JP2020009998A - Power storage device - Google Patents

Abstract

To increase the volume of a positive electrode active material layer making contribution to the rise in capacity and suppress the worsening of a low temperature rate characteristic without the need for increasing the thickness of a positive electrode active material layer.SOLUTION: A power storage device comprises an electrode body including a positive electrode, a negative electrode, an electrolyte solution and a separator. The electrode body includes one or more laminate structure units; in the laminate structure unit, a negative electrode current collector, a negative electrode active material layer, a positive electrode collection layer, a separator, and a negative electrode active material layer are laminated in this order. The positive electrode collection layer is arranged by repeatedly laminating two or more positive electrode laminate structure units, provided that in the positive electrode laminate structure unit, a separator and a positive electrode are laminated in this order.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power storage device including a positive electrode, a negative electrode, and an electrolyte.

  BACKGROUND ART Electric storage devices such as electrochemical capacitors are used, for example, as power sources for hybrid vehicles and electric vehicles. In order to improve the characteristics of the electricity storage device, the development of electrodes, electrolytes, separators, and the like, which are components thereof, is being actively promoted.

  In recent years, a further increase in the capacity of the power storage device has been demanded. For example, by increasing the thickness of the positive electrode active material layer of the electrode of the power storage device, the capacity (energy density) can be improved. However, in this case, the diffusion distance of the electrolyte solution ions (ion of the constituents of the electrolyte solution) in the electrolyte solution present in the positive electrode active material layer is increased, so that the ion diffusion resistance due to the movement of the electrolyte solution ions (hereinafter, referred to as “ion diffusion resistance”). (Referred to as "electrolyte ion diffusion resistance")). As a result, there is a problem that the low-temperature rate characteristics are reduced.

  On the other hand, Patent Literature 1 discloses a technique of forming a transmission hole (through hole) such as a cut through the electrode in an electrode (a current collector and an active material layer formed on the current collector). ing. This improves the permeability of the electrolytic solution into the positive electrode material layer, thereby compensating for a decrease in battery characteristics due to an increase in electrolytic solution ion diffusion resistance.

JP 2001-236945 A

  However, when the thickness of the positive electrode active material layer is increased in order to improve the capacity, simply forming a permeation hole in the electrode increases the diffusion distance of the electrolyte ions by the increased thickness, thereby reducing the electrolyte ion diffusion resistance. The increase cannot be suppressed. If the electrolyte ion diffusion resistance increases, the low-temperature rate characteristics deteriorate, which is not preferable.

  The present invention has been made to address the above problems. That is, one of the objects of the present invention is that, without increasing the thickness of the positive electrode active material layer, the volume of the positive electrode active material layer contributing to the improvement of the capacity can be increased, and the low-temperature rate characteristics deteriorate. Another object of the present invention is to provide a power storage device (hereinafter, may be referred to as “the power storage device of the present invention”) that can suppress the occurrence of the power storage device.

In order to solve the above problems,
The electricity storage device of the present invention
A positive electrode layer in which a positive electrode active material layer is formed on both surfaces of a positive electrode current collector layer,
A negative electrode layer in which a negative electrode active material layer is formed on both surfaces of the negative electrode current collector layer,
An electrolyte,
An electrolyte holding layer that holds the electrolyte,
Comprising an electrode body including
The electrode body is
The negative electrode current collector layer,
The negative electrode active material layer,
A positive electrode assembly layer having a stacked structure in which two or more positive electrode stacked structural units in which the electrolyte holding layer and the positive electrode layer are stacked in this order are repeatedly stacked;
An electrolyte holding layer,
A negative electrode active material layer,
Contains one or more laminated structural units laminated in this order.

In one embodiment of the power storage device of the present invention,
The positive electrode assembly layer has the laminated structure in which two positive electrode laminated structural units are repeatedly laminated.

In one embodiment of the power storage device of the present invention,
The electrode body includes a stacked structure in which two or more of the stacked structural units are repeatedly stacked.

In one embodiment of the power storage device of the present invention,
The electrolyte holding layer is a separator.

  According to the present invention, even if the thickness of the positive electrode active material layer is not increased, the volume of the positive electrode active material layer contributing to the improvement of the capacity can be increased, and the lowering of the low-temperature rate characteristic can be suppressed. .

