CN110931706A - Lithium ion battery pole piece and preparation method and application thereof - Google Patents
Lithium ion battery pole piece and preparation method and application thereof Download PDFInfo
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- CN110931706A CN110931706A CN201911227454.1A CN201911227454A CN110931706A CN 110931706 A CN110931706 A CN 110931706A CN 201911227454 A CN201911227454 A CN 201911227454A CN 110931706 A CN110931706 A CN 110931706A
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- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 49
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 47
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- 239000002904 solvent Substances 0.000 claims abstract description 59
- 239000011248 coating agent Substances 0.000 claims abstract description 40
- 238000000576 coating method Methods 0.000 claims abstract description 40
- 238000001035 drying Methods 0.000 claims abstract description 29
- 239000013543 active substance Substances 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims abstract description 22
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 57
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 35
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 24
- 239000011148 porous material Substances 0.000 claims description 20
- PUPZLCDOIYMWBV-UHFFFAOYSA-N (+/-)-1,3-Butanediol Chemical compound CC(O)CCO PUPZLCDOIYMWBV-UHFFFAOYSA-N 0.000 claims description 14
- 238000005096 rolling process Methods 0.000 claims description 13
- 238000002156 mixing Methods 0.000 claims description 10
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 8
- 239000000203 mixture Substances 0.000 claims description 8
- 235000019437 butane-1,3-diol Nutrition 0.000 claims description 7
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 5
- 238000007792 addition Methods 0.000 claims description 5
- 239000011230 binding agent Substances 0.000 claims description 4
- 125000004432 carbon atom Chemical group C* 0.000 claims description 4
- 239000006258 conductive agent Substances 0.000 claims description 4
- 239000011267 electrode slurry Substances 0.000 claims description 4
- 238000004528 spin coating Methods 0.000 claims description 2
- 238000005507 spraying Methods 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 2
- 229920000642 polymer Polymers 0.000 claims 1
- 238000009792 diffusion process Methods 0.000 abstract description 10
- 150000002500 ions Chemical class 0.000 abstract description 10
- 230000010287 polarization Effects 0.000 abstract description 8
- 238000011068 loading method Methods 0.000 abstract description 4
- 238000012546 transfer Methods 0.000 description 15
- 238000009826 distribution Methods 0.000 description 12
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 11
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- 229910052744 lithium Inorganic materials 0.000 description 9
- 239000002131 composite material Substances 0.000 description 8
- DCAYPVUWAIABOU-UHFFFAOYSA-N hexadecane Chemical compound CCCCCCCCCCCCCCCC DCAYPVUWAIABOU-UHFFFAOYSA-N 0.000 description 8
- 230000005540 biological transmission Effects 0.000 description 7
- 239000006230 acetylene black Substances 0.000 description 6
- 238000005056 compaction Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 5
- 239000001768 carboxy methyl cellulose Substances 0.000 description 5
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 5
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 5
- 239000010439 graphite Substances 0.000 description 5
- 229910002804 graphite Inorganic materials 0.000 description 5
- 239000010410 layer Substances 0.000 description 5
- 239000007791 liquid phase Substances 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 5
- 229920003048 styrene butadiene rubber Polymers 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 238000002791 soaking Methods 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 239000008367 deionised water Substances 0.000 description 2
- 229910021641 deionized water Inorganic materials 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 238000004804 winding Methods 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000034964 establishment of cell polarity Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 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
- 230000003446 memory effect Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000009718 spray deposition Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N titanium dioxide Inorganic materials O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 1
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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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
-
- 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
- H01M4/04—Processes of manufacture in general
- H01M4/043—Processes of manufacture in general involving compressing or compaction
-
- 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
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
-
- 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
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Composite Materials (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention relates to a lithium ion battery pole piece and a preparation method and application thereof, wherein the method comprises the following steps: (1) coating a solvent on the surface of the rolled pole piece to obtain a pretreated pole piece; (2) and (2) drying the pretreated pole piece obtained in the step (1) to obtain the lithium ion battery pole piece. The aperture of the pole piece is gradually enlarged from the current collector to the surface of the pole piece and is distributed in a horn-shaped gradient manner; the invention also provides a method for improving the porosity of the electrode, which is realized by coating the solvent on the surface of the rolled pole piece. The pole piece provided by the invention ensures high loading capacity, has the porosity of more than 32%, ensures the diffusion of ions and the full utilization of active substances, solves the problem of potential imbalance caused by the overcharge phenomenon on the surface of the pole piece in a full charge state, and simultaneously solves the problem that the active substances in the pole piece do not fully play a role due to the phenomenon of 'overstrain' caused by large surface polarization.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery pole piece and a preparation method and application thereof.
