Sealed prismatic storage battery

Abstract: The object of the present invention is to provide a sealed and prismatic storage battery characterized by such features as a high volumetric energy density, high compressivity and the like. A battery case 4 is made of molded plastics, each of an inner surface 9 and an outer surface 10 of each respective corner section 11 is formed of a curvature, the thickness B2 of the corner section 11 is 2.5 mm, a radius of curvature R1 of the outer surface 10 is 5.0 mm, a radius of curvature R2 of the inner surface 9 is 2.5 mm, a thickness B1 of a small thickness section 12 between the corner section 11 and the flat plane section 13 is 2.0 mm and the position of the thinnest wall section coincides with a position where the radius of a circular arc forming the inner surface of the corner section 11 crosses perpendicularly the outer side surface of the battery case.

Description: BACKGROUND OF THE INVENTION Application Areas in Industry The present invention relates to a prismatic and sealed storage battery and particularly relates to its battery case. Prior Arts Typical sealed prismatic storage batteries include such alkaline storage batteries as nickel-cadmium batteries and nickel-hydrogen storage batteries and also include lead-acid batteries. The alkaline storage batteries show a higher volumetric energy density when compared with cylindrical type batteries and many are used as electric power sources for portable equipment such as headphone stereos, portable telephones and the like, for example. On the other hand, sealed type lead-acid batteries are being increasingly used with small ones used in portable equipment and large ones in automobiles for engine starting. Recently, strong requirements have been arising for medium-sized or large batteries having a high energy density and excellent reliability for use in home appliances and electric vehicles as mobile sources of electric power. Here, the medium-sized batteries are understood to have a capacity ranging from 10 to 100 Ah and the large batteries to have a capacity exceeding 100 Ah. The number of batteries used per unit of equipment ranges from several units to several hundreds in average. Medium-sized and large batteries of non-sealed type nickel-cadmium batteries and lead-acid batteries are usually used for an energy storage purpose, UPS and the like, but there exist some inconveniences caused by the necessity of maintenance to add distilled water periodically during the life span of the batteries. As a result, there have been strong requirements for maintenance-free batteries realized by employing a sealed structure in mobile sources of electric power for home appliances, electric vehicles and the like. A typical prior art prismatic battery is illustrated in Fig. 4. In Fig. 4, each respective electrode group 31 is composed of positive electrodes 32 and negative electrodes 33 that are alternately superimposed one upon another with a separator (not shown in Fig. 4) inserted between the electrodes and then the electrode group 31 thus constructed is contained inside of a battery case 34. A positive pole 35 and a negative pole 36 are connected to the electrode group 31, respectively, and electric energy is drained to outside through the positive pole 35 and negative pole 36. A cover 38 is provided with a safety vent 37 in addition to the positive pole 35 and negative pole 36. The battery case of the foregoing batteries is made of metal or resin. In either case, the battery case is required to have high compressivity. When the internal pressure of the battery case 34 is increased, each respective side or end surface forming the prismatic battery case is exposed to outward mechanical stresses. Especially, the outward mechanical stresses concentrate to corner sections where two flat plane sections forming a prismatic battery case meet each other since outward bending moment is produced with the corners serving as the center of the bending moment. In order to improve the compressivity by overcoming the foregoing mechanical stresses, it has been considered to increase the thickness of the corner sections. Also, an employment of a curvature formed of concentric arcs for both the inner surface 39 and outer surface 40, both composing the corner section 41 together as shown in Fig. 5, has been considered as a solution to the foregoing problem. In this case, the thickness of the flat plane section 43 is made the same as that of the corner section 41. However, it becomes difficult for a sealed prismatic storage battery using a battery case with an increased case thickness to dissipate the heat produced within the battery efficiently to outside, resulting in deterioration of the battery's performance. In addition, when the battery case is produced by molding, the case is not readily formable and also the amount of the material used tends to be increased, thus ending up with numerous demerits in terms of costs. On the other hand, when a sealed prismatic storage battery is constructed so that each respective corner section thereof is formed of an outer surface and an inner surface, each of which has a curvature formed of concentric arcs, and especially the inner surface may have a