FIG. 1 is a perspective view illustrating a configuration example of a power storage device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view illustrating a configuration example of the power storage device according to the embodiment of the present invention. FIG. 3 is a plan view showing a configuration example of the positive electrode. FIG. 4 is a sectional view taken along the line I-I 'of FIG. FIG. 5 is a plan view showing a configuration example of the negative electrode. FIG. 6 is a sectional view taken along line II-II 'of FIG. FIG. 7 is a schematic cross-sectional view for explaining a configuration example of the laminate. FIG. 8 is a schematic cross-sectional view illustrating the configuration of Reference Example 1 and Reference Example 2. FIG. 9 is a graph showing the relationship between the thickness of the positive electrode and the resistance. FIG. 10 is a schematic cross-sectional view illustrating a configuration example of the power storage device of Example 1-1 and Example 1-2. FIG. 11 is a schematic cross-sectional view illustrating a configuration example of a power storage device of Comparative Examples 1-1 to 1-3. FIG. 12 is a schematic cross-sectional view illustrating a configuration example of a power storage device of Comparative Example 2. FIG. 13 is a graph summarizing the measurement results of the example and the comparative example. FIG. 14 is a graph summarizing the measurement results of the example and the comparative example.

  Hereinafter, an electric storage device according to an embodiment of the present invention (hereinafter, referred to as “the present embodiment”) will be described with reference to the drawings. In this example, the power storage device is an electrochemical capacitor (specifically, a lithium ion capacitor). Note that, in this specification, “adsorbable and desorbable” means that reversible occlusion (adsorption and insertion) and desorption (release) are possible.

  1 and 2 show the configuration of the power storage device according to the present embodiment. As shown in FIGS. 1 and 2, the power storage device includes an outer case 11 having an internal space, an electrolytic solution 12 housed inside the outer case 11, and a laminate 13. The outer case 11 is, for example, a bag-shaped laminated film in which aluminum and polypropylene are laminated.

(Electrolyte)
The electrolytic solution 12 is a non-aqueous electrolytic solution and includes an electrolyte salt and a non-aqueous solvent. The electrolyte salt is dissolved in a non-aqueous solvent. The electrolyte solution 12 may include an additive for improving the characteristics of the electrolyte solution 12 as needed.

(Electrolyte salt)
As the electrolyte salt, for example, one or more kinds selected from LiPF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N, LiClO ₄ , and other lithium salts can be used.

(Non-aqueous solvent)
Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane (DME), and tetrahydrofuran. (THF), acetonitrile (AN), γ-butyl lactone (GBL), ethyl isopropyl sulfone (EiPS), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether ( One or more selected from HFE) can be used.

(Laminate)
The laminate 13 has a structure in which a plurality of positive electrodes 21 having a rectangular planar shape and a plurality of negative electrodes 22 having a rectangular planar shape are laminated via a separator 23 having a rectangular planar shape. Further, the laminate 13 may include pre-doped metal lithium 25. The laminate 13 is also referred to as an “electrode body” for convenience.

  The laminate 13 is impregnated with the electrolyte 12 and includes the electrolyte 12. The laminated structure of the electrode member and the like constituting the laminated body 13 will be described later in detail.

(Positive electrode)
As shown in FIGS. 3 and 4, the positive electrode 21 includes a positive electrode current collector 21A having a rectangular planar shape, and a positive electrode active material layer 21B stacked on both main surfaces of the positive electrode current collector 21A. .

  The positive electrode active material layer 21B is formed on the positive electrode current collector 21A such that a part of the positive electrode current collector 21A is exposed. The exposed part 21C of the positive electrode current collector 21A functions as a terminal part that extracts a current to the outside. The exposed portion 21C is electrically connected to the positive electrode terminal tab 31 via a conductive connection member 33. The positive terminal tab 31 functions as a positive terminal of the power storage device.

  The positive electrode current collector 21A is formed of a material having good conductivity (good conductor). In the present example, for example, a porous aluminum foil can be used as the positive electrode current collector 21A.

  The positive electrode active material layer 21B contains a positive electrode active material. The positive electrode active material layer 21B may include a binder (for example, SBR (styrene butadiene rubber)) as necessary.

  The positive electrode active material is composed of a material capable of absorbing and desorbing (reversibly occluding (adsorbing) and desorbing (releasing) the electrolyte salt anion). As the positive electrode active material, for example, carbon nanotubes or activated carbon can be used. The positive electrode active material may be used alone, or two or more kinds may be used in combination.

