Inhibiting Lithium Dendrite Using a Helical Structure Soy Protein Isolate To Achieve a Janus Separator for High Performance Li–S Batteries

The propagation of lithium dendrites and the “shuttle effect” of polysulfide represent two critical challenges hindering the practical application of lithium sulfur batteries (LSBs). Herein, a dual-functional integrated Janus separator is proposed, which simultaneously inhibits the shuttle effect of polysulfide and lithium dendrites to enhance the electrochemical performance of LSBs. On the lithium metal anode interface, directional denaturation treatment was first applied to increase the α-helix content in soy protein isolate (SPI), yielding α-SPI with enhanced Li+ affinity. Phytic acid (PA) served simultaneously as cross-linker and acidity regulator, anchoring α-SPI nanoparticle onto carboxylated cellulose nanofibers (C–CNF). The resulting composite was uniformly sprayed onto the separator to construct a lithiophilic α-SPI@C–CNF framework, which homogenizes Li+ flux and suppresses lithium dendrite. At the cathode interface, the made-to-measure three-dimensional carbon (M-3DC) physically entraps lithium polysulfides and thus prevent the shuttle effect. Finally, the LSB using the Janus separator delivers a high initial capacity of 938 mAh g–1 and exhibits an excellent operation stability by retaining 537.8 mAh g–1 after 1000 cycles (with a capacity degradation rate of only 0.043% per cycle). This study presents a versatile approach to simultaneously mitigate the intrinsic limitations of both the lithium metal anode and the sulfur cathode in LSBs.