CA1233314A - Formation of dense chlorine hydrate - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method of forming chlorine hydrate is described which generally comprises, combining liquid chlorine with an aqueous liquid, and removing the heat of hydrate formation This method may also include the steps of mixing the liquid chlorine with the aqueous liquid, and cooling the chlorine hydrate to provide a pressure decrease.
However, in accordance with the present invention, no refrigeration of the aqueous liquid is required, as the heat of formation may be released to a substantially room temperature environment.

Description

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FORETOKEN OF DENSE ~DlDRINE idiot PACKG~CVND END SUP Y OF TIE INVENTION
The present invention relates generally to an improved nethcd of forming chlorine hydrate, and particularly a method of forming chlorine hydrate for a zinc-chloride secondary energy storage battery system which does not require refrigeration equiFnent.
Ike secondary energy storage systems of the type referred to herein leg., a zinc-chloride battery system or other suitable metal-halogen battery system) generally are comprised of three basic oanponents, namely an electrode stack section, an electrolyte circulation subsystem, and a store subsystem. The electrode stack section typically includes a plurality of ox ifs connected together electrically in various series and parallel oc~binatioDs to achieve a desired operating voltage and current at the battery terminals over a charge/discharge battery cycle. Each cell is comprised of a positive and negative electrode which are Roth in contact with an assess zinc-chloride electrolyte. The electrolyte circulation subsystem operates to circulate the ~inc-chloride electrolyte from a reservoir through each of the jells in the electrode stack in order to replenish the zinc and chloride electrolyte components as they are oxidized or reduced in the cells during the battery cycle. In a closed, self-contained zinc-chloricle battery system, the storage subsystem is used to contain the chlorine gas which is liberated from the cells during the charging of the battery system for subsequent return to the cells during the discharging of the beautifies system. In such a zinc-chloride battery system, chlorine gas is liberated from toe positive electrodes of the cells and stored in the form of chlorine hydrate. Chlorine hydrate is a solid which is formed by the store subsystem in a process analogous to the precuts of freezing water where chlorine is included in the i ox crystal.

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3~3~c with reference to the general operation of a zinc-chloricle battery Sistine, an electrolyte no operates to circulate the aquec~s zinc-chloride electrolyte freckle a reservoir to each of the positive "chlorille" electrodes in the electrode stack. These chlorine electrodes are typically made of porous graphite, and the electrolyte passes through the pores of the chlorine electrodes into a spate between the chlorine electrodes and the closing negative or "zinc" electrodes. The electrolyte then flows up between the opposing electrodes or otherwise out of the jells in the electrode stack and back to the electrolyte reservoir or SUTlp.
During the charging of the zinc-chloride battery system, zinc metal is deposited on the zinc electrode substrates and chlorine gas is liberated or generated at the chlorine electrode. the chlorine gas is collected in a suitable conduit, and then mixed with a chilled liquid to form chlorine hydrate. A gas plump is typically employed to draw thy chlorine gas from the electrode stack and mix it with the chilled liquid, (i.e., generally either zinc-chloride eleccrolyts or water).
I chlorine hydrate is thin deposited in a store container until ifs battery system is to be discharged.
During the discharging of the zinc-chloride battery system, the chlorine hydrate is deposed by permitting the temperature to increase, such as by circulating a warm liquid through the store container. The chlorine gas thereby recovered is returned to thy electrode stack via the electrolyte circulation subsystem, where it is reduced at tars chlorine electrodes. Si~ltaneously, the zinc metal is dissolved off of the zinc electrode substrates, and power is available at the battery terminals.
rtlher discussion of the structure and operation of zinc-chloride battery systems may be found in the following ccsnronly assigned patents: Simmons US. Patent ND. 3,713,888 entitled "Process For Electrical Energy swung Solid Halogen hydrates Simmons ills Patent , , . .. . _ _ _ .. , .. _ .

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No. 3,809,578 entitled "Process For Forming And Storing legion hydrate In Jo Battery"; Car US. Patent No. 4,100,332 entitled Cub Type Bipolar Electrode Elements And Battery Stack Thereof". Such systems are also described in published reports prep æ Ed by the assignee herein, such as "Development of the Zinc-Chloride Battery for Utility Applications," Interim Report Err, May 1980; "Development of the Zinc-Chloride Battery for Utility Applications," Interim Report Eye, April 1979, both prepared for the Electric Power Research Institute, Palo Alto, California; "Zinc-Chloride Electric Engine Unit for Four-Passenger Electric Vehicle", SUE Reprint May 1981 from Electric Pond hybrid Vehicle Progress, p-91, April 1981; and "Recent Advances In Zinc-Chloride battery Technology" published in Proceedings of Thea Power Sources Symposium, June 1982.

