Positive electrode active material, method for producing the same, secondary battery, battery module, battery pack, and electrical device

Abstract

The present application relates to a positive electrode active material, which is characterized by comprising a core and a coating layer provided on the surface of the core, wherein the core is a ternary material; and the coating layer comprises lithium tungstate and lithium borate. The positive electrode active material contains the coating layer, which reduces the degree of residual lithium on its surface, thereby improving the cycle performance of the corresponding battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and particularly to a positive electrode active material, a method for manufacturing the same, a secondary battery, a battery module, a battery pack, and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application range of lithium-ion batteries, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of lithium-ion batteries, higher requirements are also put forward for their energy density, cycle performance, etc.

[0003] Improving the rate performance and cycle performance of materials by means such as coating or doping is a relatively effective means at present. However, existing methods will all cause varying degrees of damage to the performance of lithium-ion batteries. For example, the specific capacity of lithium-ion batteries decreases, and the cycle performance deteriorates. Therefore, the existing coated or doped positive electrode active materials still need to be improved. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a positive electrode active material with a reduced residual lithium level of the positive electrode active material, thereby improving the cycle performance of the corresponding battery.

[0005] To achieve the above object, a first aspect of the present application provides a positive electrode active material, characterized in that it includes a core and a coating layer provided on the surface of the core, the core being a ternary material; wherein, the coating layer includes lithium tungstate and lithium borate.

[0006] In the present application, the positive electrode active material includes a core composed of a ternary material and a coating layer including lithium tungstate and lithium borate, so that lithium hydroxide on the surface of the ternary material reacts, reducing the residual lithium level of the positive electrode active material of the present invention, effectively preventing the electrolyte from damaging the crystal 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 air, effectively reducing the damage of water and oxygen in the air to the material, and avoiding further increase 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 the discharge process.

[0007] In any embodiment, the core includes a compound of Formula I having a single crystal structure:

[0008] LiNi x Co y Mn z O2 Formula I

[0009] Among them, x + y + z = 1, 0.3 ≤ x ≤ 1, y > 0, z > 0. Thus, further defining the nickel-cobalt-manganese ternary material with a single-crystal structure as the core can effectively avoid cracks or fractures in the obtained cathode active material during use, reduce the degree of residual lithium on the surface of the cathode active material, and thereby improve the cycling performance of the corresponding battery.

[0010] 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 each independently selected from one or both of lithium tungstate and lithium borate. Thus, further defining the coating layer as an inner and outer two-layer coating layer further reduces the degree of residual lithium on the surface of the cathode active material, and thereby improves the cycling performance of the corresponding battery.

[0011] In any embodiment, the inner coating layer includes lithium tungstate and the outer coating layer includes lithium borate. Thus, further defining the compositions of the inner and outer two-layer coating layers reduces the degree of residual lithium on the surface of the cathode active material, and thereby improves the cycling performance of the corresponding battery.

[0012] In any embodiment, the total coating amount of the coating layer is 3-5% by weight based on the weight of the cathode active material. Thus, further defining the coating amount of the coating layer reduces the degree of residual lithium on the surface of the cathode active material, and thereby improves the cycling performance of the corresponding battery.

[0013] In any embodiment, the volume average particle size Dv50 of the cathode active material is 2 μm - 6 μm, and may be 2 μm - 4 μm. Thus, further defining the particle size of the cathode active material further reduces the degree of residual lithium on the surface of the cathode active material, and thereby improves the cycling performance of the corresponding battery.

[0014] The second aspect of the present application provides a method for preparing a cathode active material, which includes

[0015] (1) providing a ternary material,

[0016] (2) treating the ternary material with a tungstate and a boron-containing acid to obtain the cathode active material;

[0017] wherein the cathode 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.

[0018] Thus, by treating the ternary material with a tungstate and a boron-containing acid simultaneously or successively, a coating layer can be formed on the surface of the ternary material, reducing the degree of residual lithium on its surface, and thereby improving the cycling performance of the corresponding battery.

[0019] 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. Thereby, a coating layer is better formed on the surface of the ternary material, reducing the residual lithium degree on its surface, and thus improving the cycling performance of the corresponding battery.

