JP2014216452A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device capable of providing high durability and safety by effectively suppressing occurrence of gas generated by decomposition of electrolyte even when excessive discharging is repeated, with high energy density being provided.SOLUTION: A power storage device includes an electrode unit in which a positive electrode where a positive electrode active material layer is formed on a positive electrode collector and a negative electrode in which a negative electrode active material layer is formed on a negative electrode collector are alternately laminated through a separator, and an electrolyte made from aprotic organic solvent electrolyte solution of lithium salt. 0.8≤a/b≤1.0 is satisfied, where, cell capacity a(mAh) is a capacity (available) after discharging from a fully charged state of the power storage device by taking time period of 0.75-1.25 hours down to a half of fully charged voltage, and perfect negative electrode capacity b(mAh) is a capacity available by discharging a negative electrode of a fully charged state of the power storage device down to a state in which a negative electrode potential comes to be 1.5 V(Li/Li).

Description

  The present invention relates to an electricity storage device.

In recent years, an electricity storage device called a hybrid capacitor, which combines the electricity storage principles of a lithium ion secondary battery and an electric double layer capacitor, has attracted attention.
As such a hybrid capacitor, a carbon material capable of inserting and extracting lithium ions is previously occluded and supported (hereinafter also referred to as “dope”) by a chemical method or an electrochemical method so that a negative electrode potential is obtained. An electricity storage device that can obtain a high energy density by lowering has been proposed (see, for example, Patent Document 1 and Patent Document 2). In addition, an electricity storage device (see, for example, Patent Document 3) having a high capacity by specifying the ratio of the positive electrode active material and the negative electrode active material so that the positive electrode potential is 2 V or less by short-circuiting the positive electrode and the negative electrode, The cell capacity when discharged to half the voltage from the state of a was set to a [mAh], and the capacity when the charged negative electrode was discharged to 1.5 V [Li / Li ⁺ ] was set to a complete negative electrode capacity b [mAh]. In some cases, an organic electrolyte capacitor (see, for example, Patent Document 4) in which the ratio between the positive electrode active material and the negative electrode active material is defined so as to satisfy 0.05 ≦ a / b ≦ 0.3 to achieve high output. Proposed.

However, although the above-described hybrid capacitor is expected to increase the output, the negative electrode potential is set to be low in advance, so that overdischarge is repeated and the positive electrode potential is lowered to 2 V or less, for example. In addition, there is a problem in that the electrolyte solution is reduced and decomposed on the surface of the positive electrode to generate gas.
As described above, it is currently difficult to put into practical use an electricity storage device that can be discharged until the cell voltage reaches 0 V while achieving high output, and ensures safety.

Japanese Patent Laid-Open No. 8-1007048 Japanese Patent No. 4015993 JP 2006-286919 A International Publication WO2005 / 031773 Pamphlet

  The present invention has been made based on the above circumstances, and its purpose is to effectively suppress the generation of gas due to the decomposition of the electrolytic solution even when repeated overdischarge is performed while obtaining a high energy density. It is an object of the present invention to provide an electricity storage device that can achieve high durability and safety.

The electricity storage device of the present invention is configured by alternately stacking a positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector and a negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector through separators. An electricity storage device comprising the electrode unit and an electrolyte solution comprising an aprotic organic solvent electrolyte solution of a lithium salt,
The capacity when discharging from the fully charged state of the electricity storage device to half the full charge voltage over 0.75 to 1.25 hours is the cell capacity a (mAh), and the state of the electricity storage device is fully charged When the capacity when the negative electrode is discharged until the negative electrode potential becomes 1.5 V (Li / Li ⁺ ) is defined as the complete negative electrode capacity b (mAh), 0.8 ≦ a / b ≦ 1.0 is satisfied. It is characterized by that.

  In the electricity storage device of the present invention, when the capacity when the negative electrode is constant current-constant voltage charged (CCCV charge) at 0 V for 12 hours is defined as the total negative electrode charge capacity c (mAh), 0.2 ≦ b / It is preferable to satisfy c ≦ 0.9.

  In the electricity storage device of the present invention, the negative electrode active material layer is a heat-treated product of graphite, non-graphitizable carbon, graphite-based composite particles, and aromatic condensation polymer, and the atomic ratio of hydrogen atoms and carbon atoms ( It is preferable that the negative electrode active material which consists of at least 1 chosen from the polyacene type organic semiconductor which has a polyacene type | system | group skeleton structure whose hydrogen atom / carbon atom) is 0.50-0.05 is contained.

  In the electricity storage device of the present invention, it is preferable that the positive electrode current collector and / or the negative electrode current collector have a through hole.

  In the electricity storage device of the present invention, the negative electrode active material layer preferably contains a negative electrode active material capable of reversibly carrying lithium ions and / or anions.

  In the electricity storage device of the present invention, the electrode unit is preferably a stacked type or a wound type.

  The electricity storage device of the present invention is preferably configured as a lithium ion capacitor.

