Separator for semi-solid-state battery and preparation method therefor

Abstract

Disclosed in the present invention are a separator for a semi-solid-state battery and a preparation method therefor. The preparation method for the separator comprises: mixing 10-40 wt% of a lithium salt with cellulose, then adding 3-10 wt% of aluminum oxide and a DMSO (dimethyl sulfoxide) solution in which 2-5 wt% of PVDF is dissolved, uniformly coating a polyolefin base membrane with the above prepared composite solid-state electrolyte coating solution in a blade coating mode, washing same with water, and drying same, thereby obtaining a separator having a composite solid-state electrolyte coating. The composite solid-state electrolyte coating obtained in the present invention is uniform, and the separator prepared therefrom can be used in a semi-solid-state battery, and can greatly reduce interface resistance in the battery, improve ionic conductivity, induce uniform deposition of lithium metal, improve the elastic modulus of the material, avoid penetration of lithium dendrites and meet usage requirements of the semi-solid-state battery.

Description

Semi-solid battery diaphragm and preparation method thereof Priority claim

[0001] The present invention claims priority to Chinese patent application No. 2023107596734, filed on June 26, 2023, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0002] The present invention relates to the field of preparation of lithium ion battery diaphragm materials, and in particular to a diaphragm for a semi-solid battery and a preparation method thereof. Background Art

[0003] Solid-state lithium metal batteries, due to their high energy density and excellent safety, have become a key development focus for lithium secondary batteries and have garnered widespread attention. However, the large-scale application of solid-state electrolytes still faces numerous challenges, including unstable solid-electrolyte interfaces, poor cycling performance, and lithium dendrite growth, hindering their application in automobiles and power grids. Therefore, before solid-state lithium metal batteries can completely replace liquid lithium-ion batteries, a transition toward semi-solid-state batteries is possible. This involves increasing the use of solid electrolytes and reducing the use of liquid electrolytes, gradually progressing toward all-solid-state batteries.

[0004] Semi-solid-state battery separators must possess excellent electrolyte wettability, interfacial stability, excellent thermal shrinkage, high modulus (≥6 GPa), and high ionic conductivity. However, currently, neither commercial polyolefin separators nor solid-state electrolytes can simultaneously meet these requirements.

[0005] Therefore, designing a separator that can meet the needs of semi-solid-state batteries has become a very critical technology. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that the current semi-solid-state battery diaphragm cannot simultaneously meet the problems of good electrolyte wettability, interface stability, excellent shrinkage performance, high modulus, and high conductivity. The present invention provides a composite solid electrolyte coating diaphragm and its preparation method that can greatly reduce the interface resistance inside the battery, improve ionic conductivity, high wettability, good thermal shrinkage performance and the high elastic modulus of the material itself, avoid the penetration of lithium dendrites, and meet the needs of semi-solid-state batteries.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] The semi-solid-state battery separator described in the present invention is prepared by mixing 10-40 wt% of lithium salt with cellulose, then adding 3-10 wt% of aluminum oxide and a DMSO (dimethyl sulfoxide) solution containing 2-5 wt% of PVDF. The composite solid electrolyte coating solution is evenly coated on a polyolefin-based film by doctor blade coating, followed by washing and drying to obtain a composite solid electrolyte-coated separator. The separator is specifically prepared according to the following steps:

[0009] (1) Preparation of composite solid electrolyte coating slurry:

[0010] First, 10-40 wt% of lithium salt and cellulose are mixed in a ratio of 1:2-1:4, and then 3-10 wt% of aluminum oxide and a DMSO (dimethyl sulfoxide) solution containing 2-5 wt% of PVDF are added thereto to obtain a composite solid electrolyte coating slurry;

[0011] (2) Preparation of semi-solid battery coated diaphragm:

[0012] A composite solid electrolyte coating liquid is evenly coated on a glass plate with a polyolefin base film by scraping. The DMSO solvent is first washed out with water, and then dried in an 80°C oven to allow the electrolyte and cellulose to completely polymerize and solidify, thereby obtaining a semi-solid battery coated diaphragm.

[0013] As a limitation of the present invention, the lithium salt in step (1) is lithium tetrafluoroborate.

[0014] As a limitation of the present invention, the cellulose in step (1) is cellulose containing hydroxyl groups or carboxyl groups.

[0015] As a limitation of the present invention, the particle size D50 of the alumina powder described in step (1) ranges from 0.2 to 1.2 μm.

[0016] As a limitation of the present invention, after washing DMSO with water in step (2), the residual amount of DMSO is less than 1 wt %.

[0017] After adopting the above technical solution, the beneficial effects achieved by the present invention are:

[0018] (1) The addition of cellulose greatly improves the wettability of the coating.

[0019] (2) The study showed that cellulose has the advantages of high dielectric constant, strong puncture resistance, good chemical stability and good thermal stability. It can form a supporting layer on the surface of polyolefin separator, which can greatly reduce the thermal shrinkage of polyolefin separator and enhance the overall puncture resistance.

