Secondary battery

Abstract

A secondary battery comprises a positive electrode plate having a positive electrode active material layer formed thereon except for a positive electrode collecting foil exposed portion along one long side of a positive electrode collecting foil, and a negative electrode plate having a negative electrode active material layer formed thereon except for a negative electrode exposed portion along one long side of a negative electrode collecting foil, a wound electrode body formed by winding the positive electrode plate with a separator interposed therebetween, a battery case accommodating the wound electrode body and an electrolyte, a positive electrode current collecting terminal electrically connected to a positive electrode collecting portion that collects the positive electrode collecting foil exposed portions, a negative electrode current collecting terminal electrically connected to a negative electrode collecting portion that collects the negative electrode collecting foil exposed portions, an area of ​​the positive electrode collecting foil exposed portion excluding the positive electrode collecting portion, and an insulating layer formed on at least one of the area of ​​the negative electrode collecting foil exposed portion excluding the negative electrode collecting portion.

Description

Technology Field

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

[0002] Japanese Patent Publication No. 2023-089639 discloses a secondary battery having a wound electrode body in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween. The positive electrode plate is pushed out from the separator on the first side in the direction of the winding axis, and a positive electrode current collector is attached to that portion. The outermost periphery of the negative electrode plate is wound on the outer side of the outermost periphery of the positive electrode plate. The portion of the separator wound on the outer side of the outermost periphery of the negative electrode plate extends to the first side and is fixed at the portion where the positive electrode current collector and the positive electrode plate are attached. Accordingly, the ingress of foreign matter into the gap between the outermost positive electrode plate and the negative electrode plate is reduced.

[0003] In Japanese Patent Publication No. 2023-089639, by extending the outermost separator and joining the separator together with the positive electrode plate to the positive electrode current collector, a short circuit in the gap between the outermost positive electrode plate and the negative electrode plate can be prevented. However, in Japanese Patent Publication No. 2023-089639, the impregnation of the wound electrode body when the electrolyte is injected is not considered, so there are cases where the impregnation of the electrolyte is reduced.

[0004] The present invention has been made in consideration of such problems. The objective of the present invention is to provide a secondary battery capable of preventing a short circuit in the gap between a positive electrode plate and a negative electrode plate interposed with a separator, while also suppressing the deterioration of the electrolyte impregnation properties of the wound electrode body.

[0005] A secondary battery related to one embodiment is,

[0006] A wound electrode body formed by winding a positive electrode plate having a positive electrode active material layer formed except for an exposed portion of the positive electrode collector foil along one long side of a strip-shaped positive electrode collector foil, and a negative electrode plate having a negative electrode active material layer formed except for an exposed portion of the negative electrode collector foil along one long side of a strip-shaped negative electrode collector foil, with a strip-shaped separator interposed therebetween;

[0007] A battery case accommodating the above-mentioned wound electrode body and electrolyte, and

[0008] A positive electrode current collecting terminal electrically connected to a positive electrode collecting part that collects the exposed portion of the above positive electrode current collecting foil, and

[0009] A negative electrode current collecting terminal electrically connected to a negative electrode collecting part that collects the exposed portion of the above negative electrode current collecting foil, and

[0010] An insulating layer is provided in at least one of the area excluding the positive electrode collecting portion of the above-mentioned positive electrode collecting foil exposure portion and the area excluding the negative electrode collecting portion of the above-mentioned negative electrode collecting foil exposure portion.

[0011] According to the present invention, it is possible to prevent a short circuit in the gap between the positive electrode plate and the negative electrode plate interposed with a separator, and at the same time, suppress the decrease in the impregnation of the electrolyte into the wound electrode body. Brief explanation of the drawing

[0012] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which the same reference numerals denote the same elements. FIG. 1 is a drawing showing the external appearance of a secondary battery related to an embodiment; FIG. 2 is a diagram illustrating the internal configuration of the secondary battery of FIG. 1; FIG. 3 is an exploded view illustrating the configuration of the wound electrode body; FIG. 4 is a side view of the wound electrode body; FIG. 5 is an enlarged view of a portion of the cross-section of the wound electrode body at the cutting line V of FIG. 4; and Figure 6 is an enlarged view of a portion of the cross-section of the wound electrode body at the cutting line VI of Figure 4. Specific details for implementing the invention

[0013] The embodiments described below are explained with reference to the drawings. Furthermore, the following embodiments are not intended to limit the technology disclosed herein. For the sake of clarity in the explanation, the following descriptions and drawings have been appropriately omitted and simplified. The dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. Additionally, in each drawing, the same reference numerals are attached to identical elements, and redundant descriptions are omitted as necessary.

