JP6607690B2 - Additive for non-aqueous electrolyte for battery, non-aqueous electrolyte for battery, and lithium secondary battery - Google Patents

Description

  The present invention relates to an additive for a non-aqueous electrolyte for a battery, a non-aqueous electrolyte for a battery, and a lithium secondary battery.

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage sources. In particular, recently, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be mounted on hybrid vehicles and electric vehicles.
The lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of occluding and releasing lithium, and a non-aqueous electrolyte for a battery containing a lithium salt and a non-aqueous solvent.
As the positive electrode active material used for the positive electrode, for example, lithium metal oxides such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , and LiFePO ₄ are used.
In addition, as the non-aqueous electrolyte, a mixed solvent (non-aqueous solvent) of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN A solution in which a Li electrolyte such as (SO ₂ CF ₂ CF ₃ ) ₂ is mixed is used.
On the other hand, negative electrode active materials used for negative electrodes include metal lithium, metal compounds capable of occluding and releasing lithium (metal simple substance, oxide, alloy with lithium, etc.) and carbon materials, particularly lithium. Lithium secondary batteries using coke, artificial graphite, and natural graphite that can be occluded and released have been put into practical use.

As an attempt to improve battery performance, it has been proposed to include various additives in a non-aqueous electrolyte for batteries.
For example, as an electrolyte for a lithium secondary battery that can improve the safety of the battery, an electrolyte for a lithium secondary battery containing an organometallic compound such as titanium oxide acetylacetonate is known (for example, a patent document). 1).
On the other hand, non-aqueous electrolysis containing titanium element as a non-aqueous electrolyte that can provide a lithium secondary battery with excellent cycle characteristics by suppressing the decomposition reaction of the solvent in the negative electrode and suppressing excessive film formation Liquids (titanium elements may be included as constituents in titanium compounds) are known (see, for example, Patent Document 2).
Further, as a non-aqueous electrolyte that can provide a lithium secondary battery capable of improving cycle characteristics (particularly suppressing a decrease in discharge capacity after charge / discharge), an organic titanate that is said to be accompanied by a strong film formation on the negative electrode A nonaqueous electrolytic solution containing a combination of an additive of vinylene carbonate and vinylene carbonate is known (see, for example, Patent Document 3).

JP-T-2004-520701 JP 2006-107796 A JP 2004-265680 A

However, in a battery using a nonaqueous electrolytic solution containing an organic titanium compound, the initial battery resistance may be increased due to the coating formed on the electrode surface.
The present invention has been made in view of the above circumstances, and is an additive for a battery non-aqueous electrolyte that can reduce the initial battery resistance, and a battery non-aqueous electrolyte containing this additive. And a lithium secondary battery.

As a result of intensive studies, the present inventor has found that by using an additive containing an inorganic titanium compound having a specific partial structure as an additive for a non-aqueous electrolyte for a battery, the initial battery resistance can be reduced. Completed the invention.
That is, the means for solving the above problems are as follows.

<1> An additive for a non-aqueous electrolyte for a battery, comprising an inorganic titanium compound having a partial structure represented by the following formula (1).

<2> The additive according to <1>, wherein the inorganic titanium compound includes a compound represented by the following formula (2).

<3> A nonaqueous electrolytic solution for batteries containing the additive according to <1> or <2>.
<4> The nonaqueous electrolyte for battery according to <3>, wherein the content of the inorganic titanium compound is 0.001% by mass to 10% by mass with respect to the total amount of the nonaqueous electrolyte for battery.
<5> a positive electrode;
Lithium metal, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped / undoped with lithium ions, transition metal nitrides that can be doped / undoped with lithium ions, and lithium A negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of ion doping and dedoping;
<3> or the nonaqueous electrolyte for batteries according to <4>,
Including lithium secondary battery.
<6> A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to <5>.

  According to the present invention, there are provided an additive for a battery non-aqueous electrolyte that can reduce initial battery resistance, and a battery non-aqueous electrolyte and a lithium secondary battery containing the additive. can do.

It is a schematic perspective view which shows an example of the laminate type battery which is an example of the lithium secondary battery of this invention. It is a schematic sectional drawing of the thickness direction of the laminated electrode body accommodated in the laminate type battery shown in FIG.

  Hereinafter, the additive of the present invention, the nonaqueous electrolyte for battery, and the lithium secondary battery will be described in detail.

[Additive (Additive A)]
The additive of the present invention (also referred to as “additive A” in the present specification) is an additive for a non-aqueous electrolyte for a battery, and has an inorganic structure represented by the following formula (1). Contains titanium compounds.

Conventionally, a technique for improving battery performance has been proposed by adding an organic titanium compound, which is an organic additive, to a battery non-aqueous electrolyte. In general, it is known that an organic additive is decomposed by charge and discharge, and the decomposed product forms a film on the electrode surface.
However, depending on the nature of the coating, the initial battery resistance may be high. When the initial battery resistance is increased, the output characteristics of the battery are deteriorated, resulting in a problem that the battery performance is deteriorated. For this reason, a battery having an initial battery resistance as low as possible is demanded.
As a result of intensive studies, the present inventors have used an additive (additive A) containing an inorganic titanium compound having a partial structure represented by the above formula (1) as an additive for a non-aqueous electrolyte for a battery. The inventors have found that the initial battery resistance can be reduced, and have completed the present invention.
That is, according to the additive (additive A) of the present invention, the initial battery resistance can be reduced.

