Stack manufacturing method

Abstract

To provide a manufacturing method of a stack, which is able to suitably control thicknesses of storage cells and to prevent decreases in stack restraining loads.SOLUTION: A technology disclosed herein relates to a manufacturing method of a stack that includes a plurality of storage cells. When the storage cells prepared herein undergo five cycles of a process, one cycle being a process that involves applying a load of up to 0.1 MPa to each of the storage cells at a speed of 0.1 mm / min in the thickness direction of each of the storage cells, and applying a load of up to 0.1 MPa to each of the storage cells prepared in the preparation process at a speed of 0.1 mm / min in the thickness direction of each of the storage cells, and then reducing the load to 0.01 MPa at a speed of 0.1 mm / min, a relationship between a storage cell thickness X1 determined relative to a surface pressure of 0.04 MPa by a pressurized side F-s curve in a first cycle and a storage cell thickness X5 determined relative to a surface pressure of 0.04 MPa by a pressurized side F-s curve in a fifth cycle satisfies the following expression: (X1-X5) / X1×100≥0.3.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a stack. [Background technology]

[0002] In recent years, stacks including multiple energy storage cells have been suitably used as drive power sources mounted on vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (BEVs). Patent Document 1 is an example of a related prior art document. Patent Document 1 discloses a technology related to a nonaqueous electrolyte secondary battery (energy storage cell) that has an electrode assembly including a housing, a nonaqueous electrolyte (nonaqueous electrolyte), a positive electrode, a negative electrode, and a separator, and the electrode assembly further includes a low spring constant membrane having a spring constant (second spring constant) lower than the spring constant (first spring constant) of the negative electrode, thereby suppressing extrusion of the nonaqueous electrolyte inside the electrode assembly due to expansion and contraction of the electrode assembly. Conventionally, stacks are used by stacking energy storage cells and applying a load to restrain them. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-055806 Summary of the Invention [Problem to be solved by the invention]

[0004] During stack use, the thickness of the energy storage cells decreases under low temperatures or low SOC (State of Charge) conditions. When the stack is in this state, the non-aqueous electrolyte extruded from the electrode assembly within the energy storage cells returns to the electrode assembly, thereby increasing the thickness of the energy storage cells and maintaining the stack's restraining load. However, if the non-aqueous electrolyte does not easily return to the electrode assembly within the energy storage cells, the energy storage cell's thickness remains small, reducing the stack's restraining load and preventing the energy storage cells from being sufficiently restrained. Therefore, when manufacturing a stack, consideration must be given not only to the extrusion of the non-aqueous electrolyte from the energy storage cells but also to the ease with which the non-aqueous electrolyte returns. In this regard, Patent Document 1, cited above, does not consider the ease with which the non-aqueous electrolyte returns to the electrode assembly, leaving room for improvement in the technology.

[0005] The technology disclosed herein has been made in consideration of the above circumstances, and its main purpose is to provide a method for manufacturing a stack that can suitably control the thickness of the storage cells stacked in the stack and suppress a decrease in the restraining load of the stack. [Means for solving the problem]

[0006] The technology disclosed herein is a method for manufacturing a stack including a plurality of rectangular energy storage cells, and includes a preparation step of preparing the energy storage cells, each of which includes a flat-shaped wound electrode body formed by stacking and winding a positive electrode and a negative electrode with a separator interposed therebetween, a non-aqueous electrolyte, and a case that houses the wound electrode body and the non-aqueous electrolyte, and a stacking step of stacking a plurality of the energy storage cells along the thickness direction of the energy storage cells. Here, when a process in which a load is applied to the storage cell prepared in the preparation step in the thickness direction of the storage cell up to 0.1 MPa at a rate of 0.1 mm / min and then the load is reduced to 0.01 MPa at a rate of 0.1 mm / min is defined as one cycle, and when this process is performed for five cycles, the relationship between the storage cell thickness X1 for a surface pressure of 0.04 MPa on the pressure-side Fs curve in the first cycle and the storage cell thickness X5 for a surface pressure of 0.04 MPa on the pressure-side Fs curve in the fifth cycle satisfies the following formula: (X1-X5) / X1×100≧0.3.

[0007] The storage cells prepared in the preparation process are storage cells that satisfy the above formula. Storage cells with this configuration have a thickness difference that allows the nonaqueous electrolyte, which is pushed out of the wound electrode body during the stacking process, to return to the inside of the wound electrode body. Therefore, the thickness of the wound electrode body increases as the storage cell re-incorporates the nonaqueous electrolyte, and the thickness of the storage cell increases. This prevents a decrease in the load applied to the storage cells, allowing a sufficient load to be maintained on the storage cells in the stack. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically illustrating a stack according to an embodiment. [Figure 2] FIG. 2 is a perspective view of the storage cell. [Figure 3] FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a perspective view that schematically shows a wound electrode body attached to a sealing plate. [Figure 5] FIG. 5 is a perspective view schematically showing a wound electrode body. [Figure 6] FIG. 6 is a schematic diagram showing the configuration of a wound electrode body. [Figure 7] FIG. 7 is a flow diagram illustrating a method for manufacturing a stack according to one embodiment. [Figure 8] FIG. 8 is an example of an Fs curve obtained in the preparation step according to one embodiment. [Figure 9] 9A and 9B are schematic diagrams illustrating thickness changes of a wound electrode assembly according to one embodiment, in which (a) shows the wound electrode assembly before stack restraint, (b) shows the wound electrode assembly when stack restraint is performed, and (c) shows the wound electrode assembly when the non-aqueous electrolyte returns to the wound electrode assembly. [Figure 10] FIG. 10 is a schematic diagram illustrating the measurement of the amount of change in cell thickness in the preparation step. [Figure 11]FIG. 11 is a flow diagram showing a method for manufacturing an energy storage cell according to one embodiment. [Figure 12] FIG. 12 is a graph plotting the change in cell thickness between the first and fifth cycles under the same load as Δcell thickness (mm) on the horizontal axis and the applied load (kN) on the vertical axis for Examples 1 and 2 and Comparative Example 2. [Figure 13] 13 is a schematic diagram illustrating thickness changes of a conventional wound electrode body, where (a) shows the wound electrode body before stack restraint, (b) shows the wound electrode body when the stack is restrained, and (c) shows the wound electrode body when the nonaqueous electrolyte returns to the wound electrode body. [Figure 14] FIG. 14 is an example of an Fs curve according to a conventional example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, some preferred embodiments of the stack disclosed herein will be described with reference to the drawings as appropriate. Matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a storage cell that does not characterize the present disclosure) can be understood as design matters for those skilled in the art based on conventional technology in the field. The stack disclosed herein can be implemented based on the contents disclosed in this specification and common technical knowledge in the field.

[0010] In the following drawings, the same reference numerals are used to designate components and parts that perform the same function, and redundant explanations may be omitted or simplified. In addition, in this specification, the expression "A to B" indicating a range means not less than A and not more than B, and also encompasses the meanings of "preferably larger than A" and "preferably smaller than B."

[0011] FIG. 1 is a perspective view schematically illustrating a stack 500 according to one embodiment. The stack 500 includes a plurality of energy storage cells 100 and a restraining mechanism 300. Although not shown here for ease of explanation, the energy storage cells 100 of the stack 500 are electrically connected by bus bars. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short-side direction (thickness direction) of the energy storage cells 100, the long-side direction (width direction) perpendicular to the short-side direction, and the up-down direction, respectively. The short-side direction X is also the arrangement direction of the energy storage cells 100. However, these directions are merely provided for ease of explanation and do not limit the installation form of the stack 500 in any way.

