Secondary battery

Abstract

Provided is a secondary battery in which an electrolyte solution is easily retained and circulated in an electrode body. A secondary battery according to the present disclosure is provided with an electrode body having a zigzag structure and an electrolyte solution. The electrode body has a first outer surface and a second outer surface. The electrolyte solution includes a remaining liquid disposed at least between the first outer surface and the case. The diaphragm has a plurality of first protrusions including first bent portions on the first outer surface, and a plurality of second protrusions including second bent portions on the second outer surface. The first protruding part is provided with a plurality of through holes. The protruding length of the second protruding portion is larger than the protruding length of the first protruding portion.

Description

Technical Field

[0001] This disclosure relates to a secondary battery. Background Technology

[0002] Previously, secondary batteries having an electrode body and an electrolyte were known, wherein the electrode body was a zigzag structure in which a strip-shaped separator was alternately folded and multiple electrodes (positive and negative electrodes) were sandwiched in (for example, see Japanese Patent Application Publication No. 2007-305464, Japanese Patent Application Publication No. 2010-157366, Japanese Patent Application Publication No. 2013-149627, Japanese Patent Application Publication No. 2016-143550, Japanese Patent Application Publication No. 2018-067396, and International Publication No. 2019 / 064740).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-305464

[0006] Patent Document 2: Japanese Patent Application Publication No. 2010-157366

[0007] Patent Document 3: Japanese Patent Application Publication No. 2013-149627

[0008] Patent Document 4: Japanese Patent Application Publication No. 2016-143550

[0009] Patent Document 5: Japanese Patent Application Publication No. 2018-067396

[0010] Patent Document 6: International Publication No. 2019 / 064740 Summary of the Invention

[0011] According to the inventors' research, in secondary batteries with a tortuous electrode body and electrolyte structure, the folded portion of the separator may obstruct the flow of electrolyte to the inner plates. This results in a localized insufficiency of electrolyte held and circulated within the electrode body, leading to problems such as electrolyte depletion or uneven salt concentration within the electrode body. This problem is particularly pronounced in applications involving repeated high-rate charge-discharge cycles, such as automotive applications.

[0012] The present invention was made in view of the above circumstances, and its main objective is to provide a secondary battery in which the electrolyte is easily maintained and circulated in the electrode body.

[0013] The disclosed secondary battery comprises: an electrode body having a zigzag structure in which a strip-shaped separator is alternately folded, and a plurality of positive electrodes and a plurality of negative electrodes are sandwiched between the zigzag separator; an electrolyte; and a housing containing the electrode body and the electrolyte. The electrode body has a pair of outer surfaces arranged facing each other, the outer surfaces including: a first outer surface on which a first end face of the positive electrode and a first end face of the negative electrode are disposed; and a second outer surface on which a second end face of the positive electrode and a second end face of the negative electrode are disposed. The electrolyte includes at least residual liquid disposed between the first outer surface and the housing. The separator has a plurality of first protrusions on the first outer surface that protrude beyond the first end face of the negative electrode, and a plurality of second protrusions on the second outer surface that protrude beyond the second end face of the negative electrode. The first protrusions include first bends in the separator, and the second protrusions include second bends in the separator. A plurality of through holes are provided in the first protrusions. The protruding length L2 of the second protrusion is greater than the protruding length L1 of the first protrusion.

[0014] Based on the above structure, it is easy to maintain and circulate the electrolyte within the electrode body. Attached Figure Description

[0015] Figure 1 This is a perspective view schematically illustrating one embodiment of a secondary battery.

[0016] Figure 2 Is to make Figure 1 A 3D diagram of a secondary battery flipped up and down.

[0017] Figure 3 It is along Figure 1 A schematic longitudinal section view of line III-III.

[0018] Figure 4 It is along Figure 1 A schematic longitudinal section view of line IV-IV.

[0019] Figure 5 This is a diagram showing a portion of a diaphragm in one example.

[0020] Figure 6 It is a variation of the example and Figure 1 A fairly accurate diagram. Detailed Implementation

[0021] Hereinafter, preferred embodiments of the present disclosure will be described with appropriate reference to the accompanying drawings. Furthermore, matters not mentioned in this specification but necessary for the implementation of this disclosure can be understood by those skilled in the art based on prior art in the field. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Additionally, in the following drawings, components and parts that perform the same function are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified. Furthermore, the expression "A~B" indicating a range in this specification includes the meaning of more than A and less than B, and also includes the meaning of "greater than A" and "less than B".

[0022] Furthermore, in this specification, "secondary battery" refers to all energy storage devices capable of repeated charging and discharging. Additionally, in this specification, "lithium-ion secondary battery" refers to a secondary battery that utilizes lithium ions as charge carriers and achieves charging and discharging through the movement of lithium ions between the positive and negative electrodes.

[0023] Figure 1 This is a perspective view of a secondary battery 100 according to one embodiment. Figure 2 Is to make Figure 1 A 3D view of a 100-cell secondary battery flipped up and down. Figure 3 It is along Figure 1 A schematic longitudinal sectional view along line III-III shows the internal structure of the secondary battery 100. The secondary battery 100, in practical use (e.g., when installed in a vehicle for automotive applications), can... Figure 1 This is the configuration. Furthermore, in the following description, the reference numerals L, R, F, Rr, U, and D in the accompanying drawings represent left, right, front, back, top, and bottom, respectively. The reference numerals X, Y, and Z in the accompanying drawings represent the short side direction, the long side direction orthogonal to the short side direction, and the up / down direction orthogonal to both the short and long side directions of the secondary battery 100, respectively. The short side direction X and the long side direction Y are typically horizontal. The up / down direction Z is typically vertical.

[0024] The secondary battery 100 in this embodiment is a lithium-ion secondary battery. Therefore, the secondary battery 100 possesses excellent battery characteristics such as high energy density and high capacity. In other embodiments, the secondary battery may be a secondary battery other than a lithium-ion secondary battery (e.g., a sodium-ion secondary battery). The secondary battery 100 is preferably a non-aqueous electrolyte secondary battery, such as a lithium-ion secondary battery.

[0025] like Figure 3 As shown, the secondary battery 100 includes a casing 10, an electrode body 20, and an electrolyte (not shown). Additionally, the secondary battery 100 also includes a positive terminal 30 and a negative terminal 40.

