CN117374410A - Lithium ion battery and method for preparing lithium ion battery - Google Patents

Lithium ion battery and method for preparing lithium ion battery Download PDF

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CN117374410A
CN117374410A CN202311305798.6A CN202311305798A CN117374410A CN 117374410 A CN117374410 A CN 117374410A CN 202311305798 A CN202311305798 A CN 202311305798A CN 117374410 A CN117374410 A CN 117374410A
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electrolyte
lithium
ion battery
lithium ion
battery
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邰子阳
蒋治亿
卢林
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Trina Energy Storage Solutions Jiangsu Co Ltd
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Trina Energy Storage Solutions Jiangsu 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
    • 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
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    • 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
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    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/446—Initial charging measures
    • 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
    • H01M4/36—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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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    • H01M2300/00—Electrolytes
    • H01M2300/0085—Immobilising or gelification of electrolyte
    • H—ELECTRICITY
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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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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • 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
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Abstract

The invention provides a method for preparing a lithium ion battery, wherein the lithium ion battery is a lithium iron manganese phosphate battery or a lithium iron phosphate battery, and the method comprises the following steps: the polymerization of the electrolyte containing the peroxide initiator is initiated by a cycle having a cycle number of at least 5 weeks. The invention also provides the lithium iron phosphate battery prepared by the method and application thereof. The method can form gel from the surface of the positive electrode material particles in situ, has mild reaction and good contact with an electrode interface, and has high peel strength of a pole piece/electrolyte combined interface and small interface resistance. In addition, divalent metal ions dissolved out by the positive electrode of the battery can be neutralized, and the high-temperature storage performance of the battery can be improved.

Description

Lithium ion battery and method for preparing lithium ion battery
Technical Field
The invention belongs to the technical field of rechargeable batteries, and particularly relates to a lithium ion battery and a method for preparing the lithium ion battery.
Background
With the rapid development of society, global energy demands are also becoming larger and larger, fossil energy is rapidly consumed, and related researches of novel high-efficiency energy storage devices attract attention of numerous scientific researchers. The secondary ion battery has gained general attention from researchers due to its extremely high power density and energy density, and has been widely used in portable electronic products, and applications in the fields of transportation and the like are expanding. The electrolyte is one of the main factors affecting the electrochemical performance of the device as a key component of the energy storage device. The electrolytes currently used are largely classified into liquid electrolytes and solid electrolytes. The liquid electrolyte has the defects of strong fluidity and difficult encapsulation, and has the risks of liquid leakage, gas expansion, explosion and the like, thereby seriously affecting the use safety of the device. The solid electrolyte can effectively improve the safety of the energy storage device and solve potential safety hazards such as liquid leakage, explosion and the like, wherein the gel electrolyte is the solid electrolyte which is most hopeful to be produced in a commercial mode due to the intrinsic flexibility and the higher ionic conductivity.
At present, in the field of in-situ initiated gel formation, a thermal initiation mode is generally selected to induce polymerization, namely, a thermal initiator is heated to generate free radicals, so that monomers are induced to begin crosslinking polymerization. Or, the gel electrolyte is converted into solid-solid phase contact (in-situ thermal initiation) after being contacted with the electrode under the action of pressure (ex-situ initiation) or solid-liquid phase, so that the interface has no binding force or weak binding force, the solid-solid interface contact resistance is high, and the electrochemical performance of the energy storage device is severely limited.
Therefore, there is a need in the art for a lithium ion battery comprising a gel electrolyte with a strong interfacial bonding force and a method for preparing the same.
Disclosure of Invention
The invention is based on the iron dissolution phenomenon in the circulation process of lithium iron phosphate, and the ferrous ions are accelerated to dissolve by using the circulation voltage, so that Fenton-like reaction is generated with a peroxide initiator in the electrolyte, and hydroxyl free radicals are generated to initiate the polymerization of monomers.
The invention firstly provides a method for preparing a lithium ion battery, wherein the lithium ion battery is a lithium iron manganese phosphate battery or a lithium iron phosphate battery, and the method comprises the following steps: the polymerization of the electrolyte containing the peroxide initiator is initiated by a cycle having a cycle number of at least 5 weeks.
In one or more embodiments, the peroxide initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, benzoyl peroxide, dibenzoyl peroxide, lauroyl peroxide, t-butyl benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, methyl ethyl ketone peroxide, di-t-butyl peroxide.
In one or more embodiments, the peroxide initiator is selected from one or more of t-butanol hydroperoxide, sodium persulfate, and dibenzoyl peroxide.
In one or more embodiments, the peroxide initiator is present in an amount of 0.01 to 0.1wt% or 0.01 to 0.05wt% based on the total weight of the electrolyte.
In one or more embodiments, the cycle is a 0.1-2C constant current constant voltage charge and discharge, a charge cut-off voltage of 2-3.65V, and a cycle of at least 10 weeks.
In one or more embodiments, the cycle is a 0.1-2C constant current constant voltage charge and discharge, a charge cut-off voltage of 3.65-4V, and a cycle of at least 5 weeks.
In one or more embodiments, the lithium ion battery includes a positive electrode tab, a negative electrode tab, a separator, and an electrolyte.
In one or more embodiments, in the positive electrode sheet, the positive electrode current collector is an aluminum foil, the positive electrode material layer comprises a positive electrode active material, a conductive agent and a binder, the positive electrode active material is lithium iron phosphate or lithium manganese iron phosphate, the conductive agent is one or more of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene and carbon nanotubes, and the binder is one or more of fluorine-containing resin, polypropylene resin, fiber type binder and polyimide type binder, preferably polyvinylidene fluoride.
