Polymer-based film for composite current collector and method of making

Abstract

The present application relates to the field of current collector film, and particularly relates to a polymer base film for composite current collector and a preparation method, the polymer base film comprises, in terms of weight percentage: 100 parts of PET resin, 2-5 parts of maleic anhydride grafted compatilizer, 4-10 parts of modified boron nitride nanosheet, 0.5-1.5 parts of lubricant, 0.3-0.8 parts of coupling agent, 0.6-1.8 parts of nucleating agent and 0.2-1 parts of antioxidant. The present application takes PET resin as base resin, adds maleic anhydride grafted compatilizer and modified boron nitride nanosheet as reinforcing modifier, and further adds lubricant, nucleating agent and other auxiliaries. The base film prepared by the present application has better improvement in mechanical strength, puncture resistance, heat resistance and stability, and can also maintain good processability, and can meet the requirements of high-performance lithium battery on composite current collector base film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of current collector films, in particular to a polymer base film for composite current collector and a preparation method. BACKGROUND

[0002] With the rapid development of new energy vehicles and electrochemical energy storage industry, the market puts forward higher requirements on the energy density, safety and cost of lithium ion batteries. As a key component of the battery, the current collector plays a core role in collecting current and supporting active materials, and its performance directly affects the overall performance of the battery.

[0003] Traditional current collectors generally use metal foils, such as copper foils for negative electrodes and aluminum foils for positive electrodes. However, metal foil current collectors have many inherent defects: first, the weight accounts for a high proportion of the total weight of the battery (about 10%-15%), which seriously limits the further improvement of the energy density of the battery; second, metal foils are easily affected by electrochemical corrosion and volume change stress during long-term cycling of the battery, especially under high-rate charging and discharging conditions, which may lead to active material shedding, increased internal resistance, and even cause fracture, posing a safety hazard; third, the ductility of metal materials is limited, and internal short circuits may occur under abuse conditions such as battery puncture and extrusion, with a high risk of thermal runaway.

[0004] To overcome the shortcomings of metal current collectors, composite current collector technology has emerged. Currently, the commonly used composite current collectors on the market usually adopt a sandwich structure of "metal-polymer base film-metal", in which the polymer base film is most commonly polyethylene terephthalate (PET). However, PET has poor thermal stability and will shrink and melt severely at high temperatures, which cannot effectively support the metal layer, ultimately leading to failure of the current collector structure.

[0005] Therefore, the development of a new type of current collector base film with excellent thermal stability and good mechanical strength is of great significance to promote the commercial application of high-performance and high-safety composite current collectors. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to provide a polymer base film for composite current collector and a preparation method.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] In a first aspect, the present application provides a polymer base film for composite current collector, comprising, by weight:

[0009] 100 parts of PET resin, 2-5 parts of maleic anhydride grafted compatibilizer, 4-10 parts of modified boron nitride nanosheet, 0.5-1.5 parts of lubricant, 0.3-0.8 parts of coupling agent, 0.6-1.8 parts of nucleating agent and 0.2-1 parts of antioxidant.

[0010] Preferably, the density of the PET resin is 1.38-1.40 g / cm 3 , and the melt index is 15-25 g / 10 min (280℃ / 2.16 kg).

[0011] Preferably, the density of the PET resin is 1.39 g / cm 3 , and the melt index is 22 g / 10 min (280℃ / 2.16 kg).

[0012] Preferably, the maleic anhydride grafted compatibilizer is POE-g-MAH, the grafting rate is 0.7%-0.9%, the density is 0.9-0.94 g / cm 3 , and the melt index is 1.2-3.6 g / 10 min (190℃ / 2.16 kg).

[0013] Preferably, the modified boron nitride nanosheet is a benzoxazine grafted modified boron nitride nanosheet, which is prepared by combining reaction of phenolic hydroxyl functionalized benzoxazine and isocyanate modified boron nitride nanosheet.

[0014] Preferably, the lubricant is at least one of stearic acid, zinc stearate, sodium stearate and calcium stearate.

