Secondary battery

Abstract

This secondary battery is provided with: an electrode group in which a positive electrode, a negative electrode provided with a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode are wound; a tape for fixing the winding end of the electrode group; an electrolyte; and a bottomed cylindrical outer casing that accommodates the electrode group, the tape, and the electrolyte. The negative electrode has an outermost peripheral part disposed on the outermost periphery of the electrode group. The tape is provided with a metal base material layer, and is attached to the negative electrode current collector at the outermost peripheral part. The negative electrode current collector at the outermost peripheral part to which the tape is attached and the outer casing are in contact with each other. The static friction coefficient of the metal base material layer with respect to the material of the outer casing is 0.8 or less.

Description

secondary battery

[0001] The present disclosure relates to a secondary battery including a wound electrode group.

[0002] The secondary battery includes an electrode group formed by winding a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, an electrolyte, and an outer can that contains the electrode group and the electrolyte. Tape (winding stop tape) is affixed to the periphery of the wound electrode group, and the winding end is fixed by the tape.

[0003] Patent Document 1 proposes a "non-aqueous electrolyte secondary battery comprising: an electrode group in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound; a tape for fixing at least the winding end of the electrode group; and a non-aqueous electrolyte, wherein, at least in a charged state, the negative electrode contains lithium metal and / or a lithium alloy, and the tape has a tensile strength of 20 N / 10 mm or less when the elongation rate is 200% or more." Patent Document 1 also describes that the base sheet of the tape is formed from a polymer such as a resin.

[0004] International Publication No. 2019 / 003641

[0005] In order to reduce the internal resistance, it is conceivable to configure the electrode assembly so that the negative electrode current collector is exposed on the outer peripheral surface of the electrode assembly that contacts the inner surface of the outer can. However, when a resin tape is used as the winding stop tape, the resin tape, which has high resistance, is interposed between the electrode assembly and the outer can, and this may prevent the internal resistance from being sufficiently reduced.

[0006] The secondary battery also includes a mechanism that, in the event of an internal short circuit, causes an increase in battery internal pressure to cause a sealing member attached to the opening of the outer can to come off, thereby ejecting the electrode group from the opening of the outer can. Operation of this mechanism suppresses an increase in battery temperature in the event of an internal short circuit. If a resin tape is attached to the outer periphery of the electrode group, the resin tape may melt in the event of an internal short circuit, delaying the ejection of the electrode group and causing an increase in battery temperature.

[0007] One aspect of the present disclosure relates to a secondary battery including: an electrode group formed by winding a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode; a tape that fixes a winding end of the electrode group; an electrolyte; and a bottomed, cylindrical outer can that accommodates the electrode group, the tape, and the electrolyte; the negative electrode has an outermost peripheral portion that is arranged at the outermost periphery of the electrode group; the tape includes a metal substrate layer and is attached to the negative electrode current collector at the outermost peripheral portion; the negative electrode current collector at the outermost peripheral portion to which the tape is attached is in contact with the outer can; and the static friction coefficient of the metal substrate layer with respect to the material of the outer can is 0.8 or less.

[0008] According to the present disclosure, in a secondary battery, it is possible to reduce the internal resistance and suppress a temperature rise during an internal short circuit.

[0009] 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] Fig. 1 is a diagram schematically showing a configuration for a friction coefficient test; Fig. 2 is a cross-sectional view schematically showing an example of a secondary battery according to an embodiment of the present disclosure; Fig. 3 is a schematic front view of a side surface of an example of a wound electrode group when viewed from the winding end side; Fig. 4 is a schematic front view of a side surface of an example of a wound electrode group when viewed from the opposite side to the winding end; Fig. 5 is a schematic top view of one end surface of an example of a wound electrode group when viewed from the winding axis direction.

[0011] Below, embodiments according to the present disclosure will be described 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 materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when numerical values ​​for specific physical properties or conditions are exemplified as lower and upper limits, 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 equal to or greater than the upper limit.

[0012] A secondary battery according to an embodiment of the present disclosure includes an electrode assembly formed by winding a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode, a tape for fixing the winding end of the electrode assembly, an electrolyte, and a cylindrical outer can with a bottom. The outer can houses the electrode assembly, the tape, and the electrolyte. The negative electrode has an outermost periphery disposed at the outermost periphery of the electrode assembly. The tape includes a metal substrate layer and is attached to the negative electrode current collector at the outermost periphery. Hereinafter, the tape including the metal substrate layer will also be referred to as "metal tape." The outermost periphery of the negative electrode current collector to which the tape is attached is in contact with the outer can. The static friction coefficient of the metal substrate layer with respect to the material of the outer can is 0.8 or less.

[0013] The outer can is in contact with the negative electrode current collector at the outermost periphery to which the tape is attached. That is, the inner surface of the outer can has a first region in contact with the negative electrode current collector and a second region in contact with the metal tape (metal substrate layer). In the second region, a low-resistance metal tape (metal substrate layer) is interposed between the electrode group (negative electrode current collector at the outermost periphery) and the outer can. The formation of the first region and the second region significantly reduces the internal resistance of the secondary battery and suppresses an increase in internal resistance that would occur if a resin tape were interposed between the electrode group and the outer can.

