WO2016125770A1

WO2016125770A1 - Electrolyte for lithium ion capacitor and lithium ion capacitor

Info

Publication number: WO2016125770A1
Application number: PCT/JP2016/052997
Authority: WO
Inventors: 高橋　昭夫
Original assignee: 日立化成株式会社
Priority date: 2015-02-02
Filing date: 2016-02-02
Publication date: 2016-08-11
Also published as: JPWO2016125770A1

Abstract

Provided are: an electrolyte for a lithium ion capacitor having improved low-temperature properties and service life; and a lithium ion capacitor using the electrolyte. The electrolyte contains a solvent formed from a cyclic carbonate comprising ethylene carbonate (EC) and propylene carbonate (PC) and a chain carbonate comprising dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). The electrolyte may further contain vinylene carbonate (VC). The lithium ion capacitor that uses the electrolyte can be configured so that the positive electrode material contains activated carbon and the negative electrode material contains a non-graphitizing carbon.

Description

Electrolyte for lithium ion capacitor and lithium ion capacitor

The present invention relates to an electrolytic solution for a lithium ion capacitor that can improve the low temperature characteristics and life of the lithium ion capacitor, and a lithium ion capacitor using the same.

For example, as a large capacity capacitor of 500 F or more, a lithium ion capacitor having both advantages of a lithium ion secondary battery and an electric double layer capacitor has been put into practical use. Recently developed lithium ion capacitors use activated carbon as the positive electrode active material and a carbon material capable of occluding and releasing lithium ions as the negative electrode active material. Has been. Therefore, in this type of lithium ion capacitor, the negative electrode potential is kept lower than a normal electric double layer capacitor (usually -1V to -1.35V) (about -3V), so that the operating voltage range of the cell can be increased. Yes (approximately 2.2V to 3.8V). Moreover, as a positive electrode charge / discharge mechanism, in addition to the adsorption of anions used in ordinary electric double layer capacitors, the adsorption of positive ions can also be used, so this type of lithium ion capacitor is compared to ordinary electric double layer capacitors, In principle, twice the capacity can be taken out.

Further, in general, a lithium ion capacitor has a smaller capacity than a lithium ion secondary battery, but has an advantage that the internal resistance is small, the output characteristics are excellent, and the life is long [Japanese Patent Laid-Open No. 2010-141217 ( Patent Document 1)].

One way to improve the characteristics of lithium ion capacitors is to improve the electrolyte. For example, Patent Document 2 discloses a lithium ion capacitor that has low internal resistance and excellent low-temperature characteristics by using an electrolytic solution that is a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). is doing.

JP 2010-141217 A JP 2012-204748 A

It is possible to use only cyclic carbonate as a solvent for the electrolyte for lithium ion capacitors. For example, propylene carbonate (PC) has the advantages of high dielectric constant and high flash point, but because of its high viscosity, In the low temperature range, the characteristics deteriorate rapidly. Moreover, when charging and discharging in a high temperature range are repeatedly used, the characteristics are gradually deteriorated, but there is a problem that the characteristics are rapidly deteriorated after a certain period.

An object of the present invention is to provide an electrolytic solution for a lithium ion capacitor having improved low-temperature characteristics and life, and a lithium ion capacitor using the same.

As a result of intensive studies on improving the low temperature characteristics of the electrolyte for lithium ion capacitors, the present inventors have found that the problem can be solved by using a composition with another organic solvent instead of a single propylene carbonate.

The properties required as an electrolyte for lithium ion capacitors include high conductivity, electrochemical stability, and high safety. These are the conditions for the electrolyte for lithium ion secondary batteries. Both have a lot in common. However, the basic reaction mechanism in the electrode is different (whether it is non-Faraday or Faraday), and the active material of the electrode that can be used is different, so it is reported that the characteristics are excellent for lithium ion secondary batteries. It is well known that an electrolytic solution or a widely used electrolytic solution for a lithium ion secondary battery cannot be immediately replaced or used for a lithium ion capacitor which is a kind of hybrid capacitor.

The inventors of the present invention conducted experiments on various organic solvents having properties suitable for an electrolyte for a lithium ion capacitor while changing the respective composition ratios, so as not to impair other performances as much as possible as compared with a single propylene carbonate. An electrolytic solution, which is a composition with improved low-temperature characteristics, was obtained and the present invention was conceived.

