Lithium secondary battery

Abstract

This lithium secondary battery comprises: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. The negative electrode has a negative electrode current collector and a negative electrode tab electrically connected to the negative electrode current collector. In the negative electrode, lithium metal is deposited on the negative electrode current collector during charging, and lithium metal is dissolved in the nonaqueous electrolyte during discharging. The negative electrode tab contains stainless steel at least in a connection portion with the negative electrode current collector.

Description

Lithium secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-146906, filed on August 28, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a lithium secondary battery comprising a lithium ion conductive non-aqueous electrolyte.

[0003] Non-aqueous electrolyte secondary batteries are used in applications such as ICT (Information Communication Technology) applications such as personal computers and smartphones, in-vehicle applications, and power storage. In these applications, non-aqueous electrolyte secondary batteries are required to have even higher capacities. Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Higher capacities in lithium-ion batteries can be achieved by using, for example, graphite and an alloy active material such as a silicon compound as the negative electrode active material. However, the capacity of lithium-ion batteries is reaching its limit.

[0004] Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with a higher capacity than lithium ion batteries. In lithium secondary batteries, lithium metal precipitates on the negative electrode during charging, and this lithium metal dissolves in the non-aqueous electrolyte during discharge.

[0005] Patent Document 1 describes a battery comprising: "a positive electrode having a positive electrode active material made of a lithium-containing transition metal oxide; a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the molar ratio of the total amount of lithium contained in the positive electrode and the negative electrode to the amount of transition metal contained in the positive electrode is 1.1 or less; a space layer is present between the negative electrode and the separator in a discharged state; and a positive electrode capacity α (mAh / cm) per unit area of ​​the positive electrode. ２and the average thickness X (μm) of the space layer satisfies 0.05≦α / X≦0.2." According to Patent Document 1, this configuration makes it possible to provide a nonaqueous electrolyte secondary battery that can suppress electrode breakage that may occur when charge-discharge cycles are repeated while realizing a high battery capacity.

[0006] International Publication No. 2019 / 087709

[0007] However, even with the method of Patent Document 1, the improvement in cycle characteristics is not sufficient, and further improvement in the charge-discharge cycle characteristics of lithium secondary batteries is desired.

[0008] One aspect of the present disclosure relates to a lithium secondary battery including: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte; the negative electrode has a negative electrode current collector and a negative electrode tab electrically connected to the negative electrode current collector; in the negative electrode, lithium metal is deposited on the negative electrode current collector during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging; and the negative electrode tab includes stainless steel at least in a portion connected to the negative electrode current collector.

[0009] According to the present disclosure, it is possible to suppress the deterioration of the cycle characteristics of a lithium secondary battery. 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.

[0010] 1 is a longitudinal cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment of the present disclosure. 2 is an enlarged view schematically illustrating a main part of the lithium secondary battery of FIG.

[0011] 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 ​​and materials may be exemplified, but other numerical values ​​and other materials 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 read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to 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. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0012] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0013] In lithium secondary batteries in which lithium metal is deposited on a negative electrode current collector in the negative electrode, the volume of the negative electrode repeatedly expands and contracts with charge and discharge. Repeated charge and discharge cycles generate repeated stress due to expansion and contraction of the negative electrode. It has been discovered that this repeated stress, when transmitted to the negative electrode tab connected to the negative electrode current collector, can cause the negative electrode tab to break or can reduce the electrical connectivity between the negative electrode current collector and the negative electrode tab, resulting in a deterioration in cycle performance. This disclosure is based on the new finding that one factor contributing to the deterioration of cycle performance of lithium secondary batteries is breakage of the negative electrode tab.

[0014] A lithium secondary battery according to one embodiment of the present disclosure includes a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode current collector and a negative electrode tab electrically connected to the negative electrode current collector. The lithium secondary battery is a secondary battery in which lithium metal is deposited on the negative electrode current collector during charging, and the deposited lithium metal dissolves from the negative electrode into the non-aqueous electrolyte during discharge. Hereinafter, the positive electrode and negative electrode may be collectively referred to as electrodes.

[0015] 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 of a lithium secondary battery 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 (e.g., graphite).

[0016] The negative electrode tab contains stainless steel (SUS) at least at the connection portion with the negative electrode current collector. The stainless steel-containing negative electrode tab suppresses breakage of the negative electrode tab due to repeated stress caused by expansion and contraction of the negative electrode with repeated charge-discharge cycles, or deterioration of electrical connectivity between the negative electrode current collector and the negative electrode tab due to repeated stress, thereby suppressing deterioration of cycle characteristics.

[0017] The negative electrode tab may have a multilayer structure in the thickness direction. For example, the negative electrode tab may have a multilayer structure including a first layer, a second layer located above the first layer, and a third layer located below the first layer. In this case, stainless steel is included in at least the first layer located on the inner side (core) of the negative electrode tab in the thickness direction. For example, the negative electrode tab may include a clad material, and the first and second layers and / or the first and third layers may be bonded together by crimping. The second and / or third layers may be plated layers formed on the first layer by plating or vapor-deposited layers formed on the first layer by vapor deposition.

