Synthesis and electrochemical properties of Na-doped LiTi2(PO4)3@carbon composite as anode for aqueous lithium ion batteries

In this paper, Li 1−x Na x Ti 2 (PO 4 ) 3 @carbon (x=0.01, 0.03, and 0.05) composites as anode for aqueous lithium ion batteries were synthesized by in situ coating approach. The doping of Na on Li sites did not break the lattice structure of LiTi 2 (PO 4 ) 3 , while the lattice volume was increased by doping of Na. Among Na-doped LiTi 2 (PO 4 ) 3 @carbon composites, Li 0.97 Na 0.03 Ti 2 (PO 4 ) 3 @carbon (LC-Na-3) demonstrated the best electrochemical properties . Compared with the pristine LiTi 2 (PO 4 ) 3 @carbon (LC) composite, LC-Na-3 composite exhibited better rate and cycling performance. LC-Na-3 composite delivered the discharge capacity of 98.5   mAh   g −1 at 0.2   C and 45.0   mAh   g −1 at 15   C, 10.9   mAh   g −1 and 32.1   mAh   g −1 larger than that of LC composite, respectively. Moreover, the discharge capacity retention for LC-Na-3 composite achieved 90.4%, 6.9% higher than that for LC composite at the rate of 2   C after 300 cycles. The improved electrochemical properties of Na-doped LiTi 2 (PO 4 ) 3 @carbon composite was ascribed to the decrease of charge transfer resistance and the acceleration of diffusion of lithium ions , resulting from the widening of diffusion channel for lithium ions, which was verified by XRD measurements.