Si anodes via dual strategies of coating Si with a rigid polymer and employing a polymer binder with improved mechanical properties

Abstract

Si undergoes significant volume change over cycles which degrades the structural integrity and stability of the electrode. This volume change is the primary barrier to the commercialization of Si anodes, and it is more pronounced for Si particle sizes over 150 nm. In this study, a crosslinked polymer binder is developed using poly(acrylic acid-co-acrylamide) (PAAM) with enhanced elasticity compared to the widely used poly(acrylic acid). PAAM is further grafted with boronic acid and dopamine, yielding PAAM-B-D, a binder with improved adhesion due to its 3D crosslinked network. Additionally, 350-nm Si is coated with cyclized polyacrylonitrile (cPAN) and heat-treated to form a conjugated structure. The cPAN-coated Si (cSi) exhibits enhanced conductivity and mechanical stiffness and is used as an active material. The developed Si anode effectively combines cPAN-coated Si with the crosslinked network formed in the PAAM-B-D polymer for enhanced adhesion. The cSi@PAAM-B-D electrode sufficiently maintains its structural integrity and mitigates the Si volume change even with the large-sized 350-nm Si. The cSi@PAAM-B-D exhibits a high initial Coulombic efficiency of 86.5 %, at a Si mass loading of 2 mg cm⁻². It also shows a capacity retention of 83.6 % and a high areal capacity of 3 mAh cm⁻² after 50 cycles.