Secondary battery

Abstract

To provide a secondary battery which is suppressed in occurrence of a short circuit due to a fragment detached from a negative electrode active material layer and excellent in impregnation of an electrolytic solution into an electrode body.SOLUTION: A secondary battery includes: an electrode body 20 that includes a plurality of first electrode plates, a plurality of second electrode plates, and a separator 25 disposed between the first electrode plate and the second electrode plate; an electrolytic solution; and a housing case. The separator is bent in a zigzag manner, and includes a first bent part 25a folded at an end part of the first electrode plate and a second bent part 25b folded at an end part of the second electrode plate. A plurality of the first bent parts are disposed on one side of a pair of side surfaces of the electrode body that face each other, and a plurality of the second bent parts are disposed on the other side thereof. The separator includes a cover part 25c that covers outer surfaces of the plurality of first bent parts, and outer surfaces of the second bent part are not covered with the separator. The separator is located on both outermost surfaces in a stacking direction of the first and second electrode plates.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to secondary batteries.

Background Art

[0002] As one form of the electrode body included in a secondary battery, a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated via a separator is known. In this laminated electrode body, a form in which the separator is folded ninety-nine times so as to be interposed between the positive electrode and the negative electrode is known (see, for example, Patent Document 1). Patent Document 1 discloses various aspects of an electrode body in which the separator is folded ninety-nine times.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the various aspects disclosed in the above prior art have at least one of the problems of the possibility of short circuit due to fragments detached from the negative electrode active material layer and the problem of poor impregnation of the electrolyte into the electrode body.

[0005] Therefore, the present disclosure provides a secondary battery that solves the problems of the prior art.

Means for Solving the Problems

[0006] The secondary battery of the present disclosure includes an electrode body including a plurality of first electrode plates, a plurality of second electrode plates having polarities different from those of the first electrode plates, and a separator disposed between the first electrode plates and the second electrode plates; an electrolytic solution; and a case that houses the electrode body and the electrolytic solution. The separator is in a strip shape and is bent in a ninety-nine fold shape. The separator includes a first bent portion folded back at an end of the first electrode plate and a second bent portion folded back at an end of the second electrode plate. A plurality of the first bent portions are disposed on one side surface side of a pair of opposing side surfaces of the electrode body. A plurality of the second bent portions are disposed on the other side surface side of the pair of opposing side surfaces of the electrode body. The separator includes a cover portion that covers an outer surface of the plurality of the first bent portions. The outer surface of the second bent portion is not covered by the separator. In the electrode body, the separator is located on both outermost surfaces in the stacking direction of the first electrode plate and the second electrode plate.

[0007] According to such a configuration, it is possible to provide a secondary battery that solves the problems of the prior art. That is, according to such a configuration, it is possible to provide a secondary battery in which a short circuit due to fragments detached from the negative electrode active material layer is suppressed and the impregnation property of the electrolytic solution into the electrode body is excellent.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0009] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. Matters not mentioned in this specification but necessary for the implementation of the present disclosure can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present disclosure can be implemented based on the content disclosed in this specification and the common general knowledge in the relevant field. In the following drawings, members and parts having the same function are denoted by the same reference numerals and described. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. Note that the numerical range expressed as "A to B" in this specification includes A and B.

[0010] In this specification, the "secondary battery" refers to a rechargeable power storage device. Also, in this specification, the "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and realizes charge and discharge by the movement of charges associated with lithium ions between the positive and negative electrodes.

[0011] FIG. 1 is a perspective view of a secondary battery 100 according to an example embodiment of the secondary battery of the present disclosure. FIG. 2 is a perspective view of the secondary battery 100 of FIG. 1 with the top and bottom reversed. FIG. 3 shows the internal structure of the secondary battery 100 of FIG. 1. In the following description, the reference numerals L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, respectively, and the reference numerals X, Y, and Z in the drawings represent the short side direction, the long side direction orthogonal to the short side direction, and the up and down direction orthogonal to the short side direction and the long side direction of the secondary battery 100, respectively.

[0012] Note that U (up) and D (down) in the drawings correspond to up and down in the normal usage form of the secondary battery 100 (especially the installation state in an in-vehicle battery), but the usage form of the secondary battery 100 is not limited thereto. For example, in other embodiments, the secondary battery 100 may be installed upside down.

[0013] The secondary battery 100 according to this embodiment is a lithium-ion secondary battery. Thereby, the secondary battery 100 can have excellent battery characteristics such as high energy density and high capacity. However, in other embodiments, the secondary battery may be a secondary battery other than a lithium-ion secondary battery (for example, a sodium-ion secondary battery, etc.).

[0014] As shown in FIGS. 1 to 3, the secondary battery 100 includes a battery case 10, an electrode body 20, and an electrolytic solution (not shown). The secondary battery 100 further includes a positive electrode terminal 30, a negative electrode terminal 40, and an insulating sheet 50.

[0015] <Battery case> The battery case 10 is a housing that houses the electrode body 20 and the electrolytic solution. As shown in FIGS. 1 and 2, the battery case 10 here has an outer shape of a flat and bottomed rectangular parallelepiped. That is, the battery case 10 is rectangular. Therefore, the secondary battery 100 in the illustrated example is a rectangular lithium-ion secondary battery. However, the shape of the battery case 10 is not limited thereto. Since the space efficiency is high when configuring a battery module using a plurality of secondary batteries 100, the battery case 10 is preferably rectangular.

[0016] The material of the battery case 10 may be the same as those conventionally used (for example, metal, resin, etc.), and there is no particular limitation. From the viewpoints of strength, heat conductivity, etc., the material of the battery case 10 is preferably metal, and more preferably aluminum, an aluminum alloy, iron, or an iron alloy. Note that the battery case 10 may be made of a laminate film.

