JP6500775B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a secondary battery, in particular to a lithium ion secondary battery, and more particularly to an electrolyte for a secondary battery, a lithium ion secondary battery using the same, and a method of manufacturing the same.

  Lithium secondary batteries are widely used in applications such as portable electronic devices and personal computers. Lithium secondary batteries are required to have improved safety such as flame retardancy, and as described in the following documents, secondary batteries using an electrolytic solution containing a phosphoric acid ester compound and a cyclic carbonate have been proposed. .

  Patent Document 1 discloses a secondary battery using an electrolytic solution composed of a phosphate compound, a cyclic carbonate containing halogen, a chain carbonate, and a lithium salt. Patent Document 1 shows that the safety can be enhanced by using this electrolytic solution, and that the irreversible capacity can be reduced by the combination of the carbon negative electrode and the electrolytic solution.

  Further, Patent Document 2 discloses an electrolyte for an alkali metal ion secondary battery containing a solution of fluoroethylene carbonate, an alkali metal dissolved in it, and propylene carbonate, and by using this electrolyte, it is possible to It has been shown that irreversible capacity loss and efficiency loss of the battery can be suppressed.

  Patent Document 3 shows that by mixing a phosphoric acid ester, high safety can be ensured even when lithium metal is deposited on the negative electrode.

  Patent Document 4 discloses a secondary battery using an electrolytic solution containing a phosphoric acid ester, a cyclic carbonate, and either a vinylene carbonate compound or a vinyl ethylene carbonate compound.

  Patent Document 5 discloses a secondary battery having an electrolyte containing a fluorine-containing phosphate.

Patent Document 6 and Patent Document 7 have the formula R ¹ O- (R ² O) _n -R ³ (R ¹ , R ³ : an alkyl group having 1 to 8 carbon atoms which may be substituted with a halogen atom, R ² : an alkylene group having 1 to 8 carbon atoms which may be substituted by a halogen atom, provided that at least one of R ¹ , R ² and R ³ must be substituted by a halogen atom, 1 ≦ n ≦ A secondary battery using an electrolytic solution containing a glycol diether represented by 4) is disclosed. Furthermore, Patent Document 6 and Patent Document 7 disclose that a phosphoric acid ester is contained in an electrolytic solution, but there is no description regarding a fluorinated phosphoric acid ester.

  In addition, while safety is required for lithium secondary batteries, improvement of the energy density of the batteries has become an important technical issue.

Several methods can be considered as a method of increasing the energy density of the lithium secondary battery, and among them, it is effective to raise the operating potential of the battery. In the conventional lithium secondary batteries using lithium cobaltate or lithium manganate as the positive electrode active material, the operating potential is 4V class (average operating potential = 3.6 to 3.8V: lithium potential). This is because the expression potential is defined by the redox reaction (Co ^{3 +} → Co ^{4 +} or Mn ^{3 +} → Mn ^{4 +} ) of Co ion or Mn ion.

On the other hand, it is known that an operating potential of 5 V class can be realized by using, for example, a spinel compound in which Mn of lithium manganate is substituted by Ni or the like as an active material. Specifically, as disclosed in Patent Document 8, it is known that a spinel compound such as LiNi _0.5 Mn _1.5 O ₄ exhibits a potential plateau in a region of 4.5 V or more. In such a spinel compound, Mn exists in a tetravalent state, and instead of the oxidation reduction of Mn ^{3 +} → → Mn ^{4 +} , the operating potential is defined by the oxidation reduction of Ni ²⁺ → → Ni ⁴⁺ .

LiNi _0.5 Mn _1.5 O ₄ has a capacity of 130 mAh / g or more and an average operating voltage of 4.6 V or more with respect to lithium metal. Although the capacity is smaller than LiCoO ₂ , the energy density of the battery is higher than that of LiCoO ₂ . For these reasons, LiNi _0.5 Mn _1.5 O ₄ is promising as a positive electrode material in the future.

Patent No. 3961597 specification Japanese Patent Publication No. 2001-501355 Patent No. 3821495 specification Patent No. 4187965 specification JP, 2008-021560, A JP, 2001-023691, A Japanese Patent Application Laid-Open No. 2001-085056 JP, 2009-123707, A

J. Electrochem. Soc. , Vol. 144, 204 (1997)

  Among the above-mentioned cyclic carbonates, ethylene carbonate (EC) has a very high dielectric constant of 90, and is known to be highly effective in ionizing lithium salts and generating ions carrying electricity. However, since ethylene carbonate has a high melting point of 37 ° C. and is solid alone at the battery operating temperature, it may cause lithium ions to be difficult to move at low temperatures, or may precipitate and affect the characteristics. Was expected. On the other hand, propylene carbonate (PC) has a fairly high dielectric constant of 65 and a melting point of -49 ° C, so it does not precipitate even at low temperatures, and may maintain the ionization of the lithium salt and the mobility of the ions. There is.

  However, it is known that propylene carbonate reacts with carbon used as a general negative electrode material to degrade the negative electrode or generate gas.

On the other hand, as a positive electrode active material, there are materials of 4V class such as LiMn ₂ O ₄ or LiCoO ₂ as disclosed in the above-mentioned Patent Documents 1 to 7. Further, as disclosed in Patent Document 8, when a spinel compound such as LiNi _0.5 Mn _1.5 O ₄ or the like is used as a positive electrode active material, a higher operating voltage can be obtained. However, under high operating voltage, the reaction between PC and the negative electrode becomes more likely to progress. Since a gas is generated by this reaction, problems in practical use such as an increase in the internal pressure of the cell in the cycle operation and a swelling of the laminate cell occur. In addition, there is also a problem that the capacity and the cycle characteristics deteriorate due to the decomposition of the electrolytic solution and the deterioration of the negative electrode.

  An object of the present invention is to provide a lithium secondary battery excellent in low temperature characteristics and in which gas generation is suppressed.

One aspect of the present invention is
A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of absorbing and releasing lithium, and a non-aqueous electrolyte containing lithium ions,
The non-aqueous electrolyte is propylene carbonate,
A fluorinated cyclic carbonate represented by the general formula (1), and
Containing one or more selected from fluorine-containing phosphate esters and fluorinated linear ethers,
The content of the propylene carbonate is 1% by volume to 50% by volume in the non-aqueous electrolytic solvent, and the content of the fluorinated cyclic carbonate is 0.1% by volume to 10% by volume in the non-aqueous electrolytic solvent The present invention relates to a lithium ion secondary battery characterized by

［式（１）中、ＡからＤは、それぞれ独立に、水素原子、フッ素原子、または、置換もしくは無置換のアルキル基であり、ＡからＤの少なくとも１つはフッ素原子またはフッ素含有アルキル基である。］

[In Formula (1), A to D are each independently a hydrogen atom, a fluorine atom, or a substituted or unsubstituted alkyl group, and at least one of A to D is a fluorine atom or a fluorine-containing alkyl group is there. ]

  According to the present invention, it is possible to provide a lithium ion secondary battery which is excellent in low temperature characteristics and in which gas generation is suppressed.

It is a figure which shows the cross-section of the secondary battery which concerns on this embodiment. It is a graph which shows the gas generation amount after the charging / discharging cycle in the Example of this invention.

  The lithium secondary battery of the present embodiment has a positive electrode, a negative electrode, and an electrolytic solution containing a non-aqueous electrolytic solvent. The non-aqueous electrolytic solvent is at least one selected from propylene carbonate (hereinafter, also described as PC), a fluorinated cyclic carbonate represented by the above formula (1), and a fluorine-containing phosphate ester and a fluorinated linear ether. Contains. In the lithium secondary battery of the present embodiment, a positive electrode active material operating at 4 V class (for example, average operating potential of 3.6 to 3.8 V: potential to lithium) may be used. A positive electrode active material operating at a potential of 5 V or more may be used. The negative electrode active material preferably contains carbon.

(Electrolyte solution)
The non-aqueous electrolyte (hereinafter also referred to as “electrolytic solution” or “non-aqueous electrolytic solution”) includes a support salt and a non-aqueous electrolytic solvent, and the non-aqueous electrolytic solvent is represented by propylene carbonate, the above formula (1) A fluorinated cyclic carbonate, and at least one selected from a fluorine-containing phosphoric acid ester and a fluorinated linear ether.

  In the present embodiment, the non-aqueous electrolytic solvent contains propylene carbonate (PC). The content of PC contained in the non-aqueous electrolytic solvent is not particularly limited, but is preferably 1% by volume or more and 50% by volume or less in the non-aqueous electrolytic solvent. When the content of PC in the non-aqueous electrolytic solvent is 1% by volume or more, the effect of enhancing the ionization of the lithium salt is further improved, and it is more preferably 5% by volume or more. It is generally considered difficult to use PC as a non-aqueous electrolytic solvent, since propylene carbonate (PC) may react with carbon to cause deterioration of the negative electrode and generate gas. However, in the non-aqueous electrolytic solvent of the present invention, the reaction between PC and carbon is suppressed, so if the content of PC in the non-aqueous electrolytic solvent is 50% by volume or less, the reaction with the negative electrode containing carbon is small. can do. As for the content rate of PC, 40 volume% or less in a non-aqueous electrolysis solvent is more preferable, and 30 volume% or less is further more preferable.

  In the present embodiment, the non-aqueous electrolytic solvent contains a fluorinated cyclic carbonate represented by the following formula (1).

式（１）で表されるフッ素化環状カーボネートにおいて、Ａ、Ｂ、ＣおよびＤは、それぞれ独立に、水素原子、フッ素原子、または、置換もしくは無置換のアルキル基であって、Ａ、Ｂ、ＣおよびＤの少なくとも１つはフッ素原子またはフッ素含有アルキル基である。

In the fluorinated cyclic carbonate represented by the formula (1), A, B, C and D each independently represent a hydrogen atom, a fluorine atom or a substituted or unsubstituted alkyl group, and A, B, At least one of C and D is a fluorine atom or a fluorine-containing alkyl group.

