WO2015005294A1

WO2015005294A1 - Power storage device

Info

Publication number: WO2015005294A1
Application number: PCT/JP2014/068090
Authority: WO
Inventors: 照明手塚; 信雄安東
Original assignee: Ｊｍエナジー株式会社
Priority date: 2013-07-12
Filing date: 2014-07-07
Publication date: 2015-01-15
Also published as: JP6487841B2; JPWO2015005294A1

Abstract

　Provided is a power storage device having high energy density, low resistance, and high durability. A power storage device provided with: an electrode unit in which a positive electrode on which a positive-electrode active-substance layer is formed and a negative electrode on which a negative-electrode active-substance layer is formed are layered in alternating fashion interposed by a separator, and an electrolyte made from an aprotic organic solvent electrolyte solution of a lithium salt. The expressions 0.35 ≤ a/b ≤ 0.95, 0.55 ≤ b/c ≤ 1.00, and 0.35 ≤ a/c ≤ 0.55 hold, where a is the cell capacity (mAh) when the power storage device is discharged from a fully charged state to a voltage that is half the fully charged voltage in 0.75 to 1.25 hours, b is the full negative-electrode capacity (mAh) when the negative electrode in the fully charged state is discharged to the point at which the negative electrode potential reaches 1.5 V (Li/Li⁺), and c is the total negative-electrode charge capacity (mAh) when the negative electrode at 0V is subjected to constant current, constant voltage (CCCV) charging over 12 hours. The electrode density of the positive-electrode active-substance layer is 0.54-0.7 g/cm³, and the electrode weight of the positive-electrode active-substance layer is 70-110 g/m².

Description

Power storage device

The present invention relates to an electricity storage device having high energy density, high output, and durability.

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.
In 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 to lower the negative electrode potential. Therefore, an electricity storage device that can obtain a high energy density has been proposed (see, for example, Patent Document 1). Also, the cell capacity when discharging from a fully charged state to half the voltage is a [mAh], and the capacity when the charged negative electrode is discharged to 1.5 V [Li / Li ⁺ ] is the complete negative electrode capacity b [ mAh], the ratio of the positive electrode active material and the negative electrode active material is regulated so as to satisfy 0.05 ≦ a / b ≦ 0.3, and an organic electrolyte capacitor with a high output (for example, patent document) 2) is also proposed.

However, when it is configured to increase the output as in Patent Document 2, the energy density is higher than that of the electric double layer capacitor, but the result is that the energy density is lower in a general lithium ion capacitor. .
Moreover, when the positive electrode active material weight is increased as in Patent Document 1, a lithium ion capacitor having a high energy density can be obtained. As described above, when the weight of the positive electrode active material is increased, the resistance at the end of discharge is increased, so that the rate characteristic is lowered and the cycle characteristic is deteriorated as compared with the conventional capacitor. The reason for this is that the load on the negative electrode is increased. If charging and discharging are repeated, it is considered that the decrease in cell capacity is accelerated due to the consumption of lithium ions in the negative electrode active material. That is, there is a trade-off relationship between higher output and higher energy density, and it has been difficult to maintain a good balance of the performance of the electricity storage device.

Japanese Patent No. 4015993 International Publication WO2005 / 031773 Pamphlet

The present invention has been made based on the above circumstances, and an object thereof is to provide a power storage device having high energy density, high output, and durability.

The inventors of the present invention have studied to achieve the above object, and have reached the present invention having the following constitution.
(1) 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 laminated via separators And an electrolytic device comprising an aprotic organic solvent solution of a lithium salt,
The capacity when the battery is discharged from 0.75 hours to 1.25 hours from the fully charged state of the storage device to half the full charge voltage is defined as the cell capacity a (mAh). The capacity when the negative electrode was discharged until the negative electrode potential became 1.5 V (Li / Li ⁺ ) was defined as the complete negative electrode capacity b (mAh), and the negative electrode was charged with constant current-constant voltage at 0 V for 12 hours. (CCCV charge) When the total negative electrode charge capacity c (mAh) is assumed, the capacity is 0.35 ≦ a / b ≦ 0.95, 0.55 ≦ b / c ≦ 1.00, 0.35 ≦ a / c ≦ 0.55 is satisfied, the electrode density of the positive electrode active material layer is 0.54 g / cm ³ to 0.7 g / cm ³ , and the electrode weight per unit area of the positive electrode active material layer is 70 g / m ² to An electricity storage device, which is 110 g / m ² .

(2) The electricity storage device according to (1), wherein the negative electrode active material layer includes graphite-based particles.
(3) The electricity storage device according to (1) or (2), wherein the positive electrode active material layer includes activated carbon.
(4) The electricity storage device according to any one of (1) to (3), wherein the separator has a thickness of 5 μm to 20 μm.
(5) The electricity storage device according to any one of (1) to (4), wherein the positive electrode current collector and / or the negative electrode current collector have a through hole.
(6) The electricity storage device according to any one of (1) to (5), wherein the electrode unit is a laminated type or a wound type.
(7) The electricity storage device according to any one of (1) to (6), wherein the negative electrode is a negative electrode doped with lithium ions in advance.
(8) The electricity storage device according to any one of (1) to (7), wherein the electricity storage device is a lithium ion capacitor.
(9) The electricity storage device according to (8), wherein the energy density is 31.5 Wh / L or more.

