JP7109950B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present disclosure relates to non-aqueous electrolyte secondary batteries.

Conventionally, non-aqueous electrolyte secondary batteries are known that include a flat electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween (see, for example, Patent Documents 1 and 2). FIG. 8 is a cross-sectional view showing a conventional flat wound electrode assembly 100 (illustration of the separator is omitted). As illustrated in FIG. 8, an electrode body 100 of a non-aqueous electrolyte secondary battery generally uses a negative electrode 102 that is one size larger than a positive electrode 101 . Therefore, the negative electrode 102 is formed with an extending portion 103 that extends inward in the winding direction from the inner end of the positive electrode 101 and does not face the positive electrode 101 .

JP 2006-278266 A Japanese Patent Application Laid-Open No. 2007-214106

The flat electrode assembly 100 is manufactured, for example, by press-molding a wound body of the positive electrode 101 and the negative electrode 102 wound with a separator (not shown) interposed therebetween. Since a gap corresponding to the thickness of the positive electrode 101 is formed in the portion overlapping with 103, it becomes difficult to press with a uniform force, and the moldability of the electrode assembly is deteriorated. Then, when the compressive force is weakened at the portion overlapping with the extension portion 103, the distance between the positive and negative electrodes is widened at this portion, and the thickness of the electrode body is partially increased. In this case, it becomes difficult to accommodate the electrode body in the battery case, and it is assumed that metallic lithium is likely to deposit during charging.

A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure has a wound structure in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and includes a flat electrode body having a flat portion and a curved portion. , a non-aqueous electrolyte secondary battery in which a mixture layer is provided on both sides of the positive electrode and the negative electrode to the inner winding end of each, wherein the inner winding end of the positive electrode and the inner winding end of the negative electrode are the flat and the negative electrode has an extending portion extending toward the curved portion from the inner winding end of the positive electrode, and the extending portion is folded back within a range not overlapping the positive electrode. characterized by

According to one aspect of the present disclosure, it is possible to provide a non-aqueous electrolyte secondary battery in which variations in the thickness of the flat portion of the electrode body are suppressed and variations in the distance between the positive and negative electrodes are suppressed. In the non-aqueous electrolyte secondary battery according to the present disclosure, for example, the electrode body can be easily accommodated in the battery case, and deposition of metallic lithium is less likely to occur during normal charging and discharging.

1 is a plan view of a non-aqueous electrolyte secondary battery that is an example of an embodiment; FIG. 1 is a front view of a non-aqueous electrolyte secondary battery that is an example of an embodiment; FIG. FIG. 1B is a sectional view along line IIA-IIA in FIG. 1A; FIG. 2B is a sectional view along line IIB-IIB in FIG. 2A; FIG. 2B is a sectional view taken along the line IIC-IIC in FIG. 2A; 1 is a front view of a positive electrode that is an example of an embodiment; FIG. 1 is a front view of a negative electrode that is an example of an embodiment; FIG. 1 is a perspective view of an electrode body that is an example of an embodiment; FIG. 1 is a cross-sectional view of an electrode body that is an example of an embodiment (illustration of a separator is omitted); FIG. FIG. 6 is an enlarged view of part A in FIG. 5; FIG. 4 is a cross-sectional view of an electrode body that is another example of an embodiment; It is a figure which shows an example of the conventional electrode body.

An example of an embodiment of the present disclosure will be described in detail below with reference to the drawings. 1A to 2C show a non-aqueous electrolyte secondary battery 10, which is a prismatic battery having a prismatic battery case, as an example of an embodiment. However, the non-aqueous electrolyte secondary battery according to the present disclosure may be a laminate battery or the like that includes an exterior body composed of a laminate sheet including a metal layer and a resin layer, for example. The drawings referred to in the description of the embodiments are all schematically described.

