One-pot Spray Pyrolysis Research Articles

Superior electrochemical properties of rutile VO2-carbon composite microspheres as a promising anode material for lithium ion batteries

We report a new process to prepare VO2(R)-carbon composite microspheres, which can be used as an anode material in lithium ion batteries. Crystalline V2O3-carbon composite microspheres prepared by a one-pot spray pyrolysis process are transformed into VO2(R)-carbon composite microspheres by heat treatment at 300°C under air atmosphere. Polyvinylpyrrolidone (PVP), which is used as the carbon source, affects the morphologies, crystal structures, and electrochemical properties of the vanadium oxide materials. The carbon content of the VO2(R)-carbon composite powders is about 12.5 wt%. The bare vanadium oxide powders prepared from the spray solution without PVP show rod-like or spherical morphologies. The initial discharge and charge capacities of the VO2(R)-carbon composite powders are 1091 and 659mAhg−1, respectively. The discharge capacity of the VO2(R)-carbon composite powders after 100 cycles is 637mAhg−1 and their capacity retention after 100 cycles measured from the second cycle is 96.0%. The high structural stability encountered during lithium insertion and extraction improves the electrochemical properties of the VO2(R)-carbon composite powders.

General formation of tin nanoparticles encapsulated in hollow carbon spheres for enhanced lithium storage capability.

A new simple process for synthesis of heterogeneous yolk-shell microspheres is introduced. The core/shell-structured microspheres are prepared by a one-pot spray pyrolysis process. The removal of one kind of metal oxide by a dry process produces heterogeneous yolk-shell microspheres. The yolk-shell Sn@C microspheres show superior electrochemical properties as anode materials for lithium-ion batteries.

Formation of core-shell-structured Zn2SnO4-carbon microspheres with superior electrochemical properties by one-pot spray pyrolysis.

Core-shell structured Zn2SnO4-carbon microspheres with different carbon contents are prepared by one-pot spray pyrolysis without any further heating process. A Zn2SnO4-carbon composite microsphere is prepared from one droplet containing Zn and Sn salts and polyvinylpyrrolidone (PVP). Melted PVP moves to the outside of the composite microsphere during the drying stage of the droplet. In addition, melting of the phase separated metal salts forms the dense core. Carbonization of the phase separated PVP forms the textured and porous thick carbon shell. The discharge capacities of the core-shell structured Zn2SnO4-carbon microspheres for the 2(nd) and 120(th) cycles at a current density of 1 A g(-1) are 864 and 770 mA h g(-1), respectively. However, the discharge capacities of the bare Zn2SnO4 microspheres prepared by the same process without PVP for the 2(nd) and 120(th) cycles are 1106 and 81 mA h g(-1), respectively. The stable and reversible discharge capacities of the Zn2SnO4-carbon composite microspheres prepared from the spray solution with 15 g PVP decrease from 894 to 528 mA h g(-1) as current density increases from 0.5 to 5 A g(-1).

Synthesis and electrochemical properties of spherical and hollow-structured NiO aggregates created by combining the Kirkendall effect and Ostwald ripening.

The Kirkendall effect and Ostwald ripening were successfully combined to prepare uniquely structured NiO aggregates. In particular, a NiO-C composite powder was first prepared using a one-pot spray pyrolysis, which was followed by a two-step post-treatment process. This resulted in the formation of micron-sized spherical and hollow-structured NiO aggregates through a synergetic effect that occurred between nanoscale Kirkendall diffusion and Ostwald ripening. The discharge capacity of the spherical and hollow-structured NiO aggregates at the 500(th) cycle was 1118 mA h g(-1) and their capacity retention, which was measured from the second cycle, was nearly 100%. However, the discharge capacities of the solid NiO aggregates and hollow NiO shells were 631 and 150 mA h g(-1), respectively, at the 500(th) cycle and their capacity retentions, which were measured from the second cycle, were 63 and 14%, respectively. As such, the spherical and hollow-structured NiO aggregates, which were formed through the synergetic effect of nanoscale Kirkendall diffusion and Ostwald ripening, have high structural stability during cycling and have excellent lithium storage properties.

