JP4784730B2 - battery - Google Patents

Description

  The present invention relates to a battery having a structure (electrode laminate) in which negative electrodes and positive electrodes wrapped with separators are alternately laminated.

  In recent years, many portable electronic devices such as a camera-integrated VTR (videotape recorder), a mobile phone, or a laptop computer have appeared, and their size and weight have been reduced. Accordingly, as a portable power source for these electronic devices, research and development for improving the energy density of batteries, particularly secondary batteries, are being actively promoted. Batteries that use non-aqueous electrolytes, especially lithium ion secondary batteries, are very promising because they have a higher energy density than lead or nickel cadmium batteries, which are conventional aqueous electrolyte secondary batteries. The market is also growing significantly.

  In particular, the characteristics of lithium ion secondary batteries such as light weight and high energy density make them suitable for electric and hybrid electric vehicle applications, so studies aimed at increasing the size and output of lithium ion secondary batteries have become active. .

  In non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries, the conductivity of the electrolyte or electrolyte is lower than that of aqueous electrolytes, so that internal resistance is reduced and higher output is achieved. The use of a thin film separator has been devised to shorten the distance between electrodes and increase the electrode reaction area. Further, in particular, in a relatively large battery, various improvements such as increasing the number of leads from the positive and negative electrode current collectors are usually made to reduce the current collecting resistance inside the battery.

  In a normal lithium ion battery, in order to achieve high productivity, a strip-like positive electrode and a negative electrode are laminated with a separator between them, and an electrode winding body wound in a cylindrical shape or a substantially elliptical shape is used as an electrolyte or The structure enclosed with exterior material with the electrolyte is taken. However, when a large number of leads are taken out from the positive electrode and negative electrode wound in a cylindrical shape or a substantially elliptical shape in order to increase the output, the element shape becomes complicated, and the number of processes and parts There has been a problem that productivity has been reduced.

In order to solve this problem, as used in gum-type alkaline storage batteries, etc., a plate-like positive electrode, a separator, and a plate-like negative electrode are used as basic laminate units, and an electrode laminate in which a plurality of these basic laminate units are stacked is used. Can be considered. In this way, since the positive and negative electrode leads can be easily taken out from each basic laminate unit, it is possible to reduce internal current collection resistance while maintaining a simple structure and high productivity. Moreover, since the shape of the electrode laminate can be approximately rectangular, a laminate film can be used as an exterior material, and the weight can be significantly reduced as compared with a metal exterior material. Therefore, it is possible to realize a battery suitable for applications in which high output and light weight are important, such as a hybrid vehicle or an electric vehicle.
Japanese Patent Laid-Open No. 2003-257496 JP 2004-71438 A

  However, when such an electrode laminate is employed, there has been a problem that the battery temperature becomes extremely high during an abnormality such as a nail penetration test due to an increase in size and output. In particular, at the time of the crush test from the direction orthogonal to the electrode stacking direction, the electrode edge portion may be short-circuited, and the battery temperature may be rapidly increased.

  Incidentally, for example, Patent Document 1 describes that an electrochemically inactive backcoat layer is provided on the outermost layer of the electrode laminate. Patent Document 2 proposes that metal electrodes electrically connected to the positive electrode and the negative electrode are laminated on the outermost layer of the electrode laminate through a separator, respectively. However, all of these conventional configurations refer only to a short circuit in the stacking direction, and there is no description of a destructive test from a direction (side surface direction) orthogonal to the stacking direction.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery capable of increasing safety by suppressing an increase in battery temperature when a crushing force is applied from the side surface direction of the electrode laminate. There is.

The battery of the present invention comprises an electrode laminate in which negative electrodes and positive electrodes wrapped in bag-like separators are alternately laminated and negative electrodes are arranged at both ends in the lamination direction, and in contact with the negative electrodes at both ends, and the lamination direction of the electrode laminate and both end surfaces of, those having an outer peripheral coating electrically conductive member covering the parallel side faces in the stacking direction, and a film package member for accommodating the electrode stack and the outer covering member.

