A lead-acid storage battery with tubular bipolar electrodes

Abstract: A storage battery of the lead-acid type is disclosed, comprising unipolar electrodes (6) and bipolar electrodes (7), having a tubular shape fastened preferably perpendicularly to separators (3, 4) made of an insulating material, which divide into two or more adjacent cells the container (1) containing the electrolyte. In a preferred embodiment, each tubular electrode (6, 7) is formed by an axial bar (8) of lead or an alloy thereof, having a circular section, surrounded by active material (9), either positive or negative, in its turn enclosed by a coaxial tubular sheath (10) in porous synthetic and insulating material, and plugs (11, 12) of plastic material. The ends (13), brought to the exterior, of the bars (8) of the unipolar tubular electrodes (6) of each of the end cells are connected to a respective external bus bar (14) for the current, constituting a pole of the storage battery (figure 2).

Description: The present invention relates a storage battery of the lead-acid kind comprising unipolar electrodes having a tubular shape, directed to the increase of the specific energy (with an attendant decrease of the weight of the non-active material) and to the improvement of the operative features, such as the internal resistance and the prolongation of the life cycle of the device. State of the art The invention has been developped in the field of research aimed at the improvement of the technical characteristics of lead-acid storage batteries for promoting their application (preferential) to electric propulsion. The bipolar arrangement has already been used, but with controversial results, due to technical difficulties connected to the practical embodiment of the related methods. Outline of the proposed system The storage battery according to the invention as set out in claim 1 comprises a container, usually of paralellepipedal shape, of a kind with boxed assembly, made of a plastic insulating material, for instance PVC, containing the electrolyte, and divided into two or more cells by means of one or more partition walls of the same insulating material, traversed by bipolar tubular electrodes, while the side walls of the container, also called end walls, parallel to the partition walls, are traversed by unipolar tubular electrodes connected to external bus bars for the current. Each tubular electrode is constituted of an axial bar of lead or an alloy thereof, surrounded by active material, in its turn surrounded by a coaxial tubular sheath of permeable insulating material, and by end plugs made of plastic material. The tubular electrodes are fastened by means of projections on the respective bars, such as coaxial disks of lead or an alloy thereof, to the partition walls or to the end walls. Said walls are preferably formed by assembling two half walls of plastic material, one of which has a cavity for receiving the corresponding projection or disk of the electrode bar, the two half walls being glued together when they are mechanically coupled in order to ensure the tightness of the cells. The tubular electrodes, supported by the walls by means of the respective bars, are arranged preferably perpendicularly to the walls and parallel to each other, respectively arranged as a comb. A storage battery structure according to the invention allows the active material of the electrodes to be distributed in such a way as to minimize the ohmic losses of the internal connections and of the electrolyte, to have a uniform current distribution in the active mass, and to have an electrolyte density that varies in a uniform manner. Finally, the advantages that derive therefrom are: a lower internal resistance, a more uniform distribution of the current density, a better use of the active material, the elimination of external and internal connections carrying current between the electrodes, a reduction of the weight of the storage battery, a high specific energy, the possibility of using a manufacturing process which is in a great part a conventional one, with small modifications in the assembly. The present invention will be better understood by a detailed disclosure of a preferred embodiment of the same, shown as a non-limiting example and with reference to the attached drawings, wherein: figure 1 is a general explanatory diagram in plan view of a storage battery having three cells according to the present invention; figure 2 is a schematic lateral view, with cut away parts, of a storage battery realized according to the principle of figure 1; figure 3 is a sectional view, in an enlarged scale, of an example of a bipolar tubular electrode, to be used in the storage battery according to the invention; figure 4 is a detail with exploded parts, of the bipolar tubular electrode of figure 3; figure 5 (a) and 5 (b) are schematic diagrams of possible arrangements of the tubular electrodes in the storage battery of the