From CO₂ to a Sustainable Aqueous Binder for Silicon/Carbon Anodes

icon/carbon (Si/C) composites are promising high-capacity anodes for lithium-ion batteries, but the large volume change of silicon during cycling pulverizes the active material and disrupts electrode integrity, causing rapid capacity decay. Poly(acrylic acid) (PAA) is a benchmark binder for Si anodes, adhering well to the silicon surface through hydrogen bonding, but its brittle chains limit long-term cycling stability. Herein, we develop an aqueous, in-situ cross-linked binder (xPAA/CPEC) that valorizes CO₂ as a covalently bound backbone component. A carboxyl-functionalized poly(ether carbonate) polyol (CPEC), synthesized from CO₂ and blended with PAA, undergoes esterification with the carboxyl groups of PAA during electrode drying, forming a three-dimensional network. This network combines the strong interfacial adhesion of PAA with elastic carbonate/ether segments that dissipate cycling-induced stress. The optimized binder, xPAA/CPEC-91, exhibited the highest peel adhesion, fracture toughness, and lowest charge-transfer resistance among the tested compositions. The resulting electrode delivered 1,753 mAh g⁻¹ with 89% initial Coulombic efficiency and retained 61% of its capacity after 200 cycles at 0.5 C, dramatically higher than that of pristine PAA (4%). This work establishes CO₂-derived polyols as viable building blocks for mechanically robust, sustainable aqueous binders in high-capacity Si/C anodes.