JP2010170730A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure the safety of a battery in the case of the generation of an external short circuit. <P>SOLUTION: In the battery, an electrode group 4 and an electrolyte solution are sealed to each other in a battery case 10. The electrode group 4 has a cathode 1 and an anode 2 wound around or laminated through a separator 3. At least either the cathode 1 or the anode 2 is equipped with a collector 2A and an active material layer 2B with an exposed part 21 of the former 2A electrically connected with the battery case 10 through a lead 16. The lead 16 has a center 16a, an end 16b contacting with the exposed part 21, and the other end 16c contacting with the battery case 10 with resistance per unit length at the center 16a lower than that at one end 16b or the other end 16c. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a battery, and more particularly to a battery having a lead.

  Conventionally, batteries having leads are known. A battery having a lead includes an electrode group in which a separator is disposed between a positive electrode and a negative electrode, a battery case that houses the electrode group (functions as a negative electrode terminal), and a sealing member that functions to seal the battery case (functions as a positive electrode terminal) And a positive electrode lead that electrically connects the positive electrode and the sealing member, and a negative electrode lead that electrically connects the negative electrode and the battery case. As the negative electrode lead, a lead made of nickel is often used.

Incidentally, it is known that when an external short circuit occurs in a battery, a large current flows between the positive electrode and the negative electrode, so that the temperature of the battery rises and the battery may generate heat. Patent Document 1 discloses a technique for suppressing heat generation caused by an external short circuit when an external short circuit occurs in a battery having leads. The technique is to form a narrowed portion narrower than other portions in a part of the negative electrode lead. Thereby, when an external short circuit occurs, the negative electrode lead is melted at the constricted portion, so that a current path of a large current can be blocked. Therefore, the heat generation inside the battery due to the external short circuit can be quickly stopped.
Japanese Patent Laid-Open No. 10-214614

  However, in the method of Patent Document 1, even if the negative electrode lead is once melted at the constricted portion, the melted portion may be re-welded. For this reason, the current path of a large current may be restored and the battery temperature may increase due to an external short circuit.

  This invention is made | formed in view of this point, The place made into the objective is to ensure the safety | security of the battery when an external short circuit generate | occur | produces.

  The battery according to the present invention is a battery in which an electrode group formed by winding or laminating a positive electrode and a negative electrode via a porous insulating layer is enclosed in a battery case together with an electrolytic solution. At least one of the positive electrode and the negative electrode has a current collector and an active material layer provided on the surface of the current collector so as to expose a part of the surface of the current collector. An exposed portion of the surface of the current collector exposed from the active material layer is electrically connected to the electrode terminal via a lead. The lead has one end that is in contact with the exposed portion, the other end that is in contact with the electrode terminal, and a central portion that is sandwiched between the one end and the other end. The resistance per unit length at the center is lower than the resistance per unit length at one end and the other end.

  As will be described later, the present inventors have recently discovered that heat is generated in the lead when an external short circuit occurs, and that the heat tends to be trapped in the center portion of the lead, thus completing the present invention. It was. In the battery described above, when an external short circuit occurs, the amount of heat generated at the center of the lead can be made smaller than the amount of heat generated at one end and the other end of the lead. Therefore, it is possible to prevent the heat generated in the lead from being trapped in the central portion of the lead.

  In a preferred embodiment described later, the lead is a flat plate, and the width of the central portion is wider than the width of one end and the other end. In another preferred embodiment described later, the lead is a flat plate, and the thickness of the central portion is larger than the thickness of one end and the other end. In another preferred embodiment described later, one end and the other end are made of a first metal, and the central portion is made of a second metal having a lower resistivity than the first metal. In either case, the resistance per unit length at the central portion can be made lower than the resistance per unit length at the one end and the other end.

  When the width of the central portion is wider than the width of one end and the other end, or when the thickness of the central portion is thicker than the thickness of the one end and the other end, the one end and the other end are made of the first metal. In the central portion, it is preferable that a portion made of the second metal having a lower resistivity than the first metal is provided on the portion made of the first metal. As a result, the resistance per unit length at the central portion is further greater than the resistance per unit length at the one end and the other end compared to the case where the one end and the other end and the central portion are made of the same metal. Can be lowered.

  In a preferred embodiment described later, the central portion is surrounded by an electrolyte solution, the negative electrode terminal is formed of a battery case, and the lead electrically connects the negative electrode exposed portion and the battery case. The battery is a lithium ion secondary battery.

  According to the present invention, it is possible to ensure the safety of a battery when an external short circuit occurs.

  Before describing the embodiments of the present invention, the background of the inventors of the present invention leading to the completion of the present invention will be described.

  It is known that it is difficult to ensure battery safety when an external short circuit occurs. Therefore, the present inventors investigated what happens in the battery when the external short circuit occurs in order to ensure the safety of the battery even when the external short circuit occurs. . Specifically, an external short circuit was caused in a cylindrical lithium ion secondary battery, and it was investigated that this occurred inside the battery. As a result, it can be seen that when an external short circuit occurs, the lead, especially the negative electrode lead, is extremely heated, and that part of the negative electrode lead is much hotter than the rest of the negative electrode lead. It was. The inventors considered two reasons for this. The two reasons will be described with reference to FIG.

  FIG. 7 is an explanatory diagram for specifying the central portion 6 a, the one end portion 6 b, and the other end portion 6 c which are parts of the negative electrode lead 6. Note that “16”, “16a”, “16b”, and “16c” in FIG. 7 are a negative electrode lead, a central portion, one end portion, and the other end portion in Embodiment 1 described later in order, and “26” in FIG. “26a”, “26b”, and “26c” are a negative electrode lead, a central portion, one end portion, and the other end portion in a first modification described later in order, and “36”, “36a”, “36b” in FIG. And “36c” are a negative electrode lead, a central portion, one end portion, and the other end portion in a second modified example, which will be described later.

