CN114744202A - Positive pole piece, preparation method thereof and lithium ion battery - Google Patents
Positive pole piece, preparation method thereof and lithium ion battery Download PDFInfo
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- CN114744202A CN114744202A CN202210571549.0A CN202210571549A CN114744202A CN 114744202 A CN114744202 A CN 114744202A CN 202210571549 A CN202210571549 A CN 202210571549A CN 114744202 A CN114744202 A CN 114744202A
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- positive pole
- positive electrode
- positive
- pole piece
- polyvinylidene fluoride
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 67
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 67
- 238000002360 preparation method Methods 0.000 title claims abstract description 46
- 239000002033 PVDF binder Substances 0.000 claims abstract description 75
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims abstract description 73
- 239000013543 active substance Substances 0.000 claims abstract description 19
- 239000011230 binding agent Substances 0.000 claims abstract description 15
- 239000000463 material Substances 0.000 claims abstract description 13
- 239000011883 electrode binding agent Substances 0.000 claims description 30
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 26
- 239000007774 positive electrode material Substances 0.000 claims description 24
- 239000002904 solvent Substances 0.000 claims description 22
- 239000011267 electrode slurry Substances 0.000 claims description 21
- 239000007787 solid Substances 0.000 claims description 18
- 239000012528 membrane Substances 0.000 claims description 17
- 239000004020 conductor Substances 0.000 claims description 16
- 238000002156 mixing Methods 0.000 claims description 14
- 229910052782 aluminium Inorganic materials 0.000 claims description 13
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 13
- 239000011888 foil Substances 0.000 claims description 13
- 238000000034 method Methods 0.000 claims description 12
- 239000011248 coating agent Substances 0.000 claims description 9
- 238000000576 coating method Methods 0.000 claims description 9
- 125000004185 ester group Chemical group 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 239000002041 carbon nanotube Substances 0.000 claims description 7
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 7
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 claims description 6
- 239000003792 electrolyte Substances 0.000 claims description 6
- 125000004435 hydrogen atom Chemical group [H]* 0.000 claims description 6
- 125000002887 hydroxy group Chemical group [H]O* 0.000 claims description 6
- 125000000449 nitro group Chemical group [O-][N+](*)=O 0.000 claims description 6
- 239000002002 slurry Substances 0.000 claims description 5
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical group [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 4
- 239000006230 acetylene black Substances 0.000 claims description 4
- 239000006229 carbon black Substances 0.000 claims description 4
- 239000011737 fluorine Substances 0.000 claims description 4
- 229910052731 fluorine Inorganic materials 0.000 claims description 4
- 229910021389 graphene Inorganic materials 0.000 claims description 4
- 229910002804 graphite Inorganic materials 0.000 claims description 4
- 239000010439 graphite Substances 0.000 claims description 4
- 229910052744 lithium Inorganic materials 0.000 claims description 4
- -1 lithium nickel cobalt manganese aluminate Chemical class 0.000 claims description 4
- 229910000572 Lithium Nickel Cobalt Manganese Oxide (NCM) Inorganic materials 0.000 claims description 3
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 claims description 3
- QTHKJEYUQSLYTH-UHFFFAOYSA-N [Co]=O.[Ni].[Li] Chemical compound [Co]=O.[Ni].[Li] QTHKJEYUQSLYTH-UHFFFAOYSA-N 0.000 claims description 3
- NKLLZZNEDKQOOB-UHFFFAOYSA-N [O-2].[Mg+2].[Ti+4].[Ni+2].[Li+] Chemical compound [O-2].[Mg+2].[Ti+4].[Ni+2].[Li+] NKLLZZNEDKQOOB-UHFFFAOYSA-N 0.000 claims description 3
- FBDMTTNVIIVBKI-UHFFFAOYSA-N [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] Chemical compound [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] FBDMTTNVIIVBKI-UHFFFAOYSA-N 0.000 claims description 3
- 125000003342 alkenyl group Chemical group 0.000 claims description 3
- 125000005907 alkyl ester group Chemical group 0.000 claims description 3
- 125000000304 alkynyl group Chemical group 0.000 claims description 3
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical compound [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 claims description 3
- 229910001428 transition metal ion Inorganic materials 0.000 abstract description 21
- 230000005540 biological transmission Effects 0.000 abstract description 9
- 230000015572 biosynthetic process Effects 0.000 abstract description 5
- 210000001787 dendrite Anatomy 0.000 abstract description 5
- 230000002035 prolonged effect Effects 0.000 abstract description 5
- 230000008961 swelling Effects 0.000 abstract description 5
- 230000005012 migration Effects 0.000 abstract description 4
- 238000013508 migration Methods 0.000 abstract description 4
- 230000035515 penetration Effects 0.000 abstract description 4
- 238000012360 testing method Methods 0.000 description 43
- 238000006116 polymerization reaction Methods 0.000 description 32
- 229910052723 transition metal Inorganic materials 0.000 description 32
- 150000003624 transition metals Chemical class 0.000 description 32
- 239000010410 layer Substances 0.000 description 30
- 238000006243 chemical reaction Methods 0.000 description 28
- 239000003999 initiator Substances 0.000 description 25
- 238000004090 dissolution Methods 0.000 description 21
- 239000000178 monomer Substances 0.000 description 17
- 230000014759 maintenance of location Effects 0.000 description 16
- 239000003995 emulsifying agent Substances 0.000 description 13
- BQCIDUSAKPWEOX-UHFFFAOYSA-N 1,1-Difluoroethene Chemical compound FC(F)=C BQCIDUSAKPWEOX-UHFFFAOYSA-N 0.000 description 9
- 230000009286 beneficial effect Effects 0.000 description 9
- 238000012661 block copolymerization Methods 0.000 description 9
- 238000000151 deposition Methods 0.000 description 8
- 230000000670 limiting effect Effects 0.000 description 8
- 239000004372 Polyvinyl alcohol Substances 0.000 description 6
- 235000019400 benzoyl peroxide Nutrition 0.000 description 6
- 239000006257 cathode slurry Substances 0.000 description 6
- 238000002425 crystallisation Methods 0.000 description 6
- 230000008025 crystallization Effects 0.000 description 6
- 230000008021 deposition Effects 0.000 description 6