According to the electricity storage device of the present invention, for example, a lithium ion capacitor, a lithium ion secondary battery, high durability is obtained without deterioration even when the load on the negative electrode is increased, high energy density is obtained, and high output Characteristics are obtained.

The electricity storage device of 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 shape, a rectangular shape, a laminate shape, or the like can be appropriately used, and is not particularly limited.
In the electricity storage device of the present invention, “positive electrode” means the electrode on the side where current flows out during discharging and current flows in during charging, and “negative electrode” refers to current flowing in during discharging. It means the pole on the side where current flows out during charging.

In this specification, “dope” means occlusion, adsorption or insertion, and 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. Further, “de-doping” means desorption and release, and refers to a phenomenon in which lithium ions or anions are desorbed from the positive electrode active material, or a phenomenon in which lithium ions are desorbed from the negative electrode active material.

In the electricity storage device of the present invention, it is preferable that at least one of the negative electrode and the positive electrode is previously doped with lithium ions. More preferably, the negative electrode is pre-doped with lithium ions.
As a method of pre-doping lithium ions into at least one of the negative electrode and the positive electrode, for example, metallic lithium or the like is disposed in the electricity storage device as a lithium electrode, and the lithium is contacted by electrochemical contact between at least one of the negative electrode and the positive electrode and the lithium electrode. A method of doping ions is used.

In the electricity storage device of the present invention, lithium ions can be uniformly doped into at least one of the negative electrode and the positive electrode also by locally arranging the lithium electrode in the cell and bringing it into electrochemical contact.

The electricity storage device of 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 having holes penetrating the front and back surfaces, a first separator, and a negative electrode current collector having holes penetrating the front and back surfaces. A negative electrode on which a negative electrode active material layer is formed, and a second separator are wound or laminated in this order, and at least one lithium electrode is disposed in an excess portion of the first separator so as not to contact the positive electrode, A lithium electrode is short-circuited to constitute an electrode unit. 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. Thereby, an electrical storage device is comprised.

Specific examples of the electricity storage device of the present invention include a lithium ion capacitor and a lithium ion secondary battery. Among these, a lithium ion capacitor is preferable.

In the present invention, the lithium ion capacitor means an electricity storage device containing lithium ions in which the positive electrode is a polarizable electrode and the negative electrode is a non-polarizable electrode.
As a positive electrode material of a lithium ion capacitor, a material having a large specific surface area such as activated carbon or polyacene is preferably used, and as a negative electrode material, the surface of core particles made of graphite, non-graphitizable carbon, or natural graphite is derived from tar or pitch. Graphite-based composite particles coated with a graphitized material and a heat-treated product of an aromatic condensation polymer having a hydrogen atom / carbon atom number ratio (hydrogen atom / carbon atom) of 0.50 to 0.00. A carbonaceous material such as a polyacene organic semiconductor (PAS) having a polyacene skeleton structure of 05, a metal oxide such as lithium titanate, a metal alloy such as silicon or tin is preferably used. As the lithium ion capacitor, the negative electrode is preferably a negative electrode doped with lithium ions in advance. A lithium ion capacitor in which the negative electrode is a negative electrode doped with lithium ions in advance is preferable because the use of the electricity storage device can be started from the charging operation. The lithium ion capacitor of the present invention preferably has an energy density of 31.5 Wh / L or more, and more preferably 33 Wh / L or more.

In the present invention, the lithium ion secondary battery means an electricity storage device containing lithium ions in which the positive electrode and the negative electrode are non-polarizable electrodes. As the positive electrode material of the lithium ion secondary battery, transition metal composite oxides such as lithium cobaltate and lithium iron phosphate are preferably used. As the negative electrode material, carbonaceous materials such as graphite and non-graphitizable carbon, metal oxides such as lithium titanate, metal alloys such as silicon and tin are preferably used.

In the electricity storage device of the present invention, the capacity when discharging from the fully charged state of the electricity storage device to half the full charge voltage over 0.75 hours to 1.25 hours is defined as a cell capacity a (mAh), The capacity when the negative electrode in a fully charged state of the electricity storage device was discharged until the negative electrode potential reached 1.5 V (Li / Li ⁺ ) was defined as the complete negative electrode capacity b (mAh), and the negative electrode was kept at 0 V for 12 hours. If the total negative charge capacity c (mAh) is constant current-constant voltage charge (CCCV charge) over 0.35 ≦ a / b ≦ 0.95, 0.55 ≦ b / c ≦ 1. 00, 0.35 ≦ a / c ≦ 0.55, the electrode density of the positive electrode active material layer is 0.54 g / cm ³ to 0.7 g / cm ³ , and the electrode weight per unit area of the positive electrode active material layer having a characteristic that but a ^{^{70g / m 2 ~ 110g / m}} 2 .

