Background technology
The features such as lithium ion battery has that operating voltage is high, energy density is large, have extended cycle life, self-discharge is little, memory-less effect, environmental friendliness, have become the ideal source of the equipment such as mobile communication, power tool, medical device at present.Along with domestic and international wideling popularize new-energy automobile, lithium ion battery, according to its unique advantage, becomes the first-selection of electric car power supply, and therefore, lithium ion battery has vast potential for future development.
LiFePO
4battery has excellent security and normal-temperature circulating performance, becomes the preferred material of batteries of electric automobile at present.But LiFePO
4also there is certain deficiency in battery high-temperature cycle performance.In electromobile, normally there are hundreds of or thousands of lithium ion batteries formation battery systems, for electromobile provides power.Battery can produce a large amount of heat in application process, if can not leave in time, the self-heating battery of meeting, reduces the cycle performance of battery; When especially using in low latitude in summer region, deterioration of battery is more obvious.Major cause is: HF during high temperature in electrolytic solution can accelerate LiFePO
4deng Fe
2+the dissolving of metal ion, under the effect of electric field, Fe
2+metal ion moves to negative pole, and reduction is deposited on negative electrode active material surface, and accelerate catalytic decomposition electrolytic solution, at SEI film (solid electrolyte film) progressive additive of negative terminal surface, interface impedance increases rapidly; Produce gas, cause inside battery to polarize and increase, cycle performance declines rapidly simultaneously.
LiFePO is improved in prior art
4the method of the high temperature circulation stability of battery mainly contains three kinds: 1) in electrolytic solution, add a small amount of additive (NSC 11801, VC additive) (Electrochemical and Solid-State Letters, 9 (2006) A537-A541); 2) at Surface coating one deck compound (AlF
3) reduce electrolytic solution and LiFePO
4the direct contact (Journal of Alloys and Compounds, 487 (2009) 214-217) of material; 3) method of doping is adopted to improve LiFePO
4high-temperature stability (Bull.Korean Chem.Soc.30 (2009) 2223-2226).These three kinds of method effects are not fine at present.
Summary of the invention
The object of this invention is to provide a kind of lithium ion battery composite separation membrane coating, apply guarantor's fluidity that this coating can significantly improve barrier film, reduce Fe
2+dissolution and transport, improve the high temperature cyclic performance of lithium ion battery.
Second object of the present invention is to provide a kind of lithium ion battery composite separation membrane using this coating.
In order to realize above object, the technical solution adopted in the present invention is: a kind of lithium ion battery composite separation membrane coating, and this coating is polyolefin backbone is connected with the polymkeric substance comprising cyanoethyl side chain.
Inorganic powder can also be added in described coating, formation polyolefin backbone is connected with and comprises the polymkeric substance of cyanoethyl side chain and the mixture of inorganic powder, the massfraction in described mixture, polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain is 5% ~ 95%.
Described inorganic powder is Al
2o
3, SiO
2, ZrO
2, TiO
2, BaSO
4, BaCO
3in any one or a few, powder granule is 0.05 ~ 5 μm.
Described polyolefin backbone is connected with the multipolymer that the polymkeric substance comprising cyanoethyl side chain is the first monomer and second comonomer, the molecular weight of this multipolymer is the mass ratio of the 10000 ~ 500000, first monomer and second comonomer is 5:1 ~ 97:3; Wherein, the first monomer is monomer 1 or monomer 2, and structural formula is:
Monomer 1:
Monomer 2:
Second comonomer is any one or two kinds in acrylic monomer, acrylic ester monomer, Acrylates monomer.
Described acrylic monomer is acrylic or methacrylic acid; Described acrylics monomer is methyl acrylate, ethyl propenoate, butyl acrylate, Isooctyl acrylate monomer, methyl methacrylate, β-dimethyl-aminoethylmethacrylate or butyl methacrylate; Described Acrylates monomer is Lithium acrylate, sodium acrylate, potassium acrylate, ammonium acrylate, lithium methacrylate, sodium methacrylate, methacrylic acid potassium or ammonium methacrylate.
Described polyolefin backbone is connected with the polymkeric substance comprising cyanoethyl side chain to be made up of following methods: by the first monomer and second comonomer, totally 100 weight parts are in a solvent dispersed, add the initiator of 0.1 ~ 5 weight part and the chain-transfer agent of 0 ~ 0.5 weight part, be heated to 60 ~ 65 DEG C of reaction 8 ~ 12h, obtain final product.
Described solvent is tetrahydrofuran (THF) or dimethyl formamide.
Described initiator is Diisopropyl azodicarboxylate or benzoyl peroxide; Described chain-transfer agent is DDM dodecyl mercaptan.
Use a lithium ion battery composite separation membrane for above-mentioned coating, this composite diaphragm applies one deck lithium ion battery composite separation membrane coating at the one or both sides of microporous polyolefin film, forms coating; The thickness of described coating is 0.5 ~ 5 μm.
