JP2010146839A - Separator for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator which includes a heat-resistant porous layer with improved stability in thermal dimension and is excellent in heat resistance and shut down function. <P>SOLUTION: The separator for nonaqueous secondary battery is characterized in that a single or both surfaces of a micro porous film formed of thermoplastic resin as a whole with a shut down function are covered with a heat resistant porous layer containing polyimide fine particles. The separator has excellent stability in thermal dimension as well as heat resistance and shut down function. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a separator for a non-aqueous secondary battery, and particularly relates to an improvement in the thermal dimensional stability of a heat-resistant porous layer, which is a constituent element of a separator for a non-aqueous secondary battery.

  Nonaqueous electrolyte batteries, particularly nonaqueous secondary batteries represented by lithium ion secondary batteries, have a high energy density and are widely used as main power sources for portable electronic devices such as mobile phones and laptop computers. This lithium ion secondary battery is required to have a higher energy density, but ensuring safety is a technical issue. The role of the separator is important in ensuring the safety of the lithium ion secondary battery, and from the viewpoint of having a shutdown function, polyolefins, particularly polyethylene microporous membranes are currently used. Here, the shutdown function refers to a function of blocking pores in the microporous membrane when the temperature of the battery rises, and blocking the current, and has a function of preventing thermal runaway of the battery.

  On the other hand, lithium ion secondary batteries have been increased in energy density year by year, and heat resistance has been required in addition to a shutdown function to ensure safety. However, the shutdown function is contrary to heat resistance because the operating principle is to close the hole by melting polyethylene. For this reason, after the shutdown function is activated, the battery may continue to be exposed to a temperature higher than the temperature at which the shutdown function is activated, whereby the separator may be melted (so-called meltdown). As a result of this meltdown, a short circuit occurs inside the battery, and as a result, a large amount of heat is generated, and the battery is exposed to dangers such as smoke, ignition, and explosion. For this reason, in addition to the shutdown function, the separator is required to have sufficient heat resistance that does not cause meltdown in the vicinity of the temperature at which the shutdown function operates.

  In this regard, conventionally, in order to achieve both heat resistance and a shutdown function, one or both surfaces (front and back surfaces) of a polyolefin microporous film are covered with a heat resistant porous layer, or a nonwoven fabric made of heat resistant fibers is laminated. The technology is proposed. For example, a non-aqueous electrolyte battery separator in which a heat-resistant porous film made of polyimide or the like is laminated on one side or both sides of a polyolefin microporous film is known (see Patent Documents 1 to 4).

  Such a non-aqueous electrolyte battery separator operates with a shutdown function near the melting point of polyethylene (about 140 ° C), and the heat-resistant porous layer exhibits sufficient heat resistance, so that meltdown occurs even at 200 ° C or higher. Therefore, it exhibits excellent heat resistance and shutdown function. However, the thermal dimensional stability of polyimide which is a component of such a heat-resistant porous layer is not sufficient, and further improvement in thermal dimensional stability has been desired.

JP 2006-155914 A JP 2006-164873 A JP 2006-348280 A JP 2007-335166 A

  Accordingly, an object of the present invention is to provide a separator having a heat-resistant porous layer with improved thermal dimensional stability and having excellent heat resistance, shutdown function, and the like.

（５） 前記有機バインダが、芳香族ポリアミド、ポリイミド、ポリエーテルスルホン、ポリスルホン、ポリエーテルケトン、ポリエーテルイミドからなる群から選ばれる１種又は２種以上のものであることを特徴とする上記（１）〜（４）のいずれかに記載の非水二次電池用セパレータ。
（６） 前記芳香族ポリアミドが、メタ型全芳香族ポリアミドであることを特徴とする上記（５）記載の非水系二次電池用セパレータ。
（７） 前記非水系二次電池用セパレータが、リチウムイオン二次電池用セパレータであることを特徴とする上記（１）〜（６）のいずれかに記載の非水系二次電池用セパレータ。
（８） リチウムのドープ・脱ドープにより起電力を得る非水系二次電池において、上記（１）〜（７）のいずれかに記載の非水系二次電池用セパレータを用いることを特徴とする非水系二次電池。 In order to solve the above problems, the present invention employs the following configuration.
(1) A separator for a non-aqueous secondary battery comprising a microporous membrane formed of a thermoplastic resin and having a shutdown function, and a heat-resistant porous layer laminated on one side or both sides of the microporous membrane. The heat-resistant porous layer comprises a polyimide fine particle, an inorganic filler, and a heat-resistant organic binder, and is a non-aqueous secondary battery separator.
(2) The heat-resistant porous layer contains 0.01 to 20% by weight of the polyimide fine particles, 50 to 95% by weight of the inorganic filler, and 4.99 to 49.99% by weight of the organic binder. The separator for non-aqueous secondary batteries according to (1) above, wherein
(3) The polyimide fine particles have a fiber diameter of 0.5 nm to 50 nm and a fiber length of 5 times or more of the fiber diameter, and are described in (1) or (2) above Non-aqueous secondary battery separator.
(4) The non-aqueous two-component resin according to any one of (1) to (3), wherein the polyimide contains a repeating unit of paraphenylenepyromellitimide represented by the following formula (1) as a main component. Secondary battery depolarizer.

