JP2010287466A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain deformation of an electrode group and dropout of a negative electrode active material from a current collector, caused by expansion of the negative electrode active material in a nonaqueous electrolyte secondary battery having the electrode group including the negative electrode active material resulting in volume change caused by occlusion and discharge of lithium ions. <P>SOLUTION: An insulating protective layer 24 is arranged so as to cover an outer peripheral surface 25 of the electrode group 10 including a positive electrode 21, the negative electrode 22 containing the negative electrode active material bringing forth a volume change, and a separator 23 interposed between them. The insulating protective layer 24 has an adhesive part adhered to the outer periphery surface 25 of the electrode group 10 and a non-adhesive part not adhered to the same. The insulating protective layer 24 has functions for relieving expansion of the electrode group 10 and protecting the electrode group 10. Thus, the nonaqueous electrolyte secondary battery capable of maintaining excellent initial battery performance and excellent initial safety at a high level for a long period can be obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention mainly relates to an improvement in the structure of an insulating protective layer of an electrode group in a non-aqueous electrolyte secondary battery that uses a negative electrode active material that undergoes a volume change with the insertion and extraction of lithium ions.

  Nonaqueous electrolyte secondary batteries have a high capacity and high energy density, and are easy to reduce in size and weight, so that they are widely used as power sources for portable electronic devices and the like. Examples of portable electronic devices include cellular phones, personal digital assistants (PDAs), notebook personal computers, video cameras, and portable game machines. A typical nonaqueous electrolyte secondary battery includes a positive electrode containing a lithium cobalt composite oxide, a negative electrode containing a carbon material such as graphite, and a polyolefin porous membrane (separator).

  Alloy-based negative electrode active materials are known as negative electrode active materials other than carbon materials. Examples of the alloy-based negative electrode active material include silicon, tin, silicon oxide, and tin oxide. The alloy-based negative electrode active material has a high discharge capacity. For example, the theoretical discharge capacity of silicon is about 11 times the theoretical discharge capacity of graphite. Therefore, the capacity of the nonaqueous electrolyte secondary battery is increased by using the alloy-based negative electrode active material.

  A non-aqueous electrolyte secondary battery containing an alloy-based negative electrode active material has excellent battery performance, but is likely to be deformed when the number of charge / discharge cycles increases. The cause is presumed to be the volume change of the alloy-based negative electrode active material. The alloy-based negative electrode active material has a large volume change (expansion and contraction) due to insertion and extraction of lithium ions, and generates a relatively large stress during the volume change. Therefore, it is desired to prevent deformation of the nonaqueous electrolyte secondary battery containing the alloy-based negative electrode active material.

  A negative electrode active material layer that is an aggregate of columnar bodies containing an alloy-based negative electrode active material has been proposed (see, for example, Patent Document 1 and Patent Document 2). The columnar body is formed so as to extend outward from the surface of the plurality of convex portions formed on the surface of the negative electrode current collector. There are voids between the columnar bodies. This void relaxes the stress accompanying the volume change of the alloy-based negative electrode active material and suppresses deformation of the negative electrode. As a result, the deformation of the battery is remarkably suppressed.

  In the techniques of Patent Documents 1 and 2, the expansion of the columnar body in the direction parallel to the surface of the negative electrode current collector is greatly mitigated by the gap. However, the expansion in the direction perpendicular to the negative electrode current collector surface has not been sufficiently relaxed. For this reason, when charging / discharging is repeated, there is a possibility that deformation of the electrode group and thus the battery may occur. That is, the techniques of Patent Documents 1 and 2 are very effective in suppressing battery deformation, but there is still room for further improvement.

  On the other hand, sticking an adhesive tape to the outer peripheral surface of the wound electrode group is performed (see, for example, Patent Document 3). The purpose is to prevent the wound electrode group from loosening, to prevent the end of the electrode group from being loosened from the outer peripheral surface of the wound electrode group, and to prevent the wound electrode group from being damaged. There are things to do. In Patent Document 3, the entire outer peripheral surface of the wound electrode group and the adhesive tape are in close contact. The pressure-sensitive adhesive tape is made of a material having high mechanical strength and relatively little stretchability.

  When the technique of Patent Document 3 is applied to the entire outer peripheral surface of a wound electrode group including a negative electrode containing an alloy-based negative electrode active material, the expansion of the alloy-based negative electrode active material, particularly the wound axis of the wound electrode group, Expansion in the vertical direction is suppressed by the adhesive tape. As a result, expansion stress accumulates inside the electrode group, and there is a risk that deformation of the negative electrode and the wound electrode group, loss of the negative electrode active material, and the like may occur.

  Such deformation and dropping deteriorate battery performance such as battery capacity, charge / discharge cycle characteristics, output characteristics, and storage characteristics. In addition, fragments of the negative electrode active material that have fallen off the current collector may cause an internal short circuit, which may reduce the safety of the battery. Further, the adhesive tape may be damaged or broken during repeated charging and discharging.

JP 2008-192594 A JP 2008-258154 A JP 2004-14374 A

  An object of the present invention is to provide a nonaqueous electrolyte that maintains a high level of battery performance and safety over a long period of time, even if the electrode group expands, deformation of the electrode group and removal of the negative electrode active material from the current collector are unlikely to occur. It is to provide a secondary battery.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, an insulating protective layer including an insulating tape is arranged on the outer peripheral surface of the electrode group, a part of the insulating tape is bonded to the outer peripheral surface of the electrode group, and the other part is not bonded to the outer peripheral surface of the electrode group. It came to do. According to this configuration, it has been found that the purpose of using the adhesive tape in the prior art can be achieved and the expansion stress of the negative electrode active material can be sufficiently relaxed. As a result, it has been found that deformation of the electrode group and dropping of the negative electrode active material from the current collector are remarkably suppressed, and a nonaqueous electrolyte secondary battery that meets the purpose can be obtained.

  That is, the present invention includes an electrode group including a positive electrode, a negative electrode, and a separator interposed therebetween, an insulating protective layer disposed so as to cover the outer peripheral surface of the electrode group, and a nonaqueous electrolyte having lithium ion conductivity. A non-aqueous electrolyte secondary battery is provided.

