Secondary battery, manufacturing method thereof, battery module, battery pack, and power device

Abstract

The invention relates to a secondary battery, the secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector, the positive film layer comprises a positive active material, the positive active material comprises an inner core and a coating layer arranged on the surface of the inner core, the inner core is a ternary material; wherein the coating layer comprises lithium tungstate and lithium borate. The positive electrode active material comprises the coating layer, so that the surface lithium residue degree is reduced, and the cycle performance of the corresponding battery is improved.

Description

[0001] This application is a divisional application with the application date of June 20, 2022, application number 202210697610.6, and the invention name being “Positive electrode active material and preparation method thereof, secondary battery, battery module, battery pack and electrical device”. Technical Field

[0002] The present application relates to the technical field of lithium batteries, and in particular to a positive electrode active material and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0003] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion batteries have achieved great development, higher requirements have been placed on their energy density, cycle performance, and other aspects.

[0004] Improving the rate capability and cycle performance of materials through coating or doping is currently a relatively effective method. However, existing methods will cause varying degrees of damage to the performance of lithium-ion batteries, such as reduced specific capacity and poor cycle performance. Therefore, existing coated or doped positive electrode active materials still need to be improved. Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material having a reduced residual lithium content, thereby improving the cycle performance of the corresponding battery.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode active material, characterized in that it includes a core and a coating layer arranged on the surface of the core, and the core is a ternary material; wherein the coating layer includes lithium tungstate and lithium borate.

[0007] The present application comprises a core composed of a ternary material and a coating layer comprising lithium tungstate and lithium borate in the positive electrode active material, so that the lithium hydroxide on the surface of the ternary material can react, reducing the residual lithium level of the positive electrode active material of the present invention, effectively preventing the electrolyte from damaging the lattice structure of the active material, thereby improving the cycle performance of the corresponding battery. The coating layer can isolate the internal material from contact with the air, effectively reducing the damage to the material by water and oxygen in the air, and avoiding further growth of residual lithium. The coating layer is a good lithium ion conductor, which can significantly reduce the surface impedance of the material and further improve the kinetic performance of the material during medium discharge.

[0008] In any embodiment, the inner core comprises a compound of Formula I having a single crystal structure:

[0009] LiNi x Co y Mn z O2 Formula I

[0010] Where x+y+z=1, 0.3≤x≤1, y>0, z>0. Therefore, further limiting the core of the nickel-cobalt-manganese ternary material to a single crystal structure can effectively prevent the resulting positive electrode active material from cracking or breaking during use, reduce the degree of residual lithium on the surface of the positive electrode active material, and thus improve the cycle performance of the corresponding battery.

[0011] In any embodiment, the coating layer includes an inner coating layer and an outer coating layer, and the inner coating layer and the outer coating layer have different compositions and are independently selected from one or both of lithium tungstate and lithium borate. Thus, further limiting the coating layer to an inner and outer coating layer further reduces the degree of residual lithium on the surface of the positive electrode active material, thereby improving the cycle performance of the corresponding battery.

[0012] In any embodiment, the inner coating layer comprises lithium tungstate and the outer coating layer comprises lithium borate. Thus, the compositions of the inner and outer coating layers are further limited, reducing the degree of residual lithium on the surface of the positive electrode active material, thereby improving the cycle performance of the corresponding battery.

[0013] In any embodiment, the total coating amount of the coating layer is 3-5% by weight based on the weight of the positive electrode active material. Thus, further limiting the coating amount of the coating layer reduces the degree of residual lithium on the surface of the positive electrode active material, thereby improving the cycle performance of the corresponding battery.

[0014] In any embodiment, the volume average particle size Dv50 of the positive electrode active material is 2 μm to 6 μm, and optionally 2 μm to 4 μm. This further limits the particle size of the positive electrode active material, further reduces the degree of residual lithium on the surface of the positive electrode active material, and thus improves the cycle performance of the corresponding battery.

