A modified positive electrode active material and its preparation method and application

Abstract

The present invention provides a modified positive electrode active material and its preparation method and application, wherein the modified positive electrode active material includes a manganese-containing positive electrode material and a polymer coating layer provided on the surface of the manganese-containing positive electrode material; the molecular structure of the polymer of the polymer coating layer contains an acidic group, and the polymer is insoluble in a first solvent, and the first solvent is N-methylpyrrolidone and / or an electrolyte solvent. The polymer coating layer is uniformly coated on the surface of the manganese-containing positive electrode material, and the acidic groups in the polymer have a complexing effect on manganese ions, effectively inhibiting the dissolution of manganese ions from the positive electrode material, so that the modified positive electrode active material has excellent structural stability and thermal stability. At the same time, the polymer is insoluble in NMP and / or the electrolyte solvent, so that the polymer coating layer continues to maintain excellent coating stability, thereby giving the modified positive electrode active material excellent performance stability and significantly improving the cycle performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery materials, and in particular relates to a modified positive electrode active material and a preparation method and application thereof. Background Art

[0002] With the development and popularization of hybrid and electric vehicles, demand for lithium-ion batteries with high energy density, high power density, and long cycle life is growing rapidly. Lithium-ion batteries are typically assembled from a positive electrode, a negative electrode, a separator, and an electrolyte. The performance of a battery is closely related to each component. As one of the core components of a battery, the positive electrode directly affects the ultimate performance of the lithium-ion battery.

[0003] Currently commercialized cathode materials include lithium iron phosphate (LiFePO4, LFP), lithium cobalt oxide (LiCoO2, LCO), lithium nickel oxide (LiNiO2, LNO), lithium manganese oxide (LiMn2O4, LMO), and nickel cobalt manganese oxide (NCM). Among them, NCM ternary materials combine the performance advantages of LCO, LNO, and LMO, offering high energy density, high discharge capacity, and good rate performance. It has become the largest cathode material in the market, enabling lithium-ion power batteries to achieve longer driving ranges, and has been attracting significant attention from the industry in recent years.

[0004] With the development of new energy technologies and the upgrading of lithium-ion batteries, it has been discovered that NCM ternary materials have significant deficiencies in electrochemical performance, thermal stability, and structural stability, which in turn affects the electrochemical performance of lithium-ion batteries. Modifying NCM ternary materials using physical or chemical means is the primary method for optimizing battery performance.

[0005] CN103474628A discloses a method for preparing a carbon-coated ternary positive electrode material, which specifically includes the following steps: S1, using nickel salt, cobalt salt and manganese salt as raw materials to prepare a ternary positive electrode material precursor; S2, dispersing conductive carbon in water containing an organic carbon source to prepare a conductive carbon dispersion system; S3, adding the ternary positive electrode material precursor and a lithium compound to the conductive carbon dispersion system to obtain a mixture; S4, drying the mixture under vacuum conditions; S5, high-temperature treatment of the dried mixture under sealed conditions or in an inert gas atmosphere to obtain a carbon-coated ternary positive electrode material. In the carbon-coated ternary positive electrode material, the conductive carbon and the ternary positive electrode material are simultaneously coated in a network-like amorphous carbon, which improves the rate performance of the positive electrode material; however, the high-temperature treatment of 500-1100°C in step S5 will partially reduce the ternary material, damage the surface structure of the material, and thus destroy the material performance.

[0006] CN108963239A discloses a method for preparing a titanium dioxide-coated lithium nickel cobalt manganate cathode material. The method comprises placing lithium nickel cobalt manganate powder in a plasma-enhanced rotary furnace, continuously introducing a titanium source gas and an oxygen-containing gas using an inert gas as a protective gas, and using pulsed microwave excitation to deposit a layer of titanium dioxide with a thickness of 10 nm to 1 μm on the surface of the lithium nickel cobalt manganate powder to obtain a titanium dioxide-coated lithium nickel cobalt manganate cathode material. This cathode material helps improve the cycle performance of lithium-ion batteries, but titanium dioxide, as a semiconductor, affects the specific capacity of the lithium nickel cobalt manganate cathode material, thereby limiting the overall capacity of the battery.