[0012] The restraint mechanism 300 is configured to apply a specified restraint pressure to the plurality of energy storage cells 100 in the thickness direction X. Here, the restraint mechanism 300 is configured with a pair of end plates 310, a pair of side plates 320, and a plurality of screws 330. The pair of end plates 310 are aligned in a predetermined thickness direction X. The pair of end plates 310 are arranged at both ends of the stack 500 in the thickness direction X. The plurality of energy storage cells 100 are arranged between the pair of end plates 310 along the thickness direction X. An insulating sheet, an inter-cell separator, or the like may be arranged between the plurality of energy storage cells 100.

[0013] The pair of side plates 320 bridge the pair of end plates 310. The pair of side plates 320 are fixed to the end plates 310 with a plurality of screws 330, for example, while applying a load to the plurality of energy storage cells 100. This applies a restraining load to the plurality of energy storage cells 100 and the plurality of porous elastic members 200 in the thickness direction X, and holds the stack 500 together. However, the restraining mechanism is not limited to this. The restraining mechanism 300 may include, for example, a plurality of restraining bands, bind bars, or the like, instead of the side plates 320.

[0014] <Storage cell 100> In this specification, the term "storage cell" refers to a device that can be repeatedly charged and discharged. Storage cells include batteries generally referred to as lithium ion batteries and lithium secondary batteries, as well as lithium polymer batteries and lithium ion capacitors. Secondary batteries generally refer to batteries that can be repeatedly charged and discharged through the movement of charge carriers between the positive and negative electrodes. Here, a lithium ion secondary battery is exemplified as one form of storage cell.

[0015] FIG. 2 is a perspective view of the energy storage cell 100. As shown in FIGS. 1 and 2, the plurality of energy storage cells 100 are arranged in the thickness direction X so that first side walls 12b, which will be described later, face each other. FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. 2. As shown in FIG. 3, the energy storage cell 100 includes a case 10, a wound electrode body 20, a non-aqueous electrolyte (not shown), a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, and a negative electrode current collector 60. Here, the energy storage cell 100 is a lithium ion secondary battery.

[0016] The case 10 is a housing that houses the wound electrode assembly 20 and the non-aqueous electrolyte. As shown in FIG. 2, the case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the case 10 may be the same as that conventionally used, and is not particularly limited. The case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 2, the case 10 includes an exterior body 12 having an opening 12h and a sealing plate (lid) 14 that seals the opening 12h. As in this embodiment, the case 10 preferably includes an exterior body 12 having an opening 12h and a sealing plate 14 that seals the opening 12h.

[0017] As shown in FIG. 2, the exterior body 12 includes a bottom 12a, a pair of first side walls 12b extending from the bottom 12a and facing each other, and a pair of second side walls 12c extending from the bottom 12a and facing each other. The bottom 12a is generally rectangular. The bottom 12a faces the opening 12h. The first side wall 12b is flat. The first side wall 12b extends from a long side of the bottom 12a. The second side wall 12c extends from a short side of the bottom 12a. In a plan view, the area of ​​the first side wall 12b is larger than the area of ​​the second side wall 12c. The size of the exterior body 12 is not particularly limited, but it is preferable that the width (long side direction Y) be 300 to 330 mm, the height (vertical direction Z) be 100 to 130 mm, and the thickness (short side direction X) be 30 to 50 mm.

[0018] The sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h of the exterior body 12. The sealing plate 14 faces the bottom 12a of the exterior body 12. The sealing plate 14 has a substantially rectangular shape in a plan view. The case 10 is integrated by joining (preferably welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The case 10 is hermetically sealed (sealed).

[0019] As shown in Fig. 3, the sealing plate 14 is provided with a liquid inlet 15, a drain valve 17, and two terminal outlet holes 18 and 19. The liquid inlet 15 is for injecting a non-aqueous electrolyte after the sealing plate 14 is assembled to the exterior body 12. The liquid inlet 15 is sealed with a sealing member 16. The drain valve 17 is configured to break when the pressure inside the case 10 reaches or exceeds a predetermined value, thereby discharging gas inside the case 10 to the outside. The terminal outlet holes 18 and 19 penetrate the sealing plate 14 in the vertical direction Z. The terminal outlet holes 18 and 19 each have an inner diameter large enough to insert the positive electrode terminal 30 and the negative electrode terminal 40 before they are attached to the sealing plate 14 (before being crimped).

[0020] The non-aqueous electrolyte may be the same as conventional ones and is not particularly limited. The non-aqueous electrolyte contains a non-aqueous solvent and a supporting salt (electrolyte salt). The non-aqueous electrolyte may further contain additives as necessary. The non-aqueous solvent includes, for example, carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The non-aqueous solvent preferably includes a carbonate. In particular, it is preferable that the non-aqueous solvent includes a cyclic carbonate and a chain carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as lithium hexafluorophosphate (LiPF6). Examples of additives that can be included in the non-aqueous electrolyte include a film-forming agent, a gas generating agent, a dispersant, and a thickener. Examples of the film-forming agent include carbonate compounds such as vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), chloroethylene carbonate, and methylphenyl carbonate; and lithium salts having an oxalato complex as the anion, such as lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiFOB), and lithium difluorobis(oxalato)phosphate (LPFO).

[0021] The positive electrode terminal 30 is disposed at one end of the sealing plate 14 in the long side direction Y (the left end in FIGS. 2 and 3). The negative electrode terminal 40 is disposed at the other end of the sealing plate 14 in the long side direction Y (the right end in FIGS. 2 and 3). As shown in FIG. 3, the positive electrode terminal 30 and the negative electrode terminal 40 extend from the inside to the outside of the sealing plate 14 through the terminal lead-out holes 18 and 19. The positive electrode terminal 30 and the negative electrode terminal 40 are fixed to the sealing plate 14. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portion surrounding the terminal lead-out holes 18 and 19 of the sealing plate 14 by crimping. Crimped portions 30c and 40c are formed at the ends of the positive electrode terminal 30 and the negative electrode terminal 40 on the exterior body 12 side (the lower end in FIG. 3).

[0022] As shown in Fig. 3, the positive electrode terminal 30 is electrically connected to the positive electrode 22 (see Fig. 6) of the wound electrode body 20 via a positive electrode current collector 50 inside the exterior body 12. The negative electrode terminal 40 is electrically connected to the negative electrode 24 (see Fig. 6) of the wound electrode body 20 via a negative electrode current collector 60 inside the exterior body 12. The positive electrode terminal 30 is insulated from the sealing plate 14 by an internal insulating member 80 and a gasket 90. The negative electrode terminal 40 is insulated from the sealing plate 14 by the internal insulating member 80 and a gasket 90.

[0023] A plate-shaped positive electrode external conductive member 32 and a plate-shaped negative electrode external conductive member 42 are attached to the outer surface of the sealing plate 14. The positive electrode external conductive member 32 is electrically connected to the positive electrode terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative electrode terminal 40. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are members to which bus bars or the like are attached that electrically connect the multiple energy storage cells 100 to each other. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external insulating member 92. Although not shown in FIG. 1 , when the stack 500 is in use, adjacent energy storage cells 100 are electrically connected to each other. For example, of adjacent energy storage cells 100, the positive electrode external conductive member 32 of one energy storage cell 100 and the negative electrode external conductive member 42 of the other energy storage cell 100 are electrically connected by a bus bar or the like. This electrically connects the stack 500. The stack 500 may be connected in series, in parallel, or in a so-called multi-series / multi-parallel connection, which is a combination of series and parallel.

