CN114374056B

CN114374056B - Polyimide composite diaphragm, preparation method thereof and lithium ion battery

Info

Publication number: CN114374056B
Application number: CN202210015035.7A
Authority: CN
Inventors: 黄佳苑; 冀亚娟; 黎中利
Original assignee: Eve Energy Co Ltd
Current assignee: Eve Energy Co Ltd
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2024-03-15
Anticipated expiration: 2042-01-07
Also published as: CN114374056A

Abstract

The invention provides a polyimide composite diaphragm, a preparation method thereof and a lithium ion battery. The polyimide composite diaphragm comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a polymer coating coated on the other side of the polyimide base film. According to the polyimide composite membrane provided by the invention, the ceramic coating and the polymer coating are respectively coated on the surface of the polyimide base membrane, the coated polymer coating can improve the thermal stability of the membrane, the mechanical strength of the membrane is improved by adding the ceramic coating, the polyimide composite membrane has better air permeability, heat-resistant stability, high ion conductivity, electrolyte wettability and electrolyte retention rate, and the cycle life and the safety performance of a lithium ion battery are further improved.

Description

Polyimide composite diaphragm, preparation method thereof and lithium ion battery

Technical Field

The invention belongs to the field of battery materials, and particularly relates to a polyimide composite diaphragm, a preparation method thereof and a lithium ion battery.

Background

With the development of electronic equipment and electric automobile industry, ceramic coated diaphragms are widely applied to the field of electric automobile batteries. In the structure of the lithium ion battery, the lithium ion battery diaphragm is taken as one of main components, can play a role in isolating the anode and the cathode and allowing lithium ions to be transmitted between the anode and the cathode, the performance of the lithium ion battery diaphragm determines the interface structure, the internal resistance, the thermal stability and the like of the battery, and directly influences the characteristics of the battery such as capacity, the cycle life, the safety and the like, and potential safety hazards such as thermal runaway, lithium dendrites and short circuit are avoided, so that the diaphragm with excellent performance has an important role in improving the comprehensive performance of the battery. However, the conventional polyolefin separator has problems of poor heat resistance, poor liquid retention and poor electrolyte wettability, so that it is necessary to develop a high-performance lithium ion battery separator.

Currently, lithium ion battery separators are mainly divided into three types: the first type is a multilayer diaphragm (PP/PE and PP/PE/PP) with higher fusing temperature and lower closed pore temperature, so that the safety performance and the cycle life of the lithium ion battery are improved; the second type is a surface modified diaphragm, for example, a silicon dioxide ceramic layer is coated on the surface of a single-layer polyethylene or polypropylene, so that the wettability and the cycle life of the diaphragm are improved, the thickness of the diaphragm and the volume of a battery are reduced, and the lightweight battery is prepared; the third class is a polymer fiber membrane, which on one hand comprises a high-porosity nanofiber membrane prepared by using an electrostatic spinning technology, and has better thermal stability and cycle performance; secondly, a polymer composite diaphragm with higher melting temperature, such as an aramid diaphragm and a modified inorganic ceramic coating (alumina), has higher thermal stability, does not generate thermal shrinkage at 200 ℃, and can keep the integrity of the diaphragm even if an organic substance base film is melted in the charging and discharging process, so that the occurrence of large-area positive/negative electrode short circuit phenomenon is prevented, and the safety of a battery is further improved; on the other hand, the polymer electrolyte diaphragm with high porosity is used for the polymer lithium ion battery to replace liquid electrolyte by solid electrolyte, so that the safety problems of liquid leakage, combustion explosion and the like are prevented. The polymer electrolyte membrane has the dual functions of electrolyte and membrane, and is generally prepared from polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) serving as a raw material or modified. However, high performance lithium ion batteries are also increasingly requiring separators. With the rapid development of power batteries for vehicles, the demand for the separator will also be greatly increased, so that development of a thinner high-performance lithium ion separator is needed.

CN107910476a discloses a preparation method of a ceramic coating composite lithium ion battery diaphragm, which at least comprises the following steps: firstly, mixing ceramic powder with a dispersing agent, adding the mixture into a solvent, performing ball milling, adding a certain mass of polymer, photo-curing resin and photoinitiator, and mechanically stirring to obtain an electrostatic spinning solution; providing a matrix film, carrying out an electrostatic spinning process by utilizing the electrostatic spinning solution to deposit nano ceramic fiber layers on the surfaces of two sides of the matrix film, and drying to obtain a composite film; finally, ultraviolet light is utilized to solidify the composite membrane, and the ceramic composite lithium ion battery diaphragm is obtained after drying treatment. The prepared ceramic composite diaphragm has the advantages of high electrolyte retention rate, high strength, high rupture temperature, uniform pore size distribution, difficult stripping of a matrix film and a nano ceramic fiber layer and the like, is beneficial to improving the cycle stability and high-rate charge and discharge performance of a lithium ion battery, and is suitable for a power lithium ion battery.

Therefore, in the art, it is desired to develop a lithium ion battery separator material having good heat resistance, wettability and ion conductivity, while the corresponding preparation method is simple, and the prepared lithium ion battery has good electrochemical properties.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a polyimide composite diaphragm, a preparation method thereof and a lithium ion battery. The invention provides a polyimide composite diaphragm, and the preparation method is simple, and is easy to realize large-scale production, and the polyimide composite diaphragm is applied to the field of lithium ion batteries, so that the cycle life, the multiplying power performance and the heat-resistant stability of the batteries are greatly improved.

In order to achieve the aim of the invention, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a polyimide composite membrane comprising a polyimide base membrane, a ceramic coating coated on one side of the polyimide base membrane, and a polymer coating coated on the other side of the polyimide base membrane.

According to the polyimide composite diaphragm provided by the invention, the ceramic coating and the polymer coating are respectively coated on the surface of the polyimide base film, and the coated polymer coating can improve the melting temperature of the diaphragm, and can not generate a thermal shrinkage phenomenon at 250 ℃, so that the thermal stability of the diaphragm is improved; the mechanical strength of the diaphragm is improved by adding the ceramic coating, meanwhile, the coating film has better air permeability and heat-resistant stability (400 ℃ and 1h: MD is less than or equal to 20.0 percent, TD is less than or equal to 17.0 percent) and higher ion conductivity by adopting a separate coating mode, the air permeability and heat-resistant stability of the coating film are poorer by mixed coating, the performance of a lithium ion battery is further unfavorable to be improved, the polyimide composite diaphragm has better air permeability, heat-resistant stability, higher ion conductivity (more than or equal to 1.9 mS/cm), electrolyte wettability and electrolyte retention rate (more than or equal to 89 percent), the cycle life and the safety performance of the lithium ion battery are improved, the occurrence of thermal runaway, lithium dendrite and short-circuit potential safety hazards of the battery is prevented, and the rapid charge and discharge under a large multiplying power can be realized.

Preferably, the polyimide composite separator has a thickness of 6 to 10 μm, for example, 6 μm,7 μm,8 μm,9 μm,10 μm.

According to the invention, the thickness of the polyimide composite diaphragm is adjusted, so that the needling strength of the coating film is better, the porosity is higher, the safety performance of the battery is improved, the danger that lithium dendrites and the diaphragm are punctured is prevented, short circuits are easy to occur when the polyimide composite diaphragm is too thin, and the internal resistance of the battery is increased when the polyimide composite diaphragm is too thick.

Preferably, the ceramic coating has a thickness of 2 μm to 3 μm, which may be, for example, 2 μm,2.1 μm,2.2 μm,2.3 μm,2.4 μm,2.5 μm,2.6 μm,2.7 μm,2.8 μm,2.9 μm or 3 μm.

According to the invention, the thickness of the ceramic coating is adjusted, so that the heat-resistant stability of the coating film is better, the ion conductivity is improved, the performance and the safety of the battery are further improved, the heat-resistant stability of the diaphragm and the ion conductivity are not improved when the ceramic coating is too thin, the safety of the battery is further affected, and conversely, the air permeability is poor and the internal impedance of the battery is increased when the ceramic coating is too thick.