In one or more embodiments, the positive electrode active material is contained in an amount of 94 to 98wt% or 96 to 98wt%, the conductive agent is contained in an amount of 0.5 to 5wt%, preferably 1 to 3wt% or 1.5 to 2.5wt%, and the binder is contained in an amount of 2 to 4wt%, preferably 1.5 to 3wt% or 2.5 to 3.5wt%, based on the total weight of the positive electrode material layer.
In one or more embodiments, in the negative electrode sheet, the negative electrode current collector is copper foil, the negative electrode material layer comprises a negative electrode active material, a conductive agent, a binder and a thickener, and the negative electrode active material is one or more of graphite, a carbon-silicon negative electrode, hard carbon and lithium titanate, preferably graphite; the conductive agent is selected from one or more of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene and carbon nano tube, and is preferably conductive carbon black; the binder is one or more selected from fluorine-containing resin, polypropylene resin, fiber-type binder, rubber-type binder and polyimide-type binder, preferably styrene-butadiene rubber; the thickener is sodium carboxymethyl cellulose.
In one or more embodiments, the negative electrode active material is contained in an amount of 90 to 98wt% or 92 to 98wt%, the conductive agent is contained in an amount of 0.5 to 5.0wt% or 1.0 to 3.0wt% or 1.5 to 2.5wt%, the binder is contained in an amount of 1.0 to 5wt% or 1.5 to 4wt%, and the thickener is contained in an amount of 0.5 to 5wt%, based on the total weight of the negative electrode material layer.
In one or more embodiments, the separator is a polymer separator, a ceramic separator, or a polymer and ceramic composite separator, the polymer separator comprising a single layer polymer separator comprising a polyethylene separator and a polypropylene separator, and a multilayer polymer separator.
In one or more embodiments, the electrolyte further includes a base electrolyte, a lithium salt, a polymeric monomer, and a crosslinking agent.
In one or more embodiments, the base electrolyte includes a solvent and optional additives.
In one or more embodiments, the solvent is selected from carbonate-based solvents or acrylate-based solvents, preferably one or more selected from dimethyl carbonate, ethylene carbonate, propylene carbonate and ethyl methyl carbonate.
In one or more embodiments, the solvents are EC, EMC, and DMC, the mass ratio of EC to DMC is (2-5): (3-6).
In one or more embodiments, the additive is a film former comprising vinylene carbonate.
In one or more embodiments, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethylsulfonate, lithium bisoxalato borate, and lithium difluorooxalato borate.
In one or more embodiments, the lithium salt is present in an amount of 10wt% to 15wt% or 12.0 to 14.0wt% based on the total mass of the electrolyte.
In one or more embodiments, the polymeric monomer is selected from one or more of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, polyethylene glycol dimethacrylate, and pentafluoropropyl acrylate.
In one or more embodiments, the polymeric monomer is selected from methyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, polyethylene glycol dimethacrylate, or pentafluoropropyl acrylate.
In one or more embodiments, the polymerized monomer is 5wt% to 15wt% or 8 to 12wt% based on the total mass of the electrolyte.
In one or more embodiments, the cross-linking agent is selected from one or more of N, N-4, 4-diphenylmethane bismaleimide, bismaleimide oligomer, polyethylene glycol-200 (PEG 200), and polyethylene glycol methacrylate (PEGA).
In one or more embodiments, the cross-linking agent is present in an amount of 0.01 to 20wt%, such as 0.1 to 5wt% or 5 to 20wt%, based on the total mass of the electrolyte.
The invention also provides a lithium ion battery prepared by the method according to any embodiment.
In one or more embodiments, the lithium ion battery has a capacity retention of greater than or equal to 95%, such as greater than or equal to 96% or greater than or equal to 97%, after 30 days of storage at 60 ℃.
In one or more embodiments, the lithium ion battery has a capacity recovery of greater than or equal to 95%, such as greater than or equal to 97% or greater than or equal to 98%, after 30 days of storage at 60 ℃.
In one or more embodiments, the peel force between the positive pre-electrolytes of the lithium ion battery is greater than or equal to 200N/m, such as greater than or equal to 300N/m or 500N/m.
In one or more embodiments, the lithium ion battery has a 100% SOC AC impedance of 70mΩ or less, such as 50mΩ or 30mΩ or less.
The invention also provides a lithium ion battery, which comprises a positive pole piece, a negative pole piece, a diaphragm and a gel electrolyte, wherein the stripping force between the gel electrolyte and the positive pole piece is more than or equal to 200N/m or more than or equal to 300N/m or more than or equal to 500N/m.
In one or more embodiments, the lithium ion battery has a capacity retention of greater than or equal to 95%, such as greater than or equal to 96% or greater than or equal to 97%, after 30 days of storage at 60 ℃.
In one or more embodiments, the lithium ion battery has a capacity recovery of greater than or equal to 95%, such as greater than or equal to 97% or greater than or equal to 98%, after 30 days of storage at 60 ℃.
In one or more embodiments, the lithium ion battery has a 100% SOC AC impedance of 70mΩ or less, such as 50mΩ or 30mΩ or less.
In one or more embodiments, in the positive electrode sheet, the positive electrode current collector is an aluminum foil, the positive electrode material layer includes a positive electrode active material, a conductive agent, and a binder, the positive electrode active material is one or more of lithium iron phosphate, lithium cobalt oxide, and lithium manganese iron phosphate, the conductive agent is one or more of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene, and carbon nanotubes, and the binder is one or more of fluorine-containing resin, polypropylene resin, fiber type binder, and polyimide type binder, preferably polyvinylidene fluoride.
In one or more embodiments, the positive electrode active material is contained in an amount of 94 to 98wt% or 96 to 98wt%, the conductive agent is contained in an amount of 0.5 to 5wt%, preferably 1 to 3wt% or 1.5 to 2.5wt%, and the binder is contained in an amount of 2 to 4wt%, preferably 1.5 to 3wt% or 2.5 to 3.5wt%, based on the total weight of the positive electrode material layer.