- 230000002349 favourable effect Effects 0.000 description 6
- 229920002451 polyvinyl alcohol Polymers 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 239000013078 crystal Substances 0.000 description 5
- WNAHIZMDSQCWRP-UHFFFAOYSA-N dodecane-1-thiol Chemical compound CCCCCCCCCCCCS WNAHIZMDSQCWRP-UHFFFAOYSA-N 0.000 description 5
- 238000010828 elution Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 239000000523 sample Substances 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 239000012298 atmosphere Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- XTXRWKRVRITETP-UHFFFAOYSA-N Vinyl acetate Chemical compound CC(=O)OC=C XTXRWKRVRITETP-UHFFFAOYSA-N 0.000 description 3
- 239000010405 anode material Substances 0.000 description 3
- 239000011247 coating layer Substances 0.000 description 3
- 239000011889 copper foil Substances 0.000 description 3
- 230000002401 inhibitory effect Effects 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 238000011056 performance test Methods 0.000 description 3
- JRKICGRDRMAZLK-UHFFFAOYSA-L peroxydisulfate Chemical compound [O-]S(=O)(=O)OOS([O-])(=O)=O JRKICGRDRMAZLK-UHFFFAOYSA-L 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 230000002269 spontaneous effect Effects 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 2
- KFDQGLPGKXUTMZ-UHFFFAOYSA-N [Mn].[Co].[Ni] Chemical compound [Mn].[Co].[Ni] KFDQGLPGKXUTMZ-UHFFFAOYSA-N 0.000 description 2
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 2
- 229910021383 artificial graphite Inorganic materials 0.000 description 2
- 239000001768 carboxy methyl cellulose Substances 0.000 description 2
- 210000004027 cell Anatomy 0.000 description 2
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 2
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 239000003292 glue Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 230000000977 initiatory effect Effects 0.000 description 2
- 229910003002 lithium salt Inorganic materials 0.000 description 2
- 159000000002 lithium salts Chemical class 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 2
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 2
- OMPJBNCRMGITSC-UHFFFAOYSA-N Benzoylperoxide Chemical compound C=1C=CC=CC=1C(=O)OOC(=O)C1=CC=CC=C1 OMPJBNCRMGITSC-UHFFFAOYSA-N 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- 229910012820 LiCoO Inorganic materials 0.000 description 1
- 229910014336 LiNi1-x-yCoxMnyO2 Inorganic materials 0.000 description 1
- 229910014446 LiNi1−x-yCoxMnyO2 Inorganic materials 0.000 description 1
- 229910014825 LiNi1−x−yCoxMnyO2 Inorganic materials 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 229910001228 Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- XSTXAVWGXDQKEL-UHFFFAOYSA-N Trichloroethylene Chemical group ClC=C(Cl)Cl XSTXAVWGXDQKEL-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 125000000217 alkyl group Chemical group 0.000 description 1
- 239000006183 anode active material Substances 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 229950005499 carbon tetrachloride Drugs 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000003013 cathode binding agent Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000007922 dissolution test Methods 0.000 description 1
- FWDBOZPQNFPOLF-UHFFFAOYSA-N ethenyl(triethoxy)silane Chemical compound CCO[Si](OCC)(OCC)C=C FWDBOZPQNFPOLF-UHFFFAOYSA-N 0.000 description 1
- NKSJNEHGWDZZQF-UHFFFAOYSA-N ethenyl(trimethoxy)silane Chemical compound CO[Si](OC)(OC)C=C NKSJNEHGWDZZQF-UHFFFAOYSA-N 0.000 description 1
- WOXXJEVNDJOOLV-UHFFFAOYSA-N ethenyl-tris(2-methoxyethoxy)silane Chemical compound COCCO[Si](OCCOC)(OCCOC)C=C WOXXJEVNDJOOLV-UHFFFAOYSA-N 0.000 description 1
- 238000001125 extrusion Methods 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000012046 mixed solvent Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 150000001451 organic peroxides Chemical class 0.000 description 1
- MMCOUVMKNAHQOY-UHFFFAOYSA-L oxido carbonate Chemical compound [O-]OC([O-])=O MMCOUVMKNAHQOY-UHFFFAOYSA-L 0.000 description 1
- 230000036961 partial effect Effects 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 238000007790 scraping Methods 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 230000007928 solubilization Effects 0.000 description 1
- 238000005063 solubilization Methods 0.000 description 1
- CIHOLLKRGTVIJN-UHFFFAOYSA-N tert‐butyl hydroperoxide Chemical compound CC(C)(C)OO CIHOLLKRGTVIJN-UHFFFAOYSA-N 0.000 description 1
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 description 1
- UBOXGVDOUJQMTN-UHFFFAOYSA-N trichloroethylene Natural products ClCC(Cl)Cl UBOXGVDOUJQMTN-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- 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
- H01M4/623—Binders being polymers fluorinated polymers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
-
- 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
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
-
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
The invention provides a positive pole piece, a preparation method thereof and a lithium ion battery. The positive pole piece comprises a positive pole current collector and a positive pole active layer positioned on the surface of the positive pole current collector, the positive pole active layer comprises a positive pole active substance and a positive pole binder used for binding the positive pole active substance, and the material of the positive pole binder comprises modified polyvinylidene fluoride with the structure shown in the formula (I). The modified polyvinylidene fluoride can capture dissolved transition metal ions, so that the electrochemical performance of the lithium ion battery is improved; meanwhile, the migration of the lithium ion battery anode can be inhibited to the surface of the cathode, the formation of dendrite is inhibited, and the penetration of a diaphragm is inhibited, so that the service life of the lithium ion battery is prolonged. The values of x, y and n are limited in the scope of the application in comparison to other ranges, respectivelyThe swelling resistance of the modified polyvinylidene fluoride can be improved; compared with the traditional polyvinylidene fluoride, the introduction of the group can effectively inhibit the increase of transmission impedance and improve the electrochemical performance, the cycle performance and the safety performance of the lithium ion battery.
Description
Technical Field
The invention relates to the technical field of lithium ion battery preparation, in particular to a positive pole piece, a preparation method thereof and a lithium ion battery.
