Surface Spinel-Coated and Polyanion-Doped Co-Free Li-Rich Layered Oxide Cathode for High-Performance Lithium-Ion Batteries

Li-rich layered oxides (LLOs) are supposed to be the most competitive cathode materials for lithium-ion batteries (LIBs), because of the high theoretical specific capacities (>250 mAh g–1). However, there are some inherent inferiorities, such as the low initial Coulombic efficiency (ICE) and the rapid capacity/voltage decay, that hinder the large-scale commercial applications of LLOs. Herein, we successfully obtained spinel-coated and phosphate-doped Co-free Li-rich layered oxides (Co-free LLOs) by cotreatment methods, using weakly acidic and alkalinity (NH4H2PO4 solution), which could effectively improve the electrochemical performance. The spinel coating could not only accelerate the movement of Li+ but also restrain O2 release, while the doping PO43– could inhibit the transition-metal (TM) migration between the oxygen octahedral site and the oxygen tetrahedral site. The optimized Co-free LLOs cathode treated with 3% NH4H2PO4 solution could deliver a high ICE of 88% and a high discharge capacity up to 159.5 mAh g–1 after 500 cycles at 1C (1C = 250 mA g–1). Moreover, the voltage fading decreases from 0.64 mV to 0.32 mV per cycle during cycling. This work provides new insights for developing high-performance Co-free LLOs cathode materials.