[0014] The secondary battery has a mechanism in which, in the event of an internal short circuit, an increase in the battery's internal pressure causes a sealing member attached to the opening of the outer can to come off, thereby ejecting the electrode group from the opening of the outer can. The metal tape has superior heat resistance compared to a resin tape having a resin substrate layer. Therefore, delays in ejection of the electrode group due to melting of the resin tape in the event of an internal short circuit and the resulting increase in battery temperature are suppressed.

[0015] The static friction coefficient of the metal substrate layer with respect to the material of the outer can is 0.8 or less. In this case, the frictional force generated between the metal substrate layer and the outer can when the electrode group ejection mechanism is activated is reduced, the electrode group is ejected smoothly, and an increase in battery temperature due to a delay in ejection of the electrode group is suppressed.

[0016] From the viewpoint of suppressing delay in discharging the electrode group, the static friction coefficient of the metal substrate layer with respect to the material of the outer can is preferably 0.6 or less.

[0017] From the viewpoint of ejection of the electrode group, the static friction coefficient of the outermost negative electrode current collector with respect to the material of the outer can is preferably 0.8 or less, and more preferably 0.6 or less.

[0018] The number of metal tapes may be one or more (for example, two). When multiple metal tapes are used, the multiple metal tapes do not include a metal tape in which the static friction coefficient of the metal substrate layer against the material of the outer can exceeds 0.8. That is, the static friction coefficient of the metal substrate layer against the material of the outer can must be 0.8 or less for all of the multiple metal tapes. If at least one of the multiple metal tapes has a metal substrate layer with a static friction coefficient of more than 0.8, the friction force between the metal substrate layer and the outer can increases, causing a delay in discharging the electrode group.

[0019] Examples of materials for the outer can include iron (Fe), aluminum (Al), copper (Cu), nickel (Ni), and alloys containing these metals. Examples of alloys containing iron include stainless steel (SUS). Among these, SUS is preferred as the material for the outer can. The outer can may have a plating layer (e.g., a Ni plating layer) on its surface. When the outer can has a plating layer on its surface, the material of the outer can in terms of the static friction coefficient refers to the material of the plating layer.

[0020] The static friction coefficient of the metal substrate layer against the material of the outer can can be determined as follows.

[0021] A friction coefficient test is performed in accordance with JIS K 7125. Specifically, as shown in FIG. 1 , a first sample 51 is fixed on a horizontal sample stage 50, a second sample 52 is placed on the first sample 51, and a weight 53 is placed on the second sample 52 as needed. In this manner, the first sample 51 and the second sample 52 are placed horizontally and in contact with each other. The total mass of the second sample 52 and the weight 53 is 500 g. If the mass of the second sample 52 is 500 g, the test is performed without using the weight 53.

[0022] One of the first sample 51 and the second sample 52 is a sample made of the same material as the metal substrate layer of the stop tape. The other of the first sample 51 and the second sample 52 is a sample made of the same material as the outer can (or the plated layer if the surface has a plated layer). Each sample may be prepared by sampling a portion of the substrate used for the metal substrate layer and the plate-shaped material used in the can manufacturing process for the outer can. The contact area between the first sample 51 and the second sample 52 is 1200 mm ２ The first sample 51 is plate-shaped. The second sample 52 is, for example, plate-shaped, and may be rectangular. The thicknesses of the first sample 51 and the second sample 52 are, for example, 0.05 to 0.5 mm. The size of the plate-shaped second sample 52 is, for example, 30 mm × 40 mm. When the second sample 52 is viewed from the normal direction of the main surface of the first sample 51, the area of ​​the second sample 52 is smaller than that of the first sample 51. The surface roughness (e.g., arithmetic mean roughness Ra) of each sample is within the range of the surface roughness of each member of the outer can or metal substrate layer used in a battery. The arithmetic mean roughness Ra of the contact surfaces of the first sample 51 and the second sample 52 is, for example, 10 μm or less (or 5 μm or less). The arithmetic mean roughness Ra is an index representing surface roughness in accordance with JIS B 0601.

[0023] A pull string 54 is attached to the second sample 52 and slid, and the load F (maximum static friction force) generated at this time is measured with a load cell. The test speed (the speed at which the second sample 52 is pulled in the direction of the arrow shown in Figure 1) is 1 mm / min. The coefficient of static friction is found by calculating (load F / normal force) based on the measured load F. The normal force is 4.9 N. The normal force is 9.8 (m / s) for the total mass (0.5 kg) of the second sample 52 and the weight 53. ２ This test is repeated five times to determine the average value of the static friction coefficient. In this way, the static friction coefficients of the first sample 51 and the second sample 52 are determined.

[0024] The static friction coefficient of the outermost negative electrode current collector against the material of the outer can can be determined by using a sample made of the same material as the negative electrode current collector for either the first sample or the second sample in the above-mentioned friction coefficient test.

[0025] The outer can may be cylindrical with a bottom or rectangular with a bottom. The wound electrode group may be columnar with a bottom or flat. A columnar electrode group may be housed in a cylindrical outer can with a bottom, and a flat electrode group may be housed in a rectangular outer can with a bottom.