(5) The above organic binder, wherein the organic binder is one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone and polyetherimide. The separator for nonaqueous secondary batteries according to any one of 1) to (4).
(6) The non-aqueous secondary battery separator according to (5), wherein the aromatic polyamide is a meta-type wholly aromatic polyamide.
(7) The nonaqueous secondary battery separator according to any one of (1) to (6), wherein the nonaqueous secondary battery separator is a lithium ion secondary battery separator.
(8) In a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, the non-aqueous secondary battery separator according to any one of (1) to (7) is used. Water-based secondary battery.

  According to the present invention, it is possible to provide a separator that has a heat-resistant porous layer with improved thermal dimensional stability and is excellent in heat resistance, shutdown function, and the like. Such a separator is effective, for example, for improving the performance of a non-aqueous secondary battery such as a lithium ion secondary battery.

[Separator for non-aqueous secondary battery]
The present invention is a separator for a non-aqueous secondary battery comprising a microporous membrane formed of a thermoplastic resin and having a shutdown function, and a heat-resistant porous layer laminated on one side or both sides of the microporous membrane. The heat-resistant porous layer is a separator for a non-aqueous secondary battery characterized in that it includes polyimide fine particles, an inorganic filler, and a heat-resistant organic binder.

  Such a separator for a non-aqueous secondary battery according to the present invention contains a heat-resistant porous layer covering a microporous membrane having a shutdown function, polyimide fine particles, an inorganic filler, and a heat-resistant organic binder. By being configured, it has excellent thermal dimensional stability in addition to heat resistance and a shutdown function. Further, in non-aqueous secondary batteries, it is known that the oxidation resistance of the electrode affects the durability of the battery itself, but the polyimide fine particles have a high oxygen index and high oxidation resistance. By using the non-aqueous secondary battery separator, it is possible to improve the durability of the non-aqueous secondary battery.

  In the present invention, the shape of the polyimide fine particles contained in the heat resistant porous layer is not particularly limited, but is preferably fibrous. As the fibrous polyimide fine particles, the fiber diameter, which is the length of the short axis when observed with a TEM (transmission electron microscope), is 0.5 to 50 nm, and the fiber length is 5 times or more the fiber diameter. What is fibrous is preferable. The fiber diameter is more preferably 1 to 40 nm, and particularly preferably 2 to 35 nm. By setting the fiber diameter to 0.5 nm or more, polyimide molecules do not completely disperse but partially aggregate to form a fine particle structure, thereby improving thermal dimensional stability. Further, by setting the fiber diameter to 50 nm or less, the polyimide fine particles are well dispersed in the heat resistant porous layer. Moreover, thermal dimensional stability can be improved by making fiber length 5 times or more of a fiber diameter.

  The polyimide fine particles of the present invention can be produced by imidizing a polyamic acid, which is a polyimide precursor, with an acid anhydride in a concentration of 0.05 to 30% by weight. As such a polyimide, what has a repeating unit of the paraphenylene pyromellitic imide shown by following formula (1) as a main component is preferable.

  Since paraphenylene pyromellitic imide has a very rigid structure, the more polymerized units of paraphenylene pyromellitic imide, the better the crystallinity and the easier it is to form polyimide fine particles. In order to develop high thermal dimensional stability, the content of the polymerization unit of paraphenylene pyromellitic imide is preferably 50 mol% or more, and more preferably 55 mol% or more. If it is less than 55 mol%, the crystallinity may be impaired, and it may be difficult to form the polyimide fine particles of the present invention.

  The components other than pyromellitic acid and paraphenylenediamine are not particularly limited. For example, an acid anhydride represented by the following formula (2) and a diamine represented by the following formula (3) are used. be able to. In formula (2), R1 represents at least a tetravalent organic group. In formula (3), R2 represents aliphatic or aromatic in general.

  Specific examples of the acid anhydride represented by the formula (2) include 1,2,3,4-benzenetetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 2, 3,4,5-thiophenetetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride, 2,3 ′, 3,4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic acid Dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-p-terphenyltetracarboxylic dianhydride, 2,2 ′, 3 3′-p-terphenyltetracarboxylic dianhydride, , 3,3 ′, 4′-p-terphenyltetracarboxylic dianhydride, 1,2,4,5-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride 1,2,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,5,6-anthracenetetracarboxylic dianhydride, 1,2,6,7-phenanthrenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, 1,2,9,10-phenanthrenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride Product, 2,6-dichroic Naphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene -1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, bis (2,3-di Carboxyphenyl) ether dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane Anhydride, bis (2,3-dicarboxyphenyl) sulfone dianhydride, bis (3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride object 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-di Carboxyphenyl) propane dianhydride, 2,6-bis (3,4-dicarboxyphenoxy) pyridine dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis (3 Examples include 4-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride, and the like, but are not limited thereto.

