JP6747191B2 - Storage element - Google Patents

Description

The present invention relates to a power storage element.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. because of their high energy density. The non-aqueous electrolyte secondary battery generally comprises an electrode body having a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between both electrodes. It is configured to be charged and discharged by performing. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors have been widely used as power storage elements other than secondary batteries.

Various additives are added to the non-aqueous electrolyte used for such an electricity storage device for the purpose of improving performance. For example, a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing a cyclic carbonate, γ-butyrolactone, fluorotoluene, etc. is proposed for the purpose of satisfying both high-temperature storage characteristics and safety during overcharge. (See Patent Document 1).

In Patent Document 1, it is said that a shutdown function at the time of overcharge is exhibited by the following action. During overcharging, heat is generated due to the oxidation reaction of the halogenated toluene, and this heat causes the resin forming the separator to plastically deform. It is said that the pores of the pallet are blocked by this, and the flow of lithium ions is blocked. In the above-mentioned Patent Document 1, in order to sufficiently function such an action, the air permeability of the separator is preferably 200 to 600 seconds/100 cm ^3, and the shutdown temperature is preferably in the range of 100 to 160°C. Is described.

International Publication No. 2004/021501

However, the present inventors have found that in a storage element using halogenated toluene, the shutdown function during overcharge cannot be sufficiently controlled by adjusting the air permeability of the separator.

The present invention has been made based on the above circumstances, and an object thereof is to provide a power storage element having a sufficient shutdown function during overcharge.

One embodiment of the present invention made to solve the above problems is a power storage element including a porous separator having a pore diameter D30 of 0.28 μm or less and a nonaqueous electrolyte containing a halogenated toluene.

ADVANTAGE OF THE INVENTION According to this invention, the electrical storage element which has a sufficient shutdown function at the time of overcharge can be provided.

FIG. 1 is an external perspective view showing a secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of secondary batteries according to an embodiment of the present invention.

One embodiment of the present invention is a power storage element including a porous separator having a pore diameter D30 of 0.28 μm or less and a nonaqueous electrolyte containing halogenated toluene.

The power storage element has a sufficient shutdown function when overcharged. The reason why such an effect occurs is presumed to be as follows. When overcharged, halogenated toluene is oxidatively decomposed to generate decomposed products. This decomposed product closes the pores of the separator and blocks the flow of ions in the electrolyte. When the pore diameter D30 of the separator exceeds 0.28 μm, the pores are not sufficiently blocked by the decomposed product, and a sufficient shutdown function is not exhibited. Note that there are separators in which the size of the pores (pore diameter D30) is greatly different even with the same degree of air permeability, and there is no correlation between the air permeability and the size/distribution of the pores.

Here, the pore diameter D30 of the separator means the pore diameter corresponding to a cumulative 30% from the larger diameter in the total pore volume (total pore volume) of the separator. Clogging of the separator occurs from small pores. For example, in the case of a separator having D30=0.28 μm, when 0.28 μm pores are clogged, it is considered that about 70% of the total pore volume is clogged. A good shutdown function is obtained by closing 70% of the total pore volume. That is, determining the upper limit value of the pore diameter D30 that includes most of the pores of the total pore volume of the separator is a suitable index for expressing a good shutdown function.

As described above, the pore diameter D30 of the pores of the separator means the pore diameter corresponding to 30% cumulative from the large diameter in the pore diameter distribution of the total pore volume (cumulative pore volume) of the separator. Specifically, it can be a measured value by the following method. An AutoPore 9400 (manufactured by Micromeritics) is used as a device for measuring the pore distribution, and the pore volume distribution is measured by the mercury injection method. The contact angle of mercury is set to 130° and the surface tension is set to 484 dynes/cm. The pore diameter range to be measured is 10 to 0.0055 μm, and the cumulative pore volume in this range is the cumulative pore volume.

It is preferable that the electricity storage element further includes a positive electrode facing the separator, and the separator has an inorganic layer formed on a surface facing the positive electrode. Further, the porosity of the inorganic layer is preferably higher than that of the resin layer. The decomposition reaction of the halogenated toluene during the overcharge occurs near the positive electrode. On the other hand, since the separator has the inorganic layer on the positive electrode side, the amount of the non-aqueous electrolyte existing near the positive electrode, that is, the halogenated toluene can be increased. As a result, the amount of oxidative decomposition of halogenated toluene during overcharge increases, and the pores of the separator are more effectively blocked.

