Softening and enriching polarity of chitosan backbone as a bifunctional binder for high-performance sulfur cathode

Abstract

Lithium-sulfur batteries have attracted much attention because of their high energy density; their long-term stability suffers from the shuttle effect of polysulfides and the volume variation of sulfur during charging and discharging process. Herein, by chemically grafting highly flexible and polar poly(N-aryloylglycamide) (PNAGA) segments onto the linear backbone of the naturally abundant, hard and brittle chitosan, a hyper-branched and 3D-linked aqueous binder was prepared, which has stronger binding strength and is more flexible than the pristine chitosan or the commercial PVDF. Moreover, owing to the presence of affluent diamide groups in the PNAGA branches, the grafted binder demonstrates much better ability for capturing polysulfides. When applied in sulfur cathode, the binder is bifunctionally effective, which can suppress the shuttle behaviors of the polysulfides and well maintain the interfacial intimacy, thus enabling excellent long-term cycling stability. After 300 cycles at 0.2 C, the relevant battery still retains 843.1 mAh g − 1, spelling a retention rate 49.4% and 69.6% higher than those using PVDF and the pristine chitosan, respectively; even under a high sulfur loading of 5.2 mg cm−2, the battery can still operate steadily more than 100 cycles at 0.2 C, maintaining a specific capacity above 620.1 mAh g − 1.