1A is a plan view of the non-aqueous electrolyte secondary battery 10, and FIG. 1B is a front view of the non-aqueous electrolyte secondary battery 10. FIG. As illustrated in FIGS. 1A and 1B , the non-aqueous electrolyte secondary battery 10 includes a rectangular bottomed cylindrical outer can 25 and a sealing plate 23 that seals the opening of the outer can 25 . The outer can 25 and the sealing plate 23 constitute a battery case. The sealing plate 23 has a substantially rectangular shape in plan view. A positive electrode terminal 18 is provided on one longitudinal end side of the sealing plate 23 with an insulating member 21 interposed therebetween, and a negative electrode terminal 20 is provided on the other longitudinal end side thereof with an insulating member 22 interposed therebetween. Further, the sealing plate 23 is provided with an electrolyte injection hole, and the electrolyte injection hole is sealed with a sealing member 26 . Further, the sealing plate 23 is provided with a gas exhaust valve 28 that is broken when the pressure inside the battery case reaches or exceeds a predetermined value.

2A to 2C are cross-sectional views of the non-aqueous electrolyte secondary battery 10. FIG. As illustrated in FIGS. 2A to 2C, the non-aqueous electrolyte secondary battery 10 includes a flat electrode body 14 housed in an outer can 25 and a non-aqueous electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents that can be used include esters, ethers, nitriles, amides, and mixed solvents of two or more thereof. The non-aqueous solvent may contain a halogen-substituted product obtained by substituting at least part of the hydrogen atoms of these solvents with halogen atoms such as fluorine.

The electrode assembly 14 has a wound structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound with a strip-shaped separator 13 interposed therebetween (see later-described FIGS. 3A, 3B, 4, etc.). Further, the electrode body 14 has a positive electrode core exposed portion 15 formed at one axial end and a negative electrode core exposed portion 16 formed at the other axial end. In this embodiment, the electrode body 14 is accommodated in the battery case so that the axial direction of the electrode body 14 is along the longitudinal direction of the battery case. The electrode body 14 may be arranged so as to. An insulating sheet 24 is arranged between the electrode body 14 and the outer can 25 so as to wrap the electrode body 14 .

In this embodiment, the positive electrode core exposed portion 15 is laminated at one axial end portion of the electrode body 14 , and the laminated portion is electrically connected to the positive electrode terminal 18 via the positive current collector plate 17 . A current interrupting mechanism 27 is provided in the conductive path between the positive electrode core exposed portion 15 and the positive electrode terminal 18 . A negative electrode substrate exposed portion 16 is laminated at the other axial end portion of the electrode body 14 , and the laminated portion is electrically connected to the negative electrode terminal 20 via the negative electrode current collector plate 19 . For example, the laminated portion of the positive electrode core exposed portion 15 is divided into two parts, and the resin-made positive electrode intermediate member 30 holding the metal positive electrode conductive member 29 is arranged between them. Similarly, the negative electrode core exposed portion 16 is divided into two parts, and a resin negative electrode intermediate member 32 holding a metal negative electrode conductive member 31 is arranged between the two parts.

The positive electrode collector plate 17 is arranged on the outer surface of the exposed portion so as to sandwich the laminated portion of the positive electrode core exposed portion 15 . Similarly, the negative electrode collector plate 19 is arranged on the outer surface of the exposed portion so as to sandwich the laminated portion of the negative electrode core exposed portion 16 . The collector plate, the exposed portion, and the conductive member are connected by, for example, resistance welding to form welded portions 15a and 16a, respectively. The shape of the core exposed portion, the current collecting structure of the electrode body, and the like are not particularly limited.

The electrode body 14 will be described in detail below with reference to FIGS. 3A to 7. FIG. 3A is a front view of the positive electrode 11, FIG. 3B is a front view of the negative electrode 12, and FIG. 4 is a perspective view of the electrode assembly 14. FIG. In addition, in FIG. 4 , the vicinity of the winding end of the electrode body 14 is developed. FIG. 5 is a sectional view of the electrode body 14 cut in a direction orthogonal to the axial direction (illustration of the separator 13 is omitted), and FIG. 6 is an enlarged view of part A in FIG.

