High-energy-density lithium ion battery and preparation method thereof

Abstract

The invention relates to the field of lithium ion batteries, and discloses a high-energy-density lithium ion battery and a preparation method thereof.The isolating membrane of the lithium ion battery comprises a base membrane and a functional coating, and the functional coating comprises ceramic powder, modified polyvinylidene fluoride and a dispersing agent; the modified polyvinylidene fluoride is prepared by mixing and hot-pressing polyvinylidene fluoride, composite polyamide acid resin, a carboxylated oligomer and an epoxy copolymer; the composite polyamide acid resin is prepared from 4, 4 '-diaminodiphenyl ether, pyromellitic dianhydride and nano aluminum oxide; the carboxylated oligomer is prepared from mercaptoacetic acid, methyl methacrylate and 4, 4 '-azobis (4-cyano valeric acid) through a reaction; and the epoxy copolymer is prepared by copolymerizing a phosphorus-containing double-bond intermediate obtained by reacting diphenyl phosphinyl chloride with hydroxyethyl acrylate and glycidyl methacrylate. The isolating membrane prepared by the preparation method disclosed by the invention is excellent in mechanical property, electrolyte wettability, heat resistance and flame retardance, and the lithium ion battery is high in energy density and good in cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a high-energy-density lithium ion battery and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries are widely used in new energy vehicles due to high energy density, fast charging and discharging capacity, long cycle life, no memory effect and other characteristics. The lithium ion battery is mainly composed of a positive electrode material, a negative electrode material, an electrolyte and a separator. The separator, as an important component of the lithium ion battery, plays an electronic insulation role between the positive and negative electrodes and ensures the free movement of ions. The separator does not directly participate in the electrochemical reaction of the battery, but its structure and performance play an important role in the cycle life, safety, energy density and power density of the battery.

[0003] Traditional lithium ion battery separators are mostly polyolefin separators, but polyolefin separators have low melting point, high shrinkage at high temperature, poor wettability with electrolyte and other problems. The existing technology considers that coating ceramic particles on the surface of the polyolefin separator is an effective strategy with controllable cost and easy large-scale production. However, the ceramic coating is mostly formed by stacking ceramic particles without distinction, and the heat resistance of the separator needs to be further improved. In a high-temperature environment, the separator will wrinkle and melt, causing the positive and negative electrodes to directly contact and causing internal short circuit of the battery. In addition, in order to meet the requirements of high-performance and high-safety batteries, the separator must have good electrolyte wettability, heat resistance and mechanical strength. SUMMARY

[0004] To solve the problems mentioned in the background, the purpose of the present application is to provide a high-energy-density lithium ion battery and a preparation method thereof. The isolation film has excellent mechanical properties, electrolyte wettability and heat resistance and flame resistance, and the prepared lithium ion battery has high energy density and good cycle performance.

[0005] The purpose of the present application can be achieved by the following technical solutions: A high-energy-density lithium ion battery comprises a negative electrode sheet, a positive electrode sheet, an electrolyte and an isolation film. The isolation film comprises a base film and a functional coating. The functional coating is arranged on at least one side surface of the base film. The functional coating comprises the following components by weight: 40-70 parts of ceramic powder, 10-30 parts of modified polyvinylidene fluoride and 2-5 parts of a dispersing agent. The modified polyvinylidene fluoride is prepared by mixing polyvinylidene fluoride, composite polyamide acid resin, carboxylated oligomer and epoxy-based copolymer in an internal mixer and then hot pressing in a flat vulcanizing machine. The composite polyamide acid resin is prepared by using 4,4'-diamino diphenyl ether and pyromellitic anhydride as monomers and nano-alumina as a filler; the carboxylated oligomer is prepared by using mercaptoacetic acid, methyl methacrylate and 4,4'-azobis(4-cyanovaleric acid) as raw materials through free radical polymerization; and the epoxy copolymer is prepared by using diphenyl phosphinic chloride and hydroxyethyl acrylate to undergo substitution reaction, and then copolymerizing the prepared phosphorus-containing double bond intermediate and glycidyl methacrylate.

[0006] Preferably, the base film is one of a polypropylene base film, a polyethylene base film and a polypropylene / polyethylene / polypropylene composite film; the ceramic powder is one or a combination of boehmite, titanium dioxide, silicon dioxide and zirconium dioxide; and the dispersant is one or a combination of sodium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyethylene glycol and hydroxyethyl cellulose.

