Secondary battery and preparation method therefor, and electric device

Abstract

A secondary battery and a preparation method therefor, and an electric device. The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a matrix material and a coating layer at least partially covering the matrix material. The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is located on the surface of the matrix material, and the second coating layer is located on the surface of the first coating layer, with the first coating layer comprising a lithium-supplementing material, and the second coating layer comprising a reductive material; or, the first coating layer comprising a reductive material, and the second coating layer comprising a lithium-supplementing material. The secondary battery has excellent cycle performance and a long service life.

Description

Secondary batteries, their preparation methods, and electrical devices

[0001] Cross-references

[0002] This application incorporates Chinese Patent Application No. 202410494041.4, filed on April 23, 2024, entitled “Secondary Battery and Method for Preparation Thereof and Electrical Device Thereof,” which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0004] Lithium-ion batteries (LIBs), as a type of rechargeable battery, possess characteristics such as high energy density, long lifespan, and energy efficiency. However, during the initial charge and discharge process of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. The formation of the SEI film consumes a large number of active lithium ions. Furthermore, during the battery's charge and discharge cycles, the cracking and fragmentation of the positive electrode active material particles, as well as the thickening and repair of the SEI film, all consume active lithium ions, easily leading to a decrease in the battery's cycle capacity and affecting its lifespan.

[0005] Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery that aims to solve the technical problem of how to improve the cycle performance of the secondary battery and extend its service life.

[0007] The first aspect of this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode active material, the positive electrode active material including a matrix material and a coating layer at least partially covering the matrix material, the coating layer including a first coating layer and a second coating layer, the first coating layer being located on the surface of the matrix material, and the second coating layer being located on the surface of the first coating layer.

[0008] The first coating layer contains a lithium-replenishing material, and the second coating layer contains a reducing material; or...

[0009] The first coating layer contains reducing materials, and the second coating layer contains lithium supplementing materials.

[0010] In this application, the lithium replenishing material in the positive electrode is present in the first coating layer of the matrix material, and the reducing material is present in the second coating layer of the matrix material; or the reducing material is present in the first coating layer of the matrix material, and the lithium replenishing material is present in the second coating layer of the matrix material. The lithium replenishing material and the reducing material can form a surface-to-surface contact, which can increase the contact area between the lithium replenishing material and the reducing material, increase the reaction degree between the lithium replenishing material and the reducing material, and improve the lithium replenishing efficiency of the lithium replenishing material. At the same time, the presence of the lithium replenishing material and the reducing material in the first or second coating layer can utilize the conductivity of the matrix material to improve the conductive network between the lithium replenishing material and the reducing material, provide more electron transport pathways, increase the reaction degree between the lithium replenishing material and the reducing material, reduce the film resistance of the electrode, and improve the kinetic performance and cycle performance of the battery.

[0011] In summary, by setting the lithium replenishing material and the reducing material on the surface of the matrix material in the first coating layer and the second coating layer, respectively, the contact area between the lithium replenishing material and the reducing material can be increased, the degree of reaction between the two can be improved, the lithium replenishing material can exert its lithium replenishing function to the maximum extent, the lithium replenishing efficiency of the lithium replenishing material can be improved, a large amount of active lithium can be provided for lithium replenishment during the cycle, the battery has excellent cycle count and long service life.

[0012] In any embodiment, the mass ratio of lithium replenishing material to reducing material is 0.5-50.

[0013] In any embodiment, the mass ratio of lithium replenishing material to reducing material is 1-20.

[0014] The mass ratio of lithium replenishing material to reducing material is within a suitable range. This allows the lithium replenishing material and reducing material to react fully and improve the lithium replenishment efficiency, while also avoiding excessive residual lithium replenishing material and / or reducing material from degrading the battery's cycle performance and energy density.

[0015] In any embodiment, the mass fraction of the lithium supplement material is 0.5%-20% based on the mass of the matrix material.

[0016] In any embodiment, the mass fraction of the lithium supplement material is 1%-10% based on the mass of the matrix material.

[0017] When the mass fraction of lithium replenishing material is within a suitable range, on the one hand, the lithium replenishing material can give full play to its lithium replenishing function and improve the cycle performance of the battery; on the other hand, it can also avoid the adverse effects of excessive lithium replenishing material on the rate performance, usable capacity and safety performance of the battery.

[0018] In any embodiment, the mass fraction of the raw material is 0.01%-10% based on the mass of the matrix material.

[0019] In any embodiment, based on the mass of the matrix material, the mass fraction of the raw material is 0.02%-5%.

[0020] When the mass fraction of reducing materials is within a suitable range, on the one hand, the lithium replenishing material reacts fully with sufficient amounts of reducing materials, allowing the lithium replenishing material to maximize its lithium replenishing effect and improve the cycle performance of the battery. On the other hand, it also avoids the adverse effects of excessive reducing materials on usable capacity and safety performance.

[0021] In any embodiment, the first coating layer and / or the second coating layer further include a conductive agent.

[0022] By adding a conductive agent to the first coating layer and / or the second coating layer, a good electron transport pathway can be formed between the reducing material and the lithium replenishing material, which significantly improves the conductive network between the lithium replenishing material and the reducing material, further enhances the reaction degree between the lithium replenishing material and the reducing material, improves the lithium replenishing efficiency of the lithium replenishing material, and extends the battery life.

[0023] In any embodiment, the mass fraction of the conductive agent is 2%-20% based on the mass of the first coating layer and / or the second coating layer containing the conductive agent.

[0024] Controlling the mass fraction of the conductive agent within a suitable range can significantly improve the conductive network between the lithium replenishment material and the reducing material, thereby increasing the lithium replenishment efficiency of the lithium replenishment material. At the same time, it can also avoid the impact of excessive conductive agent on the specific capacity of the positive electrode active material.

[0025] In any embodiment, the lithium supplementing material includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium squaric acid, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

[0026] The aforementioned lithium replenishment materials have high irreversible capacity, good lithium replenishment effect, good stability in air, and good compatibility with existing battery production processes, which is conducive to industrial production.

[0027] In any embodiment, the raw materials include one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, elemental phosphorus, metal compounds of phosphorus, elemental boron, metal compounds of boron, elemental tellurium, metal compounds of tellurium, elemental antimony, metal compounds of antimony, elemental bismuth, metal compounds of bismuth, and selenium disulfide.

[0028] The aforementioned reducing materials can chemically react with lithium replenishment materials to lower the decomposition potential of the lithium replenishment materials, achieve low-potential lithium replenishment, improve the decomposition efficiency and utilization rate of lithium replenishment materials, improve the battery capacity retention rate, and extend battery life.

[0029] In any embodiment, the lithium replenishment efficiency of the lithium replenishment material is 90%-100%.

[0030] A second aspect of this application provides a method for preparing a secondary battery, comprising the following steps:

[0031] A positive electrode sheet is obtained by coating a positive electrode slurry containing a positive electrode active material.

[0032] A secondary battery is formed by assembling the negative electrode, separator, electrolyte, and positive electrode.

[0033] The positive electrode active material includes a matrix material and a coating layer that covers at least part of the matrix material. The coating layer includes a first coating layer and a second coating layer. The first coating layer is located on the surface of the matrix material, and the second coating layer is located on the surface of the first coating layer.

[0034] The first coating layer contains lithium-replenishing material, and the second coating layer contains reducing material; or...

[0035] The first coating layer contains reducing materials, and the second coating layer contains lithium supplementing materials.

[0036] Using the above preparation method, a secondary battery with excellent cycle performance can be prepared.

[0037] In any embodiment, the preparation method of the positive electrode active material specifically includes:

[0038] Formation of the first coating layer: The matrix material raw material and the lithium supplementation material precursor are subjected to a hydrothermal reaction to obtain a composite precursor.

[0039] A first mixture comprising a composite precursor and a lithium source is subjected to a first sintering treatment to obtain the initial positive electrode active material; or...

[0040] A second sintering process is performed on a second mixture comprising a matrix material, a lithium supplementation material precursor, and a lithium source to obtain the initial positive electrode active material; or,

[0041] The initial positive electrode active material is obtained by using lithium supplementation material raw materials to perform chemical vapor deposition, physical vapor deposition, atomic layer deposition or molecular layer deposition on the matrix material;

[0042] Formation of the second coating layer: The initial positive electrode active material is coated with a first vapor containing reducing material in the gas phase to obtain the positive electrode active material; or...

[0043] The third mixture, comprising the initial positive electrode active material and the reducing material, is ball-milled to obtain the positive electrode active material; or...

