CN109560285B - Positive pole piece and secondary battery using same - Google Patents
Positive pole piece and secondary battery using same Download PDFInfo
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- CN109560285B CN109560285B CN201710889071.5A CN201710889071A CN109560285B CN 109560285 B CN109560285 B CN 109560285B CN 201710889071 A CN201710889071 A CN 201710889071A CN 109560285 B CN109560285 B CN 109560285B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application relates to a positive pole piece, wherein an extension layer containing a specific polymer and a conductive agent is arranged between a positive current collector and a positive active material layer. The extension layer comprises a polymer and a conductive agent, and the ratio of the extension rate of the extension layer to the extension rate of the positive current collector is (2-10): 1. When the electric core is abused, the extension layer can prevent the electric core from generating high-power short circuit, and the capacity of the battery can not be reduced.
Description
Technical Field
The application relates to the field of secondary batteries, in particular to a positive pole piece and a secondary battery using the positive pole piece.
Background
Secondary batteries, particularly lithium ion batteries, have characteristics of small size, high energy, no pollution, and the like, and have been widely used in mobile devices, high-power devices (such as electric vehicles), and energy storage power stations. However, how to ensure the safety of the lithium ion battery has become a major research topic of various large lithium battery manufacturers.
When a lithium ion battery collides or the battery is invaded by foreign matter, the internal short circuit of the battery is caused. At present, for the lithium ion battery, the most serious short circuit mode is that the positive current collector and the negative electrode are in short circuit, and the short circuit power is extremely high in this mode, so that the battery is easy to release heat violently to cause out of control.
Current methods for preventing thermal runaway of batteries have focused primarily on modifying the mechanical structure of the batteries. These methods, while improving the safety of the battery to some extent, can also have negative effects, such as affecting the electrochemical performance of the battery, reducing the energy density of the battery, or increasing other safety risks.
At present, the technical means for protecting the anode at home and abroad mainly comprise: coating a coating on the surface of the positive current collector to prevent the positive material from falling off and exposing the aluminum foil; or coating an insulating coating on the surfaces of the positive and negative pole pieces to prevent direct short circuit between the positive and negative poles. However, from the mechanism of short circuit in the battery cell, the most critical point for preventing the internal short circuit of the lithium ion battery from being out of control is still to prevent the positive current collector (aluminum foil) from being exposed, and the method can only prevent the surface where the aluminum foil is bonded with the positive electrode from being exposed, but cannot prevent the cross section from being exposed when the aluminum foil is broken, so that the short circuit between the positive current collector and the negative electrode cannot be completely avoided.
In view of this, the present application is specifically made.
Disclosure of Invention
In order to solve the above problems, the present applicant has made extensive studies and found that: by using an extended layer containing a specific polymer and a conductive agent on the surface of the positive current collector, the positive current collector and the negative electrode can be prevented from being short-circuited, the safety performance of the battery can be improved, and the capacity of the battery can not be reduced.
The application aims at providing a positive pole piece, which comprises a positive pole current collector and a positive pole active substance layer, wherein an extension layer is further arranged between the positive pole current collector and the positive pole active substance layer;
the spreader layer includes a polymer and a conductive agent;
the ratio of the extension rate of the extension layer to the extension rate of the positive current collector is (2-10): 1.
Preferably, the ratio of the conductivity of the extension layer to the conductivity of the positive electrode current collector is (0.1-2.0): 1.
Preferably, the polymer is a graft-modified copolymer comprising a polymer matrix and graft-modified chains.
Preferably, the polymer matrix is selected from at least one of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyacrylonitrile and polyester.
Preferably, the graft modification chain contains a flexible group, and the flexible group is selected from at least one of a siloxane group, a long-chain alkyl group, a long-chain alkenyl group and an ether group. Preferably, the long-chain alkyl is an alkyl with the carbon number not less than 8, and the long-chain alkenyl is an alkenyl with the carbon number not less than 8.