[0007] Based on current research progress, the performance of NCM ternary materials still has significant room for improvement. This is especially true in lithium-ion power batteries that require high energy density and performance. The problem of transition metal ions such as manganese ions dissolving from the cathode material is particularly prominent, especially under high-temperature testing environments. This dissolution of transition metal ions can cause the battery voltage to drop, the electrolyte to decompose, and the cycle performance to be poor, seriously affecting the battery's reliability. Therefore, the development of a cathode material with excellent cycle performance and high stability is of great practical significance. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a modified positive electrode active material and its preparation method and application. By setting a specific polymer coating layer on the surface of the manganese-containing positive electrode material, the dissolution of manganese ions from the positive electrode material can be significantly inhibited, so that the modified positive electrode active material has excellent stability, thereby improving the cycle performance of the battery.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a modified positive electrode active material, which includes a manganese-containing positive electrode material and a polymer coating layer arranged on the surface of the manganese-containing positive electrode material; the polymer of the polymer coating layer contains an acidic group in its molecular structure, and the polymer is insoluble in a first solvent, which is N-methylpyrrolidone and / or an electrolyte solvent.

[0011] In the modified positive electrode active material provided by the present invention, a polymer coating layer is provided on the surface of the manganese-containing positive electrode material. The acidic groups in the polymer have a complexing effect on the manganese ions in the manganese-containing positive electrode material, effectively inhibiting the dissolution of manganese ions from the positive electrode material, avoiding the capacity loss caused by manganese dissolution, and making the modified positive electrode active material have excellent structural stability and thermal stability. At the same time, the polymer is insoluble in N-methylpyrrolidone (NMP) and / or electrolyte solvents, can maintain the coating stability of the polymer coating layer, and will not dissolve or fall off in the positive electrode slurry and / or electrolyte. Therefore, the modified positive electrode active material is used to prepare lithium-ion batteries, which can significantly improve the cycle performance of the battery.

[0012] In the present invention, the coating of the manganese-containing positive electrode material by the polymer coating layer includes full coating or partial coating.

[0013] In the present invention, the “polymer is insoluble in the first solvent” means that the mass of the polymer that can be dissolved in 100 g of the first solvent is less than 0.01 g, that is, the solubility of the polymer in the first solvent is less than 0.01 g / 100 g.

[0014] In the present invention, the electrolyte solvent is an organic solvent for non-aqueous electrolyte known in the prior art, including any one or a combination of at least two of cyclic carbonates, chain carbonates, cyclic carboxylates, and chain carboxylates, specifically including: any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethyl acetate, ethyl propionate, propyl propionate, γ-butyrolactone, methyl acetate, methyl butyrate, ethyl butyrate or propyl butyrate.

[0015] Preferably, the manganese-containing positive electrode material includes any one of lithium nickel cobalt manganese oxide, lithium manganese oxide or lithium nickel manganese oxide, or a combination of at least two thereof, and lithium nickel cobalt manganese oxide (lithium nickel cobalt manganese oxide, NCM) is further preferred.

[0016] Preferably, the acidic group includes any one or a combination of at least two of a carboxyl group, a sulfonic acid group, a sulfate group, a sulfate ester group, a phosphoric acid group or a phosphate ester group.

[0017] Preferably, the molar percentage of acidic groups in the polymer is ≥5%, for example, it can be 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48% or 50%, etc.

[0018] Preferably, the polymer includes any one of acidic group-modified polyolefin, acidic group-modified polystyrene or acidic group-modified polyvinyl alcohol, or a combination of at least two thereof.

[0019] Preferably, the acidic group-modified polyolefin includes any one of acidic group-modified polyethylene, acidic group-modified polypropylene, acidic group-modified ethylene-propylene copolymer or acidic group-modified polybutadiene, or a combination of at least two thereof.