  In this battery, when a crushing force is applied to the side surface of the electrode laminate, the positive electrode breaks through the bag-shaped separator and comes into contact with the outer peripheral covering member, whereby the positive electrode and the negative electrode are electrically connected, and a wide range immediately after crushing. Will cause a short circuit. Therefore, the concentration of current locally and rapidly is suppressed, and the temperature does not increase rapidly. In addition, since both end surfaces and side surfaces of the electrode laminate are covered with the outer peripheral covering member, thermal diffusion is improved and local temperature rise of the battery is further suppressed.

According to the battery of the present invention, both end faces in the stacking direction of the electrode stack, is covered by the outer peripheral coating electrically conductive member and parallel side faces in the stacking direction, electrically connected to the outer periphery covering member as a negative electrode Since the electrode laminate and the outer peripheral covering member are accommodated in the film-like exterior member, a crushing force is applied from the side surface direction, and the battery temperature does not increase rapidly even when the positive electrode breaks through the separator. , Improve safety.

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

  FIG. 1 shows a configuration of a secondary battery according to an embodiment of the present invention. The secondary battery is, for example, a lithium ion secondary battery, and has a configuration in which a flat electrode laminate 20 to which the positive electrode lead 11 and the negative electrode lead 12 are attached is housed inside a film-shaped exterior member 31. ing.

  The positive electrode lead 11 and the negative electrode lead 12 are for taking out the electromotive force generated in the electrode laminate 20 to the outside, and are each in a strip shape, and are led out from the inside of the exterior member 31 to the outside, for example, in the same direction. ing. The positive electrode lead 11 is made of a metal material such as aluminum (Al), and the negative electrode lead 12 is made of a metal material such as nickel (Ni).

  The exterior member 31 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, each outer edge portion of the exterior member 31 is in close contact with each other by fusion bonding or an adhesive.

  An adhesion film 32 between the exterior member 31 and the positive electrode lead 11 and the negative electrode lead 12 for improving the adhesion between the positive electrode lead 11 and the negative electrode lead 12 and the inside of the exterior member 31 and preventing the intrusion of outside air. Has been inserted. The adhesion film 32 is made of a material having adhesion to the positive electrode lead 11 and the negative electrode lead 12. For example, when the positive electrode lead 11 and the negative electrode lead 12 are made of the metal material described above, a polyolefin such as polyethylene is used. It is preferable to be comprised with resin.

  FIG. 2 shows an appearance of the electrode laminate 20 shown in FIG. 1, and FIG. 3 shows a cross-sectional structure taken along line III-III of FIG. The electrode laminate 20 is obtained by alternately laminating positive electrodes 21 and negative electrodes 22, and the positive electrode 21 is wrapped with a bag-like separator 23. 3 shows the case where the end of the negative electrode current collector 22A and the outer peripheral covering member 41 are in contact with the side surfaces 20C and 20D, but there may be a gap here.

  FIG. 4 shows the configuration of the positive electrode 21 before lamination. The positive electrode 21 has a rectangular covering portion 21C in which an active material layer 21B is provided on both surfaces of a current collector 21A. A strip-shaped lead mounting portion 21D is extended from one corner of the covering portion 21C. In the lead attachment portion 21D, the active material layer 21B is not provided and the current collector 21A is exposed, and the positive electrode lead 11 (omitted in FIG. 4, refer to FIG. 2) is joined.

  The current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel (SUS) foil.

  The active material layer 21B includes, for example, any one or more of positive electrode materials capable of occluding and releasing lithium as an electrode reactant as a positive electrode active material, and a conductive material such as a carbon material as necessary. A binder such as a material and polyvinylidene fluoride may be included. Examples of positive electrode materials capable of occluding and releasing lithium include metal sulfides and metals that do not contain lithium, such as titanium sulfide (TiS2), molybdenum sulfide (MoS2), niobium selenide (NbSe2), or vanadium oxide (V2O5). Examples include selenides, metal oxides, and lithium-containing compounds containing lithium.