sufficiently large radius of curvature, the internal effective volume of the battery case will be decreased with a resulting reduction in the volumetric energy density of the battery. Furthermore, when an almost rectangular prism like electrode group composed of square shaped electrodes, which are superimposed one upon another, is placed in the foregoing battery case, the curved corner sections of the battery case are pressed against the edges of the electrode group, inflicting sometimes damages on the electrode group and causing the edges of positive or negative electrodes to penetrate separators, thereby bringing about the danger of electrical short circuiting. With the foregoing sealed prismatic storage battery of a battery case that has specified thicknesses for flat plane sections and corner sections, each respective flat plane section forming the prismatic battery case is exposed to an outward stress as the internal pressure in the battery case increases. Under this state, while each respective flat plane section being subjected to a tensile stress, each respective corner section, where two flat plane sections meet each other, is exposed to bending moment that works outward from the center of the corner section. Therefore, the stress is concentrated in the center of the corner section and, even when the inner surface of the corner section has a sufficiently large radius of curvature, the strength of the corner section is not strong enough with resultant insufficient compressivity. The present invention solves the foregoing problems and provides a sealed prismatic storage battery having a high volumetric energy density and using a high compressivity battery case. SUMMARY OF THE INVENTION A sealed prismatic storage battery of the present invention comprises a prismatic battery case having an opening, electrodes and electrolyte both contained in the foregoing battery case and a cover whereby the foregoing opening is closed by sealing. The afore-mentioned battery case has a plurality of almost flat plane sections, corner sections situated between two of the foregoing plurality of the almost flat plane sections and junctions existing between the foregoing corner sections and respective flat plane sections, at least the inner surface of the foregoing each respective corner section has a curvature and the thickness of the foregoing junctions is smaller than that of the foregoing flat plane sections and corner sections. In the structures as described in the above, it is particularly preferred that the afore-mentioned electrodes comprise a plurality of positive electrodes and negative electrode plates, and separators placed between positive electrodes and negative electrodes. The afore-mentioned cover is particularly preferred to have a safety vent. Each of the afore-mentioned corner sections is particularly preferred to have a curving outer surface. Each respective section between the foregoing corner sections and junctions and also between the foregoing junctions and flat plane sections is particularly preferred to change continuously in thickness. It is particularly preferred that the position where the foregoing junction becomes smallest in thickness coincides with the position of the foregoing flat plane sections where the radius of the circular arc forming the inner surface of the foregoing corner section crosses the outer surface of the flat plane section perpendicularly. It is more preferred that the thickness of the foregoing junction is larger than one half of the smallest thickness of the flat plane section as described in the above. Further, when a battery case has a radius of curvature R1 in its outer surface, a radius of curvature R2 in its inner surface, a thickness B1 in the thinnest part of a junction between a corner section and a flat plane section and a thickness B2 in the thinnest flat plane section of two or three flat plates that form a corner section of the battery case, it is most desirable that the following inequality is satisfied: R1 > R2+B1 > 0.75 R1 > B2 > B1 > 0.5 B2 When a battery case is structured as described in the above, it is made possible to prevent stresses from concentrating on a corner section of a battery case, which is composed of a plurality of almost flat plane sections. Therefore, stresses due to a tensile stress and bending moment can be prevented from concentrating only on a small area in the center of the corner section. Instead, the stresses can be dispersed to larger areas around the place where the thickness is made small. As a result, even if a battery case has the same thickness all over or a smaller thickness, the battery case can be made to show improved compressivity. According to the structures as described in the above, a reduction in thickness for the corner sections of a battery case is made possible, thereby making it possible to increase the volume for accommodating rectangular prism like electrode group and realize a battery with a high volumetric energy density. Furthermore, since an overall reduction in thickness for the battery case is achieved, it has become possible for the heat produced from the electrode group to dissipate efficiently to the outside of the battery. As a result, the charge and discharge efficiency of the electrode group is enhanced. In addition, the prevention of deterioration in electrode plates due to dissolving and the like is achieved, thus making it possible to realize a long life storage battery. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a sealed prismatic storage battery in an exemplary embodiment of the present invention. Fig. 2 shows part of a cross-sectional view of the battery case used in the prismatic storage battery of Fig. 1. Fig. 3 is an enlarged cross-sectional view of part of the battery case as shown in Fig. 2. Fig. 4 is a perspective view of a prior art sealed prismatic storage battery. Fig. 5 is an enlarged cross-sectional view of part of the battery case for an ordinary sealed prismatic storage battery. Key to Reference Numerals 1 Electrode Group 2 Positive Electrode Plate 3 Negative Electrode Plate 4 Battery Case 5 Positive Pole 6 Negative Pole 7 Safety Vent 8 Cover 9 Inner Surface 10 Outer Surface 11 Corner Section 12 Small Thickness Section 13 Plan View 16 Projected Section DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Next, a sealed prismatic storage battery will be explained in some embodiments of the present invention with reference of drawings. Fig. 1 is a perspective view of a sealed prismatic storage battery in an exemplary embodiment of the present invention. In Fig. 1, a sealed prismatic storage battery comprises electrode group 1, a battery case 4 containing the electrode group 1, electrolyte (not shown in Fig. 1) filled in the battery case 4 and with which the electrode group 1 are impregnated, and a cover 8 arranged to cover an opening of the battery case 4. The electrode group 1 is prepared as follows: A positive electrode 2 is a nickel positive electrode plate with a drainage capacity of 10 Ah per plate, which is prepared by filling an active material of nickel hydroxide powder in a foam-like nickel porous structure and then by rolling/cutting to specified dimensions. A negative electrode 3 is a negative electrode plate of hydrogen absorbing alloy having a drainage capacity of 13 Ah per plate, which is prepared by coating a punching metal with a mixture of a binder and hydrogen absorbing alloy powder which has a composition of MmNi 3.6 Co 0.7 Mn 0.4 Al 0.4 (Mm stands for misch metal) that can absorb/emit hydrogen electrochemically and then by rolling/cutting to specified dimensions. These positive and negative electrodes are wrapped in a sack like separator individually, and 10 positive electrodes and 11 negative electrodes of these separator wrapped electrodes are alternately combined to compose an electrode group 1. The electrode group 1 is made so that the thickness thereof may occupy about 5 % of the inner thickness of the battery case 4. Next, each respective positive electrode 2 is connected to a positive pole 5 and each respective negative electrode 3 is connected to a negative pole 6. Both the positive and negative poles are provided on the cover 8. The electrode group thus constructed is then placed in the battery case 4. The positive pole 5 and negative pole 6 are made of copper and nickel, respectively. Next, alkaline electrolyte in a volume of 180 cm 3 is poured in the battery case 4. After that, the opening of the battery case 4 is closed by sealing with the cover 8 which is provided with a safety vent 7 (an actuating pressure of 15 kg/cm 2 ). Thus, a battery A is completed. There are many projections 16 that are running vertically are formed on the outer side surfaces of the battery case 4. The height of the projections is about 1.5 mm. Further, the completed battery is subjected to an initial charging/discharging process (charging at 10 A for 15 hours and discharging at 20 A till the battery voltage decreases to 1.0 V). The battery thus prepared is limited to 100 Ah in the drainage capacity by the positive electrode. Fig. 2 is a cross-sectional view of the battery case 4 and Fig. 3 is an enlarged cross-sectional view of one of the corner sections of the battery case 4. The battery case in the present exemplary embodiment is of a rectangular prism like configuration and each respective corner section 11 is formed of an outer side surface and an inner side surface, each comprising a curved surface. The minimum thickness B2 of any two or three flat plane sections 13 that meet one another at a corner section 11 measures 2.5 mm, a radius of curvature R1 of the outer surface of the corner section 11 is 5.0 mm, a radius of curvature R2 of the inner surface of the corner section 11 is 2.5 mm, a thickness B1 of the thinnest part of a junction between the corner section 11 and the flat plane section 13 measures 2.0 mm and a thickness B3 of the thickest part of the corner section 11 measures 2.5 mm. Each respective thickness of the areas between the corner section 11 and the junction and between the foregoing junction and a flat plane section 13 changes continuously. In addition, the flat plane sections 13 projections 16 formed at the specified positions thereof. These projections 16 contribute to increasing the mechanical strength of the flat plane sections 13. Thus, a sealed prismatic storage battery A has been completed. Each respective curvature center of the