Background
The lithium ion battery has the advantages of high energy density, good rate capability, long cycle life and the like, so that the lithium ion battery is widely applied to the fields of mobile phones, notebook computers, new energy automobiles and the like. Positive active material (e.g., LiCoO) for lithium ion batteries2、LiNi1-x-yCoxMnyO2Ternary materials and the like), which causes that transition metal ions are easy to be dissolved out from the positive active material in the using process of the battery, especially under high temperature (not less than 45 ℃) and high voltage (not less than 4.2V), and the transition metal ions dissolved into the electrolyte can migrate to the surface of the negative electrode and are reduced into metal simple substances in the charging process. Under the catalytic action of the transition metal simple substance, the decomposition of a solid electrolyte interface film (SEI) on the surface of the negative electrode is accelerated, and the degradation of the battery performance is further aggravated. In addition, the transition metal simple substance can deposit on the surface of the negative electrode to form dendrite, and under severe conditions, the dendrite can pierce through a diaphragm to cause internal short circuit of the battery, so that the safety problem is caused. Therefore, it is very important to improve the problem of elution of the transition metal.
At present, two methods for inhibiting the dissolution of transition metal are available, one is to coat the surface of the anode active material, but the coating layer formed by coating is easy to corrode by electrolyte and lose efficacy; the other is to carry out gradient design on the positive electrode active material, but the process is complex and the cost is high. Moreover, at present, no good improvement mode exists for the problem of influence on the battery performance caused by the dissolution of materials containing transition metals such as nickel-cobalt-manganese ternary positive electrode active materials at high voltage (not less than 4.2V) and high temperature (not less than 45 ℃).
Therefore, the positive pole piece capable of capturing transition metal ions and further inhibiting the dissolution of the transition metal is developed and researched, and the positive pole piece has important significance for improving the electrochemical performance of the lithium ion battery.
Disclosure of Invention
The invention mainly aims to provide a positive pole piece, a preparation method thereof and a lithium ion battery, and aims to solve the problems of positive pole capacity loss, diaphragm resistance increase, poor cycle performance and short service life of the lithium ion battery caused by dissolution of transition metal ions in the conventional positive pole material.
In order to achieve the above object, the present invention provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode active layer located on the surface of the positive electrode current collector, wherein the positive electrode active layer includes a positive electrode active material and a positive electrode binder for binding the positive electrode active material, and the material of the positive electrode binder includes modified polyvinylidene fluoride having a structure shown in formula (I);
wherein R is1And R2Each independently selected from hydrogen atom, carboxyl, hydroxyl and C1～C7A straight-chain or branched alkyl ester group of (2), C1～C7Straight-chain or branched alkenyl ester group of (C)1～C7Straight-chain or branched alkynyl ester group of (A), C6～C12Aryl ester group or nitro group of (1); and R is1And R2Not simultaneously selected from hydrogen atoms, and not simultaneously selected from one or more of carboxyl, hydroxyl and nitro; x is any integer between 20 and 250, y is any integer between 1 and 5, and n is any integer between 200 and 480.
Further, the modified polyvinylidene fluoride has one of the following structures:
Furthermore, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder is 100 (0.5-5), preferably 100 (0.8-3), and more preferably 100 (1.2-2.5).
Further, the positive electrode active material in the positive electrode active material layer is selected from one or more of the group consisting of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganese aluminate, lithium nickel cobalt oxide, lithium nickel titanium magnesium oxide, and lithium nickel oxide.
Further, the thickness of the positive current collector is 8-20 microns, and the positive current collector is selected from one or more of the group consisting of single-optical-surface aluminum foil, double-optical-surface aluminum foil, carbon-coated aluminum foil and porous aluminum foil.
Further, the material of the positive active layer also comprises a conductive material, and the weight ratio of the total weight of the positive active layer to the conductive material is 100 (2-5); preferably, the conductive material is selected from one or more of the group consisting of carbon black, graphite, acetylene black, graphene, and carbon nanotubes.
In order to achieve the above object, another aspect of the present invention further provides a method for preparing the above positive electrode sheet provided by the present application, where the method for preparing the positive electrode sheet includes: mixing a positive electrode active substance, a positive electrode binder and a solvent to obtain positive electrode slurry; and coating the positive electrode slurry on the surface of the positive electrode current collector, and drying to obtain the positive electrode piece.
Further, the solid content of the positive electrode slurry is 45-58 wt%.
Further, the preparation method of the positive pole piece further comprises the following steps: and mixing the conductive material with the positive active substance, the positive binder and the solvent to obtain positive slurry.
The invention also provides a lithium ion battery, which comprises a positive pole piece, a negative pole piece, a diaphragm arranged between a positive pole and a negative pole, and electrolyte, wherein the positive pole piece comprises the positive pole piece provided by the application or the positive pole piece prepared by the preparation method of the positive pole piece provided by the application; optionally, the membrane is selected from modified membranes coated with the above modified polyvinylidene fluoride provided herein.
By applying the technical scheme of the invention, a strong-polarity or strong-electronegativity group is introduced into unmodified polyvinylidene fluoride to obtain the modified polyvinylidene fluoride. The introduction of the modified polyvinylidene fluoride in the positive binder layer can exert the binding performance of the positive binder on one hand, so that the positive active substance is tightly bound on the surface of the positive current collector; on the other hand, N in a group of a specific kind2-And O2-Can capture dissolved transition metal ions, further inhibit the deposition of transition metal, and further improve the cycle performance of the lithium ion battery. The modified polyvinylidene fluoride can capture dissolved transition metal ions and inhibit the transition metal from directly depositing on the surface of a positive electrode material to block an ion transmission channel, so that the electrochemical performance of the lithium ion battery is improved; meanwhile, the migration of the lithium ion battery anode can be inhibited to the surface of the cathode, the formation of dendritic crystals is inhibited, and the penetration of a diaphragm is inhibited, so that the service life of the lithium ion battery is prolonged.
Compared with other ranges, the values of x, y and n in the structural units are respectively limited in the ranges, so that a plurality of smaller crystal structures can be formed after spontaneous crystallization of the modified polyvinylidene fluoride, and the swelling resistance of the modified polyvinylidene fluoride is improved; meanwhile, compared with the traditional polyvinylidene fluoride, the introduction of the groups can break up large particles formed by crystallization to form gaps in the molecular structure of the polyvinylidene fluoride, so that the increase of transmission impedance is effectively inhibited, and the electrochemical performance, the cycle performance and the safety performance of the lithium ion battery are improved.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail with reference to examples.
