JP5334109B2 - Laminated battery - Google Patents

Description

  The present invention relates to a laminated battery having good safety when an internal pressure abnormally increases.

  In recent years, as the use of batteries has expanded, development aimed at improving battery characteristics such as higher capacity, higher energy density, and higher output has been actively conducted. In particular, the application of a battery to an application requiring high output and high capacity such as an automobile application has been required. For example, application of a lithium ion secondary battery has been studied.

  In many cases, a laminate film exterior body composed of a metal laminate film is used as an exterior body of a battery applied to such applications because of its advantage of being highly lightweight and lightweight.

  By the way, in a battery having a cylindrical or rectangular metal container (battery can) as an exterior body, for example, a part of the metal container is thinned to ensure safety when the battery internal pressure rises abnormally. In general, a vent portion is provided.

  On the other hand, the laminate type battery using the laminate film outer package has a smaller strength than the cylindrical or square metal container (battery can) and the heat fusion resin of the metal laminate film. Is sealed by heat sealing, so that the pressure resistance is lower than that of a battery having a metal container, and the battery expands or opens with a slight increase in internal pressure. For this reason, there has been an idea that in the laminated battery, it is not particularly necessary to install a vent portion.

  However, when a battery is mounted on a device, the terminal and the protection circuit are often installed near the battery, and even when there is an abnormality, the terminal and the protection circuit are corroded by leakage of the contents from the inside of the battery. Or cause secondary problems due to fever. For this reason, even in a laminated battery, it is required that only a specific portion is opened when the internal pressure of the battery is abnormally increased, and leakage of contents is suppressed only from the opened portion.

  For example, there is also a proposal of a technique for providing a vent portion in a laminated battery by disposing thin pieces between heat-sealing resin layers of upper and lower metal laminate films constituting a laminate film exterior body (Patent Document 1). According to the above-described technique, the adhesive strength between the heat-sealing resin layers of the metal laminate film (the strength of the heat seal portion) decreases in the portion where the thin piece is disposed, so the portion where the thin piece is disposed functions as a vent portion. To do.

  However, since the decrease in the adhesive strength between the heat-sealing resin layers of the metal laminate film due to the flakes is relatively large, the heat-sealing resin layers at the locations where the flakes are disposed are favorably adhered during battery manufacture and use. Not maintained, there is a risk of moisture intrusion from the outside and evaporation of the electrolyte solvent inside.

  For this reason, there is a need for development of a technique that can open only a specific portion when the battery internal pressure rises abnormally without damaging the strength of the heat seal portion of the laminate film outer package as much as possible.

JP 2001-250526 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laminated battery in which a specific portion is preferentially opened to ensure safety when the internal pressure rises abnormally.

  The laminated battery of the present invention that can achieve the above object is a polygonal battery in plan view in which an electrode body having a sheet-like positive electrode, a sheet-like negative electrode, and a separator is formed by folding a single metal laminate film in two. In the state where the positive electrode external terminal connected to the sheet-like positive electrode and the negative electrode external terminal connected to the sheet-like negative electrode are drawn out to the outside. A laminate type battery having a heat-sealed periphery and having a vent portion on the outer periphery of the laminate film exterior body, the outer periphery having a folded end of the laminate film exterior body in which a metal laminate film is folded in two Is heat sealed, and a part of the folded end is cut open, and the cut open part is defined as a vent part. It is characterized in that the.

  ADVANTAGE OF THE INVENTION According to this invention, when an internal pressure raises abnormally, a specific location can open | release preferentially and can provide the laminated battery which can ensure safety | security.

It is a top view which represents typically an example of the laminated battery of this invention. It is the sectional view on the AA line of FIG. It is the BB sectional view taken on the line of FIG.

  1 to 3 schematically show an example of a laminated battery of the present invention. 1 is a plan view of a laminated battery 1, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a cross-sectional view taken along line BB in FIG. 2 and 3, the layers of the metal laminate film constituting the laminate film outer package are not distinguished in order to avoid the complexity of the drawings, and the positive electrode mixture layer and the current collector of the sheet-like positive electrode are not distinguished. The negative electrode mixture layer and the current collector of the body and the sheet-like negative electrode are not distinguished.

