Dual‐Carbon‐Coated Na2FeP2O7 Cathode Materials for Na‐Ion Batteries with Superior High‐Rate and Cycling Stability

The iron‐based pyrophosphate Na 2 FeP 2 O 7 (NFP) is considered as one of the most promising cathodes for sodium‐ion batteries (SIBs) due to its low‐cost and superior structure stability, yet it usually suffers from poor intrinsic electronic conductivity. Herein, a two‐step carbon‐coating technique has been developed to synthesize high‐performance NFP@C cathode materials by controlling the NFP particle size and the coating layer uniformity. The first step of in‐situ carbon coating greatly restrains the excessive growth of NFP crystals with a shortened Na‐ion diffusion path. Meantime, the extra secondary carbon‐coating is adopted to repair some exposed areas, guaranteeing the full coverage of NFP particles for rapid electronic transfer. As a consequence, the as‐obtained NFP@C cathode delivers a high discharge capacity of 95.2 mAh g −1 at 0.1 C (theoretical value: 97 mAh g −1 ) and with high‐rate capability (75.2 mAh g −1 at 5 C) within 2.0–4.0 V. A capacity retention of 95.3% can be achieved even after 500 cycles at 5 C in coin‐type cells. Such superior electrochemical performances are expected to quickly promote the applications of NFP in SIBs.