TITLE OF THE INVENTION: NONAQUEOUS ELECTROLYTE,

NONAQUEOUS ELECTROLYTE ENERGY STORAGE DEVICE, AND METHOD FOR PRODUCING NONAQUEOUS ELECTROLYTE ENERGY STORAGE DEVICE

TECHNICAL FIELD

[0001]

The present invention relates to a nonaqueous electrolyte, a nonaqueous electrolyte energy storage device, and a method for producing a nonaqueous electrolyte energy storage device.

BACKGROUND ART

[0002]

Nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used for electronic devices such as personal computers and communication terminals, automobiles, and the like because of their high energy density. The nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a nonaqueous electrolyte interposed between the electrodes, and is configured to perform charge- discharge by delivering ions between the electrodes. Capacitors such as lithium ion capacitors and electric double layer capacitors are widely used as nonaqueous electrolyte energy storage device other than nonaqueous electrolyte secondary batteries.

[0003]

Various additives are added to the nonaqueous electrolyte of the nonaqueous electrolyte energy storage device for the purpose of improving performance and the like. For example, Patent Document 1 proposes a nonaqueous electrolyte battery to which phenylsilane or the like is added in order to suppress expansion of a battery at high-temperature storage. In Patent Document 2, an electrolytic solution for a secondary battery to which phenylacetylene (ethynylbenzene) is added to improve cycle characteristics and the like has been proposed.

PRIOR ART DOCUMENT PATENT DOCUMENT

[0004]

Patent Document l: JP-A-2008-210769

Patent Document 2- JP-A-2000- 195545

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005]

In the nonaqueous electrolyte energy storage device, it is desirable that good performance is maintained by repetition of charge-discharge. For example, in the nonaqueous electrolyte energy storage device, coulombic efficiency is usually improved associated with a charge-discharge cycle. The reason for this is presumably that a coating film is formed on the surface of the negative electrode due to the reductive decomposition of the nonaqueous electrolyte generated on the surface of the negative electrode, and a decomposition reaction of the nonaqueous electrolyte is gradually suppressed. However, the coulombic efficiency after repeated charge- discharge at a high voltage, specifically, at such a high voltage that the positive electrode potential at the end-of-charge voltage is 4.4 V (vs. Li/Li ⁺ ) or more or the like shows a low value. Even when the nonaqueous electrolyte to which conventional additives were added, such as the above- mentioned phenylsilane and phenylacetylene, is used, the coulombic efficiency after the charge-discharge cycles at a high voltage is not adequately improved, and it may become lower rather than the case where these additives were not added.

[0006]

The present invention has been made based on the above

circumstances, and it is an object of the present invention to provide a nonaqueous electrolyte capable of enhancing the coulombic efficiency after charge- discharge cycles at a high voltage of a nonaqueous electrolyte energy storage device, a nonaqueous electrolyte energy storage device having high coulombic efficiency after charge- discharges at a high voltage, and a method for producing such a nonaqueous electrolyte energy storage device.

MEANS FOR SOLVING THE PROBLEMS

[0007]

One embodiment of the present invention made to solve the above problem is a nonaqueous electrolyte for an energy storage device containing an aromatic compound having a silyl group or an amino group, and an acetylenediyl group.

[0008]

Another embodiment of the present invention made to solve the above problems is a nonaqueous electrolyte energy storage device including the nonaqueous electrolyte. [0009]

Another embodiment of the present invention made to solve the above problems is a method for producing a nonaqueous electrolyte energy storage device using the nonaqueous electrolyte.

ADVANTAGES OF THE INVENTION

[0010]

According to the present invention, it is possible to provide a nonaqueous electrolyte capable of enhancing the coulombic efficiency after charge- discharge cycles at a high voltage of a nonaqueous electrolyte energy storage device, a nonaqueous electrolyte energy storage device having high coulombic efficiency after charge- discharge cycles at a high voltage, and a method for producing such a nonaqueous electrolyte energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0011]

Fig. 1 is an appearance perspective view showing a nonaqueous electrolyte energy storage device according to an embodiment of the present invention.

Fig. 2 is a schematic view showing an energy storage apparatus configured by assembling a plurality of nonaqueous electrolyte energy storage devices according to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

[0012]

A nonaqueous electrolyte according to one embodiment of the present invention is a nonaqueous electrolyte for an energy storage device containing an aromatic compound having a silyl group or an amino group, and an acetylenediyl group.

[0013]

According to the nonaqueous electrolyte, the coulombic efficiency after charge- discharge cycles at a high voltage of the nonaqueous electrolyte energy storage device can be enhanced. Although the reason for this is not clear, the following reasons are presumed. It is believed that the decrease in coulombic efficiency is caused by a product produced by oxidation decomposition of the nonaqueous electrolyte or the like on the surface of the positive electrode being deposited on the negative electrode and lowering the acceptability of lithium etc. of the negative electrode. In contrast, when an aromatic compound having a silyl group or an amino group, and an acetylenediyl group is added to the nonaqueous electrolyte, it is believed that the coating on the surface of the positive electrode formed by the aromatic compound adequately causes a charge- discharge reaction, and can suppress the side reactions such as oxidative decomposition of other constituent elements contained in the nonaqueous electrolyte. The reason for this is presumed that the electron densities of the aromatic rings are increased by the highly electron-donating silyl group or the amino group and the acetylenediyl group, and the reaction tends to occur, and therefore, a coating film formation of the aromatic compound having the silyl group or the amino group, and the acetylenediyl group precedes oxidative

decomposition of other constituent elements contained in the nonaqueous electrolyte. As a result, it is presumed that the coulombic efficiency after charge- discharge cycles at a high voltage is improved.