[0026] <Shell>

[0027] The housing 10 is a frame that houses the electrode body 20 and the electrolyte. For example... Figure 1 , Figure 2 As shown, the housing 10 has a flat, bottomed cuboid shape. That is, the housing 10 is square. Therefore, the secondary battery 100 is a square lithium-ion secondary battery. However, the shape of the housing 10 is not limited to this. Since space efficiency is improved when multiple secondary batteries 100 are used to form a battery module, the housing 10 is preferably square.

[0028] The material of the housing 10 can be the same as conventionally used materials (e.g., metal, resin, etc.), without particular limitation. From the viewpoint of strength, thermal conductivity, etc., the material of the housing 10 is preferably metal, and more preferably aluminum, aluminum alloy, iron, iron alloy, etc. In addition, the housing 10 may also be made of laminated film.

[0029] like Figures 1-3 As shown, the housing 10 includes a housing body 12, a first sealing plate 14, and a second sealing plate 16. The housing body 12 is cylindrical. Figure 3 As shown, the housing body 12 has a first opening 12e at one end in the long side direction Y, and a second opening 12f at the other end in the long side direction Y. A first sealing plate 14 seals the first opening 12e, and a second sealing plate 16 seals the second opening 12f. The housing 10 is integrated by joining (e.g., welding) the first sealing plate 14 and the second sealing plate 16 at the first opening 12e and the second opening 12f of the housing body 12, respectively. The housing 10 is hermetically sealed. Thus, the secondary battery 100 is a sealed battery.

[0030] The shell 10 is hexahedral in shape, having a pair of first faces, a pair of second faces, and a pair of third faces. More specifically, as... Figure 1 As shown, the housing body 12 includes: a generally rectangular bottom surface 12a; a pair of long side surfaces 12b extending from the long side of the bottom surface 12a and facing each other; and a top surface 12c connecting the upper ends of the pair of long side surfaces 12b to each other. The top surface 12c is generally rectangular in shape. The top surface 12c faces the bottom surface 12a. Here, the bottom surface 12a and the top surface 12c form a pair of first surfaces, and the pair of long side surfaces 12b form a pair of second surfaces. The area of ​​the long side surfaces 12b is preferably larger than the area of ​​the bottom surface 12a and larger than the area of ​​the top surface 12c. The housing body 12 is formed, for example, by bending a metal sheet into a cylindrical shape and joining the seams (e.g., by welding). In the example shown, the welded joint 12d is located on the top surface 12c. Furthermore, the welded joint 12d may be located on the bottom surface 12a or on the long side surface 12b.

[0031] like Figure 2As shown, a gas discharge valve 13 is provided on the bottom surface 12a of the housing body 12. The gas discharge valve 13 is configured to break when the pressure inside the housing 10 reaches a predetermined value, thereby discharging the gas inside the housing 10 to the outside of the housing 10. Furthermore, in this embodiment, there is one gas discharge valve 13, but there may be two or more. In this embodiment, the gas discharge valve 13 is provided on the bottom surface 12a, but it is not limited to this. In other embodiments, the gas discharge valve 13 may also be provided on a surface other than the bottom surface 12a, such as the long side surface 12b, the top surface 12c, the first sealing plate 14, the second sealing plate 16, etc. Furthermore, the area of ​​the gas discharge valve 13 is arbitrary.

[0032] In this embodiment, the gas discharge valve 13 has a cross-shaped notch, but the shape of the gas discharge valve 13 is not particularly limited. In other embodiments, the gas discharge valve 13 can be a thin-walled portion, a groove, or a valve body welded to the housing 10. The gas discharge valve 13 can be, for example, a linear (only vertical or horizontal lines) notch, or a conventionally known elliptical valve (with a notch inside) or circular valve (with a notch inside). Furthermore, the size of the notch (e.g., length, depth, etc.) is arbitrary and can be appropriately determined, for example, by taking into account the pressure resistance of the housing 10.

[0033] The first sealing plate 14 and the second sealing plate 16 are plate-shaped components that seal the first opening 12e and the second opening 12f of the shell body 12. The first sealing plate 14 and the second sealing plate 16 are generally rectangular in shape when viewed from above. Here, the first sealing plate 14 and the second sealing plate 16 form a pair of third surfaces.

[0034] like Figure 1 As shown, a liquid injection hole 17 is provided in the first sealing plate 14. The liquid injection hole 17 is used to inject electrolyte into the interior of the housing 10 after the first sealing plate 14 and the second sealing plate 16 are assembled into the housing body 12. The liquid injection hole 17 is sealed by the sealing member 18 after the electrolyte is injected. In addition, in this embodiment, the liquid injection hole 17 is located below the positive terminal 30, but the location of the liquid injection hole 17 is not limited to this. In addition, in this embodiment, the liquid injection hole 17 is provided in the first sealing plate 14, but the liquid injection hole 17 can also be provided in the second sealing plate 16 or in the housing body 12.

[0035] <Electrode terminals>

[0036] The positive terminal 30 and the negative terminal 40 are respectively fixed to the housing 10. Here, the positive terminal 30 and the negative terminal 40 are fixed to opposite faces of the housing 10. More specifically, as... Figures 1-3As shown, the positive terminal 30 is mounted on the first sealing plate 14, and the negative terminal 40 is mounted on the second sealing plate 16. Specifically, the positive terminal 30 is mounted on the first sealing plate 14 in an insulated state from the first sealing plate 14. The negative terminal 40 is mounted on the second sealing plate 16 in an insulated state from the second sealing plate 16.

[0037] Furthermore, in this embodiment, the positive terminal 30 and the negative terminal 40 are respectively disposed on the first sealing plate 14 and the second sealing plate 16, but the configuration of the positive terminal 30 and the negative terminal 40 is not limited to this. In other embodiments, both the positive terminal 30 and the negative terminal 40 may be disposed on one of the first sealing plate 14 and the second sealing plate 16. The first sealing plate 14 and the second sealing plate 16 may also be disposed on the housing body 12. In addition, in this embodiment, the positive terminal 30 and the negative terminal 40 are disposed on a different surface from the gas discharge valve 13, but the positive terminal 30 and the negative terminal 40 may also be disposed on the same surface as the gas discharge valve 13.

