A green synthesis strategy for lithium/sodium-ion battery anodes: morphology and structure engineering in biochar to boost comprehensive electrochemical performance

Abstract

Spherical biochar materials emerge as potential anode candidates for the forthcoming generation of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), attributed to their chemical stability and inherent safety. However, their industrial application is limited by poor electrochemical performance and pollution from the preparation process. Focusing on these issues, this work presents a green synthesis strategy that combines both morphological and structural engineering, utilizing ultrapure water as the sole reaction medium. Through successive hydrothermal–carbonization–hydrothermal treatments, quasi-spherical biochar (CHCs-T) has been successfully synthesized. CHCs-900 exhibits a distinct and uniformly distributed quasi-spherical structure with a maximum carbon interlayer spacing (d = 4.11 Å) and the largest specific surface area (S_BET = 536.52 m² g⁻¹). When utilized as an anode material for both LIBs and SIBs, CHCs-900 demonstrates excellent comprehensive electrochemical performance. Moreover, techniques such as electrochemical kinetics analysis and ex situ physicochemical characterization reveal that the quasi-spherical design of CHCs-900 facilitates efficient Na⁺ transport and the enlarged carbon layer spacing reduces the diffusion energy barrier of Na⁺, while its large surface area and high porosity enhance charge transfer. This work underscores the importance of morphology and structure in advancing battery performance while minimizing environmental impact, aligning with global sustainability goals.