CN112786832A - Negative plate and lithium ion battery - Google Patents

Negative plate and lithium ion battery Download PDF

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Publication number
CN112786832A
CN112786832A CN202110099899.7A CN202110099899A CN112786832A CN 112786832 A CN112786832 A CN 112786832A CN 202110099899 A CN202110099899 A CN 202110099899A CN 112786832 A CN112786832 A CN 112786832A
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lithium
current collector
negative
conductive agent
protective layer
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徐雄文
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Hunan Lifang New Energy Science and Technology Co Ltd
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Hunan Lifang New Energy Science and Technology Co Ltd
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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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • 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 invention belongs to the technical field of lithium ion batteries, and particularly relates to a negative plate, which comprises: a negative current collector; the protective layer is arranged on at least one surface of the negative current collector; the protective layer includes polyimide and a conductive agent including at least one of carbon fiber, carbon nanotube, and graphene. According to the negative plate, the protective layer is arranged on the surface of the negative current collector and comprises polyimide and a conductive agent, wherein the polyimide can protect the negative current collector and can also induce lithium ions to be rapidly deposited on the negative current collector, so that the generation of lithium ion aggregation and lithium dendrite is reduced, and the generation speed of dead lithium is reduced, so that the thermal stability and the safety performance of the battery are improved; the conductive agent can enhance the conductivity of the protective layer and promote the rapid deposition of lithium ions, and can also enhance the mechanical strength and mechanical strength of the protective layer by mutually winding polyimide, thereby prolonging the cycle life of the battery.

Description

Negative plate and lithium ion battery
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a negative plate and a lithium ion battery.
Background
The lithium ion battery is widely applied to various electronic devices and electric energy storage devices due to the characteristics of high working voltage, small self-discharge, no memory effect, environmental friendliness and the like. Especially, in the application of mobile phones, the energy density of the battery is required to be higher and higher due to the lighter and thinner mobile phones. In order to improve the energy density of the lithium ion battery, the key point is to search for a high-capacity positive and negative electrode active material. The theoretical specific capacity of the metallic lithium negative electrode is 3860mAh/g, the voltage platform is-3.04V (vs standard hydrogen electrode), and the metallic lithium negative electrode has excellent conductivity and is very suitable for being used as the negative electrode of a high-energy-density battery. The main problem which troubles the lithium metal cathode is mainly the problem of lithium dendrite, in the circulation process, because of the local polarization factor, the lithium dendrite grows on the surface of the lithium metal, and when the lithium dendrite grows to a certain degree, the lithium dendrite can penetrate through a diaphragm, so that the safety problem is caused.
In view of the above, it is necessary to provide a technical solution to solve the above technical problems.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the negative plate is provided, the generation of lithium dendrites is reduced, and the safety performance of the battery is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a negative electrode sheet, comprising:
a negative current collector;
the protective layer is arranged on at least one surface of the negative current collector;
the protective layer includes polyimide and a conductive agent including at least one of carbon fiber, carbon nanotube, and graphene.
As an improvement of the negative plate, the mass ratio of the polyimide to the conductive agent is 9-99: 1.
As an improvement of the negative electrode sheet, the particle size of the polyimide is less than 1 μm.
As an improvement of the negative plate, the thickness of the protective layer is 1-20 μm.
As an improvement of the negative electrode sheet of the present invention, the negative electrode current collector includes a copper foil, a nickel foil, a stainless steel foil, a lithium foil or a lithium alloy foil.
As an improvement of the negative electrode sheet of the present invention, the protective layer is prepared by coating a conductive agent slurry on at least one surface of the negative electrode current collector, wherein the conductive agent slurry comprises a solvent, the polyimide and the conductive agent.
Another object of the present invention is to provide a lithium ion battery, including a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the negative electrode sheet is the negative electrode sheet described in any one of the above description.
As an improvement of the lithium ion battery of the present invention, the electrolyte includes an electrolyte or a solid-like electrolyte, the solid-like electrolyte is formed by in-situ polymerization of a liquid mixed solution, and the liquid mixed solution includes a lithium salt, an organic solvent, a monomer additive, an inorganic additive, and an initiator.
As an improvement of the lithium ion battery of the present invention, the inorganic additive includes at least one of nano aluminum oxide, nano magnesium oxide, nano zirconium oxide, nano silicon oxide, lithium aluminum titanium phosphate and lithium lanthanum zirconium oxide.
As an improvement of the lithium ion battery of the present invention, the lithium ion battery includes a lithium primary battery or a lithium secondary battery.