  Among these, lithium-containing compounds are preferable because some compounds can obtain a high voltage and a high energy density. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, or a phosphate compound containing lithium and a transition metal element. In particular, cobalt (Co), nickel and manganese (Mn Among these, those containing at least one of them are preferred. This is because a higher voltage can be obtained. The chemical formula is represented by, for example, Lix MIO2 or Liy MIIPO4. In the formula, MI and MII represent one or more transition metal elements. The values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

  Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Lix CoO2), lithium nickel composite oxide (Lix NiO2), and lithium nickel cobalt composite oxide (Lix Ni1-z Coz O2). (Z <1)) or lithium manganese composite oxide (LiMn2O4) having a spinel structure. Among these, a composite oxide containing nickel is preferable. This is because a high capacity can be obtained and excellent cycle characteristics can also be obtained. Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO4) or a lithium iron manganese phosphate compound (LiFe1-vMnvPO4 (v <1)).

  FIG. 5 shows the configuration of the negative electrode 22 before lamination. Similarly to the positive electrode 21, the negative electrode 22 has a configuration in which a strip-shaped lead attachment part 22D is extended from one corner of the rectangular covering part 22C. In the covering portion 22C, active material layers 22B are provided on both surfaces of the current collector 22A. In the lead attachment portion 22D, the active material layer 22B is not provided and the current collector 22A is exposed, and the negative electrode lead 12 (omitted in FIG. 5; see FIG. 2) is joined. The lead attachment portion 21D of the positive electrode 21 and the lead attachment portion 22D of the negative electrode 22 are provided at positions that do not overlap with each other in the electrode laminate 20.

  The current collector 22A is made of, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil.

  The active material layer 22B includes, for example, any one or more of negative electrode materials capable of inserting and extracting lithium as a negative electrode active material, and a binder such as polyvinylidene fluoride as necessary. May be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as non-graphitizable carbon, artificial graphite, and natural graphite. Examples of such carbon materials include non-graphitizable carbon, pyrolytic carbons, cokes, graphites, glassy carbon fibers, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Among these, coke includes pitch coke, needle coke, petroleum coke, and the like, and the organic polymer compound fired body is obtained by firing and carbonizing a phenol resin or a furan resin at an appropriate temperature. .

  Examples of the negative electrode material capable of inserting and extracting lithium and the like include materials capable of inserting and extracting lithium and including at least one of a metal element and a metalloid element as a constituent element. It is done. This is because a high energy density can be obtained by using such a material. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included.

  Examples of the metal element or metalloid element constituting the anode material include magnesium, boron, aluminum, gallium (Ga), indium (In), silicon (Si), germanium (Ge), and tin that can form an alloy with lithium. , Lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc, hafnium (Hf), zirconium, yttrium (Y), palladium (Pd) or platinum (Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or a semimetal element in the short-period type periodic table as a constituent element is preferable, and at least one of silicon and tin is particularly preferable as a constituent element. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained.

  As a negative electrode material capable of inserting and extracting lithium, a polymer compound such as polyacetylene or polypyrrole, an oxide such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, or titanium oxide, or these A nitride obtained by replacing oxygen in the oxide with nitrogen is also included.

  In addition, the negative electrode 22 is formed with a size larger than that of the positive electrode 21, and the projection surface of the active material layer 21 </ b> B is within the projection surface of the active material layer 22 </ b> B when viewed from the stacking direction A in the electrode stack 20. The relative positions of the positive electrode 21 and the negative electrode 22 are adjusted. In addition, the lithium storage capacity per unit area of the active material layer 22B on the negative electrode 22 side is set so as not to exceed the lithium release capacity per unit area of the active material layer 21B on the positive electrode 21 side.

  In this electrode laminate 20, both ends in the laminating direction A are active material layers 22B on the negative electrode 22 side. However, the active material layers 22B at both ends do not face the positive electrode 21 and do not contribute to the battery reaction. And this electrode laminated body 20 has both end surfaces 20A and 20B in the laminating direction A and side surfaces 20C and 20D parallel to the extending direction of the lead attachment portions 21D and 22D among the side surfaces parallel to the laminating direction A. The outer periphery covering member 41 is covered.