[0015] Preferably, the coupling agent is at least one of γ-aminopropyl triethoxysilane, γ-epoxypropoxypropyl trimethoxysilane and γ-methacryloyloxypropyl trimethoxysilane.

[0016] Preferably, the nucleating agent is ultra-fine talc powder, and the particle size is 100-200 nm.

[0017] Preferably, the antioxidant includes primary antioxidant 1010 and auxiliary antioxidant 168, and the mass ratio of the primary antioxidant 1010 to the auxiliary antioxidant 168 is 2-4:1.

[0018] Preferably, the preparation method of the isocyanate modified boron nitride nanosheet comprises:

[0019] S1, boron nitride nanosheet and sodium hydroxide solution are weighed and mixed, ball milling in a ball mill at a speed of 150-350 rpm for 10-20 h, filtering out the solid, washing until the washing liquid is neutral, vacuum drying, to obtain hydroxylated boron nitride nanosheet;

[0020] S2, weigh the diisocyanate and the hydroxylated boron nitride nanosheet, and put them into the toluene solution, and then ultrasonic treatment until uniform, and then stir at 60-80℃ for 6-10h, and then centrifugal, washing and drying to obtain the isocyanate-modified boron nitride nanosheet.

[0021] Preferably, in S1, the mass concentration of the sodium hydroxide solution is 5%-10%, and the ratio of the boron nitride nanosheet to the sodium hydroxide solution is 1g:(10-20)mL.

[0022] Preferably, in S2, the ratio of the diisocyanate, the hydroxylated boron nitride nanosheet and the toluene solution is (1.5-2.5)g:1g:(20-40)mL.

[0023] Preferably, the preparation method of the phenolic hydroxyl functionalized benzoxazine comprises:

[0024] Aniline and bisphenol A are added into 1,4-dioxane, and then stirred until dissolved, and then nitrogen gas is introduced as a protective gas, and then paraformaldehyde is slowly added, and then triethylamine is added, and then stirred at 90-120℃ for 6-8h, and then rotary evaporation, washing and drying are performed to obtain the phenolic hydroxyl functionalized benzoxazine (OH-BOZ).

[0025] Preferably, the ratio of aniline, bisphenol A, triethylamine, paraformaldehyde and 1,4-dioxane is 1.86g:(2.14-2.35)g:(0.3-0.6)g:(1.12-1.36)g:(60-100)mL.

[0026] Preferably, the preparation method of the modified boron nitride nanosheet comprises:

[0027] The phenolic hydroxyl functionalized benzoxazine is weighed and added into xylene, and then gradually added into the isocyanate-modified boron nitride nanosheet under the protection of nitrogen gas, and then stirred at 60-70℃ until dissolved, and then a catalyst is added, and then gradually heated to 80-90℃, and then stirred for 5-8h, and then cooled to room temperature, and then precipitated, filtered and washed, and then vacuum dried to obtain the modified boron nitride nanosheet.

[0028] Preferably, the ratio of the phenolic hydroxyl functionalized benzoxazine, the isocyanate-modified boron nitride nanosheet and xylene is (1.8-3.6)g:1g:(10-20)mL.

[0029] Preferably, the catalyst is dibutyltin dilaurate, and the amount of the catalyst is 0.3%-0.5% of the mass of the phenolic hydroxyl functionalized benzoxazine.

[0030] In a second aspect, the present application provides a preparation method of a polymer-based film for a composite current collector, comprising the following steps:

[0031] Step 1, dry the PET resin to a water content of less than 50 ppm, then mix with maleic anhydride grafted compatilizer, modified boron nitride nanosheet, antioxidant, lubricant in a high-speed mixer;

[0032] Step 2, melt blend the mixture of step 1 through a twin-screw extruder, after cooling and pelletizing, obtain a composite master batch;

[0033] Step 3, put the composite master batch into a single-screw extruder, extrude through a T-shaped flat die, shape into a cast sheet on a cooling roller, bidirectional stretch in turn, heat setting treatment, after cooling and edge cutting, wind up to obtain a composite current collector polymer base film.