Compared with the prior art, the invention has at least the following beneficial effects: the invention provides a negative plate, which comprises: a negative current collector; the protective layer is arranged on at least one surface of the negative current collector; the protective layer includes polyimide and a conductive agent including at least one of carbon fiber, carbon nanotube, and graphene.
According to the negative plate, the protective layer is arranged on the surface of the negative current collector and comprises polyimide and a conductive agent, wherein the polyimide can protect the negative current collector and can also induce lithium ions to be rapidly deposited on the negative current collector, so that the generation of lithium ion aggregation and lithium dendrite is reduced, and the generation speed of dead lithium is reduced, so that the thermal stability and the safety performance of the battery are improved;
the conductive agent can enhance the conductivity of the protective layer and promote the rapid deposition of lithium ions, and can also enhance the mechanical strength and mechanical strength of the protective layer by mutually winding polyimide, thereby prolonging the cycle life of the battery.
Detailed Description
As used in the specification and in the claims, certain terms are used to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This specification and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. "substantially" means within an acceptable error range, within which a person skilled in the art can solve the technical problem to substantially achieve the technical result.
Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.
1. Negative plate
An aspect of the present application provides a negative electrode sheet, including:
a negative current collector;
the protective layer is arranged on at least one surface of the negative current collector;
the protective layer includes polyimide and a conductive agent, and the conductive agent includes at least one of carbon fiber, carbon nanotube, and graphene.
According to the negative plate, the protective layer is arranged on the surface of the negative current collector and comprises polyimide and a conductive agent, wherein the polyimide can protect the negative current collector and can also induce lithium ions to be rapidly deposited on the negative current collector, so that the generation of lithium ion aggregation and lithium dendrite is reduced, and the generation speed of dead lithium is reduced, so that the thermal stability and the safety performance of the battery are improved;
the conductive agent can enhance the conductivity of the protective layer and promote the rapid deposition of lithium ions, and can also wrap polyimide mutually to enhance the mechanical strength and mechanical strength of the protective layer, thereby prolonging the cycle life of the battery.
In some embodiments, the mass ratio of the polyimide to the conductive agent is 9-99: 1. Since polyimide mainly serves to protect the current collector, its mass is greater than that of the conductive agent. Preferably, the mass ratio of the polyimide to the conductive agent is 9:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 99: 1.
In some embodiments, the particle size of the polyimide is <1 μm. The particle size of the polyimide is preferably on the nanometer scale, and the nanometer-scale polyimide can be uniformly distributed in the protective layer. Preferably, the particle size of the polyimide is 0.01. mu.m, 0.05. mu.m, 0.1. mu.m, 0.2. mu.m, 0.3. mu.m, 0.4. mu.m, 0.5. mu.m, 0.6. mu.m, 0.7. mu.m, 0.8. mu.m, 0.9. mu.m, or 0.99. mu.m.
In some embodiments, the thickness of the protective layer is 1 to 20 μm. The thickness of the protective layer must not be too thick, which would affect the space occupied inside the battery and the energy density of the battery. If the thickness of the protective layer is too thin, the protective layer does not function to suppress the generation of lithium dendrites, and the mechanical strength and mechanical strength of the protective layer cannot be sufficiently ensured. Preferably, the thickness of the protective layer is 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm.
In some embodiments, the negative electrode current collector comprises a copper foil, a nickel foil, a stainless steel foil, a lithium foil, or a lithium alloy foil. The lithium alloy foil includes a lithium magnesium alloy or a lithium aluminum alloy.
In some embodiments, the protective layer is formed by coating at least one surface of the negative electrode current collector with a conductive paste including a solvent, polyimide, and a conductive agent. The solvent comprises azomethylpyrrolidone. The solvent, polyimide and conductive agent are mixed in a dry environment having a dew point of no more than-35 ℃.
2. Lithium ion battery
A second aspect of the present application provides a lithium ion battery, including a positive plate, a negative plate, a diaphragm disposed between the positive plate and the negative plate, and an electrolyte, wherein the negative plate is the negative plate described in any one of the preceding paragraphs of the specification.
In some embodiments, the lithium ion battery comprises a lithium primary battery or a lithium secondary battery.
Positive plate
In the battery according to the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the material of the positive electrode current collector includes, but is not limited to, an aluminum foil, and the specific type of the positive electrode active material layer is not particularly limited and may be selected as desired.
