Self-Assembled Ion Transport Channels in Block Copolymer Electrolytes for Dendrite-Free All-Solid-State Sodium Batteries.

Sodium metal batteries are a promising low-cost alternative to lithium-based systems, offering abundant raw materials and high energy density. However, their development is hindered by challenges such as dendrite growth and interfacial instability, which compromise safety and cycling performance. To address these issues, we report a new class of fluorinated, ion conducting block copolymer electrolytes designed to self-assemble into well-defined ion transport channels. These block copolymers, composed of perfluoropolyether (PFPE) segments and charged polyethylene oxide (PEO) blocks, self-assemble into a variety of nanostructures. A three-dimensional interconnected body-centered cubic (BCC) morphology forms across a broad PFPE volume fraction range (fPFPE ≈ 0.15-0.30). Among the observed morphologies, the BCC phase stands out for its superior performance, enabling high ion conductivity (up to 1.42 × 10-4 S cm-1 at 80 °C) and forming robust electrode/electrolyte interfaces that support stable cycling in symmetric sodium cells for over 5000 h at 0.1 mA cm-2. Furthermore, in full-cell configurations using Na3V2(PO4)3 (NVP) cathodes, the block copolymer-based sodium metal battery retains >91% of its initial capacity after 1000 cycles at 0.5 C and a high Coulombic efficiency at >99.8%. This study highlights the potential of morphological control through block copolymer design to overcome key limitations in sodium metal batteries and presents a viable path toward safe, high-performance, and sustainable energy storage technologies.