Capacity Fading in Li<inf>2</inf>FeSiO<inf>4</inf> Cathode Material: Intrinsic or Extrinsic

We report the origin of capacity fading in Li2FeSiO4 cathode material, while addressing the challenges associated with the synthesis of phase-pure Li2FeSiO4 positive electrode materials in bulk and nanostructured geometries. The process has been optimized to remove iron oxide (Fe2O3) impurities and for effective carbon coating on a Li2FeSiO4 nanostructured core using a carbon source precursor during the synthesis process. X-ray diffraction measurements confirm the phase purity and nanocrystalline nature of synthesized materials. UV–visible spectroscopic measurements are carried out to understand the electronic/optical characteristics, and their correlation with materials’ electrochemical performance is investigated. The impact of iron charge state in an FeO4 tetrahedra configuration is correlated to the electrochemical performance together with the lithium-ion transporting states. The Jahn–Teller active FeO4 tetrahedra may show structural distortion in the sub-lattice of Li2FeSiO4 with different charge states and may be the main source of capacity fading in Li2FeSiO4 cathode material from the first cycle onwards.