Mechanistic Insights into the Interactions between a New Type of Hard Carbon Anode and Organic Electrolytes in Sodium-Ion Batteries

Hard carbons (HCs) are a promising class of anode materialforsodium-ion batteries (SIBs) since they exhibit excellent initial Coulombicefficiency (ICE) and rate performance with glyme-based electrolytes.However, the mechanisms behind such an excellent cell performanceremain ambiguous. Herein, we report on a combined experimental andtheoretical study to understand how and why a new type of biomass-derivedhard carbon has good compatibility with the glyme-based electrolytevs ester-based counterpart. We first show with theoretical moleculardynamics (MD) simulations that the solvation structure of glyme-Na+ has high binding energy and large volume, thus repellingthe anion (from the Na salt) away from attacking the HC anode andpromoting the formation of a stable solid electrolyte interface (SEI)layer. We then show X-ray photoelectron spectroscopy (XPS) analysis,revealing a higher concentration of inorganic materials in the SEIformed with glyme-based electrolyte. We also employ micromechanicaltesting in combination with MD simulations to demonstrate that theglyme-derived SEI possesses a higher Young's modulus and uniforminterfacial stress distribution than the ester-based counterpart.Because of these unique properties, the new HC anode with the glyme-basedelectrolyte exhibits excellent electrochemical performance, e.g.,332.8 mAh g(-1) at 0.05 C in the initial cycle with93.4% initial Coulombic efficiency (ICE), 81% capacity retention rateafter 1000 cycles at 1.0 C, and 245 mAh g(-1) rateperformance at 1.0 C. Weprepare hard carbon by reusing waste biomass raw materialsto maximize resource utilization, which is a sustainable method.