[0034] The beneficial effects of the present application are:

[0035] 1, the present application prepares a composite current collector polymer base film, PET resin is used as the base resin, maleic anhydride grafted compatilizer and modified boron nitride nanosheet are added as reinforcing modifier, in addition, lubricant, nucleating agent and other additives are also added. Compared with the traditional PET base film, the base film prepared by the present application has better improvement in mechanical strength, puncture resistance, heat resistance and other aspects, while still maintaining good processability, which can meet the requirements of high-performance lithium batteries for composite current collector base film.

[0036] 2, in the present application, the preparation process of modified boron nitride nanosheet is as follows: first, synthesize phenolic hydroxyl functionalized benzoxazine through monoamine and dihydric phenol; then, the phenolic hydroxyl group of phenolic hydroxyl functionalized benzoxazine reacts with the isocyanate group on the surface of boron nitride nanosheet to form a benzoxazine polymer chain containing urethane bond (-NH-COO-).

[0037] 3, the interface bonding ability of traditional boron nitride nanosheet and PET matrix is weak, while the modified boron nitride nanosheet prepared by the present application produces strong interface bonding with PET matrix through urethane bond, which can more effectively transfer stress from the polymer matrix to the boron nitride nanosheet, while realizing the effects of reinforcement and toughening; in addition, both boron nitride nanosheet and benzoxazine structure endow the material with extremely high thermal stability, which can also limit the movement of PET molecular chain at high temperature, significantly reducing its thermal shrinkage.

[0038] 4, after modification by the present application, the boron nitride nanosheet not only has excellent thermal stability and thermal conductivity, but also has good compatibility between the grafted benzoxazine polymer chain on its surface and PET resin, which can fundamentally solve the problems of poor compatibility and easy agglomeration of boron nitride nanosheet in PET matrix. DETAILED DESCRIPTION

[0039] The technical solutions of the present application are described below through specific examples. It should be understood that the one or more method steps mentioned in the present application do not exclude the existence of other method steps before and after the combination steps or the insertion of other method steps between the explicitly mentioned steps; it should also be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. Moreover, unless otherwise stated, the numbering of each method step is only a convenient tool to identify each method step, and not a limitation on the arrangement order or a limitation on the scope of the present application that can be implemented, the change or adjustment of the relative relationship without substantial change of the technical content is also regarded as the scope of the present application that can be implemented.

[0040] In order to better understand the above technical solutions, the exemplary embodiments of the present application are described in more detail below. Although exemplary embodiments of the present application are shown, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0041] The present application is further described below in conjunction with the following examples.

[0042] Example 1

[0043] A polymer-based film for a composite current collector, comprising, in parts by weight:

[0044] 100 parts of PET resin, 3 parts of maleic anhydride grafted compatibilizer, 7 parts of modified boron nitride nanosheet, 1 part of lubricant, 0.5 part of coupling agent, 1.2 parts of nucleating agent and 0.6 parts of antioxidant.

[0045] The density of the PET resin is 1.39 g / cm 3 , and the melt index is 22 g / 10 min (280℃ / 2.16 kg); the maleic anhydride grafted compatibilizer is POE-g-MAH, the grafting rate is 0.8%, the density is 0.92 g / cm 3 , and the melt index is 2.4 g / 10 min (190℃ / 2.16 Kg); the lubricant is zinc stearate; the coupling agent is KH-550 (γ-aminopropyl triethoxysilane); the nucleating agent is ultra-fine talc powder with a particle size of 100-200 nm; the antioxidant includes primary antioxidant 1010 and auxiliary antioxidant 168, and the mass ratio of primary antioxidant 1010 to auxiliary antioxidant 168 is 3:1.

