JP4802217B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery whose exterior material is a laminate film.

  In recent years, with the downsizing and increasing demand of electronic devices such as mobile phones and portable personal computers, there has been a demand for higher performance with respect to secondary batteries as power sources for these electronic devices. As such a secondary battery, a non-aqueous electrolyte battery using a material capable of occluding and releasing lithium, such as a carbon material, as a negative electrode material has been developed and is widely used as a power source for portable electronic devices. Unlike conventional batteries, this non-aqueous electrolyte secondary battery is characterized by being light in weight and having a high electromotive force of 4V class, and its excellent performance has attracted attention.

  Then, applying the said nonaqueous electrolyte secondary battery as power supplies, such as an electric vehicle, an electric tool, a cordless cleaner, is examined. In such applications, higher output characteristics are required as compared with conventional nonaqueous electrolyte secondary batteries.

  In order to increase the output of the battery, it is necessary to reduce the internal resistance of the battery as much as possible. For this purpose, it is important to reduce the resistance of the electrode and the battery member and increase the current collection efficiency. As one of the measures, development of a cylindrical lithium ion secondary battery or a square lithium ion secondary battery having a plurality of current collecting leads on an electrode is in progress, for example, Japanese Patent Laid-Open No. 9-92335 (patent) Document 1). With such a configuration, the current collection efficiency is improved and the internal resistance of the battery can be reduced, so that a battery with excellent output characteristics can be formed.

  However, since such a battery uses a metal container as an exterior container, there is a limit in reducing the weight of the battery. In addition, when used as a power source for an electric vehicle, a power tool, a cordless cleaner, and the like, since it is used as an assembled battery in which a plurality of unit cells are connected, an increase in weight becomes a serious problem. Therefore, a lightweight and high output battery is demanded.

  By the way, as a non-aqueous electrolyte secondary battery for portable devices such as mobile phones, a positive electrode, a negative electrode, and a polymer electrolyte layer disposed between the positive electrode and the negative electrode are used. A lithium ion secondary battery having an outer material for accommodating the electrolyte and the electrode group has been proposed and developed. This secondary battery can secure the adhesion between the positive electrode, the negative electrode and the polymer electrolyte layer even if the thickness of the exterior material is reduced. For this reason, it becomes possible to use the laminated film comprised from the thin metal layer and the polymer film as an exterior material, and can form a thin and lightweight lithium ion secondary battery. The polymer electrolyte is a gel polymer in which a non-aqueous electrolyte is held. However, since this secondary battery has a larger impedance at the electrode interface and lower lithium ion conductivity than a lithium ion secondary battery having a liquid nonaqueous electrolyte, the lithium ion having a liquid nonaqueous electrolyte is used. There is a problem that the secondary battery is inferior in large current discharge characteristics.

  For these reasons, the following proposals have been made to reduce the thickness of a lithium ion secondary battery having a liquid nonaqueous electrolyte. In the claims of Japanese Patent Application Laid-Open No. 10-177865 (Patent Document 2), a polymer gel containing a positive electrode, a negative electrode, a separator having an opposing surface holding an electrolytic solution, an electrolyte phase, and an electrolytic solution A lithium ion secondary battery comprising a phase and a mixed phase and having an adhesive resin layer for joining the positive electrode and the negative electrode to the opposing surface of the separator is described. Further, in the claims of Japanese Patent Application Laid-Open No. 10-189054 (Patent Document 3), a step of applying a binder resin solution obtained by dissolving a main component polyvinylidene fluoride in a solvent to the separator, A method for producing a thin lithium ion secondary battery comprising a step of forming a battery laminate by stacking and drying the electrodes while they are adhered and evaporating the solvent, and a step of impregnating the battery laminate with an electrolyte is described. ing. Further, in the claims of Japanese Patent Application Laid-Open No. 10-172606 (Patent Document 4), a positive electrode, a negative electrode, a separator that is disposed between the positive electrode and the negative electrode and holds an electrolytic solution containing lithium ions, A lithium ion secondary battery that holds the electrolytic solution and includes a porous adhesive resin layer that joins the positive electrode, the negative electrode, and the separator is disclosed.

  However, the lithium ion secondary battery disclosed in each publication has a problem that output characteristics are inferior due to an increase in internal resistance, and is not necessarily sufficient for high output applications.

Therefore, in order to solve the above-mentioned problems, in a thin lithium ion secondary battery, when a structure including a plurality of current collecting leads is applied as in the above-described cylindrical lithium ion secondary battery, a laminate film and a current collecting lead are applied. Since a gap is likely to be generated at the interface, the output characteristics are improved, but there is a high possibility that a nonaqueous electrolyte leaks from the gap or moisture enters the inside. As a result, there arises a problem that basic characteristics such as discharge capacity and cycle characteristics are impaired.
JP-A-9-92335 JP-A-10-177865 Japanese Patent Laid-Open No. 10-189054 JP-A-10-172606

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery that is lightweight and excellent in output characteristics, and that significantly suppresses non-aqueous electrolyte leakage and moisture intrusion from an exterior material.

A non-aqueous electrolyte secondary battery according to the present invention includes an electrode group having a laminate including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode,
A non-aqueous electrolyte held in the electrode group;
At least a part of the inner surface is made of a laminate film formed from a thermoplastic resin layer, and houses the electrode group, and heat seals the thermoplastic resin layers together to form a sealing portion. An exterior material for sealing;
A plurality of positive electrode current collecting leads having one end connected to the positive electrode of the electrode group and the other end extended from the electrode group;
A plurality of negative electrode current collector leads having one end connected to the negative electrode of the electrode group and the other end extending from the electrode group in a direction opposite to the positive electrode current collector lead;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of positive electrode current collecting leads are connected, and a positive electrode terminal extending outside through the sealing portion of the exterior material;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of negative electrode current collecting leads are connected, and a negative electrode terminal extending outside through the sealing portion of the exterior material In the non-aqueous electrolyte secondary battery
The laminate has a structure wound in a flat shape,
The length ratio calculated by the following formula (1) in the positive electrode terminal and the negative electrode terminal is 0.3 or more.

L ₁ / L ₂ (1)
However, (1) In formula, L ₁ represents the length of the current collector lead connecting portions of the sides in the positive and negative terminals, the length of the side L ₂ is along the current collecting lead connecting portion in the electrode group Indicates.

Moreover, the nonaqueous electrolyte secondary battery according to the present invention includes an electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode,
A non-aqueous electrolyte held in the electrode group;
At least a part of the inner surface is made of a laminate film formed from a thermoplastic resin layer, and houses the electrode group, and heat seals the thermoplastic resin layers together to form a sealing portion. An exterior material for sealing;
A plurality of positive electrode current collecting leads having one end connected to the positive electrode of the electrode group and the other end extended from the electrode group;
A plurality of negative electrode current collector leads having one end connected to the negative electrode of the electrode group and the other end extending from the electrode group in a direction opposite to the positive electrode current collector lead;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of positive electrode current collecting leads are connected, and a positive electrode terminal extending outside through the sealing portion of the exterior material;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of negative electrode current collecting leads are connected, and a negative electrode terminal extending outside through the sealing portion of the exterior material In the non-aqueous electrolyte secondary battery
The length ratio calculated by the following formula (1) in the positive electrode terminal and the negative electrode terminal is 0.3 or more,
The other ends of the plurality of positive current collecting leads are connected in a state aligned with the current collecting lead connecting portion of the positive terminal, and the other ends of the plurality of negative current collecting leads are connected to the negative terminal. It is characterized in that it is connected in a state where it is aligned with the current collector lead connection part.

L ₁ / L ₂ (1)
However, (1) In formula, L ₁ represents the length of the current collector lead connecting portions of the sides in the positive and negative terminals, the length of the side L ₂ is along the current collecting lead connecting portion in the electrode group Indicates.

  In the secondary battery according to the present invention, it is preferable that at least a portion of the surface of the positive electrode terminal or the negative electrode terminal that passes through the sealing portion of the laminate film is covered with a thermoplastic resin layer. The thermoplastic resin layer preferably has a thickness of 40 μm to 100 μm.

Further, in the secondary battery of the present invention, the cross-sectional area in the transverse direction of the current collector lead is preferably a 0.5 mm ² to 5 mm ^2. According to this configuration, the non-aqueous electrolyte secondary battery is light and excellent in output characteristics, and the non-aqueous electrolyte stored in the exterior material leaks to the outside or moisture enters the inside. Problems are prevented from occurring.

