WO2014072789A2

WO2014072789A2 - Porous polymer membrane, preparation method therefor, and use of same in gel polymer electrolyte

Info

Publication number: WO2014072789A2
Application number: PCT/IB2013/002452
Authority: WO
Inventors: 连芳; 任岩; 关红艳; 文炎
Original assignee: 约翰逊控制技术公司; 北京科技大学
Priority date: 2012-11-09
Filing date: 2013-11-05
Publication date: 2014-05-15
Also published as: WO2014072789A3; CN103804892A; CN103804892B

Abstract

The present invention provides a porous polymer membrane obtained through the use of a polyurethane-treated polyvinylacetal polymer, and a preparation method for said porous polymer membrane. Through-pores are evenly distributed across the porous membrane, giving said membrane excellent electrolytic liquid adsorption capabilities and allowing for a liquid adsorption rate of 300% or higher. Electrolytic liquid adsorption and swelling results in system gelation, and the porous membrane and gel system can thereby remain stable for a long period of time. The near-liquid electrolyte in the present invention has an average electro-conductivity value of 1.0 x 10-3S/cm, an electrochemical stability window of 2.0V-5.0V, markedly improved mechanical properties and electrocompatibility, and can act as a gel polymer electrolyte, thereby enhancing battery safety. The invention also renders unnecessary the use of a liquid electrolyte system or other battery system diaphragm as a support.

Description

Description Polymer porous membrane, preparation method thereof and application in gel polymer electrolyte

The invention belongs to the technical field of preparation and application of polymer films, in particular to a polymer porous film and a preparation method thereof, and a stable system for adsorbing and swelling an electrolyte as a gel polymer electrolyte: Background Art

Gel polymer is widely used as a gel polymer electrolyte system instead of a liquid electrolyte of a lithium ion battery, and has a high ion conductivity close to that of a liquid electrolyte, and has a characteristic that the solid electrolyte does not leak. It can solve the high volatility and flammability of organic electrolytes, and may cause safety problems such as cracking, fire and explosion in case of short circuit. It provides guarantee for the application of large-scale lithium-ion batteries in the field of new energy vehicles and solar energy and wind energy energy storage equipment.

At present, most of the researches are polyoxyethylene (PEO), polyacrylonitrile (PA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (P VDF) and other polar group-containing polymers. Gel polymer electrolyte.

The PEO-based gel polymer electrolyte is easy to crystallize, resulting in low electrical conductivity at room temperature. The interface between the gel polymer film and the lithium electrode in the PAN-based gel polymer electrolyte is severely deactivated, and the mechanical properties are degraded when the plasticizer content is high. It is more serious; PMMA-based gel polymer electrolyte has poor mechanical properties; PVDF-based gel polymer electrolyte has a regular polymer structure and is easy to crystallize, which is not conducive to ion conduction. It can be seen that there are widespread problems with commonly used gel polymer bases, and gel film stability, mechanical properties and compatibility with electrodes still need to be improved. In addition, the problem of oozing out of the electrolyte from the gel has not been properly solved. Summary of the invention

Polyvinyl acetal and its derivatives have the advantages of good film formability, heat resistance, water resistance and relatively stable chemical structure. They have been widely used in adhesives, chemical coatings, medical hemostatic sponges, etc. It is used in a lithium ion battery gel polymer electrolyte system. It mainly contains the following structural units (wherein R=H, methyl, ethyl or propyl):

0) (2) (3) (4) Uchida Yuji et al. In the invention patent [CN101176233A], a gel polymer electrolyte was prepared, which consisted of polyvinyl acetal or a derivative thereof, a solvent, and lithium hexafluorophosphate. Lithium hexafluorophosphate acts as a catalyst to further polymerize the polyvinyl acetal or its derivative to form a polymer electrolyte, which inhibits leakage of the electrolyte and improves discharge performance.

As for the invention patent [CN101 ² 88198A], it is mentioned that the solubility and ion conductivity of the polyvinyl condensate are improved by adjusting the composition ratio of the cyclic compound and the linear compound in the organic solvent.

In the invention patent [CN101103070A], Hiroshi Sugawara et al. mentioned that the ratio of vinyl alcohol units in polyvinyl acetal is reduced by acid modification, and acid modification not only causes intramolecular exchange reaction of acetal ring, but also is isolated. The vinyl alcohol unit becomes a plurality of linked structures, thereby improving the gelation performance of the organic solvent.

It can be seen that the polyvinyl acetal-based polymer has a good prospect for application to a lithium ion battery gel polymer, but the polyvinyl acetal and its derivative have high solubility in an organic solvent such as a carbonate, and are not stable, so When the gel polymer electrolyte is prepared by the in-situ polymerization process, the separator member must be placed, resulting in an increase in the interface.

