A lithium ion battery separator with improved ion conductivity function and a preparation method and application thereof

Abstract

The present application relates to the technical field of lithium ion battery, in particular to a kind of lithium ion battery separator of improving ion conducting function and its preparation method and application.The lithium ion battery separator includes base film and the adhesive layer located in one side or both sides of base film, the adhesive layer contains anion polymer crosslinked particles, inorganic nanoparticles;The anion polymer crosslinked particles are obtained by emulsion polymerization of reaction monomer.The anion polymer crosslinked particles provided by the present application can prevent material from deforming after being subjected to heat pressing, avoid the problem of blocking pore size.The higher ion concentration on the surface can improve the charge intensity of the separator during the battery charging and discharging process, and can also play the effect of charge compensation, which has obvious improvement effect on improving the conduction of lithium ion and stabilizing current system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery separator, in particular to a lithium ion battery separator with improved ion conduction function and its preparation method and application. BACKGROUND

[0002] In order to avoid the problem of mislayering caused by jolting and vibration during actual use, the power lithium ion battery, especially the soft package and aluminum shell structure battery, generally uses a coated film to enhance the hardness of the battery cell. However, the common problem caused by the coated film is that the glue is soft and swells greatly, so that the glue point will block the pore size after hot pressing, forming a dead zone, and the lithium ion cannot pass through, resulting in uneven current density. Over a long period of time, lithium precipitation will occur at the glue point due to the increase in liquid resistance, and eventually lithium dendrites will pierce the separator, causing the battery to sink and become scrap. This is an important reason why the current ternary lithium battery cannot complete long cycle life.

[0003] Patent technology document CN201911372686.6 discloses a kind of water-based polymer coating slurry and its application. The water-based polymer coating slurry, wherein a block anionic polyurethane is added as a dispersant, the block anionic polyurethane is composed of a hydrophobic polyurethane segment and a hydrophilic anionic polymer segment; the hydrophobic polyurethane segment is adsorbed on the polymer microspheres, and the hydrophilic anionic polymer segment is stretched in water, so that the polymer microspheres are stably suspended in water, improving the stability of the water-based polymer coating slurry; however, the hydrophilic anionic polymer segment will reduce the hardness of the coating, and will block the pore after hot pressing, affecting the cycle life of the lithium battery. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a lithium ion battery separator with improved ion conduction function and its preparation method and application to inhibit the increase in internal resistance and the growth of lithium dendrites in the cycle of the lithium ion battery, and to improve the ion conduction function and stabilize the current system.

[0005] To achieve the above purpose, the present application provides a lithium ion battery separator with improved ion conduction function, which comprises a base film and a glue coating layer on one side or both sides of the base film, and the glue coating layer contains anionic polymer cross-linked particles and inorganic nanoparticles.

[0006] Preferably, the anionic polymer cross-linked particles have a carbon chain as the main chain, and the side chains on the main chain contain carboxylic acid groups and sulfonic acid groups.

[0007] Preferably, the content of the anionic polymer cross-linked particles in the glue coating layer is greater than 5wt%.

[0008] Preferably, the anionic polymer cross-linked particles are obtained by emulsion polymerization of reaction monomers.

[0009] Preferably, the reaction monomers include, by weight fraction, 18-25 parts of methacrylic acid, 5-7 parts of methyl methacrylate, 3-4 parts of acrylamide, 42-58 parts of 2-acrylamido-2-methylpropanesulfonic acid, and 0-6 parts of a crosslinking agent.

[0010] Preferably, the crosslinking agent is a mixture of a rigid crosslinking agent and ethylene glycol diacrylate at a weight ratio of 1:1.

[0011] Preferably, the rigid crosslinking agent is prepared by dissolving 3-bromopropene in acetone to obtain a 3-bromopropene acetone solution, dissolving 4,4-bipyridine in acetone to obtain a 4,4-bipyridine acetone solution, then adding the 4,4-bipyridine acetone solution dropwise to the 3-bromopropene acetone solution at 40-45°C, reacting for 12-14 hours, cooling, collecting the precipitated product, washing it with acetone three times, and vacuum drying to obtain the rigid crosslinking agent.