[0014] The "silyl group" refers to a group in which a group represented by - S1H3, and a group in which one or more hydrogen atoms of the group represented by the -S1H3 are substituted with a substituent. That is, the "silyl group" refers to both an unsubstituted silyl group and a silyl group having a substituent. The "amino group" refers to a group in which a group represented by -NH2, and a group in which one or more hydrogen atoms of the group represented by the -NH2 are substituted with a substituent.

That is, the "amino group" refers to both an unsubstituted amino group and an amino group having a substituent.

[0015]

It is preferred that the nonaqueous electrolyte further contains an ester having a sultone structure or a cyclic sulfate structure. By further containing the above ester in the nonaqueous electrolyte, the coulombic efficiency after charge-discharge cycles can be further enhanced. The sultone structure means a cyclic sulfonic acid ester (-SO2O-) structure. In addition, the cyclic sulfate structure refers to a cyclic sulfuric acid ester (- OSO2O-) structure.

[0016]

The aromatic compound preferably has the silyl group. In this case, the coulombic efficiency after the charge- discharge cycle at a high voltage can be further enhanced.

[0017]

It is preferred that the silicon atom of the silyl group and the acetylenediyl group are bonded directly to each other. By using an aromatic compound having such a structure, charge- discharge cycle performance can be further improved. For example, the coulombic efficiency after charge-discharge cycles in the case where charge-discharge is performed with the positive electrode potential at the end-of-charge voltage being on the order of 4.3 V (vs. Li/Li ⁺ ), can also be enhanced.

[0018]

It is also preferred that the aromatic compound has the amino group. In this case, for example, the capacity retention ratio after charge- discharge cycles can also be enhanced.

[0019]

The nonaqueous electrolyte energy storage device according to one embodiment of the present invention is a nonaqueous electrolyte energy storage device including the nonaqueous electrolyte. Since the nonaqueous electrolyte energy storage device includes the nonaqueous electrolyte, the coulombic efficiency after charge- discharge cycles at a high voltage is high.

[0020]

A method for producing a nonaqueous electrolyte energy storage device according to one embodiment of the present invention is a method for producing a nonaqueous electrolyte energy storage device using the nonaqueous electrolyte. According to the production method, since the nonaqueous electrolyte is used, it is possible to produce a nonaqueous electrolyte energy storage device having high coulombic efficiency after charge- discharge cycles at a high voltage.

[0021]

Hereinafter, a nonaqueous electrolyte, a nonaqueous electrolyte energy storage device, and a method for producing a nonaqueous electrolyte energy storage device according to one embodiment of the present invention will be described in detail.

[0022]

<Nonaqueous Electrolyte>

The nonaqueous electrolyte contains a nonaqueous solvent, an electrolyte salt, and an aromatic compound having a silyl group or an amino group, and an acetylenediyl group. The nonaqueous electrolyte is used for an energy storage device. It is preferred that the nonaqueous electrolyte further contains an ester having a sultone structure or a cyclic sulfate structure. Incidentally, the nonaqueous electrolyte is not limited to a liquid. That is, the nonaqueous electrolyte is not limited to only liquids, but includes solid and gel-like ones.

[0023]

(Nonaqueous Solvent)

As the nonaqueous solvent, a publicly known nonaqueous solvent commonly used as a nonaqueous solvent of a common nonaqueous electrolyte for an energy storage device can be used. Examples of the nonaqueous solvent include cyclic carbonate, chain carbonate, ester, ether, amide, sulfone, lactone, nitrile and the like. Among these, it is preferred to use at least a cyclic carbonate or a chain carbonate, and it is more preferred to use a cyclic carbonate and a chain carbonate in combination. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio (cyclic carbonate : chain carbonate) of the cyclic carbonate and the chain carbonate is not particularly limited. However, it is preferably set to, for example, 5 : 95 or more and 50 : 50 or less [0024]

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), difluoroethylene carbonate (DFEC), styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, 1,2- diphenylvinylene carbonate, and the like, among which EC is preferred.

[0025]

Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate and the like, among which DMC and EMC are preferred.

[0026]

(Electrolyte Salt)

As the electrolyte salt, a publicly known electrolyte salt commonly used as an electrolyte salt of a common nonaqueous electrolyte for an energy storage device 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 preferred.

[0027]

Examples of the lithium salt include ^: inorganic lithium salts such as LiPF ₆ , LiP0 ₂ F ₂ , LiBF ₄ , LiC10 ₄ and LiN(S0 ₂ F) ₂ ; lithium salts having a fluorinated hydrocarbon group, such as L1SO3CF3, LiN(S0 ₂ CF3) ₂ ,

LiN(S0 ₂ C ₂ F ₅ ) ₂ , LiN(S0 ₂ CF ₃ )(S0 ₂ C ₄ F ₉ ), LiC(S0 ₂ CF ₃ ) ₃ , and LiC(S0 ₂ C ₂ F ₅ ) ₃ ; and the like. Among them, inorganic lithium salts are preferred, and L1PF6 is more preferred. [0028]

The lower limit of the content of the electrolyte salt in the

nonaqueous 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 of the content is not particularly limited; however, it is preferably 2.5 M, more preferably 2 M, and still more preferably 1.5 M.

[0029]

(Aromatic Compound Having Silyl Group or Amino Group, and

Acetylenediyl Group)

By containing the aromatic compound, the nonaqueous electrolyte can enhance the coulombic efficiency after charge- discharge cycles at a high voltage of the nonaqueous electrolyte energy storage device.