In the invention patent [CN 1800234A], Li Fangxing et al. prepared a cross-linked polyvinyl acetal polyurethane which can dissolve the network, in which dibutyltin dilaurate or dilauric acid was used as a catalyst, and 4,4'- Diphenylmethane diisocyanate (MDI) chemically crosslinks polyvinyl acetal into a network structure, which is soluble in coatings, paints, adhesives, and the like.

There have been no reports in the published articles and patents on the preparation of a polyvinyl acetal-based porous film by the method of the present invention and gelation thereof into a polymer electrolyte.

The object of the present invention is to provide a porous film of polyvinyl acetal and a derivative thereof, and a method for producing the same, which are chemically crosslinked into a three-dimensional network-like stable structure. The polymer porous film exhibits the advantages of excellent film formability, heat resistance, good water resistance, and relatively stable chemical structure of the polyvinyl acetal and its derivatives, and the above polymer porous film and preparation thereof The method solves the problem that the polyvinyl acetal and its derivative have high solubility in an organic solvent such as carbonate and cannot be stably existed, and the chemical stability is remarkable. Improve. The above polymer porous membrane has good ability of adsorbing electrolyte, and the liquid absorption rate is up to

More than 300%, the gelation of the system is achieved by adsorbing and swelling the electrolyte (including a carbonate-based electrolyte system), and the porous membrane and the gel system can be stably existed for a long period of time.

Further, it is an object of the present invention to apply the above polymer porous film to a gel polymer electrolyte, particularly to a gel polymer lithium ion battery. Since the polymer porous membrane and the formed gel polymer electrolyte can be stably existed for a long period of time, there is no problem of dissolution of the polymer porous membrane in the system and electrolyte leakage, and the above polymer porous membrane will swell in the electrolyte. Gelation or arch I found that the field polymerization is integrated with the electrolyte, and does not require the use of a liquid electrolyte system or a separator in other battery systems as a support, thereby avoiding an increase in the interface and effectively improving the ionic conductivity of the gel polymer electrolyte. . Moreover, since the polymer porous membrane achieves gelation of the system by adsorbing the swelling electrolyte (including a carbonate-based electrolyte system), when it is applied to the gel polymer electrolyte, the solid electrolyte is not provided. The characteristics of the 3⁄4 liquid; at the same time, since the transport speed of ions in the gel polymer electrolyte is greater than the transport speed in the solid electrolyte, the polymer porous membrane can be obtained in the gel polymer electrolyte, and can be obtained with respect to the solid electrolyte. High conductivity. With respect to the liquid electrolyte, the polymer porous film does not cause a liquid leakage problem in the liquid electrolyte when applied to the gel polymer electrolyte, and at the same time, a conductivity substantially equal to that of the liquid electrolyte can be obtained, and the polymer is obtained. The use of a porous membrane for a gel polymer electrolyte facilitates battery assembly. Further, polyvinyl acetal and its derivatives have conventionally been used as binders and have good bonding properties. The polymer porous film according to the present invention exhibits good adhesion properties of polyvinyl acetal and its derivatives, and therefore, the gel polymer electrolyte formed of the above polymer porous film has a polymer porous film as compared with other polymer porous films Excellent adhesion and compatibility with the electrode, reducing the electrochemical polarization of the interface, high electrochemical stability, and the electrical conductivity is close to the average value of the liquid electrolyte conductivity of 10-3⁄4/cm. Moreover, it has high mechanical properties, and the assembled battery using the gel polymer electrolyte is convenient to operate and simple in process.

The polymer porous membrane of the present invention is subjected to chemical crosslinking treatment, and the chemically crosslinked structure of the polyurethane is as follows:

(where: R = H, methyl, ethyl or propyl)

The preparation steps of the polymer porous membrane are as follows:

(a) dissolving polyvinyl formal or a homolog thereof and an organic solvent in an organic solvent in a mass ratio of 1:5 to 1:20, and disposing it as a solution;

(b) adding a diisocyanate substance capable of chemically crosslinking polyvinyl formal or a homolog thereof to the solution disposed above, and the mass ratio of the polyvinyl formal or its homologue to the diisocyanate is 10:1 - 2:1, stirring for 30min;

(c) adding a certain proportion of the non-solvent of polyvinyl acetal and its urethane product to the solution configured above, according to the non-solvent of polyvinyl formal or its homologue and polyvinyl alcohol and its chemical cross-linking product The mass ratio of the solvent is 10:1 - 1:1, and the white micelles are precipitated, and after stirring, the micelles are dissolved;

(d) after uniformly coating the solution prepared in the above step, immersing in a non-solvent bath of polyvinyl acetal and its urethane product or a mixed bath of the solvent and the non-solvent to precipitate a white film;

(e) Drying the white film to obtain a polymer porous film.

