Lithium secondary battery

Abstract

This lithium secondary battery comprises: a positive electrode provided with a long, sheet-like positive electrode current collector and a positive electrode active material layer; a negative electrode provided with a long, sheet-like negative electrode current collector; a separator; a nonaqueous electrolyte; a negative electrode external terminal electrically connected to the negative electrode current collector; and a negative electrode connection part interposed between the negative electrode current collector and the negative electrode exterior terminal. At the negative electrode, a lithium metal precipitates during charging, and the lithium metal dissolves during discharging. The positive electrode, the negative electrode, and the separator constitute a columnar wound body, and the negative electrode connection part is provided with (i) an end part running along the longitudinal direction of the negative electrode current collector projecting from one end surface of the wound body, or (ii) a plurality of negative electrode tab leads electrically connected to the negative electrode current collector and extending from one end surface of the wound body.

Description

Lithium secondary battery

[0001] The present invention relates to a lithium secondary battery.

[0002] Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with higher capacities than lithium ion batteries. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and during discharge, the lithium metal dissolves and is released as lithium ions into the non-aqueous electrolyte.

[0003] For example, Patent Document 1 proposes a lithium secondary battery comprising: a positive electrode including a positive electrode active material containing lithium; a negative electrode including a negative electrode current collector having a surface on which lithium metal is deposited in a charged state; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte solution having lithium ion conductivity that fills the space between the positive electrode and the negative electrode, wherein the negative electrode current collector includes a plurality of protrusions that protrude from the surface toward the separator, and no protrusions are present on a predetermined line on the surface of the negative electrode current collector that extends from a first end, passes through a region that extends between the plurality of protrusions, and reaches a second end that faces the first end.

[0004] On the other hand, Patent Document 2 proposes the use of a wound body unit having a ring-shaped or disk-shaped positive electrode current collector and a negative electrode current collector in a lithium ion capacitor. Each current collector is laser welded to the exposed portions of the positive electrode current collector and the negative electrode current collector. This structure has low current collection resistance and is advantageous for increasing the output of electrochemical devices.

[0005] JP 2018-195572 A International Publication No. 2012 / 036249 Pamphlet

[0006] In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging and dissolves during discharging, resulting in significant volume changes in the negative electrode. Therefore, when the positive electrode, negative electrode, and separator form an electrode group in the form of a columnar wound body, the volume change of the negative electrode causes large stresses inside the electrode group.

[0007] As the size of a lithium secondary battery increases, the number of windings of the wound body also increases, resulting in a significant increase in stress inside the electrode group. This significant increase in stress can cause defects such as localized liquid starvation (insufficient non-aqueous electrolyte), buckling, and breakage of the electrodes.

[0008] One aspect of the present invention provides a battery comprising: a positive electrode including a long sheet-like positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector; a negative electrode including a long sheet-like negative electrode current collector; a separator interposed between the positive electrode and the negative electrode; a non-aqueous electrolyte having lithium ion conductivity; a negative electrode external terminal electrically connected to the negative electrode current collector; and a negative electrode connection part interposed between the negative electrode current collector and the negative electrode external terminal, wherein the negative electrode The present invention relates to a lithium secondary battery in which lithium metal is deposited on the positive electrode, the negative electrode, and the separator, and the lithium metal dissolves during discharge; the positive electrode, the negative electrode, and the separator constitute an electrode group that is a columnar wound body; and the negative electrode connection portion comprises: (i) an end portion along the longitudinal direction of the negative electrode current collector that protrudes from one end face of the wound body; or (ii) a plurality of negative electrode tab leads that are electrically connected to the negative electrode current collector and extend from one end face of the wound body.

[0009] According to the present invention, even if the size of the lithium secondary battery increases and the electrodes break, the capacity does not drop suddenly.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] Fig. 1 is a longitudinal sectional view showing the configuration of a battery according to one embodiment of the present invention; Fig. 2 is a perspective view showing the appearance of a wound body included in a battery according to one embodiment of the present invention; Fig. 3 is a conceptual diagram showing some variations of electrodes; Fig. 4 is an enlarged view of a main part of Fig. 1; Fig. 2 is a longitudinal sectional view showing the configuration of a battery according to another embodiment of the present invention; Fig. 3 is a perspective view showing the appearance of a wound body included in a battery according to another embodiment of the present invention; Fig. 4 is a conceptual diagram showing variations of spacers.

[0012] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified. However, other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not greater than the upper limit. When multiple materials are exemplified, one of them may be selected and used alone, or two or more may be used in combination. Furthermore, the present disclosure encompasses combinations of two or more claims arbitrarily selected from the multiple claims set forth in the appended claims. In other words, as long as no technical contradiction occurs, any of the features set forth in two or more claims arbitrarily selected from the multiple claims set forth in the appended claims can be combined.

[0013] The lithium secondary battery according to the present disclosure includes a wound electrode group and a nonaqueous electrolyte having lithium ion conductivity. A battery including a wound electrode group is sometimes referred to as a wound battery. The outer shape of the wound electrode group or the wound battery is columnar, and may be, for example, cylindrical. The outer shape of a cross section perpendicular to the winding axis may be, for example, circular, elliptical, or rectangular with rounded corners (C-chamfered).

[0014] The electrode group has a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode group is constructed by winding the positive electrode and the negative electrode with the separator interposed between them around a predetermined winding core. That is, the electrode group is a columnar wound body composed of the positive electrode, the negative electrode, and the separator.

[0015] The positive electrode, negative electrode, and separator are each in the form of a long sheet. The positive electrode includes a long sheet-like positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector. The negative electrode includes a long sheet-like negative electrode current collector.

[0016] The lithium secondary battery according to the present disclosure is also called a lithium metal secondary battery. In the negative electrode of this type of battery, lithium metal is deposited during charging and dissolved during discharging. Specifically, the negative electrode only needs to have at least a negative electrode current collector, and lithium metal is deposited directly or indirectly on the negative electrode current collector.

[0017] In a lithium secondary battery, for example, 70% or more of the rated capacity is achieved by the deposition and dissolution of lithium metal. The movement of electrons at the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal at the negative electrode. Specifically, 70 to 100% (e.g., 80 to 100% or 90 to 100%) of the movement of electrons (or current from another perspective) at the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal. In other words, the negative electrode according to the present disclosure differs from a negative electrode in which the movement of electrons at the negative electrode during charging and discharging is mainly due to the absorption and release of lithium ions by the negative electrode active material (such as graphite).

