Macromolecules and Related Technologies for High-performance Lithium-sulfur Battery

Yuezhong MENG

Sun Yat-sen University

Abstract: Lithium-Sulfur (Li-S) batteries, attributed to their marvellous specific capacity (1675 mAh g-1) and breath-taking energy density (2600 Wh kg-1), are considered to be the new-generation high performance battery technologies. Meanwhile, elemental sulfur is very resourceful in nature, cost-effective, non-toxicity, and environmental benignity. In spite of these considerable advantages, the actual application of the Li-S batteries still hindered by some challenges, which mainly include the poor electrical conductivity (5*10-30 S cm-1) of sulfur, the large volumetric change during cycling (~80%), and the dissolution of lithium polysulfides (LiPSs) intermediates in the organic electrolyte solution, which results in the irreversible loss of active sulfur, low capacity retention and insufficientCoulombic efficiency during cycles.

In this respect, we focus on designing and preparing special polymers for high performance Li-S batteries, and share our ideas on the polymers used in cathode materials, in separator, as solid electrolyte and as cathode binder. In this presentation, for example, various conductive and porous carbon materials from pre-polymers have been used as the hosts for sulfur based cathode materials, which can effectively trap the LiPSs by physical/structural adsorption. Moreover, many efforts have been paid to the structure design of the electrode. In this case, the integrated sulfur cathodes with good electrochemical performance and cycling stabilities were combined with polypropylene separator or polymer electrolyte together. Regretfully, rational designs and fabrications of the high conductive network structure cathode to meet the requirement of the different sulfur loading for excellent high performance Li-S batteries.

Secondly, a strategy of a chemically heterogeneous membrane with sandwich structure has been developed by program-controlled process. The sandwich structure composite cathodes with various areal sulfur loadings of 2-16 mg cm-2 demonstrated high specific capacities, superior rate performances and cycling stabilities.

To even further enhance the long-term cycling stability, a brand new in-situ binding N-functional network binder (NFN) by the polymerization of polyethylenimine polymer (PEI) with epoxy resin (ER) was designed and applied for Li-S batteries. The unique advantages of PEI-ER binder featured with abundant N active sites and hyper-branched network structure provide strong structural and chemical affinity for the encapsulation the polysulfide intermediates. As the comprehensive influences of above-mentioned technologies, the remarkable improvement of cycling performance for Li-S batteries was successfully achieved with a high initial capacity of 1174.4mAh g-1and superiorcapacity retention of 80% over 1000 cycles, together with a super-low capacity decay of 0.02% per cycle at 0.5 C. Moreover, the batteries with high S-loading of 5.4 mg cm-2 still remain excellent capacity retention up to 77%over 500 cycles with an initial capacity of 713.4 mAh g-1 at 0.5 C. It is noteworthy that the presented strategy is not designed in any specialized manner, together with the advantages of low-cost, non-toxic and high performance, making the process absolutely commercially viable for large-scale production.

Biography: Dr. Yuezhong Meng is the Pearl-River Professor of Polymer Chemistry and Physics at Sun Yat-sen University, China, and the director of the Key Laboratory of Low-carbon Chemistry and Energy Conservation of Guangdong Province, leading a group of 56 staffs and postgraduate students. His research areas include exploratory functional polymers, chemical utilization of carbon dioxide and new energy materials.

He received his B.Sc. and M.Sc. degrees from Dalian University of Technology, China, and his Ph. D. in polymer chemistry from the same university in 1995 under the supervision of Professor Allan S. Hay (McGill University). He then joined the City University of Hong Kong as a Research Fellow from 1996 until 2003. From 1998, he had been a postdoctoral research fellow at McGill University of Canada for nearly 3 years. Dr. Meng was chosen as a member of the prestigious "Hundred Talents" by Chinese Academy of Sciences in 1998. He has authored 310 publications in refereed international journals (more than 165 papers with IF greater than 3.0) and has 5 U.S. patents and 96 Chinese patents.