JP2009135540A - Nonaqueous lithium power storage element and manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous lithium power storage element having all of a high energy density, high output and high reliability. <P>SOLUTION: The nonaqueous lithium power storage element includes a positive electrode having a positive electrode active material layer and a positive electrode collector, a negative electrode having a negative electrode active material layer and a negative electrode collector, a separator interposed between the positive electrode and the negative electrode, a nonaqueous electrolyte, and a packing body. The positive electrode active material layer contains activated carbon, and the negative electrode active material layer contains lithium ion storable carbon material. The separator has a film thickness of 15 μm to 50 μm and has a liquid resistance of ≤2.5 Ωcm<SP>2</SP>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous lithium storage element having high capacity, high output, and high reliability.

2. Description of the Related Art In recent years, a hybrid drive system (hereinafter simply referred to as a drive system) that combines an internal combustion engine or a fuel cell, a motor, and a power storage element in an automobile for the purpose of protecting the global environment and effectively using energy for resource saving. It attracts attention. One of the roles played by the power storage element for the drive system is to absorb the increase and decrease of the load of the drive system while the internal combustion engine or the fuel cell is operated at a constant output that can achieve the maximum efficiency. In other words, power that is insufficient when driven by an internal combustion engine or fuel cell alone during acceleration is supplied by supplying power from the storage element to the motor, and during deceleration, the motor is used as a generator to recover excess generated power to the storage element. It is a role to do.
The first requirement for an electric storage element used in the drive system is that input / output characteristics are excellent. This is because the duration of deceleration and acceleration in an automobile is usually about 1 minute at most, and it is important how much energy the energy storage element can absorb and release in a short time. It is.

In addition, a second requirement for these power storage elements is high energy density. If the energy density is low, the weight and volume of the electricity storage element required to supply the electric power necessary to accelerate the motor vehicle and regenerate the energy generated by the deceleration will increase, which is called an automobile. This is because it becomes difficult to efficiently store in a limited space.
Currently, nickel-metal hydride batteries are the mainstream as storage elements for such drive systems, and electric double layer capacitors and lithium ion batteries are being experimentally adopted. As the above-mentioned electric double layer capacitor, there are known an aqueous electrolyte (hereinafter referred to as an aqueous capacitor) and a non-aqueous electrolyte (hereinafter referred to as a non-aqueous capacitor). Although the water-based capacitor is excellent in input / output characteristics, there is a problem that the withstand voltage per power storage element is lowered because water as an electrolytic solution is electrolyzed and the energy density cannot be increased. In addition, since the non-aqueous capacitor has a high breakdown voltage, the energy density can be higher than that of the water-based capacitor, but the input / output characteristics are inferior to those of the water-based capacitor. Further, although the non-aqueous capacitor has a higher energy density than the water-based capacitor, the energy density is not sufficient as compared with the battery.

On the other hand, nickel-metal hydride batteries and lithium-ion batteries do not satisfy all of the input / output characteristics, energy density, and reliability, so the practical use of energy storage devices that combine high input / output, high energy density, and high reliability Is strongly demanded.
One means for further improving the energy density of the non-aqueous capacitor is to thin the separator interposed between the electrodes.
Since a separator for an electric double layer capacitor needs to have high ion conductivity, a paper separator is usually used, and its thickness is in the range of 60 to 150 μm. However, if the separator is made thin to increase the energy density, a micro short circuit is likely to occur, resulting in a problem that apparent self-discharge increases.

  The micro-short here refers to a minute short-circuit between the electrodes inside the power storage element. A power storage element with a micro short circuit is not so incapable of normal charge and discharge as a power storage element with a short circuit, but a small short circuit current always flows through a small short circuit portion generated inside. For this reason, when the storage element is stored in a charged state, the energy stored in the storage element is reduced by the self-discharge of the active material itself in the storage element without a micro short, and the voltage of the storage element gradually decreases. However, in an energy storage device having a micro short circuit, the energy stored by an internal short circuit in addition to the self discharge is reduced, so that the apparent self discharge is increased. This significantly reduces the reliability of the storage element. The cause of the micro short-circuit is considered to be that the paper-made separator is coarse and dense, and the positive electrode and negative electrode active materials cause a micro short circuit when the separator is rough.

