Composite electrode coating with reversible protection function and preparation method and application thereof

Abstract

The application provides a composite electrode coating with reversible protection function and a preparation method and application thereof, and belongs to the technical field of secondary battery composite electrodes. The application uses a high-molecular polymer A with a melt index less than 0.5 g / 10 min and a high-molecular polymer B with a melting point of 70-170 DEG C as a high-molecular matrix, and a conductive agent with a length-diameter ratio of 2-10000 to prepare the composite electrode coating with reversible protection function. The composite electrode coating has low resistivity at room temperature, suitable resistance change temperature, and large resistance increase ratio, can quickly close the electrochemical reaction of a lithium ion battery at high temperature, prevent thermal runaway, and improve the safety performance of the lithium ion battery. The lithium ion battery composite electrode based on the composite electrode coating has the advantages of stable characteristics and good room temperature electrochemical performance, and the lithium ion battery composite electrode has high compatibility with the production process of conventional lithium ion batteries, and has good application prospect.

Description

Technical Field

[0001] This invention relates to the field of composite electrode technology for secondary batteries, specifically to a composite electrode coating with reversible protection function, its preparation method, and its application. Background Technology

[0002] Although lithium-ion batteries are widely used in electric vehicles, energy storage power stations, and mobile electronic devices, safety issues remain a significant technological bottleneck restricting their large-scale application. Thermal runaway is one of the main causes of unsafe behavior in lithium-ion batteries.

[0003] Establishing self-excited thermal protection technology within the battery is an effective method to suppress thermal runaway. Currently developed technologies such as positive temperature coefficient (PTC) electrodes, thermally shut-off separators, and thermally polymerized additives can achieve a certain degree of thermal protection, but none possess reversible protection functionality. These technologies, lacking reversible protection, are incompatible with manufacturing processes and cannot be widely applied; furthermore, a single protection event sacrifices all performance, increasing operating costs. From a working mechanism perspective, technologies like thermally shut-off separators and thermally polymerized additives cannot achieve reversible protection. From an application perspective, developing PTC electrodes with reversible protection functionality is more advantageous.

[0004] The main reason why polymer substrate / conductive filler type PTC electrodes currently lack reversible functionality is the lack of interaction forces between the polymer substrate and the conductive filler, which prevents the conductive filler from reforming a good conductive network as the polymer substrate shrinks. Therefore, this invention develops a composite electrode coating with low room temperature resistivity, high resistance-to-weight ratio, and reversible protection function for thermal safety protection of lithium-ion batteries. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a composite electrode coating with reversible protection function, its preparation method, and its application. The composite electrode coating has low room temperature resistivity, suitable resistance switching temperature, high resistance-to-resistivity ratio, and a high number of reversible thermal response cycles, making it highly suitable for thermal safety protection of lithium-ion batteries.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a composite electrode coating with reversible protection function, wherein a polymer matrix and a conductive agent are mixed uniformly to obtain a composite electrode coating with reversible protection function.

[0008] The polymer matrix includes polymer A and polymer B; wherein, polymer A has a melt index of less than 0.5 g / 10 min, and polymer B has a melting point of 70~170 °C.

[0009] The aspect ratio of the conductive agent is 2 to 10000.

[0010] To address the issue that existing self-heating protection technologies lack reversible protection, this invention employs a specific polymer matrix (polymer A with a melt index less than 0.5 g / 10 min and polymer B with a melting point of 70~170 ℃) and a specific conductive agent (aspect ratio of 2~10000) to prepare a composite electrode coating with reversible protection. This composite electrode coating exhibits a large resistance-to-lift ratio, enabling rapid thermal safety protection of the battery. In the composite electrode coating of this invention, a specific conductive agent can be uniformly dispersed in a specific polymer matrix. When the temperature is below the transition temperature (below 60 °C), the conductive agents come into contact with each other to form a conductive network. Its resistivity is low and it can be regarded as a conductor, and the electrochemical reaction of the composite electrode proceeds normally. When the temperature is above the transition temperature (above 120 °C), the polymer matrix expands within a certain range, causing the conductive agents to temporarily move. The spacing between the conductive agents increases, the conductive network is destroyed, and the resistivity of the coating rises sharply. It can be regarded as an insulator, and the composite electrode loses its electrochemical activity, thereby suppressing the occurrence of thermal runaway. When the temperature drops from the high temperature back to below the transition temperature, the polymer matrix shrinks. Thanks to the interaction between the polymer matrix and the conductive agent, the conductive network is reconstructed, and the resistivity of the coating will return to the initial low level, becoming a conductor again. The electrochemical performance of the composite electrode can be restored to its initial state.

