Electrochemical performance and stability improvement of triclinic LiVOPO4 cathode material via simultaneous Y doping and YPO4 surface modification

Abstract

Here, we report the development of a facile approach in co-modification of triclinic lithium vanadyl phosphate [ε-LiVOPO4] with simultaneous yttrium (Y) doping and yttrium phosphate (YPO4) surface modification. Due to synergistic effects of YPO4 surface modification and Y doping, the resultant ε-LiVOPO4 (LVOP) exhibited significantly enhanced stability and electrochemical performance cycled in wide voltage 1.5–4.5 V. Among different proportions of Y (0, 3.5, 5, and 7 %), 5 % Y-doped sample (5 %Y-LVOP) exhibited the best electrochemical performance with a discharge capacity of 268 mAh g−1 at 0.1C and retained best cycling stability with capacity retention of 91 % after 40 cycles, showing stable high-voltage (4 V) performance with no capacity fade. The sample also showed best high-rate and long-term cycling stabilities with capacity retentions of 87 % after 40 cycles and 67 % after 200 cycles at relatively high current rates of 2C and 1C, respectively. Some of Y doped into LVOP expanded channels for Li-ion diffusion and resulted in improved ionic and electronic conductivity of 5 %Y-LVOP compared to pristine sample. In addition, YPO4 surface modification also improved cycling and thermal stability.