A new concept for advanced large-scale energy storage: secondary batteries with seawater as open self-replenishing cathode

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World-wide implementation of renewable energy sources is substantially dependent on the availability of improved technologies for the production of efficient, safe, inexpensive and eco-friendly stationary energy storage systems. This is because the power that is produced by energy sources such as solar, wind and tidal (the latter to a smaller extent) is intermittent - implying that the peak electrical output may not coincide with peak demand. For this reason large-scale energy storage is essential to provide electrical supply when and where is needed without interruptions. It is recognized that to meet all the requirements of modern society a portfolio of different storage technology are necessary, each one optimized for a given application. Many different battery technologies such as lead acid, metal-air, redox flow and lithium-ion have also been proposed as storage solution. They are each not without their issues due to their environmental impact or for the high capital and maintenance cost. For large scale energy storage the effective cost is determined by the life-time of the system and its environmental foot print, which will be transferred to the cost per MWh. Within the framework of the present call "Adventures in Energy" we aim to explore a novel technology targeted specifically to large-scale energy storage coupled with marine wind, wave and tidal power production. This involves the use of sea-water as a positive electrode (cathode) in a hybrid system which is intermediate between a secondary sodium-ion battery and a fuel cell. The salt in sea-water is an inexhaustible source of sodium ions that are transferred to the negative electrode (anode) through a fast ionic-conductor membrane while charging. During discharge the sodium ions shuffle back from the anode to the sea-water. The exciting and novel aspect of this is that a natural unlimited resource is used as an active self-replenishing component of the cell. As a consequence the system offers numerous advantages: low cost, high safety and negligible environmental impact as compared to other related technologies. The project aims to take the sea-water hybrid fuel cell from the proof-of-concept stage to a viable technology for large scale energy storage. This will be achieved through the optimisation of constituent components, development of scalable manufacturing processes and validation in a relevant environment. Our research could provide a cost-effective solution to the pressing problem of storing electricity produced in the sea by enabling the technology necessary to build large-scale semi-submerged marine energy storage parks.