JP2005183556A - Plate-type electrochemical cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate-type electrochemical cell high in energy density, small in size, easy to be thinned, free of liquid leak, and high in long-term reliability. <P>SOLUTION: The electrochemical cell at least comprises a power generating element having a pair of electrodes each serving as a positive electrode or as a negative electrode and an ion-conducting electrolyte, a bag-type outer casing for housing and for hermetically sealing the power generating element, and metal-made external leads guided out of the cell through the sealed section of the outer casing for electrically connecting the electrodes and an external circuit. It is so constituted that the sealed section width is larger at or near the part where the external lead terminals are guided out than at or near the other part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrochemical cell such as a chemical battery such as an alkaline battery, a lithium battery or a lithium ion battery, and an electric double layer capacitor, and in particular, an electrochemical cell element is housed in a bag-shaped outer package film, The present invention relates to a flat plate electrochemical cell having a structure in which an opening at a peripheral edge of an exterior body is hermetically sealed.

  In recent years, in response to the miniaturization and high-density mounting of portable electronic devices, there has been a demand for small, thin, light, and high energy density for electrochemical cells such as batteries and electric double layer capacitors as power supply elements used in them. It has been. As a method for realizing a reduction in size, thickness and weight of such an electrochemical cell, an electrochemical cell comprising a power generation element or a storage element in a bag-like outer package made of a resin film or a laminate film of a metal foil and a resin film. A flat plate electrochemical cell having a structure in which an element is housed and an opening at a peripheral edge of an outer package is hermetically sealed with heat seal or an adhesive has been proposed and partially put into practical use.

  Conventionally, this type of flat plate electrochemical cell has been made, for example, with the structure shown in FIG. The electrode acting as the positive electrode 1 or the negative electrode 2 is composed of an electrode active material, a conductive agent such as carbon for imparting conductivity, and a binder such as resin, and is made of metal foil, net, expanded metal or punched metal. The current collector 3 is made of a conductive polymer film containing a conductive filler such as metal or carbon, and is placed on or integrally laminated with the current collector 4. The current collector 3 and current collector 4 are connected to an external lead terminal 5 and an external lead terminal 6 for electrically connecting the electrodes in the cell and an external circuit after cell assembly by welding or caulking, respectively. (For example, see Patent Documents 1 and 2).

This pair of electrodes is laminated with a separator 7 made of a polymer porous film, nonwoven fabric, papermaking, etc., or a pair of strip-like electrodes laminated in this way and the separator 7 are formed into a flat shape or a cylindrical shape. The electrode body that has been pressed and turned into a flat plate shape is housed in the outer package 8. The electrode body is impregnated and occluded with an ionic conductive electrolyte after or before being housed in the exterior body to constitute an electrochemical cell. When a solid electrolyte such as a gel electrolyte, a polymer solid electrolyte, or an inorganic solid electrolyte is used as the electrolyte, these solid electrolytes are used alone or in combination with a separator. The outer package 8 is made of a resin film or a laminate film of the resin films 8a and 8c and the metal foil 8b, and an electrochemical cell element made of the electrode body and the electrolyte is housed inside the bag that is stacked in a bag shape. The peripheral portion is hermetically sealed by heat sealing, pressure bonding, adhesive, or the like. When the electrode body is housed, the metal external lead terminal is housed and sealed in a state where one end is drawn out across the sealing portion at the peripheral edge of the exterior body (see, for example, Patent Document 2).
JP-A-9-283100 (page 1-4, FIGS. 2, 3) Japanese Patent Application Laid-Open No. 11-345599 (page 2-5, FIG. 1)

  In the conventional flat type electrochemical cell, as shown in the plan views of FIGS. 5 and 6, a power generation element 10 made of an electrode body and an electrolyte is accommodated in an exterior body 8 and a sealing portion is sealed by heat sealing or the like. At this time, the sealing width of the portion where the external lead terminal 5 and the external lead terminal 6 are sealed (sealing portion B) and the other sealing portion (sealing portion C) are substantially the same in the same method. It was done in width.