[0030]

When the aromatic compound has a silyl group of the silyl group and the amino group, the coulombic efficiency after charge- discharge cycles at a high voltage can be further enhanced. On the other hand, when the aromatic compound has an amino group of the silyl group and the amino group, the capacity retention ratio after charge- discharge cycles can also be increased. Further, when the aromatic compound has the amino group, the coulombic efficiency after charge- discharge cycles in the case of performing charge- discharge at a relatively low voltage can also be enhanced. The aromatic compound may have both the silyl group and the amino group.

[0031]

The silyl group can be represented by -SiR (l). In the formula (l), each R ¹ independently represents a hydrogen atom or an optional substituent. Specific examples of R ¹ include a hydrogen atom, a halogen atom, a hydroxyl group, an amino group, a nitro group, an organic group, and the like. Here, the organic group means a group containing at least one carbon atom.

[0032]

Examples of the organic group include a hydrocarbon group, a group containing a heteroatom- containing group at the carbon- carbon or terminal of the hydrocarbon group, a group obtained by substituting a part or all of the hydrogen atoms of these groups with a substituent, a carboxy group, a cyano group and the like.

[0033]

Examples of the hydrocarbon group include aliphatic chain hydrocarbon groups such as^ alkyl groups such as a methyl group, an ethyl group, a propyl group and a butyl group! alkenyl groups such as an ethenyl group, a propenyl group and a butenyl group! and an alkynyl groups such as an ethynyl group, a propynyl group and a butynyl group, alicyclic

hydrocarbon groups such as^ cycloalkyl groups such as a cyclohexyl group! and cycloalkenyl groups such as cyclohexenyl group, and aromatic hydrocarbon groups such as a phenyl group, a naphthyl group, a biphenyl group, a benzyl group, and a phenylethynyl group (-C≡C-cp ^: φ is a phenyl group).

[0034]

Examples of the hetero atom- containing group include ^:

groups consisting solely of hetero atoms such as -0-, -S-, -SO", -SO2 -, - groups in which carbon atoms and hetero atoms are combined, such as -CO-, -COO-, -COS-, -CONH-, -OCOO-, -OCOS-, -OCONH-, -SCONH-, -SCSNH-, - SCSS-.

[0035]

Examples of the substituent include a halogen atom, a hydroxy group, a carboxy group, a nitro group, and a cyano group.

[0036]

As the R ¹ , an organic group is preferred, and a hydrocarbon group is more preferred. The hydrocarbon group is preferably a hydrocarbon group having 1 to 10 carbon atoms. More specifically, an alkyl group having 1 to 3 carbon atoms, a phenyl group, and a phenylethynyl group are preferred. All the three R ¹ s are preferably organic groups, and more preferably hydrocarbon groups.

[0037]

The number of silyl groups (silicon atoms) of the aromatic compound is not particularly limited. The number of silyl groups of the aromatic compound may be 1 or plural, but is usually 1.

[0038]

The above amino group can be represented by -NR¾ (2). In the formula (2), each R ² is independently a hydrogen atom or an optional substituent. Specific examples of R ² include a hydrogen atom, a halogen atom, a hydroxy group, an amino group, a nitro group, an organic group, and the like. Specific examples of the organic group are as described above.

[0039]

The R ² is preferably a hydrogen atom. When the aromatic compound has a group represented by -NH2, the capacity retention ratio and the coulombic efficiency after charge- discharge cycles can be further enhanced.

[0040]

The number of amino groups (nitrogen atoms) of the aromatic compound is not particularly limited. The number of amino groups of the aromatic compound may be 1 or plural, but it is usually 1.

[0041]

The aromatic compound has an acetylenediyl group (ethynediyl group! -C≡0). Further, the acetylenediyl group may be contained in the substituent of the silyl group or the amino group. The acetylenediyl group may be bonded directly to the silicon atom of the silyl group or the nitrogen atom of the amino group, or it may not be bonded directly to the silicon atom or the nitrogen atom. The acetylenediyl group is preferably directly bonded to the aromatic ring.

[0042]

The number of acetylenediyl groups of the aromatic compound is not particularly limited. The number of acetylenediyl groups of the aromatic compound may be 1 or plural, but it is preferably 1 or 2.

[0043]

The above aromatic compound refers to a compound containing an aromatic ring. The aromatic ring may be a carbocyclic ring (aromatic carbocyclic ring) or a heterocyclic ring (aromatic heterocyclic ring).

Examples of the aromatic carbocyclic ring include a benzene ring, a naphthalene ring, an anthracene ring and the like. Examples of the aromatic heterocyclic ring include a furan ring, a thiophene ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring and the like. A part or all of the hydrogen atoms of these aromatic rings may be substituted with a substituent. As the aromatic ring, an aromatic carbon ring is preferred, and a benzene ring is more preferred.

[0044]

It is preferred that at least one of the silyl group or the amino group, or the acetylenediyl group is bonded directly to the aromatic ring. This further enhances the reactivity of the aromatic compound.

[0045]

When the aromatic compound has a silyl group, it is preferred that the silicon atom of the silyl group and the acetylenediyl group are bonded directly to each other. That is, it is particularly preferred that the aromatic compound has a partial structure represented by S C≡C ^_ R ³ (R ³ represents an aromatic ring). By using the aromatic compound having such a partial structure, the coulombic efficiency can be enhanced not only after charge- discharge cycle at a high voltage but also after charge- discharge cycle under a condition of not a high voltage. An example of such an aromatic compound can be represented by SiRVC≡C-cp (R ¹ has the same meaning as R ¹ in the formula (l), and φ is a phenyl group).