Preferably, the graft-modified chain is selected from at least one of a polysiloxane group, a long-chain alkenyl group, a long-chain ether group, and a substituted or unsubstituted long-chain alkyl group, wherein the substituent is a hydroxyl group. Preferably, the long-chain alkyl is an alkyl group with a carbon number not less than 8, the long-chain alkenyl is an alkenyl group with a carbon number not less than 8, and the long-chain ether is an ether group with a carbon number not less than 8.
Preferably, the polymer is selected from at least one of styrene butadiene rubber-g-octadecene, polyacrylic acid-g-dodecanol, polyvinylidene fluoride-g-octadecene, polyacrylonitrile-g-dodecanol and polyester-g-dodecanol.
Preferably, the thickness ratio of the extension layer to the current collector is (0.05-1): 1, preferably (0.1-1): 1.
Preferably, the conductive agent is selected from at least one of conductive graphite, carbon nanotubes and graphene.
Preferably, the weight ratio of the polymer to the conductive agent in the extension layer is (1-19): 1, preferably (3-10): 1.
The application also provides a secondary battery, which comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, wherein the positive pole piece is the positive pole piece provided by the application.
The technical scheme of the application has at least the following beneficial effects:
in the positive pole piece that this application provided, be provided with the extension layer that contains specific polymer and conducting agent between positive current collector and positive active material layer. When the electric core is abused, the extension layer can prevent the electric core from generating high-power short circuit, and the capacity of the battery can not be reduced.
Detailed Description
The present application is further illustrated with reference to specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.
The positive electrode sheet of the present application is described in detail below.
In order to achieve the above object, a first aspect of the embodiments of the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer, and an extension layer is further disposed between the positive electrode current collector and the positive electrode active material layer.
[ extended layer ]
The spreader layer of embodiments of the present application includes a polymer and a conductive agent. The polymer is used for providing high ductility and covering the positive current collector to prevent the positive current collector from being exposed when the pole piece is broken. Since the polymer is generally non-conductive, it is necessary to add a conductive agent into the ductile layer to make electrical connection between the ductile layer and the positive electrode current collector, and between the ductile layer and the positive electrode active material layer.
When the lithium ion battery is impacted, extruded or invaded by foreign matters from the outside, the positive and negative pole pieces and the isolating membrane in the battery are broken under the action of external force. The following short-circuit patterns occur in the fracture zone, respectively: the method comprises the steps of firstly, generating short circuit between a positive electrode active material layer and a negative electrode active material layer, secondly, generating short circuit between the positive electrode active material layer and a negative electrode current collector (copper foil), thirdly, generating short circuit between the positive electrode current collector (aluminum foil) and the negative electrode active material layer, and fourthly, generating short circuit between the positive electrode current collector (aluminum foil) and the negative electrode current collector (copper foil). In the lithium ion battery, the two short circuit modes are the most dangerous, and because the short circuit power of the two short circuit modes is high, a large amount of heat generation can be caused at a short circuit point, and the thermal runaway of a battery core is caused. This application has added the extension layer between the mass flow body of positive pole piece and active substance layer, can be when the pole piece fracture, the extension layer that has high ductility covers the anodal mass flow body, can effectively reduce the emergence probability of two kinds of short circuit modes to fundamentally stops the emergence of electric core internal heat out of control.
In order to ensure that the extension layer has high ductility, the ratio of the extension rate of the extension layer to the positive current collector is defined as (2-10): 1. The upper limits of the ratios are 10:1, 9:1, 8:1, 6:1, and the lower limits are 2:1, 3:1, 3.5:1, 4: 1. The ratio is too low, and the effective coverage of the extension layer on the anode current collector when the pole piece is broken cannot be realized. However, the ratio is too high, which means that the content of the polymer in the ductile layer is too high, which causes processing difficulty and reduces the energy density of the cell.
As an improvement of the extension layer, the ratio of the conductivity of the extension layer to the conductivity of the positive current collector is (0.1-2.0): 1. The upper limits of the ratios are 2.0:1, 1.5:1, 1:1, 0.5:1, and the lower limits are 0.1:1, 0.5:1, 1: 1. The ratio is too low, which can reduce the transmission efficiency of lithium ions and charges in the positive pole piece. Too high a ratio means that the content of the conductive agent in the extensible layer is too high, and accordingly the content of the polymer in the extensible layer is reduced, which adversely affects the extensibility.
