Park and Veva Reilly Distinguished Seminar - "Silicon Based Nano-Architectures for Advanced Lithium-Ion Batteries" by Fathy M. Hassan, Department of Chemical Engineering, University of Waterloo

 ABSTRACT:  Silicon has the potential to revolutionize the energy storage capacities of lithium ion batteries, propelling their capabilities to meet the ever increasing power demands of next generation technologies. Silicon has a huge energy storage capacity (4200 mAh/g), ten times higher than the conventionally used graphite materials (372 mAh/g). To avoid the operational stability problems associated with the use of silicon-based anodes, the electrode structure needs to be architectured on the nanoscale. First, silicon nanowires were grown on graphene by chemical vapor deposition and used as anode materials in lithium ion batteries. This greatly improved the reversible charge capacity and its retention at high current density. Second, a novel, economical flash heat treatment (FHT) was developed to fabricate anodes based on commercially available silicon nanoparticles. The FHT resulted  in a high mass fraction of silicon, improved interfacial contact, synergistic Si02/C coating, and a  conductive  cellular network for improved electronic conductivity, as well as flexibility for stress compensation. The developed electrodes achieve first cycle efficiency of -84% and a maximum charge capacity of  3525 mAh  g-1, which  is almost 84% of silicon's theoretical maximum. Furthermore,  a stable reversible charge capacity of 1150 mA h g-1 at 1.2 A g-1 can be achieved over 500 cycles. The third project involved a synergistic physico-chemical alteration of electrode structure during its design was proposed. This capitalizes on covalent bonding of Si nanoparticles (SiNP) with sulfur-doped graphene (SG), with this composite combined with cyclized polyacrylonitrile to provide a robust nano-architecture.  This hierarchical structure stabilized the solid electrolyte interphase leading to superior reversible capacity of over  1000 mAh g·1 for 2275 cycles. Furthermore, the nano-architectured design lowered the contact of the electrolyte to the electrode, leading to not only high coulombic efficiency of 99.9% but also maintaining  high  staility even with high  electrode loading associated with  3.4 mAh  cm·2 of areal capacity. The excellent performance combined with the simplistic, scalable and non-hazardous approach render the process very attractive for commercial Li-ion battery anodes.