JP2016222641A - Lithium salt compound, and nonaqueous electrolyte, lithium ion secondary battery, and lithium ion capacitor using the lithium salt compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new lithium salt compound, a nonaqueous electrolyte excellent in high temperature cycle characteristics and output characteristics after a high temperature cycle and capable of suppressing metal elution from a positive electrode and the like, and a lithium ion secondary battery and a lithium ion capacitor using the nonaqueous electrolyte.SOLUTION: (1) A lithium salt compound consists of a difluorophosphate anion and a lithium cation having, as a ligand, one or more ether compounds selected from 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane. (2) A nonaqueous electrolyte, in which an electrolyte salt is dissolved in a nonaqueous solvent, contains the lithium salt compound. (3) A lithium ion secondary battery uses the lithium salt compound. (4) A lithium ion capacitor uses the lithium salt compound. (5) A production method of the lithium salt compound includes bringing the ether compound into contact with a lithium difluorophosphate.SELECTED DRAWING: None

Description

  The present invention relates to a novel lithium salt compound, a nonaqueous electrolytic solution using the same, a lithium ion secondary battery and a lithium ion capacitor using the nonaqueous electrolytic solution.

In recent years, power sources for automobiles such as electric cars and hybrid cars, lithium ion secondary batteries and lithium ion capacitors for idling stop have been attracting attention.
As an electrolyte for a lithium secondary battery, a non-aqueous solution in which an electrolyte such as LiPF ₆ or LiBF ₄ is dissolved in a cyclic carbonate such as ethylene carbonate or propylene carbonate and a chain carbonate such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate. A water electrolyte is used.
In order to improve battery characteristics such as load characteristics and cycle characteristics of such lithium secondary batteries, various studies have been made on non-aqueous solvents and electrolyte salts used in these non-aqueous electrolytes.

Non-Patent Document 1 proposes a complex salt having an ether compound having a specific structure as a ligand, and reports that it exhibits poor volatility, and also proposes to use the ether complex salt as an electrolyte. Has been.
Patent Document 1 discloses an electrolytic solution and a secondary battery using a complex electrolyte of glyme such as triethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether and an alkali metal salt such as lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). It is described that the thermal stability is high.
Patent Document 2 discloses a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing lithium difluorophosphate, and describes that storage characteristics are improved.

Patent Document 3 discloses a compound having a skeleton containing a heteroelement having a dielectric constant of 5 or more and a viscosity of 0.6 cP or less, such as dimethoxyethane, diethoxyethane, acetonitrile, and the like, and difluorophosphoric acid It is described that an electrolytic solution containing lithium (LiPO ₂ F ₂ ) suppresses deterioration of battery characteristics during high-temperature storage.
Patent Document 4 discloses a nonaqueous electrolytic solution containing lithium difluorophosphate, and Example 3 describes an example in which 4.6% by mass of lithium difluorophosphate is added.

JP 2010-73489 A Japanese Patent Application Laid-Open No. 11-067270 JP 2008-277002 A JP 2008-222484 A

Journal of Chemical Physics, vol.117, 5929 (2002)

  The present invention uses a novel lithium salt compound, a non-aqueous electrolyte that is excellent in high-temperature cycle characteristics using the same, and output characteristics after a high-temperature cycle, and can suppress metal elution from the positive electrode, and the non-aqueous electrolyte. An object is to provide a lithium ion secondary battery and a lithium ion capacitor.

The present inventors have examined in detail the performance of the above-described prior art non-aqueous electrolyte. As a result, in the non-aqueous electrolyte secondary battery consisting only of the glyme solvent and the alkali metal salt of Patent Document 1, the safety can be improved to some extent because of its low volatility, but LiPF is added to the cyclic carbonate and the chain carbonate. _6. Compared to non-aqueous electrolytes in which an electrolyte such as LiBF ₄ is dissolved, it has been found that the effect of the electrolyte solution is extremely high and the effect of improving the cycle characteristics is hardly exhibited.
Further, triethylene glycol dimethyl ether (2,5,8,11-tetraoxadodecane) or tetraethylene glycol dimethyl ether (2,5,8,11,14-pentaoxapentadecane) and lithium bis (trifluoromethanesulfonyl) imide [ Even in a non-aqueous electrolyte obtained by adding a complex salt obtained by mixing equimolar amounts of (CF 3 SO 2) 2 NLi: LiTFSI] to a non-aqueous electrolyte composed of LiPF ₆ , a cyclic carbonate and a chain carbonate, a glyme solvent and an alkali metal Although the viscosity of the electrolytic solution is lower than that of a non-aqueous electrolytic solution composed only of salt, it has been found that the effect is hardly exerted on the problem of improving the cycle characteristics and the output characteristics after the cycle.
Patent Document 1 describes that the oxygen portion of the ether structure of glyme is coordinated 1: 1 with an alkali metal ion, and a complex is formed in at least a part of the electrolytic solution. No mention is made of using lithium difluorophosphate as

  The nonaqueous electrolyte secondary battery of Patent Document 2 is not satisfactory in terms of improving high-temperature cycle characteristics and suppressing elution of metal ions from the positive electrode. Patent Document 2 does not describe any combination of lithium difluorophosphate and an ether compound.

In Patent Document 3, lithium difluorophosphate, short-chain dimethoxyethane, and the like are mixed, but there is no description about a suitable mixing ratio, and it is merely added to lower the viscosity of the electrolytic solution.
In Example 3 of Patent Document 4, 4.6% by mass of lithium difluorophosphate is added to a nonaqueous electrolytic solution containing a cyclic carbonate and a chain carbonate. However, this cannot completely dissolve lithium difluorophosphate uniformly.