  In the laminated battery 1, a laminated electrode body in which a plurality of sheet-like positive electrodes 7 and a plurality of sheet-like negative electrodes 8 are laminated via a separator 9, and an electrolyte solution (not shown) are rectangular laminate film exteriors in a plan view. It is housed in the body 2. A positive electrode external terminal 3 and a negative electrode external terminal 4 are drawn out from the laminate film exterior body 2. The positive electrode external terminal 3 and the negative electrode external terminal 4 are both planar, and are connected to the sheet-like positive electrode 7 and the sheet-like negative electrode 8 directly or via a lead body in the laminate film outer package 2 ( 2 and 3). FIG. 1 shows an example in which the positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn from the same side of the laminate film outer package 2, but in the battery of the present invention, the positive electrode external terminal and the negative electrode external terminal are shown. Each terminal may be drawn from a different side of the laminate film outer package.

  Laminate film outer package 2 is formed of a metal laminate film having a heat-sealing resin layer on the inner surface of the battery. More specifically, one metal laminate film is folded in two with the lower side in FIG. 1 as the folding end 5 (FIGS. 1 and 3) to form the laminate film outer package 2, and the sheet The outer periphery (including the outer periphery having the folded end 5) of the laminate film exterior body 2 is heat-sealed in a state where the electrode body and the electrolyte solution having the electrode-like positive electrode 7, the sheet-like negative electrode 8, and the separator 9 are accommodated inside. Therefore, the inside is sealed.

  And in the battery of this invention, a part of folding end 5 of the laminate film exterior body 2 is cut open, and this part is made into the vent part 6 (in FIG. 1, the vent part 6 is shown with the dotted line).

  Of the outer periphery having the folded end of the metal laminate film in the laminate film exterior body, the portion where the folded end is cut open has a lower strength than the folded end portion. Therefore, when the internal pressure of the laminated battery abnormally increases, the cut-out portion can be preferentially opened in the outer periphery having the folded end, so that this can be used as a vent portion.

  In the laminate battery of the present invention, the outer periphery having the folded end is heat-sealed in the same manner as the other outer periphery, so that the heat seal strength in the vent portion (the cut portion) is the same as that in the conventional laminate battery. The heat seal strength of the laminate film outer package can be made comparable. Therefore, for example, when the battery is manufactured or when a normal battery is used, the problem that the portion serving as the vent portion is opened can be prevented well. That is, in the laminated battery of the present invention, the heat seal strength itself of the portion that becomes the vent portion is not lowered, but the portion other than the vent portion (the portion of the folded end that remains uncut) is opened with greater strength. By adopting a structure that is difficult to perform, there is a difference between the strength of the vent portion and the strength of other portions, so that the vent portion can be preferentially opened when the internal pressure of the battery rises abnormally.

  In the laminate film exterior body, the length of the cut-off portion at the folded end where the metal laminate film is folded in half (the length in the lateral direction of the vent portion 6 in FIG. From the viewpoint of ensuring good, it is preferable that the length is 5% or more of the length of the folding end (the total length including the cut-out portion and the length in the lateral direction of the folding end 5 in FIG. 1, hereinafter the same). However, in the case of a battery of a very small size, the function of the vent part is insufficient even when the length of the cut-off portion at the folded end of the laminate film exterior body is 5% or more of the length of the folded end. Therefore, the length of the cut-off portion is preferably 3 mm or more, for example.

  In addition, if the cut-out part is too long, the opening part when functioning as a vent part becomes long, and there is a possibility that problems such as being easily spread when the battery contents leak out may occur. It is preferable that the length of the cut-off portion at the folded end of the laminate film exterior body is 10% or less of the length of the folded end.

  In addition, although the example which formed the vent part 6 in one place of the folding end 5 is shown in FIG. 1, the vent part 6 may form multiple (two, three, four, etc.), for example, 1 may be formed at both the left and right ends of the folding end 5 in FIG. In addition, when there are a plurality of vent portions, it is preferable that the total length of all the vent portions satisfy the length of the cut portion.

