Chemistry: electrical current producing apparatus – product – and – Fluid active material or two-fluid electrolyte combination... – Active material in molten state
Patent
1993-07-14
1995-03-28
Maples, John S.
Chemistry: electrical current producing apparatus, product, and
Fluid active material or two-fluid electrolyte combination...
Active material in molten state
429199, 429218, 429221, H01M 1039
Patent
active
054015936
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in high temperature secondary batteries and especially lithium aluminium iron sulphide (LAIS) batteries.
2. Discussion of Prior Art
High temperature secondary batteries have been known for some years. Compared to conventional lead/acid batteries high temperature secondary batteries can offer similar performance but at only 1/3 the weight and volume. They are formed as an electrolyte separator material sandwiched between an anode and cathode. In the case of a LAIS battery the cathode is ferrous sulphide, the electrolyte is lithium halide and the anode is lithium aluminium alloy. LAIS and related batteries utilise the high power density afforded by the lithium sulphur couple. However the use of these and other high temperature secondary batteries as high power/high energy batteries has been hampered by various factors such as maintaining conductivity efficiency over many charge/discharge cycles and problems associated with dimensional stability on heating and cooling as batteries are charged and discharged. In certain instances changes in dimensional stability are so severe as to result in internal breakdown of the battery rendering it useless. Where the effects are less severe internal expansion of the battery may cause damage by leakage of electrolyte.
SUMMARY OF THE INVENTION
Consequently there is a need to be able to produce high temperature batteries which overcome or mitigate the above disadvantages.
Accordingly there is provided a high temperature battery which comprises a cathode composed at least partly of sulphur or a metal sulphide, an anode which contains an alkali metal or alkaline earth metal or an alloy of an alkali metal or alkaline earth metal, the cathodic material being electrochemically in excess of the anodic material, and disposed between the anode and cathode an electrolyte containing at least one alkali metal halide characterised in that potassium halide selected from chloride, bromide and iodide is further added to the compositions of the anode, cathode and the electrolyte.
Preferably, the potassium halide added to the anode, cathode and electrolyte is a bromide. Preferably, potassium bromide is added to the electrolyte in excess over the amount of alkali metal halides present in the electrolyte. The inventors have found that potassium bromide can have two effects. It improves the dimensional stability of the battery with the attendant advantages described above and also acts as a part of the electrolyte. It is believed that potassium bromide improves the dimensional stability because it is a bulky constituent and when the electrolyte melts at operating temperature the potassium bromide partially melts as well.
Preferably, the cathode is a metal sulphide and ideally is ferrous sulphide or titanium disulphide, the anode is formed from an alkali metal alloy which is ideally lithium aluminium alloy and the electrolyte is a ternary mixture of lithium fluoride, lithium chloride and lithium bromide. It has been found by the inventors that an electrochemical excess of ferrous sulphide to lithium aluminium alloy results in improved dimensional stability of the battery and increases battery life expectancy whilst maintaining conductivity. Typically the lithium aluminium alloy contains 20-24% by weight of lithium. The reaction between lithium aluminium alloy and ferrous sulphide is ##STR1##
The proportion of FeS to LiA1 is in the range 1:0.6-0.9 wt to wt and preferably is about 1:0.66 wt to wt.
In the case of a high temperature secondary battery where the anode comprises lithium aluminium alloy, the cathode comprises ferrous sulphide, preferably, the ratio of lithium aluminium alloy to potassium bromide is about 1:0.23 wt to wt and the ratio of iron sulphide to potassium bromide is about 1:0.19 wt to wt.
Preferably magnesia (MgO) is added to the anode, cathode and electrolyte. Magnesia is an electrical insulator which is cheap and inert when mixed with the electrolyte. It has the effect of helping
REFERENCES:
patent: 3907589 (1975-09-01), Gay et al.
patent: 4011372 (1977-03-01), Tomczuk et al.
patent: 4013818 (1977-03-01), Askew et al.
patent: 4189529 (1980-02-01), Birt et al.
patent: 4324846 (1982-04-01), Kaun et al.
patent: 4446212 (1984-05-01), Kaun
patent: 4851306 (1989-07-01), Kaun et al.
Jones John B.
Moore David R.
Pearce Leonard J.
Maples John S.
The Secretary of State for Defence in Her Britannic Majesty's Go
LandOfFree
High temperature secondary batteries does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High temperature secondary batteries, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High temperature secondary batteries will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2249372