JP7159864B2 - NONAQUEOUS ELECTROLYTE STORAGE ELEMENT AND USAGE THEREOF - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte storage element and a method of using the same.

Non-aqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, are widely used in electronic devices such as personal computers, communication terminals, and automobiles because of their high energy density. The non-aqueous electrolyte secondary battery generally includes an electrode body having a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes, and exchanges ions between the electrodes. It is configured to charge and discharge by performing. Capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as power storage elements other than secondary batteries.

A porous resin film, a woven fabric, a non-woven fabric, and the like are widely used as a separator for such an electric storage device. For example, a secondary battery using a separator containing a polyolefin resin film having a thickness of 12 to 16 μm has been developed (see Patent Document 1).

JP 2009-302051 A

On the other hand, one of the characteristics required for electric storage elements is life characteristics. For example, it is required that the voltage drop after the float charge is performed and left for a while is small. However, according to the findings of the inventors, if the separator whose main component is polyethylene is thinned, the voltage drop may become very large, in other words, the life characteristics may be insufficient.

The present invention has been made based on the circumstances as described above, and its object is to improve life characteristics while using a separator whose main component is polyethylene, compared to a separator using the same separator. An object of the present invention is to provide a non-aqueous electrolyte storage element and a method of using such a non-aqueous electrolyte storage element.

One aspect of the present invention, which has been made to solve the above problems, includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the main component of the separator being polyethylene, and the The separator has a density of 0.5 g/cm ³ or more, and the nonaqueous electrolyte contains halogenated toluene.

Another aspect of the present invention, which has been made to solve the above problems, is a non-aqueous electrolyte that charges the non-aqueous electrolyte storage element at a positive electrode potential of 4.2 V (vs. Li/Li ⁺ ) or more. This is a method of using the storage device.

INDUSTRIAL APPLICABILITY According to the present invention, a non-aqueous electrolyte storage element using a separator whose main component is polyethylene has improved life characteristics compared to a device using the same separator, and such a non-aqueous electrolyte storage element. Can provide usage instructions.

FIG. 1 is an external perspective view showing a secondary battery according to one 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 one embodiment of the present invention.

One aspect 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, the main component of the separator is polyethylene, and the density of the separator is 0.5 g/cm ³ or more, and the nonaqueous electrolyte contains halogenated toluene. In addition, a "main component" means a component with the largest content on a mass basis.

The energy storage device uses a separator whose main component is polyethylene, but has a better lifespan than a device using the same separator. Although the reason for this is not clear, it is presumed to be due to the following effects. A separator whose main component is polyethylene is oxidized by the action of the positive electrode. The following reactions occur in this oxidation.
-CH ₂ -CH ₂ -→-CH=CH-+H ₂
Thus, the oxidation reaction produces unsaturated double bonds in polyethylene. Since unsaturated double bonds are generated at a plurality of sites to form conjugated bonds, the oxidized portion has high conductivity. Moreover, since this oxidation is caused by the action of the positive electrode, the oxidized portion grows from the surface of the separator on the positive electrode side toward the negative electrode side, that is, in the thickness direction. When the oxidized portion reaches the surface of the separator on the negative electrode side, the positive electrode and the negative electrode are electrically connected by the oxidized portion, resulting in a voltage drop between the positive electrode and the negative electrode. On the other hand, when halogenated toluene is contained in the non-aqueous electrolyte as in the electric storage device, the oxidative decomposition product of the halogenated toluene coats the surface of the positive electrode. It is presumed that this suppresses the oxidation of the separator and improves the life characteristics. Halogenated toluene is also preferable because it is an additive that hardly causes deterioration in input/output characteristics. Generally, when the separator has a relatively high density of 0.5 g/cm ³ or more, highly conductive oxidized portions are densely formed, which tends to cause a voltage drop. However, the electric storage device has good life characteristics in spite of using such a separator. In addition, since the separator has a relatively high density of 0.5 g/cm ³ or more, the amount of resin that dissolves when heat is generated in an abnormal state increases, and the resistance value can be increased. Therefore, according to the power storage device, shutdown in the event of an abnormality is likely to occur, and safety is also excellent.

