JP7051423B2 - Power storage device - Google Patents

Description

The present invention relates to a power storage device.

As a method for improving the output density in a power storage device, a power storage device (hybrid capacitor) that combines two types of positive electrodes, a positive electrode in a lithium ion battery and a positive electrode used in an electric double layer capacitor, and a negative electrode in a lithium ion battery. It has been known. For example, Patent Document 1 describes a capacitor positive electrode in which a capacitor positive electrode layer containing fine particles of activated carbon is formed on one surface of a capacitor positive electrode collector foil, and a negative electrode on one surface of a negative electrode current collector foil having through holes. A battery positive electrode containing particles of a lithium-containing metal compound on one surface of a common negative electrode on which a layer is formed, a first separator sandwiched between the capacitor positive electrode layer and the negative electrode layer, and a battery positive electrode current collector foil. A power storage device cell comprising a battery positive electrode on which a layer is formed and a second separator sandwiched between a negative electrode current collecting foil and a battery positive electrode electrode layer, wherein a common negative electrode is common to a capacitor positive electrode and a battery positive electrode. Described is a power storage device cell in which the second separator is in contact with the other surface of the negative electrode current collector foil. Further, Patent Document 2 includes a positive electrode system composed of a positive electrode including a current collector and a positive electrode mixture layer, and a negative electrode system composed of a negative electrode including a current collector and a negative electrode mixture layer. In the device, the positive electrode system has a first positive electrode having a first positive electrode mixture layer and a second positive electrode having a second positive electrode mixture layer, and the negative electrode system has a first positive electrode and a second positive electrode. It has a negative electrode arranged between them, the first positive electrode mixture layer contains a transition metal oxide, the second positive electrode mixture layer contains activated carbon, and the first positive electrode mixture layer and the second positive electrode combination. It is described that a through hole is formed in the current collector of the negative electrode arranged between the material layer and the material layer.

Patent No. 5040626 Patent No. 5091573

In the power storage device in Patent Documents 1 and 2, through holes are formed in the current collector of the negative electrode. It is said that this makes it possible to stabilize the two electrode potentials (equilibrium state) and improve the responsiveness of the power storage device by moving the ions of the negative electrodes on both sides of the current collector to each other through the through holes. ing. However, providing a through hole in the current collector complicates the manufacturing process and increases the manufacturing cost.

The present invention has been made in view of such a background, and an object of the present invention is to provide a power storage device capable of improving energy density and output density with a simple configuration.

One aspect of the present invention for achieving the above object is a first positive electrode including a first positive electrode current collector and a first positive electrode mixture layer, and a first positive electrode including a second positive electrode current collector and a second positive electrode mixture layer. It has a positive electrode system composed of two positive electrodes and a negative electrode system composed of a negative electrode current collector and a negative electrode mixture layer provided on both sides of the negative electrode current collector, which is arranged between the first positive electrode and the second positive electrode. In the power storage device, the first positive electrode mixture layer and the second positive electrode mixture layer are electrically connected, and the negative electrode current collector is provided with through holes penetrating both sides of the negative electrode current collector. However, unlike the capacity of the first positive electrode and the capacity of the second positive electrode, the amount of the negative electrode mixture facing the first positive electrode mixture layer and the amount of the negative electrode mixture facing the second positive electrode mixture layer are different from each other. It is characterized in that the amount of the negative electrode mixture layer is evenly distributed .

The present inventors have short two positive electrodes if the first positive electrode mixture layer and the second positive electrode mixture layer are electrically connected even if the negative electrode current collector is not provided with a through hole. We obtained the finding that the equilibrium potential is reached in time. That is, by configuring the power storage device as in the present invention, it is possible to improve the energy density and the output density of the power storage device without the conventional complicated configuration such as providing a through hole in the negative electrode current collector.

For example, the active material of the first positive electrode mixture layer contains a transition metal oxide, and the active material of the second positive electrode mixture layer contains activated carbon. Thereby, high energy density and output density can be realized.

According to the present invention, the energy density and the output density can be improved with a simple configuration. Other effects will be clarified in the following description.

