CN112259707A - Lithium battery negative pole piece loaded with temperature-resistant composite layer and preparation method thereof - Google Patents

Lithium battery negative pole piece loaded with temperature-resistant composite layer and preparation method thereof Download PDF

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CN112259707A
CN112259707A CN202011130329.1A CN202011130329A CN112259707A CN 112259707 A CN112259707 A CN 112259707A CN 202011130329 A CN202011130329 A CN 202011130329A CN 112259707 A CN112259707 A CN 112259707A
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negative pole
pole piece
temperature
suspension
loaded
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CN112259707B (en
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陈庆
廖健淞
白涛
李钧
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Shandong Yiwei New Material Co.,Ltd.
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Chengdu New Keli Chemical Science Co Ltd
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    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • 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
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
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    • 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
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    • H—ELECTRICITY
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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Abstract

The invention provides a lithium battery negative pole piece loaded with a temperature-resistant composite layer and a preparation method thereof, wherein the lithium battery negative pole piece is prepared by spraying a suspension B on a negative pole piece loaded with a porous conducting layer, the suspension B is prepared by adding an inorganic temperature-resistant material into a mixed solution, the negative pole piece loaded with the porous conducting layer is prepared by spraying a suspension A on the negative pole piece, the suspension A is prepared by adding an inorganic lithium ion conductor, polyethylene oxide and graphene oxide powder into a mixed solution, the negative pole piece is prepared by mixing a negative pole active material, polyvinylidene fluoride and a conductive agent and coating the mixture on a copper foil, and the mixed solution is prepared by dissolving a polyvinylidene fluoride-hexafluoropropylene copolymer in a mixed solvent of acetone and N, N-dimethylformamide. The lithium battery negative pole piece provided by the invention has the advantages of good temperature resistance, high ionic conductivity, good safety and usability, simple preparation process and suitability for industrial production.

Description

Lithium battery negative pole piece loaded with temperature-resistant composite layer and preparation method thereof
Technical Field
The invention relates to the technical field of lithium battery cathodes, in particular to a lithium battery cathode pole piece loaded with a temperature-resistant composite layer and a preparation method thereof.
Background
Lithium batteries are used as new-generation energy batteries, and have become typical representatives of new energy due to the advantages of low cost, high performance, high power, green environment and the like, and are widely applied to the fields of 3C digital products, mobile power supplies, electric vehicles and the like. In recent years, with the aggravation of environmental pollution and the guidance of national policies, the demand of the electric vehicle market mainly for electric vehicles for lithium batteries is increasing, and the lithium batteries become important development contents in new energy materials.
With the application and popularization of lithium batteries, the safety problem of the batteries is widely regarded in the process of developing a high-power lithium battery system. In recent years, safety accidents such as explosion and fire of lithium ion batteries have occurred due to problems such as technical reasons of the batteries themselves and improper use. Especially, in recent years, the demand of the electric vehicle market mainly comprising electric automobiles on lithium ion batteries is continuously increased, and the safety problem of the lithium batteries is urgently needed to be further solved in the process of developing a high-power lithium ion battery system.
In the case of fire caused by thermal runaway of the battery in recent years, the heat generation rate of the battery is far higher than the heat dissipation rate, and the heat is accumulated in a large amount and is not dissipated in time, so that the safety problem caused by the thermal runaway of the lithium battery is solved. The thermal runaway of the lithium battery is mainly caused by the temperature rise in the battery, and mainly focuses on two large aspects of the thermal instability of the electrolyte and the thermal instability of a coexisting system of the electrolyte and the positive electrode and the negative electrode. At present, from a large aspect, the safety type lithium ion battery mainly takes measures from two aspects of external management and internal design, and the internal temperature, voltage and air pressure are controlled to achieve the safety purpose. The lithium battery has the advantages that the internal design of the lithium battery is considered, the lithium ion conductivity of the lithium battery is guaranteed while the flame retardant performance of the lithium battery is improved, and the lithium battery has very important practical significance for the conventional lithium battery.
