Secondary battery, preparation method thereof and electric device

Abstract

The invention provides a secondary battery, a preparation method thereof and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive active material and an additive, the positive active material comprises a base material and a coating layer at least partially covering the base material, the coating layer comprises a lithium supplementing material or a reducing material, and the additive comprises a lithium supplementing material or a reducing material. The coating layer or the additive does not contain a lithium supplementing material and does not contain a reducing material at the same time. The secondary battery has excellent cycle performance and long service life.

Description

Secondary battery, preparation method thereof, and power-consuming device Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method thereof, and an electrical device. Background Art

[0002] Lithium-ion batteries (LIBs), a type of secondary battery, boast high energy density, long service life, and are energy-efficient and environmentally friendly. However, during the initial charge and discharge process of a lithium-ion battery, the electrolyte forms a solid electrolyte interface film (SEI) on the surface of the negative electrode. This SEI film formation consumes a large amount of active lithium ions. Furthermore, during the battery's charge and discharge cycles, the cracking and shattering of the positive electrode active material particles, and 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 shortening its service life.

[0003] Summary of the Invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery, aiming to solve the technical problem of how to improve the cycle performance of the secondary battery and extend the service life of the battery.

[0005] A first aspect of the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode active material and an additive, the positive electrode active material comprising a base material and a coating layer at least partially covering the base material, the coating layer comprising a lithium-supplementing material or a reducing material, the additive comprising a lithium-supplementing material or a reducing material, and the coating layer or the additive not comprising both a lithium-supplementing material and a reducing material.

[0006] The lithium-supplementing material in the secondary battery of the present application is present in the coating layer of the base material, the reducing material is present in the additive of the positive electrode plate or the reducing material is present in the coating layer of the base material, and the lithium-supplementing material is present in the additive of the positive electrode plate. The lithium-supplementing material and the reducing material can form point-surface contact, which can increase the contact area between the lithium-supplementing material and the reducing material, increase the reaction degree between the lithium-supplementing material and the reducing material, and improve the lithium-supplementing efficiency of the lithium-supplementing material. At the same time, the lithium-supplementing material or the reducing material is present in the coating layer, and the conductivity of the base material can be used to improve the conductive network of the lithium-supplementing material and the reducing material, provide more electron transmission pathways, increase the reaction degree between the lithium-supplementing material and the reducing material, reduce the membrane resistance of the plate, and improve the battery's dynamic performance and cycle performance.

[0007] In summary, by using the secondary battery of the present application, the contact area between the lithium-supplementing material and the reducing material is increased, and the degree of reaction between the two is increased. The lithium-supplementing material can play its lithium-supplementing role as much as possible, and the lithium-supplementing efficiency of the lithium-supplementing material is improved. A large amount of active lithium is provided for lithium replenishment during the cycle process. The battery has an excellent number of cycles and a long service life.

[0008] In any embodiment, the mass ratio of the lithium replenishing material to the reducing material is 0.5-50.

[0009] In any embodiment, the mass ratio of the lithium replenishing material to the reducing material is 1-20.

[0010] The mass ratio of the lithium replenishing material to the reducing material is within an appropriate range, which allows the lithium replenishing material and the reducing material to fully react to improve the lithium replenishing efficiency while avoiding excessive residual lithium replenishing material and / or reducing material that deteriorates the cycle performance and energy density of the battery.

[0011] In any embodiment, the mass fraction of the lithium supplementing material is 0.5%-20% based on the mass of the matrix material.

[0012] In any embodiment, the mass fraction of the lithium supplementing material is 1%-10% based on the mass of the matrix material.

[0013] The mass fraction of the lithium-supplementing material is within an appropriate range. On the one hand, the lithium-supplementing material can fully exert its lithium-supplementing effect and improve the cycle performance of the battery. On the other hand, it also avoids excessive lithium-supplementing material from having an adverse effect on the battery's rate performance, available capacity and safety performance.

[0014] In any embodiment, the mass fraction of the reducing material is 0.01% to 10% based on the mass of the matrix material.

[0015] In any embodiment, the mass fraction of the reducing material is 0.02% to 5% based on the mass of the matrix material.

[0016] The mass fraction of the reducing material is within an appropriate range. On the one hand, the lithium-supplementing material reacts fully with the reducing material under the action of a sufficient amount of the reducing material, so that the lithium-supplementing material can maximize its lithium-supplementing effect and improve the cycle performance of the battery. On the other hand, it also avoids the adverse effects of excessive reducing materials on the available capacity and safety performance.

[0017] 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 quartz, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

[0018] In any embodiment, the lithium-supplementing material includes one or more of lithium-rich nickelate, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

[0019] The lithium-supplementing material has a high irreversible capacity and a good lithium-supplementing effect. In addition, the lithium-supplementing material has good stability in the air and is compatible with the existing battery production process, which is conducive to industrial production.

[0020] In any embodiment, 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.

[0021] In any embodiment, the reducing material includes one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, and selenium disulfide.

[0022] The above-mentioned reducing materials can chemically react with the lithium supplement material to reduce the decomposition potential of the lithium supplement material, achieve low-potential lithium supplementation, improve the decomposition efficiency and utilization rate of the lithium supplement material, improve the capacity retention rate of the battery, and increase the battery life.

[0023] In any embodiment, the lithium replenishing efficiency of the lithium replenishing material is greater than or equal to 85%.

[0024] In any embodiment, the lithium replenishing material has a lithium replenishing efficiency of 90%-100%.

[0025] The second aspect of the present application provides a method for preparing a secondary battery, comprising the following steps:

[0026] Applying a positive electrode slurry containing a positive electrode active material and an additive to obtain a positive electrode sheet;

[0027] Assemble the negative electrode sheet, separator, electrolyte and positive electrode sheet to form a secondary battery.

[0028] The positive electrode active material includes a base material and a coating layer at least partially covering the base material.

[0029] The coating layer contains a lithium-supplementing material or a reducing material, the additive contains a lithium-supplementing material or a reducing material, and the coating layer and the additive do not contain both the lithium-supplementing material and the reducing material.

[0030] By adopting the above preparation method, a secondary battery with excellent cycle performance can be prepared.

[0031] In any embodiment, the method for preparing the positive electrode active material specifically includes:

[0032] The matrix material raw material and the lithium supplement material precursor are subjected to a hydrothermal reaction to obtain a composite precursor;

[0033] The composite precursor and the lithium source are subjected to a first sintering process to obtain a positive electrode active material.

[0034] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a lithium supplement material.

[0035] By utilizing hydrothermal reaction and sintering treatment, a positive electrode active material can be prepared whose coating layer contains lithium-supplementing material, so that the lithium-supplementing material in the coating layer reacts with the reducing material additive in the positive electrode plate to efficiently replenish lithium, increase the number of battery cycles, and extend the battery life.

