JP2008047303A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of preventing swelling or deformation caused by charging and discharging. <P>SOLUTION: A wound-around body 1 made by winding a laminate 2 at least containing a cathode, an anode having an anode active material layer containing Si or Sn, and a separator intercalated between these with a core material 3 at the center. In a second-round and further winding, the laminate 2 is wound around so as a distance between the anodes in a radius direction of the wound-around body 1 to satisfy the following formula (1). As to the first winding of the wound-around body 1, the laminate 2 is preferred to be wound so as not to bring forth a gap between the laminate 2 and the core material 3. Here, the formula (1) is: a distance between the anodes=a thickness of the cathode+a thickness of the separator+a thickness of the anode+a thickness of the anode active material layer×0.5 to 3.0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery such as a lithium secondary battery.

  As a form of the lithium secondary battery, a cylindrical battery is known which includes a wound body obtained by integrally winding a positive electrode and a negative electrode with a separator interposed therebetween. In the manufacture of a cylindrical battery, first, a positive electrode or the like is wound around a winding core a predetermined number of times to obtain a wound body. The wound body is removed from the winding core, and then a core material called a center pin is inserted into the center of the wound body, and the wound body is housed in a battery can together with the center pin (see, for example, Patent Document 1). However, when a battery is manufactured by this method, a gap is generated between the center portion of the wound body and the center pin. This gap may cause buckling of the electrode due to expansion and contraction of the wound body due to charging / discharging of the battery.

  Therefore, it has been proposed to manufacture a battery without inserting a center pin in the center of the wound body in a later process. For example, Patent Document 2 proposes a lithium secondary battery including an electrode winding group in which a positive electrode and a negative electrode are wound around a core member via a separator. According to the description of Patent Document 2, in this battery, since the positive electrode and the negative electrode are wound around the core material to form an electrode winding group, the electrode winding in which the positive electrode and the negative electrode are wound tightly It is said that the electrode winding group is firmly fixed in the battery outer can after the injection of the electrolytic solution, so that the electrode winding group is less likely to be displaced and the battery reliability is improved. .

  The negative electrode active material used in Patent Document 2 is a carbon-based material such as graphite. Since graphite has a small degree of expansion and contraction due to insertion and extraction of lithium, even if the negative electrode or the like is wound tightly, the influence of the expansion and contraction of the electrode winding group caused by insertion and extraction of lithium of the negative electrode active material is small. However, silicon-based materials and tin-based materials, which have been proposed as next-generation negative electrode active materials and have larger capacities than carbon-based materials, have larger volume changes caused by charging / discharging than the above-described graphite. Therefore, when a negative electrode using these materials as a negative electrode active material is tightly wound, the degree of expansion of the negative electrode active material due to lithium occlusion and release is large, which causes battery expansion and deformation. Although it is possible to suppress such expansion at the central portion where the core material is disposed in the electrode winding group, it is difficult to suppress the expansion at other parts, and as a result, deformation such as buckling of the negative electrode is difficult. Will occur.

Japanese Patent Laid-Open No. 4-332481 JP 2001-126769 A

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that can eliminate the various disadvantages of the above-described prior art.

The present invention provides a wound body in which a laminate including at least a positive electrode, a negative electrode having a negative electrode active material layer containing Si or Sn, and a separator interposed therebetween is wound around a core material. A non-aqueous electrolyte secondary battery provided,
In the second and subsequent windings, the laminate is wound such that the distance between the negative electrodes in the radial direction of the wound body satisfies the following formula (1): An electrolyte secondary battery is provided.
Distance between negative electrodes = positive electrode thickness + separator thickness + negative electrode thickness + negative electrode active material layer thickness × 0.5 to 3.0 (1)

The present invention also provides a method for producing a non-aqueous electrolyte secondary battery,
Each of which is in the form of a long strip, including at least a positive electrode, a separator, and a negative electrode that are unrolled from a roll-shaped raw material in this order and wound together around a core material,
In the first winding, the winding tension is increased so that no gap is generated around the core material.
In the second and subsequent windings, the winding tension is set lower than the winding tension during winding of the first circumferential surface.
The wound body thus obtained is accommodated in a battery can without pulling out the core material, and a method for producing a non-aqueous electrolyte secondary battery is provided.

  According to the present invention, the wound body composed of the positive electrode and the negative electrode is not in a state of being strongly wound, and has a void in the wound body. The voids can alleviate the expansion of the negative electrode caused by the negative electrode active material occludes lithium. As a result, expansion and deformation of the battery can be prevented. In addition, since the core material is provided at the center of the wound body, even if the stress caused by the expansion of the negative electrode is locally applied to the center of the wound body, the buckling of the negative electrode is caused by the core material. It is suppressed.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The nonaqueous electrolyte secondary battery of the present invention (hereinafter also simply referred to as a secondary battery or a battery) has a positive electrode, a negative electrode, and a separator disposed between them as its basic constituent members. The battery includes a wound body formed by integrally winding a positive electrode, a negative electrode, and a separator interposed therebetween. The wound body may have a circular or oval cross-sectional shape. When the positive electrode active material layer and the negative electrode active material layer are formed only on one surface of the current collector of the positive electrode and the negative electrode, a separator is interposed between the active material layers facing each other. Let these three parties wind up. When the positive electrode active material layer and the negative electrode active material layer are formed on both surfaces of the current collector of the positive electrode and the negative electrode, a separator is interposed between the positive electrode and the negative electrode facing each other. The second separator is disposed on the outer surface of the electrode or the outer surface of the negative electrode, and these four members are wound. The space between the positive electrode and the negative electrode is filled with a non-aqueous electrolyte via a separator. The battery of the present invention may be in the form of a cylinder or a square having such a wound body.

  FIG. 1 shows an embodiment of a wound body 1 in a battery of the present invention. The wound body 1 has a cylindrical shape in which a laminated body 2 including at least a positive electrode, a negative electrode, and a separator interposed therebetween is wound around a core material 3. The laminate 2 is composed of a positive electrode, a negative electrode, and a separator, or is composed of a positive electrode, a negative electrode, a first separator, and a second separator. As will be described later, in the wound body 1, the laminated body 2 is strongly wound around the first round and is loosely wound around the second round so that a gap is generated between the laminated bodies 2. In FIG. 1, for the sake of convenience, the gap is not shown.

