Metal-doped Li 2Ti 3O 7 with ramsdellite structure as high voltage anode for new generation Li-ion batteries

Abstract

Li 2Ti 3O 7 is considered to be a promising insertion material for high power battery applications because of its open structure with accessible vacancies. High-rate cycling ( C/10 and 1.5 C) has been performed and results show small irreversibility and low polarisation, but capacity losses are noticed during cycling. Partly substituting Ti IV with Fe III improves the cyclability but a significant irreversible part is obtained due to the participation of iron in the insertion mechanism. This additional reduction level lowers with a combination of two transition elements, Fe and Ni, on the ramsdellite framework sites. Moreover, lower polarisation and higher capacities are observed. In this work, Ti IV and Li are partly replaced by a combination of three elements (Fe III, Ni II and Al III) in order to further improve the electrochemical performances. The difference in charge balance is obtained by metal and oxygen vacancies, which implies new vacancies and a better accessibility to the existing vacancies for lithium insertion. Several characterisation methods have been used on three different samples (Fe, Fe/Ni and Fe/Ni/Al), which made it possible to observe wider channels in the distorted ramsdellite lattice. In this case, lithium ions circulate more easily into the channels resulting in better reversibility upon cycling, which is necessary for high-rate cycling.