[0007] Preferably, the preparation method of the modified polyvinylidene fluoride comprises the following steps: A. 4,4'-diamino diphenyl ether is added to N,N-dimethylacetamide, stirred and dissolved, then nano-alumina is added, ultrasonic dispersion is performed until uniform, then placed in an ice water bath for stirring, and pyromellitic anhydride is added in batches, stirred and reacted for 6-8 h, after the reaction is completed, vacuum degassing is performed to remove bubbles, and a composite polyamide acid resin is prepared; B. diphenyl phosphinic chloride and hydroxyethyl acrylate are taken in a reactor, nitrogen is introduced into the reactor, stirred and reacted at room temperature for 4-6 h, triethylamine is added in batches during the reaction to remove hydrogen chloride generated in the reaction, after the reaction is completed, the product is filtered, rotary evaporated, and dried to obtain a phosphorus-containing double bond intermediate; C. glycidyl methacrylate, the phosphorus-containing double bond intermediate and azobisisobutyronitrile are taken in a reactor, toluene is added, nitrogen is introduced into the reactor, the reactor is placed in an 85-95℃ water bath and reacted for 15-18 h, after the reaction is completed, the product is dissolved in acetone, precipitated in petroleum ether, and vacuum dried to obtain an epoxy copolymer; D. 4,4'-azobis(4-cyanovaleric acid), methyl methacrylate and mercaptoacetic acid are taken in a reactor, tetrahydrofuran is added, nitrogen is introduced into the reactor, the reactor is placed in a 55-70℃ water bath and reacted for 2-4 h, then diluted by adding acetone, and then precipitated in petroleum ether to remove unreacted monomers, the product is dried, dissolved in acetone, precipitated in deionized water to remove excess mercaptoacetic acid, and finally vacuum dried to obtain a carboxylated oligomer; E. polyvinylidene fluoride, the composite polyamide acid resin, the carboxylated oligomer and the epoxy copolymer are stirred and mixed, then added into a banbury mixer, after mixing, placed in a flat vulcanizing machine for hot pressing, and a modified polyvinylidene fluoride is prepared.

[0008] Preferably, in step B, the molar ratio of diphenylphosphinic chloride to hydroxyethyl acrylate is 1:1 to 1.1.

[0009] Preferably, in step C, the molar ratio of glycidyl methacrylate to the phosphorus-containing double bond intermediate is 1:3.1-3.3.

[0010] Preferably, in step D, the molar ratio of 4,4'-azobis(4-cyanovaleric acid), methyl methacrylate and thioglycolic acid is 0.01-0.02:1-1.5:0.05-0.08.

[0011] Preferably, in step E, the mass ratio of polyvinylidene fluoride, composite polyamic acid resin, carboxylated oligomer and epoxy copolymer is 1:1:0.09-0.15:0.25-0.5.

[0012] Preferably, in step E, the internal mixer temperature is 175-190° C., the mixing time is 5-10 min, the hot pressing temperature is 200-230° C., and the hot pressing time is 3-6 min.

[0013] A method for preparing a high energy density lithium ion battery comprises the following steps: S1. Weighing each component by weight, dissolving the modified polyvinylidene fluoride in N-methylpyrrolidone, then adding ceramic powder and a dispersant, mixing and dispersing the mixture in a ball mill to prepare a functional coating; S2, coating a functional coating on one side of the base film, drying and rolling it up to prepare a separator for a lithium-ion battery; S3. The positive electrode sheet, negative electrode sheet and isolation film are made into a battery cell through a winding process, and then encapsulated with aluminum-plastic film and injected with electrolyte. After going through the processes of formation, capacity, and shaping, a high-energy-density lithium-ion battery is prepared.