The reason why the above effect is obtained by the additive A is presumed as follows.
That is, in a battery using the additive A (for example, a lithium secondary battery), during the initial charge, the inorganic titanium compound having the partial structure represented by the formula (1) quickly acts on the electrode surface, and the organic component is removed. It is considered that a film having high conductivity not included is formed. It is considered that the initial battery resistance is reduced by the action of the highly conductive film.
More specifically, the inorganic titanium compound having a partial structure represented by the formula (1) (hereinafter, also referred to as “Ti—O—S structure”) includes each of Ti, O, and S with respect to the electrode surface. It is thought to act multi-point by atoms. Thereby, it is considered that a good quality and stable film is formed on the electrode surface. From the viewpoint of making this multipoint action more effective, the inorganic titanium compound preferably has an O═Ti—O—S structure.

  For the above reasons, it is considered that the initial battery resistance is reduced in the nonaqueous electrolytic solution containing the additive A as compared with the nonaqueous electrolytic solution not containing the additive A.

<Inorganic titanium compound>
The inorganic titanium compound has a partial structure (Ti—O—S structure) represented by the above formula (1).
In the above formula (1), there are no particular restrictions on the bonding state of each of the terminal titanium atom (Ti) and sulfur atom (S) (for example, the number of bonds, bond type, etc.). The above-described effects can be obtained regardless of the coupling state.

  Specific examples of inorganic titanium compounds having a Ti—O—S structure (hereinafter also referred to as “specific inorganic titanium compounds”) include titanium sulfate compounds, titanium oxysulfate compounds, titanium sulfite compounds, and titanium oxysulfite compounds. It is done.

Further, the number of Ti—O—S structures contained in one molecule of the specific inorganic titanium compound may be only one or two or more.
Examples of the inorganic titanium compound containing two or more Ti—O—S structures in one molecule include Ti (SO ₄ ) ₂ and Ti ₂ (SO ₄ ) ₃ as titanium sulfate compounds.

  The terminal Ti in the formula (1) preferably forms a Ti═O bond from the viewpoint of further reducing the initial battery resistance. That is, from the viewpoint of further reducing the initial battery resistance, the specific inorganic titanium compound preferably has an O═Ti—O—S structure (that is, an oxytitanium compound).

From the viewpoint of forming a more stable film, the terminal S in the above formula (1) is preferably a part of a sulfuric acid structure or a part of a sulfite structure. More preferably. That is, from the viewpoint of forming a more stable film, the specific inorganic titanium compound is preferably a sulfuric acid compound or a sulfite compound, and more preferably a sulfuric acid compound.
The specific inorganic titanium compound is an oxytitanium compound and a sulfuric acid compound (that is, a titanium oxysulfate compound), or an oxytitanium compound and a sulfite compound (that is, a titanium oxysulfite compound). It is more preferable that it is a titanium oxysulfate compound.

It is particularly preferable that the specific inorganic titanium compound includes a compound represented by the following formula (2). The compound represented by Formula (2) is excellent in the effect of reducing the initial battery resistance.
The compound represented by Formula (2) is a titanium oxysulfate compound.

Additive A should just contain the specific inorganic titanium compound (inorganic titanium compound which has Ti-OS structure) as an active ingredient, and the specific inorganic titanium compound contained in additive A is only one sort. May be two or more.
For example, the additive A may contain a compound represented by the formula (2) and at least one specific inorganic titanium compound other than the compound represented by the formula (2).
Additive A may contain components other than the specific inorganic titanium compound as long as the effect of the specific inorganic titanium compound is not impaired.
Examples of components other than the specific inorganic titanium compound include inorganic titanium compounds other than the specific inorganic titanium compound, organic titanium compounds, and the like.
The content of the specific inorganic titanium compound in the additive A (the total content in the case of two or more types; the same shall apply hereinafter) is preferably 50% by mass or more with respect to the total amount of the additive A, and is 80% by mass. % Or more, more preferably 90% by mass or more, and ideally 100% by mass.
In the case where the additive A contains the compound represented by the formula (2), the preferred range of the content of the compound represented by the formula (2) in the additive A is the above-described specific inorganic titanium compound in the additive A. This is the same as the preferred range of the content.

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte for batteries of the present invention (hereinafter also simply referred to as “non-aqueous electrolyte”) contains an additive A containing a specific inorganic titanium compound.
The content of the specific inorganic titanium compound in the nonaqueous electrolytic solution of the present invention (the total content in the case of two or more types; the same shall apply hereinafter) is not considered from the viewpoint of more effectively achieving the effects of the present invention. It is preferably 0.001% by mass or more, more preferably 0.001% by mass to 10% by mass, and further preferably 0.01% by mass to 8% by mass with respect to the total amount of the water electrolyte. Preferably, it is more preferable that it is 0.05 mass%-5 mass%, and it is especially preferable that it is 0.1 mass%-2 mass%.
When the nonaqueous electrolytic solution of the present invention contains the compound represented by the formula (2), the preferred range of the content of the compound represented by the formula (2) in the nonaqueous electrolytic solution of the present invention is the above-mentioned specific This is the same as the preferred range of the content of the inorganic titanium compound.

