GB2289461A

GB2289461A - Method of introducing electrolyte into an electrochemical cell

Info

Publication number: GB2289461A
Application number: GB9509958A
Authority: GB
Inventors: Peter Cook
Original assignee: AABH Patent Holdings SA
Current assignee: AABH Patent Holdings SA
Priority date: 1994-05-18
Filing date: 1995-05-17
Publication date: 1995-11-22
Also published as: DE19518152A1; GB9509958D0; JPH0845497A; ZA953934B; GB9409914D0; FR2720193A1

Description

2289461 1 Method of Introducing Ele into an Electrochemical C ctrolyte ell

Housing THIS INVENTION relates to a method of introducing electrolyte into an electrochemical cell housing. It relates also to a filling installation for introducing electrolyte into an electrochemical cell housing.

is According to a f irst aspect of the invention, there is provided a method of introducing electrolyte into an electrochemical cell housing, which method comprises drawing at least a partial vacuum in a f irst chamber located above and operatively connected to an electrochemical cell housing, so that said at least partial vacuum is thereby also drawn on the cell housing; dispensing a fluid electrolyte from a second chamber located above and operatively connected to the first chamber, and maintained under positive pressure, into the first chamber and hence into the cell housing; and on a predetermined volume of electrolyte having been dispensed from the second chamber into the first chamber, breaking said at least partial vacuum in the first chamber and pressurizing the first 2 chamber, thereby to provide additional driving force for displacing the electrolyte rapidly into the cell housing.

is The dispensing of the electrolyte from the first chamber into the cell housing, and from the second chamber into the first chamber, is thus achieved as a result of pressure differences between the housing and the first chamber, and between the chambers, assisted by gravity.

The method may include, prior to dispensing the electrolyte f rom. the second chamber into the first chamber, maintaining only a volume of electrolyte equivalent to said predetermined volume in the second chamber, so that only said predetermined volume of electrolyte is dispensed f rom the second chamber into the f irst chamber. The maintaining of said volume of electrolyte in the second chamber may be effected by transferring electrolyte into the second chamber, trapping said volume of electrolyte in the second chamber, and removing excess electrolyte from the chamber. The trapping of the electrolyte may be effected by holding it in an upright tube, or the like. The transferring of the electrolyte into the second chamber may be effected by pressurising a bulk reservoir of the electrolyte while drawing at least a partial vacuum on the second chamber, and allowing the electrolyte to pass f rom the bulk reservoir along conduit means into the second chamber. The combination of the pressurization of the bulk reservoir and said at least partial vacuum in the second chamber thus provides the required driving force for transferring the electrolyte along the conduit means.

The removing of the excess electrolyte from the second chamber may be effected by drawing at least a partial vacuum on the bulk 1 i 3 reservoir, and pressurizing the second chamber, thereby to provide a driving force for transferring the excess electrolyte from the second chamber to the bulk reservoir back along the conduit means.

While the method, at least in principle, has application on the introduction of any fluid electrolyte into an electrochemical cell housing, it is believed that it will have particular application in introducing a liquid, eg molten, electrolyte, such as molten alkali metal aluminium halide based electrolyte, having the formula MA1Ha14 where M is an alkali and Hal is a halide, and which is solid at ambient temperature, into the cell housing, which may then preferably be that of a rechargeable electrochemical cell. The electrolyte may, in particular, be NaA1C14.

The method may then include heating the bulk reservoir, the conduit means and all other components, to maintain the electrolyte in molten form.

According to a second aspect of the invention, there is provided a filling installation for introducing an electrolyte into an electrochemical cell housing, which installation comprises a first vessel providing a first chamber, the first vessel being operatively connectable to an electrochemical cell housing so that it is located above the cell housing, and the f irst vessel being adapted so that at least a partial vacuum can be drawn on its chamber; a second vessel providing a second chamber for containing fluid electrolyte, the second vessel being located above the first vessel, with the second chamber being in communication with the first 4 chamber. and the second vessel adapted so that the second chamber can be pressurized; and first valve means for closing off the second chamber from the first chamber.

The f irst vessel may thus be provided with a f itting by means of which it can be connected to vacuum drawing apparatus, eg a suction pump. The first vessel may also be provided with, at its lower end, a nozzle through which fluid electrolyte can pass, the nozzle being adapted for sealing connection thereof to the electrochemical cell housing. The nozzle may have second valve means for closing off passage of electrol- yte through it.

