CN114050372A - Diaphragm for lithium ion battery and preparation method and application thereof - Google Patents
Diaphragm for lithium ion battery and preparation method and application thereof Download PDFInfo
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- CN114050372A CN114050372A CN202111245456.0A CN202111245456A CN114050372A CN 114050372 A CN114050372 A CN 114050372A CN 202111245456 A CN202111245456 A CN 202111245456A CN 114050372 A CN114050372 A CN 114050372A
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 39
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 39
- 238000002360 preparation method Methods 0.000 title claims description 9
- 229920002678 cellulose Polymers 0.000 claims abstract description 63
- 239000001913 cellulose Substances 0.000 claims abstract description 63
- 239000004005 microsphere Substances 0.000 claims abstract description 41
- 229920000642 polymer Polymers 0.000 claims abstract description 40
- 238000004108 freeze drying Methods 0.000 claims abstract description 17
- 229920001046 Nanocellulose Polymers 0.000 claims abstract description 13
- 238000002844 melting Methods 0.000 claims abstract description 10
- 230000008018 melting Effects 0.000 claims abstract description 9
- 239000012528 membrane Substances 0.000 claims abstract description 9
- 238000005516 engineering process Methods 0.000 claims abstract description 7
- 239000002245 particle Substances 0.000 claims abstract description 7
- 239000000243 solution Substances 0.000 claims description 28
- -1 lignocellulose Polymers 0.000 claims description 25
- 239000004698 Polyethylene Substances 0.000 claims description 22
- 229920000573 polyethylene Polymers 0.000 claims description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 18
- 239000002904 solvent Substances 0.000 claims description 15
- 239000003792 electrolyte Substances 0.000 claims description 13
- 238000000498 ball milling Methods 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 12
- 239000011259 mixed solution Substances 0.000 claims description 10
- 238000001035 drying Methods 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 6
- 239000002121 nanofiber Substances 0.000 claims description 6
- 238000005096 rolling process Methods 0.000 claims description 5
- 238000003756 stirring Methods 0.000 claims description 5
- 238000004519 manufacturing process Methods 0.000 claims description 4
- 229920002749 Bacterial cellulose Polymers 0.000 claims description 3
- 229920000742 Cotton Polymers 0.000 claims description 3
- 239000004760 aramid Substances 0.000 claims description 3
- 239000005016 bacterial cellulose Substances 0.000 claims description 3
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 claims description 3
- 238000007710 freezing Methods 0.000 claims description 3
- 230000008014 freezing Effects 0.000 claims description 3
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 3
- 229920003235 aromatic polyamide Polymers 0.000 claims 1
- 239000011521 glass Substances 0.000 claims 1
- 239000007788 liquid Substances 0.000 abstract description 19
- 238000010521 absorption reaction Methods 0.000 abstract description 10
- 230000008901 benefit Effects 0.000 abstract description 8
- 239000007787 solid Substances 0.000 description 25
- 239000000839 emulsion Substances 0.000 description 13
- 239000004200 microcrystalline wax Substances 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 12
- 239000000463 material Substances 0.000 description 10
- 239000001993 wax Substances 0.000 description 9
- 239000002023 wood Substances 0.000 description 9
- 229920002125 Sokalan® Polymers 0.000 description 7
- 239000003292 glue Substances 0.000 description 7
- 239000004584 polyacrylic acid Substances 0.000 description 7
- 229920000098 polyolefin Polymers 0.000 description 7
- 239000000080 wetting agent Substances 0.000 description 7
- 239000000835 fiber Substances 0.000 description 6
- 229920001131 Pulp (paper) Polymers 0.000 description 5
- 239000008367 deionised water Substances 0.000 description 5
- 229910021641 deionized water Inorganic materials 0.000 description 5
- 239000002002 slurry Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 239000004964 aerogel Substances 0.000 description 4
- 230000014759 maintenance of location Effects 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 230000008595 infiltration Effects 0.000 description 3
- 238000001764 infiltration Methods 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 2
- 229920006231 aramid fiber Polymers 0.000 description 2
- 239000002585 base Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000003365 glass fiber Substances 0.000 description 2
- 229920001903 high density polyethylene Polymers 0.000 description 2
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- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
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- 230000009286 beneficial effect Effects 0.000 description 1
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- 238000004140 cleaning Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
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- 239000006255 coating slurry Substances 0.000 description 1
- 229920000891 common polymer Polymers 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 230000006353 environmental stress Effects 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 239000001257 hydrogen Chemical group 0.000 description 1
- 229910052739 hydrogen Chemical group 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229920001684 low density polyethylene Polymers 0.000 description 1
- 239000004702 low-density polyethylene Substances 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229920005615 natural polymer Polymers 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
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Images
Classifications
-
- 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
- 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
- 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
- H01M50/44—Fibrous material
-
- 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
- H01M50/443—Particulate material
-
- 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)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Cell Separators (AREA)
Abstract
The invention provides a diaphragm for a lithium ion battery, which comprises nano cellulose and polymer microspheres in a mass ratio of 6: 4-8.5: 1.5, wherein the particle size of the polymer microspheres is 0.1-3 mu m, and the melting point of the polymer microspheres is 100-125 ℃; the membrane for the lithium ion battery is prepared from the nano-cellulose and the polymer microspheres by a freeze-drying technology. Compared with the existing diaphragm, the diaphragm provided by the invention has the advantages of high wettability, high liquid absorption rate and high thermal stability, has a self-closing hole function, and can effectively improve the electrochemical performance and safety performance of a battery.
