Secondary battery

Abstract

An electrode for this secondary battery is characterized by comprising a core body, a mixture layer disposed on the core body, and a plurality of tabs electrically connecting the core body and an electrode terminal, wherein the plurality of tabs include a first tab on one end side in a longitudinal direction of the mixture layer, a second tab on the other end side in the longitudinal direction of the mixture layer, and a third tab disposed between the first tab and the second tab, the tab resistance of, from among the plurality of tabs, the third tab is highest in value, and the tab resistance of, from among the plurality of tabs, at least one of the first tab or the second tab is lowest in value if the ratio (Y / X) of the distance Y in the longitudinal direction from the other end of the mixture layer to the second tab to the distance X in the longitudinal direction from one end of the mixture layer to the first tab satisfies 0.95 ≤ Y / X ≤ 1.05.

Description

Secondary battery

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

[0002] Conventionally, there is a secondary battery including a wound electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. As such a secondary battery including a wound electrode body, for example, Patent Document 1 proposes a secondary battery including an electrode body in which a strip-shaped positive electrode having a plurality of positive electrode tabs and a strip-shaped negative electrode having a plurality of negative electrode tabs are wound with a separator interposed therebetween. Note that although it is a secondary battery including a laminated electrode body in which a plurality of positive and negative electrodes are alternately laminated, Patent Document 2 proposes a secondary battery in which the size of each tab connected to each of a plurality of electrodes is changed.

[0003] Japanese Unexamined Patent Application Publication No. 2016-115409, Japanese Unexamined Patent Application Publication No. 2012-181941 [[ID=ll]]

[0004] By the way, when an electrode having a plurality of tabs is used for at least one of the positive electrode and the negative electrode constituting the wound electrode body, unevenness occurs in the reaction current of the mixture layer constituting the electrode in the longitudinal direction of the electrode during charging and discharging of the battery. Particularly, when the tab resistances of the plurality of tabs are the same, the unevenness of the reaction current of the mixture layer in the longitudinal direction of the electrode becomes large. That is, the difference between the maximum value and the minimum value of the reaction current of the mixture layer in the longitudinal direction of the electrode becomes large. When the unevenness of the reaction current becomes large, there is a concern about a decrease in the life of the secondary battery. <e000102> Therefore, an object of the present disclosure is to provide a secondary battery capable of suppressing unevenness in the reaction current of the mixture layer in the longitudinal direction of the electrode in a wound electrode body using an electrode having a plurality of tabs.

[0006] A secondary battery according to one aspect of the present disclosure comprises an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound around a separator, and positive and negative electrode terminals, wherein at least one of the positive electrode and the negative electrode comprises a core body, a composite layer disposed on the core body, and a plurality of tabs electrically connecting the core body and the electrode terminals, wherein the plurality of tabs includes a first tab located closest to one end of the composite layer in the longitudinal direction, a second tab located closest to the other end of the composite layer in the longitudinal direction, and a third tab located between the first tab and the second tab, and The present invention is characterized in that, among the multiple tabs, the tab resistance of the third tab is the highest, and the ratio (Y / X) of the longitudinal distance Y from the other end of the mixture layer to the second tab to the longitudinal distance X from one end of the mixture layer to the first tab satisfies 0.95 ≤ Y / X ≤ 1.05, and among the multiple tabs, the tab resistance of at least one of the first tab and the second tab is the lowest, and if Y / X < 0.95 satisfies, the tab resistance of the first tab is the lowest, and if 1.05 < Y / X satisfies, the tab resistance of the second tab is the lowest.

[0007] According to this disclosure, a secondary battery can be provided that uses a wound electrode body with multiple tabs, which can suppress unevenness in the reaction current of the mixture layer in the longitudinal direction of the electrode.

[0008] This is a schematic cross-sectional view of a secondary battery, which is an example of an embodiment. This is a schematic plan view of an electrode, which is an example of an embodiment. This is a schematic plan view of a core, which is an example of an embodiment. This figure shows an example of the reaction current of the mixture layer in the longitudinal direction of the electrode.

[0009] Figure 1 is a schematic cross-sectional view of a secondary battery, which is an example of an embodiment. The secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound around a separator 13, an electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, respectively, and a battery case 15 that houses the above components. The battery case 15 is composed of a case body 16 and a sealing body 17 that closes the opening of the case body 16. Furthermore, the battery case 15 is not limited to a cylindrical metal case, but may be, for example, a rectangular metal case, a resin case formed by laminating a resin sheet (a so-called pouch type), etc.

[0010] The electrolyte may, for example, be ionic conductive (e.g., lithium ion conductive). The electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0011] A liquid electrolyte (electrolyte solution) includes, for example, 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. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0012] Furthermore, as the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels can be used. Examples of polymer materials include fluororesins, acrylic resins, and polyether resins. As the inorganic solid electrolyte, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Although the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may also be an aqueous electrolyte.

[0013] The case body 16 is, for example, a metal container in the shape of a bottomed cylinder. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22 that supports the sealing body 17, which is a part of the side surface that protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and its upper surface supports the sealing body 17.