  In the formula (1), the carbon number of the alkyl group represented by A, B, C or D is preferably 1 or more and 4 or less, and more preferably 1 or more and 3 or less. When the carbon number of the alkyl group is 4 or less, the increase in the viscosity of the electrolyte is suppressed, the electrolyte is easily penetrated into the pores in the electrode and the separator, and the ion conductivity is improved. This is because the current value is improved in the discharge characteristics.

  The fluorine-containing alkyl group represents an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom, and the number and position of substitution of the fluorine atom are arbitrary. In the embodiment, it is preferable that at least one of A to D is a fluorine atom or a fluorine-containing alkyl group in which 50% or more of the hydrogen atoms of the corresponding unsubstituted alkyl group are substituted with a fluorine atom. . In addition, all of A to D are a fluorine atom or a fluorine-containing alkyl group, and A to D are fluorine atoms, or fluorine in which 50% or more of the hydrogen atoms of the corresponding unsubstituted alkyl groups are substituted by fluorine atoms. It is also preferable that it is a containing alkyl group. When the content of fluorine atoms is high, the voltage resistance is further improved, and even when the positive electrode active material operating at a potential of 4.5 V or more with respect to lithium is used, the deterioration of the battery capacity after the cycle is further reduced. Because you can do it.

  Further, A to D may have a substituent in addition to the fluorine atom, and as the substituent, an amino group, a carboxy group, a hydroxy group, a cyano group, and a halogen atom (for example, a chlorine atom, a bromine atom) And at least one selected from the group consisting of In addition, said carbon number is the concept also including a substituent.

  As a fluorinated cyclic carbonate, the compound etc. which substituted one or all hydrogen atoms, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. by the fluorine atom can be mentioned, for example. For example, 4-fluoro-1,3-dioxolan-2-one (FEC) in which one of hydrogens of ethylene carbonate (EC) is substituted by fluorine, and 4,5 in which two are substituted by fluorine (cis or trans) Difluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-4 substituted with 4 fluorines Dioxolan-2-one, 4-fluoromethyl-1,3-dioxolan-2-one in which one of hydrogens of propylene carbonate (PC) is substituted by fluorine, 4-fluoro-5-methyl-1,3- Dioxolan-2-one, 4-fluoro-4-methyl-1,3-dioxolan-2-one, 3,3,3-trifluoropropylene carbonate (F (3 C), and the like.

  The content of the fluorinated cyclic carbonate contained in the non-aqueous electrolytic solvent is not particularly limited, but is preferably 0.1% by volume or more and 10% by volume or less in the non-aqueous electrolytic solvent. When the content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is 0.1% by volume or more, the effect of suppressing the reaction between PC and the negative electrode is further improved. In addition, when the content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is 10% by volume or less, gas generation due to the decomposition reaction of the fluorinated cyclic carbonate itself can be reduced. The content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is more preferably 1% by volume or more, still more preferably 1.5% by volume or more, and particularly preferably 2% by volume or more. The content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is more preferably 5% by volume or less.

  Moreover, it is preferable that it is 2 volume% or more, and, as for the content rate of the fluorinated cyclic carbonate with respect to propylene carbonate (PC), 4 volume% or more is more preferable. In addition, the content of the fluorinated cyclic carbonate relative to PC is preferably 40% by volume or less, and more preferably 20% by volume or less.

  In this embodiment, the non-aqueous electrolytic solvent is selected from, in addition to the above-mentioned fluorinated cyclic carbonate, a fluorine-containing phosphate represented by the following formula (2) and a fluorinated chain ether represented by the following formula (4) Or at least one kind of at least one kind. Each compound is described below.

  In the present embodiment, the non-aqueous electrolytic solvent can contain a fluorine-containing phosphoric acid ester represented by the following formula (2).

［式（２）において、Ｒ^１、Ｒ^２、Ｒ^３は、それぞれ独立に、アルキル基またはフッ素含有アルキル基を示し、Ｒ^１、Ｒ^２およびＲ^３の少なくとも１つがフッ素含有アルキル基である。］

[In formula (2), R ¹ , R ² and R ³ each independently represent an alkyl group or a fluorine-containing alkyl group, and at least one of R ¹ , R ² and R ³ is a fluorine-containing alkyl group. ]

The fluorine-containing alkyl group is an alkyl group having at least one fluorine atom. In the formula ^(2), the number of carbon atoms in R 1, ^{R 2} and ^{R 3} each independently is preferably 1-3. It is preferable that at least one of R ¹ , R ² and R ³ is a fluorine-containing alkyl group in which 50% or more of the hydrogen atoms of the corresponding unsubstituted alkyl group are substituted with fluorine atoms. In addition, all of R ¹ , R ² and R ³ are fluorine-containing alkyl groups, and 50% or more of the hydrogen atoms of the unsubstituted alkyl groups corresponding to R ¹ , R ² and R ³ are substituted with fluorine atoms More preferred is a fluorine-containing alkyl group. When the content of fluorine atoms is high, the voltage resistance is further improved, and even when the positive electrode active material operating at a potential of 4.5 V or more with respect to lithium is used, the deterioration of the battery capacity after the cycle is further reduced. Because you can do it. Further, the ratio of the fluorine atom in the substituent containing a hydrogen atom in the fluorine-containing alkyl group is more preferably 55% or more.

  The fluorine-containing phosphate ester is a solvent with low flammability and low reactivity. The fluorine-containing phosphate ester is not particularly limited. For example, tris (trifluoromethyl) phosphate, tris (trifluoroethyl) phosphate, tris (tetrafluoropropyl) phosphate, tris (pentafluoropropyl) phosphate And tris (heptafluorobutyl) phosphate, tris (octafluoropentyl) phosphate and the like. Further, as the fluorine-containing phosphate ester, for example, trifluoroethyl dimethyl phosphate, bis (trifluoroethyl) methyl phosphate, bis trifluoroethyl ethyl phosphate, pentafluoropropyl dimethyl phosphate, heptafluorobutyl dimethyl phosphate, Trifluoroethylethyl phosphate, Pentafluoropropylmethylethyl phosphate, Hexafluorobutylmethyl ethyl phosphate, Trifluoroethylmethyl phosphate, Pentafluoropropylmethyl propyl phosphate, Hexafluorobutyl methyl propyl phosphate, Phosphoric acid Trifluoroethyl methyl butyl, pentafluoropropyl methyl butyl phosphate, hepta fluorobutyl methyl phosphate, trifluoroethyl diethyl phosphate, pentafluoropropyl diethyl phosphate , Heptafluorobutyl diethyl phosphate, trifluoroethyl ethyl phosphate, pentafluoropropyl ethyl phosphate, heptafluorobutyl ethyl phosphate, trifluoroethyl ethyl phosphate, pentafluoropropyl ethyl phosphate, phosphoric acid Heptafluorobutylethyl butyl, trifluoroethyl dipropyl phosphate, pentafluoropropyl dipropyl phosphate, heptafluorobutyl dipropyl phosphate, trifluoroethyl propyl phosphate, pentafluoropropyl propyl phosphate, heptafluoro phosphate Examples include butyl propyl butyl, trifluoroethyl dibutyl phosphate, pentafluoro propyl dibutyl phosphate, hepta fluoro butyl dibutyl phosphate and the like. Examples of tris (tetrafluoropropyl) phosphate include tris (2,2,3,3-tetrafluoropropyl) phosphate. Examples of tris (pentafluoropropyl) phosphate include tris (2,2,3,3,3-pentafluoropropyl) phosphate. Examples of tris (trifluoroethyl) phosphate include tris (2,2,2-trifluoroethyl) phosphate (hereinafter abbreviated as TTFEP) and the like. Examples of tris (heptafluorobutyl) phosphate include tris (1H, 1H-heptafluorobutyl) phosphate and the like. Examples of tris (octafluoropentyl) phosphate include tris (1H, 1H, 5H-octafluoropentyl) phosphate and the like. Among these, tris (2,2,2-trifluoroethyl) phosphate (TTFEP) represented by the following formula (3) is preferable because the effect of suppressing electrolyte decomposition at a high potential is high. The fluorine-containing phosphate esters can be used alone or in combination of two or more.

  Although the content of the fluorine-containing phosphate ester contained in the non-aqueous electrolytic solvent is not particularly limited, it is generally 0% to 95% by volume in the non-aqueous electrolytic solvent, and 10% to 95%. Volume% or less is preferable, 15 volume% or more and 80 volume% or less are more preferable, and 20 volume% or more and 70 volume% or less are more preferable. When the content of the fluorine-containing phosphate ester in the non-aqueous electrolytic solvent is 10% by volume or more, the effect of enhancing the voltage resistance is further improved. Moreover, the ion conductivity of electrolyte solution improves that the content rate in the non-aqueous electrolysis solvent of fluorine-containing phosphate ester is 95 volume% or less, and the charge / discharge rate of a battery becomes more favorable.

  In the present embodiment, the non-aqueous electrolytic solvent can include a fluorinated linear ether.

  The fluorinated chain ether is preferably used in the case of using a positive electrode which has high oxidation resistance and operates at a high potential. As a result, it is possible to improve the capacity retention rate of charge and discharge cycles and to reduce gas generation.

  The fluorinated linear ether is not particularly limited, and for example, a structure in which part or all of hydrogen atoms of 1,2-ethoxyethane (DEE) or ethoxymethoxyethane (EME) are substituted with a fluorine atom And the like. Moreover, as the fluorinated linear ether, specifically, for example, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2 2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1H, 1H, 2'H, 3H-decafluorodipropyl ether, 1,1,1,2,3,3-hexafluoropropyl-2 , 2-difluoroethyl ether, isopropyl-1,1,2,2-tetrafluoroethyl ether, propyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2 1,2,3,3-tetrafluoropropyl ether (TFE TFPE), 1H, 1H, 5H-perfluoropentyl-1,1,2,2-tetrafluoroethyl ether 1H, 1H, 2′H-perfluorodipropyl ether, 1H-perfluorobutyl-1H-perfluoroethyl ether, methyl perfluoropentyl ether, methyl perfluorohexyl ether, methyl-1,1,3,3 , 3-Pentafluoro-2- (trifluoromethyl) propyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, ethyl nonafluorobutyl ether, ethyl- 1,1,2,3,3,3-hexafluoropropyl ether, 1H, 1H, 5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1H, 1H, 2'H-perfluoro Dipropyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether 1,1,2,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoro Ethyl ether, ethyl nonafluorobutyl ether, methyl nonafluorobutyl ether and the like can be mentioned. Among these, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H, 1H, 2'H, 3H-decafluoro from the viewpoint of withstand voltage and boiling point etc. Dipropyl ether, 1H, 1H, 2′H-perfluorodipropyl ether, ethyl nonafluorobutyl ether and the like are preferable.