  As described above in detail, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that is lightweight and excellent in large current discharge characteristics. Moreover, according to this invention, the nonaqueous electrolyte secondary battery which suppressed the leakage of the nonaqueous electrolyte from an exterior material can be provided. Therefore, it is extremely useful as a power source for portable devices, as well as a power source for electric vehicles, power tools, cordless cleaners, and the like.

  Hereinafter, a thin lithium ion secondary battery which is an example of a non-aqueous electrolyte secondary battery according to the present invention will be described in detail with reference to FIGS. However, the nonaqueous electrolyte secondary battery according to the present invention is not limited to the following embodiment as long as it is within the scope of the present invention.

  FIG. 1 is a cross-sectional view showing a nonaqueous electrolyte secondary battery (for example, a thin lithium ion secondary battery) according to the present invention, and FIG. 2 is an enlarged cross-sectional view showing part A of FIG.

  As shown in FIG. 1, the electrode group 2 is accommodated in the exterior material 1 which consists of a multilayer sheet, for example. The electrode group 2 has a structure in which a laminate composed of a positive electrode, a separator, and a negative electrode is wound in a flat shape.

  As shown in FIG. 2, the laminate includes a separator 3, a positive electrode 6 including a positive electrode active material layer 4, a positive electrode current collector 5, and a positive electrode active material layer 4 (from the lower side of the figure), a separator 3, a negative electrode active material. A negative electrode 9 including a material layer 7, a negative electrode current collector 8, and a negative electrode active material layer 7, a separator 3, a positive electrode active material layer 4, a positive electrode current collector 5, and a positive electrode 6 including a positive electrode active material layer 4; The negative electrode 9 including the negative electrode active material layer 7 and the negative electrode current collector 8 is laminated in this order. An adhesive layer (not shown) is disposed between the surface of the electrode group 2 and the inner surface of the exterior material 1. The nonaqueous electrolyte is accommodated in the exterior material 1.

  As shown in FIG. 3, the plurality of strip-like positive leads 11 housed in the exterior material 1 are connected to the positive electrode current collector 5 of the electrode group 2 and the other end is a convex positive electrode, as shown in FIG. 3. It is connected to the terminal 12. The positive electrode terminal 12 is arranged so that the connecting portion of the current collecting lead is flat and protrudes from the exterior material 1. As a method of connecting the positive electrode lead 11 to the positive electrode current collector 5, there is a method in which a solid portion that does not form an active material layer is provided on the electrode and the electrode is welded to the plain portion with a spot welder or an ultrasonic welder. It is done.

  Examples of the method for forming the plain portion include a method of performing intermittent coating using a coating apparatus having an intermittent coating function, a method of manufacturing by continuously projecting a part of the current collector or an end portion of the electrode, and the like. Can be mentioned.

  Examples of the positive electrode lead 11 include an aluminum foil, an aluminum ribbon, an aluminum plate, a stainless steel foil, a stainless steel ribbon, and a stainless steel plate having a thickness of 100 μm to 500 μm.

Sectional area in the transverse direction of the positive electrode lead is preferably a 0.5 mm ² to 5 mm ^2. By using such a positive electrode lead, the internal resistance of the battery can be reduced and the output characteristics can be improved.

  The positive electrode lead 11 is preferably bonded to the inner surface of the exterior material by an adhesive layer formed on the surface thereof. With such a configuration, the outer packaging material 1 can be fixed to the surface of the positive electrode lead 11, so that the nonaqueous electrolyte can be prevented from penetrating and leaking.

  More preferably, the surface of the positive electrode lead 11 is covered with an insulating protective sheet. With such a configuration, it is possible to prevent the positive electrode lead 11 from coming into contact with the negative electrode 9 and causing an internal short circuit.

  The insulating protective sheet is preferably formed from an organic polymer that is insoluble in the liquid non-aqueous electrolyte. Examples of such a material include at least one selected from the group consisting of a polyimide resin, a fluororesin, and a polyolefin resin. As a polyimide resin, the brand name made from duPont (duPont) can mention Kapton (Kapton), for example. On the other hand, examples of the polyolefin resin include a polyethylene resin and a polypropylene resin. Moreover, as a fluororesin, polyvinylidene fluoride (PVdF) can be mentioned, for example.

  The insulating protective sheet can be formed from a nonwoven fabric or a film. Moreover, when a porous insulating protective sheet is used, the electrolyte solution impregnation property to an electrode group can be improved. Furthermore, an adhesive may be present between the insulating protective sheet and the electrode group.

  Examples of the positive electrode terminal 12 include an aluminum foil, an aluminum plate, a stainless steel foil, and a stainless steel plate having a thickness of 100 μm to 500 μm.

  As for the said positive electrode terminal 12, it is desirable that the part which passes the sealing part of the laminate film of the surface is coat | covered with the thermoplastic resin layer 10. FIG. FIG. 4 is an enlarged cross-sectional view showing the positive terminal portion. With such a configuration, the thermoplastic resin adheres to the laminate film by thermal bonding, so that the nonaqueous electrolyte can be prevented from penetrating and leaking. The thickness of the thermoplastic resin layer 10 is preferably 40 μm to 100 μm. A more preferable range of the thickness of the thermoplastic resin layer 10 is 60 μm to 80 μm.

  The thermoplastic resin layer 10 may be formed of one type of resin or may be formed of two or more types of resins. The melting point of the thermoplastic resin is preferably 120 ° C. or higher, and a more preferable range is 140 ° C. to 250 ° C. Examples of the thermoplastic resin include polyethylene and polypropylene. In particular, polypropylene having a melting point of 150 ° C. or higher is desirable because it can improve the sealing strength of the heat seal portion.

  Examples of the shape of the positive electrode terminal include a convex shape, a rectangular shape, and a trapezoidal shape, but the shape is not particularly limited. In addition, the thickness of a part of the surface housed in the exterior material 1 and the thickness of a part extending to the outside from the exterior material 1 may be different. At that time, it is preferable to make the thickness of the part accommodated in the exterior material 1 thinner than the thickness of the part protruding to the outside from the exterior material 1.

  On the other hand, as shown in FIG. 3, the plurality of strip-like negative leads 13 housed in the exterior material 1 are arranged so as to extend in the opposite direction to the positive leads 11 through the electrode groups. One end is connected to the negative electrode current collector 8 of the electrode group 2, and the other end is connected to the convex negative electrode terminal 14. The negative electrode terminal 14 is arranged so that the connecting portion of the current collecting lead is flat and protrudes from the exterior material 1.

  As a method of connecting the negative electrode lead 13 to the negative electrode current collector 8, a method similar to the method of connecting the positive electrode lead 11 to the positive electrode current collector 5 is used.

  As the negative electrode lead 13, a copper foil, a copper ribbon, a copper plate, a nickel foil, a nickel ribbon, a nickel plate, a stainless steel foil, a stainless steel ribbon, a stainless steel plate or the like having a thickness of 100 μm to 500 μm can be used.

  More preferably, the negative electrode lead 13 is bonded to the inner surface of the exterior material 1 by an adhesive layer formed on the surface thereof. With such a configuration, the exterior material 1 can be fixed to the surface of the negative electrode lead 13, so that the nonaqueous electrolyte can be prevented from penetrating and leaking.

  The surface of the negative electrode lead 13 is preferably covered with the insulating protective sheet. By adopting such a configuration, it is possible to prevent the negative electrode lead 13 from coming into contact with the positive electrode 6 and causing an internal short circuit.

  As the negative electrode terminal 14, a copper foil, a copper plate, a nickel foil, a nickel plate, a stainless steel foil, a stainless steel plate, or the like having a thickness of 100 μm to 500 μm can be used.

  The negative electrode terminal 14 is preferably coated with the thermoplastic resin layer 10 at least on the surface of the negative electrode terminal 14 through the sealing portion of the laminate film. With such a configuration, the thermoplastic resin adheres to the laminate film by thermal bonding, so that the nonaqueous electrolyte can be prevented from penetrating and leaking. The thickness of the thermoplastic resin layer 10 is preferably 40 μm to 100 μm. A more preferable range of the thickness of the thermoplastic resin layer 10 is 60 μm to 80 μm.

  As the thermoplastic resin layer 10, the same one as the thermoplastic resin layer coated on the positive electrode terminal 12 can be used.

  Examples of the shape of the negative electrode terminal include a convex shape, a rectangular shape, and a trapezoidal shape, but the shape is not particularly limited. In addition, the thickness of a part of the surface housed in the exterior material 1 and the thickness of a part extending to the outside from the exterior material 1 may be different. In that case, it is preferable to make the thickness of the part accommodated in the exterior material 1 thinner than the thickness of the part extended to the outside from the exterior material 1.

