JP4818603B2 - Battery separator and non-aqueous electrolyte battery including the same - Google Patents

Description

  The present invention relates to a battery separator and a nonaqueous electrolyte battery including the same, and more particularly to a nonflammable battery separator made of a vinylidene fluoride polymer and a highly safe nonaqueous electrolyte battery including the separator. .

  Recently, non-aqueous electrolyte batteries such as lithium batteries and lithium ion secondary batteries have come to be widely used as power sources having high voltage and high energy density. For example, cameras, electronic watches, and various memory backups It is used as a power source for driving, a driving power source for notebook computers and mobile phones, and a main power source or auxiliary power source for electric vehicles and fuel cell vehicles. Currently, a porous film made of polyolefin such as polyethylene or polypropylene is used as a separator provided between the positive electrode and the negative electrode of these nonaqueous electrolyte batteries to prevent a short circuit between the positive and negative electrodes. However, the separator is provided with a large number of holes for allowing ions to pass during charging and discharging of the battery, and does not hinder the passage of ions under a normal use environment. However, since a polyolefin-based thin film does not have an ability to retain an electrolyte solution, a battery using the thin film as a separator has a risk of liquid leakage.

  On the other hand, in recent years, a battery using a solid electrolyte or a gel electrolyte has been proposed as a battery that does not cause a liquid leakage. In recent years, the battery has been particularly researched because it does not have to worry about liquid leakage, can be formed into a film, can be easily incorporated into an electronic device, and can effectively use space. However, since the solid electrolyte has low ionic conductivity and is difficult to put into practical use in a battery, a battery using a gel electrolyte is currently intensively studied. As such a gel electrolyte, a polymer using vinylidene fluoride as a monomer as described in JP-A No. 2002-8723 (Patent Document 1) and JP-A No. 2002-216848 (Patent Document 2) is used for non-aqueous electrolysis. A gel electrolyte impregnated and swollen with a liquid is known. And these gel electrolytes have a function as a separator for preventing the contact of a positive electrode and a negative electrode with the function as an electrolyte of a battery.

  By the way, in the battery using the gel electrolyte, similarly to the non-aqueous electrolyte battery described above, lithium metal or a lithium alloy is used as a negative electrode material, and the negative electrode is violently mixed with a compound having active protons such as water and alcohol. In order to react, the organic solvent used for the gel electrolyte is limited to aprotic organic solvents such as ester compounds and ether compounds.

  However, although the aprotic organic solvent has low reactivity with the lithium of the negative electrode active material, for example, when a battery is short-circuited, a large current flows suddenly, and when the battery abnormally generates heat, it is vaporized and decomposed. Therefore, there is a high risk of generating gas, causing the battery to rupture or ignite due to the generated gas and heat, and sparks generated during a short circuit. Further, when the battery abnormally generates heat due to a short circuit or the like, there is a risk that the vinylidene fluoride polymer is chain decomposed and the polymer itself is ignited.

JP 2002-8723 A JP 2002-216848 A

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and provide a nonflammable battery separator containing polyvinylidene fluoride and / or a vinylidene fluoride-containing copolymer. Another object of the present invention is to provide a highly safe nonaqueous electrolyte battery using such a nonflammable battery separator.

  As a result of intensive studies to achieve the above-mentioned object, the present inventors have incorporated a nonflammability imparting substance containing phosphorus into a battery separator made of polyvinylidene fluoride and / or a vinylidene fluoride-containing copolymer. The present inventors have found that the battery separator can be made nonflammable, and that the safety of the battery can be greatly improved by using the nonflammable battery separator for a nonaqueous electrolyte battery, thereby completing the present invention. It was.

That is, the battery separator of the present invention contains at least one polymer selected from the group consisting of polyvinylidene fluoride and a vinylidene fluoride-containing copolymer, and a phosphorus-containing nonflammability imparting substance , and the phosphorus-containing nonflammable material. The sex-imparting substance is at least one selected from the group consisting of phosphonate compounds and phosphinate compounds .

  In the battery separator of the present invention, the phosphorus-containing nonflammability imparting substance is preferably solid at 25 ° C.

  In the battery separator of the present invention, the polymer is preferably polyvinylidene fluoride.

  A nonaqueous electrolyte battery according to the present invention includes the battery separator, a positive electrode, a negative electrode, and a nonaqueous electrolytic solution.

