CN113794034A - Self-supporting diaphragm and preparation method thereof, composite pole piece and secondary battery - Google Patents
Self-supporting diaphragm and preparation method thereof, composite pole piece and secondary battery Download PDFInfo
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- CN113794034A CN113794034A CN202110888787.XA CN202110888787A CN113794034A CN 113794034 A CN113794034 A CN 113794034A CN 202110888787 A CN202110888787 A CN 202110888787A CN 113794034 A CN113794034 A CN 113794034A
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Images
Classifications
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- 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
- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- 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
- H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
-
- 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
- H01M50/497—Ionic conductivity
-
- 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
Abstract
The invention belongs to the technical field of secondary batteries, and particularly relates to a self-supporting diaphragm and a preparation method thereof, a composite pole piece and a secondary battery, wherein the self-supporting diaphragm comprises the following raw materials in parts by weight: 40-60 parts of ionic liquid, 30-50 parts of lignocellulose and 5-20 parts of binder. The self-supporting diaphragm provided by the invention has good thermal stability, ionic conductivity, dimensional stability and wettability, greatly reduces the conditions of short positive and negative electrodes and spontaneous combustion of a battery cell under a high-temperature condition, and improves the practicability of the diaphragm and the battery cell.
Description
Technical Field
The invention belongs to the technical field of secondary batteries, and particularly relates to a self-supporting diaphragm, a preparation method of the self-supporting diaphragm, a composite pole piece and a secondary battery.
Background
At present, polyolefin diaphragms have the advantages of being light and thin in film forming, good in flexibility and the like, so that most of the commercially used diaphragms are polyolefin diaphragms. However, the polyolefin diaphragm has high crystallinity, low surface energy and small polarity, has poor affinity, wettability and liquid retention with electrolyte, has poor contact with the surfaces of positive and negative pole pieces, and is easy to cause the internal resistance of a lithium ion battery to rise, so the existing polyolefin diaphragm mostly uses the polyolefin diaphragm coated with ceramic, although the wettability and heat resistance of the polyolefin diaphragm to the electrolyte are improved after the polyolefin diaphragm is coated with a ceramic layer, when the temperature reaches above 130 ℃, the polyolefin diaphragm can generate a hole breaking risk, the positive and negative poles are short-circuited, the battery core is spontaneous combustion, and potential safety hazards exist.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the self-supporting diaphragm is provided, has good thermal stability, ionic conductivity, dimensional stability and wettability, greatly reduces the conditions of short positive and negative electrodes and spontaneous combustion of the battery cell under the high-temperature condition, and improves the practicability of the diaphragm and the battery cell.
In order to achieve the purpose, the invention adopts the following technical scheme:
a self-supporting diaphragm comprises the following raw materials in parts by weight: 40-60 parts of ionic liquid, 30-50 parts of lignocellulose and 5-20 parts of binder.
The diaphragm provided by the invention has excellent thermal stability and high thermal decomposition temperature of ionic liquid and cellulose, and can just avoid potential safety hazards of fire, easy combustion of solvent and easy volatilization caused by thermal contraction of the diaphragm in the traditional organic electrolyte.
As an improvement of the self-supporting membrane, the thickness of the self-supporting membrane is 2-6 μm. The thickness of the self-supporting diaphragm is too thick, which affects the ion moving rate, and the thickness of the self-supporting diaphragm is too thin and is relatively soft, so that self-supporting cannot be realized.
The second purpose of the invention is: aiming at the defects of the prior art, the preparation method of the self-supporting diaphragm is provided, and has the advantages of simple operation, good controllability and high production efficiency.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method of making a self-supporting membrane comprising the steps of:
step (A): adding the ionic liquid in parts by weight into a first solvent, and uniformly stirring to obtain a first solution;
step (B): adding the lignocellulose in parts by weight into the second solution, and grinding to obtain a second solution;
step (C): adding the binder in parts by weight into a third solvent, and uniformly stirring to obtain a third solution;
step (D): adding the second solution into the first solution, uniformly stirring, adding the third solution, and uniformly stirring to obtain mixed slurry;
a step (E): and coating the mixed slurry on the surface of a bearing object, and drying to obtain the self-supporting diaphragm.