[0020] Preferably, the polymer includes any one of carboxyl-modified polyvinyl alcohol, sulfonic-modified polyvinyl alcohol, phosphate-modified polyvinyl alcohol, sulfate-modified polyvinyl alcohol, carboxyl-modified polyethylene, sulfonic-modified polyethylene, phosphate-modified polyethylene, sulfate-modified polyethylene, carboxyl-modified polybutadiene, sulfonic-modified polybutadiene, phosphate-modified polybutadiene or sulfate-modified polybutadiene, or a combination of at least two thereof.

[0021] Preferably, the polymer is soluble in at least one second solvent, which is different from the first solvent.

[0022] As a preferred technical solution of the present invention, the modified positive electrode active material can be prepared by a liquid phase coating process. Based on process considerations, the polymer is dissolved in at least one solvent different from the first solvent, namely, a second solvent.

[0023] In the present invention, the polymer is soluble in the second solvent, which means that the mass of the polymer that can be dissolved in 100g of the second solvent is ≥1g, that is, the solubility of the polymer in the second solvent is ≥1g / 100g.

[0024] Preferably, the second solvent includes any one or a combination of at least two of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, halogenated hydrocarbon solvents, alcohol solvents, ether solvents, ketone solvents, alcohol ether solvents, sulfone solvents, phenol solvents or water, and further preferably any one or a combination of at least two of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, sulfone solvents or water.

[0025] Preferably, the aromatic hydrocarbon solvent includes any one of benzene, toluene or xylene, or a combination of at least two of them.

[0026] Preferably, the aliphatic hydrocarbon solvent includes any one of pentane, hexane, octane or petroleum ether, or a combination of at least two of them.

[0027] Preferably, the alicyclic hydrocarbon solvent includes any one of cyclopentane, cyclohexane or cycloheptane, or a combination of at least two of them.

[0028] Preferably, the halogenated hydrocarbon solvent includes any one of carbon tetrachloride, chlorobenzene, dichlorobenzene, dichloromethane or chloroform, or a combination of at least two thereof.

[0029] Preferably, the alcohol solvent includes any one of methanol, ethanol, isopropanol or glycerol, or a combination of at least two of them.

[0030] Preferably, the ether solvent includes any one of diethyl ether, propylene oxide, tetrahydrofuran or dioxane, or a combination of at least two thereof.

[0031] Preferably, the ketone solvent includes any one of acetone, methyl n-butyl ketone, methyl isobutyl ketone or cyclohexanone, or a combination of at least two thereof.

[0032] Preferably, the alcohol ether solvent includes any one of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether or ethylene glycol monobutyl ether, or a combination of at least two thereof.

[0033] Preferably, the sulfone solvent includes dimethyl sulfoxide and / or sulfolane.

[0034] Preferably, the phenolic solvent comprises phenol and / or cresol.

[0035] Preferably, the second solvent includes any one of water, dimethyl sulfoxide, octane, benzene, toluene or xylene, or a combination of at least two thereof.

[0036] Preferably, based on the mass of the manganese-containing positive electrode material as 100%, the mass of the polymer coating layer is 1-10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0037] As a preferred technical solution of the present invention, in the modified positive electrode active material, the mass of the polymer coating layer is 1-10%, based on the mass of the manganese-containing positive electrode material being 100%. A uniform polymer coating layer is formed on the surface of the manganese-containing positive electrode material, thereby improving the structural stability and thermal stability of the modified positive electrode active material. If the mass of the polymer coating layer is too low, it will not form an effective coating and will not significantly inhibit the dissolution of manganese ions. If the mass of the polymer coating layer is too high and the coating layer is too thick, it will be detrimental to the transmission of lithium ions and electrons, affecting the electrochemical performance of the lithium-ion battery.

[0038] In a second aspect, the present invention provides a method for preparing the modified positive electrode active material as described in the first aspect, the preparation method comprising: mixing a manganese-containing positive electrode material with a polymer solution to obtain a slurry; and drying the slurry to obtain the modified positive electrode active material.

[0039] Preferably, the polymer solution is a mixture of a polymer and a second solvent.

[0040] Preferably, the mass ratio of the polymer to the manganese-containing positive electrode material in the slurry is (0.01-0.10):1.00, for example, it can be 0.02:1.00, 0.03:1.00, 0.04:1.00, 0.05:1.00, 0.06:1.00, 0.07:1.00, 0.08:1.00 or 0.09:1.00, etc.

