Converting sustainable biomass into a high-performance carbon anode for potassium-ion batteries (KIBs) remains mostly an empirical pursuit, hindered by an inability to tune pore hierarchy and defect density. Herein, we uncover a design principle in which the identity of the metal ion within a deep eutectic solvent (DES) governs the carbonization pathway through a precise balance of coordination and decomposition chemistry. Using a choline chloride-urea-MCl2 (M = Ca, Mg, Zn), we show that only Ca2+ guides the formation of a nitrogen-doped carbon with a kinetically ideal structure for K+ storage, featuring expanded interlayer spacing (0.376 nm), optimized defect density, and a favorable pyrrolic-N configuration. This Ca2+-regulated carbon anode achieves a superior combination of reversible capacity as high as 320 mAh g-1, exceptional rate capability of 212 mAh g-1 at 1 A g-1, and long-term stability (89% retention after 2000 cycles). This work transforms DES from passive green solvents into programmable reaction media, offering a universal principle for predictively designing biomass carbons for potassium-ion storage.
Huang et al. (Thu,) studied this question.