JP2020047830A - Capacitor - Google Patents

Abstract

To provide a power storage device capable of achieving no problems in reliability and safety even after repetitive quick charge is executed.SOLUTION: The capacitor ensures that an average value of an entropy change ΔSobtained from the following expression (1) is at least 82 J/K*mol: An average value of ΔS=ΔS+ΔS+ΔS)/3(1), where each of ΔSto ΔSis an entropy change when a voltage E(V) of the capacitor uses an upper-limit value of a rated voltage, a lower-limit value of the rated voltage or (the upper-limit value of the rated voltage + the lower-limit value of the rated voltage)/2.SELECTED DRAWING: None

Description

  The present invention relates to a capacitor.

  Power storage devices such as lithium ion secondary batteries are small and have high energy densities, and are widely used as power sources for portable electronic devices. Research and development are being actively conducted to further improve the energy density and reliability and safety.

  By the way, it is known that it is important to control the amount of heat generated during charging and discharging in order to improve the reliability and safety of lithium ion batteries. To cope with this problem, Patent Literature 1 proposes a lithium ion battery including an electrode including an electrode mixture layer in which the range of lithium capacity in which entropy heat generation during charging or discharging is negative is widened.

International Publication No. WO 2014/155496

  However, it has been found that when the lithium ion battery disclosed in Patent Literature 1 is rapidly charged, reliability (hardness of deterioration) and safety are insufficient. While the discharge speed of a power storage device such as a battery or a capacitor differs depending on the intended use, rapid charging is required for power storage devices in general. For this reason, an energy storage device that does not cause a problem in reliability and safety even after repeated rapid charging is required. However, it has been found that it is difficult to solve such a problem in a lithium ion battery due to the configuration of the electrodes. .

  In view of the above problems, an object of the present invention is to provide a power storage device that does not cause a problem in reliability and safety even when rapid charging is repeatedly performed.

  In view of such circumstances, the inventors of the present invention have conducted intensive studies, and found that a capacitor whose entropy change amount during charging is larger than that of a conventional power storage device increases the temperature due to heat generation of the power storage device as a whole charge / discharge process. Have been found to be able to solve the above problems, and have completed the present invention.

(Hereinafter also referred to as "the capacitor".) Capacitor according to an embodiment of the present invention, the average value of entropy change [Delta] S _E obtained by the following equation (1) is characterized in that at 82J / K · mol or more .
Although it is a lithium ion battery, as long as estimated from Figure 14 of Patent Document 1, the average value of the [Delta] S _E of the lithium ion battery disclosed in Patent Document 1 is about 20J / K · mol.

Average value of ΔS _E = (ΔS _Ea + ΔS _Eb + ΔS _Ec ) / 3 (1)
In the above equation (1), ΔS _Ea , ΔS _Eb and ΔS _Ec are respectively calculated by the following equation (1-1).

ΔS _E = −n × 9.65 × 10 ⁴ (C / mol) × ΔV ₀ / ΔT (1-1)
In the above formula (1-1),
ΔS _E is any of ΔS _Ea , ΔS _Eb or ΔS _Ec ,
n is the number of charges involved in the electrode reaction,
ΔV ₀ / ΔT is obtained by adjusting a capacitor adjusted at a current value of 10 C so that the voltage of the capacitor becomes E (V) in a 25 ° C. constant temperature bath at a temperature T = 20 ° C., 22 ° C., 24 ° C., 26 ° C., 28 The open circuit voltage V ₀ after leaving each in a constant temperature bath at 30 ° C. or 30 ° C. for a predetermined time was measured, and the measurement results were plotted with the horizontal axis representing T (K) and the vertical axis representing open circuit voltage V ₀ (V). In the graph shown, it means the slope of a straight line obtained by the least squares method.
The ΔS _Ea is an entropy change when the E (V) is set to the “upper limit of the rated voltage”, and the ΔS _Eb is an entropy change when the E (V) is set to the “lower limit of the rated voltage”. ΔS _Ec is an entropy change when E (V) is set to “(the upper limit value + the lower limit value) / 2”.
Note that 9.65 × 10 ⁴ (C / mol) is a Faraday constant.

The predetermined time means a longer time of the following A and B.
A: A capacitor in which the voltage of the capacitor is adjusted to the upper limit of the rated voltage by performing constant-current constant-voltage charging at a current value of 10 C for 24 hours in a constant-temperature bath of 25 ° C. Time (minutes) required for the open circuit voltage to reach the maximum value from the start of standing when left inside
B: 30 minutes when the capacitance of the capacitor is less than 2000F, and capacitance (F) / 2000 × 60 (min) when the capacitance is 2000F or more.

  Since the present capacitor has a larger heat absorption due to a change in entropy at the time of charging than a conventional power storage device, it does not easily deteriorate even after repeated rapid charging, and is excellent in safety.