[0018] In a battery in which lithium metal is deposited on the negative electrode during charging, the open circuit potential (OCV) of the negative electrode at full charge is, for example, 70 mV or less relative to lithium metal (lithium dissolution and deposition potential). A fully charged state refers to a state in which the battery is charged to a state of charge (SOC) of, for example, 0.98×C or more, where C is the rated capacity of the battery. The open circuit potential (OCV) of the negative electrode at full charge can be measured by disassembling a fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell using lithium metal as a counter electrode. The nonaqueous electrolyte of the cell may have the same composition as the nonaqueous electrolyte in the disassembled battery.

[0019] The lithium secondary battery according to the present disclosure includes a negative electrode external terminal electrically connected to the negative electrode current collector, and a negative electrode connecting part. The negative electrode connecting part is interposed between the negative electrode current collector and the negative electrode external terminal.

[0020] The negative electrode external terminal may also serve as an outer can that houses both the electrode group and the non-aqueous electrolyte. The outer can is a metal case also called a battery can. The outer can has a tubular (e.g., cylindrical) metal side portion and a bottom portion that closes one end of the side portion, and has an opening at the other end of the side portion. The side portion and the bottom portion may be formed integrally. The opening is closed by a sealing body that is a separate member from the outer can. The negative electrode external terminal may be provided in the sealing body that closes the opening of the outer can. The material of the outer can is not particularly limited, but may be metal, and stainless steel is preferable in terms of strength and durability.

[0021] In the first embodiment of the present disclosure, the negative electrode connection portion (i) includes an end portion of the negative electrode current collector extending along the longitudinal direction and protruding from one end face of the wound body. The negative electrode connection portion may include a negative electrode current collector plate. The negative electrode current collector plate is joined by welding or the like to the end portion of the negative electrode current collector extending along the longitudinal direction and protruding from one end face of the wound body. In the negative electrode connection portion, the end portion of the negative electrode current collector extending along the longitudinal direction and protruding from one end face of the wound body may be joined by welding or the like to the bottom of the outer can.

[0022] In a second embodiment of the present disclosure, the negative electrode connection portion (ii) includes a plurality of negative electrode tab leads electrically connected to the negative electrode current collector. The plurality of negative electrode tab leads each extend from one end face of the winding body. The plurality of negative electrode tab leads may each be joined to the bottom of the outer can by welding or the like. Note that, when the negative electrode external terminal is provided on the sealing body instead of the outer can, the plurality of negative electrode tab leads may each be joined to predetermined locations on the sealing body by welding or the like.

[0023] The negative electrode connection part of the first embodiment (hereinafter also referred to as the "edge current collection structure") is advantageous for increasing the output of the battery. The negative electrode connection part of the second embodiment (hereinafter also referred to as the "multi-tab structure") has a simpler structure than the edge current collection structure, and is advantageous for increasing the output of the battery and for increasing the capacity because it does not require a current collector plate. Meanwhile, in lithium secondary batteries, the edge current collection structure or the multi-tab structure not only achieves the above-mentioned effect of increasing output, but also has the separate effect of preventing a sudden decrease in capacity even if the electrode breaks.

[0024] Although lithium secondary batteries have high energy density, significant volume changes in the negative electrode make them prone to electrode buckling and breakage. In particular, as the size of lithium secondary batteries increases, the internal stress of the electrode group caused by volume changes in the negative electrode becomes significant. Conventional lithium secondary batteries experience a rapid decrease in capacity when an electrode breaks. In contrast, batteries with an end-face current collection structure or a multi-tab structure do not experience a rapid decrease in capacity even if the electrode breaks. In the case of a battery with an end-face current collection structure, even if the negative electrode breaks and the current path in the longitudinal direction of the negative electrode is interrupted, the current path in the transverse direction of the negative electrode is not affected, and therefore the capacity is not significantly affected. Furthermore, in the case of a battery with a multi-tab structure, even if the negative electrode breaks and the current path in the longitudinal direction of the negative electrode is interrupted, the capacity is not significantly affected if negative electrode tab leads are connected to each of the multiple regions formed by the break.

[0025] Furthermore, in conventional lithium secondary batteries, the longitudinal lengths of the positive and negative electrodes increase as the size increases. As a result, not only does stress increase within the electrode assembly, but current density non-uniformity becomes more pronounced. Current density non-uniformity promotes non-uniformity in the thickness of the negative electrode, facilitating electrode fracture and causing dendrite-like lithium metal deposition. In contrast, in batteries with an end-face current collection structure or multi-tab structure, current collection paths are secured in the short direction of the electrodes, making current density non-uniformity less likely to occur even if the longitudinal lengths of the positive and negative electrodes increase.

[0026] The lithium secondary battery according to the present disclosure exhibits particularly significant effects, for example, when the number of windings of the positive electrode is 29 or more, and even 70 or more. The number of windings corresponds to the number of stacked positive electrodes in the radial direction of the electrode group, which is a wound body. In other words, the number of windings corresponds to the number of times a straight line extending from the winding axis of the electrode group toward the outermost periphery of the electrode group intersects with the positive electrode. The length of the positive electrode in the longitudinal direction may be, for example, 1100 mm or more, or 3600 mm or more.

[0027] Furthermore, the lithium secondary battery according to the present disclosure is advantageous for achieving high output because it employs an end-face current collection structure or a multi-tab structure for the negative electrode, which has a higher current collection resistance than the positive electrode. That is, when an end-face current collection structure or a multi-tab structure is employed for the negative electrode, the effect of breaking the negative electrode, which is more susceptible to breakage than the positive electrode, is reduced, and the effect of reducing current collection resistance is significant.

[0028] When the negative electrode connection portion has a multi-tab structure including multiple negative electrode tab leads, the total width ln of the multiple negative electrode tab leads may be 2% or more of the longitudinal length Ln of the negative electrode. This makes it possible to achieve current collection efficiency comparable to that of an end-face current collection structure. The total width ln may be 10% or more and 80% or less of Ln.

[0029] When the negative electrode is divided into three or more (preferably four or more or five or more) regions of the same length in the longitudinal direction, it is desirable that at least one negative electrode tab lead be joined to each region. In this case, even if the negative electrode breaks and the current path in the longitudinal direction of the negative electrode is interrupted, there is a high probability that a negative electrode tab lead will be joined to each of the multiple regions formed by the break. This can effectively reduce the probability of a sudden decrease in capacity.