  That is, in this electrode laminate 20, the outer peripheral covering member 41 is in contact with the active material layers 22B at both ends of the electrode laminate 20 and is electrically connected to the negative electrode 22, as if the negative electrode covered the side surfaces 20C and 20D. It has become. Thus, the secondary battery has a function of short-circuiting the positive electrode 21 and the negative electrode 22 and suppressing a rapid temperature rise when a crushing force is applied from the side surface direction of the electrode laminate 20 and the positive electrode 21 breaks through the separator 23. I have it. Here, the active material layer 22B is provided at both ends of the electrode laminate 20, but the current collector 22A is not directly connected to the outer peripheral covering member 41 without the active material layer 22B. May be.

  The outer periphery covering member 41 is preferably formed of the same material as the current collector 22A of the negative electrode 22, for example. This is because the potential can be stabilized and the side reaction does not occur and the chemical stability is high. Moreover, the outer periphery covering member 41 is, for example, a belt-like shape, and is wound around at least one turn, and its end portion is stopped by a protective tape 42. In addition, in side 20C, 20D, the edge part of the negative electrode 22 and the outer periphery coating | coated member 41 may be in contact, and the clearance gap may be opened. The thickness of the outer periphery covering member 41 is preferably 20 μm or more and 50 μm or less, for example. This is because if the thickness is thin, thermal diffusion is not sufficient, and if the thickness is thick, it is difficult to increase the output density and energy density.

  FIG. 6 shows a configuration before lamination of the positive electrode 21 wrapped with the bag-like separator 23. The bag-like separator 23 is formed by closely adhering the outer edge portions 23B of two separators 23A larger than the positive electrode 21 at, for example, close contact portions 23C at the center of four corners and four sides. Each separator 23A is formed in the same size as the covering portion 22C of the negative electrode 22, for example. The bag-like separator 23 wraps only the covering portion 21C of the positive electrode 21 and the base end portion of the lead attachment portion 21D, and the tip portion of the lead attachment portion 21D protrudes from the bag-like separator 23.

  Such a bag-like separator 23 is composed of, for example, a porous film made of a polyolefin-based material such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. A structure in which a porous film is laminated may be used.

  Moreover, it is preferable that the thickness of the bag-shaped separator 23 is 15 micrometers or more and 30 micrometers or less, for example. If the thickness is thin, a short circuit may occur in the lead attachment portion 21D, for example, other than the edge portion of the positive electrode 21, and the battery may be extremely hot. If the thickness is thick, it is difficult to increase the output density and energy density. Here, the thickness of the bag-like separator 23 refers to the thickness of each separator 23A, not the total thickness of the two separators 23A.

  Further, the bag-like separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. For example, the electrolytic solution includes a solvent and a lithium salt that is an electrolyte salt. The solvent dissolves and dissociates the electrolyte salt. Solvents include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and 4-methyl. 1,3 dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetic acid ester, butyric acid ester or propionic acid ester, etc. are used, and any one of these or a mixture of two or more are used. May be.

  Examples of the lithium salt include LiClO 4, LiAsF 6, LiPF 6, LiBF 4, LiB (C 6 H 5) 4, CH 3 SO 3 Li, CF 3 SO 3 Li, LiCl, or LiBr, and any one or more of these are mixed. May be used.

  This secondary battery can be manufactured, for example, as follows.

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, which is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to both surfaces of the current collector 21A, dried, and compression molded to form the active material layer 21B. At this time, the active material layer 21B is formed only on the portion of the current collector 21A that becomes the covering portion 21C, and the portion that becomes the lead attachment portion 21D is left exposed without forming the active material layer 21B. In addition, the position of the application end of the active material layer 21B is made to be substantially on the same line on both surfaces of the current collector 21A. Subsequently, the positive electrode 21 is produced by cutting the current collector 21A into the shape shown in FIG.

  Further, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, which is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to both surfaces of the current collector 22A, dried, and compression molded to form the active material layer 22B, whereby the negative electrode 22 is fabricated. At this time, like the positive electrode 21, the active material layer 22B is formed only on the portion of the current collector 22A that becomes the covering portion 22C, and the portion that becomes the lead attachment portion 22D is exposed without forming the active material layer 22B. Leave. In addition, the position of the coating end of the active material layer 22B is made to be substantially on the same line on both surfaces of the current collector 22A. Subsequently, the negative electrode 22 is manufactured by cutting the current collector 22A into the shape shown in FIG.