Chinese patent application No. 201010597448.8 discloses a non-aqueous electrolyte additive for improving the high-temperature performance of a battery, which is composed of fluorine substituted carbonate and alkyl phosphate, but has limited temperature resistance and influences the lithium ion conductivity. Chinese patent application No. 201010003004.7 discloses a flame-retardant electrolyte solution including a lithium salt, a linear carbonate-based solvent, at least one ammonium cation, a phosphoric acid-based solvent, and an additive including oxalatoborate, however, the ammonium salt is very swollen when heated, a rechargeable lithium battery, and a method of manufacturing the same. Chinese patent application No. 201410474938.7 discloses an overcharge-resistant flame-retardant battery electrolyte, which comprises a non-aqueous organic solvent, a lithium salt, a film-forming and overcharge-resistant additive, however, these electrolytes have a great influence on the ionic conduction of the battery itself.
In order to improve the temperature resistance of the lithium battery, ensure the conductivity of lithium ions and effectively solve the problem of thermal runaway of the lithium battery, a novel temperature-resistant lithium battery negative plate is necessary to be provided, and the use safety of the lithium battery is further improved.
Disclosure of Invention
Aiming at the problem that thermal runaway is easy to occur in the conventional lithium battery at high temperature, the invention provides the lithium battery negative pole piece loaded with the temperature-resistant composite layer and the preparation method thereof, so that the temperature resistance of the lithium battery is improved, the ion conduction capability is ensured, and the problem of thermal runaway of the lithium battery is effectively solved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a lithium battery negative pole piece loaded with a temperature-resistant composite layer is prepared by spraying a suspension B on a negative pole piece loaded with a porous conducting layer, wherein the suspension B is prepared by adding an inorganic temperature-resistant material into a mixed solution, the negative pole piece loaded with the porous conducting layer is prepared by spraying a suspension A on the negative pole piece, the suspension A is prepared by adding an inorganic lithium ion conductor, polyethylene oxide and graphene oxide powder into a mixed solution, the negative pole piece is prepared by mixing a negative pole active material, polyvinylidene fluoride and a conductive agent and then coating the mixture on the surface of a copper foil, and the mixed solution is prepared by dissolving a polyvinylidene fluoride-hexafluoropropylene copolymer in a mixed solvent of acetone and N, N-dimethylformamide.
Preferably, the inorganic temperature-resistant material is inorganic fiber with heat-insulating property, and specifically may be one of glass fiber, rock wool, aluminum silicate fiber and vitreous silica fiber.
Further preferably, the inorganic temperature-resistant material is glass fiber.
Preferably, the inorganic lithium ion conductor is one of a Lisicon type ion conductor, a Nasicon type ion conductor, and a perovskite type lithium ion conductor.
Further preferably, the inorganic lithium ion conductor is Li6.75La3Zr1.75Ta0.25O12（LZZTO）。
Preferably, the negative electrode active material is one of a carbon material and a silicon-carbon composite material.
Preferably, the conductive agent is Super-P;
preferably, the molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 5-6 ten thousand, and the content of hexafluoropropylene is 10-15% wt.
The invention also provides a preparation method of the lithium battery negative pole piece loaded with the temperature-resistant composite layer, which comprises the following steps:
(1) uniformly mixing a negative electrode active material, polyvinylidene fluoride (PVDF) and a conductive agent, preparing to obtain slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative electrode plate;
(2) adding polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) into a mixed solvent of acetone and N, N-dimethylformamide, and then heating and stirring until the polyvinylidene fluoride-hexafluoropropylene copolymer is completely dissolved to obtain a mixed solution;
(3) adding an inorganic lithium ion conductor, polyethylene oxide (PEO) and graphene oxide powder into the obtained mixed solution to prepare a suspension A, heating and stirring the suspension A, spraying the suspension A on the surface of a negative pole piece, and drying in a vacuum oven for 30-40min to remove a solvent to obtain the negative pole piece loaded with the porous conducting layer;
(4) adding an inorganic temperature-resistant material into the obtained mixed solution to prepare a suspension B, spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, and drying in a vacuum oven for 30-40min to remove the solvent to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer.
Preferably, in the preparation of the negative electrode plate in the step (1), the raw materials comprise, by mass, 80-100 parts of a negative electrode active material, 1-4 parts of polyvinylidene fluoride and 1-5 parts of a conductive agent.