radius of curvature R1 of the battery case's outer side surface 10 and the radius of curvature R2 of the battery case's inner side surface 9 is not necessarily to be at the same position. The place of a junction where a thickness B1 of the junction is smallest coincides with a place where the radius of a circular arc forming the inner side surface 9 of a corner section 11 crosses perpendicularly the inner side surface of a flat plane section 13. The battery case 4 is made of resin. According to the same method as described in the above, sealed prismatic storage batteries B to L of various battery case configurations have been prepared. The batteries F, J and L have the corners of the outer side surfaces of the battery cases made square. The batteries D and K have been prepared using a prior art battery case as shown in Fig. 5. Table 1 shows dimensions of the battery cases used in these batteries. Thickness of Battery Case at Various Places Meas'ment Results R 1 R 2 B 1 B 2 B 3 Compressivity kg/cm 2 Battery A 5.0 2.5 2.0 2.5 2.5 12.0 Battery B 5.0 3.5 2.0 2.5 2.5 10.0 Battery C 5.0 1.5 2.0 2.5 3.5 9.0 Battery D 5.0 2.5 2.5 2.5 2.5 6.0 Battery E 5.0 2.5 1.2 2.5 2.5 5.0 Battery F - 2.5 2.0 2.5 >2.0 8.0 Battery G 4.5 2.5 1.4 2.5 2.0 8.0 Battery H 4.0 2.0 1.7 2.0 2.0 7.5 Battery I 4.0 2.0 0.9 2.0 2.0 4.0 Battery J - 2.0 1.7 2.0 >1.7 7.0 Battery K 5.0 2.0 3.0 3.0 3.0 8.0 Battery L - 2.5 2.5 2.5 >2.5 5.0 As indicated in the above table, a series of compressivity tests have been conducted using batteries A to L. The compressivity test method employed in the above is as follows: Charge a battery for 12 hours at 10 A and then let the battery standing for one hour, and further overcharge the battery at 5 A until cracks or fractures are produced on the corner sections of the battery where stresses are concentrated. Measure the internal pressure at this time. The internal pressure is measured by an internal pressure sensor attached to the battery case in advance, and the measured internal pressure values are also indicated in Table 1. Cracks were observed with the sealed prismatic storage battery A when the internal pressure reached 12 kg/cm 2 . The battery B was cracked under an internal pressure of about 10 kg/cm 2 . The battery C was cracked under an internal pressure of about 9 kg/cm 2 . The battery D was cracked under an internal pressure of about 6 kg/cm 2 . The battery E was cracked under an internal pressure of about 5 kg/cm 2 . The battery F was cracked under an internal pressure of about 8 kg/cm 2 . The battery G was cracked under an internal pressure of about 8 kg/cm 2 . The battery H was cracked under an internal pressure of about 7.5 kg/cm 2 . The battery I was cracked under an internal pressure of about 4 kg/cm 2 . The battery J was cracked under an internal pressure of about 7 kg/cm 2 . The battery K was cracked under an internal pressure of about 8 kg/cm 2 . The battery L was cracked under an internal pressure of about 5 kg/cm 2 . Table 1 reveals the fact that batteries having a smaller thickness B1 for a junction than a thickness B2 for a flat plane section and also than a thickness B3 for a corner section (such as batteries A, B, C, G and H) show an improvement in compressivity. In Table 1, the battery A shows the most enhanced compressivity. With the battery A, the existence of a section of a smaller thickness in the junction between the curved part of a corner section and a flat plane section is contributing to dispersing the stress not only to the corner section but also to the smaller thickness section. Therefore, the stress that used to concentrate on the corner section in the prior art is dispersed to larger areas. As a result, the compressivity of the battery A has been improved when compared with that of a prior art battery K in spite of the fact that the thickness of various sections of the battery A is reduced. The compressivity of the battery B is larger than that of the prior art battery D that does not have a small thickness section but smaller than that of the battery A. The reason for the above is in that a relatively large stress is imposed on the small thickness section of the junction without the uniform dispersion of stress taking place in the curved section and small thickness section since the radius of curvature R2 of the inner surface of the corner section is a little larger than that of the battery A. In other words, the radius of curvature R2 of the inner surface of the corner section is preferred to satisfy an inequality (1) as follows: R1 > R2 + B1 > B2 The compressivity of the battery C is larger than that of the battery D that does not have a small thickness section but smaller than that of the battery A. The reason for the above is in that a relatively large stress is imposed on the corner section without the uniform dispersion of stress taking place in the curved section and small thickness section since the radius of curvature R2 of the corner section is a little smaller than that of the battery A. In other words, the radius of curvature R2 of the inner surface of the corner section is preferred to satisfy an inequality (2) as follows: R1 > R2 + B1 > 0.75 R1 > B2 The battery H has been designed to have a smaller thickness