In the present invention, the state of full charge of the electricity storage device means a state of charge arbitrarily set within the range of the maximum voltage that can be used over a long period of time without causing problems such as gas generation and resistance increase. The fully charged voltage of the electricity storage device depends on the type of the electricity storage device, the material configuration of the positive and negative electrodes, and the electrolyte composition. In a lithium ion capacitor, the full charge voltage is about 3.6V to 4.0V, and in the lithium ion secondary battery, the full charge voltage is about 4.1V to 4.5V. In a lithium ion capacitor and a lithium ion secondary battery, the potential of the negative electrode is preferably 0.2 V (Li / Li ⁺ ) or less, and 0.1 V (Li / Li ⁺ ) or less when fully charged. Is more preferable. Application of a voltage higher than the fully charged voltage is not preferable because it causes deterioration of the electricity storage device.

The cell capacity a varies depending on the cell size, but can be controlled by adjusting the mass of the positive electrode active material relative to the mass of the negative electrode active material when a positive electrode active material and a negative electrode active material having a predetermined capacity are used. Specifically, for example, when the basis weight of the negative electrode active material layer constituting the negative electrode is constant, the cell capacity a can be increased as the basis weight of the positive electrode active material layer is increased.

[Measurement method of cell capacity a]
The cell capacity a is a current value (hereinafter referred to as a “current value α”) at which the discharge time is 0.75 hours to 1.25 hours when discharging from a fully charged state to half the full charged voltage. ) Measured by discharging. Specifically, first, the power storage device 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 charge in which the constant voltage of the set voltage is applied. (CCCV charge) is performed for 30 minutes until the battery is fully charged. Next, the battery is discharged from this state at a constant current of a current value α until it becomes half the set voltage. By repeating this charge / discharge five times, the storage device is brought into a steady state, and the capacity measured when the battery is discharged for the fifth time is defined as the cell capacity a.

For example, in the case of a power storage device having a cell capacity of about 200 mAh, for example, a constant voltage of 3.8 V is charged after charging the cell voltage to 3.8 V with a constant current of 200 mA (current value α). A constant current-constant voltage charge (CCCV charge) is applied for 30 minutes to achieve a fully charged state, and then the battery is discharged from this state at a constant current of 200 mA (current value α) until the cell voltage reaches 1.9V. By doing so, the cell capacity a can be measured. The time required for the discharge at this time is about 1 hour. If the discharge is performed at a constant current of 2000 mA, the discharge time is 6 minutes or less and greatly falls below 0.75 hours depending on the internal resistance of the cell. It cannot be measured.
It should be noted that 0.75 hours to 1.25 hours defined in the present invention does not mean what value can be taken, and a current value that can be discharged to half the voltage in about 1 hour is derived and discharged. It specifies the approximate time to be performed. Specifically, it is preferable to set a current value that can be discharged in a range of 0.9 hours to 1.1 hours.

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 when fully charged. Specifically, for example, as the thickness of the lithium electrode is increased, the complete negative electrode capacity b can be increased. Further, when the capacity of the positive electrode is increased, the complete negative electrode capacity b can be increased.

[Measurement method of complete negative electrode capacity b]
The complete negative electrode capacity b of the electricity storage device is the total of the negative electrode capacities obtained by the following measurements for each negative electrode in the fully charged electricity storage device.
The complete negative electrode capacity b is a constant current-constant voltage charge (CCCV charge) in which a power storage device is charged with a constant current having a current value α until the cell voltage reaches a set voltage, and then a constant voltage of a set voltage is applied. For 30 minutes until fully charged. Next, this fully charged power storage device 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 made of a lithium metal plate. Each electrode plate is used to assemble a triode cell for measuring the negative electrode capacity, and this is discharged at a constant current of β until the negative electrode potential becomes 1.5 V, and the negative electrode capacity is measured. The total negative electrode capacity b is obtained by multiplying the measured negative electrode capacity by the total number of negative electrodes.
Here, the current value β is the same value as the current value α when there is only one negative electrode constituting the electricity storage device, and there are a plurality of negative electrodes constituting the electricity storage device, and each negative electrode has the same configuration. When it has, it becomes 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 electricity storage device, a negative electrode other than the negative electrode located at the outermost part can be selected and taken out as a negative electrode for producing a three-electrode cell for measuring negative electrode capacity. Needed.

For example, in the case of an electricity storage device having a cell capacity of 200 mAh and 11 negative electrodes having the same configuration, until the cell voltage reaches 3.8 V at a constant current of 200 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 to obtain a fully charged state. Next, this fully charged power storage device is disassembled in an argon box so that the positive electrode and the negative electrode are not short-circuited, and the negative electrode located at the innermost portion is taken out. This negative electrode is used as the working electrode, and the counter electrode (both sides of the working electrode) And a three-electrode cell for measuring the negative electrode capacity using an electrode plate made of a lithium metal plate as a reference electrode, and the negative electrode at a constant current of 18.2 mA (current value β: 200 mA ÷ 11 sheets). The negative electrode capacity is measured by discharging until the potential reaches 1.5 V, and by multiplying this value by 11, the complete negative electrode capacity b can be obtained.
In the present invention, the ratio (a / b) of the cell capacity a to the complete negative electrode capacity b is 0.35 ≦ a / b ≦ 0.95. When a / b is less than 0.35, the energy density decreases. On the other hand, when a / b is larger than 0.95, lithium deposition is likely to occur during the cycle test, and the durability is deteriorated. Further, the capacity reduction due to lithium consumption is accelerated, and the characteristics are deteriorated. a / b is preferably 0.36 ≦ a / b ≦ 0.93, and particularly preferably satisfies 0.45 ≦ a / b ≦ 0.7.

