One-step Surface-to-bulk Modification of NaCrO2 Cathode for Durable Sodium-ion Batteries

NaCrO 2 is a promising O3-type cathode material in sodium-ion batteries. However, it suffers from rapid capacity fading due to the unstable structure upon cycling. This work shows that in situ carbon coating during the synthesis process has multiple synergistic effects and can effectively stabilize the material structure and improve the cyclability. It is found that sodium vacancy and carbon coating in NaCrO 2 synchronously occur, which improve its sodium-ion transport kinetics, structural stability during cycling and the air stability. More importantly, the strategy is universal in that various sources of carbon display similar effect. As a result, the asphalt-derived carbon coated material has a high initial capacity of 129 mAh g −1 at 0.1 C rate with an initial Coulombic efficiency up to 98.2 %. In addition, it shows an excellent rate capability and cycling performance with 81.1 % retention after 1000 cycles at 5 C in half cell. Moreover, a full cell has constructed by coupling with hard carbon anode, which shows a high discharge capacity of 121.9 mAh g −1 with a high Coulomb efficiency of 94.7 %, excellent rate capability and good cycling stability. This work demonstrates a general modification method on NaCrO 2 that has the potential for practical applications. Graphical In-situ carbon coating : This work shows that in situ carbon coating of NaCrO 2 cathode for sodium-ion batteries generates multiple synergistic effects and can effectively stabilize the material structure and improve the cyclability. The asphalt-derived carbon coated NaCrO 2 has a high capacity of 129 mAh g −1 at 0.1 C, excellent rate capability and cycling performance with 81.1 % retention after 1000 cycles at 5 C.