  The core material 3 in the wound body 1 is hollow or solid cylindrical. The core material 3 is preferably made of a high-strength material from the viewpoint of preventing the negative electrode buckling described later. The core material 3 is also preferably lightweight from the viewpoint of increasing the weight energy density of the battery. From these viewpoints, the core material 3 is preferably made of a polyolefin-based resin such as polyethylene or polypropylene. In that case, it is preferable to add glass fiber for strength improvement. Moreover, the core material 3 may be comprised from metals, such as copper.

The positive electrode used in the battery of the present invention has, for example, a positive electrode active material layer formed on at least one surface of a current collector. The positive electrode active material layer contains an active material. As this active material, for example, a lithium transition metal composite oxide is used. LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ or the like is used. However, it is not limited to these. These positive electrode active materials can be used singly or in combination of two or more.

  In the positive electrode used in the present invention, the positive electrode active material is suspended in a suitable solvent together with a conductive agent such as acetylene black and a binder such as polyvinylidene fluoride to produce a positive electrode mixture, which is made of aluminum foil or the like. It is obtained by rolling and pressing after applying and drying on at least one surface of the current collector.

  When the positive electrode is produced by the above method, the average value of the primary particle diameter of the lithium transition metal composite oxide is preferably 5 μm or more and 10 μm or less in view of the packing density and the reaction area. The polyvinylidene fluoride used as the binder preferably has a weight average molecular weight of 350,000 or more and 2,000,000 or less from the viewpoint of improving discharge characteristics in a low temperature environment.

  The negative electrode used in the battery of the present invention has, for example, a negative electrode active material layer formed on at least one surface of a current collector. The negative electrode active material layer contains an active material. The active material used in the present invention is a material containing Si or Sn. The negative electrode active material containing Si or Sn has a property of expanding when lithium is occluded and contracting when released. The degree of expansion and contraction is extremely large as compared with the carbon-based material that has been used as the negative electrode active material of the conventional lithium secondary battery.

  The negative electrode active material containing Si is capable of occluding and releasing lithium ions. For example, silicon alone, an alloy of silicon and metal, silicon oxide, or the like can be used. These materials can be used alone or in combination. Examples of the metal include one or more elements selected from the group consisting of Cu, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Among these metals, Cu, Ni, and Co are preferable, and Cu and Ni are preferably used from the viewpoint of excellent electronic conductivity and a low ability to form a lithium compound. Further, lithium may be occluded in an active material made of a silicon-based material before or after the negative electrode is incorporated in the battery. A particularly preferable silicon-based material is silicon or silicon oxide in view of the high occlusion amount of lithium.

  On the other hand, as an example of the negative electrode active material containing Sn, tin alone, an alloy of tin and metal, or the like can be used. These materials can be used alone or in combination. Examples of the metal that forms an alloy with tin include one or more elements selected from the group consisting of Cu, Ni, Co, Cr, Fe, Ti, Pt, W, Mo, and Au. Of these metals, Cu, Ni, and Co are preferable, and Cu and Ni are particularly preferable.

  The negative electrode active material layer can be, for example, a continuous thin film layer made of the negative electrode active material, a coating layer containing particles of the negative electrode active material, a sintered body layer containing particles of the negative electrode active material, and the like. Moreover, it may be a layer having a structure shown in FIG.

  As the separator in the battery of the present invention, a synthetic resin nonwoven fabric, a polyolefin such as polyethylene or polypropylene, or a polytetrafluoroethylene porous film is preferably used. From the viewpoint of suppressing the heat generation of the electrode that occurs when the battery is overcharged, it is preferable to use a separator in which a thin film of a ferrocene derivative is formed on one side or both sides of a polyolefin microporous membrane. The separator preferably has a puncture strength of 0.2 N / μm thickness or more and 0.49 N / μm thickness or less, and a tensile strength in the winding axis direction of 40 MPa or more and 150 MPa or less. This is because even when a negative electrode active material that greatly expands and contracts with charge and discharge is used, damage to the separator can be suppressed, and occurrence of internal short circuits can be suppressed.

The nonaqueous electrolytic solution is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. The lithium _{salt, CF 3 SO 3 Li, (} CF 3 SO 2) NLi, (C 2 F 5 SO 2) 2 NLi, LiClO 4, LiA1Cl 4, LiPF 6, LiAsF 6, LiSbF 6, LiCl, LiBr, LiI And LiC ₄ F ₉ SO ₃ . These can be used alone or in combination of two or more. Of these lithium salts, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) NLi, and (C ₂ F ₅ SO ₂ ) ₂ NLi are preferably used because of their excellent water decomposition resistance. Examples of the organic solvent include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, butylene carbonate, and the like. In particular, 0.5 to 5% by weight of vinylene carbonate and 0.1 to 1% by weight of divinyl sulfone and 0.1 to 1.5% by weight of 1,4-butanediol dimethanesulfonate with respect to the whole non-aqueous electrolyte It is preferable from the viewpoint of further improving the charge / discharge cycle characteristics. The details are not clear, but 1,4-butanediol dimethanesulfonate and divinylsulfone are decomposed stepwise to form a film on the positive electrode, so that the film containing sulfur becomes denser. It is thought that it is to become.

