With reference to alkaline batteries used on board ship:
(a) Describe the operation of a battery cell and state the materials used
(b) Describe how the cells are mounted to form a battery
(c) State the advantages and disadvantages compared with lead-acid batteries.
Structured for DG Shipping MEO Class II examination scoring criteria.
In this type of battery,
A series of alternating positive and negative plates are fully immersed in the electrolyte, separators are inserted between the interleaving plates to prevent contact/ internal short-circuiting. A non-return pressure relief valve is fitted in the housing to release the gases, which evolve especially during the period of overcharge. Relief valves are non-return type to prevent ‘poisoning’ of the electrolyte from the atmosphere.
Discharge: On discharge, nickel hydroxide losses oxygen and is reduced to a lower form, while the cadmium in the negative plates is oxidised to cadmium oxide.
Charging: On charging, the reverse of discharge occurs, the material at the positive terminal is being oxidised to nickel hydroxide and the material at the negative terminal is being reduced to cadmium.