Power storage device

Abstract

This electricity storage device (10) is provided with an electricity storage cell (20) which is provided with a positive electrode (21), a negative electrode (22), a separator (23) and a storage chamber (S) that liquid-tightly contains a liquid electrolyte, while being arranged between the positive electrode (21) and the negative electrode (22). This electricity storage device is provided with a cell stack (30) which is obtained by stacking a plurality of the electricity storage cells (20) in series; and a lateral surface of the cell stack (30), said surface being lateral to the stacking direction, is covered by a seal part (24) that is formed of a resin. A terminal positive electrode collector (21a') and a terminal negative electrode collector (22a'), which are positioned in the outermost layers of the cell stack (30), are configured from a highly heat conductive material that has a heat conductivity of 100 W / m·K or more. This electricity storage device is provided with a positive electrode cooling part (40) which cools the terminal positive electrode collector (21a') and a negative electrode cooling part (50) which cools the terminal negative electrode collector (22a'). The liquid electrolyte contains an oxalate compound.

Description

[Technical field]

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

[0002] Patent Document 1 discloses a flat-type electricity storage device constructed by stacking a plurality of individually manufactured electricity storage cells in series. The electricity 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 and arranged so that the negative electrode active material layer faces the positive electrode active material layer of the positive electrode, and a separator arranged between the positive electrode and the negative electrode.

[0003] The storage cell further includes a seal portion made of a thermoplastic resin disposed between the positive and negative electrodes and on the outer circumferential side of the positive and negative active material layers. The seal portion maintains a distance between the positive and negative current collectors to prevent short circuits between the current collectors, and also liquid-tightly seals the space between the positive and negative current collectors to form an enclosed space for accommodating a liquid electrolyte between the positive and negative current collectors.

[0004] Patent Documents 2 to 5 disclose techniques using a non-aqueous electrolyte containing lithium bis(oxalato)borate (LiBOB). When a liquid electrolyte containing LiBOB is used, a film of decomposition products is formed on the surface of the negative electrode active material, and this film acts as a protective film for the negative electrode active material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-16825 A [Patent Document 2] JP 2002-184460 A [Patent Document 3] JP 2002-110235 A [Patent Document 4] JP 2009-245828 A [Patent Document 5] JP 2014-035952 A Summary of the Invention [Problem to be solved by the invention]

[0006] Based on Patent Documents 2 to 5, the present inventors have confirmed that the life of the electricity storage device is improved as a result of adding an oxalate compound to the liquid electrolyte. However, as a result of further investigation, the present inventors have discovered a problem that when the temperature of the electricity storage device becomes high, for example, 180° C. or higher, an exothermic reaction occurs between the coating on the surface of the negative electrode active material, which is a decomposition product of the oxalate compound, and the liquid electrolyte, causing a further rise in the temperature of the electricity storage device.

[0007] In particular, in the case of a flat-type electricity storage device constructed by stacking a plurality of individually manufactured electricity storage cells in series, the chamber for accommodating the liquid electrolyte in each electricity storage cell becomes narrow, and the contact area between the liquid electrolyte and the surface of the negative electrode active material becomes relatively large, so that the temperature rise due to the exothermic reaction between the coating on the surface of the negative electrode active material and the liquid electrolyte becomes more remarkable.

[0008] The present invention has been made in view of the above circumstances, and has an object to suppress a temperature rise in an electricity storage device that uses a liquid electrolyte containing an oxalate compound. [Means for solving the problem]

[0009] an electric storage device that achieves the above-mentioned object, the electric storage device comprising: 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 provided between the positive electrode and the negative electrode for liquid-tightly storing a liquid electrolyte, the liquid electrolyte being a liquid electrolyte containing an oxalate compound; and a cell stack formed by stacking a plurality of the electric storage cells in series, the cell stack having a side surface in the stacking direction covered by a resin coating portion, the positive electrode current collector and the negative electrode current collector each comprising an end current collector located 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 portion for cooling the end current collector made of the highly thermally conductive material.

[0010] According to the above configuration, the side surface of the outer surface of the cell stack, which is formed by stacking a plurality of energy storage cells in series, in the stacking direction is covered with a resin covering portion. This suppresses heat transfer between the liquid electrolyte in the cell stack and the outside of the cell stack through the side surface of the cell stack, and limits the heat transfer portion of the outer surface of the cell stack to the outside 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 portion is provided to cool the terminal current collector made of a highly thermally conductive material.

[0011] Therefore, when the power 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, the heat is released to the outside through the end collector and the cooling portion made of a highly thermally conductive material, thereby preventing an excessive temperature rise in the liquid electrolyte. This prevents the temperature of the power storage device from rising to a temperature that would cause an exothermic reaction between the liquid electrolyte and the coating on the surface of the negative electrode active material layer formed based on the oxalate compound contained in the liquid electrolyte, and also prevents a further temperature rise in the power storage device caused by the exothermic reaction.

[0012] The oxalate compound is represented by the general formula (1)A + [BX 4-2n (C2O4) n ] - In the general formula (1), A is preferably an oxalate compound represented by the formula: + is an alkali metal cation, X is a halogen atom, and n is 1 or 2.

[0013] According to the above-mentioned configuration, the effect of improving the life of the electricity storage device can be more significantly achieved by forming a coating of the decomposition product of the oxalate compound on the surface of the negative electrode active material. The positive electrode active material layer has a coating weight of 55 mg / cm 2 or more, and the negative electrode active material layer has a weight per unit area of ​​25 mg / cm 2 It is preferable that at least one of the above conditions is satisfied.