  In FIG. 3 described above, the positive electrode current collecting lead 11 and the negative electrode current collecting lead 13 are shown as examples arranged so as to extend in opposite directions through the electrode group. It may be arranged so as to extend from the exterior material. At this time, as shown in FIG. 5, the electrode group including the positive electrode current collecting lead 11 and the negative electrode current collecting lead 13 is arranged so that a plurality of current collecting leads overlap each other when wound. It is preferable to use an electrode group having the structure described above.

  In addition, in FIG. 3 described above, an example in which both the positive and negative electrodes are provided with a plurality of current collecting leads is shown, but either the positive electrode or the negative electrode may have a structure having a plurality of current collecting leads. . In this case, a structure having a plurality of current collecting leads on the positive electrode side is preferable.

  In FIG. 1 described above, the adhesive layer is formed on the entire surface of the electrode group 2, but the adhesive layer may be formed on a part of the electrode group 2. When forming an adhesive layer on a part of the electrode group 2, it is preferable to form it on at least the surface corresponding to the outermost periphery of the electrode group 2. Further, the adhesive layer may not be provided.

  Further, in FIG. 1 described above, an example in which an electrode group having a structure in which a laminate including a plurality of positive electrodes and negative electrodes is wound in a spiral shape and then compressed in the radial direction has been described, as shown in FIG. Alternatively, an electrode group having a structure in which one positive electrode 15 and one negative electrode 16 are spirally wound through a separator 17 therebetween and then compressed in the radial direction may be used.

  In FIG. 1 described above, an example in which an electrode group having a structure in which a positive electrode and a negative electrode are wound in a spiral shape with a separator interposed therebetween and then compressed in a radial direction has been described, the positive electrode and the negative electrode are interposed with a separator. Alternatively, an electrode group having a bent structure may be used. An example of this is shown in FIG. As shown in FIG. 6, the electrode group has a structure in which the positive electrode 18 and the negative electrode 19 are bent a plurality of times (for example, five times) so that the negative electrodes 19 are in contact with each other with a separator 20 therebetween. By making the electrode group bendable, the manufacturing of the electrode group can be simplified and the mechanical strength of the electrode group can be improved.

  Hereinafter, the positive electrode, the negative electrode, the separator, the nonaqueous electrolyte, and the exterior material will be described.

(Positive electrode 6)
This positive electrode has a structure in which a positive electrode active material layer containing a positive electrode active material is supported on one side or both sides of a positive electrode current collector.

  The thickness of one surface of the positive electrode active material layer is in the range of 25 to 100 μm. Accordingly, when the positive electrode current collector is supported on both surfaces, the total thickness of the positive electrode active material is in the range of 50 μm to 200 μm. A more preferable range of the thickness of one surface is 45 to 70 μm. Within this range, the large current discharge characteristics and cycle life characteristics are greatly improved.

  The positive electrode active material may contain a conductive agent in addition to the positive electrode active material. Further, the positive electrode active material layer may include a binder that binds the positive electrode materials to each other, apart from the polymer 9 having adhesiveness.

Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt compound, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and vanadium containing lithium. Examples thereof include oxides and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among these, when a lithium-containing cobalt oxide (for example, LiCoO ₂ ), a lithium-containing nickel cobalt oxide (LiNi _0.8 Co _0.2 O ₂ ), or a lithium manganese composite oxide (LiMn ₂ O ₄ , LiMnO ₂ ) is used, a high voltage is generated. Since it is obtained, it is preferable.

  Further, as the positive electrode active material, a mixture of lithium-containing nickel oxide and lithium manganese composite oxide may be used.

Examples of the lithium-containing nickel oxide include LiNiO ₂ , LiNi _0.7 Co _0.3 O ₂ , LiCo _0.8 Ni _0.2 O ₂ , Li _1.075 Ni _0.755 Co _0.17 O _1.9 F _0.1 , Li _1.10 Ni _0.74 Co _0.16 O _1.85 F _0.15 , Li _{1.075 Ni 0.705 Co 0.17 Al 0.05 O 1.9} F 0.1, Li 1.10 Ni 0.72 Co 0.16 Nb 0.02 O 1.85 F 0.15, LiNi 1-xy Co x M y O 2 ( where M may at least selected Al, B, of Nb A lithium-containing nickel oxide represented by a seed element, where x and y are 0 <x ≦ 0.5, 0 <y <0.5, and 0 <x + y ≦ 0.5. it can. Among them, the composition formula _{LiNi 1-xy Co x M y} O 2 ( provided that at least one element M may be selected Al, B, from Nb, the x, y is 0 <x ≦ 0.5,0 <y It is preferable to use a lithium-containing nickel oxide represented by <0.5 and 0 <x + y ≦ 0.5. Specifically, LiNi _1-xy Co _x Al _y O ₂ , LiNi _1-xy Co _{x By y} O ₂ , LiNi _1-xy Co _x N _{b y} O ₂ , LiNi _1-abc Co _a Al _b Nb _c O ₂ (Wherein x and y are 0 <x ≦ 0.5, 0 <y <0.5 and 0 <x + y ≦ 0.5, and a, b and c are 0 <a ≦ 0) .5, 0 <b <0.5, 0 <c <0.5, and 0 <a + b + c ≦ 0.5). Such a lithium-containing nickel oxide is preferable because of its high thermal stability and excellent safety.

Specific examples of the lithium manganese composite oxide include Li _{1 + a} Mn _2-a O ₄ , Li _{1 + a} Mn _2-ab Co _b O ₄ , and Li _{1 + a} Mn _2-ab Al _b O _{4. , Li 1 + a Mn 2-} ab Fe b O 4, Li 1 + a Mn 2-ab Mg b O 4, Li 1 + a Mn 2-ab Ti b O 4, Li 1 + a Mn 2-ab Nb b O ₄ , Li _{1 + a} Mn _2−ab Ge _b O _{4 and the} like can be mentioned (the a represents 0 <a and 2> a + b).

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyvinylidene fluoride-tetrafluoroethylene-6-propylene terpolymer, and ethylene-propylene-diene copolymer. (EPDM) or the like can be used. When the positive electrode, the negative electrode, and the separator are integrated by a thermoforming method described later, it is desirable to use a thermosetting resin, and PVdF is particularly preferable.

  The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel. The thickness of the current collector is preferably 10 to 30 μm. This is because within this range, it is possible to balance the reduction in resistance and weight of the current collector.

(Negative electrode 9)
The negative electrode has a structure in which a negative electrode active material layer is supported on one side or both sides of a negative electrode current collector. The thickness of the single side | surface of the said negative electrode active material layer is the range of 20-100 micrometers. Therefore, when the negative electrode current collector is supported on both surfaces, the total thickness of the negative electrode active material layer is in the range of 40 to 200 μm. A more preferable range of the thickness of one side is 30 to 80 μm. Within this range, the large current discharge characteristics and cycle life characteristics are greatly improved.

  The negative electrode active material layer may contain a conductive agent in addition to the compound that absorbs and releases lithium ions. The negative electrode active material layer may contain a binder for binding the negative electrode material, in addition to the polymer 9 having adhesiveness.

  A carbonaceous material is mentioned as a compound which occludes / releases lithium ions. Examples of the carbonaceous material include (I) graphite materials such as graphite, coke, carbon fiber, and spherical carbon or carbonaceous materials, and (II) thermosetting resins, isotropic pitches, mesophase pitches, and mesophase pitch carbon fibers. Examples thereof include graphite materials or carbonaceous materials obtained by subjecting mesophase spherules to heat treatment at 500 to 3000 ° C. Among the carbonaceous materials subjected to the heat treatment, mesophase pitch-based carbon fiber graphite material or carbonaceous material, mesophase microsphere graphite material or carbonaceous material, or granular graphite material. Among such carbonaceous materials, the carbonaceous material a and the carbonaceous material b described below are preferable.

The carbonaceous material a is a graphitic material obtained by setting the temperature of the heat treatment to 2000 ° C. or more and having graphite crystals having a (002) plane spacing d ₀₀₂ of 0.340 nm or less. The shape of the graphite material is preferably granular. A non-aqueous electrolyte secondary battery including a negative electrode containing the carbonaceous material can greatly improve battery capacity and large current discharge characteristics. The spacing d ₀₀₂ is more preferably at most 0.336 nm.