[0041] Preferably, the drying method is spray drying.

[0042] Preferably, the inlet temperature of the spray drying is 200-300°C, for example, it can be 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C or 290°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and is further preferably 230-270°C.

[0043] Preferably, the outlet temperature of the spray drying is 100-200°C, for example, it can be 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C or 190°C, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range, and it is further preferably 130-170°C.

[0044] Preferably, the spray drying pressure is 0.2-0.8 MPa, for example, it can be 0.25 MPa, 0.30 MPa, 0.35 MPa, 0.40 MPa, 0.45 MPa, 0.50 MPa, 0.55 MPa, 0.60 MPa, 0.65 MPa, 0.70 MPa or 0.75 MPa, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0045] Preferably, the feed rate of the slurry in the spray drying is 5-15 mL / min, for example, it can be 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min, 11 mL / min, 12 mL / min, 13 mL / min or 14 mL / min, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0046] In a third aspect, the present invention provides a positive electrode material composition, which includes the modified positive electrode active material as described in the first aspect.

[0047] Preferably, the positive electrode material composition comprises a combination of a modified positive electrode active material, a conductive agent and a binder.

[0048] In a fourth aspect, the present invention provides a positive electrode plate, comprising a current collector and a coating disposed on the current collector, wherein the material of the coating comprises the positive electrode material composition as described in the third aspect.

[0049] In a fifth aspect, the present invention provides an electrochemical device, comprising the positive electrode sheet as described in the fourth aspect.

[0050] Preferably, the electrochemical device comprises a lithium-ion battery.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) In the modified positive electrode active material provided by the present invention, the polymer coating layer is uniformly coated on the surface of the manganese-containing positive electrode material. The acidic groups in the polymer have a complexing effect on manganese ions, effectively inhibiting the dissolution of manganese ions from the positive electrode material, and thus giving the modified positive electrode active material excellent structural stability and thermal stability. At the same time, the polymer is insoluble in NMP and / or electrolyte solvents, so that the polymer coating layer maintains excellent coating stability during the preparation process of the slurry and the electrode sheet and during the use of the battery, thereby giving the modified positive electrode active material excellent stability and cycle performance.

[0053] (2) The modified positive electrode active material is used in positive electrode sheets and lithium-ion batteries, so that the capacity retention rate of the lithium-ion battery after 100 cycles at room temperature is greater than 96%, and the capacity retention rate after 100 cycles at high temperature is greater than 94%, which effectively avoids the capacity loss caused by the dissolution of manganese in the positive electrode material and significantly improves the cycle performance of the lithium-ion battery. DETAILED DESCRIPTION

[0054] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0055] As used herein, the terms "comprises," "including," "having," "containing" or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a listed element is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0056] "Optional" or "either" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0057] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times they appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0058] The terms "one embodiment," "some embodiments," "exemplarily," "specific examples," or "some examples" used in the present invention mean that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present invention. In this document, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example.

[0059] Moreover, the technical features involved in various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0060] In the following specific embodiments of the present invention, the manganese-containing positive electrode material and polymer used are commercially available products. The manganese-containing positive electrode material is NCM ternary positive electrode material (lithium nickel cobalt manganese oxide, Nantong Ruixiang 622), and the specific information of the polymer is shown in Table 1 below:

[0061] Table 1

[0062] polymer Manufacturer's brand Mole percentage of acidic groups Carboxyl modified polyvinyl alcohol Sichuan Wei SG-182 6％ Carboxyl modified polyvinyl alcohol Sichuan Wei SG-181 6％ Sulfonic acid modified polyvinyl alcohol Sichuan Wei PS-6 6％ Carboxyl modified polybutadiene Beijing Yanshan MLPB brand 1# 20％ Carboxyl modified polybutadiene Beijing Yanshan MLPB brand 2# 20％ Carboxyl modified polybutadiene Beijing Yanshan MLPB brand 3# 20％ Carboxyl modified polyethylene Dongguan Youxin New Materials Nucerl 925 15％ Carboxyl modified polyethylene Dongguan Youxin New Materials EAA-5980 20％

[0063] Example 1

[0064] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polyvinyl alcohol (Sichuan Wei SG-181).