[0015] The second aspect of the present application provides a method for preparing a positive electrode active material, which comprises

[0016] (1) Provide ternary materials,

[0017] (2) treating the ternary material with tungstate and boron-containing acid to obtain the positive electrode active material;

[0018] The positive electrode active material includes a core and a coating layer provided on the surface of the core, and the core is a ternary material; wherein the coating layer includes lithium tungstate and lithium borate.

[0019] Therefore, by using tungstate and boron-containing acid to treat the ternary material simultaneously or successively, a coating layer can be formed on the surface of the ternary material to reduce the residual lithium content on the surface, thereby improving the cycle performance of the corresponding battery.

[0020] In any embodiment, the mass ratio of the ternary material to the tungstate is 1:8-1:1, and can be optionally 1:5-1:1. Thus, a coating layer is better formed on the surface of the ternary material, reducing the residual lithium content on the surface, thereby improving the cycle performance of the corresponding battery.

[0021] In any embodiment, the mass ratio of the ternary material to the boron-containing acid is 1:8-1:1, and can be optionally 1:5-1:1. Thus, a coating layer is better formed on the surface of the ternary material, reducing the residual lithium content on the surface, thereby improving the cycle performance of the corresponding battery.

[0022] In any embodiment, the tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; and the boron-containing acid is at least one of boric acid, metaboric acid, and a mixture of boric acid and phosphoric acid. This allows for a better coating layer to form on the surface of the ternary material, reducing the amount of residual lithium on the surface and thereby improving the cycling performance of the corresponding battery.

[0023] A third aspect of the present application provides a secondary battery, characterized in that:

[0024] The invention comprises the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method for preparing the positive electrode active material described in the second aspect of the present application.

[0025] A fourth aspect of the present application provides a battery module including the secondary battery according to the third aspect of the present application.

[0026] The fifth aspect of the present application provides a battery pack comprising the battery module of the fourth aspect of the present application.

[0027] The sixth aspect of the present application provides an electrical device comprising at least one selected from the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.

[0028] The present application forms a coating layer comprising lithium tungstate and lithium borate on the surface of the ternary material, so that the lithium hydroxide on the surface of the ternary material can react, thereby reducing the residual lithium content of the positive electrode active material of the present invention, thereby improving the cycle performance of the corresponding battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a positive electrode active material according to one embodiment of the present application.

[0030] Figure 2 Schematic diagram of a positive electrode active material according to one embodiment of the present application.

[0031] Figure 3 Schematic diagram of a secondary battery according to one embodiment of the present application.

[0032] Figure 4 yes Figure 3 FIG. 1 is an exploded view of a secondary battery according to an embodiment of the present application.

[0033] Figure 5 Schematic diagram of a battery module according to one embodiment of the present application.

[0034] Figure 6 Schematic diagram of a battery pack according to one embodiment of the present application.

[0035] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0036] Figure 8 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0037] Description of reference numerals:

[0038] A single crystal ternary material; B positive electrode active material of the present application; 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0039] Below, the embodiments of the positive electrode active material and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack and electrical device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually 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.

[0040] " 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.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] Improving the rate performance and cycle performance of materials by coating or doping is currently a relatively effective means, however, the existing methods will cause varying degrees of damage to the performance of lithium-ion batteries, for example, the specific capacity of lithium-ion batteries is reduced, the cycle performance deteriorates, etc. The existing technology cannot achieve uniform coating of agglomerated ternary materials (usually polycrystalline materials), so that the resulting agglomerated ternary materials will still undergo grain boundary cracking during the charge and discharge process, exposing a large number of new crystal planes, resulting in poor electrical performance. The applicant has found through research that the positive electrode active material of the first aspect of the present application comprises a core composed of a ternary material and a coating layer comprising lithium tungstate and lithium borate. The core is preferably a ternary material in a single crystal form, which avoids the cracking problem of the above-mentioned agglomerated ternary material, can more effectively reduce the residual lithium level of the positive electrode active material, better improve the structural stability of the positive electrode active material, and thus improve the cycle performance of the corresponding battery.

