JP2016162957A - Lithium ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion capacitor in which increase in the resistance can be suppressed even when charge and discharge are repeated a large number of times under high temperature environment, while maintaining a high capacitance and suppressing gas generation, and the initial DC resistance is small.SOLUTION: In a lithium ion capacitor including a positive electrode having a positive electrode layer containing a positive electrode active material, a negative electrode having a negative electrode layer containing a negative electrode active material, and an electrolyte solution containing an electrolyte, where at least one of the negative electrode and positive electrode is previously doped with lithium ions, the electrolyte contains a compound represented by the following formula (1). Formula (1):(X-OS-N-SO-X)Li(In the formula (1), Xand Xeach represent independently, a fluorine atom, an alkyl group of 1C-6C, or a fluoroalkyl group of 1C-6C).SELECTED DRAWING: None

Description

  The present invention relates to a lithium ion capacitor.

  Conventionally, in an electricity storage device having an electrolytic solution made of a non-aqueous electrolyte solution, there is a problem that gas is generated inside due to the influence of the decomposition reaction of the solvent on the negative electrode. As means for solving such a problem, for example, Patent Document 1 discloses a technique using an electrolytic solution in which lithium bis (fluorosulfonyl) imide is dissolved as an electrolyte in a lactone-based non-aqueous solvent. According to the nonaqueous electrolyte secondary battery described in Patent Document 1, it is said that swelling of the battery can be suppressed at high temperatures or during storage.

  However, when a lactone non-aqueous solvent is used as a solvent constituting the electrolytic solution, a SEI (Solid Electrolyte Interface) film is excessively formed in the negative electrode. Therefore, there is a problem that the direct current internal resistance increases when the thickness of the SEI film is considerably increased.

  Moreover, in a power storage device having an electrolytic solution made of a non-aqueous electrolyte solution, as means for suppressing a decrease in ion conductivity in a low temperature environment, for example, Patent Document 2 discloses a carbonate-based solvent and lithium bis (fluoro (fluorocarbon) as an electrolyte. A technique using an electrolytic solution in which sulfonyl) imide and lithium hexafluorophosphate are dissolved is disclosed. However, in the electricity storage device described in Patent Document 2, gas generation in a high temperature environment is not considered.

  Furthermore, when charge and discharge are repeated under the condition that the positive electrode potential is 4.2 V or more, the electrolytic solution is decomposed by an oxidation reaction in the positive electrode. That is, since the gas generated in the negative electrode and the gas generated in the positive electrode are integrated, it is difficult to suppress the expansion of the outer container due to the gas generation.

JP 2004-165151 A JP2013-101900A

  The object of the present invention is to suppress an increase in resistance even when charging and discharging are repeated many times in a high-temperature environment, while maintaining a high capacitance and suppressing gas generation. In addition, an object of the present invention is to provide a lithium ion capacitor having a low initial DC resistance.

The lithium ion capacitor of the present invention includes a positive electrode having a positive electrode layer containing a positive electrode active material, a negative electrode having a negative electrode layer containing a negative electrode active material,
An electrolyte containing electrolyte, and a lithium ion capacitor in which at least one of a negative electrode and a positive electrode is pre-doped with lithium ions,
The electrolyte includes a compound represented by the following formula (1).
Equation _{^{(1) :( X 1 -O 2}} S-N - -SO 2 -X 2) Li +
[In Formula (1), X < ¹ > and X < ² > show a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group each independently. ]

In the lithium ion capacitor of the present invention, the electrolyte may be LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _2, or LiN (C ₂ F ₅ SO ₂ ) as the compound represented by the formula (1). It is preferable to include at least one selected from ₂ .
The electrolyte preferably further contains LiPF ₆ in addition to the compound represented by the formula (1).
Moreover, it is preferable that the ratio of the compound represented by the said Formula (1) in the said electrolyte is 8 to 85% in molar conversion.
Moreover, it is preferable that the solvent which comprises the said electrolyte solution contains a cyclic carbonate and a chain carbonate.
Moreover, it is preferable that the ratio of the said cyclic carbonate and the said chain carbonate in the said solvent is 5: 95-80: 20 by mass ratio.
Moreover, it is preferable that the density | concentration of the compound represented by the said Formula (1) in the said electrolyte solution is 0.1-1 mol / L.
The negative electrode active material preferably includes graphite having a part or all of the surface coated with amorphous carbon.

