Lithium-ion 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

[Technical Field]

[0001] This invention relates to a lithium secondary battery. [Background technology]

[0002] Lithium-ion batteries (lithium metal batteries) are promising as high-capacity non-aqueous electrolyte secondary batteries that surpass lithium-ion batteries. In lithium-ion batteries, lithium metal is deposited 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 containing a lithium-containing positive electrode active material; a negative electrode containing a negative electrode current collector having a surface on which lithium metal is deposited when charged; a separator disposed between the positive electrode and the negative electrode; and a lithium-ion conductive non-aqueous electrolyte filling the space between the positive electrode and the negative electrode, wherein the negative electrode current collector includes a plurality of protrusions projecting from its surface toward the separator, and on a predetermined line of the surface of the negative electrode current collector, from a first end, through a region extending between the plurality of protrusions, to a second end facing the first end, there are no protrusions.

[0004] On the other hand, Patent Document 2 proposes using a wound unit having a ring-shaped or disc-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. Such a structure has low current collection resistance and is advantageous for increasing the power output of electrochemical devices. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-195572 [Patent Document 2] International Publication No. 2012 / 036249 Pamphlet [Overview of the project] [Problems that the invention aims to solve]

[0006] In lithium-ion secondary batteries, lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves during discharge, resulting in a significant change in the volume of the negative electrode. Therefore, when the positive electrode, negative electrode, and separator constitute an electrode group consisting of columnar wound bodies, the stress inside the electrode group caused by the volume change of the negative electrode becomes large.

[0007] As the size of lithium secondary batteries increases, the number of windings in the winding body also increases, leading to a significant increase in stress within the electrode group. This significantly increased stress can cause malfunctions such as localized electrolyte depletion (insufficiency of non-aqueous electrolyte), electrode buckling, and fracture. [Means for solving the problem]

[0008] One aspect of the present invention is a positive electrode comprising a long sheet-shaped positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, a negative electrode comprising a long sheet-shaped 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 portion interposed between the negative electrode current collector and the negative electrode external terminal, wherein the negative electrode, during charging... The present invention relates to a lithium secondary battery in which lithium metal is deposited, 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 along the longitudinal direction of the negative electrode current collector protruding 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. [Effects of the Invention]

[0009] According to the present invention, even if the size of the lithium secondary battery increases and electrodes break, a rapid decrease in capacity will not occur.

[0010] While the novel features of the present invention are set forth in the appended claims, the present invention, both as to organization 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. [Brief Description of the Drawings]

[0011] [Figure 1] It is a longitudinal cross-sectional view showing the configuration of a battery according to an embodiment of the present invention. [Figure 2] It is a perspective view showing the external appearance of a wound body included in the battery according to the embodiment of the present invention. [Figure 3] It is a conceptual diagram showing a part of variations of an electrode. [Figure 4] It is an enlarged view of the main part of Figure 1. [Figure 5] It is a longitudinal cross-sectional view showing the configuration of a battery according to another embodiment of the present invention. [Figure 6] It is a perspective view showing the external appearance of a wound body included in the battery according to the another embodiment of the present invention. [Figure 7] It is a conceptual diagram showing variations of a spacer. [Mode for Carrying Out the Invention]

[0012] Hereinafter, embodiments of the present disclosure will be described by way of examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials and the like may be exemplified, but other numerical values, materials and the like may be applied as long as the effects of the present disclosure can be obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "not less than numerical value A and not more than numerical value B". In the following description, when the lower and upper limits of numerical values relating to specific physical properties, conditions and the like 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 does not exceed the upper limit. When a plurality of materials are exemplified, one type may be selected and used alone, or two or more types may be used in combination. In addition, the present disclosure encompasses combinations of the matters described in two or more claims arbitrarily selected from the plurality of claims described in the appended claims. That is, as long as no technical contradiction arises, the matters described in two or more claims arbitrarily selected from the plurality of claims described in the appended claims can be combined.

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

[0014] The electrode group includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode group is configured by winding the positive electrode and the negative electrode around a predetermined winding core with the separator interposed therebetween. 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, the negative electrode and the separator are each in the form of a long sheet. The positive electrode includes a long sheet-shaped 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-shaped negative electrode current collector.

[0016] The lithium secondary battery relating to this 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 dissolves during discharge. Specifically, the negative electrode only needs to have a negative electrode current collector, and the lithium metal is deposited directly or indirectly on the negative electrode current collector.

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

[0018] In batteries that deposit lithium metal at the negative electrode during charging, the open-circuit voltage (OCV) of the negative electrode at full charge is, for example, 70mV or less relative to the lithium metal (lithium dissolution potential). Full charge refers to the state of charge (SOC) of the battery, where the rated capacity of the battery is C, for example, 0.98 × C or higher. The open-circuit voltage (OCV) of the negative electrode at full charge can be measured by disassembling the fully charged battery under an argon atmosphere, removing the negative electrode, and assembling a cell with lithium metal as the counter electrode. The non-aqueous electrolyte of the cell may have the same composition as the non-aqueous electrolyte in the disassembled battery.

[0019] The lithium secondary battery according to this disclosure comprises a negative electrode current collector, a negative electrode external terminal electrically connected to it, and a negative electrode connection portion. The negative electrode connection portion is interposed between the negative electrode current collector and the negative electrode external terminal.

