Secondary battery

Abstract

To provide a secondary battery whose reliability is high with respect to expansion of an electrode body due to charging and discharging.SOLUTION: A secondary battery disclosed herein includes a wound electrode body 20 in a flat shape in which a positive electrode 22 in a long sheet shape and a negative electrode 24 in a long sheet shape are wound with a separator 26 held therebetween, and a battery case 10 that accommodates the wound electrode body 20. The wound electrode body 20 is accommodated in the battery case 10 so that the winding axis and a height direction of the battery case 10 become substantially perpendicular. The battery case 10 includes a bottom surface 11a, a sealing plate 11d facing the bottom surface 11a, and side surfaces between the bottom surface 11a and the sealing plate 11d. The side surfaces include two flat surfaces 11b facing the flat plane of the wound electrode body 20 that is accommodated inside the case 10, and two curved surfaces 11c facing two end parts of the wound electrode body 20 in a winding axis direction. Each of the two curved surfaces 11c is a curved surface whose outer side of the battery has a convex shape.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a secondary battery. [Background technology]

[0002] In secondary batteries such as lithium-ion secondary batteries, repeated charging and discharging can cause the electrode body to expand, potentially damaging the battery case. If the thickness of the battery can is reduced to increase the internal volume of the battery can in anticipation of the expansion of the electrode body, the corners gradually become brittle during deep drawing, making it difficult to form the battery can. As an example of this type of prior art, Patent Document 1 describes a secondary battery in which expansion of the electrode body is absorbed by a thin portion in the center of the battery case, thereby preventing damage to the battery case. Furthermore, Patent Document 2 describes a secondary battery in which a curved surface facing the height direction of the battery is provided on the sealing plate, thereby preventing damage to the battery case due to expansion of the electrode body. Furthermore, Patent Document 3 describes a secondary battery in which a recess is provided on the side surface of the battery case to prevent damage to the battery case due to expansion of the electrode body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-338992 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-294012 [Patent Document 3] Japanese Patent Application Publication No. 2017-22057 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to increase the capacity of secondary batteries, development of secondary batteries using Si or Si compounds as the negative electrode active material is progressing. However, when Si or Si compounds are used as the negative electrode active material, the electrode body expands significantly during charging and discharging of the secondary battery compared to when other negative electrode active materials such as graphite are used. Therefore, there is a need for further improvement in the reliability of the electrode body against expansion of the secondary battery.

[0005] The present disclosure has been made in consideration of the above circumstances, and its main object is to provide a secondary battery that is highly reliable against expansion of an electrode assembly due to charging and discharging. [Means for solving the problem]

[0006] To solve the above problems, the secondary battery disclosed herein includes a flat wound electrode assembly in which a long sheet-like positive electrode and a long sheet-like negative electrode are wound with a separator interposed therebetween, and a battery case that houses the wound electrode assembly. The wound electrode assembly is housed in the battery case so that the winding axis and the height direction of the battery case are approximately perpendicular. The battery case is composed of a bottom surface, a sealing plate facing the bottom surface, and a side surface located between the bottom surface and the sealing plate. The side surface has two flat surfaces that face the flat surface of the wound electrode assembly housed inside the case, and two curved surfaces that face two ends of the wound electrode assembly in the winding axis direction, respectively. Both of the two curved surfaces are convex surfaces facing the outside of the battery.

[0007] In a secondary battery having the above configuration, the battery case deforms in response to the expansion of the electrode body, and the space created within the battery case by the two curved surfaces absorbs the expansion of the electrode body, thereby preventing damage to the battery case.

[0008] In a preferred embodiment of the secondary battery disclosed herein, the thickness of at least a portion of the curved surface is thinner than the thickness of the flat surface, which can promote deformation of the battery case when the electrode assembly expands, as described above, and can suitably suppress breakage of the battery case.