  The negative electrode lead 6 extends from the exposed portion 21 of the negative electrode current collector 2A to the outside of the negative electrode current collector 2A, is bent at the boundary between the inner side surface and the bottom surface of the battery case 10, and further along the bottom surface of the battery case 10 The battery case 10 extends toward the center of the bottom surface. The central portion 6a is a portion sandwiched between the one end portion 6b and the other end portion 6c, is a portion not in contact with the exposed portion 21 of the negative electrode current collector 2A and the battery case 10, and is surrounded by a nonaqueous electrolyte. It is a part surrounded by (electrolyte solution or polymer electrolyte). The one end portion 6b is a portion of the negative electrode lead 6 that is in contact with the exposed portion 21 of the negative electrode current collector 2A. The other end portion 6 c is a portion of the negative electrode lead 6 that is in contact with the bottom surface of the battery case 10.

  The first reason is that the negative electrode lead 6 has a higher resistance than the constituent members of the battery other than the negative electrode lead 6. In many cases, in the lithium ion secondary battery, the negative electrode lead 6 is made of nickel, the negative electrode current collector 2A is made of copper, and the positive electrode lead and the positive electrode current collector are made of aluminum. Since nickel has a higher specific resistance than aluminum than copper, the negative electrode lead 6 has higher resistance than the negative electrode current collector 2A, the positive electrode lead, and the positive electrode current collector. Joule heat is proportional to the resistance value. As a result, it was considered that when the external short circuit occurred in the lithium ion secondary battery, the amount of heat generated in the negative electrode lead 6 would be maximized.

  The second reason is that the central portion 6a is less likely to release heat generated in the negative electrode lead 6 due to the external short circuit than the one end portion 6b and the other end portion 6c. The central portion 6a is not in contact with the exposed portion 21 of the negative electrode current collector 2A and the battery case 10, and is surrounded by an electrolyte. One end 6b is in contact with the exposed portion 21 of the negative electrode current collector 2A, and a portion thereof is welded to the exposed portion 21 of the negative electrode current collector 2A. The other end 6 c is in contact with the bottom surface of the battery case 10, and a part thereof is welded to the battery case 10. Since the electrolyte is an organic solution, it does not have excellent thermal conductivity, and since both the negative electrode current collector 2A and the battery case 10 are made of metal, they have excellent thermal conductivity. Therefore, the heat generated in the negative electrode lead 6 easily escapes from the one end portion 6b to the negative electrode current collector 2A, and easily escapes from the other end portion 6c to the battery case 10, but it is difficult to escape from the central portion 6a. I thought.

  Based on the above findings and considerations about the discovered facts, the inventors of the present application can ensure the safety of the battery when an external short circuit occurs if the amount of heat generated in the entire negative electrode lead 6 can be reduced. I thought. As a method for reducing the amount of heat generated in the entire negative electrode lead 6, the present inventors have conceived the following two ideas.

  As a first proposal, it was considered to change the material of the negative electrode lead 6 to copper instead of nickel. Since the specific resistance of copper is lower than that of nickel, if copper is used as the negative electrode lead material, the amount of heat generated in the entire negative electrode lead 6 can be suppressed to be smaller than that in the prior art.

  However, since copper has a low specific resistance, it is very difficult to weld the negative electrode lead made of copper to the exposed portion 21 of the negative electrode current collector 2 </ b> A and the battery case 10. Even if the negative electrode lead made of copper can be welded to the exposed portion 21 of the negative electrode current collector 2 </ b> A and the battery case 10, the welding strength cannot be maintained sufficiently. Therefore, it was difficult to adopt the first plan.

  As a second proposal, it was considered not to change the material of the negative electrode lead 6 but to increase the thickness of the negative electrode lead 6 or increase the width of the negative electrode lead 6. When the thickness of the negative electrode lead 6 is increased or the width of the negative electrode lead 6 is increased, the resistance of the negative electrode lead 6 can be lowered, and therefore the amount of heat generated in the entire negative electrode lead 6 can be suppressed to be smaller than that in the conventional case.

  However, when the thickness of the negative electrode lead 6 is increased or the width of the negative electrode lead 6 is increased, the volume of the electrode group 4 increases. In addition, since the roundness of the electrode group 4 is reduced, the occupation ratio of the electrode group 4 in the battery case 10 is increased. Therefore, if the thickness of the negative electrode lead 6 is increased or the width of the negative electrode lead 6 is increased, it is difficult to ensure the amount of filling of the active material. Therefore, it was difficult to adopt the second measure. As described above, when the amount of heat generation in the entire negative electrode lead 6 is reduced, a new problem (decrease in welding strength between the lead and the exposed portion of the current collector and the electrode terminal or reduction in the filling amount of the active material) occurs. I understood.

  The inventors of the present application further examined the case where heat is remarkably generated in the positive electrode lead when an external short circuit occurs. In current lithium ion secondary batteries, in many cases, the negative electrode lead has a higher resistance than the positive electrode lead. However, if the resistance of the negative electrode lead is lower than before, the resistance may be the same between the positive electrode lead and the negative electrode lead, and the positive electrode lead may have a higher resistance than the negative electrode lead. It shows below using FIG.

  FIG. 8 is an explanatory diagram for specifying the central portion 5 a, the one end portion 5 b, and the other end portion 5 c which are parts of the positive electrode lead 5. Note that “15”, “15a”, “15b”, and “15c” in FIG. 1 are, in order, a positive electrode lead, a central portion, one end portion, and the other end portion in a third modified example that will be described later.

  The positive electrode lead 5 extends from above the exposed portion 11 of the positive electrode current collector 1 </ b> A to the outside of the positive electrode current collector 1 </ b> A and extends through the through hole 7 a of the upper insulating plate 7 to the lower surface of the sealing plate 9. The central portion 5a is a portion sandwiched between the one end portion 5b and the other end portion 5c, is a portion not in contact with the exposed portion of the positive electrode current collector 1A and the sealing plate 9, and is surrounded by a nonaqueous electrolyte. It is an enclosed part. The one end portion 5b is a portion of the positive electrode lead 5 that is in contact with the exposed portion 11 of the positive electrode current collector 1A. The other end 5 c is a portion of the positive electrode lead 5 that is in contact with the lower surface of the sealing plate 9.

