Cathode materials, methods for preparing cathode materials, lithium-ion batteries, and electrical devices.

Abstract

This application discloses a cathode material, a method for preparing the cathode material, a lithium-ion battery, and an electrical device. It relates to the field of battery cathode material technology. This application modifies the cathode material by doping high-valence cations and anions into a nickel-rich ternary cathode material. This stabilizes the bulk structure of the nickel-rich ternary cathode material under lithium insertion / extraction conditions and the interfacial stability with the electrolyte, reducing side reactions, lattice oxygen evolution, and transition metal dissolution, thereby improving cycle stability, high-temperature storage performance, and rate performance. Furthermore, a selenium-containing coating layer can be applied to the outer surface of the cathode material to reduce the content of residual lithium compounds, increase the migration rate of lithium ions on the surface, and allow the remaining selenium-containing material to combine with lattice oxygen released under high delithiation conditions, preventing the electrolyte from being oxidized and producing gas. Additionally, a conductive coating layer can be prepared on the outer surface of the selenium-containing coating layer to prevent direct contact between the selenium-containing material and the electrolyte, suppressing the occurrence of side reactions.

Description

[0001] This application is a divisional application of Chinese patent application No. 202311439210.6, entitled "Positive Electrode Material, Method for Preparing Positive Electrode Material, Lithium-ion Battery, Electrical Device", filed on November 1, 2023. Technical Field

[0002] This application relates to the field of battery cathode materials, and more particularly to a cathode material, a method for preparing the cathode material, a lithium-ion battery, and an electrical device. Background Technology

[0003] Lithium-ion batteries (LIBs) have attracted much attention due to their long lifespan, high energy density, and low maintenance costs. Currently, LIBs are widely used in electric vehicles, portable electronic devices, energy storage systems, and other fields.

[0004] However, the energy density, safety, and lifespan of LIBs are not yet fully meeting various requirements, and cathode materials are a crucial factor for breakthroughs. Ternary cathode materials, due to their high reversible capacity and low cost, have become a hot topic in industrialization in recent years. Researchers typically increase the energy density of LIBs by continuously increasing their nickel content.

[0005] However, increasing the nickel content in ternary cathode materials leads to a series of problems. On the one hand, increased nickel content reduces the material's thermal stability. Under high SOC (state of charge) delithiation, oxygen is released from the crystal lattice, internal cracks propagate, and electrolyte easily enters the particles, causing side reactions. Simultaneously, transition metal dissolution occurs, resulting in deterioration of lifespan and safety performance. On the other hand, increased nickel content leads to the formation of residual lithium compounds (RLCs) on the surface, resulting in poor interface stability and a series of side effects, including reduced first-efficiency performance, deteriorated cycle life, and storage performance. Considering the various adverse effects of RLCs on the surface of ternary cathode materials, it is necessary to remove surface RLCs and inhibit their subsequent formation. Therefore, existing nickel-rich ternary cathode materials still require improvement. Summary of the Invention

[0006] This application is made in view of the above-mentioned issues, and its purpose is to provide a cathode material, a method for preparing the cathode material, a lithium-ion battery, and an electrical device.

[0007] This application provides a cathode material having the following chemical formula: Li a Ni x Co y Mn 1-x-y M b O 2-c Q cWherein, 0.2≤a≤1.2, x≥0.6, y>0, b>0, c>0, M includes high-valence cations, Q includes anions, the high-valence cations include tetravalent or higher cations, and the anions include S 2- Se 2- Te 2- P 3- At least one of the following. High-valence cations doped into nickel-rich cathode materials can influence the crystal growth direction of the cathode material, leading to grain refinement. They can also eliminate harmful stresses caused by lattice contraction due to the H2-H3 phase transition through fracture toughening, and can eliminate local compositional inhomogeneities in the material. In addition, the doped high-valence cations can also play a pillar effect to stabilize the stability of the delithiation structure. The doped anions can replace oxygen sites, enhance metal-oxygen bonds, inhibit lattice oxygen evolution, and at the same time reduce the interaction force between the lithium layer and the oxygen layer to increase the spacing between the lithium layer and the oxygen layer, reduce the lithium ion migration barrier, and accelerate lithium ion transport. This application stabilizes the bulk structure of nickel-rich cathode materials under lithium insertion / extraction and the interfacial stability with the electrolyte by combining bulk doping of high-valence cations and surface gradient doping of anions, reducing side reactions, lattice oxygen evolution, and transition metal dissolution, and improving cycle stability, high-temperature storage performance, and rate performance.

[0008] In some embodiments of this application, the high-valence cation includes Mo. 6+ Sb 5+ Zr 4+ Ti 4+ 、Nb 5+ W 6+ Y 5+ Ta 5+ At least one of the above types of high-valence cations can affect the growth direction of cathode material crystals, leading to grain refinement. They can also eliminate harmful stress caused by lattice contraction due to H2-H3 phase transition through fracture toughening, and can eliminate the problem of local composition inhomogeneity in the material. At the same time, they can play a pillar effect to stabilize the stability of the delithiation structure.

[0009] The anions described in this application include S. 2- Se 2- Te 2- P 3-At least one of the above types of anions. These anions can replace oxygen sites, enhance the metal-oxygen bond, suppress lattice oxygen evolution, and simultaneously reduce the interaction force between the lithium and oxygen layers to increase the spacing between them, thereby lowering the lithium-ion migration barrier and accelerating lithium-ion transport. By combining bulk doping with high-valence cations and surface gradient doping with anions, the bulk structure of nickel-rich cathode materials under lithium insertion / extraction conditions and the interfacial stability with the electrolyte can be stabilized, reducing side reactions, lattice oxygen evolution, and transition metal dissolution, and improving cycle stability, high-temperature storage performance, and rate performance.