[0017] As shown in FIGS. 1 to 3, the battery case 10 includes a case body 12, a first sealing plate 14, and a second sealing plate 16. The case body 12 is in the shape of a square tube. As shown in FIG. 3, the case body 12 has a first opening 12e at one end and a second opening 12f at the other end. The first sealing plate 14 seals the first opening 12e, and the second sealing plate 16 seals the second opening 12f. The battery case 10 is integrated by joining (for example, welding) the first sealing plate 14 and the second sealing plate 16 to the case body 12 at the first opening 12e and the second opening 12f, respectively. The battery case 10 is hermetically sealed. Therefore, the secondary battery 100 is a sealed battery.

[0018] The battery case 10 has a pair of first surfaces, a pair of second surfaces, and a pair of third surfaces. As shown in FIG. 1, the case body 12 includes a substantially rectangular bottom surface 12a, a pair of long side surfaces 12b extending from the long sides 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. The top surface 12c is substantially rectangular. The top surface 12c faces the bottom surface 12a. Here, the top surface 12c and the bottom surface 12a are the pair of first surfaces, and the pair of long side surfaces 12b are the pair of second surfaces. It is preferable that the area of the long side surface 12b is larger than the area of the bottom surface 12a and larger than the area of the top surface 12c. For example, the bottom surface 12a and the top surface 12c can be the pair of short side surfaces. The case body 12 is formed, for example, by bending a single metal plate into a tubular shape and joining (for example, welding) the seams. In the illustrated example, a welding joint 12d is located on the top surface 12c. The welding joint 12d may be located on the bottom surface 12a or on the long side surface 12b.

[0019] As shown in FIG. 2, a gas discharge valve 13 is provided on the bottom surface 12a of the case body 12. The gas discharge valve 13 is configured to break when the pressure in the battery case 10 reaches a predetermined value or more and discharge the gas in the battery case 10 to the outside. In the present embodiment, the number of gas discharge valves 13 is one, but it may be two or more. Further, in the present embodiment, the gas discharge valve 13 is provided on the bottom surface 12a, but it is not limited thereto. In other embodiments, the gas discharge valve 13 may be provided on a surface other than the bottom surface 12a, for example, a long side surface 12b, a top surface 12c, a sealing plate 14, etc. Alternatively, in other embodiments, the secondary battery 100 may be installed upside down with respect to the drawing, the bottom surface 12a may be changed to the top surface 12c, and the gas discharge valve may be directed upward. Also, the area of the gas discharge valve 13 is arbitrary.

[0020] In the present embodiment, the gas discharge valve 13 is 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 may be, for example, a linear (vertical or horizontal line only) notch, or a conventionally known elliptical valve (with a notch inside) or a circular valve (with a notch inside), etc. Also, the dimensions of the notch (e.g., length, depth, etc.) are arbitrary and can be appropriately determined in consideration of, for example, the pressure resistance of the battery case 10.

[0021] The first sealing plate 14 and the second sealing plate 16 are plate-like members that seal the first opening 12e and the second opening 12f of the case body 12. The first sealing plate 14 and the second sealing plate 16 are substantially rectangular in plan view. Here, the first sealing plate 14 and the second sealing plate 16 are a pair of third surfaces.

[0022] The first sealing plate 14 is provided with a liquid injection hole 17. The liquid injection hole 17 is for injecting electrolyte into the inside of the battery case 10 after assembling the first sealing plate 14 and the second sealing plate 16 to the case body 12. The liquid injection hole 17 is provided below the positive electrode terminal 30, but the position where the liquid injection hole 17 is provided on the first sealing plate 14 is not limited to this. The liquid injection hole 17 is sealed with a sealing member 18 after the injection of the electrolyte. In this embodiment, the liquid injection hole 17 is provided on the first sealing plate 14, but the liquid injection hole 17 may be provided on the second sealing plate 16 or on the case body 12. Also, in this embodiment, the liquid injection hole 17 is provided on a surface different from the gas discharge valve 13, but the liquid injection hole 17 may be provided on the same surface as the gas discharge valve 13.

[0023] <Electrode terminal> The positive electrode terminal 30 and the negative electrode terminal 40 are respectively fixed to the battery case 10. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are respectively fixed to the opposing surfaces of the battery case 10. Specifically, the positive electrode terminal 30 is attached to the first sealing plate 14, and the negative electrode terminal 40 is attached to the second sealing plate 16.

[0024] Specifically, the first sealing plate 14 and the second sealing plate 16 have through holes, and insulating members 63, 64 (see FIG. 4) are attached to each of the through holes. The positive electrode terminal 30 is attached to the first sealing plate 14 via the insulating member 63, and the positive electrode terminal 30 is insulated from the first sealing plate 14. The negative electrode terminal 40 is attached to the second sealing plate 16 via the insulating member 64, and the negative electrode terminal 40 is insulated from the second sealing plate 16. Also, the insulating member 63 insulates the first sealing plate 14 and the electrode body 20 inside the battery case 10. The insulating member 64 insulates the second sealing plate 16 and the electrode body 20 inside the battery case 10.

[0025] In this embodiment, the positive electrode terminal 30 and the negative electrode terminal 40 are provided on the first sealing plate 14 and the second sealing plate 16, respectively. However, the arrangement of the positive electrode terminal 30 and the negative electrode terminal 40 is not limited to this. In other embodiments, both the positive electrode terminal 30 and the negative electrode terminal 40 may be provided on one of the first sealing plate 14 or the second sealing plate 16. The first sealing plate 14 and the second sealing plate 16 may be provided on the case body 12. Further, in this embodiment, the positive electrode terminal 30 and the negative electrode terminal 40 are provided on a surface different from the gas discharge valve 13. However, the positive electrode terminal 30 and the negative electrode terminal 40 may be provided on the same surface as the gas discharge valve 13.