Based on the above-mentioned present situation, the present inventors have made extensive studies to solve the above problems, and as a result, the lithium difluorophosphate is converted into a lithium salt compound of the present invention which is a novel complex, thereby obtaining difluorophosphorus. The present inventors have found a compound having significantly higher solubility in an electrolytic solution than lithium acid.
Also, one or more ether compounds selected from 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane, which are relatively long chain ether compounds, are ligands. By incorporating the lithium salt compound of the present invention consisting of the lithium cation and the difluorophosphate anion into the non-aqueous electrolyte, it has excellent high-temperature cycle characteristics and output characteristics after high-temperature cycle, and elution of metals from the positive electrode, etc. The present invention has been completed by finding that it can be suppressed.

That is, the present invention provides the following (1) to (5).
(1) a lithium cation having at least one ether compound selected from 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane as a ligand, and difluorophosphoric acid A lithium salt compound comprising an anion.
(2) A nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, wherein the lithium salt compound according to (1) is contained in the nonaqueous electrolytic solution.
(3) A lithium ion secondary battery using the lithium salt compound described in (1) above (4) A lithium ion capacitor using the lithium salt compound described in (1) above.
(5) contacting the lithium difluorophosphate with at least one ether compound selected from 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane (1) The manufacturing method of lithium salt compound as described in 2.

  According to the present invention, a novel lithium salt compound, a high-temperature cycle characteristic using the same and an output characteristic after a high-temperature cycle, a non-aqueous electrolyte solution capable of suppressing metal elution from a positive electrode, and the non-aqueous electrolyte solution are provided. The used lithium ion secondary battery and lithium ion capacitor can be provided.

[Lithium salt compound]
The lithium salt compound of the present invention is 2,5,8,11-tetraoxadodecane (hereinafter also referred to as “TOD”) and 2,5,8,11,14-pentaoxapentadecane (hereinafter also referred to as “POP”). Lithium cation (A) (hereinafter also referred to simply as “lithium cation (A)”) having at least one ether compound selected from the group consisting of a difluorophosphate anion [(PO ₂ F ₂ ) ⁻ ] It consists of.
The lithium salt compound of the present invention is typically represented by the following general formula (1) or (2). The lithium cation (A) is represented by the left part of the general formula (1) or (2).

[Li ₂ (TOD)] ²⁺ [(PO ₂ F ₂ ) ⁻ ] ₂ (1)
[Li ₂ (POP)] ²⁺ [(PO ₂ F ₂ ) ⁻ ] ₂ (2)

Since the lithium salt compound of the present invention comprises a lithium cation (A) having at least one ether compound selected from TOD and POP as a ligand and a difluorophosphate anion, it is not coordinated to a lithium ion. Complexes containing ether compounds, such as lithium bis (trifluoromethanesulfonyl) imide-TOD complex described in Patent Document 1, and lithium bis (trifluoromethanesulfonyl) imide-POP complex are less likely to be electrochemically decomposed. Has characteristics.
In addition, when the ether compound used is a short-chain ether compound such as dimethoxyethane or diethoxyethane, the effect of the lithium salt compound of the present invention is not exhibited.
The molar ratio of the ether compound (ligand: TOD and / or POP) to the lithium ion (Li ⁺ ) in the lithium cation (A) is preferably 0.1 to 0.7, more preferably 0.15 to 0. .6, more preferably 0.25 to 0.55, and most preferably 0.5.

[Method for producing lithium salt compound]
The method for producing the lithium salt compound of the present invention comprises one or more ethers selected from 2,5,8,11-tetraoxadodecane (TOD) and 2,5,8,11,14-pentaoxapentadecane (POP). It is characterized by contacting the compound with lithium difluorophosphate.
The contact between the ether compound (TOD and / or POP) and lithium difluorophosphate can be performed by a method of mixing the two and reacting them while stirring.
In the production method of the present invention, the reaction can be carried out without using a reaction solvent. For this reason, a lithium salt compound can be manufactured industrially advantageous and efficiently.

In the above reaction, the molar ratio of the ether compound (TOD and / or POP) as a ligand to the lithium ion (Li ⁺ ) is preferably 0.3 to 5, more preferably 0.4 to 3, and still more preferably. 0.45 to 2, particularly preferably 0.45 to 1.5.
By reacting at such a molar ratio, TOD and / or POP and lithium difluorophosphate can be easily reacted, and the purity of the target lithium salt compound can be increased.
The contact temperature (reaction temperature) between the ether compound and lithium difluorophosphate is preferably low in the range in which the reaction proceeds from the viewpoint of suppressing the decomposition of the lithium salt compound to be produced. Specifically, −30 to 80 ° C. is preferable, −28 to 50 ° C. is more preferable, −25 to 20 ° C. is further preferable, and −24 to 10 ° C. is particularly preferable.
The reaction pressure is not particularly limited, but is preferably from normal pressure (atmospheric pressure) to 1 MPa, more preferably from normal pressure (atmospheric pressure) to 0.3 MPa.
The reaction time is not particularly limited, but is usually 1 hour to 5 days, preferably 2 hours to 4 days, and more preferably 3 hours to 3 days.