In the electricity storage device of the present invention, it has a positive electrode terminal electrically connected to the positive electrode current collector and a negative electrode terminal electrically connected to the negative electrode current collector,
It is preferable that the positive electrode terminal and the negative electrode terminal are connected to each other through a resistor of 5 to 500Ω and short-circuited.

  In the electricity storage device of the present invention, the ratio a / b of the cell capacity a to the complete negative electrode capacity b is defined within a specific range. Therefore, high durability and safety can be obtained by effectively suppressing the generation of gas even when overdischarge is repeated until the cell voltage reaches 0 V while high energy density is obtained.

Hereinafter, a lithium ion capacitor will be described as a specific example as an electricity storage device of the present invention.
The lithium ion capacitor according to the present invention basically has an electrode unit in which the positive electrode and the negative electrode are alternately stacked or wound via a separator in the outer container. As the outer container, a cylindrical container, a rectangular container, a laminate container, or the like can be appropriately used, and is not particularly limited.
In the lithium ion capacitor according to the present invention, the “positive electrode” means the electrode on the side where current flows out during discharge and the current flows in during charging, and the “negative electrode” refers to the current flowing during discharge. Means the pole on the side where current flows in and current flows out during charging.

  In this specification, “dope” means occlusion, adsorption or insertion, and broadly refers to 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.

  As a method of pre-doping lithium ions in at least one of the negative electrode and the positive electrode, for example, metallic lithium or the like is placed in the capacitor cell as a lithium electrode, A method of doping lithium ions is used.

  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.

  The lithium ion capacitor according to the present invention includes, for example, a positive electrode in which a positive electrode active material layer is formed on a positive electrode current collector, a first separator, a negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector, and a second separator in this order. The electrode unit is configured by winding or laminating, arranging at least one lithium electrode in the surplus portion of the first separator so as not to contact the positive electrode, and short-circuiting the negative electrode current collector and the lithium electrode. After the electrode unit is sealed in a rectangular, cylindrical or laminated outer container, the electrolyte is filled to start doping of lithium ions from the lithium electrode, and the negative electrode active material layer is doped with lithium ions be able to. This constitutes a lithium ion capacitor.

In the lithium ion capacitor according to the present invention, the capacity when the lithium ion capacitor is discharged over a period of 0.75 to 1.25 hours from the fully charged state to the half voltage of the fully charged voltage is the cell capacity a. (MAh) When the fully charged negative electrode of the lithium ion capacitor is discharged until the negative electrode potential becomes 1.5 V (Li / Li ⁺ ), the capacity is defined as a complete negative electrode capacity b (mAh). It has the characteristic of satisfying 0.8 ≦ a / b ≦ 1.0.
Since the ratio a / b of the cell capacity a to the complete negative electrode capacity b is 0.8 or more, even when the cell voltage is discharged to 0 V, the generation of gas is suppressed and the lithium ion capacitor is formed. High safety is obtained. On the other hand, when a / b is less than 0.8, gas is generated when the cell voltage is discharged until it reaches 0 V, and the internal resistance increases, so that high safety cannot be obtained for the lithium ion capacitor. . In the design of the lithium ion capacitor, a / b does not exceed 1.0.

  The cell capacity a can be controlled by adjusting the mass of the positive electrode active material relative to the mass of the negative electrode active material. Specifically, for example, when the thickness of the negative electrode active material layer constituting the negative electrode is constant, the cell capacity a can be increased as the thickness of the positive electrode, that is, the thickness of the positive electrode active material layer is increased.

  The cell capacity a is preferably 400 to 800 mAh, for example.

[Measurement method of cell capacity a]
The cell capacity a is a current value (hereinafter referred to as “current value α”) at which the discharge time is 0.75 to 1.25 hours when discharging from a fully charged state to a voltage half the fully charged voltage. Measured by discharging with. Specifically, first, a lithium ion capacitor is charged at a constant current having a current value α until the cell voltage reaches a set voltage related to full charge, and then a constant current-constant voltage in which the constant voltage of the set voltage is applied. Charging (CCCV charging) is performed for 30 minutes to reach a fully charged state. Next, the battery is discharged from this state at a constant current of a current value α until it becomes half the set voltage, and the capacity measured when this discharge is made the cell capacity a. At this time, the time required for the discharge is 0.75 to 1.25 hours.

  For example, in the case of a lithium ion capacitor assumed to have a cell capacity of about 100 mAh, for example, after charging until the cell voltage reaches 3.8 V at a constant current of 100 mA (current value α), a constant voltage of 3.8 V is obtained. A constant current-constant voltage charge (CCCV charge) for applying a voltage is performed for 30 minutes until a fully charged state is reached, and then the cell voltage reaches 1.9 V at a constant current of 100 mA (current value α) from this state. The cell capacity a can be measured by discharging. The time required for the discharge at this time is about 1 hour. If it is discharged at a constant current of 1000 mA, it depends on the internal resistance of the cell, but the discharge time is about 6 minutes or less, which is much less than 0.75 hours. The capacity a cannot be measured.