[0012] Preferably, the molar ratio of 3-bromopropene to 4,4-bipyridine is 2:1.1.

[0013] Preferably, the concentration of the 3-bromopropene acetone solution is 5wt%, and the concentration of the 4,4-bipyridine acetone solution is 5wt%.

[0014] Preferably, the base film is one of polyethylene, polypropylene, polymethylpentene, polyvinylidene fluoride, polyimide, and non-woven fabric, and the porosity is 30-70%.

[0015] Preferably, the inorganic nanoparticles are one of silicon dioxide, aluminum hydroxide, magnesium hydroxide, and boehmite, and the particle size D50 is 0.1-0.5μm.

[0016] Preferably, the specific preparation steps of the anionic polymer crosslinked particles are as follows:

[0017] S1: Add the emulsifier and the rigid crosslinking agent to solvent oil D100, stir for 20-30 minutes, and obtain an oil phase;

[0018] S2: Add methacrylic acid, methyl methacrylate, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid to deionized water, adjust the pH value to 7-8 with a sodium hydroxide aqueous solution, then add ethylene glycol diacrylate, and stir for 20-30 minutes to obtain an aqueous phase;

[0019] S3: Add the aqueous phase to the oil phase, emulsify, then pass nitrogen gas for 10-20 minutes, add potassium persulfate and sodium bisulfite, and polymerize at room temperature for 5-7 hours. Finally, wash with anhydrous ethanol three times, and vacuum dry to obtain the anionic polymer crosslinked particles.

[0020] Preferably, the emulsifier in step S1 is a mixture of Tween-80 and Span-83 in a weight ratio of 1:5.

[0021] Preferably, the concentration of the aqueous sodium hydroxide solution in step S2 is 20wt%.

[0022] Preferably, the specific step of emulsification in step S3 is: stirring the pre-emulsion at room temperature at 1000-1500 rpm for 10-15 min, and then high-speed emulsification in an ice bath at 15000-20000 rpm for 3-5 min.

[0023] Further, the application also provides a preparation method of a lithium ion battery separator with improved ion conduction function, and the specific preparation method is as follows: after mixing anionic polymer crosslinked particles, inorganic nanoparticles, acrylic binder, sodium polyacrylate, polyether modified organosilicon and deionized water, the mixture is uniformly coated on one side or both sides of the base film, and then dried to obtain the lithium ion battery separator with improved ion conduction function.

[0024] Further, the application also provides an application of the lithium ion battery separator with improved ion conduction function, which can be used in lithium ion power batteries.

[0025] The beneficial effects of the application are as follows:

[0026] The battery separator prepared by the application can prevent deformation of the material after heat pressing due to the special structure of the anionic polymer crosslinked particles, and can avoid the problem of blocking the pore size. The higher ion concentration on the surface can improve the charge strength of the separator during the battery charging and discharging process, and can also have the effect of charge compensation, which can obviously improve the conduction of lithium ions and stabilize the current system.

[0027] The battery separator prepared by the application can improve the charge strength of the separator during the battery charging and discharging process due to the higher ion concentration on the surface of the anionic polymer crosslinked particles, and can also have the effect of charge compensation. In addition, the anionic polymer crosslinked particles have a unique crosslinking result inside, which can prevent deformation of the material after heat pressing, thereby blocking the pore size and causing problems such as battery cycle diving. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with specific examples. Example 1

[0029] (1) 2.4 g of 3-bromopropene was dissolved in 45.6 g of acetone to obtain a 3-bromopropene acetone solution, 1.7 g of 4,4-bipyridine was dissolved in 32.3 g of acetone to obtain a 4,4-bipyridine acetone solution, then the 4,4-bipyridine acetone solution was added dropwise into the 3-bromopropene acetone solution at 40°C, reacted for 12 h, cooled, collected the precipitated product, then washed with acetone for 3 times, and vacuum dried to obtain a rigid crosslinking agent;