[0014] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a 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 lower valve body 24 and the upper valve body 26 are connected to each other at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 towards the 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 breaks, and gas is discharged from the opening of the cap 27.

[0015] The following describes an electrode to be applied to at least one of the positive electrode 11 and negative electrode 12 that constitute the electrode body 14.

[0016] Figure 2 is a schematic plan view of an electrode as an example of an embodiment. The electrode 29 shown in Figure 2 shows the state before being wound as the electrode body 14. Also, in Figure 2, the arrow D1 is the winding direction of the electrode 29 when manufacturing the electrode body 14, and it is the longitudinal direction of the electrode 29. Further, in Figure 2, the arrow D2 orthogonal to the arrow D1 is the winding axis direction of the electrode body 14, and it is the short-side direction of the electrode 29.

[0017] The electrode 29 shown in Figure 2 includes a strip-shaped core body 30, a paste layer 32 disposed on the core body 30, and a plurality of tabs (34a, 34b, 34c). The paste layer 32 may be provided on one side of the core body 30 or may be provided on both sides of the core body 30.

[0018] When applying the electrode 29 to the positive electrode 11, as the positive electrode core body that becomes the core body 30, for example, a metal foil that is stable within the potential range of the positive electrode 11 such as aluminum, a film having the metal disposed on the surface layer, etc. can be used. Also, when applying the electrode 29 to the negative electrode 12, as the negative electrode core body that becomes the core body 30, for example, a metal foil that is stable within the potential range of the negative electrode 12 such as copper, a film having the metal disposed on the surface layer, etc. can be used.

[0019] When applying the electrode 29 to the positive electrode 11, the positive electrode paste layer that becomes the paste layer 32 contains a positive electrode active material. The positive electrode paste layer may contain a binder, a conductive agent, etc. Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, Ni, etc. The lithium transition metal oxide is, for example, Li ｘ CoO ２ 、Li ｘ NiO ２ 、Li ｘ MnO ２ 、Li ｘ Co ｙ Ni １－ｙ O ２ 、Li ｘ Co ｙ M １－ｙ O ｚ 、Li ｘ Ni １－ｙ M ｙ O ｚ 、Li ｘ Mn ２ O ４ 、Li ｘMn ２－ｙ M ｙ O ４ LiMPO ４ Li ２ MPO ４ F (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used individually or in combination of multiple types. In terms of enabling high capacity of non-aqueous electrolyte secondary batteries, the positive electrode active material is Li ｘ NiO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Ni １－ｙ M ｙ O ｚ Preferably, it contains lithium nickel composite oxides such as (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3).

[0020] Examples of conductive agents include acetylene black (AB), carbon black (CB) such as Ketjenblack, carbon nanotubes (CNTs), graphene, and carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0021] Examples of binders include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0022] When the electrode 29 is applied to the negative electrode 12, the negative electrode mixture layer 32 contains, for example, a negative electrode active material. The negative electrode mixture layer may also contain a binder, etc. Examples of negative electrode active materials include carbon materials such as graphite, metals and alloys such as Si and Sn, metal compounds containing Si and Sn, and metal oxides containing lithium. Examples of graphite include natural graphite such as flake graphite, lump graphite, and earthy graphite, lump artificial graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Examples of metal compounds containing Si include SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), Li ２ｙ SiO （２＋ｙ） Examples include Si-containing compounds in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2). Examples of metal oxides containing the element lithium include lithium titanate (Li ４ Ti ５ O １２ Examples include:

[0023] The binder included in the negative electrode mixture layer is, for example, the same as that used in the positive electrode 11. The negative electrode mixture layer may also contain a conductive agent. The conductive agent is, for example, the same as that used in the positive electrode 11.

[0024] In the electrode 29 shown in Figure 2, the composite layer 32 is not placed on the core body 30, and an exposed portion 30a is provided where the core body 30 is exposed. Multiple exposed portions 30a are provided at predetermined intervals in the longitudinal direction of the electrode 29. One end of each of the multiple tabs (34a, 34b, 34c) is welded to the core body 30 of each exposed portion 30a. When the electrode 29 is applied to the positive electrode 11, one end of each of the multiple positive electrode tabs (34a, 34b, 34c) is welded to the exposed portion of the positive electrode core body. Then, each of the multiple positive electrode tabs welded to the exposed portion of the positive electrode core body extends through a through hole provided in the insulating plate 18 to the sealing body 17, as shown in the positive electrode tab 20 in Figure 1, and is welded to the lower surface of the filter 23, which is the bottom plate of the sealing body 17. As a result, the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, becomes the positive electrode terminal. In other words, the positive electrode core and the positive electrode terminal are electrically connected by the positive electrode tab. Note that Figure 1 shows only one of the multiple positive electrode tabs. When the electrode 29 is applied to the negative electrode 12, one end of each of the multiple negative electrode tabs (34a, 34b, 34c) is welded to the exposed portion of the negative electrode core. Each of the multiple negative electrode tabs welded to the exposed portion of the negative electrode core extends through the outside of the insulating plate 19 (or through a through hole in the insulating plate 19) to the bottom of the case body 16, as shown in the negative electrode tab 21 in Figure 1, and is welded to the inner surface of the bottom of the case body 16. As a result, the case body 16 becomes the negative electrode terminal. In other words, the negative electrode core and the negative electrode terminal are electrically connected by the negative electrode tab. Note that Figure 1 shows only one of the multiple negative electrode tabs. Furthermore, in this embodiment, the components constituting the sealing body 17 are used as the positive terminal and the case body 16 is used as the negative terminal, but the invention is not limited to this, and the battery case may be provided with separate positive and negative terminals.

