Bidirectional interfacial interactions and CuxS bond formation enabled by a thiourea-crosslinked binder for high-performance micro-SiOx anodes

Abstract

Silicon suboxides (SiO_x) are promising anode materials for next-generation lithium-ion batteries (LIBs), offering high theoretical capacity and lower cost compared to nano-silicon. However, SiO_x undergoes significant volume changes during repeated lithiation and delithiation, leading to electrode delamination and interfacial instability. These issues cause contact loss among particles and degrade electrode capacity, hindering commercialization. Here, the poly(acrylic acid-co-acrylamide) backbone (PAAAM) is crosslinked with thiourea (Tu) to prepare x-PAAAM-Tu, a Tu-containing binder. The developed binder not only improves cohesion in the SiO_x electrode but also strengthens adhesion through Cu–S bond formation (Cu_xS). These interactions increase electrochemical performance and mechanical stability. Consequently, an electrode employing x-PAAAM-Tu with microsized SiO_x exhibits strong adhesion, robust cohesion, and improved structural integrity, delivering a high areal capacity of 5.9 mAh cm⁻². In addition, it maintains stable cycling up to 100 cycles, even at a 5.0 C charge rate. Notably, a full cell with an x-PAAAM-Tu-based SiO_x anode shows 38.3% higher capacity retention than the commercial CMC binder. As such, this study offers practical strategies for designing advanced binders appropriate for high-energy-density LIBs with microsized SiO_x anodes.