Regulating microstructure of walnut shell-derived hard carbon for high rate and long cycling sodium-based dual-ion batteries

Sodium-based dual-ion batteries (SDIBs) have been considered as promising candidates for large-scale energy storage applications by virtue of low cost, eco-friendliness and high cell voltage. However, due to the lack of a suitable anode to accommodate large Na+ ions, SDIBs generally suffer from poor rate capability and cycling stability. In this paper, a new strategy has been proposed to improve Na+ storage in walnut shell-derived hard carbon (WSC) by adjusting the ratio of disordered region to pseudo-graphitic region (DR/PGR) in its microstructure. The WSC sample (WSC-1200) with optimized DR/PGR ration delivered an extremely high reversible capacity of 336.5 mA h g-1 at 0.5 A/g and presented a promising high-rate cycling performance (up to 106 mA h g-1 at 10 A/g over 10,000 cycles). The assembled WSC-1200//Graphite SDIB exhibited an ultra-long cycle life over 30,000 cycles at a high rate of 5 A/g. In addition, this SDIB delivered an extremely high energy density up to 172.1 Wh kg- 1 at a power density of 68.8 W kg- 1. This work suggests that optimizing the ratio of different carbon phases can be an effective mean to pursue a relatively high specific capacity for Na+ storage.