Preferably, the thickness of the polymer coating is 2 μm-3 μm, for example, it may be 2 μm,2.1 μm,2.2 μm,2.3 μm,2.4 μm,2.5 μm,2.6 μm,2.7 μm,2.8 μm,2.9 μm or 3 μm.

In the invention, the heat-resistant stability of the coating film is greatly improved by adjusting the thickness of the polymer coating, so that the preparation of the coating film with higher surface density is realized, the improvement of the battery performance is facilitated, the improvement of the heat-resistant stability is not obvious when the polymer coating is too thin, the resistance in the battery is increased due to the too thick polymer coating, and the improvement of the battery ploidy is not facilitated.

Preferably, the thickness ratio of the ceramic coating to the polymer coating is (1.5-2.5): 1, which may be, for example, 1.5:1,1.7:1,1.9:1,2:1,2.1:1,2.2:1,2.3:1,2.4:1,2.5:1.

Preferably, the polymer coating is a meta-aramid coating.

Preferably, the glass transition temperature of meta-aramid in the meta-aramid coating is 200-450 ℃, for example, 200 ℃,220 ℃,250 ℃,270 ℃,300 ℃,320 ℃,350 ℃,370 ℃,400 ℃,420 ℃,450 ℃.

In the invention, meta-aramid is selected as the coating of the polymer, and the glass transition temperature is up to 270 ℃ and no obvious decomposition and carbonization can occur below 350 ℃, so that the thermal stability of the composite diaphragm can be greatly improved by coating the meta-aramid on the surface of the polyimide base film.

In a second aspect, the present invention provides a method for preparing the polyimide composite membrane according to the first aspect, the method comprising the steps of:

(1) Mixing ceramic and a solvent, heating until the ceramic and the solvent are dissolved, adding a surfactant for stirring and secondary heating, adding the surfactant again for secondary stirring, and filtering to obtain ceramic slurry;

(2) Mixing meta-aramid fiber, a surfactant and a solvent, and filtering to obtain polymer slurry;

(3) And coating the ceramic slurry on one side of the polyimide base film, coating the polymer slurry on the other side of the polyimide base film, and drying to obtain the polyimide composite diaphragm.

In the invention, the polyimide base film is prepared by adopting an electrostatic spinning method, and the fiber base film is prepared by adopting a separate coating method, so that the melting temperature of the diaphragm can be increased, and the thermal stability of the diaphragm is further improved.

Preferably, D of the ceramic ₁₀ The particle size is 0.3 μm to 0.4. Mu.m, for example, 0.3 μm,0.31 μm,0.32 μm,0.33 μm,0.34 μm,0.35 μm,0.36 μm,0.37 μm,0.38 μm,0.39 μm or 0.4. Mu.m.

PreferablyD of the ceramic ₅₀ The particle size is 0.6 μm to 0.7. Mu.m, for example, 0.6 μm,0.61 μm,0.62 μm,0.63 μm,0.64 μm,0.65 μm,0.66 μm,0.67 μm,0.68 μm,0.69 μm or 0.7. Mu.m.

Preferably, D of the ceramic ₉₀ The particle size is 1.3 μm to 1.4. Mu.m, for example, 1.3 μm,1.31 μm,1.32 μm,1.33 μm,1.34 μm,1.35 μm,1.36 μm,1.37 μm,1.38 μm,1.39 μm or 1.4. Mu.m.

Preferably, the ceramic has a specific surface area of 7m ² /g-8m ² /g, for example, may be 7m ² /g，7.1m ² /g，7.2m ² /g，7.3m ² /g，7.4m ² /g，7.5m ² /g，7.6m ² /g，7.7m ² /g，7.8m ² /g，7.9m ² /g or 8m ² /g。

In the invention, the air permeability and the wettability of the coating film are improved by adjusting the particle size and the specific surface area of the ceramic, if the particle size is too small, the air permeability of the coating film is poor, otherwise, the coating film is loose; when the specific surface area is too small, wettability of the coating film tends to be poor, whereas aggregation of particles tends to occur.

Preferably, the ceramic has a mass of 10g-60g, which may be, for example, 10g,12g,15g,17g,20g,22g,25g,27g,30g,32g,35g,37g,40g,42g,45g,47g,50g,52g,55g,57g or 60g.

In the invention, the heat-resistant shrinkage performance of the coating film is changed by adjusting the quality of the ceramic, and the heat-resistant shrinkage performance of the coating film is deteriorated if the added quality is too small, otherwise, the agglomeration phenomenon is generated.

Preferably, the ceramic comprises either boehmite or alumina.

Preferably, the solvent in the step (1) is deionized water.

Preferably, the deionized water has a mass of 10g to 200g, which may be, for example, 10g,20g,50g,70g,80g,100g,120g,130g,140g,150g,160g,170g,180g,190g or 200g.

Preferably, the mixing in step (1) is performed under stirring.

Preferably, the stirring rate is 700rpm-2000rpm, and may be 700rpm,720rpm,750rpm,770rpm,800rpm,820rpm,850rpm,87 rpm,900rpm,920rpm,950rpm, 460 rpm,1100rpm,1200rpm, 1500rpm, 1400rpm, 460 rpm, or 2000rpm, for example.

Preferably, the stirring time is 0.01h-12h, and may be, for example, 0.01h,0.05h,0.1h,0.5h,1h,2h,3h,4h,5h,6h,7h,8h,9h,10h,11h or 12h.

Preferably, the heating temperature in step (1) is 10 ℃ to 50 ℃, for example, 10 ℃,12 ℃,15 ℃,17 ℃,20 ℃,22 ℃,25 ℃,27 ℃,30 ℃,32 ℃,35 ℃,37 ℃,40 ℃,42 ℃,45 ℃,47 ℃, or 50 ℃.

Preferably, the heating time in step (1) is 0.1h-5h, and may be, for example, 0.1h,0.3h,0.6h,1h,1.2h,1.5h,1.7h,2h,2.2h,2.5h,2.7h,3h,3.2h,3.5h,3.7h,4h,4.2h,4.5h,4.7h or 5h.

Preferably, the surfactant in the step (1) is any two or three of polyoxyethylene ether, sodium alginate, polyvinyl acetate, polyisobutylene, polyacrylate, ethylene-vinyl acetate copolymer, alkyl polyoxyethylene ether, polyoxyethylene-polyoxypropylene block copolymer, alkyl sulfate, polyoxyethylene fatty alcohol ether, polyvinylidene fluoride, and propylene glycol methyl ether, and for example, polyoxyethylene ether, sodium alginate, polyvinyl acetate, polyisobutylene, polyacrylate, ethylene-vinyl acetate copolymer, and alkyl polyoxyethylene ether, or polyoxyethylene fatty alcohol ether, and propylene glycol methyl ether, but not limited to the listed types, and the types not listed in the surfactant range are equally applicable.

Preferably, the mass of the surfactant in the step (1) is 0.01g to 8g, for example, 0.01g,0.05g,0.1g,0.5g,1g,2g,3g,4g,5g,6g,7g or 8g.

According to the invention, the prepared slurry coating has certain viscosity by adjusting the quality of the surfactant, can be better coated on the surface of the polyimide diaphragm, and has lower surface tension; the added mass is too small, so that the phenomena of powder falling and falling of the coating are caused, otherwise, the air permeability and the ion conductivity of the coating film are influenced, and even the circulation and the multiplying power performance of the battery are influenced.

Preferably, the stirring rate in step (1) is 300rpm-2000rpm, and may be, for example, 300rpm,400rpm, 5000 rpm,600rpm,700rpm,720rpm,750rpm, 680 rpm, 5000 rpm,850rpm, 1100rpm,1200rpm, 1500rpm, 460 rpm or 2000rpm.

