Fast-growing flowering aquatic plant, Wolffia-derived porous biochar as a sustainable anode material for lithium-ion batteries

Wolffia (referred to as “Khai-phum” in Thailand) is a high-biomass-yield resource that offers advantages for energy production and future human food supplies. In this study, Wolffia was evaluated as an alternative sustainable biomass-based carbon precursor for the fabrication of anode materials in lithium-ion batteries (LIBs). Compared with the non-activated material, ZnCl 2 activation markedly eroded the WDPB surface, exposing micropores, mesopores, and macropores. At 800 °C, the specific surface area (SSA) values displayed negligible variation across all WDPBs with different ZnCl 2 ratios, owing to pore expansion and structural collapse. Notably, although WDPB1-800 exhibited the lowest R ct due to its prevalence of micropores and absence of macropores, it did not demonstrate superior electrochemical performance. While micropore structures are advantageous as they provide additional active sites for lithium storage, they also impede lithium-ion and electrolyte diffusion compared to mesopores and macropores, consequently impairing overall ion transport and electrochemical performance. Owing to its highly disordered carbon structure and hierarchical pore architecture, WDPB2-800 exhibited the best electrochemical performance as an anode in LIBs, by optimizing kinetic reactions whilst ensuring rapid ion diffusion. It achieved a remarkable specific capacity of 394.4 mAh/g, surpassing the 249.1 mAh/g recorded for WDPB1-800 after 100 cycles at 100 mA/g. This research clearly demonstrates that the integration of a highly disordered structure, elevated SSA, and hierarchical pores, coupled with a low micropore/mesopore fraction, represents one of the most promising strategies for developing high-capacity, carbon-based LIB anodes derived from sustainable biomass. • Wolffia (Khai-phum) is effectively used as a sustainable biomass precursor for lithium-ion battery anodes. • ZnCl 2 activation at 800 °C creates a hierarchical pore structure crucial for balancing Li-storage and transport. • While micropores provide more active sites, they also significantly restrict ion diffusion. • WDPB2-800 achieved the best electrochemical results of 394.4 mAh/g at 100 mA/g.