[0014] The embodiments relate to secondary batteries used as driving power sources, for example, for battery electric vehicles. In this specification, "secondary battery" refers to a general energy storage device capable of repeated charging and discharging, and includes energy storage elements such as so-called storage batteries or electric double-layer capacitors. Here, the embodiments are described in detail using a flat-sided lithium-ion secondary battery as an example. "Lithium secondary battery" refers to a secondary battery in which charging and discharging are realized by the movement of charge between lithium ions using lithium ions as a charge carrier.

[0015] FIG. 1 is a diagram showing the external shape of a secondary battery (10) related to an embodiment. FIG. 2 is a diagram explaining the internal configuration of the secondary battery (10) of FIG. 1. As shown in FIG. 1 and 2, the secondary battery (10) has a structure in which a wound electrode body (20) and an electrolyte (not shown) are contained within a battery case (11). W in the drawings indicates the width direction of the battery case (11). H in the drawings indicates the height direction of the battery case (11). Additionally, a direction orthogonal to the width direction (W) and the height direction (H) is called the thickness direction D of the battery case (11). Furthermore, these directions do not limit the installation mode of the secondary battery (10).

[0016] The battery case (11) is a rectangular container having an internal space and an external shape that is approximately rectangular. For the battery case (11), a lightweight metal material with good thermal conductivity, such as aluminum or stainless steel (SUS), is used. The battery case (11) includes a main body (12) having an opening that is open toward the top, and a cover body (13) that blocks the opening. The main body (12) has a bottom surface that is approximately rectangular in shape, a pair of wide surfaces, and a narrow surface positioned between the pair of wide surfaces. In FIG. 1, the pair of wide surfaces extend upward from the front and rear ends of the bottom surface, respectively. Additionally, the pair of narrow surfaces extend upward from the left and right ends of the bottom surface, respectively. The main body (12) and the outer edge of the opening and the cover body (13) are laser welded, and the battery case (11) is sealed.

[0017] The cover body (13) of the battery case (11) is provided with a positive electrode external terminal (14) and a negative electrode external terminal (15). Additionally, the cover body (13) is provided with an injection port not shown in the drawing for injecting an electrolyte. The injection port may be provided, for example, between the positive electrode external terminal (14) and the negative electrode external terminal (15) of the cover body (13). As shown in FIG. 2, parts of the positive electrode external terminal (14) and the negative electrode external terminal (15) are respectively connected to the positive electrode current collection terminal (16) and the negative electrode current collection terminal (17) inside the battery case (11).

[0018] The wound electrode body (20) is housed in a space enclosed by the main body (12) and the cover body (13). FIG. 3 is an exploded view illustrating the configuration of the wound electrode body (20). FIG. 4 is a side view of the wound electrode body (20). FIG. 4 shows the side of the wound electrode body (20) to which the positive electrode current collection terminal (16), indicated by the dashed line in FIG. 3, is connected.

[0019] As shown in FIG. 3, the wound electrode body (20) includes a strip-shaped first separator (1), a second separator (2), a positive electrode plate (3), and a negative electrode plate (4). The length direction of the first separator (1), the second separator (2), the positive electrode plate (3), and the negative electrode plate (4) is the long side direction, and the width direction is the short side direction. The first separator (1), the positive electrode plate (3), the second separator (2), and the negative electrode plate (4) are stacked in order with their long side directions aligned, and wound around the winding axis (X). In this embodiment, the direction of the winding axis (X) of the wound electrode body (20) coincides with the width direction (W) of the secondary battery (10). As shown in FIG. 4, the cross-section of the wound electrode body (20) has an elongated circular shape.

[0020] The positive electrode plate (3) includes a positive electrode collecting foil (30) and a positive electrode active material layer (31). The positive electrode collecting foil (30) is a supporting member for the positive electrode active material layer (31) and a conductive member for extracting electric charge from the positive electrode active material layer (31). A positive electrode collecting foil exposure portion (32) is provided in an area along one long side of the strip-shaped positive electrode collecting foil (30). The positive electrode active material layer (31) is formed in an area on the positive electrode collecting foil (30) excluding the positive electrode collecting foil exposure portion (32). The positive electrode active material layer (31) is formed in a strip shape along the other long side of the positive electrode collecting foil (30). The positive electrode active material layer (31) may be formed on one side or both sides of the positive electrode collecting foil (30). Here, the positive electrode active material layer (31) is formed on both sides of the positive electrode current collector foil (30). That is, the positive electrode plate (3) is long, and in the width direction, a wide positive electrode active material layer (31) and a narrow positive electrode current collector foil exposed portion (32) are arranged side by side.

