Improvement of stability and capacity of Co-free, Li-rich layered oxide Li_1.2Ni_0.2Mn_0.6O₂ cathode material through defect control

Layered oxides based on manganese (Mn), rich in lithium (Li), and free of cobalt (Co) are the most promising cathode candidates used for lithium-ion batteries due to their high capacity, high voltage and low cost. These types of material can be written as xLi₂MnO₃·(1 − x) LiTMO₂ (TM = Ni,Mn,etc.). Though, Li₂MnO₃ is known to have poor cycling stability and low capacity, which hinder its industrial application commercially. In this work, Li_1.2Ni_0.2Mn_0.6O₂ materials with different amounts of structural defects was successfully synthesized using powder metallurgy followed by different cooling processes in order to improve its electrochemical properties. Microstructural analyses and electrochemical measurements were carried out on the study samples synthesized by a combination of X-ray diffraction, transmission electron microscopy, and cyclic voltammetry. It is found that the disorder of the transition metal layer in Li₂MnO₃ promotes its electrochemical activity, whereas the Li/Ni antisites of the Li layer maintain the stability of its local structure. The material with optimal amount of structural defects had an initial capacity of 188.2 mAh g⁻¹, while maintaining an excellent specific capacity of 144.2 mAh g⁻¹ after 500 cycles at 1C. In comparison, Li_1.2Ni_0.2Mn_0.6O₂ without structural defect only gives a capacity of 40.8 mAh g⁻¹ after cycling. This microstructural control strategy provides a simple and effective route to develop high-performance Co-free, Li-rich Mn-based cathode materials and scale-up manufacturing.