[0030] When the negative electrode is divided into three or more regions of equal length in the longitudinal direction as described above, a planned breaking portion for preferentially breaking the negative electrode current collector may be provided at the boundary between adjacent regions. The planned breaking portion may be a plurality of slits extending in a broken line from one end to the other end in the lateral direction of the negative electrode current collector, or may be a cut extending from one end to the other end in the lateral direction of the negative electrode current collector. The cut may be at least half the length (i.e., width) of the negative electrode current collector in the lateral direction, or may be a cut that is 90% or less of the length (i.e., width) in the lateral direction.

[0031] When the negative electrode external terminal is an outer can, it is desirable that each of the multiple negative electrode tab leads be joined to the inner surface of the bottom of the outer can. Each of the multiple negative electrode tab leads extends from a desired position on one end face of the electrode assembly, and it is not easy to control the extension positions of the multiple negative electrode tab leads on the end face. However, it is easy to join multiple negative electrode tab leads extending from desired positions on the end face to the inner surface of the bottom of the outer can by welding. In this case, it is efficient to bend the tip ends of the multiple negative electrode tab leads toward the center of the electrode assembly and use the hollow along the winding axis of the electrode assembly to weld the tip ends of the multiple negative electrode tab leads together to a region including the center of the bottom of the outer can. The center of the bottom of the outer can refers to a region within a circle with a radius of 3 mm or less from the center of the bottom of the outer can. This structure does not require a current collector plate like an end-face current collection structure, contributing to simplifying the battery manufacturing process and increasing the battery capacity.

[0032] In addition, an end-face current collection structure or a multi-tab structure may be adopted not only for the negative electrode but also for the positive electrode. That is, the lithium secondary battery according to the present disclosure may include a positive electrode external terminal electrically connected to the positive electrode current collector and a positive electrode connector. The positive electrode connector is interposed between the positive electrode current collector and the positive electrode external terminal.

[0033] If the negative electrode external terminal is other than the outer can, the outer can may also serve as the positive electrode external terminal. The positive electrode external terminal may be provided on a sealing body that closes the opening of the outer can.

[0034] The positive electrode connection portion may include (i) an end portion of the positive electrode current collector extending along the longitudinal direction and protruding from the other end face of the wound body (the side on which the negative electrode connection portion is not provided). The positive electrode connection portion may include a positive electrode current collector plate. The positive electrode current collector plate is joined by welding or the like to the end portion of the positive electrode current collector extending along the longitudinal direction and protruding from the other end face of the wound body. In the positive electrode connection portion, the end portion of the positive electrode current collector extending along the longitudinal direction and protruding from the other end face of the wound body may be joined by welding or the like to the bottom of the outer can.

[0035] The positive electrode connection portion may include (ii) a plurality of positive electrode tab leads electrically connected to the positive electrode current collector. The plurality of positive electrode tab leads each extend from the other end face of the wound body (the side on which the negative electrode connection portion is not provided). When the negative electrode external terminal is provided on the sealing body rather than the outer can, the plurality of positive electrode tab leads may each be joined to the bottom of the outer can by welding or the like. When the negative electrode external terminal is an outer can, the plurality of positive electrode tab leads may each be joined to a predetermined position on the sealing body by welding or the like.

[0036] When the positive electrode connection portion has a multi-tab structure including multiple positive electrode tab leads, the total width lp of the multiple positive electrode tab leads may be 1% or more of the longitudinal length Lp of the positive electrode. This makes it possible to achieve current collection efficiency comparable to that of an end-face current collection structure. The total width lp may be 5% or more and 70% or less of Lp.

[0037] When the negative electrode connection portion has a multi-tab structure including multiple negative electrode tab leads and the positive electrode connection portion has a multi-tab structure including multiple positive electrode tab leads, the total width ln of the multiple negative electrode tab leads is desirably greater than the total width lp of the multiple positive electrode tab leads. Because the negative electrode has a higher current collection resistance than the positive electrode, satisfying ln > lp improves the balance of the current collection state of the battery and more effectively suppresses non-uniform current density. Here, the ratio of ln to lp: ln / lp is desirably 1.1 or greater, and may be 1.1 or greater and 3.0 or less.

[0038] The electrode assembly preferably has a space (hereinafter also referred to as "inter-plate space") that separates at least one of the positive electrode and the negative electrode from the separator. This significantly reduces liquid depletion and effectively suppresses reaction variations (uneven reactions) within the electrode assembly. Liquid depletion is significantly reduced because the inter-plate space absorbs the volume increase caused by expansion of the negative electrode.

[0039] The inter-plate space may exist at least in a discharged state. Here, the discharged state refers to a state after a large amount of lithium metal has dissolved from the negative electrode, and may be, for example, a state of SOC of 0.05×C or less. However, since the inter-plate space does not need to be completely filled with lithium metal in a charged state, for example, the inter-plate space may exist even in a fully charged state.

[0040] The distance between the separator and at least one of the positive electrode and the negative electrode may be, for example, 15 μm or more and 65 μm or less. The distance is the distance between the electrode surface and the separator surface defining the inter-electrode space in a direction perpendicular to the winding axis (in the case of a cylindrical electrode group, the radial direction). If the distance is 15 μm or more, sufficient space can be secured to accommodate lithium metal deposited on the negative electrode during charging, and stress during expansion of the negative electrode can be sufficiently alleviated. If the distance is 65 μm or less, or even 60 μm or less, excessive space is not formed within the electrode group, and buckling of the electrodes is less likely to occur.

[0041] The inter-electrode space may be provided by a spacer interposed between at least one of the positive electrode and the negative electrode and the separator. The spacer is provided on at least one selected from the group consisting of the surface of the positive electrode, the surface of the negative electrode, and the surface of the separator. When a spacer is provided on the surface of the positive electrode or the surface of the separator facing the positive electrode, surface pressure from the separator is easily applied to the negative electrode, making it difficult for dendritic lithium metal to precipitate, which is advantageous for improving the capacity retention rate during charge-discharge cycles.

[0042] The spacer material has insulating properties and may be non-porous or porous. The spacer may be formed, for example, from a composite containing a resin material and particles. The resin material at least functions to bind the particles together. Such a spacer may be formed using a dispersion containing the resin material and the particles.

[0043] The height of the spacer may be designed according to the desired separation distance. The height of the spacer may be 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more. The height of the spacer may be 65 μm or less, or 60 μm or less. The height of the spacer is the maximum dimension of the spacer in the thickness direction of the separator (hereinafter also referred to as direction T). The height of the spacer is determined by photographing a cross section of the spacer in direction T using a scanning electron microscope (SEM), measuring the height at any 10 points, and averaging the measurements.

