Non-aqueous electrolyte secondary battery

Abstract

To provide a non-aqueous electrolyte solution secondary battery in which formation of an ultra-high resistance region is suppressed.SOLUTION: A non-aqueous electrolyte solution secondary battery comprises wound electrode bodies and non-aqueous electrolyte solution. A negative electrode 24 includes: a negative electrode active material layer 24a containing negative electrode active material; and a plurality of negative electrode tabs 24t provided at one end in a winding axis direction Y. The plurality of negative electrode tabs 24t are connected to a negative electrode collector unit in a stacked and folded state. The negative electrode active material layer 24a includes a first high resistance region A1 that extends from the one end toward a center part in the winding axis direction Y and has a resistance value 1.5 times or more higher than that of its surrounding, and a ratio (L1 / La) of a length L1 to a length La is equal to or lower than 0.35, where La is a length of the negative electrode active material layer 24a and L1 is a length of the first high resistance region A1 in the winding axis direction Y.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Conventionally, a nonaqueous electrolyte secondary battery is known that includes a wound electrode assembly formed by stacking a strip-shaped positive electrode and a strip-shaped negative electrode with a strip-shaped separator interposed therebetween and winding them up, a nonaqueous electrolyte, a battery case that contains the wound electrode assembly and the nonaqueous electrolyte, a positive electrode terminal electrically connected to the positive electrode via a positive electrode current collector, and a negative electrode terminal electrically connected to the negative electrode via a negative electrode current collector. Related prior art documents include Patent Documents 1 and 2.

[0003] For example, Patent Document 1 describes that by providing multiple negative electrode tabs at one end of a wound electrode body in the winding axis direction, and stacking and folding these multiple negative electrode tabs and connecting them to a negative electrode current collecting part, it is possible to miniaturize the battery and improve the volumetric energy density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-127950 [Patent Document 2] JP 2014-41744 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the study by the present inventor, there is still room for improvement in the above technology from the viewpoint of reducing the resistance of the negative electrode active material layer. That is, in a non-aqueous electrolyte secondary battery, a part of the non-aqueous electrolyte is usually decomposed during initial charging, and a coating (Solid Electrolyte Interface film: SEI film) containing the decomposition product is formed on the surface of the negative electrode active material layer. This coating stabilizes the interface between the negative electrode active material layer and the non-aqueous electrolyte. However, in a wound electrode body, the non-aqueous electrolyte is supplied only from both ends in the winding axis direction. For this reason, in particular in recent high-capacity wound electrode bodies, the non-aqueous electrolyte is difficult to penetrate into the center part in the winding axis direction. As a result, the coating is difficult to form in the center part in the winding axis direction during initial charging, and the resistance is likely to be high.

[0006] In addition, according to the inventor's study, when a plurality of negative electrode tabs are connected to a negative electrode current collector in a stacked and folded state, as in Patent Document 1, a stripe-like high resistance region may be formed in the negative electrode active material layer from the end on the side where the negative electrode tabs are provided toward the center in the winding axis direction. If this high resistance region extends long in the winding axis direction and reaches the center, it may overlap with the high resistance part in the center described above to form a very high resistance region (ultra-high resistance region). This may lead to a significant decrease in battery characteristics.

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a nonaqueous electrolyte secondary battery in which the formation of an ultra-high resistance region in the negative electrode active material layer is suppressed. [Means for solving the problem]

[0008] According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising: a wound electrode body formed by stacking a strip-shaped positive electrode and a strip-shaped negative electrode with a strip-shaped separator interposed therebetween and winding the electrode body; a nonaqueous electrolyte; a battery case that contains the wound electrode body and the nonaqueous electrolyte; a positive electrode terminal electrically connected to the positive electrode via a positive electrode current collector; and a negative electrode terminal electrically connected to the negative electrode via a negative electrode current collector. The negative electrode has a negative electrode active material layer containing a negative electrode active material, and a plurality of negative electrode tabs provided at one end in the winding axis direction. The plurality of negative electrode tabs are connected to the negative electrode current collector in a stacked and folded state. The negative electrode active material layer has a first high resistance region that extends from the one end toward the center in the winding axis direction and has a resistance value 1.5 times or more higher than the surrounding area. In the winding axis direction, when the length of the negative electrode active material layer is La and the length of the first high resistance region is L1, the ratio (L1 / La) of the length L1 of the first high resistance region to the length La of the negative electrode active material layer is 0.35 or less.

[0009] By setting the ratio (L1 / La) to a predetermined value or less, it is possible to prevent the first high resistance region from reaching the center of the winding axis direction. This makes it difficult for the first high resistance region to overlap with another high resistance portion formed in the center of the winding axis direction, thereby preventing the formation of an ultra-high resistance region. As a result, it is possible to prevent a significant deterioration in the battery characteristics. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view that illustrates a nonaqueous electrolyte secondary battery according to one embodiment. [Diagram 2] FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a perspective view that shows a schematic view of an electrode assembly attached to a sealing plate. [Diagram 5] FIG. 5 is a perspective view that illustrates a schematic diagram of a wound electrode body. [Figure 6]FIG. 6 is a schematic diagram showing the configuration of a wound electrode body. [Figure 7] FIG. 7 is a schematic plan view of a negative electrode having 1.5 turns. [Figure 8] FIG. 8 is a side view that illustrates the positional relationship between the battery assembly and the pressing member in the initial charging process. [Figure 9] FIG. 9A is a graph showing the relationship between the measurement position and the resistance ratio in Example 1, and FIG. 9B is a graph showing the relationship between the measurement position and the resistance ratio in Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, some preferred embodiments of the technology disclosed herein will be described with reference to the drawings. Matters other than those specifically mentioned in this specification and necessary for carrying out the present invention (for example, the general configuration and manufacturing process of a non-aqueous electrolyte secondary battery that does not characterize the present invention) can be understood as design matters of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the field. In this specification, the expression "A to B" indicating a range includes the meaning of "greater than A" and "smaller than B" as well as the meaning of "A or more and B or less."

[0012] In this specification, the term "non-aqueous electrolyte secondary battery" refers to a general electricity storage device that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via a non-aqueous electrolyte. The concept of non-aqueous electrolyte secondary battery includes so-called storage batteries such as lithium ion secondary batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors.

[0013] <Battery 100> FIG. 1 is a perspective view of a nonaqueous electrolyte secondary battery (hereinafter, simply referred to as a battery) 100. FIG. 2 is a schematic longitudinal sectional view taken along line II-II in FIG. 1. FIG. 3 is a schematic transverse sectional view taken along line III-III in FIG. 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short side direction, the long side direction perpendicular to the short side direction, and the up-down direction perpendicular to the short side direction and the long side direction, respectively, of the battery 100. However, these directions are merely for the convenience of description, and do not limit the installation form of the battery 100 in any way.

[0014] 2, the battery 100 includes a battery case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, a negative electrode current collector 60, a positive electrode insulating member 70, a negative electrode insulating member 80, and a nonaqueous electrolyte (not shown). Here, the battery 100 is a lithium ion secondary battery. The battery 100 is preferably a lithium ion secondary battery.

[0015] The battery case 10 is a housing that contains the electrode assembly 20 and the nonaqueous electrolyte. As shown in FIG. 1, the battery case 10 has a flat, bottomed rectangular parallelepiped (rectangular) outer shape. The material of the battery case 10 may be the same as that used conventionally, and is not particularly limited. The battery case 10 is preferably made of a metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 2, the battery case 10 includes an exterior body 12 having an opening 12h, and a sealing plate (lid) 14 that closes the opening 12h. The battery case 10 preferably includes an exterior body 12 and a sealing plate 14.

[0016] 1, the exterior body 12 includes a substantially rectangular bottom wall 12a, a pair of long side walls 12b extending from the long sides of the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the short sides of the bottom wall 12a and facing each other. The bottom wall 12a faces an opening 12h. The area of ​​the long side walls 12b is larger than the area of ​​the short side walls 12c. In this specification, the term "substantially rectangular" includes not only a perfect rectangular shape (rectangular shape), but also a shape in which the corners connecting the long and short sides of the rectangle are rounded or a shape in which a notch is provided at the corner.

[0017] As shown in Fig. 1, the sealing plate 14 has a substantially rectangular shape in a plan view. As shown in Fig. 2, the sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h of the exterior body 12. The sealing plate 14 faces the bottom wall 12a of the exterior body 12. The battery case 10 is integrated by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The battery case 10 is hermetically sealed (sealed).

[0018] As shown in FIG. 2, the sealing plate 14 is provided with a liquid inlet 15, a gas exhaust valve 17, and two terminal outlet holes 18 and 19. The liquid inlet 15 is for injecting a non-aqueous electrolyte after the sealing plate 14 is assembled to the exterior body 12. The sealing plate 14 is preferably provided with the liquid inlet 15. The liquid inlet 15 is sealed with a sealing member 16. The gas exhaust valve 17 is configured to break when the pressure inside the battery case 10 reaches or exceeds a predetermined value, thereby discharging the gas inside the battery case 10 to the outside. The terminal outlet holes 18 and 19 are formed at both ends of the sealing plate 14 in the long side direction Y (the left end and the right end in FIG. 2). The terminal outlet holes 18 and 19 penetrate the sealing plate 14 in the thickness direction (the up-down direction Z). The terminal withdrawal holes 18, 19 each have an inner diameter large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to be inserted therethrough before being attached to the sealing plate 14 (before being crimped).

