A positive electrode material and its preparation method, a positive electrode sheet, and a lithium-ion battery.

Abstract

This invention discloses a cathode material, its preparation method, a cathode electrode sheet, and a lithium-ion battery, relating to the field of lithium battery cathode material technology. The cathode material comprises a layered matrix, a substituted layered matrix layer, a heterojunction layer, and a perovskite structure layer. The heterojunction layer is a gradient heterojunction with spinel and / or rock salt phases. This cathode material exhibits advantages such as low gas generation, low impedance, excellent cycle performance and safety performance, and good high-voltage stability. The preparation method involves spraying a mixed solution containing A and B sources required for the perovskite structure onto the surface of the cathode active material, followed by drying and sintering. This preparation method is simple, effectively controls the degree of ion exchange, avoids excessive lithium-ion loss leading to capacity reduction, and ensures that the prepared perovskite structure layer is uniformly distributed on the surface of the cathode material. Furthermore, the equipment is simple, the process is streamlined, and it has excellent industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode materials, and more specifically, to a cathode material, its preparation method, a cathode sheet, and a lithium-ion battery. Background Technology

[0002] With rapid economic development, people's demand for energy is gradually increasing. Layered oxide cathode materials have high capacity, discharge plateau and compaction density, and are one of the most thoroughly researched and widely used commercial lithium-ion battery cathode materials.

[0003] Taking lithium cobalt oxide as an example, its energy density can currently be improved by increasing the cutoff voltage and compaction density. The current compaction density of lithium cobalt oxide has reached 4.2 g / cm³, leaving limited room for further improvement. Further optimization can only be achieved by increasing the cutoff voltage to enhance energy density. However, as the cutoff voltage of lithium-ion batteries increases, their performance deteriorates significantly. Under high voltage, lithium cobalt oxide may undergo a structural phase transition from O₃ to H₁₃ to O₁, leading to a rapid lattice collapse. Since the 3d band of Co largely overlaps with the 2p band of O, the Fm in the high delithiation state lies on the 2p band of O, causing oxidation of lattice oxygen in the cathode material. This oxygen release, i.e., irreversible oxygen loss under high voltage, further collapses the lithium cobalt oxide structure, exacerbating structural deterioration and capacity decay during cycling. This significantly worsens the thermal stability and safety of the lithium cobalt oxide cathode material, ultimately affecting the performance and lifespan of lithium-ion batteries.

[0004] Taking ternary cathode materials as an example, ternary cathode materials are in direct contact with the electrolyte. The surface of the cathode material is easily corroded by the electrolyte, resulting in the dissolution of transition metals such as Co, Mn, and Ni. The original layered structure is destroyed, which can lead to a series of safety problems.

[0005] Surface modification of lithium-ion cathode materials can effectively reduce the contact area between the cathode material and the electrolyte, reduce the amount of transition metal dissolution, and improve the structural stability and cycling performance. Common surface modification methods include coating metal oxides, phosphates, ion-electron dual conductors, etc. Metal oxides such as ZnO, A12O3, TiO2, etc., these materials have stable structures and do not react with the electrolyte, playing a role in protecting the cathode material. However, most oxides are electron-insulating, and the coating will increase the electron conductivity impedance of the cathode material, reduce the capacity utilization, and at the same time have a limited improvement in gas generation. Metal phosphates such as AlPO4, Li3PO3, LiMgPO4, etc., the coating of these materials on the cathode material is beneficial to improve its capacity retention rate, but it cannot improve the corrosion of the electrolyte on the cathode surface at high voltages, and the protection ability is limited at high voltages. Coating ion-electron dual conductors usually refers to coating other cathode materials, such as ternary materials, lithium iron phosphate, lithium manganate, etc. These materials are either unstable at high voltages or have a risk of insufficient energy density, and at high voltages, the risk of gas generation still exists.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] In view of the fact that existing coating methods are difficult to comprehensively solve various problems of cathode materials, such as gas generation and transition metal dissolution, while maintaining good electrochemical performance of the cathode material, the present invention provides a cathode material, its preparation method, a cathode electrode and a lithium-ion battery, aiming to provide a coated and modified cathode material with high ionic conductivity, low gas generation and excellent cycling stability.

[0008] The present invention is implemented as follows:

[0009] In a first aspect, the present invention provides a cathode material, which includes a layered matrix, a substituted layered matrix layer, a heterojunction layer and a perovskite structure layer.

[0010] The layered matrix has a chemical general formula Li a M 1-b M′ b O2, where 0.98 ≤ a ≤ 1.02, 0 < b ≤ 0.1, M is at least one of Ni, Co and Mn; M′ is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb and Ca;

[0011] The substituted layered matrix layer is distributed in a direction away from the layered matrix and is connected to the layered matrix. The substituted layered matrix layer has a layered structure different from that of the layered matrix. The substituted layered matrix layer has a chemical general formula Li a-x C x M1-b M′ b O2, where 0 < x ≤ 0.3; C is metallic element A and / or metallic element B;

[0012] The heterojunction layer is distributed on the surface of the substituted layered matrix layer away from the layered matrix and is connected to the substituted layered matrix layer. The heterojunction layer includes at least one of spinel structure and rock salt phase structure.

[0013] The perovskite structure layer is distributed on the surface of the heterojunction layer away from the layered matrix and is connected to the heterojunction layer. The perovskite structure layer has the general chemical formula ABO3, where A and B are both metallic elements.

[0014] In some embodiments of the present invention, the angle of repose of the positive electrode material is ≤55°, and preferably, the angle of repose of the positive electrode material is 30°~50°.

[0015] In some embodiments of the present invention, the Li a-x C x M 1-b M′ b In O2, the value of x is 0 < x ≤ 0.1.

[0016] In some embodiments of the present invention, the total mass of elements A and B in the cathode material is less than 5% of the total mass of the cathode material; preferably, the total mass of elements A and B in the cathode material is less than 3% of the total mass of the cathode material.

[0017] In some embodiments of the present invention, A in ABO3 is at least one of Pb, Na, Sn, Sr, K, Ca, Ba, Pr, Ln, Sm, Gd and La; and B is at least one of Ti, Mg, Y, Zn, Fe, Ta, Mn, Co, Ni, Mo, Nb, W and Al.

[0018] When the M element in the layered matrix of the cathode material is the same element as the B element in the perovskite structure layer, the chemical state of the same element in the layered matrix is ​​different from that in the perovskite structure layer. The chemical state refers to the lattice position of the element and its bonding state with other element atoms.