(Negative electrode)
As shown in FIGS. 5 and 6, the negative electrode 22 includes a negative electrode current collector 22A having a rectangular planar shape, and a formed negative electrode active material layer 22B laminated on both main surfaces of the negative electrode current collector 22A. And Note that the negative electrode active material layer 22B may be formed only on one main surface of the negative electrode current collector 22A.

  The negative electrode active material layer 22B is formed on the negative electrode current collector 22A such that a part of the negative electrode current collector 22A is exposed. The exposed part 22C of the negative electrode current collector 22A functions as a terminal part that extracts a current to the outside. The exposed portion 22 </ b> C is electrically connected to the negative terminal tab 32 via the conductive connection member 34. The negative terminal tab 32 functions as a negative terminal of the power storage device.

  The negative electrode current collector 22A is formed of a material (good conductor) having good conductivity. In this example, for example, a porous copper foil can be used as the negative electrode current collector 22A.

  The negative electrode active material layer 22B includes a carbon material capable of absorbing and desorbing lithium ions (capable of reversibly occluding (adsorbing) and desorbing (releasing)) and a binder (for example, SBR (styrene butadiene rubber) or the like). . Note that the binder may be omitted. As the carbon material, for example, carbon nanotube or graphite can be used. The negative electrode active material may be used alone, or two or more kinds may be used in combination.

  In order to improve the energy density, lithium ions may be previously stored (pre-doped) in the carbon material. In the case of performing pre-doping, when the laminated body 13 is immersed in the electrolytic solution 12 after assembling the laminated body 13, lithium ions are released into the electrolytic solution 12 from the pre-doped metal lithium 25 short-circuited with the negative electrode 22. Then, the pre-doped metal lithium 25 passes through the through-holes of the positive electrode current collector 21A and the negative electrode current collector 22A and diffuses throughout the stacked body 13, and lithium ions are doped (occluded) in the carbon material. After the pre-doping, the metal lithium 25 for pre-doping has disappeared.

(Separator)
The separator 23 is an insulating porous film provided to prevent a short circuit between the positive electrode 21 and the negative electrode 22. The separator 23 is an electrolyte holding unit (also referred to as an “electrolyte holding layer”) that holds the electrolyte 12. As the separator 23, for example, polyethylene, polypropylene, other insulating porous films, or nonwoven fabric can be used.

(Structure of laminate)
The laminated structure of the laminate 13 will be described in detail with reference to FIG. FIG. 7 is a schematic sectional view of the laminate 13. In addition, illustration of the conductive connection members 33 and 34 is omitted for convenience of explanation.

  As shown in FIG. 7, the laminate 13 includes a negative electrode current collector 22A, a pre-doped metal lithium 25, a separator 23, a negative electrode 22, a separator 23, a positive electrode 21, a separator 23, a positive electrode 21, and a separator 23. A plurality of stacked units stacked in this order, a negative electrode active material layer 22B, a negative electrode current collector 22A, and a negative electrode active material layer 22B have a stacked structure in which the stacked units are stacked in this order. In FIG. 7, the doping negative electrode current collector 22A and the pre-doping metal lithium 25 are arranged on the left side of the drawing, but they may be arranged on the right side of the drawing or on both left and right sides of the drawing. Further, the stacked body 13 may have a configuration in which the negative electrode active material layer 22B disposed on the rightmost side with respect to the paper surface of FIG. 7 is not stacked.

  This laminate 13 includes one or more (six in this example) laminate structural units S. In the laminated structural unit S, a negative electrode current collector 22A (a negative electrode current collector layer), a negative electrode active material layer 22B, a separator 23 (an electrolytic solution holding layer), and a positive electrode 21 (a positive electrode layer) are laminated in this order. It has a laminated structure in which a layer in which two positive electrode laminated structural units are repeatedly laminated (also referred to as a “positive electrode assembly layer”), a separator 23, and a negative electrode active material layer 22B are laminated in this order.

  In other words, the laminated structural unit S includes the negative electrode current collector 22A, the negative electrode active material layer 22B, the separator 23, the positive electrode 21, the separator 23, the positive electrode 21, the separator 23, and the negative electrode active material layer 22B laminated in this order. It has a laminated structure. In this example, the laminate 13 includes a laminate structure in which six laminate structure units S are repeatedly laminated.