[0014] Preferably, the negative electrode sheet uses graphite, conductive carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water as the negative electrode slurry; the positive electrode sheet uses lithium cobaltate, conductive carbon black, polyvinylidene fluoride, and N-methylpyrrolidone as the positive electrode slurry; the electrolyte uses 1 mol / L lithium hexafluorophosphate as the lithium salt, and the organic solvent uses ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0015] Beneficial effects of the present invention: The application utilizes 4,4'-diamino diphenyl ether and pyromellitic anhydride as monomers, and nano-alumina as a filler to prepare a composite polyamide acid resin. A substitution reaction between chlorine atoms in diphenyl phosphinic chloride and hydroxyl groups in hydroxyethyl acrylate is utilized to prepare a phosphorus-containing double bond intermediate containing a flame-retardant phosphorus element. Then, glycidyl methacrylate and the phosphorus-containing double bond intermediate are polymerized under an azobisisobutyronitrile initiator to prepare an epoxy copolymer. In addition, a carboxylated oligomer is prepared by a free radical telomerization reaction using mercaptoacetic acid as a chain transfer agent, methyl methacrylate as a monomer, and 4,4'-azobis(4-cyanopentanoic acid) as an initiator. The carboxylated oligomer and the epoxy copolymer are added to a blend of polyvinylidene fluoride and the composite polyamide acid resin. After mixing, hot pressing is performed on a flat press to prepare modified polyvinylidene fluoride. Part of the composite polyamide acid resin can be partially cured under hot pressing conditions to improve heat resistance. The carboxyl groups on the carboxylated oligomer have a higher reactivity than the carboxyl groups on the composite polyamide acid resin. The carboxyl groups on the carboxylated oligomer react with the epoxy groups on the epoxy copolymer during melt processing, and then the carboxyl groups on the composite polyamide acid resin react with the epoxy groups on the epoxy copolymer to generate a grafted polymer in situ. The side chains of the grafted polymer can effectively entangle with polyvinylidene fluoride segments, which are not prone to migrate during processing, thereby achieving stable and efficient compatibilization of the polyvinylidene fluoride and the composite polyamide acid resin blend. This improves the interfacial adhesion between the two components, and also enables the separator film to exhibit more excellent mechanical properties, electrolyte wettability, and heat resistance and flame retardance. The prepared lithium ion battery has high energy density and good cycle performance. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0017] The preparation method of the modified polyvinylidene fluoride in Example 1 includes the following steps: A. 3 g of 4,4'-diamino diphenyl ether was added to 40 mL of N,N-dimethylacetamide, and after stirring and dissolving, 2 g of nano-alumina was added and uniformly dispersed by ultrasonic. Then, the mixture was placed in an ice water bath and stirred, and 3.27 g of pyromellitic anhydride was added in batches. After stirring for 7 h, the reaction was completed, and the bubbles were removed by vacuum degassing to prepare a composite polyamide acid resin. B, take 2.4g diphenyl phosphinic chloride and 1.2g hydroxyethyl acrylate in the reactor, the reaction is stirred under nitrogen at room temperature for 5h, during the reaction, 1.1g triethylamine is added in batches to remove the hydrogen chloride generated in the reaction, after the reaction is completed, it is prepared by filtration, rotary evaporation, drying to obtain a phosphorus-containing double bond intermediate; C, take 3g glycidyl methacrylate, 21.1g phosphorus-containing double bond intermediate and 0.15g azobisisobutyronitrile in the reactor, add 50mL toluene solvent, react under nitrogen, and react at 90℃ for 18h, after the reaction is completed, it is prepared by dissolving in acetone, precipitating in petroleum ether and vacuum drying to obtain an epoxy copolymer; D, take 0.56g 4,4'-azobis(4-cyanopentanoic acid), 20g methyl methacrylate and 0.92g mercaptoacetic acid in the reactor, add 20mL tetrahydrofuran solvent, react under nitrogen, and react at 60℃ for 4h, then add 60mL acetone for dilution, then precipitate in petroleum ether to remove unreacted monomers, after drying the reaction product, it is dissolved in 40mL acetone, then precipitated in deionized water to remove excess mercaptoacetic acid, and finally vacuum dried to obtain a carboxylated oligomer; E, take 5g polyvinylidene fluoride, 5g composite polyamide acid resin, 0.5g carboxylated oligomer and 2g epoxy copolymer, mix them after stirring, then add them into a banbury mixer, the temperature of the banbury mixer is 190℃, the rotating speed is set to 50rpm, and the mixing time is 10min, after mixing, it is hot pressed in a flat vulcanizing machine, the pressure is 10Mpa, the hot pressing temperature is 220℃, and the hot pressing time is 6min, to obtain a modified polyvinylidene fluoride.