[0047] positive electrode active material

[0048] In one embodiment of the present application, the present application provides a positive electrode active material, characterized in that it includes a core and a coating layer arranged on the surface of the core, and the core is a ternary material; wherein the coating layer includes lithium tungstate and lithium borate.

[0049] The applicant has discovered that the present application, through the positive electrode active material comprising a core composed of a ternary material and a coating layer comprising lithium tungstate and lithium borate, allows the lithium hydroxide on the surface of the ternary material to react, reducing the residual lithium level of the positive electrode active material of the present invention, effectively preventing the electrolyte from damaging the lattice structure of the active material, thereby improving the cycle performance of the corresponding battery. The coating layer can isolate the internal material from contact with the air, effectively reducing the damage to the material by water and oxygen in the air, and avoiding further growth of residual lithium. The coating layer is a good lithium ion conductor, which can significantly reduce the surface impedance of the material and can further improve the kinetic performance of the material during medium discharge.

[0050] In the present application, the term "ternary material" means a positive electrode active material containing nickel, cobalt and manganese used in batteries.

[0051] In some embodiments, the coating layer can be uniformly coated on the surface of the ternary material, or distributed in patches on the surface of the ternary material; and the coating layer can have one or more layers. If the coating layer has multiple layers, different layers can be independently selected from one or more of lithium tungstate and lithium borate, but it must be ensured that both lithium tungstate and lithium borate components exist in the coating layer.

[0052] In some embodiments, the inner core comprises a compound of Formula I having a single crystal structure:

[0053] LiNi x Co y Mn z O2 Formula I

[0054] Where x+y+z=1, 0.3≤x≤1, preferably 0.8≤x≤1; y>0, z>0. Therefore, further limiting the nickel-cobalt-manganese ternary material to a single-crystal core structure can effectively prevent the resulting positive electrode active material from cracking or breaking during use, reduce the degree of residual lithium on the surface of the positive electrode active material, and thus improve the cycle performance of the corresponding battery.

[0055] In this application, the term "single crystal" means that the lattice arrangement direction inside the particle structure is consistent and isotropic. The term "polycrystalline" means that the lattice arrangement inside the particle structure is irregular and anisotropic.

[0056] In some embodiments, the coating comprises two layers, namely, an inner coating and an outer coating, wherein the inner coating and the outer coating have different compositions and are independently selected from one or both of lithium tungstate and lithium borate. Thus, further limiting the coating to comprise inner and outer coating layers further reduces the level of residual lithium on the surface of the positive electrode active material, thereby improving the cycling performance of the corresponding battery.

[0057] In some embodiments, the inner coating layer comprises lithium tungstate and the outer coating layer comprises lithium borate. Thus, the compositions of the inner and outer coating layers are further limited, reducing the degree of residual lithium on the surface of the positive electrode active material, thereby improving the cycle performance of the corresponding battery.

[0058] In some embodiments, the total coating amount of the coating layer is 3-5% by weight based on the weight of the positive electrode active material. Thus, further limiting the coating amount of the coating layer reduces the degree of residual lithium on the surface of the positive electrode active material, thereby improving the cycle performance of the corresponding battery.

[0059] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 2 μm-6 μm, optionally 2 μm-4 μm. Thus, the particle size of the positive electrode active material is further limited, and the degree of residual lithium on the surface of the positive electrode active material is further reduced, thereby improving the cycle performance of the corresponding battery. In this application, the volume particle size and distribution of the positive electrode active material are measured using a laser particle size analyzer, for example, a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0060] The second aspect of the present application provides a method for preparing a positive electrode active material, which comprises

[0061] (1) Provide ternary materials,

[0062] (2) treating the ternary material with tungstate and boron-containing acid to obtain the positive electrode active material;

[0063] The positive electrode active material includes a core and a coating layer provided on the surface of the core, and the core is a ternary material; wherein the coating layer includes lithium tungstate and lithium borate.

[0064] Therefore, by using tungstate and boron-containing acid to treat the ternary material simultaneously or successively, a coating layer can be formed on the surface of the ternary material to reduce the residual lithium content on the surface, thereby improving the cycle performance of the corresponding battery.

