezed by moving a probe equipped with a pressure sensor, and the particle strength was recorded.

[0280] (8) Compaction density test:

[0281] Weigh 10g of positive electrode material and place it in the compaction density tester mold. The tester automatically applies 30MPa of pressure to the powder until the powder is compacted. The volume of the powder can be calculated based on the cross-sectional area of ​​the mold and the thickness of the powder at this time. According to the compaction density = mass / volume, the compaction density of the powder material can be measured.

[0282] (9) Test of whether the primary particles of the core or shell are distributed along the radial direction of the core:

[0283] The primary particles of the cathode material (particle size Dv50 ± 0.3 μm) were scanned by SEM-EDS to determine the boundary between the core and the shell, and radial lines were drawn along the core of the core in the SEM image.

[0284] Use an angle measuring instrument to measure the angle θ between 50 primary particles of the core (randomly selected) and the core radial direction. Take a total of 50 primary particles of the positive electrode material and repeat the above test to obtain the angle θ range between the primary particles of the core and the core radial direction. If the angle θ range is ±10°, the primary particles of the core are distributed along the core radial direction, otherwise they are not distributed along the core radial direction.

[0285] The angle θ between 50 primary particles of the shell (randomly selected) and the radial direction of the core was measured using an angle measuring instrument. A total of 50 primary particles of the positive electrode material were taken to repeat the above test to obtain the range of the angle θ between the primary particles of the shell and the radial direction of the core. If the range of the angle θ is ±10°, the primary particles of the shell are distributed along the radial direction of the core, otherwise they are not distributed along the radial direction of the core.

[0286] (10) Free lithium (including lithium carbonate and lithium hydroxide) content test:

[0287] Weigh 30 g of the positive electrode material, add 100 mL of pure water, stir for 30 min, let it stand for 10 min, and filter to obtain a filtrate.

[0288] The acidity and alkalinity of the sample were determined using the General Method for Determination of Chemical Reagents (GB / T 9724-2007). The filtrate was subjected to an automated two-step potentiometric titration using 0.05 mol / L dilute hydrochloric acid solution as the titrant. The following reactions occurred first: LiOH + HCl = LiCl + H2O, and Li2CO3 + HCl = LiHCO3 + LiCl. With the continued addition of dilute hydrochloric acid, all the lithium hydroxide was converted to lithium chloride and water, and all the Li2CO3 was converted to lithium bicarbonate and lithium chloride. At this point, the pH was approximately 4.0-5.0, and the potentiometric titrator exhibited an electrode potential jump, EP1. With further addition of dilute hydrochloric acid, LiHCO3 + HCl = LiCl + CO2↑ + H2O, resulting in a pH of approximately 8.0-9.0, and the potentiometric titrator exhibited an electrode potential jump, EP2. The Li2CO3 and LiOH contents in the sample were calculated using the dilute hydrochloric acid consumption corresponding to EP1 and EP2, and the chemical equation.

[0289] (11) Specific capacity test:

[0290] At 25°C, first discharge at 1 / 3C to 2.80V and hold for 30 minutes. Then charge at a constant current of 1 / 3C to 4.25V. Then discharge at 1 / 3C to 2.80V, which is recorded as C0. Finally, divide the mass of the active material by C0 to obtain the specific capacity of the material.

[0291] (12) Cycle capacity retention test:

[0292] At 25°C, the battery is charged at a constant current of 1 / 3C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, and discharged at 1 / 3C to 2.80V. This is the first cycle, and the discharge capacity of the first cycle is recorded as C0. The discharge capacity of the nth cycle is recorded as Cn, and the capacity retention rate of each cycle is Cn / C0. The capacity retention rate after 100 cycles is calculated.

[0293] (13) Capacity retention test at 60°C for 50 days:

[0294] At 25°C, the battery was charged to 4.25V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage of 4.25V, and then discharged to 2.8V at a constant current of 1 / 3C. The discharge capacity was measured and recorded as C0. The battery was again charged to 4.25V at a constant current of 1 / 3C, and then charged to 0.05C at a constant voltage of 4.25V.

[0295] A fully charged battery was placed in a 60°C constant temperature oven for 50 days and then removed. At 25°C, the battery was charged at a constant current of 1 / 3C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, and then discharged at a constant current of 1 / 3C to 2.8V. The discharge capacity was measured as Cn, and the capacity retention ratio was calculated as Cn / C0.

[0296] The above results are shown in Table 3-4.

[0297] Table 4 Battery test results of Examples 1-20 and Comparative Examples 1-3

[0298] According to the above results, we can know that:

[0299] Compared with the battery made in comparative example 1 in which the core primary particles of the positive electrode material are not distributed radially along the core and the shell primary particles are not distributed radially along the core, the batteries of Examples 1-20 of the present application have higher specific capacity, higher cycle capacity retention rate, and higher high-temperature storage performance.

[0300] Compared with the battery made in comparative example 2 in which the core primary particles of the positive electrode material are not distributed radially along the core and the shell primary particles are distributed radially along the core, the batteries of Examples 1-20 of the present application have higher specific capacity, higher cycle capacity retention rate, and higher high-temperature storage performance.