[0019] The positive electrode terminal 30 and the negative electrode terminal 40 are each fixed to the sealing plate 14 of the battery case 10. The positive electrode terminal 30 is disposed on one side of the sealing plate 14 in the long side direction Y (the left side in Figs. 1 and 2). The negative electrode terminal 40 is disposed on the other side of the sealing plate 14 in the long side direction Y (the right side in Figs. 1 and 2). As shown in Fig. 2, the positive electrode terminal 30 extends from the inside to the outside of the sealing plate 14 through the terminal pull-out hole 18, and the negative electrode terminal 40 extends from the inside to the outside of the sealing plate 14 through the terminal pull-out hole 19. The positive electrode terminal 30 and the negative electrode terminal 40 are preferably attached to the sealing plate 14. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portion surrounding the terminal pull-out holes 18 and 19 of the sealing plate 14 by crimping. The positive electrode terminal 30 and the negative electrode terminal 40 have crimping portions 30c, 40c formed at their ends on the exterior body 12 side (the lower ends in FIG. 2).

[0020] 2, the positive electrode terminal 30 is electrically connected to the positive electrode 22 (see FIG. 6, specifically, the positive electrode tab group 23) of the electrode body group 20 via the positive electrode current collecting portion 50 inside the battery case 10. The positive electrode terminal 30 is insulated from the sealing plate 14 by a positive electrode insulating member 70 and a gasket 90. The positive electrode terminal 30 is preferably made of metal, and more preferably made of, for example, aluminum or an aluminum alloy.

[0021] The negative electrode terminal 40 is electrically connected to the negative electrode 24 (see FIG. 6, specifically, the negative electrode tab group 25) of the electrode body group 20 through the negative electrode current collecting portion 60 inside the battery case 10. The negative electrode terminal 40 is insulated from the sealing plate 14 by a negative electrode insulating member 80 and a gasket 90. The negative electrode terminal 40 is preferably made of a metal, and more preferably made of, for example, copper or a copper alloy. The negative electrode terminal 40 may be configured by joining two conductive members together. For example, the portion of the negative electrode terminal 40 connected to the negative electrode current collecting portion 60 may be made of copper or a copper alloy, and the portion exposed on the outer surface of the sealing plate 14 may be made of aluminum or an aluminum alloy.

[0022] A plate-shaped positive electrode external conductive member 32 and a plate-shaped negative electrode external conductive member 42 are attached to the outer surface of the sealing plate 14. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are members to which bus bars are attached when electrically connecting a plurality of batteries 100 to each other. The positive electrode external conductive member 32 is electrically connected to the positive electrode terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative electrode terminal 40. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external resin member 92. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are preferably made of metal, and more preferably made of aluminum or an aluminum alloy, for example. However, the positive electrode external conductive member 32 and the negative electrode external conductive member 42 are not essential and may be omitted in other embodiments.

[0023] As shown in FIG. 2, the electrode assembly group 20 is accommodated inside the battery case 10 (more specifically, inside the exterior body 12). FIG. 4 is a perspective view that shows a schematic view of the electrode assembly group 20 attached to the sealing plate 14. Here, the electrode assembly group 20 has three wound electrode bodies 20a, 20b, and 20c. However, the number of wound electrode bodies arranged inside one battery case 10 is not particularly limited, and may be two or more (multiple), or may be one. The electrode assembly group 20 may be arranged inside the battery case 10 in a state where it is covered with an insulating electrode assembly holder. In other words, an electrode assembly holder may be interposed between the electrode assembly group 20 and the battery case 10 (more specifically, the exterior body 12). The electrode assembly holder is preferably made of resin.

[0024] FIG. 5 is a perspective view showing the wound electrode body 20a. FIG. 6 is a schematic diagram showing the configuration of the wound electrode body 20a. In the following, the wound electrode body 20a will be described in detail as an example, but the wound electrode bodies 20b and 20c can also have a similar configuration. As shown in FIG. 6, the wound electrode body 20a is configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with a strip-shaped separator 26 interposed therebetween and winding the strip-shaped positive electrode 22 and the strip-shaped negative electrode 24 around a winding axis WL. Although not particularly limited, the number of windings (number of turns) of the wound electrode body 20a is preferably 20 turns or more, more preferably 30 turns or more, and even more preferably 50 turns or more, and may be, for example, 150 turns or less, 100 turns or less.

[0025] As can be seen from FIG. 2 and FIG. 6, the wound electrode body 20a is disposed inside the battery case 10 with the winding axis WL oriented substantially parallel to the long side direction Y. The winding axis WL direction coincides with the long side direction Y. The wound electrode body 20a is disposed inside the battery case 10 with the winding axis WL oriented parallel to the bottom wall 12a and perpendicular to the short side wall 12c. The battery 100 has a so-called horizontal tab structure in which the positive electrode tab group 23 and the negative electrode tab group 25 are located at both ends (left and right in FIG. 2 and FIG. 4) of the wound electrode body 20a in the winding axis WL direction. However, in other embodiments, the battery 100 may have a so-called upper tab structure in which the positive electrode tab group 23 and the negative electrode tab group 25 are located at one end (for example, the upper end in FIG. 2 and FIG. 4) of the wound electrode body 20a in the winding axis WL direction. In this case, the direction of the winding axis WL may coincide with the vertical direction Z.

[0026] As shown in FIG. 5, the wound electrode body 20a has a flat outer shape. The wound electrode body 20a preferably has a flat outer shape. The wound electrode body 20a has a pair of flat portions 20f extending along the long side direction Y (winding axis WL direction) and a pair of curved portions (R portions) 20r connecting the pair of flat portions 20f. The flat portions 20f have a flat outer surface (YZ plane in FIG. 5). The curved portions 20r have a curved outer surface. In this specification, the term "flat outer surface" is not limited to a completely flat surface, and includes a case where, for example, when viewed microscopically, there is a slight step, curve, concave portion, convex portion, or the like.

[0027] 2 and 5, the pair of flat portions 20f face the pair of long side walls 12b of the exterior body 12. The flat portions 20f extend along the long side walls 12b. The pair of curved portions 20r face the bottom wall 12a and the sealing plate 14 of the exterior body 12. As in this embodiment, the wound electrode body 20a is preferably disposed inside the battery case 10 such that the stacking direction (thickness direction) of the positive electrode 22 (see FIG. 6) and the negative electrode 24 (see FIG. 6) in the flat portions 20f coincides with the short side direction X (direction perpendicular to the long side walls 12b).

[0028] The positive electrode 22 may be the same as a conventional one, and is not particularly limited. As shown in FIG. 6, the positive electrode 22 has a positive electrode collector 22c, and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed on at least one surface of the positive electrode collector 22c. However, the positive electrode protective layer 22p is not essential and can be omitted in other embodiments. The positive electrode collector 22c is strip-shaped. The positive electrode collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode collector 22c is a metal foil, specifically an aluminum foil.

[0029] A plurality of positive electrode tabs 22t are provided at one end (left end in FIG. 6) in the long side direction Y of the positive electrode collector 22c. The plurality of positive electrode tabs 22t protrude toward one side (left side in FIG. 6) in the long side direction Y. The plurality of positive electrode tabs 22t protrude in the long side direction Y beyond the separator 26. The plurality of positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the positive electrode 22. By providing the plurality of positive electrode tabs 22t, the resistance of the battery 100 can be reduced. Here, the positive electrode tab 22t is a part of the positive electrode collector 22c and is made of metal foil (aluminum foil). It is preferable that the positive electrode tab 22t is a collector exposed portion where the positive electrode active material layer 22a and the positive electrode protective layer 22p are not formed at least in a part and the positive electrode collector 22c is exposed.

[0030] As shown in FIG. 3, the positive electrode tabs 22t are stacked at one end (the left end in FIG. 3) in the long side direction Y to form a positive electrode tab group 23. The positive electrode tabs 22t are stacked and bent so that the outer ends are aligned. This improves the accommodation in the battery case 10 and reduces the size of the battery 100. In addition, the volume energy density of the battery 100 can be improved. Furthermore, as will be described later in detail, according to the study by the present inventor, when the positive electrode tab 22t is bent and curved, the inter-electrode distance between the positive electrode 22 and the negative electrode 24 tends to be locally large, for example, in the vicinity of the positive electrode tab group 23 (particularly near the base). As a result, a second high resistance region A2 (see FIG. 7) described later is likely to occur in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein. A positive electrode second current collecting portion 52 described later of the positive electrode current collecting portion 50 is attached (more specifically, joined) to the positive electrode tab group 23. The positive electrode tabs 22t are stacked and folded and connected to the positive electrode second current collecting portion 52. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collecting portion 50.