  The chain ether has an effect of reducing the viscosity of the electrolytic solution as the chain carbonate. Thus, for example, linear ethers can be used in place of linear carbonates and carboxylic esters, and can also be used in combination with linear carbonates and carboxylic esters.

  Since the chain ether tends to have a low boiling point when the carbon number is small, it may be vaporized during high temperature operation of the battery. On the other hand, when the carbon number is too large, the viscosity of the chain ether may be increased, and the conductivity of the electrolytic solution may be reduced. Therefore, it is preferable that carbon number is four or more and ten or less. For these reasons, in the present embodiment, the fluorinated linear ether is preferably represented by the following formula (4).

_{C n H 2n + 1-l} F l -O-C m H 2m + 1-k F k (4)
[In the formula (4), n is 1, 2, 3, 4, 5 or 6; m is 1, 2, 3 or 4; l is any integer from 0 to 2n + 1; Is an integer from 0 to 2m + 1, and at least one of l and k is an integer of 1 or more. ]

  In the fluorinated chain ether represented by the formula (4), when the amount of fluorine substitution is small, the fluorinated chain ether reacts with the positive electrode of high potential to lower the capacity retention of the battery or generate gas. May be On the other hand, when the amount of fluorine substitution is too large, the compatibility of the fluorinated chain ether with other solvents may be lowered, or the boiling point of the fluorinated chain ether may be lowered. From such reasons, the fluorine substitution amount is preferably 10% to 90%, more preferably 20% to 85%, and still more preferably 30% to 80%. That is, it is preferable that l, m, n of Formula (4) satisfy the following relational expressions.

  0.1 ≦ (l + k) / (2 n + 2 m + 2) ≦ 0.9

  The content of the fluorinated chain ether is not particularly limited, but is preferably 0.1% by volume or more and 70% by volume or less in the non-aqueous electrolytic solvent. The viscosity of electrolyte solution can be lowered | hung as the content rate in the non-aqueous electrolysis solvent of fluorinated chain | strand-shaped ether is 0.1 volume% or more, and electroconductivity can be improved. In addition, the effect of enhancing the oxidation resistance can be obtained. In addition, when the content of the fluorinated chain ether in the non-aqueous electrolytic solvent is 70% by volume or less, the conductivity of the electrolytic solution can be kept high, and the compatibility of the electrolytic solution is ensured. Can. Moreover, 1 volume% or more is more preferable, 5 volume% or more is more preferable, and, as for the content rate in the non-aqueous electrolysis solvent of fluorinated chain | strand-shaped ether, 10 volume% or more is especially preferable. Moreover, 65 volume% or less is more preferable, 60 volume% or less is more preferable, and, as for the content rate in the non-aqueous electrolysis solvent of fluorinated chain | strand-shaped ether, 55 volume% or less is especially preferable.

  The fluorinated linear ethers may be used alone or in combination of two or more.

  In the present embodiment, the non-aqueous electrolytic solvent may include the following in addition to the above.

  The non-aqueous electrolytic solvent may contain a fluorinated diether compound having low flammability and low reactivity.

Formula (5):
R ₁ O- (R ₂ O) _n -R ₃ (5)
In the fluorinated diether compound represented by the formula, R ₁ and R ₃ are each independently an alkyl group having 1 to 4 carbon atoms which may be substituted with a fluorine atom, and R ₂ is substituted with a fluorine atom even if an alkylene group having 1 to 4 carbon atoms, provided that at least one of the hydrogen atoms contained in R _1, R ₂ and R ₃ is substituted with a fluorine atom.

The carbon number of R ₁ and R ₃ is more preferably 1 or more and 3 or less. In a preferred embodiment, R ₁ and R ₃ are fluorine-containing alkyl groups, and examples include trifluoromethyl, trifluoroethyl, tetrafluoropropyl, pentafluoropropyl and heptafluorobutyl. The position of substitution of fluorine is arbitrary and, for example, 2,2,2-trifluoroethyl, 2,2,3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl etc. may be mentioned. Although it can be, it is not limited to these.

The carbon number of R ₂ is more preferably 1 or more and 3 or less. Mention may be made, for example, of methylene, ethylene, 1,2-propylene, 1,3-propylene, butylene and their fluorine substituents. In particular, ethylene, 1,2-propylene and 1,3-propylene are preferred. In a preferred embodiment, R ₂ is a non-substituted alkylene group. n is preferably 1 or 2, and more preferably 1.

  The fluorinated diether compound is more preferably a compound represented by the following formula (6).

CF ₃ CH ₂ OCH ₂ CH ₂ OCH ₂ CF ₃ (6)

  When the fluorinated diether compound is contained, the content in the non-aqueous electrolytic solvent is not particularly limited, but, for example, 0.1% by volume or more, more preferably 0.5% by volume or more, further preferably It is 0.9% by volume or more. On the other hand, the upper limit of the content can be appropriately changed according to the content of the fluorine-containing phosphate and the content of the other organic solvent, and typically 90% by volume or less, preferably 50% by volume or less It is. The content of the fluorinated diether compound may be relatively small, therefore in a preferred embodiment the content of the fluorinated diether compound is preferably 20% by volume, more preferably 10% by volume or less.

  The non-aqueous electrolyte can further include cyclic carbonate or linear carbonate.

  Since the cyclic carbonate has a large relative dielectric constant, the addition thereof improves the dissociability of the support salt and facilitates the provision of sufficient conductivity. Moreover, since the chain carbonate has a small viscosity, the viscosity of the electrolytic solution is lowered by the addition, so that there is an advantage that the ion mobility in the electrolytic solution is improved. In addition, cyclic carbonates and linear carbonates are suitable for mixing with fluorine-containing phosphates because of their high voltage resistance and high conductivity.

  Although it does not restrict | limit especially as cyclic carbonates other than a propylene carbonate, For example, ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC) etc. can be mentioned.

  The cyclic carbonates can be used alone or in combination of two or more.

  When the cyclic carbonate is contained, the content in the non-aqueous electrolytic solvent is preferably 0.1% by volume or more, and 5% by volume from the viewpoint of the effect of enhancing the dissociation degree of the support salt and the effect of enhancing the conductivity of the electrolytic solution. The above is more preferable, 10% by volume or more is more preferable, and 15% by volume or more is particularly preferable. From the same viewpoint, the content of the cyclic carbonate in the non-aqueous electrolytic solvent is preferably 70% by volume or less, more preferably 50% by volume or less, and still more preferably 40% by volume or less.

  The linear carbonate is not particularly limited, and examples thereof include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC) and the like. In addition, linear carbonates include fluorinated linear carbonates. As the fluorinated linear carbonate, for example, part or all of hydrogen atoms such as ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), etc. are substituted by fluorine atoms The compound etc. which have a structure can be mentioned. More specifically, as fluorinated linear carbonate, for example, bis (fluoroethyl) carbonate, 3-fluoropropyl methyl carbonate, 3,3,3-trifluoropropyl methyl carbonate, 2,2,2-trifluoro Ethyl methyl carbonate, 2,2,2-trifluoroethyl ethyl carbonate, monofluoromethyl methyl carbonate, methyl 2,2,3,3, tetrafluoropropyl carbonate, ethyl 2,2,3,3, tetrafluoropropyl carbonate, Bis (2,2,3,3, tetrafluoropropyl) carbonate, bis (2,2,2 trifluoroethyl) carbonate, 1-monofluoroethylethyl carbonate, 1-monofluoroethyl methyl carbonate, 2-monofluoroethyl Methyl car , Bis (1-mono-fluoroethyl) carbonate, bis (2-monofluoroethyl) carbonate, bis (monofluoromethyl) carbonate. Among these, dimethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, monofluoromethyl methyl carbonate, methyl 2,2,3,3, tetrafluoropropyl carbonate and the like are preferable from the viewpoint of voltage resistance and conductivity. . The linear carbonates can be used alone or in combination of two or more.

  The linear carbonate has an advantage of low viscosity when the carbon number of the substituent added to the “—OCOO—” structure is small. On the other hand, when the carbon number is too large, the viscosity of the electrolytic solution may be increased to lower the conductivity of Li ions. From such reasons, it is preferable that the total carbon number of the two substituents added to the "-OCOO-" structure of the linear carbonate is 2 or more and 6 or less. When the substituent added to the “—OCOO—” structure contains a fluorine atom, the oxidation resistance of the electrolytic solution is improved. From these reasons, the linear carbonate is preferably a fluorinated linear carbonate represented by the following formula (7).

_{C n H 2n + 1-l} F l -OCOO-C m H 2m + 1-k F k (7)
[In the formula (7), n is 1, 2 or 3; m is 1, 2 or 3; l is an integer from 0 to 2n + 1; k is from 0 to 2m + 1 And at least one of l and k is an integer of 1 or more. ]

  In the fluorinated linear carbonate represented by the formula (7), when the amount of fluorine substitution is small, the fluorinated linear carbonate reacts with the positive electrode of high potential to lower the capacity retention of the battery or generate gas. May be On the other hand, when the amount of fluorine substitution is too large, the compatibility of the linear carbonate with other solvents may be lowered, or the boiling point of the linear carbonate may be lowered. From such reasons, the fluorine substitution amount is preferably 1% to 90%, more preferably 5% to 85%, and still more preferably 10% to 80%. That is, it is preferable that l, m, n of Formula (7) satisfy the following relational expressions.