The electrolyte for a lithium ion capacitor according to the present invention includes a cyclic carbonate composed of ethylene carbonate (EC) and propylene carbonate (PC), and a chain carbonate composed of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). It is characterized by being configured.

First, in the case of the two-component system of propylene carbonate (PC) and dimethyl carbonate (DMC), and the two-component system of propylene carbonate (PC) and ethyl methyl carbonate (EMC), a large amount of gas was generated during the preliminary charge in the manufacturing process. In the case of a two-component system of ethylene carbonate (EC) and dimethyl carbonate (DMC), and a two-component system of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), the internal resistance is small at room temperature, but the characteristics are low and high. Confirmed that it would get worse.

In the research and development of lithium ion secondary batteries, it has been believed that ethylene carbonate (EC) cannot be used if the negative electrode active material is amorphous non-graphitizable carbon. It was confirmed that it can be used by mixing with carbonate.

It has been found that the cell characteristics are extremely deteriorated in the three components in which dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are blended with propylene carbonate (PC). However, it has been found that when ethylene carbonate (EC) is added to form four components, the cell characteristics are not deteriorated and the low temperature characteristics can be improved. On the other hand, the three components of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) showed little deterioration in cell characteristics but deteriorated high temperature characteristics.

As a result of repeated experiments as described above, a cyclic carbonate composed of ethylene carbonate (EC) and propylene carbonate (PC) and a chain carbonate composed of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are lithium ion capacitors. As a result, the present invention has been found to have excellent characteristics as an electrolytic solution for use in the present invention.

The content ratio of each component is not particularly limited, but the volume ratio of cyclic carbonate to chain carbonate in the solvent is preferably 1.0: 0.5 to 1.0: 4.0. Outside this range, the effect of improving the low temperature characteristics of the electrolyte for lithium ion capacitors is reduced. More preferably, it is 1.0: 1.5 to 1.0: 4.0, and the low temperature characteristics are considerably improved in this range. Desirably, it is about 1.0: 2.3, and the low temperature characteristics can be improved most remarkably.

The lithium ion capacitor electrolyte of the present invention may further contain vinylene carbonate (VC). It was confirmed that when a small amount of vinylene carbonate (VC) was added in addition to the four components, the lifetime in the high temperature range was greatly improved.

Vinylene carbonate (VC) is preferably contained in an amount of 0.5 to 5.0 weight percent based on the total amount of cyclic carbonate and chain carbonate. If it is out of this range, the effect of improving the lifetime in the high temperature range becomes weak. Desirably, when 1.0 to 2.0 weight percent is contained, the effect of improving the lifetime in the high temperature range is most effectively exhibited.

The lithium ion capacitor of the present invention is characterized by using the above-described electrolytic solution for a lithium ion capacitor, wherein the positive electrode material includes activated carbon, and the negative electrode material includes non-graphitizable carbon.

(A) is a plan view of the lithium ion capacitor of the present invention, and (b) is a cross-sectional view taken along the line IB-IB of FIG. 1 (a). It is a figure which shows the expanded view of the electrode group of the lithium ion capacitor shown in FIG. (A) And (b) is a figure which shows the example of the positive electrode plate of the lithium ion capacitor shown in FIG. 1, and a negative electrode plate. (A) And (b) is a figure which shows the example of the metallic lithium support member of the lithium ion capacitor shown in FIG. It is a figure which shows the combination of the electrode group of the lithium ion capacitor shown in FIG. 1, and a positive electrode current collection member and a negative electrode current collection member. It is the figure which showed a mode that the electrode plate group unit for lithium ion capacitors shown in FIG. 1 was accommodated in a container, and was sealed with a container lid. It is the figure which showed the relationship between content of PC, low-temperature DCR ratio, and float test DCR ratio in the lithium ion capacitor to which the electrolyte solution of this invention is applied. It is the figure which showed the relationship between the addition amount of VC, the low temperature DCR ratio, and the float test DCR ratio in the lithium ion capacitor to which the electrolytic solution of the present invention is applied.

Hereinafter, an embodiment of a lithium ion capacitor according to the present invention will be described with reference to the drawings.

(Constitution)
<Overall configuration>
FIG. 1A is a plan view showing a lithium ion capacitor 1 viewed from above the positive electrode, and FIG. 1B is a cross-sectional view taken along the line IB-IB in FIG. In FIG. 1B, the cross-sectional shape of the electrode plate group 4 is omitted, and hatching representing the cross-sectional portion is also omitted.

