JP5749116B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  With the recent development of electronic technology and increasing interest in environmental technology, various electrochemical devices are used. In particular, there are many requests for energy saving, and expectations for what can contribute to it are increasing. For example, a solar cell is mentioned as a power generation device, and a secondary battery, a capacitor, a capacitor, etc. are mentioned as an electrical storage device. Lithium ion secondary batteries, which are representative examples of power storage devices, were originally used mainly as rechargeable batteries for portable devices, but in recent years are expected to be used as batteries for hybrid vehicles and electric vehicles.

A typical lithium ion secondary battery as an electricity storage device generally has a configuration in which a positive electrode and a negative electrode mainly composed of an active material capable of inserting and extracting lithium are arranged via a separator. In the lithium ion secondary battery, the positive electrode is LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like as a positive electrode active material, carbon black or graphite as a conductive agent, polyvinylidene fluoride, latex, rubber, or the like as a binder. Is mixed with a positive electrode current collector made of aluminum or the like. The negative electrode is formed by coating a negative electrode mixture made of copper or the like with a negative electrode mixture in which coke or graphite as a negative electrode active material and polyvinylidene fluoride, latex, rubber, or the like as a binder are mixed. The The separator is made of porous polyolefin or the like, and its thickness is very thin, from several μm to several hundred μm. The positive electrode, the negative electrode, and the separator are impregnated with an electrolytic solution in the battery. Examples of the electrolytic solution include an electrolytic solution in which a lithium salt such as LiPF ₆ or LiBF ₄ is dissolved in an aprotic solvent such as propylene carbonate or ethylene carbonate or a polymer such as polyethylene oxide.

Lithium ion secondary batteries are currently mainly used as rechargeable batteries for portable devices (see, for example, Patent Document 1), but in recent years, they are expected to be widely used as batteries for automobiles such as hybrid cars and electric cars. ing. In order to expand the applications of lithium ion secondary batteries, it is necessary to reduce the size and improve the performance of the batteries. One approach is to improve separators. What is mainly used as a separator of a lithium ion secondary battery for portable devices is a microporous membrane made of synthetic resin. A synthetic resin microporous membrane is a very reliable membrane, but in order to be used as a separator for in-vehicle use, for example, improvements are required in terms of capacity, current density, heat resistance, cost, and the like. As an attempt to improve these performances, there is an example using a separator such as a nonwoven fabric or paper (for example, see Patent Documents 2 and 3). Nonwoven fabrics and paper are promising because they can produce a porous film (a film that can increase the capacity of a battery) at a low process cost and can be formed from a material having high heat resistance. There are also examples in which a synthetic resin separator is made porous or low density. Or there is an example which is considering the process aiming at the manufacturing cost reduction of the synthetic resin separator.
Furthermore, there is a research example in which a gel electrolyte obtained by gelling an electrolytic solution and a nonwoven fabric separator are combined (for example, Patent Document 4).

JP 2009-087648 A JP 2005-159283 A JP 2005-293891 A JP 2009-070605 A

However, when separators capable of increasing the capacity as described in Patent Documents 2 and 3 are used, a short circuit occurs, dendrite growth is observed, and various unstable charge / discharge behaviors are observed. There is a problem in reliability and safety.
Moreover, in the gel electrolyte using a polymer as a gelling agent as described in Patent Document 4, short circuit and dendrite growth can be reduced, but the battery performance is reduced as compared with a liquid electrolyte. It is difficult to fully exhibit.

  Therefore, the present invention has been made in view of the above circumstances, and even if a separator capable of increasing the capacity of a battery such as a nonwoven fabric is used, stable charge / discharge behavior is exhibited, and cycle characteristics and safety are also excellent. A lithium ion secondary battery is provided.

  As a result of studying various separators and electrolytes in order to achieve the above-mentioned object, the present inventors used a material having a specific pore structure for the separator and combined an electrolyte solution containing a low-molecular gelling agent. As a result, it was found that the obtained lithium ion secondary battery exhibited stable charge / discharge behavior and was excellent in cycle characteristics and safety, and the present invention was completed.

[1]
An electrolyte solution containing a non-aqueous solvent, a lithium salt, and a low-molecular gelling agent;
A positive electrode containing at least one material selected from the group consisting of materials capable of inserting and extracting lithium ions as a positive electrode active material;
A negative electrode containing at least one material selected from the group consisting of a material capable of inserting and extracting lithium ions as a negative electrode active material and metallic lithium;
A separator formed of a nonwoven fabric ;
With
Of the total number of holes of the separator, the ratio of the number of holes having a minor axis of 1.0 μm or less is 20% or less,
Of the holes present on the outermost surface of the separator, the ratio of the number of holes having a minor axis of 1.0 μm or less is 5% or less
The low-molecular gelling agent comprises one or more compounds selected from the group consisting of the following general formulas (1), (2) and (3),
^{Rf 1 -R 1 -X 1 -L 1} -R 2 (1)
Rf ¹ -R ¹ -X ¹ -L ¹ -R ³ -L ² -X ² -R ⁴ -Rf ² (2)
R ⁵ —O—Ar—X ³ —C (3)
(In the formulas (1) and (2),
Rf ¹ and Rf ² each independently represents a C 2-20 perfluoroalkyl group,
R ¹ and R ⁴ each independently represents a single bond or a divalent saturated hydrocarbon group having 1 to 6 carbon atoms,
X ¹ and X ² each independently represent a divalent functional group selected from the group consisting of the following formulas (1a) to (1e),
L ¹ and L ² are each independently a single bond, an oxyalkylene group optionally substituted with an alkyl group or a halogen atom, an oxycycloalkylene group optionally substituted with an alkyl group or a halogen atom, or an alkyl group Or a divalent oxyaromatic group optionally substituted by a halogen atom,
R ² is substituted with an alkyl group or a halogen atom (excluding a fluorine atom), an alkyl group having 1 to 20 carbon atoms, an alkyl group or a halogen atom (excluding a fluorine atom) optionally substituted with an alkyl group or a halogen atom (excluding a fluorine atom). A monovalent fluoroalkyl group, aryl group or fluoroaryl group, or one or more of these groups bonded to one or more of divalent groups corresponding to these groups The group of
R ³ represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms which may have one or more oxygen and / or sulfur atoms in the main chain and may be substituted with an alkyl group.
Moreover, in Formula (3),
R ⁵ represents a carbon hydrocarbon group having 1 to 20 carbon atoms may be substituted with a halogen atom backbone,
Ar represents an alkyl group and / or a divalent aromatic hydrocarbon group or alicyclic hydrocarbon group having 5 to 30 nucleus atoms which may be substituted with a halogen atom ,
X ³ is any divalent group of the following formulas (3a), (3b), (3e) to (3g), or any of the following formulas (3a), (3b), (3e) to (3g) Or a divalent group in which a plurality of groups are bonded,
C represents a coumarin moiety represented by the following formula (3z). In the following formula (3z), each R ^a independently represents a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom.
)
The electrolyte solution is a phase transition type gel electrolyte solution that becomes a gel at a low temperature and a sol at a high temperature,
A lithium ion secondary battery in which a phase transition temperature between the gel and the sol is in a range of 50 to 150 ° C.
[2]
An electrolyte solution containing a non-aqueous solvent, a lithium salt, and a low-molecular gelling agent;
A positive electrode containing at least one material selected from the group consisting of materials capable of inserting and extracting lithium ions as a positive electrode active material;
A negative electrode containing at least one material selected from the group consisting of a material capable of inserting and extracting lithium ions as a negative electrode active material and metallic lithium;
A separator formed of a nonwoven fabric ;
With
The lithium ion secondary battery according to [1], wherein the separator has an air permeability of 50 s / 100 cc or less.
[3]
The lithium ion secondary battery according to [1] or [2], wherein the ratio of the number of holes having a minor axis of 200 μm or more out of the total number of holes of the separator is 5% or less.
[4]
Any of [1] to [3], wherein the ratio of the number of holes having a long diameter of 150 μm or more continuous from one surface to the other surface is 5% or less among the total number of holes of the separator. The lithium ion secondary battery described in 1.
[5]
The lithium ion secondary battery according to any one of [1] to [4], wherein the separator has a thickness of 20 μm or more and 60 μm or less .
[6 ]
The lithium ion according to any one of [1] to [ 5 ], wherein X ¹ and X ² are each independently a divalent functional group represented by the formula (1a) or the formula (1d). Secondary battery.
[ 7 ]
The lithium ion secondary battery according to any one of [1] to [ 6 ], wherein X ¹ and X ² are divalent functional groups represented by the formula (1d).
[ 8 ]
The lithium ion secondary battery according to any one of [1] to [ 7 ], wherein a discharge capacity retention rate when 100 cycles of the charge / discharge cycle test at 25 ° C are performed is 80% or more.
[ 9 ]
The lithium ion secondary according to any one of [1] to [ 8 ], wherein the electrolyte is impregnated in the separator, and a part of the low-molecular gelling agent is present in the pores of the separator. battery.
[ 10 ]
The lithium ion secondary battery according to any one of [1] to [ 9 ], wherein the positive electrode includes a lithium-containing compound as the positive electrode active material.
[ 11 ]
The negative electrode contains, as the negative electrode active material, at least one material selected from the group consisting of metallic lithium, a carbon material, a material containing an element capable of forming an alloy with lithium, and a lithium-containing compound. ] The lithium ion secondary battery in any one of [ 10 ].

  According to the present invention, it is possible to provide a lithium ion secondary battery that exhibits stable charge / discharge behavior and is excellent in cycle characteristics and safety even when a separator such as a nonwoven fabric that can increase the capacity of the battery is used. .

It is sectional drawing which shows roughly an example of the lithium ion secondary battery of this embodiment.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The lithium ion secondary battery of the present embodiment includes a separator having a specific pore structure, an electrolyte containing a nonaqueous solvent, a lithium salt, and a low molecular gelling agent, and occlusion and release of lithium ions as a positive electrode active material. One or more materials selected from the group consisting of a positive electrode containing one or more materials selected from the group consisting of materials capable of absorbing, and a material capable of occluding and releasing lithium ions as the negative electrode active material and metallic lithium A negative electrode containing a material.