  FIG. 1 shows an example in which the side opposite to the side from which the positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out is a side having a folded end in which the metal laminate film is folded in two. However, in the laminated battery of the present invention, the side having the folded end obtained by folding the metal laminate film in half may be any side other than the side from which the positive electrode external terminal or the negative electrode external terminal is drawn. In the middle, either one of the left and right vertical sides can be a side having a folded end in which the metal laminate film is folded in half (side forming a vent portion). However, the position of the vent portion is, for example, to avoid adversely affecting the terminal of the device containing the laminated battery due to the electrolyte solution leaking from the location when the vent portion is activated. In addition, it is preferable to make the location as far as possible from the location where the positive electrode external terminal and the negative electrode external terminal are drawn out in the laminate film outer package. For example, as shown in FIG. 1, when the positive external terminal 3 and the negative external terminal 4 are drawn from the same side of the rectangular laminate film outer package 2 in plan view, the positive external terminal 3 and the negative external terminal 4 are It is preferable that the side opposite to the drawn side is a side having a folded end obtained by folding the metal laminate film in half, and the bent portion 6 is provided on the side portion.

  In the battery of the present invention, since the side having the folded end obtained by folding the metal laminate film in the outer periphery of the laminate film exterior body 2 is heat-sealed, the vent portion is also outside of the laminate film exterior body. It becomes a heat-sealed structure like the surroundings. Therefore, in the outer periphery other than the side where the vent part is formed (the side having the folded end where the metal laminate film is folded in half), when the battery internal pressure rises abnormally, the vent part is preferentially opened. Therefore, it is preferable that the strength of the heat seal portion is higher than that of the vent portion.

  As a method for increasing the strength of the heat seal portion in the outer periphery other than the side where the vent portion is formed, for example, the width of the heat seal portion (in FIG. The length in the vertical direction is the same for the sides of). Specifically, it is preferable to make the width of the heat seal part in the side other than the side where the vent part is formed wider than the side where the vent part is formed. More specifically, for example, from the viewpoint of improving the strength of the heat seal part in the side other than the side where the vent part is formed more favorably, the width of the heat seal part in the side other than the side where the vent part is formed is More preferably, the width is 1.1 times or more of the width of the heat seal portion at the side where the portion is formed. However, if the width of the heat seal part on the side other than the side where the vent part is formed is too wide, there arises a problem that the laminated battery becomes too large. Therefore, it is preferable that the width of the heat seal part on the side other than the side on which the vent part is formed is not more than twice the width of the heat seal part on the side on which the vent part is formed.

  In addition, as will be described in detail later, the metal laminate film constituting the laminate film outer package has a heat-sealing resin layer on the inner surface of the battery, but the positive electrode external terminal and the negative electrode external terminal, and the laminate film An adhesive layer containing the same type of resin as the heat-sealing resin contained in the heat-sealing resin layer is provided between the heat-sealing resin layer of the exterior body, and the positive electrode external terminal and the negative electrode outside are provided via this adhesive layer. It is also preferable to bond the terminal and the laminate film outer package (its heat-sealing resin layer). With respect to the side from which the positive electrode external terminal and the negative electrode external terminal are drawn, the strength of the heat seal portion can be increased also by such a method.

  In addition, it is preferable that the width | variety of the heat seal part of the outer periphery (side other than the side which formed the vent part) of a laminate film exterior body shall be 5-20 mm.

  In the sheet-like positive electrode constituting the laminate battery, for example, a layer made of a positive electrode mixture containing a positive electrode active material, a conductive additive and a binder (positive electrode mixture layer) is formed on one side or both sides of the current collector. Things can be used.

As the positive electrode active material, for example, when the laminate type battery of the present invention is a lithium ion secondary battery, an active material capable of inserting and extracting lithium ions is used. As a specific example of such a positive electrode active material, for example, a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.) Lithium-containing transition metal oxide, LiMn ₂ O ₄ and spinel-structured lithium manganese oxide obtained by substituting some of its elements with other elements, LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) Type compounds. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiNi _{3 / 5} Mn _1/5 Co _1/5 O ₂ etc.).

  As the current collector for the positive electrode, an aluminum foil or an aluminum alloy foil is suitable. The thickness of the current collector is preferably 0.01 to 0.02 mm, for example, although it depends on the size and capacity of the battery.

  In producing the positive electrode, the positive electrode active material, a conductive additive such as graphite, acetylene black, carbon black, and fibrous carbon, and a positive electrode mixture containing a binder such as polyvinylidene fluoride (PVDF), N -A paste-like or slurry-like composition uniformly dispersed using a solvent such as methyl-2-pyrrolidone (NMP) is prepared (the binder may be dissolved in the solvent), and this composition is used as the positive electrode A method of applying to the current collector and drying, and adjusting the thickness and density of the positive electrode mixture layer by pressing as necessary can be employed. However, the manufacturing method of the positive electrode according to the present invention is not limited to the above method, and other methods may be adopted.