  0.01 ≦ (l + k) / (2 n + 2 m + 2) ≦ 0.9

  The linear carbonate has the effect of lowering the viscosity of the electrolytic solution, and can increase the conductivity of the electrolytic solution. From these viewpoints, when containing a linear carbonate, the content in the non-aqueous electrolytic solvent is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and further preferably 1.0% by volume or more preferable. Moreover, 90 volume% or less is preferable, as for the content rate in the non-aqueous electrolysis solvent of a linear carbonate, 80 volume% or less is more preferable, and 70 volume% or less is more preferable.

  When the fluorinated linear carbonate is contained, the content in the non-aqueous electrolytic solvent is not particularly limited, but is preferably 0.1% by volume or more and 70% by volume or less. The viscosity of an electrolyte solution can be lowered | hung as the content rate in the non-aqueous electrolysis solvent of a fluorinated linear carbonate is 0.1 volume% or more, and electroconductivity can be improved. In addition, the effect of enhancing the oxidation resistance can be obtained. In addition, when the content of the fluorinated linear carbonate in the non-aqueous electrolytic solvent is 70% by volume or less, it is possible to keep the conductivity of the electrolytic solution high. Moreover, 1 volume% or more is more preferable, 5 volume% or more is further more preferable, and, as for the content rate in the non-aqueous electrolysis solvent of fluorinated linear carbonate, 10 volume% or more is especially preferable. Moreover, 65 volume% or less is more preferable, 60 volume% or less is further more preferable, and 55 volume% or less is especially preferable as for the content rate in the non-aqueous electrolysis solvent of fluorinated linear carbonate.

  The non-aqueous electrolytic solvent may also contain a carboxylic acid ester.

  The carboxylic acid ester is not particularly limited, and examples thereof include ethyl acetate, methyl propionate, ethyl formate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl acetate, methyl formate and the like. In addition, the carboxylic acid ester also includes a fluorinated carboxylic acid ester, and as the fluorinated carboxylic acid ester, for example, ethyl acetate, methyl propionate, ethyl formate, ethyl propionate, methyl butyrate, ethyl butyrate, ethyl butyrate, methyl acetate or formate The compound etc. which have the structure which substituted the hydrogen atom of one part or all part of methyl with the fluorine atom are mentioned. Moreover, as the fluorinated carboxylic acid ester, specifically, for example, ethyl pentafluoropropionate, ethyl 3,3,3-trifluoropropionate, methyl 2,2,3,3-tetrafluoropropionate, acetic acid 2,2-Difluoroethyl, methyl heptafluoroisobutyrate, methyl 2,3,3,3-tetrafluoropropionate, methyl pentafluoropropionate, 2- (trifluoromethyl) -3,3,3-trifluoropropion Methyl acid, ethyl heptafluorobutyrate, methyl 3,3,3-trifluoropropionate, 2,2,2-trifluoroethyl acetate, isopropyl trifluoroacetate, tert-butyl trifluoroacetate, 4,4,4-trifluoride Ethyl fluorobutyrate, methyl 4,4,4-trifluorobutyrate, 2,2-difluoro Butyl difluoroacetate, ethyl difluoroacetate, n-butyl trifluoroacetate, 2,2,3,3-tetrafluoropropyl acetate, ethyl 3- (trifluoromethyl) butyrate, methyl tetrafluoro-2- (methoxy) propionate, 3 3,3,3-trifluoropropionic acid 3,3,3 trifluoropropyl, methyl difluoroacetate, trifluoroacetate 2,2,3,3-tetrafluoropropyl, acetic acid 1H, 1H-heptafluorobutyl, methyl heptafluorobutyrate , Ethyl trifluoroacetate and the like. Among these, from the viewpoint of withstand voltage and boiling point, as the carboxylic acid ester, ethyl propionate, methyl acetate, methyl 2,2,3,3-tetrafluoropropionate, trifluoroacetic acid 2,2,3,3 -Tetrafluoropropyl is preferred. The carboxylic acid ester has an effect of reducing the viscosity of the electrolytic solution, like the linear carbonate. Thus, for example, carboxylic esters can be used instead of linear carbonates, and can also be used in combination with linear carbonates.

  The chain carboxylic acid ester has a feature that the viscosity is low when the carbon number of the substituent added to the "-COO-" structure is small, but the boiling point also tends to be low. The linear carboxylic acid ester having a low boiling point may be vaporized during high temperature operation of the battery. On the other hand, if the carbon number is too large, the viscosity of the electrolyte may be increased to lower the conductivity. From such reasons, it is preferable that the total carbon number of the two substituents added to the "-COO-" structure of the linear carboxylic acid ester is 3 or more and 8 or less.

  Moreover, when the substituent added to a "-COO-" structure contains a fluorine atom, the oxidation resistance of electrolyte solution can be improved. From these reasons, the chain carboxylic acid ester is preferably a fluorinated chain carboxylic acid ester represented by the following formula (8).

_{C n H 2n + 1-l} F l -COO-C m H 2m + 1-k F k (8)
[Wherein n is 1, 2, 3 or 4; m is 1, 2, 3 or 4; l is any integer from 0 to 2n + 1; k is 0 to 2m + 1 And at least one of l and k is an integer of 1 or more. ]

  In the fluorinated linear carboxylic acid ester represented by the formula (8), when the amount of fluorine substitution is small, the fluorinated linear carboxylic acid ester reacts with the positive electrode of high potential to lower the capacity retention of the battery, Gas may be generated. On the other hand, if the amount of fluorine substitution is too large, the compatibility of the linear carboxylic acid ester with other solvents may be reduced, or the boiling point of the fluorinated linear carboxylic acid ester may be lowered. From such reasons, the fluorine substitution amount is preferably 1% to 90%, more preferably 10% to 85%, and still more preferably 20% to 80%. That is, it is preferable that l, m, n of Formula (8) satisfy the following relational expressions.

  0.01 ≦ (l + k) / (2 n + 2 m + 2) ≦ 0.9

  When the carboxylic acid ester is contained, the content in the non-aqueous electrolytic solvent is preferably 0.1 volume or more, more preferably 0.2 volume% or more, and still more preferably 0.5 volume% or more, 1 volume% or more Is particularly preferred. The content of the carboxylic acid ester in the non-aqueous electrolytic solvent is preferably 50% by volume or less, more preferably 20% by volume or less, further preferably 15% by volume or less, and particularly preferably 10% by volume or less. By setting the content of the carboxylic acid ester to 0.1% by volume or more, the low temperature characteristics can be further improved, and the conductivity can be further improved. Moreover, when the content rate of carboxylic acid ester is 50 volume% or less, when a battery is left to stand at high temperature, it can reduce that a vapor pressure becomes high too much.

  Moreover, when it contains fluorinated chain | strand-shaped carboxylic acid ester, although the content rate in a non-aqueous electrolysis solvent is not restrict | limited in particular, 0.1 volume% or more and 50 volume% or less are preferable. The viscosity of electrolyte solution can be lowered | hung as the content rate in the non-aqueous electrolysis solvent of fluorinated chain | strand-shaped carboxylate ester is 0.1 volume% or more, and electroconductivity can be improved. In addition, the effect of enhancing the oxidation resistance can be obtained. In addition, when the content of the fluorinated linear carboxylic acid ester in the non-aqueous electrolytic solvent is 50% by volume or less, the conductivity of the electrolytic solution can be kept high, and the compatibility of the electrolytic solution is ensured. Can. Moreover, 1 volume% or more is more preferable, 5 volume% or more is further more preferable, and, as for the content rate in the non-aqueous electrolysis solvent of fluorinated linear carboxylic acid ester, 10 volume% or more is especially preferable. Moreover, 45 volume% or less is more preferable, 40 volume% or less is further more preferable, and, as for the content rate in the non-aqueous electrolysis solvent of fluorinated linear carboxylic acid ester, 35 volume% or less is especially preferable.

  The non-aqueous electrolytic solvent may contain an alkylene bis carbonate represented by the following formula (9). The oxidation resistance of the alkylene biscarbonate is equal to or slightly higher than that of the linear carbonate, and therefore, the voltage resistance of the electrolytic solution can be improved.

［式（９）中、Ｒ_４およびＲ_６は、それぞれ独立に、置換または無置換のアルキル基を表す。Ｒ_５は、置換または無置換のアルキレン基を表す。］

[In Formula (9), R ₄ and R ₆ each independently represent a substituted or unsubstituted alkyl group. R ₅ represents a substituted or unsubstituted alkylene group. ]

  In Formula (9), the alkyl group includes linear or branched ones, preferably has 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms. The alkylene group is a divalent saturated hydrocarbon group, and includes linear or branched ones, preferably having 1 to 4 carbon atoms, and more preferably 1 to 3 carbon atoms. .

  As the alkylene biscarbonate represented by the formula (9), for example, 1,2-bis (methoxycarbonyloxy) ethane, 1,2-bis (ethoxycarbonyloxy) ethane, 1,2-bis (methoxycarbonyloxy) Propane or 1-ethoxycarbonyloxy-2-methoxycarbonyloxyethane and the like can be mentioned. Among these, 1,2-bis (methoxycarbonyloxy) ethane is preferable.

  When the alkylene bis carbonate is contained, the content in the non-aqueous electrolytic solvent is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and still more preferably 1% by volume or more, 1.5% by volume The above is particularly preferable. 70 volume% or less is preferable, 60 volume% or less is more preferable, 50 volume% or less is further more preferable, and 40 volume% or less is especially preferable for the content rate in the non-aqueous electrolysis solvent of alkylene bis carbonate.

  Alkylene bis carbonate is a material with a low dielectric constant. Thus, for example, it can be used instead of or in combination with linear carbonates.

  The non-aqueous electrolytic solvent can include a linear ether.

  The chain ether is not particularly limited, and examples thereof include 1,2-ethoxyethane (DEE) and ethoxymethoxyethane (EME). The chain ether has an effect of reducing the viscosity of the electrolytic solution as the chain carbonate. Thus, for example, linear ethers can be used in place of linear carbonates and carboxylic esters, and can also be used in combination with linear carbonates and carboxylic esters.

