Battery

Abstract

Provided is a battery having excellent cycle characteristics in a low-temperature environment. This battery has an outer package can that accommodates therein: an electrode winding body that is formed by laminating, with a separator interposed therebetween, a belt-like positive electrode having a positive electrode foil and a positive electrode active material layer and a belt-like negative electrode having a negative electrode foil and a negative electrode active material layer, and that has a winding structure around the center axis; a positive electrode current collector plate; a negative electrode current collector plate; and an electrolytic solution. The electrode foils have active material covered parts in which active material layers are covered and active material non-covered parts in which the active material layers are not covered. Surfaces, where the active material non-covered parts that are bent toward the center axis are overlapped, and the current collector plates are joined. The electrolytic solution contains 7.7-11.5 mass% of fluoroethylene carbonate, 0.032-0.048 mass% of lithium tetrafluoroborate, and lithium hexafluorophosphate.

Description

[Technical Field]

[0001] The present disclosure relates to batteries. [Background technology]

[0002] Patent Document 1 describes a battery including an electrode winding body in which a strip-shaped positive electrode and a strip-shaped negative electrode are stacked and wound with a separator interposed therebetween, and the positive electrode and the negative electrode have uncovered portions that are not covered with an active material layer. Here, the uncovered portions are joined to current collector plates at the ends of the electrode winding body, bent toward the central axis of the wound structure, and overlapped.

[0003] Patent Document 2 describes that in a secondary battery, when the content of fluoroethylene carbonate (FEC) in the solvent of the nonaqueous electrolyte is 2 to 50 volume % and the content of lithium tetrafluoroborate (LiBF4) is 0.1 to 1.0 mol / L, the action of FEC can suppress the deposition of metallic lithium on the negative electrode surface, thereby improving cycle characteristics, and the action of LiBF4 can suppress the decomposition of FEC during storage in a charged state, thereby suppressing the generation of gas associated with decomposition. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 020237 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-294432 Summary of the Invention [Problem to be solved by the invention]

[0005] However, a battery with the structure shown in Patent Document 1 generates little heat during charging and discharging due to its low battery resistance. Therefore, if the composition of the electrolyte solution is that shown in Patent Document 2, it may not be possible to sufficiently suppress the deposition of metallic lithium on the negative electrode surface in a low-temperature environment, which could result in a deterioration in cycle characteristics in a low-temperature environment.

[0006] The present invention has been made in view of the above, and has an object to provide a battery that has excellent cycle characteristics in a low-temperature environment. [Means for solving the problem]

[0007] The battery according to the present invention comprises an electrode winding body having a structure in which a strip-shaped positive electrode having a positive electrode foil and a positive electrode active material layer, and a strip-shaped negative electrode having a negative electrode foil and a negative electrode active material layer are stacked with a separator interposed therebetween and wound around a central axis, a positive electrode current collector, a negative electrode current collector, and an electrolyte, all of which are housed in an outer can, wherein the positive electrode foil has a positive electrode active material coated portion coated with the positive electrode active material layer and a positive electrode active material uncoated portion not coated with the positive electrode active material layer, and the negative electrode foil has a negative electrode active material coated portion coated with the negative electrode active material layer and a negative electrode active material uncoated portion not coated with the negative electrode active material layer. The cathode active material uncoated portion has a negative electrode active material uncoated portion that is not coated with a layer, and a surface where the positive electrode active material uncoated portion bent toward the central axis overlaps is bonded to the positive electrode current collector plate, and a surface where the negative electrode active material uncoated portion bent toward the central axis overlaps is bonded to the negative electrode current collector plate, and the electrolyte contains 7.7 mass % or more and 11.5 mass % or less of fluoroethylene carbonate, 0.032 mass % or more and 0.048 mass % or less of lithium tetrafluoroborate, and lithium hexafluorophosphate. [Effects of the Invention]

[0008] According to the present invention, a battery having excellent cycle characteristics in a low-temperature environment can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view of a battery according to this embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the structure of the electrode winding body of the battery according to this embodiment before winding. [Figure 3] FIG. 3 is a plan view showing an end portion of the battery according to this embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a cross section taken along line IV-IV in FIG. [Figure 5A] FIG. 5A is a diagram showing the positive electrode current collector plate of the battery according to this embodiment. [Figure 5B] FIG. 5B is a diagram showing the negative electrode current collector plate of the battery according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described, but the present disclosure is not limited to these embodiments.

[0011] In this embodiment, a cylindrical lithium ion battery will be described as an example of the battery. However, the battery according to the present invention is not limited to this, and batteries other than lithium ion batteries or batteries other than cylindrical batteries may also be used.

[0012] FIG. 1 is a schematic cross-sectional view of a battery according to this embodiment. As shown in FIG. 1, the battery 1 according to this embodiment is, for example, a cylindrical lithium-ion battery. The battery 1 includes an outer can 11, insulating plates 12 and 13, a battery lid 14, a gasket 15, an electrode winding 20, and a safety valve mechanism 16. The battery 1 has a structure in which the insulating plates 12 and 13, the electrode winding 20, the safety valve mechanism 16, a positive electrode current collector 30A, and a negative electrode current collector 30B are housed in a space sealed by the outer can 11, the battery lid 14, and the gasket 15, and the space is filled with an electrolyte. The configuration of the battery 1 is not limited thereto, and the outer can 11 may further include, for example, a thermosensitive resistor (PTC) element, a reinforcing member, and the like.

[0013] (Outer can) The outer can 11 is a member that houses the electrode winding body 20 and the like. The outer can 11 is a cylindrical container that is open at one end in the Z direction and closed at the other end. That is, the outer can 11 has an open end 11N that is the open end. The outer can 11 is made of, for example, a metal such as iron or aluminum, or an alloy. The surface of the outer can 11 may be plated with a metal such as nickel.

