CN111916740A - Polyunsaturated carboxylic group controllable crosslinking type binder and lithium ion battery containing same - Google Patents
Polyunsaturated carboxylic group controllable crosslinking type binder and lithium ion battery containing same Download PDFInfo
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- CN111916740A CN111916740A CN202010628040.6A CN202010628040A CN111916740A CN 111916740 A CN111916740 A CN 111916740A CN 202010628040 A CN202010628040 A CN 202010628040A CN 111916740 A CN111916740 A CN 111916740A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E60/10—Energy storage using batteries
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Abstract
The invention provides a polyunsaturated carboxylic group controllable cross-linking type binder and a lithium ion battery containing the binder. The binders of the present invention are formed by crosslinking of linear unsaturated carboxylic acid-based polymers and bisoxazoline small molecules during drying. The crosslinked unsaturated carboxylic acid-based polymer forms a three-dimensional network, so that the active material can be fully coated, and the slippage among active material particles is reduced; in addition, the cross-linked unsaturated carboxylic acid-based polymer can provide more action sites, so that the polyunsaturated carboxylic acid-based controllable cross-linked binder has excellent binding power, and the cycle performance, expansion rate and rate performance of the lithium ion battery using the binder are superior to those of the lithium ion battery using the non-cross-linked binder.
Description
Technical Field
The invention relates to a polyunsaturated carboxylic group controllable cross-linking type binder and a lithium ion battery containing the binder, belonging to the technical field of lithium ion batteries, in particular to the field of binders for lithium ion batteries.
Background
The adhesive in the lithium ion battery is used as a polymer, not only has the function of bonding between active material layers, but also can be used for bonding between an active material layer and a pole piece substrate, plays an important role in the aspects of manufacturing and performance of the battery, and is one of important components of the battery.
The most used binders at present are polyvinylidene fluoride (PVDF), copolymers of Styrene and Butadiene (SBR), and polyacrylic acid (ester) type binders. The polyacrylic acid (polyacrylate) binder has rich carboxyl, and can react with active substances and hydroxyl on the pole piece, so that the peel strength is improved. However, the linear polyacrylic acid (polyacrylate) binder has insufficient active sites with the active material, and cannot sufficiently coat the active material, so that the peel strength is not high enough, and particularly, the expansion of the silicon-based negative electrode material cannot be effectively inhibited.
Disclosure of Invention
Researches find that the molecular structure with a three-dimensional network is more advantageous by synthesizing the crosslinking type polyunsaturated carboxylic acid-based binder and synthesizing the molecular structure with the polyunsaturated carboxylic acid-based binder, which mainly comes from the fact that the molecular structure can provide multiple action sites for interpenetrating networks, so that the active material is fully coated, the falling-off of active material particles is prevented, and the expansion of the electrode is effectively inhibited. However, in the prior art, the crosslinking type adhesive is mostly obtained by in-situ polymerization of an acrylic acid-based monomer and a diolefin derivative crosslinking agent, and the crosslinking type adhesive obtained by the polymerization is easy to gel, so that the problems of reduced solubility of the adhesive and complex material preparation process exist.
In order to overcome the defects of the prior art, in particular to the defects of easy gelation, low solubility and the like of the adhesive in situ polymerization in the presence of a cross-linking agent in the prior art, the invention provides the polyunsaturated carboxylic acid group controllable cross-linking adhesive and the lithium ion battery containing the adhesive.
The purpose of the invention is realized by the following technical scheme:
a binder system comprising a matrix component and a dopant component; the doped component is a bisoxazoline micromolecule, and the matrix component is an unsaturated carboxylic group polymer; in the using process, the matrix component and the doping component are subjected to a cross-linking reaction to form a three-dimensional network structure.
According to the invention, the molar ratio of the bisoxazoline small molecules to the carboxyl groups in the unsaturated carboxylic acid-based polymer is (0.01-0.50): 1.
According to the invention, the structural formula of the bisoxazoline micromolecules is shown as a formula (I),
in the formula (I), R is C1-6Alkylene of (C)6-12Arylene group of (A) or (C)6-12Heteroarylene of (A), R1Same or different, independently from each other selected from H, C1-6Alkyl group of (1).
According to the invention, the structural formula of the bisoxazoline micromolecules is shown as formula (II) -formula (V):
according to the invention, the unsaturated carboxylic acid-based polymer is an autopolymer or copolymer of at least one unsaturated carboxylic acid-based monomer; the comonomer in the copolymer comprises at least one of hydrophilic comonomer, hydrophobic comonomer and amphiphilic comonomer;
the hydrophilic comonomer accounts for 1-60% of the mole fraction of the unsaturated carboxylic acid monomer; the hydrophobic comonomer accounts for 0 to 5 percent of the mole fraction of the unsaturated carboxylic acid monomer; the amphiphilic comonomer accounts for 0 to 1 percent of the mole fraction of the unsaturated carboxylic acid monomer.