≪Capacitors≫
The present capacitor is not particularly limited, but is preferably an electrochemical capacitor. Electrochemical capacitors are non-Faraday reactions that do not involve the transfer of electrons between the electrodes and ions in the electrolyte at the electrode interface, or capacitors that use the capacitance developed due to the Faraday reaction that involves the transfer of electrons. It is.
Examples of the electrochemical capacitor include an electric double layer capacitor, a hybrid capacitor, and a redox capacitor, and a hybrid capacitor is preferable. Examples of the hybrid capacitor include a sodium ion capacitor, a lithium ion capacitor, and a magnesium ion capacitor, and among these, a lithium ion capacitor is particularly preferable.

<Average value of entropy change ΔS _E>
In the present invention, the rated voltage is the upper and lower limits of a voltage that can be used stably when a capacitor is used. For a commercially available capacitor, the rated voltage means a rated voltage described in a catalog or specification. In the case of a lithium ion capacitor, the rated voltage is usually 2.2V-3.8V.

In measuring the ΔS _E , first, the predetermined time (leaving time) is measured by the following method, and the longer one of the times obtained in A and B below is determined.
A: A constant current constant voltage (hereinafter, also referred to as “CCCV”) charging is performed at a current value of 10 C for 24 hours in a constant temperature bath at 25 ° C., so that the voltage of the capacitor is set to the upper limit of the rated voltage of the capacitor. After the adjustment, the temperature of the thermostat is set to 20 ° C., and when the thermostat is left in the thermostat at 20 ° C., the time (minutes) required from the start of standing to when the open circuit voltage shows the maximum value is measured. .
B: When the capacitance of the capacitor is less than 2000F, the time is 30 minutes. When the capacitance is 2000F or more, the capacitance is (F) / 2000 × 60 (minutes).

  Note that the capacitance of a capacitor is the capacitance obtained when the capacitor is discharged from the upper limit value to the lower limit value of the rated voltage.

After measuring or determining the predetermined time (leaving time), ΔV ₀ / ΔT is calculated as follows.
In a constant temperature bath at 25 ° C., the voltage of the capacitor is adjusted at a current value of 10 C so as to be a predetermined voltage E (V), and the capacitor after the adjustment is subjected to temperature T = 20 ° C., 22 ° C., 24 ° C., 26 ° C. The open circuit voltage V ₀ after being left in a constant temperature bath at 28 ° C. or 30 ° C. for a predetermined time is measured, and the horizontal axis is T (K), and the vertical axis is the open circuit voltage V ₀ (V). In the graph, the slope (ΔV ₀ / ΔT) of the straight line obtained by the least squares method is calculated.

More specifically, first, CCCV charging is performed at a current value of 10 C for 24 hours in a thermostat at 25 ° C., so that E (V) is adjusted to the upper limit of the rated voltage. Then, V ₀ is measured after the adjusted capacitor is left in a thermostat at T = 30 ° C. for a predetermined time. Subsequently, the temperature in the thermostatic chamber is changed to 25 ° C., and CCCV discharge is performed at a current value of 10 C for 24 hours, so that E (V) becomes the lower limit of the rated voltage. Then, V ₀ is measured after the adjusted capacitor is left in a thermostat at T = 30 ° C. for a predetermined time. The same operation is repeated at T = 28 ° C., 26 ° C., 24 ° C., 22 ° C., and 20 ° C., so that ΔV ₀ / E (V) is set to the upper limit value and the lower limit value of the rated voltage. Calculate ΔT.

Next, by changing the temperature in the thermostat to 25 ° C. and performing CCCV charging at a current value of 10 C for 24 hours, E (V) becomes “(upper limit of rated voltage + lower limit of rated voltage) / 2. "To adjust. Then, V ₀ is measured after the adjusted capacitor is left in a thermostat at T = 30 ° C. for a predetermined time. Subsequently, by performing CCCV discharge at a current value of 10 C for 24 hours, E (V) is adjusted to be the lower limit of the rated voltage. After that, the temperature in the thermostatic chamber is changed to 25 ° C., and the CCCV charging is performed at a current value of 10 C for 24 hours, so that E (V) becomes “(upper limit of rated voltage + lower limit of rated voltage) / 2”. Adjust so that Then, V ₀ is measured after leaving the adjusted capacitor in a thermostat at T = 28 ° C. for a predetermined time. By repeating the same operation at T = 26 ° C., 24 ° C., 22 ° C., and 20 ° C., when E (V) is set to “(upper limit of rated voltage + lower limit of rated voltage) / 2”, Calculate ΔV ₀ / ΔT.