The carbonaceous material b is at least one selected from a fibrous graphite material that has been heat-treated at 2000 ° C. or higher and a spherical graphite material that has been heat-treated at 2000 ° C. or higher. Among these, mesophase pitch-based carbon fiber graphite materials, vapor-grown carbon fibers such as carbon whiskers, and mesophase microsphere graphite materials are preferable. Since the negative electrode including the carbonaceous material b can reduce the interface impedance between the negative electrode and the separator even when the density is increased to 1.3 g / cm ³ or more, the large current discharge characteristics and the rapid charge of the secondary battery can be reduced. The discharge cycle performance can be improved.

  The shape of the carbonaceous material can be, for example, fibrous, spherical, or granular. The negative electrode layer contains at least one carbonaceous material selected from the group consisting of a fibrous carbonaceous material, a spherical carbonaceous material and a spherical carbonaceous material, thereby maintaining the interface resistance of the negative electrode at a close value over a long period of time. Therefore, the charge / discharge cycle life can be improved.

  The average fiber length of the fibrous carbonaceous material is preferably in the range of 5 to 200 μm. A more preferable range is 10 to 50 μm.

  The average fiber diameter of the fibrous carbonaceous material is preferably in the range of 0.1 to 20 μm. A more preferable range is 1 to 15 μm.

  The average aspect ratio of the fibrous carbonaceous material is preferably in the range of 1.5 to 200. A more preferable range is 1.5 to 50. However, the aspect ratio is the ratio of the fiber length (fiber length / fiber diameter) to the fiber diameter.

  The average particle diameter of the spherical carbonaceous material is preferably in the range of 1 to 100 μm. A more preferable range is 2 to 40 μm.

  The ratio of the minor radius to the major radius of the spherical carbonaceous material (minor radius / major axis) is preferably 1/10 or more. A more preferable range is 1/2 or more.

  The granular carbonaceous material means a carbonaceous material powder having a shape in which a ratio of a minor radius to a major radius (minor radius / major axis) is in a range of 1/100 to 1. A more preferable range of the ratio is 1/10 to 1.

  The average particle size of the granular carbonaceous material is preferably in the range of 1 to 100 μm. A more preferable range is 2 to 50 μm.

  The binder has a function of binding negative electrode materials to each other and a function of binding the negative electrode material and the negative electrode current collector. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxycellulose (CMC) and the like. Can be used. When the positive electrode, the negative electrode, and the separator are integrated by a thermoforming method described later, it is desirable to use a thermosetting resin, and PVdF is particularly preferable.

The blending ratio of the carbonaceous material and the binder is preferably in the range of 90 to 98% by weight of the carbonaceous material and 2 to 20% by weight of the binder. In particular, the content of the carbonaceous material in the negative electrode is preferably in the range of 10 to 80 g / m ^{2 on} one side. The packing density is desirably in the range of 1.20 to 1.50 g / cm ³ .

  As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel. The thickness of the current collector is preferably 5 to 20 μm. This is because within this range, it is possible to balance the reduction in resistance and weight of the current collector.

  The negative electrode active material layer may be a metal such as aluminum, magnesium, tin, or silicon, a metal oxide, a metal sulfide, or a metal nitride in addition to the carbonaceous material that occludes / releases lithium ions. It may contain a metal compound selected from those or a lithium alloy.

  Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.

  Examples of the metal sulfide include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.

  Examples of the lithium alloy include a lithium silicon alloy.

(Separator 3)
The separator is formed from a porous sheet. As the porous sheet, for example, a porous film containing polyethylene, polypropylene, or polyvinylidene fluoride (PVdF), a synthetic resin nonwoven fabric, or the like can be used. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.

  The thickness of the porous sheet is preferably 30 μm or less. If the thickness exceeds 30 μm, the distance between the positive and negative electrodes may be increased and the internal resistance may be increased. Further, the lower limit value of the thickness is preferably 5 μm. If the thickness is less than 5 μm, the strength of the separator is remarkably lowered and an internal short circuit is likely to occur. The upper limit value of the thickness is preferably 25 μm, and the lower limit value is more preferably 10 μm.

  The porous sheet preferably has a heat shrinkage of 20% or less in the presence at 120 ° C. for 1 hour. If the heat shrinkage rate exceeds 20%, it may be difficult to make the adhesion strength between the positive and negative electrodes and the separator sufficient. The heat shrinkage rate is more preferably 15% or less.

  The porous sheet preferably has a porosity in the range of 30 to 70%. This is due to the following reason. If the porosity is less than 30%, it may be difficult to obtain high electrolyte retention in the separator. On the other hand, if the porosity exceeds 70%, sufficient separator strength may not be obtained. A more preferable range of the porosity is 35 to 70%.

The porous sheet preferably has an air permeability of 500 seconds / 100 cm ³ or less. The air permeability means time (seconds) required for 100 cm ³ of air to pass through the porous sheet. If the air permeability exceeds 500 seconds / 100 cm ³ , it may be difficult to obtain high lithium ion mobility in the separator. The lower limit value of the air permeability is preferably 30 seconds / 100 cm ³ . This is because if the air permeability is less than 30 seconds / 100 cm ³ , sufficient separator strength may not be obtained. The upper limit value of the air permeability is more preferably 150 seconds / 100 cm ³ . The lower limit is more preferably 50 seconds / 100 cm ³ .

  As will be described later, when the positive electrode, the negative electrode, and the separator are integrated using an adhesive polymer, the end portion along the short direction of the separator is 0 compared to the end portion along the short direction of the negative electrode. It is desirable that a polymer having adhesiveness is present at the end of the separator that extends from 25 mm to 2 mm. By setting it as such a structure, since the intensity | strength of a separator edge part can be improved, it can suppress that an internal short circuit arises when an impact is added to a battery. Furthermore, when the battery is used in a high temperature environment of 100 ° C. or higher, the separator can be prevented from being thermally contracted, so that an internal short circuit can be suppressed and safety can be improved.

(Nonaqueous electrolyte)
This non-aqueous electrolyte is held at least by the separator. In particular, the nonaqueous electrolyte is preferably dispersed throughout the electrode group. As this non-aqueous electrolyte, a liquid non-aqueous electrolyte composed of a non-aqueous solvent in which an electrolyte is dissolved (hereinafter referred to as a non-aqueous solution), a polymer material holding the non-aqueous solution, or a solid electrolyte can be used. Examples of the polymer material in which the non-aqueous container is held include a gel-like non-aqueous electrolyte in which the non-aqueous solution is gelled, the non-aqueous solution is partially gelled and the rest remains liquid, but the non-aqueous solution And the like that are maintained in a liquid state. Among these, it is preferable to use a liquid nonaqueous electrolyte. Since the liquid non-aqueous electrolyte can increase the ionic conductivity of the electrode group, the interface resistance between the positive electrode and the separator and the interface resistance between the negative electrode and the separator can be reduced.

  The polymer material in which the non-aqueous solution is retained is prepared, for example, by mixing the non-aqueous solution, the polymer, and the gelling agent, and then performing a heat treatment to cause gelation.

  As the polymer, at least one polymer selected from polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), polyvinyl chloride (PVC), and polyacrylate (PMMA) can be used. .

  As the non-aqueous solvent, a known non-aqueous solvent can be used as a solvent for the lithium ion secondary battery, and is not particularly limited, but one kind selected from the group consisting of propylene carbonate (PC) and ethylene carbonate (EC). It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent of the first solvent and the second solvent having a lower viscosity than PC and EC. In particular, the second solvent preferably has a donor number of 16.5 or less.

  Examples of the second solvent include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, γ-butyrolactone (BL), acetonitrile (AN), ethyl acetate (EA), toluene. , Xylene, methyl acetate (MA) and the like. These second solvents can be used alone or in the form of a mixture of two or more.

  The blending amount of the first solvent in the mixed solvent is preferably 10 to 80% by volume ratio. A more preferable blending amount of the first solvent is 20 to 75% by volume ratio.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and trifluorometasulfonic acid. Examples thereof include lithium salts such as lithium (LiCF ₃ SO ₃ ) and bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ]. Of these, LiPF ₆ or LiBF ₄ is preferably used.

  The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.0 mol / L.