[0011] Furthermore, the mass ratio of polymer A to polymer B is 1:99 to 50:50.

[0012] Furthermore, the polymer A includes, but is not limited to, at least one of block copolymer polypropylene, random copolymer polypropylene, ultra-high molecular weight polyethylene, cross-linked polyethylene, and polyvinyl chloride; the polymer B includes, but is not limited to, at least one of polymethyl methacrylate, thermoplastic polyurethane rubber, low molecular weight polyethylene, polyethylene oxide, medium density polyethylene, polymethyl methacrylate, polypropylene, and polyvinyl alcohol.

[0013] Furthermore, the conductive agent includes, but is not limited to, at least one of the following: short rod-shaped carbon fibers, nickel-plated carbon fibers, carbon nanotubes, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene nanosheets, mesophase carbon microspheres, nickel nanoparticles, silver nanoparticles, silver sulfide powder, and tin powder.

[0014] Furthermore, the PTC effect of the composite electrode coating has a resistance ratio greater than or equal to 3.

[0015] Furthermore, the mass of the polymer matrix is ​​65% to 99% of the total mass of the composite electrode coating.

[0016] Furthermore, the mass of the polymer matrix is ​​80% to 97.5% of the total mass of the composite electrode coating.

[0017] Furthermore, the mass of the conductive agent is 1% to 35% of the total mass of the composite electrode coating.

[0018] Furthermore, the mass of the conductive agent is 2.5% to 20% of the total mass of the composite electrode coating.

[0019] Furthermore, the composite electrode coating has a PTC effect in a direction perpendicular to the electrode plane.

[0020] Furthermore, the composite electrode coating exhibits a reversible thermal response number greater than or equal to 2 times.

[0021] Furthermore, the composite electrode coating exhibits a reversible thermal response of at least 5 times.

[0022] Furthermore, the PTC effect resistance switching temperature of the composite electrode coating is 60 ℃ to 120 ℃. Typically, the PTC effect resistance switching temperature of the composite electrode coating is close to the melting point of the polymer matrix. This invention utilizes one or more of the following polymer matrixes: block copolymer polypropylene, random copolymer polypropylene, ultra-high molecular weight polyethylene, cross-linked polyethylene, and polyvinyl chloride with a melt index less than 0.5 g / 10 min; and one or more of the following polymer matrixes: polymethyl methacrylate, thermoplastic polyurethane rubber, low molecular weight polyethylene, polyethylene oxide, medium density polyethylene, polymethyl methacrylate, polypropylene, and polyvinyl alcohol with a melting point of 70 to 170 ℃. By combining these two in a specific ratio, the resistance switching temperature can be controlled within the range of 60 ℃ to 120 ℃.

[0023] Furthermore, the PTC effect resistance switching temperature of the composite electrode coating is 80 ℃~110 ℃.

[0024] Secondly, the present invention provides the application of the composite electrode coating with reversible protection function in the composite electrode of lithium-ion batteries.

[0025] Thirdly, the present invention provides a lithium-ion battery composite electrode, comprising the composite electrode coating with reversible protection function, a current collector, and an active material layer.

[0026] Furthermore, the thickness of the composite electrode coating accounts for 0.1% to 20% of the total thickness of the composite electrode.

[0027] Furthermore, the thickness of the composite electrode coating accounts for 0.1% to 10% of the total thickness of the composite electrode.

[0028] Furthermore, the current collector is aluminum foil or copper foil, i.e., a conventional positive or negative current collector for lithium-ion batteries.