  One end portion 5 b of the positive electrode lead 5 is welded to the exposed portion 11 of the positive electrode current collector 1 A, and the other end portion 5 c is welded to the sealing plate 9. However, the other part (central part 5a) is not in contact with the exposed part 11 and the sealing plate 9 of the positive electrode current collector 1A. For this reason, when the heat generation in the positive electrode lead 5 occurs remarkably, it may be considered that the heat does not escape from the one end portion 5b and the other end portion 5c in the central portion 5a.

  Summarizing the above, the inventors of the present invention examined in detail the behavior in the battery when an external short circuit occurred, and found that significant heat was generated in the high-resistance lead among the positive electrode lead 5 and the negative electrode lead 6. And the temperature of the exposed portion of the current collector and the portion not in contact with the electrode terminal (the central portion 5a of the positive electrode lead 5 or the central portion 6a of the negative electrode lead 6) of the high resistance lead is extremely high. I found it to be expensive. Furthermore, the inventors of the present application have considered the discovered facts in detail, and if the high resistance lead configuration is devised so as to reduce the amount of heat generated in the entire high resistance lead, the above-mentioned new problem occurs. I understood. The inventors of the present application have completed the present invention based on these.

  The lead is a member for taking out current from the battery. In the secondary battery, the lead is a member for supplying current to the battery in addition to taking out the current. Therefore, conventionally, it is considered that the lead should be welded to the exposed portion of the current collector and the electrode terminal with a certain strength or more, and the distribution of resistance per unit length in the lead is optimized. The technical idea of optimizing the distribution of resistance per unit length in the lead has never been recalled. However, the present inventors have recently discovered that heat is generated in the lead when an external short circuit occurs. In addition, when the discovered facts are considered in detail, it is considered that if the resistance per unit length is changed depending on the lead part, safety in the case of an external short circuit can be secured, and the unit length in the lead The distribution of resistance per unit was optimized. As described above, the present invention has found that heat is generated in the lead when an external short circuit is occurring, and further, a portion of the lead that is not in contact with the exposed portion of the current collector and the electrode terminal It was a completed invention because it was found that heat was difficult to escape. Without this discovery, it is not even recalled that the resistance distribution per unit length in the lead is optimized, so the optimal distribution of resistance per unit length in the lead is studied in detail I can't think of optimizing it.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to embodiment shown below. For example, in the following embodiment, a lithium ion secondary battery (hereinafter may be referred to as “battery”) will be described, but the present invention is not limited to the lithium ion secondary battery.

Embodiment 1 of the Invention
FIG. 1 is a cross-sectional view of a general wound cylindrical lithium ion secondary battery. FIGS. 2A and 2B are enlarged perspective views of the periphery of the central portion 16a of the negative electrode lead 16 in the present embodiment. The central portion 16a of the negative electrode lead 16 is viewed from the “II” direction shown in FIG. FIG.

  The wound cylindrical lithium ion secondary battery includes an electrode group 4. The electrode group 4 is a porous material that is interposed between the positive electrode 1, the negative electrode 2 disposed opposite to the positive electrode 1, the positive electrode 1 and the negative electrode 2, and prevents direct contact between the positive electrode 1 and the negative electrode 2. The positive electrode 1 and the negative electrode 2 are wound around the separator 3 and formed. Such an electrode group 4 is housed in an iron battery case 10 together with an electrolyte (not shown) having lithium ion conductivity. Inside the battery case 10, the electrode group 4 is sandwiched between the upper insulating plate 7 and the lower insulating plate 8, and the separator 3 is impregnated with the electrolyte. An opening is formed in the battery case 10, and the opening is sealed with a sealing plate 9 via an insulator.

  The positive electrode 1 has a positive electrode current collector 1A and a positive electrode active material layer 1B. The positive electrode current collector 1A is a plate or foil excellent in conductivity, and is made of, for example, aluminum. The positive electrode active material layer 1B includes a positive electrode active material (for example, nickel composite oxide), and is provided on the surface of the positive electrode current collector 1A so as to expose a part of the positive electrode current collector 1A in the longitudinal direction. At this time, the positive electrode active material layer 1B may be provided on both surfaces of the positive electrode current collector 1A, or may be provided on one surface of the positive electrode current collector 1A. A positive electrode lead 5 made of, for example, aluminum is electrically connected to a portion of the surface of the positive electrode current collector 1A exposed from the positive electrode active material layer 1B (exposed portion of the positive electrode current collector).

  The positive electrode lead 5 is formed of a flat plate and is welded to the exposed portion of the positive electrode current collector 1 </ b> A and the sealing plate 9. Such a positive electrode lead 5 extends from above the exposed portion of the positive electrode current collector 1 </ b> A to the outside of the positive electrode current collector 1 </ b> A, and extends to the sealing plate 9 through the through hole 7 a of the upper insulating plate 7.

  The negative electrode 2 has a negative electrode current collector 2A and a negative electrode active material layer 2B. The negative electrode current collector 2A is a plate or foil excellent in conductivity, and is made of, for example, copper. The negative electrode active material layer 2B contains a negative electrode active material (for example, carbon), and is provided on the surface of the negative electrode current collector 2A so as to expose a part of the negative electrode current collector 2A in the longitudinal direction. At this time, the negative electrode active material layer 2B may be provided on both surfaces of the negative electrode current collector 2A, or may be provided on one surface of the negative electrode current collector 2A. A negative electrode lead 16 is electrically connected to a portion (exposed portion of the negative electrode current collector) 21 exposed from the negative electrode active material layer 2B in the surface of the negative electrode current collector 2A.

  The negative electrode lead 16 is formed of a flat plate and is welded to the exposed portion 21 of the negative electrode current collector 2 </ b> A and the central portion of the bottom surface of the battery case 10. Such a negative electrode lead 16 extends from above the exposed portion 21 of the negative electrode current collector 2 </ b> A to the outside of the negative electrode current collector 2 </ b> A and is bent at the boundary between the inner side surface and the bottom surface of the battery case 10. Along the center of the bottom surface.

  Further, in the negative electrode lead 16, as shown in FIGS. 2A and 2B, the width of the central portion 16a is wider than the width of the one end portion 16b and the other end portion 16c. In other words, the negative electrode lead 16 has a wide portion 17 at the central portion 16a. For example, the width of the central portion 16a is not less than 2.5 mm and not more than 6 mm, whereas the widths of the one end portion 16b and the other end portion 16c are not less than 2 mm and not more than 5 mm.

