Cost-effective water-soluble three-dimensional cross-linked polymeric binder for high-performance lithium-sulfur batteries

In lithium-sulfur (Li-S) batteries, the feasible sulfur-cathode applications are limited mainly by the rapid ca-pacity loss and poor cycle life of the cathodes because of the considerable volumetric expansion, sulfur insu -lation, and polysulfide formation. To solve these problems, a water-soluble three-dimensional (3D) binder network was developed using organic poly(vinyl alcohol) (PVA) crosslinked with a boric acid (BA). Different BA concentrations (0, 0.035, 0.07, and 0.105 M) were used to compare the Li-S battery performances. The PVA-BA0.07 binder exhibited a higher strength at breakage (31 MPa) than the PVA-BA0, PVA-BA0.035, and PVA-BA0.105 binders (12, 17.5, and 19.1 MPa, respectively). To prepare the acetylene-carbon black (AB)/sulfur (S) composite (ABS), elemental S was added to acetylene-carbon black (AB) using heat diffusion. The prepared 3D-crosslinked polymeric binder effectively reduced the volumetric expansion and lithium polysulfide formation during cycling. Moreover, the boron (B), which is electron deficient, freely accepted electrons during cycling and, thus, helped form an effective solid electrolyte interface layer. The obtained lithium borate species considerably suppressed the interfacial side reactions and increased the initial coulombic efficiency. The PVA-BA0.07 binder with ABS electrode exhibited an outstanding cycling performance at a high sulfur loading. After 300 charge/ discharge cycles at 0.2 C-rate, the PVA-BA0.07 containing electrode exhibited a high discharge capacity and sulfur loading of 946.8 mAh/g and up to 3.5 mg/cm2, respectively. The study findings will enable the devel-opment of high-performance Li-S batteries using cost-effective water-soluble 3D-crosslinked polymeric binders.