[0031] As shown in Fig. 6, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (e.g., lithium transition metal composite oxide) capable of reversibly absorbing and releasing charge carriers. An example of the lithium transition metal composite oxide is a lithium manganese-containing composite oxide containing at least lithium element and manganese element. Examples of the lithium manganese-containing composite oxide include lithium manganese composite oxides (e.g., LiMn2O4, Li2MnO3) and lithium manganese nickel composite oxides in which part of the manganese is replaced with nickel (LiNi x Mn 2-xO4 (where 0 < x < 2, preferably 0 < x < 1), and further examples include lithium nickel cobalt manganese composite oxides containing cobalt. Although details will be described later, according to the study by the present inventors, when the positive electrode 22 (specifically, the positive electrode active material) contains a lithium manganese-containing composite oxide, Mn elutes into the non-aqueous electrolyte, which tends to generate the first high-resistance region A1 and / or the second high-resistance region A2 (see FIG. 7) described later in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein.

[0032] In a preferred embodiment, the positive electrode active material is doped with additive elements such as W, Zr, etc. Alternatively, a compound containing additive elements such as W, Zr, etc. (for example, an oxide such as zirconia (ZrO2)) adheres to the surface of the positive electrode active material. Although not particularly limited, the proportion of the additive element in the positive electrode active material (for example, a lithium manganese-containing composite oxide) is preferably 0.1 to 2.0% by mass, more preferably 0.2 to 1.5% by mass, and even more preferably 0.3 to 1.0% by mass. Although details will be described later, according to the study by the present inventors, when the positive electrode active material contains the zirconium (Zr) element, Zr elutes into the non-aqueous electrolyte, which tends to generate the first high-resistance region A1 and / or the second high-resistance region A2 (see FIG. 7) described later in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein.

[0033] When the total solid content of the positive electrode active material layer 22a is 100% by mass, the positive electrode active material (for example, a lithium manganese-containing composite oxide) may generally occupy 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a conductive material, a binder, various additive components, etc. As the conductive material, for example, a carbon material such as acetylene black (AB) can be used. As the binder, for example, polyvinylidene fluoride (PVdF) etc. can be used.

[0034] Although not particularly limited, in a high-capacity battery 100 used for in-vehicle applications, etc., as shown in FIG. 6, the width of the positive electrode active material layer 22a in the direction of the winding axis WL (average value, excluding the portion formed in the positive electrode tab 22t), in other words, the length Lc in the long side direction Y, is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more.

[0035] As shown in FIG. 6, the positive electrode protective layer 22p is provided between the positive electrode collector 22c and the positive electrode active material layer 22a in the long side direction Y. Here, the positive electrode protective layer 22p is provided at one end (the left end in FIG. 6) of the positive electrode collector 22c in the long side direction Y. The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). The positive electrode protective layer 22p may contain any component other than the inorganic filler, such as a conductive material, a binder, various additive components, and the like. The conductive material and the binder may be the same as those exemplified as those that may be contained in the positive electrode active material layer 22a.

[0036] As shown in FIG. 6, the negative electrode 24 has a negative electrode collector 24c and a negative electrode active material layer 24a fixed on at least one surface of the negative electrode collector 24c. The negative electrode collector 24c is strip-shaped. The negative electrode collector 24c is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode collector 24c preferably contains copper or a copper alloy. The negative electrode collector 24c is a metal foil, specifically a copper foil, here. The negative electrode collector 24c is preferably made of a copper foil or a copper alloy foil. As will be described in detail later, according to the study by the present inventors, when the negative electrode 24 (specifically the negative electrode collector 24c) contains Cu, the Cu dissolves in the nonaqueous electrolyte, and the first high resistance region A1 and / or the second high resistance region A2 (see FIG. 7) described later are likely to occur in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein.

[0037] A plurality of negative electrode tabs 24t are provided at one end (right end in FIG. 6) in the long side direction Y of the negative electrode current collector 24c. The plurality of negative electrode tabs 24t each protrude toward one side (right side in FIG. 6) in the long side direction Y. The plurality of negative electrode tabs 24t protrude in the long side direction Y beyond the separator 26. The plurality of negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the negative electrode 24. By providing the plurality of negative electrode tabs 24t, the resistance of the battery 100 can be reduced. The negative electrode tab 24t of this embodiment contains Cu. Here, the negative electrode tab 24t is a part of the negative electrode current collector 24c, and is made of a metal foil (copper foil). It is preferable that the negative electrode tab 24t is a part of the negative electrode current collector 24c. The negative electrode tab 24t is preferably a current collector exposed portion where the negative electrode active material layer 24a is not formed at least in a part thereof and the negative electrode current collector 24c is exposed.

[0038] As shown in FIG. 3, the negative electrode tabs 24t are stacked at one end (the right end in FIG. 3) in the long side direction Y to form a negative electrode tab group 25. The negative electrode tabs 24t are stacked and bent so that the outer ends are aligned. This improves the accommodation in the battery case 10 and reduces the size of the battery 100. In addition, the volume energy density of the battery 100 can be improved. Furthermore, as will be described later in detail, according to the study by the present inventor, when the negative electrode tab 24t is bent and curved, for example, in the vicinity of the negative electrode tab group 25 (particularly near the base), the inter-electrode distance between the positive electrode 22 and the negative electrode 24 tends to be locally large. As a result, a first high resistance region A1 (see FIG. 7) described later is likely to occur in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein. A negative electrode second current collecting portion 62 described later of the negative electrode current collecting portion 60 is attached to the negative electrode tab group 25. The negative electrode tabs 24t are stacked and folded and connected to the negative electrode second current collecting portion 62. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collecting portion 60.

[0039] As shown in FIG. 6, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite, or a silicon material) capable of reversibly absorbing and releasing charge carriers. When the entire solid content of the negative electrode active material layer 24a is taken as 100 mass%, the negative electrode active material may occupy approximately 80 mass% or more, typically 90 mass% or more, for example 95 mass% or more. The negative electrode active material layer 24a may contain any component other than the negative electrode active material, such as a binder, various additive components, and the like. For example, rubbers such as styrene butadiene rubber (SBR) and celluloses such as carboxymethyl cellulose (CMC) can be used as the binder.

[0040] As shown in FIG. 6, the width of the negative electrode active material layer 24a in the winding axis WL direction (average value, excluding the portion formed in the negative electrode tab 24t), in other words, the length La in the long side direction Y, is typically the same as or longer than the length Lc in the long side direction Y of the positive electrode active material layer 22a. Although not particularly limited, from the viewpoint of increasing capacity, the length La is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more. As shown in FIG. 3, in the wound electrode body 20a, the nonaqueous electrolyte is supplied only from both ends in the long side direction Y (winding axis WL direction). Therefore, the longer the length La, the greater the amount of electrolyte supplied to the center M in the long side direction Y. Y (See FIG. 7) the nonaqueous electrolyte is less likely to penetrate into the central portion including the long side direction Y. As a result, a coating is less likely to form in the central portion in the long side direction Y, and the resistance is likely to be high. Therefore, it is particularly effective to apply the technology disclosed herein. The length La may be, for example, 1000 mm or less, or 500 mm or less. This allows the effect of the technology disclosed herein to be exerted at a high level.

[0041] 5, the height Ha of the negative electrode active material layer 24a located on the flat portion 20f of the wound electrode body 20a (the same as the height of the flat portion 20f) is preferably 110 mm or less, more preferably 50 to 110 mm, even more preferably 70 to 100 mm, and particularly preferably 70 to 90 mm. In the flat portion 20f, the ratio of the length La in the long side direction Y to the height Ha of the negative electrode active material layer 24a (horizontal / vertical ratio) is preferably 1 to 10, more preferably 2 to 7, and even more preferably 3 to 5.

[0042] FIG. 7 is a schematic plan view of approximately 1.5 turns of the negative electrode 24 after it has been unwound. Y are located at the center position 0.5La from both ends in the long side direction Y (winding axis WL direction). As shown in FIG. 7, in this embodiment, the negative electrode active material layer 24a has a stripe-shaped first high resistance region A1 extending from one end (the right end in FIG. 7, specifically the first end side) in the long side direction Y where the negative electrode tab 24t is provided toward the center, and a central high resistance region AM extending in a strip-like shape in the central part in the long side direction Y. Here, there is one first high resistance region A1. However, there may be two or more (plural) first high resistance regions A1 included in one strip-shaped negative electrode 24. For example, one or two or more (plural) first high resistance regions A1 may be formed in each turn.

[0043] The first high resistance region A1 is a region whose resistance is 1.5 times higher than the surrounding area. The resistance can be measured by a conventionally known method using an AC impedance method. Details will be described in the examples below, but the resistance can be measured using, for example, the resistance inspection device disclosed in JP 2014-25850 A.