As described in the background art, the conventional positive electrode material has the problems of positive electrode capacity loss and increased sheet resistance caused by the dissolution of transition metal ions in the positive electrode material, and poor cycle performance and short service life of the lithium ion battery. In order to solve the above technical problem, the present application provides a positive electrode plate, which includes a positive current collector and a positive active layer on the surface of the positive current collector, wherein the positive active layer is located on the surface of the positive current collectorThe positive electrode active layer comprises a positive electrode active substance and a positive electrode binder for binding the positive electrode active substance, and the material of the positive electrode binder comprises modified polyvinylidene fluoride with the structure shown in the formula (I);
wherein R is1And R2Each independently include but are not limited to hydrogen atom, carboxyl, hydroxyl, C1～C7A straight-chain or branched alkyl ester group of (2), C1～C7Straight-chain or branched alkenyl ester group of (C)1～C7Straight-chain or branched alkynyl ester group of (A), C6～C12Aryl ester group or nitro group of (1); and R is1And R2Not including but not limited to hydrogen atoms, nor including but not limited to one or more of carboxyl, hydroxyl and nitro groups; x is any integer between 20 and 250, y is any integer between 1 and 5, and n is any integer between 200 and 480.
Introducing a strong-polarity or strong-electronegativity group into unmodified polyvinylidene fluoride to obtain the modified polyvinylidene fluoride. The introduction of the modified polyvinylidene fluoride in the positive binder layer can exert the binding performance of the positive binder on one hand, so that the positive active substance is tightly bound on the surface of the positive current collector; on the other hand, N in a group of a specific kind2-And O2-The dissolved transition metal ions can be captured, and then the deposition of the transition metal is inhibited, so that the cycle performance of the lithium ion battery is improved. The modified polyvinylidene fluoride can capture dissolved transition metal ions and inhibit the transition metal from being directly deposited on the surface of the anode material to block an ion transmission channel, so that the electrochemical performance of the lithium ion battery is improved; meanwhile, the migration of the lithium ion battery anode can be inhibited to the surface of the cathode, the formation of dendrite is inhibited, and the penetration of a diaphragm is inhibited, so that the service life of the lithium ion battery is prolonged.
Compared with other ranges, the values of x, y and n in the structural units are respectively limited in the ranges, so that a plurality of smaller crystal structures can be formed after spontaneous crystallization of the modified polyvinylidene fluoride, and the swelling resistance of the modified polyvinylidene fluoride is improved; meanwhile, compared with the traditional polyvinylidene fluoride, the introduction of the groups can break up large particles formed by crystallization to form gaps in the molecular structure of the polyvinylidene fluoride, so that the increase of transmission impedance is effectively inhibited, and the electrochemical performance, the cycle performance and the safety performance of the lithium ion battery are improved.
In a preferred embodiment, the modified polyvinylidene fluoride has one of the following structures:
Compared with other kinds of R1And R2Radical, using R of the above-mentioned kind1And R2The radicals being favorable for exerting N therein2-And O2-The capture effect on the transition metal ions makes the transition metal ions difficult to deposit on the surface of the anode material, and inhibits the blockage of an ion transmission channel; meanwhile, a smaller crystal structure is formed, so that the increase of transmission impedance is inhibited, the resistance of the diaphragm is reduced, and the cycle performance and the safety performance of the lithium ion battery are improved.
In a preferred embodiment, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder is 100 (0.5-5). The weight ratio of the total weight of the positive electrode active layer to the positive electrode binder includes, but is not limited to, the above range, and limiting the weight ratio to the weight of the positive electrode binder within the above range is advantageous for suppressing dissolution of transition metal ions in the positive electrode active material, thereby reducing sheet resistance, and improving electrochemical performance and cycle performance of the lithium ion battery.
In order to further suppress elution of transition metal ions in the positive electrode active material, further reduce sheet resistance, and improve electrochemical performance of the lithium ion battery, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder is preferably (0.8 to 3). In order to further suppress elution of transition metal ions in the positive electrode active material, further reduce sheet resistance, and improve electrochemical performance of the lithium ion battery, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder is more preferably (1.2 to 2.5).
The positive electrode active material used in the present application is a kind commonly used in the art. In a preferred embodiment, the positive electrode active material in the positive electrode active material layer includes, but is not limited to, one or more of the group consisting of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganese aluminate, lithium nickel cobalt oxide, lithium nickel titanium magnesium oxide, lithium nickel oxide.
In a preferred embodiment, the thickness of the positive electrode current collector is 8 to 20 μm, and the positive electrode current collector includes, but is not limited to, one or more of the group consisting of a single-sided aluminum foil, a double-sided aluminum foil, a carbon-coated aluminum foil, and a porous aluminum foil. The thickness of the positive electrode current collector includes, but is not limited to, the above range, and the limitation of the thickness in the above range is beneficial to reducing the self weight of the lithium ion battery on one hand and improving the energy density of the lithium ion battery on the other hand. Compared with other types, the positive current collector of the above type is favorable for reducing the internal resistance of the positive current collector, improving the electrical contact between the positive active material and the positive current collector, and improving the easy-processing coating performance.
The introduction of the conductive material is beneficial to improving the conductivity of the positive pole piece. In a preferred embodiment, the positive pole piece further comprises a conductive material, and the weight ratio of the total weight of the positive active layer to the conductive material is 100 (2-5). The ratio of the total weight of the positive electrode active layer to the weight of the conductive material includes, but is not limited to, the above range, and the limitation of the ratio within the above range is advantageous for further improving the conductive performance of the positive electrode sheet.
In order to further improve the conductive performance of the positive electrode sheet, preferably, the conductive material includes one or more of the group consisting of, but not limited to, carbon black, graphite, acetylene black, graphene, and carbon nanotubes.
The second aspect of the present application provides a method for preparing a positive electrode plate, which includes: mixing a positive electrode active substance, a positive electrode binder and a solvent to obtain positive electrode slurry; and coating the positive electrode slurry on the surface of the positive electrode current collector, and drying to obtain the positive electrode piece.
Mixing the positive electrode active substance, the positive electrode binder and the solvent to obtain positive electrode slurry, so as to facilitate subsequent coating processing; and coating the positive electrode slurry on the surface of the positive electrode current collector, and drying to obtain a positive electrode active layer positioned on the surface of the positive electrode current collector and obtain a positive electrode piece. The positive electrode binder includes the modified polyvinylidene fluoride provided herein.
In a preferred embodiment, the solid content of the positive electrode slurry is 45 to 58 wt%. The solid content ratio of the positive electrode slurry includes, but is not limited to, the above range, and limiting the solid content ratio within the above range is beneficial to further exerting the binding performance of the positive electrode binder, and simultaneously, is beneficial to further inhibiting the deposition of the transition metal, and is further beneficial to further improving the electrochemical performance and the service life of the lithium ion battery.