[0020] (3) On the one hand, the large number of hydroxyl polar groups on the cellulose molecules is conducive to the affinity of the electrolyte. On the other hand, the large number of hydrogen bonds easily form a dense network in the cellulose membrane, resulting in a low porosity of the diaphragm, which is not conducive to the retention of electrolyte and ion transport in the diaphragm. Therefore, inorganic particles (alumina) are added to balance the hydrogen bonding effect and increase the porosity of the diaphragm. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to the protection scope of the following embodiments. Example 1

[0022] (1) Preparation of composite solid electrolyte coating slurry:

[0023] First, 10 wt% lithium tetrafluoroborate and hydroxymethyl cellulose are mixed at a ratio of 1:4, and then 10 wt% alumina and a DMSO solution containing 4 wt% PVDF are added thereto to obtain a composite solid electrolyte coating slurry.

[0024] (2) Preparation of semi-solid battery coated diaphragm:

[0025] Polypropylene is selected as the base membrane material here. The composite solid electrolyte coating liquid is evenly coated on the polypropylene base membrane by scraping on the glass plate on which the polypropylene base membrane is laid. After washing with water, the residual DMSO amount is less than 1wt%. Then, it is dried in an 80°C oven to allow the electrolyte to be completely polymerized and solidified to obtain a semi-solid battery coated diaphragm. Example 2

[0026] (1) Preparation of composite solid electrolyte coating slurry:

[0027] First, 20 wt% lithium tetrafluoroborate and hydroxymethyl cellulose are mixed at a ratio of 1:3, and then 6 wt% alumina and a DMSO solution containing 3 wt% PVDF are added thereto to obtain a composite solid electrolyte coating slurry.

[0028] (2) Preparation of semi-solid battery coated diaphragm:

[0029] Polypropylene is selected as the base membrane material here. The composite solid electrolyte coating liquid is evenly coated on the polypropylene base membrane by scraping on the glass plate on which the polypropylene base membrane is laid. After washing with water, the residual DMSO amount is less than 1wt%. Then, it is dried in an 80°C oven to allow the electrolyte to be completely polymerized and solidified to obtain a semi-solid battery coated diaphragm. Example 3

[0030] (1) Preparation of composite solid electrolyte coating slurry:

[0031] First, 30 wt% of lithium tetrafluoroborate and hydroxymethyl cellulose are mixed in a ratio of 1:2, and then 3 wt% of aluminum oxide and a DMSO solution containing 2 wt% of PVDF are added thereto to obtain a composite solid electrolyte coating slurry.

[0032] (2) Preparation of semi-solid battery coated diaphragm:

[0033] Polypropylene is selected as the base membrane material here. The composite solid electrolyte coating liquid is evenly coated on the polypropylene base membrane by scraping on the glass plate on which the polypropylene base membrane is laid. After washing with water, the residual DMSO amount is less than 1wt%. Then, it is dried in an 80°C oven to allow the electrolyte to be completely polymerized and solidified to obtain a semi-solid battery coated diaphragm.

[0034] The performance test of the semi-solid battery coating film obtained in the above embodiment was carried out, and the test results are shown in the following table

[0035]

[0036] As can be seen from the table above, the semi-solid battery separator produced using the present invention significantly improves puncture strength, thereby suppressing the formation of lithium dendrites. It also overcomes the significant thermal shrinkage problem associated with simple polyolefin separators, significantly enhancing battery safety. The resulting improvement in wettability meets the requirements for semi-solid-state battery production, thus providing a separator suitable for semi-solid-state battery applications.

[0037] The above embodiments are merely illustrative of the principles and performance of the present invention, as well as some embodiments of its application. A person skilled in the art may make several modifications and improvements without departing from the inventive concept of the present invention, and all of these modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing a diaphragm for a semi-solid battery, characterized in that: The method is specifically carried out according to the following steps: (1) Preparation of composite solid electrolyte coating slurry: First, 10-40 wt% of lithium salt and cellulose are mixed in a ratio of 1:2-1:4, and then 3-10 wt% of aluminum oxide and 2-5 wt% of PVDF DMSO solution are added thereto to obtain a composite solid electrolyte coating slurry; (2) Preparation of semi-solid battery coated diaphragm: The polyolefin base film is spread flat on a glass plate, and the composite solid electrolyte coating slurry obtained in step 1 is evenly coated on the polyolefin base film by scraping, and the DMSO solvent is first washed out with water, and then dried in an oven at 80°C to allow the electrolyte and cellulose to completely polymerize and solidify, thereby obtaining a semi-solid battery coated diaphragm.

2. The method for preparing a diaphragm for a semi-solid battery according to claim 1, characterized in that: The lithium salt described in step 1 is lithium tetrafluoroborate.

3. The method for preparing a diaphragm for a semi-solid battery according to claim 1, characterized in that: The cellulose described in step 1 is cellulose containing hydroxyl groups or carboxyl groups.

4. The method for preparing a diaphragm for a semi-solid battery according to claim 2, characterized in that: The particle size D50 of the alumina powder described in step 1 ranges from 0.2 to 1.2 μm.

5. The method for preparing a diaphragm for a semi-solid battery according to claim 2, characterized in that: After washing the DMSO solvent with water in step 2, the residual DMSO should be less than 1 wt %.

6. A separator for a semi-solid battery prepared according to any one of claims 1 to 5.

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