<Separator>
In the lithium ion secondary battery of this embodiment, a separator is provided between the positive electrode and the negative electrode from the viewpoint of providing safety such as prevention of short circuit between the positive and negative electrodes and shutdown. As the separator, an insulating thin film having high ion permeability and excellent mechanical strength is preferable.
The separator used in the present embodiment needs to have a specific pore structure. Specifically, the ratio of the number of holes having a minor axis of 1.0 μm or less out of the total number of holes of the separator is 20% or less. Moreover, it is preferable that the air permeability of a separator is 50 s / 100 cc or less. By using a separator having such a specific pore structure in combination with an electrolyte containing a low-molecular gelling agent, the current density in the lithium ion secondary battery is locally concentrated on a part of the electrode. It is possible to suppress dendrite growth due to, and to improve an excess of charging electric capacity due to a minute short circuit.
In the separator used in this embodiment, the ratio of the number of holes having a minor axis of 1.0 μm or less is preferably 10% or less. The lower limit of the ratio of the number of holes having a minor axis of 1.0 μm or less is preferably 0.5% or more. Further, the ratio of the number of holes having a minor axis of 200 μm or more is more preferably 5% or less. Even more preferably, the ratio of the number of holes having a minor axis of 150 μm or more is 5% or less.
Moreover, it is preferable that the ratio of the number of holes having a minor axis of 1.0 μm or less among the holes present on the outermost surface of the separator is 5% or less. Furthermore, it is more preferable that the ratio of the number of holes having a long diameter of 150 μm or more continuous through holes from one surface to the other surface is 5% or less among the total number of holes of the separator used in the present embodiment. A short circuit occurs due to the ratio of the number of holes having a minor axis of 1.0 μm or less among the holes present on the outermost surface of the separator and the ratio of the holes having a major axis of through holes of 150 μm or more being 5% or less. Unstable charging / discharging behavior such as this can be further suppressed.
The air permeability of the separator used in this embodiment is preferably 50 s / 100 cc or less, and more preferably 20 s / 100 cc or less.
The thickness of the separator used in the present embodiment is preferably 20 μm or more and 60 μm or less, and more preferably 20 μm or more and 50 μm or less. The thickness of the separator is preferably 20 μm or more from the viewpoint of mechanical strength and from the viewpoint of isolating the positive and negative electrodes and suppressing short circuits. Further, from the viewpoint of increasing the output density as a battery and suppressing the decrease in energy density, the thickness of the separator is preferably 60 μm or less.
By using a separator having such a specific pore structure in combination with an electrolytic solution containing a low-molecular gelling agent, the obtained lithium ion secondary battery can exhibit stable charge / discharge behavior.
In the present embodiment, the ratio of the number of holes having a minor axis of 1.0 μm or less out of the total number of holes of the separator can be obtained by the method described in Examples described later. Further, the ratio of the number of holes having a minor axis of 200 μm or more can be determined by the method described in Examples described later. Furthermore, the ratio of the number of holes having a minor axis of 150 μm or more can be determined by the method described in Examples described later. Furthermore, out of the holes present on the outermost surface of the separator, the ratio of the number of holes having a minor axis of 1.0 μm or less, or the total number of holes of the separator, the through-holes continuous from one surface to the other surface The ratio of the number of holes having a major axis of 150 μm or more can also be determined by the method described in Examples described later.
The air permeability of the separator is the time required for 100 cc of air to permeate. An air permeability tester is used for measuring the air permeability of the separator. In the present embodiment, the air permeability of the separator is a value measured with a Gurley type air permeability meter according to JIS P-8117.
Examples of the separator used in the present embodiment include a woven fabric, a non-woven fabric, a synthetic resin microporous membrane, and papermaking. Any separator can be used as long as it can take the above-described structure. From the viewpoints of the ease of forming the pore structure and cost, woven fabrics, nonwoven fabrics and papermaking are preferred, nonwoven fabrics and papermaking are more preferred, and nonwoven fabrics are most preferred. Moreover, these separators can be manufactured by a general manufacturing method, and a manufacturing method is not ask | required. In the case of a nonwoven fabric, the separator used in the present embodiment can be made by, for example, a spunbond method, a melt blown method, or the like. In addition, the separator used in the present embodiment may be a single layer or a stack of a plurality of layers.
Examples of the material of the separator used in the present embodiment include ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, heat-resistant resin such as aramid, and cellulose. From the viewpoint of handling properties and heat resistance, polyester, polyamide, liquid crystal polyester, aramid, and cellulose are preferable. These resins and the like may be a single resin or the like, may be a copolymer resin, or may be a mixture of a plurality of resins or the like. Alternatively, a plurality of films made of a plurality of materials may be stacked. In the case of a laminated body, the material of each layer may be the same or different. When making a laminated body, it can also laminate | stack in order for every layer, and can also be made into a laminated body by bonding together the several film | membrane produced separately.

<Electrolyte>
The electrolytic solution used in the present embodiment contains (I) a nonaqueous solvent, (II) a lithium salt, and (III) a low molecular gelling agent.
(I) Although various things can be used as a non-aqueous solvent, for example, an aprotic solvent is mentioned. When used as an electrolyte solution for a lithium ion secondary battery, an aprotic polar solvent is preferable in order to increase the ionization degree of a lithium salt that is an electrolyte that contributes to the charge and discharge. Specific examples thereof include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, and trans-2,3. -Cyclic carbonates typified by pentylene carbonate, cis-2,3-pentylene carbonate, trifluoromethylethylene carbonate, fluoroethylene carbonate and 4,5-difluoroethylene carbonate; typified by γ-butyrolactone and γ-valerolactone Lactone; cyclic sulfone represented by sulfolane; cyclic ether represented by tetrahydrofuran and dioxane; methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate Bonates, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate and chain carbonate represented by methyl trifluoroethyl carbonate; nitrile represented by acetonitrile; chain ether represented by dimethyl ether; Examples thereof include a chain carboxylic acid ester represented by methyl propionate; a chain ether carbonate compound represented by dimethoxyethane. These are used singly or in combination of two or more.

  (I) The non-aqueous solvent preferably contains one or more cyclic aprotic polar solvents in order to increase the ionization degree of the lithium salt. From the same viewpoint, (I) the nonaqueous solvent more preferably contains one or more cyclic carbonates typified by ethylene carbonate and propylene carbonate. The cyclic compound has a high dielectric constant, helps ionization of the lithium salt, and enhances the gelation ability.

(I) An ionic liquid can also be used as the non-aqueous solvent. An ionic liquid is a liquid composed of ions obtained by combining an organic cation and an anion.
Examples of the organic cation include imidazolium ions such as a dialkylimidazolium cation and a trialkylimidazolium cation, a tetraalkylammonium ion, an alkylpyridinium ion, a dialkylpyrrolidinium ion, and a dialkylpiperidinium ion.

Examples of the anion serving as a counter for these organic cations include PF ₆ anion, PF ₃ (C ₂ F ₅ ) ₃ anion, PF ₃ (CF ₃ ) ₃ anion, BF ₄ anion, and BF ₂ (CF ₃ ) ₂ anion. , BF ₃ (CF ₃ ) anion, bisoxalatoborate anion, Tf (trifluoromethanesulfonyl) anion, Nf (nonafluorobutanesulfonyl) anion, bis (fluorosulfonyl) imide anion, bis (trifluoromethanesulfonyl) imide anion, bis (Pentafluoroethanesulfonyl) imide anion and dicyanoamine anion can be used.

(II) Specific examples of the lithium salt used as the electrolyte include, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{2k + 1} [k is 1-8. Integer], LiN (SO ₂ C _k F _{2k + 1} ) ₂ [k is an integer of 1 to 8], LiPF _n (C _k F _{2k + 1} ) _6-n [n is an integer of 1 to 5, k is 1 8 integer], represented by _{LiBF n ((C k F 2k} + 1) 4-n [n is an integer of 1 to 3, k is an integer of 1 to _{8], LiB (C 2 O 2)} 2 Examples thereof include lithium bisoxalyl borate, lithium difluorooxalyl borate represented by LiBF ₂ (C ₂ O ₂ ), and lithium trifluorooxalyl phosphate represented by LiPF ₃ (C ₂ O ₂ ).

Moreover, the lithium salt represented by the following general formula (a), (b), or (c) can also be used as an electrolyte.
LiC (SO ₂ R ¹¹ ) (SO ₂ R ¹² ) (SO ₂ R ¹³ ) (a)
LiN (SO ₂ OR ¹⁴ ) (SO ₂ OR ¹⁵ ) (b)
LiN (SO ₂ R ¹⁶ ) (SO ₂ OR ¹⁷ ) (c)
Here, in the formula, R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ may be the same or different from each other, and are a C 1-8 perfluoroalkyl group. Indicates.

These electrolytes are used singly or in combination of two or more. Among these electrolytes, LiPF ₆ , LiBF ₄ and LiN (SO ₂ C _k F _{2k + 1} ) ₂ [k is an integer of 1 to 8] are used from the viewpoint of enhancing gelation ability in addition to battery characteristics and stability. preferable.

  The concentration of the electrolyte is arbitrary and is not particularly limited, but the electrolyte is preferably contained in the electrolytic solution at a concentration of 0.1 to 3 mol / liter, more preferably 0.5 to 2 mol / liter.

  (III) The low molecular gelling agent is a non-polymer type gelling agent capable of sol-gel transition by reversible physical interaction. Various low molecular gelling agents are known, and any of them may be used. Examples thereof include a fluoro gelling agent described in JP-A-10-175901, an amide group-containing gelling agent described in JP-A-2007-506833, and JP-A-2009-155592.

The low molecular weight gelling agent used in the present embodiment is a group consisting of compounds represented by the following general formulas (1), (2) and (3) from the viewpoint of electrochemical stability and gelling ability with respect to an electrolytic solution. It is preferable to include one or more selected.
^{Rf 1 -R 1 -X 1 -L 1} -R 2 (1)
Rf ¹ -R ¹ -X ¹ -L ¹ -R ³ -L ² -X ² -R ⁴ -Rf ² (2)
R ⁵ —O—Ar—X ³ —C (3)

In the general formulas (1) and (2), Rf ¹ and Rf ² each independently represents a C 2-20 perfluoroalkyl group. If the said carbon number is 2-20, a raw material acquisition and a synthesis | combination will be easy. From the viewpoints of the compatibility of the compounds represented by the general formulas (1) and (2) (hereinafter also referred to as “perfluoro compounds”) into the electrolyte, the electrochemical characteristics of the electrolyte, and the gelling ability, The carbon number is preferably 2-12. Examples of the perfluoroalkyl group include perfluoroethyl group, perfluoro n-propyl group, perfluoroisopropyl group, perfluoro n-butyl group, perfluoro t-butyl group, perfluoro n-hexyl group, perfluoro n. -An octyl group, a perfluoro n-decyl group, and a perfluoro n-dodecyl group are mentioned.

In the general formulas (1) and (2), R ¹ and R ⁴ each independently represent a single bond or a divalent saturated hydrocarbon group having 1 to 6 carbon atoms, and the carbon number is 2 to 5. And preferred. When the divalent saturated hydrocarbon group has 3 or more carbon atoms, it may or may not be branched. Examples of such a divalent saturated hydrocarbon group include a methylidene group, an ethylene group, an n-propylene group, an isopropylene group, and an n-butene group.

X ¹ and X ² each independently represent a divalent functional group selected from the group consisting of the following formulas (1a) to (1g). Among these, from an electrochemical viewpoint, a divalent functional group selected from the group consisting of divalent groups represented by the following formula (1a), the following formula (1b) and the following formula (1d) is preferable. The divalent functional group represented by the formula (1a) or the following formula (1d) is more preferable, and the divalent functional group represented by the following formula (1d) is more preferable.

L ¹ and L ² may each independently be substituted with a single bond, an alkyl group or a halogen atom (that is, may be unsubstituted) an oxyalkylene group, an alkyl group or a halogen atom. A good (ie, unsubstituted) oxycycloalkylene group, or a divalent oxyaromatic group (—OAr) optionally substituted (ie, optionally substituted) with an alkyl group or a halogen atom -; Ar represents a divalent aromatic group. Examples of the oxyalkylene group include an oxyalkylene group having 2 to 10 carbon atoms, more specifically, an oxyethylene group (—C ₂ H ₄ O—) and an oxypropylene group (—C ₃ H ₆ O—). Can be mentioned. Examples of the oxycycloalkylene group include an oxycycloalkylene group having 5 to 12 carbon atoms, and more specifically, an oxycyclopentylene group, an oxycyclohexylene group, and an oxydicyclohexylene group.