[0038] However, by placing the positive terminal 30 and the negative terminal 40 on the first sealing plate 14 and the second sealing plate 16 respectively, as in this embodiment, the height (vertical dimension Z) of the secondary battery 100 can be reduced, making it easier to obtain a battery with high volumetric energy density. Furthermore, in this case, it is particularly easy to construct a battery module with high volumetric energy density for automotive applications.

[0039] The positive terminal 30 is preferably made of metal, more preferably of aluminum or an aluminum alloy. The negative terminal 40 is preferably made of metal, more preferably of copper or a copper alloy.

[0040] like Figure 3 As shown, the electrode body 20 has a convex positive electrode collector ear 23t at one end in the long side direction Y (the fifth outer surface 20e described later) that is electrically connected to the positive electrode 23. The positive electrode collector ear 23t is centrally mounted on the positive electrode current collector member 32. Additionally, the electrode body 20 has a convex negative electrode collector ear 24t at the other end in the long side direction Y (the sixth outer surface 20f described later) that is electrically connected to the negative electrode 24. The negative electrode collector ear 24t is centrally mounted on the negative electrode current collector member 42. Inside the housing 10, the positive electrode current collector member 32 is mounted on the first sealing plate 14 and electrically connected to the positive terminal 30. Inside the housing 10, the negative electrode current collector member 42 is mounted on the second sealing plate 16 and electrically connected to the negative terminal 40.

[0041] Thus, the positive terminal 30 is electrically connected to the positive electrode 23 of the electrode body 20 inside the housing 10 via the positive current collector 23t and the positive current collector 32. The negative terminal 40 is electrically connected to the negative electrode 24 of the electrode body 20 inside the housing 10 via the negative current collector 24t and the negative current collector 42. Furthermore, the configuration of electrically connecting the positive terminal 30 and the negative terminal 40 to the positive electrode 23 and the negative electrode 24 of the electrode body 20, respectively, is not limited to the configuration shown in the figure.

[0042] Electrolyte

[0043] The electrolyte and electrode body 20 are housed together inside the housing 10. In this embodiment, the electrolyte includes a liquid impregnated in the electrode body 20 (e.g., Figure 4 The upper part retains liquid 52 (described later) and the remaining liquid 50 not immersed in the electrode body 20 (see reference). Figure 4 The remaining liquid 50 is located between the electrode body 20 and the housing 10. In detail, the remaining liquid 50 is disposed at least between the first outer surface 20a of the electrode body 20 (described later) and the housing 10.

[0044] The electrolyte can be the same as that of a typical secondary battery, without particular limitations. Preferably, the electrolyte is a non-aqueous electrolyte containing a non-aqueous solvent (organic solvent) and a supporting salt (i.e., a non-aqueous electrolyte). Examples of non-aqueous solvents include carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The supporting salt, also known as the electrolyte salt, is, for example, a fluorinated lithium salt. Examples of fluorinated lithium salts include LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI). LiPF6 is preferred as the supporting salt. The electrolyte may also contain additives such as film-forming agents like vinylene carbonate (VC) and oxalic acid complexes; gas generators; thickeners; etc.

[0045] <Electrode>

[0046] The electrode body 20 is housed inside the housing 10. Figure 4 It is along Figure 1 A schematic longitudinal sectional view along line IV-IV shows the internal structure of the secondary battery 100. (See attached image.) Figure 4 As shown, in this embodiment, one electrode body 20 is housed inside a housing 10. However, the number of electrode bodies 20 housed inside a housing 10 is not particularly limited. In other embodiments, the number of electrode bodies 20 housed inside a housing 10 may be multiple (e.g., two). Additionally, the electrode body 20 may also be housed inside the housing 10 while being covered by a resin insulating sheet (electrode body support).

[0047] like Figure 4As shown, the electrode body 20 includes a plurality of positive electrodes 23, a plurality of negative electrodes 24, and a diaphragm 25 disposed between the positive electrodes 23 and the negative electrodes 24. Furthermore, Figure 4 This is a schematic diagram, therefore, it is recorded as the positive electrode 23 being separated from the diaphragm 25, and also as the negative electrode 24 being separated from the diaphragm 25. This is for the convenience of observing each component. In reality, the positive electrode 23 is in contact with the diaphragm 25, and the negative electrode 24 is in contact with the diaphragm 25.

[0048] The electrode surfaces of multiple positive electrodes 23 and multiple negative electrodes 24 extend along the YZ plane, respectively. The multiple positive electrodes 23 and multiple negative electrodes 24 are arranged along the short side direction X. The multiple positive electrodes 23 and multiple negative electrodes 24 are stacked with their orientation intersecting the vertical direction Z. Here, the short side direction X is the stacking direction of the positive electrodes 23 and negative electrodes 24. The separator 25 insulates the positive electrodes 23 and negative electrodes 24. The electrode body 20 is a stacked electrode body, which has higher electrolyte impregnation properties compared to a wound electrode body, and is particularly advantageous in terms of electrolyte injection during manufacturing. Furthermore, according to the stacked electrode body, it is easier to construct a battery with high volumetric energy density.

[0049] Furthermore, in this embodiment, the number of positive electrodes 23 is 3, the number of negative electrodes 24 is 4, and the number of separators 25 is 1. However, the number of positive electrodes 23, negative electrodes 24, and separators 25 is not particularly limited and can be appropriately determined according to the battery design. In the example shown, the number of negative electrodes 24 is one more than the number of positive electrodes 23. Therefore, in the stacked structure of positive electrodes 23 and negative electrodes 24, the outermost layer is always a negative electrode 24. In this case, the lithium contained in the positive electrode active material of the positive electrode 23 can be fully utilized, and the deposition of lithium in the negative electrode 24 can be highly prevented. Furthermore, in other embodiments, the number of positive electrodes 23 and negative electrodes 24 can be the same, or the number of positive electrodes 23 can be more than the number of negative electrodes 24. In addition, for example, the number of positive electrodes 23 and negative electrodes 24 can each be 20 or more. In addition, the number of separators 25 can also be multiple (e.g., 2).

