Synergistic effect of uniform lattice cation/anion doping to improve structural and electrochemical performance stability for Li-rich cathode materials

Abstract

There has been extensive research into lithium-rich layered oxide materials as candidates for the nextgeneration of cathode materials in lithium-ion batteries, due to their high energy density and low cost; however, their poor cycle life and fast voltage fade hinder their large-scale commercial application. Here, we propose a novel cation/anion (Na+/PO43–) co-doping approach to mitigate the discharge capacity and voltage fade of a Co-free Li1.2Ni0.2Mn0.6O2 cathode. Our results show that the synergistic effect of cation/anion doping can promote long cycle stability and rate performance by inhibiting the phase transformation of the layered structure to a spinel or rock-salt structure and stabilizing the well-ordered crystal structure during long cycles. The co-doped sample exhibits an outstanding cycle stability (capacity retention of 86.7% after 150 cycles at 1 C) and excellent rate performance (153 mAh g−1 at 5 C). The large ionic radius of Na+ can expand the Li slab to accelerate Li diffusion and the large tetrahedral PO43– polyanions with high electronegativity stabilize the local structure to improve the electrochemical performance.