Covalently cross-linked waterborne polyurethane acrylate network binder for low-expansion silicon / carbon anode

Silicon/carbon (Si/C) is considered to be the most promising anode material for use in next-generation high-energy batteries. However, Si/C-containing batteries experience significant volume expansion (>300 %) during charge and discharge, an issue which is difficult to address using the widely employed styrene–butadiene rubber (SBR) and polyacrylic acid (PAA) binders. In this study, an ultraviolet (UV)-cured waterborne polyurethane acrylate cross-linked multifunctional network (MFN) binder with high mechanical strength and electrochemical properties is developed, which is able to accommodate the volume expansion of Si/C. More specifically, its network structure with a high cross-link density effectively increases the strength of the binder (36.2 MPa) and reduces electrolyte swelling (7.8 %). Notably, it is demonstrated that during cycling, the MFN-containing cell exhibits a capacity retention of >91.7 % after 200 cycles at 0.3C. Additionally, a specific capacity of 1298.2 mAh g −1 is achieved at 5C, which represents superior performance compared to that exhibited by commercial PAA binders. Moreover, the cycle volume expansion rate and expansion force of the MFN-based cell are 6.1 % and 148.1 kg, respectively. According to density functional theory calculations, the hydrogen and covalent bond energies between the PAA and MFN molecules are calculated to be −15.09 and −121.21 kJ mol −1 , respectively. Overall, this study provides new insights into cross-linked network binders to promote the development of high-energy lithium-ion batteries.