[0014] (Caulking structure) Here, a crimping structure 11R is formed at the open end 11N of the outer can 11. The crimping structure 11R crimps the battery lid 14 and the safety valve mechanism 16 via a gasket 15. The crimping structure 11R is a so-called crimp structure. This seals the inside of the outer can 11.

[0015] (Battery cover) The battery lid 14 is a member that closes the open end 11N of the outer can 11. The area of ​​the battery lid 14 around the central axis of the battery 1 in the XY plane protrudes in the +Z direction. The area of ​​the battery lid 14 other than the protruding area is in contact with the safety valve mechanism 16. This electrically connects the battery lid 14 to the safety valve mechanism 16. The battery lid 14 contains, for example, the same material as the material from which the outer can 11 is formed.

[0016] (gasket) The gasket 15 is a member that seals the gap between the bent portion 11P and the battery lid 14. The gasket 15 is electrically insulating and contains an insulating material. This allows the gap between the bent portion 11P and the battery lid 14 to be sufficiently sealed and prevents direct contact between the outer can 11 and the battery lid 14. The type of insulating material is not particularly limited, but examples include polymer materials such as polybutylene terephthalate (PBT) and polypropylene (PP), with polybutylene terephthalate being preferred. The surface of the gasket 15 may be coated with, for example, asphalt.

[0017] (Safety valve mechanism) The safety valve mechanism 16 is a mechanism for preventing the battery from exploding. The safety valve mechanism 16 has a protrusion in the -Z direction, which is in contact with a connection portion 32B of the positive current collector plate 30A, which will be described later. This electrically connects the safety valve mechanism 16 to the positive current collector plate 30A. When the internal pressure of the outer can 11 increases due to gas generation, the safety valve mechanism 16 deforms in the +Z direction, thereby disconnecting the connection with the positive current collector plate 30A and interrupting the current. If the internal pressure of the outer can 11 increases further in this state, the safety valve mechanism 16 opens by itself, releasing the sealed state of the outer can 11 and thereby releasing the internal pressure. This prevents the battery 1 from exploding due to gas.

[0018] (insulating plate) The insulating plates 12 and 13 are dish-shaped plates having a thickness in the Z direction in a plane perpendicular to the winding axis of the electrode winding body 20. The insulating plate 12 is provided in the +Z direction of the electrode winding body 20, and the insulating plate 13 is provided in the -Z direction of the electrode winding body 20. That is, the insulating plates 12 and 13 are arranged so as to sandwich the electrode winding body 20 between them. The insulating plate 12 has a slit for passing the strip portion 32 of the positive current collector plate 30A. Similarly, the insulating plate 13 has a slit for passing the strip portion 34 of the negative current collector plate 30B.

[0019] (Electrode winding body) Fig. 2 is a diagram showing an example of the structure of an electrode winding of a battery according to this embodiment before winding. The electrode winding 20 includes a positive electrode 21, a negative electrode 22, and a separator 23. In the electrode winding 20, a laminate in which the positive electrode 21 and the negative electrode 22 sandwich the separator 23, as shown in Fig. 2, is spirally wound. Here, the laminate in which the positive electrode 21 and the negative electrode 22 of the electrode winding 20 sandwich the separator 23 has ends 41 and 42 in the Z direction that are parallel to the XY plane. The electrode winding 20 is housed in an outer can 11 and impregnated with an electrolyte.

[0020] The central axis of the electrode winding body 20 is a through hole. That is, a through hole 26 is provided in the electrode winding body 20. The through hole 26 is a hole for inserting a winding core for assembling the electrode winding body 20 and an electrode rod for welding. In the example according to this embodiment, the through hole 26 is provided with a center pin (not shown). The center pin is made of metal.

[0021] (positive electrode) The positive electrode 21 is a strip-shaped member including a positive electrode foil 211, a positive electrode active material layer 212, and an insulating layer 213. The material of the positive electrode foil 211 is, for example, a metal foil containing aluminum or an aluminum alloy, and in the example shown in this embodiment, it is an aluminum foil.

[0022] The positive electrode active material layer 212 is a layer containing a positive electrode active material. The positive electrode active material layer 212 is provided on one or both sides of the positive electrode foil 211. As shown in FIG. 2, the positive electrode active material layer 212 covers most of the positive electrode foil 211, but the periphery of one end in the minor axis direction of the strip (the end in the +Z direction) is not covered. Here, the portion of the positive electrode foil 211 that is covered with the positive electrode active material layer 212 is a positive electrode active material coated portion 211A, and the portion of the positive electrode foil 211 that is not covered with the positive electrode active material layer 212 is a positive electrode active material uncoated portion 211B. The positive electrode foil 211 has the positive electrode active material coated portion 211A and the positive electrode active material uncoated portion 211B.

[0023] The positive electrode active material layer 212 includes a positive electrode active material that absorbs and releases lithium. The positive electrode material is preferably a lithium-containing compound, more specifically, a lithium-containing composite oxide, a lithium-containing phosphate compound, or the like. The lithium-containing composite oxide is an oxide containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing composite oxide has, for example, a layered rock salt type or a spinel type crystal structure. The lithium-containing phosphate compound is a phosphate compound containing lithium and one or more elements other than lithium as constituent elements, and has, for example, an olivine type crystal structure.

[0024] The positive electrode active material layer 212 may further include a positive electrode binder. The positive electrode binder may be any material, and may include, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Examples of polymer compounds include polyvinylidene fluoride and polyimide.

[0025] The positive electrode active material layer 212 may further contain a positive electrode conductive agent. The positive electrode conductive agent may be any material, including, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and ketjen black. However, the positive electrode conductive agent is not limited to this, and may be any conductive material, such as a metal material or a conductive polymer.