Described microporous polyolefin film is any one in PP/PE/PP trilamellar membrane, PP/PP duplicature, PP/PE duplicature, PE/PE duplicature, PP unitary film, PE unitary film, and micropore size is 0.05 ~ 5 μm.
Obtained composite diaphragm is cut into the suitable width of battery, be clipped between positive and negative electrode, coat side is facing to positive pole, and adopt spirally wound or stacked or volume stacked to make battery core, be encapsulated in aluminum plastic film, inject electrolytic solution, sealing, heat-activated, shaping obtains LiFePO
4lithium ion battery.
Lithium ion battery composite separation membrane coating of the present invention, for polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain, use the lithium ion battery composite separation membrane of this coating, after electrolytic solution activation, polyolefin backbone is connected with the polymeric coating comprising cyanoethyl side chain and forms dielectric film, utilize cyanoethyl coordination, significantly improve guarantor's fluidity of barrier film, reduce Fe
2+dissolution and transport, improve the high temperature cyclic performance of lithium ion battery; Polyolefin backbone is connected with in the polymer coating comprising cyanoethyl side chain and can also adds inorganic powder, form mixture coating, use the lithium ion battery composite separation membrane of this coating, utilize cyanoethyl coordination and the effect of inorganic powder surface physical bond, reduce Fe further
2+dissolution and transport, strengthen the temperature tolerance of barrier film, improve the high temperature cyclic performance of lithium ion battery.
Embodiment
Below in conjunction with embodiment, the invention will be further described:
Embodiment 1
The lithium ion battery composite separation membrane coating of the present embodiment, for polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain, this polymkeric substance is the multipolymer of monomer 1 and acrylic ester monomer, the molecular weight of this multipolymer is 100000, acrylic ester monomer is methyl acrylate, monomer 1 is 5:1 with the mass ratio of methyl acrylate, and wherein, the structural formula of monomer 1 is:
The preparation method of this lithium ion battery composite separation membrane coating is: 50g monomer 1 and 10g methacrylate monomer are dispersed in 120g dimethyl formamide, add 0.6g Diisopropyl azodicarboxylate, is heated to 60 DEG C of reaction 8h, obtains described coating.
The lithium ion battery composite separation membrane of the use above-mentioned coating of the present embodiment, that the one side being the PP/PE/PP trilamellar membrane of 5 μm at micropore size applies polymer coating one deck polyolefin backbone being connected with and comprising cyanoethyl side chain, form coating, the thickness of coating is 0.5 μm.
Embodiment 2
The lithium ion battery composite separation membrane coating of the present embodiment, for polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain, this polymkeric substance is the multipolymer of monomer 2 and acrylic monomer, the molecular weight of this multipolymer is 10000, acrylic monomer is methacrylic acid, monomer 2 is 10:1 with the mass ratio of methacrylic acid, and wherein, the structural formula of monomer 2 is:
The preparation method of this lithium ion battery composite separation membrane coating, that 100g monomer 2 and 10g methacrylic acid monomer are dispersed in 220g tetrahydrofuran (THF), add 1.1g benzoyl peroxide, in order to Molecular regulator amount adds 0.55g DDM dodecyl mercaptan chain-transfer agent, be heated to 62 DEG C of reaction 8h, obtain described coating.
The lithium ion battery composite separation membrane of the use above-mentioned coating of the present embodiment, be the two sides of the PP/PE duplicature of 1 μm at micropore size, coating one deck polyolefin backbone is connected with the polymer coating comprising cyanoethyl side chain, and form coating, the thickness of coating is 5 μm.
Embodiment 3
The lithium ion battery composite separation membrane coating of the present embodiment, for polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain, this polymkeric substance is the multipolymer of monomer 1 and acrylic ester monomer, the molecular weight of this multipolymer is 500000, acrylic ester monomer is ethyl propenoate, methyl methacrylate, monomer 1 is 97:2:1 with the mass ratio of ethyl propenoate, methyl methacrylate, and wherein, the structural formula of monomer 1 is:
The preparation method of this composite diaphragm for lithium ion battery, that 97g monomer 1 and 2g ethyl propenoate, 1g methyl methacrylate monomer are dispersed in 200g dimethyl formamide, add 5g Diisopropyl azodicarboxylate, be heated to 65 DEG C of reaction 12h and namely obtain described coating.
The lithium ion battery composite separation membrane of the use above-mentioned coating of the present embodiment, be the one side of the PP unitary film of 0.05 μm at micropore size, coating one deck polyolefin backbone is connected with the polymer coating comprising cyanoethyl side chain, and form coating, the thickness of coating is 1 μm.
Embodiment 4
The lithium ion battery composite separation membrane coating of the present embodiment, for polyolefin backbone being connected with the polymkeric substance and Al that comprise cyanoethyl side chain
2o
3the mixture of powder.Polyolefin backbone is connected with the multipolymer that the polymkeric substance comprising cyanoethyl side chain is monomer 2 and Acrylates monomer, the molecular weight of this multipolymer is 50000, Acrylates monomer is Lithium acrylate, and monomer 2 is 5:1 with the mass ratio of Lithium acrylate, and the structural formula of monomer 2 is:
The massfraction in mixture, polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain is 5%.