Description
Technical Field
The invention relates to the field of lithium batteries, in particular to a diaphragm for a lithium ion battery and a preparation method and application thereof.
Background
At present, the polyolefin diaphragm has the advantages of strong electrochemical stability, high mechanical strength and the like, and is widely applied to commercial lithium ion battery products. But because the polarity of the polyolefin material is low, the polyolefin material has poor wettability to electrolyte, low liquid retention capacity and poor interface performance; and the polyolefin material has low self-melting point, so that the thermal stability of the diaphragm is poor.
At present, the electrolyte wettability and the thermal stability of the polyolefin diaphragm can be effectively improved by means of ceramic coating and the like on the diaphragm. However, the preparation process of the diaphragm is more complicated by the methods, the diaphragm breaking temperature of the modified diaphragm is still low, and the diaphragm still has the risk of breaking the diaphragm when the temperature reaches 130 ℃, so that the anode and the cathode are in contact with each other to form an internal short circuit, the battery is caused to fire or explode, and the safety risk exists.
In view of the above, it is necessary to provide a technical solution to the above problems.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the diaphragm for the lithium ion battery has the advantages of high wettability, high liquid absorption rate and high thermal stability, has a self-closing hole function, and can effectively improve the electrochemical performance and the safety performance of the battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
a diaphragm for a lithium ion battery comprises nanocellulose and polymer microspheres in a mass ratio of 6: 4-8.5: 1.5, wherein the particle size of the polymer microspheres is 0.1-3 mu m, and the melting point of the polymer microspheres is 100-125 ℃; the membrane for the lithium ion battery is prepared from the nano-cellulose and the polymer microspheres by a freeze-drying technology.
Preferably, the raw material of the nano-cellulose is at least one of cotton cellulose, lignocellulose, cellulose nano-fibrils, bacterial cellulose, nano-aramid fibers, nano-glass fibers and nano-polyacrylonitrile fibers.
Preferably, the polymer microsphere is polyethylene wax.
Another object of the present invention is to provide a method for preparing the separator for a lithium ion battery, including the steps of:
s1, mixing cellulose with solvent water, and performing ball milling to obtain a nano cellulose solution;
s2, mixing and stirring the polymer microspheres and the nano-cellulose solution to obtain a mixed solution, wherein the mass ratio of the nano-cellulose to the polymer microspheres is 6: 4-8.5: 1.5;
and S3, carrying out freeze drying and rolling on the mixed solution to obtain the lithium ion battery diaphragm.
Preferably, in step S1, the mixing ratio of the nanocellulose and the solvent water is 1: (40-60); the ball milling time is 1-6 h.
Preferably, in step S3, the porosity of the separator obtained by the freeze-drying technique is 65 to 85%.
Preferably, in step S3, the freezing temperature is less than or equal to 0 ℃, and the drying is carried out in a vacuum environment.
The thickness of the obtained separator is preferably 4 to 15 μm.
The invention also provides a lithium ion battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm is arranged between the positive plate and the negative plate, and the diaphragm is the diaphragm for the lithium ion battery.
Preferably, the solvent of the electrolyte is an ester solvent.