[0018] The preparation method of the positive electrode sheet of example 2 comprises the following steps: dissolving the positive electrode active material lithium cobaltate, conductive carbon black and binder polyvinylidene fluoride in N-methyl pyrrolidone according to the mass ratio of 96:2:2 to uniformly mix and prepare a positive electrode slurry, then uniformly coating the positive electrode slurry on the positive electrode current collector aluminum foil, then drying at 85℃, and then cold pressing, edge cutting, sheet cutting, striping and welding the tab to prepare the positive electrode sheet.

[0019] The preparation method of the negative electrode sheet of example 3 comprises the following steps: dissolving the graphite electrode material, conductive carbon black, binder styrene-butadiene rubber and thickening agent sodium carboxymethyl cellulose in deionized water according to the mass ratio of 92:2:5:1 to uniformly mix and prepare a negative electrode slurry, then uniformly coating the negative electrode slurry on the negative electrode current collector copper foil, then drying at 85℃, then cold pressing, and then edge cutting, sheet cutting, striping and welding the tab to prepare the negative electrode sheet.

[0020] The functional coating of example 4 comprises the following components by weight: 44 parts of silica ceramic powder, 10 parts of the modified polyvinylidene fluoride prepared in example 1, and 2.5 parts of dispersant sodium carboxymethyl cellulose.

[0021] A method for preparing a high energy density lithium ion battery, comprising the following steps: S1, each component is weighed by weight parts, the modified polyvinylidene fluoride is dissolved in N-methyl pyrrolidone, then the ceramic powder and the dispersing agent are added and mixed and dispersed in a ball mill tank to prepare a functional coating; S2, the functional coating is coated on one side surface of a polyethylene-based film, dried and wound to prepare a separator film for lithium ion batteries; S3, the positive electrode sheet prepared in Example 2, the negative electrode sheet prepared in Example 3 and the separator film (thickness of 12 μm) are subjected to a winding process to make a battery cell, then packaged with an aluminum plastic film and injected with an electrolyte, the electrolyte uses 1 mol / L lithium hexafluorophosphate as a lithium salt, and an organic solvent uses ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7, then subjected to formation, capacity, shaping and other processes to prepare a high energy density lithium ion battery.

[0022] Example 5 A functional coating comprises the following components by weight parts: 51 parts of silica ceramic powder, 17 parts of modified polyvinylidene fluoride prepared in Example 1, and 3.5 parts of dispersing agent hydroxyethyl cellulose.

[0023] A method for preparing a high energy density lithium ion battery is the same as that in Example 4.

[0024] Example 6 A functional coating comprises the following components by weight parts: 66 parts of silica ceramic powder, 25 parts of modified polyvinylidene fluoride prepared in Example 1, and 4.7 parts of dispersing agent sodium carboxymethyl cellulose.

[0025] A method for preparing a high energy density lithium ion battery is the same as that in Example 4.

[0026] A method for preparing a modified polyvinylidene fluoride comprises the following steps: A, 3g of 4,4'-diamino diphenyl ether is taken into 40mL of N,N-dimethylacetamide, stirred and dissolved, then 2g of nano alumina is added, ultrasonic dispersion is uniform, then placed in an ice water bath for stirring, 3.27g of pyromellitic anhydride is added in batches, stirred and reacted for 7h, after the reaction is completed, vacuum degassing is performed to remove bubbles, and a composite polyamide acid resin is prepared; B, 0.56g of 4,4'-azobis(4-cyanopentanoic acid), 20g of methyl methacrylate and 0.92g of mercaptoacetic acid are taken in a reactor, 20mL of tetrahydrofuran solvent is added, nitrogen is passed, and it is placed at 60℃ for 4h, then 60mL of acetone is added for dilution, then the unreacted monomers are removed by settling in petroleum ether, the reaction product is dried, then 40mL of acetone is used for dissolution, then it is settled in deionized water to remove excess mercaptoacetic acid, and finally vacuum dried to prepare a carboxylated oligomer; C. Take 5g polyvinylidene fluoride, 5g composite polyamide acid resin, 0.5g carboxylated oligomer, stir and mix, then add to the internal mixer, the temperature of the internal mixer is 190℃, set the speed to 50rpm, mixing time is 10min, after mixing, place it in the flat vulcanizing machine for hot pressing, pressure is 10Mpa, hot pressing temperature is 220℃, hot pressing time is 6min, to obtain the modified polyvinylidene fluoride.