[0026] The insulating layer 213 is laminated in a 3 mm-wide section that includes the boundary between the positive electrode active material uncoated portion 211B and the positive electrode active material layer 212. The insulating layer 213 is laminated over the entire surface of the positive electrode active material uncoated portion 211B on the separator 23 side. By providing the insulating layer 213 in this manner, it is possible to prevent the battery 1 from short-circuiting when foreign matter enters between the negative electrode active material layer 222 and the positive electrode active material uncoated portion 211B, and also to absorb the impact when the battery 1 is subjected to an impact, thereby preventing the positive electrode active material uncoated portion 211B from bending and the negative electrode 22 from short-circuiting.

[0027] (Negative electrode) The negative electrode 22 is a strip-shaped member including a negative electrode foil 221 and a negative electrode active material layer 222 .

[0028] The material of the negative electrode foil 221 is, for example, a metal foil containing nickel, a nickel alloy, copper, or a copper alloy, and in the example shown in this embodiment, it is copper foil. The surface of the negative electrode foil 221 is roughened at least in the region that comes into contact with the negative electrode active material layer 222. The roughening is achieved, for example, by forming fine particles on the surface of the negative electrode foil 221 using an electrolytic treatment method. This improves the adhesion of the negative electrode active material layer 222 to the negative electrode foil 221 due to a so-called anchor effect.

[0029] The negative electrode active material layer 222 is a layer containing a negative electrode active material. The negative electrode active material layer 222 is provided on one or both sides of the negative electrode foil 221. As shown in FIG. 2, the negative electrode active material layer 222 covers most of the negative electrode foil 221, but the periphery of the other end (the end in the −Z direction) in the minor axis direction of the strip is not covered. Here, the part of the negative electrode foil 221 that is covered with the negative electrode active material layer 222 is the negative electrode active material covered part 221A, and the part of the negative electrode foil 221 that is not covered with the negative electrode active material layer 222 is the negative electrode active material uncovered part 221B. The negative electrode foil 221 has the negative electrode active material covered part 221A and the negative electrode active material uncovered part 221B.

[0030] The negative electrode active material layer 222 contains a negative electrode active material that absorbs and releases lithium as the negative electrode active material, but may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0031] The negative electrode active material is, for example, a carbon material. In this case, the change in the crystal structure during the absorption and desorption of lithium is very small, so a high energy density can be stably obtained. In addition, the carbon material also functions as a negative electrode conductive agent, improving the conductivity of the negative electrode active material layer 222.

[0032] Examples of carbon materials used as negative electrode active materials include graphitizable carbon, non-graphitizable carbon, and graphite. More specifically, examples of carbon materials include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound calcined bodies, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Organic polymer compound calcined bodies are carbonized by calcining polymer compounds such as phenolic resins and furan resins at an appropriate temperature. When non-graphitizable carbon is used, the interplanar spacing of the (002) plane of the non-graphitizable carbon is preferably 0.37 nm to 0.34 nm. This range allows for favorable accumulation of lithium between carbon layers. However, the carbon material is not limited thereto. For example, low-crystalline carbon heat-treated at a temperature of approximately 1000°C or less, or amorphous carbon, may also be used. The carbon material may be fibrous, spherical, granular, or flaky.

[0033] The amounts of the positive electrode active material and the negative electrode active material are adjusted so that the open circuit voltage (i.e., battery voltage) of the battery 1 when fully charged is 4.25 V or higher. This results in a higher amount of lithium released per unit mass than when the open circuit voltage when fully charged is 4.20 V, even when the same positive electrode active material is used, and therefore a higher energy density can be obtained.

[0034] (separator) The separator 23 is a film that electrically insulates the positive electrode 21 from the negative electrode 22. The separator 23 is made of, for example, one or more porous films made of synthetic resins or ceramics, or may be a laminate of two or more porous films. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene.

[0035] The separator 23 may include, for example, the porous membrane or a laminated membrane of porous membranes (hereinafter referred to as a substrate layer) and a polymer compound layer provided on one or both sides of the substrate layer. The polymer compound layer includes, for example, a polymer compound such as polyvinylidene fluoride. In this case, the physical strength and chemical stability of the separator 23 can be improved. The polymer compound layer is formed, for example, by applying a solution of a polymer compound dissolved in an organic solvent to the substrate layer and then drying the substrate layer. Here, in forming the polymer compound layer, the substrate layer may be immersed in the solution and then dried. The provision of the polymer compound layer improves the adhesion of the separator 23 to the positive electrode 21 and the negative electrode 22 and suppresses distortion of the electrode winding body 20, thereby suppressing decomposition reaction of the electrolyte solution and leakage of the electrolyte solution from the substrate layer. This makes it difficult for resistance to increase even with repeated charge and discharge, and suppresses battery swelling due to gas. The material of the polymer compound layer is not limited to this, and may contain insulating inorganic particles such as aluminum oxide and aluminum nitride.

[0036] In this embodiment, the positive electrode active material uncoated portion 211B is softer than the negative electrode active material uncoated portion 221B, i.e., has a lower Young's modulus. Here, the width of the positive electrode active material uncoated portion 211B is A, the width of the negative electrode active material uncoated portion 221B is B, the length from one end of the positive electrode active material uncoated portion 211B in the +Z direction to the end of the separator 23 in the Z direction is C, and the length from one end of the negative electrode active material uncoated portion 221B in the -Z direction to the end of the separator 23 in the -Z direction is D. In this case, in this embodiment, A>B and C>D, and for example, A=7 (mm), B=4 (mm), C=4.5 (mm), and D=3 (mm).

[0037] By setting this value, when the active material uncoated portions 211B, 221B are folded simultaneously from both electrode sides with the same pressure, the length in the Z direction from the end of the separator 23 in the +Z direction to the end 41 formed by folding the positive electrode active material uncoated portion 211B can be made approximately the same as the length in the Z direction from the end of the separator 23 in the -Z direction to the end 42 formed by folding the negative electrode active material uncoated portion 221B. This allows the folded active material uncoated portions 211B, 221B to be overlapped appropriately.