In addition, the negative electrode in the electricity storage device of the present invention has a total negative electrode charge capacity c (mAh) of 0.55 ≦ b when the capacity when the negative electrode is charged with constant current-constant voltage (CCCV) at 0 V for 12 hours. It is necessary to satisfy /c≦1.00 and 0.35 ≦ a / c ≦ 0.55.
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 power storage device, and high durability is obtained. On the other hand, when b / c is less than 0.55, lithium is insufficient and cycle durability is deteriorated. On the other hand, if it exceeds 1.00, lithium is liable to precipitate and the cycle characteristics are deteriorated. 0.55 ≦ b / c ≦ 1.00 is preferable, and 0.70 ≦ b / c ≦ 0.90 is particularly preferable.

Also, when the ratio a / c of the cell capacity a to the total negative electrode charge capacity c is less than 0.35, the energy density is lowered. On the other hand, when a / c is larger than 0.55, the capacity drop during the cycle test is increased and the durability is deteriorated. 0.36 ≦ a / c ≦ 0.54 is preferable, and 0.4 ≦ a / c ≦ 0.5 is particularly preferable.

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 ratio of the negative electrode active material in the negative electrode active material layer is increased. For example, when graphite, graphite-based composite particles, and polyacene organic semiconductor (PAS) are compared with the same weight as the negative electrode active material, the total negative electrode charge capacity c increases when PAS is used.

[Measurement method of total negative electrode charge capacity c]
The total negative electrode charging capacity c of the electricity storage device is the total of the respective negative electrode capacities obtained by the following measurements relating to the respective negative electrodes constituting the electricity storage device.
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) in which a constant voltage of 0 V is applied 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 electric storage device and each negative electrode has the same configuration, the total negative electrode charge capacity c is equal to the negative electrode capacity measured in the three-electrode cell for measuring the negative electrode capacity. It is calculated | required by multiplying the number of negative electrodes contained in.

Next, each component which comprises the electrical storage device of 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, an expanded metal or a punching metal in which a through hole penetrating the back surface is formed by mechanical driving, laser processing using a CO ₂ laser, a YAG laser, a UV laser, or the like is used. A current collector in which a through hole penetrating the surface or a current collector in which a through hole is formed on the front and back surfaces by etching or electrolytic etching can be used.

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

The porosity (%) of the through holes of the positive electrode current collector is preferably 20% to 50%, more preferably 20% to 40%. Here, the porosity (%) of the positive electrode current collector can be obtained by the following 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 (1)

[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 1900 m ² / g to 3000 m ² / g, and more preferably 1950 m ² / g to 2800 m ² / g. 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 electricity storage device 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 thickness of the positive electrode active material layer is preferably 55 μm to 95 μm on one side, more preferably 60 μm to 90 μm, and particularly preferably 65 to 80 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 electricity storage device can be increased.

[Positive electrode active material layer: electrode density]
The electrode density of the positive electrode active material layer is 0.54 g / cm ³ to 0.7 g / cm ³ . When the electrode density of the positive electrode active material layer is less than 0.54 g / cm ³ , the energy density decreases. On the other hand, when the electrode density of the positive electrode active material layer is larger than 0.7 g / cm ³ , the pre-doping property is deteriorated and the cycle characteristics are deteriorated. Electrode density of the positive electrode active material layer ^is preferably from 0.54g / cm 3 ~ 0.68g / cm 3, and even more preferably 0.6g / cm 3 ~ 0.68g / cm 3.
The electrode density of the positive electrode active material layer is usually determined by washing the positive electrode obtained by disassembling the electricity storage device with diethyl carbonate and vacuum drying at 100 ° C., then the mass of the positive electrode active material layer and the outer shape of the positive electrode active material It is determined by measuring the volume (apparent volume) and dividing the mass of the positive electrode active material layer by the outer volume of the positive electrode active material layer. Here, the “external volume of the positive electrode active material layer” is a volume calculated based on the measured values of the vertical dimension, the horizontal dimension, and the thickness dimension of the positive electrode active material layer.
In addition, as a method of setting the electrode density within the above range, a method of forming by a roll press or the like can be mentioned.

[Positive electrode active material layer: basis weight]
The electrode weight per unit area of the positive electrode active material layer is 70 g / m ² to 110 g / m ² .
When the basis weight of the positive electrode active material layer is less than 70 g / cm ² , the energy density decreases. On the other hand, when the electrode weight per unit area of the positive electrode active material layer is larger than 110 g / cm ² , the resistance increases, and the cycle characteristics deteriorate. The electrode weight per unit area of the positive electrode active material layer is preferably 75 g / m ² to 110 g / m ² .
The weight per unit area of the positive electrode active material layer was determined by washing the positive electrode obtained by disassembling the electricity storage device with diethyl carbonate and drying at 100 ° C., then punching the active material layer part into a predetermined area and measuring the mass. It is calculated by peeling the active material layer, measuring the mass of the current collector, and dividing the mass of the active material layer by the area.