In some embodiments, the positive electrode active material layer includes a positive electrode active material including a compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive active material may include a composite oxide containing lithium and at least one element selected from cobalt, manganese, and nickel. In still other embodiments, the positive active material is selected from lithium cobaltate (LiCoO)2) Lithium nickel manganese cobalt ternary material and lithium manganate (LiMn)2O4) Lithium nickel manganese oxide (LiNi)0.5Mn1.5O4) Lithium iron phosphate (LiFePO)4) One or more of them.
In some embodiments, the positive electrode active material layer further comprises a positive electrode binder for improving the binding of the positive electrode active material particles to each other and also to the main body of the electrode sheet. Non-limiting examples of the positive electrode binder include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.
In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent, thereby imparting conductivity to the electrode. The positive electrode conductive agent may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
Diaphragm
In the battery according to the present application, a separator is provided between the positive electrode tab and the negative electrode tab to prevent short circuit. The material and shape of the separator used in the battery of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art.
In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.
In some embodiments, a surface treatment layer is disposed on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).
Electrolyte
In some embodiments, the electrolyte comprises an electrolytic solution.
In some embodiments, the electrolyte comprises a solid-like electrolyte formed by in-situ polymerization of a liquid mixture comprising a lithium salt, an organic solvent, a monomer additive, an inorganic additive, and an initiator.
In some embodiments, the liquid mixture includes 10 to 15 wt% of lithium salt, 80 to 85 wt% of organic solvent, 2.5 to 4.7 wt% of monomer additive, 0.3 to 2.3 wt% of inorganic additive and 0.1 to 0.2 wt% of initiator.
In some embodiments, the lithium salt comprises LiPF6、LiBF4、LiClO4LiBOB, LiFSI, LiTFSI, LiTDI and LiAsF6At least one of (1).
In some embodiments, the organic solvent includes two parts, a base solvent and a functional solvent. The base solvent is at least one of carbonate, carboxylate, fluoro carbonate, ether and fluoro ether. The functional solvent is a phosphazene solvent, and comprises pentafluoroethoxy cyclotriphosphazene or hexafluorocyclotriphosphazene. The mass ratio of the basic solvent to the functional solvent is 4-20: 1.
In some embodiments, the monomer additive is an unsaturated bond-containing monomer including at least one of polyethylene glycol diacrylate, methyl methacrylate, vinyl sulfite, ethoxylated trimethylolpropane triacrylate, vinyl acetate, and vinyl sulfite.
In some embodiments, the initiator is an azo-based initiator and/or a peroxide-based initiator. Azo initiators include, but are not limited to, at least one of azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate. Peroxide initiators include, but are not limited to, at least one of benzoyl peroxide, benzoyl t-butyl peroxide, and methyl ethyl ketone peroxide.
In some embodiments, the inorganic additive comprises at least one of nano alumina, nano magnesia, nano zirconia, nano silica, lithium aluminum titanium phosphate, and lithium lanthanum zirconium oxide. The main function of the inorganic additive is to increase the ionic conductivity of the electrolyte. In addition, the nano inorganic additive can improve the internal microstructure of the electrolyte and improve the interface compatibility of the electrolyte and a lithium cathode, thereby improving the cycle performance of the solid-state lithium metal battery.
Embodiments of the present application are illustrated below 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 claimed invention, which is not limited thereto.
Example 1
The embodiment provides a negative plate, and a preparation method of the negative plate comprises the following operations:
preparing conductive agent slurry: uniformly stirring nano polyimide powder with the average particle size of 0.5 mu m and carbon fiber VGCF (carbon fiber VGCF) in a mass ratio of 50:1 in a dry environment by taking N-methyl pyrrolidone (NMP) as a solvent to obtain conductive agent slurry;
coating the conductive agent slurry on two surfaces of a negative current collector lithium foil in a spraying or roller coating mode, wherein the coating thickness is set to be 10 mu m;
and (3) baking at the temperature of 100 ℃ to volatilize NMP, thus obtaining the negative plate with protective layers attached to the two surfaces of the lithium foil.
Example 2
The embodiment provides a negative plate, and a preparation method of the negative plate comprises the following operations:
preparing conductive agent slurry: uniformly stirring nano polyimide powder with the average particle size of 0.9 mu m and carbon fiber VGCF (carbon fiber VGCF) in a mass ratio of 70:1 in a dry environment by taking N-methyl pyrrolidone (NMP) as a solvent to obtain conductive agent slurry;
coating the conductive agent slurry on two surfaces of a negative current collector lithium foil in a spraying or roller coating mode, wherein the coating thickness is set to be 5 um;
and (3) baking at the temperature of 120 ℃ to volatilize NMP, thus obtaining the negative plate with protective layers attached to the two surfaces of the lithium foil.