Preferably, the stirring time in the step (1) is 0.1h-6h, for example, 0.1h,0.3h,0.6h,1h,1.2h,1.5h,1.7h,2h,2.2h,2.5h,2.7h,3h,3.2h,3.5h,3.7h,4h,4.2h,4.5h,4.7h,5h,5.2h,5.5h,5.7h or 6h.

Preferably, the temperature of the secondary heating in step (1) is 10 ℃ to 50 ℃, for example, 10 ℃,12 ℃,15 ℃,17 ℃,20 ℃,22 ℃,25 ℃,27 ℃,30 ℃,32 ℃,35 ℃,37 ℃,40 ℃,42 ℃,45 ℃,47 ℃ or 50 ℃.

Preferably, the time of the secondary heating in the step (1) is 0.1h-2h, for example, may be 0.1h,0.3h,0.6h,1h,1.2h,1.5h,1.7h or 2h.

Preferably, the rate of the secondary stirring in the step (1) is 100rpm to 600rpm, for example, 100rpm,150rpm,200rpm,250rpm,300rpm,350rpm,400rpm,450rpm,500rpm,550rpm or 600rpm.

Preferably, the time of the secondary stirring in the step (1) is 0.1h-6h, for example, 0.1h,0.3h,0.6h,1h,1.2h,1.5h,1.7h,2h,2.2h,2.5h,2.7h,3h,3.2h,3.5h,3.7h,4h,4.2h,4.5h,4.7h,5h,5.2h,5.5h,5.7h or 6h.

Preferably, the viscosity of the ceramic slurry in step (1) is 20cP-150cP, and may be, for example, 20cP,25cP,30cP,35cP,40cP,45cP,50cP,55cP,60cP,65cP,70cP,75cP,80cP,85cP,90cP,95cP,100cP,105cP,110cP,115cP,120cP,125cP,130cP,135cP,140cP,145cP or 150cP.

In the invention, the viscosity of the ceramic slurry is adjusted to ensure that the coating is not easy to fall off and is suitable for certain coating process conditions, and the too low viscosity can cause the coating to fall off, otherwise, the coating process of a coating film can be influenced, and the coating preparation is not facilitated.

Preferably, the dry ceramic slurry in the step (1) contains 10% -98.8% of ceramic by mass, for example, 10%,12%,15%,17%,20%,22%,25%,27%,30%,32%,35%,37%,40%,42%,45%,47%,50%,52%,55%,57%,60%,62%,65%,67%,70%,72%,75%,77%,80%,82%,85%,87%,90%,92%,95%,97%,98% or 98.8%.

In the invention, the heat-resistant stability, the air permeability and the ion conductivity of the coating film are better by adjusting the mass percentage of the ceramic in the dry material of the ceramic slurry, and the heat-resistant stability of the coating film is poor if the content is too low, and the air permeability of the coating film is poor if the content is too low.

Preferably, the mass percentage of the surfactant in the dry material of the ceramic slurry in the step (1) is 0.2% -20%, for example, may be 0.2%,0.5%,0.7%,1%,2%,5%,7%,10%,12%,15%,17% or 20%.

According to the invention, the quality percentage of the surfactant in the dry material of the ceramic slurry is adjusted, so that the peeling strength of the coating film is better, the cycle and rate performance of the lithium ion battery are better, the peeling strength of the coating film is poorer if the content is too low, the powder falling phenomenon is easy to occur, and otherwise, the cycle and rate performance of the lithium ion battery are influenced.

Preferably, the solid content of the ceramic slurry in the step (1) is 30% -50%, for example, 30%,32%,35%,37%,40%,42%,45%,47% or 50%.

In the invention, the solid content of the ceramic slurry is adjusted to be beneficial to the production of a coating process and the adjustment of the coating thickness, and if the solid content is too low, the coating thickness is smaller, otherwise, the coating process condition is not met, and the production is not beneficial.

Preferably, the mass of the intermediate aramid fiber in the step (2) is 10g-60g, for example, 10g,12g,15g,17g,20g,22g,25g,27g,30g,32g,35g,37g,40g,42g,45g,47g,50g,52g,55g,57g or 60g.

In the invention, the quality of meta-aramid fiber is adjusted, so that the high-temperature heat-resistant shrinkage rate of the coating film is better, the coating surface density is lower, the light-weight coating film is produced, the high-temperature heat-resistant shrinkage rate is higher when the added quality is too low, and otherwise, the high-temperature heat-resistant shrinkage rate is lower, and the coating surface density is higher.

Preferably, the solvent in the step (2) is deionized water.

Preferably, the surfactant in the step (2) is any two or three of polyoxyethylene ether, sodium alginate, polyvinyl acetate, polyisobutylene, polyacrylate, ethylene-vinyl acetate copolymer, alkyl polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, alkyl sulfate, polyoxyethylene fatty alcohol ether, polyvinylidene fluoride, and propylene glycol methyl ether, and for example, polyoxyethylene ether, sodium alginate, polyvinyl acetate, polyisobutylene, polyacrylate, ethylene-vinyl acetate copolymer, and alkyl polyoxyethylene ether, or polyoxyethylene fatty alcohol ether, and propylene glycol methyl ether, but not limited to the listed types, and the types not listed in the surfactant range are equally applicable.

Preferably, the surfactant in step (2) has a mass of 60g to 200g, and may be 60g,62g,65g,67g,70g,72g,75g,80g,82g,85g,87g,90g,92g,95g,97g,100g,105g,110g,115g,120g,125g,130g,135g,140g,145g,150g,155g,160g,165g,170g,175g,180g,185g,190g,195g or 200g, for example.

In the invention, the quality of the surfactant is adjusted to ensure that the air permeability and the surface density of the coating film are better, the powder falling phenomenon is avoided, the addition of too little quality can cause too large aramid fiber doping amount, the aim of low-cost production is difficult to realize, and otherwise, the circulation of the lithium ion battery and the improvement of the multiplying power performance are not facilitated.

Preferably, the mixing in step (2) is performed under stirring.

Preferably, the stirring rate is 500rpm-1400rpm, and may be, for example, 500rpm,600rpm,700rpm,720rpm,750rpm, 680 rpm,800rpm, 5000 rpm,850rpm, 1100rpm,1200rpm, 1400rpm, 750rpm, 900rpm,920rpm, 1100rpm,1200rpm, 1400rpm.

Preferably, the stirring time is 0.1h-10h, and may be, for example, 0.1h,0.3h,0.6h,1h,1.2h,1.5h,1.7h,2h,2.2h,2.5h,2.7h,3h,3.2h,3.5h,3.7h,4h,4.2h,4.5h,4.7h,5h,5.2h,5.5h,5.7h,6h,6.2h,6.5h,6.7h,7h,7.2h,7.5h, 8h,8.2h,8.5h, 9h,9.2h,9.5h,9.7h or 10h.

Preferably, the viscosity of the polymer syrup in the step (2) is 20cP to 300cP, for example, it may be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80cp,85cp,90cp,95cp,100cp,105cp,110cp,115cp,120cp,125cp,130, 135cP,140, 145, 150cP,155cp,160cP,165cP,170, 175, 180, 185, 190, 195, 200, 205, 210cp,215cP,220, 225, 230, 235, 245, 250, 255, 260, 265, or 300cP.

According to the invention, the viscosity of the polymer slurry is adjusted, so that the peeling strength of the coating film is higher, and the phenomena of falling and powder falling are not easy to occur, thereby being beneficial to preventing the occurrence of short circuit of lithium dendrites and batteries; the coating is easy to fall off and the powder falling phenomenon is caused when the viscosity is too low, so that the performance of the battery is not improved; otherwise, the coating process conditions are not met, the production is difficult, and the thickness is influenced.

Preferably, the mass percentage of the aramid fiber at the middle position of the dry material of the polymer slurry in the step (2) is 2% -50%, for example, may be 2%,5%,7%,10%,12%,15%,17%,20%,22%,25%,27%,30%,32%,35%,37%,40%,42%,45%,47% or 50%.