  Since the chain ether tends to have a low boiling point when the carbon number is small, it may be vaporized during high temperature operation of the battery. On the other hand, when the carbon number is too large, the viscosity of the chain ether may be increased, and the conductivity of the electrolytic solution may be reduced. Therefore, it is preferable that carbon number is four or more and ten or less.

  As the non-aqueous electrolytic solvent, in addition to the above, the following may be further included. The non-aqueous electrolytic solvent can include, for example, γ-lactones such as γ-butyrolactone, cyclic ethers such as tetrahydrofuran or 2-methyltetrahydrofuran, and the like. Moreover, you may include what substituted a part of hydrogen atoms of these materials by the fluorine atom. In addition, dimethyl sulfoxide, formamide, acetamide, acetamide, dimethylformamide, dioxolane (eg, 1,3-dioxolane), acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, and the like. Aprotic organic solvents such as 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone and the like May be included.

As a supporting salt, for example, LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₂ , LiN (CF ₃₎ Lithium salts such as SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl _{10 and the} like can be mentioned. In addition, examples of the supporting salt include lithium lower aliphatic carboxylic acid carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl and the like. The supporting salts can be used singly or in combination of two or more.

  Moreover, an ion conductive polymer can be added to a non-aqueous electrolysis solvent. Examples of the ion conductive polymer include polyethers such as polyethylene oxide and polypropylene oxide, and polyolefins such as polyethylene and polypropylene. Further, as the ion conductive polymer, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyvinyl chloride, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl Acetate, polyvinyl pyrrolidone, polycarbonate, polyethylene terephthalate, polyhexamethylene adipamide, polycaprolactam, polyurethane, polyethylene imine, polybutadiene, polystyrene, polyisoprene, and derivatives thereof can be mentioned. The ion conductive polymers can be used alone or in combination of two or more. Moreover, you may use the polymer containing the various monomers which comprise the said polymer.

  Further, in the present embodiment, an electrolytic solution additive may be added to the non-aqueous electrolytic solvent, if necessary.

(Positive electrode)
The positive electrode of the lithium secondary battery according to the present embodiment can use, as a positive electrode active material, a 4V class material such as LiMn ₂ O ₄ or LiCoO ₂ as disclosed in the above-mentioned Patent Documents 1 to 6 . Further, LiM1O ₂ (M1 represents at least one element selected from the group consisting of Mn, Fe, Co and Ni, a part of M1 may be substituted with Mg, Al or Ti.), LiMn Lithium such as _2-x M 2 _x O ₄ (where M 2 is at least one element selected from the group consisting of Mg, Al, Co, Ni, Fe and B, and 0 ≦ x <0.4). A composite oxide, an olivine type material represented by LiFePO ₄ , or the like can also be used.

  Further, from the viewpoint of obtaining high energy density, it is preferable to include a positive electrode active material capable of inserting or extracting lithium ions at a potential of 4.5 V or more with respect to lithium metal. As such a positive electrode active material, it is possible to use one in which at least a charging curve of the charging / discharging curve has at least a region of 4.5 V or more with respect to lithium metal. That is, an active material having at least a region of 4.5 V or more with respect to lithium metal only in the charge curve, or at least a region of 4.5 V or more with respect to lithium metal in both the charge curve and the discharge curve The active material which it has can be used.

  As measurement conditions of the charge / discharge curve, the charge / discharge current can be set to 5 mA / g, the charge termination voltage can be set to 5.2 V, and the discharge termination voltage can be set to 3 V per mass of the positive electrode active material.

  Examples of such a positive electrode active material include spinel materials, layered materials, and olivine materials.

Spinel materials include LiNi _0.5 Mn _1.5 O ₄ , LiCoMnO ₄ , LiCrMnO ₄ , LiFeMnO ₄ , LiCu _0.5 Mn _1.5 O ₄ and other lithium at a high potential of 4.5 V or more Operating materials; LiMn ₂ O ₄ with part of Mn replaced with other elements to increase the life, LiM 1 _x Mn _2-xy M 2 _y O ₄ (M 1 is from Ni, Fe, Co, Cr and Cu At least one selected, 0.4 <x <1.1, M 2 is at least one selected from Li, Al, B, Mg, Si and a transition metal, and 0 <y <0. And those obtained by substituting a part of oxygen of these materials with fluorine or chlorine.

  The spinel-based material is particularly preferably one represented by the following formula (10).

Li _a (M _x Mn _2-xy Y _y ) (O _4-w Z _w ) (10)
[Wherein, in the formula (10), 0 ≦ x ≦ 1.2, 0 ≦ y, x + y <2, 0 ≦ a ≦ 1.2, 0 ≦ w ≦ 1, M is Co, Ni, Fe, Cr and Cu Y is at least one selected from Li, B, Na, Al, Mg, Ti, Si, K and Ca, and Z is at least one of F and Cl. ]

  In particular, it is preferable that 0.4 ≦ x ≦ 1.1.

The layered material is represented by the general formula LiMO ₂ , specifically, LiCoO ₂ , LiNi _1-x M _x O ₂ (0.05 <x <0.3, M is an element containing at least Co or Al) there. material represented _{by), Li (Ni x Co y} Mn 2-x-y) O 2 (0.1 <x <0.7,0 <y <0.5), Li (M 1-z Materials represented by Mn _z ) O ₂ (0.33 ≦ z ≦ 0.7, M is at least one of Li, Co and Ni) can be mentioned.

  Moreover, the material represented by following formula (11) is especially preferable.

_{Li (Li x M 1-x} -z Mn z) O 2 (11)
[In the formula (11), 0 ≦ x <0.3, 0.3 ≦ z ≦ 0.7, M is at least one of Co and Ni. ]

As for x in Formula (11), 0 <= x <0.2 is preferable.

The olivine material has the general formula:
LiMPO ₄ (M is a transition metal)
Specifically, LiFePO ₄ , LiMnPO ₄ , LiCoPO ₄ and LiNiPO ₄ can be mentioned. It is also possible to use one in which part of these transition metals is replaced by another element or in which the oxygen moiety is replaced by fluorine. From the viewpoint of high energy density, a material represented by LiMPO ₄ (M is at least one of Co and Ni) operating at a high potential is preferable.

  Besides this, NASICON type, lithium transition metal silicon complex oxide, etc. can be used.

  Although the positive electrode active material operating at the high potential and the other normal positive electrode active materials may be used in combination, the content of the positive electrode active material operating at the high potential in the entire positive electrode active material is 60% by mass The above is preferable, 80 mass% or more is more preferable, 90 mass% or more is more preferable.

The specific surface area of these positive electrode active materials is, for example, 0.01 to ⁵ m ² / g, preferably 0.05 to ⁴ m ² / g, more preferably 0.1 to ³ m ² / g, and 0.2 to ² m. ² / g is more preferred. By setting the specific surface area to such a range, the contact area with the electrolytic solution can be adjusted to an appropriate range. That is, by setting the specific surface area to 0.01 m ² / g or more, insertion and desorption of lithium ions can be easily performed smoothly, and resistance can be further reduced. Further, by setting the specific surface area to 5 m ² / g or less, it is possible to further suppress the decomposition of the electrolyte solution and the elution of the constituent elements of the active material. The specific surface area can be measured by a conventional BET specific surface area measurement method.

The center particle diameter of the positive electrode active material is preferably 0.01 to 50 μm, and more preferably 0.02 to 40 μm. By setting the particle size to 0.02 μm or more, elution of the constituent elements of the positive electrode active material can be further suppressed, and deterioration due to contact with the electrolytic solution can be further suppressed. Further, by setting the particle diameter to 50 μm or less, insertion and desorption of lithium ions can be easily performed smoothly, and resistance can be further reduced. The central particle diameter is 50% cumulative diameter D ₅₀ (median diameter), and can be measured by a laser diffraction / scattering type particle size distribution measuring device.

  As the binder for the positive electrode, the same one as the binder for the negative electrode can be used. Among them, polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost. The amount of the positive electrode binder to be used is preferably 2 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoint of binding power and energy density in a trade-off relationship.

  As binders other than polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer rubber, polytetrafluoroethylene, polypropylene, Examples include polyethylene, polyimide and polyamideimide.

  A conductive auxiliary material may be added to the positive electrode active material layer containing the positive electrode active material for the purpose of reducing the impedance. Examples of the conductive auxiliary include carbonaceous fine particles such as graphite, carbon black and acetylene black.

  As the positive electrode current collector, aluminum, nickel, silver and their alloys are preferable. As the shape, foil, flat form, mesh form is mentioned.

  The positive electrode is obtained by dispersing and kneading the above-mentioned active material together with a conductive material and a binder in a solvent such as N-methyl-2-pyrrolidone (NMP), and applying it on a positive electrode current collector. Can.

(Negative electrode)
The negative electrode is not particularly limited as long as it contains a material capable of inserting and extracting lithium as the negative electrode active material.

  The negative electrode active material is not particularly limited, and, for example, a carbon material (a) capable of absorbing and desorbing lithium ions, a metal (b) capable of alloying with lithium, or a metal capable of absorbing and desorbing lithium ions An oxide (c) etc. is mentioned and it is preferable that it is a thing containing a carbon material (a).

  As the carbon material (a), graphite, amorphous carbon, diamond-like carbon, carbon nanotubes, or a composite thereof can be used. Here, highly crystalline graphite has high electrical conductivity, and is excellent in adhesion to a negative electrode current collector made of metal such as copper and voltage flatness. On the other hand, amorphous carbon having low crystallinity has a relatively small volume expansion, so the effect of alleviating the volume expansion of the entire negative electrode is high, and deterioration due to nonuniformity such as grain boundaries and defects hardly occurs. The carbon material (a) can be used alone or in combination with other substances. When used in combination, the carbon material (a) is preferably in the range of 2% by mass to 80% by mass in the negative electrode active material, and can be used, for example, in the range of 2% by mass to 30% by mass.