The obtained lithium salt compound can be isolated as a solid by washing with an ether solvent such as tert-butyl methyl ether, if necessary, followed by vacuum drying at room temperature.
Moreover, it can also be used as a non-aqueous electrolyte for use in lithium ion secondary batteries, lithium ion capacitors, etc. without adding an organic solvent as an electrolyte solution component such as methyl ethyl carbonate and dimethyl carbonate and isolating it as a solid. .
The structure of the lithium salt compound obtained by the production method of the present invention can be confirmed by proton nuclear magnetic resonance spectrum ( ¹ H-NMR), fluorine nuclear magnetic resonance spectrum ( ¹⁹ F-NMR), elemental analysis, etc. it can.

[Non-aqueous electrolyte]
The non-aqueous electrolyte solution of the present invention is a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent. 2,5,8,11-tetraoxadodecane (TOD) and 2,5,8,11,14 -A lithium salt compound comprising a lithium cation having at least one ether compound selected from pentaoxapentadecane (POP) as a ligand and a difluorophosphate anion is characterized.

The reason why the nonaqueous electrolytic solution of the present invention is excellent in high-temperature cycle characteristics and output characteristics after high-temperature cycles and can suppress metal elution from the positive electrode or the like is not necessarily clear, but is considered as follows.
As described above, the compound contained in the nonaqueous electrolytic solution of the present invention includes a lithium cation (A) having at least one ether compound selected from TOD and POP as a ligand, and a difluorophosphate anion [(PO ₂ F ₂ ) ⁻ ]. Here, it is considered that the lithium cation (A) is not easily decomposed electrochemically as compared with the ether compound not coordinated to the lithium ion, and the cycle characteristics can be improved. In addition, since the difluorophosphate anion reacts quickly with the active sites on the electrode, it forms a strong electrode film (Solid Electrolyte Interphase: SEI film) that does not prevent the permeation of lithium ions. For this reason, bis (trifluoromethanesulfonyl) imide ion [(CF3SO2) 2N ⁻ ], which is not a difluorophosphate anion, does not provide an effect of improving high-temperature cycle characteristics and output characteristics after high-temperature cycles. The lithium salt compound comprising (A) and the difluorophosphate anion [(PO ₂ F ₂ ) ⁻ ] is considered to be able to exhibit excellent high temperature cycle characteristics and output characteristics after high temperature cycles.

  In the non-aqueous electrolyte of the present invention, the content of the lithium salt compound comprising the lithium cation (A) and the difluorophosphate anion contained in the non-aqueous electrolyte is 0.1 to 0.1 in the non-aqueous electrolyte. It is preferable that it is 10 mass%. If the content is 10% by mass or less, a film is excessively formed on the electrode, and the output characteristics after the high temperature cycle are less likely to be deteriorated. If the content is 0.1% by mass or more, the film is sufficiently formed. In addition, since the high temperature cycle characteristics are enhanced, the above range is preferable. The content is more preferably 0.3% by mass or more in the nonaqueous electrolytic solution, further preferably 1% by mass or more, and particularly preferably 1.7% by mass or more. Moreover, the upper limit is more preferably 9% by mass or less, still more preferably 7% by mass or less, and particularly preferably 5% by mass or less.

[Nonaqueous solvent]
As the non-aqueous solvent used in the non-aqueous electrolyte solution of the present invention, one or more selected from cyclic carbonates and chain esters are preferably exemplified. In order to synergistically improve electrochemical characteristics such as a wide temperature range, particularly cycle characteristics at high temperatures, and output characteristics after cycling, it is preferable that a chain ester is included, more preferably a chain carbonate is included, It is particularly preferable that both cyclic carbonate and chain carbonate are included.
The term “chain ester” is used as a concept including a chain carbonate and a chain carboxylic acid ester.

Examples of the cyclic carbonate include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), 4-fluoro-1,3-dioxolan-2-one (FEC), and vinylene carbonate (VC).
As the combination of cyclic carbonates, a combination of EC and VC, a combination of EC and FEC, and a combination of PC and VC are particularly preferable.

In addition, when the non-aqueous solvent contains ethylene carbonate and / or propylene carbonate, the stability of the film formed on the electrode increases, the cycle characteristics when the electricity storage device is used at high temperature and high voltage, the output characteristics after the cycle, In addition, the metal elution suppression effect from the positive electrode and the like is improved, which is preferable.
The content of ethylene carbonate and / or propylene carbonate is preferably 3% by volume or more, more preferably 5% by volume or more, still more preferably 7% by volume or more with respect to the total volume of the nonaqueous solvent, and the upper limit thereof. Is preferably 40% by volume or less, more preferably 35% by volume or less, and still more preferably 25% by volume or less.

Preferred examples of the chain ester include asymmetric chain carbonates, symmetric chain carbonates, and asymmetric chain carboxylic acid esters containing an ethoxy group.
As the asymmetric chain carbonate, those having a methyl group are preferable, and specifically, methyl ethyl carbonate (MEC), methyl propyl carbonate, and methyl isopropyl carbonate are preferable, and methyl ethyl carbonate (MEC) is more preferable.
As the symmetric chain carbonate, dimethyl carbonate (DMC) and diethyl carbonate (DEC) are preferable, and as the chain carboxylic acid ester, ethyl acetate (EA) and ethyl propionate are preferable.
Among the chain esters, a combination of methyl ethyl carbonate (MEC) and dimethyl carbonate (DMC), a combination of methyl ethyl carbonate (MEC) and ethyl acetate, methyl ethyl carbonate (MEC), dimethyl carbonate (DMC) and ethyl acetate. A combination is more preferred.