Thus, attempts have been made to reduce self-discharge due to microshorts between electrodes and achieve high capacity by using a paper separator having a specific thickness, bulk density, and tensile strength (for example, Patent Documents). 1). However, also in this patent document 1, it is considered that the thickness of the paper separator is particularly preferably 60 to 90 [mu] m, and further thinning has been desired in order to improve the energy density.
On the other hand, as a thin film separator, a polyolefin-based separator used in a lithium ion secondary battery (hereinafter abbreviated as LIB) is known, and LIB has a high capacity and ensures safety (for example, patents). (Ref. 2). In order to obtain the strength for preventing the micro-short in the thin film separator, it is necessary to reduce the gap of the separator. However, as described above, a large current cannot be flowed in the LIB. Therefore, no practical problem has occurred even when a separator having a small gap is used.

  As described above, in the electric double layer capacitor, a thick separator having high ionic conductivity is used, and there remains a problem in terms of improving the energy density. On the other hand, a thin separator with low ionic conductivity is used in LIB, leaving a problem in terms of improving input / output characteristics. By the way, as a power storage element having a larger capacity than the above-described electric double layer capacitor and higher output characteristics than LIB, a power storage element using activated carbon for the positive electrode and carbonaceous material such as graphite for the negative electrode has been proposed (for example, And Patent Document 3). In addition, there has been proposed a power storage element using a composite porous material in which activated carbon is used for the positive electrode and a carbonaceous material is coated on the surface of the active carbon for the negative electrode (see, for example, Patent Document 4). However, a separator characteristic optimal for the electricity storage element that maintains the output characteristics of these electricity storage elements and also has good self-discharge characteristics has not been known.

JP 2002-231580 A Japanese Patent No. 2642206 Japanese Patent Laid-Open No. 08-1007048 JP 2001-229926 A

  An object of the present invention is to provide a non-aqueous lithium storage element having high energy density, high output, and high reliability, and a method for manufacturing the same.

Hereinafter, the “lithium ion storable carbon material” refers to a carbon material capable of occluding and releasing lithium ions among carbonaceous materials. Further, an active material used in the negative electrode of the electricity storage element described in Patent Document 4 described above, and a composite porous material in which a carbonaceous material is coated on the surface of activated carbon is simply referred to as “composite porous material”. And
As a result of earnestly examining the means for improving the capacity, the high output, and the reliability in the electric storage element composed of the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte solution, and the exterior body, the present inventors have satisfied specific conditions. It has been found that these characteristics can be achieved by using a separator.

That is, the present invention
1. From a positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and an exterior body The positive electrode active material layer contains activated carbon, the negative electrode active material layer contains a lithium ion storable carbon material, and the separator is any one selected from the group consisting of polyethylene, polypropylene, polyimide, and polyamide. A non-aqueous lithium storage element, wherein the separator has a film thickness of 15 μm or more and 50 μm or less, and the liquid resistance of the separator is 2.5 Ωcm ² or less,
2. 2. The nonaqueous lithium storage element according to 1 above, wherein the separator has a density of 0.35 g / cc or more and 0.55 g / cc or less.
3. 3. The non-aqueous lithium storage element according to 1 or 2 above, wherein the lithium ion storable carbon material is a composite porous material in which a carbonaceous material is deposited on the surface of activated carbon.
4). A positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and an exterior body The material has a film resistance of 15 μm to 50 μm and a liquid resistance of any one selected from the group consisting of a positive electrode containing activated carbon in the positive electrode active material layer, polyethylene, polypropylene, polyimide, and polyamide. A separator having a resistance of ^2.5 Ωcm ² or less and a negative electrode containing a carbon material capable of occluding lithium ions in the negative electrode active material layer are stacked or wound into an outer package, and dried by heating at a temperature not higher than the heat resistance temperature of the separator. After that, a method for producing a non-aqueous lithium storage element, characterized by injecting a non-aqueous electrolyte solution,
It is.

  According to the present invention, it is possible to provide a non-aqueous lithium storage element that has high energy density, high output, and high reliability, and a method for manufacturing the same.