[0024] FIG. 4 is a perspective view schematically showing the wound electrode body 20 attached to the sealing plate 14. Here, the wound electrode body 20 has three wound electrode bodies 20. However, the number of electrode bodies arranged inside one exterior body 12 is not particularly limited and may be one or multiple (two or more). Here, the wound electrode bodies 20 are electrically connected in parallel. The wound electrode bodies 20 are arranged inside the exterior body 12 with the winding axis WL (see FIG. 6) oriented approximately parallel to the long side direction Y. Here, the wound electrode bodies 20 are arranged side by side in a direction (short side direction X) in which the thickness direction of the wound electrode body 20 coincides with the thickness direction of the energy storage cell 100 (in other words, a direction approximately perpendicular to the first side wall 12b of the case 10). The wound electrode body 20 preferably has a flat outer shape. An end face of the wound electrode body 20 that is perpendicular to the winding axis WL (in other words, the stacking surface where the positive electrode 22 and the negative electrode 24 are stacked) faces the second side wall 12c. Although not shown, an insulating sheet is disposed between the wound electrode body 20 and the exterior body 12.

[0025] FIG. 5 is a perspective view that schematically shows a wound electrode body 20. Note that all of the wound electrode bodies 20 housed in the case 10 can have the same configuration. The wound electrode body 20 has a pair of curved portions (R portions) 20r and a flat portion 20f that connects the pair of curved portions 20r. One curved portion 20r (upper side of FIG. 5) faces the sealing plate 14, and the other curved portion 20r (lower side of FIG. 5) faces the bottom portion 12a of the exterior body 12. The flat portion 20f faces the first side wall 12b of the exterior body 12. Here, the flat portions 20f of the multiple wound electrode bodies 20 adjacent to each other in the short side direction X face each other.

[0026] 6 is a schematic diagram showing the configuration of the wound electrode body 20. The wound electrode body 20 has a positive electrode 22, a negative electrode 24, and a separator 26. In this example, the wound electrode body 20 is configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with the strip-shaped separator 26 interposed between them and winding them in the longitudinal direction around a winding axis WL. The direction of the winding axis WL is approximately parallel to the long side direction Y.

[0027] As shown in FIG. 6, the positive electrode 22 includes a positive electrode core 22c, a positive electrode active material layer 22a, and a positive electrode protective layer 22p fixed to at least one surface of the positive electrode core 22c. However, the positive electrode protective layer 22p is not essential and may be omitted in other embodiments. The positive electrode core 22c is strip-shaped. The positive electrode core 22c is preferably made of metal foil, more preferably aluminum foil or aluminum alloy foil. Here, the positive electrode core 22c is aluminum foil. The thickness of the positive electrode core 22c is not particularly limited, but is preferably 5 to 30 μm, more preferably 10 to 25 μm. The number of layers of the positive electrode 22 is preferably 30 or more.

[0028] A plurality of positive electrode tabs 22t are provided at one end of the positive electrode core 22c in the long side direction Y (the left end in FIG. 6). The plurality of positive electrode tabs 22t protrude toward one side in the long side direction Y (the left side in FIG. 6). The plurality of positive electrode tabs 22t protrude further in the long side direction Y than the separator 26. Here, the positive electrode tab 22t is part of the positive electrode core 22c and is made of metal foil (aluminum foil). As shown in FIGS. 3 to 6, the plurality of positive electrode tabs 22t are stacked at one end in the long side direction Y (the left end in FIGS. 3 to 6) to form a positive electrode tab group 23. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via a positive electrode current collector 50.

[0029] As shown in FIG. 6, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the positive electrode substrate 22c. The positive electrode active material layer 22a contains a positive electrode active material capable of reversibly absorbing and releasing charge carriers. A lithium transition metal composite oxide, for example, is preferably used as the positive electrode active material, and nickel (Ni) is particularly preferred. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as various additive components such as a binder and a conductive material. The additive components preferably include a conductive material and a binder. Examples of binders used in the positive electrode active material layer 22a include polyvinylidene fluoride (PVdF). The conductive material used in the positive electrode active material layer 22a is not particularly limited, but a carbon material is preferably used. The density of the positive electrode active material layer 22a is preferably 3.0 g / cc or more, more preferably 3.5 g / cc or more. On the other hand, the density of the positive electrode active material layer 22a is preferably 3.7 g / cc or less.

[0030] As shown in Fig. 6, the positive electrode protective layer 22p is provided at the boundary between the positive electrode core 22c and the positive electrode active material layer 22a in the long side direction Y. The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). The positive electrode protective layer 22p may contain optional components other than the inorganic filler, such as a conductive material, a binder, and various additive components.

[0031] As shown in FIG. 6, the negative electrode 24 includes a negative electrode core 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode core 24c. The negative electrode core 24c is strip-shaped. The negative electrode core 24c is preferably made of a metal foil, more preferably a copper foil or a copper alloy foil. Here, the negative electrode core 24c is a copper foil. The thickness of the negative electrode core 24c is not particularly limited, but is preferably 5 to 30 μm, more preferably 10 to 25 μm.

[0032] A plurality of negative electrode tabs 24t are provided at one end of the negative electrode core 24c in the long side direction Y (the right end in FIG. 6). The plurality of negative electrode tabs 24t protrude toward one side in the long side direction Y (the right end in FIG. 6). The plurality of negative electrode tabs 24t protrude further in the long side direction Y than the separator 26. Here, the negative electrode tab 24t is part of the negative electrode core 24c and is made of metal foil (copper foil). As shown in FIGS. 3 to 6, the plurality of negative electrode tabs 24t are stacked at one end in the long side direction Y (the right end in FIGS. 3 to 6) to form a negative electrode tab group 25. The negative electrode tab group 25 is provided at a position symmetrical to the positive electrode tab group 23 in the long side direction Y. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via a negative electrode current collector 60.

[0033] As shown in FIG. 6, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the negative electrode substrate 24c. The negative electrode active material layer 24a contains a negative electrode active material capable of reversibly absorbing and releasing charge carriers. Examples of suitable negative electrode active materials include graphite, silicon-based materials (silicon-containing materials), and mixed oxides thereof. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as various additives such as binders, thickeners, and dispersants. Examples of binders used in the negative electrode active material layer 24a include styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC). The conductive material used in the negative electrode active material layer 24a is not particularly limited, but a carbon material is preferably used. The density of the negative electrode active material layer 24a is preferably 1.3 g / cc or higher, and more preferably 1.4 g / cc or higher. On the other hand, the density of the negative electrode active material layer 24a is preferably 1.7 g / cc or less.

[0034] The length Ln of the negative electrode active material layer 24a in the width direction Y is equal to or longer than the length La of the positive electrode active material layer 22a in the width direction Y. Here, the length Ln of the negative electrode active material layer 24a in the width direction Y is preferably 20 cm or more. As will be described in detail later, this configuration allows for favorable control of the return of non-aqueous electrolyte to the wound electrode body 20. Furthermore, when the length in a direction perpendicular to the winding axis WL of the wound electrode body 20 and perpendicular to the thickness direction X of the wound electrode body 20 (here, the Z direction) is defined as the height T of the wound electrode body 20, the ratio (Ln / T) of the width direction length Ln of the negative electrode active material layer 24a to the height T of the wound electrode body 20 (hereinafter also referred to as the "electrode body aspect ratio") is preferably 2.8 to 3.2. This configuration allows for favorable control of the return of non-aqueous electrolyte to the wound electrode body 20. In the specification, "height T of the wound electrode body 20" refers to the distance in the Z direction from the uppermost end of one curved portion 20r of the wound electrode body 20 (U side in Figure 5) to the lowermost end of the other curved portion 20r (D side in Figure 5).