[0014] According to the above configuration, the energy density of the power storage device can be increased. The separator is preferably adhered to the positive electrode active material layer and the negative electrode active material layer.

[0015] According to the above configuration, the efficiency of thermal conduction between the positive electrode active material layer and the negative electrode active material layer facing each other via the separator is improved, which makes it easier for heat to be transmitted in the stacking direction of the cell stack, and allows the heat in the cell stack to be efficiently transferred to the end current collector and the cooling section and released to the outside.

[0016] The covering portion is provided with a permeable wall portion that allows carbon dioxide gas generated in the storage chamber to permeate to the outside of the cell stack, and the permeable wall portion has a density of 930 kg / m 3 It is preferred that the low density polyethylene resin be less than 1000 MPa.

[0017] When an oxalate compound containing oxalate ions in its structure is added to a liquid electrolyte, the internal pressure of the storage chamber in which the liquid electrolyte is stored may increase due to the generation of carbon dioxide gas derived from the oxalate ions. The increase in internal pressure of the storage chamber causes an increase in the temperature of the electricity storage device.

[0018] According to the above configuration, the covering portion is provided with a permeable wall portion made of a low-density polyethylene resin that has the property of allowing carbon dioxide gas to pass therethrough. As a result, when carbon dioxide gas originating from the oxalate ions that constitute the oxalate compound is generated in the storage chamber, the carbon dioxide gas in the storage chamber can be discharged to the outside of the cell stack through the permeable wall portion. As a result, an increase in the internal pressure of the storage chamber can be suppressed, and a temperature increase in the power storage device due to an increase in the internal pressure of the storage chamber can be suppressed.

[0019] The transparent wall portion is preferably provided around the entire periphery of the covering portion. According to the above configuration, it is possible to allow carbon dioxide gas to pass through from any position in the circumferential direction of the inner surface of the covering portion, and it is possible to prevent the generated carbon dioxide gas from continuing to accumulate in parts of the storage chamber, such as corner portions, without being discharged. Effect of the Invention

[0020] According to the present invention, it is possible to suppress a temperature rise in an electricity storage device that uses a liquid electrolyte containing an oxalate compound. [Brief description of the drawings]

[0021] [Figure 1] FIG. [Diagram 2] FIG. 11 is a partial cross-sectional view of a peripheral portion of a cell stack according to a modified example. [Diagram 3] FIG. 11 is a cross-sectional view of a power storage device according to a modified example. [Figure 4] 6 is a graph showing a change in temperature of a cell stack during discharge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The power storage device 10 shown in Fig. 1 is, for example, a power storage module used in batteries of various vehicles such as forklifts, hybrid cars, and electric cars. The power storage device 10 is, for example, a secondary battery such as a lithium ion secondary battery. The power storage device 10 may be an electric double layer capacitor. In this embodiment, the case where the power storage device 10 is a lithium ion secondary battery is illustrated.

[0023] As shown in Fig. 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.

[0024] The positive electrode 21 includes a positive electrode collector 21a and a positive electrode active material layer 21b provided on a first surface 21a1 of the positive electrode collector 21a. In a plan view 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 collector 21a. The peripheral portion of the first surface 21a1 of the positive electrode collector 21a in the plan view 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 so as to surround the periphery of the positive electrode active material layer 21b in the plan view.

[0025] 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. The negative electrode uncoated portion 22c is disposed so as to surround the periphery of the negative electrode active material layer 22b in a plan view.

[0026] 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 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 in a plan view.

[0027] The positive electrode current collector 21a has a second surface 21a2 opposite to the first surface 21a1. The positive electrode 21 is an electrode having a monopolar structure 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 an electrode having a monopolar structure 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.

[0028] 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 a short circuit due to contact between the two electrodes, while allowing charge carriers such as lithium ions to pass through.

[0029] The separator 23 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains a liquid electrolyte. Examples of materials constituting 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.

[0030] 1, in this embodiment, a sheet-like separator 23 having adhesive layers 23a on both surfaces is used. The adhesive layer 23a on one surface (the surface on the lower side of the drawing) of the separator 23 is in contact with the first surface of the positive electrode current collector 21a. 21a1 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.

[0031] The seal portion 24 is a first surface of the positive electrode current collector 21a of the positive electrode 21. 21a1 and the first surface 22a1 of the negative electrode current collector 22a of the negative electrode 22, and is disposed on the outer circumferential 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 prevents a short circuit between the current collectors by insulating between the positive electrode current collector 21a and the negative electrode current collector 22a.

[0032] The sealing portion 24 extends along the peripheral portions of the positive electrode current collector 21a and the negative electrode current collector 22a in a plan view, and is formed in a frame shape surrounding the periphery of the positive electrode active material layer 21b and the negative electrode active material layer 22b. The sealing portion 24 is disposed between the positive electrode uncoated portion 21c of the first surface 21a1 of the positive electrode current collector 21a and the negative electrode uncoated portion 22c of the first surface 22a1 of the negative electrode current collector 22a.

[0033] 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 portion 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.

[0034] The storage chamber S has a flat shape that spreads in the planar direction of the first surface 21a1 of the positive electrode current collector 21a and the first surface 22a1 of the negative electrode current collector 22a and has a short length in the stacking direction. For example, when the length of the storage chamber S in the stacking direction is L and the volume of the storage chamber S is V, the ratio (V / L) of the length L to the volume V is preferably 0.025 or more, and more preferably 0.035 or more. Moreover, the ratio (V / L) is, for example, 0.4 or less.