  Among these, a divalent oxyaromatic group is preferable from the viewpoint of gelling ability and improving the safety of the electrolytic solution. The divalent aromatic group in the divalent oxyaromatic group which may be substituted with an alkyl group or a halogen atom is a cyclic divalent group exhibiting so-called “aromaticity”. The divalent aromatic group may be a carbocyclic group or a heterocyclic group. The carbocyclic group has 6 to 30 nuclear atoms, and may be substituted with an alkyl group or a halogen atom as described above, or may not be substituted. Specific examples thereof include a divalent group having a nucleus represented by a phenylene group, a biphenylene group, a terphenylene group, a naphthylene group, an anthranylene group, a phenanthrylene group, a pyrenylene group, a chrysenylene group, and a fluoranthenylene group. It is done.

The heterocyclic group has 5 to 30 nuclear atoms, and includes, for example, a nucleus represented by a pyrrolene group, a furylene group, a thiophenylene group, a triazolen group, an oxadiazolene group, a pyridylene group, and a pyrimidylene group. And a divalent group. Among these, as the divalent aromatic group, a phenylene group, a biphenylene group, or a naphthylene group is preferable. Examples of the alkyl group that is a substituent include a methyl group and an ethyl group, and examples of the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom.
The oxycycloalkylene group and the oxyaromatic group include those in which a plurality of rings are connected. Examples of such a group include an oxybiphenylene group, an oxyterphenylene group, and an oxycycloalkylphenylene group.

R ² in the general formula (1) is an alkyl group having 1 to 20 carbon atoms, an alkyl group, or a halogen atom (provided that it may be substituted with an alkyl group or a halogen atom (excluding a fluorine atom)). A fluoroalkyl group, an aryl group, or a fluoroaryl group optionally substituted with a fluorine atom), or one or more of these groups and one of divalent groups corresponding to these groups A monovalent group bonded to a species or more is shown. R ² is more specifically a methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-decyl group. And an alkyl group having 1 to 12 carbon atoms represented by This alkyl group may or may not be further substituted with an alkyl group or a halogen atom (excluding a fluorine atom).

  As a fluoroalkyl group, a C1-C12 fluoroalkyl group (however, except a perfluoroalkyl group) or a C1-C12 perfluoroalkyl group is preferable. Specific examples of the fluoroalkyl group having 1 to 12 carbon atoms (excluding the perfluoroalkyl group) and the perfluoroalkyl group having 1 to 12 carbon atoms include a trifluoromethyl group, 1,1,1,2 , 2-pentafluoroethyl group, 1,1,2,2-tetrafluoroethyl group, 1,1,1,2,2,3,3-heptafluoron-butyl group, 1,1,2,2, 3,3,4,4,5,5,6,6-dodecafluoro n-hexyl group and 1,1,1,2,2,3,3,4,4,5,5,6,6-tri A decafluoro n-decyl group is mentioned. The fluoroalkyl group may be further substituted with an alkyl group or a halogen atom (excluding a fluorine atom), or may not be substituted.

As an aryl group, for example, an aryl group having 6 to 12 nuclear atoms represented by a phenyl group, a biphenyl group, and a naphthyl group, and a fluoroaryl group, for example, a monofluorophenyl group, a difluorophenyl group, a tetrafluorophenyl Examples thereof include a fluoroaryl group having 6 to 12 nuclear atoms represented by the group.
R ² represents one or more of the aforementioned alkyl group, fluoroalkyl group, aryl group and fluoroaryl group, and a divalent group corresponding to these groups, that is, an alkylene group, a fluoroalkylene group, an arylene group. A monovalent group in which one or more of a group and a fluoroarylene group are bonded may be used. Examples of such a group include a group in which an alkylene group and a perfluoroalkyl group are bonded (however, this group is also a kind of fluoroalkyl group), a group in which an alkylene group and an aryl group are bonded, fluoro Examples include a group in which an alkyl group and a fluoroarylene group are bonded.

R ² is preferably an alkyl group or a fluoroalkyl group from the viewpoint of more effectively and reliably achieving the effects of the present embodiment, and is an alkyl group having 1 to 12 carbon atoms or a fluoroalkyl group having 1 to 12 carbon atoms (provided that Or a perfluoroalkyl group having 1 to 12 carbon atoms, more preferably an alkyl group having 1 to 8 carbon atoms or a fluoroalkyl group having 2 to 10 carbon atoms (provided that the perfluoroalkyl group is a perfluoroalkyl group). It is more preferable that the group is excluded.

R ³ in the general formula (2) may or may not have one or more oxygen and / or sulfur atoms in the main chain, and may or may not be substituted with an alkyl group. A divalent saturated hydrocarbon group having 1 to 18 carbon atoms is shown. The said carbon number is preferable in it being 1-16, and more preferable in it being 2-14. The gelling ability can also be controlled by the number of carbon atoms in R ³ . Moreover, the carbon number of the said range is preferable from a viewpoint of a synthesis | combination and raw material acquisition.

Examples of the gelling agent having a perfluoro group include Rf ¹ -R ¹ —O—R ² , Rf ¹ —R ¹ —S—R ² , Rf ¹ —R ¹ —SO ₂ —R ² , Rf ¹ —. R ¹ —OCO—R ² , Rf ¹ —R ¹ —O—Ar—O—R ² (wherein Ar represents a divalent aromatic group; the same shall apply hereinafter), Rf ¹ —R ¹ —SO ₂ —Ar—O—R ² , Rf ¹ —R ¹ —SO ₂ —Ar—O—Rf ⁴ , Rf ¹ —R ¹ —SO ₂ —Ar—O—Rf ³ —Rf ⁴ (where Rf ³ represents fluoro An alkylene group, Rf ⁴ represents a fluoroalkyl group.), Rf ¹ -R ¹ -SO-Ar-O-R ² , Rf ¹ -R ¹ -S-Ar-O-R ² , Rf ¹ -R ^1- O—R ⁵ —O—R ² (where R ⁵ represents an alkylene group), Rf ¹ —R ¹ —CONH—R ² , Rf ¹ —R ¹ —SO ₂ —Ar ¹ —O—R ³ -O-Ar ² -SO _2- R ⁴ -Rf ² (wherein Ar ¹ and Ar ² each independently represents a divalent aromatic group; the same shall apply hereinafter), Rf ¹ -R ¹ -O-Ar ¹ -O-R ³ —O—Ar ² —O—R ⁴ —Rf ² , Rf ¹ —R ¹ —SO ₂ —Ar ¹ —O—R ⁶ —O—R ⁷ —O—Ar ² —O—R ⁴ —Rf ² (here And R ⁶ and R ⁷ each independently represents an alkylene group, the same shall apply hereinafter). More specifically, Rf ¹ and Rf ² are each independently a perfluoroalkyl group having 2 to 10 carbon atoms, R ¹ is an alkylene group having 2 to 4 carbon atoms, Ar is (or Ar ¹ and Ar ² are each Independently, a p-phenylene group or a p-biphenylene group, a compound represented by each of the above general formulas wherein R ² is an alkyl group having 4 to 8 carbon atoms, and a dimer structure thereof, for example, Rf ¹ -R ^1- O—Ar—O—R ² , Rf ¹ —R ¹ —SO ₂ —Ar—O—R ² , Rf ¹ —R ¹ —O—Ar ¹ —O—R ³ —O—Ar ² —O— R ⁴ —Rf ² , Rf ¹ —R ¹ —SO ₂ —Ar ¹ —O—R ⁶ —O—R ⁷ —O—Ar ² —O—R ⁴ —Rf ² are exemplified. It is done.

  In the general formula (3), Ar represents a substituted or unsubstituted divalent aromatic hydrocarbon group or alicyclic hydrocarbon group having 5 to 30 nuclear atoms. The divalent aromatic hydrocarbon group is a cyclic divalent group exhibiting so-called “aromaticity”. This divalent aromatic hydrocarbon group may be a carbocyclic group or a heterocyclic group. These divalent aromatic hydrocarbon groups may be substituted with a substituent or may be an unsubstituted one that is not substituted. A substituent of the divalent aromatic hydrocarbon group can be selected from the viewpoint of synthesis or availability of raw materials. Alternatively, the substituent of the divalent aromatic hydrocarbon group can be selected from the viewpoint of the melting temperature and gelling ability of the gelling agent.

The carbocyclic group has 6 to 30 nuclear atoms, may be substituted with a substituent, or may be unsubstituted or unsubstituted. Specific examples thereof include divalent groups having a nucleus represented by a phenylene group, a biphenylene group, a terphenylene group, a naphthylene group, an anthranylene group, a phenanthrylene group, a pyrenylene group, a chrysenylene group, and a fluoranthenylene group. It is done.
The heterocyclic group has 5 to 30 nuclear atoms, and includes, for example, a nucleus represented by a pyrrolene group, a furylene group, a thiophenylene group, a triazolen group, an oxadiazolene group, a pyridylene group, and a pyrimidylene group. And a divalent group.
Ar is preferably a substituted or unsubstituted divalent aromatic hydrocarbon group having 6 to 20 nuclear atoms, from the viewpoints of availability of raw materials and ease of synthesis, and gelation ability in an electrolyte solution. A group selected from the group consisting of a group, a biphenylene group, a naphthylene group, a terphenylene group, and an anthranylene group is more preferable.
Moreover, as said substituent, the alkyl group represented by the methyl group and the ethyl group, and a halogen atom are mentioned.

  The alicyclic hydrocarbon group has 5 to 30 atoms, and examples thereof include a cyclopentyl group, a cyclohexyl group, and a cyclooctyl group.

  An aromatic hydrocarbon group or an alicyclic hydrocarbon group, if the number of each atom is within the range, a plurality of groups are connected, or both a carbocyclic ring and a heterocyclic ring, It can also have both an alicyclic group.

In the general formula (3), R ⁵ represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms in the main chain, and may be saturated or unsaturated. R ⁵ may be an aliphatic hydrocarbon group and may further have an aromatic hydrocarbon group. Part or all of the hydrocarbon group may be substituted with a halogen atom. When this hydrocarbon group is a monovalent aliphatic hydrocarbon group, it may be branched or unbranched, and a part or all of the branched chain may be substituted with a halogen atom. The hydrocarbon group chain may contain an oxygen atom and / or a sulfur atom. Furthermore, when the monovalent hydrocarbon group has an aromatic hydrocarbon group, this aromatic hydrocarbon group may or may not further have a substituent. However, this monovalent hydrocarbon group is an electrolytic solution in which a compound represented by the above general formula (3) (hereinafter also referred to as “compound (3)”) is dissolved in a nonaqueous solvent and contains the nonaqueous solvent. In order to gel the liquid, it is necessary to be a hydrocarbon group that can dissolve the compound (3) in a non-aqueous solvent, such as an arylalkyl group typified by a benzyl group. When the monovalent hydrocarbon group has 21 or more carbon atoms, it becomes difficult to obtain the raw material. The monovalent hydrocarbon group represented by R ⁵ is preferably an alkyl group having 4 to 18 carbon atoms, and an alkyl group having 4 to 14 carbon atoms from the viewpoint of more effectively and reliably achieving the above effects in the present embodiment. Is more preferable. R ⁵ is preferably a linear alkyl group from the viewpoint of gelling ability and handling properties.

In the general formula (3), X ³ is a divalent group in which any one of the following formulas (3a) to (3g) or any one of the following formulas (3a) to (3g) is bonded. The group of is shown. A divalent group of any one of the following formulas (3a), (3e), and (3g) is preferable.
In the above general formula (3), X ³ must be selected from the point of being stable over a long period of time and the gelling ability when the compound (3) is used in a lithium ion secondary battery. When X ³ is a group represented by the above formula (3a), a very stable gel tends to be formed. When X ³ is a group represented by the above formula (3e), the gel-sol transition can be induced not only by temperature but also by light irradiation, leading to expansion of applications.

