title: Amorphous GeOx-Coated Reduced Graphene Oxide Balls with Sandwich Structure for Long-Life Lithium-Ion Batteries.
abstract: Amorphous GeOx-coated reduced graphene oxide (rGO) balls with sandwich structure are prepared via a spray-pyrolysis process using polystyrene (PS) nanobeads as sacrificial templates. This sandwich structure is formed by uniformly coating the exterior and interior of few-layer rGO with amorphous GeOx layers. X-ray photoelectron spectroscopy analysis reveals a Ge:O stoichiometry ratio of 1:1.7. The amorphous GeOx-coated rGO balls with sandwich structure have low charge-transfer resistance and fast Li(+)-ion diffusion rate. For example, at a current density of 2 A g(-1), the GeOx-coated rGO balls with sandwich and filled structures and the commercial GeO2 powders exhibit initial charge capacities of 795, 651, and 634 mA h g(-1), respectively; the corresponding 700th-cycle charge capacities are 758, 579, and 361 mA h g(-1). In addition, at a current density of 5 A g(-1), the rGO balls with sandwich structure have a 1600th-cycle reversible charge capacity of 629 mA h g(-1) and a corresponding capacity retention of 90.7%, as measured from the maximum reversible capacity at the 100th cycle.
authors.affiliation: †Department of Materials Science and Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136-713, Republic of Korea.
authors.forename: Seung Ho
authors.initials: SH
authors.lastname: Choi
authors.affiliation: ‡Department of Chemical Engineering, Kongju National University, 275 Budae-dong, Cheonan, Chungnam 330-717, Republic of Korea.
authors.forename: Kyeong Youl
authors.initials: KY
authors.lastname: Jung
authors.affiliation: †Department of Materials Science and Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 136-713, Republic of Korea.
authors.forename: Yun Chan
authors.initials: YC
authors.lastname: Kang
keywords: anode material; germanium oxide; graphene composite; lithium-ion battery; spray pyrolysis