In the case where an additive A containing a specific inorganic titanium compound is used as an additive for a non-aqueous electrolyte, a battery is actually produced, the produced battery is disassembled, and the non-aqueous electrolyte is taken out again. The content of the specific inorganic titanium compound in the electrolytic solution may be significantly reduced. Therefore, when at least the specific inorganic titanium compound is detected from the non-aqueous electrolyte extracted from the battery, it can be considered that the additive A is contained in the non-aqueous electrolyte.
In the present specification, the term “content” and the term “addition amount” both mean the content relative to the total amount of the non-aqueous electrolyte.

<Additive B>
The nonaqueous electrolytic solution of the present invention is at least one selected from the group consisting of a carbonate compound having a carbon-carbon unsaturated bond, a carbonate compound having a fluorine atom, a fluorophosphate compound, an oxalato compound, and a sultone compound. It is preferable to contain an additive B.
When the nonaqueous electrolytic solution of the present invention contains the additive B, the effect of the additive A described above is more effectively achieved. This is because the additive B forms a film on the electrode surface or strengthens the film formed by the additive A, so that decomposition of the solvent on the electrode surface is more effectively suppressed. it is conceivable that.

(Carbonate compound having a carbon-carbon unsaturated bond)
Examples of the carbonate compound having a carbon-carbon unsaturated bond include methyl vinyl carbonate, ethyl vinyl carbonate, divinyl carbonate, methyl propynyl carbonate, ethyl propynyl carbonate, dipropynyl carbonate, methyl phenyl carbonate, ethyl phenyl carbonate, and diphenyl carbonate. Carbonates; vinylene carbonate, methyl vinylene carbonate, 4,4-dimethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, ethynyl ethylene carbonate, 4,4-diethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, propylene Le ethylene carbonate, 4,4-propynyl carbonate, cyclic carbonates such as 4,5-di-propynyl carbonate; and the like. Among these, preferably, methyl phenyl carbonate, ethyl phenyl carbonate, diphenyl carbonate, vinylene carbonate, vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, more preferably vinylene carbonate, Vinyl ethylene carbonate.

(Carbonate compound having fluorine atom)
Examples of the carbonate compound having a fluorine atom include methyl trifluoromethyl carbonate, ethyl trifluoromethyl carbonate, bis (trifluoromethyl) carbonate, methyl (2,2,2-trifluoroethyl) carbonate, ethyl (2,2,2). -Chain carbonates such as trifluoroethyl) carbonate and bis (2,2,2-trifluoroethyl) carbonate; 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4 -Cyclic carbonates such as trifluoromethylethylene carbonate; Of these, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, and 4,5-difluoroethylene carbonate are preferable.

(Fluorophosphate compound)
Examples of the fluorophosphate compound include lithium difluorophosphate, lithium monofluorophosphate, difluorophosphoric acid, monofluorophosphoric acid, methyl difluorophosphate, ethyl difluorophosphate, dimethyl fluorophosphate, and diethyl fluorophosphate. . Of these, lithium difluorophosphate and lithium monofluorophosphate are preferred.

(Oxalato compound)
Examples of the oxalato compound include lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, tris (oxalato) lithium phosphate, lithium difluoro (oxalato) borate, and lithium bisoxalatoborate. Of these, lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, and lithium bisoxalatoborate are preferable.

(Sultone compound)
Examples of sultone compounds include 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1-methyl-1,3-propene sultone, 2-methyl-1,3-propene sultone, and 3-methyl. Examples include sultone such as -1,3-propene sultone. Of these, 1,3-propane sultone and 1,3-propene sultone are preferable.

  The additive B mentioned above is vinylene carbonate, vinyl ethylene carbonate, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, lithium monofluorophosphate, lithium difluorophosphate, difluorobis ( Oxalato) lithium phosphate, tetrafluoro (oxalato) lithium phosphate, tris (oxalato) lithium phosphate, lithium difluoro (oxalato) borate, lithium bisoxalatoborate, 1,3-propane sultone, and 1,3-propene Particularly preferred is at least one selected from the group consisting of sultone.

When the nonaqueous electrolytic solution of the present invention contains the additive B, the additive B contained may be only one kind or two or more kinds.
When the non-aqueous electrolyte of the present invention contains the additive B, its content (total content when there are two or more) is not particularly limited, but the effect of the additive A is more effective. From the viewpoint of performance, it is preferably 0.001% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass with respect to the total amount of the non-aqueous electrolyte. More preferably, it is in the range of 1% by mass to 4% by mass, more preferably in the range of 0.1% by mass to 2% by mass, and particularly preferably in the range of 0.1% by mass to 1% by mass. preferable.