The content of halogenated toluene in the non-aqueous electrolyte is preferably 2% by mass or more. As a result, a particularly sufficient amount of decomposition products are generated during overcharge, and the pores of the separator are more effectively blocked.

The halogenated toluene is preferably o-fluorotoluene (orthofluorotoluene). o-Fluorotoluene has a higher oxidation voltage than other additives. Therefore, it is possible to suppress the generation of decomposed products during normal charge and discharge and maintain good characteristics.

<Storage element>
An electricity storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery will be described as an example of a power storage element. The positive electrode, the separator, and the negative electrode usually form an electrode body that is superposed by stacking or winding. The electrode body is housed in a case, and the nonaqueous electrolyte is filled in the case. In the secondary battery, the non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, the non-aqueous electrolyte is impregnated in a separator arranged between the positive electrode and the negative electrode. As the case, a known aluminum case, resin case, or the like that is usually used as a case of a secondary battery can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer disposed on the positive electrode base material directly or via an intermediate layer. The positive electrode is a sheet (film) having the above laminated structure.

The positive electrode base material has conductivity. As the material of the base material, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance between potential resistance, high conductivity and cost. In addition, examples of the form of forming the positive electrode substrate include a foil and a vapor deposition film, and the foil is preferable from the viewpoint of cost. That is, the positive electrode base material is preferably an aluminum foil. Examples of aluminum or aluminum alloy include A1085P, A3003P and the like specified in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer. The structure of the intermediate layer is not particularly limited, and can be formed of, for example, a composition containing a resin binder and conductive particles. In addition, having "conductivity" means that the volume resistivity measured according to JIS-H-0505 (1975) is 10< ⁷ > ohm*cm or less, and it says "non-conductivity." Means that the volume resistivity is more than 10 ⁷ Ω·cm.

The positive electrode active material layer is formed of a so-called positive electrode mixture containing a positive electrode active material. In addition, the positive electrode mixture material forming the positive electrode active material layer contains an optional component such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary.

Examples of the positive electrode active material include a composite oxide represented by Li _x MO _y (M represents at least one kind of transition metal) (Li _x CoO ₂ , Li _x NiO having a layered α-NaFeO ₂ type crystal structure). _{2, Li x MnO 3, Li} x Ni α Co (1-α) O 2, Li x Ni α Mn β Co (1-α-β) O 2 , etc., _Li x _Mn 2 _{O 4} having a spinel type crystal structure , Li _x Ni _α Mn _(2-α) O ₄ etc.), Li _w Me _x (XO _y ) _z (Me represents at least one transition metal, and X represents P, Si, B, V, etc.) in represented by polyanionic compounds _{(LiFePO 4, LiMnPO 4, LiNiPO} 4, LiCoPO 4, Li 3 V 2 (PO 4) 3, Li 2 MnSiO 4, Li 2 CoPO 4 F , etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species. In the positive electrode active material layer, one kind of these compounds may be used alone, or two or more kinds thereof may be mixed and used.

The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the battery performance. Examples of such a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black, and Ketjen black, metal, and conductive ceramics. Examples of the shape of the conductive agent include powder and fibrous shapes.

Examples of the binder (binder) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, polyimide; ethylene-propylene-diene rubber (EPDM), Examples include elastomers such as sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; polysaccharide polymers and the like.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group by methylation or the like in advance.

The filler is not particularly limited as long as it does not adversely affect the battery performance. Examples of the main component of the filler include polyolefin such as polypropylene and polyethylene, silica, alumina, zeolite, glass and carbon.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer disposed on the negative electrode base material directly or via an intermediate layer. The negative electrode is a sheet (film) having the above laminated structure. The intermediate layer may have the same structure as the intermediate layer of the positive electrode.

The negative electrode base material may have the same configuration as the positive electrode base material, but as the material, a metal such as copper, nickel, stainless steel, or nickel plated steel or an alloy thereof is used, and copper or a copper alloy is used. preferable. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The negative electrode active material layer is formed of a so-called negative electrode mixture containing the negative electrode active material. Further, the negative electrode mixture material forming the negative electrode active material layer contains an optional component such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary. As the optional components such as the conductive agent, the binder, the thickener, and the filler, those similar to the positive electrode active material layer can be used.