[0035] The length L of the storage chamber S in the stacking direction is, for example, 400 μm or more and 1000 μm or less, and preferably 500 μm or more and 750 μm or less. The volume V of the storage chamber S is, for example, 25 cc or more and 150 cc or less, preferably 40 cc or more and 120 cc or less, and more preferably 50 cc or more and 100 cc or less. The length L is 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.

[0036] The cell stack 30 has a structure in which a plurality of storage cells 20 are stacked such 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. As a result, the plurality of storage cells 20 constituting the cell stack 30 are connected in series.

[0037] Here, in the cell stack 30, two storage cells 20 adjacent to each other in the stacking direction form a pseudo bipolar electrode 25 in which the positive electrode current collector 21a and the negative electrode current collector 22a in contact with each other are regarded as one current collector. The pseudo bipolar electrode 25 includes a current collector having a structure in which the positive electrode current collector 21a and the 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.

[0038] 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. The outer peripheral portion 24a protrudes in a direction perpendicular to the stacking direction 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 portions 24a of the seal portions 24 of the storage cells 20 adjacent to each other in the stacking direction are integrated together by bonding the outer peripheral portions 24a of the seal portions 24 to each other.

[0039] 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 examples of a method for bonding adjacent seal portions 24 to each other include known welding methods such as heat welding, ultrasonic welding, and infrared welding.

[0040] 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 respectively referred to as a terminal positive electrode current collector 21a' and a terminal negative electrode current collector 22a' as terminal current collectors. A positive electrode cooling unit 40 for cooling the terminal positive electrode current collector 21a' is attached to a second surface 21a2' of the terminal positive electrode current collector 21a'. In addition, a negative electrode cooling unit 50 for cooling the terminal negative electrode current collector 22a' is attached to a second surface 22a2' of the terminal negative electrode current collector 22a'.

[0041] The positive electrode cooling section 40 and the negative electrode cooling section 50 cool the terminal positive electrode current collector 21a' to, for example, 60°C or less. The specific configuration of the positive electrode cooling section 40 and the negative electrode cooling section 50 is not particularly limited, and a known cooling section used for cooling an electricity storage device can be used. An example of a known cooling section is a cooling section that has a structure such as fins that enhances heat transfer efficiency and cools an object to be cooled by exchanging heat with a cooling medium.

[0042] In this embodiment, the positive electrode cooling section 40 and the negative electrode cooling section 50 are configured to function as current-carrying plates. That is, the positive electrode cooling section 40 and the negative electrode cooling section 50 are configured from a material having 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. The charge and discharge of the electricity storage device 10 is performed through terminals provided on the positive electrode cooling section 40 and the negative electrode cooling section 50, respectively. As the material for forming the positive electrode cooling section 40 and the negative electrode cooling section 50, for example, the same material as the material for forming the positive electrode current collector 21a and the negative electrode current collector 22a described later can be used.

[0043] 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.

[0044] There are no particular limitations on the specific configuration of the restraining member 60, so long as it is capable of applying a restraining load to the cell stack 30. Fig. 1 illustrates, as an example, 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 bias the restraining plates 61 in directions in which they approach each other, thereby applying a restraining load to the cell stack 30 in the stacking direction.

[0045] 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 for continuing to pass current to 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.

[0046] 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 the highly thermally conductive material include metal materials such as silver, copper, gold, and aluminum. The thermal conductivity of the highly thermally conductive material is, for example, 500 W / m·K or less.

[0047] From the viewpoint of thermal 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.

[0048] 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 Above 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 Less than 2.2m 2 It is preferable that:

[0049] 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.

[0050] Examples of materials that can be used to form 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) include metal materials, conductive resin materials, and conductive inorganic materials.

[0051] 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 in which a conductive filler is added to a conductive polymer material or a non-conductive polymer material as necessary.

[0052] 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. Moreover, 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.

[0053] From the viewpoint of thermal conduction to the terminal positive electrode current collector 21a' and the terminal 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 the length 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. 2 Preferably less than 2.2m 2 It is more preferable that:

[0054] 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. 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.

[0055] 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'. Either or both of the positive electrode collector 21a and the negative electrode collector 22a may have a plurality of layers including one or more layers containing the above-mentioned metal material or conductive resin material. Either or both of the surfaces of the positive electrode collector 21a and the negative electrode collector 22a may be covered with a known protective layer. Either or both of the surfaces of the positive electrode collector 21a and the negative electrode collector 22a may be surface-treated by a known method such as plating. Examples of the surface treatment include chromate treatment and chromate phosphate treatment.

[0056] 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 they are foils, sheets, or films, their thickness is, for example, 1 to 100 μm.

[0057] In this 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.

[0058] <Positive Electrode Active Material Layer and Negative Electrode Active Material Layer> The positive electrode active material layer 21b includes a positive electrode active material capable of absorbing and releasing charge carriers such as lithium ions. As the positive electrode active material, any material that can be used as a positive electrode active material for a lithium ion secondary battery, 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, may be used. Two or more types of positive electrode active materials may be used in combination. In this embodiment, the positive electrode active material layer 21b includes olivine-type lithium iron phosphate (LiFePO4) as a polyanion-based compound.