  Specific examples of the diamine represented by the formula (3) include m-phenylenediamine, p-phenylenediamine, 1,4-diaminonaphthalene, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene, and 2,6-diamino. Naphthalene, 2,7-diaminonaphthalene, 2,6-diaminoanthracene, 2,7-diaminoanthracene, 1,8-diaminoanthracene, 2,4-diaminotoluene, 2,5-diamino (m-xylene), 2, 5-diaminopyridine, 2,6-diaminopyridine, 3,5-diaminopyridine, 2,4-diaminotoluenebenzidine, 3,3′-diaminobiphenyl, 3,3′-dichlorobenzidine, 3,3′-dimethylbenzidine 3,3′-dimethoxybenzidine, 2,2′-diaminobenzophenone, 4,4′-diamidine Benzophenone, 3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylsulfone 4,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl sulfide, 4,4′-diaminodiphenyl thioether, 4,4′-diamino-3,3 ′, 5 , 5′-tetramethyldiphenyl ether, 4,4′-diamino-3,3 ′, 5,5′-tetraethyldiphenyl ether, 4,4′-diamino-3,3 ′, 5,5′-tetramethyldiphenylmethane, , 3-bis (3-aminophenoxy) benzene, 1, -Bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 2,6-bis (3-aminophenoxy) pyridine, , 4-bis (3-aminophenylsulfonyl) benzene, 1,4-bis (4-aminophenylsulfonyl) benzene, 1,4-bis (3-aminophenylthioether) benzene, 1,4-bis (4-amino) Phenylthioether) benzene, 4,4′-bis (3-aminophenoxy) diphenylsulfone, 4,4′-bis (4-aminophenoxy) diphenylsulfone, bis (4-aminophenyl) aminebis (4-aminophenyl)- N-methylamine bis (4-aminophenyl) -N-phenylamine bis (4-aminophenyl) phos Fin oxide, 1,1-bis (3-aminophenyl) ethane, 1,1-bis (4-aminophenyl) ethane, 2,2-bis (3-aminophenyl) propane, 2,2-bis (4- Aminophenyl) propane, 2,2-bis (4-amino-3,5-dimethylphenyl) propane, 4,4′-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] Sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] methane, bis [3-methyl- 4- (4-aminophenoxy) phenyl] methane, bis [3-chloro-4- (4-aminophenoxy) phenyl] methane, bis [3,5-dimethyl- -(4-aminophenoxy) phenyl] methane, 1,1-bis [4- (4-aminophenoxy) phenyl] ethane, 1,1-bis [3-methyl-4- (4-aminophenoxy) phenyl] ethane 1,1-bis [3-chloro-4- (4-aminophenoxy) phenyl] ethane, 1,1-bis [3,5-dimethyl-4- (4-aminophenoxy) phenyl] ethane, 2,2 -Bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [3-methyl-4- (4-aminophenoxy) phenyl] propane, 2,2-bis [3-chloro-4- ( 4-aminophenoxy) phenyl] propane, 2,2-bis [3,5-dimethyl-4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) pheny ] Butane, 2,2-bis [3-methyl-4- (4-aminophenoxy) phenyl] butane, 2,2-bis [3,5-dimethyl-4- (4-aminophenoxy) phenyl] butane, , 2-bis [3,5-dibromo-4- (4-aminophenoxy) phenyl] butane, 1,1,1,3,3,3-hexafluoro-2,2-bis (4-aminophenyl) propane 1,1,1,3,3,3-hexafluoro-2,2-bis [3-methyl-4- (4-aminophenoxy) phenyl] propane and the like. These may be used alone or in combination.

  Polyamic acid polymers are obtained from the reaction of diamines and acids in solution. In the polymerization of polyamic acid, the main component as an acid component, that is, 55 mol% or more is used as pyromellitic dianhydride. In the case of 55 mol% or less, it is difficult to obtain a polyimide filler that exhibits the desired high modulus of elasticity. Other acid components are as described above. As a diamine component, 50 mol% or more of paraphenylenediamine is used. When it is less than 50 mol%, it is difficult to obtain polyimide fine particles that exhibit the desired thermal dimensional stability. Preferably 55 mol% or more of paraphenylenediamine is used. Other diamine components are as described above.

  The solvent for polymerizing the polyamic acid is not particularly limited as long as it dissolves well without decomposing the polyamic acid. Specific examples include N, N-dimethylformamide, N, N-dimethylacetamide, and N-methyl. Amide-type aprotic polar solvents such as pyrrolidone and hexamethylphosphoramide, 1,3-dimethylimidazolidinone, tetramethylurea, 1,3-dipropylimidazolidinone, N-methylcaprolactam, dimethylsulfoxide, dimethyl Aprotic polar solvents such as sulfone, tetramethylsulfone, pyridine, 2-picoline, 3-picoline, 4-picoline, 2,3-lutidine, 2,4-lutidine, 2,5-lutidine, 2,6- Complex compounds such as lutidine, 3,4-lutidine, 3,5-lutidine, 2,6-lutidine, etc. Family compounds, cresols, ethylene glycol, and the like diols such as tetramethylene glycol.

  These solvents are carbon tetrachloride, chloroform, dichloromethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane. , Organic halides such as trichloroethylene and tetrachloroethylene, benzene, toluene, benzonitrile, xylene, solvent naphtha, and other solvents such as dioxane can also be used.

  In order to obtain the polyamic acid in the present invention, the molecular weight can be controlled by controlling the ratio of the amount of diamine used in the organic solvent to the number of moles of acid anhydride. A preferable molar balance is 0.6 to 1.4 mol of the diamine component with respect to 1 mol of the acid anhydride component. In the case of 0.6 mol or less or 1.4 or less, the molar balance is greatly collapsed, the molecular weight is too low, and it may be difficult to form a fiber state.

  In order to seal the end of the polymer in this polymer, it is preferable to use a compound that acts as a monofunctional group for the polymerization of polyimide. Examples of the acid component include acid anhydrides having only one structure of an acid anhydride having 8 to 20 carbon atoms, such as phthalic anhydride and substituted products thereof, hexahydrophthalic anhydride and substituted products thereof, succinic anhydride and substituted products thereof. Body, 1,8-naphthalenedicarboxylic acid anhydride and substituted product thereof, 2,3-naphthalenedicarboxylic acid anhydride and substituted product thereof, and the like. Examples of the amine component include compounds having only one amino group having 1 to 20 carbon atoms, such as methylamine, aniline, cyclohexylamine, aminodiphenyl, aminonaphthalene and substituted products thereof.

