Low-Cost and Environmentally Friendly Biopolymer Binders for Li–S Batteries

Lithium–sulfur batteries (LSBs) have drawn tremendous attention for their superior theoretical energy density. Nevertheless, the "shuttle effect" originating from the dissolution and migration of lithium polysulfide (LiPS) in electrolytes limits the cycling stability of LSBs. To deal with this challenge, a biopolymer network PPG with a three-dimensional (3D) cross-linked structure, on the basis of guar gum (GG), phytic acid (PA), and soy protein isolate (SPI), has been explored as a cathode binder for LSBs. The robust adsorption ability to capture LiPS presented by the PPG binder has been demonstrated through the ultraviolet–visible (UV–vis) measurement and further been certified by calculation with the density functional theory (DFT). Its outstanding mechanical and adhesion performance is also beneficial to sustain the integrality of sulfur electrodes during the cycle life test. PPG binder-based LSBs exhibit significant promotion in prolonged cycling tests with a 79.7% capacity retention after 700 cycles at 1 C. The capacity of PPG binder-based LSBs can still maintain 933.6 mAh g–1 (at 0.1 C) after 50 cycles even with a high sulfur mass loading of 4.9 mg cm–2. This result demonstrates the significance of a natural polymer in the design of a binder for a sulfur cathode to achieve LSBs with splendid cycling performance.