[0029] Furthermore, the active material layer comprises the following components by mass percentage: 90-97% active material, 0.5-5% binder, and 0.5-5% conductive carbon.

[0030] Furthermore, the active material is lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium manganese oxide (LiMnO2), or lithium nickel cobalt aluminum ternary composite material (LiNi). 1-x-y Co x Al y O2), lithium nickel manganese cobalt ternary composite material (LiNi) x Mn y Co z One of O2, graphite, or MCMB, which are conventional positive or negative electrode materials for lithium-ion batteries.

[0031] Fourthly, the present invention provides a method for preparing the lithium-ion battery composite electrode, comprising the following steps:

[0032] S1: The conductive agent is blended with the polymer matrix by solution method or melt method to obtain a polymer matrix / conductive agent complex;

[0033] S2: The polymer matrix / conductive agent composite is uniformly coated onto the current collector by solution coating or hot pressing, and the current collector-coating composite is obtained after drying.

[0034] S3: A layer of active material slurry is coated on the current collector-coating composite, and after drying, a lithium-ion battery composite electrode is obtained.

[0035] Furthermore, during the blending process using the aforementioned melt method, the temperature is raised to 10°C to 50°C above the melting point of the polymer matrix.

[0036] Furthermore, when using the solution method for blending, stirring is employed to ensure that the polymer matrix and the conductive agent are mixed evenly.

[0037] Furthermore, when the solution method is used for blending, the polymer matrix / conductive agent composite is coated onto the current collector using a solution coating method; when the melt method is used for blending, the polymer matrix / conductive agent composite is hot-pressed onto the current collector using a hot-pressing method.

[0038] Compared with the prior art, the advantages of the present invention are:

[0039] (1) The composite electrode coating provided by the present invention has low resistivity at room temperature, suitable resistance switching temperature, high resistance ratio, and many reversible thermal response times. It can shut down the electrochemical reaction of lithium-ion battery at a set temperature, prevent thermal runaway, and improve the safety performance of lithium-ion battery.

[0040] (2) The lithium-ion battery composite electrode based on the composite electrode coating has the advantages of stable characteristics and good electrochemical performance at room temperature. At the same time, the lithium-ion battery composite electrode is highly compatible with the production process of conventional lithium-ion batteries and has good application prospects. Attached Figure Description

[0041] Figure 1 , Figure 2 These are all schematic diagrams of the composite electrode coating structure with reversible protection function of the present invention. Detailed Implementation

[0042] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In a first aspect, the present invention provides a composite electrode coating with reversible protection function, wherein a polymer matrix and a conductive agent are mixed uniformly to obtain a composite electrode coating with reversible protection function.

[0044] The polymer matrix includes polymer A and polymer B; wherein, polymer A has a melt index of less than 0.5 g / 10 min, and polymer B has a melting point of 70~170 °C.

[0045] The aspect ratio of the conductive agent is 2 to 10000.

[0046] In some examples, the mass ratio of polymer A to polymer B is 1:99 to 50:50.

[0047] In some examples, the polymer A includes, but is not limited to, at least one of block copolymer polypropylene, random copolymer polypropylene, ultra-high molecular weight polyethylene, cross-linked polyethylene, and polyvinyl chloride; the polymer B includes, but is not limited to, at least one of polymethyl methacrylate, thermoplastic polyurethane rubber, low molecular weight polyethylene, polyethylene oxide, medium density polyethylene, polymethyl methacrylate, polypropylene, and polyvinyl alcohol.

[0048] In some examples, the conductive agent includes, but is not limited to, at least one of short rod-shaped carbon fibers, nickel-plated carbon fibers, carbon nanotubes, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene nanosheets, mesophase carbon microspheres, nickel nanoparticles, silver nanoparticles, silver sulfide powder, and tin powder.

[0049] In some examples, the rise-to-resistance ratio of the PTC effect of the composite electrode coating is greater than or equal to 3.

[0050] In some examples, the mass of the polymer matrix is ​​65% to 99% of the total mass of the composite electrode coating.

[0051] In some examples, the mass of the conductive agent is 1% to 35% of the total mass of the composite electrode coating.