Hereinafter, embodiments of the present invention will be described in detail.
In general, a power storage element includes a positive electrode, a separator, a negative electrode, an electrolytic solution, and an exterior body as main components. However, the power storage element of the present invention is a non-aqueous lithium that uses an organic solvent in which a lithium salt is dissolved as an electrolytic solution. Type storage element.
The positive electrode used in the electricity storage device of the present invention is obtained by providing a positive electrode active material layer on a positive electrode current collector. The positive electrode current collector is preferably a metal foil, and more preferably an aluminum foil having a thickness of 1 to 100 μm.
The positive electrode active material layer contains a positive electrode active material and a binder, and optionally contains a conductive filler. Activated carbon is preferably used as the positive electrode active material. The activated carbon is not particularly limited as long as it exhibits desired characteristics, and commercial products obtained from various raw materials such as petroleum-based, coal-based, plant-based, and polymer-based can be used. It is preferable to use activated carbon powder having an average particle size of about 1 to 500 μm, more preferably 1 to 50 μm. When the particle size is large, it becomes difficult to produce an electrode by a coating method, and when the particle size is small, a large amount of binder is required for coating and fixing, so that the volume energy density is lowered. As the binder, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), fluororubber, styrene-butadiene copolymer, and the like can be used.

  In addition to the activated carbon and the binder, a conductive filler made of a conductive carbonaceous material having higher conductivity than the positive electrode active material can be mixed in the positive electrode active material layer as necessary. As such a conductive filler, ketjen black, acetylene black, vapor grown carbon fiber, graphite, a mixture thereof and the like are preferable. 0-20 mass% is preferable with respect to a positive electrode active material, and, as for the mixing amount of the conductive filler in a positive electrode active material layer, the range of 1-15 mass% is more preferable. The conductive filler is preferably mixed from the viewpoint of high input, but if the mixing amount is more than 20% by mass, the content of the positive electrode active material in the positive electrode active material layer is reduced, so that the energy density per volume decreases. This is not preferable. The thickness of the positive electrode active material layer is usually about 50 to 200 μm. For the positive electrode, a paste in which a positive electrode active material and a binder (conductive filler as necessary) are dispersed in a solvent is prepared, this paste is applied onto the positive electrode current collector, dried, and if necessary It is obtained by pressing. Examples of the coating method include a bar coating method, a transfer roll method, a T-die method, a screen printing method, and the like, and a coating method according to the physical properties and coating thickness of the paste can be appropriately selected.

The negative electrode used in the electricity storage device of the present invention is obtained by providing a negative electrode active material layer on a negative electrode current collector. The negative electrode current collector is preferably a metal foil, more preferably a copper foil having a thickness of 1 to 100 μm.
The negative electrode active material layer contains a negative electrode active material and a binder, and optionally contains a conductive filler. The negative electrode active material is a lithium ion storable carbon material. As the lithium ion storable carbon material, a carbonaceous material having a specific surface area of 1 to 1500 m ² / g by BET method such as natural graphite, artificial graphite, coke, non-graphite carbon, and composite porous material is preferably used. Can be used. A carbonaceous material having a specific surface area exceeding 1500 m ² / g by the BET method, such as acetylene black, carbon black, and activated carbon, is not preferable as the negative electrode active material of the present invention. Among the lithium ion storable carbon materials, a composite porous material can be most preferably used.
The shape of the lithium ion storable carbon material preferably has an average particle size of about 1 to 500 μm, more preferably 1 to 50 μm.

The lithium-ion storable carbon material, natural graphite, artificial graphite, coke, and for any of the non-graphitizable carbon has a specific surface area by BET method is preferably ^{1~200m 2 / g, 3~100m 2 /} g Is more preferable. If the specific surface area is less than 1 m ² / g, there will be a problem that discharging and charging with a large current will not be possible, and if the specific surface area is greater than 200 m ² / g, the particle size will be too fine and it will be difficult to make an electrode. A problem occurs.
On the other hand, the lithium ion storable carbon material, in the case of composite porous material preferably has a specific surface area of 10~1500m ² / g, more preferably ^{10~1000m 2 / g, 20~800m 2 /} g Is more preferable. When the specific surface area is less than 10 m ² / g, there arises a problem that discharging and charging due to a large current cannot be performed. When the specific surface area is more than 1500 m ² / g, the reaction between lithium ions in the electrolyte and the composite porous material occurs. Increases, and it is difficult to increase the energy density of the energy storage device.

