Positive electrode material and preparation method thereof, positive electrode plate, battery and electric device

Abstract

The invention provides a positive electrode material, a method for preparing the positive electrode material, a positive electrode plate, a battery and an electric device. The positive electrode material comprises an inner core and a shell wrapping the inner core, each of the inner core and the shell comprises primary particles, most of the primary particles in the inner core are distributed in the radial direction of the inner core, and the distribution of most of the primary particles in the shell is different from the radial distribution of the inner core. The particle strength of the positive electrode material is improved, so that the cycle life, the high-temperature storage performance and the energy density of the battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly relates to a cathode material, a method for preparing the cathode material, a cathode electrode sheet, a battery, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application scope of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic power plants, thermal power plants, wind power plants, and solar power plants, as well as in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary batteries, higher requirements are also put forward for their energy density, cycle performance, rate performance, etc. Summary of the Invention

[0003] The present application is made in view of the above problems, and its purpose is to provide a cathode material, a method for preparing the cathode material, a cathode electrode sheet, a battery, and an electrical device. The stress distribution caused by lattice contraction and expansion during charge and discharge of the cathode material of the present application is more uniform, the particle strength of the material is improved, thereby improving the cycle life, high-temperature storage performance, and energy density of the battery.

[0004] To achieve the above object, a first aspect of the present application provides a cathode material, including 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;

[0005] The core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ; where

[0006] M1 of the core and the shell independently includes one or two elements in Group IIIA and Group VIIB,

[0007] M2 of the core and the shell independently includes one or more elements in Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB,

[0008] a of the core and the shell independently is greater than 0.9 and less than 1.2,

[0009] x of the core and the shell independently is greater than or equal to 0.5 and less than 1,

[0010] y of the core and the shell is independently greater than 0 and less than or equal to 0.2,

[0011] 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.50,

[0012] b of the core and the shell is independently greater than 0 and less than or equal to 0.02,

[0013] z of the core and the shell is independently greater than 1.8 and less than 2.2.

[0014] Thus, overall, it is beneficial to improve the particle strength of the positive electrode material, thereby improving the cycle life, high - temperature storage performance, and energy density of the battery.

[0015] In any embodiment, a of the core and the shell is independently 1; and / or,

[0016] 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,

[0017] 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,

[0018] 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.3; and / or,

[0019] z of the core and the shell is independently 2; and / or,

[0020] M1 of the core and the shell independently includes one or two elements of Mn and Al; and / or,

[0021] 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.

[0022] In any embodiment, 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.

[0023] During the cycling process, the core is prone to cracking, and the shell mainly undergoes interfacial ion exchange with the electrolyte. By doping specific elements into the core and the shell, it is beneficial to improve the strength of the core, improve the cycle life of the battery, and is also beneficial to increase the lithium - ion migration rate, improve the kinetic performance of the battery, and is also beneficial to improve the structural stability and corrosion resistance of the positive electrode material.

[0024] In any embodiment, the aspect ratio of the primary particles of the core is greater than that of the primary particles of the shell.

[0025] In any embodiment, 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, and is optionally greater than or equal to 1.8 and less than or equal to 5.

[0026] Thus, the aspect ratio of the primary particles of the core being greater than that of the primary particles of the shell is beneficial to improving the cycle performance, high-temperature storage performance, and rate performance of the battery.

[0027] In any embodiment, the x of the core is greater than the x of the shell.

[0028] In any embodiment, the ratio of the x of the core to the x of the shell is greater than 1 and less than 2.

[0029] Thus, it is beneficial to improve the electrochemical activity of the positive electrode material; it is beneficial to reduce the lithium concentration difference between the core and the shell during charge and discharge to improve the cycle performance of the battery; it is beneficial to reduce the lattice deformation of the shell to protect the core structure and reduce the corrosion of the core by the electrolyte and the occurrence of side reactions to improve the cycle performance, specific capacity, and high-temperature storage performance of the battery.

[0030] In any embodiment, the ratio of the average diameter of the 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.

[0031] Thus, cracking and shedding of the shell of the positive electrode material during charge and discharge are reduced, corrosion of the core by the electrolyte is reduced, and the cycle performance, high-temperature storage performance, and energy density of the battery are improved.

[0032] In any embodiment, the positive electrode material further includes a first coating layer covering the shell and a second coating layer covering the first coating layer; wherein, the first coating layer covers the shell in an island shape, and / or, the second coating layer continuously covers the first coating layer.

[0033] Thus, the island-shaped covering of the first coating layer improves the adhesion between the primary particles of the shell, thereby improving the structural strength of the positive electrode material. The arrangement of the two coating layers is beneficial to enhancing the migration rate of lithium ions in the positive electrode material and the ion exchange rate between the positive electrode material and the electrolyte, and is beneficial to reducing the side reactions between the positive electrode material and the electrolyte, thereby improving the cycle life of the battery.

[0034] In any embodiment, 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.

[0035] Thereby, the energy density, cycle life, and storage life of the battery are improved.

[0036] In any implementation, 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 selected to be greater than 5 μm and less than or equal to 15 μm; and / or,

[0037] 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 selected to be greater than or equal to 0.5 and less than or equal to 2, where,

[0038] The Span of the positive electrode material = (Dv90 particle size - Dv10 particle size) / Dv50 particle size; and / or,

[0039] The BET specific surface area of the positive electrode material at liquid nitrogen temperature is 0.3 - 1.5 cm 2 / g, and can be selected to be 0.36–0.89 cm 2 / g; and / or,

[0040] The tap density of the positive electrode material under 30 Mpa is 3.2–3.5 g / cm 3 .

[0041] When the Dv50 particle size of the positive electrode material is within the above range, the tap density and volume energy density of the positive electrode material are improved, and the material cracking phenomenon during the cycle is reduced, thereby improving the cycle life and high-temperature storage performance of the battery.

[0042] When the Span value of the positive electrode material is within the above range, the tap density of the positive electrode material is improved, thereby improving the energy density of the battery.

[0043] When the BET of the positive electrode material is within the above range, the electrochemically active sites of the positive electrode material are increased, and at the same time, the side reaction between the positive electrode material and the electrolyte is inhibited, thereby improving the energy density and cycle performance of the battery.

