A High Rate and Stable Hybrid Li/Na‐Ion Battery Based on a Hydrated Molten Inorganic Salt Electrolyte

Abstract Taking into the consideration safety, environmental impact, and economic issue, the construction of aqueous batteries based on aqueous electrolyte has become an indispensable technical option for large‐scale electrical energy storage. The narrow electrochemical window is the main problem of conventional aqueous electrolyte. Here, an economical room‐temperature inorganic hydrated molten salt (RTMS) electrolyte with a large electrochemical stability window of 3.1 V is proposed. Compared with organic fluorinated molten salts, RTMS is composed of lithium nitrate hydrate and sodium nitrate with much lower cost. Based on the RTMS electrolyte, a hybrid Li/Na‐ion full battery is fabricated from cobalt hexacyanoferrate cathode (NaCoHCF) and perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA) anode. The full cell with the RTMS electrolyte exhibits a fantastic performance with high capacity of 139 mAh g⁻¹ at 1 C, 90 mAh g⁻¹ at 20 C, and capacity retention of 94.7% over 500 cycles at 3 C. The excellent performances are contributed to the unique properties of RTMS with a large electrochemical window, solvated H₂O free and high mobility of Li⁺, which exhibits excellent Li‐ions insertion and extraction capacity of NaCoHCF. This RTMS cell provides a new economic choice for large‐scale energy storage.