Flame-made Lithium Transition Metal Orthosilicates

Abstract

Li2MSiO4 (M = Fe, Mn, Co) compounds have since their discovery gained increased attention as alternative, inexpensive and inherently safe positive electrodes for Li-ion batteries. To meet the required performance for an electrode, sophisticated, complex and time-consuming synthesis measures are required at present. Here, we present a time-efficient and scalable aerosol combustion method with subsequent annealing, leading to nanoscale and carbon-coated Li2FeSiO4 and Li2Fe0.5Mn0.5SiO4. Using liquid-feed flame spray pyrolysis, we demonstrate synthesis of orthosilicate materials, with phase purities exceeding 95 wt. % according to Rietveld quantifications, in a relatively short time. The importance of the precursor concentration, in order to obtain loosely agglomerated nanoparticles, is discussed and the long-term performance is investigated. In the case of Li2FeSiO4, the optimised precursor concentration yielded particles of about 30 nm, which delivered an initial discharge capacity of up to 150 mAhg−1 at 60 °C and C/20. Furthermore, over 50% of the capacity is retained at a high rate of 5C, and long-term cycling showed outstanding capacity retention of over 90% after 300 cycles at a moderate rate of C/2. Li2Fe0.5Mn0.5SiO4 on the other hand, was shown to suffer from a severe capacity fade, and upon prolonged cycling the redox activity can be attributed solely to Fe.