[0035] The separator 26 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. The separator 26 forms the outer surface of the wound electrode body 20. The length Ls of the separator 26 in the long side direction Y is equal to or longer than the length Ln of the negative electrode active material layer 24a in the long side direction Y. The separator 26 has a substrate portion. The separator 26 may be formed on at least one surface of the substrate portion, and a heat-resistant layer containing, for example, inorganic particles and a heat-resistant layer binder may be formed thereon. The separator 26 may also be formed on at least one surface of the substrate portion with an adhesive layer containing an adhesive layer binder. The adhesive layer may further contain inorganic particles in addition to the adhesive layer binder. The adhesive layer may be formed in a shape such as dots, stripes, waves, bands (lines), dashed lines, or a combination thereof in a planar view. Although not shown in the drawings, in this embodiment, a heat-resistant layer is provided on the surface of the substrate portion of the separator 26, and an adhesive layer is further provided on the heat-resistant layer. The separator 26 preferably has a heat-resistant layer and an adhesive layer. Alternatively, the separator 26 preferably has an adhesive layer containing inorganic particles.

[0036] The substrate of separator 26 is a sheet-like member of a microporous membrane. Separator 26 is preferably made of a polyolefin resin. Examples of polyolefin resins that can be used include polyethylene (PE), polypropylene (PP), and mixtures thereof.

[0037] There are no particular limitations on the thickness of the separator 26. When a non-aqueous electrolyte is not present in the separator 26, the thickness of the separator 26 is preferably about 10 to 30 μm. In this specification, the "thickness of the separator 26" refers to the thickness including the adhesive layer and the heat-resistant layer when the separator 26 has an adhesive layer and a heat-resistant layer in addition to the base material, and refers to the thickness before press-molding unless otherwise specified.

[0038] When separator 26 has an adhesive layer, the adhesive layer binder used in the adhesive layer can be any binder that has been conventionally used for this type of application, without particular limitation, and examples thereof include acrylic resins, fluorine-based resins (e.g., PVdF), rubber-based resins (e.g., styrene butadiene rubber (SBR)), urethane-based resins, silicone-based resins, and epoxy-based resins. These may be used alone or in combination of two or more. Furthermore, when the adhesive layer contains inorganic particles, the proportion of the inorganic particles relative to the total mass of the heat-resistant layer is preferably about 5 to 20 mass%, more preferably about 10 to 15 mass%.

[0039] When the separator 26 has a heat-resistant layer, the proportion of inorganic particles relative to the total mass of the heat-resistant layer is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The heat-resistant layer binder used in the heat-resistant layer can be any binder conventionally used for this type of application, without particular limitation, and examples thereof include acrylic resins, fluorine-based resins, epoxy resins, urethane resins, and ethylene vinyl acetate resins. These may be used alone or in combination of two or more. The heat-resistant layer binder and the adhesive layer binder may be the same or different.

[0040] The inorganic particles used in the heat-resistant layer and adhesive layer of the separator 26 can be any conventionally known particles used for this type of application, but preferably include, for example, insulating ceramic particles. Among these, from the viewpoint of heat resistance, inorganic oxides such as alumina, zirconia, silica, and titania, metal hydroxides such as aluminum hydroxide, and clay minerals such as boehmite are preferred, with alumina and boehmite being more preferred. Furthermore, from the viewpoint of suppressing thermal shrinkage of the separator 26, compounds containing aluminum are particularly preferred.

[0041] As shown in FIG. 3, the positive electrode current collecting part 50 forms a conductive path that electrically connects the positive electrode tab group 23 consisting of multiple positive electrode tabs 22t to the positive electrode terminal 30. The positive electrode current collecting part 50 includes a positive electrode first current collecting part 51 and a positive electrode second current collecting part 52. The positive electrode first current collecting part 51 is attached to the inner surface of the sealing plate 14. The positive electrode second current collecting part 52 extends along the second side wall 12c of the exterior body 12. As shown in FIGS. 3 to 5, the positive electrode second current collecting part 52 is attached to the wound electrode body 20.

[0042] 3, the negative electrode current collecting part 60 forms a conductive path that electrically connects the negative electrode tab group 25 consisting of the multiple negative electrode tabs 24t to the negative electrode terminal 40. The negative electrode current collecting part 60 includes a negative electrode first current collecting part 61 and a negative electrode second current collecting part 62. The configurations of the negative electrode first current collecting part 61 and the negative electrode second current collecting part 62 may be the same as those of the positive electrode first current collecting part 51 and the positive electrode second current collecting part 52 of the positive electrode current collecting part 50.

[0043] <Stack 500 manufacturing method> 7 is a flow diagram showing a method for manufacturing a stack 500 according to one embodiment. The stack 500 disclosed herein can be manufactured by a manufacturing method including a preparation step S10 and a stacking step S20, and is characterized by performing the preparation step S10. Furthermore, the manufacturing method for the stack 500 disclosed herein may include other steps at any stage in addition to the above steps, and the remaining manufacturing process may be the same as conventional methods.

[0044] (Preparation step S10) In the preparation step S10, an energy storage cell 100 is prepared, which includes the above-described wound electrode body 20, a non-aqueous electrolyte, and a case 10. In the preparation step S10, the energy storage cell 100 may be purchased and prepared, or the energy storage cell 100 may be manufactured and prepared.

[0045] Here, the energy storage cell 100 prepared in the preparation step S10 is characterized in that, when five cycles of a load application process are performed in the thickness direction of the energy storage cell 100 (the X direction in FIG. 1 ), where a load is applied to the energy storage cell 100 at a rate of 0.1 mm / min up to 0.1 MPa and then the load is reduced to 0.01 MPa at a rate of 0.1 mm / min, the relationship between the energy storage cell thickness X1 at a surface pressure of 0.04 MPa on the pressure-side Fs curve in the first cycle and the energy storage cell thickness X5 at a surface pressure of 0.04 MPa on the pressure-side Fs curve in the fifth cycle satisfies the following formula: (X1-X5) / X1×100≧0.3. Hereinafter, (X1-X5) / X1×100 is also referred to as the "cell thickness change." Note that, in this specification, the "cell thickness change" is determined by measurement using an autograph.

[0046] FIG. 8 shows an example of an Fs curve obtained in the preparation step S10 in one embodiment. Here, the Fs curve for the first cycle corresponds to the Fs curve of the storage cell at the time of shipment (i.e., before use as a stack). On the other hand, the Fs curve for the fifth cycle corresponds to the Fs curve of the storage cell from which the nonaqueous electrolyte held inside the wound electrode body has been removed. Therefore, the difference between X1 and X5 (X1-X5) corresponds to the thickness of the nonaqueous electrolyte held inside the wound electrode body at the time of shipment. In this embodiment, the "change in cell thickness" is the rate of decrease in cell thickness at a surface pressure of 0.04 MPa and serves as an index indicating the amount of nonaqueous electrolyte held inside the wound electrode body.

[0047] FIG. 9 is a schematic diagram illustrating thickness changes in the wound electrode assembly 20 according to one embodiment. FIG. 13 is a schematic diagram illustrating thickness changes in the wound electrode assembly 20 according to a conventional example. In FIGS. 9 and 13, (a) shows the wound electrode assembly 20 before stack restraint, (b) shows the wound electrode assembly 20 when the stack is restrained, and (c) shows the wound electrode assembly 20 when the non-aqueous electrolyte returns to the wound electrode assembly 20. FIG. 14 is an example of an Fs curve according to a conventional example. FIG. 14 corresponds to FIG. 8. In FIGS. 9 and 13, a portion of the wound electrode assembly 20 is partially enlarged.