  In particular, non-aqueous electrolytes include 4-fluoro-1,3-dioxolan-2-one, 4-chloro-1,3-dioxolan-2-one or 4-trifluoromethyl-1,3-dioxolane-2- It is also preferable to use a high dielectric constant solvent having a relative dielectric constant of 30 or more, such as a cyclic carbonate derivative having a halogen atom such as ON. This is because it has high resistance to reduction and is not easily decomposed. Further, an electrolytic solution obtained by mixing the high dielectric constant solvent and a low viscosity solvent having a viscosity of 1 mPa · s or less such as dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate is also preferable. This is because higher ionic conductivity can be obtained. Furthermore, it is also preferable that the content of fluorine ions in the electrolytic solution is in the range of 14 mass ppm to 1290 mass ppm. This is because, when an appropriate amount of fluorine ions is contained in the electrolytic solution, a coating film such as lithium fluoride derived from fluorine ions is formed on the negative electrode, and it is considered that the decomposition reaction of the electrolytic solution in the negative electrode can be suppressed. . Furthermore, it is preferable that at least one additive selected from the group consisting of acid anhydrides and derivatives thereof is contained in an amount of 0.001 wt% to 10 wt%. This is because a film is formed on the surface of the negative electrode, and the decomposition reaction of the electrolytic solution can be suppressed. As this additive, a cyclic compound containing a —C (═O) —O—C (═O) — group in the ring is preferable. For example, succinic anhydride, glutaric anhydride, maleic anhydride, phthalic anhydride, anhydrous Phthalic anhydride derivatives such as 2-sulfobenzoic acid, citraconic anhydride, itaconic anhydride, diglycolic anhydride, hexafluoroglutaric anhydride, 3-fluorophthalic anhydride, 4-fluorophthalic anhydride, or anhydrous 3,6 -Epoxy-1,2,3,6-tetrahydrophthalic acid, 1,8-naphthalic anhydride, 2,3-naphthalene carboxylic acid anhydride, 1,2-cyclopentane dicarboxylic acid anhydride, 1,2-cyclohexane dicarboxylic acid, etc. 1,2-cycloalkanedicarboxylic anhydride, or cis-1,2,3,6-tetrahydrophthalic anhydride or 3,4,5,6-tetrahydrophthal Tetrahydrophthalic anhydride such as acid anhydride, or hexahydrophthalic anhydride (cis isomer, trans isomer), 3,4,5,6-tetrachlorophthalic anhydride, 1,2,4-benzene Examples thereof include tricarboxylic acid anhydride, dianhydropyromellitic acid, and derivatives thereof.

The wound body 1 in the battery of this embodiment is characterized by its wound state. Details are as follows. In the winding of the first round of the wound body 1, the laminated body 2 is wound so that a substantial gap does not occur between the laminated body 2 and the core material 3. Further, in the second and subsequent windings, the laminate 2 is wound so that the distance between the negative electrodes in the radial direction of the wound body 1 satisfies the following formula (1). In addition, the winding state demonstrated here is a thing regarding the state before a battery is charged / discharged.
Distance between negative electrodes = positive electrode thickness + separator thickness + negative electrode thickness + negative electrode active material layer thickness × 0.5 to 3.0 (1)

  In this embodiment, the technical significance of winding the laminate 2 as described above is as follows. First, for winding of the first round, the stress generated due to the expansion of the negative electrode active material by winding the laminated body 2 so that no gap is generated between the laminated body 2 and the core material 3. Even if it is locally applied to the center of the wound body 1, the core material 3 can receive the stress. As a result, buckling of the negative electrode is suppressed by the core material 3. When a gap is generated between the laminate 2 and the core material in the first winding, the negative electrode is deformed toward the gap due to expansion of the negative electrode active material, and buckling occurs. End up.

  Next, with respect to winding after the second round, winding the laminated body so as to satisfy the above formula (1) is performed so that voids are generated in the laminated body 2 after winding the second round. Means to do. Since the laminate 2 includes the positive electrode, the negative electrode, and the separator, the generation of voids in the laminate 2 is the same as the generation of voids between these members. Therefore, in the above formula (1), the left side is the distance between the negative electrodes, but even if this is the distance between the positive electrodes or the distance between the separators, there is no change to the formula on the right side. In addition, the distance between negative electrodes is the distance between the thickness direction center parts of a negative electrode. The same applies to the distance between the positive electrodes and the distance between the separators.

  The degree of the above-described void is expressed by the term [negative electrode active material layer thickness × 0.5 to 3.0] in the above formula (1). By performing winding so that such voids are generated, the expansion of the negative electrode caused by the negative electrode active material occlusion of lithium can be reduced by the voids. As a result, expansion and deformation of the battery can be prevented. If the degree of voids is less than [negative electrode active material layer thickness x 0.5], the expansion of the negative electrode due to the occlusion of lithium cannot be reliably relieved, and the battery will expand and deform. . If the degree of voids exceeds [negative electrode active material layer thickness x 3.0], the winding of the laminate 2 in the wound body 1 tends to be displaced, and the reliability of the battery decreases. From the viewpoint of further reducing the expansion of the negative electrode and preventing the winding of the laminate 2 from shifting, the degree of voids is preferably [negative electrode active material layer thickness × 0.5 to 1.5]. . In addition, the negative electrode active material layer thickness in the case where the active material layer is formed on each surface of the current collector is the sum of the thicknesses of the active material layers.

  It is most preferable that the voids exist uniformly over the entire radial direction of the wound body 1, but within a range that does not impair the effects of the present invention, the gap is partially in the radial direction of the wound body 1. It is not prevented that there is a portion that does not fill the void.

  FIG. 2 schematically shows an example of a method for manufacturing a wound body in the battery of the present embodiment, and FIG. 3 shows an enlarged view of the main part in FIG. In this embodiment, as shown in FIG. 2, first, the members constituting the battery are overlapped. The constituent members used here are the four members of the first separator S1, the second separator S2, the positive electrode C, and the negative electrode A. All of these members have a long strip shape. The widths of the first separator S1 and the second separator S2 are wider than the widths of the positive electrode C and the negative electrode A.

  In FIG. 2, spacer members P1 and P2, which will be described later, are already attached to the negative electrode A before winding, but this is shown for convenience in understanding the invention. Actually, the spacer members P1 and P2 are not attached to the negative electrode A before winding.

  In the four members, the positive electrode C, the first separator S1, and the negative electrode A are overlapped in this order, and the second separator S2 is overlapped on the outer surface of the negative electrode A. And the laminated body which consists of these four members is integrally wound around the core material. In overlapping of each member, adjacent members are in contact only by overlapping, and are not joined by a joining means such as an adhesive. That is, each member is only in contact with each other so as to be mechanically peelable.

  The above-mentioned members are superposed in the order described above and wound to obtain a wound body (not shown). As shown in FIG. 2, the winding is performed so that the positive electrode C side faces inward. By winding in this way, in the wound body, the positive electrode C, the first separator S1, the negative electrode A, and the second separator S2 are arranged in layers in this order.

  The positive electrode C is formed by forming an active material layer (not shown) containing a positive electrode active material on each surface of a current collector (not shown). On the other hand, the negative electrode A is formed by forming an active material layer (not shown) containing a negative electrode active material capable of occluding and releasing lithium on each surface of a current collector (not shown).