[0019] In some embodiments of the present invention, the median particle size Dv50 of the cathode material is 12~18 μm;

[0020] In some embodiments of the present invention, the thickness of the replacement layer of the layered matrix is ​​less than 50 nm;

[0021] In some embodiments of the present invention, the thickness of the heterojunction layer is less than 10 nm;

[0022] In some embodiments of the present invention, the thickness of the perovskite structure layer is less than 10 nm.

[0023] Secondly, the present invention provides a method for preparing a cathode material according to any of the above embodiments, comprising the following steps:

[0024] Prepare positive electrode active material; prepare a mixed solution of source A and source B;

[0025] The mixed solution is sprayed onto the surface of the positive electrode active material under stirring, and dried to obtain a spray-coated positive electrode material;

[0026] The positive electrode material is obtained by sintering the sprayed coating and then crushing it.

[0027] In some embodiments of the present invention, the preparation method of the positive electrode active material includes the following steps: mixing lithium source, M source and M′ source and calcining, and then crushing to obtain the positive electrode active material.

[0028] In some embodiments, the calcination temperature is 600–1100°C, preferably 800–1090°C; the calcination time is 5–15 h, preferably 7–14 h.

[0029] In some embodiments, the primary particle size of the positive electrode active material is 2–25 μm;

[0030] In some embodiments, the lithium source is at least one selected from lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxalate;

[0031] In some embodiments, the M source is at least one of an oxide or hydroxide containing M; the M is at least one of Ni, Co, and Mn; preferably, the M source is at least one of cobalt tetroxide, cobalt hydroxyoxide, cobalt hydroxide, nickel cobalt manganese oxide, nickel cobalt manganese hydroxide, manganese hydroxide, nickel hydroxide, nickel oxide, and manganese oxide.

[0032] In some embodiments, the M′ source is at least one of oxides, hydroxides, acetates, carbonates, and basic carbonates containing M′; and M′ is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, and Ca.

[0033] In some embodiments of the present invention, the A source is at least one of acetate, carbonate and basic carbonate containing A, and A is at least one of Pb, Na, Sn, Sr, K, Ca, Ba, Ln, Pr, Sm, Gd and La.

[0034] In some embodiments of the present invention, the B source is at least one of acetate, carbonate and basic carbonate containing B, and the B is at least one of Ti, Mg, Y, Zn, Fe, Ta, Mn, Co, Ni, Mo, Nb, W and Al.

[0035] In some embodiments of the present invention, the mixed solution is an aqueous solution of source A and source B.

[0036] In some embodiments of the present invention, the molar ratio of element A to element B in the mixed solution is (1~1.1):(1~1.1).

[0037] In some embodiments of the present invention, the mixed solution is sprayed onto the surface of the aluminum source and the positive electrode active material under stirring, and then dried to obtain the spray-coated positive electrode material.

[0038] In some embodiments, the aluminum source includes at least one of aluminum oxide, aluminum hydroxide, and aluminum hydroxyaluminate.

[0039] In some embodiments of the present invention, the stirring speed is 300~1500 r / min;

[0040] In some embodiments of the present invention, the spraying time is 10-60 minutes;

[0041] In some embodiments of the present invention, the drying temperature is 40~150℃, preferably 40℃; the drying time is 0.5~3h, preferably 0.5h.

[0042] In some embodiments of the present invention, the sintering temperature is 350–700°C, preferably 550°C; the sintering time is 2–10 h, preferably 4 h;

[0043] In some embodiments of the present invention, the crushing is performed using at least one of a vibrating screen, a mechanical mill, and an air jet mill.

[0044] Thirdly, the present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material obtained in any of the above embodiments.

[0045] Fourthly, the present invention provides a lithium-ion battery, including the above-mentioned positive electrode, as well as a negative electrode, an electrolyte, and a separator.

[0046] Fifthly, the present invention provides an electronic device including the aforementioned lithium-ion battery.

[0047] The present invention has the following beneficial effects:

[0048] (1) This invention provides a surface-coated modified cathode material, comprising a layered matrix, a substituted layered matrix layer, a heterojunction layer, and a perovskite structure layer. The heterojunction layer is a gradient heterojunction with spinel and / or rock salt phases, which can improve the phase interface, alleviate the irreversible oxygen loss problem of the cathode material under high voltage, and enable the cathode material to have better high voltage stability during cycling, thereby enabling the lithium-ion battery to achieve high voltage cycle capacity retention. In addition, the perovskite structure coating layer, as a fast ion conductor, has the characteristics of high electronic conductivity, high lithium-ion conductivity, and low oxygen-ion conductivity, which significantly improves the OER (oxygen production reaction) overpotential on the material surface, and can realize the reversible storage of high-valence oxygen in its oxygen vacancies under high voltage, thereby significantly improving the cycle stability of the layered oxide cathode material under high voltage. Therefore, the cathode material with the above characteristics provided by this invention has the advantages of low gas production, low impedance, excellent cycle performance and safety performance, and good high voltage stability.

[0049] (2) This invention provides a method for preparing a cathode material. The method involves spraying a mixed solution containing a source A and a source B required for a perovskite structure onto the surface of the cathode active material. At a certain temperature, metal ions in the mixed solution exchange with lithium ions in the cathode active material, resulting in partial substitution of lithium ions to the surface layer, thus forming a substituted layered matrix. Further spraying and coating of the cathode material, followed by sintering, sequentially forms a heterojunction layer and a perovskite structure layer on the surface of the substituted layered matrix, thereby forming a structure consisting of a layered matrix, a substituted layered matrix, a heterojunction layer, and a perovskite structure layer. The preparation method of this invention is simple, effectively controls the degree of ion exchange, and avoids excessive lithium ion loss leading to capacity reduction. Furthermore, the prepared perovskite structure layer is uniformly distributed on the surface of the cathode material, and the equipment is simple with few process steps, showing great promise for industrialization. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 SEM image of the cathode material prepared in Example 1;

[0052] Figure 2 SEM image of the cathode material prepared in Example 5;

[0053] Figure 3 Here is a SEM image of the cathode material prepared in Comparative Example 1;

[0054] Figure 4 Here is a SEM image of the cathode material prepared in Comparative Example 10;

[0055] Figure 5 This is a TEM image of the cathode material prepared in Example 5. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0057] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.

[0058] The term "embodiment" in this document means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0059] In the embodiments of this application, the term "and / or" is only a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0060] Additionally, the character " / " in this article generally indicates that the objects before and after it are in an "or" relationship.