Extensive efforts have been taken over many years to develop techniques for forming a halogen hydrate. Indeed, these efforts have given rise to several inventions for which commonly assigned patents I have been granted or aye currently pending, including: US. Patent Nos.
3,713,888 and 3,809,578 identified above; Bjorkman US. Patent Jo.
3,783,027 entitled "Apparatus And method For Making Chlorine hydrate From High Energy density artery Electrolyte And Lorraine"; 3ehling US.
Patent Jo. 3~793/077 entitled "Battery Including Apparatus For Making Halogen hydrate", Bjorkman US. Patent Jo. 3,814,630 entitled "Filter/Store For electric Energy Storage Device"; Bjorkman US. Patent No. 3,823,036 entitled "Secondary Battery uprising Means For Forming halogen hydrate ode ~ukble Shells"; Bjorkman US. Patent No. 3,840,650 entitled "Stable Chlorine E~7drate"; Simmons US. Patent Jo. 3,907,592 entitled "Halogen hydrates"; Sweeney US. Patent Jo. 3,908,001 entitled "Manufacture of Chlorine E~7drate"; Simmons US. Patent I. 37935,024 entitled "Halogen Hydr~tes"J Simmons USE Patent No. 3,940,283 entitled along Hydrates Car et at US. Patent No. 4,146,68G entitled I

"Operational Zinc Chlorine Battery Based On A Water Store";
Belling US. Patent No, ~,115,529 entitled "~lalocJen hydrate Formation From Halogen end Finely Divided Aqueous Droplets";
US. Patent No. 4,306,000 entitled "Method Of Cooling Zinc Halogen Batteries"; Coddle Canadian Patent Application Serial No. 412,550 filed September 30, 1982 entitled "Metal Halogen Battery Construction With Improved Technique For Producing Halogen Hydrate"; Canadian Patent Application Serial No.
420,731 filed February 2, 1983 entitled "Halogen Hydrate Storage Device For mobile Zinc-Chloride Battery System";
Canadian Patent Application Serial No. 419,350 filed January 12, 1983 entitled "Multiple Stage Multiple Filter Hydrate Store"; US. Patent No. 4,389l468 granted June 21, 1983 entitled "Metal Halogen Battery System With Multiple Outlet Nozzle For Hydrate Generally speaking, it is desirable to concentrate or otherwise form a dense chlorine hydrate in order to reduce the size and/or weight of the hydrate store. This consideration is particularly important when the zinc-chloride battery is used to power an electric vehicle, where the size and weight of the hydrate store will have a significant effect on the operating range of the electric vehicle. Although highly compressed chlorine hydrate has been employed in the past to reduce the size and weight of the hydrate store, one of the principal techniques for increasing the density of the chlorine hydrate is to employ filtration in the hydrate store compartment. Examples of such filtration techniques may be found in the US. patent No. 3,814,630 and the Canadian Patent Application Serial No. 419,350 identified above.

The purpose of the filter in the hydrate store is to separate the compressible particulate chlorine hydrate from the liquid used in the hydrate formation process. As the chloride hydrate enters the store, it is in the form of a dilute slurry, of which approximately three (33 to seven (7) percent is hydrate crystal. However, due to the mob/