The organic solvent described in the above preparation step (a) is preferably at least one of N-methylpyrrolidone, hydrazine, hydrazine-dimethylformamide, chloroform, tetrahydrofuran, and polyethylene according to a similar compatibility principle. An organic solvent having a solubility difference of acetal or a homolog thereof of 1.7 to 2; the diisocyanate material described in the above production process step (b) is preferably 4,4'-diphenylmethane diisocyanate or toluene-2. At least one of 4-diisocyanate, toluene 2,6-diisocyanate, hexamethylene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate; non-described in the above preparation process step (c) The solvent is preferably at least one of deionized water, anhydrous methanol, and anhydrous ethanol; the drying step described in the preparation step (e) is blast drying or vacuum drying at 30 ° C - 60 ° C. . The above polymer porous film can be applied to a gel polymer electrolyte, and the polymer porous film adsorbs and swells the electrolyte to effect gelation to form a gel polymer electrolyte. Among them, the main component of the electrolytic solution is a lithium salt or an organic solvent.

A lithium ion battery can be assembled by using the gel polymer electrolyte formed of the above polymer porous film. The positive electrode in the lithium ion battery system is at least one selected from the group consisting of lithium iron phosphate, nickel cobalt manganese ternary material, spinel lithium manganate, high capacity lithium-rich manganese-based material, and the negative electrode is selected from the following materials. At least one of: graphite, hard carbon, lithium titanate, silicon based compounds and alloys.

The lithium salt in the electrolyte used in the lithium ion battery system is at least one selected from the group consisting of LiPF ₆ , LiC 10 ₄ , LiBF ₄ , LiAsF ₆ , LiAlCl ₄ , LiCF ₃ S〇 ₃ , LiN (S〇 ₂ CF ₃ ) ₂ LiBOB, LiSbF ₆ , LiSCN, LiSnF ₆ , LiGeF ₆ , LiTaF ₆ .

The organic solvent in the electrolyte used in the lithium ion battery system is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinyl sulfite, sulfurous acid. Propylene ester, dimethyl sulfite, diethyl linoleate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, Ethyl propionate, ethyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, dioxolane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, acetonitrile, two Sulfoxide, acetone, hydrazine, hydrazine-dimethylformamide, sulfolane, dimethyl sulfone.

The lithium ion battery is mainly composed of a gel polymer electrolyte layer formed by the polymer porous film of the present invention, a positive electrode pole piece, a negative electrode pole piece, a positive electrode tab, a negative electrode tab, and the like, and the battery can be assembled in a winding type. Or a laminated type, that is, a manufacturing method generally used for a lithium ion battery, and a schematic structural view thereof is shown in FIG. The invention has the following advantages:

The polyvinyl acetal and its derivative of the polymer porous film of the present invention are non-irritating, non-toxic, environmentally friendly, non-flammable, and highly safe. The porous polymer membrane prepared by the technique of the present invention is chemically crosslinked, has good chemical stability, is not dissolved in an organic solvent such as carbonate, and is chemically stable. The interconnected pores of the polymer porous membrane can quickly adsorb the electrolyte, and form a long-term stable gel polymer electrolyte as a host material and support. This is related to polyvinyl acetal and its derivatives as a gelling agent. There is an essential difference in the gelation process. The polymer porous film of the present invention does not dissolve in an electrolyte system including a carbonate as a main solvent, and both mechanical properties and compatibility with electrodes are improved. Therefore, high chemical stability and mechanical strength bring greater convenience to the battery process, and do not require the use of a liquid electrolyte system or a separator of other battery systems as a support, thereby avoiding widespread use at present. The use of a diaphragm member in a gel polymer lithium ion battery effectively reduces the number of interfaces in the lithium ion battery structure, which is close to the average value of the liquid electrolyte of 10 - ³ S/cm. DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing the structure of a lithium battery cell of a gel polymer electrolyte layer formed by using the polymer porous film of the present invention.

Fig. 2 is a view showing the appearance of a polyvinyl formal (PVFM polymer porous film) by chemically crosslinking 4,4'-diphenylmethane diisocyanate (MDI) prepared in Example 1.

Fig. 3 is a microscopic top view of a polyvinyl butyral (PVB) polymer porous film of MDI chemically crosslinked prepared in Example 2.

Fig. 4 is a view showing the appearance of a polyvinyl formal (PVFM) polymer porous film prepared in Comparative Example 1.

Figure 5 is a graph showing the results of an electrochemical stabilization window by linear sweep voltammetry after the polymer porous membrane prepared in Example 1 was initiated as a gel polymer electrolyte.