[0030] (2) 2 g of Tween-80, 10 g of Span-83 and 1 g of the rigid crosslinking agent were added into 65 g of solvent oil D100, stirred for 20 min to obtain an oil phase;

[0031] (3) 18 g of methacrylic acid, 5 g of methyl methacrylate, 3 g of acrylamide and 42 g of 2-acrylamido-2-methylpropanesulfonic acid were added into 70 g of deionized water, and the pH value was adjusted to 7.1 by using a sodium hydroxide aqueous solution, then 1 g of ethylene glycol diacrylate was added, and stirred for 20 min to obtain an aqueous phase;

[0032] (4) The aqueous phase was added into the oil phase, pre-emulsified at room temperature and 1000 rpm for 15 min, then high-speed emulsified in an ice bath at 15000 rpm for 5 min, and then nitrogen was passed for 10 min, 10 g of potassium persulfate and 5 g of sodium bisulfite were added, and polymerized at room temperature for 5 h, finally washed with anhydrous ethanol for 3 times, and vacuum dried to obtain an anionic polymer crosslinked particle;

[0033] (5) 10 g of the anionic polymer crosslinked particle, 100 g of inorganic nanoparticles with a particle size D50 of 0.28 μm, 3 g of polymethyl methacrylate, 1 g of sodium polyacrylate, 0.5 g of polyether modified silicone and 20 g of deionized water were mixed, and uniformly coated on one side of a polypropylene base film with a porosity of 45%, and then dried to obtain a lithium ion battery separator with improved ion conduction function. Example 2:

[0034] (1) 2.4 g of 3-bromopropene was dissolved in 45.6 g of acetone to obtain a 3-bromopropene acetone solution, 1.7 g of 4,4-bipyridine was dissolved in 32.3 g of acetone to obtain a 4,4-bipyridine acetone solution, then the 4,4-bipyridine acetone solution was added dropwise into the 3-bromopropene acetone solution at 40°C, reacted for 12 h, cooled, collected the precipitated product, then washed with acetone for 3 times, and vacuum dried to obtain a rigid crosslinking agent;

[0035] (2) 2.5 g of Tween-80, 12 g of Span-83 and 2 g of the rigid crosslinking agent were added into 75 g of solvent oil D100, stirred for 20 min to obtain an oil phase;

[0036] (3) 22 g of methacrylic acid, 6 g of methyl methacrylate, 3.5 g of acrylamide and 50 g of 2-acrylamido-2-methylpropanesulfonic acid were added to 80 g of deionized water, and the pH value was adjusted to 7.4 with sodium hydroxide aqueous solution, then 2 g of ethylene glycol diacrylate was added, and stirred for 25 min to obtain an aqueous phase;

[0037] (4) The aqueous phase was added to the oil phase, stirred at room temperature at 1500 rpm for 10 min, then emulsified at high speed at 20000 rpm in an ice bath for 3 min, then nitrogen was passed for 10-20 min, 12 g of potassium persulfate and 6 g of sodium bisulfite were added, and polymerized at room temperature for 6 h, and finally washed with anhydrous ethanol for 3 times, vacuum dried to obtain anionic polymer cross-linked particles;

[0038] (5) 20 g of anionic polymer cross-linked particles, 150 g of inorganic nanoparticles with a particle size D50 of 0.28 μm, 4 g of polymethyl methacrylate, 2 g of sodium polyacrylate, 0.8 g of polyether modified silicone and 30 g of deionized water were mixed and uniformly coated on both sides of a polypropylene base film with a porosity of 45%, and then dried to obtain a lithium ion battery separator with improved ion conduction function. Example 3:

[0039] (1) 2.4 g of 3-bromopropene was dissolved in 45.6 g of acetone to obtain a 3-bromopropene acetone solution, then 1.7 g of 4,4-bipyridine was dissolved in 32.3 g of acetone to obtain a 4,4-bipyridine acetone solution, then the 4,4-bipyridine acetone solution was added dropwise to the 3-bromopropene acetone solution at 45°C, and reacted for 14 h, cooled, collected the precipitated product, then washed with acetone for 3 times, and vacuum dried to obtain a rigid cross-linking agent;

[0040] (2) 3 g of Tween-80, 15 g of Span-83 and 3 g of rigid cross-linking agent were added to 80 g of solvent oil D100, and stirred for 30 min to obtain an oil phase;

[0041] (3) 25 g of methacrylic acid, 7 g of methyl methacrylate, 4 g of acrylamide and 58 g of 2-acrylamido-2-methylpropanesulfonic acid were added to 90 g of deionized water, and the pH value was adjusted to 7.8 with sodium hydroxide aqueous solution, then 3 g of ethylene glycol diacrylate was added, and stirred for 30 min to obtain an aqueous phase;

[0042] (4) The aqueous phase was added to the oil phase, stirred at room temperature at 1500 rpm for 15 min, then emulsified at high speed at 20000 rpm in an ice bath for 5 min, then nitrogen was passed for 20 min, 14 g of potassium persulfate and 7 g of sodium bisulfite were added, and polymerized at room temperature for 7 h, and finally washed with anhydrous ethanol for 3 times, vacuum dried to obtain anionic polymer cross-linked particles;

[0043] (5) 30 g of the anionic polymer crosslinked particles, 200 g of inorganic nanoparticles with a particle size D50 of 0.28 μm, 5 g of polymethyl methacrylate, 3 g of sodium polyacrylate, 1 g of polyether-modified silicone, and 40 g of deionized water are mixed and uniformly coated on both sides of a polypropylene-based film with a porosity of 45%, and then dried to obtain a lithium ion battery separator with improved ion conduction function. Example 4:

[0044] (1) 2.5 g of Tween-80, 12 g of Span-83, and 75 g of solvent oil D100 are stirred for 20 min to obtain an oil phase;

[0045] (2) 22 g of methacrylic acid, 6 g of methyl methacrylate, 3.5 g of acrylamide, and 50 g of 2-acrylamido-2-methylpropanesulfonic acid are added to 80 g of deionized water, and the pH value is adjusted to 7.3 with a sodium hydroxide aqueous solution, and then 4 g of ethylene glycol diacrylate is added and stirred for 25 min to obtain an aqueous phase;

[0046] (3) The aqueous phase is added to the oil phase, stirred at room temperature at 1500 rpm for 10 min, then emulsified at high speed at 20000 rpm in an ice bath for 3 min, and then nitrogen is passed for 10-20 min, 12 g of potassium persulfate and 6 g of sodium bisulfite are added, and polymerization is carried out at room temperature for 6 h, and finally washed with anhydrous ethanol 3 times and vacuum dried to obtain anionic polymer crosslinked particles;

[0047] (4) 20 g of the anionic polymer crosslinked particles, 150 g of inorganic nanoparticles with a particle size D50 of 0.28 μm, 4 g of polymethyl methacrylate, 2 g of sodium polyacrylate, 0.8 g of polyether-modified silicone, and 30 g of deionized water are mixed and uniformly coated on both sides of a polypropylene-based film with a porosity of 45%, and then dried to obtain a lithium ion battery separator. Example 5:

[0048] (1) 2.5 g of Tween-80, 12 g of Span-83, and 75 g of solvent oil D100 are stirred for 20 min to obtain an oil phase;

[0049] (2) 22 g of methacrylic acid, 6 g of methyl methacrylate, 3.5 g of acrylamide, and 50 g of 2-acrylamido-2-methylpropanesulfonic acid are added to 80 g of deionized water, and the pH value is adjusted to 7.5 with a sodium hydroxide aqueous solution to obtain an aqueous phase;

