Electrode-customized separator membranes based on self-assembled chiral nematic liquid crystalline cellulose nanocrystals as a natural material strategy for sustainable Li-metal batteries

Abstract

Despite their enormous potential as a high-energy-density power source, practical applications of Li-metal batteries have been plagued mainly by poor electrochemical longevity. Here, we present an electrode-customized separator (EC separator) based on self-assembled chiral nematic liquid crystalline cellulose nanocrystal (LC-CNC) as a natural material strategy to simultaneously address the electrochemical reversibility issues of both Li-metal anodes and high-capacity cathodes in Li-metal full cells. The EC separator (thickness similar to 10 mu m) com-prises a 3-glycidyloxypropyl trimethoxysilane (GPTMS)-modified LC-CNC layer on a polyethylene (PE) separator support layer. The LC-CNC layer enables facile/uniform Li+ flux toward Li-metal anodes owing to its ordered nanoporous channels and nanofluidic ion migration effect, thus improving Li plating/stripping cyclability. The GPTMS of the LC-CNC layer chelates heavy metal ions dissolved from high-capacity LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes, thereby enhancing structural stability of the cathodes. The resulting EC separator enables a Li-metal full cell to improve the volumetric energy density (1016 Wh L-cell(-1)), cycling retention (84% after 100 cycles vs. 0% for the pristine PE separator), and dimensional stability of the Li-metal anode under constrained cell conditions (thin Li-metal anode (20 mu m)/high-capacity NCM811 cathode), which outperform those of previously reported synthetic material-based separators for Li-metal full cells.