[0038] (end) 3 is a plan view showing the ends of the battery according to this embodiment. Ends 41 and 42 are surfaces formed by bending the active material uncoated portions 211B and 221B. That is, one end 41 of the electrode wound body 20 is an end made of the positive electrode active material uncoated portion 211B, and the other end 42 of the electrode wound body 20 is an end made of the negative electrode active material uncoated portion 221B. Ends 41 and 42 have flat surfaces that do not affect the bonding with the current collector plates 30A and 30B.

[0039] FIG. 4 is a diagram showing an example of a cross section taken along line IV-IV in FIG. 3. The structure of end portion 41 will be described in detail below with reference to FIG. 4. As shown in FIG. 4, end portion 41 has a surface formed by positive electrode active material uncoated portions 211B bent in the direction of the central axis. With this structure, the radial lines from the central axis (the radius of the electrode winding), i.e., the multiple positive electrode active material uncoated portions 211B on line IV-IV, are stacked in the Z direction. This allows positive electrode 21 to come into contact with the positive electrode current collector plate 30A over a wide area, thereby reducing battery resistance.

[0040] The end 42 has the same structure as the end 41. That is, as shown in FIG. 4, the end 42 has a surface on which the negative electrode active material uncoated portions 221B bent in the direction of the central axis are formed. With this structure, the multiple negative electrode active material uncoated portions 221B radially extending from the central axis are stacked in the Z direction. The negative electrode 22 comes into contact with the negative electrode current collector plate 30B over a wide area, thereby reducing the battery resistance.

[0041] 5B, grooves 43 are provided in the end portions 41, 42. The grooves 43 extend from the outer peripheries of the end portions 41, 42 to the through-hole 26 having the central axis. The grooves 43 are provided to prevent the end portions 41, 42 from having an uneven surface due to wrinkles or distortions of the positive electrode active material uncoated portion 211B and the negative electrode active material uncoated portion 221B when the positive electrode active material uncoated portion 211B and the negative electrode active material uncoated portion 221B are bent. This prevents deterioration of the bond between the end portions 41, 42 and the current collector plates, and reduces the resistance between the end portions 41, 42 and the current collector plates 30A, 30B.

[0042] More specifically, if the positive electrode active material uncoated portion 211B and the negative electrode active material uncoated portion 221B are bent without previously forming the grooves 43 in the end portions 41 and 42, wrinkles and distortions may occur in the positive electrode active material uncoated portion 211B and the negative electrode active material uncoated portion 221B. On the other hand, if the positive electrode active material uncoated portion 211B and the negative electrode active material uncoated portion 221B are bent after previously forming the grooves 43 in the end portions 41 and 42, the occurrence of wrinkles during folding can be suppressed. This allows the end portions 41 and 42 to have flat surfaces with few irregularities.

[0043] (Positive current collector plate) 5A is a diagram showing a positive electrode current collector plate of a battery according to this embodiment. The material of the positive electrode current collector plate 30A is a metal plate made of, for example, aluminum or an aluminum alloy, or a composite material. As shown in FIG. 5A, the positive electrode current collector plate 30A includes a sector-shaped portion 31 and a strip-shaped portion 32.

[0044] The sectorial portion 31 is a portion that is connected to the positive electrode active material uncoated portion 211B. Holes 35 are provided in the sectorial portion 31. The sectorial portion 31 is provided between the end portion 41 and the insulating plate 12 in the battery 1. The sectorial portion 31 is welded to the end portion 41 at multiple points, thereby suppressing the internal resistance of the battery. The means for joining the positive electrode current collector plate 30A and the end portion 41 is not particularly limited, and may be laser welding, for example.

[0045] Hole 35 is provided at a position that overlaps with through-hole 26 in the Z direction when attached to end 41. This structure allows the electrolyte to smoothly penetrate into electrode wound body 20 when assembling the battery, and also makes it easier to release gas generated when the battery is in an abnormally high temperature state or overcharged state.

[0046] The strip-shaped portion 32 is provided on a linear portion of the sector-shaped portion 31. The strip-shaped portion 32 includes an insulating portion 32A and a connecting portion 32B. The strip-shaped portion 32 is provided in the battery 1 so as to penetrate the insulating plate 12 in the Z direction. The insulating portion 32A is a portion of the strip-shaped portion 32 whose surface is covered with an insulator. Insulating tape is attached to the insulating portion 32A, or an insulating material is applied to the insulating portion 32A. The insulating portion 32A is provided at the base of the strip-shaped portion 32, i.e., between the connecting portion 32B and the sector-shaped portion 31. The connecting portion 32B is a portion that connects to the safety valve mechanism 16. The connecting portion 32B is provided at the tip of the strip-shaped portion 32. Note that if a center pin is not provided in the through-hole 26, the strip-shaped portion 32 is unlikely to come into contact with a portion at the negative electrode potential, and therefore the insulating portion 32A may not be provided. In this case, the width of the positive electrode 21 and the negative electrode 22 in the Z direction can be increased by an amount corresponding to the thickness of the insulating portion 32A, thereby making it possible to further increase the charge / discharge capacity.

[0047] (negative electrode current collector plate) 5B is a diagram showing the negative electrode current collector of the battery according to this embodiment. The material of the negative electrode current collector 30B is a metal plate made of, for example, nickel, a nickel alloy, copper, or a copper alloy, or a composite material. As shown in FIG. 5B, the negative electrode current collector 30B has a sector-shaped portion 33 and a strip-shaped portion 34.

[0048] The sectorial portion 33 is a portion that is connected to the negative electrode active material uncovered portion 221B. Holes 36 are provided in the sectorial portion 33. The sectorial portion 33 is provided in the battery 1 between the end portion 42 and the insulating plate 13. The negative electrode current collector 30B is joined in the -Z direction of the end portion 42. The sectorial portion 33 is welded to the end portion 42 at multiple points. There are no particular limitations on the means for joining the negative electrode current collector 30B and the end portion 42, and laser welding may be used, for example. This can reduce the internal resistance of the battery.