Fig. 6 shows the results of charge and discharge cycle test of the lithium ion battery prepared in Example 8, with a voltage range of 2.5 V to 4.25 V and a charge and discharge rate of 0.1 C. detailed description

The parameter determination of the present invention is described as follows: Determination of liquid absorption rate

Gelation can be achieved by MDI chemically crosslinked PVFM porous membranes. During the gelation process, the electrolyte gradually immersed in the interior of the polymer porous membrane to swell the polymer, and the white film gradually became transparent. After immersing in the electrolyte for 30 mmir, the formed gel polymer porous film was taken out from the electrolytic solution, drained, and the residual electrolyte on the surface of the gel polymer porous film was blotted with a filter paper to measure the liquid absorption rate.

The liquid absorption rate (absorbance / porous film mass) X 100% where the amount of liquid absorption is the difference between the mass of the porous film before and after the electrolyte is soaked. Calculation method of conductivity

The gel polymer electrolyte to be tested was clamped with a stainless steel sheet to form a battery of I stainless steel I GPE I stainless steel I structure, and the electrochemical interface impedance was measured. The ionic conductivity σ of the gel polymer film was calculated according to the following formula: a=L/AR

Where L is the thickness of the polymer film, A is the contact area of the film with the stainless steel working electrode, and R is the solution resistance of the gel polymer electrolyte. Example 1

0.1015 g of polyvinyl formal (PVFM) was dissolved in 1.0125 g of N-methylpyrrolidone (MP), magnetically stirred at 45 ° C until the PVFM was completely dissolved, and 0.0300 g of 4,4'-diphenylmethane was added to the solution. Diisocyanate (MDI), stirred at 75 ° C for 30 min, and then added 0.1295 g of deionized water as a non-solvent for polyvinyl acetal and its urethane product, white gums were precipitated, and white micelles were dissolved and dissolved. The magnetic stirring was continued for 30 min, and the mixed solution was prepared. The mixed solution was coated with a film, immersed in deionized water to prepare a porous film, and the obtained porous film was dried for 1 hour. The method of drying the porous film may be, for example, but not limited to, placing the porous film at 30 ° C - 60 ° C, by air drying or vacuum drying. Figure 2 is a microscopic appearance of the PVFM polymer porous membrane prepared in Example 1, and the uniformly distributed interconnected pores brought a high liquid absorption rate of 593%. The PVFM polymer porous membrane prepared in Example 1 has high liquid absorption rate and high chemical stability, and is a prerequisite and basis for forming a stable gel electrolyte system and obtaining high electrical conductivity. The conductivity of the gel electrolyte systems PVFM porous polymer membrane prepared in Example 1 was formed a stable ^{1.25 X l (X 3 S /} cm, the conductivity of the liquid electrolyte is slightly higher than the average 1CT ³ S / _C m. And The linear sweep voltammetry test results of Figure 5 show that the electrochemical stability window of the stable gel electrolyte system formed by the PVFM polymer porous membrane prepared in Example 1 is in the range of 2.0V~5.0V, which is higher than that of the liquid electrolyte. The chemical stability window is 2.0V~4.3V, and the electrochemical stability is better than that of the liquid electrolyte.

0.1049 g of polyvinyl butyral (PVB) was dissolved in 1.9975 g of N-methylpyrrolidone (NMP), magnetically stirred at 45 ° C until the PVB was completely dissolved, and 0.0111 g of 4,4 '-diphenyl was added to the solution. Methane diisocyanate (MDI), stirred at 75 ° C for 30 min, and then added dropwise 0.01971 g of deionized water to precipitate white micelles. The white micelles were dissolved by stirring to dissolve, and magnetic stirring was continued for 30 min. The mixed solution was prepared. The mixed solution was coated with a film and immersed in deionized water to prepare a porous film, and the obtained porous film was dried for 1 hour. The method of drying the porous film may be, for example, but not limited to, placing the porous film at 30 ° C - 60 ° C, by air drying or vacuum drying. 3 is a microscopic morphology of the PVB polymer porous film prepared in Example 2, and the uniformly distributed interconnected pores bring a high liquid absorption rate of 610%. The high liquid absorption rate and high chemical stability of the PVB polymer porous membrane form a stable gel electrolyte system and obtain higher electricity. The premise and basis of the conductivity. The PVB polymer porous membrane prepared in Example 2 formed a stable gel electrolyte system having a conductivity of 1.33 X 10- ³ S/cm, which is slightly higher than the average value of the liquid electrolyte conductivity of 10 - ³ S/cm. Example 3

