Extending the pyrophosphate chemistry for rechargeable Na-ion batteries, here we report the synthesis and electrochemical characterization of Na 2FeP 2O 7, a novel Fe-based cathode material for sodium batteries. Prepared by conventional solid-state as well as solution-combustion synthesis (at 600 °C), the Na 2FeP 2O 7 adopts a triclinic structure (space group: P-1) with three-dimensional channels running along , [- 110] and [01-1] directions. With no further optimization, the as-synthesized Na 2FeP 2O 7 cathode was found to be electrochemically active, delivering a reversible capacity of 82 mAh·g - 1 with the Fe 3 +/Fe 2 + redox potential centered around 3 V (vs. Na/Na +). With its theoretical capacity of ~ 100 mAh·g - 1 and potential high rate-capability, Na 2FeP 2O 7 forms a promising novel cathode material, with the distinction of being the first ever pyrophosphate-class of cathode for sodium-ion batteries.
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