Example 3
The embodiment provides a negative plate, and a preparation method of the negative plate comprises the following operations:
preparing conductive agent slurry: uniformly stirring nano polyimide powder with the average particle size of 0.3 mu m and carbon fiber VGCF (carbon fiber VGCF) in a mass ratio of 80:1 in a dry environment by taking N-methyl pyrrolidone (NMP) as a solvent to obtain conductive agent slurry;
coating the conductive agent slurry on two surfaces of a negative current collector lithium foil in a spraying or roller coating mode, wherein the coating thickness is set to be 20 mu m;
and (3) baking at the temperature of 80 ℃ to volatilize NMP, thus obtaining the negative plate with protective layers attached to the two surfaces of the lithium foil.
Example 4
The embodiment provides a negative plate, and a preparation method of the negative plate comprises the following operations:
preparing conductive agent slurry: uniformly stirring nano polyimide powder with the average particle size of 0.2 mu m and carbon fiber VGCF (carbon fiber VGCF) in a mass ratio of 20:1 in a dry environment by taking N-methyl pyrrolidone (NMP) as a solvent to obtain conductive agent slurry;
coating the conductive agent slurry on two surfaces of a negative current collector lithium foil in a spraying or roller coating mode, wherein the coating thickness is set to be 15 mu m;
and (3) baking at the temperature of 70 ℃ to volatilize NMP, thus obtaining the negative plate with protective layers attached to the two surfaces of the lithium foil.
Example 5
The embodiment provides a negative plate, and a preparation method of the negative plate comprises the following operations:
preparing conductive agent slurry: uniformly stirring nano polyimide powder with the average particle size of 0.6 mu m and carbon fiber VGCF (carbon fiber VGCF) in a mass ratio of 10:1 in a dry environment by taking N-methyl pyrrolidone (NMP) as a solvent to obtain conductive agent slurry;
coating the conductive agent slurry on two surfaces of a negative current collector lithium foil in a spraying or roller coating mode, wherein the coating thickness is set to be 2 um;
and (3) baking at the temperature of 80 ℃ to volatilize NMP, thus obtaining the negative plate with protective layers attached to the two surfaces of the lithium foil.
Example 6
The embodiment provides a lithium ion battery, and a preparation method thereof comprises the following operations:
1) preparing a negative plate: prepared using the method described in example 1.
2) Preparing a positive plate:
preparation of positive electrode active material slurry: mixing a lithium nickel manganese cobalt ternary material (NCM523), a conductive agent SuperP and a binder polyvinylidene fluoride according to a weight ratio of 97:1.4:1.6, adding N-methylpyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the system is uniform to obtain positive active material slurry with the solid content of 72%.
Positive plate: taking a positive current collector, dividing the positive current collector into a pole piece main body area and a pole lug area, dividing the pole lug area into a connection area and a pole lug main body area, and connecting the pole lug main body area with the pole piece main body area through the connection area; coating the positive active material slurry on at least one surface of the pole piece main body area, and drying at 85 ℃ to obtain a positive active material layer; and (4) drying the anode plate for 24 hours in a vacuum at the temperature of 60 ℃ in a drying environment to obtain the anode plate.
3) Preparation of the separator
A commercial polypropylene film with the thickness of 16 mu m is taken as a diaphragm and dried for 24 hours in vacuum at the temperature of 60 ℃ in a drying environment.
4) Preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonate, 4 wt% of hexachlorocyclotriphosphazene, 3.8 wt% of polyethylene glycol bisacrylamide, 2 wt% of lithium lanthanum zirconium oxide and 0.2 wt% of azobisisobutyronitrile.
5) Assembling a negative plate, a positive plate and a diaphragm into a bare cell by adopting a lamination process according to the form of negative electrode/diaphragm/positive electrode/diaphragm/negative electrode, filling the bare cell with a liquid mixed solution after the bare cell is placed in a shell, and heating the bare cell for 1-5 hours at 60-85 ℃ after the liquid mixed solution is fully soaked, so that the liquid mixed solution is subjected to in-situ polymerization reaction to form the quasi-solid electrolyte.
6) And (3) carrying out formation, degassing and vacuum packaging to finish the preparation of the solid-state-like lithium metal battery.