In addition to the lithium ion storable carbon material and the binder, a conductive filler made of a carbonaceous material having higher conductivity than the negative electrode active material can be mixed in the negative electrode active material layer as necessary. Examples of the conductive filler include acetylene black, ketjen black, vapor grown carbon fiber, and mixtures thereof. The mixed amount of the conductive filler is preferably 0 to 20% by mass, more preferably 1 to 15% by mass with respect to the negative electrode active material. The conductive filler is preferably mixed from the viewpoint of high input, but if the mixing amount is more than 20% by mass, the content of the negative electrode active material in the negative electrode active material layer decreases, so the energy density per volume decreases. This is not preferable.
For the negative electrode, create a paste in which a lithium ion storable carbon material and a binder (conductive filler, if necessary) are dispersed in a solvent, apply this paste on the negative electrode current collector, dry it, and then Can be obtained by pressing according to the above. As a coating method, the same method as that for the positive electrode can be used, and a coating method according to the physical properties and coating thickness of the paste can be appropriately selected. The thickness of the negative electrode active material layer is usually about 50 to 200 μm.

The separator used in the electricity storage device of the present invention insulates the positive electrode and the negative electrode from being in direct electrical contact with each other, and retains the electrolytic solution in the internal gap to form a lithium ion conduction path between the electrodes. Take on. Examples of raw materials for forming the separator include polyethylene, polypropylene, cellulose, polyimide, polyamide and the like. As a method for producing a separator from these raw materials, a known method can be used. For example, a method of making a crushed fibrous material, a method of opening a hole by stretching after film formation, a method of forming a film by mixing with an inorganic substance or an organic substance, and then eluting the inorganic substance or organic substance to open a hole, etc. Can be mentioned.
The film thickness of the separator needs to be 15 μm or more and 50 μm or less. When the thickness is less than 15 μm, the ability to electrically insulate the positive electrode and the negative electrode is lowered, and the resulting micro short circuit cannot be prevented, and a self-discharge large storage element is likely to occur. In addition, if it exceeds 50 μm, the separator itself does not generate energy, so not only the wasteful volume is consumed and the energy density of the electricity storage device is reduced, but also the internal resistance of the electricity storage device increases due to the distance between the electrodes being increased, High output characteristics are difficult to obtain.

Further, it is important that the liquid resistance of the separator is 2.5 Ωcm ² or less, preferably 2.0 Ωcm ² or less. A separator having a liquid resistance larger than 2.5 Ωcm ² has a small gap for holding the electrolyte, ie, a small number of holes or a small number of holes. Since the internal resistance of the electricity storage element increases, the output characteristics deteriorate.
The separator liquid resistance (Ωcm ² ) in the present invention is defined as a resistance value calculated as follows.
Two SUS plates having a thickness of 0.5 to 1 mm, a width of 1.5 cm, and a height of 5 cm are prepared as electrodes. One side of one plate is covered with a tape having a thickness of 50 μm while leaving the lower part 1 cm from the end, and is electrically insulated. Next, the electrode covered with the tape and the electrode not covered with the tape are overlapped and fixed so that the tape is interposed therebetween, thereby forming an electrode pair. Then, 1.5 cm ² that is not covered with the tape is an effective electrode area that can be energized. The electrode pair is immersed in an electrolytic solution in which LiBF ₄ is dissolved at a concentration of 1 mol / L in a solvent in which propylene carbonate: ethylene carbonate: γ-butyrolactone is mixed at a volume ratio of 1: 1: 2, and the frequency is 1 kHz. Measure AC resistance. The measured value at this time is defined as a resistance value R1 (see FIG. 1- (A)).

Next, the electrode pair used in the above measurement is unfixed, the separator for measuring the liquid resistance is cut into a size that covers the electrode, sandwiched between the two plates to be the electrode, and fixed again. The electrode pair including this separator is immersed in an electrolytic solution having the same composition as that used in the above measurement, and the AC resistance is measured at a frequency of 1 kHz. The measured value at this time is defined as a resistance value R2 (see FIG. 1- (B)).
The liquid resistance (Ωcm ² ) of the separator is calculated from these measured values as follows.
When the thickness of the separator is x μm, the resistance value Rx of the electrolyte solution between the electrodes when the electrode area is 1.5 cm ² and the distance between the electrodes is (50 + x) μm is proportional to the distance between the electrodes. Is calculated in proportion to the resistance value Rx = [(50 + x) / 50] × resistance value R1.
The difference (R2-Rx) between the calculated value (Rx) and the resistance value R2 when the separator is actually sandwiched is an increase in resistance due to the presence of the separator instead of the electrolyte.
By multiplying the resistance increase value by 1.5 cm ² which is an effective electrode area, the liquid resistance of the separator can be determined in units of Ωcm ² .