[0018] At least one of the second layer and the third layer may contain copper (Cu). The copper-containing second layer (and / or the third layer) suppresses an increase in the resistance of the negative electrode tab containing stainless steel, thereby improving the material strength of the negative electrode tab while maintaining low resistance of the negative electrode tab. The copper-containing second layer (and / or the third layer) may be pure copper (e.g., oxygen-free copper) or a copper alloy. The copper content in the copper alloy may be, for example, 70% by mass or more, or even 85% by mass or more. The copper alloy may contain, as an element other than copper, at least one selected from the group consisting of Zn, Sn, Al, Ni, Fe, Mn, and P.

[0019] At least one of the second layer and the third layer may contain nickel (Ni). The nickel-containing second layer (and / or the third layer) facilitates welding a bond between the negative electrode tab and the negative electrode current collector or the negative electrode-side sealing member, thereby improving the bond strength.

[0020] The negative electrode tab may have a multilayer structure of four or more layers in the thickness direction. For example, the negative electrode tab may have a multilayer structure in which copper-containing layers are formed on both sides of a stainless steel plate (first layer), and a nickel layer is further formed on the copper-containing layers.

[0021] The ratio T1 / T0 of the thickness T1 of the first layer to the overall thickness T0 of the negative electrode tab may be 25% or more and 50% or less, which makes it easy to achieve both low resistance of the negative electrode tab and improved material strength of the negative electrode tab, and to easily suppress deterioration of cycle characteristics.

[0022] The stainless steel is not particularly limited, and may be ferritic stainless steel, or any of austenitic stainless steel, martensitic stainless steel, austenitic-ferritic stainless steel, and precipitation hardening stainless steel. Ferritic stainless steel has excellent rupture strength. Austenitic stainless steel may also be used because of its excellent corrosion resistance. Ferritic stainless steel includes SUS430. Austenitic stainless steel includes SUS304, SUS301, SUS310S, SUS316, etc.

[0023] The breaking strength is measured by a tensile strength test in accordance with JIS Z 2241:2011. However, because the negative electrode tab is small, the specific test conditions are changed from JIS Z 2241. A strip-shaped negative electrode tab removed from a battery is used as the test specimen. The test is conducted at room temperature with a tensile speed (crosshead displacement) of 0.042 mm / min. Tests that break near the grip are excluded. The tensile strength is calculated from the maximum load and the cross-sectional area of ​​the tab, and the average value for five negative electrode tabs is calculated.

[0024] The negative electrode may include a lithium layer containing lithium metal and / or a lithium alloy. In this case, the negative electrode tab may be in contact with the lithium layer rather than directly with the negative electrode current collector. That is, the negative electrode tab may be electrically connected to the negative electrode current collector via the lithium layer. By joining the negative electrode tab to the lithium layer, resistance can be reduced and high cycle characteristics can be maintained. The lithium alloy may include Mg or Al as an element other than lithium.

[0025] In order to effectively prevent the negative electrode tab from breaking due to repeated stress caused by expansion and contraction of the negative electrode with repeated charge-discharge cycles, the breaking strength of the negative electrode tab is preferably 350 MPa or more, and more preferably 450 MPa or more.

[0026] The lithium secondary battery may include an electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and in this case, the positive electrode, the negative electrode, and the separator have a length L1 in a first direction D1 parallel to the winding axis and a length L2 in a second direction D2 perpendicular to the first direction, with the length L1 being shorter than the length L2 (L1<L2).

[0027] The electrode group and a nonaqueous electrolyte may be housed in a cylindrical case to form a lithium secondary battery. In this case, the negative electrode tab is preferably disposed closer to the inner periphery of the electrode group (closer to the central axis of the winding) than to the outer periphery of the winding, since this facilitates suppression of breakage of the negative electrode tab due to expansion and contraction of the negative electrode. Specifically, when the radius of the electrode group is r, the negative electrode tab is preferably disposed in a region that is 0.7r or less away from the center of the electrode group in a plane perpendicular to the winding axis direction of the electrode group. In other words, the negative electrode tab is preferably disposed in a region within a circle with a radius of 0.7r centered on the central axis of the winding in a plane perpendicular to the winding axis direction of the electrode group.

[0028] The lithium secondary battery preferably further includes a spacer layer having a protrusion between at least one of the positive electrode and the negative electrode and the separator. The protrusion provides a space between at least one of the positive electrode and the negative electrode and the separator. The spacer layer may be provided on at least one member selected from the group consisting of the positive electrode, the negative electrode, and the separator. The spacer layer forms a space between the positive electrode and the separator or between the negative electrode and the separator, and suppresses expansion of the negative electrode during charge and discharge.

