Perfect reversibility of the lithium insertion in FeS2: The combined effects of all-solid-state and thin film cell configurations

Abstract All-solid-state thin film batteries based on sputtered pyrite electrodes, a lithium phosphorus oxynitride electrolyte and a lithium anode were prepared and characterized. The successive reduction of both S 2 2 − and Fe 2 + species led to an impressive volumetric discharge capacity, five times higher than the one for LiCoO 2 . Excellent reversibility and capacity retention were obtained during the first and the subsequent 800 charge–discharge cycles. A continuous cycling in the low voltage domain was found to be detrimental to the reversibility of the conversion reaction, suggesting a progressive evolution of the phase distribution inside the electrode. The initial capacity was easily recovered after few full oxidation cycles.