  A particularly preferable non-aqueous solution is a solution in which an electrolyte (for example, lithium salt) is dissolved in a mixed non-aqueous solvent containing γ-butyrolactone (BL), and the BL composition ratio is 20% by volume or more and 80% by volume of the mixed non-aqueous solvent. It is as follows. In the mixed non-aqueous solvent, it is preferable that the BL composition ratio is maximized. If the ratio is less than 20% by volume, gas tends to be generated at high temperatures. In addition, when the mixed non-aqueous solvent contains BL and cyclic carbonate, the ratio of the cyclic carbonate becomes relatively high, and thus the solvent viscosity may be remarkably increased. When the solvent viscosity increases, the conductivity and permeability of the non-aqueous electrolyte decrease, so that the charge / discharge cycle characteristics, the large current discharge characteristics, and the discharge characteristics under a low temperature environment around −20 ° C. decrease. On the other hand, if the ratio exceeds 80% by volume, the reaction between the negative electrode and BL tends to occur, and the charge / discharge cycle may be reduced. That is, when the negative electrode (for example, containing a carbonaceous material that occludes and releases lithium ions) reacts with BL to cause reductive decomposition of the nonaqueous electrolyte, a coating that inhibits the charge / discharge reaction is formed on the surface of the negative electrode. . As a result, current concentration is likely to occur in the negative electrode, so that lithium metal is deposited on the negative electrode surface, or the impedance of the negative electrode interface is increased, the charge / discharge efficiency of the negative electrode is reduced, and charge / discharge cycle characteristics are deteriorated. A more preferable range is 40% by volume or more and 75% by volume or less. By setting it within this range, it is possible to further increase the effect of suppressing gas generation during high-temperature storage, and to further improve the discharge capacity in a low temperature environment around −20 ° C.

  As a solvent mixed with BL, a cyclic carbonate is desirable in terms of increasing the charge / discharge efficiency of the negative electrode.

  As the cyclic carbonate, propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), trifluoropropylene carbonate (TFPC) and the like are desirable. In particular, when EC is used as a solvent mixed with BL, charge / discharge cycle characteristics and large current discharge characteristics can be greatly improved. Other solvents mixed with BL include a third solvent consisting of at least one selected from the group consisting of PC, VC and TFPC, diethyl carbonate (DEC), methyl ethyl carbonate (MEC) and aromatic compounds, and EC. It is desirable that it is a mixed solvent with the above in terms of enhancing charge / discharge cycle characteristics.

  Furthermore, you may contain 20 volume% or less of low-viscosity solvents from a viewpoint of reducing a solvent viscosity. Examples of the low viscosity solvent include chain carbonates, chain ethers, and cyclic ethers.

  More preferred compositions of the non-aqueous solvent according to the present invention are BL and EC, BL and PC, BL and EC and DEC, BL and EC and MEC, or BL and EC and MEC and VC. At this time, the volume ratio of EC is preferably 5 to 40% by volume. This is due to the following reason. If the EC ratio is less than 5% by volume, it may be difficult to cover the negative electrode surface densely with a protective film, so that the reaction between the negative electrode and BL occurs, and the charge / discharge cycle characteristics can be sufficiently improved. It can be difficult. On the other hand, if the volume ratio of EC exceeds 40% by volume, the viscosity of the non-aqueous solution increases and the ionic conductivity may decrease, so the charge / discharge cycle characteristics, large current discharge characteristics, and low temperature discharge characteristics are sufficiently improved. Can be difficult to do. A more preferable range of the EC ratio is 10 to 35% by volume. Moreover, it is preferable that the ratio of the solvent which consists of at least 1 type chosen from DEC, MEC, and VC shall be in the range of 0.01-10 volume%.

Examples of the electrolyte include the same ones as described above. Of these, LiPF ₆ or LiBF ₄ is preferably used. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.0 mol / L.

  The viscosity of the non-aqueous solution at 20 ° C. is preferably in the range of 3 cp to 20 cp. This is due to the following reason. If the viscosity is less than 3 cp, the vapor pressure increases when the secondary battery is stored in a high temperature environment, or the amount of gas generated increases, and the exterior material may expand. On the other hand, when the viscosity exceeds 20 cp, the permeability of the non-aqueous solution is lowered, so that the internal resistance may be increased. A more preferable range of the viscosity is 4 cp to 15 cp. A more preferable range is 6 to 8 cp.

  Among non-aqueous solvents having a viscosity at 20 ° C. in the range of 3 cp to 20 cp, solvent A consisting of at least one selected from the group consisting of propylene carbonate (PC), γ-butyrolactone (BL) and diethyl carbonate (DEC) It is preferable to use an electrolyte dissolved in a nonaqueous solvent containing ethylene carbonate (EC).

  The volume ratio of the solvent A in the non-aqueous solvent is preferably 50 to 90% by volume. This is due to the following reason. If the volume ratio is less than 50% by volume, the low-temperature discharge characteristics may be deteriorated, and gas may be easily generated at a high temperature. When reductive decomposition of the non-aqueous electrolyte occurs, a film that inhibits the charge / discharge reaction is formed on the surface of the negative electrode, and current concentration tends to occur in the negative electrode, so that lithium metal is deposited on the negative electrode surface or the impedance of the negative electrode interface Becomes higher, the charge / discharge efficiency of the negative electrode is lowered, and the charge / discharge cycle characteristics are lowered. A more preferable range is 60% by volume or more and 80% by volume or less.

  The volume ratio of EC in the non-aqueous solvent is preferably 5 to 40% by volume. This is due to the following reason. If the EC ratio is less than 5% by volume, it is difficult to densely cover the negative electrode surface with a protective film, and reductive decomposition of the non-aqueous electrolyte is likely to occur. Therefore, it is difficult to sufficiently improve the charge / discharge cycle characteristics. There is a possibility. On the other hand, if the EC ratio exceeds 40% by volume, the solvent A ratio is relatively low, and the amount of gas generated when the secondary battery is stored at high temperature may increase. A more preferable range of the EC ratio is 10 to 35% by volume.

  The nonaqueous solvent preferably further contains vinylene carbonate (VC). The ratio of VC in the non-aqueous solvent is preferably in the range of 0.01 to 10% by volume.

Examples of the electrolyte include the same ones as described above. Of these, LiPF ₆ or LiBF ₄ is preferably used. The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 mol / L to 2.0 mol / L.

  The amount of the liquid non-aqueous electrolyte having each composition described above is preferably 0.2 to 0.6 g per 100 mAh of battery unit capacity. This is due to the following reason. If the amount of the liquid non-aqueous electrolyte is less than 0.2 g / 100 mAh, the ionic conductivity of the positive electrode and the negative electrode may not be sufficiently maintained. On the other hand, when the amount of the liquid non-aqueous electrolyte exceeds 0.6 g / 100 mAh, the amount of the electrolyte becomes large, which may make sealing difficult when a sheet-made exterior material is used. A preferable range of the amount of the liquid non-aqueous electrolyte is 0.4 to 0.55 g / 100 mAh.

(Exterior material 1)
The exterior material 1 is a sheet having a thickness of 0.5 mm or less including a resin layer. The resin layer of the exterior material 1 can be formed from a thermoplastic resin, for example. Examples of the thermoplastic resin include polyethylene and polypropylene.

  Examples of the exterior material 1 include a multilayer sheet including a metal layer and resin layers formed on both surfaces of the metal layer.

  Examples of the metal layer include aluminum, stainless steel, iron, copper, nickel, and the like. Among these, aluminum that is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, but may be formed from a combination of two or more types of metal layers.

  The resin layer serving as the inner surface of the exterior material 1 has a function as a heat seal surface and a function of preventing the metal layer from being corroded by the nonaqueous electrolyte. Moreover, the resin layer used as the outer surface of an exterior material plays the role which prevents damage to a metal layer. Each resin layer may be formed from one type of resin, or may be formed from two or more types of resins. Each resin layer is preferably formed from a thermoplastic resin. The melting point of the thermoplastic resin that forms the resin layer serving as the inner surface of the exterior surface is preferably 120 ° C. or higher, and more preferably in the range of 140 ° C. to 250 ° C. Examples of the thermoplastic resin include polyethylene and polypropylene. In particular, polypropylene having a melting point of 150 ° C. or higher is desirable because it can improve the sealing strength of the heat seal portion.

  When the thickness of the outer packaging material 1 exceeds 0.5 mm, the capacity per weight of the battery and the capacity per volume of the battery are lowered. The thickness of the exterior material 1 is preferably 0.3 mm or less, more preferably 0.25 mm or less, and most preferably 0.2 mm or less. On the other hand, if the thickness is less than 0.05 mm, deformation or breakage tends to occur. For this reason, the lower limit value of the thickness is preferably 0.05 mm.