According to the invention, the unsaturated carboxylic acid-based polymer has a decomposition temperature of 300-400 ℃ (TG test) and a glass transition temperature of 100-200 ℃ (DSC test).
The invention provides a pole piece which comprises an adhesive formed by the adhesive system.
According to the invention, the pole piece is prepared by coating a slurry on one or both surfaces of a current collector, the slurry comprising 0.5-5 wt% of the above-mentioned binder system.
According to the invention, the peel strength of the adhesive in the pole piece is more than 60N/m, for example, 60-100N/m.
The invention provides a lithium ion battery which comprises the pole piece.
The invention has the beneficial effects that:
the invention provides a polyunsaturated carboxylic group controllable cross-linking type binder and a lithium ion battery containing the binder. The binders of the present invention are formed by crosslinking of linear unsaturated carboxylic acid-based polymers and bisoxazoline small molecules during drying. The crosslinked unsaturated carboxylic acid-based polymer forms a three-dimensional network, so that the active material can be fully coated, and the slippage among active material particles is reduced; in addition, the cross-linked unsaturated carboxylic acid-based polymer can provide more action sites, so that the polyunsaturated carboxylic acid-based controllable cross-linked binder has excellent binding power, and the cycle performance, expansion rate and rate performance of the lithium ion battery using the binder are better than those of the lithium ion battery using a non-cross-linked binder.
Drawings
Fig. 1 is a schematic diagram of an apparatus for testing the peel strength of an adhesive.
Fig. 2 is a graph showing peel strength versus displacement for examples 1,2, 3, 4, 1.1, and 1.2.
Fig. 3 is a graph of peel strength versus displacement for comparative example 1, comparative example 2, and comparative example 3.
Fig. 4 is a graph of peel strength versus displacement for comparative example 4 and comparative example 5.
Detailed Description
[ Binder System ]
As previously mentioned, the present invention provides a binder system comprising a matrix component and a dopant component; the doped component is a bisoxazoline micromolecule, and the matrix component is an unsaturated carboxylic group polymer; in the using process, the matrix component and the doping component are subjected to a cross-linking reaction to form a three-dimensional network structure.
Specifically, in the using process, the carboxyl group of the unsaturated carboxylic acid-based polymer in the matrix component and the bisoxazoline micromolecules in the doping component can perform a crosslinking reaction, and the reaction process and the three-dimensional network structure are shown as follows:
wherein R and R1The definition of (A) is as follows.
In a particular embodiment, the matrix component and the dopant component are capable of undergoing a cross-linking reaction during drying to form a three-dimensional network structure.
In a specific embodiment, the molar ratio of the bisoxazoline small molecule to the carboxyl groups in the unsaturated carboxylic acid-based polymer is (0.01-0.50):1, preferably (0.01-0.20):1, for example 0.01:1, 0.02:1, 0.05:1, 0.08:1, 0.10:1, 0.12:1, 0.15:1, 0.18:1, 0.20:1, 0.23:1, 0.25:1, 0.30:1, 0.35:1, 0.40:1, 0.45:1, 0.50: 1.
In a specific embodiment, the structural formula of the bisoxazoline micromolecule is shown as a formula (I),
in the formula (I), R is C1-6Alkylene of (C)6-12Arylene group of (A) or (C)6-12Heteroarylene of (A), R1Same or different, independently from each other selected from H, C1-6Alkyl group of (1).
For example, R is methylene (-CH)2-) ethylene (-CH2CH2-), phenylene (1, 2-linked, 1, 3-linked or 1, 4-linked) or pyridylene, R1Identical or different, independently of one another, from H, methyl or ethyl.
Illustratively, the structural formula of the bisoxazoline micromolecules is shown as formula (II) to formula (V):
in a particular embodiment, the unsaturated carboxylic acid based polymer is an autopolymer or copolymer of at least one unsaturated carboxylic acid based monomer.
Illustratively, the unsaturated carboxylic monomers include, but are not limited to, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, or the like as illustrative examples; also included are carboxylates formed from the carboxylic acids, i.e., (meth) acrylates, crotonates, itaconates, maleates, or the like.
Illustratively, the comonomer in the copolymer includes, but is not limited to, at least one of a hydrophilic comonomer, a hydrophobic comonomer, and an amphiphilic comonomer, as examples.
Illustratively, the hydrophilic comonomer includes, but is not limited to, as illustrative examples, at least one of (meth) acrylamide, N-methylol (meth) acrylamide, N-dimethylacrylamide, sodium p-styrenesulfonate, sodium vinylsulfonate, sodium allylsulfonate, sodium 2-methallylsulfonate, sodium ethylmethacrylate sulfonate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, dimethyldiallylammonium chloride, and the like.
