Mg/Ta dual-site doping of high-nickel layered cathode material LiNi0.9Co0.1O2 for extended cycling and thermal stability

Abstract

Due to its high specific capacity and low cost, high-nickel layered oxide LiNi0.9Co0.1O2 has found promising application as the cathode materials for lithium-ion batteries. However, the crystallographic instability induced by Li+/Ni2+ anti-site exchange, the interfacial parasitic reactions and the microcracking caused by internal stress jointly contribute to the mechano-chemical failure of LiNi0.9Co0.1O2, leading to its fast capacity decay and high thermal stability concern. In this regard, a Mg/Ta dual-site doping strategy was proposed for LiNi0.9Co0.1O2, for which Mg2+ was doped in situ during the synthesis of cathode precursor, while Ta5+ ions were incorporated after the precursor synthesis. This novel synthesis approach leads to unique dual-site occupations of Mg2+ and Ta5+ in the 3a and 3b crystallographic sites respectively. The Mg2+ ions residing in 3a site can function as pillar ions by preventing the Li+/Ni2+ anti-site exchange and inhibiting layered to rock-salt phase transition. The Ta5+ ions occupying 3b site not only leads to the expanded lithium layer spacing but also creates interfacial protection and well-ordered microstructure in LiNi0.9Co0.1O2. Consequently, the dual-site-doped LiNi0.9Co0.1O2 outperforms the pristine and single-site-doped samples. For instance, its full cell shows a greatly enhanced cycling stability from 57.3 % to 90.5 % after 300 cycles at 1C/1C and well improved thermal stability from 205.2 °C to 225.6 °C, compared to the pristine sample. This Mg/Ta dual-site doping strategy provides a facile and practical way to improve the electrochemical and thermal performances of high-nickel layered cathode material LiNi0.9Co0.1O2.