Browsing by Author "Abbas, Syed Ali"

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High-performance graphene/sulphur electrodes for flexible Li-ion batteries using the low-temperature spraying method
(2015-01-01)
Kumar, Pushpendra
;
Wu, Feng-Yu
;
Hu, Lung-Hao
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Abbas, Syed Ali
;
Ming, Jun
Elementary sulphur (S) has been shown to be an excellent cathode material in energy storage devices such as Li-S batteries owing to its very high capacity. The major challenges associated with the sulphur cathodes are structural degradation, poor cycling performance and instability of the solid-electrolyte interphase caused by the dissolution of polysulfides during cycling. Tremendous efforts made by others have demonstrated that encapsulation of S materials improves their cycling performance. To make this approach practical for large scale applications, the use of low-cost technology and materials has become a crucial and new focus of S-based Li-ion batteries. Herein, we propose to use a low temperature spraying process to fabricate graphene/S electrode material, where the ink is composed of graphene flakes and the micron-sized S particles prepared by grinding of low-cost S powders. The S particles are found to be well hosted by highly conductive graphene flakes and consequently superior cyclability (similar to 70% capacity retention after 250 cycles), good coulombic efficiency (similar to 98%) and high capacity (similar to 1500 mA h g(-1)) are obtained. The proposed approach does not require high temperature annealing or baking; hence, another great advantage is to make flexible Li-ion batteries. We have also demonstrated two types of flexible batteries using sprayed graphene/S electrodes.
Mitigating Metal Dendrite Formation in Lithium-Sulfur Batteries via Morphology-Tunable Graphene Oxide Interfaces
(2019-01-16)
Chen, Yu-Ting
;
Abbas, Syed Ali
;
Kaisar, Nahid
;
Wu, Sheng Hui
;
Chen, Hsin-An
Despite issues related to dendrite formation, research on Li metal anodes has resurged because of their high energy density. In this study, graphene oxide (GO) layers are decorated onto Li metal anodes through a simple process of drop-casting and spray-coating. The self-assembly of GO is exploited to synthesize coatings having compact, mesoporous, and macroporous morphologies. The abilities of the GO coatings to suppress dendrite formation are compared through Li vertical bar Li symmetrical cell charging at a current density of 5 mA cm(-2) for 2000 cycles-a particularly abusive test. The macroporous structure possesses the lowest impedance, whereas the compact structure excels in terms of stability. Moreover, GO exhibits a low nucleation overpotential and is transformed into reduced GO with enhanced conductivity during the operation of the cells; both factors synergistically mitigate the issue of dendrite formation. Li-S batteries incorporating the GO-decorated Li anodes exhibit an initial capacity of 850 mA h g(-1) and maintain their stability for 800 cycles at a C-rate of 1 C (1675 mA h g(-1)), suggesting the applicability of GO in future rechargeable batteries.