  Prior to the superposition of these four members, the first spacer member P1 is disposed between the first separator S1 and the negative electrode A over the longitudinal direction of these members. At the same time, a second spacer member P2 is disposed between the second separator S2 and the negative electrode A over the longitudinal direction of these members. However, these spacer members P1 and P2 are not arranged in the first round of winding, but are arranged in the second and subsequent rounds. In the first round of winding, these four members are wound around the core material so that no gap is generated between the four members. Both spacer members P1 and P2 are discontinuously arranged at a predetermined interval over the entire lengthwise direction of the negative electrode A or the like. The first spacer member P1 and the second spacer member P2 may have the same shape or different shapes. Further, the same material or different materials may be used. In the present embodiment, the first spacer member P1 and the second spacer member P2 have the same shape and the same material. Both spacer members P1, P2 are rectangular, and are arranged so that their long sides coincide with the width direction of the negative electrode A or the like.

  The long sides of the first and second spacer members P1, P2 are larger than the width of the negative electrode A or the like. Both spacer members P1 and P2 having such a shape are arranged between the negative electrode A and the separators S1 and S2 so that their longitudinal ends extend from the side edges of the negative electrode A or the like. . Specifically, as shown in FIG. 3, with respect to the arrangement position of the first spacer member P1, the first short side M1 and the first side edge L1 such as the negative electrode A coincide with each other, and the second short side The end portion on the M2 side is arranged to extend from the second side edge L2 of the negative electrode A or the like. Regarding the second spacer member P2, the first short side N1 and the second side edge L2 of the negative electrode A and the like coincide with each other, and the end on the second short side N2 side is the first side of the negative electrode A and the like. It is arranged to extend from the edge L1.

  As shown in FIG. 3, the first spacer member P1 and the second spacer member P2 are arranged so as to have a positional relationship that does not overlap with each other when viewed in plan in a state before winding. The The spacer members P1 and P2 are arranged such that a gap G is formed between their adjacent long sides when they are viewed in plan before winding. By arranging both spacer members P1 and P2 in this way, when a cylindrical wound body is configured, an excessive space is prevented from being formed between the negative electrode A and both separators S1 and S2. be able to. If excessive space is formed, sagging may occur in the wound body. Moreover, it can prevent that an unevenness | corrugation is formed in the surrounding surface of a cylindrical winding body by arrange | positioning both spacer members P1 and P2 in this way.

  By arranging the first and second spacer members P1 and P2 in this way, the wound body R in the state shown in FIG. 4A is obtained. The wound body R has a cylindrical shape, and the end portions of both spacer members P1, P2 protrude from the upper and lower surfaces thereof. In the wound body R, the negative electrode A and the separators S1 and S2 are separated from each other by the thickness of the spacer members P1 and P2.

  Next, both spacer members P1, P2 are removed from the wound body R in the state shown in FIG. As a means for removing both spacer members P1, P2 from the wound body R, in this embodiment, a method of pulling out and removing both spacer members P1, P2 from the wound body R is adopted. In this case, the first spacer member P1 and the second spacer member P2 are pulled out simultaneously and at the same speed in directions opposite to each other by 180 degrees. By pulling out both spacer members P1, P2 under such conditions, both spacer members P1, P2 can be successfully removed without impairing the winding state of the wound body R. By removing both spacer members P1, P2, a space corresponding to the thickness of the removed spacer members P1, P2 is formed between the negative electrode A and both separators S1, S2. The wound body R from which the spacer members P1 and P2 are removed is accommodated in the battery can without pulling out the core material.

  As described above, the spacer members P1 and P2 used in this embodiment are made of a material that is not occluded by the active material of the negative electrode A. Specifically, both spacer members P1, P2 can be made of plastic or paper. Both spacer members P1, P2 can also be made of metal. When producing a 18650 type battery, it is sufficient that the spacer members P1 and P2 have a thickness of 10 to 200 μm, particularly 15 to 100 μm, between the negative electrode A and the separators S1 and S2. It is preferable from the point that a simple space can be formed. The spacer members P1 and P2 have a short side length of 5 to 100 mm, particularly preferably 5 to 30 mm. The gap G between adjacent long sides of the spacer members P1 and P2 is preferably 3 to 60 mm, particularly preferably 5 to 50 mm.

  FIG. 5 shows another example of a method for manufacturing a wound body in the battery of the present embodiment. The points described above with reference to FIGS. 2 to 4 are appropriately applied to points that are not particularly described with respect to this manufacturing method. Also in this manufacturing method, the laminated body formed by laminating the positive electrode C, the first separator S1, the negative electrode A, and the second separator S2 is wound to obtain the wound body R. However, in this manufacturing method, unlike the manufacturing methods shown in FIGS. 2 to 4, the spacer members P1 and P2 are not used. In this manufacturing method, instead of using the spacer members P1 and P2, in the manufacturing method, the feeding tension of the positive electrode C, the first separator S1, the negative electrode A, and the second separator S2 is individually controlled to increase the strength of the winding. You are controlling.

  Specifically, the rotations of the feeding devices for the positive electrode C, the first separator S1, the negative electrode A, and the second separator S2 are controlled by individual motors. That is, the positive electrode C, the first separator S1, the negative electrode A, and the second separator S2 are not drawn out by the rotation. By individually controlling the feeding speed of these members with a motor, their tensions are individually controlled. As a result, the strength of winding of these members in the wound body R is controlled.

  Specifically, when each of the positive electrode C, the first separator S1, the negative electrode A, and the second separator S2 each having a long strip shape is unwound from a roll-shaped raw material and wound, In the winding of the circumference, the winding tension is increased so that no gap is generated around the core material. In the second and subsequent windings, the winding is performed with the feeding tension set lower than the feeding tension during winding of the first circumferential surface. And the winding body obtained in this way is accommodated in a battery can, without pulling out a core material.

  FIG. 6 shows a schematic diagram of a cross-sectional structure of a preferred embodiment of the negative electrode used in the present invention. The negative electrode 10 of this embodiment includes a current collector 11 and an active material layer 12 formed on at least one surface thereof. 6 shows a state in which the active material layer 12 is formed only on one surface of the current collector 11 for convenience, the active material layer may be formed on both surfaces of the current collector. .