[0020] 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. Thereby, a coating layer is better formed on the surface of the ternary material, reducing the residual lithium degree on its surface, and thus improving the cycling performance of the corresponding battery.

[0021] In any embodiment, the tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; the boron-containing acid is at least one of boric acid, metaboric acid, and a mixture of boric acid and phosphoric acid. Thereby, a coating layer is better formed on the surface of the ternary material, reducing the residual lithium degree on its surface, and thus improving the cycling performance of the corresponding battery.

[0022] The third aspect of the present application provides a secondary battery, characterized in that

[0023] it includes 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.

[0024] The fourth aspect of the present application provides a battery module, including the secondary battery of the third aspect of the present application.

[0025] The fifth aspect of the present application provides a battery pack, including the battery module of the fourth aspect of the present application.

[0026] The sixth aspect of the present application provides an electrical device, including 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.

[0027] By forming a coating layer containing lithium tungstate and lithium borate on the surface of the ternary material in the present application, the lithium hydroxide on the surface of the ternary material can react, reducing the residual lithium degree of the positive electrode active material of the present invention, and thus improving the cycling performance of the corresponding battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the positive electrode active material of an embodiment of the present application.

[0029] Figure 2 It is a schematic diagram of the positive electrode active material of an embodiment of the present application.

[0030] Figure 3 It is a schematic diagram of the secondary battery of an embodiment of the present application.

[0031] Figure 4 is Figure 3 An exploded view of a secondary battery according to an embodiment of the present application as shown.

[0032] Figure 5 A schematic diagram of a battery module according to an embodiment of the present application.

[0033] Figure 6 A schematic diagram of a battery pack according to an embodiment of the present application.

[0034] Figure 7 is Figure 6 An exploded view of a battery pack according to an embodiment of the present application as shown.

[0035] Figure 8 A schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0036] Description of reference numerals:

[0037] A single crystal ternary material; B the positive electrode active material of the present application; 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly Detailed description of specific embodiments

[0038] Hereinafter, embodiments of the positive electrode active material of the present application, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device will be specifically disclosed 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 identical structures are omitted. This is to avoid the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the accompanying 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 recited in the claims.

[0039] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form a new technical solution.

[0041] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0042] If there is no special instruction, all steps of this application can be carried out in sequence or randomly, and preferably in sequence. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0043] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0044] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or present) and B is false (or absent); A is false (or absent) while B is true (or present); or both A and B are true (or present).

[0045] Improving the rate performance and cycling performance of materials by means such as coating or doping is currently a relatively effective method. However, existing methods will all cause varying degrees of damage to the performance of lithium-ion batteries. For example, the specific capacity of lithium-ion batteries decreases, and the cycling performance deteriorates. The prior art cannot achieve uniform coating of aggregated ternary materials (usually polycrystalline materials), resulting in grain boundary cracking of the obtained aggregated ternary materials during charge and discharge, exposing a large number of new crystal planes and leading to poor electrical performance. The applicant has found through research that the positive electrode active material of the first aspect of this application includes a core composed of a ternary material and a coating layer containing lithium tungstate and lithium borate. Preferably, the core is a ternary material in single crystal form, avoiding the cracking problem of the above-mentioned aggregated ternary materials, being able to more effectively reduce the residual lithium degree of the positive electrode active material, better improving the structural stability of the positive electrode active material, and thus improving the cycling performance of the corresponding battery.

[0046] Positive electrode active material

[0047] In one embodiment of this application, this application provides a positive electrode active material, characterized in that it includes a core and a coating layer provided on the surface of the core, the core being a ternary material; wherein, the coating layer includes lithium tungstate and lithium borate.

[0048] The applicant has found through research that in this application, the positive electrode active material includes a core composed of a ternary material and a coating layer containing lithium tungstate and lithium borate, enabling the lithium hydroxide on the surface of the ternary material to react, reducing the residual lithium degree 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 cycling performance of the corresponding battery. The coating layer can isolate the internal material from contact with air, effectively reducing the damage of water and oxygen in the air to the material and avoiding further increase of residual lithium. The coating layer is a good lithium ion conductor, can significantly reduce the surface impedance of the material, and can further improve the kinetic performance of the material during the discharge process.