When removing the separator from the electricity storage device to measure the liquid resistance (Ωcm ² ) of the separator, use a separator that is thoroughly washed with dimethoxyethane and methanol and blown dry at room temperature. Can do.
The density of the separator is preferably 0.35 g / cc or more and 0.55 g / cc or less (the density here refers to the bulk density). Since the true specific gravity of the material forming the separator is about 1 g / cc, at this density, there is a gap for holding the electrolyte sufficiently. Although related to the film thickness of the separator, if the density of the separator is greater than 0.55 g / cc, the amount of electrolyte impregnated in the separator decreases, resulting in an increase in the liquid resistance of the separator and a decrease in output characteristics. Resulting in. Similarly, when the density of the separator is less than 0.35 g / cc, there are too many voids in the separator, and micro short-circuiting easily occurs, and the self-discharge characteristics are deteriorated.

Further, when the heat resistant temperature of the separator is 70 ° C. or higher, preferably 80 ° C. or higher, more preferably 100 ° C. or higher, the reliability of the power storage element is improved. If the heat resistant temperature of the separator is less than 70 ° C., there is a possibility that sufficient drying cannot be performed by heating in the production process of the electricity storage device, which is not preferable. There is no upper limit on the heat-resistant temperature of the separator, but for example, when a polypropylene-aluminum laminate film is used as the exterior body, the heat-resistant temperature of the exterior body is limited by the heat-resistant temperature of the exterior body. There is no need for more.
The heat resistant temperature of the separator in the present invention refers to the Gurley resistance of the separator before and after heating when the separator is returned to room temperature for 10 minutes (the air permeability specified in JIS P8117: 1998). Means the resistance (Gurley) (the time required for 100 ml of air to pass through a paper or paperboard with an area of 642 mm ² , hereinafter, also simply referred to as “resistance”) and means the maximum temperature at which the increase is 20% or less. Shall. That is, when the heat resistant temperature is 100 ° C. or higher, it means that the resistance after the heat treatment at 100 ° C. or higher for 10 minutes is within 1.2 times the resistance before heating. For example, in the case of a separator having a Gurley resistance before heating of 600 seconds, it may be 600 to 720 seconds after the heat treatment.

The electricity storage device of the present invention is prepared by preparing an electrode body in which a positive electrode and a negative electrode are wound or laminated with a separator interposed therebetween, and mounting an exterior body such as a can or a polypropylene-aluminum laminate film on the electrode body. It heat-drys with the dryer set to the temperature below heat-resistant temperature, and inject | pours electrolyte solution. Alternatively, after the electrode body is heated and dried in advance, an exterior body may be attached and the electrolytic solution may be injected. When performing heat drying, it is more preferable to heat dry under reduced pressure conditions because the drying time can be shortened.
For example, the separator used in LIB is mainly polyethylene, and when such a separator is used for the electricity storage device of the present invention, it may be heated and dried at 80 ° C. Moreover, if it is a cellulose-type separator, what is called a paper separator, it can be heat-dried at the temperature of 120 degreeC or more. By setting such temperature conditions, the electrode body before injecting the electrolyte solution can be dried without blocking the pores opened in the separator, and the output characteristics of the storage element are maintained. Reliability can be improved. Although the details of the reason why the reliability of the electricity storage element is improved by heating and drying the electrode body before injection is not clear, it is considered that the amount of water contained in the positive electrode and the negative electrode can be reduced.

Examples of the solvent for the non-aqueous electrolyte used in the electricity storage device of the present invention include cyclic carbonates represented by ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl carbonate. A chain carbonate represented by methyl (MEC), lactones such as γ-butyrolactone (γBL), and a mixed solvent thereof can be used.
As a salt dissolved in these solvents, lithium salts such as LiBF ₄ and LiPF ₆ can be used. The salt concentration of the electrolytic solution is preferably in the range of 0.5 to 2.0 mol / L. If it is less than 0.5 mol / L, the anion is insufficient and the capacity of the electricity storage device decreases. On the other hand, if it exceeds 2.0 mol / L, undissolved salt may remain in the electrolytic solution, or the viscosity of the electrolytic solution increases and the conductivity decreases. The negative electrode used in the electricity storage device of the present invention can be doped with lithium in advance. By doping with lithium, it is possible to control the initial efficiency, capacity, and output characteristics of the power storage element.

