THIN BATTERY

Abstract: A sealing body (4) is improved in a thin battery comprising a generating element wherein the active material for a negative electrode, an electrolyte, and the active material for a positive electrode are superposed on each other in a form of layers (1, 2, 3), terminal plates (5, 6) which are provided on and under the generating element and serve both as a collector and a battery jar, and the frame-like sealing body (4) by which the generating element is sealed in a space between the terminal plates and the plates are insulated from each other. The sealing body is characterized in that it has a vertical multilayer structure comprising layers (41, 42), at least one of which is made of metal, and a layer (43) made of electric insulator. Thereby, the mechanical strength of the sealing body and as a result, that of the battery are increased, and they are hard to be bent. Therefore, the outside air or the electrolyte can be prevented from penetrating or leaking through the sealing part, and the performance of the battery can be prevented from deteriorating, and further, the long-term reliability of the battery can be improved.

Description: Technical Field This invention relates to a film type battery for use in a portable electric equipment and a battery powered equipment etc., and especially to improvement of a sealing material. Background Art In recent years, the portable electric equipment and the battery powered equipment have been minimized in size and thickness rapidly, and demands for minimizing size and thickness of batteries for use in these equipments have been increased in proportion to the above tendency. Especially, a demand for film type battery with a high reliability and having a thickness of under 0.5 mm incl. is increasing. As for a film type battery using light metal represented by lithium as a negative active material, a battery having a thickness of as small as 0.1 mm is produced at present, and in this battery thicknesses of a current collector and a sealing portion become comparatively thin as small as tens of microns. Fig. 13 is a vertical sectional view showing an example of a conventional film type battery. In the figure, 1 denotes a negative active material layer, 2 denotes a positive active material layer, and 3 denotes an ion conductive electrolyte layer; and a generating element is composed of these components. Metallic lithium, for example, is used for the negative active material. 5 denotes a negative terminal plate, 6 denotes a positive terminal plate, and the terminal plates 5 and 6 serve also as a current collector and a container. A stainless steel plate and a nickel plate etc. having a thickness of 15 to 30 microns are used for the terminal plates 5 and 6. A frame-shaped sealing material 4, which seals the above generating element in between the both terminal plates 5 and 6 and insulates the terminal plate 5 from the terminal plate 6, is installed on peripheral edges of the terminal plates 5 and 6. The sealing material 4 is made of denatured polypropylene resin. EP-A-228 757 discloses a Film type battery having an alternative polymeric multi-layer sealing material. The film type battery, which utilizes a light metal represented by the lithium as the negative active material, is frequently used for portable electric equipments. In- such a case, a reliability i.e. a hardness to be bent and a durability to long service, in other words a long-term reliability, is required for the film type battery. However, since the sealing material 4 is made of the denatured polypropylene resin in the film type battery having the above-mentioned construction, its mechanical strength is small so that it is apt to be bent and a clearance is easily produced at a sealing portion. For this reason, when the film type battery having the above construction has been put in service for a long period, there has been such a trouble that a battery performance has been deteriorated due to a leakage of electrolyte or an ingress of moisture and oxygen from the sealing portion. If moisture enters the battery, it reacts with the metallic lithium forming the negative active material so that a battery capacity is lessened. Further, when installing the sealing material 4 in the film type battery having the above-mentioned construction, the terminal plates 5 and 6 have been thermally bonded to the sealing material 4 after installing the sealing material 4 on the peripheral edges of the terminal plates 5 and 6. However, since a thermal shrinkage factor of the sealing material 4 is different from those of the terminal plates 5 and 6, there has been such a trouble in the same way as the above that a battery performance has been deteriorated due to wrinkles formed on the sealing portion as shown by Fig. 14, so that residual stresses have been produced and a part of the sealing portion has been opened by a stress applied thereon during use of battery so as to permit atmosphere to enter an inside of battery. A film type battery including the sealing material 4 having a double-layer structure as illustrated in Fig. 15 is also well known. 