[0049] In this application, the term "ternary material" means a positive electrode active material containing nickel, cobalt, and manganese used in a battery.

[0050] In some embodiments, the coating layer can uniformly coat the surface of the ternary material or be 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 independently be selected from one or more of lithium tungstate and lithium borate, but it is necessary to ensure that both lithium tungstate and lithium borate are present in the coating layer.

[0051] In some embodiments, the core includes a compound of Formula I having a single crystal structure:

[0052] LiNi x Co y Mn z O2 Formula I

[0053] Wherein, x + y + z = 1, 0.3 ≤ x ≤ 1, preferably 0.8 ≤ x ≤ 1; y > 0, z > 0. Thus, further defining the core as a single crystal structure nickel-cobalt-manganese ternary material can effectively avoid cracks or fractures in the obtained positive electrode active material during use, reduce the degree of residual lithium on the surface of the positive electrode active material, and thereby improve the cycle performance of the corresponding battery.

[0054] In the present application, the term "single crystal" means that the lattice arrangement direction inside the particle structure is consistent and has isotropy. The "polycrystalline" means that the lattice arrangement inside the particle structure is irregular and has anisotropy.

[0055] In some embodiments, the coating layer has two coating layers, namely an inner coating layer and an outer coating layer, and the compositions of the inner coating layer and the outer coating layer are different, and they are independently selected from one or two of lithium tungstate and lithium borate respectively. Thus, further defining the coating layer as an inner and outer two-layer coating layer further reduces the degree of residual lithium on the surface of the positive electrode active material, and thereby improves the cycle performance of the corresponding battery.

[0056] In some embodiments, the inner coating layer includes lithium tungstate and the outer coating layer includes lithium borate. Thus, further defining the compositions of the inner and outer two-layer coating layers reduces the degree of residual lithium on the surface of the positive electrode active material, and thereby improves the cycle performance of the corresponding battery.

[0057] 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 defining the coating amount of the coating layer reduces the degree of residual lithium on the surface of the positive electrode active material, and thereby improves the cycle performance of the corresponding battery.

[0058] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 2 μm - 6 μm, and may be optionally 2 μm - 4 μm. Thereby, the particle size of the positive electrode active material is further defined, 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, a laser particle size analyzer is used to measure the volume particle size and its distribution of the positive electrode active material. For example, a Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited, UK, is used.

[0059] The second aspect of this application provides a method for preparing a positive electrode active material, which includes

[0060] (1) providing a ternary material,

[0061] (2) treating the ternary material with a tungstate and a boron-containing acid to obtain the positive electrode active material;

[0062] wherein 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.

[0063] Thereby, by treating the ternary material with a tungstate and a boron-containing acid simultaneously or successively, a coating layer can be formed on the surface of the ternary material, reducing the degree of residual lithium on its surface, thereby improving the cycle performance of the corresponding battery.

[0064] In some embodiments, in the method, the ternary material can be treated with a tungstate and a boron-containing acid simultaneously or successively in sequence, and preferably the ternary material is treated with a tungstate and a boron-containing acid successively in sequence.

[0065] In some preferred embodiments, the ternary material is first treated with a tungstate, and then the treated ternary material is further treated with a boron-containing acid.

[0066] In some embodiments, the mass ratio of the ternary material to the tungstate is 1:8 - 1:1, and may be optionally 1:5 - 1:1. Thereby, a coating layer can be better formed on the surface of the ternary material, reducing the degree of residual lithium on its surface, thereby improving the cycle performance of the corresponding battery.

[0067] In some embodiments, the mass ratio of the ternary material to the boron-containing acid is 1:8 - 1:1, and may be optionally 1:5 - 1:1. Thereby, a coating layer can be better formed on the surface of the ternary material, reducing the degree of residual lithium on its surface, thereby improving the cycle performance of the corresponding battery.

[0068] In some embodiments, the tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; the boron-containing acid is at least one of boric acid, metaboric acid, and a mixture of boric acid and phosphoric acid. Thus, a coating layer is better formed on the surface of the ternary material, reducing the degree of residual lithium on its surface, thereby improving the cycling performance of the corresponding battery.