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

[0021] In the first embodiment of this disclosure, the negative electrode connection portion comprises (i) an end portion of a negative electrode current collector that protrudes from one end face of the winding body along the longitudinal direction. The negative electrode connection portion may also comprise a negative electrode current collector plate. The negative electrode current collector plate is joined to the end portion of the negative electrode current collector that protrudes from one end face of the winding body along the longitudinal direction by welding or the like. In the negative electrode connection portion, the end portion of the negative electrode current collector that protrudes from one end face of the winding body along the longitudinal direction may be joined to the bottom of the outer casing by welding or the like.

[0022] In a second embodiment of the present disclosure, the negative electrode connection portion comprises (ii) a plurality of negative electrode tab leads electrically connected to a negative electrode current collector. Each of the plurality of negative electrode tab leads extends from one end face of the winding body. Each of the plurality of negative electrode tab leads may be joined to the bottom of the outer casing by welding or the like. If the negative electrode external terminal is provided on the sealing body instead of the outer casing, each of the plurality of negative electrode tab leads may be joined to a predetermined location on the sealing body by welding or the like.

[0023] The negative electrode connection section of the first embodiment (hereinafter also referred to as the "end-face current collection structure") is advantageous for increasing the output power of the battery. Furthermore, the negative electrode connection section of the second embodiment (hereinafter also referred to as the "multi-tab structure") has a simpler structure than the end-face current collection structure and is advantageous for increasing the capacity in addition to increasing the output power of the battery, as it does not require a current collection plate. On the other hand, in lithium secondary batteries, the end-face current collection structure or the multi-tab structure have the effect of not causing a sudden decrease in capacity even if the electrode breaks, in addition to the effect of increasing the output power mentioned above.

[0024] While lithium-ion batteries have a high energy density, the volume change of the negative electrode is significant, making them prone to electrode buckling and fracture. In particular, as the size of the lithium-ion battery increases, the stress inside the electrode group caused by the volume change of the negative electrode becomes significant. In conventional lithium-ion batteries, electrode fracture results in a rapid decrease in capacity. 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 an electrode fractures. In the case of batteries with an end-face current collection structure, even if the negative electrode fractures and the current path in the longitudinal direction of the negative electrode is interrupted, the current path in the short direction of the negative electrode is not affected, and therefore the capacity is not significantly affected. Also, in the case of batteries with a multi-tab structure, even if the negative electrode fractures and the current path in the longitudinal direction of the negative electrode is interrupted, if negative electrode tab leads are joined to each of the multiple regions formed by the fracture, the capacity is not significantly affected.

[0025] Furthermore, in conventional lithium secondary batteries, the longitudinal length of the positive and negative electrodes increases as the size increases. As a result, in addition to an increase in stress within the electrode group, the non-uniformity of current density becomes more pronounced. This non-uniformity of current density promotes non-uniformity in the thickness of the negative electrode, which encourages electrode fracture and causes the deposition of lithium metal in a dendrite-like manner. In contrast, in batteries with an end-face current collection structure or a multi-tab structure, even if the longitudinal length of the positive and negative electrodes increases, a current collection path is secured in the short direction of the electrodes, making it less likely for non-uniformity of current density to occur.

[0026] The lithium secondary battery according to this disclosure exhibits particularly remarkable effects when, for example, the number of turns of the positive electrode is 29 or more, and more specifically, 70 or more. The number of turns corresponds to the number of stacks of positive electrodes in the radial direction of the electrode group, which is a wound body. That is, the number of turns corresponds to the number of times a straight line extending from the winding axis of the electrode group to the outermost circumference of the electrode group intersects with the positive electrode. The longitudinal length of the positive electrode may be, for example, 1100 mm or more, or 3600 mm or more.

[0027] Furthermore, the lithium secondary battery according to this disclosure employs an end-face current collection structure or a multi-tab structure for the negative electrode, which has higher current collection resistance than the positive electrode, making it advantageous for increasing power output. In other words, when an end-face current collection structure or a multi-tab structure is adopted for the negative electrode, it not only reduces the impact of fracture of the negative electrode, which is more prone to breakage than the positive electrode, but also significantly reduces current collection resistance.

[0028] When the negative electrode connection section has a multi-tab structure comprising 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 of Ln, or 80% or less.

[0029] When the negative electrode is divided into three or more (preferably four or five or more) regions of the same length in the longitudinal direction, it is desirable that at least one negative electrode tab lead is connected 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, the probability that negative electrode tab leads are connected to each of the multiple regions formed by the break increases. Therefore, the probability of a sudden drop in capacitance can be effectively reduced.

[0030] As described above, when the negative electrode is divided into three or more regions of the same length in the longitudinal direction, a fracture-predicted portion may be provided at the boundary between adjacent regions to preferentially fracture the negative electrode current collector. The fracture-predicted portion may be a plurality of slits extending in a dashed line from one end to the other in the short direction of the negative electrode current collector, or it may be a cut extending from one end to the other in the short direction of the negative electrode current collector. The cut may be more than half the length (i.e., width) of the negative electrode current collector in the short direction, or it may be 90% or less of the length (i.e., width) in the short direction.

