Electrochemically active metals and metal oxides such as Sn, [1] Si, [2] SnO 2 , [3] and Co 3 O 4 [4] have long been considered as anode materials for lithium ion batteries because of their high theoretical capacities. However, a large specific volume change commonly occurs in the host matrix of these metals and metal oxides during the cycling processes, thus leading to pulverization of the electrodes and rapid capacity decay. [1][2][3] To circumvent these obstacles, carbonaceous materials with high electrical conductivity and fair ductility have been widely chosen as matrices for metals and metal oxides to improve their cycle performance. In particular, graphene, which is a monolayer of carbon atoms arranged in a honeycomb network, is becoming one of the most appealing matrices because of its unique properties such as superior electrical conductivity, [5] excellent mechanical flexibility, [6] large surface area (2630 m 2 g À1 ), [7] and high thermal and chemical stability. [8] In this regard, Si/graphene, [9] SnO 2 /graphene, [10] TiO 2 /graphene, [11] and Co 3 O 4 /graphene [12] hybrids or composites, in which metals or metal oxides are distributed onto the surface of graphene or between the graphene layers, have been fabricated by restacking graphene sheets in the presence of guest nanoparticles or corresponding organometallic precursors. Compared to other carbon matrices such as graphite, [13] carbon black, [14] and carbon nanotubes, [15] graphene sheets can more effectively buffer the strain from the volume change of metals or metal oxides during the charging-discharging processes and preserve the high electrical conductivity of the overall electrode. Nevertheless, the metal and metal oxide nanoparticles are still prone to strong aggregation during the cycle processes because of nonintimate contact between graphene layers and active nanoparticles. [7][8][9][10] This leads to a decrease in capacity of most metal or metal oxide/graphene composites by 20-50 % of their first reversible capacity after 30 cycles. [9][10] One of the most promising strategies to tackle the aggregation problem of metal and metal oxides in lithium ion batteries is to confine them within individual carbon shells. [16][17][18][19] A key challenge in this strategy is the achievement of both high electrical conductivity and a low-weight fraction of thin carbon layers on the surface of metal or metal oxide nanoparticles.Herein we describe a novel strategy for the fabrication of graphene-encapsulated metal oxide (GE-MO) by coassembly between negatively charged graphene oxide and positively charged oxide nanoparticles. The process is driven by the mutual electrostatic interactions of the two species, and is followed by chemical reduction. The resulting GE-MO possesses flexible and ultrathin graphene shells that effectively enwrap the oxide nanoparticles. This unique hybrid architecture can 1) suppress the aggregation of oxide nanoparticles, 2) accommodate the volume change during the cycle processes, 3) give rise to a high oxide content i...

Electrochemically active metals and metal oxides such as Sn, [1] Si, [2] SnO 2 , [3] and Co 3 O 4 [4] have long been considered as anode materials for lithium ion batteries because of their high theoretical capacities. However, a large specific volume change commonly occurs in the host matrix of these metals and metal oxides during the cycling processes, thus leading to pulverization of the electrodes and rapid capacity decay. [1][2][3] To circumvent these obstacles, carbonaceous materials with high electrical conductivity and fair ductility have been widely chosen as matrices for metals and metal oxides to improve their cycle performance. In particular, graphene, which is a monolayer of carbon atoms arranged in a honeycomb network, is becoming one of the most appealing matrices because of its unique properties such as superior electrical conductivity, [5] excellent mechanical flexibility, [6] large surface area (2630 m 2 g À1 ), [7] and high thermal and chemical stability. [8] In this regard, Si/graphene, [9] SnO 2 /graphene, [10] TiO 2 /graphene, [11] and Co 3 O 4 /graphene [12] hybrids or composites, in which metals or metal oxides are distributed onto the surface of graphene or between the graphene layers, have been fabricated by restacking graphene sheets in the presence of guest nanoparticles or corresponding organometallic precursors. Compared to other carbon matrices such as graphite, [13] carbon black, [14] and carbon nanotubes, [15] graphene sheets can more effectively buffer the strain from the volume change of metals or metal oxides during the charging-discharging processes and preserve the high electrical conductivity of the overall electrode. Nevertheless, the metal and metal oxide nanoparticles are still prone to strong aggregation during the cycle processes because of nonintimate contact between graphene layers and active nanoparticles. [7][8][9][10] This leads to a decrease in capacity of most metal or metal oxide/graphene composites by 20-50 % of their first reversible capacity after 30 cycles. [9][10] One of the most promising strategies to tackle the aggregation problem of metal and metal oxides in lithium ion batteries is to confine them within individual carbon shells. [16][17][18][19] A key challenge in this strategy is the achievement of both high electrical conductivity and a low-weight fraction of thin carbon layers on the surface of metal or metal oxide nanoparticles.Herein we describe a novel strategy for the fabrication of graphene-encapsulated metal oxide (GE-MO) by coassembly between negatively charged graphene oxide and positively charged oxide nanoparticles. The process is driven by the mutual electrostatic interactions of the two species, and is followed by chemical reduction. The resulting GE-MO possesses flexible and ultrathin graphene shells that effectively enwrap the oxide nanoparticles. This unique hybrid architecture can 1) suppress the aggregation of oxide nanoparticles, 2) accommodate the volume change during the cycle processes, 3) give rise to a high oxide content i...

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Anisotropic surface modification of TiO2 nanoparticles was achieved applying a Pickering emulsion approach. TiO2 nanoparticles were prepared by sol-gel routes which allowed an excellent control over their size and morphology. The obtained colloids were further used as stabilizers in the formation of oil-in-water Pickering emulsion. For reasons of comparison, also commercially available titanium dioxide nanoparticles (Evonik AEROXIDE TiO2 P25) were used in the functionalization experiments. An organophosphorus coupling agent present in the oil phase coordinated to the surface of the anatase nanoparticles. In such a way an anisotropic surface modification of the particles was achieved which increased the stability of the Pickering emulsion. Spectroscopic studies revealed the presence of organophosphorus coupling agents which exhibited a covalent bonding to the surface of the particles. Thermogravimetric analyses confirmed a lower surface coverage of the particles modified in emulsion compared to those modified in suspension. Reactions of organophosphorus coupling agents containing an additional methacrylate group applying an organic monomer (methyl methacrylate) as the oil phase of the Pickering emulsion resulted in hybrid TiO2@polymer spheres. Spectroscopic characterization of the resulting particles revealed that the phosphonates were coordinated to the TiO2 surface and at the same time copolymerized with the MMA within the oil droplet. Morphological investigations of the isolated final product showed that the material was composed of polymer spheres with the stabilizing TiO2 nanoparticles on their surface.

Well-defined complexes of Ti and Zr alkoxides and β-keto ester ligands carrying polymerizable double bonds were copolymerized with methyl methacrylate applying atom transfer radical polymerization. The structure and the morphology of the obtained hybrid polymers were investigated using NMR, FT-IR, and size exclusion chromatography. All methods revealed an incorporation of both comonomers in the polymer backbone. NMR and FT-IR analyses demonstrated that after polymerization the chemical linkage between the metal alkoxides and the organic macromolecules was preserved. The alkoxide-containing macromolecules were used as precursors in the formation of metal oxide-containing nanocomposites applying the sol−gel process. The decomposition temperature of the final nanocomposites increased depending on the chemical composition of the materials. Small-angle X-ray scattering investigations revealed a short-range order for the polymers containing Ti-alkoxides which disappeared after carrying out the sol−gel process due to the hydrolysis of the well-defined complexes. Transmission electron microscopy showed the formation of amorphous metal oxide nanoparticles inside the polymer network with diameters of a few nanometers. The particles were highly dispersed due to the low mobility of the alkoxides in the matrix during the sol−gel process.