amount of chlorine gas which is liberated during the charging of the battery, it is not practical to store the chlorine hydrate Particles in this dilute slurry. Accordingly, a filter is used to provide a hydrate concentration system for removing as such of the ox ox so liquid as possible. thus, it will be appreciated that the increase in the density of the hydrate particles in the store will result in a decrease in the size and weight of the battery system.
The practical levels of chlorine hydrate packing by filtration in a zinc-chloride battery system having a capacity on the order 50 queue appear to be approximately 0.15 - 0.17 gym Clime of total chlorine and water stored. These levels should be compared with the maximum theoretical chlorine hydrate densities of 0.33 gym Clime where the hydrate is comprised of CLUE 8H20 and 0.4 gym Clime where the hydrate is oc~,prised of CLUE 6~20.
Accordingly/ it is a principal object of the present invention to provide a method of forming chlorine hydrate which more closely approaches the maximum theoretical density levels.
It is another object of the present invention to provide a method of forming highly dense chlorite hydrate without requiring a refrigeration system.
It is a further object of the present invention to provide a method of forming highly dense chlorine hydrate for which the heat of formation may be revved directly to the environment.
It is an additional object of the present invention to prcNide a method of forming highly dense chlorine hydrate in situ.
It is another object of the present invention to provide a method of forming highly dsns2 chlorine hydrate such that a relatively taller hydrate store volume is required.
It is yet another object of the present invention to provide a method of forming highly dense chlorine hydrate as part of a method of .~;3~;3~' charging a zinc chloride battery systelll used to Rowe an electric vehicle.
To achieve the foregoing objects r the present invention provides a method of forming chlorine hydrate as part of a method of charging a zinc-chloride battery contained in an electric vehicle, comprising the steps of: (a) providing a vessel capable of being sealed off from the ambient environment; (b) adding a predetermined quantity of an aqueous liquid to the vessel; (c) adding liquid chlorine into the vessel in a quantity such that a portion of the liquid chlorine evaporates until the pressure in the vessel is below 100 prig, but above those chlorine vapor pressures necessary for the formation of chlorine hydrate in the temperature range +6C to +20C and the pressure is maintained throughout the formation of chlorine hydrate; (d) sealing the vessel (e) allowing the quantity of aqueous liquid to react with the liquid chlorine to form chlorine hydrate; and (f) removing the heat of hydrate formation to a substantially ambient room temperature environment up to approximately +2~C.
Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiments which makes reference to the following set of drawings in which:
BRIEF Dissolution OF 'Roy DRAWINGS
Figure 1 is a graph of an equilibrium diagram with respect to chlorine end various chlorine hydrate formulations.
Figure 2 is a simplified view, partially in cross section of a chlorine hydrate store container in accordance with the present invention.
In its broader aspects, chlorine hydrate may be formed in accordance with the present invention by combining liquid chlorine with an aqueous liquid, and removing the heat of hydrate formation. The aqueous liquid may be any suitable wa~er-based liquid which will facilitate the formation of chlorine hydrate. Thus, while water is preferred as the aqueous liquid, other suitable water-based liquids may be employed, such as zinc-chloride electrolyte.

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On,- of the principal advantages of this metallic', of furrowing chlorine hydrate it that no refrigeration is required, as in previous methods where the aqueous liquid had to be chilled to a temperature typically between I to 6C in order to form hydrate with chlorine in a gaseous state. Thus, the aqueous liquid may be combined with the liquid chlorine at room or substantially ambient temperatures.
'err the method of forming chlorine hydrate in accordant ox with the present invention is used as part of a method of charging a zinc-chloride outwore, it will be -appreciated that the gaseous chlorine generated in the stack section must first be converted to liquid chlorine. Although the energy expended in this conversion may offset at least in part the energy saved by eliminating the refrigeration equipment, it is important to nuts that the chlorine hydrate furrowed in accorclanoe with the present invention is considerably more dense no the chlorine hydrate typically formed via refrigeration and condensed by filtration. For example, sxpsimentation }was Chicano that a chloxins hydrate density of 0.32 gym Clime of total chlorine and water stored (where the hydrate is comprised of C~2 8.4H20) is achievable. must another advantage of the present invention is that thy size and weight of the hyclrats store may by reduced. This consideration is, of courts, very impotent when a 2inc-chloride battery is used to purer an electric vehicle. A smaller and lighter hydrate store will not only increase the operating range of the electric vehicle, but will also permit the zinc-chloride battery to be employed if, relatively compact-sizec.
electric vehicles Another advantage of the preset-; invention is that the chlorine hydrate nay be formed "if situ". That is, the chlorine hydrate may be forehand in the same vessel or container in which the liquid chlorine and the aqueous liquid are ccn'c,inedO In prior hydrate connation processes where the chlorine hydrate is first funned in a pup or conduit and conveyed to a store cony eta, there was a tendency for ., .. _ _ _ . .. , . . _ , , _ , _ _ . , ... . . _ ~23~ I

