FeP Quantum Dots Confined in Carbon-Nanotube-Grafted P-Doped Carbon Octahedra for High-Rate Sodium Storage and Full-Cell Applications

Transition metal phosphides (TMPs) possess high theoretical sodium storage capacities, but suffer from poor rate performance, due to their intrinsic low conductivity and large volume expansion upon sodiation/desodiation. Compositing TMPs with carbon materials or downsizing their feature size are recognized as efficient approaches to address the above issues. Nevertheless the surface-controlled capacitive behavior is generally dominated, which inevitably compromises the charge/discharge platform, and decreases the operational potential window in full-cell constructions. In this work, a novel architecture (FeP@OCF) with FeP quantum dots confined in P-doped 3D octahedral carbon framework/carbon nanotube is rationally designed. Such structure enables a simultaneous enhancement on the diffusion-controlled capacity in the platform region (2.3 folds), and the surface-controlled capacity in the slope region (2.9 folds) as compared to that of pure FeP. As a result, an excellent reversible capacity (674 mAh g(-1)@ 0.1 A g(-1)) and a record high-rate performance (262 mAh g(-1) @ 20 A g(-1)) are achieved. A full-cell FeP@OCF// Na3V2(PO4)(3) is also constructed showing an outstandingly high energy density of 185 Wh kg(-1) (based on the total mass of active materials in both electrodes), which outperforms the state-of-the art TMP-based sodium-ion battery full cells.