[0049] The holes 36 are provided at positions that overlap with the through-holes 26 in the Z direction when the end portions 42 are bonded. This structure allows the electrolyte to smoothly penetrate into the electrode wound body 20 when assembling the battery, and also makes it easier to release gas generated when the battery is in an abnormally high temperature state or an overcharged state.

[0050] The strip-shaped portion 34 is provided on a linear portion of the sector-shaped portion 33. The strip-shaped portion 34 is provided in the battery 1 so as to penetrate the insulating plate 13 in the Z direction. The strip-shaped portion 34 of the negative current collector 30B is shorter than the strip-shaped portion 32 of the positive current collector 30A. The strip-shaped portion 34 is provided with a round projection 37 that is convex in the thickness direction. As a result, during resistance welding in the manufacturing process of the battery 1, the projection 37 melts due to current concentration, allowing the strip-shaped portion 34 to be welded to the closure portion of the outer can 11.

[0051] (electrolyte) The electrolyte solution according to this embodiment contains a solvent and a solute. In the following description, the content of the electrolyte solution components in the battery 1 refers to the content in the electrolyte solution after the battery 1 is fully discharged. The content of the electrolyte solution components in the battery 1 can be determined by gas chromatography mass spectrometry or inductively coupled plasma atomic emission spectrometry. The gas chromatograph mass spectrometer used was a 5977B manufactured by Agilent Technologies. The inductively coupled plasma atomic emission spectrometer used was a PS3500DDII manufactured by Hitachi High-Tech Science.

[0052] The solvent includes a non-aqueous solvent such as an organic solvent, for example, a cyclic carbonate such as ethylene carbonate (EC) or dimethyl carbonate (DMC), a chain carbonate, a lactone, a chain carboxylic acid ester, and a nitrile (mononitrile).

[0053] The solvent further contains fluoroethylene carbonate (FEC). By including FEC, when a metallic lithium layer precipitates on the surface of the negative electrode during charging in a low-temperature environment, the metallic lithium layer on the surface of the negative electrode is covered with a film made of a solvent decomposition product, which can suppress deterioration of low-temperature cycle characteristics. This is because covering with the film can prevent the progression of metallic lithium precipitation.

[0054] The content of FEC in the electrolyte solution in Battery 1 is 7.7% by mass or more. This range provides a coating thick enough to cover the metallic lithium layer, thereby sufficiently suppressing deterioration in low-temperature cycle characteristics.

[0055] On the other hand, if the battery 1 contains an excess amount of FEC, the generation of hydrogen fluoride (HF) is promoted when the temperature of the battery 1 rises. Hydrogen fluoride can react with lithium carbonate (Li2CO3) and other substances present on the surface of the positive electrode, generating large amounts of carbon dioxide and hydrocarbon gases. If a large amount of gas is generated and the internal pressure of the battery rises, the safety valve mechanism breaks and the current is cut off.

[0056] The content of FEC in the battery 1 is 11.5 mass % or less relative to the electrolyte solution. By setting the content within this range, excessive generation of hydrogen fluoride (HF) can be suppressed, and therefore gas generation can be suppressed.

[0057] The solute contains 14% by mass or more and 18% by mass of lithium hexafluorophosphate (LiPF6).

[0058] The solute further contains lithium tetrafluoroborate (LiBF4), which forms a coating on the positive electrode and prevents contact between the lithium carbonate present in the positive electrode and the hydrogen fluoride in the electrolyte, thereby further suppressing the generation of carbon dioxide gas.

[0059] The content of LiBF4 in the battery 1 is 0.032 mass % or more relative to the electrolyte solution. By setting the content within this range, the generation of carbon dioxide gas can be more sufficiently suppressed.

[0060] On the other hand, the content of LiBF4 in the battery 1 is 0.048 mass % or less with respect to the electrolyte solution. By setting the content within this range, it is possible to prevent the coating of the positive electrode from becoming excessively thick, which can prevent an increase in battery resistance.

[0061] The solvent further contains succinonitrile (SN). By including SN, the SN captures metal ions in the electrolyte, which can prevent the battery 1 from short-circuiting. The mechanism by which SN prevents the battery 1 from short-circuiting will be described in detail below with reference to FIG. 4.

[0062] 4 , in the battery 1 according to this embodiment, the positive electrode active material uncoated portion 211B is bent in the central axis direction. Therefore, the positive electrode active material coated portion 211A near the end 41 is also pulled in the central axis direction, which may cause a difference in the layer spacing between the adjacent positive electrode and negative electrode. More specifically, at the outermost periphery of the electrode wound body 20, the negative electrode 22 is disposed outside the positive electrode 21. Therefore, a local increase in the layer spacing may occur between the upper end 21A of the positive electrode 21 in the outermost peripheral portion of the electrode wound body 20 and the upper end 22B of the negative electrode 22 in the outermost peripheral portion of the electrode wound body 20. Here, the upper end 21A of the positive electrode 21 refers to the end of the positive electrode active material coated portion 211A and the positive electrode active material layer 212 in the +Z direction, and the +Z upper end 22A of the negative electrode 22 refers to the end of the negative electrode 22, i.e., the negative electrode active material coated portion 221A and the negative electrode active material layer 222 in the +Z direction.