[0301] Compared with the comparative example 3 in which neither the core nor the shell of the positive electrode material is doped with the M2 element, the batteries of Examples 1-20 of the present application have a higher specific capacity, a higher cycle capacity retention rate, and a higher high-temperature storage performance.

[0302] Compared with the battery made from the positive electrode material of Example 13 having a higher aspect ratio of the core primary particles, the batteries of Examples 1, 5-6 of the present application have a higher cycle capacity retention rate and higher high-temperature storage performance.

[0303] Compared with the battery made from the positive electrode material of Example 16 with a smaller Dv50 particle size, the batteries of Examples 9 and 10 of the present application have a higher cycle capacity retention rate and higher high-temperature storage performance.

[0304] Compared with the battery made from the positive electrode material of Example 17 with a larger Dv50 particle size, the batteries of Examples 9 and 10 of the present application have a higher cycle capacity retention rate and higher high-temperature storage performance.

[0305] Compared with the battery made in Example 20 in which the ratio of the core nickel content to the shell nickel content of the positive electrode material is less than 1, the battery in Example 1 of the present application has a higher specific capacity, a higher cycle capacity retention rate, and a higher high-temperature storage performance.

[0306] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode material comprising a core and a shell coating the core, wherein both the core and the shell comprise primary particles, wherein, Most of the primary particles in the core are distributed radially along the core, and the distribution of most of the primary particles in the shell is different from the radial distribution of the core; The core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ; wherein, M1 of the core and the shell independently includes one or two elements of Mn and Al; M2 of the core and the shell independently includes one or more elements of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, P; a of the core and the shell is independently greater than 0.9 and less than 1.2; x of the core and the shell is independently greater than or equal to 0.5 and less than 1; y of the core and the shell is independently greater than 0 and less than or equal to 0.2; 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.50; b of the core and the shell is independently greater than 0 and less than or equal to 0.02; z of the core and the shell is independently greater than 1.8 and less than 2.

2.

2. The positive electrode material according to claim 1, wherein, a of the core and the shell is independently 1; and / or, x of the core and the shell is independently greater than or equal to 0.5 and less than or equal to 0.9; and / or, y of the core and the shell is independently greater than or equal to 0.05 and less than or equal to 0.2; and / or, 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.3; and / or, z of the core and the shell is independently 2.

3. The cathode material according to claim 1 or 2, wherein, M2 of the core includes one or more elements of Zr, Sr, Y, Na, K, W, Nb, Sb, La, Ti, Mo; M2 of the shell includes one or more elements of Zr, Sr, Sb, La, F, Cl, B, P, Ti, Te.

4. The cathode material according to any one of claims 1 to 3, wherein, The aspect ratio of the primary particles of the core is greater than that of the primary particles of the shell.

5. The cathode material according to any one of claims 1 to 4, wherein, The aspect ratio of the primary particles of the core is greater than or equal to 1.5 and less than or equal to 8.

6. The cathode material according to any one of claims 1 to 5, wherein, x of the core is greater than x of the shell.

7. The cathode material according to any one of claims 1 to 6, wherein, The ratio of x of the core to x of the shell is greater than 1 and less than 2.

8. The cathode material according to any one of claims 1 to 7, wherein, The ratio of the average diameter of the core to the average thickness of the shell is 1:1 - 100:

1.

9. The cathode material according to any one of claims 1 to 8 further includes a first coating layer covering the shell and a second coating layer covering the first coating layer; wherein, The first coating layer coats the shell in an island shape, and / or, the second coating layer continuously coats the first coating layer.

10. The cathode material according to claim 9, wherein The first coating layer and the second coating layer independently include one or more elements of Sr, B, Al, Ti, Zr, Nb, W, F, La, Ce, C, Co.

11. The cathode material according to any one of claims 1 to 10, wherein, The Dv50 particle size of the positive electrode material is greater than or equal to 5 μm and less than or equal to 20 μm; and / or, The Span of the positive electrode material is greater than or equal to 0.4 and less than or equal to 5, where, The Span of the positive electrode material = (Dv90 particle size - Dv10 particle size) / Dv50 particle size; and / or, The BET specific surface area of the positive electrode material at liquid nitrogen temperature is 0.3-1.5 cm 2 / g; and / or, The tap density of the positive electrode material under 30 Mpa is 3.2–3.5 g / cm 3 .

12. The positive electrode material according to any one of claims 1 to 11, wherein, The mass content of free lithium in the positive electrode material is less than 3000 ppm.

13. A method for preparing a positive electrode material, comprising the following steps: Add the first solution to the base or its solution for reaction, with the addition rate of the first solution being 12 - 29 L / h to obtain precursor 1; wherein, The first solution includes a nickel source, a cobalt source, and a source of element M1; Add the second solution to the precursor 1 and the base or its solution for reaction, with the addition rate of the second solution being 12 - 25 L / h, to obtain precursor 2; wherein, the second solution includes a nickel source, a cobalt source, and a source of element M1; Mix the precursor 2, a lithium source, and a source of element M2, and sinter to obtain a sintered product, which is the cathode material.