FIG. 1 is a diagram schematically showing an example of an internal structure of a power storage device 100 and a circuit configuration including a power storage device 100 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the internal structure of the sample of Example 2. FIG. 3 is a cross-sectional view schematically showing the internal structure of the comparative example 1 sample. FIG. 4 is a graph showing the results of evaluation experiment 2. FIG. 5 is a diagram showing an internal structure of the power storage device 300, which is another configuration example different from the power storage device 100.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(overall structure)
FIG. 1 is a diagram schematically showing an example of an internal structure of a power storage device 100 and a circuit configuration including a power storage device 100 according to an embodiment of the present invention. As shown in the figure, the power storage device 100 includes a positive electrode system composed of a first positive electrode 10 and a second positive electrode 20, and a negative electrode system 50 (common negative electrode) provided between the first positive electrode 10 and the second positive electrode 20. It is a power storage device configured to include.

The first positive electrode 10 has a foil-shaped first positive electrode current collector 12 and a first positive electrode mixture layer 14 formed by coating or the like on the surface thereof. The second positive electrode 20 has a foil-shaped second positive electrode current collector 22 and a second positive electrode mixture layer 24 formed by coating or the like on this surface.

On the other hand, the negative electrode system 50 includes a foil-shaped negative electrode current collector 54 and a negative electrode mixture layer 52. The negative electrode mixture layer 52 is formed by being applied to both sides of the negative electrode current collector 54, respectively. The negative electrode mixture layer 52a on the first positive electrode 10 side of the negative electrode current collector 54 faces the first positive electrode mixture layer 14 via the separator 30, and the negative electrode mixture on the second positive electrode 20 side of the negative electrode current collector 54. The layer 52b faces the second positive electrode mixture layer 24 via the separator 40.

The first positive electrode 10, the second positive electrode 20, and the negative electrode system 50 are housed in a predetermined packaging material 70 (for example, a laminated film or a metal can), and the electrolytic solution 80 is injected into the packaging material 70 and sealed.

Further, the first positive electrode current collector 12 and the second positive electrode current collector 22 electrically connected to each other by the lead wire 60 are connected to a predetermined circuit 200 (for example, a charger) via the lead wire 62 connected to the lead wire 60. , Discharger, and other power-consuming loads) are electrically connected to the positive electrode terminal 201, while the negative electrode terminal 202 of the circuit 200 is connected to the negative electrode current collector 54 in the negative electrode system 50 via a lead wire 64. Is electrically connected to the negative electrode system 50.

The positive electrode active material of the first positive electrode mixture layer 14 is, for example, an active material that can constitute the positive electrode of the battery, and specifically, for example, activated carbon, a transition metal oxide, or the like used in a lithium ion battery. .. More specifically, it is, for example, a transition metal oxide such as cobalt, manganese, vanadium, titanium, nickel (for example, lithium cobalt oxide (LiCoO ₂ )) or a sulfide.

The positive electrode active material of the second positive electrode mixture layer 24 is, for example, a positive electrode active material constituting the positive electrode of the electric double layer capacitor, and specifically, for example, a positive electrode active material used in a lithium ion capacitor (for example, activated carbon). ).

The negative electrode active material of the negative electrode mixture layer 52 is, for example, an active material that can constitute the negative electrode of the battery, and specifically, for example, a carbon-based material (for example, graphite) or tin used for the negative electrode of a lithium ion battery. Oxides, silicon oxides, etc.

The material of the first positive electrode current collector 12 and the second positive electrode current collector 22 is, for example, an electrode such as aluminum or stainless steel. The material of the negative electrode current collector 54 is, for example, an electrode made of stainless steel, copper, nickel, or the like.

The separators 30 and 40 are non-woven fabrics and the like having no electron conductivity, and are, for example, fibers made of cellulose, polyethylene, or polypropylene.

The electrolytic solution 80 is, for example, a solution having electrical conductivity, for example, an electrolytic solution containing a lithium salt. The lithium salt in this case is, for example, LiClO ₄ , LiAsF ₆ , LiBF ₄ , and LiPF ₆ . The solvent is, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate.

Here, the negative electrode current collector 54 has a through hole that enables mutual movement of ions generated by the first positive electrode mixture layer 14 and the second positive electrode mixture layer 24, which are provided in the conventional power storage device. Is not provided. On the other hand, as described above, the first positive electrode current collector 12 and the second positive electrode current collector 22 are electrically connected by the lead wire 60.