[0026] However, when the positive electrode terminal 30 and the negative electrode terminal 40 are provided on the first sealing plate 14 and the second sealing plate 16, respectively, as in this embodiment, the height of the secondary battery 100 (i.e., the dimension in the Z direction of the drawing) can be reduced, and it becomes easy to obtain a battery with a high volume energy density. Further, in this case, it becomes easy to configure a battery module with a high volume energy density, particularly in in-vehicle applications.

[0027] The positive electrode terminal 30 and the negative electrode terminal 40 are exposed on the outer surfaces of the first sealing plate 14 and the second sealing plate 16, respectively. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are arranged on an axis extending in the long side direction Y and passing through the centers of the first sealing plate 14 and the second sealing plate 16. However, in other embodiments, the axis may be displaced, for example, in the short side direction X from the centers of the first sealing plate 14 and the second sealing plate 16. Further, the positive electrode terminal 30 and the negative electrode terminal 40 do not have to be arranged on the axis. For example, one of the positive electrode terminal 30 and the negative electrode terminal 40 may be displaced to one side in the short side direction X, and the other may be displaced to the other side in the short side direction X.

[0028] The positive electrode terminal 30 is preferably made of metal, and more preferably made of aluminum or an aluminum alloy. The negative electrode terminal 40 is preferably made of metal, and more preferably made of copper or a copper alloy.

[0029] The electrode body 20 has a positive current collector tab electrically connected to the positive electrode 23 at one end, and the positive current collector tabs are bundled and attached to the positive current collector member 32. The electrode body 20 has a negative current collector tab electrically connected to the negative electrode 24 at the other end, and the negative current collector tabs are bundled and attached to the negative current collector member 42. Inside the battery case 10, the positive current collector member 32 is attached to the first sealing plate 14 and is electrically connected to the positive terminal 30. Inside the battery case 10, the negative current collector member 42 is attached to the second sealing plate 16 and is electrically connected to the negative terminal 40.

[0030] In this way, the positive terminal 30 is electrically connected to the positive electrode 23 of the electrode body 20 through the positive current collector tab and the positive current collector member 32 inside the battery case 10. The negative terminal 40 is electrically connected to the negative electrode 24 of the electrode body 20 through the negative current collector tab and the negative current collector member 42 inside the battery case 10. Note that the structure for 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 one shown in the figure.

[0031] <Electrode body> The electrode body 20 is housed inside the battery case 10. FIG. 4 is a perspective view of the secondary battery 100, schematically showing the case body 12 in a perspective manner. FIG. 5 is a schematic cross-sectional view of the electrode body 20 along the thickness direction of the electrode body 20, described in a simplified manner while changing the orientation of the electrode body 20. FIG. 6 is a cross-sectional view of the electrode body 20 schematically showing the internal structure of the battery case 10 in a simplified manner, and is a cross-sectional view along the X direction (the thickness direction of the electrode body 20, in other words, the stacking direction of the positive electrode 23 and the negative electrode 24) and the Z direction in FIG. 1.

[0032] Note that since these drawings are schematic diagrams, the main surface of the positive electrode 23 and the separator 25 are shown separately, and the main surface of the negative electrode 24 and the separator 25 are also shown separately. This is for the ease of visual recognition of each member. In reality, the main surface of the positive electrode 23 and the separator 25 are in contact, and the main surface of the negative electrode 24 and the separator 25 are in contact. Also, in reality, the parts of the separator 25 can also be in contact with each other.

[0033] As shown in FIGS. 4 and 6, the electrode body 20 is disposed inside the battery case 10 in a state of being covered with an insulating sheet 50 described later. In the present embodiment, a plurality of electrode bodies 20 are accommodated inside one battery case 10. In the example shown in FIGS. 4 and 6, two electrode bodies 20 are accommodated inside one battery case 10. When there are a plurality of electrode bodies 20 in this way, a flow path for the electrolytic solution and the generated gas can be formed between the electrode body 20 and the adjacent electrode body 20. Note that the number of electrode bodies 20 accommodated inside one battery case 10 is not particularly limited. In other embodiments, the number of electrode bodies 20 accommodated inside one battery case 10 may be three or more, or may be one.

[0034] The electrode body 20 includes a plurality of positive electrodes 23 (positive electrode plates 23) as the first electrode plate, a plurality of negative electrodes 24 (negative electrode plates 24) as the second electrode plate having a polarity different from that of the first electrode plate, and a single separator 25. The single separator 25 is disposed between the plurality of positive electrodes 23 and the plurality of negative electrodes 24, thereby insulating the positive electrode 23 and the negative electrode 24. Note that in other embodiments, the first electrode plate may be configured as the negative electrode 24 and the second electrode plate may be configured as the positive electrode 23. The electrode body 20 is a laminated electrode body, and has higher impregnation property of the electrolytic solution than a wound electrode body, and is particularly advantageous in terms of the injection property of the electrolytic solution during manufacturing. Further, according to the laminated electrode body, it is easy to configure a battery having a high volume energy density.

[0035] In the example shown in FIG. 5, the number of positive electrodes 23 is three, and the number of negative electrodes 24 is four. However, the number of positive electrodes 23 and negative electrodes 24 is not particularly limited and can be appropriately determined according to the battery design. In the illustrated example, the number of negative electrodes 24 is one more than the number of positive electrodes 23. Therefore, in the electrode laminate structure of the positive electrode 23 and the negative electrode 24, the outermost layers are both the 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 precipitation of lithium in the negative electrode 24 can be highly prevented. In other embodiments, the number of positive electrodes 23 and the number of negative electrodes 24 may be the same, or the number of positive electrodes 23 may be more than the number of negative electrodes 24. For example, the number of positive electrodes 23 and negative electrodes 24 can be 20 or more, respectively.

