High-heat-resistance battery diaphragm and preparation method thereof

Abstract

The invention discloses a high-heat-resistance battery diaphragm and a preparation method thereof, and relates to the technical field of lithium ion battery diaphragms. The high heat-resistant battery diaphragm is prepared from the following components in parts by mass: 40 to 60 parts of heat-resistant polymer matrix, 20 to 40 parts of inorganic heat-resistant filler, 5 to 15 parts of pore-forming agent, 3 to 10 parts of flexibilizer, 2 to 10 parts of stabilizer and 0.5 to 5 parts of coupling agent. Through the synergistic effect of the stabilizer with a specific structure and the formula, the high-temperature resistance of the diaphragm is remarkably enhanced, high-temperature deformation and thermal degradation are inhibited, and meanwhile, the flame retardance is greatly improved. The dispersity of the inorganic filler is improved through the synergistic effect of the stabilizer and the coupling agent, a more uniform through micropore structure is formed by combining the reasonable proportion of the pore-forming agent and the flexibilizer, and the porosity and the liquid absorption rate are remarkably improved. While high heat resistance is maintained, the problem that mechanical strength is reduced or an ion channel is blocked due to a traditional modification technology is avoided, and synchronous optimization of heat resistance, electrolyte wettability and mechanical flexibility is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery separators, and in particular to a high-heat-resistant battery separator and a preparation method thereof. Background Art

[0002] With the rapid development of new energy technologies, lithium-ion batteries, as efficient, rechargeable energy storage devices, have been widely used in electric vehicles, energy storage systems, and consumer electronics. However, battery safety and reliability remain key factors restricting their further development. Battery separators, as a crucial component of lithium-ion batteries, play a vital role in their performance, safety, and lifespan.

[0003] Traditional battery separators typically use polyolefin materials, such as polypropylene (PP) and polyethylene (PE), which offer excellent chemical stability and a certain degree of mechanical strength. However, at high temperatures, polyolefin separators are prone to shrinkage, deformation, and even melting, leading to internal short circuits in the battery, thermal runaway, and potentially fires, explosions, and other safety incidents, seriously threatening the safety of users and property. Furthermore, polyolefin separators have limited oxidation resistance, making them difficult to meet the stringent requirements placed on separators during the charging and discharging processes of high-energy-density batteries.

[0004] During the development of high-energy-density batteries, the redox reaction within the battery becomes more intense, generating more heat and oxidizing substances. The separator needs to possess higher heat and oxidation resistance to maintain the stability of the battery's internal structure and ensure smooth lithium-ion transmission channels. At the same time, with the continuous expansion of battery application scenarios, such as rapid charging of electric vehicles, operation in high-temperature environments, and long-term charge and discharge cycles in energy storage systems, the comprehensive performance requirements for battery separators are becoming increasingly stringent.

[0005] Currently, industry research on improving the heat and oxidation resistance of battery separators is primarily focused on material modification and composite technologies. For example, inorganic heat-resistant fillers are added to the polyolefin matrix to improve the separator's heat resistance, while surface coating technology is used to enhance the separator's oxidation resistance. However, existing technologies still have many shortcomings: on the one hand, some modification methods are complex and costly, making large-scale industrial production difficult; on the other hand, while improving certain properties, some composite separators often lead to degradation of other properties, such as reduced mechanical strength and decreased lithium-ion conductivity. This makes it impossible to achieve a performance balance, thus limiting their widespread application in the field of high-end batteries.