[0044] Although it is not intended to be particularly limited, according to the study of the present inventor, it is presumed that the first high resistance region A1 is generated by a mechanism different from that of the central high resistance region AM. That is, the central high resistance region AM is a region where the resistance is considered to be high due to a small amount of coating. In detail, in the battery 100, a part of the nonaqueous electrolyte is decomposed during initial charging, and a coating (SEI film) containing the decomposition product is formed on the surface of the negative electrode active material layer 24a. This coating stabilizes the interface between the negative electrode active material layer 24a and the nonaqueous electrolyte. However, in the wound electrode body 20a with a particularly high capacity, the nonaqueous electrolyte is difficult to penetrate into the center of the long side direction Y, so that the coating is difficult to form in the center of the long side direction Y during initial charging. As a result, it is considered that the central high resistance region AM is formed.

[0045] On the other hand, the first high resistance region A1 is a region where the resistance is considered to be high due to the bending of the negative electrode tabs 24t. In detail, when the wound electrode body 20a is impregnated with a nonaqueous electrolyte, for example, moisture or oxygen in the electrolyte may affect the nonaqueous electrolyte, and metal ions may be eluted from the wound electrode body 20a. For example, Cu constituting the negative electrode current collector 24c (or the negative electrode tab 24t) may be eluted from the negative electrode 24. A transition metal element (particularly Mn) or an additive element (for example Zr), which is a constituent element of the positive electrode active material, may be eluted from the positive electrode 22. At this time, if the negative electrode tab 24t is bent and curved (in other words, if an external force is applied), the interelectrode distance between the positive electrode 22 and the negative electrode 24 is likely to be locally large at that location. Then, a large amount of nonaqueous electrolyte containing the above metal ions is likely to accumulate in the area where the electrode gap is locally wide. When initial charging is performed in this state, the potential of the negative electrode 24 drops, and metals such as Mn, Zr, and Cu that have dissolved into the nonaqueous electrolyte are deposited on the negative electrode active material layer 24a. If there is excess nonaqueous electrolyte (excess liquid) outside the wound electrode body 20a at this time, the dissolved metal ions also accumulate in the excess liquid, and the amount of metal deposition increases closer to the end of the long side direction Y of the wound electrode body 20a. As a result, decomposition of the nonaqueous solvent is promoted in the area where the metal is deposited, and the amount of organic coating becomes greater than in the surrounding area, which is thought to form the first high-resistance region A1.

[0046] The central high resistance region AM is formed by adjusting the conditions of the pressurized impregnation step (step 2) in the manufacturing method described later, for example, so that the central M in the long side direction Y (winding axis WL direction) Y It is possible to suppress this to within a range of ±15%. However, it is very difficult to completely eliminate it. Therefore, if the first high resistance region A1 extends long in the long side direction Y and overlaps with the central high resistance region AM, there is a risk that a region with extremely high resistance (ultra-high resistance region) will be formed.

[0047] In this embodiment, as shown in Fig. 7, when the length (total length) of the negative electrode active material layer 24a in the long side direction Y (winding axis WL direction, direction perpendicular to the first end side) is La and the length of the first high resistance region A1 is L1, the ratio (L1 / La) of the length L1 of the first high resistance region A1 to the length La of the negative electrode active material layer 24a is set to 0.35 or less. This makes it difficult for the first high resistance region A1 to overlap with the central high resistance region AM, thereby preventing the formation of an ultra-high resistance region. This in turn prevents a significant decrease in battery characteristics.

[0048] From the viewpoint of exerting the effect of the technology disclosed herein at a high level, the ratio (L1 / La) is preferably 0.31 or less, more preferably 0.3 or less, and even more preferably 0.2 or less. The ratio (L1 / La) may typically exceed 0, for example, 0.05 or more. In the case where there are two or more (plural) first high-resistance regions A1, if at least one first high-resistance region A1 satisfies the ratio (L1 / La), the effect of the technology disclosed herein is exerted, but it is more preferable that half or more, or even all of the first high-resistance regions A1 satisfy the ratio (L1 / La). In addition, when the length La of the negative electrode active material layer 24a in the long side direction Y is long as in the present embodiment, the ratio (L1 / La) may be 0.1 or more, 0.2 or more.

[0049] In this embodiment, the negative electrode active material layer 24a further has a stripe-shaped second high resistance region A2 extending from the other end (the left end in FIG. 7, specifically the second end side) in the long side direction Y where the positive electrode tab 22t is provided toward the center. However, for example, when the positive electrode tab group 23 and the negative electrode tab group 25 are provided at the end on the same side in the long side direction Y, the second high resistance region A2 may not be formed at the other end in the long side direction Y. Also, here, there is one second high resistance region A2 each. However, the number of second high resistance regions A2 included in one strip-shaped negative electrode 24 may be two or more (plural). For example, one or two or more (plural) second high resistance regions A2 may be formed in each turn.

[0050] The second high resistance region A2 is a region having a resistance value 1.5 times or more higher than the surrounding area, similar to the first high resistance region A1 formed at the end opposite to the long side direction Y. The second high resistance region A2 is a region where the resistance is considered to be high due to the bending and curvature of the multiple positive electrode tabs 22t, similar to the first high resistance region A1. As shown in FIG. 7, in the long side direction Y (winding axis WL direction), when the length of the negative electrode active material layer 24a is La and the length of the second high resistance region A2 is L2, it is preferable that the ratio (L2 / La) of the length L2 of the second high resistance region A2 to the length La of the negative electrode active material layer 24a is 0.35 or less. This makes it difficult for even the second high resistance region A2 to overlap with the central high resistance region AM, and the formation of a region with a very high resistance can be suppressed to a high level. In turn, a significant decrease in the battery characteristics can be suppressed to a high level.

[0051] From the viewpoint of exerting the effect of the technology disclosed herein at a high level, the ratio (L2 / La) is preferably 0.31 or less, more preferably 0.3 or less, and even more preferably 0.2 or less. The ratio (L2 / La) may typically exceed 0, for example, 0.05 or more. When there are two or more (plural) second high-resistance regions A2, it is preferable that at least one second high-resistance region A2 satisfies the ratio (L2 / La), and it is more preferable that more than half, or even all, of the second high-resistance regions A2 satisfy the ratio (L2 / La). In addition, when the length La of the negative electrode active material layer 24a in the long side direction Y is long as in this embodiment, the ratio (L2 / La) may be 0.1 or more, 0.2 or more.

[0052] The method for measuring the lengths L1 and L2 will be described in detail in the Examples below, but the high resistance region can also be visually identified as "color unevenness." The ratio (L1 / La) can be adjusted by the length La and / or the length L1, and the ratio (L2 / La) can be adjusted by the length La and / or the length L2. The values ​​of the lengths L1 and L2 can be suitably adjusted, for example, by the conditions of the initial charging step (step 3) in the manufacturing method described below, particularly the restraining position and restraining load of the battery case 10 in the initial charging step.

[0053] From the viewpoint of improving the battery characteristics, it is preferable that the resistance of the central high resistance region AM is reduced as much as possible. When the resistance distribution measurement is performed along the long side direction Y (winding axis WL direction) in the part where the first high resistance region A1 of the negative electrode active material layer 24a is not formed, the resistance value Rm at the center position 0.5 La from one end (the right end in FIG. 7) (i.e., the position where the resistance is estimated to be the highest in the central high resistance region AM) is preferably 1.5 times or less than the resistance value Rs at the reference position 0.25 La from one end (i.e., the position where the first high resistance region A1 and the central high resistance region AM are not formed). This can reduce unevenness in the coating in the long side direction Y of the negative electrode active material layer 24a. In addition, the central high resistance region AM is prevented from spreading in the long side direction Y, and the formation of an ultra-high resistance region can be suppressed to a higher level. When the length La of the negative electrode active material layer 24a in the long side direction Y is long as in this embodiment, the resistance value Rm can be 1.3 times or more, or 1.4 times or more, the resistance value Rs. The resistance ratio can be suitably adjusted, for example, by the conditions of the pressure impregnation step (step 2) in the manufacturing method described later.

[0054] As shown in FIG. 6, the separator 26 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. The width of the separator 26 in the winding axis WL direction, in other words, the length Ls in the long side direction Y, is typically equal to or longer than the length La in the long side direction Y of the negative electrode active material layer 24a. The separator 26 is preferably a resin porous sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may have an adhesive layer or a heat resistance layer (HRL) on the surface of the base material portion made of a resin porous sheet. The adhesive layer is a layer containing a binder. The heat resistance layer is a layer containing an inorganic filler such as alumina, silica, boehmite, magnesia, titania, or the like, and a binder such as PVdF. The heat resistance layer can also serve as an adhesive layer. The heat-resistant layer and the adhesive layer may have the same configuration as those of the conventional ones.

[0055] The separator 26 preferably has an adhesive layer on the surface facing the negative electrode 24. The adhesive layer has a function of, for example, melting during press molding of the wound electrode body 20a, and bonding (pressing) the negative electrode 24 and the separator 26. The negative electrode 24 and the separator 26 are preferably bonded by an adhesive layer. This makes it possible to suppress the interelectrode distance from becoming locally large even when the positive electrode tab 22t or the negative electrode tab 24t is bent and curved. In addition, if the negative electrode 24 and the separator 26 are strongly bonded, the nonaqueous electrolyte is less likely to penetrate into the center of the long side direction Y, and a coating is less likely to be formed. As a result, the center of the long side direction Y is likely to have high resistance. Therefore, it is particularly effective to apply the technology disclosed herein. Here, an adhesive layer is provided on the surface of the separator 26 facing the negative electrode 24; however, in other embodiments, an adhesive layer can be provided on the surface of the negative electrode 24 facing the separator 26, or an adhesive layer can be provided on the surface of the separator 26 facing the positive electrode 22.