Like a battery, a capacitor generates or absorbs heat due to a charge / discharge reaction.
Takamasa Oshima, et al., "Exothermic Behavior of Small Lithium-Ion Secondary Batteries During Rapid Charge / Discharge", IEEJ Transactions on Materials, B, 2004, Vol. 124, No. 12, p. With reference to 1521-1527, the endothermic heat generation in this reaction is related to TΔS in a thermodynamic relational expression ΔG = ΔH−TΔS under a constant temperature and a constant pressure in an ideal reversible state. For this reason, in the present invention, the entropy change ΔS is considered as an endothermic factor.
Here, from the relational expression [−ΔS = δ (ΔG) / ΔT] between the Gibbs energy change and the entropy change and the relational expression [−ΔG = nFE] between the Gibbs energy change and the battery electromotive force, ΔS is represented by the following expression. be able to.
ΔS = n · F · (ΔE / ΔT)
[N: number of charges involved in electrode reaction, F: Faraday constant (C / mol), E: electromotive force (V) of battery]

Assuming that the electromotive force E of the battery can be approximated to the open circuit voltage V ₀ (V), the amount of heat accompanying the entropy change at the time of charging the capacitor can be approximately expressed by the following equation (1-1).
ΔS _E = −n · 9.65 × 10 ⁴ · (ΔV ₀ / ΔT) (1-1)

N in the formula (1-1) is, for example, n = 1 when a monovalent lithium ion or sodium ion participates in the electrode reaction, and a divalent magnesium ion participates in the electrode reaction. In this case, n = 2. This equation (1-1), by substituting [Delta] V ₀ / [Delta] T calculated above, can be calculated [Delta] S _E at a predetermined voltage E (V).

In the present invention, as the predetermined voltage E (V), “the upper limit value of the rated voltage”, “the lower limit value of the rated voltage”, and “(the upper limit value + the lower limit value) / 2” are employed. Using ΔS _Ea , ΔS _Eb, and ΔS _Ec in each case, the average value was calculated by the following equation (1). The present inventors have found that by setting this average value to 82 J / K · mol or more, it is possible to provide a capacitor that does not cause a problem in reliability and safety even after repeated rapid charging.
Average value of ΔS _E = (ΔS _Ea + ΔS _Eb + ΔS _Ec ) / 3 (1)

When the present capacitor is a lithium ion capacitor, the “upper limit value of rated voltage”, “lower limit value of rated voltage” and “(the upper limit value + the lower limit value) / 2” are 3.8V, 2. It is preferably 2 V and 3.0 V. In this case, ΔS _Ea = ΔS _3.8 , ΔS _Eb = ΔS _2.2 , ΔS _Ec = ΔS _3.0 , and the above equation (1) is as follows.
Average value of ΔS _E = (ΔS _3.8 + ΔS _2.2 + ΔS _3.0 ) / 3

The lower limit of the average value of [Delta] S _E is preferably 83J / K · mol, more preferably 84J / K · mol, particularly preferably 85J / K · mol. On the other hand, the upper limit value of the average value of [Delta] S _E is preferably 200 J / K · mol, particularly preferably 150J / K · mol.
If the average value is less than 82 J / K · mol, a desired effect may not be obtained. On the other hand, if the average value is too large, the heat generated at the time of discharge will be too large. Therefore, when charging and discharging are repeated, the capacitor cells may be liable to deteriorate.

  Factors that greatly affect the average value include a combination of a positive electrode active material, a negative electrode active material, and an electrolyte described below. By adjusting these factors, the average value can be set within a predetermined range.

<Configuration of capacitor>
The present capacitor usually includes a positive electrode, a negative electrode, and an electrolyte.

[Positive electrode]
The positive electrode usually contains a positive electrode active material.
The positive electrode active material is not particularly limited, but is preferably a positive electrode active material capable of storing and releasing anions, and more preferably activated carbon and carbon nanotubes.
The positive electrode active material used for the positive electrode may be one type or two or more types.

Examples of the positive electrode include a laminate in which a positive electrode active material layer containing the positive electrode active material is formed on a positive electrode current collector.
The positive electrode active material layer can be usually manufactured by preparing a slurry containing a positive electrode active material, a binder, and the like, applying the slurry on a current collector, and drying the slurry.
Further, the positive electrode may have a conductive layer.

The positive electrode current collector used for the positive electrode is preferably a plate-like body such as aluminum or stainless steel, and may have a through hole penetrating the front and back surfaces.
The thickness of the positive electrode current collector is usually 10 to 50 μm.

Examples of the binder include a rubber-based binder such as styrene-butadiene rubber (SBR) and NBR; polytetrafluoroethylene, polyvinylidene fluoride (PVDF), and fluorine as disclosed in JP-A-2009-246137. Fluorine binders such as a modified (meth) acrylic binder; polypropylene; polyethylene.
As the binder, one kind may be used, or two or more kinds may be used.

The positive electrode active material layer further includes a conductive agent such as carbon black, carbon fiber, graphite, and metal powder; carboxymethyl cellulose (CMC), its Na salt or ammonium salt, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, Thickeners such as oxidized starch, phosphorylated starch, and casein may be included.
These may be used alone or in combination of two or more.

