UNDERWATER BATTERIES PROVIDED WITH LIQUID SEPARATING MEANS BETWEEN INTERNAL ELECTROCHEMICAL ENVIRONMENT AND EXTERNAL LIQUID ENVIRONMENT

Abstract: A battery for underwater use comprising a plurality of elements, each having a positive electrode (14) and a negative electrode (15) in a liquid electrolyte (S), is disclosed, characterised in that said elements are series connected and in that each element is provided with an aperture (19) communicating with the external liquid environment (E), and in that liquid means (A) for separating the electrolyte and the external liquid environment therebetween, said liquid means consisting of a non-ionised liquid, non-reacting with said electrolyte as well as with said external liquid environment, are provided.

Description: UNDERWATER BATTERIES PROVIDED WITH LIQUID SEPARATING MEANS BETWEEN INTERNAL ELECTROCHEMICAL ENVIRONMENT AND EXTERNAL LIQUID ENVIRONMENT DESCRIPTION The present invention relates to batteries for underwater use provided with liquid means for separating the internal electrochemical environment and the external liquid environment therebetween. Primary batteries, as well as storage batteries, can be used as power sources in underwater engineering, to operate motors, for lighting, to power-feed electrical apparatuses and the like. However, at present secondary (storage) batteries, mainly of the lead/sulphuric acid type, and in some instances nickel-iron or nickel-cadmium batteries having an alkaline electrolyte, are widely used. Currently available storage batteries, both the sealed and the non-sealed ones, have a recess, inside the individual cell units and above the electrolyte, containing air and the gases (hydrogen and oxygen) that can be gradually produced at the electrodes . Non-sealed batteries have plugs provided with a gas vent. Both battery types, although provided with satisfactorily insulated liquid-tight clips, cannot directly be immersed at sea or lake depths, as salty, brackish or fresh water would enter the non-sealed batteries, entailing the leaking of the electrolyte, whereas sealed batteries would collapse under the external environment pressure. Both instances would entail a voltage drop and a permanent damage of the electrodes, not to mention the relevant environmental damage. Therefore, the state of the art discloses the use of heavy and expensive steel casings, containing, in case of non-sealed batteries, platinum catalysts for hydrogen and oxygen recombination. In light of the liquid near-incompressibility principle, the subject matter of the present invention is a system that provides the filling of the recess located above the electrolyte of the cell units of a battery with a liquid meeting specific requisites. An object of the present invention is that of providing an arrangement for liquid electrolyte batteries allowing the immersion thereof even at great depths, without the occurrence of the above-mentioned drawbacks, up to date solely avoidable by means of costly devices . According to the present invention, an assembly exploiting the near-incompressibility of the liquids and using a non-ionised liquid separating layer, non-reactive with the battery electrolyte and with the aqueous environment, is provided. The separating layer is arranged in the recess located above the electrolyte solution level in the cell units of the battery, thereby allowing the assembly to be pressurised even at great depths due to the immersion, without introducing significant stresses inside the battery casing. Other objects, features and advantages of the present invention will be made apparent in the following description, given by way of example and not for limiting purposes, of several presently preferred embodiments thereof and making reference to the Figures of the annexed drawings, wherein: FIG. 1 is a schematic view of a multiple-cell or element battery provided with liquid separating means (layer) according to the invention and with free apertures, at the top of the individual cell units, communicating with the external liquid environment; FIG. 2 is a schematic view analogous to that of FIG. 1 and referring to a second embodiment, in which check valves are provided at the apertures at the top of the individual cells or cell units, toward the external liquid environment; FIG. 3 shows a third embodiment of a battery assembly in which a manifold is provided between the vents of the individual cell units of the battery, the manifold being provided, at the top portion thereof, with a check valve at an individual aperture communicating with the external liquid environment; FIG. 4 schematically shows a further embodiment of the battery according to the present invention, in which a multiple-cell battery is housed into a container filled up with the liquid separating means (layer) and the container being provided, at the top portion thereof, with a check valve at an individual aperture communicating with the external liquid environment; FIGS. 5, 6 and 7 show voltage/time charts for batteries according to the invention under a closed circuit voltage condition. In light of the aforementioned, and taking into account the Figures of the annexed drawings that will hereinafter be detailed, the object of the present invention is based on the liquid near-incompressibility principle, and it provides a liquid separating layer according to the already outlined conditions. The liquid separating layer performs the following tasks : a) it allows the escape of the gases evolved within the battery towards the external environment; b) it avoids short circuit current between the electrodes of different battery cells. In the following disclosure the electrolyte solution of the battery will be indicated with S, a liquid floating onto the solution S will