[0006] Therefore, the development of a battery separator and its preparation method that has high heat resistance and oxidation resistance, excellent comprehensive performance and is suitable for large-scale production has become a key issue that needs to be urgently solved in the current field of battery separator technology, and it has extremely important practical significance for promoting the sustainable development of the new energy industry. Summary of the Invention

[0007] The purpose of the present invention is to provide a highly heat-resistant and oxidation-resistant battery separator that takes into account both mechanical strength and ionic conductivity, so as to solve the performance degradation problem of existing separators in high temperature and oxidative environments and improve the safety and service life of the battery.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a high heat-resistant battery separator, comprising the following components in the following weight ratios: a heat-resistant polymer matrix: 40-60 parts, an inorganic heat-resistant filler: 20-40 parts, a pore-forming agent: 5-15 parts, a toughening agent: 3-10 parts, a stabilizer: 2-10 parts, and a coupling agent: 0.5-5 parts; The stabilizer is a compound represented by Formula 1; Formula 1; The R1 is selected from the group consisting of: methyl, ethyl, propyl, tert-butyl, phenyl, and methoxy.

[0009] Furthermore, the heat-resistant polymer matrix is ​​selected from: polyimide or polyetheretherketone.

[0010] Furthermore, the inorganic heat-resistant filler is selected from: alumina and / or silica, with an average particle size ranging from 50 to 500 nm.

[0011] Furthermore, the pore-forming agent is selected from polyethylene glycol or polyvinyl pyrrolidone.

[0012] Furthermore, the toughening agent is selected from: dioctyl phthalate.

[0013] Furthermore, the stabilizer is selected from any one of the compounds shown in the following structures: ; .

[0014] Furthermore, the synthesis method of the stabilizer is: ; Step 1: Raw materials 1 and 2 are reacted by Williamson reaction to synthesize intermediate 1; Step 2: Intermediate 1 and raw material 3 are subjected to Buchwald-Hartwig arylation reaction to synthesize a stabilizer.

[0015] Furthermore, the coupling agent is selected from: γ-aminopropyltriethoxysilane.

[0016] A method for preparing a high-heat-resistant battery separator comprises the following steps: S1. The heat-resistant polymer matrix is ​​dissolved in a solvent at 80-100 ℃ to form a glue having a mass concentration of 10-20%; S2. Adding an inorganic heat-resistant filler, a pore-forming agent, a toughening agent, a stabilizer and a coupling agent to the glue solution and homogeneously dispersing the coating slurry; S3. The coating slurry is applied to the substrate and dried to form a film; S4. After extracting the pore-forming agent, drying is performed to obtain a highly heat-resistant battery separator.

[0017] Furthermore, the solvent is N-methylpyrrolidone.

[0018] Furthermore, the homogeneous dispersion is carried out using a shear emulsifier at 1500-2000 rpm for 0.5-2 h.

[0019] Furthermore, the drying temperature is 80-150° C., and the drying time is 1-3 hours.

[0020] Furthermore, the extraction solvent is deionized water or ethanol, and the extraction time is 10-30 minutes.

[0021] The molecular structure of the stabilizer described in the present invention contains a rigid aromatic ring and an electron-donating group. The phenolic hydroxyl group and / or nitrogen-containing heterocyclic structure in the molecular structure can provide hydrogen atoms to quench the free radicals generated during the charge and discharge process of the battery and interrupt the oxidation chain reaction. Large steric groups (such as tert-butyl and phenyl) slow down the molecular chain breakage of the polymer matrix at high temperature through the spatial steric effect, thereby inhibiting the thermal degradation of the diaphragm. The polar groups in the stabilizer form hydrogen bonds with the surface of the inorganic filler, and at the same time, through the synergistic effect of the coupling agent, the following are achieved: reducing filler agglomeration and improving dispersion uniformity; strengthening the filler-polymer interface bonding force and preventing the failure of the diaphragm structure caused by interface peeling at high temperature. The low oxidation potential characteristics of the stabilizer can preferentially cause a passivation reaction on the electrode surface to form a stable solid electrolyte interface film, reduce electrolyte side reactions, and extend the battery cycle life.