[0046]

On the other hand, an example of an aromatic compound in which the silicon atom of the silyl group is not bonded directly to the acetylenediyl group can be represented by SiRVR ⁴ -C≡C-(p (R ¹ has the same meaning as R ¹ in the formula (l), R ⁴ is a divalent hydrocarbon group, and φ is a phenyl group). Examples of the divalent hydrocarbon group include a

methanediyl group, an ethanediyl group, a benzenediyl group (phenylene group) and the like, and a benzenediyl group is preferred. The number of carbon atoms of the divalent hydrocarbon group is preferably 1 to 10, for example.

[0047]

When the aromatic compound has an amino group, one example of such an aromatic compound can be represented by NRVcp ^_ C≡C-R ⁵ (R ² has the same meaning as R ² in the formula (2), R ⁵ is a hydrogen atom or a monovalent hydrocarbon group, and φ is a benzenediyl group). The number of carbon atoms of the monovalent hydrocarbon group represented by the R ⁵ is, for example, preferably 1 to 10, and more preferably 1 to 3. The R ⁵ is preferably a hydrogen atom.

[0048]

Examples of the aromatic compound having a silyl group and an acetylenediyl group include phenylethynyl trimethylsilane, phenylethynyl triethylsilane, naphthylethynyl trimethylsilane, 4- (trimethylsilyl)diphenylacetylene, dimethylbis(phenylethynyl)silane, diphenylbis(phenylethynyl)silane, and the like.

[0049]

Examples of the aromatic compound having an amino group and an acetylenediyl group include ethynylaniline, 4-(phenylethynyl)aniline, N,N- dimethylethynylaniline, N,N-dimethyl-4-(l-propynyl)aniline, 2- ((trimethylsilyl)ethynyl)aniline, 3-((trimethylsilyl)ethynyl)aniline, 2,5- diethynylaniline, 2-ethynyl-4-aminotoluene, 2-phenylethynyl-phenylamine, 3,3'-(buta-l,3-diyne-l,4-diyl)dianiline, 4-((4- ((trimethylsilyl)ethynyl)phenyl)ethynyl)aniline, and the like.

[0050]

The lower limit of the content of the aromatic compound in the nonaqueous electrolyte is preferably 0.01% by mass, more preferably 0.05% by mass, and still more preferably 0.1% by mass. On the other hand, the upper limit of the content is preferably, for example, 5% by mass, preferably 3% by mass, and more preferably 1% by mass. By setting the content of the aromatic compound to the above-mentioned lower limit or more and the above-mentioned upper limit or less, the coulombic efficiency after charge- discharge cycles at a high voltage of the nonaqueous electrolyte energy storage device can be further enhanced.

[0051]

(Ester Having Sultone Structure or Cyclic Sulfate Structure)

When the nonaqueous electrolyte further contains the above esters, it is possible to further enhance the coulombic efficiency after charge- discharge cycles at a high voltage of the nonaqueous electrolyte energy storage device. As the above-mentioned esters, esters having a cyclic sulfate structure are more preferred since the above-mentioned effect is further increased.

[0052]

The number of carbon atoms of the ester can be, for example, 2 to 10. The number of ring members of the sultone structure and the cyclic sulfate structure can be, for example, 4 to 6, and is preferably a five-membered ring.

[0053]

Examples of the ester having the sultone structure include 1,3- propanesultone, 1,4-butanesultone, 2,4-butanesultone, 1,3-propenesultone, 1,4-butenesultone, l-methyl-l,3-propanesultone, 3-methyl-l,3- propanesultone, l-fluoro-l,3-propanesultone, 3-fluoro-l,3-propanesultone, methylene methane disulfonic acid ester and the like. As the ester having the sultone structure, unsaturated sultone is preferred, and 1,3- propenesultone is more preferred.

[0054]

Esters having the cyclic sulfate structure include ethylene sulfate, 4- methyl"2,2-dioxo- 1,3,2-dioxathiolane, 4-ethyl-2,2-dioxo- 1,3,2-dioxathiolane, 4-propyl"2,2-dioxo- 1,3,2-dioxathiolane, 4-methylsulfonyloxymethyl-2,2- dioxo- 1,3,2-dioxathiolane, 4-ethylsulfonyloxymethyl-2,2- 1,3,2- dioxathiolane, bis((2,2-dioxo-l,3,2-dioxathiolane-4-yl)methyl)sulfate, 4,4'- bis(2,2-dioxo- 1,3,2-dioxathiolane) and the like. As the ester having a cyclic sulfate structure, a compound having a plurality of sulfate structures is preferred, a compound having a plurality of cyclic sulfate structures is more preferred, and 4, 4'-bis(2,2-dioxo- 1,3,2-dioxathiolane) is further preferred.

[0055]

The lower limit of the content of the ester in the nonaqueous electrolyte is preferably 0.05% by mass, more preferably 0.2% by mass, and still more preferably 0.5% by mass. On the other hand, the upper limit of the content is preferably, for example, 10% by mass, preferably 5 mass%, and more preferably 3% by mass. By setting the content of the ester to the above-mentioned lower limit or more and the above-mentioned upper limit or less, the coulombic efficiency after charge- discharge cycles can be further enhanced.

[0056]

(Additive)

As long as the effect of the present invention is not impaired, the nonaqueous electrolyte may further contains, as an additive, a component other than the nonaqueous solvent, the electrolyte salt, the aromatic compound having a silyl group or an amino group, and an acetylenediyl group, and the ester having a sultone structure or a cyclic sulfate structure. As the additive, various additives contained in a common nonaqueous electrolyte for an energy storage device can be mentioned. The upper limit of the content of the additive in the nonaqueous electrolyte is preferably 5% by mass, and sometimes more preferably 1% by mass, more preferably 0.4% by mass, and still more preferably 0.1% by mass. These additives may affect various performances of the charge- discharge cycle.

