Untangling the potential of non-entangled bottlebrush block copolymers as separator coating materials for high-rate and long-life sodium metal batteries

Abstract

Sodium (Na) metal batteries are of great interest as next-generation battery systems due to the high energy density, natural abundance, and cost advantages of Na metal. However, Na metal systems face significant challenges, primarily due to uncontrolled Na electrodeposition and unstable electrolyte-electrode interphases, leading to collateral cell failures. Herein, we introduce a bottlebrush block copolymer (BBP), consisting of oligomeric poly(ethylene oxide) (PEO) and polystyrene blocks, as a coating material for conventional glass fiber (GF) separators. The BBP exhibits a controlled hexagonal cylindrical morphology and non-entangled topology, which significantly enhances ion-conducting properties and mechanical robustness through well-defined microphase separation. Additionally, the non-entangled topology of the BBP, facilitated by its bottlebrush structure, promotes effective PEO-Na+ coordination, thereby effectively regulating Na+ flux at the electrolyte-electrode interphases. This uniform Na+ flux achieved by the BBP coating ultimately leads to dendrite-free Na deposition and stable electrode interphases, resulting in high-rate and long-lasting Na metal batteries. This study highlights the potential of non-entangled bottlebrush-structured polymers as viable separator coating materials for Na metal battery systems.