Yuseong gu, South Korea
Yuseong gu, South Korea

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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.

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.

Suk J.,Center for Advanced Battery Materials | Lee Y.H.,Center for Advanced Battery Materials | Lee Y.H.,Sungkyunkwan University | Kim D.Y.,Center for Advanced Battery Materials | And 4 more authors.
Journal of Power Sources | Year: 2016

We developed highly promising solid polymer electrolytes (SPEs) based on a novel cross-linker containing star-shaped phosphazene with poly(ethylene oxide) (PEO) branches with very high ionic conductivity (7.6 × 10−4 S cm−1), improved mechanical stability, and good electrochemical stability for all-solid-state lithium batteries. In particular, allyl groups were introduced at the ends of the cross-linker in order to overcome the easy self-polymerization of existing cross-linking acrylate end groups. A novel semi-interpenetrating network (semi-IPN) SPE was prepared by in-situ radical polymerization of a precursor solution containing lithium salt, poly(ethylene glycol) dimethyl ether as a plasticizer, and a mixture of pentaerythritol tetrakis(3-mercaptopropionate) and a synthesized hexakis(allyloxy)cyclotriphosphazene (thiol-ene PAL) as the cross-linker. Batteries employing LiFePO4 as the cathode, lithium foil as the anode, and the SPE thin film as the electrolyte were assembled and tested. At ambient temperature, the initial discharge capacity was 147 mAh/g at 0.1 °C and 132 mAh/g at 0.5 °C, and 97% of the capacity was retained at the 100th cycle. All-solid-state pouch-package lithium cells assembled with the SPEs exhibited stable electrochemical performance, even under a severely wrinkled state. These outstanding properties of SPEs based on thiol-ene PAL demonstrate feasibility for practical battery applications with improved reliability and safety. © 2016

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