  The concentration at the time of polymerization is preferably 0.05 to 30% by weight. When the concentration at the time of polymerization is 0.05% by weight or less, it is not preferable because a lot of cost is required for removing the solvent and productivity is lowered. The content of 30% by weight or less is preferable because rapid heat generation during polymerization can be suppressed. The concentration at the time of polymerization is preferably 0.05 to 20% by weight, more preferably 0.05 to 10% by weight.

The polymerization reaction temperature is preferably −10 to 50 ° C., more preferably −10 to 30 ° C. By reacting at a low temperature, it is possible to suppress a decrease in molecular weight due to hydrolysis and incomplete end-capping. However, if the temperature is too low, the solubility of the monomer and the solubility of the acid anhydride are obtained. Since it is not high, the reaction may not proceed.
Imidization in the solution is performed by adding a dehydrating condensing agent to the polyamic acid solution thus obtained.

  At this time, as the condensing agent, acid anhydrides such as acetic anhydride, benzoic anhydride, trifluoroacetic acid dianhydride; chlorides such as phosgene, thionyl chloride, tosyl chloride, nicotyl chloride; phosphorus trichloride, triphenyl phosphite, Phosphorus compounds such as diethyl phosphate cyanide; condensing agents such as N, N′-disubstituted carbodiimides such as N, N′-dicyclohexylcarbodiimide can be raised. The amount of the dehydrating condensing agent may be an amount that sufficiently imidizes the polyamic acid. The amount is 0.8 mol to 50 mol, preferably 0.9 mol to 30 mol, and more preferably 1 mol to 10 mol with respect to 1 mol of the amic acid bond.

  An amine catalyst may be used in the dehydration condensation reaction. As an amine catalyst, a tertiary aliphatic amine such as trimethylamine, triethylamine, tributylamine, diisopropylethylamine, triethylenediamine; N, N-dimethylaniline, 1,8-bis (N , N-dimethylamino) aromatic compounds such as naphthalene, heterocyclic compounds such as pyridine, lutidine, quinoline, isoquinoline, 1,8-diazabicyclo [5.4.0] undecene, and N, N-dimethylaminopyridine. As an accelerator. For example, when triethylenediamineamine or N, N-dimethylaminopyridine is used, imidization in the solution can be accelerated. The addition amount of the catalyst is not particularly specified, but is 0.005 mol equivalent% to 100 mol equivalent% with respect to the dehydration condensing agent.

  The polyamic acid concentration during the dehydration condensation reaction is preferably 0.05 to 30% by weight. When the concentration at the time of reaction is 0.05% by weight or less, productivity is lowered, which is not preferable. By setting it to 30% by weight or less, it becomes possible to suppress entanglement of molecular chains and to produce fibrous polyimide fine particles. The concentration during the reaction is preferably 0.05 to 20% by weight, more preferably 0.05 to 10% by weight.

The reaction temperature between the dehydrating condensing agent and the polyamic acid is not particularly limited as long as it is in a temperature range where the reaction proceeds sufficiently, but is generally -10 to 220 ° C. In this case, it is preferable to sufficiently disperse. The dispersion method is not particularly specified, but high-speed stirring, ultrasonic treatment, high shear dispersion equipment, or the like may be used. Thus, polyimide fine particles effective for improving various physical properties such as the thermal dimensional stability of the heat resistant porous layer can be obtained.
The polyimide fine particles thus obtained can be isolated and used for the heat-resistant porous layer. Moreover, you may mix an organic binder and an inorganic filler with the state of a solution.

  In the separator for a non-aqueous secondary battery of the present invention, the content of the polyimide fine particles, the inorganic filler and the heat-resistant organic binder in the heat-resistant porous layer is not particularly limited, but in the heat-resistant porous layer, It is preferable that 0.01 to 20% by weight of polyimide fine particles, 50 to 95% by weight of inorganic filler, and 4.99 to 49.99% by weight of organic binder are contained. The polyimide fine particles can drastically improve the thermal dimensional stability even with a small content, and if 0.01% by weight is contained, the effect can be obtained. On the other hand, if the content of the polyimide fine particles exceeds 20% by weight, the adhesiveness is lowered, which is not preferable. Also, when the content of the inorganic filler is less than 50% by weight, the thermal dimensional stability is lowered, which is not preferable. On the other hand, when the content of the inorganic filler exceeds 95% by weight, the strength of the heat-resistant porous layer is insufficient, and powder falling is likely to occur, which is not preferable. Moreover, it is not preferable that the content of the organic binder is less than 4.99% by weight because powder falling or the like tends to occur. On the other hand, if the content of the organic binder exceeds 49.99% by weight, it is not preferable because the desired amount of polyimide fine particles and inorganic filler cannot be added.