[Negative electrode current collector]
As the negative electrode current collector, stainless steel, copper, nickel, or the like can be used.
The thickness of the negative electrode current collector is not particularly limited, but is usually 1 μm to 50 μm, preferably 5 μm to 40 μm, and particularly preferably 10 μm to 30 μm.

The negative electrode current collector preferably has a hole penetrating the front and back surfaces, and the hole diameter of the through hole is, for example, 0.5 μm to 400 μm, preferably 0.5 μm to 350 μm, and preferably 1 μm. It is particularly preferred that the particle diameter is ˜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).
Porosity (%) = [1- (Mass of negative electrode current collector / true specific gravity of negative electrode current collector) / (apparent volume of negative electrode current collector)] × 100 (2)
Examples of the negative electrode current collector having a through hole include, for example, an expanded metal or a punching metal in which a through hole penetrating the back surface is formed by mechanical driving, laser processing using a CO ₂ laser, a YAG laser, a UV laser, or the like. A current collector in which a through-hole penetrating the back surface or a current collector in which a through-hole is formed on the front and back surfaces by etching can be used.

[Negative electrode active material]
As the negative electrode active material, it is preferable to use graphite particles among materials that can be reversibly doped / dedoped with lithium ions. Specifically, graphite-based composite particles in which the surface of core particles made of graphite, non-graphitizable carbon, and natural graphite are 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 the group consisting of polyacene-based organic semiconductors (PAS) having a polyacene-based skeleton structure in which the atomic ratio of hydrogen atoms to carbon atoms (hydrogen atom / carbon atom) is 0.50 to 0.05 Is preferably used. In the case of PAS, when the atomic ratio of hydrogen atoms to carbon atoms exceeds 0.50, the electron conductivity is lowered, so that the internal resistance of the cell may be lowered. On the other hand, when the atomic ratio is less than 0.05, the capacity per unit weight is lowered, so that the energy density of the cell may be lowered.
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, the particle size is preferably graphite particles having a 50% volume cumulative diameter (D50) in the range of 1.0 μm to 10 μm from the viewpoint of improving the output, and graphite particles in the range of 2 μm to 5 μm. More preferred. 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 an electricity storage device having a sufficiently low internal resistance.
The negative electrode active material preferably has a specific surface area of 0.1 m ² / g to 200 m ² / g, more preferably 0.5 m ² / g to 50 m 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 electricity storage device 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 electricity storage device to be increased is high, and gas may be generated at the time of charging, which may reduce durability.
The 50% volume cumulative diameter (D50) of the graphite-based particles is a value determined by, for example, a 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 preferable 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 μm to 80 μm, preferably 10 μm to 65 μm, and more preferably 10 μm to 50 μm. 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.

[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, examples of the binder include a rubber-based binder such as SBR, a fluorine-containing resin obtained by seed polymerization of polytetrafluoroethylene, polyvinylidene fluoride, etc. with an acrylic resin, or an acrylic resin. 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 to be added varies depending on the electric conductivity of the active material used, the shape of the electrode to be produced, etc., but both are usually preferably 2% by mass to 20% by mass with respect to the active material, In particular, 2% by mass to 10% by mass is more preferable.

[Separator]
As the separator in the electricity storage device of the present invention, a material having an air permeability measured by a method based on JISP8117 in the range of 1 sec to 200 sec can be used. Specifically, for example, it can be appropriately selected from non-woven fabrics and microporous membranes composed of polyethylene, polypropylene, polyester, cellulose, polyolefin, cellulose / rayon, etc., and particularly polyethylene, polypropylene, cellulose / It is preferable to use a rayon nonwoven fabric.
The thickness of the separator is, for example, 5 μm to 20 μm, and preferably 5 μm to 15 μm. When the thickness of the separator is less than 5 μm, a short circuit is likely to occur. On the other hand, when it is larger than 20 μm, the resistance becomes high.

[Electrolyte]
In the electricity storage device of the present invention, an aprotic organic solvent electrolyte solution of lithium salt is used as the electrolyte.

[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 , LiN (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 can be obtained.

The electricity storage device of the present invention has a capacity retention rate of 95% or more after 10,000 cycles of constant current charge / discharge at a time rate of 10 C in a voltage range of 3.8 V to 2.2 V. Furthermore, in the electricity storage device of the present invention, the rate of increase in the internal resistance after 10000 cycles of constant current charge / discharge at a time rate of 10 C in the voltage range of 3.8 V to 2.2 V is 3% or less. This is because the electricity storage device of the present invention satisfies 0.35 ≦ a / b ≦ 0.95, 0.55 ≦ b / c ≦ 1.00, 0.35 ≦ a / c ≦ 0.55, and the positive electrode When the electrode density of the active material layer is 0.54 g / cm ³ to 0.7 g / cm ³ and the electrode weight per unit area of the positive electrode active material layer satisfies 70 g / m ² to 110 g / m ² , higher capacity can be obtained. This shows that the maintenance rate can be maintained and the increase in internal resistance can be suppressed. By configuring the power storage device of the present invention, it is possible to maintain a good balance between the trade-off relationship between higher output and higher energy density.