[0069] In some embodiments, the tungstate and the boron-containing acid are usually used in the form of their suspensions or solutions, and the solvents used are usually water or alcohols such as ethanol, n-propanol, isopropanol, ethylene glycol, or glycerol. The concentration of the tungstate solution is 5-20 mg / ml; the concentration of the boron-containing acid solution is 6-24 mg / ml.

[0070] In a preferred embodiment, the single-crystal ternary material is added to the tungstate suspension, stirred for 5-40 minutes, and then left to stand, for example, for 5 minutes; the lower-layer precipitate is taken, dried, and then placed in an oxygen atmosphere and heated at a temperature of 400-600 °C for 2-6 h to obtain a primary residual-lithium-reducing material;

[0071] Then, the obtained primary residual-lithium-reducing material is dispersed in the boron-containing acid solution, stirred for 5-40 minutes, and then left to stand, for example, for 5 minutes; the lower-layer precipitate is taken, dried, and then placed in an oxygen atmosphere and heated at a temperature of 300-600 °C for 2-6 h to obtain the positive electrode active material of the present application.

[0072] The third aspect of the present application provides a secondary battery, characterized in that

[0073] it includes the positive electrode active material described in the first aspect of the present application or the positive electrode active material obtained by the method for preparing the positive electrode active material described in the second aspect of the present application.

[0074] The secondary battery, battery module, battery pack, and electrical device of the present application will be described below with appropriate reference to the drawings.

[0075] In one embodiment of the present application, a secondary battery is provided.

[0076] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0077] [Positive electrode plate]

[0078] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.

[0079] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0080] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as 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.).

[0081] In some embodiments, the positive electrode active material may further include positive electrode active materials known in the art for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphate 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 conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, 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 (which can also be abbreviated as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be abbreviated as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn0.1 O2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of the lithium-containing phosphate with olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of composite materials of lithium manganese iron phosphate and carbon.

[0082] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder 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 fluorinated acrylate resin.

[0083] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an 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.

[0084] In some embodiments, the positive electrode plate can be prepared in the following manner: dispersing the above components for preparing the positive electrode plate, such as positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0085] [Negative electrode plate]

[0086] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0087] As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0088] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper 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.).

[0089] In some embodiments, the negative electrode active material can be a negative electrode active material for batteries well-known in the art. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based materials can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials can 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 conventional materials that can be used as battery negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0090] In some embodiments, the negative electrode film layer may also optionally include a binder. The binder can 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).

[0091] In some embodiments, the negative electrode film layer may also optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0092] In some embodiments, the negative electrode film layer may also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0093] In some embodiments, the negative electrode plate can be prepared in the following manner: Dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; Coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0094] [Electrolyte]

[0095] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like or all-solid state.

[0096] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0097] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluorooxalate phosphate.

[0098] 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, methyl propyl carbonate, ethyl propyl 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0099] In some embodiments, the electrolytic solution may also optionally include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0100] [Separator membrane]

[0101] In some embodiments, the secondary battery further includes a separator membrane. There is no particular limitation on the type of separator membrane in this application, and any well-known porous structure separator membrane with good chemical stability and mechanical stability can be selected.

[0102] In some embodiments, the material of the separator membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane can be a single-layer thin film or a multi-layer composite thin film, without particular limitation. When the separator membrane is a multi-layer composite thin film, the materials of each layer can be the same or different, without particular limitation.

[0103] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator membrane can be made into an electrode assembly through a winding process or a stacking process.

[0104] In some embodiments, the secondary battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0105] In some embodiments, the outer packaging of the secondary battery can be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer packaging of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0106] The present application places no particular limitation on the shape of the secondary battery, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 is a secondary battery 5 with a square structure as an example.

[0107] In some embodiments, referring to Figure 4 , the outer packaging can include a housing 51 and a cover plate 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 through a winding process or a stacking 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.

[0108] In some embodiments, the secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0109] Figure 5 is a battery module 4 as an example. Referring to Figure 5 , in the battery module 4, multiple secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple secondary batteries 5 can be fixed by fasteners.