Illustratively, the hydrophobic comonomer includes, but is not limited to, at least one of methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, styrene, acrylonitrile, and the like, as exemplary.
Illustratively, the amphiphilic comonomer includes, but is not limited to, at least one of stearic acid polyoxyethylene ether (meth) acrylate, nonylphenol polyoxyethylene ether (meth) acrylate, lauryl alcohol polyoxyethylene ether (meth) acrylate, or the like, as exemplary ones.
Illustratively, the hydrophilic comonomer comprises 1 to 60% by mole of the unsaturated carboxylic monomer, illustratively 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%. The hydrophilic comonomer can provide more functional groups such as hydroxyl, amino and sulfonic groups for the adhesive, so that the adhesive effect of the adhesive on the pole piece and the active material is increased, but the content of the hydrophilic comonomer is not high enough, and is not beneficial to the crosslinking reaction of the bisoxazoline micromolecules and the carboxyl when the content is more than 60 percent.
Illustratively, the hydrophobic comonomer comprises 0 to 5% of the mole fraction of the unsaturated carboxylic monomer, illustratively 0%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%. When the mole fraction of the hydrophobic comonomer in the unsaturated carboxylic acid monomer is more than 5%, the solubility of the copolymer is reduced, and the copolymer is easy to precipitate and separate out in the polymerization process.
Illustratively, the amphiphilic comonomer comprises 0 to 1% of the mole fraction of the unsaturated carboxylic monomer, illustratively 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%. A small amount of amphiphilic comonomer plays a role in reducing the surface activity and is beneficial to the polymerization reaction.
In a particular embodiment, the unsaturated carboxylic acid based polymer has a weight average molecular weight of from 50 to 1000, preferably from 80 to 300, ten thousand.
In a specific embodiment, the unsaturated carboxylic acid-based polymer has a decomposition temperature of 300-.
In a particular embodiment, the binder system further includes a solvent component selected from water, such as deionized water. When water is selected as a solvent component, the binder system has the characteristics of no solvent release, environmental requirement conformity, no combustion, low cost, safe use and the like.
In a specific embodiment, the amount of the solvent component added is not particularly defined, and the preparation of the binder system may be achieved and a binder system having a specific solids content, viscosity and pH may be obtained.
In a particular embodiment, the binder system has a solids content of 0.1 to 10 wt.%, preferably 0.3 to 5 wt.%.
In a particular embodiment, the viscosity of the binder system is 100-.
In a particular embodiment, the binder system has a pH of 5 to 7.
In one embodiment, the binder system is a polyunsaturated carboxylic acid based controlled crosslinking binder system.
In a specific embodiment, in order to endow the pole piece with better flexibility, the adhesive system further comprises an SBR emulsion type adhesive, and the addition amount of the SBR emulsion type adhesive is 10-100 wt% of the total mass of the adhesive system.
[ unsaturated carboxylic acid-based Polymer and preparation thereof ]
As mentioned above, the unsaturated carboxylic acid based polymer is an autopolymer or copolymer of at least one of the above unsaturated carboxylic acid based monomers.
Illustratively, the copolymer is a copolymer of at least one of the above-mentioned unsaturated carboxylic acid-based monomers and at least one of the above-mentioned hydrophilic comonomers, or is a copolymer of at least one of the unsaturated carboxylic acid-based monomers and at least one of the hydrophobic comonomers, or is a copolymer of at least one of the unsaturated carboxylic acid-based monomers, at least one of the hydrophilic comonomers and at least one of the hydrophobic comonomers; further, the copolymer also comprises an amphiphilic comonomer.
In one embodiment, the unsaturated carboxylic acid-based polymer is a copolymer of at least one unsaturated carboxylic acid-based monomer and at least one hydrophilic comonomer; the unsaturated carboxylic acid monomers are (methyl) acrylic acid, crotonic acid, itaconic acid and maleic acid, but are not limited to the unsaturated carboxylic acid monomers; the hydrophilic comonomer is at least one of (meth) acrylamide, N-methylol (meth) acrylamide, N-dimethylacrylamide, sodium p-styrenesulfonate, sodium vinylsulfonate, sodium allylsulfonate, sodium 2-methallylsulfonate, sodium ethylmethacrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, or dimethyldiallylammonium chloride, but is not limited to the exemplary hydrophilic comonomer.
In one embodiment, the unsaturated carboxylic acid-based polymer is a copolymer of at least one unsaturated carboxylic acid-based monomer and at least one hydrophobic comonomer; the unsaturated carboxylic acid monomers are (methyl) acrylic acid, crotonic acid, itaconic acid and maleic acid, but are not limited to the unsaturated carboxylic acid monomers; the hydrophobic comonomer is at least one of methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, styrene, acrylonitrile, but is not limited to the exemplified hydrophobic comonomers.