The preparation method of this lithium ion battery composite separation membrane coating, that 50g monomer 2 and 10g Lithium acrylate monomer are dispersed in 1200g tetrahydrofuran (THF), add 0.6g benzoyl peroxide, be heated to 61 DEG C of reaction 9h and obtain polymers soln polyolefin backbone being connected with and comprising cyanoethyl side chain; By the Al of 1140g
2o
3powder adds in polymers soln, namely obtains described coating after dispersed.
The lithium ion battery composite separation membrane of the use above-mentioned coating of the present embodiment is the two sides at PP/PP duplicature, and coating one deck polyolefin backbone is connected with the polymkeric substance and Al that comprise cyanoethyl side chain
2o
3the mixture coating of powder, form coating, the thickness of coating is 5 μm.
Embodiment 5
The lithium ion battery composite separation membrane coating of the present embodiment, for polyolefin backbone being connected with the polymkeric substance and SiO that comprise cyanoethyl side chain
2powder, BaSO
4the mixture of powder.Polyolefin backbone is connected with the multipolymer that the polymkeric substance comprising cyanoethyl side chain is monomer 1 and acrylic ester monomer, the molecular weight of this multipolymer is 400000, acrylic ester monomer is Isooctyl acrylate monomer, and monomer 1 is 8.5:1 with the mass ratio of Isooctyl acrylate monomer, and the structural formula of monomer 1 is:
The massfraction in mixture, polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain is 95%.
The preparation method of this lithium ion battery composite separation membrane coating, that 85g monomer 1 and 10g Isooctyl acrylate monomer monomer are dispersed in 180g dimethyl formamide, add 0.95g Diisopropyl azodicarboxylate, in order to Molecular regulator amount adds 0.095g DDM dodecyl mercaptan chain-transfer agent, be heated to 63 DEG C of reaction 11h and obtain polymers soln polyolefin backbone being connected with and comprising cyanoethyl side chain; Again by 3g SiO
2, 2g BaSO
4powder adds in polymers soln, namely obtains described coating after dispersed.
The lithium ion battery composite separation membrane of the use above-mentioned coating of the present embodiment is the one side at PE/PE duplicature, and coating one deck polyolefin backbone is connected with the polymkeric substance and SiO that comprise cyanoethyl side chain
2powder, BaSO
4the mixture coating of powder, form coating, the thickness of coating is 2 μm.
Embodiment 6
The lithium ion battery composite separation membrane coating of the present embodiment, for polyolefin backbone being connected with the polymkeric substance and TiO that comprise cyanoethyl side chain
2the mixture of powder.Polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain is monomer 2 and the multipolymer of acrylic monomer, acrylic ester monomer, the molecular weight of this multipolymer is 120000, acrylic monomer is vinylformic acid, acrylic ester monomer is butyl methacrylate, monomer 2 is 97:1:2 with the mass ratio of vinylformic acid, butyl methacrylate, and the structure of monomer 2 is:
The massfraction in mixture, polyolefin backbone being connected with the polymkeric substance comprising cyanoethyl side chain is 50%.
The preparation method of this lithium ion battery composite separation membrane coating, that 97g monomer 2 and 1g vinylformic acid, 2g butylmethacrylate monomer are dispersed in 200g tetrahydrofuran (THF), add 1g benzoyl peroxide, be heated to 64 DEG C of reaction 12h and obtain polymers soln polyolefin backbone being connected with and comprising cyanoethyl side chain; Again by the TiO of 100g
2powder adds in polymers soln, namely obtains described coating after dispersed.
The lithium ion battery composite separation membrane of the use above-mentioned coating of the present embodiment is the two sides at PE duplicature, and coating one deck polyolefin backbone is connected with the polymkeric substance and TiO that comprise cyanoethyl side chain
2the mixture coating of powder, form coating, the thickness of coating is 0.5 μm.
Experimental example
Composite diaphragm obtained for embodiment 1 ~ 6 is cut into the suitable width of battery, is clipped between positive and negative electrode, coat side is facing to positive pole, and adopt volume stacked to make battery core, be encapsulated in aluminum plastic film, inject electrolytic solution, sealing, heat-activated, shaping obtains LiFePO
4lithium ion battery.
By the LiFePO using the obtained composite diaphragm of embodiment 1 ~ 6 to prepare
4lithium ion battery and the LiFePO using conventional separator (microporous polyolefin film) to obtain by same procedure
4lithium ion battery carries out high temperature (45 DEG C) cycle performance test experiments, and result is as shown in table 1.Experimental result illustrates, high temperature (45 DEG C) cycle performance of the composite diaphragm lithium ion battery using embodiment 1 ~ 6 obtained is relative to conventional separator (microporous polyolefin film), and tool increases significantly.
Composite diaphragm lithium ion battery 45 DEG C of cycle performance test results that table 1 uses embodiment 1 ~ 6 obtained