As an improvement of the extension layer, the thickness ratio of the extension layer to the current collector is (0.05-1): 1, preferably (0.1-1): 1. The upper limits of the ratios are 1:1, 0.8:1, 0.5:1, 0.1:1, and the lower limits are 0.05:1, 0.1:1, 0.5: 1. The thickness of the extension layer is too small, the wrapping of the current collector is limited when the pole piece is broken, and short circuit can not be effectively prevented. The thickness of the extension layer is too large, which affects the transmission rate of lithium ions and charges in the positive pole piece and reduces the energy density of the battery cell.
As an improvement of the extension layer, the conductive agent is at least one selected from conductive graphite, carbon nano-tube and graphene.
As an improvement of the extension layer, the weight ratio of the polymer to the conductive agent in the extension layer is (1-19): 1, the upper limit of the ratio is 19:1, 15:1, 10:1, 5:1, and the lower limit of the ratio is 1:1, 2:1, 3:1, 4:1, preferably (3-10): 1. Too low of this ratio means that the content of polymer in the extensible layer is too low, which has a negative effect on the extensibility. Too high of this ratio may reduce the transmission efficiency of lithium ions and charges in the positive electrode sheet.
The extension layer can be obtained by mixing the polymer and the conductive agent, adding the solvent, uniformly stirring to obtain extension layer slurry, and then coating the extension layer slurry on the surface of the positive current collector. If an oily polymer is used, N-methylpyrrolidone may be used as the solvent, and if an aqueous polymer is used, deionized water may be used as the solvent.
The applicant has found that the polymer in the ductile layer, which is styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyacrylonitrile or polyester, has a certain ductility but cannot completely prevent thermal runaway. However, when the polymer contains a flexible group, the ductility can be further improved. The flexible group may be at least one selected from a siloxane bond, a long-chain alkyl group, a long-chain alkylene group, and an ether bond.
Further, when the polymer in the present application is a graft-modified copolymer, it has better ductility and safety properties when it is used in a battery. The graft modified copolymer can be obtained by connecting a graft modified chain on a polymer matrix, and the specific means comprises chemical grafting and graft polymerization initiated by plasma, high-energy radiation, ultraviolet light and the like.
As an improvement of the graft modified copolymer, the polymer matrix is selected from at least one of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyacrylonitrile and polyester. Wherein polyester mainly refers to polyethylene terephthalate (PET).
As an improvement of the graft modified copolymer, the graft modified chain contains a flexible group, and the flexible group is selected from at least one of a siloxy group, a long-chain alkyl group, a long-chain alkenyl group and an ether group. Preferably, the long-chain alkyl group is an alkyl group having not less than 8 carbon atoms, and the long-chain alkenyl group is an alkenyl group having not less than 8 carbon atoms.
As an improvement of the graft-modified copolymer, the graft-modified chain is selected from at least one of a polysiloxane group, a long-chain alkenyl group, a long-chain ether group, and a substituted or unsubstituted long-chain alkyl group, wherein the substituent is a hydroxyl group. Preferably, the long-chain alkyl group is an alkyl group having not less than 8 carbon atoms, the long-chain alkenyl group is an alkenyl group having not less than 8 carbon atoms, and the long-chain ether group is an ether group having not less than 8 carbon atoms. Further preferably, the long-chain alkyl group, the long-chain alkenyl group, and the long-chain ether group each contain a main chain having 8 to 30 carbon atoms.
The above graft copolymer can be obtained by copolymerizing a monomer for forming a polymer base and a graft-modifying monomer for forming a graft-modified chain. Wherein, the grafting modified monomer is selected from at least one of polysiloxane, long-chain alkane, long-chain alkene, long-chain enol and long-chain ether. Preferably, the long-chain alkane is an alkane having not less than 8 carbon atoms, the long-chain alkene is an alkene having not less than 8 carbon atoms, the long-chain enol is an enol having not less than 8 carbon atoms, and the long-chain ether is an ether having not less than 8 carbon atoms.