[0048] When a nonaqueous electrolyte is present inside the wound electrode body 20, for example, the nonaqueous electrolyte is present inside the voids 26s of the separator 26 of the wound electrode body 20. In the state shown in FIG. 13(a), the nonaqueous electrolyte is held in the voids 26s of the wound electrode body 20 in the energy storage cell 100 before being restrained. During stack manufacturing, when the energy storage cell 100 is restrained, a load is applied to the energy storage cell 100 in the thickness direction X. As a result, as shown in FIG. 13(b), the voids 26s of the wound electrode body 20 are crushed, and the nonaqueous electrolyte held inside the voids 26s is pushed out of the wound electrode body 20. Meanwhile, when the stack 500 is used, for example, during initial charging, in a low-temperature environment, or under a low SOC condition, the thickness of the wound electrode body 20 decreases. In particular, when the conditions of a low-temperature environment, a low SOC, and initial charging are met, the thickness of the wound electrode body 20 decreases significantly. This reduces the restraining load applied to the energy storage cell 100 by the restraining mechanism 300. Then, as shown in FIG. 13(c), the nonaqueous electrolyte that was outside the wound electrode body 20 attempts to return to the inside of the wound electrode body 20 by the amount corresponding to the reduced restraining load. The amount of nonaqueous electrolyte that returns to the inside of the wound electrode body 20 is affected by the amount of voids 26s in the wound electrode body 20. In other words, when the amount of voids 26s in the wound electrode body 20 of the energy storage cell 100 is small, the amount of nonaqueous electrolyte that returns to the inside of the wound electrode body 20 is small. As shown in FIG. 14, in the conventional energy storage cell 100, the difference between X1 and X5 is small. In other words, there are few voids 26s for the nonaqueous electrolyte present outside the wound electrode body 20 to return to the inside of the wound electrode body 20. In this way, when the amount of voids 26s in the wound electrode body 20 of the energy storage cell 100 is small, the amount of non-aqueous electrolyte returning to the wound electrode body 20 is small, so the thickness of the wound electrode body 20 does not increase effectively, and the thickness of the energy storage cell 100 remains thin. As a result, the load applied to the energy storage cell 100 decreases, and it is no longer possible to restrain it with a sufficient load.

[0049] Here, the stack 500 according to this embodiment is characterized in that, in the preparation step S10, energy storage cells having a cell thickness change (%) of 0.3% or more (≧0.3) are prepared. For the energy storage cells 100, a sufficient difference between X1 and X5 is provided. In other words, as shown in FIG. 9(a), the wound electrode body 20 has a sufficient thickness to accommodate the nonaqueous electrolyte retained inside the wound electrode body at the time of shipment. As shown in FIG. 9(c), sufficient voids 26s are provided for the nonaqueous electrolyte present outside the wound electrode body 20 to return to the inside of the wound electrode body 20. Therefore, by re-incorporating the nonaqueous electrolyte, the thickness of the wound electrode body 20 increases, and the thickness of the energy storage cells 100 also increases. This prevents a decrease in the load applied to the energy storage cells 100, and a sufficient load is maintained on the energy storage cells 100 in the stack 500.

[0050] FIG. 10 is a schematic diagram illustrating measurement of the amount of change in cell thickness in the preparation step S10. In FIG. 10, the direction in which the autograph 600 applies a load in the thickness direction of the energy storage cell 100 is indicated by a hollow arrow. As shown in FIG. 8, first, the energy storage cell 100 is set in the autograph 600 so that a load is applied in the thickness direction (the direction of the hollow arrow). As shown in FIG. 10, the energy storage cell 100 is set so that a pair of first side walls 12b of the energy storage cell 100 abut against the autograph 600. When viewed horizontally, the energy storage cell 100 is set so that the load from the autograph 600 is applied to the flat portion 20f of the wound electrode body 20. Here, the energy storage cell 100 is set in the autograph 600 so that the load is applied to the location indicated by the imaginary line in FIG. 3. The means for measuring the thickness displacement of the energy storage cell 100 is not particularly limited, and for example, a laser displacement meter (for example, Keyence Corporation, product name: LK-G157, etc.) or the like can be used. Furthermore, the thickness of the energy storage cell 100 may be measured at one location or multiple locations (two or more locations). A load is applied to the energy storage cell 100 in the thickness direction of the energy storage cell 100 (indicated by the white arrow) at a rate of 0.1 mm / min. When the load reaches 0.1 MPa, the load is reduced to 0.01 MPa at a rate of 0.1 mm / min. The above cycle counts as one cycle, and this process is repeated five times. At this time, Fs curves (load-displacement curves) on the pressurized side for the first and fifth cycles are obtained (see FIG. 8). Based on the obtained Fs curve, the storage cell thickness at 0.04 MPa in the first cycle is plotted and designated as X1. Meanwhile, based on the obtained Fs curve, the storage cell thickness at 0.04 MPa in the fifth cycle is plotted and designated as X5. Then, the cell thickness change (%) is calculated using the following formula (i): (X1-X5) / X1×100...Formula (i)

[0051] There are no particular limitations on the method for controlling the numerical range of the cell thickness change amount of the energy storage cell 100, and it can be controlled by various methods. For example, the cell thickness change amount of the energy storage cell 100 can be controlled by adjusting the gap 26s of the separator 26, the size of the wound electrode body 20, etc.

[0052] The method for controlling the numerical range of the cell thickness change of the energy storage cell 100 is not limited thereto, but it can be controlled, for example, by adjusting the length Ln of the negative electrode active material layer 24a in the width direction Y of the wound electrode assembly 20. In this case, the length Ln of the negative electrode active material layer 24a in the width direction Y is preferably 20 cm or more. This configuration makes it possible to suitably control the inflow and outflow of non-aqueous electrolyte into and from the wound electrode assembly 20. That is, it is possible to control the numerical range of the cell thickness change of the energy storage cell 100. Similarly, the numerical range of the cell thickness change of the energy storage cell 100 can be controlled by adjusting the ratio (Ln / T) of the width direction length Ln of the negative electrode active material layer 24a to the height T of the wound electrode assembly 20 (electrode assembly aspect ratio). In this case, it is preferable that the electrode assembly aspect ratio is 2.8 to 3.2. This configuration also makes it possible to suitably control the inflow and outflow of non-aqueous electrolyte into and from the wound electrode assembly 20.

[0053] The method for controlling the numerical range of the cell thickness change of the energy storage cell 100 is not limited thereto. For example, when an adhesive layer is present on the surface of the separator 26, the thickness change can be controlled by adjusting the ratio of the area where the adhesive layer is formed (area of ​​the adhesive layer formation region / area of ​​the separator × 100). In this case, the ratio of the area where the adhesive layer is formed is preferably about 3 to 30%, and more preferably about 5 to 15%. It is also preferable to apply the adhesive layer to the surface of the separator 26 in a dot pattern. This suitably increases the voids 26s in the separator 26, thereby increasing the amount of non-aqueous electrolyte retained. The ratio of the volume of the adhesive layer to the volume between the electrode (positive electrode or negative electrode) and the separator substrate (Vol%) (volume of the adhesive layer on the separator / volume between the electrode and the separator substrate × 100) is preferably 50 to 97 vol%, and more preferably 85 to 95 vol%. By employing a wound electrode body having such a numerical range, the numerical range of the amount of change in cell thickness of the energy storage cell 100 can be controlled to a suitable numerical range.

[0054] The method for controlling the numerical range of the cell thickness change of the energy storage cell 100 is not limited to the above, and can also be controlled, for example, by adjusting the particle size (D50) of the inorganic particles contained in the adhesive layer and the heat-resistant layer. In this case, the particle size (D50) of the inorganic particles contained in the adhesive layer and the heat-resistant layer is preferably about 0.1 to 0.6 μm. In this specification, the particle size (D50) of the inorganic particles refers to the average particle diameter of 50 wt% of the particles, calculated from the smallest particle size, in the particle size distribution measured by laser diffraction.