  The thickness of the packaging material 1 is measured by the method described below. That is, in the region excluding the heat seal sealing portion of the exterior material 1, three points that are separated from each other by 1 cm or more are arbitrarily selected, the thickness of each point is measured, an average value is calculated, and this value is calculated. The thickness of the material. In addition, when the foreign material (for example, resin) has adhered to the surface of the said exterior material, thickness is measured after removing this foreign material. For example, when PVdF adheres to the surface of the exterior material, the PVdF is removed by wiping the surface of the exterior material with a dimethylformamide solution, and then the thickness is measured. When the exterior material 1 is composed of a multilayer sheet, it is desirable that the electrode group is adhered to the inner surface of the exterior material by an adhesive layer formed on at least a part of the surface thereof. With such a configuration, since the exterior material can be fixed to the surface of the electrode group, it is possible to prevent the electrolyte from penetrating between the electrode group and the exterior material.

  For the adhesive layer, the same material as the polymer having adhesiveness described later can be used. The adhesive layer may have a porous structure. The porous adhesive layer can hold the nonaqueous electrolyte in the voids.

  The nonaqueous electrolyte secondary battery according to the present invention is manufactured by the method described below.

(1) Thermoforming method (first step)
An electrode group is produced by the method described in the following (a) to (c).

  (A) A separator is interposed as a separator between the positive electrode and the negative electrode and wound in a spiral shape.

  (B) A separator as a separator is interposed between the positive electrode and the negative electrode, and then wound in a spiral shape, and then compressed in the radial direction.

  (C) Bending twice or more with a separator interposed between the positive electrode and the negative electrode.

  The positive electrode is produced, for example, by suspending a conductive agent and a binder in an appropriate solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate. Examples of the positive electrode active material, the conductive agent, the binder, and the current collector include the same materials as those described in the section of (1) Positive electrode described above.

  The negative electrode, for example, kneads lithium ion storage and release carbonaceous material and a binder in the presence of a solvent, applies the obtained suspension to a current collector, dries, and then at a desired pressure. It is produced by pressing once or performing multistage pressing 2 to 5 times.

  Examples of the carbonaceous material, the binder, and the current collector include the same materials as those described in the section of (2) Negative electrode.

  Examples of the porous sheet of the separator include the same as those described in the section of (3) Separator described above.

(Second step)
After the electrode group is accommodated in the exterior material, heat forming is performed.

  The atmosphere for performing the heat forming is preferably a reduced pressure atmosphere including a vacuum or a normal pressure atmosphere.

  The heating temperature is preferably 30 ° C. or higher. A more preferable range is 60 ° C to 100 ° C. Moreover, when it shape | molds at the temperature of 60-100 degreeC in a pressure-reduced atmosphere, an electrode group can be dried simultaneously with shaping | molding.

  The molding is compressed in the radial direction when the electrode group is produced by the method (a), and compressed in the laminating direction when the electrode group is produced by the method (b) or (c). It is desirable to do so.

  The molding can be performed by, for example, press molding or insertion into a molding die.

The pressure applied during molding is preferably in the range of 0.01 to 20 kg / cm ² . When the pressure exceeds 20 kg / cm ² , an internal short circuit is likely to occur. A more preferable range is 0.01 to 15 kg / cm ² . When the pressure is in the range of 0.01 to 15 kg / cm ² , the integration can be easily performed.

  The heat molding time is preferably in the range of 2 seconds to 120 minutes.

  When the electrode group is thermoformed, the binder contained in the positive electrode and the negative electrode can be thermoset, so that the positive electrode, the negative electrode, and the separator can be integrated. The peel strength between the separator and the negative electrode layer and the peel strength between the negative electrode layer and the negative electrode current collector are integrated while the positive electrode, the negative electrode and the separator are integrated by adjusting the heat molding temperature, the molding pressure and the molding time. It can be made lower than

(Third step)
A non-aqueous electrolyte secondary battery according to the present invention is obtained by impregnating a liquid non-electrolyte into an electrode group in the exterior material and sealing an opening of the exterior material.

  In addition, after performing the heat forming without housing the electrode group in the exterior material, this electrode group is accommodated in the exterior material, the electrode group in the exterior material is impregnated with a liquid nonaqueous electrolyte, and the sealing treatment The nonaqueous electrolyte secondary battery according to the present invention can be obtained.

(2) Method of using an adhesive polymer (first step)
A group of electrodes is prepared by interposing a porous sheet as a separator between the positive electrode and the negative electrode.

  The electrode group is preferably produced by the same method as described in the above-described thermoforming method. When produced by such a method, in the second step to be described later, while the polymer solution having adhesiveness is infiltrated into the positive electrode, the negative electrode, and the separator, the solution is applied to the entire boundary between the positive electrode and the separator and between the negative electrode and the separator. Infiltration can be prevented. As a result, it is possible to intersperse the polymer having adhesiveness to the positive electrode, the negative electrode and the separator, and to interpose the polymer having adhesiveness to the boundary between the positive electrode and the separator and the boundary between the negative electrode and the separator. it can.

  The positive electrode and the negative electrode are produced by the same method as described in the thermoforming method described above. As the porous sheet of the separator, the same sheet as described in the section of (3) Separator described above can be used.

(Second step)
The electrode group is accommodated in a bag-shaped exterior material so that the laminated surface can be seen from the opening. A solution obtained by dissolving a polymer having adhesiveness in a solvent is injected into the electrode group in the exterior material from the opening, and the electrode group is impregnated with the solution.

  The polymer having adhesiveness is desirably a polymer that can maintain high adhesiveness while holding the nonaqueous electrolyte. Furthermore, it is more preferable that such a polymer has high lithium ion conductivity. Specific examples include polyacrylonitrile (PAN), polyacrylate (PMMA), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and polyethylene oxide (PEO). In particular, polyvinylidene fluoride (PVdF) is preferable. Polyvinylidene fluoride (PVdF) can hold a non-aqueous electrolyte, and if it contains a non-aqueous electrolyte, it partially gels, so that the ionic conductivity in the positive electrode can be further improved.

  As the solvent, it is desirable to use an organic solvent having a boiling point of 200 ° C. or lower. Examples of such an organic solvent include dimethylformamide (boiling point 153 ° C.). If the boiling point of the organic solvent exceeds 200 ° C., the drying time may take longer when the heating temperature described below is set to 100 ° C. or lower. The lower limit of the boiling point of the organic solvent is preferably 50 ° C. If the boiling point of the organic solvent is less than 50 ° C., the organic solvent may evaporate while the solution is injected into the electrode group. The upper limit of the boiling point is more preferably 180 ° C., and the lower limit of the boiling point is further preferably 100 ° C.

  The concentration of the polymer having adhesiveness in the solution is preferably in the range of 0.05 to 2.5% by weight. This is due to the following reason. If the concentration is less than 0.05% by weight, it may be difficult to bond the positive and negative electrodes and the separator with sufficient strength. On the other hand, if the concentration exceeds 2.5% by weight, it may be difficult to obtain a sufficient porosity to hold the non-aqueous electrolyte, and the interface impedance of the electrode may be significantly increased. As the interface impedance increases, the capacity and large current discharge characteristics are significantly reduced. A more preferable range of the concentration is 0.1 to 1.5% by weight.

  The injection amount of the solution is preferably in the range of 0.1 to 2 mL per 100 mAh of battery capacity when the concentration of the polymer having adhesiveness in the solution is 0.05 to 2.5% by weight. This is due to the following reason. If the amount of liquid injection is less than 0.1 mL, it may be difficult to sufficiently improve the adhesion between the positive electrode, the negative electrode, and the separator. On the other hand, if the injection volume exceeds 2 mL, the lithium ion conductivity of the secondary battery may decrease and the internal resistance may increase, and the discharge capacity, large current discharge characteristics, and charge / discharge cycle characteristics should be improved. May be difficult. A preferable range of the injection amount is 0.15 to 1 mL per 100 mAh of battery capacity.

(Third step)
Apply heat forming.

  The atmosphere in which the heat forming is performed is preferably a reduced pressure atmosphere including a vacuum or a normal pressure atmosphere.

  The heating temperature is preferably 30 ° C. or higher. A more preferable range is 60 ° C to 100 ° C. Moreover, when it shape | molds in the pressure reduction atmosphere at the temperature of 60 to 100 degreeC, an electrode group can be dried simultaneously with shaping | molding.

  The molding is compressed in the radial direction when the electrode group is produced by the method (a), and compressed in the laminating direction when the electrode group is produced by the method (b) or (c). It is desirable to do so.

  The molding can be performed by, for example, press molding or insertion into a molding die.

The pressure applied during molding is preferably in the range of 0.01 to 20 kg / cm ² . A more preferable range is 0.01 to 15 kg / cm ² .

  The heat molding time is preferably in the range of 2 seconds to 120 minutes.