[0036] In any embodiment, the reaction temperature of the hydrothermal reaction is 120° C.-220° C.; and / or the reaction time of the hydrothermal reaction is 8 h-24 h.

[0037] The appropriate reaction temperature and / or reaction time of the hydrothermal reaction enables the lithium-replenishing material precursor to form a coating layer on the matrix material raw material, and the two have good bonding strength. After subsequent sintering treatment, the lithium-replenishing material forms a structurally complete coating layer on the surface of the matrix material.

[0038] In any embodiment, the temperature of the first sintering process is 600° C.-1000° C.; and / or the time of the first sintering process is 4 hours-24 hours.

[0039] The appropriate first sintering temperature and / or time allows the composite precursor to fully react with the lithium source to obtain a positive electrode active material with a stable structure and high phase purity.

[0040] In any embodiment, the method for preparing the positive electrode active material specifically includes:

[0041] The mixture comprising the matrix material, the lithium supplement material precursor and the lithium source is subjected to a second sintering treatment to obtain a positive electrode active material.

[0042] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a lithium supplement material.

[0043] By using a one-step sintering process, a positive electrode active material with a coating layer containing a lithium-supplementing material can be prepared, so that the lithium-supplementing material in the coating layer of the base material reacts with the additive containing the reducing material in the positive electrode plate to efficiently replenish lithium, increase the number of battery cycles, and extend the battery life.

[0044] The molar ratio of the lithium-supplementing material precursor to the lithium source is within an appropriate range, which is conducive to a lithium-supplementing material coating layer of appropriate quality, thereby improving the material basis for long-cycle batteries.

[0045] In any embodiment, the temperature of the second sintering process is 600° C.-900° C.; and / or the time of the second sintering process is 4 hours-24 hours.

[0046] The appropriate second sintering temperature and / or time allows the lithium-supplementing material precursor to fully react with the lithium source to obtain a coating layer with a stable structure and high phase purity.

[0047] In any embodiment, the method for preparing the positive electrode active material specifically includes:

[0048] The base material and the reducing material vapor are vapor-coated to obtain the positive electrode active material.

[0049] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a reducing material.

[0050] By utilizing the vapor coating process, the reducing material can be uniformly coated on the surface of the base material in the vapor phase to obtain a positive electrode active material whose coating layer contains the reducing material, so that the reducing material in the coating layer reacts with the additive containing the lithium replenishing material in the positive electrode plate to efficiently replenish lithium, increase the number of battery cycles, and extend the battery life.

[0051] In any embodiment, the mass ratio of the matrix material to the reducing material vapor is 10:1000.

[0052] The mass ratio of the matrix material to the reducing material vapor is within an appropriate range, so that the coating layer contains sufficient reducing material to react with the lithium-supplementing material, thereby achieving the purpose of reducing the decomposition potential of the lithium-supplementing material. At the same time, it also avoids the coating layer being too thick, which has an adverse effect on the transmission of lithium ions and affects the kinetic performance of the battery.

[0053] A third aspect of the present application provides an electrical device, comprising the secondary battery of the first aspect and the secondary battery prepared by the preparation method of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] FIG1 is a schematic diagram of a positive electrode active material and additives in one embodiment of the present application;

[0055] FIG2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0056] FIG3 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG2 ;

[0057] FIG4 is a schematic diagram of a battery module according to an embodiment of the present application;

[0058] FIG5 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0059] FIG6 is an exploded view of the battery pack shown in FIG5 according to an embodiment of the present application;

[0060] FIG. 7 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0061] Reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate; 6 positive electrode active material; 61 matrix material; 62 coating layer; 7 additives. DETAILED DESCRIPTION

[0062] Below, the embodiments of the secondary battery, its preparation method, and the electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0063] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0064] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0065] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0066] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0067] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0068] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0069] All active lithium in lithium-ion batteries is provided by the positive electrode active material. However, during the initial charge of a lithium-ion battery, the formation of a solid electrolyte interphase (SEI) on the negative electrode surface and other chemical side reactions during subsequent charge and discharge cycles consume active lithium ions, degrading the battery's cycling performance. To improve the cycling performance of lithium-ion batteries, a common solution in the industry is to add positive electrode lithium-supplementing materials to the battery's positive electrode. Commonly used positive electrode lithium-supplementing materials generally include binary lithium-containing compounds, ternary lithium-containing compounds, or organic lithium salts. However, most positive electrode lithium-supplementing materials with high lithium capacity also have high decomposition voltages, which can affect the battery's cycling performance and safety. To address the high decomposition potential of positive electrode lithium-supplementing materials, both the lithium-supplementing material and the reducing material are often added to the positive electrode plate as additives. However, the reducing material and the lithium-supplementing material are both in particle form, and their contact is point-to-point. Furthermore, the conductive agent and the positive electrode active material in the plate isolate them from each other, preventing sufficient contact and reaction between the reducing material and the lithium-supplementing material. Consequently, the lithium-supplementing material cannot fully exert its lithium-supplementing function, resulting in low lithium-supplementing efficiency. To address this technical issue, the industry will also coat the surface of the lithium-supplementing material with a reducing material to form a core-shell structure lithium-supplementing composition with the core structure being the lithium-supplementing material and the shell structure being the reducing material. However, the common lithium-supplementing materials and reducing materials have poor electronic conductivity. The core-structured lithium-supplementing material cannot form an effective electron pathway for electron gain and loss, resulting in poor battery kinetic performance and poor lithium-supplementing efficiency. In addition, since the core-structured lithium-supplementing material cannot be effectively utilized, the shell-structured reducing material will undergo irreversible side reactions with the electrolyte or the positive electrode active material, thereby deteriorating the reversible capacity of the battery and the cycle performance of the battery.

[0070] [Secondary battery]

[0071] The present application provides a secondary battery, including a positive electrode plate, the positive electrode plate including a positive electrode active material and an additive, the positive electrode active material including a base material and a coating layer at least partially covering the base material, the coating layer including a lithium-supplementing material or a reducing material, the additive including a lithium-supplementing material or a reducing material, and the coating layer and the additive do not contain both the lithium-supplementing material and the reducing material.

[0072] As shown in FIG1 , the positive electrode sheet includes a positive electrode active material 6 and an additive 7 . The positive electrode active material 6 includes a base material 61 and a coating layer 62 at least partially covering the base material 61 .

[0073] In some embodiments, the positive electrode active material includes a base material and a coating layer at least partially covering the base material, the coating layer includes a lithium supplementing material, and the additive includes a reducing material.

[0074] In some embodiments, the positive electrode active material includes a base material and a coating layer at least partially covering the base material, the coating layer includes a reducing material, and the additive includes a lithium supplementing material.