[0027] The preparation method of the modified polyvinylidene fluoride of Comparative Example 2 comprises the following steps: A. Take 3g 4,4'-diamino diphenyl ether and add it to 40mL N,N-dimethylacetamide, stir and dissolve, then add 2g nano alumina, ultrasonic dispersion, then place it in an ice water bath and keep stirring, add 3.27g pyromellitic anhydride in batches, stir and react for 7h, after the reaction is completed, perform vacuum degassing to remove bubbles, to obtain the composite polyamide acid resin; B. Take 2.4g diphenylphosphine chloride and 1.2g hydroxyethyl acrylate in a reactor, react under nitrogen, stir at room temperature for 5h, add 1.1g triethylamine in batches during the reaction to remove the hydrogen chloride generated in the reaction, after the reaction is completed, perform filtration, rotary evaporation and drying, to obtain the phosphorus-containing double bond intermediate; C. Take 3g glycidyl methacrylate, 21.1g phosphorus-containing double bond intermediate and 0.15g azobisisobutyronitrile in a reactor, add 50mL toluene solvent, react under nitrogen, place it in a 90℃ oven and react for 18h, after the reaction is completed, use acetone to dissolve, petroleum ether to settle, and vacuum drying, to obtain the epoxy copolymer; D. Take 5g polyvinylidene fluoride, 5g composite polyamide acid resin, 2g epoxy copolymer, stir and mix, then add to the internal mixer, the temperature of the internal mixer is 190℃, set the speed to 50rpm, mixing time is 10min, after mixing, place it in the flat vulcanizing machine for hot pressing, pressure is 10Mpa, hot pressing temperature is 220℃, hot pressing time is 6min, to obtain the modified polyvinylidene fluoride.

[0028] The functional coating of Comparative Example 3 comprises the following components by weight: 66 parts of silica ceramic powder, 25 parts of the modified polyvinylidene fluoride prepared in Comparative Example 1, and 4.7 parts of the dispersant carboxymethyl cellulose sodium.

[0029] The preparation method of the high-energy-density lithium ion battery is the same as that of Example 4.

[0030] The functional coating of Comparative Example 4 comprises the following components by weight: 66 parts of silica ceramic powder, 25 parts of the modified polyvinylidene fluoride prepared in Comparative Example 2, and 4.7 parts of the dispersant carboxymethyl cellulose sodium.

[0031] The preparation method of the high-energy-density lithium ion battery is the same as that of Example 4.

[0032] Comparative Example 5 A functional coating comprising the following parts by weight: silica ceramic powder 66 parts, polyvinylidene fluoride 25 parts, dispersing agent sodium carboxymethyl cellulose 4.7 parts.

[0033] A method for preparing a high energy density lithium ion battery as in Example 4.

[0034] Performance testing A, the lithium ion battery prepared by example 4-6 and comparative example 3-5 was tested for performance with the separator film: (1) heat shrinkage rate test: the separator film sample was cut into 2x2cm size, heated in a vacuum drying oven at 170℃ for 30min, and the size change of the separator film was observed, and the data results are shown in Table 1.

[0035] (2) tensile strength test: the separator film sample was cut into 45x5mm size, stretched at a rate of 5mm / min, five samples in each group, and the average value was the final result, and the data results are shown in Table 1.

[0036] (3) electrolyte absorption rate test: determined by contact angle and electrolyte holding rate, contact angle test is to drop 5-20μL electrolyte on the surface of the separator film, record the included angle between the electrolyte and the separator, the smaller the angle, the better the electrolyte spreads on the surface of the separator, the stronger the affinity between them; electrolyte holding rate test is to weigh the mass of the unwetted separator film as M1, then completely immerse the separator film in electrolyte for 1h, wipe off the excess electrolyte on the surface, weigh the mass of the soaked separator film as M2, calculate by the formula: electrolyte absorption rate=(M2-M1) / M1x100%, and the data results are shown in Table 1.

[0037] (4) flame retardant performance test: the separator film was cut into a circular sample with a diameter of 20mm, then a lighter was used to ignite continuously for 10s, and the performance of the separator film was observed to determine the flame retardant ability of the separator film, and the data results are shown in Table 1.

