CN117352963A - Separator, preparation method thereof, secondary battery and electric equipment - Google Patents
Separator, preparation method thereof, secondary battery and electric equipment Download PDFInfo
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- CN117352963A CN117352963A CN202210734208.0A CN202210734208A CN117352963A CN 117352963 A CN117352963 A CN 117352963A CN 202210734208 A CN202210734208 A CN 202210734208A CN 117352963 A CN117352963 A CN 117352963A
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- aramid fiber
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- 238000002360 preparation method Methods 0.000 title abstract description 14
- 239000011148 porous material Substances 0.000 claims abstract description 155
- 239000011248 coating agent Substances 0.000 claims abstract description 147
- 238000000576 coating method Methods 0.000 claims abstract description 147
- 229920006231 aramid fiber Polymers 0.000 claims abstract description 105
- 239000012528 membrane Substances 0.000 claims abstract description 39
- 238000000605 extraction Methods 0.000 claims description 173
- 229920003235 aromatic polyamide Polymers 0.000 claims description 115
- 239000004760 aramid Substances 0.000 claims description 114
- 239000002904 solvent Substances 0.000 claims description 53
- 239000010954 inorganic particle Substances 0.000 claims description 37
- 238000001035 drying Methods 0.000 claims description 18
- 239000002245 particle Substances 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 11
- 238000004519 manufacturing process Methods 0.000 claims description 2
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 description 52
- 238000012360 testing method Methods 0.000 description 22
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 20
- 239000006185 dispersion Substances 0.000 description 17
- 239000000243 solution Substances 0.000 description 17
- 239000011347 resin Substances 0.000 description 16
- 229920005989 resin Polymers 0.000 description 16
- 238000009826 distribution Methods 0.000 description 15
- 239000007788 liquid Substances 0.000 description 14
- 238000003756 stirring Methods 0.000 description 14
- 239000002002 slurry Substances 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 11
- 239000003795 chemical substances by application Substances 0.000 description 10
- 238000007711 solidification Methods 0.000 description 9
- 230000008023 solidification Effects 0.000 description 9
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 8
- 239000001110 calcium chloride Substances 0.000 description 8
- 229910001628 calcium chloride Inorganic materials 0.000 description 8
- 239000006184 cosolvent Substances 0.000 description 8
- 150000002500 ions Chemical class 0.000 description 8
- 238000000227 grinding Methods 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 239000011259 mixed solution Substances 0.000 description 7
- 238000002156 mixing Methods 0.000 description 7
- 230000035699 permeability Effects 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- 230000005540 biological transmission Effects 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 5
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 5
- 238000005524 ceramic coating Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 238000005070 sampling Methods 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical group [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 4
- 239000011247 coating layer Substances 0.000 description 4
- 230000001186 cumulative effect Effects 0.000 description 4
- 238000005520 cutting process Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- 229910052744 lithium Inorganic materials 0.000 description 4
- 229920000098 polyolefin Polymers 0.000 description 4
- 230000008569 process Effects 0.000 description 4
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 238000009423 ventilation Methods 0.000 description 4
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 3
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 3
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 3
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000002349 favourable effect Effects 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 2
- 239000012752 auxiliary agent Substances 0.000 description 2
- 238000005345 coagulation Methods 0.000 description 2
- 230000015271 coagulation Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000005191 phase separation Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000003860 storage Methods 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 230000001502 supplementing effect Effects 0.000 description 2
- 238000009827 uniform distribution Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910018626 Al(OH) Inorganic materials 0.000 description 1
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 1
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 1
- 229910019440 Mg(OH) Inorganic materials 0.000 description 1
- NPYPAHLBTDXSSS-UHFFFAOYSA-N Potassium ion Chemical compound [K+] NPYPAHLBTDXSSS-UHFFFAOYSA-N 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 229910006404 SnO 2 Inorganic materials 0.000 description 1
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 1
- 229910002367 SrTiO Inorganic materials 0.000 description 1
- 229910010413 TiO 2 Inorganic materials 0.000 description 1
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 1
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 229910001424 calcium ion Inorganic materials 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- 238000003618 dip coating Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000005485 electric heating Methods 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 238000012983 electrochemical energy storage Methods 0.000 description 1
- 238000007765 extrusion coating Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- -1 for example 3 Inorganic materials 0.000 description 1
- 229910021389 graphene Inorganic materials 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 125000000623 heterocyclic group Chemical group 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000037427 ion transport Effects 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 229910001629 magnesium chloride Inorganic materials 0.000 description 1
- 229910001425 magnesium ion Inorganic materials 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000012982 microporous membrane Substances 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 229910001414 potassium ion Inorganic materials 0.000 description 1
- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 229910001415 sodium ion Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000005406 washing Methods 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
- 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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
-
- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Cell Separators (AREA)
- Secondary Cells (AREA)
Abstract
The application provides a diaphragm, a preparation method thereof, a secondary battery and electric equipment. The membrane comprises a base membrane and an aramid fiber coating coated on at least one side surface of the base membrane, wherein the aramid fiber coating is a porous structure coating, the pore diameter of a surface pore of the aramid fiber coating is a first pore diameter, the pore diameter D50 of an inner pore of the aramid fiber coating is a second pore diameter, the D50 of the first pore diameter is 0.8-1.5 times of the D50 of the second pore diameter, and the first pore diameter and the second pore diameter are both smaller than 1 mu m. The thermal shrinkage rate of the diaphragm at 150 ℃ is controlled within 10 percent, and the rupture temperature of the diaphragm is more than 200 ℃.
Description
Technical Field
The application relates to the field of batteries, in particular to a diaphragm, a preparation method thereof, a secondary battery and electric equipment.
Background
The secondary lithium battery is used as an electrochemical energy storage device and is widely applied to a plurality of fields such as portable intelligent equipment, electric vehicles and the like. With the development of industry, the battery requirements of high energy density and high safety are more and more vigorous. The diaphragm is used as an important component of the secondary battery, provides a moving channel for ion transmission, blocks positive and negative electrodes, and provides guarantee for the safety of the battery. With the increasingly prominent problem of battery safety, the requirements of industry on the performance of the separator are gradually increased. In order to improve the safety of the conventional separator, an aramid coating or a ceramic coating is generally coated on the surface of the polyolefin separator. However, in practical application, the high temperature resistance of the separator coated with the aramid fiber coating or the ceramic coating is not guaranteed, the heat shrinkage of the separator at about 130 ℃ can be controlled to be below 3.5%, but after the temperature is raised to 150 ℃, the heat shrinkage performance of the separator can be greatly reduced, the heat shrinkage rate can be more than 10%, and the rupture temperature of the separator is generally below 200 ℃. In order to improve the high temperature resistance of the diaphragm, in the prior study, though the shrinkage resistance of the diaphragm at 150 ℃ and the diaphragm breaking temperature of the diaphragm can be improved by various coating modes, the thickness, quality, process complexity and production efficiency of the diaphragm can be seriously influenced by various coating modes, so how to realize the high temperature resistance of the diaphragm on the basis of single-layer coating, the heat shrinkage rate of the diaphragm at 150 ℃ is controlled within 10 percent, and the diaphragm breaking temperature is improved to more than 200 ℃ is a key for effectively improving the safety of the diaphragm and realizing commercialization.