  When an external short circuit occurs in the lithium ion secondary battery according to the present embodiment, the negative electrode lead 16 has a higher resistance than the positive electrode lead 5, so that it is expected that significant heat generation occurs in the negative electrode lead 16. However, since the width of the central portion 16a of the negative electrode lead 16 in this embodiment is wider than the width of the one end portion 16b and the other end portion 16c, the resistance per unit length in the central portion 16a is reduced to the one end portion 16b and the other end portion 16c. It can be made lower than the resistance per unit length. Therefore, when an external short circuit occurs, the amount of heat generated at the central portion 16a can be made smaller than the amount of heat generated at the one end portion 16b and the other end portion 16c. Therefore, even when the negative electrode lead 16 generates heat due to the occurrence of an external short circuit, the temperature rise in the central portion 16a can be suppressed more than before, so that the temperature rise of the lithium ion secondary battery is higher than before. Can also be suppressed. Thereby, the safety | security of the battery when an external short circuit generate | occur | produces can be ensured.

  The wider the width of the central portion 16a than the width of the one end portion 16b and the other end portion 16c, the more the resistance per unit length in the central portion 16a than the resistance per unit length in the one end portion 16b and the other end portion 16c. Can also be lowered. However, if the width of the central portion 16a is too wider than the width of the one end portion 16b and the other end portion 16c, it becomes difficult to produce the negative electrode lead 16, and the shape of the electrode group 4 in the battery case 10 becomes distorted. This causes problems such as the negative electrode lead 16 being difficult to be bent or the electrode group 4 being unable to be accommodated in the battery case 10. Considering these, the width of the central portion 16a is preferably 1.1 to 2 times the width of the one end portion 16b and the other end portion 16c, and is 1 of the width of the one end portion 16b and the other end portion 16c. It is preferable that it is 1 to 1.5 times.

  As a first method of forming the negative electrode lead 16 in the present embodiment, a negative electrode lead body made of a first metal (for example, nickel) and having substantially the same width in the longitudinal direction is prepared. What is necessary is just to provide the part which consists of a 1st metal on the side surface of the part corresponded to a center part. Thereby, as shown in FIG. 2A, in the central portion 16a, the portion 17b made of the first metal on the side surface of the portion (the portion made of the first metal) 17a corresponding to the central portion of the negative electrode lead body. Is formed. That is, in the negative electrode lead 16 shown in FIG. 2A, not only the one end portion 16b and the other end portion 16c but also the central portion 16a is made of the first metal.

  As a second method of forming the negative electrode lead 16 in the present embodiment, a portion made of the second metal may be provided on the side surface of the portion corresponding to the central portion of the negative electrode lead body. As a result, as shown in FIG. 2B, in the central portion 16a, the portion 17c made of the second metal is formed on the side surface of the portion 17a corresponding to the central portion of the negative electrode lead body.

  Here, although the first metal may be used as the second metal, it is preferable to select a metal (for example, copper or gold) having a lower resistivity than the first metal. Thereby, the resistance per unit length in the central portion 16a is lower in the case shown in FIG. 2B than in the case shown in FIG. 2A, so that the amount of heat generated in the central portion 16a is reduced. Can do. Accordingly, when an external short circuit occurs in the lithium ion secondary battery having the negative electrode lead 16 having the central portion 16a shown in FIG. 2B, the negative electrode lead 16 having the central portion 16a shown in FIG. 2A is provided. Compared with the case where an external short circuit occurs in a lithium ion secondary battery, the safety of the battery can be further ensured.

  As described above, in the lithium ion secondary battery according to this embodiment, the resistance per unit length in the central portion 16a can be made lower than the resistance per unit length in the one end portion 16b and the other end portion 16c. it can. Therefore, even if heat is generated in the negative electrode lead 16 due to the occurrence of an external short circuit, the heat can be prevented from being trapped in the central portion 16a. Therefore, it is possible to ensure the safety of the battery when an external short circuit occurs.

  In the lithium ion secondary battery according to the present embodiment, the one end portion 16b and the other end portion 16c are both made of nickel, so that the negative electrode lead 16, the exposed portion 21 of the negative electrode current collector 2A, and the battery case 10 are welded. Strength can be secured.

  Furthermore, in the lithium ion secondary battery according to the present embodiment, the wide portion 17 is formed only in the central portion 16a. Therefore, as compared with the case where the entire negative electrode lead 16 is widened, an increase in the volume of the electrode group 4 can be minimized, and the distortion of the electrode group 4 can be minimized.

  Hereinafter, the materials of the battery case 10, the positive electrode current collector 1A, the positive electrode active material layer 1B, the separator 3, the nonaqueous electrolyte, the negative electrode current collector 2A, and the negative electrode active material layer 2B are listed in order.

  As a material of the battery case 10, iron, nickel, copper, or aluminum is used.

  As a material of the positive electrode current collector 1A, aluminum (Al), carbon, or a conductive resin can be used. When aluminum or a conductive resin is used as the material of the positive electrode current collector, the surface of the positive electrode current collector may be treated with carbon.

The positive electrode active material layer 1B contains a positive electrode active material. As the positive electrode active material, LiCoO ₂ , LiNiO _2, or Li ₂ MnO ₄ may be used alone, or two or more of these may be used, and a composite oxide containing lithium may be used. As the composite oxide containing lithium, in addition to LiCoO ₂ , LiNiO ₂ and Li ₂ MnO ₄ , an olivine-type lithium phosphate represented by the general formula of LiMPO ₄ (M = V, Fe, Ni, Mn) or Li Lithium fluorophosphate represented by a general formula of ₂ MPO ₄ F (M = V, Fe, Ni, Mn) can be used. Moreover, as a positive electrode active material, you may use what substituted a part of metal element which comprises the complex oxide containing the said lithium with another metal element. Further, as the positive electrode active material, the composite oxide containing lithium may be surface-treated with a metal oxide, lithium oxide, or a conductive agent, and the composite oxide containing lithium is treated with a hydrophobic treatment. It may be what was done.