0.1012 g of polyvinyl formal (PVFM) was dissolved in 1.0343 g of N-methylpyrrolidone (NMP), magnetically stirred at 45 ° C until the PVFM was completely dissolved, and 0.015 g of 4,4 '-diphenylmethane was added to the solution. The diisocyanate (MDI) was stirred at 75 ° C for 30 min, and 0.0114 g of deionized water was added dropwise to precipitate a white micelle. The white micelles were dissolved by stirring to dissolve, and the magnetic stirring was continued for 30 min. The mixed solution was prepared. The mixed solution was coated with a film, immersed in deionized water to prepare a porous film, and the obtained porous film was dried for 1 hour. The method of drying the porous film may be, for example, but not limited to, placing the porous film at 30 ° C - 60 ° C, by air drying or vacuum drying. The synthetic PVFM polymer porous membrane prepared in Example 3 has a high liquid absorption rate of 411% and high chemical stability, and provides a prerequisite for stable gel electrolyte system formation and high electrical conductivity. The conductivity of the stabilized gel electrolyte system formed by the PVFM polymer porous film prepared in Example 3 had an electrical conductivity of 1.03 Χ 10· ³ S/cm, which was close to the average value of the liquid electrolyte conductivity of 10· /η. Example 4

0.0989 g of polyvinyl formal (PVFM) was dissolved in 0.9987 g of N-methylpyrrolidone (NMP), magnetically stirred at 45 ° C until the PVFM was completely dissolved, and 0.0319 g of 4,4 '-diphenylmethane was added to the solution. The diisocyanate (MDI) was stirred at 75 ° C for 30 min, and then OJ OlOg anhydrous ethanol was added dropwise to precipitate a white micelle. The white micelle was dissolved by stirring to dissolve, and the magnetic stirring was continued for 30 min. The mixed solution was prepared. The mixed solution was coated with a film, immersed in absolute ethanol to prepare a porous film, and the obtained porous film was dried for 1 hour. The method of drying the porous film may be, for example, but not limited to, placing the porous film at 30 ° C - 60 ° C, by air drying or vacuum drying. The PVFM polymer porous membrane prepared in Example 4 has a high liquid absorption rate of 352% and high chemical stability, and provides a prerequisite for the formation of a stable gel electrolyte system and the acquisition of higher electrical conductivity. The conductivity of the stabilized gel electrolyte system formed by the PVFM polymer porous membrane prepared in Example 1 had an electrical conductivity of 0.97 X 10- ³ S/cm, which was close to the average value of the liquid electrolyte conductivity of 10 _ ³ S/cm. Example 5

Dissolve 0.1018 g of polyvinyl formal (PVFM) in 0.7857 g of N-methylpyrrolidine In the ketone (NMP), magnetically stir at 45 ° C until the PVFM is completely dissolved. Add 0.0305 g of 4,4'-diphenylmethane diisocyanate (MDI) to the solution, stir at 75 ° C for 30 min, then add 0.1016 g to the solution. Ionized water, white gums were precipitated, and the white micelles were dissolved by stirring to dissolve. The magnetic stirring was continued for 30 minutes, and the mixed solution was prepared. The mixed solution was coated with a film, immersed in deionized water to prepare a porous film, and the obtained porous film was dried for 1 hour. The method of drying the porous film may be, for example, but not limited to, placing the porous film at 30 ° C - 60 ° C, by air drying or vacuum drying. The high chemical stability of the PVFM polymer porous membrane prepared in Example 5 and the high liquid absorption rate of 00% promoted the formation of a stable gel electrolyte system. The electrical conductivity of the system was 1.28 X 10- ³ S/cm, slightly higher than that of the liquid electrolyte. The average value of the electrical conductivity is 10" ³ S/cm. Example 6

0.0977 g of polyvinyl formal (PVFM) was dissolved in 0.9805 g of N-methylpyrrolidone (NMP), magnetically stirred at 45 ° C until PVFM was completely dissolved, and 0.0306 g of 4,4 '-diphenylmethane was added to the solution. The diisocyanate (MDI) was stirred at 75 ° C for 30 min, and then added dropwise 0.0230 g of deionized water to precipitate a white micelle. The white micelle was dissolved by stirring to dissolve, and the magnetic stirring was continued for 30 min. The mixed solution was prepared. The mixed solution was coated with a film and immersed in deionized water to prepare a porous film, and the obtained porous film was dried for 1 hour. The method of drying the porous film may be, for example, but not limited to, placing the porous film at 30 ° C - 60 ° C, by air drying or vacuum drying. The high chemical stability of the PVFM polymer porous membrane prepared in Example 6, and the high liquid absorption rate of 45% promoted the formation of a stable gel electrolyte system. The conductivity of the system was 1.12 X 10-S/cm, slightly higher than that of the liquid electrolyte. The average conductivity is 103⁄4/cm.