  In the nonaqueous electrolyte secondary battery of the present invention, the positive electrode includes a positive electrode active material layer containing a positive electrode active material capable of inserting and extracting lithium ions and a positive electrode current collector. The negative electrode includes a negative electrode active material layer containing a negative electrode active material that expands and contracts due to insertion and extraction of lithium ions, and a negative electrode current collector. The insulating protective layer has an adhesive portion bonded to the outer peripheral surface of the electrode group and a non-adhesive portion not bonded to the outer peripheral surface of the electrode group.

In a preferred embodiment of the present invention, the electrode group is obtained by winding with a separator interposed between the positive electrode and the negative electrode, one end along the width direction is located at the center of the electrode group, and the width direction The other end along the outer peripheral surface of the electrode group is a wound-type electrode group, and the insulating protective layer fixes the other end of the electrode group to the electrode group at least on the outer peripheral surface of the electrode group It has the adhesion part arranged in.
The non-bonded portion has at least one free end portion protruding outward from the outer peripheral surface of the electrode group, and there is a gap between the non-bonded portion and the outer peripheral surface of the electrode group at the free end portion. Is preferred.

When the electrode group is a flat electrode group obtained by press-molding a wound electrode group, it is preferable that the free end portion is provided at an end in the width direction of the flat electrode group.
More preferably, the free end portions are provided at both ends in the width direction of the flat electrode group so as to face each other through the flat electrode group.
When the electrode group is a flat electrode group obtained by press-molding a wound electrode group, the free end portion is disposed at both ends in the thickness direction of the flat electrode group via the flat electrode group. It is preferable to be provided so as to face each other.

The insulating protective layer includes an insulating tape, and the insulating tape preferably contains at least one elastic material selected from synthetic resins and rubbers.
More preferably, the elastic modulus of the elastic material is 0.01 to 1.0 GPa.
The negative electrode active material is preferably a carbon material or an alloy-based negative electrode active material.

  The nonaqueous electrolyte secondary battery of the present invention has high capacity and high output, is excellent in battery performance, and has high safety. In addition, the nonaqueous electrolyte secondary battery of the present invention is less susceptible to deformation of the electrode group due to the expansion of the electrode group and falling off of the negative electrode active material from the current collector. Maintained.

It is a perspective view showing typically the composition of the nonaqueous electrolyte secondary battery which is one of the embodiments of the present invention. It is a cross-sectional view which shows typically the structure of the electrode group and insulating protective layer which are contained in the nonaqueous electrolyte secondary battery shown in FIG. It is a cross-sectional view which shows typically the structure of the insulating protective layer of another form. It is a side view which shows typically the structure of a vacuum evaporation system.

  FIG. 1 is a perspective view schematically showing a configuration of a nonaqueous electrolyte secondary battery 1 which is one embodiment of the present invention. In FIG. 1, in order to show the structure of the principal part of the nonaqueous electrolyte secondary battery 1, a part is notched. FIG. 2 is a cross-sectional view schematically showing the configuration of the electrode group 10 and the insulating protective layer 24 included in the nonaqueous electrolyte secondary battery 1 shown in FIG. FIG. 2 is a cross-sectional view of the electrode group 10 in a direction perpendicular to the winding axis. A nonaqueous electrolyte secondary battery 1 shown in FIG. 1 is a prismatic battery in which an electrode group 10 is accommodated in a prismatic battery case 11.

  The electrode group 10 includes a positive electrode 21, a negative electrode 22, and a separator 23. The positive electrode lead 12 makes the positive electrode current collector of the positive electrode 21 and the sealing plate 14 functioning as a positive electrode terminal conductive. The negative electrode lead 13 conducts the negative electrode current collector of the negative electrode 22 and the external negative electrode terminal 15. The gasket 16 insulates the sealing plate 14 from the external negative electrode terminal 15. The sealing plate 14 is joined to the opening end of the battery case 11 and seals the battery case 11. A liquid injection hole (not shown) is formed in the sealing plate 14. The liquid injection hole is closed by a plug 17 after the nonaqueous electrolyte is injected into the battery case 11.

As shown in FIG. 2, the electrode group 10 is a flat electrode group including a positive electrode 21, a negative electrode 22, and a separator 23 interposed therebetween.
At the center of the electrode group 10, one end portion (one end portion in the longitudinal direction) 26 is positioned along the width direction of the electrode laminate in which the separator 23 is interposed between the positive electrode 21 and the negative electrode 22. The other end portion (the other end portion in the longitudinal direction) 27 along the width direction of the electrode laminate is located on the outer peripheral surface 25 of the electrode group 10.

  The electrode group 10 is obtained by press-molding a wound electrode group into a flat shape. Pressurization or the like can be used for pressurization of the wound electrode group. The wound electrode group is produced by laminating the separator 23 between the positive electrode 21 and the negative electrode 22 and winding the resultant electrode stack along the width direction of the one end portion 26 along the width direction. it can. The positive electrode 21, the negative electrode 22, and the separator 23 are all strip-shaped. Moreover, the electrode group 10 can also be produced by stacking the electrode laminate on a plate.

The positive electrode 21 includes a positive electrode current collector and a positive electrode active material layer (not shown).
A conductive substrate can be used for the positive electrode current collector. The material of the conductive substrate is a metal material such as stainless steel, titanium, aluminum, aluminum alloy, or a conductive resin. In addition, the conductive substrate includes a porous conductive substrate and a non-porous conductive substrate. Examples of porous conductive substrates include mesh bodies, net bodies, punching sheets, lath bodies, porous bodies, foams, and nonwoven fabrics. Non-porous conductive substrates include foils, sheets and films. The thickness of the conductive substrate is usually 5 to 100 μm, preferably 8 to 50 μm.

The positive electrode active material layer is provided on one or both surfaces in the thickness direction of the positive electrode current collector, and contains a positive electrode active material. The positive electrode active material layer may contain a conductive agent, a binder and the like together with the positive electrode active material. In the present embodiment, the positive electrode active material layer is provided on both surfaces of the positive electrode current collector.
As the positive electrode active material, those commonly used in the field of non-aqueous electrolyte secondary batteries can be used, and among these, lithium-containing composite oxides, olivine-type lithium phosphate, and the like are preferable.