In one or more embodiments, in the negative electrode sheet, the negative electrode current collector is copper foil, the negative electrode material layer comprises a negative electrode active material, a conductive agent, a binder and a thickener, and the negative electrode active material is one or more of graphite, a carbon-silicon negative electrode, hard carbon and lithium titanate, preferably graphite; the conductive agent is selected from one or more of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene and carbon nano tube, and is preferably conductive carbon black; the binder is one or more selected from fluorine-containing resin, polypropylene resin, fiber-type binder, rubber-type binder and polyimide-type binder, preferably styrene-butadiene rubber; the thickener is sodium carboxymethyl cellulose.
In one or more embodiments, the negative electrode active material is contained in an amount of 90 to 98wt% or 92 to 98wt%, the conductive agent is contained in an amount of 0.5 to 5.0wt% or 1.0 to 3.0wt% or 1.5 to 2.5wt%, the binder is contained in an amount of 1.0 to 5wt% or 1.5 to 4wt%, and the thickener is contained in an amount of 0.5 to 5wt%, based on the total weight of the negative electrode material layer.
In one or more embodiments, the separator is a polymer separator, a ceramic separator, or a polymer and ceramic composite separator, the polymer separator comprising a single layer polymer separator comprising a polyethylene separator and a polypropylene separator, and a multilayer polymer separator.
In one or more embodiments, the gel electrolyte initiates polymerization from an electrolyte containing a peroxide initiator by a cycle having a cycle number of at least 5 weeks; the peroxide initiator is selected from one or more of tert-butyl hydroperoxide, sodium persulfate and dibenzoyl peroxide.
In one or more embodiments, the cycle is a 0.1-2C constant current constant voltage charge and discharge, a charge cut-off voltage of 2-3.65V, and a cycle of at least 10 weeks.
In one or more embodiments, the cycle is a 0.1-2C constant current constant voltage charge and discharge, a charge cut-off voltage of 3.65-4V, and a cycle of at least 5 weeks.
The invention also provides the application of the method in any embodiment in improving the capacity retention rate and capacity recovery rate of a lithium ion battery, increasing the stripping force between the positive electrode and the electrolyte and reducing the alternating current impedance of the battery.
Detailed Description
So that those skilled in the art can appreciate the features and effects of the present invention, a general description and definition of the terms and expressions set forth in the specification and claims follows. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and in the event of a conflict, the present specification shall control.
The theory or mechanism described and disclosed herein, whether right or wrong, is not meant to limit the scope of the invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
Herein, "comprising," "including," "containing," and similar terms are intended to cover the meaning of "consisting essentially of … …" and "consisting of … …," e.g., "a consisting essentially of B and C" and "a consisting of B and C" should be considered to have been disclosed herein when "a comprises B and C" is disclosed herein.
In this document, all features such as values, amounts, and concentrations that are defined as ranges of values or percentages are for brevity and convenience only. Accordingly, the description of a numerical range or percentage range should be considered to cover and specifically disclose all possible sub-ranges and individual values (including integers and fractions) within the range.
Herein, unless otherwise specified, percentages refer to mass percentages, and proportions refer to mass ratios.
The sum of the percentages of the components of the composition is 100% herein.
Herein, when embodiments or examples are described, it should be understood that they are not intended to limit the invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described herein are intended to be included within the scope of the invention as defined by the appended claims.
In this context, not all possible combinations of the individual technical features in the individual embodiments or examples are described in order to simplify the description. Accordingly, as long as there is no contradiction between the combinations of these technical features, any combination of the technical features in the respective embodiments or examples is possible, and all possible combinations should be considered as being within the scope of the present specification.
Conventional gel electrolyte initiation methods are thermal initiation, photoinitiation, radiation polymerization, etc., most commonly thermal initiation, and high temperature baking is used to impregnate the electrolyte. Through intensive researches, the inventor finds that the Fenton-like reaction between divalent metal ions and a peroxide initiator occurs through circularly accelerating the dissolution of positive metal ions, the monomer crosslinking polymerization can be induced without heating at room temperature, and the battery performance is higher than that of a gel electrolyte battery obtained by standing at room temperature. In addition, as Fenton-like reaction occurs due to the dissolution of metal ions of the positive electrode, the gel electrolyte precursor can be polymerized in situ from the surface of the positive electrode material, the electrode electrolyte interface of the prepared battery core has good contact, and the metal ions dissolved by the positive electrode can be neutralized, so that the high-temperature storage performance of the battery is improved.
In situ polymerization process
The invention provides a method for preparing a lithium ion battery by in-situ polymerization, which comprises the steps of initiating polymerization by circulation after liquid injection, wherein the polymerization condition is that the room temperature is maintained, and electrolyte is initiated to form gel electrolyte by constant-current constant-pressure circulation for at least 5 weeks, and the electrolyte comprises a peroxide initiator. Specifically, the polymerization conditions are to maintain room temperature such as (10-30 ℃), to charge and discharge at a constant current and constant voltage of 0.1C-2C, to charge for at least 10 weeks at a cut-off voltage of 2V-3.65V, or to charge for at least 5 weeks at a cut-off voltage of 3.65-4V.
In the method, after electrolyte is injected, iron ions in the battery anode material are dissolved out through circulation at room temperature, the electrolyte containing peroxide initiator is induced to crosslink and polymerize to form gel electrolyte, and the room temperature is kept all the time in the initiation process without high-temperature heating. It is understood that high temperature generally means a temperature of 60℃or higher.