this conduit to become plugged or blocked with hydrate during the latter part of the battery charging prove so. Sin ox the chlorine hydrate is former in the sloe vessel where the luckily chlorine and the aqueous liquid are ccNbined, there is no need -to convey the hydrate Jo another ocmFartment~ thereby eliminating any possible blockage that could otherwise occur in the conduit used to convey the hydrate.
A further advantage of the present invention is that the heat of hydrate formation may be removed to a foam temperature or substantially ambient temperature environment outside of the vessel in which the hydrate is former. Thus, the need to insulate the hydrate store from the environment in order to maintain the chlorine hydrate at a chiller temperature is considerably reduced or elfin m axed. thus, it may be advisable to construct the stows oompartm~nt such that it is capable of releasing heat to the environment.
While it should be appreciated that in the appropriate application it may be advisable to assist the removal of the heat of hydrate formation by providing some cooling during or after the chlorine hydrate is formed, it should be understood that this step is not essential to practicing the present invention. Similarly, while it may also be appropriate to control the temperature of the aqueous liquid before or during the formation of chlorine hydrate, such as cooling the aqueous liquid until a predetermined temperature is reached, again it should be understood that this step is not essential to practicing the present invention.
An additional step by the present method which is preferred, but may not be essential under the appropriate circumstances, is to mix the liquid chlorine with the aqueous liquid. This sling may be achieved by a variety of suitable means, such as agitating, stirring, shaking, blending, intermingling, ox otherwise bringing the liquid chlorine and the aqueous liquid in close association or intimate contact. Preferably, the mixing step should occur concomitantly with . _ . . _ _ . , . . . _ . _ . . _ _ . _ .. _ . _ . _ .

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the step of removing the heat of hydrate formation. Indeed, the steps of ccm:oining the liquid chlorine with the aqueous liquid touch as by adding these two components to a vessel), sling these two oonponents together, and removing the heat of hydrate formation may all occur ooncomit~ntly. however, other suitable timing relationships may also be provided in the appropriate application.
Referring to Figure 1, an equilibrium diagram with respect to chlorine and various chlorine hydrate formulations is Chicano. The curves contained in this equilibrium diagram are used to illustrate the pressure and temperature relationships associated with the present invention. For example, the cry labeled "A" represents the chlorine vapor pressure over chlorine liquid with respect to temperature. Curve "A" illustrates that when the liquid chlorine is added or otherwise introduce d to the vessel in which the hydrate is to be formed, it will be under a relatively high pressure.
Assuming that the vessel is at a lower pressure than that of the liquid chlorine prior to its introduction to the vessel, a portion of the liquid chlorine will evaporate as it is introduced to the vessel.
This evaporation will continue until the pressure in the vessel rapidly rises to a level depending upon the quantity of liquid chlorine supplied to the vessel. For example, the pressure in the vessel will typically increase to a range generally between 70 and 85 PI whereby a substantial portion of the liquid chlorine supplied will remain in its initial liguified state Curves "B" through "E" represent the temperatures and pressures required in order to form chlorine hydrate where various aqueous liquids are employed. Curve "B" represents chlorine hydrate formed with water, while curves "C" through NEW represent chlorine hydrate formed with mixtures of water with zinc-chloride electrolyte.
Thus, for example, curve "C" represents chlorine hydrate formed with a 16~ cono~ntration of zinc-chloride in water, while curve YE" represents _ . _, _ ., . _ . . . , . _ .. , . _ _ I

chlorine Hitler formed with a 40~ concentration of zinc-chloride in water.
accordingly, it may be seen from curves "I" through "E" that chlorine hydrate may be formed at a low pressure when the tenFerature is also appropriately low. ~dtlitionally, it may be seen that chlorine hydrate may be formed at a high pressure where the temperature is also appropriately high. These prior krx~n pressure and temperature relationships indicate, for expel, that after the chlorine hydrate is formed in accordance with the present invention, the pressure in the vessel may be decreased by providing some cooling to the chlorine hydrate. This cooling may be provided by any conventional means, swept as by heat exchange with a cold or tooled liquid it water).
It should also be noted that it may be advisable to control the relative quantities of liquid chlorine and the aqueous liquid being added to the vessel in order to convert as much of these components to chlorine hydrate as possible. ill erratically, the liquid chlorine and the aquec~ls liquid should be predate i Ed amounts which will ensure a complete conversion to chlorine hydrate. however, as a practical matter, if precise control over these quantities cannot be obtained, or if the liquid chlorine and the awakes liquid are not sufficiently mixed, a complete conversion will not occur and same free liquid chlorine and/or Skye free aqueous liquid will remain. Thus, for example, a situation could arise after the hydrate formation process is generally ctrnpleted where there is Rome liquid chlorine left at the bottom of the vessel, very dense chlorine hydrate adjacent to this liquid chlorine, less dense chlorine hydrate near the lap of the vessel, some aqueous liquid trapped between layers of hydrate, and some gaseous chlorine at the top of the vessel above the hydrate.
While the pressure in the vessel at the end of the chlorine hydrate formation process will be dependent upon the typewrote within the vessel, this pressure should typically be between 50-70 SUE.

