Low-Temperature Treated Lignin as Both Binder and Conductive Additive for Silicon Nanoparticle Composite Electrodes in Lithium-Ion Batteries

This work demonstrates a high-performance and durable silicon nanoparticle-based negative electrode in which conventional polymer binder and carbon black additive are replaced with lignin. The mixture of silicon nanoparticles and lignin, a low cost, renewable, and widely available biopolymer, was coated on a copper substrate using the conventional slurry mixing and coating method and subsequently heat-treated to form the composite electrode. The composite electrode showed excellent electrochemical performance with an initial discharge capacity of up to 3086 mAh g^-1 and retaining 2378 mAh g^-1 after 100 cycles at 1 A g^-1. Even at a relatively high areal loading of ∼1 mg cm^-2, an areal capacity of ∼2 mAh cm^-2 was achieved. The composite electrode also displayed excellent rate capability and performance in a full-cell setup. Through synergistic analysis of X-ray photoelectron spectroscopy, Raman, and nanoindentation experiment results, we attribute the amazing properties of Si/lignin electrodes to the judicious choice of heat treatment temperature at 600 °C. At this temperature, lignin undergoes complex compositional change during which a balance between development of conductivity and retaining of polymer flexibility is realized. We hope this work could lead to practicable silicon-based negative electrodes and stimulate the interest in the utilization of biorenewable resources in advanced energy applications.