The preparation method is simple and easy to operate, the uniform and complete diaphragm integrated pole piece can be obtained by coating the mixed slurry on the pole piece on a machine, and the pole piece is dried in vacuum for 30min at 60 ℃ after coating and is stored in a sealing way. The adhesive uses polyacrylic acid adhesive, the polyacrylic acid is a water-soluble polymer, contains rich carboxyl functional groups, can tightly and firmly adhere the gel electrolyte and the pole piece, and has weak hydrogen bond action with the needle-leaved lignocellulose (BWF), and the hydrogen bond is mainly formed by carboxyl of the polyacrylic acid and hydroxyl of the needle-leaved lignocellulose (BWF). The first solvent, the second solvent and the third solvent are deionized water. The solid content of the first solution is 15-25%, the mass fraction of the second solution is 30-50%, and the solid content of the third solution is 10-15%. The support can be a smooth glass sheet, a metal sheet and the like, and when the support is a pole piece, the support can be prepared into a diaphragm integrated pole piece, so that the thickness between the diaphragm and the pole piece is reduced, and preferably, the diaphragm is combined with the negative pole piece. And (D) adding the second solution into the first solution in the step (D), stirring for 1 hour, adding the third solution, and stirring for 2 hours, so that the preparation effect is better.
As an improvement of the preparation method of the self-supporting diaphragm, in the step (B), a ball milling tank is used for milling, and the ratio of balls to materials for milling is 40-60: 0.5-2, and a rotation speed of 1000-1200 r/min. The unreasonable setting of the ball-material ratio and the rotating speed can easily cause the direct destruction of ground lignocellulose, and can not form rich hydroxyl groups to weaken the film-forming property.
As an improvement of the preparation method of the self-supporting diaphragm, the ionic liquid is at least one of quaternary ammonium salt ionic liquid, quaternary phosphorus salt ionic liquid, quaternary sulfur salt ionic liquid or nitrogen heterocyclic ionic liquid. The ionic liquid of the present invention is a salt completely composed of anions and cations, which is in a liquid state at or near room temperature, and is also referred to as a low-temperature molten salt. The main reason why the ionic liquid is used as an ionic compound and has a low melting point is that ions cannot be regularly accumulated into crystals due to the asymmetry of certain substituents in the structure of the ionic liquid. Preferably, the ionic liquid is a nitrogen heterocyclic ionic liquid, preferably, the ionic liquid is an imidazole ionic liquid, preferably, the ionic liquid is [ BMIM ]]BF4(1-butyl-3-methylimidazolium tetrafluoroborate), the specific advantages of the ionic liquid are mainly as follows: (1) the ionic conductivity is good, the solubility to inorganic salt and polymer is good, and the ionic conductivity of the polymer electrolyte can be obviously improved; (2) the thermal decomposition temperature is high, the material is not flammable, and the potential safety hazard that the solvent in the traditional organic electrolyte is flammable and volatile can be avoided; (3) good chemical stability,The electrochemical stability window is wide, and can provide a foundation for the use of the battery in an extreme environment.
As an improvement of the preparation method of the self-supporting diaphragm, the azacyclo-ionic liquid comprises imidazole ionic liquid, pyridine ionic liquid and pyrrole ionic liquid.
As an improvement of the preparation method of the self-supporting membrane, the lignocellulose comprises at least one of coniferous lignocellulose, broadleaf lignocellulose and grass wood lignocellulose. Lignocellulose is an organic fiber substance obtained by chemical treatment and mechanical processing of natural renewable wood, and is nontoxic, tasteless, pollution-free and radioactivity-free. The lignocellulose has small specific gravity, large specific surface area, excellent heat preservation, heat insulation, sound insulation, insulation and air permeability, uniform thermal expansion, no shell and no cracking. When the working temperature of the product reaches 150 ℃, the product can insulate heat for several days, can insulate heat for dozens of hours when reaching 200 ℃, and can insulate heat for several hours when exceeding 220 ℃. The needle leaf lignocellulose has long fiber, tight tissue structure and low content of hybrid cells, and the hybrid cells in the chemical pulp are mostly lost during washing, so the pulp has good quality and the formed paper has strong mechanical property. Under an electron microscope, the needle leaf lignocellulose can be clearly observed to be densely and compactly arranged, the needle leaf lignocellulose fibers subjected to ball milling have different lengths and are mutually wound, and the finest fibers are only about dozens of nanometers. The needle-leaved lignocellulose (BWF) has strong film-forming property and is rich in carboxyl and hydroxyl after being ground.