According to the invention, the high heat-resistant stability of the coating film and the development of the low-cost diaphragm are realized by adjusting the mass percentage content of the aramid fiber at the middle position of the dry material of the polymer slurry, and if the content is too low, the improvement of the heat-resistant stability is not facilitated, otherwise, the diaphragm cost is too high, and the aim of mass production is not facilitated.

Preferably, the mass percentage of the surfactant in the dry material of the polymer slurry in the step (2) is 20% -90%, for example, 20%,22%,25%,27%,30%,32%,35%,37%,40%,42%,45%,47%,50%,52%,55%,57%,60%,62%,65%,67%,70%,72%,75%,77%,80%,82%,85%,87% or 90%.

According to the invention, the air permeability and the surface density of the coating film are better and the powder falling phenomenon is avoided by adjusting the mass percentage of the surfactant in the dry material of the polymer slurry, so that the aim of low-cost production is difficult to realize due to the excessively large doping amount of the aramid fiber caused by the excessively small added mass, and the circulation and the improvement of the multiplying power performance of the lithium ion battery are not facilitated otherwise.

Preferably, the solids content of the polymer slurry in step (2) is 10% -40%, for example, 10%,12%,15%,17%,20%,22%,25%,27%,30%,32%,35%,37% or 40%.

In the invention, the solid content of the polymer slurry is adjusted to be beneficial to the production of a coating process and the adjustment of the coating thickness, and if the solid content is too low, the coating thickness is smaller, otherwise, the coating process condition is not met, and the production is not beneficial.

Preferably, the ceramic slurry in the step (3) is coated by roll coating.

Preferably, the polymer slurry in the step (3) is coated by spraying.

Preferably, the spray coating temperature is 10 ℃ to 80 ℃, for example, 10 ℃,12 ℃,15 ℃,17 ℃,20 ℃,22 ℃,25 ℃,27 ℃,30 ℃,32 ℃,35 ℃,37 ℃,40 ℃,42 ℃,45 ℃,47 ℃,50 ℃,52 ℃,55 ℃,57 ℃,60 ℃,62 ℃,65 ℃,67 ℃,70 ℃,72 ℃,75 ℃,77 ℃, or 80 ℃.

Preferably, the drying temperature in step (3) is 30-80 ℃, for example 30 ℃,32 ℃,35 ℃,37 ℃,40 ℃,42 ℃,45 ℃,47 ℃,50 ℃,52 ℃,55 ℃,57 ℃,60 ℃,62 ℃,65 ℃,67 ℃,70 ℃,72 ℃,75 ℃,77 ℃, or 80 ℃.

In a third aspect, the present invention provides a lithium ion battery, the lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, the separator being the polyimide composite separator according to the first aspect.

The polyimide composite membrane provided by the invention has good ionic conductivity, air permeability, thermal stability, electrolyte wettability and liquid retention rate, so that the cycle stability and the service life of the lithium ion battery are improved.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a polyimide composite diaphragm, which comprises a polyimide base film capable of tolerating high temperature up to 300 ℃, and having almost zero thermal shrinkage under 200 ℃, and also having a porosity up to 50%, thereby preventing the formation of lithium dendrites, so that the polyimide base film has good air permeability and heat-resistant stability, and on the basis, the ceramic coating and the polymer coating are coated on the surface of the base film separately, so that the porosity is between 40% and 44%, and the tensile strength is over 300Kgf/cm ² The situation that the current density is too high due to the fact that the porosity is too high is prevented from happening, and then lithium dendrites are generated is avoided, and the safety of the battery is effectively improved; by further preferably using meta-aramid as the polymer coating material, the glass transition temperature is up to 270 ℃ and no obvious decomposition and carbonization can occur below 350 ℃, so that the meta-aramid can be coated on the surface of the polyimide base film Greatly improves the thermal stability of the composite diaphragm; in addition, the electrolyte infiltration performance and the electrolyte retention rate of the composite diaphragm can be improved by adopting a high-performance ceramic material, so that the cycle stability and the service life of the lithium ion battery are improved. In addition, the polyimide composite membrane provided by the invention has better electrolyte liquid absorption rate and liquid retention rate, so that the capacity retention rate, the cycle stability and the service life of the battery are greatly improved, and meanwhile, compared with a commercial membrane, the polyimide composite membrane has better air permeability and ion conductivity, and is beneficial to improving the rate capability and the cycle capability of the battery.

The preparation method of the polyimide composite diaphragm is simple, and the preparation process, the coating and the cutting process of the slurry can solve the problem of the surface defect of the diaphragm, so that the composite diaphragm with a flat film surface, no granular feel, no scratch and no fold is prepared; is beneficial to preventing the growth of lithium dendrite of the battery and improving the safety and the cycle life of the lithium ion battery.

The battery prepared by the polyimide composite diaphragm provided by the invention has better capacity retention rate, circulation stability and service life, reduces the resistance of the battery, improves the rate performance, heat-resistant stability and safety performance of the battery, can realize high-rate charge and discharge, and is applied to the field of power automobiles.

Drawings

FIG. 1 is a schematic structural view of a polyimide composite separator according to examples 1 to 6, wherein 11 is a polyimide base film, 12 is a ceramic coating layer, and 13 is a polymer coating layer;

fig. 2 is an assembly flow chart of the lithium ion battery prepared by application examples 1 to 6 and comparative application examples 1 to 18, wherein 1 is a negative electrode shell, 2 is an elastic sheet, 3 is a gasket, 4 is a lithium sheet, 5 is a polyimide composite separator, 6 is a lithium iron phosphate positive electrode, 7 is a gasket, and 8 is a positive electrode shell.

Detailed Description

The technical scheme of the invention is further described below by combining the attached drawings and the specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Example 1

The embodiment provides a polyimide composite diaphragm, which comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a meta-aramid polymer coating coated on the other side of the polyimide base film. The thickness of the polyimide composite diaphragm is 6 mu m, the thickness of the ceramic coating is 2 mu m, the thickness of the polymer coating is 2 mu m, and the glass transition temperature of meta-aramid in the meta-aramid coating is 400 ℃.

The preparation method comprises the following steps:

(1) Will D ₁₀ Particle diameter of 0.3 μm, D ₅₀ Particle diameter of 0.6 μm, D ₉₀ Particle diameter of 1.3 μm and specific surface area of 7m ² Stirring 30g of boehmite (purity of 99.95%) and 45g of deionized water at a high speed at a stirring speed of 1000rpm for 4 hours, stirring by a magnetic stirring mode for 6 hours, performing ultrasonic dispersion for 1 hour, heating at 30 ℃ for 0.5 hour, adding 0.24g of alkyl polyoxyethylene ether (solid content of 90%) and 1.2g of polyvinyl acetate (solid content of 15%) surfactant after dissolution, stirring and performing secondary heating, wherein the stirring speed is 600rpm, the stirring time is 1 hour, the secondary heating temperature is 30 ℃, the secondary heating time is 0.5 hour, adding 4g of polyacrylate surfactant again for secondary stirring, wherein the secondary stirring speed is 600rpm, the secondary stirring time is 2 hours, and filtering to obtain ceramic slurry with the viscosity of 150cP and the solid content of 38%, wherein the mass percentage of boehmite in the dry material of the ceramic slurry is 84.6%; the mass percentage of alkyl polyoxyethylene ether, polyvinyl acetate and polyacrylate surfactant in the dry material of the ceramic slurry is 0.7%, 3.4% and 11.3% respectively;

(2) Stirring 10g of meta-aramid (purchased from the company of the new materials and the tobacco station Co., ltd.), 60g of alkyl sulfate surfactant, 30g of sodium alginate surfactant and 30g of deionized water, wherein the stirring speed is 1400rpm, the stirring time is 4 hours, and the polymer slurry with the viscosity of 80cP and the solid content of 20% is obtained after filtration, wherein the mass percentage of the dry material middle aramid of the polymer slurry is 10%; the mass percentage of the alkyl sulfate and the sodium alginate surfactant in the dry material of the polymer slurry is 60% and 30% respectively;

(3) The ceramic slurry is coated on one side of a polyimide base film in a roller way, rewound and dried, and the polymer slurry is sprayed on the other side of the polyimide base film at the temperature of 10 ℃ and dried at the temperature of 30 ℃ to obtain the polyimide composite diaphragm, wherein the coating and unreeling tension is 0.01N, the reeling tension is 0.1N, the stretching speed is 0.01m/min, and the contact pressure is 0.01N; secondly, rewinding process parameters, rewinding stretching speed difference 0.1, winding and unwinding tension 0.01N, rewinding temperature 30 ℃, rewinding speed 0.01m/min and contact pressure 0.01N; the slitting winding and unwinding tension is 1N, the slitting speed is 0.01m/min, and the contact pressure is 0.01N; and (5) placing the slit film in a purification workshop with the temperature of 40 ℃ after slitting to obtain a finished slit film.