[0044] A third sintering process is performed on a fourth mixture containing the initial positive electrode active material and the reducing material to obtain the positive electrode active material.

[0045] The first coating layer includes a lithium replenishing material, and the second coating layer includes a reducing material.

[0046] According to the above preparation method, a first coating layer containing lithium replenishing material and a second coating layer containing reducing material can be obtained, which can improve the reaction degree between reducing material and lithium replenishing material, achieve efficient lithium replenishment, increase the number of battery cycles, and extend the battery life.

[0047] In any embodiment, the first mixture or the second mixture further includes a carbon source; or, the third mixture or the fourth mixture further includes a conductive agent.

[0048] By adding a carbon source or conductive agent during the synthesis of the first coating layer and / or the second coating layer, a first coating layer and / or a second coating layer containing a conductive agent can be obtained. This is beneficial to further improve the conductive network of the lithium replenishing material and the reducing material, increase the degree of reaction between the two, and achieve the purpose of efficient lithium replenishment.

[0049] In any embodiment, the hydrothermal reaction temperature is 120°C-220°C; and / or, the hydrothermal reaction time is 8h-24h.

[0050] The appropriate hydrothermal reaction temperature and / or reaction time enable the lithium supplement material precursor to form a coating layer on the base material raw material, and the two have good bonding force. After subsequent sintering treatment, the lithium supplement material forms a structurally complete coating layer on the surface of the base material.

[0051] In any embodiment, the temperature of the first sintering treatment is 600°C-1000°C; and / or, the time of the first sintering treatment is 4h-24h.

[0052] A suitable temperature and / or time for the first sintering allows the composite precursor to react fully with the lithium source, resulting in a cathode active material with stable structure and high phase purity.

[0053] In any embodiment, the temperature of the second sintering treatment is 600℃-900℃; and / or, the time of the second sintering treatment is 4h-24h.

[0054] A suitable second sintering temperature and / or time allows the lithium supplement material precursor to react fully with the lithium source, resulting in a lithium supplement material coating layer with stable structure and high phase purity.

[0055] In any embodiment, the temperature of the third sintering treatment is 120°C-350°C; and / or, the time of the third sintering treatment is 4h-48h.

[0056] A suitable temperature and / or time for the third sintering is beneficial for forming a dense and uniform reducing material coating layer.

[0057] In any embodiment, the preparation method of the positive electrode active material specifically includes:

[0058] Formation of the first coating layer: The matrix material is vapor-coated with a second vapor containing reducing materials to obtain an intermediate material; or...

[0059] A fifth mixture containing the matrix material and the reducing material is ball-milled to obtain an intermediate material; or...

[0060] The sixth mixture, which contains the matrix material and the reducing material, is subjected to a fourth sintering process to obtain the intermediate material;

[0061] The formation of the second coating layer: A fifth sintering process is performed on a seventh mixture comprising intermediate materials, lithium supplementation material precursors, and a lithium source to obtain the positive electrode active material; or,

[0062] Using lithium-supplementing material raw materials, intermediate materials are subjected to chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition to obtain positive electrode active materials;

[0063] The first coating layer includes reducing materials, and the second coating layer includes lithium replenishing materials.

[0064] According to the above preparation method, a first coating layer containing reducing materials and a second coating layer containing lithium replenishing materials can be obtained, which can improve the reaction degree between reducing materials and lithium replenishing materials, achieve efficient lithium replenishment, increase the number of battery cycles, and extend the battery life.

[0065] In any embodiment, the seventh mixture further includes a carbon source; or, the fifth or sixth mixture further includes a conductive agent.

[0066] By adding a carbon source or conductive agent during the synthesis of the first coating layer and / or the second coating layer, a first coating layer and / or a second coating layer containing a conductive agent can be obtained. This is beneficial to further improve the conductive network of the lithium replenishing material and the reducing material, increase the degree of reaction between the two, and achieve the purpose of efficient lithium replenishment.

[0067] In any embodiment, the temperature of the fourth sintering treatment is 120°C-350°C; and / or, the time of the fourth sintering treatment is 4h-48h.

[0068] A suitable sintering temperature and / or sintering time is beneficial for reducing materials to form a uniform and dense first coating layer on the surface of the matrix material.

[0069] In any embodiment, the temperature of the fifth sintering treatment is 200°C-500°C; and / or, the time of the fifth sintering treatment is 4h-48h.

[0070] Appropriate sintering temperature and / or sintering time allow the lithium supplement material precursor to react fully with the lithium source, resulting in a lithium supplement material coating layer with stable structure and high phase purity.

[0071] A third aspect of this application provides an electrical device comprising a secondary battery according to the first aspect and a secondary battery prepared by the preparation method of the second aspect. Attached Figure Description

[0072] Figure 1 is a schematic diagram of the positive electrode active material in one embodiment of this application;

[0073] Figure 2 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0074] Figure 3 is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 2;

[0075] Figure 4 is a schematic diagram of a battery module according to an embodiment of this application;

[0076] Figure 5 is a schematic diagram of a battery pack according to an embodiment of this application;

[0077] Figure 6 is an exploded view of the battery pack of one embodiment of this application shown in Figure 5;

[0078] Figure 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0079] Reference numerals: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Positive electrode active material; 60 Substrate material; 61 Coating layer; 611 First coating layer; 612 Second coating layer. Detailed Implementation

[0080] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, its preparation method, and its power-consuming device. However, unnecessary details may be omitted. For example, detailed descriptions of well-known facts 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 enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0081] 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.

[0082] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0083] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0084] 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.

[0085] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0086] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0087] All active lithium in a lithium-ion battery is provided by the positive electrode active material. However, the formation of the solid electrolyte interphase (SEI) film on the negative electrode surface during the first charge of a lithium-ion battery and other chemical side reactions during subsequent charge-discharge cycles consume active lithium ions, deteriorating the battery's cycle performance. To improve the cycle performance of lithium-ion batteries, a common industry solution is to add positive electrode lithium replenishing materials to the positive electrode. Commonly used positive electrode lithium replenishing materials generally include binary lithium compounds, ternary lithium compounds, or organic lithium salts. However, most positive electrode lithium replenishing materials with high lithium capacity also have high decomposition voltages, which affect the battery's cycle performance and safety performance. To address the high decomposition potential of positive electrode lithium replenishing materials, both the replenishing material and reducing agent are often added to the positive electrode sheet as additives. However, both the reducing agent and the lithium replenishing material are in particulate form, and their contact is point-to-point. Furthermore, the conductive agent and positive electrode active material in the electrode sheet isolate the two, preventing sufficient contact and reaction between the reducing agent and the lithium replenishing material. Consequently, the lithium replenishing material cannot perform its lithium replenishing function, resulting in low lithium replenishment efficiency. To address this technical issue, the industry also attempts to coat the surface of the lithium replenishment material with reducing materials, forming a core-shell lithium replenishment composition where the core structure is the lithium replenishment material and the shell structure is the reducing material. However, common lithium replenishment materials and reducing materials have poor electronic conductivity, and the core-structured lithium replenishment material cannot form an effective electronic pathway for electron gain and loss, resulting in poor battery kinetic performance and low lithium replenishment efficiency. Furthermore, since the core-structured lithium replenishment material cannot be effectively utilized, the reducing material in the shell structure will undergo irreversible side reactions with the electrolyte or positive electrode active material, deteriorating the battery's reversible capacity and cycle performance.

[0088] [Rechargeable Battery]

[0089] This application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode active material and an additive, the positive electrode active material including a matrix material and a coating layer at least partially covering the matrix material, the coating layer including a first coating layer and a second coating layer, the first coating layer being located on the surface of the matrix material, and the second coating layer being located on the surface of the first coating layer;

[0090] Wherein, the first coating layer comprises a lithium-replenishing material, and the second coating layer comprises a reducing material; or...

[0091] The first coating layer contains the reducing material, and the second coating layer contains the lithium replenishing material.

[0092] As shown in Figure 1, the positive electrode active material 6 includes a substrate material 60 and a coating layer 61 that covers at least part of the substrate material 60. The coating layer 61 includes a first coating layer 611 and a second coating layer 612, wherein the first coating layer 611 is located on the surface of the substrate material 60 and the second coating layer 612 is located on the surface of the first coating layer 611.

[0093] In some embodiments, the first coating layer 611 comprises a lithium replenishing material, and the second coating layer 612 comprises a reducing material.

[0094] In some embodiments, the first coating layer 611 contains the reducing material, and the second coating layer 612 contains the lithium replenishing material.

