Time-programmed microbe-mediated precursor engineering enables closed-pore and interlayer spacing optimization in hard carbon for sodium-ion batteries.

Abstract

Biomass-derived hard carbon represents a highly promising anode material for sodium-ion batteries. However, its large-scale commercialization is severely hindered by critical drawbacks, including low reversible specific capacity and poor cycling stability at high current densities, which originate from an insufficient closed-pore architecture and narrow interlayer spacing. Herein, we developed a time-programmed microbe-mediated precursor engineering strategy based on Bacillus subtilis. Utilizing the microbial enzyme system, the lignocellulosic components of the precursor are selectively degraded under mild conditions. By tuning the microbial treatment duration, we achieved accurate regulation of the precursor's chemical composition, which in turn synergistically governs the expansion of interlayer spacing, the construction of closed-pore architecture, and the formation of oxygen-containing carbonyl functional groups in the resulting hard carbon. The optimized hard carbon (HC-BT3D) exhibits synergistically enhanced electrochemical performance. It delivers a reversible specific capacity of 361.1 mAh g-1 with an initial coulombic efficiency of 89.9% and retains 88.5% of the initial capacity even after 1000 cycles at the increased current density of 1 A g-1. In addition, in situ analyses precisely reveal that the sodium storage process of hard carbon follows the mechanism of "adsorption-intercalation-filling". This work integrates time-programmed microbe-mediated control into hard carbon precursor engineering, provides a green methodological approach for the synergistic optimization of multiscale structural parameters, and offers valuable insights for the structural design of high-performance hard carbon anodes.