[0061] In the embodiments of this application, "multiple" means two or more (including two), similarly, "multiple groups" means two or more (including two groups), and "multiple layers" means two or more (including two layers), unless otherwise explicitly specified and limited.

[0062] In the embodiments of this application, "at least one" means one or more.

[0063] In the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed in a specific orientation, etc. It should not be construed as a limitation to the embodiments of the present application. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application according to specific circumstances.

[0064] In a first aspect, the present invention provides a positive electrode material, which includes a layered matrix, a substituted layered matrix layer, a heterojunction layer, and a perovskite structure layer.

[0065] The layered matrix has a chemical general formula Li a M 1-b M′ b O2, where 0.98 ≤ a ≤ 1.02, 0 < b ≤ 0.1, M is at least one of Ni, Co, and Mn; M′ is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, and Ca;

[0066] The substituted layered matrix layer is distributed in the direction away from the layered matrix and is connected to the layered matrix. The substituted layered matrix layer has a layered structure different from that of the layered matrix; the substituted layered matrix layer has a chemical general formula Li a-x C x M 1-b M′ b O2, where 0 < x ≤ 0.3, preferably 0 < x ≤ 0.1; C is metal element A or / and metal element B;

[0067] The heterojunction layer is distributed on the surface of the substituted layered matrix layer in the direction away from the layered matrix and is connected to the substituted layered matrix layer. The heterojunction layer includes at least one of a spinel structure and a rock salt phase structure;

[0068] The perovskite structure layer is distributed on the surface of the heterojunction layer in the direction away from the layered matrix and is connected to the heterojunction layer. The perovskite structure layer has a chemical general formula ABO3, where both A and B are metal elements.

[0069] The lithium content of the positive electrode material provided by the present invention gradually decreases along the directions of the layered matrix, the substituted layered matrix layer, the heterojunction layer, and the perovskite structure layer.

[0070] Under high-voltage delithiation, cathode materials are prone to lattice oxygen oxidation and gas generation. This can cause the crystal structure of the cathode material to collapse, leading to capacity decay. Furthermore, it poses a significant safety hazard, as gas accumulation can cause battery explosion. Additionally, the cathode material is in direct contact with the electrolyte, making its surface susceptible to corrosion and the dissolution of transition metals such as Co, Mn, and Ni. Surface coating of the cathode material can partially mitigate these problems, but may still lead to capacity reduction and increased impedance.

[0071] The cathode material provided by this invention contains a heterojunction layer, which is a gradient heterojunction with spinel and / or rock salt phases. This heterojunction layer can improve the phase interface between the layered matrix layer, the heterojunction layer, and the perovskite structure layer, alleviate the irreversible oxygen loss problem of the cathode material under high voltage, and enable the cathode material to have better high voltage stability during cycling. This, in turn, enables the lithium-ion battery to achieve high voltage cycle capacity retention. In addition, the perovskite structure coating layer, as a fast ion conductor, has the characteristics of high electronic conductivity, high lithium-ion conductivity, and low oxygen ion conductivity. This significantly improves the OER (oxygen production reaction) overpotential on the material surface and enables the reversible storage of high-valence oxygen in its oxygen vacancies under high voltage, thereby significantly improving the cycle stability of the layered oxide cathode material under high voltage.

[0072] Therefore, the cathode material with the above-mentioned characteristics provided by the present invention has the advantages of low gas production, low impedance, excellent cycle performance and safety performance, and good high-voltage stability.

[0073] In some embodiments of the present invention, the angle of repose of the positive electrode material is ≤55°, and preferably, the angle of repose of the positive electrode material is 30°~50°.

[0074] The angle of repose can reflect the uniformity of the coating of the cathode material. The higher the uniformity of the coating, the smaller the interaction force between the particles, that is, the smaller the friction between the material particles, the greater the fluidity of the material particles, and the smaller the angle of repose.

[0075] The cathode material provided by this invention has a suitable angle of repose, and the perovskite structure layer on the outer surface of the cathode material is a uniform coating layer. The coating structure of the cathode material can be observed from the scanning electron microscope (SEM) image, which includes film-like coating and a small number of island-like coatings, with good uniformity. Good coating uniformity is beneficial to reducing interfacial side reactions, reducing gas production, improving structural stability, and improving cycle stability.

[0076] Layered matrix Li a M 1-b M′ b O2 undergoes a displacement reaction with the metal salt solution; at this time, a portion of the Li core... a M 1-b M′ bO2, as the bulk, does not react and remains in an ordered, layered state; while Li a M 1-b M′ b Li exists on the surface of O2. + Loss, Li + The lost vacancies are partially replaced by metal C ions from the metal salt solution, thus yielding Li a-x C x M 1-b M′ b O2 layer.

[0077] If the mass percentage of carbon is too high, it will lead to excessive lithium loss and a decrease in specific capacity; if the mass percentage of carbon is too low, it will lead to a low lithium replacement rate and a decrease in the effect of suppressing gas production.

[0078] In some embodiments of the present invention, the total mass of element A and element B in the cathode material is less than 5% of the total mass of the cathode material; preferably, the total mass of element A and element B in the cathode material is less than 3% of the total mass of the cathode material.

[0079] Low levels of elements A and B indicate fewer perovskite structural layers, resulting in insufficient coating and decreased gas production suppression and cycle stability. Conversely, high levels of elements A and B lead to greater ion exchange with the layered matrix, resulting in increased Li... + The large loss leads to a decrease in the specific capacity of the cathode material.

[0080] In some embodiments of the present invention, A in ABO3 is at least one of Pb, Na, Sn, K, Ca, Ba, Sr, Ln, Pr, Sm, Gd, and La; and B is at least one of Ti, Mg, Y, Zn, Fe, Ta, Mn, Co, Ni, Mo, Nb, W, and Al.

[0081] When the M element in the layered matrix of the cathode material is the same element as the B element in the perovskite structure layer, the chemical state of the same element in the layered matrix is ​​different from the chemical state in the perovskite structure layer.

[0082] In some embodiments of the present invention, the median particle size Dv50 of the cathode material is 12~18 μm;

[0083] In some embodiments of the present invention, the thickness of the replacement layered matrix is ​​less than 50 nm;

[0084] In some embodiments of the present invention, the thickness of the heterojunction layer is less than 10 nm;

[0085] In some embodiments of the present invention, the thickness of the perovskite structure layer is less than 10 nm.

[0086] The cathode material provided by this invention has a multilayer structure, wherein the thickness of the substituted layered matrix layer, the heterojunction layer, and the perovskite structure layer is relatively small. Therefore, the specific capacity of the cathode material does not decrease due to the coating modification and still maintains a high specific capacity.

