Effects of physical and operating parameters on the performance of a concentration gradient battery for saltwater-based energy storage

Abstract

Concentration gradient batteries (CGBs) use electrodialysis and reverse electrodialysis to charge and discharge, respectively. An important factor hindering CGB efficiency is osmosis through ion exchange membranes (IEMs); however, adding an osmotic ballast to the dilute compartment reduces osmosis and improves CGB efficiency. Despite the importance of osmosis in CGB performance, there has been no evaluation of the effects of CGB parameters on performance with and without an osmotic ballast. Accordingly, our goal was to evaluate the effects of selected CGB parameters on various CGB performance metrics to inform future optimization of CGB designs. Results showed ballast addition improved current and round-trip energy efficiency and stabilized CGB performance across multi-cycle operation. However, ballast addition caused lower average (net) power densities due to its impact on IEM stack resistance and solution viscosity. Increasing the flowrate and decreasing the spacer thickness led to decreases in average net power densities. Importantly, the effect of IEM properties on CGB performance varied with ballast addition: low water permeability IEMs had greater and lower round-trip energy efficiencies without and with ballast, respectively, compared to low resistance IEMs. This work informs CGB parameter selection, demonstrates tradeoffs associated with osmotic ballast addition, and shows multi-cycle CGB operation is feasible.