K + -Intercalated Na x Fe 0.2 Mn 0.8 O 2 Cathodes Synthesized by Room-Temperature Sodium Reduction for Sodium-Ion Batteries

Layered metal oxides are promising cathode materials for sodium-ion batteries, and K + intercalation modification of layered Na x TMO 2 -based (TM refers to transition metal) cathodes has been widely reported. Our previous work synthesized K + -intercalated Na x TMO 2 via a two-step high-temperature method, which suffers from severe side reactions and material loss. Herein, a room-temperature sodium metal reduction strategy was developed to prepare K + -intercalated Na x Fe 0.2 Mn 0.8 O 2 . This low-temperature approach achieves effective K + intercalation, which results in expanded interlayer spacing and enhanced Na + diffusion coefficients while suppressing side reactions and material loss induced by high-temperature treatment. The as-prepared material delivers 161.6 mAh g –1, retains 64.9 mAh g –1 at 5 C, maintains 77.2% capacity after 200 cycles, and exhibits electrochemical performance comparable to that of the counterpart synthesized via the two-step high-temperature method.