  The positive electrode active material layer 1B contains a conductive agent and a binder in addition to the positive electrode active material. Examples of the conductive agent include natural graphite or artificial graphite graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black; conductive fibers such as carbon fiber or metal fiber; Carbon powder; metal powder such as aluminum; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; organic conductive materials such as phenylene derivatives can be used.

  Examples of the binder include PVDF (poly (vinylidene fluoride)), polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, poly Acrylic acid ethyl ester, polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoro Polymers such as polypropylene, styrene butadiene rubber or carboxymethyl cellulose can be used. The binder is selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid and hexadiene. Also, a copolymer of two or more materials can be used. As the binder, two or more selected from the above-mentioned polymers and copolymers can be mixed and used.

  As the non-aqueous electrolyte, an electrolyte solution in which a solute is dissolved in an organic solvent, or a so-called polymer electrolyte in which an electrolyte solution is made non-fluidized by a polymer can be used. When at least an electrolyte solution is used as the nonaqueous electrolyte, a separator 3 such as a nonwoven fabric or a microporous membrane made of polyethylene, polypropylene, aramid resin, amideimide, polyphenylene sulfide, polyimide, or the like is provided between the positive electrode 1 and the negative electrode 2. The separator is preferably impregnated with an electrolyte solution. Further, a heat-resistant member such as alumina, magnesia, silica, or titania may be provided inside or on the surface of the separator 3. Apart from the separator 3, a heat-resistant layer composed of the heat-resistant member and a binder similar to the binder provided on the positive electrode 1 and the negative electrode 2 may be provided.

The non-aqueous electrolyte material is selected based on the redox potential of each active material. Solutes preferably used for non-aqueous electrolytes include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiNCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lower aliphatic. Lithium carboxylate, LiF, LiCl, LiBr, LiI, lithium chloroborane, bis (1,2-benzenediolate (2-)-O, O ′) lithium borate, bis (2,3-naphthalenedioleate (2 -)-O, O ') lithium borate, bis (2,2'-biphenyldiolate (2-)-O, O') lithium borate, bis (5-fluoro-2-olate-1-benzenesulfone) acid -O, O ') borate salts such as lithium _{borate, (CF 3 SO 2) 2} NLi, LiN (CF 3 SO 2) (C 4 ₉ SO _2), applicable salts used in _(C 2 _{F 5} SO _2), such as 2 NLi or tetraphenyl lithium borate can be used, generally lithium ion secondary battery.

  Furthermore, as an organic solvent for dissolving the salt, ethylene carbonate (EC), propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate (EMC: ethyl methyl carbonate) carbonate), dipropyl carbonate, methyl formate, methyl acetate, methyl propionate, ethyl propionate, dimethoxymethane, γ-butyrolactone, γ-valerolactone, 1,2-diethoxyethane, 1,2-dimethoxyethane, ethoxymethoxy Ethane, trimethoxymethane, tetrahydrofuran, tetrahydrofuran derivatives (eg 2-methyltetrahydrofuran), dimethyl sulfoxide, dioxolane derivatives (eg 1,3-dioxo) Or 4-methyl-1,3-dioxolane), formamide, acetamide, dimethylformamide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, acetate ester, propionate ester, sulfolane, 3-methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, ethyl ether, diethyl ether, 1,3-propane sultone, anisole or fluorobenzene, or two of them A mixture of seeds or more can be used, and a solvent generally used in lithium ion secondary batteries can be applied.

  Furthermore, the organic solvent for dissolving the salt is vinylene carbonate, cyclohexyl benzene, biphenyl, diphenyl ether, vinyl ethylene carbonate, divinyl ethylene carbonate, phenyl ethylene carbonate, diallyl carbonate, fluoroethylene carbonate, catechol carbonate, vinyl acetate, ethylene sulfite, Additives such as propane sultone, trifluoropropylene carbonate, dibenisofuran, 2,4-difluoroanisole, o-terphenyl or m-terphenyl may be included.

The nonaqueous electrolyte may be one of polymer materials such as polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride or polyhexafluoropropylene, or a mixture of two or more thereof. A solid electrolyte in which the above solute is mixed can also be used. Moreover, as a nonaqueous electrolyte, the gel form in which the said organic solvent was mixed with the said polymeric material can also be used. Further, lithium nitride, lithium halide, lithium oxyacid _{salt, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, Li 3 PO 4 -Li 4 SiO 4, Li 2 SiS 3, Li 3 PO 4 -Li An inorganic material such as ₂ S—SiS ₂ or a phosphorus sulfide compound may be used as the solid electrolyte. When a gel-like non-aqueous electrolyte is used as the non-aqueous electrolyte, the gel-like non-aqueous electrolyte may be provided between the positive electrode 1 and the negative electrode 2 instead of the separator 3 and is adjacent to the separator 3. It may be provided.

  As the negative electrode current collector 2A, a metal foil such as stainless steel, nickel, copper, or titanium may be used, or a thin film of carbon or conductive resin may be used. These metal foils or thin films may be surface-treated with carbon, nickel, titanium, or the like.

The negative electrode active material layer 2B contains a negative electrode active material. Examples of the negative electrode active material include carbon materials (for example, various natural graphites or artificial graphite), substances containing Si (for example, Si simple substance, Si alloy or SiO _x (0 <x <2)), and substances containing Sn (for example, Sn simple substance). Sn alloy or SnO) or lithium metal can be used. Lithium metal includes lithium alloys containing Al, Zn, Mg, etc. in addition to lithium alone. As the negative electrode active material, one of the above may be used alone, or two or more may be used in combination.

  The negative electrode active material layer 2B contains a binder in addition to the negative electrode active material. As this binder, the same binder as that contained in the positive electrode active material layer can be used.

  As described above, in this embodiment, since the width of the central portion of the negative electrode lead is wider than the width of one end portion and the other end portion of the negative electrode lead, the resistance per unit length in the central portion of the negative electrode lead is reduced. The resistance per unit length at one end and the other end can be lower. In the following first modified example and second modified example described later, the resistance per unit length in the central part of the negative electrode lead is different per unit length in the one end part and the other end part of the negative electrode lead by another configuration. It is lower than the resistance.

(First modification)
3A and 3B are cross-sectional views in which the periphery of the central portion 26a of the negative electrode lead 26 in the present modification is enlarged.

