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

NaCrO2 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 NaCrO2 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 NaCrO2 that has the potential for practical applications.

Automated summary

This work demonstrates that in situ carbon coating can effectively stabilize the structure of NaCrO2 and improve its cyclability in sodium-ion batteries. It shows excellent rate capability, cycling performance, and air stability. The strategy of carbon coating is universal and various carbon sources can achieve similar effects. The modified NaCrO2 has potential for practical applications in electrochemical energy storage systems.