[0026] The negative electrode may include a negative electrode composite layer supported on a negative electrode current collector. In this case, the negative electrode does not have the negative electrode composite layer supported on at least a portion of the region facing the outer can at the outermost periphery (the negative electrode current collector is exposed). The negative electrode composite layer may be formed on the surface of the negative electrode current collector facing the positive electrode (positive electrode composite layer). It is preferable that the negative electrode composite layer is not supported on 70% or more or 80% or more of the area of ​​the region facing the outer can at the outermost periphery. It is more preferable that the negative electrode composite layer is not supported on the entire region facing the outer can at the outermost periphery. It is preferable that the negative electrode composite layer is not supported on 70% or more or 80% or more of the area of ​​the region where the tape is attached at the outermost periphery. It is more preferable that the negative electrode composite layer is not supported on the entire region where the tape is attached at the outermost periphery.

[0027] Examples of secondary batteries include nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries and lithium metal secondary batteries. The negative electrode of a lithium ion secondary battery includes a negative electrode composite layer supported on a negative electrode current collector. The negative electrode composite layer includes a negative electrode active material that occludes lithium ions during charging and releases lithium ions during discharging. The negative electrode of a lithium metal secondary battery is a negative electrode in which lithium metal precipitates during charging and dissolves in an electrolyte during discharging. The negative electrode may be composed of only a negative electrode current collector, or lithium metal may precipitate on the surface of the negative electrode current collector during charging. The negative electrode of a lithium metal secondary battery may have a thin negative electrode composite layer supported on the surface of the negative electrode current collector.

[0028] (Winding Stop Tape) The metal substrate layer is composed of, for example, a foil- or sheet-shaped substrate. The metal substrate layer may contain one or more metals. The metal substrate layer may be an alloy layer containing two or more metals. The metal substrate layer preferably contains at least one metal selected from the group consisting of nickel (Ni), iron (Fe), copper (Cu), titanium (Ti), zinc (Zn), silver (Ag), gold (Au), and stainless steel (SUS). In this case, the electrical conductivity and heat resistance of the metal tape are likely to be improved, and the static friction coefficient against the outer can material can be easily controlled to 0.8 or less.

[0029] From the viewpoint of fixing the electrode group, the tape preferably includes an adhesive layer. The adhesive layer is preferably disposed on one surface (the surface on the outermost periphery side) of the metal substrate layer. In this case, the outermost negative electrode current collector and the metal substrate layer are in close contact with each other via the adhesive layer. The adhesive layer is formed of an adhesive. Examples of adhesives include acrylic adhesives, silicone adhesives, rubber adhesives, etc. Among them, acrylic adhesives are preferred from the viewpoint of heat resistance, etc. The ratio of the thickness of the adhesive layer to the thickness of the metal substrate layer is, for example, 5 to 25%. From the viewpoint of reducing internal resistance, the thickness of the adhesive layer is, for example, 75 μm or less. Even if the adhesive layer included in the tape has low conductivity, it can be thinned to a level where the influence of the adhesive layer on the conductivity of the tape is almost negligible by being compressed between the inner surface of the outer can and the electrode group inside the battery.

[0030] The adhesive layer may be conductive and may be formed from a conductive adhesive (e.g., an adhesive containing conductive particles). Examples of conductive particles include metal particles, composite particles containing resin particles and a metal coating layer covering the surfaces of the resin particles, etc. Examples of metals contained in the metal particles and the metal coating layer include Ni, Cu, Ag, Fe, etc. The metal particles and the metal coating layer may contain one type of metal, or two or more types of metals. Examples of resins contained in the resin particles include acrylic resin, polystyrene, etc.

[0031] From the viewpoint of easily reducing internal resistance and easily ensuring energy density (battery capacity), the thickness of the tape is preferably 250 μm or less, more preferably 200 μm or less. From the viewpoint of suppressing breakage of the tape, the thickness of the tape is, for example, 50 μm or more. The thickness of the tape is the total thickness of the metal substrate layer and the adhesive layer.

[0032] When the winding end is fixed with multiple tapes, it is preferable that each of the multiple tapes (e.g., tapes 41 and 42 in Fig. 3) has a thickness within the above-mentioned preferred range. Furthermore, the thicknesses of the multiple tapes may be different from each other as long as the effect of the tapes in reducing internal resistance is not impaired, but from the viewpoints of reducing internal resistance and ensuring uniformity of the surface pressure of the electrode group, it is preferable that the thicknesses of the multiple tapes are approximately the same.

[0033] The width of the tape is preferably 4 mm or more and 12 mm or less, in which case the winding end can be stably fixed with the tape and a sufficient contact area between the outer can and the outermost periphery can be easily ensured.

[0034] When the winding end is fixed with multiple tapes, it is preferable that each of the multiple tapes (e.g., tapes 41 and 42 in Fig. 3) has a width within the above-mentioned preferred range. Furthermore, the widths of the multiple tapes may be different from each other as long as the effect of the tapes in reducing internal resistance is not impaired, but from the viewpoints of reducing internal resistance and ensuring uniformity of the surface pressure of the electrode group, it is preferable that the widths of the multiple tapes are approximately the same.