  By the way, the present inventor has attempted to increase the capacity of a power storage device including a unit cell in which a pair of a positive electrode 21 and a negative electrode 22 are stacked with a separator 23 interposed therebetween, as in Reference Example 1 shown in FIG. In order to achieve this, it was studied to make the positive electrode active material layer 21B thicker than in Reference Example 1 as in Reference Example 2.

  In this case, as shown by the line p1 in FIG. 9, the diffusion distance of the electrolyte solution ions (ion of the component of the electrolyte solution 12) in the electrolyte solution present in the cathode active material layer 21B is increased, so that the positive electrode is increased. It was found that the ion diffusion resistance of the electrolyte in the active material layer 21B increased. For this reason, it was found that when the positive electrode active material layer 21B was made thicker than in Reference Example 1 as in Reference Example 2, low-temperature rate characteristics (particularly, high-rate low-temperature rate characteristics) deteriorated.

  FIG. 9 shows the third arc from the left in the Cole-Cole plot considered to correspond to the electrolyte ion diffusion resistance when the power storage device is measured by the AC impedance method in an environment of −40 ° C. It is the graph which plotted the magnitude | size (diameter) with respect to the positive electrode active material layer (thickness for two positive electrode active material layers 21B).

  On the other hand, the laminated structural unit S of the laminated body 13 of the present power storage device includes two opposed positive electrodes 21 (four positive electrode active material layers 21B) between a pair of negative electrode active material layers 22B. A separator 23 (electrolyte holding unit) is provided between the two opposed positive electrodes 21.

  Therefore, without increasing the thickness of the positive electrode active material layer 21B, the total (thickness D1) of the thicknesses d1 to d4 of the four positive electrode active material layers 21B becomes the unit cell unit including the pair of the positive electrode 21 and the negative electrode 22. It can be the total thickness of the positive electrode active material layer 21B. In other words, even if the thickness of the positive electrode active material layer 21B is not increased, the volume of the positive electrode active material layer 21B contributing to the improvement of the capacity per unit cell can be increased. Thus, the capacity of the power storage device can be increased as in the case of increasing the thickness of the positive electrode active material layer 21B as in Reference Example 2 without increasing the thickness of the positive electrode active material layer 21B.

  Further, since the thickness of the positive electrode active material layer 21B does not increase, it is possible to suppress an increase in the diffusion distance of electrolyte ions in the electrolyte solution 12 existing in the positive electrode active material layer 21B. Accordingly, it is possible to suppress a decrease in the low-temperature rate characteristic (high-rate low-temperature rate characteristic) when the thickness of the positive electrode active material layer 21B generated in Reference Example 2 is increased.

  Further, in the laminated structure unit S, a separator 23 (electrolyte holding portion) holding the electrolyte 12 is interposed between a pair of positive electrodes 21 facing each other. Accordingly, the electrolyte salt anion migrates from the separator 23 between the pair of positive electrodes 21 (a pair of positive electrodes 21 sandwiching the separator 23) due to the electrochemical reaction, whereby the electrolyte salt anion migrates between the pair of positive electrodes 21 sandwiching the separator 23. 21 is supplied to each positive electrode active material layer 21B. Thereby, it can be suppressed that the supply of the electrolyte salt anion from the electrolyte solution 12 to the positive electrode active material layer 21B becomes insufficient and the resistance increases.

  Further, the laminate 13 including the six laminate structural units S includes a pair of the positive electrode 21 and the negative electrode 22 with the separator 23 interposed therebetween (the negative electrode 22 in which the negative electrode active material layer 22B is formed only on one surface of the negative electrode current collector 22A). ) Is repeatedly laminated. Therefore, the capacity of the pair of positive electrodes 21 sandwiching the separator 23 can be more effectively utilized.

  Furthermore, the stacked body 13 including the six stacked structural units S can be configured such that the number of the negative electrode current collectors 22A is smaller than the number of the positive electrode current collectors 21A. Therefore, for example, in the case of using a relatively expensive negative electrode current collector 22A that needs to be subjected to a drilling process or the like, it is possible to suppress an increase in cost.

(Operation of power storage device (lithium ion capacitor))
In the electric storage device having the above-described configuration, charging and discharging of electric energy is performed at the negative electrode 22 by an electrochemical reaction (Faraday reaction) of lithium, and charging and discharging of electric energy at the positive electrode 21 by adsorption and release of an electrolyte salt anion. Is performed.