Background
The lithium ion battery is an environment-friendly battery with high energy density and power density, long cycle life, small self-discharge and no memory effect, and is widely applied to the fields of portable electronic equipment such as smart phones, notebooks and tablet computers, electric vehicles, energy storage and the like. With the development of social economy, higher requirements are put on the specific energy, the service life and the safety of the lithium ion battery.
At present, increasing the energy density of lithium ion batteries is one of the important directions in the development of lithium ion batteries, and the most direct means is to adopt electrodes with larger coating thickness and higher compaction density, so that the quantity of active substances in a unit area is increased, and the proportion of inactive substances is reduced. However, when the thick electrode technology pole piece works, ion diffusion is limited, so that an overcharge phenomenon can occur in advance on an interface on the surface of the pole piece in a full charge state, and at the moment, an active substance in the pole piece does not reach a completely embedded state, and the potential is unbalanced, so that a phenomenon of surface lithium precipitation can be caused; when the charging is carried out, the higher the positive electrode potential is, the lower the negative electrode is, but the current on the surface of the negative electrode is the largest, the larger the polarization is, the largest liquid phase polarization is, so that the 'overstrain' phenomenon appears on the surface of the negative electrode plate, and the internal substances do not fully play a role. In order to ensure the ion diffusion rate and the full utilization of active materials while ensuring high loading, it is more important to design and optimize the microstructure of the electrode.
At present, a Japanese equipment company reforms equipment to enable a winding pole piece to pass through a winding roller with a burr-shaped surface, changes the structural state of the surface of a negative coating layer in a mechanical friction mode, and then plays a role in opening the surface of the pole piece and achieving the effect of improving the surface pore distribution of the negative pole piece due to rolling. In actual use, the pole piece is easy to be subjected to powder removal and material falling through the traditional mechanical friction mode, and the performance of the pole piece in actual use is influenced. In addition, the cost incurred by changing the number of rollers of different meshes is also increased.
Huang et al, which uses supersonic suspension atomization and automatic spray deposition processes to prepare a double-layer coating, first prepare a layer of porous titanium-based material coating with a thickness of about 6.1 μm on a current collector, the particle size of the material is about 200nm, the pore size is 40nm, and then deposit a layer of non-porous titanium-based material on the coating. Porous TiO2The internal pores are beneficial to the diffusion of lithium ions, thereby improving the rate characteristic. (Atwo layer electrode structure for improved Li Ion dispersion and volumetric efficiency in Li Ion batteries. Huang C, Young N P, Zhang J, et al. Nano Energy, Vol31, pp:377-385,2016.) the article uses a two-layer electrode structure to ensure both high volumetric Energy density and high power density characteristics, but reduces the electrode packing density.
In view of the problems existing in the prior art, how to not destroy the surface structure of the electrode on the premise of not changing the coating thickness and the compaction density of the electrode, the porosity of the surface of the electrode is improved, the transmission of a liquid phase is facilitated, the potential balance of the lower surface and the inner part of a pole piece in a working state is promoted, the lithium precipitation on the surface of the electrode is avoided, the polarization phenomenon on the surface of the electrode is reduced, the 'overstrain' phenomenon on the surface is improved, and the problem to be solved urgently is solved.
Disclosure of Invention
In view of the problems in the prior art, the invention provides a lithium ion battery pole piece and a preparation method and application thereof. According to the method, the rolled pole piece surface is coated with a water-based solvent, and the solvent is volatilized during drying, so that the pole piece surface is loosened, the effect of expanding surface pores is achieved, the porosity of the pole piece surface is increased, the liquid phase transmission is facilitated, the problem that the potential on the surface and the potential in the electrode are unbalanced due to the overcharge phenomenon on the interface of the electrode surface, and lithium is separated out is solved, the polarization phenomenon of the electrode surface layer is reduced, and the surface overwork phenomenon is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a lithium ion battery pole piece, comprising the following steps:
(1) coating a solvent on the surface of the rolled pole piece to obtain a pretreated pole piece;
(2) and (2) drying the pretreated pole piece obtained in the step (1) to obtain the lithium ion battery pole piece.