  The amount of the polymer component such as a binder and a thickener that can be contained in the positive electrode active material layer is preferably 1 to 20 parts by mass, particularly preferably 2 to 15 parts by mass with respect to 100 parts by mass of the positive electrode active material. is there.

[Negative electrode]
The negative electrode of the present capacitor usually contains a negative electrode active material.
The negative electrode active material is not particularly limited, but is preferably a negative electrode active material capable of storing and releasing cations, and particularly preferably a negative electrode active material capable of storing and releasing lithium ions, sodium ions, and magnesium ions. More specifically, a carbon material such as graphite, graphitizable carbon, non-graphitizable carbon, a composite carbon material in which graphite particles are coated with pitch or resin carbide; a metal which can be alloyed with lithium, sodium or magnesium or Semimetals or materials containing oxides of these metals or semimetals; lithium titanate is preferred.
The negative electrode active material used for the negative electrode may be one type or two or more types.

As the negative electrode, similarly to the positive electrode, for example, a laminate in which a negative electrode active material layer containing the negative electrode active material is formed on a negative electrode current collector is given.
The negative electrode current collector used for the negative electrode is preferably a plate-like body such as copper, nickel, and stainless steel, and may have a through hole penetrating the front and back surfaces.
The thickness of the negative electrode current collector is usually 10 to 50 μm.
The negative electrode active material layer may contain a binder and other components as in the case of the positive electrode, and specific examples and the amounts thereof are the same as in the case of the positive electrode.

[Electrolytes]
The electrolyte is not particularly limited, and examples thereof include lithium salts, sodium salts, magnesium salts, and organic onium salts. Of these, lithium salts, sodium salts, and magnesium salts are preferred.
Examples of the anion portion constituting the electrolyte include PF ₆ ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , PF ₃ (CF ₃ ) ₃ ⁻ , BF ₄ ⁻ , BF ₂ (CF) ₂ ⁻ , and BF ₃ ( ^{_{CF 3) -, B (CN}} ) 4 -, N (FSO 2) 2 -, N (CF 3 SO 2) 2 -, N (C 2 F 5 SO 2) 2 -, Cl -, Br -, ClO 4 ^-
As the electrolyte, one kind may be used, or two or more kinds may be used.

The electrolyte is usually used in a state of an electrolytic solution dissolved in a solvent. As a solvent for dissolving the electrolyte, an aprotic organic solvent is preferable. Examples of the aprotic organic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolan, methylene chloride, and sulfolane. These solvents may be used alone or in combination of two or more.
It is preferable to use a mixed solvent of a cyclic carbonate and a chain carbonate as the solvent from the viewpoint that an electrolyte having a low viscosity and a high ionic conductivity can be obtained.

  The concentration of the electrolyte in the electrolyte is preferably 0.1 mol / L or more, more preferably 0.5 to 1.5 mol / L, in order to reduce the internal resistance due to the electrolyte. The electrolyte may be in a gel or solid state. In this case, electrolyte leakage can be suppressed.

  When the present capacitor is a lithium ion capacitor, it is preferable to use an electrolyte containing lithium fluorophosphate (at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate). The lower limit of the content ratio of lithium fluorophosphate in the electrolytic solution is preferably 0.01% by mass, and particularly preferably 0.05% by mass. On the other hand, the upper limit of the content ratio of lithium fluorophosphate in the electrolytic solution is preferably 10% by mass, more preferably 5% by mass, and particularly preferably 3% by mass.

When the present capacitor is a lithium ion capacitor, it is preferable to further add sultones to the electrolytic solution. One or two or more sultones may be used.
Note that sultones may be decomposed as the capacitor is charged or discharged, but in this specification, if the electrolyte used for manufacturing the capacitor includes the sultone, the electrolyte includes the sultone.

  Examples of the sultones include compounds represented by the following formulas (B) and (C).

In the formula (B), R ^{B1 to} R ^B6 are each independently a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms which may be substituted by a halogen atom, and n is an integer of 0 to 3 It is.
The halogen atom is preferably a fluorine atom, the alkyl group having 1 to 6 carbon atoms is preferably an alkyl group having 1 to 3 carbon atoms, and n is preferably 1 to 3, more preferably 1 to 2, and 1 Is particularly preferred.

In the formula (C), R ^{C1 to} R ^C4 are each independently a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms which may be substituted by a halogen atom, and n is an integer of 0 to 3 It is.
Preferred examples of the halogen atom, the alkyl group having 1 to 6 carbon atoms and n are the same as the preferred examples in the formula (B).

  As the sultones, propane sultone and 1-propene 1,3-sultone are preferred.

