CN115832240A

CN115832240A - Positive electrode active material, method for producing same, secondary battery, battery module, battery pack, and electric device

Info

Publication number: CN115832240A
Application number: CN202210697610.6A
Authority: CN
Inventors: 李月微; 严观福生; 任苗苗; 代志鹏; 靳超; 尤龙震
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-06-20
Filing date: 2022-06-20
Publication date: 2023-03-21

Abstract

The application relates to a positive active material, which is characterized by comprising an inner core and a coating layer arranged on the surface of the inner core, wherein the inner core is a ternary material; wherein the coating layer comprises lithium tungstate and lithium borate. The positive active material comprises a coating layer, so that the residual lithium degree on the surface of the positive active material is reduced, and the cycle performance of a corresponding battery is improved.

Description

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

Technical Field

The present disclosure relates to lithium battery technologies, and more particularly, to a positive active material, a method for manufacturing the positive active material, a secondary battery, a battery module, a battery pack, and an electric device.

Background

In recent years, with the application range of lithium ion batteries becoming wider, lithium ion batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment and aerospace. As lithium ion batteries have been greatly developed, higher requirements are also put forward on energy density, cycle performance, and the like.

The method of improving the rate capability and cycle performance of the material by means of coating or doping is currently an effective means, but the existing methods all cause damage to the performance of the lithium ion battery to different degrees, for example, the gram capacity of the lithium ion battery is reduced, the cycle performance is deteriorated, and the like. Therefore, the existing coated or doped positive electrode active material still remains to be improved.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a positive electrode active material having a reduced level of residual lithium in the positive electrode active material, and having improved cycle performance of the battery.

In order to achieve the above object, a first aspect of the present application provides a positive electrode active material, including an inner core and a coating layer disposed on a surface of the inner core, wherein the inner core is a ternary material; wherein the coating layer comprises lithium tungstate and lithium borate.

According to the invention, the anode active material comprises the core composed of the ternary material and the coating layer containing the lithium tungstate and the lithium borate, so that the lithium hydroxide on the surface of the ternary material is reacted, the residual lithium degree of the anode active material is reduced, the damage of an electrolyte to the lattice structure of the active material is effectively prevented, and the cycle performance of a corresponding battery is improved. The coating can completely cut off interior material and air contact, can effectively reduce the destruction of water oxygen in the air to the material, avoids the further increase of incomplete lithium. The coating layer is a good lithium ion conductor, so that the surface impedance of the material can be remarkably reduced, and the dynamic performance of the material in the middle discharge process can be further improved.

In any embodiment, the inner core comprises a compound of formula I having a single crystal structure:

LiNi _x Co _y Mn _z O ₂ formula I

Wherein x + y + z =1, 0.3. Ltoreq. X.ltoreq.1, y 0, z 0. Therefore, the nickel-cobalt-manganese ternary material with the single-crystal structure as the inner core is further limited, the obtained positive active material can be effectively prevented from cracking or breaking in the using process, the degree of residual lithium on the surface of the positive active material is reduced, and the cycle performance of the corresponding battery is improved.

In any embodiment, the coating comprises an inner coating and an outer coating, and the inner coating and the outer coating are different in composition and are each independently selected from one or both of lithium tungstate and lithium borate. Therefore, the coating layer is further limited to be an inner coating layer and an outer coating layer, the degree of residual lithium on the surface of the positive active material is further reduced, and the cycle performance of the corresponding battery is improved.

In any embodiment, the inner cladding comprises lithium tungstate and the outer cladding comprises lithium borate. Therefore, the composition of the inner and outer coating layers is further limited, the degree of residual lithium on the surface of the positive active material is reduced, and the cycle performance of the corresponding battery is improved.

In any embodiment, the total coating amount of the coating layers is 3 to 5wt% based on the weight of the positive electrode active material. Therefore, the coating amount of the coating layer is further limited, the degree of residual lithium on the surface of the positive active material is reduced, and the cycle performance of the corresponding battery is improved.

In any embodiment, the volume average particle diameter Dv50 of the positive electrode active material is from 2 μm to 6 μm, and optionally from 2 μm to 4 μm. Therefore, the particle size of the positive electrode active material is further limited, the residual lithium degree on the surface of the positive electrode active material is further reduced, and the cycle performance of the corresponding battery is improved.