[0095] In this application, the lithium replenishing material in the positive electrode is present in the first coating layer of the matrix material, and the reducing material is present in the second coating layer of the matrix material; or the reducing material is present in the first coating layer of the matrix material, and the lithium replenishing material is present in the second coating layer of the matrix material. Compared with traditional methods where both the lithium replenishing material and the reducing material exist as additives, forming point-to-point contact or no contact at all, the lithium replenishing material and the reducing material in this application can form surface-to-surface contact, which can increase the contact area between the lithium replenishing material and the reducing material, increase the degree of reaction between the lithium replenishing material and the reducing material, and improve the lithium replenishing efficiency of the lithium replenishing material. At the same time, the presence of the lithium replenishing material and the reducing material in the first coating layer and the second coating layer can utilize the conductivity of the matrix material to improve the conductive network between the lithium replenishing material and the reducing material, provide more electron transport paths, reduce the film resistance of the electrode, and improve the kinetic performance of the battery. By constructing an excellent conductive network through the inter-positional relationship between the lithium replenishing material, the reducing material, and the matrix material, the kinetic performance of the battery is improved. This allows the lithium replenishing material to fully exert its lithium replenishing function and improve the lithium replenishment efficiency. In addition, due to the excellent conductive network of the electrode and the improved contact sites between the lithium replenishing material and the reducing material, the lithium replenishing material can gain and lose electrons and fully participate in the electrochemical reaction. Under the action of the reducing material, it can undergo a decomposition reaction at a low potential, releasing enough active lithium ions to replenish the lithium ions lost during the cycle, thus achieving the lithium replenishment effect. This also reduces the possibility of side reactions between the reducing material and the positive electrode active material or electrolyte, thereby improving the cycle performance of the battery.

[0096] In summary, the secondary battery using this application allows the lithium replenishment material to maximize its lithium replenishment function, improves the lithium replenishment efficiency of the lithium replenishment material, provides sufficient active lithium to replenish the lithium ions lost during cycling, and the battery has excellent cycle count and long service life.

[0097] In some embodiments, the mass ratio of lithium replenishing material to reducing material is 0.5-50. In some embodiments, the mass ratio of lithium replenishing material to reducing material can be selected as 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or any range between the two.

[0098] In some embodiments, the mass ratio of lithium replenishing material to reducing material is 1-20. In some embodiments, the mass ratio of lithium replenishing material to reducing material can be selected as 1, 5, 10, 15, 20, or any value range between the two.

[0099] The mass ratio of lithium replenishing material to reducing material is within a suitable range. This allows the lithium replenishing material and reducing material to react fully and improve the lithium replenishment efficiency, while also avoiding excessive residual lithium replenishing material and reducing material from degrading the battery's cycle performance and energy density.

[0100] In some embodiments, the mass fraction of the lithium-supplementing material is 0.5%-20% based on the mass of the matrix material. In some embodiments, the mass fraction of the lithium-supplementing material can be selected from 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range between the two, based on the mass of the matrix material.

[0101] In some embodiments, the mass fraction of the lithium-replenishing material is 1%-10% based on the mass of the matrix material. In some embodiments, the mass fraction of the lithium-replenishing material can be selected as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value range between the two, based on the mass of the matrix material.

[0102] When the mass fraction of lithium replenishing material is within a suitable range, on the one hand, the lithium replenishing material can give full play to its lithium replenishing function and improve the cycle performance of the battery; on the other hand, it can also avoid the adverse effects of excessive lithium replenishing material on the rate performance, usable capacity and safety performance of the battery.

[0103] In some embodiments, the mass fraction of the reducing agent is 0.01%-10% based on the mass of the matrix material. In some embodiments, the mass fraction of the reducing agent can be selected from 0.01%, 0.05%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range between the two, based on the mass of the matrix material.

[0104] In some embodiments, the mass fraction of the reducing agent is 0.02%-5% based on the mass of the matrix material. In some embodiments, the mass fraction of the reducing agent can be selected as 0.02%, 0.05%, 1%, 2%, 3%, 4%, 5%, or any value range between the two, based on the mass of the matrix material.

[0105] When the mass fraction of reducing materials is within a suitable range, on the one hand, the lithium replenishing material reacts fully with sufficient amounts of reducing materials, allowing the lithium replenishing material to maximize its lithium replenishing effect and improve the cycle performance of the battery. On the other hand, it also avoids the adverse effects of excessive reducing materials on usable capacity and safety performance.

[0106] In some embodiments, the first coating layer and / or the second coating layer further include a conductive agent.

[0107] In some embodiments, the first coating layer further includes a conductive agent.

[0108] In some embodiments, the second coating layer further includes a conductive agent.

[0109] In some embodiments, both the first coating layer and the second coating layer include a conductive agent.

[0110] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers, and carbon.

[0111] By adding a conductive agent to the first coating layer and / or the second coating layer, a good electron transport pathway can be formed between the reducing material and the lithium replenishing material, which significantly improves the conductive network between the lithium replenishing material and the reducing material, further enhances the reaction degree between the lithium replenishing material and the reducing material, improves the lithium replenishing efficiency of the lithium replenishing material, and extends the battery life.

[0112] In some embodiments, the first coating layer comprises a conductive agent, and the mass fraction of the conductive agent is 2%-20% based on the mass of the first coating layer. In some embodiments, the first coating layer comprises a conductive agent, and the mass fraction of the conductive agent may be selected as 2%, 3%, 4%, 5%, 10%, 15%, 20%, or any value range between the two, based on the mass of the first coating layer.

[0113] In some embodiments, the second coating layer comprises a conductive agent, and the mass fraction of the conductive agent is 2%-20% based on the mass of the second coating layer. In some embodiments, the second coating layer comprises a conductive agent, and the mass fraction of the conductive agent may be selected as 2%, 3%, 4%, 5%, 10%, 15%, 20%, or any value range between the two, based on the mass of the second coating layer.

[0114] In some embodiments, both the first and second coating layers contain a conductive agent, and the mass fraction of the conductive agent is 2%-20% based on the mass of the first and second coating layers. In some embodiments, both the first and second coating layers contain a conductive agent, and the mass fraction of the conductive agent can be selected from 2%, 3%, 4%, 5%, 10%, 15%, 20%, or any value range between the two, based on the mass of the first and second coating layers.

[0115] In some embodiments, the lithium supplementation material includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium squaric acid, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

[0116] The aforementioned lithium replenishment materials have high irreversible capacity, good lithium replenishment effect, good stability in air, and good compatibility with existing battery production processes, which is conducive to industrial production.

[0117] In some embodiments, the lithium supplementation material includes one or more of lithium-rich nickel oxide, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

[0118] The appropriate combination of lithium-replenishing materials and reducing agents can lower the decomposition potential of the lithium-replenishing materials, fully leveraging their lithium-replenishing function. Furthermore, the reaction products of these materials and reducing agents do not contain gases such as oxygen, carbon dioxide, or nitrogen, reducing the likelihood of gas generation in the battery and minimizing the impact of these gases on battery safety and cycle performance. Additionally, the decomposition products of these lithium-replenishing materials, including silicon oxide, nickel oxide, lithium oxide, boron oxide, or lithium sulfate, possess good ion conductivity, which helps improve the ion conductivity of the electrodes, thereby enhancing the battery's rate performance and cycle performance.

[0119] In some implementations, the lithium supplementation material includes one or both of lithium metasilicate and lithium orthosilicate.

[0120] The low decomposition potential of lithium metasilicate or lithium orthosilicate allows for a wider range of applications for high-capacity lithium replenishment materials. Furthermore, the decomposition products, including silicon dioxide and lithium sulfate, have good ion conductivity, which can improve the ion conductivity of the positive electrode and enhance the rate performance and cycle performance of the battery.

[0121] In some embodiments, the reducing material includes one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, elemental phosphorus, metal compounds of phosphorus, elemental boron, metal compounds of boron, elemental tellurium, metal compounds of tellurium, elemental antimony, metal compounds of antimony, elemental bismuth, metal compounds of bismuth, and selenium disulfide.

[0122] In this paper, the term "metallic compounds of selenium" refers to compounds formed by selenium and metallic elements, in which selenium has a negative chemical valence. These metallic compounds of selenium include, but are not limited to, lithium selenide, sodium selenide, or calcium selenide.

[0123] In this paper, the term "metallic compounds of sulfur" refers to compounds formed by sulfur and metallic elements, in which sulfur has a negative chemical valence state. These metallic compounds of sulfur include, but are not limited to, calcium sulfide, lithium sulfide, sodium sulfide, zinc sulfide, or iron sulfide.

