Ultrafast synthesis of hard carbon anodes for sodium-ion batteries

Hard carbons (HCs) are a significantly promising anode material for alkali metal-ion batteries. However, long calcination time and much energy consumption are required for the traditional fabrication way, resulting in an obstacle for high-throughput synthesis and structure regulation of HCs. Herein, we report an emerging sintering method to rapidly fabricate HCs from different carbon precursors at an ultrafast heating rate (300 to 500 °C min^-1) under one minute by a multifield-regulated spark plasma sintering (SPS) technology. HCs prepared via the SPS possess significantly fewer defects, lower porosity, and less oxygen content than those pyrolyzed in traditional sintering ways. The molecular dynamics simulations are employed to elucidate the mechanism of the remarkably accelerated pyrolysis from the quickly increased carbon sp² content under the multifield effect. As a proof of concept, the SPS-derived HC exhibits an improved initial Coulombic efficiency (88.9%), a larger reversible capacity (299.4 mAh⋅g^-1), and remarkably enhanced rate capacities (136.6 mAh⋅g^-1 at 5 A⋅g^-1) than anode materials derived from a traditional route for Na-ion batteries.