  In the negative electrode lead 26 in this modification, as shown in FIGS. 3A and 3B, the width of the central portion 26a is larger than the width of the one end portion 26b and the other end portion 26c. In other words, the negative electrode lead 26 in this modification has a thick portion 27 at the central portion 26a. For example, the thickness of the central portion 26a is not less than 0.11 mm and not more than 0.3 mm, whereas the thickness of the one end portion 26b and the other end portion 26c is not less than 0.1 mm and not more than 0.15 mm. Thereby, also in this modified example, the resistance per unit length in the central portion 26a can be made lower than the resistance per unit length in the one end portion 26b and the other end portion 26c, and thus obtained in the first embodiment. The same effect as that obtained can be obtained.

  As the width of the central portion 26a is made thicker than the width of the one end portion 26b and the other end portion 26c, the resistance per unit length in the central portion 26a becomes the resistance per unit length in the one end portion 26b and the other end portion 26c. Can be lower. However, if the width of the central portion 26a is made too thicker than the widths of the one end portion 26b and the other end portion 26c, it becomes difficult to produce the negative electrode lead 26, and the shape of the electrode group 4 in the battery case 10 becomes distorted. It becomes difficult to bend the negative electrode lead 26, or the height of the electrode group 4 increases, which causes problems such as the electrode group 4 becoming difficult to enter the battery case 10. Considering these, the thickness of the central portion 26a is preferably 1.1 to 3 times the thickness of the one end portion 26b and the other end portion 26c, and is 1 of the thickness of the one end portion 26b and the other end portion 26c. It is preferable that it is 1 to 2 times.

  As a first method of forming the negative electrode lead 26 in this modification, a negative electrode lead body made of a first metal (for example, nickel) and having substantially the same width in the longitudinal direction is prepared. What is necessary is just to provide the part which consists of a 1st metal on the upper surface and lower surface of the part corresponded to a center part. As a result, as shown in FIG. 3A, in the central portion 26a, portions 27b made of the first metal are formed on the upper surface and the lower surface of the portion 27a corresponding to the central portion of the negative electrode lead body. That is, in the negative electrode lead 26 shown in FIG. 3A, not only the one end portion 26b and the other end portion 26c but also the central portion 26a is made of the first metal.

  As a second method of forming the negative electrode lead 26 in the present embodiment, a portion made of the second metal may be provided on the upper surface and the lower surface of the portion corresponding to the central portion of the negative electrode lead body. Thereby, as shown in FIG.3 (b), in the center part 26a, the part 27c which consists of a 2nd metal is formed on the upper surface and lower surface of the part 27a equivalent to a center part among negative electrode lead main bodies.

  Here, although the first metal may be used as the second metal, it is preferable to select a metal (for example, copper or gold) having a lower resistivity than the first metal. Accordingly, the resistance per unit length in the central portion 26a shown in FIG. 3B is lower than the resistance per unit length in the central portion 26a shown in FIG. Accordingly, when an external short circuit occurs in the lithium ion secondary battery having the negative electrode lead 26 having the central portion 26a shown in FIG. 3B, the negative electrode lead 26 having the central portion 26a shown in FIG. 3A is provided. Compared with the case where an external short circuit occurs in a lithium ion secondary battery, the safety of the battery can be further ensured.

  Note that, in the negative electrode lead in this modification, it is preferable that the central portion is formed so as to be wider and thicker than the one end portion and the other end portion. Thereby, compared with the said Embodiment 1 and this modification, the resistance per unit length of the center part of a negative electrode lead is made still lower than the resistance per unit length in the one end part and other end part of a negative electrode lead. Therefore, the temperature rise in the central portion of the negative electrode lead due to the occurrence of an external short circuit can be further suppressed.

(Second modification)
FIG. 4 is an enlarged cross-sectional view of the periphery of the central portion 36a of the negative electrode lead 36 in the second modification.

  In the negative electrode lead 36 in this modification, the central portion 36a is made of a material having a lower resistivity than the one end portion 36b and the other end portion 36c. Thereby, also in this modification, since the resistance per unit length in the center part 36a can be made lower than the resistance per unit length in the one end part 36b and the other end part 36c, it is obtained in the first embodiment. The same effect as that obtained can be obtained.

  Specifically, when the one end portion 36b and the other end portion 36c are made of nickel, the central portion 36a may be made of a metal having a resistivity lower than that of nickel (for example, copper or gold), or made of nickel. The part may be plated with a metal having a resistivity lower than that of nickel. The latter can form the negative electrode lead 36 more easily than the former.

  Note that, in the negative electrode lead in this modification, it is preferable that the central portion is formed wider than the one end portion and the other end portion, and is made of a material having a low resistivity. Alternatively, it is preferable that the central portion is formed thicker than the one end portion and the other end portion, and is made of a material having a low resistivity. Thereby, compared with the said Embodiment 1, the said 1st modification, and this modification, the resistance per unit length in the center part of a negative electrode lead is reduced per unit length in the one end part and other end part of a negative electrode lead. Since the resistance can be made lower than the resistance, the temperature rise in the central portion of the negative electrode lead due to the occurrence of the external short circuit can be further suppressed. More preferably, in the negative electrode lead, the central portion is formed of a material that is wider and thicker than the one end and the other end and has a low resistivity.

(Third Modification)
In the batteries according to Embodiment 1 and the first to second modifications, the negative electrode lead has a higher resistance than the positive electrode lead. In the battery according to the third modification, the positive electrode lead has a higher resistance than the negative electrode lead. FIG. 5 is an enlarged perspective view of the peripheral edge of the central portion of the positive electrode lead in this modification.

  In the positive electrode lead 15 in this modification, since the width of the central portion 15a is wider than the width of the one end portion 15b and the other end portion 15c, the resistance per unit length in the central portion 15a is reduced in the one end portion 15b and the other end portion 15c. It can be lower than the resistance per unit length. Therefore, the temperature rise in the central portion 15a of the positive electrode lead 15 due to the occurrence of the external short circuit can be suppressed low. Therefore, even when an external short circuit occurs, the safety of the lithium ion secondary battery can be ensured.