  By subjecting the electrode group to thermoforming, the solvent can be evaporated, and the positive electrode, the negative electrode, and the separator can be integrated. In this thermoforming, the adhesive high molecular weight, heating temperature, molding pressure and thermoforming time are adjusted to integrate the positive electrode, the negative electrode and the separator, and the peel strength between the separator and the negative electrode layer. Can be made lower than the peel strength between the negative electrode layer and the negative electrode current collector.

(4th process)
A nonaqueous electrolyte secondary battery according to the present invention is obtained by impregnating a liquid nonaqueous electrolyte into an electrode group in the outer packaging material and performing a sealing treatment.

  Further, before the electrode group is housed in the exterior material, the electrode group is impregnated with a solution in which an adhesive polymer is dissolved, and the electrode group is subjected to thermoforming, and then the electrode group is attached to the exterior material. The nonaqueous electrolyte secondary battery according to the present invention can be obtained by storing the battery in a container, injecting a nonaqueous electrolyte, and performing sealing or the like. Furthermore, the electrode group may be accommodated in the exterior material after an adhesive is applied to the outer peripheral surface of the electrode group. Thereby, an electrode group can be adhere | attached on the inner surface of an exterior material.

  In the case of producing a battery by a method using an adhesive polymer, the total amount of the polymer having adhesiveness contained in the battery (including those contained in an adhesive part described later) is 0.1 per 100 mAh of battery capacity. ˜6 mg is preferred. This is due to the following reason. If the total amount of the adhesive polymer is less than 0.1 mg per 100 mAh, it may be difficult to sufficiently improve the adhesion between the positive electrode, the separator and the negative electrode. On the other hand, if the total amount exceeds 6 mg per 100 mAh, the lithium ion conductivity of the secondary battery may decrease and the internal resistance may increase, and the discharge capacity, large current discharge characteristics, and charge / discharge cycle characteristics should be improved. May be difficult. A more preferable range of the total amount of the polymer having adhesiveness is 0.2 to 1 mg per 100 mAh of battery capacity.

  When manufacturing a battery by the method using the adhesive polymer, it is desirable that the adhesive polymer is held in the voids of the positive electrode layer, the separator, or the negative electrode layer. Moreover, it is preferable that the polymer having adhesiveness is scattered in the electrode group because the internal resistance of the battery can be reduced.

  The polymer having adhesiveness preferably has a porous structure having fine pores in the gaps of the positive electrode, the negative electrode, and the separator. The polymer having adhesiveness having a porous structure can hold a large amount of non-aqueous electrolyte. Furthermore, it is desirable that the electrode group is uniformly dispersed and scattered.

[Example]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings described above.

Example 1
<Preparation of positive electrode>
First, 90.5% by weight of lithium cobalt oxide (Li _x CoO ₂ ; x is 0 ≦ x ≦ 1) powder, 2.5% by weight of acetylene black, 3% by weight of graphite, 4% by weight of polyvinylidene fluoride (PVdF) % And an N-methyl-2-pyrrolidone (NMP) solution were added and mixed to prepare a slurry. The slurry was intermittently applied to a positive electrode current collector made of an aluminum foil having a thickness of 15 μm at regular intervals in the longitudinal direction of the electrode, dried, and then roll-pressed.

Then, a positive electrode lead (short side) made of aluminum having a thickness of 0.2 mm, a width of 5 mm, and a length of 50 mm is applied to an uncoated portion of the positive electrode layer formed at both ends and a central portion of the positive electrode in the longitudinal direction. A total of three cross-sectional areas in the direction of 1 mm ² ) were welded, and the weld was covered with insulating tape to produce a positive electrode.

The obtained positive electrode had a structure in which a positive electrode layer having a thickness of 50 μm was supported on both surfaces of the positive electrode current collector. The total thickness of the positive electrode layer is 100 μm and the packing density is 3.3 g / cm ³ .

<Production of negative electrode>
A mesophase pitch carbon fiber heat-treated at 3000 ° C. was prepared as a carbonaceous material. The carbon fiber had an average fiber diameter of 8 μm, an average fiber length of 20 μm, and an average interplanar spacing (d ₀₀₂ ) of 0.3360 nm. A slurry was prepared by mixing 93% by weight of the carbonaceous powder, 7% by weight of polyvinylidene fluoride (PVDF) as a binder, and an NMP solution. The obtained slurry was intermittently applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 12 μm in the longitudinal direction of the electrode, dried and roll-pressed.

Next, when the negative electrode is divided into four in the longitudinal direction, a thickness of 0.2 mm × width is applied to an uncoated portion of the negative electrode layer formed at a length of 1/4 and 3/4 from the end. A total of two 5 mm × 50 mm Cu negative electrode leads (cross-sectional area of 1 mm ^{2 in the} short direction) were welded, and the weld was covered with insulating tape to produce a negative electrode.

A negative electrode having an electrode density of 1.4 g / cm ³ was produced. The obtained negative electrode had a structure in which a negative electrode layer having a thickness of 48 μm was supported on both surfaces of the negative electrode current collector. The total thickness of the negative electrode layer is 96 μm.

<Production of electrode group>
A polyethylene separator having a thickness of 15 μm and a porosity of 50% was prepared. A separator is interposed between the positive electrode and the negative electrode, and the positive electrode lead and the negative electrode lead are wound in a spiral shape so as to extend in opposite directions, and then pressed in the radial direction to a thickness of 2.7 mm. And formed into a flat shape having a width of 120 mm and a height of 200 mm.

  As the positive electrode terminal and the negative electrode terminal, a convex positive electrode terminal made of aluminum (projection thickness 0.5 mm, lead connection thickness 0.2 mm) and copper negative electrode terminal (projection thickness 0. 5 mm, the thickness of the lead connection part 0.2 mm).

Next, after three positive leads and two negative leads were welded to the lead connection portions of the positive electrode terminal and the negative electrode terminal, respectively, the lead connection portion side of the protruding portion was covered with polypropylene. The thickness of the polypropylene layer was 100 μm. In this way, an electrode group was produced. The obtained electrode group has a side length L ₁ = 35.5 mm of the current collecting lead connecting portion, a side length L ₂ = 120 mm along the current collecting lead connecting portion of the electrode group, and L ₁ / L ₂ = It was 0.3.

<Preparation of non-aqueous electrolyte>
Lithium tetrafluoroborate (LiBF ₄ ) is dissolved in a mixed solvent of ethylene carbonate (EC) and γ-butyrolactone (BL) (mixing volume ratio 40:60) at 1.5 mol / L to prepare a non-aqueous electrolyte (liquid Non-aqueous electrolyte) was prepared.

<Battery assembly>
A 100 μm-thick laminate film in which both sides of an aluminum foil are covered with polypropylene is formed into a cylindrical shape, the electrode group is accommodated in this, and the obtained product is sandwiched between holders so that the battery thickness is 2.7 mm. . Polyvinylidene fluoride (PVdF), which is an adhesive polymer, was dissolved in 0.3% by weight in dimethylformamide (DMF) (boiling point: 153 ° C.), which is an organic solvent. The obtained solution was injected into the electrode group in the laminate film so as to have a capacity of 0.6 mL per 100 mAh of battery capacity, and the solution was infiltrated into the electrode group, and the electrode group, the positive electrode lead, and the negative electrode lead. Adhered to the entire surface.

  Next, the electrode group in the laminate film is subjected to vacuum drying at 80 ° C. for 12 hours to evaporate the organic solvent, and the adhesive polymer is held in the voids of the positive electrode, the negative electrode, and the separator, and the positive electrode, the negative electrode, and The separator was integrated, and a porous adhesive portion was formed on the surface of the electrode group.

  The holder was then released. The time during which the electrode group was sandwiched between the holders was 120 minutes. The non-aqueous electrolyte is injected into the electrode group in the laminate film so that the amount per battery capacity of 1 Ah is 4.1 g, and has the structure shown in FIGS. A thin non-aqueous electrolyte secondary battery having a thickness of 150 mm and a height of 250 mm was assembled.

Example 2
The thickness L is 3 mm and the width is the same as in Example 1 except that the length L ₁ of the side of the current collecting lead connecting portion at the positive electrode terminal and the negative electrode terminal is 60 mm and L ₁ / L ₂ = 0.5. A thin non-aqueous electrolyte secondary battery having a thickness of 150 mm and a height of 250 mm was assembled.

Example 3
The thickness L is 3 mm and the width is the same as in Example 1 except that the length L ₁ of the side of the current collector lead connecting portion at the positive electrode terminal and the negative electrode terminal is 90 mm and L ₁ / L ₂ = 0.75. A thin non-aqueous electrolyte secondary battery having a thickness of 150 mm and a height of 250 mm was assembled.