[0010] In some embodiments of this application, 0.0005 ≤ b ≤ 0.01, and / or 0.001 ≤ c ≤ 0.1. Doping amounts of high-valence cations and anions in the cathode material within the above ranges are beneficial for stabilizing the bulk structure of the nickel-rich cathode material during lithium insertion / extraction and for improving the interfacial stability with the electrolyte. This reduces side reactions, lattice oxygen evolution, and transition metal dissolution, thereby improving cycle stability, high-temperature storage performance, and rate performance. It is less likely that insufficient doping will prevent the above effects from being achieved, and excessive doping will not affect the battery capacity or lead to a decrease in the battery's electrochemical performance.

[0011] In some embodiments of this application, the outer surface of the cathode material further includes a first coating layer, which comprises a selenium-containing substance. The selenium-containing substance can react in situ with impure lithium ions (RCLs) on the surface of the nickel-rich cathode material to form lithium selenate selenoselenoate (Li₂Se₂O₃) and lithium selenoate (Li₂SeO₄) and other CEIs, thereby increasing the migration rate of lithium ions on the surface. Simultaneously, the remaining selenium-containing substance can combine with lattice oxygen released during the high delithiation state to prevent the electrolyte from being oxidized and generating gas.

[0012] In some embodiments of this application, the selenium-containing material includes at least one of elemental selenium (Se), selenium oxide (SeO2), selenium sulfide (SeS2), and tellurium selenide (TeSe). These types of selenium-containing materials readily react with impure lithium on the surface of nickel-rich cathode materials to form lithium selenate selenate and lithium selenate, etc., in situ for the formation of CEI (electrolyte interface).

[0013] In some embodiments of this application, the selenium content in the cathode material containing the first coating layer is 0.03%–5%. It should be noted that the content here refers to the mass percentage.

[0014] In some embodiments of this application, based on 100% of the total mass of the cathode material, the amount of selenium-containing material added ranges from 0.1% to 5%. Within this range, the selenium-containing material is less likely to fail to remove RLCs due to insufficient addition, resulting in insignificant improvement in cathode material performance. Conversely, excessive addition is less likely to reduce the proportion of active material, decrease battery capacity, or even cause excessive selenium-containing material to catalyze the decomposition of electrolyte solvents and generate gas.

[0015] In some embodiments of this application, based on 100% of the total mass of the cathode material, the amount of selenium-containing substance added ranges from 0.5% to 2%.

[0016] In some embodiments of this application, the particle size Dv50 of the selenium-containing material is 100nm-1000nm. If the particle size of the selenium-containing material is too large, it is not conducive to the reaction with RLCs and a large amount of RLCs are easily left behind. Nanoscale selenium-containing materials, on the other hand, have a larger specific surface area, which can increase the reaction contact area and form a dense selenium-containing material coating layer.

[0017] In some embodiments of this application, the particle size Dv50 of the selenium-containing substance is 100nm-500nm.

[0018] In some embodiments of this application, the positive electrode material further includes a second coating layer, which coats the surface of the first coating layer. The second coating layer comprises a conductive polymer. Since selenium-containing substances readily catalyze the decomposition of electrolyte ester solvents to generate oxidizing gases, the conductive polymer in the second coating layer can isolate the selenium-containing substances from direct contact with the electrolyte, suppressing side reactions. Simultaneously, the excellent conductivity of the conductive polymer enhances the electronic conductivity of the material, reduces interfacial impedance, and improves the battery's cycle performance.

[0019] In some embodiments of this application, the conductive polymer includes at least one of polyaniline, polypyrrole, polypyridine, and polythiophene. These types of conductive polymers readily react to form a coating layer, which helps prevent direct contact between selenium-containing substances and the electrolyte, suppressing side reactions. Furthermore, these conductive polymers also possess excellent conductivity, enhancing the electronic conductivity of the cathode material, reducing interfacial impedance, and improving battery cycle performance.

[0020] In some embodiments of this application, the thickness of the second coating layer is 50nm-500nm. It is not easy for the thickness to affect the lithium-ion transport effect of the battery due to being too thick, nor is it easy for the thickness to be too thin to achieve the purpose of reducing side reactions by reducing the contact between selenium-containing substances and electrolyte.

[0021] In some embodiments of this application, the thickness of the second coating layer is 50nm-200nm.

[0022] A second aspect of this application provides a method for preparing a cathode material, comprising the following steps:

[0023] The method for preparing the cathode material includes the following steps:

[0024] A nickel-rich ternary cathode material precursor is mixed with a high-valence cation dopant and sintered to obtain a high-valence cation doped cathode material A. The cathode material A is mixed with an anion dopant and sintered to obtain the cathode material. The cathode material is referred to as cathode material C. Cathode material C contains high-valence cations and anions. The high-valence cations include tetravalent or higher cations.

[0025] or,

[0026] The method for preparing the cathode material includes the following steps:

[0027] A nickel-containing cathode material precursor is mixed with an anion dopant and sintered to obtain anion-doped cathode material B. The cathode material B is mixed with a high-valence cation dopant and sintered to obtain the cathode material. The cathode material is referred to as cathode material C. Cathode material C contains high-valence cations and anions, and the high-valence cations include tetravalent or higher cations.

[0028] This application obtains a cathode material C co-doped with high-valence cations and anions by first doping a high-valence cation with an anion, or by first doping anion with a high-valence cation, resulting in a cathode material C with good stability. It should be noted that the mixing of high-valence cation dopants and sintering in this application is to imbue the final cathode material with the high-valence cations, while the mixing of anion dopants and sintering is to imbue the final cathode material with the anions.

[0029] In some embodiments of this application, in the step of preparing the positive electrode material A, the sintering includes primary sintering and secondary sintering. The temperature of primary sintering is 350℃-500℃ and the primary sintering time is 2-7h. The temperature of secondary sintering is 600℃-800℃ and the secondary sintering time is 3-6h.

[0030] In some embodiments of this application, the sintering temperature in the step of preparing the positive electrode material B is 400°C–650°C.

[0031] A third aspect of this application provides a method for preparing a cathode material, comprising the following steps:

[0032] The cathode material C described above is mixed with a selenium-containing substance and heated to obtain a cathode material, which is referred to as cathode material D. The surface of cathode material D has a selenium-containing substance coating layer.