  The complete negative electrode capacity b can be controlled by adjusting the amount of lithium ions doped in the negative electrode active material constituting the negative electrode. Specifically, for example, as the thickness of the lithium electrode is increased, the complete negative electrode capacity b can be increased.

  The complete negative electrode capacity b is preferably 400 to 1,000 mAh, for example.

[Measurement method of complete negative electrode capacity b]
The complete negative electrode capacity b of the lithium ion capacitor is the total of the negative electrode capacities obtained by the following measurements for each negative electrode in the fully charged lithium ion capacitor.
The complete negative electrode capacity b is a constant current-constant voltage charge (CCCV charge) in which a lithium ion capacitor is charged at a constant current of a current value α until the cell voltage reaches a set voltage, and then a constant voltage of the set voltage is applied. ) For 30 minutes until fully charged. Next, the fully charged lithium ion capacitor is decomposed in an argon box so that the positive electrode and the negative electrode are not short-circuited, and the negative electrode is taken out. The negative electrode is used as a working electrode, and the counter electrode and the reference electrode are electrodes made of a lithium metal plate. A three-electrode cell for negative electrode capacity measurement is assembled using each plate, and the negative electrode capacity is measured by discharging the negative electrode potential at a constant current of β until the negative electrode potential becomes 1.5 V. b is obtained.
Here, the current value β is a current at which the discharge time is 0.75 to 1.25 hours when discharging to half the voltage of the lithium ion capacitor in a fully charged state. It is the electric current value at the time of discharging the said negative electrode used for the polar cell. When there is only one negative electrode constituting the lithium ion capacitor, the current value β is the same as the current value α, there are a plurality of negative electrodes constituting the lithium ion capacitor, and each negative electrode has the same configuration Is a value obtained by dividing the current value α by the number of negative electrodes.
When three or more negative electrodes are contained in the lithium ion capacitor, a negative electrode other than the negative electrode located at the outermost part is selected and taken out as a negative electrode for producing a three-electrode cell for measuring the negative electrode capacity. Is needed. When two or more negative electrodes are contained in the lithium ion capacitor and each negative electrode has the same configuration, the complete negative electrode capacity b is the negative electrode capacity measured in the three-electrode cell for measuring the negative electrode capacity, It is obtained by multiplying the number of negative electrodes contained in the lithium ion capacitor.

  For example, in the case of a lithium ion capacitor having a cell capacity of 100 mAh and having five negative electrodes of the same configuration, the cell voltage becomes 3.8 V at a constant current of 100 mA (current value α). After charging, constant current-constant voltage charging (CCCV charging) for applying a constant voltage of 3.8 V is performed for 30 minutes until it is fully charged, and then this fully charged lithium ion capacitor is placed in an argon box. Disassemble the positive electrode and the negative electrode so that they do not short-circuit, take out the negative electrode located at the innermost part, use this negative electrode as the working electrode, and use an electrode plate made of a lithium metal plate for the counter electrode and the reference electrode, respectively. A three-electrode cell was assembled, and this was discharged at a constant current of 20 mA (current value β) until the negative electrode potential became 1.5 V. The negative electrode capacity was measured, and this value was multiplied by five to complete. The total negative electrode capacity b can be obtained.

Further, the negative electrode in the lithium ion capacitor according to the present invention has a total negative electrode charge capacity c (mAh) of 0.28 when the negative electrode is charged at a constant current-constant voltage (CCCV) for 12 hours at 0 V. It is preferable to satisfy ≦ b / c ≦ 0.9.
When the ratio b / c of the complete negative electrode capacity b to the total negative electrode charge capacity c is in the above range, a high capacity retention rate is obtained for the lithium ion capacitor and high durability is obtained. On the other hand, if b / c is less than 0.2 or exceeds 0.9, high durability cannot be obtained for the lithium ion capacitor.

  The total negative electrode charge capacity c can be controlled by adjusting the type and mass of the negative electrode active material contained in the negative electrode. Specifically, for example, the total negative electrode charge capacity c can be increased as the mass of the negative electrode active material is increased. For example, when graphite and polyacene organic semiconductor (PAS) are compared with the same weight as the negative electrode active material, the total negative electrode charge capacity c becomes larger when PAS is used.

  The total negative electrode charging capacity c is preferably 400 to 5,000 mAh, for example.

[Measurement method of total negative electrode charge capacity c]
The total negative electrode charge capacity c of the lithium ion capacitor is the total of the negative electrode capacities obtained by the following measurement relating to the respective negative electrodes constituting the lithium ion capacitor.
Specifically, the total negative electrode charge capacity c is first charged by charging a negative electrode capacity measurement tripolar cell for measuring the complete negative electrode capacity b until the negative electrode potential becomes 0 V at a constant current of β. Then, constant current-constant voltage charging (CCCV charging) for applying a constant voltage of 0 V is performed for 12 hours, and the negative electrode capacity at this time is measured, whereby the total negative electrode charging capacity c is obtained.
When a plurality of negative electrodes are contained in the lithium ion capacitor and each negative electrode has the same configuration, the total negative electrode charge capacity c is the negative electrode capacity measured in the three-electrode cell for negative electrode capacity measurement. It is obtained by multiplying the number of negative electrodes contained in the lithium ion capacitor.