[0075] The lithium-supplementing material in the secondary battery of the present application is present in the coating layer of the base material. When the reducing material is present in the form of an additive or the reducing material is present in the coating layer of the base material, when the lithium-supplementing material is present in the form of an additive, compared to the traditional lithium-supplementing material and the reducing material both being present in the form of additives, the two forming point-point contact or direct non-contact, the lithium-supplementing material and the reducing material of the present application can form point-surface contact, which can increase the contact area between the lithium-supplementing material and the reducing material, increase the reaction degree between the lithium-supplementing material and the reducing material, and improve the lithium-supplementing efficiency of the lithium-supplementing material. At the same time, the lithium-supplementing material or the reducing material is present in the coating layer, and the conductivity of the base material can be used to improve the conductive network of the lithium-supplementing material and the reducing material, provide more electron transmission paths, reduce the sheet resistance of the electrode, and improve the dynamic performance of the battery. Without introducing an additional carbon layer or conductive agent, an excellent conductive network is constructed through the mutual positional relationship of the lithium-supplementing material, the reducing material and the matrix material, thereby improving the kinetic performance of the battery and enabling the lithium-supplementing material to fully exert its lithium-supplementing effect and improve the lithium-supplementing efficiency. In addition, since the electrode has an excellent conductive network and the contact sites between the lithium-supplementing material and the reducing material are improved, the lithium-supplementing material can gain and lose electrons and fully participate in the electrochemical reaction. Under the action of the reducing material, a decomposition reaction can occur at a low potential, releasing sufficient active lithium ions to replenish the lithium ions lost during the cycle process, thereby achieving the lithium-supplementing effect and reducing the possibility of side reactions between the reducing material and the positive electrode active material or the electrolyte, thereby improving the cycle performance of the battery.

[0076] In summary, by using the secondary battery of the present application, the lithium-supplementing material can play its lithium-supplementing role as much as possible, improve the lithium-supplementing efficiency of the lithium-supplementing material, provide sufficient active lithium during the cycle to replenish the lithium ions lost during the cycle, and the battery has an excellent number of cycles and a long service life.

[0077] In some embodiments, the mass ratio of the lithium replenishing material to the reducing material is 0.5-50. In some embodiments, the mass ratio of the lithium replenishing material to the reducing material can be selected from 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or any range therebetween.

[0078] In some embodiments, the mass ratio of the lithium-supplementing material to the reducing material is 1 to 20. In some embodiments, the mass ratio of the lithium-supplementing material to the reducing material can be selected from 1, 5, 10, 15, 20 or any range therebetween.

[0079] The mass ratio of the lithium replenishing material to the reducing material is within an appropriate range, which allows the lithium replenishing material and the reducing material to fully react to improve the lithium replenishing efficiency while avoiding excessive residual lithium replenishing material and reducing material from deteriorating the battery's cycle performance and energy density.

[0080] 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 is 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 therebetween, based on the mass of the matrix material.

[0081] In some embodiments, the mass fraction of the lithium-supplementing material is 1%-10% based on the mass of the matrix material. In some embodiments, the mass fraction of the lithium-supplementing material is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range therebetween, based on the mass of the matrix material.

[0082] The mass fraction of the lithium-supplementing material is within an appropriate range. On the one hand, the lithium-supplementing material can fully exert its lithium-supplementing effect and improve the cycle performance of the battery. On the other hand, it also avoids excessive lithium-supplementing material from having an adverse effect on the battery's rate performance, available capacity and safety performance.

[0083] In some embodiments, the mass fraction of the reducing material is 0.01%-10% based on the mass of the matrix material. In some embodiments, the mass fraction of the reducing material is 0.01%, 0.05%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range therebetween based on the mass of the matrix material.

[0084] In some embodiments, the mass fraction of the reducing material is 0.02%-5% based on the mass of the matrix material. In some embodiments, the mass fraction of the reducing material is 0.02%, 0.05%, 1%, 2%, 3%, 4%, 5% or any range therebetween based on the mass of the matrix material.

[0085] The mass fraction of the reducing material is within an appropriate range. On the one hand, the lithium-supplementing material reacts fully with the reducing material under the action of a sufficient amount of the reducing material, so that the lithium-supplementing material can maximize its lithium-supplementing effect and improve the cycle performance of the battery. On the other hand, it also avoids the adverse effects of excessive reducing materials on the available capacity and safety performance.

[0086] In some embodiments, the lithium-supplementing material includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium quartz, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

[0087] The lithium-supplementing material has a high irreversible capacity and a good lithium-supplementing effect. In addition, the lithium-supplementing material has good stability in the air and is compatible with the existing battery production process, which is conducive to industrial production.

[0088] In some embodiments, the lithium-supplementing material includes one or more of lithium-rich nickelate, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

[0089] The combination of suitable lithium-supplementing materials and reducing materials can not only reduce the decomposition potential of the lithium-supplementing materials and fully utilize their lithium-supplementing properties, but also eliminate the presence of gases such as oxygen, carbon dioxide, or nitrogen in the reaction products, thereby reducing the likelihood of gassing in the battery and minimizing their impact on battery safety and cycle performance. Furthermore, the decomposition products of the lithium-supplementing materials, such as silicon oxide, nickel oxide, lithium oxide, boron oxide, or lithium sulfate, possess excellent ionic conductivity, which helps improve the ion conductivity of the electrode, thereby enhancing the battery's rate capability and cycle performance.

[0090] In some embodiments, the lithium supplementing material includes one or both of lithium metasilicate and lithium orthosilicate.

[0091] The decomposition potential of lithium metasilicate or lithium orthosilicate is low, which enables lithium-supplementing materials with higher capacity to have a stronger application space. The decomposition products contain silicon dioxide and lithium sulfate, which have good ion conductivity, can enhance the ion conductivity of the positive electrode sheet, and improve the rate performance and cycle performance of the battery.

[0092] 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.

[0093] As used herein, the term "selenium metal compound" refers to a compound formed by selenium and a metal element, wherein the chemical valence of selenium in the selenium metal compound is negative, wherein the selenium metal compound includes but is not limited to lithium selenide, sodium selenide or calcium selenide.

[0094] As used herein, the term "sulfur metal compound" refers to a compound formed by sulfur and a metal element, wherein the chemical valence of sulfur in the sulfur metal compound is negative, wherein the sulfur metal compound includes but is not limited to calcium sulfide, lithium sulfide, sodium sulfide, zinc sulfide or iron sulfide.

[0095] As used herein, the term "phosphorus metal compound" refers to a compound formed by phosphorus and a metal element, wherein the chemical valence state of phosphorus in the phosphorus metal compound is negative, wherein the phosphorus metal compound includes but is not limited to lithium phosphide, sodium phosphide, iron phosphide, calcium phosphide, zinc phosphide, aluminum phosphide or copper phosphide.

