Gd3+-doped NaTi2(PO4)3@C negative material with superior Na-storage property for sodium-ion batteries

The pristine NaTi2(PO4)3 negative electrode material has a poor electrical conductivity, which significantly inhibits its application in sodium-ion batteries. Herein, carbon coating and Gd3+ doping are simultaneously applied to promote the electrical conductivity of NaTi2(PO4)3 through a simple sol-gel approach. The conductive carbon coating promotes apparent conductivity, while Gd3+-doping effectively improves intrinsic conductivity. Therefore, the resulting Gd3+-doped NaTi2−xGdx(PO4)3@C (x=1%, 3%, 5%, 7%) composites display superior high-rate capabilities for sodium energy storage. A typical obtained NaTi1.95Gd0.05(PO4)3@C anode presents high capacities of 105.9 and 93.1 mAh g−1 at 5 and 10 C, respectively. Furthermore, this anode shows a high capacity retention ratio of 95.2% at 20 C over 500 cycles. These results suggest that this carbon coating and doping strategy is highly effective and can be adopted to enhance the battery properties of other electrode materials.