Cylindrical battery

Abstract

A negative electrode mixture layer (52) has: a first layer (52a) disposed on a winding outer surface (50a) in a thickness direction of a negative electrode core body (50); a second layer (52b) having a density smaller than that of the first layer (52a) and disposed on the side, of the first layer (52a), opposite from the winding outer surface (50a) side; a third layer (52c) disposed on a winding inner surface (50b) in the thickness direction of the negative electrode core body (50) and having a density substantially the same as the density of the first layer (52a); and a fourth layer (52d) having a density substantially the same as the density of the second layer (52b) and disposed on the side, of the third layer (52c), opposite from the winding inner surface (50b) side. The ratio of the thickness of the second layer (52b) to the thickness of the first layer (52a) is different from the ratio of the thickness of the fourth layer (52d) to the thickness of the third layer (52c).

Description

Cylindrical battery

[0001] The present disclosure relates to a cylindrical battery.

[0002] Conventionally, as a cylindrical battery, there is one described in Patent Document 1. This cylindrical battery includes an electrode body in which a long positive electrode including a positive electrode core and a positive electrode mixture layer and a long negative electrode including a negative electrode core and a negative electrode mixture layer are wound via a separator, an electrolyte, a bottomed cylindrical outer can that houses the electrode body and the electrolyte, and a sealing body that is caulked and fixed to the opening of the outer can via a gasket.

[0003] Japanese Patent Application Laid-Open No. 2013-016328

[0004] FIG. 6 is a schematic cross-sectional view when the negative electrode 112 of the cylindrical battery 110 of a reference example, which is not a prior art, is cut in a plane including the center in the negative electrode width direction and the negative electrode thickness direction. As shown in FIG. 6, in the negative electrode 112, the same negative electrode mixture layer 152e and negative electrode mixture layer 152f are provided on the negative electrode core 50 on the outer winding side and the inner winding side. Further, the negative electrode 112 has a negative electrode longitudinal direction region 180 in which the negative electrode core 50 is exposed and is adjacent to the negative electrode mixture layer 152e in the negative electrode longitudinal direction on the outer winding side in the thickness direction. In other words, the negative electrode 112 has a negative electrode core exposed portion 151 that is continuous via a step portion 153 on the first surface 185 on the outer winding side in the thickness direction of the negative electrode mixture layer 152e.

[0005] The inventor of the present invention has found that when the same negative electrode mixture layer 152e and negative electrode mixture layer 152f are provided on the negative electrode core 50 on the outer winding side and the inner winding side, the negative electrode 112 has a negative electrode core exposed portion adjacent to the negative electrode mixture layer 152a on at least one of the outer winding side and the inner winding side, the linear pressure of the corner portion 155 on the negative electrode core exposed portion 151 side in the negative electrode mixture layer 152e tends to become excessive during rolling by a pair of rolling rolls 15a and 15b after applying a negative electrode mixture slurry on the negative electrode core 50, the corner portion 155 is likely to be damaged, and the active material is likely to fall off around the corner portion. Here, the problem that the above-mentioned corner portion 155 is likely to be damaged can also occur in the positive electrode. Therefore, an object of the present disclosure is to provide a cylindrical battery in which the corner portion on the side of the first electrode core exposed portion of the first electrode mixture layer is difficult to be damaged.

[0006] To solve the above problems, the cylindrical battery according to the present disclosure comprises an electrode body in which a long first electrode including a first electrode core and a first electrode mixture layer, and a long second electrode including a second electrode core and a second electrode mixture layer are wound around a separator, an electrolyte, and an outer container for housing the electrode body and the electrolyte, wherein the first electrode has a first electrode longitudinal region in the thickness direction where the first electrode core is exposed on the first side, the first electrode mixture layer has a first layer disposed on a first surface in the thickness direction of the first electrode core, a second layer having a density smaller than the density of the first layer and disposed on the side opposite to the first surface of the first layer, a third layer disposed on a second surface in the thickness direction of the first electrode core and having a density substantially the same as the density of the first layer, and a fourth layer having a density substantially the same as the density of the second layer and disposed on the side opposite to the second surface of the third layer, wherein the ratio of the thickness of the second layer to the thickness of the first layer is different from the ratio of the thickness of the fourth layer to the thickness of the third layer.

[0007] According to the cylindrical battery described herein, the corners of the first electrode mixture layer on the side where the first electrode core is exposed are less likely to be damaged.