The cylindrical lithium ion capacitor 1 has a bottomed cylindrical container (can) 3 made of steel plated with nickel. In the container 3, the electrode plate group unit 2 for a lithium ion capacitor, which is a combination of the electrode plate group 4, the positive electrode current collecting member 26 and the negative electrode current collecting member 36 is housed. As shown in FIGS. 1B and 2, the electrode plate group 4 includes a hollow cylindrical polypropylene shaft core 5, a strip-like positive electrode plate 21 and a negative electrode plate 31, a first separator 6 and a second separator 7. It is configured to be wound through. As the first and

second separators

6 and 7, a porous substrate such as kraft paper can be used.

<Positive electrode plate>
As shown in FIG. 3, the positive electrode plate 21 is configured, for example, by coating a positive electrode active material mixture 23 on both surfaces of an aluminum foil (positive electrode current collector) 22. In the present specification, the aluminum foil includes an aluminum alloy foil. As the positive electrode active material mixture 23, for example, a mixture of activated carbon, a binder composed of an acrylic binder, and a dispersant composed of carboxymethylcellulose (CMC) can be used. The aluminum foil 22 has a coating portion 24 in which a number of through-holes are formed and a positive electrode active material mixture is applied, and an uncoated portion that is formed along the longitudinal direction of the coating portion 24 and has no through-holes. It has a work part 25. The positive electrode active material mixture 23 is applied to the coating portion 24 with a length that is less than the length in the width direction of the coating portion. That is, the uncoated portion 25 of the aluminum foil is left exposed along the coating layer of the positive electrode active material mixture 23.

<Negative electrode plate>
The negative electrode plate 31 also has the same structure as the positive electrode plate 21 shown in FIG. That is, the negative electrode plate 31 has a structure in which the negative electrode active material mixture 33 is applied to both surfaces of a copper foil (negative electrode current collector) 32. In the present specification, the copper foil includes not only a pure copper foil but also a copper alloy foil. Examples of the negative electrode active material mixture 33 include a non-graphitizable carbon that is an amorphous carbon capable of occluding and releasing lithium ions, a binder made of polyvinylidene fluoride (PVDF), and a conductive assistant such as acetylene black. Mixtures with materials can be used. The copper foil 32 has a coated part 34 in which a large number of through holes are formed, and an uncoated part 35 that is formed along the longitudinal direction of the coated part 34 and has no through holes. A negative electrode active material mixture 33 is applied to the coating part 34 in a length that is less than the length of the coating part 34 in the width direction. That is, the uncoated part 35 of the copper foil is left exposed along the coating layer of the negative electrode active material mixture 33.

<Metal lithium support member>
The metal lithium support member 41 is for occluding (doping) lithium ions in the negative electrode active material (in this example, amorphous carbon) of the negative electrode plate 31. As shown in FIGS. 4A and 4B, the metal lithium support member 41 is composed of a thin plate-like metal lithium 42, a copper foil 43, and a nickel-plated copper foil 44 (support). . The copper foil 43 can be used by cutting the same copper foil 32 that constitutes the negative electrode plate 31 into a predetermined dimension. The copper foil 43 and the nickel-plated copper foil 44 are formed with a large number of through holes (not shown), and the metal lithium 42 is formed with a large number of through holes of the two

supports

43 and 44. It is sandwiched between the two

supports

43 and 44 so as to contact the part.

<Plate group>
As shown in FIG. 2, the electrode plate group 4 has a spiral cross section with the shaft core 5 as the center through two

separators

6 and 7 so that the positive electrode plate 21 and the negative electrode plate 31 are not in direct contact with each other. It is made up of wounds. The positive electrode plate 21 and the negative electrode plate 31 are arranged so that the respective uncoated portions (uncoated portions 25 and 35) protrude outward from the

separators

6 and 7 in the opposite direction. In addition, the winding terminal part of the electrode plate group 4 is fixed by sticking an adhesive tape across the winding terminal part and the outer peripheral surface of the electrode plate group in order to prevent unwinding.