  Therefore, in the sealing part C from which the external lead terminal is not drawn out, uniform and sufficient adhesive force and sealing performance can be obtained by heat fusion of the same resin, but in the sealing part B from which the external lead terminal is drawn out, The external lead terminal metal and the resin inside the exterior body are joined differently, and the adhesion and sealing properties are insufficient, so the joint between this external lead terminal and the exterior body during storage after cell fabrication or during use Therefore, there are problems such as leakage of the electrolyte from the outside, moisture, oxygen, and the like from the external environment entering the cell, causing an increase in the internal resistance of the cell and a significant decrease in charge / discharge performance. In particular, in the case of a non-aqueous electric double layer capacitor that uses activated carbon as an electrode active material and a non-aqueous electrolyte as an electrolyte as a power generation element of an electrochemical cell, if water enters the cell, the electrolyte solution is applied when a charging voltage is applied. This lack of sealing was an important problem because it promoted the decomposition of the catalyst and the reaction with the activated carbon electrode, leading to significant cell performance degradation and a reduction in withstand voltage.

  On the other hand, if the sealing width is increased in order to improve the sealing performance, the size of the power generation element is reduced correspondingly to obtain an electrochemical cell of a certain size, and the energy density per cell volume is reduced. was there.

  In order to solve the above-described problems, the flat type electrochemical cell of the present invention has a structure in which the sealing portion where the external lead terminal is sealed is wider than the other sealing portions.

  A flat plate electrochemical cell according to the present invention includes a pair of electrodes functioning as a positive electrode or a negative electrode, an ion conductive electrolyte, an exterior body that houses and seals the electrode and the electrolyte, the electrode, and an external circuit And an external lead terminal for electrically connecting the external lead terminal, and a sealing portion in which the external lead terminal is sealed has a structure that is wider than other sealing portions.

  Preferably, the outer package is made of a metal foil, a multilayer laminate film of three or more layers having a weather resistant resin layer on the outer side and a thermoplastic resin layer on the inner side, and the outer package is hermetically sealed by thermal fusion.

  Particularly preferably, the metal foil constituting the multilayer laminate film is an aluminum or aluminum alloy foil, the weather-resistant resin disposed on the outside is polyamide or polyester, and the thermoplastic resin disposed on the inside is a polyolefin resin. .

  The flat plate electrochemical cell is preferably a non-aqueous electric double layer capacitor.

  The flat plate electrochemical cell of the present invention has a structure in which the sealing portion where the external lead terminal is sealed is wider than the other sealing portions. With this structure, most of the sealing portions from which the external lead terminals on the outer periphery of the exterior body are not pulled out can be suppressed to the minimum width at which necessary sealing performance can be obtained without increasing the sealing width. On the other hand, since the sealing portion from which the external lead terminal is drawn out can take a sufficiently large bonding area between the external lead terminal and the resin on the inner surface of the exterior body, a sufficient adhesive force and sealing performance as a whole electrochemical cell is ensured, and Since the storage space for the power generation element can be increased, there is an effect that a flat electrochemical cell having a small size, a high energy density, no leakage, and high reliability can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a flat plate electrochemical cell according to the present invention.

  Each of the electrodes acting as the positive electrode 1 or the negative electrode 2 is composed of an electrode active material, a conductive agent such as carbon for imparting conductivity and a binder such as a resin, if necessary, and is made of metal foil, net, expanded metal, Each of the current collector 3 and the current collector 4 made of a conductive polymer film containing a conductive filler such as punched metal or carbon is placed or integrally laminated. To these current collectors, external lead terminals 5 and external lead terminals 6 for electrically connecting the electrodes in the cell and external circuits after cell assembly are connected by welding or caulking, etc., respectively.

  The external lead terminal is formed by punching or cutting into a predetermined lead shape in advance, leaving an exposed portion of the current collector that does not form an electrode at its end when forming the electrode layer on the current collector. A lead made of a metal foil, a plate, a net or a wire is fixed by welding or the like. Further, the exposed portion of the current collector can be formed into an external lead terminal portion in which a part of the metal current collector formed by punching or cutting into a predetermined lead shape is extended, and is particularly suitable for a thin cell. .