[0033] In some embodiments of this application, the heating temperature is 230°C–500°C;

[0034] And / or, the heating time is 15 min to 120 min.

[0035] The fourth aspect of this application also provides a method for preparing a cathode material, comprising the following steps:

[0036] A conductive polymer is dissolved in an organic solvent to obtain a conductive polymer solution. The conductive polymer solution, an initiator, and the positive electrode material D described above are mixed, reacted, filtered, washed, and dried to obtain a positive electrode material, which is referred to as positive electrode material E. The surface of positive electrode material E has a conductive material coating layer.

[0037] It should be noted that the above preparation method can be understood as preparing a conductive material coating layer on the outer surface of the selenium-containing material coating layer of the cathode material D, thereby forming the cathode material E, which contains both the selenium-containing material coating layer and the conductive material coating layer.

[0038] In some embodiments of this application, based on 100% of the total mass of the positive electrode material D, the amount of the conductive polymer added is 0.5%-10%. It is not easy to affect the lithium-ion transport effect of the battery due to excessive addition, nor is it easy to achieve the purpose of reducing side reactions by reducing the contact between selenium-containing substances and electrolyte due to insufficient addition.

[0039] The fifth aspect of this application also provides a lithium-ion battery, the battery comprising the positive electrode material described above in this application, and the battery comprising any one of a battery cell, a battery module, and a battery pack.

[0040] A fifth aspect of this application also provides an electrical device, the electrical device comprising the lithium-ion battery described above.

[0041] The beneficial effects that this application can achieve are:

[0042] This invention provides a cathode material that utilizes co-doping with high-valence cations and anions. The high-valence cations doped into the nickel-rich cathode material influence the crystal growth direction, leading to grain refinement. This process eliminates harmful stresses caused by lattice contraction during the H2-H3 phase transition through fracture toughening, and also eliminates localized compositional inhomogeneities. Furthermore, the doped high-valence cations act as a support structure, stabilizing the stability of the delithiation structure. The doped anions can replace oxygen sites, strengthening metal-oxygen bonds, suppressing lattice oxygen evolution, and simultaneously reducing the interaction force between the lithium and oxygen layers to increase the spacing between them, lowering the lithium-ion migration barrier and accelerating lithium-ion transport. By combining bulk doping with high-valence cations and surface gradient doping with anions, the bulk structure of the nickel-rich cathode material under lithium insertion / extraction conditions and its interfacial stability with the electrolyte are stabilized. This reduces side reactions, lattice oxygen evolution, and transition metal dissolution, improving cycle stability, high-temperature storage performance, and rate performance.

[0043] In addition, a first coating layer containing selenium can be prepared on the outer surface of the cathode material. The selenium-containing material can undergo a redox reaction with the lithium ions (RCLs) on the surface of the nickel-rich cathode material to remove some of the RCLs and form lithium selenate (Li2Se2O3) and lithium selenate (Li2SeO4) and other CEIs (electrolyte interfaces) in situ, which is beneficial to improve the migration rate of lithium ions on the surface. At the same time, the remaining selenium-containing material can combine with the lattice oxygen released under the high delithiation state to prevent the electrolyte from being oxidized and producing gas. The remaining RCLs can be further reacted and converted into active lithium for secondary utilization during the formation process after the battery cell is made.

[0044] Furthermore, a second coating layer, a conductive material coating layer, can be prepared on the surface of the selenium-containing material coating layer of the cathode material. This conductive material coating layer can prevent the selenium-containing material from directly contacting the electrolyte, suppressing side reactions. At the same time, the excellent conductivity of the conductive polymer can enhance the electronic conductivity of the cathode material, reduce interfacial impedance, and improve the cycle performance of the battery. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the cathode material structure according to one embodiment of this application.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1. Active substance; 2. Selenium-containing coating layer; 3. Conductive coating layer.

[0048] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0049] The following detailed description, with appropriate reference to the accompanying drawings, discloses the insulating thermal radiation coating and its preparation method, the insulating thermal radiation coating layer and its preparation method, the battery casing, the battery, and the electrical device. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of providing a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0052] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0053] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0054] As the nickel content in cathode materials increases, a series of problems arise. On the one hand, the increased nickel content leads to a decrease in the thermal stability of the material. Under high SOC delithiation state, oxygen is released from the crystal lattice, internal cracks propagate, and electrolyte easily enters the particle interior, causing side reactions. At the same time, transition metal dissolution occurs, resulting in a deterioration in lifespan and safety performance.

[0055] In view of this, this application proposes a cathode material having the following chemical formula: Li a Nix Co y Mn 1-x- y M b O 2-c Q c Wherein, 0.2≤a≤1.2, x≥0.6, y>0, b>0, c>0, M includes high-valence cations, Q includes anions, the high-valence cations include tetravalent or higher cations; the anions include S 2- Se 2- Te 2- P 3- At least one of them.

[0056] In some embodiments, high-valence cations include Mo 6+ Sb 5+ Zr 4+ Ti 4+ 、Nb 5+ W 6+ Y 5+ Ta 5+ At least one of the above types of high-valence cations can affect the growth direction of the cathode material crystal, leading to grain refinement. They can also eliminate harmful stress caused by H2-H3 phase transition lattice shrinkage through fracture toughening, and can eliminate the problem of local component inhomogeneity in the material. At the same time, they can play a pillar effect to stabilize the stability of the delithiation structure.

[0057] The anions in the aforementioned cathode material of this application include S. 2- Se 2- Te 2- P 3- At least one of the above types of anions. These anions can replace oxygen sites, enhance the metal-oxygen bond, suppress lattice oxygen evolution, and simultaneously reduce the interaction force between the lithium and oxygen layers to increase the spacing between them, thereby lowering the lithium-ion migration barrier and accelerating lithium-ion transport. By combining bulk doping with high-valence cations and surface gradient doping with anions, the bulk structure of nickel-rich cathode materials under lithium insertion / extraction conditions and the interfacial stability with the electrolyte can be stabilized, reducing side reactions, lattice oxygen evolution, and transition metal dissolution, and improving cycle stability, high-temperature storage performance, and rate performance.