As an improvement of the preparation method of the self-supporting membrane, the solid content of the mixed slurry is 40-60%. The mixed slurry with a certain solid content is beneficial to thickness control and leveling property during coating.
The third purpose of the invention is that: aiming at the defects of the prior art, the composite pole piece comprises a pole piece and a self-supporting diaphragm arranged on at least one side surface of the pole piece, the thickness of the battery core is greatly reduced, the overall battery density is improved, and the self-supporting diaphragm is heat-resistant and high-temperature-resistant and is not easy to burn.
In order to achieve the purpose, the invention adopts the following technical scheme:
a composite pole piece comprises a pole piece and a coating layer arranged on at least one side face of the pole piece, wherein the coating layer is the self-supporting diaphragm. The thickness of the traditional diaphragm and pole piece is 8-15 um/layer, and the composite pole piece can be thinner by 3-10 um/layer than the traditional structure by using the composite pole piece, so that the integral energy density of the battery cell can be improved.
The fourth purpose of the invention is that: aiming at the defects of the prior art, the secondary battery has the advantages of good thermal stability, good ionic conductivity, high temperature resistance, good safety and long service life.
In order to achieve the purpose, the invention adopts the following technical scheme:
the secondary battery is characterized by comprising a positive electrode, a negative electrode, electrolyte and a shell, wherein the positive electrode and/or the negative electrode is/are the composite pole piece. When the battery is assembled, the materials are punched and cut into proper sizes, the battery is assembled in a glove box, and at least 20mg of electrolyte is required to be dripped into every 1mg of positive active material.
Compared with the prior art, the invention has the beneficial effects that: the self-supporting diaphragm provided by the invention has good thermal stability, ionic conductivity, dimensional stability and wettability, greatly reduces the conditions of short positive and negative electrodes and spontaneous combustion of a battery cell under a high-temperature condition, and improves the practicability of the diaphragm and the battery cell.
Drawings
Fig. 1 is a comparison of a layer structure of a battery cell prepared by using the composite pole piece of the present invention and a layer structure of a conventional battery cell.
Fig. 2 is a graph comparing EIS curves for a battery prepared using the self-supporting separator of the present invention and a battery prepared using a polypropylene separator.
FIG. 3 is a physical comparison of the self-supporting membrane of the present invention with a polypropylene membrane after being left at 180 ℃ for 30 min.
FIG. 4 is a diagram of a composite electrode sheet prepared according to the present invention.
Wherein, 1, anode; 2. a negative electrode; 3. a diaphragm; 4. and (5) compounding the pole piece.
Detailed Description
The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, but the embodiments of the invention are not limited thereto.
Example 1
A method for preparing a self-supporting membrane 3, comprising the steps of:
step (A): adding ionic liquid into a first solvent, and uniformly stirring to obtain a first solution;
step (B): adding lignocellulose into the second solution, and grinding to obtain a second solution;
step (C): adding the binder into the third solvent, and uniformly stirring to obtain a third solution;
step (D): adding the second solution into the first solution, uniformly stirring, adding the third solution, and uniformly stirring to obtain mixed slurry; the solid content of the prepared mixed slurry was 40%.
A step (E): the mixed slurry is coated on the surface of a bearing object and dried to obtain the self-supporting membrane 3.
Wherein, the ball milling tank is used for milling in the step (B), and the ball-material ratio of milling is 50: 1, rotation speed 1032 r/min.
Wherein the ionic liquid is [ BMIM ]]BF4(1-butyl-3-methylimidazole tetrafluoroborate), the lignocellulose is coniferous lignocellulose, and the binder is polyacrylic acid binder.