It should be noted that although only the polyvinyl acetal and polyvinyl butyral are used in the examples to prepare the polymer porous film of the present invention, those skilled in the art should be aware of polyvinyl formal and its homologues. All have the (1)-(4) basic structural unit as set forth in the description of the specification, the main structural features are similar, and both have certain hydroxyl groups, and the polyurethane of the polymer porous film of the present invention listed in the Summary of the Invention can be formed. The chemical cross-linking structure can be used, and other homologues of polyvinyl formal can be used to prepare the polymer porous film of the present invention. Although the examples of the present invention only describe the dissolution of polyvinyl formal or its homologues using N-methylpyrrolidone (NMP), the organic solvent is preferably N-methylpyrrolidone, N,N-dimethylformamide, chloroform. At least one of tetrahydrofuran, an organic solvent having a solubility difference of <1.7-2 in the field is also feasible. In addition to 4,4'-diphenylmethane diisocyanate (MDI), any other diisocyanate may be used to chemically crosslink with polyvinyl formal or a homolog thereof. In addition to preferred deionization In addition to water, anhydrous methanol, anhydrous ethanol, such as a cheap and readily available non-solvent, it is also possible to add other polyvinyl formal or its homologue to a solution of polyvinyl formal or its homologue and diisocyanate. A non-solvent for the polyurethaneized product. The mass ratio of polyvinyl formal or its homologue to its organic solvent may be any ratio between 1:5 and 1:20. The mass ratio of polyvinyl formal or its homologue to diisocyanate may be any ratio between 10:1 and 2:1. The mass ratio of the polyethylol formal or its homologue to the non-solvent of the polyvinyl acetal and its chemically crosslinked product is any ratio between 10:1 and 1:1. t匕 is lower than column 1

0.1953g of polyacetol formall (PVFM) was dissolved in 2.0156g of N-methylpyrrolidone (NMP), magnetically stirred at 45 °C until PVFM was completely dissolved, 0.1980g of deionized water was added to the solution, and white glue was precipitated. The pellet was continuously magnetically stirred at 45 ° C until the precipitate was dissolved. The solution was coated and immersed in deionized water to prepare a porous film, and the obtained porous film was dried for 1 hour. Figure 4 is a microscopic topography of a porous polymer membrane. The porous membrane has a porous honeycomb shape and has a large pore diameter of about 25 μm. The polymer wall composed of large pores is also uniformly distributed, and the diameter is about 1-2 μm. Small pores. The PVFM polymer porous film which is not chemically crosslinked is rapidly dissolved in an electrolyte containing an organic solvent such as LiPF ₆ /EC+DMC (3:7 in Vol.), and a stable gel electrolyte system cannot be formed.

Comparison of liquid absorption rate and conductivity

By comparison, it was found that the composition of the polymer porous film of the present invention is chemically crosslinked, has good chemical stability, and the polymer porous film is not dissolved in the organic solvent component of the electrolytic solution. The connected pores of the porous membrane can quickly adsorb the electrolyte and form a gel polymer electrolyte to effectively prevent the electrolyte from being missed. At the same time, the gel polymer electrolyte has high conductivity and reaches and approaches the average value of the liquid electrolyte conductivity of 1.12 Χ 10· ³ . Example 7 The porous polymer membrane prepared in Example 1 was immersed in 1 mol/L LiPF ₆ dissolved in an electrolyte solution of EC:DMC=3:7 (V/V), or a few drops of lithium ion battery were dropped onto the surface of the polymer porous membrane. Electrolyte. After the porous membrane adsorbs and swells the electrolyte, a gel polymer electrolyte is obtained, which avoids the use of the separator component which must be placed in the conventional gel polymer lithium ion battery, thereby effectively reducing the number of interfaces in the lithium ion battery structure and facilitating the improvement of the ionic conductivity. . Through the linear sweep voltammetry test, the electrochemical stability window of the gel polymer electrolyte is 2.0V~5.0V, and the result is shown in FIG. 5. The impedance of the solution is 5.0Ω through the AC impedance test, and the conductance is calculated according to the above formula. The rate is 1.25 X 10- /cm. The main components of the electrolytic solution used are a lithium salt and an organic solvent. The lithium salt is selected from at least one of the following: LiPF ₆ , LiC10 ₄ LiBF ₄ , LiAsF ₆ , LiAlCl ₄ , LiCF ₃ S〇 ₃ , LiN(S0 ₂ CF ₃ ) ₂ , LiBOB, LiSbF ₆ , LiSCN, LiSnF ₆ , LiGeF ₆ , LiTaF ₆ . The organic solvent is selected from at least one of the following: ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite Ester, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, methyl acetate, ethyl acetate, ethyl propionate, ethyl butyrate, tetrahydrofuran, 2-methyl Tetrahydrofuran, tetrahydropyran, dioxolane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, acetonitrile, dimethyl sulfoxide, acetone, hydrazine, hydrazine-dimethylformamidine Amine, sulfolane, dimethyl sulfone. Example 8