Compared with the prior art, the invention has the beneficial effects that:
1) the diaphragm provided by the invention takes the nano-cellulose as the main body of the base material, is environment-friendly, can save the cost, has extremely high thermal stability, still has the performances of no thermal shrinkage and no rupture of the diaphragm at about 300 ℃, and can greatly improve the thermal safety performance of the battery; meanwhile, the arrangement of the polymer microspheres is increased, the polymer microspheres are added, so that the integral diaphragm has a self-hole-closing function, the reaction of the battery can be effectively stopped when the thermal runaway occurs, and the safety of the battery can be further improved.
2) In addition, the diaphragm provided by the invention is prepared by adopting a freeze drying technology, the diaphragm has larger porosity by adopting the method, and the wettability, the liquid absorption rate and the liquid retention rate of the diaphragm can be improved because the nanocellulose has rich hydroxyl functional groups, so that the interface performance of the diaphragm can be effectively improved, and the electrochemical performance of the battery can be improved.
Drawings
Fig. 1 is a molecular structure diagram of a nanofiber membrane of the present invention.
FIG. 2 is an electron microscope image of the nanofiber membrane of the present invention.
Figure 3 is a schematic representation of the closing mechanism of the membrane of the present invention.
Fig. 4 is a graph comparing thermal stability before and after baking at 200 c of the separators of example 1 and comparative example 1.
Figure 5 is a graph comparing the wettability of the membranes of example 1 and comparative example 1.
Fig. 6 is a graph comparing the cycle capacity at 1C rate performance for the cells of example 1 and comparative example 1.
Detailed Description
1. Diaphragm for lithium ion battery and preparation method thereof
The first aspect of the invention provides a diaphragm for a lithium ion battery, which comprises nano-cellulose and polymer microspheres in a mass ratio of 6: 4-8.5: 1.5, wherein the particle size of the polymer microspheres is 0.1-3 mu m, and the melting point of the polymer microspheres is 100-125 ℃; the membrane for the lithium ion battery is prepared from the nano-cellulose and the polymer microspheres by a freeze-drying technology.
The invention adopts the nano-cellulose as the main material of the diaphragm, and the nano-cellulose is used as a natural polymer material, has wide source and convenient processing, thereby having great cost advantage for the nano-cellulose as the diaphragm base material. As shown in fig. 1, cellulose chain molecules have a large number of hydroxyl functional groups, and hydrogen bonds formed between the functional groups have strong intermolecular forces, so that the rigidity of the material is increased. Therefore, the cellulose material has a high thermal stability (about 300 ℃).
In addition, the nano-cellulose is used as the main material of the diaphragm, the diaphragm has higher porosity and thinner thickness, the porosity can reach more than 70%, and the porosity of the common polymer diaphragm is only 40%.
The polymer microspheres adopted by the invention are selected to have the particle size of 0.1-3 mu m and the melting point of 100-125 ℃, and can be converted into a molten state after reaching the melting point when the battery generates abnormal heat, so that the purpose of closing pores of the diaphragm to stop the further reaction of the battery is achieved, the thermal stability of the cellulose-based diaphragm is further improved, and the safety performance of the battery is improved, and the schematic diagram can be shown in fig. 3.
In addition, the invention adopts the freeze-drying technology to obtain the separator with high porosity similar to that of aerogel. Aerogel is a nano-scale porous solid material formed by replacing liquid phase in gel with gas in a certain drying way. It can be understood that after the solute is dissolved in the solvent, the solvent is completely replaced by gas in the original volume of the solution by a specific drying mode (such as freeze drying), and the nanoscale solid multi-control material with extremely high porosity is formed.
The water solution obtained by mixing the nano-cellulose and the polymer microspheres is frozen, the water solvent is frozen into ice, then the ice is dried and sublimated in a vacuum environment, the ice is directly sublimated into gas, after the drying is finished, the moisture in the ice block is completely replaced by air, and the remaining solute forms a diaphragm with high porosity similar to aerogel. Compared with a drying method at normal temperature, the freeze drying method can obtain the cellulose-based diaphragm with high porosity and high liquid retention.
Preferably, the raw material of the nano-cellulose is at least one of cotton cellulose, lignocellulose, cellulose nano-fibrils, bacterial cellulose, nano-aramid fibers, nano-glass fibers and nano-polyacrylonitrile fibers. As shown in figure 2, the cellulose provided by the invention contains a large number of linear structures which can be obviously seen from an electron microscope image, and the cellulose can form nano-fibers after ball milling, so that the requirement for preparing the diaphragm is met.