[0065] In some embodiments, in the method, the ternary material may be treated with tungstate and the boron-containing acid simultaneously or sequentially, preferably, the ternary material may be treated with tungstate and the boron-containing acid sequentially.

[0066] In some preferred embodiments, the ternary material is first treated with tungstate, and then the treated ternary material is treated with boron-containing acid.

[0067] In some embodiments, the mass ratio of the ternary material to the tungstate is 1:8-1:1, optionally 1:5-1:1. Thus, a coating layer is better formed on the surface of the ternary material, reducing the residual lithium content on the surface, thereby improving the cycle performance of the corresponding battery.

[0068] In some embodiments, the mass ratio of the ternary material to the boron-containing acid is 1:8-1:1, and can be 1:5-1:1. This allows for a better coating layer to be formed on the surface of the ternary material, reducing the residual lithium content on the surface and improving the cycle performance of the corresponding battery.

[0069] In some embodiments, the tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; and the boron-containing acid is at least one of boric acid, metaboric acid, and a mixture of boric acid and phosphoric acid. This allows for a better coating layer to form on the surface of the ternary material, reducing the amount of residual lithium on the surface and thereby improving the cycling performance of the corresponding battery.

[0070] In some embodiments, the tungstate and the boric acid are typically used in the form of a suspension or solution, and the solvent used is typically water or an alcohol such as ethanol, n-propanol, isopropanol, ethylene glycol, or glycerol. The concentration of the tungstate solution is 5 to 20 mg / ml; the concentration of the boric acid solution is 6 to 24 mg / ml.

[0071] In a preferred embodiment, a single crystal ternary material is added to a tungstate suspension, stirred for 5-40 minutes, and then allowed to stand, for example, for 5 minutes; the lower precipitate is removed, dried, and then placed in an oxygen atmosphere and heated at a temperature of 400-600° C. for 2-6 hours to obtain a primary residual lithium reduction material;

[0072] Then, the obtained primary residual lithium reduction material is dispersed in a boron-containing acid solution, stirred for 5-40 minutes, and allowed to stand, for example, for 5 minutes; the lower layer of precipitate is removed, dried, and then placed in an oxygen atmosphere and heated at a temperature of 300-600°C for 2-6 hours to obtain the positive electrode active material of the present application.

[0073] A third aspect of the present application provides a secondary battery, characterized in that:

[0074] The invention comprises the positive electrode active material described in the first aspect of the present application or the positive electrode active material prepared by the method for preparing the positive electrode active material described in the second aspect of the present application.

[0075] The secondary battery, battery module, battery pack, and electric device of the present application are described below with reference to the accompanying drawings as appropriate.

[0076] In one embodiment of the present application, a secondary battery is provided.

[0077] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0078] [Positive electrode]

[0079] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0080] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0081] 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 a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] In some embodiments, the positive electrode active material may also include positive electrode active materials for batteries that are well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.10 Al 0.05 O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0083] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0084] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder 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 current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0086] [Negative electrode]

[0087] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0088] 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.

[0089] 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.).

[0090] 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.

[0091] 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).

[0092] 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.

[0093] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0094] 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.

[0095] [Electrolytes]

[0096] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0097] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] [Isolation film]

[0102] 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.

[0103] 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.

[0104] 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.

[0105] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0106] 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.

[0107] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 3 The secondary battery 5 is a square structure as an example.

[0108] In some embodiments, reference Figure 4 , the outer packaging 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 isolation membrane can form 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.

[0109] 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.

[0110] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0111] 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.

[0112] 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.

[0113] Figure 6 and Figure 7 The battery pack 1 is used as an example. Figure 6 and Figure 7The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0114] In addition, the present application also provides an electric 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 electric device, and can also be used as an energy storage unit for the electric device. The electric 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.

[0115] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0116] Figure 8 This is 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.

[0117] 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.

