Tailoring Pseudo-Graphitic Domain by Molybdenum Modification to Boost Sodium Storage Capacity and Durability for Hard Carbon.

Abstract

Hard carbon (HC) stands out as the most prospective anode for sodium-ion batteries (SIBs) with significant potential for commercial applications. However, some long-standing and intractable obstacles, like low first coulombic efficiency (ICE), poor rate capability, storage capacity, and cycling stability, have severely hindered the conversion process from laboratory to commercialization. The above-mentioned issues are closely related to Na+ transfer kinetics, surface chemistry, and internal pseudo-graphitic carbon content. Herein, constructing molybdenum-modified hard carbon solid spheres (Mo2C/HC-5.0), both the ion transfer kinetics, surface chemistry, and internal pseudo-graphitic carbon content are comprehensively improved. Specifically, Mo2C/HC-5.0 with higher pseudo-graphitic carbon content provides a large number of active sites and a more stable layer structure, resulting in improved sodium storage capacity, rate performance, and cycling stability. Moreover, the lower defect density and specific surface area of Mo2C/HC-5.0 further enhance ICE and sodium storage capacity. Consequently, the Mo2C/HC-5.0 anode achieves a high capacity of 410.7mA h g-1 and an ICE of 83.9% at 50mA g-1. Furthermore, the material exhibits exceptional rate capability and cycling stability, maintaining a capacity of 202.8mA h g-1 at 2 A g-1 and 214.9mA h g-1 after 800 cycles at 1 A g-1.