  In the active material layer 12, at least a part of the surface of the active material particles 12 a containing Si is covered with a metal material having a low lithium compound forming ability. The metal material 13 is a material different from the constituent material of the particles 12a. Gaps are formed between the particles 12a coated with the metal material. That is, the metal material covers the surface of the particle 12a in a state in which a gap is ensured so that the non-aqueous electrolyte containing lithium ions can reach the particle 12a. In FIG. 6, the metal material 13 is conveniently represented as a thick line surrounding the periphery of the particle 12a. This figure is a schematic view of the active material layer 12 viewed two-dimensionally. In reality, each particle is in direct contact with other particles or through a metal material 13. “Low lithium compound forming ability” means that lithium does not form an intermetallic compound or solid solution, or even if formed, lithium is in a very small amount or very unstable.

  The metal material 13 has conductivity, and examples thereof include copper, nickel, iron, cobalt, and alloys of these metals. In particular, the metal material 13 is preferably a highly ductile material in which even if the active material particles 12a expand and contract, the coating on the surface of the particles 12a is not easily broken. It is preferable to use copper as such a material.

  The metal material 13 is preferably present on the surface of the active material particles 12 a over the entire thickness direction of the active material layer 12. The active material particles 12 a are preferably present in the matrix of the metal material 13. Thus, even if the particles 12a are pulverized due to expansion and contraction due to charge / discharge, the particles are less likely to fall off. In addition, since the electronic conductivity of the entire active material layer 12 is ensured through the metal material 13, the electrically isolated active material particles 12 a are generated, and in particular, the electrically isolated active material is deep in the active material layer 12. Generation of the particles 12a of the substance is effectively prevented. The presence of the metal material 13 on the surface of the active material particles 12a over the entire thickness direction of the active material layer 12 can be confirmed by electron microscope mapping using the material 13 as a measurement target.

  The metal material 13 coats the surface of the particle 12a continuously or discontinuously. When the metal material 13 continuously covers the surfaces of the particles 12a, it is preferable to form fine voids in the coating of the metal material 13 that allow the non-aqueous electrolyte to flow. When the metal material 13 discontinuously coats the surface of the particle 12a, the non-aqueous electrolyte is supplied to the particle 12a through a portion of the surface of the particle 12a that is not covered with the metal material 13. In order to form the coating of the metal material 13 having such a structure, the metal material 13 may be deposited on the surfaces of the particles 12a by, for example, electrolytic plating in accordance with conditions described later.

  The average thickness of the metal material 13 covering the surface of the active material particles 12a is preferably 0.05 to 2 μm, more preferably 0.1 to 0.25 μm. That is, the metal material 13 covers the surface of the active material particles 12a with a minimum thickness. As a result, while the energy density is increased, the particles 12a are prevented from falling off due to expansion / contraction and pulverization due to charge / discharge. Here, the “average thickness” is a value calculated based on a portion of the surface of the active material particle 12 a that is actually covered with the metal material 13. Accordingly, the portion of the surface of the active material particle 12a that is not covered with the metal material 13 is not used as a basis for calculating the average value.

  The voids formed between the particles 12a coated with the metal material 13 have a function as a flow path of the non-aqueous electrolyte containing lithium ions. Since the non-aqueous electrolyte smoothly flows in the thickness direction of the active material layer 12 due to the presence of the voids, cycle characteristics can be improved. Further, the voids formed between the particles 12a also have a function as a space for relieving stress caused by the volume change of the active material particles 12a due to charge and discharge. The increase in the volume of the active material particles 12a whose volume has been increased by charging is absorbed by the voids. As a result, pulverization of the particles 12a is difficult to occur, and significant deformation of the negative electrode 10 is effectively prevented.

  As described later, the active material layer 12 is preferably electrolyzed using a predetermined plating bath on a coating film obtained by applying a slurry containing particles 12a and a binder onto a current collector and drying the slurry. It forms by plating and depositing the metal material 13 between the particle | grains 12a.

  In order to form necessary and sufficient voids in the active material layer 12 in which the non-aqueous electrolyte can be circulated, it is preferable to sufficiently infiltrate the plating solution into the coating film. In addition to this, it is preferable to make conditions suitable for depositing the metal material 13 by electrolytic plating using the plating solution. The plating conditions include the composition of the plating bath, the pH of the plating bath, and the current density of electrolysis. Regarding the pH of the plating bath, it is preferable to adjust this to 7.1-11. By controlling the pH within this range, the dissolution of the active material particles 12a is suppressed, the surface of the particles 12a is cleaned, and plating on the particle surface is promoted. Is formed. The value of pH is measured at the temperature at the time of plating.

When using copper as the metal material 13 for plating, it is preferable to use a copper pyrophosphate bath. When nickel is used as the metal material, for example, an alkaline nickel bath is preferably used. In particular, it is preferable to use a copper pyrophosphate bath, even if the active material layer 12 is thick, because the voids can be easily formed over the entire thickness direction of the layer. Further, since the metal material 13 is deposited on the surface of the active material particles 12a and the metal material 13 is less likely to be deposited between the particles 12a, the voids between the particles 12a are also successfully formed. preferable. When using a copper pyrophosphate bath, the bath composition, electrolysis conditions and pH are preferably as follows.
Copper pyrophosphate trihydrate: 85-120 g / l
-Potassium pyrophosphate: 300-600 g / l
-Potassium nitrate: 15-65 g / l
-Bath temperature: 45-60 ° C
・ Current density: 1 to 7 A / dm ²
PH: Ammonia water and polyphosphoric acid are added to adjust the pH to 7.1 to 9.5.

In particular, when a copper pyrophosphate bath is used, it is preferable to use one having a P ratio defined by a ratio of P ₂ O ₇ weight to Cu weight (P ₂ O ₇ / Cu) of 5 to 12. . When the P ratio is less than 5, the metal material 13 covering the active material particles 12a tends to be thick, and it may be difficult to form desired voids between the particles 12a. Further, when a P ratio exceeding 12 is used, current efficiency is deteriorated, and gas generation is likely to occur, so that production stability may be lowered. When a copper pyrophosphate bath having a P ratio of 6.5 to 10.5 is used as a more preferable copper pyrophosphate bath, the size and number of voids formed between the active material particles 12a may be reduced. This is very advantageous for the flow of the water electrolyte.