[0118] Example

[0119] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0120] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0121] 1. Preparation of positive electrode active materials

[0122] Example 1.1

[0123] 1. Disperse 0.5 g of ammonium metatungstate (500 nm average particle size) in 50 ml of ethanol and stir thoroughly to obtain a 10 mg / ml suspension A. Dissolve 0.75 g of boric acid in 50 ml of ethanol to obtain a 15 mg / ml solution B.

[0124] 2. In a magnetic stirring device with a stirrer, 100g of LiNi 0.95 Co 0.03 Mn 0.02 O2 is added to the above suspension A, mixed at a solid-liquid ratio of 1:2 (mass ratio), and stirred for 20 minutes. During this process, the residual lithium reacts with ammonium metatungstate to form lithium tungstate, which is coated on the surface of the material.

[0125] 3. Let the suspension stand for 5 minutes, allow the suspension to separate into separate layers, and then collect the slurry and solid powder by pouring. Dry the solid powder in a vacuum oven (Model OV-11 / 12, Lab companion) for 10 hours, until the weight of the solid powder changes by no more than 5% by weight within half an hour. The solid powder is then heated in a tube furnace at 500°C for 5 hours under an oxygen atmosphere to obtain a primary residual lithium reduction material.

[0126] 4. In a magnetic stirring apparatus equipped with a stirrer, disperse the primary residual lithium reduction material obtained above into Solution B at a solid-to-liquid ratio of 1:2 (mass ratio) and continue stirring for 20 minutes. During this process, the remaining small amount of residual lithium reacts with boric acid to form lithium borate, which is coated on the surface of the material.

[0127] 5. Let the suspension stand for 5 minutes. After separation, pour out the suspension and solid powder to collect. Dry the solid powder in a vacuum oven (Model OV-11 / 12, Lab companion) for 5 hours, until the weight of the solid powder changes by no more than 5% by weight within half an hour. Then, heat the solid powder in a tube furnace at 500°C for 5 hours under an oxygen atmosphere to obtain the positive electrode active material.

[0128] The particle size Dv50 of the obtained positive electrode active material was 4 μm; the total coating amount of the coating layer was 4 wt % based on the weight of the positive electrode active material.

[0129] Preparation Example 2-8

[0130] The preparation method of the positive electrode active material is similar to that of Preparation Example 1, but the type and amount of the coating layer material are adjusted. The different preparation conditions are detailed in Table 1, and the different product parameters are detailed in Table 2.

[0131] Preparation Example 9

[0132] The preparation method of the positive electrode active material is similar to that of Preparation Example 1, except that the continuous stirring time in steps 2 and 4 is adjusted to 15 minutes. The different preparation conditions are detailed in Table 1, and the different product parameters are detailed in Table 2.

[0133] Preparation Example 10

[0134] The preparation method of the positive electrode active material is similar to that of Preparation Example 1, except that the continuous stirring time in steps 2 and 4 is adjusted to 30 minutes. The different preparation conditions are detailed in Table 1, and the different product parameters are detailed in Table 2.

[0135] Preparation Examples 11-12

[0136] The preparation method of the positive electrode active material is similar to that of Preparation Example 1, but the volume average particle size of the positive electrode active material is adjusted. The different preparation conditions are detailed in Table 1, and the different product parameters are detailed in Table 2.

[0137] Preparation Example 13

[0138] The preparation method of the positive electrode active material is similar to that of Preparation Example 1, but steps 4 and 5 are performed first, and then steps 2 and 3. The different preparation conditions are detailed in Table 1, and the different product parameters are detailed in Table 2.

[0139] Preparation Example 14

[0140] Similar to the preparation method of the positive electrode active material of Preparation Example 1, but steps 2-5 are carried out at the same time, that is, suspension A and suspension B are added to the ternary material at the same time, mixed with the ternary material, and then allowed to stand for 5 minutes. After stratification, the suspension and solid powder are collected by pouring. The solid powder is dried in a vacuum oven (model OV-11 / 12, manufacturer Lab companion) for 5 hours until the weight of the solid powder changes by no more than 5% by weight in half an hour. The solid powder is then placed in a tube furnace and heated at 500°C for 5 hours under an oxygen atmosphere to obtain a positive electrode active material. Different preparation conditions are detailed in Table 1, and different product parameters are detailed in Table 2.