  In the nonaqueous electrolyte battery of the present invention, it is preferable that the nonaqueous electrolyte is held in the battery separator to form a gel electrolyte. In this case, in addition to preventing liquid leakage from the battery, the battery can be formed into a film, and the space in the electronic device can be effectively utilized by improving the incorporation into the electronic device.

  ADVANTAGE OF THE INVENTION According to this invention, the nonflammable battery separator containing a polyvinylidene fluoride and / or a vinylidene fluoride containing copolymer and a phosphorus containing nonflammability provision substance can be provided. In addition, a highly safe nonaqueous electrolyte battery including the separator can be provided.

The present invention is described in detail below. The battery separator of the present invention contains at least one polymer selected from the group consisting of polyvinylidene fluoride and a vinylidene fluoride-containing copolymer, and a phosphorus-containing incombustibility imparting substance , and the phosphorus-containing incombustibility imparted The substance is at least one selected from the group consisting of phosphonate compounds and phosphinate compounds . The battery separator of the present invention contains a phosphorous-containing nonflammability imparting substance and is therefore nonflammable. When the separator is applied to a battery, the separator itself burns when the battery abnormally generates heat due to a short circuit or the like. This can reliably prevent thermal runaway of the battery.

  The polymer constituting the battery separator of the present invention is polyvinylidene fluoride (PVDF) and / or a vinylidene fluoride-containing copolymer. These polymers may be used alone or in combination of two or more. May be. The vinylidene fluoride-containing copolymer is a copolymer of vinylidene fluoride and other monomers, and monomers copolymerized with vinylidene fluoride include hexafluoropropylene, maleic acid, maleic acid ester, maleic anhydride Examples include acids, tetrafluoroethylene, trifluoroethylene, fluoroethylene, ethylene, propylene, trifluoropropylene, and the like. Among these, hexafluoropropylene is preferable. The polymer used in the battery separator of the present invention is preferably polyvinylidene fluoride and a vinylidene fluoride-hexafluoropropylene copolymer, and more preferably polyvinylidene fluoride.

The nonflammability-imparting substance used for the battery separator of the present invention needs to contain phosphorus and is preferably solid at 25 ° C. (room temperature). Here, the nonflammability imparting substance is selected from the group consisting of a phosphonate compound and a phosphinate compound, and these phosphorus-containing compounds may be used singly or in combination of two or more. These compounds containing phosphorus in the molecule generate phosphate esters when the separator burns, and make the separator incombustible by the action of the phosphate esters. Moreover, since phosphorus has the effect | action which suppresses the chain decomposition of the said polyvinylidene fluoride which is a raw material of a separator, and a vinylidene fluoride containing copolymer, the danger of the combustion of a separator can be reduced effectively.

  The content of the nonflammability imparting substance in the battery separator of the present invention is preferably in the range of 3 to 20% by mass, and more preferably in the range of 5 to 15% by mass. When the content of the nonflammability imparting substance is less than 3% by mass, the effect of reducing the risk of burning the separator is small, and when it exceeds 20% by mass, the mechanical strength of the separator is lowered.

［式中、Ｒ^6aは、それぞれ独立して一価の置換基を示し；Ｒ^6bは、一価の置換基又はハロゲン元素を示す］で表される化合物が好ましく、上記ホスフィネート化合物としては、下記式(VII)：

［式中、Ｒ^7aは、一価の置換基を示し；Ｒ^7bは、それぞれ独立して一価の置換基又はハロゲン元素を示す］で表される化合物が好ましい。これらホスホネート化合物及びホスフィネート化合物は、１種単独で用いても、２種以上を混合して用いてもよく、ホスホネート化合物とホスフィネート化合物とを組み合わせて用いてもよい。 Examples of the phosphonate compound include the following formula (VI):

[Wherein R ^6a independently represents a monovalent substituent; R ^6b represents a monovalent substituent or a halogen element] is preferable, and examples of the phosphinate compound include the following: Formula (VII):

[Wherein, R ^7a represents a monovalent substituent; R ^7b independently represents a monovalent substituent or a halogen element] is preferable. These phosphonate compounds and phosphinate compounds may be used singly or in combination of two or more, or a phosphonate compound and a phosphinate compound may be used in combination.