A second aspect of the present application provides a method of preparing a positive electrode active material, which includes

(1) A ternary material is provided which is,

(2) Treating the ternary material with tungstate and boron-containing acid to obtain the positive active material;

the positive active material comprises an inner core and a coating layer arranged on the surface of the inner core, wherein the inner core is a ternary material; wherein the coating layer comprises lithium tungstate and lithium borate.

Therefore, by respectively treating the ternary material with tungstate and boric acid simultaneously or sequentially, a coating layer can be formed on the surface of the ternary material, so that the residual lithium degree on the surface of the ternary material is reduced, and the cycle performance of the corresponding battery is improved.

In any embodiment, the mass ratio of the ternary material to tungstate is 1. Therefore, a coating layer is better formed on the surface of the ternary material, the residual lithium degree on the surface of the ternary material is reduced, and the corresponding cycle performance of the battery is improved.

In any embodiment, the mass ratio of the ternary material to the boron-containing acid is 1. Therefore, a coating layer is better formed on the surface of the ternary material, the residual lithium degree on the surface of the ternary material is reduced, and the cycle performance of the corresponding battery is improved.

In any embodiment, the tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; the boric acid is at least one of boric acid, metaboric acid and a mixture of boric acid and phosphoric acid. Therefore, a coating layer is better formed on the surface of the ternary material, the residual lithium degree on the surface of the ternary material is reduced, and the cycle performance of the corresponding battery is improved.

A third aspect of the present application provides a secondary battery characterized in that,

a positive electrode active material comprising the positive electrode active material according to the first aspect of the present application or a positive electrode active material produced by the method for producing a positive electrode active material according to the second aspect of the present application.

A fourth aspect of the present application provides a battery module including the secondary battery of the third aspect of the present application.

A fifth aspect of the present application provides a battery pack including the battery module of the fourth aspect of the present application.

A sixth aspect of the present application provides an electric 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.

According to the invention, the coating layer containing lithium tungstate and lithium borate is formed on the surface of the ternary material, so that lithium hydroxide on the surface of the ternary material is reacted, the residual lithium degree of the positive electrode active material is reduced, and the cycle performance of the corresponding battery is improved.

Drawings

Fig. 1 is a schematic view of a positive electrode active material according to an embodiment of the present application.

Fig. 2 is a schematic view of a positive electrode active material according to an embodiment of the present application.

Fig. 3 is a schematic view of a secondary battery according to an embodiment of the present application.

Fig. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in fig. 3.

Fig. 5 is a schematic view of a battery module according to an embodiment of the present application.

Fig. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

Fig. 7 is an exploded view of the battery pack according to the embodiment of the present application shown in fig. 6.

Fig. 8 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Description of reference numerals:

a single crystal ternary material; b a positive electrode active material of the present application; 1, a battery pack; 2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 Top cover Assembly

Detailed Description

Hereinafter, embodiments of the positive electrode active material and the method for producing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application are specifically disclosed in detail with reference to the drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. 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 recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is only a shorthand representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not specifically mentioned.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

The method of improving the rate capability and cycle performance of the material by means of coating or doping is currently an effective means, but the existing methods all cause damage to the performance of the lithium ion battery to different degrees, for example, the gram capacity of the lithium ion battery is reduced, the cycle performance is deteriorated, and the like. In the prior art, the agglomerated ternary material (usually a polycrystalline material) cannot be uniformly coated, so that the agglomerated ternary material still has crystal boundary cracking in the charge-discharge process, a large number of new crystal faces are exposed, and the electrical property is poor. The applicant finds that the positive active material of the first aspect of the present application includes a core made of a ternary material and a coating layer made of lithium tungstate and lithium borate, and preferably, the core is a single-crystal ternary material, so as to avoid the cracking problem of the above-mentioned aggregated ternary material, reduce the residual lithium level of the positive active material more effectively, and improve the structural stability of the positive active material, thereby improving the cycle performance of the corresponding battery.

Positive electrode active material

In one embodiment of the present application, a positive electrode active material is provided, which is characterized by comprising an inner core and a coating layer disposed on the surface of the inner core, wherein the inner core is a ternary material; wherein the coating layer comprises lithium tungstate and lithium borate.

The applicant researches and discovers that according to the lithium-ion battery, the positive active material comprises an inner core made of a ternary material and a coating layer containing lithium tungstate and lithium borate, so that lithium hydroxide on the surface of the ternary material is reacted, the residual lithium degree of the positive active material is reduced, the damage of an electrolyte to the lattice structure of the active material is effectively prevented, and the cycle performance of the corresponding battery is improved. The coating can completely cut off interior material and air contact, can effectively reduce the destruction of water oxygen in the air to the material, avoids the further increase of incomplete lithium. The coating layer is a good lithium ion conductor, so that the surface impedance of the material can be remarkably reduced, and the dynamic performance of the material in the middle discharge process can be further improved.