In a particular embodiment, the unsaturated carboxylic acid-based polymer is a copolymer of at least one unsaturated carboxylic acid-based monomer, at least one hydrophilic comonomer, and at least one hydrophobic comonomer; the unsaturated carboxylic acid monomers are (methyl) acrylic acid, crotonic acid, itaconic acid and maleic acid, but are not limited to the unsaturated carboxylic acid monomers; the hydrophilic comonomer is at least one of (meth) acrylamide, N-methylol (meth) acrylamide, N-dimethylacrylamide, sodium p-styrenesulfonate, sodium vinylsulfonate, sodium allylsulfonate, sodium 2-methallylsulfonate, sodium ethylmethacrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, or dimethyldiallylammonium chloride, but is not limited to the exemplary hydrophilic comonomer. The hydrophilic comonomer comprises 1 to 60% by mole of the unsaturated carboxylic monomer, illustratively 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%. The hydrophobic comonomer is at least one of methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, styrene, acrylonitrile, but is not limited to the exemplified hydrophobic comonomers. The hydrophobic comonomer comprises 0 to 5%, illustratively 0%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the total mole fraction of the unsaturated carboxylic monomer and the hydrophilic comonomer.
In a specific embodiment, the unsaturated carboxylic acid-based polymer further comprises an amphiphilic comonomer selected from at least one of stearic acid polyoxyethylene ether (meth) acrylate, nonylphenol polyoxyethylene ether (meth) acrylate, and lauryl alcohol polyoxyethylene ether (meth) acrylate. The amphiphilic comonomer comprises 0 to 1% of the mole fraction of the unsaturated carboxylic monomer, illustratively 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%.
Illustratively, the unsaturated carboxylic acid-based polymer is prepared, for example, by:
at least one unsaturated carboxylic acid monomer, optional hydrophilic comonomer, optional hydrophobic comonomer and optional amphiphilic comonomer are mixed and dissolved in water (such as deionized water), inert gas is used for protection, mechanical stirring is carried out, and an initiator is added to initiate polymerization, so as to prepare the unsaturated carboxylic acid-based polymer.
The temperature of the dissolution is, for example, room temperature.
Wherein the polymerization reaction temperature is 30-100 ℃, preferably 40-80 ℃.
Wherein, the stirring speed is 300-1000rpm, preferably 500-800 rpm.
Wherein, the inert gas is high-purity nitrogen or argon.
The initiator is at least one of potassium persulfate, ammonium persulfate, sodium persulfate, tetravalent cerium salt (ammonium ceric nitrate), potassium permanganate, sodium persulfate/sodium bisulfite, ferrous sulfate/hydrogen peroxide, ammonium persulfate/tetramethylethylenediamine and ammonium persulfate/sodium sulfite, and the addition amount of the initiator is 0.1-2 wt% of the total mass of the comonomer.
[ Pole pieces ]
As mentioned above, the present invention provides a pole piece comprising an adhesive formed from the above adhesive system.
In a specific embodiment, the pole piece is prepared by coating a slurry on one or both surfaces of a current collector, wherein the slurry comprises an active material, an additive and the binder system.
Illustratively, the slurry comprises 0.5-5 wt% of the above-mentioned binder system, preferably 0.8-2.5 wt% of the above-mentioned binder system, and further preferably 1.5-2.5 wt% of the above-mentioned binder system.
In a specific embodiment, the binder in the pole piece has a three-dimensional network structure formed by a cross-linking reaction.
In a particular embodiment, the peel strength of the adhesive in the pole piece is 60N/m or more, for example 60-100N/m.
In a specific embodiment, the pole piece is, for example, a positive pole piece or a negative pole piece.
In a specific embodiment, in the positive electrode plate, the current collector is a single-optical-surface aluminum foil, a double-optical-surface aluminum foil or a porous aluminum foil, the active material in the slurry is at least one of lithium iron phosphate, a ternary positive electrode material and lithium cobaltate, the additive is a conductive agent, and the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotubes.
In a specific embodiment, in the negative electrode plate, the current collector is a single-optical-surface copper foil, a double-optical-surface copper foil or a porous copper foil, the active material in the slurry is at least one of artificial graphite, natural graphite, mesophase carbon spheres, silicon oxide, nano silicon powder, silicon oxide, silicon carbon, silicon-doped graphite and lithium titanate, the additive is a conductive agent and a dispersing agent, the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotubes, and the dispersing agent is sodium carboxymethyl cellulose.