Example 2

The embodiment provides a polyimide composite diaphragm, which comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a meta-aramid polymer coating coated on the other side of the polyimide base film. The thickness of the polyimide composite membrane is 8 mu m, the thickness of the ceramic coating is 2.5 mu m, the thickness of the polymer coating is 2.5 mu m, and the glass transition temperature of meta-aramid in the meta-aramid coating is 320 ℃.

The preparation method comprises the following steps:

(1) Will D ₁₀ Particle diameter of 0.35 μm, D ₅₀ Particle diameter of 0.65 μm and D ₉₀ Particle diameter of 1.35 μm and specific surface area of 7.5m ² Stirring 35g of boehmite per gram and 70g of deionized water at a high speed at a stirring speed of 1000rpm for 6h, stirring by a magnetic stirring mode for 6h, performing ultrasonic dispersion for 1h, heating at 35 ℃ for 1.5h, adding 2.5g of propylene glycol methyl ether surfactant respectively after dissolution, stirring at a stirring speed of 1000rpm for 3h, heating at a secondary heating temperature of 35 ℃ for 1h, and adding 4g of polyacrylate surfactant again The sex agent is subjected to secondary stirring, wherein the speed of the secondary stirring is 350rpm, the time of the secondary stirring is 3 hours, and ceramic slurry with the viscosity of 85cP and the solid content of 40% is obtained after filtering, wherein the mass percentage of boehmite in the dry material of the ceramic slurry is 84.3%; the mass percentage of the propylene glycol methyl ether and the polyacrylate surfactant in the dry material of the ceramic slurry is 6 percent and 9.7 percent respectively;

(2) Stirring 35g of meta-aramid, 60g of ethylene-vinyl acetate copolymer surfactant, 40g of sodium alginate surfactant and 100g of deionized water, wherein the stirring speed is 900rpm, the stirring time is 5 hours, and the polymer slurry with the viscosity of 150cP and the solid content of 30% is obtained after filtration, wherein the mass percentage of the dry material intermediate aramid of the polymer slurry is 26%; the mass percentage of the ethylene-vinyl acetate copolymer and the sodium alginate surfactant in the dry material of the polymer slurry is 44.4 percent and 29.6 percent respectively;

(3) The ceramic slurry is coated on one side of a polyimide base film in a roller way, rewound and dried, and the polymer slurry is sprayed on the other side of the polyimide base film at 45 ℃ and dried at 55 ℃ to obtain the polyimide composite diaphragm, wherein the coating and unreeling tension is 0.01N, the reeling tension is 0.1N, the stretching speed is 0.01m/min, and the contact pressure is 0.01N; secondly, rewinding process parameters, rewinding stretching speed difference 0.1, winding and unwinding tension 0.01N, rewinding temperature 30 ℃, rewinding speed 0.01m/min and contact pressure 0.01N; the slitting winding and unwinding tension is 1N, the slitting speed is 0.01m/min, and the contact pressure is 0.01N; and (5) placing the slit film in a purification workshop with the temperature of 40 ℃ after slitting to obtain a finished slit film.

Example 3

The embodiment provides a polyimide composite diaphragm, which comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a meta-aramid polymer coating coated on the other side of the polyimide base film. The thickness of the polyimide composite membrane is 10 mu m, the thickness of the ceramic coating is 2.2 mu m, the thickness of the polymer coating is 2.2 mu m, and the glass transition temperature of meta-aramid in the meta-aramid coating is 260 ℃.

The preparation method comprises the following steps:

(1) Will D ₁₀ Particle diameter of 0.32 μm, D ₅₀ Particle diameter of 0.62 μm, D ₉₀ Particle diameter of 1.32 μm and specific surface area of 7.2m ² Stirring 20g of aluminum oxide per gram and 60g of deionized water at a high speed at a stirring speed of 800rpm for 9h, stirring for 6h by a magnetic stirring mode, performing ultrasonic dispersion for 1h, heating at 20 ℃ for 3h until 1g of polyisobutene is added after dissolution, stirring and secondary heating are performed, wherein the stirring speed is 600rpm, the stirring time is 4h, the secondary heating temperature is 20 ℃, the secondary heating time is 1.5h, adding 1g of polyoxyethylene fatty alcohol ether surfactant again for secondary stirring, the secondary stirring speed is 200rpm, the secondary stirring time is 4h, and filtering to obtain ceramic slurry with a viscosity of 55cP and a solid content of 35%, wherein the mass percentage of aluminum oxide in the dry material of the ceramic slurry is 90.9%; the mass percentage of the polyisobutene and the polyoxyethylene fatty alcohol ether surfactant in the dry material of the ceramic slurry is 4.55 percent and 4.55 percent respectively;

(2) Stirring 20g of meta-aramid fiber, 40g of ethylene-vinyl acetate copolymer surfactant, 40g of sodium alginate surfactant and 80g of deionized water, wherein the stirring speed is 700rpm, the stirring time is 7h, and the polymer slurry with the viscosity of 85cP and the solid content of 15% is obtained after filtration, wherein the mass percentage of the dry material intermediate aramid fiber of the polymer slurry is 20%; the mass percentage of the ethylene-vinyl acetate copolymer and the sodium alginate surfactant in the dry material of the polymer slurry is 40 percent and 40 percent respectively;

(3) The ceramic slurry is coated on one side of a polyimide base film in a roller way, rewound and dried, and the polymer slurry is sprayed on the other side of the polyimide base film at 25 ℃ and dried at 45 ℃ to obtain the polyimide composite diaphragm, wherein the coating and unreeling tension is 0.01N, the reeling tension is 0.1N, the stretching speed is 0.01m/min, and the contact pressure is 0.01N; secondly, rewinding process parameters, rewinding stretching speed difference 0.1, winding and unwinding tension 0.01N, rewinding temperature 30 ℃, rewinding speed 0.01m/min and contact pressure 0.01N; the slitting winding and unwinding tension is 1N, the slitting speed is 0.01m/min, and the contact pressure is 0.01N; and (5) placing the slit film in a purification workshop with the temperature of 40 ℃ after slitting to obtain a finished slit film.

Example 4

The embodiment provides a polyimide composite diaphragm, which comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a meta-aramid polymer coating coated on the other side of the polyimide base film. The thickness of the polyimide composite membrane is 10 mu m, the thickness of the ceramic coating is 2.8 mu m, the thickness of the polymer coating is 2.8 mu m, and the glass transition temperature of meta-aramid in the meta-aramid coating is 350 ℃.