  The lithium-containing composite oxide is a metal oxide containing lithium and a transition element or an oxide in which a part of the transition element in the metal oxide is substituted with a different element. Examples of the transition element include Sc, Y, Mn, Fe, Co, Ni, Cu, and Cr, and Mn, Co, Ni, and the like are preferable. Examples of different elements include Na, Mg, Zn, Al, Pb, Sb, and B, and Mg and Al are preferable. A transition element and a different element can be used individually by 1 type or in combination of 2 or more types, respectively.

Specific examples of the lithium-containing composite _{oxide, Li l CoO 2, Li l} NiO 2, Li l MnO 2, Li l Co m Ni 1-m O 2, Li l Co m M 1-m O n, Li l Ni _1-m M _m O _n , Li _l Mn ₂ O ₄ , Li _l Mn _2−m M _n O ₄ (wherein M is Sc, Y, Mn, Fe, Co, Ni, Cu, Cr, It represents at least one element selected from the group consisting of Na, Mg, Zn, Al, Pb, Sb and B. 0 <l ≦ 1.2, m = 0 to 0.9, n = 2.0 to 2. 3).

The value of l indicating the molar ratio of lithium is a value immediately after the production of the positive electrode active material, and increases or decreases due to charge / discharge. Among these, (wherein, M, l, m and n are the _{same.) Li l Co m M 1} -m O n is preferred. Note that the lithium-containing composite oxide may include an oxygen defect portion or an oxygen excess portion.

Examples of the olivine type lithium phosphate include LiXPO ₄ and Li ₂ XPO ₄ F (wherein X is at least one selected from the group consisting of Co, Ni, Mn and Fe).
A positive electrode active material can be used individually by 1 type, or can be used in combination of 2 or more type as needed.

  Conductive agents include graphite such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and conductive fibers such as carbon fiber and metal fiber. Metal powders such as aluminum, conductive metal oxides such as titanium oxide, and carbon fluoride. A conductive agent can be used individually by 1 type or in combination of 2 or more types.

  The binders include polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene, polypropylene, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyacryl Acid hexyl, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyether, polyether sulfone, styrene butadiene rubber, modified acrylic rubber, polyvinyl pyrrolidone, carboxymethyl cellulose, etc. .

Moreover, the copolymer containing 2 or more types of monomer compounds can be used as a binder. Examples of the monomer compound include tetrafluoroethylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, hexafluoropropylene, pentafluoropropylene, acrylic acid, and hexadiene.
A binder can be used individually by 1 type or in combination of 2 or more types.

  The positive electrode active material layer can be formed, for example, by applying a positive electrode mixture slurry to the surface of the positive electrode current collector, drying, and rolling. The positive electrode mixture slurry can be prepared by dissolving or dispersing a positive electrode active material and, if necessary, a conductive agent and a binder in an organic solvent or water. Examples of the organic solvent include dimethylformamide, dimethylacetamide, methylformamide, N-methyl-2-pyrrolidone (NMP), dimethylamine, acetone, and cyclohexanone.

The negative electrode 22 includes a negative electrode current collector and a negative electrode active material layer.
A non-porous conductive substrate can be used for the negative electrode current collector. The material of the conductive substrate is, for example, a metal material such as stainless steel, nickel, copper, or a copper alloy, or a conductive resin. Non-porous conductive substrates include foils, sheets and films. The thickness of the conductive substrate is usually 5 to 100 μm, preferably 8 to 50 μm.

  The negative electrode active material layer contains a negative electrode active material that causes a volume change (expansion and contraction) in accordance with insertion and extraction of lithium ions, and is formed on one or both surfaces in the thickness direction of the negative electrode current collector. . In the present embodiment, the negative electrode active material layer is formed on both surfaces in the thickness direction of the negative electrode current collector. In addition, the negative electrode active material layer includes, together with the negative electrode active material, a negative electrode active material, a conductive agent, a binder, a thickener, and the like other than those described above as long as the battery performance of the nonaqueous electrolyte secondary battery 1 is not impaired. You may go out.

Examples of the negative electrode active material include carbon materials and alloy-based negative electrode active materials.
Examples of the carbon material include natural graphite, artificial graphite, coke, graphitized carbon, carbon fiber, spherical carbon, and amorphous carbon.
The alloy-based negative electrode active material is a material that occludes lithium by alloying with lithium and reversibly occludes and releases lithium under a negative electrode potential. The alloy-based negative electrode active material includes an alloy-based negative electrode active material containing silicon and an alloy-based negative electrode active material containing tin.

The alloy-based negative electrode active material containing silicon is represented by silicon, silicon oxide represented by the formula SiO _a (0.05 <a <1.95), and formula SiC _b (0 <b <1). Examples thereof include silicon carbide, silicon nitride represented by the formula SiN _c (0 <c <4/3), silicon alloy, silicon compound, and solid solutions thereof. A silicon alloy is an alloy of silicon and an element other than silicon. Elements other than silicon include Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti.

A silicon compound is a compound in which part of silicon contained in silicon, silicon oxide, silicon carbide, silicon nitride, or silicon alloy is substituted with one or more elements. These elements include B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn.
Among alloy-based negative electrode active materials containing silicon, silicon and silicon oxide are preferable.

The alloy-based negative electrode active material containing tin includes tin, tin oxide represented by the formula SnO _d (0 <d <2), tin dioxide (SnO ₂ ), tin nitride, tin alloy, tin compound, and these There is a solid solution. Examples of the tin alloy include a Ni—Sn alloy, a Mg—Sn alloy, a Fe—Sn alloy, a Cu—Sn alloy, and a Ti—Sn alloy. Examples of the tin compound include SnSiO ₃ , Ni ₂ Sn ₄ , and Mg ₂ Sn. Among alloy-based negative electrode active materials containing tin, tin oxide, tin alloy, tin compound, and the like are preferable.
Among alloy-based negative electrode active materials, silicon, silicon oxide, tin, tin oxide and the like are preferable, and silicon, silicon oxide and the like are particularly preferable.

