JPWO2018056188A1 - Non-aqueous electrolyte storage element and method of using the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte storage element having improved life characteristics as compared with those in which the same separator is used while using a separator whose main component is polyethylene, and a method of using such a non-aqueous electrolyte storage element. provide. One aspect of the present invention comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the main component of the separator is polyethylene, and the density of the separator is zero. A non-aqueous electrolyte storage element having a concentration of not less than 5 g / cm 3 and the non-aqueous electrolyte containing a halogenated toluene. [Selected figure] Figure 1

Description

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

  BACKGROUND OF THE INVENTION Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc., due to 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 delivers ions between the two electrodes. It is configured to charge and discharge by performing. Moreover, capacitors, such as a lithium ion capacitor and an electric double layer capacitor, are also prevailing widely as electrical storage elements other than a secondary battery.

  A resin porous film, a woven fabric, a non-woven fabric, etc. are widely used as a separator used for such an electrical storage element. For example, a secondary battery using a separator including 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 the storage element is the life characteristic. For example, it is required that the voltage drop after float charging and leaving for a while is small. However, according to the findings of the inventors, the separator whose main component is polyethylene may have a very large voltage drop when it is thinned, in other words, the life characteristics may be insufficient.

  The present invention has been made based on the above circumstances, and the object of the present invention is to improve the life characteristics as compared with those in which the same separator is used while using a separator whose main component is polyethylene. A non-aqueous electrolyte storage device and a method of using such a non-aqueous electrolyte storage device.

One embodiment of the present invention made to solve the above problems comprises 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, The density of a separator is 0.5 g / cm ³ or more, and the above-mentioned nonaqueous electrolyte is a nonaqueous electrolyte electricity storage element containing halogenated toluene.

Another aspect of the present invention made to solve the above problems is a non-aqueous electrolyte in which the non-aqueous electrolyte storage element is charged at a positive electrode potential of 4.2 V (vs. Li ^/ Li ⁺ ) or more It is a usage method of a storage element.

  According to the present invention, there is provided a non-aqueous electrolyte storage element having improved life characteristics as compared with those in which the same separator is used while using a separator whose main component is polyethylene, and such a non-aqueous electrolyte storage element. How to use 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 view showing a power storage device configured by collecting a plurality of secondary batteries according to an embodiment of the present invention.

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, the main component of the separator is polyethylene, and the density of the separator is 0.5 g / cm. ³ or more, and the non-aqueous electrolyte is a non-aqueous electrolyte storage element containing a halogenated toluene (hereinafter, also simply referred to as "storage element"). In addition, a "main component" means the component with most content on a mass basis.

The storage element has good life characteristics as compared with those in which the same separator is used while using a separator whose main component is polyethylene. Although this reason is not certain, it is guessed to be by the following effect | action. The separator mainly composed of 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 above-mentioned oxidation reaction produces unsaturated double bonds in polyethylene. The formation of unsaturated double bonds at a plurality of places results in the formation of a conjugated bond, whereby the oxidized portion becomes highly conductive. Further, since this oxidation occurs by the action of the positive electrode, the oxidized portion grows from the positive electrode side surface of the separator toward the negative electrode side, that is, in the thickness direction. When the oxidized portion reaches the negative electrode side surface of the separator, the positive electrode and the negative electrode are electrically conducted by the oxidized portion, and a voltage drop between the positive and negative electrodes occurs. On the other hand, when the non-aqueous electrolyte contains halogenated toluene as in the storage element, the oxidized decomposition product of the halogenated toluene coats the surface of the positive electrode. As a result, it is presumed that the oxidation of the separator is suppressed and the life characteristics are improved. Halogenated toluene is also preferable because it is an additive that hardly causes deterioration of input / output characteristics. Generally, when the density of the separator is a relatively high density of 0.5 g / cm ³ or more, the oxidized portion having high conductivity is densely formed, so that a voltage drop easily occurs. However, the storage element has good life characteristics despite the use of such a separator. In addition, when the density of the separator is relatively high, such as 0.5 g / cm ³ or more, the amount of resin dissolved in the abnormal heat generation increases, and the resistance value can be increased. Therefore, according to the storage element, shutdown at the time of abnormality is likely to occur, and the safety is also excellent.

  The average thickness of the separator may be 20 μm or less. In the case of a thin separator, since the oxidized portion easily reaches the negative electrode side, the life is usually shortened. On the other hand, according to the storage element, even with such a separator having an average thickness of 20 μm or less, sufficient life characteristics can be exhibited. In addition, by using a separator having an average thickness of 20 μm or less, the storage element can be made thinner and lighter. In addition, "average thickness" means the average value of the thickness of ten places selected arbitrarily.