[0044] When a spacer is present, the negative electrode is divided into a first region facing the spacer and a second region not facing the spacer. The inter-electrode space is formed corresponding to the second region. The ratio of the area of ​​the first region to the total area of ​​the first and second regions is not particularly limited, but may be, for example, 5% to 30% or 5% to 20% in consideration of the balance between cycle characteristics and internal resistance. The larger the area ratio of the first region, the more likely it is that the amount of lithium metal deposited per unit area in the second region will be. Therefore, the amount of change in thickness of the negative electrode will be greater.

[0045] The first region facing the spacer is desirably arranged on the negative electrode in a state as uniform and dispersed as possible. This reduces the number of areas where lithium metal can be locally deposited in large amounts while suppressing an increase in internal resistance, making it easier to suppress deformation of the electrode assembly. Typically, the positive electrode and the negative electrode have a long (strip-like) shape having long and short sides. When the length (width) of the short side of the strip-like negative electrode is L, and a circular region having a diameter of any L / 3 is set on the surface of the negative electrode, it is desirable that the first region and the second region always coexist in such a circular region.

[0046] When the positive electrode connection portion has an end-face current collecting structure including a positive electrode current collector plate, a portion of the spacer may be disposed in a region of the positive electrode current collector between the positive electrode current collector plate and the positive electrode active material layer. With this structure, the exposed portion of the positive electrode current collector is protected by the spacer, which is an insulating member. Protecting the exposed portion of the positive electrode current collector with an insulating member can efficiently improve the safety of the battery.

[0047] Hereinafter, embodiments of the battery according to the present disclosure will be further described with reference to the drawings. In each drawing, the shape or features of each component do not necessarily reflect the actual dimensions, and are not necessarily drawn to the same scale. The same components in each drawing are designated by the same reference numerals.

[0048] [Lithium Secondary Battery] (First Embodiment) Fig. 1 is a longitudinal sectional view showing the configuration of a lithium secondary battery 200 according to a first embodiment of the present invention. Fig. 2 is a perspective view showing the appearance of a wound body 100 included in the lithium secondary battery 200. Fig. 3 is a conceptual diagram showing some variations of the electrodes. The positive electrode 10 and the negative electrode 20 constituting the wound body 100 are electrodes of the type shown in Fig. 3(a).

[0049] The battery 200 includes a wound body 100 formed into a columnar shape by winding a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, a non-aqueous electrolyte (not shown), a metal battery case 210 with a bottom that houses the wound body 100 and the non-aqueous electrolyte, and a sealing plate 220 that seals the opening of the battery case 210. A gasket 221 is disposed on the periphery of the sealing plate 220, and the inside of the battery case 210 is sealed by crimping the open end of the battery case 210 to the gasket 221.

[0050] The positive electrode 10 is in the form of a long sheet and includes a positive electrode current collector 11 and a positive electrode active material layer 12 supported thereon. The positive electrode active material layer 12 is formed on both sides of the positive electrode current collector 11. However, one end of the positive electrode current collector 11 along the longitudinal direction is formed with a positive electrode current collector exposed portion 11x that does not have the positive electrode active material layer 12.

[0051] The negative electrode 20 is in the form of a long sheet and includes a negative electrode current collector 21. The negative electrode 20 may include a lithium ion occlusion layer 22 (a layer that generates capacity by occlusion and release of lithium ions by a negative electrode active material (such as graphite)) supported on the negative electrode current collector 21. In this case, the open circuit potential of the negative electrode when fully charged may be 70 mV or less relative to lithium metal (lithium dissolution and deposition potential). If the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion occlusion layer when fully charged. In other words, the negative electrode generates capacity by the deposition and dissolution of lithium metal.

[0052] 1 is configured into a columnar shape by winding a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween. When winding, the positive electrode current collector exposed portion 11x is positioned so that it protrudes from one end face of the wound body 100, and the negative electrode current collector exposed portion 21x protrudes from the other end face of the wound body 100. The separator 30 is wound around the outermost periphery of the wound body 100.

[0053] The positive electrode current collector exposed portion 11x protruding from one end face of the wound body 100 is connected to the positive electrode current collector plate 13 by welding or the like. The negative electrode current collector exposed portion 21x protruding from the other end face of the wound body 100 is connected to the negative electrode current collector plate 23 by welding or the like. In other words, both the positive electrode connection portion and the negative electrode connection portion have an end face current collection structure.

[0054] The material of the positive electrode current collector 13 is, for example, aluminum, aluminum alloy, titanium, stainless steel, etc. The material of the positive electrode current collector 13 may be the same as the material of the positive electrode current collector 11. The material of the negative electrode current collector 23 is, for example, copper, copper alloy, nickel, stainless steel, etc. The material of the negative electrode current collector 23 may be the same as the material of the negative electrode current collector 21.

[0055] One end of the positive electrode tab 15 is connected to the positive electrode current collector 13, and the other end is connected to the inner surface of the sealing plate 220. Therefore, the sealing plate 220 functions as an external positive electrode terminal. The positive electrode current collector 13 is connected to an end portion along the longitudinal direction of the positive electrode current collector that protrudes from one end face of the wound body 100, thereby forming a positive electrode connection portion.

[0056] The negative electrode current collector 23 is welded to a welding member 25 provided on the inner bottom surface of the battery case 210. Therefore, the battery case 210 functions as an external negative electrode terminal. The negative electrode current collector 23 is connected to an end portion along the longitudinal direction of the negative electrode current collector that protrudes from the other end face of the wound body 100, thereby forming a negative electrode connection portion.

[0057] FIG. 4 is an enlarged view schematically illustrating the discharged state of the main portion of FIG. 1 . A spacer 40 is provided between the positive electrode 10 and the separator 30. The spacer 40 ensures a space S between the plates. The spacer 40 is composed of linear protrusions 41 arranged along the long side of the separator 30. In the discharged state, no lithium metal is deposited on the surface of the negative electrode current collector 21, and a space is maintained between the positive electrode 10 and the separator 30. On the other hand, in the charged state, lithium metal is deposited on the surface of the negative electrode current collector 21 and is accommodated in the space between the negative electrode 20 and the separator 30 while being subjected to the pressing force of the separator 30. Here, the negative electrode 20 includes the negative electrode current collector 21 in the discharged state, and includes the negative electrode current collector 21 and lithium metal deposited on its surface in the charged state. However, this configuration is merely an example, and the negative electrode 20 may include lithium metal not only on the negative electrode current collector 21 but also on its surface, even in the discharged state.