[0087] Secondly, the present invention provides a method for preparing a cathode material according to any of the above embodiments, comprising the following steps:

[0088] Prepare positive electrode active material; prepare a mixed solution of source A and source B;

[0089] The mixed solution is sprayed onto the surface of the positive electrode active material under stirring, and dried to obtain a spray-coated positive electrode material;

[0090] The positive electrode material is obtained by sintering the sprayed coating and then crushing it.

[0091] This invention applies a mixed solution containing source A and source B to the surface of the positive electrode active material by spraying, which facilitates control over the degree of ion exchange between the positive electrode material and the mixed solution, resulting in a substituted layered matrix layer (Li) with 0 < x ≤ 0.3. a-x C x M 1-b M′ b (O2); In addition, the spraying method allows for control over the thickness of the obtained substituted layered matrix layer, keeping it relatively thin and avoiding excessive impact on the specific capacity of the cathode material. Furthermore, spraying the mixed solution onto the cathode surface while stirring ensures that elements A and B are uniformly distributed on the cathode material surface, resulting in a uniform distribution of the perovskite structure layer on the cathode material surface, greatly improving the coating uniformity and effectiveness.

[0092] It should be noted that the general chemical formula of the positive electrode active material described in this invention is Li. a M 1-b M′ b O2, by spraying a mixed solution onto its surface, causes partial ion exchange of the positive electrode active material to obtain the layered matrix layer and the original substituted layered matrix layer. After the sprayed positive electrode material is sintered, part of the original substituted layered matrix layer reacts to form a heterojunction layer, thereby obtaining the substituted layered matrix layer and the heterojunction layer.

[0093] Ion exchange is a liquid-solid phase reaction process involving the diffusion of substances in liquid and solid phases. A mixed solution is uniformly sprayed onto the surface of the cathode material through spraying and stirring. At a certain temperature, metal ions in the mixed solution exchange with lithium ions in the cathode active material, resulting in the partial replacement of lithium ions with the surface layer, thus forming a substituted layered matrix.

[0094] Further coating of the cathode material with spraying and sintering creates a heterojunction layer and a calcite-ironite structure layer sequentially on the surface of the replaced layered matrix, thus forming a structure consisting of a layered matrix, a replaced layered matrix, a heterojunction layer, and a calcite-ironite structure layer. The heterojunction layer is a partially replaced layered matrix (Li... a-x C x M 1-b M′ b The heterojunction layer is formed by the reaction of O2 with a portion of the perovskite structure (ABO3) at high temperature. The heterojunction layer is a gradient heterojunction with spinel and / or rock salt phases.

[0095] The preparation method of this invention is simple, the equipment is simple, and the process is simple, which has a good prospect for industrialization.

[0096] In some embodiments of the present invention, the preparation method of the positive electrode active material includes the following steps: mixing lithium source, M source and M′ source and calcining, and then crushing to obtain the positive electrode active material.

[0097] It should be noted that the preparation method of the positive electrode active material described in this invention is not limited to the above-mentioned solid-phase method, and may also employ methods such as salt decomposition, co-precipitation, sol-gel method, hydrothermal method, reverse emulsion method, and template method.

[0098] In some embodiments, the calcination temperature is 600-1100℃, preferably 800-1090℃; the calcination time is 5-15h, preferably 7-14h.

[0099] In some embodiments, the primary particle size of the positive electrode active material is 2–25 μm;

[0100] In some embodiments, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxalate;

[0101] In some embodiments, the M source is at least one of an oxide or hydroxide containing M; the M is at least one of Ni, Co, and Mn; preferably, the M source is at least one of cobalt tetroxide, cobalt hydroxyl oxide, cobalt hydroxide, nickel cobalt manganese oxide, nickel cobalt manganese hydroxide, manganese hydroxide, nickel hydroxide, nickel oxide, and manganese oxide.

[0102] In some embodiments, the M′ source is at least one of oxides, hydroxides, acetates, carbonates, and basic carbonates containing M′; and M′ is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, and Ca.

[0103] In some embodiments of the present invention, the A source is at least one of acetate, carbonate and basic carbonate containing A, and A is at least one of Pb, Na, Sn, Sr, K, Ca, Ba, Ln, Pr, Sm, Gd and La.

[0104] In some embodiments of the present invention, the B source is at least one of acetate, carbonate and basic carbonate containing B, and the B is at least one of Ti, Mg, Y, Zn, Fe, Ta, Mn, Co, Ni, Mo, Nb, W and Al.

[0105] In some embodiments of the present invention, the mixed solution is an aqueous solution of source A and source B.

[0106] In some embodiments of the present invention, the molar ratio of element A to element B in the mixed solution is (1~1.1):(1~1.1).

[0107] In some embodiments of the present invention, the mixed solution is sprayed onto the surface of the aluminum source and the positive electrode active material under stirring, and after drying, a spray-coated positive electrode material is obtained.

[0108] In some embodiments, the aluminum source includes at least one of aluminum oxide, aluminum hydroxide, and aluminum hydroxyaluminate.

[0109] The addition of an aluminum source during sintering in this invention is beneficial for improving the cycle stability of the cathode material.

[0110] In some embodiments of the present invention, the stirring speed is 300~1500 r / min;

[0111] In some embodiments of the present invention, the spraying time is 10 to 60 minutes;

[0112] In some embodiments of the present invention, the drying temperature is 40~150℃, preferably 40℃; the drying time is 0.5~3h, preferably 0.5h.

[0113] In some embodiments of the present invention, the sintering temperature is 350-700°C, preferably 550°C; and the sintering time is 2-10 hours, preferably 4 hours.

[0114] In some embodiments of the present invention, the crushing is performed using at least one of a vibrating screen, a mechanical mill, and an air jet mill.

[0115] Thirdly, the present invention provides a positive electrode sheet, which comprises the positive electrode material obtained in any of the above embodiments. The positive electrode sheet comprises a positive current collector and a positive active material layer, wherein the positive active material layer comprises the positive electrode material provided in the first aspect of the present invention. The positive current collector is typically a sheet-like structure, and the positive active material layer typically covers at least partially the surface of the positive current collector, and may also be a layer extending along the surface of the positive current collector. The positive current collector is typically a structure or component that collects current, for example, it may be a metal foil (e.g., copper foil, aluminum foil, etc.). Those skilled in the art can select a suitable method to prepare the positive electrode sheet, for example, it may include the following steps: mixing the positive active material, binder, and conductive agent to form a slurry, and then coating it onto the positive current collector.