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here this process is employed in a zinc-chloride battery, it should lo noted that this pressure will be quickly reduced live. within -the first 10~ of discharge) to operating pressures between 0-10 PI through the release of chlorine to the battery stack section. P~iditionally, this pressure may also be reduced by providing cooling after the hydrate is form-d. Indeed, sufficient cooling may be provided to reduce the pressure within the vessel to ambient pressure, if desired.
Additionally, it should be appreciated that while no refrigeration equipment is required to form the chlorine hydrate a typical room temperatures, the temperature of top surrounding environment may be sufficiently high (i.e. generally greater than 28.3C~ that some cooling or refrigeration equipment may be needed in order to rewove the heat of hydrate formation. i~svsrtheless, thy amount of such tooling or refrigeration Gould be substantially less than that required to chill the aqueous liquid to a temperature typically between -8 to -I 6C as in previous chlorine hydrate formation methods.
qbrning now to a description of a store container or vessel utilized to practice the present invention, it should be understood that this vessel was constructed for experimental and demonstration proses and that the present invention is not limited to any particular vessel shape or design. Thus, for example, while the vessel described herein is cylindrical, thy vessel may also by circle in shape, and so forth.
Referring to Figure 2, a simplified view of a chlorine hydrate store container 10 in accordance with the present invention is shown.
The store container 10 generally comprises a glass tube 12, a plastic top cover 14, and a plastic bass plate 16. The top over 14 is secured to the tube 12 by a pair of clamping rings 20-22, and a plurality of circumferential spaced bolts 24 and nuts 26. A split-ring fibrous grommet 27 is interposed between the clamping ring 22 and the glass tube 12 in a conventional manner. Thy base plate 16 is also E~x~lred to the tube 12 in thy same way as described above for the top oovsr 14. A pair of gaskets 2B-30 are also provided to facilitate a fluid-tight foal one the tune 12 and the tap craver 14 and between the tube 12 and the oases plate 16.
Roy top cover 14 is provided with Rio apertures 32-34 for permitting access to the internal chamber 36 defined by the tube 12, the top craver 14 and the base plate 15. For ex~nple, the aperture 32 is used to introduce or otherwise add an aqueous liquid to the chamber 36, and the aperture 34 is used to introduce or otherwise add liquid chlorine to the chamber 36. ED hermetically seal the aperture 32 and permit the chanter 36 to Boone pressurized during the hydrate formation process, a plastic plug 38 is inserted into the aperture. Similarly, the aperture 34 is sealed by a volleyer 40 which is mounted to the store container 10 via a threaded connection.
In order to introduce liglud chlorine to the chamber 36, a suitable source of liquid chlorine, such as a conventional chlorine cylinder 42 is coupled to the valve 40 by a coupling 44. Liquid chlorine may then be supplied to the chamber 36 by opening Roth the chlorine cylinder valve 46 and the store container valve 40. where the present invention is practiced in a zinc-chloride battery, it should be appreciated that the source of liquid chlorine would be derived Fran the battery stack section rather than a chlorine cylinder.
Roy store container 10 may be made from any suitable material which will be chemically resistive or inert to the chemical entities with which it will acme into contact, such as liyuid/gaseous chlorine and the aqueous liquid. must for example, the top cover 14, the base plate 16, the plug 38, and so forth Jay be made Fran a variety of neutrals. these materials include, without limitation, Teflon (a Dupont trademark), Conner (a Penlight trademark), and Bolt Ron polyvinychloride (4008-2124~ Ned by the General wire Rubber Corp.
Other examples of suitable n~terials may be furrowed in the 19~0 "Development of the Zinc-Chloride Battery Err Utility Applications"
report identified previously.
With respect to the tube 12, this tube may also be made in whole or Fart from one of the avow materials. However, it should be noted that in one form of the present invention, the tube 12 should be constructed such that it is capable of releasing heat from the chamber 36 to the environment. It m y also be noted that the store container 10 is provided with a plastic cylinder-shaped shield 48, which includes a plurality of apertures for facilitating the removal of heat from the Shari 36.
Additionally, the gaskets 28 and 30 may be made from any Seattle sealing material, which is also chemically resistive or inert to the chemical entities with which it will come into contact. Employs of such sealing materials are polytetra-fluoroethylene and Vito flyer lastcn3ers, Other examples of suitable materials may be found in the 1980 'development of the Zinc-Chloride Eater Err Utility Applications'` report identified previously.
In one form of the present invention the aqueous liquid is added to ale store container 10 before liquid chlorine is added. The aqueous liquid my be added to same appropriate level, such as the level indicate by reference numeral 50. M ditionally, before the plug 38 is used to seal the aperture 32, it may be advantageous to purge all or substantially all of the air from the cuber 36. This purging is preferably achieved by replacing the air in the gas spa ox of chamber 36 with gaseous chlorine.
When the valves 40 and 46 are opened, a portion of the liquid chlorine supplied to the chamber 36 will evaporate. This evaporation is an endothermic reaction with a heat of chlorine evaporation being -4.8 K Coulomb at atmospheric pressure. this will cause some cooling to occur in the chamber 36. however, this tooling will be offset by the heat of hydrate formation, which is 18.6 X Cal/ to at atmospheric _ .. , .. .. ... _ _ .. . . . . . . _ . _ _ . . _ 3~3~