  When a predetermined voltage is applied between the positive electrode current collector 21A and the negative electrode current collector 22A of the power storage device having the above-described configuration, the electrolyte salt anion in the electrolytic solution 12 is adsorbed (occluded) on the positive electrode 21 side. On the other hand, lithium ions are adsorbed (occluded) on the negative electrode 22 side. Thus, the power storage device is charged.

  When a power load (electric resistance) is connected between the positive electrode current collector 21A and the negative electrode current collector 22A of the power storage device having the above-described configuration, an electrolyte salt anion is released from the positive electrode active material into the electrolyte solution 12 and Then, lithium ions are released from the negative electrode 22 (carbon material) into the electrolytic solution 12. Thereby, the power storage device is discharged.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

<Example 1-1>
The power storage device (lithium ion capacitor) of Example 1-1 was manufactured as follows.

(Preparation of positive electrode)
A slurry solution of a positive electrode mixture obtained by mixing activated carbon as a positive electrode active material, acetylene black as a conductive additive, and SBR as a binder in an aqueous solution in which carboxymethyl cellulose (CMC) is dispersed (negative electrode mixture slurry) Was prepared. The mixing ratio was adjusted so that activated carbon was 89% by weight, acetylene black was 5% by weight, CMC was 2% by weight, and SBR was 4% by weight.

  Next, the prepared positive electrode mixture slurry solution was applied to an aluminum foil (a structure having a porosity (air permeability of 40 seconds) having a rectangular portion (exposed portion 21C) projecting from a part of one side of the rectangular shape as the positive electrode current collector 21A. / 100 mL) and a thickness of 30 μm) (a rectangular area excluding the exposed part 21C).

  After that, water is removed from the positive electrode material mixture slurry by drying, and then rolled by a roll press to obtain an aluminum foil with a positive electrode active material layer 21B having an exposed portion 21C (uncoated portion) as a positive electrode terminal portion (ie, The positive electrode 21 (165 mm × 95 mm) shown in FIGS. 3 and 4 was obtained.

(Preparation of negative electrode)
A slurry solution of a negative electrode mixture obtained by mixing graphite as an anode active material, acetylene black as a conductive additive, and SBR as a binder in an aqueous solution in which carboxymethyl cellulose (CMC) is dispersed (negative electrode mixture slurry) Was prepared. The mixing ratio was adjusted so as to be 94% by weight of graphite, 2% by weight of acetylene black, 2% by weight of CMC and 2% by weight of SBR.

  Next, the prepared negative electrode mixture slurry solution is applied to a copper foil having a rectangular portion (exposed portion 22C) protruding from a part of one side of the rectangular shape as the negative electrode current collector 22A (a structure having porosity (opening ratio: 10%)). , A thickness of 18 μm) on both surfaces (a rectangular region excluding the convex portion).

  Then, after removing the water by drying the negative electrode mixture slurry solution, the negative electrode active material layer 22B having a thickness of 85 μm and having the exposed portion 22C (uncoated portion) as a negative electrode terminal portion is formed by rolling with a roll press. (That is, the negative electrode 22 (175 mm × 100 mm) shown in FIGS. 5 and 6).

(Preparation of electrolyte solution)
The electrolyte was prepared as follows. First, as a non-aqueous solvent, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of EC: PC: EMC: DEC = 30: 10. : 46.7: 23.3 to prepare a mixed solvent. Next, lithium hexafluorophosphate (LiPF ₆ ) was used as an electrolyte salt and dissolved in the prepared mixed solvent such that the electrolyte salt concentration became 1.0 mol / L. Thus, an electrolytic solution was obtained.

(Assembly of power storage device)
Next, as shown in FIG. 10, the prepared two positive electrodes 21, one negative electrode 22, and a polypropylene-made separator 23 having a thickness of 20 μm were combined with the negative electrode 22 / separator 23 / positive electrode 21 / separator 23 / positive electrode 21. A stacked body was formed by stacking in the order of / separator 23 / negative electrode 22. This laminate includes one laminated structural unit S (negative electrode current collector 22B / negative electrode active material layer 22B / separator 23 / positive electrode 21 / separator 23 / positive electrode 21 / separator 23 / negative electrode active material layer 22B).