[0021] Additionally, although not shown in the drawing of FIG. 3, the negative electrode plate (4) includes a negative electrode collecting foil (40) and a negative electrode active material layer (41) (see FIG. 5). The negative electrode collecting foil (40) is a supporting member for the negative electrode active material layer (41) and a conductive member for extracting charge from the negative electrode active material layer (41). An exposed portion of the negative electrode collecting foil is provided in an area along one long side of the strip-shaped negative electrode collecting foil (40). The negative electrode active material layer (41) is formed in an area on the negative electrode collecting foil (40) excluding the exposed portion of the negative electrode collecting foil. The negative electrode active material layer (41) is formed in a strip shape along the other long side of the negative electrode collecting foil (40). The negative electrode active material layer (41) may be formed on one side or both sides of the negative electrode collecting foil (40). Here, the negative electrode active material layer (41) is formed on both sides of the negative electrode current collector foil (40). That is, the negative electrode plate (4) is long, and in the width direction, a wide negative electrode active material layer (41) and a narrow negative electrode current collector foil exposed portion are arranged side by side.

[0022] The components and materials constituting the secondary battery (10) are those used in widely known lithium-ion secondary batteries and are not particularly limited. An example of the components and materials constituting the secondary battery (10) is shown below.

[0023] As for the positive electrode current collector foil (30) constituting the positive electrode plate (3), examples include aluminum foil (including aluminum alloy). Examples of positive electrode active materials included in the positive electrode active material layer (31) include lithium transition metal oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 Examples include O4, etc.), lithium transition metal phosphate compounds (e.g., LiFePO4, etc.). The positive electrode active material layer (31) may include components other than the active material, such as a conductive material or a binder. As a conductive material, carbon black such as acetylene black (AB) or other carbon materials (e.g., graphite, etc.) may be used. As a binder, polyvinylidene fluoride (PVdF), etc. may be used.

[0024] As the negative electrode current collector foil (40) constituting the negative electrode plate (4), examples include copper foil. As the negative electrode active material included in the negative electrode active material layer (41), carbon materials such as graphite, hard carbon, and soft carbon can be used. When graphite is used as the negative electrode active material, the negative electrode active material may be natural graphite or artificial graphite, and may be coated with an amorphous carbon material. The negative electrode active material layer (41) may include components other than the active material, such as a binder or a thickener. As the binder, styrene butadiene rubber (SBR) may be used, for example. As the thickener, carboxymethylcellulose (CMC) may be used, for example.

[0025] The first separator (1) and the second separator (2) insulate the positive electrode plate (3) and the negative electrode plate (4), and also provide a path for the movement of a charge carrier between the positive electrode active material layer (31) and the negative electrode active material layer (41). As the first separator (1) and the second separator (2), a porous sheet (film) made of polyolefin such as polyethylene (PE) or polypropylene (PP) may be used. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the first separator (1) and the second separator (2).

[0026] The electrolyte typically comprises a non-aqueous solvent and a supporting salt. As the non-aqueous solvent, known solvents used as non-aqueous solvents for lithium-ion secondary batteries may be used. Examples of non-aqueous solvents include carbonates, ethers, esters, nitriles, sulfones, lactones, etc. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), etc. Such non-aqueous solvents may be used as a single type or in combination of two or more types.

[0027] As a supporting salt, lithium salts such as LiPF6, LiBF4, and LiClO4 (preferably LiPF6) are suitably used. The electrolyte may contain other components. Examples of other components include gas-generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB), film-forming agents, dispersants, and thickeners.

[0028] In the central part of the winding axis (X) direction of the wound electrode body (20), a positive electrode active material layer (31) and a negative electrode active material layer (41) are laminated, and a core part in which a charge / discharge reaction is performed is formed. In addition, in the wound electrode body (20), at one end of the winding axis (X) direction (left end in FIG. 3), a positive electrode current collector foil laminated part (33) exists in which the positive electrode current collector foil exposed part (32) is laminated in a state where it is pushed out from the negative electrode plate (4). In addition, in the wound electrode body (20), at the other end of the winding axis (X) direction (the right end in FIG. 3, although not shown in the drawing), a negative electrode current collector foil laminated part exists in which the negative electrode current collector foil exposed part is laminated in a state where it is pushed out from the positive electrode plate (3).

