Electricity storage device

Abstract

To provide a technique for enhancing impregnation efficiency of a nonaqueous electrolyte to an electrode body while enhancing energy density of a power storage device SOLUTION: According to the technique disclosed herein, there is provided a power storage device including an electrode body, a nonaqueous electrolytic solution, and a case. The electrode assembly includes an electrode having an electrode active material layer containing an electrode active material. The case has a bottom surface, an upper surface, and a side surface. The electrode has a first region on the bottom surface side and a second region on the upper surface side. The first region is provided with a first electrode active material layer having a relatively high density. The second region is provided with a second electrode active material layer having a relatively low density. The second electrode active material layer is provided to a position of at least 40% from a first end on an upper surface side toward a second end on a bottom surface side in the electrode active material layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] An example of an electricity storage device is a secondary battery such as a lithium-ion secondary battery. In recent years, this type of electricity storage device has been suitably used as a power source for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] Japanese Patent Laid-Open Publication No. 2009-259502 discloses a nonaqueous electrolyte secondary battery including positive and negative electrode plates each having an active material mixture applied to a current collector. At least one of the positive and negative electrode plates has a density change portion in which the density of the active material mixture changes at a substantially constant rate from one side to the other in the planar direction. The publication states that such a configuration in which at least one of the positive and negative electrode plates has a density change portion increases the active material ratio in the high-density portion, thereby improving energy density, and also ensures voids in the low-density portion for infiltration of the nonaqueous electrolyte, thereby improving input / output characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-259502 Summary of the Invention [Problem to be solved by the invention]

[0005] Increasing the density of the electrode active material layer has been considered to increase the energy density of an electricity storage device. However, as the density of the electrode active material layer increases, the porosity of the electrode tends to decrease. Therefore, it is necessary to devise a way to increase the efficiency of impregnation of the electrode assembly with a non-aqueous electrolyte. Therefore, the present inventors wanted to increase the efficiency of impregnation of the electrode assembly with a non-aqueous electrolyte while increasing the energy density of the electricity storage device. [Means for solving the problem]

[0006] The technology disclosed herein provides an electricity storage device having an electrode assembly, a non-aqueous electrolyte, and a case. The electrode assembly includes an electrode having an electrode active material layer containing an electrode active material. The case accommodates the electrode assembly and the non-aqueous electrolyte and has a bottom surface, a top surface opposite the bottom surface, and a side surface provided between the bottom surface and the top surface. The electrode has a first region on the bottom surface side and a second region on the top surface side. A first electrode active material layer having a relatively high density is provided in the first region. A second electrode active material layer having a relatively low density is provided in the second region. The second electrode active material layer is provided in a position at least 40% of the way from a first end on the top surface side of the electrode active material layer toward a second end on the bottom surface side. This configuration can increase the energy density of the electricity storage device while improving the efficiency of impregnation of the electrode assembly with the non-aqueous electrolyte. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic perspective view of an electricity storage device 100. As shown in FIG. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 3] FIG. 3 is a partial perspective view of the electrode body 20. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram of the electrode body 220. [Figure 5] FIG. 5 is a schematic perspective view of the power storage device 3100. As shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7]FIG. 7 is a partial perspective view of the electrode body 320. As shown in FIG. [Figure 8] FIG. 8 is a schematic diagram of the electrode body 420. [Figure 9] FIG. 9 is a plan view of the positive electrode 422. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the energy storage device disclosed herein is described below. The embodiment described herein does not particularly limit the technology disclosed herein. The technology disclosed herein is not limited to the embodiment described herein unless otherwise specified. The drawings are schematic and do not necessarily reflect the actual product. Components and parts that perform the same function are appropriately designated with the same reference numerals, and redundant explanations may be omitted. The reference numerals "R," "L," "U," "D," "F," and "Rr" in the drawings represent "right," "left," "up," "down," "front," and "rear," respectively. The notation "A to B" indicating a numerical range means "greater than A and less than B" unless otherwise specified, and also encompasses the meaning of "greater than A and less than B."

[0009] In this specification, the term "electricity storage device" refers to a device in which charge and discharge occur by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. Electricity storage devices include secondary batteries such as lithium ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium ion capacitors and electric double layer capacitors. The electricity storage device may be, for example, a lithium ion secondary battery.

[0010] First Embodiment FIG. 1 is a schematic perspective view of an electricity storage device 100. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1. In this embodiment, the electricity storage device 100 is a lithium-ion secondary battery. As shown in FIGS. 1 and 2, the electricity storage device 100 includes a case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, a negative electrode current collector 60, and insulating members 92 and 94. The case 10 is, for example, an outer container that houses the electrode assembly 20 and a nonaqueous electrolyte solution 80. Here, the case 10 is a flat, rectangular case. As shown in FIGS. 1 and 2, the case 10 includes a main body 12 and a sealing plate 14. In this embodiment, the main body 12 includes a bottom surface 12a, an opening 12h, and a pair of opposing first side surfaces 12b and a pair of opposing second side surfaces 12c. The bottom surface 12a is, for example, rectangular (including substantially rectangular; the same applies below) and constitutes the lower surface of the case 10. The opening 12h faces the bottom surface 12a and is closed by the sealing plate 14. Therefore, the sealing plate 14 disposed at the opening 12h constitutes the upper surface of the case 10. The pair of opposing first side surfaces 12b and the pair of opposing second side surfaces 12c are provided between the bottom surface 12a and the sealing plate 14 (upper surface) here. The pair of opposing first side surfaces 12b extend from a pair of opposing long sides of the bottom surface 12a. The pair of opposing second side surfaces 12c extend from a pair of opposing short sides of the bottom surface 12a.

[0011] The sealing plate 14 is, for example, a member that closes the opening 12h of the case 10. In this embodiment, the sealing plate 14 is flat and has a shape (here, rectangular) corresponding to the shape of the opening 12h. As shown in FIGS. 1 and 2 , the sealing plate 14 has a liquid inlet 15, a gas release valve 17, and terminal outlet holes 18 and 19. The liquid inlet 15 is, for example, a through-hole for injecting nonaqueous electrolyte 80 into the case 10. In this example, the liquid inlet 15 is sealed with a sealing member 16. The gas release valve 17 is, for example, a thin-walled portion that breaks when the pressure inside the case 10 reaches or exceeds a predetermined value, thereby releasing gas inside the case 10 to the outside. The terminal outlet hole 18 is, for example, a through-hole through which a portion of the positive electrode terminal 30 is inserted. The terminal outlet hole 19 is, for example, a through-hole through which a portion of the negative electrode terminal 40 is inserted.

[0012] The electrode assembly 20 is, for example, a power generating element of the electricity storage device 100 and includes a positive electrode 22 and a negative electrode 24. FIG. 3 is a partial perspective view of the electrode assembly 20. FIG. 3 shows a portion of the laminated structure of the electrode assembly 20, which includes the positive electrode 22, the negative electrode 24, and the separator 26. As shown in FIG. 3, the electrode assembly 20 is a laminated electrode assembly including a sheet-shaped positive electrode 22, a sheet-shaped negative electrode 24, and a sheet-shaped separator 26 interposed between the positive electrode 22 and the negative electrode 24. In this embodiment, the electrode assembly 20 has four laminated surfaces on which the positive electrodes 22 and the negative electrodes 24 are laminated. As shown in FIG. 2, these four laminated surfaces face the bottom surface 12a, a pair of opposing second side surfaces 12c, and the sealing plate 14 within the case 10. Of these four stacking surfaces, a positive electrode tab group 23 and a negative electrode tab group 25 are provided on the stacking surface facing the sealing plate 14.

[0013] As shown in FIG. 3, the positive electrode 22 includes a positive electrode active material layer 22a, a positive electrode current collector foil 22c, and a protective layer 22p. The positive electrode current collector foil 22c is, for example, a sheet-like aluminum foil. In this embodiment, the positive electrode current collector foil 22c has a rectangular main body and a positive electrode tab 22t protruding from the main body. The positive electrode current collector foil 22c has a region where the positive electrode active material layer 22a is provided and a region where the positive electrode active material layer 22a is not provided. The region where the positive electrode active material layer 22a is not provided includes, for example, a region where the protective layer 22p is provided and a region where the positive electrode current collector foil 22c is exposed.

[0014] 3, the positive electrode active material layer 22a is provided in a rectangular shape on the positive electrode current collector foil 22c. Here, the positive electrode active material layer 22a is not provided in the region along the long side of the positive electrode current collector foil 22c on the positive electrode tab 22t side. The positive electrode active material layer 22a may be provided, for example, on one or both sides (both sides in this case) of the positive electrode current collector foil 22c.

[0015] The positive electrode active material layer 22a contains, for example, a positive electrode active material. Examples of the positive electrode active material include lithium composite oxides and lithium transition metal phosphate compounds. The crystal structure of the positive electrode active material is not particularly limited and may be a layered structure, a spinel structure, an olivine structure, or the like. The lithium composite oxide is preferably a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn as a transition metal element. Examples of the lithium transition metal composite oxide include lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium iron nickel manganese composite oxides. These positive electrode active materials may be used alone or in combination of two or more.

[0016] In this specification, the term "lithium nickel cobalt manganese composite oxide" refers to oxides containing Li, Ni, Co, Mn, and O as constituent elements, as well as oxides containing one or more additional elements. Examples of the additional elements include transition metal elements and typical metal elements, such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. The additional elements may also be metalloid elements, such as B, C, Si, and P; or nonmetallic elements, such as S, F, Cl, Br, and I. This also applies to the lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide.

[0017] Examples of the lithium transition metal phosphate compound include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate. Examples of the positive electrode active material include LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4 and the like can be preferably used.

[0018] The positive electrode active material layer 22a may contain, in addition to the positive electrode active material, a conductive material, a binder, and the like. Examples of the conductive material include carbon black such as acetylene black (AB) and other carbon materials such as graphite. Examples of the binder include polyvinylidene fluoride (PVdF). The content of the positive electrode active material in the positive electrode active material layer 22a is, for example, preferably 70 mass % or more, more preferably 80 mass % to 97 mass %, and even more preferably 85 mass % to 96 mass %. The content of the conductive material in the positive electrode active material layer 22a is, for example, 0.1 mass % to 20 mass %. The content of the binder in the positive electrode active material layer 22a is, for example, 0.5 mass % to 15 mass %.

[0019] In this embodiment, the positive electrode active material layer 22a includes a first positive electrode active material layer 22a1 and a second positive electrode active material layer 22a2. The first positive electrode active material layer 22a1 is provided, for example, in a first region R1 on the bottom surface 12a side. The second positive electrode active material layer 22a2 is provided, for example, in a second region R2 on the top surface (here, the sealing plate 14) side. In this embodiment, the second positive electrode active material layer 22a2 is provided from a first end 22e1 on the top surface (here, the sealing plate 14) side of the positive electrode active material layer 22a to a position at least 40% of the way toward a second end 22e2 on the bottom surface 12a side, where 100% is the shortest distance from the first end 22e1 to the second end 22e2 (see FIGS. 2 and 3). Although not particularly limited, for example, from the viewpoint of further increasing the efficiency of impregnation of the nonaqueous electrolyte solution 80 into the electrode body 20, the second positive electrode active material layer 22a2 is preferably provided to a position at least 43%, preferably at least 45%, and more preferably at least 47%, of the shortest distance from the first end 22e1 to the second end 22e2, when the shortest distance from the first end 22e1 to the second end 22e2 is taken as 100%, but is not particularly limited, for example, from the viewpoint of further achieving the energy density of the power storage device 100, the second positive electrode active material layer 22a2 is provided to a position at least 70%, preferably at least 65%, more preferably at least 60%, and even more preferably at least 55%, of the shortest distance from the first end 22e1 to the second end 22e2, when the shortest distance from the first end 22e1 to the second end 22e2 is taken as 100%.

[0020] In this embodiment, the density of the first positive electrode active material layer 22a1 is set to be greater than the density of the second positive electrode active material layer 22a2. The density of the first positive electrode active material layer 22a1 is, for example, 3 times or less, preferably 2.5 times or less, more preferably 2 times or less, and even more preferably 1.5 times or less that of the second positive electrode active material layer 22a2. For example, from the viewpoint of increasing the energy density of the power storage device 100, the density of the first positive electrode active material layer 22a1 is greater than 1 time, preferably 1.05 times or more, more preferably 1.1 times or more, and even more preferably 1.15 times or more that of the second positive electrode active material layer 22a2. Although not particularly limited, the density of the first positive electrode active material layer 22a1 is set to be approximately 2 g / cc to 5 g / cc, and preferably 3 g / cc to 4 g / cc. The density of the second positive electrode active material layer 22a2 is set to about 2 g / cc to 5 g / cc, and preferably 2.5 g / cc to 3.5 g / cc.

[0021] In this embodiment, the thickness of the first positive electrode active material layer 22a1 and the thickness of the second positive electrode active material layer 22a2 are preferably the same. Therefore, for example, in the process of providing the positive electrode active material layer 22a, a relatively large amount of a positive electrode active material layer-forming slurry (hereinafter also referred to as "positive electrode slurry") is applied to the region of the positive electrode current collector foil 22c that will become the first region R1, and a relatively small amount of the positive electrode slurry is applied to the region that will become the second region R2, and the coating is then pressed. In this manner, the first positive electrode active material layer 22a1 and the second positive electrode active material layer 22a2 are preferably provided. The pressing pressure at this time can be appropriately set so that both layers have the same thickness. In this embodiment, the positive electrode active material contained in the first positive electrode active material layer 22a1 can be greater than the positive electrode active material contained in the second positive electrode active material layer 22a2.

[0022] The protective layer 22p may be provided, for example, closer to the upper surface (here, the sealing plate 14) than the second region R2. In the embodiment shown in FIGS. 2 and 3, the protective layer 22p is provided along one of a pair of opposing long sides of the positive current collector foil 22c, on which the positive electrode tab 22t is provided, and is provided on the base end side of the positive electrode tab 22t. The base end of the positive electrode tab 22t here refers to the boundary between the positive electrode tab 22t and the rectangular main body of the positive electrode current collector foil 22c. The protective layer 22p includes, for example, an insulating inorganic filler (e.g., alumina). Note that the protective layer 22p does not necessarily have to be provided. For this reason, in other embodiments, the protective layer 22p is not provided (see the third and fourth embodiments described below).

[0023] The positive electrode tab 22t is, for example, a portion connected to the positive electrode current collector 50. In the embodiment shown in FIG. 2, the positive electrode tab 22t protrudes from the long side of a pair of opposing long sides of the positive electrode current collector foil 22c that is closer to the upper surface (here, the sealing plate 14). Neither the positive electrode active material layer 22a nor the protective layer 22p is provided on the protruding tip side of the positive electrode tab 22t. In this embodiment, in the electrode assembly 20, the positive electrode tabs 22t of the respective positive electrodes 22 are stacked to form a positive electrode tab group 23.

[0024] As shown in Fig. 3, the negative electrode 24 includes a negative electrode active material layer 24a and a negative electrode current collector foil 24c. The negative electrode current collector foil 24c is, for example, a sheet-like copper foil. The negative electrode current collector foil 24c has a rectangular main body and a negative electrode tab 24t protruding from the main body. The negative electrode current collector foil 24c has a region where the negative electrode active material layer 24a is provided and a region where the negative electrode active material layer 24a is not provided. The region where the negative electrode active material layer 24a is not provided is, for example, a region where the negative electrode current collector foil 24c is exposed.

[0025] 3, the negative electrode active material layer 24a is provided in a rectangular shape on the entire negative electrode current collector foil 24c except for the negative electrode tab 24t. The negative electrode active material layer 24a may be provided on, for example, one or both surfaces (both surfaces in this example) of the negative electrode current collector foil 24c.

[0026] The negative electrode active material layer 24a contains, for example, a negative electrode active material. Examples of the negative electrode active material include carbon materials such as natural graphite and artificial graphite; silicon; and the like. The negative electrode active material layer 24a may contain, in addition to the negative electrode active material, for example, a binder, a thickener, and the like. Examples of the binder include styrene butadiene rubber (SBR). Examples of the thickener include carboxymethyl cellulose (CMC). The content of the negative electrode active material relative to the entire negative electrode active material layer 24a is, for example, 70% by mass or more, preferably 80% by mass or more, more preferably 90% to 99% by mass, and may be 95% to 99% by mass. The content of the binder relative to the entire negative electrode active material layer 24a is, for example, 0.5% to 10% by mass.

[0027] Although not shown and described, in this embodiment, the negative electrode active material layer 24a has the same structure as the positive electrode active material layer 22a. The negative electrode active material layer 224a has, for example, a first negative electrode active material layer and a second negative electrode active material layer.

[0028] The negative electrode tab 24t is a portion that is connected to, for example, the negative electrode current collector 60. In the embodiment shown in FIG. 2, the negative electrode tab 24t protrudes from the long side of a pair of opposing long sides of the negative electrode current collector foil 24c that is closer to the upper surface (here, the sealing plate 14). The negative electrode tab 24t is not provided with a negative electrode active material layer 24a. In this embodiment, the negative electrode tabs 24t of the respective negative electrodes 24 are stacked on top of each other in the electrode assembly 20 to form a negative electrode tab group 25.

[0029] Examples of separator 26 include porous sheets (films) made of resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of separator 26.

[0030] The nonaqueous electrolyte 80 includes, for example, a nonaqueous solvent and a supporting salt. Examples of the nonaqueous solvent include organic solvents used in this type of application, such as carbonates, ethers, esters, nitriles, sulfones, and lactones. Among these, carbonates are preferably used. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC). As the nonaqueous solvent, one type of nonaqueous solvent may be used alone, or two or more types of nonaqueous solvents may be used in combination. Examples of the supporting salt include lithium salts such as LiPF6. The concentration of the supporting salt may be, for example, 0.7 mol / L to 1.4 mol / L. The nonaqueous electrolyte 80 may contain additives used in this type of application, if necessary.

[0031] The positive electrode terminal 30 is, for example, a portion electrically connected to the positive electrode 22 of the electrode assembly 20. As shown in FIGS. 1 and 2, the positive electrode terminal 30 is attached to the sealing plate 14. As shown in FIG. 2, the positive electrode terminal 30 is inserted through the terminal pull-out hole 18, with a portion of the positive electrode terminal 30 being disposed inside the case 10 and a portion of the positive electrode terminal 30 being disposed outside the case 10. The portion of the positive electrode terminal 30 that is disposed inside the case 10 is connected to the positive electrode current collector 50.

[0032] The negative electrode terminal 40 is, for example, a portion electrically connected to the negative electrode 24 of the electrode assembly 20. As shown in FIGS. 1 and 2, the negative electrode terminal 40 is attached to the sealing plate 14. As shown in FIG. 2, the negative electrode terminal 40 is inserted through the terminal pull-out hole 19, with a portion of the negative electrode terminal 40 being disposed inside the case 10 and a portion of the negative electrode terminal 40 being disposed outside the case 10. The portion of the negative electrode terminal 40 that is disposed inside the case 10 is connected to the negative electrode current collector 60.

[0033] The positive electrode current collector 50 is, for example, a portion electrically connected to the positive electrode 22 of the electrode assembly 20. As shown in FIG. 2, the positive electrode current collector 50 is flat and arranged along the inner surface of the sealing plate 14. In this example, the positive electrode tab group 23 is connected (welded) to the positive electrode current collector 50, and the tip 30c of the positive electrode terminal 30 is also connected to the positive electrode current collector 50. The positive electrode current collector 50 is made of, for example, aluminum or an aluminum alloy.

[0034] The negative electrode current collector 60 is, for example, a portion electrically connected to the negative electrode 24 of the electrode assembly 20. As shown in FIG. 2, the negative electrode current collector 60 is flat and arranged along the inner surface of the sealing plate 14. In this example, the negative electrode tab group 25 is connected (welded) to the negative electrode current collector 60, and the tip 40c of the negative electrode terminal 40 is also connected to the negative electrode current collector 60. The negative electrode current collector 60 is made of, for example, copper or a copper alloy.

[0035] The insulating member 92 is a member that prevents electrical conduction between the positive electrode terminal 30 and the sealing plate 14 and between the negative electrode terminal 40 and the sealing plate 14. As shown in FIGS. 1 and 2 , the insulating member 92 has a portion that is arranged along the outer surface of the sealing plate 14 and a portion that is arranged along the inner periphery of the terminal lead-out hole 18 or 19. The insulating member 94 is a member that prevents electrical conduction between the positive electrode current collector 50 and the sealing plate 14 and between the negative electrode current collector 60 and the sealing plate 14. As shown in FIG. 2 , the insulating member 94 is arranged along the inner surface of the sealing plate 14. Although not shown, the electricity storage device 100 may also include an electrode assembly holder. The electrode assembly holder is a member that prevents electrical conduction between the electrode assembly 20 and the case 10. The electrode assembly holder may be housed in the case 10 with the electrode assembly 20 housed therein. Although not particularly limited, examples of constituent materials of various insulating members include polyolefin resins such as polypropylene (PP) and polyethylene (PE); fluorine-based resins such as perfluoroalkoxyalkane and polytetrafluoroethylene (PTFE); and the like.

[0036] As described above, the power storage device 100 includes an electrode assembly 20, a non-aqueous electrolyte solution 80, and a case 10. The electrode assembly 20 includes a positive electrode 22 having a positive electrode active material layer 22a containing a positive electrode active material. The case 10 accommodates the electrode assembly 20 and the non-aqueous electrolyte solution 80 and has a bottom surface 12a, an upper surface (here, the sealing plate 14) facing the bottom surface 12a, and side surfaces (here, a first side surface 12b and a second side surface 12c) provided between the bottom surface 12a and the upper surface (here, the sealing plate 14). The positive electrode 22 has a first region R1 on the bottom surface 12a side and a second region R2 on the upper surface (here, the sealing plate 14) side. A first positive electrode active material layer 22a1 having a relatively high density is provided in the first region R1. A second positive electrode active material layer 22a2 having a relatively low density is provided in the second region R2. Here, the second positive electrode active material layer 22a2 is provided to a position at least 40% from the first end 22e1 on the top surface (here, sealing plate 14) side of the positive electrode active material layer 22a toward the second end 22e2 on the bottom surface 12a side.

[0037] In the electricity storage device 100, a first positive electrode active material layer 22a1 having a relatively high density is provided in a first region R1 on the bottom surface 12a side. A second positive electrode active material layer 22a2 having a relatively low density is provided in a second region R2 on the top surface (here, the sealing plate 14) side. In other words, a first positive electrode active material layer 22a1 having a relatively high porosity and being relatively difficult to be impregnated with the nonaqueous electrolyte solution 80 is provided in the first region R1 on the bottom surface 12a side. A second positive electrode active material layer 22a2 having a relatively low porosity and being relatively easy to be impregnated with the nonaqueous electrolyte solution 80 is provided in the second region R2 on the top surface (here, the sealing plate 14) side. In the manufacturing process of the electricity storage device 100, the nonaqueous electrolyte solution 80 is poured so that the liquid level is located higher (here, on the sealing plate 14 side) than the upper end 20e (see FIG. 2) of the electrode body 20, for example. Thereafter, an impregnation step of the nonaqueous electrolyte solution 80 is carried out, for example, over several hours to several days. As described above, in the electricity storage device 100, the second positive electrode active material layer 22a2, which is relatively easily impregnated with the nonaqueous electrolyte solution 80, is provided in the second region R2. Therefore, for example, the efficiency with which the nonaqueous electrolyte solution 80 impregnates the electrode assembly 20 in the impregnation step can be increased via the second positive electrode active material layer 22a2. In addition, in the electricity storage device 100, the first positive electrode active material layer 22a1, which is relatively difficult to impregnate with the nonaqueous electrolyte solution 80, is provided in the first region R1. Therefore, in the impregnation step, the contact time between the nonaqueous electrolyte solution 80 and the first positive electrode active material layer 22a1 can be longer, and as a result, the efficiency with which the nonaqueous electrolyte solution 80 impregnates the electrode assembly 20 via the first positive electrode active material layer 22a1 can be increased. This makes it possible to increase the energy density of the electricity storage device 100 and also to increase the efficiency with which the electrode body 20 is impregnated with the non-aqueous electrolyte solution 80 .

[0038] The case 10 may have a rectangular bottom surface 12a, a pair of first side surfaces 12b, and a pair of second side surfaces 12c. The pair of first side surfaces 12b may extend from a pair of opposing long sides of the bottom surface 12a. The pair of second side surfaces 12c may extend from a pair of opposing short sides of the bottom surface 12a. The case 10 may have a positive electrode terminal 30 and a negative electrode terminal 40 on its top surface (here, the sealing plate 14). In an electricity storage device 100 having a case 10 configured in this manner, the effects of the technology disclosed herein can be appropriately achieved.

[0039] The power storage device 100 may include, as the electrode assembly 20, a laminated electrode assembly including a sheet-shaped positive electrode 22, a sheet-shaped negative electrode 24, and a sheet-shaped separator 26 interposed between the positive electrode 22 and the negative electrode 24. In the laminated electrode assembly, four side surfaces are stacking surfaces (open surfaces) of the electrodes. For this reason, the laminated electrode assembly is an electrode assembly that is more advantageous for impregnation with a nonaqueous electrolyte solution, for example. This allows the effects of the technology disclosed herein to be more preferably realized.

[0040] The density of the first positive electrode active material layer 22a1 may be three times or less the density of the second positive electrode active material layer 22a2. By setting the density of the first positive electrode active material layer 22a1 within this range, the efficiency of impregnation of the nonaqueous electrolyte solution 80 through the first positive electrode active material layer 22a1 can be further increased.

[0041] Although one embodiment of the technology disclosed herein has been described above, the above embodiment is merely an example. The technology disclosed herein may include modifications and alterations of the above embodiment. Note that in the embodiments described below, descriptions of parts common to the above embodiment will be omitted to avoid duplication.

[0042] Second Embodiment In the first embodiment described above, the power storage device 100 includes the electrode assembly 20, which is a laminated electrode assembly. However, the technology disclosed herein is not limited to this. The power storage device 100 may include, for example, an electrode assembly 220 shown in FIG. 4 instead of the electrode assembly 20. FIG. 4 is a schematic diagram of the electrode assembly 220. As shown in FIG. 4, the electrode assembly 220 is a wound electrode assembly in which a long sheet-like positive electrode 222 and a long sheet-like negative electrode 224 are wound around a winding axis WL with a long sheet-like separator 226 interposed therebetween. In this embodiment, the electrode assembly 220 has two laminated surfaces (open surfaces) where the positive electrode 222 and the negative electrode 224 are laminated. In this embodiment, these two laminated surfaces face the bottom surface 12a and the sealing plate 14 inside the case 10 (see FIG. 2). Of these two stacking surfaces, a positive electrode tab group and a negative electrode tab group may be provided on the stacking surface facing the sealing plate 14. In the embodiment shown in Fig. 4, the positive electrode tab group may be composed of a plurality of positive electrode tabs 222t. The negative electrode tab group may be composed of a plurality of negative electrode tabs 224t.

[0043] As shown in FIG. 4, the positive electrode 222 includes a positive electrode active material layer 222a, a positive electrode current collector foil 222c, and a protective layer 222p. The positive electrode current collector foil 222c is, for example, a long sheet of aluminum foil. In this embodiment, the positive electrode current collector foil 222c has a long, strip-shaped main body and a positive electrode tab 222t protruding from the main body. The positive electrode current collector foil 222c has a region where the positive electrode active material layer 222a is provided and a region where the positive electrode active material layer 222a is not provided. The region where the positive electrode active material layer 222a is not provided includes, for example, a region where the protective layer 222p is provided and a region where the positive electrode current collector foil 222c is exposed.

[0044] In the embodiment shown in Fig. 4, the positive electrode active material layer 222a is provided in a strip shape on the positive electrode current collector foil 222c along the longitudinal direction LD. Here, the positive electrode active material layer 222a is not provided in the region along the longitudinal direction LD of the positive electrode current collector foil 222c on the positive electrode tab 222t side. The positive electrode active material layer 222a may be provided on, for example, one or both sides (here, both sides) of the positive electrode current collector foil 222c. In this embodiment, the positive electrode active material layer 222a has a first positive electrode active material layer 222a1 and a second positive electrode active material layer 222a2.

[0045] In the embodiment shown in FIG. 4, the first positive electrode active material layer 222a1 is provided in the first region R21. The first region R21 is provided, for example, on the bottom surface 12a side of the case 10 (see FIG. 2). In this embodiment, the first region R21 can be set in a portion along the longitudinal direction LD of the positive electrode 222 on the side opposite the positive electrode tab 222t. The first positive electrode active material layer 222a1 is provided, for example, in a strip shape along the longitudinal direction LD of the positive electrode 222 on the side opposite the positive electrode tab 222t. In the embodiment shown in FIG. 4, the second positive electrode active material layer 222a2 is provided in the second region R22. The second region R22 is provided, for example, on the top surface (here, the sealing plate 14) side of the case 10 (see FIG. 2). In this embodiment, the second region R22 can be set in a portion along the longitudinal direction LD of the positive electrode 222 on the positive electrode tab 222t side. The second positive electrode active material layer 222a2 is provided, for example, on the positive electrode tab 222t side in a strip shape along the longitudinal direction LD of the positive electrode 222. In Fig. 4, reference numeral "222e1" denotes a first end portion, and reference numeral "222e2" denotes a second end portion.

[0046] The protective layer 222p may be provided, for example, closer to the upper surface (here, the sealing plate 14) than the second region R22. In the embodiment shown in Fig. 4, the protective layer 222p is provided in a strip shape along the longitudinal direction LD on the positive electrode tab 222t side of the positive electrode current collector foil 222c, and is provided on the base end side of the positive electrode tab 222t. The base end of the positive electrode tab 222t here refers to the boundary between the positive electrode tab 222t and the main body of the positive electrode current collector foil 222c.

[0047] In the embodiment shown in FIG. 4, the positive electrode tabs 222t protrude outward (in the U direction in the vertical direction Z in FIG. 4) from one end side of the positive electrode current collector foil 222c in the winding axis direction WD. The positive electrode tabs 222t are provided at predetermined intervals (intermittently) along the longitudinal direction LD. Neither the positive electrode active material layer 222a nor the protective layer 222p is provided on the protruding tip side of the positive electrode tab 222t. In this embodiment, a plurality of positive electrode tabs 222t are stacked in the electrode assembly 220 to form a positive electrode tab group. This positive electrode tab group is connected to the positive electrode current collector 50 (see FIG. 2). The positive electrode tabs 222t may, for example, differ from one another in size or shape.

[0048] As shown in FIG. 4, the negative electrode 224 includes a negative electrode active material layer 224a and a negative electrode current collector foil 224c. The negative electrode current collector foil 224c is, for example, a long sheet-like copper foil. In this embodiment, the negative electrode current collector foil 224c has a long, strip-like main body and a negative electrode tab 224t protruding from the main body. The negative electrode current collector foil 224c has a region where the negative electrode active material layer 224a is provided and a region where the negative electrode active material layer 224a is not provided. The region where the negative electrode active material layer 224a is not provided includes, for example, a region where the negative electrode current collector foil 224c is exposed.

[0049] 4, the negative electrode active material layer 224a is provided in a strip shape on the negative electrode current collector foil 224c along the longitudinal direction LD. Here, the negative electrode active material layer 224a is provided over the entire body of the negative electrode current collector foil 224c along the longitudinal direction LD. The negative electrode active material layer 224a may be provided on, for example, one or both sides (both sides in this case) of the negative electrode current collector foil 224c.

[0050] In the embodiment shown in FIG. 4, the negative electrode tab 224t protrudes outward (in the U direction in the up-down direction Z in FIG. 4) from one end side of the negative electrode current collector foil 224c in the winding axis direction WD. The negative electrode tabs 224t are provided at predetermined intervals (intermittently) along the longitudinal direction LD. No negative electrode active material layer 224a is provided on the protruding tip side of the negative electrode tab 224t. In this embodiment, a plurality of negative electrode tabs 224t are stacked in the electrode body 220 to form a negative electrode tab group. This negative electrode tab group is connected to the negative electrode current collector 60 (see FIG. 2). The negative electrode tabs 224t may, for example, differ from one another in size or shape.

[0051] As described above, the electricity storage device 100 may include the electrode assembly 220, which is a wound electrode assembly. This can, for example, further increase the energy density of the electricity storage device 100. In addition, the wound electrode assembly has, for example, superior liquid retention properties for the nonaqueous electrolyte solution 80. This can improve the battery performance of the electricity storage device 100.

[0052] <Third embodiment> In the first and second embodiments, the electricity storage device 100 includes a positive electrode terminal 30 and a negative electrode terminal 40 on the sealing plate 14, which is the upper surface. However, the technology disclosed herein is not limited to this. FIG. 5 is a schematic perspective view of an electricity storage device 3100. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 5. As shown in FIGS. 5 and 6, the electricity storage device 3100 includes a case 310, an electrode assembly 320, a positive electrode terminal 330, a negative electrode terminal 340, a positive electrode current collector 350, a negative electrode current collector 360, a nonaqueous electrolyte 370, and various insulating members (not shown). Here, the case 310 is a flat, rectangular case. As shown in FIGS. 5 and 6, the case 310 includes a main body 312 and two sealing plates 314. In this embodiment, the main body 312 has a rectangular cylindrical shape and includes a bottom surface 312a, a pair of opposing first side surfaces 312b, a top surface 312d, and two openings 312h. The bottom surface 312a is, for example, rectangular and constitutes the lower surface of the case 310. The pair of opposing first side surfaces 312b extend from a pair of opposing long sides of the bottom surface 312a. The top surface 312d faces the bottom surface 312a. In this embodiment, the area surrounded by the bottom surface 312a, the pair of opposing first side surfaces 312b, and the top surface 312d constitutes the opening 312h. A sealing plate 314 is attached to each of the two openings 312h, forming a pair of opposing second side surfaces 312c. The pair of opposing second side surfaces 312c extend from a pair of opposing short sides of the bottom surface 312a.

[0053] The main body 312 can be produced, for example, by bending a single metal plate into a cylindrical shape and joining (for example, welding) the seams. Therefore, as shown in Fig. 5, the main body 312 has a joint 312w on the top surface 312d thereof that extends along the left-right direction Y.

[0054] The sealing plate 314 is, for example, a member that closes the opening 312h of the case 310. In this embodiment, the sealing plate 314 is flat and has a shape (here, rectangular) that corresponds to the shape of the opening 312h. In the embodiment shown in FIGS. 5 and 6, one of the sealing plates 314 (here, the sealing plate 314 to which the positive electrode terminal 330 is attached) is provided with a liquid inlet 315. In this embodiment, the liquid inlet 315 is provided closer to the upper surface 312d than the positive electrode terminal 330. The liquid inlet 315 is sealed with, for example, a sealing plug 316. Although not shown, each sealing plate 314 is provided with a terminal lead-out hole.

[0055] Fig. 7 is a partial perspective view of the electrode assembly 320. Fig. 7 shows a portion of the laminated structure of the positive electrode 322, the negative electrode 324, and the separator 326 in the electrode assembly 320. As shown in Fig. 7, the electrode assembly 320 is a laminated electrode assembly including a sheet-shaped positive electrode 322, a sheet-shaped negative electrode 324, and a sheet-shaped separator 326 interposed between the positive electrode 322 and the negative electrode 324.

[0056] 7, the positive electrode 322 includes a positive electrode active material layer 322a and a positive electrode current collector foil 322c. In this embodiment, the positive electrode active material layer 322a includes a first positive electrode active material layer 322a1 and a second positive electrode active material layer 322a2.

[0057] The first positive electrode active material layer 322a1 is provided, for example, in the first region R31 on the bottom surface 312a side (see FIGS. 6 and 7). The second positive electrode active material layer 322a2 is provided, for example, in the second region R32 on the top surface 312d side (see FIGS. 6 and 7). In FIG. 7, the reference numeral "322e1" denotes a first end portion, and the reference numeral "322e2" denotes a second end portion.

[0058] 7, the positive electrode tab 322t protrudes from one of a pair of opposing short sides of the positive electrode current collector foil 322c. As shown in FIGS. 6 and 7, in the electrode assembly 320, the positive electrode tabs 322t of the positive electrodes 322 are stacked to form a positive electrode tab group 323.

[0059] As shown in Fig. 7, the negative electrode 324 includes a negative electrode active material layer 324a and a negative electrode current collector foil 324c. In the embodiment shown in Fig. 7, the negative electrode tab 324t protrudes from one of a pair of opposing short sides of the negative electrode current collector foil 324c. As shown in Figs. 6 and 7, in the electrode assembly 320, the negative electrode tabs 324t of the negative electrodes 324 are stacked to form a negative electrode tab group 325.

[0060] In this embodiment, the positive electrode terminal 330 is provided on one of a pair of opposing second side surfaces 312c (here, a pair of opposing sealing plates 314). As shown in Fig. 6, the positive electrode terminal 330 is inserted into a terminal lead-out hole (not shown) provided in the sealing plate 314, and a portion of the positive electrode terminal 330 is disposed inside the case 310 and a portion of the positive electrode terminal 330 is disposed outside the case 310. The portion of the positive electrode terminal 330 disposed inside the case 310 is connected to the positive electrode current collector 350.

[0061] In this embodiment, the negative electrode terminal 340 is provided on the other of the pair of opposing second side surfaces 312c (here, the pair of opposing sealing plates 314). As shown in Fig. 6, the negative electrode terminal 340 is inserted into a terminal lead-out hole (not shown) provided in the sealing plate 314, and a portion of the negative electrode terminal 340 is disposed inside the case 310 and a portion of the negative electrode terminal 340 is disposed outside the case 310. The portion of the negative electrode terminal 340 that is disposed inside the case 310 is connected to the negative electrode current collector 360.

[0062] 6, the positive electrode current collector 350 is flat and disposed along the inner surface of one of a pair of opposing second side surfaces 312c (here, a pair of opposing sealing plates 314). In this case, the positive electrode current collector 350 is connected (welded) to the positive electrode tab group 323, and also to the tip of the positive electrode terminal 330.

[0063] 6, the negative electrode current collector 360 has a flat plate shape and is disposed along the inner surface of the other of the pair of opposing second side surfaces 312c (here, the pair of opposing sealing plates 314). In this case, the negative electrode current collector 360 is connected (welded) to the negative electrode tab group 325 and also to the tip of the negative electrode terminal 340.

[0064] Although not shown in the drawings, the power storage device 3100 may have an insulating member similar to that described in the first embodiment.

[0065] As described above, the case 310 may have a rectangular bottom surface 312a, a pair of first side surfaces 312b, and a pair of second side surfaces 312c. The pair of first side surfaces 312b may extend from a pair of opposing long sides of the bottom surface 312a. The pair of second side surfaces 312c may extend from a pair of opposing short sides of the bottom surface 312a. The case 310 may have a positive terminal 330 and a negative terminal 340 on the second side surfaces 312c.

[0066] In this embodiment, in the manufacturing process for the electricity storage device 3100 having the above-described configuration, after the nonaqueous electrolyte solution 370 is poured, the impregnation step is performed with the bottom surface 312a of the case 310 positioned downward in the direction of gravity. As described above, in the electricity storage device 3100, the second positive electrode active material layer 322a2, which is relatively easily impregnated with the nonaqueous electrolyte solution 370, is provided in the second region R32. Therefore, for example, the efficiency with which the nonaqueous electrolyte solution 370 impregnates the electrode body 320 in the impregnation step can be increased via the second positive electrode active material layer 322a2. In addition, in the electricity storage device 3100, the first positive electrode active material layer 322a1, which is relatively difficult to impregnate with the nonaqueous electrolyte solution 370, is provided in the first region R31. This makes it possible to increase the contact time between the nonaqueous electrolyte solution 370 and the first positive electrode active material layer 322a1 in the impregnation step, thereby increasing the efficiency with which the nonaqueous electrolyte solution 370 impregnates the electrode assembly 320 with the nonaqueous electrolyte solution 370 via the first positive electrode active material layer 322a1. This increases the energy density of the electricity storage device 3100 and also increases the efficiency with which the nonaqueous electrolyte solution 370 impregnates the electrode assembly 320.

[0067] <Fourth embodiment> In the third embodiment described above, the power storage device 3100 includes the electrode assembly 320, which is a laminated electrode assembly. However, the technology disclosed herein is not limited to this. The power storage device 3100 may include, for example, an electrode assembly 420 shown in FIG. 8 instead of the electrode assembly 320. FIG. 8 is a schematic diagram of the electrode assembly 420. As shown in FIG. 8, the electrode assembly 420 is a wound electrode assembly in which a long sheet-like positive electrode 422 and a long sheet-like negative electrode 424 are wound around a winding axis WL with a long sheet-like separator 426 interposed therebetween.

[0068] FIG. 9 is a plan view of the positive electrode 422. As shown in FIGS. 8 and 9, the positive electrode 422 includes a positive electrode active material layer 422a and a positive electrode current collector foil 422c. The positive electrode current collector foil 422c is, for example, a long sheet-like aluminum foil. In this embodiment, the positive electrode current collector foil 422c has a long, strip-like main body and a positive electrode tab 422t protruding from the main body. The positive electrode current collector foil 422c has a region where the positive electrode active material layer 422a is provided and a region where the positive electrode active material layer 422a is not provided. The region where the positive electrode active material layer 422a is not provided includes, for example, a region where the positive electrode current collector foil 422c is exposed.

[0069] 8 and 9, the positive electrode active material layer 422a is provided in a strip shape on the positive electrode current collector foil 422c along the longitudinal direction LD. Here, the positive electrode active material layer 422a is not provided on the positive electrode tab 422t. The positive electrode active material layer 422a may be provided on, for example, one or both sides (here, both sides) of the positive electrode current collector foil 422c. In this embodiment, the positive electrode active material layer 422a has a first positive electrode active material layer 422a1 and a second positive electrode active material layer 422a2.

[0070] In this embodiment, the first positive electrode active material layer 422a1 is provided in a first region R41 on the bottom surface 312a side of the electrode assembly 420 (see FIGS. 6, 8, and 9). The second positive electrode active material layer 422a2 is provided, for example, in a second region R42 on the top surface 312d side (see FIGS. 6, 8, and 9). As shown in FIG. 9, in the positive electrode 422, the first positive electrode active material layers 422a1 and the second positive electrode active material layers 422a2 are provided alternately from a starting end 4221 to a terminal end 4222 in the longitudinal direction LD. The starting end 4221 may be, for example, the end where winding begins and may be located inside the electrode assembly 420. The terminal end 4222 may be, for example, the end where winding ends and may be located on the outer periphery of the electrode assembly 420.

[0071] As shown in FIGS. 8 and 9, the positive electrode tabs 422t protrude outward (in the R direction in the left-right direction Y in FIG. 8) from one end of the positive electrode current collector foil 422c along the longitudinal direction LD. The positive electrode tabs 422t are provided at predetermined intervals (intermittently) along the longitudinal direction LD. No positive electrode active material layer 422a is provided on the protruding tip side of the positive electrode tab 422t. In this embodiment, a plurality of positive electrode tabs 422t are stacked in the electrode body 420 to form a positive electrode tab group.

[0072] As shown in FIG. 8, the negative electrode 424 includes a negative electrode active material layer 424a and a negative electrode current collector foil 424c. The negative electrode current collector foil 424c is, for example, a long sheet-like copper foil. In this embodiment, the negative electrode current collector foil 424c has a long, strip-like main body and a negative electrode tab 424t protruding from the main body. The negative electrode current collector foil 424c has a region where the negative electrode active material layer 424a is provided and a region where the negative electrode active material layer 424a is not provided. The region where the negative electrode active material layer 424a is not provided includes, for example, a region where the negative electrode current collector foil 424c is exposed.