Design and synthesis of micron-sized spherical aggregates composed of hollow Fe2O3 nanospheres for use in lithium-ion batteries.

A novel structure denoted a "hollow nanosphere aggregate" is synthesized by introducing nanoscale Kirkendall diffusion to the spray pyrolysis process. The hollow Fe2O3 nanosphere aggregates with spherical shape and micron size are synthesized as the first target material. A solid iron oxide-carbon composite powder that is prepared by a one-pot spray pyrolysis process is transformed into the hollow Fe2O3 nanosphere aggregates by sequential post-pyrolysis treatments under reducing and oxidizing atmospheres. The nanoscale Kirkendall diffusion plays a key role in the formation of the hollow Fe2O3 nanosphere aggregates with spherical shape and micron size. The unique structure of the hollow Fe2O3 nanosphere aggregates results in their superior electrochemical properties as an anode material for lithium ion batteries by improving the structural stability during cycling. The hollow metal oxide nanosphere aggregates with various compositions for wide applications including energy storage can be prepared by the simple fabrication method introduced in this study.

Superior electrochemical performances of double-shelled CuO yolk–shell powders formed from spherical copper nitrate–polyvinylpyrrolidone composite powders

Spherical copper nitrate–polyvinylpyrrolidone (PVP) composite powders coated with a copper nitrate hydroxide [Cu2(OH)3NO3]–carbon composite are prepared by a one-pot spray pyrolysis process. In this, Cu2(OH)3NO3 and carbon are formed by dehydration of copper nitrate and carbonization of PVP, respectively. Thermal decomposition of the composite powders is then performed at 300 °C under an air atmosphere, producing the final yolk–shell-structured CuO powders. The electrochemical properties of these powders are then compared with those of commercial CuO nanopowders. The discharge capacities of the CuO yolk–shell powders and the commercial CuO nanopowders after 240 cycles at a current density of 500 mA g−1 are 590 and 302 mA h g−1, respectively. Furthermore, the discharge capacity of the CuO yolk–shell powders is as high as 615 mA h g−1, even after 1000 cycles at a current density of 1000 mA g−1. Electrochemical impedance spectroscopy reveals that the structural stability of the CuO yolk–shell powders during cycling lowers the charge transfer resistance, and thereby improves the lithium ion diffusion rate.

Electrochemical properties of tin oxide flake/reduced graphene oxide/carbon composite powders as anode materials for lithium-ion batteries.

Hierarchically structured tin oxide/reduced graphene oxide (RGO)/carbon composite powders are prepared through a one-pot spray pyrolysis process. SnO nanoflakes of several hundred nanometers in diameter and a few nanometers in thickness are uniformly distributed over the micrometer-sized spherical powder particles. The initial discharge and charge capacities of the tin oxide/RGO/carbon composite powders at a current density of 1000 mA g(-1) are 1543 and 1060 mA h g(-1), respectively. The discharge capacity of the tin oxide/RGO/carbon composite powders after 175 cycles is 844 mA h g(-1), and the capacity retention measured from the second cycle is 80%. The transformation during cycling of SnO nanoflakes, uniformly dispersed in the tin oxide/RGO/carbon composite powder, into ultrafine nanocrystals results in hollow nanovoids that act as buffers for the large volume changes that occur during cycling, thereby improving the cycling and rate performances of the tin oxide/RGO/carbon composite powders.

Rapid continuous synthesis of spherical reduced graphene ball-nickel oxide composite for lithium ion batteries.

In this study, we synthesized a powder consisting of core-shell-structured Ni/NiO nanocluster-decorated graphene (Ni/NiO-graphene) by a simple process for use as an anodic material for lithium-ion batteries. First, a crumpled graphene powder consisting of uniformly distributed Ni nanoclusters was prepared by one-pot spray pyrolysis. This powder was subsequently transformed into the Ni/NiO-graphene composite by annealing at 300°C in air. The Ni/NiO-graphene composite powder exhibited better electrochemical properties than those of the hollow-structured NiO-Ni composite and pure NiO powders. The initial discharge and charge capacities of the Ni/NiO-graphene composite powder were 1156 and 845 mA h g−1, respectively, and the corresponding initial coulombic efficiency was 73%. The discharge capacities of the Ni/NiO-graphene, NiO-Ni, and pure NiO powders after 300 cycles were 863, 647, and 439 mA h g−1, respectively. The high stability of the Ni/NiO-graphene composite powder, attributable to the unique structure of its particles, resulted in it exhibiting long-term cycling stability even at a current density of 1500 mA g−1, as well as good rate performance. The structural stability of the Ni/NiO-graphene composite powder particles during cycling lowered the charge transfer resistance and improved the Li-ion diffusion rate.

