Meliorating the sodium storage properties of NaTi2(PO4)3/C by rational structural design

Sodium-ion battery is considered to be a potential replacement for lithium-ion battery due to abundant sodium reserve and low cost. NASICON-type NaTi2(PO4)3 possesses three-dimensional channels, which makes it show excellent sodium storage performance. And it is a prospective anode for sodium-ion battery. In this paper, sodium storage property of NaTi2(PO4)3/C was further improved by rational structural design. We prepared NaTi2(PO4)3-xCl3x/C (x = 0, 0.05, 0.1, 0.2) by sol-gel method and applied it to anode materials for sodium-ion battery. Cl doping on PO43− site has no significant effect on the crystalline structure and particle agglomeration of materials. It is clear that electrochemical performances of all Cl-doped samples are better than those of blank sample. As the doping amount increases, the performance first enhances and then declines. For the rate performance of all samples, NaTi2(PO4)2.9Cl0.3 (NC/Cl-30) delivers discharge capacities of 257.8, 212.7, 169.5, and 146.3 mAh g−1 at 0.1, 0.4, 2, and 4 A g−1, with marked enhancement of 133.7, 124.4, 113.2, and 112.2 mAh g−1 compared with NaTi2(PO4)3/C (NC). In addition, NC/Cl-30 also exhibits outstanding cycling performance. The discharge capacity of NC/Cl-30 at 1 A g−1 after 1000 cycles reaches up to 142.2 mAh g−1, 62.9 mAh g−1 larger than that of NC. NC/Cl-30 presents higher capacity resulting from proper Cl doping. Our work provides some references for optimizing performance of NaTi2(PO4)3 in sodium-ion battery through a method of anion doping.