CN101638490A - Polyimide porous membrane and preparation method and lithium ion battery thereof - Google Patents
Polyimide porous membrane and preparation method and lithium ion battery thereof Download PDFInfo
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Abstract
The invention provides a polyimide porous membrane and the pore distribution of the polyimide porous membrane is as follows: the pore volume of 50-300nm of pores is above 75% of the total pore volumeand the pore volume of less than 50nm and more than 300nm of pores is below 25%. The invention also provides a preparation method of the polyimide porous membrane and a lithium ion battery using the porous membrane as diaphragm. The polyimide porous membrane provided by the invention has uniform pore distribution and higher mechanical strength so that the lithium ion battery prepared by using theporous membrane as diaphragm has higher service life, processing yield and thermal stability and the safety performance of the cell is greatly improved.
Description
Technical field
The present invention relates to a kind of polyimide porous membrane, also relate to the preparation method of this polyimide porous membrane, also relate to and use the lithium ion battery of this porous-film as battery diaphragm.
Background technology
So far, use the lithium-ion secondary cell of liquid electrolyte to be widely used.Yet, because liquid electrolyte need be packaged in the metal casing of sealing, under the situation of some improper use, outside heat was delivered to inside battery by metal shell when for example battery was worked under hot environment, inside battery heat release when perhaps discharging current is big, inside battery or outside are understood overheated and inner pressure of battery are increased considerably, thereby, the liquid electrolyte thermally labile blasts owing to making battery, therefore use the lithium-ion secondary cell of liquid electrolyte to have potential safety hazard, limit further developing of liquid electrolyte lithium-ion secondary cell, therefore improved the key that lithium ion battery security is the research and development lithium-ion secondary cell.
One of Security Countermeasures of lithium-ion secondary cell are to make the electric current blocking, wherein battery diaphragm plays important effect, barrier film with polymkeric substance of vesicular structure melts under comparatively high temps, thereby cause vesicular structure to be closed, impedance increases sharply and make electric current blocking, this temperature is called blocking (Shut-Down) temperature, claims self-closing temperature again.In addition, behind the membranous bore closure, if battery temperature continue to raise, when surpassing membranous heat resisting temperature, barrier film can take place to melt fully, destroy, and causes positive pole, negative pole directly to contact and short circuit, and this temperature is called film destroy (break-out) temperature.(as the membranous self-closing temperature of PE is 130-140 ℃ because temperature of fusion is lower than 200 ℃ for battery diaphragm commonly used now such as polyethylene (PE), polypropylene (PP), the membranous self-closing temperature of PP is about 170 ℃), in some cases, for example outside temperature is too high, discharging current is excessive or electrolytic solution is subjected under the situation of the thermal inertia in the thermal process, even electric current is interdicted, the temperature of battery also may continue to raise, therefore barrier film may be destroyed fully and cause battery short circuit, thereby cause battery explosion or catch fire.Therefore, adopt PE barrier film and the membranous security of PP lower.
Along with the development of lithium-ion secondary cell in recent years, the requirement of high-capacity battery is increasing, and when using high-capacity battery, needs to reduce the internal resistance of cell, thereby the factor that the inside battery heat is increased increases, and the safety performance that therefore improves battery becomes even more important.
JP11310658A2 discloses a kind of polyimide porous membrane and preparation method thereof, this preparation method comprises, with the film and the porous-film lamination of polyamic acid solution, then this laminar structure is immersed in the lean solvent, obtaining bore dia is the porous polyimide film of 0.01-10 μ m.Described porous-film is the conventional polyolefins film that is used for battery diaphragm.Though the film that is prepared by this method can improve the thermotolerance of battery diaphragm to a certain extent, yet, when temperature surpasses the fusing point (about as 180 ℃) of polyolefine material, polyolefine material melts, the polyimide layer that causes being laminated on this polyolefins film comes off thereupon, this polyimide porous membrane still dangerous property during as the barrier film of battery.
CN101000951A discloses a kind of preparation method who is used as the polyimide porous membrane of battery diaphragm, this method comprises and will contain the solution film forming of polyimide, pore-forming material and solvent, and remove the pore-forming material being lower than under the polyimide glass temperature, method by two-way stretch stretches to polyimide then, makes the hole typing.Described pore-forming material is that various and base material have excellent compatibility and can be being lower than the material of removing under the substrate glass temperature, as non-volatile organic solvent, as nonane, decane, undecane, dodecane, whiteruss or mineral oil.Though aforesaid method can obtain the micropore on the polyimide film by the effusion of pore-forming material, this method is difficult to thoroughly remove the pore-forming material, thereby is easy to cause the pore size of polyimide porous membrane inhomogeneous.
Summary of the invention
The objective of the invention is to overcome the uneven shortcoming of pore size of above-mentioned polyimide film of the prior art, uniform polyimide porous membrane of a kind of pore size and preparation method thereof is provided, a kind of lithium ion battery that uses this porous-film as battery diaphragm also is provided.
The invention provides a kind of polyimide porous membrane, the pore size distribution of this polyimide porous membrane is, bore dia is that the pore volume in the hole of 50-300 nanometer accounts for more than 75% of total pore volume, and bore dia accounts for below 25% of total pore volume less than 50 nanometers and bore dia greater than the pore volume in the hole of 300 nanometers.
The present invention also provides a kind of preparation method of polyimide porous membrane, this method comprises that the mixture that will contain polyamic acid, pore-forming material and solvent forms polyamide acid film, this polyamide acid film is contacted with solidification liquid, and carry out imidization, described solvent is for dissolving polyamic acid but slightly soluble or do not dissolve the solvent of pore shaping object matter, and described solidification liquid is for dissolving pore-forming material but slightly soluble or the insoluble liquid of separating polyamic acid.
The present invention also provides a kind of lithium ion battery, this battery comprises battery case and is encapsulated in the electrode group and the electrolytic solution of this enclosure, described electrode group comprises reels or stacked positive pole, barrier film and negative pole successively, and wherein, described barrier film is a polyimide porous membrane provided by the invention.