[0056] As shown in FIG. 2, the positive electrode current collecting part 50 constitutes a conductive path that electrically connects the positive electrode tab group 23 consisting of a plurality of positive electrode tabs 22t to the positive electrode terminal 30. The positive electrode current collecting part 50 may be made of the same metal type as the positive electrode current collector 22c, for example, a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The positive electrode current collecting part 50 includes a positive electrode first current collecting part 51 connected to the positive electrode terminal 30, and a positive electrode second current collecting part 52 connected to the positive electrode tab group 23. The positive electrode first current collecting part 51 is attached to the inner surface of the sealing plate 14.

[0057] The positive electrode second current collecting portion 52 extends along the short side wall 12c of the exterior body 12. The positive electrode second current collecting portion 52 is attached to the positive electrode tab group 23 of the wound electrode body 20a. As shown in FIG. 3, the positive electrode second current collecting portion 52 has a joint J with the positive electrode tab group 23. The joint J is a welded joint formed by welding such as ultrasonic welding, resistance welding, and laser welding in a state where the multiple positive electrode tabs 22t are stacked. The joint J is arranged by bringing the multiple positive electrode tabs 22t closer to one side (the front side in FIG. 3) in the short side direction X of the wound electrode bodies 20a, 20b, and 20c. This allows the multiple positive electrode tabs 22t to be folded appropriately in a stacked state, and the curved positive electrode tab group 23 to be stably formed.

[0058] As shown in FIG. 2, the negative electrode current collecting part 60 constitutes a conductive path that electrically connects the negative electrode tab group 25 consisting of a plurality of negative electrode tabs 24t to the negative electrode terminal 40. The negative electrode current collecting part 60 may be made of the same metal type as the negative electrode current collector 24c, for example, a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode current collecting part 60 includes a negative electrode first current collecting part 61 connected to the negative electrode terminal 40 and a negative electrode second current collecting part 62 connected to the negative electrode tab group 25. The configuration and arrangement of the negative electrode first current collecting part 61 and the negative electrode second current collecting part 62 may be the same as those of the positive electrode first current collecting part 51 and the positive electrode second current collecting part 52 of the positive electrode current collecting part 50.

[0059] The negative electrode second current collecting portion 62 is attached to the negative electrode tab group 25 of the wound electrode body 20a. As shown in FIG. 3, the negative electrode second current collecting portion 62 has a joint J with the negative electrode tab group 25. The joint J is a welded joint formed by welding such as ultrasonic welding, resistance welding, and laser welding in a state where the multiple negative electrode tabs 24t are stacked, as in the case of the positive electrode side. The joint J is arranged by bringing the multiple negative electrode tabs 24t closer to one side (the front side in FIG. 3) in the short side direction X of the wound electrode bodies 20a, 20b, and 20c. This allows the multiple negative electrode tabs 24t to be folded appropriately in a stacked state, and the curved negative electrode tab group 25 to be stably formed.

[0060] 2, the positive electrode insulating member 70 is a member that insulates the sealing plate 14 from the positive electrode first current collecting part 51. The positive electrode insulating member 70 is made of a resin material that has resistance to the electrolyte used and electrical insulation properties and is elastically deformable, and is preferably made of, for example, a polyolefin resin such as polypropylene (PP), a fluorinated resin such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene sulfide (PPS), or the like.

[0061] 2, the negative electrode insulating member 80 is a member that insulates the sealing plate 14 and the negative electrode first current collecting portion 61. The negative electrode insulating member 80 is disposed symmetrically with the positive electrode insulating member 70 with respect to the center CL in the long side direction Y of the wound electrode body 20a. The material, configuration, etc. of the negative electrode insulating member 80 may be the same as those of the positive electrode insulating member 70.

[0062] The nonaqueous electrolyte typically contains a nonaqueous solvent and a supporting salt (electrolyte salt). As the nonaqueous solvent, one or more of those that are known to be usable in nonaqueous electrolyte secondary batteries can be used. Examples of the nonaqueous solvent include organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. The nonaqueous solvent preferably contains a carbonate. Examples of the carbonate include chain carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and cyclic carbonates such as propylene carbonate (PC).

[0063] The supporting salt is not particularly limited as long as it contains a charge carrier (typically lithium ion), and one or more of the salts that are known to be usable in non-aqueous electrolyte secondary batteries can be used. Examples of the supporting salt include fluorine-containing lithium salts such as LiPF6 and LiBF4. The supporting salt preferably contains LiPF6.

[0064] The non-aqueous electrolyte may further contain additional components (additives). As the additives, one or more of those that have been known to be added to non-aqueous electrolytes can be used. Examples of the additives include boron-based additives containing boron element such as lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiODFB); phosphorus-based additives containing phosphorus element such as lithium difluorophosphate (lithium difluorophosphate, LiPO2F2) and lithium difluorooxalate phosphate (LiDFOP); sulfur-based additives containing sulfur element such as lithium fluorosulfonate (LiSO3F), lithium ethyl sulfate, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); and the like. These additives may be so-called film-forming agents that decompose (at a low potential) prior to the non-aqueous solvent and / or supporting salt during initial charging and form a film on the surface of the negative electrode active material layer 24a.

[0065] In a preferred embodiment, the non-aqueous electrolyte contains a lithium salt containing phosphorus (P) (P-containing lithium salt). Examples of the P-containing lithium salt include LiPF6, which is exemplified above as a supporting salt, and LiPO2F2, LiDFOP, and the like, which are exemplified above as additives. According to the study by the present inventors, when the non-aqueous electrolyte contains a P-containing lithium salt, the first high resistance region A1 and / or the second high resistance region A2 may be easily generated in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein.

[0066] In a preferred embodiment, the non-aqueous electrolyte contains a lithium salt (B-containing lithium salt) containing boron element (B). Examples of the B-containing lithium salt include LiBF4, which is exemplified above as the supporting salt, and LiBOB and LiODFB, which are exemplified above as the additive. According to the study by the present inventors, when the non-aqueous electrolyte contains a B-containing lithium salt, the first high resistance region A1 and / or the second high resistance region A2 may be easily generated in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein.

[0067] In a preferred embodiment, the non-aqueous electrolyte contains a lithium salt containing sulfur element (S) (S-containing lithium salt). Examples of the S-containing lithium salt include LiSO3F, lithium ethyl sulfate, LiTFSI, LiFSI, and the like, which are listed above as additives. According to the inventor's study, when the non-aqueous electrolyte contains an S-containing lithium salt, the first high resistance region A1 and / or the second high resistance region A2 may be easily generated in the negative electrode active material layer 24a. Therefore, it is particularly effective to apply the technology disclosed herein.

[0068] However, additives in the nonaqueous electrolyte (for example, the above-mentioned boron-based additives, phosphorus-based additives, and sulfur-based additives) are typically electrically decomposed by initial charging during battery manufacture, and consumed to form a coating on the negative electrode active material layer 24a, etc. Therefore, in the state of the battery 100, the nonaqueous electrolyte may or may not contain (remain) additives such as those described above.

[0069] <Manufacturing method of battery 100> The battery 100 can be manufactured by a manufacturing method including, for example, the following steps: a battery assembly construction step (step 1), a pressurized impregnation step (step 2), an initial charging step (step 3), a degassing step (step 4), and a liquid injection hole sealing step (step 5) in this order. However, the pressurized impregnation step (step 2) and the degassing step (step 4) are optional and may be omitted in other embodiments. Furthermore, other steps may be included at any stage.

[0070] In the construction step (step 1), the electrode body group 20 (wound electrode bodies 20a, 20b, 20c) and non-aqueous electrolyte are accommodated in the battery case 10 in a glove box to construct a battery assembly 100A (see FIG. 8). In this specification, the term "battery assembly" refers to an intermediate product that has been assembled to a state prior to the initial charging step (step 3) in the manufacturing process of the battery 100. The order in which the electrode body group 20 and the non-aqueous electrolyte are accommodated in the battery case 10 is not particularly limited. For example, the electrode body group 20 may be accommodated in the battery case 10, and then the non-aqueous electrolyte may be poured into the battery case 10.

[0071] In a preferred embodiment, this process includes an electrode group arrangement process (step 1-1), a welding and bonding process (step 1-2), a drying process (step 1-3), and a liquid injection process (step 1-4), typically in this order. However, the drying process (step 1-3) is optional and may be omitted in other embodiments. In other embodiments, the order of the welding and bonding process (step 1-2) and the drying process (step 1-3) may be reversed, and the order of the welding and bonding process (step 1-2) and the liquid injection process (step 1-4) may be reversed. Furthermore, other processes may be included at any stage.