[0008] This is an axial cross-sectional view of a cylindrical battery according to one embodiment of the present disclosure. This is a perspective view showing an example of the electrode body of the cylindrical battery. This is a schematic cross-sectional view when a long, unfolded negative electrode is cut by a plane including the center in the negative electrode width direction and the negative electrode thickness direction. This is an enlarged schematic cross-sectional view of the negative electrode longitudinal region where the negative electrode mixture layer exists on both the outer and inner sides of the winding with respect to the negative electrode longitudinal direction. This is an enlarged schematic cross-sectional view corresponding to Figure 4 of the cylindrical battery of the reference example. This is a schematic cross-sectional view corresponding to Figure 3 illustrating the problems in the cylindrical battery of the reference example.

[0009] Hereinafter, embodiments of the cylindrical battery according to this disclosure will be described in detail with reference to the drawings. The cylindrical battery of this disclosure may be a primary battery or a secondary battery. Furthermore, the cylindrical battery of this disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a cylindrical lithium-ion secondary battery using a non-aqueous electrolyte will be given as an example of one embodiment of the cylindrical battery 10, but the cylindrical battery of this disclosure is not limited to this.

[0010] It is intended from the outset that new embodiments can be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. In addition, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. In this specification, the axial (height direction) sealing body 17 side of the cylindrical battery 10 is referred to as "upper," and the axial bottom 68 side of the outer casing 16 is referred to as "lower." Among the components described below, components that are not described in the independent claim indicating the highest-level concept are optional components and are not essential components.

[0011] Figure 1 is an axial cross-sectional view of a cylindrical battery 10 according to one embodiment of the present disclosure, and Figure 2 is a perspective view showing an example of an electrode body 14 of the cylindrical battery 10. As shown in Figure 1, the cylindrical battery (hereinafter simply referred to as "battery") 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), a metal outer casing 16 that houses the electrode body 14 and the non-aqueous electrolyte, and a sealing body 17 that closes the axial upper opening of the outer casing 16. In the example shown in Figure 1, the outer casing 16 has a bottomed cylindrical shape, but the outer casing may have a cylindrical shape, and the battery may have a structure in which the openings on both sides of the outer casing are sealed.

[0012] As shown in Figure 2, the electrode body 14 has a wound structure in which a long positive electrode 11 and a long negative electrode 12 are wound around two long separators 13. The negative electrode 12 is an example of a first electrode, and the positive electrode 11 is an example of a second electrode. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and widthwise (short-side) directions. The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The negative electrode 12 may constitute the starting end of the winding of the electrode body 14. However, generally, the separators 13 extend beyond the starting end of the winding of the negative electrode 12, and the starting end of the winding of the separators 13 becomes the starting end of the winding of the electrode body 14.

[0013] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes. Liquid electrolytes (electrolytes) contain a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. Non-aqueous solvents may contain halogen-substituted compounds (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0014] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0015] The positive electrode 11 comprises a positive electrode core and positive electrode mixture layers arranged on both sides of the positive electrode core. The positive electrode core can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its surface. The positive electrode mixture layers contain a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it to arrange the positive electrode mixture layers on both sides of the positive electrode core.

[0016] The positive electrode active material is mainly composed of a lithium-containing composite oxide. Examples of metal elements contained in the lithium-containing composite oxide (lithium-containing metal composite oxide) include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. A preferred example of a lithium-containing composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. The lithium-containing composite oxide may have a spinel structure or an olivine structure. However, it is preferable that the lithium-containing composite oxide has a layered rock salt structure because it makes it easier to produce a positive electrode with a large discharge capacity.

[0017] Examples of conductive agents included in the positive electrode mixture layer include carbon black such as acetylene black and Ketjen black, and carbon materials such as graphite. Examples of binders included in the positive electrode mixture layer 42 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0018] The negative electrode 12 comprises a negative electrode core 50 (see Figures 3 and 4) and negative electrode mixture layers 52 (see Figures 3 and 4) arranged on both sides of the negative electrode core 50. The negative electrode mixture layer 52 is an example of a first electrode mixture layer. The negative electrode core 50 can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 52 contains a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 50, drying the coating, and then compressing it to arrange the negative electrode mixture layer 52 on both sides of the negative electrode core 50.