The half cell is assembled with 1^1⁄2?〇 ₄ as the positive electrode and Li as the negative electrode. The battery uses a CR2032 button battery. A separator member was not added to the battery, and instead, the polymer porous film prepared in Example 1 was used. During the assembly process, a small amount of electrolyte is added dropwise to infiltrate the polymer porous membrane and the electrode material, and the electrolyte is swollen to gel. The polymer porous membrane prepared in Example 1 was applied to a gel polymer electrolyte, and a half-cell assembled using lithium iron phosphate as a positive electrode battery. After charging and discharging test, the results shown in FIG. 6 indicate that the embodiment was employed. 1 The prepared polymer porous membrane is applied to the gel polymer electrolyte with good chemical stability, excellent cycle stability of the battery, battery cycle 80 times, capacity retention rate of 95.4%, close to the liquid electrolyte cycle 80 times, capacity The application rate of 97.6% is maintained, and the application requirements in the battery system are achieved.

The polymer porous film prepared in Example 1 can also be used for a lithium ion battery in which positive and negative electrodes are composed of other materials. For example, the positive electrode of the lithium ion battery is at least one selected from the group consisting of lithium iron phosphate, nickel cobalt manganese ternary material, spinel lithium manganate, high capacity lithium-rich manganese-based material, and the negative electrode is at least one selected from the group consisting of One: graphite, hard carbon, lithium niobate, silicon based compounds and alloys. Fig. 1 shows an embodiment of a lithium ion battery cell structure obtained by using the polymer porous film of the present invention as a gel polymer electrolyte. The lithium ion battery cell is a laminated type or a wound type, and includes a positive electrode tab 1, a positive electrode tab 2 welded to one end of the positive electrode tab 1, a negative electrode tab 3, and a sum welded to the negative electrode tab 3. The negative electrode tab 4 at the same end of the positive electrode tab 2 and the gel polymer electrolyte layer 5 formed of the polymer porous film of the present invention between the positive and negative electrode tabs. Those skilled in the art will be aware of lithium ion batteries obtained from solid electrolyte lithium gel-free polymer electrolytes. ' ^b using the polymer porous membrane of the present invention as a gel polymer electrolyte, the lithium ion battery is deintercalated from the structure of the active material of the negative electrode tab 3 during discharge, and the active material of the negative electrode tab 3 is The solvation occurs at the interface of the gel polymer electrolyte layer 5, and migrates to the side of the positive electrode tab 1 in the gel polymer electrolyte layer 5, and the interface between the active material of the positive electrode tab 1 and the gel polymer electrolyte layer 5 The upper side is desolvated and then embedded in the structure of the material of the positive electrode tab 1, and the electrons are passed from the negative electrode tab 4 to the positive electrode tab 2 via an external circuit to form an directional movement of electrons, that is, an electric current. In the charging process, in contrast to the above process, lithium ions are deintercalated from the active material of the positive electrode tab 1 and traverse the interface between the gel polymer electrolyte layer 5 and the positive electrode tab 1 and the negative electrode tab 3, and then embedded in the negative electrode tab. 3 The structure of the active substance.

Unlike a liquid electrolyte lithium ion battery, for a gel polymer lithium ion battery, since a polymer porous film having a certain mechanical strength is used to adsorb-swell a gel polymer electrolyte formed after the electrolyte, the use of a separator is avoided. It reduces the multiple interfaces during lithium ion migration and the obstacles caused by the separator, which is more conducive to the migration of lithium ions and reduces the internal resistance of lithium ion batteries. At the same time, the shape of the battery is not limited by the liquid electrolyte, but it can be made according to the design requirements.

Claims

Claim

A polymer porous film characterized in that the component is a urethane product of at least one of polyvinyl formal or a homolog thereof, and is stably present in the form of a porous film.

2. A porous polymer membrane according to claim 1, wherein the chemically crosslinked structure of the polyurethane is as follows:

(where: R = H, methyl, ethyl or propyl)

3. A method of producing a polymer porous membrane, characterized in that the preparation of the polymer porous membrane is carried out by the following process steps:

(1) dissolving polyvinyl formal or a homolog thereof in an organic solvent in a certain ratio, and disposing it as a solution;

(2) adding a certain proportion of a diisocyanate substance which is chemically crosslinked to a solution of the above-mentioned configuration, or a homologue thereof, and stirring until it is dissolved;

(3) adding a certain proportion of a non-solvent of a polyvinyl acetal and a polyurethane product thereof to the solution disposed above, and separating a white micelle, and stirring to dissolve the micelle;

(4) after the solution prepared by the above steps is uniformly coated, immersed in a non-solvent bath of polyvinyl acetal and its urethane product or a mixed bath of the solvent and the non-solvent to precipitate a white film;

(5) The white film was dried to obtain a polymer porous film.