The effect of the charge cut-off voltage on the life of the battery is critical, and the lower the charge cut-off voltage is, the more advantageous the battery life, so the charge voltage of the lithium iron phosphate battery is usually around 3.65V. In the polymerization conditions herein, the charging voltage may range from 2V to 3.65V, preferably from 3V to 3.65V. The battery or battery pack may gradually decrease in capacity after a number of cycles, and may be considered to be at the end of battery life when the capacity decreases to some extent, and thus the number of cycles may be at least 10 weeks. Herein, if the charge voltage in the polymerization conditions is increased to 3.65V-4V, it is necessary to correspondingly reduce the cycle number to extend the battery life, which may be at least 5 weeks.
Gel electrolyte
The electrolyte suitable for the present invention includes a base electrolyte, a lithium salt, a polymeric monomer, a crosslinking agent, and a peroxide initiator selected from one or more of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, benzoyl peroxide, dibenzoyl peroxide, lauroyl peroxide, t-butyl benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, methyl ethyl ketone peroxide, di-t-butyl peroxide, preferably, one or more of t-butyl hydroperoxide (TBH), sodium Persulfate (PDS), and dibenzoyl peroxide (BPO). The peroxide initiator may be present in an amount of less than 2.00wt%, preferably from 0.01wt% to 0.1wt%, more preferably from 0.01wt% to 0.05wt%, based on the total weight of the electrolyte. It is understood that in this context, the peroxide initiator forms a Fenton-like reaction with the divalent metal ion eluted from the positive electrode to form hydroxyl radicals, by which the monomer is initiated to polymerize, forming a gel electrolyte.
Herein, the base electrolyte includes a solvent and optional additives. Solvents suitable for use in the present invention are conventional in the art, preferably selected from one or more of carbonates, acrylates, such as dimethyl carbonate (DMC), ethylene Carbonate (EC), propylene Carbonate (PC) and Ethyl Methyl Carbonate (EMC). In some embodiments, the solvent comprises EC, EMC, DMC, the ratio of which can be adjusted according to the actual needs, such as EC: EMC: the mass ratio of DMC may be (2-5): (3-6), such as 3:3:4. The additives may be conventional in the art, such as film formers. Useful film formers include Vinylene Carbonate (VC). In the present invention, when the base electrolyte contains a film forming agent, the mass fraction of the film forming agent in the base electrolyte may be 2wt% to 5wt%, preferably 2wt% to 3wt%, based on the total weight of the base electrolyte.
The lithium salts suitable for use in the present invention are conventional in the art and may preferably be selected from lithium hexafluorophosphate (LiPF 6 ) One or more of lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethane sulfonate, lithium bisoxalato borate (LiBOB), and lithium difluorooxalato borate (lidaob). In the electrolyte, the mass fraction of the lithium salt can be 10-15 wt% or 12.0-14.0 wt% based on the total weight of the electrolyte.
Herein, the polymeric monomer includes an acrylic monomer, preferably selected from: one or more of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl Methacrylate (MMA), ethyl methacrylate, propyl methacrylate, butyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, polyethylene glycol dimethacrylate and pentafluoropropyl acrylate. In the electrolyte, the mass fraction of the polymerized monomer may be 5wt% to 15wt% or 8 to 12wt%, for example 7wt%, 9wt%, 10wt%, 12wt%, based on the total weight of the electrolyte.
Herein, the crosslinking agent is preferably selected from one or more of N, N-4, 4-diphenylmethane bismaleimide, bismaleimide oligomer, polyethylene glycol-200 (PEG 200) and polyethylene glycol methacrylate (PEGA). In the electrolyte, the cross-linking agent may be present in an amount of 0.01 to 20wt%, for example 0.1 to 5wt% or 5 to 20wt%, based on the total weight of the electrolyte.
Lithium ion battery
The lithium ion battery prepared by the in-situ initiation gel forming method can improve the stripping force of the positive electrode of the battery and reduce the iron ion leaching amount, thereby reducing the alternating current impedance of the lithium ion battery and improving the high-temperature storage performance of the lithium ion battery. Herein, the high temperature storage performance is embodied by the capacity retention rate and the capacity recovery rate.
Therefore, the invention also provides a lithium ion battery prepared by the in-situ initiated gel forming method according to any embodiment. In some embodiments, the invention also provides the use of an in situ initiated gel forming process as described in any of the embodiments herein in the preparation of a lithium ion battery. The capacity retention rate of the lithium ion battery is more than or equal to 95%, preferably more than or equal to 96%, more preferably more than or equal to 97%, and the capacity recovery rate of the lithium ion battery is more than or equal to 95%, preferably more than or equal to 97%, more preferably more than or equal to 98%. The 100% SOC AC impedance of the lithium ion battery is less than 70mΩ, preferably less than or equal to 50mΩ, and more preferably less than or equal to 35mΩ. In a preferred embodiment, the interfacial bonding force between the positive electrode plate and the electrolyte of the lithium ion battery is more than 200N/m, preferably more than 300N/m, more preferably more than or equal to 500N/m, and the leaching amount of the positive iron ions after the 1C/1C cycle of the lithium ion battery is less than or equal to 500ppm, preferably less than or equal to 450ppm, more preferably less than or equal to 400ppm. In an exemplary embodiment, the capacity retention rate of the lithium ion battery is more than or equal to 97.5%, the 100% SOC alternating current impedance is less than or equal to 30mΩ, the positive electrode iron ion leaching amount is less than or equal to 80ppm after 1C/1C circulation for 500 weeks, and the stripping force of the positive electrode plate and the electrolyte is more than or equal to 550N/m.
Lithium ion batteries generally include a battery cell including a positive electrode sheet, a negative electrode sheet, and a separator, and an electrolyte, which may be an electrolyte as described in any of the embodiments herein. And laminating the positive pole piece, the negative pole piece and the diaphragm according to design requirements (such as Z-shaped lamination or winding lamination) to obtain the battery core of the lithium ion battery.