[0059] 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. For example, the negative electrode active material can be Li, carbon, a metal compound, Or, Examples of the element that can be alloyed with lithium include an element or a compound thereof. Examples of carbon include natural graphite, artificial graphite, hard carbon (hardly graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of the element that can be alloyed with lithium include silicon and tin. In this embodiment, the negative electrode active material layer 22b includes graphite as a carbon-based material.

[0060] 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 assistant for enhancing electrical conductivity, a binder, an electrolyte (polymer matrix, ion-conductive polymer, liquid electrolyte, etc.), an electrolyte supporting salt for enhancing ion conductivity (lithium salt), etc. The components contained in the active material layer and the compounding ratio of the components are not particularly limited, and conventionally known knowledge about lithium ion secondary batteries may be appropriately referred to.

[0061] The conductive assistant is added to increase the conductivity of the positive electrode 21 or the negative electrode 22. Examples of the conductive assistant include acetylene black, carbon black, and graphite. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, 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 the solvent or dispersion medium include water and N-methyl-2-pyrrolidone.

[0062] To form the active material layers on the surfaces of the positive electrode current collector 21a and the negative electrode current collector 22a, a conventionally known method such as a roll coating method 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.

[0063] The thickness and basis weight of the active material layer are not particularly limited, and conventionally known knowledge about lithium ion secondary batteries may be appropriately referred to. 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.

[0064] 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 More than 70 mg / cm 2 The weight per unit area of ​​the positive electrode active material layer 21b is preferably 90 mg / cm or more. 2 In 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:

[0065] 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 More than 30 mg / cm 2 The weight per unit area of ​​the negative electrode active material layer 22b is preferably 45 mg / cm or more. 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:

[0066] <Sealing part (covering part)> The seal portion 24 has a density of 930 kg / m 3 The low density polyethylene resin has a density of, for example, 900 kg / m 3 or more, preferably 910 kg / m 3 The above density is a density conforming to JIS K6922.

[0067] Polyethylene resins are classified by density, for example, in JIS K6922. In this classification, 3 A polyethylene resin having a density exceeding this is considered to be medium density polyethylene. The low density polyethylene resin constituting the seal portion 24 is a polyethylene resin having a density lower than that of medium density polyethylene. Examples of the low density polyethylene resin include high pressure low density polyethylene and linear low density polyethylene. The low density polyethylene resin is preferably high pressure low density polyethylene. The thermal conductivity of the seal portion 24 is, for example, 0.28 to 0.38 W / m K.

[0068] <Liquid electrolyte> The liquid electrolyte may, for example, include a liquid electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the electrolyte salt, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 may be used. As the non-aqueous solvent, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers may be used. Two or more of these known solvent materials may be used in combination.

[0069] The liquid electrolyte contains an oxalate compound. The oxalate compound means a compound containing an oxalate ion in its structure. Examples of the oxalate compound include those represented by the general formula (1)A + [BX 4-2n (C2O4) n ] - In the general formula (1), A + is an alkali metal cation such as a lithium ion, X is a halogen atom such as a fluorine atom, and n is 1 or 2.

[0070] Specific examples of the compound represented by the general formula (1) include lithium difluorooxalate borate (LiDFOB) and lithium bisoxalate borate (LiBOB). The oxalate compound may be any of the oxalate compounds disclosed in Patent Documents 2 to 5. These oxalate compounds may be used alone or in combination.

[0071] The mixing ratio of the oxalate compound in the liquid electrolyte is, for example, preferably 0.1 to 5 parts by mass, more preferably 0.3 to 4 parts by mass, even more preferably 0.5 to 3 parts by mass, and most preferably 1 to 2 parts by mass, relative to 100 parts by mass of the total mass of components other than the oxalate compound contained in the liquid electrolyte.

[0072] The electricity storage device 10 is manufactured by sequentially performing an electrode formation process, an electricity storage cell formation process, and a cell stack formation process. Here, as an example, a case will be described in which all the positive electrode current collectors 21a including the terminal positive electrode current collector 21a' are made of aluminum foil, and all the negative electrode current collectors 22a including the terminal negative electrode current collector 22a' are made of copper foil.

[0073] <Electrode formation process> The electrode formation process includes a positive electrode formation process for forming the positive electrode 21 and a negative electrode formation process for forming the negative electrode 22.

[0074] The positive electrode formation step is not particularly limited, and may be a known method applied to the formation of the positive electrode 21 including the positive electrode collector 21a and the positive electrode active material layer 21b. For example, the positive electrode 21 can be formed by attaching a positive electrode mixture, which will become the positive electrode active material layer 21b when solidified, to a first surface 21a1 of an aluminum foil serving as the positive electrode collector 21a to a predetermined thickness, and then performing a solidification process appropriate for the positive electrode mixture.

[0075] The negative electrode forming step is not particularly limited, and may be any known method applicable to the formation of the negative electrode 22 including the negative electrode current collector 22a and the negative electrode active material layer 22b. 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 22b when solidified, to a predetermined thickness on the first surface 22a1 of the copper foil serving as the negative electrode current collector 22a, and then performing a solidification process appropriate for the negative electrode composite material.

[0076] <Storage cell formation process> In the 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 side of the positive electrode collector 21a and the negative electrode collector 22a.

[0077] Thereafter, the positive electrode 21, the negative electrode 22, the separator 23, and the sealing material are bonded by welding 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 a method for welding the sealing material include known welding methods such as heat welding, ultrasonic welding, and infrared welding.

