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I4.03 - High Performance Hybrid Nanostructures for Lithium Ion Battery Anode 
April 8, 2015   9:30am - 9:45am

Presently, LIBs have got tremendous attention due to their high energy densities and have been considered as promising power source for future EV. In this regard, metallic Si, Ge and Sn are considered as potential substitute to the conventional graphite (372 mAh/g) due to their high theoretical capacities 4200, 1600 and 992 mAh/g, respectively and thermal stability. However, structural disintegration, limited access to redox sites and loss of electrical contact have long been identified as primary reasons for capacity loss and poor cyclic life of these materials. Although nanotechnology plays critical role by developing nanostructures but simple reduction in size introduce new fundamental issues like side reactions and thermally less stable. Furthermore, formations of unstable SEI film due to the decomposition of the organic electrolyte at ?0.5 V vs. Li/Li+. Thus, a careful design that can inhibit the side reaction by surface protection, make all redox sites accessible by increasing the intrinsic conductivity, maintain a continues network for ionic and electronic flow and keeps the structural integrity, resulting improved performance and excellent capacity retention with long cyclic life to meet the requirements set by USABC for LIBs use in EVs. Here, we have developed hybrid structures of Si and Sn using two strategies to overcome the aforementioned problems. The encapsulation of the NPs/NTs in the shell of inactive metal and dual protection was provided by the overcoat of NG. The second strategy accounts the surface protection by C shell and dual protection by soft matrix of porous carbon (PC). The intrinsic conductivity is increased by the backbone of highly conductive metal that efficiently transfers the electron to all redox sites inside the nanostructure and acts as stress relaxer due to its hard nature. Furthermore, these hybrids also took the advantages of Li+ storage at the grain boundaries that brings additional capacity. The high performance of the composite based on the synergistic effect of several components in the nanodesign. Moreover, NG/PC increases the contact area between electrolyte and electrode for better performance because of their high surface area. In addition, due to the high conductivity and fast ions transfer mobility, graphene/porous carbon maintains the fast electrical flow of the composites. As a result these hybrids possess extraordinary performance with capacity retention of ~100% after long cyclic life of 2000 cycles. These strategies to combine the different property enhancing factors in one composite with engineered structures will bring the realization of the LIBs in EVs. Li, Q.; Mahmood, N.; Jinghan, Z.; Hou, Y., Sun, S., Nonotoday, 2014, DOI:10.1016/j.nantod.2014.09.002. Mahmood, N.; Zhang, C.; Liu, F.; Jinghan, Z.; Hou, Y., ACS Nano 2013, 7, 10307-10318. Zhang, C.; Mahmood, N.; Yin, H.; Liu, F.; Hou, Y., Adv Mater 2013, 25, 4932-4937. Mahmood, N.; Zhang, C.; Hou, Y., Small 2013, 9, 1321-1328.

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