Eco-friendly utilization of sawdust: Ionic liquid-modified biochar for enhanced Li+ storage of TiO2

Highlights: • Sawdust modified by [Bmim]H₂PO₄ converted into high performance anodes. • N-O-Ti/N-Ti-O and P-O-Ti bonds in biochar/TiO₂ interface detected by XPS. • Biochar/TiO₂ interface bonding enhanced anodic structural/cyclic stability. • IL-assisted low-temperature carbonization is environmental-friendly. In China, forestry logging and wood processing produce hundreds of thousands of tons of sawdust every year, which is either discarded or burned. These nonecofriendly practices result in some challenges associated with greenhouse gas emissions. Sawdust-based biochar tailored for anodes of lithium-ion batteries (LIBs) can effectively realize value-added utilization of sawdust. The purpose of the current work is to prepare TiO₂/biochar nanocomposites to improve the electrical conductivity and structural stability of the anode. However, poor interfacial interaction between TiO₂ and carbon in the TiO₂/C composites arising from their heterogeneous nature leads to structural deformation of the composites used as anodes of lithium-ion batteries (LIBs). A strategy of constructing ionic liquid-coupled biochar/TiO₂ interfaces is proposed to obtain chemically bonded interfaces between TiO₂ and sawdust-derived biochar. In this study, TiO₂/C-880 composites are prepared by one-step carbonization of TiO₂ nanoparticles (NPs) and sawdust at 880 °C previously dissolved in 1-butyl-3-methyl-imidazolium ([Bmim]H₂PO₄)/dimethyl sulfoxide (DMSO). The morphologies of TiO₂/C-880 demonstrate that the TiO₂ is encapsulated by porous biochar with intimate interfaces, and the X-ray photoelectron spectroscopy (XPS) results indicate the formation of N-Ti-O/N-O-Ti and Ti-O-P bonds that bridge the two components. TiO₂/C-880 electrodes have high reversible specific capacities (404 mAh g⁻¹ at 0.1 A g⁻¹) and desirable long-term cyclic stability (100 mAh g⁻¹ at 2 A g⁻¹ throughout 2500 cycles). Moreover, large diffusion coefficients (D_Li⁺) ranging from 5.9 × 10⁻¹¹ to 1.2 × 10⁻⁹ cm² s⁻¹ are obtained from galvanostatic intermittent titration (GITT) curves. The N-Ti-O/N-O-Ti and Ti-O-P bonds at the interfaces offer routes for fast Li⁺/electron transport, which account for the high performance of the TiO₂/C-880 electrodes.