[0046] The preparation method of the modified boron nitride nanosheet includes:

[0047] S1, preparation of isocyanate modified boron nitride nanosheet (BNNS-NCO):

[0048] Take 1 g of boron nitride nanosheet and 15 mL of 6 wt% sodium hydroxide solution, ball mill in a ball mill at 250 rpm for 15 h, filter out the solid, wash until the washing liquid is neutral, vacuum drying, get hydroxylated boron nitride nanosheet (BNNS-OH); take 2 g of diisocyanate and 1 g of hydroxylated boron nitride nanosheet (BNNS-OH); put into 30 mL of toluene solution, ultrasonic uniform, then stir at 70℃ for 8 h, after centrifugation, washing and drying, get isocyanate modified boron nitride nanosheet (BNNS-NCO).

[0049] S2, preparation of phenolic hydroxyl functionalized benzoxazine (OH-BOZ):

[0050] Take 1.86 g of aniline and 2.28 g of bisphenol A into 80 mL of 1,4-dioxane, fully stir to dissolve, then introduce nitrogen as protective gas, slowly add 1.2 g of paraformaldehyde (molecular weight 30 g / mol), then add 0.45 g of triethylamine, stir at 110℃ for 7 h, after reaction, remove the solvent by rotary evaporation, and wash with n-hexane for 3 times, dry in vacuum oven at 60℃ for 18 h, get phenolic hydroxyl functionalized benzoxazine (OH-BOZ).

[0051] S3, preparation of modified boron nitride nanosheet:

[0052] Take 2.5 g of phenolic hydroxyl functionalized benzoxazine (OH-BOZ) into 15 mL of xylene, under the protection of nitrogen, stir at 65℃ until uniform dissolution, then gradually add 1 g of isocyanate modified boron nitride nanosheet (BNNS-NCO), continuously stir during the process, after the BNNS-NCO is completely added, add 0.4% of the mass of OH-BOZ of dibutyltin dilaurate (DBTDL), gradually increase the temperature to 85℃, and stir for 6 h, after reaction, cool the reaction liquid to room temperature, pour into 5 times the volume of 70 wt% ethanol solution, collect the precipitate, filter and wash with ethanol for at least 3 times, dry in vacuum oven at 60℃, get benzoxazine grafted modified boron nitride nanosheet (BZ-g-BNNS), which is the modified boron nitride nanosheet.

[0053] The above method for preparing the composite current collector polymer base film comprises the following steps:

[0054] Step 1, dry the PET resin at 130℃ to a water content of less than 50 ppm, then mix with maleic anhydride grafting compatibilizer, modified boron nitride nanosheet, antioxidant, lubricant in a high-speed mixer, stir for 8 min;

[0055] Step 2, melt blend the mixture of Step 1 by a twin-screw extruder, set the temperature interval of the extruder to 250-275℃, and the screw rotation speed to 300 rpm, after cooling and granulation, obtain the composite master batch;

[0056] Step 3, put the composite master batch into a single-screw extruder, extrude by a T-shaped flat die, shape into a cast sheet on a cooling roller, sequentially stretch in the longitudinal direction (MD) and the transverse direction (TD), the longitudinal stretching temperature is 90℃, the stretching ratio is 3:1; the transverse stretching temperature is 105℃, the stretching ratio is 3:1; then perform heat setting treatment at 230℃, after cooling and edge cutting, wind up to obtain a composite current collector polymer base film with a thickness of 10μm.

[0057] Example 2

[0058] A composite current collector polymer base film, comprising, by weight fraction:

[0059] 100 parts of PET resin, 2 parts of maleic anhydride grafted compatibilizer, 4 parts of modified boron nitride nanosheet, 0.5 parts of lubricant, 0.3 parts of coupling agent, 0.6 parts of nucleating agent, and 0.2 parts of antioxidant.

[0060] The density of the PET resin is 1.39g / cm 3 , and the melt index is 22g / 10min (280℃ / 2.16kg); the maleic anhydride grafted compatibilizer is POE-g-MAH, the grafting rate is 0.8%, the density is 0.92g / cm 3 , and the melt index is 2.4g / 10min (190℃ / 2.16Kg); the lubricant is stearic acid; the coupling agent is KH-560 (γ-glycidoxypropyltrimethoxysilane); the nucleating agent is ultra-fine talc powder, the particle size is 100-200nm; the antioxidant includes main antioxidant 1010 and auxiliary antioxidant 168, the mass ratio of main antioxidant 1010 to auxiliary antioxidant 168 is 2:1. The preparation method of the modified boron nitride nanosheet is the same as that of Example 1.