[0038] Table 1 performance test results of samples

[0039] As can be seen from the data in Table 1, the separators prepared in Examples 4-6 have high tensile strength, small contact angle, high electrolyte retention rate, excellent electrolyte wettability, low thermal shrinkage rate, good thermal stability, and good heat-resistant and flame-retardant properties. The tensile strength and electrolyte retention rate of the separators prepared in Comparative Examples 3-4 are lower than those of the separators prepared in Examples 4-6, and the thermal shrinkage rate is higher than that of the separators prepared in Examples 4-6, indicating that the introduction of the epoxy-based copolymer and the carboxylated oligomer can synergistically improve the thermal stability, mechanical properties and electrolyte wettability of the separators. The separator prepared in Comparative Example 3 starts to shrink and burns after being burned by a flame for 3 seconds, indicating that the introduction of the epoxy-based copolymer can improve the flame-retardant properties of the separator to some extent. The properties of the separator prepared in Comparative Example 5 are significantly lower than those of the separators prepared in Examples 4-6, indicating that the modification of the polyvinylidene fluoride component can improve the mechanical properties, electrolyte wettability and heat-resistant and flame-retardant properties of the separator.

[0040] B. Performance detection of the lithium ion batteries prepared in Examples 4-6 and Comparative Examples 3-5: (1) Energy density test: The capacity value and voltage of the battery cell after capacity distribution were obtained, and the energy value was calculated according to the capacity value x voltage = energy value. The length, width and thickness of the battery cell were measured, and the volume was calculated. The ratio of the energy value to the volume was the volume energy density. The data results are shown in Table 2.

[0041] (2) Cycle performance test: The test temperature was 25±3°C, the charging current was 1C, the discharging current was 0.5C, and the cycle number was 500 cycles. The data results are shown in Table 2.

[0042] Table 2. Performance detection results of samples

[0043] As can be seen from the data in Table 2, the lithium ion batteries prepared in Examples 4-6 have more excellent energy density and cycle performance than the batteries prepared in Comparative Examples 3-5.

[0044] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" 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 does not necessarily refer 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.

[0045] The foregoing is considered as illustrative only of the principles of the application. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the application to the exact construction and practice described. Accordingly, all such variations and modifications are intended to be included within the scope of the application as defined in the following claims.

Claims

1. A high energy density lithium ion battery, characterized in that: The invention comprises a negative electrode sheet, a positive electrode sheet, an electrolyte and a separator, wherein the separator comprises a base film and a functional coating, wherein the functional coating is provided on at least one side of the base film, and the functional coating comprises the following components in parts by weight: 40 to 70 parts of ceramic powder, 10 to 30 parts of modified polyvinylidene fluoride, and 2 to 5 parts of a dispersant; The modified polyvinylidene fluoride is prepared by mixing polyvinylidene fluoride, composite polyamic acid resin, carboxyl oligomer and epoxy copolymer in an internal mixer and then hot pressing in a flat vulcanizer. The composite polyamic acid resin is prepared by using 4,4'-diaminodiphenyl ether and pyromellitic anhydride as monomers and nano-alumina as filler; the carboxylated oligomer is prepared by using thioglycolic acid, methyl methacrylate, and 4,4'-azobis(4-cyanovaleric acid) as raw materials through a free radical polymerization reaction; the epoxy copolymer is prepared by using diphenylphosphinyl chloride and hydroxyethyl acrylate to undergo a substitution reaction, and then copolymerizing the prepared phosphorus-containing double bond intermediate with glycidyl methacrylate.

2. The high energy density lithium ion battery according to claim 1, characterized in that The base film is one of a polypropylene base film, a polyethylene base film, and a polypropylene / polyethylene / polypropylene composite film; the ceramic powder is one or more combinations of boehmite, titanium dioxide, silicon dioxide, and zirconium dioxide; and the dispersant is one or more combinations of sodium carboxymethyl cellulose, polyacrylic acid, sodium polyacrylate, polyethylene glycol, and hydroxyethyl cellulose.