[0058] In this application, the cathode material Li a Ni x Co y Mn 1-x-y M b O 2-c Q cIn this context, 0.2 ≤ a ≤ 1.2, where a can be any value within the range of 0.2 to 1.2, such as 0.2, 0.25, 0.28, 0.3, 0.32, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.18, or 1.2. It should be noted that the above range of lithium molar content in the cathode material includes the lithium molar content of the battery using this cathode material under different charge and discharge states.

[0059] In some embodiments, 0.0005 ≤ b ≤ 0.01, and / or 0.001 ≤ c ≤ 0.1. For example, b can be any value in the range of 0.0005 to 0.01, such as 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01; c can be any value in the range of 0.001 to 0.1, such as 0.001, 0.003, 0.005, 0.006, 0.008, 0.009, 0.01, 0.015, 0.02, 0.03, 0.04, 0.05, 0.055, 0.06, 0.07, 0.08, 0.085, 0.09, 0.095, 0.01. Within the above-mentioned range, the doping amount of high-valence cations and anions in the cathode material is beneficial to stabilizing the bulk structure of the nickel-rich cathode material under lithium insertion / extraction and the interfacial stability with the electrolyte, reducing side reactions, lattice oxygen evolution and transition metal dissolution, improving cycle stability, high-temperature storage performance and rate performance. It is not easy to exert the above effects due to insufficient doping amount, nor is it easy to affect the battery capacity and cause the battery's electrochemical performance to decline due to excessive doping amount.

[0060] On the other hand, as the nickel content increases, it leads to the formation of RLCs (residual lithium compounds on the surface) and poor interface stability in the electrode, resulting in a series of side effects, including first-efficiency degradation, deterioration of cycle and storage performance. Considering the various adverse effects of RLCs on the surface of the aforementioned ternary cathode material, it is necessary to remove surface RLCs and suppress their subsequent formation.

[0061] In view of this, in the above-mentioned cathode material doped with anions and high-valence cations, this application also designs a first coating layer on the outer surface of the cathode material, the first coating layer including a selenium-containing substance.

[0062] Selenium-containing substances can undergo redox reactions with lithium ions (RCLs) on the surface of nickel-rich cathode materials to remove some RCLs and form lithium selenate (Li2Se2O3) and lithium selenate (Li2SeO4) CEI (electrolyte interface) in situ, which is beneficial to improving the migration rate of lithium ions on the surface. At the same time, the remaining selenium-containing substances can combine with lattice oxygen released under high delithiation state to prevent the electrolyte from being oxidized and producing gas. The remaining RCLs can be further reacted and converted into active lithium for secondary utilization during the formation process after the battery cell is made.

[0063] In some embodiments, the selenium-containing material includes at least one of elemental selenium (Se), selenium oxide (SeO2), selenium sulfide (SeS2), and tellurium selenide (TeSe). These types of selenium-containing materials readily undergo redox reactions with impure lithium ions (RCLs) on the surface of nickel-rich cathode materials to form lithium selenate selenoate and lithium selenoate (CEI) in situ. This removes some RCLs, preventing excessive RCL content from affecting the interface stability of the lithium-ion battery and causing a series of side effects such as poor initial efficiency, deteriorated cycle life, and reduced storage performance.

[0064] In this embodiment, the selenium content in the cathode material including the first coating layer ranges from 0.03% to 5%, for example, it can be 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 0.9%, 1%, 1.05%, 1.1%, 1.2%, 1.3%, 1.5%. Any value within the range of 0.03% to 5%, including 1.8%, 1.9%, 1.91%, 1.95%, 2%, 2.2%, 2.3%, 2.5%, 2.6%, 2.7%, 2.76%, 2.8%, 2.9%, 3%, 3.5%, 3.56%, 3.6%, 3.7%, 3.9%, 4%, 4.2%, 4.5%, 4.8%, 4.9%, and 5%.

[0065] In some embodiments, based on 100% of the total mass of the cathode material, the amount of selenium-containing material added ranges from 0.1% to 5%, and further, from 0.5% to 2%. For example, it can be any value within the range of 0.1% to 5%, such as 0.1%, 0.3%, 0.4%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.6%, 2.9%, 3%, 3.3%, 3.5%, 3.8%, 3.9%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, 4.9%, and 5%. It is understood that the total mass of the cathode material mentioned in this embodiment refers to the material having the above chemical formula Li. a Ni x Co y Mn1-x-y M b O 2-c Q c The total mass of the cathode material, i.e., the cathode material for which the first coating layer has not yet been prepared.

[0066] This application does not limit the particle size Dv50 of the selenium-containing material. In some embodiments, the particle size Dv50 of the selenium-containing material is 100nm-1000nm, or it can be 100nm-500nm. For example, it can be any value in the 100nm-1000nm range, such as 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, etc.

[0067] However, selenium-containing substances can easily catalyze the decomposition of electrolyte ester solvents to generate oxidizing gases. Therefore, in some embodiments, the above-mentioned positive electrode material containing the first coating layer further includes a second coating layer, which coats the surface of the first coating layer and includes a conductive polymer.

[0068] The conductive polymer in the second coating layer can prevent selenium-containing substances from directly contacting the electrolyte and suppress side reactions. At the same time, the excellent conductivity of the conductive polymer enhances the electronic conductivity of the cathode material, reduces interfacial impedance, and improves the cycle performance of the battery.

[0069] In some embodiments, the conductive polymer includes at least one of polyaniline, polypyrrole, polypyridine, and polythiophene. These types of conductive polymers readily react to form a coating layer, which helps prevent direct contact between selenium-containing substances and the electrolyte, suppressing side reactions. Furthermore, these conductive polymers also possess excellent conductivity, enhancing the electronic conductivity of the cathode material, reducing interfacial impedance, and improving battery cycle performance.