[0065] The modified positive electrode active material was prepared as follows: 2 parts carboxyl-modified polyvinyl alcohol was dissolved in 100 parts dimethyl sulfoxide. 98 parts NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0066] Example 2

[0067] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is sulfonic acid group-modified polyvinyl alcohol (Sichuan Wei PS-6).

[0068] The modified positive electrode active material was prepared as follows: 3 parts of sulfonic acid-modified polyvinyl alcohol was dissolved in 100 parts of dimethyl sulfoxide. 97 parts of NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0069] Example 3

[0070] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polybutadiene (Beijing Yanshan MLPB brand 1#).

[0071] The modified positive electrode active material was prepared as follows: 5 parts carboxyl-modified polybutadiene was dissolved in 100 parts toluene. 95 parts NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0072] Example 4

[0073] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polyethylene (Dongguan Youxin New Materials Nucerl 925).

[0074] The modified positive electrode active material was prepared as follows: 8 parts of carboxyl-modified polyethylene was dissolved in 100 parts of n-octane. 92 parts of NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0075] Example 5

[0076] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polyethylene (Dongguan Youxin New Materials EAA-5980).

[0077] The modified positive electrode active material was prepared as follows: 7 parts of carboxyl-modified polyethylene was dissolved in 100 parts of n-octane. 93 parts of NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0078] Example 6

[0079] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polybutadiene (Beijing Yanshan MLPB brand 2#).

[0080] The modified positive electrode active material was prepared as follows: 6 parts of carboxyl-modified polybutadiene was dissolved in 100 parts of toluene. 94 parts of NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0081] Example 7

[0082] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polybutadiene (Beijing Yanshan MLPB brand 3#).

[0083] The modified positive electrode active material was prepared as follows: 4 parts carboxyl-modified polybutadiene was dissolved in 100 parts toluene. 96 parts NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0084] Example 8

[0085] A modified positive electrode active material and a preparation method thereof, wherein the modified positive electrode active material comprises an NCM ternary positive electrode material and a polymer coating layer arranged on the surface of the NCM ternary positive electrode material, wherein the polymer is carboxyl-modified polyvinyl alcohol (Sichuan Wei SG-182).

[0086] The modified positive electrode active material was prepared as follows: 1 part carboxyl-modified polyvinyl alcohol was dissolved in 100 parts dimethyl sulfoxide. 99 parts NCM ternary cathode material powder was added while stirring at 1000 rpm. After 30 minutes, a uniformly dispersed slurry was obtained. The slurry was spray-dried using the following parameters: inlet temperature of 250°C, outlet temperature of 150°C, slurry feed rate of 10 mL / min, and air pressure of 0.5 MPa. After spray drying, the collected particles constituted the modified positive electrode active material.

[0087] Comparative Example 1

[0088] A modified positive electrode active material is different from Example 1 only in that the polymer of the polymer coating layer is polyvinyl alcohol; the types, amounts and preparation methods of other materials are the same as those in Example 1.

[0089] Comparative Example 2

[0090] A modified positive electrode active material, which differs from Example 2 only in that the polymer of the polymer coating layer is sulfonic acid anion-doped polypyrrole; the sulfonic acid anion-doped polypyrrole is prepared by reacting pyrrole, naphthalenesulfonic acid and ammonium persulfate, and its preparation method refers to the prior art CN114695852A; the types, amounts and preparation methods of other materials are the same as those in Example 2.

[0091] Comparative Example 3

[0092] A positive electrode active material, namely the uncoated NCM ternary positive electrode material in Example 1.

[0093] Application Examples 1-8, Comparative Application Examples 1-3

[0094] A positive electrode plate comprises a current collector (Al foil) and a coating disposed on the current collector, wherein the coating is made of a positive electrode material composition; the positive electrode material composition comprises a positive electrode active material, a conductive agent (conductive carbon black), and a binder (polyvinylidene fluoride, PVDF) in a mass ratio of 95.5:2.0:2.5; wherein the positive electrode active material is the positive electrode active material provided in Examples 1-8 and Comparative Examples 1-3, respectively.