In the general formula (3), C represents a coumarin moiety, and in the following formula (3z), each R ^a independently represents a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom.

  The low molecular gelling agent mentioned above is used individually by 1 type or in combination of 2 or more types.

  The content of the low-molecular gelling agent in the electrolytic solution used in the present embodiment is arbitrary, but the content ratio with respect to the nonaqueous solvent is 0.1: 99. .9 to 10:90, preferably 0.3: 99.7 to 5:95. When the content ratio of these components is within the range, the lithium ion secondary battery using the electrolytic solution exhibits particularly high battery characteristics. Moreover, when the low molecular weight gelling agent acts as a gelling agent, both the gelling ability and the handling property can be improved because the content ratio of the above components is within the range. In addition, as the content of the gelling agent in the electrolytic solution is larger, the electrolytic solution has a higher phase transition point and becomes a firm gel. As the content of the gelling agent is smaller, the viscosity of the electrolytic solution is lower and easier to handle.

  Among the gelling agents used in the present embodiment, those having a perfluoro group include, for example, International Publication No. 2007/083843, Japanese Patent Application Laid-Open No. 2007-191626, Japanese Patent Application Laid-Open No. 2007-191627, and Japanese Patent Application Laid-Open No. 2007-191627. It can manufacture with reference to the method as described in 2007-191661 gazette.

Moreover, the gelling agent which has a perfluoro group used for this embodiment is compoundable with the following scheme, for example.
That is, first, a compound represented by the following formula (II) is synthesized as follows from a compound represented by the following formula (I) for which a commercially available product is available.

The compound represented by the above formula (I) (4-hydroxy-4′-mercaptophenyl) may be replaced with 4-hydroxy-4′-mercaptobiphenyl, but in the following description, 4-hydroxy-4 ′ -An example using mercaptophenyl is shown. Next, the compound represented by the formula (II) is dimerized as follows to obtain the compound represented by the formula (III).

In this case, as the compound represented by the formula (II), compounds having different carbon numbers of the perfluoroalkyl group may be used (for example, one n is replaced with a different numerical value m), and R ¹ May be changed to R ³ which is a different divalent hydrocarbon group. However, since they do not necessarily react at a molar ratio of 1: 1, it is preferable to use the same compound as the compound represented by formula (II) from the viewpoint of stably obtaining a desired compound. .
Here, the compound represented by the formula (III) has a gelling ability. However, as shown in the following reaction formula, the compound represented by the following formula (IV) can be obtained by oxidizing the thioether moiety to sulfonylation or sulfoxide formation. A gelling agent having the perfluoro group represented is obtained.

As long as in the production scheme of a gelling agent having a perfluoroalkyl group represented by the general formula (IV), n represents an integer of 2 to 18, in each of R ¹ and R ³ are independently a single bond or a main 1 represents a substituted or unsubstituted divalent hydrocarbon group having 1 to 6 carbon atoms in the chain, and R ² is a substituted or unsubstituted 3 to 18 carbon atom in the main chain which may have an ether group or a thioether group In the formula, each X independently represents an SO group or an SO ₂ group.

Furthermore, the gelling agent having a perfluoro group used in the present embodiment can be synthesized by the following scheme, for example. First, a thiol compound represented by the following general formula (11a) is sulfided with a compound represented by the following general formula (11b) in the presence of a base such as triethylamine in a solvent such as dry THF. The compound represented by (11c) is obtained.
HS-Ar-OH (11a)
C _m F _{2m + 1} C _p H _2p X ¹ (11b)
_{C m F 2m + 1 C p} H 2p -S-Ar-OH (11c)

Next, the compound represented by the general formula (11c) is etherified with a compound represented by the following general formula (11d) in the presence of an alkali metal compound such as K ₂ CO _{3 in} a solvent such as 3-pentanone. To obtain a compound represented by the following general formula (11e).
R ¹ X ² (11d)
_{C m F 2m + 1 C p} H 2p -S-Ar-O-R 1 (11e)

Then, the perfluoro compound represented by the following general formula (11j) is obtained by oxidizing the compound represented by the general formula (11e) with an oxidizing agent such as hydrogen peroxide in the presence of a catalyst such as acetic acid. Is obtained.
_{C m F 2m + 1 C p} H 2p -SO 2 -Ar-O-R 1 (11j)
Here, as long as in the production scheme of the perfluoro compound represented by the general formula (11j), Ar represents a substituted or unsubstituted divalent aromatic group having 8 to 30 nuclear atoms, and R ¹ is saturated or An unsaturated monovalent hydrocarbon group having 1 to 20 carbon atoms, m represents a natural number of 2 to 16, and p represents an integer of 0 to 6. X ¹ represents a halogen atom such as an iodine atom, and X ² represents a halogen atom such as a bromine atom.

  As such a synthesis method, for example, the synthesis method described in International Publication No. 2009/78268 can be referred to.

Further, when Ar is a group in which a plurality of aromatic rings such as a biphenylene group or a terphenylene group are bonded by a single bond, a perfluoro compound represented by the above general formula (11j) is obtained by the following synthesis method, for example. Can do. First, a thiol compound represented by the following general formula (11f) is sulfided with a compound represented by the above general formula (11b) in the presence of a base such as triethylamine in a solvent such as dry THF. A compound represented by (11 g) is obtained. Here, in the formulas (11f) and (11g), m and p are as defined in the formula (11j), X ³ represents a halogen atom such as a bromine atom, and Ar ² represents the above formula (11j). ) Represents a part of the divalent aromatic hydrocarbon group constituting Ar.
^{HS-Ar 2 -X 3 (11f} )
_{C m F 2m + 1 C p} H 2p -S-Ar 2 -X 3 (11g)

Next, the following compound (11h) is obtained by oxidizing the compound represented by the general formula (11g) with an oxidizing agent such as hydrogen peroxide in the presence of a catalyst such as acetic acid. Here, in the formula (11h), Ar ² , X ³ , m and p are as defined in the formula (11g).
_{C m F 2m + 1 C p} H 2p -SO 2 -Ar 2 -X 3 (11h)

Then, from the compound represented by the above general formula (11h) and the compound represented by the following general formula (11i), in the presence of a palladium catalyst in a basic aqueous solution such as K ₂ CO ₃ , Suzuki-Miyaura coupling To obtain the perfluoro compound represented by the general formula (11j). Here, in the formula (11i), R ¹ has the same meaning as in the formula (11j), Ar ³ is Ar ² a divalent aromatic hydrocarbon group constituting Ar in the formula (11j) A part different from is shown, and Ar ² and Ar ³ bonded by a single bond is Ar.
R ¹ —O—Ar ³ —B (OH) ₂ (11i)

Moreover, the gelling agent which has a perfluoro group used for this embodiment is compoundable with the following scheme, for example. That is, from the compound represented by the following general formula (Ia) and the compound represented by the following general formula (IIa), by dehydration condensation such as Mitsunobu reaction, it is a kind of gelling agent having a perfluoro group A compound represented by the formula (IIIa) can be synthesized. Here, in the formula, Y ¹ and Y ² are each independently an S atom or an O atom.
^{Rf 1 -R 1 -Y 1 -Z-} Y 2 H (Ia)
Rf ² R ² OH (IIa)
^{Rf 1 -R 1 -Y 1 -Z-} Y 2 -R 2 -Rf 2 (IIIa)

Further, in the compound represented by the above general formula (IIIa), when Y ¹ and / or Y ² is an S atom, the S atom is further sulfonylated or sulfoxided to form a gel having a perfluoro group A compound represented by the following general formula (IVa), which is another kind of agent, can be synthesized. Here, at least one of Y ³ and Y ⁴ is an SO group or SO ₂ group, and when one of Y ³ and Y ⁴ is an SO group or SO ₂ group, the other is an S atom or an O atom.
^{Rf 1 -R 1 -Y 3 -Z-} Y 4 -R 2 -Rf 2 (IVa)

The compound represented by the general formula (Ia) is, for example, a perfluoroalkane halide (thiol group or a hydrogen atom of a hydroxyl group) of a compound represented by the following formula (Va) under alkaline conditions ( For example, it can be synthesized by substitution with a perfluoroalkyl group of iodide.
HY ¹ -ZY ² H (Va)
The compound represented by the above formula (IIa) can be synthesized by further reducing the halide of alkanol obtained by the addition reaction of perfluoroalkane halide (for example, iodide) to alkenol.

Here, as long as in the production scheme of the perfluoro compound represented by the general formula (IIIa) or (IVa), Rf ¹ and Rf ² are each independently substituted or unsubstituted having 2 to 18 carbon atoms in the main chain. Represents a perfluoroalkyl group, R ¹ and R ² each independently represents a single bond or a substituted or unsubstituted divalent hydrocarbon group having 1 to 8 carbon atoms in the main chain, and Z represents a substituted or unsubstituted group. A divalent aromatic hydrocarbon group or alicyclic hydrocarbon group having 5 to 30 nucleus atoms is shown.

  However, the method for synthesizing the gelling agent having a perfluoro group used in the present embodiment is not limited to the above method.

  In addition, as the coumarin-type gelling agent (compound (3)) used in the present embodiment, for example, the compounds described in the liquid crystal discussion conference proceedings collection p44 (2007) can be used.

Moreover, the compound (3) which has an azo group is compoundable by the following reaction pathways, for example.
Examples of the compound (3) having an azo group synthesized as described above are represented by the following formula (3I) (hereinafter also referred to as “compound (3I)”) and the following formula (3II). (Hereinafter also referred to as “compound (3II)”).
Hereinafter, the synthesis methods of the compounds (3I) and (3II) will be described in detail.
[Method for Synthesizing Compound (3I)]
Step 1: Synthesis of compound (a)
Add a mixed solution of concentrated nitric acid and concentrated sulfuric acid to the eggplant flask. While cooling the eggplant flask in an ice bath, coumarin is gradually added so that the temperature of the mixed solution does not exceed 20 ° C. When all the coumarin has been added, remove the ice bath and stir at room temperature for 1 hour to react. The reaction solution is poured into water, and the precipitated solid is collected by filtration. The solid collected by filtration is recrystallized from toluene to obtain a light yellow solid compound (a).
Step 2: Synthesis of compound (b)
In an eggplant flask, the compound (a) is dissolved in a mixed solution of ethanol and toluene, and a hydrogenation reaction is performed in the presence of Pd / C. After the hydrogenation reaction, Pd / C is collected by filtration, and the filtrate is concentrated by an evaporator. The precipitated solid is recrystallized from toluene to obtain a yellow solid compound (b).
Step 3: Synthesis of compound (c)
In an eggplant flask, an aqueous solution of 12N hydrochloric acid and water is prepared under ice-cooling at 5 ° C. Compound (b) and sodium nitrite (NaNO ₂ ) are added to the aqueous solution and stirred for 20 minutes. Further, a mixed solution of phenol, sodium hydroxide and water is added and stirred. The precipitated solid is recrystallized from toluene to obtain compound (c).
Step 4: Synthesis of Compound (3I)
In an eggplant flask, compound (c) is dissolved in 3-pentanone. 1-Bromooctane and potassium carbonate are added to the obtained solution and refluxed for 15 hours. The obtained solid is recrystallized from toluene and purified by column chromatography to obtain compound (3I). In the column chromatography, silica gel is used as a filler and chloroform is used as a developing solvent.
[Method for Synthesizing Compound (3II)]
In an eggplant flask, compound (c) is dissolved in 3-pentanone. 1-Bromohexane and potassium carbonate are added to the obtained solution and refluxed for 15 hours. The obtained solid is recrystallized from toluene and purified by column chromatography to obtain compound (3II). In the column chromatography, silica gel is used as a filler and chloroform is used as a developing solvent.