[0036] In this embodiment, the size of the negative electrode 24 is larger than the size of the positive electrode 23. In FIG. 5, the width of the negative electrode 24 (i.e., the dimension in the Z direction of the drawing) is larger than the width of the positive electrode 23. Thereby, the precipitation of lithium in the negative electrode 24 can be highly prevented. In other embodiments, the width of the negative electrode 24 may be the same as the width of the positive electrode 23, or may be smaller.

[0037] The electrode body 20 has a substantially rectangular parallelepiped shape. As shown in FIGS. 3 and 4, the electrode body 20 has a first side surface 20a facing the bottom surface 12a of the case body 12. The electrode body 20 has a second side surface 20c facing the top surface 12c of the case body 12. The first side surface 20a and the second side surface 20c are a pair of side surfaces facing each other. In addition to this, the electrode body 20 has a pair of main surfaces facing the pair of long side surfaces 12b of the case body 12. The electrode body 20 has a pair of side surfaces facing the first sealing plate 14 and the second sealing plate 16.

[0038] The separator 25 is strip-shaped. That is, the separator 25 is long and narrow. The separator 25 is bent in a ninety-nine-fold shape. Specifically, the separator 25 is folded back alternately at the ends of the positive electrode 23 and the negative electrode 24. Therefore, as shown in FIG. 5, the separator 25 has a flat portion along the electrode and a bent portion folded back at the end of the electrode. As a result, each of the plurality of positive electrodes 23 is sandwiched by the separator 25, and each of the plurality of negative electrodes 24 is sandwiched by the separator 25. Since the separator 25 is in a ninety-nine-fold shape, the manufacturing efficiency of the laminated electrode body can be increased.

[0039] Therefore, as shown in FIG. 5, the bent portion of the separator 25 is defined as a first bent portion 25a folded back at the end of the positive electrode 23, and a second bent portion 25b folded back at the end of the negative electrode 24. As shown in FIG. 6, the plurality of first bent portions 25a are arranged on the side of the second side surface 20c facing the top surface 12c of the case body 12. The portion of the plurality of first bent portions 25a facing the top surface 12c faces the outside of the electrode body 20 and constitutes the outer surface of the plurality of first bent portions 25a. The plurality of second bent portions 25b are arranged on the side of the first side surface 20a facing the bottom surface 12a of the case body 12. The portion of the plurality of second bent portions 25b facing the bottom surface 12a faces the outside of the electrode body 20 and constitutes the outer surface of the plurality of second bent portions 25b.

[0040] In the present embodiment, in the electrode body 20, separators 25 are positioned on both outermost surfaces in the stacking direction of the positive electrode 23 and the negative electrode 24. According to such a configuration, since the negative electrode 24, which is the outermost electrode in the electrode body 20, is covered by the separator 25, that is, it is not exposed, damage to the negative electrode 24 can be suppressed. Further, even when the negative electrode 24 is damaged and a part of the negative electrode active material layer peels off, the separator 25 can suppress the fragments peeled off from the negative electrode active material layer from moving within the secondary battery 100. Thus, in the secondary battery 100 according to the present embodiment, damage and detachment of the active material layer (negative electrode active material layer in the illustrated example) of the electrode plate (negative electrode 24 in the illustrated example) located outermost in the stacking direction of the positive electrode 23 and the negative electrode 24 in the electrode body 20 can be suppressed, and even when detachment of the active material layer occurs, a short circuit due to the detached active material layer can be suppressed.

[0041] On the other hand, in a secondary battery, improvement in the impregnation property of the electrolyte into the electrode body is required. Particularly in an in-vehicle battery, when the secondary battery is enlarged to extend the cruising range of the vehicle, the time for impregnating the electrolyte into the electrode body during the manufacture of the secondary battery becomes long (that is, the injection property becomes low), and there is a problem that the production efficiency decreases. Further, when the secondary battery is repeatedly charged and discharged at a high rate, the electrolyte is discharged from the electrode body due to the expansion / contraction of the active material layer, and thus there is also a problem that the lithium ion concentration in the electrode body tends to become non-uniform. Therefore, in an in-vehicle battery, it is desirable to improve the impregnation property of the electrolyte into the electrode body.

[0042] Therefore, in the present embodiment, the outer surface of the second bent portion 25b is not covered by the separator 25. Accordingly, the end portion of the positive electrode active material layer of the positive electrode 23 is exposed between the adjacent second bent portions 25b. For this reason, the electrolyte easily penetrates into the electrode body 20 from the end portion of the exposed positive electrode active material layer. Thereby, in the secondary battery 100, the impregnation property of the electrolyte into the electrode body 20 is extremely enhanced.

[0043] In addition, there is also an advantage that the gas generated inside the electrode body 20 is easily discharged to the outside of the electrode body 20 from the end of the exposed positive electrode active material layer. Also, in the example shown in FIG. 6, a gas discharge valve 13 is provided on the outer surface side of the second bent portion 25b, in other words, on the bottom surface 12a side of the case body 12. In this case, when the amount of gas generated inside the electrode body 20 is large, it is particularly advantageous because the large amount of gas generated by the gas discharge valve 13 can be easily discharged to the outside of the battery case 10.

[0044] In the illustrated example, the second side surface 20c of the electrode body 20 on the side where the first bent portion 25a is arranged faces the top surface 12c of the case body 12, and the first side surface 20a of the electrode body 20 on the side where the second bent portion 25b is arranged faces the bottom surface 12a of the case body 12, and the electrode body 20 is housed in the battery case 10. However, the orientation of the electrode body 20 when it is housed in the battery case 10 is not limited to that of the illustrated example.

