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

Abstract 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 (≈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 ≈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 Na 3 V 2 PO 4 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 .