[0078] 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 electricity storage cell 20 is formed. <Cell stack formation process> In the cell stack forming process, first, the multiple 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 face each other. Then, the multiple 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.

[0079] Next, the positive electrode cooling section 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 on the outermost side at one end of the stacking direction. Similarly, the negative electrode cooling section 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 on the outermost side at the other end of the stacking direction. In this way, the cell stack 30 is formed. Thereafter, the restraining member 60 is attached to the cell stack 30. For example, after arranging restraining plates 61 at both ends of the cell stack 30 in the stacking direction, the restraining plates 61 are fastened to each other by fastening members 62.

[0080] Next, the operation of this embodiment will be described. In the electricity storage device 10 of this embodiment, a liquid electrolyte containing an oxalate compound is used as the liquid electrolyte. As a result, a coating of a decomposition product of the oxalate compound is formed on the surface of the negative electrode active material layer 22b. This coating functions as a protective film for the negative electrode active material layer 22b, thereby improving the life of the electricity storage device 10.

[0081] In addition, the side of the outer surface of the cell stack 30 formed by stacking a plurality of the storage cells 20 in series in the stacking direction is covered with a resin seal portion 24 (coating 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 of the cell stack 30, and limits the heat transfer portion of the outer surface of the cell stack 30 to the outside to the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' located at the end faces in the stacking direction. In addition, the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' are made of a highly heat conductive material, and a positive electrode cooling portion 40 and a negative electrode cooling portion 50 that cool the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' are provided.

[0082] When the electricity 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, the heat is released to the outside through the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a', which are made of a highly heat-conductive material, as well as the positive electrode cooling portion 40 and the negative electrode cooling portion 50. This can prevent an excessive temperature rise in the liquid electrolyte. As a result, it is possible to prevent a temperature rise in the electricity storage device 10 that reaches a temperature that causes an exothermic reaction between the liquid electrolyte and the coating on the surface of the negative electrode active material layer 22b formed based on the oxalate compound contained in the liquid electrolyte, and also to prevent a further temperature rise in the electricity storage device 10 caused by the exothermic reaction.

[0083] According to this embodiment, the following effects can be obtained. (1) The electricity storage device 10 includes an electricity 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 is a liquid electrolyte containing an oxalate compound.

[0084] The cell stack 30 is made up of a plurality of storage cells 20 stacked in series, the side surfaces of the cell stack 30 in the stacking direction are covered with resin seal parts 24, and the terminal positive current collector 21a' and terminal negative current collector 22a' located in the outermost layers of the cell stack 30 are made of a highly heat-conductive material with a thermal conductivity of 100 W / m K or more. A positive electrode cooling part 40 that cools the terminal positive electrode current collector 21a' and a negative electrode cooling part 50 that cools the terminal negative electrode current collector 22a' are provided.

[0085] According to the above-mentioned configuration, a coating of a decomposition product of the oxalate compound is formed on the surface of the negative electrode active material layer 22b, thereby improving the life of the electricity storage device 10. In addition, it is possible to suppress a temperature rise in the electricity storage device 10 that would cause an exothermic reaction between the liquid electrolyte and the coating on the surface of the negative electrode active material layer 22b, which is formed based on the oxalate compound contained in the liquid electrolyte, and to suppress a further temperature rise in the electricity storage device 10 caused by the exothermic reaction.

[0086] (2) The oxalate compound is represented by the general formula (1)A + [BX 4-2n (C2O4) n ] - It is an oxalate compound represented by the formula: According to the above-mentioned configuration, a film of the decomposition product of the oxalate compound is formed on the surface of the negative electrode active material. This film acts as a protective film for the negative electrode active material. As a result, the battery performance of the electricity storage device 10 is improved.

[0087] According to the above-mentioned configuration, the effect of improving the life of the electricity storage device 10 can be more significantly achieved by forming a coating of a decomposition product of the oxalate compound on the surface of the negative electrode active material layer 22b.

[0088] (3) The weight of the positive electrode active material layer 21b is 55 mg / cm 2 The negative electrode active material layer 22b has a coating weight of 25 mg / cm 2 That's all. According to the above configuration, the energy density of the power storage device 10 can be increased.

[0089] (4) The separator 23 is bonded to the positive electrode active material layer 21b and the negative electrode active material layer 22b. According to the above configuration, the efficiency of thermal conduction between the positive electrode active material layer 21b and the negative electrode active material layer 22b facing each other via the separator 23 is improved. This makes it easier for heat to be transmitted in the stacking direction of the cell stack 30, and the heat in the cell stack 30 can 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 released to the outside. Furthermore, since 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 suppress an increase in the distance in the stacking direction between the positive electrode active material layer 21b and the negative electrode active material layer 22b during charging and discharging, and thus it is possible to suppress an increase in the resistance of the storage cell 20.

[0090] (5) The entire sealing portion 24, which is the covering portion, is a permeable wall portion that allows carbon dioxide gas generated in the storage chamber S to pass through to the outside of the cell stack 30, and has a density of 930 kg / m 3 It is composed of low-density polyethylene resin less than 100%.

[0091] When an oxalate compound containing oxalate ions in its structure is added to the liquid electrolyte, the internal pressure of the storage chamber S in which the liquid electrolyte is stored may increase due to the generation of carbon dioxide gas derived from the oxalate ions. The increase in the internal pressure of the storage chamber S causes the temperature of the electricity storage device 10 to increase.