The positive electrode tab generally includes a positive electrode current collector and a positive electrode material layer formed on a surface of the positive electrode current collector. The positive electrode current collector may be copper foil, aluminum foil, titanium foil, nickel foil, iron foil, zinc foil, or the like, and is preferably aluminum foil. In some embodiments, the positive electrode current collector is an aluminized composite film current collector. The positive electrode material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode material layer is obtained by coating positive electrode slurry comprising positive electrode active material, conductive agent, binder and solvent on a positive electrode current collector, and rolling, die cutting and baking. The solvent may be N-methylpyrrolidone. In an exemplary embodiment, the binder powder may be dissolved in a solvent, and then the positive electrode active material and the conductive agent may be added to prepare a positive electrode slurry. The solid content of the positive electrode slurry may be 55 to 65wt%, such as 57 to 61wt%, and the viscosity of the positive electrode slurry may be 5000 to 15000mpa·s, such as 5000 to 10000mpa·s or 10000 to 15000mpa·s. The positive electrode active material in the positive electrode material layer suitable for the positive electrode sheet herein may be a lithium-containing transition metal oxide or phosphide commonly used in the art, such as lithium iron phosphate or lithium manganese iron phosphate, and the like. The conductive agent may be commonly used in the art, and is preferably selected from one or more of conductive carbon black (SP), carbon Fiber (CF), acetylene black, ketjen black, graphene, and carbon nanotubes. The binder may be one or more selected from the group consisting of fluorine-containing resins, polypropylene resins, fibrous binders and polyimide-type binders, which are commonly used in the art. In some embodiments, the fluorine-containing resin is polyvinylidene fluoride (PVDF). The mass of the positive electrode active material may be 94wt% to 98wt%, preferably 96wt% to 98wt%, the content of the conductive agent may be 0.5wt% to 5wt%, preferably 1wt% to 3wt%, for example 1wt%, 1.5wt%, 2wt%, 2.5wt%, and the content of the binder may be 2wt% to 4wt%, preferably 1.5wt% to 3wt%, for example 2.5wt%, 3wt%, 3.5wt%, based on the total weight of the positive electrode material layer.
The negative pole piece comprises a negative pole current collector and a negative pole material layer arranged on the surface of the negative pole current collector. The negative electrode current collector may be a material having excellent conductivity, such as copper foil, which is commonly used in the art. The anode material layer includes an anode active material, a conductive agent, and a binder. The negative electrode material layer is prepared by coating negative electrode slurry containing a negative electrode active material, a conductive agent, a binder and a solvent on a negative electrode current collector, and then rolling, die cutting and baking. The negative electrode material layer or negative electrode slurry may further include an optional thickener and/or dispersant. The negative electrode active material, the conductive agent and the binder can be sequentially added into a solvent to prepare negative electrode slurry, and further prepare a negative electrode plate. In an exemplary embodiment, the thickener is dissolved in a solvent, and then the anode active material, the conductive agent, and the binder are added to be uniformly mixed. The solvent may be a solvent conventional in the art, such as deionized water. The solid content of the anode slurry may be 45 to 55wt%, such as 46 to 50wt%, and the viscosity of the anode slurry may be 3000 to 9000mpa·s, such as 3000 to 6000mpa·s or 6000 to 9000mpa·s. The negative electrode active material may be one or more selected from the group consisting of graphite (including artificial graphite, natural graphite), silicon carbon negative electrode, hard carbon, and lithium titanate, the conductive agent is preferably one or more selected from the group consisting of conductive carbon black, carbon fiber, acetylene black, ketjen black, graphene, and carbon nanotube, and the binder is preferably one or more selected from the group consisting of fluorine-containing resin, polypropylene resin, fiber-type binder, rubber-type binder, and polyimide-type binder, such as styrene-butadiene rubber (SBR). In some embodiments, the negative electrode active material in the negative electrode material layer is graphite, the conductive agent is conductive carbon black, the binder is styrene-butadiene rubber, and the thickener is sodium carboxymethyl cellulose (CMC). The mass ratio of each component in the anode material layer may be conventional, for example, the content of the anode active material may be 90wt% to 98wt%, preferably 92wt% to 98wt%, for example 93wt%, 95wt%, 95.7wt%, 96wt%, 97wt%, the content of the conductive agent may be 0.5wt% to 5wt%, preferably 1.0wt% to 3wt%, for example 1wt%, 1.5wt%, 2wt%, 2.5wt%, the content of the binder may be 1.0wt% to 5wt%, preferably 1.5 to 4wt%, for example 1.8wt%, 2.0wt%, 2.5wt%, 3wt%, 3.5wt%, and the content of the thickener may be 0.5 to 5wt%, for example 1wt%, 1.5wt%, 2wt%, 2.5wt%, based on the total weight of the anode material layer.
The membrane may be a polymer membrane, a ceramic membrane or a polymer and ceramic composite membrane. The polymer separator includes a single layer polymer separator and a multi-layer polymer separator. The single layer polymer separator includes a Polyethylene (PE) separator and a polypropylene (PP) separator.
And after the battery cell is obtained, packaging the battery cell in a shell, and drying, injecting liquid (injecting electrolyte), packaging, standing, forming and shaping to obtain the lithium ion battery. The form of the lithium ion battery of the present invention is not particularly limited, and may be a cylindrical lithium ion battery, a soft pack lithium ion battery, or an aluminum case lithium ion battery.
The capacity retention rate and the capacity recovery rate of the lithium ion battery are improved, the stripping force between the positive electrode and the electrolyte is increased, and the reduction is realized Method for reducing AC impedance of battery
The lithium ion battery prepared by the preparation method has the advantages that the capacity retention rate and the capacity recovery rate are improved, the stripping force between the positive electrode and the electrolyte is increased, and the alternating current impedance is reduced. Therefore, the invention also provides a method for improving the capacity retention rate and the capacity recovery rate of a lithium ion battery, increasing the stripping force between the positive electrode and the electrolyte and reducing the alternating current impedance of the battery, and/or the application of the method in improving the capacity retention rate and the capacity recovery rate of the lithium ion battery, increasing the stripping force between the positive electrode and the electrolyte and reducing the alternating current impedance of the battery.