[0052] In some examples, the PTC effect resistive switching temperature of the composite electrode coating is 60 ℃ to 120 ℃.

[0053] Secondly, the present invention provides the application of the composite electrode coating with reversible protection function in the composite electrode of lithium-ion batteries.

[0054] Thirdly, the present invention provides a lithium-ion battery composite electrode, comprising the composite electrode coating with reversible protection function, a current collector, and an active material layer.

[0055] In some examples, the thickness of the composite electrode coating accounts for 0.1% to 20% of the total thickness of the composite electrode.

[0056] In some examples, the current collector is aluminum foil or copper foil, i.e., the current collector of a conventional lithium-ion battery positive or negative electrode.

[0057] In some examples, the active material layer comprises the following components by mass percentage: 90-97% active material, 0.5-5% binder, and 0.5-5% conductive carbon.

[0058] In some examples, the active material is lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium manganese oxide (LiMnO2), or lithium nickel cobalt aluminum ternary composite material (LiNi). 1-x-y Co x Al y O2), lithium nickel manganese cobalt ternary composite material (LiNi) x Mn y Co z One of O2, graphite, or MCMB, which are conventional positive or negative electrode materials for lithium-ion batteries.

[0059] The method for preparing the lithium-ion battery composite electrode includes the following steps:

[0060] S1: The conductive agent is blended with the polymer matrix by solution method or melt method to obtain a polymer matrix / conductive agent complex;

[0061] S2: The polymer matrix / conductive agent composite is uniformly coated onto the current collector by solution coating or hot pressing, and the current collector-coating composite is obtained after drying.

[0062] S3: A layer of active material slurry is coated on the current collector-coating composite, and after drying, a lithium-ion battery composite electrode is obtained.

[0063] Example 1

[0064] A composite electrode (positive electrode) for lithium-ion batteries

[0065] (1) Preparation of polymer matrix / conductive agent complex:

[0066] By mass fraction, 48.5% polyvinyl chloride (melt index 0.3 g / 10 min), 48.5% polymethyl methacrylate (melting point 125 ℃), and 3% multi-walled carbon nanotubes (aspect ratio 2000) were added to N,N-dimethylformamide (DMF) and mixed to obtain a uniformly dispersed slurry.

[0067] (2) Preparation of the positive electrode:

[0068] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0069] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0070] Example 2

[0071] A composite electrode (positive electrode) for lithium-ion batteries

[0072] (1) Preparation of polymer matrix / conductive agent complex:

[0073] By mass fraction, 24% ultra-high molecular weight polyethylene (melt index of 0.01 g / 10 min), 56% medium density polyethylene (melting point of 126 ℃), and 20% graphene nanosheets (aspect ratio of 1200) were added to xylene and mixed, while heating to 130 ℃ and stirring to obtain a uniformly dispersed slurry.

[0074] (2) Preparation of the positive electrode:

[0075] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0076] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0077] Example 3

[0078] A composite electrode (positive electrode) for lithium-ion batteries

[0079] (1) Preparation of polymer matrix / conductive agent complex:

[0080] By mass fraction, 24% polyvinyl chloride (melt index 0.3 g / 10 min), 56% polypropylene (melting point 162 ℃), and 20% single-walled carbon nanotubes (aspect ratio 1500) were added to an internal mixer with parameters set at 180 ℃ and 100 rpm. After uniform mixing, the mixture was granulated. The resulting polymer matrix / conductive agent composite particles were then hot-pressed with parameters set at 180 ℃ and 20 MPa to obtain a uniform polymer matrix / conductive agent composite film with a thickness of 15 μm.

[0081] (2) Preparation of the positive electrode:

[0082] The polymer matrix / conductive agent composite film obtained in step (1) was hot-pressed onto both sides of the 16 μm positive current collector Al foil using a hot-pressing method. The hot-pressing parameters were set to 180 ℃ and 2.5 MPa to obtain the current collector-coating composite, wherein the coating thickness was 15 μm.