[0029] As shown in FIG. 4, the central part in the height direction (H) of the positive electrode collecting foil stacking part (33) is formed by the positive electrode collecting foil exposure part (32) being gathered (hereinafter referred to as "collecting"), thereby forming a positive electrode collecting part (34). FIG. 5 is an enlarged view of a part of the cross-section of the wound electrode body at the cutting line V of FIG. 4. FIG. 5 shows the vicinity of the positive electrode collecting part (34) at the cutting line V as viewed from the upper side (white arrow side). As shown in FIG. 4, the positive electrode collecting terminal (16) is electrically connected to the positive electrode collecting part (34) by means of ultrasonic welding, etc. As shown in FIG. 5, since adjacent positive electrode collecting foils (30) are collected in the positive electrode collecting part (34), foreign matter does not enter between the positive electrode plate (3) and the negative electrode plate (4).

[0030] Likewise, the central part in the height direction (H) of the negative electrode collecting foil stacking section is formed by the exposure portions of the negative electrode collecting foils being gathered to form a negative electrode collecting section. A negative electrode collecting terminal (17) is electrically connected to the negative electrode collecting section. Since adjacent negative electrode collecting foils are collected in the negative electrode collecting section, foreign matter does not enter between the positive electrode plate (3) and the negative electrode plate (4).

[0031] An insulating layer (35) is formed in at least one of the area excluding the positive electrode collecting portion (34) of the positive electrode collecting foil exposed portion (32) and the area excluding the negative electrode collecting portion of the negative electrode collecting foil exposed portion. It is preferable that the insulating layer (35) be formed in both the area excluding the positive electrode collecting portion (34) of the positive electrode collecting foil exposed portion (32) and the area excluding the negative electrode collecting portion of the negative electrode collecting foil exposed portion.

[0032] Hereinafter, the insulating layer (35) formed on the positive electrode current collector exposed portion (32) will be described in detail. Also, since the insulating layer (35) is formed on the negative electrode current collector exposed portion in the same way as on the positive electrode current collector exposed portion (32), the description is omitted. The insulating layer (35) is, for example, a cured body of a liquid insulating paste. The insulating paste may include, for example, an inorganic material having insulating properties, a solvent for the insulating paste, and a resin component. The inorganic material may be at least one of powdered alumina, boehmite, and titania. As the solvent for the insulating paste, an NMP solution, which is an example of an organic solvent, is used. The resin component functions as a binder in the insulating layer (35). The resin component may be at least one selected from the group consisting of PVDF, PVA, and acrylic, which are polymer materials soluble in NMP. It is preferable that the insulating layer (35) has flexibility when collecting the positive electrode current collector exposed portion (32).

[0033] As shown in FIG. 3, the insulating layer (35) is formed at a predetermined interval along the long side direction of the positive electrode current collector exposed portion (32). The "predetermined interval" at which the insulating layer (35) is formed is preferably a pitch such that when the positive electrode plate (3) is wound, the insulating layer (35) is formed over the entire area excluding the positive electrode collecting portion (34) of the positive electrode current collector exposed portion (32). Additionally, the insulating layer (35) is formed on both sides of the positive electrode current collector exposed portion (32). Accordingly, when the positive electrode plate (3) is wound to form a wound electrode body (20), the positive electrode current collector (30) is exposed only at the positive electrode collecting portion (34).

[0034] FIG. 6 is an enlarged view of a portion of the cross-section of the wound electrode body at cutting line VI of FIG. 4. FIG. 6 shows the vicinity of the positive electrode current collector foil stacking portion (33) at cutting line VI, viewed from the upper side (white arrow side). As shown in FIG. 6, in the positive electrode current collector foil stacking portion (33), an insulating layer (35) is formed on both sides of the positive electrode current collector foil exposed portion (32).

[0035] Generally, it is known that during battery manufacturing, metal foreign matter such as welding sputter is generated and enters the secondary battery (10) through the injection port. The metal foreign matter that enters the secondary battery (10) may cause a short circuit by connecting the battery case (11) to the wound electrode body (20) or between the positive electrode and the negative electrode within the wound electrode body (20).