In some embodiments, the lithium ion battery has a capacity retention of greater than or equal to 95%, such as greater than or equal to 96% or greater than or equal to 97%, after 30 days of storage at 60 ℃. In some embodiments, the lithium ion battery has a capacity recovery of greater than or equal to 95%, such as greater than or equal to 97% or greater than or equal to 98%, after 30 days of storage at 60 ℃. In some embodiments, the peel force between the positive pre-electrolytes of the lithium ion battery is greater than or equal to 200N/m, such as greater than or equal to 300N/m or 500N/m. In some embodiments, the lithium ion battery has a 100% SOC AC impedance of 70mΩ or less, such as 50mΩ or 30mΩ or less.
The invention has the following beneficial effects:
the invention provides a lithium iron phosphate battery containing gel electrolyte, which is formed by in-situ gel forming from the surface of positive electrode material particles, has mild reaction and good contact with an electrode interface, and has high peel strength of a pole piece/electrolyte combined interface and small interface resistance. In addition, the in-situ gel forming method can neutralize divalent metal ions dissolved out by the positive electrode of the battery, and improves the high-temperature storage performance of the battery.
The invention will be further illustrated by means of specific examples. It should be understood that these examples are illustrative only and are not intended to limit the scope of the invention. The methods and reagents used in the examples are, unless otherwise indicated, conventional in the art.
Detection method
Iron ion elution test
And disassembling the battery after circulation, taking out the negative plate, scraping off powder, and testing the iron ion content in the negative powder digestion solution (concentrated nitric acid: concentrated hydrochloric acid volume ratio is 1:3) by using an Inductively Coupled Plasma (ICP). Thus, the detected iron ion content is actually the content of remaining unneutralized iron ions after the Fenton reaction.
60 ℃ high temperature storage 30D test
a) The battery was charged to 3.65V at a constant current of 0.5C (constant voltage cut-off current of 0.02C) at normal temperature, left to stand for 10 minutes, discharged to 3.0V at a constant current of 1C, left to stand for 10 minutes, and this capacity was recorded as the original capacity C 0 ；
b) Placing 100% SOC battery in a 60 ℃ incubator, and storing for 30 days;
c) Taking out the battery after high-temperature storage, standing at room temperature for 8h, discharging to 2.0V with 1C constant current, and recording the capacity as C 1 Then charged to 3.65V at a constant current of 0.5C (constant voltage cut-off current of 0.02C), left standing for 10 minutes, discharged to 2.0V at a constant current of 1C, left standing for 10 minutes, and charged and discharged 3 times in this way, the maximum discharge capacity was recorded as C 2 ；
d) Capacity retention = C 1 /C 0 X 100%; capacity recovery rate=c 2 /C 0 ×100％。
AC impedance
The frequency was tested using a daily BT3554 instrument, test frequency 1kHz.
Positive electrode/electrolyte peel force (adhesion)
The detection reference willNational standard GB/T7122-1996. The cuboid gel electrolyte/positive plate composite layer with the thickness of 1mm, the length of 10cm and the width of 2cm is fixed on a steel plate of a stripping force test fixture by double faced adhesive tape, and the positive plate faces downwards. The stripping test mainly relies on the traction effect of the clamp above, and the clamp clamps the electrolyte layer to complete the construction of the whole adhesion test device. During test, the upward traction angle of the clamp is 90 degrees, and the traction rate is 2mm min -1 。
Preparing a positive pole piece and a negative pole piece
1) Preparation of positive electrode: 210g of PVDF powder was dissolved in 2791g of NMP, and uniformly stirred to prepare a PVDF gel solution with 7wt% solids for use. Mixing and stirring 10kg of lithium iron phosphate and 0.3kg of conductive carbon black uniformly, adding the PVDF glue solution into the mixed dry material, regulating the slurry to 59% of solid content after stirring uniformly, ensuring that the viscosity is 15000 mPa.S, and coating the slurry on a 9 mu m thick aluminum-plated composite film current collector to obtain a positive electrode plate;
2) Preparation of the negative electrode: a gum solution having a solids content of 1.8wt% was prepared by dissolving 72g CMC powder in 3928g deionized water. And (3) mixing 5kg of artificial graphite and 0.17kg of conductive carbon black, stirring uniformly, adding a proper amount of CMC glue solution and SBR, stirring uniformly, regulating the solid content of the slurry to 48%, adjusting the viscosity to 8000 mPa.S, and coating on a copper foil current collector with the thickness of 6 mu m to obtain the negative electrode plate.
Preparation of a base electrolyte
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): first, ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a ratio of 3:3:4, uniformly mixing the components in mass ratio to prepare a basic electrolyte solvent, taking 97.5wt% of the solvent based on the total mass of the basic electrolyte, adding 2.5wt% of a film-forming additive Vinylene Carbonate (VC), and uniformly mixing to obtain the required basic electrolyte.
Example 1
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): 77.38wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of Methyl Methacrylate (MMA) monomer, 0.1wt% of a cross-linking agent polyethylene glycol diacrylate (molecular weight 200) cross-linking agent (PEG 200) and 0.02wt% of a peroxide initiator tert-butyl hydroperoxide (tert-Butyl hydroperoxide, TBH) are uniformly mixed to prepare the required electrolyte.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, and is charged to 3.65V at constant current and constant voltage for 10 weeks to accelerate the dissolution of positive ions to initiate polymerization, so as to form gel electrolyte.