[0050] (3) The water phase is added to the oil phase, pre-emulsified at room temperature for 10 min at 1500 rpm, high-speed emulsified in an ice bath for 3 min at 20000 rpm, and then nitrogen is passed for 10-20 min. 12 g of potassium persulfate and 6 g of sodium bisulfite are added, and polymerization is carried out at room temperature for 6 h. Finally, the anionic polymer crosslinked particles are washed with anhydrous ethanol for 3 times and vacuum dried to obtain the anionic polymer crosslinked particles;

[0051] (4) 20 g of the anionic polymer crosslinked particles, 150 g of inorganic nanoparticles with a particle size D50 of 0.28 μm, 4 g of polymethyl methacrylate, 2 g of sodium polyacrylate, 0.8 g of polyether modified silicone and 30 g of deionized water are mixed and uniformly coated on both sides of the polypropylene-based film with a porosity of 45%, and then dried to obtain a lithium ion battery separator with improved ion conduction function.

[0052] Comparative Example 1:

[0053] 150 g of inorganic nanoparticles with a particle size D50 of 0.28 μm, 4 g of polymethyl methacrylate, 2 g of sodium polyacrylate, 0.8 g of polyether modified silicone and 30 g of deionized water are mixed and uniformly coated on both sides of the polypropylene-based film with a porosity of 45%, and then dried to obtain a lithium ion battery separator.

[0054] Performance test:

[0055] According to the GB / T6672-2001 "Plastic Film and Sheet Thickness Determination Mechanical Measurement Method" standard, the thickness (μ) of each group of samples in Examples 1-3 and Comparative Examples 1-3 is tested by THI-1801 thickness tester;

[0056] According to the GB / T135I9-2016 standard, the thermal shrinkage rate (%) of each group of samples in Examples 1-3 and Comparative Examples 1-3 is measured by FST-3102 film thermal shrinkage tester after being placed at 130°C for 1 h;

[0057] According to the ISO15105-1:2007 "Plastics-Film and Sheeting Part 1: Diferential pressure Methods" standard, the air permeability value (s / 100ml) of each group of samples in Examples 1-3 and Comparative Examples 1-3 is measured by GTR-704R air permeability tester;

[0058] Each group of samples in Examples 1-3 and Comparative Examples 1-3 is sandwiched between two PET films; the temperature of the hot roller is tested with a temperature measuring gun, and after the set temperature is reached, the roller switch is turned on, and the film is placed parallel into the plastic packaging machine. After the film leaves the plastic packaging machine, the PET film is peeled off, and the adhesion between the separators is tested by a universal testing machine (N / m);

[0059] Conventional and post-heat pressing impedance: tested by impedance analyzer.

[0060] The test results are shown in Table 1.

[0061] Table 1 Performance test results

[0062]

[0063] Data analysis:

[0064] As can be seen from the performance data of Examples 1-5, the lithium ion battery separator prepared by the present application has a lower air permeability value and a higher temperature resistance, and has a higher ion conductivity function, can stabilize the current system, and most importantly, still has a high ion conductivity function after heat pressing, which is mainly due to the high surface ion concentration of the anionic polymer crosslinked particles, which can improve the charge strength of the separator during the battery charging and discharging process, and also has the effect of charge compensation, and due to its unique internal crosslinked structure, it will not block the pore channel after heat pressing.

[0065] As can be seen from the performance data of Examples 2 and 4-5, the polymer particles prepared by using the rigid crosslinking agent provided by the present application can effectively improve the temperature resistance and ion conductivity, and also have a significant contribution to the ion conductivity after heat pressing, which is mainly due to the rigid structure and fully crosslinked internal structure of the polymer particles given by the rigid crosslinking agent, and the coulomb effect between the rigid crosslinking agent and the sulfonic acid group also further improves the compactness of the polymer particles, so that it has a high anion concentration and a low swelling rate, and will not block the pore channel after heat pressing.

