High-temperature battery systems

At first sight high-temperature batteries would seem to be at a disadvantage compared with ambient-temperature batteries. Provided however, that the application is one which requires a stored energy greater than 10 kW h, hot batteries have attractive characteristics-they have high specific energies and their performance is independent of the ambient temperature. Cooling is also easier because of the large temperature difference between the battery and the coolant. Two types of cell have been used: molten salt electrolyte cells and solid electrolyte cells. In the former lithium is the negative electrode and in the latter, sodium. The only molten salt electrolyte cell which has been developed to the battery stage is the lithium-aluminium iron sulphide cell, whereas two solid electrolyte cells have reached this stage: the sodium-sulphur cell and the sodium-nickel chloride cell. The emphasis in this paper will be on these latter two systems as these are now in pilot production and on test in a variety of electric vehicles.