Power storage device

Abstract

To provide a power storage device using a liquid electrolyte containing an ester compound which is hardly affected by heat of outside air under a high temperature environment.SOLUTION: A power storage device 10 includes a positive electrode 21, a negative electrode 22, a separator 23, and power storage cells 20 having storage chambers S liquid-tightly storing a liquid electrolyte. A ratio of an ester compound to a total non-aqueous solvent in the liquid electrolyte is 70 vol.% or more. The power storage device 10 includes a cell stack 30 in which the plurality of power storage cells 20 is stacked in series, wherein side surfaces with respect to a stacking direction of the cell stacks 30 are covered with a resin seal part 24. A terminal positive electrode current collector 21a' and a terminal negative electrode current collector 22a' which are positioned on an outermost layer of the cell stack 30 are composed of a high thermal conductive material having thermal conductivity of 100 W / m K or more. The power storage device 10 includes a positive electrode cooling part 40 for cooling the terminal positive electrode current collector 21a' and a negative electrode cooling part 50 for cooling the terminal negative electrode current collector 22a'.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electricity storage device. [Background technology]

[0002] Patent Document 1 discloses a flat-type energy storage device constructed by stacking a plurality of individually manufactured energy storage cells in series. The energy storage cell includes a positive electrode having a positive electrode active material layer formed in the center of one side of a positive electrode current collector made of resin, a negative electrode having a negative electrode active material layer formed in the center of one side of a negative electrode current collector made of resin, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode, and a separator disposed between the positive electrode and the negative electrode.

[0003] The energy storage cell further includes a seal made of a thermoplastic resin, which is disposed between the positive electrode and the negative electrode and on the outer circumferential side of the positive electrode active material layer and the negative electrode active material layer. The seal maintains a gap between the positive electrode current collector and the negative electrode current collector to prevent short circuits between the current collectors, and also liquid-tightly seals the gap between the positive electrode current collector and the negative electrode current collector, thereby forming an enclosed space for containing a liquid electrolyte between the positive electrode current collector and the negative electrode current collector. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-16825 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have found that by using a liquid electrolyte whose viscosity has been reduced by containing an ester compound, it is possible to suppress an increase in the diffusion resistance of charge carriers in the active material layer.

[0006] However, since ester compounds have a low boiling point, there is a risk that the ester compounds contained in the liquid electrolyte will volatilize when the temperature inside the electricity storage device rises due to the influence of heat from the outside air in a high-temperature environment, and therefore electricity storage devices using liquid electrolytes containing ester compounds have the problem of being susceptible to the influence of heat from the outside air in high-temperature environments.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electricity storage device that uses a liquid electrolyte containing an ester compound and is less susceptible to the influence of heat from the outside air in a high-temperature environment. [Means for solving the problem]

[0008] The electricity storage device that achieves the above object is an electricity storage device that includes an electricity storage cell including: a positive electrode having a positive electrode active material layer bonded to a first surface of a positive electrode current collector; a negative electrode having a negative electrode active material layer bonded to a first surface of a negative electrode current collector, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode; a separator disposed between the positive electrode active material layer and the negative electrode active material layer; and a storage chamber that is provided between the positive electrode and the negative electrode and that liquid-tightly stores a liquid electrolyte, the liquid electrolyte containing an ester compound, a ratio of the ester compound to the total non-aqueous solvent in the battery is 70% by volume or more; the battery comprises a cell stack formed by stacking a plurality of the energy storage cells in series, wherein the side surfaces of the cell stack in the stacking direction are covered with resin coverings; the positive electrode current collector and the negative electrode current collector each comprise an end current collector located in the outermost layer of the cell stack; at least one of the end current collectors is made of a highly thermally conductive material having a thermal conductivity of 100 W / m K or more; and the battery comprises a cooling unit that cools the end current collector made of the highly thermally conductive material.

[0009] According to the above-described configuration, the liquid electrolyte contains an ester compound to reduce the viscosity, thereby making it possible to suppress an increase in the diffusion resistance of charge carriers in the active material layer. Furthermore, the outer surface of the cell stack, which is made by stacking multiple energy storage cells in series, is covered with a resin coating on the side facing the stacking direction. This suppresses heat transfer between the liquid electrolyte in the cell stack and the outside of the cell stack through the side of the cell stack, and limits the heat transfer portion of the outer surface of the cell stack to the terminal current collector located at the end face in the stacking direction. In addition, the terminal current collector is made of a highly thermally conductive material, and a cooling section is provided to cool the terminal current collector made of a highly thermally conductive material.

[0010] Therefore, when the energy storage device is used in a high-temperature environment, the covering portion can prevent heat from the outside air from being transferred to the liquid electrolyte in the cell stack. Even if the temperature of the liquid electrolyte rises due to the influence of the heat from the outside air, the heat is released to the outside through the terminal current collector and the cooling portion, which are made of a highly thermally conductive material, thereby preventing an excessive temperature rise in the liquid electrolyte. Therefore, the energy storage device is less susceptible to the influence of heat from the outside air, and the effect of the ester compound contained in the liquid electrolyte in preventing an increase in the diffusion resistance of charge carriers in the active material layer can be continuously obtained, even in a high-temperature environment.

[0011] The ester compound is preferably at least one selected from methyl acetate, ethyl acetate, and methyl propionate. The separator is preferably adhered to the positive electrode active material layer and the negative electrode active material layer.

[0012] This configuration improves the efficiency of thermal conduction between the positive electrode active material layer and the negative electrode active material layer that face each other via the separator, facilitating heat transfer in the stacking direction of the cell stack and enabling the heat in the cell stack to be efficiently transferred to the terminal current collector and the cooling section and then released to the outside.

[0013] It is preferable that the positive electrode current collector and the negative electrode current collector are stacked so that a second surface thereof, which is the surface opposite to the first surface, is in contact with each other. [Effects of the Invention]

[0014] According to the present invention, it is possible to reduce the influence of heat from the outside air in a high-temperature environment. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. [Figure 2] FIG. 10 is a partial cross-sectional view of a peripheral portion of a cell stack according to a modified example. [Figure 3] FIG. 10 is a cross-sectional view of a power storage device according to a modified example. [Figure 4] 6 is a graph showing the temperature change of the cell stack during discharge. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will now be described with reference to the drawings. The power storage device 10 shown in Fig. 1 is a power storage module used in batteries for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The power storage device 10 is, for example, a secondary battery such as a lithium ion secondary battery. The power storage device 10 may also be an electric double layer capacitor. In this embodiment, the power storage device 10 is illustrated as a lithium ion secondary battery.

[0017] 1, the energy storage device 10 includes a cell stack 30 (laminate) in which a plurality of energy storage cells 20 are stacked in a stacking direction. Hereinafter, the stacking direction of the plurality of energy storage cells 20 will be simply referred to as the stacking direction. Each energy storage cell 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and a seal portion 24.

[0018] The positive electrode 21 includes a positive electrode current collector 21a and a positive electrode active material layer 21b provided on a first surface 21a1 of the positive electrode current collector 21a. In a plan view seen from the stacking direction (hereinafter simply referred to as a plan view), the positive electrode active material layer 21b is formed in the center of the first surface 21a1 of the positive electrode current collector 21a. In a plan view, the peripheral portion of the first surface 21a1 of the positive electrode current collector 21a is a positive electrode uncoated portion 21c where the positive electrode active material layer 21b is not provided. The positive electrode uncoated portion 21c is arranged to surround the periphery of the positive electrode active material layer 21b in a plan view.

