Investigating the particle size effect on the electrochemical performance and degradation of cobalt-free lithium-rich layered oxide Li1.2Ni0.2Mn0.6O2

Abstract

Lithium-rich layered oxides (LRLOs) as Li-ion battery positive electrode materials promise to deliver superior specific capacity (> 270 mAh g−1) boosting the driving range of electric vehicles (EVs). Interestingly, these materials do not strictly require cobalt in their formulation, solving the supply, environmental, and ethical issues associated to this metal. Herein the synthesis of Co-free Li1.2Ni0.2Mn0.6O2 (LRNM) via lab-scale co-precipitation and solid-state reaction is reported, employing transition metal salts with different anions. These yield to different morphological features of the resulting LRNMs, also impacting the physicochemical characteristics and electrochemical performance. The use of sulfate TMs results in a material (LRNM-S) with smaller crystallite and particle sizes, which displays very high specific capacity (more than 270 mAh g−1 at C/20) and excellent rate capability (109 mAh g−1 at 10C). However, its capacity and voltage fading are also more pronounced than for the acetate-based material (LNRM-A), which owns twice as large crystallites achieving capacity and voltage retention both higher than 97% over 100 cycles. Our investigation unveiled the prevalent trade-off between full activation and exploitation of the LRLOs high specific capacity and anion redox against structural degradation and accelerated ageing of the materials.