Example 7
The present embodiment provides a lithium ion battery, which is different from embodiment 6 in the following preparation method:
1) preparing a negative plate: prepared using the method described in example 2.
4) Preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonic ester, 4 wt% of pentafluoroethoxycyclotriphosphazene and 3.8Mixing methyl methacrylate in weight percent, nano-magnesia in 2 percent and azobisisoheptonitrile in 0.2 percent to obtain liquid mixed liquid.
The rest is the same as embodiment 6, and the description is omitted here.
Example 8
The present embodiment provides a lithium ion battery, which is different from embodiment 6 in the following preparation method:
1) preparing a negative plate: prepared using the method described in example 3.
4) Preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonate, 4 wt% of hexachlorocyclotriphosphazene, 3.8 wt% of ethoxylated trimethylolpropane triacrylate, 2 wt% of lithium aluminum titanium phosphate and 0.2 wt% of benzoyl peroxide to obtain a liquid mixed solution.
The rest is the same as embodiment 6, and the description is omitted here.
Example 9
The present embodiment provides a lithium ion battery, which is different from embodiment 6 in the following preparation method:
1) preparing a negative plate: prepared using the method described in example 4.
4) Preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonate, 4 wt% of hexachlorocyclotriphosphazene, 3.8 wt% of vinyl sulfite, 2 wt% of nano-zirconia and 0.2 wt% of azobisisobutyronitrile.
The rest is the same as embodiment 6, and the description is omitted here.
Example 10
The present embodiment provides a lithium ion battery, which is different from embodiment 6 in the following preparation method:
1) preparing a negative plate: prepared using the method described in example 5.
4) Preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonate, 4 wt% of hexachlorocyclotriphosphazene, 3.8 wt% of polyethylene glycol diacrylate, 2 wt% of nano magnesium oxide and 0.2 wt% of azobisisobutyronitrile.
The rest is the same as embodiment 6, and the description is omitted here.
Comparative example 1
The negative electrode sheet provided by the comparative example is the negative electrode current collector lithium foil in example 1.
Comparative example 2
The present comparative example provides a lithium ion battery, the preparation method of which comprises the following operations:
1) preparing a negative plate: the negative electrode sheet provided in comparative example 1 was used.
2) Preparing a positive plate:
preparation of positive electrode active material slurry: mixing a lithium nickel manganese cobalt ternary material (NCM523), a conductive agent SuperP and a binder polyvinylidene fluoride according to a weight ratio of 97:1.4:1.6, adding N-methylpyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the system is uniform to obtain positive active material slurry with the solid content of 72%.
Positive plate: taking a positive current collector, dividing the positive current collector into a pole piece main body area and a pole lug area, dividing the pole lug area into a connection area and a pole lug main body area, and connecting the pole lug main body area with the pole piece main body area through the connection area; coating the positive active material slurry on at least one surface of the pole piece main body area, and drying at 85 ℃ to obtain a positive active material layer; and (4) drying the anode plate for 24 hours in a vacuum at the temperature of 60 ℃ in a drying environment to obtain the anode plate.
3) Preparation of the separator
A commercial polypropylene film with the thickness of 16 mu m is taken as a diaphragm and dried for 24 hours in vacuum at the temperature of 60 ℃ in a drying environment.
4) Preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonate, 4 wt% of hexachlorocyclotriphosphazene, 3.8 wt% of polyethylene glycol bisacrylamide, 2 wt% of lithium lanthanum zirconium oxide and 0.2 wt% of azobisisobutyronitrile.
5) Assembling a negative plate, a positive plate and a diaphragm into a bare cell by adopting a lamination process according to the form of negative electrode/diaphragm/positive electrode/diaphragm/negative electrode, filling the bare cell with a liquid mixed solution after the bare cell is placed in a shell, and heating the bare cell for 1-5 hours at 60-85 ℃ after the liquid mixed solution is fully soaked, so that the liquid mixed solution is subjected to in-situ polymerization reaction to form the quasi-solid electrolyte.
6) And (3) carrying out formation, degassing and vacuum packaging to finish the preparation of the solid-state-like lithium metal battery.
Comparative example 3
This comparative example provides a lithium ion battery, which was prepared by a method different from that of example 6:
4) preparing liquid mixed liquid: mixing 10 wt% LiPF6And 90 wt% of carbonate to obtain a liquid mixture.
The rest is the same as embodiment 6, and the description is omitted here.