  In the lithium ion capacitor according to the present invention, when the cell voltage is set to 0 V, a positive electrode terminal electrically connected to the positive electrode current collector, and a negative electrode terminal electrically connected to the negative electrode current collector Are preferably connected and short-circuited via a resistor of 5 to 500Ω. By doing so, the cell voltage can be set to 0 V simply and quickly with high safety. When the positive electrode terminal and the negative electrode terminal are connected via a resistance exceeding 500Ω, a long time is required until the cell voltage reaches 0V. In addition, it is dangerous to connect via a resistance lower than 5Ω because a large current is generated at the time of short circuit.

  Below, each component which comprises the lithium ion capacitor which concerns on this invention is demonstrated.

[Current collector]
The positive electrode and the negative electrode are respectively provided with a positive electrode current collector and a negative electrode current collector that receive and distribute electricity. As such a positive electrode current collector and a negative electrode current collector, it is preferable to use a current collector in which through holes are formed. The form and number of through holes in the positive electrode current collector and the negative electrode current collector are not particularly limited, and lithium ions and electrolysis supplied electrochemically from a lithium electrode arranged to face at least one of the positive electrode and the negative electrode It can set so that the lithium ion in a liquid can move between the front and back of an electrode, without interrupted | blocked by each electrode electrical power collector.

[Positive electrode current collector]
As the positive electrode current collector, a porous current collector having through holes can be used.
As the positive electrode current collector having a through hole, for example, the back surface is obtained by laser processing such as expanded metal, punching metal, CO ₂ laser, YAG laser or UV laser in which a through hole penetrating the back surface is formed by mechanical implantation. It is possible to use a current collector in which a through-hole penetrating through is formed.

  As the material of the positive electrode current collector, aluminum, stainless steel, or the like can be used, and aluminum is particularly preferable. Moreover, the thickness of the positive electrode current collector is not particularly limited, but may be usually 1 to 50 μm, preferably 5 to 40 μm, and particularly preferably 10 to 40 μm.

The porosity (%) of the through holes of the positive electrode current collector is preferably 20 to 50%, and more preferably 20 to 40%. Here, the porosity (%) of the positive electrode current collector can be obtained by the following formula (1).
Formula (1): Porosity (%) = [1- (mass of positive electrode current collector / true specific gravity of positive electrode current collector) / (apparent volume of positive electrode current collector)] × 100

[Positive electrode active material]
As the positive electrode active material, a material capable of reversibly doping and dedoping at least one kind of anion such as lithium ion and tetrafluoroborate is used, and examples thereof include activated carbon powder. The specific surface area of the activated carbon is preferably 1900m ² / g~3000m ² / g, further preferably a 1950m ² / g~2800m ² / g. In addition, the 50% volume cumulative diameter (D50) of the activated carbon is preferably 2 μm to 8 μm, particularly preferably 2 μm to 5 μm, from the viewpoint of the packing density of the activated carbon. When the specific surface area and 50% volume cumulative diameter (D50) of the activated carbon are in the above ranges, the energy density of the lithium ion capacitor can be further improved. Here, the value of the 50% volume cumulative diameter (D50) is obtained by, for example, the microtrack method.

[Positive electrode active material layer]
The positive electrode active material layer is formed by attaching the positive electrode active material to the positive electrode current collector by coating, printing, injection, spraying, vapor deposition, pressure bonding, or the like. The positive electrode active material layer may have a thickness of one surface of 20 to 500 μm, preferably 25 to 350 μm, and more preferably 25 to 250 μm. By setting the thickness of the positive electrode active material layer in the above range, the diffusion resistance of ions moving in the positive electrode active material layer can be reduced, and thereby the internal resistance can be lowered. Since the positive electrode capacity can be increased, the cell capacity can be increased, and as a result, the capacity of the lithium ion capacitor can be increased.

[Negative electrode current collector]
As the negative electrode current collector, stainless steel, copper, nickel, or the like can be used. Although the thickness of a negative electrode collector is not specifically limited, Usually, what is necessary is just 1-50 micrometers, it is preferable that it is 5-40 micrometers, and it is especially preferable that it is 10-30 micrometers.