<Positive electrode current collector>
The positive electrode current collecting member 26 is made of aluminum (including an aluminum alloy), and has a ring shape in which a circular hole is formed in the central portion as shown in FIG. As shown in FIG. 1B, the hole has a diameter that fits the upper end of the shaft core 5 so that the positive electrode current collecting member 26 does not deviate from the center of the electrode plate group 4. The positive electrode current collecting member 26 is welded to the uncoated portion 25 of the positive electrode plate 21 included in the electrode plate group 4. Therefore, as shown in FIG. 6, the positive electrode current collecting member 26 is brought closer to the electrode plate group 4 from the upper side of the electrode plate group 4 where the uncoated portion 25 of the positive electrode plate 21 is located, and the aluminum foil of the positive electrode plate 21. The positive electrode current collecting member 26 is placed on the uncoated portion 25 of 22. The uncoated portion 25 and the positive electrode current collecting member 26 are welded by laser welding. For laser welding, the positive electrode current collecting member 26 is provided with four grooves that are convex toward the direction in contact with the electrode plate group 4 and that form a recess for welding so as to open away from the electrode plate group 4. It has been. These grooves are formed by press working, and extend radially linearly around the virtual center point of the positive electrode current collector 26. In addition, the positive electrode terminal part 27b welded to the positive electrode current collection member 26 in FIG. 5 is welded to the positive electrode terminal part 27a of the container lid 51 shown in FIG. As shown in FIG. 1B, a rubber insulating ring member for electrically insulating the container 3 is attached to the outer peripheral edge portion of the positive electrode current collecting member 26 during assembly.

<Negative electrode current collector>
The negative electrode current collecting member 36 is formed of nickel or a metal material obtained by applying nickel plating to copper. In the present embodiment, the negative electrode current collector 36 is formed of a metal material obtained by applying nickel plating to copper. As shown in FIG. 5, the negative electrode current collecting member 36 has a disk shape in which a circular depression is formed in the central portion. This recess is formed so as to accommodate the lower end of the shaft core 5. As shown in FIG. 5, the negative electrode current collecting member 36 is moved closer to the electrode plate group 4 from the side where the uncoated portion 35 of the copper foil of the negative electrode plate 31 of the electrode plate group 4 is located, It is placed on the coating part 35. And the negative electrode current collection member 36 and the uncoated part 35 of the copper foil 32 are laser-welded. Similarly to the positive electrode current collecting member 26, the negative electrode current collecting member 36 is also provided with four grooves that constitute a concave portion for welding so as to protrude toward the electrode plate group 4 and open in a direction away from the electrode plate group 4. It has been. These grooves are formed by pressing, and extend linearly and radially about the virtual center point of the negative electrode current collector 36.

<Welding of electrode plate group and current collecting member>
Laser light is used for welding the

uncoated portions

25 and 35 of the electrode plate group 4 and the current collecting members (the positive current collecting member 26 and the negative current collecting member 36). In the present embodiment, a direct focusing semiconductor laser device (DLL, not shown) that continuously generates laser light can be used. The case where the negative electrode current collector 36 is welded will be described as an example. Using a direct-collecting semiconductor laser device that continuously generates laser light, the laser light is collected along the groove of the negative electrode current collector 36. The negative electrode current collecting member 36 is melted locally by continuously irradiating from the outer peripheral side of the electric member 36 toward the center, and the uncoated portion 35 of the copper foil of the negative electrode plate and the negative electrode current collecting member 36 are melted by the molten metal. Weld. A good welding result can be similarly obtained even if a fiber light guiding type semiconductor laser device is used instead of the direct focusing type semiconductor laser device.

<Storing the electrode plate group in a container>
A metal lithium support member 41 is disposed on the outer periphery of the electrode plate group 4 to which the current collecting member is welded, that is, the electrode plate group unit 2 for a lithium ion capacitor, and is accommodated in the container 3. In a state in which the lithium ion capacitor electrode plate group unit 2 is housed, the recess of the negative electrode current collecting member 36 and the bottom of the container 3 are joined and electrically connected by joint welding. A predetermined amount of epoxy resin is injected using the inner periphery of the shaft core 5. When a predetermined time elapses, the epoxy resin is solidified to fix the inner bottom portion of the container and the negative electrode current collecting member 36. Next, the metallic lithium support member 41 and the side surface portion of the container 3 are joined by resistance welding to be electrically connected to the negative electrode current collector 36 (negative electrode plate 31) via the container 3. Thus, lithium ions can be occluded (doped) in the negative electrode active material (in this example, amorphous carbon) of the negative electrode plate 31.