Polyimide porous membrane provided by the invention and preparation method thereof can make the pore diameter distribution of this porous-film even, thereby improved the work-ing life of the lithium ion battery of being made as battery diaphragm by this porous-film; Also make this porous-film have higher physical strength, thereby the processed finished products rate of the lithium ion battery of being made as battery diaphragm by this porous-film is improved.Have higher thermostability in addition, improved the safety performance of battery greatly.The work-ing life of lithium ion battery provided by the invention is higher, and the processed finished products rate is higher, and the safety performance of battery is fine, can be applied in the high-capacity power battery.
Description of drawings
The electron scanning micrograph on the polyimide porous membrane surface that Fig. 1 makes for the embodiment of the invention 1.
Embodiment
According to polyimide porous membrane provided by the invention, the pore size distribution of described porous-film is, bore dia is that the pore volume in the hole of 50-300 nanometer accounts for more than 75% of total pore volume, and bore dia accounts for below 25% of total pore volume less than 50 nanometers and bore dia greater than the pore volume in the hole of 300 nanometers.The measurement of above-mentioned bore dia all adopts mercury penetration method to carry out, and concrete measuring method is conventionally known to one of skill in the art.
According to porous-film provided by the invention, when porous-film of the present invention is used for battery diaphragm, be that average pore diameter is the 0.01-5 micron, be preferably the 0.05-2 micron to the requirement of battery diaphragm; Porosity is 10-60 volume %, be preferably 25-45 volume %; Thickness is the 5-50 micron, be preferably the 12-25 micron; Ventilation property is 10-200 second/100cc, be preferably 20-180 second/100cc.Described porosity is meant that the cumulative volume of polyimide porous membrane mesopore accounts for the per-cent of the volume of polyimide porous membrane.Described porosity adopts mercury penetration method to measure.The pore structure of polyimide film of the present invention is more even.Because the homogeneity in the hole of this porous-film is fine, and ventilation property is fine, therefore can make better as the safety performance of the lithium ion battery of battery diaphragm by this porous-film.
The preparation method of polyimide porous membrane provided by the invention comprises that the mixture that will contain polyamic acid, pore-forming material and solvent forms polyamide acid film, this polyamide acid film is contacted with solidification liquid, and carry out imidization, described solvent is for dissolving polyamic acid but slightly soluble or do not dissolve the solvent of pore shaping object matter, and described solidification liquid is for dissolving pore-forming material but slightly soluble or the insoluble liquid of separating polyamic acid.25 ℃ of solubleness of " slightly soluble " described herein expression are less than 1% (w/w) and greater than 0.01% (w/w); " do not dissolve " 25 ℃ of solubleness of expression less than 0.01% (w/w).
According to preparation method provided by the invention, in the preferred case, the weight ratio of described pore-forming material and described polyamic acid is 0.01-0.3: 1, the weight ratio of polyamic acid and described solvent is 1: 4.5-10, the weight ratio of polyamic acid and described solidification liquid is 1: 20-200, be preferably 1: 40-50.
According to preparation method provided by the invention, the described mode that polyamide acid film is contacted with solidification liquid is for to be immersed in polyamide acid film in the solidification liquid, the temperature of described solidification liquid is 0-50 ℃, and the time of described polyamide acid film being immersed described solidification liquid is 20-120 minute.At this moment, this polyamide acid film solidifies and removes the pore-forming material, has formed the porous-film of polyamic acid.
The pore-forming principle of this polyamic acid porous-film has following two kinds, a kind ofly be, pore-forming material and polyamic acid are immiscible, can produce reaction with the pore-forming material but do not remove the pore-forming material with the material of polyamic acid reaction by using, thereby form micropore in polyamide acid film; Another kind is that pore-forming material and polyamic acid are immiscible, can dissolve the pore-forming material but the insoluble material of separating polyamic acid by adopting, and with the pore-forming substance dissolves, thereby form micropore in polyamide acid film.
According to preparation method provided by the invention, according to above-mentioned first kind of pore-forming principle, described pore-forming material is selected from one or more in oxyhydroxide, aluminium hydroxide, alkali-metal phosphoric acid salt and the tripoly phosphate sodium STPP of alkali earth metal, and mean particle size is the 0.01-2 micron.Wherein, the oxyhydroxide of described alkali earth metal is magnesium hydroxide and/or calcium hydroxide; Described alkali-metal phosphoric acid salt is tertiary sodium phosphate and Tripotassium phosphate, and described solidification liquid is one or more in hydrochloric acid, sulfuric acid and the phosphoric acid.Experiment showed, that in hydrochloric acid, sulfuric acid and the phosphoric acid one or more all are not more than 1% (w/w) to one or more the 25 ℃ of solubleness in the above-mentioned oxyhydroxide that is selected from alkali earth metal as the pore-forming material, aluminium hydroxide, alkali-metal phosphoric acid salt and the tripoly phosphate sodium STPP.
According to preparation method provided by the invention, the concentration of described hydrochloric acid is 5-35 weight %, and the concentration of described aqueous sulfuric acid is 5-98 weight %, and the concentration of described phosphate aqueous solution is 5-98 weight %.
According to preparation method provided by the invention, according to above-mentioned second kind of pore-forming principle, it is the phthalic acid dialkyl of 13-18 and in the methylin acetic ester one or more that described pore-forming material is selected from saturated carboxylic acid, phenylformic acid polyol ester, carbonatoms that carbonatoms is 5-15; Described solidification liquid is one or more in methyl alcohol, ethanol, methyl ether, ether, acetone and the methyl propanediol.Wherein, described carbonatoms is that the saturated carboxylic acid of 5-15 is one or more in valeric acid, caproic acid, enanthic acid, sad, n-nonanoic acid, capric acid and their isomer; Described phenylformic acid polyol ester is phenylformic acid one condensed ethandiol ester and/or phenylformic acid one propylene glycol ester that contracts; Described carbonatoms is that the phthalic acid dialkyl of 13-18 is terephthalic acid diamyl ester and/or m-phthalic acid two capronates; Described methylin acetic ester is 1-Methoxy-2-propyl acetate and/or glycol methyl ether acetate.Experiment showed, that in methyl alcohol, ethanol, methyl ether, ether, acetone and the methyl propanediol one or more are that the phthalic acid dialkyl of 13-18 and one or more the 25 ℃ of solubleness in the methylin acetic ester all are not more than 1% (w/w) to above-mentioned be selected from saturated carboxylic acid, phenylformic acid polyol ester, carbonatoms that carbonatoms is 5-15 as the pore-forming material.