The average thickness of the separator may be 20 μm or less. In the case of a thin separator, the oxidized portion tends to reach the negative electrode side, so the life of the separator is generally shortened. On the other hand, according to the electric storage element, even a separator having an average thickness of 20 μm or less can exhibit sufficient life characteristics. In addition, by using a separator having an average thickness of 20 μm or less, it is possible to reduce the thickness and weight of the electric storage element. In addition, "average thickness" means the average value of the thickness of ten arbitrarily selected places.

The separator may have a density of 0.58 g/cm ³ or more. As described above, when the density of the separator is high, voltage drop tends to occur. However, even when such a separator is used in the electric storage element, it has good life characteristics equivalent to those with a density of less than 0.58 g/cm ³ . Further, by using a separator having a density of 0.58 g/cm ³ or more, the shutdown function can be further improved, and safety can be improved. The "density" of the separator is the mass per unit volume calculated from the average thickness and the mass per unit area, and refers to the density measured in accordance with JIS-P-8118 (1998). .

The content of halogenated toluene in the non-aqueous electrolyte is preferably 0.1% by mass or more. By using a separator having a halogenated toluene content of 0.1% by mass or more and preferably having a density of 0.58 g/cm ³ or more, life characteristics can be exhibited more fully.

The halogenated toluene is preferably fluorinated toluene. By using fluorinated toluene, the life characteristics become more sufficient.

The fluorinated toluene is preferably orthofluorotoluene (o-fluorotoluene) or metafluorotoluene (m-fluorotoluene). By using o-fluorotoluene or m-fluorotoluene, the life characteristics become more sufficient. More preferably, it is metafluorotoluene (m-fluorotoluene).

The power storage element preferably has a positive electrode potential of 4.2 V (vs. Li/Li ⁺ ) or more in a fully charged state. As described above, when the positive electrode potential in the fully charged state is high, the separator is usually easily oxidized, and the life tends to be shortened. However, the power storage device has good life characteristics even when it is used after being charged to such a high potential. In addition, since the positive electrode potential in the fully charged state is 4.2 V (vs. Li/Li ⁺ ) or higher, the charge/discharge capacity can be increased.

Another aspect of the present invention is a method of using a non-aqueous electrolyte storage element, in which the non-aqueous electrolyte storage element is charged at a positive electrode potential of 4.2 V (vs. Li/Li ⁺ ) or higher. When the positive electrode potential during charging is 4.2 V (vs. Li/Li ⁺ ) or more, the charge/discharge capacity can be increased. In addition, even when the battery is charged at such a high potential and used, voltage drop after charging is suppressed, and the storage device can be used for a long period of time.

<Non-aqueous electrolyte storage element>
A power storage device according to one 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. A non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a “secondary battery”) will be described below as an example of a storage element. The positive electrode, separator, and negative electrode generally form an electrode assembly that is superimposed by lamination or winding. The electrode body is housed in a case, and the case is filled with the non-aqueous electrolyte. In the secondary battery, the non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. The non-aqueous electrolyte is filled in the case and impregnated into the separator. As the case, a known SUS case (stainless steel case), an aluminum case, a resin case, or the like, which is usually used as a secondary battery case, can be used.

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

The said positive electrode base material has electroconductivity. As the material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of the balance between potential resistance, high conductivity and cost. In addition, as a form of forming the positive electrode base material, a foil, a deposited film, and the like can be mentioned, and a foil is preferable from the viewpoint of cost. In other words, aluminum foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloy include A1085P and A3003P defined in JIS-H-4000 (2014).

The intermediate layer is a coating layer on the surface of the positive electrode substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode mixture layer. The structure of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles. It should be noted that having "conductivity" means having a volume resistivity of 10 ⁷ Ω cm or less as measured in accordance with JIS-H-0505 (1975). means that the volume resistivity is greater than 10 ⁷ Ω·cm.