Disclosure of Invention
The application provides a diaphragm, a preparation method thereof, a secondary battery and electric equipment, so as to improve the high temperature resistance of the diaphragm, control the thermal shrinkage rate of the diaphragm at 150 ℃ to be within 10 percent, and improve the rupture temperature of the diaphragm to be above 200 ℃.
In a first aspect, the present application provides a separator comprising a base film and an aramid coating applied to at least one side surface of the base film, wherein the aramid coating is a porous structure coating, the pore diameter of the surface pores of the aramid coating is a first pore diameter, the pore diameter of the inner pores of the aramid coating is a second pore diameter, the D50 of the first pore diameter is 0.8-1.5 times the D50 of the second pore diameter, and both the first pore diameter and the second pore diameter are smaller than 1 μm.
According to the diaphragm, the aramid fiber coating is arranged on the surface of at least one side of the base film, wherein the ratio of the D50 of the first aperture to the D50 of the second aperture of the aramid fiber coating is 0.8-1.5, so that the aperture of each part of the aramid fiber coating is ensured to be relatively close, namely the aperture of the surface aperture and the aperture of the internal aperture of the aramid fiber coating are controlled in a similar range. The aperture of the surface hole and the aperture of the inner hole in the aramid fiber coating are controlled within the above range, so that three-dimensional holes with uniform aperture are formed in the aramid fiber coating, more arch structures can be formed in the aramid fiber coating, the flexural strength of the diaphragm is improved, the heat shrinkage performance of the diaphragm is improved, the heat shrinkage rate of the diaphragm at 150 ℃ is reduced, and the rupture temperature of the diaphragm can be improved.
In addition, in the aramid fiber coating of the existing diaphragm, due to the limitation of the preparation process, the pore sizes of all parts are different, the pore size difference between the pore size of the surface pore and the pore size of the internal pore is larger, and the pore size of the surface pore is smaller generally, so that the transmission of active ions is not facilitated, and the quick charge performance of the battery is not facilitated to be improved; when the aperture of the surface hole meets the transmission requirement of active ions, the aperture of the inner hole of the aramid fiber coating is easily oversized at the moment, and the self-discharge of the secondary battery is easily aggravated. The aperture D50 of the surface hole of the aramid fiber coating and the aperture D50 of the internal hole of the surface hole are kept in the proportion range limited by the application, so that the aperture of each part in the aramid fiber coating is more consistent, and each part is beneficial to the transmission of active ions, thereby being more beneficial to improving the quick charge performance of the secondary battery and not aggravating the self-discharge of the secondary battery.
In one possible implementation, the ratio of the pore diameter D75 of the surface pores and the pore diameter D25 of the surface pores of the aramid coating is less than or equal to 2, preferably 1.8, and more preferably 1.5; the ratio of the pore diameter D75 of the inner pores to the pore diameter D25 of the inner pores of the aramid coating is 2 or less, preferably 1.8, and more preferably 1.5. Wherein, aperture D75 represents that 75% of the pores are smaller than the aperture, aperture D25 represents that 25% of the pores are smaller than the aperture, and a great amount of experimental statistics prove that when the ratio of aperture D75 of the surface pores to aperture D25 of the surface pores is controlled within 2, the aperture distribution of the surface pores of the aramid coating can be more uniform, and likewise, the ratio of aperture D75 of the inner pores to aperture D25 of the inner pores is controlled within 2, the uniformity of the aperture distribution of the inner pores in the aramid coating can be more favorable for improving the heat resistance and mechanical property of the diaphragm. The closer D75 and D25 are, the better the pore diameter uniformity is, the heat shrinkage resistance and the membrane rupture temperature of the membrane can be obviously improved, the membrane has better air permeability and the capability of transmitting active ions, and the self-discharge of the secondary battery can be reduced and the charging performance of the secondary battery can be improved when the membrane is used in the secondary battery.
In one possible implementation, the D50 of the first pore size and the D50 of the second pore size are both 50-350nm. By controlling the D50 of the first aperture and the D50 of the second aperture within the range of 50-350nm, a uniformly arranged nanoscale small pore structure can be formed in the aramid fiber coating, so that the passage of transmitted ions is facilitated, the phenomenon of stress concentration in the aramid fiber coating can be avoided, and the heat-resistant shrinkage performance of the diaphragm is improved under the condition of not increasing the internal resistance of the diaphragm.
In one possible implementation, the density of pores on the surface and any cross section of the aramid coating is 8000000-13000000/mm 2 . The holes of the aramid fiber coating can be uniformly distributed on the surface and the inside of the aramid fiber coating, the distribution of the holes of any section of the surface and the inside of the aramid fiber coating is more uniform, the high temperature resistance of the diaphragm can be further improved, the heat shrinkage rate is reduced, the mechanical property of the diaphragm can be improved, and the rupture temperature of the diaphragm is improved.
In one possible implementation, the intrinsic viscosity of the aramid in the aramid coating is 1.1-1.8dL/g. The larger the intrinsic viscosity value of the aramid fiber, the larger the molecular weight thereof. The molecular weight of the aramid fiber can influence the pore-forming effect of the aramid fiber, and the phase separation speed is faster as the molecular weight is larger. However, if the molecular weight is too large, pore forming is difficult, a compact layer is easy to generate on the surface of the porous membrane, the air permeability of the porous membrane is poor, and the internal resistance is influenced; if the molecular weight is too low, the ideal mechanical strength cannot be achieved, so that the intrinsic viscosity of the aramid fiber is controlled within the range of 1.1-1.8dL/g, and the obtained aramid fiber coating can maintain certain mechanical strength and has holes with specific size, so that the aramid fiber coating has certain air permeability and smaller internal resistance.
In one possible implementation, the aramid coating has a thickness of 1-4 μm. The thickness of the whole diaphragm can be kept at a lower level by coating the micro-scale aramid fiber coating, so that the diaphragm quality is prevented from being increased due to the fact that the thickness of the aramid fiber coating is too high.
In one possible implementation, the aramid coating contains inorganic particles in an amount of 50% to 90%, preferably 50% to 85%, and more preferably 50% to 80% by weight of the aramid coating. By adding inorganic particles, the compactness of the aramid fiber coating can be improved, so that the heat shrinkage performance of the diaphragm is further improved, and the diaphragm can maintain a higher rupture temperature. In one possible implementation, the particle size D50 of the inorganic particles is 600nm or less, preferably 500nm or less, further preferably 100-400nm. The particle diameter D50 of the inorganic particles is controlled within 600nm, so that the aramid fiber coating can form small holes with the pore diameter smaller than 1 mu m, and meanwhile, the smaller particle diameter of the inorganic particles is favorable for improving the heat-resistant shrinkage performance of the diaphragm. In addition, by adding inorganic particles, the electrostatic effect in the aramid fiber coating is effectively improved, the volume difference of the aramid fiber coating before and after drying is reduced, and the curling problem of the diaphragm is improved.