One-pot synthesis of manganese oxide-carbon composite microspheres with three dimensional channels for Li-ion batteries

The fabrication of manganese oxide-carbon composite microspheres with open nanochannels and their electrochemical performance as anode materials for lithium ion batteries are investigated. Amorphous-like Mn3O4 nanoparticles embedded in a carbon matrix with three-dimensional channels are fabricated by one-pot spray pyrolysis. The electrochemical properties of the Mn3O4 nanopowders are also compared with those of the Mn3O4-C composite microspheres possessing macropores resembling ant-cave networks. The discharge capacity of the Mn3O4-C composite microspheres at a current density of 500 mA g−1 is 622 mA h g−1 after 700 cycles. However, the discharge capacity of the Mn3O4 nanopowders is as low as 219 mA h g−1 after 100 cycles. The Mn3O4-C composite microspheres with structural advantages and high electrical conductivity have higher initial discharge and charge capacities and better cycling and rate performances compared to those of the Mn3O4 nanopowders.

Electrochemical properties of ultrafine Sb nanocrystals embedded in carbon microspheres for use as Na-ion battery anode materials.

Ultrafine Sb nanocrystals, uniformly distributed in a carbon matrix with a microspherical morphology, were synthesized by one-pot spray pyrolysis. The Sb-carbon composite microspheres exhibited good Na-storage properties with stable cyclability, a capacity retention of 90% over 100 cycles, and good rate performance.

Macroporous Fe3O4/carbon composite microspheres with a short Li+ diffusion pathway for the fast charge/discharge of lithium ion batteries.

Macroporous Fe3O4/carbon composite and core-shell Fe3O4@carbon composite microspheres have been prepared by means of one-pot spray pyrolysis. The addition of polystyrene (PS) nanobeads to a spray solution containing an iron salt and poly(vinylpyrrolidone) (PVP) led to macroporous Fe3O4/carbon composite microspheres, the carbon and iron components of which are uniformly distributed over the entire composite microsphere. The pore-size distribution curve for the macroporous Fe3O4/carbon composite shows distinct peaks at around 10 and 80 nm. An electrode prepared from the macroporous Fe3O4/carbon composite microspheres showed better cycling and rate performances than an electrode formed from core-shell Fe3O4@carbon composite microspheres. The initial discharge and charge capacities of the macroporous Fe3O4/carbon composite microsphere electrode were determined to be 1258 and 908 mA h g(-1) at 2 A g(-1), respectively, and the corresponding initial coulombic efficiency was 72 %. The composite microsphere electrode cycled 500 times at 5 A g(-1) showed a high discharge capacity of 733 mA h g(-1).

Uniform Decoration of Vanadium Oxide Nanocrystals on Reduced Graphene‐Oxide Balls by an Aerosol Process for Lithium‐Ion Battery Cathode Material

VO2-decorated reduced graphene balls were prepared by a one-pot spray-pyrolysis process from a colloidal spray solution of well-dispersed graphene oxide and ammonium vanadate. The graphene-VO2 composite powders prepared directly by spray pyrolysis had poor electrochemical properties. Therefore, the graphene-VO2 composite powders were transformed into a reduced graphene ball (RGB)-V2O5 (RGB) composite by post-treatment at 300 °C in an air atmosphere. The TEM and dot-mapping images showed a uniform distribution of V and C components, originating from V2O5 and graphene, consisting the composite. The graphene content of the RGB-V2O5 composite, measured by thermogravimetric analysis, was approximately 5 wt %. The initial discharge and charge capacities of RGB-V2O5 composite were 282 and 280 mA h g(-1), respectively, and the corresponding Coulombic efficiency was approximately 100 %. On the other hand, the initial discharge and charge capacities of macroporous V2O5 powders were 205 and 221 mA h g(-1), respectively, and the corresponding Coulombic efficiency was approximately 93 %. The RGB-V2O5 composite showed a better rate performance than the macroporous V2O5 powders.