be indicated with A, the water of the external environment (sea, lake, etc.) will be indicated with E, and the densities of S, A and E will be indicated with d s , d A , d E , respectively. Three conditions underlying the present invention are : 1) The density of A must be lower than the density of S, i.e., d A < d s ; 2) A and S must be immiscible therebetween; 3) A and S must be non-reactive therebetween; When d A > d E , and always providing the requisites 1- 3 are met, the check valve is superfluous and the liquids A and E can be in contact therebetween. In this instance, besides performing the tasks a) and b) , the liquid A further performs the following: c) it prevents the interdiffusion between the solution S and the water E of the external environment; d) it allows that the internal pressure of each individual cell of the battery be equal to that of the external environment. It is to be noted that when the batteries according to the present invention use a check valve d A can be lower or equal to d E (d A ≤ d E ) . The assembly subject matter of the present invention will hereinafter be described with reference to various embodiments thereof. FIGS. 1, 2, 3 and 4 show schematic views of such embodiments, that are to be construed as non-limiting illustrative examples of the invention itself . FIGS. 1-3 are mere sketches, in which a highlighting of the thickness of the battery casing was omitted. Instead, the latter, as well as the thickness of the container utilised in the fourth embodiment, are highlighted in FIG. 4. For the device of FIG. 1, in which the liquid A directly contacts the external environment water, i.e., E, a further requirement must be met, precisely: 4) The density of A must be greater than the density of E, hence, taking condition 1) into account, it must be d E <d A <d s ; FIG. 1 schematically shows a longitudinal section of the battery according to a first embodiment thereof. Therein, a 6-cell or 6-element assembly, providing a rated voltage equal to 12 V for lead/acid batteries, is shown. The battery comprises a casing, globally indicated with 10, partitioned into six cell units by partitions 11 extending from the bottom panel 12 of the battery to the top panel 13. Positive and negative plates 14 and 15 are housed within the six cell units, in case spaced apart by known spacers, not shown. The positive and negative plates 14, 15 are interconnected by jumpers 16, sealingly bridging the partitions 11. The space described by the individual cell units or elements is filled up to a height hi with an electrolyte S. In a lead/acid battery the solution S is made of a H 2 0/H 2 S0 4 solution. In the traditional batteries, the electrolyte S is exposed to air which contains H 2 and is enriched with 0 2 , the various gas ratios thereof being variable and depending on the operating conditions of the battery, as it is well-known to those skilled in the art. According to the present invention, on the electrolyte S a liquid separating layer A, of a thickness h 2 , non-ionised and non-reactive with the electrolyte S or with the external liquid environment (salty, brackish or fresh water) , is located. The battery is also provided with terminals 17 and 18 for the connection to an electric load (not shown) and, if needed, to a well-known battery recharger. The terminals 17 and 18 are insulated from the external environment, e.g., with silicone or epoxy resins. At the top portion of each cell unit, elements 19 for communicating the layer A and the external environment E therebetween, comprising an expansion chamber 20 delimited by chokes 21 and 22, are located. The communication elements 19 allow a pressure compensation of the external environment E with the internal environment of the battery S+A. The presence of the chambers 20 and of the chokes 21 and 22 enables to prevent the external leaking of S+A in case the battery is tilted during the handling or the use. For the embodiments indicated in FIGS. 2-4, the walls of the battery casing have to be elastic rather than stiff, in order to adapt to the volumetric changes in the battery content, essentially due to the volumetric changes of S+A at the increase of the external environment pressure. Thus, e.g., 100 atm changes in the external pressure yield volumetric changes lower than 1%, typically of 0.4-0.5%. In fact, liquids are not strictly incompressible, the compressibility value thereof depending on their nature. Hence, different liquids such as E and the S+A complex could have slightly different compressibility, and also the volumetric changes due to such differences are assessable at 0.4-0.5% for pressure changes equal to 100 atm, therefore such as to easily be compensated by the elasticity of the walls of the battery casing. In fact, under such conditions, a cubic battery having a 20 cm corner would undergo linear dimension changes in the order of the millimetre. In the embodiment of FIG. 1, non-stiff walls are not required for the battery casing, since, according to the Pascal principle, the internal pressure of each individual cell battery equals that of the external environment . In the construction of the embodiment of FIG. 2, where corresponding elements are indicated with reference numbers equal to those of FIG. 1, check valves Vi, V δ , arranged so as to allow the escape of the gases that might evolve from the electrodes 14 and 15 during the battery operation, while preserving the hydrostatic balance among S, A, and E as already indicated, are provided. In the construction of the embodiment of FIG. 3, in which corresponding elements are indicated with the same reference numbers of FIGS. 2 and 3, the top end of the elements 19 is connected to a manifold pipe network, globally indicated with 23, provided with branches, 