[0092] According to the above configuration, the covering portion is made of a low-density polyethylene resin having a property of allowing carbon dioxide gas to pass therethrough, thereby serving as a permeable wall portion that allows carbon dioxide gas generated in the storage chamber S to pass therethrough to the outside of the cell stack 30. As a result, when carbon dioxide gas derived from the oxalate ions that constitute the oxalate compound is generated in the storage chamber S, the carbon dioxide gas in the storage chamber S can be discharged to the outside of the cell stack 30 through the covering portion that serves as a permeable wall portion. As a result, an increase in the internal pressure of the storage chamber S can be suppressed, and a temperature increase in the electricity storage device 10 due to an increase in the internal pressure of the storage chamber S can be suppressed.

[0093] Furthermore, the low-density polyethylene resin has a low water vapor permeability in addition to a carbon dioxide gas permeability, so that it is possible to prevent moisture from entering the storage chamber S from the outside through the covering portion acting as a permeable wall portion.

[0094] (6) The entire sealing portion 24, which is the covering portion, is a permeable wall portion that allows carbon dioxide gas to pass through. Therefore, the permeable wall portion is located on the entire periphery of the covering portion. According to the above configuration, carbon dioxide gas can be transmitted through any position in the circumferential direction of the covering portion, and it is possible to prevent the generated carbon dioxide gas from continuing to accumulate without being discharged in corners of the storage chamber S, for example.

[0095] (7) The positive electrode 21, the negative electrode 22, and the separator 23 are repeatedly stacked in a stacked structure, and a second surface 21a2 opposite to the first surface 21a1 of the positive electrode current collector 21a is in contact with a second surface 22a2 opposite to the first surface 22a1 of the negative electrode current collector 22a.

[0096] In this case, if the internal pressure of the storage chamber S increases excessively and the storage chamber S expands, the positive electrode current collector 21a and the negative electrode current collector 22a may be deformed, and the contact area between the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a may decrease, increasing the resistance. In other words, the increase in the internal pressure of the storage chamber S may cause the battery performance to decrease. Therefore, when the above techniques (5) to (6) are applied to such a configuration, in addition to the effect of suppressing the increase in the internal pressure of the storage chamber S, the effect of suppressing the decrease in the battery performance can also be obtained.

[0097] (8) 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 It is.

[0098] 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, and the contact area with the negative electrode current collector 22a of the adjacent power storage cell 20 is prevented from becoming smaller. This makes it possible to prevent a decrease in the efficiency of thermal conduction between the power storage cells 20 caused by the reduction in the contact area.

[0099] (9) The negative electrode current collector 22a is in the form of a foil having a thickness of 0.005 to 0.02 mm, and the negative electrode active material layer 22b has a basis weight 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 It is.

[0100] According to the above configuration, the same effect as that of (4) above can be obtained with respect to the negative electrode 22. (10) 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 2 The thickness is 0.005 mm or more and 0.05 mm or less. In other words, the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' are current collectors whose thickness is significantly small relative to their area. Therefore, the amount of heat conduction from the positive electrode cooling section 40 and the negative electrode cooling section 50 can be increased, and the inside of the cell stack 30 can be efficiently cooled.

[0101] (11) 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 compared to their area. Therefore, the heat in the cell stack 30 can be more efficiently transferred to the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a'.

[0102] This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs. The permeable wall portion, which is made of the low-density polyethylene resin and allows carbon dioxide gas generated in the storage chamber S to permeate to the outside of the cell stack 30, may be partially provided as part of the seal portion 24. Examples of the part of the seal portion 24 where the permeable wall portion is provided include a part of the seal portion 24 in the stacking direction and a part of the seal portion 24 in the circumferential direction.

[0103] For example, the seal portion 24 has a multi-layer structure in which a first resin layer made of the low-density polyethylene resin and a second resin layer made of another resin are stacked in the stacking direction, and the first resin layer is the permeable wall portion. In addition, in the case of a cell stack 30 formed by stacking energy storage cells 20 each having a polygonal shape in a plan view, the cell stack 30 has three or more side surfaces in the stacking direction. The seal portion 24 constituting one of the side surfaces is made of the low-density polyethylene resin and is the permeable wall portion, and the seal portions 24 constituting the other side surfaces are made of another resin.

[0104] Examples of the other resins include polyolefin resins. Examples of the 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 the modified polyethylene include acid-modified polyethylene and epoxy-modified polyethylene. Examples of the modified polypropylene include acid-modified polypropylene and epoxy-modified polypropylene. These known polyolefin resins may be used in combination of two or more kinds. The polyolefin resin may be a thermoplastic resin or a thermosetting resin. In this case, the thermal conductivity of the seal portion 24 is, for example, 0.17 to 0.19 W / m·K.

[0105] For example, the entire seal portion 24 may be made of a resin other than the low-density polyethylene resin. 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, but a covering portion may be provided separately from the sealing portion 24. For example, the outer peripheral portion 24a of the sealing portion 24 is omitted, and a resin layer that covers the side surface of the cell stack 30 in the stacking direction is 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 the resin that constitutes the sealing portion 24, or it may be different.