Examples of the monovalent substituent in R ^6a and R ^{6b in} the above formula (VI) and R ^7a and R ^7b in the formula (VII) include an alkoxy group, an aryloxy group, an alkyl group, an aryl group, an acyl group, a substituted or non-substituted group. Examples thereof include a substituted amino group, an alkylthio group, and an arylthio group. Among these, an alkoxy group and an aryloxy group are preferable in terms of excellent nonflammability. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, an allyloxy group containing a double bond, an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group, and the like. Examples of the aryloxy group include a phenoxy group, a methylphenoxy group, and a methoxyphenoxy group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Includes a phenyl group, a tolyl group, a naphthyl group, and the substituted or unsubstituted amino group includes an amino group, a methylamino group, a dimethylamino group, an ethylamino group, a diethylamino group, an aziridyl group, and a pyrrolidyl group. Examples of the alkylthio group include methylthio group, ethylthio group It includes groups such as the above-described arylthio group, a phenylthio group, and the like. The hydrogen element in these monovalent substituents may be substituted with a halogen element, and is preferably substituted with fluorine.

On the other hand, examples of the halogen element in R ^{6b of} the above formula (VI) and R ^7b of the formula (VII) include fluorine, chlorine, bromine, etc. Among these, fluorine is preferable.

  Specific examples of the phosphonate compound of the above formula (VI) include dimethyl fluorophosphate, diethyl fluorophosphate, bistrifluoroethyl fluorophosphate, dipropyl fluorophosphate, diallyl fluorophosphate, dibutyl fluorophosphate, and fluorophosphoric acid. Examples thereof include diphenyl and difluorophenyl fluorophosphate.

  On the other hand, as the phosphinate compound of the above formula (VII), specifically, methyl chlorofluorophosphate, ethyl chlorofluorophosphate, trifluoroethyl chlorofluorophosphate, propyl chlorofluorophosphate, allyl chlorofluorophosphate, chloro Butyl fluorophosphate, methoxyethyl chlorofluorophosphate, methoxyethoxyethyl chlorofluorophosphate, phenyl chlorofluorophosphate, fluorophenyl chlorofluorophosphate, methyl difluorophosphate, ethyl difluorophosphate, trifluoroethyl difluorophosphate, Propyl difluorophosphate, allyl difluorophosphate, butyl difluorophosphate, methoxyethyl difluorophosphate, methoxyethoxyethyl difluorophosphate, phenyl difluorophosphate, fluorinated difluorophosphate Phenyl, and the like. Among these, methyl difluorophosphate, ethyl difluorophosphate, trifluoroethyl difluorophosphate, propyl difluorophosphate, and phenyl difluorophosphate are preferable.

  The battery separator of the present invention includes, for example, a plasticizer and a volatile organic solvent added to the polymer and the phosphorus-containing nonflammability imparting substance, and uniformly mixed to obtain a mixed solution. The mixed solution is placed on a glass plate or the like. Then, it is heated and dried to volatilize the volatile organic solvent to form a film, and then the plasticizer can be extracted with an extraction solvent. Here, examples of the plasticizer include dibutyl phthalate (DBP), examples of the volatile organic solvent include acetone, and examples of the extraction solvent include the polymer used and phosphorus-containing nonflammability. A solvent having a low solubility of the substance and an excellent solubility of the plasticizer used is appropriately selected and used. The film-like separator thus obtained has micropores formed by extraction of a plasticizer, and is excellent in non-aqueous electrolyte retention described later.

  The non-aqueous electrolyte battery of the present invention includes the above-described battery separator, positive electrode, negative electrode, and non-aqueous electrolyte solution, and is otherwise used in the technical field of non-aqueous electrolyte batteries as required. The member is provided.

