Free-Standing Soft Carbon Fibers with High Orientation for Na⁺ Storage to Achieve High Volumetric Capacity

Noncrystalline carbon materials typically encounter challenges of low volumetric capacity, high discharge plateau, and poor rate capability when utilized as sodium-storage anode materials. The effect of the orientation of carbon layers in noncrystalline carbon materials on sodium storage behavior remains unclear. This study clarifies the sodium storage behavior of high-carbon layer orientation soft carbon fiber materials and reveals the desolvation process of their ordered carbon layer structures as well as pore structure filling and sodium deposition processes, which enhanced the sodium storage capacity. When employed as a sodium-storage anode material, it demonstrates a plateau capacity of 218.9 mAh g^-1 and a volumetric capacity of 316.5 mAh cm^-3 at 50 mA g^-1. Remarkably, the material still exhibits a reversible capacity of 97.9 mAh g^-1 at a rate of 2 A g^-1. This study demonstrates the impact of carbon layer orientation on sodium storage behavior in carbon-based electrode materials and also provides a new insight for designing high-volumetric-capacity noncrystalline carbon materials.