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

Examples of the positive electrode active material include composite oxides represented by Li _x MO _y (M represents at least one transition metal) ₍ Li _x CoO ₂ , Li _x NiO 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 and other Li _x Mn ₂ O ₄ having a spinel crystal structure , Li _x Ni _α Mn _(2-α) O ₄ etc.), Li _{w Mex (XO y ) z} (Me represents at least one transition metal, and X represents, for example, P, Si, B, V, etc.) and polyanion compounds represented by _{( LiFePO4} , _{LiMnPO4 , LiNiPO4} , _{LiCoPO4, Li3V2(PO4)3 , Li2MnSiO4 , Li2CoPO4F , etc.} ). Elements or polyanions in these compounds may be partially substituted with other elements or anionic species. In the positive electrode mixture layer, one type of these compounds may be used alone, or two or more types 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 battery performance. Examples of such conductive agents include natural or artificial graphite, furnace black, acetylene black, carbon black such as ketjen black, metals, and conductive ceramics. The shape of the conductive agent may be powdery, fibrous, or the like.

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

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

The filler is not particularly limited as long as it does not adversely affect battery performance. Main components of the filler include polyolefins 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 mixture layer disposed on the negative electrode base material directly or via an intermediate layer. The negative electrode is a sheet (film) having the laminated structure. The intermediate layer can have the same structure as the intermediate layer of the positive electrode.

The negative electrode substrate can have the same structure as the positive electrode substrate, but as a material, a metal such as copper, nickel, stainless steel, 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 substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The negative electrode mixture layer is formed from a so-called negative electrode mixture containing a negative electrode active material. In addition, the negative electrode mixture forming the negative electrode mixture layer contains optional components such as a conductive agent, a binder (binding agent), a thickener, and a filler, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler may be the same as those used for the positive electrode mixture layer.

A material capable of intercalating and deintercalating lithium ions is usually used as the negative electrode active material. Specific negative electrode active materials include, for example, Si, Sn and other metals or semimetals; Si oxides, Sn oxides and other metal oxides or semimetal oxides; polyphosphate compounds; graphite, amorphous Examples thereof include carbon materials such as carbon (easily graphitizable carbon or non-graphitizable carbon).

Furthermore, the negative electrode mixture (negative electrode mixture layer) includes typical nonmetallic elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W.

(separator)
The separator is mainly composed of polyethylene and has a density of 0.5 g/cm ³ or more. The separator is a polyethylene porous resin film, a polyethylene fiber nonwoven fabric, a woven fabric, or the like, preferably a polyethylene porous film.

The above polyethylene may be either high-density polyethylene, low-density polyethylene, or the like. The polyethylene is not limited to an ethylene homopolymer, and may be a copolymer of ethylene as a main monomer and other monomers (for example, 5 mol % or less of other monomers).

The lower limit of the content of polyethylene in the separator is preferably 50% by mass, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit of this content may be 100% by mass.

In the above separator, other components than polyethylene that may be contained include resins other than polyethylene, fillers, and the like.

The upper limit of the average thickness of the separator may be, for example, 30 μm, preferably 25 μm, more preferably 20 μm. By making the average thickness of the separator equal to or less than the above upper limit, it becomes possible to reduce the thickness and weight of the electric storage device. In addition, according to the electric storage element, it is possible to suppress the shortening of life, which is likely to occur remarkably by making the separator thinner. On the other hand, the lower limit of the average thickness can be, for example, 10 μm from the viewpoint of preventing a short circuit between the positive and negative electrodes, and may be 15 μm.

The lower limit of the density of the separator is 0.5 g/cm ³ , preferably 0.53 g/cm ³ , more preferably 0.55 g/cm ³ and even more preferably 0.58 g/cm ³ . By making the density of the separator equal to or higher than the above lower limit, the shutdown function can be improved, and safety can be improved. Moreover, according to the electric storage element, it is possible to suppress the shortening of the life of the electric storage element, which tends to occur when the density of the separator is increased. On the other hand, the upper limit of this density is preferably 0.7 g/cm ³ and may be 0.65 g/cm ³ from the viewpoint of ensuring sufficient conductivity of ions (non-aqueous electrolyte). It may be 0.6 g/cm ³ .