Moreover, the nonaqueous electrolytic solution of the present invention may contain other additives other than those described above.
Examples of other additives include difluorophosphates other than the above-mentioned lithium difluorophosphate, monofluorophosphates other than lithium monofluorophosphate, and fluorosulfonates.
Other additives include, for example, International Publication No. 2012/053644, Japanese Patent No. 4033074, Japanese Patent No. 4819409, Japanese Patent Laid-Open No. 2012-226878, Japanese Patent No. 5353923, Japanese Patent No. 4424895, and the like. Can be appropriately selected from the additives described in 1.

Next, other components of the nonaqueous electrolytic solution will be described.
The nonaqueous electrolytic solution generally contains an electrolyte and a nonaqueous solvent.

<Non-aqueous solvent>
Various known solvents can be appropriately selected as the nonaqueous solvent, but it is preferable to use a cyclic aprotic solvent and / or a chain aprotic solvent.
In order to improve the safety of the battery, when aiming to improve the flash point of the solvent, it is preferable to use a cyclic aprotic solvent as the non-aqueous solvent.

(Cyclic aprotic solvent)
As the cyclic aprotic solvent, cyclic carbonate, cyclic carboxylic acid ester, cyclic sulfone, and cyclic ether can be used.
The cyclic aprotic solvent may be used alone or in combination of two or more.
The mixing ratio of the cyclic aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass. By setting it as such a ratio, the electroconductivity of the electrolyte solution relating to the charge / discharge characteristics of the battery can be increased.
Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate having a high dielectric constant are preferably used. In the case of a battery using graphite as the negative electrode active material, ethylene carbonate is more preferable. Moreover, you may use these cyclic carbonates in mixture of 2 or more types.

Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone, δ-valerolactone, alkyl substitution products such as methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.
The cyclic carboxylic acid ester has a low vapor pressure, a low viscosity, a high dielectric constant, and can lower the viscosity of the electrolytic solution without lowering the degree of dissociation between the flash point of the electrolytic solution and the electrolyte. For this reason, since it has the feature that the conductivity of the electrolytic solution, which is an index related to the discharge characteristics of the battery, can be increased without increasing the flammability of the electrolytic solution, when aiming to improve the flash point of the solvent, It is preferable to use a cyclic carboxylic acid ester as the cyclic aprotic solvent. Of the cyclic carboxylic acid esters, γ-butyrolactone is most preferred.
The cyclic carboxylic acid ester is preferably used by mixing with another cyclic aprotic solvent. For example, a mixture of a cyclic carboxylic acid ester and a cyclic carbonate and / or a chain carbonate can be mentioned.

Examples of the cyclic sulfone include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, dipropyl sulfone, methylethyl sulfone, methylpropyl sulfone and the like.
An example of a cyclic ether is dioxolane.

(Chain aprotic solvent)
As the chain aprotic solvent, a chain carbonate, a chain carboxylic acid ester, a chain ether, a chain phosphate, or the like can be used.
The mixing ratio of the chain aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.
Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, Examples include ethyl pentyl carbonate, dipentyl carbonate, methyl heptyl carbonate, ethyl heptyl carbonate, diheptyl carbonate, methyl hexyl carbonate, ethyl hexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate, dioctyl carbonate, and methyltrifluoroethyl carbonate. These chain carbonates may be used as a mixture of two or more.

  Specific examples of the chain carboxylic acid ester include methyl pivalate. Specific examples of the chain ether include dimethoxyethane. Specific examples of the chain phosphate ester include trimethyl phosphate.

(Solvent combination)
The non-aqueous solvent may be used alone or in combination.
Further, only one or more types of cyclic aprotic solvents may be used, or only one or more types of chain aprotic solvents may be used, or cyclic aprotic solvents and chain proticity may be used. You may mix and use a solvent. When the load characteristics and low temperature characteristics of the battery are particularly intended to be improved, it is preferable to use a combination of a cyclic aprotic solvent and a chain aprotic solvent as the nonaqueous solvent.
Furthermore, in view of the electrochemical stability of the electrolytic solution, it is most preferable to apply a cyclic carbonate to the cyclic aprotic solvent and a chain carbonate to the chain aprotic solvent. Further, the conductivity of the electrolytic solution related to the charge / discharge characteristics of the battery can be increased by a combination of the cyclic carboxylic acid ester and the cyclic carbonate and / or the chain carbonate.

As a combination of cyclic carbonate and chain carbonate, specifically, ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, propylene carbonate and Diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate Diethyl carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate and methyl ethyl carbonate And diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.
The mixing ratio of the cyclic carbonate and the chain carbonate is expressed by mass ratio, and the cyclic carbonate: chain carbonate is 5:95 to 80:20, more preferably 10:90 to 70:30, and particularly preferably 15:85. ~ 55: 45. By setting it as such a ratio, since the raise of the viscosity of electrolyte solution can be suppressed and the dissociation degree of electrolyte can be raised, the conductivity of the electrolyte solution in connection with the charge / discharge characteristic of a battery can be raised. In addition, the solubility of the electrolyte can be further increased. Therefore, since it can be set as the electrolyte solution excellent in the electrical conductivity in normal temperature or low temperature, the load characteristic of the battery from normal temperature to low temperature can be improved.