As described above, the present inventors quickly reach the equilibrium state of the potentials of the first positive electrode mixture layer 14 and the second positive electrode mixture layer 24 without providing a through hole in the negative electrode current collector 54, and the battery reaction occurs. We obtained the finding that it progresses stably.

Hereinafter, the evaluation experiment conducted by the present inventors in order to demonstrate this will be described.

<< Evaluation experiment >>
1. 1. Preparation of Samples First, based on the power storage device 100 shown in FIG. 1, three types of lithium ion battery samples (Example 1 sample, Example 2 sample, Comparative Example 1 sample) described below were prepared.

<Preparation of Example 1 sample>
The sample of Example 1 is a sample of a power storage device having no through hole in any of the current collectors, and each constituent material was prepared as follows.

(1st positive electrode)
As the first positive electrode current collector 12 in the first positive electrode 10, aluminum having no through hole was used. A slurry containing LiFePO ₄ as the active material of the first positive electrode mixture layer 14 was applied to one side of the aluminum foil obtained by pressing this at a grain size of 115 g / m ² on one side, and after drying, 5.0 cm × 3.0 cm. A first positive electrode 10 (positive electrode) was obtained by cutting a rectangular portion (excluding the terminal welded portion).

(Second positive electrode)
As the second positive electrode current collector 22 in the second positive electrode 20, aluminum having no through hole was used. On one side of the aluminum foil obtained by pressing this, a slurry of activated carbon as the active material of the second positive electrode mixture layer 24 was applied at a grain size of 45 g / m ² on one side, and after drying, a rectangular portion of 5.0 cm × 3.0 cm. A second positive electrode 20 (positive electrode) was obtained by cutting (excluding the terminal welded portion).

(Common negative electrode)
As the negative electrode current collector 54 in the negative electrode system 50, a copper foil having no through hole was used. A slurry obtained by mixing 100 parts by weight of pitch-coated graphite, 5.5 parts by weight of a conductive material, 2.0 parts by weight of a thickener, and 5.0 parts by weight of a binder on both sides of this copper foil is used as a negative electrode mixture layer 52, and has a single-sided amount. A negative electrode system 50 (common negative electrode) was obtained by applying at 39.5 g / m ² and drying, and then cutting a 5.2 cm × 3.2 cm rectangular portion (excluding the terminal welded portion).

(Separator)
As the separators 30 and 40, a non-woven fabric made of cellulose having a thickness of 35 μm was used.

A laminated body was produced by laminating the above constituent materials in the order of the first positive electrode 10, the separator 30, the negative electrode system 50, the separator 40, and the second positive electrode 20. The obtained laminated body was inserted into a laminated film as an exterior material, and a cell was assembled. Then, an electrolytic solution (a solution in which LiPF ₆ is dissolved in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a weight ratio of 1: 2 so as to have a concentration of 1 mol / L) is injected into this cell, and after impregnation under reduced pressure. , Vacuum sealed.

<Preparation of Example 2 sample>
In the second example sample, as in the first sample, no through hole is provided in any of the current collectors, and further, the thickness of the first negative electrode mixture layer 52a on the first positive electrode 10 side in the common negative electrode is large. It is larger than the thickness of the second negative electrode mixture layer 52b on the second positive electrode 20 side.

FIG. 2 is a cross-sectional view schematically showing the internal structure of the sample of Example 2. First, the constituent materials of the Example 2 sample were prepared as described below.

(1st positive electrode)
The same first positive electrode 10 as in Example 1 sample was prepared.

(Second positive electrode)
A second positive electrode 20 similar to that of Example 1 sample was prepared.

(Common negative electrode)
The slurry is applied to one surface (hereinafter referred to as the first surface) of the copper foil (negative electrode current collector 54) with a one-sided grain amount of 59 g / m ² to prepare a negative electrode mixture layer 52a, and the other surface of the copper foil is prepared. A negative electrode system 50 (common negative electrode) similar to that of Example 1 sample was prepared except that the slurry was applied to (hereinafter referred to as the second surface) at a grain size of 21 g / m ² on one side to prepare a negative electrode mixture layer 52b. ..

(Separator)
Separator 30 and 40 similar to those of Example 1 sample were prepared.

