Seawater battery is a new concept energy storage device that uses seawater as a cathode material, one of the most abundant resources on the earth. It is crucial to design cells and optimize key components for the high performance rechargeable seawater batteries. Seawater batteries, which utilize natural seawater as the active material in an open-structured cathode, require a new platform for building and testing the cells other than existing Li-ion coin-type or pouch-type cells. So, we designed the coin-type seawater battery of a new platform, and we would like to introduce new findings based on our optimized cell. Engineering the cathode components—improving the wettability of cathode current collector and seawater catholyte flow—improves the voltage efficiency. In order to get reliable data from the materials that are the key elements in seawater batteries, a coin-type cell, a flow-cell tester, and their key compartments were designed and fabricated by trial and error and the testing environment was also determined.

We examined the wettability of seawater on the carbon felt (CF) cathode current collector and its effect on the charge-discharge cycling performance. The air-heating process of CFs made the surface hydrophilic, resulting in a reduced ΔV of the cell (~1.4 V) at a current rate of 0.025 mA cm^-2, compared to the cell using a pristine CF (~1.6 V). We also showed that the flow of the seawater reduced ΔV (~0.7 V) by 36% from ~1.1 V under no flow state. Through these various experiments, we optimized the key factors affecting the seawater battery. Therefore, further experiments on promising materials in seawater batteries can be conducted using the customized coin-type cell, which is an essential prerequisite for the practical implementation of seawater batteries as the next generation Energy storage system (ESS).