  According to the present invention, an electrolytic solution containing a specific electrolyte is used, and at least one of the negative electrode and the positive electrode is pre-doped with lithium ions. As a result, a high capacity retention rate can be obtained, gas generation can be suppressed, and a lithium ion capacitor with low initial DC resistance can be obtained.

Embodiments of a lithium ion capacitor according to the present invention will be described below.
[Basic configuration of lithium ion capacitor]
The lithium ion capacitor according to the present invention basically has a configuration in which an electrode unit in which a positive electrode and a negative electrode are alternately stacked or further wound via a separator is disposed in an outer container. As the outer container, a container of a cylindrical shape, a rectangular shape, a laminate shape, or the like can be used as appropriate, and is not particularly limited.

  In the lithium ion capacitor according to the present invention, at least one of the negative electrode and the positive electrode is previously doped with lithium ions. As a method for doping lithium ions, for example, a lithium ion supply source such as metallic lithium is disposed in a capacitor cell as a lithium electrode, and the lithium ion supply source is electrochemically contacted with at least one of a negative electrode and a positive electrode and a lithium ion supply source. A method of doping ions is preferably used. When lithium ions are not doped in advance in either the negative electrode or the positive electrode, a high capacity retention rate cannot be obtained and the generation of gas cannot be suppressed in repeated charge and discharge in high and low temperature environments. .

  In this specification, “dope” also means occlusion, adsorption, or insertion, and is widely a phenomenon in which at least one of lithium ions and anions enters the positive electrode active material, or a phenomenon in which lithium ions enter the negative electrode active material. Say. “De-doping” also means desorption and release, and refers to a phenomenon in which lithium ions or anions are desorbed from the positive electrode active material, or a phenomenon in which lithium ions are desorbed from the negative electrode active material.

In the lithium ion capacitor according to the present invention, it is possible to uniformly dope lithium ions into at least one of the negative electrode and the positive electrode also by locally disposing the lithium electrode in the cell and bringing it into electrochemical contact.
Therefore, even when a large-capacity cell in which the positive electrode and the negative electrode are laminated or further wound is formed, at least one of the negative electrode and the positive electrode can be smoothly and uniformly doped with lithium ions.

[Current collector]
Each of the positive electrode and the negative electrode is provided with a positive electrode current collector or a negative electrode current collector (hereinafter collectively referred to as “current collector”) that receives and distributes electricity. The current collector is preferably formed with a through-hole penetrating the front and back surfaces. The shape, number, etc. of the through holes in the current collector are not particularly limited, and lithium ions electrochemically supplied from a lithium electrode arranged to face at least one of the positive electrode and the negative electrode and lithium ions in the electrolytic solution It can set so that it can move between the front and back of an electrode, without interrupted | blocked by each electrical power collector.

  Even if the current collector has a through-hole formed by etching or the like, such as an electrolytic etching foil, the through-hole can be formed by mechanical driving or other mechanical processing such as punching metal or expanded metal. May be formed. The diameter of the through hole of the current collector is, for example, 0.1 μm to 100 μm, preferably 0.5 to 80 μm, and particularly preferably 1 to 50 μm.

As a material constituting the current collector, a material generally used for a lithium battery can be used. For example, as a material constituting the positive electrode current collector, aluminum, a stainless steel net, or the like can be used. On the other hand, as a material constituting the negative electrode current collector, stainless steel mesh, copper, nickel, or the like can be used.
Although the thickness of a collector is not specifically limited, Usually, what is necessary is just 2-100 micrometers, 5-80 micrometers is preferable and 10-50 micrometers is especially preferable.