Example 2
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): the required electrolyte is prepared by uniformly mixing 77.39wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of methyl methacrylate monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent and 0.01wt% of a peroxide initiator PDS.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, and is charged to 3.65V at constant current and constant voltage for 10 weeks to accelerate the dissolution of positive ions to initiate polymerization, so as to form gel electrolyte.
Example 3
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): the required electrolyte is prepared by uniformly mixing 77.39wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of methyl methacrylate monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent and 0.01wt% of a peroxide initiator PDS.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, and is charged to 4.0V at constant current and constant voltage for 5 weeks to accelerate the dissolution of positive ions to initiate polymerization, so as to form gel electrolyte.
Example 4
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): the required electrolyte is prepared by uniformly mixing 77.35wt% of base electrolyte, 12.5wt% of LiPF6, 10wt% of methyl methacrylate monomer, 0.1wt% of cross-linking agent polyethylene glycol diacrylate (molecular weight 200) cross-linking agent and 0.05wt% of peroxide initiator PDS.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, is charged to 4.0V at constant current and constant voltage, circulates for 5 weeks to accelerate the dissolution of positive ions to initiate polymerization, and forms gel electrolyte.
Comparative example 1
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): the required electrolyte is prepared by uniformly mixing 77.39wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of methyl methacrylate monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent and 0.01wt% of a peroxide initiator PDS.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is put into an oven and heated for 6 hours at 60 ℃ to initiate polymerization, so as to form gel electrolyte.
Comparative example 2
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): 77.38wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of methyl methacrylate monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent and 0.02wt% of an azo initiator AIBN are uniformly mixed to prepare the required electrolyte.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is put into an oven and heated for 6 hours at 60 ℃ to initiate polymerization, so as to form gel electrolyte.
Comparative example 3
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): 77.38wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of Methyl Methacrylate (MMA) monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent (PEG 200) and 0.02wt% of an azo initiator AIBN are uniformly mixed to prepare the required electrolyte.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, and is charged to 3.65V at constant current and constant voltage for 10 weeks to accelerate the dissolution of positive ions to initiate polymerization, so that gel electrolyte is not formed.
Comparative example 4 (standing)
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): 77.38wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of Methyl Methacrylate (MMA) monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent (PEG 200) and 0.02wt% of a peroxide initiator tert-butyl alcohol peroxide TBH are uniformly mixed to prepare the required electrolyte.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
Standing at room temperature for 45 days until gel electrolyte is formed.
Comparative example 5
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): 77.38wt% of a base electrolyte, 12.5wt% of LiPF6, 10wt% of Methyl Methacrylate (MMA) monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent (PEG 200) and 0.02wt% of a peroxide initiator tert-butyl hydroperoxide TBH are uniformly mixed to prepare the required electrolyte.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, and is charged to 3.65V at constant current and constant voltage for 2 weeks to accelerate the dissolution of positive ions to initiate polymerization, so that gel electrolyte is not formed.
Comparative example 6
Lithium ion battery electrolyte was prepared in a glove box (moisture < 0.01ppm, oxygen content < 0.01 ppm): the required electrolyte was prepared by uniformly mixing 77.39wt% of the base electrolyte, 12.5wt% of LiPF6, 10wt% of methyl methacrylate monomer, 0.1wt% of a crosslinking agent polyethylene glycol diacrylate (molecular weight 200) crosslinking agent, and 2.00wt% of a peroxide initiator PDS.
Sequentially carrying out rolling, die cutting, drying, winding, assembling and injecting on the positive and negative pole pieces to obtain electrolyte, sealing, forming and sealing to obtain the 4060D0-2.0Ah square soft package lithium ion battery.
The lithium ion battery is placed at room temperature, and is charged to 4.0V at constant current and constant voltage for 5 weeks to accelerate the dissolution of positive ions to initiate polymerization, so as to form gel electrolyte.
Battery cycle test
The results of performance tests of the cells prepared from the electrolytes of the respective examples and comparative examples are shown in table 1 below.
Table 1: battery performance results
Note that: "/" indicates that no glue was formed and no peel force was applied.
As can be seen from table 1:
a) Compared with the traditional thermal initiation, the battery prepared by combining the peroxide initiator with the cyclic initiation mode has better performance: the gel electrolyte prepared by the traditional thermal initiation mode (comparative examples 1 and 2) has low interfacial binding force and high alternating current impedance, can not neutralize iron ions dissolved out by the positive electrode after the battery is circulated, the battery capacity is reduced, and the gel electrolyte prepared by the peroxide initiator circulation initiation mode (example 2) has high interfacial binding force (positive electrode/electrolyte stripping force), low alternating current impedance, can neutralize iron ions dissolved out by the battery after the battery is circulated, and has higher battery capacity retention rate and capacity recovery rate;
b) Peroxide initiators are capable of neutralizing the cyclically leached iron ions, but the initiator content should not be excessive: the cycle initiation mode is the same, the peroxide initiator TBH or BPO (examples 1 and 5) can neutralize the circularly dissolved iron ions, while the azo initiator AIBN (comparative example 3) cannot, and the dissolution amount of the iron ions is high, so that the prepared battery capacity retention rate and recovery rate are relatively low; meanwhile, in a certain range, the higher the content of the peroxide initiator (examples 3-4), the more active sites for initiating reaction can be increased, the interface binding force can be increased, and more iron ions dissolved out by the positive electrode can be neutralized, so that the high-temperature storage performance of the battery is further improved, but if the content of the peroxide initiator is excessive (for example, more than or equal to 2wt percent, compared with example 6), the iron ions can be neutralized, the interface binding force is improved, but the capacity performance of the battery is reduced, and the inventor speculates that the possible reason is that the peroxide initiator is a high-reactivity substance, and the excessive residual components can cause the increase of side reactions of the battery under the condition that the initiation stage cannot be completely consumed;
c) The cyclic initiation mode can increase the interface binding force, but the voltage and the cyclic period number of the cyclic initiation mode need to meet certain conditions: when the battery is left standing for a long time at room temperature (for example, 45 days, comparative example 4), the iron ions of the positive electrode are slowly dissolved out and are neutralized by a small amount of peroxide initiator to finally form gel, but the interfacial binding force is lower (174N/m), and the specific reason is that the standing time is too long, so that the peroxide is degraded, and the gel is uneven due to too low initiator content. Meanwhile, when the battery cores are disassembled for peeling force test, the internal glue forming (soft adhesion) mechanical strength of the battery is lower, which is probably due to the fact that part of monomers undergo self-polymerization reaction in the overlong standing process, so that polymerization is uneven, part of contact interfaces are still in liquid contact, and therefore the battery has lower alternating current internal resistance under the condition of lower peeling force. Therefore, the cyclic initiation mode (example 1) of the invention can enhance the interfacial bonding force (327N/m > 174N/m) of the battery, has lower alternating current impedance, and further enhances the capacity retention rate and the capacity recovery rate of the battery; meanwhile, if the cycle number is reduced, the voltage is increased to increase the dissolution rate of iron ions to initiate polymerization (examples 2-3), and if the cycle number is too small (comparative example 5), a gel electrolyte cannot be formed and is still a liquid electrolyte, so that the defects of strong fluidity and difficult encapsulation are present, and risks such as liquid leakage, gas expansion and explosion are easy to occur, thereby influencing the use safety.