[0083] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to the solvent N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0084] Example 4

[0085] A composite electrode (positive electrode) for lithium-ion batteries

[0086] (1) Preparation of polymer matrix / conductive agent complex:

[0087] By mass fraction, 48.5% polyvinyl chloride (melt index 0.3 g / 10 min), 48.5% polymethacrylic acid (melting point 125 ℃), and 3% multi-walled carbon nanotubes (aspect ratio 2000) were added to N,N-dimethylformamide (DMF) and mixed to obtain a uniformly dispersed slurry.

[0088] (2) Preparation of the positive electrode:

[0089] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0090] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0091] Example 5

[0092] A composite electrode (positive electrode) for lithium-ion batteries

[0093] (1) Preparation of polymer matrix / conductive agent complex:

[0094] By mass fraction, 42% polyvinyl chloride (melt index 0.3 g / 10 min), 42% polymethyl methacrylate (melting point 125 ℃), and 18% short rod carbon fibers (length-to-diameter ratio 10) were added to N,N-dimethylformamide (DMF) and mixed to obtain a uniformly dispersed slurry.

[0095] (2) Preparation of the positive electrode:

[0096] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0097] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0098] Example 6

[0099] A composite electrode (positive electrode) for lithium-ion batteries

[0100] (1) Preparation of polymer matrix / conductive agent complex:

[0101] By mass fraction, 42% ultra-high molecular weight polyethylene (melt index of 0.01 g / 10 min), 42% medium density polyethylene (melting point of 126 ℃), and 18% short rod carbon fibers (length-to-diameter ratio of 10) were added to xylene and mixed while heating to 130 ℃ and stirring to obtain a uniformly dispersed slurry.

[0102] (2) Preparation of the positive electrode:

[0103] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0104] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0105] Example 7

[0106] A composite electrode (positive electrode) for lithium-ion batteries

[0107] (1) Preparation of polymer matrix / conductive agent complex:

[0108] By mass fraction, 24% ultra-high molecular weight polyethylene (melt index of 0.01 g / 10 min), 56% medium density polyethylene (melting point of 126 ℃), and 20% carbon nanofibers (length-to-diameter ratio of 500) were added to xylene and mixed while being heated to 130 ℃ and stirred to obtain a uniformly dispersed slurry.

[0109] (2) Preparation of the positive electrode:

[0110] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0111] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0112] Example 8

[0113] A composite electrode (positive electrode) for lithium-ion batteries

[0114] (1) Preparation of polymer matrix / conductive agent complex:

[0115] By mass fraction, 24% ultra-high molecular weight polyethylene (melt index of 0.01 g / 10 min), 56% medium density polyethylene (melting point of 126 ℃), and 20% mesophase carbon microspheres (aspect ratio of 2) were added to xylene and mixed, while heating to 130 ℃ and stirring to obtain a uniformly dispersed slurry.

[0116] (2) Preparation of the positive electrode:

[0117] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0118] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0119] Example 9

[0120] A composite electrode (positive electrode) for lithium-ion batteries

[0121] (1) Preparation of polymer matrix / conductive agent complex:

[0122] By mass fraction, 24% ultra-high molecular weight polyethylene (melt index of 0.01 g / 10 min), 56% thermoplastic polyurethane rubber (melting point of 80 ℃), and 20% short rod carbon fiber (length-to-diameter ratio of 10) were added to xylene and mixed while heating to 130 ℃ and stirring to obtain a uniformly dispersed slurry.

[0123] (2) Preparation of the positive electrode:

[0124] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0125] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0126] Example 10

[0127] A composite electrode (positive electrode) for lithium-ion batteries

[0128] (1) Preparation of polymer matrix / conductive agent complex:

[0129] By mass fraction, 24% ultra-high molecular weight polyethylene (melt index of 0.01 g / 10 min), 56% low molecular weight polyethylene (melting point of 113 ℃), and 20% short rod carbon fibers (length-to-diameter ratio of 10) were added to xylene and mixed while heating to 130 ℃ and stirring to obtain a uniformly dispersed slurry.