However, the manufacturing method of a compound (3) is not limited to the said method.
The electrolyte used in the present embodiment is preferably a phase transition type gel electrolyte solution that is a gel at a low temperature and a sol at a high temperature. In the lithium ion secondary battery of this embodiment, when the electrolytic solution is a gel electrolyte solution, the handling property such as injection is excellent and the safety such as the reduction of leakage tends to be secured at a high level. Among these, the phase transition temperature between the gel and the sol is more preferably in the range of 50 to 150 ° C.

It is preferable that the electrolyte used in the present embodiment is sufficiently impregnated in the separator, and a part of the low-molecular gelling agent in the electrolyte is present in the pores of the separator. The low-molecular gelling agent adheres to the separator surface or is impregnated in the electrode, but it is preferable that the low-molecular gelling agent is also present in the pores of the separator.
For example, by filling the whole or a part of the pores of the nonwoven fabric with the low molecular gelling agent aggregate, the pore size unique to the nonwoven fabric and the nonuniformity of the pore size distribution can be improved. That is, it is possible to prevent an internal short circuit between the electrodes due to the expansion and contraction of the positive electrode and the negative electrode due to charge / discharge and an internal short circuit due to the lithium dendrite generated due to the nonuniformity of the current density. Therefore, a lithium ion secondary battery including a composite of a nonwoven fabric having a certain pore structure and a low molecular gelling agent exhibits stable charge / discharge characteristics.

  The mixing ratio of the nonaqueous solvent, the lithium salt, and the low molecular gelling agent can be selected according to the purpose, but the electrolyte concentration and the content of the low molecular gelling agent are all within the above-mentioned preferable range, and more preferably the above range. It is desirable to be in By producing an electrolytic solution with such a composition, battery characteristics and handleability can be further improved.

The method for preparing the electrolytic solution used in the present embodiment is not particularly limited as long as the above components are mixed, and the mixing order of the electrolyte, the nonaqueous solvent, and the low molecular gelling agent is not limited. For example, after preparing a preliminary electrolyte by mixing a predetermined amount of electrolyte and a non-aqueous solvent, a low molecular gelling agent can be mixed with the preliminary electrolyte to obtain the electrolyte used in this embodiment. . Alternatively, it is possible to obtain an electrolytic solution used in the present embodiment by simultaneously mixing all the components in a predetermined amount. It is preferable to heat the electrolytic solution containing the low-molecular gelling agent once and cool it to room temperature in a state where each component in the mixture is uniform.
The electrolyte used in the present embodiment is particularly excellent in satisfying safety and battery characteristics required for a lithium ion secondary battery, and is preferably used in a lithium ion secondary battery.

<Positive electrode>
In the lithium ion secondary battery of this embodiment, the positive electrode uses a material containing one or more materials selected from the group consisting of materials capable of inserting and extracting lithium ions as the positive electrode active material. Examples of such materials include composite oxides represented by the following general formulas (6a) and (6b), metal chalcogenides and metal oxides having a tunnel structure and a layered structure, and olivine-type phosphate compounds.
Li _x MO ₂ (6a)
Li _y M ₂ O ₄ (6b)
Here, in the formula, M represents one or more metals selected from transition metals, x represents a number from 0 to 1, and y represents a number from 0 to 2.

More specifically, for example, lithium cobalt oxide typified by LiCoO ₂ ; lithium manganese oxide typified by LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ ; lithium nickel typified by LiNiO ₂ Oxide; represented by Li _z MO ₂ (M represents two or more elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2). And lithium-containing composite metal oxide; and iron phosphate olivine represented by LiFePO ₄ . Further, as the positive electrode active material, for example, a metal other than lithium represented by S, MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ and NbSe ₂ is used. Oxides are also exemplified. Furthermore, conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole are also exemplified as the positive electrode active material.
In the lithium ion secondary battery of this embodiment, the positive electrode preferably includes a lithium-containing compound as a positive electrode active material.

Further, it is preferable to use a lithium-containing compound as the positive electrode active material because a high voltage and a high energy density tend to be obtained. As such a lithium-containing compound, any compound containing lithium may be used. For example, a composite oxide containing lithium and a transition metal element, a phosphate compound containing lithium and a transition metal element, and lithium and a transition metal element (For example, Li _{t Mu} SiO ₄ , where M is as defined in the above formula (6a), t is a number from 0 to 1, and u is a number from 0 to 2). . From the viewpoint of obtaining a higher voltage, lithium, cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium ( V) and composite oxides containing at least one transition metal element selected from the group consisting of titanium (Ti) and phosphate compounds are preferred.

More specifically, the lithium-containing compound is preferably a metal oxide having lithium, a metal chalcogenide having lithium, and a metal phosphate compound having lithium. For example, the lithium-containing compounds are represented by the following general formulas (7a) and (7b). The compound which is made is mentioned.
^{_{Li v M I O 2 (7a}} )
Li _w M ^II PO ₄ (7b)
Here, in the formula, M ^I and M ^II each represent one or more transition metal elements, and the values of v and w vary depending on the charge / discharge state of the battery, but usually v is 0.05 to 1.10, w Indicates a number from 0.05 to 1.10.

  The compound represented by the general formula (7a) generally has a layered structure, and the compound represented by the general formula (7b) generally has an olivine structure. In these compounds, for the purpose of stabilizing the structure, a part of the transition metal element is substituted with Al, Mg, other transition metal elements or included in the crystal grain boundary, a part of the oxygen atom And those substituted with a fluorine atom or the like. Furthermore, what coat | covered the other positive electrode active material to at least one part of the positive electrode active material surface is mentioned.

  A positive electrode active material is used individually by 1 type or in combination of 2 or more types.

  The number average particle diameter (primary particle diameter) of the positive electrode active material is preferably 0.05 μm to 100 μm, more preferably 1 μm to 10 μm. The number average particle size of the positive electrode active material can be measured by a wet particle size measuring device (for example, a laser diffraction / scattering particle size distribution meter, a dynamic light scattering particle size distribution meter). Alternatively, 100 particles observed with a transmission electron microscope are randomly extracted and analyzed with image analysis software (for example, image analysis software manufactured by Asahi Kasei Engineering Co., Ltd., trade name “A Image-kun”). It can also be obtained by calculating an average. In this case, when the number average particle diameter differs between measurement methods for the same sample, a calibration curve created for the standard sample may be used.

The positive electrode is obtained, for example, as follows. That is, first, a positive electrode mixture-containing paste is prepared by dispersing, in a solvent, a positive electrode mixture obtained by adding a conductive additive, a binder, or the like to the positive electrode active material as necessary. Next, this positive electrode mixture-containing paste is applied to a positive electrode current collector and dried to form a positive electrode mixture layer, which is pressurized as necessary to adjust the thickness, thereby producing a positive electrode.
Here, the solid content concentration in the positive electrode mixture-containing paste is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass.
The positive electrode current collector is made of, for example, a metal foil such as an aluminum foil or a stainless steel foil.

<Negative electrode>
In the lithium ion secondary battery of the present embodiment, the negative electrode uses one or more materials selected from the group consisting of a material capable of inserting and extracting lithium ions and a metallic lithium as a negative electrode active material. In the lithium ion secondary battery of this embodiment, the negative electrode is one type selected from the group consisting of metallic lithium, a carbon material, a material containing an element capable of forming an alloy with lithium, and a lithium-containing compound as a negative electrode active material. It is preferable to contain the above materials. Examples of such materials include lithium metal, hard carbon, soft carbon, artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, organic polymer compound fired body, mesocarbon microbeads. Carbon materials represented by carbon fiber, activated carbon, graphite, carbon colloid, and carbon black. Among these, examples of the coke include pitch coke, needle coke, and petroleum coke. Further, the fired body of the organic polymer compound is obtained by firing and polymerizing a polymer material such as a phenol resin or a furan resin at an appropriate temperature. In the present embodiment, a battery employing metallic lithium as the negative electrode active material is also included in the lithium ion secondary battery.

  Further, examples of the material capable of inserting and extracting lithium ions include a material containing an element capable of forming an alloy with lithium. This material may be a single metal or semi-metal, an alloy or a compound, and may have at least a part of one or more of these phases. .

  In the present specification, the “alloy” includes an alloy having one or more metal elements and one or more metalloid elements in addition to an alloy composed of two or more metal elements. In addition, the alloy may have a nonmetallic element as long as the alloy has metallic properties as a whole. In the alloy structure, a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of these coexist.

  Examples of such metal elements and metalloid elements include titanium (Ti), tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), and antimony (Sb). Bismuth (Bi), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr) and yttrium (Y).

  Among these, metal elements and metalloid elements of Group 4 or 14 in the long-period periodic table are preferable, and titanium, silicon, and tin are particularly preferable.

  As an alloy of tin, for example, as a second constituent element other than tin, silicon, magnesium (Mg), nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, Examples thereof include those having one or more elements selected from the group consisting of antimony and chromium (Cr).

  Examples of the silicon alloy include, as the second constituent element other than silicon, tin, magnesium, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Those having one or more elements selected from the above are listed.

Examples of the titanium compound, the tin compound, and the silicon compound include those having oxygen (O) or carbon (C), and in addition to titanium, tin, or silicon, the second constituent element described above is included. It may be.
Moreover, a lithium containing compound is also mentioned as a material which can occlude and release lithium ions. As the lithium-containing compound, the same compounds as those exemplified as the positive electrode material can be used.

  A negative electrode active material is used individually by 1 type or in combination of 2 or more types.

  The number average particle diameter (primary particle diameter) of the negative electrode active material is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm. The number average particle size of the negative electrode active material is measured in the same manner as the number average particle size of the positive electrode active material.

A negative electrode is obtained as follows, for example. That is, first, a negative electrode mixture-containing paste is prepared by dispersing, in a solvent, a negative electrode mixture prepared by adding a conductive additive or a binder to the negative electrode active material, if necessary. Next, the negative electrode mixture-containing paste is applied to a negative electrode current collector and dried to form a negative electrode mixture layer, which is pressurized as necessary to adjust the thickness, thereby producing a negative electrode.
Here, the solid content concentration in the negative electrode mixture-containing paste is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass.
The negative electrode current collector is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  Examples of the conductive aid used as necessary in the production of the positive electrode and the negative electrode include graphite, carbon black typified by acetylene black and ketjen black, and carbon fiber. The number average particle size (primary particle size) of the conductive assistant is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm, and is measured in the same manner as the number average particle size of the positive electrode active material. Examples of the binder include polyvinylidene fluoride (PVDF), a copolymer containing polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polyacrylic acid, styrene butadiene rubber, and fluorine rubber.

  The lithium ion secondary battery of the present embodiment is, for example, a lithium ion secondary battery that schematically shows a cross-sectional view in FIG. A lithium ion secondary battery 100 shown in FIG. 1 includes a separator 110, a positive electrode 120 and a negative electrode 130 that sandwich the separator 110 from both sides, and a positive electrode current collector 140 that sandwiches a laminate thereof (arranged outside the positive electrode). And a negative electrode current collector 150 (arranged outside the negative electrode) and a battery outer case 160 for housing them. A laminate in which the positive electrode 120, the separator 110, and the negative electrode 130 are laminated is impregnated with the above-described electrolytic solution. As each of these members, if the electrolyte solution and the separator are combined as described above, other members can be those provided in a conventional lithium ion secondary battery, for example, those described above. Also good.