  The thickness of the positive electrode mixture layer in the sheet-like positive electrode is preferably 30 to 100 μm per side. Moreover, it is preferable that content of each structural component in a positive mix layer shall be positive electrode active material: 90-98 mass%, conductive support agent: 1-5 mass%, and binder: 1-5 mass%.

  The positive electrode external terminal is preferably made of aluminum or an aluminum alloy from the viewpoint of ease of connection with the equipment used. The thickness of the positive external terminal is preferably 50 to 300 μm. That is, by setting the thickness of the positive external terminal to 50 μm or more, it is possible to prevent cutting during welding of the positive external terminal and to prevent tearing due to pulling and bending. In addition, by setting the thickness of the positive external terminal to 300 μm or less, it is possible to prevent a gap in the thickness direction from being generated in the heat seal portion of the laminate film exterior body. As described above, an adhesive layer is provided between the laminate film exterior body and the positive electrode external terminal in order to increase the strength of the heat seal portion on the side where the positive electrode external terminal is drawn out of the outer periphery of the laminate film exterior body. Although it can interpose, you may provide the said contact bonding layer previously in the location planned to be located in the heat seal part in a positive electrode external terminal.

  The sheet-like positive electrode and the positive electrode external terminal may be connected by directly connecting the sheet-like positive electrode current collector and the positive electrode external terminal. For example, the sheet-like positive electrode collector may be connected via an aluminum lead body. It can also be performed by connecting the electric body and the positive external terminal. The thickness of the aluminum lead body is preferably 50 to 300 μm, like the positive external terminal. Such a lead body is preferably used when the aluminum foil as the positive electrode current collector is particularly thin and the strength is insufficient for direct connection with the positive electrode external terminal.

  Examples of the method of connecting the current collector in the sheet-like positive electrode or the aluminum lead connected to the current collector and the positive external terminal include, for example, resistance welding, ultrasonic welding, laser welding, caulking, and conductive adhesive Various methods can be employed, such as the method by, but ultrasonic welding is particularly suitable.

As the sheet-like negative electrode constituting the laminated battery, for example, when the laminated battery of the present invention is a lithium ion secondary battery, one containing an active material capable of inserting and extracting lithium ions is used. Examples of such negative electrode active materials include graphite, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, mesocarbon microbeads (MCMB), and carbon fibers. One or a mixture of two or more releasable carbon-based materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and their alloys, lithium-containing nitrides, or compounds that can be charged and discharged at a low voltage close to lithium metals such as oxides (such as LiTi ₅ O ₁₂ ), or Lithium metal or lithium / aluminum alloy can also be used as the negative electrode active material. These negative electrode active materials include conductive assistants (carbon materials exemplified as conductive assistants related to positive electrodes) and binders (mixed binders of rubber binders such as PVDF and styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC). Etc.] or the like, and a finished product (negative electrode mixture layer) using the current collector as a core material, or the above-mentioned various alloys and lithium metal foils are laminated on the surface of the current collector And the like are used as a sheet-like negative electrode.

  For example, in the case of a sheet-like negative electrode having a negative electrode mixture layer, a negative electrode mixture containing the negative electrode active material, the binder, and a conductive auxiliary agent such as graphite, acetylene black, and carbon black, if necessary, A paste-like or slurry-like composition uniformly dispersed using a solvent such as NMP is prepared (the binder may be dissolved in the solvent), and this composition is applied onto the negative electrode current collector. The method of drying and adjusting the thickness and density of a negative mix layer layer by press processing as needed can be employ | adopted. However, the method for producing the sheet-like negative electrode according to the present invention is not limited to the above method, and other methods may be adopted.

  As the current collector for the negative electrode, a copper foil is suitable. The thickness of the current collector is preferably 0.05 to 0.02 mm, for example, although it depends on the size and capacity of the battery.