Example 2 sample of the laminated body was prepared by laminating the above-mentioned constituent materials in the order of the first positive electrode 10, the separator 30, the negative electrode system 50, the separator 40, and the second positive electrode 20. In this case, the coated surface of the first positive electrode 10 and the first surface of the common negative electrode (negative electrode system 50) are made to face each other, and the coated surface of the second positive electrode 20 and the second surface of the common negative electrode (negative electrode system 50) are relative to each other. I let you.

<Preparation of Comparative Example 1 sample>
Comparative Example 1 sample is a sample of a conventional power storage device in which a through hole 56 is provided in a negative electrode current collector 54.

FIG. 3 is a cross-sectional view schematically showing the internal structure of the comparative example 1 sample. First, as described below, the constituent materials of the comparative example 1 sample were prepared.

(1st positive electrode)
The same first positive electrode 10 as in Example 1 sample was prepared.

(Second positive electrode)
A second positive electrode 20 similar to that of Example 1 sample was prepared.

(Common negative electrode)
A common negative electrode (negative electrode system 50) similar to that of the sample in Example 1 was produced except that a copper current collector having a through hole 56 formed was used as the negative electrode current collector 54.

(Separator)
Separator 30 and 40 similar to those of Example 1 sample were prepared.

By laminating the above constituent materials in the order of the first positive electrode 10, the separator 30, the negative electrode system 50, the separator 40, and the second positive electrode 20, a sample of Comparative Example 1 of the laminated body was prepared.

2. 2. Characteristic evaluation experiment The evaluation experiment described below was performed on the Example 1 sample, Example 2 sample, and Comparative Example 1 sample prepared as described above.

(Evaluation experiment 1)
The target sample (cell) is charged with a constant current of 3 mA until the cell voltage reaches 3.8 V, and then a constant current-constant voltage charge of 3.8 V is applied, and the convergent current becomes 1.5 mA. Went up to. Then, it was discharged with a constant current of 3 mA until the cell voltage became 2.2 V. Such a 3.8V-2.2V charge / discharge test is performed not only for the above-mentioned discharge current ( 3 mA) but also for each of the cases of 300 mA, 450 mA, 600 mA, and 900 mA, and the discharge capacity of the cell is appropriately measured. bottom. In addition, this evaluation experiment was carried out for each of Example 1 sample, Example 2 sample, and Comparative Example 1 sample.

(Evaluation experiment 2)
As shown in FIG. 2, first, a predetermined position 60a (A in the figure) on the first positive electrode 10 side of the conductor 62 and a predetermined position 60b (B in the figure) on the second positive electrode 20 side of the conductor 60. , A current sensor was connected to each of the predetermined positions 60c (C in the figure) of the conducting wire 62. Then, the target sample (cell) is charged with a constant current of 28 mA until the cell voltage reaches 3.8 V, then pauses for 10 minutes, and then discharged with a constant current of 28 mA until the cell voltage reaches 2.2 V. After that, it was rested for 10 minutes. Then, the current value during this period was measured by the current sensors (A, B, C). This evaluation experiment 2 was performed on the sample of Example 1.

3. 3. Experimental results and examination <Evaluation experiment 1>
The following is a table showing the results of evaluation experiment 1.

As shown in this table, in Example 1, as the discharge current increases to 3 mA, 300 mA, 450 mA, 600 mA, and 900 mA, the discharge capacity of the cell is 19.4 mAh, 16.0 mAh (note that the rate of change). (Relative discharge capacity [%] when the discharge capacity is 100 when the discharge current is 3 mA) is 82.2), 10.9 mAh (change rate is 55.9), 8.0 mAh (change). The rate decreased to 41.2) and 5.5 mAh (rate of change was 28.3).

In Example 2, as the discharge current increases to 3 mA, 300 mA, 450 mA, 600 mA, and 900 mA, the discharge capacities of the cells are 19.5 mAh, 13.7 mAh (change rate is 82.2), and 8.4 mAh. (The rate of change was 42.9), 6.0 mAh (the rate of change was 30.8), and 3.7 mAh (the rate of change was 19.2 ).

In Comparative Example 1, as the discharge current increases to 3 mA, 300 mA, 450 mA, 600 mA, and 900 mA, the discharge capacities of the cells are 19.5 mAh, 15.6 mAh (change rate is 80.4), and 9.9 mAh. (The rate of change was 50.8), 7.2 mAh (the rate of change was 37.2), and 4.4 mAh (the rate of change was 22.6 ).