[0066] It should be understood by those of ordinary skill in the art that the above discussion of any of the embodiments is only exemplary and is not intended to suggest that the scope of the present application is limited to these examples; under the idea of the present application, the above embodiments or technical features in different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail.

Claims

1. A lithium ion battery separator with improved ionically conductive function, characterized in that, The base film and the adhesive layer on one side or both sides of the base film are included, the adhesive layer contains anionic polymer cross-linked particles and inorganic nano-particles, the anionic polymer cross-linked particles have carbon chain as main chain, and the side chain on the main chain contains carboxylic acid group and sulfonic acid group, the monomers of the anionic polymer cross-linked particles include 18-25 parts of methacrylic acid, 5-7 parts of methyl methacrylate, 3-4 parts of acrylamide, 42-58 parts of 2-acrylamide-2-methylpropanesulfonic acid and 0-6 parts of cross-linking agent.

2. The lithium-ion battery separator with improved ionic conduction function according to claim 1, wherein, The cross-linking agent is a mixture of rigid cross-linking agent and ethylene glycol diacrylate at a weight ratio of 1:

1.

3. The lithium-ion battery separator with improved ionic conduction function according to claim 2, wherein, The preparation method of the rigid cross-linking agent is as follows: 3-bromopropylene is dissolved in acetone to obtain a 3-bromopropylene acetone solution, 4,4-bipyridine is dissolved in acetone to obtain a 4,4-bipyridine acetone solution, then the 4,4-bipyridine acetone solution is added dropwise into the 3-bromopropylene acetone solution at 40-45℃, and the reaction is carried out for 12-14 hours, the precipitated product is collected, washed with acetone for 3 times and dried under vacuum to obtain the rigid cross-linking agent; the molar ratio of 3-bromopropylene to 4,4-bipyridine is 2:1.1; the concentration of the 3-bromopropylene acetone solution is 5wt%, and the concentration of the 4,4-bipyridine acetone solution is 5wt%.

4. The lithium-ion battery separator with improved ionic conduction function according to claim 1, wherein, The base film is one of polyethylene, polypropylene, polymethylpentene, polyvinylidene fluoride, polyimide and non-woven fabric, and the porosity is 30-70%.

5. The lithium-ion battery separator with improved ionic conduction function according to claim 1, wherein, The inorganic nano-particles are one of silicon dioxide, aluminum hydroxide, magnesium hydroxide and boehmite, and the particle size D50 is 0.1-0.5μm.

6. The lithium-ion battery separator with improved ionic conduction function according to claim 1, wherein, The specific preparation steps of the anionic polymer cross-linked particles are as follows: S1: the emulsifier and the rigid cross-linking agent are added into solvent oil D100, stirred for 20-30 minutes to obtain an oil phase; S2: methacrylic acid, methyl methacrylate, acrylamide and 2-acrylamide-2-methylpropanesulfonic acid are added into deionized water, and the pH value is adjusted to 7-8 by using sodium hydroxide aqueous solution, then ethylene glycol diacrylate is added, and stirred for 20-30 minutes to obtain an aqueous phase; S3: the aqueous phase is added into the oil phase, emulsified, and then nitrogen is passed for 10-20 minutes, and potassium persulfate and sodium bisulfite are added, and the polymerization is carried out at room temperature for 5-7 hours, finally washed with anhydrous ethanol for 3 times, and dried under vacuum to obtain the anionic polymer cross-linked particles.

7. A method for producing a lithium ion battery separator having improved ion conductivity according to any one of claims 1 to 6, characterized by, The specific preparation method is as follows: the anionic polymer cross-linked particles, inorganic nano-particles, acrylic adhesive, polyacrylic acid sodium, polyether modified silicone and deionized water are mixed, and then uniformly coated on one side or both sides of the base film, and dried to obtain the lithium ion battery separator with improved ion conduction function.

8. The application of the lithium ion battery separator with improved ion conduction function according to any one of claims 1-6 in lithium ion power battery.

Images