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

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

  It is preferable that the said halogenated toluene is fluorinated toluene. Use of fluorinated toluene results in more sufficient life characteristics.

  The fluorinated toluene is preferably orthofluorotoluene (o-fluorotoluene) or metafluorotoluene (m-fluorotoluene). The use of o-fluorotoluene or m-fluorotoluene results in more satisfactory life characteristics. And more preferably, it is metafluorotoluene (m-fluorotoluene).

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

Another aspect of the present invention is a method of using the 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 more. When the positive electrode potential at the time of charge is 4.2 V (vs. Li ^/ Li ⁺ ) or more, the charge / discharge capacity can be increased. In addition, also in the case of using with such high potential, the voltage drop after charging is suppressed, and the storage element can be used for a long time.

<Non-aqueous electrolyte storage element>
A storage element 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 (hereinafter, also simply referred to as “secondary battery”) will be described as an example of the storage element. The positive electrode, the separator and the negative electrode usually form an electrode body which is superposed by lamination 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. Further, the non-aqueous electrolyte is filled in the case and impregnated in the separator. As said case, the well-known SUS case (stainless steel case), aluminum case, resin case etc. which are normally 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 mixture layer disposed directly or via an intermediate layer on the positive electrode base material. The positive electrode is a sheet (film) of the laminated structure.

  The said positive electrode base material has electroconductivity. As a material of a base material, metals, such as aluminum, titanium, a tantalum, stainless steel, or those alloys are used. Among these, aluminum and aluminum alloys are preferable in terms of the balance of potential resistance, conductivity height and cost. Moreover, a foil, a vapor deposition film, etc. are mentioned as a formation form of a positive electrode base material, From the surface of cost, a foil is preferable. That is, an aluminum foil is preferable as the positive electrode substrate. In addition, as aluminum or aluminum alloy, A1085P, A3003P etc. which are prescribed | regulated to JIS-H-4000 (2014) can be illustrated.

The intermediate layer is a coating layer on the surface of the positive electrode base material, and reduces the contact resistance between the positive electrode base material and the positive electrode mixture layer by containing conductive particles such as carbon particles. The configuration 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 based on JIS-H-0505 (1975) is 10 < ⁷ > ohm * cm or less, and "non-conductivity" Means that the above-mentioned volume resistivity is more than 10 ⁷ Ω · cm.

  The positive electrode mixture layer is formed of 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 (binder), a thickener, and a filler, as necessary.

As the positive electrode active material, for example, a complex oxide represented by Li _x MO _y (M represents at least one 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, X represents for example P, Si, B, and V, etc.) And polyanion 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 element or anion species. In the positive electrode mixture layer, one of these compounds may be used alone, or two or more thereof may be mixed and used.

  The conductive agent is not particularly limited as long as the conductive material 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, metals, conductive ceramics and the like. The shape of the conductive agent may, for example, be powdery or fibrous.

  As said binder (binder), Thermoplastic resins, such as a fluororesin (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) etc.), polyethylene, a polypropylene, a polyimide; Ethylene-propylene-diene rubber (EPDM), Elastomers such as sulfonated EPDM, styrene butadiene rubber (SBR), fluoro rubber, etc .; polysaccharide polymers and the like.

  Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. 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 the battery performance. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, carbon and the like.

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

  The above-mentioned negative electrode substrate can be made to have the same configuration as the positive electrode substrate, but as materials, metals such as copper, nickel, stainless steel, nickel plated steel or alloys thereof are used, and copper or copper alloy preferable. That is, copper foil is preferable as the negative electrode substrate. As a copper foil, a rolled copper foil, an electrolytic copper foil, etc. are illustrated.

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

  As the negative electrode active material, usually, a material capable of inserting and extracting lithium ions is used. Specific examples of the negative electrode active material include metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide and Sn oxide; polyphosphoric acid compounds; graphite (graphite), amorphous Carbon materials such as carbon (graphitizable carbon or non-graphitizable carbon) and the like can be mentioned.

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

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

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

  As a minimum of content of polyethylene in the above-mentioned separator, 50 mass% is preferred, 80 mass% or more is more preferred, 90 mass% or more is more preferred, and 95 mass% or more is especially preferred. The upper limit of this content may be 100% by mass.