[0029] The spacer layer ensures a space for lithium metal to deposit on the negative electrode surface, reducing volumetric changes in the negative electrode associated with lithium metal deposition. The spacer layer is provided as a convex portion on at least one of the positive electrode, negative electrode, and separator. The spacer layer or convex portion may be provided on the surface of the positive electrode, the surface of the negative electrode, or the surface of the separator facing the positive electrode or negative electrode. The convex portion provided on the surface of the positive electrode and / or the surface of the separator facing the positive electrode forms a space between the positive electrode and the separator, while the convex portion provided on the surface of the negative electrode and / or the surface of the separator facing the negative electrode forms a space between the negative electrode and the separator. The space suppresses expansion of the negative electrode during charge and discharge, thereby suppressing deterioration of cycle characteristics.

[0030] The spacer layer may have convex portions arranged in a predetermined repeating pattern. The predetermined repeating pattern may be a straight or curved line pattern, a dot pattern, or a mesh pattern. A mesh pattern is obtained by connecting a plurality of straight and / or curved line patterns to form a mesh. A dot pattern corresponds to a case where the extension length (length of the straight or curved lines) of the line convex portions is as short as the line width of the line convex portions.

[0031] The spacer layer may include at least a first linear portion along a first geometric pattern and a second linear portion along a second geometric pattern. In addition to the first and second portions, the spacer layer may include a third linear portion along a third geometric pattern. The first and second portions may be disposed in a first region and a second region, respectively, on the surface of at least one member selected from the group consisting of a positive electrode, a negative electrode, and a separator. The first region is a portion closer to the center in a first direction parallel to the winding axis. The second region is located further outward from the center than the first region in the first direction parallel to the winding axis.

[0032] The first geometric pattern may be, for example, a substantially linear pattern extending along the second direction, or a pattern in which a plurality of linear protrusions are arranged (continuously or intermittently) along a plurality of straight lines substantially parallel to the second direction.

[0033] The second geometric pattern may be, for example, a substantially linear pattern extending along the second direction, or may be a mesh pattern. The second geometric pattern as a linear pattern may be, for example, a pattern in which a plurality of linear protrusions are intermittently arranged along a plurality of straight lines substantially parallel to the second direction. In this case, the plurality of linear protrusions may be arranged in a staggered pattern.

[0034] The shape of the mesh of the mesh pattern is not particularly limited, but may be polygonal, preferably rectangular or hexagonal. From the viewpoint of suppressing unevenness of the space between the electrode and the separator, the interior angle of the polygon may be 120° or less. The quadrangular mesh may be rectangular or square, or may be rhombic.

[0035] From the viewpoint of ensuring the minimum necessary space between the electrode and the separator, the average height h of the convex portions may be 0.02 mm or more and 0.09 mm or less, or 0.015 mm or more and 0.01 mm or less, depending on the battery size. The average height h of the convex portions is determined by averaging the measured values ​​at any 10 points.

[0036] From the viewpoint of improving the liquid circulation of the non-aqueous electrolyte on the negative electrode surface, the height of some of the protrusions may be different from the height of the remaining protrusions, and the heights of adjacent protrusions may be different. The multiple protrusions may include a protrusion with a height h1 and a protrusion with a height h2 smaller than the height h1. In this case, the ratio of the height h2 to the height h1 (h2 / h1) may be, for example, 0.8 or more and less than 1.0, or 0.8 or more and 0.95 or less. The width of the protrusions (the width in the direction perpendicular to the extension direction of the line-shaped protrusions) is, for example, 1 mm or less, and may be 0.1 mm or more and 1 mm or less.

[0037] From the viewpoint of suppressing deposition of lithium metal on the surface of the projections, the projections may be made of a material having lower conductivity than the electrodes, or may be made of a resin material.

[0038] The material constituting the spacer layer is not particularly limited. The spacer layer may be composed of a conductive material and / or an insulating material. Among these, an insulating material is preferable. Since lithium metal is less likely to deposit on the surface of an insulating material, the effect of suppressing expansion of the negative electrode can be enhanced.

[0039] The conductive material can be appropriately selected from the materials for the negative electrode current collector or the positive electrode current collector described below. Such a spacer layer may be provided by forming convex portions on the negative electrode current collector by pressing or the like. Alternatively, a conductive paint may be applied to the surface of the separator or electrode, or a conductive tape may be attached to the surface of the separator or electrode.

[0040] Examples of insulating materials include resin materials. Examples of resin materials include polyolefin resin, acrylic resin, polyamide resin, polyimide resin, silicone resin, fluorine-based resin, urethane resin, melamine resin, and urea resin. As the resin material, a cured product of a curable resin such as an epoxy resin may be used. Furthermore, inorganic fillers may be mixed into these resin materials.

[0041] The material constituting the spacer layer is preferably a material having a Young's modulus of 0.01 GPa or more and 10 GPa or less. This makes it easier to alleviate stress due to expansion and contraction of the negative electrode and to maintain the space for accommodating lithium metal. In addition, damage to the electrode caused by the spacer layer is easily suppressed. Examples of insulating materials having a Young's modulus in the above range include cured products of the above-mentioned curable resins.