  As the metal (b), metals mainly composed of Al, Si, Pb, Sn, Zn, Cd, Sb, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, La, etc., or metals thereof Two or more types of alloys, or an alloy of these metals or alloys with lithium can be used. In particular, it is preferable to include silicon (Si) as the metal (b). The metal (b) can be used alone or in combination with other substances, but is preferably in the range of 5% by mass to 90% by mass in the negative electrode active material, and is 20% by mass to 50% by mass. The following range is more preferable.

  As the metal oxide (c), silicon oxide, aluminum oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, or a composite thereof can be used. In particular, silicon oxide is preferably contained as the metal oxide (c). This is because silicon oxide is relatively stable and hardly causes reaction with other compounds. In addition, one or two or more elements selected from nitrogen, boron and sulfur can be added to the metal oxide (c), for example, 0.1 to 5% by mass. By doing this, the electrical conductivity of the metal oxide (c) can be improved. The metal oxide (c) can be used alone or in combination with other substances, but it is preferably in the range of 5% by mass to 90% by mass in the negative electrode active material, and preferably 40% by mass to 70%. More preferably, it is in the range of mass% or less.

Specific examples of the metal oxide (c) include, for example, LiFe ₂ O ₃ , WO ₂ , MoO ₂ , SiO, SiO ₂ , CuO, SnO, SnO ₂ , Nb ₃ O ₅ , Li _x Ti _2-x O ₄ (1 ≦ x ≦ 4/3), PbO ₂ , Pb ₂ O _{5 and the} like.

Moreover, as a negative electrode active material, the metal sulfide (d) which can occlude and discharge | release lithium ion is mentioned other than that, for example. Examples of the metal sulfide (d) include SnS and FeS ₂ . As the anode active material, other features, e.g., metal lithium or lithium alloy, polyacene or polythiophene or _{Li 5, (Li 3 N)} , Li 7 MnN 4, Li 3 FeN 2, Li 2.5 Co 0. Examples include lithium nitride such as ₅ N or Li ₃ CoN.

  The above negative electrode active materials can be used singly or in combination of two or more.

  In one embodiment, the negative electrode active material can be configured to include a carbon material (a), a metal (b), and a metal oxide (c). Hereinafter, this negative electrode active material will be described.

  It is preferable that all or a part of the metal oxide (c) have an amorphous structure. The metal oxide (c) of the amorphous structure can suppress the volume expansion of the carbon material (a) and the metal (b), and can suppress the decomposition of the electrolytic solution. This mechanism is presumed to have some influence on the formation of a film on the interface between the carbon material (a) and the electrolyte because the metal oxide (c) has an amorphous structure. In addition, it is considered that the amorphous structure has relatively few elements due to nonuniformity such as grain boundaries and defects. The fact that all or part of the metal oxide (c) has an amorphous structure can be confirmed by X-ray diffraction measurement (general XRD measurement). Specifically, when the metal oxide (c) does not have an amorphous structure, a peak specific to the metal oxide (c) is observed, but all or part of the metal oxide (c) is amorphous. In the case of having a structure, the characteristic peak is observed as broadened in the metal oxide (c).

  The metal oxide (c) is preferably an oxide of the metal constituting the metal (b). The metal (b) and the metal oxide (c) are preferably silicon (Si) and silicon oxide (SiO), respectively.

  The metal (b) is preferably dispersed in whole or in part in the metal oxide (c). By dispersing at least a part of the metal (b) in the metal oxide (c), the volume expansion of the whole negative electrode can be further suppressed, and the decomposition of the electrolytic solution can also be suppressed. The fact that all or part of the metal (b) is dispersed in the metal oxide (c) can be determined by transmission electron microscopy (general TEM observation) and energy dispersive X-ray spectroscopy (general) This can be confirmed by using the Specifically, the cross section of a sample containing metal (b) particles is observed, the oxygen concentration of the metal (b) particles dispersed in the metal oxide (c) is measured, and the metal (b) particles are formed. It can be confirmed that the metal in question is not an oxide.

  As described above, the contents of the respective carbon material (a), metal (b) and metal oxide (c) to the total of carbon material (a), metal (b) and metal oxide (c) are It is preferable that they are 2 mass% or more and 80 mass% or less, 5 mass% or more and 90 mass% or less, and 5 mass% or more and 90 mass% or less, respectively. In addition, the contents of the carbon material (a), the metal (b) and the metal oxide (c) with respect to the total of the carbon material (a), the metal (b) and the metal oxide (c) are respectively It is more preferable that they are 2 mass% or more and 30 mass% or less, 20 mass% or more and 50 mass% or less, and 40 mass% or more and 70 mass% or less.

  An anode active material in which all or part of the metal oxide (c) has an amorphous structure and all or part of the metal (b) is dispersed in the metal oxide (c) is disclosed, for example, in It can produce by the method as disclosed by the 2004-47404 gazette. That is, the metal oxide (c) is subjected to a CVD process in an atmosphere containing an organic gas such as methane gas, whereby the metal (b) in the metal oxide (c) is nanoclustered and the surface is a carbon material (a) ) Coated composites can be obtained. Moreover, the said negative electrode active material can also be produced by mixing a carbon material (a), a metal (b), and a metal oxide (c) by mechanical milling.

  The carbon material (a), the metal (b), and the metal oxide (c) are not particularly limited, but particulate materials can be used. For example, the average particle size of the metal (b) can be smaller than the average particle size of the carbon material (a) and the average particle size of the metal oxide (c). In this way, the metal (b) having a large volume change due to charge and discharge has a relatively small particle size, and the carbon material (a) and the metal oxide (c) having a small volume change have a relatively large particle size. Thus, dendrite formation and alloy pulverization are more effectively suppressed. Further, lithium is occluded and released in the order of particles of large particle size, particles of small particle size and particles of large particle size in the process of charge and discharge, from this point as well, generation of residual stress and residual strain is suppressed Be done. The average particle size of the metal (b) can be, for example, 20 μm or less, and preferably 15 μm or less.

  The average particle size of the metal oxide (c) is preferably 1/2 or less of the average particle size of the carbon material (a), and the average particle size of the metal (b) is the average of the metal oxide (c) The particle diameter is preferably 1/2 or less. Furthermore, the average particle size of the metal oxide (c) is 1/2 or less of the average particle size of the carbon material (a), and the average particle size of the metal (b) is the average particle size of the metal oxide (c) It is more preferable that it is 1/2 or less of. If the average particle size is controlled to such a range, the effect of alleviating the volumetric expansion of metal and alloy phase can be more effectively obtained, and a secondary battery excellent in the balance of energy density, cycle life and efficiency is obtained. Can. More specifically, the average particle size of silicon oxide (c) is set to 1/2 or less of the average particle size of graphite (a), and the average particle size of silicon (b) is the average particle of silicon oxide (c) It is preferable to set it as 1/2 or less of a diameter. More specifically, the average particle diameter of silicon (b) can be, for example, 20 μm or less, and preferably 15 μm or less.

  The binder for the negative electrode is not particularly limited, and polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene copolymer, etc. Polymerized rubber, polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide imide and the like can be mentioned.

  The content of the negative electrode binder is preferably in the range of 1 to 30% by mass, and more preferably 2 to 25% by mass, based on the total amount of the negative electrode active material and the negative electrode binder. By setting the content to 1% by mass or more, the adhesion between the active materials or between the active material and the current collector is improved, and the cycle characteristics are improved. Further, by setting the content to 30% by mass or less, the active material ratio can be improved, and the negative electrode capacity can be improved.

  The negative electrode current collector is not particularly limited, but aluminum, nickel, copper, silver, and their alloys are preferable from the viewpoint of electrochemical stability. As the shape, foil, flat form, mesh form is mentioned.

  The negative electrode can be manufactured by forming a negative electrode active material layer containing a negative electrode active material and a binder for a negative electrode on a negative electrode current collector. Examples of the method of forming the negative electrode active material layer include a doctor blade method, a die coater method, a CVD method, and a sputtering method. After a negative electrode active material layer is formed in advance, a thin film of aluminum, nickel, or an alloy thereof may be formed by a method such as vapor deposition or sputtering to form a negative electrode current collector.

(Separator)
The secondary battery may be composed of a combination of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Examples of the separator include woven fabrics, nonwoven fabrics, polyolefins such as polyethylene and polypropylene, porous polymers such as polyimide and porous polyvinylidene fluoride, and ion conductive polymer electrolyte membranes. These can be used alone or in combination.

(Shape and exterior of battery)
Examples of the shape of the battery include cylindrical, square, coin, button, and laminate types.

  In the case of the laminate type, the electrode and the separator are stacked in a planar shape, and there is no small R portion (a region close to the winding core of the winding structure or a region corresponding to a folding portion of the flat winding structure). Therefore, when an active material having a large volume change due to charge and discharge is used, it is less likely to be adversely affected by the volume change of the electrode due to charge and discharge as compared with a battery having a wound structure.

  As an exterior body of a battery, stainless steel, iron, aluminum, titanium, or these alloys, or these plating processed goods are mentioned, for example. For example, nickel plating can be used as the plating. When the battery is a laminate type, a laminate film is preferred as the outer package.

  As a metal foil layer on the resin base material layer of a laminate film, aluminum, aluminum alloy, titanium foil is mentioned, for example. As a material of the heat welding layer of a laminate film, thermoplastic polymer materials, such as polyethylene, a polypropylene, a polyethylene terephthalate, are mentioned, for example. Moreover, the resin base material layer and metal foil layer of a laminate film are not limited to one layer, respectively, Two or more layers may be sufficient. From the viewpoint of versatility and cost, an aluminum laminate film is preferable.