The content of the chain ester is not particularly limited, but it is preferably used in the range of 60 to 90% by volume with respect to the total volume of the nonaqueous solvent. If the content is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, and if it is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte is lowered and the temperature is wide, particularly at high temperatures. The above range is preferable because there is little risk of deterioration of electrochemical characteristics such as cycle characteristics and output characteristics after cycling.
Among the chain esters, the proportion of volume occupied by ethyl acetate (EA) is preferably 1% by volume or more, more preferably 2% by volume or more, and still more preferably 3% by volume or more. The upper limit is preferably 10% by volume or less, more preferably 8% by volume or less, and still more preferably 6% by volume or less.
In the case of the said composition, since it is excellent in the high temperature cycle characteristic and the output characteristic after a high temperature cycle, and metal elution from a positive electrode etc. can be suppressed, it is preferable.
The ratio of the cyclic carbonate to the chain ester is preferably 10/90 to 45/55 in terms of the volume ratio of (cyclic carbonate / chain ester), from the viewpoint of improving electrochemical characteristics in a wide temperature range, particularly at high temperatures. / 85 to 40/60 is more preferable, and 20/80 to 35/65 is still more preferable.

(Additive)
In the non-aqueous electrolyte of the present invention, as an additive that can be used in combination with the lithium salt compound of the present invention, an SO ₂ group-containing compound, an aromatic compound, a carbon-carbon triple bond-containing compound, a lithium-containing ionic compound And one or more selected from phosphazene compounds.

The SO ₂ group-containing compound is not particularly limited as long as it is a compound having “SO ₂ group” in the molecule. Specific examples thereof include 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, 2,2-dioxide-1,2-oxathiolane- One or more kinds selected from 4-yl acetate, ethylene sulfate, propylene sulfate, butane-1,4-diyl dimethanesulfonate, methylenemethane disulfonate, and the like are preferable.

  The aromatic compound is not particularly limited as long as it is a compound having a “benzene ring” in the molecule. Specific examples thereof include cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, biphenyl, terphenyl (o-, m-, p-isomer), fluorobenzene, hexafluorobenzene, octafluorotoluene, pentafluorophenylmethane. One or more selected from sulfonate, 2-phenylphenyl dimethyl phosphate, 2-phenylphenyl diethyl phosphate, methylphenyl carbonate, ethylphenyl carbonate, methyl 2-phenylphenyl carbonate, phenyl 2-phenylphenyl carbonate, and the like are preferable. Can be mentioned.

  The carbon-carbon triple bond-containing compound is not particularly limited as long as it is a compound having a “carbon-carbon triple bond” in the molecule. Specific examples thereof include methyl 2-propynyl carbonate, 2-propynyl methanesulfonate, 2-propynyl vinylsulfonate, di (2-propynyl) oxalate, ethynyl ethylene carbonate, 2-propynyl 2-oxo-1,3-dioxolane. One or more kinds selected from -4-carboxylate, 2-butyne-1,4-diyl dimethanesulfonate, and the like are preferable.

  The type of lithium-containing ionic compound is not particularly limited as long as it is a compound having “lithium” as a cationic species. Specific examples thereof include lithium difluorophosphate, lithium fluorosulfonate, difluorobis [oxalate-O, O ′] lithium phosphate (LiPFO), lithium tetrafluoro [oxalate-O, O ′] lithium phosphate, and bis [oxalate. -O, O '] lithium borate (LiBOB), difluoro [oxalate-O, O'] lithium borate, lithium methyl sulfate, lithium ethyl sulfate, lithium 2,2,2-trifluoroethyl sulfate, etc. One or more types are preferably mentioned, and two or more types are more preferably used in combination.

  The type of the phosphazene compound is not particularly limited as long as it is a compound having “N═PN group” in the molecule. Specific examples thereof include methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, ethoxyheptafluorocyclotetraphosphazene, dimethylaminopentafluorocyclotriphosphazene, and diethylaminopentafluorocyclotriphosphazene. 1 or more types chosen from are mentioned suitably.

The content of the SO ₂ group-containing compound, aromatic compound, carbon-carbon triple bond-containing compound, lithium-containing ionic compound, or phosphazene compound is preferably 0.001 to 5% by mass in the non-aqueous electrolyte. In this range, the film is sufficiently formed without becoming too thick, and the high temperature cycle characteristics and the output characteristics after the high temperature cycle are enhanced. The content is more preferably 0.01% by mass or more, more preferably 0.1% by mass or more in the non-aqueous electrolyte, and the upper limit thereof is more preferably 3.5% by mass or less, and 2.5% by mass. The following is more preferable.

Moreover, it is preferable to use together 2 or more types of compounds used in combination with the lithium salt compound of this invention. Among the combinations, it is more preferable to use a lithium-containing ionic compound in combination with at least one selected from an SO ₂ group-containing compound, an aromatic compound, a carbon-carbon triple bond-containing compound, and a phosphazene compound.

From the viewpoint of improving the output of the lithium ion secondary battery and the lithium ion capacitor, the lower limit of the HF concentration contained in the non-aqueous electrolyte of the present invention is preferably 1 ppm or more, more preferably 2 ppm or more, and the upper limit of the HF concentration. Is preferably 50 ppm or less, more preferably 20 ppm or less, and still more preferably 8 ppm or less.
From the viewpoint of improving the output of the lithium ion secondary battery and the lithium ion capacitor, the lower limit of the alcohol content contained in the non-aqueous electrolyte of the present invention is preferably 1 ppm or more, more preferably 2 ppm or more. Is preferably 50 ppm or less, more preferably 20 ppm or less, still more preferably 8 ppm or less.