[Positive electrode active material]
The positive electrode is configured by forming a positive electrode layer containing a positive electrode active material on one surface or both surfaces of a positive electrode current collector.
As the positive electrode active material, a material capable of reversibly adsorbing and desorbing at least one kind of anion such as lithium ion and tetrafluoroborate is used, and specific examples thereof include activated carbon powder. The positive electrode active material preferably has a number average particle diameter D50 of 2 μm or more, more preferably 2 to 50 μm, and particularly preferably 2 to 20 μm. Further, the positive electrode active material preferably has an average pore diameter of 10 nm or less, and preferably has a BET specific surface area of 600 to 3000 m ² / g, more preferably 1300 to 2500 m ² / g.

[Negative electrode active material]
The negative electrode is configured by forming a negative electrode layer containing a negative electrode active material on one surface or both surfaces of a negative electrode current collector.
As the negative electrode active material, it is preferable to use graphite (coated graphite particles) whose surface is partially or entirely coated with amorphous carbon among materials capable of reversibly doping and dedoping lithium ions. . The coated graphite particles exemplified as the negative electrode active material include, for example, hard carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fiber (carbon fiber) whose surface of graphite-based particles such as natural graphite and artificial graphite is fired at 1500 ° C. or less. Manufactured by coating with amorphous carbon such as MCF). These negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 or more type.
In the coated graphite particles exemplified as the negative electrode active material, the presence or absence of tar or pitch-derived coating on the particle surface can be confirmed by measurement of Raman spectrum, XRD, or the like. The covering structure can be confirmed by cutting a part of the particles with a focused ion beam (FIB) and observing the cross section with a transmission electron microscope (TEM).

The graphite constituting the negative electrode active material has an average interplanar spacing (d002) of (002) plane of 3.357 mm by X-ray wide angle diffraction method, and 1355 cm ^{−1 with} respect to a peak near 1580 cm ⁻¹ by argon laser Raman. A graphite having an intensity ratio (I1355 / I1580) of a nearby peak of, for example, 0.25 and crystallite sizes Lc and La determined by X-ray diffraction of 100 nm or more can be suitably used. The coated graphite particles constituting the negative electrode active material have an intensity ratio of a peak near 1355 cm ^{−1 to} a peak near 1580 cm ⁻¹ by an argon laser Raman, for example, 1.03.

  The coating amount of amorphous carbon in the coated graphite particles exemplified as the negative electrode active material is preferably 5 to 200% by mass, and more preferably 10 to 100% by mass. Here, the coating amount of the amorphous carbon in the coated graphite particles is a value obtained by (mass of amorphous carbon in the coated graphite particles / mass of graphite in the coated graphite particles) × 100 (mass%). . When the coating amount of amorphous carbon is too small, the active sites of graphite with high crystallinity are likely to be exposed on the surface of the coated graphite particles, so that reductive decomposition of the electrolyte proceeds when charging and discharging are repeated. However, a large amount of gas is likely to be generated. On the other hand, when the coating amount of amorphous carbon is excessive, the surface of the graphite particles is excessively covered with carbon having low crystallinity, so that lithium ions are difficult to intercalate with graphite. Therefore, the charge transfer resistance between the graphite particles or between the graphite particles and the electrolyte is increased, and the resistance of the lithium ion capacitor is increased.

  Preferable examples of the coated graphite particles include particles obtained by coating the surface of natural graphite with, for example, 10% by mass of amorphous carbon based on the mass of natural graphite by a chemical vapor deposition method using toluene gas as a carbon raw material.

As the negative electrode active material, a powdered material is used in the same manner as the positive electrode active material, and the particle size is preferably 0.1 to 5 μm in number average particle size D50. A negative electrode active material having a number average particle diameter D50 of less than 0.1 μm is difficult to produce. On the other hand, with a negative electrode active material having a number average particle diameter D50 exceeding 5 μm, it may be difficult to obtain a lithium ion capacitor having a sufficiently low internal resistance. The negative electrode active material preferably has a BET specific surface area of 0.1 to 2000 m ² / g, more preferably 0.1 to 600 m ² / g.