[0025] If the tabs (34a, 34b, 34c) shown in Figure 2 are positive electrode tabs, then metal plates such as aluminum, titanium, nickel, or alloys thereof can be used as tabs (34a, 34b, 34c). Similarly, if the tabs (34a, 34b, 34c) shown in Figure 2 are negative electrode tabs, then metal plates such as nickel, copper, or alloys thereof can be used as tabs (34a, 34b, 34c).

[0026] Figure 3 is a schematic plan view of a core body, which is an example of an embodiment. The multiple tabs (34a, 34b, 34c) shown in Figure 3 are formed by cutting the core body 30 into a tab shape. In other words, a part of the core body 30 is used as tabs (34a, 34b, 34c).

[0027] In this embodiment, the tabs (34a, 34b, 34c) may be composed of a separate component from the core body 30, as shown in Figure 2, or they may be composed of a part of the core body 30, as shown in Figure 3.

[0028] As shown in Figures 2 and 3, the multiple tabs consist of a first tab 34a, a second tab 34b, and a third tab 34c. The first tab 34a is positioned closest to one end of the composite layer 32 in the longitudinal direction (32a shown in Figure 2) among the multiple tabs. The second tab 34b is positioned closest to the other end of the composite layer 32 in the longitudinal direction (32b shown in Figure 2) among the multiple tabs. The third tab 34c is positioned between the first tab 34a and the second tab 34b. The tab resistance of the third tab 34c is the highest among the multiple tabs. Furthermore, the tab resistances of the first tab 34a and the second tab 34b satisfy one of the following conditions (1) to (3). Specifically, the ratio (Y / X) of the longitudinal distance X from one end of the mixture layer 32 to the first tab 34a to the longitudinal distance Y from the other end of the mixture layer 32 to the second tab 34b satisfies the following conditions: (1) If 0.95 ≤ Y / X ≤ 1.05, then the tab resistance of at least one of the tabs, the first tab 34a or the second tab 34b, is the lowest; (2) If Y / X < 0.95, then the tab resistance of the first tab 34a is the lowest; and (3) If 1.05 < Y / X, then the tab resistance of the second tab 34b is the lowest.

[0029] Figure 4 shows an example of the reaction current of an electrode in the longitudinal direction of the electrode. The horizontal axis of the graph in Figure 4 represents the longitudinal position of the electrode 29, and the vertical axis of the graph in Figure 4 represents the reaction current of the electrode 29 during charging and discharging of the secondary battery. In the curve shown in the graph in Figure 4, the dashed line represents the reaction current of the exposed portion 30a, but since there is no composite layer 32 in the exposed portion 30a, no reaction occurs and the reaction current is 0. In the curve shown in the graph in Figure 4, the solid line represents the reaction current of the composite layer 32. As shown by the solid line in the curve of Figure 4, in an electrode 29 having multiple tabs, the reaction current of the composite layer 32 around the third tab 34c, which is between the first tab 34a and the second tab 34b, tends to be high, while the reaction current of the composite layer 32 between one longitudinal end of the electrode 29 and the first tab 34a, or between the other longitudinal end of the electrode 29 and the second tab 34b, tends to be low. Furthermore, the difference between the maximum and minimum values ​​of the reaction current of the compound layer 32 in the longitudinal direction of the electrode 29 (so-called reaction current unevenness) is particularly pronounced in the reaction current of the compound layer 32, especially when the tab resistances of multiple tabs are the same, and the above tendency increases, leading to increased reaction current unevenness. However, as in this embodiment, by using the first tab 34a, second tab 34b, and third tab 34c that satisfy the above tab resistance conditions, the above tendency is suppressed, for example, in the reaction current of the compound layer 32, and reaction current unevenness is reduced.

[0030] The tab resistance in this disclosure is the resistance value in the length direction from one end of the tab on the core body 30 side to the other end on the terminal side. For example, when a separate component from the core body 30 is used as a tab, as shown in Figure 2, one terminal of the resistance meter is brought into contact with one end of the tab on the core body 30, and the other terminal of the resistance meter is brought into contact with the other end of the tab on the sealing body 17 to measure the resistance value, and this value is taken as the tab resistance. Also, for example, when a part of the core body 30 is used as a tab, as shown in Figure 3, one terminal of the resistance meter is brought into contact with the tab as close as possible to the composite layer 32 on the core body 30, and the other terminal of the resistance meter is brought into contact with the other end of the tab on the sealing body 17 to measure the resistance value, and this value is taken as the tab resistance. The resistance meter is a microtester (manufactured by HIOKI E.E. CORPORATION, model number RM3545).