[0035] The tape is preferably wound around the electrode assembly so that both ends do not overlap. When the winding end is fixed with multiple tapes, it is preferable that each of the multiple tapes is wound around the electrode assembly so that both ends do not overlap. The length of the tape (the dimension in the longitudinal direction of the strip-shaped tape) is preferably shorter than the outer periphery of the electrode assembly by 1 mm or more and 7 mm or less. The tape is preferably wound, for example, 0.8 to 0.99 times around the outer periphery of the electrode assembly. In this case, the effect of fixing the electrode assembly is enhanced, stress associated with expansion and contraction of the electrode assembly is easily alleviated, and damage to the positive and negative electrodes (particularly breakage of the negative electrode current collector) associated with expansion and contraction of the electrode assembly is easily suppressed.

[0036] The tape includes a first tape and a second tape attached to the outermost negative electrode current collector at one end side and the other end side in the winding axis direction of the electrode group, respectively, and the first tape and the second tape each preferably have a metal substrate layer having a static friction coefficient of 0.8 or less with respect to the material of the outer can. This allows the outermost negative electrode current collector to be in contact with the outer can at the center in the winding axis direction of the electrode group. The first tape and the second tape described above make it easy to reduce internal resistance and more stably fix the winding end of the electrode group.

[0037] Examples of components of a nonaqueous electrolyte secondary battery are described below, although the secondary battery is not limited to the examples described below.

[0038] (Negative Electrode) The negative electrode includes, for example, a negative electrode current collector and a negative electrode composite layer supported on the surface of the negative electrode current collector. The negative electrode composite layer includes, for example, a negative electrode active material, a binder, and a thickener. The negative electrode is obtained, for example, by applying a negative electrode slurry to both sides of the negative electrode current collector, drying the coating, and then rolling to form a negative electrode composite layer. The negative electrode slurry includes a negative electrode composite and a dispersion medium (e.g., water). The negative electrode composite layer may be formed on only one side of the negative electrode current collector or on both sides. In this case, the negative electrode current collector may be exposed in a predetermined region on the surface (the surface region facing the outer can) without being coated with the negative electrode slurry. Alternatively, the negative electrode current collector may be exposed in the predetermined region by, for example, scraping off the negative electrode composite layer. In the case of a lithium metal secondary battery, the negative electrode may be formed only with the negative electrode current collector, or lithium foil may be pressure-bonded to the negative electrode current collector.

[0039] The negative electrode mixture contains at least a negative electrode active material and may contain other components as needed, such as a binder, a thickener, and a conductive material.

[0040] The negative electrode active material may be a material that reversibly absorbs and releases lithium ions. Examples of the negative electrode active material 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 the carbonaceous material include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon).

[0041] Examples of the negative electrode active material include a carbonaceous material, a Si-containing material, and a Sn-containing material. The negative electrode may contain one or more negative electrode active materials. Examples of the carbonaceous material include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon).

[0042] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0043] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber polymers, etc. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride, etc. Examples of thickeners include carboxymethyl cellulose (CMC), sodium salt of CMC, etc.

[0044] The negative electrode current collector may be a conductive sheet, such as a foil or film.

[0045] Examples of materials for the negative electrode current collector (conductive sheet) include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys, which have high electrical conductivity, are preferred.

[0046] 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.

[0047] (Positive Electrode) The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode is obtained, for example, by applying a positive electrode 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 the coating to form a positive electrode mixture layer. The positive electrode slurry includes a positive electrode mixture and a dispersion medium (for example, N-methyl-2-pyrrolidone). The positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides.

[0048] The positive electrode mixture contains at least a positive electrode active material and may contain other components as needed, such as a binder and a conductive material.

[0049] 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.

[0050] 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 Ni, Co, 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.

[0051] Among the lithium-containing transition metal oxides, composite oxides containing Ni, Co and / or Mn as transition metal elements, which may contain Al as an optional component, and which have a layered rock-salt type crystal structure are preferred in terms of obtaining high capacity.

[0052] As the binder, conductive material, etc., for example, those exemplified for the negative electrode can be used. The shape and thickness of the positive electrode current collector can be selected from the shape and range of the positive electrode current collector.

[0053] Examples of materials for the positive electrode current collector (conductive sheet) include aluminum (Al), titanium (Ti), iron (Fe), and alloys containing these metal elements. The alloy may be an Al alloy, a Ti alloy, an Fe alloy, or the like. The Fe alloy may be stainless steel (SUS).

[0054] 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.

[0055] (Separator) A porous sheet having ion permeability and insulating properties is used for the separator. Examples of porous sheets include thin films, woven fabrics, nonwoven fabrics, etc. having micropores. The material of the separator is not particularly limited, and a polymeric material may be used. Examples of polymeric materials include olefin resins, polyamide resins, cellulose, etc. Examples of olefin resins include polyethylene, polypropylene, and ethylene-propylene copolymers, etc. The separator may contain additives (such as inorganic fillers) as necessary. The thickness of the separator is not particularly limited, and is, for example, 5 μm or more and 100 μm or less.

[0056] (Electrolyte) A non-aqueous electrolyte having lithium ion conductivity can be used as the electrolyte. The non-aqueous electrolyte is not particularly limited, and a non-aqueous electrolyte used in a known non-aqueous electrolyte secondary battery can be used. The non-aqueous electrolyte 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.