[Positive electrode layer and negative electrode layer]
The positive electrode layer and the negative electrode layer are formed using a slurry containing the positive electrode active material or the negative electrode active material and a binder, or by depositing the positive electrode active material or the negative electrode active material on a current collector. be able to. The thickness of the positive electrode layer and the negative electrode layer is usually 1 to 100 μm, preferably 1 to 80 μm, more preferably 2 to 70 μm.

[Binder]
In the case where the positive electrode layer including the positive electrode active material and the negative electrode layer including the negative electrode active material as described above are formed using a slurry containing the positive electrode active material or the negative electrode active material and a binder, the slurry is a positive electrode active material. It is prepared by mixing a material or negative electrode active material, a binder, and a conductive material, carboxymethyl cellulose (CMC) (including carboxymethyl cellulose salt), etc., used as necessary, in addition to water or an organic solvent. .
Then, the positive electrode or the negative electrode is manufactured by applying the obtained slurry to the positive electrode current collector or the negative electrode current collector, or by forming the slurry into a sheet shape and pasting the slurry on the positive electrode current collector or the negative electrode current collector. can do.

In the production of the positive electrode or the negative electrode, examples of the binder include rubber-based binders such as SBR, fluorine-containing resins such as polytetrafluoroethylene and polyvinylidene fluoride, thermoplastic resins such as polypropylene and polyethylene, and acrylic resins. Etc. can be used.
Examples of the conductive material include carbon black such as acetylene black and ketjen black, graphite, and metal powder.
The amount of each of the binder and the conductive material to be added varies depending on the electrical conductivity of the positive electrode active material or negative electrode active material used, the shape of the electrode to be produced, etc. It is preferable that it is 2-40 mass%.

[Separator]
As a separator in the lithium ion capacitor according to the present invention, it is preferable to use a material having an air permeability measured by a method in accordance with JIS P8117 within a range of 1 to 200 sec. As such a separator, for example, those appropriately selected from non-woven fabrics and microporous membranes composed of polyethylene, polypropylene, polyester, cellulose, polyolefin, cellulose / rayon, etc. can be used, cycle characteristics and From the viewpoint of electrolytic solution impregnation, it is particularly preferable to use a film in which silica is coated on polyethylene. Moreover, the thickness of a separator is 5-100 micrometers, for example, and 10-50 micrometers is preferable.

[Electrolyte]
In the lithium ion capacitor according to the present invention, a non-protonic organic solvent electrolyte solution of lithium salt is used as the electrolytic solution. Below, each component in electrolyte solution is demonstrated.

[Aprotic organic solvent]
Examples of the aprotic organic solvent constituting the electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate ( Chain carbonates such as DEC), methylpropyl carbonate (MPC), and methylbutyl carbonate (MBC) can be used. A mixed solvent in which two or more of these are mixed may be used, and in particular, an electrolyte solution having a low viscosity, a high degree of dissociation, and a high ionic conductivity is obtained, and therefore includes a cyclic carbonate and a chain carbonate. It is preferable to use a mixed solvent.
Further, the non-prototronic organic solvent constituting the electrolytic solution is preferably composed only of a carbonate-based solvent (cyclic carbonate and chain carbonate). Contains organic solvents other than system solvents, for example, cyclic esters such as γ-butyrolactone, cyclic sulfones such as sulfolane, cyclic ethers such as dioxolane, chain carboxylic acid esters such as ethyl propionate, and chain ethers such as dimethoxyethane. May be.

  The ratio of the cyclic carbonate and the chain carbonate in the aprotic organic solvent is preferably a mass ratio of 5:95 to 80:20, more preferably 10:90 to 70: 30. By using an aprotic organic solvent containing cyclic carbonate and chain carbonate at such a ratio, the increase in the viscosity of the electrolyte can be suppressed and the degree of dissociation of the electrolyte can be increased. The conductivity of the electrolytic solution can be increased, and the solubility of the electrolyte can be further increased.