24, 25, 26, 27, 28, 29, converging towards a common connection spot 30, at which a check valve VK, having the same purpose of the valves V x , ... V 6 of FIG. 2, is arranged. As it is apparent from the drawing of FIG. 3, the arrangement of the various branchings allows the gas produced from the battery to converge to the collection vertex 30. In the construction of the embodiment of FIG. 4, in which corresponding elements are indicated with the same reference numbers of FIGS. 1, 2 and 3, the casing of the battery 10 is accommodated within a watertight case 31. Said watertight case 31 is provided with a perimetric lip 32 registered with a corresponding perimetric lip 33 onto the bottom portion of an upwards-tapered pyramid-shaped element 34 for collecting the gases evolved at the electrodes 14 and 15 of the various cell units of the battery. At the apex of the pyramid-shaped element 34 a check valve VN is located. At the lips 32 and 33, fastened therebetween with bolts 36, a seal 35 is located. Within the element 34, seal feedthroughs 37 and 38 for the passage of connection cables to the terminals 17 and 18 of the battery are provided. The entire space around and above the battery casing 10, as well as the space over the electrolyte S is filled up with the separating liquid A, having the already described characteristics and that will hereinafter be better detailed. Further, it has to be pointed out that the battery housed within the case 31 as shown in FIG. 4 could be replaced by a number of batteries. The characteristics and the nature of the liquid forming the separating layer A (liquid separating means) between the electrolyte S and the external environment E will hereinafter be disclosed. As above-disclosed, the liquid A must be non-ionised in order to be insulating. It has to be pointed out that the density of the electrolyte solution of a lead/sulphuric acid battery depends on the battery type and charge. Thus, e.g., the electrolyte density in an electric car battery during the discharge ranges from 1.33 to 1.21 g/ml, whereas in a battery for stationary plants the density ranges from 1.225 to 1.08 g/ml. In a nickel-iron battery with an alkaline electrolyte (20-30% KOH, 50 g/1 LiOH) the density usually exceeds 1.16 g/ml. Therefore, considering that the seawater density is usually lower than 1.025 g/ml, it can be stated that a separating liquid A having a density ranging from 1.04 to 1.07 g/ml, immiscible with aqueous solutions and non-reactive in an acidic or alkaline environment, proves to be an all-purpose separating liquid for storage batteries with an acidic or alkaline electrolyte, to be used according to the embodiment sketched in FIG. 1. However, for any acidic or alkaline electrolyte battery to be used according to the embodiment of FIG. 1, a liquid A, immiscible and non reactive with the electrolyte solution, having a density smaller than the minimum density evidenced by said solution during the discharge process, yet greater than that of the external environment water, can always be found. Substances useful as separating liquid A, covering the electrolyte solution, in the embodiment of FIG. 1 can be selected also from the following substance classes: chlorinated hydrocarbons, like, e.g., 1,1,1- trichloroethane, chlorobenzene, 1,1,2,2- tetrachloroethane, 1, 2-dichlorobenzene, carbon tetrachloride, trichloroethylene, 2-chlorotoluene, 4- chlorotoluene; bromidrated hydrocarbons, like, e.g., 1-bromodecane, bromobenzene, 1-bromohexane, bromocyclohexane; nitroderivatives of hydrocarbons, like, e.g., nitrobenzene; silicones, like, e.g., the silicone oil 710. These substances can be utilised as such or as mixtures thereof, or even admixed to hydrocarbons. Even solid substances belonging to the first three substance classes like, e.g., solid 1, -dichlorobenzene, could be dissolved in other liquid substances of the same class or in hydrocarbons. The solution having the required density can easily be obtained carrying out the admixture of the various substances in presence of a densimeter. In the embodiments shown in FIGS. 2-4, check valves are provided, preventing the external environment water from entering the battery, as a covering liquid A, besides the substances belonging to the above-mentioned groups, immiscible and non-reactive liquids, the density of which being lower than that of the external environment water, like, e.g., a hydrocarbon mixture like oil, naphtha, kerosene, Nujol or liquid paraffin, (with a density being generally comprised in the range 0.76-0.88 g/ml) or their mixtures can suitably be utilised. The discharge curves, i.e. the CCV (closed circuit voltage) versus time, of some batteries available on the market modified according to the present invention are shown in FIGS. 5-7. FIG. 5 shows the discharge of a 12V/35Ah lead/sulphuric acid battery, connected to a water-cooled 0.33 ohm/300 W load resistor, the electrolyte solution thereof having been covered according to the embodiment of FIG. 1 with a liquid mixture of several substances belonging to the aforementioned groups, by way of demonstration of the compatibility of said substances with the electrolyte. FIG. 6 shows the discharge of a 1.3V/5Ah nickel-iron battery connected to a 1.74 ohm/4 W load resistor, whereas FIG. 7 shows the discharge of a cadmium-nickel battery, made of seven 1.2V/3Ah cell units, connected to a 12 ohm/20 W load resistor. Both batteries were of the alkaline electrolyte type, and were filled with liquid paraffin according to the embodiments of FIGS. 2 and 4, respectively. All the above-mentioned curves were obtained with the batteries immersed at a 50 m depth in sea water. Identical discharge curves were obtained for the in-air discharge of the same batteries with the same load resistors .

