Sealed lead acid dipolar battery

Abstract: A sealed lead acid dipolar storage battery, in which one or more dipolar electrodes (11) consist of lead or lead alloy foils (13) or of other electroconductive material. The foils (13) are provided with a reticular print (14) for keeping a layer of positive active compound (15) on one side of the foil (13) and a layer of negative active compound (15) on the other side. The electrodes (11) are stacked one on top of the other so as to alternate the different polarities; a series of separators in microfiber glass with a high porosity are interposed between the electrodes (11) in series.

Description: The present invention refers to a lead acid storage battery with dipolar electrodes. In the field of lead storage batteries there are already some gas recombination systems with a starved electrolyte. This kind of battery is maintenance-free and avoids the risk of electrolyte leakage, and they are used for electronic applications and for stationary batteries. A traditional lead storage battery is composed by lead electrodes with a layer of positive active compound opposed to other electrodes with a layer of negative active compound. Several electrodes with the same polarity are welded together and immersed in an electrolytic bath. The end poles come out of the cell and are connected to the adjacent cell. The most common limits of this configuration devices are a low specific energy of the battery due to the high lead content, that is not an active material. It is also difficult to utilise the active compound on the lead grids completely. Another drawback is concerned with the connections between the cells, where the greatest part of the voltage drop occurs. Many efforts have been made in the field of lead storage batteries in order to reach better performances. Although present construction techniques give quite good results, they are still far from the full exploitation of the power that lead systems can offer. A solution for this problem is to use a new kind of electrode that eliminates the above mentioned limits. A high power density bipolar lead acid battery system is known from Extended Abstracts Of The Electrochemical Society, Fall Meeting, Pittsburgh, Pa., 15-20 Oct. 1978, no. 2, abstract n. 80, pages 208-209. The disclosed battery system comprises a plurality of dipolar electrodes being stacked one on top of the other so as to alternate the different polarities. The electrodes consist of lead sheets rolled so as to provide relief crests and low relieves on either side of the sheet for keeping a layer of positive active compound on one side of the sheet and a layer of negative active compound on the other side. A series of microporous glass fibre separators are interposed between the electrodes. DE-A-3907741 refers to a battery wherein crests and channels cover the surface of the electrodes except for a non-imprinted channel on the edges of the electrodes. The non-imprinted channel is adapted for fitting perimetral gaskets performing sealing action between the electrodes. The gaskets provide a plurality of perimetral electrolyte communicating channels in which the electrolyte can circulate between adjacent cells through inlet and outlet bores obtained in the electrodes. It is an object of the present invention to propose an accumulator with a low internal resistance, eliminating the actual connections between the cells where most of the voltage drops are concentrated. It is also a purpose to reach a better distribution of the current density due to an enlarged active surface of the conductive material contacting the active compounds, that can be therefore utilised in the best way. Another purpose of this invention is to reduce the total weight of the accumulator by eliminating the connections and reducing the non active supporting material. These and other objects are attained according to the invention by a sealed lead acid dipolar storage battery according to claim 1. The accumulator according to the invention will now be described with reference to the enclosed drawing, that is an exploded perspective view of the dipolar accumulator. Referring to the drawing, a substantially parallelepipedal housing 10 contains all the components of the accumulator. A stack of dipolar electrodes 11 shaped like rectangular plates, is located inside the housing 10. The electrodes are stacked adjacent with special separators 12 interposed between them. The separators can also be made of glass microfibre or of the kind used for sealed batteries. Each electrode 11 is composed of a thin foil 13 made of lead or a lead compound, with a particular reticular print 14 designed for holding the active compound 15. This is generally lead oxide, and it is spread out onto the reticular print 14 that represents a good support and consequently an excellent electric contact between the lamina 13 and the active compound 15 applied thereto. The reticular print 14 does not cover the whole area of the lamina 13; as a matter of fact a side edge 16 is left uncovered for the application of a gasket (not shown) on the perimeter for the purpose of sealing or for the application of thermoplastic resins. The separator 12 does not contact the perimetral packing so as to leave a narrow perimetral channel that is useful for introducing the electrolyte and that allows an easier filling also in the places that are more distant from the inlet valve. For the execution of the laminas 13, a special polymeric material with an electroconductive matrix can be used instead of lead and lead alloys, reducing considerably the weight of the non-active parts. This special compound has to be light, with a high electric conductivity and ionic impermeability. The reticular print 14 is characterized by relief crests of the same material as the lamina 13 and by low relieves on which the active compound is applied. The relief crests of a surface, with respect to the opposite one, are displaced by half a pitch so as to render the structure stiffer. The height of the relief crests obtained in the reticular print determines the thickness and the amount of the active compound 15 to be applied. Each dipolar electrode 11 supports positive active compound spread on one of its sides, while the other side supports the negative active compound. The electrodes are stacked one on top of the other in such a way that the polarities are alternatively disposed. The microfiber glass microfibre separators 12 are interposed between the electrodes 11 and retain the necessary quantity of electrolyte. The various bipolar electrodes 11, that are sealed against the housing 10, determine a series of cells that must be water-tight to prevent infiltration from the other cells and to avoid short- circuits. The cells are filled with an electrolytic liquid, usually a sulphuric acid solution. The passage of the electric current between the cells occurs orthogonal with respect to the surface of the foil 13 with no need of intermediate electrical connections. Two monopolar electrodes 17 and 18 are fitted at the ends of the stack of dipolar electrodes 11, forming the terminal parts of the battery. These electrodes have a reticular print 13, identical to the ones of the other dipolar electrodes, on the side that is facing the inside of the battery, and the active compound is present on the outside faces of the monopolar electrodes 17 and 18. Two collectors 19 and 20 are applied to these faces and are moreover connected to respective poles 21 and 22 sticking out of the housing 10 for the utilisation of the battery. The microfiber glass separators 12 retain the electrolyte inside and allow the recombination of the gasses that are present in the cells. The thickness of the separators 12 is sized according to the amount of acid that is necessary. The separators 12 allow the battery to be used in closed area, which is the most important feature of sealed storage batteries. If the cell is not completely filled up with electrolyte, the separator 12 operates according to the gas recombination principle, allowing the oxygen that is developed at the positive monopolar electrode to flow through its own microporous structure during the recharge stage. For improving the electric performance of the battery it is necessary to press the electrodes 11 and the separators 12 as a whole. In fact a greater capacity is obtained by increasing the contact between the electrolyte and the active compounds 15. This also causes an improvement of the electrochemical formation and a longer life of the battery. The battery is fitted with vent plug 23 for the gas inside the cells; the sulphuric acid electrolyte is introduced through these valves, which are provided with a neoprene rubber cap 24 that lets the gas out of the battery at determined pressure values. A plastic lid 25 completes the upper part of valve 23. The adjustment of the valves 23 is carried out by using each time rubber with different levels of hardness. A load compensator 26 is inserted between the stack of electrodes 11 and the housing 10 for the purpose of recuperating the loss of compression on the unit formed by electrodes 11 and separators 12 that occurs when the acid is introduced. In this way the pressure that is required for the electrodes is maintained during the volume variations of the separator. In fact when the electrolyte is introduced, the microfiber glass separator shrinks slightly, reducing the load that is imposed to the electrodes. Moreover the pressure variations that occur during the loading and unloading of the battery get compensated. It is known that when the glass microfibre separators 12 are filled up they shrink and in doing so reduce the value of the compression that is given. The load compensator 26, that consists of a plate in poliuretanic material, when it is freed it restores the value of the pressure that was lost during the load decrease. Among the advantages that are offered by the present invention, some components of traditional accumulators have been eliminated, such as the collectors between the cells. This simplifies the operation of the assembly machines. The compression between electrodes and separators prolongs the life of the battery as it impedes the shedding of the active compounds from the foils. The voltage rating of the battery described here does not represent a restrictive example as it is possible to put "n" electrodes in series until the desired voltage is reached.

