Freeze-Dried Cellulose Separators: Enabling Stable Cathode- and Anode- Electrolyte Interphase in High-Performance...

Extensive research efforts have been focusing on lithium metal batteries (LMBs) for their higher energy density compared to Li-ion batteries, offering promising applicability in robotics and electric vehicles. Despite this potential as the next generation energy storage, conventional polyolefin-based separators used in LMBs suffer from inadequate mechanical strength, poor thermal stability, and susceptibility to Li dendrite penetration, alongside environmental concerns due to their fossil fuel origins. Fabrication of separators with cellulose, a type of biodegradable polymers derived from nature, has been attracting many interests, but that by a fully aqueous method has not been well developed. This study presents a novel, cellulose-based separator fabricated via an all-water-based freeze-drying process, eliminating toxic chemicals and promoting sustainability. Moreover, the cellulose separator exhibits enhanced wettability and lower interfacial energy for electrolytes compared to conventional polyolefin separators, in part due to its hydrophilic functional groups. These properties also contribute to the formation of stable anode- and cathode-electrolyte interfacial layers, suppressing dendrite growth and improving LMB performance and longevity. Superior Li-metal battery performance is demonstrated when both LiFePO₄ and carbon-sulfur (CS) composite electrodes were employed with the cellulose separator, underscoring the potential of freeze-dried cellulose separators for future applications.