[0044] In any implementation, the free lithium mass content in the positive electrode material is less than 3000 ppm.

[0045] When the free lithium mass content of the positive electrode material is within the above range, the gel risk during the electrode sheet processing is reduced, the processability is improved, the side reaction between the positive electrode material and the electrolyte is reduced, and the side reaction gas generation amount is reduced.

[0046] The second aspect of the present application provides a method for preparing a positive electrode material, including the following steps:

[0047] Add the first solution to the alkali 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;

[0048] Add the second solution to precursor 1 and the alkali 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;

[0049] Mix precursor 2, a lithium source, and a source of element M2, and sinter them to obtain a sintered product, which is the cathode material.

[0050] Thus, overall, it is beneficial to improve the particle strength of the cathode material, thereby improving the cycle life, high-temperature storage performance, and energy density of the battery.

[0051] In any implementation, 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,

[0052] M1 of the core and the shell independently includes one or two elements from Group IIIA and Group VIIB,

[0053] M2 of the core and the shell independently includes one or more elements from Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB,

[0054] a of the core and the shell independently is greater than 0.9 and less than 1.2,

[0055] x of the core and the shell independently is greater than or equal to 0.5 and less than 1,

[0056] y of the core and the shell independently is greater than 0 and less than or equal to 0.2,

[0057] 1 - x - y of the core and the shell independently is greater than 0 and less than or equal to 0.50,

[0058] b of the core and the shell independently is greater than 0 and less than or equal to 0.02,

[0059] z of the core and the shell is independently greater than 1.8 and less than 2.2.

[0060] In any embodiment, the method further comprises the following steps:

[0061] Mix the sintered product with a first coating raw material and sinter to obtain an intermediate product;

[0062] Mix the intermediate product with a second coating raw material and sinter to obtain a cathode material comprising two coating layers;

[0063] The cathode material comprises 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 comprise 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 contain Li a (Ni x Co y M1 (1-x-y ) 1-b M2 b O z , and the first coating layer and the second coating layer independently comprise one or more elements of Group IIA, Group IIIA, Group IVB, Group VB, Group VIB, Group VIIA, Group IIIB, Group IVA, and Group VIII, and may be selected to comprise one or more elements of Sr, B, Al, Zr, Nb, W, F, La, Ce, C, and Co; Among them,

[0064] M1 of the core and the shell independently comprises one or two elements of Group IIIA and Group VIIB,

[0065] M2 of the core and the shell independently comprises one or more elements of Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, and Group VB,

[0066] a of the core and the shell is independently greater than 0.9 and less than 1.2,

[0067] x of the core and the shell is independently greater than or equal to 0.5 and less than 1,

[0068] y of the core and the shell is independently greater than 0 and less than or equal to 0.2,

[0069] 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.50,

[0070] b of the core and the shell is independently greater than 0 and less than or equal to 0.02,

[0071] The z of the core and the shell is independently greater than 1.8 and less than 2.2.

[0072] In any embodiment, in the step of preparing the precursor 2, after the reaction, the reaction product is aged to obtain the precursor 2.

[0073] In any embodiment, in the step of preparing the precursor 2, the temperature of the aging is 30°C - 80°C, and / or the time of the aging is 5 - 24 h.

[0074] In any embodiment,

[0075] 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,

[0076] In the steps of preparing the precursor 1 and the precursor 2, the reaction is carried out in an inert gas atmosphere; and / or,

[0077] 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,

[0078] In the step of preparing the precursor 2, after the reaction or aging, the reaction product is washed and dried, the temperature of the drying is 100°C - 180°C, and the time of the drying is 5 - 15 h; and / or,

[0079] In the step of preparing the sintered product, the temperature of the sintering is 750°C - 950°C; and / or,

[0080] In the step of preparing the sintered product, the time of the sintering is 10 - 30 h; and / or,

[0081] In the step of preparing the sintered product, the sintering is carried out in an atmosphere containing oxygen; and / or,

[0082] In the steps of preparing the intermediate product and the cathode material including two coating layers, the temperature of the sintering is independently 250°C - 700°C; and / or,

[0083] In the steps of preparing the intermediate product and the cathode material including two coating layers, the time of the sintering is independently 5 - 20 h; and / or,

[0084] 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.

[0085] In any embodiment,

[0086] The Dv50 particle size of the precursor 1 is 4.3–17.3 μm; and / or,

[0087] The Dv50 particle size of the precursor 2 is 5 - 20 μm; and / or,

[0088] 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,

[0089] 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,

[0090] 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,

[0091] 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, where 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,

[0092] 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,

[0093] 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%.

[0094] The third aspect of the present application provides a positive electrode sheet, including 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.

[0095] The fourth aspect of the present application provides a battery, including 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.

[0096] The fifth aspect of the present application provides an electrical device, including the battery of the fourth aspect of the present application. Description of the Drawings

[0097] Figure 1 is a schematic structural diagram of the radial distribution of the primary particles of the present application along the inner core.

[0098] Figure 2 is a schematic diagram of a battery cell of an embodiment of the present application.

[0099] Figure 3 is Figure 2 the exploded view of the battery cell of an embodiment of the present application shown.

[0100] Figure 4 is a schematic diagram of a battery module of an embodiment of the present application.

[0101] Figure 5 It is a schematic diagram of a battery pack according to an embodiment of the present application.

[0102] Figure 6 is Figure 5 an exploded view of the battery pack according to an embodiment of the present application shown in the figure.

[0103] Figure 7 It is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0104] Figure 8 It is a schematic diagram of the distribution directions of the core primary particles and the shell primary particles of the positive electrode material in Example 1 of the present application.

[0105] Explanation of reference numerals:

[0106] 1 battery pack; 2 upper box body; 3 lower box body; 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. Specific embodiments

[0107] Hereinafter, embodiments of the negative electrode active material, its manufacturing method, positive electrode sheet, negative electrode sheet, battery cell, battery module, battery pack, and electrical device of the present application will be specifically disclosed 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 identical structures are omitted. This is to avoid the following description from becoming unnecessarily long 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 recited in the claims.