[Electrolyte salt]
A preferable example of the electrolyte salt used in the present invention is a lithium salt.
The lithium _{salt, LiPF 6, LiBF 4, LiN} (SO 2 F) 2, and _LiN (SO 2 _{CF 3)} is preferably one or more selected from _2, LiPF ₆ is more preferable.
The concentration of the lithium salt is usually preferably 0.8 M or more, more preferably 1.0 M or more, and further preferably 1.2 M or more with respect to the non-aqueous solvent. Moreover, the upper limit is preferably 1.6 M or less, more preferably 1.5 M or less, and even more preferably 1.4 M or less.

[Production of non-aqueous electrolyte]
The nonaqueous electrolytic solution of the present invention includes, for example, the above-mentioned nonaqueous solvent mixed therein, and the lithium salt comprising the lithium cation (A) and the difluorophosphate anion with respect to the electrolyte salt and the nonaqueous electrolytic solution. It can be obtained by adding a salt compound.
At this time, it is preferable that the compound added to the non-aqueous solvent and the non-aqueous electrolyte to be used is one that is purified in advance and has as few impurities as possible within a range that does not significantly reduce the productivity.

  The nonaqueous electrolytic solution of the present invention can be used in the following first and second electric storage devices, and as the nonaqueous electrolyte, not only a liquid but also a gelled one can be used. Furthermore, the non-aqueous electrolyte of the present invention can be used for a solid polymer electrolyte. In particular, it is preferably used for a first electricity storage device (ie, for a lithium battery) or a second electricity storage device (ie, for a lithium ion capacitor) using a lithium salt as an electrolyte salt, and is used for a lithium battery. More preferably, it is more preferably used for a lithium secondary battery.

[First power storage device (lithium secondary battery)]
The lithium secondary battery of the present invention is composed of the nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent. Components other than the non-aqueous electrolyte, such as a positive electrode and a negative electrode, can be used without particular limitation.
For example, as the positive electrode active material for a lithium secondary battery, a composite metal oxide with lithium containing one or more selected from the group consisting of cobalt, manganese, and nickel is used. These positive electrode active materials can be used alone or in combination of two or more.
Examples of such lithium composite metal oxides include LiCoO ₂ , LiCo _1-x M _x O ₂ (where M is Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and One or more elements selected from Cu, 0.001 ≦ x ≦ 0.05), LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Mn _0.1 Co _0.1 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , Li ₂ MnO ₃ and LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe), and LiNi _1/2 Mn _3/2 O 1 or more is preferably used selected from ₄ It is done. Moreover, LiCoO ₂ and LiMn ₂ O _4, LiCoO ₂ and LiNiO _2, may be used in combination as LiMn ₂ O ₄ and LiNiO _2.

Among these, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _1/2 Mn _3/2 O ₄ , Li ₂ MnO ₃ LiMO ₂ (M is a transition metal such as Co, Ni, Mn, Fe, etc.) and a lithium mixed metal oxide that can be used at a voltage of 4.4 V (positive electrode Li reference potential is 4.5 V) or more LiNi _0.5 Mn _0.3 Co _0.2 O ₂ and LiNi _1/2 Mn _3/2 O ₄ having a high Ni content are particularly preferable. When a positive electrode containing Ni or Mn is used, the amount of Ni or Mn eluted from the positive electrode as metal ions increases, and the catalytic effect of Ni or Mn deposited on the negative electrode accelerates the decomposition of the electrolyte on the negative electrode. As a result, electrochemical characteristics such as high-temperature cycle characteristics deteriorate. However, an electricity storage device using the non-aqueous electrolyte of the present invention is preferable because deterioration of electrochemical characteristics such as cycle characteristics at high temperatures and output characteristics after cycling and metal elution from the positive electrode can be suppressed.

The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and one or more selected from carbon nanotubes Examples thereof include carbon materials. Further, graphite, carbon black, and carbon nanotubes may be appropriately mixed and used.
The amount of the conductive agent added to the positive electrode mixture is preferably 1 to 10% by mass, more preferably 2 to 5% by mass.

The positive electrode is composed of a conductive agent such as acetylene black and carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene. This is mixed with a binder such as copolymer (NBR), carboxymethyl cellulose (CMC), or ethylene propylene diene terpolymer, and a high boiling point solvent such as 1-methyl-2-pyrrolidone is added thereto and kneaded. After forming this agent, this positive electrode mixture is applied to an aluminum foil as a current collector or a stainless steel lath plate, etc., dried and pressure-molded, and then vacuumed at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. It can produce by heat-processing with.
The density of the part except the collector of the positive electrode is usually at 1.5 g / cm ³ or more, to further enhance the capacity of the battery, preferably 2 g / cm ³ or more, more preferably 3 g / cm ³ or more, further Preferably it is 3.6 g / cm ³ or more. The upper limit is preferably 4 g / cm ³ or less.

Examples of the negative electrode active material for a lithium secondary battery include lithium metal, a lithium alloy, and a carbon material that can occlude and release lithium (e.g., graphitizable carbon, or a (002) plane spacing of 0.37 nm or more. Non-graphitizable carbon, graphite with (002) plane spacing of 0.34 nm or less, etc.], tin (single), tin compound, silicon (single), silicon compound, lithium titanate such as Li ₄ Ti ₅ O ₁₂ One or two or more selected from compounds and the like can be used in combination. Particularly preferred combinations are graphite and silicon, or graphite and silicon compound.
When graphite and silicon or graphite and silicon compound are used in combination as the negative electrode active material, the content of silicon and silicon compound in the total negative electrode active material is preferably 1 to 45% by mass, more preferably 2 to 15%. % By mass. It is preferable for the content to be in the above-mentioned range since the capacity can be increased while suppressing a decrease in electrochemical characteristics and an increase in electrode thickness of the lithium secondary battery according to the present invention.