  Examples of the inorganic filler in the present invention include metal hydroxide, metal oxide, metal nitride, carbonate, sulfate, clay mineral and the like. Examples of the metal hydroxide include aluminum hydroxide, magnesium hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, nickel hydroxide, boron hydroxide, and boehmite. Examples of the metal oxide include aluminum oxide, oxidized Titanium, zinc oxide, silicon oxide, yttrium oxide, cerium oxide, tin oxide, iron oxide, etc., as metal nitride, aluminum nitride, boron nitride, titanium nitride, etc., as carbonate, calcium carbonate, magnesium carbonate, barium carbonate Etc., sulfate as barium sulfate, calcium sulfate, etc., clay mineral as calcium silicate, talc, mica, montmorillonite, hydrotalcite, bentonite, zeolite, sepiolite, kaolin, hectorite, saponite, stevensite, beidellite, etc. But Or a combination of two or more of these.

  In the separator configuration of the present invention, the heat-resistant porous layer has a function of imparting heat resistance to the separator. By adding an inorganic filler as described above to this layer, such as prevention of short circuit at high temperatures and dimensional stability, etc. From the viewpoint, the heat resistance of the heat resistant porous layer can be further improved. In general, a separator coated with a heat-resistant porous layer tends to be strongly charged with static electricity, and handling properties are often not preferable from such a viewpoint. Here, when an inorganic filler such as a metal hydroxide is added to the heat-resistant porous layer, since the charged charge decays quickly, the charge can be kept at a low level and the handling property is improved. . For these reasons, it is preferable to add such an inorganic filler into the heat-resistant porous layer.

  In the present invention, the average particle size of the inorganic filler in the heat resistant porous layer is not particularly limited, but is preferably in the range of 0.1 to 1 μm. When the average particle diameter of the inorganic filler exceeds 1 μm, the short circuit resistance at high temperature of the heat resistant porous layer is lowered, which is not preferable. Further, there is a problem that it hinders the formation of the heat-resistant porous layer with an appropriate thickness. Moreover, when the average particle diameter of the inorganic filler is smaller than 0.1 μm, not only the coating strength is reduced and the problem of powder falling occurs, but using such a small one is substantially from the viewpoint of cost. Have difficulty.

  In the heat-resistant porous layer in the present invention, it is necessary to contain a heat-resistant organic binder from the viewpoints of strength, shape maintenance and the like of the heat-resistant porous layer. As such an organic binder, a polymer having a melting point of 200 ° C. or higher or a polymer having no melting point but a decomposition temperature of 200 ° C. or higher is suitable, and preferably aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyether One or more selected from the group consisting of ketones and polyetherimides. In particular, aromatic polyamides are preferable from the viewpoint of high-temperature oxidation resistance and durability, and meta-type wholly aromatic polyamides such as polymetaphenylene isophthalamide are more preferable from the viewpoint of easily forming a porous layer.

  In the present invention, the heat-resistant porous layer has a large number of micropores inside and has a structure in which these micropores are connected, and gas or liquid can pass from one surface to the other. It means the layer that became. The porosity of the heat resistant porous layer is preferably in the range of 60 to 90%. When the porosity of the heat resistant porous layer exceeds 90%, the heat resistance tends to be insufficient, which is not preferable. On the other hand, if it is lower than 60%, the cycle characteristics, storage characteristics and discharge properties tend to decrease, which is not preferable. It should be noted that the organic binder may be mainly composed of the polymer as described above, ie, about 90% by weight or more, and contains about 10% by weight or less of other components that do not affect the battery characteristics. Also good.

  As the thermoplastic resin used for the microporous membrane in the present invention, a thermoplastic resin having a melting point of less than 200 ° C. is suitable, preferably a polyolefin, and particularly preferably polyethylene. The polyethylene used in the present invention is not particularly limited, but high-density polyethylene or a mixture of high-density polyethylene and ultrahigh molecular weight polyethylene is suitable. For example, in addition to polyethylene, other polyolefins such as polypropylene and polymethylpentene may be mixed and used. A microporous membrane means a membrane that has a large number of micropores inside and has a structure in which these micropores are connected, allowing gas or liquid to pass from one surface to the other. To do. The microporous membrane may be mainly composed of a thermoplastic resin in an amount of about 90% by weight or more, and may contain about 10% by weight or less of other components that do not affect the battery characteristics. good.

  The film thickness of the microporous film such as polyethylene is preferably 5 μm or more. If the thickness of the microporous film is less than 5 μm, mechanical properties such as tensile strength and puncture strength are insufficient, which is not preferable. The thickness of the heat resistant porous layer is preferably 2 μm or more. When the thickness of the heat-resistant porous layer is less than 2 μm, it becomes difficult to obtain sufficient heat resistance.

  The porosity of the microporous membrane is preferably 20 to 60%. When the porosity of the microporous membrane is less than 20%, the membrane resistance of the separator becomes too high, and the output of the battery is remarkably reduced. On the other hand, if it exceeds 60%, the shutdown characteristic is remarkably deteriorated. The Gurley value (JIS P8117) indicating the air permeability of the microporous membrane is preferably 10 to 500 sec / 100 cc. If the Gurley value of the microporous membrane is higher than 500 sec / 100 cc, the ion permeability is insufficient and the resistance of the separator increases. When the Gurley value of the microporous film is lower than 10 sec / 100 cc, the shutdown function is remarkably not practical.

  In the present invention, the heat-resistant porous layer may be formed on at least one surface of the microporous membrane, but from the viewpoint of handling properties, durability, and the effect of suppressing heat shrinkage, it is more preferable to form the heat-resistant porous layer on both front and back surfaces. preferable.