[0108] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0109] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0110] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0111] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, and preferably in sequence. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0112] If there is no special instruction, the Dv50 particle size in this application refers to the particle size when the cumulative volume distribution value is 50%.

[0113] [Battery cell]

[0114] A battery cell, also known as a rechargeable battery or a storage battery, refers to a battery that can activate the active material and continue to be used after being charged after the battery discharges.

[0115] Under normal circumstances, a battery cell includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (such as lithium ions) are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing active ions to pass through. The electrolyte is between the positive electrode plate and the negative electrode plate, mainly functioning to conduct active ions.

[0116] [Positive electrode material]

[0117] An embodiment of the present application provides a positive electrode material, including a core and a shell coating the core, both the core and the shell including 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;

[0118] The core and the shell independently include Li a (Ni x Co y M1 (1-x-y) ) 1-b M2 b O z ; wherein,

[0119] M1 of the core and the shell independently includes one or two elements from Group IIIA and Group VIIB,

[0120] M2 of the core and the shell independently includes one or more elements from Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB,

[0121] a of the core and the shell independently is greater than 0.9 and less than 1.2 (such as 0.95, 1, 1.05, 1.1, 1.15, 1.18, or a range composed of any of the above values),

[0122] x of the core and the shell independently is greater than or equal to 0.5 and less than 1 (such as 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or a range composed of any of the above values),

[0123] y of the core and the shell independently is greater than 0 and less than or equal to 0.2 (such as 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 composed of any of the above values),

[0124] 1 - x - y of the core and the shell is 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 composed of any of the above values).

[0125] b of the core and the shell is 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 composed of any of the above values).

[0126] z of the core and the shell is independently greater than 1.8 and less than 2.2 (e.g., 1.85, 1.9, 1.95, 2, 2.1, 2.15, or a range composed of any of the above values).

[0127] Traditional high - nickel polycrystalline ternary cathode materials are prone to cracking during cycling; under high - voltage conditions, as the charge - discharge depth increases, the cracking phenomenon of the material becomes more serious; as a result, more unmodified active surfaces will be exposed, leading to an accelerated cycle decay of the material or even a "diving" phenomenon.

[0128] Although the mechanism is not yet clear, the applicant unexpectedly found that: most of the primary particles in the core of the cathode material of the present application are radially distributed along the core, which is beneficial to improving the transport and diffusion of lithium ions; most of the primary particles in the shell are not radially distributed along 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 insertion of lithium ions during charge - discharge, reducing the cracking and inactivation of the cathode material; overall, it is beneficial to improving the uneven stress distribution caused by lattice contraction and expansion during charge - discharge of the cathode material, so as to enhance the particle strength of the material, thereby improving the cycle life, high - temperature storage performance, and energy density of the battery.

[0129] In the present application, the primary particle has a major - axis direction, and the major - axis direction refers to the direction of the maximum length of the largest surface of the primary particle. The radial distribution has a well - known definition in the art. Specifically, in some embodiments, the primary particles being radially distributed along the core may refer to the major - axis direction of the primary particles being arranged within an angle of about ±10° with respect to the direction (R) towards the core center, as Figure 1 shown.

[0130] In this application, whether the primary particles of the core or the shell are distributed along the radial direction of the core can be tested by conventional methods in the art; for example, a surface scan of the primary particles of the cathode material is performed using a combined SEM-EDS instrument to determine the boundary between the core and the shell, and a radial line is drawn along the core of the core in the scanning electron micrograph; a protractor is used to measure the angle θ between multiple primary particles of the core / shell 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 it is determined whether the primary particles of the core are distributed along the radial direction of the core according to the range of the angle θ.

[0131] In this application, "majority" means greater than 50% in quantity, and can be optionally 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, greater than or equal to 99.9% in quantity.

[0132] In this application, "the radial direction of the core" is the direction of the line connecting the core of the core and the edge of the core.

[0133] In some embodiments, a of the core and the shell is independently 1; and / or,

[0134] 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,

[0135] 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,

[0136] 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.3; and / or,

[0137] z of the core and the shell is independently 2; and / or,

[0138] M1 of the core and the shell independently includes one or two elements of Mn and Al, and can be optionally Mn; and / or,

[0139] 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, and can be optionally including one or more elements of Zr and Y.

[0140] In some embodiments, 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.

[0141] During the cycling process, the core is prone to cracking. The shell mainly undergoes interfacial ion exchange with the electrolyte. By doping specific elements into the core and the shell, it is beneficial to enhance the strength of the core, improve the cycle life of the battery, increase the lithium ion migration rate, enhance the kinetic performance of the battery, and also improve the structural stability and corrosion resistance of the cathode material.

[0142] In some embodiments, the aspect ratio of the primary particles of the core is greater than that of the primary particles of the shell;

[0143] Optionally, 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, and can be selected as greater than or equal to 1.8 and less than or equal to 5, such as 1.5, 2, 3, 4, 5, 6, 7, 8 or the range composed of any of the above values.

[0144] Thus, the aspect ratio of the primary particles of the core being greater than that of the primary particles of the shell is beneficial to improving the cycle performance, high-temperature storage performance and rate performance of the battery.

[0145] 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, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 1.8, 1.9 or the range composed of any of the above values.

[0146] Thus, it is beneficial to improve the electrochemical activity of the cathode material; it is beneficial to reduce the lithium concentration difference between the core and the shell during charge and discharge to improve the cycle performance of the battery; it is beneficial to reduce the lattice deformation of the shell to protect the core structure and reduce the corrosion of the core by the electrolyte and the occurrence of side reactions to improve the cycle performance, specific capacity and high-temperature storage performance of the battery.

[0147] In some embodiments, the ratio of the average diameter of the core to the average thickness of the shell is 1:1 - 100:1, and can be selected as 1:1 - 20:1, and more preferably 3:1 - 10:1, such as 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 the range composed of any of the above values.

[0148] Thus, the cracking and shedding of the shell of the cathode material during charge and discharge are reduced, the corrosion of the core by the electrolyte is reduced, and the cycle performance, high-temperature storage performance and energy density of the battery are improved.