  Specific examples of combinations of cyclic carboxylic acid esters and cyclic carbonates and / or chain carbonates include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate, and γ-butyrolactone and ethylene carbonate and methylethyl. Carbonate, γ-butyrolactone and ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and propylene carbonate and dimethyl carbonate, γ-butyrolactone and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and propylene carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, γ-butyrolactone, Tylene carbonate and propylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate, propylene carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate And professional Ren carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate Propylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and sulfolane, γ-butyrolactone and ethylene carbonate and sulfolane, γ-butyrolactone and propylene carbonate and sulfolane, γ-butyrolactone, ethylene carbonate, propylene carbonate and sulfolane, γ -Butyrolactone and sul Such as orchids and dimethyl carbonate.

(Other solvents)
The nonaqueous electrolytic solution of the present invention may contain a solvent other than the above as a nonaqueous solvent.
Specific examples of the other solvent include amides such as dimethylformamide, chain carbamates such as methyl-N, N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, N, N-dimethylimidazolidinone and the like. Examples thereof include boron compounds such as cyclic urea, trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, trimethylsilyl borate, and polyethylene glycol derivatives represented by the following general formula.
HO (CH ₂ CH ₂ O) _a H
HO [CH ₂ CH (CH ₃ ) O] _b H
CH ₃ O (CH ₂ CH ₂ O) _c H
CH ₃ O [CH ₂ CH (CH ₃ ) O] _d H
CH ₃ O (CH ₂ CH ₂ O) _e CH ₃
CH ₃ O [CH ₂ CH (CH ₃ ) O] _f CH _{3
C 9 H 19 PhO (CH 2} CH 2 O) g [CH (CH 3) O] h CH 3
(Ph is a phenyl group)
CH ₃ O [CH ₂ CH (CH ₃ ) O] _i CO [OCH (CH ₃ ) CH ₂ ] _j OCH ₃
In the above formula, a to f are integers of 5 to 250, g to j are integers of 2 to 249, 5 ≦ g + h ≦ 250, and 5 ≦ i + j ≦ 250.

<Electrolyte>
The nonaqueous electrolytic solution of the present invention can contain various known electrolytes.
Any electrolyte can be used as long as it is normally used as an electrolyte for a non-aqueous electrolyte.
Specific examples of the electrolyte include (C ₂ H ₅ ) ₄ NPF ₆ , (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NAsF ₆ , (C ₂ H ₅ ) ₄ N ₂ SiF ₆ , (C ₂ H ₅ ) ₄ NOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), (C ₂ H ₅ ) ₄ NPF _n [C _k F _{(2k + 1)} ] _(6-n) Tetraalkylammonium salts such as (n = 1 to 5, k = 1 to 8), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F Lithium salts such as _{(2k + 1)} (k = 1 to 8), LiPF _n [C _k F _{(2k + 1)} ] _(6-n) (n = 1 to 5, k = 1 to 8) are included. . Moreover, the lithium salt represented by the following general formula can also be used.

_{^{LiC (SO 2 R 27) (}} SO 2 R 28) (SO 2 R 29), LiN (SO 2 OR 30) (SO 2 OR 31), LiN (SO 2 R 32) (SO 2 R 33) ( where R ^{27 to} R ³³ may be the same as or different from each other, and are a C 1-8 perfluoroalkyl group). These electrolytes may be used alone or in combination of two or more.
Of these, lithium salts are particularly desirable, and LiPF ₆ , LiBF ₄ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiClO ₄ , LiAsF ₆ , LiNSO ₂ [C _k F _{( 2k + 1)] 2 (k} = 1~8 _{integer), LiPF n [C k F} (2k + 1)] (6-n) (n = 1~5, k = 1~8 integer) are preferred.
The electrolyte is usually preferably contained in the nonaqueous electrolytic solution at a concentration of 0.1 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L.

In the nonaqueous electrolytic solution, when a cyclic carboxylic acid ester such as γ-butyrolactone is used in combination as the nonaqueous solvent, it is particularly desirable to contain LiPF ₆ .
Since LiPF ₆ has a high degree of dissociation, the conductivity of the electrolytic solution can be increased, and the reductive decomposition reaction of the electrolytic solution on the negative electrode can be suppressed. LiPF ₆ may be used alone, or LiPF ₆ and other electrolytes may be used. Any other electrolyte can be used as long as it is normally used as an electrolyte for a non-aqueous electrolyte, but lithium salts other than LiPF ₆ are preferred among the specific examples of the lithium salts described above. .
Specific examples include LiPF ₆ and LiBF ₄ , LiPF ₆ and LiN [SO ₂ C _k F _{(2k + 1)} ] ₂ (k = 1 to 8), LiPF ₆ , LiBF ₄ and LiN [SO ₂ C _k F _{( 2k + 1)} ] (k = 1 to 8).

The ratio of LiPF _{6 in} the lithium salt is 1% by mass to 100% by mass, preferably 10% by mass to 100% by mass, and more preferably 50% by mass to 100% by mass. Such an electrolyte is preferably contained in the nonaqueous electrolytic solution at a concentration of 0.1 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L.