[0031] Tab resistance can be adjusted, for example, by changing the cross-sectional area (width × thickness), length, material of the tab, and the contact resistance between the tab and the core or between the tab and the terminal. Contact resistance can be adjusted, for example, by changing the welding area between the tab and the core or between the tab and the terminal. Therefore, each of the first tab 34a, second tab 34b, and third tab 34c is designed to satisfy the above tab resistance conditions by changing, for example, at least one of the cross-sectional area (width × thickness), length, material, and contact resistance between the tab and the core or between the tab and the terminal.

[0032] The third tab 34c is preferably positioned in the longitudinal center of the compound layer 32. The longitudinal center of the compound layer 32 refers to the region from position 0.4 to position 0.6, where one end of the compound layer 32 is defined as position 0 and the other end as position 1. By positioning the third tab 34c, which exhibits the highest tab resistance, in the longitudinal center of the compound layer 32, for example, the maximum value of the reaction current of the compound layer 32 in the longitudinal direction of the electrode 29 can be suppressed, thereby further suppressing unevenness in the reaction current of the compound layer 32 in the longitudinal direction of the electrode 29.

[0033] When multiple tabs are metal plates, it is preferable that the welding area between the metal plate of the third tab 34c and the core body 30 is the smallest among the welding areas between each metal plate and the core body 30. By making the welding area between the metal plate of the third tab 34c and the core body 30 the smallest, for example, the maximum value of the reaction current of the composite layer 32 in the longitudinal direction of the electrode 29 can be suppressed, and the unevenness of the reaction current of the composite layer 32 in the longitudinal direction of the electrode can be further suppressed.

[0034] In addition to the third tab 34c, additional tabs such as a fourth tab and a fifth tab may be provided between the first tab 34a and the second tab 34b. The tab resistance of the additional tabs should be greater than or equal to the minimum value indicated by the first tab 34a and the second tab 34b, and less than or equal to the maximum value indicated by the third tab 34c. In this disclosure, if an additional tab with the same resistance value as the tab resistance of the third tab 34c is provided between the first tab 34a and the second tab 34b, the tab closest to the longitudinal center of the mixture layer 32 is defined as the third tab 34c.

[0035] The number of additional tabs is not particularly limited. However, in order to further suppress the unevenness of the reaction current of the mixture layer 32 in the longitudinal direction of the electrode 29, for example, the plurality of tabs may have 2N+1 tabs (where N is 1 or more) spaced apart along the longitudinal direction between the first tab 34a and the second tab 34b, and of these 2N+1 tabs, the (N+1)th tab 34 from the first tab 34a or the (N+1)th tab from the second tab 34b is preferably a tab with a lower tab resistance than the third tab 34c.

[0036] Furthermore, in order to further suppress the unevenness of the reaction current of the mixture layer 32 in the longitudinal direction of the electrode 29, for example, the plurality of tabs have 2N+1 (N is 1 or more) tabs spaced apart along the longitudinal direction between the first tab 34a and the second tab 34b, and of these 2N+1 tabs, the (N+1)th tab from the first tab 34a or the (N+1)th tab from the second tab 34b is the third tab 34c, and it is preferable that the tab resistance of all tabs other than the third tab 34c is lower than the tab resistance of the third tab 34c.

[0037] The above conditions (1) to (3) regarding the tab resistance of the first tab 34a and the second tab 34b will be described in more detail. (1) When 0.95 ≤ Y / X ≤ 1.05 is satisfied, it is sufficient that the tab resistance of at least one of the tabs, the first tab 34a and the second tab 34b, be the lowest among the multiple tabs. However, it is preferable that the tab resistances of both the first tab 34a and the second tab 34b are the lowest in order to further suppress the unevenness of the reaction current of the mixture layer 32 in the longitudinal direction of the electrode 29. If only the tab resistance of one of the tabs, the first tab 34a or the second tab 34b, is the lowest, it is preferable that the tab resistance of the other tab, the first tab 34a or the second tab 34b, is, for example, greater than the lowest value, less than or equal to the highest value indicated by the third tab 34c, and less than or equal to twice the lowest value. (2) When Y / X < 0.95 is satisfied, it is sufficient that the tab resistance of the first tab 34a is the lowest among the multiple tabs. Therefore, the tab resistance of the second tab 34b should be greater than or equal to the minimum value indicated by the first tab 34a and less than or equal to the maximum value indicated by the third tab 34c. However, in order to further suppress the unevenness of the reaction current of the mixture layer 32 in the longitudinal direction of the electrode 29, it is preferable that the tab resistance of the second tab 34b is greater than the minimum value indicated by the first tab 34a, less than or equal to the maximum value indicated by the third tab 34c, and less than or equal to twice the minimum value. (3) If 1.05 < Y / X is satisfied, then the tab resistance of the second tab 34b should be the lowest among the multiple tabs. Therefore, the tab resistance of the first tab 34a should be greater than or equal to the minimum value indicated by the second tab 34b and less than or equal to the maximum value indicated by the third tab 34c. However, in order to further suppress the unevenness of the reaction current of the mixture layer 32 in the longitudinal direction of the electrode 29, it is preferable that the tab resistance of the first tab 34a is greater than the minimum value shown by the second tab 34b, less than or equal to the maximum value shown by the third tab 34c, and less than or equal to twice the minimum value.