[0055] In the preparation step S10, the storage cell 100 may be prepared in which the numerical range of the cell thickness change is 0.3% or more (≧0.3), or the cell thickness change may be measured in the preparation step S10 using the method described above to confirm that the numerical range of the cell thickness change of the storage cell 100 is 0.3% or more (≧0.3).

[0056] Although there is no particular upper limit to the amount of change in cell thickness, the thickness of the energy storage cells 100 in the pre-constraint state (before stack assembly) increases accordingly as the amount of change in cell thickness increases. Therefore, from the viewpoint of downsizing the assembly device in the stacking step S20 and saving labor in the stacking step S20, it is preferable that the amount of change in cell thickness be 2.0% or less.

[0057] (Lamination step S20) In the stacking step S20, a plurality of energy storage cells 100 are stacked along the thickness direction X of the energy storage cells 100. The stacking step S20 may be the same as a conventionally known stack manufacturing method. Here, the plurality of energy storage cells 100 are sandwiched between a pair of end plates 310 in the arrangement direction X, and are constrained by side plates 320 and a plurality of screws 330. At this time, a restraining load is applied in the stacking direction of the energy storage cells 100 by the restraining mechanism 300. In this manner, the stack 500 according to this embodiment is manufactured. The restraining load during cell stacking in the stacking step S20 may be, for example, 2 to 30 kN, and preferably 3 to 20 kN.

[0058] <Method of manufacturing the energy storage cell 100> Although not particularly limited, the energy storage cell 100 in the preparation step S10 can be prepared, for example, by the manufacturing method described below. The manufacturing method of the energy storage cell 100 described below is an example of the preparation step S10 in this specification. FIG. 11 is a flow diagram showing a manufacturing method of the energy storage cell 100 according to one embodiment. As shown in FIG. 11 , although not particularly limited, the energy storage cell 100 can be manufactured by a manufacturing method that typically includes, for example, an assembly step S101, a drying step S102, a liquid injection step S103, a degassing and charging step S104, a pressure reduction step S105, a liquid injection hole sealing step S106, an activation step S107, and an aging step S108, in this order. Furthermore, the manufacturing method of the energy storage cell 100 disclosed herein may include other steps at any stage in addition to the above steps, and the remaining manufacturing process may be the same as conventional methods.

[0059] (Assembly process S101) In the assembly step S101, the wound electrode body 20 is placed in the case 10 (exterior body 12) to prepare an assembly. In this specification, the term "assembly" refers to an energy storage cell that has been assembled to a state prior to the liquid injection hole sealing step described below.

[0060] In the assembly process S101, the positive electrode second current collecting portion 52 is attached to the positive electrode tab group 23 of the wound electrode body 20, and further, the negative electrode current collecting portion 60 and the negative electrode second current collecting portion 62 are attached to the negative electrode tab group 25. Next, the positive electrode terminal 30 and the negative electrode terminal 40 are attached to the sealing plate 14. Next, the positive electrode terminal 30 and the positive electrode first current collecting portion 51, and the negative electrode terminal 40 and the negative electrode first current collecting portion 61 are respectively joined by a conventionally known method (e.g., ultrasonic welding, resistance welding, laser welding, etc.). Next, the wound electrode body 20 is housed in an insulating sheet. The insulating sheet can be prepared, for example, by folding an insulating resin sheet made of a resin material such as polyethylene (PE) into a bag or box shape. Then, it is preferable to house (insert) the wound electrode body 20 covered with the insulating sheet into the internal space of the exterior body 12. Then, the exterior body 12 of the case 10 and the sealing plate 14 are joined to produce an assembly. Such joining can be performed by welding, for example, laser welding, etc. In the assembly step S101, the liquid injection hole 15 is not sealed.

[0061] In the assembly step S101, the wound electrode body 20 is preferably arranged in a direction (short side direction X) in which the thickness direction of the energy storage cell 100 (in other words, a direction approximately perpendicular to the first side wall 12b of the case 10) coincides with the thickness direction of the wound electrode body 20. In other words, the wound electrode body 20 is preferably arranged inside the exterior body 12 so that the winding axis WL is parallel to the bottom 12a of the exterior body 12.

[0062] (Drying process S102) In the drying step S102, the assembly is dried to remove moisture contained in the assembly (for example, the inside of the wound electrode body 20, etc.). Such drying can be performed by a known method. For example, the drying step S102 can be performed by transporting the assembly (the case 10 containing the wound electrode body 20) to a drying furnace (not shown) and heating it.

[0063] The drying temperature and drying time in the drying step S102 can be adjusted as appropriate depending on the amount of moisture contained in the wound electrode assembly 20, etc. The drying temperature is not particularly limited as long as it is within a range that can remove moisture, but it is desirable to dry at a temperature that does not damage the separator 26 of the wound electrode assembly 20. Furthermore, the drying step S102 is preferably performed in a reduced pressure atmosphere. This allows the drying time in the drying step S102 to be shortened. However, this is not a limitation, and the drying step S102 may also be performed in an atmospheric pressure atmosphere. Note that the drying step S102 is not an essential step in the technology disclosed herein. In some preferred embodiments, the drying step S102 can be omitted.

[0064] (Liquid injection process S103) In the liquid injection step S103, a nonaqueous electrolyte is injected into the case 10 housing the wound electrode body 20 through an injection hole 15 provided in the sealing plate 14. The liquid injection step S103 may be performed in an atmospheric pressure atmosphere or a reduced-pressure atmosphere, but is preferably performed in a reduced-pressure atmosphere. This improves the impregnation of the nonaqueous electrolyte into the wound electrode body 20, allowing the liquid injection step S103 to be completed in a shorter time. In the liquid injection step S103, the nonaqueous electrolyte is injected in an amount that will spread throughout the entire wound electrode body 20. A conventionally known nonaqueous electrolyte injection device can be used as appropriate for the liquid injection step S103. Note that, as with conventional methods, examples of pressurized gases that can be used to pressure-feed the nonaqueous electrolyte include inert gases such as nitrogen (N2) and dry air. After the liquid injection step S103 is completed, it is preferable to appropriately pressurize or depressurize the inside of the case 10.

[0065] (Gas removal and charging process S104) In the degassing and charging step S104, the assembly is charged. This allows a coating to be formed on the surface of the negative electrode active material layer 24a. Furthermore, by discharging gas generated during charging and discharging to the outside of the case 10, the amount of gas generated inside the case 10 after the liquid inlet 15 is sealed is reduced, and gas retention within the wound electrode body 20 after the liquid inlet 15 is sealed can be suppressed. The charging conditions in this step are not particularly limited and may be the same as those in conventional manufacturing methods. Although not particularly limited, for example, the degassing and charging step S104 can be performed by charging at a current of about 0.05 C to 10 C in a room temperature environment (e.g., 25°C) until the SOC (State of Charge) reaches about 20% to 90%.

[0066] The degassing and charging step S104 is preferably performed with the case 10 restrained and a load applied to the case 10. This facilitates the expulsion of gas from the case 10, thereby suppressing gas buildup within the electrode body. When restraining the case 10 in the degassing and charging step S104, a load is preferably applied to the first side wall 12b of the case 10. Furthermore, when restraining the case 10 in this manner, it is preferable that the center CP of the wound electrode body 20 (see FIG. 3) and the center of the restrained region are substantially aligned when viewed from the front from the first side wall 12b of the case 10. The restrained region is not particularly limited, but it is preferable that an area of ​​the first side wall 12b of the case 10, centered on the center CP of the wound electrode body 20, be restrained over a length of 280 to 295 mm in the long side direction Y and a length of 85 to 95 mm in the up-down direction Z. The load applied to the case 10 is not particularly limited, but is preferably 0.25 to 0.80 MPa. In this specification, the "center CP of the wound electrode body 20" refers to the point where the center MY in the long side direction Y and the center MZ in the up-down direction Z intersect perpendicularly on the surface of the wound electrode body 20 having the flat portion 20f (the surface facing the first side wall 12b of the case 10), as shown in Figure 3.