  When sultones are used, the lower limit of the amount of the sultones added to the electrolytic solution is preferably 0.01% by mass with respect to 100% by mass of the electrolytic solution. On the other hand, the upper limit of the amount of sultones added to the electrolytic solution is preferably 10% by mass, more preferably 5% by mass, and particularly preferably 2% by mass, based on 100% by mass of the electrolytic solution. Note that this addition amount refers to the addition amount to the electrolytic solution used when manufacturing the capacitor.

When the electrolyte is used in the form of an electrolytic solution, a separator is usually used between the positive electrode and the negative electrode so that the positive electrode and the negative electrode do not physically contact each other.
Examples of the separator include a nonwoven fabric or a porous film made of cellulose rayon, polyethylene, polypropylene, polyamide, polyester, polyimide, or the like.

As the structure of the capacitor, for example, a laminated cell in which a laminate in which a plate-shaped positive electrode and a negative electrode are laminated via a separator or a gel or solid electrolyte is enclosed in an exterior film or the like, a band-shaped positive electrode and A wound cell in which a laminate obtained by winding a negative electrode with a separator or a gel or solid electrolyte through a container such as a square or cylindrical container can be given.
As a structure of the capacitor, a hyperbolic (bipolar) type cell in which a positive electrode is formed on one surface of a plate-shaped current collector and an electrode having a negative electrode formed on the other surface is laminated with a separator interposed therebetween. You can also mention.
In particular, when the capacitor is a wound cell housed in a rectangular or cylindrical container, the capacitor is suitable because it is easily affected by heat generation.

  When the present capacitor is a lithium ion capacitor, it is preferable that the negative electrode is doped with lithium ions in advance. For the method of doping lithium ions in advance, for example, International Patent Publication Nos. WO 1998/033227 and WO 2000/007255 may be referred to.

  Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
<Preparation of positive electrode>
92 parts by mass of a commercially available activated carbon powder having a specific surface area of 2000 m ² / g, 6 parts by mass of acetylene black powder, 7 parts by mass of an acrylic resin binder, 4 parts by mass of CMC and 200 parts by mass of water were stirred and mixed to prepare a slurry.
A non-aqueous carbon-based conductive paint is applied on both sides of an aluminum expanded metal (positive electrode current collector) having a porosity of 47% and a thickness of 38 μm using a roll coater, and then dried in a vacuum to form a conductive layer having a total thickness of 52 μm. To obtain a positive electrode current collector. The slurry was applied to both sides of the positive electrode current collector with a conductive layer by a roll coater, and then dried in vacuum to obtain a laminate having a total thickness of 200 μm. Note that both the front and back surfaces of the positive electrode current collector, a portion where the conductive layer and the positive electrode active material layer are stacked (hereinafter, also referred to as a “coated portion”), and a portion where neither layer is formed (hereinafter, “ The conductive layer and the electrode layer were formed so as to generate an “uncoated portion”. In addition, the through-hole of the positive electrode current collector in the coating part was almost closed by the conductive layer. The thus obtained laminate is cut into a size of 98 mm × 141 mm so that the coated portion has a size of 98 mm × 126 mm and the uncoated portion has a size of 98 mm × 15 mm, thereby producing a positive electrode. did.

<Preparation of negative electrode>
100 parts by mass of a graphite powder having an average particle diameter of 4 μm and 50 parts by mass of an optically isotropic pitch having a softening point of 110 ° C. and a mesophase amount (QI (quinoline insoluble matter) amount) of 13% are kneaded with a heating kneader, and this is kneaded. It was fired at 800 ° C. in an oxidizing atmosphere. The obtained fired product was pulverized so that the average particle diameter became 8 μm, and fired again at 1000 ° C. in a non-oxidizing atmosphere to obtain a negative electrode active material. 92 parts by mass of the obtained negative electrode active material, 6 parts by mass of acetylene black powder, 5 parts by mass of SBR, 3 parts by mass of CMC and 200 parts by mass of water were stirred and mixed to prepare a slurry. The obtained slurry was applied to both surfaces of a negative electrode current collector made of copper expanded metal having a porosity of 57% and a thickness of 32 μm using a roll coater, and then dried under vacuum to obtain a laminate having a total thickness of 80 μm. . A negative electrode is prepared by cutting the thus obtained laminate into a size of 100 mm x 143 mm so that the coated portion has a size of 100 mm x 128 mm and the uncoated portion has a size of 100 mm x 15 mm. did.

