Double‐Carbon‐Layer Coated Na 4 MnV(PO 4 ) 3 Towards High‐Performance Sodium‐Ion Full Batteries

Abstract As an improved structure of NASICON‐type Na 3 V 2 (PO 4 ) 3 cathode for sodium‐ion batteries, Na 4 MnV(PO 4 ) 3 (NMVP) has series advantages of low cost and weak biological toxicity through partial elemental substitution of manganese for vanadium. However, the low electronic conductivity and poor cycle stability of NMVP need to be solved for the purpose of practical application. Herein, the electronic conductivity and structural stability of NMVP material are enhanced through a double‐carbon‐layer coating strategy by a simple sol‐gel synthesis method. The coated double‐carbon layer can construct a conductive network and reduce the electrolytic corrosion for NMVP active material. Attributed to the robust structure and fast electrochemical kinetics, the decorated NMVP electrode exhibited an excellent sodium storage ability. It delivered a high capacity of 99.8 mAh g −1 at 1 C with a cumulative efficiency of 72.3% over 500 cycles, and the specific capacity can reach 81.3 mAh g −1 at a high rate of 10 C. The high cumulative efficiency of the half‐cell gives the NMVP full‐cell superior performance, which delivered a high capacity of 93.8 mAh g −1 with capacity retention of 86.1% over 100 cycles at 1 C when assembled with a hard carbon anode.