[0019] Generally, carbon materials that reversibly intercept and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphite such as natural graphite such as flake graphite, lump graphite, and clay graphite, and artificial graphite such as lump graphite and graphitized mesophase carbon microbeads. In order to effectively increase the discharge capacity of the negative electrode mixture layer 52, it is preferable that the negative electrode mixture layer 52 contains a silicon-containing material containing silicon (Si) as the negative electrode active material.

[0020] If the weight ratio of silicon element to the negative electrode mixture layer 52 is 7% by mass or more, the discharge capacity tends to increase, and the battery 10 tends to have a high output. Furthermore, if the weight ratio of silicon element to the negative electrode mixture layer 52 is 12% by mass or more, the battery output tends to increase even further. Since the volume change of the negative electrode mixture layer 52 during charging and discharging can be reduced and the expansion and contraction of the electrode body 14 during charging and discharging can be suppressed, the durability (long-term reliability) of the battery 10 tends to be good, it is preferable that the weight ratio of silicon element to the negative electrode mixture layer 52 is 50% by mass or less. The negative electrode active material may include metals other than Si that alloy with lithium, alloys containing such metals, compounds containing such metals, etc.

[0021] The binder contained in the negative electrode mixture layer 52 may be fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) or a modified version thereof is used. In addition to SBR, the negative electrode mixture layer 52 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0022] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably polyethylene, polyolefin resins such as polypropylene, or cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be placed on the surface of the separator 13.

[0023] As shown in Figure 1, a positive electrode lead 20 is joined to the positive electrode 11, and a negative electrode lead 21 is joined to the end of the negative electrode 12 on the winding start side in the longitudinal direction. The battery 10 has an insulating plate 18 above the electrode body 14 and an insulating plate 19 below the electrode body 14. The positive electrode lead 20 extends towards the sealing body 17 through a through hole in the insulating plate 18, and the negative electrode lead 21 extends towards the bottom 68 of the outer casing 16 through a through hole in the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the sealing plate 23 of the sealing body 17 by welding or the like. The terminal cap 27 that constitutes the top plate of the sealing body 17 is electrically connected to the sealing plate 23, and the terminal cap 27 becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 68 of the metal outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0024] More specifically, the outer surface of the winding of the positive electrode 11 has a first positive electrode core exposed portion located at a distance in the longitudinal direction of the positive electrode from both ends in the longitudinal direction of the positive electrode. The first positive electrode core exposed portion is provided so as to be sandwiched between positive electrode mixture layers in the longitudinal direction of the positive electrode. Furthermore, the inner surface of the winding of the positive electrode 11 has a second positive electrode core exposed portion located at a distance in the longitudinal direction of the positive electrode from both ends in the longitudinal direction of the positive electrode. The second positive electrode core exposed portion is provided so as to be sandwiched between positive electrode mixture layers in the longitudinal direction of the positive electrode.

[0025] The first positive electrode core exposure portion and the second positive electrode core exposure portion are located in substantially the same region along the longitudinal direction of the positive electrode. The positive electrode lead is joined to the first positive electrode core exposure portion or the second positive electrode core exposure portion by ultrasonic welding or the like. Briefly, the positive electrode 11 has a first positive electrode core exposure portion and a second positive electrode core exposure portion in which the positive electrode core is exposed in an intermediate part such as the center in the winding direction, and the positive electrode lead 20 is electrically connected to the first positive electrode core exposure portion or the second positive electrode core exposure portion.

[0026] Figure 3 is a schematic cross-sectional view of a negative electrode 12 unfolded in a long shape, cut by a plane that includes the center in the negative electrode width direction and the negative electrode thickness direction. As shown in Figure 3, the negative electrode 12 has a negative electrode longitudinal region 80a on the first side (outside the winding) in the thickness direction in which the negative electrode core body 51 is exposed, and a negative electrode longitudinal region 80b on the second side (inside the winding) in the thickness direction in which the negative electrode core body 51 is exposed.

[0027] More specifically, the outer surface 12a of the negative electrode 12 has a first negative electrode core exposure portion 51a at the end on the winding start side in the longitudinal direction of the negative electrode, where the negative electrode core body 50 is exposed, and a second negative electrode core exposure portion 51b at the end on the winding end side in the longitudinal direction of the negative electrode, where the negative electrode core body 50 is exposed. Furthermore, the inner surface 12b of the negative electrode 12 has a third negative electrode core exposure portion 51c at the end on the winding start side in the longitudinal direction of the negative electrode, where the negative electrode core body 50 is exposed, and a fourth negative electrode core exposure portion 51d at the end on the winding end side in the longitudinal direction of the negative electrode, where the negative electrode core body 50 is exposed.