[0149] In some embodiments, the positive electrode material further includes a first coating layer that coats the shell and a second coating layer that coats 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.

[0150] Thus, the island-shaped coating of the first coating layer improves the adhesion between the primary particles of the shell, thereby improving the structural strength of the positive electrode material. The arrangement of the two coating layers is conducive to enhancing the migration rate of lithium ions in the positive electrode material and the ion exchange rate between the positive electrode material and the electrolyte, and is conducive to reducing the side reactions between the positive electrode material and the electrolyte, thereby enhancing the cycle life of the battery.

[0151] In some embodiments, 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, and may be selected to include one or more elements selected from B, Al, and Ti.

[0152] Thereby, the energy density, cycle life, and storage life of the battery are improved.

[0153] 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 may be selected to be greater than 5 μm and less than or equal to 15 μm, such as 5 μm, 7 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 17 μm, 18 μm, 20 μm, or a range composed of any of the above values; and / or,

[0154] The Span of the positive electrode material is greater than or equal to 0.4 and less than or equal to 5, and may be selected to 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 composed of any of the above values, wherein,

[0155] The Span of the positive electrode material = (Dv90 particle size - Dv10 particle size) / Dv50 particle size; and / or,

[0156] The BET specific surface area of the positive electrode material at liquid nitrogen temperature is 0.3 - 1.5 cm 2 / g, and may be selected to be 0.36–0.89 cm 2 / g, such as 0.3 cm 2 / g, 0.5 cm 2 / g, 0.7 cm 2 / g, 0.8 cm 2 / g, 0.9 cm 2 / g, 1.0 cm 2 / g, 1.1 cm 2 / g, 1.2 cm2 / g, 1.3 cm 2 / g, 1.4 cm 2 / g, 1.5 cm 2 / g or a range composed of any of the above values; and / or,

[0157] The tap density of the positive electrode material under 30 Mpa is 3.2–3.5 g / cm 3 , such as 3.2 g / cm 3 , 3.3 g / cm 3 , 3.4 g / cm 3 , 3.5 g / cm 3 or a range composed of any of the above values.

[0158] When the Dv50 particle size of the positive electrode material is within the above range, the tap density and volumetric energy density of the positive electrode material are improved, the phenomenon of material cracking during the cycling process is reduced, thereby improving the cycle life and high-temperature storage performance of the battery.

[0159] When the Span value of the positive electrode material is within the above range, the tap density of the positive electrode material is improved, thereby improving the energy density of the battery.

[0160] When the BET of the positive electrode material is within the above range, the electrochemically active sites of the positive electrode material are increased, and at the same time, the side reaction between the positive electrode material and the electrolyte is inhibited, thereby improving the energy density and cycling performance of the battery.

[0161] In some embodiments,

[0162] The mass content of free lithium in the positive electrode material is less than 3000 ppm.

[0163] When the mass content of free lithium in the positive electrode material is within the above range, the gel risk during the electrode sheet processing is reduced, the processability is improved, the side reaction between the positive electrode material and the electrolyte is reduced, and the gas generation amount of the side reaction is reduced.

[0164] In this application, the aspect ratio of the primary particles of the core / shell is measured by a conventional method in the art; for example, the boundary between the core and the shell is determined by scanning the primary particles of the positive electrode material with a SEM-EDS combined instrument, and then the aspect ratios of multiple primary particles of the core and multiple primary particles of the shell are observed respectively through the scanning electron micrographs. 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.

[0165] In this application, the volume distribution particle sizes Dv10, Dv50, and Dv90 are measured by conventional methods in the art; for example, the sample is completely dispersed, and then the sample is measured by a laser particle size analyzer according to the standard of GB / T 19077-2016 / ISO 13320:2009.

[0166] In this application, the average diameter of the core and the average thickness of the shell are measured by conventional methods in the art; for example, the primary particles of the cathode material are subjected to area scanning by a combined SEM-EDS instrument to determine the boundary between the core and the shell. The distance from the core of the core to the boundary and the distance from the core of the core to the outermost edge of the shell are measured in the scanning electron micrograph. The measurement is repeated with random orientation multiple times, and then the above test is repeated for multiple primary particles of the cathode material. Twice the average value of the distance from the core of the core to the boundary 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 is the average thickness of the shell.

[0167] In this application, the BET specific surface area is measured by conventional methods in the art; for example, it is measured by the nitrogen adsorption specific surface area analysis test method and calculated by the BET method. Among them, the nitrogen adsorption specific surface area analysis test can be carried out by a specific surface area and pore analyzer, and the test steps can refer to GB / T 19587-2004.

[0168] In this application, the particle strength of the cathode material is measured by conventional methods in the art; for example, a microhardness tester is used. The secondary particles of the cathode material are selected, and the particles are extruded by the movement of a probe equipped with a pressure sensor to record the particle strength.

[0169] In this application, the tap density of the cathode material is measured by conventional methods in the art; for example, the cathode material is placed in the mold of a tap density tester, and the tester automatically applies a certain pressure to the powder to compact it. 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 the tap density = mass / volume, the tap density of the powder material can be measured.

[0170] [Method for preparing cathode material]

[0171] One embodiment of this application provides a method for preparing a cathode material, including the following steps:

[0172] Adding the first solution to the alkali or its solution for reaction, 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 composed of any of the above values) to obtain precursor 1; wherein, the first solution includes a nickel source, a cobalt source, and a source of element M1;

[0173] Add the second solution to the precursor 1 and the base or its solution for reaction. The addition rate of the second solution is 12 - 25 L / h (the addition rate of the second solution is 12 - 25 L / h, such as 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 composed of any of the above values) to obtain precursor 2; wherein, the second solution includes a nickel source, a cobalt source, and a source of element M1;

[0174] Mix the precursor 2, a lithium source, and a source of element M2, and sinter to obtain a sintered product, which is the positive electrode material.

[0175] Thus, most of the primary particles in the core are distributed along the radial direction of the core, which is beneficial to improving the transport 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 insertion of lithium ions during charge and discharge, and reducing the cracking and inactivation of the positive electrode material; overall, it is beneficial to improving the uneven stress distribution caused by lattice contraction and expansion during charge and discharge of the positive electrode material, 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.