  The thickness of the negative electrode mixture layer in the sheet-like negative electrode is preferably 30 to 100 μm per side. Moreover, it is preferable that content of each structural component in a negative mix layer shall be negative electrode active material: 90-98 mass%, binder: 1-5 mass%. Moreover, when using a conductive support agent for a negative electrode, it is preferable that content of the conductive support agent in a negative mix layer shall be 1-5 mass%.

  For the negative electrode external terminal, a metal foil or ribbon such as nickel, nickel-plated copper, or nickel-copper clad is preferable. Further, the thickness of the negative electrode external terminal is preferably 50 to 300 μm similarly to the positive electrode external terminal. That is, by setting the thickness of the negative electrode external terminal to 50 μm or more, it is possible to prevent cutting during welding of the negative electrode external terminal and to prevent tearing due to pulling and bending. In addition, by setting the thickness of the negative electrode external terminal to 300 μm or less, it is possible to prevent a gap in the thickness direction from being generated in the heat seal portion of the laminate film exterior body. In addition, as described above, an adhesive layer is provided between the laminate film exterior body and the negative electrode external terminal in order to increase the strength of the heat seal portion on the side where the negative electrode external terminal is drawn out of the outer periphery of the laminate film exterior body. Although it can interpose, you may provide the said adhesive layer previously in the location planned to be located in the heat seal part in a negative electrode external terminal.

  The sheet-like negative electrode and the negative electrode external terminal may be connected by directly connecting the sheet-like negative electrode current collector and the negative electrode external terminal. For example, the sheet-like negative electrode current collector may be connected via a copper lead. It can also be performed by connecting the body and the negative electrode external terminal. The thickness of the copper lead body is preferably 50 to 300 μm, similarly to the negative electrode external terminal. Such a lead body is preferably used when the copper foil as the negative electrode current collector is particularly thin and the strength is insufficient for direct connection with the negative electrode external terminal.

  Examples of the method of connecting the current collector in the sheet-like negative electrode or the copper lead connected to the current collector include various methods such as resistance welding, ultrasonic welding, laser welding, caulking, and a method using a conductive adhesive. Although methods can be employed, ultrasonic welding is particularly suitable.

  In the laminated battery of the present invention, the sheet-like positive electrode and the sheet-like negative electrode are laminated with a separator interposed therebetween, or a winding wound in a spiral shape after being overlapped with a separator. It can be used as an electrode body. In the laminated electrode body and the wound electrode body, a plurality of sheet-like positive electrodes and sheet-like negative electrodes can be used as necessary. In the case of a wound electrode body, the cross section may be shaped to be flat as necessary.

  Examples of the separator relating to the laminated battery include a porous film and a nonwoven fabric made of polyethylene, polypropylene, a fusion of polyethylene and polypropylene, polyethylene terephthalate, polybutylene terephthalate, and the like. The thickness of the separator is preferably 10 to 50 μm, and the porosity is preferably 30 to 70%. Moreover, the effect which prevents a short circuit can be improved and the reliability of a battery can be improved more by using several separators, such as overlapping a porous film and a nonwoven fabric.

As an electrolyte solution for a laminate type battery, when the laminate type battery of the present invention is a lithium ion secondary battery, for example, a high dielectric constant such as ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (BL), etc. A solution in which a solute such as LiPF ₆ or LiBF ₄ is dissolved in a solvent or an organic solvent such as a linear solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (EMC). Non-aqueous electrolyte). In addition, it is more preferable to use the mixed solvent of the said high dielectric constant solvent and a low-viscosity solvent as an electrolyte solution solvent. PVDF, rubber-based material, alicyclic epoxy, oxetane-based material having a three-dimensional cross-linked structure, and the like may be mixed and solidified into the above solution to form a polymer electrolyte.

  The laminate film outer package of the laminate type battery is composed of a metal laminate film, and examples thereof include a three-layer metal laminate film composed of an outer resin layer / a metal layer / a heat-sealing resin layer. Nylon film (such as nylon 66 film), polyester film (such as PET film), etc. as the exterior resin layer in the metal laminate film, aluminum film, stainless steel film, etc. as the metal layer, modified as the heat sealing resin layer Polyolefin film (modified polyolefin ionomer film etc.) etc. are mentioned.

  In the metal laminate film, the thickness of the exterior resin layer is preferably 20 to 100 μm, the thickness of the metal layer is preferably 10 to 150 μm, and the thickness of the heat-sealing resin layer is 20 to 100 μm. preferable.