  The thickness (total thickness) D1 of the positive electrode active material layer 21B of the laminate is the thickness d1 of the positive electrode active material layer 21B, the thickness d2 of the positive electrode active material layer 21B, the thickness d3 of the positive electrode active material layer 21B, and This is the sum of the thickness d4 of the positive electrode active material layers 21B. That is, the thickness (total thickness) D1 of the cathode active material layer 21B = the thickness d1 of the cathode active material layer 21B + the thickness d2 of the cathode active material layer 21B + the thickness d3 of the cathode active material layer 21B + the thickness of the cathode active material layer 21B. The thickness is d4.

  In Example 1-1, by adjusting the coating amount of the positive electrode mixture slurry solution and the like, the positive electrode active material layer 21B was adjusted so that the thickness (total thickness) D1 of the positive electrode active material layer 21B became 195 μm. Was adjusted in thickness.

  Next, the laminate was placed in an exterior body made of an aluminum laminate film, and then an electrolyte was injected into the exterior body, and the laminate was immersed in the electrolyte. Thereafter, the exterior body was sealed to obtain the power storage device (lithium ion capacitor) of Example 1. When the laminate is placed in the package, a negative electrode current collector layer 22A (not shown in FIG. 10), metal lithium 25 for pre-doping (not shown in FIG. 10), a separator 23 (not shown in FIG. 10) was inserted into the laminated body. Thereafter, a pre-doping process was performed by short-circuiting the negative electrode 22 and the metal lithium 25.

<Example 2>
A power storage device of Example 2 was manufactured in the same manner as in Example 1, except that the thickness (total thickness) D1 of the positive electrode active material layer 21B was changed to 198 μm.

<Comparative Example 1-1>
A positive electrode 21 was produced in the same manner as in Example 1, except that the thickness of the positive electrode active material layer 21B was changed so that the thickness (total thickness) D1 of the positive electrode active material layer 21B was 80 μm.

  In the process of assembling the electricity storage device, one produced positive electrode 21, two negative electrodes 22 and two separators 23 were divided into negative electrode 22 / separator 23 / positive electrode 21 / separator 23 / negative electrode 22 as shown in FIG. 11. To produce a laminated body. This laminated body does not include the laminated structural unit S.

  Note that the thickness (total thickness) D1 of the positive electrode active material layer 21B of this laminate is the sum of the thickness d11 of the positive electrode active material layer 21B and the thickness d12 of the positive electrode active material layer 21B. That is, the thickness (total thickness) D1 of the positive electrode active material layer 21B = the thickness d11 of the positive electrode active material layer 21B + the thickness d12 of the positive electrode active material layer 21B. Except for the above, an electricity storage device was manufactured in the same manner as in Example 1.

<Comparative Example 1-2>
Comparative Example 1 was performed in the same manner as in Comparative Example 1-1, except that the thickness of the positive electrode active material layer 21B was changed so that the thickness (total thickness) D1 of the positive electrode active material layer 21B was 149 μm. 2 power storage devices were produced.

<Comparative Example 1-3>
Comparative Example 1 was performed in the same manner as in Comparative Example 1-1, except that the thickness of the positive electrode active material layer 21B was changed so that the thickness (total thickness) D1 of the positive electrode active material layer 21B was 243 μm. 3 power storage devices were produced.

<Comparative Example 2>
The positive electrode 21 was produced in the same manner as in Example 1 except that the thickness of the positive electrode active material layer 21B was changed so that the thickness (total thickness) D1 of the positive electrode active material layer 21B was 198 μm. In the process of assembling the electricity storage device, the two produced positive electrodes 21, one negative electrode 22, and the separator 23 are divided into the negative electrode 22 / separator 23 / positive electrode 21 / positive electrode 21 / separator 23 / negative electrode 22 as shown in FIG. Were produced in this order. This laminated body does not include the laminated structural unit S.

  The thickness (total thickness) D1 of the positive electrode active material layer 21B of the laminate is a thickness d21 of the positive electrode active material layer 21B, a thickness d22 of the positive electrode active material layer 21B, a thickness d23 of the positive electrode active material layer 21B, and This is the sum of the thickness d24 of the positive electrode active material layer 21B. That is, the thickness (total thickness) D1 of the cathode active material layer 21B = the thickness d21 of the cathode active material layer 21B + the thickness d22 of the cathode active material layer 21B + the thickness d23 of the cathode active material layer 21B + the thickness of the cathode active material layer 21B. The thickness is d24. Except for the above, an electricity storage device of Comparative Example 2 was manufactured in the same manner as in Example 1.