[0176] In some embodiments, the positive electrode material includes a core and a shell coating the core. 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 comprises one or two elements selected from Group IIIA and Group VIIB, M2 of the core and the shell independently comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB, a of the core and the shell is 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 composed of any of the above values), x of the core and the shell is 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 composed of any of the above values), y of the core and the shell is independently greater than 0 and less than or equal to 0.2 (e.g., 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 composed of any of the above values), 1 - x - y of the core and the shell is independently greater than 0 and less than or equal to 0.50 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5 or a range composed of any of the above values), b of the core and the shell is 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, 0.019 or a range composed of any of the above values), and z of the core and the shell is independently greater than 1.8 and less than 2.2 (e.g., 1.85, 1.9, 1.95, 2, 2.1, 2.15 or a range composed of any of the above values).

[0177] In some embodiments, the method further comprises the following steps:

[0178] Mixing the sintered product with a first coating raw material and sintering to obtain an intermediate product;

[0179] Mixing the intermediate product with a second coating raw material and sintering to obtain a cathode material comprising two coating layers;

[0180] The cathode material comprises 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 comprise 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 comprise 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 comprise one or more elements of Group IIA, Group IIIA, Group IVB, Group VB, Group VIB, Group VIIA, Group IIIB, Group IVA, and Group VIII, and may optionally comprise one or more elements of Sr, B, Al, Zr, Nb, W, F, La, Ce, C, Co; wherein, M1 of the core and the shell independently comprises one or two elements of Group IIIA and Group VIIB, M2 of the core and the shell independently comprises one or more elements of Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, and Group VB, a of the core and the shell independently is greater than 0.9 and less than 1.2 (for example, 0.95, 1, 1.05, 1.1, 1.15, 1.18 or the range composed 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 (for example, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or the range composed 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 (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 the range composed of any of the above values), 1 - x - y of the core and the shell independently is greater than 0 and less than or equal to 0.50 (for example, 0.1, 0.2, 0.3, 0.4, 0.5 or the range composed of any of the above values), b of the core and the shell independently 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, 0.019 or the range composed of any of the above values), and z of the core and the shell independently is greater than 1.8 and less than 2.2 (for example, 1.85, 1.9, 1.95, 2, 2.1, 2.15 or the range composed of any of the above values).

[0181] In some embodiments, in the step of preparing the precursor 2, after the reaction, the reaction product is aged to obtain the precursor 2.

[0182] In some embodiments, in the step of preparing the precursor 2, the temperature of the aging is 30°C - 80°C, such as 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or the range composed of any of the above values.

[0183] In some embodiments, in the step of preparing the precursor 2, the time of the aging is 5 - 24 h, such as 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 17, 19, 20, 21, 22, 23, 24 h or the range composed of any of the above values.

[0184] In some embodiments, in the steps of preparing the precursor 1 and the precursor 2, the temperature of the reaction is independently 40°C - 80°C, such as 40°C, 50°C, 60°C, 70°C, 80°C or a range composed of any of the above values.

[0185] In some embodiments, in the steps of preparing the precursor 1 and the precursor 2, the reaction is carried out in an inert gas atmosphere.

[0186] In some embodiments, 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 (such as 9, 9.5, 10, 10.5, 11, 11.5, 12 or a range composed of any of the above values).

[0187] In some embodiments, in the steps of preparing the precursor 2, after the reaction or aging, the reaction product is washed and dried. Optionally, the drying temperature is 100°C - 180°C, such as 100°C, 120°C, 140°C, 150°C, 170°C, 180°C or a range composed of any of the above values. Optionally, the drying time is 5 - 15h, such as 5, 6, 7, 8, 9, 10, 11, 13, 15h or a range composed of any of the above values.

[0188] In some embodiments, in the steps of preparing the sintered product, the sintering temperature is 750°C - 950°C, such as 750°C, 800°C, 850°C, 900°C, 950°C or a range composed of any of the above values.

[0189] In some embodiments, in the steps of preparing the sintered product, the sintering time is 10 - 30h, such as 10, 15, 20, 25, 30h or a range composed of any of the above values.

[0190] In some embodiments, in the steps of preparing the sintered product, the sintering is carried out in an atmosphere containing oxygen.

[0191] In some embodiments, 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, such as 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C or a range composed of any of the above values.

[0192] In some embodiments, in the steps of preparing the intermediate product and the cathode material including two coating layers, the sintering time is independently 5 - 20h, such as 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 17, 18, 19, 20h or a range composed of any of the above values.

[0193] In some embodiments, 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.

[0194] In some embodiments, the Dv50 particle size of the precursor 1 is 4.3–17.3 μm, such as 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 composed of any of the above values.

[0195] In some embodiments, the Dv50 particle size of the precursor 2 is 5-20 μm, such as 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 composed of any of the above values.

[0196] In some embodiments, 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.

[0197] 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, such as 0.01, 0.05, 0.08, 0.1, 0.12, 0.14, 0.15, 0.18, 0.19, or a range composed of any of the above values.

[0198] In some embodiments, the molar ratio of the lithium element in the precursor 2 to the lithium element in the lithium source is 5:6 - 10:9, such as 5:6, 1:1.06, 1:1, 1.05:1, 10:9, or a range composed of any of the above values.

[0199] 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, where a is greater than 0.9 and less than 1.2, such as 0.95, 1, 1.05, 1.1, 1.15, 1.18, or a range composed of any of the above values, and b is greater than 0 and less than or equal to 0.02, such as 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 composed of any of the above values.

[0200] In some embodiments, the mass ratio of the first coating material to the sintered product is greater than 0 and less than or equal to 1%, optionally greater than 0 and less than or equal to 0.5%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any of the above values.

[0201] In some embodiments, the mass ratio of the second coating material to the intermediate product is greater than 0 and less than or equal to 1%, optionally greater than 0 and less than or equal to 0.5%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range composed of any of the above values.

[0202] [Positive electrode plate]

[0203] The positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0204] During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode materials in the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li will change.

[0205] In the listing of the positive electrode materials in the present application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations.

[0206] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0207] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as 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.).

