Surface characterization and stability phenomena in Li2FeSiO4 studied by PES/XPS

Abstract

Photoelectron spectroscopy (PES) has been used to characterise the surface of Li₂FeSiO₄ cathodes extracted from lithium-ion batteries. Pristine, uncycled, air-exposed electrodes were first analysed and found to carry significantly greater amounts of Li₂CO₃ on their surfaces than electrodes stored under inert atmosphere. The surface film formed on electrochemical cycling of Li₂FeSiO₄ electrodes at 60 °C using a LiN(SO₂CF₃)₂ salt based electrolyte revealed high salt stability and only small amounts of solvent reaction products. These were mainly of Li-carboxylate type; neither carbonates nor LiF were found. The excellent capacity retention (<3% over 120 cycles) and minimal irreversible capacity during the first cycle are probably a direct result of this very thin surface film. Li₂FeSiO₄ must therefore be seen as a most promising (and potentially cheap) positive electrode material for future large-scale Li-ion battery applications.