[0042] The spacer layer can be formed, for example, by attaching a resin adhesive tape to the surface of the separator or electrode. Alternatively, the spacer layer can be formed by applying a solution or dispersion containing a resin material to the surface of the separator or electrode and drying it. The spacer layer can also be formed by applying a curable resin to the surface of the separator or electrode in a desired shape and curing it. Alternatively, the spacer layer can be formed by scattering particles of a resin material in a desired shape on the surface of the separator or electrode.

[0043] The lithium secondary battery may include a stacked electrode group configured by stacking a positive electrode and a negative electrode with a separator interposed therebetween, or may include a wound electrode group configured by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween.

[0044] 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 current collector upon charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode current collector upon charging to become lithium metal, which is then deposited on the surface of the negative electrode current collector. The lithium metal deposited on the surface of the negative electrode current collector 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.

[0045] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0046] The surface of the conductive sheet may be smooth. This makes it easier for lithium metal from the positive electrode to deposit evenly on the conductive sheet during charging. "Smooth" means that the maximum height roughness Rz of the conductive sheet is 20 μm or less. The maximum height roughness Rz of the conductive sheet may be 10 μm or less. The maximum height roughness Rz is measured in accordance with JIS B 0601:2013.

[0047] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloys. The conductive material may be a metallic material such as a metal or alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form an alloy or an intermetallic compound with lithium is preferred. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, as well as graphite with a preferentially exposed basal plane. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0048] The thickness of the negative electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0049] The surface of the negative electrode current collector may have the aforementioned lithium layer formed thereon, or a negative electrode composite layer (not shown) may be formed thereon. The negative electrode composite layer is formed, for example, by applying a paste containing a negative electrode active material such as graphite to at least a portion of the surface of the negative electrode current collector. However, from the viewpoint of achieving a high-capacity lithium secondary battery exceeding that of a lithium ion battery, the thickness of the negative electrode composite layer is set to be sufficiently thin so that lithium metal can be precipitated at the negative electrode. In this case, the open-circuit potential of the negative electrode at full charge may be 70 mV or less relative to lithium metal (lithium dissolution and deposition potential). When the open-circuit potential of the negative electrode at full charge is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion absorption layer at full charge. In other words, the negative electrode exhibits capacity due to the precipitation and dissolution of lithium metal.

[0050] [Positive Electrode] The positive electrode includes, for example, a positive electrode current collector and a positive electrode composite layer supported on the positive electrode current collector. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode composite layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode composite 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.

[0051] 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.

[0052] Examples of transition metal elements contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Co, Ni, and / or Mn. 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, etc.

[0053] Among lithium-containing transition metal oxides, composite oxides containing Co, Ni, and / or Mn as transition metal elements, and optionally containing Al, and having a layered rock-salt crystal structure are preferred in terms of obtaining high capacity. In this case, in the lithium secondary battery, the molar ratio mLi / mM of the total amount of lithium contained in the positive electrode and negative electrode to the amount mM of metal M other than lithium contained in the positive electrode is set to, for example, 1.1 or less.

[0054] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0055] 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.

[0056] The positive electrode current collector may be a conductive sheet. Examples of the conductive sheet include foil and film. The surface of the positive electrode current collector may be coated with a carbon material.

[0057] Examples of the material of the positive electrode current collector (conductive sheet) include metal materials containing Al, Ti, Fe, etc. The metal material may be Al, an Al alloy, Ti, a Ti alloy, an Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0058] 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.

[0059] [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 spacer layer described above may be formed on the surface of the separator. 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.

[0060] [Non-aqueous electrolyte] The 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 in a liquid state or a gel state.

[0061] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0062] The gel-like non-aqueous electrolyte contains a lithium salt and a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. The matrix polymer is, for example, a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin.

[0063] As the lithium salt or anion, any known material used in non-aqueous electrolytes for 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 SO ２ ) ｙ － (m and n are each independently an integer of 0 or 1 or more, and x and y are each independently 0, 1, or 2, satisfying the relationship x+y=2.) The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion, BF ２ (C ２ O ４ ) － , P.F. ４ (C ２ O ４ ) － , P.F. ２ (C ２ O ４ ) ２ － The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0064] 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. The interaction between the anion of the oxalate complex and lithium facilitates the uniform deposition of lithium metal in the form of fine particles. This facilitates the suppression of localized deposition of lithium metal. The anion of the oxalate complex may be combined with another anion. The other anion may be PF ６ － and / or an anion of an imide.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] The concentration of the lithium salt in the non-aqueous electrolyte is, 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. Furthermore, 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.

[0069] The non-aqueous electrolyte may contain an additive. The additive may form a coating on the negative electrode. The formation of a coating derived from the additive on the negative electrode makes it easier to suppress the formation of dendrites. Examples of such additives include vinylene carbonate, FEC, and vinyl ethyl carbonate (VEC).

[0070] The configuration of a lithium secondary battery according to the present disclosure will be described below with reference to the drawings, taking as an example a cylindrical battery including a wound electrode group, although the present disclosure is not limited to the following configuration.