[0009] In a preferred embodiment of the secondary battery disclosed herein, the negative electrode contains Si or a Si compound as a negative electrode active material, which allows for a high-performance secondary battery to be provided with a high capacity. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view schematically illustrating a secondary battery according to an embodiment. [Figure 2] FIG. 1 is a perspective view schematically illustrating a battery case according to one embodiment. [Figure 3] FIG. 2 is a schematic diagram showing the configuration of an electrode body according to one embodiment. [Figure 4] FIG. 1 is a top view schematically illustrating a secondary battery according to an embodiment. [Figure 5] FIG. 2 is a top view schematically illustrating expansion of a battery case in accordance with expansion of an electrode body of a secondary battery according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the technology disclosed herein are described below. Matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification, can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the drawings described in this specification, components and parts that perform the same function are denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not necessarily reflect the actual dimensional relationships.

[0012] In this specification, the term "secondary battery" refers to a general term for an electricity storage device that can be repeatedly charged and discharged with the movement of charge carriers between positive and negative electrodes, and is a concept that encompasses so-called storage batteries (chemical batteries) such as lithium ion secondary batteries and sodium ion secondary batteries, and capacitors (physical batteries) such as lithium ion capacitors (LIC). Below, each of the main constituent materials of the secondary battery according to the present disclosure will be described. It should be noted that conventionally known materials can be used for constituent materials of secondary batteries not described here.

[0013] (1) Overall configuration of a secondary battery according to an embodiment Fig. 1 is a perspective view of a secondary battery 100 according to one embodiment. Fig. 2 is a perspective view schematically showing a battery case according to one embodiment. As shown in FIG. 1, the secondary battery 100 is composed of a battery case 10 (described later) and an electrode assembly 20 (not shown) housed inside the case. The battery case 10 is integrated by joining (for example, welding) a sealing plate 11d to the periphery of an opening 11h of the exterior body 11. The exterior body 11 is composed of a bottom surface 11a, a sealing plate 11d facing the bottom surface 11a, and side surfaces 11b and 11c located between the bottom surface 11a and the sealing plate 11d. The sealing plate 11d is provided with a liquid inlet 15, a gas release valve 17, and two terminal outlet holes (not shown). The liquid inlet 15 is for injecting the electrolyte after the sealing plate 11d is assembled to the exterior body 11. The liquid inlet 15 is sealed with a sealing member 16. The gas release valve 17 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby releasing gas inside the battery case 10 to the outside. The two terminal lead-out holes are formed at both ends of the sealing plate 11d in the long side direction Y. The terminal lead-out holes penetrate the sealing plate 11d in the up-down direction Z. The terminal lead-out holes each have an inner diameter large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to be inserted therethrough before they are attached to the sealing plate 11d (before they are crimped).

[0014] (2) Battery case 2, the battery case 10 is a housing that houses the electrode assembly 20 (not shown). The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The battery 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.

[0015] From the viewpoint of promoting deformation of the battery case in response to expansion of the electrode assembly, as described below, the Young's modulus of the members of the battery case 10 is preferably 220 GPa or less, more preferably 100 GPa or less, and particularly preferably 70 GPa or less.

[0016] The battery case 10 is composed of a bottom surface 11a, a sealing plate 11d facing the bottom surface 11a, and side surfaces 11b and 11c located between the bottom surface 11a and the sealing plate 11d. The side surfaces 11b and 11c each have two flat surfaces 11b facing the flat surfaces of the electrode assembly 20 (not shown) housed in the case, and two curved surfaces 11c facing the two ends of the electrode assembly 20 (not shown) in the winding axis direction, respectively, and having convex surfaces facing the outside of the battery. In this disclosure, the R value is used as an index representing the area of ​​the curved surfaces. The R value can be calculated using the top view of the battery shown in Figure 4 and the following formula: R={(w / 2) 2 +h 2} / 2h R: R value w: The length of the chord AB for the arc AB that makes up the entire surface h: The maximum distance from the arc AB to the perpendicular to the chord AB When h is constant, the larger the R value (the larger w), the larger the area of ​​the curved surface. From the viewpoint of absorbing the expansion of the electrode body 20 due to the space generated within the battery case 10 by providing a curved surface on the side surface 11c of the battery case 10, the R value of the curved surface (when h = 5) is preferably 5.0 or more, more preferably 6.5 or more, and particularly preferably 8.0 or more. Furthermore, from the viewpoint of preventing the space from becoming excess space due to providing an excessive curved surface, the R value (when h = 5) is preferably 12.0 or less, more preferably 11.0 or less, and particularly preferably 10.0 or less.