[0036] Typically, when impregnating with an electrolyte, the electrolyte penetrates from the upper and lower positive electrode collecting foil stacking portions (33) of the positive electrode collecting portion (34) to the center of the wound electrode body (20). When a metal foreign substance that has entered the interior of the secondary battery (10) through the injection port causes a short circuit between the positive electrode and the negative electrode within the wound electrode body (20), a route can be conceived through which the metal foreign substance moves along the flow of the electrolyte penetrating the wound electrode body (20). As a means to prevent a short circuit caused by this route, it is possible to prevent the metal foreign substance from entering between the positive electrode and the negative electrode.

[0037] In Japanese Patent Publication No. 2023-089639, the intrusion of metallic foreign matter is suppressed by extending the outermost separator and joining the separator together with the positive electrode plate to the positive electrode current collector. However, there is a concern that the impregnation properties of the electrolyte may be reduced as it is covered by the separator.

[0038] In this regard, in the embodiment, an insulating layer (35) is formed in the area excluding the positive electrode collecting part (34) in the positive electrode collecting foil exposed part (32). Because of this, when the electrolyte is injected, even if a metal foreign substance (F) is introduced into the gap between the positive electrode plate (3) and the negative electrode plate (4) of the wound electrode body (20), the occurrence of a short circuit can be suppressed. In addition, as shown in FIG. 6, in the positive electrode collecting foil stacking part (33), the positive electrode plate (3) and the separator are not joined as in Japanese Patent Publication No. 2023-089639, so when the electrode is collected, a gap is formed in the positive electrode collecting foil stacking part (33) other than the positive electrode collecting part (34). Because of this, it is possible to impregnate the wound electrode body (20) with the electrolyte without changing the electrolyte injection conditions.

[0039] Furthermore, the present invention is not limited to the above embodiments, and appropriate modifications are possible within the scope of the intent without departing from the spirit.

Claims

Claim 1 A secondary battery comprising: a positive electrode plate having a positive electrode active material layer formed thereon except for a strip-shaped positive electrode collector foil exposed portion along one long side of a strip-shaped positive electrode collector foil; a negative electrode plate having a negative electrode active material layer formed thereon except for a strip-shaped negative electrode collector foil exposed portion along one long side of a strip-shaped negative electrode collector foil; a wound electrode body formed by winding the positive electrode plate having a negative electrode active material layer formed thereon except for a strip-shaped negative electrode collector foil exposed portion along one long side of a strip-shaped negative electrode collector foil; a battery case accommodating the wound electrode body and an electrolyte; a positive electrode current collecting terminal electrically connected to a positive electrode collector foil portion that collects the positive electrode collector foil exposed portions; a negative electrode current collecting terminal electrically connected to a negative electrode collector foil portion that collects the negative electrode collector foil exposed portions; an area of ​​the positive electrode collector foil exposed portion excluding the positive electrode collector foil portion; and an insulating layer formed on at least one of the area of ​​the negative electrode collector foil exposed portion excluding the negative electrode collector foil portion. Claim 2 In claim 1, the insulating layer is formed at predetermined intervals along the long side direction of the positive electrode current collector or the negative electrode current collector. Claim 3 A secondary battery according to claim 1, wherein the insulating layer is formed on both the region excluding the positive electrode collecting portion of the positive electrode collecting foil exposure portion and the region excluding the negative electrode collecting portion of the negative electrode collecting foil exposure portion. Claim 4 A secondary battery according to claim 1, wherein the separator comprises a first separator and a second separator, and the first separator and the positive electrode plate and the second separator and the negative electrode plate are stacked in order with the long side direction aligned and wound around a winding axis set along the short side direction. Claim 5 In claim 4, the battery case is a rectangular case having a rectangular outer shape, the wound electrode body has a flat rectangular outer shape, at one end in the direction of the winding axis, the positive electrode current collector foil exposed portion protrudes onto the negative electrode plate and is arranged in a stacked manner, and at the other end in the direction of the winding axis, the negative electrode current collector foil exposed portion protrudes onto the positive electrode plate and is arranged in a stacked manner, and the wound electrode body is a secondary battery accommodated in the battery case such that the winding axis direction extends in the width direction of the battery case. Claim 6 A secondary battery according to claim 1, wherein the positive electrode plate is long and, in the width direction, the positive electrode active material layer and the positive electrode current collector foil exposed portion are arranged side by side, and the positive electrode current collector foil exposed portion is arranged along the entire length direction of the positive electrode plate.

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