As illustrated in FIG. 3A, the positive electrode 11 has a positive electrode core 11a and a positive electrode mixture layer 11b provided on the positive electrode core 11a. For the positive electrode core 11a, a foil of a metal such as aluminum or an aluminum alloy that is stable in the potential range of the positive electrode 11, a film having the metal on the surface layer, or the like can be used. The thickness of the positive electrode core 11a is, for example, 10 to 20 μm. The positive electrode mixture layer 11b contains a positive electrode active material, a conductive material such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably provided on both surfaces of the positive electrode core 11a. The thickness of the positive electrode mixture layer 11b is, for example, 50 to 200 μm in total on both sides of the positive electrode core 11a. The positive electrode 11 is formed by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive material, a binder, and the like on the positive electrode core 11a, drying the coating film, and then compressing the positive electrode mixture layer 11b to form a positive electrode. It can be produced by forming on both sides of the core body 11a.

For example, a lithium metal composite oxide is used as the positive electrode active material. Metal elements contained in the lithium metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. are mentioned. An example of a suitable lithium metal composite oxide is a lithium metal composite oxide containing at least one of Ni, Co and Mn. Specific examples include lithium metal composite oxides containing Ni, Co and Mn, and lithium metal composite oxides containing Ni, Co and Al. Inorganic compound particles such as tungsten oxide, aluminum oxide, and lanthanide-containing compounds may adhere to the surfaces of the lithium metal composite oxide particles.

As illustrated in FIG. 3B, the negative electrode 12 has a negative electrode core 12a and a negative electrode mixture layer 12b provided on the negative electrode core 12a. For the negative electrode core 12a, a foil of a metal such as copper or a copper alloy that is stable in the potential range of the negative electrode 12, a film having the metal on the surface layer, or the like can be used. The thickness of the negative electrode core 12a is, for example, 5 to 15 μm. The negative electrode mixture layer 12b contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably provided on both surfaces of the negative electrode core 12a. The total thickness of the negative electrode mixture layer 12b on both sides of the negative electrode core 12a is, for example, 50 to 200 μm. The negative electrode 12 is formed by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. onto the negative electrode core 12a, drying the coating film, and then compressing the negative electrode mixture layer 12b to the negative electrode core 12a. can be produced by forming on both sides of the

As the negative electrode active material, for example, graphite such as natural graphite such as flake graphite, massive graphite, and earthy graphite, massive artificial graphite, and artificial graphite such as graphitized mesophase carbon microbeads is used. As the negative electrode active material, metals such as Si and Sn that are alloyed with lithium, alloys containing such metals, compounds containing such metals, and the like may be used, and these may be used in combination with graphite. Specific examples of the compound include silicon compounds represented by SiO _x (0.5≦x≦1.6).

As illustrated in FIG. 4 , the electrode body 14 includes the positive electrode 11 and the negative electrode 12 with the separator 13 interposed therebetween such that the positive electrode core exposed portion 15 and the negative electrode core exposed portion 16 are positioned on opposite sides in the axial direction. It has a wound structure. The electrode body 14 has, for example, an axial length of 50 to 150 mm, a width of 50 to 150 mm, and a thickness of 10 to 25 mm. A porous sheet having ion permeability and insulation is used for the separator 13 . Specific examples of porous sheets include microporous thin films, woven fabrics, and non-woven fabrics. Suitable materials for the separator 13 include olefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure, and a heat-resistant layer or the like may be formed on the surface of the separator 13 .

In the electrode body 14, the negative electrode 12 is one size larger than the positive electrode 11, and is arranged so that the negative electrode mixture layer 12b always exists in the region facing the positive electrode mixture layer 11b. In the present embodiment, the positive electrode mixture layer 11b is provided on both surfaces of the positive electrode core 11a from the outer end 40 of the positive electrode 11 to the inner end 41 (see FIG. 6 described later), that is, from both ends in the longitudinal direction of the positive electrode 11. there is Similarly, the negative electrode composite material layer 12b is provided on both surfaces of the negative electrode core 12a from the winding outer end 50 to the winding inner end 51 of the negative electrode 12, that is, over both longitudinal ends of the negative electrode 12. As shown in FIG.