  When a laminate film is used as the exterior body, the volume change of the battery and the distortion of the electrode due to the generation of gas are more likely to occur than when the metal can is used as the exterior body. This is because the laminate film is more easily deformed by the internal pressure of the battery than the metal can. Furthermore, when sealing a secondary battery using a laminate film as an outer package, usually, the internal pressure of the battery is made lower than the atmospheric pressure, and there is no extra space inside, so gas is generated inside the battery. It easily leads to a change in volume of the battery and deformation of the electrode. Moreover, in the case of a laminate type battery, the gap between the electrodes tends to widen because the gas tends to stay between the electrodes when a gas is generated between the electrodes, as compared with a battery having a wound structure. When used, this tendency is more pronounced. According to the present embodiment, it is possible to suppress the occurrence of such a problem, and to provide a non-aqueous electrolyte secondary battery excellent in long-term reliability even in a laminate type battery using a laminate film outer package. be able to.

(Basic structure of battery)
A cross-sectional view of a laminate-type lithium secondary battery according to the present embodiment is shown in FIG. As shown in FIG. 1, the lithium secondary battery according to the present embodiment comprises a positive electrode current collector 3 made of metal such as aluminum foil and a positive electrode active material layer 1 containing a positive electrode active material provided thereon And a negative electrode current collector 4 made of a metal such as copper foil, and a negative electrode active material layer 2 provided on the negative electrode current collector 4 and containing a negative electrode active material. The positive electrode and the negative electrode are laminated via a separator 5 made of non-woven fabric or a microporous polypropylene film so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. The electrode pair is accommodated in a container formed of an exterior body 6, 7 such as an aluminum laminate film. A positive electrode tab 9 is connected to the positive electrode current collector 3, a negative electrode tab 8 is connected to the negative electrode current collector 4, and these tabs are drawn out of the container. An electrolytic solution is injected into the container and sealed. An electrode group in which a plurality of electrode pairs are stacked may be accommodated in a container.

  Hereinafter, although the specific Example to which this invention is applied is described, this invention is not limited to a present Example, It can be suitably changed and implemented in the range which does not exceed the main point. .

  The abbreviations of the compounds used in the following examples are described.

PC: propylene carbonate EC: ethylene carbonate TFE TFPE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether TTFEP: tris (2,2,2-trifluoroethyl) phosphate
DMC: Dimethyl carbonate FEC: Fluoro ethylene carbonate FPC: 3, 3, 3- trifluoro propylene carbonate

Example 1-1
LiNi _0.5 Mn _1.5 O ₄ (90% by mass) as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder (5% by mass), and carbon black (5% by mass) as a conductive agent And were mixed to obtain a positive electrode mixture. The positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry. The positive electrode slurry was uniformly applied on one side of a 20 μm thick aluminum current collector. The thickness of the coated film was adjusted so that the initial charge capacity per unit area was 2.5 mAh / cm ² . After drying, the positive electrode was produced by compression molding using a roll press.

Artificial graphite was used as the negative electrode active material. Artificial graphite was dispersed in PVdF dissolved in N-methyl pyrrolidone to prepare a slurry for the negative electrode. The mass ratio of the negative electrode active material to the binder was 90/10. The negative electrode slurry was uniformly applied on a 10 μm thick Cu current collector. The thickness of the coating film was adjusted so that the initial charge capacity was 3.0 mAh / cm ² . After drying, the negative electrode was produced by compression molding using a roll press.

  The positive electrode and negative electrode cut out into 3 cm × 3 cm were disposed to face each other via a separator. For the separator, a 25 μm thick microporous polypropylene film was used.

The electrolytic solution is propylene carbonate (PC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TFETFPE), tris (2,2,2-trifluoro phosphate) 0.8 mol / l of lithium salt LiPF ₆ is added to a solvent consisting of ethyl) (TTFEP) and dimethyl carbonate (DMC) in PC / TFETFPE / TTFEP / DMC = 50/30/20/3 (volume ratio), Further, fluoroethylene carbonate (FEC) was added so as to have a volume ratio of 2 in the above solvent composition.

  The positive electrode, the negative electrode, the separator, and the electrolytic solution described above were disposed in a laminate outer package, and the laminate was sealed to fabricate a lithium secondary battery. The positive electrode and the negative electrode were connected to tabs and electrically connected from the outside of the laminate.

  The lithium secondary battery was charged at 100 mA, and after the upper limit voltage reached 4.8 V, it was charged at a constant voltage until the total charge time reached 2.5 hours. Thereafter, it was discharged at a constant current until the lower limit voltage was 3 V at 100 mA. This charge and discharge were repeated 100 times. The charge and discharge were carried out in a 45 ° C. thermostat.

(Gas generation evaluation)
The amount of gas generation was evaluated by measuring the change in cell volume before and after charge and discharge cycles. The cell volume was measured using the Archimedes method, and the amount of gas generation was calculated by examining the difference before and after charge and discharge cycles. Although not shown here, the amount of gas generation was very large when no FEC was added.

Example 1-2
A lithium secondary battery was produced in the same manner as in Example 1-1 except that fluoroethylene carbonate (FEC) was added so as to have a volume ratio of 3 in the above solvent composition, and the gas generation amount was measured.

Example 1-3
A lithium secondary battery was produced in the same manner as in Example 1-1 except that fluoroethylene carbonate (FEC) was added so as to have a volume ratio of 5 in the above solvent composition, and the gas generation amount was measured.

Example 1-4
A lithium secondary battery was produced in the same manner as in Example 1-1 except that fluoroethylene carbonate (FEC) was added so as to have a volume ratio of 10 in the above solvent composition, and the gas generation amount was measured.

  FIG. 2 shows the gas generation amount in the charge and discharge cycle by the addition amount of fluoroethylene carbonate (FEC) which is a fluorinated cyclic carbonate (Examples 1-1 to 1-4). By adding an appropriate amount of FEC, the amount of gas generation is minimized, and when it is further added, it tends to increase. In the present embodiment, even in the electrolytic solvent composition containing nearly 50% by volume of PC, gas generation is well suppressed when the content of FEC in the electrolytic solution is in the range of approximately 2 to 6% by volume, particularly around 3% by volume. The Further, it is understood from Table 1 and FIG. 2 that the suppression of gas generation was good when the content ratio (volume ratio) of FEC to PC was in the range of 4 to 12%, particularly around 6%.

Example 2-1
As an electrolyte, PC / TFETFPE / TTFEP = 38 /20/40 ( volume ratio) the structure was in a solvent of 1,3-propane sultone 0.1 mol / l was added, the addition of lithium salt LiPF ₆ 0.8 mol / l . Furthermore, 3, 3, 3- trifluoro propylene carbonate (FPC) which is fluorinated cyclic carbonate was added so that it might be 2 volume%. Except for the electrolytic solution, a lithium secondary battery was produced in the same manner as in Example 1-1, and the amount of gas generation was measured after 300 cycles of a 45 ° C. charge and discharge cycle.

Example 2-2
The composition of the solvent of the electrolytic solution is changed to PC / TFETFPE / TTFEP = 38/20/40 (volume ratio) to make PC / TFETFPE / TTFEP = 30/20/40 (volume ratio), and the FPC is changed to 2% by volume A lithium secondary battery was produced in the same manner as in Example 2-1 except that 10% by volume of the lithium secondary battery was added, and the amount of gas generation was measured, to be 0.42 cc.

Comparative Example A
A lithium secondary battery was produced in the same manner as in Example 2-1 except that the composition of the solvent of the electrolytic solution was PC / TFETFPE / TTFEP = 40/20/40 and no FPC was added, and gas generation was performed. The amount was measured and found to be 0.72 cc.

  In Example 2-1 and Example 2-2, gas generation was suppressed by the addition of the FPC. The content of the FPC in the electrolyte solution seems to be optimum around 2% by volume. In addition, it is considered that gas generation can be favorably suppressed when the content ratio (volume ratio) of the FPC to the PC is around 5% to around 33%.

Example 3-1
Lithium was prepared in the same manner as Example 1-1 except that the composition of the solvent of the electrolytic solution was PC / TFETFPE / DMC = 30/70/1 and FEC was added so as to have a volume ratio of 2 in the above solvent composition ratio. The following battery was fabricated, and the amount of gas generation after 300 cycles of the 45 ° C. charge / discharge cycle was measured to be 0.32 cc.

Example 3-2
The composition of the solvent of the electrolytic solution is PC / TFETFPE / TTFEP / DMC = 30/50/20/1, and the FEC is added to have a volume ratio of 2 in the above solvent composition ratio, as in Example 1-1. The lithium secondary battery was manufactured, and the amount of gas generation after 300 cycles of the charge and discharge cycle at 45.degree. C. was measured to be 0.17 cc.

  According to a comparison between Example 3-1 and Example 3-2, the amount of gas generation is smaller when TTFEP is added, and by mixing the fluorine-containing phosphate ester, the gas generation suppressing effect can be further obtained. The It can be said that the effect of suppressing gas generation is good when the content ratio (volume ratio) of FEC to PC is around 7%. Moreover, when 2 volume% of FEC and 3 volume% were compared, the direction of 2 volume% of FEC has a smaller amount of gas, and the suppression effect of gas generation was favorable in 2 volume% vicinity with respect to electrolyte solution.

Example 4-1
In the same manner as Example 1-1 except that the composition of the solvent of the electrolytic solution is PC / TFETFPE / TTFEP / DMC = 30/20/50/3 and FEC is added so as to have a volume ratio of 3 in the above solvent composition. A lithium secondary battery was manufactured, and the gas generation amount was measured after 50 cycles of 45 ° C. charge and discharge cycles, and it was 0.25 cc.

  In addition, the same lithium secondary battery as in this example is fabricated, charged at 45 mA with a constant current of 50 mA to 4.75 V, charged for 2.5 hours with constant voltage, and then discharged to 3.0 V. The Thereafter, the battery was charged again under the same conditions, and then discharged to 3.0 V at 50 mA at 25 ° C., and the discharge capacity at this time was 56 mAh.

Example 4-2
Example 1-1 except that the composition of the solvent of the electrolytic solution is EC / PC / TFETFPE / TTFEP / DMC = 10/20/20/50/3 and FEC is added so as to have a volume ratio of 3 in the solvent composition. A lithium secondary battery was produced in the same manner as above, and the amount of gas generation was measured after 50 cycles of 45.degree. C. charge and discharge cycles, and it was 0.26 cc.