[0072] In the electrode assembly arrangement step (step 1-1), the electrode assembly group 20 is arranged inside the exterior body 12. More specifically, the electrode assembly group 20 is accommodated inside the exterior body 12 through the opening 12h. Next, in the welding and joining step (step 1-2), the sealing plate 14 is welded to the periphery of the opening 12h of the exterior body 12 to integrate the exterior body 12 and the sealing plate 14. Next, in the drying step (step 1-3), the exterior body 12 in which the electrode assembly group 20 is accommodated is dried with the liquid injection hole 15 open to remove moisture inside the exterior body 12. In particular, moisture inside the electrode assembly group 20 is removed. The moisture can be removed in the same manner as in the past, using a heating and drying device, a vacuum drying device, or the like, by performing operations such as heating and decompression alone or in appropriate combination. The heating temperature is preferably set to a temperature at which moisture can be appropriately evaporated, for example, under reduced pressure, and at which the separator 26 of the electrode assembly group 20 and the like are not thermally deteriorated. The heating temperature can be set, for example, within a range of 50 to 200°C.

[0073] Next, in the liquid injection step (step 1-4), a nonaqueous electrolyte is prepared. The nonaqueous electrolyte typically contains a nonaqueous solvent and a supporting salt as essential components, and may further contain one or more of the additives described above. Although not particularly limited, the concentration of each additive in the nonaqueous electrolyte is preferably 0.01 mol / L or more, and more preferably 0.05 mol / L or more, for each type, because it is easy to form a suitable coating on the surface of the negative electrode active material layer 24a. On the other hand, from the viewpoint of suppressing an increase in the battery resistance, the concentration of each additive in the nonaqueous electrolyte is preferably 1 mol / L or less, more preferably 0.5 mol / L or less, and even more preferably 0.1 mol / L or less, for each type (or the total). Then, the nonaqueous electrolyte is injected into the battery case 10 through the liquid injection hole 15 of the sealing plate 14. The injection is preferably carried out with the pressure inside the battery case 10 reduced in order to improve the impregnation of the non-aqueous electrolyte into the electrode assembly group 20 (wound electrode bodies 20a, 20b, 20c).

[0074] In the pressurized impregnation step (step 2), after the construction step (more specifically, the liquid injection step) of the battery assembly 100A (see FIG. 8), the battery assembly 100A is housed in a pressure-adjustable chamber, and pressurization and depressurization are repeated a predetermined number of times with the liquid injection hole 15 open (in other words, with no pressure difference between the inside and outside of the battery case 10). This allows the inside of each of the wound electrode bodies 20a, 20b, 20c, particularly the central portion in the long side direction Y, to be thoroughly impregnated with the nonaqueous electrolyte. As a result, the resistance of the central high-resistance region AM can be reduced, and unevenness in the coating in the long side direction Y can be reduced.

[0075] The pressure during pressurization depends on, for example, the length La of the negative electrode active material layer 24a in the long side direction Y, and is preferably 0.5 MPa or more, and more preferably 0.8 MPa or more. The time to hold the pressurized state depends on, for example, the length La of the negative electrode active material layer 24a in the long side direction Y, and is preferably 5 minutes or more, and more preferably 6 minutes or more. After pressurization, the pressure is released to return to normal pressure (about 0 MPa), and the time to hold the normal pressure state is preferably 1 minute or more. The number of times that pressurization and release are repeated is preferably 10 times or more, more preferably 15 times or more, and even more preferably 20 times or more. This process may be performed in a room temperature environment (for example, about 25°C ± 10°C, 25°C ± 5°C).

[0076] In the initial charging step (step 3), the battery assembly 100A (see FIG. 8) is charged at least once after the pressure impregnation step. The initial charging electrolyzes the nonaqueous electrolyte (e.g., additive), and forms a coating (SEI film) containing a decomposition product on the surface of the negative electrode active material layer 24a. The initial charging is preferably performed in a state where a predetermined area of ​​the battery case 10 is pressed. Specifically, it is preferable to perform the initial charging in a state where a portion of the flat portion 20f where the positive electrode active material layer 22a and the negative electrode active material layer 24a face each other is pressed. In particular, it is preferable to perform the initial charging in a state where a portion where the first high resistance region A1 and / or the second high resistance region A2 is likely to occur (in other words, a portion where the interelectrode distance is locally increased and the nonaqueous electrolyte is likely to accumulate) is pressed. In particular, it is effective to press the vicinity of the positive electrode tab group 23 (particularly near the base) and the vicinity of the negative electrode tab group 25 (particularly near the base). This makes it possible to prevent the inter-electrode distance from becoming locally large, and allows the length L1 of the first high-resistance region A1 and / or the length L2 of the second high-resistance region A2 to be suitably adjusted to a predetermined value or less (for example, 0.35 or less).

[0077] In a preferred embodiment, a cell press equipped with a pair of restraining plates is first prepared. A pressing member 200 for pressing a predetermined area of ​​the battery case 10 is also prepared. FIG. 8 is a side view that shows a schematic positional relationship between the battery assembly 100A (specifically, the long side wall 12b of the battery case 10) and the pressing member 200 in this step. The pressing member 200 is rectangular in side view. The pressing member 200 is rectangular parallelepiped in shape. In FIG. 8, the wound electrode body 20a in the battery case 10 is shown by a hidden line (dotted line).

[0078] As shown in FIG. 8, the size of the pressing member 200 is preferably smaller than the long side wall 12b of the battery case 10, and is preferably smaller than the wound electrode body 20a in the battery case 10. The pressing member 200 is preferably long enough to press the positive electrode tab group 23 and the negative electrode tab group 25 in the long side direction Y without pressing them too much, from the vicinity of the base of the positive electrode tab group 23 to the vicinity of the base of the negative electrode tab group 25. In the long side direction Y, the length L of the pressing member 200 is preferably equal to or longer than the length of the portion where the positive electrode active material layer 22a and the negative electrode active material layer 24a face each other (here, the length Lc of the positive electrode active material layer 22a). This makes it possible to suppress the interelectrode distance from becoming locally large at a high level. In this embodiment, the length L of the pressing member 200 is longer than the length La of the negative electrode active material layer 24a. Here, the pressing member 200 is long enough to press almost the entire negative electrode active material layer 24a in the long side direction Y. The length L of the pressing member 200 is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 250 mm or more.

[0079] In this embodiment, the height H of the pressing member 200 in the height direction Z is smaller than the overall height of the wound electrode body 20a and smaller than the height Ha of the negative electrode active material layer 24a (height of the flat portion 20f). This ensures a flow path for the nonaqueous electrolyte, and allows initial charging to be performed in a state in which the electrode body group 20 (wound electrode bodies 20a, 20b, 20c) is sufficiently impregnated with the nonaqueous electrolyte. The height H of the pressing member 200 is preferably 100 mm or less, more preferably 50 to 100 mm, even more preferably 60 to 90 mm, and particularly preferably 70 to 80 mm.

[0080] In this step, the pair of long side walls 12b of the battery assembly 100A are then sandwiched between two pressing members 200 from the short side direction X. Specifically, the battery assembly 100A and the pressing member 200 are opposed to each other so that the center position CP of the long side walls 12b of the battery case 10 coincides with the center of the pressing member 200. In this state, the battery assembly 100A is placed between a pair of restraining plates of a press machine, and charging is performed with a predetermined restraining load applied to the battery assembly 100A. From the viewpoint of exerting the effects of the technology disclosed herein at a high level, the restraining load is preferably 20 kN or more, and more preferably 25 kN or more (surface pressure of 1.2 MPa or more).

[0081] With the battery case 10 pressed in this manner, the battery assembly 100A is charged. The battery assembly 100A can be charged in the same manner as in the past. Typically, an external power source is connected between the positive and negative terminals of the battery assembly 100A, and charging is performed until a predetermined voltage is reached between the positive and negative terminals. The battery assembly 100A is preferably charged until the state of charge (SOC) is 5% or more, more preferably 10% or more. The state of charge (SOC) of the battery assembly 100A in this step is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less. When the nonaqueous electrolyte contains an additive, it is preferable to charge at least to the decomposition potential of the additive. The voltage to be reached may be set to about 3V or more, typically 3.5V or more, for example 4V or more, when the negative electrode active material is a carbon material. The charging rate may be, for example, about 0.1C to 2C. Charging may be performed once, or may be repeated two or more times, for example, with a discharge in between. This step may be performed in a room temperature environment (for example, about 25°C ± 10°C, about 25°C ± 5°C) or in a high temperature environment, for example, about 45°C. Charging in a high temperature environment can promote the formation of the coating.

[0082] In the degassing step (step 4), after the initial charging step, gas inside the battery case 10, such as air or gas generated by decomposition of the non-aqueous electrolyte in the initial charging step, is exhausted to the outside of the battery case 10. The gas can be exhausted, for example, by reducing the pressure inside the battery case 10. Then, in the liquid injection hole sealing step (step 5), the liquid injection hole 15 is sealed with a sealing member 16 while the pressure inside the battery case 10 is kept at normal pressure or reduced. This causes the battery case 10 to be airtightly sealed (hermetically sealed). In this manner, the battery 100 can be suitably manufactured.