[0141] 2. Preparation of Secondary Batteries

[0142] Example 1

[0143] 1) Preparation of positive electrode sheet

[0144] The finished positive electrode active material prepared in Example 1.1 was used as the positive electrode material. It was thoroughly stirred and mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system at a weight ratio of 94:3:3. The mixture was then coated on aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet. The coating amount of the positive electrode sheet was 8 mg / cm 2 .

[0145] 2) Preparation of negative electrode sheet

[0146] Artificial graphite as the negative electrode active material, acetylene black as the conductive agent, styrene butadiene rubber (SBR) as the binder, and carbon methyl cellulose sodium (CMC) as the thickener were mixed thoroughly in a deionized water solvent system according to a weight ratio of 90:5:2:1, and then coated on a copper foil, dried, and cold pressed to obtain a negative electrode sheet. The coating amount of the negative electrode sheet was 10 mg / cm 2 .

[0147] 3) Isolation film

[0148] A porous polymer film made of polyethylene (PE) is used as the separator.

[0149] 4) Preparation of electrolyte

[0150] The electrolyte is 1 mol / L LiPF6 / (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1).

[0151] 5) Battery Preparation

[0152] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to provide isolation, and then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with the above-mentioned electrolyte, and packaged to obtain a secondary battery.

[0153] The secondary batteries of Examples 2-15 and Comparative Examples 1-2 were prepared in a similar manner to the secondary battery of Example 1, except that the positive electrode active materials were adjusted to the active materials of the corresponding preparation examples. The different product parameters are detailed in Table 2.

[0154] Comparative Example 3

[0155] The secondary battery preparation method is similar to that of Example 1, but the positive electrode active material is an uncoated ternary material. Product parameters are detailed in Table 2.

[0156] 3. Battery performance test

[0157] 1. Capacity retention rate determination

[0158] At 25°C, the prepared battery was charged to 4.25V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 4.25V, left for 30 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity was recorded as the initial capacity C0. Repeat the above steps for the same battery, and simultaneously record the discharge capacity Cn of the battery after the nth cycle. Record the capacity retention rate Rn = Cn / C0*100% of the battery after the 100th cycle as a measurement result characterizing the effective service life of the battery. The 0.33C capacity retention rates of all embodiments and comparative examples after 100 cycles are summarized in Table 1 below, where higher values ​​indicate better battery performance.

[0159] 2. Determination of residual lithium

[0160] The test was performed by acid-base titration using a potentiometric titrator.

[0161] (1) Pre-test treatment: Weigh 30 g of positive electrode active material powder, add 100 ml of pure water, stir for 30 min, let it stand for 10 min, filter and remove a certain amount of filtrate;

[0162] (2) Test: Select 0.05 mol / L hydrochloric acid standard solution, drain the liquid to remove the bubbles in the burette, select the corresponding sensor and program to start automatic detection and conversion into residual lithium amount.

[0163] 4. Test results of various embodiments and comparative examples

[0164] Batteries of various examples and comparative examples were prepared according to the above methods, and their performance parameters were measured. The results are shown in Table 2 below.

[0165] Table 1 Preparation conditions of positive electrode active materials of various examples and comparative examples

[0166]

[0167]

[0168]

[0169] As can be seen from Examples 1 to 14 in Table 2, the positive electrode active material containing both lithium tungstate and lithium borate in the coating layer exhibits a lower surface residual lithium content, even as low as 0.1wt%; while maintaining a higher capacity retention rate. This is because tungstate and boric acid allow the lithium hydroxide on the surface of the ternary material to react, reducing the residual lithium content of the positive electrode active material of the present invention, effectively preventing the electrolyte from damaging the lattice structure of the active material, and thus improving the cycle performance of the corresponding battery. The coating layer can isolate the internal material from contact with the air, effectively reducing the damage to the material caused by water and oxygen in the air, and avoiding further growth of residual lithium. In addition, the coating layer is a good lithium ion conductor, which can significantly reduce the surface impedance of the material and further improve the kinetic performance of the material during medium discharge.