The electrode body 14 has a flat shape with a flat portion 14a and a curved portion 14b. Although the details will be described later, the electrode body 14 is manufactured by press-molding a wound body of the positive electrode 11 and the negative electrode 12 wound with the separator 13 interposed therebetween. The flat portion 14a is a portion where the outer surface of the electrode body 14 is substantially flat. The curved portion 14b is a portion curved so that the outer surface of the electrode body 14 is convex outward. At the curved portion 14b, the positive electrode 11 and the negative electrode 12 are curved so as to protrude outward. The curved portions 14b are formed on both sides of the flat portion 14a.

As illustrated in FIGS. 5 and 6 , the winding inner end 41 of the positive electrode 11 and the winding inner end 51 of the negative electrode 12 are arranged on the flat portion 14 a of the electrode body 14 . As described above, the positive electrode 11 and the negative electrode 12 are provided with composite material layers on both sides up to the winding inner ends 41 and 51, respectively. Therefore, the winding inner end 41 of the positive electrode 11 and the winding inner end of the positive electrode mixture layer 11b are aligned. Further, the winding inner end 51 of the negative electrode 12 and the winding inner end of the negative electrode mixture layer 12b are aligned. Therefore, the inner end of the positive electrode mixture layer 11b and the inner end of the negative electrode mixture layer 12b are also arranged on the flat portion 14a. It is preferable that the winding inner ends 41 and 51 be positioned near the curved portion 14b within a range not overlapping the curved portion 14b. The winding inner ends 41 and 51 are arranged, for example, within a range of 10 mm from the end of the flat portion 14a (the boundary with the curved portion 14b). The inner end of the separator 13 may be arranged at either the flat portion 14a or the curved portion 14b.

The negative electrode 12 has an extension portion 52 that extends from the winding inner end 41 of the positive electrode 11 toward the curved portion 14b. The extending portion 52 is a portion that extends inward in the winding direction of the electrode body 14 from the winding inner end 41 of the positive electrode 11 and does not face the positive electrode 11 . By providing the extending portion 52, even if the positive electrode 11 and the negative electrode 12 are slightly deviated from the intended arrangement, the negative electrode mixture layer 12b is arranged to face the entire surface of the positive electrode mixture layer 11b. The length of the extending portion 52 (the length along the longitudinal direction of the negative electrode 12) is preferably 3 to 135 mm, more preferably 5 to 60 mm, in consideration of manufacturing errors, formation of folded portions to be described later, and the like.

The extending portion 52 of the negative electrode 12 is folded back so as not to overlap the positive electrode 11 . That is, the extending portion 52 is bent toward the winding inner end 41 side of the positive electrode 11 , and a bent portion 53 is formed in the intermediate portion of the extending portion 52 . The winding inner end 51 of the negative electrode 12 exists closer to the winding inner end 41 than the bent portion 53, or exists at a position coinciding with the winding inner end 41 of the positive electrode 11 in the thickness direction of the flat portion 14a. The bent portion 53 is preferably formed in a substantially linear shape along the width direction of the negative electrode 12 (the axial direction of the electrode body 14) and arranged on the flat portion 14a.

In the electrode body 14 , the thickness of the negative electrode 12 is increased in at least part of the extension portion 52 by folding the extension portion 52 . Specifically, by folding the negative electrode 12 between the winding inner end 51 and the bent portion 53 , the thickness of the extension portion 52 at that portion becomes twice the thickness of the other portion. Therefore, in the electrode body 14 , the gap corresponding to the thickness of the positive electrode 101 , which is formed in the conventional electrode body 100 at the portion overlapping with the extending portion 103 , can be filled with the folded portion of the negative electrode 12 . Therefore, when manufacturing the flat electrode body 14, it becomes easy to press with a uniform force, and good formability can be obtained. The electrode body structure in which the extending portion 52 is folded is particularly effective when the width and thickness of the electrode body 14 are small.