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

[0032] Furthermore, 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. In other words, the lithium secondary battery according to this disclosure may include a positive electrode external terminal electrically connected to the positive electrode current collector and a positive electrode connection portion. The positive electrode connection portion is interposed between the positive electrode current collector and the positive electrode external terminal.

[0033] The positive external terminal may also be the outer casing, if the negative external terminal is not the outer casing. The positive external terminal may also be provided on the sealing body that closes the opening of the outer casing.

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

[0035] The positive electrode connection section may (ii) comprise a plurality of positive electrode tab leads electrically connected to the positive electrode current collector. Each of the plurality of positive electrode tab leads extends from the other end face of the winding body (the side on which the negative electrode connection section is not provided). If the negative electrode external terminal is provided on the sealing body rather than the outer casing, each of the plurality of positive electrode tab leads may be joined to the bottom of the outer casing by welding or the like. If the negative electrode external terminal is on the outer casing, each of the plurality of positive electrode tab leads may be joined to a predetermined location on the sealing body by welding or the like.

[0036] When the positive electrode connection section has a multi-tab structure comprising 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 of Lp, or 70% or less.

[0037] When the negative electrode connection section has a multi-tab structure comprising multiple negative electrode tab leads, and the positive electrode connection section has a multi-tab structure comprising multiple positive electrode tab leads, it is desirable that the total width ln of the multiple negative electrode tab leads is greater than the total width lp of the multiple positive electrode tab leads. Since the negative electrode has a higher current collection resistance than the positive electrode, setting ln > lp improves the balance of the battery's current collection state and more effectively suppresses non-uniformity of current density. Here, the ratio of ln to lp: ln / lp is preferably 1.1 or greater, and may be between 1.1 and 3.0.

[0038] It is desirable that the electrode group has a space (hereinafter also referred to as the "inter-plate space") that separates and faces at least one of the positive and negative electrodes from the separator. This significantly reduces liquid depletion and effectively suppresses variations in the reaction (reaction unevenness) within the electrode group. Liquid depletion is significantly reduced because the inter-plate space plays a role in absorbing the volume increase when the negative electrode expands.

[0039] The interplate space only needs to exist at least in the discharge state. Here, the discharge state is the state after a large amount of lithium metal has dissolved from the negative electrode, and may be, for example, a state of charge (SOC) of 0.05 × C or less. However, the interplate space does not need to be completely filled with lithium metal in the charge state; for example, the interplate space may exist even in a fully charged state.

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

[0041] The space between the electrode plates 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. Providing the spacer on the surface of the positive electrode or the positive electrode side surface of the separator makes it easier for surface pressure from the separator to be applied to the negative electrode, making it difficult for dendrite-shaped lithium metal to precipitate, which is advantageous for improving the capacity retention rate during charge-discharge cycles.

[0042] The spacer material is insulating and may be non-porous or porous. The spacer may be formed, for example, from a composite material containing a resin material and particles. The resin material plays at least a role in binding the particles together. Such a spacer may also be formed using a dispersion containing the resin material and particles.

[0043] The spacer height should be designed to match the desired spacing distance. The spacer height may be 15 μm or more, 20 μm or more, 25 μm or more, or 30 μm or more. The spacer height may also be 65 μm or less, or 60 μm or less. The spacer height is the maximum dimension of the spacer in the thickness direction of the separator (hereinafter also referred to as direction T). The spacer height is determined by taking a cross-section of the spacer in direction T using a scanning electron microscope (SEM), measuring the height at 10 arbitrary points, and taking the average value.

[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 space between the electrode plates is formed corresponding to the second region. The ratio of the area of ​​the first region to the total area of ​​the second region is not particularly limited, but considering the balance between cycle characteristics and internal resistance, it may be, for example, 5% or more and 30% or less, or 5% or more and 20% or less. The larger the ratio of the area of ​​the first region, the greater the amount of lithium metal deposited per unit area in the second region tends to be. Therefore, the change in the thickness of the negative electrode becomes larger.

[0045] It is desirable that the first region facing the spacer be arranged on the negative electrode in a state that is as uniform and dispersed as possible. This reduces the areas where lithium metal can be deposited in large quantities locally, while suppressing an increase in internal resistance, and makes it easier to suppress deformation of the electrode group. Typically, the positive and negative electrodes have a long (strip-like) shape with a long side and a short side. When the length (width) in the short side direction of the strip-shaped negative electrode is L, and a circular region with an arbitrary diameter of 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 has an end-face current collection structure equipped with a positive electrode current collector plate, a portion of the spacer may be positioned in the region between the positive electrode current collector plate and the positive electrode active material layer of the positive electrode current collector. With such a structure, the exposed portion of the positive electrode current collector is protected by the spacer, which is an insulating material. By protecting the exposed portion of the positive electrode current collector with an insulating material, the safety of the battery can be efficiently enhanced.

[0047] Embodiments of the battery according to this disclosure will be further described below 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 shown at the same scale. The same reference numerals are used for the same components in each drawing.

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

[0049] The battery 200 comprises a wound body 100 formed in a columnar shape by winding a positive electrode 10 and a negative electrode 20 with a separator 30 in between, a non-aqueous electrolyte (not shown), a metal bottomed battery case 210 housing 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 placed on the periphery of the sealing plate 220, and the inside of the battery case 210 is sealed by crimping the opening end of the battery case 210 to the gasket 221.