[0124] In this article, the term "metallic compounds of phosphorus" refers to compounds formed by phosphorus and metal elements in which phosphorus has a negative chemical valence. These metallic compounds of phosphorus include, but are not limited to, lithium phosphide, sodium phosphide, iron phosphide, calcium phosphide, zinc phosphide, aluminum phosphide, or copper phosphide.

[0125] In this paper, the term "metallic compounds of boron" refers to compounds formed by boron and metallic elements in which boron has a negative chemical valence state. These metallic compounds of boron include, but are not limited to, titanium diboride, calcium hexaboride, molybdenum boride, or cobalt boride.

[0126] In this paper, the term "metallic compounds of tellurium" refers to compounds formed by tellurium and metallic elements, in which the chemical oxidation state of tellurium is negative. Metallic compounds of tellurium include, but are not limited to, copper telluride or molybdenum telluride.

[0127] In this paper, the term "metallic compounds of antimony" refers to compounds formed by antimony and metallic elements, wherein the chemical valence of antimony in metallic compounds of antimony is negative, and such metallic compounds of antimony include, but are not limited to, lithium antimony, sodium antimony, or indium antimony.

[0128] In this paper, the term "metallic compounds of bismuth" refers to compounds formed by bismuth and metallic elements, in which bismuth has a negative chemical valence state, including but not limited to sodium bismuthide.

[0129] The aforementioned reducing materials can chemically react with lithium replenishment materials to lower the decomposition potential of the lithium replenishment materials, achieve low-potential lithium replenishment, improve the decomposition efficiency and utilization rate of lithium replenishment materials, improve the battery capacity retention rate, and extend battery life.

[0130] In some embodiments, the reducing material includes one or more of elemental selenium, non-transition metal compounds of selenium, elemental sulfur, non-transition metal compounds of sulfur, elemental phosphorus, non-transition metal compounds of phosphorus, elemental boron, non-transition metal compounds of boron, elemental tellurium, non-transition metal compounds of tellurium, elemental antimony, non-transition metal compounds of antimony, elemental bismuth, non-transition metal compounds of bismuth, and selenium disulfide.

[0131] In this paper, the term "non-transition metal compounds of selenium" refers to compounds formed by selenium and non-transition metal elements, in which selenium has a negative chemical valence. These metal compounds of selenium include, but are not limited to, lithium selenide, sodium selenide, or calcium selenide.

[0132] In this paper, the term "non-transition metal compounds of sulfur" refers to compounds formed by sulfur and non-transition metal elements, in which sulfur has a negative chemical valence. These non-transition metal compounds of sulfur include, but are not limited to, calcium sulfide, lithium sulfide, or sodium sulfide.

[0133] In this paper, the term "non-transition metal compound of phosphorus" refers to a compound formed by phosphorus and a non-transition metal element, wherein the chemical valence of phosphorus in the non-transition metal compound of phosphorus is negative. The non-transition metal compounds of phosphorus include, but are not limited to, lithium phosphide, sodium phosphide, iron phosphide, calcium phosphide, and aluminum phosphide.

[0134] In this paper, the term "non-transition metal compound of boron" refers to a compound formed by boron and a non-transition metal element, wherein the chemical valence of boron in the non-transition metal compound of boron is negative, and the non-transition metal compound of boron includes, but is not limited to, calcium hexaboride.

[0135] In this paper, the term "non-transition metal compound of tellurium" refers to a compound formed by tellurium and a non-transition metal element, in which the chemical oxidation state of tellurium is negative. Non-transition metal compounds of tellurium include, but are not limited to, lithium telluride and sodium telluride.

[0136] In this paper, the term "antimony non-transition metal compound" refers to a compound formed by antimony and a non-transition metal element, wherein the chemical valence of antimony in the antimony non-transition metal compound is negative, and the antimony non-transition metal compound includes, but is not limited to, lithium antimony, sodium antimony, or indium antimony.

[0137] In this paper, the term "bismuth non-transition metal compound" refers to a compound formed by bismuth and a non-transition metal element, wherein the chemical valence of bismuth in the bismuth non-transition metal compound is negative, and the bismuth non-transition metal compound includes, but is not limited to, sodium bismuthide.

[0138] The aforementioned reducing materials do not contain transition metal elements, which can reduce the impact of catalytic oxidation reactions between transition metal elements and electrolytes on the battery's cycle or safety performance.

[0139] In some embodiments, the reducing material includes one or more of elemental selenium, elemental sulfur, elemental phosphorus, elemental boron, elemental tellurium, elemental antimony, elemental bismuth, and selenium disulfide.

[0140] The aforementioned reducing materials are elemental, which can reduce the impact of the catalytic oxidation reaction between transition metal elements and electrolyte on the battery's cycle or safety performance. At the same time, the elemental reducing materials have a low relative molecular mass, so the same mass content of reducing agent can react with more lithium-replenishing materials, thus improving the mass utilization rate of the reducing agent.

[0141] In some embodiments, the lithium replenishment efficiency of the lithium replenishment material is 90%-100%. In some embodiments, the lithium replenishment efficiency of the lithium replenishment material can be selected as 90%, 94%, 95%, 97%, 98%, 99%, 100%, or any value range between the two.

[0142] Lithium replenishment materials have high lithium replenishment efficiency, improve battery cycle performance, and extend battery life.

[0143] In some embodiments, the matrix material includes olivine-structured lithium phosphates, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials; these matrix materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4). 4( It can also be abbreviated as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites, at least one of the following:

[0144] In some embodiments, the matrix material includes lithium iron phosphate or a modified form of lithium iron phosphate, said modified form including one or more of doping modification and coating modification.

[0145] Some embodiments of this application provide a method for preparing a secondary battery, comprising the following steps:

[0146] A positive electrode sheet is obtained by coating a positive electrode slurry containing a positive electrode active material.

[0147] The negative electrode, separator, electrolyte, and positive electrode are assembled to form a secondary battery.

[0148] The positive electrode active material includes a matrix material and a coating layer that covers at least part of the matrix material. The coating layer includes a first coating layer and a second coating layer. The first coating layer is located on the surface of the matrix material, and the second coating layer is located on the surface of the first coating layer.

[0149] The first coating layer contains a lithium-replenishing material, and the second coating layer contains a reducing material; or,

[0150] The first coating layer contains the reducing material, and the second coating layer contains the lithium replenishing material.

[0151] In some implementations, the negative electrode, separator, and electrolyte can be conventionally configured in the art and can be selected by those skilled in the art according to actual needs.

[0152] Using the above preparation method, a secondary battery with excellent cycle performance can be prepared.

[0153] In some embodiments, the preparation method of the positive electrode active material specifically includes:

[0154] Formation of the first coating layer: The matrix material raw material and the lithium supplementation material precursor are subjected to a hydrothermal reaction to obtain a composite precursor.

[0155] The first mixture comprising the composite precursor and the lithium source is subjected to a first sintering treatment to obtain the initial positive electrode active material; or...

[0156] A second sintering treatment is performed on a second mixture comprising a matrix material, the lithium supplementation material precursor, and the lithium source to obtain the initial positive electrode active material; or,

[0157] The initial positive electrode active material is obtained by performing chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition on the matrix material using lithium supplementation material raw materials;

[0158] Formation of the second coating layer: The initial positive electrode active material is coated with a first vapor containing reducing material in the gas phase to obtain the positive electrode active material; or...

[0159] The third mixture comprising the initial positive electrode active material and the reducing material is ball-milled to obtain the positive electrode active material; or...

[0160] The fourth mixture containing the initial positive electrode active material and the reducing material is subjected to a third sintering treatment to obtain the positive electrode active material;

[0161] The first coating layer includes a lithium replenishing material, and the second coating layer includes a reducing material.

[0162] According to the above preparation method, a first coating layer containing lithium replenishing material and a second coating layer containing reducing material can be obtained, which can improve the reaction degree between reducing material and lithium replenishing material, achieve efficient lithium replenishment, increase the number of battery cycles, and extend the battery life.

[0163] In some embodiments, the initial positive electrode active material is prepared as follows:

[0164] A composite precursor is obtained by hydrothermal reaction of the matrix material raw material and the lithium supplementation material precursor.

[0165] The first mixture containing the composite precursor and the lithium source is subjected to a first sintering treatment to obtain the initial positive electrode active material.

[0166] The initial positive electrode active material includes a matrix material and a first coating layer that at least partially covers the matrix material, wherein the first coating layer includes a lithium supplement material.