[0116] Fourthly, the present invention provides a lithium-ion battery, comprising the positive electrode material provided in the first aspect of the present invention, or the positive electrode sheet provided in the third aspect of the present invention.

[0117] The lithium-ion battery provided by this invention typically includes a positive electrode, a negative electrode, a separator spaced between the positive and negative electrodes, and an electrolyte. Methods for preparing the lithium-ion battery should be known to those skilled in the art. For example, the positive electrode, separator, and negative electrode can each be a sheet, which can be cut to a target size and stacked sequentially, or wound to a target size to form a cell, and further combined with an electrolyte to form a lithium-ion battery.

[0118] In the lithium-ion battery provided by this invention, the negative electrode typically includes a negative current collector and a negative active material layer located on the surface of the negative current collector. The negative active material layer typically includes a negative active material. The negative active material can be any material suitable for lithium-ion batteries, including, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. Specifically, the graphite can be selected from one or more combinations of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more combinations of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material can be selected from one or more combinations of elemental tin, tin oxide compounds, and tin alloys. The negative current collector is typically a structure or component that collects current. The negative current collector can be any material suitable for use as a negative current collector in a lithium-ion battery, including, but not limited to, metal foil, and more specifically, copper foil.

[0119] In the lithium-ion battery provided by the present invention, the separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be one or more of the following: polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0120] In the lithium-ion battery provided by this invention, the electrolyte can be any electrolyte suitable for lithium-ion batteries in the art. For example, the electrolyte typically includes an electrolyte and a solvent. The electrolyte typically includes lithium salts, and more specifically, the lithium salt can be inorganic lithium salts and / or organic lithium salts. The lithium salt can be selected from one or more combinations of LiPF6, LiBF4, LiN(SO2F)2 (abbreviated as LiFSI), LiN(CF3SO2)2 (abbreviated as LiTFSI), LiClO4, LiAsF6, LiB(C2O4)2 (abbreviated as LiBOB), and LiBF2C2O4 (abbreviated as LiDFOB). For another example, the concentration of the electrolyte can be between 0.8 mol / L and 1.5 mol / L. The solvent can be any solvent suitable for lithium-ion batteries in the art. The solvent of the electrolyte is usually a non-aqueous solvent, preferably an organic solvent, specifically including but not limited to ethylene carbonate, propylene carbonate, butene carbonate, pentene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, etc., or one or more of their halogenated derivatives.

[0121] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0122] Example 1

[0123] A method for preparing a positive electrode material includes the following steps:

[0124] (1) Preparation of positive electrode active material: Lithium carbonate, cobalt tetroxide, titanium oxide, and aluminum oxide were weighed and uniformly mixed in a molar ratio of n(Li):n(Co):n(Ti):n(Al) = 1.07:1:0.002:0.020. The mixture was sintered at 1020℃ for 10h, and then crushed to obtain lithium cobalt oxide, which is the positive electrode active material with the chemical formula LiCo. 0.9785 Ti 0.0020 Al 0.0195 O2.

[0125] (2) Preparation of mixed solution: Lanthanum acetate and aluminum nitrate were weighed according to the molar ratio n(La):n(Al)=1:1 and dissolved in deionized water to obtain a mixed solution with a total mass percentage of 2% of La and Al elements.

[0126] (3) Preparation of spray-coated positive electrode material: The positive electrode active material and alumina are placed in a high-speed mixing device and premixed at 1000r / min for 5min to obtain solid material. The mixed solution is sprayed while stirring. The spraying is completed in 10min. Then, the material is discharged after mixing for another 5min. Then, it is further dried at 40℃ for 30min to obtain the spray-coated positive electrode material. The mass of alumina is 0.2% of the mass of the positive electrode active material, and the feeding ratio of solid material to mixed solution is 5kg:400mL.

[0127] (4) Preparation of positive electrode material: The positive electrode material coated by spraying is placed in a box furnace and sintered at 550°C for 4 hours. After crushing, it is passed through a 400-mesh sieve to obtain the positive electrode material.

[0128] Example 2

[0129] A method for preparing a positive electrode material includes the following steps:

[0130] (1) Same as Example 1.

[0131] (2) Preparation of mixed solution: Strontium acetate and titanium glycolate were weighed according to the molar ratio n(Sr):n(Ti)=1:1 and dissolved in deionized water to obtain a mixed solution with a total mass percentage of 2% of Sr and Ti elements.

[0132] (3) Preparation of spray-coated positive electrode material: The positive electrode active material and alumina are placed in a high-speed mixing device and premixed at 1500r / min for 5min to obtain solid material. The mixed solution is sprayed while stirring. The spraying is completed in 10min. Then, the material is discharged after mixing for 5min. Then, it is further dried at 40℃ for 30min to obtain the spray-coated positive electrode material. The mass of alumina is 0.2% of the mass of the positive electrode active material, and the feeding ratio of solid material to mixed solution is 5kg:400mL.

[0133] (4) Same as in Example 1.

[0134] Example 3

[0135] (1) Preparation of positive electrode active material: Weigh lithium carbonate and NCM622 (Ni+Co+Mn):n(W):n(Al) in a molar ratio of n(Li):n(Ni+Co+Mn):n(W):n(Al) = 1.065: 1.00: 0.0008:0.0075. 0.6 Co 0.2 Mn 0.2 OH2), tungsten oxide, and aluminum oxide are uniformly mixed and sintered at 1020℃ for 10 hours. The mixture is then crushed to obtain doped lithium nickel cobalt manganese oxide, which is the positive electrode active material with the chemical formula LiNi. 0.595 Co 0.198 Mn 0.199 W 0.0007 Al 0.0073 O2.

[0136] (2) to (4) are the same as in Example 1.

[0137] Example 4

[0138] (1) Same as in Example 1;

[0139] (2) Preparation of mixed solution: Lanthanum acetate and molybdenum nitrate were weighed according to the molar ratio n(La):n(Mo)=1:1 and dissolved in deionized water to obtain a mixed solution with a total mass percentage of 2% of La and Mo elements.

[0140] (3)~(4) are the same as in Example 1.

[0141] Example 5

[0142] (1) Same as Example 1.

[0143] (2) Preparation of mixed solution: Lanthanum acetate, calcium nitrate and yttrium nitrate were weighed and dissolved in deionized water according to the molar ratio n(La):n(Ca):n(Y) = 0.5:0.5:1 to obtain a mixed solution with a total mass percentage of 3% of metal elements.