<Production method of battery>
The lithium ion secondary battery of this embodiment is produced by a known method using the above-described specific separator and electrolyte, a positive electrode, and a negative electrode. For example, a plurality of positive electrodes in which a positive electrode and a negative electrode are wound in a laminated state with a separator interposed therebetween to be formed into a laminate having a wound structure, or they are alternately laminated by bending or laminating a plurality of layers. Or a laminate in which a separator is interposed between the electrode and the negative electrode. Next, the laminated body is accommodated in a battery case (exterior), the electrolytic solution used in the present embodiment is injected into the case, and the laminated body is immersed in the electrolytic solution and sealed. The lithium ion secondary battery can be manufactured. Alternatively, an electrolyte membrane containing a gelled electrolyte solution is prepared in advance, and a positive electrode, a negative electrode, an electrolyte membrane, and a separator as necessary are formed by bending or stacking as described above, and then a battery case A lithium ion secondary battery can also be produced by being housed inside. The shape of the lithium ion secondary battery of the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a rectangular tube shape, a button shape, a coin shape, a flat shape, and a laminated shape are suitably employed.

  Since the electrolytic solution used in the present embodiment can achieve high conductivity and high safety (for example, flame retardancy and liquid retention), a lithium ion secondary battery including the electrolytic solution and the specific separator described above. Has high battery characteristics (for example, charge / discharge characteristics, low temperature operability, high temperature durability, etc.) and at the same time realizes high safety. Specifically, since the electrolytic solution contains a gelling agent having a small influence on its properties, the lithium ion secondary battery including the specific electrolytic solution and the separator described above has been particularly found in conventional polymer batteries. Such a significant decrease in conductivity and battery characteristics can be suppressed. In addition, since the electrolyte contains an additive having a function of acting as a gelling agent and a combustion suppressing action, leakage of the electrolyte to the outside of the battery can be prevented, as well as the lithium ion secondary of this embodiment. The battery can further reduce the danger of lithium dendrite and the danger of combustion. By using both of these additives in combination, it is possible to suppress a decrease in charge / discharge cycle characteristics derived from the additive and to achieve high safety that cannot be achieved with a single additive.

  In the lithium ion secondary battery according to the present embodiment, the discharge capacity maintenance rate when the charge / discharge cycle test at 25 ° C. is performed 100 cycles is preferably 80% or more, and more preferably 85% or more. More preferably, it is 90% or more. In the present embodiment, the charge / discharge cycle test indicates a case where charge / discharge of the produced battery is performed under 1C conditions. When the battery is charged and discharged once, it is counted as one cycle, and the discharge capacity maintenance rate is calculated with the discharge capacity at the second cycle as 100%.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said embodiment. The present invention can be variously modified without departing from the gist thereof.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. Various characteristics of the lithium ion secondary battery were measured and evaluated as follows.

(I) Separation of pore size of separator The pore size of the separator used for evaluation was measured with a digital microscope. VHX-500F made by Keyence is used for the digital microscope, and the entire range of the separator used for battery evaluation is observed with a field of view of 300 times. Of 1000 holes, the short diameter is 1.0 μm or less. The number of was measured. From the number of the holes, the ratio of the number of holes having a minor axis of 1.0 μm or less out of 1000 holes was obtained. The said ratio was made into the ratio of the number of the holes whose minor axis is 1.0 micrometer or less among the total number of holes which a separator has.
Similarly, the ratio of the number of holes having a minor axis of 200 μm or more was similarly determined by measuring the number of holes having a minor axis of 200 μm or more among arbitrary 1000 holes.
Similarly, the ratio of the number of holes having a minor axis of 150 μm or more was similarly determined by measuring the number of holes having a minor axis of 150 μm or more among arbitrary 1000 holes.
Further, among the holes present on the outermost surface of the separator, the ratio of the number of holes having a minor axis of 1.0 μm or less, and the total number of holes of the separator, the through-holes continuous from one surface to the other surface Similarly, the ratio of holes having a long diameter of 150 μm or more was measured in the same manner, and the number of holes having a short diameter of 1.0 μm or less and the number of holes having a long diameter of 150 μm or more among arbitrary 1000 holes was measured. Was determined by
Moreover, the short diameter and long diameter of the hole of the nonwoven fabric which is a separator were defined as follows. When the holes of the nonwoven fabric are triangular, the major axis is the length of the longest line segment connecting the midpoints of the two sides, and the minor axis is the shortest segment of the line segments connecting the midpoints of the two sides. Defined as length. When the hole of the nonwoven fabric was a quadrangle, the longest line segment among the line segments connecting the midpoints of the opposite sides was defined as the major axis, and the shortest segment was defined as the minor axis. When the holes of the nonwoven fabric were polygonal, the major axis was defined as the longest vertex distance, and the minor axis was defined as the shortest vertex distance.

(Ii) Air permeability measurement of separator It measured with the Gurley type air permeability meter based on JIS P-8117.
(Iii) Film thickness of separator The film thickness of the separator used for evaluation was measured using a film thickness meter. As a film thickness meter, a Digimatic indicator manufactured by Mitutoyo was used to measure the film thickness at three arbitrary points in the separator, and the average value was taken as the film thickness of the separator.

(Iv) Charging and discharging capacity measurement of a lithium ion secondary battery The charging capacity and discharging capacity at a specific charging current and discharging current were measured as follows to evaluate the charging / discharging characteristics of the lithium ion secondary battery.
As a lithium ion secondary battery for measurement, a small battery with 1C = 3 mA was prepared and used. The charge and discharge capacity of the lithium ion secondary battery was measured using a charge / discharge device ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. and a thermostat PLM-63S (trade name) manufactured by Futaba Kagaku.
(Measurement 1) After charging at a constant current of 1 mA and reaching 4.2 V, charging was performed at a constant voltage of 4.2 V for a total of 8 hours. Thereafter, after a pause of 10 minutes, the discharge capacity when discharged to 3.0 V at 1 mA was measured.
(Measurement 2) Subsequently, after charging at a constant current of 3 mA and reaching 4.2 V, charging was performed at a constant voltage of 4.2 V for a total of 3 hours. Then, after 10 minutes of rest, the discharge capacity was measured when discharged to 3.0 V at 3 mA.
The battery ambient temperature at this time was set to 25 ° C.
(Iv-A) Charging / discharging efficiency measurement The charging / discharging measurement 1 as described in said (iv) charge and discharge capacity measurement of a lithium ion secondary battery was performed once, and charging / discharging of the measurement 2 was performed 4 times after that. The charge / discharge efficiency for the fourth time was calculated by the following formula. In addition, a battery characteristic is excellent, so that the value of this charging / discharging efficiency is large.
Charging / discharging efficiency (%) = capacity during discharging / capacity during charging x 100
(Iv-i) Voltage change The voltage change during the 10-minute rest period from the fourth charge to the fourth discharge was monitored. The battery has more stable performance as the voltage change is smaller.

(V) Evaluation of Charging Behavior of Laminated Lithium Ion Secondary Battery The initial charge / discharge characteristics of the laminated lithium ion secondary battery were evaluated as follows. As a lithium ion secondary battery for measurement, a single-layer laminated battery with 1C = 48.0 mA was prepared and used. The measurement was performed using a charge / discharge device ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. After charging with a constant current of 15.0 mA and reaching 4.2 V, charging was performed for a total of 8 hours while changing the current value so as to be a constant voltage of 4.2 V. The battery ambient temperature at this time was set to 25 ° C. A battery that was stably charged for the first time under the charging conditions was evaluated as “good”, and a battery whose voltage dropped during charging or could not be stably charged was evaluated as “poor”. If charging cannot be performed at a constant voltage without reaching 4.2 V, charging at a constant voltage of 4.2 V without convergence of the current value despite reaching 4.2 V. It was determined that charging could not be performed stably when the battery could not be charged and when it was apparently charged beyond the rated battery capacity.

(Vi) Lithium ion secondary battery capacity maintenance rate measurement (cycle test)
The capacity retention rate was measured using a charge / discharge device ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. and a thermostat PLM-63S (trade name) manufactured by Futaba Kagaku Co., Ltd. As a lithium ion secondary battery for measurement, (iv) a battery produced in the same manner as the measurement of charging and discharging capacity of a lithium ion secondary battery was used. In the charge / discharge cycle test, as the first cycle, the battery was charged at a constant current of 3 mA, reached 4.2 V, and then charged at a constant voltage of 4.2 V for a total of 3 hours. Then, after 10 minutes of rest, the battery was discharged at a constant current of 1 mA, and when it reached 3.0 V, it was rested again for 10 minutes. Subsequently, after the second cycle, the battery was charged with a constant current of 3 mA, and after reaching 4.2 V, the battery was charged with a constant voltage of 4.2 V for a total of 3 hours. Thereafter, after 10 minutes of rest, the battery was discharged at a constant current of 3 mA, and when it reached 3.0 V, it was rested again for 10 minutes. Charging and discharging were performed once each as one cycle, and 100 cycles of charging and discharging were performed. The ratio of the discharge capacity at the 100th cycle when the discharge capacity at the second cycle was 100% was taken as the capacity retention rate. The ambient temperature of the battery was set to 25 ° C.

(Vii) High temperature durability test of lithium ion secondary battery Except that the ambient temperature of the battery was set to 50 ° C., the same as “(vi) Lithium ion secondary battery capacity maintenance rate measurement (cycle test)” The charge / discharge cycle test was conducted up to 100 cycles, and the capacity retention rate at high temperature was measured.

(Viii) Overcharge test of single-layer laminate type lithium ion secondary battery For the overcharge test, a single-layer laminate type lithium ion secondary battery with 1C = 45.0 mA was prepared and used. The measurement was performed using a charge / discharge device ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. The battery charged to a charging rate of 100% was further charged at a constant current of 45.0 mA, and the charging rate at which a voltage drop was observed was determined. The fact that a voltage drop is observed means that a short circuit has occurred.