〔Electrolytes〕
The electrolyte in the electrolytic solution contains a compound represented by the following formula (1) (hereinafter referred to as “specific lithium salt”).
Equation _{^{(1) :( X 1 -O 2}} S-N - -SO 2 -X 2) Li +
[In Formula (1), X < ¹ > and X < ² > show a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group each independently. ]

In X ¹ and X ² represented by the above formula (1), specific examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, sec-butyl group, t- Examples thereof include a butyl group, a pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-methyl-2-methylpropyl group, a 2,2-dimethylpropyl group, and a hexyl group.
In X ¹ and X ² shown in the above formula (1), specific examples of the fluoroalkyl group having 1 to 6 carbon atoms include a difluoromethyl group, a monofluoromethyl group, a trifluoromethyl group, a trifluoroethyl group, Examples thereof include a difluoroethyl group, a pentafluoroethyl group, a pentafluoropropyl group, a tetrafluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

As the specific lithium salt, it is preferable to use one in which X ¹ and X ² shown in the above formula (1) are a fluorine atom or a fluoroalkyl group having 1 to 6 carbon atoms. Preferable specific examples of such a specific lithium salt include lithium bis (fluorosulfonyl) imide [LiN (FSO ₂ ) ₂ ], lithium bis (pentafluoroethanesulfonyl) imide [LiN (C ₂ F ₅ SO ₂ ) _2. ], Lithium bis (trifluoromethanesulfonyl) imide [LiN (CF ₃ SO ₂ ) ₂ ] and the like. Among these, lithium bis (fluorosulfonyl) imide [LiN (FSO ₂ ) ₂ ] is particularly preferable because of its high ion conductivity and low resistance.

The electrolyte in the electrolytic solution may include a lithium salt other than the specific lithium salt (hereinafter referred to as “other lithium salt”). Specific examples of such other etium salts include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6 and the} like. Among these, LiPF ₆ is preferable because of its high ion conductivity and low resistance.

  The concentration of the electrolyte (specific lithium salt and other lithium salt) in the electrolytic solution is preferably 0.1 mol / L or more because low internal resistance is obtained, and is 0.5 to 1.5 mol / L. More preferably, it is more preferably 0.6 to 1.2 mol / L.

  The concentration of the specific lithium salt in the electrolytic solution is preferably 0.1 mol / L or more, and more preferably 0.1 to 1.0 mol / L because low internal resistance is obtained. When the concentration of the specific lithium salt is too low, the resulting lithium ion capacitor is likely to expand, and the DC resistance may increase. On the other hand, when the concentration of the specific lithium salt is excessive, the viscosity of the obtained electrolytic solution is increased, so that the internal resistance may be increased.

  Moreover, it is preferable that the ratio of the specific lithium salt in electrolyte is 8% or more in conversion of a mole, More preferably, it is 8 to 85%. If the ratio of the specific lithium salt is too small, the effect of suppressing gas generation becomes small, and the effect of reducing the initial direct current resistance may not be sufficiently obtained. On the other hand, if the ratio of the specific lithium salt is excessive, the durability of the cycle characteristics, high-temperature float characteristics, etc. may be deteriorated due to corrosion of the positive electrode current collector.

[Structure of lithium ion capacitor]
As a structure of the lithium ion capacitor according to the present invention, a wound-type, plate-shaped or sheet-shaped positive electrode and negative electrode having an electrode unit wound in a state where a strip-shaped positive electrode and a negative electrode are laminated via a palator are provided. Examples include a laminated type having an electrode unit in which three or more layers are alternately laminated via a separator, and a film type in which the above electrode unit is enclosed in an exterior film. The structures of these lithium ion capacitors are known, for example, from Japanese Patent Application Laid-Open No. 2004-266091, and can have the same configuration as those capacitors including a pre-doping method.

  According to the present invention, an electrolytic solution containing a specific electrolyte is used, and at least one of the negative electrode and the positive electrode is preliminarily doped with lithium ions. Therefore, an increase in resistance can be suppressed in a high temperature and low temperature environment, Even when charging / discharging is repeated many times, a high capacitance is maintained, generation of gas can be suppressed, and a lithium ion capacitor with low initial DC resistance can be obtained.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by these Examples.