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

In some embodiments, the coating layer can be uniformly coated on the surface of the ternary material, and can also be distributed on the surface of the ternary material in a patch shape; and the coating layer may have one or more layers, and if the coating layer has multiple layers, the different layers may be independently selected from one or more of lithium tungstate and lithium borate, but it is necessary to ensure that both components of lithium tungstate and lithium borate are present in the coating layer.

In some embodiments, the inner core comprises a compound of formula I having a single crystal structure:

LiNi _x Co _y Mn _z O ₂ formula I

Wherein x + y + z =1, 0.3. Ltoreq. X.ltoreq.1, preferably 0.8. Ltoreq. X.ltoreq.1; y >0, z >. Therefore, the nickel-cobalt-manganese ternary material with the single-crystal structure as the inner core is further limited, the obtained positive active material can be effectively prevented from cracking or breaking in the using process, the degree of residual lithium on the surface of the positive active material is reduced, and the cycle performance of the corresponding battery is improved.

In the present application, the term "single crystal" means that the crystal lattice inside the particle structure is aligned in a uniform direction and has isotropy. The term "polycrystalline" means that the lattice arrangement inside the grain structure is irregular and anisotropic.

In some embodiments, the coating has two layers of coating, including an inner coating and an outer coating, and the inner coating and the outer coating are different in composition and are each independently selected from one or both of lithium tungstate and lithium borate. Therefore, the coating layers are further limited to be an inner coating layer and an outer coating layer, the degree of residual lithium on the surface of the positive active material is further reduced, and the cycle performance of the corresponding battery is improved.

In some embodiments, the inner cladding comprises lithium tungstate and the outer cladding comprises lithium borate. Therefore, the composition of the inner and outer coating layers is further limited, the degree of residual lithium on the surface of the positive active material is reduced, and the cycle performance of the corresponding battery is improved.

In some embodiments, the total coating amount of the coating layers is 3 to 5wt% based on the weight of the positive electrode active material. Therefore, the coating amount of the coating layer is further limited, the degree of residual lithium on the surface of the positive active material is reduced, and the cycle performance of the corresponding battery is improved.

In some embodiments, the volume average particle diameter Dv50 of the positive electrode active material is 2 μm to 6 μm, and may be selected from 2 μm to 4 μm. Therefore, the particle size of the positive electrode active material is further limited, the degree of residual lithium on the surface of the positive electrode active material is further reduced, and the cycle performance of the corresponding battery is improved. In the present application, the volume particle diameter of the positive electrode active material and the distribution thereof are measured by using a laser particle size analyzer, for example, a Mastersizer3000 type laser particle size analyzer of malvern instruments ltd, u.k.a.

(1) A ternary material is provided which is,

Therefore, by using tungstate and boracic acid to treat the ternary material simultaneously or sequentially, a coating layer can be formed on the surface of the ternary material, so that the residual lithium degree on the surface of the ternary material is reduced, and the cycle performance of a corresponding battery is improved.

In some embodiments, the ternary material may be treated with tungstate and boron-containing acid simultaneously or sequentially in the process, preferably the ternary material is treated with tungstate and boron-containing acid sequentially.

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

In some embodiments, the weight ratio of the ternary material to tungstate is 1. Therefore, a coating layer is better formed on the surface of the ternary material, the residual lithium degree on the surface of the ternary material is reduced, and the cycle performance of the corresponding battery is improved.

In some embodiments, the mass ratio of the ternary material to the boron-containing acid is 1. Therefore, a coating layer is better formed on the surface of the ternary material, the residual lithium degree on the surface of the ternary material is reduced, and the corresponding cycle performance of the battery is improved.

In some embodiments, the tungstate is at least one of ammonium metatungstate, ammonium tungstate, ammonium phosphotungstate; the boric acid is at least one of boric acid, metaboric acid and a mixture of boric acid and phosphoric acid. Therefore, a coating layer is better formed on the surface of the ternary material, the residual lithium degree on the surface of the ternary material is reduced, and the cycle performance of the corresponding battery is improved.