[0057] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

[0058] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof. The non-aqueous electrolyte may contain only one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted derivatives include fluorides. Examples of lithium salts include LiPF ６ The concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less.

[0059] (Exterior Body) The exterior body (battery case) houses the electrode group and the nonaqueous electrolyte. The exterior body is not particularly limited, and a known exterior body may be used. The exterior body usually includes an exterior can and a sealing body that seals the opening of the exterior can. The exterior can is formed, for example, by performing a predetermined can-making process using a plate-shaped material such as a stainless steel plate. The surface of the stainless steel plate may be nickel-plated. The exterior can functions as a negative electrode terminal. The sealing body (sealing plate) functions as a positive electrode terminal. The sealing body may include a sealing plate and a gasket. The gasket is interposed between the sealing plate and the open end of the exterior can to electrically insulate them.

[0060] (Positive electrode lead, negative electrode lead) The positive electrode and the sealing body are electrically connected via a positive electrode lead. Examples of the material for the positive electrode lead include aluminum and aluminum alloys. The negative electrode and the outer can are electrically connected by the contact between the outermost negative electrode current collector to which the tape is attached and the outer can. The negative electrode and the outer can may also be electrically connected via a negative electrode lead. Examples of the material for the negative electrode lead include nickel and nickel alloys.

[0061] FIG. 2 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment of the present disclosure. Although a stop tape 40 is wound around the peripheral surface of the electrode group 14, the stop tape 40 is omitted from FIG. 2. FIGS. 3 to 5 are front views illustrating an example of a wound electrode group in which the winding end is secured with tape. FIGS. 3 and 4 are side views of the electrode group, with FIG. 3 being a view from the X1 direction in FIG. 5 and FIG. 4 being a view from the X2 direction in FIG. 5. FIG. 5 is a view of the electrode group from the winding axis direction, and a view from the Y direction in FIGS. 3 and 4. The secondary battery according to the present disclosure is not limited to this.

[0062] The cylindrical secondary battery 10 includes a cylindrical exterior body (battery case) 30 with a bottom, and a wound electrode group 14 and an electrolyte (not shown) housed within the exterior body 30. The exterior body 30 includes an exterior can 38 and a sealing body (sealing plate 31 and gasket 37) that seals the opening of the exterior can 38. The exterior can 38 is a cylindrical case with a bottom made of metal (e.g., SUS). A gasket 37 is disposed between the exterior can 38 and the sealing plate 31. Within the exterior can 38, insulating plates 17 and 18 are disposed at both ends of the electrode group 14.

[0063] The sealing plate 31 includes a filter 32, a lower valve body 33, an insulating member 34, an upper valve body 35, and a cap 36. All of the members except for the insulating member 34 are electrically connected to one another.

[0064] The cylindrical electrode group 14 is formed by winding the positive electrode 11, the negative electrode 12, and the separator 13 so that the separator 13 is disposed between the positive electrode 11 and the negative electrode 12. The positive electrode 11, the negative electrode 12, and the separator 13 are each strip-shaped. The positive electrode 11 includes a positive electrode current collector and a positive electrode composite layer formed on both sides of the positive electrode current collector. The negative electrode 12 includes a negative electrode current collector and a negative electrode composite layer formed on both sides of the negative electrode current collector. However, the negative electrode composite layer is not supported on the entire surface region of the negative electrode 12 facing the exterior can 38 (the surface of the negative electrode current collector facing the exterior can), and the negative electrode current collector is exposed.

[0065] One end of the positive electrode lead 19 is connected to the positive electrode 11, and the other end of the positive electrode lead 19 is connected to the sealing plate 31 (filter 32). That is, the positive electrode 11 is electrically connected to a cap 36 that also serves as a positive electrode terminal. One end of the negative electrode lead 20 is connected to the negative electrode 12, and the other end of the negative electrode lead 20 is connected to an outer can 38 that also serves as a negative electrode terminal.

[0066] The bottomed cylindrical outer can 38 contains the electrode group 14, whose winding end 14e is secured by tape 40, and an electrolyte (not shown). The secondary battery 10 has a mechanism whereby, in the event of an internal short circuit, the sealing body (sealing plate 31) attached to the opening of the outer can 38 comes off, and the electrode group 14, whose winding end 14e is secured by tape 40, is ejected from the opening of the outer can 38.

[0067] Negative electrode 12 has an outermost peripheral portion 12a that is disposed at the outermost periphery 14s of electrode group 14. In the entire surface region of outermost peripheral portion 12a that faces outer can 38, the negative electrode composite material layer is not supported, and the negative electrode current collector is exposed.

[0068] The tape 40 includes a first tape 41 and a second tape 42 attached to the negative electrode current collector of the outermost peripheral portion 12 a at one end 141 side and the other end 142 side in the winding axis direction of the electrode group 14 , respectively.