[0019] The negative electrode 22 includes a negative electrode current collector 22a and a negative electrode active material layer 22b provided on a first surface 22a1 of the negative electrode current collector 22a. In a plan view, the negative electrode active material layer 22b is formed in the center of the first surface 22a1 of the negative electrode current collector 22a. In a plan view, the peripheral portion of the first surface 22a1 of the negative electrode current collector 22a is a negative electrode uncoated portion 22c where the negative electrode active material layer 22b is not provided. In a plan view, the negative electrode uncoated portion 22c is arranged to surround the periphery of the negative electrode active material layer 22b.

[0020] The positive electrode 21 and the negative electrode 22 are arranged such that the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other in the stacking direction. That is, the facing direction of the positive electrode 21 and the negative electrode 22 coincides with the stacking direction. The negative electrode active material layer 22b is formed to be slightly larger than the positive electrode active material layer 21b, and in a plan view, the entire formation region of the positive electrode active material layer 21b is located within the formation region of the negative electrode active material layer 22b.

[0021] The positive electrode current collector 21a has a second surface 21a2 opposite to the first surface 21a1. The positive electrode 21 is a monopolar electrode in which neither the positive electrode active material layer 21b nor the negative electrode active material layer 22b is formed on the second surface 21a2 of the positive electrode current collector 21a. The negative electrode current collector 22a has a second surface 22a2 opposite to the first surface 22a1. The negative electrode 22 is a monopolar electrode in which neither the positive electrode active material layer 21b nor the negative electrode active material layer 22b is formed on the second surface 21a2 of the negative electrode current collector 22a.

[0022] The separator 23 is disposed between the positive electrode 21 and the negative electrode 22, and is a component that separates the positive electrode 21 and the negative electrode 22 to prevent short circuits due to contact between the two electrodes, while allowing charge carriers such as lithium ions to pass through.

[0023] The separator 23 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains the liquid electrolyte. Examples of materials that make up the separator 23 include polypropylene, polyethylene, polyolefin, and polyester. The separator 23 may have a single-layer structure or a multi-layer structure. The multi-layer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and the like.

[0024] 1, this embodiment uses a sheet-like separator 23 having adhesive layers 23a provided on both surfaces. The adhesive layer 23a provided on one surface (the surface on the lower side of the paper) of the separator 23 is adhered to the first surface 21a1 of the positive electrode current collector 21a and the positive electrode active material layer 21b. The adhesive layer 23a provided on the other surface (the surface on the upper side of the paper) of the separator 23 is adhered to the negative electrode active material layer 22b.

[0025] The seal portion 24 is disposed between the first surface 21a1 of the positive electrode current collector 21a of the positive electrode 21 and the first surface 22a1 of the negative electrode current collector 22a of the negative electrode 22, and is disposed on the outer peripheral side of the positive electrode active material layer 21b and the negative electrode active material layer 22b, and is bonded to both the positive electrode current collector 21a and the negative electrode current collector 22a. The seal portion 24 insulates the positive electrode current collector 21a from the negative electrode current collector 22a, thereby preventing a short circuit between the current collectors.

[0026] The sealing portion 24 extends along the peripheral edges of the positive electrode current collector 21 a and the negative electrode current collector 22 a in a plan view, and is formed in a frame shape surrounding the peripheries of the positive electrode active material layer 21 b and the negative electrode active material layer 22 b. The sealing portion 24 is disposed between the positive electrode uncoated portion 21 c on the first surface 21 a 1 of the positive electrode current collector 21 a and the negative electrode uncoated portion 22 c on the first surface 22 a 1 of the negative electrode current collector 22 a.

[0027] A storage chamber S is formed inside the energy storage cell 20 and is partitioned by a frame-shaped seal portion 24, the positive electrode 21, and the negative electrode 22. The storage chamber S is a liquid-tight sealed space surrounded by the frame-shaped seal portion 24, the positive electrode 21, and the negative electrode 22. The storage chamber S contains a positive electrode active material layer 21b, a negative electrode active material layer 22b, a separator 23, and a liquid electrolyte. The peripheral edge of the separator 23 is embedded in the seal portion 24. The seal portion 24 seals the gap between the positive electrode 21 and the negative electrode 22, thereby preventing the liquid electrolyte contained in the storage chamber S from permeating to the outside.

[0028] The cell stack 30 has a structure in which a plurality of the energy storage cells 20 are stacked so that the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a are in contact with each other, whereby the plurality of energy storage cells 20 constituting the cell stack 30 are connected in series.

[0029] Here, in the cell stack 30, two adjacent energy storage cells 20 in the stacking direction form a pseudo bipolar electrode 25 in which the mutually contacting positive electrode current collector 21a and negative electrode current collector 22a are regarded as a single current collector. The pseudo bipolar electrode 25 includes a current collector having a structure in which the positive electrode current collector 21a and negative electrode current collector 22a are stacked, a positive electrode active material layer 21b formed on one surface of the current collector, and a negative electrode active material layer 22b formed on the other surface.

[0030] The seal portion 24 of each storage cell 20 has an outer peripheral portion 24a that extends outward beyond the edges of the positive electrode current collector 21a and the negative electrode current collector 22a. When viewed from the stacking direction, the outer peripheral portion 24a protrudes beyond the edges of the positive electrode current collector 21a and the negative electrode current collector 22a in a direction perpendicular to the stacking direction. The storage cells 20 adjacent to each other in the stacking direction are integrated by bonding the outer peripheral portions 24a of the seal portions 24 together.

[0031] Therefore, the peripheral surface of the cell stack 30, i.e., the side surface in the stacking direction, is entirely covered by the seal portion 24. In this embodiment, the seal portion 24 forms a covering portion that covers the side surface in the stacking direction of the cell stack 30. Note that adjacent seal portions 24 can be bonded to each other by known welding methods such as heat welding, ultrasonic welding, or infrared welding.

[0032] 1, the positive electrode current collector 21a and the negative electrode current collector 22a located in the outermost layers in the stacking direction of the cell stack 30 are referred to as the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a', respectively. A positive electrode cooling unit 40 that cools the terminal positive electrode current collector 21a' is attached to the second surface 21a2' of the terminal positive electrode current collector 21a'. Furthermore, a negative electrode cooling unit 50 that cools the terminal negative electrode current collector 22a' is attached to the second surface 22a2' of the terminal negative electrode current collector 22a'.

[0033] The positive electrode cooling unit 40 and the negative electrode cooling unit 50 cool the terminal positive electrode current collector 21a' to, for example, 60°C or less. The specific configurations of the positive electrode cooling unit 40 and the negative electrode cooling unit 50 are not particularly limited, and known cooling units used for cooling power storage devices can be used. Examples of known cooling units include cooling units that have a structure, such as fins, that enhances heat transfer efficiency and cools the cooling target by exchanging heat with a cooling medium.

