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

• All-solid-state lithium cells comprising a pyrite thin film were made by sputtering.
• The reversibility of the reaction of FeS2 with lithium is excellent.
• The capacity of pyrite thin films is five times higher than the one for LiCoO2.
• Capacity fading occurs during continuous cycling in the conversion reaction domain.
• The recovery of the initial behavior is achieved by a full charge of the battery.

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 S22 − and Fe2 + species led to an impressive volumetric discharge capacity, five times higher than the one for LiCoO2. 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.

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