When an alkaline nickel bath is used, the bath composition, electrolysis conditions and pH are preferably as follows.
Nickel sulfate: 100 to 250 g / l
Ammonium chloride: 15-30 g / l
・ Boric acid: 15-45 g / l
-Bath temperature: 45-60 ° C
・ Current density: 1 to 7 A / dm ²
-PH: 25% by weight ammonia water: Adjust to pH 8-11 within the range of 100-300 g / l.
When this alkaline nickel bath and the above-described copper pyrophosphate bath are compared, there is a tendency that moderate voids are formed in the active material layer 12 when the copper pyrophosphate bath is used, and the life of the negative electrode is increased. It is preferable because it is easy to achieve.

  The characteristics of the metal material 13 can be appropriately adjusted by adding various additives used in the electrolytic solution for producing copper foil such as protein, active sulfur compound, and cellulose to the above various plating baths.

  The ratio of the voids in the entire active material layer formed by the various methods described above, that is, the void ratio is preferably about 15 to 45% by volume, particularly about 20 to 40% by volume. By setting the porosity within this range, it is possible to form necessary and sufficient voids in the active material layer 12 that allow the nonaqueous electrolyte to flow. The void amount of the active material layer 12 is measured by a mercury intrusion method (JIS R 1655). The mercury intrusion method is a method for obtaining information on the physical shape of a solid by measuring the size and volume of pores in the solid. The principle of the mercury intrusion method is to apply a pressure to mercury to inject it into the pores of the object to be measured, and to measure the relationship between the pressure applied at that time and the volume of mercury that has been pushed in (intruded). In this case, mercury enters sequentially from the large voids present in the active material layer 12. In the present invention, the void amount measured at a pressure of 90 MPa is regarded as the entire void amount. The porosity (%) of the active material layer 12 is obtained by dividing the void amount per unit area measured by the above method by the apparent volume of the active material layer 12 per unit area and multiplying it by 100. .

The porosity can also be controlled by appropriately selecting the particle size of the active material particles 12a. From this viewpoint, the particle 12a has a maximum particle size of preferably 30 μm or less, more preferably 10 μm or less. Moreover, when the particle diameter of the particle is expressed by a D ₅₀ value, it is preferably 0.1 to 8 μm, particularly preferably 0.3 to 4 μm. The particle size of the particles is measured by laser diffraction / scattering particle size distribution measurement and electron microscope observation (SEM observation).

  If the amount of the active material relative to the whole negative electrode is too small, it is difficult to sufficiently improve the energy density of the battery. Conversely, if the amount is too large, the strength decreases and the active material tends to fall off. Considering these, the thickness of the active material layer is 10 to 40 μm, preferably 15 to 30 μm, and more preferably 18 to 25 μm.

  In the negative electrode 10 of the present embodiment, a thin surface layer (not shown) may be formed on the surface of the active material layer 12. Further, the negative electrode 10 may not have such a surface layer. The thickness of the surface layer is 0.25 μm or less, preferably 0.1 μm or less. There is no restriction | limiting in the lower limit of the thickness of a surface layer. By forming the surface layer, the pulverized active material particles 12a can be further prevented from falling off. However, in the present embodiment, by setting the porosity of the active material layer 12 within the above-described range, it is possible to sufficiently prevent the pulverized active material particles 12a from dropping without using a surface layer. Is possible.

  When the negative electrode 10 has the thin surface layer or does not have the surface layer, a secondary battery is assembled using the negative electrode 10 to reduce the overvoltage when the battery is initially charged. Can do. This means that lithium can be prevented from being reduced on the surface of the negative electrode 10 when the secondary battery is charged. The reduction of lithium leads to the generation of dendrites that cause a short circuit between the two electrodes.

  When the negative electrode 10 has a surface layer, the surface layer covers the surface of the active material layer 12 continuously or discontinuously. When the surface layer continuously covers the surface of the active material layer 12, the surface layer has a large number of microscopic voids (not shown) that are open at the surface and communicate with the active material layer 12. It is preferable. The fine voids are preferably present in the surface layer so as to extend in the thickness direction of the surface layer. The fine voids allow the non-aqueous electrolyte to flow. The role of the fine voids is to supply a non-aqueous electrolyte into the active material layer 12. When the surface of the negative electrode 10 is viewed in plan by electron microscope observation, the fine voids are such that the ratio of the area covered with the metal material 13, that is, the coverage is 95% or less, particularly 80% or less, especially 60% or less. It is preferable that the size is large. When the coverage exceeds 95%, it is difficult for the non-aqueous electrolyte having high viscosity to enter, and the range of selection of the non-aqueous electrolyte may be narrowed.

  The surface layer is made of a metal material having a low lithium compound forming ability. This metal material may be the same as or different from the metal material 13 present in the active material layer 12. The surface layer may have a structure of two or more layers made of two or more different metal materials. Considering the ease of manufacture of the negative electrode 10, the metal material 13 present in the active material layer 12 and the metal material constituting the surface layer are preferably the same type.

  In the negative electrode 10 of this embodiment, when the porosity in the active material layer 12 has the above-described value, the resistance of the negative electrode 10 to bending increases. Specifically, the MIT folding resistance measured according to JIS C 6471 is preferably 30 times or more, more preferably 50 times or more. High folding resistance is extremely advantageous because the negative electrode 10 is less likely to be folded when the negative electrode 10 is folded or wound and accommodated in a battery container. As the MIT folding endurance device, for example, a film folding endurance fatigue tester (product number 549) manufactured by Toyo Seiki Seisakusho is used, and measurement can be performed with a bending radius of 0.8 mm, a load of 0.5 kgf and a sample size of 15 × 150 mm. it can.

  As the current collector 11 in the negative electrode 10, the same one as conventionally used as the current collector of the negative electrode for the non-aqueous electrolyte secondary battery can be used. The current collector 11 is preferably made of a metal material having a low lithium compound forming ability as described above. Examples of such metallic materials are as already described. In particular, it is preferably made of copper, nickel, stainless steel or the like. Also, it is possible to use a copper alloy foil represented by a Corson alloy foil. Further, as the current collector, a metal foil having a normal tensile strength (JIS C 2318) of preferably 500 MPa or more, for example, a copper film layer formed on at least one surface of the aforementioned Corson alloy foil can be used. Furthermore, it is preferable to use a current collector having a normal elongation (JIS C 2318) of 4% or more. This is because when the tensile strength is low, wrinkles are generated due to stress when the active material expands, and when the elongation is low, the current collector may crack. By using these current collectors, it is possible to further improve the folding resistance of the negative electrode 10 described above. The thickness of the current collector 11 is preferably 9 to 35 μm considering the balance between maintaining the strength of the negative electrode 10 and improving the energy density. In addition, when using copper foil as the electrical power collector 11, it is preferable to give the rust prevention process using organic compounds, such as a chromate process and a triazole type compound and an imidazole type compound.

