K <b> ⁺ </b> -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 NaxTMO2-based (TM refers to transition metal) cathodes has been widely reported. Our previous work synthesized K+-intercalated NaxTMO2 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 NaxFe0.2Mn0.8O2. 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.