New materials for Li-ion batteries: synthesis and spectroscopic characterization of Li-2(FeMnCo)SiO4 cathode materials

Improving cathode materials is mandatory for next-generation Li-ion batteries. Exploring polyanion compounds with high theoretical capacity such as the lithium metal orthosilicates, Li2MSiO4 is of great importance. In particular, mixed silicates represent an advancement with practical applications. Here we present results on a rapid solid state synthesis of mixed Li-2(FeMnCo)SiO4 samples in a wide compositional range. The solid solution in the P2(1)/n space group was found to be stable for high iron concentration or for a cobalt content up to about 0.3 atom per formula unit. Other compositions led to a mixture of polymorphs, namely Pmn2(1) and Pbn2(1). All the samples contained a variable amount of Fe3+ ions that was quantified by Mossbauer spectroscopy and confirmed by the T-N values of the paramagnetic to antiferromagnetic transition. Preliminary characterization by cyclic voltammetry revealed the effect of Fe3+ on the electrochemical response. Further work is required to determine the impact of these electrode materials on lithium batteries.