The separator can be produced by a known method, and the density and thickness can be adjusted by a known method. Moreover, the above separator can be a commercially available one.

(Non-aqueous electrolyte)
The non-aqueous electrolyte is obtained by dissolving an electrolyte salt in a non-aqueous solvent. The non-aqueous electrolyte contains halogenated toluene.

(halogenated toluene)
The halogenated toluene is a compound in which some or all of the hydrogen atoms of toluene are replaced with halogen atoms. A halogenated toluene can be used individually by 1 type or in mixture of 2 or more types.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and the like, and a fluorine atom is preferred. When the halogen atom is a fluorine atom, that is, when fluorinated toluene is used as the halogenated toluene, the positive electrode is more effectively coated with oxidative decomposition products, and thus the life characteristics can be further 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 or 2, more preferably 1. When one halogenated toluene has a plurality of halogen atoms, the plurality of halogen atoms may be the same or different.

As the halogenated toluene, halogenated toluene in which a hydrogen atom on a benzene ring (aromatic ring) is substituted with a halogen atom is preferable. In the case of such a halogenated toluene, the bonding position of the halogen atom is preferably ortho-position or meta-position relative to the methyl group, more preferably meta-position.

Specific examples of the halogenated toluene include fluorotoluene (o-fluorotoluene, m-fluorotoluene, p-fluorotoluene, α-fluorotoluene), chlorotoluene, bromotoluene, difluorotoluene, dichlorotoluene, dibromotoluene, Fluorotoluene, trichlorotoluene, tribromotoluene, chlorofluorotoluene, bromofluorotoluene and the like can be mentioned.

Among these, fluorotoluene is preferred, o-fluorotoluene (2-fluorotoluene), m-fluorotoluene (3-fluorotoluene) and p-fluorotoluene (4-fluorotoluene) are more preferred, o-fluorotoluene and m -fluorotoluene is more preferred, and m-fluorotoluene is particularly preferred. Such fluorinated toluene has a small voltage drop in the float test. That is, by using such fluorinated toluene, the life characteristics of the power storage element can be further improved.

The content of the halogenated toluene in the nonaqueous electrolyte is not particularly limited, and the lower limit is, for example, preferably 0.1% by mass, more preferably 0.3% by mass, further preferably 0.5% by mass, and 1% by mass. % is more preferred, and 3% by mass is even more preferred. By setting the content of the halogenated toluene to the above lower limit or more, it is possible to sufficiently exhibit the life characteristics. In particular, when the density of the separator is 0.58 g/cm ³ or more, the content of halogenated toluene is set to the above lower limit or more, so that the life characteristics can be exhibited more sufficiently. The halogenated toluene content in the non-aqueous electrolyte refers to the mass of the halogenated toluene relative to the mass of the entire non-aqueous electrolyte.

On the other hand, the upper limit of the content of this halogenated toluene can be, for example, 10% by mass, preferably 8% by mass, and more preferably 6% by mass. By setting the content of the halogenated toluene to the above upper limit or less, a certain ionic conductivity can be ensured.

(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 an electric storage device can be used. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones, nitriles and the like. Among these, it is preferable to use at least a cyclic carbonate or a chain carbonate, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is not particularly limited, but may be, for example, 5:95 or more and 50:50 or less. is preferred.

Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and 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 preferred.

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, etc. Among them, EMC is preferred.

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

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 Fluorinated hydrocarbon groups such as _2C2F5 ) _{2 ,} LiN _{( SO2CF3} ) _{( SO2C4F9} ) _{, LiC ( SO2CF3} ) ₃ , _{LiC ( SO2C2F5} ) ₃ Lithium salt etc. which have can be mentioned. Among these, inorganic lithium salts are preferred, and _LiPF6 is more preferred.

