JP6652072B2 - Nonaqueous electrolyte, power storage element and method for manufacturing power storage element - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte, a power storage device, and a method for manufacturing a power storage device.

  Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and 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 transfers ions between the two electrodes. The battery is configured to be charged and discharged. In addition, capacitors such as a lithium ion capacitor and an electric double layer capacitor are widely used as power storage elements other than the nonaqueous electrolyte secondary battery.

  Various additives are added to the non-aqueous electrolyte used for such a storage element for the purpose of improving performance and the like. Specifically, a non-aqueous electrolyte to which a benzotriazole derivative has been added in order to improve the storage performance at high temperatures has been proposed (see Patent Document 1).

JP 2013-066966 A

  However, at the present time when the need for high-energy-density energy storage devices has been increasing in recent years, the above-mentioned requirements for performance have been further increased, and the above-mentioned conventional non-aqueous electrolyte has been able to satisfy these requirements. Absent.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte capable of suppressing a decrease in discharge capacity after high-temperature storage of a power storage element, and a storage battery including the non-aqueous electrolyte. An object of the present invention is to provide an element and a method for manufacturing the electric storage element.

  One embodiment of the present invention made to solve the above problem is a nonaqueous electrolyte containing a compound represented by the following formula (1) or (2).

（式（１）中、Ｒ^１、Ｒ^２、Ｒ^３及びＲ^４は、それぞれ独立して水素原子、ハロゲン原子、ヒドロキシ基、アミノ基、ニトロ基、スルホン酸基、チオール基、リン酸基、１価の有機基又は１価のイオン性基である。式（２）中、Ｒ^５、Ｒ^６、Ｒ^７及びＲ^８は、それぞれ独立して水素原子、ハロゲン原子、ヒドロキシ基、アミノ基、ニトロ基、スルホン酸基、チオール基、リン酸基、１価の有機基又は１価のイオン性基である。）

(In the formula (1), R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a nitro group, a sulfonic group, a thiol group, a phosphate group, In the formula (2), R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent a hydrogen atom, a halogen atom, a hydroxy group, an amino group, or a monovalent organic group or a monovalent ionic group. A nitro group, a sulfonic group, a thiol group, a phosphate group, a monovalent organic group or a monovalent ionic group.)

  Another embodiment of the present invention is a power storage element including the nonaqueous electrolyte.

  Another embodiment of the present invention is a method for manufacturing a power storage element using the nonaqueous electrolyte.

  ADVANTAGE OF THE INVENTION According to this invention, the non-aqueous electrolyte which can suppress the fall of the discharge capacity after preservation | save of an electric storage element at high temperature, the electric storage element provided with this non-aqueous electrolyte, and the manufacturing method of this electric storage element can be provided.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a power storage device including a plurality of non-aqueous electrolyte secondary batteries according to an embodiment of the present invention.

  One embodiment of the present invention is a nonaqueous electrolyte containing a compound represented by the following formula (1) or (2).

In the above formula (1), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a nitro group, a sulfonic group, a thiol group, a phosphate group, It is a monovalent organic group or a monovalent ionic group.

In the above formula (2), R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a nitro group, a sulfonic group, a thiol group, a phosphate group, It is a monovalent organic group or a monovalent ionic group.

  According to the nonaqueous electrolyte, a decrease in the discharge capacity after storage of the power storage element at a high temperature can be suppressed. The reason why such an effect occurs is not clear, but the compound contained in the nonaqueous electrolyte is a compound in which the carbon atom at the 4-position of the 6-membered ring of 1,2,3-benzotriazole is substituted with a nitrogen atom. By having an azabenzotriazole structure, the free charge of the compound increases and the reducibility increases. As a result, the film is easily decomposed and reduced on the negative electrode surface at the time of the first charge, and the film protects the negative electrode surface. This is presumed to improve the effect of suppressing a decrease in discharge capacity after storage of the power storage element at high temperature. Here, the “ionic group” refers to a group formed by a combination of a cation group and an anion or a combination of an anion group and a cation.