[0096] As used herein, the term "boron metal compound" refers to a compound formed by boron and a metal element, wherein the chemical valence of boron in the boron metal compound is negative, wherein the boron metal compound includes but is not limited to titanium diboride, calcium hexaboride, molybdenum boride or cobalt boride.

[0097] Herein, the term "tellurium metal compound" refers to a compound formed by tellurium and a metal element, wherein the chemical valence state of tellurium in the tellurium metal compound is negative, wherein the tellurium metal compound includes but is not limited to copper telluride or molybdenum telluride.

[0098] Herein, the term "antimony metal compound" refers to a compound formed by antimony and a metal element, wherein the chemical valence of antimony in the antimony metal compound is negative, wherein the antimony metal compound includes but is not limited to lithium antimonide, sodium antimonide or indium antimonide.

[0099] Herein, the term "bismuth metal compound" refers to a compound formed by bismuth and a metal element, wherein the chemical valence state of bismuth in the bismuth metal compound is negative, wherein the bismuth metal compound includes but is not limited to sodium bismuthide.

[0100] The above-mentioned reducing materials can chemically react with the lithium supplement material to reduce the decomposition potential of the lithium supplement material, achieve low-potential lithium supplementation, improve the decomposition efficiency and utilization rate of the lithium supplement material, improve the capacity retention rate of the battery, and increase the battery life.

[0101] 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.

[0102] In this article, the term "non-transition metal compound of selenium" refers to a compound formed by selenium and a non-transition metal element, wherein the chemical valence state of selenium in the non-transition metal compound of selenium is negative, wherein the metal compound of selenium includes but is not limited to lithium selenide, sodium selenide or calcium selenide.

[0103] As used herein, the term "non-transition metal compound of sulfur" refers to a compound formed by sulfur and a non-transition metal element, wherein the chemical valence of sulfur in the non-transition metal compound of sulfur is negative, wherein the non-transition metal compound of sulfur includes but is not limited to calcium sulfide, lithium sulfide or sodium sulfide.

[0104] As used herein, 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 state of phosphorus in the non-transition metal compound of phosphorus is negative, and the non-transition metal compound of phosphorus includes but is not limited to lithium phosphide, sodium phosphide, iron phosphide, calcium phosphide, and aluminum phosphide.

[0105] As used herein, 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 state of boron in the non-transition metal compound of boron is negative, wherein the non-transition metal compound of boron includes but is not limited to calcium hexaboride.

[0106] As used herein, the term "non-transition metal compound of tellurium" refers to a compound formed by tellurium and a non-transition metal element, wherein the chemical valence state of tellurium in the non-transition metal compound of tellurium is negative, and the non-transition metal compound of tellurium includes but is not limited to lithium telluride and sodium telluride.

[0107] In this article, the term "non-transition compound of antimony" refers to a compound formed by antimony and a non-transition metal element, wherein the chemical valence state of antimony in the non-transition metal compound of antimony is negative, wherein the non-transition metal compound of antimony includes but is not limited to lithium antimonide, sodium antimonide or indium antimonide.

[0108] Herein, the term "non-transition metal compound of bismuth" refers to a compound formed by bismuth and a non-transition metal element, wherein the chemical valence state of bismuth in the non-transition metal compound of bismuth is negative, wherein the non-transition metal compound of bismuth includes but is not limited to sodium bismuth.

[0109] The above-mentioned reducing material does not contain transition metal elements, which can reduce the impact of the catalytic oxidation reaction between the transition metal elements and the electrolyte on the cycle or safety performance of the battery.

[0110] 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.

[0111] The above-mentioned reducing material is a single substance, which can reduce the impact of the catalytic oxidation reaction between the transition metal element and the electrolyte on the cycle or safety performance of the battery. At the same time, the relative molecular mass of the single substance reducing material is low, and the same mass content of the reducing agent can react with more lithium supplement materials, thereby improving the mass utilization rate of the reducing agent.

[0112] In some embodiments, the reducing material includes one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, and selenium disulfide.

[0113] The above-mentioned reducing material has strong reducing property. When added in low amount, it can achieve the purpose of reducing the decomposition potential of the lithium-supplementing material, give full play to the lithium-supplementing effect of the lithium-supplementing material, improve the lithium-supplementing efficiency of the lithium-supplementing material, and increase the cycle number of the battery.

[0114] In some embodiments, the lithium replenishment efficiency of the lithium replenishment material is greater than or equal to 85%, and can be 90%-100%. In some embodiments, the lithium replenishment efficiency of the lithium replenishment material can be 85%, 87%, 90%, 94%, 95%, 97%, 98%, 99%, 100%, or any range therebetween.

[0115] Lithium replenishing materials have high lithium replenishing efficiency, improve the cycle performance of the battery and extend the service life of the battery.

[0116] In some embodiments, the matrix material includes a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials. These matrix materials can be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium phosphates containing olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO4( It can also be referred to as LFP), at least one of a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0117] In some embodiments, the matrix material includes lithium iron phosphate or a modified form of lithium iron phosphate, wherein the modified form includes one or more of doping modification and coating modification.

[0118] In some embodiments of the present application, a method for preparing a secondary battery is provided, comprising the following steps:

[0119] Applying a positive electrode slurry containing a positive electrode active material and an additive to obtain a positive electrode sheet;

[0120] Assemble the negative electrode sheet, separator, electrolyte and positive electrode sheet to form a secondary battery.

[0121] The positive electrode active material includes a base material and a coating layer at least partially covering the base material.

[0122] The coating layer contains a lithium-supplementing material or a reducing material, the additive contains a lithium-supplementing material or a reducing material, and the coating layer and the additive do not contain both the lithium-supplementing material and the reducing material.

[0123] In some embodiments, the negative electrode plate, separator, and electrolyte may be conventionally configured in the art and may be selected by those skilled in the art according to actual needs.

[0124] In some embodiments, a method for preparing a secondary battery includes the following steps:

[0125] Applying a positive electrode slurry containing a positive electrode active material and an additive to obtain a positive electrode sheet;

[0126] Assemble the negative electrode sheet, separator, electrolyte and positive electrode sheet to form a secondary battery.

[0127] The positive electrode active material includes a base material and a coating layer at least partially covering the base material.

[0128] The coating layer contains lithium-supplementing materials, and the additive contains reducing materials.

[0129] In some embodiments, coating of the positive electrode slurry is a conventional step in the art and can be selected by those skilled in the art according to actual needs.

[0130] In some embodiments, a method for preparing a secondary battery includes the following steps:

[0131] Applying a positive electrode slurry containing a positive electrode active material and an additive to obtain a positive electrode sheet;

[0132] Assemble the negative electrode sheet, separator, electrolyte and positive electrode sheet to form a secondary battery.

