Ultrahighly Elastic Lignin-Based Copolymers as an Effective Binder for Silicon Anodes of Lithium-Ion Batteries

The three-dimensional structure of natural lignin is destroyed during the extraction and separation processes to generate the fractions with low molecular weight, which cannot be directly applied as high value-added binders for lithium-ion batteries because of its electrolyte solubility. Besides, the elasticity of polymeric binders is quite important to accommodate the large volume change of electrode materials during discharge and charge processes, whereas this problem is neglected. In this work, three-dimensional lignin (L)-polyacrylic acid (PAA) copolymeric binders (L- co-PAA) are designed and synthesized through esterification reaction between aliphatic -OH groups of L and -COOH groups of PAA. The L-co-PAA films with the mass ratio (1:3) of L to PAA possess the ultrahigh elasticity with 400 and 600% stretching for 300 cycles and tensile strain of 630%, mainly because the copolymerizing of L and PAA can weaken hydrogen bonding forces between PAA chains and the rotation of -C-O- single bond within ester linkage can further increase their elasticity, which contributes to maintain the integrity of the electrodes for lithium-ion batteries, especially for silicon-based electrodes. The silicon-based electrodes using L-co-PAA as binders display high initial coulombic efficiency (84%) and excellent cycling stability (939 mA h g(-1) after 1000 cycles). This study offers a facile method for the fabrication of the low-cost polymeric binders with ultrahigh tensile strain and the implementation of the high-value utilization of lignin.