Electrochemical properties of graphene-MnO composite and hollow-structured MnO powders prepared by a simple one-pot spray pyrolysis process

Graphene-MnO composite and hollow-structured MnO powders are prepared by a simple one-pot spray pyrolysis process. The graphene content in the graphene-MnO composite powder is estimated to be 10wt.%. The fine MnO crystals of size several tens of nanometers are uniformly distributed all over the graphene. The BET specific surface areas of the graphene-MnO composite and hollow-structured MnO powders are found to be 20 and 5 m2g−1, respectively. The graphene-MnO composite powders have high initial discharge and charge capacities of 1207 and 849mA h g−1, respectively, at a current density of 500mAg−1. The initial discharge and charge capacities of the hollow-structured MnO powders are 1004 and 673mA h g−1, respectively. The discharge capacities of the graphene-MnO composite and hollow-structured MnO powders for the 130th cycle are 1313 and 701mA h g−1, respectively.

Superior cycling and rate performances of rattle-type CoMoO4 microspheres prepared by one-pot spray pyrolysis

Rattle-type CoMoO4 and CoMoO4–carbon composite microspheres were prepared by one-pot spray pyrolysis at temperatures of 850 and 700 °C, respectively. The XRD patterns of both the samples corresponded to the pure crystal structure of β-CoMoO4. The CoMoO4–carbon composite microspheres exhibited broad diffraction peaks with relatively lower intensities, when compared to those of rattle-type CoMoO4 microspheres. This indicates the poor crystallinity of the carbon composite powders, despite the similar preparation conditions. In the initial cycles, the rattle-type CoMoO4 microspheres and CoMoO4–carbon composite microspheres delivered discharge capacities of 1221 and 1245 mA h g−1, respectively at a current density of 500 mA g−1, and charge capacities of 1019 and 896 mA h g−1, respectively, corresponding to Coulombic efficiencies of 83 and 72%, respectively. After 150 cycles, the discharge capacities of the rattle-type and carbon composite microspheres were 1065 and 833 mA h g−1, respectively, and the corresponding capacity retentions measured after the first cycles were 100 and 90%, respectively. The morphology of the rattle-type CoMoO4 microsphere was maintained, despite repeated Li+ insertion and extraction processes, even at a high current density of 500 mA g−1.

Electrochemical Properties of Hollow‐Structured MnS–Carbon Nanocomposite Powders Prepared by a One‐Pot Spray Pyrolysis Process

Spherical, hollow MnS-C composite powders were prepared from a solution of manganese salt, thiourea, and sucrose by one-pot spray pyrolysis. The MnS-C composite powders were generated by direct sulfidation of MnO with hydrogen sulfide gas generated in situ by decomposition of thiourea during spray pyrolysis. Sucrose, which is used as a carbon source material, plays a key role in the formation of the MnS-C composite powders by improving the reducing atmosphere around the powders. Dot-mapping images of the composite powders demonstrated uniform distribution of the manganese, sulfur, and carbon components within the MnS-C composite powder. Fine crystals of MnS were uniformly mixed with carbon derived from polymerization and carbonization of sucrose. The carbon content of the MnS-C composite powders was 26 wt%. The discharge capacities of the MnS-C composite powders in the 2nd and 200th cycles were 863 and 967 mA h g(-1), respectively, at a current density of 1000 mA g(-1). The spherical and hollow morphology of the MnS-C composite powders was completely retained, even after 200 cycles. The enhanced cycling and rate performance of the MnS-C composite powders is ascribed to the structural stability of the composite powders.