Claims: A sealed lead acid dipolar storage battery, comprising: a housing (10); a plurality of dipolar electrodes (11) being stacked one on top of the other so as to alternate the different polarities, said electrodes consisting of foils (13) of electroconductive material provided with relief crests and low reliefs on either side of the foil for keeping a layer of positive active compound (15) on one side of the foil (13) and a layer of negative active compound (15) on the other side; a series of high porosity microfiber glass separators (12) being interposed between the electrodes (11) in series; said relief crests and low reliefs leave a non-imprinted channel on the edges of the foils (13) adapted for fitting perimetral gaskets performing sealing action against the housing (10) and between the electrodes (11); said relief crests and low reliefs forming a reticular print (14) wherein the relief crests on one surface are fitted displaced of half a pitch with respect to the opposite surface for stiffening the structure; said gaskets providing a plurality of impermeable cells containing the separators (12) being filled with electrolytic liquid; the separators (12) being disposed so as not to contact the respective perimetral gasket, leaving a narrow perimetral channel for introducing the electrolyte and allowing an easier filling also in places that are more distant from the inlet valve; a load compensator plate (26) for maintaining the required pressure on the electrodes (11), said load compensator plate being inserted between one end of the stack of electrodes (11) and the housing (10).

Inventors: GINATTA MARCO VINCENZO, ROSSETTI FURIO, GINATTA, MARCO VINCENZO, ROSSETTI, FURIO
Applicants: EDISON TERMOELETTRICA SPA, EDISON TERMOELETTRICA S.P.A.
Application year: 1991
Main classification: H01M10
IPC codes: H01M10