Further preferably, the long-chain alkane, the long-chain alkene, the long-chain enol, or the long-chain ether contains a main chain having 8 to 30 carbon atoms, that is, the long-chain alkane may be C8～C30The long-chain olefin may be C8～C30The long-chain alkenol of (A) may be C8～C30The enol or long-chain ether of (A) may be C8～C30An ether of (a).
In the above graft-modified monomers, the backbone of the polyoxosilane is Si-O-Si, which is similar in nature to quartz, except that it has pendant groups to which organic groups are attached. Utensil for cleaning buttockExamples of bodies include polydimethylsiloxane. Preferred polysiloxanes have the formula I, wherein R is1～R4Is hydrogen or alkyl with the carbon atom number more than or equal to 2, and x is an integer of 1000-10000.
The nomenclature of the graft polymers is generally adopted by customary nomenclature. To indicate the arrangement of the monomer units in the copolymer structure, the grafting is indicated by the letter "g" (gtaft). Such as: PS-g-PMMA. In general, the components preceding g represent the main chain and the components following g represent the branches. The above designations refer to graft copolymers having a polystyrene backbone and polymethyl methacrylate branches.
In the embodiment of the present application, the graft-modified copolymer may be selected from at least one of styrene-butadiene rubber-g-octadecene, polyacrylic acid-g-dodecanol, polyvinylidene fluoride-g-octadecene, polyacrylonitrile-g-dodecanol, and polyester-g-dodecanol.
In the above graft copolymer, styrene-butadiene rubber-g-octadecene and polyacrylic acid-g-dodecanol are water-soluble, and polyvinylidene fluoride-g-octadecene, polyacrylonitrile-g-dodecanol, polyester-g-dodecanol are oil-soluble.
The preparation method of the graft polymer is mainly divided into two methods:
the method comprises the following steps: the pre-polymerized polymer is activated chemically or physico-chemically to generate active center (expressed as free radical, positive or negative ion) on the main chain. Then, it initiates the polymerization of monomer M to form a graft copolymer, which is called a method of grafting branches to macromolecules.
The second method comprises the following steps: and adding the grafting monomer while initiating the polymerization of the main chain monomer, so that the main chain monomer and the grafting modified monomer M are polymerized simultaneously to form the grafting modified polymer.
Among them, if M itself has a polymerization functional group such as C ═ C or — OH and can cause a polymerization reaction as a graft-modified monomer, method two can be adopted. If M itself does not contain groups capable of participating in the polymerization reaction, method one is used, i.e.the active sites are generated on the polymer matrix and the polymerization of M is then initiated to form the graft copolymer.
For example, butadiene styrene rubber-g-octadecene can be obtained by taking butadiene and styrene containing double bond functional groups as main chain monomers, taking octadecene as a grafting monomer, utilizing double bonds and allyl groups contained in the main chain, and adding an initiator for polymerization reaction.
The polyacrylic acid-g-dodecanol can be prepared by taking acrylic acid containing active points as a main chain monomer and taking dodecenol as a grafting monomer in an aqueous solution through a graft copolymerization method.
The polyvinylidene fluoride-g-octadecene can be prepared by taking vinylidene fluoride containing active points as a main chain monomer, taking octadecene as a grafting monomer, adding water, an initiator, a dispersant and a chain transfer agent, and performing emulsion graft copolymerization.
The polyacrylonitrile-g-dodecanol can be prepared by taking acrylonitrile as a main chain monomer and dodecenol as a grafting monomer, adding water, an initiator, a dispersant and a chain transfer agent, and carrying out emulsion graft copolymerization.
The polyester-g-dodecanol can be prepared by taking ethylene terephthalate containing double bond functional groups as a main chain monomer, taking dodecenol as a grafting monomer, adding water, an initiator, a dispersant and a chain transfer agent, and carrying out emulsion graft copolymerization.