The preparation method comprises the following steps:

(1) Will D ₁₀ Particle diameter of 0.37 μm, D ₅₀ Particle diameter of 0.67 μm, D ₉₀ Particle diameter of 1.37 μm and specific surface area of 7.7m ² Stirring 45g of per gram of aluminum oxide and 150g of deionized water at a high speed at a stirring speed of 1500rpm for 3h, stirring for 6h by a magnetic stirring mode, performing ultrasonic dispersion for 1h, heating at 40 ℃ for 1.5h, adding 3g of polyisobutene for stirring and secondary heating after dissolving, wherein the stirring speed is 1500rpm, the stirring time is 1.5h, the secondary heating temperature is 40 ℃, the secondary heating time is 0.5h, adding 3g of polyoxyethylene fatty alcohol ether surfactant for secondary stirring again, wherein the secondary stirring speed is 500rpm, the secondary stirring time is 2h, and filtering to obtain ceramic slurry with a viscosity of 120cP and a solid content of 45%, wherein the mass percentage of aluminum oxide in a dry material of the ceramic slurry is 88.2%; the mass percentage of the polyisobutene and the polyoxyethylene fatty alcohol ether surfactant in the dry material of the ceramic slurry is 5.9 percent and 5.9 percent respectively;

(2) Stirring 48g of meta-aramid, 75g of ethylene-vinyl acetate copolymer surfactant, 75g of sodium alginate surfactant and 150g of deionized water, wherein the stirring speed is 1200rpm, the stirring time is 3 hours, and the polymer slurry with the viscosity of 230cP and the solid content of 32% is obtained after filtration, wherein the mass percentage of the dry material intermediate aramid of the polymer slurry is 24.2%; the mass percentage of the ethylene-vinyl acetate copolymer and the sodium alginate surfactant in the dry material of the polymer slurry is 37.9 percent and 37.9 percent respectively;

(3) The ceramic slurry is coated on one side of a polyimide base film in a roller way, rewound and dried, and the polymer slurry is sprayed on the other side of the polyimide base film at 65 ℃ and dried at 70 ℃ to obtain the polyimide composite diaphragm, wherein the coating and unreeling tension is 0.01N, the reeling tension is 0.1N, the stretching speed is 0.01m/min, and the contact pressure is 0.01N; secondly, rewinding process parameters, rewinding stretching speed difference 0.1, winding and unwinding tension 0.01N, rewinding temperature 30 ℃, rewinding speed 0.01m/min and contact pressure 0.01N; the slitting winding and unwinding tension is 1N, the slitting speed is 0.01m/min, and the contact pressure is 0.01N; and (5) placing the slit film in a purification workshop with the temperature of 40 ℃ after slitting to obtain a finished slit film.

Example 5

The embodiment provides a polyimide composite diaphragm, which comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a meta-aramid polymer coating coated on the other side of the polyimide base film. The thickness of the polyimide composite diaphragm is 10 mu m, the thickness of the ceramic coating is 2 mu m, the thickness of the polymer coating is 2 mu m, and the glass transition temperature of meta-aramid in the meta-aramid coating is 200 ℃.

The preparation method comprises the following steps:

(1) Will D ₁₀ Particle diameter of 0.3 μm, D ₅₀ Particle diameter of 0.6 μm, D ₉₀ Particle diameter of 1.3 μm and specific surface area of 7m ² Stirring/g of 10g of boehmite and 10g of deionized water at a stirring speed of 700rpm for 12h, heating at 10 ℃ for 5h until the mixture is dissolved, adding 0.05g of alkyl polyoxyethylene ether and 0.3g of polyvinyl acetate surfactant, stirring and secondary heating, wherein the stirring speed is 300rpm, and the stirring time is equal to the stirring timeThe temperature of the secondary heating is 10 ℃, the time of the secondary heating is 2 hours, the polyacrylate surfactant with the mass of 0.05g is added again for secondary stirring, wherein the speed of the secondary stirring is 100rpm, the time of the secondary stirring is 6 hours, and the ceramic slurry with the viscosity of 20cP and the solid content of 30 percent is obtained after filtering, wherein the mass percent of ceramic in the dry material of the ceramic slurry is 96.6 percent; the mass percentage of the alkyl polyoxyethylene ether surfactant in the dry material of the ceramic slurry is 0.5 percent, the mass percentage of the polyvinyl acetate surfactant is 2.9 percent, and the mass percentage of the polyacrylate surfactant is 0.48 percent;

(2) Stirring 10g of meta-aramid, 30g of alkyl sulfate, 30g of sodium alginate surfactant and 10g of deionized water respectively, wherein the stirring speed is 500rpm, the stirring time is 10 hours, and the polymer slurry with the viscosity of 20cP and the solid content of 10% is obtained after filtration, wherein the mass percentage of the dry material middle-position aramid of the polymer slurry is 14.4%; the mass percentage of the alkyl sulfate surfactant in the dry material of the polymer slurry is 42.8 percent, and the mass percentage of the sodium alginate surfactant is 42.8 percent;

(3) The ceramic slurry is roller-coated on one side of a polyimide base film, the polymer slurry is sprayed on the other side of the polyimide base film at the temperature of 10 ℃, and the polyimide composite diaphragm is obtained after drying at the temperature of 30 ℃, wherein the coating and unreeling tension is 0.01N, the reeling tension is 0.1N, the stretching speed is 0.01m/min, and the contact pressure is 0.01N; secondly, rewinding process parameters, rewinding stretching speed difference 0.1, winding and unwinding tension 0.01N, rewinding temperature 30 ℃, rewinding speed 0.01m/min and contact pressure 0.01N; the slitting winding and unwinding tension is 1N, the slitting speed is 0.01m/min, and the contact pressure is 0.01N; and (5) placing the slit film in a purification workshop with the temperature of 40 ℃ after slitting to obtain a finished slit film.

Example 6

The embodiment provides a polyimide composite diaphragm, which comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a meta-aramid polymer coating coated on the other side of the polyimide base film. The thickness of the polyimide composite diaphragm is 10 mu m, the thickness of the ceramic coating is 3 mu m, the thickness of the polymer coating is 3 mu m, and the glass transition temperature of meta-aramid in the meta-aramid coating is 450 ℃.

The preparation method comprises the following steps:

(1) Will D ₁₀ Particle diameter of 0.4 μm, D ₅₀ Particle diameter of 0.7 μm, D ₉₀ Particle diameter of 1.4 μm and specific surface area of 8m ² Stirring per gram of 60g of boehmite and 200g of deionized water at a stirring speed of 2000rpm for 0.02h, heating at 50 ℃ for 0.2h until 5g of alkyl polyoxyethylene ether surfactant is added after dissolution, stirring and secondary heating are carried out, wherein the stirring speed is 2000rpm, the stirring time is 0.2h, the secondary heating temperature is 50 ℃, the secondary heating time is 0.2h, 8g of polyacrylate surfactant is added again for secondary stirring, the secondary stirring speed is 600rpm, the secondary stirring time is 0.2h, and ceramic slurry with the viscosity of 150cP and the solid content of 50% is obtained after filtration, wherein the mass percentage of ceramic in the dry material of the ceramic slurry is 82.2%; the mass percentage of the alkyl polyoxyethylene ether surfactant in the dry material of the ceramic slurry is 6.8 percent, and the mass percentage of the polyacrylate surfactant is 11 percent;

(2) Stirring 60g of meta-aramid, 100g of alkyl sulfate, 100g of sodium alginate surfactant and 200g of deionized water respectively, wherein the stirring speed is 1400rpm, the stirring time is 0.2h, and filtering to obtain polymer slurry with the viscosity of 300cP and the solid content of 40%, wherein the mass percentage of the dry material intermediate aramid of the polymer slurry is 23%; the mass percentage of the alkyl sulfate surfactant in the dry material of the polymer slurry is 38.5 percent, and the mass percentage of the sodium alginate surfactant is 38.5 percent;

(3) The ceramic slurry is roller-coated on one side of a polyimide base film, the polymer slurry is sprayed on the other side of the polyimide base film at 80 ℃, and the polyimide composite diaphragm is obtained after drying at 80 ℃, wherein the coating and unreeling tension is 0.01N, the reeling tension is 0.1N, the stretching speed is 0.01m/min, and the contact pressure is 0.01N; secondly, rewinding process parameters, rewinding stretching speed difference 0.1, winding and unwinding tension 0.01N, rewinding temperature 30 ℃, rewinding speed 0.01m/min and contact pressure 0.01N; the slitting winding and unwinding tension is 1N, the slitting speed is 0.01m/min, and the contact pressure is 0.01N; and (5) placing the slit film in a purification workshop with the temperature of 40 ℃ after slitting to obtain a finished slit film.