14. The method according to claim 13, wherein The cathode material includes a core and a shell coating the core, and both the core and the shell include primary particles. Among them, most of the primary particles in the core are distributed along the radial direction of the core, and the distribution of most of the primary particles in the shell is different from the radial distribution of the core; The core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ; wherein, M1 of the core and the shell independently includes one or two elements of Mn and Al; M2 of the core and the shell independently includes one or more elements of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, P; a of the core and the shell independently is greater than 0.9 and less than 1.2; x of the core and the shell independently is greater than or equal to 0.5 and less than 1; y of the core and the shell independently is greater than 0 and less than or equal to 0.2; 1 - x - y of the core and the shell independently is greater than 0 and less than or equal to 0.50; b of the core and the shell independently is greater than 0 and less than or equal to 0.02; z of the core and the shell independently is greater than 1.8 and less than 2.

2.

15. The method according to claim 13, further comprising the following steps: Mix the sintered product with a first coating raw material and sinter to obtain an intermediate product; Mix the intermediate product with a second coating raw material and sinter to obtain a cathode material including two coating layers; The positive electrode material includes a core, a shell coating the core, a first coating layer coating the shell, and a second coating layer coating the first coating layer. Both the core and the shell include primary particles, wherein, Most of the primary particles in the core are distributed along the radial direction of the core, and the distribution of most of the primary particles in the shell is different from the radial distribution of the core; The core and the shell independently include Li a (Ni x Co y M1 (1-x-y ) 1-b M2 b O z , the first coating layer and the second coating layer independently include one or more elements selected from Sr, B, Al, Ti, Zr, Nb, W, F, La, Ce, C, and Co; wherein, M1 of the core and the shell independently includes one or two elements of Mn and Al; M2 of the core and the shell independently includes one or more elements of Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, P; a of the core and the shell independently is greater than 0.9 and less than 1.2; x of the core and the shell independently is greater than or equal to 0.5 and less than 1; y of the core and the shell independently is greater than 0 and less than or equal to 0.2; 1 - x - y of the core and the shell independently is greater than 0 and less than or equal to 0.50; b of the core and the shell independently is greater than 0 and less than or equal to 0.02; z of the core and the shell independently is greater than 1.8 and less than 2.

2.

16. The method according to any one of claims 13 to 15, wherein In the step of preparing the precursor 2, after the reaction, age the reaction product to obtain the precursor 2.

17. The method according to claim 16, wherein, In the step of preparing the precursor 2, the aging temperature is 30°C - 80°C, and / or the aging time is 5 - 24 h.

18. The method according to any one of claims 13 to 17, wherein, In the steps of preparing the precursor 1 and the precursor 2, the temperature of the reaction is independently 40°C - 80°C; and / or, In the steps of preparing the precursor 1 and the precursor 2, the reaction is carried out in an inert gas atmosphere; and / or, In the steps of preparing the precursor 1 and the precursor 2, the reaction is carried out under the condition that the pH value is 9 - 12; and / or, In the steps of preparing the precursor 2, after the reaction or aging, the reaction product is washed and dried, the drying temperature is 100°C - 180°C, and the drying time is 5 - 15 h; and / or, In the steps of preparing the sintered product, the sintering temperature is 750°C - 950°C; and / or, In the steps of preparing the sintered product, the sintering time is 10 - 30 h; and / or, In the steps of preparing the sintered product, the sintering is carried out in an atmosphere containing oxygen; and / or, In the steps of preparing the intermediate product and the cathode material including two coating layers, the sintering temperature is independently 250°C - 700°C; and / or, In the steps of preparing the intermediate product and the cathode material including two coating layers, the sintering time is independently 5 - 20 h; and / or, In the steps of preparing the intermediate product and the cathode material including two coating layers, the sintering is carried out in an atmosphere containing oxygen.

19. According to the method according to any one of claims 13 to 18, wherein, The Dv50 particle size of the precursor 1 is 4.3–17.3 μm; and / or, The Dv50 particle size of the precursor 2 is 5 - 20 μm; and / or, In the first solution and the second solution, the molar percentage of nickel element in the total metal elements is independently greater than 0.5 and less than 1; and / or, In the first solution and the second solution, the molar percentage of cobalt element in the total metal elements is independently greater than 0 and less than 0.2; and / or, The molar ratio of the lithium element in the precursor 2 to the lithium element in the lithium source is 5:6 - 10:9; and / or, The molar ratio of the lithium element in the lithium source to the M2 element in the source of the M2 element is a:b, wherein a is greater than 0.9 and less than 1.2, and b is greater than 0 and less than or equal to 0.02; and / or, The mass ratio of the first coating raw material to the sintered product is greater than 0 and less than or equal to 1%; and / or, The mass ratio of the second coating raw material to the intermediate product is greater than 0 and less than or equal to 1%.

20. A cathode electrode sheet, comprising the cathode material according to any one of claims 1 to 12 or the cathode material prepared by the method according to any one of claims 13 to 19.

21. A battery, comprising the cathode material according to any one of claims 1 to 12, the cathode material prepared by the method according to any one of claims 13 to 19, or the cathode electrode sheet according to claim 20.

22. An electrical device, comprising the battery according to claim 21.

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