In a second aspect, the present application further provides a preparation method of the above-mentioned separator, where the preparation method includes:
the base film coated with the aramid pulp is subjected to multistage extraction and then is subjected to drying treatment to obtain a diaphragm; the multi-stage extraction at least comprises a first-stage extraction, a second-stage extraction and a third-stage extraction, wherein the mass concentration of the good solvent in the first-stage extraction is 35-58%, the mass concentration of the good solvent in the second-stage extraction is 20-35%, and the mass concentration of the good solvent in the third-stage extraction is less than or equal to 2.5%. In the first stage extraction, the aramid pulp is not completely cured, and by controlling the mass concentration of the good solvent in the first stage extraction to be in the range of 35-55%, the formation of a pore structure with uniform pore diameter can be facilitated in the thickness direction of the aramid coating. In the second stage of extraction, the aramid pulp is completely solidified, and the mass concentration of the good solvent in the second stage of extraction is controlled within the range of 20-35%, so that the formation of macropores in the aramid coating can be avoided, and the formation of a compact coating on the aramid coating can be avoided. The good solvent remaining on the coated separator can be removed by controlling the mass concentration of the good solvent in the third extraction stage to 2.5% or less.
In a preferred implementation, the mass concentration of the good solvent in the first stage extraction is 35-55%, more preferably 35-53%; the mass concentration of the good solvent in the second extraction is 20 to 33%, more preferably 20 to 30%. By further optimizing the concentration of good solvent in the first stage extraction and the second stage extraction, the uniformity of pore size in the aramid coating can be further improved.
In an alternative implementation, the multi-stage extraction comprises: placing the base film coated with the aramid pulp into a multi-section extraction tank for extraction; wherein, multistage extraction groove is including the first extraction groove, second extraction groove and the third extraction groove that set gradually at least, and in multistage extraction, the base film that is coated with aramid pulp carries out the extraction through first extraction groove, second extraction groove and third extraction groove in proper order. The first extraction tank is also referred to as a coagulation bath, and the aramid pulp is coagulated in the first extraction tank. Wherein the concentration of the good solvent in the first extraction tank gradually decreases along the moving direction of the base film in the first extraction tank, and the difference between the highest concentration value and the lowest concentration value of the good solvent in the first extraction tank is 5-15wt%, preferably 6-13wt%, and more preferably 7-12wt%. Illustratively, the concentration of the good solvent in the first extraction tank is distributed in a gradient along the moving direction of the base film in the first extraction tank, and the concentration gradually decreases. The good solvent with gradually reduced concentration is arranged in the first extraction tank, and the difference value between the highest concentration value and the lowest concentration value of the good solvent in the first extraction tank is controlled within the range of 5-15wt%, so that the diffusion rates of the good solvent and the poor solvent are kept consistent along the thickness direction of the aramid fiber coating along the time change, holes with high pore diameter consistency are formed in the aramid fiber coating, the distribution of the holes is more uniform, and the ventilation increment of the diaphragm can be obviously improved under the condition of improving the thermal shrinkage and the rupture temperature of the diaphragm.
In an alternative implementation, the extraction time of the first extraction and the extraction time of the second extraction are both 5-15s.
The data in the above possible implementations of the present application, such as the data of the first pore diameter, the second pore diameter, the aramid coating thickness, the particle diameter of the inorganic particles, the addition amount, and the like, should be understood as values within the engineering measurement error range during measurement, and are all within the range defined in the present application.
In a third aspect, the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator may be a separator of the first aspect of the present application.
The secondary battery that this application provided, owing to including the diaphragm of this application first aspect, under the condition that this application diaphragm possesses high heat resistance, the secondary battery of this application can obtain better security, simultaneously, owing to the diaphragm of this application has higher ventilative value, consequently, the secondary battery of this application still can obtain higher quick charge performance.
In a fourth aspect, the present application provides an electrical consumer comprising the secondary battery of the third aspect of the present application.
Among them, the electric equipment includes but is not limited to electronic devices, electric vehicles, electric power storage systems, etc. On the basis that the secondary battery of each possible implementation mode of the application has better safety and quick charge performance, the same effect can be obtained by using the secondary battery as electric equipment of a driving power supply.
Drawings
FIG. 1 is a schematic view showing a cross-sectional structure of a separator according to an embodiment of the present application in a thickness direction;
FIG. 2 is a surface SEM image of a separator of example 1 of the present application;
FIG. 3 is an SEM image of a cross section of the separator of example 1 along its thickness direction;
FIG. 4 is a graph showing the surface pore size distribution of the separator of example 1;
FIG. 5 is an internal pore size distribution plot at a cross-section of the separator of example 1;
FIG. 6 is a graph showing the rupture temperature of the separator of example 1.
Reference numerals: 11-base film; 12-aramid coating; 121-surface pores; 122-internal holes.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present application more apparent, the present application will be described in further detail with reference to the accompanying drawings.
For ease of understanding, the relevant terms referred to in this application are explained first below.
And (3) a secondary battery: by using the difference in the electric potential of the two electrodes, a potential difference is generated, thereby causing electrons to flow, and a current is generated, which can convert chemical energy into electric energy.
A diaphragm: the medium is used for separating the positive electrode from the negative electrode in the battery cell and preventing the positive electrode and the negative electrode from being directly contacted to short-circuit. The basic properties of the separator are porosity (channels that provide ion transport) and electrical insulation (to prevent leakage).
Heat shrinkage rate: the dimensional change rate of the separator in the longitudinal (machine direction, MD), i.e., in the long side direction of the separator)/transverse (transverse direction, TD, perpendicular to the MD, i.e., in the short side direction of the separator) direction before and after heating is shown.
Rupture of membranes temperature: the separator melts to such an extent that rupture occurs, resulting in a temperature at which the secondary battery is locally or comprehensively short-circuited.
D50: also called median pore diameter, the pore diameter corresponding to a cumulative pore diameter distribution percentage of 50% is physically defined as the pore diameter being less than 50% of its pores and the pore diameter being greater than 50% of its pores.
D75: the physical meaning of the pore diameter corresponding to the cumulative pore diameter distribution percentage reaching 75% is that the pore diameter is smaller than 75% of the pores and larger than 25% of the pores.
D25: the physical meaning of the pore diameter corresponding to the cumulative pore diameter distribution percentage reaching 25% is that the pore diameter is smaller than 25% of the pores and larger than 75% of the pores.