[0070] This application does not limit the thickness of the second coating layer. In some embodiments, the thickness of the second coating layer is 50nm-500nm, or even 50nm-200nm. For example, the thickness of the second coating layer can be any value within the 50nm-500nm range, such as 50nm, 80nm, 100nm, 120nm, 150nm, 180nm, 200nm, 250nm, 300nm, 350nm, 400nm, 420nm, 450nm, 480nm, 490nm, and 500nm. Within the above thickness range, the second coating layer is less likely to affect the lithium-ion transport effect of the battery due to excessive thickness, and less likely to fail to achieve the purpose of reducing side reactions by reducing the contact between selenium-containing substances and the electrolyte due to excessive thinness.

[0071] A second aspect of this application provides a method for preparing a cathode material, the method comprising the following steps:

[0072] A nickel-rich ternary cathode material precursor is mixed with a high-valence cation dopant and sintered to obtain a high-valence cation doped cathode material A. Cathode material A is mixed with an anion dopant and sintered to obtain the above cathode material. This cathode material is referred to as cathode material C. Cathode material C contains high-valence cations and anions, wherein the high-valence cations include tetravalent or higher cations.

[0073] or,

[0074] The preparation method of this cathode material includes the following steps:

[0075] A nickel-containing cathode material precursor is mixed with an anion dopant and sintered to obtain anion-doped cathode material B. Cathode material B is mixed with a high-valence cation dopant and sintered to obtain the above-mentioned cathode material. This cathode material is referred to as cathode material C. Cathode material C contains high-valence cations and anions, wherein the high-valence cations include tetravalent or higher cations.

[0076] It should be noted that the cathode material C prepared by this method has the chemical formula described above in this application: Li a Ni x Co y Mn1-x-yM b O 2-c Q c Wherein, 0.2≤a≤1.2, x≥0.6, y>0, b>0, c>0, M includes high-valence cations, Q includes anions, the high-valence cations include tetravalent or higher cations, and the anions include S 2- Se 2- Te 2- P 3- At least one of them.

[0077] It is understood that the purpose of mixing high-valence cation dopants and sintering in this application is to ensure that the final cathode material carries the aforementioned high-valence cations, while the purpose of mixing anion dopants and sintering is to ensure that the final cathode material also carries the aforementioned anions. This invention does not limit the doping order of high-valence cations and anions. Cathode material A can be prepared by first doping a high-valence cation dopant into a nickel-rich ternary cathode material precursor, and then anion doping can be performed on cathode material A to obtain a cathode material C co-doped with high-valence cations and anions. Alternatively, anion dopants can be added to a nickel-rich ternary cathode material precursor to prepare an anion-doped cathode material B, and then high-valence cation dopants can be added to cathode material B to prepare a cathode material C co-doped with high-valence cations and anions. The cathode material C prepared by these two methods can be understood as the same type of cathode material, namely, a cathode material co-doped with high-valence cations and anions.

[0078] In some embodiments, high-valence cations are first doped into a nickel-rich ternary cathode material precursor to prepare cathode material A. During the preparation of cathode material A, the sintering process includes primary sintering and secondary sintering. The primary sintering temperature is 350℃–500℃, and the primary sintering time is 2–7 h. The secondary sintering temperature is 600℃–800℃, and the secondary sintering time is 3 h–6 h.

[0079] In some embodiments, anions are first doped into a nickel-rich ternary cathode material precursor to prepare cathode material B. During the preparation of cathode material B, the sintering temperature is 400℃–650℃.

[0080] In some embodiments, the nickel-rich ternary cathode material precursor is mixed with a high-valence cation dopant and then ball-milled in a ball mill jar to obtain mixed powder a. Sintering the mixed powder a helps to improve the sintering efficiency and makes the nickel-rich ternary cathode material precursor and the high-valence cation dopant more uniformly mixed.

[0081] In some embodiments, the nickel-rich ternary cathode material precursor and the cathode dopant are mixed and then ball-milled in a ball mill jar to obtain mixed powder b. Sintering the mixed powder b is beneficial to improving the sintering effect and making the nickel-rich ternary cathode material precursor and the anion dopant more uniformly mixed.

[0082] Similarly, after mixing cathode material A, which is doped with high-valence cations, with anion dopant, or after mixing cathode material B, which is doped with anion, with high-valence cation dopant, the sintering speed can be increased by ball milling, so that the raw materials are mixed more evenly.

[0083] Based on the method for preparing a cathode material C co-doped with high-valence cations and anions proposed in the second aspect of this application, the third aspect of this application also proposes a method for preparing a cathode material, comprising the following steps:

[0084] The cathode material C described above is mixed with a selenium-containing substance and heated to obtain a cathode material, which is referred to as cathode material D. The surface of cathode material D has a selenium-containing substance coating layer.

[0085] It should be noted that the above preparation method can be understood as preparing a selenium-containing coating layer on the outer surface of the cathode material C, thereby forming the cathode material D.

[0086] This application prepares a selenium-containing coating layer on the surface of a cathode material C co-doped with high-valence cations and anions. The selenium-containing material can undergo a redox reaction with the lithium ions (RCLs) on the surface of the nickel-rich cathode material to remove some of the RCLs and form lithium selenate (Li2Se2O3) and lithium selenate (Li2SeO4) and other CEIs (electrolyte interfaces) in situ, which is beneficial to improving the migration rate of lithium ions on the surface. At the same time, the remaining selenium-containing material can combine with the lattice oxygen released under the high delithiation state to prevent the electrolyte from being oxidized and producing gas. The remaining RCLs can be further reacted and converted into active lithium for secondary utilization during the formation process after the battery cell is made.

[0087] Under heating conditions, the selenium-containing material melts and diffuses uniformly on the surface of the cathode material C, forming a dense coating layer. In some embodiments, the heating temperature is 230℃–500℃, for example, any temperature value within the range of 230℃–500℃, such as 230℃, 240℃, 250℃, 280℃, 300℃, 350℃, 400℃, 420℃, 450℃, 480℃, or 500℃. These temperature conditions allow selenium-containing materials such as elemental selenium (Se), selenium oxide (SeO2), selenium sulfide (SeS2), and tellurium selenide (TeSe) to melt, which is beneficial for encapsulating the co-doped cathode material and forming a uniform selenium-containing coating layer on its surface.

