Spongy composite lithium ion battery separator

Abstract

The present application relates to the technical field of lithium battery, in particular to a kind of sponge composite lithium ion battery separator, including separator layer and polymer coating, the separator layer is polyolefin porous membrane or ceramic coating modified polyolefin porous membrane, the polymer coating is formed after coating sizing material is coated on one side or both sides of separator layer by solution phase inversion method, the polymer coating has sponge porous continuous skeleton structure filled with ceramic particles, the polymer coating prepared has been greatly improved relative to conventional water-based PVDF coating separator product adhesion, simultaneously, the overall air permeability of the separator after coating the coating is greatly reduced relative to traditional acetone system PVDF coating separator, is advantageous to improve lithium ion transport capacity, the present application is applicable to lithium ion battery, sodium ion battery and other new type secondary battery.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a sponge-like composite lithium-ion battery separator. Background Technology

[0002] PVDF-coated separators possess excellent electrochemical stability and electrolyte wettability, which can improve the cycle performance and lifespan of lithium-ion batteries. They also have good adhesion, allowing the positive electrode, negative electrode, and separator to be integrated into a single structure through hot pressing. This significantly reduces battery assembly time and effectively lowers the overall battery production cost, while also effectively suppressing cell expansion and deformation, greatly improving battery safety performance. They are widely used in power, energy storage, and 3C lithium-ion battery fields.

[0003] Currently, water-based PVDF coatings are the most widely used, but there are still significant gaps in terms of adhesion between the separator and the electrode, as well as electrolyte wetting ability, making it difficult to meet the requirements of large-size power batteries (especially soft-pack batteries) and 3C consumer batteries. While traditional acetone-based PVDF coated separators have significantly improved adhesion, they employ a dip-coating process, which has drawbacks such as low production efficiency, high manufacturing costs, high static electricity, high separator permeability, and difficulty in controlling coating thickness and pore structure. These limitations restrict their application in the power battery field, and their application is becoming increasingly limited as consumers demand higher charging and rate performance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to propose a sponge-like composite lithium-ion battery separator to solve the problems of high air permeability and poor adhesion of traditional PVDF coated separators.

[0005] To achieve the above objectives, the present invention provides a sponge-like composite lithium-ion battery separator, comprising a separator layer and a polymer coating. The separator layer is a polyolefin porous membrane or a ceramic-coated modified polyolefin porous membrane, and the polymer coating is formed by coating a slurry onto one or both sides of the separator layer and then performing a solution phase inversion method.

[0006] The coating slurry comprises the following raw materials in parts by weight: 3-10 parts adhesive polymer, 5-20 parts ceramic particles, 40-150 parts organic solvent, 0.5-3 parts deionized water and 0.3-1.8 parts N-palmitoyl dopamine.

[0007] The polymer coating has a sponge-like porous continuous skeleton structure filled with ceramic particles.

[0008] Furthermore, the porosity of the polyolefin porous membrane and the ceramic-coated modified polyolefin porous membrane is 30-70%, preferably 40-60%.

[0009] Furthermore, the adhesive polymer is one or both of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0010] Furthermore, the ceramic particles are one or both of alumina or boehmite, with a particle size of 0.1-1.0 μm, preferably 0.3-0.8 μm.

[0011] Furthermore, the organic solvent is one of DMAC, NMP, NMF or DMSO, preferably DMAC or NMP which have lower toxicity.

[0012] Furthermore, the coating method is one of microgravure coating, bar coating, or slit coating, preferably double-sided simultaneous coating.

[0013] Furthermore, the coating thickness is 0.2-2μm, the air permeability of the coating is less than 200s / 100ml, and the adhesion force between the coating and the electrode is 20-30N / m.

[0014] Furthermore, the sponge-like composite lithium-ion battery separator is suitable for novel secondary batteries such as lithium-ion batteries and sodium-ion batteries.

