Open source all-iron battery 2.0.

In this work we present significant improvements to the open-source all-iron battery. We show higher power density and simpler fabrication. We also show a more reproducible procedure for preparing the electrolytes. The results are a highly rechargeable electrochemical cell based on iron, chloride, sulfate, and potassium ions in water at near-neutral pH. The cell is stable for thousands of cycles. It displays modest energy density consistent with the previous all-iron battery. The current is improved by a factor of 10 to a practical level of 500 mA/L and is able to deliver a maximal power of 250 mW/L. While this is modest performance compared to commercial rechargeable batteries, its low cost, simple synthesis, and safe manufacturing may make it suitable for storing renewable energy.