[0133] The positive electrode active material includes a base material and a coating layer at least partially covering the base material.

[0134] The coating layer contains reducing materials, and the additive contains lithium-supplementing materials.

[0135] By adopting the above preparation method, a secondary battery with excellent cycle performance can be prepared.

[0136] In some embodiments, the method for preparing the positive electrode active material specifically includes:

[0137] The matrix material raw material and the lithium supplement material precursor are subjected to a hydrothermal reaction to obtain a composite precursor;

[0138] The composite precursor and the lithium source are subjected to a first sintering process to obtain a positive electrode active material.

[0139] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a lithium supplement material.

[0140] In some embodiments, the matrix material raw material includes a raw material for synthesizing a matrix material precursor or a matrix material precursor. For example, if the matrix material is lithium iron phosphate, the matrix material raw material includes 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 material includes a nickel source, a cobalt source, and a manganese source or nickel cobalt manganese hydroxide. The matrix material raw material can be selected according to the type of matrix material.

[0141] In some embodiments, the lithium-supplementing material precursor includes raw materials for synthesizing lithium-supplementing materials, for example, the lithium-supplementing material is lithium metasilicate, and the lithium-supplementing material precursor is tetraethyl orthosilicate or silicon dioxide; the lithium-supplementing material is lithium orthosilicate, and the lithium-supplementing material precursor is tetraethyl orthosilicate or silicon dioxide; the lithium-supplementing material is lithium-rich lithium ferrite, and the lithium-supplementing material precursor is iron oxide; the lithium-supplementing material precursor is lithium borate, and the lithium-supplementing material precursor is boron oxide; the lithium-supplementing material precursor is lithium metaborate, and the lithium-supplementing material precursor is boron oxide; the lithium-supplementing material precursor can be selected according to the type of lithium-supplementing material.

[0142] In some embodiments, 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.

[0143] In some embodiments, the amount of matrix material raw material, lithium supplement material precursor or lithium source added depends on the mass content of the matrix material and lithium supplement material in the target product positive electrode active material.

[0144] By using hydrothermal reaction and sintering treatment, a positive electrode active material with a coating layer containing a lithium-supplementing material can be prepared, so that the lithium-supplementing material in the coating layer reacts with the additive containing a reducing material in the positive electrode plate to efficiently replenish lithium, increase the number of battery cycles, and extend the battery life.

[0145] In some embodiments, the reaction temperature of the hydrothermal reaction is 120° C.-220° C. In some embodiments, the reaction temperature of the hydrothermal reaction can be selected from 120° C., 140° C., 160° C., 180° C., 200° C., 220° C., or any range therebetween.

[0146] In some embodiments, the reaction time of the hydrothermal reaction is 8 h to 24 h. In some embodiments, the reaction time of the hydrothermal reaction can be selected from 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, or any range therebetween.

[0147] The appropriate reaction temperature and / or reaction time of the hydrothermal reaction enables the lithium-replenishing material precursor to form a coating layer on the matrix material raw material, and the two have good bonding strength. After subsequent sintering treatment, the lithium-replenishing material forms a structurally complete coating layer on the surface of the matrix material.

[0148] In some embodiments, the temperature of the first sintering process is 600° C.-1000° C. In some embodiments, the temperature of the first sintering process can be selected from 600° C., 700° C., 800° C., 900° C., 1000° C., or any range therebetween.

[0149] In some embodiments, the first sintering treatment time is 4 hours to 24 hours. In some embodiments, the first sintering treatment time can be selected from 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, or any range therebetween.

[0150] The appropriate first sintering temperature and / or time allows the composite precursor to fully react with the lithium source to obtain a positive electrode active material with a stable structure and high phase purity.

[0151] In some embodiments, the method for preparing the positive electrode active material specifically includes:

[0152] The mixture containing the matrix material, the lithium supplement material precursor and the lithium source is sintered to obtain the positive electrode active material.

[0153] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a lithium supplement material.

[0154] In some embodiments, the matrix material includes lithium iron phosphate or a modified form of lithium iron phosphate, wherein the modified form includes one or more of doping modification and coating modification.

[0155] By using a one-step sintering process, a positive electrode active material with a coating layer containing a lithium-supplementing material can be prepared, so that the lithium-supplementing material in the coating layer reacts with the additive containing the reducing material in the positive electrode plate to efficiently replenish lithium, increase the number of battery cycles, and extend the battery life.

[0156] In some embodiments, the temperature of the second sintering process is 600° C.-900° C. In some embodiments, the temperature of the second sintering process can be selected from 600° C., 700° C., 800° C., 900° C., or any range therebetween.

[0157] In some embodiments, the second sintering treatment time is 4 hours to 24 hours. In some embodiments, the second sintering treatment time can be selected from 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, or any range therebetween.

[0158] The appropriate second sintering temperature and / or time allows the lithium-supplementing material precursor to fully react with the lithium source to obtain a coating layer with a stable structure and high phase purity.

[0159] In some embodiments, the method for preparing the positive electrode active material specifically includes:

[0160] The base material and the reducing material vapor are vapor-coated to obtain the positive electrode active material.

[0161] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a reducing material.

[0162] In some embodiments, the method for preparing the positive electrode active material specifically includes:

[0163] treating the reducing material into a reducing material vapor;

[0164] The base material and the reducing material vapor are vapor-coated to obtain the positive electrode active material.

[0165] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a reducing material.

[0166] In some embodiments, the reduced material may be treated to form reduced material vapor by conventional means in the art, including but not limited to heating treatment.

[0167] In some embodiments, the method for preparing the positive electrode active material specifically includes:

[0168] The matrix material and the reducing material are mixed and then mechanically ball milled to obtain the positive electrode active material.

[0169] During the mechanical ball milling process, the reducing material is converted into reducing material vapor to perform gas phase coating on the base material.

[0170] The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a reducing material.

[0171] By utilizing the vapor coating process, the reducing material can be uniformly coated on the surface of the base material in the vapor phase to obtain a positive electrode active material whose coating layer contains the reducing material, so that the reducing material in the coating layer reacts with the additive containing the lithium replenishing material in the positive electrode plate to efficiently replenish lithium, increase the number of battery cycles, and extend the battery life.

[0172] In some embodiments, the mass ratio of the matrix material to the reducing material is 10: 1-1000: 1. In some embodiments, the mass ratio of the matrix material to the reducing material can be 10: 1, 50: 1, 100: 1, 200: 1, 300: 1, 400: 1, 500: 1, 600: 1, 700: 1, 800: 1, 900: 1, 1000: 1, or any range therebetween.