The film thickness of the separator for a non-aqueous secondary battery of the present invention is preferably 30 μm or less, more preferably 25 μm or less. When the thickness of the separator exceeds 30 μm, the energy density and output characteristics of a battery to which the separator is applied are undesirably lowered. As a physical property of the separator for non-aqueous secondary batteries, the Gurley value (JIS P8117) is 10 to 1000 sec / 100 cc, preferably 100 to 400 sec / 100 cc. When the Gurley value is less than 10 sec / 100 cc, the Gurley value of the microporous membrane is too low, and the deterioration of the shutdown function is remarkably impractical. When the Gurley value exceeds 1000 sec / 100 cc, the ion permeability becomes insufficient, resulting in a problem that the membrane resistance of the separator is increased and the output of the battery is lowered. The membrane resistance is 0.5 to 10 ohm · cm ² , preferably 1 to 5 ohm · cm ² . The puncture strength is in the range of 10 to 1000 g, preferably 200 to 600 g.

[Method for producing separator for non-aqueous secondary battery]
Although the manufacturing method of the separator for non-aqueous secondary batteries of this invention is not specifically limited, For example, it is possible to manufacture through the following processes (i)-(iv). That is, (i) a step of dispersing a polyimide fine particle and an inorganic filler in a water-soluble organic solvent solution of an organic binder to prepare a coating slurry; and (ii) the obtained coating slurry is mainly made from a polyolefin resin. (Iii) the coated microporous membrane is immersed in a coagulating liquid comprising water or a mixture of water and the organic solvent to form an organic binder. It is a manufacturing method comprising: a solidifying step; and (iv) a step of washing and drying the microporous membrane after the solidifying step.

  In the step (i), the water-soluble organic solvent is not particularly limited, but a good solvent for an organic binder is preferable. Specifically, a polar solvent is preferable, and examples thereof include N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. In addition, a solvent that is a poor solvent for the organic binder may be mixed with these polar solvents. By applying such a solvent, a microphase separation structure is induced, and the formation of a heat-resistant porous layer is facilitated. As the poor solvent, alcohols are preferable, and polyhydric alcohols such as glycol are particularly preferable.

  In step (ii), a coating solution for forming a heat-resistant porous layer is applied to at least one surface of the microporous membrane. In the present invention, it is preferable to apply on both surfaces of the microporous membrane. The concentration of the coating solution is preferably 4 to 9% by weight. Examples of the coating method include knife coater method, gravure coater method, screen printing method, Mayer bar method, die coater method, reverse roll coater method, ink jet method, spray method, roll coater method and the like. From the viewpoint of uniformly applying the coating film, the reverse roll coater method is particularly suitable. More specifically, for example, when applying a coating solution for forming a heat-resistant porous layer on both sides of a polyethylene microporous membrane, it is applied excessively on both sides of the polyethylene microporous membrane through a pair of Meyer bars. There is a method in which a working liquid is applied, this is passed between a pair of reverse roll coaters, and an excessive coating liquid is scraped off to precisely measure.

  In the step (iii), the coated microporous film is immersed in a coagulating liquid capable of coagulating the organic binder, thereby coagulating the organic binder and forming a porous layer. Examples of the coagulation method include a method of spraying a coagulation liquid with a spray and a method of immersing in a bath (coagulation bath) containing the coagulation liquid. The coagulation liquid is not particularly limited as long as it can coagulate the organic binder, but is preferably a mixture of water or an appropriate amount of water in the organic solvent used in the coating liquid. Here, the mixing amount of water is preferably 40 to 80% by weight with respect to the coagulation liquid. When the amount of water is less than 40% by weight, there arises a problem that the time required for solidifying the organic binder becomes long or solidification becomes insufficient. On the other hand, when the amount is more than 80% by weight, there arises a problem that the cost for solvent recovery becomes high, or the surface that comes into contact with the coagulating liquid is solidified too quickly and the surface is not sufficiently porous.

  Step (iv) is a step of removing the coagulating liquid from the obtained separator by washing with water, and then drying, following step (iii). The drying method is not particularly limited, but the drying temperature is suitably 50 to 80 ° C. When a high drying temperature is applied, a method of contacting the roll in order to prevent dimensional change due to heat shrinkage. Is preferably applied.

[Non-aqueous secondary battery]
The above-described separator for a non-aqueous secondary battery of the present invention can be applied to any known non-aqueous secondary battery, and a battery excellent in safety and thermal dimensional stability can be obtained.
The type and configuration of the applied non-aqueous secondary battery is not limited in any way, but the non-aqueous secondary battery separator of the present invention is a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium. It can be suitably applied to a battery. Among these, application to a lithium ion secondary battery is preferable.

In general, a non-aqueous secondary battery means a battery element in which a negative electrode and a positive electrode are opposed to each other with a separator interposed therebetween and an electrolytic solution is impregnated, and this is enclosed in an exterior. The negative electrode has a structure in which a negative electrode mixture composed of a negative electrode active material, a conductive additive, and a binder is formed on a current collector (copper foil, stainless steel foil, nickel foil, etc.). As the negative electrode active material, a material capable of electrochemically doping lithium, for example, a carbon material, silicon, aluminum, or tin is used. The positive electrode has a structure in which a positive electrode mixture composed of a positive electrode active material, a conductive additive, and a binder is formed on a current collector. Examples of the positive electrode active material include lithium-containing transition metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMn _0.5 Ni _0.5 O ₂ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiMn ₂ O. ₄ and LiFePO ₄ are used. The electrolytic solution has a configuration in which a lithium salt, for example, LiPF ₆ , LiBF ₄ , or LiClO ₄ is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, and vinylene carbonate. Examples of the exterior material include a metal can or an aluminum laminate pack. The shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the separator of the present invention can be suitably applied to any shape.