[0170] In contrast, the positive electrode active materials in Comparative Examples 1 and 2, which included a coating layer containing only lithium tungstate or lithium borate, had significantly higher residual lithium levels on their surfaces than the examples of the present invention, reaching 0.5 wt %. Furthermore, the cycling performance of these batteries was also lower than that of the present invention. Furthermore, the positive electrode active material in Comparative Example 3, which had no coating layer, had a residual lithium level of 1 wt %, which is more than three times higher than that of the examples of the present invention. Therefore, the positive electrode material of the present invention has a reduced level of residual lithium.

[0171] 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 sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes: A core and a coating layer provided on the surface of the core, wherein the core is a ternary material; Wherein, the coating layer includes lithium tungstate and lithium borate.

2. The secondary battery according to claim 1, wherein The core includes a compound having a single crystal structure.

3. The secondary battery according to claim 1 or 2, characterized in that In the ternary material, the molar ratio of Ni is 0.3-1 based on the total amount of Ni, Co and Mn.

4. The secondary battery according to any one of claims 1 to 3, characterized in that The core comprises a compound of formula I: LiNi x Co y Mn z O2 Formula I Among them, x+y+z=1, 0.3≤x<1.

5. The secondary battery according to any one of claims 1 to 4, characterized in that The coating layer includes an inner coating layer and an outer coating layer, and the inner coating layer and the outer coating layer have different compositions, and each of the inner coating layer and the outer coating layer independently includes one or both of lithium tungstate and lithium borate.

6. The secondary battery according to claim 5, characterized in that The inner coating layer includes lithium tungstate, and the outer coating layer includes lithium borate.

7. The secondary battery according to any one of claims 1 to 6, characterized in that The total coating amount of the coating layer is 3-5 wt % based on the weight of the positive electrode active material.

8. The secondary battery according to any one of claims 1 to 7, characterized in that The volume average particle size Dv50 of the positive electrode active material is 2 μm to 6 μm.

9. The secondary battery according to claim 8, characterized in that The volume average particle size Dv50 of the positive electrode active material is 2 μm to 4 μm.

10. The secondary battery according to any one of claims 1 to 9, characterized in that The amount of residual lithium on the surface of the positive electrode active material is 0.1 wt % to 0.3 wt %.

11. A method for preparing a secondary battery, comprising preparing a positive electrode active material, wherein the preparing the positive electrode active material comprises: (1) Provide ternary materials, (2) treating the ternary material with tungstate and boron-containing acid to obtain the positive electrode active material; The positive electrode active material includes a core and a coating layer provided on the surface of the core, and the core is a ternary material; wherein the coating layer includes lithium tungstate and lithium borate.

12. The method according to claim 11, characterized in that The mass ratio of the ternary material to tungstate is 1:8-1:

1.

13. The method according to claim 11 or 12, characterized in that The mass ratio of the ternary material to tungstate is 1:5-1:

1.

14. The method according to any one of claims 11 to 13, characterized in that The mass ratio of the ternary material to the boron-containing acid is 1:8-1:

1.

15. The method according to any one of claims 11 to 14, characterized in that The mass ratio of the ternary material to the boron-containing acid is 1:5-1:

1.

16. The method according to any one of claims 11 to 15, characterized in that The tungstate includes at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; and the boron-containing acid includes at least one of boric acid, metaboric acid, and a mixture of boric acid and phosphoric acid.

17. A battery module, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 10 or a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 11 to 16.

18. A battery pack, characterized in that: A battery module comprising the battery module according to claim 17.

19. An electrical device, characterized in that: The invention comprises at least one selected from the group consisting of the secondary battery according to any one of claims 1 to 10, the secondary battery prepared by the method for preparing a secondary battery according to any one of claims 11 to 16, the battery module according to claim 17, or the battery pack according to claim 18.

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