According to preparation method provided by the invention, described solvent can be the various solvents that can dissolve polyamic acid, the example of this solvent comprises N-2-methyl-2-pyrrolidone (NMP), N, N-N,N-DIMETHYLACETAMIDE (DMAc), tetrahydrofuran (THF) (THF), N, one or more in dinethylformamide (DMF), m-cresol, dimethyl sulfoxide (DMSO) (DMSO) and the methyl alcohol.Experiment showed, that above-mentioned solvent all is not more than 1% (w/w) to 25 ℃ of solubleness of aforementioned pore-forming material.
According to preparation method provided by the invention, described polyamic acid can be commercially available, also can obtain by tetracarboxylic dianhydride and organic diamine are reacted in solvent.When adopting tetracarboxylic dianhydride and organic diamine in solvent during the prepared in reaction polyamic acid solution, described pore-forming material can be before reaction, any stage after the reaction neutralization reaction adds, the pore-forming material is mixed more equably with polyamic acid solution, and the present invention adds the pore-forming material before being chosen in reaction.The preparation method who is described polyamic acid solution comprises tetracarboxylic dianhydride, organic diamine, pore-forming material and solvent, obtain uniform mixture, this mixture is formed polyamide acid film, and be lower than drying under the second-order transition temperature of polyamic acid, with removing the pore-forming material in the dried described polyamide acid film immersion solidification liquid, then carry out imidization.
According to preparation method provided by the invention, in the preferred case, the mol ratio of described tetracarboxylic dianhydride and organic diamine is 0.8-1.2,1.00-1.02 more preferably, the weight ratio of the total amount of tetracarboxylic dianhydride and organic diamine and pore-forming material is 1: 0.01-0.3, the total amount of tetracarboxylic dianhydride and organic diamine and the weight ratio of described solvent are 1: 4.5-10.
According to preparation method provided by the invention, in the preferred case, the temperature of tetracarboxylic dianhydride, organic diamine, pore-forming material and solvent being carried out condensation reaction is 20-70 ℃, and the time of contact is 3-15 hour.
According to the present invention, can utilize various technology well known in the art to make polyamic acid solution form polyamide acid film, for example, the mixture that contains polyamic acid, pore-forming material and solvent can be coated on the supporter, dry except that after desolvating, can obtain polyamide acid film.The polyamide acid film that obtain this moment is the low-down film of porosity of non-porous film or film, is not the porous-film on the ordinary meaning, can not satisfy the requirement of battery diaphragm to porosity, aperture and pore distribution.
The step that polyamic acid solution is coated on the supporter is that 10-40 ℃, relative humidity are to carry out under the condition of 20-80% in temperature preferably.
The method that applies can be a whole bag of tricks well known in the art, for example spin-coating method, spread coating, casting method, dip coating etc.The amount that applies depends on thickness or the thickness of polyimide film and the concentration of polyamic acid solution of the polyamide acid film that will obtain.Generally speaking, to make the thickness of final gained polyimide porous membrane be the 5-50 micron to the amount of coating.The gauge control that experiment showed, the polyamide acid film that will form is in the 10-60 micrometer range, and the thickness that can make final gained polyimide porous membrane is the 5-50 micron.Thickness determine and the known situation of polyamic acid solution concentration under, those skilled in the art are easy to grasp the coated weight of polyamic acid solution.
Described supporter can be selected from a kind of in stainless steel plate, polyethylene film, polypropylene film, polyester film, Copper Foil and the aluminium foil.
Removing the method for desolvating can be for well known to a person skilled in the art the whole bag of tricks, and as methods such as seasoning, heat drying, vacuum-dryings, the exsiccant condition comprises that temperature can be 20-150 ℃, and the time can be 5-20 minute.
Thereby improve the quality of the final polyimide porous membrane that obtains for the quality that further improves polyamide acid film, under the preferable case, the polyamic acid solution described in the method provided by the invention is the polyamic acid solution of process at 15-40 ℃ of following vacuum outgas 1-12 hour preferred 1-2 hour.In other words, under the preferable case, method provided by the invention also is included in before the polyamic acid solution film forming, earlier with polyamic acid solution at 15-40 ℃ of following vacuum outgas 1-12 hour, preferred 1-2 hour, to remove the bubble that may exist in the solution.The vacuum tightness of described vacuum outgas can guarantee the non-volatile or a small amount of volatilization of polyamic acid solution, and under the preferable case, described vacuum tightness is the 0.001-0.1 MPa.
According to the present invention, in order further to improve the quality of polyimide porous membrane, prevent that solidification liquid from causing disadvantageous effect to polyimide porous membrane, under the preferable case, method provided by the invention comprises that also the porous polyamide acid film that will obtain cleans with clean-out system.Described clean-out system can be that carbonatoms is alcohol and/or the ketone of 2-8, is preferably ethanol, acetone or the mixture of the two.The temperature of cleaning can be 0-60 ℃, is preferably 20-50 ℃.The mode of described cleaning can be with clean-out system the porous polyamide acid film to be carried out drip washing and/or dipping.The number of times of drip washing is preferably 3-5 time, and the time of dipping can be 3-6 hour.Can utilize the auxiliary cleaning of ultrasonic wave during dipping.
Among the present invention, the condition of the porous polyamide acid film being carried out imidization can be the condition of the amido acid imidization of routine, concrete working method also has been conventionally known to one of skill in the art, for example, can realize in 2-7 hour by the porous polyamide acid film is heated down at 70-400 ℃.
Can directly heat up and also can adopt program mode to heat up to raise the temperature to 70-400 ℃, the present invention preferably adopts with 4-8 ℃/minute temperature rise rate temperature programming to 70-400 ℃, so that the abundant imidization of polyamic acid generates required polyimide.Further preferably make the porous polyamide acid film be 70-200 ℃ of maintenance 0.5-4 hour down, keep realizing in 0.5-3 hour imidization down at 200 ℃-400 ℃ in temperature by programmed temperature method.Experimental results show that, the amido acid dehydration only takes place under this condition generate imido reaction, can't cause the distribution in above-mentioned in type hole, the variation of size, thereby the polyimide film that obtains still keeps the vesicular structure in the porous polyamide acid film, become polyimide porous membrane.