B2 for the flat plane section thereof than the thickness of the prior art battery D. Since the junction's thickness B1 is smaller than B2, the stress imposed is dispersed to larger areas. As a result, the compressivity of the battery H has been improved when compared with that of the prior art battery D in spite of the fact that the thickness of the battery case is reduced. In contrast, the compressivity of the batteries D, E and I is markedly reduced. The battery D has the thickness B1 for the junction, the thickness B2 for the flat plane section and the thickness B3 for the corner section all made equal to one another, and the tensile stress and curvature moment, which develop as the internal pressure of the battery D increases, are concentrated on a small area of the curved surface of the corner section, resulting in cracking in spite of the relatively low internal pressure produced in the battery D. The compressivity of the battery E is further reduced from that of the battery D. The reason for the above is in that the thickness B1 for the junction of the battery E is extremely small and stress has been concentrated on the small thickness section. The compressivity of the battery I is further reduced from that of the battery H. The reason for the above is in that the thickness B1 for the junction of the battery I is extremely small when compared with the wall thickness B1 of the battery H and stress has been concentrated on the small thickness section. Next, the performance of the batteries F, J and L, all of which have square corner sections on the outer surfaces of each respective battery case, will be examined by comparing one with another. The compressivity of the batteries F and J wherein the junction thickness B1 is made smaller than the thickness B2 of the flat plane section is higher than that of the battery L having the same thickness for both the junction thickness B1 and the thickness B2 of the flat plane section. When the thickness B2 of the flat plane section 13 is increased, the resulting compressivity is improved. However, the inside volume of the battery case 4 that can afford to accommodate an electrode group will be reduced, thereby causing the drainage capacity of the battery to be reduced tremendously and also making it difficult for the heat produced in the battery to dissipate to the outside. Therefore, it is not desirable to increase the thickness B2 of the flat plane section 13. Also, as the radius of curvature R2 of the inner surface 9 of the battery case 4 increases, the extent of protrusion of the corner sections towards the inside of the battery is increased, thereby causing the volume, where an electrode group can occupy, to be reduced and decreasing the drainage capacity of the battery. Therefore, it is not desirable to increase the radius of curvature R2 of the inner surface 9 of the battery case 4 too much. From the evaluation results as described in the above, it can be concluded that a battery case should be comprising a plurality of almost flat plane sections, corner sections formed of the foregoing plurality of almost flat plane sections and junctions situated between each respective corner section and flat plane section of the foregoing, and the thickness of the foregoing junctions needs to be smaller than that of the foregoing flat plane sections and corner sections. Furthermore, the battery case to be employed is particularly preferred to be a sealed prismatic battery case having corner sections, each of which is formed of an outer surface and an inner surface both comprising a curvature. It is most preferred that the radius of curvature R1 of battery case's outer surface, the radius curvature R2 of battery case's inner surface, the thickness B1 of a small thickness section of a junction situated between a corner section and a flat plane section and the thickness B2 of two or three flat plane sections forming corner sections satisfy the following inequality (3): R1 > R2 + B1 > 0.75 R1 > B2 > B1 > 0.5 B2 In addition, the place where the wall thickness becomes smallest as mentioned in the above should coincide with the place, where the radius of a circular arc forming an inner surface of a corner section, crosses the flat plane on the outer side surface of the battery case. There are dangers of having the edges of the electrode group pressed against the inside surfaces of the corner sections and even damaged in a battery using a battery case that has the inner and outer surfaces of the corner sections formed of concentric circular arcs. Furthermore, the edges of positive electrodes or negative electrodes may break through the separators with a resulting danger of short-circuiting the electrodes. As opposed to the above, the battery case of a prismatic storage battery of the present invention has small thickness sections in the corner sections thereof, thereby eliminating the possibilities of pressing the edges of the electrode group against the inner surfaces of the battery case and the possible dangers of short-circuiting. Furthermore, even if the structures in the foregoing exemplary embodiments do not have any curvatures on the outer surfaces, the same effects as achieved with the present exemplary embodiment