The hole diameter of the through-hole of the negative electrode current collector is, for example, 0.5 to 400 μm, preferably 0.5 to 350 μm, and particularly preferably 1 to 330 μm.
Further, the porosity (%) of the through holes of the negative electrode current collector is preferably 20 to 70%, and more preferably 20 to 60%. Here, the porosity (%) of the negative electrode current collector can be obtained by the following formula (2).
Formula (2): Porosity (%) = [1- (Mass of negative electrode current collector / true specific gravity of negative electrode current collector) / (apparent volume of negative electrode current collector)] × 100

[Negative electrode active material]
As the negative electrode active material, graphite-based particles are used among materials that can be reversibly doped and dedoped with lithium ions. Specifically, graphite-based composite particles in which the surface of core particles made of graphite, non-graphitizable carbon, or natural graphite is coated with a graphitized substance derived from tar or pitch, and a heat-treated product of an aromatic condensation polymer. And at least one selected from polyacene-based organic semiconductors (PAS) having a polyacene-based skeleton structure in which the number ratio of hydrogen atoms to carbon atoms (hydrogen atom / carbon atom) is 0.50 to 0.05. Is preferred. In PAS, when the atomic ratio of hydrogen atoms to carbon atoms exceeds 0.50, the electronic conductivity of the PAS is lowered, and thus the internal resistance of the cell may be lowered. On the other hand, if it is less than 0.05, the capacity per unit weight is lowered, and therefore the energy density of the cell may be lowered.
Here, the aromatic condensation polymer refers to a condensate of an aromatic hydrocarbon compound and aldehydes. Examples of the aromatic hydrocarbon compound include phenol, cresol, and xylenol, and examples of the aldehyde include formaldehyde, acetaldehyde, and furfural.

As the negative electrode active material, it is preferable to use graphite-based particles having a 50% volume cumulative diameter (D50) in the range of 1.0 to 10 μm from the viewpoint of improving output, and 50% volume cumulative diameter (D50). Is more preferable in the range of 2 to 5 μm. Graphite-based particles having a 50% volume cumulative diameter (D50) of less than 1.0 μm are difficult to produce, and the durability may be reduced due to gas generation during charging. On the other hand, with graphite-based particles having a 50% volume cumulative diameter (D50) exceeding 10 μm, it is difficult to obtain a lithium ion capacitor having a sufficiently low internal resistance. Moreover, the negative electrode active material preferably has a specific surface area of 0.1~200m ² / g, more preferably 0.5~50m ² / g. When the specific surface area of the negative electrode active material is less than 0.1 m ² / g, the resistance of the obtained lithium ion capacitor is increased, while when the specific surface area of the negative electrode active material exceeds 200 m ² / g, The irreversible capacity at the time of charging of the obtained lithium ion capacitor becomes high, and there is a possibility that durability may be lowered due to generation of gas at the time of charging.
In the above, the 50% volume cumulative diameter (D50) of the graphite-based particles is a value determined by, for example, the microtrack method.

[Negative electrode active material layer]
The negative electrode active material layer is formed by adhering the negative electrode active material to the negative electrode current collector by coating, printing, injection, spraying, vapor deposition, pressure bonding, or the like. The preferred range of the thickness of the negative electrode active material layer varies depending on the balance with the mass of the positive electrode active material layer, but the thickness on one side may be 10 to 80 μm, preferably 10 to 65 μm, and preferably 10 to 50 μm. It is more preferable that By making the layer thickness of the negative electrode active material layer in the above range, the required negative electrode capacity can be secured, and the diffusion resistance of ions moving in the negative electrode active material layer can be reduced. The internal resistance can be lowered.

  The amount of lithium ions doped into the negative electrode is determined in consideration of the capacitance, internal resistance and durability required for the electricity storage device. In particular, in order to set the cell capacity a, the complete negative electrode capacity b, and the total negative electrode charge capacity c within a predetermined range, for example, 100 to 800 mAh is preferable.

[Binder]
The positive electrode having the positive electrode active material layer and the negative electrode having the negative electrode active material layer as described above can be produced by a known method that is usually used.
For example, each electrode (positive electrode or negative electrode) includes each active material powder (positive electrode active material or negative electrode active material), a binder, and, if necessary, a conductive material, a thickener such as carboxymethyl cellulose (CMC), The slurry can be produced by mixing with water or an organic solvent and applying the resulting slurry to a current collector, or by forming the slurry into a sheet and sticking it to the current collector.

In the production of each of the above electrodes, as the binder, for example, a rubber-based binder such as SBR, a fluorine-containing resin obtained by seed polymerization of polytetrafluoroethylene, polyvinylidene fluoride, or the like with an acrylic resin, an acrylic resin, or the like is used. Can be used.
Examples of the conductive material include acetylene black, ketjen black, graphite, and metal powder.
The amount of each of the binder and the conductive material added varies depending on the electrical conductivity of the active material to be used, the shape of the electrode to be produced, and the like. .

[Separator]
As a separator in the lithium ion capacitor according to the present invention, a material having an air permeability measured by a method according to JISP8117 in a range of 1 to 200 sec can be used. Specifically, for example, polyethylene, polypropylene, A nonwoven fabric composed of polyester, cellulose, polyolefin, cellulose / rayon, or the like, or a microporous membrane can be appropriately selected and used, and it is particularly preferable to use a nonwoven fabric made of polyethylene, polypropylene, or cellulose / rayon.
The thickness of a separator is 1-100 micrometers, for example, and it is preferable that it is 5-50 micrometers.

[Electrolyte]
In the lithium ion capacitor according to the present invention, an aprotic organic solvent electrolyte solution of a lithium salt is used as the electrolytic solution.