[0058] Because the lithium metal is accommodated in the inter-plate space between the positive electrode 10 and the separator 30, the apparent volume change of the electrode assembly due to the precipitation of lithium metal during charge-discharge cycles is reduced, thereby suppressing the stress applied to the negative electrode current collector 21. Furthermore, because pressure is applied from the separator 30 to the lithium metal accommodated between the negative electrode 20 and the separator 30, the precipitation state of the lithium metal is controlled, making it less likely for the lithium metal to become isolated, and suppressing a decrease in charge-discharge efficiency.

[0059] In the illustrated example, the cross-sectional shape of the spacer 40 is trapezoidal. However, embodiments of the present disclosure are not limited thereto and may be, for example, a rectangle, a rectangle with at least one curved corner, an ellipse, or a partial ellipse. Furthermore, in the illustrated example, the spacer 40 is provided between the positive electrode 10 and the separator 30, but embodiments of the present disclosure are not limited thereto. The spacer 40 may be provided only between the negative electrode 20 and the separator 30, or may be provided between the positive electrode 10 and the separator 30, or between the negative electrode 20 and the separator 30. The spacer 40 is provided on at least one surface selected from the group consisting of the surface of the positive electrode, the surface of the negative electrode, and the surface of the separator. Providing a spacer on the surface of the positive electrode or the surface of the separator facing the positive electrode facilitates the application of surface pressure from the separator to the negative electrode, making it less likely that dendritic lithium metal will precipitate, which is advantageous for improving the capacity retention rate during charge-discharge cycles.

[0060] In the illustrated example, the positive electrode 10 and the negative electrode 20 are each an electrode of the type shown in FIG. 3( a), but are not limited thereto. For example, as shown in FIG. 3( b), the current collector exposed portion 11x (21x) may be processed to have irregularities. Furthermore, as shown in FIG. 3( e), a spacer 40 may be formed on the surface of the positive electrode 10 or the negative electrode 20. In FIG. 3( e), a portion of the spacer 40 is formed on the current collector exposed portion 11x (21x). With this structure, the exposed portion of the positive electrode current collector can be protected by the spacer 40, which is an insulating member.

[0061] Second Embodiment Fig. 5 is a longitudinal cross-sectional view showing the configuration of a lithium secondary battery 200A according to a second embodiment of the present invention. Fig. 6 is a perspective view showing the appearance of a wound body 100A included in the lithium secondary battery 200A. The positive electrode 10 constituting the wound body 100 is an electrode of the type shown in Fig. 3(a), and the negative electrode 20 is an electrode of the type shown in Fig. 3(c), (d), or (f). In this embodiment, the positive electrode connection part has an end face current collection structure, and the negative electrode connection part has a multi-tab structure.

[0062] The negative electrode 20 of the type shown in Figure 3(c), (d), or (f) has at least a long sheet-like negative electrode current collector 21, and a lithium ion occlusion layer 22 carried on the negative electrode current collector 21 or a sheet-like lithium metal or lithium alloy layer 22 in close contact with the surface of the negative electrode current collector 21. However, regardless of the illustrated example, the negative electrode 20 may be composed of only the negative electrode current collector 21. One longitudinal end of the negative electrode current collector 21 is formed with a negative electrode current collector exposed portion 21x that does not have these layers. A plurality of tab leads 24 are connected to the negative electrode current collector exposed portion 21x. Each of the plurality of tab leads 24 extends from one end face of the wound body 100A.

[0063] Of the multiple tab leads 24, the tab leads 24 connected to the outer periphery of the winding 100A are longer than the tab leads 24 connected closer to the inner periphery, and protrude a greater distance from the end face of the winding 100A. The tab leads 24 may protrude from the end face of the winding 100A by a length that allows the tab leads 24 to reach near the center of the winding 100A when the tab leads 24 are bent toward the center of the winding 100A. The tab leads 24 extending from any position on the end face of the winding 100A can be welded to the inner surface of the bottom of the battery case 210 by utilizing the hollow in the center of the winding 100A. For example, the necessary welding can be performed by inserting a welding electrode into the hollow in the winding 100A.

[0064] As described above, when the negative electrode connection portion has a multi-tab structure, a negative electrode current collector plate is not required, which is desirable in that it is possible to simultaneously obtain the effects of increasing capacity and improving the current collection efficiency of the negative electrode, which has a large current collection resistance. Furthermore, since the negative electrode external terminal is an outer can, the process of joining the multiple tab leads 24 to the inner surface of the bottom of the outer can is a conventional process, and there is no need to rigorously align the multiple tab leads 24.

[0065] 3(c), (d), or (f), the positive electrode 10 may also have a multi-tab structure with a plurality of tab leads 14. Alternatively, only the positive electrode connection part may have a multi-tab structure, and the negative electrode connection part may have an end-face current collection structure.

[0066] The electrode type shown in FIG. 3( c) is suitable for both positive and negative electrodes. When the electrode is divided into three longitudinal regions R1, R2, and R3 of equal length, one tab lead is connected to each region. The electrode type shown in FIG. 3( d) is particularly suitable for positive electrodes. The electrode type shown in FIG. 3( f) has a breakable portion 35 that preferentially breaks the current collector and is suitable for both positive and negative electrodes. The breakable portion 35 in the illustrated example is a plurality of slits extending in a dashed line from one end of the current collector to the other end in the short direction, but is not limited thereto. By designing the electrode so that tab leads 14 (24) are connected to each of the regions R1 to R3 formed by breaking at the breakable portion 35, a sudden decrease in capacity is prevented even if the electrode breaks.

[0067] In the illustrated example, a cylindrical lithium secondary battery has been described, but the shape of the lithium secondary battery is not limited to this and may be rectangular, and various shapes may be appropriately selected depending on the application, etc. Also, known configurations other than those described above may be used without particular limitation.

[0068] For example, the battery case is not limited to an outer can. For example, the battery case may be a film case. A film case is a case formed into a bag or the like from a laminate (laminate film) of a barrier layer such as a metal foil and a resin layer. The barrier layer has a stronger blocking effect against external air or moisture than resin, and is formed from a metal foil, metal oxide layer, or the like.

