Improving the electrochemical properties of Ni-based cation-disordered cathode by Fe and F co-doping

Cation-disordered rock-salt cathodes have attracted extensive attention due to their high capacity and energy density . However, the excessive redox reaction of O 2- causes a severe impairment of Ni capacity and the release of O 2 , leading to the poor cycle stability and voltage decay for Li-Ni-Nb-O cathodes. In our work, the oxyfluoride compounds Li 1.23 Ni 0.3 Nb x Fe y O 2- z F z with various doping concentrations of Fe and F are successfully synthesized by solid state reaction using high-energy ball milling. Apart from observing the plateau at around 4 V with the redox reaction of Ni, a new plateau at approximately 2.6 V is observed due to the redox reaction of Fe. The doping of Fe on Nb increases the discharge capability and the co-doping of F on O further improves cycle stability. With the optimized doping amount of Fe ( y  = 0.16) and F ( z  = 0.15), Li 1.23 Ni 0.3 Nb 0.30 Fe 0.16 O 0.85 F 0.15 can deliver a discharge capacity of 347.1 mAh/g at a current density of 20 mA/g after the activation process in subsequent cycles. After 20 cycles at 20 mA/g, the capacity retention is 181.6 mAh/g, and after 100 cycles at 50 mA/g, the discharge capacity remains 102.2 mAh/g.