Enabling high working voltage and rate capability of NASICON cathode via moderately regulating coordination environment

Sodium super ionic conductor (NASICON)-type Na 3 V 2 (PO 4 ) 3 (NVP) has been considered as a promising cathode candidate for sodium ion batteries (SIBs) due to its three dimensional (3D) ionic diffusion channels, high structural and thermal stability. However, such cathode usually involves a two-electron reaction with the V 4+ /V 3+ couple at ~3.4 V, showing a limited specific capacity. Moreover, NVP always suffers from poor electronic conductivity and sluggish Na + diffusion kinetics , resulting in poor rate capability. Herein, a V-site Mn (15 mol%) regulation strategy together with 3D interconnected porous carbon/graphene framework has been developed for constructing Na 3.3 V 1.7 Mn 0.3 (PO 4 ) 3 @3D porous hybrids (3DP-NVMP-Mn0.3) for not only enhancing working voltage of the V 4+ /V 3+ couple but also activating electrochemical activity of the V 5+ /V 4+ couple in NVP cathode. Compared to 3DP-NVMP-Mn0.1 (5 mol% Mn) and 3DP-NVMP-Mn0.5 (25 mol% Mn), 3DP-NVMP-Mn0.3 exhibits the highest specific capacity of 119.8 mAh g −1 and the highest energy density of 413.0 Wh kg −1 at the material level at 0.1C, better rate capability up to 20C (89.2 mAh g −1 ), and a capacity retention of 75.87 % after 8000 cycles at 20C, outperforming the theoretical capacity (117 mAh g −1 ) and energy density (397 Wh kg −1 ) of NVP. • A moderate Mn regulation strategy has been developed in manipulating Na 3 V 2 (PO 4 ) 3 . • Na 3.3 V 1.7 Mn 0.3 (PO 4 ) 3 @3D porous hybrids enhance working voltage of V 4+ /V 3+ couple. • Such hybrids also activate electrochemical activity of V 5+ /V 4+ couple. • A capacity (119.8 mAh g −1 ) exceeding theoretical capacity of NVP has been achieved. • Such hybrids exhibit the highest energy density (413.0 Wh kg −1 ) at a material level.