Claims (10)

1. A method of making a lithium ion battery, wherein the lithium ion battery is a lithium iron manganese phosphate battery or a lithium iron phosphate battery, the method comprising: initiating polymerization of the electrolyte containing peroxide initiator by cycle, the cycle number being at least 5 weeks;
wherein the peroxide initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, benzoyl peroxide, dibenzoyl peroxide, lauroyl peroxide, tert-butyl benzoyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, methyl ethyl ketone peroxide and di-tert-butyl peroxide.
2. The method of claim 1, wherein the peroxide initiator is present in an amount of 0.01 to 0.1wt%, based on the total weight of the electrolyte.
3. The method according to claim 1, wherein the cycle is 0.1 to 2C constant current constant voltage charge and discharge, the charge cut-off voltage is 2 to 3.65V, the cycle is at least 10 weeks, or
The cycle is 0.1-2C constant-current constant-voltage charge and discharge, the charge cut-off voltage is 3.65-4V, and the cycle is at least 5 weeks.
4. The method of claim 1, wherein the electrolyte further comprises a base electrolyte, a lithium salt, a polymeric monomer, and a crosslinking agent;
Wherein the base electrolyte comprises a solvent and optionally additives;
the solvent is selected from carbonate solvents or acrylic ester solvents, preferably one or more selected from dimethyl carbonate, ethylene carbonate, propylene carbonate and methyl ethyl carbonate;
the solvent is EC, EMC and DMC, the mass ratio of EC to DMC is (2-5) (3-6);
the additive is a film forming agent, and the film forming agent contains vinylene carbonate.
5. The method of claim 4, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethane sulfonate, lithium bis (oxalato) borate, and lithium difluoro (oxalato) borate;
the mass of the lithium salt is 10-15 wt% based on the total mass of the electrolyte.
6. The method of claim 4, wherein the polymeric monomer is selected from one or more of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, polyethylene glycol dimethacrylate, and pentafluoropropyl acrylate;
The mass percentage of the polymerized monomer is 5-15 wt% based on the total mass of the electrolyte.
7. The method of claim 4, wherein the cross-linking agent is selected from one or more of N, N-4, 4-diphenylmethane bismaleimide, bismaleimide oligomer, polyethylene glycol-200 (PEG 200), and polyethylene glycol methacrylate (PEGA);
the weight percentage of the cross-linking agent is 0.01-20wt% based on the total weight of the electrolyte.
8. A lithium ion battery prepared by the method according to any one of claims 1 to 7, characterized in that,
after the lithium ion battery is stored for 30 days at 60 ℃, the capacity retention rate is more than or equal to 95%;
after the lithium ion battery is stored for 30 days at 60 ℃, the capacity recovery rate is more than or equal to 95%.
9. A lithium ion battery is characterized by comprising a positive pole piece, a negative pole piece, a diaphragm and a gel electrolyte, wherein the stripping force between the gel electrolyte and the positive pole piece is more than or equal to 200N/m,
the gel electrolyte initiates polymerization from an electrolyte containing a peroxide initiator by a cycle having a cycle number of at least 5 weeks; the peroxide initiator is selected from one or more of tert-butyl hydroperoxide, sodium persulfate and dibenzoyl peroxide.
10. The lithium-ion battery of claim 9, wherein the battery is configured to provide the battery with a battery power,
the cycle is 0.1-2C constant-current constant-voltage charge and discharge, the charge cut-off voltage is 2-3.65V, and the cycle is at least 10 weeks;
or the cycle is 0.1-2C constant-current constant-voltage charge and discharge, the charge cut-off voltage is 3.65-4V, and the cycle is at least 5 weeks.
CN202311305798.6A 2023-10-10 2023-10-10 Lithium ion battery and method for preparing lithium ion battery Pending CN117374410A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117638200A (en) * 2024-01-24 2024-03-01 宁德新能源科技有限公司 Lithium ion battery and electronic device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117638200A (en) * 2024-01-24 2024-03-01 宁德新能源科技有限公司 Lithium ion battery and electronic device
CN117638200B (en) * 2024-01-24 2024-04-30 宁德新能源科技有限公司 Lithium ion battery and electronic device

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