[ preparation of Pole pieces ]
The invention also provides a preparation method of the pole piece, which comprises the following steps:
a) preparing the binder system comprising: preparing a matrix component, wherein the matrix component is an unsaturated carboxylic acid-based polymer; preparing a doping component which is a bisoxazoline micromolecule.
In a specific embodiment, the preparation method of the pole piece comprises the following steps:
a) preparing the binder system comprising: preparing a matrix component, wherein the matrix component is an unsaturated carboxylic acid-based polymer; preparing a doping component, wherein the doping component is a bisoxazoline micromolecule;
b) uniformly mixing an active material, a conductive agent and the binder system obtained in the step a) to obtain slurry;
c) coating the slurry obtained in the step b) on the surface of at least one side of a current collector, and drying to obtain the pole piece.
In a specific embodiment, the electrode plate is a positive electrode plate, and the preparation method comprises the following steps:
a) preparing the binder system comprising: preparing a matrix component, wherein the matrix component is an unsaturated carboxylic acid-based polymer; preparing a doping component, wherein the doping component is a bisoxazoline micromolecule;
b) uniformly mixing a positive electrode active material (such as 96.2 wt% of lithium cobaltate), a conductive agent (such as 2 wt% of carbon black) and the binder system (1.8 wt%) to obtain positive electrode slurry;
c) and coating the positive electrode slurry on the surface of at least one side of the current collector, and drying to obtain the positive electrode piece.
In a specific embodiment, the electrode plate is a negative electrode plate, and the preparation method comprises the following steps:
a) preparing the binder system comprising: preparing a matrix component, wherein the matrix component is an unsaturated carboxylic acid-based polymer; preparing a doping component, wherein the doping component is a bisoxazoline micromolecule;
b) uniformly mixing a negative electrode active material (such as 96.5 wt% of graphite), a conductive agent (such as 1 wt% of carbon black), a dispersing agent (such as 1 wt% of sodium carboxymethyl cellulose) and the binder system (such as 1.5 wt%) to obtain negative electrode slurry;
c) and coating the negative electrode slurry on at least one side surface of the current collector, and drying to obtain the negative electrode piece.
In a specific embodiment, step a) further comprises: and mixing the doping component and the matrix component to obtain the binder system.
In a specific embodiment, step a) specifically comprises: preparing a matrix component, wherein the matrix component is an unsaturated carboxylic acid-based polymer, and dissolving the matrix component in water to form an aqueous solution of the matrix component; preparing a doping component, wherein the doping component is a bisoxazoline micromolecule; and adding the bisoxazoline micromolecules into the aqueous solution of the matrix component, and fully stirring and mixing to prepare the binder system.
In step a), the temperature of the mixing is 25-40 ℃.
In the step a), the stirring speed is 300-1000 rpm.
[ lithium ion Battery ]
As described above, the present invention provides a lithium ion battery, which includes the above-mentioned pole piece.
In a specific embodiment, the positive electrode plate, the negative electrode plate and the diaphragm are assembled into the battery cell in a winding or laminating manner, then are packaged by an aluminum plastic film, and then are subjected to baking, electrolyte injection, formation and secondary sealing in sequence to obtain the lithium ion battery.
In a specific embodiment, the capacity retention rate after 100 cycles of 0.5C charge and discharge at 25 ℃ at room temperature is 90% or more (e.g., 91% or more), as calculated as 100 cycles.
In one specific embodiment, the expansion rate is 6% or less after 100 cycles of 0.5C charge and discharge at 25 ℃ at room temperature, calculated as 100 cycles.
The lithium ion battery with the pole piece can have better cycle performance.
The polyunsaturated carboxylic group controllable cross-linking type adhesive is used for manufacturing the pole piece of the lithium ion battery according to the pole piece production process commonly used in the industry. The lithium ion battery comprises a positive pole piece, a negative pole piece, a diaphragm and electrolyte, and is assembled into an aluminum plastic film flexible package battery.
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
The peel strengths referred to in the following examples were measured as follows:
coating the negative electrode slurry on the surface of a current collector (such as copper foil), drying and cold-pressing to form a pole piece, and cutting the prepared pole piece into a test sample with the size of 20 multiplied by 100mm for later use; bonding the pole piece to the surface to be tested by using a double-sided adhesive tape, and compacting by using a compression roller to ensure that the pole piece is completely attached to the pole piece; the other side of the double-sided adhesive tape of the sample is adhered to the surface of the stainless steel, and one end of the sample is reversely bent, wherein the bending angle is 180 degrees; the testing is carried out by adopting a high-speed rail tensile machine, one end of stainless steel is fixed on a clamp below the tensile machine, the bent tail end of a sample is fixed on an upper clamp, the angle of the sample is adjusted to ensure that the upper end and the lower end are positioned at the vertical position, then the sample is stretched at the speed of 50mm/min until the sample is completely peeled off from a substrate, the displacement and the acting force in the process are recorded, and the force when the stress is balanced is generally regarded as the peeling strength of a pole piece, and the schematic diagram of the device is shown.
