Modulating Intrinsic Defect Structure of Fibrous Hard Carbon for Super-Fast and High-Areal Sodium Energy Storage

Creating defects by heteroatom doping is commonly approved in respect of enhancing fast sodium-ion storage of carbonaceous anodes ascribing to rich external defects, but the contribution of intrinsic carbon defects (e.g., vacancy) in improving rate-capability has rarely been investigated. Here, a bio-derived fibrous hard carbon with high-reversible intrinsic defects is synthesized via metal-assisted-catalytic strategy. It is found that sp(2)-hybridized carbon is united through catalytic-tuning during thermal-etching process along with the formation of low-potential planar intrinsic carbon defects (vacancies and non-hexagonal carbon rings) by sacrificing poor-reversible carbon edges. Such integrated structures greatly improve the reversibility of defective sites and charge transfer kinetics, thus enhancing the slope sodium-storage capacity of carbon below 1 V even at high current densities. Thus-obtained fibrous carbon anodes enable boosted initial coulombic efficiency (approximate to 90%) and ultrahigh-rate capability in both half- (222.2 mAh g(-1)at 50 A g(-1)) and full-cell (200 C, charged/discharged in approximate to 10 s). Interestingly, compared with meso-/macroporous structures, such micropore-dominated carbon fibers are more beneficial for fabricating high-mass-loading, crack-free thick electrodes (>10 mg cm(-2)) with considerable areal-capacity over 3.0 mAh cm(-2). Paired with high-loading Na3V2PO4 cathode (14.4 mg cm(-2)), full-cell achieves admirable areal-capacity over 1.4 mAh cm(-2) and peak areal-energy/power-density of 3.2/74 mW cm(-2).