[0028] In the example shown in Figure 3, the first negative electrode core exposed portion 51a and the third negative electrode core exposed portion 51c are located in substantially the same negative electrode longitudinal region. However, the negative electrode longitudinal length of the first negative electrode core exposed portion 51a may be longer than the negative electrode longitudinal length of the third negative electrode core exposed portion 51c. Also, in the example shown in Figure 3, the negative electrode longitudinal length of the second negative electrode core exposed portion 51b is longer than the negative electrode longitudinal length of the fourth negative electrode core exposed portion 51d. However, the second negative electrode core exposed portion 51b and the fourth negative electrode core exposed portion 51d may be located in substantially the same negative electrode longitudinal region. The winding end of the negative electrode 12 is included in the negative electrode longitudinal region 80a, which is an example of the first electrode longitudinal region.

[0029] The second negative electrode core exposed portion 51b includes a portion that is included in the outermost surface of the electrode body 14 and includes a portion that contacts the inner surface of the outer can 16. Furthermore, a negative electrode lead 21 (see Figure 1) is joined to the first negative electrode core exposed portion 51a by ultrasonic welding or the like. The negative electrode lead 21 may also be joined to the third negative electrode core exposed portion 51c. In this embodiment, since both the winding start side and the winding end side of the negative electrode 12 are electrically connected to the negative electrode terminal, the current path on the negative electrode side can be reduced, and electrical resistance can be reduced.

[0030] Insulating tape (not shown) is applied to the exposed portion of the first positive electrode core and the exposed portion of the second positive electrode core, for example, so as to overlap the positive electrode mixture layer located on both sides in the longitudinal direction of the positive electrode. Insulating tape (not shown) is also applied to the exposed portion of the first negative electrode core 51a so as to cover at least the negative electrode lead 21. The insulating tape is provided for the purpose of preventing short circuits and preventing the active material from falling off. The insulating tape can be made of, for example, a tape with a polyimide film as the base material and a silicone adhesive, but it may be made of any material as long as it is insulating and can be applied.

[0031] The outermost surface of the electrode body may be composed of a separator, and the exposed portion of the negative electrode core may not come into contact with the inner surface of the outer can. The negative electrode lead may be joined at any position in the negative electrode width direction. Alternatively, only one negative electrode lead may be joined to the negative electrode, or two or more negative electrode leads may be joined to the negative electrode at intervals in the negative electrode width direction. Similarly, the positive electrode lead may be joined at any position in the positive electrode width direction. Alternatively, only one positive electrode lead may be joined to the positive electrode, or two or more positive electrode leads may be joined to the positive electrode at intervals in the positive electrode width direction. The lower end of the electrode body in the height direction may be composed of an exposed portion of the negative electrode core, and this exposed portion may be joined to the bottom of the outer can via a current collector plate. The upper end of the electrode body in the height direction may be composed of an exposed portion of the positive electrode core, and the positive electrode may be electrically connected to the sealing body by joining this exposed portion to a current collector plate.

[0032] Referring again to Figure 1, the battery 10 further comprises a resin gasket 28 positioned between the outer casing 16 and the sealing body 17. The sealing body 17 is crimped and fixed to the opening of the outer casing 16 via the gasket 28. This seals the internal space of the battery 10. The gasket 28 is sandwiched between the outer casing 16 and the sealing body 17, insulating the sealing body 17 from the outer casing 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer casing 16 and the sealing body 17.

[0033] The outer can 16 has a cylindrical portion 30 and a bottom portion 68, and the cylindrical portion 30 includes an annular shoulder portion 38 and an annular grooved portion 34. The grooved portion 34 is formed, for example, by spinning a part of the side surface of the outer can 16 radially inward along the entire circumference to create an annular recess on the radially inward side. The shoulder portion 38 is formed when the sealing body 17 is crimped and fixed to the outer can 16, by bending the upper end of the outer can 16 inward along the entire circumference towards the peripheral edge 45 of the sealing body 17.

[0034] The sealing body 17 has a structure in which a sealing plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a terminal cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The sealing plate 23 has at least one through hole 23a. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges.