[0130] (2) Preparation of the positive electrode:

[0131] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0132] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0133] Example 11

[0134] A composite electrode (negative electrode) for lithium-ion batteries

[0135] (1) Preparation of polymer matrix / conductive agent complex:

[0136] By mass fraction, 48.5% polyvinyl chloride (melt index 0.3 g / 10 min), 48.5% polymethyl methacrylate (melting point 125 ℃), and 3% multi-walled carbon nanotubes (aspect ratio 2000) were added to N,N-dimethylformamide (DMF) and mixed to obtain a uniformly dispersed slurry.

[0137] (2) Preparation of negative electrode:

[0138] The slurry prepared in step (1) was uniformly coated on both sides of the negative electrode current collector Cu foil with a thickness of 12 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0139] By mass fraction, 97.7% of the negative electrode active material graphite, 1.3% of the thickener CMC, and 1.0% of the binder SBR were added to the solvent deionized water and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the negative electrode tabs were welded to obtain the negative electrode sheet.

[0140] Comparative Example 1

[0141] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto both sides of a 16 μm thick Al foil positive electrode current collector using a roller coating method. After drying, the above electrode sheet was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0142] Comparative Example 2

[0143] (1) 97% polymethyl methacrylate (melting point 125 °C) and 3% multi-walled carbon nanotubes (length-to-diameter ratio 2000) were added to N,N-dimethylformamide (DMF) by mass fraction and mixed to obtain a uniformly dispersed slurry.

[0144] (2) Preparation of the positive electrode:

[0145] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0146] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0147] Comparative Example 3

[0148] (1) 97% polyvinyl chloride (melt index of 0.3 g / 10 min) and 3% multi-walled carbon nanotubes (length-to-diameter ratio of 2000) were added to N,N-dimethylformamide (DMF) and mixed to obtain a uniformly dispersed slurry.

[0149] (2) Preparation of the positive electrode:

[0150] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0151] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0152] Comparative Example 4

[0153] (1) Preparation of polymer matrix / conductive agent complex:

[0154] By mass fraction, 48.5% polyvinyl chloride (melt index 0.3 g / 10 min), 48.5% polymethyl methacrylate (melting point 125 ℃), and 3% mesophase carbon microspheres (aspect ratio 1) were added to N,N-dimethylformamide (DMF) and mixed to obtain a uniformly dispersed slurry.

[0155] (2) Preparation of the positive electrode:

[0156] The slurry prepared in step (1) was uniformly coated on both sides of the positive electrode current collector Al foil with a thickness of 16 μm using a solution coating method. After drying, a current collector-coating composite was obtained, wherein the coating thickness was 10 μm.

[0157] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto the current collector-coating composite by roller coating. After drying, the electrode was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0158] Assemble lithium-ion secondary batteries

[0159] The positive electrode sheets prepared in Examples 1-10 and Comparative Examples 1-4 were assembled into lithium-ion secondary batteries according to the following method:

[0160] By mass fraction, 97.7% of the negative electrode active material graphite, 1.3% of the thickener CMC, and 1.0% of the binder SBR were added to the solvent deionized water and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was coated onto both sides of a 12 μm thick negative electrode current collector Cu foil using a roller coating method. After drying, the above electrode sheet was cold-pressed, trimmed, cut, slit, and welded with negative electrode tabs to obtain the negative electrode sheet.

[0161] 1.15M LiPF6 was dissolved in a mixed solution of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and fluorobenzene (volume ratio of 30:30:35:5) to serve as the electrolyte.

[0162] Using polyethylene as a separator, the positive electrode sheets prepared in Examples 1-10 and Comparative Examples 1-4 were assembled with the above-mentioned negative electrode sheets and electrolyte to form a lithium-ion secondary battery. The battery size was 50 mm (length) × 42 mm (width) × 34 mm (height), and the rated capacity of the battery was 3410 mAh.

[0163] The negative electrode sheet prepared in Example 11 was assembled into a lithium-ion secondary battery according to the following steps:

[0164] By mass fraction, 97% of the positive electrode active material LiCoO2, 1.5% of the conductive agent Super-P, and 1.5% of the binder PVDF were added to the solvent N-methylpyrrolidone (NMP) and mixed. After planetary ball milling, a uniformly dispersed black slurry was obtained. This black slurry was uniformly coated onto both sides of a 16 μm thick Al foil positive electrode current collector using a roller coating method. After drying, the above electrode sheet was cold-pressed, trimmed, cut, slit, and the positive electrode tabs were welded to obtain the positive electrode sheet.