  The negative electrode active material layer can be formed, for example, by applying a negative electrode mixture slurry to the surface of the negative electrode current collector, drying, and rolling. The negative electrode mixture slurry includes a negative electrode active material and an organic solvent, and may further include a binder, a conductive agent, a thickener, and the like. The same organic solvent, binder and conductive agent as those contained in the positive electrode active material layer can be used. Further, water may be used in place of the organic solvent. As the thickener, carboxymethyl cellulose or the like can be used.

When the negative electrode active material is an alloy-based negative electrode active material, the negative electrode active material layer may be formed by a vapor phase method. The negative electrode active material layer formed by a vapor phase method is preferably an amorphous or low crystalline thin film having a thickness of 3 to 50 μm. Vapor deposition methods include vacuum deposition, sputtering, ion plating, laser ablation, chemical vapor deposition (CVD), plasma chemical vapor deposition, and thermal spraying.
In the present embodiment, the negative electrode active material layer is formed as a thin solid film, but is not limited thereto, and may be formed as a pattern shape such as a lattice or an aggregate of a plurality of columnar bodies.

  The separator 23 is a lithium ion permeable insulating layer disposed so as to be interposed between the positive electrode 21 and the negative electrode 22. The separator 23 may have lithium ion conductivity. A porous film can be used for the separator 23. Examples of the porous film include a microporous film, a woven fabric, and a non-woven fabric. The microporous film may be either a single layer film or a multilayer film (composite film). Further, two or more layers of microporous membrane, woven fabric, non-woven fabric, etc. may be laminated.

  Various resin materials can be used as the material of the separator 23, but polyolefins such as polyethylene and polypropylene are preferable in view of durability, shutdown function, battery safety, and the like. The thickness of the separator 23 is usually 5 to 300 μm, preferably 8 to 40 μm. The porosity of the separator 23 is preferably 30 to 70%, more preferably 35 to 60%.

  The insulating protective layer 24 is disposed so as to cover the entire outer peripheral surface 25 of the electrode group 10. Preferably, the insulating protective layer 24 is arranged so that the dimension of the insulating protective layer 24 is longer than the dimension of the electrode group 10 in the winding axis direction of the electrode group 10.

  The insulating protective layer 24 is bonded to the outer peripheral surface 25 of the electrode group 10 in the outer peripheral region 28 of the electrode group 10. This portion is an adhesive portion of the insulating protective layer 24. In the outer peripheral region 28, the other end portion 27 of the electrode laminate constituting the electrode group 10 is exposed on the outer peripheral surface 25 of the electrode group 10. The outer peripheral region 28 extends to both ends of the electrode group 10 in the winding axis direction of the electrode group 10. For bonding the insulating protective layer 24 to the outer peripheral region 28, a general adhesive used in the battery field can be used.

  The portions other than the bonding portion of the insulating protective layer 24 are not bonded to the outer peripheral surface 25 of the electrode group 10, and are disposed so as to have a slight gap between the electrode group 10. This portion is a non-bonded portion of the insulating protective layer 24. The size of the gap between the insulating protective layer 24 and the outer peripheral surface 25 of the electrode group 10 in the thickness direction of the electrode group 10 is not particularly limited, but considering workability when the electrode group 10 is accommodated in the battery case 11, etc. , Preferably 3 mm or less.

  In the present embodiment, the insulating protective layer 24 is bonded to the outer peripheral surface 25 of the electrode group 10 with one bonding portion. Thereby, the other end portion 27 is released from the outer peripheral surface 25 of the electrode group 10, and the electrode group 10 is prevented from being loosened. Furthermore, since the entire outer peripheral surface 25 of the electrode group 10 is covered with the insulating protective layer 24, the electrode group 10 can be protected. When carrying a portable electronic device equipped with the nonaqueous electrolyte secondary battery 1 including the electrode group 10, a relatively large stress may be applied to the nonaqueous electrolyte secondary battery 1 due to dropping, collision, contact, or the like. At this time, damage to the electrode group 10 can be prevented.

  Further, the non-bonded portion of the insulating protective layer 24 is not bonded to the outer peripheral surface 25 of the electrode group 10, and is disposed along the outer peripheral surface 25 of the electrode group 10. In portions other than the outer peripheral region 28, there is a gap between the outer peripheral surface 25 of the electrode group 10 and the insulating protective layer 24. Thereby, the expansion stress of the electrode group 10 at the time of charge, especially the expansion stress in the direction perpendicular to the negative electrode current collector can be relaxed. For this reason, a deformation | transformation of the electrode group 10 is suppressed and the drop-off | omission from the collector of a negative electrode active material can fully be suppressed.

  As a result, the advantage of including a high-capacity negative electrode active material (particularly an alloy-based negative electrode active material) is maintained over a long period of time. Specifically, the nonaqueous electrolyte secondary battery 1 including the negative electrode 22 containing a high-capacity negative electrode active material has high capacity and high output, and battery performance such as output characteristics, charge / discharge cycle characteristics, and storage characteristics. Is excellent. In particular, the high-level battery performance at the initial stage of use is maintained substantially the same over a long period of time. In addition, since the negative electrode active material is hardly removed from the current collector as a cause of internal short circuit, the nonaqueous electrolyte secondary battery 1 has very high performance in terms of safety.

  The insulating protective layer 24 includes, for example, an insulating tape. The insulating tape is made of at least one material selected from the group consisting of synthetic resins and rubbers. As the synthetic resin, fluororesin, polyurethane, chlorinated polyisoprene, chlorosulfonated polyethylene, polypropylene and the like can be used. As rubbers, chloroprene rubber, silicone rubber, natural rubber, styrene butadiene rubber, nitrile rubber, ethylene-propylene rubber, acrylonitrile-butadiene rubber, fluorine rubber, butyl rubber, urethane rubber, hydrogenated polybutadiene, and the like can be used.

  The synthetic resin and rubber constituting the insulating tape preferably have a Young's modulus of 0.01 GPa to 1.0 GPa, more preferably 0.05 GPa to 1.0 GPa. By setting the Young's modulus from the above range, the protection function of the electrode group 10 and the relaxation function of the expansion stress during charging of the electrode group 10 are compatible at a high level. As a result, the battery performance and safety of the nonaqueous electrolyte secondary battery 1 can be maintained at a high level throughout the usable period. In this specification, the Young's modulus is a value calculated from an inclination from a point at which stress is generated to a point at which the sample extends by 2% after a tensile test based on JIS K 6301.