According to the invention, the rolled surface of the pole piece is coated with a solvent which is volatile, the solvent penetrates through the surface of the pole piece to the inside through infiltration, and then drying is combined to volatilize the solvent from the electrode, so that the surface of the electrode becomes loose and the pore state of the surface of the pole piece is improved, the effect of improving the pore distribution of the pole piece is achieved, more mass transfer channels are provided, pole pieces with different porosity can be obtained by adjusting the using amount of the solvent, and the problems that the surface of the pole piece is pressed too tightly by adopting a process with larger coating thickness and compaction density, liquid phase transmission is not facilitated, active substances are not fully utilized when the pole piece works, and lithium precipitation or 'overstrain' occurs on the surface of the electrode are solved.
Preferably, the pole pieces rolled in step (1) are positive pole pieces and/or negative pole pieces.
Preferably, the solvent coated on the surface of the positive plate comprises N-methyl pyrrolidone.
Preferably, the solvent coated on the surface of the negative electrode sheet comprises water and/or alcohol with 1-4 carbon atoms, preferably any one or a combination of at least two of water, ethanol, isopropanol, 1, 3-butanediol or ethylene glycol, wherein the combination is typically but not limited to: water and ethanol, water and ethylene glycol, water and 1, 3-butanediol, ethanol and ethylene glycol, and the like.
In the invention, the type of water is not particularly limited, and the water can be pure water, deionized water or distilled water, and the water can be any type commonly used by a person skilled in the art, can achieve the effect of expanding the surface porosity of the pole piece, and can increase the surface porosity of the pole piece, so that the invention is suitable for the pole piece.
Preferably, the volume ratio of alcohol to water is 1-9%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or 9%, etc., preferably 3-7%.
Preferably, the solvent is added in the step (1) in an amount of 90-150mg/m2For example, it may be 90mg/m2、95mg/m2、100mg/m2、105mg/m2、110mg/m2、115mg/m2、120mg/m2、125mg/m2、130mg/m2、135mg/m2、140mg/m2、145mg/m2Or 150mg/m2Etc., preferably 100-135mg/m2If the addition amount is less than 90mg/m2The surface of the pole piece cannot be completely coated, so that pores on the surface of the pole piece are not uniformly distributed; the addition amount is more than 150mg/m2Excessive damage to the pole pieces can occur.
Preferably, the solvent coating in step (1) comprises any one or a combination of at least two of coating, spray coating or spin coating, preferably coating.
Preferably, the width of the pole piece surface coating is the same as the width of the baffle of the coating machine.
Preferably, the temperature of the drying in the step (2) is 45-70 ℃, for example, 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃ or 70 ℃ and the like, preferably 60-65 ℃. If the temperature is lower than 45 ℃, the aim of drying the pole piece cannot be fulfilled, and the solvent cannot be sufficiently dried, so that the residual moisture of the pole piece is too high; the temperature is higher than 70 ℃, so that the pole piece is excessively dried, and the phenomena of pole piece cracking, pole piece edge bulging and the like are caused.
Preferably, the drying apparatus comprises a forced air dryer.
Preferably, the speed of the pretreated pole piece entering and exiting the blast dryer is 1-10m/min, such as 1m/min, 2m/min, 4m/min, 6m/min, 8m/min, 9m/min or 10m/min, and preferably 2-8 m/min. If the speed is less than 1m/min, the time for the pole piece to stay in the blast dryer is too long, so that the pole piece is excessively dried, the pole piece is cracked, the edge of the pole piece is bulged and the like; the speed is more than 10m/min, the solvent can not be fully dried, and the residual moisture of the pole piece is overhigh.
Preferably, the blast dryer is divided into three zones, and the temperature of the first zone, the second zone and the third zone is independently 45-70 ℃, for example, the temperature of the first zone is 45 ℃, the temperature of the second zone may be 45 ℃, 60 ℃, 70 ℃, the temperature of the third zone may be 50 ℃, 65 ℃, 70 ℃ or the like, and the like, which are not affected each other.