[0071] FIG. 1 is a longitudinal cross-sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery including a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a nonaqueous electrolyte (not shown). The battery case is composed of a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15. The case body 15 has an annular step 21 formed by partially pressing the side wall near the opening from the outside. The sealing body 16 is supported by the surface of the step 21 facing the opening. A gasket 27 is disposed between the case body 15 and the sealing body 16, thereby ensuring the hermeticity of the battery case. Within the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction.

[0072] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The cap 26 is disposed outside the case body 15, and the filter 22 is disposed inside the case body 15. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with an insulating member 24 interposed between their respective peripheral edges. The filter 22 and the lower valve body 23 are connected to each other at their respective peripheral edges. The upper valve body 25 and the cap 26 are connected to each other at their respective peripheral edges. The lower valve body 23 has an air vent. If the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 bulges toward the cap 26 and separates from the lower valve body 23. This breaks the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure increases further, the upper valve body 25 breaks, and gas is discharged through an opening formed in the cap 26.

[0073] The electrode group 14 is composed of a positive electrode 110, a negative electrode (negative electrode current collector) 120, and a separator 300. The positive electrode 110, the negative electrode 120, and the separator 300 interposed therebetween are all strip-shaped, and are spirally wound so that their width directions are parallel to the winding axis.

[0074] The positive electrode 110 is electrically connected to a cap 26, which also serves as a positive electrode terminal, via a positive electrode lead 19. One end of the positive electrode lead 19 is connected, for example, near the center in the longitudinal direction of the positive electrode 110. The other end of the positive electrode lead 19 extending from the positive electrode 110 is welded to the inner surface of the filter 22 through a through-hole formed in the insulating plate 17.

[0075] The negative electrode 120 is electrically connected to the case body 15, which also serves as a negative electrode terminal, via a negative electrode lead 20, which is a negative electrode tab. One end of the negative electrode lead 20 is connected to an end of the negative electrode 120 in the longitudinal direction, for example, and the other end is welded to the inner bottom surface of the case body 15.

[0076] 2 is an enlarged view schematically illustrating the discharge state of region X surrounded by a dashed line in FIG. 1 . In the illustrated example, the cross-sectional shape of the spacer layer is trapezoidal. However, embodiments of the present disclosure are not limited to this. In the illustrated example, the spacer layer is provided between the positive electrode and the separator. However, embodiments of the present disclosure are not limited to this, and the spacer layer may be provided between the negative electrode and the separator, or between the positive electrode, negative electrode, and the separator.

[0077] The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode composite layer 112. A spacer layer 400 is provided between the positive electrode composite layer 112 and the separator 300. The spacer layer 400 includes linear protrusions 401 arranged along the second direction D2 (longitudinal direction) of the separator 300. In a discharged state, lithium metal is not deposited on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300. On the other hand, in a charged state, lithium metal is deposited on the surface of the negative electrode current collector 121 and is accommodated in the space between the positive electrode 110 and the separator 300 while being subjected to the pressing force of the separator 300. That is, the negative electrode 120 includes the negative electrode current collector 121 in a discharged state, and includes the negative electrode current collector 121 and lithium metal deposited on its surface in a charged state.

[0078] Because the lithium metal is accommodated in the space between the positive electrode 110 and the separator 300, the apparent volume change of the electrode assembly due to the precipitation of the lithium metal during charge / discharge cycles is reduced, thereby suppressing the stress applied to the negative electrode current collector 121. Furthermore, because pressure is applied from the separator 300 to the lithium metal accommodated between the positive electrode 110 and the separator 300, 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.

[0079] In the illustrated example, a cylindrical lithium secondary battery having a wound electrode group has been described, but the shape of the lithium secondary battery is not limited to this and can be appropriately selected from various shapes such as a cylindrical shape, a coin shape, a square shape, a sheet shape, a flat shape, etc., depending on the application, etc. The shape of the electrode group is also not particularly limited and may be a laminated type. In addition, known configurations other than the electrode group and non-aqueous electrolyte of the lithium secondary battery can be used without particular limitation.