Moreover, the non-aqueous electrolyte can also contain an overcharge inhibitor.
As the overcharge preventing agent, biphenyl, alkylbiphenyl, terphenyl (o-, m-, p-isomer), partially hydrogenated terphenyl (o-, m-, p-isomer) (for example, 1, 2) -Dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl), cyclohexylbenzene, t-butylbenzene, 1,3-di-t-butylbenzene, t-amylbenzene, diphenylether, dibenzofuran Aromatic compounds such as fluorotoluene (o-, m-, p-isomer), difluorotoluene, trifluorotoluene, tetrafluorotoluene, pentafluorotoluene, fluorobenzene, difluorobenzene (o-, m-, p-isomer) ), 1-fluoro-4-t-butylbenzene, 2-fluoro Partially fluorinated products of aromatic compounds such as phenyl and fluorocyclohexylbenzene (for example, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene); 2,4-difluoro Examples thereof include fluorine-containing anisole compounds such as anisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole.
Among these, the aromatic compounds exemplified above are preferable.
Moreover, an overcharge inhibitor may be used individually by 1 type, or may use 2 or more types together.
When two or more kinds are used in combination, in particular, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, Using at least one selected from aromatic compounds not containing oxygen, such as t-amylbenzene, and at least one selected from oxygen-containing aromatic compounds such as diphenyl ether, dibenzofuran, and the like is an overcharge prevention property and a high temperature storage property. From the standpoint of balance.

When the non-aqueous electrolyte contains an overcharge inhibitor, the content of the overcharge inhibitor is not particularly limited, but for example 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0. .3% by mass or more, particularly preferably 0.5% by mass or more.
Moreover, content of the said overcharge inhibitor is 10 mass% or less, for example, Preferably it is 5 mass% or less, More preferably, it is 3 mass% or less, More preferably, it is 2 mass% or less.

The nonaqueous electrolytic solution may contain at least one compound other than the above-described compounds as an additive as long as the object of the present invention is not hindered.
Specific examples of other compounds include sulfate esters such as dimethyl sulfate, diethyl sulfate, ethylene sulfate, propylene sulfate, butene sulfate, pentene sulfate and vinylene sulfate; and sulfur compounds such as sulfolane, 3-sulfolene and divinyl sulfone, Can be mentioned.
These compounds may be used alone or in combination of two or more.
Of these, ethylene sulfate, propylene sulfate, butene sulfate, and pentene sulfate are preferred.

[Lithium secondary battery]
The lithium secondary battery of the present invention includes a negative electrode, a positive electrode, and the nonaqueous electrolytic solution of the present invention.
Usually, a separator is provided between the negative electrode and the positive electrode.

(Negative electrode)
The negative electrode active material constituting the negative electrode includes metallic lithium, a lithium-containing alloy, a metal or alloy that can be alloyed with lithium, an oxide that can be doped / undoped with lithium ions, and a doped / undoped lithium ion. At least one selected from the group consisting of possible transition metal nitrides and carbon materials capable of doping and dedoping lithium ions (may be used alone or a mixture containing two or more thereof) May be used).
Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, and tin alloys. Further, lithium titanate may be used.
Among these, carbon materials that can be doped / undoped with lithium ions are preferable. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The form of the carbon material may be any of a fibrous form, a spherical form, a potato form, and a flake form.

Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or less, and mesopause bitch carbon fiber (MCF).
Examples of the graphite material include natural graphite and artificial graphite. As artificial graphite, graphitized MCMB, graphitized MCF, and the like are used. Further, as the graphite material, a material containing boron can be used. As the graphite material, those coated with a metal such as gold, platinum, silver, copper and tin, those coated with amorphous carbon, and those obtained by mixing amorphous carbon and graphite can be used.

These carbon materials may be used alone or in combination of two or more.
As the carbon material, a carbon material having a (002) plane distance d (002) of 0.340 nm or less as measured by X-ray analysis is particularly preferable. Further, as the carbon material, graphite having a true density of 1.70 g / cm ³ or more or a highly crystalline carbon material having properties close thereto is also preferable. When the carbon material as described above is used, the energy density of the battery can be further increased.

(Positive electrode)
Examples of the positive electrode active material constituting the positive electrode include transition metal oxides or transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _X Co _(1-X) O ₂ [0 <X <1], Li _{1 + α} Me _1-α O ₂ having a α-NaFeO ₂ type crystal structure (Me is a transition metal element containing Mn, Ni and Co, 1.0 ≦ (1 + α) / (1-α) ≦ 1.6), LiNi _x Co _y Mn _z O ₂ [x + y + z = 1, 0 <x <1, 0 <y <1, 0 <z <1] (For example, LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O _2, etc.), LiFePO ₄ , LiMnPO _4, etc., a composite comprising lithium and a transition metal Oxide, polyaniline Emissions, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazoles, conductive polymers such as polyaniline complex, and the like. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can be used as the positive electrode. In addition, a mixture of a composite oxide of lithium and a transition metal and a carbon material can be used as the positive electrode.
Said positive electrode active material may be used by 1 type, and may mix and use 2 or more types. When the positive electrode active material has insufficient conductivity, it can be used together with a conductive auxiliary agent to constitute a positive electrode. Examples of the conductive assistant include carbon materials such as carbon black, amorphous whiskers, and graphite.