[0061] The preparation method of the above-mentioned composite current collector polymer base film comprises the following steps:

[0062] Step 1, dry the PET resin at 120℃ to a water content of less than 50ppm, then mix the maleic anhydride grafted compatibilizer, the modified boron nitride nanosheet, the antioxidant, and the lubricant in a high-speed mixer, and stir for 5min;

[0063] Step 2, melt blend the mixture of Step 1 by a twin-screw extruder, set the temperature interval of the extruder to 250-275℃, and the screw rotation speed to 200 rpm, after cooling and granulation, obtain the composite master batch;

[0064] Step 3, the composite master batch is put into a single screw extruder, extruded through a T-shaped flat die, shaped into a cast sheet on a cooling roller, sequentially stretched in the machine direction (MD) and the transverse direction (TD), the machine direction stretching temperature is 85℃, the stretching ratio is 2.5:1; the transverse direction stretching temperature is 100℃, the stretching ratio is 2.5:1; then heat setting treatment is carried out at 220℃, after cooling, edge cutting and winding, a composite current collector polymer base film with a thickness of 6μm is obtained.

[0065] Example 3

[0066] A composite current collector polymer base film, comprising, by weight fraction:

[0067] 100 parts of PET resin, 5 parts of maleic anhydride grafted compatibilizer, 10 parts of modified boron nitride nanosheet, 1.5 parts of lubricant, 0.8 parts of coupling agent, 1.8 parts of nucleating agent and 1 part of antioxidant.

[0068] The density of the PET resin is 1.39g / cm 3 , the melt index is 22g / 10min (280℃ / 2.16kg); the maleic anhydride grafted compatibilizer is POE-g-MAH, the grafting rate is 0.8%, the density is 0.92g / cm 3 , the melt index is 2.4g / 10min (190℃ / 2.16Kg); the lubricant is sodium stearate; the coupling agent is KH-570 (γ-methacryloxypropyltrimethoxysilane); the nucleating agent is ultra-fine talc powder, the particle size is 100-200nm; the antioxidant includes main antioxidant 1010 and auxiliary antioxidant 168, the mass ratio of main antioxidant 1010 to auxiliary antioxidant 168 is 4:1. The preparation method of the modified boron nitride nanosheet is the same as that of Example 1.

[0069] The preparation method of the above-mentioned composite current collector polymer base film comprises the following steps:

[0070] Step 1, the PET resin is dried at 140℃ to a water content of less than 50ppm, then mixed with the maleic anhydride grafted compatibilizer, the modified boron nitride nanosheet, the antioxidant and the lubricant in a high-speed mixer for 10min;

[0071] Step 2, the mixture of Step 1 is melt blended through a twin screw extruder, the temperature interval of the extruder is set to 250-275℃, the screw rotation speed is 350rpm, after cooling and granulation, a composite master batch is obtained;

[0072] Step 3, the composite master batch was put into a single screw extruder, extruded through a T-shaped flat die, and formed into a cast sheet on a cooling roller. The cast sheet was sequentially stretched in the machine direction (MD) and the transverse direction (TD) at a stretching temperature of 95°C and a stretching ratio of 3.5:1 in the MD and a stretching temperature of 110°C and a stretching ratio of 3.5:1 in the TD. Then, the cast sheet was subjected to heat setting at 240°C, cooled, trimmed, and wound to obtain a polymer base film for a composite current collector with a thickness of 14 μm.

[0073] Example 4

[0074] A polymer base film for a composite current collector, which is different from that of Example 1 only in that the preparation method of the modified boron nitride nanosheet is different.