[0083] <Uses of Battery 100> The battery 100 can be used for various purposes, but for example, because of its high capacity and excellent battery characteristics, it can be suitably used as a power source (driving power source) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, but examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). The battery 100 can also be suitably used as a battery pack in which a plurality of batteries 100 are arranged in a predetermined arrangement direction and a load is applied from the arrangement direction by a restraining mechanism.

[0084] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these examples.

[0085] <Preparation of evaluation battery> In the construction step (step 1), a plurality of battery assemblies (Examples 1 to 3, Comparative Examples 1 to 3) having the same configuration were constructed. Specifically, first, a lithium nickel cobalt manganese composite oxide (LiNi 0.6 Co 0.2 Mn 0.2O2, NCM-Zr) were prepared. A positive electrode active material layer containing this positive electrode active material, a carbon material (AB) as a conductive material, and PVdF as a binder in a mass ratio of NCM-Zr:AB:PVdF=97.5:1.5:1.0 was prepared on an aluminum foil as a positive electrode current collector to prepare a strip-shaped positive electrode sheet. A negative electrode active material layer containing graphite (C) as a negative electrode active material, SBR and CMC as binders in a mass ratio of C:(SBR+CMC)=98.5:1.5 was prepared on a copper foil as a negative electrode current collector to prepare a strip-shaped negative electrode sheet.

[0086] Next, the positive electrode sheet and the negative electrode sheet prepared above were faced to each other with a separator sheet interposed therebetween, and wound into a flat shape to prepare a wound electrode body. The separator sheet used had a heat-resistant layer (also serving as an adhesive layer) containing alumina and PVdF on the surface of a PE substrate. The overall height of the wound electrode body, including the curved portion, was 94 mm, the height of the flat portion (height of the negative electrode active material layer) Ha was 81 mm, and the length La of the negative electrode active material layer in the long side direction was 286 mm.

[0087] Next, a non-aqueous electrolyte was prepared by dissolving LiPF6 in a mixed solvent of EC, EMC, and DMC, and further adding LiBOB, LiSO3F, and LiPO2F2 as additives to a concentration of 0.05 mol / L. The wound electrode body and the non-aqueous electrolyte were then housed in a battery case to construct a rectangular parallelepiped battery assembly. In this manner, a number of battery assemblies with the same configuration were constructed.

[0088] In the pressurized impregnation step (step 2), pressurization and depressurization shown in Table 1 were repeated the number of times shown in Table 1. In Examples 1 and 2 and Comparative Examples 1 and 2, the battery assembly was housed in a pressure-adjustable chamber, and with the injection hole open, the pressure was increased from normal pressure to 0.8 MPa in one minute, the pressure was maintained at 0.8 MPa for six minutes, the pressure was then decreased to normal pressure in one minute, and the normal pressure state was maintained for one minute. This operation was repeated a total of 20 times. On the other hand, in Example 3 and Comparative Example 3, as shown in Table 1, this step was not performed (this step was omitted).

[0089] In the initial charging step (step 3), first, a pressing member as shown in FIG. 8 was prepared. Here, the length L of the pressing member in the long side direction was 290 mm, which was longer than the length La (286 mm) of the negative electrode active material layer in the long side direction, and the height H of the pressing member was 75 mm, which was shorter than the height Ha (81 mm) of the flat part of the wound electrode body. Next, the pressing member was arranged based on the center of the long side wall of the battery assembly constructed above, and the battery assembly and the pressing member were restrained with the restraining load shown in Table 1. As a result, the pressing member was applied to the part of the flat part of the wound electrode body where the positive electrode active material layer and the negative electrode active material layer faced each other. In the long side direction, the flat part of the wound electrode body is pressed by the pressing member from the vicinity of the root of the positive electrode tab group to the vicinity of the root of the negative electrode tab group. In the long side direction, the left and right ends of the pressing member are each 9 mm away from the short side wall. In the height direction, the upper end of the pressing member was 14 mm away from the sealing plate, and the lower end of the pressing member was 14 mm away from the bottom wall. Next, the battery assembly with the restraining load applied was charged to an SOC of 12% at a charge rate of 0.2 C. In this manner, the evaluation batteries (Examples 1 to 3, Comparative Examples 1 to 3) were produced.

[0090] [Table 1]

[0091] <Disassembly of the evaluation battery> First, the evaluation battery after the initial charge was discharged until the voltage reached 3.0 V, and then disassembled in a dry air atmosphere (for example, with a dew point of about -50°C) to remove the wound electrode body from the battery case. Then, the wound electrode body was unwound and the negative electrode was separated.

[0092] <Measurement of the resistance ratio (Rm / Rs) of the central high resistance area> First, the negative electrode was cut out in a suitable size (see, for example, FIG. 7) along the width direction (the same as the long side direction of the evaluation battery), and washed with DMC to prepare a test specimen for resistance measurement. Next, a resistance inspection device was prepared that includes a mounting section that accommodates the test specimen and non-aqueous electrolyte, a probe that contacts the measurement point, and an AC impedance measurement section. For the device configuration of the resistance inspection device, for example, JP 2014-25850 A can be referred to. The probe includes, for example, a cylindrical main body section that accommodates the non-aqueous electrolyte and a counter electrode (metal Li), and a measurement section that is connected to the lower end of the main body and contacts a part (measurement point) of the negative electrode active material layer of the test specimen, and is configured to be movable along the width direction of the test specimen. The diameter of the measurement section is, for example, about Φ1 mm to 10 mm. The AC impedance measurement section is configured to input an AC current or AC voltage between the working electrode that is in contact with the negative electrode tab and the measurement point (counter electrode) that is in contact with the measurement section of the probe, to measure impedance.

[0093] Next, the placement part of the resistance inspection device was filled with a non-aqueous electrolyte (only a non-aqueous solvent and a supporting salt, no additives added), and the test specimen was placed in the placement part. Next, a part (i.e., a part where a high resistance region is not formed) at one end of the negative electrode active material layer (the end on the side where the negative electrode tab is provided, the right end in FIG. 7) that was not dark black was selected by visual inspection. Then, with the working electrode in contact with the negative electrode tab, the probe was moved at a predetermined interval along the width direction of the negative electrode active material layer, and the resistance of the surface of the negative electrode active material layer was measured in spots by the AC impedance method. Specifically, for each measurement point, the difference in resistance from the direct current to the impedance arc end was obtained. The measurement interval was about 10 mm, and measurements were performed at a total of 30 points. Next, the value of the reaction resistance was read from the Cole-Cole plot, and the resistance value Rs at the reference position 0.25 La from one end was set as the reference (1) and standardized. Then, a resistance distribution showing the relationship between the measurement position and the resistance ratio was created. As an example, Fig. 9(A) shows the resistance distribution of Example 1, and Fig. 9(B) shows the resistance distribution of Example 3. In addition, for Examples 1 to 3, Table 1 shows the ratio (Rm / Rs) of the resistance value Rm at the center position of 0.5 La to the resistance value Rs at the reference position of 0.25 La.

[0094] As shown in Table 1, in Example 3 where the pressurized infiltration step (step 2) was not performed, the resistance ratio (Rm / Rs) was 1.7, and the resistance value Rm at the center position was 1.7 times larger than the resistance value Rs at the reference position. In contrast, in Examples 1 and 2 where the pressurized infiltration step (step 2) was performed, the resistance ratio (Rm / Rs) was 1.49, and the resistance value Rm at the center position was suppressed to 1.49 times the resistance value Rs at the reference position. Therefore, it was found that the resistance value Rm at the center position can be suitably adjusted by the pressurized infiltration step. Also, here, by applying pressure and reducing the pressure as shown in Table 1 in the pressurized infiltration step, the resistance ratio (Rm / Rs) could be made 1.5 or less.

[0095] <Measurement of the length of the first high resistance region> The presence or absence of a first high resistance region (a high resistance region extending from the end on the side where the negative electrode tab is provided toward the center in the width direction) was confirmed by the following procedure. First, (1) an end on one side of the negative electrode active material layer (the end on the side where the negative electrode tab is provided, the right end in FIG. 7) was visually confirmed to have a region that was darker black than the surroundings. Next, (2) of the dark black region, the central M of the negative electrode active material layer was visually confirmed to have a darker black than the surroundings. Y (See FIG. 7) for the center side end portion closest to the center M. Next, (3) the resistance (resistance value A) was measured in the same manner as above. Y The resistance (resistance value B) was measured in the same manner as above for the area close to the reference position (outside the dark black area). Then, (4) if the ratio of resistance value A to resistance value Rs at the reference position (resistance value A / Rs) was 1.5 or more and the ratio of resistance value B to resistance value Rs at the reference position (resistance value B / Rs) was less than 1.5, the first high resistance area was determined to be "present." The results are shown in Table 1.