[0063] As a result, the potential of the positive electrode 21 increases. When the potential of the positive electrode 21 exceeds the dissolution potential of a transition metal (e.g., nickel) in the positive electrode active material, the transition metal in the positive electrode active material dissolves into the electrolyte. If SN is not contained in the electrolyte, metal ions dissolved into the electrolyte may precipitate on the surface of the negative electrode 22. If the precipitate penetrates the separator 23, it may reach the positive electrode 21, causing a short circuit. On the other hand, if SN is contained in the electrolyte, it is thought that SN captures the metal ions in the electrolyte and forms a complex containing the metal ions, preventing them from depositing on the surface of the negative electrode 22. Therefore, by including SN in the electrolyte, it is possible to prevent metal ions in the electrolyte from depositing on the surface of the negative electrode 22, thereby preventing a short circuit in the battery.

[0064] The content of SN in the battery 1 is 0.392 mass % or more relative to the electrolyte. By setting the content in this range, the SN can sufficiently capture metal ions in the electrolyte, thereby preventing the battery 1 from short-circuiting.

[0065] On the other hand, the SN content of the battery 1 is 0.588 mass % or less with respect to the electrolyte solution. By setting the content within this range, it is possible to prevent the coating on the surface of the negative electrode 22 from becoming excessively thick, which can prevent an increase in battery resistance.

[0066] The solute of the electrolyte is not limited to those listed above, and may include, for example, electrolyte salts such as lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium tetraphenylborate (LiB(CH)), lithium methanesulfonate (LiCHSO), lithium trifluoromethanesulfonate (LiCFSO), lithium tetrachloroaluminate (LiAlCl), dilithium hexafluorosilicate (LiSiF), lithium chloride (LiCl), and lithium bromide (LiBr).

[0067] As described above, the battery 1 according to this embodiment is a battery in which the electrode wound body 20 having a structure in which the strip-shaped positive electrode 21 including the positive electrode foil 211 and the positive electrode active material layer 212 and the strip-shaped negative electrode 22 including the negative electrode foil 221 and the negative electrode active material layer 222 are stacked with the separator 23 interposed therebetween and wound around the central axis, the positive electrode current collector 30A, the negative electrode current collector 30B, and the electrolyte are housed in the outer can 11, in which the positive electrode foil 211 has the positive electrode active material coated portion 211A coated with the positive electrode active material layer 212 and the positive electrode active material uncoated portion 211B not coated with the positive electrode active material layer 212, and the negative electrode foil 221 has the negative electrode active material coated portion 22 1A and anode active material uncoated portions 221B that are not coated with anode active material layer 222, and a surface (edge ​​41) where the cathode active material uncoated portions 211B bent toward the central axis overlap with the cathode current collector 30A, and a surface (edge ​​42) where the anode active material uncoated portions 221B bent toward the central axis overlap with the anode current collector 30B, and the electrolyte contains 7.7 mass % or more and 11.5 mass % or less of fluoroethylene carbonate (FEC), 0.032 mass % or more and 0.048 mass % or less of lithium tetrafluoroborate (LiBF4), and lithium hexafluorophosphate (LiPF6).

[0068] As a result, the positive electrode 21 and the negative electrode 22 have active material-uncoated portions 211B and 221B that are not coated with the active material layers 212 and 222. The active material-uncoated portions 211B and 221B are joined to the current collector plates 30A and 30B at the ends 41 and 42 of the electrode winding 20, bent toward the central axis of the wound structure, and overlapped. This reduces the internal resistance of the battery compared to a typical battery in which current extraction leads are welded to the positive electrode 21 and the negative electrode 22, respectively. This prevents the battery from overheating and reaching high temperatures during discharge, enabling high-rate discharge. Furthermore, by using FEC in an amount within the range disclosed herein, cycle characteristics in low-temperature environments can be improved without excessive gas generation. By using LiBF4 in an amount within the range disclosed herein, gas generation due to FEC decomposition can be suppressed while suppressing an increase in resistance. This allows for improved cycle characteristics in low-temperature environments while suppressing gas generation and an increase in resistance.

[0069] In a preferred embodiment, the electrolyte solution further contains 0.392 mass % to 0.588 mass % of succinonitrile (SN), which allows SN to capture metal ions in the electrolyte solution and accumulate them on the surface of the negative electrode 22, thereby suppressing an increase in battery resistance and preventing short circuits in the battery due to the deposition of transition metals.

[0070] (Example) Examples will be described below, but the present invention is not limited to the examples described below.

[0071] Table 1 shows the measurement results of the batteries according to Test Examples 1-1 to 1-7.

[0072] [Table 1]

[0073] (Test Example 1-1) The battery according to Test Example 1-1 was fabricated in the following manner.

[0074] A positive electrode active material was applied to a portion of the surface of the positive electrode foil 211 to provide a positive electrode active material coated portion 211A and a positive electrode active material uncoated portion 211B. Similarly, a negative electrode active material was applied to a portion of the surface of the negative electrode foil 221 to provide a negative electrode active material coated portion 221A and a negative electrode active material uncoated portion 221B. At this time, notches were provided in portions of the active material uncoated portions 211B, 221B that corresponded to the central axis.

[0075] Then, the positive electrode 21 and the negative electrode 22, which had been pretreated by drying or the like, were stacked with the separator 23 interposed therebetween, and wound in a spiral shape so as to form a through-hole 26 in the central axis, thereby producing the wound electrode body 20.

[0076] Next, a load was applied locally to the ends 41, 42 formed by winding the active material uncoated portions 211B, 221B, thereby forming grooves 43. A load was then applied from the outer circumferential direction of the ends 41, 42 so that the active material uncoated portions 211B, 221B would bend toward the through-holes 26. The same pressure was then applied to the active material uncoated portions 211B, 221B simultaneously from both sides in the Z direction, thereby forming the ends 41, 42 into flat surfaces. Thereafter, the sector-shaped portion 31 of the positive electrode current collector 30A was laser-welded to the end 41, and the sector-shaped portion 33 of the negative electrode current collector 30B was laser-welded to the end 42.