The compound is represented by the formula (1), wherein R ¹ is a hydrogen atom or an electron-withdrawing group, and R ² , R ³ , and R ⁴ are hydrogen atoms, or represented by 2), the ^{R 5} is an electron withdrawing group, said ^R 6, ^{R 7} and ^{R 8} is preferably a hydrogen atom. When the compound has such a structure, a decrease in discharge capacity after storage of the power storage element at a high temperature can be more effectively suppressed, and an increase in resistance can be suppressed.

  The compound is 4-azabenzotriazole (1H-1,2,3-triazolo [4,5-b] pyridine), 1-acetyl-1H-1,2,3-triazolo [4,5-b] pyridine Alternatively, a combination of these is preferable. When the compound has the above structure, a decrease in discharge capacity and an increase in resistance after storage of the power storage element at a high temperature can be more effectively suppressed.

  Another embodiment of the present invention is a power storage element including the nonaqueous electrolyte. Since the power storage element includes the nonaqueous electrolyte, a decrease in discharge capacity after high-temperature storage can be suppressed.

The positive electrode potential at the charge termination voltage during normal use of the power storage element is preferably 4.4 V (vs. Li ^/ Li ⁺ ) or higher. When the positive electrode potential at the end-of-charge voltage during normal use is in the above range, the power storage element can more effectively exhibit the effect of suppressing a decrease in discharge capacity after high-temperature storage. Here, the normal use refers to a case where the storage element is used by adopting a recommended or specified charging condition for the storage element, and a case where a charger for the storage element is prepared. Refers to the case where the power storage element is used by applying the charger.

  Another embodiment of the present invention is a method for manufacturing a power storage element using the nonaqueous electrolyte. According to the method for manufacturing a power storage element, since the nonaqueous electrolyte is used, a power storage element capable of suppressing a decrease in discharge capacity after high-temperature storage can be obtained.

<Non-aqueous electrolyte>
The non-aqueous electrolyte according to one embodiment of the present invention is used for a power storage device and contains a compound represented by the above formula (1) or the above formula (2). The non-aqueous electrolyte generally contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Further, the non-aqueous electrolyte may be solid.

  Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferred. When the halogen atom is a fluorine atom, the discharge capacity retention ratio can be increased.

  The monovalent organic group is not particularly limited, but is preferably a monovalent organic group having 1 to 10 carbon atoms. As the monovalent organic group having 1 to 10 carbon atoms, for example, a monovalent hydrocarbon group having 1 to 10 carbon atoms, a divalent heteroatom at the carbon-carbon or at the terminal on the bond side of the hydrocarbon group or Examples include a group (g) containing a hetero atom-containing group, a group in which part or all of the hydrogen atoms of the hydrocarbon group and the group (g) are substituted with a hetero atom or a hetero atom-containing group.

Examples of the monovalent hydrocarbon group having 1 to 10 carbon atoms include a group having a chain hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group.
As the chain hydrocarbon group,
Alkyl groups such as methyl group, ethyl group, propyl group, butyl group and pentyl group;
Alkenyl groups such as an ethenyl group, a propenyl group and a butenyl group;
Alkynyl groups such as an ethynyl group, a propynyl group and a butynyl group are exemplified.
As the alicyclic hydrocarbon group,
Cycloalkyl groups such as cyclopentyl group and cyclohexyl group;
Cycloalkenyl groups such as cyclopropenyl group, cyclopentenyl group, cyclohexenyl group;
And a bridged ring hydrocarbon group such as a norbornyl group and an adamantyl group.
As the group having an aromatic hydrocarbon group,
Aryl groups such as phenyl, tolyl, xylyl and naphthyl;
And aralkyl groups such as benzyl group and phenethyl group.

  Examples of the hetero atom constituting the hetero atom or the hetero atom-containing group include an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a silicon atom, a halogen atom and the like. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  The monovalent ionic group is represented by the following formula (3) or (4).

In the above formula (3), X ⁺ is a monovalent group containing a monovalent cation. Y ^- is a monovalent anion.

Examples of the monovalent cation contained in the monovalent group represented by X ⁺ include a uronium cation, an ammonium cation, a phosphonium cation, an iodonium cation, and an oxonium cation.

Examples of the monovalent anion represented by Y ⁻ include an anion of an electrolyte salt used for a non-aqueous electrolyte of a general electric storage element, such as a hexafluorophosphate anion and a tetrafluoroborate anion. .

