Thermally Controlled Dual Stabilization Mechanisms of Modified Kenaf-Derived Lignin-Based Aqueous Binders for Silicon Electrodes Used in Lithium-ion Batteries

Abstract

Silicon (Si) is a promising anode material of lithium-ion batteries due to its high lithium storage capacity; however, severe volume expansion during the charge-discharge cycling causes electrode degradation and rapid capacity fading. While binders are essential for maintaining electrode integrity, high-performance binders are often costly, complex to process, and dependent on organic solvents. Aqueous binders derived from natural polymers therefore represent attractive alternatives in terms of cost, sustainability, and environmental compatibility. Although chemically modified lignin binders are promising for Si electrodes, previous studies have only suggested the existence of two distinct thermal treatment approaches—low- and high-temperature processing—and no study has systematically compared these two methods. Herein, we report a modified kenaf-derived lignin copolymerized with polyacrylamide (KL-PAM) as an aqueous binder for Si electrodes and systematically investigated the effect of thermal treatment temperature on its stabilization mechanisms. Low-temperature-treated at 200 °C KL-PAM electrodes accommodated Si volume expansion through binder flexibility and adhesion, whereas high-temperature-treated electrodes were stabilized by carbonization-induced hardening of KL-PAM, which also enhanced electronic conductivity. As a result, high-temperature-treated at 600 °C electrodes exhibited superior rate capability, while capacity retention was comparable between the two regimes. Intermediate-temperature treatment was ineffective, leading to binder failure. This study clears thermally controlled dual stabilization mechanisms of lignin-based binders and provides guidance for the development of sustainable binders for Si electrodes of lithium-ion batteries.