[0057]

The nonaqueous electrolyte can be usually obtained by adding components such as an electrolyte salt and an aromatic compound having a silyl group or an amino group, and an acetylenediyl group to the

nonaqueous solvent and dissolving them.

[0058]

<Nonaqueous Electrolyte Energy Storage Device>

A nonaqueous electrolyte energy storage device according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. Hereinafter, a

nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte energy storage device. In general, the positive electrode and the negative electrode form an electrode assembly which is alternately superimposed by lamination or winding with a separator interposed between the positive electrode and the negative electrode. The electrode assembly is housed in a case, and the nonaqueous electrolyte is filled in the case. As the nonaqueous electrolyte, the above-mentioned nonaqueous electrolyte according to one embodiment of the present invention is used. The nonaqueous electrolyte is interposed between the positive electrode and the negative electrode. As the case, it is possible to use a publicly known metal case, resin case, or the like which is commonly used as a case of a nonaqueous electrolyte secondary battery. Hereinafter, constituent elements of the nonaqueous electrolyte secondary battery other than the nonaqueous electrolyte will be described.

[0059]

<Positive Electrode>

The positive electrode has a positive substrate and a positive active material layer disposed directly or with an intermediate layer interposed therebetween on the positive substrate.

[0060]

The positive substrate has conductivity. As a material of the substrate, metals such as aluminum, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and an aluminum alloy are preferred from the viewpoint of balance among an electric potential resistance, high conductivity and a cost. Further, examples of the formation form of the positive substrate include a foil, a vapor deposition film, and the like, and from the viewpoint of cost, a foil is preferred. That is, an aluminum foil is preferred as the positive substrate. Examples of aluminum or aluminum alloy include A1085P, A3003P, and the like prescribed in JIS H 4000 (2014).

[0061]

The intermediate layer is a coating layer on the surface of the positive substrate, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive substrate and the positive active material layer. The constitution of the intermediate layer is not particularly limited, and it can be formed, for example, from a composition containing a resin binder and conductive particles. In addition, "having conductivity" means that the volume resistivity measured in accordance with JIS H 0505 (1975) is 10 ⁷ Q'cm or less, and "non- conductive" means that the volume resistivity is more than 10 ⁷ Ω·οηι.

[0062]

The positive active material layer is formed of a so-called positive composite containing a positive active material. The positive composite for forming the positive active material layer contains optional components such as a conductive agent, a binder, a thickener, a filler and the like, as required.

[0063]

Examples of the positive active material include composite oxides (Li _x Co02, Li _x Ni02, Li _x Mn03, Li _x Ni _a Co(i- _a )02, Li _x Ni _a CopAl(i- _a -p)02, LixNi _a MnpCo(i-a-p)02, Lii+ _x (Ni _a MnpCo(i- _a -p))i- _x 02, and the like having a layered orNaFe02 type crystal structure, Li _x Mn204, Li _x Ni _a Mn(2- _a )04, and the like having a spinel type crystal structure) represented by Li _x MO _y (M represents at least one kind of transition metal), and polyanion compounds (LiFeP0 ₄ , LiMnP0 ₄ , LiNiP0 ₄ , LiCoP0 ₄ , Li ₃ V ₂ (P0 ₄ ) ₃ , Li ₂ MnSi0 ₄ ,

Li2CoP0 ₄ F, and the like) represented by Li _w Me _x (XOy) _z (Me represents at least one transition metal, and X represents, for example, P, Si, B, V, and the like). Elements or polyanions in these compounds may be partially substituted with other elements or anionic species. In the positive active material layer, one of these compounds may be used alone, or two or more of these compounds may be used in a mixture.

[0064]

The positive active material preferably contains a positive active material which can make the positive electrode potential at the end-of- charge voltage during normal use of the nonaqueous electrolyte secondary battery nobler than 4.4 V (vs. Li/Li ⁺ ). Since the nonaqueous electrolyte secondary battery (energy storage device) includes the nonaqueous electrolyte, the coulombic efficiency after charge- discharge cycles at a high voltage is high. Accordingly, by using a positive active material which can be a potential nobler than 4.4 V (vs. Li/Li ⁺ ), a nonaqueous electrolyte secondary battery having increased energy density and high coulombic efficiency after charge-discharge cycles can be formed.

[0065]

The positive active material whose positive electrode potential at the end-of-charge voltage during normal use can be nobler than 4.4 V (vs. Li/Li ⁺ ) may be a positive active material capable of inserting and removing reversible lithium ion after reaching a potential nobler than 4.4 V (vs.

Li/Li ⁺ ) Examples of such a positive active material include ^:

Lii+x(Ni _a Mn Co(i-a- ))i-x02 (x > 0, β > 0.5) having a layered orNaFeO2 type crystal structure! LiNio.5Mn1.5O4 which is an example of Li _x Ni _a Mn(2- _a )O4 having a spinel type crystal structure! LiNiPO4, L1C0PO4, L12C0PO4F or Li2MnSiO4 which is an example of a polyanion compound! and the like.

[0066]

Here, the case of "during normal use" means a case where the nonaqueous electrolyte secondary battery is used by adopting the charging condition recommended for or designated to the nonaqueous electrolyte secondary battery, and when a charger for the nonaqueous electrolyte secondary battery is prepared, the case means a case where the nonaqueous electrolyte secondary battery is used by applying the charger. For example, in a nonaqueous electrolyte secondary battery using graphite as a negative active material, the positive electrode potential is about 4.45 V (vs. Li/Li ⁺ ) when the end-of-charge voltage is 4.35 V although it depends on the design.

[0067]

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 a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black and Ketjen black, metal, conductive ceramics, and the like, and the acetylene black is preferred.

