Impact of the Mechanical Properties of a Functionalized Cross-linked Binder on the Longevity of Li-S Batteries.

One of the very challenging aspects of Li-S battery development is fabrication of a sulfur electrode with high areal loading using conventional Li-ion binders. Herein we report a new multifunctional polymeric binder - synthesized by the free radical cross-linking polymerization of 2-(acryloyloxy)ethyl]trimethylammonium chloride (AETMAC) and ethylene glycol diacrylate (EGDA) to form poly(AETMAC-co-EGDA) - that not only helps to confine the soluble polysulfide species, but also has the desired mechanical properties to allow stable cycling of high-sulfur loading cathodes. Through a combination of spectroscopic and electrochemical studies, we elucidate the chemical interactions that inhibit polysulfide shuttling. We show that extensive cross-linkage enables this polymeric binder to exhibit a low degree of swelling, as well as high tensile and toughness moduli. These attributes are essential to maintain the architectural integrity of the sulfur cathode during extended cycling. Using this material, Li-S cells with high sulfur loading (6.0 mg∙cm-2), and a low-intermediate electrolyte/sulfur ratio (7 μL:1 mg) achieve an areal capacity of 5.4 mAh.cm2, and can be (dis)charged for 300 cycles with stable reversible redox behavior after the initial cycles.