The cycle retention referred to in the following examples was tested using the following method: the capacity retention rate and the expansion rate of the battery after 100 times of charge-discharge cycles at 0.5C/0.5C at a normal temperature of 25 ℃ were calculated for 100 times.
The rate capability (rate discharge) referred to in the following examples was tested using the following method: the full-electricity batteries are respectively discharged to cut-off voltage at 0.2C/0.5C/1.0C/1.5C/2.0C, and the capacity retention rate (the capacity retention rate discharged compared with 0.2C) is calculated, namely the values of 0.5C/0.2C, 1.0C/0.2C, 1.5C/0.2C and 2C/0.2C.
The viscosities referred to in the following examples were measured using a common digital display rotational viscometer.
Example 1
Preparation of the binder system:
dispersing 10g of acrylic acid in 190g of deionized water, mechanically stirring at 800rpm, heating to 40 ℃, preserving heat for 30min, introducing nitrogen, adding 0.05g of sodium persulfate and 0.2g of sodium bisulfite, and continuing to react for 10 h. After the reaction is finished, the temperature is reduced to 30 ℃ to obtain an unsaturated carboxylic acid-based polymer, then 2g of bisoxazoline micromolecule shown in the formula (II) is added, and mechanical stirring is carried out for 30min at 500rpm to obtain a binder system, wherein the viscosity is 3500mPa & s.
The prepared unsaturated carboxylic acid-based polymer is characterized, and the weight average molecular weight is 100 ten thousand; the decomposition temperature was 325 ℃ (TG test) and the glass transition temperature was 106 ℃ (DSC test).
Preparing a negative pole piece: compounding a negative active material silicon-based/graphite composite negative material (SiOx/artificial graphite is compounded to prepare the negative active material with the gram volume of 450mAh/g), the prepared polyunsaturated carboxylic group controllable crosslinking binder and conductive carbonAnd black is dispersed in deionized water, and uniformly dispersed negative electrode slurry is obtained after stirring, wherein the solid components comprise 96.5 wt% of silicon-based/graphite composite negative electrode material, 1.5 wt% of the prepared binder system, 1 wt% of sodium carboxymethylcellulose and 1 wt% of conductive carbon black, the solid content of the negative electrode slurry is 45 wt%, and the viscosity is 3500-5500mPa & s. The negative electrode slurry is evenly coated on two sides of a copper foil after passing through a gauze with 150 meshes, dried for 4 hours at 80-130 ℃, and compacted by a roller press with the compaction density of 1.5-1.7g/cm3And obtaining the negative pole piece.
Preparing a positive pole piece: dispersing a positive electrode active material lithium cobaltate, a binder PVDF and conductive carbon black in N-methyl pyrrolidone, and stirring to obtain uniformly dispersed positive electrode slurry, wherein the solid components comprise 96.5 wt% of lithium cobaltate, 1.5 wt% of PVDF and 2 wt% of conductive carbon black, the solid content of the positive electrode slurry is 68 wt%, and the viscosity is 21505mPa & s. Uniformly coating the anode slurry on two surfaces of an aluminum foil, drying at the temperature of 100 ℃ and 130 ℃ for 4h, compacting the aluminum foil by using a roller press, wherein the compaction density is 2.8-3.5g/cm3And obtaining the positive pole piece.
Preparing a lithium ion battery: and (3) winding the positive plate, the negative plate and a diaphragm (a PP/PE/PP composite membrane with the thickness of 9 mu m and the porosity of 41%) into a battery cell, then baking, injecting electrolyte, forming and secondary sealing to obtain the lithium ion battery.
Example 1.1
Different from example 1, the amount of the added bisoxazoline small molecules is 1g, and the other conditions are the same.
Example 1.2
The difference from example 1 was that the amount of the bisoxazoline small molecule to be added was 3g, and the other conditions were the same.
Example 2
Preparation of the binder system:
dispersing 8g of acrylic acid and 2g of acrylamide in 190g of deionized water, mechanically stirring at 800rpm, heating to 70 ℃, preserving heat for 30min, introducing nitrogen, adding 0.05g of potassium persulfate, and continuing to react for 10 h. After the reaction, the temperature was reduced to 30 ℃ to obtain an unsaturated carboxylic acid based polymer, and then 1.4g of a bisoxazoline small molecule represented by the formula (III) was added thereto, and the mixture was mechanically stirred at 500rpm for 30 minutes to obtain a binder system having a viscosity of 4200 mPas.