The positive electrode active material of the nonaqueous electrolyte battery of the present invention is partially different between a primary battery and a secondary battery. For example, in the case of a primary battery, as the positive electrode active material, fluorinated graphite [(CF _x ) _n ], MnO ₂ (electrochemical synthesis or chemical synthesis), V ₂ O ₅ , MoO ₃ , Ag ₂ CrO ₄ , CuO, CuS, FeS ₂ , SO ₂ , SOCl ₂ , TiS ₂ etc. are preferred Among these, MnO ₂ and fluorinated graphite are preferable from the viewpoints of high capacity and high safety, and high discharge potential and excellent wettability of the electrolytic solution. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

On the other hand, in the case of a secondary battery, as the positive electrode active material, metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , MnO ₃ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO ₂ and LiFePO _{2 are used.} Preferable examples include lithium-containing composite oxides such as ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, and Ni. In this case, the composite oxide includes: LiFe _x Co _y Ni (wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1) (1-xy) O 2, or represented by LiMn _x Fe _y O _2-xy like. Among these, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are particularly preferable in terms of high capacity, high safety, and excellent electrolyte wettability. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The negative electrode active material of the non-aqueous electrolyte battery of the present invention is partially different between a primary battery and a secondary battery. For example, in the case of a primary battery, examples of the negative electrode active material include lithium metal itself and lithium alloys. . Examples of the metal that forms an alloy with lithium include Sn, Si, Pb, Al, Au, Pt, In, Zn, Cd, Ag, and Mg. Among these, Al, Zn, and Mg are preferable from the viewpoints of rich reserves and toxicity. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  On the other hand, in the case of a secondary battery, preferred examples of the negative electrode active material include lithium metal itself, an alloy of lithium and Al, In, Sn, Si, Pb, Zn, or the like, or a carbon material such as graphite doped with lithium. Among these, carbon materials such as graphite are preferable, and graphite is particularly preferable in terms of higher safety and excellent wettability of the electrolytic solution. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black, and the binder includes polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.

  Moreover, there is no restriction | limiting in particular as a shape of the said positive electrode and a negative electrode, It can select suitably from well-known shapes as an electrode. For example, a sheet shape, a columnar shape, a plate shape, a spiral shape, and the like can be given.

The non-aqueous electrolyte used for the non-aqueous electrolyte battery of the present invention contains a non-aqueous solvent and a supporting salt as main components. Here, examples of the non-aqueous solvent include aprotic organic solvents, and liquids at 25 ° C. (room temperature) can be selected and used from the phosphonate compounds and phosphinate compounds described above. A mixed solution of a protic organic solvent and at least one of a phosphonate compound and a phosphinate compound can also be used. Here, specific examples of the aprotic organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and vinylene. Carbonates such as carbonate (VC), ethers such as 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), diethyl ether (DEE), phenylmethyl ether, γ-butyrolactone (GBL), γ-valerolactone Carboxylic acid esters such as methyl formate (MF), nitriles such as acetonitrile, amides such as dimethylformamide, and sulfones such as dimethyl sulfoxide. These aprotic organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

Moreover, as said support salt, the support salt used as the ion source of lithium ion is preferable. The supporting salt is not particularly limited, and for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and Li ( Preferable examples include lithium salts such as C ₂ F ₅ SO ₂ ) ₂ N. Among these, LiPF ₆ is more preferable in terms of excellent nonflammability. These supporting salts may be used alone or in combination of two or more. The concentration of the supporting salt in the non-aqueous electrolyte is preferably 0.2 to 1.5 mol / L (M), more preferably 0.5 to 1 mol / L. If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .

  In the nonaqueous electrolyte battery of the present invention, the amount of the nonaqueous electrolyte used for the separator is adjusted, or the type of the nonaqueous solvent used for the nonaqueous electrolyte is selected, and the nonaqueous electrolyte is added to the separator. By holding and forming a gel electrolyte from the separator and the non-aqueous electrolyte, liquid leakage from the battery can be prevented. Further, in this case, the battery can be made into a film, the incorporation into the electronic device can be greatly improved, and the space in the electronic device can be used effectively.

  The form of the non-aqueous electrolyte battery of the present invention described above is not particularly limited, and various known forms such as a coin-type, button-type, paper-type, square-type or spiral-type cylindrical battery are preferably cited. It is done. In the case of the button type, a non-aqueous electrolyte battery can be produced by preparing a sheet-like positive electrode and negative electrode, sandwiching a separator between the positive electrode and negative electrode, and impregnating with a non-aqueous electrolyte. In the case of a spiral structure, for example, a non-aqueous electrolyte battery can be manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and stacking and winding up the sheet-like negative electrode on the current collector. .