  Next, the preferable manufacturing method of the negative electrode 10 of this embodiment is demonstrated, referring FIG. In this manufacturing method, a coating film is formed on the current collector 11 using a slurry containing particles of an active material and a binder, and then electrolytic plating is performed on the coating film.

  First, a current collector 11 is prepared as shown in FIG. Then, a slurry containing active material particles 12 a is applied onto the current collector 11 to form a coating film 15. The surface roughness of the coating film forming surface of the current collector 11 is preferably 0.5 to 4 μm at the maximum height of the contour curve. If the maximum height exceeds 4 μm, the formation accuracy of the coating film 15 is lowered and current concentration of the permeation plating tends to occur on the convex portions. When the maximum height is less than 0.5 μm, the adhesion of the active material layer 12 tends to be lowered. As the active material particles 12a, those having the above-described particle size distribution and average particle size are preferably used.

  The slurry contains a binder and a diluting solvent in addition to the active material particles. The slurry may contain a small amount of conductive carbon material particles such as acetylene black and graphite. In particular, when the active material particles 12a are made of a silicon-based material, the conductive carbon material is preferably contained in an amount of 1 to 3% by weight based on the weight of the active material particles 12a. When the content of the conductive carbon material is less than 1% by weight, the viscosity of the slurry is lowered and the sedimentation of the active material particles 12a is promoted, so that it is difficult to form a good coating film 15 and uniform voids. . On the other hand, if the content of the conductive carbon material exceeds 3% by weight, plating nuclei concentrate on the surface of the conductive carbon material, and it becomes difficult to form a good coating.

  As the binder, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene propylene diene monomer (EPDM), or the like is used. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used. The amount of the active material particles 12a in the slurry is preferably about 30 to 70% by weight. The amount of the binder is preferably about 0.4 to 4% by weight. A dilution solvent is added to these to form a slurry.

  The formed coating film 15 has a large number of minute spaces between the particles 12a. The current collector 11 on which the coating film 15 is formed is immersed in a plating bath containing a metal material having a low lithium compound forming ability. By immersion in the plating bath, the plating solution enters the minute space in the coating film 15 and reaches the interface between the coating film 15 and the current collector 11. Under this condition, electrolytic plating is performed to deposit plating metal species on the surfaces of the particles 12a (hereinafter, this plating is also referred to as permeation plating). The osmotic plating is performed by using the current collector 11 as a cathode, immersing a counter electrode as an anode in a plating bath, and connecting both electrodes to a power source.

  The deposition of the metal material by the osmotic plating is preferably progressed from one side of the coating film 15 to the other side. Specifically, as shown in FIGS. 7B to 7D, electrolytic plating is performed so that deposition of the metal material 13 proceeds from the interface between the coating film 15 and the current collector 11 toward the surface of the coating film. I do. By precipitating the metal material 13 in this way, the surface of the active material particles 12a can be successfully coated with the metal material 13, and a void is successfully formed between the particles 12a coated with the metal material 13. be able to.

  As described above, the conditions of the infiltration plating for depositing the metal material 13 include the composition of the plating bath, the pH of the plating bath, the current density of electrolysis, and the like. Such conditions are as already described.

  As shown in FIGS. 7B to 7D, when plating is performed so that the deposition of the metal material 13 proceeds from the interface between the coating film 15 and the current collector 11 toward the surface of the coating film. In the forefront portion of the precipitation reaction, fine particles 13a made of plating nuclei of the metal material 13 are present in layers with a substantially constant thickness. As the deposition of the metal material 13 proceeds, adjacent microparticles 13a combine to form larger particles, and when the deposition proceeds further, the particles combine to continuously cover the surface of the active material particles 12a. It becomes like this.

  The permeation plating is terminated when the metal material 13 is deposited on the entire thickness direction of the coating film 15. By adjusting the end point of plating, a surface layer (not shown) can be formed on the upper surface of the active material layer 12. In this way, the target negative electrode is obtained as shown in FIG.

  It is also preferable to subject the negative electrode 10 to rust prevention after the osmotic plating. As the rust prevention treatment, for example, organic rust prevention using triazole compounds such as benzotriazole, carboxybenzotriazole, tolyltriazole, and imidazole, and inorganic rust prevention using cobalt, nickel, chromate and the like can be employed.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
A current collector made of an electrolytic copper foil having a thickness of 18 μm was acid washed at room temperature for 30 seconds. After the treatment, it was washed with pure water for 15 seconds. A slurry containing particles made of silicon was applied on both surfaces of the current collector to a thickness of 20 μm to form a coating film. The composition of the slurry was particles: styrene butadiene rubber (binder): acetylene black = 100: 1.7: 2 (weight ratio). The average particle diameter D ₅₀ of the particles was 2 μm. The average particle diameter D ₅₀ was measured using a Microtrac particle size distribution measuring device (No. 9320-X100) manufactured by Nikkiso Co., Ltd.

The current collector on which the coating film was formed was immersed in a copper pyrophosphate bath having the following bath composition, and copper was permeated to the coating film by electrolysis to form an active material layer. The electrolysis conditions were as follows. DSE was used for the anode. A DC power source was used as the power source.
Copper pyrophosphate trihydrate: 105 g / l
-Potassium pyrophosphate: 450 g / l
・ Potassium nitrate: 30 g / l
-P ratio: 7.7
・ Bath temperature: 50 ° C
・ Current density: 3 A / dm ²
-PH: Ammonia water and polyphosphoric acid were added to adjust to pH 8.2.

  The permeation plating was terminated when copper was deposited over the entire thickness direction of the coating film. In this way, a target negative electrode was obtained. SEM observation of the longitudinal section of the active material layer confirmed that the active material particles were covered with a copper film having an average thickness of 240 nm in the active material layer. The porosity of the active material layer was 30%. The thickness of the active material layer was 20 μm.

LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ was used as the positive electrode active material. This was suspended in polyvinylpyrrolidone as a solvent together with acetylene black and polyvinylidene fluoride to obtain a positive electrode mixture. The positive electrode mixture was applied to a current collector made of aluminum foil and dried, followed by roll rolling and pressing to obtain a positive electrode. The total thickness of the positive electrode including the current collector and the active material layer was 160 μm. Polypropylene porous films having a thickness of 20 μm were used as the first and second separators.

The negative electrode, the positive electrode, and the first and second separators were formed in a long band shape having a width of 60 mm. These members were overlapped in the order shown in FIG. 2 and wound around a core material made of a polypropylene cylindrical tube having a diameter of 4.2 mm. One member of the wound surface wound these members around the core material without any gaps. From the second round onward, first and second spacer members made of nickel were disposed between the negative electrode and the first and second separators. The spacer member had a long side length of 80 mm, a short side length of 2.5 mm, and a thickness of 100 μm. The gap G shown in FIG. 3 was set to 50 mm. The spacer member was pulled out and removed from the wound body, and then the wound body was accommodated in a battery can. The core material was not pulled out when the wound body was accommodated. As the electrolytic solution, a solution obtained by adding 2% by volume of vinylene carbonate to a solution of 1 mol / l LiPF ₆ dissolved in a 1: 1 volume% mixed solvent of ethylene carbonate and diethyl carbonate was used. After filling the electrolytic solution, the battery can was sealed to obtain a lithium secondary battery. The battery had a diameter of 18 mm and a height of 65 mm (type 18650). When the cross section of the battery was CT scanned and the distance between the negative electrodes in the wound body was measured, it was 280 μm.

[Comparative Example 1]
Using the same positive electrode and negative electrode as in Example 1 and the first and second separators, these members were wound around the same core material as in Example 1 to obtain a wound body. The winding was performed so that no gap was generated between these members. After completion of winding, the cylindrical tube was pulled out from the wound body. The wound body after the cylindrical tube was pulled out was housed in a battery can in the same manner as in Example 1 to obtain a lithium secondary battery.

[Evaluation]
The batteries obtained in Examples and Comparative Examples were charged and discharged for 50 cycles. The charging conditions were 0.5 C, final voltage 4.2 V, and constant current / constant voltage (CCCV). The discharge conditions were 0.5 C, final voltage 2.7 V, and constant current (CC). However, charge / discharge at the first cycle is 0.05C, charge / discharge at the second to fourth cycles is 0.1C, charge / discharge at the fifth to seventh cycles is 0.5C, and charge / discharge at the eighth to tenth cycles is 1C. It was. About the battery after 50 cycles of charging / discharging, the cross section was CT-scanned and the state of the wound body was observed nondestructively. The results are shown in FIG. 8 (Example 1) and FIG. 9 (Comparative Example 1). 8 and 9 also show a CT scan image of the battery before charging and discharging.

  As is apparent from the results shown in FIGS. 8 and 9, in the battery of the example, the negative electrode and the like are hardly deformed after 50 cycles of charging and discharging, whereas in the battery of the comparative example, 50 cycles. It can be seen that severe buckling occurs in the negative electrode and the like after charging and discharging. In addition, since the core material used in Example 1 is a product made from a polypropylene, the core material does not appear in FIG. 8 which is the CT scan image.

It is a schematic diagram which shows the structure of the cross section of the winding body in one Embodiment of the battery of this invention. It is a schematic diagram which shows an example of the manufacturing method of the winding body shown in FIG. It is a schematic diagram which shows the arrangement | positioning state by the planar view of a spacer member. It is a perspective view which shows the winding body which has a spacer member. It is a schematic diagram which shows the other example of the manufacturing method of the winding body shown in FIG. It is a schematic diagram which shows the cross-section of one Embodiment of the negative electrode used for this invention. It is process drawing which shows the manufacturing method of the negative electrode shown in FIG. 2 is a CT scan image of a cross section of the battery obtained in Example 1. FIG. 4 is a CT scan image of a cross section of the battery obtained in Comparative Example 1. FIG.

Explanation of symbols

A Negative electrode C Positive electrode S1 1st separator S2 2nd separator P1 1st spacer member P2 2nd spacer member 1 Winding body 2 Laminate 3 Core material 10 Negative electrode for nonaqueous electrolyte secondary battery 11 Current collector DESCRIPTION OF SYMBOLS 12 Active material layer 12a Active material particle 13 Metal material with low lithium compound formation ability 15 Coating film

Claims (6)

Non-water provided with a wound body in which a laminate including at least a positive electrode, a negative electrode having a negative electrode active material layer containing Si or Sn, and a separator interposed therebetween is wound around a core material An electrolyte secondary battery,
In the second and subsequent windings, the laminate is wound such that the distance between the negative electrodes in the radial direction of the wound body satisfies the following formula (1): Electrolyte secondary battery.
Distance between negative electrodes = positive electrode thickness + separator thickness + negative electrode thickness + negative electrode active material layer thickness × 0.5 to 3.0 (1)   2. The nonaqueous electrolytic solution according to claim 1, wherein, in the first winding of the wound body, the laminated body is wound so that no gap is formed between the laminated body and the core member. Secondary battery.   The negative electrode active material layer contains particles of an active material containing Si or Sn, and at least a part of the surface of the particles is coated with a metal material having a low lithium compound forming ability and coated with the metal material. The nonaqueous electrolyte secondary battery according to claim 1, wherein voids are formed between the particles.   The non-aqueous electrolyte secondary battery according to claim 3, wherein the metal material is present on the surface of the particles over the entire thickness direction of the negative electrode active material layer.   The nonaqueous electrolyte secondary battery according to claim 3 or 4, wherein the negative electrode active material layer has a porosity of 15 to 45% by volume. Each of which is in the form of a long strip, including at least a positive electrode, a separator, and a negative electrode that are unrolled from a roll-shaped raw material in this order and wound together around a core material,
In the first winding, the winding tension is increased so that no gap is generated around the core material.
In the second and subsequent windings, the winding tension is set lower than the winding tension during winding of the first circumferential surface.
A method for producing a non-aqueous electrolyte secondary battery, wherein the wound body thus obtained is accommodated in a battery can without pulling out the core material.