Fig. 1 is a schematic structural view of a polyimide composite membrane provided in examples 1 to 6, which comprises a polyimide base film 11, a ceramic coating layer 12 coated on one side of the polyimide base film, and a polymer coating layer 13 coated on the other side of the polyimide base film.

Comparative example 1

This comparative example differs from example 1 in that only the ceramic coating layer was applied to the polyimide base film, and the meta-aramid polymer layer was not applied, all of which were the same as in example 1.

Comparative example 2

This comparative example differs from example 1 in that only the meta-aramid coating layer was applied to the polyimide-based film, and the ceramic coating layer was not applied, all of which are the same as in example 1.

Comparative example 3

This comparative example differs from example 1 in that D is used ₁₀ 0.1 μm, D ₅₀ 0.3 μm, D ₉₀ 1.0 μm and a specific surface area of 4m ² Boehmite per g, otherwise the same as in example 1.

Comparative example 4

This comparative example differs from example 1 in that D is used ₁₀ 0.5 μm, D ₅₀ 0.8 μm, D ₉₀ 1.6 μm and a specific surface area of 5m ² Boehmite per g, otherwise the same as in example 1.

Comparative example 5

This comparative example differs from example 1 in that the ceramic coating had a thickness of 0.5 μm and the polymer coating had a thickness of 0.5 μm, all of which were identical to example 1.

Comparative example 6

This comparative example differs from example 1 in that the ceramic coating layer has a thickness of 5 μm and the polymer coating layer has a thickness of 5 μm, all other than that of example 1.

Comparative example 7

The comparative example was different from example 1 in that the mass percentage of the ceramic in the dry material of the ceramic slurry was 5%, the mass percentage of the surfactant in the dry material of the ceramic slurry was 95%, and the other was the same as in example 1.

Comparative example 8

This comparative example differs from example 1 in that the viscosity of the ceramic slurry is 10cP, and the other is the same as example 1.

Comparative example 9

This comparative example differs from example 1 in that the viscosity of the ceramic slurry is 160cP, and the other is the same as example 1.

Comparative example 10

This comparative example is different from example 1 in that the ceramic slurry has a solid content of 20%, and the other is the same as example 1.

Comparative example 11

This comparative example is different from example 1 in that the ceramic slurry has a solid content of 60%, and the other is the same as example 1.

Comparative example 12

The comparative example is different from example 1 in that the mass percentage of the aramid fiber at the middle position of the dry material of the polymer slurry is 60%, the mass percentage of the surfactant in the polymer slurry is 40%, and the other components are the same as in example 1.

Comparative example 13

This comparative example differs from example 1 in that the viscosity of the polymer syrup was 10cP, and the other was the same as in example 1.

Comparative example 14

This comparative example differs from example 1 in that the viscosity of the polymer syrup was 310cP, and the other was the same as in example 1.

Comparative example 15

This comparative example differs from example 1 in that the polymer syrup has a solids content of 5%, the remainder being the same as in example 1.

Comparative example 16

This comparative example differs from example 1 in that the polymer syrup has a solids content of 45%, the remainder being the same as in example 1.

Comparative example 17

This comparative example differs from example 1 in that the ceramic coating had a thickness of 0.5 μm and the polymer coating had a thickness of 3.5 μm, all of which were identical to example 1.

Comparative example 18

This comparative example differs from example 1 in that the ceramic coating had a thickness of 3.5 μm and the polymer coating had a thickness of 0.5 μm, all of which were the same as in example 1.

Application examples 1 to 6 and comparative application examples 1 to 18

The polyimide composite separators provided in examples 1 to 6 and comparative examples 1 to 18 were prepared to obtain lithium ion batteries, and the preparation method was as follows:

preparation of a positive plate: adding lithium iron phosphate as a positive electrode material, acetylene black as a conductive agent and polyvinylidene fluoride as a binder into a solvent according to the ratio of 8:1:1, fully stirring to obtain mixed slurry, uniformly coating the mixed slurry onto an aluminum foil, and drying, rolling and cutting to obtain a required positive electrode sheet;

Preparing a negative plate: the negative electrode material is lithium sheet;

electrolyte solution: drying the dried lithium hexafluorophosphate LiPF ₆ Dissolved in a mixed solvent (ethylene carbonate/dimethyl carbonate/ethylmethyl carbonate) with a volume ratio of 1:1:1, liPF ₆ The concentration of (C) was 1mol/L.

Preparation of a lithium ion battery: in a glove box filled with argon, the prepared negative electrode sheet, diaphragm, positive electrode sheet and electrolyte are assembled to obtain a button-type battery, and as shown in fig. 2, the assembling sequence is as follows: the cathode shell 1-the elastic sheet 2-the gasket 3-the lithium sheet 4-the electrolyte-the diaphragm 5-the electrolyte-the lithium iron phosphate 6-the gasket 7-the anode shell 8 of the anode, and then the CR2032 button cell is assembled and compressed and sealed by a button cell sealing machine. And placing the assembled button cell for 24 hours, and carrying out electrochemical performance test after the pole piece, the electrolyte and the diaphragm are fully wetted.

Test conditions

The polyimide composite separators provided in examples 1 to 6 and comparative examples 1 to 18 were subjected to performance test as follows:

(1) Heat shrinkage rate: the test sample sizes were 10CM long and 10CM wide; oven heating was used, the test temperature was 400 ℃, and the test time was 1 hour.

(2) Ventilation value: the test sample sizes were 5CM long and 5CM wide; the gas permeation tester was used to test the seconds required for 100ml of gas to permeate the membrane.

(3) Ion conductivity: the size of the test sample is 18mm in diameter; punching for standby; adopting an electrochemical workstation to test EIS; the buckling assembly sequence is as follows: negative electrode shell-gasket-electrolyte-coating film-electrolyte-gasket-elastic sheet-positive electrode shell

(4) Electrolyte absorption rate: the test sample sizes were 3CM long and 3CM wide; the coating film before soaking was weighed to be M ₀ Soaking the coating film in electrolyte for 30 min, wiping the electrolyte on the surface with non-woven fabric, and weighing to M ₁ The method comprises the steps of carrying out a first treatment on the surface of the Then the liquid absorption= (M ₁ -M ₀ )/M ₀ ×100％。

(5) Electrolyte retention rate: the test sample sizes were 3CM long and 3CM wide; the coating film before soaking was weighed to be M ₀ Soaking the coating film in electrolyte for 30 min, wiping the electrolyte on the surface of the coating film with non-woven fabric, and weighing to M ₁ The method comprises the steps of carrying out a first treatment on the surface of the Soaking the coating film in electrolyte for 12 hr, wiping the electrolyte on the surface of the coating film with non-woven fabric, weighing to obtain M _x Then the liquid retention rate= (M _x -M ₀ )/(M ₁ -M ₀ )×100％。

(6) Porosity: determining the void volume of the coating film as V according to the weight change before and after the coating film soaks water _Hole(s) The method comprises the steps of carrying out a first treatment on the surface of the The framework volume of the membrane is V _{Membrane framework} Obtainable by raw material density and dry film weight; porosity of the coated film=v _Hole(s) /V _{Membrane framework} ＝V _Hole(s) /(V _Hole(s) +V _{Membrane framework} )。

(7) Tensile strength: the test sample has a length of 10CM and a width of 2CM, and a universal tester is adopted, wherein the test speed is 100m/min; the pulling force was 1KN.

The lithium ion batteries provided in application examples 1 to 6 and comparative application examples 1 to 18 were subjected to the electrochemical performance test as follows:

(1) Cycle performance: the electrochemical workstation battery test system is tested at 45 ℃, the tested current density is 1C, and the charging and discharging voltage window is 2.6V-4.2V.