In the formula (4), Y ^'- is a monovalent group comprising a monovalent anion. X ' ⁺ is a monovalent cation.

The Y ^'- as the monovalent anions contained in the monovalent group represented by the amide anion, sulfite anions, and the like.

Examples of the monovalent cation represented by X ′ ⁺ include cations of an electrolyte salt used for a non-aqueous electrolyte of a general electric storage element, such as a lithium cation, a sodium cation, a potassium cation, and an onium cation. Can be

  Examples of the monovalent ionic group include groups represented by the following formulas (5) and (6).

In the formula (1), R ¹ is preferably a hydrogen atom or an electron-withdrawing group, and R ² , R ³ and R ⁴ are preferably hydrogen atoms. Examples of the electron-withdrawing group include an acyl group, a nitro group, a cyano group, a tosyl group, a mesyl group and the like, and among these, an acyl group is preferable. As the acyl group, an acetyl group and a propionyl group are particularly preferable.

In the above formula (2), R ⁵ is preferably an electron withdrawing group, more preferably a monovalent ionic group, and R ⁶ , R ⁷ and R ⁸ are preferably hydrogen atoms. As the monovalent ionic group, for example, groups represented by the above formulas (5) and (6) are preferable.

  Examples of the compound include 4-azabenzotriazole (1H-1,2,3-triazolo [4,5-b] pyridine) and 1-acetyl-1H-1,2,3-triazolo [4,5-b ] Pyridine, 6-bromo-1H-1,2,3-triazolo [4,5-b] pyridine, O- (7-azabenzotriazol-1-yl) -N, N, N ′, N′-tetra Methyluronium hexafluorophosphate (HATU), (7-azabenzotriazol-1-yloxy) tris (dimethylamino) phosphonium hexafluorophosphate (AOP) and the like. Among them, 4-azabenzotriazole (1H-1,2,3-triazolo [4,5-b] pyridine), 1-acetyl-1H-1,2,3-triazolo [4,5-b] Preference is given to pyridine or a combination thereof.

  The mass (content) of the compound with respect to the total mass of the nonaqueous electrolyte is not particularly limited, but the lower limit is preferably 0.01% by mass, and more preferably 0.1% by mass. When the content of the compound is equal to or more than the above lower limit, the effect of suppressing a decrease in the discharge capacity after storage of the power storage element at a high temperature can be more sufficiently exerted. On the other hand, the upper limit of the mass (content) of the compound relative to the total mass of the nonaqueous electrolyte is preferably 2% by mass, more preferably 1% by mass, from the viewpoint of suppressing an increase in resistance due to excessive decomposition of the compound.

(Non-aqueous solvent)
As the non-aqueous solvent, a known non-aqueous solvent generally used as a non-aqueous solvent in a non-aqueous electrolyte of a general electric storage element can be used. Examples of the non-aqueous solvent include cyclic carbonate, chain carbonate, ester, ether, amide, sulfone, lactone, nitrile 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 the cyclic carbonate and the chain carbonate are used in combination, the volume ratio between 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.

  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), and difluoroethylene. Examples thereof include carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among them, EC is preferable.

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

(Electrolyte salt)
As the electrolyte salt, a known electrolyte salt that is generally used as an electrolyte salt in a nonaqueous electrolyte of a general electric storage element can be used. Examples of the electrolyte salt include a lithium salt, a sodium salt, a potassium salt, a magnesium salt, an onium salt and the like, 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 , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO _{2 2 C 2 F 5) 2,} LiN (SO 2 CF 3) (SO 2 C 4 F 9), LiC (SO 2 CF 3) substituted with _{3, LiC (SO 2 C 2} F 5) hydrogen ₃ or the like is fluorine And a lithium salt having a hydrocarbon group. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

  As a minimum of content of the above-mentioned electrolyte salt in the 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 2.5 M, more preferably 2 M, and still more preferably 1.5 M.

  The non-aqueous electrolyte may contain components other than the compound, 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 a nonaqueous electrolyte of a general electric storage element. 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 and dissolving the electrolyte salt and the compound to the non-aqueous solvent.