[0075] The preparation method of the modified boron nitride nanosheet comprises:

[0076] S1, preparation of isocyanate-modified boron nitride nanosheet (BNNS-NCO):

[0077] 1 g of boron nitride nanosheet was mixed with 10 mL of 5 wt% sodium hydroxide solution, ball milled in a ball mill at a speed of 150 rpm for 10 h, and the solid was filtered out, washed until the washing liquid was neutral, and vacuum dried to obtain hydroxylated boron nitride nanosheet (BNNS-OH); 1.5 g of diisocyanate and 1 g of hydroxylated boron nitride nanosheet (BNNS-OH) were put into 20 mL of toluene solution, uniformly ultrasonicated, and then stirred at 60°C for 6 h. After centrifugation, washing, and drying, isocyanate-modified boron nitride nanosheet (BNNS-NCO) was obtained.

[0078] S2, preparation of phenolic hydroxyl functionalized benzoxazine (OH-BOZ):

[0079] 1.98 g of 4,4'-diaminodiphenyl methane and 2.14 g of bisphenol A were added to (60-100) mL of 1,4-dioxane, fully stirred and dissolved, and then nitrogen was introduced as a protective gas. 1.12 g of paraformaldehyde (molecular weight 30 g / mol) was slowly added, followed by the addition of 0.3 g of triethylamine. The mixture was stirred at 110°C for 7 h. After the reaction was completed, the solvent was removed by rotary evaporation, and the product was washed with n-hexane for 3 times. The product was dried in a vacuum oven at 60°C for 18 h to obtain phenolic hydroxyl functionalized benzoxazine (OH-BOZ).

[0080] S3, preparation of modified boron nitride nanosheet:

[0081] Take 1.8 g of phenolic hydroxyl functionalized benzoxazine (OH-BOZ) into 10 mL of xylene, stir at 60°C under the protection of nitrogen until it is uniformly dissolved, then gradually add 1 g of isocyanate modified boron nitride nanosheet (BNNS-NCO), continuously stir during the process, after the BNNS-NCO is completely added, add 0.3% of the mass of OH-BOZ of dibutyltin dilaurate (DBTDL), gradually warm up to 80°C, and keep stirring for 5 h. After the reaction is completed, cool the reaction liquid to room temperature, pour it into 5 times the volume of 70 wt% ethanol solution, collect the precipitate, filter and wash with ethanol at least 3 times, and dry in a vacuum oven at 60°C to obtain benzoxazine grafted modified boron nitride nanosheet (BZ-g-BNNS), which is a modified boron nitride nanosheet.

[0082] Example 5

[0083] A composite current collector polymer base film, which is only different from example 1 in that the preparation method of the modified boron nitride nanosheet is different.

[0084] The preparation method of the modified boron nitride nanosheet comprises:

[0085] S1, preparation of isocyanate modified boron nitride nanosheet (BNNS-NCO):

[0086] Take 1 g of boron nitride nanosheet and mix with 20 mL of 10 wt% sodium hydroxide solution, ball mill in a ball mill at a speed of 350 rpm for 20 h, filter out the solid, wash until the washing liquid is neutral, and vacuum dry to obtain hydroxylated boron nitride nanosheet (BNNS-OH); take 2.5 g of diisocyanate and 1 g of hydroxylated boron nitride nanosheet (BNNS-OH); pour into 40 mL of toluene solution, ultrasonically uniform, then stir at 80°C for 10 h, after centrifugation, washing and drying, obtain isocyanate modified boron nitride nanosheet (BNNS-NCO).

[0087] S2, preparation of phenolic hydroxyl functionalized benzoxazine (OH-BOZ):

[0088] Take 1.98 g of 4,4'-diaminodiphenyl methane and 2.35 g of bisphenol A into (60-100) mL of 1,4-dioxane, stir to dissolve, then introduce nitrogen as a protective gas, slowly add 1.36 g of paraformaldehyde (molecular weight 30 g / mol), then add 0.6 g of triethylamine, stir at 110°C for 7 h, after the reaction is completed, remove the solvent by rotary evaporation, and wash with n-hexane 3 times, dry in a vacuum oven at 60°C for 18 h to obtain phenolic hydroxyl functionalized benzoxazine (OH-BOZ).