  When forming the active material layer 21B and the active material layer 22B, the lithium storage capacity per weight of the negative electrode mixture and the lithium release capacity per weight of the positive electrode mixture are measured in advance, and the active material layer The lithium storage capacity per unit area of 22B should not exceed the lithium release capacity per unit area of the active material layer 21B.

  After that, the positive electrode 21 is sandwiched between two separators 23A larger than the positive electrode 21, and the outer edge portions 23B of the two separators 23A are connected to each other at, for example, the close contact portions 23C at the four corners and the center of the four sides by, for example, heat fusion. In close contact. Thus, the positive electrode 21 is wrapped with the bag-shaped separator 23 as shown in FIG.

  After the positive electrode 21 is wrapped with the bag-like separator 23, for example, three types of the positive electrode 21 wrapped with the bag-like separator 23 and, for example, four negative electrodes 22 are prepared, and these are prepared as the negative electrode 22 and the bag-like separator. The electrode stack 20 is formed by laminating the positive electrode 21, the negative electrode 22, the negative electrode 22, the positive electrode 21, the negative electrode 22, the positive electrode 21, the negative electrode 22, and the negative electrode 22. . As a result, an electrode laminate 20 including, for example, six units of the basic laminate unit of the active material layer 21B, the bag-like separator 23, and the active material layer 22B is formed, and the active material layers 22B are disposed at both ends in the lamination direction A. Is done. Furthermore, when forming the electrode laminate 20, the relative positions of the negative electrode 22 and the positive electrode 21 so that the projection surface of the active material layer 21 </ b> B is within the projection surface of the active material layer 22 </ b> B when viewed from the lamination direction A. Adjust the position.

  After forming the electrode laminate 20, the outer periphery covering member 41 is wound around the electrode laminate 20 at least once, and the end portion is stopped with the protective tape 42. Thereby, both end surfaces 20A and 20B and side surfaces 20C and 20D in the stacking direction A of the electrode stack 20 are covered with the outer periphery covering member 41. Subsequently, the three positive electrode leads 11 are joined to the lead mounting portion 21D of the positive electrode 21 simultaneously by, for example, ultrasonic welding. Similarly, four negative leads 12 are joined to the lead attachment portion 22D of the negative electrode 22 simultaneously by, for example, ultrasonic welding.

  After the positive electrode lead 11 and the negative electrode lead 12 are joined, the electrode laminate 20 is impregnated with the electrolyte solution, the electrode laminate 20 is sandwiched between the exterior members 31, and the outer edges of the exterior member 31 are adhered to each other by heat fusion or the like. And enclose. At that time, an adhesive film 32 is inserted between the positive electrode lead 11, the negative electrode lead 12, and the exterior member 31. Thereby, the secondary battery shown in FIG. 1 is completed.

  In this secondary battery, when a crushing force is applied to the side surfaces 20C and 20D of the electrode laminate 20, the positive electrode 21 breaks through the bag-like separator 23 and comes into contact with the outer periphery covering member 41. As a result, the positive electrode 21 and the negative electrode 22 are connected. Short circuit electrically. Here, since the outer periphery covering member 41 covers the entire outer periphery of the electrode laminate 20, a short circuit occurs over a wide range. Therefore, the current does not concentrate rapidly locally, and a rapid temperature rise can be prevented. In addition, since both end surfaces 20A and 20B and side surfaces 20C and 20D of the electrode laminate 20 are covered with the outer periphery covering member 41, thermal diffusion is improved and the temperature rise of the battery is further suppressed.

  As described above, in the present embodiment, since the outer periphery covering member 41 includes not only the both end surfaces 20A and 20B in the stacking direction A of the electrode laminate 20 but also the side surfaces 20C and 20D, the side surfaces 20C and 20D are crushed. Even when force is applied, it is possible to suppress a sudden rise in battery temperature and enhance safety.