[0034] In this embodiment, the positive electrode cooling section 40 and the negative electrode cooling section 50 are configured to also function as current-carrying plates. That is, the positive electrode cooling section 40 and the negative electrode cooling section 50 are made of a material that has high thermal conductivity and electrical conductivity, and are electrically connected to the second surface 21a2' of the terminal positive electrode current collector 21a' and the second surface 22a2' of the terminal negative electrode current collector 22a', respectively. Charging and discharging of the energy storage device 10 are performed through terminals provided on the positive electrode cooling section 40 and the negative electrode cooling section 50, respectively. The positive electrode cooling section 40 and the negative electrode cooling section 50 may be made of the same material as the material for the positive electrode current collector 21a and the negative electrode current collector 22a, which will be described later.

[0035] The energy storage device 10 includes a restraining member 60 that restrains the cell stack 30. The restraining member 60 applies a restraining load to a region where the energy storage cells 20 face each other in the stacking direction of the cell stack 30, particularly to a region where the range where the positive electrode active material layer 21b is provided overlaps with the range where the negative electrode active material layer 22b is provided in a plan view.

[0036] There are no particular limitations on the specific configuration of the restraining member 60, as long as it is capable of applying a restraining load to the cell stack 30. As an example, Fig. 1 illustrates a restraining member 60 including plate-shaped restraining plates 61 arranged at both ends of the cell stack 30 in the stacking direction so as to sandwich the cell stack 30, and fastening members 62 consisting of bolts and nuts that fasten the restraining plates 61 together. The fastening members 62 urge the restraining plates 61 in directions that bring them closer to each other, thereby applying a restraining load to the cell stack 30 in the stacking direction.

[0037] Next, the positive electrode current collector 21a, the negative electrode current collector 22a, the positive electrode active material layer 21b, the negative electrode active material layer 22b, the liquid electrolyte, and the seal portion 24 will be described in detail. <Positive electrode current collector and negative electrode current collector> The positive electrode current collector 21a and the negative electrode current collector 22a are chemically inactive electrical conductors that allow current to continue to flow through the positive electrode active material layer 21b and the negative electrode active material layer 22b during discharging or charging of the lithium ion secondary battery.

[0038] The material constituting the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' is a highly thermally conductive material having a thermal conductivity of 100 W / m·K or more. Examples of such highly thermally conductive materials include metal materials such as silver, copper, gold, and aluminum. The thermal conductivity of such highly thermally conductive materials is, for example, 500 W / m·K or less.

[0039] From the viewpoint of heat conduction to the positive electrode cooling section 40 and the negative electrode cooling section 50, it is preferable that the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' have a large area in a plan view (hereinafter simply referred to as area) and a small thickness.

[0040] From the above viewpoint, the area of ​​the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' is, for example, 1 m 2 More than 1.3m 2 The area of ​​the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' is preferably 2.5 m or more, for example. 2 is less than 2.2m 2 It is preferable that:

[0041] The thickness of the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' is, for example, 0.003 mm or more, preferably 0.005 mm or more, and more preferably 0.01 mm or more. The thickness of the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' is, for example, 0.06 mm or less, preferably 0.05 mm or less, and more preferably 0.04 mm or less.

[0042] The positive electrode current collector 21a other than the terminal positive electrode current collector 21a′ (hereinafter referred to as a general positive electrode current collector) and the negative electrode current collector 22a other than the terminal negative electrode current collector 22a′ (hereinafter referred to as a general negative electrode current collector) may be made of, for example, a metal material, a conductive resin material, a conductive inorganic material, or the like.

[0043] Examples of the metal material include copper, aluminum, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, and SUS304 as specified in JIS G 4305:2015). Examples of the conductive resin material include resins obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material as needed.

[0044] The thermal conductivity of the material constituting the general positive electrode current collector and the general negative electrode current collector is not particularly limited, but is preferably 100 W / m K or more. The general positive electrode current collector and the general negative electrode current collector are also preferably made of the above-mentioned highly thermally conductive material.

[0045] From the viewpoint of heat conduction to the terminating positive electrode current collector 21a' and the terminating negative electrode current collector 22a', it is preferable that the general positive electrode current collector and the general negative electrode current collector have a large area and a small thickness. From the above viewpoint, the area of ​​the general positive electrode current collector and the general negative electrode current collector is, for example, 1 m 2 It is preferable that it is 1.3m or more. 2 The area of ​​the general positive electrode current collector and the general negative electrode current collector is preferably 2.5 m or more, for example. 2 Preferably, it is 2.2m or less. 2 More preferably, it is:

[0046] The thickness of the general positive electrode current collector and the general negative electrode current collector is, for example, preferably 0.003 mm or more, more preferably 0.005 mm or more, and even more preferably 0.01 mm or more, and the thickness of the general positive electrode current collector and the general negative electrode current collector is, for example, preferably 0.06 mm or less, more preferably 0.05 mm or less, and even more preferably 0.04 mm or less.

[0047] The area and thickness of the general positive electrode current collector and the general negative electrode current collector are preferably configured similarly to those of the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a'. One or both of the positive electrode current collector 21a and the negative electrode current collector 22a may have multiple layers, including one or more layers containing the above-mentioned metal material or conductive resin material. The surface of one or both of the positive electrode current collector 21a and the negative electrode current collector 22a may be coated with a known protective layer. The surface of one or both of the positive electrode current collector 21a and the negative electrode current collector 22a may be surface-treated by a known method such as plating. Examples of such surface treatments include chromate treatment and chromate phosphate treatment.

[0048] The positive electrode current collector 21a and the negative electrode current collector 22a may each independently have the form of, for example, a foil, a sheet, a film, a wire, a rod, a mesh, a clad material, etc. When in the form of a foil, a sheet, or a film, the thickness is, for example, 1 to 100 μm.

[0049] In the present embodiment, the positive electrode current collector 21a and the negative electrode current collector 22a are configured such that the general positive electrode current collector is made of aluminum foil, the terminal positive electrode current collector 21a' is made of aluminum foil, the general negative electrode current collector is made of copper foil, and the terminal negative electrode current collector 22a' is made of copper foil.

[0050] <Positive Electrode Active Material Layer and Negative Electrode Active Material Layer> The positive electrode active material layer 21b contains a positive electrode active material capable of absorbing and releasing charge carriers such as lithium ions. The positive electrode active material may be any material that can be used as a positive electrode active material for lithium ion secondary batteries, such as a lithium composite metal oxide having a layered rock salt structure, a metal oxide having a spinel structure, or a polyanion-based compound. Two or more positive electrode active materials may also be used in combination. In this embodiment, the positive electrode active material layer 21b contains olivine-type lithium iron phosphate (LiFePO4) as a polyanion-based compound.

[0051] The negative electrode active material layer 22b can be made of any element, alloy, or compound capable of absorbing and releasing charge carriers such as lithium ions. Examples of the negative electrode active material include Li, carbon, metal compounds, and elements or compounds thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin. In this embodiment, the negative electrode active material layer 22b contains graphite as a carbon-based material.

[0052] The positive electrode active material layer 21b and the negative electrode active material layer 22b (hereinafter also simply referred to as the active material layer) may each further contain, as necessary, a conductive aid for improving electrical conductivity, a binder, an electrolyte (a polymer matrix, an ion-conductive polymer, a liquid electrolyte, etc.), an electrolyte supporting salt (lithium salt) for improving ion conductivity, etc. The components contained in the active material layer and the blending ratio of these components are not particularly limited, and conventionally known knowledge about lithium ion secondary batteries may be referred to as appropriate.