Preferably, the thicknesses of the laminated pole piece and the lithium ion battery pole piece are independently 240-250 μm and 265-275 μm, for example, the thickness of the laminated pole piece can be 240 μm, 245 μm, 248 μm or 250 μm, and the thickness of the lithium ion battery pole piece can be 265 μm, 268 μm, 270 μm, 272 μm or 275 μm.
Preferably, the compacted density of the rolled pole piece and the lithium ion battery pole piece is independently 1.3-1.8mg/cm3And 1.1-1.5mg/cm3For example, the compacted density of the rolled pole piece may be 1.3mg/cm3、1.5mg/cm3Or 1.8mg/cm3And the compaction density of the lithium ion battery pole piece can be 1.1mg/cm3、1.3mg/cm3Or 1.5mg/cm3And the like.
Preferably, the rolled pole piece in step (1) is prepared by the following steps:
(a) mixing an electrode active substance, a conductive agent and a binder to prepare electrode slurry;
(b) coating the electrode slurry obtained in the step (a) on a current collector, and drying to obtain a dry pole piece;
(c) and (c) rolling the dried pole piece obtained in the step (b) to obtain a rolled pole piece.
In the invention, the rolled pole piece is not specifically limited, and any pole piece commonly used by those skilled in the art is suitable for the invention.
Preferably, the preparation method comprises the following steps:
(1) mixing an electrode active substance, a conductive agent and a binder, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) coating a solvent on the surface of the rolled pole piece obtained in the step (1) by using a coating machine, and controlling the addition amount of the solvent to be 90-150mg/m2Obtaining a pretreated pole piece;
(3) and (2) enabling the pretreated pole piece obtained in the step (1) to enter and exit a 45-70 ℃ blast dryer at a speed of 1-10m/min, wherein the temperatures of a first area, a second area and a third area of the blast dryer are independently 45-70 ℃, and drying to obtain the lithium ion battery pole piece.
In a second aspect, the present invention provides the lithium ion battery pole piece obtained by the preparation method according to the first aspect, wherein the aperture of the pole piece gradually increases from the current collector to the surface of the pole piece, and the pole piece is distributed in a "horn" shape in a gradient manner.
The pole piece provided by the invention has the advantages that the surface is loose and porous, the pores are large, the pores close to a current collector are small, the pore diameters are distributed in a horn-shaped gradient manner, the requirements of the pole piece surface to be pressed to be too tight and the channel for ion transmission caused by a large compaction density process are balanced, so that when the electrode is thick, the overcharge phenomenon cannot occur in advance in a full-charge state on the interface of the surface, the electrode surface and the internal potential are kept balanced, and the phenomenon of lithium precipitation cannot occur; the polarization phenomenon in the charging and discharging process is reduced, the phenomenon of overstrain on the surface of the pole piece is avoided, and the internal substances of the pole piece are ensured to fully play a role.
In a third aspect, the present invention provides a lithium ion battery, comprising the electrode plate according to the second aspect.
According to the lithium ion battery provided by the invention, the pole pieces with the aperture in the horn-shaped gradient distribution are adopted, so that the high loading capacity is ensured, the ion diffusion and the full utilization of active substances are ensured, the utilization rate of the active substances is improved, the ion diffusion rate and the electronic conductivity are accelerated, and the electrochemical performances of the lithium ion battery, such as specific capacity, rate capability, cycle life and the like, are improved.
In a fourth aspect, the invention provides a method for improving electrode porosity, which comprises the step of coating a solvent on the surface of a rolled pole piece.
According to the method for improving the porosity of the electrode, provided by the invention, the adopted solvent is a volatile solvent, so that the problems that the surface of a pole piece is too compact, the porosity is low and ion diffusion is not facilitated are solved, the surface of the electrode is loose and porous, the pore diameter is in gradient distribution, the ion diffusion is facilitated, and active substances are fully utilized. The method has the advantages of simple and effective raw materials, convenient operation and easy industrial production.
Preferably, the rolled pole piece is a positive pole piece and/or a negative pole piece.
Preferably, the solvent coated on the surface of the positive plate comprises N-methyl pyrrolidone.