[0015] Furthermore, the present invention also provides a method for preparing the above-mentioned sponge-like composite lithium-ion battery separator, the specific steps of which are as follows:

[0016] A. Mix 30-60% of the organic solvent, deionized water and N-palmitoyl dopamine in the raw materials and stir for 10-30 minutes to obtain mixture I;

[0017] B. Add ceramic particles to mixture I and stir for 30-90 minutes to obtain mixture II;

[0018] C. Mix the adhesive polymer and the remaining organic solvent in the raw materials, and stir for 30-60 minutes to obtain mixture III;

[0019] D. Add mixture II to mixture III and stir for 30-60 minutes to obtain mixture IV;

[0020] E. Pass the mixture IV through a magnetic filter device, stir for 5-20 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry;

[0021] F. Apply the coating slurry to one or both sides of the membrane layer to obtain a coated membrane;

[0022] G. The coated film is subjected to a coagulation bath, washed with water multiple times, and dried at 40-70℃ to obtain a sponge-like composite lithium-ion battery separator.

[0023] Preferably, the coagulation bath in step G is a mixture of organic solvent and deionized water in a weight ratio of 25-35:65-75.

[0024] The beneficial effects of this invention are:

[0025] The sponge-like composite lithium-ion battery separator prepared by this invention has an air permeability value of less than 200s / 100mL and an adhesion strength of more than 29.2 / N / m. Its air permeability value is much lower than that of separators prepared by traditional acetone and aqueous PVDF, and its adhesion strength is much greater than that of separators prepared by aqueous PVDF, and is superior to that of separators prepared by acetone PVDF.

[0026] In the phase transformation process, N-palmitoyl dopamine dissolves in deionized water and adsorbs onto the pore surface during pore formation, forming pore modification, which in turn leads to the formation of a sponge-like coating structure. Furthermore, the introduction of the dopamine structure also improves the adhesion of the coating.

[0027] This invention uses microgravure, wire rod, or slot coating methods to replace dip coating, making it suitable for high-speed, continuous, stable, and large-scale production. It also uses solution phase inversion instead of gas phase inversion, providing greater process variability and allowing for better adjustment of the coating structure and performance according to the application scenario. Its application scope is not limited to the 3C consumer battery field. In addition, this process uses DMAC instead of acetone, which reduces the risk of combustion and explosion. After being treated by the solvent recovery system, it can be recycled, further reducing production costs. Attached Figure Description

[0028] Figure 1 This is a scanning electron microscope image of the coating surface in Embodiment 1 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0030] In the embodiments of the present invention, the ceramic-coated modified polyolefin porous membrane described in the comparative example has a thickness of 9 μm and a porosity of 46%. The ceramic coating is applied to one side of the polyolefin porous membrane with a thickness of 3 μm, and the alumina particle size is 0.5 μm.

[0031] Example 1

[0032] A sponge-like composite lithium-ion battery separator, the preparation method of which includes the following steps:

[0033] A. Mix 20g DMAC, 0.5g deionized water and 0.3g N-palmitoyl dopamine, stir for 10min to obtain mixture I;

[0034] B. Add 5g of aluminum oxide to mixture I and stir for 30 minutes to obtain mixture II;

[0035] C. Mix 3g PVDF and 20g DMAC and stir for 30min to obtain mixture III;

[0036] D. Add mixture II to mixture III and stir for 30 minutes to obtain mixture IV;

[0037] E. Pass the mixture IV through a magnetic filter device, stir for 5 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry;

[0038] F. Coating the coating slurry onto both sides of the ceramic-coated modified polyolefin porous membrane to obtain the coated membrane;

[0039] G. The coated membrane is subjected to a coagulation bath containing 25g DMAC and 75g deionized water, washed multiple times with water, and dried at 40°C to obtain a sponge-like composite lithium-ion battery separator.

[0040] Example 2

[0041] A sponge-like composite lithium-ion battery separator, the preparation method of which includes the following steps:

[0042] A. Mix 50g DMAC, 1.5g deionized water and 1g N-palmitoyl dopamine, stir for 20min to obtain mixture I;

[0043] B. Add 13g of aluminum oxide to mixture I and stir for 60 minutes to obtain mixture II;

[0044] C. Mix 6g PVDF and 50g DMAC and stir for 45min to obtain mixture III;

[0045] D. Add mixture II to mixture III and stir for 45 minutes to obtain mixture IV;

[0046] E. Pass the mixture IV through a magnetic filter device, stir for 12 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry.