[0208] In some embodiments, the positive electrode material may further include positive electrode materials for batteries that are well-known in the art. By way of example, the positive electrode material may include at least one of the following materials: lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional 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. Among them, examples of the lithium transition metal oxide 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 (which may also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which may also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which may also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which may also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which may also be abbreviated 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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0209] In some embodiments, the positive electrode film layer may optionally further include a binder. By way of example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0210] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an 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.

[0211] In some embodiments, the positive electrode plate can be prepared in the following manner: dispersing the components for preparing the positive electrode plate described above, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0212] [Negative electrode plate]

[0213] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0214] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0215] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0216] In some embodiments, the negative electrode active material can be a negative electrode active material for a battery 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, etc. The silicon-based materials can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0217] In some embodiments, the negative electrode film layer may further optionally include a binder. As an 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).

[0218] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. As an 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.

[0219] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0220] In some embodiments, the negative electrode plate can be prepared by the following method: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0221] [Electrolyte]

[0222] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of the electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0223] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0224] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluoro bis(oxalate) phosphate, and lithium tetrafluorooxalate phosphate.

[0225] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0226] In some embodiments, the electrolyte may further optionally include additives. By way of example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, and the like.

[0227] [Separator film]

[0228] In some embodiments, the battery cell further includes a separator film. The present application does not particularly limit the type of the separator film, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0229] In some embodiments, the material of the separator film may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0230] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film may be made into an electrode assembly by a winding process or a stacking process.

[0231] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0232] In some embodiments, the outer package of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic, and as plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be cited.

[0233] The present application does not particularly limit the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 2 is a battery cell 5 with a square structure as an example.

[0234] In some embodiments, referring to Figure 3 , the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with 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 separator film may form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates into the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0235] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0236] Figure 4 is a battery module 4 as an example. Refer to Figure 4 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0237] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0238] In some embodiments, the above battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0239] Figure 5 and Figure 6 is a battery pack 1 as an example. Refer to Figure 5 and Figure 6 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0240] In addition, the present application also provides an electrical device. The electrical device includes at least one of the battery cell, battery module, or battery pack provided by the present application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can 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, satellites, energy storage systems, etc., but is not limited thereto.

[0241] As the electrical device, the battery cell, battery module, or battery pack can be selected according to its usage requirements.

[0242] Figure 7 is an electrical device as an example. The electrical device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high-power and high-energy density requirements of the electrical device for the battery cell, a battery pack or battery module can be adopted.

[0243] [Embodiment]

[0244] The embodiments of the present application will be described below. The following described embodiments are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific techniques or conditions noted in the embodiments, the techniques or conditions described in the literature in this field or according to the product specifications are followed. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchases.

[0245] Embodiment 1

[0246] (1) Preparation of the positive electrode material:

[0247] Nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in deionized water at a molar ratio of 8:1:1 to obtain a first solution with a total concentration of 1 mol / L;

[0248] Nickel sulfate, cobalt sulfate and manganese sulfate are dissolved in deionized water at a molar ratio of 6:2:2 to obtain a second solution with a total concentration of 1 mol / L;

[0249] The concentration of ammonia water is 5 g / L.

[0250] ① In a nitrogen atmosphere, the first solution and sodium hydroxide are introduced into a 500 L reaction kettle, the temperature of the reaction kettle is controlled at 60 °C, the rotation speed is maintained at 200 - 300 rpm, the flow rate of the first solution is 15 - 25 L / h, the pH value of the reaction system is maintained at 11, and as the particle size grows, the flow rate of the first solution is gradually reduced, and ammonia water is introduced simultaneously to maintain the ammonia concentration in the kettle at 5 g / L, obtaining a precursor 1 with a Dv50 particle size of 8 μm, namely Ni 0.8 Co 0.1 Mn 0.1 (OH)2;

[0251] ② Keeping other conditions the same as in step ①, introducing the second solution, controlling the flow rate at 12 - 16 L / h, continuing to grow, aging at 60 °C for 10 h, filtering, washing the filter residue, and drying at 100 °C for 15 h, obtaining a precursor 2 with a Dv50 particle size of 10 μm, namely Ni 0.6 Co 0.2 Mn 0.2 (OH)2 coated with Ni 0.8 Co 0.1 Mn 0.1 (OH)2;

[0252] ③ Mix the precursor 2, LiOH·H2O and ZrO2 in a mixer at a molar ratio of 0.99:1.00:0.01, and sinter at 800 °C for 18 h in an oxygen atmosphere;

[0253] ④Mix the sintered product with alumina at a molar ratio of 1:0.01, and then sinter at 500 °C for 10 h in an oxygen atmosphere to obtain the cathode material.

[0254] In the cathode material, the distribution directions of the primary particles of the core and the primary particles of the shell can be observed by scanning electron microscopy. The schematic diagrams of the distribution directions of the primary particles 81 of the core and the primary particles 82 of the shell are shown in Figure 8 .

[0255] (2) Preparation of the cathode electrode sheet:

[0256] Mix the cathode material, polyvinylidene fluoride, and conductive carbon black in a mass ratio of 90:5:5, then add N-methylpyrrolidone (NMP), stir for 2 h, and then stir it in a homogenizer at 1000 r / min until it is uniformly mixed. Then, uniformly coat it on both sides of a 13-μm-thick aluminum foil current collector. After coating, dry it in an oven at 100 °C, cold press it, and slit it to obtain the cathode electrode sheet.

[0257] (3) Preparation of the electrolyte:

[0258] Mix ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:2 to obtain a mixed solvent. Then, in a glove box under an argon atmosphere, dissolve the thoroughly dried lithium hexafluorophosphate in the mixed solvent and mix it evenly to obtain the electrolyte. The lithium salt concentration in the electrolyte is 1 mol / L.

[0259] (4) Preparation of the anode electrode sheet:

[0260] Mix the anode active material graphite, sodium carboxymethyl cellulose, styrene-butadiene rubber, and acetylene black in a mass ratio of 96:1:1:2, add deionized water, stir evenly in a blender, and then coat the slurry on both sides of an 8-μm-thick copper foil. Dry it in an oven at 100 °C, cold press it, and slit it to obtain the anode electrode sheet.