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

In a preferred embodiment, the single crystal ternary material is added to the tungstate suspension, stirred for 5-40 minutes, and then kept stand, for example, for 5 minutes; taking the lower-layer precipitate, drying, then placing in an oxygen atmosphere, and heating at the temperature of 400-600 ℃ for 2-6 h to obtain a first-stage residual lithium reduction material;

then, dispersing the obtained first-stage lithium residue reducing material in a boron-containing acid solution, stirring for 5-40 minutes, and standing for 5 minutes, for example; and (3) taking the lower-layer precipitate, drying, then placing in an oxygen atmosphere, and heating at the temperature of 300-600 ℃ for 2-6 h to obtain the cathode active material.

The secondary battery, the battery module, the battery pack, and the electric device according to the present invention will be described below with reference to the drawings as appropriate.

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

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

[ Positive electrode sheet ]

The positive pole piece includes the anodal mass flow body and sets up the anodal rete on anodal mass flow body at least one surface, anodal rete includes the anodal active material of the first aspect of this application.

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

In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may 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 may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the positive active material may further include a positive active material for a battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, 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 a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g., liNiO) ₂ ) Lithium manganese oxide (e.g., liMnO) ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (may also be abbreviated as NCM) ₃₃₃ )、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (may also be abbreviated as NCM) ₅₂₃ )、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (may also be abbreviated as NCM) ₂₁₁ )、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (may also be abbreviated as NCM) ₆₂₂ )、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (may also be abbreviated as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxides (e.g., liNi) _0.85 Co _0.15 Al _0.05 O ₂ ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) ₄ (also referred to as LFP for short)), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., liMnPO) ₄ ) At least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer further optionally includes 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 fluoroacrylate resin.

In some embodiments, the positive electrode film layer further optionally includes 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.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.

[ negative electrode sheet ]

The negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on the negative pole mass flow body at least one surface, the negative pole rete includes negative pole active material.

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

In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. 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 alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative active material may employ a negative active material for a battery known in the art. As an example, the anode 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 and the like. The silicon-based material can be at least one selected from elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the anode film layer further optionally includes a binder. The binder may be at least one selected from 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).

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode film layer may also optionally include other adjuvants, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In some embodiments, the negative electrode sheet can be prepared by: dispersing the components for preparing the negative electrode plate, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (such as deionized water) to form negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and drying, cold pressing and the like to obtain the negative electrode pole piece.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be liquid, gel, or all solid.

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

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorodioxaoxalato phosphate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may 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, dimethylsulfone, methylethylsulfone, and diethylsulfone.

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include a negative electrode film forming additive, a positive electrode film forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

[ isolation film ]

In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In some embodiments, the material of the isolation film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and electrolyte.

In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other shape. For example, fig. 3 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to fig. 4, the overwrap may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and a cover plate 53 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.

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

Fig. 5 is a battery module 4 as an example. Referring to fig. 5, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.

Fig. 6 and 7 are a battery pack 1 as an example. Referring to fig. 6 and 7, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.

In addition, this application still provides a power consumption device, power consumption device includes at least one in secondary battery, battery module or the battery package that this application provided. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.

Fig. 8 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

As another example, the device may be a cell phone, a tablet, a laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.

Examples

In order to make the technical problems, technical solutions and advantages solved by the present application clearer, the present application will be described in further detail below with reference to embodiments and drawings. It should be apparent that the described embodiments are only a few embodiments of the present application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application and its applications. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without any inventive step are within the scope of the present application.

The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

1. Preparation of positive electrode active material

Example 1.1

1. 0.5g of ammonium metatungstate with an average particle size of 500 nm was dispersed in 50ml of ethanol and sufficiently stirred to obtain 10mg/ml of suspension A for use. 0.75g of boric acid is dissolved in 50ml of ethanol to obtain a solution B with the concentration of 15mg/ml for later use.

2. In a magnetic stirring apparatus with a stirrer, 100g of LiNi was added _0.95 Co _0.03 Mn _0.02 O ₂ The suspension a was added and mixed at a solid-to-liquid ratio of 1 (mass ratio) for 20 minutes with stirring. In the process, the residual lithium reacts with the ammonium metatungstate to generate lithium tungstate, and the lithium tungstate is coated on the surface of the material.

3. Standing for 5 minutes, and pouring and collecting the suspension and the solid powder after layering. The solid powder was dried in a vacuum oven (model OV-11/12, manufacturer Lab company) for 10 hours until the solid powder weight did not change more than 5% by weight within half an hour. And then placing the solid powder in a tube furnace, and heating for 5 hours at 500 ℃ in an oxygen atmosphere to obtain a first-stage residual lithium reduction material.