(Separator)
The separator is a film that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and examples thereof include a porous film and a polymer electrolyte.
A microporous polymer film is preferably used as the porous film, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, and polyester.
In particular, porous polyolefin is preferable. Specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film can be exemplified. On the porous polyolefin film, other resin excellent in thermal stability may be coated.
Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, a polymer swollen with an electrolytic solution, and the like.
The nonaqueous electrolytic solution of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer.

(Battery configuration)
The lithium secondary battery of the present invention can take various known shapes, and can be formed into a cylindrical shape, a coin shape, a square shape, a laminate shape, a film shape, or any other shape. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose.

As an example of the lithium secondary battery (non-aqueous electrolyte secondary battery) of the present invention, a laminate type battery can be mentioned.
FIG. 1 is a schematic perspective view showing an example of a laminated battery as an example of the lithium secondary battery of the present invention, and FIG. 2 shows the thickness of the laminated electrode body accommodated in the laminated battery shown in FIG. It is a schematic sectional drawing of a direction.
The laminate type battery shown in FIG. 1 contains a non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1) inside, and the periphery is sealed. The laminate outer package 1 is sealed inside. As the laminate exterior body 1, for example, an aluminum laminate exterior body is used.
As shown in FIG. 2, the laminated electrode body accommodated in the laminate outer package 1 includes a laminated body in which positive plates 5 and negative plates 6 are alternately laminated with separators 7 interposed therebetween. And a separator 8 surrounding the periphery. The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the non-aqueous electrolyte of the present invention.
The plurality of positive electrode plates 5 in the laminated electrode body are all electrically connected to the positive electrode terminal 2 via a positive electrode tab (not shown), and a part of the positive electrode terminal 2 is part of the laminate outer package 1. It protrudes outward from the peripheral end (FIG. 1). The portion where the positive electrode terminal 2 protrudes at the peripheral end of the laminate outer package 1 is sealed with an insulating seal 4.
Similarly, each of the plurality of negative electrode plates 6 in the laminated electrode body is electrically connected to the negative electrode terminal 3 through a negative electrode tab (not shown), and a part of the negative electrode terminal 3 is part of the laminate exterior. It protrudes outward from the peripheral edge of the body 1 (FIG. 1). The portion where the negative electrode terminal 3 protrudes at the peripheral end of the laminate outer package 1 is sealed with an insulating seal 4.
In the laminate type battery according to the above example, the number of the positive plates 5 is 5 and the number of the negative plates 6 is 6. All the outer layers are laminated in an arrangement to be the negative electrode plate 6. However, it is needless to say that the number of positive plates, the number of negative plates, and the arrangement in the laminated battery are not limited to this example, and various changes may be made.

The lithium secondary battery of the present invention is obtained by charging / discharging a lithium secondary battery (lithium secondary battery before charge / discharge) including a negative electrode, a positive electrode, and the non-aqueous electrolyte of the present invention. Lithium secondary batteries may be used.
That is, the lithium secondary battery of the present invention is prepared by first preparing a lithium secondary battery before charging / discharging including the negative electrode, the positive electrode, and the non-aqueous electrolyte of the present invention, and then before charging / discharging. It may be a lithium secondary battery (charged / discharged lithium secondary battery) produced by charging / discharging the lithium secondary battery one or more times.

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. For example, notebook computers, mobile computers, mobile phones, headphone stereos, video movies, LCD TVs, handy cleaners, electronic notebooks, calculators, radios, backup power supply applications, motors, automobiles, electric cars, motorcycles, electric bikes, bicycles, electric motors Bicycles, lighting equipment, game machines, watches, electric tools, cameras, and other small portable devices and large devices can be widely used.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples.
In the following examples, “wt%” represents mass%.
In the following examples, “addition amount” represents the content in the finally obtained non-aqueous electrolyte (that is, the amount relative to the total amount of the finally obtained non-aqueous electrolyte).

[Example 1]
In the following procedure, a laminate type battery having the same configuration as the laminate type battery shown in FIG. 1 was prepared as a lithium secondary battery.

<Production of negative electrode>
98 parts by mass of artificial graphite, 1 part by mass of carboxymethylcellulose and 1 part by mass of SBR latex were kneaded with an aqueous solvent to prepare a paste-like negative electrode mixture slurry.
Next, the negative electrode mixture slurry is applied to both sides of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 12 μm, dried, and then compressed by a roll press to form a sheet formed of a negative electrode current collector and a negative electrode active material layer. Negative electrode (negative electrode plate) was obtained. The coating density of the negative electrode active material layer at this time was 12 mg / cm ² , and the packing density was 1.45 g / ml.
Six negative electrode plates as described above were produced, and a negative electrode tab was attached to each of the obtained six negative electrode plates.