[0144] (3) Preparation of spray-coated positive electrode material: The positive electrode active material and alumina are placed in a high-speed mixing device and premixed at 300 r / min for 5 min to obtain solid material. The mixed solution is sprayed while stirring. The spraying is completed in 60 min. Then, the material is discharged after mixing for another 5 min. Then, it is further dried at 150℃ for 30 min to obtain the spray-coated positive electrode material. The mass of alumina is 0.2% of the mass of the positive electrode active material, and the feeding ratio of solid material to mixed solution is 5 kg: 267 mL.

[0145] (4) Same as in Example 1.

[0146] Example 6

[0147] (1) Same as Example 1.

[0148] (2) Preparation of mixed solution: Lanthanum acetate, calcium nitrate, yttrium nitrate and magnesium acetate were weighed according to the molar ratio n(La):n(Ca):n(Y):n(Mg)=1:1:1:1 and dissolved in deionized water to obtain a mixed solution with a total mass percentage of 2% of metal elements.

[0149] (3) Preparation of spray-coated positive electrode material: The positive electrode active material and alumina are placed in a high-speed mixing device and premixed at 1000r / min for 5min to obtain solid material. The mixed solution is sprayed while stirring. The spraying is completed in 10min. Then, the material is discharged after mixing for 5min. Then, it is further dried at 40℃ for 3h to obtain the spray-coated positive electrode material. The mass of alumina is 0.2% of the mass of the positive electrode active material, and the feeding ratio of solid material to mixed solution is 5kg:400mL.

[0150] (4) Preparation of positive electrode material: The positive electrode material coated by spraying is placed in a box furnace and sintered at 700°C for 2 hours. After crushing, it is passed through a 400-mesh sieve to obtain the positive electrode material.

[0151] Example 7

[0152] The difference from Example 1 is that the total mass percentage of metal elements in the mixed solution in step (2) is 4%, and the feeding ratio of solid material to mixed solution is 5kg:200mL.

[0153] Example 8

[0154] The difference from Example 1 is that the drying temperature in step (3) is 60°C.

[0155] Example 9

[0156] The difference from Example 1 is that the sintering temperature in step (4) is 350°C and the sintering time is 4 hours.

[0157] Example 10

[0158] The difference from Example 1 is that the sintering temperature in step (4) is 550°C and the sintering time is 8h.

[0159] Comparative Example 1

[0160] The difference from Example 1 is that source A and source B are not added. The specific steps are as follows:

[0161] (1) Same as Example 1.

[0162] (2) Place the positive electrode active material and alumina in a high-speed mixing device and mix at 1000 r / min for 20 min to obtain solid material, wherein the mass of alumina is 0.2% of the mass of the positive electrode active material.

[0163] (3) Preparation of cathode material: The solid material is placed in a box furnace and sintered at 550°C for 4 hours. After crushing, it is passed through a 400-mesh sieve to obtain the cathode material.

[0164] Comparative Example 2

[0165] The difference from Example 1 is that source A and source B are dry-mixed with the positive electrode active material, and the specific steps are as follows:

[0166] (1) Same as Example 1.

[0167] (2) Mix the positive electrode active material and dopant at a mass ratio of 5 kg: 8 g, wherein the dopant has a molar ratio of n

[0168] A mixture of lanthanum oxide (La):n(Al) = 1:1 and aluminum oxide is mixed with 0.2% (by mass) aluminum oxide of the positive electrode active material. The mixture is then stirred at 1000 r / min for 20 min and discharged to obtain the spray-coated positive electrode material.

[0169] (3) is the same as step (4) in Example 1.

[0170] Comparative Example 3

[0171] The difference from Example 1 is that no aluminum source is added. The specific steps are as follows:

[0172] (1) Same as Example 1.

[0173] (2) Dissolve lanthanum acetate in water to obtain an aqueous solution with a lanthanum element mass percentage of 2%, and obtain a lanthanum source solution.

[0174] (3) Use lanthanum source solution instead of mixed solution for spraying.

[0175] (4) Same as in Example 1.

[0176] Comparative Example 4

[0177] The difference from Example 1 is that no lanthanum source is added. The specific steps are as follows:

[0178] (1) Same as Example 1.

[0179] (2) Dissolve aluminum nitrate in water to obtain an aqueous solution with an aluminum content of 2% by mass, and obtain an aluminum source solution.

[0180] (3) Use aluminum source solution instead of mixed solution for spraying.

[0181] (4) Same as in Example 1.

[0182] Comparative Example 5

[0183] The difference from Example 1 is that the sintering temperature in step (4) is 900°C.

[0184] Comparative Example 6

[0185] The difference from Example 1 is that the drying temperature in step (3) is 300°C.

[0186] Comparative Example 7

[0187] The difference from Example 5 is that source A and source B are dry-mixed with the positive electrode active material, and the specific steps are as follows:

[0188] (1) Same as Example 5.

[0189] (2) Mix the positive electrode active material and dopant at a mass ratio of 5 kg: 8 g, wherein the dopant is a mixture of lanthanum oxide, calcium oxide and yttrium oxide with a molar ratio of n(La):n(Ca):n(Y) = 0.5:0.5:1, and add 0.2% aluminum oxide by mass of the positive electrode active material. Mix at 1000 r / min for 20 min and discharge to obtain the spray-coated positive electrode material.

[0190] (3) is the same as step (4) in Example 5.

[0191] Comparative Example 8

[0192] The difference from Example 3 is that the mixed solution of source A and source B is not added.

[0193] Comparative Example 9

[0194] The difference from Example 3 is that source A and source B are dry-mixed with the positive electrode active material, and the specific steps are as follows:

[0195] (1) Same as Example 3.

[0196] (2) Mix the positive electrode active material and dopant at a mass ratio of 5kg:8g, wherein the dopant is a mixture of lanthanum oxide and aluminum oxide with a molar ratio of n(La):n(Al):=1:1, and add 0.2% of aluminum hydroxide by mass of the positive electrode active material. Mix at 1000r / min for 20min and discharge to obtain the spray-coated positive electrode material.

[0197] (3) Same as step (4) in Example 3

[0198] Comparative Example 10

[0199] The difference from Example 5 is that in step (3), the positive electrode active material is dispersed in the mixed solution, and the specific steps are as follows:

[0200] (1) Same as Example 5.

[0201] (2) Lanthanum acetate, calcium nitrate and yttrium nitrate were weighed and dissolved in deionized water according to the molar ratio n(La):n(Ca):n(Y) = 0.5:0.5:1 to obtain a mixed solution with a total mass percentage of 3% of the metal elements.