<Production of lithium-ion capacitor element>
First, 10 positive electrodes, 11 negative electrodes, and 22 separators each having a thickness of 50 μm were prepared. The coated portions of the positive electrode and the negative electrode were overlapped with each other, but the uncoated portions were on opposite sides and did not overlap. , A separator, a negative electrode, a separator, and a positive electrode were stacked in this order, and four sides of the obtained stacked body were fixed with a tape to prepare an electrode stacked body. Then, a lithium foil having a thickness of 100 μm is cut and pressed on a stainless steel net having a thickness of 40 μm to prepare a lithium ion supply member. The lithium ion supply member faces one of the electrode stacks with a negative electrode via a separator. Thus, an electrode stacking unit was obtained. An aluminum positive electrode having a width of 50 mm, a length of 50 mm, and a thickness of 0.2 mm, in which a sealant film was previously heat-sealed to the uncoated portion of each of the ten positive electrodes of the produced electrode stacking unit at the sealing portion. The power supply tabs were overlapped and ultrasonically welded. On the other hand, the uncoated portion and the lithium-ion supply member of each of the 11 negative electrodes of the electrode stacking unit were previously heat-sealed with a sealant film to the sealing portion in a seal 50 mm in width, 50 mm in length, and 0.2 mm in thickness. The negative electrode power supply tabs were overlapped and resistance welded. As described above, a lithium ion capacitor element was manufactured.

<Production of lithium ion capacitor>
Next, a polypropylene (PP) layer, an aluminum layer and a nylon layer are laminated, and the dimensions are 125 mm (length) × 160 mm (width) × 0.15 mm (thickness), and 105 mm (length) × 140 mm (width) of the upper exterior film subjected to drawing processing (width of the outer peripheral edge serving as a joining portion is 10 mm), a PP layer, an aluminum layer, and a nylon layer are laminated, and the dimension is 125 mm (length). A lower exterior film of × 160 mm (width) × 0.15 mm (thickness) was produced. Next, the lithium ion capacitor element is arranged at a position to be a housing portion on the lower exterior film, and each of the positive electrode power tab and the negative electrode power tab is arranged to protrude outward from an end of the lower exterior film, The upper exterior film is superimposed on this lithium ion capacitor element, and three sides (two sides where the power tab for the positive electrode and the power tab for the negative electrode protrude and one side in the longitudinal direction) at the outer peripheral edges of the upper exterior film and the lower exterior film. Was heat-fused to form a joint around the housing on the three sides.

As an aprotic organic solvent, a mixed solvent of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio: 3: 4: 3, respectively) was used to prepare a solution containing LiPF ₆ having a concentration of 1.2 mol / L. Thereafter, an additive (lithium difluorophosphate) was added in an amount of 0.5% by mass based on the electrolytic solution to obtain an electrolytic solution.

  Next, after injecting the obtained electrolytic solution into the accommodating portion between the exterior films, the other side of the outer peripheral edge of the exterior film was heat-sealed. Then, in this state, the negative electrode was doped with lithium ions from a lithium foil (lithium ion supply member) by being left for 10 days. In this way, a laminated lithium ion capacitor for a test laminate was produced.

<Evaluation of cell characteristics>
The lithium-ion capacitor is charged at a constant current of 10 A until the cell voltage reaches the upper limit value of the rated voltage of 3.8 V, and then a constant current-constant voltage charging of applying a constant voltage of 3.8 V is performed for 0.5. Time went. Next, the capacitance when the cell was discharged at a constant current of 10 A until the voltage of the cell reached the lower limit value of 2.2 V of the rated voltage was measured. The measurement result of the capacitance was 1110F.
At this time, the value obtained by dividing the difference between the voltage immediately before the discharge and the voltage 100 msec after the start of the discharge by the discharge current was defined as the internal resistance. The measurement result of the internal resistance was 1.2 mΩ.
Table 1 shows the results. In Table 1, the results of the capacitance and the internal resistance of Example 2 and Comparative Examples 1 and 2 are relative values when the values of the capacitance and the internal resistance in Example 1 are each 100.

<Measurement of ΔS _E>
First, the following measurement was performed in order to determine a predetermined time to be left in a thermostat. CCCV charging was performed at a current value of 10 C for 24 hours at a charging voltage (upper limit of the rated voltage) of 3.8 V in a constant temperature bath at 25 ° C. After that, when the temperature in the thermostat was changed to 20 ° C., the open circuit voltage (OCV) of the lithium ion capacitor showed the maximum value after 30 minutes.
The ΔS _E during charging of the lithium ion capacitor cell was calculated by Takamasa Oshima et al., “Heat generation behavior during rapid charge / discharge of a small lithium ion secondary battery”, IEEJ Transactions on Science, B, 2004, Vol. 124, No. 12, p. . It measured as follows with reference to 1521-1527.

CCCV charging was performed at a current value of 10 C for 24 hours in a thermostat at 25 ° C. with E = 3.8 V (upper limit of the rated voltage). Then, the temperature T in the thermostat was changed to 30 ° C., and after 30 minutes, the OCV of the lithium ion capacitor was measured. Subsequently, the temperature in the thermostat was changed to 25 ° C., and CCCV discharge was performed at a current value of 10 C for 24 hours with E = 2.2 V (lower limit value of the rated voltage). Then, the temperature T in the thermostat was changed to 30 ° C., and after 30 minutes, the OCV of the lithium ion capacitor was measured.
These measurements,
E = 3.8V; T = 30 ° C.
E = 2.2V; T = 30 ° C.
It expresses.
Thereafter, the OCV measurement was similarly performed in the following order. In addition, the temperature of the thermostat at the time of CCCV charge and CCCV discharge other than performing OCV measurement was set to 25 ° C.