  In the said separator, resin other than polyethylene, a filler, etc. can be mentioned as another component which may be contained other than polyethylene.

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

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, more preferably 0.58 g / cm ^3. By setting the density of the separator to the above lower limit or more, the shutdown function can be enhanced and safety can be enhanced. Moreover, according to the storage element, it is possible to suppress the shortening of the life of the storage element which is likely to be generated by densifying the separator. On the other hand, the upper limit of the density is preferably 0.7 g / cm ^{3 and} may be 0.65 g / cm ³ in terms of securing sufficient conductivity of ions (non-aqueous electrolyte), etc. It may be 0.6 g / cm ³ .

The said separator can be manufactured by a well-known method, and adjustment of density and thickness can also be performed by a well-known method. Moreover, the said separator can use what is marketed.

(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 said halogenated toluene means the compound by which one part or all part of the hydrogen atom which toluene has was substituted by the halogen atom. The halogenated toluene can be used alone or in combination of two or more.

  As said halogen atom, although a fluorine atom, a chlorine atom, a bromine atom etc. can be mentioned, a fluorine atom is preferable. When the halogen atom is a fluorine atom, that is, when fluorinated toluene is used as the halogenated toluene, the life characteristics can be further enhanced by the coating of the oxidized decomposition product on the positive electrode being more effectively generated.

  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, and 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 said halogenated toluene, the halogenated toluene by which the hydrogen atom on the benzene ring (aromatic ring) was substituted by the halogen atom is preferable. In the case of such halogenated toluene, as a bonding position of a halogen atom, an ortho position and a meta position with respect to a methyl group are preferable, and a meta position is more preferable.

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

  Among these, fluorotoluene is preferable, o-fluorotoluene (2-fluorotoluene), m-fluorotoluene (3-fluorotoluene) and p-fluorotoluene (4-fluorotoluene) are more preferable, 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 storage element can be further improved.

The content of halogenated toluene in the non-aqueous electrolyte is not particularly limited, and the lower limit is, for example, preferably 0.1% by mass, more preferably 0.3% by mass, and still more preferably 0.5% by mass. % Is more preferable, and 3% by mass is further preferable. By making content of halogenated toluene more than the said lower limit, a lifetime characteristic can fully be exhibited. In particular, when the density of the separator is 0.58 g / cm ³ or more, by setting the content of the halogenated toluene to the above lower limit or more, the life characteristics can be more sufficiently exhibited. The content of halogenated toluene in the non-aqueous electrolyte refers to the mass of halogenated toluene with respect to the mass of the whole non-aqueous electrolyte.

On the other hand, the upper limit of the content of the halogenated toluene can be, for example, 10% by mass, preferably 8% by mass, and more preferably 6% by mass. By setting the content of halogenated toluene below the above-mentioned upper limit, a constant ion conductivity can be secured.

(Non-aqueous solvent)
As said non-aqueous solvent, the well-known non-aqueous solvent generally used can be used as a non-aqueous solvent of general nonaqueous electrolyte for electrical storage elements. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, esters, ethers, amides, sulfones, lactones and nitriles. Among these, it is preferable to use at least cyclic carbonate or linear carbonate, and it is more preferable to use cyclic carbonate and linear carbonate in combination. When using cyclic carbonate and chain carbonate in combination, the volume ratio of cyclic carbonate and chain carbonate (cyclic carbonate: chain carbonate) is not particularly limited, but 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), 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), ethyl methyl carbonate (EMC), diphenyl carbonate and the like, and among these, EMC is preferable.

(Electrolyte salt)
As said electrolyte salt, the well-known electrolyte salt normally used can be used as electrolyte salt of general nonaqueous electrolyte for electrical storage elements. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like, and lithium salt is preferable.

As the lithium salt, inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₄ ) _{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, And lithium salts and the like. Among these, inorganic lithium salts are preferable, and LiPF ₆ is more preferable.

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

  The non-aqueous electrolyte may contain components other than the above-described halogenated toluene, non-aqueous solvent, and electrolyte salt as long as the effects of the present invention are not impaired. As said other component, various additives, such as 2-fluoro- 6-nitrotoluene, contained in the general nonaqueous electrolyte for electrical storage elements can also be mentioned, for example. However, as content of these other components, 5 mass% or less may be preferable, and 1 mass% or less may be more preferable.

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

(Positive electrode potential)
In the storage element, the fully charged positive electrode potential 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 storage element has good life characteristics even when used after being charged to such a high potential. In addition, since the fully charged positive electrode potential is high as described above, the charge / discharge capacity can be increased. The upper limit of the fully charged positive electrode potential is, for example, 5 V (vs. Li ^/ Li ⁺ ).