(Evaluation)
Evaluations described below were performed on the manufactured power storage devices of the examples and the comparative examples.

(Capacity measurement)
(Measurement of capacity 1)
CC-CV charging (constant current constant voltage charging) was performed for 30 minutes at a temperature of 25 ° C. and a charging voltage of 3.8 V and a constant current of 1 C at a temperature of 25 ° C. Thereafter, CC discharge (constant current discharge) was performed at a discharge current of 1 C to a voltage of 2.2 V. Thereby, the discharge capacity (hereinafter, also referred to as “1 C capacity (25 ° C.)”) was measured.

  Then, the capacity ratio to the capacity of Comparative Example 1-1 (= “1 C capacity (25 ° C.) of each example or each comparative example) ÷“ 1 C capacity (25 ° C.) of Comparative Example 1-1) is calculated as capacity 1. did.

(Measurement of capacity 2)
CC-CV charging (constant current constant voltage charging) was performed for 30 minutes at a temperature of −10 ° C. and a charging current of 3.8 V and a constant current of 1 C. Thereafter, CC discharge (constant current discharge) was performed with a discharge current of 5 C to a voltage of 2.2 V. Thereby, the discharge capacity (hereinafter, also referred to as “5C capacity (−10 ° C.)”) was measured.

  Then, the capacity ratio to the capacity of Comparative Example 1-1 (= “5C capacity (−10 ° C.) of each example or each comparative example) ÷“ 5C capacity (−10 ° C.) of Comparative Example 1-1 ”) Calculated as 2.

  Note that 1C is a current value at which the theoretical capacity is discharged (or charged) in one hour. 5C is a current value at which the theoretical capacity is discharged (or charged) in 0.2 hours.

(Capacity retention rate)
(Measurement of capacity retention ratio 1)
CC-CV charging (constant current constant voltage charging) was performed for 30 minutes at a temperature of −10 ° C. and a charging current of 3.8 V and a constant current of 1 C. Thereafter, CC discharge (constant current discharge) was performed at a discharge current of 1 C to a voltage of 2.2 V. Thereby, the discharge capacity (hereinafter, referred to as “1 C capacity (−10 ° C.)”) was measured.

Then, for each example and each comparative example, the percentage of “1C capacity (−10 ° C.)” to “1C capacity (25 ° C.)” measured as described above was defined as the capacity retention ratio 1 according to the following equation (1). Calculated.

Capacity retention 1 = {“1C capacity of example (comparative example) X (−10 ° C.)” ”“ 1C capacity of example (comparative example) X same as above (25 ° C.) ”} × 100% (1)

(Measurement of capacity retention ratio 2)
For each example and each comparative example, the percentage of “5C capacity (−10 ° C.)” to “1C capacity (25 ° C.)” measured as described above was calculated as the capacity retention ratio 2 by the following equation (2). .

Capacity retention ratio 2 = {“5C capacity of Example (Comparative Example) X (−10 ° C.)” ”“ 1 C capacity of Example (Comparative Example) X same as above (25 ° C.) ”} × 100% (2)

  The measurement results are shown in Table 1 and FIGS.

  As shown in Table 1, and FIGS. 13 and 14, Examples 1 and 2 can increase the total volume of the positive electrode active material layer 21B without increasing the thickness of the positive electrode active material layer 21B, As a result, the capacity could be improved.

  Further, as shown in Table 1, FIG. 13 and FIG. 14, in Example 1 and Example 2, even when the thickness (total thickness) D1 of the cathode active material layer 21B is large, the low-temperature rate characteristics (high-rate It was confirmed that the deterioration of (characteristics) could be suppressed. 13 and 14 show, as reference values, the predicted values based on the data of the comparative example in the case of the cell configuration of FIG. 11 and the thickness (total thickness) D1 of the positive electrode active material layer 21B of 200 μm. (Calculated value).

<Modification>
As mentioned above, although embodiment and each Example of this invention were described concretely, this invention is not limited to said Embodiment and each Example, Various deformation | transformation based on the technical idea of this invention are carried out. Is possible.

  For example, the configurations, methods, steps, shapes, materials, numerical values, and the like described in the above-described embodiment and each example are merely examples, and different configurations, methods, steps, shapes, materials, and numerical values may be used as necessary. Etc. may be used.

  Further, the configurations, methods, steps, shapes, materials, numerical values, and the like of the above-described embodiment and each example can be combined with each other without departing from the gist of the present invention.