[0261] (5) Separator: Use a polypropylene membrane.

[0262] (6) Preparation of the secondary battery:

[0263] Stack and wind the above-mentioned cathode electrode sheet, separator, and anode electrode sheet in sequence to obtain an electrode assembly; put the electrode assembly into an outer package, add the above-prepared electrolyte, and after processes such as encapsulation, standing, formation, and aging, obtain the secondary battery.

[0264] The preparation methods, 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.

[0265]

[0266]

[0267]

[0268]

[0269]

[0270]

[0271] Material and Battery Tests

[0272] (1) Tests on the chemical formulas of the core and shell and the elements contained in the coating layer:

[0273] Perform a surface scan on the primary particles (particle size is Dv50 particle size ± 0.3 μm) of the cathode material through a combined SEM-EDS instrument to determine the boundaries of the core, shell, and coating layer. Then, in the form of point scanning through the combined SEM-EDS instrument, select ten points in the core, shell, and coating layer respectively and take the average value to further determine the chemical formulas of the core and shell and the elements contained in the coating layer.

[0274] (2) Tests on 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 cathode material:

[0275] Perform a surface scan on the primary particles (particle size is Dv50 particle size ± 0.3 μm) of the cathode material through a combined SEM-EDS instrument to determine the boundary between the core and the shell. Then, observe the aspect ratios of 50 primary particles of the core and 50 primary particles of the shell respectively through the SEM images. Repeat the above tests for a total of 50 primary particles of the cathode material and take the average value as the aspect ratio of the primary particles of the core and the aspect ratio of the primary particles of the shell.

[0276] Take the primary particles of the cathode material (particle size is Dv50 particle size ± 0.3 μm), observe the aspect ratio of the primary particles through the SEM images. Repeat the above tests for a total of 50 primary particles of the cathode material and take the average value as the aspect ratio of the primary particles of the cathode material.

[0277] (3) Tests on whether the coating layer is island-shaped coating or continuous coating:

[0278] Use electron probe X-ray microscopy (EPMA) to analyze the coating layer. If the display area of the coating layer elements is less than 1 μm 2 and the distribution is non-continuous, the test result is island-shaped coating, otherwise it is layered coating.

[0279] (4) Tests on volume distribution particle sizes Dv10, Dv50, and Dv90:

[0280] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T 19077-2016 / ISO 13320:2009.

[0281] Detailed test process: Take an appropriate amount of the washed sample (the sample concentration ensures a light transmittance of 8% - 12%), add 20 mL of absolute ethanol, and ultrasonically treat for 5 min (53 KHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to the standard of GB / T 19077-2016 / ISO 13320:2009.

[0282] (5) Measurement of the average diameter of the core and the average thickness of the shell:

[0283] Perform a surface scan on the primary particles (particle size is Dv50 particle size ± 0.3 μm) of the cathode material through a combined SEM-EDS instrument to determine the boundary between the core and the shell. Measure the distance from the core of the core to the boundary and the distance from the core of the core to the outermost edge of the shell in the scanning electron micrograph. Randomly orient and measure 50 times, and then repeat the above test on 50 primary particles of the cathode material. Twice the average value of the distance from the core of the core to the boundary 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 is the average thickness of the shell.

[0284] (6) Measurement of the BET specific surface area:

[0285] Test using the nitrogen adsorption specific surface area analysis test method and calculate it by the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be carried out through the TriStarII specific surface and pore analyzer of Micromeritics Company in the United States, and the test steps can refer to GB / T 19587-2004.

[0286] The detailed steps are as follows: Dry the sample to be tested in a vacuum drying oven at 200 °C for 2 hours; weigh 1 g of the sample to be tested and place it in the test tube. Fill the liquid nitrogen cup with liquid nitrogen and put it on the test tube. Use nitrogen as the adsorption gas, and map the adsorption and desorption curve with a relative pressure P / P0 of 0 - 0.99 through the specific surface and pore analyzer. P is the equilibrium adsorption pressure, and P0 is the saturated vapor pressure. Calculate the BET specific surface area of the cathode active material by the BET method.

[0287] (7) Measurement of the particle strength of the cathode material:

[0288] Use a microhardness tester (Shimadzu DUH-211S), select the secondary particles of the cathode material with a particle size of Dv50 particle size ± 0.3 μm, squeeze the particles by the movement of the probe equipped with a pressure sensor, and record the particle strength.

[0289] (8) Compaction density test:

[0290] Weigh 10 g of the cathode material and place it in the mold of the compaction density tester. The tester automatically applies a pressure of 30 MPa to the powder until it 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 the compaction density = mass / volume, the compaction density of the powder material can be measured.

[0291] (9) Test on whether the primary particles of the core or shell are distributed radially along the core:

[0292] Perform a surface scan on the primary particles (with a particle size of Dv50 particle size ± 0.3 μm) of the cathode material using a combined SEM-EDS instrument to determine the boundary between the core and the shell. Draw a radial line along the core of the core in the scanning electron microscope image;

[0293] Use a protractor to measure the angle θ between the primary particles of 50 cores (randomly selected) and the core radius. Repeat the above test for a total of 50 primary particles of the cathode material to obtain the range of the angle θ between the primary particles of the core and the core radius. If the range of the angle θ is ±10°, then the primary particles of the core are distributed radially along the core; otherwise, they are not.

[0294] Use a protractor to measure the angle θ between the primary particles of 50 shells (randomly selected) and the core radius. Repeat the above test for a total of 50 primary particles of the cathode material to obtain the range of the angle θ between the primary particles of the shell and the core radius. If the range of the angle θ is ±10°, then the primary particles of the shell are distributed radially along the core; otherwise, they are not.

[0295] (10) Test on the content of free lithium (including lithium carbonate and lithium hydroxide):

[0296] Weigh 30 g of the cathode material, add 100 mL of pure water, stir for 30 min, let it stand for 10 min, and then filter by suction to obtain the filtrate.