[0045] However, the electrolytic solution includes the one impregnated in the electrode body 20 and the surplus solution not impregnated in the electrode body 20. The surplus solution is located between the battery case 10 and the electrode body 20. Therefore, the surplus solution is located on the first side surface 20a side of the electrode body 20 facing the bottom surface 12a of the case body 12. Therefore, as in the example shown in FIG. 6, when the first side surface 20a of the electrode body 20 is on the side where the first bent portion 25a is arranged, the surplus solution is likely to impregnate from the end of the positive electrode active material layer of the exposed positive electrode 23, so that the impregnation property of the electrolytic solution into the electrode body 20 becomes particularly high.

[0046] As shown in FIG. 5, in the present embodiment, in the longitudinal direction of the separator 25, the tip 25e on the cover portion 25c side is disposed on one of the pair of opposing main surfaces of the electrode body 20. In this case, it is possible to more reliably suppress the lamination misalignment of the positive electrode 23, the negative electrode 24, and the separator 25 in the electrode body 20 as a whole. The tip 25e on the cover portion 25c side of the separator 25 is preferably in a region where the positive electrode 23 and the negative electrode 24 face each other. In particular, in the illustrated example, since the width of the negative electrode 24 is larger than the width of the positive electrode 23, the negative electrode 24 has a region at its edge that does not face the positive electrode 23 and a region at its center that faces the positive electrode 23. Therefore, when the tip 25e on the cover portion 25c side of the separator 25 is in a region where the positive electrode 23 and the negative electrode 24 face each other, it becomes easier to suppress the lamination misalignment.

[0047] In the present embodiment, a region 25d of the separator 25 that is located on the tip 25e side with respect to the cover portion 25c (in other words, a region of the separator 25 that is folded back along the main surface of the electrode body 20 from the end of the cover portion 25c) is adhered to a region that exists inside the region 25d of the separator 25 that is located on the tip 25e side with respect to the cover portion 25c (that is, on the electrode body 20 side). The region that exists inside is a region of the separator 25 that is on the inner layer side of the region 25d of the electrode body 20 that is located on the tip 25e side with respect to the cover portion 25c. In other words, the region that exists inside is a part of the separator 25 that covers the negative electrode 24, which is the outermost layer of the electrode lamination structure included in the electrode body 20. In this case, the region 25d located on the tip side with respect to the cover portion 25c can be efficiently fixed to the electrode body 20. That is, it is easy to fix the separator 25.

[0048] At this time, preferably, the region 25d located on the tip 25e side rather than the cover portion 25c is fixed in the separator 25 without using a tape on the inner side of the region 25d located on the tip 25e side. Therefore, no tape is attached on the main surface of the electrode body 20. In this case, generation of a large step portion caused by the thickness of the tape can be suppressed. When the electrode body 20 of the secondary battery 100 expands and the electrode body 20 comes into contact with the battery case 10, or when the secondary battery 100 is used with pressure applied in its thickness direction, a pressure difference applied to the electrode body 20 may occur due to the step portion caused by the thickness of the tape. This pressure difference may be a factor that makes the battery reaction non-uniform or a factor that causes lithium precipitation. Therefore, by not using a tape as described above and not generating a step portion due to the thickness of the tape, effects such as improvement in the uniformity of the battery reaction and suppression of lithium precipitation can be obtained.

[0049] As a specific method for fixing the region 25d located on the tip 25e side of the separator 25 without using a tape, for example, a method using an adhesive, particularly a method of press bonding, can be mentioned. When performing press bonding, it is preferable that the separator 25 has an adhesive layer described later. Note that an adhesive may be applied only to the fixed portion of the separator 25. Press bonding may be performed at room temperature or at a high temperature (for example, 50°C to 100°C).

[0050] Alternatively, the tip 25e on the cover portion 25c side of the separator 25 may be disposed on one of the pair of opposing side surfaces of the electrode body 20. In this case, generation of a step due to the separator 25 on the main surface of the electrode body 20 can be suppressed.

[0051] In the present embodiment, since the folded-back portion of the separator 25 at the end of the positive electrode 23 is the first bent portion 25a, the separator 25 has a cover portion 25c that covers the outer surface of the first bent portion 25a. Therefore, on the side of the side surface 20c of the electrode body 20, the outside of the portion where the end of the negative electrode active material layer of the negative electrode 24 is exposed is covered by the cover portion 25c of the separator 25. Thereby, even when a part of the negative electrode active material layer of the negative electrode 24 is detached, it is possible to suppress the fragments of the detached negative electrode active material layer from moving greatly from the position where they are detached by the cover portion 25c of the separator 25. As a result, it is possible to effectively suppress the occurrence of a short circuit due to the fragments of the detached negative electrode active material layer.

[0052] In a lithium-ion secondary battery, detachment of a part of the active material layer is much more likely to occur at the negative electrode than at the positive electrode. Therefore, by adopting the present embodiment, even if a part of the negative electrode active material layer that is more likely to be detached is detached, it is possible to more effectively suppress a short circuit caused by the detached negative electrode active material layer.

[0053] Next, the materials constituting the positive electrode 23, the negative electrode 24, and the separator 25 will be described. The positive electrode 23 typically has a positive electrode current collector and a positive electrode active material layer fixed on at least one surface of the positive electrode current collector. The positive electrode current collector is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode current collector is a metal foil, specifically an aluminum foil. In the present embodiment, in the positive electrode 23, a portion where the positive electrode current collector is exposed without forming the positive electrode active material layer is formed, and the exposed portion constitutes a current collecting tab. However, the method of configuring the current collecting tab is not limited to this.