[0080] <<Appendix>> The above embodiments disclose the following technologies. (Technology 1) A lithium secondary battery including a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode current collector and a negative electrode tab electrically connected to the negative electrode current collector, wherein lithium metal deposits on the negative electrode current collector during charging and dissolves in the non-aqueous electrolyte during discharging, and wherein the negative electrode tab contains stainless steel at least in a portion connected to the negative electrode current collector. (Technology 2) The lithium secondary battery according to Technology 1, wherein the negative electrode tab has a multilayer structure including, in a thickness direction, a first layer, a second layer located above the first layer, and a third layer located below the first layer, and wherein the first layer contains the stainless steel. (Technology 3) The lithium secondary battery according to Technology 2, wherein the ratio T1 / T0 of the thickness T1 of the first layer to the overall thickness T0 of the negative electrode tab is 25% or more and 50% or less. (Technology 4) The lithium secondary battery according to Technology 2 or 3, wherein at least one of the second layer and the third layer contains copper. (Technology 5) The lithium secondary battery according to any one of Technology 1 to 4, wherein the stainless steel contains austenitic stainless steel. (Technology 6) The lithium secondary battery according to any one of Technology 1 to 5, wherein the negative electrode includes a lithium layer containing lithium metal and / or a lithium alloy, and wherein the negative electrode tab is not in direct contact with the negative electrode current collector and is electrically connected to the negative electrode current collector via the lithium layer. (Technology 7) The lithium secondary battery according to any one of Technology 1 to 6, wherein the breaking strength of the negative electrode tab is 350 MPa or more. (Technology 8) The lithium secondary battery according to any one of Technologies 1 to 7, comprising an electrode group in which the positive electrode and the negative electrode are wound with the separator interposed therebetween, and a cylindrical case that houses the electrode group and the non-aqueous electrolyte, wherein, when the radius of the electrode group is r, the negative electrode tab is disposed in a region that is distanced 0.7r or less from the center of the electrode group on a plane perpendicular to the direction of the winding axis of the electrode group.(Technology 9) The lithium secondary battery according to any one of Techniques 1 to 8, further comprising a spacer layer having convex portions between the separator and at least one of the positive electrode and the negative electrode, and a space is provided between the separator and at least one of the positive electrode and the negative electrode. (Technology 10) The lithium secondary battery according to Technique 9, wherein the spacer layer has the convex portions arranged in a predetermined repeating pattern.

[0081] [Examples] The lithium secondary battery according to the present disclosure will be specifically described below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0082] Example 1 (1) Preparation of Positive Electrode A rock salt type lithium-containing transition metal oxide (NCA; positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0) and having a layered structure, acetylene black (AB; conductive material), and polyvinylidene fluoride (PVdF; binder) were mixed in a mass ratio of NCA:AB:PVdF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a positive electrode mixture slurry. Next, the obtained positive electrode mixture slurry was applied to both sides of an Al foil (positive electrode current collector), dried, and the coating of the positive electrode mixture was rolled using a roller. Finally, the resulting laminate of the positive electrode current collector and the positive electrode mixture was cut to a predetermined electrode size to prepare a positive electrode having a positive electrode mixture layer on both sides of the positive electrode current collector.

[0083] (2) Preparation of Separator (Preparation of Substrate) A strip-shaped porous film made of polyethylene (average thickness 10 μm) was prepared as a separator substrate.

[0084] (Formation of First Spacer Layer) A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) was dispensed onto one surface (negative electrode side surface) of the separator using a dispenser. The coating liquid was then vacuum dried. In this manner, a spacer layer (first spacer layer) having a honeycomb-shaped mesh pattern was formed on one surface of the separator.

[0085] The mesh shape of the first spacer layer was a regular hexagon. The height of the linear convex portions constituting the first spacer layer was set to 30 μm (thickness of the first spacer layer: 30 μm). The spacing between two opposing sides of the regular hexagonal mesh was approximately 4.5 mm. The width of the linear convex portions was 0.25 mm. In the opposing region of the separator between the positive electrode and the negative electrode, the area S1 of the first spacer layer was 10% of the area S0 of the opposing region.

[0086] (Formation of second spacer layer) A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) was dispensed onto both sides of the positive electrode using a dispenser. The coating liquid was then vacuum dried. In this way, spacer layers (second spacer layers) having a honeycomb mesh pattern were formed on both sides of the positive electrode.

[0087] The mesh shape of the second spacer layer was a regular hexagon. The height of the linear convex portions constituting the second spacer layer was set to 10 μm (thickness of the second spacer layer: 10 μm). The spacing between two opposing sides of the regular hexagonal mesh was approximately 4.5 mm. The width of the linear convex portions was 0.25 mm. The area S2 of the second spacer layer was 10% of the area S0 of the region of the positive electrode facing the negative electrode.

[0088] (3) Fabrication of Negative Electrode (Preparation of Negative Electrode Current Collector) A strip of SUS foil (thickness 10 μm) with rolled lithium metal layers (thickness 20 μm) on both sides was used as the negative electrode current collector. (Welding of Negative Electrode Tab) A negative electrode tab (Ni / SUS304 / Ni, width 3 mm, thickness 100 μm) was welded to the negative electrode current collector from above the rolled lithium metal using an ultrasonic welding machine.

[0089] When the electrode group described below was formed, the negative electrode tab was positioned at a distance of 0.56r from the center of the electrode group in a plane perpendicular to the winding axis direction of the electrode group, where r is the radius of the electrode group.

[0090] (4) Preparation of non-aqueous electrolyte: Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC=30:70, and LiPF was added to the resulting mixed solvent. ６ 1 mol / L, LiBF ２ (C ２ O４ ) were dissolved in a concentration of 0.1 mol / L to prepare liquid non-aqueous electrolytes.

[0091] (5) Assembling the Battery In a dry atmosphere with a dew point of -30°C or less, the positive electrode and negative electrode current collectors were spirally wound with the separator interposed therebetween to prepare an electrode group.