In the copolymer, the mass ratio of the main chain monomer to the grafting monomer can be (0.1-20): 1.
[ Positive electrode active material layer ]
The positive electrode active material in the embodiment of the present application is selected from at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, and a high nickel material.
Wherein the chemical formula of the high nickel material is LiaNixCoyMzO2Wherein M is at least one of Mn, Al, Zr, Ti, V, Mg, Fe and Mo, a is more than or equal to 0.95 and less than or equal to 1.2, x is more than or equal to 0.5, y is more than or equal to 0, z is more than or equal to 0, and x + y + z is 1. Commercially available nickel-rich materials include NCM622, NCA811, NCM 111.
As an improvement of the positive electrode active material layer, it further comprises a binder and a conductive agent.
Examples of the binder include at least one selected from the group consisting of polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, sodium carboxymethylcellulose, a water-based acrylic resin, an ethylene-vinyl acetate copolymer, styrene-butadiene rubber, fluorinated rubber, and polyurethane.
The conductive agent may be at least one selected from carbon materials, graphite, carbon black, graphene, and carbon nanotube conductive fibers. Commonly used conductive agents include Ketjen black (ultra fine conductive carbon black, particle size 30-40nm), SP (Super P, small particle conductive carbon black, particle size 30-40 μm), S-O (ultra fine graphite powder, particle size 3-4 μm), KS-6 (large particle graphite powder, particle size 6.5 μm), acetylene black, VGCF (vapor grown carbon fiber, particle size 3-20 μm). The optional conductive agent also includes metal powder, conductive whisker, conductive metal compound, conductive polymer, etc.
As an improvement of the positive electrode active material layer, in the positive electrode active material layer, the mass percentage of the positive electrode active material is 80-98%, the mass percentage of the binder is 1-10%, and the mass percentage of the conductive agent is 1-10%.
The secondary battery of the present application is explained in detail below.
A second aspect of the embodiments of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, where the positive electrode plate is the positive electrode plate provided in the embodiments of the present application.
In the secondary battery, the positive pole piece comprises a positive pole current collector, an extension layer and a positive pole active substance layer; the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer, and the electrolyte comprises an organic solvent and electrolyte salt dissolved in the organic solvent.
Further, the secondary battery of the embodiment of the present application is preferably a lithium ion battery, and the lithium ion battery may be a wound or stacked lithium ion battery.
When the secondary battery is a lithium ion battery, a conventional lithium ion battery preparation method can be adopted, and the method at least comprises the following steps:
coating extension layer slurry comprising a polymer and a conductive agent on the surface of a positive current collector to form an extension layer;
coating positive electrode slurry comprising a positive electrode active substance, a conductive agent and a binder on the surface of the extension layer, and drying to form a positive electrode active substance layer to obtain a positive electrode piece;
coating the negative electrode slurry comprising a negative electrode active substance, a binder and a thickening agent on the surface of a negative electrode current collector, and drying to form a negative electrode active substance layer to obtain a negative electrode plate;
and step four, sequentially stacking the positive pole piece, the isolating membrane and the negative pole piece, then winding or pressing to obtain a bare cell, then injecting electrolyte, and packaging to obtain the secondary battery.
[ negative electrode active material layer ]
In the anode active material layer of the embodiment of the present application, it includes an anode active material, a binder, and a thickener.
The negative electrode active material may be at least one metal selected from the group consisting of soft carbon, hard carbon, artificial graphite, natural graphite, silicon oxide, silicon-carbon composite, lithium titanate, and a metal capable of forming an alloy with lithium. Wherein the silicon oxide is SiOx，0.5<x<2. The silicon-carbon composite is selected from graphite-hard carbon mixed material, graphite-silicon material composite material and graphite-hard carbon-silicon material composite material.
Examples of the binder include at least one selected from the group consisting of polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, aqueous acrylic resin, ethylene-vinyl acetate copolymer, styrene-butadiene rubber, fluorinated rubber, and polyurethane.
As the thickener, a surfactant such as sodium carboxymethylcellulose (CMC) may be mentioned.