Preferably, the temperature of the heating and stirring in the step (2) is 30-60 ℃, and the stirring is carried out for 50-100 min.
Preferably, in the preparation of the mixed solution in the step (2), the raw materials comprise, by mass, 10-20 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 30-50 parts of acetone and 50-70 parts of N, N-dimethylformamide.
More preferably, the total of the parts by mass of acetone and N, N-dimethylformamide is 100 parts.
Preferably, in the step (3), in the preparation of the suspension A, the raw materials comprise, by mass, 10-35 parts of an inorganic lithium ion conductor, 1-5 parts of polyethylene oxide, 1-3 parts of graphene oxide powder and 150 parts of a mixed solution.
Preferably, the temperature of the heating and stirring in the step (3) is 50-80 ℃, and the stirring is carried out for 1-2 h.
Preferably, in the step (4), in the preparation of the suspension B, the inorganic temperature-resistant material is 10-35 parts by weight, and the mixed solution is 100-150 parts by weight.
Preferably, the spraying process in the steps (3) and (4) selects high-pressure spraying to form a film, and the film thickness is 20-30 μm.
It is known that thermal runaway of lithium batteries is mainly caused by an increase in the internal temperature of the battery. Most of the solvents of the current commonly used lithium battery electrolyte have the problems of high volatility, low flash point and high possibility of burning, when an internal short circuit is caused by collision or deformation, high-rate charge and discharge and overcharge generate a large amount of heat, so that the temperature of the battery rises, when a certain temperature is reached, a protective layer SEI film is damaged, a negative electrode reacts with the solvents and the binders, the temperature rises, a diaphragm melts and closes, internal electrolytes and the like begin to be decomposed in a series, heat is continuously released, the battery is further heated, positive electrode materials are further decomposed, a large amount of heat and gas are released, the temperature is continuously raised, the negative electrode and the positive electrode react with the electrolytes violently, so that the thermal balance of the battery is damaged, the temperature of the battery rises sharply, namely thermal runaway is caused, and the battery is finally burnt and even explodes in severe cases. The invention creatively improves the temperature resistance of the SEI film, solves the problem of lithium ion conductivity of the traditional temperature-resistant additive after the SEI film is formed, finally obtains the negative pole piece with high temperature resistance and ion conductivity, and can effectively solve the problem of thermal runaway when being used for a lithium battery.
Firstly, preparing a negative electrode active material, polyvinylidene fluoride and a conductive agent to obtain slurry, wherein the negative electrode active material is a carbon material or a silicon-carbon composite material, and the conductive agent is Super-P (conductive carbon black); and coating the slurry on the surface of the copper foil to prepare the conventional negative pole piece.
Further, dissolving the polyvinylidene fluoride-hexafluoropropylene copolymer in a mixed solvent of acetone and N, N-dimethylformamide to prepare a mixed solution. The polyvinylidene fluoride-hexafluoropropylene copolymer has good high temperature resistance, chemical corrosion resistance, oxidation resistance, weather resistance and corrosion resistance, and also has good piezoelectricity, dielectricity and pyroelectricity, and the obtained mixed solution can play an important role in the preparation of the negative pole piece as a raw material of functional slurry in the subsequent process.
Further, adding inorganic lithium ion conductor, polyoxyethylene and graphene oxide powder into the mixed solution to prepare turbid liquid A, and spraying the turbid liquid A on the obtained negative pole piece to obtain the negative pole piece loaded with the porous conducting layer; the PVDF-HFP material is doped by the PEO and the graphene oxide, so that the formed film layer has a three-dimensional porous structure, and the graphene oxide has good conductivity, so that the ion conductivity can be remarkably improved.
And further, adding an inorganic temperature-resistant material into the mixed solution to prepare a suspension B, and spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer. The inorganic heat-resistant material selects inorganic fiber with heat-insulating property, preferably glass fiber, and the heat-insulating inorganic fiber can be compounded with a base film, so that an inorganic lithium ion conductor and the heat-resistant material are sprayed on the surface of a negative active material to effectively compound to form an SEI film framework, a PVDF-HFP load temperature-resistant layer is formed on the surface of a conductive layer again, and a double-layer porous composite film is formed after drying and removing a solvent, thereby realizing the composite temperature-resistant layer with ion conduction and temperature-resistant functions, not only inhibiting the heat exchange between the film material and an electrolyte when the film material is out of control due to heat, inhibiting the generation of side reactions, but also improving the physical strength, enabling the formed SEI film not to deform when being heated, and obviously improving the safety of a negative pole piece and even a lithium battery.