  In the positive electrode lead in this modification, the central portion may be formed wider than the one end and the other end in accordance with the first modification, and in accordance with the second modification. You may be comprised from the material whose resistivity is lower than one end part and the other end part. In any case, the same effect as that in the present modification can be obtained.

  Furthermore, in the positive electrode lead in this modification, the central portion is preferably formed wider and thicker than the one end and the other end, and wider than the one end and the other end. In addition, it is preferably made of a material having a low resistivity, or it is preferably made of a material having a higher thickness than the one end and the other end and having a low resistivity. As a result, the resistance per unit length in the central portion can be made lower than the resistance per unit length in the one end portion and the other end portion, as compared with the present modification example, resulting in the occurrence of an external short circuit. The temperature rise at the central portion of the positive electrode lead can be further reduced.

  More preferably, in the positive electrode lead in the present modification, the central portion is formed of a material that is wider and thicker than the one end portion and the other end portion and has a low resistivity. .

<< Other Embodiments >>
The first embodiment and the first to third modifications may be configured as follows.

  In the first embodiment and the first to third modifications, the example is applied to the cylindrical wound lithium ion secondary battery, but the present invention can also be applied to a prismatic lithium ion secondary battery. When an external short circuit occurs in a prismatic lithium ion secondary battery, the heat generated in the lead is likely to be trapped in the exposed part of the lead and the part that is not in contact with the electrode terminal (that is, the central part) Therefore, the thickness of the central portion of the lead may be thicker than the thickness of one end and the other end, and the width of the central portion of the lead may be wider than the width of the one end and the other end. The part may be formed of a material having a lower resistivity than the one end and the other end. In the electrode group provided in the prismatic lithium ion secondary battery, the positive electrode and the negative electrode may be wound via a separator, or the positive electrode and the negative electrode may be stacked via a separator.

  In the positive electrode in Embodiment 1 and the first to third modifications, two or more exposed portions of the positive electrode current collector are provided, and one positive electrode lead is provided in each of the exposed portions of the positive electrode current collector. It may be welded. Similarly, in the negative electrode, two or more exposed portions of the negative electrode current collector are provided, and one negative electrode lead may be welded to each of the exposed portions of the negative electrode current collector. Even in the case where a plurality of positive leads and negative leads are provided, each lead may be constituted by the lead in the first embodiment or any one of the first to third modifications.

  The positive electrode lead in the first embodiment and the first to second modifications may be the positive electrode lead in the third modification, and the conventional positive electrode lead (in the central portion, one end portion, and the other end portion). It may be a positive electrode lead whose width, thickness and material are the same. Similarly, the negative electrode lead in the third modification example may be the negative electrode lead in the first embodiment and the first to second modification examples described above, and a conventional negative electrode lead (central portion, one end portion, and the other end). The negative electrode lead having the same width, thickness and material may be used.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, the content described here is only the illustration of this invention, and this invention is not limited to these.
-Manufacturing method of lithium ion secondary battery-
Example 1
The cylindrical lithium ion secondary battery shown in FIG. 1 was produced by the following procedure.
(1) Production of positive electrode An appropriate amount of N-methyl- is added to 100 parts by weight of lithium cobaltate (LiCoO ₂ ) having an average particle diameter of 10 μm as a positive electrode active material, 8 parts by weight of PVDF as a binder and 3 parts by weight of acetylene black as a conductive agent. 2-Pyrrolidone (NMP: N-methylpyrrolidone) was added and mixed to obtain a positive electrode mixture paste.

  This positive electrode mixture paste was applied to both surfaces of a positive electrode current collector made of an aluminum foil (length 600 mm, width 54 mm, thickness 20 μm). At this time, the positive electrode mixture slurry was not applied to the vicinity of the center in the longitudinal direction of the aluminum foil (the portion of the aluminum foil where the positive electrode lead is welded, that is, the exposed portion of the positive electrode current collector). The positive electrode mixture slurry was dried to obtain a laminate in which the positive electrode mixture slurry was applied to both surfaces of the positive electrode current collector. This laminate was rolled so that each positive electrode active material layer had a thickness of 70 μm. In this way, a positive electrode plate was produced.

After that, an aluminum positive electrode lead (length 50 mm, width 3 mm, thickness 0.1 mm) was prepared, and one end of the positive electrode lead was placed on one surface of the exposed portion of the positive electrode current collector by ultrasonic welding. Connected.
(2) Production of negative electrode An appropriate amount of water was added to and mixed with 100 parts by weight of artificial graphite having an average particle diameter of 20 μm as a negative electrode active material, 1 part by weight of styrene butadiene rubber as a binder and 1 part by weight of carboxymethyl cellulose as a thickener. Thus, a negative electrode mixture paste was obtained.

  This negative electrode mixture paste was applied to both surfaces of a negative electrode current collector made of copper foil (length 630 mm, width 56 mm, thickness 10 μm). At this time, the negative electrode mixture slurry was not applied to the vicinity of the end portion on the winding end side of the copper foil (the portion of the copper foil where the negative electrode lead is welded, that is, the exposed portion of the negative electrode current collector). The negative electrode mixture slurry was dried to obtain a laminate in which the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector. This laminated body was rolled so that each negative electrode active material layer had a thickness of 65 μm. In this way, a negative electrode plate was produced.

After that, a nickel negative electrode lead (length: 50 mm, width: 3 mm, thickness: 0.1 mm) was prepared, and a wide portion 17 (width: 4 mm, thickness: 0.1 mm) in the central portion of the negative electrode lead 16. Formed. One end of the negative electrode lead was connected to one surface of the exposed portion of the negative electrode current collector by ultrasonic welding.
(3) Battery assembly A separator made of a polyethylene microporous membrane (manufactured by Asahi Kasei Co., Ltd., thickness 20 μm) is interposed between the positive electrode 1 and the negative electrode 2, and the positive electrode 1, the negative electrode 2, and the separator are wound. Electrode group 4 was obtained. At this time, the positive electrode 1 and the negative electrode 2 were disposed so that the portion of the negative electrode 2 to which the negative electrode lead 16 was connected was located on the winding end side. Further, the positive electrode 1 and the negative electrode 2 were arranged so that the positive electrode lead 5 extended upward from the electrode group 4 and the negative electrode lead 16 extended downward from the electrode group 4.