Preferably, the solvent coated on the surface of the negative electrode sheet comprises water and/or alcohol with 1-4 carbon atoms, preferably any one or a combination of at least two of water, ethanol, isopropanol, 1, 3-butanediol or ethylene glycol.
Compared with the prior art, the invention has at least the following beneficial effects:
(1) the pole piece provided by the invention has larger surface pores, smaller pores close to a current collector, and the pore diameters are distributed in a horn-shaped gradient manner, the porosity is more than 32%, compared with the pole piece which is not coated with a solvent after rolling, the porosity is improved by more than 2.75%, the high loading capacity is ensured, the diffusion of ions and the full utilization of active substances are ensured, the problem of potential imbalance caused by the phenomenon of overcharge on the surface and the situation that the internal active substances are not completely embedded in the pole piece in a full charge state is solved, and the problem that the internal active substances are not fully exerted due to the phenomenon of overstrain caused by larger surface polarization of the pole piece in the charge and discharge process is also solved;
(2) according to the preparation method of the pole piece, the solvent is coated on the surface of the rolled pole piece, the solvent is a volatile solvent, and then drying is carried out, so that the solvent is removed from the electrode, the surface of the electrode becomes loose, the pore state of the surface of the pole piece is improved, the effect of improving the pore distribution of the pole piece is achieved, more mass transfer channels are provided, and the problem that the transmission of a liquid phase is not facilitated due to the fact that the surface of the pole piece is pressed too tightly by adopting a large coating thickness and compaction density process is solved;
(3) according to the lithium ion battery provided by the invention, the pole pieces with the gradient-distributed pore diameters are adopted, so that the utilization rate of active substances is improved, the ion diffusion rate and the electronic conductivity are accelerated, and the electrochemical properties such as the specific capacity, the rate capability, the cycle life and the like of the lithium ion battery are improved;
(4) according to the method for improving the porosity of the electrode, the problems that the surface of the pole piece is too compact and the porosity is low are solved by adopting the solvent, so that the surface of the electrode is loose and porous, the pore diameter is in horn-shaped gradient distribution, and active substances can fully play a role. The method has the advantages of simple and effective raw materials, convenient operation and easy industrial production.
Drawings
Fig. 1 is an SEM image of the rolled pole piece provided in example 1.
Fig. 2 is an SEM image of the solvent coated pole piece provided in example 1.
Detailed Description
The following further describes the technical means of the present invention to achieve the predetermined technical effects by means of embodiments with reference to the accompanying drawings, and the embodiments of the present invention are described in detail as follows.
Example 1
This embodiment provides a lithium ion battery pole piece, pole piece aperture is from the mass flow body to pole piece surface grow gradually, is "loudspeaker" form gradient distribution, pole piece porosity is 32.66%.
The preparation method of the pole piece comprises the following steps:
(1) mixing a graphite active substance, acetylene black, styrene butadiene rubber and carboxymethyl cellulose according to a mass ratio of 96.3:1:1.5:1.2, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) adding a composite solvent of ethanol and pure water into a trough of a transfer coater, wherein the volume ratio of the ethanol to the pure water is 3%, and the transfer solvent amount of a transfer roller is 100mg/m2；
(3) And (3) feeding the pretreated pole piece obtained in the step (2) into a blast dryer at a speed of 4m/min of a driving belt, wherein the temperature of a first area of the blast dryer is 50 ℃, the temperature of a second area of the blast dryer is 55 ℃, and the temperature of a third area of the blast dryer is 50 ℃, and drying to obtain the lithium ion battery pole piece.
As shown in fig. 1, the SEM image of the rolled pole piece obtained in this example shows that the surface of the pole piece is in a tight state; as shown in fig. 2, the SEM image of the pole piece coated with the composite solvent of ethanol and pure water shows that the surface of the pole piece is in a loose state, which indicates that the composite solvent coated with ethanol and pure water has the effect of expanding surface pores, so that the porosity of the surface of the pole piece is increased.
Example 2
This embodiment provides a lithium ion battery pole piece, pole piece aperture is from the mass flow body to pole piece surface grow gradually, is "loudspeaker" form gradient distribution, pole piece surface porosity is 35.48%.