[Example 1]
(1) Production of positive electrode By applying a conductive coating on both sides of an aluminum expanded metal, which is a positive electrode current collector precursor, using a vertical die type double-side coating machine, and then drying under reduced pressure. A conductive layer was formed on the front and back surfaces of the positive electrode current collector precursor.
Next, activated carbon powder (number average particle diameter D50 = 4 μm, average pore diameter = 2 nm, BET specific surface area = 2100 m ² / g) as a positive electrode active material on the conductive layers formed on the front and back surfaces of the positive electrode current collector precursor. The slurry containing was coated on both sides using a vertical die type double-side coating machine, and then dried under reduced pressure to form a positive electrode layer on the conductive layer. The thickness of the positive electrode layer was 90 μm.
The material obtained by laminating the conductive layer and the positive electrode layer on a portion of the positive electrode current collector precursor thus obtained was used as the portion where the conductive layer and the positive electrode layer were laminated (hereinafter referred to as “coating part”). The positive electrode current collector is cut into an appropriate size by cutting a positive electrode precursor containing a portion in which no layer is formed (hereinafter, also referred to as “uncoated portion” for the positive electrode). A positive electrode having a positive electrode layer formed on both sides was prepared.

(2) Production of Negative Electrode Coated graphite particles coated with amorphous carbon having a number average particle diameter D50 of 4 μm as the negative electrode active material are contained on both surfaces of the copper expanded metal as the negative electrode current collector precursor. The slurry was coated on both sides using a vertical die type double-side coating machine, and then dried under reduced pressure to form negative electrode layers on the front and back surfaces of the negative electrode current collector precursor.
The material in which the negative electrode layer is formed on a part of the current collector precursor thus obtained is the portion where the negative electrode layer is formed (hereinafter, also referred to as “coating part” for the negative electrode), the negative electrode. By cutting the negative electrode precursor including a portion where the electrode layer is not formed (hereinafter, also referred to as “uncoated portion” for the negative electrode) to an appropriate size, the negative electrode layer is formed on both surfaces of the negative electrode current collector. The formed negative electrode was produced. The thickness of the negative electrode layer was 65 μm.
The coated graphite particles used here were produced as follows.
50 parts by mass of pitch as a precursor is mixed with 100 parts by mass of fine graphite powder having a number average particle diameter D50 of 2.5 μm with a kneader, and the temperature is increased at a rate of 5 ° C./min in a nitrogen atmosphere. It baked by heating and hold | maintaining at 1000 degreeC temperature for 6 hours. The obtained fired product was pulverized to a value of number average particle diameter D50 of 4 μm to produce coated graphite particles. The coated amount of amorphous carbon in the coated graphite particles is 50% by mass.

(3) Production of Separator A film of cellulose / rayon composite material was cut so that the vertical and horizontal widths were larger than those of the positive electrode and the negative electrode to produce a separator (hereinafter, this separator is referred to as “separator A”). did.

(4) Production of Lithium Ion Capacitor Element First, 10 positive electrodes, 11 negative electrodes, and 24 separators are prepared. The positive electrode and the negative electrode are overlapped with each other, but the uncoated portions are opposite to each other. In an aligned state so as not to overlap each other, the separator, the negative electrode, the separator, and the positive electrode were stacked in this order, and the four sides of the stacked body were fixed with a tape to produce an electrode laminate unit.
Next, the lithium foil is cut and crimped to a copper mesh to produce a lithium ion supply member, and this lithium ion supply member is disposed on the upper side of the electrode stacking unit so as to face the negative electrode through two separators. .
Then, a rectangular aluminum power supply tab for positive electrode, in which a sealant film was heat-sealed to the seal portion in advance, was overlapped and welded to each uncoated portion of the 10 positive electrodes in the produced electrode laminate unit. On the other hand, a rectangular copper negative electrode power tab with a sealant film heat-sealed in advance on the seal portion is welded to each of the uncoated portion of each of the eleven negative electrodes of the electrode laminate unit and the lithium ion supply member. Thus, a lithium ion capacitor element was produced.