  In the above-described embodiment, a matrix polymer compound (so-called gel electrolyte) holding the electrolyte solution 12 may be used as the electrolyte solution holding unit instead of the separator 23.

  On the other hand, in the above-described embodiment, the stacked structural unit S may have a structure including three or more positive electrode stacked structural units (separator 23 / positive electrode 21). For example, the laminated structural unit S may have a laminated structure in which three positive electrode laminated structural units are repeatedly laminated between a pair of opposed negative electrode active material layers 22B. That is, the laminated structural unit S is the negative electrode current collector layer 21A / the negative electrode active material layer 22B / the separator 23 / the positive electrode 21 / the separator 23 / the positive electrode 21 / the separator 23 / the positive electrode 21 / the separator 23 / the negative electrode active material layer 22B. Is also good.

  Further, for example, the stacked structural unit S may have a stacked structure in which four or more positive electrode stacked structural units are repeatedly stacked between a pair of opposed negative electrode active material layers 22B. In addition, two or more positive electrode laminated structural units are also referred to as “positive electrode assembly layers” for convenience.

  In the above embodiment, for example, instead of the laminate 13, for example, two long positive electrodes 21 and one long negative electrode 22 are stacked together with the long separator 23 (for example, the positive electrode 21 / separator 23 / Negative electrode 22 / separator 23 / positive electrode 21 / separator 23 in that order), and a wound body (electrode body) may be used. In this case, the wound body may include one or more laminated structural units S from the radially inner circumferential side to the outer circumferential side of the wound body.

  In the above-described embodiment, various laminated structures can be adopted as the laminated structure of the electrode member of the laminated body 13 as long as the laminated structure unit S is included.

  In the above-described embodiment, the stacked body 13 may include one or more (for example, six) other stacked structural units instead of the stacked structural unit S. Another laminated structural unit is a layer in which two positive electrode laminated structural units in which a negative electrode 22 (a negative electrode layer), a separator 23 (an electrolytic solution holding layer), and a positive electrode 21 (a positive electrode layer) are laminated in this order are repeatedly laminated. (Positive electrode assembly layer) has a laminated structure laminated in this order. As for the laminated structure of the electrode member of the laminated body 13, various laminated structures can be adopted as long as the laminated member includes one or more other laminated structural units. In addition, another laminated structural unit may have a structure including three or more positive electrode laminated structural units (separator 23 / positive electrode 21). Further, the wound body may include one or more other laminated structural units from the radially inner circumferential side to the outer circumferential side of the wound body.

  In the above embodiment, the power storage device is a power storage device using a material capable of absorbing and desorbing an electrolyte salt anion (capable of reversible storage (adsorption) and desorption (release)) as a positive electrode active material. Alternatively, another power storage device other than the lithium ion capacitor may be used. A power storage module may be configured by connecting a plurality of power storage devices.

  DESCRIPTION OF SYMBOLS 11 ... exterior case, 12 ... electrolyte solution, 13 ... laminated body, 21 ... positive electrode, 21A ... positive electrode current collector layer, 21B ... positive electrode active material layer, 22 ... negative electrode, 22A ... negative electrode current collector layer, 22B ... negative electrode active Material layer, 23 ... separator

Claims (4)

A positive electrode layer in which a positive electrode active material layer is formed on both surfaces of a positive electrode current collector layer,
A negative electrode layer in which a negative electrode active material layer is formed on both surfaces of the negative electrode current collector layer,
An electrolyte,
An electrolyte holding layer that holds the electrolyte,
Comprising an electrode body including
The electrode body is
The negative electrode current collector layer,
The negative electrode active material layer,
A positive electrode assembly layer having a stacked structure in which two or more positive electrode stacked structural units in which the electrolyte holding layer and the positive electrode layer are stacked in this order are repeatedly stacked;
An electrolyte holding layer,
A negative electrode active material layer,
Contains one or more laminated structural units laminated in this order,
Power storage device. The power storage device according to claim 1,
The positive electrode assembly layer has a stacked structure in which the two positive electrode stacked structural units are repeatedly stacked.
Power storage device. The power storage device according to claim 1 or 2,
The electrode body includes a laminated structure in which two or more of the laminated structural units are repeatedly laminated.
Power storage device. The power storage device according to any one of claims 1 to 3,
The electrolyte holding layer is a separator,
Power storage device.

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