The preparation method of the pole piece comprises the following steps:
(1) mixing a graphite active substance, acetylene black, styrene butadiene rubber and carboxymethyl cellulose according to a mass ratio of 96.3:1:1.5:1.2, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) deionized water is added into a trough of the transfer coater, and the amount of solvent transferred by a transfer roller is 114.9mg/m2；
(3) And (3) feeding the pretreated pole piece obtained in the step (2) into a blast dryer at a speed of a transmission belt of 2m/min, wherein the temperature of a first area of the blast dryer is 50 ℃, the temperature of a second area of the blast dryer is 55 ℃, and the temperature of a third area of the blast dryer is 50 ℃, and drying to obtain the lithium ion battery pole piece.
Example 3
This embodiment provides a lithium ion battery pole piece, pole piece aperture is from the mass flow body to pole piece surface grow gradually, is "loudspeaker" form gradient distribution, pole piece surface porosity is 36.19%.
The preparation method of the pole piece comprises the following steps:
(1) mixing lithium iron phosphate, acetylene black and PVDF according to the mass ratio of 8:1:1, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) adding N-methyl pyrrolidone into the trough of the transfer coater, wherein the amount of solvent transferred by a transfer roller is 135mg/m2；
(3) And (3) feeding the pretreated pole piece obtained in the step (2) into a blast dryer at a speed of 4m/min of a driving belt, wherein the temperature of a first area of the blast dryer is 50 ℃, the temperature of a second area of the blast dryer is 55 ℃, and the temperature of a third area of the blast dryer is 50 ℃, and drying to obtain the lithium ion battery pole piece.
Example 4
The only difference compared to example 1 was that by replacing the belt speed in step (3) by 6m/min from 4m/min, a pole piece was produced with a porosity close to that of example 1 of 33.48%.
Example 5
Compared with example 1, the difference is only that the temperatures of the different zones of the blast dryer in step (3) are adjusted to: the first zone temperature was 60 deg.c, the second zone temperature was 65 deg.c, and the third zone temperature was 60 deg.c, producing a pole piece porosity close to that of example 1 at 32.99%.
Example 6
Compared with example 1, the difference is only that the volume ratio of ethanol to pure water in step (2) is replaced by 10%, and the porosity of the prepared pole piece is 32.46%.
Example 7
This embodiment provides a lithium ion battery pole piece, pole piece aperture is from the mass flow body to pole piece surface grow gradually, is "loudspeaker" form gradient distribution, pole piece surface porosity is 33.76%.
(1) Mixing a graphite active substance, acetylene black, styrene butadiene rubber and carboxymethyl cellulose according to a mass ratio of 96.3:1:1.5:1.2, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) adding a composite solvent of ethylene glycol and pure water into a trough of a transfer coater, wherein the volume ratio of the ethylene glycol to the pure water is 5%, and the amount of the solvent transferred by a transfer roller is 95mg/m2；
(3) And (3) feeding the pretreated pole piece obtained in the step (2) into a blast dryer at a speed of a transmission belt of 8m/min, wherein the temperature of a first area of the blast dryer is 55 ℃, the temperature of a second area of the blast dryer is 60 ℃, and the temperature of a third area of the blast dryer is 55 ℃, and drying to obtain the lithium ion battery pole piece.
Example 8
This embodiment provides a lithium ion battery pole piece, pole piece aperture is from the mass flow body to pole piece surface grow gradually, is "loudspeaker" form gradient distribution, pole piece surface porosity is 33.88%.
(1) Mixing a graphite active substance, acetylene black, styrene butadiene rubber and carboxymethyl cellulose according to a mass ratio of 96.3:1:1.5:1.2, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) adding a composite solvent of 1, 3-butanediol and pure water into a trough of a transfer coating machine, wherein the volume ratio of the 1, 3-butanediol to the pure water is 7%, and the amount of the solvent transferred by a transfer roller is 145mg/m2；
(3) And (3) feeding the pretreated pole piece obtained in the step (2) into a blast dryer at a speed of a driving belt of 1m/min, wherein the temperature of a first area of the blast dryer is 65 ℃, the temperature of a second area of the blast dryer is 70 ℃, and the temperature of a third area of the blast dryer is 65 ℃, and drying to obtain the lithium ion battery pole piece.