Can improve the transformation efficiency that polyamic acid is converted into polyimide by raising temperature of reaction, prolongation reaction times.Under the above-mentioned condition of the present invention, polyamic acid is converted into the transformation efficiency of polyimide greater than 99%, and owing to the present invention improves the pore-forming mode of polyimide porous membrane, the mode that is transformed into polyimide by polyamic acid then adopts usual manner, therefore in the specific embodiment of the invention not the amount to polyamic acid make special requirement.In addition, the existence of a small amount of polyamic acid does not have much affect to thermotolerance, ventilation property and the percent thermal shrinkage of polyimide porous membrane, therefore has the polyamic acid below 2% in the polyimide porous membrane that allows to obtain.
Preferably adopt binary organic acid acid anhydride and organic diamine to carry out condensation reaction in the specific embodiment of the invention and prepare polyamic acid.The example of described binary organic acid acid anhydride includes but not limited to as BPDA (s-BPDA), benzophenone tetracarboxylic dianhydride (BTDA), pyromellitic acid anhydride (PMDA), oxygen biphenyl tetracarboxylic acid anhydrides (ODPA) and dihydroxyphenyl propane two ether dianhydrides (BPADA).The example of described organic diamine includes but not limited to 4,4 '-diaminodiphenyl oxide (4,4 '-ODA), 3,4 '-diaminodiphenyl oxide (3,4 '-ODA), Ursol D (PDA), mphenylenediamine (mDA), 3,3 '-sulfobenzide diamines, 4,4 '-sulfobenzide diamines.
The mol ratio of described polynary organic carboxyl acid or derivatives thereof and organic diamine is preferably 0.8-1.2, more preferably 1.00-1.02.Under the preferable case, the weight ratio of total feeding quantity of the feeding quantity of described solvent and polynary organic carboxyl acid or derivatives thereof and organic diamine is 4.5-10.The temperature of condensation reaction is preferably 20-70 ℃, and the time is preferably 3-15 hour.
Among the present invention, described polyimide can be the polymkeric substance that contains imide group in the various repeating units of this area routine, and under the preferable case, described polyimide is the polyimide with following structural formula,
Wherein, wherein, A
1Be preferably the aryl of following structure:
Described diamines can be to have NH
2-A
2-NH
2The diamines of the structure of expression, A
2Can be the aryl of following structure:
Polymerization degree n can be 50-10000, and heat decomposition temperature is more than 420 ℃.
One skilled in the art will appreciate that because general polyimide (PI) is a kind of insoluble high molecular polymer its polymerization degree is difficult to accurately measure, and the limiting viscosity of another the physical parameter polyamic acid directly related with the polymerization degree is closely related.Polyamic acid is by the intermediate in acid dianhydride and the amine prepared in reaction polyimide reaction process, discover, by control polyamic acid limiting viscosity within the specific limits, can obtain the polyimide of the required polymerization degree or desired physical properties, and limiting viscosity be one with the irrelevant physical parameter that can objectively respond the polyamic acid polymerization degree of measuring condition, so this area uses the limiting viscosity of polyamic acid to represent the polymerization degree of polyamic acid and polyimide usually.The present invention continues to use the polymerization degree that aforesaid method characterizes Kapton at this.The present inventor discovers, as long as being controlled at 100-200 milliliter/gram, the limiting viscosity of polyamic acid that will be corresponding with this polyimide preferably can realize purpose of the present invention at 140-190 milliliter/gram, therefore, among the present invention, be that 100-200 milliliter/gram is preferably 140-190 milliliter/gram as long as make the limiting viscosity of the polyamic acid corresponding with this polyimide.
Under the preferable case, described polyimide is one or more in the PMMI corresponding with tetracarboxylic dianhydride and diamines, poly-biphenyl tetracarboxylic imide, the poly-benzophenone tetramethyl imide.Preferred described PMMI is selected from one or more in the poly-equal diimides of N-phenyl, the poly-equal diimides of N-xenyl, the poly-equal diimides of N-hexichol ether; Described poly-biphenyl tetracarboxylic imide is selected from one or more in poly-N-phenyl biphenyl tetracarboxylic imide, poly-N-xenyl biphenyl tetracarboxylic imide, the poly-N-hexichol ether biphenyl tetracarboxylic imide; Described poly-benzophenone tetramethyl imide is selected from one or more in poly-N-phenyl benzophenone tetramethyl imide, poly-N-xenyl benzophenone tetramethyl imide, the poly-N-hexichol ether benzophenone tetramethyl imide.
A preferred embodiment of the invention, the preparation method of polyimide porous membrane provided by the invention comprises the steps:
(1) with tetracarboxylic dianhydride and organic diamine according to mol ratio 0.8-1.2: 1 ratio adds in the solvent, it is 5-40 weight % that the consumption of solvent makes the concentration of the polyamic acid that obtains, after 20-70 ℃ of following stirring reaction 3-15 hour, add the pore-forming material, the pore-forming material is 0.01-0.3 with the weight ratio of the polyamic acid that obtains: 1; Under uniform temp, obtained polyamic acid solution in vacuum outgas 1-12 hour;
(2) be that 10-40 ℃, relative humidity are under the 20-80% condition in temperature, above-mentioned polyamic acid solution be coated on stainless steel or the glass support, 20-200 ℃ dry down, remove the polyamide acid film that obtains the 5-50 micron after desolvating;
(3) supporter of above-mentioned polyamide acid film is put into 10-50 ℃ solidification liquid dipping 20-120 minute, obtained the porous polyamide acid film;
(4) with the above-mentioned porous polyamide acid film that obtains in 10-50 ℃ clean-out system soaking and washing 3-6 hour, the progressively mode of imidization of gradient increased temperature is adopted in dry back, heating is converted into polyimide with polyamic acid under nitrogen, argon gas or vacuum, obtains polyimide porous membrane.The temperature of heating is 100-200 ℃ and keeps down 0.5-1.5 hour, 180-250 ℃ to keep 0.5-1.5 hour, 230-280 ℃ to keep 0.5-1.5 hour, 260-350 ℃ to keep 0.5-1.5 hour down down down.
