Feng Gong

Effective thermal transport properties in multiphase biological systems containing carbon nanomaterials

Here we report computational results from an off-lattice Monte Carlo investigation of the effective thermal transport properties in multiphase biological systems containing carbon nanomaterials. A three-phase system that consists of a cell, healthy tissue and carbon nanotubes (CNTs) was built in silico for this study. The CNTs were embedded in both the cell and the healthy tissue. The effective thermal conductivity (Keff) of such biological systems can be predicted by taking into account the dispersion of the CNTs and the interfacial thermal resistances (ITRs) between any pair of components. We quantitatively investigated the effects of the distribution (CNTs at different locations in the system), concentration (0.01–0.1 vol%), and morphology (diameter of 2–10 nm, length of 200–800 nm) of the CNTs on the Keff of the biological systems. Additionally, we studied the effects of the ITRs between any pair of components (0.05–76.5 × 10−8 m2 K W−1) on the Keff of the biological systems. The results showed that greater enhancement of the Keff values of the biological systems can be achieved by using longer CNTs in higher concentration, and reducing the ITRs between the CNTs and their surroundings. Finally, CNTs embedded on the cell membrane have a stronger effect than being dispersed within the cell or in the tissue surrounding the cell.

Facile and controllable synthesis of solid Co3V2O8 micro-pencils as a highly efficient anode for Li-ion batteries

Mixed metal vanadate oxides are promising superior anode materials for lithium ion batteries due to their high specific capacities, improved cycling performance and excellent rate properties. In this work, we demonstrate a facile and controllable synthesis of solid Co3V2O8 micro-particles with different morphologies through a hydrothermal method. By controlling the reaction time, either Co3V2O8 micro-plates or micro-pencils could be fabricated. Characterization via X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrated the pure phase and solid morphology of the Co3V2O8 micro-pencils. Scanning electron microscopy (SEM) images of the products obtained at different stages clearly revealed the formation process of the Co3V2O8 micro-pencils. Electrochemical measurements of the Co3V2O8 micro-pencils showed an excellent lithium storage capacity (1137 mAxa0h g−1 at 200 mA g−1), good cycling retention (∼670 mA h g−1 after 330 cycles), desirable coulombic efficiency (∼100% for 350 cycles) and notable rate capability (300 mA h g−1 at 2000 mA g−1). The improved electrochemical performances of the solid Co3V2O8 micro-pencils indicate their great potential as high-performance anode materials for lithium ion batteries.

Enhanced Electrochemical and Thermal Transport Properties of Graphene/MoS2 Heterostructures for Energy Storage: Insights from Multiscale Modeling

Graphene has been combined with molybdenum disulfide (MoS2) to ameliorate the poor cycling stability and rate performance of MoS2 in lithium ion batteries, yet the underlying mechanisms remain less explored. Here, we develop multiscale modeling to investigate the enhanced electrochemical and thermal transport properties of graphene/MoS2 heterostructures (GM-Hs) with a complex morphology. The calculated electronic structures demonstrate the greatly improved electrical conductivity of GM-Hs compared to MoS2. Increasing the graphene layers in GM-Hs not only improves the electrical conductivity but also stabilizes the intercalated Li atoms in GM-Hs. It is also found that GM-Hs with three graphene layers could achieve and maintain a high thermal conductivity of 85.5 W/(m·K) at a large temperature range (100-500 K), nearly 6 times that of pure MoS2 [∼15 W/(m·K)], which may accelerate the heat conduction from electrodes to the ambient. Our quantitative findings may shed light on the enhanced battery performances of various graphene/transition-metal chalcogenide composites in energy storage devices.

An in situ iodine-doped graphene/silicon composite paper as a highly conductive and self-supporting electrode for lithium-ion batteries

A graphene/silicon composite paper is considered as a promising anode material for flexible batteries. Herein, a highly conductive, flexible, self-supporting, and binder-free graphene/Si composite paper has been prepared via in situ iodine doping and simultaneous reduction of a graphene oxide/silicon composite slice with a solution of hydrohalic (HI) acid as a reducing agent. The in situ iodine doping not only increases the electrical conductivity of the graphene/silicon composite paper, but also improves the strength of the graphene matrix; this results in high capacity and enhanced cycling stability. The in situ iodine-doped composite paper is used as a flexible, self-supporting, and binder-free electrode. The composite paper exhibits a stable capacity retention of 805 mAxa0h g−1 after 100 cycles and an enhanced rate capability, which shows superior performance as compared to the common thermally reduced rGO/Si composites. The high flexibility and high conductivity as well as improved electrochemical performance of this binder-free self-supporting paper anode make it attractive for LIB applications in flexible storage devices.

Graphene coated Co3V2O8 micro-pencils for enhanced-performance in lithium ion batteries

Transition metal vanadates have attracted much attention for high capacity anodes of lithium ion batteries (LIBs). However, they have obvious drawbacks (short cycle-lives and low rate performance) because of the intrinsically low electronic conductivity and serious volume variation during Li-ion desorption and insertion. In particular, pure Co3V2O8 micro-pencils (pCVO MPs) have a stable and regular crystal structure, large tap density and uniform grain size, but, unfortunately, they have not exhibited expected electrochemical performance. Herein, we report the successful preparation of reduced graphene oxide coated Co3V2O8 micro-pencils (rGO@CVO MPs) through a facile approach combining hydrothermal synthesis with thermal reduction. When tested as anodes for LIBs, rGO@CVO MPs exhibit superior electrochemical performance compared to that of pure Co3V2O8 micro-pencils (pCVO MPs). The anodes of rGO@CVO MPs show a high reversible capacity of 760 mA h g−1 over 200 cycles at 200 mA g−1, and 500 mA h g−1 can remain after 500 cycles at 1000 mA g−1, with an increase in 200 mA h g−1 in contrast to the pCVO MPs. It is consequently demonstrated that the composite material (rGO@CVO MPs) is a promising anode material for LIBs.

Predictions of the thermal conductivity of multiphase nanocomposites with complex structures

Multiphase nanocomposites have drawn substantial attention due to their advanced functionality, including high thermal conductivity. Herein, theoretical models are developed based on modifications of the effective medium theory and then validated to predict the effective thermal conductivity (Keff) of three common multiphase nanocomposites: nanosheet/nanoparticle/polymer, nanotube/nanoparticle/polymer, and nanosheet/nanotube/polymer. Case studies showed that the predicted Keff agreed well with available experimental data, validating the developed models. Moreover, quantifiable material properties, like the thermal conductivity of nanofillers, the morphology of nanofillers, and the interfacial thermal resistance around nanofillers, were used to investigate their effects on the Keff of multiphase nanocomposites. This quantitative study not only can provide simplified strategy to predict the Keff for diverse multiphase nanocomposites, but it can also guide the design of multiphase nanocomposites with enhanced thermal conductivity.