A self-supporting membrane 3 comprises the following raw materials in parts by weight: 60 parts of ionic liquid, 30 parts of lignocellulose and 10 parts of binder, and the thickness is 5 microns.
A composite pole piece 4 comprises a pole piece and coating layers arranged on two side surfaces of the pole piece, wherein the coating layers are the self-supporting diaphragm 3, and are shown in figure 4.
A secondary battery comprises a positive electrode 1, a negative electrode 2, electrolyte and a shell, wherein the negative electrode 2 is the composite pole piece 4, and the positive electrode 1 and the negative electrode 2 are sequentially stacked. The secondary battery may be a lithium ion battery, a sodium ion battery, or the like.
Example 2
The difference from example 1 is that:
the weight part ratio of the ionic liquid to the lignocellulose to the binder is 50 parts: 40 parts of: 10 parts.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
The difference from example 1 is that:
the weight part ratio of the ionic liquid, the lignocellulose and the binder is 40 parts: 50 parts of: 10 parts.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
The difference from example 1 is that:
the weight part ratio of the ionic liquid to the lignocellulose to the binder is 45 parts: 40 parts of: 15 parts.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
The difference from example 1 is that:
the weight part ratio of the ionic liquid, the lignocellulose and the binder is 40 parts: 45 parts of: 15 parts.
The rest is the same as embodiment 1, and the description is omitted here.
Example 6
The difference from example 1 is that:
the weight part ratio of the ionic liquid, the lignocellulose and the binder is 40 parts: 40 parts of: and 20 parts.
The rest is the same as embodiment 1, and the description is omitted here.
Example 7
The difference from example 1 is that:
the weight part ratio of the ionic liquid to the lignocellulose to the binder is 50 parts: 45 parts of: 5 parts of the raw materials.
The rest is the same as embodiment 1, and the description is omitted here.
Example 8
The difference from example 1 is that:
the weight part ratio of the ionic liquid to the lignocellulose to the binder is 45 parts: 50 parts of: 5 parts of the raw materials.
The rest is the same as embodiment 1, and the description is omitted here.
Example 9
The difference from example 1 is that:
the positive electrode 1 is the composite pole piece 4.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1 is a polypropylene separator 3.
Performance testing
1. The thermal shrinkage and rupture temperatures of the separators 3 prepared in examples 1 to 8 and comparative example 1 were measured, and the test results are shown in table 1.
TABLE 1
| Item | Example 1 | Example 2 | Example 3 | Example 4 | Example 5 |
| |
2 | 2.4 | 2.6 | 2.5 | 2.4 |
| Temperature of membrane rupture | 196 | 191 | 193 | 192 | 194 |
| Item | Example 6 | Example 7 | Example 8 | Example 9 | Comparative example 1 |
| Thermal shrinkage rate | 2.3 | 2.2 | 2.4 | 3 | 7 |
| Temperature of membrane rupture | 194 | 194 | 193 | 180 | 130 |
As can be seen from table 1, the diaphragm 3 prepared by the invention has a lower thermal shrinkage rate and a higher film breaking temperature, so that the diaphragm 3 is not easily damaged at a high temperature, thereby greatly reducing the situations of short positive and negative electrodes 2 and spontaneous combustion of the battery cell at a high temperature, and improving the safety, the practicability and the service life of the battery cell of the diaphragm 3. And the membrane rupture temperature of the membrane 3 of the invention is obviously higher than that of the polypropylene membrane 3 of the comparative example 1, the membrane can resist the temperature of more than 190 ℃, and the heat resistance is good. As can be seen from the comparison of fig. 3, the self-supporting membrane 3 of the present invention still does not deform after standing at 180 ℃ for 30min, has a clear boundary and good dimensional stability, while the polypropylene membrane 3 of the reference 1 deforms, has a fuzzy boundary, has risks of burning and volatilization, and is poor in safety. From the comparison between the embodiment 1 and the embodiment 9, when the self-supporting diaphragm is arranged on the negative electrode, the prepared composite pole piece and the battery cell have better performances. From the comparison of examples 1 to 6 in table 1, when the weight part ratio of the ionic liquid, the lignocellulose and the binder is set to 60 parts: 30 parts of: when 10 parts of the modified polypropylene resin is used, the prepared diaphragm 3 has better performance, lower thermal shrinkage and higher diaphragm breaking temperature.