Preferably, the polymer microsphere is polyethylene wax. More preferably, the polyethylene wax is a high density polyethylene wax. High density polyethylene has the following advantages: 1) the paint has good heat resistance, cold resistance, wear resistance, electrical insulation and good chemical stability, is insoluble in any organic solvent at room temperature, and resists corrosion of acid, alkali and various salts; 2) the rigidity and toughness are high, and the mechanical strength is good; 3) the environmental stress cracking resistance is also good, and the dielectric property is good; 4) the hardness, tensile strength and creep properties are superior to low density polyethylene. Polyethylene wax is used as the polymer microsphere, the particle size of the polyethylene wax is about 1 mu m, the melting point of the polyethylene wax is 110 ℃, the polyethylene wax can be well mixed with the aqueous solution of cellulose, the slurry is uniformly mixed, the effect of melting and closing pores of the polyethylene wax can be more uniformly exerted in the abnormal heat production process of the battery, and the safety of the battery is further improved.
The second aspect of the present invention provides a method for preparing the separator, comprising the steps of:
s1, mixing cellulose with solvent water, and performing ball milling to obtain a nano cellulose solution;
s2, mixing and stirring the polymer microspheres and the nano-cellulose solution to obtain a mixed solution, wherein the mass ratio of the nano-cellulose to the polymer microspheres is 6: 4-8.5: 1.5;
and S3, carrying out freeze drying and rolling on the mixed solution to obtain the lithium ion battery diaphragm.
Due to the viscosity problem of the nano-cellulose solution, the total solid content of the slurry designed by the preparation method is 5-15%, so that the problems of overhigh viscosity, poor leveling property of the coating slurry and uneven film surface caused by overhigh solid content can be avoided on one hand, and the requirement of coating thickness can be hardly met due to overhigh solid content on the other hand.
Specifically, the mass ratio of the nanocellulose to the polymer microspheres can be 6:4, 6.5:3.5, 7:3, 7.5: 2.5, 8:2 or 8.5: 1.5; the above-mentioned mass ratio is a mass ratio of both solid contents. Through a large number of experiments, the inventor finds that when the mass proportion of the polymer microspheres reaches more than 20%, the polymer microspheres can achieve the effect of completely closing pores when being baked at 150 ℃, but the mass proportion of the polymer microspheres cannot be too high, and the electrochemical performance of the battery under normal use can be influenced by the too high proportion.
Preferably, in step S1, the mixing ratio of the cellulose and the solvent water is 1: (40-60); the ball milling time is 1-6 h. More preferably, the mixing ratio of the cellulose and the solvent water is 1: and 50, ball milling for 2-5 h.
Specifically, step S1 may be: adding the crude cellulose and deionized water into an agate ball-milling tank according to the mass ratio of 1:50, wherein the mass ratio of the coarse cellulose to the deionized water is 2: 1, adding an agate ball mill, sealing the tank body, and then placing the tank body in a planetary ball mill for ball milling for 2-5 hours to obtain the nano cellulose solution.
Preferably, in step S3, the porosity of the separator obtained by the freeze-drying technique is 65 to 85%.
Preferably, in step S3, the freezing temperature is less than or equal to 0 ℃, and the drying is carried out in a vacuum environment.
Preferably, the thickness of the obtained separator is 4 to 15 μm. The finally obtained cellulose-based diaphragm has the performances of high liquid absorption rate, high heat resistance and self-closed pore. The thickness of the common PP diaphragm can only reach 8 mu m, while the cellulose-based diaphragm can reach 4-8 mu m, and the cellulose-based diaphragm has lower thickness and wider application range.
2. Lithium ion battery
The third aspect of the present invention provides a lithium ion battery, including a positive plate, a negative plate, a separator interposed between the positive plate and the negative plate, and an electrolyte, wherein the separator is the separator for a lithium ion battery described in any one of the above.
Preferably, the solvent of the electrolyte is an ester solvent. The electrolyte solvent of ester is a strong polar molecule like cellulose, and has a large attraction between the electrolyte solvent and the cellulose, so that the wetting of the cellulose-based diaphragm on the electrolyte can be accelerated, and the liquid absorption and retention capacity of the diaphragm can be improved.