[0053] The conductive additive is added to increase the conductivity of the positive electrode 21 or the negative electrode 22. Examples of the conductive additive include acetylene black, carbon black, and graphite. Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as polyacrylic acid and methacrylic acid; styrene-butadiene rubber; carboxymethyl cellulose; alginates such as sodium alginate and ammonium alginate; water-soluble cellulose ester crosslinked bodies; and starch-acrylic acid graft polymers. These binders can be used alone or in combination. Examples of solvents or dispersion media include water and N-methyl-2-pyrrolidone.

[0054] To form the active material layer on the surface of the positive electrode current collector 21a and the negative electrode current collector 22a, a conventionally known method such as roll coating may be used. In order to improve the thermal stability of the positive electrode 21 or the negative electrode 22, the above-mentioned heat-resistant layer may be provided on the surface of the active material layer.

[0055] The thickness and basis weight of the active material layer are not particularly limited, and conventionally known knowledge about lithium ion secondary batteries can be referred to as appropriate. However, from the viewpoint of increasing the energy density of the storage cell 20, it is preferable to increase the basis weight of the active material layer.

[0056] Specifically, the thickness of the positive electrode active material layer 21b is, for example, 250 μm or more, and preferably 400 μm or more. The thickness of the positive electrode active material layer 21b is, for example, 600 μm or less. The basis weight of the positive electrode active material layer 21b is, for example, 55 mg / cm 2 or more, 70 mg / cm 2 The weight per unit area of ​​the positive electrode active material layer 21b is preferably 90 mg / cm or more, for example. 2In order to increase the rigidity of the positive electrode 21, when the positive electrode current collector 21a is in the form of a foil having a thickness of 0.015 to 0.05 mm, the weight of the positive electrode active material layer 21b is set to 55 to 90 mg / cm 2 and the density of the positive electrode active material layer 21b is 1.6 to 2.1 g / cm 3 It is preferable that:

[0057] The thickness of the negative electrode active material layer 22b is, for example, 150 μm or more, preferably 200 μm or more, and more preferably 250 μm or more. The thickness of the negative electrode active material layer 22b is, for example, 400 μm or less. The basis weight of the negative electrode active material layer 22b is, for example, 25 mg / cm 2 or more, 30 mg / cm 2 The weight of the negative electrode active material layer 22b is preferably 45 mg / cm or more, for example. 2 In order to increase the rigidity of the negative electrode 22, when the negative electrode current collector 22a is in the form of a foil having a thickness of 0.005 to 0.02 mm, the weight of the negative electrode active material layer 22b is set to 25 to 45 mg / cm. 2 and the density of the negative electrode active material layer 22b is 1.1 to 1.5 g / cm 3 It is preferable that:

[0058] <Sealing part (covering part)> The seal portion 24 is made of a polyolefin resin. Examples of polyolefin resins include polyethylene (PE), polypropylene (PP), modified polyethylene (modified PE), modified polypropylene (modified PP), isoprene, modified isoprene, polybutene, modified polybutene, and polybutadiene. Examples of modified polyethylene include acid-modified polyethylene and epoxy-modified polyethylene. Examples of modified polypropylene include acid-modified polypropylene and epoxy-modified polypropylene. Two or more of these known polyolefin resins may be used in combination. The polyolefin resin may be a thermoplastic resin or a thermosetting resin. The thermal conductivity of the seal portion 24 is, for example, 0.17 to 0.19 W / m K.

[0059] <Liquid electrolyte> Examples of liquid electrolytes include those containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. Known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may be used in combination.

[0060] The liquid electrolyte contains an ester compound as a non-aqueous solvent. Examples of the ester compound include methyl acetate, ethyl acetate, and methyl propionate. Two or more types of ester compounds may be used in combination. The problem of volatilization of the ester compound contained in the liquid electrolyte when the temperature inside the power storage device 10 rises is more likely to occur the lower the boiling point of the ester compound, for example, when the boiling point is 90°C or lower. The boiling point of methyl acetate is 57°C, the boiling point of ethyl acetate is 77.1°C, and the boiling point of methyl propionate is 80°C.

[0061] The ester compound is contained in the liquid electrolyte to reduce the viscosity of the liquid electrolyte and improve its ionic conductivity. The viscosity of the liquid electrolyte at 25°C is, for example, preferably 7 mPa·s or less, and more preferably 6 mPa·s or less. The viscosity of the liquid electrolyte at 25°C is, for example, 0.8 mPa·s or more. Note that 1 mPa·s = 1 cP.

[0062] The ionic conductivity of the liquid electrolyte at 25° C. is preferably, for example, 5 mS / cm or more. Suitable ranges of ionic conductivity include, for example, a range of 6 to 30 mS / cm, a range of 7 to 25 mS / cm, a range of 10 to 25 mS / cm, a range of 12 to 25 mS / cm, and a range of 13 to 20 mS / cm.

[0063] The ratio of the ester compound to the total non-aqueous solvent in the liquid electrolyte is, for example, preferably 30 to 95% by volume, more preferably 40 to 90% by volume, even more preferably 50 to 89% by volume, particularly preferably 60 to 88% by volume, and most preferably 70 to 87% by volume.

[0064] The energy storage device 10 is manufactured by sequentially performing an electrode formation process, an energy storage cell formation process, and a cell stack formation process. Here, as an example, a case will be described in which all of the positive electrode current collectors 21a, including the terminal positive electrode current collector 21a', are made of aluminum foil, and all of the negative electrode current collectors 22a, including the terminal negative electrode current collector 22a', are made of copper foil.

[0065] <Electrode formation process> The electrode forming step includes a positive electrode forming step of forming the positive electrode 21 and a negative electrode forming step of forming the negative electrode 22.

[0066] The positive electrode formation step is not particularly limited, and any known method applicable to forming the positive electrode 21 including the positive electrode current collector 21a and the positive electrode active material layer 21b can be used. For example, the positive electrode 21 can be formed by adhering a positive electrode composite, which will become the positive electrode active material layer 21b upon solidification, to a first surface 21a1 of an aluminum foil serving as the positive electrode current collector 21a to a predetermined thickness, and then performing a solidification treatment appropriate for the positive electrode composite.

[0067] The negative electrode formation step is not particularly limited, and may be any known method applicable to forming the negative electrode 22 including the negative electrode current collector 22 a and the negative electrode active material layer 22 b. For example, the negative electrode 22 can be formed by adhering a negative electrode composite material, which will become the negative electrode active material layer 22 b when solidified, to a first surface 22 a 1 of copper foil serving as the negative electrode current collector 22 a to a predetermined thickness, and then performing a solidification treatment appropriate for the negative electrode composite material.

[0068] <Storage cell formation process> In the energy storage cell formation process, first, the positive electrode 21 and the negative electrode 22 are arranged so that the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other in the stacking direction with the separator 23 sandwiched therebetween, and a sealing material that becomes the sealing portion 24, for example, a sheet made of the above-mentioned low-density polyethylene resin, is arranged between the positive electrode 21 and the negative electrode 22 and on the outer periphery of the positive electrode current collector 21a and the negative electrode current collector 22a.