[0035] If the battery 10 overheats and its internal pressure rises, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the terminal cap 27, thus interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is released from the through-hole 27a of the terminal cap 27. This release of gas prevents the battery 10 from rupturing due to an excessive rise in internal pressure, thereby increasing the safety of the battery 10.

[0036] The case described above has been one in which the sealing body 17 has a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and has a convex terminal cap 27 covering the rupture plates. However, the sealing body may consist only of rupture plates, or it may have a structure in which an internal terminal plate, an annular insulating plate, and a rupture plate are laminated in order from the electrode body side. Alternatively, the sealing body may not have rupture plates, and the bottom of the outer casing may have a thin, easily breakable portion that breaks when the battery overheats abnormally.

[0037] Figure 4 is an enlarged schematic cross-sectional view of the negative electrode longitudinal region where negative electrode mixture layers exist on both the outer and inner sides of the winding with respect to the negative electrode longitudinal direction. As shown in Figure 4, the negative electrode mixture layer 52 has a first layer 52a disposed on the outer surface 50a of the negative electrode core 50 in the thickness direction, and a second layer 52b having a density lower than that of the first layer 52a and disposed on the opposite side of the first layer 52a from the outer surface 50a. The negative electrode mixture layer 52 also has a third layer 52c disposed on the inner surface 50b of the negative electrode core 50 in the thickness direction and having a density approximately the same as that of the first layer 52a, and a fourth layer 52d having a density approximately the same as that of the second layer 52b and disposed on the opposite side of the third layer 52c from the inner surface 50b. The outer surface 50a is an example of the first surface in the thickness direction of the negative electrode core 50, and the inner surface 50b is an example of the second surface in the thickness direction of the negative electrode core 50.

[0038] In Figure 4 and Figure 5 (described later), the length of t, which is indicated in multiple places, is the same. The ratio of the thickness of the second layer 52b to the thickness of the first layer 52a is different from the ratio of the thickness of the fourth layer 52d to the thickness of the third layer 52c. In this embodiment, the sum of the masses of the first layer 52a and the second layer 52b arranged on a unit area of ​​the outer surface 50a of the winding is approximately equal to the sum of the masses of the third layer 52c and the fourth layer 52d arranged on a unit area of ​​the inner surface 50b of the winding. In this embodiment, the sum of the thicknesses of the first layer 52a and the second layer 52b is approximately equal to the sum of the thicknesses of the third layer 52c and the fourth layer 52d.

[0039] That is, when the density of the first layer 52a is g1, the density of the second layer 52b is g2, the thickness of the first layer 52a is d1, the thickness of the second layer 52b is d2, the thickness of the third layer 52c is d3, and the thickness of the fourth layer 52d is d4, then g1 > g2 and d2 / d1 is different from d4 / d3. Also, (g1・d1 + g2・d2) = (g1・d3 + g2・d4) and (d1 + d2) = (d3 + d4). In the example shown in Figure 4, d2 / d1 = 7 / 3 and d4 / d3 = 1. In this embodiment, (g1・d1+g2・d2)=(g1・d3+g2・d4) and (d1+d2)=(d3+d4) are true, but it is not necessary for either (g1・d1+g2・d2)=(g1・d3+g2・d4) or (d1+d2)=(d3+d4) or both to be true.

[0040] Next, the effects of battery 10 will be explained. Figure 5 is a schematic cross-sectional view of the cylindrical battery 110 of the reference example, corresponding to Figure 4. The cylindrical battery 110 of the reference example (hereinafter simply referred to as battery) differs from battery 10 in that when the thickness of the first layer 152a is d1', the thickness of the second layer 152b is d2', the thickness of the third layer 152c is d3', and the thickness of the second layer 152d is d4', the relationship d2' / d1' = d4' / d3' holds true. The other configurations are the same as battery 10. In the example shown in Figure 5, d2' / d1' = d4' / d3' = 3 / 2.

[0041] In the negative electrode 112 of the battery 110, with respect to the negative electrode mixture layer 152, the density of the second and fourth layers 152b and 152d on the side opposite to the negative electrode core 50 is lower than the density of the first and third layers 152a and 152c on the negative electrode core 50 side, both on the outer and inner sides of the negative electrode core 50. Therefore, the non-aqueous electrolyte can easily penetrate to the negative electrode core 50 side of the negative electrode mixture layer 152, both on the outer and inner sides of the negative electrode core 50, allowing the charge and discharge reaction to occur efficiently.