The method for preparing a polymer porous film according to claim 3, wherein the organic solvent is preferably at least one of Ν-methylpyrrolidone, hydrazine, hydrazine-dimethylformamide, chloroform or tetrahydrofuran. And an organic solvent having a solubility difference of < 1.7 - 2 according to the principle of similar compatibility with polyvinyl formal or a homolog thereof, and polyvinyl formal or The mass ratio of its homologue to organic solvent is 1:5 - 1:20.

The method for producing a polymer porous film according to claim 3, wherein the diisocyanate is preferably 4,4'-diphenylmethane diisocyanate, toluene-2,4-diisocyanate or toluene 2 , at least one of 6-diisocyanate, hexamethylene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, and other diisocyanates, polyvinyl formal or a homolog thereof and diisocyanate The mass ratio of the substances is 10:1 - 2:1.

The method for preparing a polymer porous film according to claim 3, wherein the non-solvent is preferably at least one of deionized water, anhydrous methanol, and anhydrous ethanol, polyvinyl formal or a homologous system thereof. The mass ratio of the substance to the non-solvent of the polyvinyl acetal and its chemically crosslinked product is 10:1 - 1:1.

The method for producing a polymer porous film according to claim 3, wherein the drying step is blast drying or vacuum drying at 30 ° C - 60 ° C.

The method for preparing a polymer porous membrane according to claim 3, wherein the organic solvent comprises N-methylpyrrolidone, hydrazine, hydrazine-dimethylformamide, chloroform, tetrahydrofuran, and the like. The compatibility principle is different from the solubility of polyvinyl formal or its homologue of 1. ⁷ - ² organic solvent, and the mass ratio of polyvinyl formal or its homologue to organic solvent is 1:5 - 1:20 .

The method for producing a polymer porous film according to claim 3, wherein the diisocyanate substance comprises 4,4'-diphenylmethane diisocyanate, toluene-2,4-diisocyanate, toluene 2 , 6-diisocyanate, hexamethylene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, and other diisocyanates, polyvinyl formal or its homologues and diisocyanate mass ratio Is 1 (Η - 2:1.

The method for preparing a polymer porous membrane according to claim 3, wherein the non-solvent comprises deionized water, anhydrous methanol, absolute ethanol, polyvinyl formal or a homolog thereof and polyvinyl alcohol. The non-solvent mass ratio of the acetal and its chemically crosslinked product is from 10:1 to 1:1.

A lithium ion battery using the polymer porous film according to claim 1, wherein the positive electrode in the lithium ion battery system is at least one selected from the group consisting of lithium iron phosphate and nickel cobalt manganese ternary material. , spinel lithium manganate, high capacity lithium-rich manganese-based material, the negative electrode is at least one selected from the group consisting of graphite, hard carbon, lithium titanate, silicon-based compounds and alloys.

12. The use of a polymer porous membrane according to claim 1 in a gel polymer electrolyte, characterized in that the polymer porous membrane adsorbs and swells the electrolyte to effect gelation to form a gel polymer electrolyte, wherein The main components of the electrolyte are a lithium salt and an organic solvent.

13. The use according to claim 12, wherein the lithium salt is at least one selected from the group consisting of LiPF6, LiC104, LiBF4, LiAsF6, IiAlC14, LiCF3S〇3, LiN(S〇2CF3)2, LiBOB. , LiSbF6, LiSCN, LiSnF6, LiGeF6, LiTaF6o

The use according to claim 12, wherein the organic solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and vinyl succinic acid. Ester, propylene acrylate, dimethyl benzoate, diethyl succinate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, acetic acid Ester, ethyl acetate, ethyl propionate, ethyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, dioxolane, 1,2-dimethoxyethane, diethylene glycol Methyl ether, acetonitrile, dimethyl sulfoxide, acetone, hydrazine, hydrazine-dimethylformamide, sulfolane, dimethyl sulfone.

A battery cell using a lithium ion battery of the polymer porous film according to claim 1, the battery core comprising:

a positive electrode tab and a positive electrode tab welded on the positive pole tab;

a negative pole piece and a negative electrode tab spliced on the negative pole piece;

The polymer electrolyte layer is a polymer porous film according to claim 1.

The lithium ion battery according to claim 15, wherein the battery of the lithium ion battery is a laminated type or a wound type.

17. A lithium ion battery comprising the cells of weights 15 or 10.