[Structure of electricity storage device]
As the structure of the electricity storage device of the present invention, in particular, a wound-type, plate-like or sheet-like positive electrode and negative electrode in which a belt-like positive electrode and a negative electrode are wound through a separator are laminated in three or more layers via a separator. And a laminated type in which a unit having such a laminated structure is enclosed in an outer film or a rectangular outer can.
The structures of these power storage devices are known, for example, from Japanese Patent Application Laid-Open No. 2004-266091, and can have the same configuration as those power storage devices.

As mentioned above, although embodiment of this invention was described concretely, 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 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 construed as being limited to these examples.

[Example 1 (S1): Cell production example 1]
(1) Fabrication of positive electrode Conductive paint (Nippon Graphite Bunny Height T-602DEFK) 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. Using a processing machine, the coating width was set to 100 mm, the coating thickness of both sides combined was set to 125 μm, and both sides were coated, followed by drying under reduced pressure to form conductive layers on the front and back surfaces of the positive electrode current collector.
Next, activated carbon particles having a 50% volume cumulative diameter (D50) value of 3 μm and a specific surface area of 2000 m ² / g on the conductive layer formed on the front and back surfaces of the positive electrode current collector (Cataler Co., Ltd .: -CEP21K) (Positive electrode active material) 43 wt%, binder 1.5 wt% (manufactured by JSR: TRD201B), carboxylmethylcellulose sodium salt (Daicel 1120) 2 wt%, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) HS100) A slurry containing 2.5 wt% and water 51 wt% was coated on both sides using a vertical die type double-side coating machine, then dried under reduced pressure and roll pressed to form an electrode on the conductive layer. 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.

(2) Production of Negative Electrode Graphite particles having a 50% volume cumulative diameter (D50) of 6 μm on both sides of a negative electrode current collector made of a copper chemical etching foil having a through-hole diameter of 300 μm, a porosity of 55%, and a thickness of 25 μm. Graphite-based composite particles having a pitch-coated surface (1) (Nippon Carbon Co., Ltd .: AGP30) (negative electrode active material) 40 wt%, SBR binder (JSR Co., Ltd .: TRD2001) 1 wt% and carboxymethyl cellulose sodium salt (Daicel) 1120) A slurry containing 1.5 wt%, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd .: HS100) 2 wt%, and water 55.5 wt% was coated on both sides using a vertical die type double-side coating machine. Then, it was made to dry and roll-pressed, and the negative electrode active material layer which is an electrode layer was formed in the front and back of a negative electrode collector.
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”. .

(3) Production of Separator A film made of a cellulose / rayon composite material having a thickness of 15 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, 10 positive electrodes, 11 negative electrodes, and 22 separators are prepared, and the positive electrode and the negative electrode are overlapped with each other, but the respective uncoated portions are opposite to each other. 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 laminate were fixed with a tape to produce an electrode laminate unit.
Next, a lithium ion supply member is prepared by cutting the foil-like lithium metal having a thickness of 46 μm so that the size of the foil-like lithium metal is 65 mm × 85 mm and pressing the copper foil on 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 as to oppose a negative electrode through the separator of an electrode lamination | stacking unit.
And 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 10 positive electrodes of the produced electrode laminate unit The power tabs were stacked and welded. On the other hand, each of the 11 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 (vertical width) × 127 mm (horizontal width) × 0.15 mm (thickness), and 72 mm (vertical width) × One exterior film that has been subjected to a drawing process of 105 mm (width), and a polypropylene layer, an aluminum layer, and a nylon layer are laminated, and the other dimension is 90 mm (length) × 127 mm (width) × 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. Arranged. One exterior film was overlapped on this electrode laminate unit, and three sides (including two sides from which the positive electrode terminal and the negative electrode terminal protrude) at the outer peripheral edge of one exterior film and the other exterior film were heat-sealed.
On the other hand, an electrolytic solution containing LiPF ₆ at a concentration of 1.2 mol / L using a mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate (3: 1: 4 by volume, respectively) as an aprotic organic solvent. Prepared.
Subsequently, after inject | pouring the said electrolyte solution between one exterior film and the other exterior film, the remaining one side in the outer periphery part of one exterior film and the other exterior film was heat-seal | fused. 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 outer lithium ion capacitor (hereinafter referred to as cell 1) was produced. A total of four similar cells 1 were produced.
The average cell capacity of the obtained cell 1 was 190 mAh.

[Positive electrode active material layer: density]
A positive electrode obtained by disassembling one cell 1 is immersed in a container containing diethyl carbonate for 30 minutes for washing treatment, vacuum-dried at 100 ° C., and then placed in any place where an active material layer exists. Two pieces having a size of 2 cm ² were cut out, the weight of one cut out positive electrode was measured with an electronic balance, and the thickness was measured with a micrometer. Next, only the current collector in the uncoated region where no active material layer was present was cut into the same size, the weight was measured with an electronic balance, and the thickness was measured with a micrometer. The weight of the positive electrode active material layer was calculated by subtracting the weight of the obtained current collector from the weight of the positive electrode. Next, the thickness of only the obtained current collector was subtracted from the thickness of the positive electrode to calculate the thickness of the positive electrode active material layer, and the external volume (apparent volume) of the positive electrode active material was calculated. Next, the positive electrode active material layer density was determined by dividing the mass of the positive electrode active material layer by the outer volume of the positive electrode active material layer.