[0042] However, the inventor of the present invention has found experimentally that when d2' / d1' = d4' / d3 holds on both the outer and inner sides of the winding of the negative electrode core 50 as in the battery 110 of the reference example, if there is a negative electrode core exposed portion 151 (see FIG. 6) adjacent to the negative electrode binder layer 152e (see FIG. 6) in the negative electrode longitudinal direction, when the negative electrode binder slurry is applied onto the negative electrode core 50 and then rolled by a pair of rolling rolls 15a, 15b (see FIG. 6), the linear pressure at the corner 155 (see FIG. 6) on the side of the negative electrode core exposed portion 151 in the negative electrode binder layer 152e tends to become excessive, the corner 155 is likely to be damaged, and the active material is likely to fall off around the corner.

[0043] On the other hand, as in the present embodiment, when d2 / d1 is made different from d4 / d3 on both the outer and inner sides of the winding of the negative electrode core 50, when rolling by the rolling rolls 15a, 15b after applying the negative electrode binder slurry onto the negative electrode core 50, it is easy to reduce the linear pressure at the corner 55 (see FIG. 3) on the side of the negative electrode core exposed portion 51 in the negative electrode binder layer 52, damage to the corner 55 can be suppressed, and it has been found experimentally that the active material is less likely to fall off around the corner.

[0044] The inventor of the present invention speculates that if the ratio of the thickness of the high-density layer on the negative electrode core side to the low-density layer on the side opposite to the negative electrode core side is intentionally made different and unbalanced on the outer and inner sides of the winding of the negative electrode core, when pressed by the rolling roll 15, the negative electrode binder layer 52 is likely to move flexibly in the thickness direction, and the linear pressure at the corner 55 on the side of the negative electrode core exposed portion 51 in the negative electrode binder layer 52 is reduced.

[0045] Since the charge-discharge reaction is likely to occur efficiently and evenly in the winding direction of the electrode body 14, it is preferable that the sum of the mass of the first layer 52a and the mass of the second layer 52b arranged on the unit area of the outer winding surface 50a substantially coincides with the sum of the mass of the third layer 52c and the mass of the fourth layer 52d arranged on the unit area of the inner winding surface 50b. Also, since the roundness of the electrode body 14 is likely to be high and the reliability and battery performance of the battery 10 are likely to be high, it is preferable that the sum of the thickness of the first layer 52a and the thickness of the second layer 52b substantially coincides with the sum of the thickness of the third layer 52c and the thickness of the fourth layer 52d.

[0046] The present disclosure is not limited to the above-described embodiments and their modifications, and various improvements and changes can be made within the scope of the matters described in the claims of the present application and their equivalent scope. For example, in the above embodiment, the case where the first electrode is the negative electrode 12 and the first electrode active material layer is the negative electrode active material layer 52 has been described. However, the first electrode may be the positive electrode and the first electrode active material layer may be the positive electrode active material layer.

[0047] Specifically, the positive electrode may have a positive electrode longitudinal direction region where the positive electrode core is exposed on the first side in the positive electrode thickness direction, and the positive electrode active material layer may include a first layer disposed on the first surface of the positive electrode core in the positive electrode thickness direction, a second layer having a density smaller than that of the first layer and disposed on the side opposite to the first surface side in the first layer, a third layer disposed on the second surface of the positive electrode core in the positive electrode thickness direction and having a density substantially the same as that of the first layer, and a fourth layer having a density substantially the same as that of the second layer and disposed on the side opposite to the second surface side in the third layer. And the ratio of the thickness of the second layer to the thickness of the first layer may be different from the ratio of the thickness of the fourth layer to the thickness of the third layer. Even in this case, similar to the negative electrode, damage at the corners of the positive electrode active material layer can be effectively suppressed.

[0048] Also, in this case, since the charge-discharge reaction is likely to occur efficiently and evenly in the winding direction of the electrode body, it is preferable that the total mass of the first layer and the second layer disposed on the unit area of the first surface of the positive electrode core substantially coincides with the total mass of the third layer and the fourth layer disposed on the unit area of the second surface of the positive electrode core. Further, since the roundness of the electrode body is likely to be high and the reliability and performance of the battery are likely to be high, with respect to the positive electrode active material layer, it is preferable that the sum of the thickness of the first layer and the thickness of the second layer substantially coincides with the sum of the thickness of the third layer and the thickness of the fourth layer.

