Oxidized bacterial cellulose functionalized with SiO₂ nanoparticles as a separator for lithium-metal and lithium–sulfur batteries

It is highly desirable to develop lithium-metal batteries (LMBs), including lithium–sulfur batteries (LSBs), as the next-generation high-energy batteries. However, issues related to Li metal anodes and sulfur cathodes, such as non-uniform Li deposition and polysulfide shuttling, must be addressed. Here we report the study of bacterial cellulose (BC), modified by SiO₂ nanoparticles (NPs), as a separator material for LMBs and LSBs. To achieve uniform decoration of SiO₂ NPs on BC nanofibers, we oxidize and partly hydrolyze BC by introducing carboxyl groups and tetraethyl orthosilicate. Electrochemical studies confirm that the composite BC film can smoothen the Li⁺ flux, regulate the Li deposition, and curb the polysulfide shuttling due to the strong interaction of oxygen functional groups on oxidized BC and SiO₂ with Li⁺ and polysulfides. As a separator used in lithium plating and stripping, the composite BC/SiO₂ film offers much better stability, lower polarization voltage, and higher Coulombic efficiency than conventional separators. When applied in Li//S and Li//LiFePO₄ batteries, it also demonstrates much-improved performance. Such a functionalized BC separator is very promising in LMB and LSB applications. Graphical abstract: [Figure not available: see fulltext.].