[0050] The positive electrode 23 can be the same as before, without any particular limitation. The positive electrode 23 typically has a positive current collector and a layer of positive active material fixed to at least one surface of the positive current collector. The positive current collector is preferably made of metal, for example, a metal foil such as aluminum foil. In this embodiment, as... Figure 3 As shown, in the positive electrode 23, there is a portion where the positive electrode active material layer is not formed and the positive electrode current collector is exposed. This exposed portion constitutes the positive electrode current collector tab 23t.

[0051] The positive electrode active material layer contains a positive electrode active material capable of reversibly adsorbing and releasing charge carriers. Preferably, the positive electrode active material is an oxide containing at least one of Ni, Co, and Mn; examples include lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel manganese composite oxide, and lithium nickel cobalt manganese composite oxide, etc., which are lithium transition metal composite oxides. The positive electrode active material layer may also contain conductive materials, binders, etc., as needed. Furthermore, carbon materials such as carbon black and carbon nanotubes are preferred as conductive materials. Additionally, resin binders such as polyvinylidene fluoride are preferred as binders.

[0052] The negative electrode 24 can be the same as before, without any particular limitation. The negative electrode 24 typically has a negative current collector and a layer of negative active material fixed to at least one surface of the negative current collector. The negative current collector is preferably made of metal, such as copper foil or other metal foil. In this embodiment, as... Figure 3 As shown, in the negative electrode 24, there is a portion where the negative electrode active material layer is not formed and the negative electrode current collector is exposed. This exposed portion constitutes the negative electrode current collector tab 24t.

[0053] The negative electrode active material layer contains a negative electrode active material capable of reversibly absorbing and releasing charge carriers. Examples of negative electrode active materials include carbon materials such as graphite, hard carbon, and soft carbon; Si-containing materials such as Si and silicon oxide; Sn-containing materials such as Sn; and so on. The negative electrode active material layer may also contain conductive materials, thickeners, binders, etc., as needed. As a binder, styrene-butadiene rubber, carboxymethyl cellulose, etc., are preferred.

[0054] The separator 25 is a component that insulates the positive electrode active material layer from the negative electrode active material layer. The separator 25 preferably comprises a porous resin sheet made of resin. As a porous resin sheet, a porous resin sheet made of polyolefin resins such as polyethylene (PE), polypropylene (PP), or mixtures thereof is preferred. The porous resin sheet can be a single-layer structure or a multi-layer structure (e.g., a three-layer structure of PP / PE / PP).

[0055] Functional layers such as adhesive layers and heat resistance layers (HRL) can be formed on the surface of porous resin sheets as needed. Adhesive layers may contain adhesive resins such as acrylic resin and polyvinylidene fluoride. Heat resistance layers may contain ceramic particles such as alumina, boehmite, aluminum hydroxide, and titanium dioxide. Preferably, the heat resistance layer also includes an adhesive resin. The heat resistance layer can also serve as an adhesive layer.

[0056] In one embodiment, the diaphragm 25 includes a substrate made of a porous resin sheet and adhesive layers disposed on both sides of the substrate. In another embodiment, the diaphragm 25 includes a substrate made of a porous resin sheet, an adhesive layer disposed on one side of the substrate, and a heat-resistant layer disposed on the other side of the substrate. In this embodiment, the heat-resistant layer may also function as an adhesive layer. In yet another embodiment, the diaphragm 25 includes a substrate made of a porous resin sheet, an adhesive layer disposed on one side of the substrate, and a heat-resistant layer disposed on the other side of the substrate, and further includes a second adhesive layer disposed on the heat-resistant layer.

[0057] like Figure 4 As shown, the electrode body 20 has a first outer surface 20a and a second outer surface 20c as a pair of opposite outer surfaces. Here, the first outer surface 20a is the lower outer surface in the vertical direction, facing the bottom surface 12a of the housing 10. The first end face 231 (lower end face) of the positive electrode 23 and the first end face 241 (lower end face) of the negative electrode 24 are disposed on the first outer surface 20a. Here, the second outer surface 20c is the upper outer surface in the vertical direction, facing the top surface 12c of the housing 10. The second end face 232 (upper end face) of the positive electrode 23 and the second end face 242 (upper end face) of the negative electrode 24 are disposed on the second outer surface 20c. Preferably, the positive electrode collector tab 23t and the negative electrode collector tab 24t are not provided on the first outer surface 20a and the second outer surface 20c.

[0058] Furthermore, the electrode body 20 has a third outer surface 20b1 and a fourth outer surface 20b2 as a pair of main surfaces of the two outer surfaces constituting the stacking direction (short side direction X) of the positive electrode 23 and the negative electrode 24. The third outer surface 20b1 and the fourth outer surface 20b2 face a pair of long side surfaces 12b of the housing body 12. In this embodiment, the third outer surface 20b1 and the fourth outer surface 20b2 of the electrode body 20 are formed by a diaphragm 25. Figure 4 In cross-sectional observation, a pair of main surfaces (the third outer surface 20b1 and the fourth outer surface 20b2) are connected by the first outer surface 20a and the second outer surface 20c. Additionally, as... Figure 3 As shown, the electrode body 20 also has a fifth outer surface 20e and a sixth outer surface 20f as a pair of outer surfaces facing the first sealing plate 14 and the second sealing plate 16. A positive electrode collector ear 23t is provided on the fifth outer surface 20e. A negative electrode collector ear 24t is provided on the sixth outer surface 20f.

[0059] In this embodiment, from the viewpoint of charge carrier acceptability, when viewed from above, the size of the negative electrode 24 is formed to be larger than the size of the positive electrode 23. The area of ​​the negative electrode 24 (the area of ​​the negative electrode active material layer) is larger than the area of ​​the positive electrode 23 (the area of ​​the positive electrode active material layer). Figure 4As shown, the width (Z dimension in the vertical direction) of the negative electrode 24 is larger than the width of the positive electrode 23. This effectively prevents lithium deposition in the negative electrode 24. Furthermore, in other embodiments, the width of the negative electrode 24 may be the same as or smaller than the width of the positive electrode 23.