Claims: CLAIMS 1. A battery for underwater use comprising a plurality of elements, each having a positive electrode and a negative electrode in a liquid electrolyte, characterised in that said elements are series connected and in that each element is provided with an aperture communicating with the external liquid environment, and in that liquid separating means are provided between the electrolyte and the external liquid environment, consisting of a liquid that is non-ionised, insoluble and non-reactive both in respect of said electrolyte and in respect of said external liquid environment. 2. The battery according to claim 1, characterised in that said elements are made of cell units and in that said liquid separating means have a density intermediate between that of said electrolyte and that of the external liquid means, made of fresh or salty water. 3. The battery according to claim 1 or 2, characterised in that at the top of each element or cell unit an aperture communicating with the external liquid environment is provided in order to allow a hydrostatic pressure balancing between the interior and the exterior of the battery, said aperture being chamber-shaped and vented at the top thereof, and with one or more narrow openings in order to avoid the leaking toward the external environment of the liquid separating means and of the electrolyte when said battery is tilted. 4. The battery according to one or more of the claims 1 to 3, characterised in that said apertures at the top of each element or cell unit are connected to a manifold having an individual aperture in correspondence of the external environment. 5. The battery according to one or more of the preceding claims, characterised in that it comprises a secondary casing housing said battery, wherein the space between the battery and said casing is filled up with said liquid separating means and it is provided with an individual aperture communicating with the external environment, there being also provided insulated and liquid-tight thorough-leads for connecting said battery to an electric load or to a battery recharger. 6. The battery according to one or more of the preceding claims, characterised in that said liquid separating means which are non-ionised and non-reactive with the electrolyte of the battery and with the external liquid environment and have an intermediate density between that of the battery electrolyte and that of the external liquid environment, consisting of fresh or salt water, are selected from one or more of the following substance classes: chlorinated hydrocarbons, like, e.g., 1,1,1- trichloroethane, chlorobenzene, 1,1,2,2- tetrachloroethane, 1, 2-dichlorobenzene, carbon tetrachloride, trichloroethylene, 2-chlorotoluene, 4- chlorotoluene; bromidrated hydrocarbons, like, e.g., 1-bromodecane, bromobenzene, 1-bromohexane, bromocyclohexane; nitroderivatives of hydrocarbons, like, e.g., nitrobenzene; silicones, like, e.g., the silicone oil 710. 7. The battery according to claim 1, characterised in that said elements are made of cell units and in that said liquid separating means have a density that is lower than that of the electrolyte, and in that at the top of each element or cell unit a check valve is provided, arranged so as to allow the escape of gases produced during the operation of the battery and to prevent the entering of the external liquid environment. 8. The battery according to claim 7, characterised in that said apertures at the top of each element or cell unit are connected to a manifold having a individual check valve. 9. The battery according to claim 7 and/or 8 characterised in that said liquid separating means have a density that is lower than that of the electrolyte and also of the external liquid environment and consist of oil, naphtha, kerosene, mineral oil (Nujol), liquid paraffin and mixtures thereof. 10. The battery according to one or more of the preceding claims, characterised in that said elements or cell units are of the lead/sulphoric acid type or the nickel-iron or nickel-cadmium type. 11. The battery according to one or more of the preceding claims, characterised in that, in the assemblies provided with check valves, the casing of the battery and/or said secondary casing are made of a relatively yielding material, in order to compensate the different compressibility between the external liquid means and the complex electrolyte/separating liquid.

Inventors: ZOCCHI FERNANDO, ZOCCHI, FERNANDO
Applicants: A L A ELETTRONICA S R L ALSO K, CONSIGLIO NAZIONALE RICERCHE, ZOCCHI FERNANDO, A.L.A. ELETTRONICA S.R.L. ALSO KNOWN AS ALA ELETTRONICA S.R.L., CONSIGLIO NAZIONALE DELLE RICERCHE, ZOCCHI, FERNANDO
Application year: 2000
Main classification: H01M2
IPC codes: H01M2, H01M10