At present, secondary batteries, such as lithium ion batteries, are commonly used diaphragms which are polyolefin diaphragms, and the melting point temperature range of the diaphragms is only 130-165 ℃, so that the operation safety of high-power lithium batteries is difficult to ensure. To improve the safety performance of the separator, the polyolefin separator is generally modified by an aramid coating or ceramic coating. Among them, ceramic coating improves heat-resistant shrinkage performance of the separator more remarkably at a certain temperature, but at a higher temperature, ceramic coating loses mechanical strength and thus loses protective ability. The aramid fiber coating material has high decomposition temperature and can still maintain strength at a higher temperature, so that the aramid fiber coating material has higher rupture temperature, but the heat-resistant shrinkage performance of the aramid fiber coating is poorer, a certain amount of inorganic particles are required to be added to improve the compactness of the coating, so that the heat-resistant shrinkage performance of the diaphragm is improved, but the mechanical strength of the aramid fiber coating is easily lost by adding the inorganic particles, so that the corresponding rupture temperature cannot be maintained. Thus, the current single-coated separator has not achieved an improvement in the combination of low shrinkage and high rupture temperature.
In order to solve the technical problems, the application provides a diaphragm. Fig. 1 is a schematic cross-sectional structure in a thickness direction of a separator, which includes a base film 11 and an aramid coating layer 12 coated on at least one side surface of the base film 11, as shown in fig. 1. In the separator shown in fig. 1, one side surface of the base film 11 is coated with an aramid coating 12. It is understood that the aramid coating 12 may be provided on one side surface of the base film 11 alone, or may be provided on both side surfaces of the base film 11. The diaphragm provided with only one aramid coating layer 12 will be explained below with reference to fig. 1, but the diaphragms provided with the aramid coating layers 12 on both sides of the base film 11 are also within the scope of the present application.
Referring to fig. 1, the base film 11 is a microporous film structure, and may provide porosity and insulation to facilitate the passage of transported ions and maintain insulation between the positive and negative electrode sheets of the secondary battery. The base film 11 may be a polyolefin-based film, and the thickness of the base film 11 may be 4 to 20 μm, which may provide the separator with substantial tensile strength and puncture resistance.
With continued reference to FIG. 1, the aramid coating 12 is a porous structured coating, which may have a thickness of, for example, 1-4 μm. The aperture of the surface pores 121 of the aramid fiber coating 12 is a first aperture, and the aperture of the inner pores 122 of the aramid fiber coating 12 is a second aperture. The surface hole 121 of the aramid fiber coating 12 is a hole that can be observed from any surface of the aramid fiber coating, and the surface of the aramid fiber coating 12 may be a surface parallel to the base film 11 and far from the base film 11, or may be a side surface of the aramid fiber coating 12, i.e., a surface perpendicular to the base film 11. The inner hole 122 of the aramid fiber coating 12 is a hole corresponding to any cross section of the aramid fiber coating 12, and any cross section of the aramid fiber coating 12 may be any cross section of the aramid fiber coating 12 parallel to the thickness direction of the aramid fiber coating 12, may be a cross section perpendicular to the thickness direction of the aramid fiber coating 12, may be an inclined cross section, or may be a cross section obtained by cutting the aramid fiber coating 12 along any direction. The pore diameter of the pore corresponding to the cross section is the pore diameter of the inner pore 122 of the aramid coating 12.
In the aramid coating 12 of the embodiment of the present application, D50 of the first pore diameter is 0.8 to 1.5 times, preferably 0.8 to 1.4 times, more preferably 0.8 to 1.3 times that of the second pore diameter, and both the first pore diameter and the second pore diameter are smaller than 1 μm, preferably smaller than 800nm, more preferably smaller than 600nm. Illustratively, the D50 of the first pore size and the D50 of the second pore size both satisfy 50-350nm. The ratio of the D50 of the first pore size to the D50 of the second pore size may be, for example, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5. The D50 of the first pore size and the D50 of the second pore size may be, for example, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 200nm, 220nm, 250nm, 300nm, 320nm or 350nm.
The ratio of the pore diameter D50 of the surface pore to the pore diameter D50 of the internal pore corresponding to any section is limited within the range of 0.8-1.5 times, so that the sizes of the surface pore and the internal pore of the aramid fiber coating 12 are closer, the pore diameter distribution is narrower, and three-dimensional pores with uniform pore diameters can be formed in the aramid fiber coating 12, thereby facilitating the transmission of the transmission ions in the aramid fiber coating 12 to be smoother and improving the quick charge capacity of the secondary battery. Holes meeting the above range can form more arch structures in the aramid fiber coating 12, so that the flexural strength of the diaphragm is improved, the heat shrinkage performance of the diaphragm is improved, the heat shrinkage rate of the diaphragm at 150 ℃ is reduced, and the rupture temperature of the diaphragm can be improved.
In an alternative embodiment, the ratio of the pore diameter D75 of the surface pores of the aramid coating 12 to the pore diameter D25 thereof is 2 or less; the ratio of the pore diameter D75 and the pore diameter D25 of the internal pores corresponding to any section of the aramid coating 12 is less than or equal to 2. The ratio range can lead the pore diameter of each part of the aramid fiber coating to be more uniform.
In an alternative embodiment, the intrinsic viscosity of the aramid in the aramid coating 12 is 1.1-1.8dL/g. For example, the intrinsic viscosity of the aramid fiber may be, for example, 1.1dL/g, 1.2dL/g, 1.3dL/g, 1.4dL/g, 1.5dL/g, 1.6dL/g, 1.7dL/g, or 1.8dL/g. The aramid fiber can be at least one of meta-aramid fiber, para-aramid fiber, other heterocyclic aramid fiber and modified aramid fiber.
In one possible implementation, the density of pores on the surface and any cross section of the aramid coating is 8000000-13000000/mm 2 Exemplary may be 8000000/mm, for example 2 9000000 pieces/mm 2 10000000 pieces/mm 2 11000000 pieces/mm 2 12000000 pieces/mm 2 Or 13000000/mm 2 。
In an alternative embodiment, the aramid coating 12 contains inorganic particles in an amount of 50% to 90%, preferably 70% to 90% by weight of the aramid coating 12. Illustratively, the inorganic particles may be present in the aramid coating 12 at a weight ratio of, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%. The aramid coating 12 comprises the rest of the aramid except the inorganic particles in the weight proportion. Wherein the particle diameter D50 of the inorganic particles may be 600nm or less. Wherein the inorganic particles may be SrTiO, for example 3 、SnO 2 、Mg(OH) 2 、MgO、Al(OH) 3 、Al 2 O 3 、SiO 2 、BaSO 4 Or TiO 2 At least one of them.