[Aprotic organic solvent of electrolyte]
Examples of the aprotic organic solvent constituting the electrolytic solution include ethylene carbonate (hereinafter also referred to as “EC”), propylene carbonate (hereinafter also referred to as “PC”), cyclic carbonates such as butylene carbonate, and dimethyl carbonate. (Hereinafter also referred to as “DMC”), chain carbonates such as ethyl methyl carbonate (hereinafter also referred to as “EMC”), diethyl carbonate (hereinafter also referred to as “DEC”), and methylpropyl carbonate. You may use the mixed solvent which mixed 2 or more types of these.

  In the present invention, the aprotic organic solvent constituting the electrolytic solution is an organic solvent other than cyclic carbonate and chain carbonate, for example, cyclic ester such as γ-butyrolactone, cyclic sulfone such as sulfolane, cyclic ether such as dioxolane, propionic acid, etc. It may contain a chain carboxylic acid ester such as ethyl and a chain ether such as dimethoxyethane.

〔Electrolytes〕
Examples of the lithium salt of the electrolyte in the electrolytic solution include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , Li (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _2, etc. LiPF ₆ is preferably used because of its high ion conductivity and low resistance. The concentration of the lithium salt in the electrolytic solution is preferably 0.1 mol / L or more, more preferably 0.5 to 1.5 mol / L, because low internal resistance is obtained.

[Structure of lithium ion capacitor]
As the lithium ion capacitor structure according to the present invention, in particular, three or more layers each of a wound-type, plate-shaped or sheet-shaped positive electrode and negative electrode in which a belt-like positive electrode and a negative electrode are wound through a separator via a separator. Examples of the laminated type include a laminated type, and a laminated type in which units having such a laminated structure are enclosed in an outer film or a rectangular outer can.
These capacitor structures are known from Japanese Patent Application Laid-Open No. 2004-266091 and the like, and can be configured similarly to those capacitors.

As mentioned above, although embodiment of this invention was described concretely, embodiment of this invention is not limited to said example, A various change can be added.
For example, the electricity storage device of the present invention is not limited to a wound or stacked lithium ion capacitor, and can be suitably applied to an electric double layer capacitor, a lithium ion secondary battery, and other electricity storage devices.

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

[Example 1: Cell production example 1]
(1) Production of positive electrode A conductive paint is applied to both sides of a current collector material made of aluminum electrolytic etching foil having a pore diameter of 1 μm and a thickness of 30 μm, and a coating width is set using a vertical die type double-side coating machine. Under the coating conditions of 100 mm and a coating speed of 8 m / min, the coating thickness target value on both sides is set to 10 μm, and after coating on both sides, drying is performed under reduced pressure to conduct electricity on the front and back surfaces of the positive electrode current collector. A layer was formed.
Next, a slurry containing activated carbon particles (positive electrode active material) having a number average particle diameter D50 of 3 μm on the conductive layers formed on the front and back surfaces of the positive electrode current collector is a vertical die type double-side coating machine. , And the coating thickness of 8 m / min is applied on both sides with the target value of the combined thickness (total thickness) set to 471 μm. A positive electrode active material layer as a layer was formed.
The portion obtained by laminating the conductive layer and electrode layer of the positive electrode current collector thus obtained (hereinafter also referred to as “coating portion” for the positive electrode) is 60 mm × 80 mm, and no layers are formed. The electrode layer is formed on both surfaces of the positive electrode current collector by cutting into a size of 60 mm × 95 mm so that the portion (hereinafter also referred to as “uncoated part” for the positive electrode) is 60 mm × 15 mm. A positive electrode was produced. The thickness of the positive electrode including the thickness of the current collector was 471 μm.

(2) Production of negative electrode Pitch coat the surface of graphite with a number average particle diameter D50 of 6 μm on both sides of a negative electrode current collector made of a copper chemical etching foil with a through-hole diameter of 300 μm, a porosity of 55%, and a thickness of 25 μm. The slurry containing the graphite-based composite particles (1) (negative electrode active material) and SBR binder (manufactured by JSR Corporation: TRD2001) is applied to a coating width of 100 mm using a vertical die type double-side coating machine. By setting the target value of the coating thickness (total thickness) on both sides to 117 μm under the coating conditions with a working speed of 8 m / min, applying both sides, and drying under reduced pressure, the front and back surfaces of the negative electrode current collector A negative electrode active material layer as an electrode layer was formed.
The portion where the electrode layer of the negative electrode current collector thus obtained (hereinafter also referred to as “coating portion” for the negative electrode) is 65 mm × 85 mm, and the portion where the electrode layer is not formed (hereinafter, A negative electrode having electrode layers formed on both sides of a negative electrode current collector was prepared by cutting into a size of 65 mm × 100 mm so that the negative electrode was also referred to as an “uncoated part”. . The thickness of the negative electrode including the thickness of the current collector was 117 μm.

(3) Production of Separator A film made of a cellulose / rayon composite material having a thickness of 35 μm and an air permeability of 100 sec was cut into 70 mm × 91 mm to produce a separator.