  The material of the current collector and the external lead terminal may be any material that is chemically stable with respect to the electrolyte and the electrode material, electrochemically stable with respect to charging and overdischarge, and has corrosion resistance. Nickel, stainless steel and the like are preferable. This pair of electrodes is laminated with a separator 7 made of a polymer porous film, nonwoven fabric, papermaking, etc., or a pair of strip-like electrodes laminated in this way and the separator 7 are formed into a flat shape or a cylindrical shape. The electrode body that has been pressed and turned into a flat plate shape is housed in the outer package 8.

  The electrode body is impregnated and occluded with an ionic conductive electrolyte after or before being housed in the exterior body to constitute an electrochemical cell. When a solid electrolyte such as a gel electrolyte, a polymer solid electrolyte, or an inorganic solid electrolyte is used as the electrolyte, these solid electrolytes are used alone or in combination with a separator. The exterior body 8 is made of a laminate film of resin films 8a and 8c and a metal foil 8b. The electrochemical cell element made of the electrode body and the electrolyte is housed inside the laminated film in a bag shape. Is hermetically sealed by heat sealing, pressure bonding or adhesive. When the electrode body is housed, the metal external lead terminal is housed and sealed in a state where one end is drawn out across the sealing portion at the peripheral edge of the exterior body. In the flat electrochemical cell of the present invention, the sealing portion A where the external lead terminal is sealed is wider than the sealing portion C.

  The resin constituting the exterior body may be any weather-resistant resin that does not deteriorate due to humidity or temperature in the use environment and has mechanical strength. For example, polyamide resin such as nylon, polyimide, polyester, polyolefin resin, etc. Can be used. In particular, the resin disposed on the inner surface is preferably a thermoplastic resin that can be melted and softened by heating and heat-bonded to each other, and can be hermetically sealed by heat sealing with a simple process and high reliability. Polyolefin resins such as polypropylene and polyerylene and acid-modified polyolefins are suitable.

  In particular, when a cell using a non-aqueous electrolyte such as a lithium battery, a lithium ion battery, or an electric double layer capacitor is configured as an electrochemical cell, if external moisture (moisture) enters the cell from the exterior body, It causes significant performance degradation and decomposition of moisture and electrolytes that have entered during charging, and causes cell expansion and rupture in severe cases. As described above, polyamide resin such as nylon, polyimide, polyester, polyolefin resin, etc. A highly weather resistant resin and a moisture-impermeable metal foil such as aluminum and a thermoplastic resin that can be heat-sealed such as a polyolefin resin such as polypropylene and polyerylene and its copolymer on the inner surface are laminated and integrated. Using the laminated film, the method of bonding and sealing the outer peripheral edge of the exterior body by heat sealing is Particularly preferred are possible more reliable hermetic seal is simple.

  Further, in order to house the above electrode body in the exterior body and sandwich and seal the external lead terminal between the exterior body films by heat sealing, between the resin inside the exterior body film and the external lead terminal, It is particularly preferable to interpose a sealing agent 9 made of an acid-modified polyolefin resin having high adhesiveness to a metal or an acid-modified polyolefin on the side in contact with the external lead terminal and a resin in which the side in contact with the exterior body film is polyolefin. The sealing agent 9 is interposed by placing an acid-modified polyolefin resin on the resin layer on the innermost surface of the outer package film, or using an acid-modified polyolefin on the external lead terminal in advance or an acid-modified polyolefin on the side in contact with at least the external lead terminal. It is possible by heat-sealing using a resin having a polyolefin resin on the side in contact with the outer packaging film.