[0069] Thereafter, the positive electrode 21, the negative electrode 22, the separator 23, and the sealing material are welded together to form an assembly in which the positive electrode 21, the negative electrode 22, the separator 23, and the sealing portion 24 are integrated together. Examples of methods for welding the sealing material include known welding methods such as heat welding, ultrasonic welding, and infrared welding.

[0070] Next, a liquid electrolyte is injected into the storage chamber S inside the assembly through an injection port provided in a part of the seal portion 24, and then the injection port is sealed. In this way, the energy storage cell 20 is formed. <Cell stack formation process> In the cell stack forming process, first, the plurality of energy storage cells 20 are stacked on top of each other so that the second surfaces 21a2 of the positive electrode current collectors 21a and the second surfaces 22a2 of the negative electrode current collectors 22a face each other. Then, the plurality of energy storage cells 20 are integrated by bonding the outer circumferential portions 24a of the seal portions 24 of the energy storage cells 20 adjacent to each other in the stacking direction.

[0071] Next, the positive electrode cooling unit 40 is overlapped and fixed in an electrically connected state to the second surface 21a2 of the positive electrode current collector 21a of the positive electrode 21 arranged outermost at one end in the stacking direction. Similarly, the negative electrode cooling unit 50 is overlapped and fixed in an electrically connected state to the second surface 22a2 of the negative electrode current collector 22a of the negative electrode 22 arranged outermost at the other end in the stacking direction. This completes the cell stack 30. Thereafter, a restraining member 60 is attached to the cell stack 30. For example, after placing restraining plates 61 on both ends of the cell stack 30 in the stacking direction, the restraining plates 61 are fastened together with fastening members 62.

[0072] Next, the operation of this embodiment will be described. In the electricity storage device 10 of this embodiment, a liquid electrolyte containing an ester compound to reduce viscosity is used as the liquid electrolyte, which makes it possible to increase the basis weight of the active material layer while suppressing an increase in the diffusion resistance of charge carriers in the active material layer.

[0073] Furthermore, the outer surface of the cell stack 30, which is formed by stacking a plurality of energy storage cells 20 in series, on the side surface in the stacking direction is covered with a resin seal portion 24 (covering portion). This suppresses heat transfer between the liquid electrolyte in the cell stack 30 and the outside of the cell stack 30 through the side surface of the cell stack 30, and limits the heat transfer portion with the outside on the outer surface of the cell stack 30 to the terminating positive electrode current collector 21 a' and the terminating negative electrode current collector 22 a' located at the end faces in the stacking direction. In addition, the terminating positive electrode current collector 21 a' and the terminating negative electrode current collector 22 a' are made of a highly thermally conductive material, and a positive electrode cooling portion 40 and a negative electrode cooling portion 50 are provided to cool the terminating positive electrode current collector 21 a' and the terminating negative electrode current collector 22 a'.

[0074] When the energy storage device 10 is used in a high-temperature environment, the resin seal portion 24 (coating portion) can prevent heat from the outside air from being transferred to the liquid electrolyte in the cell stack 30. Even if the temperature of the liquid electrolyte rises due to the influence of the heat from the outside air, the heat is released to the outside through the terminal positive electrode current collector 21a' and terminal negative electrode current collector 22a', which are made of a highly thermally conductive material, as well as the positive electrode cooling portion 40 and the negative electrode cooling portion 50. This makes it possible to prevent an excessive temperature rise in the liquid electrolyte, resulting in an energy storage device 10 that is less susceptible to the influence of the heat from the outside air.

[0075] According to this embodiment, the following effects can be obtained. (1) The energy storage device 10 includes an energy storage cell 20 including a positive electrode 21 having a positive electrode current collector 21a and a positive electrode active material layer 21b, a negative electrode 22 having a negative electrode current collector 22a and a negative electrode active material layer 22b, a separator 23 disposed between the positive electrode active material layer 21b and the negative electrode active material layer 22b, and a storage chamber S provided between the positive electrode 21 and the negative electrode 22 and liquid-tightly storing a liquid electrolyte. The liquid electrolyte contains an ester compound.

[0076] The battery includes a cell stack 30 formed by stacking a plurality of energy storage cells 20 in series, the side surfaces of the cell stack 30 in the stacking direction being covered with resin seals 24, and the terminal positive electrode current collector 21a' and terminal negative electrode current collector 22a' positioned in the outermost layers of the cell stack 30 are made of a highly thermally conductive material with a thermal conductivity of 100 W / m K or more. The battery also includes a positive electrode cooling section 40 that cools the terminal positive electrode current collector 21a' and a negative electrode cooling section 50 that cools the terminal negative electrode current collector 22a'.

[0077] According to the above configuration, the energy storage device 10 is less susceptible to the effects of heat from the outside air, and even in a high-temperature environment, the effect of suppressing an increase in the diffusion resistance of charge carriers in the active material layer due to the ester compound contained in the liquid electrolyte can be continuously obtained.

[0078] (2) The weight of the positive electrode active material layer 21b is 55 mg / cm 2 The weight of the negative electrode active material layer 22b is 25 mg / cm 2 That's all. The greater the basis weight of the active material layer, the higher the diffusion resistance of charge carriers such as lithium ions in the active material layer. Therefore, when the basis weight of the active material layer is large as described above, the effect (1) achieved by including an ester compound in the liquid electrolyte is more pronounced.

[0079] (3) The separator 23 is bonded to the positive electrode active material layer 21b and the negative electrode active material layer 22b. The above configuration improves the efficiency of thermal conduction between the positive electrode active material layer 21b and the negative electrode active material layer 22b, which face each other via the separator 23. This facilitates heat transfer in the stacking direction of the cell stack 30, allowing the heat within the cell stack 30 to be efficiently transferred to the terminal positive electrode current collector 21a', the terminal negative electrode current collector 22a', the positive electrode cooling section 40, and the negative electrode cooling section 50, and then released to the outside. Furthermore, because the separator 23 is bonded to the positive electrode active material layer 21b and the negative electrode active material layer 22b, it is possible to prevent the distance between the positive electrode active material layer 21b and the negative electrode active material layer 22b in the stacking direction from increasing during charge and discharge, and therefore it is possible to prevent an increase in the resistance of the energy storage cell 20.

[0080] (4) The positive electrode current collector 21a is in the form of a foil having a thickness of 0.015 to 0.05 mm, and the positive electrode active material layer 21b has a basis weight of 55 to 90 mg / cm 2 and the density of the positive electrode active material layer 21b is 1.6 to 2.1 g / cm 3 is.

[0081] According to the above configuration, the provision of the positive electrode active material layer 21b increases the rigidity of the foil-shaped positive electrode current collector 21a. Therefore, when the internal pressure of the storage chamber S increases, the positive electrode 21 is prevented from warping and deforming, which reduces the contact area with the negative electrode current collector 22a of the adjacent energy storage cell 20. This prevents a decrease in the efficiency of heat conduction between the energy storage cells 20 due to the reduction in the contact area.