[0167] A first coating layer containing lithium-supplementing material can be prepared by using hydrothermal reaction and sintering.

[0168] In some embodiments, the matrix material raw materials include raw materials or matrix material precursors used to synthesize the matrix material precursor. For example, if the matrix material is lithium iron phosphate, the matrix material raw materials include a phosphorus source and an iron source or iron phosphate; or if the matrix material is lithium nickel cobalt manganese oxide, the matrix material raw materials include a nickel source, a cobalt source, and a manganese source or nickel cobalt manganese hydroxide. The matrix material raw materials can be selected according to the type of matrix material.

[0169] In some embodiments, the lithium replenishment material precursor includes raw materials for synthesizing the lithium replenishment material. For example, the lithium replenishment material is lithium metasilicate, and the lithium replenishment material precursor is tetraethyl orthosilicate or silicon dioxide; the lithium replenishment material is lithium orthosilicate, and the lithium replenishment material precursor is tetraethyl orthosilicate or silicon dioxide; the lithium replenishment material is lithium-rich lithium iron phosphate, and the lithium replenishment material precursor is iron oxide; the lithium replenishment material precursor is lithium borate, and the lithium replenishment material precursor is boron oxide; the lithium replenishment material precursor is lithium metaborate, and the lithium replenishment material precursor is boron oxide; the lithium replenishment material precursor can be selected according to the type of lithium replenishment material.

[0170] In some implementations, the lithium source is a conventional choice in the art, including but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium hydroxide, lithium phosphate, or lithium dihydrogen phosphate.

[0171] In some implementations, the amount of matrix material raw material, lithium supplementation material precursor, or lithium source added depends on the respective mass content of the matrix material and lithium supplementation material in the target product cathode active material.

[0172] In some embodiments, the hydrothermal reaction temperature is 120°C to 220°C. In some embodiments, the hydrothermal reaction temperature can be selected from 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, or any value between two of these.

[0173] In some embodiments, the hydrothermal reaction time is 8 hours (h) to 24 hours. In some embodiments, the hydrothermal reaction time can be selected as 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, or any value range between the two.

[0174] The appropriate hydrothermal reaction temperature and / or reaction time enable the lithium supplement material precursor to form a coating layer on the base material raw material, and the two have good bonding force. After subsequent sintering treatment, the lithium supplement material forms a structurally complete coating layer on the surface of the base material.

[0175] In some embodiments, the temperature of the first sintering treatment is 600°C-1000°C. In some embodiments, the temperature of the first sintering treatment can be selected from 600°C, 700°C, 800°C, 900°C, 1000°C, or any value range between two of them.

[0176] In some embodiments, the first sintering treatment time is 4h-24h. In some embodiments, the first sintering treatment time can be selected as 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h or any value range between the two.

[0177] A suitable temperature and / or time for the first sintering allows the composite precursor to react fully with the lithium source, resulting in a cathode active material with stable structure and high phase purity.

[0178] In some embodiments, the initial positive electrode active material is prepared as follows:

[0179] A second sintering process is performed on a second mixture comprising a matrix material, the lithium supplementation material precursor, and the lithium source to obtain the initial positive electrode active material.

[0180] In some embodiments, the matrix material includes lithium iron phosphate or a modified form of lithium iron phosphate, said modified form including one or more of doping modification and coating modification.

[0181] By using a one-step sintering process, an initial positive electrode active material containing lithium-supplementing material in the first coating layer can be prepared.

[0182] In some embodiments, the temperature of the second sintering treatment is 600°C-900°C. In some embodiments, the temperature of the second sintering treatment can be selected as 600°C, 700°C, 800°C, 900°C, or any value range between two of them.

[0183] In some embodiments, the second sintering treatment time is 4h-24h. In some embodiments, the second sintering treatment time can be selected as 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h or any value range between the two.

[0184] A suitable second sintering temperature and / or time allows the lithium supplementation material precursor to react fully with the lithium source, resulting in a coating layer with stable structure and high phase purity.

[0185] In some embodiments, the initial positive electrode active material is prepared as follows:

[0186] The initial positive electrode active material is obtained by performing chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition on the matrix material using lithium-supplementing material raw materials.

[0187] In some implementations, physical vapor deposition includes thermal evaporation, magnetron sputtering, or ion plating.

[0188] Chemical vapor deposition, physical vapor deposition, atomic layer deposition, and molecular layer deposition are all conventional processes. The appropriate process and raw materials for lithium replenishment are selected according to the type of lithium replenishment material to prepare the first coating layer.

[0189] The raw materials for lithium replenishment materials can be conventionally selected based on the type of target lithium replenishment material and the preparation process. For example, if the target lithium replenishment material is lithium metasilicate and the selected process is atomic layer deposition, then the raw materials are lithium oxide and silicon dioxide. If the target lithium replenishment material is a lithium metasilicate thin film and the selected process is chemical vapor deposition, then the raw materials are lithium carbonate and tetramethyl orthosilicate. If the target lithium replenishment material is lithium silicate and the selected process is physical vapor deposition, then the raw materials are lithium silicate.

[0190] The above-mentioned chemical vapor deposition, physical vapor deposition, atomic layer deposition, and molecular layer deposition can form a uniform and dense first coating layer on the substrate material.

[0191] In some embodiments, the preparation method of the positive electrode active material is as follows:

[0192] The initial positive electrode active material is coated with a first vapor containing reducing material in the gas phase to obtain the positive electrode active material.

[0193] In some embodiments, the reducing material can be processed into vapor using conventional methods in the art, including but not limited to heat treatment.

[0194] By using vapor phase coating, the reducing material can be uniformly coated onto the surface of the initial positive electrode active material in vapor phase, forming a second coating layer containing the reducing material.

[0195] In some embodiments, the preparation method of the positive electrode active material is as follows:

[0196] The third mixture, comprising the initial positive electrode active material and the reducing material, is ball-milled to obtain the positive electrode active material.

[0197] During the mechanical ball milling process, the raw materials are converted into reducing material vapor, which then coats the initial positive electrode active material in the gas phase.

[0198] In some embodiments, the preparation method of the positive electrode active material is as follows:

[0199] The fourth mixture, comprising the initial positive electrode active material and the reducing material, is subjected to a third sintering treatment to obtain the positive electrode active material.

[0200] Sintering is beneficial for converting reducing materials into a gaseous state and for forming a uniform and dense second coating layer on the initial positive electrode active material.

[0201] In some embodiments, the temperature of the third sintering treatment is 120°C-350°C; and / or, the time of the third sintering treatment is 4h-48h.

[0202] A suitable temperature and / or time for the third sintering is beneficial for forming a dense and uniform reducing material coating layer.

[0203] In some embodiments, the first mixture or the second mixture further includes a carbon source.

[0204] In some embodiments, the first mixture or the second mixture further includes at least one of glucose, sucrose, fructose, polyethylene glycol, starch, polydopamine, polyvinylpyrrolidone, or tannic acid.

[0205] In some embodiments, the third or fourth mixture further includes a conductive agent.

[0206] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0207] By adding a carbon source or conductive agent during the synthesis of the first coating layer and / or the second coating layer, a first coating layer and / or a second coating layer containing a conductive agent can be obtained. This is beneficial to further improve the conductive network of the lithium replenishing material and the reducing material, increase the degree of reaction between the two, and achieve the purpose of efficient lithium replenishment.

[0208] In some embodiments, the preparation method of the positive electrode active material specifically includes:

[0209] Formation of the first coating layer: The matrix material is vapor-phase coated with a second vapor containing reducing material to obtain an intermediate material; or...

[0210] The fifth mixture comprising the matrix material and the reducing material is ball-milled to obtain the intermediate material; or...

[0211] The sixth mixture containing the matrix material and the reducing material is subjected to a fourth sintering process to obtain the intermediate material.

[0212] Formation of the second coating layer: A fifth sintering treatment is performed on a seventh mixture comprising the intermediate material, the lithium supplementation material precursor, and the lithium source to obtain the positive electrode active material; or,

[0213] The intermediate material is obtained by performing chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition on the lithium supplementation material raw material to obtain the positive electrode active material.

[0214] The first coating layer comprises reducing material, and the second coating layer comprises lithium replenishing material.

[0215] According to the above preparation method, a first coating layer containing reducing materials and a second coating layer containing lithium replenishing materials can be obtained, which can improve the reaction degree between reducing materials and lithium replenishing materials, achieve efficient lithium replenishment, increase the number of battery cycles, and extend the battery life.