[0202] (3) Disperse the positive electrode active material and alumina in the mixed solution, stir for 30 min, stir in an oil bath at 100℃ and evaporate the solvent to obtain the spray-coated positive electrode material; wherein the mass of alumina is 0.2% of the mass of the positive electrode active material, and the ratio of the total amount of positive electrode active material and alumina to the amount of mixed solution is 5 kg: 267 mL.

[0203] (4) Same as Example 5.

[0204] The test results of this invention are as follows:

[0205] (1) Electrochemical performance testing:

[0206] ① Electrode preparation: Positive electrode material, SP (conductive agent), and PVDF (binder) are mixed in a mass ratio of 92:4:4, NMP (N-methylpyrrolidone) is added, and the mixture is stirred to form a slurry. This slurry is then coated onto aluminum foil and dried at 80°C to form the positive electrode sheet. Graphite, SP (conductive agent), binder, and dispersant are mixed in a mass ratio of 95.5:1.5:1.5:1.5, water is added, and the mixture is stirred to form a slurry. This slurry is then coated onto aluminum foil and dried at 80°C to form the negative electrode sheet.

[0207] ② Pouch battery assembly: Assemble the positive electrode, negative electrode, electrolyte and separator into a pouch battery;

[0208] ③ Capacity Test (25℃, 0.2C): At room temperature (25℃), charge at a constant current rate of 0.2C to V2 voltage, then further charge at a constant voltage of V2 until the current drops below 0.05C, bringing it to a fully charged state at V2. Then discharge at a constant current rate of 0.2C to V1 to obtain the discharge capacity. The discharge specific capacity at 0.2C / 0.2C rate is obtained using the following formula: Discharge specific capacity = Discharge capacity / Mass of cathode material.

[0209] Among them, the V1 of lithium cobalt oxide cathode material is 3.0V and the V2 is 4.48V, while the V1 of lithium nickel cobalt manganese oxide (Ni:Co:Mn=6:2:2) cathode material is 2.8V and the V2 is 4.0V.

[0210] ④ Capacity retention test (45℃, 1.0C): The cycle capacity retention performance of the cathode material is evaluated by the number of cycles in which the capacity drops to 80%. One cycle includes: the battery under test is left to stand for 120 minutes, then charged at a constant current of 1C to V2, then charged at a constant voltage of V2 to 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to V1. The discharge capacity is recorded. The above steps are repeated until the battery capacity drops to 80%, and the number of cycles is recorded. The battery capacity drops to 80% because the ratio of the discharge capacity after n cycles to the discharge capacity of the first cycle is 80%.

[0211] Among them, the V1 of lithium cobalt oxide cathode material is 3.0V and the V2 is 4.48V, while the V1 of lithium nickel cobalt manganese oxide (Ni:Co:Mn=6:2:2) cathode material is 2.8V and the V2 is 4.0V.

[0212] ⑤ Storage Gas Generation Test: The battery under test is fully charged at 1C and then stored at 70℃. The battery is periodically removed and cooled to room temperature before its thickness is measured. The thickness increase over different storage times is calculated, and the gas generation of the cathode material is evaluated based on the thickness increase. The test period is 0, 7, 15, 30, 60, and 100 days. Taking 100 days as an example, the storage gas generation rate of the cathode material on the 100th day can be calculated using the following formula: (H 100 -H0) / H0, where H 100 H0 and H0 are the thicknesses of the battery measured on day 100 and day 0, respectively.

[0213] (2) Transmission electron microscopy (TEM) test: The present invention uses Thermo Fisher Scientific transmission electron microscope to observe and analyze the crystal structure of the cathode material.

[0214] (3) Scanning electron microscopy (SEM) test: The Nova NanoSEM 450 electron scanning electron microscope was used to observe and analyze the surface morphology of the cathode material.

[0215] (4) Particle size test: The Dv50 of the cathode material was tested using a laser particle size analyzer in accordance with GB / T 19077-2016.

[0216] (5) Angle of repose test: The angle of repose of the cathode material shall be tested in accordance with GB / T 16913-2008.

[0217] Instruction manual attached Figure 1 , 2 Figures 3 and 4 show the SEM images of the cathode materials prepared in Examples 1 and 5 and Comparative Examples 1 and 10, respectively. As can be seen from the figures, in Comparative Example 1, because the cathode material particles were not mixed with sources A and B for surface coating modification, the surface of the cathode material particles was smooth and had sharp edges. In Comparative Example 10, the cathode active material was directly dispersed in a mixed solution containing sources A and B, and then the solvent was evaporated to obtain the coated cathode material. Therefore, the surface roughness of the obtained cathode material was relatively high, and the perovskite structure layer mainly covered the material surface in island-like shapes, resulting in poor coating uniformity. In contrast, the cathode material particles prepared in Examples 1 and 5 were more rounded in shape than those in Comparative Example 1, indicating successful coating. Furthermore, compared to Comparative Example 10, the perovskite structure layer mostly covered the surface in a film-like manner, greatly reducing the surface roughness of the cathode material particles and resulting in higher coating uniformity.

[0218] Instruction manual attached Figure 5 The image shows a TEM image of the cathode material prepared in Example 5. As can be seen from the image, the cathode material consists of four layers: a layered structure, a substituted layered structure, a spinel / rock salt phase, and a perovskite structure, corresponding to the layered matrix, the substituted layered matrix layer, the heterojunction layer, and the perovskite structure layer, respectively. In addition, it can be seen from the image that the thickness of the substituted layered matrix layer is less than 50 nm, the thickness of the heterojunction layer is less than 10 nm, and the thickness of the perovskite structure layer is less than 10 nm.

[0219] The Dv50 of the cathode materials prepared in the embodiments and comparative examples of this invention is 12~18μm. The angle of repose of the cathode materials prepared in the embodiments of this invention is 25~55°, while the angles of repose of comparative examples 2, 7, and 10 are 58°, 60°, and 57°, respectively. In comparative examples 2 and 7, the cathode active materials are dry-mixed with oxides of source A and source B. In comparative example 10, the cathode material is dispersed in a mixed solution containing source A and source B, and then the solvent is evaporated to obtain the spray-coated cathode material. Compared with the spraying method of this invention, the two methods of the comparative examples (dry method and solution mixing) result in cathode materials with higher surface roughness, and therefore higher angles of repose.

[0220] The performance of the cathode materials prepared in each embodiment and comparative example is shown in Table 1 and Table 2, where Table 1 shows the test results of lithium cobalt oxide cathode materials and Table 2 shows the test results of lithium nickel cobalt manganese oxide cathode materials.