[0054] The positive electrode active material layer contains a positive electrode active material capable of reversibly occluding and releasing charge carriers. As the positive electrode active material, an oxide containing at least one of Ni, Co, and Mn is preferable, and examples thereof include lithium transition metal composite oxides such as lithium cobalt oxide, lithium manganate, lithium nickelate, lithium nickel manganese composite oxide, and lithium nickel cobalt manganese composite oxide. The positive electrode active material is more preferably a lithium composite oxide containing Ni (in other words, a Ni-containing lithium composite oxide). In the Ni-containing lithium composite oxide, the Ni content is preferably in the range of 70 to 100 mol% with respect to the total number of moles of metals other than Li. In the lithium transition metal composite oxide, a part of Ni, Co, and Mn may be substituted with Al, Ti, Zr, P, B, Si, Nb, C, etc. Further, the positive electrode active material may be one in which the particle surface of the lithium transition metal composite oxide is coated with a compound containing Al, Ti, Zr, W, P, B, Si, Nb, C, etc. The total substitution amount and addition amount are about 0.1 to 7% by mass. On the other hand, as the positive electrode active material, a lithium transition metal phosphate compound such as lithium iron phosphate can also be used. The positive electrode active material layer may contain a conductive material, a binder, and the like. As the conductive material, a carbon material such as carbon black or carbon nanotube is preferable. As the binder, a resin binder such as polyvinylidene fluoride is preferable.

[0055] The negative electrode 24 typically has a negative electrode current collector and a negative electrode active material layer fixed on at least one surface of the negative electrode current collector. The negative electrode current collector is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode current collector is a metal foil here, specifically a copper foil. In the present embodiment, in the negative electrode 24, a portion where the negative electrode current collector is exposed without forming the negative electrode active material layer is formed, and the exposed portion constitutes the current collecting tab. However, the method of configuring the current collecting tab is not limited to this.

[0056] The negative electrode active material layer contains a negative electrode active material capable of reversibly occluding and releasing charge carriers. Examples of the negative electrode active material include carbon-based negative electrode active materials such as graphite, hard carbon, and soft carbon; Si-based negative electrode active materials such as Si and silicon oxide; silicon-carbon composite negative electrode active materials; and Sn-based negative electrode active materials such as Sn. The negative electrode active material layer may contain a conductive material, a thickening material, a binder, etc. It is preferable to include styrene-butadiene rubber, carboxymethyl cellulose, etc. as the binder.

[0057] The separator 25 is a member that insulates the positive electrode active material layer and the negative electrode active material layer. As the separator 25, for example, a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) is suitable. The porous resin sheet may have a single-layer structure or a multilayer structure (e.g., a three-layer structure of PP / PE / PP).

[0058] It is preferable that an adhesive layer is provided on the surface of the separator 25. The adhesive layer contains, for example, an adhesive resin such as an acrylic resin or polyvinylidene fluoride. When the separator 25 has an adhesive layer, it is easy to suppress the lamination shift between the separator 25 and the electrode. The adhesive layer may be provided on the entire surface of the separator 25 or may be pattern-coated.

[0059] A heat resistance layer (HRL) containing ceramic particles may be provided on the surface of the separator 25. Examples of the material of the ceramic particles include alumina, boehmite, aluminum hydroxide, titania, etc. The heat resistance layer preferably further contains a resin binder. The resin binder may be an adhesive resin such as an acrylic resin or polyvinylidene fluoride. By adding an appropriate amount of the resin binder into the heat resistance layer, the heat resistance layer can also function as an adhesive layer.

[0060] As one embodiment of the separator 25, the separator 25 includes a base material of a porous resin sheet and adhesive layers on both surfaces of the base material. As another embodiment of the separator 25, the separator 25 includes a base material of a porous resin sheet, an adhesive layer on one surface of the base material, and a heat-resistant layer on the other surface of the base material. In this embodiment, the heat-resistant layer may have the function of the adhesive layer. As yet another embodiment of the separator 25, the separator 25 includes a base material of a porous resin sheet, an adhesive layer on one surface of the base material, and a heat-resistant layer on the other surface of the base material, and further includes an adhesive layer on this heat-resistant layer.

[0061] <Insulating sheet> As shown in FIGS. 4 and 6, the insulating sheet 50 is housed inside the battery case 10 together with the electrode body 20. The insulating sheet 50 is disposed between the battery case 10 and the electrode body 20. The insulating sheet 50 covers the periphery of the electrode body 20. Preferably, the insulating sheet 50 covers at least the main surface of the electrode body 20, the first side surface 20a, and the second side surface 20c.

[0062] The insulating sheet 50 is made of an insulating material and is preferably made of resin. Examples of the resin include olefin resins such as polyethylene (PE), polypropylene (PP), and polymethylpentene (PMP / TPX (trademark)); polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); acrylic resin (PMMA); polyimide (PI); polyphenylene ether (PPE); triacetate (TAC); polyphenylene sulfide resin (PPS); polycarbonate (PC); nylon; and fluorine resins such as polytetrafluoroethylene (PTFE). Among them, PE and PP are preferred.

[0063] Fig. 7 shows a developed view of the insulating sheet 50. In the present embodiment, the insulating sheet 50 is composed of a single sheet-like member. The insulating sheet 50 is formed by bending this sheet-like member into a rectangular tube shape corresponding to the shape of the electrode body 20. As shown in Fig. 6, at both ends in the circumferential direction of the electrode body 20, there is an overlapping portion 50a where the bent sheet ends overlap. In the insulating sheet 50, at this overlapping portion 50a, both ends of the bent sheet are fixed by joining or the like. The joining can be performed, for example, by welding such as thermal welding or ultrasonic welding; adhesion with an adhesive; fixing with an adhesive tape, etc. At this overlapping portion 50a, only a part of both ends of the bent sheet may be joined. For example, a total of two locations at both ends of the overlapping portion 50a are joined, or a total of three locations including both ends and the central portion of the overlapping portion 50a are joined. At this overlapping portion 50a, it may be joined over the entire length of the overlapping portion 50a.