<Preparation of positive electrode>
A paste-like positive electrode mixture slurry was prepared by kneading 98 parts by mass of LiCoO ₂ , 1 part by mass of acetylene black and 1 part by mass of polyvinylidene fluoride using N-methylpyrrolidinone as a solvent.
Next, this positive electrode mixture slurry was applied to both sides of a positive electrode current collector of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to form a sheet-like material comprising a positive electrode current collector and a positive electrode active material. A positive electrode (positive electrode plate) was obtained. Coated weight of the positive electrode active material layer at this time was 25 mg / cm ^2, the filling density was 3.6 g / ml.
Five positive electrode plates as described above were produced, and a positive electrode tab was attached to each of the obtained five positive electrode plates.

<Preparation of non-aqueous electrolyte>
As a nonaqueous solvent, ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:35:35 (mass ratio), respectively, to obtain a mixed solvent.
In the obtained mixed solvent, LiPF ₆ as an electrolyte was dissolved so that the electrolyte concentration in the finally obtained nonaqueous electrolytic solution was 1 mol / liter.
To the solution obtained above, a compound represented by the formula (2) (addition amount 0.5 wt%) was added as an additive A to obtain a nonaqueous electrolytic solution.

<Production of laminated electrode body>
The positive electrode tab and the negative electrode tab are placed on the same side of the six negative electrode plates attached with the negative electrode tab and the five positive electrode plates attached with the positive electrode tab through a microporous polyethylene film (thickness 20 μm; separator). It was laminated in the direction of arrangement. At this time, the positive electrode plate and the negative electrode plate were alternately laminated so that the outermost layers on both sides were both negative electrode plates. An insulating tape (separator) was wound around the obtained laminated body to maintain the shape, thereby obtaining a laminated electrode body.

<Attachment of positive terminal and negative terminal>
Six negative electrode tabs extending from each of the six negative electrode plates were attached to one negative electrode terminal made of copper foil by ultrasonic welding.
Five positive electrode tabs extending from each of the five positive electrode plates were attached to one positive electrode terminal made of aluminum foil by ultrasonic welding.

<Production of laminated laminated battery>
The laminated electrode body to which the positive electrode terminal and the negative electrode terminal were attached was accommodated in an aluminum laminate outer body, and one side of the laminate outer body to which the positive electrode terminal and the negative electrode terminal were attached was heat-sealed. At this time, a part of the positive electrode terminal and a part of the negative electrode terminal protruded from the peripheral end of the laminate outer package. The portions where the positive electrode terminal and the negative electrode terminal protrude were each sealed with an insulating seal.
Next, two of the remaining three sides of the laminate outer package were heat-sealed.
Next, the nonaqueous electrolyte solution is injected into the laminate exterior body from one side of the laminate exterior body that is not thermally fused, and the positive electrode plate, each negative electrode plate, and each separator are impregnated with the nonaqueous electrolyte solution. I let you. Next, the laminate outer package was sealed by heat-sealing one side that was not heat-sealed. Thus, a laminate type battery was obtained.
Each measurement was implemented about the obtained lamination type battery (battery for a test).

[Evaluation methods]
<Charge / discharge characteristics of battery: initial discharge capacity>
The laminate type battery was charged at a constant current of 500 mA and a constant voltage of 4.4 V in a constant temperature bath at 25 ° C., and the discharge capacity when discharged to 3.3 V at a constant current of 500 mA in the constant temperature bath of 25 ° C. was measured. The initial discharge capacity [mAh].
The obtained results are shown in Table 1.

[Comparative Example 1]
In Example 1, a nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the compound represented by the formula (2) was not added (that is, there was no additive). The production and evaluation of the battery were performed in the same manner as in Example 1. The obtained results are shown in Table 1.

[Example 2]
In Example 1, as the additive A, a nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the amount of the compound represented by the formula (2) was changed to 0.2 wt%. The production and evaluation of the battery were performed in the same manner as in Example 1. The obtained results are shown in Table 1.

  As shown in Table 1, in Examples 1 and 2 using the additive A, the initial discharge capacity was increased by 10% as compared with the comparative example 1 in which the additive A was not used. That is, in Examples 1-2, it was confirmed that the initial battery resistance was reduced.

DESCRIPTION OF SYMBOLS 1 Laminate exterior body 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulation seal 5 Positive electrode plate 6 Negative electrode plate 7, 8 Separator

Claims (4)

A battery non-aqueous electrolyte containing an additive for a battery non-aqueous electrolyte , the additive comprising an inorganic titanium compound having a partial structure represented by the following formula (1):
The inorganic titanium compound is a sulfuric acid compound having an O = Ti-O-S structure, or a sulfite compound having an O = Ti-O-S structure,
A nonaqueous electrolytic solution for a battery, wherein the content of the inorganic titanium compound is 0.05% by mass to 5% by mass with respect to the total amount of the nonaqueous electrolytic solution for a battery .
The non-aqueous electrolyte for a battery according to claim 1, wherein the inorganic titanium compound contains a compound represented by the following formula (2).
A positive electrode;
Lithium metal, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped / undoped with lithium ions, transition metal nitrides that can be doped / undoped with lithium ions, and A negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of doping and dedoping lithium ions;
A non-aqueous electrolyte for a battery according to claim 1 or 2 ,

Including lithium secondary battery. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 3 .