[0096] As shown in Table 1, the first high resistance region was confirmed in all test examples. Therefore, the length from one end of the negative electrode active material layer to the central end of the dark black region (2) above was measured with a ruler, and this was taken as the length L1 in the width direction (winding axis direction) of the first high resistance region. Then, the ratio (L1 / La) of the length L1 of the first high resistance region to the total length La (286 mm) in the width direction of the negative electrode active material layer was calculated. The results are shown in Table 1.

[0097] As shown in Table 1, in Comparative Examples 1 to 3, the ratio (L1 / La) was relatively large, and in Comparative Example 3 in particular, L1 extended to a length substantially equal to the total widthwise length La of the negative electrode active material layer. In contrast, in Examples 1 to 3 in which a high restraining load was applied to the battery assembly in the initial charging step, the ratio (L1 / La) was kept relatively small. Therefore, it was found that the length L1 can be suitably adjusted, for example, by the conditions of the pressurized impregnation step and the conditions of the initial charging step, particularly the restraining position and restraining load in the initial charging step. In addition, here, in the initial charging step, a pressing member having a size of 290 mm wide x 75 mm high was used, and a restraining load of 25 kN or more was applied to the battery assembly from the long side wall side, whereby the ratio (L1 / La) could be set to 0.35 or less.

[0098] Although detailed explanation is omitted, the present inventors performed a component analysis of the first high resistance region using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and found that it contained a large amount of components such as B, P, S, Mn, Zr, and Cu. B, P, and S are components derived from the non-aqueous electrolyte (e.g., additives). From this, it was inferred that a large amount of non-aqueous electrolyte was present in the vicinity of the first high resistance region. Furthermore, Mn and Zr are components derived from the positive electrode active material, and Cu is a component derived from the negative electrode current collector. It can be seen that in the area where a large amount of non-aqueous electrolyte was present, there was also a large amount of metal deposition such as Mn, Zr, and Cu.

[0099] In addition, when the first high-resistance region and the non-discolored portion (portion other than the first high-resistance region) were analyzed by nuclear magnetic resonance (NMR), the first high-resistance region had a relatively larger amount of organic coating. From this, it was considered that in the portion where metals such as Mn, Zr, and Cu were precipitated, side reactions such as decomposition of the non-aqueous solvent were promoted, resulting in an increase in the organic coating and the formation of the first high-resistance region A1.

[0100] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field. The technology described in the claims includes various modifications and changes of the above-exemplified embodiments. For example, it is possible to replace a part of the above-mentioned embodiment with another modification, and it is also possible to add another modification to the above-mentioned embodiment. Furthermore, if a technical feature is not described as essential, it can be appropriately deleted.

[0101] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A wound electrode assembly formed by stacking a strip-shaped positive electrode and a strip-shaped negative electrode with a strip-shaped separator interposed therebetween and winding the electrode assembly, a non-aqueous electrolyte, a battery case that accommodates the wound electrode assembly and the non-aqueous electrolyte, a positive electrode terminal that is electrically connected to the positive electrode via a positive electrode current collector, and a negative electrode terminal that is electrically connected to the negative electrode via a negative electrode current collector, wherein the negative electrode has a negative electrode active material layer that includes a negative electrode active material, and a plurality of negative electrode tabs that are provided at one end in the winding axis direction, the negative electrode active material layer has a first high-resistance region extending from the one end toward a central portion in the winding axis direction and having a resistance value 1.5 times or more higher than that of its surroundings, and wherein, in the winding axis direction, when a length of the negative electrode active material layer is La and a length of the first high-resistance region is L1, a ratio (L1 / La) of the length L1 of the first high-resistance region to the length La of the negative electrode active material layer is 0.35 or less. Item 2: The nonaqueous electrolyte secondary battery according to item 1, wherein the negative electrode active material layer has a length La in the winding axis direction of 200 mm or more. Item 3: The nonaqueous electrolyte secondary battery according to item 1 or 2, wherein the negative electrode has a negative electrode current collector containing copper or a copper alloy. Item 4: The nonaqueous electrolyte secondary battery according to any one of Items 1 to 3, wherein the positive electrode contains a lithium-manganese-containing composite oxide as a positive electrode active material. Item 5: The nonaqueous electrolyte secondary battery according to Item 4, wherein the positive electrode active material contains elemental zirconium. Item 6: The nonaqueous electrolyte secondary battery according to any one of Items 1 to 5, wherein the nonaqueous electrolyte contains a lithium salt containing element phosphorus. Item 7: The nonaqueous electrolyte secondary battery according to any one of Items 1 to 6, wherein the nonaqueous electrolyte contains a lithium salt containing elemental boron. Item 8: The nonaqueous electrolyte secondary battery according to any one of items 1 to 7, wherein the nonaqueous electrolyte contains a lithium salt containing elemental sulfur. Item 9: The nonaqueous electrolyte secondary battery according to any one of items 1 to 8, wherein the negative electrode and the separator are bonded to each other via an adhesive layer. Item 10: The nonaqueous electrolyte secondary battery according to any one of items 1 to 9, wherein, in a portion of the negative electrode active material layer where the first high-resistance region is not formed, when a resistance distribution measurement is performed along the winding axis direction, a resistance value at a central position 0.5 La from the one end is 1.5 times or less than a resistance value at a reference position 0.25 La from the one end. Item 11: The nonaqueous electrolyte secondary battery according to any one of items 1 to 10, wherein the positive electrode has a plurality of positive electrode tabs provided at the other end in the winding axis direction, and the plurality of positive electrode tabs are connected to the positive electrode current collector in a stacked and folded state, the negative electrode active material layer has a second high-resistance region extending from the other end toward a central portion in the winding axis direction and having a resistance value 1.5 times or more higher than that of its surroundings, and when a length of the second high-resistance region is L2 in the winding axis direction, a ratio (L2 / La) of the length L2 of the second high-resistance region to the length La of the negative electrode active material layer is 0.35 or less. [Explanation of symbols]

[0102] 10 Battery case 20 Electrode group 20a, 20b, 20c wound electrode body 22 Positive electrode 22t Positive electrode tab 23 Positive electrode tab group 24 Negative electrode 24a Negative active material layer 24c Negative electrode current collector 24t negative electrode tab 25 Negative electrode tab group 26 Separator 100 batteries A1 1st high resistance region A2 2nd high resistance region La Length of negative electrode active material layer L1 Length of the first high resistance region L2 Length of the second high resistance region

Claims

1. a wound electrode body formed by stacking a strip-shaped positive electrode and a strip-shaped negative electrode with a strip-shaped separator interposed therebetween and winding the electrode; A non-aqueous electrolyte; a battery case that contains the wound electrode body and the nonaqueous electrolyte; a positive electrode terminal electrically connected to the positive electrode via a positive electrode current collecting portion; a negative electrode terminal electrically connected to the negative electrode via a negative electrode current collecting portion; Equipped with the negative electrode has a negative electrode active material layer including a negative electrode active material and a plurality of negative electrode tabs provided at one end in a winding axis direction, the negative electrode tabs are connected to the negative electrode current collecting portion in a stacked and folded state; the negative electrode active material layer has a first high resistance region extending from the one end toward a center portion in the winding axis direction and having a resistance value 1.5 times or more higher than that of a surrounding area, In the winding axis direction, when a length of the negative electrode active material layer is La and a length of the first high resistance region is L1, a ratio (L1 / La) of the length L1 of the first high resistance region to the length La of the negative electrode active material layer is 0.35 or less. Nonaqueous electrolyte secondary battery.

2. The length La of the negative electrode active material layer in the winding axis direction is 200 mm or more. The nonaqueous electrolyte secondary battery according to claim 1 .

3. The negative electrode has a negative electrode current collector containing copper or a copper alloy.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

4. The positive electrode contains a lithium manganese-containing composite oxide as a positive electrode active material.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

5. The positive electrode active material contains zirconium element. The nonaqueous electrolyte secondary battery according to claim 4 .

6. The non-aqueous electrolyte contains a lithium salt containing a phosphorus element.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

7. The non-aqueous electrolyte contains a lithium salt containing elemental boron.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

8. The non-aqueous electrolyte contains a lithium salt containing elemental sulfur.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

9. The negative electrode and the separator are bonded to each other by an adhesive layer.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

10. When a resistance distribution measurement is performed along the winding axis direction in a portion of the negative electrode active material layer where the first high resistance region is not formed, a resistance value at a central position 0.5 La from the one end is 1.5 times or less than a resistance value at a reference position 0.25 La from the one end.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

11. The positive electrode has a plurality of positive electrode tabs provided at the other end in the winding axis direction, The positive electrode tabs are connected to the positive electrode current collecting portion in a stacked and folded state, the negative electrode active material layer has a second high-resistance region extending from the other end toward a center portion in the winding axis direction and having a resistance value 1.5 times or more higher than that of a surrounding area, In the winding axis direction, when the length of the second high resistance region is L2, a ratio (L2 / La) of the length L2 of the second high resistance region to the length La of the negative electrode active material layer is 0.35 or less.

3. The nonaqueous electrolyte secondary battery according to claim 1 or 2.

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