[0050] The positive electrode 10 is in the form of a long sheet and comprises 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 its longitudinal direction has a positive electrode current collector exposed portion 11x which does not have the positive electrode active material layer 12.

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

[0052] The winding body 100 in Figure 1 is constructed in a columnar shape by winding a positive electrode 10 and a negative electrode 20 with a separator 30 in between. During winding, the positive electrode current collector exposed portion 11x protrudes from one end face of the winding body 100, and the negative electrode current collector exposed portion 21x protrudes from the other end face of the winding body 100. The separator 30 is wound around the outermost circumference of the winding body 100.

[0053] The exposed positive electrode current collector portion 11x protruding from one end face of the winding body 100 is connected to the positive electrode current collector plate 13 by welding or the like. The exposed negative electrode current collector portion 21x protruding from the other end face of the winding 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 plate 13 may be, for example, aluminum, aluminum alloy, titanium, or stainless steel. The material of the positive electrode current collector plate may be the same as the material of the positive electrode current collector body 11. The material of the negative electrode current collector plate 23 may be, for example, copper, copper alloy, nickel, or stainless steel. The material of the negative electrode current collector plate 23 may be the same as the material of the negative electrode current collector body 21.

[0055] The other end of the positive electrode tab 15, one end of which is connected to the positive electrode current collector plate 13, 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 connection portion is formed when the positive electrode current collector plate 13 is connected to the end of the positive electrode current collector that protrudes from one end face of the wound body 100 along the longitudinal direction.

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

[0057] Figure 4 is a schematic enlarged view showing the discharge state of the main part in Figure 1. A spacer 40 is provided between the positive electrode 10 and the separator 30. The spacer 40 ensures a space S between the electrode plates. The spacer 40 consists of a linear protrusion 41 provided along the long side direction of the separator 30. In the discharge state, lithium metal is not 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 charging state, lithium metal is deposited on the surface of the negative electrode current collector 21 and is housed in the space between the negative electrode 20 and the separator 30 while receiving the pressing force of the separator 30. Here, the negative electrode 20 comprises the negative electrode current collector 21 in the discharge state and the negative electrode current collector 21 and the lithium metal deposited on its surface in the charging state. However, this configuration is merely an example, and the negative electrode 20 may have lithium metal on its surface in addition to the negative electrode current collector 21 even in the discharge state.

[0058] Since the lithium metal is contained in the interplate space between the positive electrode 10 and the separator 30, the apparent volume change of the electrode group due to the deposition of lithium metal during the charge-discharge cycle is reduced. Therefore, the stress applied to the negative electrode current collector 21 is also suppressed. Furthermore, since pressure is applied from the separator 30 to the lithium metal contained between the negative electrode 20 and the separator 30, the deposition 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 this disclosure are not limited thereto, and may be, for example, rectangular, rectangular with a curve at least one corner, elliptical, or part of an ellipse. Also, in the illustrated example, the spacer 40 is provided between the positive electrode 10 and the separator 30, but embodiments of this disclosure are not limited thereto. The spacer 40 may be provided only between the negative electrode 20 and the separator 30, or it may be provided between the positive electrode 10 and the negative electrode 20 and the separator 30 respectively. The spacer 40 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. Providing the spacer on the surface of the positive electrode or the positive electrode side surface of the separator makes it easier for surface pressure from the separator to be applied to the negative electrode, making it difficult for dendrite-shaped lithium metal to precipitate, which is advantageous for improving the capacity retention rate in charge-discharge cycles.

[0060] In the illustrated example, the positive electrode 10 and the negative electrode 20 are electrodes of the type shown in Figure 3(a), but are not limited to these. For example, as shown in Figure 3(b), the exposed portion 11x(21x) of the current collector may be processed to have irregularities. Alternatively, as shown in Figure 3(e), a spacer 40 may be formed on the surface of the positive electrode 10 or the negative electrode 20. In Figure 3(e), a portion of the spacer 40 is formed on the exposed portion 11x(21x) of the current collector. This structure allows the exposed portion of the positive electrode current collector to be protected by the spacer 40, which is an insulating material.

[0061] (Second Embodiment) Figure 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. Figure 6 is a perspective view showing the external 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 Figure 3(a), and the negative electrode 20 is an electrode of the type shown in Figure 3(c), (d), or (f). In this embodiment, the positive electrode connection portion has an end-face current collection structure, and the negative electrode connection portion 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 storage layer 22 supported on the negative electrode current collector 21 or a sheet-like layer 22 of lithium metal or lithium alloy in close contact with the surface of the negative electrode current collector 21. However, notwithstanding the illustrated example, the negative electrode 20 may consist only of the negative electrode current collector 21. At one end of the negative electrode current collector 21 along the longitudinal direction, a negative electrode current collector exposed portion 21x without these layers is formed. Multiple tab leads 24 are connected to the negative electrode current collector exposed portion 21x. Each of the multiple tab leads 24 extends from one end face of the winding body 100A.