[0089] S3, preparation of modified boron nitride nanosheet:

[0090] Take 3.6 g of phenolic hydroxyl functionalized benzoxazine (OH-BOZ) into 20 mL of xylene, stir at 70°C under the protection of nitrogen until it is uniformly dissolved, then gradually add 1 g of isocyanate-modified boron nitride nanosheet (BNNS-NCO), continuously stirring during the process, after the BNNS-NCO is completely added, add 0.5% of the mass of OH-BOZ of dibutyltin dilaurate (DBTDL), gradually warm up to 90°C, and keep stirring for 8 h. After the reaction is completed, cool the reaction liquid to room temperature, pour it into 5 times the volume of 70 wt% ethanol solution, collect the precipitate, filter and wash with ethanol at least 3 times, and dry in a vacuum oven at 60°C to obtain benzoxazine grafted modified boron nitride nanosheet (BZ-g-BNNS), which is a modified boron nitride nanosheet.

[0091] Comparative Example 1

[0092] A composite current collector polymer base film, which is the same as Example 1 except that the modified boron nitride nanosheet is replaced by isocyanate-modified boron nitride nanosheet (BNNS-NCO).

[0093] Comparative Example 2

[0094] A composite current collector polymer base film, which is the same as Example 1 except that the modified boron nitride nanosheet is replaced by conventional boron nitride nanosheet and phenolic hydroxyl functionalized benzoxazine (OH-BOZ), and the mass ratio of boron nitride nanosheet to phenolic hydroxyl functionalized benzoxazine (OH-BOZ) is 1:2.5, and the preparation of phenolic hydroxyl functionalized benzoxazine (OH-BOZ) is the same as Example 1.

[0095] Experimental Example

[0096] The performance of the polymer base film prepared in Example 1, Comparative Examples 1-2 was tested, and the tests were conducted in accordance with the national or international standard.

[0097] The detection items include:

[0098] Tensile strength (referring to GB / T 1040.3-2006), elongation at break (referring to GB / T 1040.3-2006), elastic modulus (referring to GB / T 1040.3-2006); puncture strength (referring to GB / T 10004-2008); thermal shrinkage (150°C, 30 min, referring to GB / T 12027-2004).

[0099] The test results are shown in Table 1:

[0100] Table 1 Performance test results of polymer base film

[0101]

[0102] From the detection results of Table 1, it can be seen that the mechanical properties, puncture resistance and thermal stability of the polymer-based film prepared in Example 1 are all excellent. The strength, thermal stability and puncture resistance of Comparative Example 1 are all poorer than those of Example 1, indicating that the isocyanate-modified boron nitride nanosheet alone performs worse than the modified boron nitride nanosheet; Comparative Example 2, although introducing phenolic hydroxyl functionalized benzoxazine, performs the worst, and the most likely reason is that the dispersion of boron nitride nanosheet is poor, resulting in weak interfacial bonding, which becomes a defect of the overall stress.

[0103] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and integrate different embodiments or examples described in the present specification.

[0104] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A polymer-based membrane for composite current collectors, characterized in that, Calculated by weight, including: 100 parts PET resin, 2-5 parts maleic anhydride graft compatibilizer, 4-10 parts modified boron nitride nanosheets, 0.5-1.5 parts lubricant, 0.3-0.8 parts coupling agent, 0.6-1.8 parts nucleating agent and 0.2-1 parts antioxidant; The modified boron nitride nanosheets are benzoxazine-grafted modified boron nitride nanosheets, which are prepared by combining phenolic hydroxyl-functionalized benzoxazine with isocyanate-modified boron nitride nanosheets.

2. The polymer-based membrane for composite current collectors according to claim 1, characterized in that, The density of the PET resin is 1.38-1.40 g / cm³. 3 The melt flow index is 15-25 g / 10 min at 280℃ and 2.16 kg; the maleic anhydride graft compatibilizer is POE-g-MAH, with a grafting rate of 0.7%-0.9% and a density of 0.9-0.94 g / cm³. 3 The melt index is 1.2-3.6 g / 10 min at 190℃ and 2.16 kg.