[0069] The main components of a lithium secondary battery are further described below. [Spacer] The spacer 40, which is provided between the positive electrode 10 and / or negative electrode 20 and the separator 30, forms an inter-plate space S for accommodating deposited lithium metal. The separator 30 is typically in the form of a long sheet (strip) having long and short sides. Here, the direction along the short side of the separator 30 is designated D1. In a cross section (hereinafter referred to as the reference cross section) parallel to the direction T and the direction D1 of the spacer, the contact length (width of the first region) between the separator 30, the positive electrode 10, or the negative electrode 20 and the spacer 40 is not particularly limited, but is, for example, 500 μm or more and 2000 μm or less. When the contact length is within this range, stress applied to the spacer 40 is more likely to be uniformly distributed among the separator 30, the positive electrode 10, and the negative electrode 20. Furthermore, the first region facing the spacer 40 is likely to be disposed in a uniform and dispersed state facing the positive electrode 10 or the negative electrode 20. The contact length is the average value of the contact lengths at five different reference cross sections.

[0070] There are no particular limitations on the shape of the spacer 40 in the reference cross section, and the shape of the spacer in the reference cross section may be, for example, a rectangle, a rectangle having at least one curved corner, a trapezoid, an ellipse, a part of an ellipse, or a shape similar to these.

[0071] The material constituting the spacer 40 is not particularly limited. The spacer 40 may be formed, for example, by applying a solution or dispersion containing a resin material or the like to the surface of the separator 30, the positive electrode 10, or the negative electrode 20 and drying the applied solution. The solvent or dispersion medium is not particularly limited, and N-methyl-2-pyrrolidone (NMP), for example, can be used. The spacer 40 may also be formed by dispersing particles in a desired shape on the surface of the separator 30, the positive electrode 10, or the negative electrode 20. The spacer 40 may also be formed by applying a curable resin in a desired shape to the surface of the separator 30, the positive electrode 10, or the negative electrode 20 and curing the resin. The spacer 40 may also be formed by attaching adhesive tape to the surface of the separator 30, the positive electrode 10, or the negative electrode 20. Among the above methods, a method using a solution or dispersion containing a resin material is preferred. Of these, a method using a dispersion containing a resin material and particles is particularly preferred. In this case, the spacer is formed from a composite containing a resin material and particles.

[0072] Examples of resin materials include fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene, fluorine-containing rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer, styrene-butadiene copolymer or its hydrogenated product, acrylonitrile-butadiene copolymer or its hydrogenated product, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate, and ethyl cellulose. cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; acrylic resins such as acrylic acid-methacrylic acid copolymers; polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyimide, polyamides such as wholly aromatic polyamide (aramid), polyimide, polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymethacrylic acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

[0073] The particles may be inorganic or organic. Examples of inorganic particles include insulating metal oxides, metal hydroxides, metal nitrides, metal carbides, and metal sulfides. Examples of metal oxides include aluminum oxide (alumina and boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, and silicon oxide (silica). Examples of metal hydroxides include aluminum hydroxide. Examples of metal nitrides include silicon nitride, aluminum nitride, boron nitride, and titanium nitride. Examples of metal carbides include silicon carbide and boron carbide. Examples of metal sulfides include barium sulfate. Minerals such as aluminosilicates, layered silicates, barium titanate, and strontium titanate may also be used. Among these, alumina, silica, and titania are preferred.

[0074] The average particle size of the particles is not particularly limited, but is preferably 10 μm or less, and more preferably 0.1 μm or more and 2.0 μm or less. The average particle size can be determined by photographing a cross section of the spacer in direction T inside the secondary battery with an electron microscope, identifying the particle portion by performing image processing such as binarization of the photographed image, and calculating the average diameter of an equivalent circle having the same area as each particle. It is desirable to calculate the average from, for example, 100 or more particles.

[0075] In a composite containing a resin material and particles, the particles are preferably contained in an amount of 70 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the resin material, which makes it easier to ensure sufficient strength of the spacer.

[0076] The arrangement of the spacers is not particularly limited. For example, when viewed from direction T (the normal direction of the main surface of the separator), the spacers are preferably arranged so that a straight line SL can be drawn along direction D1 passing through three or more (preferably four or more, and even five or more) spacers. In this case, lithium metal is less likely to deposit unevenly or in a dendritic form on the negative electrode. Furthermore, local expansion of the negative electrode is suppressed, making electrode damage less likely to occur. In addition, the spacers increase the number of fulcrums that support the separator and electrode, so that the separator and electrode receive stress relatively evenly from the spacers. Therefore, electrode damage is further suppressed. Furthermore, the separator can apply a more uniform pressing force to the entire deposited lithium metal. Therefore, the deposition direction of lithium metal is more easily controlled toward the surface of the negative electrode.

[0077] When viewed from the direction T, the ratio d / h of the minimum distance d (μm) between adjacent spacers to the spacer height h (μm) on the straight line SL may be, for example, 10 or more and 800 or less, or may be 40 or more and 400 or less. By controlling the d / h ratio within the above range, it becomes easier to ensure sufficient space to accommodate lithium metal. Furthermore, a more uniform pressing force can be applied from the separator to the entire deposited lithium metal. The minimum distance d between adjacent spacers can be determined by measuring one location on each of any 10 straight lines SL and averaging the measurements.

[0078] The spacer may be, for example, a plurality of linear protrusions arranged in a stripe pattern on the surface of the electrode or separator, intersecting direction D1. For example, one protrusion may be provided on each end of the separator surface in direction D1, extending along the long side of the separator (hereinafter referred to as direction D2), and one or more protrusions may be provided between the two ends along direction D2. In this case, a straight line SL can be drawn so as to pass through the spacer at three or more points in total, including two points at both ends and one or more points between the two ends. Such spacers consisting of a plurality of linear protrusions can be formed relatively easily on the surface of the separator or electrode. Furthermore, parameters such as the height h and the d / h ratio can be easily controlled.

[0079] Next, the arrangement of the spacers will be described with reference to Fig. 7. In the illustrated example, the spacers are provided on the surface of the separator. However, the embodiment of the present disclosure is not limited to this, and the spacers may be provided on the surface of the electrode.

[0080] 7A is a plan view schematically illustrating a spacer disposed on the surface of a separator. The spacer 40 includes linear protrusions 41 extending along direction D2 at both ends of the surface of the separator 30 in direction D1, and a linear protrusion 41 extending along direction D2 at the center between the ends. That is, the spacer 40 includes a total of three linear protrusions 41 that are substantially parallel to each other. Therefore, a straight line SL drawn along direction D1 passes through the spacer 40 at three points. Note that "substantially parallel" means roughly parallel, and the linear protrusions 41 may intersect at an angle of, for example, 0° to 20° or 0° to 10°.