The inorganic particles with the weight ratio are added into the aramid fiber coating 12, so that the compactness of the aramid fiber coating 12 can be improved, and the heat-resistant shrinkage performance of the diaphragm can be improved. However, the excessively high inorganic particle content easily causes the aramid fiber coating 12 to lose mechanical strength, so that the corresponding rupture temperature cannot be maintained at high temperature, and therefore, the mechanical strength of the diaphragm can be improved and the aramid fiber coating 12 can be maintained at a higher rupture temperature by adding 50-90% of inorganic particles by mass ratio. In addition, the particle size of the inorganic particles in the aramid fiber coating 12 cannot be too large, and the excessively large inorganic particles are not beneficial to reducing the thermal shrinkage, and possibly reduce the mechanical strength of the aramid fiber coating 12, so that the designed rupture temperature cannot be reached, therefore, the inorganic particles with the weight ratio of 50-90% are added in the aramid fiber coating 12, the particle size D50 of the inorganic particles is limited to be less than or equal to 600nm, and the heat-resistant shrinkage performance of the diaphragm and the rupture temperature of the diaphragm can be improved while the mechanical strength of the aramid fiber coating 12 is effectively improved. For example, the separator of the embodiment of the application can have a heat shrinkage of 10% or less at 150 ℃, a rupture temperature of 200% or more, and a ventilation value of 200s/100ml or less.
The structure and composition of the separator are described above, and a specific preparation method of the separator will be explained below.
The preparation method of the diaphragm provided by the application comprises the following steps: the membrane can be obtained by multistage extraction and drying of the base membrane coated with the aramid pulp. Wherein the multi-stage extraction may be a coagulation bath extraction.
Wherein, the aramid pulp can comprise aramid resin, inorganic particles and one or more good solvents. When the aramid fiber slurry is prepared, the aramid fiber resin and the inorganic particles can be simultaneously dissolved in a good solvent, and the aramid fiber slurry can be obtained after uniform dispersion; in addition, a solution of an aramid resin and a dispersion of inorganic particles may be prepared separately, and then the solution of an aramid resin and the dispersion of inorganic particles may be mixed to obtain an aramid slurry. The good solvent may be at least one of N-methylpyrrolidone (N-Methyl-2-pyrrosidone NMP), N-Dimethylacetamide (DMAC), and N, N-Dimethylformamide (DMF).
It is understood that the aramid slurry may include a co-solvent, a pore-forming agent, a poor solvent for the aramid resin, etc. in addition to the aramid resin and the inorganic particles. Wherein the cosolvent or pore-forming agent is selected from one or a combination of at least two of lithium chloride, magnesium chloride, calcium carbonate and calcium chloride. The poor solvent may be selected from one or a combination of at least another of water, methanol, ethanol, propanol, acetone, ethyl acetate, dichloromethane, and petroleum ether.
As an exemplary illustration, in one embodiment of the present application, the resulting aramid pulp may have an aramid resin weight ratio of 2-10%, an inorganic particle weight ratio of 0-30%, a co-solvent weight ratio of 0-8%, a poor solvent weight ratio of 0-5%, and a good solvent weight ratio of 60-85%.
The aramid pulp may be coated on at least one surface of the base film on which the aramid pulp is coated. The coating mode can be one of gravure roll coating, bar coating, extrusion coating or dip coating.
The base film coated with the aramid fiber coating can be sequentially immersed in multi-stage extraction tanks with different concentrations for multi-stage extraction and solidification, so as to form the aramid fiber coating with the required aperture on the surface of the base film. The multistage extraction tank at least comprises a first extraction tank, a second extraction tank and a third extraction tank which are sequentially arranged, and in multistage extraction, the base film coated with the aramid pulp is sequentially extracted and solidified through the first extraction tank, the second extraction tank and the third extraction tank. The extraction in the first extraction tank is the first-stage extraction, the extraction in the second extraction tank is the second-stage extraction, and the extraction in the third extraction tank is the third-stage extraction. Wherein, the mass concentration of the good solvent in the first extraction tank is 35-55%, the mass concentration of the good solvent in the second extraction tank is 20-35%, and the mass concentration of the good solvent in the third extraction tank is less than or equal to 2.5%. The good solvent may be, for example, at least one of NMP, DMAC or DMF, and the choice of the particular good solvent may be selected in combination with the type of co-solvent or pore former, and is not particularly limited herein. The poor solvent in the multi-stage extraction tank can be water. Wherein, the extraction time of the first extraction stage and the extraction time of the second extraction stage can be 5-15s.
The multi-stage extraction tank used in the multi-stage extraction process at least comprises three stages of extraction tanks, namely a first extraction tank, a second extraction tank and a third extraction tank, and the multi-stage extraction tank can also comprise other extraction tanks besides the three stages of extraction tanks. When other sections of extraction tanks are provided, the added extraction tank can be arranged between the second extraction tank and the third extraction tank, so long as the good solvent concentration of the last section of extraction tank, namely the third extraction tank, meets the range defined by the embodiment of the application.
In one embodiment of the present application, the concentration of the good solvent in the first extraction tank gradually decreases along the moving direction of the base film in the first extraction tank, and the difference between the highest concentration value and the lowest concentration value of the good solvent in the first extraction tank is 5-15wt%. According to the preparation method, the pore diameters of the holes formed in the obtained aramid fiber coating are more consistent in the thickness direction of the aramid fiber coating by controlling the concentration gradient of the good solvent in the first extraction tank, and the aim of small ventilation increment is fulfilled under the condition of effectively improving the heat shrinkage performance and the rupture temperature of the diaphragm.
The concentration of the good solvent in the first extraction tank may be stepwise distributed by the following method:
1) For example, a baffle plate and other parts can be arranged in the moving direction of the base film, so that the diffusion efficiency of the poor solvent in the extraction tank can be slowed down;
2) Continuously supplementing a small amount of good solvent at the water inlet position of the base film in the first extraction tank;
3) When the poor solvent, such as water, is normally supplemented in the first extraction tank, the supplementing amount of the poor solvent can be supplemented in a gradient distribution manner.
It is to be understood that the above methods are merely exemplary, and any method that allows for a gradient of the good solvent in the first extraction tank is to be understood as falling within the scope of the present application.
In one embodiment of the present application, an oven may be used for drying after the multi-stage extraction is completed. Wherein, the oven can be a three-stage oven, and the temperatures of the three-stage oven can be 50 ℃, 55 ℃ and 60 ℃ respectively.
The preparation method of the separator is explained above, and the properties of the separator of the present application will be further described in detail with reference to specific examples and comparative examples.
Example 1
This example is a membrane, the membrane being prepared by the steps of:
step S11, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid values are fully dissolved to obtain an aramid solution;
Step S12, adding 2.0kg of alumina with the particle size of 0.2 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
step S13, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
s14, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and then, the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 40-50%, the DMAC concentration at the position where the base film enters the tank is 50%, the DMAC concentration at the position where the base film exits the tank is 40%, the DMAC content in a second extraction tank is 30%, the DMAC content in a third extraction tank is less than or equal to 2.5%, and the time for a diaphragm to pass through each extraction tank is 8S;
and S15, drying by using three-stage ovens, wherein the temperatures of the ovens at the three stages are 50 ℃, 55 ℃ and 60 ℃ respectively, and drying to obtain the membrane with the diameter of 10 mu m.