pressure, heat of hydrate formation will be readily removed from the chamber 36 through the glass tube 12 to toe room temperature environment surrounding the store container 10.
he various ~mbodlments which have been set forth above err for the purpose of illustration and were not intended to limit the invention. It will be appreciated by those skilled in the art that various changes and notifications may be made to these e~bcdiments described in this specification without deputing from the spirit end scope of the invention as defined by the appended claims.

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of forming chlorine hydrate comprising the steps of:
(a) providing a vessel capable of being sealed off from the ambient environment;
(b) adding a quantity of an aqueous liquid to said vessel;
(c) adding liquid chlorine into said vessel in a quantity such that a portion of the liquid chlorine evaporates until the pressure in said vessel is below 100 psig, but above those chlorine vapor pressures necessary for the formation of chlorine hydrate in the temperature range +6°C to +20°C, and said pressure is maintained throughout the formation of chlorine hydrate;
(d) sealing the vessel;
(e) allowing the quantity of aqueous liquid to react with the remaining liquid chlorine to form chlorine hydrate;
and (f) removing the heat of hydrate formation to an environment having a temperature of approximately +6°C up to a room temperature of approximately +26°C.

2. The method according to claim 1 wherein said aqueous liquid is added to said vessel before said liquid chlorine is added to said vessel.

3. The method according to claim 1 further including the step of mixing said liquid chlorine with said aqueous liquid.

4. The method according to claim 3, wherein said mixing step occurs concomitantly with said step of removing the heat of hydrate formation.

5. The method according to claim 1, wherein said step of adding said liquid chlorine to said vessel, said step of adding said aqueous liquid to said vessel and said step of mixing said liquid chlorine with said aqueous liquid all occur concomitantly.

6. The method according to claim 1 wherein said aqueous liquid is water.

7. The method according to claim 1 wherein said aqueous liquid is an aqueous electrolyte.

8. The method according to claim 1, further including the step of maintaining the temperature of said aqueous liquid within the temperature range +6°C to +20°C
before said aqueous liquid is combined with said liquid chlorine.

9. The method according to claim 1 including the step of cooling said chlorine hydrate such that the pressure inside said vessel decreases.

10. The method according to claim 1, wherein said method of forming chlorine hydrate forms part of a method for charging a zinc-chloride battery.

11. A method of forming chlorine hydrate as part of a method of charging a zinc-chloride battery contained in an electric vehicle, comprising the steps of:
(a) providing a vessel capable of being sealed off from the ambient environment;
(b) adding a predetermined quantity of an aqueous liquid to said vessel;
(c) adding liquid chlorine into said vessel in a quantity such that a portion of the liquid chlorine evaporates until the pressure in said vessel is below 100 psig, but above those chlorine vapor pressures, specified in figure 1, necessary for the formation of chlorine hydrate in the temperature range +6°C to +20°C and said pressure is maintained throughout the formation of chlorine hydrate;
(d) sealing the vessel;
(e) allowing the quantity of aqueous liquid to react with the liquid chlorine to form chlorine hydrate; and (f) removing the heat of hydrate formation to a substantially ambient room temperature environment up to approximately +26°C.

12. The method according to claim 11, including the step of cooling said chlorine hydrate, such that the pressure inside said vessel decreases.