(Synthesis Example 1)
As a gelling agent, a compound represented by the following structural formula (I) (hereinafter also referred to as “compound (I)”. The same shall apply hereinafter) was synthesized as follows.
First, compound (a) was obtained according to the following scheme. Specifically, in a 200 mL eggplant flask, a solution of 29.89 g (63 mmol) of 2- (perfluorohexyl) ethyl iodide and 11.34 g ((60 mmol) of p-bromothiophenol (100 mmol) in a 100 mL solution of dry tetrahydrofuran (dryTHF). Then, 9.09 g (90 mmol) of triethylamine was added, and the mixture was refluxed for 10 hours in an oil bath at 84 ° C. After returning to room temperature, a solid was confirmed in the solution, and thus the solid was removed by suction filtration.
After the filtrate was transferred to a 300 mL separatory funnel, cyclopentyl methyl ether was added, the organic layer was washed twice with water, and anhydrous magnesium sulfate was added to the organic layer and dried. Anhydrous magnesium sulfate was removed by fold filtration. The obtained filtrate was concentrated under reduced pressure, and the residue was recrystallized from ethanol. As a result, 31.87 g of compound (a) was obtained (yield 99.3%).
Next, the compound (b) was obtained according to the following scheme. Specifically, in a 300 mL eggplant flask, 13 mL (151 mmol) of 35% aqueous hydrogen peroxide was added to 100 mL of a glacial acetic acid solution of 32.82 g (61.3 mmol) of the above compound (a), and the oil bath at 70 ° C. Stirring was performed for 2 hours. After returning to room temperature, 5 mL of 20% aqueous sodium hydrogen sulfite solution was added to reduce unreacted hydrogen peroxide. At this time, a solid had already precipitated in the solution, but when 90 mL of water was added, a solid further precipitated. After performing suction filtration, the solid was washed with water. As a result, 26.34 g of compound (b) was obtained (yield 75%).
And the compound (a) was obtained like the following scheme. Specifically, in a 100 mL eggplant flask, 1.39 g (6.58 mmol) of 4-hexoxyphenylboronic acid, 3.7 g (6.58 mmol) of compound (b), 30 mL of 2M aqueous sodium carbonate solution, dioxane 60 mL (amount added until solid dissolved) was added. To this was added 0.295 g (1.31 mmol) of palladium acetate and 1.18 g (4.5 mmol) of triphenylphosphine, and then a Dimroth tube was attached to the eggplant flask, and vigorously at 95 ° C. for 2.5 hours under N ₂ atmosphere. Stir. After cooling to room temperature, 50 mL of water was added and stirred at room temperature for 2.5 hours. After transferring to a 300 mL separatory funnel, 80 mL of ethyl acetate was added as an organic solvent, and the aqueous layer was removed. This aqueous layer was extracted twice with 50 mL of ethyl acetate. These organic layers were combined and washed once with 120 mL of saturated aqueous sodium hydrogen carbonate solution and twice with saturated brine. After the organic layer was transferred to a 200 mL Erlenmeyer flask, 0.2 g of activated carbon was added and stirred at room temperature for 30 minutes. Further, sodium sulfate was added and stirred at room temperature for 1 hour.
Celite was spread to a depth of 1 cm in Nutsche, and the solid was removed by suction filtration using the celite. The filtrate was transferred to a 200 mL eggplant flask and then concentrated under reduced pressure to obtain a solid (c). Petroleum ether (20 mL) and methanol (30 mL) were added to the solid (c), but they were not completely dissolved. The filtrate was concentrated under reduced pressure to give a solid (e). As a result of measuring ¹ H-NMR spectra of the solids (d) and (e), it was found that the main component of the solid (d) was the target product. When the solid (d) was dissolved in chloroform, black microcrystals were confirmed in the solution, and the microcrystals were removed by passing through a cylinder filter (pore diameter 0.45 μm, diameter 13 mm). The solution passed through the filter was concentrated under reduced pressure and recrystallized with chloroform. In order to increase the yield, the filtrate after recrystallization was concentrated under reduced pressure and recrystallized twice with chloroform and ethanol. As a result of recrystallization three times in total, 2.38 g of compound (I) was obtained (yield 54%).
As the gelling agent, the following compound (b), compound (c), and compound (d) were synthesized in the same manner.

(Production Example 1)
<Preparation of electrolyte>
Ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 2 to obtain a mixed solution. LiPF ₆ was added to this mixed solution so as to have a concentration of 1 mol / L to prepare a non-gelled electrolytic solution (A) (hereinafter, the electrolytic solution before addition of the gelling agent is referred to as “mother electrolytic solution”). ). To the mother electrolyte (A), the compound (a) synthesized as above is added as a gelling agent, heated to 90 ° C. and uniformly mixed, and then cooled to 25 ° C. to obtain the compound (a) An electrolytic solution (a) containing 1% by mass was obtained.

Example 1
<Preparation of positive electrode>
Lithium nickel, manganese and cobalt mixed oxide having a number average particle diameter of 11 μm as a positive electrode active material, graphite carbon powder having a number average particle diameter of 6.5 μm and acetylene black powder having a number average particle diameter of 48 nm as a conductive auxiliary agent, and a binder Polyvinylidene fluoride (PVDF) as a mixed oxide: graphite carbon powder: acetylene black powder: PVDF = 100: 4.2: 1.8: 4.6. N-methyl-2-pyrrolidone was added to the obtained mixture so as to have a solid content of 68% by mass and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was dried and removed, followed by rolling with a roll press. The rolled product was punched into a disk shape having a diameter of 16 mm to obtain a positive electrode (α).

<Production of negative electrode>
Graphite carbon powder I having a number average particle diameter of 12.7 μm and graphite carbon powder II having a number average particle diameter of 6.5 μm as a negative electrode active material, a carboxymethylcellulose solution (solid content concentration 1.83% by mass) as a binder, and a diene system Rubber (glass transition temperature: −5 ° C., number average particle size upon drying: 120 nm, dispersion medium: water, solid content concentration 40% by mass), graphite carbon powder I: graphite carbon powder II: carboxymethyl cellulose solution: diene A rubber-like rubber was mixed at a solid content mass ratio of 90: 10: 1.44: 1.76 so that the total solid content concentration was 45% by mass to prepare a slurry-like solution. The slurry solution was applied to one side of a 10 μm thick copper foil, and the solvent was removed by drying, followed by rolling with a roll press. The rolled product was punched into a disk shape with a diameter of 16 mm to obtain a negative electrode (β).

<Preparation of separator>
A nonwoven fabric (film thickness 54 μm, basis weight 21 g / m ² ) made of polyethylene terephthalate and aramid was selected as a separator and punched into a disk shape having a diameter of 24 mm to obtain a separator (γ). The pore size and air permeability of the obtained separator were measured as described above. The results are shown in Table 1.

<Battery assembly>
A laminate in which the positive electrode (α) and the negative electrode (β) produced as described above were superimposed on both sides of the separator (γ) was inserted into a SUS disk-type battery case. Next, 0.5 mL of the electrolytic solution (a) heated to 90 ° C. was injected into the battery case, and the laminate was immersed in the electrolytic solution (a). Thereafter, the battery case was sealed to produce a lithium ion secondary battery (small battery). The lithium ion secondary battery was held at 80 ° C. for 1 hour, and then cooled to 25 ° C. to obtain a lithium ion secondary battery (1).

(Example 2)
A lithium ion secondary battery (2) was obtained in the same manner as in Example 1 except that the separator was changed to a nonwoven fabric (δ) made of polyethylene terephthalate (film thickness: 24 μm, basis weight: 17 g / m ² ).

(Example 3)
A lithium ion secondary battery (3) was obtained in the same manner as in Example 1 except that the separator was changed to a nonwoven fabric (ε) made of polyethylene terephthalate (film thickness 32 μm, basis weight 19 g / m ² ).

  The lithium ion secondary batteries (1) to (3) produced in Examples 1 to 3 were evaluated as described in “(iv) Lithium ion secondary battery charge and discharge capacity measurement”. The results are shown in Table 1.

(Comparative Example 1)
A lithium ion secondary battery (4) was obtained in the same manner as in Example 1 except that the mother electrolyte (A) was used as it was instead of the electrolyte (a).

(Comparative Example 2)
A lithium ion secondary battery (5) was obtained in the same manner as in Example 2, except that the mother electrolyte (A) was used as it was instead of the electrolyte (a).

(Comparative Example 3)
A lithium ion secondary battery (6) was obtained in the same manner as in Example 3 except that the mother electrolyte (A) was used as it was instead of the electrolyte (a).

(Comparative Example 4)
The separator was changed to a non-woven fabric (ζ) made of polyolefin (film thickness 40 μm, basis weight 6.0 g / m ² ), and the mother electrolyte (A) was used as the electrolyte instead of the electrolyte (a). Obtained a lithium ion secondary battery (7) in the same manner as in Example 1.

The lithium ion secondary batteries (4) to (7) produced in Comparative Examples 1 to 4 were evaluated as described in “(iv) Lithium ion secondary battery charge and discharge capacity measurement”. The results are shown in Table 1.

  As can be seen from Table 1, lithium ion secondary batteries (1) to (3) using a material exhibiting a specific pore structure of the present embodiment for the separator and using an electrolytic solution containing a specific low molecular gelling agent. ) Shows a stable charge / discharge behavior without short-circuiting, as compared with lithium ion secondary batteries (4) to (7) that do not use a separator having a specific pore structure and a low molecular gelling agent. I understood.

Example 4
<Preparation of positive electrode>
Lithium nickel, manganese and cobalt mixed oxide having a number average particle diameter of 11 μm as a positive electrode active material, graphite carbon powder having a number average particle diameter of 6.5 μm and acetylene black powder having a number average particle diameter of 48 nm as a conductive auxiliary agent, and a binder And polyvinylidene fluoride (PVdF) were mixed at a mass ratio of 100: 4.2: 1.8: 4.6. N-methyl-2-pyrrolidone was added to the obtained mixture so as to have a solid content of 68% by mass and further mixed to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was dried and removed, followed by rolling with a roll press. The rolled product was punched into a rectangular shape with a length of 50 mm and a width of 30 mm to obtain a positive electrode (η).

<Production of negative electrode>
Graphite carbon powder having a number average particle diameter of 12.7 μm and graphite carbon powder having a number average particle diameter of 6.5 μm as a negative electrode active material, a carboxymethylcellulose solution (solid content concentration 1.83% by mass) as a binder, and a diene rubber ( Glass transition temperature: −5 ° C., number average particle size upon drying: 120 nm, dispersion medium: water, solid content concentration of 40% by mass) at a solid content mass ratio of 90: 10: 1.44: 1.76 A slurry-like solution was prepared by mixing so that the total solid concentration was 45% by mass. This slurry-like solution was applied to one side of a copper foil having a thickness of 18 μm, and the solvent was removed by drying, followed by rolling with a roll press. The rolled product was punched into a rectangular shape with a length of 52 mm and a width of 32 mm to obtain a negative electrode (θ).

<Battery assembly>
Two cup-formed packaging materials (size of rectangular outer end: 68 mm × 48 mm) were stacked so that the opening sides face each other, and the three sides of the periphery were sealed to prepare a laminate cell exterior. Subsequently, a separator (ε) was prepared, and a laminate obtained by alternately stacking the positive electrode (η) and the negative electrode (θ) produced as described above via the separator (ε) was used as a laminate cell exterior. Placed in. Subsequently, gel electrolyte solution (b) (gelator content: obtained by adding the compound (a) synthesized as described above as a gelling agent to the mother electrolyte (A) in the cell exterior. 3% by mass), and the remaining side of the laminate cell exterior was sealed under reduced pressure to obtain a lithium ion secondary battery. The obtained lithium ion secondary battery was held at 95 ° C. under reduced pressure for 4 hours, and then cooled to 25 ° C. Then, this type of sealing was performed under reduced pressure to obtain laminated lithium ion secondary batteries (8-1) to (8-3).

  The laminated lithium ion secondary batteries (8-1) to (8-3) obtained as described above were evaluated as described in "(v) Evaluation of charging behavior of laminated lithium ion secondary battery". It was. The results are shown in Table 2.

(Comparative Example 5)
A laminated lithium ion secondary battery was obtained in the same manner as in Example 4 except that the mother electrolyte (A) was used instead of the electrolyte (b). In addition, injection | pouring of mother electrolyte solution (A) was performed repeating the atmospheric pressure and the pressure reduction of 100 mmHg until there was no bubble generation. In this way, single layer laminate type lithium ion secondary batteries (9-1) to (9-3) were obtained.

The laminated lithium ion secondary batteries (9-1) to (9-3) obtained as described above are evaluated as described in "(v) Evaluation of charging behavior of laminated lithium ion secondary battery". It was. The results are shown in Table 2.

  As can be seen from Table 2, a laminate type lithium ion secondary battery (8-) using a material exhibiting a specific pore structure of the present embodiment for a separator and using an electrolytic solution containing a specific low molecular gelling agent. 1) to (8-3) are stable without short-circuiting, compared with the laminated lithium ion secondary batteries (9-1) and (9-2) that do not use a specific low-molecular gelling agent. It was found to show charge / discharge behavior.