[0063] Of the multiple tab leads 24, the tab leads 24 connected to the outer circumference of the winding body 100A are longer than the tab leads 24 connected to the inner circumference, and have a greater protrusion distance from the end face of the winding body 100A. The protrusion length of the tab leads 24 from the end face of the winding body 100A should be such that, for example, when the tab lead 24 is bent toward the center of the winding body 100A, the tab lead 24 reaches near the center of the winding body 100A. Tab leads 24 extending from any position on the end face of the winding body 100A can be welded to the inner surface of the bottom of the battery case 210 by utilizing the hollow space in the center of the winding body 100A. For example, welding electrodes can be inserted into the hollow space of the winding body 100A and the necessary welding can be performed.

[0064] As described above, when the negative electrode connection section is made into a multi-tab structure, a negative electrode current collector plate is not required, which is desirable because it allows for the simultaneous achievement of increased capacity and improved current collection efficiency of the negative electrode, which has high current collection resistance. Furthermore, since the negative electrode external terminal is the outer casing, the process of joining the multiple tab leads 24 to the inner surface of the bottom of the outer casing is the same as conventional processes, and there is no need to precisely align the multiple tab leads 24.

[0065] Furthermore, the positive electrode 10 may be of the type shown in Figures 3(c), (d), or (f), and the positive electrode connection portion may also have a multi-tab structure with multiple tab leads 14, rather than being limited to the negative electrode 20. Alternatively, only the positive electrode connection portion may have a multi-tab structure, while the negative electrode connection portion may have an end-face current collection structure.

[0066] The electrode type shown in Figure 3(c) is suitable for both positive and negative electrodes. When the electrode is divided into three regions R1, R2, and R3 of the same length in the longitudinal direction, one tab lead is joined to each region. The electrode type shown in Figure 3(d) is particularly suitable for positive electrodes. The electrode type shown in Figure 3(f) has a fracture zone 35 that preferentially fractures the current collector and is suitable for both positive and negative electrodes. The fracture zone 35 in the illustrated example is a plurality of slits extending in a dashed line from one end to the other in the short direction of the current collector, but is not limited to this. By designing the electrode so that a tab lead 14 (24) is connected to each of the regions R1 to R3 formed by fracture at the fracture zone 35, even if the electrode fractures, a sudden drop in capacity will not occur.

[0067] Although the illustrated example describes a cylindrical lithium secondary battery, the shape of the lithium secondary battery is not limited to this; it may also be rectangular, and various shapes can be appropriately selected depending on the application. Furthermore, other known configurations can be used without any particular restrictions.

[0068] For example, the battery case is not limited to using an outer tin. For example, the battery case may be a film case. A film case is a case formed in the shape of a bag or similar using a laminate film, which is a laminate of a barrier layer such as metal foil and a resin layer. The barrier layer has a higher ability to block outside air or moisture than the resin and is formed from metal foil, a metal oxide layer, etc.

[0069] The following provides a further explanation of the main components of lithium-ion batteries. [Spacer] The spacer 40, provided between the positive electrode 10 and / or negative electrode 20 and the separator 30, forms an interplate space S that accommodates the deposited lithium metal. The separator 30 is usually a long sheet (strip) having a long side and a short side. Here, the direction along the short side of the separator 30 is denoted as D1. In a cross section parallel to the direction T of the spacer and parallel to direction D1 (hereinafter referred to as the reference cross section), the contact length (width of the first region) between the separator 30, the positive electrode 10 or negative electrode 20 and the spacer 40 is not particularly limited, but for example, it is 500 μm or more and 2000 μm or less. When the contact length is within this range, the stress on the spacer 40 is easily distributed uniformly across the separator 30, the positive electrode 10 and the negative electrode 20. In addition, the first region facing the spacer 40 is easily positioned facing the positive electrode 10 or the negative electrode 20 in a uniform and distributed state. Note that the contact length is the average value of the contact lengths at five different reference cross-sections.

[0070] The shape of the spacer 40 in the reference cross-section is not particularly limited. The shape of the spacer in the reference cross-section may be, for example, a rectangle, a rectangle with a curve at least one corner, a trapezoid, an ellipse, a part of an ellipse, or a similar shape.

[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 to the surface of the separator 30, positive electrode 10, or negative electrode 20 and drying it. The solvent or dispersion medium is not particularly limited, but for example, N-methyl-2-pyrrolidone (NMP) can be used. Alternatively, the spacer 40 may be formed by scattering particles in a desired shape on the surface of the separator 30, positive electrode 10, or 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, positive electrode 10, or negative electrode 20 and curing it. Alternatively, the spacer 40 may be formed by attaching adhesive tape to the surface of the separator 30, positive electrode 10, or negative electrode 20. Among the above methods, the method using a solution or dispersion containing a resin material is preferred. In particular, the method using a dispersion containing a resin material and particles is 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, ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate and other rubbers, and ethylcellulose. Examples include cellulose derivatives such as methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; acrylic resins such as acrylic acid-metharyl acid copolymers; polyamides such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyimide, and fully aromatic polyamides (aramids); polyimide, polyamideimide, polyacrylonitrile, polyvinyl alcohol, polyether, polyacrylic acid, polymetharyl acid, polyester, polyolefin, silicone resin, urethane resin, melamine resin, urea resin, and epoxy resin.