(4) Production of Lithium Ion Capacitor Element First, 7 positive electrodes, 8 negative electrodes, and 16 separators are prepared, and the positive electrode and the negative electrode are overlapped on each other, but the respective uncoated portions are on the opposite side. In order 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 stack were fixed with a tape to produce an electrode laminate unit.
Next, a lithium ion supply member is produced by cutting the foil-like lithium metal having a thickness of 44 μm so that the area of the lithium metal is 65 mm × 85 mm and pressing it onto a copper foil having a thickness of 25 μm (manufactured by Nippon Foil Co., Ltd.). And this lithium ion supply member was arrange | positioned so that the negative electrode might be opposed to the upper side of an electrode lamination | stacking unit.
For the positive electrode made of aluminum having a width of 50 mm, a length of 50 mm, and a thickness of 0.15 mm in which a sealant film is heat-sealed in advance to the uncoated portion of each of the seven positive electrodes of the produced electrode laminate unit. The power tabs were stacked and welded. On the other hand, each of the eight negative electrodes of the electrode laminate unit, each of the uncoated portion and the lithium ion supply member, having a width of 50 mm, a length of 50 mm, and a thickness of 0.2 mm, in which a sealant film is heat-sealed to the seal portion in advance. A copper negative electrode power tab was stacked and welded. Thereby, a lithium ion capacitor element was obtained.

(5) Production of Lithium Ion Capacitor A polypropylene layer, an aluminum layer, and a nylon layer are laminated, the dimensions are 90 mm (length) x 117 mm (width) x 0.15 mm (thickness), and 70 mm (length) x in the center portion 97 mm (horizontal width) one exterior film and polypropylene layer, aluminum layer and nylon layer are laminated, and the other dimension is 90 mm (vertical width) x 117 mm (horizontal width) x 0.15 mm (thickness) An exterior film was prepared.

Next, the positive electrode terminal and the negative electrode terminal of the electrode laminate unit project outward from the end portion of the other exterior film at the position serving as the housing portion on the other exterior film. 1 outer film is placed on this electrode laminate unit, and three sides (including two sides from which the positive electrode terminal and the negative electrode terminal protrude) are heat-melted on one outer film and the other outer film. I wore it.
On the other hand, an electrolytic solution containing LiPF ₆ having a concentration of 1.2 mol / L was prepared using a mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate (3: 1: 4 by volume) as an aprotic organic solvent.
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. 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.
As described above, a test laminate external lithium ion capacitor (hereinafter referred to as “cell 1”) was produced.
A total of three similar cells 1 were produced.

[Evaluation of cell performance]
About the obtained cell 1, while measuring the cell capacity | capacitance a, the complete negative electrode capacity | capacitance b, the total negative electrode charge capacity | capacitance c, and an energy density as follows, an overdischarge test and a durability test were done, and the characteristic was evaluated. It was.

(I) Measurement of cell capacity a and calculation of energy density After charging one cell 1 at a constant current of 0.4 A (current value α) until the cell voltage becomes 3.8 V, 3.8 V The charging / discharging operation of discharging until the cell voltage became 1.9 V at a constant current of 0.4 A was repeated 5 times after performing the constant voltage charging for 30 minutes. The capacity at the time of discharge in the fifth charge / discharge operation was defined as cell capacity a. Table 1 shows the cell capacity a. The time required for the discharge in the fifth charge / discharge operation was 1.04 hours.
Table 1 shows a value obtained by dividing the product of the obtained cell capacity a and the average cell voltage by the volume of the cell 1 as energy density ED (Wh / L).

(Ii) Measurement of complete negative electrode capacity b After measurement of the above cell capacity a, the cell 1 is charged with a constant current of 0.4 A until the cell voltage becomes 3.8 V, and then charged with a constant voltage of 3.8 V. Fully charged by going for 30 minutes. The fully charged cell 1 is disassembled to take out the negative electrode, and a negative electrode capacity measurement cell using a lithium metal plate as a counter electrode is assembled. The negative electrode potential is 1.5 V (Li / Li ⁺⁾ at a constant current of 50 mA. The value obtained by multiplying the negative electrode capacity by 8 (the number of negative electrodes) when discharged until the complete negative electrode capacity b was obtained. Table 1 shows the complete negative electrode capacity b.

(Iii) Measurement of the total negative electrode charge capacity c For the negative electrode capacity measurement cell, after the measurement of the complete negative electrode capacity b, the cell voltage was measured at a constant current of 0.4 A in the same manner as the measurement of the cell capacity a. Was charged until the voltage became 0 V, and then constant voltage charging at 0 V was performed for 12 hours. A value obtained by multiplying the negative electrode capacity at this time by 8 (the number of negative electrodes) was defined as a total negative electrode charge capacity c. Table 1 shows the total negative electrode charge capacity c.

(Iv) Overdischarge test Another cell 1 is discharged at a constant current of 4A until the cell voltage reaches 0V, and then charged at a constant current of 4A until the cell voltage reaches 3.8V. The overdischarge cycle was repeated 5 times. After the overdischarge cycle, the presence or absence of gas generation was confirmed. Table 1 shows the case where gas is generated as “X” and the case where gas is not generated as “◯”.