[0060] like Figure 4 As shown, in this embodiment, the electrode body 20 has a zigzag structure. That is, the diaphragm 25 is strip-shaped. In other words, the diaphragm 25 is elongated. Here, the diaphragm 25 is formed into a zigzag shape (also called a corrugated shape) that is alternately folded at predetermined intervals (length La). The diaphragm 25 is alternately folded at the ends of the electrodes (positive electrode 23 and negative electrode 24). The diaphragm 25 has a first bend and a second bend. The length La is the overall length of the electrode body 20 in the vertical direction Z. The plurality of positive electrodes 23 and the plurality of negative electrodes 24 are alternately sandwiched between the folded portions of the diaphragm 25. By making the diaphragm 25 zigzag, the manufacturing efficiency of the stacked electrode body can be improved.

[0061] The diaphragm 25 has an electrode-facing portion with a generally I-shaped cross-section facing the electrodes (positive electrode 23 and negative electrode 24) and a pair of protrusions with a generally U-shaped cross-section folded at the ends of the electrodes. The electrode-facing portion is the part facing at least one of the positive electrode 23 (typically a positive electrode active material layer) and the negative electrode 24 (typically a negative electrode active material layer). The electrode-facing portion is located at the center of the electrode body 20 in the vertical direction Z. Here, the electrode-facing portion extends along the YZ plane. The electrode-facing portion extends along the long side surface 12b of the housing 10. In addition, the pair of protrusions of the diaphragm 25 have a plurality of first protrusions 25a on the first outer surface 20a of the electrode body 20, protruding beyond the first end face 241 of the negative electrode 24, and a plurality of second protrusions 25c on the second outer surface 20c of the electrode body 20, protruding beyond the second end face 242 of the negative electrode 24. The first protrusion 25a and the second protrusion 25c are portions that do not face the main surfaces of the electrodes (positive electrode 23 and negative electrode 24). Here, the first protrusion 25a and the second protrusion 25c are formed by a diaphragm 25. They are protrusions that extend in a Z-direction upwards and downwards from the end faces 241 and 242 of the negative electrode 24.

[0062] The first protrusion 25a includes a folded portion (first bend) of the diaphragm 25. Here, the first protrusion 25a is folded in such a way that it covers the first end face 231 of the positive electrode 23. The first protrusion 25a extends toward the bottom surface 12a of the housing body 12. The first protrusion 25a faces the bottom surface 12a of the housing 10. The distance L0 from the bottom surface 12a of the housing body 12 to the front end (lower end, the folded portion of the diaphragm 25) of the first protrusion 25a is preferably, for example, 0.1 to 2.0 mm.

[0063] A plurality of through holes 25h are formed in the first protrusion 25a of the separator 25. In this embodiment, there is residual liquid 50 between the first outer surface 20a of the housing 10 and the electrode body 20 that is not impregnated in the electrode body 20. Therefore, by providing a plurality of through holes 25h in the first protrusion 25a of the separator 25 on the side of the first outer surface 20a of the electrode body 20 where the residual liquid 50 exists (the lower side in the vertical direction), the electrolyte can easily penetrate into the electrode body 20 through the through holes 25h. As a result, the impregnation of the electrolyte can be effectively improved in the secondary battery 100, especially on the side of the first outer surface 20a of the electrode body 20 (the lower side). Furthermore, even with repeated charging and discharging, the occurrence of liquid depletion can be effectively suppressed, and the electrolyte can be easily circulated within the electrode body 20.

[0064] Here, multiple through holes 25h are provided in the folded portion (bend) of the diaphragm 25. Preferably, the multiple through holes 25h are straight and short in the thickness direction of the diaphragm 25 when viewed in cross-section. This improves the electrolyte circulation efficiency. For example, the ratio (Lt) of the shortest path length (Lt) of the through holes 25h in the thickness direction of the diaphragm 25 to the thickness (t) of the diaphragm 25 is preferably less than 1.5, more preferably less than 1.2, and even more preferably less than 1.1. Lt / t can also be 1. Furthermore, while multiple fine through holes (micropores) capable of allowing charge carriers to pass through are typically irregularly formed in the diaphragm 25, the "through holes 25h" referred to herein differs from the aforementioned micropores and are typically regularly arranged, for example, with a larger pore diameter (e.g., width W or length D1 described later).

[0065] Figure 5 This is a developed diagram showing a portion of a septum 25 in one example. For example... Figure 5 As shown, the plurality of through holes 25h are perforated or wire-like cuts. These perforated or wire-like cuts are regularly arranged at predetermined intervals of 2La along the length of the strip-shaped diaphragm 25 (a direction orthogonal to the long side direction Y). Here, the plurality of through holes 25h are rectangular in shape and arranged in a linear pattern, spaced apart along the long side direction Y. However, in other embodiments, they may also be arranged in a linear pattern, spaced apart along the length direction. Such a plurality of through holes 25h can be formed using conventionally known methods, such as laser cutting or piercing with a knife. The size of the through holes 25h is not particularly limited and can be appropriately adjusted, for example, depending on the type of diaphragm 25 and the type of electrolyte used.

[0066] While not particularly limited, the width W (length of the shorter side in the X direction) of the rectangular through-hole 25h is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. The length D1 of the longer side of the rectangular through-hole 25h is preferably 0.1 mm or more, more preferably 0.5 mm or more, and even more preferably 1 mm or more. Furthermore, while the shape of the plurality of through-holes 25h is rectangular, other shapes (e.g., square, circular) are also possible. From the viewpoint of improving impregnation, the plurality of through-holes 25h are preferably arranged in a linear pattern (e.g., straight line). From the viewpoint of uniformly distributing the electrolyte across the electrode body 20, the plurality of through-holes 25h are preferably arranged regularly (at certain intervals). From the viewpoint of uniformly distributing the electrolyte across the electrode body 20, the interval D2 of the plurality of through-holes 25h is preferably 5 mm or less, more preferably 2 mm or less.

[0067] Furthermore, there is no particular limitation on the timing of forming the multiple through holes 25h in the separator 25. The multiple through holes 25h can be formed in advance in the separator 25, or, for example, a separator without through holes 25h can be prepared, and the multiple through holes 25h can be formed in the separator during the process of stacking the multiple positive electrodes 23 and the multiple negative electrodes 24, or at the same time as stacking the multiple positive electrodes 23 and the multiple negative electrodes 24.