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

[0074] The average particle size 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 taking an electron microscope image of the cross-section of the spacer in direction T inside the secondary battery, performing image processing such as binarization of the image to identify the particle portion, and calculating the average diameter of the equivalent circle having the same area as each particle. It is desirable to obtain the average from, for example, 100 or more particles.

[0075] In composite materials containing resin material and particles, it is desirable that the particles be present in a ratio of 70 parts by mass or more and 100 parts by mass or less per 100 parts by mass of resin material. This makes it easier to ensure sufficient strength of the spacer.

[0076] The arrangement of the spacers is not particularly limited. For example, it is preferable that the spacers are arranged such that a straight line SL along direction D1 can be drawn so as to pass through three or more (preferably four or more, and even more preferably five or more) spacers when viewed from direction T (the direction normal to the main surface of the separator). In this case, lithium metal is less likely to precipitate unevenly or in a dendrite-like manner on the negative electrode. Furthermore, local expansion of the negative electrode is suppressed, making electrode damage less likely. In addition, the spacers provide more support points for the separator and the electrode, so that the separator and the electrode receive stress relatively evenly from the spacers. Therefore, electrode damage is further suppressed. Moreover, a more uniform pressing force can be applied from the separator to the entire precipitated lithium metal. Therefore, the deposition direction of lithium metal can be more easily controlled toward the surface of the negative electrode.

[0077] When viewed from direction T, the ratio d / h of the minimum distance d (μm) between adjacent spacers to the height h (μm) of the spacers in a straight line SL can be, for example, between 10 and 800, or between 40 and 400. By controlling the d / h ratio within the above range, it becomes easier to secure sufficient space for accommodating the 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 measured at one point in each of any 10 straight lines SL and the average value can be obtained.

[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 so as to intersect with direction D1. For example, one protrusion may be provided at each end of the separator surface in direction D1, along the direction of the long side of the separator (hereinafter referred to as direction D2), and one or more protrusions along direction D2 may be provided between these ends. In this case, a straight line SL can be drawn so as to pass through the spacer at a total of three or more locations: two locations at both ends and one or more locations between these ends. Such a spacer consisting of multiple linear protrusions can be formed on the surface of the separator or electrode relatively easily. Furthermore, it is easy to control parameters such as height h and d / h ratio.

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

[0080] Figure 7(a) is a schematic plan view showing a spacer arranged on the surface of a separator. The spacer 40 comprises line-shaped protrusions 41 along direction D2, provided at both ends of the surface of the separator 30 in direction D1, and a line-shaped protrusion 41 along direction D2, provided in the center between the two ends. In other words, the spacer 40 consists of a total of three substantially parallel line-shaped protrusions 41. Therefore, the straight line SL drawn along direction D1 passes through the spacer 40 at three points. Note that substantially parallel means approximately parallel, and the line-shaped protrusions 41 may intersect at angles such as 0° to 20° or 0° to 10°.

[0081] Figure 7(b) is a schematic plan view showing other spacers arranged on the surface of the separator. The spacer 40 consists of a plurality of line-shaped protrusions 41 arranged in a stripe pattern on the surface of the separator 30 along direction D2. In this case, a straight line SL can be drawn along direction D1, passing through the same number of locations as the line-shaped protrusions 41 (7 locations in the illustrated example).

[0082] Figure 7(c) is a schematic plan view showing yet another spacer arranged on the surface of the separator. The spacer 40 consists of a plurality of spot-shaped protrusions 41 arranged to be evenly distributed on the surface of the separator 30. In the illustrated example, when drawing a straight line SL along direction D1, the number of spot-shaped protrusions 41 that the line SL passes through differs depending on its position. Straight line SL1 passes through 4 protrusions 41, and straight line SL2 passes through 5 protrusions 41. In such cases, it is sufficient that at least one of the multiple straight lines SL that can be drawn in different ways passes through 3 or more protrusions.

[0083] Figure 7(d) is a schematic plan view showing yet another spacer arranged on the surface of the separator. Spacer 40 is a continuum of honeycomb-shaped ribs evenly distributed on the surface of separator 30. In this case as well, when drawing a straight line SL along direction D1, the number of ribs passed through differs depending on the position of the straight line SL. Straight line SL1 passes through ribs at 5 locations, and straight line SL2 passes through ribs at 4 locations.

[0084] Figure 7(e) is a schematic plan view showing yet another spacer arranged on the surface of the separator. The spacer 40 consists of a plurality of linear protrusions 41 evenly distributed on the surface of the separator 30. The linear protrusions 41 are arranged to intersect alternately along direction D1. In this case as well, when drawing a straight line along direction D1, the number of linear protrusions 41 that the line passes through will differ depending on the position of the line SL. For example, line SL1 passes through 3 or 4 protrusions 41, line SL2 passes through 3 protrusions 41, and line SL3 passes through 2 protrusions 41.

[0085] The following provides a more detailed explanation of each component of a lithium-ion secondary battery. [Negative electrode] The negative electrode is equipped with a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode during charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons on the negative electrode during charging, becoming lithium metal, and depositing 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 during discharge. The lithium ions contained in the non-aqueous electrolyte may originate from lithium salts added to the non-aqueous electrolyte, or they may be supplied from the positive electrode active material during charging, or both.