[0038] The minimum and maximum values ​​of the tab resistance are not particularly limited, as the optimal values ​​vary depending on the longitudinal length of the composite layer 32, the conductivity of the composite layer 32, etc. However, for example, the ratio of the maximum value to the minimum value is preferably in the range of 2 to 7, and more preferably in the range of 3 to 7.

[0039] The electrode 29 of this embodiment described above may be applied to at least one of the positive electrode 11 and the negative electrode 12, but it is preferable that it be applied to at least the positive electrode 11. In the case of the positive electrode 11 or negative electrode 12 to which the electrode 29 of this embodiment is not applied, the form of the electrode may be that of a conventional electrode and is not particularly limited, but for example, it may be an electrode having a single tab or an electrode having multiple tabs with the same tab resistance.

[0040] The separator 13 constituting the electrode body 14 may be made of, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator.

[0041] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0042] <Example 1> [Preparation of positive electrode] Lithium cobalt oxide, carbon black, and polyvinylidene fluoride (PVDF) were mixed in a solid content mass ratio of 98:1:1, an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added, and the mixture was kneaded to prepare a positive electrode mixture slurry.

[0043] By intermittently applying a positive electrode mixture slurry along the longitudinal direction of a positive electrode core made of aluminum foil, a positive electrode mixture layer and three exposed areas without the positive electrode mixture layer were created, spaced apart along the longitudinal direction of the positive electrode core. Aluminum positive electrode tabs were welded to each exposed area. In this way, a positive electrode having three tabs, namely the first tab, second tab, and third tab, was obtained. The first, second, and third tabs used were the same length, but their cross-sectional areas were in the order of first tab = second tab > third tab.

[0044] In the positive electrode, when the position of one end of the positive electrode mixture layer in the longitudinal direction is set to 0 and the position of the other end of the positive electrode mixture layer in the longitudinal direction is set to 1, the first tab is at position 0.34, the second tab is at position 0.83, and the third tab is at position 0.50. That is, the ratio (Y / X) of the longitudinal distance Y from the other end of the positive electrode mixture layer to the second tab to the longitudinal distance X from one end of the positive electrode mixture layer to the first tab is less than 0.95. Furthermore, when the tab resistance of each tab was measured with the tabs connected to the sealing body as described later, the first and second tabs were 1.0 mΩ, and the third tab was 4.0 mΩ.

[0045] [Preparation of the negative electrode] Natural graphite, sodium carboxymethylcellulose (CMC-Na), and styrene-butadiene rubber (SBR) were mixed in an aqueous solution in a solid content mass ratio of 100:1:1 to prepare a negative electrode mixture slurry.

[0046] The longitudinal ends of a negative electrode core made of copper foil were set as uncoated areas, and the negative electrode mixture slurry was applied to the negative electrode core other than the uncoated areas, thereby creating a negative electrode mixture layer and exposed areas without the negative electrode mixture layer at both longitudinal ends of the negative electrode core. Nickel negative electrode tabs were welded to each exposed area. In this way, a negative electrode with two tabs was obtained. The length and cross-sectional area of ​​the two tabs are the same.

[0047] [Preparation of Non-Aqueous Electrolyte] A mixed solvent is prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF) is added to this mixed solvent. ６ A non-aqueous electrolyte was prepared by dissolving ) at a concentration of 1.0 mol / liter.

[0048] [Fabrication of Secondary Battery] The positive electrode and the negative electrode described above were wound in a spiral shape via a polyolefin separator to create a wound electrode body. The fabricated electrode body was placed inside the case body, the negative electrode tab was welded to the bottom of the case body, and the positive electrode lead was welded to the sealing body. After injecting a non-aqueous electrolyte into the case body, the opening of the case body was sealed with the sealing body via a gasket to fabricate a secondary battery.

[0049] Using COMSOL Multiphysics software from COMSOL Corporation, a simulation model of this battery system was created by modifying various material parameters such as exchange current density, diffusion coefficient, and curvature to fit the battery characteristics, such as the C rate dependence and temperature dependence during charging and discharging, to match the measured values ​​of the fabricated secondary battery. The tab resistance of each tab measured above was input into the created simulation model to determine the reaction current distribution of the positive electrode mixture layer in the longitudinal direction of the positive electrode, and the minimum value of the reaction current of the positive electrode mixture layer (I) was determined. ｍｉｎ The maximum value of the reaction current of the positive electrode mixture layer relative to (I ｍａｘ ) ratio (I ｍａｘ / I ｍｉｎ ) was calculated.

