Copolymerized Sulfur with Intrinsically Ionic Conductivity, Superior Dispersibility, and Compatibility for All-Solid-State Lithium Batteries
Fan Zhang, Yingwu Luo, Xiang Gao, Rui Wang
Abstract
Elemental sulfur is ionic-insulating and incompatible with most solvents and other additives in the electrode. When it is used in all-solid-state lithium batteries, there is always high resistance to lithium ion transfer, leading to a poor rate and cycle performance. In this work, polymeric sulfur is synthesized to resolve this problem. Sulfur is copolymerized with poly(ethylene glycol) methyl ether methacrylate (PMEMA) and 1,3-diisopropenylbenzene (DIB). PMEMA is an acrylate monomer, which can undergo radical copolymerization with sulfur diradicals. Its oligoethylene oxide side chain can transfer lithium ions, providing an intrinsic ion-conducting character, good dispersibility, and compatibility for the final polymeric sulfur material, named poly(S–PMEMA–DIB). It is applied to all-solid-state lithium batteries as the positive material, with the Li1.5Al0.5Ge1.5(PO4)3 (LAGP)/polyethylene oxide (PEO) composite as the all-solid-state electrolyte. Because poly(S–PMEMA–DIB) can disperse well in acetonitrile and shows good compatibility with LAGP, the electrode can be prepared easily with a uniform structure. Also, because of the intrinsically ionic conductivity of this polymeric sulfur, the interfacial resistance of the electrode is reduced. All-solid-state batteries made from poly(S–PMEMA–DIB) demonstrate an improved rate and cycle performance compared with those made from elemental sulfur, delivering high reversible capacities of 1140 mA h g–1 at 0.1 C and 600 mA h g–1 at 0.5 C.