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

• Multi-redox triclinic lithium vanadyl phosphate ε -LiVOPO 4 (LVOP) • Simultaneous yttrium (Y) doping and yttrium phosphate (YPO 4 ) surface modification. • 5% Y-doped sample (5%Y-LVOP) exhibited discharge capacity of 268 mAh g -1 at 0.1C. • Stable high-voltage (4 V) performance with no capacity fade. • ε -LiVOPO 4 showed enhanced stability and electrochemical performance. Here, we report the development of a facile approach in co-modification of triclinic lithium vanadyl phosphate [ ε -LiVOPO 4 ] with simultaneous yttrium (Y) doping and yttrium phosphate (YPO 4 ) surface modification. Due to synergistic effects of YPO 4 surface modification and Y doping, the resultant ε -LiVOPO 4 (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 0.1 C 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 2 C and 1 C, 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, YPO 4 surface modification also improved cycling and thermal stability.