Method provided by the invention can be qualitatively judged according to the ABC of organic synthesis and polyimide film can be accessed.Certainly, also can carry out qualitative sign according to infrared spectra.1720cm in the infrared spectra
-1Near strong peak is a C=O stretching vibration absorption peak, 1380cm
-1Strong peak is a C-N stretching vibration absorption peak in neighbouring.If occur above-mentioned peak in the infrared spectra, then can illustrate to have obtained polyimide.Described infrared spectra spectrogram can adopt the U.S. NEXUS470 of Nicolet company type fourier transform infrared spectroscopy, Potassium Bromide coating to obtain.The said determination method has been conventionally known to one of skill in the art, does not repeat them here.Owing to adopt very sophisticated method synthesis of polyimides among the present invention, just the pore-forming mode is improved, so especially the structure of polyimide film is not characterized in an embodiment.
Size, porosity and the ventilation property in the formed polyimide of the present invention hole all has relation with polyamic acid solution concentration, solidification liquid, film-forming temperature, humidity, can realize control to the polyimide porous membrane quality by regulating these parameters.
Lithium ion battery provided by the invention comprises battery case and the electrode group and the electrolytic solution that are encapsulated in this enclosure, and described electrode group comprises reels or stacked positive pole, barrier film and negative pole successively, and wherein, described barrier film is a polyimide porous membrane provided by the invention.
According to lithium ion battery provided by the invention, the positive pole of described battery, negative pole and electrolytic solution all can adopt and well known to a person skilled in the art various positive poles, negative pole and electrolytic solution, and specifically prescription and preparation method do not repeat them here.
The following examples will the invention will be further described.In an embodiment, among the embodiment there be used main raw material:
Pyromellitic acid anhydride: SHANGHAI RESEARCH INSTITUTE OF SYNTHETIC RESINS;
Benzophenone tetracarboxylic dianhydride: SHANGHAI RESEARCH INSTITUTE OF SYNTHETIC RESINS;
Dihydroxyphenyl propane two ether dianhydrides: Shanghai synthetic resins institute;
Oxygen bibenzene tetracarboxylic dianhydride: Shanghai chemical reagents corporation;
Ursol D: chemical reagent purchase and supply 5-linked chemical plant, Shanghai;
N,N-dimethylacetamide, N-Methyl pyrrolidone: Shanghai chemical reagent work.
Embodiment 1
(1) with 4,4 '-diaminodiphenyl oxide and pyromellitic acid anhydride join in 300 milliliters of N,N-dimethylacetamide with 1: 1 mol ratio, and wherein solid content is 10 weight %.25 ℃ of following stirring reactions 8 hours, add 3 gram 1-Methoxy-2-propyl acetates then, and vacuum outgas 1 hour under this temperature, obtain thick mixture, the limiting viscosity η of this mixture
Int=150 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content);
(2) be that 10 ℃, relative humidity are under 50% condition in temperature, said mixture is coated on the stainless steel plate, remove after dry 20 minutes down at 100 ℃ and desolvate, obtain polyamide acid film;
(3) the above-mentioned stainless steel plate that has polyamide acid film was flooded 60 minutes down at 20 ℃ in 100 milliliters of solidification liquids of being made up of ethanol, ether and acetone (volume ratio of ethanol, ether and acetone is 3: 2: 1), be cured, pore-forming, 40 ℃ dry 20 hours down, ultrasonic cleaning 1 hour in 25 ℃ water then, descended dry 20 hours at 40 ℃ afterwards, obtain the porous polyamide acid film;
(4) adopt the progressively mode of imidization of gradient increased temperature, above-mentioned porous polyamide acid film is heated in nitrogen carry out imidization, obtain thickness and be 33 microns polyimide porous membrane.The mode of heating is to keep 1 hour down at 150 ℃, and 200 ℃ kept 1 hour down, and 250 ℃ kept 1 hour down, and 320 ℃ kept 1 hour down.
Adopt scanning electronic microscope to observe the pore distribution of the above-mentioned polyimide porous membrane that obtains, resultant electron scanning micrograph as shown in Figure 1.As can be seen from the figure, the surface of film and inner crisscross a large amount of hole that distributing, hole be circle or oval, and the distribution in hole and aperture are all comparatively even, and the pattern in hole is better.
The pore volume of bore dia in the hole of 110-130 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 93% of total pore volume, and the average pore diameter of this film is 125 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 2
Method according to embodiment 1 prepares polyimide porous membrane, and different is that the amount of the pore-forming material 1-Methoxy-2-propyl acetate that adds in step (1) is 6 grams, obtains thick mixture, the limiting viscosity η of this mixture
Int=180 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content).Finally obtain thickness and be 19 microns polyimide porous membrane.
The pore volume of bore dia in the hole of 160-190 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 78% of total pore volume, and the average pore diameter of this film is 175 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 3
Method according to embodiment 1 prepares polyimide porous membrane, and different is that the amount of the pore-forming material 1-Methoxy-2-propyl acetate that adds in step (1) is 5 grams, obtains thick mixture, the limiting viscosity η of this mixture
Int=160 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content).Finally obtain thickness and be 14 microns polyimide porous membrane.
The pore volume of bore dia in the hole of 160-210 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 88% of total pore volume, and the average pore diameter of this film is 195 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 4
(1) with 4,4 '-diaminodiphenyl oxide and benzophenone tetracarboxylic dianhydride (BTDA) join in 300 milliliters of N,N-dimethylacetamide with 1: 1 mol ratio, and wherein solid content is 12 weight %.40 ℃ of following stirring reactions 10 hours, add 4 gram capric acid then, and back vacuum outgas 1 hour under this temperature, obtain thick mixture, the limiting viscosity η of this mixture
Int=188 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content);
(2) be that 20 ℃, relative humidity are under 60% condition in temperature, said mixture is coated on the stainless steel plate, obtain polyamide acid film after dry 10 minutes down at 120 ℃;
(3) the above-mentioned stainless steel plate that has polyamide acid film was flooded 60 minutes down at 25 ℃ in 500 milliliters of solidification liquids of being made up of ethanol and ether (volume ratio of ethanol and ether is 2: 1), be cured, pore-forming, 40 ℃ dry 5 hours down, ultrasonic cleaning 1 hour in 25 ℃ of water then, descended dry 20 hours at 40 ℃ afterwards, obtain the porous polyamide acid film;
(4) adopt the progressively mode of imidization of gradient increased temperature, above-mentioned porous polyamide acid film is heated in nitrogen carry out imidization, obtain thickness and be 26 microns polyimide porous membrane.The mode of heating is to keep 1 hour down at 160 ℃, and 210 ℃ kept 0.8 hour down, and 230 ℃ kept 1.2 hours down, and 320 ℃ kept 1 hour down.