[0110] Optionally, the battery module 4 can further include a housing with a receiving space, and multiple secondary batteries 5 are accommodated in the receiving space.

[0111] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0112] Figure 6 and Figure 7 is a battery pack 1 as an example. Referring to Figure 6 and Figure 7, the battery pack 1 may include a battery box and a plurality of 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 be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0113] 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 by the present application. The secondary battery, battery module, or battery pack can be used as the power source of the electric device or as the energy storage unit of the electric device. The electric device can 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, satellites, energy storage systems, etc., but are not limited thereto.

[0114] As the electric device, the secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0115] Figure 8 is an example of an electric device. The electric device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for this electric device, a battery pack or battery module can be used.

[0116] Another example of the device can be a mobile phone, tablet computer, laptop, etc. This device usually requires being thin and light, and a secondary battery can be used as the power source.

[0117] Embodiment

[0118] In order to make the technical problems, technical solutions, and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation to the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0119] For those not specified in the embodiments in terms of specific techniques or conditions, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. For the reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0120] I. Preparation of the positive electrode active material

[0121] Example 1.1

[0122] 1. Disperse 0.5 g of ammonium metatungstate with an average particle size of 500 nm in 50 ml of ethanol, stir well to obtain suspension A with a concentration of 10 mg / ml for later use. Dissolve 0.75 g of boric acid in 50 ml of ethanol to obtain solution B with a concentration of 15 mg / ml for later use.

[0123] 2. In a magnetic stirring device equipped with a stirrer, add 100 g of LiNi 0.95 Co 0.03 Mn 0.02 O2 to the above suspension A, mix at a solid-liquid ratio of 1:2 (mass ratio), and continuously stir for 20 minutes. During this process, residual lithium reacts with ammonium metatungstate to form lithium tungstate and coat the surface of the material.

[0124] 3. Let it stand for 5 minutes. After stratification, pour and collect the suspension and solid powder. Dry the solid powder in a vacuum oven (model OV-11 / 12, manufacturer Lab companion) for 10 hours until the weight of the solid powder changes by no more than 5 wt% within half an hour. Then place the solid powder in a tube furnace and heat it at 500 °C for 5 h in an oxygen atmosphere to obtain the primary residual-lithium-reduced material.

[0125] 4. In a magnetic stirring device equipped with a stirrer, disperse the primary residual-lithium-reduced material obtained above in solution B at a solid-liquid ratio of 1:2 (mass ratio), and continuously stir for 20 minutes. During this process, the remaining small amount of residual lithium reacts with boric acid to form lithium borate and coat the surface of the material.

[0126] 5. Let it stand for 5 minutes. After stratification, pour and collect the suspension and solid powder. Dry the solid powder 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 wt% within half an hour. Then place the solid powder in a tube furnace and heat it at 500 °C for 5 h in an oxygen atmosphere to obtain the positive electrode active material.

[0127] The obtained positive electrode active material has a Dv50 particle size of 4 μm; the total coating amount of the coating layer is 4 wt%, based on the weight of the positive electrode active material.

[0128] Preparation Examples 2 - 8

[0129] Similar to the preparation method of the positive electrode active material in Preparation Example 1, but the types and amounts of the coating layer materials are adjusted. The different preparation conditions are shown in Table 1, and the different product parameters are shown in Table 2.

[0130] Preparation Example 9

[0131] Similar to the preparation method of the positive electrode active material in Preparation Example 1, but the continuous stirring time in Steps 2 and 4 was adjusted to 15 minutes. The different preparation conditions are shown in Table 1, and the different product parameters are shown in Table 2.

[0132] Preparation Example 10

[0133] Similar to the preparation method of the positive electrode active material in Preparation Example 1, but the continuous stirring time in Steps 2 and 4 was adjusted to 30 minutes. The different preparation conditions are shown in Table 1, and the different product parameters are shown in Table 2.

[0134] Preparation Examples 11 - 12

[0135] Similar to the preparation method of the positive electrode active material in Preparation Example 1, but the volume average particle diameter of the positive electrode active material was adjusted. The different preparation conditions are shown in Table 1, and the different product parameters are shown in Table 2.