[0050] <Example 2> A secondary battery was fabricated in the same manner as in Example 1, except that the cross-sectional area of ​​the positive electrode tabs was arranged as follows: 1st tab > 2nd tab > 3rd tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the 1st tab was 1.0 mΩ, the 2nd tab was 2.0 mΩ, and the 3rd tab was 3.0 mΩ. The tab resistances of each tab measured above were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0051] <Comparative Example 1> A secondary battery was manufactured in the same manner as in Example 1, except that the cross-sectional areas of the positive electrode tabs were set to 1st tab = 2nd tab = 3rd tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the 1st tab, 2nd tab, and 3rd tab were all 2.0 mΩ. The measured tab resistances of each tab were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0052] <Comparative Example 2> A secondary battery was fabricated in the same manner as in Example 1, except that the cross-sectional area of ​​the positive electrode tabs was arranged as follows: second tab > third tab > first tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the first tab was 3.0 mΩ, the second tab was 1.0 mΩ, and the third tab was 2.0 mΩ. The tab resistances of each tab measured above were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0053] <Comparative Example 3> A secondary battery was fabricated in the same manner as in Example 1, except that the cross-sectional area of ​​the positive electrode tabs was set to third tab > first tab = second tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the first tab was 2.5 mΩ, the second tab was 2.5 mΩ, and the third tab was 1.0 mΩ. The tab resistances of each tab measured above were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0054] Table 1 shows the first examples of Examples 1-2 and Comparative Examples 1-3. ｍａｘ / I ｍｉｎ The results were summarized.

[0055]

[0056] As shown in Table 1, Examples 1 and 2 are all better than Comparative Examples 1 to 3. ｍａｘ / I ｍｉｎ The value was low. From these results, it can be said that when Y / X < 0.95 is satisfied, by using an electrode with the tab resistance of the first tab set to the lowest value and the tab resistance of the third tab set to the highest value, it is possible to suppress the unevenness of the reaction current of the mixture layer in the longitudinal direction of the electrode.

[0057] <Example 3> A secondary battery was manufactured in the same manner as in Example 1, except for the following difference in the manufacturing of the positive electrode. Five exposed sections without a positive electrode mixture layer were created at intervals along the longitudinal direction of the positive electrode core. Aluminum positive electrode tabs were welded to each exposed section to obtain a positive electrode having tabs 1 to 5. The lengths of the tabs 1 to 5 used were the same, but the cross-sectional areas were 1st tab = 2nd tab > 4th tab = 5th tab > 3rd tab. In this positive electrode, when the position of one end of the positive electrode mixture layer in the longitudinal direction is set to 0 and the position of the other end of the positive electrode mixture layer in the longitudinal direction is set to 1, the 1st tab is at position 0.17, the 2nd tab is at position 0.83, the 3rd tab is at position 0.50, the 4th tab is at position 0.34, and the 5th tab is at position 0.66. In other words, the ratio (Y / X) of the longitudinal distance Y from the other end of the positive electrode mixture layer to the second tab to the longitudinal distance X from one end of the positive electrode mixture layer to the first tab is within the range of 0.95 to 1.05. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the first and second tabs were 1.0 mΩ, the third tab was 7.0 mΩ, and the fourth and fifth tabs were 3.0 mΩ.

[0058] Furthermore, the tab resistance of each tab measured above was input to the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0059] <Example 4> A secondary battery was fabricated in the same manner as in Example 3, except that the cross-sectional area of ​​the positive electrode tabs was set as follows: 1st tab = 2nd tab = 5th tab > 3rd tab = 4th tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the 1st tab, 2nd tab and 5th tab were 2.0 mΩ, and the 3rd tab and 4th tab were 4.5 mΩ. The tab resistance of each tab measured above was input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0060] <Example 5> A secondary battery was manufactured in the same manner as in Example 3, except that the cross-sectional areas of the positive electrode tabs were set as follows: 1st tab = 2nd tab > 4th tab > 3rd tab = 5th tab, and in the positive electrode, when the position of one end of the positive electrode mixture layer in the longitudinal direction is set to 0 and the position of the other end in the longitudinal direction of the positive electrode mixture layer is set to 1, the 1st tab was at position 0.17, the 2nd tab at position 0.83, the 3rd tab at position 0.34, the 4th tab at position 0.50, and the 5th tab at position 0.66. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the 1st and 2nd tabs were 1.0 mΩ, the 3rd and 5th tabs were 5.0 mΩ, and the 4th tab was 3.0 mΩ. The tab resistance of each tab measured above was input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0061] <Example 6> A secondary battery was fabricated in the same manner as in Example 3, except that the cross-sectional area of ​​the positive electrode tabs was set as follows: 1st tab > 2nd tab > 4th tab = 5th tab > 3rd tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the results were 0.8 mΩ for the 1st tab, 1.2 mΩ for the 2nd tab, 7.0 mΩ for the 3rd tab, and 3.0 mΩ for the 4th and 5th tabs. The measured tab resistances of each tab were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0062] <Comparative Example 4> A secondary battery was manufactured in the same manner as in Example 3, except that the cross-sectional areas of the positive electrode tabs were set as follows: 1st tab = 2nd tab = 3rd tab = 4th tab = 5th tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the 1st tab to the 5th tab were all 3.0 mΩ. The tab resistance of each tab measured above was input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0063] <Comparative Example 5> A secondary battery was manufactured in the same manner as in Example 3, except that the cross-sectional areas of the positive electrode tabs were arranged as follows: 1st tab > 4th tab > 3rd tab > 5th tab > 2nd tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the results were 1.0 mΩ for the 1st tab, 5.0 mΩ for the 2nd tab, 3.0 mΩ for the 3rd tab, 2.0 mΩ for the 4th tab, and 4.0 mΩ for the 5th tab. The tab resistances of each tab measured above were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0064] <Comparative Example 6> A secondary battery was manufactured in the same manner as in Example 3, except that the cross-sectional area of ​​the positive electrode tabs was set as follows: 3rd tab > 4th tab = 5th tab > 1st tab = 2nd tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the 1st and 2nd tabs were 5.0 mΩ, the 3rd tab was 1.0 mΩ, and the 4th and 5th tabs were 2.0 mΩ. The measured tab resistances of each tab were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0065] Table 2 shows the I of Examples 3-6 and Comparative Examples 4-6. ｍａｘ / I ｍｉｎ The results were summarized.