[0088] In some embodiments, the heating time is 15 min–120 min. For example, the heating time can be any value within the range of 15 min–120 min, such as 15 min, 20 min, 50 min, 60 min, 80 min, 90 min, 100 min, 110 min, or 120 min. Under the above heating time conditions, the selenium-containing material can be molten and encapsulate the co-doped cathode material, forming a uniform selenium-containing material coating layer on its surface. At the same time, it is less likely to damage other substances in the co-doped cathode material due to excessively long heating time.

[0089] In some embodiments, heating in a tube furnace helps to make the selenium-containing material and the cathode material C heat more evenly, promotes the melting of the selenium-containing material, and forms a uniform first coating layer on the surface of the cathode material C: a selenium-containing material coating layer.

[0090] In some embodiments, the heating step is carried out in a protective atmosphere, such as an argon atmosphere, which helps to accelerate the melting of the selenium-containing material and prevents air from reacting with the selenium-containing material to generate other impurities that could affect the performance of the selenium-containing material coating layer.

[0091] Based on the method for preparing cathode material D with a selenium-containing coating layer proposed in the third aspect of this application, the fourth aspect of this application provides another method for preparing cathode material, including the following steps:

[0092] The conductive polymer is dissolved in an organic solvent to obtain a conductive polymer solution. The conductive polymer solution, the initiator, and the above-mentioned positive electrode material D are mixed and reacted, filtered, washed, and dried to obtain a positive electrode material, which is referred to as positive electrode material E. The surface of positive electrode material E has a conductive material coating layer.

[0093] It should be noted that the above preparation method can be understood as preparing a conductive material coating layer on the outer surface of the selenium-containing material coating layer of the cathode material D, thereby forming the cathode material E, which contains both the selenium-containing material coating layer and the conductive material coating layer.

[0094] Since selenium-containing substances readily catalyze the decomposition of ester solvents in the electrolyte to generate oxidizing gases, coating the outermost layer of the cathode material with a conductive polymer can prevent direct contact between the selenium-containing substances and the electrolyte, suppressing side reactions. At the same time, the excellent conductivity of the conductive polymer can enhance the electronic conductivity of the cathode material, reduce interfacial impedance, and improve the cycle performance of the battery.

[0095] In some embodiments, based on 100% of the total mass of the positive electrode material D, the amount of conductive polymer added is 0.5%–10%. For example, the amount added can be any value within the range of 0.5%–10%, such as 0.5%, 1%, 2%, 3%, 5%, 6%, 7%, 8%, 9%, 9.5%, 10%, etc. Within the above range, it is beneficial to completely encapsulate the positive electrode material containing selenium to form a dense conductive polymer coating layer, isolating the selenium-containing material from direct contact with the electrolyte, suppressing side reactions, and simultaneously providing conductivity to enhance the electronic conductivity of the positive electrode material, reduce interfacial impedance, and improve the cycle performance of the battery.

[0096] In some embodiments, the organic solvent includes NMP (N-methylpyrrolidone). These organic solvents can rapidly and uniformly dissolve the conductive polymer.

[0097] In some embodiments, the initiator includes hydrogen peroxide, ammonium persulfate, potassium persulfate, and azobisisobutyronitrile.

[0098] In some embodiments, the reaction between the conductive polymer and the positive electrode material D is carried out under a protective atmosphere, such as a nitrogen atmosphere.

[0099] In some embodiments, refer to Figure 1 The cathode material comprises an active material 1, a selenium-containing coating layer 2 encapsulating the active material 1, and an outermost conductive coating layer 3. The active material 1 is a nickel-rich ternary cathode material doped with high-valence cations and anions, namely the cathode material C described in this application. This nickel-rich ternary cathode material has the following chemical formula: Li a Ni x Co y Mn 1-x-y M b O 2-c Q c Wherein, 0.2≤a≤1.2, x≥0.6, y>0, b>0, c>0, M includes high-valence cations, Q includes anions, and the high-valence cations include tetravalent or higher cations.

[0100] The cathode material in this embodiment utilizes high-valence cations to influence the crystal growth direction, resulting in grain refinement. Fracture toughening eliminates harmful stresses caused by lattice contraction during the H2-H3 phase transition, and also eliminates localized compositional inhomogeneities in the cathode material. Furthermore, the doped high-valence cations act as a pillar effect, stabilizing the stability of the delithiation structure. The doped anions can replace oxygen sites, strengthening metal-oxygen bonds, suppressing lattice oxygen evolution, and simultaneously reducing the interaction force between the lithium and oxygen layers to increase the spacing between them, lowering the lithium-ion migration barrier and accelerating lithium-ion transport. This application, by combining bulk doping with high-valence cations and surface gradient doping with anions, stabilizes the bulk structure of the nickel-rich cathode material during lithium insertion / extraction and the interfacial stability with the electrolyte, reducing side reactions, lattice oxygen evolution, and transition metal dissolution, thereby improving cycle stability, high-temperature storage performance, and rate performance.

[0101] Furthermore, in this embodiment, the selenium-containing material in the selenium-containing coating layer 2 of the cathode material can react in situ with the lithium residues (RCLs) on the surface of the nickel-rich cathode material to form lithium selenate (Li2Se2O3) and lithium selenate (Li2SeO4) and other CEIs, thereby increasing the migration rate of lithium ions on the surface. Simultaneously, the remaining selenium-containing material can combine with the lattice oxygen released under high delithiation state to prevent the electrolyte from being oxidized and generating gas. Further, the outermost conductive coating layer 3 of the cathode material can prevent direct contact between the selenium-containing material and the electrolyte, suppressing side reactions. At the same time, the excellent conductivity of the conductive polymer can enhance the electronic conductivity of the cathode material, reduce interfacial impedance, and improve the cycle performance of the battery.