Comparative example 4
This comparative example provides a lithium ion battery, which was prepared by a method different from that of example 6:
4) preparing liquid mixed liquid: mixing 10 wt% LiPF680 wt% of carbonate, 6 wt% of hexachlorocyclotriphosphazene, 3.8 wt% of polyethylene glycol bisacrylamide and 0.2 wt% of azobisisobutyronitrile are mixed to obtain a liquid mixed solution.
The rest is the same as embodiment 6, and the description is omitted here.
And (3) performance testing:
the following performance tests were performed on the batteries prepared above:
1) and (3) carrying out cycle performance test at normal temperature under the current density of 0.5C, wherein the voltage is 3.0-4.5V, and calculating the discharge capacity and the capacity retention rate after 200 cycles.
2) The battery was stored at room temperature for various periods of time and the impedance change was measured.
3) The battery is subjected to safety performance tests such as thermal shock, acupuncture, heavy object impact and the like, and phenomena such as ignition and explosion do not occur
It is determined as pass (check), otherwise it is determined as not pass (x).
The test results are shown in table 1.
TABLE 1 test results
Figure BDA0002915386380000161
Figure BDA0002915386380000171
As can be seen from example 6 and comparative example 2, after the protective layer is attached to the surface of the negative electrode sheet, the thermal stability, safety performance, and cycle life of the battery are improved, because the polyimide can protect the negative electrode current collector, and can also induce lithium ions to be rapidly deposited on the negative electrode current collector, thereby reducing the aggregation of lithium ions and the generation of lithium dendrites, and simultaneously reducing the generation speed of dead lithium, thereby improving the thermal stability and safety performance of the battery; and the conductive agent can enhance the conductivity of the protective layer and promote the lithium ions to be rapidly deposited, and can also enhance the mechanical strength and the mechanical strength of the protective layer by mutually winding the polyimide, thereby prolonging the cycle life of the battery.
It can be seen from example 6 and comparative example 3 that, compared with the common electrolyte, the electrolyte adopts the in-situ polymerized solid-like electrolyte, the safety performance is obviously improved, the solid-like electrolyte can inhibit the growth of lithium dendrites, and the solid-like electrolyte has high compatibility with the electrode interface and small impedance.
It can be seen from example 6 and comparative example 4 that the cycle performance of the battery is significantly improved by adding the lithium lanthanum zirconium oxygen nano inorganic additive in a proper ratio to the liquid mixed solution, because the inorganic additive increases the ionic conductivity of the electrolyte. In addition, the nano inorganic additive improves the internal microstructure of the electrolyte, improves the interface compatibility of the electrolyte and the lithium cathode, and obviously improves the cycle performance of the battery.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (10)

1. A negative electrode sheet, comprising:
a negative current collector;
the protective layer is arranged on at least one surface of the negative current collector;
the protective layer includes polyimide and a conductive agent including at least one of carbon fiber, carbon nanotube, and graphene.
2. The negative electrode sheet according to claim 1, wherein the mass ratio of the polyimide to the conductive agent is 9-99: 1.
3. The negative electrode sheet according to claim 1, wherein the particle size of the polyimide is <1 μm.
4. The negative electrode sheet according to claim 1, wherein the protective layer has a thickness of 1 to 20 μm.
5. The negative electrode sheet according to claim 1, wherein the negative electrode current collector comprises a copper foil, a nickel foil, a stainless steel foil, a lithium foil, or a lithium alloy foil.
6. The negative electrode sheet according to claim 1, wherein the protective layer is formed by coating a conductive agent paste on at least one surface of the negative electrode current collector, the conductive agent paste including a solvent, the polyimide, and the conductive agent.
7. A lithium ion battery is characterized by comprising a positive plate, a negative plate, a diaphragm arranged between the positive plate and the negative plate and electrolyte, wherein the negative plate is the negative plate of any one of claims 1 to 6.
8. The lithium ion battery of claim 7, wherein the electrolyte comprises an electrolyte solution or a solid-like electrolyte formed by in-situ polymerization of a liquid mixture comprising a lithium salt, an organic solvent, a monomer additive, an inorganic additive, and an initiator.
9. The lithium ion battery of claim 8, wherein the inorganic additive comprises at least one of nano alumina, nano magnesia, nano zirconia, nano silica, lithium aluminum titanium phosphate, and lithium lanthanum zirconium oxide.
10. The lithium ion battery of claim 7, wherein the lithium ion battery comprises a lithium primary battery or a lithium secondary battery.
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Application publication date: 20210511