Cathode formulation for survivor locator light

Abstract

A Water Activated Battery characterized by a) At least one anode selected from the group consisting of magnesium, aluminum, zinc and alloys thereof; b) A cathode comprising at least one basic copper salt comprising Cu(OH).sub.2combined with a copper salt CuX (with (n1) the molar ratio between the CuX and the Cu(OH).sub.2in the basic copper salt), such that a discharge reaction in saline versus a Mg anode could be written nMg+Cu(OH).sub.2.(n1)CuX=Mg(OH).sub.2+(n1)MgX+nCu) on a skeletal frame, the cathode further comprising a non-hygroscopic soluble, ionically conductive material; c) at least one cavity separating said cathode and said at least one anode; and d) at least one aperture leading to said at least one cavity for the ingress of an electrolyte-forming, aqueous liquid.

Claims

1. A cathode material for an activated, deferred-action battery, said cathode material comprising on a skeletal frame, a readily soluble non-hygroscopic ionic salt, and at least one basic copper salt comprising at least one of basic copper sulfate and basic copper carbonate.

2. The cathode material of claim 1 wherein the readily soluble non-hygroscopic ionic salt is selected from the group comprising Copper(II) formate monohydrate [Cu(HCO.sub.2).sub.2.H.sub.2O], Sodium ferrocyanide decahydrate [Na.sub.4Fe(CN).sub.6.10H.sub.2O], Potassium ferricyanide[K.sub.3Fe(CN).sub.6], Potassium sulfate [K.sub.2SO.sub.4], Calcium lactate pentahydrate [[CH.sub.3CH(OH)COO].sub.2Ca.5H.sub.2O], Sodium citrate monobasic [HOC(COONa)(COONa)(CH.sub.2COOH).sub.2] and Magnesium formate dihydrate [C.sub.2H.sub.2MgO.sub.4.2H.sub.2O].

3. The cathode material of claim 1 further comprising a kaolin.

4. The cathode material of claim 1 further comprising an electronically conductive material that is optionally selected from the group comprising graphite, carbon black and carbon fibers.

5. The cathode material of claim 1 further comprising a binder material.

6. The cathode material of claim 5, wherein the binder material comprises a polymer, a wax or sulfur.

7. A Water Activated Battery characterized by A housing containing; a) at least one anode selected from the group consisting of magnesium, aluminum, zinc and alloys thereof; b) at least one cathode comprising a readily soluble non-hygroscopic ionic salt and at least one basic copper salt selected from the group of basic copper sulfate and basic copper carbonate; c) at least one cavity separating said cathode and said at least one anode; and d) at least one aperture through said housing leading to said at least one cavity for the ingress of an electrolyte-forming, aqueous liquid.

8. The water-activated, deferred-action battery of claim 7, wherein the basic copper salt of the cathode is compacted and fused to itself and to a skeletal frame to form a heat-fused, conductive, electrochemically active material.

9. The water-activated, deferred-action battery of claim 7, wherein a portion of a surface of the cathode is formed as open spaces.

10. The water-activated, deferred-action battery of claim 7 wherein the cathode material further comprises an electronically conductive material optionally selected from the group comprising graphite, carbon black and carbon fibers.

11. The water-activated, deferred-action battery of claim 7, wherein the cathode material further comprises a kaolin.

12. The water-activated, deferred-action battery according to claim 7 wherein the cathode further comprises a binder material optionally comprising a polymer, a wax or sulfur.

13. The water-activated, deferred-action battery according to claim 7 wherein the cathode material is fused to itself by heating during or after compression.

14. The water-activated, deferred-action battery according to claim 7, where the anode and cathode are configured as parallel flat plates.

15. The water-activated, deferred-action battery according to claim 7, where the anode is configured as a hollow cylinder and the cathode is configured as a smaller cylinder nested within the anode without contact between the anode and cathode.

16. The water-activated, deferred-action battery according to claim 7, where the cathode is configured as a hollow cylinder and the anode is configured as a smaller cylinder nested within the cathode without contact between the anode and cathode.

17. A method of fabricating a cathode from comprising a readily soluble non-hygroscopic ionic salt and at least one basic copper salt selected from the group of basic copper sulfate and basic copper carbonate on a skeletal frame, comprising fusing the cathode material to itself by heating during or after compression.

Description

BRIEF DESCRIPTION OF FIGURES

(1) The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

(2) With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in, the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

(3) In the drawings:

(4) FIG. 1 is a perspective, fragmented view of a preferred embodiment of the battery according to the invention;

(5) FIG. 2 is a perspective, fragmented view of the cathode; and

(6) FIG. 3 is a photograph showing a reference cathode comprising NaCl together with a second cathode comprising a non-hygroscopic but readily soluble ionic salt, both after exposure to a super-saturated condensing humid environment.

DESCRIPTION OF EMBODIMENTS

(7) The present invention relates to water-activated, deferred-action batteries and to a method for producing a cathode for such batteries.

(8) More particularly the present invention relates to a deferred-action battery which is adapted to be activated by immersing it in water. Such batteries may be used for automatically powering emergency lamps and sirens on life-jackets and in case of flooding, for example.