As another negative electrode active material for a lithium secondary battery, an oxide containing titanium is preferable, and a lithium titanate compound having a spinel structure such as Li ₄ Ti ₅ O ₁₂ is preferable. It is preferable to use an oxide containing titanium as the negative electrode active material and the nonaqueous electrolytic solution of the present invention because the cycle characteristics at high temperatures and the output characteristics after cycling of the lithium ion secondary battery can be further improved.
In addition, it is preferable to use carbon nanotubes as the conductive assistant because the above effects are more easily exhibited.
The specific surface area of the oxide containing titanium is preferably 4 m ² / g or more and 100 m ² / g or less, and the volume-based average particle diameter determined by the laser diffraction / scattering method is preferably 0.1 μm or more and 50 μm or less.

The negative electrode is kneaded using the same conductive agent, binder, and high-boiling solvent as in the production of the positive electrode, and then the negative electrode mixture is applied to the copper foil of the current collector. After being dried and pressure-molded, it can be produced by heat treatment under vacuum at a temperature of about 50 ° C. to 250 ° C. for about 2 hours.
The density of the portion excluding the current collector of the negative electrode is usually 1.1 g / cm ³ or more, and preferably 1.5 g / cm ³ or more in order to further increase the capacity of the battery. The upper limit is preferably 2 g / cm ³ or less.

Although there is no restriction | limiting in particular as a battery separator, The monolayer or laminated | stacked microporous film, woven fabric, or nonwoven fabric etc. of polyolefin, such as a polypropylene, polyethylene, an ethylene propylene copolymer, can be used. As the lamination of polyolefin, a lamination of polyethylene and polypropylene is preferable, and a three-layer structure of polypropylene / polyethylene / polypropylene is more preferable.
The thickness of a separator becomes like this. Preferably it is 2 micrometers or more, More preferably, it is 3 micrometers or more, More preferably, it is 4 micrometers or more, Moreover, the upper limit becomes like this. Preferably it is 30 micrometers or less, More preferably, it is 20 micrometers or less, More preferably, it is 15 micrometers or less.

  The structure of the lithium battery is not particularly limited, and a coin-type battery, a cylindrical battery, a square battery, a laminate battery, or the like can be applied.

  The lithium secondary battery according to the present invention has excellent electrochemical characteristics in a wide temperature range even when the end-of-charge voltage is 4.2 V or more, particularly 4.3 V or more, and the characteristics are also good at 4.4 V or more. is there. The end-of-discharge voltage is usually 2.8 V or more, and further 2.5 V or more, but the lithium secondary battery in the present invention can be 2.0 V or more. Although it does not specifically limit about an electric current value, Usually, it uses in the range of 0.1-30C. Moreover, the lithium battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is -10-80 degreeC.

  In the present invention, as a countermeasure against an increase in the internal pressure of the lithium battery, a method of providing a safety valve on the battery lid or cutting a member such as a battery can or a gasket can be employed. Further, as a safety measure for preventing overcharge, the battery lid can be provided with a current interruption mechanism that senses the internal pressure of the battery and interrupts the current.

[Second power storage device (lithium ion capacitor)]
A second electricity storage device of the present invention is an electricity storage device that stores the energy by using intercalation of lithium ions to a carbon material such as graphite, which is a negative electrode, containing the non-aqueous electrolyte of the present invention. It is called an ion capacitor (LIC). Examples of the positive electrode include those using an electric double layer between an activated carbon electrode and an electrolytic solution, and those using a π-conjugated polymer electrode doping / dedoping reaction. The electrolytic solution contains at least a lithium salt such as LiPF ₆ .
In the lithium ion capacitor, a negative electrode potential can be kept lower than that of a normal electric double layer capacitor by using a carbon material in which lithium titanate or lithium ions are previously inserted or doped instead of activated carbon as the negative electrode material. As a result, the cell operating voltage range can be widened.
If the non-aqueous electrolyte of the present invention is used, a lithium ion capacitor excellent in high-temperature cycle characteristics and output characteristics after high-temperature cycles can be provided.

Synthesis example 1
Synthesis of bis (difluorophosphoryl) (2,5,8,11-tetraoxadodecane) dilithium In a 100 ml flask, 20.0 g (112 mmol) of 2,5,8,11-tetraoxadodecane and 12.0 g of lithium difluorophosphate (111 mmol) was charged. The mixture was stirred at room temperature for 3 hours and then cooled to -20 ° C. After standing for 2 days, the precipitate was filtered, and the residue was washed with tert-butyl methyl ether. The obtained solid was vacuum-dried at room temperature to obtain 19.33 g of bis (difluorophosphoryl) (2,5,8,11-tetraoxadodecane) dilithium as a white solid (yield 88.4%).
The obtained bis (difluorophosphoryl) (2,5,8,11-tetraoxadodecane) dilithium was measured by ¹ H-NMR, ¹⁹ F-NMR, and elemental analysis to confirm its structure. The results are shown below.
^<1 H-NMR measurement results>
¹ H-NMR (400 MHz, CD ₃ CN): 3.55 to 3.60 (8H, m), 3.49 to 3.55 (4H, m), 3.33 (6H, s)
< ¹⁹ F-NMR measurement result>
¹⁹ F-NMR (376.5 MHz, CD ₃ CN): 84.60 (4F, d, J = 928.2 Hz)
<Results of elemental analysis>
Anal. _{Calcd For C 8 H 18 F 4} Li 2 O 8 P 2: C, 24.39; H, 4.60. Found: C, 24.05; H, 4.62.