  When the Young's modulus of the insulating tape is less than 0.01 GPa, the mechanical strength of the insulating protective layer 24 is improved, but the elasticity is lowered. For this reason, there exists a possibility that the function to relieve the expansion stress at the time of charge of the electrode group 10 may fall. Further, when the electrode group 10 is repeatedly expanded, the insulating protective layer 24 is stretched, and the protective function of the electrode group 10 may be reduced. If the Young's modulus of the insulating tape exceeds 1.0 GPa, the mechanical strength of the insulating protective layer 24 becomes insufficient, and the protective function of the electrode group 10 may be reduced. In addition, the expansion stress of the electrode group 10 cannot be appropriately suppressed, and the nonaqueous electrolyte secondary battery 1 may be swollen.

  Synthetic resins and rubbers may contain general fillers in order to improve their mechanical strength, flame retardancy, and the like. Examples of the filler include silica, alumina, talc, zircon, calcium silicate, calcium carbonate, silicon carbide, boron nitride, beryllia, zirconia, titanium oxide, and titania.

  The thickness of the insulating tape is preferably 10 to 300 μm, more preferably 20 to 150 μm. If the thickness is less than 10 μm, the expansion stress of the electrode group 10 cannot be moderately moderated, and the nonaqueous electrolyte secondary battery 1 may be swollen. Further, when the electrode group 10 repeatedly expands, the insulating protective layer 24 that is an insulating tape is in an extended state, and the protective function of the electrode group 10 may be reduced. On the other hand, when the thickness exceeds 300 μm, the mechanical strength of the insulating protective layer 24, which is an insulating tape, increases, and the function of relaxing the expansion stress during charging of the electrode group 10 becomes insufficient. There is a risk of dropping off.

  In the present embodiment, the insulating protective layer 24 is bonded to the outer peripheral surface 25 of the electrode group 10 only in the outer peripheral region 28, but is not limited thereto. The insulating protective layer 24 is not particularly limited in the number of adhesive portions as long as the insulating protective layer 24 has an adhesive portion that adheres to the outer peripheral surface 25 of the electrode group 10 and a non-adhesive portion that does not adhere to the outer peripheral surface 25 of the electrode group 10. . For example, it is possible to provide an arbitrary number of two or more adhesive portions. In that case, a non-adhesion part exists between an adhesion part and an adhesion part. However, from the viewpoint of alleviating the expansion stress of the electrode group 10, the number of adhesion portions is preferably 1 to 5, and more preferably 1 to 2.

  The electrode group 10 is impregnated with a nonaqueous electrolyte. In the present embodiment, a liquid nonaqueous electrolyte is used as the nonaqueous electrolyte. The liquid non-aqueous electrolyte contains a solute (supporting salt) and a non-aqueous solvent, and further contains various additives as necessary.

The _{solute, LiClO 4, LiBF 4, LiPF} 6, LiAlCl 4, LiSbF 6, LiSCN, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiB 10 Cl 10, lower aliphatic lithium carboxylate, LiCl, LiBr, Examples include LiI, chloroborane lithium, borates, imide salts, and the like. Solutes can be used alone or in combination of two or more. The solute is preferably added at a ratio of 0.5 to 2 moles per liter of the nonaqueous solvent.

  Non-aqueous solvents include cyclic carbonates, chain carbonates, and cyclic carboxylic acid esters. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate. Examples of chain carbonic acid esters include diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate. Examples of the cyclic carboxylic acid ester include γ-butyrolactone and γ-valerolactone. A non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types.

  Examples of the additive include vinylene carbonate compounds (hereinafter referred to as “VC compounds”), benzene compounds, and the like. Examples of the VC compound include vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, and the like. The VC compound may contain a fluorine atom. Examples of the benzene compound include cyclohexylbenzene, biphenyl, diphenyl ether and the like.

  In the present embodiment, a nonaqueous electrolyte secondary battery 1 having a square shape is described. However, the nonaqueous electrolyte secondary battery of the present invention is not limited to a prismatic battery. The non-aqueous electrolyte secondary battery of the present invention includes various types such as a cylindrical battery including a wound electrode group, a laminated pack battery including a wound, flat or stacked electrode, and a coin battery including a stacked electrode. It can be formed into a battery having the shape of

FIG. 3 is a longitudinal sectional view schematically showing the configuration of another form of the insulating protective layer 24a.
The insulating protective layer 24a is similar to the insulating protective layer 24 in that the outer peripheral region 28 of the electrode group 10 has an adhesive portion and the other portions are non-adhesive portions. It has a free end portion 29 at one end in the width direction (direction perpendicular to the thickness direction).

  The free end portion 29 is a portion protruding outward from the outer peripheral surface 25 of the electrode group 10. In the free end portion 29, a gap exists between the insulating protective layer 24 a and the outer peripheral surface 25 of the electrode group 10. The gap of the free end portion 29 is larger than the gap between the insulating protective layer 24 a and the outer peripheral surface 25 of the electrode group 10 in the non-bonded portion other than the free end portion 29. The free end portion 29 is usually folded and exists along the outer peripheral surface 25 of the electrode group 10. And the electrode group 10 can be expanded moderately at the time of charge.

  Since the end in the width direction of the electrode group 10 has an R shape, stresses directed in various directions are generated with the expansion of the negative electrode active material. As a result, the stress applied to the end portion in the width direction of the electrode group 10 is larger than the stress applied to the center portion in the width direction (flat portion of the electrode group 10) of the electrode group 10, and in particular, the negative electrode active material is removed. Etc. are likely to occur. At this time, by providing the free end portion 29, a relatively large expansion stress at the end portion in the width direction of the electrode group 10 can be sufficiently relaxed. For this reason, the falling off of the negative electrode active material can be remarkably suppressed. Moreover, since the expansion stress of the whole electrode group 10 is relieved to substantially the same extent, the deformation | transformation as the whole electrode group 10 can be suppressed notably.