  Further, the same lithium secondary battery as that of this example was produced, and the discharge capacity at 25 ° C. was measured in the same manner as in Example 4-1, and it was 55 mAh.

実施例４−１および実施例４−２のいずれにおいてもガス発生が抑制されている。電解液に、より多くＰＣを含む実施例４−１は、ガス発生がより抑制されており、かつ、電池容量もＰＣの一部をＥＣに置き換えた実施例４−２と同等以上であった。

Gas generation is suppressed in any of Example 4-1 and Example 4-2. In Example 4-1 containing more PC in the electrolytic solution, gas generation was further suppressed, and the battery capacity was also equal to or higher than Example 4-2 in which a part of PC was replaced with EC. .

  The comparative example of the solvent composition which does not contain a propylene carbonate below is shown.

Comparative Example B-1
A lithium secondary battery was produced in the same manner as in Example 1-1 except that the solvent composition of the electrolytic solution was changed to FEC / TFETFPE / TTFEP = 30/40/30, and the resistance of the electrode was increased to operate the battery. I did not.

Comparative Example B-2
A lithium secondary battery was produced in the same manner as in Example 1-1 except that the solvent composition of the electrolytic solution was changed to FEC / TFE TFPE = 30/70. As a result, the electrode resistance increased and the battery did not operate.

Comparative Example B-3
A lithium secondary battery was produced in the same manner as in Example 1-1 except that the solvent composition of the electrolytic solution was changed to FEC / TTFEP = 30/70. As a result, the electrode resistance increased and the battery did not operate.

Comparative Example C
A lithium secondary battery is produced in the same manner as Example 1-1 except that the composition of the solvent of the electrolytic solution is set to EC / FEC / TFETFPE = 30/20/50, and gas generation after 50 cycles of 45 ° C. charge / discharge cycles The amount was measured and found to be 1.73 cc.

比較例Ｂ−１〜Ｂ−３においては、ＰＣを含まない電解溶媒の組成とした場合、電極の抵抗が増大し電池が動作しない結果となった。また、比較例Ｃにおいて、ＰＣを含まずにＥＣを含む電解溶媒の組成とした場合はガス発生量が上記の各実施例よりも多い結果となった。

In Comparative Examples B-1 to B-3, when the composition of the electrolytic solvent containing no PC was used, the resistance of the electrode increased and the battery did not operate. In Comparative Example C, when the composition of the electrolytic solvent containing EC was used without containing PC, the gas generation amount was larger than that of each of the above-described Examples.

  As described above, according to the present embodiment, it is possible to expect good characteristics at low temperatures, and to obtain a lithium secondary battery in which gas generation is suppressed.

  The lithium secondary battery of the present embodiment is a secondary battery which can be expected to have good characteristics at low temperatures and has reduced gas generation, and any industrial field requiring a power source, as well as transport, storage and electric energy. It can be used in the industrial field related to supply. Specifically, it can be used as a power supply of mobile devices, a power supply of a medium for transportation and transportation, a backup power supply, a storage facility for storing electric power generated by solar power generation, wind power generation and the like.

DESCRIPTION OF SYMBOLS 1 positive electrode active material layer 2 negative electrode active material layer 3 positive electrode collector 4 negative electrode collector 5 separator 6 laminate outer package 7 laminate outer package 8 negative electrode tab 9 positive electrode tab

Claims (21)

A lithium ion secondary battery comprising a positive electrode and a negative electrode capable of absorbing and releasing lithium, and a non-aqueous electrolyte containing lithium ions,
The non-aqueous electrolyte is propylene carbonate,
A fluorinated cyclic carbonate represented by the general formula (1) ,
Off Tsu-containing phosphoric acid ester le, and
Fluorinated linear ether
Contain,
The content of propylene carbonate is less than 50 vol% 1 vol% or more nonaqueous solvent, the content of the fluorinated cyclic carbonate is Ri nonaqueous der 0.1 vol% to 10 vol% solvent The content of the fluorine-containing phosphate ester is 15% to 70% by volume in the non-aqueous electrolytic solvent, and the content of the fluorinated chain ether is 10% to 70% by volume in the non-aqueous electrolytic solvent The lithium ion secondary battery characterized by being.

[In Formula (1), A to D are each independently a hydrogen atom, a fluorine atom, or a substituted or unsubstituted alkyl group, and at least one of A to D is a fluorine atom or a fluorine-containing alkyl group is there. ] The lithium ion secondary battery according to claim 1, wherein the content of propylene carbonate in the non-aqueous electrolytic solvent is 5% by volume or more. The lithium ion secondary battery according to claim 1 or 2 , wherein the content of propylene carbonate in the non-aqueous electrolytic solvent is 28.3% by volume or more. The lithium ion secondary battery according to any one of claims 1 to 3 , wherein the content of propylene carbonate in the non-aqueous electrolytic solvent is 40% by volume or less. The lithium ion secondary battery according to any one of claims 1 to 4 , wherein the content of propylene carbonate in the non-aqueous electrolytic solvent is 30% by volume or less. The lithium ion secondary battery according to any one of claims 1 to 5 , wherein the content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is 1% by volume or more. The lithium ion secondary battery according to any one of claims 1 to 6 , wherein the content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is 2% by volume or more. The lithium ion secondary battery according to any one of claims 1 to 7 , wherein the content of the fluorinated cyclic carbonate in the non-aqueous electrolytic solvent is 5% by volume or less. The lithium ion secondary battery according to any one of claims 1 to 8 , wherein a content of the fluorinated cyclic carbonate to propylene carbonate is 2% by volume or more and 40% by volume or less. The lithium ion secondary battery according to any one of claims 1 to 9 , wherein a content of the fluorinated cyclic carbonate to propylene carbonate is 20% by volume or less. The lithium ion secondary battery according to any one of claims 1 to 10 , wherein a content of the fluorinated cyclic carbonate to propylene carbonate is 4% by volume or more. The fluorinated cyclic carbonate is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and a compound having a structure in which part or all of hydrogen atoms of butylene carbonate are substituted by fluorine atoms. lithium-ion secondary battery according to any one of claims 1 to 11. The lithium ion secondary battery according to claim 12 , wherein the fluorinated cyclic carbonate contains at least one selected from fluoroethylene carbonate and fluoropropylene carbonate. Wherein the fluorinated chain ether, a lithium ion secondary battery according to any one of claims 1 to 13, characterized by being represented by the following formula (2).
_{C n H 2n + 1-l} F l -O-C m H 2m + 1-k F k (2)
[In the formula (2), n is 1, 2, 3, 4, 5 or 6; m is 1, 2, 3 or 4; l is any integer from 0 to 2n + 1; Is an integer from 0 to 2m + 1, and at least one of l and k is an integer of 1 or more. ] The fluorine-containing phosphoric acid ester, a lithium ion secondary battery according to any one of claims 1 to 14, characterized by being represented by the following formula (3).

[In formula (3), R ¹ , R ² and R ³ each independently represent an alkyl group or a fluorine-containing alkyl group, and at least one of R ¹ , R ² and R ³ is a fluorine-containing alkyl group. ] The lithium ion secondary battery according to any one of claims 1 to 15 , wherein the positive electrode active material contained in the positive electrode contains a lithium manganese composite oxide represented by the following formula (4).
Li _a (M _x Mn _2-x Y _y ) (O _4-w Z _w ) (4)
(Wherein 0 ≦ x ≦ 1.2, 0 ≦ y, x + y <2, 0 ≦ a ≦ 1.2, 0 ≦ w ≦ 1. M is composed of Co, Ni, Fe, Cr and Cu) At least one member selected from the group: Y is at least one member selected from the group consisting of Li, B, Na, Al, Mg, Ti, Si, K and Ca; and Z is selected from the group consisting of F and Cl It is at least one kind of choice.) The lithium ion secondary battery according to claim 16 , wherein the lithium manganese composite oxide contains at least Ni as M. The positive electrode active material contained in the positive electrode according to any one of claims 1 to 17, characterized in that it comprises at least one lithium-metal composite oxide represented by the following formula (5) or (6) Lithium ion secondary battery.
LiMPO ₄ (5)
[In Formula (5), M is at least 1 sort (s) of Co and Ni. ]
_{Li (Li x M 1-x} -z Mn z) O 2 (6)
[In the formula (6), 0 ≦ x <0.3, 0.3 ≦ z ≦ 0.7, M is at least one of Co and Ni] The lithium ion secondary battery according to any one of claims 1 to 18 , further comprising an outer package including the positive electrode, the negative electrode, and the non-aqueous electrolyte, wherein the outer package is made of an aluminum laminate. . The lithium ion secondary battery according to any one of claims 1 to 19 , wherein the content of the fluorinated chain ether in the non-aqueous electrolytic solvent is 10 to 60% by volume. A method of manufacturing a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, comprising:
Arranging the positive electrode and the negative electrode in opposition via a separator,
Housing the positive electrode and the negative electrode disposed opposite to each other in an outer package together with the non-aqueous electrolyte;
Sealing the outer package, wherein the non-aqueous electrolyte is propylene carbonate,
Fluorinated cyclic carbonate represented by the general formula (7),
Off Tsu-containing phosphoric acid ester, and
Fluorinated linear ether
Contain,
The content of propylene carbonate is less than 50 vol% 1 vol% or more nonaqueous solvent, the content of the fluorinated cyclic carbonate is Ri nonaqueous der 0.1 vol% to 10 vol% solvent The content of the fluorine-containing phosphate ester is 15% to 70% by volume in the non-aqueous electrolytic solvent, and the content of the fluorinated chain ether is 10% to 70% by volume in the non-aqueous electrolytic solvent method for manufacturing a lithium ion secondary battery, characterized in that it.

[In Formula (7), A to D are each independently a hydrogen atom, a fluorine atom, or a substituted or unsubstituted alkyl group, and at least one of A to D is a fluorine atom or a fluorine-containing alkyl group is there. ]

Images