[0082] (5) The negative electrode current collector 22a is foil-shaped and has a thickness of 0.005 to 0.02 mm, and the negative electrode active material layer 22b has a weight per unit area of ​​25 to 45 mg / cm 2 and the density of the negative electrode active material layer 22b is 1.1 to 1.5 g / cm 3 is.

[0083] According to the above configuration, the same effect as that of the above (4) can be obtained with respect to the negative electrode 22. (6) The area of ​​the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' located in the outermost layer of the cell stack 30 is 1 m 2 More than 2.5m 2The thickness is 0.005 mm or more and 0.05 mm or less. In other words, the terminal positive electrode current collector 21 a' and the terminal negative electrode current collector 22 a' are current collectors whose thickness is significantly small relative to their area. This increases the amount of heat conduction from the positive electrode cooling section 40 and the negative electrode cooling section 50, allowing the inside of the cell stack 30 to be cooled efficiently.

[0084] (7) The area of ​​the general positive electrode current collector and the general negative electrode current collector is 1 m 2 More than 2.5m 2 The thickness is 0.005 mm or more and 0.05 mm or less. In other words, the general positive electrode current collector and the general negative electrode current collector are current collectors whose thickness is significantly small relative to their area. This allows heat within the cell stack 30 to be more efficiently transferred to the terminal positive electrode current collector 21 a' and the terminal negative electrode current collector 22 a'.

[0085] This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. In the above embodiment, the sealing portion 24 constitutes a covering portion that covers the side surface of the cell stack 30 in the stacking direction. However, a covering portion may be provided separately from the sealing portion 24. For example, the outer peripheral portion 24a of the sealing portion 24 may be omitted, and a resin layer that covers the side surface of the cell stack 30 in the stacking direction may be provided as the covering portion. The resin that constitutes this resin layer is the same as that of the sealing portion 24. Furthermore, when a covering portion is provided separately from the sealing portion 24, the resin that constitutes the covering portion may be the same as or different from the resin that constitutes the sealing portion 24.

[0086] In the above embodiment, the storage chamber S is formed to be partitioned by the frame-shaped seal portion 24, the positive electrode 21, and the negative electrode 22. However, the configuration for forming the storage chamber S is not limited to the above embodiment. For example, the storage chamber S may be formed to be partitioned by the positive electrode 21, the negative electrode 22, and a resin layer serving as a covering portion that covers the side surface of the cell stack 30 in the stacking direction.

[0087] In this case, the resin layer serving as the coating is adhered to each side surface of the positive electrode current collector 21a and the negative electrode current collector 22a. The side surface of the positive electrode current collector 21a is a side edge of the positive electrode current collector 21a, for example, a surface perpendicular to the first surface 21a1 and the second surface 21a2 of the positive electrode current collector 21a, and the side surface of the negative electrode current collector 22a is a side edge of the negative electrode current collector 22a, for example, a surface perpendicular to the first surface 22a1 and the second surface 22a2 of the negative electrode current collector 22a.

[0088] In this case, the sealing portion 24 may or may not be provided. Examples of the sealing portion 24 that may be provided include a sealing portion that is not bonded to either the positive electrode current collector 21a or the negative electrode current collector 22a but is bonded to the resin layer, a sealing portion that is bonded to the positive electrode current collector 21a and the resin layer but is not bonded to the negative electrode current collector 22a, and a sealing portion that is bonded to the negative electrode current collector 22a and the resin layer but is not bonded to the positive electrode current collector 21a. Two or more of these sealing portions may be used in combination.

[0089] Only one of the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' may be made of a highly heat-conductive material, and the other may be made of the same material as the general positive electrode current collector and the general negative electrode current collector.

[0090] In the above embodiment, the positive electrode cooling unit 40 and the negative electrode cooling unit 50 are provided as cooling units, but one of the positive electrode cooling unit 40 and the negative electrode cooling unit 50 may be omitted. However, if only one of the terminal positive electrode current collector 21 a' and the terminal negative electrode current collector 22 a' is made of a highly thermally conductive material, a cooling unit is provided to cool the terminal positive electrode current collector 21 a' or the terminal negative electrode current collector 22 a' made of a highly thermally conductive material.

[0091] The separator 23 may be configured to be bonded to only one of the positive electrode 21 and the negative electrode 22 , or may be configured to be bonded to neither the positive electrode 21 nor the negative electrode 22 . The planar shapes of the positive electrode current collector 21a and the positive electrode active material layer 21b are not particularly limited. They may be polygonal, such as rectangular, or may be circular or elliptical. The same applies to the negative electrode current collector 22a and the negative electrode active material layer 22b.

[0092] The shape of the seal portion 24 in plan view is not particularly limited, and may be a polygonal shape such as a rectangle, or may be a circle or an ellipse. The seal portion 24 may be made up of multiple components. For example, the seal portion 24 may be made up of two components, the outer peripheral portion 24a and a portion other than the outer peripheral portion, and the seal portion 24 may be made up by welding the two components. Alternatively, the seal portion 24 may be made up of multiple components stacked in the stacking direction. Furthermore, the seal portion 24 may be made up of two components, the outer peripheral portion 24a and a portion other than the outer peripheral portion, and the portion other than the outer peripheral portion may be made up of multiple components stacked in the stacking direction.

[0093] In the above embodiment, the restraining member 60 is provided for the cell stack 30. However, the restraining member 60 may be omitted. As shown in FIG. 2 , the distance between the first surface 21a1 of the positive electrode current collector 21a and the first surface 22a1 of the negative electrode current collector 22a in the energy storage cell 20 may vary depending on the location. The distance between the first surface 21a1 of the positive electrode current collector 21a and the first surface 22a1 of the negative electrode current collector 22a in the stacking direction, where the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other, is defined as a first distance D1. The first distance D1 corresponds to the sum of the thicknesses of the positive electrode active material layer 21b, the negative electrode active material layer 22b, and the separator 23. The distance between the first surface 21a1 of the positive electrode current collector 21a and the first surface 22a1 of the negative electrode current collector 22a in the stacking direction, where the seal portion 24 is bonded, is defined as a second distance D2. The second distance D2 corresponds to the thickness of the seal portion 24 between the peripheral edge of the first surface 21a1 of the positive electrode current collector 21a and the peripheral edge of the first surface 22a1 of the negative electrode current collector 22a.

[0094] It is preferable that the second distance D2 is smaller than the first distance D1, that is, smaller than the thickness of the seal portion 24. In this case, with respect to the region where the range where the positive electrode active material layer 21b is provided and the range where the negative electrode active material layer 22b is provided overlap in the facing region of the cell stack 30, the restraining member 60 can more efficiently apply a restraining load. On the other hand, if the second distance D2 is made excessively smaller than the first distance D1, the stress applied to the interface between the positive electrode current collector 21a and the negative electrode current collector 22a and the seal portion 24 increases, and there is a risk that the seal portion 24 will easily peel off from the positive electrode current collector 21a and the negative electrode current collector 22a.

[0095] From the above viewpoints, it is preferable that the first distance D1 and the second distance D2 satisfy the relationship of 0.6D1 ≤ D2 < D1, more preferably satisfy the relationship of 0.7D1 ≤ D2 ≤ 0.95D1, and even more preferably satisfy the relationship of 0.8D1 ≤ D2 ≤ 0.9D1.