[0136] Preparation Example 13

[0137] Similar to the preparation method of the positive electrode active material in Preparation Example 1, but Steps 4 and 5 were carried out first, and then Steps 2 and 3 were carried out. The different preparation conditions are shown in Table 1, and the different product parameters are shown in Table 2.

[0138] Preparation Example 14

[0139] Similar to the preparation method of the positive electrode active material in Preparation Example 1, but Steps 2 - 5 were carried out simultaneously, that is, suspension A and suspension B were added to the ternary material at the same time, mixed with the ternary material, and then left standing for 5 minutes. After stratification, the suspension and the solid powder were poured and collected. The solid powder was dried in a vacuum oven (model OV - 11 / 12, manufacturer Lab companion) for 5 hours until the weight of the solid powder changed by no more than 5 wt% within half an hour. Then the solid powder was placed in a tube furnace and heated at 500 °C in an oxygen atmosphere for 5 h to obtain the positive electrode active material. The different preparation conditions are shown in Table 1, and the different product parameters are shown in Table 2.

[0140] II. Preparation of secondary battery

[0141] Example 1

[0142] 1) Preparation of positive electrode plate

[0143] Using the finished product of the positive electrode active material prepared in Preparation Example 1.1 as the positive electrode material, it was fully stirred and mixed evenly with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 94:3:3 in an N - methylpyrrolidone solvent system, and then coated on an aluminum foil, dried, and cold - pressed to obtain a positive electrode plate. The coating amount of the positive electrode plate was 8 mg / cm 2 。

[0144] 2) Preparation of the negative electrode sheet

[0145] Artificial graphite as the negative active material, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were fully stirred and mixed evenly 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 .

[0146] 3) Separator

[0147] A porous polymer film made of polyethylene (PE) was used as the separator.

[0148] 4) Preparation of the electrolyte

[0149] The electrolyte was 1 mol / L LiPF6 / (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1).

[0150] 5) Preparation of the battery

[0151] The positive electrode sheet, separator, and negative electrode sheet were overlapped in sequence, with the separator placed between the positive and negative electrodes to play a separating role, and then wound to obtain a bare battery core. The bare battery core was placed in an outer package, the above-mentioned electrolyte was injected and sealed to obtain a secondary battery.

[0152] The preparation methods of the secondary batteries in Examples 2-15 and Comparative Examples 1-2 were similar to that of the secondary battery in Example 1, but the positive active material was adjusted to the active material of the corresponding preparation example. The specific product parameters are shown in Table 2.

[0153] Comparative Example 3

[0154] The preparation method of the secondary battery was similar to that of the secondary battery in Example 1, but the positive active material was an uncoated ternary material. The specific product parameters are shown in Table 2.

[0155] III. Battery performance test

[0156] 1. Determination of capacity retention rate

[0157] At 25 °C, the prepared battery was charged at a constant current of 1 / 3C to 4.25V, then charged at a constant voltage of 4.25V until the current reached 0.05C, left standing for 30 min, and then discharged at 1 / 3C to 2.8V. The obtained capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded simultaneously. The capacity retention rate Rn = Cn / C0 * 100% after the 100th cycle was recorded as the measurement result characterizing the effective service life of the battery. The 0.33C capacity retention rates after 100 cycles for all examples and comparative examples are summarized in Table 1 below, where higher values indicate better battery performance.

[0158] 2. Determination of residual lithium content

[0159] The test was carried out by acid-base titration using a potentiometric titrator.

[0160] (1) Pretreatment before testing: Weigh 30 g of the positive electrode active material powder, add 100 ml of pure water, stir for 30 min, let it stand for 10 min, filter by suction, and then transfer a certain amount of the filtrate.

[0161] (2) Testing: Select a hydrochloric acid standard solution with a concentration of 0.05 mol / L, drain the air bubbles in the burette, select the corresponding sensor and program to start automatic detection and convert it into the residual lithium content.

[0162] IV. Test results of each example and comparative example

[0163] The batteries of each example and comparative example were prepared according to the above method, and their performance parameters were measured. The results are shown in Table 2 below.

