JP2010062299A - Electricity storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electricity storage device that is capable of preventing a reduction in volume energy density while achieving high power output even when using a positive electrode including particles of activated carbon or the like which have pores. <P>SOLUTION: In the electricity storage device, a closed container 4 contains a power generation cell, in which a positive electrode 2 and a negative electrode 1 are opposed to each other across a separator, and a lithium metal electrically connected to the negative electrode with the power generation cell and the lithium metal immersed in a nonaqueous electrolyte solvent 40. The negative electrode is pre-doped, and the positive electrode includes at least a positive-electrode active material, a conductive material, and a binder. When the converted specific surface area of the positive-electrode active material, which is measured by a laser diffraction/scatter type particle size distribution measuring apparatus, is defined as CS1, the real density of the positive-electrode active material is defined as ρ1, the ratio by weight of the positive-electrode active material is defined as W1, the converted specific surface area of the conductive material, which is measured by the apparatus, is defined as CS2, the real density of the conductive material is defined as ρ2, and the ratio by weight of the conductive material is defined as W2, the following formula is satisfied: 0.5<R=(CS2/ρ2×W2)/(CS1/ρ1×W1)<2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention particularly relates to a power storage device such as a lithium ion capacitor including a positive electrode in which particles having pores such as activated carbon are used as a positive electrode active material.

  In recent years, as environmental problems have been highlighted, research on distributed power sources in which small-scale power supply facilities are distributed in power demand areas and the development of new environmentally friendly energy sources have been conducted. As part of these efforts, the power generated by solar and wind power generation is attracting attention as a clean energy source that can be used as a distributed power source and has a low environmental burden. In order to use these clean energy on a daily basis instead of the energy source that can be obtained, an electricity storage device that accumulates the obtained electric power and can stably discharge the necessary amount when necessary is required. Become.

Therefore, use of a lithium ion capacitor or the like is expected as such an electricity storage device.
In this lithium ion capacitor, for example, a plurality of positive electrode plates and negative electrode plates are laminated with a separator interposed therebetween, and the lithium ion capacitor is schematically configured by being accommodated in an airtight container while being immersed in an electrolytic solution. .

  In this positive electrode plate, a positive electrode mixture layer is formed on both surfaces of a current collector made of a metal foil such as a nickel foil or an aluminum foil. The positive electrode mixture layer includes at least a positive electrode active material, a conductive agent, and In addition to containing a binder, carbon such as activated carbon capable of reversibly supporting lithium ions and / or anions is used as the positive electrode active material.

  On the other hand, a negative electrode mixture layer made of a carbon material capable of occluding and releasing alkali metal ions such as lithium ions is formed on both sides of a current collector made of a metal foil such as a copper foil. Further, in this sealed container, lithium metal or the like is attached to a current collector or the like of the negative electrode, and the negative electrode plate occludes / releases lithium ions eluted from the lithium metal into the electrolytic solution. .

  As a result, the lithium ion capacitor is charged / discharged by reversible loading of lithium ions and / or anions at the positive electrode and insertion / release of lithium ions etc. at the negative electrode, and thus has a smaller electric capacity than a lithium ion secondary battery. However, since it does not involve a chemical reaction, it has low resistance, that is, high output and high charge / discharge speed, and has durability against repeated charge / discharge, and is excellent in charge / discharge characteristics. In addition, the energy capacity can be increased by pre-doping the negative electrode mixture layer in advance with lithium ions or the like to increase the operating voltage.

  In addition to this, the lithium ion capacitor has a withstand voltage of an electric double layer capacitor even when compared with a single electric double layer capacitor in which a large number of plate-like electrodes and separators used for large current applications are laminated. Is about 1.3 V for aqueous electrolytes and about 2.5 V for organic solvent electrolytes, so the energy density is low, but it can be used as a high-capacity small space power source. In other words, the lithium ion capacitor is a power storage device that has a charge / discharge characteristic superior to that of the lithium ion secondary battery and high output, and has a higher capacity and a smaller space than the electric double layer capacitor.

  For this reason, this lithium-ion capacitor is used as an in-vehicle power supply instead of a lead battery, as well as a hybrid electric vehicle that replaces a gasoline vehicle. Use in various applications is also being considered because it is easy to respond to changes in the form and is not subject to restrictions on installation location, such as expected to be used as a driving power source for fuel vehicles.

Japanese Patent Laid-Open No. 2005-197084

  By the way, if this lithium ion capacitor pursues further higher output, the particle size of the positive electrode active material is reduced and the surface area is increased, but in that case, an excessive amount of conductive material and binder are required. As the volume of the positive electrode increases, there is a problem that the energy capacity per volume, that is, the volume energy density is reduced.