[0092] The electrode group was inserted into a cylindrical battery can (case body) with a bottom, a nonaqueous electrolyte was poured into it, and the opening of the battery can was sealed with a sealing member. At this time, the positive electrode lead was connected to the sealing member, and the negative electrode lead was connected to the battery can. A gasket was placed between the sealing member and the battery can. In this way, a cylindrical lithium secondary battery was completed, and lithium secondary battery A1 according to Example 1 was obtained.

[0093] Examples 2 to 6, Comparative Example 1 Lithium secondary batteries A2 to A5 according to Examples 2 to 5 and lithium secondary battery B1 according to Comparative Example 1 were obtained in the same manner as battery A1 according to Example 1, except that the material of the negative electrode tab was changed to the material shown in Table 1.

[0094] In Example 1, a clad material in which Ni layers were pressure-bonded to both sides of an austenitic stainless steel SUS304 foil was used as the negative electrode tab. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:SUS304:Ni layer was 1:2:1. The ratio T1 / T0 of the thickness T1 of the stainless steel layer to the total thickness T0 of the negative electrode tab was 50%.

[0095] In Example 2, a clad material was used as the negative electrode tab, in which both sides of a ferritic stainless steel SUS430 foil were crimped with Ni layers. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:SUS430:Ni layer was 1:2:1. The ratio T1 / T0 of the thickness T1 of the stainless steel layer to the total thickness T0 of the negative electrode tab was 50%.

[0096] In Example 3, a clad material was used as the negative electrode tab, in which Cu layers were pressure-bonded to both sides of a SUS304 foil and Ni layers were pressure-bonded to both sides of the Cu layers. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:Cu layer:SUS304:Cu layer:Ni layer was 2:2:3:2:2. The ratio T1 / T0 of the thickness T1 of the stainless steel layer to the total thickness T0 of the negative electrode tab was 27%.

[0097] In Example 4, a clad material was used as the negative electrode tab, in which a Cu layer was pressure-bonded to one side of a SUS304 foil and a Ni layer was pressure-bonded to the other side. The surface of the negative electrode tab with the Ni layer was welded to the negative electrode current collector. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:SUS304:Cu layer was 2:3:5. The ratio T1 / T0 of the thickness T1 of the stainless steel layer to the total thickness T0 of the negative electrode tab was 30%.

[0098] In Example 5, a clad material in which Ni layers were pressure-bonded to both sides of a SUS304 foil was used as the negative electrode tab. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:SUS304:Ni layer was 1:3:1, which was different from Example 1. The ratio T1 / T0 of the thickness T1 of the stainless steel-containing layer to the total thickness T0 of the negative electrode tab was 60%.

[0099] In Example 6, a clad material in which Ni layers were pressure-bonded to both sides of a SUS304 foil was used as the negative electrode tab. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:SUS304:Ni layer was 1:2:1, as in Example 1. The ratio T1 / T0 of the thickness T1 of the layer containing stainless steel to the total thickness T0 of the negative electrode tab was 50%. When the electrode group was formed, the negative electrode tab was positioned at a distance of 0.25r from the center of the electrode group on a plane perpendicular to the winding axis direction of the electrode group, where r is the radius of the electrode group.

[0100] In Comparative Example 1, a clad material in which Ni layers were pressure-bonded to both sides of copper foil was used as the negative electrode tab. The total thickness of the negative electrode tab was 100 μm, and the thickness ratio of the Ni layer:Cu layer:Ni layer was 1:2:1. The ratio T1 / T0 of the thickness T1 of the stainless steel-containing layer to the total thickness T0 of the negative electrode tab was 50%.

[0101] Reference Example 1 In the preparation of a negative electrode, graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and lithium polyacrylate were mixed in a mass ratio of 96.5:1:1.5:1 as the negative electrode active material, and the mixture was stirred after adding water to prepare a negative electrode composite slurry. Next, the obtained negative electrode composite slurry was applied to both sides of copper foil, dried, and the coating film of the negative electrode composite was rolled using a roller. Finally, the obtained laminate of the negative electrode current collector and the negative electrode composite was cut to a predetermined electrode size, and a negative electrode having a negative electrode composite layer on both sides of the negative electrode current collector was prepared.

[0102] The positive electrode and the negative electrode were spirally wound with a separator interposed therebetween to prepare an electrode group, without forming a first spacer layer and a second spacer layer. A lithium ion secondary battery was completed in the same manner as in Example 1, and a secondary battery C1 according to Reference Example 1 was obtained.

[0103] [Evaluation 1] (Charge-discharge cycle test) Each battery was subjected to a charge-discharge cycle test at 25° C. Charging and discharging were performed under the following conditions, with a 20-minute break between charging and discharging. The ratio of the discharge capacity at the 40th cycle to the discharge capacity at the 1st cycle (MR40) was calculated as the capacity retention rate (%).