[0067] (Decompression step S105) In the depressurization step S105, the pressure inside the case 10 is reduced, thereby further discharging gas present inside the case 10 (for example, air or gas generated in the degassing / charging step S104) to the outside of the case 10. The depressurization step S105 may be the same as the means used in the depressurization step in conventional manufacturing methods of this type, and does not particularly characterize the technology disclosed herein, so further detailed description will be omitted. Note that the depressurization step S105 is not an essential step in the technology disclosed herein. In some preferred embodiments, the depressurization step S105 can be omitted.

[0068] (Injection hole sealing process S106) In the liquid inlet hole sealing step S106, the liquid inlet 15 of the assembly is sealed. The liquid inlet hole sealing step S106 may be the same as a conventionally known method for manufacturing the energy storage cell 100, and is not particularly limited. Here, the liquid inlet 15 is sealed with a metallic sealing member 16, and the sealing is performed by welding the metal portion of the sealing member 16 to the sealing plate 14 (the peripheral edge of the liquid inlet 15). However, the method for sealing the liquid inlet 15 is not limited to this. Although not shown in the drawings, the liquid inlet 15 may also be sealed with a rivet such as a blind rivet.

[0069] (Activation step S107) In the activation step S107, the energy storage cell 100, whose liquid injection hole 15 has been sealed through the liquid injection hole sealing step S106, is charged while a load is applied in the thickness direction of the energy storage cell 100. This causes a coating to be formed on the surface of the negative electrode active material layer 24a. The activation step S107 is included as an example of the "preparation step S10" in this specification.

[0070] The charging conditions in the activation step S107 are not particularly limited and may be the same as those in conventional manufacturing methods. For example, the activation step S107 can be performed by charging at a current of about 0.05 C to 10 C in a room temperature environment (e.g., 25°C) until the SOC (State of Charge) reaches about 20% to 90%.

[0071] In the activation step S107, the load applied to the energy storage cell 100 is preferably 0.5 to 0.7 MPa. This configuration allows the amount of change in cell thickness to fall within a more suitable range. The method for applying the load to the energy storage cell 100 is not particularly limited, and any general means that can be employed in conventional energy storage cell manufacturing methods can be used. For example, the load can be applied to the energy storage cell 100 by sandwiching the pair of first side walls 12b of the energy storage cell 100 between restraining plates and connecting the restraining plates with a bridging member.

[0072] (Aging process S108) In the aging step S108, the energy storage cell 100 that has undergone the activation step S107 is stored in a predetermined temperature environment for a predetermined time while maintaining the charged state. This allows a coating to be more suitably formed on the surface of the negative electrode active material layer 24a. Note that the aging step S108 is not an essential step in the technology disclosed herein. In some preferred embodiments, the aging step S108 can be omitted.

[0073] The conditions for the aging step S108 can be adjusted appropriately depending on the desired form of coating formation and are not particularly limited. For example, the cell temperature (aging temperature) in the aging step S108 can be set to 30°C or higher, preferably 40°C or higher, for example 50°C or higher, or even 60°C or higher. There is no particular upper limit to the aging temperature, but a temperature of approximately 70°C or lower can be used as a guide. Temperature control in the aging step S108 can be performed using, for example, a thermostatic bath. The duration of the aging step S108 (aging time) can be changed appropriately depending on, for example, the aging temperature and is not particularly limited. For example, when the aging temperature is set to approximately 45 to 65°C, the aging time is preferably set to approximately 3 to 30 hours.

[0074] Furthermore, in the aging step S108, aging is preferably performed while applying a load in the thickness direction X of the energy storage cell 100. The amount of load applied to the energy storage cell in the aging step S108 is not particularly limited, but is preferably 0.5 to 0.7 MPa. Furthermore, the process may proceed to the aging step S108 while maintaining the load applied in the activation step S107.

[0075] The stack 500 can be used for various purposes, and can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car, a truck, etc. The type of vehicle is not particularly limited, and examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0076] Hereinafter, examples of the technology disclosed herein will be described, but the technology disclosed herein is not intended to be limited to these examples.

[0077] <Preparing the storage cells> First, three energy storage cells for constructing a stack according to the example were prepared. The wound electrode assembly housed in the energy storage cell according to the example had a pair of curved portions as shown in FIG. 5, and a strip-shaped positive electrode and a strip-shaped negative electrode were stacked via a strip-shaped separator and wound in the longitudinal direction. The separator used in Example 1 had an adhesive layer and a heat-resistant layer, the adhesive layer had an area ratio of 30%, and the inorganic particles contained in the heat-resistant layer had a particle size of 0.5 μm. The width of the negative electrode active material layer formation region of the energy storage cell according to the example was 29 cm, and the electrode assembly aspect ratio (the ratio (Ln / T) of the width direction length Ln of the negative electrode active material layer to the height T of the wound electrode assembly) was 3.0. The number of stacked positive electrodes in the wound electrode assembly was 33.

[0078] Next, as Example 2, three storage cells of Example 2 were prepared, which were the same as the storage cell of Example 1 except that a separator was used in which the adhesive layer formation area ratio was 7% and the particle size of the inorganic particles in the adhesive layer was 0.3 μm.

[0079] As Comparative Example 1, three energy storage cells according to Comparative Example 1 were prepared, which were the same as the energy storage cell according to Example 1 except that a separator was used in which the proportion of the area in which the adhesive layer was formed was 100% and the particle size of the inorganic particles in the adhesive layer was 1.0 μm. Similarly, as Comparative Example 2, three energy storage cells according to Comparative Example 2 were prepared, which were the same as the energy storage cell according to Example 1 except that a separator similar to that of Comparative Example 1 was used and that charging and discharging were performed while applying a load of 0.4 MPa in the thickness direction of the energy storage cell in the activation step. Furthermore, as Comparative Example 3, three storage cells according to Comparative Example 3 were prepared, which were the same as the storage cell according to Example 1 except that an electrode body (i.e., an electrode body that was not a wound electrode body) having a so-called laminated structure in which a substantially rectangular positive electrode and a substantially rectangular negative electrode were laminated in the thickness direction X of the storage cell via a substantially rectangular separator was used, the aspect ratio of the electrode body was 1.6, the shape of the case was changed in conjunction with the change in the electrode body (however, the plate thickness and material were not changed), and charging and discharging were performed while applying a load of 0.18 MPa in the thickness direction of the storage cell during the activation process.