[0068] The second protrusion 25c includes a folded portion (second bend) of the diaphragm 25. Here, the second protrusion 25c is folded to cover the second end face 242 of the negative electrode 24. The second protrusion 25c extends toward the top surface 12c of the housing body 12. The second protrusion 25c faces the top surface 12c of the housing 10. In some embodiments, it is preferable not to form multiple through holes in the second protrusion 25c of the diaphragm 25. This facilitates the retention of electrolyte in the second protrusion 25c (upper liquid retention 52). However, in other embodiments, through holes may be formed in the second protrusion 25c of the diaphragm 25 in a fewer number than, for example, fewer than in the first protrusion 25a.

[0069] like Figure 4As shown, in this embodiment, the protrusion length L2 of the second protrusion 25c in the separator 25 is greater than the protrusion length L1 of the first protrusion 25a. That is, L1 < L2. In particular, it is difficult for residual liquid 50 to exist on the second outer surface 20c side (the upper side in the vertical direction) of the electrode body 20, but by increasing the protrusion length L2 of the second protrusion 25c, it is easy to retain electrolyte in the second protrusion 25c (the upper part retains liquid 52). Therefore, in the secondary battery 100, especially on the second outer surface 20c side (the upper side) of the electrode body 20, the electrolyte retention can be effectively improved. Furthermore, even with repeated charging and discharging at high rates, the occurrence of liquid depletion can be effectively suppressed. In addition, it is possible to suppress large deviations in the amount of electrolyte retained in each electrode (positive electrode 23 and negative electrode 24).

[0070] In addition, such as Figure 4 As shown, the protrusion lengths L1 and L2 are the straight protrusion lengths of the protrusions 25a and 25c. In this embodiment, the protrusion length L1 of the first protrusion 25a is the length protruding downward from the first end face 241 of the adjacent negative electrode 24 (more specifically, the lower end of the negative electrode active material layer) (in the direction in which the negative electrode 24 extends). The protrusion length L2 of the second protrusion 25c is the length protruding upward from the second end face 242 of the negative electrode 24 (more specifically, the upper end of the negative electrode active material layer) (in the direction in which the negative electrode 24 extends). Furthermore, in the secondary battery 100, the protrusion 25a may also be in a state where it is flattened under the weight of the electrode body 20, thus reducing the protrusion length L1.

[0071] While not specifically limited, the protrusion length L2 of the second protrusion 25c is preferably 0.5 mm or more, more preferably 1.0 to 5.0 mm. By making the protrusion length L2 a predetermined value or more, more electrolyte can be retained in the second protrusion 25c, and the effects disclosed herein can be achieved at a higher level. In addition, by making the protrusion length L2 less than a predetermined value, the charge-discharge capacity increases, thereby improving the volumetric energy density. Furthermore, the protrusion length L1 of the first protrusion 25a is preferably 0.5 to 2.0 mm. Furthermore, the ratio of protrusion length L2 to protrusion length L1 (L2 / L1) is preferably 1.2 or more, more preferably 1.5 or more, and even more preferably 2.0 to 5.0.

[0072] like Figure 4 As shown, in some embodiments, the extension length L'2 of the second protrusion 25c along the extension direction of the diaphragm 25 is preferably greater than the extension length L'1 of the first protrusion 25a along the extension direction. That is, it is preferable that L'1 < L'2. As a result, electrolyte retention can be improved more effectively, especially on the second outer surface 20c side (upper side) of the electrode body 20.

[0073] In addition, such as Figure 4 As shown, the extension lengths L'1 and L'2 are the lengths of the protrusions 25a and 25c along the diaphragm 25 (the lengths along the generally U-shaped bend in cross-section). More specifically, for example, the extension length L'1 is the length along the bend of the diaphragm 25 from the position of the root of one of the first protrusions 25a (the portion connected to the electrode facing portion) facing the first end face 241 of the negative electrode 24 to the position of the root of the other protrusion (the portion connected to the electrode facing portion) facing the first end face 241 of the negative electrode 24.

[0074] While not specifically limited, the extension length L'2 of the second protrusion 25c is typically more than twice the protrusion length L2 of the second protrusion 25c, preferably 1 mm or more, more preferably 2.0 to 11.0 mm. By making the extension length L'2 a predetermined value or more, more electrolyte can be retained in the second protrusion 25c, and the effects disclosed herein can be achieved at a higher level. Furthermore, the extension length L'1 of the first protrusion 25a is preferably 1.0 to 5.0 mm. Additionally, the ratio of the extension length L'2 to the extension length L'1 (L'2 / L'1) is preferably 1.2 or more, more preferably 1.5 or more, and even more preferably 2.0 to 5.0.

[0075] In some embodiments, the liquid level H of the remaining liquid 50 is preferably located above the front end (lower end, the folded portion of the separator 25) of the first protrusion 25a of the separator 25 when the state of charge (SOC) of the secondary battery 100 is 0%. The height of the liquid level H of the remaining liquid 50 fluctuates depending on the state of charge of the secondary battery 100, but is generally lowest when the SOC = 0%. Therefore, if the liquid level H is adjusted so that it is located above the first protrusion 25a of the separator 25 when the SOC = 0%, the immersion of the remaining liquid 50 from the first protrusion 25a will proceed smoothly. Thus, the aforementioned effects can be achieved to a higher degree.

[0076] In some embodiments, the liquid level H of the remaining liquid 50 is more preferably located above the through hole 25h provided in the first protrusion 25a of the separator 25 when the charge rate of the secondary battery 100 is 0%. Therefore, during the charging and discharging of the secondary battery 100, the remaining liquid 50 can be maintained in a state of circulation (in and out) through the through hole 25h, and the aforementioned effects can be achieved to a higher level.

[0077] In some embodiments, the liquid level H of the remaining liquid 50 is more preferably located above the first end face 241 of the negative electrode 24 when the charge rate of the secondary battery 100 is 0%. This allows the remaining liquid 50 to smoothly immerse and circulate from the first end face 241 of the negative electrode 24, achieving the aforementioned effects at a particularly high level.

[0078] In some embodiments, the gas discharge valve 13 is preferably disposed in the housing 10 on a surface facing the first outer surface 20a of the electrode body 20 (here, the bottom surface 12a). This allows the gas generated within the electrode body 20 to easily move towards the gas discharge valve 13 through the through-hole 25h of the diaphragm 25. Consequently, the generated gas is easily discharged outside the housing 10.