[0066]

[0067] As shown in Table 2, all of Examples 3 to 6 are superior to Comparative Examples 4 to 6. ｍａｘ / I ｍｉｎ The value was low. From these results, it can be said that when 0.95 ≤ Y / X ≤ 1.05 is satisfied, by using an electrode in which the tab resistance of at least one of the tabs (the first tab and the second tab) is set to the lowest value and the tab resistance of the third resistor is set to the highest value, it is possible to suppress the unevenness of the reaction current of the mixture layer in the longitudinal direction of the electrode.

[0068] Among Examples 3 to 6, Examples 3 and 5 I ｍａｘ / I ｍｉｎThe value was low. From the results of Example 5, when there are 2N+1 tabs (N is 1 or more) arranged with spacing along the longitudinal direction between the first tab and the second tab, it is preferable that the (N+1)th tab from the first tab among the 2N+1 tabs has a tab resistance lower than the third tab, which has the highest tab resistance. Also, from the results of Example 3, when there are 2N+1 tabs (N is 1 or more) arranged with spacing along the longitudinal direction between the first tab and the second tab, it is preferable that the (N+1)th tab from the first tab among the 2N+1 tabs is the third tab, which has the highest tab resistance, and the tab resistances of all tabs other than the third tab are lower than the tab resistance of the third tab.

[0069] <Example 7> The secondary battery was manufactured in the same manner as in Example 1, except for the following difference in the preparation of the positive electrode. In the positive electrode, when the position of one end of the positive electrode mixture layer in the longitudinal direction is set to 0 and the position of the other end of the positive electrode mixture layer in the longitudinal direction is set to 1, the first tab was set to the position of 0.17, the second tab to the position of 0.66, and the third tab to the position of 0.50. That is, the ratio (Y / X) of the longitudinal distance Y from the other end of the positive electrode mixture layer to the second tab to the longitudinal distance X from one end of the positive electrode mixture layer to the first tab is greater than 1.05. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the first and second tabs were 1.0 mΩ and the third tab was 4.0 mΩ.

[0070] Furthermore, the tab resistance of each tab measured above was input to the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0071] <Example 8> A secondary battery was fabricated in the same manner as in Example 7, except that the cross-sectional area of ​​the positive electrode tabs was arranged as follows: second tab > first tab > third tab. When the tab resistance of each tab was measured with the tabs connected to the sealing body, the first tab was 2.0 mΩ, the second tab was 1.0 mΩ, and the third tab was 3.0 mΩ. The tab resistances of each tab measured above were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ The result was calculated.

[0072] <Comparative Example 7> A secondary battery was fabricated in the same manner as in Example 7, except that the cross-sectional areas of the tabs on the positive electrode side were made equal, i.e., the first tab = the second tab = the third tab. When the tab resistances of the respective tabs were measured in a state where the tabs were connected to the sealing body, the tab resistances of all of the first tab, the second tab, and the third tab were 2.0 mΩ. The tab resistances of the respective tabs measured above were input into the simulation model created in the same manner as in Example 1, and I ｍａｘ / I ｍｉｎ was calculated.

[0073] Table 3 summarizes the results of I ｍａｘ / I ｍｉｎ for Examples 7 to 8 and Comparative Example 7.