Small-particle-size inorganic particles which are conducive to pore formation are selected, the ratio of the inorganic particles is increased, and two sections of extraction tanks with high good solvent concentration are matched to ensure that pores are formed uniformly in the aramid fiber precipitation process, and the pore sizes of the surfaces and the inside are close. In the DMAC concentration of 45% in the first extraction tank, the aramid pulp coating is not completely solidified, the liquid-liquid phase separation time is sufficient, the gradient uniform pore diameter is formed along the thickness direction, the aramid pulp coating in the second extraction tank is completely solidified, the 30% solvent concentration is moderate, no macropores are formed, and no compact coating is formed. The holes in the aramid fiber coating are uniformly distributed, so that defect points are avoided, the aramid fiber coating can keep higher mechanical strength under the condition of high inorganic particle content, and meanwhile, the membrane breaking temperature and the heat-resistant shrinkage performance are improved.
Example 2
This example is a membrane, the membrane being prepared by the steps of:
s21, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid value is fully dissolved to obtain an aramid solution;
step S22, adding 2.0kg of alumina with the particle size of 0.2 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
s23, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
s24, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and then, the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 40-50%, the DMAC concentration at the position of the base film entering the tank is 50%, the concentration of a solvent at the position of a groove outlet is 40%, the DMAC content in a second extraction tank is 20%, the DMAC content in a third extraction tank is less than or equal to 2.5%, and the time for a diaphragm to pass through each extraction tank is 8S;
and S25, drying by using three-stage ovens, wherein the temperatures of the ovens at the three stages are 50 ℃, 55 ℃ and 60 ℃ respectively, and drying to obtain the membrane with the diameter of 10 mu m.
Example 3
This example is a membrane, the membrane being prepared by the steps of:
s31, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid value is fully dissolved to obtain an aramid solution;
step S32, adding 1.6kg of alumina with the particle size of 0.2 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
s33, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
step S34, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and then, the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 40-50%, the good solvent concentration at the position where the base film enters the tank is 50%, the DMAC concentration at the position where the base film exits the tank is 40%, the DMAC content in a second extraction tank is 20%, the DMAC content in a third extraction tank is less than or equal to 2.5%, and the time for a diaphragm to pass through each extraction tank is 8S;
and step S35, drying by using three-stage ovens, wherein the temperatures of the ovens at the three stages are respectively 50 ℃, 55 ℃ and 60 ℃, and drying to obtain the membrane with the diameter of 10 mu m.
Example 4
This example is a membrane, the membrane being prepared by the steps of:
s41, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid value is fully dissolved to obtain an aramid solution;
step S42, adding 2.0kg of alumina with the particle size of 0.4 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
step S43, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
step S44, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and then, the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 40-50%, the DMAC concentration at the position where the base film enters the tank is 50%, the DMAC concentration at the position where the base film exits the tank is 40%, the DMAC content in a second extraction tank is 20%, the DMAC content in a third extraction tank is less than or equal to 2.5%, and the time for a diaphragm to pass through each extraction tank is 8S;
and step S45, drying by using three-stage ovens, wherein the temperatures of the ovens at the three stages are respectively 50 ℃, 55 ℃ and 60 ℃, and drying to obtain the membrane with the diameter of 10 mu m.
Comparative example 1
This example is a membrane, the membrane being prepared by the steps of:
s101, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid value is fully dissolved to obtain an aramid solution;
step S102, adding 2kg of alumina with the particle size of 0.2 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
step S103, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
step S104, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 20%, the DMAC content in a second extraction tank is 5%, the DMAC content in a third extraction tank is less than or equal to 2.5%, and the time for a diaphragm to pass through each extraction tank is 8S;
step S105, drying by using three-stage ovens, wherein the temperatures of the ovens at the three stages are 50 ℃, 55 ℃ and 60 ℃ respectively, and drying to obtain the membrane with the diameter of 10 mu m.
Comparative example 2
This example is a membrane, the membrane being prepared by the steps of:
Step S201, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid values are fully dissolved to obtain an aramid solution;
step S202, adding 2.0kg of alumina with the particle size of 0.4 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
step S203, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
step S204, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 60%, the DMAC content in a second extraction tank is 50%, the DMAC content in a third extraction tank is 40%, and the time for a diaphragm to pass through each extraction tank is 8S;
step S205, after extraction and solidification, the mixture enters a fourth extraction tank and a fifth extraction tank for water washing, the concentration of a good solvent in the fourth extraction tank is 2%, the concentration of a good solvent in the fifth extraction tank is 2%, then three-stage baking ovens are used for drying, the temperatures of the three-stage baking ovens are respectively 50 ℃, 55 ℃ and 60 ℃, and a 10-mu m diaphragm is obtained after the baking.
Comparative example 3
This example is a membrane, the membrane being prepared by the steps of:
step S301, adding 0.4kg of pore-forming agent calcium chloride into 6kg of DMAC, fully stirring and dissolving, then adding 0.6kg of meta-aramid resin powder, and stirring in a constant-temperature water bath environment at 40 ℃ for 1h until the aramid values are fully dissolved to obtain an aramid solution;
step S302, adding 2.0kg of alumina with the particle size of 0.4 mu m into 9kg of DMAC, and fully grinding and dispersing to obtain alumina dispersion liquid;
step S303, mixing an aramid fiber solution and an alumina dispersion liquid to prepare an aramid fiber slurry;
step S304, coating aramid pulp on two sides of a PE base film with the thickness of 7 mu m by using a gravure roll, wherein the coating speed is 30m/min, and the coated aramid pulp enters a mixed solution of DMAC and water for multistage extraction and solidification, wherein the DMAC content in a first extraction tank is 60%, the DMAC content in a second extraction tank is 20%, the DMAC content in a third extraction tank is 2%, and the time for a diaphragm to pass through each extraction tank is 8S;
and step S305, drying by using three-stage ovens, wherein the temperatures of the ovens at the three stages are 50 ℃, 55 ℃ and 60 ℃ respectively, and drying to obtain the membrane with the diameter of 10 mu m.
The dimensions and performance parameters of the separators of each of the examples and comparative examples were tested, and the test items include the thickness of the base film in the separator, the thickness of the aramid coating, the first pore size, the second pore size, the surface maximum pore size, the cross-sectional maximum pore size, the heat shrinkage at 150 ℃, the rupture temperature, and the air permeability value. The specific test process of each item is as follows:
1) Thickness measurement of base film and aramid coating
A. Sampling: for the diaphragm with the width less than 200mm, determining a point every 40mm plus or minus 5mm along the longitudinal direction, wherein the number of test points is not less than 10, the number of test points can be determined according to the width of the diaphragm, and the distance between a measurement start point and an edge is not less than 20mm;
for the diaphragm with the width more than or equal to 200mm, a point is determined every 80mm plus or minus 5mm along the transverse direction, the number of test points is not less than 10, the number of test points can be determined according to the width of the diaphragm, and the distance between the measurement start point and the edge is not less than 20mm.