The conventional cell structure includes a positive electrode 1, a negative electrode 2, and a separator 3, as shown by D in fig. 11The thickness includes the thickness of the three and the thickness of the gap connecting the three, as shown in figure 1D2The battery cell structure comprises a positive electrode 1 and a composite pole piece 4, wherein the composite pole piece 4 comprises a negative pole 2 pole piece and a self-supporting diaphragm 3 arranged on one side surface of the negative pole 2 pole piece, the thickness of each layer is 3-10um thinner than that of each traditional layer of battery cell structure, and when the battery cell is provided with multiple layers, the battery cell can be 300-1000um thinner than that of the traditional battery cell, so that the energy density of the battery is greatly increased.
As can be taken from fig. 2, the EIS plots for both the cell made with the self-supporting separator 3 and the cell made with the polypropylene separator 3 have a semicircle in the medium-high frequency region, which mainly indicates the charge transfer at the electrode/electrolyte interface. The charge transfer resistances (i.e., semi-circle diameters) for the lithium ion battery and the PP separator 3 battery of the self-supporting separator 3 of the present invention were 54.6 Ω and 101.8 Ω, respectively, which demonstrates that the battery of the self-supporting separator 3 of the present invention can accelerate the charge transfer to reduce the interface resistance. Ionic liquids in membranes 3 of the invention, i.e., [ BMIM ]]BF4 (1-butyl-3-methylimidazolium tetrafluoroborate) has high ionic conductivity, and is calculated to be 1.58 x 10 after adding certain amount of softwood lignocellulose (BWF) and binder (PAA)-3S/cm, good ionic conductivity.
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. A self-supporting diaphragm is characterized by comprising the following raw materials in parts by weight: 40-60 parts of ionic liquid, 30-50 parts of lignocellulose and 5-20 parts of binder.
2. The self-supporting membrane according to claim 1, wherein the thickness of the self-supporting membrane is 2 to 6 μm.
3. Method for the preparation of a self-supporting membrane according to claim 1, characterized in that it comprises the following steps:
step (A): adding the ionic liquid in parts by weight into a first solvent, and uniformly stirring to obtain a first solution;
step (B): adding the lignocellulose in parts by weight into the second solution, and grinding to obtain a second solution;
step (C): adding the binder in parts by weight into a third solvent, and uniformly stirring to obtain a third solution;
step (D): adding the second solution into the first solution, uniformly stirring, adding the third solution, and uniformly stirring to obtain mixed slurry;
a step (E): and coating the mixed slurry on the surface of a bearing object, and drying to obtain the self-supporting diaphragm.
4. The preparation method of the self-supporting membrane according to claim 3, wherein the grinding in the step (B) is performed by using a ball mill pot, and the ball-to-material ratio of grinding is 40-60: 0.5-2, and a rotation speed of 1000-1200 r/min.
5. The method for preparing a self-supporting membrane according to claim 3, wherein the ionic liquid is at least one of quaternary ammonium salt ionic liquid, quaternary phosphorus salt ionic liquid, quaternary sulfur salt ionic liquid and nitrogen heterocyclic ionic liquid.
6. The method of making a self-supporting membrane according to claim 5, wherein the azacyclo-ionic liquid comprises at least one of an imidazole-ionic liquid, a pyridine-ionic liquid, and a pyrrole-ionic liquid.
7. The method of making a self-supporting membrane according to claim 3, wherein the ligno-cellulose comprises at least one of coniferous ligno-cellulose, broadleaf ligno-cellulose, and vegetation ligno-cellulose.
8. The method for preparing a self-supporting membrane according to claim 3, wherein the solid content of the mixed slurry is 40 to 60%.
9. A composite pole piece, comprising a pole piece and a coating layer disposed on at least one side of the pole piece, wherein the coating layer is the self-supporting separator of any one of claims 1-2.
10. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a case, wherein the positive electrode and/or the negative electrode is the composite electrode sheet according to claim 9.
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