  FIG. 3 is a plan view of a flat plate electrochemical cell using the present invention. The exterior body 8 is folded back to accommodate and seal the power generation element 10. Of the sealing portions of the outer package 8, the sealing width of the sealing portion A from which the external lead terminals are drawn out is wider than the sealing width of the external lead terminals 5 and other sealing portions C from which the external lead terminals 6 are not drawn. In addition, the adhesive strength between the external lead terminal and the resin on the inner surface of the exterior body and the sealing performance are secured, and the sealing width of the sealing portion C is kept to a minimum and the entire space of the sealing portion is minimized. . The sealing width of the sealing part C from which the external lead terminal is not drawn out is 2 mm or more, more preferably 2.5 mm in order to suppress cell deterioration due to leakage or moisture intrusion from the external environment. The above is good. The sealing width of the sealing portion A from which the external lead terminal is drawn depends on the material and size of the external lead terminal and the resin material on the side surface of the exterior body, but usually requires 3 mm or more, preferably 5 mm or more. FIG. 4 is a plan view of a flat type electrochemical cell using the present invention, which is an example in which four sides are sealed.

  Moreover, as a separator used for this invention, what is normally used for an electrochemical cell is applicable. That is, when configuring a non-aqueous electrolyte battery such as a lithium battery or a lithium ion battery, a polyolefin-based polymer porous film such as polypropylene or polyethylene, a mixed paper with a nonwoven fabric or glass fiber, etc. For electric double layer capacitors, such as rayon paper making, graft polymerized polyethylene, etc., non-woven fabrics made from fibers such as cellulose, polyester, polyolefin resin and glass, paper making or polyolefin porous films can be suitably used.

In general, basic electrochemical characteristics such as operating voltage and maximum theoretical capacity of an electrochemical system as a power generation element or a storage element are defined by an electrode active material and an electrolyte described later. In the case of constituting a nonaqueous electrolyte battery such as a lithium battery or a lithium ion secondary battery in the flat electrochemical cell of the present invention, lithium metal, an alloy of lithium and other metals such as aluminum and tin as the negative electrode active material Occlusion and release of lithium ions such as carbonaceous materials obtained by firing oxides, nitrides, sulfides, graphite or organic substances such as silicon, tin, tungsten, titanium, iron, and conductive polymers such as polyacene and polyacetylene In the case where an alkaline battery is formed using a possible substance, a metal such as zinc, cadmium, or a hydrogen storage alloy can be used. As the positive electrode active material, in the case of lithium batteries or lithium ion secondary battery, CF _X and _{TiS 2,} MoS _2, NbSe _3, etc. of metal _{chalcogenide, MnO 2, MoO 3, V} 2 O 5, Li X CoO ₂ , Li _X NiO ₂ , Li _X Ni _y Co _1-y O ₂ , Li _x Mn ₂ O _{4 and} other metal oxides, reaction with lithium ions such as conductive polymers such as polyaniline, polypyrrole and polyparaphenylene Alternatively, a substance capable of occluding and releasing lithium ions can be used. In the case of an alkaline battery, oxides such as silver oxide, manganese dioxide, nickel hydroxide and nickel oxyhydroxide, hydroxides and the like are used.

  In the case of an electric double layer capacitor, a material having a large specific surface area such as a carbon material such as activated carbon or carbon black, a metal or another oxide can be used as an electrode active material for both the positive electrode and the negative electrode. When using the above metals such as lithium and zinc as the electrode active material, the conductive agent and the binder can be obtained by using a plate or foil that is integrally formed in a predetermined shape directly on the current collector. It is unnecessary. The present invention is not limited to these examples of electrode active materials, but can be applied to chemical cells using other electrode active materials, electric double layer capacitors, and electrochemical cells composed of power generating elements or power storage elements that combine these. I can do it.

This electrode body is impregnated and occluded with an ionic conductive electrolyte after being stored in the exterior body or before being stored in advance to constitute an electrochemical cell element. As the electrolyte, for example, in the case of an organic electrolyte battery, γ-butyrolactone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, 1, Lithium ion dissociating salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ as a supporting electrolyte in an organic solvent such as 2-dimethoxyethane, tetrahydrofuran, dioxolane, dimethylformamide, sulfolane, acetonitrile or a mixed solvent. Lithium ions such as a dissolved non-aqueous (organic) electrolyte, a polymer solid electrolyte in which the lithium salt is dissolved in a polymer such as polyethylene oxide or a crosslinked polyphosphazene, or an inorganic solid electrolyte such as Li ₃ N or LiI Conductive A non-aqueous electrolyte can be used.