When the electrode group 10 is not expanded, the free end portion 29 exists along the outer peripheral surface 25 of the electrode group 10, so that the protective function of the electrode group 10 does not deteriorate.
In the present embodiment, one free end portion 29 is provided. However, the present invention is not limited to this, and the free end portions 29 may be provided in an arbitrary number of 2 or more. For example, it is preferable to provide one free end portion 29 at each of both end portions in the width direction of the electrode group 10. That is, it is preferable to provide the two free end portions 29 so as to be opposed to both end portions in the width direction of the electrode group 10 through the electrode group 10.

  Further, the free end portion 29 may be provided in the thickness direction of the electrode group 10 so as to face each other with the electrode group 10 interposed therebetween. At this time, the number of free end portions 29 on one side is preferably the same as the number of free end portions 29 on the other side. The electrode group 10 tends to be greatly expanded and deformed in the thickness direction. Therefore, providing the free end portion 29 in the above-described arrangement is effective in reducing the expansion stress of the electrode group 10 and suppressing the deformation of the electrode group 10 in the thickness direction.

  In consideration of the workability when the electrode group 10 covered with the insulating protective layer 24a is accommodated in the battery case 11, the protection of the electrode group 10 by the insulating protective layer 24a, etc., the number of free end portions 29 is as follows. About 1 to 4 is preferable, and 1 to 2 is more preferable.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
Example 1
(1) Preparation NiSO ₄ aqueous solution of the positive electrode, Ni: Co = 8.5: to prepare an aqueous solution of metal ion concentration 2 mol / L so as to 1.5 (molar ratio) was added cobalt sulfate. While stirring, a 2 mol / L sodium hydroxide solution is gradually added dropwise to the aqueous solution to neutralize, thereby coprecipitation of a binary precipitate having a composition represented by Ni _0.85 Co _0.15 (OH) _2. Was generated by This precipitate was separated by filtration, washed with water, and dried at 80 ° C. to obtain a composite hydroxide.

This composite hydroxide was heated in the atmosphere at 900 ° C. for 10 hours for heat treatment to obtain a composite oxide having a composition represented by Ni _0.85 Co _0.15 O. Here, lithium hydroxide monohydrate is added so that the sum of the number of atoms of Ni and Co and the number of atoms of Li are equal, and heat treatment is performed at 800 ° C. for 10 hours in air. Thus, a lithium nickel-containing composite oxide having a composition represented by LiNi _0.85 Co _0.15 O ₂ was obtained. Thus, a positive electrode active material having an average secondary particle size of 10 μm was obtained.

  Thoroughly mix 93 g of the positive electrode active material powder obtained above, 3 g of acetylene black (conductive agent), 4 g of polyvinylidene fluoride powder (binder) and 50 ml of N-methyl-2-pyrrolidone (NMP). An agent paste was prepared. This positive electrode mixture paste was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, dried, and rolled to form a positive electrode active material layer having a thickness of 120 μm. The obtained positive electrode was cut into 30 mm × 600 mm to obtain a positive electrode plate.

(2) Production of negative electrode A vacuum deposition apparatus 30 shown in FIG. 4 was used for production of the negative electrode. FIG. 4 is a side view schematically showing the configuration of the vacuum vapor deposition apparatus 30. In FIG. 4, each constituent member disposed inside the vacuum vessel 31 is indicated by a solid line. The vacuum deposition apparatus 30 includes a vacuum container 31, an unwinding roll 32, a plurality of transporting rolls 33, film forming rolls 34a and 34b, a winding roll 35, masks 36a, 36b, 36c, and 36d, vapor deposition sources 37a and 37b, and an oxygen nozzle. 38a and 38b and a vacuum pump 39 are included.

The vacuum vessel 31 is a pressure vessel, and includes an unwinding roll 32, a plurality of transport rolls 33, film forming rolls 34a and 34b, a winding roll 35, masks 36a, 36b, 36c, and 36d, vapor deposition sources 37a and 37b, and an oxygen nozzle 38a. , 38b are accommodated therein.
A strip-shaped current collector 40 is wound around the unwinding roll 32. The plurality of transport rolls 33 transport the belt-like current collector 40 wound around the unwinding roll 32 to the take-up roll 35 via the film forming rolls 34a and 34b.

  The film forming rolls 34a and 34b are provided to face the vapor deposition sources 37a and 37b, respectively, in the vertical direction. A cooling device (not shown) is disposed inside the film forming rolls 34a and 34b to cool the peripheral surfaces of the film forming rolls 34a and 34b. Masks 36a and 36b are arranged below the film forming roll 34a in the vertical direction. On the exposed surface of the film forming roll 34a not blocked by the masks 36a and 36b, the vapor of the negative electrode active material layer or a mixture of the vapor and oxygen is formed on one surface of the belt-like current collector 40 running on the exposed surface. Is vapor-deposited, cooled and solidified to form a negative electrode active material layer.

  Masks 36c and 36d are arranged below the film forming roll 34b in the vertical direction. On the exposed surface of the film-forming roll 34b not blocked by the masks 36c and 36d, the vapor of the negative electrode active material layer or a mixture of the vapor and oxygen is formed on the other surface of the strip-shaped current collector 40 running on the exposed surface. Is deposited to form a negative electrode active material layer. Thereby, the negative electrode 41 in which the negative electrode active material layers are formed on both surfaces in the thickness direction of the belt-like current collector 40 is obtained.

  The take-up roll 35 is provided so as to be rotationally driven by a driving means (not shown). The winding roll 35 winds and stores the negative electrode 41. One end of the belt-like current collector 40 in the longitudinal direction is sent out from the winding roll 32 according to the path shown in FIG. 4 and fixed to the peripheral surface of the winding roll 35. In this state, the winding roll 35 is rotated to start the winding operation, whereby the deposition of the negative electrode active material on the strip-shaped current collector 40 is started.

  The vapor deposition sources 37a and 37b contain an alloy-based negative electrode active material such as silicon or tin as a target. By heating the target, vapor of the target is generated and rises toward the exposed surfaces of the film forming rolls 34a and 34b. For heating the target, heating by a heating element, heating by electron beam irradiation, or the like can be used.