The lower limit of the content of the electrolyte salt in the nonaqueous electrolyte is preferably 0.1M, more preferably 0.3M, still more preferably 0.5M, and particularly preferably 0.7M. On the other hand, the upper limit is not particularly limited, but is preferably 2.5M, more preferably 2M, and even more preferably 1.5M.

The non-aqueous electrolyte may contain components other than the halogenated toluene, non-aqueous solvent, and electrolyte salt as long as the effects of the present invention are not impaired. Examples of other components include various additives such as 2-fluoro-6-nitrotoluene, which are contained in general non-aqueous 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.

(Positive electrode potential)
The positive electrode potential in the fully charged state of the storage element is preferably 4.2 V (vs. Li/Li ⁺ ) or higher (noble), and is 4.3 V (vs. Li/Li ⁺ ) or higher. is more preferred. The power storage device has good life characteristics even when it is used after being charged to such a high potential. In addition, since the positive electrode potential in the fully charged state is high as described above, the charge/discharge capacity can be increased. The upper limit of the positive electrode potential in the fully charged state is, for example, 5 V (vs. Li/Li ⁺ ).

From the same point of view, the positive electrode potential at the end of charge voltage during normal use is preferably 4.2 V (vs. Li/Li ⁺ ) or higher (higher), and 4.3 V (vs. Li/Li ⁺ ). Or, it is more preferable to be more noble (higher) than this. The upper limit of the positive electrode potential at the charge termination voltage during normal use is, for example, 5 V (vs. Li/Li ⁺ ). Here, the term "during normal use" refers to the case where the storage element is used under the charging conditions recommended or specified for the storage element, and when a charger for the storage element is prepared. means that the charger is applied to use the quality storage element.

(Manufacturing method of power storage element)
The electric storage element can be obtained by a method according to a known electric storage element manufacturing method. For example, the method for manufacturing the electric storage element includes a step of housing an electrode assembly having a positive electrode, a negative electrode, and a separator in a case, and a step of injecting the non-aqueous electrolyte into the case. The injection can be performed by a known method. After the injection, the injection port is sealed to obtain an electric storage device. The details of each element constituting the storage element (secondary battery) obtained by the manufacturing method are as described above.

<How to use the non-aqueous electrolyte storage element>
The usage method of the electric storage element is not particularly limited, and it can be used in the same manner as a known electric storage element. In addition, it is preferable to charge the electric storage element at a positive electrode potential of 4.2 V (vs. Li/Li ⁺ ) or higher, and the charging is performed at a positive electrode potential of 4.3 V (vs. Li/Li ⁺ ) or higher. It is more preferable to do so. By increasing the positive electrode potential during charging in this manner, the charge/discharge capacity can be increased. Moreover, even when the battery is charged at such a high potential and used, a voltage drop is suppressed, and the storage device can be used for a long period of time. On the other hand, the upper limit of the positive electrode potential in the fully charged state is, for example, 5 V (vs. Li/Li ⁺ ).

Similarly, it is preferable to charge the electric storage element so that the positive electrode potential at the charging end voltage is 4.2 V (vs. Li/Li ⁺ ) or more, and is 4.3 V (vs. Li/Li ⁺ ) or higher. It is more preferable to charge to become more noble. The upper limit of the positive electrode potential at this charging end voltage is, for example, 5 V (vs. Li/Li ⁺ ).

<Other embodiments>
The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved modes in addition to the above-described modes. For example, the intermediate layer may not be provided in the positive electrode or negative electrode. Further, in the above-described embodiments, the storage element is mainly described as a secondary battery, but other 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 diagram of a rectangular secondary battery 1 that is an embodiment of the storage element according to the present invention. In addition, the same figure is taken as the figure which saw through the inside of a container. A secondary battery 1 shown in FIG. 1 has an electrode assembly 2 housed in a 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 a positive terminal 4 via a positive lead 4', and the negative electrode is electrically connected to a negative terminal 5 via a negative lead 5'.