Comparing the experimental results of Example 1 sample and Comparative Example 1 sample, it was shown that there was almost no difference in the discharge capacities between the two, and that Example 1 sample was rather better. That is, it can be confirmed that even if a current collector having no through hole is used, there is no influence on the characteristics of the power storage device, or the characteristics of the power storage device may be improved.

Next, comparing the experimental results of Example 1 sample and Example 2 sample, Example 2 sample is not superior to Example 1 sample in terms of discharge capacity, but rather Example 1 sample. Is superior to the example 2 sample. From this, it can be seen that in the common negative electrode, it is not necessary to adjust the basis weight of the negative electrode mixture on each surface according to the capacity of the positive electrodes facing each other. That is, when the current collector of Example 1 is not provided with a through hole, the power storage device can be improved by a simple manufacturing process such as equalizing the basis weight of each negative electrode mixture in the common negative electrode.

<Evaluation experiment 2>
FIG. 4 is a graph showing the results of evaluation experiment 2. The horizontal axis represents the time (seconds) after the start of charging, the vertical axis on the left side represents the current (A), and the vertical axis on the right side represents the voltage (V) of the cell (sample). As shown in the figure, when a voltage is applied and the charging current 401 (coarse broken line in the figure) starts to flow in the power storage device 100, immediately after that, the current value 403 of the current on the second positive electrode 20 side (solid line in the figure). ) Increases, and then the current value 405 (fine broken line in the figure) of the current on the first positive electrode 10 side gradually increases. That is, immediately after charging, charging is started by the current on the second positive electrode 20 side having high responsiveness, and then charging is performed by the current on the first positive electrode 10 side having a large capacity.

When the charging current 411 is stopped about 2500 seconds after the start of charging, the current value 407 of the current on the second positive electrode 20 side decreases immediately after that, and then the current value 409 of the current on the first positive electrode 10 side. Gradually decreases. That is, immediately after the charging is stopped, the discharge by the current on the second positive electrode 20 side having high responsiveness is started, and then the discharge by the current on the first positive electrode 10 side having a large capacity is performed. After that, charging and discharging of the same behavior are repeated.

According to this evaluation experiment 2, a current is flowing between the first positive electrode mixture layer 14 of the first positive electrode 10 and the second positive electrode mixture layer 24 of the second positive electrode 20 even during the pause immediately after charging and discharging. Understand. That is, it can be seen that the potential difference between the two positive electrodes can be eliminated even when the through hole 56 is not formed in the common negative electrode (negative electrode current collector 54). From this, it can be seen that the energy density can be increased without impairing the output density.

The reason why the potential difference between the two poles can be eliminated and the responsiveness of the power storage device 100 can be stabilized without providing the through hole 56 can be described below.

That is, in the conventional power storage device provided with a through hole, for example, lithium ions and the like move between the negative electrode mixtures existing on both sides of the negative electrode current collector by the through hole to eliminate the potential difference between the two positive electrodes. Was supposed to be. However, according to this evaluation experiment, even if a through hole through which ions can move is not provided, for example, as shown in the power storage device 100 of FIG. 1, the first positive electrode mixture layer 14 and the second positive electrode mixture layer 24 It has been found that if the electrons are electrically connected by the conductor 60 or the like, the potential difference can be sufficiently eliminated by the movement of electrons through the conductor 60. That is, this means that in the negative electrode current collector 54 provided with the first positive electrode mixture layer 14 and the second positive electrode mixture layer 24 interposed therebetween, it is not necessary to provide a through hole through both the negative electrode mixture. Means. Since the battery reaction (oxidation-reduction reaction) related to ions in the power storage device 100 is performed between the active material and the electrolytic solution, it is considered that the battery reaction is not substantially inhibited even if the through hole is not provided.

As described above, in the power storage device 100 of the present embodiment, the first positive electrode mixture layer 14 and the second positive electrode mixture layer 24 are electrically connected to each other, while the negative electrode current collector 54 is connected to the negative electrode current collector 54. Since the through hole is not provided, the energy density and the output density of the power storage device 100 can be improved without the conventional complicated configuration such as providing the through hole in the negative electrode current collector 54.