[0096] Note that when the second distance D2 is made smaller than the first distance D1 as described above, in addition to the seal portion 24, a resin layer 70 is provided as a covering portion that covers the side surface of the cell stack 30 in the stacking direction.

[0097] ○ A conductive layer that adheres to the positive electrode current collector 21a may be disposed between the positive electrode cooling portion 40 and the positive electrode current collector 21a in order to improve the conductive contact between the two members. Examples of the conductive layer include a layer containing carbon such as acetylene black or graphite, and a layer having a hardness lower than that of the positive electrode current collector 21a such as a plating layer containing Au or the like. Similarly, a similar conductive layer may be disposed between the negative electrode cooling portion 50 and the negative electrode current collector 22a.

[0098] 〇 The number of power storage cells 20 constituting the power storage device 10 is not particularly limited. The number of power storage cells 20 constituting the power storage device 10 may be 1. 〇 A positive electrode active material layer 21b or a negative electrode active material layer 22b may be provided on the second surface 21a2 of the positive electrode current collector 21a. Also, a positive electrode active material layer 21b or a negative electrode active material layer 22b may be provided on the second surface 22a2 of the negative electrode current collector 22a.

[0099] The electrode may be a bipolar electrode in which the positive electrode current collector 21a and the negative electrode current collector 22a are combined into a single current collector. Examples of the current collector for a bipolar electrode include stainless steel foil (e.g., SUS304, SUS316, SUS301, SUS304, etc., as specified in JIS G 4305:2015), copper foil, aluminum foil, and nickel foil. Other current collectors may include clad materials of two or more metals, such as copper and aluminum, plated materials of two or more metals, such as copper and aluminum, and laminated metal foils of two or more metals. For example, when a copper-aluminum plated material having a copper layer and an aluminum layer is used as the current collector for a bipolar electrode, the aluminum layer may function as the positive electrode current collector 21a, and the copper layer may function as the negative electrode current collector 22a.

[0100] In the cell stack 30, the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a, which are contact portions between adjacent power storage cells 20 in the stacking direction, may be bonded to each other. Examples of a method for bonding the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a include a method using a conductive adhesive.

[0101] As shown in Fig. 3, the energy storage device 10 may be configured to include a cell stack body 31 formed by stacking a plurality of cell stacks 30. In the cell stack body 31, the plurality of cell stacks 30 are stacked so that the terminating positive electrode current collector 21a' and the terminating negative electrode current collector 22a' face each other. The cell stack body 31 may be formed by stacking, for example, one to eight cell stacks 30. When the energy storage device 10 includes the cell stack body 31, it is preferable that the restraining member 60 is configured to apply a restraining load to the cell stack body 31.

[0102] In the energy storage device 10 shown in FIG. 3 , the positive electrode cooling section 40 and the negative electrode cooling section 50 are omitted. Cooling sections 80 are provided between all layers of the cell stacks 30 and between the cell stacks 30 and the restraining plates 61 of the restraining members 60. The cooling sections 80 provided between the layers of the cell stacks 30 cool both the terminal positive electrode current collector 21 a′ and the terminal negative electrode current collector 22 a′ that face each other across the cooling section 80. The specific configuration of the cooling section 80 is similar to that of the positive electrode cooling section 40 and the negative electrode cooling section 50, except that the cooling section 80 is provided so as to contact both the terminal positive electrode current collector 21 a′ and the terminal negative electrode current collector 22 a′ that face each other across the cooling section 80. Note that, although the cooling sections 80 are provided between all layers of the cell stacks 30 in the example shown in FIG. 3 , the cooling sections 80 may be provided only between some layers of the cell stacks 30.

[0103] The cell stack 31 may be configured so that the positive electrode cooling section 40 also functions as the negative electrode cooling section 50. For example, the cell stack 31 may be configured by stacking cell stacks 30 from which the negative electrode cooling section 50 is omitted. The cell stacks 30 are then stacked such that the positive electrode cooling section 40 of one cell stack 30 is in contact with the terminal negative electrode current collector 22a' of the other cell stack 30 between the layers. In this case, the positive electrode cooling section 40 also functions as the negative electrode cooling section 50 that cools the terminal negative electrode current collector 22a' of the adjacent cell stack 30. Similarly, the cell stack 31 may be configured so that the negative electrode cooling section 50 also functions as the positive electrode cooling section 40.

[0104] The cell stack laminate 31 may include a cell stack 30 in which the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' are both made of a material other than the above-mentioned high thermal conductivity material. [Example]

[0105] The electricity storage device 10 was actually fabricated, and the temperature change during discharge of the fabricated electricity storage device 10 was measured. <Configuration of energy storage cell> A storage cell 20 having the following configuration was fabricated.

[0106] (Positive electrode material) Positive electrode current collector: 0.050 mm thick aluminum foil. Positive electrode active material layer: A mixture of olivine-type lithium iron phosphate (LiFePO4), acetylene black (AB), and polyvinylidene fluoride (PVdF).

[0107] Mass ratio of the positive electrode active material layer: 90:5:5 (LiFePO4:AB:PVdF) Amount of positive electrode active material layer: 55.5 mg / cm 2 Density of the positive electrode active material layer: 2 g / cm 3 (Anode material) Negative electrode current collector: 0.015 mm thick copper foil.

[0108] Negative electrode active material layer: a mixture of artificial graphite (C), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). Mass ratio of negative electrode active material layer: 94.8:0.8:4.4 (C:CMC:SBR) Amount of negative electrode active material layer: 26.5 mg / cm 2 Density of negative electrode active material layer: 1.3 mg / cm 2 (Other ingredients) Separator: 18 μm thick porous sheet with a ceramic layer.

[0109] Sealing part: Acid-modified polyethylene Liquid electrolyte: A liquid electrolyte prepared by dissolving LiN(FSO2)2 to a mixed solvent of ethylene carbonate and methyl propionate in a volume ratio of 15:85, to which 1.2M of LiN(FSO2)2 was added, and adding 5.7% by mass of vinylene carbonate and 1% by mass of lithium difluorooxalatoborate (LiDFOB).

[0110] (Storage cell size) Planar area of ​​the positive electrode active material layer: 780mm long x 1024mm wide Thickness of the positive electrode active material layer: 277.5 μm Planar area of ​​the negative electrode active material layer: 822mm long x 1055mm wide Negative electrode active material layer thickness: 203.8 μm Containment chamber volume: 29.3cm 3 <Cell stack and energy storage device> Twenty-four of the produced power storage cells 20 were stacked in series to produce one cell stack 30. The produced cell stack 30 was used to produce a power storage device 10.

[0111] As shown in Fig. 3, the energy storage device 10 has a structure in which four cell stacks 30 are stacked. Cooling sections 80 are arranged between all of the layers of the cell stacks 30 in the energy storage device 10, and between the cell stacks 30 and the restraining members 60 located at both ends in the stacking direction. Aluminum plates are used for the cooling sections 80. In the following, the cooling sections 80 located between the layers of the cell stacks 30 are referred to as inner cooling sections, and the cooling sections 80 located between the cell stacks 30 and the restraining members 60 are referred to as outer cooling sections.