The pore volume of bore dia in the hole of 275-300 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 87% of total pore volume, and the average pore diameter of this film is 290 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 5
(1) with 4,4 '-diaminodiphenyl oxide and pyromellitic acid anhydride join among 300 milliliters of NMP with 1: 1 mol ratio, and wherein solid content is 12 weight %., add 1 gram magnesium hydroxide and 1.5 gram aluminium hydroxides (mean particle size is 0.05 micron) then, and obtain thick mixture, the limiting viscosity η of this mixture after 15 hours at 25 ℃ of following stirring reactions
Int=143 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content);
(2) be that 30 ℃, relative humidity are under 80% condition in temperature, said mixture is coated on the stainless steel plate, dry naturally after 10 minutes and obtain polyamide acid film;
(3) the above-mentioned stainless steel plate that has polyamide acid film was flooded 80 minutes down at 25 ℃ in 600 milliliters of solidification liquids of being made up of hydrochloric acid and phosphoric acid (volume ratio of hydrochloric acid and phosphoric acid is 2: 1), be cured, pore-forming, in 25 ℃ water, cleaned 10 hours, descended dry 10 hours at 40 ℃ afterwards, obtain the porous polyamide acid film;
(4) adopt the progressively mode of imidization of gradient increased temperature, above-mentioned porous polyamide acid film is heated in nitrogen carry out imidization, obtain thickness and be 35 microns polyimide porous membrane.The mode of heating is to keep 1 hour down at 80 ℃, and 120 ℃ kept 1 hour down, and 180 ℃ kept 1 hour down, and 250 ℃ kept 1 hour down, and 300 ℃ kept 1 hour down, and 350 ℃ kept 1 hour down.
The pore volume of bore dia in the hole of 50-75 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 80% of total pore volume, and the average pore diameter of this film is 60 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 6
(1) with 4,4 '-diaminodiphenyl oxide and bibenzene tetracarboxylic dianhydride join among 100 milliliters of NMP with 1: 1 mol ratio, and wherein solid content is 12 weight %.55 ℃ of following stirring reactions 8 hours, the mixture (volume ratio is 4: 3: 1) that adds 1 gram Dinonylphthalate, capric acid and dioctyl phthalate (DOP) then, and vacuum outgas 2 hours under this temperature, obtain thick mixture, the limiting viscosity η of this mixture
Int=145 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content);
(2) be that 30 ℃, relative humidity are under 70% condition in temperature, said mixture is coated on the stainless steel plate, obtain polyamide acid film after dry 10 minutes down at 100 ℃;
(3) with the above-mentioned stainless steel plate that has a polyamide acid film in 1000 milliliters of acetone at 25 ℃ of dippings 30 minutes down, be cured, pore-forming, 40 ℃ dry 10 hours down, obtain the porous polyamide acid film;
(4) adopt the progressively mode of imidization of gradient increased temperature, above-mentioned porous polyamide acid film is heated in nitrogen carry out imidization, obtain thickness and be 23 microns polyimide porous membrane.The mode of heating is to keep 1 hour down at 150 ℃, and 200 ℃ kept 1 hour down, and 250 ℃ kept 1 hour down, and 300 ℃ kept 1 hour down.
The pore volume of bore dia in the hole of 50-80 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 79% of total pore volume, and the average pore diameter of this film is 68 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 7
(1) with 4,4 '-diaminodiphenyl oxide and bibenzene tetracarboxylic dianhydride join among 100 milliliters of DMF with 1: 1 mol ratio, and wherein solid content is 15 weight %.20 ℃ of following stirring reactions 8 hours, add 3 gram Dinonylphthalates then, and, obtain thick mixture, the limiting viscosity η of this mixture 15 ℃ of following vacuum outgass 2 hours
Int=166 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content);
(2) be that 30 ℃, relative humidity are under 40% condition in temperature, said mixture is coated on the stainless steel plate, dry naturally after 60 minutes and obtain polyamide acid film;
(3) with the above-mentioned stainless steel plate that has a polyamide acid film in 500 milliliters of ethanol at 25 ℃ of dippings 60 minutes down, be cured, pore-forming, 40 ℃ dry 10 hours down, obtain the porous polyamide acid film;
(4) adopt the progressively mode of imidization of gradient increased temperature, above-mentioned porous polyamide acid film is heated in nitrogen carry out imidization, obtain thickness and be 45 microns polyimide porous membrane.The mode of heating is to keep 1 hour down at 150 ℃, and 200 ℃ kept 1 hour down, and 250 ℃ kept 1 hour down, and 320 ℃ kept 1 hour down.
The pore volume of bore dia in the hole of 80-110 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 85% of total pore volume, and the average pore diameter of this film is 97 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Embodiment 8
(1) with 4,4 '-diaminodiphenyl oxide and bibenzene tetracarboxylic dianhydride join 100 milliliters of N with 1: 1 mol ratio, in the N-N,N-DIMETHYLACETAMIDE (DMAc), solid content is 10 weight %, 20 ℃ of following stirring reactions 4 hours, add 2.5 gram tertiary sodium phosphates (mean particle size is 1.5 microns) then, and 15 ℃ of following vacuum outgass 2 hours, obtain thick mixture, the limiting viscosity η of this mixture
Int=178 milliliters/gram (condition determination: Ubbelodhe viscometer, 30 ℃ of constant temperature, mixture diluted is 0.005 grams per milliliter to solid content);
(2) be that 30 ℃, relative humidity are under 40% condition in temperature, said mixture is coated on the stainless steel plate, dry naturally after 60 minutes and obtain polyamide acid film;
(3) with the above-mentioned stainless steel plate that has a polyamide acid film in 1000 milliliters of sulfuric acid at 25 ℃ of dippings 45 minutes down, be cured, pore-forming, dipping 10 hours in 30 ℃ acetone then, afterwards 70 ℃ dry 10 hours down, obtain the porous polyamide acid film;
(4) adopt the progressively mode of imidization of gradient increased temperature, above-mentioned porous polyamide acid film is heated in nitrogen carry out imidization, obtain thickness and be 18 microns polyimide porous membrane.The mode of heating is to keep 1 hour down at 150 ℃, and 200 ℃ kept 1 hour down, and 250 ℃ kept 1 hour down, and 320 ℃ kept 1.5 hours down.
