Low-cost, resilient, and non-flammable rechargeable Fe-ion batteries with scalable fabrication and long cycle life†

Abstract

Aqueous Fe-ion batteries remain largely unexplored owing to their short cycle life despite their extremely low material cost. Furthermore, their working mechanisms are mostly undisclosed with only a few experimental studies available. In this study, we fabricated Fe-ion batteries, which delivered an impressive specific capacity of 225 mA h g⁻¹ at a relatively low rate of 5C and exhibited an extremely long cycle life of up to 27 000 cycles with a capacity retention of 82% at 15C. Furthermore, the overall setup included a carbon steel foil anode (moderate-purity Fe source), along with scalable cathodes and low-cost FeSO₄ electrolyte, offering cost-effective solutions. Our theoretical study revealed that the Fe incorporation processes in the cathode, along with the corresponding voltage profiles during cycling, are primarily influenced by the formation energy of Fe on the emptied N sites of polyaniline and the structural deformations caused by Fe attachment. Notably, our batteries were shown to be free from fire hazard and failure due to short circuits. As manufacturing-friendly sandwich-type or 3D cylindrical cathodes eliminate multi-stack electrodes, our batteries are cost-effective, long-lasting, and safe for stationary energy storage systems.