4. In a magnetic stirring apparatus with a stirrer, the primary lithium residue reduction material obtained above was dispersed in the solution B in a solid-to-liquid ratio of 1. In the process, the residual small amount of residual lithium reacts with boric acid to generate lithium borate and coat the surface of the material.

5. Standing for 5 minutes, and pouring and collecting the suspension and the solid powder after layering. The solid powder was dried in a vacuum oven (model OV-11/12, manufacturer Lab company) for 5 hours until the solid powder weight did not change more than 5% by weight within half an hour. And then placing the solid powder in a tube furnace, and heating the solid powder for 5 hours at 500 ℃ in an oxygen atmosphere to obtain the positive active material.

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

Preparation examples 2 to 8

Similar to the preparation method of the positive active material of preparation example 1, but the kind and amount of the coating material were adjusted, the preparation conditions were detailed in table 1, and the product parameters were detailed in table 2.

Preparation example 9

Similar to the preparation method of the positive active material of preparation example 1, but the continuous stirring time in

steps

2 and 4 was adjusted to 15 minutes. The different preparation conditions are detailed in table 1 and the different product parameters are detailed in table 2.

Preparation example 10

steps

2 and 4 was adjusted to 30 minutes. The different preparation conditions are detailed in table 1 and the different product parameters are detailed in table 2.

Preparation examples 11 to 12

A method similar to that of preparation example 1 was used to prepare a positive electrode active material, but the volume average particle diameter of the positive electrode active material was adjusted. The different preparation conditions are detailed in table 1 and the different product parameters are detailed in table 2.

Preparation example 13

Similar to the positive active material preparation method of preparation example 1, but steps 4 and 5 were performed first, and then steps 2 and 3 were performed. The different preparation conditions are detailed in table 1 and the different product parameters are detailed in table 2.

Preparation example 14

Similar to the method of preparing the positive active material of preparation example 1, but simultaneously performing steps 2-5, namely, simultaneously adding the suspension a and the suspension B to the ternary material, mixing with the ternary material, then standing for 5 minutes, and after layering, pouring and collecting the suspension and the solid powder. The solid powder was dried in a vacuum oven (model OV-11/12, manufacturer Lab company) for 5 hours until the solid powder weight did not change more than 5% by weight within half an hour. And then placing the solid powder in a tube furnace, and heating the solid powder for 5 hours at 500 ℃ in an oxygen atmosphere to obtain the positive active material. The different preparation conditions are detailed in table 1 and the different product parameters are detailed in table 2.

2. Preparation of secondary battery

Example 1

1) Preparation of positive pole piece

The finished product of the positive electrode active material of preparation example 1.1 was used as a positive electrode material, and acetylene was used as a conductive agentBlack, binder polyvinylidene fluoride (PVDF) in a weight ratio of 94:3:3, fully stirring and uniformly mixing in an N-methyl pyrrolidone solvent system, coating on an aluminum foil, drying and cold pressing to obtain the positive pole piece, wherein the coating amount of the positive pole piece is 8mg/cm ² 。

2) Preparation of negative pole piece

Artificial graphite serving as a negative electrode active material, acetylene black serving as a conductive agent, styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) serving as a thickening agent are mixed according to a weight ratio of 90:5:2:1, fully stirring and uniformly mixing in a deionized water solvent system, coating on a copper foil, drying and cold pressing to obtain a negative pole piece, wherein the coating amount of the negative pole piece is 10mg/cm ² 。

3) Isolation film

A porous polymer film made of Polyethylene (PE) was used as a separator.

4) Preparation of the electrolyte

The electrolyte is 1mol/L LiPF ₆ V (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1.

5) Preparation of the Battery

And overlapping the positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive and negative electrodes to play an isolating role, and winding to obtain the bare cell. And placing the bare cell in an outer package, injecting the electrolyte and packaging to obtain the secondary battery.

The secondary batteries of examples 2 to 15 and comparative examples 1 to 2 were fabricated in a similar manner to the secondary battery of example 1, except that the positive active material was adjusted to the active material of the corresponding fabrication example, and various product parameters were specified in table 2.

Comparative example 3

A secondary battery similar to that of example 1 was prepared, but the positive electrode active material was an uncoated ternary material. Product parameters are detailed in table 2.