  Further, specific embodiments of the present invention will be described in detail.

(Examples 1-3)
The secondary battery described in the embodiment was manufactured. First, 42 parts by weight of lithium / cobalt composite oxide (LiCoO 2) as a positive electrode active material, 42 parts by weight of lithium / manganese composite oxide (LiMn 2 O 4), 4 parts by weight of polyvinylidene fluoride as a binder, A positive electrode mixture was prepared by mixing 2 parts by weight of artificial graphite as an agent. Subsequently, the positive electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which was applied to both surfaces of a current collector 21A made of a strip-shaped aluminum foil having a thickness of 15 μm, and dried. The active material layer 21B was formed by compression molding with pressure. At this time, the active material layer 21B was formed only on the portion of the current collector 21A that became the covering portion 21C, and the portion that became the lead attachment portion 21D was left exposed without forming the active material layer 21B. In addition, the position of the coating end of the active material layer 21B was made to be substantially on the same line on both surfaces of the current collector 21A. Then, the positive electrode 21 was produced by cutting the current collector 21A into the shape shown in FIG.

  Further, as a negative electrode active material, 90 parts by weight of artificial graphite and 10 parts by weight of polyvinylidene fluoride as a binder are mixed to prepare a negative electrode mixture, which is dispersed in N-methyl-2-pyrrolidone as a solvent. Thus, a negative electrode mixture slurry was obtained. This negative electrode mixture slurry was applied to both surfaces of a current collector 22A made of a strip-shaped copper foil having a thickness of 15 μm, dried, and then compression molded at a constant pressure to form an active material layer 22B. At this time, like the positive electrode 21, the active material layer 22B is formed only on the portion of the current collector 22A that becomes the covering portion 22C, and the portion that becomes the lead attachment portion 22D is exposed without forming the active material layer 22B. I left it. In addition, the position of the coating end of the active material layer 22B was made to be substantially on the same line on both surfaces of the current collector 22A. Subsequently, the current collector 22A was cut into the shape shown in FIG.

  When forming the active material layer 21B and the active material layer 22B, the lithium storage capacity per weight of the negative electrode mixture and the lithium release capacity per weight of the positive electrode mixture are measured in advance, and the active material layer The lithium storage capacity per unit area of 22B was made not to exceed the lithium release capacity per unit area of the active material layer 21B.

  After that, the polypropylene microporous film was cut into a rectangular shape having the same size as the covering portion 22C of the negative electrode 22 to form two separators 23A. The positive electrode 21 was sandwiched between the two separators 23A, and the outer edge portions 23B were adhered to each other by thermal fusion at the close contact portions 23C at the four corners and the center of the four sides. Thus, the positive electrode 21 was wrapped with the bag-like separator 23 as shown in FIG. The thickness of the bag-like separator 23 was 25 μm in Example 1 and Example 2, and 12 μm in Example 3.

  After wrapping the positive electrode 21 with the bag-like separator 23, three types of the positive electrode 21 thus wrapped with the bag-like separator 23 and four negative electrodes 22 are prepared. The positive electrode 21, the negative electrode 22, and the positive electrode 21 wrapped with the bag-like separator 23, the negative electrode 22, the positive electrode 21 wrapped with the bag-like separator 23, and the negative electrode 22 were laminated in this order to form the electrode laminate 20. As a result, an electrode laminate 20 is formed that encloses six units of the basic laminate unit of the active material layer 21B, the bag-like separator 23, and the active material layer 22B, and the active material layers 22B are disposed at both ends in the lamination direction A. It was. When forming the electrode stack 20, the relative positions of the negative electrode 22 and the positive electrode 21 are set so that the projection surface of the active material layer 21 </ b> B is within the projection surface of the active material layer 22 </ b> B when viewed from the stacking direction A. It was adjusted.

  After the electrode laminate 20 is formed, the outer periphery covering member 41 made of a strip-like copper foil is wound around the electrode laminate 20 in the same manner as the current collector 22A of the negative electrode 22 at least once, and both end faces 20A and 20B in the laminating direction A Then, the side surfaces 20C and 20D were covered, and the end portions were fixed with a protective tape 42 made of polypropylene. The thickness of the outer periphery covering member 41 was 20 μm in Example 1 and Example 3, and 15 μm in Example 2.

