Mechanochemistry transforming high-surface-area coal-based activated carbon into densified carbon with optimized multi-scale structures for enhanced sodium/potassium ion storage

Practical sodium/potassium-ion batteries require carbon anodes with both high gravimetric and volumetric performances, for which engineering carbon material with simultaneous high-density architecture and well-organized structures is the key. Herein, a simple and scalable strategy via a mechanochemistry process is developed to transform high-surface-area activated carbon into densified carbon with optimized multi-scale structures in term of greatly decreased ineffective pores, a shorten carbon lattice and modified carboxyl-dominant functional groups. In the mechanochemical process, the rearrangement of ineffective pores was achieved by high-energy collision and shear effects between grinding balls and particles, in which micropores were concentrated at ∼0.5 nm, followed by carboxylic modification on the fresh edges in air atmosphere (CO2). The reduced ineffective pores and enriched functional groups have improved reversibility and kinetics of Na/K ions storage in carbon matrix, resulting in large reversible capacities, excellent rate capabilities even at a high-loading mass of 5 mg·cm−2. Electrochemical kinetic analysis and ex-situ X-ray diffraction reveal the dominant capacitive storage mechanism for Na+, and theorical calculations demonstrate that the grafted carboxyl groups in carbon matrix promote Na+ reversible storage with multi-ion adsorption configuration, thus improving capacitive storage capacities. This work demonstrates the feasibility of transforming coal-based porous carbon into high-performance anode materials.