The existing lithium battery has the problem of easy occurrence of thermal runaway at high temperature, and the application of the existing lithium battery is limited. In view of the above, the invention provides a lithium battery negative pole piece loaded with a temperature-resistant composite layer and a preparation method thereof, wherein a negative active material, polyvinylidene fluoride and a conductive agent are mixed according to a proportion to prepare a slurry, and then the slurry is coated on the surface of copper foil and dried to obtain a negative pole piece; dissolving polyvinylidene fluoride-hexafluoropropylene copolymer in a mixed solvent of acetone and N, N-dimethylformamide, and stirring and mixing until the polyvinylidene fluoride-hexafluoropropylene copolymer is completely dissolved to obtain a mixed solution for later use; adding an inorganic lithium ion conductor, polyoxyethylene and graphene oxide powder into the obtained solution to prepare a suspension A, spraying the suspension A on the surface of the obtained negative pole piece, and drying in a vacuum oven to remove the solvent to form the negative pole piece loaded with the porous conducting layer; adding an inorganic temperature-resistant material into the obtained solution to prepare a suspension B, spraying the suspension B on the surface of the obtained negative pole piece loaded with the porous conducting layer, and drying in a vacuum oven to remove the solvent to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer. The lithium battery negative pole piece provided by the invention has the advantages of good temperature resistance, high ionic conductivity, good safety and usability, simple preparation process and suitability for industrial production.
Compared with the prior art, the invention provides a lithium battery negative pole piece loaded with a temperature-resistant composite layer and a preparation method thereof, and the outstanding characteristics and excellent effects are as follows:
1. the lithium battery negative pole piece prepared by the invention has the advantages of good temperature resistance, high ionic conductivity, good safety and usability, simple preparation process and suitability for industrial production.
2. According to the invention, the lithium ion conductor and the temperature-resistant material are sprayed on the surface of the active material to form the SEI film skeleton, the formed SEI film has excellent temperature resistance, and the negative influence of the reduction of the lithium ion conductivity of the traditional temperature-resistant additive in the SEI film forming process can be avoided.
3. The preparation method mainly comprises the steps of copolymerizing PVDF-HFP and PEO, forming a conductive layer by loading a lithium ion conductor and graphene oxide, forming a PVDF-HFP loaded temperature-resistant layer on the surface of the conductive layer again, and drying to remove a solvent to form a double-layer porous composite film, so that the composite temperature-resistant layer with high ion conductivity and good temperature resistance is realized.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.
Example 1
(1) Uniformly mixing 90kg of carbon material, 2.5kg of polyvinylidene fluoride and 3kg of super-P, preparing to obtain slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative pole piece;
(2) adding 15kg of polyvinylidene fluoride-hexafluoropropylene copolymer into a mixed solvent of 40kg of acetone and 60kg of N, N-dimethylformamide, and then stirring for 75min at 345 ℃ until the mixture is completely dissolved to obtain a mixed solution;
(3) mixing 22kgLi6.75La3Zr1.75Ta0.25O12Adding 3kg of polyethylene oxide and 2kg of graphene oxide powder into 125kg of the obtained mixed solution to prepare a suspension A, heating the suspension A to 65 ℃, stirring for 1.5h, then spraying the suspension A on the surface of a negative pole piece at high pressure, and drying in a vacuum oven for 35min to remove the solvent to obtain the negative pole piece loaded with the porous conductive layer, wherein the average thickness of the film layer is 25 microns;
(4) adding 22kg of glass fiber into the obtained 125kg of mixed solution to prepare suspension B, then spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, drying in a vacuum oven for 35min to remove the solvent, forming a film layer with the average thickness of 25 mu m again to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer, and finally assembling the negative pole piece of the lithium battery with the LFP positive pole, the lithium hexafluorophosphate/carbonate electrolyte and the diaphragm to form the button cell.