(2) Rate capability: the current density of the test is 0.5C, 1C, 2C, 3C and 4C, and the charge-discharge voltage window is 2.6V-4.2V when the test is carried out on an electrochemical workstation battery test system under the condition of 45 ℃.

The results of the tests are shown in tables 1 and 2:

TABLE 1

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TABLE 2

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As can be seen from the data in Table 1, the polyimide composite membranes provided in examples 1 to 6 of the present invention have a heat shrinkage of not more than 20%, a gas permeation value of not more than 206s/100ml, an ionic conductivity of not less than 1.9mS/cm, a liquid absorption of up to 280% or more, a liquid retention of up to 89% or more, a porosity of up to 40% and a tensile strength of not less than 190Kgf/cm ² Meanwhile, the polyimide composite membrane provided in the embodiment 2 has the optimal comprehensive performance, and the prepared coating membrane has better performances.

Comparative examples 1 and 2 are single-layer coated separators having much greater heat shrinkage than the polyimide composite separator provided in example 1, as compared to example 1; in the case that the physical properties of the ceramics are out of range, the comparative example 3 and the comparative example 4 provide diaphragms with reduced ionic conductivity, liquid absorption, liquid retention and porosity; the separators provided in comparative examples 5 to 18 were reduced in ion conductivity, liquid absorption, liquid retention, and porosity as compared to example 1.

As can be seen from the data of table 2, the lithium ion batteries provided in application examples 1 to 6 of the present invention have a capacity retention rate of not less than 83% after 500 cycles at 1C and a capacity retention rate of not less than 80% after 500 cycles at 2C.

Comparative application example 1 and comparative application example 2 are single-layer coated separators having much lower capacity retention at 1C and 2C than the lithium ion battery provided in application example 1, as compared to example 1; the comprehensive performance of the lithium ion battery provided by other comparative application examples is not as good as that of application example 1, and the polyimide composite diaphragm provided by the invention is favorable for preventing the growth of lithium dendrites of the battery and improving the safety and the cycle life of the lithium ion battery.

The applicant states that the process of the invention is illustrated by the above examples, but the invention is not limited to, i.e. does not mean that the invention must be carried out in dependence on the above process steps. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of selected raw materials, addition of auxiliary components, selection of specific modes, etc. fall within the scope of the present invention and the scope of disclosure.

Claims

1. The preparation method of the polyimide composite diaphragm is characterized in that the polyimide composite diaphragm comprises a polyimide base film, a ceramic coating coated on one side of the polyimide base film and a polymer coating coated on the other side of the polyimide base film; the polymer coating is a meta-aramid coating, and the glass transition temperature of meta-aramid in the meta-aramid coating is 200-450 ℃;

the preparation method comprises the following steps:

(1) Mixing ceramic and deionized water, heating until the ceramic and the deionized water are dissolved, adding a surfactant for stirring and secondary heating, adding the surfactant again for secondary stirring, and filtering to obtain ceramic slurry;

(2) Mixing meta-aramid fiber, a surfactant and deionized water, and filtering to obtain polymer slurry with a solid content of 10% -40%;

(3) Coating ceramic slurry on one side of a polyimide base film, coating polymer slurry on the other side of the polyimide base film, and drying to obtain the polyimide composite diaphragm;

the ceramic in step (1) comprises boehmite or alumina; d of the ceramic ₁₀ The grain diameter is 0.3-0.4 μm, D ₅₀ The grain diameter is 0.6-0.7 mu m, D ₉₀ The grain diameter is 1.3 μm-1.4 μm; the specific surface area of the ceramic is 7m ² /g-8m ² /g；

The viscosity of the ceramic slurry obtained in the step (1) is 20-150 cP, and the solid content of the ceramic slurry is 30-50%;

the surfactant in the step (1) and the step (2) is respectively and independently selected from any two or three of polyoxyethylene ether, sodium alginate, polyvinyl acetate, polyisobutylene, polyacrylate, ethylene-vinyl acetate copolymer, alkyl polyoxyethylene ether, polyoxyethylene-polyoxypropylene segmented copolymer, alkyl sulfate, polyoxyethylene fatty alcohol ether, polyvinylidene fluoride and propylene glycol methyl ether.

2. The method of manufacturing according to claim 1, wherein the polyimide composite separator has a thickness of 6 to 10 μm.

3. The method of claim 1, wherein the ceramic coating has a thickness of 2 μm to 3 μm.

4. The method of claim 1, wherein the polymer coating has a thickness of 2 μm to 3 μm.

5. The method of claim 1, wherein the ratio of the thickness of the ceramic coating to the thickness of the polymer coating is (1.5-2.5): 1.

6. The method according to claim 1, wherein the ceramic has a mass of 10g to 60g.

7. The method according to claim 1, wherein the deionized water has a mass of 10g to 200g.

8. The method according to claim 1, wherein the mixing in step (1) is performed under stirring.

9. The method of claim 8, wherein the stirring is at a rate of 700rpm to 2000rpm.

10. The method of claim 8, wherein the stirring is for a period of 0.01h to 12h.

11. The method according to claim 1, wherein the heating temperature in the step (1) is 10 ℃ to 50 ℃.

12. The method according to claim 1, wherein the heating time in the step (1) is 0.1h to 5h.

13. The method according to claim 1, wherein the mass of the surfactant in the step (1) is 0.01g to 8g.

14. The method according to claim 1, wherein the stirring rate in the step (1) is 300rpm to 2000rpm.

15. The method according to claim 1, wherein the stirring time in the step (1) is 0.1h to 6h.

16. The method according to claim 1, wherein the secondary heating in the step (1) is performed at a temperature of 10 ℃ to 50 ℃.

17. The method according to claim 1, wherein the time of the secondary heating in the step (1) is 0.1h to 2h.

18. The method according to claim 1, wherein the rate of the secondary stirring in the step (1) is 100rpm to 600rpm.

19. The method according to claim 1, wherein the time of the secondary stirring in the step (1) is 0.1h to 6h.

20. The method according to claim 1, wherein the viscosity of the ceramic slurry in the step (1) is 20cP to 150cP.

21. The method according to claim 1, wherein the ceramic slurry in step (1) contains 10 to 98.8% by mass of ceramic in dry material.

22. The preparation method according to claim 1, wherein the mass percentage of the surfactant in the dry material of the ceramic slurry in the step (1) is 0.2% -20%.

23. The preparation method according to claim 1, wherein the mass of the intermediate aramid fiber in the step (2) is 10g-60g.

24. The method according to claim 1, wherein the deionized water has a mass of 10g to 200g.

25. The preparation method according to claim 1, wherein the mass of the surfactant is 60g-200g.

26. The method of claim 1, wherein the mixing is performed with stirring.

27. The method of claim 26, wherein the stirring is at a rate of 500rpm to 1400rpm.

28. The method of claim 26, wherein the stirring is for a period of 0.1h to 10h.

29. The method of claim 1, wherein the viscosity of the polymer syrup in the step (2) is 20cP to 300cP.

30. The preparation method according to claim 1, wherein the mass percentage of the aramid fiber in the middle position of the dry material of the polymer slurry in the step (2) is 2% -50%.

31. The preparation method according to claim 1, wherein the mass percentage of the surfactant in the dry material of the polymer slurry in the step (2) is 20% -90%.

32. The method of claim 1, wherein the ceramic slurry in step (3) is applied by roll coating.

33. The method of claim 1, wherein the polymer slurry in step (3) is applied by spraying.

34. The method of claim 33, wherein the spray coating is at a temperature of 10 ℃ to 80 ℃.

35. The method according to claim 1, wherein the drying temperature in the step (3) is 30 ℃ to 80 ℃.

36. A polyimide composite membrane, which is prepared by the preparation method of any one of claims 1 to 35.

37. A lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator is the polyimide composite separator according to claim 36.