From the same point of view, it is preferable that the positive electrode potential at the charge termination voltage during normal use be 4.2 V (vs. Li ^/ Li ⁺ ) or higher (it becomes higher), and 4.3 V (vs. Li ^/ Li ⁺ ) Or more noble (more expensive) is more preferable. 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 normal use time is a case where the storage element is used by adopting a charging condition recommended or specified for the storage element, and a charger for the storage element is prepared. Means the case where the charger is applied and the quality storage element is used.

(Method of manufacturing storage element)
The said electrical storage element can be obtained by the method according to the manufacturing method of a well-known electrical storage element. For example, the method of manufacturing the storage element includes a step of housing an electrode body 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 above injection can be performed by a known method. After injection, a storage element can be obtained by sealing the injection port. The details of each element constituting the storage element (secondary battery) obtained by the manufacturing method are as described above.

<How to use non-aqueous electrolyte storage element>
The usage method of the said electrical storage element is not specifically limited, It can use by the method similar to a well-known electrical storage element. Note that it is preferable to charge the storage element at a positive electrode potential of 4.2 V (vs. Li ^/ Li ⁺ ) or higher, and charge at a positive electrode potential of 4.3 V (vs. Li ^/ Li ⁺ ) or higher. It is more preferable to do. By raising the positive electrode potential at the time of charging in this manner, the charge / discharge capacity can be increased. In addition, also in the case of using by charging with such a high potential, the voltage drop is suppressed, and the storage element can be used for a long time. On the other hand, the upper limit of the fully charged positive electrode potential is, for example, 5 V (vs. Li ^/ Li ⁺ ).

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

<Other Embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment. For example, the intermediate layer may not be provided in the positive electrode or the negative electrode. Moreover, in the said embodiment, although the electrical storage element was demonstrated centering on the form which is a secondary battery, another electrical storage element may be sufficient. 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 a storage element according to the present invention. In addition, the same figure is a view seen through the inside of the container. In the secondary battery 1 shown in FIG. 1, the electrode body 2 is accommodated in a battery case 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 via a separator. 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 storage element according to the present invention is not particularly limited, and a cylindrical battery, a rectangular battery (rectangular battery), a flat battery and the like can be mentioned as an example. The present invention can also be realized as a power storage device provided with a plurality of the above power storage elements. One embodiment of a power storage device is shown in FIG. In FIG. 2, power storage device 30 includes a plurality of power storage units 20. Each storage unit 20 includes a plurality of secondary batteries 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), and a plug-in hybrid vehicle (PHEV).

  Hereinafter, the present invention will be more specifically described by way of examples, 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 at a mass ratio of 65: 35 as a positive electrode active material, acetylene black as a conductive agent, And polyvinylidene fluoride (PVDF) was used as a binder. Adjust the viscosity by adding an appropriate amount of N-methyl-2-pyrrolidone (NMP) to a mixture of 90% by mass, 5% by mass and 5% by mass of the positive electrode active material, the conductive additive and the binder, respectively. A paste-like positive electrode mixture was produced. The positive electrode mixture was applied to both surfaces of an aluminum foil (positive electrode substrate) 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 substrate. The positive electrode mixture layer was not formed on the positive electrode plate, and the exposed portion of the positive electrode substrate was provided, and the exposed portion of the positive electrode substrate was joined to the positive electrode lead.

(2) Production of Negative Electrode Plate Graphite (graphite) was used as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener. An appropriate amount of water was added to a mixture of 95% by mass, 3% by mass and 2% by mass of the negative electrode active material, the binder and the thickener, respectively, to adjust the viscosity to prepare a paste-like negative electrode mixture. The negative electrode mixture was applied to both sides of a copper foil (negative electrode base material) having a thickness of 10 μm and dried to prepare a negative electrode plate. A negative electrode composite was not formed on the negative electrode plate, and a portion where the negative electrode substrate was exposed was provided, and a portion where the negative electrode substrate was exposed and the negative electrode plate lead were joined.