The installation may include a bulk electrolyte reservoir, with a conduit leading f rom the inside of the bulk reservoir near its bottom into the second chamber, near its bottom. The second vessel may include a tube protruding upwardly from the bottom of the chamber, with the lower end of the tube being closed off by the first valve means and the upper end of the tube being open.

The bulk electrolyte reservoir may be adapted to be pressurized, with it and the second chamber being connected to a supply of inert gas under pressure, eg a pressurized nitrogen supply. The bulk reservoir may also be adapted so that at least a partial vacuum can be drawn thereon, while the second vessel may also be adapted so that at least a partial vacuum can be drawn thereon. The bulk reservoir and the second vessel may thus be provided with suitable fittings for connecting them to vacuum drawing apparatus, such as a suction pump.

is The installation may include control means for automatically controlling the drawing of said at least partial vacuum, and the pressurization of the bulk reservoir and the second chamber. Thus, to transfer electrolyte into the measuring tube, the bulk reservoir may be pressurized with nitrogen, while at least a partial vacuum is drawn on the second chamber. This will cause electrolyte to pass along the conduit into the second chamber, with sufficient electrolyte being transferred so that the second chamber is filled with electrolyte to a level above the upper end of the measuring tube. Thereafter, the second chamber is pressurized with nitrogen, while at least a partial vacuum is drawn on the bulk reservoir. This will cause excess electrolyte to flow back along the conduit from the second chamber to the bulk reservoir. The control means my thus include sensing means, eg electrodes, for sensing the level of electrolyte in the second chamber. Thus, an electrode may be provided, with automatic pressurization of the second chamber and the drawing of said at least partial vacuum on the reservoir being effected once the electrode has sensed that the level of the electrolyte has risen to above the upper end of the measuring tube. The control means may include a second electrode in the second chamber, the second electrode being adapted to sense when the level of the electrolyte has fallen below the upper end of the measuring tube, and that the automatic electrolyte dispensing cycle provided by the installation has been completed.

The electrolyte may be a molten salt electrolyte as hereinbef ore described.

6 The invention will now be described by way of example with reference to the accompanying diagrammatic drawing of a filling installation according to the invention.

In the drawing, reference numeral 10 generally indicates a filling installation according to the invention.

is The filling installation 10 includes a vessel 12 providing a chamber 14, with a nozzle 16 leading f rom the bottom of the chamber 14. The nozzle 16 is fitted with a valve 18. The nozzle is of a self-sealing type which is connectable fluid tightly to a filling opening 22 of an electrochemical cell housing 20 so that the vessel 12 is located above the cell housing. The vessel 12 is provided with a fitting in the form of a length of conduit 24 which is operatively connected to a vacuum drawing device (not shown) such as a suction pump.

The installation 10 also includes a second vessel 26, providing a chamber 28 located above the vessel 12. The vessel 26 includes an upright open ended measuring tube 30, the operatively lower end of which is in communication with the chamber 14. A valve 32 is provided at the lower end of the tube 30. A pair of electrodes 34, 36 protrude into the chamber 28, as does a displacement rod 38.

The vessel 26 is provided with a fitting 40 which is operatively connected, by means of a conduit 42, to a vacuum drawing device 44, which may be a suction pump or the like.

9 7 The vessel 26 also has a further fitting 46 which is operatively connected, by means of a conduit 48, to a source 50 of pressurized nitrogen.

The installation 10 further includes a bulk electrolyte reservoir 52.

The reservoir 52 has a fitting 54 connected by means of a conduit 56 to the vacuum drawing device 44, as well as a fitting 58 connected by means of a conduit 60 to the pressurized nitrogen supply 50.

A conduit 62, fitted with a filter 64, leads from near the bottom of the bulk reservoir 52, to the chamber 28 at or near the bottom thereof.

The bulk reservoir 52 is provided with thermostatically controlled heating means (not shown) for maintaining a bulk supply of NaA1C14 in molten form therein. Thus, the heating means typically maintains the bulk reservoir at about 2000C, which is above the melting point of about 1570C of NaA1C14 electrolyte.

By means of the bulk nitrogen supply 50, a blanket of dry nitrogen at low positive pressure is normally provided in the bulk reservoir, so that atmospheric air is thereby excluded from the reservoir.

The installation 10 also includes heating means (not shown)for maintaining all components at elevated temperature, typically at about 2000C.