The prepared unsaturated carboxylic acid-based polymer is characterized, and the weight average molecular weight is 240 ten thousand; the decomposition temperature was 338 ℃ (TG test) and the glass transition temperature was 118 ℃ (DSC test).
The battery pole piece fabrication and battery assembly process were the same as in example 1.
Example 3
Preparation of the binder system:
dispersing 10g of methacrylic acid, 2g of hydroxyethyl acrylate and 0.2g of acrylonitrile in 210g of deionized water, mechanically stirring at 800rpm, heating to 40 ℃, keeping the temperature for 30min, introducing nitrogen, adding 0.06g of ammonium persulfate and 0.03g of tetramethylethylenediamine, and continuing to react for 12 h. After the reaction is finished, the temperature is reduced to 30 ℃ to obtain an unsaturated carboxylic acid-based polymer, and then 2.5g of bisoxazoline micromolecules shown in the formula (IV) are added, and the mixture is mechanically stirred at 500rpm for 30min to obtain a binder system with the viscosity of 5130 mPas.
The prepared unsaturated carboxylic acid-based polymer is characterized, and the weight average molecular weight is 310 ten thousand; the decomposition temperature was 346 deg.C (TG test) and the glass transition temperature was 124 deg.C (DSC test).
The battery pole piece fabrication and battery assembly process were the same as in example 1.
Example 4
Preparation of the binder system:
dispersing 10g of methacrylic acid, 2g of N-hydroxymethyl acrylamide, 0.2g of butyl acrylate and 0.1 part of stearic acid polyoxyethylene ether acrylate into 210g of deionized water, mechanically stirring at 800rpm, heating to 70 ℃, preserving heat for 30min, introducing nitrogen, adding 0.08g of sodium persulfate, and continuing to react for 12 h. After the reaction is finished, the temperature is reduced to 30 ℃ to obtain an unsaturated carboxylic group polymer, then 3g of bisoxazoline micromolecules shown in the formula (V) are added, and the mixture is mechanically stirred for 30min at 500rpm to obtain a binder system with the viscosity of 8335 mPas.
The prepared unsaturated carboxylic acid-based polymer is characterized, and the weight average molecular weight is 380 ten thousand; the decomposition temperature was 358 deg.C (TG test) and the glass transition temperature was 133 deg.C (DSC test).
The battery pole piece fabrication and battery assembly process were the same as in example 1.
Example 5
Preparation of the binder system:
dispersing 9g of acrylic acid, 1g of sodium acrylate and 1g of acrylamide in 189g of deionized water, mechanically stirring at 800rpm, heating to 40 ℃, preserving heat for 30min, introducing nitrogen, adding 0.055g of sodium persulfate and 0.2g of sodium bisulfite, and continuing to react for 10 h. After the reaction is finished, the temperature is reduced to 30 ℃ to obtain an unsaturated carboxylic group polymer, then 2g of bisoxazoline micromolecules shown in the formula (II) are added, and the mixture is mechanically stirred for 30min at 500rpm to obtain a binder system with the viscosity of 4210 mPas.
The prepared unsaturated carboxylic acid-based polymer is characterized, and the weight average molecular weight is 108 ten thousand; the decomposition temperature was 324 ℃ (TG test) and the glass transition temperature was 109 ℃ (DSC test).
Comparative example 1
Unlike example 1, the bis-oxazoline small molecule was not added, and the conditions were the same.
Comparative example 2
Unlike example 2, the bis-oxazoline small molecule was not added, and the conditions were the same.
Comparative example 3
Unlike example 3, the bis-oxazoline small molecule was not added, and the conditions were the same.
Comparative example 4
Unlike example 4, the bis-oxazoline small molecule was not added, and the conditions were the same.
Comparative example 5
Unlike example 1, a commercial non-crosslinked binder (Raynaud's BM-1100H) was used in the negative electrode formulation process, as was the case with the other conditions.
Test example 1
The lithium ion batteries prepared in the above examples and comparative examples were subjected to performance tests using the above test methods, in which peel strength-displacement graphs are shown in fig. 2 to 4, and the test data are summarized in tables 1 and 2.