[0017] The thickness of at least one of the two curved surfaces is thinner than the thickness of the flat end surface. From the viewpoint of promoting deformation of the battery case 10 in response to the expansion of the electrode body 20, as described below, the ratio of the thickness of the curved surface 11c to the thickness of the flat surface 11b is preferably 0.9 or less, more preferably 0.85 or less, and particularly preferably 0.8 or less. On the other hand, from the viewpoint of preventing the strength of the battery case 10 from being insufficient due to an excessive thinning of the thickness of the side surface 11c, the ratio of the thickness of the curved surface to the thickness of the flat surface 11b is preferably 0.2 or more, more preferably 0.25 or more, and particularly preferably 0.3 or more.

[0018] (2) Wound electrode body 3 is a schematic diagram showing the configuration of an electrode assembly according to one embodiment. The electrode assembly 20 has a positive electrode 22 and a negative electrode 24. In this example, the electrode assembly 20 is a flat wound electrode assembly in which a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 are stacked with a strip-shaped separator 26 interposed therebetween and wound around a winding axis WL.

[0019] As shown in FIG. 3, the positive electrode 22 has a positive electrode core 22c and a positive electrode active material layer 22a formed on at least one surface (both surfaces in this case) of the positive electrode core 22c.

[0020] The positive electrode core 22c is strip-shaped and made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode core 22c is a metal foil, specifically an aluminum foil.

[0021] As shown in FIG. 3, the positive electrode active material layer 22a is provided in a strip-like shape along the longitudinal direction of the strip-shaped 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. The positive electrode active material preferably contains at least one of Ni, Co, and Mn. For example, a lithium transition metal composite oxide such as a lithium nickel cobalt manganese composite oxide may be used. When the total solid content of the positive electrode active material layer 22a is taken as 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a conductive material, a binder, various additives, etc. Examples of the conductive material include carbon materials such as carbon black (e.g., acetylene black (AB)). Examples of the binder include PVdF.

[0022] As shown in Fig. 3, the positive electrode tabs 22t protrude from the end of the electrode assembly 20 in the long side direction Y. The positive electrode tabs 22t are provided at intervals along the longitudinal direction of the strip-shaped positive electrode 22. The tabs are rectangular in shape here, but may also have various other shapes (for example, trapezoidal). In at least a portion of the positive electrode tab 22t, a region is formed in which the positive electrode active material layer 22a is not formed and the positive electrode core 22c is exposed.

[0023] As shown in FIG. 3, the negative electrode 24 has a negative electrode core 24c and a negative electrode active material layer 24a formed on at least one surface (both surfaces in this case) of the negative electrode core 24c.

[0024] The negative electrode core 24c is strip-shaped and made of a conductive metal such as copper, a copper alloy, nickel, stainless steel, etc. Here, the negative electrode core 24c is a metal foil, specifically a copper foil.

[0025] The negative active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode core 24c. The negative active material layer 24a contains a negative active material (for example, a carbon material such as graphite, a Si compound such as Si or SiO) that can reversibly occlude and release charge carriers. As the Si compound, SiO x silicon oxide represented by (0.05 < x < 1.95), Li x Si y O z lithium silicon oxide represented by (x, y, z independently satisfy 0 ≤ x, y, z ≤ 1), Li 21 a lithium-containing lithium-silicon alloy represented by LiSi5, etc. may be used. When the total solid content of the negative active material layer 24a is 100% by mass, the negative active material may occupy generally 80% by mass or more, typically 90% by mass or more, for example 95% by mass or more. The negative active material layer 24a may contain optional components other than the negative active material, for example, a binder, a dispersant, various additive components, etc. As the binder, for example, rubbers such as styrene-butadiene rubber (SBR) may be used. As the dispersant, for example, celluloses such as carboxymethyl cellulose (CMC) may be used.