Comparative example 1
Compared with example 1, the difference is only that the comparative example provides a lithium ion battery pole piece, and no solvent is coated on the surface of the pole piece after rolling.
The preparation method of the pole piece comprises the following steps:
(1) mixing a graphite active substance, acetylene black, styrene butadiene rubber and carboxymethyl cellulose according to a mass ratio of 96.3:1:1.5:1.2, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) adding a composite solvent of ethanol and pure water into a trough of a transfer coating machine, and transferring the solvent by a transfer roller with the amount of 0mg/m2；
(3) And (3) feeding the pretreated pole piece obtained in the step (2) into a blast dryer at a speed of 4m/min of a driving belt, wherein the temperature of a first area of the blast dryer is 50 ℃, the temperature of a second area of the blast dryer is 55 ℃, the temperature of a third area of the blast dryer is 50 ℃, and drying is carried out to obtain the lithium ion battery pole piece, wherein the porosity of the pole piece prepared by the method is 31.59%.
Evaluating the performance of the pole piece:
the porosity of the electrode sheets prepared in examples 1-8 and comparative example 1 was tested, and the system and method for testing the porosity of the electrode sheets were performedThe method comprises the following steps: the test method cited in CN103134744A said method comprising the steps of: cutting a proper amount of pole piece, and measuring the mass M of the pole piece0(ii) a Measuring the volume V of the pole piece; placing the pole piece into a container, wherein hexadecane is arranged in the container, and completely soaking the pole piece by the hexadecane for a certain time; taking out the pole piece, placing on filter paper, sucking and wiping to constant weight, and measuring the mass M of the pole piece1(ii) a According to the formula: ε ═ M1-M0) Calculating the porosity epsilon of the pole piece according to the rho/Vx 100 percent; wherein the cutting pole piece is a cuboid pole piece; the volume V of the pole piece is equal to length, width and thickness; the thickness is equal to the thickness of the thick foil of the pole piece; the hexadecane is analytically pure; rho is the density of the hexadecane at normal temperature; the soaking time is 1 hour, and the container is covered by a cover during soaking.
The test results are shown in table 1.
TABLE 1
The following points can be seen from table 1:
(1) as can be seen from the examples 1 to 8, in the examples 1 to 8, the solvent is coated on the surface of the rolled pole piece, so that the porosity of the pole piece is more than 32%; compared with different embodiments, the porosity of the pole piece is increased from 31.59% to 36.19% before and after the pole piece is processed, the increase rate is 14.56%, the effect of increasing the porosity is achieved, the surface porosity of the pole piece is increased, the capacity of accommodating more lithium ions in a short time can be met, the 'overstrain' of the pole piece is reduced, the polarization of the lithium battery is reduced, and the problem that potential imbalance caused by the overcharge phenomenon on the surface of the pole piece in a full charge state causes local lithium precipitation is solved;
(2) it can be seen from the combination of examples 1 and 6 that, the volume ratio of ethanol to pure water in example 1 is 3%, the porosity of the obtained pole piece is 32.66%, and the volume ratio of ethanol to pure water in example 6 is 10%, and the porosity of the obtained pole piece is 32.46%, which indicates that the volume ratio of ethanol to pure water in example 1 is more favorable for increasing the porosity of the pole piece;
(3) as can be seen from example 1 and comparative example 1, in example 1, the porosity of the pole piece obtained by coating the surface of the rolled pole piece with the composite solvent of ethanol and pure water is 32.66%, and compared with the pole piece not coated with the solvent in comparative example 1, the porosity of the pole piece in comparative example 1 is 31.59%, which shows that in example 1, the porosity of the pole piece is increased by coating the surface of the pole piece with the composite solvent of ethanol and pure water.
In conclusion, the lithium ion battery pole piece provided by the invention has the advantages that the solvent is coated on the surface of the rolled pole piece, the solvent is a volatile solvent, the porosity of the pole piece is increased from 31.59% to 36.19%, the increase rate is 14.56%, and the effect of increasing the porosity is achieved. The pole piece surface porosity grow, make pole piece surface aperture is great, and the aperture that is close to the mass flow body is less, is "loudspeaker" form gradient distribution, can satisfy the ability of accepting more lithium ions in the short time, reduces pole piece "strain", reduces lithium cell polarization, solves the pole piece under full charge state, and the potential unbalance that the phenomenon of overcharging and lead to appears in the surface causes the emergence of local lithium of separating out.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. A preparation method of a lithium ion battery pole piece is characterized by comprising the following steps:
(1) coating a solvent on the surface of the rolled pole piece to obtain a pretreated pole piece;
(2) and (2) drying the pretreated pole piece obtained in the step (1) to obtain the lithium ion battery pole piece.