[0079] As described above, in the secondary battery 100, a plurality of through holes 25h are formed in the first protrusion 25a of the separator 25, allowing the remaining liquid 50 to easily enter and exit through the through holes 25h. This is particularly effective on the first outer surface 20a side (lower side) of the electrode body 20, improving the impregnation properties of the electrolyte. Furthermore, in the secondary battery 100, the protrusion length L2 of the second protrusion 25c of the separator 25 is greater than the protrusion length L1 of the first protrusion 25a. This facilitates the retention of electrolyte in the second protrusion 25c (with liquid 52 retained in the upper part).

[0080] Such synergistic effects, according to the technology disclosed herein, even in situations such as Figure 4 When the secondary battery 100 is charged and discharged with the positive electrode 23 and negative electrode 24 arranged along the vertical direction (short side direction X), electrolyte depletion is less likely to occur in the electrode body 20. Furthermore, fluctuations in salt concentration within the electrode body 20 are more easily mitigated. Therefore, performance degradation and lithium deposition caused by charge-discharge cycles can be suppressed.

[0081] The secondary battery 100 can be used for various applications. Preferred applications include automotive applications, specifically, as a power source for driving electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Additionally, the secondary battery 100 can be used as a battery, such as a small energy storage device. The secondary battery 100 can also typically be used as a battery module formed by connecting multiple batteries in series and / or in parallel.

[0082] The following describes some test examples related to the present invention, but it is not intended to limit the present invention to these test examples.

[0083] <Making a Secondary Battery>

[0084] It was made with the following features Figure 4The stacked electrode body shown is a prismatic lithium-ion battery (width 308mm × depth 30mm × height 90mm, capacity 140Ah). The stacked electrode body is a zigzag structure formed by alternately folding a strip-shaped separator in the vertical direction during use. The stacked electrode body is assembled such that the length of the first protrusion of the separator protruding from the lower end face (first end face) of the negative electrode (vertical length to the fold line of the separator) is L1 in Table 1 below, and the length of the second protrusion of the separator protruding from the upper end face (second end face) of the negative electrode (vertical length to the fold line of the separator) is L2 in Table 1 below. In addition, multiple widths W are formed at certain intervals D2 on the fold line portion of the separator (the front end of the first protrusion). Figure 4 A through hole of rectangular shape with a length D1 (in the direction of the shorter side). The dimensions of the through hole are shown in Table 1 below.

[0085] The electrolyte level was adjusted so that the remaining liquid level H at the start of a charge-discharge cycle after battery completion was at a specified position above the bottom surface of the inner surface of the casing. In all test examples, the distance L0 from the bottom surface of the casing to the fold line of the separator (the front end of the first protrusion) and the position of the remaining liquid level H were consistent. In all test examples, the height of the remaining liquid level was adjusted so that even at its lowest point (zero charge), it was positioned above the lower end of the negative electrode. Batteries were manufactured in this manner (Examples 1 and 2, and Comparative Examples 1 and 2).

[0086] <Evaluation of Cyclic Characteristics>

[0087] First, the battery was adjusted to 50% SOC at 25°C. A discharge pulse load of 10 seconds was applied with a discharge current value I. The initial resistance IV was calculated by averaging the voltage drop ΔV obtained by dividing the voltage drop ΔV over 10 seconds by the discharge current value I. Here, the discharge current value I was measured at currents of 140A, 280A, and 420A (C1, 2, and 3C), and the average of the calculated initial resistance IV was set as the initial resistance IV.

[0088] Then, at 25°C, the fabricated battery was charged at a constant current rate of 70A (0.5C) until the charging cutoff voltage of 4.2V was reached, followed by a constant current discharge at a discharge rate of 70A (0.5C) until the discharge cutoff voltage of 2.5V was reached. This charge-discharge cycle was defined as 1 cycle, with a 60-second pause between charge and discharge cycles. This cycle was repeated 1000 times. After the cycle test, the IV resistance was measured in the same manner as the initial resistance. The resistance rise rate (%) was calculated based on the ratio of the IV resistance after the cycle test to the initial resistance (IV resistance after the cycle test / initial resistance). The results are shown in Table 1.

[0089] Table 1

[0090] Table 1

[0091]

[0092] As shown in Table 1, the resistance rise rate was highest in Comparative Example 1, where the first protrusion of the diaphragm did not have a through hole. Furthermore, the resistance rise rate was also high in Comparative Example 2, where L2 < L1. This can be attributed to insufficient electrolyte volume maintained and circulated within the electrode body. In practical applications, a resistance rise rate of less than 10% is preferable.

[0093] Compared to these comparative examples, in Examples 1 and 2, where the first protrusion of the diaphragm has a through-hole and L1 < L2, the rate of increase in resistance is significantly improved. This is because the depletion of the electrolyte and fluctuations in salt concentration within the electrode body are suppressed. Specifically, it is understood that the remaining liquid in the lower part of the electrode body (first outer surface side) easily enters from the electrode end face through the through-hole and circulates within the electrode body, and the electrolyte in the upper part of the electrode body (second outer surface side) is easily retained in the second protrusion of the diaphragm and easily circulates from the electrode end face into the electrode body. In particular, in Example 2, by lengthening L2 compared to Example 1, the amount of electrolyte retained in the second protrusion increases, thereby further suppressing the rate of increase in resistance. These results demonstrate the technical significance of the technology disclosed herein.

[0094] The above provides detailed examples of this disclosure, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes technologies obtained by various modifications and alterations to the above-described examples.

[0095] For example, the ends of the electrodes (positive electrode 23 and negative electrode 24) covered by each protrusion can be changed instead of the above. Figure 4 One possible implementation is that the bent portion of the diaphragm 25 included in the first protrusion 25a on the first outer surface 20a side (below) covers the first end face 241 of the negative electrode 24, and the bent portion of the diaphragm 25 included in the second protrusion 25c on the second outer surface 20c side (above) covers the second end face 232 of the positive electrode 23.

[0096] For example, in the above Figure 4 In one embodiment, an example is shown where the remaining liquid 50 exists only on the side of the first outer surface 20a (below), but it is also possible that the remaining liquid exists on the side of the second outer surface 20c (above). In this case, the amount of remaining liquid on the side of the first outer surface 20a (below) is greater than the amount of remaining liquid on the side of the second outer surface 20c (above).