(9) Embodiments of the invention are directed to such survivor locator lights and their batteries.

(10) There are standard humidity tests such as SAE International Aerospace Standard (AS) 4492 Survivor Locator Lights, December 1995 and reaffirmed Nov. 18, 2004, RTCA/DO-160C and RTCA/DO-160E that such batteries and lamps must pass.

(11) There is an interest in prolonging the product life of survivor locator lights in high humidity storage conditions, shortening the period for the light to come on following immersion, and reducing unit costs while being fully compliant with International Aerospace Standards.

(12) Embodiments of the invention are directed to such survivor locator lights and their batteries.

(13) With reference to FIG. 1 a water-activated, deferred-action battery 10 having a single cell is shown. The battery 10 consists of two spaced-apart anodes 12, each having the form of a thin plate. Anodes 12 are made of a metal selected from the group comprising magnesium, aluminum, zinc, and alloys thereof. Particularly preferred is a magnesium alloy.

(14) Each anode 12 is held in parallel, adjacent relationship to a major inner face 14 of a plastic battery housing 16. Both anodes 12 are connected in parallel to a negative terminal 18, accessible from outside housing 16.

(15) A cathode plate 20 that is typically thicker than the anodes 12, but has about the same area as each anode 12, is positioned between the anodes 12. A cavity 22 containing air and, optionally, separator layers (not shown) is included between the cathode plate 20 and each anode 12 to electrically insulate the cathode 20 from the anode 12 while the battery 10 is in its inactivated state. The battery has a housing 16 that is typically plastic. Two apertures 23, 28 are provided in the case 14, a lower aperture 23 near the base of the housing 16, and an upper aperture 28 near the top of the housing 16. Both apertures 23, 28 connect the cavity 22 to the environment outside the housing 16 and ensure that if the battery 10 is immersed in water, the water can penetrate via the apertures 23, 28 into the housing 16, flooding the cavity 22. The aperture 23 at the base of the housing 16 not only serves for the ingress of the electrolyte-forming aqueous liquid, typically water but also allows reaction products such as solid hydroxides and oxides to be emitted from the cavity 22. The second aperture 28 is an outlet near the top of the housing 16 that, on immersion of the battery 10 into water, serves to allow air to escape from the housing 16 so that water can enter the battery 10 to start power-producing operation. When connected to a lifejacket worn by a person, the battery is typically substantially vertical, so that the lower aperture 23 is below the upper aperture 28. The upper aperture 28 allows hydrogen generated in the cell to escape the housing 16. In a preferred embodiment, the higher aperture 28 is located on an opposite surface of the housing 16 from the lower aperture 28. In some embodiments, more than one venting aperture 28 is provided, such as one on each side of the top end of the housing 16.

(16) The battery 10 is usually directly and switchlessly connected to a lamp 50 and is generally attached to a lifejacket (not shown). On immersion into water, the battery 10 is activated and the lamp is illuminated.

(17) The cathode plate 20 may include a basic copper salt such as basic copper sulfate or basic copper carbonate. Water activated batteries that include basic copper salts are disclosed in pending application PCT/IL2017/050026 and corresponding U.S. application Ser. No. 15/041,401 also to Epsilor Electric Fuel. The basic copper salt has a low aqueous solubility, so usefully, unlike the battery described in U.S. Pat. No. 5,424,147 to Khasin et al, the apertures 23, 28 of batteries in accordance with the present battery 10 do not require sealing by a water soluble film or mechanical plugs to protect the battery 10 before use to extend its shelf-life. The absence of this film decreases the activation time, decreases the product complexity, thereby lowering the fabrication costs.

(18) To provide a ready source of ions, the active cathode material 20 has traditionally included a readily soluble salt, which invariably was table salt (NaCl) or calcium sulfate.

(19) Humidity tests with these materials have shown condensation of water droplets on the surface of the electrode. It has been hypothesized that the hygroscopic nature of the readily soluble salt has encouraged condensation of water on the cathode surface and that this is a key contributor to the short shelf life of such batteries in humid conditions, such as those prevalent in Florida, Jamaica, Hong Kong and South China in the monsoon season.

(20) In embodiments of the present invention and in contradistinction to the prior art, in addition to a basic copper salt the active cathode material 20 further includes a non-hygroscopic but readily soluble water-ionizable salt. The readily soluble, water ionizable non-hygroscopic salt is provided to provide ions on immersion into fresh water, such as a lake, for example.

(21) The active cathode material 20 may further include carbon to provide electrons, sulfur, a polymeric binder such as a Fluoropolymer, wax. The carbon may suitably be provided as graphite, carbon fibers or carbon black, where carbon black is preferred.

(22) The discharge reaction against a Mg based anode in water could be:
CuSO.sub.4+Mg.fwdarw.Cu+MgSO.sub.4 together with
Cu(OH).sub.2+Mg.fwdarw.Cu+Mg(OH).sub.2

(23) The reason that sulfur may be added is that sulfur present in the cathode converts any copper produced by these discharge reactions to CuS, which increases the energy content of the battery.