[0077] Thereafter, strip-shaped portions 32 and 34 of current collector plates 30A and 30B were folded, and insulating plates 12 and 13 were attached to positive current collector plate 30A and negative current collector plate 30B. Electrode wound body 20 assembled through the above steps was inserted into outer can 11, and the bottom of outer can 11 was welded. Electrolyte was poured into outer can 11, and then it was sealed with gasket 15 and battery lid 14.

[0078] Here, the fabricated battery according to Test Example 1-1 was fully discharged, and then the outer can 11 was punctured and centrifuged to analyze the collected electrolyte solution. As a result, the contents of FEC, LiBF4, and SN were as shown in Table 1. Here, the contents of other components shown in Table 1 in the electrolyte solution according to Test Example 1-1 were 11.4 mass% for EC, 59.87 mass% for DMC, and 16.2 mass% for LiPF6. The analysis of the electrolyte solution was performed using a gas chromatography mass spectrometer.

[0079] (Test Examples 1-2 to 1-7) The batteries according to Test Examples 1-2 to 1-7 were fabricated in the same manner as in Example 1-1, except that the FEC content of the electrolyte solution was adjusted to the content shown in Table 1. In addition, among the components of the electrolyte solutions according to Test Examples 1-2 to 1-7, the contents of the other components shown in Table 1 were adjusted so that the mass ratio of (EC+FEC):DMC and the molar concentration of LiPF6 (mol / kg) were the same as those of the electrolyte solution according to Test Example 1-1.

[0080] (evaluation) The number of low-temperature cycles was measured for the batteries fabricated in Test Examples 1-1 to 1-7. The number of low-temperature cycles was defined as the number of charge / discharge cycles at which the charge / discharge capacity of the battery first became less than 40% of that at the initial charge / discharge, and the measurement was performed under the following conditions. Charging was performed using the CCCV method until the current became equal to the charge cutoff current. Discharging was performed using the CC method until the voltage reached the discharge cutoff voltage. ·Measurement temperature: 0℃ Charging voltage: 4.2V ·Charging current: 6.5A Charging cutoff current: 0.1A ·Discharge current: 15A Discharge cut-off voltage: 2.5V Rest time between charges and discharges: 30 minutes

[0081] The high temperature cutoff time was measured for the batteries fabricated according to Test Examples 1-1 to 1-7. The high temperature cutoff time was measured by leaving the battery in an incubator at 80° C. Here, the high temperature cutoff time was defined as the time from when the battery was placed in the incubator until the safety valve mechanism 16 ruptured.

[0082] For the batteries according to Test Examples 1-1 to 1-7, those that had a low-temperature cycle count of 500 or more and a high-temperature cutoff time of 100 hours or more were rated as passing (rating A), and the others were rated as failing (rating B).

[0083] (result) As shown in Table 1, Test Examples 1-2 to 1-6, which are working examples, were judged to have passed the test because the number of low-temperature cycles was 500 or more and the high-temperature cutoff time was 100 or more hours. It can be seen that the batteries according to Test Examples 1-2 to 1-6 can increase the number of low-temperature cycles while suppressing gas generation. On the other hand, Test Example 1-1, which is a comparative example, was judged to have failed the test because the high-temperature cutoff time was 20 hours. It can be seen that the battery according to Test Example 1-1 cannot suppress gas generation due to the excessive FEC content. Furthermore, Test Example 1-7, which is a comparative example, was judged to have failed the test because the low-temperature cycles were 300 times. It can be seen that the battery according to Test Example 1-7 cannot improve the low-temperature cycle characteristics due to the insufficient FEC content.

[0084] Table 2 shows the measurement results of the batteries according to Test Examples 2-1 to 2-7.

[0085] [Table 2]

[0086] (Test Examples 2-1 to 2-7) The batteries according to Test Examples 2-1 to 2-7 were fabricated in the same manner as in Example 1-1, except that the FEC and LiBF4 contents in the electrolytes were adjusted to the contents shown in Table 2. In addition, the contents of the other components shown in Table 2 among the components of the electrolytes according to Test Examples 2-1 to 2-7 were adjusted so that the mass ratio of (EC+FEC):DMC and the molar concentration of LiPF6 (mol / kg) were the same as those of the electrolyte according to Test Example 1-1.

[0087] (evaluation) The battery resistance was measured for the batteries fabricated in Test Examples 2-1 to 2-7. The battery resistance was determined by measuring the AC impedance of the fabricated batteries at 1 kHz over a voltage range of 3.35 V to 3.55 V. A HIOKI Battery HiTester 3561 was used to measure the battery resistance.

[0088] The storage life of the batteries fabricated in Test Examples 2-1 to 2-7 was measured. The storage life was measured by leaving the fabricated batteries in a fully charged state at a high temperature of 60°C. The storage life was defined as the time from when the battery was placed in a thermostatic chamber at 60°C until the voltage fell below 4.0V due to a short circuit.

[0089] For the batteries according to Test Examples 2-1 to 2-7, those having a battery resistance of 6.2 mΩ or less and a storage life of 600 hours or more were rated as passing (evaluation A), and others were rated as failing (evaluation B).

[0090] (result) As shown in Table 2, Test Examples 2-2 to 2-6, which are working examples, were judged to have passed the test because the battery resistance was 6.2 mΩ or less and the storage life was 600 hours or more. It can be seen that the batteries according to Test Examples 2-2 to 2-6 can improve the storage life while suppressing an increase in battery resistance. On the other hand, Test Example 2-1, which is a comparative example, was judged to have failed the test because the battery resistance was 6.9 mΩ. It can be seen that the battery according to Test Example 2-1 contains an excessive amount of LiBF4, which increases the resistance. Furthermore, Test Example 2-7, which is a comparative example, was judged to have failed the test because the storage life was 400 hours. It can be seen that the battery according to Test Example 2-7 has a short storage life due to a lack of LiBF4.

[0091] Table 3 shows the measurement results of the batteries according to Test Examples 3-1 to 3-7.