  Hereinafter, the present invention will be described in detail by way of examples. Various physical property values and methods for measuring performance are as follows.

[Fiber diameter and fiber length of polyimide fine particles]
Morphological observation was performed using a transmission microscope (TEM) H-800 manufactured by Hitachi, Ltd., and the fiber diameter and length of 20 fine particles were measured and the average was calculated.

[Film thickness]
It was determined by measuring 20 points with a contact-type film thickness meter (manufactured by Mitutoyo Co., Ltd.) and averaging them. Here, the contact terminal used was a cylindrical one having a bottom surface of 0.5 cm in diameter, and measurement was performed under a condition that a load of 1.2 kg / cm ² was applied to the contact terminal.

[Gurley value]
The Gurley value (second / 100 cc) was measured according to JIS P8117.

[Porosity] The constituent material consists of a, b, c..., N, the weight of the constituent material is Wa, Wb, Wc..., Wn (g · cm ² ), and the respective true densities are da, db, When dc ..., dn (g / cm ³ ) and the film thickness of the layer of interest is t (cm), the porosity ε (%) is ε = {1− (Wa / da + Wb / db + Wc / dc +... + Wn / Dn) / t} × 100
I asked more.

[Shutdown (SD) characteristics]
First, the separator is punched to Φ19 mm, dipped in a 3% by weight methanol solution of a nonionic surfactant (manufactured by Kao Corporation; Emulgen 210P), and air-dried. Then, the separator was impregnated with the electrolytic solution and sandwiched between SUS plates (Φ15.5 mm). Here, 1 M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) was used as the electrolytic solution. This was enclosed in a 2032 type coin cell. I took the lead from the coin cell, put a thermocouple, and put it in the oven. The temperature of the cell is measured at a rate of temperature increase of 1.6 ° C / min. Simultaneously, alternating current with an amplitude of 10 mV and a frequency of 1 kHz is applied to measure the resistance of the cell. evaluated. Various performances are summarized in Table 1.

[Heat shrinkage]
A sample is cut into 18 cm (MD direction) × 6 cm (TD direction). Mark 2 cm and 17 cm points (Point A, Point B) from the top on a line that bisects the TD direction. Also, mark the points 1 cm and 5 cm (point C, point D) from the left on the line that bisects the MD direction. A clip is attached to this (the place where the clip is attached is within 2 cm in the upper part in the MD direction), and it is hung in an oven adjusted to 175 ° C. and heat-treated for 30 minutes under no tension. The length between the two points AB and the CD was measured before and after the heat treatment, and the thermal shrinkage rate was obtained from the following equation.
MD direction thermal shrinkage = {(AB length before heat treatment−AB length after heat treatment) / AB length before heat treatment} × 100
TD direction thermal contraction rate = {(length of CD before heat treatment−length of CD after heat treatment) / length of CD before heat treatment} × 100

[Adjustment of polyimide fine particles]
Into a reaction vessel equipped with a thermometer / stirring device and a raw material inlet, 600 mL of dimethylacetamide (DMAc) dehydrated with molecular sieves in a nitrogen atmosphere was added, and 0.21 g of paraphenyldiamine was further added and completely dissolved. Cooled to 0 ° C. in a bath. To this cooled diamine solution, 0.41 g of pyromellitic dianhydride and 0.057 g of phthalic anhydride were added and reacted. The reaction was allowed to proceed for 8 hours in an ice bath. To the polyamic acid solution thus obtained, 0.043 g of triethylenediamine was added and completely dissolved, and then heated to 60 ° C., and a solution consisting of 1 ml of acetic anhydride and 40 ml of dimethylacetamide (DMAc) was added dropwise with high-speed stirring. Thereafter, the target polyimide fine particles were obtained by holding at 10 ° C. for 10 hours. From the TEM photograph, the average diameter was 20 nm, and the fiber length was 1 μm. The polyimide particles extracted in reprecipitate from solution was subjected to IR measurement of a sample dried under vacuum at 80 ° C. and washed with acetone, the peak of the peak and 720 cm ^-1 distinctive 1780 cm ^-1 is observed imide It was done. The concentration of the polyimide fine particles in this solution was 0.09% by weight.

[Example 1]
As polyethylene powder, GUR2126 (weight average molecular weight 41.50 million, melting point 141 ° C.) and GRX143 (weight average molecular weight 560,000, melting point 135 ° C.) manufactured by Ticona were used. A polyethylene solution was prepared by dissolving GUR2126 and GURX143 in a mixed solvent of liquid paraffin and decalin such that the polyethylene concentration was 30% by weight so that the ratio was 1: 9 (weight ratio). The composition of the polyethylene solution is polyethylene: liquid paraffin: decalin = 30: 45: 25 (weight ratio). This polyethylene solution was extruded from a die at 148 ° C., cooled in a water bath, and dried at 60 ° C. for 8 minutes and at 95 ° C. for 15 minutes to produce a gel tape (base tape). The base tape was stretched by biaxial stretching, which was sequentially performed with longitudinal stretching and lateral stretching. Here, the longitudinal stretching was 5.5 times, the stretching temperature was 90 ° C., the transverse stretching was 11.0 times the stretching ratio, and the stretching temperature was 105 ° C. After transverse stretching, heat setting was performed at 125 ° C. Next, this was immersed in a methylene chloride bath to extract liquid paraffin and decalin. Then, it dried at 50 degreeC and obtained the polyethylene microporous film by annealing at 120 degreeC. The properties of this polyethylene microporous membrane were a film thickness of 12.0 μm, a porosity of 36%, and an air permeability of 301 seconds / 100 cc.

