Bifunctional polymer electrolyte with higher lithium-ion transference number for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have attracted enormous interest due to their super-high theoretical energy density (2600 W · h/kg) in recent years. However, issues such as lithium dendrites and the shuttle effect severely hampered the large-scale application of Li-S batteries. Herein, a novel bifunctional gel polymer electrolyte, poly(N,N-diallyl-N, N-dimethylammonium bis(trifluoromethylsulfonylimide))-P(VDF-HFP) (PDDA-TFSI-P(VDF-HFP), PTP), was prepared by anion exchange reaction to tackle the above problems. Benefited from the interaction between TFSI− and quaternary ammonium ion in PTP, a higher lithium-ion transference number was obtained, which could availably protect Li metal anodes. Meanwhile, due to the adsorption interactions between PDDA-TFSI and polysulfides (LiPSs), the shuttle effect of Li-S batteries could be alleviated effectively. Consequently, the Li symmetric batteries assembled with PTP cycled more than 1000 h and lithium metal anodes were protected effectively. Li-S batteries assembled with this polymer electrolyte show a discharge specific capacity of 813 mA·h/g after 200 cycles and 467 mA·h/g at 3C, exhibiting excellent cycling stability and C-rates performance.