Examples 1-13, Comparative Examples 1-4
[Production of lithium ion secondary battery]
94% by mass of LiNi _0.34 Mn _0.33 Co _0.33 O _{2 and} 3% by mass of acetylene black (conductive agent) are mixed, and 3% by mass of polyvinylidene fluoride (binder) is previously added to 1-methyl-2- A positive electrode mixture paste was prepared by adding to and mixing with the solution dissolved in pyrrolidone. This positive electrode mixture paste was applied to both surfaces of an aluminum foil (current collector), dried and pressurized, and cut into a predetermined size to produce a belt-like positive electrode sheet. The density of the portion excluding the current collector of the positive electrode was 3.6 g / cm ³ .
Further, 5% by mass of SiO (negative electrode active material) and 90% by mass of artificial graphite (d ₀₀₂ = 0.335 nm, negative electrode active material) were mixed, and 5% by mass of polyvinylidene fluoride (binder) was previously added to 1-methyl- In addition to the solution dissolved in 2-pyrrolidone, the mixture was mixed to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to both surfaces of a copper foil (current collector), dried and pressurized, and cut into a predetermined size to produce a strip-shaped negative electrode sheet. The density of the portion excluding the current collector of the negative electrode was 1.55 g / cm ³ .
As a result of X-ray diffraction measurement using this electrode sheet, the ratio of the peak intensity I (110) of the (110) plane of the graphite crystal to the peak intensity I (004) of the (004) plane [I (110) / I (004)] was 0.1.
And it laminated | stacked in order of the positive electrode sheet obtained above, the separator made from a microporous polyethylene film, and the negative electrode sheet obtained above, and wound this in the shape of a spiral. The wound body was housed in an iron cylindrical battery can plated with nickel which also serves as a negative electrode terminal. Further, a nonaqueous electrolytic solution having the composition shown in Tables 1 and 2 was injected, and the battery lid having the positive electrode terminal was caulked through a gasket to produce an 18650 type cylindrical battery. The positive electrode terminal was previously connected inside the battery using a positive electrode sheet and an aluminum lead tab, and the negative electrode can was previously connected using a negative electrode sheet and a nickel lead tab.

[Evaluation of high-temperature cycle characteristics]
Using the cylindrical battery produced by the above method, in a constant temperature bath of 55 ° C., charge at a constant current of 1 C and a constant voltage for 3 hours to a final voltage of 4.25 V (positive electrode Li reference potential is 4.35 V), Next, discharging to a discharge voltage of 3.0 V under a constant current of 1 C was defined as one cycle, and this was repeated until 300 cycles were reached. And the discharge capacity maintenance factor after a cycle was calculated | required by the following formula, and the high temperature cycling characteristic was evaluated.
Discharge capacity retention ratio (%) = (discharge capacity at 300th cycle / discharge capacity at 1st cycle) × 100

[Evaluation of output characteristics after high-temperature cycle]
The cylindrical battery after the high temperature cycle was charged in a constant temperature bath at 25 ° C. with a constant current and a constant voltage of 1 C for 3 hours to a final voltage of 4.25 V, and then discharged to a discharge voltage of 3.0 V under a constant current of 1 C. (1C capacity). Thereafter, the battery was charged with a constant current and a constant voltage of 1 C to a final voltage of 4.25 V for 3 hours, and discharged to a discharge voltage of 3.0 V under a constant current of 5 C (5 C capacity). The capacity ratio (5C capacity / 1C capacity) was defined as output characteristics after the cycle.
As for the output characteristics after the high temperature cycle, relative output characteristics were evaluated based on the output characteristics of Comparative Example 1 as 100%.

[Evaluation of metal dissolution after high-temperature cycle]
The amount of metal elution after the high-temperature cycle was determined by identifying the amount of metal deposited on the negative electrode. The amount of metal deposited on the negative electrode was dismantled from the cylindrical battery after the high temperature cycle, dissolved the washed negative electrode sheet with acid, and then ICP (high frequency inductively coupled plasma) emission spectroscopy (manufactured by Hitachi High-Tech Science Co., Ltd., The total metal elution amount of Ni, Mn and Co was analyzed by “SPS3520UV”).
The metal elution amount was evaluated based on the total metal elution amount of Ni, Mn and Co in Comparative Example 1 as 100%.
The production conditions and battery characteristics of the battery are shown in Tables 1-2.
Incidentally, in Table _{1~2, Li 2 (TOD) (} PO 2 F 2) 2 , the bis (difluoromethyl phosphoryl) (2,5,8,11-tetra oxa dodecane) is an abbreviation of dilithium, Li (G3 ₁ TFSI is an abbreviation for lithium bis (trifluoromethanesulfonyl) imide-2,5,8,11-tetraoxadodecane.
The same applies to Tables 3 to 5.

Example 14 and Comparative Example 5
A positive electrode sheet was produced using LiNi _1/2 Mn _3/2 O ₄ (positive electrode active material) instead of the positive electrode active material used in Example 5 and Comparative Example 1. 94% by mass of LiNi _1/2 Mn _3/2 O ₄ coated with amorphous carbon and 3% by mass of acetylene black (conductive agent) are mixed, and 3% by mass of polyvinylidene fluoride (binder) is pre- A positive electrode mixture paste was prepared by adding to and mixing with the solution dissolved in methyl-2-pyrrolidone.
This positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried and pressurized, and cut into a predetermined size to produce a positive electrode sheet. A cylindrical battery was fabricated in the same manner as in Example 1 and Comparative Example 1, except that the discharge end voltage was 4.9 V, the discharge end voltage was 2.7 V, and the composition of the nonaqueous electrolyte was changed to a predetermined one. Battery evaluation was performed.
The metal elution amount was determined based on the metal elution amount of Comparative Example 5 as 100%.
The results are shown in Table 3.