4a is a negative-side sealing material and 4b is a positive-side sealing material. In this film type battery, in order to avoid an external short-circuiting due to contact of the terminal plate 5 with the terminal plate 6 at their peripheral edges, outside dimensions of the terminal plates 5 and 6 are made smaller than outside dimensions of the sealing materials 4a and 4b. Such a junction of the sealing material 4a with the terminal plate 5 and a junction of the sealing material 4b with the terminal plate 6, have been manufactured simultaneously and consecutively through processes shown by Fig. 16 through Fig. 19. Namely, in the first place, a grid 20 as illustrated by Fig. 16 is prepared, and the grid 20 is welded to a stainless plate 21, for example, forming the terminal plate. Incidentally, the grid 20 is made of the same material as that of the sealing material 4, has the same thickness as those of the sealing materials 4a and 4b, and has a structure including many sealing materials 4a and 4b integrally. In the second place, the grid 20 is placed on a hard ground film 11 as illustrated by Fig. 17, and a cut is made into the grid 20 by a half cutter 10 so as to separate it as shown by Fig. 18. In Fig. 18, for example, a right side is assumed as a junction of the sealing material 4a with the terminal plate 5, and a left side is assumed as a junction of the sealing material 4b with the terminal plate 6. Fig. 17 through Fig. 19 correspond to a sectional view taken on the line XVII - XVII of Fig. 16. Then, cuts are made only into the terminal plates 5 and 6 respectively by the half cutter 10 as illustrated by Fig. 18, so that the terminal plates 5 and 6 are removed from the cut lines as illustrated by Fig. 19. In such a manufacturing method, however, since the terminal plates 5 and 6 have been hard and the sealing materials 4a and 4b have been soft, there has been a possibility that the cuts have been made up to the sealing materials 4a and 4b so as to break them separately in the process of Fig. 18. If junctions in which the cuts are made up to the sealing materials 4a and 4b are used in the process of Fig. 18, there is a possibility that the external short-circuiting would occur due to the contact of the terminal plate 5 with the terminal plate 6 at their peripheral edges. That is, in the film type battery constructed as shown by Fig. 15, the external short-circuiting has not been prevented sufficiently, and the productivity has been worse because it has been a hard work to make cuts only into the terminal plates 5 and 6 in the process of Fig. 18. Disclosure of the Invention A first object of this invention is to provide a film type battery which is excellent in a long-term reliability. A second object of this invention is to provide a film type battery which can prevent an external short-circuiting sufficiently and is easily produced. In order to accomplish the above first object, the present invention provides a film type battery comprising a generating element which is formed by laminating a negative active material, an electrolyte and a positive active material into a layer shape, terminal plates which are installed respectively above and below the generating element and serve also as a current collector and a container, and a frame-shaped sealing material which is installed on peripheral edges of the terminal plates, seals the generating element in between both terminal plates and insulates one terminal plate from the other; characterized by that the sealing material comprises a multi-layer structure in which at least one layer is made of metal and the others are made of an electrical insulator, the metal layer having a thermal skrinkage factor closes to that of the terminal plates than that of the electrical insulator, said layers being stacked vertically. A metal layer is included in the multi-layer structure of the sealing material so that the sealing material or a battery is increased in its mechanical strength and becomes hard to be bent. Consequently, the clearance is not produced at the sealing portion so that the deterioration of battery performance due to the ingress of atmosphere or the leakage of electrolyte can be prevented. Since the metal layer is sandwiched between the adhesive agent layers, wrinkles become very small which are produced when the terminal plates are thermally bonded to the sealing material, so that the problem of residual stress can be solved. Accordingly, the deterioration of battery performance due to the ingress of atmosphere and the leakage of electrolyte can be prevented. Brief Description of the Drawings Fig. 1 is a vertical sectional view showing a film type battery of an embodiment. Fig. 2 is a diagram showing a preservation performance of the battery of the embodiment in comparison with that of a battery of comparison example. Fig. 3 is an oblique view showing a film type battery of an embodiment 2. Fig. 4 is a sectional view taken on a line IV - IV of Fig. 3. Fig. 5 is a discharge characteristic diagram of the battery of an illustrative example. Fig. 6 is a discharge characteristic diagram of a battery of comparison example in the illustrative example. Fig. 7 through Fig. 12 are vertical sectional views showing a part of manufacturing process, in order, of the film type battery of embodiment 4. Fig. 13 is a vertical sectional view showing a conventional film type battery. Fig. 14 is a vertical sectional view showing controversial points of the conventional film type battery. Fig. 15 is a vertical sectional view showing an another conventional film type battery. Fig. 16 is an oblique view showing a starting material for use in manufacture of the sealing material and the terminal plate. Fig. 17 through Fig. 19 are vertical sectional partial views showing a part of manufacturing process, in order, of the film type battery of Fig. 15. Best Mode for carrying Out the Invention (Embodiment 1) Fig. 1 is a vertical sectional view showing a film type battery of this embodiment. In the figure, 1 denotes a negative active material layer, 2 denotes a positive active material layer, and 3 denotes an electrolyte layer; and a generating element is composed of these components. Metallic lithium is used for the negative active material. A principal component of the positive active material is manganese dioxide. The electrolyte layer 3 is composed of a solid-polymer electrolyte comprising polyethylene oxide added with lithium perchlorate. 