A gel polymer electrolyte with multiple hydrogen bonding for pressure-free Ah silicon-based pouch cells

Silicon stands out as promising negative electrode for future lithium-ion batteries owing to its high specific capacity. However, drastic volume change during cycling results in significant loss of electronic/ionic conduction and poor cycling life, necessitating external stack pressure to confine volume expansion. In this work, we develop a gel polymer electrolyte by in situ co-polymerizing methyl methacrylate and 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate to enable pressure-free and energy-dense silicon-based lithium-ion batteries. Benefiting from the crosslinked polymer structure and self-healing property, the SiO_x particles experience limited volume expansion and maintain robust interfacial contact with the gel electrolyte, leading to a capacity retention of 90.2% after 400 cycles (0.3 C, 500 mA g^-1). Additionally, the gel electrolytes effectively supress electrode swelling and the formation of "dead silicon", endowing 1000 cycles (0.5 C, 0.8 A) for Ah-scale silicon-based pouch cells free from external stack pressure. Such gel electrolytes also demonstrate safety superiority to conventional liquid electrolytes, which promotes the commercial viability of high-energy-density silicon-based batteries.