[0049] Furthermore, the cylindrical battery of this disclosure may have the following configuration: Configuration 1: An electrode body in which a long first electrode including a first electrode core and a first electrode mixture layer, and a long second electrode including a second electrode core and a second electrode mixture layer are wound around a separator, an electrolyte, and an outer casing for housing the electrode body and the electrolyte, wherein the first electrode has a first electrode longitudinal region in the first electrode thickness direction in which the first electrode core is exposed, and the first electrode mixture layer has a first layer disposed on the first surface of the first electrode core in the first electrode thickness direction, and a density higher than that of the first layer A cylindrical battery comprising: a second layer having a low density and positioned on the opposite side of the first surface of the first layer; a third layer positioned on the second surface in the first electrode thickness direction of the first electrode core and having approximately the same density as the first layer; and a fourth layer having approximately the same density as the second layer and positioned on the opposite side of the second surface of the third layer, wherein the ratio of the thickness of the second layer to the thickness of the first layer is different from the ratio of the thickness of the fourth layer to the thickness of the third layer. Configuration 2: The cylindrical battery according to Configuration 1, wherein the sum of the mass of the first layer and the mass of the second layer positioned on a unit area of ​​the first surface is approximately equal to the sum of the mass of the third layer and the mass of the fourth layer positioned on a unit area of ​​the second surface. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein the sum of the thickness of the first layer and the thickness of the second layer is approximately equal to the sum of the thickness of the third layer and the thickness of the fourth layer. Configuration 4: The cylindrical battery according to any one of Configurations 1 to 3, wherein the first electrode is the negative electrode and the longitudinal region of the first electrode includes the winding end of the negative electrode.

[0050] 10 Battery, 11 Positive electrode, 12 Negative electrode, 12a Outer surface of negative electrode winding, 12b Inner surface of negative electrode core winding, 13 Separator, 14 Electrode body, 15a, 15b Rolling roll, 16 Outer can, 17 Sealing body, 18 Insulating plate, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 23 Sealing plate, 23a Through hole, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Terminal cap, 27a Through hole, 28 Gasket, 30 Cylindrical part, 34 Grooved part, 38 Shoulder part, 42 Positive electrode mixture layer, 45 Peripheral part, 50 Negative electrode core, 50a Outer surface of negative electrode core winding, 50b 51 Inner surface of the negative electrode core, 51a Exposed portion of the negative electrode core, 51b Exposed portion of the first negative electrode core, 51c Exposed portion of the third negative electrode core, 51d Exposed portion of the fourth negative electrode core, 52 Negative electrode mixture layer, 52a First layer, 52b Second layer, 52c Third layer, 52d Fourth layer, 55 Corner portion, 68 Bottom portion, 80a, 80b Negative electrode longitudinal region, 15 Rolling roll.

Claims

1. An electrode body comprising: an elongated first electrode including a first electrode core and a first electrode mixture layer; an elongated second electrode including a second electrode core and a second electrode mixture layer, wound around a separator; an electrolyte; and an outer container for housing the electrode body and the electrolyte, wherein the first electrode has a longitudinal region of the first electrode where the first electrode core is exposed on the first side in the thickness direction of the first electrode; the first electrode mixture layer comprises: a first layer disposed on the first surface of the first electrode core in the thickness direction of the first electrode; a second layer having a density smaller than that of the first layer and disposed on the side opposite to the first surface of the first layer; a third layer disposed on the second surface of the first electrode core in the thickness direction of the first electrode and having a density approximately the same as that of the first layer; and a fourth layer having a density approximately the same as that of the second layer and disposed on the side opposite to the second surface of the third layer. A cylindrical battery in which the ratio of the thickness of the second layer to the thickness of the first layer is different from the ratio of the thickness of the fourth layer to the thickness of the third layer.

2. The cylindrical battery according to claim 1, wherein the sum of the mass of the first layer and the mass of the second layer arranged on a unit area of ​​the first surface is substantially equal to the sum of the mass of the third layer and the mass of the fourth layer arranged on a unit area of ​​the second surface.

3. The cylindrical battery according to claim 1 or 2, wherein the sum of the thickness of the first layer and the thickness of the second layer is substantially equal to the sum of the thickness of the third layer and the thickness of the fourth layer.

4. The cylindrical battery according to claim 1 or 2, wherein the first electrode is a negative electrode, and the longitudinal region of the first electrode includes the end of the winding that is finished on the negative electrode side.

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