[0026] When using Si or a Si compound in particular as the above-mentioned negative active material, since the amount of insertion / desorption of charge carriers (such as lithium ions) per unit area is large, it becomes possible to provide a high-performance secondary battery that realizes high capacity. When using Si or a Si compound as the negative active material, since the volume change accompanying the insertion / desorption of charge carriers (such as lithium ions) is large, the electrode body expands significantly during charge and discharge, and as a result, the battery case is likely to be damaged. However, the secondary battery according to the present disclosure can use Si or a Si compound as the negative active material in order to prevent the battery case from being damaged due to the expansion of the electrode body accompanying charge and discharge.

[0027] As shown in Fig. 3, the negative electrode tabs 24t protrude from the end of the electrode body 20 in the long side direction Y. The negative electrode tabs 24t are provided at intervals along the longitudinal direction of the strip-shaped negative electrode 24. The shape of the tabs is rectangular here, but they may also be various other shapes (for example, trapezoidal). In at least a part of the negative electrode tab 24t, a region is formed in which the negative electrode active material layer 24a is not formed and the negative electrode core 24c is exposed.

[0028] 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. A porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable for the separator 26. The separator 26 may have a heat resistance layer (HRL) containing an inorganic filler provided on the surface of the resin sheet. Examples of inorganic fillers that can be used include alumina, boehmite, aluminum hydroxide, and titania. An adhesive layer is preferably provided on one or both surfaces of the separator 26. The adhesive layer improves adhesion to the contacting positive electrode active material layer or negative electrode active material layer. The adhesive layer contains, for example, polyvinylidene fluoride (PVdF) as an adhesive component. The adhesive layer may also contain inorganic particles such as alumina and boehmite. The adhesive layer may be provided on the surface of the resin sheet or on the surface of the HRL.

[0029] <Expansion of the electrode body> As described above, in this type of secondary battery, the electrode assembly housed inside the battery case may expand during charging and discharging. Excessive expansion may result in damage to the battery case.

[0030] In particular, when Si or a Si compound is used as the negative electrode active material, the volume change associated with the insertion / extraction of charge carriers (lithium ions, etc.) is large, and therefore excessive expansion of the electrode body associated with charging and discharging of the secondary battery is more likely to occur than when other types of negative electrode active materials (e.g., graphite) are used.

[0031] When excessive expansion of the electrode body occurs due to charging and discharging of the secondary battery, the degree of expansion in the direction from the flat surface of the wound electrode body toward the outside of the battery is relatively large, and the degree of expansion in the direction from the curved surface toward the outside of the battery is relatively small. Therefore, the battery case used in the secondary battery disclosed herein is devised as described below.

[0032] <Prevention of battery case damage> The principle of suppressing damage to the battery case due to expansion of the electrode assembly according to the present disclosure will be explained below while comparing it with conventional batteries.

[0033] (1) Orientation of the wound electrode assembly In a secondary battery according to one embodiment, the wound electrode body 20 is housed in the battery case 10 so that the winding axis WL of the wound electrode body 20 is approximately perpendicular to the height direction of the battery case 10. That is, the flat surface 11b of the battery case 10 and the flat surface of the wound electrode body 20 face each other, and the wound electrode body 20 is housed so that the positive electrode 22 and the negative electrode 24 of the wound electrode body 20 are on the side of the two curved surfaces 11c of the side surfaces 11b, 11c of the battery case 10. In this specification and claims, the "height direction" refers to the direction in which the side surfaces 11b and 11c rise from the bottom surface 11a of the hexahedral battery case 10 including the sealing plate 11d (i.e., the Z direction in FIG. 2), and is not limited to the direction of gravity (vertical direction). For example, if the secondary battery 100 (battery case 10) is placed so that one flat surface 11b is below (the bottom) in the direction of gravity, it should be noted that the height direction here is the same as the horizontal direction intersecting with the direction of gravity.

[0034] In some conventional secondary batteries, the wound electrode body is housed in the battery case so that the winding axis of the wound electrode body is approximately parallel to the height direction of this type of hexahedral battery case. In this electrode body housing mode, the orientation in which the wound electrode body is housed in the battery case differs by 90° from the height direction of the battery compared to the secondary battery according to the present disclosure.

[0035] (2) Battery case structure As shown in FIG. 1, the two curved surfaces 11c of the battery case 10 according to one embodiment are formed so that the areas near the positive and negative electrode terminals of the wound electrode body 20 are convex surfaces facing outward from the battery.