[0173] The mass ratio of the matrix material to the reducing material vapor is within an appropriate range, so that the coating layer contains sufficient reducing material to react with the lithium-supplementing material, thereby achieving the purpose of reducing the decomposition potential of the lithium-supplementing material. At the same time, it also avoids the coating layer being too thick, which has an adverse effect on the transmission of lithium ions and affects the kinetic performance of the battery.

[0174] In one embodiment, the secondary battery comprises a lithium-ion battery. Specifically, it comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive and negative electrodes. During the battery's charge and discharge processes, active ions are intercalated and released between the positive and negative electrodes. The electrolyte acts as an ion conductor 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.

[0175] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

[0176] In some embodiments, the positive electrode film layer includes a positive electrode active material and an additive.

[0177] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0178] In some embodiments, the positive electrode plate 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.

[0179] In some embodiments, the positive electrode plate further includes a binder, which may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0180] In some embodiments, the positive electrode sheet can be prepared by the following method: the positive electrode active material in the above embodiment, the additives in the above embodiment, the binder, the conductive agent and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0181] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0182] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0183] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0184] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0185] In some embodiments, the negative electrode film layer may further 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).

[0186] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0187] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0188] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0189] In some embodiments, the electrolyte acts as a conductive medium between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on specific needs. For example, the electrolyte may be liquid, gel, or solid.

[0190] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0191] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0192] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0193] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0194] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0195] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0196] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0197] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0198] 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0199] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0200] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0201] 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. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0202] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG2 shows a secondary battery 5 having a square structure as an example.

[0203] In some embodiments, referring to FIG3 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0204] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0205] Figure 4 shows an example battery module 4. Referring to Figure 4 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0206] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0207] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0208] Figures 5 and 6 illustrate an example battery pack 1. Referring to Figures 5 and 6 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0209] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0210] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0211] Figure 7 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0212] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0213] Example

[0214] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0215] 1. Preparation method

[0216] Example 1

[0217] 1) Preparation of positive electrode sheet

[0218] 100 g of ferrous oxalate, 91.66 g of ammonium dihydrogen phosphate and 8.82 g of ethyl orthosilicate were mixed and dispersed in an ethanol solution, and subjected to a hydrothermal reaction at 180° C. for 12 h.

[0219] The reaction solution was centrifuged to obtain a composite precursor, which was then mixed with 33.05 g of lithium hydroxide monohydrate and dispersed in an ethanol solution. After drying, the composite precursor was sintered in a tube furnace at 800° C. for 12 hours under a nitrogen atmosphere to obtain lithium iron phosphate coated with lithium metasilicate. The mass content of lithium metasilicate was 3.445% based on the mass of the lithium iron phosphate.

[0220] Take 95.2g of lithium iron phosphate coated with lithium metasilicate, 0.8g of reducing material elemental sulfur, 2g of conductive carbon (SP), and 2g of polyvinylidene fluoride binder and dissolve them in solvent N-methylpyrrolidone (NMP). After fully stirring and mixing, prepare a positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain the positive electrode sheet.

[0221] 2) Preparation of negative electrode sheet

[0222] The active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are thoroughly stirred and mixed in an appropriate amount of deionized water solvent system in a weight ratio of 96.5%:0.7%:1.8%:1% to obtain a negative electrode slurry. The negative electrode slurry is then coated on a Cu foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0223] 3) Isolation film

[0224] A polyethylene porous polymer film is used as the separator.

[0225] 4) Preparation of electrolyte

[0226] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0227] 6) Preparation of batteries

[0228] The positive electrode sheet, separator, and negative electrode sheet are stacked in order and wound to obtain a battery cell. The battery cell is placed in an outer package, and the above-mentioned electrolyte is added. After packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0229] Example 2

[0230] Compared with Example 1, Example 2 differs in that the preparation method of the positive electrode sheet is adjusted, as follows:

[0231] 0.87 g of elemental sulfur was treated at 155° C. to generate sulfur vapor, which was then diffused onto the surface of 100 g of lithium iron phosphate, so that the elemental sulfur was uniformly coated on the surface of the lithium iron phosphate in the form of vapor, thereby forming sulfur-coated lithium iron phosphate. The mass fraction of the sulfur coating layer was 0.87% based on the mass of the lithium iron phosphate.

[0232] Sulfur-coated lithium iron phosphate, lithium metasilicate, conductive carbon (SP), and a binder are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 92.8%:3.2%:2%:2%, and the mixture is thoroughly stirred and mixed to prepare a positive electrode film slurry. The positive electrode film slurry is coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain a positive electrode sheet.

[0233] Example 3

[0234] Compared with Example 1, Example 3 differs in that the preparation method of the positive electrode sheet is adjusted, as follows:

[0235] 100 g of lithium iron phosphate and 0.87 g of elemental sulfur were mixed and added to a ball mill for ball milling. The ball mill speed was set to 500 rpm and the ball milling time was 4 hours. During the ball milling process, the elemental sulfur was uniformly coated on the surface of the lithium iron phosphate in the form of vapor to form lithium iron phosphate coated with elemental sulfur. The mass fraction of the sulfur coating layer was 0.87% based on the mass of the lithium iron phosphate.

[0236] Sulfur-coated lithium iron phosphate, lithium metasilicate, conductive carbon (SP), and a binder are dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 92.8%:3.2%:2%:2%, and the mixture is thoroughly stirred and mixed to prepare a positive electrode film slurry. The positive electrode film slurry is coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain a positive electrode sheet.

[0237] Example 4

[0238] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0239] 100 g of lithium iron phosphate material was dispersed in a mixed organic solvent of ethanol and water, and then 6 g of ethyl orthosilicate and 4.846 g of lithium hydroxide monohydrate were added. After drying, the mixture was placed in a tube furnace and sintered at 800° C. for 12 h under a nitrogen atmosphere to obtain a lithium orthosilicate-coated lithium iron phosphate positive electrode active material. The mass content of lithium orthosilicate based on the mass of lithium iron phosphate was 3.45%;

[0240] 95.2 g of lithium iron phosphate coated with lithium orthosilicate, 0.8 g of reducing material elemental sulfur, 2 g of conductive carbon (SP), and 2 g of binder were dissolved in solvent N-methylpyrrolidone (NMP), stirred and mixed thoroughly to prepare a positive electrode slurry, which was coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain positive electrode sheets.