(V) Durability test After charging another one of the cells 1 at a constant current of 4A until the cell voltage becomes 3.8V, the cell voltage becomes 2.85V at a constant current of 4A. The cycle test was repeated 10,000 times for the charge / discharge cycle to discharge up to. The ratio of the capacity at the 10,000th cycle to the capacity at the first cycle in this cycle test is shown in Table 1 as a capacity retention rate. Table 1 shows “◯” when the capacity retention rate is 90% or more, “Δ” when 80% or more and less than 90%, and “X” when less than 80%.

[Examples 2 to 10 and Comparative Examples 1 and 2: Cell Production Examples 2 to 12]
In Example 1 of the cell of Example 1, the thickness of the positive electrode active material layer was changed to change the thickness of the positive electrode as shown in Table 1, and the lithium metal thickness was changed according to Table 1 in the same manner. Thus, three cells 2 to 12 were produced. In addition, with respect to the lithium metal whose thickness is 30 micrometers or less, it adjusted to predetermined thickness by vacuum deposition on copper foil.
For these cells 2 to 12, in the same manner as in Example 1, the cell capacity a, the complete negative electrode capacity b, the total negative electrode charge capacity c and the energy density were measured, and an overdischarge test and a durability test were performed. Was evaluated. However, the current value α in the measurement of the cell capacity a, the complete negative electrode capacity b, the total negative electrode charge capacity c, and the energy density was as shown in Table 1. In addition, the current value related to charging / discharging in the overdischarge test and the durability test was set to a value 10 times the current value α used for measuring the cell capacity a shown in Table 1.
In the measurement of the cell capacity a, the time required for discharging was within 0.75 to 1.25 hours.
The results are shown in Table 1.

Example 11
Four cells similar to Example 1 were prototyped, fully charged and connected to resistors of 1Ω, 5Ω, 100Ω, and 500Ω, respectively, short-circuited, and allowed to stand for 1 day, and then the cell voltage was measured. The cell connected to the 100Ω resistor had dropped to 1V or less, but the cell connected to the 500Ω resistor had a voltage of about 2V, and it took a long time to reduce the voltage. I understood that. Also, since a slight spark occurred when connecting a 1Ω resistor, a large current flows when the resistance value is small.

As apparent from the results in Table 1, according to the cell satisfying 0.8 ≦ a / b ≦ 1.0, the generation of gas is suppressed even when the overdischarge is repeated until the cell voltage reaches 0V. It was confirmed that Further, it was confirmed that high durability can be obtained according to the cell satisfying 0.2 ≦ b / c ≦ 0.9.

Claims (8)

An electrode unit in which a positive electrode having a positive electrode active material layer formed on a positive electrode current collector and a negative electrode having a negative electrode active material layer formed on a negative electrode current collector are alternately stacked via a separator; and lithium An electricity storage device comprising an electrolyte solution comprising an aprotic organic solvent electrolyte solution of a salt,
The capacity when discharging from the fully charged state of the electricity storage device to half the full charge voltage over 0.75 to 1.25 hours is the cell capacity a (mAh), and the state of the electricity storage device is fully charged When the capacity when the negative electrode is discharged until the negative electrode potential becomes 1.5 V (Li / Li ⁺ ) is defined as the complete negative electrode capacity b (mAh), 0.8 ≦ a / b ≦ 1.0 is satisfied. An electricity storage device characterized by the above.   When the negative electrode is charged with constant current-constant voltage (CCCV charge) for 12 hours at 0 V, the total negative electrode charge capacity c (mAh) is satisfied, and 0.2 ≦ b / c ≦ 0.9 is satisfied. The power storage device according to claim 1.   The negative electrode active material layer is a heat-treated product of graphite, non-graphitizable carbon, graphite-based composite particles, and aromatic condensation polymer, and the atomic ratio of hydrogen atoms to carbon atoms (hydrogen atoms / carbon atoms) is 0 3. The electricity storage device according to claim 1, comprising a negative electrode active material composed of at least one selected from polyacene organic semiconductors having a polyacene skeleton structure of .50 to 0.05.   The power storage device according to any one of claims 1 to 3, wherein the positive electrode current collector and / or the negative electrode current collector have a through hole.   The power storage device according to any one of claims 1 to 4, wherein the negative electrode active material layer contains a negative electrode active material capable of reversibly supporting lithium ions and / or anions. .   The power storage device according to claim 1, wherein the electrode unit is a stacked type or a wound type.   It is comprised as a lithium ion capacitor, The electrical storage device of any one of Claims 1-6 characterized by the above-mentioned. A positive electrode terminal electrically connected to the positive electrode current collector and a negative electrode terminal electrically connected to the negative electrode current collector;
The power storage device according to any one of claims 1 to 7, wherein the positive electrode terminal and the negative electrode terminal are connected to each other through a resistor of 5 to 500Ω and short-circuited.