Electrochemical properties of bare nickel sulfide and nickel sulfide–carbon composites prepared by one-pot spray pyrolysis as anode materials for lithium secondary batteries

Spherical bare nickel sulfide and nickel sulfide–carbon composite powders are prepared by a one-step spray pyrolysis. Submicron bare nickel sulfide particles with a dense structure have mixed crystal phases of NiS, Ni7S6, and NixS6. The nickel sulfide–carbon composite powders prepared from a spray solution containing 0.1 M sucrose have a main crystal structure of Ni7S6 phase with small impurity peaks of NixS6 phase. A nickel oxide–carbon composite powder is first formed as an intermediate product in the front part of the reactor at 800 °C. Fast decomposition of thiourea at this high temperature results in the evolution of hydrogen sulfide gas, which then forms the nickel sulfide–carbon composite powders by direct sulfidation of nickel oxide under the reducing atmosphere. Nickel sulfide nanocrystals with a size of a few nanometers are uniformly distributed inside the spherical carbon matrix. The nickel sulfide–carbon composite powders prepared with 0.1 M sucrose have an excellent discharge capacity of 472 mA h g−1 at a high current density of 1000 mA g−1, even after 500 cycles, with the corresponding capacity retention measured after the first cycle being 86%.

Electrochemical Properties of Yolk-Shell-Structured CuO-Fe2O3Powders with Various Cu/Fe Molar Ratios Prepared by One-Pot Spray Pyrolysis

Several yolk-shell-structured CuO-Fe2 O3 powders with various Cu/Fe molar ratios have been successfully prepared under equivalent reaction conditions using a one-pot spray pyrolysis process. The Cu and Fe components are uniformly distributed throughout the powders, irrespective of composition. The Brunauer-Emmett-Teller surface areas of the yolk-shell CuO-Fe2 O3 systems increased from 5 to 16 m(2) g(-1) if the Cu/Fe molar ratios are decreased from 3:1 to 1:3. The initial discharge and charge capacities of the yolk-shell CuO-Fe2 O3 system (Cu/Fe=1:2), showing maximum values at a constant current density of 1000 mA g(-1) , are 1436 and 1012 mA h g(-1) , respectively. After 130 cycles, the discharge capacities of the yolk-shell CuO-Fe2 O3 powders with Cu/Fe molar ratios of 1:3, 1:2, 1:1, 2:1, and 3:1 are 1159, 1151, 755, 655, and 651 mA h g(-1) , respectively. The discharge capacities of the yolk-shell and dense powder samples after 50 cycles, when subjected to a series of current density increases from 500 to 5000 mA g(-1) , are 735 and 495 mA h g(-1) , respectively.

Electrochemical Properties of ZrO2-Doped V2O5 Amorphous Powders with Spherical Shape and Fine Size

Amorphous V2O5 powders with zirconia (ZrO2) dopant are prepared by one-pot spray pyrolysis at temperatures above the melting temperature of V2O5. The powders with 7 wt % ZrO2 are completely spherical and dense with a clean surface, on which crystals of pure V2O5 powders are scarcely observed. The V2O5 powders with 7 wt % ZrO2 have uniformly distributed V and Zr components. The uniformly distributed Zr component disturbs the crystallization of V2O5 during the quenching of the melted powders. These powders also give smooth initial discharge curves with a single slope, which is typical to amorphous materials. The discharge capacities of the V2O5 powders with 7 wt % ZrO2 are 309, 269, and 222 mA h g(-1) after the first, second, and 50th cycles, respectively, even at a high current density of 294 mA g(-1). The capacity retention measured after the first cycle is 83% after 50 cycles.

Superior electrochemical properties of Co3O4 yolk–shell powders with a filled core and multishells prepared by a one-pot spray pyrolysis

Highly crystalline Co3O4 yolk-shell powders with a filled core and various shell numbers are prepared by a simple one-pot spray pyrolysis process. Co3O4 yolk-shell powders exhibited a high initial discharge capacity of 548 mA h g(-1) and retained their capacities very well, even at a high discharge rate of 10,000 mA g(-1).

One-pot synthesis of Fe2O3 yolk–shell particles with two, three, and four shells for application as an anode material in lithium-ion batteries

Fe2O3 yolk-shell particles with two, three, and four shells are prepared by one-pot spray pyrolysis. The discharge capacity of the Fe2O3 yolk-shell particles with two shells showing the best electrochemical properties is as high as 848 mA h g(-1) after 80 cycles at a current density of 300 mA g(-1).