The configuration of the electric storage device according to the present invention is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries (rectangular batteries), flat batteries, and the like. The present invention can also be implemented as a power storage device including a plurality of the above power storage elements. One embodiment of a 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 mounted as a power supply for automobiles such as electric vehicles (EV), hybrid vehicles (HEV), and plug-in hybrid vehicles (PHEV).

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

[Example 1]
(1) Production of positive electrode plate A mixture of LiMn ₂ O ₄ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ in a mass ratio of 65:35 as a positive electrode active material, acetylene black as a conductive aid, And polyvinylidene fluoride (PVDF) was used as a binder. An appropriate amount of N-methyl-2-pyrrolidone (NMP) is added to a mixture in which the proportions of the positive electrode active material, conductive aid, and binder are 90% by mass, 5% by mass, and 5% by mass, respectively, to adjust the viscosity, A pasty positive electrode mixture was produced. This positive electrode mixture was applied to both sides of an aluminum foil (positive electrode base material) having a thickness of 15 μm and dried to prepare a positive electrode plate in which a positive electrode mixture layer was formed on the positive electrode base material. A portion where the positive electrode substrate was exposed was provided on the positive electrode plate without forming the positive electrode mixture layer, and the portion where the positive electrode substrate was exposed and the positive electrode lead were joined.

(2) Production of Negative Electrode Plate Graphite (black lead) was used as the negative electrode active material, styrene-butadiene rubber (SBR) was used as the binder, and carboxymethyl cellulose (CMC) was used as the thickener. An appropriate amount of water was added to a mixture containing 95 mass %, 3 mass %, and 2 mass % of the negative electrode active material, the binder, and the thickener, respectively, to adjust the viscosity, and a pasty negative electrode mixture was produced. This negative electrode mixture was applied to both sides of a copper foil (negative electrode substrate) having a thickness of 10 μm and dried to prepare a negative electrode plate. A portion where the negative electrode substrate was exposed was provided on the negative electrode plate without forming the negative electrode mixture, and the portion where the negative electrode substrate was exposed and the negative electrode plate lead were joined.

(3) Preparation of non-injected battery A separator consisting of only a base layer is interposed between the positive electrode plate and the negative electrode plate prepared as described above, and the positive electrode plate and the negative electrode plate are wound to form an electrode. A body (power generation element) was produced. A microporous film made of polyethylene (PE), which is a thermoplastic resin, having an average thickness of 20 μm and a density of 0.58 g/cm ³ was used as the separator consisting only of the substrate layer. The electrode body was accommodated inside the battery case through the opening of the battery case. Next, the positive plate lead was joined to the battery lid, and the negative plate lead was joined to the negative terminal. After that, the battery lid was fitted into the opening of the battery case, and the battery case and the battery lid were joined by laser welding to produce a non-injected battery in which no non-aqueous electrolyte was injected.

(4) Preparation and injection of non-aqueous electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:70 to prepare a non-aqueous solvent. A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in this non-aqueous solvent at a concentration of 1 mol/L and adding orthofluorotoluene (OFT) in an amount of 5% by mass based on the mass of the non-aqueous electrolyte. This non-aqueous electrolyte is injected into the battery case through an injection port provided on the side surface of the battery case, and the injection port is sealed with a plug to obtain a non-aqueous electrolyte storage element of Example 1 having a nominal capacity of 600 mAh. (hereinafter sometimes simply referred to as “battery”).

[Examples 2 to 12, Comparative Examples 1 to 4]
Examples 2 to 12 were carried out in the same manner as in Example 1 except that the types and amounts of additives added to the non-aqueous solvent, and the average thickness and density of the separator used were as shown in Tables 1 and 2. , and Comparative Examples 1 to 4 were produced. In the table, "OFT" indicates o-fluorotoluene, "MFT" indicates m-fluorotoluene, and "PFT" indicates p-fluorotoluene. In addition, "-" indicates that no additive was added or evaluation was not performed.