The installation 10 further includes an electrical control system (not shown) which is operatively connected to the electrodes 36 and 8 34 as well as to the pressurized nitrogen supply 50 and the vacuum drawing device 44. If desired, the control system can also be operatively connected to the valves 18 and 32 and to the vacuum drawing device connected to the chamber 14, so that the entire operation of the installation 10 can take place automatically. The displacement rod 38 allows small adjustments to be made in the volume of electrolyte retained in the measuring tube 30.

is In use, by means of the control system, a partial vacuum is applied to the chamber 28. This, together with the low pressure nitrogen blanket in the bulk reservoir 52, provides a driving force for transferring molten NaA1C14 from the reservoir 52 into the chamber 28 along the conduit 62. The electrode 34 senses the level of the electrolyte in the chamber 28 and when the level has reached the electrode 34, indicative that the measuring tube 30 is flooded with molten electrolyte, the control system causes the partial vacuum in the chamber 28 to be broken, and a low positive pressure nitrogen blanket to be introduced into the chamber 28, thereby restoring the pressure in the chamber 28 to near atmospheric pressure. The control system simultaneously causes a partial vacuum to be drawn on the bulk reservoir 52. This pressure difference, assisted by gravity, causes excess electrolyte in the chamber 28, ie electrolyte which is not contained in the measuring tube 30, to be transferred back into the reservoir 52 so that the measured volume of electrolyte is trapped in the measuring tube 30. The electrode 36 senses when the electrolyte level is below the upper end of the measuring tube 30, whereupon the control system causes the partial vacuum applied to the bulk reservoir 52 to be broken and low positive pressure nitrogen to i 9 be introduced into the reservoir 52. during these operations.

The valve 32 will be closed Thereafter, to dispense electrolyte into the cell housing 20, the valve 18 is opened, while at least a partial vacuum is drawn on the chamber 14. Simultaneously, said at least partial vacuum will also be drawn on the cell housing 20. The cell housing 20 and the chamber 14 are typically evacuated to 20 to 30 millibars absolute pressure, which typically takes about 7 seconds.

The valve 32 is then opened, and molten electrolyte flows from the measuring tube 30, into and through the chamber 14, and into the cell housing 20. When all the electrolyte has been dispensed from the measuring tube 30, the vacuum in the chamber 14 breaks, and nitrogen from the chamber 28 raises the pressure in the chamber 14 to near atmospheric pressure, thereby assisting in driving the electrolyte into the cell housing 20. The transfer of the electrolyte from the measuring tube 30 into the cell housing 20 typically takes about 4 seconds.

The valves 18, 32 are thereafter closed, the cell housing 20 disconnected, and the operation repeated for subsequent cell housings.

The control system thus uses pressure and vacuum sensors and level detecting electrodes. A logic system, which may use relay logic or a programmable logic controller to operate electro -mechanical valves, controls the application of vacuum, the flow of nitrogen, and may control the opening and closing of the valves 18 and 32. Automatic means, which may include robotics, may present unfilled cell housings to the installation and remove filled cell housings, thus providing a totally automatic process of filling cell housings with electrolyte, without the need for a human operator.

The Applicant believes that the installation 10 provides a means for accurately and rapidly measuring and dispensing liquid sodium aluminium chloride electrolyte into secondary cell housings.

NaA1C14 normally presents difficulties in manufacture, storage and handling. For example, if it is allowed to come into contact with moisture, such as water vapour in the atmosphere, hydrochloric acid is formed which both contaminates it and increases its corrosive nature. Furthermore, it is a solid below 1570C, and thus requires heating to above 1570C to render it fluid. In molten form, it has a low viscosity, and a specific gravity of approximately 1,7 at is 2000C.

The Applicant believes that, by using the installation 10 to introduce NaA1C14, the following advantages arise:

the electrolyte is isolated from contamination at all times during transfer into the cell housing; there involved in reservoir 52; is no potentially contaminating mechanical pumping transferring the electrolyte to and from the bulk vacuum is used in preference to pressure for transferring the electrolyte for safety reasons; the positive pressures employed in the various steps through use of pressurized nitrogen are thus of A 11 much smaller magnitude than the partial vacuums used and are generally less than 40 millibars or 4 kPa(g); the reversal of the electrolyte f low inherent in the system during f illing of the measuring tube 30, automatically cleans the filter 64 during each cycle; the installation accurately delivers measured volumes of electrolyte automatically and rapidly as a step in the manufacture of secondary cells.

Impregnation of the electrolyte into the cell housing is, surprisingly, very rapid and takes place within a few seconds. It has been found that the combination of pre-evacuation of the cell housing, and pressure due to the nitrogen blanket applied in the chamber 28 results in fast complete accurate loading of the electrolyte into the cell housing.