[0064] Here, in the present embodiment, in the overlapping portion 50a of the insulating sheet 50, there is a region through which the electrolytic solution and gas can pass. In this case, it is advantageous from the viewpoints of high impregnation of the electrolytic solution into the electrode body 20 and rapid discharge of gas from the electrode body 20. The region through which the electrolytic solution and gas can pass can be provided by joining only a part of the overlapping portion 50a. That is, the non-joined portion in the overlapping portion 50a becomes the region through which the electrolytic solution and gas can pass. Alternatively, by providing a through-hole in the insulating sheet while joining over the entire length of the overlapping portion 50a, etc., a region through which the electrolytic solution and gas can pass can also be provided. The region through which the electrolytic solution and gas can pass in the overlapping portion 50a preferably has a dimension of 1 / 5L or more, more preferably 1 / 3L or more, and even more preferably 1 / 2L or more in the extending direction of the overlapping portion 50a, where the total length of the overlapping portion is L. The region through which the electrolytic solution and gas can pass in the overlapping portion 50a of the insulating sheet 50 may be always open or may be a region that opens under stress.

[0065] In this embodiment, the overlapping portion 50a of the insulating sheet 50 faces the first side surface 20a, which is the side where the second bent portion 25b of the electrode body 20 is located. In the second bent portion 25b, the positive electrode active material layer of the positive electrode 23 is exposed, enhancing the impregnation property of the electrolytic solution into the electrode body. Therefore, when the overlapping portion 50a faces the first side surface 20a, it is advantageous in terms of further enhancing the impregnation property of the electrolytic solution into the electrode body. At this time, it is more advantageous that there is a region in the overlapping portion 50a of the insulating sheet 50 through which the electrolytic solution and gas can pass.

[0066] In this embodiment, the overlapping portion 50a of the insulating sheet 50 is on the side of the bottom surface 12a of the case body 12 of the battery case 10. Since the surplus liquid of the electrolytic solution not impregnated in the electrode body 20 exists on the bottom surface 12a side of the case body 12 within the battery case 10, when the overlapping portion 50a faces the bottom surface 12a, it is advantageous for supplying this surplus liquid to the electrode body 20. Therefore, in this embodiment, it is preferable that the overlapping portion 50a of the insulating sheet 50 is on the side where the surplus liquid of the electrolytic solution exists. At this time, it is more advantageous that there is a region in the overlapping portion 50a of the insulating sheet 50 through which the electrolytic solution can pass. Note that the overlapping portion 50a of the insulating sheet 50 may face a surface other than the bottom surface 12a of the case body 12 of the battery case 10.

[0067] In this embodiment, the overlapping portion 50a faces the bottom surface 12a of the case body 12 having the gas discharge valve 13. Thus, it is preferable that the overlapping portion 50a faces the surface of the battery case 10 having the gas discharge valve 13. In this case, when gas rapidly generates within the electrode body 20, it is easy to discharge the gas outside the battery case 10 through the gas discharge valve 13. At this time, it is more advantageous that there is a region in the overlapping portion 50a of the insulating sheet 50 through which the gas can pass. Note that the overlapping portion 50a of the insulating sheet 50 may face a surface of the case body 12 of the battery case 10 that does not have the gas discharge valve 13.

[0068] <Electrolytic solution> The electrolyte is housed inside the battery case 10 together with the electrode body 20. The electrolyte may be the same as that of a general secondary battery and is not particularly limited. Typically, the electrolyte is a non-aqueous liquid electrolyte (i.e., non-aqueous electrolyte) containing a non-aqueous solvent and a supporting salt. The non-aqueous solvent includes, for example, carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The non-aqueous solvent is preferably a mixture of EC, EMC, and DMC in the range of 1 to 99% by volume each so that the total ratio is 100% by volume. The non-aqueous solvent may further contain carboxylic acid esters such as methyl acetate. The supporting salt, also called an electrolyte salt, is, for example, a fluorine-containing lithium salt. Examples of the fluorine-containing lithium salt include LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI), etc. The supporting salt preferably contains LiPF6. The concentration of the supporting salt is not particularly limited, but is preferably 0.6 to 1.8 mol / L, and more preferably 0.7 mol / L to 1.3 mol / L. The electrolyte may further contain additives, specific examples such as film-forming agents such as vinylene carbonate (VC) and oxalato complexes; gas generators; thickeners, etc.

[0069] The secondary battery 100 can be used for various applications. Suitable applications include in-vehicle applications, specifically, power sources for driving mounted on vehicles such as battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV). Also, the secondary battery 100 can be used as a storage battery such as a small power storage device. The secondary battery 100 can typically also be used in the form of a battery module formed by connecting a plurality of them in series and / or in parallel.

