Bottlebrush Architecture Suppresses Crystallization to Enable Soft, Stretchable Solid-State Polymer Electrolyte for Lithium-Metal Batteries

Abstract

High-performance solid-state electrolytes are essential for safe, high-energy-density lithium batteries, yet achieving high ionic conductivity and mechanical resilience at room temperature remains challenging. Polyethylene glycol (PEG)-based electrolytes show promise but crystallize below ∼42 °C, which suppresses segmental dynamics and ion transport. Here, we show that bottlebrush architecture suppresses crystallization in high-molecular-weight PEG, enabling solvent-free polymer electrolytes that combine high conductivity, softness, and stretchability. Bottlebrush polymer electrolytes exhibit smooth temperature-dependent conductivity and achieve room-temperature conductivities more than two orders of magnitude higher than linear PEG systems. The Li+ transport number increases by nearly 20% relative to that of linear PEG–salt electrolytes. Covalently cross-linked bottlebrush networks retain ionic mobility while providing exceptional mechanical robustness, including stable conductivity under compression, extensibility up to 500% strain, and negligible hysteresis over hundreds of mechanical loading–unloading cycles. The bottlebrush PEG electrolyte supports stable lithium-metal battery operation in Li‖NMC811 cells and long-term (>800 h), low-overpotential (100 mV) lithium plating–stripping in symmetric Li‖Li cells. Moreover, the bottlebrush PEG elastomer serves as both the electrolyte and separator in separator-free Li‖NMC811 cells and enables operation at both 333 and 298 K, while promoting dense, nondendritic lithium deposition and a stable solid electrolyte interphase. These results establish bottlebrush PEG as a versatile platform for deformable, high-performance, and stable solid polymer electrolytes.