Capacity Fading in Li₂FeSiO₄ 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.