[0216] In some embodiments, the intermediate material is prepared as follows:

[0217] Formation of the first coating layer: The matrix material is coated with a second vapor containing reducing material in the gas phase to obtain an intermediate material.

[0218] In some embodiments, the reducing material can be processed into a second vapor using conventional methods in the art, including but not limited to heat treatment.

[0219] By using vapor phase coating, the reducing material vapor phase can be uniformly coated onto the surface of the matrix material to obtain a first coating layer containing the reducing material.

[0220] In some embodiments, the intermediate material is prepared as follows:

[0221] The fifth mixture, comprising the matrix material and the reducing material, is ball-milled to obtain the intermediate material.

[0222] Ball milling can convert reducing materials into a gaseous state, and the gaseous reducing materials can be used to coat the matrix material to form a reducing material coating layer.

[0223] In some embodiments, the intermediate material is prepared as follows:

[0224] The sixth mixture, comprising the matrix material and the reducing material, is subjected to a fourth sintering process to obtain the intermediate material.

[0225] Sintering is beneficial for converting reducing materials into a gaseous state, which is conducive to forming a uniform and dense first coating layer on the matrix material.

[0226] In some embodiments, the temperature of the fourth sintering treatment is 120°C-350°C; and / or the time of the fourth sintering treatment is 4h-48h.

[0227] In some embodiments, the preparation method of the positive electrode active material is as follows:

[0228] The seventh mixture, comprising the intermediate material, the lithium supplementation material precursor, and the lithium source, is subjected to a fifth sintering treatment to obtain the positive electrode active material.

[0229] In some embodiments, the lithium replenishment material precursor includes raw materials for synthesizing the lithium replenishment material. For example, the lithium replenishment material is lithium metasilicate, and the lithium replenishment material precursor is tetraethyl orthosilicate or silicon dioxide; the lithium replenishment material is lithium orthosilicate, and the lithium replenishment material precursor is tetraethyl orthosilicate or silicon dioxide; the lithium replenishment material is lithium-rich lithium iron phosphate, and the lithium replenishment material precursor is iron oxide; the lithium replenishment material precursor is lithium borate, and the lithium replenishment material precursor is boron oxide; the lithium replenishment material precursor is lithium metaborate, and the lithium replenishment material precursor is boron oxide; the lithium replenishment material precursor can be selected according to the type of lithium replenishment material.

[0230] In some implementations, the lithium source is a conventional choice in the art, including but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium hydroxide, lithium phosphate, or lithium dihydrogen phosphate.

[0231] In some embodiments, the temperature of the fifth sintering treatment is 200°C-500°C; and / or the time of the fifth sintering treatment is 4h-48h.

[0232] In some embodiments, the preparation method of the positive electrode active material is as follows:

[0233] The intermediate material is obtained by performing chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition on the lithium-supplementing material raw material.

[0234] In some implementations, physical vapor deposition includes thermal evaporation, magnetron sputtering, or ion plating.

[0235] Chemical vapor deposition, physical vapor deposition, atomic layer deposition, and molecular layer deposition are all conventional processes. The appropriate process and raw materials for lithium replenishment are selected according to the type of lithium replenishment material to prepare the first coating layer.

[0236] The raw materials for lithium replenishment materials can be conventionally selected based on the type of target lithium replenishment material and the preparation process. For example, if the target lithium replenishment material is lithium metasilicate and the selected process is atomic layer deposition, then the raw materials are lithium oxide and silicon dioxide. If the target lithium replenishment material is a lithium metasilicate thin film and the selected process is chemical vapor deposition, then the raw materials are lithium carbonate and tetramethyl orthosilicate. If the target lithium replenishment material is lithium silicate and the selected process is physical vapor deposition, then the raw materials are lithium silicate.

[0237] Using the above-mentioned chemical vapor deposition, physical vapor deposition, atomic layer deposition, and molecular layer deposition, a uniform and dense second coating layer can be formed on the surface of the intermediate material.

[0238] In some embodiments, the seventh mixture further includes a carbon source.

[0239] In some embodiments, the carbon source includes bitumen or biomass carbon.

[0240] In some embodiments, the fifth or sixth mixture further includes a conductive agent.

[0241] In some embodiments, the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0242] In one embodiment, the secondary battery includes a lithium-ion battery. Specifically, it includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0243] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0244] In some embodiments, the positive electrode film layer includes a positive electrode active material.

[0245] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0246] In some embodiments, the positive electrode further includes a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0247] In some embodiments, the positive electrode sheet further includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0248] In some embodiments, the positive electrode sheet can be prepared by dispersing the positive active material, binder, conductive agent and any other components in the above embodiments in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0249] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0250] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0251] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0252] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0253] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0254] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0255] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0256] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0257] In some embodiments, the electrolyte acts as a conductor of ions between the positive and negative electrode plates. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0258] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0259] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0260] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0261] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0262] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0263] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0264] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0265] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0266] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0267] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0268] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0269] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0270] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 shows a square-structured secondary battery 5 as an example.

[0271] In some embodiments, referring to FIG3, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0272] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0273] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0274] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0275] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0276] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0277] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0278] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0279] Figure 7 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0280] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0281] Example

[0282] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0283] I. Preparation Method

[0284] Example 1

[0285] 1) Preparation of positive electrode active materials

[0286] 100g of lithium iron phosphate material was dispersed in a mixed organic solvent of ethanol and water, and then 7.4g of tetraethyl orthosilicate and 3.0g of lithium hydroxide monohydrate were added. After drying, the mixture was sintered in a tube furnace at 800℃ for 12h under a nitrogen atmosphere to obtain lithium iron phosphate positive electrode active material coated with lithium metasilicate. Based on the mass of lithium iron phosphate, the mass content of lithium metasilicate was 3.2%.

[0287] 103.2g of lithium iron phosphate coated with lithium metasilicate was mixed with 0.8g of reducing material elemental sulfur and then treated at 155°C for 12h under an inert atmosphere to obtain a positive electrode active material with lithium metasilicate as the first coating layer and elemental sulfur as the second coating layer.

[0288] 2) Preparation of positive electrode sheet

[0289] The positive electrode active material, conductive carbon (SP), and binder prepared above were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96%:2%:2%. After thorough mixing, a positive electrode film slurry was prepared. The positive electrode film slurry was coated onto the positive electrode current collector aluminum foil, and then dried at 100°C, cold-pressed at 40T, and slit to obtain the positive electrode sheet.

[0290] 2) Preparation of negative electrode sheet

[0291] The active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in an appropriate amount of deionized water solvent system at a weight ratio of 96.5%:0.7%:1.8%:1% to obtain a negative electrode slurry. The negative electrode slurry is then coated onto Cu foil, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0292] 3) Separating membrane

[0293] Polyethylene porous polymer film is used as the separator.

[0294] 4) Preparation of electrolyte

[0295] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte with a concentration of 1 mol / L.

[0296] 6) Battery manufacturing

[0297] The positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain a battery cell. The battery cell is then placed in an outer packaging, and the electrolyte mentioned above is added. After processes such as encapsulation, settling, formation, and aging, a secondary battery is obtained.

[0298] Example 2

[0299] Example 2 differs from Example 1 in that the preparation method of the positive electrode active material is adjusted, as follows:

[0300] 0.80g of elemental sulfur was treated at 155℃ to obtain sulfur vapor. The sulfur vapor was diffused onto the surface of 100g of lithium iron phosphate, so that elemental sulfur was uniformly coated on the surface of lithium iron phosphate in the form of vapor, forming sulfur-coated lithium iron phosphate. Based on the mass of lithium iron phosphate, the mass fraction of the sulfur coating layer was 0.80%.

[0301] A lithium metasilicate coating layer was formed on the surface of sulfur-coated lithium iron phosphate using atomic layer deposition (ALD) technology, involving lithium oxide and silicon dioxide. The specific process is as follows: First, under a nitrogen atmosphere, lithium tert-butoxide / H₂O and tetraethyl orthosilicate / H₂O were alternately introduced into the first and second chambers, respectively, to obtain lithium oxide precursor and silicon dioxide precursor, respectively. The reaction temperature of lithium tert-butoxide / H₂O was 170℃, and the reaction temperature of tetraethyl orthosilicate / H₂O was 65℃. The lithium tert-butoxide and tetraethyl orthosilicate / H₂O precursors were then reacted. The introduction and diffusion times of tetraethyl silicate, H2O, and H2O were 1s / 15s, 2s / 15s, and 2s / 20s, respectively. Under an N2 atmosphere, 100.8g of sulfur-coated lithium iron phosphate was placed in the sample chamber of an atomic layer deposition apparatus and heated to 235°C. The lithium oxide precursor and silica precursor obtained above were alternately introduced as one cycle. The amount of lithium metasilicate generated was monitored by controlling the number of cycles, so that the target weight of lithium metasilicate was 3.2g.