Examples of a shape of the conductive agent include powder, fiber, or the like. [0068]

Examples of the binder include ^: thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride

(PVDF), etc.), polyethylene, polypropylene, polyimide and the like! elastomers such as ethylene-propylene- diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluorine rubber and the like! polysaccharide polymers! and the like.

[0069]

Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group which reacts with lithium, it is preferred to

previously deactivate the functional group by methylation or the like.

[0070]

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

[0071]

<Negative Electrode>

The negative electrode has a negative substrate and a negative active material layer disposed directly or with an intermediate layer interposed therebetween on the negative substrate. The intermediate layer can have the same structure as the intermediate layer of the positive electrode.

[0072] The negative substrate may have the same structure as that of the positive substrate. However, as a material of the negative substrate, a metal such as copper, nickel, stainless steel or nickel-plated steel, or an alloy thereof is used, and copper or a copper alloy is preferred. That is, a copper foil is preferred as the negative substrate. As the copper foil, a rolled copper foil, an electrolytic copper foil, and the like are exemplified.

[0073]

The negative active material layer is formed of a so-called negative composite containing a negative active material. The negative composite for forming the negative active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as required. As optional components such as a conductive agent, a binder, a thickener, and a filler, the same materials as those of the positive active material layer can be used.

[0074]

As the negative active material, a material which can absorb and release lithium ions is usually used. Specific examples of the negative active material include ^: metals or semi-metals such as Si and Sn! metal oxides or semi-metal oxides such as Si oxide and Sn oxide! polyphosphate compounds! carbon materials such as graphite and amorphous carbon (graphitizable carbon or non-graphitizable carbon); and the like.

[0075]

Further, the negative composite (negative active material layer) may contain: a typical nonmetallic element such as B, N, P, F, CI, Br and L a typical metallic element such as Li, Na, Mg, Al, K, Ca, Zn, Ga and Ge! or a transition metal element such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr,

Ta, Hf, Nb or W.

[0076]

<Separator>

As a material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film or the like is used. Among them, a porous resin film is preferred from the viewpoint of strength, and a nonwoven fabric is preferred from the viewpoint of a liquid retaining property of the nonaqueous electrolyte. From the viewpoint of strength, polyolefins such as polyethylene and polypropylene are preferred as a main component of the separator, and polyimide, aramid or the like are preferred from the viewpoint of resistance to oxidation decomposition. Further, these resins may be combined.

[0077]

In addition, an inorganic layer may be provided between the separator and the electrode (usually, the positive electrode). The inorganic layer is a porous layer also called a heat resistant layer or the like. A separator having an inorganic layer formed on one surface of a porous resin film can also be used. The inorganic layer is usually composed of inorganic particles and a binder, and other components may be contained.

[0078]

<Maximum Achieved Potential>

The nonaqueous electrolyte energy storage device (secondary battery) can be used with the maximum achieved potential of the positive electrode charged to 4.4 V (vs. Li/Li ⁺ ) or more. The maximum achieved potential of the positive electrode may be 4.45 V (vs. Li/Li ⁺ ) or more. As described above, since the maximum achieved potential of the positive electrode is high, high energy density can be achieved. In addition, according to the nonaqueous electrolyte secondary battery, the coulombic efficiency after the charge-discharge cycle is high even when it is used with the maximum achieved potential of the positive electrode being 4.4 V (vs. Li/Li ⁺ ) or more. The upper limit of the maximum achieved potential of the positive electrode is, for example, 5.0 V (vs. Li/Li ⁺ ), and may be 4.8 V (vs. Li/Li ⁺ ) or may be 4.6 V (vs. Li/Li ⁺ ). Further, the maximum achieved potential of the positive electrode may be the positive electrode potential at the end-of-charge voltage during normal use.

[0079]

<Method for Producing Nonaqueous Electrolyte Energy Storage Device> A method for producing a nonaqueous electrolyte energy storage device according to one embodiment of the present invention is a method for producing a nonaqueous electrolyte energy storage device using the nonaqueous electrolyte. The production method is not particularly limited except that a nonaqueous electrolyte containing an aromatic compound having a silyl group or an amino group, and an acetylenediyl group is used. In the case of the above- described nonaqueous electrolyte secondary battery, the above production method includes, for example, a step of preparing a positive electrode, a step of preparing a negative electrode, a step of preparing a nonaqueous electrolyte, a step of forming an electrode assembly alternately superimposed by laminating or winding a positive electrode and a negative electrode with a separator interposed therebetween, a step of housing the positive electrode and the negative electrode (electrode assembly) in a container, and a step of injecting the nonaqueous electrolyte into the container. After injection, a nonaqueous electrolyte secondary battery can be produced by sealing an injection hole.

[0080]

<Other Embodiments>

The present invention is not limited to the above-mentioned embodiment, but may be implemented in aspects with various modifications and improvements besides the above embodiment. For example, in the positive electrode and the negative electrode, it is not necessary to provide the intermediate layer, and it may not have a definite layer structure. For example, the positive electrode and the negative electrode may have a structure in which an active material is supported on a mesh-like substrate, or the like. Further, in the above-mentioned embodiment, an aspect in which the nonaqueous electrolyte energy storage device is a nonaqueous electrolyte secondary battery has been chiefly described, but other nonaqueous electrolyte energy storage devices may be used. Examples of other nonaqueous electrolyte energy storage devices include capacitors (electric double-layer capacitors, lithium ion capacitors), and the like.