[0102] The fifth aspect of this application provides a lithium-ion battery comprising the positive electrode material as described above, namely, a positive electrode material C comprising co-doped high-valence cations and anions, a positive electrode material D comprising a selenium-containing coating layer, and a positive electrode material E comprising a conductive polymer coating layer.

[0103] In some embodiments, the lithium-ion battery described above includes any one of a battery cell, a battery module, and a battery pack.

[0104] The sixth aspect of this application provides an electrical device that includes the lithium-ion battery described above. The electrical device of this application has at least all the beneficial effects of the lithium-ion battery described above, which will not be repeated here.

[0105] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0106] Examples 1 to 20

[0107] 1. Modification of positive electrode active materials

[0108] S1: According to Table 1, the nickel-rich ternary cathode material NCM is mixed with a high-valence cation dopant and added to a ball mill jar to obtain mixed powder a. Mixed powder a is placed in an alumina crucible and sintered once at 350℃-500℃ for 2-7 hours, followed by a second sintering at 600℃-800℃ for 3-6 hours to obtain cathode material A. The doping amount of the high-valence cation is 0.1% of the total molar mass of the nickel-rich ternary cathode material NCM.

[0109] S2: According to Table 1, the cathode material A and the cathode dopant are mixed and added to a ball mill jar for ball milling to obtain mixed powder b. Mixed powder b is then sintered at 400℃-650℃ to obtain cathode material C co-doped with high-valence cations and anions; wherein, the anion doping amount is 0.5% of the total molar mass of nickel-rich ternary cathode material NCM.

[0110] S3: According to Table 1, the positive electrode material C and selenium-containing material with a particle size Dv50 of 100nm-1000nm are mixed and added to a ball mill jar to obtain mixed powder c. The mixed powder c is placed in an alumina crucible, placed in a tube furnace, and heated to 230℃-500℃ under an argon atmosphere for 15min-120min. The selenium-containing material becomes molten and diffuses uniformly on the surface of the positive electrode material C to form a dense coating layer, thus obtaining the positive electrode material D with a first coating layer of selenium-containing material coating on the surface. Wherein, the first coating layer content (wt%) in Table 1 refers to the amount of selenium-containing material added based on 100% of the total mass of the positive electrode material C.

[0111] S4: Dissolve the conductive polymer in N-methylpyrrolidone to obtain a conductive polymer solution. Mix the positive electrode material D, the conductive polymer solution, and the initiator hydrogen peroxide, react, filter, and wash to obtain a positive electrode material E with a second coating layer of conductive material with a thickness of 50nm-500nm. In Table 1, the content of the second coating layer (wt%) refers to the amount of conductive polymer added based on 100% of the total mass of the positive electrode material D.

[0112] The aforementioned cathode material E is a modified cathode material co-doped with high-valence cations and anions, and possesses a selenium-containing coating layer and a conductive coating layer, as described above. Figure 1 The modified cathode material contains an active material 1, a selenium-containing coating layer 2, and a conductive coating layer 3. The active material 1 is a nickel-rich ternary cathode material doped with high-valence cations and anions.

[0113] 2. Preparation of lithium-ion batteries

[0114] 1) Positive electrode plate

[0115] The modified positive electrode active material, nickel-cobalt-manganese ternary positive electrode material NCM, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were dissolved in solvent N-methylpyrrolidone (NMP) at a weight ratio of 96.5:1.5:2 and thoroughly stirred to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector with a primer, and then dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0116] 2) Negative electrode plate

[0117] The active material graphite, silicon, conductive agent acetylene black, polymer, and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water in a weight ratio of 90:5:2:2:1 to prepare a negative electrode slurry. The slurry is then coated onto copper foil, dried, and cold-pressed to obtain the anode sheet.

[0118] 3) Diaphragm

[0119] The diaphragm is a PE diaphragm with a PVDF and alumina coating on the surface to improve adhesion and heat resistance.

[0120] 4) Electrolyte

[0121] To obtain the electrolyte, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6:LiFSI (2:8) was uniformly dissolved in the above solution. The concentration of lithium salt in this electrolyte was 1 mol / L.

[0122] 5) Assemble the battery

[0123] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product.

[0124] Example 21

[0125] Example 21: Modified nickel-rich ternary cathode material C, doped with high-valence cations and anions, was prepared according to steps S1 and S2 of Example 1. Then, a lithium-ion battery was prepared according to the steps for preparing a lithium-ion battery in Example 1.

[0126] Example 22

[0127] Example 22: Following steps S1 to S3 of Example 1, a modified nickel-rich ternary cathode material D, doped with high-valence cations and anions and possessing a first coating layer of selenium-containing material, was prepared. Then, a lithium-ion battery was prepared following the steps of preparing a lithium-ion battery in Example 1.

[0128] Comparative Example 1

[0129] In Comparative Example 1, the cathode material used in the lithium-ion battery was the nickel-rich ternary cathode material NCM from Example 1, which was not modified. Other aspects were the same as in Example 1.

[0130] Comparative Example 2

[0131] The positive electrode material in the lithium-ion battery of Comparative Example 2 is the same as that in Example 1, except that Comparative Example 2 only prepares the first coating layer containing selenium material according to step S3 of Example 1, without doping with high-valence cations and anions, and does not prepare the second coating layer containing conductive material.

[0132] Performance testing:

[0133] The capacity retention rate at 0.33C (100 cycles), the capacity retention rate (%) after 100 days of storage at 100% SOC at 60°C, and the number of days (days) during which gas production reaches 0.4 MPa at 100% SOC at 60°C were measured for the lithium-ion batteries obtained in the examples and comparative examples.