[0069] The negative electrode current collector of the outermost peripheral portion 12a, to which the tape 40 (first tape 41, second tape 42) is attached, is in contact with the outer can 38. At one end 141 of the electrode group 14 in the winding axis direction, the negative electrode current collector of the outermost peripheral portion 12a has a region in contact with the outer can 38 via the first tape 41. At one end 142 of the electrode group 14 in the winding axis direction, the negative electrode current collector of the outermost peripheral portion 12a has a region in contact with the outer can 38 via the second tape 42. At a central portion 143 of the electrode group 14 in the winding axis direction, the negative electrode current collector of the outermost peripheral portion 12a is in direct contact with the outer can 38. This makes it possible to more stably fix the winding end end 14e of the electrode group 14 and facilitates reducing internal resistance.

[0070] The first tape 41 includes a first substrate layer. The second tape 42 includes a second substrate layer. The first substrate layer and the second substrate layer are each a metal substrate layer having a static friction coefficient of 0.8 or less against the material of the outer can 38. The static friction coefficients of the first substrate layer and the second substrate layer may be approximately the same or different. The metal species contained in the first substrate layer and the second substrate layer may be the same or different.

[0071] The first tape 41 includes a first adhesive layer disposed on one surface (the surface on the outermost periphery) of the first base layer. The second tape 42 includes a second adhesive layer disposed on one surface (the surface on the outermost periphery) of the second base layer. The first adhesive layer and the second adhesive layer may each be conductive. The first adhesive layer and the second adhesive layer may be made of the same or different materials.

[0072] The tapes 41, 42 are each wrapped around the electrode group 41 so that both ends do not overlap. That is, in the wrapping direction of the tapes 41, 42, there are portions 41a, 42a on the outer circumferential surface of the electrode group 14 where the tapes 41, 42 are not wrapped. The length of the tapes 41, 42 (the dimension in the length direction of the strip-shaped tapes 41, 42) is preferably shorter than the outer circumferential length of the electrode group 14 by 1 mm or more and 7 mm or less. The tapes 41, 42 are preferably wrapped around the outer circumferential surface of the electrode group 14 by, for example, 0.8 to 0.99 revolutions.

[0073] As shown in FIG. 3 , the distance L1 between the tape 41 and one end 141 of the electrode group 14 in the winding axis direction and the distance L2 between the tape 42 and the other end 142 of the electrode group 14 in the winding axis direction may each be, for example, 2 to 5 mm. While L1 and L2 may be different, from the viewpoint of facilitating stable fixation of the electrode group, it is preferable that L1 and L2 are approximately the same. As shown in FIG. 3 , the distance L3 between the tape 41 and the tape 42 is preferably 18 to 46 mm. In this case, it is easy to ensure a sufficient area for direct contact between the negative electrode current collector of the outermost peripheral portion 12 a and the outer can 38 at the central portion 143 in the winding axis direction of the electrode group 14.

[0074] Although the negative electrode lead 20 is provided in the illustrated example, it is not necessary to provide the negative electrode lead 20. Even when the negative electrode lead 20 is not provided, the negative electrode 12 and the outer can 38 are electrically connected by contact between the inner surface of the outer can 38 and the electrode group 14 (outermost peripheral portion 12 a) to which the winding end 14 e is fixed by the tape 40, and the internal resistance can be sufficiently reduced.

[0075] In the illustrated example, both the first tape and the second tape include a metal substrate layer, but either the first tape or the second tape may include a resin substrate layer. In this case, the effect of the resin tape is small, and the metal tape reduces internal resistance and suppresses delays in discharging the electrode group. Examples of resins contained in the resin substrate layer include polypropylene resin. The resin substrate layer preferably has a static friction coefficient of 0.8 or less against the material of the outer can. If either the first tape or the second tape includes a metal substrate layer whose static friction coefficient against the material of the outer can exceeds 0.8, delays in discharging the electrode group will occur.

[0076] <<Appendix>> The above embodiments disclose the following technologies. (Technology 1) A secondary battery comprising: an electrode group formed by winding a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode; tape for fixing the winding end of the electrode group; an electrolyte; and a cylindrical outer can with a bottom that houses the electrode group, the tape, and the electrolyte, wherein the negative electrode has an outermost peripheral portion that is arranged at the outermost periphery of the electrode group, the tape has a metal substrate layer and is attached to the negative electrode current collector at the outermost peripheral portion, the negative electrode current collector at the outermost peripheral portion to which the tape is attached is in contact with the outer can, and the static friction coefficient of the metal substrate layer with respect to the material of the outer can is 0.8 or less. (Technology 2) The secondary battery according to Technology 1, wherein the static friction coefficient of the metal substrate layer with respect to the material of the outer can is 0.6 or less. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the negative electrode comprises a negative electrode composite layer supported on the negative electrode current collector, and wherein the negative electrode composite layer is not supported in at least a portion of the region of the outermost periphery facing the outer can. (Technology 4) The secondary battery according to any one of Technology 1 to 3, wherein the metal substrate layer contains at least one selected from the group consisting of nickel, iron, copper, titanium, zinc, silver, gold, and stainless steel. (Technology 5) The secondary battery according to any one of Technology 1 to 4, wherein the material of the outer can contains stainless steel. (Technology 6) The secondary battery according to any one of Technology 1 to 5, wherein the tape comprises an adhesive layer, and wherein the adhesive layer is disposed on the surface of the metal substrate layer on the outermost periphery side. (Technology 7) The secondary battery according to any one of Technology 1 to 6, wherein the thickness of the tape is 250 μm or less. (Technology 8) The secondary battery according to any one of Technology 1 to 7, wherein the width of the tape is 4 mm or more and 12 mm or less. (Technology 9) The secondary battery according to any one of Techniques 1 to 8, wherein the length of the tape is shorter than the outer periphery of the electrode group by 1 mm or more and 7 mm or less.(Technology 10) The secondary battery according to any one of Techniques 1 to 9, wherein the tape includes a first tape and a second tape attached to the outermost negative electrode current collector at one end side and the other end side in the winding axis direction of the electrode group, respectively, the first tape and the second tape each have the metal base layer having a static friction coefficient of 0.8 or less with respect to a material of the outer can, and the outermost negative electrode current collector and the outer can are in contact at a center in the winding axis direction of the electrode group.