  After winding the outer periphery covering member 41, three positive electrode leads 11 made of aluminum were joined to the lead attachment portion 21D of the positive electrode 21 simultaneously by ultrasonic welding. Further, four negative electrode leads 12 made of nickel were simultaneously joined to the lead attachment portion 22D of the negative electrode 22 by ultrasonic welding.

  After joining the positive electrode lead 11 and the negative electrode lead 12, 1 mol / l of LiPF6 as an electrolyte salt was dissolved in an equal volume mixed solvent of ethylene carbonate and propylene carbonate to prepare an electrolytic solution. The electrode laminate 20 is impregnated with this electrolytic solution, the electrode laminate 20 is sandwiched between the exterior members 31 made of a laminate film, and the outer edges of the exterior members 31 are brought into close contact with each other by thermal fusion or the like and sealed under reduced pressure. . At this time, the positive electrode lead 11 and the negative electrode lead 12 were led out of the exterior member 31, and an adhesion film 32 was inserted between them and the exterior member 31. Through the above steps, the secondary battery having the design capacity of 1 Ah shown in FIGS. 1 to 3 was obtained.

  Further, except that the outer periphery covering member 41 is not provided as Comparative Example 1, and further, only the both end faces 20A and 20B in the stacking direction A of the electrode laminate 20 are covered with the outer periphery covering member 41 as Comparative Example 2. A secondary battery was fabricated in the same manner as in Example 1 except for the above.

  Ten secondary batteries of the obtained examples and comparative examples were prepared, and the battery voltage normally became 4.3 V, which is not increased by the protection circuit, with the protection circuit removed for each battery. After carrying out constant current charging at 200 mA until, the constant voltage charging at 4.3 V was performed until the charging current value attenuated to 10 mA, and an overcharged state was obtained.

  After that, a flat plate crushing test was conducted as an abnormal use environment test. At that time, as shown in FIG. 7, the flat plate 50 was crushed from the direction B orthogonal to the stacking direction A of the electrode stack 20, and the temperature was the highest among the 10 tested in each Example and Comparative Example. The highest temperature of the battery that became higher (hereinafter referred to as the highest battery temperature during the test) was examined. The obtained results are shown in Table 1.

  As can be seen from Table 1, in Example 1, the maximum battery temperature during the test was lower than in Comparative Examples 1 and 2, and the safety in abnormal environments was improved. That is, when both end faces 20A, 20B in the stacking direction A of the electrode laminate 20 and the side faces 20C, 20D are covered with the outer peripheral covering member 41, a crushing force is applied from the direction B perpendicular to the stacking direction A. It was found that the increase in battery temperature can be suppressed and safety can be improved.

  Further, in Example 2 in which the thickness of the outer peripheral covering member 41 was 15 μm, the maximum temperature during the test was higher than in Example 1 in which the thickness was 20 μm. This is considered to be because thermal diffusion was not sufficient because the outer peripheral covering member 41 was thinned. That is, it was found that if the thickness of the outer periphery covering member 41 is 20 μm or more, the effect of suppressing the rise in battery temperature can be enhanced.

  Similarly, in Example 3 in which the thickness of the bag-shaped separator 23 was 12 μm, the maximum temperature during the test was higher than in Example 1 in which the thickness was 25 μm. This is presumably because the bag-shaped separator 23 was too thin and a short circuit occurred at, for example, the lead attachment portion 21D other than the edge portion of the positive electrode 21 to raise the battery temperature. That is, it has been found that if the thickness of the bag-like separator 23 is 15 μm or more, an increase in battery temperature can be sufficiently suppressed.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiment and examples, the case where both end surfaces 20A and 20B in the stacking direction A of the electrode stack 20 and the side surfaces 20C and 20D are covered with the outer periphery covering member 41 has been described. , 20D may be covered with an outer peripheral covering member.

