Room‐Temperature Rechargeable Ca‐Ion Based Hybrid Batteries with High Rate Capability and Long‐Term Cycling Life

Calcium‐ion batteries (CIBs) are promising energy storage devices due to the merits of natural abundance, similar standard reduction potential to lithium, and bivalent‐ion characteristic of calcium. However, the development of CIBs is hindered by the low rate capability and poor cycling performance at room temperature. Here, a highly reversible room‐temperature calcium‐ion based hybrid battery is realized by a tri‐ion strategy, which significantly improves the diffusion kinetics of calcium ions. The optimized CIB shows high rate capability of 15 C as well as excellent cycling stability over 1500 cycles with 86% capacity retention at 5 C, at room temperature, which is the best result of reported calcium‐ion based full batteries.