invention; figure 6 shows in elevation two half walls to be coupled by means of glueing or welding in order to form a single wall; figure 7 is an elevation view that shows schematically the system of box-like assembly of the container forming the storage battery, with walls and tubular electrodes shown in the preceding figures; figure 8 is a diagram which represents the experimental capacity in function of the charge/discharge cycles at 40°C of a storage battery according to the invention; and figure 9 is a comparison diagram of the trend of the voltage versus time in a storage battery of the lead-acid type of the prior art with respect to a similar storage battery according to the present invention. With reference to figures 1 to 7, an exemple of storage battery according to the invention comprises a container, generally shown in 1, made of an insulating material, of parallelepipedal shape with a box-like assembly, having two vertical longitudinal walls 2, two transversal vertical end walls 3, partition walls 4, in this case two walls 4, the storage battery being divided into three cells, and three plates 5 forming the bottom of the container and inserted between the end and partition walls 3, 4 and the longitudinal walls 2. In the container 1 several horizontal unipolar tubular electrodes 6 are assembled, at an end thereof, perpendicularly to the end walls 3, so as to extend to the interior of the end cells of the storage battery, and several horizontal bipolar tubular electrodes 7 are assembled, at their half length, perpendicularly to the partition walls 4 so that they extend from one side and the other into the interior of two relative cells placed side by side. Both the unipolar electrodes 6 and the bipolar electrodes 7, as one may understand from figures 2, 6 and 7, are parallelly supported in groups with a mesh arrangement that is reciprocally meshing, the unipolar electrodes 6 extending into the free spaces left by the bipolar electrodes 7, and vice versa. An arrangement of this kind with offset meshes may be of any type, for instance with a square mesh or a triangular mesh, as it is shown in figures 5 (a) and 5 (b), with equal distances p between the axes of the electrodes of each group. Against a greater construction complexity, the triangular mesh arrangement offers, with respect to the arrangement with a square mesh, a more uniform distribution of the electrodes on the transversal section of each cell, and consequently better operation of the storage battery. As a matter of fact, a more uniform distribution of the electrodes also leads to a more homogeneous distribution of the layer of electrolyte around each electrode. Moreover, in this kind of arrangement, each electrode is surrounded by four electrodes of the opposit polarity, offering a greater surface of ionic exchange with a consequent improvement of the electrical behaviour, in particular under a fast discharge. Each bipolar electrode (see figures 3 and 4) has an axial bar 8 carrying current, having a circular sectional shape, for instance having a diameter of about 2mm, made of lead or an alloy thereof, preferably an alloy of the kind Pb/Sb with a low content of Sb, and refined with Se; the amount of Sb is preferably 1.7 - 3%. The reduction of the content of Sb limits the phenomenon of self-discharge, and the alloy that uses Se as a refining agent shows moreover a mechanical resistance suitable for assembling the bars in the wall of plastic material. Around the axial bar 8, which operates as a support for the electrode, active material 9, positive (PbO 2 ) or negative (spongy Pb) is placed, obtained in a conventional way from a slurry. The active material 9 is surrounded by a tubular sheath 10, having for instance a diameter of about 8mm and having a thickness of about 0.3mm, of a porous plastic material (for instance a porous synthetic fiber), coaxial with the bar 8. Each tubular sheath 10 is closed by end plugs, which may be of the kind with a central through-hole, as shown in 11, at the end of a sheath 10 adjacent to an end or partition wall, or of a kind with a central blind hole, as shown in 12, at the free end of the sheath 10, in order to maintain the bar 8 centered with respect to the tubular sheath 10. The ends 13 of the bars 8 of the unipolar tubular electrodes 6, protruding outside the end walls 3 of the storage battery through the plugs 11, are connected at the exterior with a conducting plate 14 in common (figure 3), usually made of copper, which forms the actual current bus bar or pole of the storage battery. The assembly of the tubular electrodes (unipolar 6 and bipolar 7) on the respective walls (end wall 3 and partition walls 4) is performed in the following way. Each bar 8 carrying current and acting as a support, has a projection, in this case a concentric disk 15 of lead or an alloy thereof, located near an end of the electrode, in the case of a unipolar electrode 6, or half way