Low-Cost and Sustainable Cross-Linked Polyvinyl Alcohol–Tartaric Acid Composite Binder for High-Performance Lithium–Sulfur Batteries

Abstract

A high specific energy density in lithium–sulfur (Li-S) batteries can be achieved by constructing high-sulfur-loading electrodes. However, this electrode type leads to fast capacity decay owing to the formation of large cracks on its surface. Consequently, the optimization of polymeric binders is considered an effective strategy to decrease the volume expansion of sulfur electrodes during cycling. In this study, a three-dimensional (3D) cross-linked polymeric binder was prepared via the polymerization of polyvinyl alcohol (PVA) and tartaric acid (TA). Acetylene carbon black (C) and elemental sulfur (S) were mixed and melt-diffused to prepare a CS composite. The developed 3D cross-linked PVA-TA composite binder films exhibited improved breaking strengths and swelling degrees. Moreover, the inter/intramolecular reactions between the hydroxyl groups of the PVA and TA molecules effectively reduced expansion and suppressed lithium polysulfides (LiPSs) during cycling. The synthesized composite binder also improved the adhesion of the active material and mechanical properties, which decreased the self-discharge and overpotential polarization and increased the lithium-ion diffusion coefficient. The CS electrode (78% sulfur, 3.3–3.5 mg/cm2 sulfur loading) with PVA-TA composite binder exhibited a high initial discharge specific capacity of 537.7 mAh/g and maintained 463.99 mAh/g after 400 cycles at 1.0 C-rate with the decay rate of 0.14%. The outstanding electrochemical performance is due to the 3D cross-linked polymeric network and the excellent adsorption ability. To the best of our knowledge, a sulfur electrode with low-cost and sustainable 3D cross-linked PVA-TA composite binder with excellent electrochemical properties was used for the first time in Li-S batteries.