As the negative electrode active material, a material capable of inserting and extracting lithium ions is usually used. Specific negative electrode active materials include, for example, metals such as Si and Sn or semimetals; metal oxides or semimetal oxides such as Si oxides and Sn oxides; polyphosphoric acid compounds; graphite (graphite) and amorphous. Examples thereof include carbon materials such as carbon (graphitizable carbon or non-graphitizable carbon).

Further, the negative electrode mixture (negative electrode active material layer) is a typical non-metal element such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge. And the like, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W may be contained.

(Separator)
The separator is a porous sheet (film) having a pore diameter D30 of 0.28 μm or less.

The upper limit of the pore diameter D30 of the separator is 0.28 μm, more preferably 0.18 μm. By setting the pore diameter D30 of the separator to the upper limit or less, the shutdown function at the time of overcharge can be enhanced. On the other hand, as the lower limit, for example, 0.03 μm is preferable, and 0.05 μm is more preferable. By setting the pore diameter D30 of the separator to be equal to or more than the above lower limit, it is possible to secure sufficient ion mobility and the like under normal conditions.

The upper limit of the pore diameter D10 of the separator is preferably 0.75 μm, more preferably 0.37 μm, and further preferably 0.3 μm. When the pore diameter D10 of the separator is less than or equal to the above upper limit, the diameter of most of the pores is less than or equal to the above upper limit. Therefore, by setting the pore diameter D10 to be equal to or less than the above upper limit, it is possible to enhance the certainty that the decomposed product blocks most of the pores when overcharge occurs, and further enhance the shutdown function. The lower limit of the pore diameter D10 is, for example, 0.1 μm, preferably 0.2 μm. The pore diameter D10 of the separator means a pore diameter corresponding to a cumulative 10% from a large diameter in the volume-based pore diameter distribution measured according to the above-described measurement method of the pore diameter D30.

The upper limit of the pore diameter D50 (median diameter) of the separator is preferably 0.15 μm, more preferably 0.11 μm. By setting the pore diameter D50 of the separator to be equal to or less than the above upper limit, the shutdown function can be further enhanced. The lower limit of the pore diameter D50 is, for example, 0.01 μm, preferably 0.03 μm. The pore diameter D50 of the separator means the pore diameter corresponding to a cumulative 50% from the large diameter in the volume-based pore diameter distribution measured according to the above-described measuring method of the pore diameter D30.

The average thickness of the separator is not particularly limited, but the lower limit is preferably 5 μm, more preferably 10 μm. On the other hand, the upper limit of this average thickness is preferably 40 μm, more preferably 30 μm. By setting the average thickness of the separator within the above range, the function of the separator can be sufficiently ensured, and the shutdown function at the time of overcharge can be more sufficiently exhibited. The average thickness means an average value of thicknesses measured at arbitrary ten points (the same applies hereinafter).

The separator may be composed of, for example, a resin layer alone, or may have a layered structure including a resin layer and an inorganic layer. Both the resin layer and the inorganic layer are porous.

As the material of the resin layer, for example, woven cloth, non-woven cloth, porous resin film or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of liquid retention of the nonaqueous electrolyte. As the main component of the separator, polyolefin such as polyethylene or polypropylene is preferable from the viewpoint of strength, and polyimide or aramid is preferable from the viewpoint of resistance to oxidative decomposition. Further, these resins may be combined.

The resin layer is preferably made of a resin having a melting point or softening point of 100° C. or higher, more preferably 130° C. or higher. By using a separator having such a resin layer, good output characteristics can be exhibited in a high temperature environment.

When the separator has an inorganic layer together with the resin layer, the inorganic layer is usually arranged on the side facing the positive electrode. This inorganic layer can be formed, for example, by applying an inorganic layer forming material on the surface of the resin layer and drying.

The inorganic layer usually contains inorganic particles and a binder that binds the inorganic particles. As the inorganic particles, silica, alumina, titania, zirconia, magnesia, ceria, yttria, zinc oxide, inorganic oxides such as iron oxide, silicon nitride, titanium nitride, inorganic nitride such as boron nitride, other, silicon carbide, carbonic acid. Calcium, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, aluminosilicate, calcium silicate, silicic acid Examples thereof include magnesium, diatomaceous earth, silica sand, glass and the like.

As the binder, one that can fix inorganic particles, does not dissolve in a non-aqueous solvent, and is electrochemically stable in the range of use is usually used. Examples of the binder include those described above as the binder used in the positive electrode active material layer.

