Rechargeable Potassium‐Ion Full Cells Operating at −40 °C

Abstract Potassium‐ion batteries (PIBs) are promising for cryogenic energy storage. However, current researches on low‐temperature PIBs are limited to half cells utilizing potassium metal as an anode, and realizing rechargeable full cells is challenged by lacking viable anode materials and compatible electrolytes. Herein, a hard carbon (HC)‐based low‐temperature potassium‐ion full cell is successfully fabricated for the first time. Experimental evidence and theoretical analysis revealed that potassium storage behaviors of HC anodes in the matched low‐temperature electrolyte involve defect adsorption, interlayer co‐intercalation, and nanopore filling. Notably, these unique potassiation processes exhibited low interfacial resistances and small reaction activation energies, enabling an excellent cycling performance of HC with a capacity of 175 mAh g −1 at −40 °C (68 % of its room‐temperature capacity). Consequently, the HC‐based full cells demonstrated impressive rechargeability and high energy density above 100 Wh kg −1 cathode at −40 °C, representing a significant advancement in the development of PIBs.