along the electrode, in the case of a bipolar electrode 7. Each end wall 3 or partition walls 4 is formed by coupling two half walls 3a, 3b and 4a, 4b, respectively (figures 4 and 6) in plastic material, such as PVC, one of these half walls of the pair having a cavity 16 for housing the relative disk 15 of the bar 8. The two half walls of each pair are glued or welded to each other at their internal facing surfaces, in order to block the disk 15 in the cavity 16. The respective adjacent bored plugs 11 of the tubular electrodes are also glued or welded on the respective half walls (4a and 4b in figure 4). As electrolyte contained in the storage battery, in this case sulphuric acid is used, either in free form or gelled, with a specific density between 1.240 and 1.300 g/cm 2 . In experimental operations, the modalities of electro-chemical formation have been examined, i.e. the quality and quantity of the immission of acid and electric current for the transformation of Pb into PbO 2 (positive electrodes) and spongy Pb (negative electrodes). Electrical tests have been performed for charge and discharge, after the substitution of the formation electrolyte with the working electrolyte. These tests have been carried out under temperatures of 25°C and 40°C (figure 8). Moreover, tests of mechanical stress have been performed according to the CEI standards of 25.08.1983 (vertical vibration, 30-50 Hz, 30 m/s 2 , for 2 hours with a rest time of 4 hours, discharge current of 180 A, duration of the discharge 60 s), obtaining 1,33 volt/element > 1,2 volt/element. Also a comparison has been made with a conventional storage battery having a slightly smaller size, with ten cycles of charge/slow discharge (2A) and fast discharge (6A), with the results shown by the curves I and II of figure 9. From the experimental tests it has been shown that with the storage battery according to the present invention the advantages mentioned at the beginning of the present disclosure may be obtained.

Claims: A lead-acid storage battery, comprising a container (1) for the electrolyte, divided into two or more cells by means of one or more partition walls (4) of insulating material, traversed by bars (8)of a conducting material, which operate as supports for corresponding bipolar tubular electrodes (7), said container being delimited laterally by end walls (3) traversed by other bars (8) of conducting material, which operate as supports for corresponding unipolar tubular electrodes (6), said electrodes (6, 7) being arranged parallel to each other and reciprocally intercalated, each of said walls (3, 4) being formed by two half walls (3a, 3b; 4a, 4b) coupled to each other, said storage battery being characterized in that one of said two half walls has a cavity (16), each conducting bar (8) has a projection such as a coaxial circular disk (15) of the same material as the bar and of the same sizes as said cavity and each of said half walls is provided with holes sized as the corresponding bars and only allowing the passage of the bars, said projection being housed in said cavity so as to lock said bar (8) on the respective wall (3, 4) upon coupling said two half walls together by gluing or welding directly. A storage battery according to claim 1 characterized in that each tubular electrode is formed by a bar (8) surrounded by positive and/or negative active material (9), which is surrounded by a coaxial tubular sheath (10) of a porous synthetic material, as well as by end plugs (11, 12) of a plastic material, having suitable holes for receiving the respective bar (8). A storage battery according to claim 1 or 2, characterized in that said bars (8) are formed by lead or an alloy thereof. A storage battery according to claim 3, wherein said bars (8) are formed by an alloy Pb/Sb with a low content of Sb, 1.7 - 3%, and refined with Se, in order to reduce the phenomenon of self-discharge and to have a mechanical resistance suitable for assembling the bars on the respective walls. A storage battery according to any of the preceding claims, wherein the electrolyte is free or gelled sulphuric acid, having a specific density between 1.240 and 1.300 g/cm 3 . A storage battery according to any of the preceding claims, characterized in that the ends (13) of the bars (8) of the unipolar tubular electrodes (6) which extend through each end wall (3) of the container (1) are connected, outside said container, with a bus collector (14) which forms the relative pole of the storage battery.

Inventors: GINATTA MARCO VINCENZO, MAJA MARIO, ORSELLO GIANMICHELE, PEROTTI PIERANGELO, ROSETTI FURIO, ZAMPOLLI MARCO, GINATTA,MARCO VINCENZO, MAJA,MARIO, ORSELLO,GIANMICHELE, PEROTTI,PIERANGELO, ROSETTI,FURIO, ZAMPOLLI,MARCO
Applicants: EDISON TERMOELETTRICA SPA, ENEA ENTE NUOVE TEC, EDISON TERMOELETTRICA S.P.A., ENTE PER LE NUOVE TECNOLOGIE, L'ENERGIA E L'AMBIENTE ( ENEA)
Application year: 1991
Main classification: H01M10
IPC codes: H01M10