Fabrication of polyacrylic acid-based composite binders with strong binding forces on copper foils for silicon anodes in lithium-ion batteries

The commercial application of silicon (Si) anodes with high theoretical capacity is hampered by the poor cyclic stability because the huge volume change of Si during discharge/charge processes results in the pulverization of electrode materials and the electric contact loss of electrode materials with copper (Cu) foils. Binders play an important role for adhering active materials and conductive additives together onto Cu foils. Herein, we design and develop a three-dimensional networked composite binder (PAA-co-SN) via an amidation reaction between polyacrylic acid (PAA) and thiourea (SN). The granular anchors (Cu_xS) are constructed at the interface between PAA-co-SN binders and Cu foils, resulting from the reaction of S and Cu during the drying processes of Si electrodes. When used as binders for Si nanoparticles, they exhibit stable cyclic performance (1580 mAh g⁻¹ after 500 cycles). The anchoring mechanism between composite binders and Cu foils provides a strategy for the improvement of electrochemical properties of Si-based anodes for lithium-ion batteries.