Architecturally Engineered Polyelectrolyte Binders: Property-Matching for Solid-State Battery Composite Cathodes

Polymer binders in solid-state composite cathodes must provide ionic conductivity while maintaining mechanical integrity and interfacial contact, but the relative importance of these properties to battery performance is poorly understood. Here, we show that initial capacity for LiNi0.8 Mn0.1Co0.1O2/Li6PS5Cl/Li4Ti5O12 batteries correlates with polyelectrolyte binder ionic conductivity and interfacial resistance, while retention depends on plateau modulus (Gp’) and damping factor (tanδ). Varying lithium borate polycarbonate with 10 wt % poly(ethylene oxide) (PEO) from linear to star and graft architectures generates conductivity-matched binder sets with distinct mechanical and interfacial properties. Linear binders combining high ionic conductivity (10–4 S cm–1) and low interfacial resistance achieve the highest capacity (210 mAh g–1), while graft architectures with long PEO side-chains deliver superior capacity retention (98% vs 92% for linear) through low Gp’ (∼146 kPa) and high tanδ (∼0.8). Property-matching in one-dimension while using architecture to predictably vary others provides a generalizable design approach for multifunctional polymers in energy storage, extendable to solid polymer electrolytes and other systems requiring simultaneous optimization of transport and mechanical properties.