The new electrochemical reaction mechanism of Na/FeS2 cell at ambient temperature

• We have fabricated the FeS2 particle by hydrothermal process.
• We have examined the electrochemical behaviors of FeS2 with sodium.
• We have clarified the charge reaction mechanism of Na/FeS2 cell for the first time.

FeS2 synthesized by hydrothermal method was used for sodium batteries for the first time. A large initial discharge capacity of 771 mAh g−1 and a high reversible capacity of 521 mAh g−1 were obtained. The reaction mechanism of electrochemical de-sodiation (charge) was investigated after the initial discharge. Our results have demonstrated that the composition and structure of electrode after the charging to 3.0 V could not recover its original state of FeS2 and a new phase of NaFeS2 was revealed. This should be responsible to the large irreversible capacity in the first cycle and the high discharge and charge plateaus after the initial cycle.