Zn/Ti dual concentration-gradients surface doping to improve the stability and kinetics for Li-rich layered oxides cathode

Abstract

Li-rich layered oxides (LLOs) with high specific capacity and low cost are potential cathode materials for next-generation lithium-ion batteries (LIBs). However, surface side reactions and structural instability at high operating voltages lead to poor cycling performance and sluggish kinetics. Herein, we report a novel Zn/Ti dual concentration-gradients surface modification strategy for LLOs, in which the Ti content gradually increases from the interface to the particle interior while the Zn content gradually decreases and finally remains at a relatively stable level. This strategy successfully induces the formation of functionalized surfaces and the Ti doping is more favorable to stabilize Mn4+, while the subsequent Zn doping is more benign to Ni3+. In addition, the strong Ti-O bond serves to stabilize the oxygen framework, while the blocking effect of Zn2+ in the Li layer inhibits the migration path of transition metal (TM) elements. In conclusion, the synergistic effect of double ion co-doping stabilizes the surface structure, improves the redox kinetics, and mitigates the degradation of electrochemical performance, with 24.1% increase in capacity retention compared to the pristine LLOs after 150 cycles at 0.5 C. This study provides an effective strategy for the design of robust LLOs cathode materials for LIBs.