[0022] The heat-resistant polymer matrix described in the present invention provides a rigid skeleton with a glass transition temperature much higher than that of traditional polyolefins. As a continuous phase, it supports the stability of the diaphragm structure and resists high-temperature deformation. The inorganic heat-resistant filler inhibits heat conduction through physical barriers, reduces the risk of melting, forms hydrogen bonds with the polar groups of the stabilizer, and improves dispersibility; the coupling agent strengthens the interface bonding with the polymer to prevent the filler from falling off at high temperatures. The stabilizer contains a phenolic hydroxyl / nitrogen-containing heterocyclic structure to provide triple protection: the phenolic hydroxyl group captures the free radicals generated by battery charging and discharging, interrupting the oxidation chain reaction; large steric groups such as tert-butyl / phenyl shield the polymer main chain and inhibit high-temperature chain scission; the polar group forms a hydrogen bond network with the filler surface; and together with the coupling agent, optimizes the filler-matrix interface to reduce interfacial thermal stress failure. The siloxane group of the coupling agent is hydrolyzed and bonds with the filler, bridging the inorganic filler and the organic phase, and improving the interfacial compatibility at high temperatures. After extraction, the pore former and toughening agent form through micropores to ensure ionic conductivity; the plasticizing effect offsets the brittleness caused by the filler and maintains the flexibility of the diaphragm. The pores formed by the pore former and the toughening agent work together to avoid ion channel blockage and mechanical property degradation caused by high filler content.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. Synergistically improve thermal stability and flame retardancy: Through the synergistic effect of stabilizers with specific structures and formulas, the high-temperature resistance of the diaphragm is significantly enhanced, high-temperature deformation and thermal degradation are inhibited, and flame retardancy is greatly improved.

[0024] 2. Optimize pore structure and electrolyte wettability: The synergistic effect of stabilizer and coupling agent improves the dispersibility of inorganic filler. Combined with the reasonable ratio of pore former and toughening agent, a more uniform through-microporous structure is formed, which significantly improves porosity and liquid absorption rate.

[0025] 3. Breakthrough in performance balance bottleneck: While maintaining high heat resistance, avoid the problems of mechanical strength degradation or ion channel blockage caused by traditional modification technologies, and achieve simultaneous optimization of heat resistance, electrolyte wettability and mechanical flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The stabilizer 1 of the present invention 1 HNMR spectrum.

[0027] Figure 2 The invention relates to a method for synthesizing the stabilizer. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Synthesis example 1 Synthesis of stabilizer 1: ; Step 1: Under a nitrogen atmosphere, 20 g of raw material 1, 17.65 g of raw material 2, 0.07 g of pyridine-2-carboxylic acid, 0.6 g of CuI, 32.85 g of potassium phosphate trihydrate, and 250 g of DMSO were added to the reaction system, and the mixture was heated to 85° C. and reacted for 16 hours; after cooling, the reaction mixture was extracted with an ammonia solution and methyl tert-butyl ether, and the organic phase was washed five times with water and then twice with a saturated NaCl solution; finally, the combined organic phase was dried over anhydrous magnesium sulfate, spin-dried, and chromatographed on a silica gel column using a mixture of petroleum ether and ethyl acetate as an eluent to obtain 22.12 g of intermediate 1.

[0030] Step 2: Under a nitrogen atmosphere, 22.45 g of intermediate 1, 23.95 g of raw material 3, 8.44 g of sodium tert-butoxide, 1.21 g of tris(dibenzylideneacetone)dipalladium, 0.4 g of tri-tert-butylphosphine and 250 g of toluene were added to the reaction system, stirred evenly, heated to 110 ° C, and refluxed for 12 hours; after the reaction was completed, the temperature was slightly lowered, and diatomaceous earth was used for filtration to remove salt and catalyst. After the filtrate was cooled to room temperature, it was washed three times with water, the organic phase was retained, and the aqueous phase was extracted with ethyl acetate; after the organic phases were combined, they were dried with anhydrous magnesium sulfate, spin-dried, and chromatographed on a silica gel column using a mixture of petroleum ether and ethyl acetate as an eluent to obtain 29.91 g of stabilizer 1.