[0070] As described above, specific examples of the present disclosure have been described in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

[0071] That is, the secondary battery of the present disclosure is as follows in items [1] to

[10] . [1] An electrode body including a plurality of first electrode plates, a plurality of second electrode plates having polarities different from those of the first electrode plates, and a separator disposed between the first electrode plates and the second electrode plates, an electrolytic solution, a case for housing the electrode body and the electrolytic solution, and a secondary battery comprising: the separator is strip-shaped and is bent in a ninety-fold shape, the separator includes a first bent portion folded back at an end of the first electrode plate and a second bent portion folded back at an end of the second electrode plate, a plurality of the first bent portions are disposed on one side surface of a pair of opposing side surfaces of the electrode body, a plurality of the second bent portions are disposed on the other side surface of a pair of opposing side surfaces of the electrode body, the separator includes a cover portion covering an outer surface of the plurality of the first bent portions, the outer surface of the second bent portion is not covered by the separator, in the electrode body, the separator is located on both outermost surfaces in the stacking direction of the first electrode plate and the second electrode plate, a secondary battery. [2] The case includes a pair of opposing first surfaces, a pair of opposing second surfaces, and a pair of opposing third surfaces, the first bent portion and the cover portion are disposed on one side of the pair of first surfaces, the secondary battery according to item [1], wherein the second bent portion is disposed on the other side of the pair of first surfaces. [3] On the other side of the pair of first surfaces, a gas discharge valve is provided which breaks when the pressure in the case becomes a predetermined value or more and discharges the gas in the case to the outside of the case. The secondary battery according to item [2]. [4] The electrolytic solution includes an excess liquid located between the case and the electrode body, the secondary battery according to item [2] or [3], wherein the excess liquid is located on the other side of the pair of first surfaces. [5] The outer surface of the electrode body is covered with an insulating sheet, The insulating sheet has an overlapping portion of the insulating sheet on the other side of the pair of the first surfaces. The secondary battery according to any one of items [2] to [4], wherein a region through which the electrolytic solution and gas can pass exists in the overlapping portion. [6] The electrode body has a first electrode tab electrically connected to the first electrode plate at one end, and a second electrode tab electrically connected to the second electrode plate at the other end. The case includes a case body having a first opening at one end and a second opening at the other end, a first sealing plate for sealing the first opening, and a second sealing plate for sealing the second opening. The secondary battery according to any one of items [1] to [5], wherein a first electrode terminal electrically connected to the first electrode plate is provided on the first sealing plate, and a second electrode terminal electrically connected to the second electrode plate is provided on the second sealing plate. [7] In the longitudinal direction of the separator, the tip on the cover portion side is disposed on one of the pair of main surfaces of the electrode body facing each other. The secondary battery according to any one of items [1] to [6]. [8] The region located on the tip side of the cover portion is adhered to the region existing inside the region located on the tip side of the cover portion in the separator. The secondary battery according to item [7]. [9] The region located on the tip side of the cover portion is fixed without using a tape inside the region located on the tip side of the cover portion in the separator. The secondary battery according to item [8].

[10] In the longitudinal direction of the separator, the tip on the cover portion side is disposed on one of the pair of side surfaces of the electrode body facing each other. The secondary battery according to any one of items [1] to [6].

Explanation of Reference Numerals

[0072] 10 Battery case 12 Case body 12a Bottom surface 13 Gas discharge valve 14 First sealing plate 16 Second sealing plate 20 Electrode body 23 Positive electrode 24 Negative electrode 25 Separator 50 Insulating sheet 100 Secondary battery

Claims

1. An electrode body including a plurality of first electrode plates, a plurality of second electrode plates having polarities different from those of the first electrode plates, and a separator disposed between the first electrode plates and the second electrode plates; An electrolytic solution; A case for housing the electrode body and the electrolytic solution; A secondary battery comprising: The separator is strip-shaped and bent in a ninety-fold shape; The separator includes a first bent portion folded back at an end of the first electrode plate and a second bent portion folded back at an end of the second electrode plate; A plurality of the first bent portions are disposed on one side surface of a pair of opposing side surfaces of the electrode body; A plurality of the second bent portions are disposed on the other side surface of a pair of opposing side surfaces of the electrode body; The separator includes a cover portion covering an outer surface of the plurality of the first bent portions; The outer surface of the second bent portion is not covered by the separator; In the electrode body, the separator is located on both outermost surfaces in the stacking direction of the first electrode plate and the second electrode plate; A secondary battery.

2. The case includes a pair of opposing first surfaces, a pair of opposing second surfaces, and a pair of opposing third surfaces; The first bent portion and the cover portion are disposed on one side of the pair of first surfaces; The secondary battery according to claim 1, wherein the second bent portion is disposed on the other side of the pair of first surfaces.

3. The secondary battery according to claim 2, wherein a gas discharge valve is provided on the other side of the pair of first surfaces, which breaks when the pressure in the case becomes a predetermined value or more and discharges the gas in the case to the outside of the case.

4. The electrolytic solution includes surplus liquid located between the case and the electrode body; The secondary battery according to claim 2, wherein the surplus liquid is located on the other side of the pair of first surfaces.

5. The outer surface of the electrode body is covered with an insulating sheet; The insulating sheet has an overlapping portion on the other side of the pair of first surfaces; The secondary battery according to claim 2, wherein a region through which the electrolytic solution and gas can pass exists in the overlapping portion.

6. The electrode body has a first electrode tab electrically connected to the first electrode plate at one end and a second electrode tab electrically connected to the second electrode plate at the other end. The case includes a case body having a first opening at one end and a second opening at the other end, a first sealing plate for sealing the first opening, and a second sealing plate for sealing the second opening. The secondary battery according to claim 1, wherein a first electrode terminal electrically connected to the first electrode plate is provided on the first sealing plate, and a second electrode terminal electrically connected to the second electrode plate is provided on the second sealing plate.

7. The secondary battery according to claim 1, wherein, in the longitudinal direction of the separator, the tip on the cover portion side is disposed on one of the pair of main surfaces of the electrode body that face each other.

8. The secondary battery according to claim 7, wherein a region located on the tip side of the cover portion is adhered to a region existing inside a region located on the tip side of the cover portion in the separator.

9. The secondary battery according to claim 8, wherein a region located on the tip side of the cover portion is fixed inside a region located on the tip side of the cover portion in the separator without using a tape.

10. The secondary battery according to claim 1, wherein, in the longitudinal direction of the separator, the tip on the cover portion side is disposed on one of the pair of side surfaces of the electrode body that face each other.

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