The introduction of the conductive material is beneficial to improving the conductivity of the positive pole piece and reducing the resistance of the diaphragm, and in a preferred embodiment, the preparation method of the positive pole piece further comprises the following steps: and mixing the conductive material with the positive active substance, the positive binder and the solvent to obtain the positive slurry.
In order to further improve the conductive performance of the positive electrode sheet, preferably, the conductive material includes one or more of the group consisting of, but not limited to, carbon black, graphite, acetylene black, graphene, and carbon nanotubes.
The third aspect of the present application further provides a preparation method of modified polyvinylidene fluoride, including: mixing a vinylidene fluoride monomer, a first emulsifier, a first solvent, a first molecular weight regulator and a first initiator under the condition of a first inert atmosphere, carrying out first polymerization to obtain a first polymerization product, controlling the first polymerization reaction to carry out for 2-6 h, and stopping the reaction to obtain a first reaction system containing a first prepolymer; under the condition of a second inert atmosphere, a polymerized monomer, a second emulsifier, a second solvent, a second molecular weight regulator and a second initiatorMixing and carrying out second polymerization to obtain a second polymerization product, controlling the second polymerization reaction to carry out for 2-6 h, and stopping the reaction to obtain a second reaction system containing a second prepolymer; the polymerized monomer has the chemical structure of formula (II): CH (CH)2＝CR1R2(II)；R1And R2Respectively have the same definitions as the above; and under the condition of a third inert atmosphere, mixing the first reaction system, the second reaction system and a third initiator, carrying out block copolymerization, controlling the block copolymerization reaction for 2-6 hours, and stopping the reaction to obtain the modified polyvinylidene fluoride provided by the application.
The modified polyvinylidene fluoride prepared by the preparation method has uniform molecular weight distribution (generally reaching 1.5-1.8), high product yield and simple operation.
In a preferred embodiment, the weight ratio of the vinylidene fluoride monomer, the first emulsifier, the first solvent, the first molecular weight regulator and the first initiator is 100 (0.1-0.2): 300-1000): 0.0001-0.001): 0.05-1.5); the weight ratio of the polymerization monomer, the second emulsifier, the second solvent, the second molecular weight regulator and the second initiator is 100 (0.1-0.2): (300-1000): (0.0001-0.001): (0.05-1.5).
Preferably, the weight ratio of the vinylidene fluoride monomer, the first emulsifier, the first solvent, the first molecular weight regulator and the first initiator is 100 (0.1-0.2): 300-600): 0.0001-0.001): 0.15-1.0; the weight ratio of the polymerized monomer, the second emulsifier, the second solvent, the second molecular weight regulator and the second initiator is 100 (0.1-0.2): 300-600): 0.0001-0.001): 0.15-1.0.
In order to further improve the yield and the uniformity of the molecular weight distribution of the vinylidene fluoride oligomer and the second polymerization product, the weight ratio of the vinylidene fluoride monomer, the first emulsifier, the first solvent, the first molecular weight regulator and the first initiator is preferably 100 (0.1-0.2): 300-600): 0.0001-0.001): 0.15-1.0; the weight ratio of the polymerized monomer, the second emulsifier, the second solvent, the second molecular weight regulator and the second initiator is 100 (0.1-0.2): 300-600): 0.0001-0.001): 0.15-1.0.
In a preferred embodiment, the first initiator, the second initiator and the third initiator each independently include, but are not limited to, inorganic and/or organic peroxides of the persulfate type; more preferably one or more of the group consisting of peroxycarbonate, t-butyl hydroperoxide, alkyl diperoxide. Compared with other types of initiators, the initiator has higher pertinence to the first polymerization reaction, the second polymerization reaction and the block copolymerization reaction, and is favorable for further improving the generation rate of the modified polyvinylidene fluoride.
In a preferred embodiment, the first molecular weight regulator and the second molecular weight regulator each independently include, but are not limited to, one or more of the group consisting of dodecyl mercaptan, trichloroethylene, and tetrachloromethane. Compared with other types, the molecular weight regulator is favorable for more accurately controlling the molecular weight of a polymerization product to be within a target range, and is favorable for improving the uniformity of molecular weight distribution, thereby being favorable for obtaining the modified polyvinylidene fluoride with better swelling resistance and better transition metal ion capture performance.
In a preferred embodiment, the first and second emulsifiers include, but are not limited to, polyvinyl alcohol and/or alkali metal perfluorooctanoates. Compared with other emulsifiers, the preferred emulsifiers are beneficial to playing the role of solubilization, promoting the dissolution of reaction monomers in a reaction system and further accelerating the reaction.
In a preferred embodiment, the first solvent and the second solvent each independently include, but are not limited to, water having a conductivity of ≦ 3 μ s/cm.
In a preferred embodiment, the temperatures during the first polymerization, the second polymerization and the block copolymerization independently include, but are not limited to, 70 to 85 ℃ and the times independently include, but are not limited to, 2 to 6 hours. The temperature and time during the first polymerization, the second polymerization and the block copolymerization include, but are not limited to, the above ranges, and limiting the same to the above ranges is advantageous for increasing the polymerization rate of the vinylidene fluoride monomer, and simultaneously for increasing the yield and the uniformity of the molecular weight distribution of the product. Alternatively, the temperature in the first polymerization, the second polymerization and the block copolymerization process may be 70 ℃, 72 ℃, 75 ℃, 78 ℃, 79 ℃, 80 ℃, 82 ℃ or 85 ℃ respectively, and the time may be 2h, 2.5h, 3h, 3.5h, 4h, 5h, 5.5h or 6h respectively.
In a preferred embodiment, when the third initiator is a persulfate-based inorganic, the block copolymerization process further comprises: mixing the first reaction system, the second reaction system, the third initiator and the auxiliary initiator; the weight percentage of the co-initiator is 0.1-2% based on the total weight of the first polymerization product and the second polymerization product in the first reaction system and the second reaction system. When the third initiator is persulfate inorganic matter, the introduction of the auxiliary initiator is beneficial to improving the initiation efficiency, and further beneficial to improving the block polymerization reaction rate; meanwhile, it is advantageous to limit the amount of the co-initiator to the above range in comparison with other ranges in order to increase the conversion rates of the first polymerization product in the first reaction system and the second polymerization product in the second reaction system.