<Storage element>
An energy storage device according to one embodiment of the present invention has a positive electrode, a 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 and the negative electrode usually form an electrode body that is alternately superimposed by lamination or winding via a separator. The electrode body is housed in a case, and the case is filled with the nonaqueous electrolyte. In the non-aqueous electrolyte secondary battery, the above-described non-aqueous electrolyte is used as the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the case, a known metal case or the like usually used as a case of a non-aqueous electrolyte secondary battery can be used.

  According to the non-aqueous electrolyte secondary battery (electric storage element), since the non-aqueous electrolyte containing the compound is used, a decrease in discharge capacity after high-temperature storage is suppressed.

(Positive electrode)
The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate.

  The positive electrode substrate has conductivity. As the material of the base material, a metal such as aluminum, titanium, tantalum, stainless steel or an alloy thereof is used. Among these, aluminum and an aluminum alloy are preferable in view of the balance between potential resistance, high conductivity, and cost. Examples of the form of forming the positive electrode substrate include a foil and a vapor-deposited film, and a foil is preferable in terms of cost. That is, an aluminum foil is preferable as the positive electrode substrate. In addition, as aluminum or an aluminum alloy, A1085P, A3003P, etc. specified in JIS-H-4000 (2014) can be exemplified.

The intermediate layer is a coating layer on the surface of the positive electrode base material, and reduces contact resistance between the positive electrode base material and the positive electrode active material layer by containing conductive particles such as carbon particles. The configuration of the intermediate layer is not particularly limited, and can be formed, for example, from a composition containing a resin binder and conductive particles. Note that having “conductive” means that the volume resistivity measured according to JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “non-conductive”. Means that the volume resistivity is greater than 10 ⁷ Ω · cm.

  The positive electrode active material 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 active material 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 composite 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.) (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 anionic species. In the positive electrode active material layer, one kind of these compounds may be used alone, or two or more kinds may be used in combination.

  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, conductive ceramics, and the like. Examples of the shape of the conductive agent include powder, fiber, and the like.

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

The lower limit of the positive electrode potential at the charge termination voltage during normal use of the power storage element is preferably 4.2 V (vs. Li ^/ Li ⁺ ), more preferably 4.3 V (vs. Li ^/ Li ⁺ ). 4 V (vs. Li ^/ Li ⁺ ) is more preferable, and 4.45 V (vs. Li ^/ Li ⁺ ) is particularly preferable. On the other hand, the upper limit of the positive electrode potential at the charge termination voltage is preferably 5.0 V (vs. Li ^/ Li ⁺ ), and more preferably 4.6 V (vs. Li ^/ Li ⁺ ). When the positive electrode potential at the end-of-charge voltage during normal use is applied to the above range, the power storage element can effectively exhibit the ability to suppress a decrease in discharge capacity after storage at high temperatures.

  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 inactivate 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. The 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 substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The intermediate layer can have the same configuration as the intermediate layer of the positive electrode.

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

  The negative electrode active material layer is formed from a so-called negative electrode mixture containing the negative electrode active material. In addition, the negative electrode mixture forming the negative electrode active material layer contains optional components such as a conductive agent, a binder (binder), a thickener, and a filler, if necessary. As the optional components such as a conductive agent, a binder, a thickener, and a filler, the same components as those of 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 examples of the negative electrode active material include metals or semimetals such as Si and Sn;
Metal oxides or semimetal oxides such as Si oxides and Sn oxides;
Polyphosphate compound;
Carbon materials such as graphite (graphite) and amorphous carbon (easy graphitizable carbon or hardly graphitizable carbon);
And a lithium metal composite oxide such as lithium titanate.

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

(Separator)
As the material of the separator, for example, a woven fabric, a nonwoven fabric, a 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 a main component of the separator, for example, a 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.

<Method of manufacturing power storage element>
A method for manufacturing a power storage device according to one embodiment of the present invention is a method for manufacturing a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte is used as the nonaqueous electrolyte. The manufacturing method includes, for example, a step of housing a positive electrode and a 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 nonaqueous electrolyte secondary battery can be obtained by sealing the injection port. Details of each element constituting the non-aqueous electrolyte secondary battery obtained by the manufacturing method are as described above. According to the manufacturing method, by using the nonaqueous electrolyte, it is possible to obtain a nonaqueous electrolyte secondary battery (electric storage element) in which a decrease in discharge capacity after high-temperature storage is suppressed.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be embodied in modes in which various changes and improvements are made in addition to the above-described modes. For example, it is not necessary to provide an intermediate layer in the positive electrode or the negative electrode. Further, in the above-described embodiment, the description has been made mainly on the form in which the electric storage element is a non-aqueous electrolyte secondary battery, but other electric storage elements may be used. As other power storage elements, a capacitor (electric double layer capacitor, lithium ion capacitor) or the like can be given.