As an improvement of the negative electrode active material layer, in the negative electrode active material layer, the mass percentage content of the negative electrode active material is 93.5-98%, the mass percentage content of the binder is 1-5%, and the mass percentage content of the thickening agent is 0.5-1.5%.
[ isolating film ]
In the embodiment of the present application, the material of the isolation film is not particularly limited, and may be a polymer isolation film. The polymeric barrier film may be selected from one of polyethylene, polypropylene and ethylene-propylene copolymer.
[ electrolyte ]
In the embodiment of the present application, the electrolytic solution includes an organic solvent and an electrolyte salt dissolved in the organic solvent.
Further, the organic solvent in the embodiment of the present application may contain one or more of cyclic carbonate, linear carbonate, chain carboxylate, and sulfone organic solvents. The organic solvent which can be specifically selected from the following is not limited thereto: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, propyl formate, butyl formate, pentyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, pentyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, methyl butyrate, methyl valerate, methyl acrylate, sulfolane, dimethyl sulfone.
In the embodiment of the present application, when the secondary battery is a lithium ion battery, the electrolyte is a lithium salt selected from at least one of inorganic lithium salts and organic lithium salts.
Wherein the inorganic lithium salt is selected from lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium hexafluoroarsenate (LiAsF)6) Lithium perchlorate (LiClO)4) At least one of (1). The organic lithium salt may be selected from lithium bis (oxalato) borate (LiB (C)2O4)2Abbreviated as LiBOB), lithium bis (fluorosulfonyl) imide (LiFSI), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI).
The electrolyte of the embodiment of the application can also contain additives.
The additive may be one or more selected from fluorine-containing compounds, sulfur-containing compounds and unsaturated double bond-containing compounds. The following substances can be selected in particular and are not limited thereto: fluoroethylene carbonate, ethylene sulfite, propane sultone, N-methyl pyrrolidone, N-methyl formamide, N-methyl acetamide, acetonitrile, acrylonitrile, gamma-butyrolactone and methyl sulfide.
In the following specific examples of the embodiments of the present application, only examples of the lithium ion battery are shown, but the embodiments of the present application are not limited thereto. The present application is further illustrated below with reference to examples of lithium ion batteries. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application. In the following examples and comparative examples, the positive electrode active material NCM111(Li [ Ni ]1/3Co1/3Mn1/3]O2)、NCM622(Li[Ni0.6Co0.2Mn0.2]O2)、NCM811(Li[Ni0.8Co0.1Mn0.1]O2)、LiCoO2Are all commercially available. Other reagents, materials and equipment used are commercially available unless otherwise specified.
Example 1
Preparation of the ductile layer
And mixing the polymer and the conductive agent, adding a solvent, uniformly stirring to obtain extension layer slurry, coating the extension layer slurry on the surfaces of two sides of the positive current collector, and drying to obtain extension layers 1-13. Wherein the oily polymer adopts N-methyl pyrrolidone as a solvent, and the water-based polymer adopts deionized water as a solvent. The positive electrode current collector adopts aluminum foil, and the thickness is 12 mu m. The types of the polymer and the conductive agent, the mass ratio of the polymer and the conductive agent, the thickness of the extension layer, the ratio of the extension rate of the extension layer to the positive current collector and the ratio of the conductivity of the extension layer to the positive current collector are shown in table 1. In the polymer column, taking styrene-butadiene rubber-g-octadecene, 6.3:1 as an example, the mass ratio of styrene-butadiene rubber to octadecene in the polymer is 6.3: 1.
TABLE 1
In Table 1, the elongation test method is referred to GB1040-1/2, and the conductivity test method is referred to GB 11007-1989.
Preparation of positive pole piece
Mixing a positive electrode active substance, a conductive agent acetylene black and a binder polyvinylidene fluoride (PVDF), wherein the mixing weight ratio of the positive electrode active substance to the conductive agent acetylene black to the binder PVDF is 94: 3: 3. adding solvent N-methyl pyrrolidone, and mixing and stirring uniformly to obtain the anode slurry. And uniformly coating the positive electrode slurry on the extension layers on the two sides of the positive electrode current collector, drying at 85 ℃, cold pressing, slitting and cutting into pieces, and drying at 85 ℃ for 4 hours under a vacuum condition to obtain the positive electrode piece. Specific types of the positive electrode active material used therein are shown in table 2.
