SnO2 coating to stabilize Mn-based layered oxide cathode materials for sodium-ion batteries

Thanks to high theoretical capacity and good ionic conductivity, Mn-based layered metal oxides are considered to be promising cathode materials for sodium-ion batteries (SIBs). However, the irreversible structural change and oxygen loss during sodiation/desodiation processes lead to rapid capacity attenuation. Herein, SnO2 surface coating was adopted for the first time to improve the Na-storage performance of Na0.6[Li0.2Mn0.8]O2 (NLMO) through solid-phase heat treatment with a subsequent liquid-phase method. The optimized 1 wt% SnO2 coated NLMO demonstrated a capacity of 103 mAh/g at a high rate of 1C (1C = 176 mA/g) and 88 mAh/g after 40 cycles with a capacity retention of 85.4%. The SnO2 coating layer endows the NLMO structure with stable ion transport interface to facilitate sodium-ion transfer and an isolated shielding layer to inhibit oxygen loss, thus contributing to stable cycling performance and high capacity even at a high rate. This surface-coating strategy is expected to be applicable to other layered metal oxides as cathode materials to achieve good cycling stability and high-rate capacity. This work is significant for the electrochemical performance improvement of layered metal oxides applied in SIBs.