  Using the prepared polyimide fine particle solution, Conex (registered trademark; made by Teijin Techno Products), polyimide fine particles and aluminum hydroxide (made by Showa Denko; H-43M), which is a meta-type wholly aromatic polyamide, are in a weight ratio. 20: 0.1: 79.9, and the weight of dimethylacetamide (DMAc) and tripropylene glycol (TPG) was adjusted so that the concentration of the meta-type wholly aromatic polyamide was 5.5% by weight. A slurry for coating was obtained by mixing in a mixed solvent having a ratio of 50:50.

A pair of Meyer bars (count # 6) was confronted with a clearance of 20 μm. An appropriate amount of the above slurry for coating was placed on a Mayer bar, and the coating slurry was applied to both sides of the polyethylene microporous membrane by passing the polyethylene microporous membrane between a pair of Meyer bars. This was immersed in a coagulating liquid having a weight ratio of water: DMAc: TPG = 50: 25: 25 and 40 ° C. Next, washing with water and drying were performed to form heat-resistant porous layers on the front and back of the polyethylene microporous membrane, thereby obtaining a separator for a non-aqueous secondary battery of the present invention.
The film thickness of the obtained separator was 20.3 μm, the porosity of the heat-resistant porous layer was 72%, and the air permeability was 420 seconds / 100 cc. The separator had shutdown characteristics, and the thermal shrinkage rate of the separator was MD 14% and TD 12%.

[Example 2]
A non-aqueous secondary battery as in Example 1 except that the composition of the coating slurry was such that the polyimide fine particles, aluminum hydroxide, and meta-type wholly aromatic polyamide were in a weight ratio of 10:40:50. A separator was prepared. The film thickness of the obtained separator was 20.1 μm, the porosity of the heat-resistant porous layer was 68%, and the air permeability was 431 seconds / 100 cc. The separator had shutdown characteristics, and the thermal shrinkage rate of the separator was MD18% and TD16%.

[Example 3]
The non-aqueous secondary battery as in Example 1 except that the composition of the coating slurry is such that the polyimide fine particles, aluminum hydroxide, and meta-type wholly aromatic polyamide are in a weight ratio of 10:80:10. A separator was prepared. The film thickness of the obtained separator was 19.8 μm, the porosity of the heat-resistant porous layer was 71%, and the air permeability was 410 seconds / 100 cc. The separator had shutdown characteristics, and the thermal shrinkage rate of the separator was MD11% and TD10%.

[Comparative Example 1]
The non-aqueous secondary as in Example 1 except that the composition of the slurry for coating does not use polyimide fine particles and the weight ratio of meta-type wholly aromatic polyamide and aluminum hydroxide is 20:80. A battery separator was produced. The film thickness of the obtained separator was 20.0 μm, the porosity of the heat-resistant porous layer was 70%, and the air permeability was 414 seconds / 100 cc. The separator had shutdown characteristics, and the thermal shrinkage rate of the separator was MD21% and TD18%.

[Comparative Example 2]
The composition of the coating slurry was the same as in Example 1 except that aluminum hydroxide was not used and the polyimide fine particles and the meta-type wholly aromatic polyamide were in a weight ratio of 0.1: 99.9. A separator for a non-aqueous secondary battery was produced. The thickness of the obtained separator was 20.2 μm, the porosity of the heat-resistant porous layer was 71%, and the air permeability was 455 seconds / 100 cc. The separator had shutdown characteristics, and the thermal contraction rate of the separator was MD 30% and TD 15%.

Claims (8)

A separator for a non-aqueous secondary battery comprising a microporous membrane formed of a thermoplastic resin and having a shutdown function, and a heat-resistant porous layer laminated on one or both sides of the microporous membrane,
The heat-resistant porous layer comprises a polyimide fine particle, an inorganic filler, and a heat-resistant organic binder, and is a non-aqueous secondary battery separator.   The heat-resistant porous layer contains 0.01 to 20% by weight of the polyimide fine particles, 50 to 95% by weight of the inorganic filler, and 4.99 to 49.99% by weight of the organic binder. The separator for non-aqueous secondary batteries according to claim 1.   3. The nonaqueous secondary battery according to claim 1, wherein the polyimide fine particles are in a fibrous form having a fiber diameter of 0.5 nm to 50 nm and a fiber length of 5 times or more of the fiber diameter. Separator for use. The depolarizer for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the polyimide contains a repeating unit of paraphenylene pyromellitic imide represented by the following formula (1) as a main component.

  The organic binder is one or more selected from the group consisting of aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. The separator for non-aqueous secondary batteries in any one of.   The non-aqueous secondary battery separator according to claim 5, wherein the aromatic polyamide is a meta-type wholly aromatic polyamide.   The said separator for non-aqueous secondary batteries is a separator for lithium ion secondary batteries, The separator for non-aqueous secondary batteries in any one of Claims 1-6 characterized by the above-mentioned.   A non-aqueous secondary battery using the separator for a non-aqueous secondary battery according to claim 1 in a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium.