title: General strategy to synthesize uniform mesoporous TiO2/graphene/mesoporous TiO2 sandwich-like nanosheets for highly reversible lithium storage.
abstract: Uniform oxide deposition on graphene to form a sandwich-like configuration is a well-known challenge mainly due to their large lattice mismatches and poor affinities. Herein, we report a general strategy to synthesize uniform mesoporous TiO2/graphene/mesoporous TiO2 sandwich-like nanosheets (denoted as G@mTiO2), which cannot be achieved by conventional one-pot synthetic methods. We show that by rational control of hydrolysis and condensation of Ti precursors in a slow way, GO sheets can be conformably coated by amorphous TiO2 shells, which then can be facilely transformed into the well-defined G@mTiO2 nanosheets by annealing. This amorphous-to-crystalline strategy conveniently allows bypassing strain fields that would inevitably arise if direct growth of mesoporous anatase shells on graphene. As distinct from the most common structures of graphene-based composites (mixed, wrapped, or anchored models), the resultant materials display a uniform sandwich-like configuration: few-layer graphene conformably encapsulated by mesoporous TiO2 shells. This new G@mTiO2 nanosheet exhibits ultrathin nature (∼34 nm), small size and high crystalline nanocrystals (∼6 nm), high surface areas (∼252 m(2)/g) and uniform mesopores (∼3.4 nm). We further show that the thickness of mesoporous TiO2 shells can be facilely adjusted as desired by controlling the ammonia content, and this facile strategy can be easily extended to design other oxide/graphene/oxide sandwich-like materials. More importantly, we showcase the benefits of the resultant G@mTiO2 nanosheets as anodes in lithium ion batteries: they deliver an extra high capacity, an excellent high-rate capability, and long cycle life.
authors.affiliation: Department of Chemistry, Laboratory of Advanced Materials, Shanghai Key Lab of Molecular Catalysis and Innovative Materials, and State Key Laboratory of Molecular Engineering of Polymers, Fudan University , Shanghai 200433, P. R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.forename: Yupu
authors.initials: Y
authors.lastname: Liu
authors.forename: Jinxiu
authors.initials: J
authors.lastname: Wang
authors.forename: Jianping
authors.initials: J
authors.lastname: Yang
authors.forename: Lijuan
authors.initials: L
authors.lastname: Zhang
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Elzatahry
authors.forename: Daifallah
authors.initials: D
authors.lastname: Al-Dahyan
authors.forename: Yongyao
authors.initials: Y
authors.lastname: Xia
authors.forename: Dongyuan
authors.initials: D
authors.lastname: Zhao
keywords: coating; graphene; lithium-ion batteries; mesoporous TiO2; sandwich-like sheets