2. The preparation method according to claim 1, wherein the rolled pole piece in step (1) is a positive pole piece and/or a negative pole piece;
preferably, the solvent coated on the surface of the positive plate comprises N-methyl pyrrolidone;
preferably, the solvent coated on the surface of the negative electrode sheet comprises water and/or alcohol with 1-4 carbon atoms, preferably any one or a combination of at least two of water, ethanol, isopropanol, 1, 3-butanediol or ethylene glycol;
preferably, the volume ratio of alcohol to water is 1-9%, preferably 3-7%.
3. The production method according to claim 1 or 2, wherein the solvent is added in the amount of 90 to 150mg/m in the step (1)2Preferably 100-135mg/m2。
4. The production method according to any one of claims 1 to 3, wherein the solvent coating in step (1) comprises any one of coating, spray coating or spin coating or a combination of at least two thereof, preferably coating;
preferably, the width of the pole piece surface coating is the same as the width of the baffle of the coating machine.
5. The method according to any one of claims 1 to 4, wherein the temperature of the drying in the step (2) is 45 to 70 ℃, preferably 60 to 65 ℃;
preferably, the apparatus for drying comprises a forced air dryer;
preferably, the speed of the pretreated pole pieces entering and exiting the blast dryer in the step (2) is 1-10m/min, preferably 2-8 m/min;
preferably, the blast dryer is divided into three zones, the temperature of the first zone, the second zone and the third zone being independently 45-70 ℃;
preferably, the thicknesses of the rolled pole piece and the lithium ion battery pole piece are respectively 240-250 μm and 265-275 μm;
preferably, the compacted density of the rolled pole piece and the lithium ion battery pole piece is independently 1.3-1.8mg/cm3And 1.1-1.5mg/cm3。
6. The preparation method according to any one of claims 1 to 5, wherein the rolled pole piece in the step (1) is prepared by the following steps:
(a) mixing an electrode active substance, a conductive agent and a binder to prepare electrode slurry;
(b) coating the electrode slurry obtained in the step (a) on a current collector, and drying to obtain a dry pole piece;
(c) and (c) rolling the dried pole piece obtained in the step (b) to obtain a rolled pole piece.
7. The method for preparing a polymer according to any one of claims 1 to 6, comprising the steps of:
(1) mixing an electrode active substance, a conductive agent and a binder, coating the mixture on a current collector, drying, and then rolling to obtain a rolled pole piece;
(2) coating a solvent on the surface of the rolled pole piece obtained in the step (1) by using a coating machine, and controlling the addition amount of the solvent to be 90-150mg/m2Obtaining a pretreated pole piece;
(3) and (2) enabling the pretreated pole piece obtained in the step (1) to enter and exit a 45-70 ℃ blast dryer at a speed of 1-10m/min, wherein the temperatures of a first area, a second area and a third area of the blast dryer are independently 45-70 ℃, and drying to obtain the lithium ion battery pole piece.
8. The lithium ion battery pole piece obtained by the preparation method according to any one of claims 1 to 7, wherein the pore diameter of the pole piece gradually increases from the current collector to the surface of the pole piece and is distributed in a horn-shaped gradient manner.
9. A lithium ion battery comprising the pole piece of claim 8.
10. A method for improving electrode porosity is characterized in that a solvent is coated on the surface of a rolled pole piece;
preferably, the rolled pole piece is a positive pole piece and/or a negative pole piece;
preferably, the solvent coated on the surface of the positive plate comprises N-methyl pyrrolidone;
preferably, the solvent coated on the surface of the negative electrode sheet comprises water and/or alcohol with 1-4 carbon atoms, preferably any one or a combination of at least two of water, ethanol, isopropanol, 1, 3-butanediol or ethylene glycol.
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