An insulating ring member for electrically insulating the positive current collecting member 26 and the container 3 is attached to the outer peripheral edge of the positive current collecting member 26. The container 3 is subjected to drawing processing in the vicinity of the opening, and the electrode group unit 2 for lithium ion capacitors is fixed in the container 3 as shown in FIG.

A container lid 51 constituting a positive electrode terminal is disposed above the positive electrode current collecting member 26. The container lid 51 includes a lid body 52 disposed on the positive electrode current collector 26 and a lid cap 53 combined with the lid body 52. The lid main body 52 is made of aluminum, and the lid cap 53 is made of steel plated with nickel as in the case of the container 3. The lid cap 53 has an annular flat part and a convex part protruding from the center part of the flat part. The container lid 51 is configured such that the outer peripheral portion of the flat portion of the lid cap 53 is curled (curled) on the edge of the lid body 52. A gap is formed between the convex portion of the lid cap 53 and the lid body 52.

One end of one positive electrode terminal portion 27a out of two positive electrode terminal portions 27 formed by laminating a ribbon-like aluminum foil is joined to the upper surface of the positive electrode current collecting member 26. The other positive electrode terminal portion 27 b of the positive electrode terminal portion 27 is welded to the outer bottom surface of the lid body 52 constituting the container lid 51. Also, the other ends of the two positive

terminal portions

27a and 27b are joined together. Thereby, the lid body 52 is electrically connected to one electrode plate (positive electrode plate 21) of the electrode plate group 4.

As described above, an annular step portion is formed in the drawn container, and the container lid 51 is electrically insulated on the container lid 51 and the container 3. It arrange | positions through a member. The opening end portion is curled (caulked) so as to approach the container lid 51. As a result, the container lid 51 is fixed in a state where the container lid 51 is sandwiched between the opening end portion and the stepped portion that are curled. Thereby, the inside of the lithium ion capacitor 1 is sealed.

<Injection of electrolyte>
Actually, after injecting an amount of nonaqueous electrolyte (not shown) that can infiltrate the entire lithium ion capacitor electrode group unit 2 into the container 3, a container lid 51 is placed in the opening and curled. And seal. As the non-aqueous electrolyte, the present invention is composed of a cyclic carbonate composed of ethylene carbonate (EC) and propylene carbonate (PC), and a chain carbonate composed of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). The electrolyte solution for lithium ion capacitors can be used.

Hereinafter, examples of the electrolytic solution for a lithium ion capacitor according to the present invention will be described.

(Example 1)
<Method for producing positive electrode>
Weight of active carbon having a specific surface area of 1000 m ² / g or more as a positive electrode active material, an acrylic binder as a binder, carboxymethyl cellulose (CMC) as a dispersing agent, and acetylene black of conductive carbon powder as a conductive auxiliary agent ( (Mass) ratio was 85: 7: 3: 5, and water (dispersion solvent) was added and kneaded to prepare a positive electrode slurry. The slurry was applied to both surfaces of an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode.

<Method for producing negative electrode>
Weight of non-graphitizable carbon that is amorphous carbon capable of occluding and releasing lithium ions as negative electrode active material, polyvinylidene fluoride (PVDF) as binder, and acetylene black of conductive carbon powder as conductive aid (Mass) ratio is 90: 5: 5, and the dispersion solvent N-methylpyrrolidone (NMP) (Wako Pure Chemical Industries, Ltd., purity 99%) is added and kneaded to prepare the negative electrode slurry. Produced. The slurry was applied to both sides of a 15 μm thick copper foil, dried and pressed to obtain a negative electrode.

<Metal lithium support member>
Metal lithium (Honjo Metal Co., Ltd., purity 95%), copper foil constituting the negative electrode plate, and nickel-plated copper foil were cut into predetermined dimensions. Metal lithium was sandwiched between two supports so as to come into contact with a portion of the support where a large number of through holes were formed.

<Turn>
The electrode plate group is wound so that the positive electrode plate and the negative electrode plate are not in direct contact via the two separators and the positive electrode plate and the two laminates are not in direct contact via the two separators with the axial center as the winding center. Wound using a machine (Minato Seisakusho Co., Ltd.). At this time, the positive electrode plate, the negative electrode plate, and the separator are cut to a predetermined size so that the diameter becomes 38 mm, and an unwinding prevention adhesive tape is provided along the longitudinal direction of the separator wound around the outer periphery of the electrode plate group. Pasted.

