Three‐Armed Polycaprolactone‐Based Polyurethane for High‐Performance Composite Solid‐State Electrolytes

ABSTRACT To mitigate the aggregation of inorganic fillers in composite solid electrolytes, we synthesized a three‐armed polyester polyurethane oligomer (TAPU) through a two‐step polymerization. The curing degree of TAPU was quantitatively analyzed based on the infrared absorption of isocyanate groups, and the curing kinetics were investigated and integrated with the crystalline properties of the cured TAPU. TAPU had a strong solvation ability for lithium salt, and the ionic conductivity of the electrolyte reached 1.48 × 10 −4 S cm −1 at room temperature, which is much higher than that of linear polycaprolactone electrolytes. The LLZTO particles modified with TAPU exhibited enhanced dispersion stability in the composite electrolyte system, effectively suppressing nanoparticle aggregation and improving interfacial compatibility between the ceramic fillers and polymer matrix. The Li//5% LLZTO‐TAPU//Li coin cells were prepared by in situ curing and had excellent cycle stability of up to 768 h at 50°C, which was five times higher than that of PCL electrolytes. Compared with linear polymer solid electrolytes, nonlinear topological polymer provided more functional groups for high ion conduction and cycling stability in lithium batteries.