Na_0.44MnO₂ coated with In₂O₃ as a high-voltage cathode for sodium-ion batteries

Na_0.44MnO₂ microrods with high crystallinity have been prepared by a simple solid-phase method and then coated with In₂O₃ by precipitation method. 1 wt% In₂O₃ coating could improve the sodium-storage capability of Na_0.44MnO₂ microrods significantly. The original Na_0.44MnO₂ microrods could provide the maximum discharge capacity of 100.3 mAh g⁻¹ under a wide voltage of 2.0–4.5 V at 1 C, but the discharge capacity rapidly decreases to 70.4 mAh g⁻¹ after 400 cycles, which was only 70.3% of the maximum capacity. However, the Na_0.44MnO₂ coated with 1 wt% In₂O₃ exhibited a high discharge capacity of 90.9 mAh g⁻¹ after 400 cycles, with high-capacity retention of 86.7% in the same case. Moreover, compared with Na_0.44MnO₂, 1 wt% In₂O₃ coated Na_0.44MnO₂ shows better rate capability. Even at a high current density of 10 C, the discharge capacity is 63.6 mAh g⁻¹, much larger than the 32.9 mAh g⁻¹ of the pristine Na_0.44MnO₂. The mechanism of In₂O₃ coating improving the electrochemical performance of Na_0.44MnO₂ microrods was studied in detail.