Host-Guest Engineering for Advanced Batteries.

The performance of advanced batteries is governed not only by the intrinsic properties of electrodes and electrolytes, but also by the dynamic states of ionic, molecular, and reactive species during operation. Conventional materials-centered strategies, however, often provide insufficient molecular-level control over these local and transient states, limiting precise regulation of ion association, solvation/desolvation, interfacial transfer, and reaction-intermediate conversion. Host-guest engineering offers a molecular design strategy to address this challenge by selectively recognizing, coordinating, confining, or redistributing target guests within defined host environments. This Review organizes host-guest engineering across liquid electrolytes, solid-state and quasi-solid-state electrolytes, electrode-electrolyte interfaces, and solid-liquid conversion cathodes, and compares how different host environments regulate transport, interfacial chemistry, and conversion processes. A cross-scenario quantitative comparison further links molecular-level regulation with battery performance. Across these scenarios, effective regulation is shown to require an appropriate balance between guest-regulation effectiveness and guest-dynamic flexibility rather than simply maximizing binding or confinement. Finally, future opportunities are discussed in integrated host architectures, broader battery systems, adaptive host environments, and the quantitative determination of process-specific host-guest interaction windows.