(3) Preparation of Non-Fluid Solution Battery A separator consisting of only a base material layer is interposed between the positive electrode plate and the negative electrode plate manufactured as described above, and the electrode is formed by winding the positive electrode plate and the negative electrode plate. The body (power generation element) was produced. As a separator which consists only of a base material layer, it consists of polyethylene (PE) which is a thermoplastic resin, and the average thickness 20 micrometers and the microporous film of the density 0.58 g / cm < ³ > were employ | adopted. The electrode body was housed inside the battery case from the opening of the battery case. Then, the positive electrode plate lead was joined to the battery lid, and the negative electrode plate lead was joined to the negative electrode terminal. After that, the battery cover was fitted into the opening of the battery case, and the battery case and the battery cover were joined by laser welding to produce a non-aqueous electrolyte battery in which the non-aqueous electrolyte was not injected.

(4) Preparation of Nonaqueous Electrolyte and Injection The nonaqueous solvent was prepared by mixing ethylene carbonate (EC) and ethylmethyl carbonate (EMC) in a volume ratio of 30:70. A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in this non-aqueous solvent and adding 5% by mass of orthofluorotoluene (OFT) with respect to the mass of the non-aqueous electrolyte. The nonaqueous electrolyte storage element of Example 1 having a nominal capacity of 600 mAh by injecting the nonaqueous electrolyte into the inside of the battery case from a liquid injection port provided on the side of the battery case and sealing the liquid injection port with a plug. (Hereafter, it may only be called a "battery") was produced.

[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 each battery of Comparative Examples 1-4. In the table, "OFT" indicates o-fluorotoluene, "MFT" indicates m-fluorotoluene, and "PFT" indicates p-fluorotoluene. Moreover, "-" shows that the additive is not added or evaluation is not performed.

[Evaluation]
Evaluation test (Confirmation of voltage drop after float test)
The confirmation test of the 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 conducted 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 for a total of 3 hours at a predetermined constant voltage. Thereafter, it was placed in a thermostatic bath of a predetermined temperature (60 ° C. or 70 ° C.), and charging for 6 days and rest for 1 day were repeated at a predetermined constant voltage. The amount of voltage drop (mV) was confirmed from the value of the voltage after one day of rest. The results are shown in Table 1. In the battery used for this evaluation, the positive electrode potential is 4.2 V (vs. Li ^/ Li ⁺ ) when the voltage is 4.1 V, and the positive electrode potential is 4.3 V (4.2 V). vs. Li ^/ Li ⁺ ).

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

As shown in Table 1, it can be seen that the batteries of Examples 1 to 9 have a smaller voltage drop after the float test as compared to those of Comparative Examples 1 to 4 having the same average thickness and density. In particular, Comparative Example 2 having a high density of 0.58 g / cm ³ has a large voltage drop. On the other hand, it is understood that the voltage drop can be suppressed to the extent that it is not different from other separators by adding the OFT as in Example 1 and the like.

  Further, as shown in Table 2, it can be seen that the addition of the halogenated toluene has the effect of suppressing the 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. Moreover, although Example 12 using p-fluorotoluene has a voltage drop a little large from the beginning, it turns out that the voltage drop after that is suppressed and the life characteristic is improved.

  The present invention can be applied to non-aqueous electrolyte storage devices including non-aqueous electric field secondary batteries used as power sources for personal computers, communication terminals and other electronic devices, and 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 storage unit 30 storage device

Claims (9)

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 above separator is polyethylene,
The density of the above separator is 0.5 g / cm ³ or more,
The nonaqueous electrolyte electrical storage element in which the said nonaqueous electrolyte contains halogenated toluene.   The nonaqueous electrolyte storage device according to claim 1, wherein the average thickness of the separator is 20 μm or less. The density of the said separator is 0.58 g / cm < ³ > or more, The nonaqueous electrolyte electrical storage element of Claim 1 or Claim 2.   The nonaqueous electrolyte storage device according to claim 3, wherein the content of halogenated toluene in the nonaqueous electrolyte is 0.1% by mass or more.   The nonaqueous electrolyte storage device according to any one of claims 1 to 4, wherein the halogenated toluene is fluorinated toluene.   The non-aqueous electrolyte storage device according to claim 5, wherein the fluorinated toluene is orthofluorotoluene or metafluorotoluene.   6. The non-aqueous electrolyte storage device according to claim 5, wherein said fluorinated toluene is metafluorotoluene. The nonaqueous electrolyte storage element according to any one of claims 1 to 7, wherein the positive electrode potential in a fully charged state is 4.2 V (vs. Li ^/ Li ⁺ ) or more. A method of using a non-aqueous electrolyte storage device, comprising: charging the non-aqueous electrolyte storage device according to any one of claims 1 to 8 at a positive electrode potential of 4.2 V (vs. Li ^/ Li ⁺ ) or more.

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