In order to make the technical solutions and advantages of the present invention clearer, the present invention and its advantages will be described in further detail below with reference to the following detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
Example 1
A diaphragm for a lithium ion battery comprises nanocellulose and polymer microspheres in a mass ratio of 6: 4-8.5: 1.5, wherein the particle size of the polymer microspheres is 0.1-3 mu m, and the melting point of the polymer microspheres is 100-125 ℃; the membrane for the lithium ion battery is prepared from the nano-cellulose and the polymer microspheres by a freeze-drying technology.
Specifically, the raw material adopted by the nano-cellulose is wood nano-cellulose, the raw material of the polymer microsphere is polyethylene micro-wax emulsion (solid content is 20%), the total designed solid content of the diaphragm slurry is 10%, and 100g of slurry is prepared, and the specific preparation method comprises the following steps:
1) taking a proper amount of wood pulp board, ultrasonically cleaning the wood pulp board for three times by using deionized water and ethanol respectively, drying the wood pulp board, and crushing the wood pulp board into crude fibers by a crusher, wherein the mass ratio of the wood pulp board to the crude fibers is 1:50, adding the crude fiber and deionized water into an agate ball milling tank, adding a wetting agent (with the solid content of 10%) and mixing together, wherein the weight ratio of the coarse fiber to the deionized water is 2: 1 adding agate ball mill, sealing the tank body, placing the tank body in a planetary ball mill, and carrying out ball milling for 2 hours, wherein the obtained solution is a wood nano-cellulose solution (WPC).
2) Adding polyethylene micro-wax emulsion (WPE) into wood nano-cellulose solution (WPC), and fully stirring to obtain mixed solution; continuously adding polyacrylic acid glue solution (solid content is 20%) into the mixed solution, and uniformly stirring to obtain uniform diaphragm slurry; wherein, according to the actual solid content ratio in the liquid, the wood nano-cellulose solution: polyethylene micro-wax emulsion: wetting agent: the mass ratio of the polyacrylic acid glue solution is 6.93:1.5:0.03: 0.04;
3) and adding the mixed solution into a container, putting the container into a freeze dryer for freeze drying to obtain a diaphragm with extremely high porosity and similar to aerogel, putting the diaphragm into a roller press for rolling, and controlling the rolled diaphragm to be between 10 and 15 mu m to obtain the diaphragm CPS for the lithium ion battery.
Example 2
Different from example 1, the solid content of the polyethylene micro-wax emulsion is 5%, namely, the solid content of the wood nano-cellulose solution is calculated according to the actual solid content ratio in the liquid: polyethylene micro-wax emulsion: wetting agent: the mass ratio of the polyacrylic acid glue solution is 6.93:0.375:0.03: 0.04.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
Different from example 1, the solid content of the polyethylene micro-wax emulsion is 10%, namely, the solid content of the wood nano-cellulose solution is calculated according to the actual solid content ratio in the liquid: polyethylene micro-wax emulsion: wetting agent: the mass ratio of the polyacrylic acid glue solution is 6.93:0.75:0.03: 0.04.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
Different from example 1, the solid content of the polyethylene micro-wax emulsion is 15%, namely, the solid content of the wood nano-cellulose solution is calculated according to the actual solid content ratio in the liquid: polyethylene micro-wax emulsion: wetting agent: the mass ratio of the polyacrylic acid glue solution is 6.93:1.13:0.03: 0.04.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
Different from example 1, the solid content of the polyethylene micro-wax emulsion is 25%, namely, the solid content of the wood nano-cellulose solution is calculated according to the actual solid content ratio in the liquid: polyethylene micro-wax emulsion: wetting agent: the mass ratio of the polyacrylic acid glue solution is 6.93:1.88:0.03: 0.04.
The rest is the same as embodiment 1, and the description is omitted here.
Example 6
Different from example 1, the solid content of the polyethylene micro-wax emulsion is 40%, namely, the solid content of the wood nano-cellulose solution is calculated according to the actual solid content ratio in the liquid: polyethylene micro-wax emulsion: wetting agent: the mass ratio of the polyacrylic acid glue solution is 6.93:3:0.03: 0.04.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1
Unlike example 1, this comparative example is a conventional polyolefin PP separator.
Comparative example 2
Different from example 1 is a preparation method S3 of the separator.
3) And adding the mixed solution into a container, and drying and rolling to obtain the diaphragm with the thickness of 20 mu m for the lithium ion battery.
The rest is the same as embodiment 1, and the description is omitted here.