E = 3.8V; T = 28 ° C.
E = 2.2V; T = 28 ° C.
E = 3.8V; T = 26 ° C.
E = 2.2V; T = 26 ° C.
E = 3.8V; T = 24 ° C.
E = 2.2V; T = 24 ° C.
E = 3.8V; T = 22 ° C.
E = 2.2V; T = 22 ° C.
E = 3.8V; T = 20 ° C.
E = 2.2V; T = 20 ° C.

The relationship of the OCV value with respect to each temperature T (K) in the thermostat measured as described above is plotted for each of the cases of E = 3.8 V and E = 2.2 V, and the OCV is calculated by the least square method. Was calculated (ΔV ₀ / ΔT), and ΔS _E (J / K · mol) was calculated by the above equation (1-1). As a result, ΔS _{E at} E = 3.8 V and E = 2.2 V were 55.5 J / K · mol and 112.4 J / K · mol, respectively.

  CCCV charging was performed at a current value of 10 C for 24 hours in a 25 ° C. constant temperature bath at E = 3.0 V. Then, the temperature T in the thermostat was changed to 30 ° C., and after 30 minutes, the OCV (at E = 3.0 V; T = 30 ° C.) of the lithium ion capacitor was measured. Subsequently, CCCV discharge was performed at a current value of 10 C for 24 hours at a set voltage of 2.2 V. Thereafter, the temperature in the thermostat was changed to 25 ° C., and CCCV charging was performed at a current value of 10 C for 24 hours with E = 3.0 V. Subsequently, the temperature T in the thermostat was changed to 28 ° C., and after 30 minutes, the OCV (at E = 3.0 V; T = 28 ° C.) of the lithium ion capacitor was measured. By repeating the same operation, E = 3.0 V; T = 26 ° C., E = 3.0 V; T = 24 ° C., E = 3.0 V; T = 22 ° C., E = 3.0 V; T = 20 ° C. OCV measurement was performed.

As a result, [Delta] S _E in the E = 3.0 V was 93.0J / K · mol. From the above, E = 3.8 V, the average value of [Delta] S _E in the three points E = 3.0 V and E = 2.2V was 87.0J / K · mol. Table 1 shows the results.

<Measurement of calorific value when charged with large current>
The amount of heat generated when the lithium ion capacitor was adiabatically charged from a lower limit value of 2.2 V to an upper limit value of 3.8 V at a current of 100 A under an environment of 25 ° C. was measured using a thermocouple attached to the surface of the cell. And the heat capacity of the cell. As a result, the calorific value becomes -210 J. Even when the battery is charged with such a large current, the charging process is substantially an endothermic process, and is a power storage device in which deterioration due to (rapid) charging and discharging is suppressed. Was confirmed. Table 1 shows the results.

<Cycle test with quick charge>
A charge-discharge cycle test was performed in which the lithium-ion capacitor was charged at 60 ° C. at 100 A to the upper limit of the rated voltage of 3.8 V, and then discharged at 10 A to the lower limit of the rated voltage of 2.2 V. This charge / discharge was defined as one cycle, and the cell thickness after 10,000 cycles was measured. Table 1 shows the results. In Table 1, the results of the cycle tests of Example 2 and Comparative Examples 1 and 2 are relative values when the increase in the thickness of the cell after the cycle test using the cell of Example 1 is 100. . The smaller the value, the more difficult it is to deteriorate even after repeated rapid charging, and the better the safety.

[Example 2]
In the same manner as in Example 1, except that the additive added to the electrolytic solution was changed to 1% by mass of lithium difluorophosphate and 0.05% by mass of 1-propene 1,3-sultone. To produce a lithium ion capacitor, and various evaluations were made. Table 1 shows the results.

[Comparative Example 1]
In Example 1, a lithium ion capacitor was produced in the same manner as in Example 1 except that no additive was added to the electrolytic solution, and various evaluations were performed. Table 1 shows the results.

[Comparative Example 2]
Example 1 Example 1 was repeated except that the negative electrode had the same structure as the positive electrode of Example 1 and that no lithium ion supply member was used (that is, lithium ions were not doped into the negative electrode). In the same manner as in the above, a capacitor cell was produced.
The capacitor obtained in Comparative Example 2 was an electric double layer capacitor, and the upper limit of the rated voltage was 1.6 V and the lower limit was 0 V. In the measurement of ΔS _E , the average value at three points of E = 1.6 V, E = 0.8 V, and E = 0 V was obtained. In the evaluation of the cell characteristics, the measurement of the calorific value when charged with a large current, and the cycle test in rapid charging, the evaluation was performed at 0 to 1.6 V. Table 1 shows the evaluation results.