(5) Production of Lithium Ion Capacitor Next, one exterior film in which a polypropylene layer, an aluminum layer, and a nylon layer are laminated and drawn to a size that can accommodate a lithium ion capacitor element at the center, and the polypropylene layer The other exterior film in which the aluminum layer and the nylon layer were laminated was produced.

Subsequently, the lithium ion capacitor element was disposed at a position serving as a housing portion on the other exterior film so that each of the positive electrode terminal and the negative electrode terminal protruded outward from the end of the other exterior film. One exterior film is overlaid on this lithium ion capacitor element, and three sides (including two sides from which the positive electrode terminal and the negative electrode terminal protrude) are heat-sealed at the outer peripheral edge of one exterior film and the other exterior film. did.
On the other hand, in a mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate (3: 1: 4 by mass ratio), LiN (FSO ₂ ) _{2 having a} concentration of 0.6 mol / L and LiPF _{6 having a} concentration of 0.6 mol / L. An electrolytic solution in which was dissolved was prepared.
Subsequently, after inject | pouring the said electrolyte solution between one exterior film and the other exterior film, the remaining one side in the outer periphery part of one exterior film and the other exterior film was heat-seal | fused.
As described above, a laminate-coated lithium ion capacitor (hereinafter referred to as “cell”) was produced.

[Examples 2 to 7 and Comparative Example 1]
A cell was produced in the same manner as in Example 1 except that the electrolyte solution was prepared by changing the type and concentration of the electrolyte according to the following Table 1 in the production of the lithium ion capacitor.

[Comparative Example 2]
A cell was produced in the same manner as in Example 1 except that in the production of the lithium ion capacitor element, the lithium ion supply member was not disposed.

[Initial characteristic test]
About the cell which concerns on Examples 1-7 and Comparative Examples 1-2, after performing constant current charge of 1A to 3.8V in 25 degreeC environment, it performed constant voltage charge of 3.8V for 1 hour, and then Then, a constant current discharge of 10 A was performed up to 2.2 V, and the capacitance (F), DC resistance (mΩ) and capacity (mAh) of the cell were calculated based on the obtained data. The results are shown in Table 1.

[Low temperature characteristics test]
1. Discharge characteristics The cells according to Examples 1 to 7 and Comparative Examples 1 and 2 were charged at a constant current of 1 A up to 3.8 V in a -30 ° C environment, and then charged at a constant voltage of 3.8 V for 1 hour. Then, a constant current discharge of 10 A was performed up to 2.2 V, and the DC resistance (mΩ) and capacity (mAh) of the cell were calculated based on the obtained data. The results are shown in Table 1.
2. Charging characteristics For cells according to Examples 1 to 7 and Comparative Examples 1 and 2, in a -30 ° C environment, a constant current discharge was performed at 1 A up to 2.2 V, followed by a constant voltage discharge at 2.2 V for 1 hour. Then, 10 A constant current charging to 3.8 V was performed, and based on the obtained data, the direct current resistance (mΩ) and capacity (mAh) of the cell were calculated. The results are shown in Table 1.

[High temperature load test (float test)]
About the cell which concerns on Examples 1-7 and Comparative Examples 1-2, the high temperature load test was done on condition of the following. Before and after the high temperature load test, the cell volume, DC resistance and capacitance were measured, and the ratio (%) of the measured value after the test to the measured value before the test was determined. Here, the volume of the cell was measured by the following method. The results are shown in Table 1.
(Test conditions)
Test equipment: DC power supply device (PW8-3AQP) manufactured by TEXIO, Yamato Scientific thermostat (DKN812)
Test temperature: 70 ° C
Test voltage: 3.8V
Test time: 1000 hours (cell volume measurement method)
A state in which a container containing water (density 1 g / cm ³ ) is placed on a balance is defined as wind body 0, and the cell before and after the test is hung with a wire that can ignore the volume. Immerse in water and measure the mass. The volume is calculated from the obtained measurement value based on the Archimedes principle.