(24) There is also some parasitic reaction of Mg with water, giving hydrogen.
Mg+2H.sub.2O.fwdarw.Mg(OH).sub.2+H.sub.2

(25) Referring now to FIG. 2, one embodiment of the cathode plate 20 is shown in further detail. The cathode plate 20 comprises a skeletal frame 24 including a conductive metal and having a portion of its surface area formed as open spaces 30. The main bulk of the cathode plate 20 comprises a heat-pressed, rigid, static bed 32 of active cathode material including a basic copper salt such as basic copper sulfate or basic copper carbonate encompassing the skeletal frame 24 together with about 10% by weight of a readily soluble water ionizable non-hygroscopic salt.

(26) Under pressure and heat, the cathode plate 20 is compacted and fused to itself and to the skeletal frame 24, to form a heat-fused, conductive, electrochemically-active phase. As with many sintering operations, the strength of the form thus produced can be improved by the addition of a suitable binder material; advantageously, fluorinated ethylene propylene and/or kaolin may be added to act as a supplementary binder. The skeletal frame 24 is electrically connected to a positive terminal 33 which is accessible from outside the housing 16.

(27) For the battery to be activated by immersion in water, a readily water ionizable salt is required. However, it has been found that water ionizable salts used in the past, such as NaCl, CaSO.sub.4 or mixtures thereof, being hygroscopic, absorb moisture from the air which may be very humid in some parts of the world, such as Florida, the Caribbean, Hong Kong, and so on. This may cause the nucleation and growth of water droplets on the surface of the cathode, which, if they bridge the gap to the anode which is typically less than a millimeter away, cause current leakage and adversely affects the shelf-life of the battery.

(28) Embodiments of the invention are directed to a solution to this problem. Instead of NaCl, CaSO.sub.4 or mixtures thereof, non-hygroscopic but still readily soluble salts may be used.

(29) The following table lists various non-hygroscopic but still readily soluble ionic salts that were tested.

(30) TABLE-US-00001 Salt Formula CAS Copper(II) formate hydrate Cu(HCO.sub.2).sub.2H.sub.2O 133386-04-6 Sodium ferrocyanide K.sub.4Fe(CN).sub.610H.sub.2O 14434-22-1 decahydrate Magnesium formate Mg(HCO.sub.2)2H.sub.2O 6150-82-9 dehydrate Potassium ferricyanide K.sub.3Fe(CN).sub.6 13746-66-2 Potassium sulfate K.sub.2SO.sub.4 7778-80-5 Calcium lactate [CH.sub.3CH(OH)COO].sub.2Ca5H.sub.2O 5743-47-5 pentahydrate Sodium Citrate Monobasic HOC(COONa)(CH.sub.2COOH).sub.2 18996-35-5

(31) Basic copper sulfate cathodes 20 were prepared as follows:

(32) CuSO.sub.4.3Cu(OH).sub.2.H.sub.2O 4 gm (Northern Michigan Aquatics), sulfur 1.2 gm (Aldrich), carbon black 1 gm (Cabot), 1 gm of a non-hygroscopic but readily soluble ionic salt, and FEP powder 0.8 gm (DuPont) were weighed into a Pascal blender and blended for two hours. The 8 g mix was transferred to the cylinder of a piston and cylinder type die, wherein the cylinder had a die recess with an open area of 72.5 mm. First, 4 gm of the mix was poured into the die cylinder and leveled, then the cathode current collector (a pre-tabbed copper expanded metal sheet, approximately 20 mesh, obtained from the Dexmet Corp. or a Titanium strip) was laid over this, and a further 4 g portion of mix added to the die cylinder and leveled.

(33) The standard die was then closed with its mating piston section. The closed die was then heated to 110 C. in a 5 ton press with heated platens (PHI), and the mix pressed for four minutes. After cooling and removing the compact from the die, the cathode was observed to be robust and uniform, with a thickness of 5 mm.

(34) When assembled into the battery 10 and circuit shown in FIG. 1, it was subjected to the high humidity testing conditions defined in the AS4492 standard, and then immersed in water. Within five minutes of immersion, the lamp 50 lit up and continued to provide light for over 10 hours.

(35) In contrast to similar anodes used in the past that includes table salt as a readily soluble ionic salt, the present invention uses non-hygroscopic ionic salts such as one of the salts listed above:

(36) FIG. 3 shows a cathode with a non-hygroscopic salt on the left. In the figure, the non-hygroscopic salt being magnesium formate dihydrate. A control cathode with 10% by weight of NaCl is shown on right.

(37) After the humidity test, cathodes made with non-hygroscopic salts did not have condensed water droplets on their surface. However, the control cathodes made with table salt, had water droplets condensed on their surface. Further testing has shown that that such droplets also form in humid environments over time, and that they bridge between the cathode and anode thereby draining the battery.

(38) It is believed that batteries including only non-hygroscopic ionic salts have indefinite storage time in real conditions of temperature/relative humidity such as those found in places such as Jamaica, Florida, Hong Kong and the like.

(39) It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.