  FIG. 1 is a schematic view of a rectangular non-aqueous electrolyte secondary battery 1 which is an embodiment of a power storage device according to the present invention. The figure is a view in which the inside of the container is seen through. In a nonaqueous electrolyte secondary battery 1 shown in FIG. 1, an electrode body 2 is 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 via a separator. The positive electrode is electrically connected to the positive terminal 4 via a positive electrode lead 4 ', and the negative electrode is electrically connected to the negative terminal 5 via a negative lead 5'. Further, the non-aqueous electrolyte according to one embodiment of the present invention is injected into the battery container 3.

  The configuration of the storage element according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square 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. FIG. 2 illustrates an embodiment of a power storage device. 2, power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of non-aqueous electrolyte 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 described more specifically 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. To this, 4-azabenzotriazole was further added in a saturated amount (less than 1% by mass) to obtain a non-aqueous electrolyte of Example 1.

(Production of power storage device)
A positive electrode plate was manufactured using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ having an α-NaFeO ₂ type crystal structure as a positive electrode active material. Further, a negative electrode plate using graphite as a negative electrode active material was produced. Next, the positive electrode plate and the negative electrode plate were laminated via a separator made of a polyethylene microporous membrane, and wound into a flat shape to produce an electrode body. The electrode body was housed in an aluminum rectangular battery case, and a positive electrode terminal and a negative electrode terminal were attached. After injecting the non-aqueous electrolyte into the container (square battery case), the container was sealed to obtain a power storage element (square lithium ion secondary battery having a designed capacity of 850 mAh).

[Examples 2 to 5, Comparative Example 1]
Except that the kind and content of the compound used were as described in Table 1, the nonaqueous electrolytes of Examples 2 to 5 and Comparative Example 1 and the electricity storage element were obtained in the same manner as in Example 1. In addition, each compound was added so as to have a content of 1% by mass. When the compound was not completely dissolved, insoluble components were removed by filtration. "Saturated dissolution" in the column of "content" in Table 1 indicates that the content is the saturated dissolution amount, that is, the content is less than 1% by mass.

[Evaluation]
(High temperature storage test)
With respect to each of the obtained electric storage elements, the initial charge / discharge was performed twice at a charge end voltage of 4.35V. The positive electrode potential at the charging end voltage at this time was about 4.45 V (vs. Li / Li ⁺ ). At the first time, the battery was charged at a constant current of 170 mA up to 4.35 V at 25 ° C., and then charged at a constant voltage of 4.35 V. The condition for terminating the charging was until the total charging time reached 8 hours. After a pause of 10 minutes after charging, the battery was discharged at 25 ° C. to 2.75 V at a constant current of 170 mA. The second time, the battery was charged at a constant current of 170 mA up to 4.35 V at 25 ° C., and then was charged at a constant voltage of 4.35 V. The condition for terminating the charging was until the total charging time reached 8 hours. After a pause of 10 minutes after charging, the battery was discharged at 25 ° C. to 2.75 V at a constant current of 850 mA. The second discharge capacity was defined as “initial discharge capacity”.
Next, the battery was charged at a constant current of 850 mA up to 4.35 V at 25 ° C., and then charged at a constant voltage of 4.35 V. The condition for terminating the charging was until the total charging time became 3 hours. Thereafter, a high-temperature storage test was performed at 45 ° C. for 180 days. Thereafter, the following capacity maintenance rate, discharge capacity recovery rate, and DCR increase rate were evaluated. Table 1 shows the results of these evaluations.

(Capacity maintenance rate)
The storage element after the high-temperature storage test was held at 25 ° C. for 4 hours or more, and then discharged at 25 ° C. to 2.75 V at a constant current of 850 mA. The discharge capacity at this time was defined as “remaining discharge capacity”. The ratio of the remaining discharge capacity to the initial discharge capacity was determined as “capacity maintenance rate (%)”.