[0297] The determination is carried out by the general method for the determination of acidity and alkalinity of chemical reagents (GB / T 9724-2007). An automatic two-step potentiometric titration is performed on the filtrate using a 0.05 mol / L dilute hydrochloric acid solution as the titrant. First, the following reactions occur: LiOH + HCl = LiCl + H2O, Li2CO3 + HCl = LiHCO3 + LiCl. As the dilute hydrochloric acid solution is continuously added, all lithium hydroxide is converted into lithium chloride and water, and all Li2CO3 is converted into lithium bicarbonate and lithium chloride. At this time, the pH value is about 4.0 - 5.0, and the potentiometric titrator shows an electrode potential jump point EP1. As the dilute hydrochloric acid solution is continuously added, LiHCO3 + HCl = LiCl + CO2↑ + H2O. At this time, the pH value is about 8.0 - 9.0, and the potentiometric titrator shows an electrode potential jump point EP2. The contents of Li2CO3 and LiOH in the sample are calculated based on the consumption of the dilute hydrochloric acid corresponding to EP1 and EP2 and the chemical equations.

[0298] (11) Test of specific capacity:

[0299] At 25°C, first discharge at 1 / 3C to 2.80V and hold for 30 min. Then charge at a constant current of 1 / 3C to 4.25V, and 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.

[0300] (12) Test of cycle capacity retention rate:

[0301] 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, which is the first cycle. The discharge capacity of the first cycle is recorded as C0; cycle according to the above, the discharge capacity of the nth cycle is recorded as Cn, and the capacity retention rate of each cycle is Cn / C0. Calculate the capacity retention rate after 100 cycles.

[0302] (13) Test of capacity retention rate after storage at 60°C for 50 days:

[0303] 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 then discharged at a constant current of 1 / 3C to 2.8V. The measured discharge capacity is recorded as C0. The battery is charged again at a constant current of 1 / 3C to 4.25V, and then charged at a constant voltage of 4.25V to 0.05C.

[0304] Take out the fully charged battery after storing it in a 60°C constant temperature oven for 50 days. 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 then discharged at a constant current of 1 / 3C to 2.8V. The measured discharge capacity is Cn. Calculate the capacity retention rate = Cn / C0.

[0305] The above results are shown in Table 3-4.

[0306] Table 4 Battery test results of Examples 1-20 and Comparative Examples 1-3

[0307]

[0308]

[0309] It can be seen from the above results that:

[0310] Compared with the battery made of the core primary particles of the positive electrode material of Comparative Example 1 not being distributed along the radial direction of the core and the shell primary particles not being distributed along the radial direction of the core, the specific capacity, cycle capacity retention rate, and high-temperature storage performance of the batteries of Examples 1-20 of the present application are higher.

[0311] Compared with the battery made of the core primary particles of the positive electrode material of Comparative Example 2 not being distributed along the radial direction of the core and the shell primary particles being distributed along the radial direction of the core, the specific capacity, cycle capacity retention rate, and high-temperature storage performance of the batteries of Examples 1-20 of the present application are higher.

[0312] Compared with the battery made of the positive electrode material of Comparative Example 3 without doping the M2 element in both the core and the shell, the specific capacity, cycle capacity retention rate, and high-temperature storage performance of the batteries of Examples 1-20 of the present application are higher.

[0313] Compared with the battery made of the positive electrode material of Example 13 having a relatively high aspect ratio of the core primary particles, the cycle capacity retention rate and high-temperature storage performance of the batteries of Examples 1, 5-6 of the present application are higher.

[0314] Compared with the battery made of the positive electrode material of Example 16 having a relatively small Dv50 particle size, the cycle capacity retention rate and high-temperature storage performance of the batteries of Examples 9, 10 of the present application are higher.

[0315] Compared with the battery made of the positive electrode material of Example 17 having a relatively large Dv50 particle size, the cycle capacity retention rate and high-temperature storage performance of the batteries of Examples 9, 10 of the present application are higher.

[0316] Compared with the battery made of the positive electrode material of Example 20 having a ratio of the nickel content in the core to the nickel content in the shell less than 1, the specific capacity, cycle capacity retention rate, and high-temperature storage performance of the battery of Example 1 of the present application are higher.

[0317] It should be noted that this application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having the same composition and achieving the same effects as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A cathode material comprising a core and a shell coating the core, both the core and the shell comprising 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 selected from Group IIIA and Group VIIB; M2 of the core and the shell independently includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB; 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 cathode 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; and / or, M1 of the core and the shell independently includes one or two elements selected from Mn and Al; and / or, M2 of the core and the shell independently includes one or more elements selected from Ti, Na, K, Zr, Sr, Sb, Mo, W, Nb, Y, Te, La, B, F, Cl, and P.

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

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

5. The cathode material according to any one of claims 1 to 4, wherein, The aspect ratio of the primary particles in 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 positive electrode material according to claim 9, wherein, 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.

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: React by adding the first solution to the base or its solution, 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; Adding the second solution to the precursor 1 and the base or its solution for reaction, 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; Mixing the precursor 2, a lithium source, and a source of element M2, and sintering to obtain a sintered product, which is the positive electrode material.

14. The method according to claim 13, wherein The positive electrode material includes a core and a shell coating the core, both the core and the shell including 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 ; wherein, M1 of the core and the shell independently includes one or two elements selected from Group IIIA and Group VIIB; M2 of the core and the shell independently includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB; 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: Mixing the sintered product with a first coating raw material and sintering to obtain an intermediate product; Mixing the intermediate product with a second coating raw material and sintering to obtain a positive electrode 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 of Group IIA, Group IIIA, Group IVB, Group VB, Group VIB, Group VIIA, Group IIIB, Group IVA, and Group VIII; wherein, M1 of the core and the shell independently includes one or two elements selected from Group IIIA and Group VIIB; M2 of the core and the shell independently includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group VA, Group VIA, Group VIIA, Group IIIB, Group IVB, Group VB, and Group VIB; 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, the reaction product is aged 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 reaction temperature 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 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 h; and / or in the step of preparing the sintered product, the sintering temperature is 750°C - 950°C; and / or in the step of preparing the sintered product, the sintering time is 10 - 30 h; and / or in the step 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 positive electrode 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 positive electrode 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 positive electrode material including two coating layers, the sintering is carried out in an atmosphere containing oxygen.

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

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

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

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