The average thickness of the inorganic layer is not particularly limited, but the lower limit is preferably 1 μm, more preferably 3 μm. The upper limit is preferably 10 μm, more preferably 6 μm. By setting the average thickness of the inorganic layer to the above lower limit or more, it is possible to impregnate the inorganic layer with a sufficient amount of non-aqueous electrolyte (halogenated toluene) and increase the decomposition amount of halogenated toluene during overcharge. be able to. In addition, by setting the average thickness of the inorganic layer to be equal to or less than the above upper limit, it is possible to reduce the thickness of the electrode body as a whole and to increase the energy density of the electricity storage element.

The separator can be manufactured by a known method, and the pore size can be adjusted by a known method. Moreover, as the separator, a commercially available one can be used.

(Non-aqueous electrolyte)
The non-aqueous electrolyte is one in which an electrolyte salt is dissolved in a non-aqueous solvent. The non-aqueous electrolyte contains halogenated toluene.

(Halogenated toluene)
The halogenated toluene means a compound in which some or all of the hydrogen atoms contained in toluene are replaced with halogen atoms. Halogenated toluene may be used alone or in combination of two or more.

Examples of the halogen atom include a fluorine atom, a chlorine atom and a bromine atom, and a fluorine atom is preferable. When the halogen atom is a fluorine atom, a decomposition reaction at the time of overcharge and adhesion of the decomposed product to the separator occur more suitably, and the shutdown function can be enhanced.

The number of halogen atoms in the halogenated toluene is not particularly limited and is, for example, 1 or more and 4 or less, preferably 1 and 2, and more preferably 1. When one halogenated toluene has plural halogen atoms, plural kinds of halogen atoms may be the same or different.

The halogenated toluene is preferably halogenated toluene in which a hydrogen atom on a benzene ring (aromatic ring) is replaced with a halogen atom. In the case of such a halogenated toluene, the bonding position of the halogen atom is preferably the ortho position and the para position with respect to the methyl group, and more preferably the ortho position.

Specific examples of the halogenated toluene include fluorotoluene (o-fluorotoluene, m-fluorotoluene, p-fluorotoluene), chlorotoluene, bromotoluene, difluorotoluene, dichlorotoluene, dibromotoluene, trifluorotoluene, trichlorotoluene. , Tribromotoluene, chlorofluorotoluene, bromofluorotoluene and the like.

Among these, fluorotoluene is preferable, o-fluorotoluene (2-fluorotoluene) and p-fluorotoluene (4-fluorotoluene) are preferable, and o-fluorotoluene is more preferable. Such halogenated toluene has a higher oxidation voltage than other additives. Therefore, it is possible to suppress the generation of decomposed products during normal charge and discharge and maintain good characteristics.

The mass (content) of the halogenated toluene with respect to the total mass of the non-aqueous electrolyte is not particularly limited, and the lower limit is preferably 2 mass% and more preferably 3 mass %. By setting the content of the halogenated toluene to the above lower limit or more, a particularly sufficient amount of decomposition products are generated during overcharge, and the pores of the separator are more effectively blocked.

The upper limit of the mass (content) of halogenated toluene with respect to the total mass of the non-aqueous electrolyte may be, for example, 10 mass %, but is preferably 7 mass %. By setting the content of the halogenated toluene to the above upper limit or less, the function of the non-aqueous electrolyte during normal use can be sufficiently exhibited.

(Non-aqueous solvent)
As the non-aqueous solvent, a known non-aqueous solvent that is usually used as a non-aqueous solvent for a general non-aqueous electrolyte for a storage element can be used. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, ester, ether, amide, sulfone, lactone and nitrile. Among these, it is preferable to use at least cyclic carbonate or chain carbonate, and it is more preferable to use cyclic carbonate and chain carbonate in combination. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate and the chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but is, for example, 5:95 or more and 50:50 or less. Is preferred.

Further, the upper limit of the content of the non-aqueous solvent other than the cyclic carbonate and the chain carbonate in the non-aqueous solvent is preferably 30% by volume, sometimes 10% by volume, and preferably 1% by volume. There is also. By setting the content of the non-aqueous solvent other than the cyclic carbonate and the chain carbonate to the above upper limit or less, it is difficult to suppress the oxidative decomposition of halogenated toluene during overcharge and the adhesion of the decomposed product to the separator, and the shutdown function is more effective. It is expressed with high certainty.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene. Carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like can be mentioned, and among these, EC is preferable.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diphenyl carbonate, and the like. Among these, EMC is preferable.