[0081] 7(b) is a plan view schematically illustrating another spacer 40 arranged on the surface of the separator 30. The spacer 40 is composed of a plurality of linear protrusions 41 arranged in a stripe pattern on the surface of the separator 30 along the direction D2. In this case, a straight line SL can be drawn along the direction D1 so as to pass through the same number of locations as the linear protrusions 41 (seven locations in the illustrated example).

[0082] 7(c) is a plan view schematically illustrating yet another spacer disposed on the surface of the separator. The spacer 40 is composed of a plurality of spot-like protrusions 41 evenly distributed on the surface of the separator 30. In the illustrated example, when a straight line SL is drawn along the direction D1, the number of spot-like protrusions 41 passing through the straight line SL varies depending on the position of the straight line SL. The straight line SL1 passes through four protrusions 41, and the straight line SL2 passes through five protrusions 41. In such a case, it is sufficient that the number of protrusions passed through by at least one of the multiple straight lines SL that can be drawn in different ways is three or more.

[0083] 7(d) is a plan view schematically showing yet another spacer arranged on the surface of the separator. The spacer 40 is a continuous body of honeycomb-shaped ribs evenly distributed on the surface of the separator 30. In this case, too, when a straight line SL is drawn along the direction D1, the number of ribs that the line SL passes through varies depending on its position. The straight line SL1 passes through the ribs at five points, and the straight line SL2 passes through the ribs at four points.

[0084] 7( e) is a plan view schematically illustrating yet another spacer disposed on the surface of the separator. The spacer 40 is composed of a plurality of linear protrusions 41 evenly distributed on the surface of the separator 30. The linear protrusions 41 are arranged so as to intersect alternately along the direction D1. In this case as well, when a straight line is drawn along the direction D1, the number of linear protrusions 41 passing through varies depending on the position of the line SL. For example, the line SL1 passes through three or four protrusions 41, the line SL2 passes through three protrusions 41, and the line SL3 passes through two protrusions 41.

[0085] Each component of the lithium secondary battery will be described in more detail below. [Negative Electrode] The negative electrode includes a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode upon charging to become lithium metal, which is then deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves as lithium ions in the non-aqueous electrolyte upon discharging. The lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte, may be supplied from the positive electrode active material upon charging, or may be both.

[0086] The negative electrode may include a negative electrode current collector and a sheet of lithium metal or lithium alloy in close contact with the surface of the negative electrode current collector. That is, the negative electrode current collector may be provided with a lithium metal-containing underlayer (a lithium metal or lithium alloy layer (hereinafter also referred to as a "lithium underlayer")) in advance. The lithium alloy may contain elements such as aluminum, magnesium, indium, and zinc in addition to lithium. By providing a lithium metal underlayer and depositing lithium metal on it during charging, dendritic deposition can be more effectively suppressed. The thickness of the lithium metal underlayer is not particularly limited, but may be, for example, in the range of 5 μm to 25 μm.

[0087] The negative electrode may include a lithium ion occlusion layer (a layer that develops capacity by occlusion and release of lithium ions by a negative electrode active material (such as graphite)) supported on a negative electrode current collector. In this case, the open circuit potential of the negative electrode when fully charged may be 70 mV or less relative to lithium metal (dissolution and deposition potential of lithium). If the open circuit potential of the negative electrode when fully charged is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion occlusion layer when fully charged. In other words, the negative electrode develops capacity by deposition and dissolution of lithium metal.

[0088] The lithium ion occlusion layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture may contain a binder, a thickener, a conductive agent, etc. in addition to the negative electrode active material.

[0089] Examples of the negative electrode active material include a carbonaceous material, a Si-containing material, and a Sn-containing material. The negative electrode may contain one or more negative electrode active materials. Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0090] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0091] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber polymer, etc. Examples of the fluororesin include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0092] The negative electrode current collector may be a conductive sheet. Examples of the conductive sheet include metal foil and metal film. The material of the negative electrode current collector may be any metal material other than lithium metal and lithium alloys, such as Cu, Ni, Fe, or an alloy containing these metal elements. Examples of alloys include Cu alloys and Fe alloys (such as stainless steel (SUS)). Among these, copper foil or copper alloy foil is preferably used for the negative electrode current collector, but is not particularly limited thereto.

[0093] The thickness of the negative electrode current collector is not particularly limited, and may be, for example, 5 μm or more and 300 μm or less, or 10 μm or more and 100 μm or less.

[0094] [Positive Electrode] The positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector. The positive electrode active material layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode active material layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode can be obtained, for example, by applying a positive electrode mixture slurry including the positive electrode active material, the conductive material, and the binder to both sides of the positive electrode current collector, drying the coating, and then rolling. For example, known materials can be used as the positive electrode active material, the binder, the conductive material, and the like.

[0095] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred because of their low production cost and high average discharge voltage.

[0096] The lithium-containing transition metal oxide is a composite oxide containing lithium and a metal other than lithium, Me, where the metal Me contains at least a transition metal. Among the lithium-containing transition metal oxides, composite oxides having a rock salt type crystal structure with a layered structure (layered rock salt type) are preferred in terms of obtaining a high capacity.

[0097] The metal Me may contain, as a transition metal element, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. The lithium-containing transition metal oxide may contain one or more transition metal elements. The metal Me preferably contains, as a transition metal element, at least one selected from the group consisting of Co, Ni, and Mn, and preferably contains at least Ni as the transition metal.

[0098] The lithium-containing transition metal oxide may contain one or more typical elements as needed. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al. That is, the metal Me may contain Al as an optional component.

[0099] The lithium-containing transition metal oxide is, for example, a lithium-containing transition metal oxide represented by the general formula (1): Li ａ Ni ｂ M １－ｂ O ２ In general formula (1), 0.9≦a≦1.2 and 0.65≦b≦1 are satisfied, and M is at least one element selected from the group consisting of Co, Mn, Al, Ti, Fe, Nb, B, Mg, Ca, Sr, Zr, and W.

[0100] The molar ratio mLi / mMe of the total amount mLi of Li contained in the positive electrode and negative electrode to the amount mMe of metal Me contained in the lithium-containing transition metal oxide is, for example, 1.2 or less, and may be 1.1 or less.

[0101] The positive electrode current collector may be any conductive sheet. Examples of the conductive sheet include metal foil and metal film. The material of the positive electrode current collector may be, for example, Al, Al alloy, Ti, Ti alloy, or Fe alloy (stainless steel (SUS), etc.). Among these, aluminum foil or aluminum alloy foil is preferred for the positive electrode current collector, but is not particularly limited thereto.