[Positive electrode active material layer: basis weight]
The weight of the remaining 2 cm × 2 cm positive electrode made when measuring the density of the positive electrode active material layer was measured with an electronic balance, the active material layer was peeled off, the mass of the current collector was measured, and the active material layer The mass per unit area of the positive electrode active material layer was calculated by dividing the mass by the area.

[Evaluation of cell performance]
With respect to the remaining three cells 1 obtained, the cell capacity a, the complete negative electrode capacity b, the total negative electrode charge capacity c, the energy density and the DC-IR were measured and the durability test was performed as follows. Was evaluated.

(I) Measurement of cell capacity a and calculation of energy density After charging one cell 1 with a constant current of 0.19 A (current value α) until the cell voltage becomes 3.8 V, 3.8 V After performing the constant voltage charging for 30 minutes, the charging / discharging operation of discharging until the cell voltage became 1.9 V at a constant current of 0.19 A was repeated 5 times. The capacity at the time of discharge in the fifth charge / discharge operation was defined as cell capacity a. The results based on the cell capacity a are shown in Table 1. The time required for the discharge in the fifth charge / discharge operation was 1.04 hours.
Table 1 shows the energy density (Wh / L) as 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.

(Ii) Measurement of complete negative electrode capacity b After measurement of the above cell capacity a, the cell 1 was charged with a constant current of 0.19 A until the cell voltage reached 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 measuring cell using a lithium metal plate as a counter electrode is assembled. The negative electrode potential is 1.5 V (Li / L) at a constant current of 0.0173 A. The value obtained by multiplying the negative electrode capacity of 11 (the number of negative electrodes) by 11 (the number of negative electrodes) when discharging until Li ⁺ ) is defined as the complete negative electrode capacity b, and Table 1 shows the results based on 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 at a constant current of 0.0173 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. The value obtained by multiplying the negative electrode capacity at this time by 11 (the number of negative electrodes) is the total negative electrode charge capacity c, and Table 1 shows the results based on the total negative electrode charge capacity c.

(Iv) Measurement of DC-IR The cell before the capacity retention rate measurement is charged with a constant current of 1.9 A (time rate 10 C) until the cell voltage reaches 3.8 V before the cycle test is started, and then 3. A constant current-constant voltage charge applying a constant voltage of 8 V was performed for 0.5 hour, and then discharged at a constant current of 19 A (time ratio 100 C) until the cell voltage reached 2.2 V. At that time, the approximate straight lines of the voltage after 1 second and 3 seconds are taken and extrapolated to 0 second, and the difference between the extrapolated voltage and 3.8V (ΔV) divided by the current value 19A is DC. Internal resistance (DC-IR).

(V) Cycle characteristic test:
[Capacity maintenance rate]
The cell 1 is charged at a constant current of 1.9 A (time rate 10 C) until the cell voltage becomes 3.8 V, and then the cell voltage becomes 2.2 V at a constant current of 1.9 A. 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 maintenance ratio is 95% or more, “Δ” when 90% or more and less than 95%, and “x” when less than 90%.
[Rate of increase in resistance]
The cell for measuring the capacity retention rate is charged with a constant current of 1.9 A (time rate 10 C) before and after the start of the cycle test until the cell voltage becomes 3.8 V, and then a constant voltage of 3.8 V is applied. Current-constant voltage charging was performed for 0.5 hour, and then discharging was performed at a constant current of 19 A (time rate 100 C) until the cell voltage reached 2.2 V. This cycle of 3.8V-2.2V was repeated, and the DC internal resistance at the 10th time was measured. Table 1 shows the case where the rate of increase in resistance before and after the cycle test is 3% or less as “◯”, the case where it is greater than 3% and 5% or less as “Δ”, and the case where it is greater than 5% as “X”.

〔Comprehensive judgment〕
If the fabricated cell operates without any problems such as short-circuiting, the initial DC-IR is 10.35 mΩ or less, and the energy density is greater than 31.5 Wh / L, it is marked as ◯. Furthermore, when the capacity maintenance rate is 95% or more and the resistance increase rate is 3% or less, it is marked as ◯. When it is out of the above range, it is x.

[Examples of manufacturing cells of Example 2 (S2) to Example 13 (S13) and Comparative Examples 1 (C1) to 10 (S10)]
In the cell production example 1 of Example 1, the electrode density and basis weight of the positive electrode active material layer, a / b, b / c, and a / c are set as shown in Table 1, and the separator thickness is changed according to Table 1. Except for the above, four S2-S13 and four C1-C10 were prepared in the same manner.
For these S2 to S13, the cell capacity a, the complete negative electrode capacity b, the total negative electrode charge capacity c, the energy density and the DC-IR were measured in the same manner as in Example 1, and a cycle characteristic test was conducted to evaluate the characteristics. Went. In the DC-IR measurement and the cycle characteristic test, the current value was changed in accordance with the capacity of each cell so that the time rate was the same as that in Example 1.
The results based on these results are shown in Table 1.