Note that the negative electrode 12 has an extension portion that extends outward in the winding direction from the outer end 40 of the positive electrode 11 , but the extension portion on the outer side of the winding is larger than the extension portion 52 on the inner side of the winding. It is not folded in this embodiment as it has little effect on the formability of body 14 .

A distance L between the winding inner end 41 of the positive electrode 11 and the winding inner end 51 of the negative electrode 12 is, for example, 0 to 30 mm. Here, 0 mm means that the winding inner ends 41 and 51 are aligned in the thickness direction of the flat portion 14a. Considering manufacturing errors, press formability, etc., the inner winding end 51 is preferably located closer to the curved portion 14b than the inner winding end 41 within a range where the distance L does not exceed 30 mm. Specifically, the distance L is preferably 0.5 to 20 mm, more preferably 1 to 10 mm, and more preferably 1 mm to 5 mm.

In the example shown in FIGS. 5 and 6, the extending portion 52 is folded back toward the inner side of the electrode body 14, that is, toward the center of the winding. The extending portion 52 may be folded to the outside of the electrode body 14, but the folded shape to the inside of the electrode body 14 can be formed by changing the pressing conditions, for example, and folding is easy. Regardless of whether the extending portion 52 is folded back inside or outside the electrode body 14, the influence of the thickness difference of the electrode at the portion where the extending portion 52 is formed can be reduced, and good formability can be obtained.

As illustrated in FIG. 7, the electrode body 14 may have a structure in which the winding outer end 40 of the positive electrode 11 and the winding outer end 50 of the negative electrode 12 are arranged in the curved portion 14b. In this case, since the extending portion of the negative electrode 12 on the winding outer side is positioned at the curved portion 14b, the moldability of the electrode assembly 14 is further improved. In the example shown in FIG. 7, the outer winding ends 40, 50 are arranged on one curved portion 14b near the inner winding ends 41, 51, but the outer winding ends 40, 50 are far from the inner winding ends 41, 51. It may be arranged on the curved portion 14b on the other side.

The electrode body 14 is manufactured by flattening the wound body of the positive electrode 11 and the negative electrode 12 wound with the separator 13 interposed therebetween, as described above. In this case, for example, a cylindrical wound body is manufactured using a substantially cylindrical winding core, and after the winding core is removed, the wound body is radially pressed. Alternatively, the positive electrode 11 and the negative electrode 12 may be flatly wound using a flat winding core. Also in this case, after removing the winding core, it is further pressed into a flat shape. In addition, by winding in a state in which one longitudinal end of the negative electrode 12 serving as the winding inner end 51 extends from one longitudinal end of the positive electrode 11 serving as the winding inner end 41 , the electrode body 14 extends to the winding inner end. An exit 52 is formed.

The extension 52 may be folded before manufacturing the roll or before pressing the roll, or the roll may be pressed such that the extension 52 is bent. In either case, the extension portion 52 is press-molded so as to be positioned on the flat portion 14a of the electrode body 14. As shown in FIG. When the wound body is pressed so that the extending portion 52 is bent, the extending portion 52 is folded back inside the electrode body 14 . The distance L between the winding inner end 41 of the positive electrode 11 and the winding inner end 51 of the negative electrode 12 can be adjusted by adjusting the length of the extending portion 52, the arrangement of the winding inner end 41, and the like.

Here, the effect of folding the extension portion 52 will be shown by the following examples and comparative examples.

<Example>
The positive electrode 11 provided with the positive electrode mixture layer 11b extending to both ends in the longitudinal direction and the negative electrode 12 provided with the negative electrode mixture layer 12b extending to both ends in the longitudinal direction were wound with the separator 13 interposed therebetween. A substantially cylindrical core was used for the core. At this time, the positive electrode core exposed portion 15 and the negative electrode core exposed portion 16 are positioned on opposite sides in the axial direction, and one end in the longitudinal direction of the negative electrode 12, which becomes the winding inner end 51, is arranged to become the winding inner end 41. A wound body having an extending portion 52 formed thereon was obtained by winding while extending from one end in the longitudinal direction. Next, the winding core is removed from the wound body, and the extending portion 52 is pressed so that it is positioned near the curved portion 14b of the flat portion 14a of the electrode body 14 and the extending portion 52 is bent. A flat electrode body 14 having an axial length of 116.3 mm, a width of 52.7 mm, and a plate thickness of 10.4 mm was produced. The extending portion 52 was bent inwardly of the electrode body 14 and formed with a folded portion having the distance L of 3 mm.