Preparation of negative pole piece
Preparing negative active material artificial graphite, conductive agent acetylene black, binder Styrene Butadiene Rubber (SBR), and thickener carboxymethylcellulose sodium (CMC) according to a weight ratio of 95: 2: 2:1, adding solvent deionized water, and stirring and mixing uniformly to obtain the cathode slurry. And uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector, drying at 80-90 ℃ after coating, cold pressing, slitting and cutting, and drying for 4 hours at 110 ℃ under a vacuum condition to obtain a negative electrode pole piece.
Preparation of electrolyte
Preparing a basic electrolyte, wherein the basic electrolyte comprises dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC) and Ethylene Carbonate (EC), and the mass ratio of the dimethyl carbonate to the ethyl methyl carbonate to the ethylene carbonate is 5:2: 3. Then, an electrolyte salt was added so that the concentration of lithium hexafluorophosphate in the electrolyte solution was 1 mol/L.
Lithium ion battery preparation
And the negative pole piece, the isolation film and the positive pole piece are sequentially stacked, the isolation film is positioned between the positive pole piece and the negative pole piece, and then the positive pole piece and the negative pole piece are wound into a square bare cell with the thickness of 8mm, the width of 60mm and the length of 130 mm. And (2) filling the bare cell into an aluminum foil packaging bag, baking for 10h at 75 ℃, injecting a non-aqueous electrolyte, carrying out vacuum packaging, standing for 24h, charging to 4.2V by using a constant current of 0.1C (160mA), then charging to 0.05C (80mA) by using a constant voltage of 4.2V until the current is reduced to 0.05V, then discharging to 3.0V by using a constant current of 0.1C (160mA), repeating the charging and discharging for 2 times, and finally charging to 3.8V by using a constant current of 0.1C (160mA), thus completing the preparation of the lithium ion secondary battery. The batteries 1-15 are obtained by adopting the mode. The positive electrode active material and the spreading layer used in the battery are shown in table 2.
TABLE 2
Comparative example 1
The preparation process of batteries 1# to 5# is shown in table 3:
TABLE 3
Test example
The batteries prepared in example 1 and comparative example 1 were subjected to battery needling and extrusion tests in accordance with the standard "GB/T-31485 Power storage batteries for electric vehicles safety requirements and test methods". If no fire and no explosion were considered to pass the test, the test results are listed in tables 4 and 5.
TABLE 4 needling test
TABLE 5 extrusion test
Through analyzing batteries 1-4 and batteries 1# and 2#, it can be seen from the test results of needling and extrusion that when the surface of the positive current collector has an extension layer, two short circuit modes can be effectively prevented from occurring, and therefore the failure of the battery due to thermal runaway is avoided. In terms of mechanism, when the thickness of the extension layer is increased, the extension layer has good extensibility, and when the battery core is acted by external force, the positive current collector can be wrapped more tightly along with the extension layer of the pole piece, so that short circuit is prevented better. And the battery capacity did not change significantly compared to the comparative example where no spreading layer was used.
As can be seen from the analysis of the batteries 1, 5, 14, and 15, when different positive electrode active materials were used, the spreading layer on the surface of the positive electrode current collector functioned, and the batteries were effectively protected.
By analyzing the batteries 6 and 7, it can be seen that: the content of the polymer in the extension layer is reduced, the protection effect of the extension layer on the positive current collector is weakened, and the safety performance of the battery is reduced. If the content of the polymer is too high, the safety performance is further improved, but the transmission efficiency of lithium ions and charges in the positive electrode plate is reduced, and the battery capacity is reduced.