[0074]

[0075] As shown in Table 3, in Examples 7 to 8, I ｍａｘ / I ｍｉｎ was a lower value than in Comparative Example 7. From these results, it can be said that when 1.05 < Y / X is satisfied, by using an electrode in which the tab resistance of the second tab is the minimum value and the tab resistance of the third tab is the maximum value, it is possible to suppress the unevenness of the reaction current in the active material layer in the longitudinal direction of the electrode.

[0076] This disclosure is further illustrated by the following embodiments. Configuration 1: A secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator, and positive and negative electrode terminals, wherein at least one of the positive electrode and the negative electrode comprises a core body, a compound layer disposed on the core body, and a plurality of tabs electrically connecting the core body and the electrode terminals, wherein the plurality of tabs includes, among the plurality of tabs, a first tab located closest to one end of the compound layer in the longitudinal direction, a second tab located closest to the other end of the compound layer in the longitudinal direction, and a third tab located between the first tab and the second tab, wherein among the plurality of tabs, the tab resistance of the third tab is the highest, and the ratio (Y / X) of the longitudinal distance Y from the other end of the compound layer to the second tab to the longitudinal distance X from the one end of the compound layer to the first tab is, A secondary battery in which, when 0.95 ≤ Y / X ≤ 1.05 is satisfied, the tab resistance of at least one of the first tab and the second tab among the plurality of tabs is the lowest value, when Y / X < 0.95 is satisfied, the tab resistance of the first tab among the plurality of tabs is the lowest value, and when 1.05 < Y / X is satisfied, the tab resistance of the second tab among the plurality of tabs is the lowest value. Configuration 2: The secondary battery according to Configuration 1, wherein the third tab is located in the center of the longitudinal direction of the mixture layer. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the plurality of tabs have 2N+1 (N is 1 or more) tabs spaced apart along the longitudinal direction between the first tab and the second tab, and of the 2N+1 tabs, the (N+1)th tab from the first tab is a tab with a lower tab resistance than the third tab. Configuration 4: The plurality of tabs have 2N+1 (N is 1 or more) tabs spaced apart along the longitudinal direction between the first tab and the second tab, and of the 2N+1 tabs, the (N+1)th tab from the first tab is the third tab, and the tab resistance of all tabs other than the third tab is lower than the tab resistance of the third tab, as described in Configuration 1 or 2.Configuration 5: A secondary battery according to any one of Configurations 1 to 4, wherein each of the plurality of tabs is a metal plate welded onto the core, and the welding area between the metal plate of the third tab and the core is the smallest of the welding areas between each of the metal plates and the core. Configuration 6: A secondary battery according to any one of Configurations 1 to 5, wherein the ratio of the maximum value (maximum value / minimum value) of the tab resistance to the minimum value is in the range of 2 or more and 7 or less.

[0077] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 29 Electrode, 30 Core body, 30a Exposed part, 32 Mixture layer, 32a One end, 32b Other end, 34a First tab, 34b Second tab, 34c Third tab.

Claims

1. A secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator in between, and positive and negative electrode terminals, wherein at least one of the positive electrode and the negative electrode comprises a core body, a composite layer disposed on the core body, and a plurality of tabs electrically connecting the core body and the electrode terminals, wherein the plurality of tabs includes a first tab located closest to one end of the composite layer in the longitudinal direction, a second tab located closest to the other end of the composite layer in the longitudinal direction, and a third tab located between the first tab and the second tab, wherein the tab resistance of the third tab is the highest, and the ratio (Y / X) of the longitudinal distance Y from the other end of the composite layer to the second tab to the longitudinal distance X from the one end of the composite layer to the first tab is, A secondary battery in which, when 0.95 ≤ Y / X ≤ 1.05 is satisfied, the tab resistance of at least one of the tabs, the first tab and the second tab, is the lowest among the multiple tabs; when Y / X < 0.95 is satisfied, the tab resistance of the first tab is the lowest among the multiple tabs; and when 1.05 < Y / X is satisfied, the tab resistance of the second tab is the lowest among the multiple tabs.

2. The secondary battery according to claim 1, wherein the third tab is located in the longitudinal center of the mixture layer.

3. The secondary battery according to claim 1 or 2, wherein the plurality of tabs have 2N+1 (N is 1 or more) tabs spaced apart along the longitudinal direction between the first tab and the second tab, and of the 2N+1 tabs, the (N+1)th tab from the first tab is a tab with lower tab resistance than the third tab.

4. The secondary battery according to claim 1 or 2, wherein the plurality of tabs have 2N+1 (N is 1 or more) tabs spaced apart along the longitudinal direction between the first tab and the second tab, the (N+1)th tab from the first tab among the 2N+1 tabs is the third tab, and the tab resistance of all tabs other than the third tab is lower than the tab resistance of the third tab.

5. The secondary battery according to claim 1 or 2, wherein each of the plurality of tabs is a metal plate welded onto the core, and the welding area between the metal plate of the third tab and the core is the smallest of the welding areas between each of the metal plates and the core.

6. The secondary battery according to claim 1 or 2, wherein the ratio of the maximum value (maximum value / minimum value) of the tab resistor to the minimum value is in the range of 2 or more and 7 or less.

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