[0106] It should be noted that a permeable wall section can also be provided in a configuration in which a covering section is provided separately from the sealing section 24. For example, a first permeable wall section made of the low-density polyethylene resin is provided for the sealing section 24 so as to reach the outer surface from the inner surface of the sealing section 24. Then, a second permeable wall section made of the low-density polyethylene resin is provided for the covering section so as to reach the outer surface of the covering section from a contactable portion of the inner surface of the covering section with the gas that has permeated the first permeable wall section. In this case, carbon dioxide gas generated in the storage chamber S permeates to the outside of the sealing section 24 through the first permeable wall section, and then permeates to the outside of the covering section through the second permeable wall section.

[0107] In the above embodiment, the storage chamber S is defined by the frame-shaped seal portion 24, the positive electrode 21, and the negative electrode 22. However, the configuration for defining the storage chamber S is not limited to the above embodiment. For example, the storage chamber S may be defined 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.

[0108] In this case, the resin layer, which is the covering portion, 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.

[0109] In this case, the seal part 24 may be provided or may not be provided. Examples of the seal part 24 include a seal part that is not attached to either the positive electrode current collector 21a or the negative electrode current collector 22a but is attached to the resin layer, a seal part that is attached to the positive electrode current collector 21a and the resin layer but is not attached to the negative electrode current collector 22a, and a seal part that is attached to the negative electrode current collector 22a and the resin layer but is not attached to the positive electrode current collector 21a. Two or more of these seal parts may be used in combination.

[0110] 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.

[0111] 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, when only one of the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' is made of a highly thermally conductive material, a cooling unit is provided to cool the terminal positive electrode current collector 21a' or the terminal negative electrode current collector 22a' made of a highly thermally conductive material.

[0112] 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 is true for the negative electrode current collector 22a and the negative electrode active material layer 22b.

[0113] The shape of the seal portion 24 in a 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 composed of a plurality of members. For example, the seal portion 24 may be composed of two members, the outer peripheral portion 24a and a portion other than the outer peripheral portion, and the seal portion 24 may be composed by welding the two members. Alternatively, the seal portion 24 may be composed of a plurality of members stacked in the stacking direction. Furthermore, the seal portion 24 may be composed of two members, 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 composed of a plurality of members stacked in the stacking direction.

[0114] 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 collector 21a and the first surface 22a1 of the negative electrode collector 22a in the storage cell 20 may be different for each portion. In the stacking direction, the distance between the first surface 21a1 of the positive electrode collector 21a and the first surface 22a1 of the negative electrode collector 22a in the portion 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 thickness of the positive electrode active material layer 21b, the thickness of the negative electrode active material layer 22b, and the thickness of the separator 23. In addition, in the stacking direction, the distance between the first surface 21a1 of the positive electrode collector 21a and the first surface 22a1 of the negative electrode collector 22a in the portion 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 portion of the first surface 21a1 of the positive electrode current collector 21a and the peripheral portion of the first surface 22a1 of the negative electrode current collector 22a.

[0115] It is preferable to make the second distance D2 smaller than the first distance D1, that is, smaller than the thickness of the seal portion 24. In this case, the restraining load by the restraining member 60 can be applied more efficiently 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 opposing region of the cell stack 30. 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 becomes large, and there is a risk that the seal portion 24 will be easily peeled off from the positive electrode current collector 21a and the negative electrode current collector 22a.

[0116] 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 still more preferably satisfy the relationship of 0.8D1 ≤ D2 ≤ 0.9D1.

[0117] In addition, 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.

[0118] ○ 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 lower hardness than 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.

[0119] 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.

[0120] ○ The electrode may be a bipolar electrode in which the positive electrode current collector 21a and the negative electrode current collector 22a are used as one current collector. Examples of the current collector of the bipolar electrode include stainless steel foil (e.g., JIS Examples of the current collector include SUS304, SUS316, SUS301, SUS304, etc., as specified in JIS G 4305:2015, copper foil, aluminum foil, and nickel foil. In addition, a clad material of two or more metals such as copper and aluminum, a plated material of two or more metals such as copper and aluminum, and a current collector in which two or more metal foils are bonded together may be used. For example, when a copper-aluminum plated material having a copper layer and an aluminum layer is used as a current collector of a bipolar electrode, the aluminum layer can function as the positive electrode current collector 21a, and the copper layer can function as the negative electrode current collector 22a.

[0121] 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 the power storage cells 20 adjacent 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.

[0122] As shown in Fig. 3, the energy storage device 10 may be configured to include a cell stack laminate 31 formed by stacking a plurality of cell stacks 30. In the cell stack laminate 31, the plurality of cell stacks 30 are stacked such that the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' face each other. The cell stack laminate 31 may include, for example, 1 to 8 cell stacks 30. When the energy storage device 10 includes the cell stack laminate 31, it is preferable that the restraining member 60 is configured to apply a restraining load to the cell stack laminate 31.

[0123] 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. The cooling section 80 is provided between all layers of the cell stacks 30 and between the cell stack 30 and the restraining plate 61 of the restraining member 60. The cooling section 80 provided between the layers of the cell stacks 30 cools both the terminal positive electrode current collector 21a' and the terminal negative electrode current collector 22a' that face each other with the cooling section 80 in between. The specific configuration of the cooling section 80 is the same as 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 21a' and the terminal negative electrode current collector 22a' that face each other with the cooling section 80 in between. In the example shown in FIG. 3, the cooling section 80 is provided between all layers of the cell stacks 30, but the cooling section 80 may be provided only between some layers of the cell stacks 30.

[0124] The cell stack laminate 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 laminate 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 laminate 31 may be configured so that the negative electrode cooling section 50 also functions as the positive electrode cooling section 40.