<Assembly>
The positive electrode current collecting member and the negative electrode current collector member were fitted to both ends of the shaft core, respectively, and the positive electrode (negative electrode) plate uncoated portion and the positive electrode (negative electrode) current collector member were welded by laser welding. A metal lithium support member was wound around the outer periphery of the electrode plate group, and then inserted into the container, and the inner bottom portion of the container and the negative electrode current collecting member were joined by resistance welding. Further, a predetermined amount of epoxy resin was injected into the inner periphery of the shaft core, and after waiting for a predetermined time until solidification, the metallic lithium support member and the side surface portion of the container were joined by resistance welding. Next, a positive electrode current collecting member welded to the positive electrode terminal portion in advance and a container lid for sealing the container were joined.

<Injection of electrolyte>
A predetermined amount of non-aqueous electrolyte was injected into the container using the inner periphery of the shaft core. The non-aqueous electrolyte is phosphorus hexafluoride as an electrolyte in a solvent in which PC, EC, DMC and EMC (Wako Pure Chemical Industries, Ltd., purity 98%) are mixed at a volume ratio of 33: 33: 17: 17. An electrolytic solution was prepared by dissolving lithium oxide (LiPF ₆ ) (Wako Pure Chemical Industries, Ltd., purity 99%) at a 1.0 molar concentration.

<Sealing container>
After the gasket was fitted to the container, the container was covered and sealed so that the positive electrode terminal portion was folded with the container lid, and a lithium ion capacitor was produced.

<Occlusion of lithium in negative electrode active material>
By leaving the lithium ion capacitor in a storage room controlled at a predetermined temperature (60 ° C. or lower) for one month, lithium ions were occluded in the negative electrode active material, and a lithium ion capacitor in which the negative electrode was charged was obtained.

(Example 2)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 30: 30: 20: 20 as the electrolytic solution.

(Example 3)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 25: 25: 25: 25 as the electrolytic solution.

Example 4
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 20: 20: 30: 30 as the electrolytic solution.

(Example 5)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 15: 15: 35: 35 as the electrolytic solution.

(Example 6)
A lithium ion capacitor was manufactured in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 10: 10: 40: 40 as the electrolytic solution.

(Example 7)
A lithium ion capacitor was fabricated in the same manner as in Example 4 except that vinylene carbonate (VC) was added at 0.5 wt% as an additive for the electrolytic solution.

(Example 8)
A lithium ion capacitor was fabricated in the same manner as in Example 4 except that vinylene carbonate (VC) was added at 1% by weight as an additive for the electrolytic solution.

Example 9
A lithium ion capacitor was fabricated in the same manner as in Example 4 except that vinylene carbonate (VC) was added at 2% by weight as an additive for the electrolytic solution.

(Example 10)
A lithium ion capacitor was fabricated in the same manner as in Example 4 except that vinylene carbonate (VC) was added at 5% by weight as an additive for the electrolytic solution.

(Example 11)
A lithium ion capacitor was fabricated in the same manner as in Example 4 except that vinylene carbonate (VC) was added at 10% by weight as an additive for the electrolytic solution.

(Comparative Example 1)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except that the electrolytic solution was a PC solvent.

(Comparative Example 2)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 45: 45: 5: 5 as the electrolytic solution.

(Comparative Example 3)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 40: 40: 10: 10 as the electrolytic solution.

(Comparative Example 4)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 35: 35: 15: 15 as the electrolytic solution.

(Comparative Example 5)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 5: 5: 45: 45.

(Comparative Example 6)
A lithium ion capacitor was fabricated in the same manner as in Example 1 except for the solvent in which PC, EC, DMC, and EMC were mixed at a volume ratio of 3: 3: 47: 47 as the electrolytic solution.

(Comparative Example 7)
A lithium ion capacitor was fabricated in the same manner as in Comparative Example 1 except that vinylene carbonate (VC) was added at 1% by weight as an additive for the electrolytic solution.