  On the other hand, in the lithium ion secondary battery, as shown in Patent Document 1, the ratio of the total surface area of the conductive material to the total surface area of the positive electrode active material is calculated from the BET specific surface area, and the appropriate amount of the conductive material is determined. By specifying, a method for preventing a decrease in volume energy density while obtaining a high output has been proposed.

  However, even if this method of calculating from the BET specific surface area is used, in the lithium ion capacitor, since the positive electrode mixture layer is made of activated carbon or the like, the surface area is added to the surface in the pores of the particles that have nothing to do with the output. It will be.

  The present invention has been made in view of such circumstances, and even when using a positive electrode in which particles such as activated carbon have pores, while specifying an appropriate amount of active material and amount of conductive material to obtain high output It is an object of the present invention to provide an electricity storage device that can prevent a decrease in volume energy density.

  In other words, the power generation cell in which the positive electrode capable of reversibly carrying lithium ions or anions and the negative electrode capable of occluding and releasing lithium ions are arranged opposite to each other with a separator interposed therebetween. In the electricity storage device housed in a sealed container in a state of being immersed in an electrolyte solution containing lithium salt together with lithium metal electrically connected to the negative electrode, the negative electrode is pre-doped to previously store lithium ions, The positive electrode is composed of at least a positive electrode active material, a conductive material, and a binder. The converted specific surface area of the positive electrode active material measured by a laser diffraction scattering particle size distribution analyzer is CS1, the true density is ρ1, and the weight ratio is W1. And the converted specific surface area of the conductive material measured by the laser diffraction / scattering particle size distribution analyzer is CS2, Is the ratio of the total picture surface area of the conductive material to the total surface area of the positive electrode active material, R = (CS2 / ρ2 × W2) / (CS1 / ρ1 × W1) is 0. It is characterized by 5 <R <2.

  According to a second aspect of the present invention, in the electricity storage device according to the first aspect, the power generation cell includes a plurality of sets in which the positive electrode and the negative electrode are alternately stacked via a separator between each other. It is characterized by being provided.

  According to the electricity storage device according to claim 1, the ratio R = (CS2 / ρ2 × W2) / (CS1 / ρ1 × W1) of the total surface area of the conductive material to the total surface area of the positive electrode active material is 0.5. Since <R <2, it is possible to prevent a decrease in volume energy density while obtaining a high output. In particular, as in the electricity storage device according to claim 2, by increasing the energy capacity by providing a plurality of pairs of positive electrodes and negative electrodes alternately stacked via separators between each other, , Can increase the output.

Hereinafter, a lithium ion capacitor according to the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the lithium ion capacitor of this embodiment includes a negative electrode plate 1 in which a negative electrode mixture layer 11 is formed on the front and back surfaces of a rectangular thin plate-like current collector 10, and a positive electrode mixture layer 21. Are arranged on the front and back surfaces of the current collector 20 in the shape of a rectangular thin plate, the plate surfaces thereof are arranged in the vertical direction, and a plurality (alternately) of the positive electrode plates 2 are interposed with separators 3 interposed therebetween. In the embodiment, three sheets are laminated). The negative electrode plate 1 and the positive electrode plate 2 are immersed in the non-aqueous electrolyte 40 and accommodated in the sealed container 4. The non-aqueous electrolyte 40 is not suitable for the negative electrode plate 1 and the positive electrode plate 2. A solution in which a lithium salt such as LiBF ₄ or LiPF ₆ is dissolved in an active organic solvent is used.

  In the negative electrode plate 1, carbon capable of occluding and releasing lithium ions is used as the negative electrode mixture layer 11, and the negative electrode mixture layer 11 is formed on the front and back surfaces of the current collector 10 as shown in FIG. 3. It is formed on substantially the entire surface except for the central portion in the width direction. A copper foil is used as the current collector 10 and is electrically connected to the negative electrode mixture layer 11 at the center of the current collector 10 where the negative electrode mixture layer 11 is not formed. An elongated plate-like lithium metal 12 is stuck in the vertical direction. Further, the current collector 10 is provided with a tab 10a made of the same material as that of the current collector 10 at one upper corner (upper right corner in FIG. 1).

  On the other hand, in the positive electrode plate 2, as shown in FIG. 4, the positive electrode mixture layer 21 is formed on the front and back surfaces of the current collector 20 on the substantially entire surface except for the center part in the width direction, that is, the corresponding part of the lithium metal 12. ing. The positive electrode mixture layer 21 contains at least a positive electrode active material, a conductive material, and a binder. The positive electrode active material can reversibly carry lithium ions and / or anions in the non-aqueous electrolyte 40. Carbon such as activated carbon is used.