[0081]

Fig. 1 shows a schematic view of a rectangular nonaqueous electrolyte energy storage device 1 (nonaqueous electrolyte secondary battery) of an embodiment of the nonaqueous electrolyte energy storage device according to the present invention. Fig. 1 is a perspective view of the inside of a container. In the nonaqueous electrolyte energy storage device 1 shown in Fig. 1, an electrode assembly 2 is housed in a container 3. The electrode assembly 2 is configured by winding a positive electrode including a positive active material and a negative electrode including a negative active material with a separator interposed therebetween. The positive electrode is electrically connected to a positive electrode terminal 4 through a positive electrode lead 4', and the negative electrode is electrically connected to a negative electrode terminal 5 through a negative electrode lead 5'.

[0082]

Further, the configuration of the nonaqueous electrolyte energy storage device according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as an energy storage apparatus having a plurality of the nonaqueous electrolyte energy storage devices. An embodiment of the energy storage apparatus is shown in Fig. 2. In Fig. 2, the energy storage apparatus 30 includes a plurality of energy storage units 20. Each of the energy storage units 20 includes a plurality of nonaqueous electrolyte energy storage devices 1. The energy storage apparatus 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid automobiles (HEV), plug-in hybrid automobiles (PHEV) and the like.

EXAMPLES

[0083]

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

[0084]

The additives used in Examples and Comparative Examples are shown below.

(Aromatic Compound)

Aromatic compound A: Phenylethynyl trimethylsilane represented by the following formula (A)

Aromatic compound B: 4-(trimethylsilyl)diphenylacetylene represented by the following formula (B)

Aromatic compound C ^: Dimethylbis(phenylethynyl)silane

represented by the following formula (C)

Aromatic compound D: Dipheny Ibis (phenylethynyl) silane

represented by the following formula (D)

Aromatic compound E: Ethynylaniline represented by the following formula (E)

Aromatic compound X: Ethynylbenzene represented by the following formula (X)

Aromatic compound Y- Phenylsilane represented by the following formula (Y)

[0085]

[Chem. Formula l]

(A) (B)

(C) ( D)

[0086]

(Ester Having Sultone Structure or Cyclic Sulfate Structure)

Ester a'- 4,4'-bis(2,2-dioxo-l,3,2-dioxathiolane) represented by the following formula (a)

[0087]

[Chem. Formula 2]

( a )

[0088]

[Example l]

(Preparation of Nonaqueous Electrolyte)

LiPF6 as an electrolyte salt was dissolved at a concentration of 1.2 mol/L in a nonaqueous solvent in which EC, DMC and EMC were mixed in a volume ratio of 30 : 40 : 30, and to the resulting mixture, 0.5% by mass of the aromatic compound A and 1% by mass of the ester a were added to prepare a nonaqueous electrolyte of Example 1.

[0089]

(Production of Positive Electrode Plate)

Li _x Ni _a Co Al(i-a- )02 was used as a positive active material. A positive electrode paste containing the positive active material,

polyvinylidene fluoride (PVdF) and acetylene black (AB) in proportions of 90 ^: 5 ^: 5 by mass (on solid equivalent basis), and using N-methylpyrrolidone as a dispersion medium, was prepared. The positive electrode paste was applied onto both surfaces of a band-shaped aluminum foil as a positive substrate so that the positive active material was contained in an amount of 15 mg/cm ² per unit electrode area. This was pressed by a roller press machine to form the positive active material layer, and then dried under reduced pressure at 100°C for 10 hours to remove the liquid content in the electrode plate. In this manner, a positive electrode plate was prepared.

[0090]

(Production of Negative Electrode Plate)

Graphite was used as a negative active material. A negative electrode paste containing graphite, styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in proportions of 96 : 2 : 2 by mass (on solid equivalent basis), and using water as a dispersion medium, was prepared. The negative electrode paste was applied to both surfaces of a band-like copper foil as a negative substrate so as to contain the negative active material in an amount of 10.0 mg/cm ² per unit electrode area. This was pressed by a roller press machine to form a negative active material layer, and then dried under reduced pressure at 100° C for 12 hours to remove moisture in the electrode plate. In this way, a negative electrode plate was obtained.

[0091]

(Production of Nonaqueous Electrolyte Energy Storage Device)

As a separator, a microporous polyolefin membrane having an inorganic layer formed on its surface was used. The positive electrode plate and the negative electrode plate were laminated with the separator interposed therebetween to produce an electrode assembly. The electrode assembly was housed in a metal-resin composite film case, the nonaqueous electrolyte was injected into the case, and then the electrode assembly was sealed by heat welding to obtain a nonaqueous electrolyte energy storage device (secondary battery) of Example 1.

[0092]

[Examples 2 to 5, Comparative Examples 1 to 3]

Nonaqueous electrolyte energy storage devices of Examples 2 to 5 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1 except that the aromatic compound having the type and the amount shown in Table 1 was added as the aromatic compound or no aromatic compound was added. In Table 1, " ^■ " indicates that no additive is added.

[0093]

[Example 6, Comparative Example 4]

Nonaqueous electrolyte energy storage devices of Example 6 and Comparative Example 4 were obtained in the same manner as in Example 1 except that a nonaqueous solvent in which EC and EMC were mixed at a volume ratio of 20 ^: 80 was used, and the aromatic compound having the type and the amount shown in Table 2 was added or no aromatic compound was added. In Table 2, "-" indicates that no additive was added.