The oxygen nozzles 38a and 38b are respectively provided between the film forming rolls 34a and 34b and the vapor deposition sources 37a and 37b in the vertical direction, and supply oxygen. When forming a negative electrode active material layer made of only silicon or tin, supply of oxygen is stopped.
The vacuum pump 39 is connected to the vacuum vessel 31 and puts the inside of the vacuum vessel 31 into a vacuum state (depressurized state).

  In the vacuum deposition apparatus 30, the following conditions are set, and a 5 μm-thick silicon vapor deposition layer (a negative electrode active material layer made of an alloy-based negative electrode active material) is formed on both surfaces of the belt-like current collector 40 in the thickness direction. A negative electrode 41 was produced. Note that an electron beam irradiation apparatus was used for heating the target. The obtained negative electrode 41 was cut into 31 mm × 650 mm to prepare a negative electrode plate.

Degree of vacuum in the vacuum vessel 31: 5 × 10 ⁻³ Pa
Band-shaped current collector 40: electrolytic copper foil having a length of 50 m, a width of 10 cm, and a thickness of 35 μm (manufactured by Furukawa Circuit Foil Co., Ltd.)
Winding speed of belt-shaped current collector 40 by winding roller 35 (conveying speed of belt-shaped current collector 40): 2 cm / min.
Temperature of the peripheral surfaces of the film forming rolls 34a and 34b: 20 ° C.

Oxygen gas: not supplied.
Vapor deposition sources 37a and 37b: silicon single crystal with a purity of 99.9999% (manufactured by Shin-Etsu Chemical Co., Ltd.)
Electron beam acceleration voltage: 10 kV
Emission of electron beam: 500mA

(3) Production of flat electrode group In the positive electrode plate obtained above, a positive electrode current collector was exposed at a predetermined position, and one end of an aluminum positive electrode lead was connected to the exposed portion. In the negative electrode plate obtained above, the negative electrode current collector was exposed at a predetermined position, and a nickel negative electrode lead was connected to the exposed portion. An electrode laminate in which a polyethylene porous sheet (separator, trade name: Hypore, manufactured by Asahi Kasei Co., Ltd.) having a thickness of 16 μm is interposed between the positive electrode plate and the negative electrode plate is wound around one end along the width direction. In this way, a wound electrode group was produced.

  The other end portion (hereinafter, simply referred to as “other end portion”) along the width direction of the electrode laminate was exposed on the outer peripheral surface of the obtained wound electrode group. The obtained wound electrode group was pressed under an environment of 25 ° C. to produce a flat electrode group. The press pressure was 0.5 MPa. The length of the flat electrode group in the winding axis direction was 33 mm, and the outer peripheral length was 75 mm.

  A polypropylene insulating adhesive tape (thickness 40 μm, Young's modulus 1.0 GPa, manufactured by Teraoka Seisakusho Co., Ltd.) was cut into a length of 90 mm and a width of 35 mm. The adhesive layer extending at a width of 5 mm in the width direction was left at both ends in the longitudinal direction of the insulating pressure-sensitive adhesive tape, and the other part of the adhesive layer was removed with a solvent. This insulating adhesive tape was arranged around the flat electrode group obtained above. Subsequently, the adhesive layer left at both ends of the adhesive tape was attached to the outer peripheral region including the other end exposed on the outer peripheral surface of the flat electrode group, and the other end was fixed to the outer peripheral surface of the flat electrode group.

  The insulating adhesive tape is bonded to the outer peripheral surface of the flat electrode group in the outer peripheral region where the other end is located, and forms an adhesive protective layer, but the other part of the insulating adhesive tape is a flat electrode. It was not bonded to the outer peripheral surface of the group, and a non-bonded portion of the insulating protective layer was formed. In the non-bonded portion, there was a gap of 1 mm or less between the insulating tape layer and the outer peripheral surface of the flat electrode group.

(4) Preparation of non-aqueous electrolyte 1 wt% vinylene carbonate was added to a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 3 to obtain a mixed solution. Thereafter, LiPF ₆ was dissolved in the mixed solution so that the concentration became 1.0 mol / L to prepare a non-aqueous electrolyte.

(5) Assembling the battery Using the flat electrode group (hereinafter simply referred to as “electrode group”) and the non-aqueous electrolyte obtained above, a rectangular shape having the same structure as shown in FIG. A battery was produced.
The electrode group was inserted into a rectangular battery case. A resin frame (not shown) was mounted on the upper part of the electrode group. The resin frame separates the electrode group and the sealing plate and prevents the positive electrode lead and the negative electrode lead from contacting the battery case. The other end of the aluminum positive electrode lead was connected to the lower surface of the sealing plate. The other end of the nickel negative electrode lead was connected to the external negative electrode terminal. The external negative electrode terminal was disposed on the sealing plate via a resin gasket. A sealing plate was placed in the opening of the battery case and welded. A predetermined amount of nonaqueous electrolyte was injected into the battery case from the injection hole of the sealing plate. Thereafter, the non-aqueous electrolyte secondary battery of the present invention was produced by closing the liquid injection port with a plug.

(Example 2)
Example of manufacturing the negative electrode 41 by forming negative electrode active material layers on both surfaces of the strip-shaped current collector 40, except that oxygen is supplied from the oxygen nozzles 38a and 38b and the oxygen supply rate is set to 100 sccm. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery of the present invention was produced.

(Example 3)
A nonaqueous electrolyte of the present invention was produced in the same manner as in Example 1 except that a negative electrode produced as described below was used instead of the negative electrode 41.

[Production of negative electrode]
The flaky artificial graphite was pulverized and classified to adjust the volume average particle diameter to 20 μm, thereby obtaining a negative electrode active material. 100 parts by weight of the negative electrode active material, 1 part by weight of styrene butadiene rubber (binder), and 100 parts by weight of a 1% by weight aqueous solution of carboxymethyl cellulose were mixed with a double-arm kneader to prepare a negative electrode mixture paste. . The negative electrode mixture paste was applied to both sides of a 10 μm thick copper foil (negative electrode current collector), dried, and then rolled to prepare a negative electrode. The total thickness of the negative electrode active material layers on both sides and the negative electrode current collector was 155 μm.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that a polypropylene insulating pressure-sensitive adhesive tape having an adhesive layer on the entire surface of one side was used instead of the polypropylene insulating pressure-sensitive adhesive tape from which a part of the adhesive layer was removed with a solvent. A non-aqueous electrolyte secondary battery was produced. In addition, the protective layer which consists of a polypropylene insulating adhesive tape was adhere | attached on the whole outer peripheral surface of the electrode group contained in this nonaqueous electrolyte secondary battery.