[0086] The negative electrode may comprise a negative electrode current collector and a sheet-like 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 pre-existing underlayer containing lithium metal (a layer of lithium metal or lithium alloy (hereinafter also referred to as the "lithium underlayer")). The lithium alloy may contain elements other than lithium, such as aluminum, magnesium, indium, and zinc. By providing a lithium metal underlayer and allowing lithium metal to deposit on it during charging, dendrite-like deposition can be suppressed even more effectively. The thickness of the lithium metal underlayer is not particularly limited, but may be in the range of, for example, 5 μm to 25 μm.

[0087] The negative electrode may include a lithium ion storage layer supported on the negative electrode current collector (a layer that exhibits capacity through the intercalation and release of lithium ions by the negative electrode active material (such as graphite)). In this case, the open-circuit potential of the negative electrode at full charge may be 70 mV or less relative to the lithium metal (lithium dissolution potential). When the open-circuit potential of the negative electrode at full charge is 70 mV or less relative to the lithium metal, lithium metal is present on the surface of the lithium ion storage layer at full charge. That is, the negative electrode exhibits capacity through the deposition and dissolution of lithium metal.

[0088] The lithium-ion storage layer is formed by creating layers of a negative electrode composite material containing a negative electrode active material. In addition to the negative electrode active material, the negative electrode composite material may also contain binders, thickeners, conductive agents, etc.

[0089] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material, or a combination of two or more types. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0090] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, carbon nanotubes, and graphite.

[0091] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0092] The negative electrode current collector can be any conductive sheet. Examples of conductive sheets include metal foil and metal film. The material of the negative electrode current collector can be any metallic material other than lithium metal and lithium alloys; for example, Cu, Ni, Fe, or alloys containing these metallic elements. Examples of alloys include Cu alloys and Fe alloys (stainless steel (SUS), etc.). Among these, it is preferable to use copper foil or copper alloy foil for the negative electrode current collector, but it is not particularly limited.

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

[0094] [Positive electrode] The positive electrode comprises, for example, a positive electrode current collector and a positive electrode active material layer supported by 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 on both sides. The positive electrode can be obtained, for example, by applying a positive electrode composite slurry containing the positive electrode active material, conductive material, and binder to both sides of the positive electrode current collector, drying the coating, and then rolling it. For example, known materials can be used as the positive electrode active material, binder, conductive material, etc.

[0095] The positive electrode active material is a material that intercepts and releases lithium ions. Examples of positive electrode active materials 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 they have low manufacturing costs and a high average discharge voltage.

[0096] Lithium-containing transition metal oxides are composite oxides containing lithium and a metal other than lithium, where the metal Me contains at least one transition metal. Among lithium-containing transition metal oxides, composite oxides having a layered rock salt type (layered rock salt type) crystal structure are preferred for obtaining high capacity.

[0097] Metallic Me may contain transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one transition metal element or two or more. It is desirable that metallic Me contains at least one transition metal element selected from the group consisting of Co, Ni, and Mn, and it is desirable that it contains at least Ni as a transition metal.

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

[0099] Lithium-containing transition metal oxides include, for example, those with the general formula (1):Li a Ni b M 1-b It is represented as O2. 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 of the total amount of Li (mLi) in the positive and negative electrodes to the amount of metallic Me (mMe) in the lithium-containing transition metal oxide, mLi / mMe, is, for example, 1.2 or less, and may also be 1.1 or less.

[0101] The positive electrode current collector can be any conductive sheet. Examples of conductive sheets 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 preferable for the positive electrode current collector, but it is not particularly limited.

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

[0103] [Separator] A porous sheet having ion permeability and insulating properties is used as the separator. Examples of porous sheets include thin films, woven fabrics, and nonwoven fabrics with microporous properties. The material of the separator is not particularly limited, but it 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 electrolytes] A non-aqueous electrolyte having lithium ion conductivity includes, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in liquid or gel form. A liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. When the lithium salt dissolves in the non-aqueous solvent, lithium ions and anions are generated.

[0106] As the lithium salt or anion, known materials used in non-aqueous electrolytes for lithium secondary batteries can be used. Specifically, BF4 - ClO4 - PF6 -, CF3SO3 - , CF3CO2 - , anions of imides, anions of oxalate complexes, and the like. Examples of the anions of imides include N(SO2CF3)2 - , N(C m F 2m+1 SO2) x (C n F 2n+1 SO2)y - (m and n are each independently 0 or an integer of 1 or more, x and y are each independently 0, 1 or 2, and satisfy x+y=2.) and the like. The anion of the oxalate complex may contain boron and / or phosphorus. The non-aqueous electrolyte may contain one type of these anions alone, or may contain two or more types.

[0107] From the viewpoint of suppressing the precipitation of lithium metal in a dendritic form, the non-aqueous electrolyte preferably contains at least an anion of an oxalate complex, and particularly desirably contains an oxalate complex anion having fluorine. The interaction between the oxalate complex anion having fluorine and lithium facilitates uniform precipitation of lithium metal in the form of fine particles. This makes it easier to suppress local precipitation of lithium metal. The oxalate complex anion having fluorine may be combined with other anions. The other anions may be PF6 - and / or anions of imides. Examples of the anion of the oxalate complex include bis(oxalate)borate anion, difluoro(oxalate)borate anion (BF2(C2O4) - ), PF4(C2O4) - , PF2(C2O4)2 - and the like, and it is desirable to use at least the difluoro(oxalate)borate anion.

