Building a Long-Lifespan Aqueous K-Ion Battery Operating at −35 °C

Aqueous potassium-ion batteries (AKIBs) are promising low-cost and high-safety candidates for large-scale energy storage applications. However, most AKIBs can only operate above −20 °C with a short lifespan at low temperatures (8–300 cycles at −20 °C) owing to the high freezing point of KCF 3 SO 3 -based electrolytes and severe electrode dissolution. Here, we developed an AKIB consisting of K 1.55 Fe[Fe(CN) 6 ] 0.95 ·1.03H 2 O/10 m KCF 3 COO/3,4,9,10-perylenetetracarboxylic diimide. The newly proposed 10 m KCF 3 COO electrolyte has a low freezing point (−35.5 °C) owing to a large H-bond breakage degree and a high average ice formation energy. Both electrodes exhibit low solubility in the 10 m KCF 3 COO electrolyte. As a result, the full cell delivers high energy density (56.3 Wh kg –1 at 25 °C, 41.9 Wh kg –1 at −35 °C) and a long low-temperature lifespan (87.5% capacity retention over 1000 cycles at −35 °C). This work marks a milestone development of AKIBs for low-temperature applications.