[0102] The thickness of the positive electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0103] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator. Examples of porous sheets include thin films, woven fabrics, and nonwoven fabrics having micropores. The material of the separator is not particularly limited, but may be a polymer material. Examples of polymer materials include olefin resins, polyamide resins, and cellulose. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may contain additives as needed. Examples of additives include inorganic fillers.

[0104] The thickness of the separator is not particularly limited, but is, for example, 5 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.

[0105] [Non-aqueous electrolyte] A non-aqueous electrolyte having lithium ion conductivity contains, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be liquid or gel-like. A liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. The dissolution of the lithium salt in the non-aqueous solvent generates lithium ions and anions.

[0106] As the lithium salt or anion, known materials used in non-aqueous electrolytes of lithium secondary batteries can be used. Specifically, BF ４ － , ClO ４ － , P.F. ６ － , C.F. ３ SO ３ － , C.F. ３ CO ２ － , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides include N(SO ２ CF ３ ) ２ － , N(C ｍ F ２ｍ＋１ SO ２ ) ｘ (C ｎ F ２ｎ＋１ SO２ ) y － (m and n are each independently an integer of 0 or 1 or greater, and x and y are each independently 0, 1, or 2, satisfying x+y=2.) The anion of the oxalate complex may contain boron and / or phosphorus. The non-aqueous electrolyte may contain one or more of these anions.

[0107] From the viewpoint of suppressing the deposition of lithium metal in a dendritic form, the nonaqueous electrolyte preferably contains at least an anion of an oxalate complex, and more preferably contains an oxalate complex anion having fluorine. The interaction between the oxalate complex anion having fluorine and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This makes it easier to suppress local deposition of lithium metal. The oxalate complex anion having fluorine may be combined with another anion. The other anion may be PF ６ － and / or anions of imides. Examples of the anion of the oxalate complex include bisoxalate borate anion and difluorooxalate borate anion (BF ２ (C ２ O ４ ) － ), P.F. ４ (C ２ O ４ ) － , P.F. ２ (C ２ O ４ ) ２ － and the like, and it is desirable to use at least a difluorooxalatoborate anion.

[0108] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain one or more of these non-aqueous solvents. Examples of halogen-substituted derivatives include fluorides.

[0109] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0110] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0111] The concentration of the lithium salt in the non-aqueous electrolyte may be, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. The concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0112] The lithium secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and home storage batteries.

[0113] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0114] 100, 100A: Wound body (electrode group) 10: Positive electrode 11: Positive electrode current collector 11x: Positive electrode current collector exposed portion 12: Positive electrode active material layer 13: Positive electrode current collector plate 15: Positive electrode tab 20: Negative electrode 21: Negative electrode current collector 21x: Negative electrode current collector exposed portion 22: Negative electrode active material layer 23: Negative electrode current collector plate 25: Welding member 30: Separator 40: Spacer 41: Convex portion 200, 200A: Battery 210: Battery case 220: Sealing plate 221: Gasket

Claims

1. a positive electrode including a long sheet-like positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector; a negative electrode including a long sheet-like negative electrode current collector; a separator interposed between the positive electrode and the negative electrode; a non-aqueous electrolyte having lithium ion conductivity; a negative electrode external terminal electrically connected to the negative electrode current collector; a negative electrode connection portion interposed between the negative electrode current collector and the negative electrode external terminal; Equipped with In the negative electrode, lithium metal is precipitated during charging, and the lithium metal is dissolved during discharging, the positive electrode, the negative electrode, and the separator constitute an electrode group that is a columnar wound body, The negative electrode connection portion is (i) an end portion along the longitudinal direction of the negative electrode current collector protruding from one end face of the wound body, or (ii) A lithium secondary battery comprising a plurality of negative electrode tab leads electrically connected to the negative electrode current collector and extending from one end face of the wound body.

2. the negative electrode connection portion includes the plurality of negative electrode tab leads, 2. The lithium secondary battery according to claim 1, wherein a total width ln of the plurality of negative electrode tab leads is 2% or more of a length Ln in the longitudinal direction of the negative electrode.

3. The lithium secondary battery according to claim 2 , wherein when the negative electrode is divided into three or more regions of equal length in the longitudinal direction, at least one negative electrode tab lead is joined to each of the regions.

4. The lithium secondary battery according to claim 3 , wherein a breakable portion for preferentially breaking the negative electrode current collector is provided at a boundary between the adjacent regions.

5. the negative electrode external terminal includes an exterior can that accommodates the electrode group, the nonaqueous electrolyte, and the negative electrode connection portion, the outer can has a cylindrical side portion and a bottom portion closing one end of the side portion, and has an opening at the other end of the side portion; 5. The lithium secondary battery according to claim 3, wherein each of the negative electrode tab leads is joined to an inner surface of the bottom of the outer can.

6. a positive electrode external terminal electrically connected to the positive electrode current collector; a positive electrode connection portion interposed between the positive electrode current collector and the positive electrode external terminal; Equipped with The positive electrode connection portion is (i) an end portion along the longitudinal direction of the positive electrode current collector protruding from the other end face of the wound body, or (ii) The lithium secondary battery according to any one of claims 1 to 3, further comprising a plurality of positive electrode tab leads electrically connected to the positive electrode current collector and extending from the other end face of the wound body.

7. The positive electrode connection portion includes the plurality of positive electrode tab leads, 7. The lithium secondary battery according to claim 6, wherein a total width lp of the plurality of positive electrode tab leads is 1% or more of a longitudinal length Lp of the positive electrode.

8. the negative electrode connection portion includes the plurality of negative electrode tab leads, The positive electrode connection portion includes the plurality of positive electrode tab leads, 7. The lithium secondary battery according to claim 6, wherein a total width ln of the plurality of negative electrode tab leads is greater than a total width lp of the plurality of positive electrode tab leads.

9. 5. The lithium secondary battery according to claim 1, wherein the electrode group has a space that separates and faces at least one of the positive electrode and the negative electrode from the separator.

10. 10. The lithium secondary battery according to claim 9, further comprising a spacer interposed between at least one of the positive electrode and the negative electrode and the separator, the space being provided by the spacer.

11. The lithium secondary battery according to claim 10 , wherein the spacer is insulating, and a part of the spacer is disposed in the connection portion.

12. The positive electrode includes a composite oxide including lithium and a metal other than lithium (Me), The lithium secondary battery according to any one of claims 1 to 4, wherein the molar ratio mLi / mMe of the total amount mLi of Li contained in the positive electrode and the negative electrode to the amount mMe of the metal Me contained in the composite oxide is 1.1 or less.