<Comparative example>
A flat electrode body was manufactured in the same manner as in Example except that the extending portion was not folded back.

The plate thickness of each electrode body of Examples and Comparative Examples immediately after production, the plate thickness after standing for 60 minutes, and the height gauge thickness were measured by the following methods. The height gauge thickness of the electrode body was measured at one end in the width direction of the flat portion where the extending portion was located and at the other end in the width direction of the flat portion. Table 1 shows the evaluation results.
Plate thickness: The entire electrode body placed on the flat ground is sandwiched between flat plates parallel to the ground and larger than the electrode body, and the numerical value of the gap between the ground and the flat plate Height gauge thickness: The electrode placed on the flat ground A numerical value of the gap between the ground and the tip of the rod when the body is sandwiched between rods that are parallel to the ground and have a circular tip with a diameter of 5 mm.

As shown in Table 1, in the electrode body of the comparative example in which the extending portion was not folded back, the change in thickness was large immediately after production and after standing for 60 minutes, and the thickness difference between one end in the width direction and the other end in the width direction was large. is large. On the other hand, in the electrode body of the example in which the extending part was folded back, the thickness did not substantially change immediately after the production and after being left for 60 minutes. The thickness difference at the edge is small. In the electrode body of the comparative example, as a result of the insufficient compression of the wound body at the portion overlapping with the extending portion, it is considered that the structure of the wound body was loosened and the thickness increased particularly at one end in the width direction. If the electrode body of the comparative example has a large variation in thickness, it may be difficult to accommodate the electrode body in a battery case, and metallic lithium is likely to precipitate during charging.

It is believed that in the electrode bodies of the examples, due to the effect of folding back the extending portions, a sufficient compressive force was secured in the entire wound body, and good moldability was obtained. The electrode bodies of Examples have a substantially uniform thickness, and the variation in the distance between the positive and negative electrodes is sufficiently suppressed. Therefore, it is easy to accommodate the electrode assembly in a battery case, and deposition of metallic lithium is less likely to occur during normal charging and discharging of a battery using the electrode assembly.

10 nonaqueous electrolyte secondary battery 11 positive electrode 11a positive electrode core 11b positive electrode mixture layer 12 negative electrode 12a negative electrode core 12b negative electrode mixture layer 13 separator 14 electrode body 15 positive electrode core exposed portion 15a, 16a welded portion 16 negative electrode core exposed portion 17 positive current collector plate 18 positive electrode terminal 19 negative electrode current collector plate 20 negative electrode terminal 21, 22 insulating member 23 sealing plate 24 insulating sheet 25 outer can , 26 sealing member, 27 current interrupting mechanism, 28 gas discharge valve, 29 positive electrode conductive member, 30 positive electrode intermediate member, 31 negative electrode conductive member, 32 negative electrode intermediate member, 40, 50 winding outer ends, 41, 51 winding inner end, 52 extension

Claims (4)

It has a winding structure in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. A non-aqueous electrolyte secondary battery having material layers on both sides,
The winding inner end of the positive electrode and the winding inner end of the negative electrode are arranged on the flat portion,
the negative electrode has an extending portion extending toward the curved portion from the inner winding end of the positive electrode;
The non-aqueous electrolyte secondary battery, wherein the extending portion is folded back so as not to overlap the positive electrode. 2. The non-aqueous electrolyte secondary according to claim 1, wherein the distance between the inner winding end of the positive electrode and the inner winding end of the negative electrode when the winding structure is viewed from the thickness direction of the flat portion is 0 to 30 mm. battery. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a winding outer end of said positive electrode and a winding outer end of said negative electrode are arranged in said curved portion. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein said extending portion is folded inside said electrode body.

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