[0031] Product structure identification: MS [MS+1] of intermediate 1: 504; MS of stabilizer 1 [MS+1]: 918; 1HNMR of stabilizer 1-dChloroform- Figure 1: δ8.17(dd,2H),8.05(d,2H),7.87-7.79(m,1H),7.73(m,1H),7.68-7.55(m,6H),7.44-7.31(m,6H),7.23(m,2H),7.09(m,1H) ,6.94(dd,1H),6.39(p,1H),4.80(d,1H),4.56-4.48(m,1H),4.39(d,1H),4.06-3.55(m,9H),2.49(d,3H),1.07-1.00(m,9H).

[0032] Synthesis Example 2-Synthesis Example 6 Synthesis Examples 2-6: Stabilizers 2-6 were synthesized sequentially, following the same method as in Synthesis Example 1 except that Raw Material 2 was substituted. The structures of Raw Material 2, Stabilizers 2-6, and MS [MS+1] data are shown in Table 2.

[0033] Table 2. Structure of starting material 2, stabilizer 2-stabilizer 6 and MS [MS+1] data involved in Synthesis Examples 2-6.

[0034]

[0035] Example 1 Preparation of a high heat-resistant battery separator: 1. Raw materials mass ratio: 50 parts of heat-resistant polymer matrix (polyimide), 30 parts of inorganic heat-resistant filler (aluminum oxide, average particle size range 200nm), 10 parts of pore-forming agent (polyethylene glycol), 5 parts of toughening agent (dioctyl phthalate), 5 parts of stabilizer (stabilizer 1 prepared in Synthesis Example 1), 2 parts of coupling agent (γ-aminopropyltriethoxysilane) 2. Preparation method: S1. The heat-resistant polymer matrix was added to the reactor, 400 parts of N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred and dissolved at 90 ° C for 2 hours to form a glue solution with a mass concentration of 12.5%; S2. An inorganic heat-resistant filler, a pore-forming agent, a toughening agent, a stabilizer and a coupling agent were added to the glue solution and homogenized and dispersed at a speed of 1800 rpm using a shear emulsifier for 1.5 hours to obtain a uniform and stable coating slurry; S3. The coating slurry is coated on a polyethylene terephthalate (PET) substrate, and the wet film thickness is controlled at 200 μm; dried at 120 ° C for 2 hours to form an initial diaphragm; S4. The initial separator was immersed in deionized water and extracted at room temperature for 20 minutes to remove the polyethylene glycol pore-forming agent; after removal, the separator was vacuum-dried at 100°C for 1 hour to obtain a final high-heat-resistant battery separator.

[0036] Example 2-Example 6 A high heat-resistant battery separator was prepared by referring to the preparation method of Example 1, wherein the stabilizer was replaced with stabilizer 2 to stabilizer 6 prepared in Synthesis Examples 2 to 6 in sequence, and the rest remained the same as Example 1.

[0037] Comparative Example 1 A high heat-resistant battery separator was prepared by referring to the preparation method of Example 1, except that the stabilizer was replaced by comparative compound 1, and the rest remained the same as Example 1.

[0038] Comparative compound 1: .

[0039] Comparative Example 2 A high heat-resistant battery separator was prepared by referring to the preparation method of Example 1, except that the stabilizer was not added, and the rest of the steps were the same as those of Example 1.

[0040] Comparative Example 3 A high heat-resistant battery separator was prepared by referring to the preparation method of Example 1, except that the mass fraction of the heat-resistant polymer matrix was changed to 65 parts, and the rest remained the same as Example 1.

[0041] Performance testing: 1. Porosity: The high heat-resistant battery separators prepared in the examples and comparative examples were tested for porosity according to the standard GB / T21650.2-2008.