[0095] The preparation method of the positive electrode sheet is as follows: the positive electrode active material, the conductive agent and the binder are mixed in a mass ratio of 95.5:2.0:2.5, and the mixture is added into N-methylpyrrolidone (NMP) at a ratio of 50 wt% of the solid content of the system, and the mixture is stirred and mixed to prepare a uniform positive electrode slurry. After passing through a 100 mesh screen, the mixture is coated on the positive electrode current collector Al foil, dried, and rolled using a roller with a 10×10 4 The positive electrode sheet is obtained by rolling the sample with a unit length load of N / m.

[0096] A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet is the aforementioned positive electrode sheet; and a method for preparing the lithium-ion battery is as follows:

[0097] (1) Preparation of positive electrode: as described above;

[0098] (1) Preparation of negative electrode sheet: The negative electrode active material (artificial graphite), conductive agent (conductive carbon black SP), binder (styrene-butadiene rubber, SBR) and thickener (sodium carboxymethyl cellulose, CMC) were mixed in a mass ratio of 95.0:1.0:2.5:1.5, added to deionized water at a solid content of 40 wt%, and stirred thoroughly to prepare a uniform negative electrode slurry. After passing through a 100 mesh sieve, the slurry was coated on the negative electrode current collector Cu foil, dried, and rolled with a roller at a speed of 10 × 10 4 The negative electrode sheet was obtained by rolling the negative electrode sheet with a unit length load of N / m.

[0099] (3) Diaphragm: PE porous polymer film (Shenzhen Xingyuan Material Technology Co., Ltd.) was used as the diaphragm;

[0100] (4) Assembly of lithium-ion batteries: The positive electrode sheet, the separator, and the negative electrode sheet are wound in sequence to obtain a battery cell; the battery cell is encapsulated with an aluminum-plastic film, baked to remove water, and then injected with an electrolyte. After vacuum packaging, shelving, formation, secondary sealing, and shaping, the lithium-ion battery is obtained.

[0101] Performance testing:

[0102] (1) Normal temperature cycle performance

[0103] The lithium-ion battery prepared above was charged to 4.20V at a constant current of 0.33C, then charged at a constant voltage to a cutoff current of 0.02C, and discharged at 0.33C to 2.50V; left for 5 minutes, charged to 4.20V at a constant current of 0.33C, then charged at a constant voltage to a cutoff current of 0.02C, and discharged at 0.33C to 2.50V, thereby performing initial adjustment.

[0104] At 25°C, charge the initially conditioned lithium-ion battery at a constant current of 0.50C to 4.20V, then charge at a constant voltage to a cutoff current of 0.02C, rest for 5 minutes, and then discharge at a constant current of 1C to 2.50V, rest for 5 minutes. Measure the discharge capacity of the first cycle. Repeat this cycle for 100 charge / discharge cycles, measure the discharge capacity of the 100th cycle, and calculate the capacity retention rate at the 100th cycle using the following formula:

[0105] Capacity retention rate after 100 cycles at room temperature (%) = 100% × 100th cycle discharge capacity / first cycle discharge capacity.

[0106] (2) High temperature cycle performance

[0107] At 45°C, charge the initially conditioned lithium-ion battery at a constant current of 0.50C to 4.20V, then charge at a constant voltage to a cutoff current of 0.02C, rest for 5 minutes, and then discharge at a constant current of 1C to 2.50V, rest for 5 minutes. Measure the discharge capacity of the first cycle. Repeat this charge / discharge cycle for 100 cycles, measure the discharge capacity of the 100th cycle, and calculate the capacity retention rate at the 100th cycle using the following formula:

[0108] Capacity retention rate after 100 cycles of high-temperature cycling (%) = 100% × 100th cycle discharge capacity / first cycle discharge capacity.

[0109] The test results are shown in Table 2; in Table 2, the % data in the polymer coating layer column represents the mass of the polymer coating layer based on the mass of the NCM ternary positive electrode material as 100%.

