Designing a new battery system using NaCl aqueous solution as cathode

Abstract

The importance of Electrical Energy Storage (EES) for integration with renewable sources has increased gradually in accordance with rising environmental concerns and energy demands. Although research and development in EES technologies has been progressing, some challenges, such as improved performances, cost, location, etc., still remain before they can be successful. The cost-competition is expected to significantly affect the broad market penetration of EES. The eco-friendly seawater battery, employing seawater to a cathode material, is cost-effective, thus addressing the cost issue. As a seawater cathode provides Na ions of the energy source continuously and finally, a seawater battery can have high energy density despite having low salt (NaCl) concentration (~0.46 M). That is to say, it should be located near the ocean. In addition, renewable sources, possibly integrated with the seawater battery, are limited owing to the locational constraint. Herein, a rechargeable saltwater battery is proposed for the first time, which utilizes NaCl aqueous solution as an active material while it has typically served as electrolyte to conduct ions, in batteries or electrolysis. Using cheap and safe saltwater as catholyte allows the battery to be located anywhere, and also offers a significant reduction in production costs which is one of the requisitions for large-scale EES systems. In addition, changing salt levels in water enables the control of the working potential of the cell and energy density (up to 423 Wh/kg at 6 M NaCl). This ultimately provides the flexibilities of the saltwater battery for different applications. The cell design and components (e.g. change of material components) significantly affected its electrochemical performances. Thus, this research also focused on designing the new cell and the key components (a solid electrolyte and a carbon-based cathode electrode) to test saltwater cathode. The electrochemical mechanism and performances were therefore investigated. In addition, some catalysts were applied to improve cell performances. Lastly, a cost analysis of a saltwater battery was examined, by comparing it to other batteries, to demonstrate its feasibility as a next-generation EES technology.