Example 4
A thin non-aqueous electrolyte secondary battery having a thickness of 3 mm, a width of 150 mm, and a height of 250 mm in the same manner as in Example 3 except that the thickness of the polypropylene layer covering the positive electrode terminal and the negative electrode terminal is 40 μm. Assembled.

Comparative Example 1
Except that the positive electrode lead made of aluminum and the negative electrode lead made of Cu were welded one by one to the uncoated part of the active material layer formed at one end in the longitudinal direction, respectively, in the same manner as in Example 1. Thus, a positive electrode and a negative electrode were produced.

  The positive electrode and the negative electrode are interposed between the same separators as in Example 1, wound in a spiral shape so that the positive electrode lead and the negative electrode lead extend in the same direction, and then pressed in the radial direction. An electrode group having a thickness of 2.7 mm, a width of 120 mm, and a height of 200 mm was formed into a flat shape. In this electrode group, the positive electrode current collector was located on the outermost periphery of the electrode group. Further, the positive electrode current collecting lead and the negative electrode current collecting lead were not connected to the positive electrode terminal and the negative electrode terminal.

  A laminate film having a thickness of 100 μm in which both surfaces of an aluminum foil were covered with polypropylene was formed into a bag shape, and the electrode group was accommodated in the bag.

  Thereafter, a thin non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1.

Comparative Example 2
A thin nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that the positive electrode terminal and the negative electrode terminal were not connected.

Comparative Example 3
The length L ₁ of the side of the current collector lead connecting portion in the positive electrode terminal and the negative electrode terminal is 25 mm, L ₁ / L ₂ = 0.21, and the thickness of the polypropylene layer covering the positive electrode terminal and the negative electrode terminal is 30 μm. A thin nonaqueous electrolyte secondary battery having a thickness of 3 mm, a width of 150 mm, and a height of 250 mm was assembled in the same manner as in Example 1 except that.

  The following treatment was performed as an initial charging step on the obtained secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3. First, after being left in a high temperature environment of 40 ° C. for 5 hours, constant current / constant voltage charging was performed for 10 hours to 4.2 V at 0.2 C (2 A) in that environment. Thereafter, the battery was discharged at 0.2 C to 2.7 V, and the second cycle was charged under the same conditions as in the first cycle to obtain a nonaqueous electrolyte secondary battery.

  Next, for the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3, large current discharge characteristics were measured, and the results are shown in Table 1. As a method for defining this large current discharge characteristic, here, a method for defining by the ratio of each discharge capacity obtained when discharging at two current values was adopted. That is, when the current of 10 A that discharges 10 Ah, which is the nominal capacity of the battery in 1 hour, is 1 C, the discharge capacity when discharged at 0.2 C (0.2 C), the discharge capacity when discharged at 10 C (10 C ), And the ratio of the two discharge capacities, which is the ratio of discharge capacity (10C) / discharge capacity (0.2C), is defined as the large current discharge capacity ratio, and will be used hereinafter.

Subsequently, 20 secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared and stored in a constant temperature bath at 60 ° C. for a certain period. The number of batteries in which abnormalities occurred was examined, and the results are also shown in Table 1.

  As is apparent from Table 1, in the batteries of Examples 1 to 4, the occurrence rate of batteries in which abnormalities such as leakage and swelling were observed was greatly suppressed, and in particular, Examples 1 to 3 However, in the batteries of Comparative Example 2 and Comparative Example 3, the abnormality occurrence rate is high. Moreover, although the incidence rate of abnormality is low in Comparative Example 1, it can be seen that the large current discharge ratio is significantly reduced as compared with Examples 1 to 4.

Sectional drawing which shows an example of the nonaqueous electrolyte secondary battery concerning this invention. The expanded sectional view which shows the A section of FIG. The expanded sectional view which shows the positive electrode terminal part of the nonaqueous electrolyte secondary battery of FIG. The non-aqueous electrolyte secondary battery of FIG. The perspective view which shows another example of the electrode group integrated in the nonaqueous electrolyte secondary battery of FIG. The side view which shows another example of the electrode group integrated in the nonaqueous electrolyte secondary battery of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Exterior material, 2 ... Electrode group, 3 ... Separator, 4 ... Positive electrode active material layer, 5 ... Positive electrode collector, 6 ... Positive electrode, 7 ... Negative electrode active material layer, 8 ... Negative electrode collector, 9 ... Negative electrode, DESCRIPTION OF SYMBOLS 10 ... Thermoplastic resin layer, 11 ... Positive electrode lead, 12 ... Positive electrode terminal, 13 ... Negative electrode lead, 14 ... Negative electrode terminal, 15 ... Positive electrode, 16 ... Negative electrode, 17 ... Separator, 18 ... Positive electrode, 19 ... Negative electrode, 20 ... Separator .

Claims (9)

An electrode group having a laminate including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte held in the electrode group;
At least a part of the inner surface is made of a laminate film formed from a thermoplastic resin layer, and houses the electrode group, and heat seals the thermoplastic resin layers together to form a sealing portion. An exterior material for sealing;
A plurality of positive electrode current collecting leads having one end connected to the positive electrode of the electrode group and the other end extended from the electrode group;
A plurality of negative electrode current collector leads having one end connected to the negative electrode of the electrode group and the other end extending from the electrode group in a direction opposite to the positive electrode current collector lead;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of positive electrode current collecting leads are connected, and a positive electrode terminal extending outside through the sealing portion of the exterior material;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of negative electrode current collecting leads are connected, and a negative electrode terminal extending outside through the sealing portion of the exterior material In the non-aqueous electrolyte secondary battery
The laminate has a structure wound in a flat shape,
The length ratio calculated by the following formula (1) in the positive electrode terminal and the negative electrode terminal is 0.3 or more, and the nonaqueous electrolyte secondary battery is characterized in that:
L ₁ / L ₂ (1)
However, (1) In formula, L ₁ represents the length of the current collector lead connecting portions of the sides in the positive and negative terminals, the length of the side L ₂ is along the current collecting lead connecting portion in the electrode group Indicates. An electrode group including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte held in the electrode group;
At least a part of the inner surface is made of a laminate film formed from a thermoplastic resin layer, and houses the electrode group, and heat seals the thermoplastic resin layers together to form a sealing portion. An exterior material for sealing;
A plurality of positive electrode current collecting leads having one end connected to the positive electrode of the electrode group and the other end extended from the electrode group;
A plurality of negative electrode current collector leads having one end connected to the negative electrode of the electrode group and the other end extending from the electrode group in a direction opposite to the positive electrode current collector lead;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of positive electrode current collecting leads are connected, and a positive electrode terminal extending outside through the sealing portion of the exterior material;
A plate-like current collecting lead connecting portion to which the other ends of the plurality of negative electrode current collecting leads are connected, and a negative electrode terminal extending outside through the sealing portion of the exterior material In the non-aqueous electrolyte secondary battery
The length ratio calculated by the following formula (1) in the positive electrode terminal and the negative electrode terminal is 0.3 or more,
The other ends of the plurality of positive current collecting leads are connected in a state aligned with the current collecting lead connecting portion of the positive terminal, and the other ends of the plurality of negative current collecting leads are connected to the negative terminal. A non-aqueous electrolyte secondary battery, which is connected in a state of being arranged in a current collector lead connection portion.
L ₁ / L ₂ (1)
However, (1) In formula, L ₁ represents the length of the current collector lead connecting portions of the sides in the positive and negative terminals, the length of the side L ₂ is along the current collecting lead connecting portion in the electrode group Indicates.   3. The nonaqueous electrolyte secondary battery according to claim 1, wherein at least a portion of the surface of the positive electrode terminal or the negative electrode terminal that passes through the sealing portion is covered with a thermoplastic resin layer. .   4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thermoplastic resin layer has a thickness of 40 μm to 100 μm. Shorter cross-sectional area of the direction claims 1-4 non-aqueous electrolyte secondary battery of any one of claims, which is a 0.5 mm ² to 5 mm ² of the current collector lead.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains lithium titanium oxide.   The thickness of the said positive electrode terminal and the said negative electrode terminal is 100 micrometers-500 micrometers, The nonaqueous electrolyte secondary battery of any one of Claims 1-6 characterized by the above-mentioned.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode includes a mixture of a lithium-containing nickel oxide and a lithium manganese composite oxide.   9. The nonaqueous electrolyte secondary battery according to claim 1, wherein a thickness of the exterior material is in a range of 0.05 mm to 0.5 mm.

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