In the case of an electric double layer capacitor, (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NPF ₄ , (C ₂ H ₅ ) ₄ instead of or in addition to the above supporting electrolyte. Ammonium salts such as NClO ₄ , (C ₂ H ₅ ) ₃ CH ₃ NBF ₄ , and (CH ₃ ) ₄ NBF ₄ , phosphonium salts, and the like are used. When a solid electrolyte such as a gel electrolyte, a polymer solid electrolyte, or an inorganic solid electrolyte is used as the electrolyte, these solid electrolytes can be used alone or in combination with a separator instead of the separator.

Hereinafter, embodiments will be described with reference to the drawings.
(Example 1)
In this embodiment, an electric double layer capacitor having the basic structure shown in FIGS. 1 and 3 is configured as a flat plate electrochemical cell according to the present invention. A strip electrode sheet having a thickness of 100 μm and a width of 50 mm was prepared by mixing and kneading polytetrafluoroethylene (PTFE) using activated carbon powder and carbon black as a conductivity-imparting agent and binder. This electrode sheet is bonded and laminated with a conductive adhesive containing carbon as a conductive filler on one side of a current collector made of aluminum foil having a thickness of 40 μm, leaving an exposed portion of 28 mm on each side, and then exposed. An external lead terminal made of an aluminum plate having a thickness of 70 μm and a width of 4 mm was joined to the part by ultrasonic welding. Next, the electrode laminate was cut to have a width of 50 mm and a length of 90 mm to produce a laminate of a pair of electrodes and a current collector. After winding the laminated body of the pair of electrodes and the current collector with the electrode formation surfaces facing each other with a separator interposed therebetween, using a flat core having a width of 28 mm and a thickness of 2 mm The electrode body was pressed at a load of 4 kg / cm ² .

  As the outer package, an insulating laminate film having a thickness of about 110 μm in which nylon was bonded to the outer surface of the aluminum foil and polypropylene was bonded and laminated to the inner surface was folded into a bag shape with the polypropylene layer as the inner surface. Next, the electrode body is placed so that the external lead terminal is on the side facing the folded side of the exterior film, and the external lead terminal is drawn out and stored from the sealing portion of the opening side facing the folded side. . First, the peripheral edge of one side of the two sides perpendicular to the side from which the external lead terminal was drawn out of the openings at the three peripheral edge portions was heat-sealed (pressurized heat fusion).

  Next, an electrolyte solution in which 1 mol / l tetraethylammonium tetrafluoroborate is dissolved in propylene carbonate is injected from the other opening side perpendicular to the folded side of the exterior film, and the pressure is reduced to apply the electrolyte to the electrode and separator. After impregnation, the periphery of the opening was heat sealed and hermetically sealed. In this example, the sealing width by heat sealing of the sealing portion (thermal fusion width of the outer package film) is 2.5 mm in the sealing portion C where the external lead terminal is not pulled out, and the sealing is performed by pulling out the external lead terminal. In part A, it was 5 mm. In this manner, 30 flat plate electrochemical cells of this example having a width of 40 mm, a length of 61 mm, and a thickness of 2.2 mm were produced.

  In addition, the external lead terminal is a polypropylene in which the side in contact with the external lead terminal is previously subjected to acid-denaturation treatment in a portion corresponding to the sealing portion of the outer package at the time of heat sealing, before being stored in the outer package. A resin having a thickness of 100 μm and a width of 5 mm, which is polypropylene on the side in contact with the film, was thermally bonded, and acid-modified polypropylene was interposed between the external lead terminal and the polypropylene film layer on the side surface of the exterior body in heat sealing.

The average value of the capacitance of the flat plate electrochemical cell of this example thus produced was 14.2 F, the capacity per unit volume was 2.65 F / cm ³ , and the average value of internal resistance was 98 mΩ. . In addition, even after an accelerated deterioration test that is stored for 1000 hours in a high-temperature and high-humidity environment at a temperature of 60 ° C. and a relative humidity of 90% RH, no electrolyte leakage (leakage) occurred from the sealed portion, and internal resistance Was 115 mΩ and the capacitance was 14.1 F, and substantially no deterioration was observed.

