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

Abstract

The iron‐based pyrophosphate Na2FeP2O7 (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.