[0094]

[Evaluation]

(Charge-Discharge Cycle Test: 4.35 V)

The nonaqueous electrolyte energy storage devices of Examples 1 to 6 and Comparative Examples 1 to 4 were used and the following cycle test was conducted. At 45°C, the battery was charged at constant current and constant voltage with a charge current of 1.0 C and an end-of-charge voltage of 4.35 V. The termination condition of the charge was made until the total charging time reached 3 hours. Thereafter, a rest period of 10 minutes was provided. Thereafter, a constant current discharge was performed with a discharge current of 1.0 C and an end-of-discharge voltage of 2.50 V, and then a rest period of 10 minutes was provided. This charge- discharge was performed for 50 cycles. In addition, the positive electrode potential (maximum achieved potential of the positive electrode) at the end-of-charge voltage in the charge- discharge cycle test using graphite as the negative electrode is about 4.45 V (vs. Li/Li ⁺ ).

[0095]

After the cycle test, the capacity check test was conducted under the following conditions. The battery was charged at a constant current of 1.0 C up to 4.35 V at 25°C and then charged at a constant voltage of 4.35 V. The termination condition of the charge was made until the total charging time reached 3 hours. After a 10-minute rest period after charging, constant current discharge was carried out at 1.0 C to 2.50 V at 25°C.

Thereby, coulombic efficiency (%) was determined by measuring an amount of charge and a discharge capacity and dividing the discharge capacity by the amount of charge. The obtained coulombic efficiency is shown in Tables 1 and 2.

[0096]

(Charge-Discharge Cycle Test: 4.20 V)

Using each of the nonaqueous electrolyte energy storage devices of Examples 1 to 5 and Comparative Examples 1 to 3, a capacity check test was conducted under the following conditions before the cycle test. The battery was charged at a constant current of 1.0 C up to 4.20 V at 25°C and then charged at a constant voltage of 4.20 V. The termination condition of the charge was made until the total charging time reached 3 hours. After a 10-minute rest period after charging, constant current discharge was carried out at 1.0 C to 2.50 V at 25°C. Thereby, the discharge capacity was measured.

[0097]

Next, the following cycle test was conducted. At 45°C, the battery was charged at constant current and constant voltage with a charge current of 1.0 C and an end-of-charge voltage of 4.20 V. The termination condition of the charge was made until the total charging time reached 3 hours.

Thereafter, a rest period of 10 minutes was provided. Thereafter, a constant current discharge was performed with a discharge current of 1.0 C and an end-of-discharge voltage of 2.50 V, and then a rest period of 10 minutes was provided. This charge- discharge was performed for 500 cycles. The positive electrode potential (maximum achieved potential of the positive electrode) at the end-of-charge voltage in the charge- discharge cycle test using graphite as the negative electrode was about 4.30 V (vs. Li/Li ⁺ ).

[0098]

After the cycle test, the capacity check test was conducted under the same conditions as before the cycle test. As the capacity retention ratio (%), the ratio of the discharge capacity after the cycle test to the discharge capacity before the cycle test was determined. Also, the coulombic efficiency (%) after the cycle test was determined. These are shown in Tables 1 and 2. [0099]

[Table l]

[0100]

[Table 2]

[0101]

As shown in the above Tables 1 and 2, in Examples 1 to 6 using aromatic compounds A to E having a silyl group or an amino group, and an acetylenediyl group, the coulombic efficiency after charge- discharge cycles at 4.35 V (maximum achieved potential of the positive electrode^ about 4.45 V (vs. Li/Li ⁺ )) exceeds 60%. On the other hand, in Comparative Examples 1 and 2 in which the aromatic compounds were not added, and Comparative Examples 2 and 3 in which the aromatic compounds X and Y having only one of the silyl group or the amino group and the acetylenediyl group were used, the coulombic efficiency after charge- discharge cycles at 4.35 V is as low as 60% or less.

[0102]

Focusing attention on Comparative Examples 2 and 3 using the aromatic compounds X and Y, although the coulombic efficiency after the charge- discharge cycles at 4.20 V is high, the coulombic efficiency after the charge- discharge cycles at 4.35 V is low. That is, the effect that the coulombic efficiency after charge- discharge cycles at a high voltage can be enhanced can be said to be a peculiar effect produced when an aromatic compound having a silyl group or an amino group, and an acetylenediyl group is used. As shown in Comparative Example 3, even when the aromatic compound X having an acetylenediyl group and the aromatic compound Y having a silyl group were used in combination, the coulombic efficiency after the charge-discharge cycles at 4.35 V was low. That is, it is understood that coulombic efficiency after charge- discharge cycles at 4.35 V is enhanced by using an aromatic compound having both the silyl group or amino group, and the acetylenediyl group.

[0103]

As shown in Table 1, in Examples 1 to 4 using aromatic compounds A to D having a silyl group and an acetylenediyl group, the coulombic efficiency after charge-discharge cycles at 4.35 V is particularly high. Furthermore, in Examples 1, 3, and 4 using aromatic compounds A, C, and D in which the silicon atom of the silyl group and the acetylenediyl group are bonded directly to each other, the coulombic efficiency after charge- discharge cycles at 4.20 V is also higher than that of Comparative Example 1 in which no aromatic compound was added. On the other hand, in Example 5 using the aromatic compound E having an amino group and an acetylenediyl group, the coulombic efficiency and the capacity retention ratio after charge- discharge cycles at 4.20 V are higher than those of Comparative Example 1 in which no aromatic compound was added.

INDUSTRIAL APPLICABILITY

[0104]

The present invention is applicable to a nonaqueous electrolyte energy storage device used as a power source for electronic devices such as personal computers and communication terminals, automobiles, and the like.

DESCRIPTION OF REFERENCE SIGNS

[0105]

l: Nonaqueous electrolyte energy storage device

2 ^' · Electrode assembly

3 ^: Container

4 ^' · Positive electrode terminal

4' ^' · Positive electrode lead

5^ Negative electrode terminal

5': Negative electrode lead

20^ Energy storage unit : Energy storage apparatus