Example 2
(1) Uniformly mixing 85kg of silicon-carbon composite material, 3kg of polyvinylidene fluoride and 4kg of super-P, preparing to obtain slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative pole piece;
(2) adding 13kg of polyvinylidene fluoride-hexafluoropropylene copolymer into a mixed solvent of 35kg of acetone and 65kg of N, N-dimethylformamide, and then stirring for 90min at 40 ℃ until the mixture is completely dissolved to obtain a mixed solution;
(3) 20kgLi6.75La3Zr1.75Ta0.25O12Adding 2kg of polyethylene oxide and 1.5kg of graphene oxide powder into 140kg of the obtained mixed solution to prepare a suspension A, heating the suspension A to 60 ℃, stirring for 2h, then spraying the suspension A on the surface of a negative electrode plate at high pressure, and drying in a vacuum oven for 32min to remove the solvent to obtain the negative electrode plate loaded with the porous conductive layer, wherein the average thickness of the film layer is 22 microns;
(4) adding 20kg of glass fiber into the obtained 140kg of mixed solution to prepare suspension B, then spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, drying in a vacuum oven for 32min to remove the solvent, forming a film layer with the average thickness of 22 mu m again to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer, and finally assembling the negative pole piece of the lithium battery with the LFP positive pole, the lithium hexafluorophosphate/carbonate electrolyte and the diaphragm to form the button cell.
Example 3
(1) Uniformly mixing 95kg of carbon material, 2kg of polyvinylidene fluoride and 2kg of super-P, preparing slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative pole piece;
(2) adding 18kg of polyvinylidene fluoride-hexafluoropropylene copolymer into a mixed solvent of 45kg of acetone and 55kg of N, N-dimethylformamide, and then stirring for 60min at 50 ℃ until the mixture is completely dissolved to obtain a mixed solution;
(3) mixing 25kgLi6.75La3Zr1.75Ta0.25O12Adding 4kg of polyethylene oxide and 2.5kg of graphene oxide powder into 110kg of the obtained mixed solution to prepare a suspension A, heating the suspension A to 70 ℃, stirring for 1h, then spraying the suspension A on the surface of a negative pole piece at high pressure, and drying in a vacuum oven for 38min to remove the solvent to obtain the negative pole piece loaded with the porous conductive layer, wherein the average thickness of the film layer is 28 microns;
(4) adding 25kg of glass fiber into the obtained 110kg of mixed solution to prepare suspension B, then spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, drying in a vacuum oven for 38min to remove the solvent, forming a film layer with the average thickness of 28 microns again to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer, and finally assembling the negative pole piece of the lithium battery with the LFP positive pole, the lithium hexafluorophosphate/carbonate electrolyte and the diaphragm to form the button cell.
Example 4
(1) Uniformly mixing 80kg of silicon-carbon composite material, 4kg of ethylene polyvinylidene fluoride and 5kg of super-P, preparing to obtain slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative pole piece;
(2) adding 10kg of polyvinylidene fluoride-hexafluoropropylene copolymer into a mixed solvent of 50kg of acetone and 50kg of N, N-dimethylformamide, and then stirring for 100min at 30 ℃ until the mixture is completely dissolved to obtain a mixed solution;
(3) mixing 10kgLi6.75La3Zr1.75Ta0.25O12Adding 1kg of polyethylene oxide and 1kg of graphene oxide powder into 150kg of the obtained mixed solution to prepare a suspension A, heating the suspension A to 50 ℃, stirring for h, spraying the suspension A on the surface of a negative pole piece at high pressure, and drying in a vacuum oven for 30min to remove the solvent to obtain the negative pole piece loaded with the porous conducting layer, wherein the average thickness of the film layer is 20 microns;
(4) adding 10kg of glass fiber into the obtained 150kg of mixed solution to prepare suspension B, then spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, drying in a vacuum oven for 30min to remove the solvent, forming a film layer with the average thickness of 20 mu m again to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer, and finally assembling the negative pole piece of the lithium battery with the LFP positive pole, the lithium hexafluorophosphate/carbonate electrolyte and the diaphragm to form the button cell.