(Examples 5 to 16, Comparative Examples 6 to 17)
With respect to the mother electrolyte (A), any one of the gelling agents represented by the above compound (a), compound (b), compound (c), and compound (d) is shown in Table 3 The electrolytes (b), (c), (d), (e), (f), (g), and (g) were added in the same manner as in Example 1 except that the total amount of the solution was added to the base. h) was prepared respectively. Of the electrolytes (a) to (h), the separator (ε) as the separator, and the total number of holes of the separator, the separator (ι) (polyethylene having a minor axis of 1.0 μm or less is 100% Lithium ion secondary batteries (10) to (33) were produced in the same manner as in Example 1 using any one of the microporous membranes and the film thickness: 25 μm. About lithium ion secondary battery (10)-(25), the measurement as described in said "(vi) Lithium ion secondary battery capacity maintenance factor measurement (cycle test)" was performed. For the lithium ion secondary batteries (26) to (33), the above “(vii) High temperature durability test of lithium ion secondary battery” was performed. The results are shown in Table 3.

  As shown in Table 3, lithium ion secondary batteries (10) to (10) to (10) to (10) using an electrolyte solution containing a specific low-molecular gelling agent and using a nonwoven fabric showing a specific pore structure of this embodiment as a separator. 17) and (26) to (29) are excellent in cycle characteristics as compared with lithium ion secondary batteries (18) to (25) and (30) to (33) that do not use a nonwoven fabric having a specific structure. I understood.

(Example 17)
<Preparation of positive electrode>
Lithium cobalt acid (LiCoO ₂ ) having a number average particle diameter of 10.8 μm as a positive electrode active material, acetylene black powder having a number average particle diameter of 42 nm as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder are 89.5. : 6.5: 6.0 mixed at a mass ratio. N-methyl-2-pyrrolidone was further mixed with the obtained mixture to prepare a slurry solution. This slurry-like solution was applied to one side of an aluminum foil having a thickness of 20 μm, and the solvent was removed by drying, followed by rolling with a roll press. A positive electrode (κ) was obtained by punching into a rectangular shape of × 30 mm. In addition, about the compound material after the vacuum drying in the obtained electrode, the amount per unit area is 24.8 g / cm ² ± 3%, the thickness on one side is 82.6 μm ± 3%, and the density is 3.0 g / The slurry-like solution was prepared while adjusting the amount of the solvent (N-methyl-2-pyrrolidone) so that cm ³ ± 3% and the coating width was 150 mm with respect to the width of 200 mm of the aluminum foil.

<Production of negative electrode>
Graphite carbon powder (trade name “MCMB25-28”, manufactured by Osaka Gas Chemical Co., Ltd.) as a negative electrode active material, acetylene black powder having a number average particle diameter of 42 nm as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder Were mixed at a mass ratio of 93.0: 2.0: 5.0. N-methyl-2-pyrrolidone was further mixed with the obtained mixture to prepare a slurry solution. This slurry solution was applied to a copper foil having a thickness of 14 μm and a width of 200 mm, and the solvent was dried and removed, followed by rolling with a roll press. Further, the rolled product was vacuum-dried at 150 ° C. for 10 hours and punched into a 52 mm × 32 mm rectangular shape to obtain a negative electrode (λ). In addition, about the compound material after vacuum drying in the obtained electrode, the amount per unit area is 11.8 g / cm ² ± 3%, the thickness on one side is 84.6 μm ± 3%, and the density is 1.4 g / The slurry-like solution was prepared while adjusting the amount of solvent (N-methyl-2-pyrrolidone) so that cm ³ ± 3% and the coating width was 150 mm with respect to the width of 200 mm of the copper foil.

<Creation of electrolyte>
To the mother electrolyte (A), the compound (a) synthesized as described above as a gelling agent and fluoroethylene carbonate are added, heated to 90 ° C. and uniformly mixed, and then cooled to 25 ° C. Thus, an electrolytic solution (h) (compound (I): 3% by mass, fluoroethylene carbonate: 3% by mass) was obtained.

<Battery assembly>
Two rectangular laminate films (no drawing, thickness 120μm, 68mm x 48mm) laminated with an aluminum layer and a resin layer are stacked with the aluminum layer side facing out, and the three sides of the periphery are sealed and laminated A cell exterior was prepared. Subsequently, a separator (ε) produced in the same manner as in Example 3 was prepared, and a laminate in which a plurality of positive electrodes (κ) and negative electrodes (λ) produced as described above were alternately stacked via separators. Was placed in the laminate cell exterior. Next, the electrolytic solution (h) was charged into the cell exterior, and the remaining side of the laminate cell was temporarily sealed. Next, the whole cell was heated at 90 ° C. for 2 hours, so that the laminate of the electrode and the separator was impregnated with the electrolytic solution. After slow cooling, the temporarily sealed side of the laminate cell was finally sealed to obtain a laminate type lithium ion secondary battery (34). With respect to this battery (34), the measurement described in the above “(viii) Overcharge test of laminate type single layer lithium ion secondary battery” was performed. The results are shown in Table 4.

(Comparative Example 18)
Instead of the electrolyte solution (h), the same procedure as in Example 17 was used except that the mother electrolyte solution (B) (fluoroethylene carbonate: 3% by mass) obtained by adding fluoroethylene carbonate to the mother electrolyte solution (A) was used. A laminated lithium ion secondary battery was obtained. In addition, injection | pouring of mother electrolyte (B) was performed, repeating atmospheric pressure and pressure reduction of 100 mmHg until a bubble generation | occurrence | production disappeared. In this way, a single layer laminate type lithium ion secondary battery (35) was obtained. With respect to this battery (35), the measurement described in the above “(viii) Overcharge test of laminate type single layer lithium ion secondary battery” was performed. The results are shown in Table 4.

  As shown in Table 4, the lithium ion secondary battery (34) using the nonwoven fabric showing the specific pore structure of the present embodiment as a separator and using an electrolytic solution containing a specific low molecular gelling agent, It was found that even when overcharge is abnormal, the short circuit is delayed and the battery becomes safer.

  The lithium ion secondary battery of the present invention is expected to be used as a rechargeable battery for automobiles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, in addition to portable devices such as mobile phones, portable audio devices, and personal computers.

  DESCRIPTION OF SYMBOLS 100 ... Lithium ion secondary battery, 110 ... Separator, 120 ... Positive electrode, 130 ... Negative electrode, 140 ... Positive electrode collector, 150 ... Negative electrode collector, 160 ... Battery exterior.

Claims (11)

An electrolyte solution containing a non-aqueous solvent, a lithium salt, and a low-molecular gelling agent;
A positive electrode containing at least one material selected from the group consisting of materials capable of inserting and extracting lithium ions as a positive electrode active material;
A negative electrode containing at least one material selected from the group consisting of a material capable of inserting and extracting lithium ions as a negative electrode active material and metallic lithium;
A separator formed of a nonwoven fabric ;
With
Of the total number of holes of the separator, the ratio of the number of holes having a minor axis of 1.0 μm or less is 20% or less,
Of the holes present on the outermost surface of the separator, the ratio of the number of holes having a minor axis of 1.0 μm or less is 5% or less
The low-molecular gelling agent comprises one or more compounds selected from the group consisting of the following general formulas (1), (2) and (3),
^{Rf 1 -R 1 -X 1 -L 1} -R 2 (1)
Rf ¹ -R ¹ -X ¹ -L ¹ -R ³ -L ² -X ² -R ⁴ -Rf ² (2)
R ⁵ —O—Ar—X ³ —C (3)
(In the formulas (1) and (2),
Rf ¹ and Rf ² each independently represents a C 2-20 perfluoroalkyl group,
R ¹ and R ⁴ each independently represents a single bond or a divalent saturated hydrocarbon group having 1 to 6 carbon atoms,
X ¹ and X ² each independently represent a divalent functional group selected from the group consisting of the following formulas (1a) to (1e),
L ¹ and L ² are each independently a single bond, an oxyalkylene group optionally substituted with an alkyl group or a halogen atom, an oxycycloalkylene group optionally substituted with an alkyl group or a halogen atom, or an alkyl group Or a divalent oxyaromatic group optionally substituted by a halogen atom,
R ² is substituted with an alkyl group or a halogen atom (excluding a fluorine atom), an alkyl group having 1 to 20 carbon atoms, an alkyl group or a halogen atom (excluding a fluorine atom) optionally substituted with an alkyl group or a halogen atom (excluding a fluorine atom). A monovalent fluoroalkyl group, aryl group or fluoroaryl group, or one or more of these groups bonded to one or more of divalent groups corresponding to these groups The group of
R ³ represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms which may have one or more oxygen and / or sulfur atoms in the main chain and may be substituted with an alkyl group.
Moreover, in Formula (3),
R ⁵ represents a carbon hydrocarbon group having 1 to 20 carbon atoms may be substituted with a halogen atom backbone,
Ar represents an alkyl group and / or a divalent aromatic hydrocarbon group or alicyclic hydrocarbon group having 5 to 30 nucleus atoms which may be substituted with a halogen atom ,
X ³ is any divalent group of the following formulas (3a), (3b), (3e) to (3g), or any of the following formulas (3a), (3b), (3e) to (3g) Or a divalent group in which a plurality of groups are bonded,
C represents a coumarin moiety represented by the following formula (3z). In the following formula (3z), each R ^a independently represents a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom.
)
The electrolyte solution is a phase transition type gel electrolyte solution that becomes a gel at a low temperature and a sol at a high temperature,
A lithium ion secondary battery in which a phase transition temperature between the gel and the sol is in a range of 50 to 150 ° C. An electrolyte solution containing a non-aqueous solvent, a lithium salt, and a low-molecular gelling agent;
A positive electrode containing at least one material selected from the group consisting of materials capable of inserting and extracting lithium ions as a positive electrode active material;
A negative electrode containing at least one material selected from the group consisting of a material capable of inserting and extracting lithium ions as a negative electrode active material and metallic lithium;
A separator formed of a nonwoven fabric ;
With
The lithium ion secondary battery according to claim 1, wherein the separator has an air permeability of 50 s / 100 cc or less.   3. The lithium ion secondary battery according to claim 1, wherein a ratio of the number of holes having a minor axis of 200 μm or more out of the total number of holes of the separator is 5% or less.   4. The ratio of the number of holes having a long diameter of 150 μm or more continuous from one surface to the other surface of the total number of holes of the separator is 5% or less. 5. The lithium ion secondary battery described in 1.   The lithium ion secondary battery as described in any one of Claims 1-4 whose film thickness of the said separator is 20 micrometers or more and 60 micrometers or less. Wherein X ¹ and X ² are, each independently, the formula (1a) or said a divalent functional group represented by formula (1d), the lithium ion according to any one of claims 1 to 5 Secondary battery. The lithium ion secondary battery according to any one of claims 1 to 6 , wherein X ¹ and X ² are a divalent functional group represented by the formula (1d). Discharge capacity retention of 80% or more, the lithium ion secondary battery according to any one of claims 1 to 7 when when performing 100 cycles of charge and discharge cycle test at 25 ° C.. The lithium ion secondary according to any one of claims 1 to 8 , wherein the electrolyte is impregnated in the separator, and a part of the low-molecular gelling agent is present in the pores of the separator. battery. The lithium ion secondary battery according to any one of claims 1 to 9 , wherein the positive electrode includes a lithium-containing compound as the positive electrode active material. The negative electrode contains, as the negative electrode active material, at least one material selected from the group consisting of metallic lithium, a carbon material, a material containing an element capable of forming an alloy with lithium, and a lithium-containing compound. The lithium ion secondary battery as described in any one of 1-10 .