[0112] The manufactured energy storage device 10 is also fitted with a plurality of first temperature sensors and a plurality of second temperature sensors for measuring the temperature of the cell stacks 30. The first temperature sensors are thermistor sensors that measure the temperature of each surface facing the inner cooling portion in each cell stack 30. The second temperature sensors are thermistor sensors that measure the temperature of each surface facing the outer cooling portion in each cell stack 30 located at both ends in the stacking direction.

[0113] <Temperature measurement of power storage device> The fabricated energy storage device 10 was charged with a charging current of 3.78 A until one of the energy storage cells 20 reached 3.75 V. The charged energy storage device 10 was then left at a temperature of 25°C, and the temperature of the energy storage device 10 was adjusted so that the temperatures measured by the first temperature sensors and the second temperature sensors were 25°C. Next, at a temperature of 25°C, the charged energy storage device 10 was discharged with a discharge current of 40 A, with an initial SOC of 100%, until the discharge capacity reached 50 Ah. The temperatures of each portion of the cell stack 30 of the energy storage device 10 during discharge were measured with the first temperature sensor and the second temperature sensor. The results are shown in FIG. 4.

[0114] Although the graph in Fig. 4 shows only one of the measurement results from the multiple first temperature sensors, all of the measurement results from the first temperature sensor were similar to the measurement results from the first temperature sensor shown in the graph. Also, although the graph in Fig. 4 shows only one of the measurement results from the multiple second temperature sensors, all of the measurement results from the second temperature sensor were similar to the measurement results from the second temperature sensor shown in the graph.

[0115] 4, the temperature of each cell stack 30 of the energy storage device 10 gradually increased as the discharge progressed. During discharge, the temperature of the energy storage device 10 measured by the first temperature sensor was higher than the temperature of the energy storage device 10 measured by the second temperature sensor.

[0116] As described above, although the temperature of the energy storage device 10 rises as the device discharges, neither the temperature inside the energy storage device 10 measured by the first temperature sensor nor the temperature outside the energy storage device 10 measured by the second temperature sensor exceeds 40° C. This result shows that the provision of the cooling unit 80 can suppress the temperature rise in the cell stack 30.

[0117] [Note] the positive electrode active material layer is bonded to a first surface of the positive electrode current collector; the negative electrode having the negative electrode active material layer bonded to a first surface of the negative electrode current collector, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode; a separator disposed between the positive electrode active material layer and the negative electrode active material layer; and a storage chamber disposed between the positive electrode and the negative electrode for liquid-tightly storing a liquid electrolyte, the liquid electrolyte containing an ester compound. The energy storage device includes a storage cell including: a positive electrode having a positive electrode active material layer bonded to a first surface of the positive electrode current collector; a negative electrode having a negative electrode active material layer bonded to a first surface of the negative electrode current collector, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode; a separator disposed between the positive electrode active material layer and the negative electrode active material layer; and a storage chamber disposed between the positive electrode and the negative electrode for liquid-tightly storing a liquid electrolyte, the liquid electrolyte containing an ester compound. The energy storage device includes a cell stack formed by stacking the storage cells in series, the cell stack having side surfaces in the stacking direction covered with resin coatings, the positive electrode current collector and the negative electrode current collector each including an end current collector positioned in the outermost layer of the cell stack, at least one of the end current collectors being made of a highly thermally conductive material having a thermal conductivity of 100 W / m·K or more; and a cooling unit for cooling the end current collector made of the highly thermally conductive material.

[0118] According to the above-described configuration, the liquid electrolyte contains an ester compound to reduce the viscosity, thereby increasing the basis weight of the active material layer while suppressing an increase in the diffusion resistance of charge carriers in the active material layer.

[0119] Furthermore, the outer surface of the cell stack, which is made by stacking multiple energy storage cells in series, is covered with a resin coating on the side facing the stacking direction. This suppresses heat transfer between the liquid electrolyte in the cell stack and the outside of the cell stack through the side of the cell stack, and limits the heat transfer portion of the outer surface of the cell stack to the terminal current collector located at the end face in the stacking direction. In addition, the terminal current collector is made of a highly thermally conductive material, and a cooling section is provided to cool the terminal current collector made of a highly thermally conductive material.

[0120] Therefore, when the energy storage device is used in a high-temperature environment, the covering portion can prevent heat from the outside air from being transferred to the liquid electrolyte in the cell stack. Even if the temperature of the liquid electrolyte rises due to the influence of the heat from the outside air, the heat is released to the outside through the terminal current collector and the cooling portion, which are made of a highly thermally conductive material, thereby preventing an excessive temperature rise in the liquid electrolyte. Therefore, the energy storage device is less susceptible to the influence of heat from the outside air, and the effect of the ester compound contained in the liquid electrolyte in preventing an increase in the diffusion resistance of charge carriers in the active material layer can be continuously obtained, even in a high-temperature environment.

[0121] The weight of the positive electrode active material layer is 55 mg / cm 2 or more, and the weight of the negative electrode active material layer is 25 mg / cm 2 It is preferable that at least one of the above conditions is satisfied. The larger the basis weight of the active material layer, which is one or both of the positive electrode active material layer and the negative electrode active material layer, the higher the diffusion resistance of charge carriers such as lithium ions in the active material layer. Therefore, when the basis weight of the active material layer is large as described above, the above-mentioned effect of including an ester compound in the liquid electrolyte is more pronounced. [Explanation of symbols]

[0122] S...accommodation chamber, 10...energy storage device, 20...energy storage cell, 21...positive electrode, 21a...positive electrode current collector, 21a'...terminal positive electrode current collector, 21b...positive electrode active material layer, 22...negative electrode, 22a...negative electrode current collector, 22a'...terminal negative electrode current collector, 22b...negative electrode active material layer, 23...separator, 24...sealing portion, 30...cell stack, 40...positive electrode cooling portion, 50...negative electrode cooling portion.

Claims

1. a positive electrode having a positive electrode active material layer adhered to a first surface of a positive electrode current collector; a negative electrode having a negative electrode active material layer bonded to a first surface of a negative electrode current collector, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode; a separator disposed between the positive electrode active material layer and the negative electrode active material layer; An electricity storage device including an electricity storage cell having a storage chamber provided between the positive electrode and the negative electrode and configured to liquid-tightly store a liquid electrolyte, the liquid electrolyte is a liquid electrolyte containing an ester compound, a ratio of the ester compound to the total non-aqueous solvent in the liquid electrolyte is 70% by volume or more; a cell stack formed by stacking a plurality of the storage cells in series, the cell stack has a side surface in the stacking direction covered with a resin covering portion, the positive electrode current collector and the negative electrode current collector each include an end current collector located in the outermost layer of the cell stack, At least one of the terminal current collectors is made of a high thermal conductivity material having a thermal conductivity of 100 W / m K or more, The electricity storage device further comprises a cooling unit that cools the terminal current collector made of the highly thermally conductive material.

2. The electricity storage device according to claim 1 , wherein the ester compound is at least one selected from the group consisting of methyl acetate, ethyl acetate, and methyl propionate.

3. 3. The power storage device according to claim 1, wherein the separator is bonded to the positive electrode active material layer and the negative electrode active material layer.

4. 4. The power storage device according to claim 1, wherein a second surface of the positive electrode current collector opposite to the first surface and a second surface of the negative electrode current collector opposite to the first surface are superimposed so as to be in contact with each other.

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