The positive electrode mixture layer 21 has a converted specific surface area measured by a laser diffraction / scattering particle size distribution measuring device of the positive electrode active material, CS1 (m ² / cc), a true density ρ1 (g / cc) of the positive electrode active material, The converted specific surface area measured by the laser diffraction / scattering particle size distribution measuring device of the conductive material with the weight ratio W1 of the positive electrode active material is CS2 (m ² / cc), the true density ρ2 (g / cc) of the conductive material, the conductive material When the weight ratio of the material is W2, R = (CS2 / ρ2 × W2) / (CS1 / ρ1 × W1), which is the ratio of the total surface area of the conductive material to the total surface area of the positive electrode active material, is 0.5 <R <. 2 is prepared. Here, the weight ratios W1 and W2 are the weights of the positive electrode active material or the conductive material when the total weight of the three components of the positive electrode active material, the conductive material, and the binder is 100, and the weight ratio with respect to the three components is That means.

  Thus, the particles are spherical from the particle size distribution obtained from the particle diameter, the number, the surface area, and the volume of the powder of the positive electrode active material or the conductive material by measuring with a laser diffraction scattering type particle size distribution measuring device. Assuming that, the converted specific surface area is obtained. For this reason, by adjusting the R so that 0.5 <R <2, it is possible to obtain a lithium ion capacitor in which the volume energy density does not decrease while obtaining high output even when the powder has pores. can get.

  The current collector 20 is made of nickel foil, aluminum foil, or the like, and the remaining upper corner portion (FIG. 1) that does not overlap with the tab 10a of the negative electrode plate 1 when laminated as described above. A tab 20a made of the same material as that of the current collector 20 is provided integrally with the upper left corner).

  The tabs 20a of all the positive electrode plates 2 are welded and electrically connected to a common positive electrode terminal plate 42 penetrating the sealed container 4, and the tabs 10a of all the negative electrode plates 1 are connected to the sealed container 4. It welds and is electrically connected to the common negative electrode terminal plate 41 which penetrates.

  The airtight container 4 is made of a flexible material obtained by processing an airtight soft packaging material such as a laminate film into a rectangular bag shape by fusion or the like. The inside of the airtight container 4 includes a positive terminal plate 42 and Even if the negative electrode terminal plate 41 penetrates, airtightness is maintained.

  In the lithium ion capacitor configured as described above, the ratio R = (CS2 / ρ2 × W2) / (CS1 / ρ1 × W1) of the total surface area of the conductive material to the total surface area of the positive electrode active material is 0.5 <R. Since <2, it is possible to prevent a decrease in volume energy density while obtaining a high output.

  Note that the present invention is not limited to the above-described embodiment, and other than the lithium ion capacitor, that is, by specifying an appropriate amount of active material and amount of conductive material to obtain a high output while reducing the output density. The present invention is also applicable to other power storage devices such as lithium secondary batteries that are expected to have an effect of preventing the above.

  Next, the lithium ion capacitors of Examples 1 to 3 and Comparative Examples 1 to 6 having the positive electrode plate 2 having the positive electrode mixture layers 21 having different R are prepared, and 0.5 <R <2 is satisfied. It was confirmed as follows that a decrease in volume energy density can be prevented while obtaining a high output, that is, a low resistance value.

[Preparation of positive electrode plate 2]
First, in order to produce each of the positive electrode plates 2 of Examples 1 to 3 and Comparative Examples 1 to 6, activated carbon powders as cathode active materials having different CS1 and ρ1 shown in Table 1 and conductive materials having different CS2 and ρ2 are used. The above activated carbon powder, acetylene black, and polyvinylidene fluoride powder as a binder were mixed at different ratios shown in Table 1, respectively.
CS1 and CS2 are values measured using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Nikkiso Co., Ltd.).

  Next, a mixture obtained by adding N-methylpyrrolidone to these mixtures and kneading them into a paste was applied to both sides of the belt-like aluminum foil and then dried to form the positive electrode mixture layer 21. After the aluminum foil on which the positive electrode mixture layer 21 is formed is cut into a predetermined shape according to the outer shapes of the current collector 20 and the tab 20a, the positive electrode mixture layer in the center in the width direction on the front and back surfaces of the current collector 20 By stripping 21, 10 positive electrode plates 2 of Examples 1 to 3 and Comparative Examples 1 to 6 in which the positive electrode mixture layer 21 was not formed at the center of the current collector 20 were obtained.

[Preparation of Negative Electrode Plate 1]
A non-graphitizable carbon material and polyvinylidene fluoride powder were mixed at a weight ratio of 95: 5, N methylpyrrolidone was added, and the mixture was kneaded into a paste form on both sides of the strip-shaped copper foil. The negative electrode mixture layer 11 was formed by drying after coating the entire surface.