  In addition, if the laminate film exterior body is a polygon in plan view, the shape is not particularly limited, and if necessary, in a plan view, a triangle, a tetragon, a pentagon, a hexagon, a heptagon, Various shapes such as an octagon can be taken, but a quadrangle (rectangle or square) is common in plan view.

  The laminate type battery of the present invention is preferably manufactured, for example, by the following method. First, an electrode body having a sheet-like positive electrode, a sheet-like negative electrode, and a separator is placed on a metal laminate film, the metal laminate film is folded in two so as to wrap the electrode body, and one side and a bent end for injecting an electrolyte solution are formed. The remaining outer periphery is heat-sealed, leaving the edges it has. Next, in order to inject the electrolyte solution, the electrolyte solution is injected from one side left without heat sealing, and the one side is heat sealed while decompressing the inside of the laminate film outer package.

  After that, usually, the battery is aged and subjected to chemical conversion treatment. However, gas may be generated in the battery at that time. Therefore, a part of the outer periphery of the laminate film exterior body related to the battery is opened and laminated under reduced pressure. It is preferable to remove the gas from the film outer package. Therefore, in producing the laminated battery of the present invention, it is preferable to open a part of the folded end obtained by folding the metal laminate film in half and degas, and then heat-seal the side having the folded end. In this case, the portion where the folding end is cut open can be used as a vent portion as it is.

  The laminated battery of the present invention is a conventionally known laminated battery (especially a laminated battery) such as a power supply for various electronic devices, including applications requiring high output and high capacity batteries such as automobile applications. It can be used for the same applications as various applications in which lithium ion secondary batteries) are used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
LiCoO ₂ : 96 parts by mass, acetylene black: 2 parts by mass, and PVDF: 2 parts by mass were mixed, and NMP was further added to prepare a positive electrode mixture-containing paste. The obtained positive electrode mixture-containing paste was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried, and then subjected to a press treatment to form a positive electrode mixture layer, whereby a sheet-like positive electrode was obtained. The thickness of the positive electrode mixture layer of the obtained sheet-like positive electrode was 60 μm per one side of the current collector. Thereafter, the obtained sheet-like positive electrode was cut into a shape in which a portion where the positive electrode mixture layer was formed had a width of 105 mm and a length of 200 mm, and also included an exposed portion of a positive electrode current collector serving as a current collecting tab.

<Production of negative electrode>
Graphite: 98% by mass, SBR: 1.5% by mass and CMC: 0.5% by mass were added and mixed, and further water was added to prepare a negative electrode mixture-containing paste. The obtained negative electrode mixture-containing paste was applied to both sides of a current collector made of a copper foil having a thickness of 10 μm, dried, and then subjected to a press treatment to form a negative electrode mixture layer, whereby a sheet-like negative electrode was obtained. The thickness of the negative electrode mixture layer of the obtained sheet-like negative electrode was 60 μm per one side of the current collector. Thereafter, the obtained sheet-like negative electrode was cut into a shape in which a portion where the negative electrode mixture layer was formed had a width of 110 mm and a length of 205 mm, and also included an exposed portion of the negative electrode current collector that became a current collecting tab.

<Battery assembly>
10 sheets of the sheet-like positive electrode and 11 sheets of the sheet-like negative electrode were laminated via a separator (a polyolefin microporous film having a thickness of 25 μm) to obtain a laminated electrode body. In addition, it laminated | stacked so that both ends of a laminated electrode body might become a negative electrode. Next, the current collecting tabs of each sheet-like positive electrode according to the laminated electrode body are ultrasonically welded to the positive electrode external terminal made of aluminum, and the current collecting tabs of each sheet-like negative electrode are ultrasonically welded to the negative electrode external terminal made of copper. did. The positive electrode external terminal and the negative electrode external terminal have the same modification as the resin constituting the heat-sealing resin layer of the laminate film exterior body on both sides of the place where the heat seal portion of the laminate film exterior body is expected to be located. An adhesive layer made of polyolefin was disposed.