[0125] 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 highly thermally conductive material. EXAMPLES

[0126] An electricity storage device 10 was actually fabricated, and the temperature change during discharging of the fabricated electricity storage device 10 was measured. <Structure of Energy Storage Cell> A storage cell 20 having the following configuration was fabricated.

[0127] (Positive electrode material) Positive electrode current collector: Aluminum foil with a thickness of 0.050 mm. Positive electrode active material layer: A mixture of olivine-type lithium iron phosphate (LiFePO4), acetylene black (AB), and polyvinylidene fluoride (PVdF).

[0128] Mass ratio of positive electrode active material layer: 90:5:5 (LiFePO4:AB:PVdF) Weight of positive electrode active material layer: 55.5 mg / cm 2 Density of the positive electrode active material layer: 2g / cm 3 (Negative electrode material) Negative electrode current collector: 0.015 mm thick copper foil.

[0129] 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) Weight of negative electrode active material layer: 26.5 mg / cm 2 Density of negative electrode active material layer: 1.3 mg / cm 2 (Other materials) Separator: 18 μm thick porous sheet with a ceramic layer.

[0130] Sealing part: Acid-modified polyethylene Liquid electrolyte: A liquid electrolyte prepared by dissolving LiN(FSO2)2 to a concentration of 1.2M in a mixed solvent of ethylene carbonate and methyl propionate in a volume ratio of 15:85, and adding 5.7% by mass of vinylene carbonate and 1% by mass of lithium difluorooxalatoborate (LiDFOB).

[0131] (Storage cell size) Planar area of ​​the positive electrode active material layer: 780 mm long x 1024 mm wide Thickness of the positive electrode active material layer: 277.5 μm Planar area of ​​the negative electrode active material layer: 822 mm long x 1055 mm wide Negative electrode active material layer thickness: 203.8 μm Containment chamber volume: 29.3cm 3 <Cell stack and power storage device> 24 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.

[0132] 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 layers of the cell stacks 30 in the energy storage device 10 and between the cell stacks 30 and the binding members 60 located at both ends in the stacking direction. Aluminum plate material is 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 binding members 60 are referred to as outer cooling sections.

[0133] Furthermore, the manufactured power storage device 10 is 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.

[0134] <Temperature measurement of power storage device> The produced energy storage device 10 was charged with a charging current of 3.78A until any one of the energy storage cells 20 reached 3.75V. The charged energy storage device 10 was then left at a temperature of 25°C to adjust the temperature of the energy storage device 10 so that the temperature measured by each of the first temperature sensors and each of the second temperature sensors was 25°C. Next, at a temperature of 25°C, the charged energy storage device 10 was discharged with a discharge current of 40A until the discharge capacity reached 50Ah, with the initial SOC set to 100%. The temperature of each portion of the cell stack 30 of the energy storage device 10 during discharging was measured by the first temperature sensor and the second temperature sensor. The results are shown in FIG. 4.

[0135] Note that the graph in Fig. 4 shows only one of the measurement results from the multiple first temperature sensors, but 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, the graph in Fig. 4 shows only one of the measurement results from the multiple second temperature sensors, but 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.

[0136] As shown in Fig. 4, the temperature of each cell stack 30 of the energy storage device 10 gradually increased as the discharge progressed. Regarding the temperature of the energy storage device 10 during discharge, the temperature inside the energy storage device 10 measured by the first temperature sensor was higher than the temperature outside the energy storage device 10 measured by the second temperature sensor.

[0137] As described above, although the temperature of the electricity storage device 10 rises with discharge, neither the temperature inside the electricity storage device 10 measured by the first temperature sensor nor the temperature outside the electricity 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 of the cell stack 30. It is also shown that when an oxalate compound is contained in the liquid electrolyte, the temperature rise of the electricity storage device 10 can be suppressed to a temperature that causes an exothermic reaction between the liquid electrolyte and the coating on the surface of the negative electrode active material layer 22b formed based on the oxalate compound. [Explanation of symbols]

[0138] S... storage 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; A power storage device including a power 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 oxalate compound, A cell stack is provided in which a plurality of the storage cells are stacked in series, the cell stack has a side surface in a stacking direction covered with a resin covering portion, the positive electrode current collector and the negative electrode current collector each include a terminal current collector located in an outermost layer of the cell stack, At least one of the terminal collectors is made of a highly thermally conductive material having a thermal conductivity of 100 W / m K or more; a cooling unit that cools the terminal current collector made of the highly thermally conductive material, the covering portion is provided with a permeable wall portion that allows carbon dioxide gas generated in the storage chamber to permeate to the outside of the cell stack, The electricity storage device, wherein the permeable wall portion is made of a low-density polyethylene resin having a density of less than 930 kg / m 3 .

2. The oxalate compound is represented by the general formula (1)A ＋ [B.X. ４－２ｎ (C ２ O ４ ) ｎ ] － (A in the formula ＋ 2. The electricity storage device according to claim 1, wherein the compound is an oxalate compound represented by the formula:

3. The positive electrode active material layer has a weight per unit area of ​​55 mg / cm ２ or more, and the weight of the negative electrode active material layer is 25 mg / cm ２ The power storage device according to claim 1 or 2, which satisfies at least one of the above conditions.

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

5. The power storage device according to any one of claims 1 to 4, wherein the permeable wall portion is provided around the entire periphery of the covering portion.

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