  The electrode group 4 was accommodated in a bottomed cylindrical iron battery case 10. After that, the end portion (the other end portion 5c) of the positive electrode lead 5 is connected to the lower surface of the sealing plate 9 by a laser welding method, and the end portion (the other end portion 16c) of the negative electrode lead 16 is connected to the battery case 10 by a resistance welding method. Connected to the inner bottom. At this time, as shown in FIGS. 2A and 2B, the negative electrode lead 16 was bent at both ends of the wide portion 17.

An upper insulating plate 7 made of polypropylene is provided on the electrode group 4, and a lower insulating plate 8 made of polypropylene is provided below the electrode group 4. After that, a nonaqueous electrolyte was injected into the battery case 10. The non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1.

A step portion was formed at a position 5 mm below the opening end of the battery case 10, and the sealing plate 9 was disposed on the step portion of the battery case 10 via a ring-shaped gasket. After that, the opening of the battery case 10 was sealed by caulking the peripheral edge of the sealing plate 9 to the opening end of the battery case 10 via a gasket. In this way, a cylindrical lithium ion secondary battery (diameter 18 mm, height 65 mm, design capacity 2600 mAh) was produced.
<< Comparative Example 1 >>
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the wide portion was not formed on the negative electrode lead.
-Evaluation method of lithium ion secondary battery-
An external short circuit test was carried out by the following method.

  Ten batteries of Examples and Comparative Examples were prepared and charged at a constant current of 1500 A under a 25 ° C. environment until the battery voltage reached 4.25V. After charging, the battery was left in an environment of 60 ° C. for 1 hour. Thereafter, the positive electrode and negative electrode of the battery after charging were externally short-circuited for 10 seconds using a predetermined test circuit (resistance value: 0.005Ω) in an environment of 60 ° C. At this time, the number of batteries whose battery surface temperature (hereinafter simply referred to as battery temperature) exceeded 80 ° C. was examined. And in this external short circuit test, it was judged that the battery whose battery temperature does not exceed 80 degreeC is the battery which has the outstanding safety | security.

  The result is shown in FIG. As can be seen from FIG. 6, in all of the examples, the battery temperature was 80 ° C. or less. On the other hand, in the comparative example, the battery temperature exceeded 80 ° C. in any of the batteries. Thereby, it was confirmed that the battery of the example was a battery having excellent safety.

  Since the battery of the present invention can maintain high safety even when a short circuit occurs in the battery, it is suitable as a power source for all devices. The battery of the present invention assists a power source of a portable electronic device (for example, a personal computer, a mobile phone, a mobile device, a personal digital assistant (PDA), a portable game device or a video camera), and a battery motor. It is preferably used as a power source for a power source (power source for a hybrid electric vehicle or a fuel cell vehicle), a power source for driving (a power source for an electric tool, a vacuum cleaner, a robot, etc.) or a power source for a plug-in HEV (Hybrid Electric Vehicle). In addition, the battery of the present invention is generally applicable to batteries, but is particularly useful for lithium ion secondary batteries.

It is a schematic longitudinal cross-sectional view of the cylindrical lithium ion secondary battery which is one Embodiment of the battery of this invention. (A) And (b) is the perspective view to which the periphery of the center part of the negative electrode lead in 1st Embodiment was expanded. (A) And (b) is sectional drawing to which the periphery of the center part of the negative electrode lead in a 1st modification was expanded. It is sectional drawing to which the periphery of the center part of the negative electrode lead in a 2nd modification was expanded. It is the perspective view which expanded the periphery of the center part of the positive electrode lead in a 3rd modification. It is a table | surface which shows the measurement result of the temperature in an Example and a comparative example. It is explanatory drawing for pinpointing the center part which is a part of negative electrode lead, one end part, and the other end part. It is explanatory drawing for pinpointing the center part which is a part of positive electrode lead, one end part, and the other end part.

1 Positive electrode
1A Positive electrode current collector
1B Positive electrode active material layer
2 Negative electrode
2A Negative electrode current collector
2B Negative electrode active material layer
3 Separator (porous insulation layer)
4 Electrode group
5,15 Positive lead
5a, 15a center
5b, 15b One end 5c, 15c The other end 6, 16, 26, 36 Negative electrode lead
6a, 16a, 26a, 36a Central part
6b, 16b, 26b, 36b One end
6c, 16c, 26c, 36c The other end
10 Battery case
11 Exposed part
17 Wide part
21 Exposed part
27 Thick part

Claims (8)

An electrode group formed by winding or laminating a positive electrode and a negative electrode via a porous insulating layer is a battery enclosed in a battery case together with an electrolyte solution,
At least one of the positive electrode and the negative electrode has a current collector, and an active material layer provided on the surface of the current collector so as to expose a part of the surface of the current collector,
Of the surface of the current collector, an exposed portion exposed from the active material layer is electrically connected to an electrode terminal via a lead,
The lead has one end abutted against the exposed portion, the other end abutted against the electrode terminal, and a center portion sandwiched between the one end and the other end. And
The battery according to claim 1, wherein a resistance per unit length in the central portion is lower than a resistance per unit length in the one end and the other end. The lead is a flat plate,
The battery according to claim 1, wherein a width of the central portion is wider than a width of the one end portion and the other end portion. The lead is a flat plate,
2. The battery according to claim 1, wherein a thickness of the central portion is larger than thicknesses of the one end portion and the other end portion. The one end and the other end are made of a first metal,
The said center part is provided with the part which consists of a 2nd metal whose resistivity is lower than the said 1st metal on the part which consists of a said 1st metal. battery. The one end and the other end are made of a first metal,
The battery according to claim 1, wherein the central portion is made of a second metal having a lower resistivity than the first metal.   The battery according to claim 1, wherein the central portion is surrounded by the electrolytic solution. The electrode terminal of the negative electrode is composed of the battery case,
The battery according to claim 1, wherein the lead electrically connects the exposed portion of the negative electrode and the battery case.   It is a lithium ion secondary battery, The battery as described in any one of Claim 1 to 7 characterized by the above-mentioned.

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