Efficient electrode materials, that combine high power and high energy, are the crucial requisites of sodium‐ion batteries (SIBs), which have unwrapped new possibilities in the areas of grid‐scale energy storage. Hard carbons (HCs) are considered as the leading candidate anode materials for SIBs, however, the primary challenge of slow charge‐transfer kinetics at the low potential region (<0.1 V) remains unresolved till date, and the underlying structure–performance correlation is under debate. Herein, ultrafast sodium storage in the whole‐voltage‐region (0.01–2 V), with the Na+ diffusion coefficient enhanced by 2 orders of magnitude (≈10–7 cm2 s–1) through rationally deploying the physical parameters of HCs using a ZnO‐assisted bulk etching strategy is reported. It is unveiled that the Na+ adsorption energy (Ea) and diffusion barrier (Eb) are in a positive and negative linear relationship with the carbon p‐band center, respectively, and balance of Ea and Eb is critical in enhancing the charge‐storage kinetics. The charge‐storage mechanism in HCs is evidenced through comprehensive in(ex) situ techniques. The as prepared HCs microspheres deliver a record high rate performance of 107 mAh g–1 @ 50 A g–1 and unprecedented electrochemical performance at extremely low temperature (426 mAh g–1 @ −40 °C).
Resin derived hard carbons (HCs) generally demonstrate remarkable electrochemical performance for both sodium ion batteries (SIBs) and potassium‐ion batteries (KIBs), but their practical applications are hindered by their high price and high temperature pyrolysis (≈1500 °C). Herein, low‐cost pitch is coated on the resin surface to compromise the cost, and meanwhile manipulate the microstructure at a relatively low pyrolysis temperature (1000 °C). HC‐0.2P‐1000 has a large number of short graphitic layer structures and a relatively large interlayer spacing of 0.3743 nm, as well as ≈1 nm sized nanopores suitable for sodium storage. Consequently, the as produced material demonstrates a superior reversible capacity (349.9 mAh g−1 for SIBs and 321.9 mAh g−1 for KIBs) and excellent rate performance (145.1 mAh g−1 at 20 A g−1 for SIBs, 48.5 mAh g−1 at 20 A g−1 for KIBs). Furthermore, when coupled with Na3V2(PO4)3 as cathode, the full cell exhibits a high energy density of 251.1 Wh kg−1 and excellent stability with a capacity retention of 73.3% after 450 cycles at 1 A g−1.
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