[0134] Table 1: Parameter results of Examples 1-22 and Comparative Examples 1-2

[0135]

[0136]

[0137] As shown in Table 1, this application stabilizes the bulk structure of the nickel-rich cathode material during lithium insertion / extraction and the interfacial stability with the electrolyte by combining bulk doping of high-valence cations and surface gradient doping of anions. This reduces side reactions, lattice oxygen evolution, and transition metal dissolution, thereby improving the cycle stability, high-temperature storage performance, and rate performance of the lithium-ion battery. Furthermore, by preparing a selenium-containing coating layer and a conductive coating layer on the outer surface of the cathode material, some RLCs are removed, preventing excessive RLC content from affecting the interfacial stability of the lithium-ion battery and causing a series of side effects such as poor first-time efficiency, deteriorated cycle performance, and reduced storage performance. The conductive coating layer prevents direct contact between the selenium-containing material and the electrolyte, suppressing side reactions. Simultaneously, the excellent conductivity of the conductive polymer enhances the electronic conductivity of the cathode material, reduces interfacial impedance, and improves the battery's cycle performance. Therefore, the lithium-ion batteries prepared in Examples 1 to 22 have a capacity retention rate of over 96.5% at 0.33C (100 cycles), a capacity retention rate of over 91.5% after 100 days of storage at 100% SOC at 60°C, and a gas production rate of over 0.4 MPa for over 220 days at 100% SOC at 60°C.

[0138] Comparative Example 1, without modification of the cathode material, exhibited poor capacity retention and stability in its lithium-ion battery.

[0139] In Comparative Example 2, the cathode material was only coated with a selenium-containing material, without doping with high-valence cations and anions, and without a conductive material coating. As a result, the capacity retention and stability of the lithium-ion battery also decreased.

[0140] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode material, characterized in that, The cathode material has the following chemical formula: Li a Ni x Co y Mn 1-x-y M b O 2-c Q c Wherein, 0.2≤a≤1.2, x≥0.6, y>0, b>0, c>0, M includes high-valence cations, Q includes anions, the high-valence cations include tetravalent or higher cations, and the anions include S 2- Se 2- Te 2- P 3- At least one of the following; the outer surface of the positive electrode material further includes a first coating layer, the first coating layer including a selenium-containing substance; the positive electrode material further includes a second coating layer, the second coating layer coating the surface of the first coating layer, the second coating layer including a conductive polymer; the high-valence cation includes Mo. 6+ Sb 5+ Zr 4+ Ti 4+ 、Nb 5+ W 6+ Y 5+ Ta 5+ At least one of them; The selenium-containing material partially combines with the released lattice oxygen and partially reacts with the impure lithium RCLs on the surface of the cathode material to form lithium selenoselenate Li2Se2O3 and lithium selenoselenate Li2SeO4.

2. The cathode material according to claim 1, characterized in that, 0.0005≤b≤0.01, and / or, 0.001≤c≤0.

1.

3. The cathode material according to claim 1, characterized in that, The selenium-containing substance includes at least one of elemental selenium (Se), selenium oxide (SeO2), selenium sulfide (SeS2), and tellurium selenide (TeSe).

4. The cathode material according to claim 1, characterized in that, The content of selenium in the cathode material containing the first coating layer is 0.03%-5%.

5. The positive electrode material according to claim 1, characterized in that, Based on 100% of the total mass of the cathode material, the amount of selenium-containing substance added ranges from 0.1% to 5%.

6. The cathode material according to claim 5, characterized in that, Based on 100% of the total mass of the cathode material, the amount of selenium-containing substance added ranges from 0.5% to 2%.

7. The positive electrode material according to claim 1, characterized in that, The particle size Dv50 of the selenium-containing substance is 100nm-1000nm.

8. The cathode material according to claim 7, characterized in that, The particle size Dv50 of the selenium-containing substance is 100nm-500nm.

9. The positive electrode material according to claim 1, characterized in that, The conductive polymer includes at least one of polyaniline, polypyrrole, polypyridine, and polythiophene.

10. The cathode material according to claim 9, characterized in that, The thickness of the second coating layer is 50nm-500nm.

11. The cathode material according to claim 10, characterized in that, The thickness of the second coating layer is 50nm-200nm.

12. A method for preparing the positive electrode material according to any one of claims 1 to 11, characterized in that, The preparation method of the cathode material C includes the following steps: A nickel-rich ternary cathode material precursor is mixed with a high-valence cation dopant and sintered to obtain a high-valence cation doped cathode material A. The cathode material A is mixed with an anion dopant and sintered to obtain the cathode material C. The cathode material C contains high-valence cations and anions, and the high-valence cations include tetravalent or higher cations. or, The preparation method of the cathode material C includes the following steps: A nickel-containing cathode material precursor is mixed with an anion dopant and sintered to obtain anion-doped cathode material B. The cathode material B is mixed with a high-valence cation dopant and sintered to obtain cathode material C. Cathode material C contains high-valence cations and anions, and the high-valence cations include tetravalent or higher cations. The cathode material C is mixed with a selenium-containing substance and heated to obtain cathode material D, wherein the surface of cathode material D has a selenium-containing substance coating layer. A conductive polymer is dissolved in an organic solvent to obtain a conductive polymer solution. The conductive polymer solution, an initiator, and the positive electrode material D are mixed and reacted, filtered, washed, and dried to obtain a positive electrode material, which is denoted as positive electrode material E. The surface of positive electrode material E has a conductive material coating layer.

13. The method for preparing the cathode material according to claim 12, characterized in that, In the step of preparing the cathode material A, the sintering includes primary sintering and secondary sintering. The temperature of primary sintering is 350-500℃ and the time is 2-7h. The temperature of secondary sintering is 600-800℃ and the time is 3-6h.

14. The method for preparing the cathode material according to claim 12, characterized in that, In the step of preparing the positive electrode material B, the sintering temperature is 400℃-650℃.

15. The method for preparing the cathode material according to claim 12, characterized in that, The heating temperature is 230℃—500℃; And / or, the heating time is 15 min to 120 min.

16. The method for preparing the cathode material according to claim 12, characterized in that, Based on 100% of the total mass of the positive electrode material D, the amount of conductive polymer added is 0.5%–10%.

17. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in any one of claims 1 to 11.

18. An electrical appliance, characterized in that, The electrical device includes the lithium-ion battery as described in claim 17.

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