[evaluation]
Evaluation test (confirmation of voltage drop after float test)
A confirmation test of voltage drop after the float test of each battery of Examples 1 to 9 and Comparative Examples 1 to 4 shown in Table 1 was performed by the following method. Each battery was charged at a constant current of 600 mA at 25° C. to a predetermined voltage (4.1 V or 4.2 V) and further charged at a predetermined constant voltage for a total of 3 hours. After that, it was placed in a constant temperature bath at a predetermined temperature (60° C. or 70° C.), and was repeatedly charged for 6 days and rested for 1 day at a predetermined constant voltage. The amount of voltage drop (mV) was confirmed from the value of the voltage after resting for one day. Table 1 shows the results. In the battery used for this evaluation, when the voltage is 4.1 V, the positive electrode potential is 4.2 V (vs. Li/Li ⁺ ), and when the voltage is 4.2 V, the positive electrode potential is 4.3 V ( vs. Li/Li ⁺ ).

A confirmation test of voltage drop after the float test of each battery of Examples 10 to 12 and Comparative Example 1 shown in Table 2 was performed by the following method. Each battery was charged to a predetermined voltage (4.2 V) at a constant current of 600 mA at 25° C., and further charged at a predetermined constant voltage for a total of 3 hours. After that, it was placed in a constant temperature bath at a predetermined temperature (70° C.), and was repeatedly charged at a predetermined constant voltage for 2 days and rested for 1 day. The amount of voltage drop (mV) was confirmed from the value of the voltage after resting for one day. Table 2 shows the results.

As shown in Table 1, the batteries of Examples 1-9 show less voltage drop after the float test than those of Comparative Examples 1-4 having the same average thickness and density. In particular, Comparative Example 2, which has a high density of 0.58 g/cm ³ , has a large voltage drop. On the other hand, it can be seen that by adding OFT as in Example 1, the voltage drop can be suppressed to the same extent as other separators.

Moreover, as shown in Table 2, it can be seen that the addition of halogenated toluene has the effect of suppressing a voltage drop regardless of the substitution position of the halogen atom. Among them, o-fluorotoluene (Example 10) and m-fluorotoluene (Example 11) have a large voltage drop suppressing effect, and m-fluorotoluene (Example 11) has a particularly large voltage drop suppressing effect. Recognize. Further, in Example 12 using p-fluorotoluene, the voltage drop was slightly large from the initial stage, but the voltage drop thereafter was suppressed, and the life characteristics were improved.

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

1 secondary battery 2 electrode assembly 3 battery container 4 positive electrode terminal 4' positive electrode lead 5 negative electrode terminal 5' negative electrode lead 20 power storage unit 30 power storage device

Claims (7)

A positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,
The main component of the separator is polyethylene,
The separator has a density of 0.5 g/cm ³ or more,
The non-aqueous electrolyte contains halogenated toluene,
The halogenated toluene has one halogen atom , and the halogen atom is bonded to the methyl group at the meta position,
The separator is a porous film,
A non-aqueous electrolyte storage element, wherein the separator has an average thickness of 25 μm or less. 2. The non-aqueous electrolyte storage element according to claim 1, wherein said separator has an average thickness of 20 [mu]m or less. 3. The non-aqueous electrolyte storage element according to claim 1, wherein said separator has a density of 0.58 g/cm< ³ > or more. 4. The non-aqueous electrolyte storage element according to claim 3, wherein the content of halogenated toluene in said non-aqueous electrolyte is 0.1% by mass or more. 5. The non-aqueous electrolyte storage element according to claim 1, wherein said halogenated toluene is metafluorotoluene . 6. The non-aqueous electrolyte storage element according to any one of claims 1 to 5 , wherein the positive electrode potential in a fully charged state is 4.2 V (vs. Li/Li ⁺ ) or higher. A method of using a non-aqueous electrolyte storage element according to any one of claims 1 to 6 , wherein the non-aqueous electrolyte storage element is charged at a positive electrode potential of 4.2 V (vs. Li/Li ⁺ ) or higher.

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