The cells according to Examples 1, 3, and 4 have electrolytes that use LiN (FSO ₂ ) ₂ and LiPF ₆ in combination as electrolytes, so both initial characteristics and low-temperature characteristics are good, and in the float test It is understood that the expansion of the cell is suppressed and the increase in DC resistance is also suppressed.
The cell according to the second embodiment, since having a LiN (CF ₃ SO _{2) 2} and combination with the electrolyte solution LiPF ₆ as an electrolyte, the initial characteristics and low temperature characteristics are both good, and in the float test cell It is understood that the expansion of the DC is suppressed and the increase of the DC resistance is also suppressed.
The cell according to Example 5, because it has a LiN electrolyte using only (FSO _{2) 2} as an electrolyte, the initial characteristics and low temperature characteristics are both good, also the expansion of the cell is suppressed in the float tests It is understood that However, the DC resistance increased in the float test.
The cell according to Example 6, since it has a LiN (FSO _{2) 2} and LiPF ₆ the combination with the electrolytic solution as the electrolyte, low-temperature characteristics initial characteristics excluding the size of the good and the time of charging is good, the floating test It is understood that cell expansion is suppressed. However, since the ratio of LiN (FSO ₂ ) ₂ in the electrolyte was small, the capacity during charging was lowered in the low temperature characteristics, and the DC resistance was increased in the float test.
The cell according to Example 7, LiN order to have (FSO _{2) 2} and combination with the electrolyte solution LiPF _6, is that the initial characteristics and the low-temperature characteristics are both good is understood as the electrolyte. However, since the ratio of LiN (FSO ₂ ) ₂ in the electrolyte was large, cell expansion was not suppressed in the float test, and an increase in DC resistance occurred.
The cell according to Comparative Example 1 has an electrolytic solution using only LiPF ₆ as an electrolyte, so that both initial characteristics and low-temperature characteristics are not good, and in the float test, cell expansion is not suppressed. The DC resistance increased.
For the cell according to Comparative Example 2, since the negative electrode was not pre-doped with lithium ions, both the initial characteristics and the low temperature characteristics were not good, and in the float test, the cell expanded greatly and the DC resistance The rise of is occurring.

Claims (8)

A positive electrode having a positive electrode layer containing a positive electrode active material;
A negative electrode having a negative electrode layer containing a negative electrode active material;
An electrolyte containing electrolyte, and a lithium ion capacitor in which at least one of a negative electrode and a positive electrode is pre-doped with lithium ions,
The said electrolyte contains the compound represented by following formula (1), The lithium ion capacitor characterized by the above-mentioned.
Equation _{^{(1) :( X 1 -O 2}} S-N - -SO 2 -X 2) Li +
[In Formula (1), X < ¹ > and X < ² > show a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group each independently. ] The electrolyte contains at least one selected from LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ as the compound represented by the formula (1). The lithium ion capacitor according to claim 1. The lithium ion capacitor according to claim 1, wherein the electrolyte further contains LiPF ₆ in addition to the compound represented by the formula (1).   4. The lithium ion capacitor according to claim 1, wherein a ratio of the compound represented by the formula (1) in the electrolyte is 8 to 85% in terms of mole. 5.   The lithium ion capacitor according to any one of claims 1 to 4, wherein the solvent constituting the electrolytic solution includes a cyclic carbonate and a chain carbonate.   6. The lithium ion capacitor according to claim 5, wherein a ratio of the cyclic carbonate and the chain carbonate in the solvent is 5:95 to 80:20 by mass ratio.   The lithium ion capacitor according to claim 1, wherein the concentration of the compound represented by the formula (1) in the electrolytic solution is 0.1 to 1 mol / L.   The lithium ion capacitor according to any one of claims 1 to 7, wherein the negative electrode active material includes graphite having a part or all of the surface thereof coated with amorphous carbon.