[0077] [Examples] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0078] Secondary Batteries E1 to E9, R1 to R3 (Preparation of Positive Electrode) Positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone was added and stirred to prepare a positive electrode slurry. A lithium-containing transition metal oxide containing nickel, cobalt, and aluminum was used as the positive electrode active material. The positive electrode slurry was then applied to both sides of aluminum foil serving as a positive electrode current collector. The coating was dried and rolled with a roller to form a positive electrode composite layer. The positive electrode current collector with the positive electrode composite layer formed on both sides was then cut to a predetermined size to prepare a positive electrode.

[0079] (Preparation of Negative Electrode) Graphite (negative electrode active material), styrene-butadiene copolymer rubber (SBR), and carboxymethyl cellulose Na salt (CMC-Na) were mixed in a mass ratio of 98:1:1, and an appropriate amount of water was added and stirred to prepare a negative electrode slurry. The negative electrode slurry was then applied to both sides of copper foil serving as a negative electrode current collector, the coating was dried, and the mixture was rolled with a roller to form a negative electrode composite layer. The negative electrode current collector with the negative electrode composite layer formed on both sides was cut to a predetermined size to prepare a negative electrode. On one surface of the region that would become the outermost periphery of the negative electrode (the entire region facing the outer can), the negative electrode current collector was exposed without forming a negative electrode composite layer.

[0080] The static friction coefficient of the outermost negative electrode current collector against the material of the outer can was 0.6 or less.

[0081] (Preparation of non-aqueous electrolyte) LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 3:7). ６ was dissolved in a solution at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[0082] (Preparation of Electrode Assembly) One end of an aluminum positive electrode lead was attached to the positive electrode. One end of a nickel negative electrode lead was attached to the negative electrode. In an inert gas atmosphere, the positive electrode and negative electrode were spirally wound with a polyethylene porous film as a separator therebetween to prepare an electrode assembly.

[0083] (Fixing the winding end of the electrode group) The winding end of the electrode group was fixed with tape. Specifically, as shown in Figures 3 to 5, a first tape 41 and a second tape 42 were attached to two locations on the outer periphery 14s of the electrode group 14 (one end 141 side of the winding axis and the other end 142 side). The first tape 41 included a first base material layer and a first adhesive layer formed on one surface (the surface on the outermost periphery side) of the first base material layer. The second tape 42 included a second base material layer and a second adhesive layer formed on one surface (the surface on the outermost periphery side) of the second base material layer.

[0084] The materials for the first base material layer and the second base material layer were the materials shown in Table 1. Note that PP in Table 1 stands for polypropylene resin. The static friction coefficients of the first base material layer against the material of the outer can and the static friction coefficients of the second base material layer against the material of the outer can were the values ​​shown in Table 1.

[0085] The thickness of the first tape 41 and the second tape 42 was 150 μm when the metal substrate layer was included, and 30 μm when the PP substrate layer was included. The width of the first tape 41 and the second tape 42 was 9 mm.

[0086] The lengths of the first tape 41 and the second tape 42 were each 2 mm shorter than the length of the outer periphery 14s of the electrode group 14. The distance L1 between the first tape 41 and one end 141 of the electrode group 14 in the winding axis direction and the distance L2 between the second tape 42 and the other end 142 of the electrode group 14 in the winding axis direction were each 5 mm. The distance L3 between the first tape 41 and the second tape 42 was 36 mm.

[0087] The thickness of the first adhesive layer and the second adhesive layer was 30 μm for the metal substrate layer and 10 μm for the PP substrate layer. The first adhesive layer and the second adhesive layer were each made of an acrylic adhesive.

[0088] (Assembly of Secondary Battery) A cylindrical, bottomed stainless steel (SUS) outer can was prepared. The electrode group was housed in the outer can. At this time, the other end of the positive electrode lead was connected to a sealing plate, and the other end of the negative electrode lead was connected to the inner bottom surface of the outer can. After injecting a nonaqueous electrolyte, the opening of the outer can was sealed by covering it with a sealing plate. At this time, a gasket was interposed between the sealing plate and the open end of the outer can. In this way, a cylindrical nonaqueous electrolyte secondary battery was fabricated.