<Characteristic measurement>
In an environment of 25 ° C. and −20 ° C., charge at a constant current of 10 A until the cell voltage of the lithium ion capacitor reaches 3.8 V, and then apply a constant voltage of 3.8 V to 30 constant current-constant voltage charging. Went for a minute. Next, the battery was discharged at a constant current of 10 A until the cell voltage reached 2.2V. The direct current internal resistance (DCR) of the cell in this discharge was measured (Toyo System Co., Ltd. TOSCAT-3200).

The DC internal resistance (DCR) is obtained by calculating an approximate straight line from the voltage at 1 second and 2 seconds after the start of discharge, and the voltage drop at the start is obtained by extrapolation of this line, and this voltage drop is divided by the discharge current. Determined by

10 cells each of the lithium ion capacitors manufactured by the methods of Examples 1 to 10 and Comparative Examples 1 to 9 were measured, and the average values before and after the float test are shown in Tables 1 and 2.

<Float test>
In a constant temperature bath at 80 ° C., charging was performed at a constant current of 5 A until the cell voltage of the lithium ion capacitor reached 3.8 V, and then a constant current-constant voltage charging for applying a constant voltage of 3.8 V was performed for 1000 hours. .

<Characteristic evaluation>
The DCR ratio (change rate of direct current internal resistance) was calculated by the following formula.
DCR ratio = DC internal resistance after test (DCR) / DC internal resistance before test (DCR)
Table 1 and FIG. 7 show the results of the lithium ion capacitors to which the electrolytic solution of the present invention was applied, that is, Examples 1 to 6 and Comparative Examples 1 to 6. Moreover, the lithium ion capacitor which applied vinylene carbonate (VC) to the additive of this invention, ie, the result from Example 7 to Example 10 and Comparative Example 1 and Comparative Example 7 to Comparative Example 9, is shown in Table 2 and FIG. Show.

Comprehensive judgment was judged by comparing with the characteristic value of the comparative example.

◎: The characteristics are much better than the comparative example.

○: The characteristics are superior to the comparative example.

△: The characteristics are equivalent to those of the comparative example.

X: The characteristic is worse than the comparative example.

The electrolyte solution for lithium ion capacitors of the present invention is an electrolyte solution that combines the characteristics of each solvent well by optimizing the composition ratio. By using this, the lithium ion has excellent low-temperature characteristics and long life. A capacitor can be obtained.

DESCRIPTION OF SYMBOLS 1 Lithium ion capacitor 3 Container 4 Electrode plate group 5

Shaft core

6,7 Separator

Claims

The solvent is composed of cyclic carbonate composed of ethylene carbonate and propylene carbonate, chain carbonate composed of dimethyl carbonate and ethylmethyl carbonate, and vinylene carbonate,
The volume ratio of the annular carbonate and the chain carbonate is 1.0: 0.5 to 1.0: 4.0,
An electrolytic solution for a lithium ion capacitor, wherein the vinylene carbonate is contained in an amount of 0.5 to 5.0 weight percent with respect to the total amount of the cyclic carbonate and the chain carbonate.
The solvent is composed of a cyclic carbonate composed of ethylene carbonate and propylene carbonate, and a chain carbonate composed of dimethyl carbonate and ethylmethyl carbonate, and the volume ratio of the cyclic carbonate to the chain carbonate is 1.0: 0.5. 1.0 to 4.0, an electrolyte for a lithium ion capacitor.
Furthermore, the electrolyte solution for lithium ion capacitors of Claim 2 containing vinylene carbonate.
The electrolyte solution for a lithium ion capacitor according to claim 3, wherein the volume ratio of the annular carbonate to the chain carbonate is 1.0: 1.5 to 1.0: 4.0.
The electrolyte solution for a lithium ion capacitor according to claim 3, wherein the volume ratio of the annular carbonate and the chain carbonate is about 1.0: 2.3.
The electrolyte solution for a lithium ion capacitor according to claim 3, wherein the vinylene carbonate is contained in an amount of 0.5 to 5.0 weight percent with respect to the total amount of the cyclic carbonate and the chain carbonate.
The electrolyte solution for a lithium ion capacitor according to claim 3, wherein the vinylene carbonate is contained in an amount of 1.0 to 2.0 weight percent with respect to the total amount of the cyclic carbonate and the chain carbonate.
A lithium ion capacitor using the electrolyte for a lithium ion capacitor according to any one of claims 1 to 7, wherein the positive electrode material includes activated carbon, and the negative electrode material includes non-graphitizable carbon. .