Water-Based Dual-Cross-Linked Polymer Binders for High-Energy-Density Lithium-Sulfur Batteries

High-mass-loading electrodes with long-term stability have long been a great challenge for lithium-sulfur batteries (LSBs), since the conventional binders are unable to cope with the shuttling of lithium polysulfides and the structural damage in an electrode. Here, a novel water-based polymer, polyphosphate acid cross-linked chitosan ethylamide carbamide (PACEC), is developed as a binder to construct high-energy-density sulfur cathode and flexible LSBs. With a dual-cross-linked network, the PACEC shows excellent affinity with lithium polysulfides to relieve the shuttle effect and robust mechanical properties to stabilize the electrode. The sulfur cathode based on PACEC demonstrates a high sulfur loading of 14.8 mg cm^-2, the areal initial capacity of 17.5 mAh cm^-2, and Coulombic efficiency of 99.3%, while the amount of electrolyte is strictly limited to 6 μL mg^-1. More importantly, a robust pouch cell with an area of 6 cm² and only 177% oversized lithium can successfully integrate the energy density of 6.5 mAh cm^-2 with the cycling retention per cycle of 99.74% during 270 cycles and flexibility at a curvature of 3 mm. This study provides inspirations for the design of eco-friendly polymer binders and paving new ways for the development of LSBs.