In a preferred embodiment, the co-initiator includes, but is not limited to, one or more of the group consisting of vinyltriethoxysilane, vinyltrimethoxysilane and vinyltris (β -methoxyethoxy) silane. Co-initiators include, but are not limited to, the ranges described above, and limiting them to the ranges described above advantageously reduces activation energy, increases initiation efficiency, and thus increases the rate of block polymerization.
The fourth aspect of the present application further provides a lithium ion battery, which includes a positive electrode plate, a negative electrode plate, a diaphragm disposed between the positive electrode and the negative electrode, and an electrolyte, where the positive electrode plate includes the positive electrode plate provided in the present application or the positive electrode plate prepared by the preparation method of the positive electrode plate provided in the present application.
The prepared positive pole piece is applied to the lithium ion battery, so that the internal resistance of the lithium ion battery can be reduced, the electrochemical performance of the lithium ion battery can be improved, and the service life of the lithium ion battery can be prolonged.
In a preferred embodiment, the membrane includes, but is not limited to, a modified membrane coated on the surface with the above-described modified polyvinylidene fluoride provided herein.The modified polyvinylidene fluoride provided by the application is coated on the surface of a diaphragm, and N in the modified polyvinylidene fluoride2-And O2-The dissolved transition metal ions can be further captured, and the transition metal ions are further inhibited from penetrating through the diaphragm and depositing on the negative electrode, so that the electrochemical performance and the service life of the lithium ion battery are further improved.
The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.
It should be noted that the following tests were performed on all of the lithium ion batteries prepared in the examples and comparative examples in this application, including:
(1) high temperature capacity retention performance test:
the thickness of the full-electricity cell is tested before testing and is recorded as D0. Placing the lithium ion battery in an environment with the temperature of (45 +/-3) DEG C, standing for 3h, after the temperature of the battery reaches 45 ℃, charging to 4.3V at constant voltage according to a constant current of 1C/1C, charging at constant voltage until the cut-off current is 0.05C, and standing for 5 min; discharging to 3V at 1C, and recording initial capacity Q0(ii) a The continuous circulation reaches 900 circles and the discharge capacity Q is recorded900TStopping the cycle until the capacity fade rate is equal to 80%; then the battery is fully charged, the battery core is taken out and is kept stand at the normal temperature (25 +/-3) DEG C for 3 hours, and the full charge thickness D is tested2And the thickness change rate (%) was calculated.
The calculation formula is as follows: retention ratio of circulating capacity (Q)900T/Q0X 100%, thickness expansion ratio ((D)900T-D0)/D0)×100％。
(2) Testing the resistance performance of the diaphragm:
the membrane resistance was tested using a four-probe method with a two-probe resistance tester. Cut into the positive pole piece that the size is 4cm 8cm with positive pole piece, then place the positive pole piece after cuting below two probes of resistance tester, make two probes pass through two utmost point posts and be connected with the resistance meter, rotate the testing arrangement handle, the probe receives steady pressure extrusion pole piece, and pressure size passes through pressure gauge control, reachs the pressure value 200Pa of settlement and reads resistance data after stable, and this data is positive pole piece resistance relative value.
(3) Transition metal dissolution test:
and (3) disassembling the 0% SOC lithium ion battery after 45 ℃ circulation, taking out the negative pole piece, scraping the negative active powder on the carbon-coated copper foil, and carrying out ICP test.
Example 1
A preparation method of modified polyvinylidene fluoride comprises the following steps:
(1) mixing vinylidene fluoride monomer, polyvinyl alcohol, water and dodecyl mercaptan, stirring in the atmosphere of high-purity nitrogen (the purity is more than 99.999%), heating a reaction system to 70 ℃, adding dibenzoyl peroxide (BPO), starting a first polymerization reaction, and finishing the reaction for 2 hours to obtain a first polymerization product with the polymerization degree of 30;
in the first reaction system, the weight ratio of vinylidene fluoride monomer (VDF monomer), polyvinyl alcohol (first emulsifier), water (first solvent), dodecyl mercaptan (first molecular weight regulator) and BPO (first initiator) is 30:0.5:100:0.0001: 0.2;
(2) mixing vinyl acetate (CH)2＝CHCOOCH3) Mixing water, polyvinyl alcohol and dodecyl mercaptan, stirring in a high-purity (the purity is more than 99.999%) nitrogen atmosphere, raising the temperature of a reaction system to 70 ℃, adding BPO, starting a second polymerization reaction, and finishing the reaction after 2 hours; evaporating and removing the solvent in the product while the product is hot, and transferring the product to a drying oven at 55 ℃ for drying for 20 hours to obtain a second polymerization product with the polymerization degree of 4;
in the second reaction system, the weight ratio of vinyl acetate (polymerized monomer), polyvinyl alcohol (second emulsifier), water (second solvent), dodecyl mercaptan (second molecular weight regulator) and BPO (second initiator) is 30:0.5:100:0.0002: 0.2;
(3) and mixing the first reaction system and the second reaction system, re-emulsifying by using the residual polyvinyl alcohol, heating to 80 ℃, adding BPO (third initiator) to enable the A chain segment and the B chain segment to generate block copolymerization, evaporating and removing the solvent in the block copolymerization product while the product is hot after 4 hours of reaction, and transferring to a drying oven at 55 ℃ for drying for 20 hours to obtain the modified polyvinylidene fluoride.
The modified polyvinylidene fluoride prepared in example 1 has the following structure:
A preparation method of a positive pole piece comprises the following steps:
the positive electrode active material NCM811, the modified polyvinylidene fluoride (positive electrode binder), conductive carbon black and carbon nanotubes (the diameter of the carbon nanotubes is 11nm, and the specific surface area is 200 m)2(g, the manufacturer is cabot), dispersing in N-methyl pyrrolidone (NMP), and stirring to obtain positive electrode slurry; wherein the weight ratio of the positive electrode active substance NCM811, the modified polyvinylidene fluoride, the conductive carbon black and the carbon nano tube is 93:3:3: 1;
the solid content of the positive electrode slurry is 52 wt%, and the viscosity is 5360mPa & s; coating the positive electrode slurry on the two side surfaces of a carbon-coated aluminum foil (with the thickness of 12 mu m), baking for 4 hours at 130 ℃, and rolling with the compaction density of 2.5g/cm3And obtaining the positive pole piece.