5 denotes a negative terminal plate, 6 denotes a positive terminal plate, and the terminal plates 5 and 6 serve also as a current collector and a container. A stainless plate is used for the terminal plates 5 and 6. A frame-shaped sealing material 4, which seals the above generating element in between the both terminal plates 5 and 6 and insulates the terminal plate 5 from the terminal plate 6, is installed on peripheral edges of the terminal plates 5 and 6. The sealing material 4 has a triple-layer structure in which an electric insulator layer 43 is sandwiched between two metallic layers 41 and 42. The metallic layers 41 and 42 are composed of cobar (Ni: 28%, Co: 18%, Fe: 54%). The electric insulator layer 43 is composed of alumina ceramics. The metallic layers 41 and 42 are adhered to the electric insulator layer 43 by means of thermal bonding or through adhesive agent. The sealing material 4 is melt bonded to the terminal plates 5 and 6 by means of laser welding. On the other hand, a film type battery was prepared as a comparison example, which had the same structure as that of this embodiment except for the sealing material 4 including a single-layer structure comprising denatured polypropylene resin. That is, the film type battery of comparison example has the same structure as that of the battery shown in Fig. 13. Fig. 2 is a diagram showing a preservation performance of the battery of this embodiment in comparison with that of the battery of comparison example. An axis of abscissa represents a preservation day and an axis of ordinate represents a discharge capacity ratio (%). The preservation performance was examined by measuring a successive change of battery capacity when the battery was left as it was in an atmosphere of 60 °C temperature and 90% relative humidity. In this diagram, an initial capacity is assumed as 100. As seen from Fig. 2, the battery of this embodiment brings about a small change in capacity i.e. a small deterioration in performance when left as it is for a long period, so that it provides a long-term reliability as compared with the battery of comparison example. Since the sealing material 4 includes the metallic layers 41 and 42 in the battery of this embodiment, the mechanical strength of the battery is larger than that of the battery of comparison example so that this battery is hard to be bent. Accordingly, in the battery of this embodiment, air-tightness is satisfactorily secured between the sealing material 4 and the terminal plates 5 and 6. Especially, since the cobar forming component material of the metallic layers 41 and 42 has an approximately same coefficient of thermal expansion as that of the alumina ceramics forming component material of the electrical insulator layer 43, the battery of this embodiment is stable against temperature change so that the air-tightness between the sealing material 4 and the terminal plates 5 and 6 is secured well. Therefore, permeabilities of moisture, oxygen, carbon dioxide gas, nitrogen etc. are extremely small in the battery of this embodiment as compared with the battery of comparison example, so that the performance deterioration is small and the long-term reliability is excellent. As described above, in the battery of this embodiment, the sealing material 4 has the vertical-type triple-layer structure and the metallic layers 41 and 42 are included therein, so that the mechanical strength can be made large, the performance deterioration due to ingress of atmosphere can be prevented, and the long-term reliability can be improved. Further, the sealing material 4 may be of a triple-layer structure, in which two electric insulator layers are installed and one metallic layer is sandwiched between them. Moreover, the sealing material 4 is not limited to the triple-layer structure, but may be of a multi-layer structure having at least one metallic layer. However, it goes without saying that the electric insulation layer is so installed as to insulate the terminal plate 5 from the terminal plate 6. Furthermore, the sealing material 4 may be melt bonded to the terminal plates 5 and 6 by means of electron beam welding or resistance welding. Aluminium, Fe-Ni alloy (Ni: 42% with Fe: 58%, for instance), stainless steel, copper, nickel etc. may be used for the component material of the metallic layer. In addition, ceramics other than the alumina ceramics or synthetic resin may be used for the component material of the electric insulator layer. Sulfide-group adhesive agent is preferable for the synthetic resin, and polysulfide denatured epoxy resin (Trade name: "FLEP", made by TORAY THIOKOL CO.), polysulfide polymer (Trade name: "THIOKOL LP", made by TORAY THIOKOL CO.) etc., for instance, may be used therefor. The following is an illustrative example of a structure which could be used, when a metal layer is employed, to embody the invention. Fig. 3 is an oblique view showing a film type battery of this embodiment. Fig. 4 is a sectional view taken on a line IV - IV of Fig. 3. In these figures, components same with or similar to those of Fig. 1 are attached with the same symbols. In the battery of this embodiment, the sealing material 4 has a triple-layer structure in which a foreign material layer 46, comprising a material a thermal shrinkage factor of which is closer to the terminal plates 5 and 6 rather than that of denatured polyolefin-group thermoplastic resin, is sandwiched between adhesive agent layers 44 and 45 comprising the denatured polyolefin-group thermoplastic resin. A material formed by graft polymerizing maleic anhydride to polypropylene resin is used for the denatured polyolefin-group thermoplastic resin forming the component material of the adhesive agent layers 44 and 45, and in this illustrative example polypropylene resin is used for the component material of the foreign material layer 46. The polypropylene resin can be considered as a material which is formed by removing a functional group having adhesive function from the denatured polyolefin-group