3. Battery performance testing

1. Capacity retention ratio measurement

The obtained battery was charged at 25 ℃ to 4.25V at a constant current of 1/3C, charged at a constant voltage of 4.25V to a current of 0.05C, left for 30min, and discharged at 1/3C to 2.8V, and the obtained capacity was designated as initial capacity C0. The above steps were repeated for the same cell and the discharge capacity Cn of the cell after the nth cycle was recorded at the same time. The capacity retention Rn = Cn/C0 x 100% of the cell after the 100 th cycle was recorded and as a measure characterizing the useful service life of the cell, the 0.33C capacity retention of all examples and comparative examples after 100 cycles is summarized in table 1 below, where higher values indicate better cell performance.

2. Measurement of residual lithium amount

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

(1) Pretreatment in testing: weighing 30g of positive electrode active material powder, adding 100ml of pure water, stirring for 30min, standing for 10min, performing suction filtration, and transferring a certain amount of filtrate;

(2) And (3) testing: selecting 0.05mol/L hydrochloric acid standard solution, discharging liquid and discharging bubbles in the burette, selecting a corresponding sensor and a program to start automatic detection and converting the detection into the residual lithium amount.

4. Test results of examples and comparative examples

Batteries of examples and comparative examples were prepared according to the above-described methods, respectively, and the performance parameters were measured, with the results shown in table 2 below.

Table 1 preparation conditions of positive electrode active materials of respective examples and comparative examples

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 exhibited a lower amount of surface residual lithium, even as low as 0.1wt%; while maintaining a higher capacity retention. The reason is that the tungstate and the boric acid enable lithium hydroxide on the surface of the ternary material to react, the residual lithium degree of the anode active material is reduced, and the damage of electrolyte to the lattice structure of the active material is effectively prevented, so that the cycle performance of the corresponding battery is improved. The coating can completely cut off interior material and air contact, can effectively reduce the destruction of water oxygen in the air to the material, avoids the further increase of incomplete lithium. And the coating layer is a good lithium ion conductor, so that the surface impedance of the material can be remarkably reduced, and the dynamic performance of the material in the middle discharge process can be further improved.

In contrast, the positive active materials of comparative examples 1 and 2, which include the coating layer containing only lithium tungstate or lithium borate, had a significantly higher amount of residual lithium on the surface than the examples of the present invention, up to 0.5wt%, and also had lower cycle performance than the batteries of the present invention. Furthermore, the positive active material of comparative example 3, which has no coating layer, has a residual lithium amount of 1wt%, which is more than 3 times higher than that of the example of the present invention. Therefore, the positive electrode material of the present invention has a reduced level of residual lithium.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.

Claims

1. A positive electrode active material, comprising:

the core is made of ternary materials;

wherein the coating layer comprises lithium tungstate and lithium borate.

2. The positive electrode active material according to claim 1, wherein the inner core comprises a compound of formula I having a single crystal structure:

LiNi _x Co _y Mn _z O ₂ formula I

Wherein x + y + z =1, 0.3. Ltoreq. X.ltoreq.1, y 0, z 0.

3. The positive electrode active material according to claim 1 or 2, wherein the coating layer comprises an inner coating layer and an outer coating layer, and the inner coating layer and the outer coating layer are different in composition and are independently selected from one or both of lithium tungstate and lithium borate, respectively.

4. The positive electrode active material according to claim 3, wherein the inner cladding layer comprises lithium tungstate, and the outer cladding layer comprises lithium borate.

5. The positive electrode active material according to any one of claims 1 to 4, wherein the total coating amount of the coating layer is 3 to 5% by weight based on the weight of the positive electrode active material.

6. The positive electrode active material according to any one of claims 1 to 5, wherein the volume average particle diameter Dv50 of the positive electrode active material is from 2 μm to 6 μm, optionally from 2 μm to 4 μm.

7. A method of preparing a positive electrode active material, comprising

(1) A ternary material is provided which is,

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

9. The method according to claim 7, characterized in that the mass ratio of the ternary material to the boron-containing acid is 1.

10. The method of any of claims 7-9, wherein the tungstate is at least one of ammonium metatungstate, ammonium tungstate, and ammonium phosphotungstate; the boric acid is at least one of boric acid, metaboric acid and a mixture of boric acid and phosphoric acid.

11. A secondary battery is characterized in that,

a positive electrode active material comprising the positive electrode active material according to any one of claims 1 to 6 or produced by the method for producing a positive electrode active material according to any one of claims 7 to 10.

12. A battery module characterized by comprising the secondary battery according to claim 11.

13. A battery pack comprising the battery module according to claim 12.

14. An electric device comprising at least one selected from the secondary battery according to claim 11, the battery module according to claim 12, and the battery pack according to claim 13.