Example 5
(1) Uniformly mixing 100kg of carbon material, 1kg of polyvinylidene fluoride and 1kg of super-P, preparing slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative pole piece;
(2) adding 20kg of polyvinylidene fluoride-hexafluoropropylene copolymer into a mixed solvent of 30kg of acetone and 70kg of N, N-dimethylformamide, and then stirring for 50min at 60 ℃ until the mixture is completely dissolved to obtain a mixed solution;
(3) mixing 35kgLi6.75La3Zr1.75Ta0.25O12Adding 5kg of polyethylene oxide and 3kg of graphene oxide powder into 100kg of the obtained mixed solution to prepare a suspension A, heating the suspension A to 80 ℃, stirring for 1h, then spraying the suspension A on the surface of a negative pole piece at high pressure, and drying in a vacuum oven for 40min to remove the solvent to obtain the negative pole piece loaded with the porous conducting layer, wherein the average thickness of the film layer is 30 microns;
(4) adding 35kg of glass fiber into 100kg of the obtained mixed solution to prepare suspension B, spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, drying in a vacuum oven for 40min to remove the solvent, forming a film layer with the average thickness of 30 mu m again to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer, and finally assembling the negative pole piece of the lithium battery with the LFP positive pole, the lithium hexafluorophosphate/carbonate electrolyte and the diaphragm to form the button cell.
Comparative example 1
Compared with the embodiment 1, the button cell is assembled by directly using the negative pole piece prepared in the step (1), an LFP positive pole, lithium hexafluorophosphate/carbonate electrolyte and a diaphragm.
Comparative example 2
Compared with the embodiment 1, the negative pole piece prepared in the step (1) is directly used, the fluoro-carbonate is used as a temperature-resistant additive to be added into the electrolyte, and the electrolyte, the LFP positive pole, the lithium hexafluorophosphate/carbonate electrolyte and the diaphragm are assembled into the button cell.
The test method comprises the following steps:
ion conductivity test: the internal resistance of the button cell prepared in the embodiments 1-5 and the comparative examples 1-2 of the invention is directly tested by using an ohmmeter to represent the ion conductivity of the cell, particularly the negative pole piece, and the test results are shown in table 1;
testing temperature resistance: the button cell prepared in the embodiments 1-5 and the comparative examples 1-2 of the invention is connected to a tester, the button cell is discharged at a current density of 0.04mA/g, the working state of the cell is kept, the temperature of the cell is slowly raised from room temperature to 200 ℃ at a speed of 3 ℃/min, the external current is tested, the short-circuit temperature of the cell is recorded, the temperature resistance of the cell, particularly the negative pole piece is represented, and the test results are shown in Table 1.
Table 1:
Figure 207348DEST_PATH_IMAGE002
as can be seen from table 1, when the button cell obtained in examples 1 to 5 and comparative examples 1 to 2 of the present invention is subjected to performance tests, the internal resistance of the cell in examples 1 to 5 is very close to the internal resistance of the cell in comparative example 1, which indicates that the temperature-resistant layer added in example 1 has little influence on the resistance of the cell itself, and the short-circuit temperature thereof is significantly increased, which indicates that the added temperature-resistant layer can effectively increase the operating temperature of the cell. In contrast, in comparative example 1, only the negative electrode sheet prepared in step (1) is used, and although the internal resistance of the battery is low, the temperature resistance is poor, and a large risk of thermal runaway exists. Comparative example 2 the fluoro-carbonate is added in the electrolyte as a temperature-resistant additive, so that the temperature resistance of the battery is improved, but the improvement is limited, and meanwhile, the internal resistance of the battery is greatly influenced, and the service performance of the battery is influenced.

Claims (10)

1. The lithium battery negative pole piece loaded with the temperature-resistant composite layer is characterized in that a suspension B is sprayed on a negative pole piece loaded with a porous conducting layer, the suspension B is prepared by adding an inorganic temperature-resistant material into a mixed solution, the negative pole piece loaded with the porous conducting layer is prepared by spraying a suspension A on the negative pole piece, the suspension A is prepared by adding an inorganic lithium ion conductor, polyethylene oxide and graphene oxide powder into a mixed solution, the negative pole piece is prepared by mixing a negative active material, polyvinylidene fluoride and a conductive agent and then coating the mixture on the surface of a copper foil, and the mixed solution is prepared by dissolving a polyvinylidene fluoride-hexafluoropropylene copolymer in a mixed solvent of acetone and N, N-dimethylformamide.