[0165] 1.15M LiPF6 was dissolved in a mixed solution of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and fluorobenzene (volume ratio of 30:30:35:5) to serve as the electrolyte.

[0166] Using polyethylene as a separator, the negative electrode sheet prepared in Example 11 was assembled with the above-mentioned positive electrode sheet and electrolyte to form a lithium-ion secondary battery. The battery dimensions were 50 mm (length) × 42 mm (width) × 34 mm (height), and the rated capacity of the battery was 3410 mAh.

[0167] Performance testing

[0168] 1. Performance testing of lithium-ion secondary batteries

[0169] (1) Safety performance test of lithium-ion secondary batteries through nail penetration

[0170] In the nail penetration test, the nail diameter D = 3 mm and the penetration speed V = 80 mm / s.

[0171] The pass rate of lithium-ion secondary batteries was calculated based on the criteria of not igniting, burning, or exploding. The test results are shown in Table 1.

[0172] (2) Thermal shock safety performance test of lithium-ion secondary batteries

[0173] In the thermal shock test, the battery was charged to 4.4 V at a constant current rate of 0.5C at 25 ℃, and then charged to 0.05 C at a constant voltage of 4.4 V. The battery was then placed in a constant temperature chamber, and the temperature chamber was heated to 150 ℃ at a heating rate of 5 ℃ / min and maintained at 150 ℃ for 1 hour.

[0174] The pass rate of lithium-ion secondary batteries was calculated based on the criteria of not igniting, burning, or exploding. The test results are shown in Table 1.

[0175] (3) Thermal response protection reversibility test of lithium-ion secondary batteries

[0176] In the thermal response protection reversibility test, the battery was charged to 4.4 V at a constant current of 0.5C at 25 ℃, and then charged to 0.05 C at a constant voltage of 4.4 V. The battery was then placed in a constant temperature chamber, and the temperature chamber was heated to 120 ℃ at a heating rate of 5 ℃ / min and maintained at 120 ℃ for 1 hour. After that, the battery was removed and returned to 25 ℃, and discharged to 3.0 V at a constant current of 0.5C.

[0177] The pass rate of lithium-ion secondary batteries was calculated based on the criterion that the constant current discharge specific capacity reached more than 80% of the charge specific capacity. The test results are shown in Table 1.

[0178] Table 1: Performance Test Results of Lithium-ion Secondary Batteries

[0179]

[0180] The data in Table 1 for Examples 1 and 11 show that the composite electrode coating with reversible protection function of the present invention can improve the safety performance of lithium-ion batteries whether it is applied to the composite positive electrode or the composite negative electrode of lithium-ion batteries. However, the reversibility on the negative electrode side is slightly worse than that on the positive electrode side, which may be related to the destruction of the SEI layer on the surface of the negative electrode at high temperature.

[0181] The data in Examples 1, 4, 5, and 6 in Table 1 show that by selecting different polymers, the resistivity switching temperature and the reversibility of the PTC effect of the composite electrode coating with reversible protection function can be adjusted, thereby improving the safety performance of lithium-ion secondary batteries.

[0182] The data in Table 1 for Examples 2, 7, and 8 and Comparative Example 4 show that by selecting conductive carbon with a larger aspect ratio, the resistance ratio of the polymer matrix / conductive agent composite electrode coating can be improved, making the thermal shut-off performance of the lithium-ion battery composite electrode more reliable, thereby improving the safety of lithium-ion secondary batteries.

[0183] As can be seen from the data of Examples 3, 9 and 10 in Table 1, by replacing polypropylene with thermoplastic polyurethane rubber or low molecular weight polyethylene with a lower melting point, the resistivity switching temperature of the polymer matrix / conductive agent composite electrode coating is in the range of 80 ℃ to 110 ℃, which can shut down the electrode reaction before thermal runaway begins, thereby improving the safety of lithium-ion secondary batteries.