3. The high energy density lithium ion battery according to claim 1, characterized in that The preparation method of the modified polyvinylidene fluoride comprises the following steps: A. Add 4,4'-diaminodiphenyl ether to N,N-dimethylacetamide, stir and dissolve, then add nano-alumina, ultrasonically disperse evenly, place in an ice-water bath and keep stirring, add pyromellitic anhydride in batches, stir and react for 6-8 hours, and after the reaction is completed, vacuum and remove bubbles to prepare a composite polyamic acid resin; B. Diphenylphosphinic acid chloride and hydroxyethyl acrylate were placed in a reactor, nitrogen was passed through the reactor, and the reaction was stirred at room temperature for 4 to 6 hours. During the reaction, triethylamine was added in batches to remove hydrogen chloride produced by the reaction. After the reaction was completed, the mixture was filtered, rotary evaporated, and dried to obtain a phosphorus-containing double bond intermediate. C. Glycidyl methacrylate, a phosphorus-containing double bond intermediate, and azobisisobutyronitrile were placed in a reactor, toluene solvent was added, nitrogen was passed through the reactor, and the reaction was carried out at 85-95° C. for 15-18 hours. After the reaction was completed, the epoxy copolymer was dissolved in acetone, settled with petroleum ether, and dried in vacuo to obtain the epoxy copolymer. D. 4,4'-azobis(4-cyanovaleric acid), methyl methacrylate, and thioglycolic acid were placed in a reactor, tetrahydrofuran solvent was added, nitrogen was passed through the reaction, and the reaction was carried out at 55-70°C for 2-4 hours. Acetone was then added to dissolve and dilute the mixture, and the unreacted monomers were subsequently precipitated in petroleum ether to remove the reaction product. The reaction product was dried, dissolved in acetone, and then precipitated in deionized water to remove excess thioglycolic acid. Finally, the reaction product was dried in vacuo to obtain a carboxylated oligomer. E. Take polyvinylidene fluoride, composite polyamic acid resin, carboxyl oligomer and epoxy copolymer, stir and mix them, and then add them into an internal mixer. After the mixing is completed, place them into a flat vulcanizer for hot pressing to prepare modified polyvinylidene fluoride.

4. The high energy density lithium ion battery according to claim 3, characterized in that In step B, the molar ratio of diphenylphosphinic chloride to hydroxyethyl acrylate is 1:1-1.

1.

5. The high energy density lithium ion battery according to claim 3, characterized in that: In the step C, the molar ratio of glycidyl methacrylate to the phosphorus-containing double bond intermediate is 1:3.1-3.

3.

6. The high energy density lithium ion battery according to claim 3, characterized in that: In the step D, the molar ratio of 4,4'-azobis(4-cyanovaleric acid), methyl methacrylate and thioglycolic acid is 0.01-0.02: 1-1.5: 0.05-0.

08.

7. The high energy density lithium ion battery according to claim 3, characterized in that: In the step E, the mass ratio of polyvinylidene fluoride, composite polyamic acid resin, carboxylated oligomer and epoxy copolymer is 1:1:0.09-0.15:0.25-0.

5.

8. The high energy density lithium ion battery according to claim 3, characterized in that: In the step E, the internal mixer temperature is 175-190° C., the mixing time is 5-10 min, the hot pressing temperature is 200-230° C., and the hot pressing time is 3-6 min.

9. A method for preparing a high energy density lithium ion battery according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Weighing each component by weight, dissolving the modified polyvinylidene fluoride in N-methylpyrrolidone, then adding ceramic powder and a dispersant, mixing and dispersing the mixture in a ball mill to prepare a functional coating; S2, coating a functional coating on one side of the base film, drying and rolling it up to prepare a separator for a lithium-ion battery; S3. The positive electrode sheet, negative electrode sheet and isolation film are made into a battery cell through a winding process, and then encapsulated with aluminum-plastic film and injected with electrolyte. After going through the processes of formation, capacity, and shaping, a high-energy-density lithium-ion battery is prepared.

10. The method for preparing a high energy density lithium ion battery according to claim 9, wherein: The negative electrode sheet uses graphite, conductive carbon black, styrene-butadiene rubber, sodium carboxymethyl cellulose, and deionized water as the negative electrode slurry; the positive electrode sheet uses lithium cobalt oxide, conductive carbon black, polyvinylidene fluoride, and N-methylpyrrolidone as the positive electrode slurry; the electrolyte uses 1 mol / L lithium hexafluorophosphate as the lithium salt, and the organic solvent uses ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

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