Reference examples, examples, and comparative examples are shown below to further clarify the features of the present invention.
<Reference Example 1>
150 g of commercially available pitch-based activated carbon (BET specific surface area 1955 m ² / g) is placed in a stainless steel mesh basket and placed on a stainless steel bat containing 300 g of coal-based pitch, and an electric furnace (effective size in the furnace 300 mm × 300 mm) × 300 mm) and heat treatment was performed. In the heat treatment, the temperature was raised to 670 ° C. in 4 hours in a nitrogen atmosphere, maintained at the same temperature for 4 hours, then cooled to 60 ° C. by natural cooling, and then taken out from the furnace.
The obtained product had a BET specific surface area of 240 m ² / g.
Next, 83.4 parts by mass of the composite porous material obtained above, 8.3 parts by mass of acetylene black, 8.3 parts by mass of PVdF (polyvinylidene fluoride) and NMP (N-methylpyrrolidone) were mixed, and the slurry was mixed. Obtained. Next, the obtained slurry was applied to one side of a copper foil having a thickness of 14 μm, dried, and pressed to obtain a negative electrode having a thickness of about 87 μm.

Next, 81.6 parts by mass of commercially available pitch-based activated carbon identical to the raw material of the composite porous material of the negative electrode, 6.1 parts by mass of Ketjen black and 12.3 parts by mass of PVdF and NMP were mixed with Al having a thickness of 30 μm. The foil was coated on both sides and dried to obtain a positive electrode having a thickness of about 340 μm.
One of the positive electrodes and two of the negative electrodes were cut out from the electrode obtained above so that the geometric area of the portion where the active material was applied was 3 cm ² . A lithium metal having the same area and a thickness of 20 μm is pressed so as to contact the composite porous material of the two negative electrodes, and a cellulose separator (Nippon Advanced Co., Ltd.) having a thickness of 30 μm between the positive electrode and the two negative electrodes with the positive electrode as the center. A product name: TF40-30) made by paper industry was sandwiched to prepare an electrode body. The separator had a liquid resistance of 1.17 Ωcm ² and a density of 0.40 g / cc. The prepared electrode body is put into a container formed of a laminate film made of PP (polypropylene) and aluminum, and heated and dried at 110 ° C. for 10 minutes under a reduced pressure condition in a vacuum dryer, and then EC and DEC are in a volume ratio of 3: 7. A nonaqueous electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L was injected into the mixed solvent and sealed to prepare an electricity storage device. In addition, it was confirmed by measuring the sample of only the separator prepared separately that there was no change of the resistance of the separator before and behind this heat drying.

The created storage element is charged with constant current and constant voltage for 2 hours at a maximum current of 3 mA and a maximum voltage of 4.0 V in a thermostatic chamber set at 25 ° C., the discharge current is 3 mA, and the voltage of the storage element is 2 V. The battery was discharged at a constant current until a reference capacity was confirmed.
Next, constant current and constant voltage charging is performed at a maximum current of 50 mA and a maximum voltage of 4.0 V for 10 minutes. The discharge current is set to 200 mA and discharged at a constant current until the voltage of the storage element shows 2 V. At this time, the capacity is 3 mA. The output characteristics were calculated from the ratio of capacity when discharged.
Next, constant current and constant voltage charging was performed for 2 hours at a maximum current of 50 mA and a maximum voltage of 4.0 V. After the charging was completed, the storage element was moved to a constant temperature bath at 60 ° C. At this time, the open terminal voltage (OCV) of the electricity storage element was 4.0V. The storage element was taken out of the thermostat after 100 hours and the open terminal voltage was measured and found to be 3.85V. The above results are summarized in Table 1.
In Table 1, the output characteristics and the open terminals after 100 hours are expressed as “200 mA / 3 mA output maintenance rate (%)” and “OCV (V) after 100 hours”, respectively.