thermoplastic resin forming the component material of the adhesive agent layers 44 and 45. The adhesive agent layers 44 and 45 are bonded to the foreign material layer 46 by means of thermal bonding or through adhesive agent. The sealing material 4 is thermally bonded to the terminal plates 5 and 6. On the other hand, a film type battery was prepared as a comparison example, which had the same structure as that of this illustrative example except for the sealing material 4 including a single-layer structure comprising the same material as that of the adhesive agent layers 44 and 45. That is, the film type battery of comparison example has the same structure as that of the battery shown in Fig. 13. Discharge capacities of 0.2 Ah batteries of this embodiment and comparison example were measured at constant discharge current of 20mA for both cases of initial discharge and discharge after 20 days preservation at 60 °C, respectively. Fig. 5 shows a result of the battery of this illustrative example, and Fig. 6 shows a result of the battery of the comparison example. As seen from Fig. 5 and Fig. 6, the battery of this embodiment presents little decrease in the capacity even after preservation at high temperature, but the battery of comparison example presents a decrease in the discharge capacity to about 70% of the initial discharge capacity after the preservation at high temperature. In the battery of this illustrative example, the thermal shrinkage factor of the foreign material layer 46 is smaller than those of the adhesive agent layers 44 and 45 and close to those of the terminal plates 5 and 6, so that wrinkles produced when thermally bonding the sealing material 4 to the terminal plates 5 and 6 become extremely small as compared with wrinkles of the battery of comparison example. Namely, it follows that stresses do not remain on sealing portions of the battery of this illustrative example, Consequently, in the battery of this illustrative example, a part of the sealing material does not open due to a stress applied on the sealing portion during use of battery and the battery performance does not deteriorate due to the ingress of atmosphere in the battery, so that the long-term reliability of battery of this illustrative example, is improved. Further, since a principal-chain structure of the component material for the adhesive agent layers 44 and 45 is same as that of the component material for the foreign material layer 46, they are adhered by means of the melt bonding so that they are connected closely each other. In addition, the principal-chain structure is of polyolefin-group type so that the moisture permeability in the sealing material 4 becomes small. Accordingly, the deterioration of battery performance due to the ingress of atmosphere such as moisture in the battery can be prevented preferably. As described above, since the sealing material 4 has the vertical-type triple-layer structure and the foreign material layer 46 is sandwiched in between the adhesive agent layers 44 and 45 in the battery of this embodiment, wrinkles produced when thermally bonding the sealing material 4 to the terminal plates 5 and 6 can be prevented, i.e. the problem of residual stress can be solved, so that the performance deterioration due to the ingress of atmosphere can be prevented and the long-term reliability can be improved. The structure of the sealing material 4 is not limited to the triple-layer structure, but may be of a quintuple-layer structure in which the adhesive agent layer and the foreign material layer laminated one another by turns, or may be of a multi-layer structure including more layers. The material of foreign material layer is not limited to the polyolefin-group thermoplastic resin, but may be a metal if its thermal shrinkage factor is close to that of the terminal plate, and the structure may thus be used to embody the invention.

Claims: A film type battery comprising a generating element which is formed by laminating a negative active material, an electrolyte and a positive active material into a layer shape, terminal plates which are installed respectively above and below the generating element and serve also as a current collector and a container, and a frame-shaped sealing material which is installed on peripheral edges of the terminal plates, seals the generating element in between both terminal plates and insulates one terminal plate from the other; characterized in that the sealing material comprises a multi-layer structure in which at least one layer is made of metal and the others are made of an electrical insulator, said layers being stacked vertically. A film type battery as set forth in claim 1, in which the metallic layer of the sealing material is composed of aluminium, cobar (Ni : 28%, Co : 18%, Fe : 54%), Fe-Ni alloy, stainless steel, copper or nickel. A film type battery as set forth in claim 1 or claim 2, in which the electric insulator layer of the sealing material is composed of ceramics or synthetic resin. A film type battery as set forth in any one of claims 1 to 3, in which the sealing material comprises a synthetic resin of a sulfide-group adhesive agent. A film type battery according to any one of the preceding claims wherein the electric insulator layer comprises a denatured polyolefin-group resin. A film type battery as set forth in any one of the preceding claims, in which the multi-layer is triple-layer. A film type battery as set forth in any one of the preceding claims, in which the metal layer has a thermal shrinkage factor closer to that of the terminal plates than that of the electrical insulator.

Inventors: IZUCHI SYUICHI, KATO SHIRO, MURATA KAZUO, TAKEUCHI KENICHI, IZUCHI, SYUICHI, KATO, SHIRO, MURATA, KAZUO, TAKEUCHI, KENICHI
Applicants: YUASA BATTERY CO LTD, YUASA CORPORATION
Application year: 1992
Main classification: H01M2
IPC codes: H01M2