The separators obtained in the above examples 1 to 6 and comparative examples 1 to 2 were applied to lithium ion batteries.
The separators obtained in example 1 and comparative example 1 were subjected to a thermal stability test, and both were baked at 200 ℃ to obtain the results shown in FIG. 4. After being baked at 200 ℃, the common polyolefin PP diaphragm is completely melted, and the structure of the cellulose-based diaphragm still keeps complete, so that the cellulose-based diaphragm has good thermal stability and higher safety.
The wetting property test of the diaphragms obtained in the example 1 and the comparative example 1 is continued, the same two electrolytes are dripped into the two diaphragms, the infiltration conditions of the two diaphragms are observed after a period of time, and the infiltration result is shown in a figure 5.
In addition, the liquid absorption rate after 1 hour of the diaphragms of the examples 1 to 6 and the diaphragm of the comparative example 1 and the sum of the air permeability value after baking at 150 ℃ are also detected, and the detection results are shown in table 1. Wherein, the liquid absorption rate is obtained by calculating the mass of the weighing diaphragm before and after infiltration.
As is apparent from the above test results, the cellulose-based separator provided by the present invention has a good liquid absorption rate. In addition, the test of the air permeability value after being baked at 150 ℃ shows that the high-analysis microsphere added in the invention has a good hole plugging function, and the thermal stability of the diaphragm is effectively ensured. Preferably, the dry weight ratio of the polymer microspheres in the cellulose-based separator of the present invention is preferably 20 to 30% in consideration of wettability with an electrolyte and a closed-cell effect. In addition, it can be seen from the test results of example 1 and comparative example 2 that the cellulose-based separator obtained by the freeze-drying technique has better porosity and liquid absorption rate.
The performance test of the lithium ion batteries composed of the separators obtained in example 1 and comparative example 1 was continued, and the test results are shown in fig. 6, which shows that the cellulose-based separator of the present invention is also more excellent in cycle performance.
Therefore, the diaphragm provided by the invention has the advantages of high wettability, high liquid absorption rate and high thermal stability, has a self-closing hole function, and can effectively improve the electrochemical performance and safety performance of a battery.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (10)
1. The diaphragm for the lithium ion battery is characterized by comprising nano cellulose and polymer microspheres in a mass ratio of 6: 4-8.5: 1.5, wherein the particle size of the polymer microspheres is 0.1-3 mu m, and the melting point of the polymer microspheres is 100-125 ℃; the membrane for the lithium ion battery is prepared from the nano-cellulose and the polymer microspheres by a freeze-drying technology.
2. The lithium ion battery separator according to claim 1, wherein the nanocellulose is at least one of cotton cellulose, lignocellulose, cellulose nanofibrils, bacterial cellulose, aramid nanofibers, glass nanofibers, and polyacrylonitrile nanofibers.
3. The separator for a lithium ion battery according to claim 1, wherein the polymer microsphere is polyethylene wax.
4. A preparation method of the separator for the lithium ion battery according to any one of claims 1 to 3, characterized by comprising the steps of:
s1, mixing cellulose with solvent water, and performing ball milling to obtain a nano cellulose solution;
s2, mixing and stirring the polymer microspheres and the nano-cellulose solution to obtain a mixed solution, wherein the mass ratio of the nano-cellulose to the polymer microspheres is 6: 4-8.5: 1.5;
and S3, carrying out freeze drying and rolling on the mixed solution to obtain the lithium ion battery diaphragm.
5. The method for preparing the separator for the lithium ion battery according to claim 4, wherein in step S1, the mixing ratio of the nanocellulose to the solvent water is 1: (40-60); the ball milling time is 1-6 h.
6. The method for producing the separator for lithium ion batteries according to claim 4, wherein in step S3, the porosity of the separator obtained by the freeze-drying technique is 65 to 85%.
7. The method for producing a separator for a lithium ion battery according to claim 4 or 6, wherein the freezing temperature is 0 ℃ or lower in step S3, and the drying is performed in a vacuum atmosphere.
8. The method for producing a separator for a lithium ion battery according to claim 4, wherein the thickness of the obtained separator is 4 to 15 μm.
9. A lithium ion battery, comprising a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm is arranged between the positive plate and the negative plate, and is characterized in that the diaphragm is the diaphragm for the lithium ion battery according to any one of claims 1 to 3.
10. The lithium ion battery of claim 9, wherein the solvent of the electrolyte is an ester solvent.
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