3. The polymer-based membrane for composite current collectors according to claim 1, characterized in that, The lubricant is at least one of stearic acid, zinc stearate, sodium stearate, and calcium stearate; the coupling agent is at least one of γ-aminopropyltriethoxysilane, γ-epoxypropoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

4. The polymer-based membrane for composite current collectors according to claim 1, characterized in that, The nucleating agent is ultrafine talc powder with a particle size of 100-200 nm; the antioxidant includes primary antioxidant 1010 and secondary antioxidant 168, and the mass ratio of primary antioxidant 1010 to secondary antioxidant 168 is 2-4:

1.

5. The polymer-based membrane for composite current collectors according to claim 1, characterized in that, The method for preparing the modified boron nitride nanosheets includes: Phenolic hydroxyl-functionalized benzoxazine was weighed and added to xylene. Under nitrogen protection, the mixture was stirred at 60-70℃ until it was uniformly dissolved. Isocyanate-modified boron nitride nanosheets were gradually added, followed by a catalyst. The temperature was gradually increased to 80-90℃ and stirred for 5-8 hours. After the reaction was completed, the mixture was cooled to room temperature, precipitated, filtered, washed, and vacuum dried to obtain modified boron nitride nanosheets.

6. The polymer-based membrane for composite current collectors according to claim 5, characterized in that, The ratio of phenol hydroxyl-functionalized benzoxazine, isocyanate-modified boron nitride nanosheets, and xylene was (1.8-3.6) g:1 g:(10-20) mL; the catalyst was dibutyltin dilaurate, and the amount added was 0.3%-0.5% of the mass of phenol hydroxyl-functionalized benzoxazine.

7. The polymer-based membrane for composite current collectors according to claim 1, characterized in that, The method for preparing the isocyanate-modified boron nitride nanosheets includes: Boron nitride nanosheets were weighed and mixed with sodium hydroxide solution, ball-milled, washed, and vacuum dried to obtain hydroxylated boron nitride nanosheets; diisocyanate and hydroxylated boron nitride nanosheets were weighed and added to toluene, ultrasonically homogenized, stirred at 60-80℃ for 6-10 h, and after centrifugation, washing and drying, isocyanate-modified boron nitride nanosheets were obtained; wherein the ratio of diisocyanate, hydroxylated boron nitride nanosheets and toluene was (1.5-2.5) g: 1 g: (20-40) mL.

8. The polymer-based membrane for composite current collectors according to claim 1, characterized in that, The preparation method of the phenolic hydroxyl-functionalized benzoxazine includes: Aniline and bisphenol A were added to 1,4-dioxane and stirred until dissolved. Nitrogen gas was introduced as a protective gas, and paraformaldehyde was slowly added, followed by triethylamine. The mixture was stirred and reacted at 90-120°C for 6-8 hours. After the reaction was completed, the mixture was rotary evaporated, washed, and dried to obtain phenol-hydroxyl-functionalized benzoxazine.

9. A polymer-based membrane for composite current collectors according to claim 8, characterized in that, The ratio of aniline, bisphenol A, triethylamine, paraformaldehyde and 1,4-dioxane is 1.86 g:(2.14-2.35) g:(0.3-0.6) g:(1.12-1.36) g:(60-100) mL.

10. A method for preparing a polymer-based film for composite current collectors according to claim 1, characterized in that, Includes the following steps: Step 1: Dry the PET resin to a moisture content of less than 50 ppm, and then mix it with maleic anhydride graft compatibilizer, modified boron nitride nanosheets, antioxidant, and lubricant in a high-speed mixer. Step 2: The mixture from Step 1 is melt-blended using a twin-screw extruder. After cooling and pelletizing, a composite masterbatch is obtained. Step 3: The composite masterbatch is fed into a single-screw extruder and extruded through a T-die. It is then formed into a cast sheet on a cooling roller, stretched bidirectionally, heat-set, cooled, trimmed, and wound up to obtain a polymer-based film for composite current collectors.

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