[0104] (Charging) 10mA / cm until the voltage reaches 4.1V ２ After that, the current value was increased to 4 mA / cm ２ The battery was charged at a constant voltage of 4.1 V until the battery reached a voltage of 0.1 V.

[0105] (Discharge) 10 mA / cm until the voltage reaches 3.0 V ２ A constant current discharge was carried out at a current of .

[0106] The ratio of the discharge capacity at the 40th cycle to the discharge capacity at the 1st cycle (MR40) was determined for the two batteries, and the average value of the MR40 values ​​for the two batteries was calculated as the capacity retention rate (%).

[0107] After the charge-discharge cycle test, the battery was subjected to X-ray CT photography, and the presence or absence of fracture of the negative electrode tab was examined from a three-dimensional constructed image.

[0108] The evaluation results are shown in Table 1. Table 1 also shows the material of the negative electrode tab used in each battery and its breaking strength.

[0109]

[0110] Batteries B1 and C1 were compared. Batteries B1 and C1 used copper foil as the negative electrode tab. Battery C1 is a lithium-ion battery that does not rely on lithium deposition on the negative electrode, and the negative electrode tab did not break as the number of charge-discharge cycles increased. In contrast, with the number of charge-discharge cycles increased, Battery B1 experienced a rapid drop in capacity retention at the 35th cycle, making subsequent charge-discharge cycles difficult. When the battery was examined after the charge-discharge cycle test, the negative electrode tab was found to have broken. This is thought to be because Battery B1 is a lithium secondary battery in which metallic lithium is deposited on the negative electrode during charging and the deposited metallic lithium dissolves in the electrolyte during discharging. Therefore, the negative electrode (and electrode group) repeatedly expands and contracts during charging and discharging. The repeated stress associated with the expansion and contraction of the negative electrode was applied to the negative electrode tab, leading to its breakage.

[0111] However, in batteries A1 to A5, which used a material containing stainless steel (SUS) for the negative electrode tab, even in lithium secondary batteries in which metallic lithium precipitates in the negative electrode during charging and the precipitated metallic lithium dissolves in the electrolyte during discharge, breakage of the negative electrode tab was suppressed and a high capacity retention rate was achieved.

[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 including hybrids and plug-in hybrids, and home storage batteries combined with solar cells.

[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] REFERENCE SIGNS LIST 10 Lithium secondary battery 14 Electrode group 15 Case body 16 Sealing body 17, 18 Insulating plate 19 Positive electrode lead 20 Negative electrode lead 21 Step portion 22 Filter 23 Lower valve body 24 Insulating member 25 Upper valve body 26 Cap 27 Gasket 100 Electrode 110 Positive electrode 111 Positive electrode current collector 112 Positive electrode composite layer 120 Negative electrode 121 Negative electrode current collector 300 Separator 400 Spacer layer 401 Convex portion

Claims

1. A lithium secondary battery comprising: a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte; wherein the negative electrode has a negative electrode current collector and a negative electrode tab electrically connected to the negative electrode current collector; wherein, in the negative electrode, lithium metal is deposited on the negative electrode current collector during charging and the lithium metal dissolves in the non-aqueous electrolyte during discharging; and the negative electrode tab contains stainless steel at least at a portion connected to the negative electrode current collector.

2. The lithium secondary battery according to claim 1, wherein the negative electrode tab has a multilayer structure including, in the thickness direction, a first layer, a second layer located above the first layer, and a third layer located below the first layer, and the first layer includes the stainless steel.

3. The lithium secondary battery according to claim 2, wherein the ratio T1 / T0 of the thickness T1 of the first layer to the total thickness T0 of the negative electrode tab is 25% or more and 50% or less.

4. The lithium secondary battery according to claim 2, wherein at least one of the second layer and the third layer contains copper.

5. The lithium secondary battery according to any one of claims 1 to 4, wherein the stainless steel includes an austenitic stainless steel.

6. The lithium secondary battery according to any one of claims 1 to 4, wherein the negative electrode includes a lithium layer containing lithium metal and / or a lithium alloy, and the negative electrode tab is not in direct contact with the negative electrode current collector, but is electrically connected to the negative electrode current collector via the lithium layer.

7. The lithium secondary battery according to any one of claims 1 to 4, wherein the breaking strength of the negative electrode tab is 350 MPa or more.

8. The lithium secondary battery according to any one of claims 1 to 4, comprising an electrode group in which the positive electrode and the negative electrode are wound with the separator interposed therebetween, and a cylindrical case that houses the electrode group and the non-aqueous electrolyte, wherein, when the radius of the electrode group is r, the negative electrode tab is disposed in a region that is 0.7r or less away from the center of the electrode group on a plane perpendicular to the direction of the winding axis of the electrode group.

9. The lithium secondary battery according to any one of claims 1 to 4, further comprising a spacer layer having a convex portion between the separator and at least one of the positive electrode and the negative electrode, and a space is provided between the separator and at least one of the positive electrode and the negative electrode.

10. The lithium secondary battery according to claim 9, wherein the spacer layer has the protrusions arranged in a predetermined repeating pattern.

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