Enhanced Cycling Performance of Li–S Cells by Mitigation of Lithium Polysulfides Encompassing Palladated Porous Aromatic Polymer-Coated Membranes
Natarajan Angulakhsmi, S. Sundar, N. Karthik, Murugavel Kathiresan, Ramasamy Santhosh Kumar, Dong Jin Yoo, A. Manuel Stephan
Abstract
Although lithium–sulfur (Li–S) batteries are expected to replace lithium-ion batteries due to their high theoretical capacity, low cost, and environmental friendliness, the poor electronic conductivity of sulfur, shuttling of lithium polysulfide (LiPS) between the electrodes, and tendency to self-discharge have delayed attempts to commercialize the technology. Introduction of a permselective and functionalized membrane has been recognized as a potential strategy to mitigate LiPS shuttling. Earlier reports found that biphenyl groups form a passive layer that improves the performance of Li–S batteries and that Pd(PPh 3 ) 4 can serve as an efficient catalyst for the conversion of LiPS. In this study, a porous organic polymer comprising both biphenyls and Pd(PPh 3 ) 4 interconnected via a Friedel–Crafts alkylation reaction (BP-POP) was synthesized and coated onto a commercially available porous Celgard 2320 membrane, and its electrochemical performance was investigated. For comparison purposes, a phenyl derivative (instead of biphenyl), MP-POP, was also synthesized and evaluated. The introduced membrane not only blocked the shuttling of LiPS and prevented self-discharge but also accelerated the catalytic conversion of LiPS. The superior performance of the BP-POP-coated membrane compared with the MP-POP-coated and uncoated Celgard 2320 membranes can be attributed to the synergistic effects of the catalytic activities of the biphenyl group and Pd(PPh 3 ) 4 .