Amphipathic emulsion binder for enhanced performance of lithium–sulfur batteries

Abstract

The application of polyvinylidene fluoride (PVDF) binder in lithium–sulfur batteries faces challenges due to inadequate adhesion, undesirable conductivities, limited lithium polysulfides absorbability, and its dependence on the use of toxic N-methyl-2-pyrrolidone solvent. Here, a polysaccharide emulsion binder (HBEA) is synthesized by polymerizing and grafting hydrophilic lithiated acrylic acid, 2-hydroxyethyl acrylate, and hydrophobic butyl acrylate onto the backbone of sodium hyaluronate. The amphipathic nature of the synthesized binder enables outstanding affinity to electrode materials, ensuring exceptional adhesion compared to PVDF in various destructive tests. Additionally, the abundant polar groups in HBEA facilitate effective absorption of lithium polysulfides, leading to enhanced sulfur utilization and improved protection of the lithium anode. Furthermore, the presence of lithiated acrylic acid in HBEA leads to a Li⁺ diffusion coefficient 0.6–1 times larger than that of PVDF in the HBEA binder-based cells. As a result, the high-loading HBEA cell (5 mg cm⁻²) demonstrates an initial discharge capacity of 3.3 mA h cm⁻² at 0.5C and maintains an 87.8% capacity retention after 75 cycles. This work offers an environmentally friendly and easily producible emulsion binder for high-mass-loading sulfur cathodes.