2. The negative pole piece of the lithium battery loaded with the temperature-resistant composite layer according to claim 1, wherein,
the inorganic temperature-resistant material is inorganic fiber with heat-insulating property, and specifically can be one of glass fiber, rock wool, asbestos, aluminum silicate fiber and vitreous silicon fiber;
the inorganic lithium ion conductor is one of a Lisicon type ion conductor, a Nasicon type ion conductor and a perovskite type lithium ion conductor;
the negative active material is one of a carbon material and a silicon-carbon composite material;
the conductive agent is Super-P;
the molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 5-6 ten thousand, and the content of hexafluoropropylene is 10-15% wt.
3. The preparation method of the negative pole piece of the lithium battery loaded with the temperature-resistant composite layer according to any one of claims 1 to 2, which is characterized by comprising the following steps:
(1) uniformly mixing a negative electrode active material, polyvinylidene fluoride and a conductive agent, preparing to obtain slurry, coating the slurry on the surface of copper foil, drying, and collecting to obtain a negative electrode plate;
(2) adding the polyvinylidene fluoride-hexafluoropropylene copolymer into a mixed solvent of acetone and N, N-dimethylformamide, and then heating and stirring until the polyvinylidene fluoride-hexafluoropropylene copolymer is completely dissolved to obtain a mixed solution;
(3) adding an inorganic lithium ion conductor, polyoxyethylene and graphene oxide powder into the obtained mixed solution to prepare a suspension A, heating and stirring the suspension A, spraying the suspension A on the surface of a negative pole piece, and drying in a vacuum oven for 30-40min to remove a solvent to obtain the negative pole piece loaded with the porous conducting layer;
(4) adding an inorganic temperature-resistant material into the obtained mixed solution to prepare a suspension B, spraying the suspension B on the surface of the negative pole piece loaded with the porous conducting layer, and drying in a vacuum oven for 30-40min to remove the solvent to obtain the negative pole piece of the lithium battery loaded with the porous temperature-resistant composite layer.
4. The preparation method of the temperature-resistant composite layer-loaded lithium battery negative electrode piece according to claim 3, characterized in that in the preparation of the negative electrode piece in the step (1), the raw materials comprise, by mass, 80-100 parts of a negative electrode active material, 1-4 parts of polyvinylidene fluoride and 1-5 parts of a conductive agent.
5. The method for preparing the negative pole piece of the lithium battery loaded with the temperature-resistant composite layer according to claim 3, wherein the temperature raising and stirring in the step (2) is at 30-60 ℃ and is stirred for 50-100 min.
6. The method for preparing the temperature-resistant composite layer-loaded negative electrode plate of the lithium battery as claimed in claim 3, wherein in the step (2), the mixed solution is prepared from, by mass, 10-20 parts of polyvinylidene fluoride-hexafluoropropylene copolymer, 30-50 parts of acetone, 50-70 parts of N, N-dimethylformamide, and 100 parts of acetone and N, N-dimethylformamide.
7. The method for preparing the lithium battery negative electrode plate loaded with the temperature-resistant composite layer according to claim 3, wherein in the step (3), the suspension A is prepared from 10-35 parts by mass of an inorganic lithium ion conductor, 1-5 parts by mass of polyethylene oxide, 1-3 parts by mass of graphene oxide powder and 150 parts by mass of a mixed solution.
8. The method for preparing the negative pole piece of the lithium battery loaded with the temperature-resistant composite layer according to claim 3, wherein the temperature raising and stirring in the step (3) is 50-80 ℃, and the stirring is carried out for 1-2 hours.
9. The method for preparing the lithium battery negative electrode plate loaded with the temperature-resistant composite layer according to claim 3, wherein in the step (4), in the preparation of the suspension B, 10-35 parts by mass of the inorganic temperature-resistant material and 150 parts by mass of the mixed solution are added.
10. The method for preparing the lithium battery negative pole piece loaded with the temperature-resistant composite layer according to claim 3, wherein the spraying process in the steps (3) and (4) selects high-pressure spraying to form a film, and the thickness of the formed film is 20-30 μm.
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