(Comparative Example 2)
The same procedure as in Example 2 was performed except that a polypropylene insulating pressure-sensitive adhesive tape having an adhesive layer on the entire surface of one side was used instead of the polypropylene insulating pressure-sensitive adhesive tape from which a part of the adhesive layer was removed with a solvent. A non-aqueous electrolyte secondary battery was produced. In addition, the protective layer which consists of a polypropylene insulating adhesive tape was adhere | attached on the whole outer peripheral surface of the electrode group contained in this nonaqueous electrolyte secondary battery.

(Test Example 1)
The following evaluation test was implemented about the nonaqueous electrolyte secondary battery obtained in Examples 1-3 and Comparative Examples 1-2.
[Battery capacity evaluation test]
About the nonaqueous electrolyte secondary battery of Examples 1-3 and Comparative Examples 1-2, the charge / discharge cycle was performed twice on condition of the following, and discharge capacity was calculated | required. The results are shown in Table 1.
Constant current charging: 800 mA (1.0 C), final voltage 4.15 V.
Constant voltage charging: end current 40 mA (0.05 C), rest time 20 minutes.
Constant current discharge: current 160 mA (0.2 C), end voltage 2.0 V, rest time 20 minutes.

[Charge / discharge cycle characteristics test]
In a 25 ° C. environment, the battery was charged at a constant current of 800 mA (1.0 C) to 4.15 V, then charged at a constant current of 40 mA (0.05 C) at a final current, and discharged at a constant current of 160 mA (0.2 C) to 2 V. The discharge capacity at this time was defined as the initial discharge capacity. Then, the current value at the time of discharge was set to 800 mA (1 C), and the charge / discharge cycle was repeated. After 100 cycles, constant current discharge was performed at 160 mA (0.2 C) to obtain a discharge capacity after 100 cycles. Then, the percentage of the discharge capacity after 100 cycles with respect to the initial discharge capacity (cycle capacity maintenance rate,%) was determined. The results are shown in Table 1.

[Battery swelling test]
The difference between the battery thickness during charging in the first cycle of the charge / discharge cycle characteristic test and the battery thickness during charging in the 100th cycle was defined as the swelling of the battery.

  From Table 1, it can be seen that the batteries of Examples 1 to 3 have little deterioration in charge / discharge cycle characteristics and the swelling of the battery is suppressed.

  The non-aqueous electrolyte secondary battery of the present invention can be used in the same applications as conventional non-aqueous electrolyte secondary batteries, and is particularly useful as a power source for portable electronic devices. Examples of portable electronic devices include personal computers, mobile phones, mobile devices, personal digital assistants (PDAs), portable game devices, and video cameras. The non-aqueous electrolyte secondary battery of the present invention includes a main power source or auxiliary power source for driving an electric motor in a hybrid electric vehicle, a fuel cell vehicle, a plug-in HEV, etc., a driving power source for an electric tool, a vacuum cleaner, a robot, etc. The use as is expected.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 10 Electrode group 11 Battery case 12 Positive electrode lead 13 Negative electrode lead 14 Sealing plate 15 External negative electrode terminal 16 Gasket 17 Sealing 21 Positive electrode 22 Negative electrode 23 Separator 24, 24a Insulating protective layer 25 Electrode group outer peripheral surface 26 Electrode group one end portion 27 Electrode group other end portion 28 Electrode group outer peripheral region 29 Free end portion 30 Vacuum deposition apparatus

Claims (9)

An electrode group including a positive electrode, a negative electrode, and a separator interposed therebetween, an insulating protective layer disposed so as to cover an outer peripheral surface of the electrode group, and a non-aqueous electrolyte having lithium ion conductivity,
The positive electrode includes a positive electrode active material layer containing a positive electrode active material capable of inserting and extracting lithium ions and a positive electrode current collector,
The negative electrode includes a negative electrode active material layer containing a negative electrode active material that expands and contracts due to insertion and extraction of lithium ions and a negative electrode current collector,
The said insulating protective layer is a non-aqueous electrolyte secondary battery which has the adhesion part adhere | attached on the outer peripheral surface of the said electrode group, and the non-adhesion part which is not adhere | attached on the said outer peripheral surface of the said electrode group. The electrode group is obtained by winding with the separator interposed between the positive electrode and the negative electrode, and one end along the width direction is located at the center of the electrode group, and the other is along the width direction. The wound electrode group whose end is located on the outer peripheral surface of the electrode group,
2. The non-aqueous solution according to claim 1, wherein the insulating protective layer includes the adhesive portion disposed so as to fix the other end portion of the electrode group to the electrode group at least on an outer peripheral surface of the electrode group. Electrolyte secondary battery.   The non-adhering portion has at least one free end portion protruding outward from the outer peripheral surface of the electrode group, and the free end portion is between the non-adhesive portion and the outer peripheral surface of the electrode group. The nonaqueous electrolyte secondary battery according to claim 1, wherein voids are present.   The electrode group is a flat electrode group obtained by pressure-molding the wound electrode group, and the free end portion is provided at an end in the width direction of the flat electrode group. 4. The nonaqueous electrolyte secondary battery according to 3.   5. The nonaqueous electrolyte secondary battery according to claim 3, wherein the free end portion is provided at both end portions in the width direction of the flat electrode group so as to face each other through the flat electrode group.   The electrode group is a flat electrode group obtained by pressure-molding the wound electrode group, and the free end portions are provided at both ends in the thickness direction of the flat electrode group. The nonaqueous electrolyte secondary battery according to claim 3, wherein the nonaqueous electrolyte secondary battery is provided so as to face each other across the group.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the insulating protective layer includes an insulating tape, and the insulating tape contains at least one elastic material selected from synthetic resins and rubbers.   The non-aqueous electrolyte secondary battery according to claim 7, wherein the elastic material has a Young's modulus of 0.01 GPa to 1.0 GPa.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is a carbon material or an alloy-based negative electrode active material.

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