A High-Performance Layered Cr-Based Cathode for Sodium-ion Batteries

Abstract Sodium-ion batteries (SIBs) are the popular alternative for grid-scale energy storage due to the abundant resources and wide distribution of sodium. However, NaCrO2, one of the most promising layered oxides for cathode materials, suffers from a serious capacity decrease by charging to the potential higher than 3.6 V, attributed to the irreversible chromium ions migration from CrO6 slabs to sodium layers during the initial charge process. Herein we synthesize a novel O3-type layered Na0.88Cr0.88Ru0.12O2 material, which could be well operated at elevated potential 3.8 V. The Na0.88Cr0.88Ru0.12O2 electrode delivers an extended reversible discharge capacity of 156 mAh g-1 and superior rate capability. Moreover, Na0.88Cr0.88Ru0.12O2 electrode shows excellent cycling performance, illustrated by 80.7% capacity retention over 1100 cycles. The results of high-angle annular dark-field scanning transmission electron microscopy measurement indicate that the undesired migration of Cr ions during sodium extraction can be suppressed via Ru doping, which can significantly improve the electrochemical properties of Na0.88Cr0.88Ru0.12O2 compared to NaCrO2. Our findings provide new insights for the common transition-metal migration during cycling layered cathodes, and motivate a new design strategy for high-performance SIBs.