<Example 1>
Reference Example, except that a polyethylene separator (prototype manufactured by Asahi Kasei Co., Ltd.) having a thickness of 22 μm, a liquid resistance of 1.86 Ωcm ² and a density of 0.50 g / cc was used, and the heating and drying temperature was set to 80 ° C. A power storage device was prepared and evaluated in the same manner as in 1. The results are summarized in Table 1. It was confirmed in the same manner as in Reference Example 1 that there was no change in the resistance of the separator before and after heat drying.
<Example 2>
Reference Example, except that a polyethylene separator having a thickness of 25 μm, a liquid resistance of 2.13 Ωcm ² , and a density of 0.56 g / cc (prototype manufactured by Asahi Kasei Co., Ltd.) was used and the heating and drying temperature was 80 ° C. A power storage device was prepared and evaluated in the same manner as in 1. The results are summarized in Table 1. It was confirmed in the same manner as in Reference Example 1 that there was no change in the resistance of the separator before and after heat drying.
<Reference Example 2>
The same as Reference Example 1 except that a cellulose separator (trade name: TF40-50, manufactured by Nippon Kogyo Paper Industries Co., Ltd.) having a thickness of 50 μm, a liquid resistance of 1.53 Ωcm ² and a density of 0.42 g / cc was used. A storage element was created and evaluated. The results are summarized in Table 1. It was confirmed in the same manner as in Reference Example 1 that there was no change in the resistance of the separator before and after heat drying.

<Comparative Example 1>
The same as Reference Example 1 except that a cellulose separator (trade name: CTW57-55 manufactured by Nippon Kogyo Paper Industries Co., Ltd.) having a film thickness of 55 μm, a liquid resistance of 3.15 Ωcm ² and a density of 0.61 g / cc was used. A power storage device was prepared and evaluated. The results are summarized in Table 1. As is clear from Table 1, the output characteristics of the electricity storage device were not good. It was confirmed in the same manner as in Reference Example 1 that there was no change in the resistance of the separator before and after heat drying.
<Comparative example 2>
The film thickness is 14 μm, the liquid resistance is 1.33 Ωcm ² , and the density is 0.51 g / cc. A polyethylene separator (prototype manufactured by Asahi Kasei Co., Ltd.) is used. A device was prepared and evaluated in the same manner as in Example 1. The results are summarized in Table 1. As is clear from Table 1, the storage characteristics of the electricity storage device were not good. It was confirmed in the same manner as in Reference Example 1 that there was no change in the resistance of the separator before and after heat drying.

The above results are summarized in Table 1. In Table 1, the output retention ratio (A) / (B) per unit volume of the element was calculated as the volume of the electricity storage element and the pseudo energy density. This seems that there is no significant difference in the energy density between the electricity storage elements at a current value as small as 3 mA, but when the current is as large as 200 mA, which is actually used, the influence on the energy density between the electricity storage elements is large. Therefore, such an index is calculated.
From Table 1, it can be seen that the power storage elements of the examples all have good output characteristics and a large pseudo energy density (A) / (B). On the other hand, in Comparative Example 1, the liquid resistance is large and the film thickness is large, the output characteristics are lowered, and the pseudo energy density is also low. On the other hand, it can be seen that the liquid resistance as in Comparative Example 2 has good output characteristics, but the film thickness is small and micro-shorts occur, and the self-discharge characteristics (OCV after 100 hours) decrease.

  The non-aqueous lithium storage element of the present invention can be suitably used as a storage element for a hybrid drive system.

It is a diagram for explaining a method of measuring the resistance value R1 and the resistance value R2 for calculating the liquid resistance of the separator (Ωcm ^2).

Claims (4)

From a positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and an exterior body The positive electrode active material layer contains activated carbon, the negative electrode active material layer contains a lithium ion storable carbon material, and the separator is any one selected from the group consisting of polyethylene, polypropylene, polyimide, and polyamide. A non-aqueous lithium storage element, characterized in that the material of the separator is 15 μm or more and 50 μm or less and the liquid resistance of the separator is 2.5 Ωcm ² or less.   The density of a separator is 0.35 g / cc or more and 0.55 g / cc or less, The nonaqueous lithium storage element according to claim 1 characterized by things.   3. The non-aqueous lithium storage element according to claim 1, wherein the lithium ion storable carbon material is a composite porous material in which a carbonaceous material is deposited on the surface of activated carbon. A positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte, and an exterior body The material has a film resistance of 15 μm to 50 μm and a liquid resistance of any one selected from the group consisting of a positive electrode containing activated carbon in the positive electrode active material layer, polyethylene, polypropylene, polyimide, and polyamide. A separator having a resistance of ^2.5 Ωcm ² or less and a negative electrode containing a carbon material capable of occluding lithium ions in the negative electrode active material layer are stacked or wound into an outer package, and dried by heating at a temperature not higher than the heat resistance temperature of the separator. And then injecting a non-aqueous electrolyte solution, a method for producing a non-aqueous lithium storage element.

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