[0184] The ordinary lithium-ion secondary battery in Comparative Example 1 does not have a polymer matrix / conductive agent composite electrode coating, and therefore has the worst safety performance.

[0185] In Comparative Example 2, the polymer matrix of the composite electrode coating is made of only Class B polymers with a melting point of 70~170 ℃, which has thermal protection and good safety performance, but does not have reversibility.

[0186] In Comparative Example 3, the polymer matrix of the composite electrode coating only uses Class A polymers with a melt index of less than 0.5 g / 10min. Since this type of polymer hardly expands near its melting point, the material has low PTC strength, cannot achieve thermal shutdown, has poor safety performance, and is not reversible.

[0187] In summary, this invention uses polymer A with a melt index less than 0.5 g / 10 min and polymer B with a melting point of 70-170 °C as polymer matrices, and prepares a composite electrode coating with reversible protection function using a conductive agent with an aspect ratio of 2-10000. This composite electrode coating has low resistivity at room temperature, a suitable resistance switching temperature, and a large resistance-to-resistance ratio, enabling it to rapidly shut down the electrochemical reaction of lithium-ion batteries at high temperatures, preventing thermal runaway and improving the safety performance of lithium-ion batteries. The lithium-ion battery composite electrode based on this composite electrode coating has the advantages of stable characteristics and good electrochemical performance at room temperature. Furthermore, the lithium-ion battery composite electrode has high compatibility with conventional lithium-ion battery manufacturing processes and has good application prospects.

[0188] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A composite electrode coating with reversible protection function, characterized in that, A composite electrode coating with reversible protective function is obtained by uniformly mixing a polymer matrix with a conductive agent. The polymer matrix includes polymer A and polymer B; wherein, polymer A has a melt index of less than 0.5 g / 10 min, and polymer B has a melting point of 70~170 °C. The aspect ratio of the conductive agent is 2 to 10000; The polymer A includes at least one of block copolymer polypropylene, random copolymer polypropylene, ultra-high molecular weight polyethylene, cross-linked polyethylene, and polyvinyl chloride; the polymer B includes at least one of polymethyl methacrylate, thermoplastic polyurethane rubber, low molecular weight polyethylene, polyethylene oxide, medium density polyethylene, polymethyl methacrylate, polypropylene, and polyvinyl alcohol. The conductive agent includes at least one of the following: short rod-shaped carbon fiber, nickel-plated carbon fiber, carbon nanotubes, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene nanosheets, mesophase carbon microspheres, nano-nickel particles, nano-silver particles, silver sulfide powder, and tin powder.

2. The composite electrode coating with reversible protection function according to claim 1, characterized in that, The mass of the polymer matrix is ​​65% to 99% of the total mass of the composite electrode coating; the mass of the conductive agent is 1% to 35% of the total mass of the composite electrode coating.

3. The composite electrode coating with reversible protection function according to claim 1, characterized in that, The PTC effect resistance switching temperature of the composite electrode coating is 60 ℃~120 ℃.

4. The composite electrode coating with reversible protection function according to claim 1, characterized in that, The PTC effect of the composite electrode coating has a resistance ratio greater than or equal to 3.

5. The application of the composite electrode coating with reversible protection function as described in any one of claims 1 to 4 in the composite electrode of a lithium-ion battery.

6. A lithium-ion battery composite electrode, characterized in that, It includes the composite electrode coating, current collector, and active material layer with reversible protection function as described in any one of claims 1 to 4.

7. A lithium-ion battery composite electrode according to claim 6, characterized in that, The thickness of the composite electrode coating accounts for 0.1% to 20% of the total thickness of the composite electrode.

8. The method for preparing a lithium-ion battery composite electrode as described in claim 6, characterized in that, Includes the following steps: S1: The conductive agent is blended with the polymer matrix by solution method or melt method to obtain a polymer matrix / conductive agent complex; S2: The polymer matrix / conductive agent composite is uniformly coated onto the current collector by solution coating or hot pressing, and the current collector-coating composite is obtained after drying. S3: A layer of active material slurry is coated on the current collector-coating composite, and after drying, a lithium-ion battery composite electrode is obtained.

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