[0047] F. Coating the coating slurry onto both sides of the ceramic-coated modified polyolefin porous membrane to obtain the coated membrane;

[0048] G. The coated membrane is subjected to a coagulation bath containing 30g DMAC and 70g deionized water, washed multiple times with water, and dried at 55°C to obtain a sponge-like composite lithium-ion battery separator.

[0049] Example 3

[0050] A sponge-like composite lithium-ion battery separator, the preparation method of which includes the following steps:

[0051] A. Mix 75g DMAC, 3g deionized water and 1.8g N-palmitoyl dopamine and stir for 30 minutes to obtain mixture I;

[0052] B. Add 20g of aluminum oxide to mixture I and stir for 90min to obtain mixture II;

[0053] C. Mix 10g PVDF and 75g DMAC and stir for 60min to obtain mixture III;

[0054] D. Add mixture II to mixture III and stir for 60 minutes to obtain mixture IV;

[0055] E. Pass the mixture IV through a magnetic filter device, stir for 20 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry.

[0056] F. Coating the coating slurry onto both sides of the ceramic-coated modified polyolefin porous membrane to obtain the coated membrane;

[0057] G. The coated membrane is subjected to a coagulation bath containing 35 DMAC and 65 g of deionized water, washed multiple times with water, and dried at 70°C to obtain a sponge-like composite lithium-ion battery separator.

[0058] Comparative Example 1

[0059] A lithium-ion battery separator, the preparation method of which includes the following steps:

[0060] A. Mix 6g PVDF and 100g acetone and stir for 45min to obtain mixture I;

[0061] B. Add 13g of aluminum oxide to mixture I and stir for 20 minutes. This yields mixture II.

[0062] C. Pass mixture II through a magnetic filter device, stir for 12 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry;

[0063] D. The coating slurry is coated on both sides of the ceramic-coated modified polyolefin porous membrane to obtain a coated membrane, which is then dried at 55°C to obtain a lithium-ion battery separator.

[0064] Comparative Example 2

[0065] A lithium-ion battery separator, the preparation method of which includes the following steps:

[0066] A. Mix 6g of aqueous PVDF and 100g of deionized water and stir for 45min to obtain mixture I;

[0067] B. Add 13g of aluminum oxide to mixture I and stir for 20 minutes. This yields mixture II.

[0068] C. Pass mixture II through a magnetic filter device, stir for 12 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry;

[0069] D. The coating slurry is sprayed onto both sides of the ceramic-coated modified polyolefin porous membrane to obtain a coated membrane, which is then dried at 55°C to obtain a lithium-ion battery separator.

[0070] Comparative Example 3

[0071] A lithium-ion battery separator, the preparation method of which includes the following steps:

[0072] A. Mix 50g DMAC and 1.5g deionized water and stir for 20 minutes to obtain mixture I;

[0073] BG, same as Example 2.

[0074] Performance testing

[0075] Breathability test: Using a Wang Yan-style breathability meter, the test time is 5 seconds, and the standard atmospheric pressure is used.

[0076] Heat shrinkage test: Use a forced-air drying oven, set the temperature to 130℃, and the time to 1 hour. Sample size: 10cm*10cm, sandwiched between 5 layers of A4 paper on the top and bottom.

[0077] Adhesion test: Fold the diaphragm in half and pass it through a laminator at a temperature of 120℃. Cut a sample to size of 15mm*15cm and perform a peel strength test using a universal tensile testing machine at a speed of 300mm / min.

[0078] The test results are shown in Table 1.