  Further, for example, in the above-described embodiments and examples, the case where an electrolytic solution that is a liquid electrolyte is used has been described, but other electrolytes may be used instead of the electrolytic solution. Other electrolytes include, for example, a gel electrolyte in which an electrolyte is held in a polymer compound, a solid electrolyte having ionic conductivity, a mixture of a solid electrolyte and an electrolyte, or a solid electrolyte and a gel electrolyte. And a mixture thereof.

  Note that various polymer compounds can be used for the gel electrolyte as long as it absorbs the electrolyte and gels. Examples of such a polymer compound include a fluorine-based polymer compound such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, an ether-based polymer such as polyethylene oxide or a crosslinked product containing polyethylene oxide. A molecular compound, polyacrylonitrile, etc. are mentioned. In particular, a fluorine-based polymer compound is desirable from the viewpoint of redox stability.

  As the solid electrolyte, for example, an organic solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, or an inorganic solid electrolyte made of ion conductive glass or ionic crystals can be used. At this time, as the polymer compound, for example, an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate, an acrylate polymer compound alone or mixed, Alternatively, it can be used by copolymerizing in the molecule. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

  Moreover, in the said embodiment and Example, although the laminated structure was demonstrated about the battery provided in the inside of the exterior member 31 which consists of a laminate film, this invention applies any if it is a battery provided with the laminated structure. Can do. Moreover, not only a secondary battery but a primary battery is applicable.

  Furthermore, in the above-described embodiments and examples, the material constituting each constituent element such as the positive electrode 21, the negative electrode 22, or the electrolyte has been described as an example, but other materials may be used. In addition, although the so-called lithium ion secondary battery has been described in the above embodiments and examples, the present invention can be similarly applied to a battery using other electrode reactions. Other batteries include, for example, so-called lithium metal batteries that use lithium precipitation / dissolution in the negative electrode, or lithium storage / release and precipitation / dissolution in the negative electrode. It is a battery represented by the sum of a component and a capacity component by precipitation / dissolution. Further, other light metals other than lithium as the electrode reactant, for example, other group 1 elements in the long-period periodic table such as sodium (Na) or potassium (K), or long-period type such as magnesium or calcium (Ca) Examples include batteries using Group 2 elements in the periodic table or other light metals such as aluminum.

1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention. It is a perspective view showing the external appearance of the electrode laminated body shown in FIG. It is sectional drawing along the III-III line of the electrode laminated body. It is a top view showing the structure before lamination | stacking of a positive electrode. It is a top view showing the structure before lamination | stacking of a negative electrode. It is a top view showing the structure before lamination | stacking of the positive electrode wrapped with the bag-shaped separator. It is a top view for demonstrating the method of the flat plate crushing test of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Positive electrode lead, 12 ... Negative electrode lead, 20 ... Electrode laminated body, 21 ... Positive electrode, 21A ... Current collector, 21B ... Active material layer, 21C, 22C ... Covering part, 21D, 22D ... Lead attachment part, 22 ... Negative electrode , 22A ... current collector, 22B ... active material layer, 23 ... bag-like separator, 23A ... separator, 23B ... outer edge part, 23C ... adhesion part, 31 ... exterior member, 32 ... adhesion film, 41 ... outer periphery covering member, 42 ... protective tape.

Claims (5)

An electrode laminate in which negative electrodes and positive electrodes wrapped in bag-like separators are alternately stacked and negative electrodes are arranged at both ends in the stacking direction;
Contact with the negative electrode of said end, and both end surfaces in the laminating direction of the electrode stack, and the outer covering member of the conductive covering the parallel side faces in the stacking direction,
Batteries comprising a film package member for accommodating the electrode stack and the outer peripheral cover member. The peripheral covering member, that is formed by the current collector and the same material of the negative electrode
請 Motomeko 1 battery described. The bag-like separator, the outer edges of the large two separators than the positive electrode, Ru der those in close contact with at least a portion
請 Motomeko 1 battery described. The thickness of the bag-like separator Ru der than 30μm below 15μm
請 Motomeko 1 battery described. The thickness of the outer peripheral cover member Ru der than 50μm below 20μm
請 Motomeko 1 battery described.

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