[0092] [Table 3]

[0093] (Test Examples 3-1 to 3-7) The batteries according to Test Examples 3-1 to 3-7 were fabricated in the same manner as in Example 1-1, except that the FEC and SN contents of the electrolytes were adjusted to the contents shown in Table 3. In addition, the contents of the other components shown in Table 3 among the components of the electrolytes according to Test Examples 3-1 to 3-7 were adjusted so that the mass ratio of (EC+FEC):DMC and the molar concentration of LiPF6 (mol / kg) were the same as those of the electrolyte according to Test Example 1-1.

[0094] (evaluation) The battery resistance and storage life of the fabricated batteries according to Test Examples 3-1 to 3-7 were measured in the same manner as in Test Examples 2-1 to 2-7.

[0095] For the batteries according to Test Examples 3-1 to 3-7, those having a battery resistance of 6.2 mΩ or less and a storage life of 600 hours or more were rated as passing (evaluation A), and others were rated as failing (evaluation B).

[0096] (result) As shown in Table 3, Test Examples 3-2 to 3-6, which are working examples, were deemed to have passed the test because the battery resistance was 6.2 mΩ or less and the storage life was 600 hours or more. It can be seen that the batteries according to Test Examples 3-2 to 3-6 were able to improve the storage life while suppressing an increase in battery resistance. On the other hand, Test Example 3-1, which is a comparative example, was deemed to have failed the test because the battery resistance was 7.4 mΩ. It can be seen that the battery according to Test Example 3-1 had an increased resistance due to the excessive amount of SN in the electrolyte. Furthermore, Test Example 3-7, which is a comparative example, was deemed to have failed the test because its storage life was 500 hours. It can be seen that the battery according to Test Example 3-7 had a short storage life due to a lack of SN.

[0097] The above-described embodiments are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present disclosure.

[0098] For example, a battery 1 according to another embodiment of the present invention includes an electrode winding body 20 having a structure in which a strip-shaped positive electrode 21 including a positive electrode foil 211 and a positive electrode active material layer 212, and a strip-shaped negative electrode 22 including a negative electrode foil 221 and a negative electrode active material layer 222 are stacked and wound with a separator 23 interposed therebetween, a positive electrode current collector 30A, a negative electrode current collector 30B, and an electrolyte, all of which are housed in an outer can 11. The positive electrode foil 211 has a positive electrode active material coated portion 211A coated with the positive electrode active material layer 212 and a positive electrode active material uncoated portion 211B not coated with the positive electrode active material layer 212, and the negative electrode foil 221 has an anode active material coated portion 221A coated with the anode active material layer 222 and a cathode active material uncoated portion 211B not coated with the anode active material layer 222. The electrode winding body 20 has a negative electrode active material uncoated portion 221B that is not covered with a positive electrode active material, the positive electrode active material uncoated portion 211B being joined to the positive electrode current collector 30A at one end 41 of the electrode winding body 20, and the negative electrode active material uncoated portion 221B being joined to the negative electrode current collector 30B at the other end 42 of the electrode winding body 20, the one end 41 forming a surface where the positive electrode active material uncoated portions 211B bent toward the central axis of the wound structure overlap, and the other end 42 forming a surface where the negative electrode active material uncoated portions 221B bent toward the central axis of the wound structure overlap, and the electrolyte further contains 0.392 mass % or more and 0.588 mass % or less of succinonitrile (SN). As a result, SN captures metal ions in the electrolyte and prevents them from depositing on the surface of the negative electrode 22, thereby suppressing an increase in battery resistance and suppressing battery short-circuiting due to deposition of transition metals. [Explanation of symbols]

[0099] 1 battery 11 Outer can 11N open end 11P Bending part 11R crimped structure 12, 13 Insulating plate 14 Battery cover 15 Gasket 16 Safety valve mechanism 20 Electrode winding body 21 Positive electrode 21A top end 211 Positive electrode foil 212 Cathode active material layer 211A Positive electrode active material coating 211B Positive electrode active material uncoated part 213 Insulating Layer 22 Negative electrode 22A top end 221 Negative electrode foil 222 Negative electrode active material layer 221A Negative electrode active material coating 221B Negative electrode active material uncoated part 23 Separator 26 Through hole 30A positive current collector 30B Negative current collector plate 31 Fan-shaped section 32 Belt 32A Insulation 32B connection 33 Fan-shaped section 34 Belt 35, 36 holes 37 Protrusion 41, 42 End 43 Groove

Claims

1. a rolled electrode body having a structure in which a strip-shaped positive electrode including a positive electrode foil and a positive electrode active material layer and a strip-shaped negative electrode including a negative electrode foil and a negative electrode active material layer are stacked with a separator interposed therebetween and wound around a central axis; A positive electrode current collector plate; A negative electrode current collector plate; An electrolyte; However, in a battery housed in an outer can, the positive electrode foil has a positive electrode active material coated portion that is coated with the positive electrode active material layer and a positive electrode active material uncoated portion that is not coated with the positive electrode active material layer, the negative electrode foil has a negative electrode active material coated portion that is coated with the negative electrode active material layer and a negative electrode active material uncoated portion that is not coated with the negative electrode active material layer, a surface where the positive electrode active material uncovered portion bent toward the central axis overlaps with the positive electrode current collector plate and is joined to the positive electrode active material uncovered portion; a surface where the negative electrode active material uncovered portion bent toward the central axis overlaps with the negative electrode current collector plate and is joined to the negative electrode active material uncovered portion; The battery, wherein the electrolyte solution contains 7.7% by mass or more and 11.5% by mass or less of fluoroethylene carbonate, 0.032% by mass or more and 0.048% by mass or less of lithium tetrafluoroborate, and lithium hexafluorophosphate.

2. 2. The battery according to claim 1, wherein the electrolyte further contains 0.392% by mass or more and 0.588% by mass or less of succinonitrile.

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