As shown in Table 1, the positive electrode active material satisfying 0.35 ≦ a / b ≦ 0.95, 0.55 ≦ b / c ≦ 1.00, and 0.35 ≦ a / c ≦ 0.55 If the cell has a layer electrode density of 0.54 g / cm ³ to 0.7 g / cm ³ and a positive electrode active material layer electrode weight of 70 g / m ² to 110 g / m ² , a DC-IR In other words, it was possible to obtain an electric storage device having a low balance, that is, a large output, a high energy density, and a good balance of performance capable of suppressing a decrease in capacity and an increase in resistance after cycle testing.

Since the C / C cell had a / c larger than 0.54, the capacity drop during the cycle test became large and the characteristics deteriorated.
The C2 cell had an a / c of less than 0.35, so the energy density decreased.
Since the C3 cell had a b / c value exceeding 1.00, the capacity drop during the cycle test was large and the cell characteristics deteriorated.
Since the C4 cell had a b / c of less than 0.55, the capacity decreased and the resistance increased during the cycle test, and the characteristics deteriorated.
In the C5 cell, since the electrode weight per unit area of the positive electrode active material layer was larger than 110 g / cm ² , the initial DC-IR was high, the resistance increased during the cycle test, the capacity decreased, and the cell characteristics deteriorated.
Since the C6 cell has an electrode weight per unit area of the positive electrode active material layer of less than 70 g / cm ² , the energy density was lowered.
In the C7 cell, since the electrode density of the positive electrode active material layer was larger than 0.7 g / cm ³ , the initial DC-IR was high, the capacity decreased and the resistance increased during the cycle test, and the cell characteristics deteriorated.
On the other hand, the C8 cell had a lower energy density because the positive electrode active material layer had an electrode density of less than 0.54 g / cm ³ .
In the C9 cell, since a / b was larger than 0.95, the capacity decreased and the resistance increased during the cycle test, and the cell characteristics deteriorated.
Since the a / b of the C10 cell was less than 0.35, the capacity decreased and the resistance increased during the cycle test, and the cell characteristics deteriorated.
From the above results, each of Comparative Examples C1 to C10 was an electricity storage device that did not satisfy any of the configurations of the present invention. Therefore, the target output of the present application was large, the energy density was high, the capacity decreased after the cycle test, An electric storage device with a good balance of performance that can suppress an increase in resistance could not be obtained.

The electricity storage device of the present invention can be used as a lithium ion capacitor, a lithium ion secondary battery, etc., with high energy density and high output characteristics without deterioration even when the capacity of the negative electrode is increased. The
The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2013-146835 filed on July 12, 2013 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims

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 solution of a salt,
The capacity when discharging from the fully charged state of the electricity storage device to half the voltage of the full charge over 0.75 to 1.25 hours is defined as the cell capacity a (mAh). The capacity when the negative electrode was discharged until the negative electrode potential reached 1.5 V (Li / Li + ) was defined as a complete negative electrode capacity b (mAh), and the negative electrode was charged at constant current-constant voltage at 0 V for 12 hours ( When the capacity when CCCV charging is set to the total negative electrode charging capacity c (mAh), 0.35 ≦ a / b ≦ 0.95, 0.55 ≦ b / c ≦ 1.00, 0.35 ≦ a / c ≦ 0.55 is satisfied, the electrode density of the positive electrode active material layer is 0.54 g / cm 3 to 0.7 g / cm 3 , and the electrode weight per unit area of the positive electrode active material layer is 70 g / m 2 to 110 g / A power storage device characterized by being m 2 .
The electricity storage device according to claim 1, wherein the negative electrode active material layer includes graphite-based particles.
The electric storage device according to claim 1 or 2, wherein the positive electrode active material layer includes activated carbon.
The electricity storage device according to any one of claims 1 to 3, wherein the separator has a thickness of 5 袖 m to 20 袖 m.
The electricity storage device according to any one of claims 1 to 4, wherein the positive electrode current collector and / or the negative electrode current collector has a through hole.
The electricity storage device according to any one of claims 1 to 5, wherein the electrode unit is a stacked type or a wound type.
The electricity storage device according to any one of claims 1 to 6, wherein the negative electrode is a negative electrode doped with lithium ions in advance.
The electricity storage device according to any one of claims 1 to 7, wherein the electricity storage device is a lithium ion capacitor.
The energy storage device according to claim 8, wherein the energy density is 31.5 Wh / L or more.
The capacity maintenance ratio after performing 10,000 cycles of constant current charge / discharge at a time rate of 10 C in a voltage range of 3.8 V to 2.2 V is 95% or more, according to any one of claims 1 to 9. Power storage device.
11. The rate of increase in internal resistance after 10,000 cycles of constant current charge / discharge at a time rate of 10 C in a voltage range of 3.8 V to 2.2 V is 3% or less. The electricity storage device described in 1.