[0110] Table 2

[0111] positive electrode active material polymer coating Normal temperature cycle performance (%) High temperature cycle performance (%) Example 1 2% carboxyl-modified polyvinyl alcohol 97.0 94.9 Example 2 3% sulfonic acid modified polyvinyl alcohol 97.5 95.4 Example 3 5% carboxyl modified polybutadiene 98.3 96.1 Example 4 8% carboxyl modified polyethylene 96.8 94.6 Example 5 7% carboxyl modified polyethylene 97.3 95.1 Example 6 6% carboxyl modified polybutadiene 97.8 95.6 Example 7 4% carboxyl modified polybutadiene 98.0 95.8 Example 8 1% carboxyl-modified polyvinyl alcohol 96.5 94.4 Comparative Example 1 2% polyvinyl alcohol 91.5 89.2 Comparative Example 2 3% sulfonic acid anion doped polypyrrole 93.2 90.9 Comparative Example 3 -- 91.4 89.1

[0112] Combined with the performance test data in Table 2, it can be seen that compared with the conventional NCM ternary positive electrode material in Comparative Example 3, the modified positive electrode active material provided by the present invention has excellent structural stability, thermal stability and cycle performance, so that the capacity retention rate of the lithium ion battery containing it after 100 cycles at room temperature is 96.5-98.3%, and the capacity retention rate after 100 cycles at high temperature is 94.4-96.1%, which has excellent cycle performance.

[0113] In the present invention, a polymer coating layer of a specific material is uniformly coated on the surface of the manganese-containing positive electrode material. Since the polymer is insoluble in NMP and / or the electrolyte solvent, the stability of the polymer coating layer can be continuously maintained; at the same time, the acidic groups in the polymer can complex manganese ions, effectively inhibiting the capacity loss caused by manganese dissolution in the positive electrode material, so that the modified positive electrode active material has excellent stability and cycle performance. In Comparative Example 1, polyvinyl alcohol was used to coat the NCM ternary positive electrode material. Since polyvinyl alcohol does not have a complexing effect, it cannot inhibit the dissolution of manganese in the positive electrode material, resulting in poor battery cycle performance; in Comparative Example 2, the sulfonic acid anion-doped polypyrrole is soluble in NMP, causing the polymer coating layer to fall off during the preparation of the positive electrode slurry, and it cannot continuously and effectively play the role of inhibiting the dissolution of manganese ions, resulting in low battery cycle performance.

[0114] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the modified positive electrode active material, its preparation method, and its application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacement of various raw materials in the product of the present invention, addition of auxiliary components, selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. A modified positive electrode active material, characterized in that The modified positive electrode active material comprises a manganese-containing positive electrode material and a polymer coating layer disposed on the surface of the manganese-containing positive electrode material; The manganese-containing positive electrode material includes any one of lithium nickel cobalt manganese oxide, lithium manganese oxide or lithium nickel manganese oxide, or a combination of at least two thereof; The polymer molecular structure of the polymer coating layer contains an acidic group, and the polymer is insoluble in a first solvent. The first solvent is N -Methylpyrrolidone and electrolyte solvent; The polymer includes any one or a combination of at least two of acid group-modified polyolefin, acid group-modified polystyrene or acid group-modified polyvinyl alcohol; The acidic group includes any one or a combination of at least two of a carboxyl group, a sulfonic acid group, a sulfate group, a sulfate ester group, a phosphoric acid group or a phosphate ester group; Based on the mass of the manganese-containing positive electrode material being 100%, the mass of the polymer coating layer is 2-10%; The polymer is soluble in at least one second solvent, the second solvent being different from the first solvent; The method for preparing the modified positive electrode active material comprises the following steps: The manganese-containing positive electrode material is mixed with a solution formed by dissolving a polymer in a second solvent to obtain a slurry; and the slurry is dried to obtain the modified positive electrode active material.

2. The modified positive electrode active material according to claim 1, characterized in that The manganese-containing positive electrode material includes lithium nickel cobalt manganese oxide.