(Electrolyte salt)
As the above-mentioned electrolyte salt, a known electrolyte salt that is usually used as an electrolyte salt of a general non-aqueous electrolyte for a storage element can be used. Examples of the electrolyte salt include a lithium salt, a sodium salt, a potassium salt, a magnesium salt, and an onium salt, and a lithium salt is preferable.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , and LiN(SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO. _{2 C 2 F 5) 2,} LiN (SO 2 CF 3) (SO 2 C 4 F 9), LiC (SO 2 CF 3) 3, LiC (SO 2 C 2 F 5) 3 fluorinated hydrocarbon group, Examples thereof include a lithium salt having Among these, inorganic lithium salts are preferable, and LiPF ₆ is more preferable.

As a minimum of content of the above-mentioned electrolyte salt in the above-mentioned nonaqueous electrolyte, 0.1M is preferred, 0.3M is more preferred, 0.5M is still more preferred, and 0.7M is especially preferred. On the other hand, the upper limit is not particularly limited, but is preferably 2.5M, more preferably 2M, even more preferably 1.5M.

The non-aqueous electrolyte may contain components other than the halogenated toluene, the non-aqueous solvent, and the electrolyte salt as long as the effects of the present invention are not impaired. Examples of the other components include various additives contained in general nonaqueous electrolytes for electric storage devices. However, the content of these other components may be preferably 5% by mass or less, and more preferably 1% by mass or less.

The non-aqueous electrolyte can be obtained by adding the electrolyte salt and halogenated toluene to the non-aqueous solvent and dissolving them.

<Method of manufacturing storage element>
The power storage element can be obtained by a method similar to a known method for manufacturing a power storage element. For example, the method for manufacturing the electricity storage device includes a step of housing the positive electrode and the negative electrode (electrode body) in a case, and a step of injecting the nonaqueous electrolyte into the case.

The injection can be performed by a known method. After the injection, the storage port can be obtained by sealing the injection port. The details of each element constituting the electricity storage device (secondary battery) obtained by the manufacturing method are as described above.

<Other embodiments>
The present invention is not limited to the above embodiment, and can be carried out in various modified and improved modes in addition to the above modes. For example, the intermediate layer may not be provided in the positive electrode or the negative electrode. Further, in the above-described embodiment, the description has been centered on the form in which the power storage element is a secondary battery, but other power storage elements may be used. Other storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic view of a rectangular secondary battery 1 which is an embodiment of the electricity storage device according to the present invention. It should be noted that the figure is a perspective view of the inside of the container. In the secondary battery 1 shown in FIG. 1, the electrode body 2 is housed in the battery container 3. The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material with a separator interposed therebetween. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'.

The configuration of the electricity storage device according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above power storage elements. An embodiment of the power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of secondary batteries 1. The power storage device 30 can be installed as a power source for vehicles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV).

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

[Example 1]
(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved at a concentration of 1.0 M in a solvent in which EC and EMC were mixed at a volume ratio of 30:70. O-Fluorotoluene (OFT) was further added to this as an additive so that it might be 5 mass %, and the non-aqueous electrolyte was obtained.

(Production of power storage element)
By applying a slurry obtained by mixing LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as a positive electrode active material, acetylene black as a conductive aid, and polyvinylidene fluoride as a binder to an aluminum foil, and drying. A positive electrode plate was produced. The mass ratio of the positive electrode active material, the conductive additive, and the binder was 94:3:3, respectively. A negative electrode plate was prepared by applying a slurry prepared by mixing graphite as a negative electrode active material, styrene-butadiene rubber as a binder, and CMC as a thickener to a copper foil and drying the slurry. The mass ratio of graphite and the binder was set to 97:3, respectively. Then, a separator (total thickness 21 μm) was prepared in which a porous inorganic layer having a thickness of 5 μm was laminated on one surface of a resin layer (softening point 135° C.) made of a polyethylene microporous film. The pore diameter D10 of the separator was 0.25 μm, the pore diameter D30 was 0.13 μm, and the pore diameter D50 was 0.07 μm. These measurements were performed by the method described above. Further, the air permeability of the separator was measured according to JIS-P8117:2009.