The pore volume of bore dia in the hole of 195-220 nanometer that adopts mercury penetration method to measure the above-mentioned polyimide porous membrane that obtains accounts for 89% of total pore volume, and the average pore diameter of this film is 210 nanometers.The pore size distribution that this polyimide porous membrane is described is very even.
Comparative Examples 1
Pyromellitic acid anhydride, diaminodiphenyl oxide, polymeric chain one end are contained amino polystyrene, and (weight-average molecular weight is 15000, available from Aldrich company) join 100 milliliters of N-2-methyl-2-pyrrolidones (NMP) with 1: 1: 0.008 mol ratio and at room temperature mix, obtain the solution of homogeneous, the solid content of this solution is 10 weight %, film with the I-shaped spreader of filming then, obtain thickness and be 0.5 millimeter film.
This film was removed solvent in 2 hours 120 ℃ of heating, ℃ carried out imidization 3 hours with 5 ℃ of/minute temperature programmings to 300 then, being warmed up to 350 ℃ again kept 1.5 hours, be cooled to 120 ℃ at last and carry out the biaxial stretching processing simultaneously, draw speed 10 mm/min, stretch ratio vertically (MD) is 2 times, and laterally (TD) is 2 times, obtains porous-film thus.
Wherein there is 1720cm in the fourier-transform infrared spectrogram
-1Near strong peak is C=O stretching vibration absorption peak, 1380cm
-1Strong peak is a C-N stretching vibration absorption peak in neighbouring, and illustrating has imide group in the product, has 1600 centimetres in the spectrogram
-1, 1575 centimetres
-1, 1490 centimetres
-1, 1450 centimetres
-1Absorption peak (phenyl ring characteristic peak), illustrate to have phenyl ring in the product.
The pore volume of bore dia in the hole of 30-65 nanometer that adopts mercury penetration method to measure the above-mentioned porous-film that obtains accounts for 45% of total pore volume, and the average pore diameter of this film is 50 nanometers.The aperture that this polyimide porous membrane is described is very inhomogeneous.
Performance test
1, film properties test
(1), the thickness of test membrane
Adopt measured film thickness instrument (Shanghai six water chestnut instrument plants, CH-1-
ST SType) thickness of mensuration membrane sample is chosen 5 point measurements on the membrane sample arbitrarily, and is averaged.
(2), the porosity of test membrane and mean pore size
Adopt mercury penetration method to use mercury injection apparatus (DEMO AutoPore 9500, the U.S.) to measure the porosity and the mean pore size of membrane sample.
(3), the tensile strength of test membrane and elongation
Come the tensile strength and the elongation of test membrane sample according to the plastic tensile test method of GB1040-79.
(4), testing air permeable
Measure the ventilation property of membrane sample according to the method for describing among the JIS P8117.
According to above-mentioned testing method resulting polyimide porous membrane in embodiment 1-8 and the Comparative Examples 1 is carried out performance test, gained the results are shown in the table 1.
Table 1
| Embodiment | Thickness (micron) | Mean pore size (nanometer) | Porosity (%) | Ventilation property (second/100cc) | Elongation (%) | Intensity (MPa) |
| Embodiment 1 | ??33 | ??125 | ??65 | ??180 | ??5.6 | ??78 |
| Embodiment 2 | ??19 | ??175 | ??33 | ??150 | ??6.0 | ??34 |
| Embodiment 3 | ??14 | ??195 | ??45 | ??23 | ??12.2 | ??66 |
| Embodiment 4 | ??26 | ??290 | ??29 | ??47 | ??8.5 | ??43 |
| Embodiment 5 | ??35 | ??60 | ??55 | ??73 | ??15.5 | ??120 |
| Embodiment 6 | ??23 | ??68 | ??36 | ??143 | ??7.8 | ??97 |
| Embodiment 7 | ??45 | ??97 | ??24 | ??110 | ??9.0 | ??52 |
| Embodiment 8 | ??18 | ??210 | ??71 | ??64 | ??4.0 | ??86 |
| Comparative Examples 1 | ??18 | ??50 | ??50 | ??450 | ??3.6 | ??70 |
From the result of table 1 as can be seen, the mean pore size of polyimide porous membrane that adopts method preparation provided by the invention is between 50 to 300 nanometers, and porosity, ventilation property and physical strength are all very good, meet the requirement of lithium ion battery separator to the aperture.From the test data of Comparative Examples 1 and embodiment 8 more as can be seen, the porosity of the polyimide porous membrane that obtains in the Comparative Examples 1, ventilation property and physical strength are all relatively poor.
2, test battery performance
(1) anodal preparation
With 100 gram positive active material LiCoO
2, 2 gram tackiness agent vinylidene fluorides (PVDF), 3 gram conductive agent acetylene blacks mixtures join in the 40 gram N-N-methyl-2-2-pyrrolidone N-s (NMP), in vacuum mixer, stir then and form uniform anode sizing agent.
This slurry is coated on the aluminium foil equably, 150 ℃ of following oven dry, roll-ins then, cuts to make and be of a size of 390 millimeters * 40 millimeters * 18 microns positive pole, wherein contain 5.8 gram activeconstituents LiCoO
2
(2) preparation of negative pole
The mixture of 100 gram negative electrode active material natural graphites, 1.5 gram tackiness agent polytetrafluoroethylene (PTFE)s and 1.5 gram carboxymethyl celluloses (CMC) is joined in the 100 gram water, in vacuum mixer, stir then and form uniform cathode size.
This cathode size is coated on equably on the both sides of Copper Foil,, roll-in, cuts to make and be of a size of 395 millimeters * 41 millimeters * 12 microns negative pole, wherein contain 2.6 gram activeconstituents natural graphites then 90 ℃ of down oven dry.
(3) make battery with barrier film of the present invention
To include in after the above-mentioned positive pole that obtains, negative pole and barrier film lamination successively and the winding in 4.0 millimeters * 34 millimeters * 46 millimeters the square aluminum hull.Described barrier film is respectively the porous polyimide porous-film that makes by in embodiment 1-7 and the Comparative Examples 1.