Claims (7)

A capacitor having an average value of the entropy change ΔS _E obtained by the following equation (1) of 82 J / K · mol or more.
Average value of ΔS _E = (ΔS _Ea + ΔS _Eb + ΔS _Ec ) / 3 (1)
[In equation (1), ΔS _Ea , ΔS _Eb, and ΔS _Ec are each calculated by the following equation (1-1). ]
ΔS _E = −n × 9.65 × 10 ⁴ (C / mol) × ΔV ₀ / ΔT (1-1)
[In the formula (1-1),
ΔS _E is any of ΔS _Ea , ΔS _Eb or ΔS _Ec ,
n is the number of charges involved in the electrode reaction,
ΔV ₀ / ΔT is obtained by adjusting a capacitor adjusted at a current value of 10 C so that the voltage of the capacitor becomes E (V) in a 25 ° C. constant temperature bath at a temperature T = 20 ° C., 22 ° C., 24 ° C., 26 ° C., 28 The open circuit voltage V ₀ after leaving each in a constant temperature bath at 30 ° C. or 30 ° C. for a predetermined time was measured, and the measurement results were plotted with the horizontal axis representing T (K) and the vertical axis representing open circuit voltage V ₀ (V). In the graph shown, it means the slope of a straight line obtained by the least squares method.
The ΔS _Ea is an entropy change when the E (V) is set to the “upper limit of the rated voltage”,
The ΔS _Eb is an entropy change when the E (V) is set to “the lower limit of the rated voltage”,
The ΔS _Ec is an entropy change when the E (V) is set to “(the upper limit value + the lower limit value) / 2”.
The predetermined time means a longer time of the following A and B.
A: A capacitor whose voltage has been adjusted to the upper limit of the rated voltage by performing constant-current constant-voltage charging at a current value of 10 C for 24 hours in a 25 ° C. constant temperature bath in a 25 ° C. constant temperature bath. Time (minutes) required for the open circuit voltage to reach the maximum value from the start of standing when left inside
B: 30 minutes when the capacitance of the capacitor is less than 2000F, and capacitance (F) / 2000 × 60 (min) when the capacitance is 2000F or more]   The capacitor according to claim 1, further comprising an electrolyte containing at least one selected from the group consisting of a lithium salt, a sodium salt, a magnesium salt, and an organic onium salt. 3. The capacitor according to claim 1, wherein the average value of the entropy change ΔS _E is 200 J / K · mol or less. 4. A lithium ion capacitor in which the average value of the entropy change ΔS _E obtained by the following equation (1) is 82 J / K · mol or more.
Average value of ΔS _E = (ΔS _3.8 + ΔS _3.0 + ΔS _2.2 ) / 3 (1)
[In equation (1), ΔS _3.8 , ΔS _3.0 and ΔS _2.2 are each calculated by the following equation (1-1). ]
ΔS _E = −9.65 × 10 ⁴ (C / mol) × ΔV ₀ / ΔT (1-1)
[In the formula (1-1),
ΔS _E is any of ΔS _3.8 , ΔS _3.0 or ΔS _2.2 ,
ΔV ₀ / ΔT is obtained by adjusting a lithium ion capacitor adjusted at a current value of 10 C so that the voltage of the lithium ion capacitor becomes E (V) in a thermostat at 25 ° C., at a temperature T = 20 ° C., 22 ° C., 24 ° C. The open circuit voltage V ₀ after being left in a constant temperature bath at 26 ° C., 28 ° C. or 30 ° C. for a predetermined time was measured, and the horizontal axis was T (K), and the vertical axis was the open circuit voltage V ₀ (V). In a graph in which the measurement results are plotted, it means the slope of a straight line obtained by the least squares method.
ΔS _3.8 is an entropy change when the E (V) is set to 3.8 V,
The ΔS _3.0 is an entropy change when the E (V) is set to 3.0 V,
ΔS _2.2 is an entropy change when E (V) is set to 2.2V.
The predetermined time means a longer time of the following A and B.
A: A lithium ion capacitor whose voltage was adjusted to 3.8 V by performing constant current constant voltage charging at a current value of 10 C for 24 hours in a constant temperature bath of 25 ° C. was heated at a constant temperature of 20 ° C. Time (minutes) required for the open circuit voltage to reach the maximum value from the start of standing when left in the bath
B: 30 minutes when the capacitance of the lithium ion capacitor is less than 2000F, and capacitance (F) / 2000 × 60 (min) when the capacitance is 2000F or more]   The lithium ion capacitor according to claim 4, further comprising an electrolytic solution containing lithium fluorophosphate.   The lithium ion capacitor according to claim 5, wherein the electrolyte further includes sultones. The lithium ion capacitor according to claim 4, wherein the average value of the entropy change ΔS _E is 200 J / K · mol or less.