[0097] The technology disclosed herein is more effective when the secondary battery 100 is used in an orientation in which the first outer surface 20a is positioned lower than the second outer surface 20c in the vertical direction. The technology disclosed herein is particularly effective when the secondary battery 100 is used in an orientation in which the stacking direction of the electrodes (positive electrode 23 and negative electrode 24) is perpendicular to the vertical direction.

[0098] For example, in the above Figures 1-3 In this embodiment, the positive terminal 30 is mounted on the first sealing plate 14, and the negative terminal 40 is mounted on the second sealing plate 16. Additionally, as... Figure 2 As shown, the gas discharge valve 13 is disposed on the bottom surface 12a of the housing 10. However, it is not limited to this.

[0099] Figure 6 It is a variation of the example and Figure 1 A comparable diagram. (For example...) Figure 6 As shown, in this modified example, the secondary battery 200 includes a housing 110. Here, the housing 110 includes a housing body 112 having an opening on one side (the upper side) and a sealing plate 114 that blocks the opening of the housing body 112. The housing body 112 includes: a generally rectangular bottom surface 112a; a pair of long side surfaces 112b extending from a pair of long sides of the bottom surface 112a and facing each other; and a pair of short side surfaces 112c extending from a pair of short sides of the bottom surface 112a and facing each other. Here, the positive terminal 130, the negative terminal 140, and the gas discharge valve 113 are mounted on the sealing plate 114 (the same side of the housing 10). In such a secondary battery 200, the technology disclosed herein can also be preferably applied.

[0100] As described above, the following are examples of specific methods that can be used as specific examples of the technology disclosed herein.

[0101] [1] A secondary battery, comprising: an electrode body having a zigzag structure in which a strip-shaped separator is alternately folded and a plurality of positive electrodes and a plurality of negative electrodes are sandwiched between the zigzag separator; an electrolyte; and a housing containing the electrode body and the electrolyte, the electrode body having a pair of outer surfaces arranged facing each other, the outer surfaces including: a first outer surface on which a first end face of the positive electrode and a first end face of the negative electrode are disposed; and a second outer surface on which a second end face of the positive electrode and a second end face of the negative electrode are disposed. The electrolyte includes at least the remaining liquid disposed between the first outer surface and the housing. The diaphragm has a plurality of first protrusions on the first outer surface that protrude beyond the first end face of the negative electrode, and a plurality of second protrusions on the second outer surface that protrude beyond the second end face of the negative electrode. The first protrusion includes a first bend in the diaphragm, and the second protrusion includes a second bend in the diaphragm. A plurality of through holes are provided in the first protrusion. The protrusion length L2 of the second protrusion is greater than the protrusion length L1 of the first protrusion.

[0102] [2] In the secondary battery described in item [1], the extension length L'2 of the second protrusion along the extension direction of the separator is greater than the extension length L'1 of the first protrusion along the extension direction.

[0103] [3] In the secondary battery described in item [1] or [2], a gas discharge valve is provided in the housing, the gas discharge valve is configured to break when the pressure inside the housing reaches a predetermined value or above, and discharge the gas inside the housing to the outside of the housing, the gas discharge valve is provided in the housing on the surface facing the first outer surface of the electrode body.

[0104] [4] In any one of the secondary batteries described in [1] to [3], the liquid level of the remaining liquid is located above the through hole of the diaphragm when the charge rate of the secondary battery is 0%.

[0105] [5] In any one of the secondary batteries described in [1] to [4], the liquid level of the remaining liquid is located above the first end face of the negative electrode when the charge rate of the secondary battery is 0%.

[0106] Explanation of reference numerals in the attached figures

[0107] 10 housing

[0108] 12 Shell Body

[0109] 12a Bottom surface

[0110] 12c Top surface

[0111] 13 Gas discharge valve

[0112] 14 First sealing plate

[0113] 16 Second sealing plate

[0114] 20 electrode body

[0115] 23 Positive Electrode

[0116] 24 negative electrode

[0117] 25 diaphragm

[0118] 25a First protrusion

[0119] 25c Second protrusion

[0120] 25h through hole

[0121] 50% remaining liquid

[0122] 52 Upper part retains liquid

[0123] 100 rechargeable battery.

Claims

1. A secondary battery, wherein, The secondary battery has the following features: An electrode body having a tortuous structure in which a strip-shaped diaphragm is formed by alternating folds and multiple positive and multiple negative electrodes are sandwiched between the tortuous diaphragm; Electrolyte; as well as The housing contains the electrode body and the electrolyte. The electrode body has an outer surface arranged in a counter-facing manner, the outer surface comprising: A first outer surface having the first end face of the positive electrode and the first end face of the negative electrode configured thereon; as well as The second outer surface is configured with the second end face of the positive electrode and the second end face of the negative electrode. The electrolyte includes at least the remaining liquid disposed between the first outer surface and the housing. The diaphragm The first outer surface has a plurality of first protrusions that protrude beyond the first end face of the negative electrode. The second outer surface has a plurality of second protrusions that protrude beyond the second end face of the negative electrode. The first protrusion includes a first bend in the diaphragm. The second protrusion includes a second bend in the diaphragm. Multiple through holes are provided in the first protrusion. The protrusion length L2 of the second protrusion is greater than the protrusion length L1 of the first protrusion.

2. The secondary battery according to claim 1, wherein, The extension length L'2 of the second protrusion along the extension direction of the diaphragm is greater than the extension length L'1 of the first protrusion along the extension direction.

3. The secondary battery according to claim 1 or 2, wherein, A gas discharge valve is provided in the housing, and the gas discharge valve is configured to break when the pressure inside the housing reaches a predetermined value, thereby discharging the gas inside the housing to the outside of the housing. The gas discharge valve is disposed in the housing on the surface facing the first outer surface of the electrode body.

4. The secondary battery according to claim 1 or 2, wherein, When the secondary battery is at a charge rate of 0%, the level of the remaining liquid is located above the through hole of the diaphragm.

5. The secondary battery according to claim 4, wherein, When the secondary battery is charged at 0%, the level of the remaining liquid is located above the first end face of the negative electrode.

Images