[0042] 2. Liquid absorption rate test: A high heat-resistant battery separator prepared in the embodiment and comparative example was immersed in the electrolyte, taken out and weighed after 2 hours, and the liquid absorption rate was calculated based on the weight change before and after. The electrolyte composition was: 1 mol / L LiPF6 ethylene carbonate and dimethyl carbonate solution, wherein the volume ratio of the solvent ethylene carbonate and dimethyl carbonate was 1:1.

[0043] 3. Limiting Oxygen Index: The high heat-resistant battery separators prepared in the examples and comparative examples were tested for limiting oxygen index according to the standard JIS-K7201-3-2008.

[0044] See Table 2 for data.

[0045] Table 2. Porosity, liquid absorption rate, and limiting oxygen index data of a high-heat-resistant battery separator prepared in the examples and comparative examples.

[0046]

[0047] The porosity, liquid absorption rate and limiting oxygen index of the embodiments of the present invention are significantly better than those of the comparative examples. The porosity and liquid absorption rate of the embodiments are generally higher, while those of the comparative examples are significantly lower; the limiting oxygen index of the embodiments is generally much higher than that of the comparative examples, indicating that they have better thermal stability. When the comparative examples do not add stabilizers or use invalid stabilizers, the performance deteriorates overall, and the liquid absorption rate drops sharply when the matrix ratio is adjusted. This shows that the stabilizer and formula design of the present invention can synergistically improve the comprehensive performance of the diaphragm, and have significant advantages in maintaining a high porosity structure, electrolyte wettability and flame retardancy.

[0048] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A high heat-resistant battery separator, characterized in that: The invention comprises the following components in the following mass ratios: heat-resistant polymer matrix: 40-60 parts, inorganic heat-resistant filler: 20-40 parts, pore-forming agent: 5-15 parts, toughening agent: 3-10 parts, stabilizer: 2-10 parts, coupling agent: 0.5-5 parts; The stabilizer is a compound represented by Formula 1; Formula 1; The R1 is selected from the group consisting of: methyl, ethyl, propyl, tert-butyl, phenyl, and methoxy.

2. A high heat-resistant battery separator according to claim 1, characterized in that: The heat-resistant polymer matrix is ​​selected from: polyimide or polyetheretherketone.

3. A high heat-resistant battery separator according to claim 1, characterized in that: The inorganic heat-resistant filler is selected from: alumina and / or silica, and has an average particle size range of 50-500 nm.

4. A high heat-resistant battery separator according to claim 1, characterized in that: The pore-forming agent is selected from polyethylene glycol or polyvinyl pyrrolidone.

5. A high heat-resistant battery separator according to claim 1, characterized in that: The toughening agent is selected from: dioctyl phthalate.

6. A high heat-resistant battery separator according to claim 1, characterized in that: The stabilizer is selected from any one of the compounds shown in the following structures: ； 。 7. The high heat-resistant battery separator according to claim 1, characterized in that: The coupling agent is selected from: γ-aminopropyltriethoxysilane.

8. A method for preparing a high heat-resistant battery separator according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. The heat-resistant polymer matrix is ​​dissolved in a solvent at 80-100 ℃ to form a glue having a mass concentration of 10-20%; S2. Adding an inorganic heat-resistant filler, a pore-forming agent, a toughening agent, a stabilizer and a coupling agent to the glue solution, and homogeneously dispersing the coating slurry; S3. The coating slurry is applied to the substrate and dried to form a film; S4. After extracting the pore-forming agent, drying is performed to obtain a highly heat-resistant battery separator.

9. The method for preparing a high heat-resistant battery separator according to claim 8, characterized in that: The solvent is N-methylpyrrolidone; the homogeneous dispersion is carried out using a shear emulsifier at 1500-2000 rpm for 0.5-2 hours.

10. The method for preparing a high heat-resistant battery separator according to claim 8, characterized in that: The drying temperature is 80-150° C., and the drying time is 1-3 hours. The extraction solvent is deionized water or ethanol, and the extraction time is 10-30 minutes.

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