[0302] Example 3

[0303] Example 3 differs from Example 1 in that the preparation method of the positive electrode active material is adjusted, as follows:

[0304] 100g of lithium iron phosphate material was dispersed in a mixed organic solvent of ethanol and water, and then 7.4g of tetraethyl orthosilicate, 3.0g of lithium hydroxide monohydrate and 0.4g of glucose were added. After drying, the material was sintered in a tube furnace at 800℃ for 12h under a nitrogen atmosphere to obtain a positive electrode active material of lithium iron phosphate coated with lithium metasilicate and carbon conductive agent. Based on the mass of lithium iron phosphate, the mass content of lithium metasilicate was 3.2%, and based on the mass of the first coating layer, the mass fraction of carbon was 4.8%.

[0305] 103.36g of lithium metasilicate, carbon-coated lithium iron phosphate, and 0.8g of reducing agent elemental sulfur were mixed and treated at 155°C for 12h under an inert atmosphere to obtain the positive electrode active material.

[0306] Example 4

[0307] Example 4 differs from Example 1 in that the preparation method of the positive electrode active material is adjusted, as follows:

[0308] 0.16g of conductive carbon black was thoroughly mixed with 0.8g of elemental sulfur, and then further mixed with 100g of lithium iron phosphate. The mixture was then treated at 155°C for 24 hours to obtain an intermediate material.

[0309] Lithium oxide and silicon dioxide were deposited on the surface of an intermediate material using atomic layer deposition to form a lithium metasilicate coating layer. The specific process is as follows: First, in a nitrogen atmosphere, lithium tert-butoxide / H2O and tetraethyl orthosilicate / H2O were alternately introduced into the first chamber and the second chamber, respectively, to obtain lithium oxide precursor and silicon dioxide precursor, respectively. The reaction temperature of lithium tert-butoxide / H2O was 170℃, and the reaction temperature of tetraethyl orthosilicate / H2O was 65℃. The introduction and diffusion times of lithium tert-butoxide, tetraethyl orthosilicate, and H2O were 1s / 15s, 2s / 15s, and 2s / 20s, respectively. Under an N2 atmosphere, 100.96 g of elemental sulfur and carbon-coated lithium iron phosphate were placed in the sample chamber of an atomic layer deposition apparatus and heated to 235 °C. The lithium oxide precursor and silicon dioxide precursor obtained above were alternately introduced as one cycle. The amount of lithium metasilicate generated was monitored by controlling the number of cycles, so that the target weight of lithium metasilicate was 3.2 g.

[0310] Example 5

[0311] Compared with Example 1, the preparation method of the positive electrode active material was adjusted, as follows:

[0312] 100g of ferrous oxalate, 91.66g of diammonium hydrogen phosphate and 8.11g of tetraethyl orthosilicate were mixed and dispersed in an ethanol solution and subjected to a hydrothermal reaction at 180°C for 12 hours.

[0313] The reaction solution was centrifuged to obtain a composite precursor. The composite precursor was mixed with 32.42 g of lithium hydroxide monohydrate and dispersed in an ethanol solution. After drying, it was sintered in a tube furnace at 800 °C for 12 h under a nitrogen atmosphere to obtain lithium iron phosphate coated with lithium metasilicate. Based on the mass of lithium iron phosphate, the mass content of lithium metasilicate was 3.2%.

[0314] 103.2g of lithium iron phosphate coated with lithium metasilicate was thoroughly mixed with 0.8g of selenium powder and 0.16g of conductive carbon black, and then treated at 240℃ for 12h to obtain the positive electrode active material.

[0315] Example 6

[0316] Compared with Example 1, the preparation method of the positive electrode active material was adjusted, as follows:

[0317] 100g of lithium iron phosphate material was dispersed in a mixed organic solvent of ethanol and water, and then 5.55g of tetraethyl orthosilicate, 4.48g of lithium hydroxide monohydrate and 0.8g of glucose were added. After drying, the mixture was sintered in a tube furnace at 800℃ for 12h under a nitrogen atmosphere to obtain lithium orthosilicate and carbon-coated lithium iron phosphate. Based on the mass of lithium iron phosphate, the mass content of lithium orthosilicate was 3.2%, and based on the mass of the first coating layer, the mass fraction of carbon was 9.1%.

[0318] 0.8 g of boron vapor was reacted with 103.52 g of lithium orthosilicate and carbon-coated lithium iron phosphate to form a second coating layer of boron. The mass fraction of boron was 0.80% based on the mass of lithium iron phosphate.

[0319] Example 7

[0320] 100g of lithium iron phosphate and 0.8g of selenium disulfide were mixed and added to a ball mill for ball milling. The ball mill speed was set to 500rpm and the ball milling time was 4h. During the ball milling process, selenium disulfide was uniformly coated on the surface of lithium iron phosphate in the form of vapor to form the first coating layer of selenium disulfide. Based on the mass of lithium iron phosphate, the mass fraction of selenium disulfide was 0.80%.

[0321] 100.8 g of selenium disulfide-coated lithium iron phosphate was dispersed in a mixed organic solvent of ethanol and water, and then 1.40 g of boron oxide, 5.04 g of lithium hydroxide monohydrate and 0.8 g of glucose were added. After drying, the mixture was sintered in a tube furnace at 800 °C for 12 h under a nitrogen atmosphere to obtain the positive electrode active material.

[0322] Comparative Example 1

[0323] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted, as follows:

[0324] Lithium iron phosphate, conductive carbon (SP), and binder are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96%:2%:2%. After thorough mixing, a positive electrode film slurry is prepared. The positive electrode film slurry is coated onto the positive electrode current collector aluminum foil, and then dried at 100°C, cold-pressed, and slit to obtain the positive electrode sheet.

[0325] Comparative Example 2

[0326] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted, as follows:

[0327] 92g of lithium iron phosphate, 3.2g of lithium metasilicate, 0.8g of elemental sulfur, 2g of conductive carbon (SP), and 2g of binder were dissolved in the solvent N-methylpyrrolidone (NMP). After thorough mixing, a positive electrode slurry was prepared. The positive electrode slurry was coated onto the positive electrode current collector aluminum foil, and then dried at 100℃, cold-pressed, and slit to obtain the positive electrode sheet.

[0328] Comparative Example 3

[0329] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted, as follows:

[0330] Lithium metasilicate and elemental sulfur were mixed in a mass ratio of 8:2 and then mechanically ball-milled to obtain sulfur-coated lithium metasilicate material.

[0331] 92g of lithium iron phosphate, 4g of sulfur-coated lithium metasilicate, 2g of conductive carbon (SP), and 2g of binder were dissolved in N-methylpyrrolidone (NMP) solvent and thoroughly mixed to prepare a positive electrode slurry. The positive electrode slurry was coated onto the positive electrode current collector aluminum foil, and then dried at 100℃, cold-pressed, and slit to obtain the positive electrode sheet.

[0332] II. Testing Methods

[0333] 1. Battery cycle count

[0334] The secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.5C to the charging cutoff voltage of 4.0V, then charged at a constant voltage until the current ≤0.05C, and allowed to stand for 5 minutes. They were then discharged at a constant current rate of 0.33C to the discharge cutoff voltage of 2V, and allowed to stand for 5 minutes. This constituted the first charge-discharge cycle. Starting from the second cycle, the charging voltage was reduced to 3.8V, while other parameters remained unchanged. The batteries were then subjected to cyclic charge-discharge tests using this method until the battery capacity decreased to 80%. The number of cycles at this point represents the battery's cycle life at 25°C.

[0335] 2. Lithium replenishment efficiency of lithium replenishment materials

[0336] The lithium-ion batteries of the examples and comparative examples were charged to 4.5V at 0.05C rate at 25°C, and the charging capacity C1 was recorded. The mass of the lithium replenishing material in the positive electrode film layer was recorded as m0, and the mass of the substrate material was recorded as m1.

[0337] The lithium-ion battery of Comparative Example 1 is used as a blank control. Its charging capacity measured under the above test conditions is recorded as C2. The mass of the matrix material in the positive electrode film layer of Comparative Example 1 is recorded as m2. Then the specific capacity of the matrix material is B = C2 / m2.

