Porous structure-tuned cellulose nanofiber paper separators (designated as S-CNP separators) are
demonstrated as a promising alternative to commercial polyolefin separators for use in lithium-ion batteries.
A new architectural strategy based on colloidal silica (SiO2) nanoparticle-assisted structural control
is presented to overcome the difficulty in forming controllable porous structure of pure cellulose nanofiber
paper separators (designated as CNP separators) from densely-packed cellulose nanofibers (CNFs). The
new S-CNP separators proposed herein incorporate SiO2 nanoparticles as a CNF-disassembling agent (i.e.,
as non-conductive spacer particles). This structural uniqueness allows loose packing of CNFs, thereby
facilitating the evolution of more porous structure. The unusual porous structure of S-CNP separators can
be fine-tuned by varying SiO2 contents in the CNF suspension. Notably, the S-CNP separator (fabricated
with 5 wt.% SiO2 content) exhibits the highest ionic conduction due to the well-balanced combination of
nanoporous structure and separator thickness, thus contributing to excellent cell performance. This study
underlines that the colloidal SiO2 nanoparticle-directed structural tuning of CNPs offers a promising route
for the fabrication of advanced paper separators with optimized attributes and functionality