The positive electrode plate to which the lead was attached, the separator and the negative electrode plate to which the lead was attached were laminated in this order to produce an electrode assembly. The inorganic layer of the separator was laminated so as to face the positive electrode plate. This electrode body was housed in a laminate outer package, and at this time, the positive electrode lead and the negative electrode lead were allowed to come out from the outer package. The non-aqueous electrolyte was injected into the inside of the outer package and then sealed to obtain the electricity storage device (lithium ion secondary battery) of Example 1.

[Examples 2 to 4, Comparative Examples 1 to 4]
Electric storage of Examples 2 to 4 and Comparative Examples 1 to 4 in the same manner as in Example 1 except that the additive described in Table 1 and the separator having the thickness and the pore size described in Table 1 were used. The device was obtained. In addition, "-" in the column of the inorganic layer in the table indicates that a single resin layer separator having no inorganic layer was used. In addition, "-" in the column of additive in the table indicates that the corresponding additive was not added. Further, in the table, OFT represents o-fluorotoluene, FB represents fluorobenzene, and CHB represents cyclohexylbenzene.

[Evaluation]
Each of the obtained power storage devices was charged to 100% SOC (state of charge) and then charged to a constant current for 8 hours at a charging current of 0.1 CA in an environment of 25° C. to bring the battery into an overcharged state. After that, the battery was discharged, the power storage element was disassembled, and the separator was taken out. The air permeability of the taken out overcharged separator was measured in the same manner as above. Table 1 shows the air permeability of the initial separator and the increase rate (%) of the air permeability of the separator after overcharge with respect to the air permeability of the initial separator. Table 1 also shows the rate of increase in air permeability (%/μm) per unit thickness of the separator.

As shown in Table 1 above, in the electricity storage devices of Examples 1 to 4, the air permeability of the separator after overcharging greatly increased. That is, according to the electricity storage devices of Examples 1 to 4, it is understood that the pores are closed during overcharge, and an excellent shutdown function is generated. On the other hand, in Comparative Example 1 in which the pore diameter D30 of the separator is 0.29 μm, the air permeability after overcharging does not significantly increase. On the other hand, in Example 3 in which the pore diameter D30 is 0.28 μm, the air permeability greatly increases after overcharge. In particular, these are remarkable when compared with the rate of increase in air permeability per unit thickness, and it is shown that a remarkable effect is produced by setting the pore diameter D30 to 0.28 μm or less.

Further, in Comparative Example 2 in which the additive is not added and Comparative Examples 3 and 4 in which the additive other than the halogenated toluene is added, the air permeability of the separator after overcharge is not significantly increased. That is, an excellent shutdown function at the time of overcharge is exhibited only when a porous separator having a pore diameter D30 of 0.28 μm or less and a non-aqueous electrolyte containing halogenated toluene are used in combination. It can be said that it is a thing.

Further, comparing Example 2 and Example 3 in which the thickness of the entire separator and the thickness of the inorganic layer are equal, Example 2 having a low air permeability has a higher increase rate of the air permeability after overcharge. It's getting bigger. That is, it can be seen that the shutdown function does not depend on the size of the air permeability, but depends on the pore diameter D30 of the separator. From this, it is considered that there are separators that exhibit the shutdown function and separators that do not exhibit the shutdown function even if the air permeability is about the same.

INDUSTRIAL APPLICABILITY The present invention can be applied to electronic equipment such as personal computers and communication terminals, non-aqueous electrolyte storage elements including non-aqueous electric field secondary batteries used as power sources for automobiles, and the like.

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Electrode body 3 Battery container 4 Positive electrode terminal 4'Positive electrode lead 5 Negative electrode terminal 5'Negative electrode lead 20 Electric storage unit 30 Electric storage device

Claims (3)

A porous separator having a pore diameter D30 of 0.28 μm or less and a pore diameter D10 of 0.75 μm or less ;
And a non-aqueous electrolyte containing halogenated toluene ,
Storage element content of the halogenated toluene in the nonaqueous electrolyte Ru der least 2 wt%. Further comprising a positive electrode facing the separator,
The electricity storage device according to claim 1, wherein the separator has an inorganic layer formed on a surface facing the positive electrode. The electricity storage device according to claim 1 or 2 , wherein the halogenated toluene is o-fluorotoluene.

Images