(Discharge capacity recovery rate)
After the measurement of the remaining discharge capacity, each storage element was charged at 25 ° C. at a constant current of 850 mA to 4.35 V, and then charged at a constant voltage of 4.35 V. The termination condition of the charging was set until the total charging time became 3 hours. After a pause of 10 minutes, the battery was discharged at 25 ° C. to 2.75 V at a constant current of 850 mA. The discharge capacity at this time was defined as “recovery discharge capacity”. The ratio of the recovery discharge capacity to the initial discharge capacity was determined as “discharge capacity recovery rate (%)”.

(DCR increase rate)
The DCR (DC resistance) before the start of the high-temperature storage test and the DCR of the storage element after the execution of the high-temperature storage test were evaluated. After the measurement of the initial discharge capacity and the measurement of the recovery discharge capacity, each of the storage elements was charged at a constant current of 850 mA up to 3.70 V at 25 ° C., and then charged at a constant voltage of 3.70 V. The termination condition of the charging was set until the total charging time became 3 hours. After setting the SOC (State of Charge) of the battery to 50% under the above conditions, the battery was discharged at current values of 170 mA, 425 mA, and 850 mA for 10 seconds, and the voltage at 10 seconds after the start of discharge was plotted on the vertical axis, and the discharge current value was plotted horizontally. From a graph of the current-voltage characteristics obtained by plotting on the axis, a DCR (direct current resistance) value corresponding to the gradient was obtained. Then, the ratio of “DCR after high-temperature storage test” to “DCR before high-temperature storage test” (“DCR after high-temperature storage test” / “DCR before high-temperature storage test”) is calculated, and “DCR Increase rate (%) "was obtained.

  As shown in Table 1 above, in Comparative Examples 1 containing 1,2,3-benzotriazole, in Examples 1 to 5 containing the compound of the present invention, the capacity retention of the electricity storage element after high-temperature storage was observed. And the discharge capacity recovery rate were good. In particular, Examples 1 and 2 containing the compound represented by the above formula (1) are excellent in the capacity retention rate and the discharge capacity recovery rate after high-temperature storage of the storage element, and also excellent in the DCR increase suppression effect. Was.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a power storage element including a non-aqueous electrolyte such as a non-aqueous electrolyte secondary battery used as a power source for a personal computer, an electronic device such as a communication terminal, a car, and the like, and a non-aqueous electrolyte included in the storage element. .

(Explanation of symbols)
DESCRIPTION OF SYMBOLS 1 Non-aqueous electrolyte secondary battery 2 Electrode body 3 Battery case 4 Positive terminal 4 'Positive lead 5 Negative terminal 5' Negative lead 20 Power storage unit 30 Power storage device

Claims (6)

A non-aqueous electrolyte containing a compound represented by the following formula (1) or (2).

(In the formula (1), R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a nitro group, a sulfonic group, a thiol group, a phosphate group, In the formula (2), R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent a hydrogen atom, a halogen atom, a hydroxy group, an amino group, or a monovalent organic group or a monovalent ionic group. A nitro group, a sulfonic group, a thiol group, a phosphate group, a monovalent organic group or a monovalent ionic group.) The compound is represented by the formula (1), wherein R ¹ is a hydrogen atom or an electron-withdrawing group, and R ² , R ³ , and R ⁴ are hydrogen atoms, or the compound is The non-aqueous electrolyte according to claim 1, wherein R ⁵ is an electron-withdrawing group, and R ⁶ , R ^7, and R ⁸ are hydrogen atoms.   The compound is 4-azabenzotriazole (1H-1,2,3-triazolo [4,5-b] pyridine), 1-acetyl-1H-1,2,3-triazolo [4,5-b] pyridine 3. The non-aqueous electrolyte according to claim 2, which is a combination thereof.   An electric storage device comprising the non-aqueous electrolyte according to claim 1. The power storage device according to claim 4, wherein a positive electrode potential at a charge end voltage in normal use is 4.4 V (vs. Li ^/ Li ⁺ ) or more.   A method for manufacturing a power storage device using the non-aqueous electrolyte according to claim 1.

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