[0221] Table 1: Lithium Cobalt Oxide Cathode Materials

[0222]

[0223] Table 2: Lithium Nickel Cobalt Manganese Oxide Cathode Materials

[0224]

[0225] As shown in Table 1, Examples 1, 2, and 3, which underwent surface coating modification, exhibited higher capacity and cycle stability, as well as lower gas production. In contrast, Comparative Example 1, which did not undergo surface coating modification, showed lower cycle stability and significantly worsened gas production. This indicates that surface coating modification has a significant effect on improving the surface layer of the cathode material.

[0226] Compared with Example 1, increasing the solute concentration in the mixed solution resulted in a decrease in capacity and a slight deterioration in gas production. Comparing Examples 1, 9, and 10, decreasing the sintering temperature or extending the sintering time resulted in a slight decrease in capacity and cycle stability; decreasing the sintering temperature worsened gas production. Comparing Example 1 with Comparative Example 2, and Example 3 with Comparative Example 8, the dry mixing of source A and source B with the cathode material in oxide form resulted in a deterioration in capacity, cycle stability, and gas production, indicating that wet spraying is beneficial for forming an effective coating modification layer, thereby improving capacity, cycle stability, and gas production. Comparing Examples 1, 3, and 4, it can be seen that using a single element for coating modification has poor results. Comparing Examples 1, 5, and 6, it can be seen that increasing the sintering temperature and drying temperature tends to worsen the electrical performance.

[0227] In Comparative Example 10, the positive electrode active material was dispersed in a mixed solution containing source A and source B. With this mixing method, the degree of ion exchange between the positive electrode active material and the liquid phase is high, the amount of lithium ion loss is large, resulting in a decrease in the capacity of the final positive electrode material, poor cycle stability and a large amount of gas production.

[0228] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that, The positive electrode material includes a layered matrix, a substituted layered matrix layer, a heterojunction layer, and a perovskite structure layer; the layered matrix has a chemical general formula Li a M 1-b M′ b O2, where 0.98 ≤ a ≤ 1.02, 0 < b ≤ 0.1, M is at least one of Ni, Co, and Mn; M′ is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb, and Ca; The substituted layered matrix is ​​distributed in a direction away from the layered matrix and is connected to the layered matrix, and the substituted layered matrix has a layered structure different from that of the layered matrix; The heterojunction layer is distributed on the surface of the substituted layered matrix layer away from the layered matrix and is connected to the substituted layered matrix layer. The heterojunction layer includes at least one of spinel structure and rock salt phase structure. The perovskite structure layer is distributed on the surface of the heterojunction layer away from the layered matrix and is connected to the heterojunction layer. The perovskite structure layer has the chemical formula ABO3, where A and B are both metallic elements. The thickness of the substituted layered matrix layer is less than 50 nm; the thickness of the heterojunction layer is less than 10 nm; the thickness of the perovskite structure layer is less than 10 nm. The method for preparing the cathode material includes the following steps: Prepare positive electrode active material; prepare a mixed solution of source A and source B; The mixed solution is sprayed onto the surface of the positive electrode active material under stirring, and dried to obtain a spray-coated positive electrode material; The positive electrode material is obtained by sintering the sprayed coating and then crushing it. By spraying the mixed solution onto the surface of the positive electrode active material, some of the positive electrode active material undergoes ion exchange to obtain the layered matrix layer and the original substituted layered matrix layer. After the sprayed positive electrode material is sintered, some of the original substituted layered matrix layer reacts to form a heterojunction layer, thereby obtaining the substituted layered matrix layer and the heterojunction layer.

2. The cathode material according to claim 1, characterized in that, The angle of repose of the positive electrode material is ≤55°.

3. A positive electrode material according to claim 1 or 2, characterized in that, A is at least one of Pb, Na, Sn, Sr, K, Ca, Ba, Ln, Pr, Sm, Gd, and La; B is at least one of Ti, Mg, Y, Zn, Fe, Ta, Mn, Co, Ni, Mo, Nb, W, and Al. Or / and, the total mass of element A and element B in the cathode material is less than 5% of the total mass of the cathode material; Or / and, the median particle size Dv50 of the cathode material is 12~18μm.

4. The method for preparing the cathode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Prepare positive electrode active material; prepare a mixed solution of source A and source B; The mixed solution is sprayed onto the surface of the positive electrode active material under stirring, and dried to obtain a spray-coated positive electrode material; The positive electrode material is obtained by sintering the sprayed coating and then crushing it.

5. The method for preparing the cathode material according to claim 4, characterized in that, The preparation method of the positive electrode active material includes the following steps: mixing lithium source, M source and M′ source and calcining them, and then crushing them to obtain the positive electrode active material; The calcination temperature is 600–1100℃, and the time is 5–15 hours; Or / and, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium oxalate; Or / and, the source of M is at least one of an oxide or hydroxide containing M; wherein M is at least one of Ni, Co, and Mn; Or / and, the M′ source is at least one of oxides, hydroxides, acetates, carbonates and basic carbonates containing M′; the M′ is at least one of Ba, La, Ti, Zr, V, Nb, Cu, Mg, B, Sr, Al, Sc, Y, Ga, Zn, W, Mo, Si, Sb and Ca.

6. The method for preparing the cathode material according to claim 4, characterized in that, The A source is at least one of acetate, carbonate and basic carbonate containing A, and A is at least one of Pb, Na, Sn, Sr, K, Ca, Ba, Ln, Pr, Sm, Gd and La; Or / and, the source of B is at least one of acetate, carbonate and basic carbonate containing B, wherein B is at least one of Ti, Mg, Y, Zn, Fe, Ta, Mn, Co, Ni, Mo, Nb, W and Al; Or / and, the mixed solution is an aqueous solution of source A and source B; Or / and, the molar ratio of element A to element B in the mixed solution is (1~1.1):(1~1.1).

7. The method for preparing the cathode material according to claim 4, characterized in that, The mixed solution is sprayed onto the surface of the aluminum source and the positive electrode active material under stirring, and then dried to obtain the spray-coated positive electrode material.

8. The method for preparing the cathode material according to any one of claims 4 to 7, characterized in that, The preparation method satisfies at least one of the following characteristics: Or / and, the stirring speed of the stirring is 300~1500 r / min; Or / and, the spraying time is 10~60 min; Or / and, the drying temperature is 40~150℃, and the time is 0.5~3h; Or / and, the sintering temperature is 350–700°C, and the time is 2–10 h.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 3.

10. A lithium-ion battery, characterized in that, It includes the positive electrode, negative electrode, electrolyte, and separator as described in claim 9.

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