3. The modified positive electrode active material according to claim 1, characterized in that The molar percentage of acidic groups in the polymer is ≥5%.

4. The modified positive electrode active material according to claim 1, characterized in that The acidic group-modified polyolefin includes any one of acidic group-modified polyethylene, acidic group-modified polypropylene, acidic group-modified ethylene-propylene copolymer, or acidic group-modified polybutadiene, or a combination of at least two thereof.

5. The modified positive electrode active material according to claim 1, characterized in that The second solvent includes any one or a combination of at least two of aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, halogenated hydrocarbon solvents, alcohol solvents, ether solvents, ketone solvents, alcohol ether solvents, sulfone solvents, phenol solvents or water.

6. The modified positive electrode active material according to claim 5, characterized in that The second solvent includes any one of an aromatic hydrocarbon solvent, an aliphatic hydrocarbon solvent, a sulfone solvent or water, or a combination of at least two thereof.

7. The modified positive electrode active material according to claim 5, characterized in that The aromatic hydrocarbon solvent includes any one of benzene, toluene or xylene, or a combination of at least two of them.

8. The modified positive electrode active material according to claim 5, characterized in that The aliphatic hydrocarbon solvent includes any one of pentane, hexane, octane or petroleum ether, or a combination of at least two of them.

9. The modified positive electrode active material according to claim 5, characterized in that The alicyclic hydrocarbon solvent includes any one of cyclopentane, cyclohexane or cycloheptane, or a combination of at least two of them.

10. The modified positive electrode active material according to claim 5, characterized in that The halogenated hydrocarbon solvent includes any one of carbon tetrachloride, chlorobenzene, dichlorobenzene, dichloromethane or chloroform, or a combination of at least two thereof.

11. The modified positive electrode active material according to claim 5, characterized in that The alcohol solvent includes any one of methanol, ethanol, isopropanol or glycerol, or a combination of at least two of them.

12. The modified positive electrode active material according to claim 5, characterized in that The ether solvent includes any one of diethyl ether, propylene oxide, tetrahydrofuran or dioxane, or a combination of at least two thereof.

13. The modified positive electrode active material according to claim 5, characterized in that The ketone solvent includes any one of acetone, methyl n-butyl ketone, methyl isobutyl ketone or cyclohexanone, or a combination of at least two thereof.

14. The modified positive electrode active material according to claim 5, characterized in that The alcohol ether solvent includes any one of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether or ethylene glycol monobutyl ether, or a combination of at least two of them.

15. The modified positive electrode active material according to claim 5, characterized in that The sulfone solvent includes dimethyl sulfoxide and / or sulfolane.

16. The modified positive electrode active material according to claim 5, characterized in that The phenolic solvent includes phenol and / or cresol.

17. A method for preparing the modified positive electrode active material according to any one of claims 1 to 16, characterized in that: The preparation method comprises: mixing a manganese-containing positive electrode material with a solution formed by dissolving a polymer in a second solvent to obtain a slurry; and drying the slurry to obtain the modified positive electrode active material.

18. The preparation method according to claim 17, characterized in that: The drying method is spray drying.

19. The preparation method according to claim 18, characterized in that The inlet temperature of the spray drying is 200-300°C.

20. The preparation method according to claim 18, characterized in that The outlet temperature of the spray drying is 100-200°C.

21. The preparation method according to claim 18, characterized in that The spray drying pressure is 0.2-0.8 MPa.

22. The preparation method according to claim 18, characterized in that The feed rate of the slurry in the spray drying process is 5-15 mL / min.

23. A positive electrode material composition, characterized in that The positive electrode material composition includes the modified positive electrode active material according to any one of claims 1 to 16.

24. The positive electrode material composition according to claim 23, characterized in that The positive electrode material composition includes a combination of a modified positive electrode active material, a conductive agent, and a binder.

25. A positive electrode plate, characterized in that: The positive electrode plate includes a current collector and a coating disposed on the current collector, and the material of the coating includes the positive electrode material composition according to claim 23 or 24.

26. An electrochemical device, characterized in that The electrochemical device comprises the positive electrode sheet according to claim 25.