Ether-based electrolyte enabled Na/FeS2 rechargeable batteries

• The cyclability of Na/FeS2 system is greatly improved by the use of ether-based electrolyte for the first time.
• A sodiation capacity of 450 mAh/g is retained for FeS2 after 100 cycles.
• This work provides a new way to develop conversion reaction based materials for sodium ion batteries.

We demonstrate for the first time that by simply substituting ether-based electrolyte (1.0 M NaCF3SO3 in diglyme) for the commonly used carbonate-based electrolyte, the cyclability of FeS2 towards sodium storage can be significantly improved. A sodiation capacity over 600 mAh/g and a discharge energy density higher than 750 Wh/kg are obtained for FeS2 at 20 mA/g. When tested at 60 mA/g, FeS2 presents a sodiation capacity of 530 mAh/g and retains 450 mAh/g after 100 cycles, much better than the cycling performance of Na/FeS2 tested in carbonate-based electrolyte.

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