Preferably all piping and metal work in the installation 10 are of nickel, with couplings being made up of flanges and 0-ring seals. In this fashion, the Applicant believes, corrosion, or stress corrosion and consequent cracking, is largely eliminated.

12

Claims

CLAIMS:

1. A method of introducing electrolyte into an electrochemical cell housing, which method comprises drawing at least a partial vacuum in a f irst chamber located above and operatively connected to an electrochemical cell housing, so that said at least partial vacuum is thereby also drawn on the cell housing; dispensing a f luid electrolyte from a second chamber located above and operatively connected to the first chamber, and maintained under positive pressure, into the first chamber and hence into the cell housing; and on a predetermined volume of electrolyte having been dispensed f rom the second chamber into the f irst chamber, breaking said at least partial vacuum in the first chamber and pressurizing the first is chamber, thereby to provide additional driving force for displacing the electrolyte rapidly into the cell housing.

2. A method according to Claim 1, which includes, prior to dispensing the electrolyte from the second chamber into the first chamber, maintaining only a volume of electrolyte equivalent to said predetermined volume in the second chamber, so that only said predetermined volume of electrolyte is dispensed from the second chamber into the first chamber.

3. A method according to Claim 2, wherein the maintaining of said volume of electrolyte in the second chamber is effected by transferring electrolyte into the second chamber, trapping said 13 volume of electrolyte in the second chamber, and removing excess electrolyte from the chamber.

4. A method according to Claim 3, wherein the transferring of the electrolyte into the second chamber is effected by pressurising a bulk reservoir of the electrolyte while drawing at least a partial vacuum on the second chamber, and allowing the electrolyte to pass from the bulk reservoir along conduit means into the second chamber.

5. A method according to Claim 4, wherein the removing of the excess electrolyte from the second chamber is effected by drawing at least a partial vacuum on the bulk reservoir, and pressurizing the second chamber, thereby to provide a driving force for transferring the excess electrolyte from the second chamber to the bulk reservoir back along the conduit means.

is

6. A filling installation for introducing an electrolyte into an electrochemical cell housing, which installation comprises a first vessel providing a first chamber, the first vessel being operatively connectable to an electrochemical cell housing so that it is located above the cell housing, and the first vessel being adapted so that at least a partial vacuum can be drawn on its chamber; a second vessel providing a second chamber for containing fluid electrolyte, the second vessel being located above the first vessel, with the second chamber being in communication with the first chamber, and the second vessel adapted so that the second chamber can be pressurized; and 14 first valve means for closing off the second chamber from the first chamber.

is

7. An installation according to Claim 6, wherein the f irst vessel is provided with a f itting by means of which it can be connected to vacuum drawing apparatus, as well as with, at its lower end, a nozzle through which fluid electrolyte can pass, the nozzle being adapted for sealing connection thereof to the electrochemical cell housing, and having second valve means for closing off passage of electrolyte through it.

8. An installation according to Claim 6 or Claim 7, which includes a bulk electrolyte reservoir, with a conduit leading from the inside of the bulk reservoir near its bottom into the second chamber, near its bottom.

9. An installation according to Claim 8, wherein the second vessel includes a tube protruding upwardly f rom the bottom of the chamber, with the lower end of the tube being closed off by the first valve means and the upper end of the tube being open.

10. An installation according to Claim 9, wherein the bulk electrolyte reservoir is adapted to be pressurized, with it and the second chamber being connected to a supply of inert gas under pressure.

11. An installation according to Claim 9 or Claim 10, wherein the bulk reservoir is adapted so that a vacuum can be drawn thereon, with the second vessel also being adapted so that at least a partial is vacuum can be drawn thereon, and with the bulk reservoir and the second vessel being provided with suitable fittings for connecting them to vacuum drawing apparatus.

12. An installation according to claim 11, which includes control means for automatically controlling the drawing of said at least partial vacuum, and the pressurization of the bulk reservoir and the second chamber, the control means including sensing means for sensing the level of electrolyte in the second chamber.

13. An installation according to Claim 12, wherein the sensing means includes a first electrode in the second chamber for sensing when the level of the electrolyte has risen to above the upper end of the measuring tube, and a second electrode in the second chamber for sensing when the level of the electrolyte has fallen below the upper end of the tube.

is

14. A novel method of introducing electrolyte into an electrochemical cell housing, substantially as described and illustrated herein.

is. A novel filling installation for introducing an electrolyte into an electrochemical cell housing, substantially as described and illustrated herein.