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 Lit but also restrain O-2 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.

Automated summary

In this study, spinel-coated and phosphate-doped Co-free Li-rich layered oxides (Co-free LLOs) were successfully prepared using cotreatment methods, which showed improved electrochemical performance. The spinel coating accelerated the ion movement and restrained oxygen release, while the doping of phosphate inhibited transition metal migration. The optimized Co-free LLOs cathode treated with 3% NH4H2PO4 solution exhibited high initial Coulombic efficiency and discharge capacity, as well as reduced voltage fading during cycling.