A 150-μm thick three-layered metal laminate film (rectangular, size 130 mm × 230 mm) made of polyester film / aluminum film / modified polyolefin film was prepared. Then, the laminated electrode body is placed on the modified polyolefin film layer in the metal laminate film so that a part of the positive electrode external terminal and the negative electrode external terminal protrude from the same side of the metal laminate film as shown in FIG. The metal laminate film is folded in two so as to wrap the electrode body, the side from which the positive electrode external terminal and the negative electrode external terminal are drawn, the two vertical sides on the right side in FIG. It was set as the exterior body and vacuum-dried at 70 degreeC for 15 hours. Thereafter, a non-aqueous electrolyte was injected from the left vertical side in FIG. 1, and the vertical side was heat-sealed and sealed under reduced pressure. Note that the nonaqueous electrolytic solution, a solution was used in which a LiPF ₆ in a solvent mixture to 1: 3 to EC and DEC at a volume ratio at a concentration 1.0 mol / l. The width of the heat seal on the three sides of the laminate film outer package was 10 mm, and the width of the heat seal on the side having the folded end was 5 mm.

  The laminated film outer package after sealing (laminated electrode outer body and laminate film outer package containing a non-aqueous electrolyte solution) is aged for 24 hours, and then charged for 1 hour at a current value of 0.1 C. The chemical conversion treatment was performed by carrying out constant current-constant voltage charging (constant current charging: 0.5 C, constant voltage charging: 4.2 V) with a charging time of 4 hours. Next, a portion of the folded end of the laminate film outer package in which the metal laminate film was folded in half was cut out from one end to 10 mm, and a laminated lithium ion secondary battery having the cut-out portion as a vent portion was obtained.

Example 2
After performing the chemical conversion treatment in the same manner as in Example 1, the portion of the folded end of the laminate film outer package in which the metal laminate film is folded in half is cut open from one end to 10 mm, and the degassing in the laminate film outer package is performed under reduced pressure. Subsequently, the side having the folded end was heat-sealed to obtain a laminated lithium ion secondary battery having the cut-out portion as a vent portion. Since the non-aqueous electrolyte is partly attached to the open part used for degassing and the heat seal strength may be lowered, the width of the heat seal on the side having the folded end is 7 mm. It was wider than in Example 1.

Comparative Example 1
A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that the side having the folded end obtained by folding the metal laminate film in the laminate film outer package was not heat-sealed or cut open.

  The laminated lithium ion secondary batteries of Examples 1 and 2 and Comparative Example 1 were fully charged at 4.2V, and then an overcharge test was performed under the conditions of 12V and 2C. The opening position was confirmed. These results are shown in Table 1 together with the situation of the outer periphery of the laminate film exterior body according to each battery.

  In Table 1, “presence / absence of degassing” means presence / absence of degassing after chemical conversion treatment, and “other than folding end” in the “opening position after overcharge test” column is a laminate film It means that the package is opened at the outer periphery other than the side having the folded end of the exterior body.

  As is clear from Table 1, in the batteries of Examples 1 and 2, the unsealing of the laminate film outer package during the overcharge test occurred only at the vent portion, but in the battery of Comparative Example 1, the laminate film outer package was No opening has occurred in a specific area around the outside.

DESCRIPTION OF SYMBOLS 1 Laminated battery 2 Laminate film exterior body 3 Positive electrode external terminal 4 Negative electrode external terminal 5 Folding end 6 Vent part 7 Sheet-like positive electrode 8 Sheet-like negative electrode 9 Separator

Claims (3)

An electrode body having a sheet-like positive electrode, a sheet-like negative electrode, and a separator is accommodated in a polygonal laminate film outer package formed by folding a single metal laminate film in two, and the sheet-like positive electrode The outer periphery of the laminate film exterior body is heat-sealed in a state where the positive electrode external terminal connected to the negative electrode external terminal connected to the sheet-like negative electrode is drawn to the outside, and the laminate film exterior body A laminated battery having a vent portion on the outer periphery,
The outer periphery of the laminate film exterior body having a folded end obtained by folding the metal laminate film in half is heat-sealed, and a part of the folded end is cut open, and the cut open portion is defined as a vent portion. A laminated battery characterized by that.   The laminate film exterior body is obtained by performing gas venting in a state in which a part of a folded end obtained by folding a metal laminate film into two is opened, and then heat-sealing the outer periphery having the folded end. Laminated battery.   3. The laminated battery according to claim 1, wherein a length of a cut-off portion of a folded end of the laminate film outer package in which the metal laminate film is folded in half is 5 to 10% of the length of the folded end. .

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