(Comparative Example 1)
Using the same electrode body and exterior body film as in Example 1, the sealing portion C and the external lead that do not draw out the external lead terminals as the sealing width by heat sealing of the sealing portion (thermal fusion width of the exterior body film) Thirty electrochemical cells of Comparative Example 1 according to the conventional method were produced in the same manner as in Example 1 except that both the sealing portions B from which the terminals were drawn out were 3 mm. The size of the cell thus produced was 41 mm wide, 59 mm long, and 2.2 mm thick. The average capacitance immediately after production was 14.2 F, and the capacity per unit volume was 2.67 F / cm ^3. The average value of the internal resistance was 100 mΩ, which was almost the same as that of Example 1. However, after the accelerated deterioration test that was stored in a high-temperature and high-humidity environment at a temperature of 60 ° C. and a relative humidity of 90% RH, Three leakages (leakage) of the electrolytic solution from the external lead terminal lead portion of B occurred.

(Comparative Example 2)
The conventional method is the same as in Example 1 except that the sealing width by heat sealing of the sealing portion is 5 mm for both the sealing portion C from which the external lead terminal is not pulled out and the sealing portion B from which the external lead terminal is pulled out. 30 electrochemical cells of Comparative Example 2 were prepared. The size of the cell thus produced is 45 mm in width, 61 mm in length, and 2.2 mm in thickness. The average value of capacitance immediately after production is 14.2 F, and the capacity per unit volume is 2.35 F / cm. ^3. The average value of the internal resistance was 99 mΩ, and the capacity per unit volume was 12% smaller than that of the cell according to the present invention in Example 1.

  However, after an accelerated deterioration test that is stored for 1000 hours in a high-temperature and high-humidity environment at a temperature of 60 ° C. and a relative humidity of 90% RH, leakage of the electrolyte from the external lead terminal lead-out portion (leakage) of the sealing portion B occurs. Was 0, the internal resistance was 113 mΩ, and the capacitance was 14.1 F, so that substantial deterioration was hardly observed.

  As described above, the first embodiment according to the present invention is less likely to cause leakage or charge / discharge from the sealing portion of the exterior body without substantially reducing the capacity per unit volume as compared with the comparative example according to the conventional method. It can be seen that a flat plate electrochemical cell with significantly improved performance degradation and high long-term reliability can be obtained.

It is sectional drawing of the flat type electrochemical cell by this invention. It is a top view which shows the electrode, collector, and external lead terminal which are used with the flat type electrochemical cell by this invention. It is a top view of the flat type electrochemical cell by this invention. It is a top view of the flat type electrochemical cell by this invention. It is a top view of the conventional flat type electrochemical cell. It is a top view of the conventional flat type electrochemical cell. It is sectional drawing of the conventional flat type electrochemical cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Current collector 4 Current collector 5 External lead terminal 6 External lead terminal 7 Separator 8 Exterior body 8a Resin film 8b Metal foil 8c Resin film 9 Sealant 10 Power generation element

Claims (4)

  A pair of electrodes functioning as a positive electrode or a negative electrode, an ion conductive electrolyte, an exterior body that houses and seals the electrode and the electrolyte, and an external lead for electrically connecting the electrode and an external circuit A flat plate electrochemical cell having a structure in which a sealing portion in which the external lead terminal is sealed is wider than other sealing portions.   The exterior body is made of a metal foil, a multilayer laminate film of three or more layers having a weather resistant resin layer on the outside and a thermoplastic resin layer on the inside, and the exterior body is hermetically sealed by thermal fusion. The flat plate electrochemical cell according to claim 1.   The metal foil constituting the multilayer laminate film is an aluminum or aluminum alloy foil, the weather-resistant resin disposed on the outside is polyamide or polyester, and the thermoplastic resin disposed on the inside is a polyolefin resin. The flat plate electrochemical cell according to claim 2.   The flat plate electrochemical cell according to any one of claims 1 to 3, wherein the flat plate electrochemical cell is a non-aqueous electric double layer capacitor.

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