can be obtained provided that the inner surface configurations of the corner sections of the battery case used are the same as the ones of the present exemplary embodiment. In addition, it is particularly preferred that the sealed prismatic storage batteries of the present invention are an alkaline storage battery such as a nickel·hydrogen battery or a nickel-cadmium battery, and a lead-acid battery. Also, it is particularly preferred that the sealed prismatic storage batteries of the present invention are medium size and large size storage batteries with an energy density exceeding 10 Ah. As described in the above, the sealed prismatic storage battery of the present invention is characterized by showing the following effects: (1) Achieving a high degree of compressivity without reducing the drainage capacity of a storage battery. (2) Eliminating the possibilities of battery case's inner surfaces being pressed against the edges of the electrode group and resultant dangers of short-circuiting the electrodes by employing a battery case wherein the inner and outer curved surfaces at corner sections are not formed of concentric circular arcs and small thickness sections are provided. (3) Making it possible to make battery case's wall thickness small, thereby facilitating the dissipation of the heat produced in a storage battery to outside and consequently contributing to the suppression of battery's heat generation. The foregoing effect will be particularly multiplied by producing the battery case using plastic materials that are easy to mold, inexpensive and low in thermal conductivity. (4) Realizing sealed prismatic storage batteries of medium size and large size showing a high energy density and all the advantages of the foregoing (1) to (3).

Claims: A sealed prismatic storage battery comprising: a prismatic battery case having an opening; an electrode and an electrolyte contained in said battery case; and a cover closing said battery case's opening by sealing, wherein said battery case has a plurality of flat plane sections, a corner section situated between each flat plane section of said plurality of flat plane sections, and a junction section situated between said corner section and said each flat plane section, said corner section has a curvature at least on the inner surface thereof, and said junction section has a thickness that is smaller than that of said flat plane section and also that of said corner section. The sealed prismatic strage battery according to Claim 1, wherein said flat plane section has an almost flat plane shape. The sealed prismatic storage battery according to Claim 1, wherein said prismatic battery case has an almost rectangular prism like shape. The sealed prismatic storage battery according to Claim 3, wherein a position of the thinnest section of said junction section coincides with a position where a radius of a circular arc forming an inner surface of said corner section crosses perpendicularly an inner surface of said flat plane section. The sealed prismatic storage battery according to Claim 1, wherein a thickness of said junction section is larger than 1/2 of the smallest thickness of said flat plane section. The sealed prismatic storage battery according to Claim 1, wherein said electrode includes a plurality of positive and negative electrodes and a separator placed between respective positive and negative electrode of said plurality of electrodes. The sealed prismatic storage battery according to Claim 1, wherein said cover is provided with a safety vent. The sealed prismatic storage battery according to Claim 1, wherein said battery case is made of at least one selected from molded plastics and molded metals. The sealed prismatic storage battery according to Claim 1, wherein said corner section has an outer surface with a curvature. The sealed prismatic storage battery according to Claim 9, wherein a thinnest place of said junction section coincides with a place where a radius of a circular arc forming an inner surface of said corner section crosses perpendicularly an outer surface of said flat plane section. The sealed prismatic storage battery according to Claim 9, wherein a thickness of said junction is larger than 1/2 of the thickness of said flat plane section. The sealed prismatic storage battery according to Claim 8, wherein a radius of curvature R1 of said outer surface of said corner section, a radius of curvature R2 of said inner surface of said corner section, a thickness B1 of said junction section and a thickness B2 of said flat plane section satisfy the following inequality: R1 > R2 + B1 > 0.75 R1 > B2 > B1 > 0.5 B2 The sealed prismatic storage battery according to Claim 1, wherein a thickness of a first section between said corner section and said junction section changes continuously along a length of said first sections, and a thickness of a second section between said junction section and said flat plane section changes continuously along a length of said second section.

Inventors: HAMADA SHINJI, IKOMA MUNEHISA, MORISHITA NOBUYASU, OKAMOTO MIHO, HAMADA, SHINJI, IKOMA, MUNEHISA, MORISHITA, NOBUYASU, OKAMOTO, MIHO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: H01M2
IPC codes: H01M10, H01M2