[0036] On the other hand, in conventional secondary batteries, all four side surfaces of the hexahedral battery case are flat, making them so-called box-shaped (or prismatic) battery cases. Therefore, it can be said that such a battery case falls outside the scope of the technical concept of the present disclosure. For example, in a hexahedral box-shaped battery case, if two opposing side surfaces are curved, and the winding axis of the wound electrode assembly is housed in a manner such that it is approximately parallel to the height direction of the battery, it is not possible to achieve an effect equivalent to the breakage prevention effect of the battery case according to the present disclosure.

[0037] (3) Preventing damage to the battery case due to expansion of the electrode body In one embodiment of the secondary battery, by combining the above (1) orientation of the wound electrode body 20 and the above (2) structure of the battery case 10, damage to the battery case 10 due to expansion of the wound electrode body 20 is suppressed.

[0038] 5, in a battery case 10 according to one embodiment, when the wound electrode assembly 20 expands due to charging and discharging of the secondary battery, the battery case 10 follows the expansion of the electrode assembly 20 in the thickness direction of the battery (the stacking direction of the electrode assembly) and deforms in the direction of arrow A. Before the expansion of the electrode assembly 20 occurs, the battery case 10 has the shape indicated by the solid line, and as it follows the expansion of the electrode assembly 20, it deforms into the shape indicated by the dotted line.

[0039] At this time, if the thickness of the curved surface 11c of the battery case 10 is thinner than the thickness of the flat surface 11b, the deformation of the battery case 10 can occur more significantly, which effectively prevents damage to the battery case 10.

[0040] Furthermore, when the wound electrode body 20 (not shown) expands due to charging and discharging of the secondary battery, the expansion of the electrode body 20 can be absorbed in the internal space created by the two curved surfaces of the side surface 11c of the battery case 10.

[0041] The battery case 10 according to one embodiment achieves the above-described effects to suppress damage to the battery case 10 caused by expansion of the electrode body 20 accompanying charging and discharging of the secondary battery.

[0042] As described above, the housing configuration of the electrode assembly 20 and the battery case 10 according to one embodiment take into consideration the expansion of the electrode assembly 20 in the thickness direction (the stacking direction of the electrode assembly) and the width direction (the long side direction of the electrode assembly) of the battery, and therefore have high reliability against expansion of the secondary battery. Therefore, when used as the negative electrode active material, Si or a Si compound, which exhibits a large degree of expansion of the electrode assembly during charge and discharge, can be used as the negative electrode active material, making it possible to provide a high-capacity secondary battery.

[0043] Although the present invention has been described in detail above using specific embodiments, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the above-described embodiments. [Explanation of symbols]

[0044] 10 Battery case 11a Bottom 11b Side (two flat surfaces) 11c Side (two curved surfaces) 11d Sealing plate 11h opening 20 Electrode body 22 Positive electrode 22a Cathode active material layer 22c positive electrode active core 22t Positive electrode tab 24 Negative electrode 24a Negative electrode active material layer 24c negative electrode core 24t negative electrode tab 26 Separator 30 Positive terminal 40 Negative terminal

Claims

1. a flat wound electrode body in which a long sheet-like positive electrode and a long sheet-like negative electrode are wound with a separator interposed therebetween; a battery case that houses the wound electrode body; A secondary battery comprising: the wound electrode body is housed in the battery case so that the winding axis and the height direction of the battery case are approximately perpendicular to each other; the battery case is composed of a bottom surface, a sealing plate facing the bottom surface, and a side surface between the bottom surface and the sealing plate, the side surface includes two flat surfaces facing the flat surfaces of the wound electrode body housed inside the case, and two curved surfaces facing two ends of the wound electrode body in the winding axis direction, The two curved surfaces each constitute a curved surface that is convex on the outer side of the battery. Secondary battery.

2. The secondary battery according to claim 1 , wherein a thickness of at least a part of the curved surface is thinner than a thickness of the flat surface.

3. The secondary battery according to claim 1 , wherein the negative electrode contains Si or a Si compound as a negative electrode active material.

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