[0241] Example 5

[0242] Compared with Example 4, the preparation method of the positive electrode sheet was adjusted as follows:

[0243] 100 g of lithium iron phosphate material was dispersed in a mixed organic solvent of ethanol and water, and then 1.51 g of boron oxide and 5.457 g of lithium hydroxide monohydrate were added. After drying, the material was placed in a tube furnace and sintered at 800° C. for 12 h under a nitrogen atmosphere to obtain a lithium borate-coated lithium iron phosphate positive electrode active material. The mass content of lithium borate based on the mass of lithium iron phosphate was 3.45%;

[0244] 95.2 g of lithium borate-coated lithium iron phosphate, 0.8 g of reducing material elemental phosphorus, 2 g of conductive carbon (SP), and 2 g of binder were dissolved in solvent N-methylpyrrolidone (NMP), stirred and mixed thoroughly to prepare a positive electrode slurry, which was coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain positive electrode sheets.

[0245] Example 6

[0246] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0247] 100 g of ferrous oxalate, 91.66 g of ammonium dihydrogen phosphate and 2 g of ferric oxide were mixed and dispersed in an ethanol solution, and subjected to a hydrothermal reaction at 180° C. for 12 h.

[0248] The reaction solution was centrifuged to obtain a product, and the obtained product was mixed with 34.41 g of lithium hydroxide monohydrate and dispersed in an ethanol solution. After drying, the mixture was placed in a tube furnace and sintered at 800° C. for 12 h under a nitrogen atmosphere to obtain a positive electrode active material of lithium iron phosphate coated with lithium iron phosphate-rich lithium iron phosphate. The mass content of the lithium iron phosphate-rich lithium iron phosphate was 3.53% based on the mass of the lithium iron phosphate.

[0249] Lithium iron phosphate coated with lithium-rich lithium iron phosphate, reducing material elemental sulfur, conductive carbon (SP), and binder are dissolved in solvent N-methylpyrrolidone (NMP) in a mass ratio of 95.2%:0.8%:2%:2%, and the mixture is fully stirred and mixed to prepare a positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain a positive electrode sheet.

[0250] Examples 7-10

[0251] Compared with Example 1, Examples 7-10 replace the additive with elemental selenium, selenium disulfide, elemental antimony or calcium sulfide. See Table 1 for specific parameters.

[0252] Example 11

[0253] Compared with Example 4, Example 11 replaces the additive with elemental tellurium. For specific parameters, see Table 1.

[0254] Comparative Example 1

[0255] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0256] Lithium iron phosphate, conductive carbon (SP), and binder were dissolved in N-methylpyrrolidone (NMP) solvent in a mass ratio of 96%:2%:2%, and the mixture was thoroughly stirred and mixed to prepare a positive electrode film slurry. The positive electrode film slurry was coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain the positive electrode sheet.

[0257] Comparative Example 2

[0258] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0259] 96 g of lithium iron phosphate coated with lithium metasilicate prepared in Example 1, 2 g of conductive carbon (SP), and 2 g of binder were dissolved in a solvent of N-methylpyrrolidone (NMP), and the mixture was thoroughly stirred and mixed to prepare a positive electrode slurry. The positive electrode slurry was coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain a positive electrode sheet.

[0260] Comparative Example 3

[0261] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0262] 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 solvent N-methylpyrrolidone (NMP), stirred and mixed thoroughly to prepare a positive electrode slurry, which was coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain positive electrode sheets.

[0263] Comparative Example 4

[0264] Compared with Example 1, the preparation method of the positive electrode sheet was adjusted as follows:

[0265] Lithium metasilicate and sulfur were mixed in a mass ratio of 8:2, and then mechanically ball milled to obtain sulfur-coated lithium metasilicate material.

[0266] 92g of lithium iron phosphate, 4g of sulfur-coated lithium metasilicate material, 2g of conductive carbon (SP), and 2g of binder were dissolved in solvent N-methylpyrrolidone (NMP), stirred and mixed thoroughly to prepare a positive electrode slurry, which was coated on the positive electrode current collector aluminum foil, and then dried at 100°C, cold pressed, and cut to obtain positive electrode sheets.

[0267] 2. Test Method

[0268] 1. Number of battery cycles

[0269] The secondary batteries prepared in each example and comparative example were charged at a constant current rate of 0.5C to a charge cutoff voltage of 4.0V. They were then charged at a constant voltage rate to a current of ≤0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage of 2V. The batteries were allowed to rest for 5 minutes. This constituted the first charge-discharge cycle. At the beginning of the second cycle, the charge voltage was reduced to 3.8V, while all other parameters remained unchanged. The batteries were cyclically charged and discharged according to this method until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0270] 2. Diaphragm resistance of the electrode

[0271] Cut the dried electrode sheet at the left, center, and right sides of the electrode into small discs with a diameter of 10mm. Turn on the Yuanneng Technology electrode resistance meter, place it in the appropriate position on the "probe" of the electrode resistance meter, click the "Start" button, and wait for the reading to stabilize before reading. Test two positions on each small disc, and calculate the average of the six measurements to obtain the film resistance of the electrode.

[0272] 3. Lithium replenishment efficiency of lithium replenishment materials

[0273] The lithium-ion batteries of the embodiment and comparative example were charged to 4.5V at 0.05C rate at 25°C, and the charge capacity C1 was recorded, where the mass of the lithium supplement material in the positive electrode film layer was recorded as m0, and the mass of the matrix material was recorded as m1;

[0274] The lithium-ion battery of Comparative Example 1 is used as a blank control. The charge capacity thereof 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 gram capacity of the matrix material B = C2 / m2;

[0275] The actual gram capacity of the lithium-supplementing material A1 = (C1-B×m1) / m0, where the theoretical gram capacity of the lithium-supplementing material is A0. The lithium-supplementing efficiency of the lithium-supplementing material = the actual gram capacity of the lithium-supplementing material / theoretical gram capacity of the lithium-supplementing material = A1 / A0×100%.

[0276] 4. Upper limit decomposition voltage of lithium supplement materials

[0277] At 25°C, the batteries of the embodiment and comparative example were charged at a constant current of 0.05V to 4.5V, and then charged at a constant voltage of 4.5V to 0.04C. The lithium replenishment efficiency during this process was calculated, and the potential corresponding to the lithium replenishment efficiency reaching 100% was regarded as the upper limit decomposition voltage of the lithium replenishment material.

[0278] 5. Gas production of the battery

[0279] The battery cell was immersed in silicone oil and the test temperature was controlled at 25°C using a constant temperature water bath. The cell mass (Mx) was measured and the volume change (Vx) was calculated using the Archimedean principle to obtain the gas production. At 25°C, the batteries of the examples and comparative examples were charged at a constant current of 0.05C to 4.5V, then at a constant voltage of 4.5V to 0.05V. The volume change (Vx) was recorded over time and voltage to obtain the formation gas production per unit capacity at the cutoff voltage.

[0280] 3. Analysis of test results of various embodiments and comparative examples

[0281] Secondary batteries of various examples and comparative examples were prepared according to the above methods, and various parameters were measured. The results are shown in the table below.

