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Kim D.Y.,Center for Advanced Battery Materials | Kim M.,KAIST | Kim M.,Samsung | Kim D.W.,Center for Advanced Battery Materials | And 3 more authors.
Carbon | Year: 2015

In this study, free-standing porous graphene papers for high-capacity and reversible Li-O2 battery cathodes are investigated. The graphene paper-like films were fabricated by the assembling of graphene nanoplatelets (GNPs) with the aid of graphene oxides (GOs) as a stabilizer, using a vacuum-assisted filtration method. By using GOs as a stabilizer, the GNP/GO films were fabricated with a paper-like form and they exhibited a highly wrinkled and disordered morphology. Moreover, the use of GNPs as a basic material eliminated the need for a post-annealing to recover the intrinsic electrical conductivity of graphene sheets. Subsequently, the GNP/GO paper could be directly used as a Li-O2 battery cathode without any conducting additives and binders. The GNP/GO paper electrode showed a much higher discharge capacity in comparison to the reduced-GO paper and commercially available carbon papers. We also found that toroidal Li2O2 mainly nucleated and grew on discharge, and decomposed on charge with a relatively high O2 evolution/consumption efficiency of 87%. However, a large number of Li2O2 particles grew inside the GNP/GO paper electrode, resulting in severe volume expansion of the electrode. This volume expansion could be the primary reason for the capacity fading on cycling. © 2015 Elsevier Ltd. All rights reserved. Source


Kim D.Y.,Center for Advanced Battery Materials | Kim M.,KAIST | Kim D.W.,Center for Advanced Battery Materials | Suk J.,Center for Advanced Battery Materials | And 3 more authors.
Carbon | Year: 2016

In non-aqueous Li-O2 batteries, relatively large amounts of discharge products are formed on air cathodes. As such, the expansion of air cathodes is a critical issue that remains to be solved. Here, we report the fabrication of highly porous free-standing graphene paper by introducing macropores within the paper using polystyrene colloidal particles as a sacrificial template. The as-prepared macroporous graphene paper (mp-GP) have a large Brunauer-Emmett-Teller (BET) surface area (ca. 373 m2 g-1), a large pore volume (ca. 10.9 cm3 g-1), and a high porosity (91.6%). Owing to the high surface area and large pore volume, the mp-GPs exhibit a high specific capacity of ca. 12,200 mAh g-1 at a current density of 200 mA g-1, as well as good rate capability, when used as an air cathode in a non-aqueous Li-O2 battery. Moreover, the mp-GP shows good stability up to 100 and 78 cycles at a current density of 500 mA g-1 and 2000 mA g-1 respectively, with a limiting capacity of 1000 mAh g-1. It is found that formation and decomposition of the discharge product, Li2O2, occur within the macropores, and thus, the mp-GP maintains its original structure without considerable expansion during cycling. © 2016 Elsevier Ltd. All rights reserved. Source

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