[0338] The actual specific capacity of the lithium replenishment material is A1 = (C1 - B × m1) / m0, where the theoretical specific capacity of the lithium replenishment material is A0. The lithium replenishment efficiency of the lithium replenishment material = actual specific capacity of the lithium replenishment material / theoretical specific capacity of the lithium replenishment material = A1 / A0 × 100%.

[0339] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0340] The positive electrode active materials and secondary batteries of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in the table below.

[0341] Table 1

[0342] As shown in Table 1, the positive electrode active material in Examples 1-7 includes lithium iron phosphate and a coating layer that covers at least part of the lithium iron phosphate. The coating layer includes a first coating layer and a second coating layer. The first coating layer is located on the surface of the lithium iron phosphate, and the second coating layer is located on the surface of the first coating layer. The first coating layer contains lithium metasilicate or lithium orthosilicate, and the second coating layer contains elemental sulfur, elemental selenium, or elemental boron; or the first coating layer contains elemental sulfur or selenium disulfide, and the second coating layer contains lithium metasilicate or lithium borate.

[0343] As can be seen from the comparison between Examples 1-7 and Comparative Example 1, coating the surface of the positive electrode active material with lithium replenishing material and reducing material can increase the cycle number of the battery and extend its service life.

[0344] As can be seen from the comparison between Examples 1-7 and Comparative Example 2, compared with adding lithium replenishing materials and reducing materials to the positive electrode film layer, this application coats the lithium replenishing materials and reducing materials on the surface of lithium iron phosphate, which can further improve the lithium replenishing efficiency of the lithium replenishing materials and extend the cycle number of the battery.

[0345] As can be seen from the comparison between Examples 1-7 and Comparative Example 3, compared with adding core-shell structured lithium replenishing materials and reducing materials to the positive electrode film layer, this application coats the lithium replenishing materials and reducing materials onto the surface of lithium iron phosphate in the form of a double-layer coating, which can further improve the lithium replenishing efficiency of the lithium replenishing materials and extend the cycle number of the battery.

[0346] As can be seen from the comparison between Example 3 and Example 1, and Example 4 and Example 2, the inclusion of a conductive agent in the first or second coating layer can further improve the lithium replenishment efficiency of the lithium replenishment material and improve the cycle performance of the battery.

[0347] 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 secondary battery, comprising a positive electrode, characterized in that, The positive electrode sheet includes a positive electrode active material, the positive electrode active material includes a matrix material and a coating layer that covers at least part of the matrix material, the coating layer includes a first coating layer and a second coating layer, the first coating layer is located on the surface of the matrix material, and the second coating layer is located on the surface of the first coating layer; Wherein, the first coating layer comprises a lithium-replenishing material, and the second coating layer comprises a reducing material; or... The first coating layer contains the reducing material, and the second coating layer contains the lithium replenishing material.

2. The secondary battery according to claim 1, characterized in that, The mass ratio of the lithium replenishing material to the reducing material is 0.5-50.

3. The secondary battery according to claim 1, characterized in that, The mass ratio of the lithium replenishing material to the reducing material is 1-20.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, Based on the mass of the matrix material, the mass fraction of the lithium supplement material is 0.5%-20%.

5. The secondary battery according to any one of claims 1 to 3, characterized in that, Based on the mass of the matrix material, the mass fraction of the lithium supplement material is 1%-10%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that, Based on the mass of the matrix material, the mass fraction of the reducing material is 0.01%-10%.

7. The secondary battery according to any one of claims 1 to 5, characterized in that, Based on the mass of the matrix material, the mass fraction of the reducing material is 0.02%-5%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The first coating layer and / or the second coating layer further include a conductive agent.

9. The secondary battery according to any one of claims 1 to 7, characterized in that, Based on the mass of the first coating layer and / or the second coating layer containing the conductive agent, the mass fraction of the conductive agent is 2%-20%.

10. The secondary battery according to any one of claims 1 to 9, characterized in that, The lithium supplementing material includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium squaric acid, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

11. The secondary battery according to any one of claims 1 to 10, characterized in that, The reducing materials include one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, elemental phosphorus, metal compounds of phosphorus, elemental boron, metal compounds of boron, elemental tellurium, metal compounds of tellurium, elemental antimony, metal compounds of antimony, elemental bismuth, metal compounds of bismuth, and selenium disulfide.

12. The secondary battery according to any one of claims 1 to 10, characterized in that, The lithium replenishment efficiency of the lithium replenishment material is 90%-100%.

13. A method for preparing a secondary battery, characterized in that, Includes the following steps, A positive electrode sheet is obtained by coating a positive electrode slurry containing a positive electrode active material. The negative electrode, separator, electrolyte, and positive electrode are assembled to form a secondary battery. The positive electrode active material includes a matrix material and a coating layer that at least partially covers the matrix material. The coating layer includes a first coating layer and a second coating layer. The first coating layer is located on the surface of the matrix material, and the second coating layer is located on the surface of the matrix material. The surface of the first coating layer; The first coating layer contains a lithium-replenishing material, and the second coating layer contains a reducing material; or, The first coating layer contains the reducing material, and the second coating layer contains the lithium replenishing material.

14. The preparation method according to claim 13, characterized in that, The preparation method of the positive electrode active material specifically includes: Formation of the first coating layer: The matrix material raw material and the lithium supplementation material precursor are subjected to a hydrothermal reaction to obtain a composite precursor. The first mixture comprising the composite precursor and the lithium source is subjected to a first sintering treatment to obtain the initial positive electrode active material; or... A second sintering treatment is performed on a second mixture comprising a matrix material, the lithium supplementation material precursor, and the lithium source to obtain the initial positive electrode active material; or, The initial positive electrode active material is obtained by performing chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition on the matrix material using lithium supplementation material raw materials. Formation of the second coating layer: The initial positive electrode active material is vapor-phase coated with a first vapor containing reducing material to obtain the positive electrode active material; or... The third mixture comprising the initial positive electrode active material and the reducing material is ball-milled to obtain the positive electrode active material; or... The fourth mixture containing the initial positive electrode active material and the reducing material is subjected to a third sintering treatment to obtain the positive electrode active material; The first coating layer includes a lithium replenishing material, and the second coating layer includes a reducing material.

15. The preparation method according to claim 14, characterized in that, The first mixture or the second mixture further includes a carbon source; or, The third or fourth mixture also includes a conductive agent.

16. The preparation method according to claim 14 or 15, characterized in that, The hydrothermal reaction temperature is 120℃-220℃; and / or, the hydrothermal reaction time is 8h-24h.

17. The preparation method according to any one of claims 14 to 16, characterized in that, The temperature of the first sintering treatment is 600℃-1000℃; and / or the time of the first sintering treatment is 4h-24h.

18. The preparation method according to any one of claims 14 to 17, characterized in that, The temperature of the second sintering treatment is 600℃-900℃; and / or the time of the second sintering treatment is 4h-24h.

19. The preparation method according to any one of claims 14 to 18, characterized in that, The temperature of the third sintering treatment is 120℃-350℃; and / or the time of the third sintering treatment is 4h-48h.

20. The preparation method according to claim 13, characterized in that, The preparation method of the positive electrode active material specifically includes: Formation of the first coating layer: The matrix material is vapor-phase coated with a second vapor containing reducing material to obtain an intermediate material; or... The fifth mixture comprising the matrix material and the reducing material is ball-milled to obtain the intermediate material; or... The sixth mixture containing the matrix material and the reducing material is subjected to a fourth sintering process to obtain the intermediate material. Formation of the second coating layer: A fifth sintering treatment is performed on a seventh mixture comprising the intermediate material, the lithium supplementation material precursor, and the lithium source to obtain the positive electrode active material; or, The intermediate material is obtained by performing chemical vapor deposition, physical vapor deposition, atomic layer deposition, or molecular layer deposition on the lithium supplementation material raw material to obtain the positive electrode active material. The first coating layer comprises reducing material, and the second coating layer comprises lithium replenishing material.

21. The preparation method according to claim 20, characterized in that, The seventh mixture further includes a carbon source; or... The fifth or sixth mixture also includes a conductive agent.

22. The preparation method according to claim 20 or 21, characterized in that, The temperature of the fourth sintering treatment is 120℃-350℃; and / or the time of the fourth sintering treatment is 4h-48h.

23. The preparation method according to claim 20 or 21, characterized in that, The temperature of the fifth sintering treatment is 200℃-500℃; and / or the time of the fifth sintering treatment is 4h-48h.

24. An electrical appliance, characterized in that, The secondary battery includes any one of claims 1 to 13 or a secondary battery prepared by any one of claims 14 to 23.

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