A method of making a lithium ion battery, comprising:
(1) dispersing a negative active material artificial graphite, a negative binder SBR, conductive carbon black and sodium carboxymethyl cellulose in solvent water, and stirring to obtain negative electrode slurry; wherein the weight ratio of the artificial graphite, the cathode binder SBR, the conductive carbon black and the sodium carboxymethylcellulose is 95:1.8:2: 1.2; coating the negative electrode slurry on the surfaces of two sides of the carbon-coated copper foil, and rolling the carbon-coated copper foil by using a roller press to obtain a negative electrode plate;
(2) the positive electrode plate and the negative electrode plate prepared in the embodiment, and the diaphragm (glue coating layer/base material/glue coating layer) prepared in the above manner were assembled into a cell by zigzag lamination (in the order of diaphragm/negative electrode/diaphragm/positive electrode), and then an electrolyte (LiPF) was injected6As lithium salt, dimethyl carbonate DMC and diethyl carbonate DEC with the lithium salt concentration of 1mol/L and the mixed solvent weight ratio of 3:1 are subjected to chemical composition and partial volume procedures to obtain lithium ionsAnd a sub-battery.
The lithium ion battery prepared in example 1 was subjected to a high-temperature capacity retention performance test, a sheet resistance performance test, and a transition metal elution amount test, and the test results are summarized in tables 1 and 2.
Example 2
The preparation method of the modified polyvinylidene fluoride is the same as that of the example 1, and the difference from the example 1 is that: the polymerized monomer used in the second polymerization process is CH2CHCOOH; the finally prepared modified polyvinylidene fluoride has the following structure:
The preparation methods of the positive electrode plate and the lithium ion battery are respectively the same as that in example 1, and the solid content of the prepared positive electrode slurry is 52 wt%. The test results of the high-temperature capacity retention performance and the resistance performance of the diaphragm are shown in table 1, and the test results of the transition metal dissolution condition are shown in table 2.
Example 3
The preparation method of the modified polyvinylidene fluoride is the same as that of the example 1, and the difference from the example 1 is that: the polymerized monomer used in the second polymerization process is C (NO)2) H ═ CHCOOH; the finally prepared modified polyvinylidene fluoride has the following structure:
The preparation methods of the positive pole piece and the lithium ion battery are respectively the same as that in the example 1, and the solid content of the prepared positive pole slurry is 52 wt%. The test results of the high-temperature capacity retention performance and the resistance performance of the diaphragm are shown in table 1, and the test results of the transition metal dissolution condition are shown in table 2.
Example 4
The modified polyvinylidene fluoride is the same as that in the example 1, the preparation method of the positive pole piece is the same as that in the example 1, and the difference from the example 1 is as follows: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 0.5; the solid content of the prepared cathode slurry was 56 wt%.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 5
The modified polyvinylidene fluoride is the same as that in the embodiment 1, the preparation method of the positive pole piece is the same as that in the embodiment 1, and the difference from the embodiment 1 is that: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 5; the solid content of the obtained positive electrode slurry was 46 wt%.
The preparation method of the lithium ion battery is the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 6
The modified polyvinylidene fluoride is the same as that in the embodiment 1, the preparation method of the positive pole piece is the same as that in the embodiment 1, and the difference from the embodiment 1 is that: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 6; the solid content of the obtained cathode slurry was 43 wt%.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 7
The modified polyvinylidene fluoride is the same as that in the embodiment 1, the preparation method of the positive pole piece is the same as that in the embodiment 1, and the difference from the embodiment 1 is that: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 0.8; the solid content of the obtained cathode slurry was 51 wt%.
The preparation method of the lithium ion battery is the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 8
The modified polyvinylidene fluoride is the same as that in the embodiment 1, the preparation method of the positive pole piece is the same as that in the embodiment 1, and the difference from the embodiment 1 is that: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 3; the solid content of the obtained positive electrode slurry was 48 wt%.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 9
The modified polyvinylidene fluoride is the same as that in the embodiment 1, the preparation method of the positive pole piece is the same as that in the embodiment 1, and the difference from the embodiment 1 is that: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 1.2; the solid content of the obtained positive electrode slurry was 50 wt%.
The preparation method of the lithium ion battery is the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 10
The modified polyvinylidene fluoride is the same as that in the embodiment 1, the preparation method of the positive pole piece is the same as that in the embodiment 1, and the difference from the embodiment 1 is that: the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder modified polyvinylidene fluoride is 100: 2.5; the solid content of the obtained cathode slurry was 47 wt%.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 11
The preparation method of the positive pole piece is the same as that of the embodiment 1, and the difference from the embodiment 1 is that: the positive active substance adopted in the preparation process of the positive pole piece is NCM622 material; the solid content of the obtained cathode slurry was 52 wt%.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Example 12
The preparation method of the positive pole piece is the same as that of the embodiment 1, and the difference from the embodiment 1 is that: the positive active substance adopted in the preparation process of the positive pole piece is NCM111 material; the solid content of the obtained cathode slurry was 52 wt%.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Comparative example 1
The difference from example 1 is that: the binder used in the preparation process of the positive pole piece is a traditional unmodified PVDF binder.
The preparation methods of the lithium ion battery are respectively the same as that of the embodiment 1, the test result of the high-temperature capacity retention performance and the test result of the membrane resistance performance are shown in table 1, and the test result of the transition metal dissolution condition is shown in table 2.
Comparative example 2
The preparation method of the modified polyvinylidene fluoride is the same as that of the example 1, and the difference from the example 1 is that: the prepared modified polyvinylidene fluoride has the following structure:
The preparation methods of the positive electrode plate and the lithium ion battery are respectively the same as that in example 1, and the solid content of the prepared positive electrode slurry is 52 wt%. The test results of the high-temperature capacity retention performance and the resistance performance of the diaphragm are shown in table 1, and the test results of the transition metal dissolution condition are shown in table 2.