That is, since the through hole has a shape for circulating ions generated from the first positive electrode mixture layer 14 or the second positive electrode mixture layer 24, the through hole complicates the manufacturing process such as circulating such ions. According to the power storage device 100 of the present embodiment, the energy density and the output density of the power storage device 100 can be improved even if the holes are not provided in the positive electrode.

Further, in the power storage device 100 of the embodiment, the active material of the first positive electrode mixture layer 14 may contain a transition metal oxide, and the active material of the second positive electrode mixture layer 24 may contain activated carbon. Thereby, high energy density and output density can be realized.

The above description of the embodiment is for facilitating the understanding of the present invention, and does not limit the present invention. The present invention can be modified and improved without departing from the spirit thereof, and the present invention includes its equivalents.

For example, FIG. 5 is a diagram showing an internal structure of a power storage device 300, which is another configuration example different from the power storage device 100. The same parts as those of the power storage device 100 are designated by the same reference numerals. The power storage device 300 is a power storage device including two negative electrode systems 350 and a positive electrode system 310 provided between the two negative electrode systems 350.

Each of the two negative electrode systems 350 has a foil-shaped negative electrode current collector 54 and a negative electrode mixture layer 52 formed by coating or the like on this surface.

On the other hand, the positive electrode system 310 includes a foil-shaped positive electrode current collector 312, a first positive electrode mixture layer 14 formed by being applied to one surface of the positive electrode current collector 312, and a positive electrode current collector 312. The second positive electrode mixture layer 24 formed by being applied or the like to the other surface of the above is provided. The first positive electrode mixture layer 14 faces one negative electrode system 350 via the separator 30, and the second positive electrode mixture layer 24 faces the other negative electrode system 350 via the separator 40.

Further, the two negative electrode current collectors 54 electrically connected to each other by the conductor 90 are electrically connected to the negative electrode terminal 202 of the predetermined circuit 200 via the conductor 92 connected to the conductor 90, and the other. The positive electrode terminal 201 of the circuit 200 is electrically connected to the positive electrode system 310 via a lead wire 94 connected to the positive electrode current collector 312 in the positive electrode system 310.

Further, the positive electrode current collector 312 is not provided with a through hole that enables mutual movement of ions generated by the first positive electrode mixture layer 14 and the second positive electrode mixture layer 24. On the other hand, the two negative electrode mixture layers 52 are electrically connected by a lead wire 90. Even with such a configuration, the same effect as that of the power storage device 100 can be obtained.

100 Power storage device, 10 1st positive electrode, 12 1st positive electrode current collector, 14 1st positive electrode mixture layer, 20 2nd positive electrode, 22 2nd positive electrode current collector, 24 2nd positive electrode mixture layer, 30 separator, 40 Separator, 50 Negative electrode system, 52 Negative electrode mixture layer, 52a 1st Negative electrode mixture layer, 52b 2nd Negative electrode mixture layer, 54 Negative electrode current collector, 56 Through holes, 60 conductors, 70 packaging material, 80 electrolyte, 90 Lead wire, 200 circuits, 201 positive electrode terminal, 202 negative electrode terminal, 300 storage device, 310 positive electrode system, 312 positive electrode current collector, 350 negative electrode system

Claims (2)

A positive electrode system including a first positive electrode including a first positive electrode current collector and a first positive electrode mixture layer, and a second positive electrode including a second positive electrode current collector and a second positive electrode mixture layer, and the first positive electrode. A power storage device having a negative electrode system arranged between a positive electrode and the second positive electrode and composed of a negative electrode current collector and a negative electrode mixture layer provided on both sides thereof.
The first positive electrode mixture layer and the second positive electrode mixture layer are electrically connected, and the negative electrode current collector is not provided with through holes penetrating both sides of the negative electrode current collector.
Unlike the capacity of the first positive electrode and the capacity of the second positive electrode,
The basis weight of the negative electrode mixture layer facing the first positive electrode mixture layer and the basis weight of the negative electrode mixture layer facing the second positive electrode mixture layer are equal.
A power storage device characterized by that. The power storage device according to claim 1 , wherein the active material of the first positive electrode mixture layer contains a transition metal oxide, and the active material of the second positive electrode mixture layer contains activated carbon.

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