B. And (3) testing: each test point was tested by a thickness gauge at a temperature of 23.+ -. 2 ℃ with a measuring face diameter of between 2.5mm and 10mm and a load applied to the test sample of between 0.5N and 1.0N.
C. And (3) data processing: and taking an actual measurement value of the thickness of each test point and taking an arithmetic average value.
2) D50 for first aperture, D50 for second aperture, surface maximum aperture, cross-section maximum aperture measurement
A. And equally dividing a roll of diaphragm in the TD and MD directions in three equal intervals to form nine grids, and randomly selecting samples with the size of 1cm to 1cm cut in each grid, wherein the total number of the samples is 9.
B. Taking pictures of the section and the surface of each sample by using SEM, and selecting pictures under the magnification of 20K for later use;
C. Importing the SEM picture into Image J software;
D. setting a corresponding scale proportion in the Image J according to the SEM picture scale;
E. the section and the surface electron microscope of each sample are respectively provided with a rectangular area with the diameter of 6.0 μm and the diameter of 1.5 μm, the pore size is marked in sequence, all obvious pores are marked as far as possible during marking, and no record is carried out on the pores which are below 20nm and cannot be effectively identified;
F. when the surface electron microscope of the aramid fiber coating observes unevenness, when a plurality of layers of holes are overlapped in the thickness gradient direction at the same position at the height fluctuation position, the outermost holes are selected for recording; the irregular hole takes the maximum diameter as a record value; the pores are connected together, and if the length exceeds 500nm, the pores are characterized respectively;
G. respectively accumulating the surface and section apertures of 9 samples to prepare a number aperture distribution diagram of the surface and the section; d50 is the pore size at which the cumulative number of all pore diameters of 9 samples is 50%, and D50 of the first pore diameter and D50 of the second pore diameter are obtained, respectively.
3) Heat shrinkage at 150 DEG C
A. Sampling: randomly taking 6 samples across the full width of the membrane, a specific sampling of each sample may include: cutting 100mm along the MD direction of the diaphragm; when the TD direction of the separator is greater than 100mm, the length of the test sample in the TD direction may be 100mm; when the TD direction of the microporous membrane is less than 100mm, the length of the test sample in the TD direction may be practically equal.
B. And (3) testing: marking longitudinal and transverse marks of the samples, and measuring and recording the longitudinal and transverse dimensions of each sample; the sample is horizontally placed in a paper jacket layer, and the sample has no folding, wrinkling, adhesion and other conditions; placing the paper sleeve (the number of layers can be 10 for example) with the sample in the middle of the constant temperature oven flatly (the door opening time is not more than 3s for example); heating the sample to 150 ℃ by an electric heating constant temperature box for 1h; after taking out the sample, the sample was cooled to room temperature, and the longitudinal length and the transverse length were measured.
C. And (3) data processing:
the heat shrinkage of each sample was calculated:
T＝(L 0 -L)/L 0 ×100％，
wherein T is the heat shrinkage (%), L of the sample 0 For the size (mm) of the sample before heating, L is the size (mm) of the sample after heating. An arithmetic average of the heat shrinkage of the samples was calculated. The heat shrinkage in table 1 of the present application is the average of shrinkage in both TD and MD directions.
4) Rupture of membranes temperature
Using TMA equipment to test, cutting a diaphragm sample with the length of 8mm and the width of 4mm along the TD/MD direction, applying a constant load of 0.02N on the length direction, carrying out temperature programming at 5 ℃/min, recording the deformation of the diaphragm, when the deformation reaches the maximum, meaning that the diaphragm breaks, recording the point as a broken film point, and the corresponding temperature is the broken film temperature of the TD/MD direction.
5) Ventilation value
According to the method 6.5.4 in GB/T36363-2018, the specific method is as follows: and cutting three diaphragms on the film roll at intervals of 150mm longitudinally, wherein the sampling size is 100mm multiplied by 100mm when the width of the diaphragm is more than or equal to 100mm, and the sampling size is 100mm multiplied by the width of the diaphragm when the width of the diaphragm is less than 100 mm. The air permeability test is carried out by placing the diaphragm in a test head of an air permeability instrument which is suitable for the test range, and the average value of 3 test results is taken as the air permeability of the diaphragm.
The test results of each of the above test items are shown in Table 1. Wherein, for ease of understanding, the relevant test data may be understood in connection with fig. 2-6. Fig. 2 is a surface SEM image of the separator of example 1, fig. 3 is a SEM image of a cross section of the separator of example 1 in the thickness direction thereof, fig. 4 is a surface pore diameter distribution chart of the separator of example 1, fig. 5 is an internal pore diameter distribution chart at the cross section of the separator of example 1, and fig. 6 is a rupture temperature test chart of the separator of example 1.
As shown in fig. 2 to 5, the separator of example 1 has substantially uniform pore diameters of the surface pores and the inner pores and substantially uniform median pore diameter D50, which means that the separator obtained by the preparation method of the present application has uniform pore diameter distribution and uniform size of pores throughout the aramid coating. In addition, as can be seen from fig. 6, the separator of example 1 has a high rupture temperature. Wherein specific data can be referred to in table 1.
TABLE 1
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As is clear from the comparison data of examples 1 and 2, when the concentration of the good solvent in the second extraction tank was changed, the pore size in the aramid coating was increased, and the rupture temperature of the separator was further affected. From the comparative data of example 2 and example 3, it is understood that the heat shrinkage resistance of the separator is reduced when the ratio of the inorganic particles in the aramid coating layer is changed. As is clear from the comparative data of example 2 and example 4, increasing the particle diameter of the inorganic particles also has a certain effect on the heat shrinkage resistance of the separator.
As can be seen from the comparative data of example 1 and comparative examples 1-2 of table 1, the performance of the separator obtained by the extraction process of comparative examples 1 and 2, i.e., the concentration of the good solvent in each of the first, second and third extraction tanks, was far lower than that of example 1. In the separator obtained in comparative example 1, the difference between the surface pore diameter and the internal pore diameter at the cross section was large, the rupture temperature of the obtained separator was low, and the heat shrinkage at 150 ℃ was also much higher than in example 1.
In summary, the aramid fiber coating with uniform pore diameter and uniform distribution can be obtained by selecting a proper multistage extraction process. In the preparation process of the diaphragm, the smaller the particle size of the inorganic particles in the aramid fiber slurry is, the more uniform distribution of holes is realized, the content of the inorganic particles is increased, the content of the aramid fiber is relatively reduced, the volume change of the aramid fiber coating is small in the extraction curing process, the size of the formed holes is reduced, and the formation of the holes with uniform pore diameters is facilitated.
In addition, in the aramid pulp, the higher the molecular weight of the aramid, the faster the precipitation speed, the more favorable the formation of macropores, and the too low molecular weight cannot achieve the necessary mechanical strength, so the molecular weight of the aramid is controlled within a proper range. When the molecular weight of the aramid fiber is high, a proper amount of cosolvent can be added for cosolvent dissolution, and the cosolvent can be eluted by water in the extraction process. The size and uniformity of the aperture in the aramid fiber coating can be improved by selecting a proper cosolvent or pore-forming agent and a proper concentration of an auxiliary agent.