TABLE 1
TABLE 2
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
it can be seen from comparison of examples 1 to 3 and comparative example 1 that the modified polyvinylidene fluoride described above is obtained by introducing a strongly polar or strongly electronegative group into polyvinylidene fluoride. The introduction of the modified polyvinylidene fluoride in the positive binder layer can exert the binding performance of the positive binder on one hand, so that the positive active substance is tightly bound on the surface of the positive current collector; on the other hand, N in a group of a specific kind2-And O2-Can capture dissolved transition metal ions, further inhibit the deposition of transition metal, and further improve the cycle performance of the lithium ion battery. The modified polyvinylidene fluoride can capture dissolved transition metal ions and inhibit the transition metal from being directly deposited on the surface of the anode material to block an ion transmission channel, so that the electrochemical performance of the lithium ion battery is improved; meanwhile, the migration of the lithium ion battery anode can be inhibited to the surface of the cathode, the formation of dendrite is inhibited, and the penetration of a diaphragm is inhibited, so that the service life of the lithium ion battery is prolonged.
As can be seen from comparison between example 1 and comparative example 2, limiting the values of x, y, and n in the structural unit to the above ranges respectively enables formation of a plurality of smaller crystal structures after spontaneous crystallization of modified polyvinylidene fluoride, as compared to other ranges, and improves the swelling resistance of modified polyvinylidene fluoride; meanwhile, compared with the traditional polyvinylidene fluoride, the introduction of the groups can break up large particles formed by crystallization to form gaps in the molecular structure of the polyvinylidene fluoride, so that the increase of transmission impedance is effectively inhibited, and the electrochemical performance, the cycle performance and the safety performance of the lithium ion battery are improved.
As can be seen from comparison of examples 1 and 4 to 6, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder includes, but is not limited to, the preferred range of the present application, and limiting the weight ratio to the preferred range of the present application is advantageous for suppressing elution of transition metal ions in the positive electrode active material, thereby reducing the sheet resistance and improving the electrochemical performance and cycle performance of the lithium ion battery.
As can be seen from comparison of examples 1, 7 and 8, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder includes, but is not limited to, the more preferable range of the present application, and limiting the weight ratio to the more preferable range of the present application is advantageous for further exhibiting the binding performance of the positive electrode binder, and for further suppressing the deposition of the transition metal, and further for further improving the electrochemical performance and the service life of the lithium ion battery.
As can be seen from comparison of examples 1, 9 and 10, the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder includes, but is not limited to, the more preferable range of the present application, and it is limited to the more preferable range of the present application, which is advantageous for further exhibiting the binding property of the positive electrode binder while further suppressing the deposition of the transition metal.
It is understood from comparison of examples 1, 11 and 12 that the higher the content of Co in the nickel-cobalt-manganese ternary positive electrode material, the less the transition metal is eluted, because the cobalt element can maintain the layered structure of the positive electrode active material well and stabilize the structure.
In conclusion, the positive pole piece provided by the application can effectively inhibit the problem of dissolution of transition metal of the positive pole material, and remarkably improves the high-temperature cycle performance and service life of the lithium ion battery.
It is noted that the terms first, second and the like in the description and in the claims of the present application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described or illustrated herein.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. 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. The positive pole piece is characterized by comprising a positive pole current collector and a positive pole active layer positioned on the surface of the positive pole current collector, wherein the positive pole active layer comprises a positive pole active substance and a positive pole binder used for binding the positive pole active substance, and the material of the positive pole binder comprises modified polyvinylidene fluoride with the structure shown in the formula (I);
wherein R is1And R2Each independently selected from hydrogen atom, carboxyl, hydroxyl and C1～C7Straight or branched alkyl ester group of (2), C1～C7Straight-chain or branched alkenyl ester group of (C)1～C7Straight-chain or branched alkynyl ester group of (A), C6～C12Aryl ester group or nitro group of (1); and said R is1And said R2Is not simultaneously selected from hydrogen atoms, or one or more of carboxyl, hydroxyl and nitro;
x is any integer between 20 and 250, y is any integer between 1 and 5, and n is any integer between 200 and 480.
2. The positive electrode sheet according to claim 1, wherein the modified polyvinylidene fluoride has one of the following structures:
wherein x is140 to 200, y1Is 2 to 4, n1240 to 370; x is a radical of a fluorine atom240 to 250, y2Is 3 to 5, n2200 to 480; x is a radical of a fluorine atom3Is 80 to 150, y3Is 4 to 5, n3220 to 280.
3. The positive electrode plate as claimed in claim 1 or 2, wherein the weight ratio of the total weight of the positive electrode active layer to the positive electrode binder is 100 (0.5-5), preferably 100 (0.8-3), and more preferably 100 (1.2-2.5).
4. The positive electrode sheet according to any one of claims 1 to 3, wherein the positive electrode active material in the positive electrode active material layer is one or more selected from the group consisting of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese aluminate, lithium nickel cobalt oxide, lithium nickel titanium magnesium oxide, and lithium nickel oxide.
5. The positive electrode plate as claimed in claim 4, wherein the positive electrode current collector has a thickness of 8-20 μm, and is selected from one or more of the group consisting of a single-optical-surface aluminum foil, a double-optical-surface aluminum foil, a carbon-coated aluminum foil and a porous aluminum foil.
6. The positive pole piece of claim 5, wherein the material of the positive active layer further comprises a conductive material, and the weight ratio of the total weight of the positive active layer to the conductive material is 100 (2-5);
preferably, the conductive material is selected from one or more of the group consisting of carbon black, graphite, acetylene black, graphene, and carbon nanotubes.
7. The preparation method of the positive pole piece according to any one of claims 1 to 6, wherein the preparation method of the positive pole piece comprises the following steps:
mixing a positive electrode active substance, a positive electrode binder and a solvent to obtain positive electrode slurry;
and coating the positive electrode slurry on the surface of the positive electrode current collector, and drying to obtain the positive electrode piece.
8. The preparation method of the positive pole piece according to claim 7, wherein the solid content of the positive pole slurry is 45-58 wt%.
9. The method for preparing the positive pole piece according to claim 8, further comprising:
and mixing a conductive material with the positive active substance, the positive binder and the solvent to obtain positive slurry.
10. A lithium ion battery comprises a positive pole piece, a negative pole piece, a diaphragm arranged between a positive pole and a negative pole, and electrolyte, and is characterized in that the positive pole piece comprises the positive pole piece in any one of claims 1 to 6 or the positive pole piece prepared by the preparation method of the positive pole piece in any one of claims 7 to 9; optionally, the membrane is selected from modified membranes of which the surfaces are coated with the modified polyvinylidene fluoride in claim 1.
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Cited By (1)
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| CN115117359A (en) * | 2022-08-30 | 2022-09-27 | 宁德时代新能源科技股份有限公司 | Binder, preparation method, positive pole piece, secondary battery and electricity utilization device |
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