TABLE 1
| Peel strength (N/m) | Capacity retention (%) | Swelling ratio (%) | |
| Example 1 | 65 | 96 | 5.5 |
| Example 1.1 | 59 | 91 | 5.9 |
| Example 1.2 | 67 | 96 | 5.4 |
| Comparative example 1 | 30 | 82 | 8.3 |
| Comparative example 5 | 34 | 90 | 7.9 |
| Example 2 | 71 | 95 | 5.3 |
| Comparative example 2 | 32 | 75 | 8.4 |
| Example 3 | 80 | 95 | 5.2 |
| Comparative example 3 | 38 | 79 | 8.7 |
| Example 4 | 83 | 98 | 5.4 |
| Comparative example 4 | 34 | 87 | 8.2 |
TABLE 2 Rate Properties of batteries prepared in examples and comparative examples
As can be seen from tables 1 and 2 above, the pole piece peel strength using the binders according to examples 1-4, and examples 1.1 and 1.2 of the present invention is high compared to the single component polyunsaturated carboxylic acid based controlled cross-linking binder without added cross-linking agent, and the peel strength data are obtained by reading the average values in figures 2-4. After 100-week charge/discharge cycles, the capacity retention rate was high, and the performance was improved to some extent as compared with that of a commercial non-crosslinked binder. In addition, comparing examples 1, 1.1 and 1.2, it can be seen that the increase of the amount of the crosslinking agent increases the number of crosslinking sites, increases the peel strength, and has a good effect of suppressing swelling, but the capacity retention rate in example 1.2 is not improved because the capacity of the binder to absorb the electrolyte is reduced after the number of crosslinking sites is increased, which affects the transmission of lithium ions, and the amount of the crosslinking agent added can be adjusted reasonably as required in practical application. In conclusion, the polyunsaturated carboxylic acid group controllable crosslinking type binder can well stabilize the active material on the pole piece, so that the capacity retention rate is higher.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A binder system, wherein the binder system comprises a matrix component and a dopant component; the doped component is a bisoxazoline micromolecule, and the matrix component is an unsaturated carboxylic group polymer; in the using process, the matrix component and the doping component are subjected to a cross-linking reaction to form a three-dimensional network structure.
2. The binder system of claim 1 wherein the molar ratio of the bisoxazoline small molecules to the carboxyl groups of the unsaturated carboxylic acid-based polymer is (0.01-0.50): 1.
3. The binder system of claim 1 or 2, wherein the bisoxazoline small molecules have a structural formula as shown in formula (I),
in the formula (I), R is C1-6Alkylene of (C)6-12Arylene group of (A) or (C)6-12Heteroarylene of (A), R1Same or different, independently from each other selected from H, C1-6Alkyl group of (1).
4. The binder system of claim 3 wherein the bisoxazoline small molecules have a formula of (II) to (V):
5. the binder system of any one of claims 1-4, wherein the unsaturated carboxylic acid-based polymer is an autopolymer or copolymer of at least one unsaturated carboxylic acid-based monomer; the comonomer in the copolymer comprises at least one of hydrophilic comonomer, hydrophobic comonomer and amphiphilic comonomer;
the hydrophilic comonomer accounts for 1-60% of the mole fraction of the unsaturated carboxylic acid monomer; the hydrophobic comonomer accounts for 0 to 5 percent of the mole fraction of the unsaturated carboxylic acid monomer; the amphiphilic comonomer accounts for 0 to 1 percent of the mole fraction of the unsaturated carboxylic acid monomer.
6. The binder system of any of claims 1-5, wherein the unsaturated carboxylic acid-based polymer has a decomposition temperature of 300-.
7. A pole piece, wherein the pole piece comprises an adhesive formed from the adhesive system of any one of claims 1-6.
8. The pole piece according to claim 7, wherein the pole piece is prepared by coating a slurry on one or both surfaces of a current collector, the slurry comprising 0.5-5 wt% of the above binder system.
9. The pole piece according to claim 7 or 8, wherein the peel strength of the adhesive in the pole piece is 60N/m or more.
10. A lithium ion battery comprising the pole piece of any one of claims 7-9.
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| CN112851374A (en) * | 2021-01-25 | 2021-05-28 | 上海佰奥聚新材料科技有限公司 | Dispersion binder combination for nano zirconia ceramic and application thereof |
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| CN1360584A (en) * | 1999-07-12 | 2002-07-24 | Dsm有限公司 | Preparation of aromatic bisoxazoline |
| CN107534150A (en) * | 2015-04-22 | 2018-01-02 | 东亚合成株式会社 | Rechargeable nonaqueous electrolytic battery electrode binding agent and application thereof |
| CN108368294A (en) * | 2015-12-07 | 2018-08-03 | 纳幕尔杜邦公司 | The curing agent of fluorinated elastomer |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1360584A (en) * | 1999-07-12 | 2002-07-24 | Dsm有限公司 | Preparation of aromatic bisoxazoline |
| CN107534150A (en) * | 2015-04-22 | 2018-01-02 | 东亚合成株式会社 | Rechargeable nonaqueous electrolytic battery electrode binding agent and application thereof |
| CN108368294A (en) * | 2015-12-07 | 2018-08-03 | 纳幕尔杜邦公司 | The curing agent of fluorinated elastomer |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112851374A (en) * | 2021-01-25 | 2021-05-28 | 上海佰奥聚新材料科技有限公司 | Dispersion binder combination for nano zirconia ceramic and application thereof |
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