Cellulose nanofiber separator for suppressing shuttle effect and Li dendrite formation in lithium-sulfur batteries

Lithium-sulfur battery (LSB) has high energy density but is limited by the polysulfides shuttle and dendrite growth during cycling. Herein, a free-standing cellulose nanofiber (CNF) separator is designed and fabricated in isopropanol/water suspension through vacuum filtration progress. CNFs with abundant polar oxygen-containing functional groups can chemically immobilize the polysulfides, and suppress the formation of the dendrites by controlling the surface morphology of the SEI on lithium metal in LSB. The isopropanol content in a suspension can fine-tune the pore structure of the membrane to achieve optimal electrochemical performance. The prepared separator displays integrated advantages of an ultrathin thickness (19 μm), lightweight (0.87 mg cm⁻²), extremely high porosity (98.05%), and decent electrolyte affinity. As a result, the discharge capacity of the LSB with CNF separator at the first and 100th cycle is 1.4 and 1.3 times that of PP separator, respectively. Our research provides an environmental-friendly and facile strategy for the preparation of multifunctional separators for LSBs.