Dongsheng Guan

A scalable graphene sulfur composite synthesis for rechargeable lithium batteries with good capacity and excellent columbic efficiency.

Sulfur nanoparticles wrapped with a conductive graphene framework was synthesized with a high sulfur loading through a scalable one-step process. The graphene-coated sulfur nanostructured composite, when used as cathode for lithium sulfur battery, shows a reversible capacity of 808 mAh g(-1) at a rate of 210 mA g(-1) and an average columbic efficiency of ∼98.3% over 100 cycles. It is found that graphene oxide (GO) with a porous structure offers flexible confinement function that helps prevent the loss of active materials, thus extending the cycling life of the electrode. Moreover, reduced graphene oxide provides a conductive network surrounding the sulfur particles, which facilitates both electron transport and ion transportation. This novel one-step, all-solution-based process is scalable and provides a promising approach for potential industrial applications.

A Multilayered Silicon-Reduced Graphene Oxide Electrode for High Performance Lithium-Ion Batteries

A multilayered structural silicon-reduced graphene oxide electrode with superior electrochemical performance was synthesized from bulk Si particles through inexpensive electroless etching and graphene self-encapsulating approach. The prepared composite electrode presents a stable charge-discharge performance with high rate, showing a reversible capacity of 2787 mAh g(-1) at a charging rate of 100 mA g(-1), and a stable capacity over 1000 mAh g(-1) was retained at 1 A g(-1) after 50 cycles with a high columbic efficiency of 99% during the whole cycling process. This superior performance can be attributed to its novel multilayered structure with porous Si particles encapsulated, which can effectively accommodate the large volume change during the lithiation process and provide increased electrical conductivity. This facile low-cost approach offers a promising route to develop an optimized carbon encapsulated Si electrode for future industrial applications.

Enhanced photovoltaic performance of perovskite CH₃NH₃PbI₃ solar cells with freestanding TiO₂ nanotube array films.

Freestanding TiO2 nanotube array films are fabricated and first applied as electrodes in perovskite CH3NH3PbI3 sensitized solar cells. The device demonstrates improved light absorption with more than 90% of light absorbed in the whole visible range and a reduced charge recombination rate, leading to a significant improvement of the photocurrent and efficiency. This study suggests a promising way of improving the conversion efficiency of perovskite solar cells through novel electrodes.

Effects of amorphous and crystalline MoO3 coatings on the Li-ion insertion behavior of a TiO2 nanotube anode for lithium ion batteries

Amorphous and crystalline MoO3 coatings are synthesized on anodic TiO2 nanotube arrays by electrodeposition, as a self-standing, binder-free anode material in Li-ion batteries for enhancing the Li-ion insertion performance. The amorphous MoO3 layer is uniform and conformal with a thickness of 10 nm, and is converted into crystalline nanoparticles via thermal treatment. Our results show that both the coated TiO2 nanotubes deliver much higher areal capacities than bare nanotubes or a dense crystalline α-MoO3 film, while the crystalline α-MoO3 coating greatly increases the areal capacity of TiO2 nanotubes compared to the amorphous. The results are obtained at 1340 μA h cm−2 initial capacity for nanotubes with a crystalline coating, 977 μA h cm−2 for those with an amorphous coating and 342 μA h cm−2 for the bare ones. The significant enhancement is due to a combination of MoO3 with high specific capacity and TiO2 nanotube arrays with large surface area allowing uniform MoO3 deposition and rapid ionic transfer. Crystalline α-MoO3 is better than amorphous MoO3 and the coating medium is discussed in terms of chemical state, crystal defects, capacitive contributions and the charge–discharge kinetics in coated TiO2 nanotube electrodes.

Carbon nanotube-assisted growth of single-/multi-layer SnS2 and SnO2 nanoflakes for high-performance lithium storage

SnS2 nanoparticles and SnS2 nanoflake/CNTs composite are prepared by a low-cost facile hydrothermal method for their use in rechargeable Li-ion batteries. It is found that the presence of multi-walled CNTs during synthesis greatly affects the morphology of as-formed SnS2 nanostructures, and circinal single-layer and multilayer SnS2 nanoflakes enwrapped by CNTs are produced. The composite is further oxidized to porous SnO2 nanoflake/CNTs hybrid by annealing at 500 °C in air. The formation mechanism of SnS2/CNTs and SnO2/CNTs composites is examined. All the three materials are used as the anode in Li-ion batteries. The SnS2/CNTs composite delivers stronger cycling stability than the pure SnS2 anode. In tests the former exhibits excellent capacity retention of 91.5% at 100 mA g−1 over 50 cycles, while the latter displays 66.8%. The rate capability of SnS2/CNTs composite is much better than pure SnS2 as well. Redox reaction characteristics and Li-ion transfer kinetics at the two SnS2 anodes are studied by differential capacity plots and electrochemical impedance spectroscopy. It is discovered that the SnS2/CNTs composite with larger surface area allows faster Li-ion transfer kinetics, effective cushion of volume changes, and thus gains the improved Li-ion intercalation behaviours. The capacity of the tin-based anode can be further raised by transformation to a SnO2/CNTs hybrid that also delivers excellent rate and cycling performances.

Atomic Layer Deposition Process Modeling and Experimental Investigation for Sustainable Manufacturing of Nano Thin Films

This paper studies the adverse environmental impacts of atomic layer deposition (ALD) nano-manufacturing technology on ALD of Al2O3 nano-scale thin films. Numerical simulations with detailed ALD surface reaction mechanism developed based on Density Functional Theory (DFT), and atomic-level calculations are performed to investigate the effects of four process parameters including process temperature, pulse time, purge time, and carrier gas flow rate on ALD film deposition rate, process emissions and wastes. Full-cycle ALD simulations reveal that the depositions of nano-thin-films in ALD are in essence the chemisorption of the gaseous species and the conversion of surface species. Methane emissions are positively proportional to the film deposition process. The studies show that process temperature fundamentally affects the ALD chemical process by changing the energy states of the surface species. Pulse time is directly related to the precursor dosage. Purge time influences the ALD process by changing the gas-surface interaction time, and higher carrier gas flow rate alters the ALD flow field by accelerating the convective heat and mass transfer in ALD process.

Laser ablation on lithium-ion battery electrode solid electrolyte interface removal

The formation of a solid electrolyte interface (SEI) on a Li-ion battery electrode during usage cycling is a critical reason for battery capacity loss. In this paper, laser ablation technology is applied to remove SEI from a graphite electrode surface. Characterization methods including scanning electron microscopy, Raman microscopy, and Fourier transform infrared spectroscopy are used to study the structure and morphology changes of the SEI on the electrode surface. The results show that laser ablation can successfully remove the SEI, indicating a feasible method to clean the electrode surface.