Towards rational design of high performance Ni-rich layered oxide cathodes: The interplay of borate-doping and excess lithium

Abstract

Ni-rich layered oxide cathodes have received extensive attention because of their high specific capacities and cost-effectiveness resulting from a reduction in Co usage. However, Ni-rich layered oxide still suffer from the challenge of limited rate capability, capacity/voltage fading and safety issues that are mainly induced by significant Li/Ni cation mixing and structural instability during extended cycling. Herein, we demonstrate a fine-tuning of the surface structure and chemistry to facilitate the electrochemical kinetics and cycling stability of Ni-rich layered oxide through incorporation of borate doping and appropriate excess Li. The modified LiNi0.6Co0.2Mn0.2O2 cathode delivers a high reversible capacity of 188.2 mA h g−1, has enhanced cyclability with a capacity retention of 86% after 200 cycles, and has less voltage drop. Complimentary electron microscopy and spectroscopy techniques reveal that the interplay of borate polyanions and excess Li results in reduced cation mixing that induces fast kinetics, and stabilization of the oxygen close-packed structure that accounts for robust cycling stability. This work provides a promising strategy for designing high-performance layered oxide cathode materials.