Etching amorphous components to optimize carbon crystalline micro-environment in hard carbon and boosting of low-potential sodium-ion storage with improved rate capability

The energy density of sodium-ion batteries depends significantly on advanced carbon anodes design, where optimizing crystallinity and porosity is critical for improving both Na⁺ storage and rate capability. Herein, a facile pre-etching strategy is proposed to prepare high-performance coal-based hard carbon to selectively remove amorphous components and reconstruct carbon crystalline micro-environment, thereby enabling all-round improvements in Na⁺ storage properties. Pre-etching at 400°C selectively decomposes the unripe components including aliphatic and hydrogenated sidechain structures within complex coal matrix to release spatial freedom for coal-based microcrystalline rearrangement, thereby enabling the formation of isotropic-oriented carbon microcrystalline with enlarged interlayer spacing, reduced amorphous carbon and augmented sub-nanopores. Particularly, benefiting from the optimized microcrystalline and porosity, the obtained carbon anode achieves the state-of-the-art comprehensive performance for coal-derived hard carbons, delivering a reversible capacity up to 333 mAh g⁻¹ with a greatly upgraded low-potential plateau of 248 mAh g⁻¹ and an improved rate capability (203 mAh g⁻¹ at 1 C). The constructed full battery can exhibit an energy density of 240 Wh kg⁻¹ with a voltage of 3.23 V. Our strategy is easily compatible with existing production lines, and achieves a comprehensive yield exceeding 60 %, holding significant potentials for directly converting coal precursor to advanced carbon anodes.