[0108] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and halogen-substituted products thereof. The non-aqueous electrolyte may contain one type of these non-aqueous solvents alone, or may contain two or more types. Examples of the halogen-substituted products include fluorides and the like.

[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 linear 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 linear carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

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

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

[0112] The lithium secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablet devices, as well as in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and home energy storage systems.

[0113] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of Symbols]

[0114] 100, 100A: Winded body (electrode group) 10: Positive electrode 11: Positive electrode current collector 11x: Positive electrode current collector exposed part 12: Positive electrode active material layer 13: Positive electrode current collector plate 15: Positive Tab 20: Negative electrode 21: Negative electrode current collector 21x: Negative electrode current collector exposed part 22: Negative electrode active material layer 23: Negative electrode current collector plate 25: Welding components 30: Separator 40: Spacer 41 protrusions 200, 200A: battery 210: Battery case 220: Sealing board 221: Gasket

Claims

1. A positive electrode comprising a long sheet-shaped positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, A negative electrode comprising a long, sheet-shaped negative electrode current collector, A separator interposed between the positive electrode and the negative electrode, A non-aqueous electrolyte having lithium ion conductivity, The negative electrode current collector and the negative electrode external terminals electrically connected, A negative electrode connection portion interposed between the negative electrode current collector and the negative electrode external terminal, It is equipped with, In the aforementioned negative electrode, lithium metal is deposited during charging, 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. The negative electrode connection part is (i) The end portion of the negative electrode current collector that protrudes from one end face of the winding body along the longitudinal direction, (ii) A lithium secondary battery comprising a plurality of negative electrode tab leads, which are electrically connected to the negative electrode current collector and extend from one end face of the winding body, wherein when the negative electrode is divided into three or more regions of the same length in the longitudinal direction, at least one of the negative electrode tab leads is joined to each region.

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

3. The lithium secondary battery according to claim 1 or 2, wherein the boundary between adjacent regions has a planned fracture portion that preferentially fractures the negative electrode current collector.

4. The negative electrode external terminal comprises an outer casing that houses the electrode group, the non-aqueous electrolyte, and the negative electrode connection portion. The outer can comprises a cylindrical 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 lithium secondary battery according to claim 1 or 2, wherein each of the plurality of negative electrode tab leads is joined to the inner surface of the bottom of the outer casing.

5. Furthermore, the positive electrode external terminal is 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, It is equipped with, The positive electrode connection part is, (i) The end portion of the positive electrode current collector that protrudes from the other end face of the winding body along the longitudinal direction, (ii) The lithium secondary battery according to claim 1 or 2, 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 winding body.

6. The positive electrode connection portion comprises the plurality of positive electrode tab leads, The lithium secondary battery according to claim 5, wherein the total width lp of the plurality of positive electrode tab leads is 1% or more of the longitudinal length Lp of the positive electrode.

7. The negative electrode connection portion comprises the plurality of negative electrode tab leads, The positive electrode connection portion comprises the plurality of positive electrode tab leads, The lithium secondary battery according to claim 5, wherein the total width ln of the plurality of negative electrode tab leads is greater than the total width lp of the plurality of positive electrode tab leads.

8. The lithium secondary battery according to claim 1 or 2, 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.

9. Furthermore, the lithium secondary battery according to claim 8, further comprising a spacer interposed between at least one of the positive electrode and the negative electrode and the separator, wherein the spacer provides the space.

10. The aforementioned spacer is insulating, The negative electrode connection portion comprises an end portion that protrudes from one end face of the wound body and is aligned with the longitudinal direction of the negative electrode current collector, A lithium secondary battery according to claim 9, wherein a portion of the spacer is arranged at the end of the negative electrode current collector that protrudes from one end face of the wound body, which is provided by the negative electrode connection portion, and is along the longitudinal direction of the negative electrode current collector.

11. The lithium secondary battery according to claim 5, 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.

12. The lithium secondary battery according to claim 11, further comprising a spacer interposed between at least one of the positive electrode and the negative electrode and the separator, wherein the spacer provides the space.

13. The spacer is insulating, The positive electrode connection portion comprises an end portion that protrudes from the other end face of the winding body and is aligned with the longitudinal direction of the positive electrode current collector, A lithium secondary battery according to claim 12, wherein a portion of the spacer is arranged at the end of the positive electrode current collector that protrudes from the other end face of the winding body, which is provided by the positive electrode connection portion, and is aligned with the longitudinal direction of the positive electrode current collector.

14. The positive electrode comprises a composite oxide containing lithium and a metal other than lithium, Me. The lithium secondary battery according to claim 1 or 2, wherein the molar ratio of the total amount of Li contained in the positive electrode and the negative electrode, mLi / mMe, to the amount of metal Me contained in the composite oxide, mLi / mMe, is 1.1 or less.

15. The lithium secondary battery according to claim 1 or 2, wherein the length of the positive electrode in the longitudinal direction is 1100 mm or more.

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