According to the diaphragm provided by the embodiment of the application, the proportion of the aramid resin, the stepless particles and the auxiliary agent is adjusted by selecting the proper aramid resin and the inorganic particles, and the proper multistage extraction process conditions are selected for use, so that the aramid coating with the surface aperture and the internal aperture which are compounded with the requirements of the application can be prepared, and the purposes of improving the heat-resistant shrinkage performance and the rupture temperature of the diaphragm are further achieved.
According to the same object, the present application also provides a secondary battery, which may include a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte is filled between the positive electrode sheet and the negative electrode sheet and wets the separator. Wherein, the diaphragm can be the diaphragm that this application provided.
The secondary battery that this application provided, because including the diaphragm of this application, under the condition that this application diaphragm possesses high heat resistance, the secondary battery of this application can obtain better security, simultaneously, because the diaphragm of this application has higher ventilative value, consequently, the secondary battery of this application still can obtain higher quick charge performance.
It is to be understood that the secondary battery of the present application may be a lithium ion battery, a sodium ion battery, a potassium ion battery, a magnesium ion battery, a calcium ion battery, or the like, and the type of the specific secondary battery is not limited as long as the secondary battery can be assembled using the separator of the present application. In addition, the specific types of the positive electrode sheet and the negative electrode sheet can be selected according to the specific type of the secondary battery, and taking a lithium ion battery as an example, the positive electrode active material in the positive electrode sheet comprises, but is not limited to, lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, lithium nickel cobalt manganate or lithium nickel cobalt aluminate, and the negative electrode active material in the negative electrode sheet comprises, but is not limited to, graphite, activated carbon, graphene or the like. Specifically, the selection may be made according to the performance of the secondary battery.
Based on the same object, the application also provides electric equipment, and the electric equipment comprises the secondary battery. The secondary battery can provide power for the electric equipment so as to drive the electric equipment to normally operate.
Among them, the electric equipment includes but is not limited to electronic devices, electric vehicles, electric power storage systems, etc. On the basis that the secondary battery of each possible implementation mode of the application has better safety and quick charge performance, the same effect can be obtained by using the secondary battery as electric equipment of a driving power supply.
The terminology used in the above embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the specification and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include, for example, "one or more" such forms of expression, unless the context clearly indicates to the contrary.
Reference in the specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," and the like in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless expressly specified otherwise.
The foregoing is merely specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think about changes or substitutions within the technical scope of the present application, and the changes or substitutions are intended to be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (11)
1. The membrane is characterized by comprising a base membrane and an aramid fiber coating coated on at least one side surface of the base membrane, wherein the aramid fiber coating is a porous structure coating, the pore diameter of a surface pore of the aramid fiber coating is a first pore diameter, the pore diameter of an inner pore of the aramid fiber coating is a second pore diameter, the D50 of the first pore diameter is 0.8-1.5 times of the D50 of the second pore diameter, and the first pore diameter and the second pore diameter are smaller than 1 mu m.
2. The separator of claim 1, wherein the ratio of D75 to D25 of the first pore size is 2 or less; the ratio of D75 to D25 of the second aperture is less than or equal to 2.
3. The membrane of claim 1 or 2, wherein the D50 of the first pore size and the D50 of the second pore size are both 50-350nm.
4. A separator according to any one of claims 1-3, wherein the aramid coating has a thickness of 1-4 μm.
5. The separator according to any one of claims 1 to 4, wherein the aramid coating contains inorganic particles in an amount of 50 to 90% by weight of the aramid coating.
6. The separator according to claim 5, wherein the inorganic particles have a particle diameter d50.ltoreq.600 nm.
7. A method of making the separator of any one of claims 1-6, comprising:
the base film coated with the aramid pulp is subjected to multistage extraction and then is subjected to drying treatment to obtain the diaphragm; the multi-stage extraction at least comprises a first-stage extraction, a second-stage extraction and a third-stage extraction, wherein the mass concentration of the good solvent in the first-stage extraction is 35-58%, the mass concentration of the good solvent in the second-stage extraction is 20-35%, and the mass concentration of the good solvent in the third-stage extraction is less than or equal to 2.5%.
8. The method of claim 7, wherein the multistage extraction comprises: placing the base film coated with the aramid pulp into a multi-section extraction tank for extraction; wherein,
The multistage extraction tank at least comprises a first extraction tank, a second extraction tank and a third extraction tank which are sequentially arranged, and in the multistage extraction, a base film coated with aramid pulp is sequentially extracted through the first extraction tank, the second extraction tank and the third extraction tank;
wherein, along the moving direction of the base film in the first extraction tank, the mass concentration of the good solvent in the first extraction tank is gradually reduced, and the difference between the highest concentration value and the lowest concentration value of the good solvent in the first extraction tank is 5-15wt%.
9. The method according to claim 7 or 8, wherein the extraction time of the first extraction and the extraction time of the second extraction are each 5 to 15s.
10. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and the separator according to any one of claims 1 to 6 disposed between the positive electrode sheet and the negative electrode sheet.
11. A powered device comprising the secondary battery of claim 10.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210734208.0A CN117352963A (en) | 2022-06-27 | 2022-06-27 | Separator, preparation method thereof, secondary battery and electric equipment |
| PCT/CN2023/100283 WO2024001794A1 (en) | 2022-06-27 | 2023-06-14 | Separator and preparation method therefor, secondary battery, and electric device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210734208.0A CN117352963A (en) | 2022-06-27 | 2022-06-27 | Separator, preparation method thereof, secondary battery and electric equipment |
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| CN117352963A true CN117352963A (en) | 2024-01-05 |
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| CN202210734208.0A Pending CN117352963A (en) | 2022-06-27 | 2022-06-27 | Separator, preparation method thereof, secondary battery and electric equipment |
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| WO (1) | WO2024001794A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004031084A (en) * | 2002-06-25 | 2004-01-29 | Oji Paper Co Ltd | Separator for lithium ion secondary battery and battery using it |
| CN112635918A (en) * | 2020-12-26 | 2021-04-09 | 宁德卓高新材料科技有限公司 | Diaphragm, preparation method thereof and battery |
| CN113054324A (en) * | 2021-04-21 | 2021-06-29 | 上海恩捷新材料科技有限公司 | High-safety diaphragm and battery |
| CN114024095B (en) * | 2021-10-27 | 2022-08-05 | 长园泽晖新能源材料研究院(珠海)有限公司 | Coating diaphragm with special pore structure and preparation method thereof |
| CN114243093B (en) * | 2022-02-25 | 2022-05-13 | 湖南中锂新材料科技有限公司 | High-breakdown-strength aramid fiber diaphragm and preparation method and application thereof |
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2022
- 2022-06-27 CN CN202210734208.0A patent/CN117352963A/en active Pending
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