Example 15 and Comparative Example 6
A negative electrode sheet was prepared using lithium titanate (Li ₄ Ti ₅ O ₁₂ ; negative electrode active material) instead of the negative electrode active material used in Example 5 and Comparative Example 1.
90% by mass of lithium titanate, 4% by mass of acetylene black (conductive agent) and 1% by mass of carbon nanotubes (conductive agent) are mixed, and 5% by mass of polyvinylidene fluoride (binder) is previously added to 1-methyl-2-pyrrolidone. The negative electrode mixture paste was prepared by adding to and mixing with the solution previously dissolved in the mixture.
This negative electrode mixture paste was applied onto a copper foil (current collector), dried, pressurized and cut into a predetermined size to produce a negative electrode sheet, and the end-of-charge voltage during battery evaluation was 2 A cylindrical battery was produced in the same manner as in Example 1 and Comparative Example 1 except that the discharge end voltage was set to 0.8 V, the discharge end voltage was set to 1.2 V, and the composition of the nonaqueous electrolyte was changed to a predetermined one. Went.
The results are shown in Table 4.

Examples 16-17, Comparative Example 7
[Solubility test]
A predetermined amount of bis (difluorophosphoryl) (2,5,8,11-tetraoxadodecane) dilithium obtained by the same production method as in Synthesis Example 1 was added to 50 g of the electrolytic solution used in Comparative Example 1, and 10% at 25 ° C. The mixture was stirred for a minute (Examples 16 and 17).
Further, 0.75 g of lithium difluorophosphate was added to 50 g of the nonaqueous electrolytic solution used in Comparative Example 1, and the mixture was stirred at 25 ° C. for 10 minutes (Comparative Example 7).
When a completely uniform liquid with no undissolved residue was obtained after stirring, the solubility was evaluated as o, and when it remained undissolved, the solubility was evaluated as x. The results are shown in Table 5.

Each of the lithium secondary batteries of Examples 1 to 13 using a non-aqueous electrolyte containing a lithium cation having a specific ether compound as a ligand and a lithium salt compound composed of a difluorophosphate anion is Comparative Examples 1 to 1. Compared with the lithium secondary battery of No. 4, the high temperature cycle characteristics, the output characteristics after the high temperature cycle, and the metal elution suppression effect from the positive electrode are improved.
Further, from the comparison between Example 14 and Comparative Example 5 and the comparison between Example 15 and Comparative Example 6, when LiNi _1/2 Mn _3/2 O ₄ is used for the positive electrode or when lithium titanate is used for the negative electrode Since the same effect is also observed, it is clear that the effect is not dependent on a specific positive electrode or negative electrode.
Further, from the comparison between Examples 16 and 17 and Comparative Example 7, a lithium cation compound composed of an ether compound as a ligand and a lithium salt compound composed of a difluorophosphate anion has much higher solubility than lithium difluorophosphate. It can be seen that there is an improvement.
The nonaqueous electrolytic solution of the present invention has an effect of improving high temperature cycle characteristics, output characteristics after high temperature cycling, and the like as a nonaqueous electrolytic solution for an electricity storage device such as a lithium ion capacitor.

  If the non-aqueous electrolyte of the present invention is used, it is possible to obtain an electricity storage device that is excellent in high-temperature cycle characteristics and output characteristics after high-temperature cycles and that can suppress metal elution from the positive electrode and the like. Power storage devices such as lithium-ion secondary batteries and lithium-ion capacitors that are particularly likely to be used at high temperatures, such as hybrid electric vehicles, plug-in hybrid electric vehicles, battery electric vehicles, tablet terminals, and ultrabooks When used as a nonaqueous electrolytic solution, it is possible to obtain an electricity storage device that is excellent in high-temperature cycle characteristics and output characteristics after high-temperature cycles, and that can suppress metal elution from the positive electrode or the like.

Claims (8)

  From a lithium cation having at least one ether compound selected from 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane as a ligand, and a difluorophosphate anion A lithium salt compound. The lithium salt compound according to claim 1, wherein a molar ratio of the ether compound to lithium ions (Li ⁺ ) in the lithium cation is 0.1 to 0.7.   3. Bis (difluorophosphoryl) (2,5,8,11-tetraoxadodecane) dilithium or bis (difluorophosphoryl) (2,5,8,11,14-pentaoxapentadecane) dilithium The lithium salt compound described in 1.   A non-aqueous electrolytic solution in which an electrolyte salt is dissolved in a non-aqueous solvent, wherein the lithium salt compound according to any one of claims 1 to 3 is contained in the non-aqueous electrolytic solution.   The nonaqueous electrolytic solution according to claim 4, comprising a nonaqueous solvent containing one or more selected from cyclic carbonates and chain carbonates.   A lithium ion secondary battery using the nonaqueous electrolytic solution according to claim 4.   A lithium ion capacitor using the nonaqueous electrolytic solution according to claim 4.   Any one of the ether compounds chosen from 2,5,8,11-tetraoxadodecane and 2,5,8,11,14-pentaoxapentadecane and lithium difluorophosphate are brought into contact. A method for producing a lithium salt compound according to claim 1.