Simultaneously promoting the surface/bulk structural stability of Fe/Mn-based layered cathode for sodium ion batteries

Layered sodium iron manganese oxide cathodes have attracted great interest owing to their high specific capacity and cost-effective metal resources, while the detrimental phase transitions and surface structural degradation severely limit their commercial applications. In this work, the bulk and surface structure stability of a P 2-Na 0.67 Fe 0.5 Mn 0.5 O 2 cathode can be synergically enhanced by a one-step Li/Nb co-doping strategy. Structural characterizations reveal that Li doping promotes the formation of P 2/O3 biphasic structure and makes the unfavorable P 2-OP4 phase transition convert into a smooth solid-solution reaction. Nb doping enhances the mobility of sodium ions and forms strong Nb-O bonds, thereby enhancing the stability of the TMO 2 layer structure. In particular, the Nb element induces the surface reorganization of an atomic-scale NaNbO 3 coating layer, which could effectively prevent the dissolution of metals and surface side reactions. The synergistic mechanism of enhanced electrochemical performance is proved by multiple characterizations during cycling. As a result, the as-prepared Na 0.67 Li 0.1 Fe 0.5 Mn 0.38 Nb 0.02 O 2 exhibits improved capacity retention of 85.4 % than raw material (45.7 %) after 100 cycles at 0.5C (1C = 174 mA g −1 ) within 2.0–4.0 V. This co-regulating strategy provides a promising approach to designing highly stable sodium-ion battery cathodes. Furthermore, a full cell of Na 0.67 Li 0.1 Fe 0.5 Mn 0.38 Nb 0.02 O 2 with hard carbon displays excellent cycling stability (85.1 % capacity retention after 100 cycles), making its commercial operation possible. This synergistic strategy of biphasic structure and surface reorganization is a critical route to accelerate the application of layer oxide cathodes.