Probing Sn substitution in Li1.2Ni0.13Co0.13Mn0.54-xSnxO2 as a cathode material for Li-ion batteries

Abstract

Layered Li-rich/Mn-rich NMC is characterized by a high initial capacity of more than 250 mAh/h and a lower cost and higher thermal stability than LiCoO2.1 However, its commercialisation is currently still hampered by significant voltage fade, most certainly related to irreversible transition metal migration upon electrochemical cycling.2 For example the reduction of Mn4+ to Mn3+ and subsequent migration causes a transition from a layered to a spinel structure, having a devastating effect on the electrochemical properties. Substitution of Mn4+ by isovalent, redox inactive cations which are supposed to be not prone to migration upon charging, is believed to be a valuable strategy to stabilize the layered structure upon charging.3 Here, we probe the partial substitution of Sn4+ for Mn4+ in Li-rich/Mn-rich NMC. Via an extended series of characterization techniques, including XRD, STEM-EDX, HAADF-STEM and ABF-STEM, the structural properties, including substitution limit, layeredness and cation ordering, of Sn substituted Li1.2Ni0.13Co0.13Mn0.54-xSnxO2 are investigated and correlated with both synthesis method and electrochemical performance.