[0089] [Evaluation] A secondary battery in a fully charged state was obtained by constant current charging at a current of 500 mA until the voltage reached 4.2 V. The internal resistance at this time was measured. An internal short circuit test was also conducted by heating. Specifically, the fully charged secondary battery was placed in a furnace at 200°C, and the electrode group ejection mechanism was activated. A thermocouple was used to measure the temperature near the center of the side surface of the cylindrical battery, and the maximum temperature at this time was measured.

[0090]

[0091] In secondary batteries E1 and E2, in which one of the first tape and the second tape was a Cu tape and the other of the first tape and the second tape was a PP tape, internal resistance was reduced and temperature rise during an internal short circuit was suppressed. In secondary battery E3, in which both the first tape and the second tape were Cu tape, internal resistance was further reduced and temperature rise during an internal short circuit was further suppressed.

[0092] In secondary batteries E4 and E5, in which one of the first tape and the second tape was SUS tape and the other of the first tape and the second tape was PP tape, internal resistance was reduced and temperature rise during an internal short circuit was suppressed. In secondary battery E6, in which both the first tape and the second tape were SUS tape, internal resistance was further reduced and temperature rise during an internal short circuit was further suppressed.

[0093] In secondary batteries E7 and E8, in which one of the first tape and the second tape was Ni tape and the other of the first tape and the second tape was PP tape, internal resistance was reduced and temperature rise during an internal short circuit was suppressed. In secondary battery E9, in which both the first tape and the second tape were Ni tape, internal resistance was further reduced and temperature rise during an internal short circuit was further suppressed.

[0094] In the secondary battery R1 in which both the first tape and the second tape were PP tapes, the PP tape with high resistance was interposed between the outer can and the electrode group, and therefore the internal resistance increased.

[0095] In secondary battery R1, both the first and second tapes were PP tapes, so the impact of PP melting during a short circuit was significant (a large amount of PP was welded between the outer can and the electrode group), which delayed ejection of the electrode group and increased the maximum temperature during a short circuit. On the other hand, in secondary batteries E1, E2, E4, E5, E7, and E8, either the first or second tape was PP tape, and the other was Cu tape, SUS tape, or Ni tape. Therefore, the impact of PP melting during a short circuit was small, and the temperature increase during a short circuit was suppressed.

[0096] In secondary battery R2, where both the first and second tapes were Al tapes, the maximum temperature during short circuiting increased significantly due to the large static friction coefficient of the Al tapes (greater than 0.8). In secondary battery R3, where the first tape was Cu tape but the second tape was Al tape (greater than 0.8) with a large static friction coefficient, the maximum temperature during short circuiting increased due to the large static friction coefficient of the electrode groups.

[0097] The present disclosure can be used in a secondary battery in which a wound electrode group is housed in an outer can.

[0098] 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.

[0099] 10: secondary battery, 11: positive electrode, 12: negative electrode, 12a: outermost periphery of negative electrode, 13: separator, 14: electrode group, 14s: outermost periphery of electrode group, 14e: winding end of electrode group, 31: sealing plate, 38: outer can, 40: tape, 41: first tape, 42: second tape

Claims

1. A secondary battery comprising: an electrode group in which a positive electrode, a negative electrode including a negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode are wound; a tape for fixing the wound end portion of the electrode group; an electrolyte; and a bottomed cylindrical exterior can for housing the electrode group, the tape, and the electrolyte, wherein the negative electrode has an outermost peripheral portion disposed on the outermost periphery of the electrode group, the tape includes a metal base material layer and is attached to the negative electrode current collector of the outermost peripheral portion, the negative electrode current collector of the outermost peripheral portion to which the tape is attached is in contact with the exterior can, and the static friction coefficient of the metal base material layer with respect to the material of the exterior can is 0.8 or less.

2. The secondary battery according to claim 1, wherein the static friction coefficient of the metal base material layer with respect to the material of the exterior can is 0.6 or less.

3. The secondary battery according to claim 1, wherein the negative electrode includes a negative electrode composite material layer supported by the negative electrode current collector, and the negative electrode composite material layer is not supported at least in part of a region facing the exterior can of the outermost peripheral portion.

4. The secondary battery according to claim 1, wherein the metal base material layer includes at least one selected from the group consisting of nickel, iron, copper, titanium, zinc, silver, gold, and stainless steel.

5. The secondary battery according to claim 1, wherein the material of the exterior can includes stainless steel.

6. The secondary battery according to claim 1, wherein the tape includes an adhesive layer, and the adhesive layer is disposed on the surface of the metal base material layer on the outermost peripheral portion side.

7. The secondary battery according to claim 1, wherein the thickness of the tape is 250 μm or less.

8. The secondary battery according to claim 1, wherein the width of the tape is 4 mm or more and 12 mm or less.

9. The secondary battery according to claim 1, wherein the length of the tape is shorter than the length of the outer periphery of the electrode group by 1 mm or more and 7 mm or less.

10. The secondary battery according to claim 1, wherein the tape includes a first tape and a second tape attached to the negative electrode current collector of the outermost peripheral portion on one end side and the other end side in the winding axis direction of the electrode group, respectively, the first tape and the second tape each include the metal base material layer having a static friction coefficient of 0.8 or less with respect to the material of the exterior can, and at the central portion in the winding axis direction of the electrode group, the negative electrode current collector of the outermost peripheral portion is in contact with the exterior can.

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