  The copper foil on which the negative electrode mixture layer 11 is formed is cut into a predetermined shape according to the outer shapes of the current collector 10 and the tab 10a, and then the negative electrode mixture layer at the center in the width direction on the front and back surfaces of the current collector 10 The negative electrode plate 1 in which the negative electrode mixture layer 11 was not formed in the central portion of the current collector 10 was obtained by peeling off each of 11. Next, lithium metal 12 was attached to the surface of the current collector 10 of the negative electrode plate 1. As a result, as the negative electrode plates 1 of Examples 1 to 3 and Comparative Examples 1 to 6, 9 sets of 10 identical sheets were prepared.

Next, 10 sets of power generation cells constructed by alternately laminating 10 positive plates 2 and 10 negative plates 1 of Example 1 with separators 3 interposed between each other are assembled. After that, all the tabs 20a are welded to the positive terminal plate 42 and all the tabs 10a are welded to the negative terminal plate 41, respectively. Subsequently, the whole is sandwiched from both ends in the laminating direction by two aluminum laminate films except for a part of the negative electrode terminal plate 41 and the positive electrode terminal plate 42, and then the terminal plates 41, 42 are sealed by heat sealing. After sealing three sides excluding one side, polypyrene carbonate having a concentration of LiPF ₆ adjusted to 1 mol / L as the electrolyte 40 is injected, and the remaining one side on the terminal plates 41 and 42 side is injected. The sealed container 4 was formed by sealing, and the lithium ion capacitor of Example 1 was produced.
Similarly, lithium ion capacitors of Examples 2 to 3 and Comparative Examples 1 to 6 were produced using the 10 positive plates 2 and 10 negative plates 1 described above.

Except for the positive electrode plate 2 described above, the volume energy density and resistance of the lithium ion capacitors of Examples 1 to 3 and Comparative Examples 1 to 6 having the same configuration were measured. The volume energy density is the amount of electric power when a lithium ion capacitor is left for 10 days and then charged at a current value of 1 A up to 3.8 V at 25 ° C., and discharged at a current value of 1 A up to 2.2 V after resting for 1 minute. The resistance was calculated by dividing by the volume of the cell, and the resistance was calculated in the same manner as the volume energy density, and then discharging was performed at a current value of 100 A, and the direct current resistance was calculated from the initial voltage drop after the discharge was started.
The results are shown in Table 2.

  As can be seen from Table 2, the lithium ion capacitors of Examples 1 to 3 can prevent a decrease in volume energy density while keeping the resistance low. On the other hand, although the lithium ion capacitors of Comparative Examples 1 to 6 have low resistance, the volume energy density is too low, and when a large capacity is required, the lithium ion capacitors are practically hindered. is there.

It is a fracture | rupture front view which shows the lithium ion capacitor of this embodiment. FIG. 2 is a cutaway side view showing the lithium ion capacitor of the present embodiment, and is a cross-sectional view taken along line AA of FIG. 1. It is a front schematic diagram of the negative electrode plate 1 of this embodiment. It is a front schematic diagram of the positive electrode plate 2 of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode plate 2 Positive electrode plate 3 Separator 4 Airtight container 10 Current collector of negative electrode plate 1 11 Negative electrode mixture layer 20 Current collector for positive electrode plate 21 Positive electrode mixture layer

Claims (2)

A power generation cell in which a positive electrode capable of reversibly carrying lithium ions or anions and a negative electrode capable of occluding and releasing lithium ions are arranged opposite to each other via a separator.
With the lithium metal electrically connected to the negative electrode, in an electricity storage device housed in a sealed container in a state immersed in an electrolyte containing a lithium salt,
The negative electrode is pre-doped to previously store lithium ions,
The positive electrode comprises at least a positive electrode active material, a conductive material and a binder,
The converted specific surface area measured by the laser diffraction scattering type particle size distribution measuring device of the positive electrode active material is CS1, the true density is ρ1, the weight ratio is W1, and the conductive material is measured by the laser diffraction scattering type particle size distribution measuring device. When the converted specific surface area is CS2, the true density is ρ2, and the weight ratio is W2,
R = (CS2 / ρ2 × W2) / (CS1 / ρ1 × W1), which is a ratio of the total surface area of the conductive material to the total surface area of the positive electrode active material, satisfies 0.5 <R <2. device.   2. The power storage device according to claim 1, wherein a plurality of sets of the power generation cells are provided by alternately stacking a plurality of the positive electrodes and the negative electrodes with a separator interposed between each other.

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