General Strategy to Synthesize Uniform Mesoporous TiO₂/Graphene/Mesoporous TiO₂Sandwich-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.

Mesoporous materials for energy conversion and storage devices

“…Other carbon materials (such as hollow carbon spheres, carbon nanotubes and graphene) have also been introduced into LIBs as mesostructured electrodes [125][126][127][128] . For example, a pomegranate-like meso structure consisting of silicon nanoparticles encapsulated in a hollow carbon framework (Si@C) has shown a high Coulombic efficiency (99.87%) and volumetric capacity (1,270 mAh cm −3 ), and good cyclability 119 .…”

Critical Insight into the Relentless Progression Toward Graphene and Graphene‐Containing Materials for Lithium‐Ion Battery Anodes

“…Following the trend begun in 2014, this year was mainly characterized by a large number of works focused on long-term cyclability tests (e.g., ≥1000 cycles), generally performed at medium/high currents (e.g., ≥1 A g −1 ). Indeed, graphene-containing insertion (e.g., Li 3 VO 4 , [351][352][353] TiO 2 [ 354,355 ] and LTO [ 356 ] ), conversion (e.g., CoFe 2 O 4 , [ 357 ] Co 3 O 4 , [ 358 ] FeS 2 , [ 359 ] ) and alloying (e.g., Si [360][361][362] and SnO 2 [ 363 ] ) binary hybrids, as well as ternary analogues, [364][365][366][367] showed remarkable results in terms of specifi c gravimetric capacity retained after long cycling. Moreover, other intermetallic compounds (e.g., SnSb [ 368,369 ] ) and metal oxides (e.g., Fe 3 O 4 [ 370,371 ] and MnO [ 372 ] ), when combined with graphene, showed improved cycling stability with respect to their bare analogues.…”

Amorphous Vanadium Titanates as a Negative Electrode for Lithium-ion Batteries

“…The morphology of aVTO powder is advantageous in high-power applications because it provides a short Li + diffusion path and a larger contact area with the electrolyte solution [13][14][15][16][17]. Fig.…”

“…It is intuitive that phase transitions can be suppressed by introducing disorder, for instance, structural defects such as vacancies and void spaces on the surface of nanostructured materials or in the bulk of amorphous materials [12]. Moreover, nanostructuring of electrode materials is expected to be a promising strategy to increase the power density of cells by shortening the Li + diffusion path within the bulk materials [13][14][15][16][17]. In addition to suppressing unwanted phase transitions, amorphization of electrode materials has also been proven effective for increasing the number of Li + storage sites and facilitating solid-state Li + diffusion through the abundant void spaces [18][19][20][21].…”