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

( Reference Example 1 )
<Preparation of battery separator>
Polyvinylidene fluoride (PVDF) 45 g, phosphazene compound A [formula (II) below :
(NPR ² ₂ ) _n ... (II)
In the above, a cyclic phosphazene compound in which n is 3, and all six R ² are Cl] 5 g, 50 mL of dibutyl phthalate (DBP) and 50 mL of N-methylpyrrolidone are mixed to obtain a uniform solution. After casting the mixed solution on a glass plate, N-methylpyrrolidone is volatilized by heating to form a film, and then dibutyl phthalate is extracted with ethyl methyl carbonate (extraction solvent), dried, and separated into a battery separator. Manufactured. Moreover, the safety | security and critical oxygen index of the obtained separator were evaluated by the following method. The results are shown in Table 1.

(1) Safety The safety of the separator was evaluated from the combustion behavior of flames ignited in an atmospheric environment by the method of arranging UL (underlighting laboratory) standard UL94HB method. At that time, ignitability, combustibility, formation of carbides, and secondary ignition phenomena were also observed. Specifically, based on the UL test standard, a 127 mm × 12.7 mm test piece was produced from the separator. Here, when the test flame does not ignite the test piece (combustion length: 0 mm), it is “non-flammable”, and when the ignited flame does not reach the 25 mm line and the fallen object is not ignited, “flame retardant” The case where the ignited flame was extinguished on the 25 to 100 mm line and the fallen object was not ignited was evaluated as “self-extinguishing”, and the case where the ignited flame exceeded the 100 mm line was evaluated as “combustible”.

(2) Critical oxygen index The critical oxygen index of the separator was measured according to JIS K7201. A larger critical oxygen index indicates that the separator is less likely to burn. Specifically, a 127 mm × 12.7 mm test piece was prepared from the separator, the test piece was perpendicular to the test piece support, and a combustion cylinder (inner diameter 75 mm, height 450 mm, diameter 4 mm of glass particles from the bottom 100) It is attached so that it is located at a distance of 100 mm or more from the upper end of a metal net that is evenly filled with a thickness of ± 5 mm, and then oxygen (JIS K 1101 or this) is attached to the combustion cylinder. Equivalent or better) and nitrogen (JIS K 1107 grade 2 or better), and the test piece is ignited under a predetermined oxygen concentration (the heat source is JIS K 2240 Type 1 No. 1) and burned I checked the condition. However, the total flow rate in the combustion cylinder is 11.4 L / min. This test was performed three times, and the average value is shown in Table 1. The oxygen index refers to the value of the minimum oxygen concentration expressed by the volume percent necessary for the material to continue burning. In this application, the test piece burns continuously for 3 minutes or longer, From the minimum oxygen flow rate required for burning 50 mm or more and the nitrogen flow rate at that time, the following formula:
Critical oxygen index = (oxygen flow rate) / [(oxygen flow rate) + (nitrogen flow rate)] × 100 (volume%)
The limiting oxygen index was calculated according to

(Examples 5-6 , Reference Examples 2-4, and Comparative Examples 1-2)
Phosphazene A, phosphazene B [cyclic phosphazene compound in which n is 3 and all six R ² are phenoxy groups (—OPh) in formula (II)], trifluoroethyl difluorophosphate, bistrifluoroethyl chlorophosphate Was used in the same amount as shown in Table 1, and a battery separator was produced in the same manner as in Reference Example 1 . Moreover, the safety | security and critical oxygen index of the obtained separator were evaluated by the following method. The results are shown in Table 1.

  As apparent from Table 1, the separator of the comparative example was flammable and had a low critical oxygen index, whereas the separator of the example was nonflammable and had a very high critical oxygen index.

Claims (5)

Containing at least one polymer selected from the group consisting of polyvinylidene fluoride and a vinylidene fluoride-containing copolymer, and a phosphorus-containing incombustibility imparting substance ,
The battery separator, wherein the phosphorus-containing incombustibility imparting substance is at least one selected from the group consisting of a phosphonate compound and a phosphinate compound . The battery separator according to claim 1 , wherein the phosphorus-containing nonflammability imparting substance is solid at 25 ° C.   The battery separator according to claim 1, wherein the polymer is polyvinylidene fluoride. A nonaqueous electrolyte battery comprising the battery separator according to claim 1 , a positive electrode, a negative electrode, and a nonaqueous electrolytic solution. The nonaqueous electrolyte battery according to claim 4 , wherein the nonaqueous electrolyte is retained in the battery separator to form a gel electrolyte.