[0073] 8, the negative electrode active material layer 424a is provided in a strip shape on the negative electrode current collector foil 424c along the longitudinal direction LD. Here, the negative electrode active material layer 424a is not provided on the negative electrode tab 424t. The negative electrode active material layer 424a may be provided on, for example, one or both sides (both sides in this case) of the negative electrode current collector foil 424c.

[0074] As shown in FIG. 8, the negative electrode tabs 424t protrude outward (in the L direction in the left-right direction Y in FIG. 8) from one end of the negative electrode current collector foil 424c along the longitudinal direction LD. The negative electrode tabs 424t are provided at predetermined intervals (intermittently) along the longitudinal direction LD. No negative electrode active material layer 424a is provided on the protruding tip side of the negative electrode tab 424t. In this embodiment, a plurality of negative electrode tabs 424t are stacked in the electrode body 420 to form a negative electrode tab group.

[0075] <Other embodiments> In the above-described embodiment, both the positive electrode and the negative electrode are provided with a first electrode active material layer and a second electrode active material layer. However, the technology disclosed herein is not limited to this. In other embodiments, at least one of the positive electrode and the negative electrode may be provided with a first electrode active material layer and a second electrode active material layer. Furthermore, the case in the above-described embodiment is rectangular. However, the technology disclosed herein is not limited to this configuration. The case may be cylindrical, for example.

[0076] Suitable applications of the electricity storage devices in all the above-described embodiments include drive power sources mounted on vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (BEVs). Alternatively, the electricity storage devices in all the above-described embodiments may be used as a single cell in an electricity storage module including a plurality of single cells.

[0077] The technology disclosed herein may include aspects described in the following items. Section 1: an electrode body including an electrode having an electrode active material layer including an electrode active material; a nonaqueous electrolyte; a case that houses the electrode assembly and the nonaqueous electrolyte solution, the case having a bottom surface, an upper surface opposite to the bottom surface, and a side surface provided between the bottom surface and the upper surface; An electricity storage device comprising: the electrode has a first region on the bottom surface side and a second region on the top surface side, a first electrode active material layer having a relatively high density is provided in the first region; a second electrode active material layer having a relatively low density is provided in the second region; Here, the second electrode active material layer is provided in the electrode active material layer from the first end on the top surface side to a position that is at least 40% of the way toward the second end on the bottom surface side. Section 2: The case is The container has a rectangular bottom surface, a pair of first side surfaces extending from a pair of opposing long sides of the bottom surface, and a pair of second side surfaces extending from a pair of opposing short sides of the bottom surface, Item 2. The electricity storage device according to item 1, having a positive electrode terminal and a negative electrode terminal on the upper surface. Section 3: The case is The container has a rectangular bottom surface, a pair of first side surfaces extending from a pair of opposing long sides of the bottom surface, and a pair of second side surfaces extending from a pair of opposing short sides of the bottom surface, Item 1. The electricity storage device according to item 1, having a positive electrode terminal and a negative electrode terminal on the second side surface. Section 4: 4. The power storage device according to any one of items 1 to 3, comprising, as the electrode body, a laminated electrode body including a sheet-shaped positive electrode, a sheet-shaped negative electrode, and a sheet-shaped separator interposed between the positive electrode and the negative electrode. Section 5: 4. The power storage device according to any one of items 1 to 3, wherein the electrode body comprises a wound electrode body in which a long sheet-like positive electrode and a long sheet-like negative electrode are wound around a winding axis with a long sheet-like separator interposed therebetween. Item 6: Item 6. The electricity storage device according to any one of items 1 to 5, wherein the density of the first electrode active material layer is three times or less the density of the second electrode active material layer. [Explanation of symbols]

[0078] 100, 3100 Energy storage device 10,310 cases 20, 220, 320, 420 electrode body 22, 222, 322, 422 positive electrode 22a, 222a, 322a, 422a Cathode active material layer 22a1, 222a1, 322a1, 422a1 First positive electrode active material layer 22a2, 222a2, 322a2, 422a2 Second positive electrode active material layer R1, R21, R31, R41 1st area R2, R22, R32, R42 2nd area 22c, 222c, 322c, 422c positive electrode current collector foil 24, 224, 324, 424 negative electrode 80, 370 Nonaqueous electrolyte

Claims

1. an electrode body including an electrode having an electrode active material layer including an electrode active material; a nonaqueous electrolyte; a case that houses the electrode assembly and the nonaqueous electrolyte solution, the case having a bottom surface, an upper surface opposite to the bottom surface, and a side surface provided between the bottom surface and the upper surface; An electricity storage device comprising: the electrode has a first region on the bottom surface side and a second region on the top surface side, a first electrode active material layer having a relatively high density is provided in the first region; a second electrode active material layer having a relatively low density is provided in the second region; Here, the second electrode active material layer is provided in the electrode active material layer from the first end on the top surface side to a position that is at least 40% of the way toward the second end on the bottom surface side.

2. The case is The container has a rectangular bottom surface, a pair of first side surfaces extending from a pair of opposing long sides of the bottom surface, and a pair of second side surfaces extending from a pair of opposing short sides of the bottom surface, The electricity storage device according to claim 1 , further comprising a positive electrode terminal and a negative electrode terminal on the upper surface.

3. The case is The container has a rectangular bottom surface, a pair of first side surfaces extending from a pair of opposing long sides of the bottom surface, and a pair of second side surfaces extending from a pair of opposing short sides of the bottom surface, The power storage device according to claim 1 , further comprising a positive electrode terminal and a negative electrode terminal on the second side surface.

4. The electrode body is a laminated electrode body including a sheet-shaped positive electrode, a sheet-shaped negative electrode, and a sheet-shaped separator interposed between the positive electrode and the negative electrode. The power storage device according to any one of claims 1 to 3.

5. The electrode body includes a wound electrode body in which a long sheet-shaped positive electrode and a long sheet-shaped negative electrode are wound around a winding axis with a long sheet-shaped separator interposed therebetween. The power storage device according to any one of claims 1 to 3.

6. 4. The power storage device according to claim 1, wherein the density of the first electrode active material layer is three times or less the density of the second electrode active material layer.

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