[0080] <Evaluation of cell thickness change> The amount of change in cell thickness was evaluated for the energy storage cells according to Examples 1 and 2 and Comparative Examples 1 to 3 using the method described above. The autograph used was a precision universal testing machine (Autograph AGX-V) manufactured by Shimadzu Corporation. The cell thickness was measured using a laser displacement meter LK-G157 manufactured by Keyence Corporation. First, as shown in FIG. 10 , the energy storage cell was set in the autograph. Then, a load was applied to the energy storage cell in the thickness direction (indicated by the white arrow) at a rate of 0.1 mm / min. After the load applied to the energy storage cell reached 0.1 MPa, the load was reduced to 0.01 MPa at a rate of 0.1 mm / min. This process constituted one cycle, and five cycles of this process were performed. In this manner, Fs curves (load-displacement curves) for the first and fifth cycles were obtained. From the obtained Fs curve, the cell thickness X1 at the first cycle when the surface pressure was 0.04 MPa and the cell thickness X5 at the fifth cycle when the surface pressure was 0.04 MPa were obtained, and the cell thickness change (%) was calculated using X1 and X5 according to formula (i). The results are shown in Table 1. Cell thickness change (%) = (X1 - X5) / X1 × 100 Equation (i)

[0081] [Table 1]

[0082] <0.3~3kN spring constant> A "0.3 to 3 kN spring constant" was calculated for the energy storage cells according to Examples 1 and 2 and Comparative Examples 1 to 3. In this specification, the "0.3 to 3 kN spring constant" is an index showing the degree of release of the stack restraint load when the cell thickness is reduced. Specifically, based on the Fs curve obtained above, a graph was created in which the change in cell thickness between the first and fifth cycles under the same load was plotted on the horizontal axis as Δcell thickness (mm) and the applied load (kN) on the vertical axis. Then, the spring constant when the load range was 0.3 to 3 kN was calculated as the "0.3 to 3 kN spring constant (kN / mm)." The "0.3 to 3 kN spring constant" was calculated using the following formula (ii). The results are shown in Table 1. 0.3~3kN spring constant (kN / mm) = -((3-0.3)(kN) / (Δ cell thickness at 3kN - Δ cell thickness at 0.3kN))(mm) Equation (ii) 12 is a graph plotting the change in cell thickness between the first and fifth cycles under the same load as Δcell thickness (mm) on the horizontal axis and the applied load (kN) on the vertical axis for Examples 1 and 2 and Comparative Example 2. In the graph of FIG. 12, the region where the load is between 0.3 and 3 kN is indicated by a thick line.

[0083] <Result> As can be seen from Table 1, Examples 1 and 2, in which the cell thickness change was 0.3% or more (≧0.3), had a lower "0.3 to 3 kN spring constant" compared to Comparative Examples 1 to 3. This indicates that even when the cell thickness is reduced due to a low temperature environment, low SOC conditions, or the like, the thickness of the energy storage cell is suitably controlled (the energy storage cell thickness increases again), thereby minimizing the degree of loss of the stack restraint load. Therefore, in a stack manufactured using energy storage cells in which the cell thickness change was 0.3% or more (≧0.3), even when the energy storage cell thickness is reduced, the energy storage cell thickness is suitably controlled, thereby minimizing the decrease in the stack restraint load (minimizing loss of the restraint load).

[0084] Although preferred embodiments of the present disclosure have been described above, the above embodiments are merely examples. The present disclosure can be implemented in various other forms. The present disclosure can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modifications, and it is also possible to add other modifications to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it can be deleted as appropriate.

[0085] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A method for manufacturing a stack including a plurality of rectangular storage cells, the method comprising: a preparation step of preparing the storage cells including a flat wound electrode body formed by stacking and winding a positive electrode and a negative electrode with a separator interposed therebetween, a non-aqueous electrolyte, and a case that accommodates the wound electrode body and the non-aqueous electrolyte; and a stacking step of stacking the plurality of storage cells in a thickness direction of the storage cells, wherein a load of 0.1 mm is applied to the storage cells prepared in the preparation step in the thickness direction of the storage cells. a storage cell thickness X1 at a surface pressure of 0.04 MPa on the pressure-side Fs curve in the first cycle and a storage cell thickness X5 at a surface pressure of 0.04 MPa on the pressure-side Fs curve in the fifth cycle satisfying the following formula: (X1-X5) / X1×100≧0.3. Item 2: The method for manufacturing a stack according to Item 1, wherein the negative electrode comprises a negative electrode core and a negative electrode active material layer formed on the negative electrode core, and the length Ln of the negative electrode active material layer in a width direction perpendicular to the longitudinal direction of the wound electrode body is 20 cm or more. Item 3: The method for producing a stack according to Item 2, wherein, when the length of the wound electrode body in a direction perpendicular to the winding axis direction and perpendicular to the thickness direction of the wound electrode body is defined as a height T of the wound electrode body, a ratio (Ln / T) of the length Ln in the width direction of the negative electrode active material layer to the height T of the wound electrode body is 2.8 to 3.2. Item 4: The method for manufacturing a stack according to any one of items 1 to 3, wherein the preparation step includes an activation step of charging the storage cells while applying a load to the storage cells in a thickness direction of the storage cells, and the load applied to the storage cells in the activation step is 0.5 to 0.7 MPa. Item 5: The method for producing a stack according to any one of Items 1 to 4, wherein the number of stacked positive electrodes is 30 or more. Item 6: The method for manufacturing a stack according to any one of Items 1 to 5, wherein the relationship between the storage cell thickness X1 at a surface pressure of 0.04 MPa on the pressure-side Fs curve in the first cycle and the storage cell thickness X5 at a surface pressure of 0.04 MPa on the pressure-side Fs curve in the fifth cycle further satisfies the following formula: (X1-X5) / X1×100≦2.0. [Explanation of symbols]

[0086] 10 cases 12 Exterior body 14 Sealing plate 20 Wound electrode body 22 Positive electrode 24 Negative electrode 26 Separator 26s void 100 storage cells 300 Restraint mechanism 500 stacks 600 Autograph S10 Preparation process S20 Lamination Process S101 Assembly process S102 Drying process S103 Liquid injection process S104 Gas removal and charging process S105 Decompression process S106 Liquid injection hole sealing process S107 Activation process S108 Aging process

Claims

1. A method for manufacturing a stack including a plurality of rectangular energy storage cells, The battery comprises a flat wound electrode body formed by stacking and winding a positive electrode and a negative electrode with a separator interposed therebetween, a non-aqueous electrolyte, and a case that accommodates the wound electrode body and the non-aqueous electrolyte, the negative electrode includes a negative electrode core and a negative electrode active material layer formed on the negative electrode core, a width direction length Ln of the negative electrode active material layer perpendicular to the longitudinal direction of the wound electrode body is 20 cm or more; a preparation step of preparing the storage cell in which the number of stacked layers of the positive electrode is 30 or more; a stacking step of stacking a plurality of the energy storage cells along a thickness direction of the energy storage cells, When a process of applying a load to the storage cell prepared in the preparing step in a thickness direction of the storage cell at a rate of 0.1 mm / min up to 0.1 MPa and then reducing the load to 0.01 MPa at a rate of 0.1 mm / min was defined as one cycle and the process was performed for five cycles, The relationship between the storage cell thickness X1 at a surface pressure of 0.04 MPa on the pressure-side F-s curve in the first cycle and the storage cell thickness X5 at a surface pressure of 0.04 MPa on the pressure-side F-s curve in the fifth cycle is The following formula: (X1-X5) / X1×100≧0.3 fulfill, Stack manufacturing method.

2. When the length in a direction perpendicular to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is defined as the height T of the wound electrode body, a ratio (Ln / T) of a length Ln in the width direction of the negative electrode active material layer to a height T of the wound electrode body is 2.8 to 3.2; A method for manufacturing the stack of claim 1 .

3. the preparation step includes an activation step of charging the storage cell while applying a load in a thickness direction of the storage cell, In the activation step, a load applied to the storage cell is 0.5 to 0.7 MPa. A method for manufacturing a stack according to claim 1 or 2.

4. The relationship between the storage cell thickness X1 at a surface pressure of 0.04 MPa on the pressure-side F-s curve in the first cycle and the storage cell thickness X5 at a surface pressure of 0.04 MPa on the pressure-side F-s curve in the fifth cycle is The following formula: (X1-X5) / X1×100≦2.0 Further satisfying the A method for manufacturing a stack according to claim 1 or 2.

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