[0282] Table 1

[0283] As can be seen from Table 1 above, the secondary batteries in Examples 1-11 of the present application include a positive electrode plate, the positive electrode plate contains a positive electrode active material and an additive, the positive electrode active material includes a lithium iron phosphate matrix material and a coating layer at least partially covering the lithium iron phosphate matrix, the coating layer includes a lithium metasilicate, lithium-rich lithium ferrite, lithium borate or lithium orthosilicate lithium supplementary material, and the additive includes elemental sulfur, elemental selenium, selenium disulfide, elemental antimony, elemental tellurium or elemental phosphorus reducing material; or the coating layer includes an elemental sulfur reducing material, and the additive includes a lithium metasilicate lithium supplementary material.

[0284] From the comparison of Examples 1-11 and Comparative Example 1, it can be seen that compared with the positive electrode sheet in the secondary battery without adding lithium supplementing material and reducing material, the secondary battery of the present application can increase the number of battery cycles and extend the battery life.

[0285] From the comparison of Examples 1-11 and Comparative Example 2, it can be seen that compared with the secondary battery in which the positive electrode plate only contains lithium replenishing material, the secondary battery of the present application can improve the lithium replenishing efficiency of the lithium replenishing material, increase the number of battery cycles, and extend the battery life.

[0286] From the comparison of Examples 1-11 and Comparative Example 3, it can be seen that compared with the secondary battery in which the lithium replenishing material and the reducing material are present in the form of additives in the positive electrode plate, the secondary battery of the present application can reduce the decomposition potential of the lithium replenishing material, improve the lithium replenishing efficiency of the lithium replenishing material, increase the number of battery cycles, and extend the service life of the battery.

[0287] Table 2

[0288] As can be seen from Table 2, compared with secondary batteries in which lithium metasilicate lithium replenishing materials and elemental sulfur reducing materials exist in the form of a core-shell structure, the secondary battery of the present application can reduce the membrane resistance of the electrode, improve the lithium replenishing efficiency of the lithium replenishing material, increase the number of battery cycles, and extend the service life of the battery.

[0289] Table 3

[0290] As can be seen from Table 3, compared with lithium-rich iron phosphate lithium-supplementing materials, the use of lithium metasilicate or lithium orthosilicate lithium-supplementing materials can reduce battery gas production, increase the number of battery cycles, and improve the battery's cycle performance and safety performance.

[0291] From the comparison of Examples 1, 7-8, 10 with Example 9, and the comparison of Example 4 with Example 11, it can be seen that the reducing material includes elemental selenium, elemental sulfur, selenium disulfide or sulfur metal oxide calcium sulfide, which can further improve the lithium replenishment efficiency of the lithium replenishment material and improve the cycle performance of the battery.

[0292] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a positive electrode plate, characterized in that: The positive electrode plate includes a positive electrode active material and an additive, wherein the positive electrode active material includes a base material and a coating layer at least partially covering the base material. The coating layer contains a lithium-supplementing material or a reducing material, the additive contains the lithium-supplementing material or the reducing material, and the coating layer or the additive do not contain the lithium-supplementing material and the reducing material at the same time.

2. The secondary battery according to claim 1, wherein The mass ratio of the lithium supplementing material to the reducing material is 0.5-50.

3. The secondary battery according to claim 1, wherein The mass of the lithium supplementing material and 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 supplementing 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 lithium supplement material includes one or more of lithium nickelate, lithium-rich lithium nickelate, lithium ferrite, lithium-rich lithium ferrite, lithium oxalate, lithium quartz, lithium metasilicate, lithium orthosilicate, lithium carbonate, lithium sulfate, lithium hydroxide, lithium phosphate, lithium oxide, lithium peroxide, lithium borate, and lithium metaborate.

9. The secondary battery according to any one of claims 1 to 7, characterized in that The lithium supplement material includes one or more of lithium-rich nickelate, lithium metasilicate, lithium orthosilicate, lithium sulfate, lithium hydroxide, lithium borate, lithium metaborate, and lithium phosphate.

10. The secondary battery according to any one of claims 1 to 9, characterized in that The reducing material includes one or more of elemental selenium, its metal compound, elemental sulfur, its metal compound, elemental phosphorus, its metal compound, elemental boron, its metal compound, elemental tellurium, its metal compound, elemental antimony, its metal compound, elemental bismuth, its metal compound, and selenium disulfide.

11. The secondary battery according to any one of claims 1 to 9, characterized in that: The reducing material includes one or more of elemental selenium, metal compounds of selenium, elemental sulfur, metal compounds of sulfur, and selenium disulfide.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The lithium replenishing efficiency of the lithium replenishing material is greater than or equal to 85%.

13. The secondary battery according to any one of claims 1 to 11, characterized in that The lithium replenishing efficiency of the lithium replenishing material is 90%-100%.

14. A method for preparing a secondary battery, characterized in that: The following steps are included: Applying a positive electrode slurry containing a positive electrode active material and an additive to obtain a positive electrode sheet; Assembling the negative electrode sheet, separator, electrolyte and the positive electrode sheet to form a secondary battery, The positive electrode active material includes a base material and a coating layer at least partially covering the base material. The coating layer contains a lithium-supplementing material or a reducing material, the additive contains a lithium-supplementing material or a reducing material, and the coating layer or the additive do not contain the lithium-supplementing material and the reducing material at the same time.

15. The preparation method according to claim 14, characterized in that The preparation method of the positive electrode active material specifically includes: The matrix material raw material and the lithium supplement material precursor are subjected to a hydrothermal reaction to obtain a composite precursor; The composite precursor is subjected to a first sintering process with a lithium source to obtain a positive electrode active material, The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a lithium supplement material.

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

17. The preparation method according to claim 15 or 16, characterized in that: The temperature of the first sintering treatment is 600° C.-1000° C.; and / or the time of the first sintering treatment is 4 hours-24 hours.

18. The preparation method according to claim 14, characterized in that The preparation method of the positive electrode active material specifically includes: The mixture comprising the matrix material, the lithium supplement material precursor and the lithium source is subjected to a second sintering treatment to obtain a positive electrode active material. The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a lithium supplement material.

19. The preparation method according to claim 18, characterized in that The temperature of the second sintering treatment is 600° C.-900° C.; and / or the time of the second sintering treatment is 4 hours-24 hours.

20. The preparation method according to claim 14, characterized in that The preparation method of the positive electrode active material specifically includes: The base material and the reducing material vapor are vapor-coated to obtain the positive electrode active material. The positive electrode active material includes a base material and a coating layer at least partially covering the base material, and the coating layer contains a reducing material.

21. The preparation method according to claim 20, characterized in that The mass ratio of the matrix material to the reducing material vapor is 10:1000.

22. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 21.

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