By analyzing the cells 8 and 9: the thickness of the extension layer is too small, the wrapping of the current collector is limited when the pole piece is broken, and short circuit can not be effectively prevented. The thickness of the extension layer is too large, which can affect the transmission rate of lithium ions and charges in the positive pole piece, reduce the energy density of the battery core and reduce the battery capacity.
Through analysis of batteries 10-13 and batteries 3# -5 #, it can be known that: the safety performance of the battery can be improved well by changing the types of the polymers and only by grafting the modified copolymer. In contrast, when the polymer is only a general homopolymer or copolymer, improvement of the safety performance of the battery is limited because ductility cannot meet the requirement.
The preferred embodiments disclosed above are not intended to limit the scope of the claims. A number of possible variations and modifications can be made by anyone skilled in the art without departing from the concept of the present application, and the scope of protection of the present application shall therefore be subject to the ambit defined by the claims.
Claims (12)
1. A positive pole piece comprises a positive current collector and a positive active material layer, and is characterized in that an extension layer is arranged between the positive current collector and the positive active material layer;
the spreader layer includes a polymer and a conductive agent;
the ratio of the extensibility of the extension layer to the extensibility of the positive current collector is (2-10): 1;
the thickness ratio of the extension layer to the positive current collector is (0.05-1): 1.
2. The positive pole piece according to claim 1, wherein the ratio of the conductivity of the extension layer to the positive current collector is (0.1-2.0): 1.
3. The positive electrode sheet according to claim 1, wherein the polymer is a graft-modified copolymer comprising a polymer matrix and a graft-modified chain.
4. The positive electrode plate as claimed in claim 3, wherein the polymer matrix is at least one selected from styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyacrylonitrile, and polyester.
5. The positive electrode plate according to claim 3, wherein the graft modification chain contains a flexible group, the flexible group is at least one selected from a siloxane group, a long chain alkyl group, a long chain alkenyl group and an ether group, the long chain alkyl group is an alkyl group with a carbon atom number of not less than 8, and the long chain alkenyl group is an alkenyl group with a carbon atom number of not less than 8.
6. The positive electrode plate according to claim 5, wherein the graft modification chain is at least one selected from polysiloxane, long chain alkenyl, long chain ether group, and substituted or unsubstituted long chain alkyl group, wherein the substituent in the substituted long chain alkyl group is hydroxyl, the long chain alkyl group is an alkyl group with a carbon atom number of not less than 8, the long chain alkenyl group is an alkenyl group with a carbon atom number of not less than 8, and the long chain ether group is an ether group with a carbon atom number of not less than 8.
7. The positive electrode sheet according to any one of claims 3 to 6, wherein the polymer is at least one selected from styrene-butadiene rubber-g-octadecene, polyacrylic acid-g-dodecanol, polyvinylidene fluoride-g-octadecene, polyacrylonitrile-g-dodecanol, and polyester-g-dodecanol.
8. The positive pole piece according to claim 1, wherein the thickness ratio of the extension layer to the positive current collector is (0.1-1): 1.
9. The positive electrode sheet according to claim 1, wherein the conductive agent is at least one selected from conductive graphite, carbon nanotubes, and graphene.
10. The positive pole piece according to claim 1, wherein the weight ratio of the polymer to the conductive agent in the extension layer is (1-19): 1.
11. The positive pole piece according to claim 10, wherein the weight ratio of the polymer to the conductive agent in the extension layer is (3-10): 1.
12. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet is the positive electrode sheet according to any one of claims 1 to 11.
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| CN111740177B (en) * | 2019-07-26 | 2022-09-16 | 眉山茵地乐科技有限公司 | Positive electrode material, positive electrode, battery, and battery pack |
| CN110364681A (en) * | 2019-07-27 | 2019-10-22 | 珠海冠宇电池有限公司 | A kind of based lithium-ion battery positive plate of the high security of triple protection |
| CN114512678A (en) * | 2020-11-16 | 2022-05-17 | Oppo广东移动通信有限公司 | Current collector, battery and electronic equipment |
| CN113809278B (en) * | 2021-09-15 | 2023-05-16 | 珠海冠宇电池股份有限公司 | Electrode assembly and application thereof |
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