[0164] Table 1 Preparation conditions of the positive electrode active materials of each example and comparative example

[0165]

[0166]

[0167]

[0168] As can be seen from Examples 1 to 14 in Table 2, the cathode active materials containing both lithium tungstate and lithium borate in the coating layer exhibit a lower residual lithium amount on the surface, even as low as 0.1 wt%; meanwhile, a higher capacity retention rate is maintained. This is because the tungstate and boric acid react with lithium hydroxide on the surface of the ternary material, reducing the residual lithium degree of the cathode 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 air, effectively reducing the damage of water and oxygen in the air to the material and avoiding the further increase of residual lithium. And 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 the discharge process.

[0169] Relatively speaking, in Comparative Examples 1 and 2, the cathode active materials contain coating layers containing only lithium tungstate or lithium borate, and the residual lithium amount on their surfaces is significantly higher than that of the examples of the present invention, reaching 0.5 wt%, and the cycle performance of their batteries is also lower than that of the present invention. Moreover, in Comparative Example 3, the cathode active material has no coating layer, and its residual lithium amount reaches 1 wt%, which is more than 3 times higher than the residual lithium amount of the examples of the present invention. Therefore, the cathode material of the present invention has a reduced residual lithium degree.

[0170] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same constitution and the same effect as the technical idea within the technical scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, Comprising: a core and a coating layer provided on the surface of the core, the core being a ternary material; wherein the coating layer comprises lithium tungstate and lithium borate; wherein the coating layer comprises an inner coating layer and an outer coating layer, and the inner coating layer and the outer coating layer have different compositions, which are independently selected from one or two of lithium tungstate and lithium borate.

2. The cathode active material according to claim 1, wherein The core comprises a compound of Formula I having a single crystal structure: LiNi x Co y Mn z O2 formula I wherein x + y + z = 1, 0.3 ≤ x < 1, y > 0, z > 0.

3. The cathode active material according to claim 1 or 2, characterized in that, The inner coating layer comprises lithium tungstate and the outer coating layer comprises lithium borate.

4. The positive electrode active material according to claim 1 or 2, characterized in that, The total coating amount of the coating layer is 3-5% by weight based on the weight of the positive electrode active material.

5. The cathode active material according to claim 1 or 2, characterized in that, The volume average particle diameter Dv50 of the positive electrode active material is 2 μm - 6 μm.

6. The cathode active material according to claim 1 or 2, characterized in that, The volume average particle diameter Dv50 of the positive electrode active material is 2 μm - 4 μm.

7. A method for preparing a positive electrode active material, which comprises (1) providing a ternary material, (2) treating the ternary material successively with a tungstate and a boron-containing acid to obtain the positive electrode active material; Wherein the positive electrode active material includes a core and a coating layer provided on the surface of the core, the core being a ternary material; wherein the coating layer includes lithium tungstate and lithium borate; wherein, The coating layer comprises an inner coating layer and an outer coating layer, and the inner coating layer and the outer coating layer have different compositions, which are independently selected from one or two of lithium tungstate and lithium borate.

8. The method according to claim 7, wherein The mass ratio of the ternary material to the tungstate is 1:8 - 1:

1.

9. The method according to claim 7, wherein The mass ratio of the ternary material to the tungstate is 1:5 - 1:

1.

10. The method according to claim 7, wherein The mass ratio of the ternary material to the boron-containing acid is 1:8 - 1:

1.

11. The method according to claim 7, wherein The mass ratio of the ternary material to the boron-containing acid is 1:5 - 1:

1.

12. The method according to any one of claims 7-11, characterized in that, The tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; the boron-containing acid is at least one of boric acid, metaboric acid, and a mixture of boric acid and phosphoric acid.

13. A secondary battery, characterized in that it comprises the positive electrode active material according to any one of claims 1-6 or the positive electrode active material prepared by the method for preparing a positive electrode active material according to any one of claims 7-12.

14. A battery module, characterized in that, Comprising the secondary battery according to claim 13.

15. A battery pack, characterized in that, Comprising the battery module according to claim 14.

16. An electrical device, characterized in that, Comprising at least one selected from the secondary battery according to claim 13, the battery module according to claim 14, or the battery pack according to claim 15.

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