[0079]

[0080] Data Analysis: As can be seen from Examples 1-3, the sponge-like composite lithium-ion battery separator prepared by this invention has an air permeability value of less than 200s / 100mL and an adhesion strength of more than 29.2 / N / m. Its air permeability value is much lower than that of separators prepared by traditional acetone and aqueous PVDF, and its adhesion strength is much greater than that of separators prepared by aqueous PVDF, and superior to that of separators prepared by acetone PVDF. The decrease in air permeability is mainly due to the modification of pores and the formation of sponge-like coating structure by N-palmitoyl dopamine during the solution phase inversion process. The increase in adhesion strength is mainly due to the phase inversion process and the promotion of coating adhesion by N-palmitoyl dopamine.

[0081] Electrochemical performance test: The separator prepared in Example 2 and the separator prepared in the comparative example were used to make soft-pack lithium-ion battery chips using the same process. The electrolyte was 1M LiPF6 dissolved in (ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (volume ratio 1:1:1)). The electrolyte was tested for 500 cycles using a constant current discharge of 1.0C. The test results are shown in Table 2.

[0082] Table 2. Battery performance test results for the separators prepared in Examples 2 and Comparative Examples 1-3.

[0083]

[0084] Data analysis shows that, as can be seen from Example 2 above, the battery prepared using the sponge-like composite lithium-ion battery separator of the present invention still retains 97.5% of its capacity after 500 cycles.

[0085] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0086] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A sponge-like composite lithium-ion battery separator, characterized in that, It includes a membrane layer and a polymer coating. The membrane layer is a polyolefin porous membrane or a ceramic-coated modified polyolefin porous membrane. The polymer coating is formed by coating a slurry onto one or both sides of the membrane layer and then performing a solution phase inversion method. The coating slurry comprises the following raw materials in parts by weight: 3-10 parts adhesive polymer, 5-20 parts ceramic particles, 40-150 parts organic solvent, 0.5-3 parts deionized water and 0.3-1.8 parts N-palmitoyl dopamine; The polymer coating has a sponge-like porous continuous skeleton structure filled with ceramic particles.

2. The sponge-like composite lithium-ion battery separator according to claim 1, characterized in that, The porosity of the polyolefin porous membrane and the ceramic-coated modified polyolefin porous membrane is 30-70%.

3. The sponge-like composite lithium-ion battery separator according to claim 1, characterized in that, The adhesive polymer is one or both of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

4. The sponge-like composite lithium-ion battery separator according to claim 1, characterized in that, The ceramic particles are one or both of alumina or borax, with a particle size of 0.1-1.0 μm.

5. The sponge-like composite lithium-ion battery separator according to claim 1, characterized in that, The organic solvent is one of DMAC, NMP, NMF or DMSO.

6. The sponge-like composite lithium-ion battery separator according to claim 1, characterized in that, The coating method is one of microgravure coating, bar coating, or slit coating.

7. The sponge-like composite lithium-ion battery separator according to claim 1, characterized in that, The coating has a thickness of 0.2-2 μm and an air permeability of less than 200 s / 100 mL.

8. A method for preparing a sponge-like composite lithium-ion battery separator according to any one of claims 1-7, characterized in that, The specific steps are as follows: A. Mix deionized water, N-palmitoyl dopamine and 30-60% of the organic solvent in the raw material, and stir for 10-30 minutes to obtain mixture I; B. Add ceramic particles to mixture I and stir for 30-90 minutes to obtain mixture II; C. Mix the adhesive polymer and the remaining organic solvent in the raw materials, and stir for 30-60 minutes to obtain mixture III; D. Add mixture II to mixture III and stir for 30-60 minutes to obtain mixture IV; E. Pass the mixture IV through a magnetic filter device, stir for 5-20 minutes, and then filter it through a 250-mesh filter to obtain the coating slurry; F. Apply the coating slurry to one or both sides of the membrane layer to obtain a coated membrane; G. The coated film is subjected to a coagulation bath, washed with water multiple times, and dried at 40-70℃ to obtain a sponge-like composite lithium-ion battery separator.

9. The method for preparing the sponge-like composite lithium-ion battery separator according to claim 8, characterized in that, The coagulation bath in step G is a mixture of organic solvent and deionized water, with a weight ratio of organic solvent to deionized water of 25-35:65-75.

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