To in solvent (ethylene carbonate: methylethyl carbonic ether: diethyl carbonate (EC/EMC/DEC) volume ratio is 1: 1: 1), contain 1 mole lithium hexafluoro phosphate (LiPF
6) about 2.4 grams of electrolytic solution inject above-mentioned battery, and ageing in a conventional manner, the sealed cell aluminum hull promptly obtains lithium-ion secondary cell.The design capacity of this battery is 750 MAHs.
(4) battery resistance to elevated temperatures test
Testing method is as follows: battery is carried out 1C be charged to 100% Charging state, be placed in the baking oven, oven temperature is elevated to 150 ℃ and kept 10 minutes with 5 ℃/minute from room temperature, continue when short-circuit conditions not occurring to be increased to 180 ℃ and kept 10 minutes, observe battery and short circuit whether occurs with 5 ℃/minute.Wherein cell voltage falls greater than 0.2 volt and is considered as short circuit.
(5) battery life test
Testing method is as follows: under 25 ℃ ± 5 ℃, with after 1C constant current charge to 3.7 volt, constant voltage charge then is discharged to 2.5 volts with 1C to 20 milliamperes of cut-off currents with battery; Repeat then to be discharged to 2.5 volts charge and discharge process again with 1C with 1C constant current charge to 3.7 volt, carry out cycle charge-discharge 500 times after, write down dump energy.Dump energy is high more, and battery life is long more.
To carry out battery resistance to elevated temperatures and life test according to above-mentioned testing method with the battery of polyimide porous membrane making made in embodiment 1-8 and the Comparative Examples 1, resulting the results are shown in Table 2.
Table 2
From the result of table 2 as can be seen, the lithium ion battery with the barrier film preparation of lithium-ion secondary cell of the present invention has better security and longer work-ing life.
Claims (14)
1, a kind of polyimide porous membrane, it is characterized in that, the pore size distribution of this polyimide porous membrane is, bore dia is that the pore volume in the hole of 50-300 nanometer accounts for more than 75% of total pore volume, bore dia accounts for below 25% of total pore volume less than 50 nanometers and bore dia greater than the pore volume in the hole of 300 nanometers, and described bore dia adopts mercury penetration method to record.
2, porous-film according to claim 1, wherein, the ventilation property of described porous-film is 10-200 second/100cc.
3, porous-film according to claim 2, wherein, the ventilation property of described porous membrane is 20-180 second/100cc.
4, the preparation method of the described polyimide porous membrane of claim 1, it is characterized in that, this method comprises that the mixture that will contain polyamic acid, pore-forming material and solvent forms polyamide acid film, this polyamide acid film is contacted with solidification liquid, and carry out imidization, described solvent is for dissolving polyamic acid but slightly soluble or do not dissolve the solvent of pore shaping object matter, and described solidification liquid is for dissolving pore-forming material but slightly soluble or the insoluble liquid of separating polyamic acid.
5, preparation method according to claim 4, wherein, the weight ratio of described pore-forming material and described polyamic acid is 0.01-0.3: 1, and the weight ratio of polyamic acid and described solvent is 1: 4.5-10, the weight ratio of polyamic acid and described solidification liquid is 1: 20-200.
6, according to claim 4 or 5 described preparation methods, wherein, described pore-forming material is selected from one or more in oxyhydroxide, aluminium hydroxide, alkali-metal phosphoric acid salt and the tripoly phosphate sodium STPP of alkali earth metal, and mean particle size is the 0.01-2 micron; Described solidification liquid is one or more in hydrochloric acid, sulfuric acid and the phosphate aqueous solution.
7, preparation method according to claim 6, wherein, the oxyhydroxide of described alkali earth metal is magnesium hydroxide and/or calcium hydroxide; Described alkali-metal phosphoric acid salt is tertiary sodium phosphate and/or Tripotassium phosphate.
8, preparation method according to claim 6, wherein, the concentration of described hydrochloric acid is 5-35 weight %, and the concentration of described aqueous sulfuric acid is 5-98 weight %, and the concentration of described phosphate aqueous solution is 5-98 weight %.
9, according to claim 4 or 5 described preparation methods, wherein, to be selected from saturated carboxylic acid, phenylformic acid polyol ester, carbonatoms that carbonatoms is 5-15 be the phthalic acid dialkyl of 13-18 and in the methylin acetic ester one or more to described pore-forming material; Described solidification liquid is one or more in methyl alcohol, ethanol, methyl ether, ether, acetone and the methyl propanediol.
10, preparation method according to claim 9, wherein, described carbonatoms is that the saturated carboxylic acid of 5-15 is one or more in valeric acid, caproic acid, enanthic acid, sad, n-nonanoic acid, capric acid and their isomer; Described phenylformic acid polyol ester is phenylformic acid one condensed ethandiol ester and/or phenylformic acid one propylene glycol ester that contracts; Described carbonatoms is that the phthalic acid dialkyl of 13-18 is terephthalic acid diamyl ester and/or m-phthalic acid two capronates; Described methylin acetic ester is 1-Methoxy-2-propyl acetate and/or glycol methyl ether acetate.
11, according to claim 4 or 5 described preparation methods, wherein, described polyamic acid is one or more in poly-equal benzene tetramethyl amido acid, poly-biphenyl tetracarboxylic amido acid and the poly-benzophenone tetramethyl amido acid; Described solvent is N-2-methyl-2-pyrrolidone, N,N-dimethylacetamide, tetrahydrofuran (THF), N, one or more in dinethylformamide, m-cresol, dimethyl sulfoxide (DMSO) and the methyl alcohol.
12, preparation method according to claim 4, wherein, the described mode that polyamide acid film is contacted with solidification liquid is for to be immersed in polyamide acid film in the solidification liquid, and the temperature of described solidification liquid is 0-50 ℃, and the time of dipping is 20-120 minute.
13, preparation method according to claim 4, wherein, the method for described imidization be included in keep under 70-200 ℃ the temperature 0.5-4 hour, under 200-400 ℃ temperature, kept 0.5-3 hour.
14, a kind of lithium ion battery, this battery comprises battery case and is encapsulated in the electrode group and the electrolytic solution of this enclosure, described electrode group comprises reels or stacked positive pole, barrier film and negative pole successively, it is characterized in that described barrier film is any described polyimide porous membrane among the claim 1-3.
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