Dewei Rao

Ultrahigh energy storage and ultrafast ion diffusion in borophene-based anodes for rechargeable metal ion batteries

Since the turn of the new century, the increasing demand for high-performance energy storage systems has generated considerable interest in rechargeable ion batteries (IBs). However, current IB technologies are not entirely satisfactory, especially the electrodes. We report here, via density functional theory calculations and first principles molecular dynamics simulations, that a borophene anode material has the fascinating properties of ultrahigh energy storage and ultrafast ion diffusion in metal (Li, Na, K, Mg, Al) IBs. Particularly for Li IBs with a borophene anode, a specific density of 3306 mA h g−1 and a high charging voltage of 1.46 V can be maintained at room temperature. Furthermore, non-ideal borophene anodes, including those with defects or oxidation and nanoribbon samples, still possess good properties for practical applications. This theoretical exploration will provide helpful guidance in searching for available or novel boron nanosheets as promising anode materials to advance commercial IB technology.

Separator modified by Ketjen black for enhanced electrochemical performance of lithium–sulfur batteries

A routine separator modified by a Ketjen black (KB) layer on the cathode side has been investigated to improve the electrochemical performances of Li–S batteries. The KB modified separator was prepared by a facile slurry coating method which offers a low-cost approach to solve the difficulties of Li–S batteries. Li–S cells assembled with this KB coated separator present excellent electrochemical performances in comparison with that of cells with a routine separator. The initial discharge capacity reaches 1318 mA h g−1 at 0.1C, and the reversible discharge capacity is maintained at 815 mA h g−1 after 100 cycles at 1C implying high capacity retention. Meanwhile, it achieves a discharge capacity of 934 mA h g−1 even at 2C demonstrating an excellent rate performance. Furthermore, electrochemical impedance spectroscopy (EIS) shows that the KB separator sample displays a lower charge transfer resistance which is beneficial for the electrochemical kinetics. The improved performance is supposed to be attributed to the porous architecture of the Ketjen black (KB) layer on the routine separator, which served as a physical barrier to block dissolved lithium polysulfides and an upper current collector to facilitate the transition of ions and electrons.

N-substituted defective graphene sheets: promising electrode materials for Na-ion batteries

Using density functional theory calculations, we have investigated the adsorption of Na on pristine and N-substituted defective graphene sheets (graphitic, pyridinic, and pyrrolic structures) and explored their application in Na-ion batteries. The adsorption energy and the charge transfer of Na on the various types of sheet were calculated. The effects of N-substitution were also studied by electronic structure analysis, including the total electronic density of states, partial electron density of states, and charge density differences. The results show that electron-rich structures have a negative influence on Na binding, while electron-deficient structures are beneficial. The Na storage capacities of different sheets were evaluated by optimizing multiple Na atom adsorbed structures. We found that more Na atoms can be stored on electron-deficient sheets, making them promising for practical application as electrode materials in Na-ion batteries.

Lithium decoration of three dimensional boron-doped graphene frameworks for high-capacity hydrogen storage

Based on density functional theory and the first principles molecular dynamics simulations, a three-dimensional B-doped graphene-interconnected framework has been constructed that shows good thermal stability even after metal loading. The average binding energy of adsorbed Li atoms on the proposed material (2.64 eV) is considerably larger than the cohesive energy per atom of bulk Li metal (1.60 eV). This value is ideal for atomically dispersed Li doping in experiments. From grand canonical Monte Carlo simulations, high hydrogen storage capacities of 5.9 wt% and 52.6 g/L in the Li-decorated material are attained at 298 K and 100 bars.

Graphdiyne as a High-Efficiency Membrane for Separating Oxygen from Harmful Gases: A First-Principles Study

We theoretically explored the adsorption and diffusion properties of oxygen and several harmful gases penetrating the graphdiyne monolayer. According to our first-principles calculations, the oxidation of the acetylenic bond in graphdiyne needs to surmount an energy barrier of ca. 1.97 eV, implying that graphdiyne remains unaffected under oxygen-rich conditions. In a broad temperature range, graphdiyne with well-defined nanosized pores exhibits a perfect performance for oxygen separation from typical noxious gases, which should be of great potential in medical treatment and industry.

Zn-MOF derived micro/meso porous carbon nanorod for high performance lithium–sulfur battery

In order to solve the problems of poor cycling stability and low coulombic efficiency in lithium–sulfur battery, induced by the low conductivity of sulfur and the shuttle effect of soluble polysulfides, a unique micro/meso porous carbon nanorod (MPCN) was fabricated by carbonizing a zinc metal–organic framework (Zn-MOF) precursor, which was prepared by a facile aqueous solution method at room temperature. The mesopores in the MPCN are beneficial for the infiltration of electrolyte and the transportation of Li ions, and the micropores are sufficient to encapsulate sulfur and adsorb the soluble polysulfides. The MPCN–S cathode displays a discharge capacity of about 1000 mA h g−1 at the current rate of 0.5C and retains 740 mA h g−1 after 200 cycles with the coulombic efficiency up to 95%. Moreover, it still has a discharge capacity as high as 850 mA h g−1 when the current rate increased to 2C, which demonstrates a nice rate capability.

CeO2 nanodots decorated ketjen black for high performance lithium–sulfur batteries

A CeO2 nanodots decorated ketjen black composite was fabricated by a simple wet impregnation method and used as the host of sulfur for a lithium–sulfur battery. The microstructure and chemical components were evaluated by XRD, SEM, TEM, surface area analysis and thermogravimetric analysis. Electrochemical tests and microanalysis demonstrated that CeO2 nanodots served as the sulfur fixation spots as well as the catalytic agent compared with the reference sample without CeO2 nanodots. The CeO2/KB–S cathode material with the CeO2/KB mass ratio of approximately 15/85 shows a high initial discharge capacity of 905 mA h g−1 at the current rate of 1C and remains at 710 mA h g−1 after 300 cycles. Furthermore, the CeO2/KB–S cathode shows a promising rate performance with the discharge capacity of 800 mA h g−1 even at the current rate of 2C.

Nanoporous MoS2 monolayer as a promising membrane for purifying hydrogen and enriching methane

We present a theoretical prediction of a highly efficient membrane for hydrogen purification and natural gas upgrading, i.e. laminar MoS2 material with triangular sulfur-edged nanopores. We calculated from first principles the diffusion barriers of H2 and CO2 across monolayer MoS2 to be, respectively, 0.07 eV and 0.17 eV, which are low enough to warrant their great permeability. The permeance values for H2 and CO2 far exceed the industrially accepted standard. Meanwhile, such a porous MoS2 membrane shows excellent selectivity in terms of H2/CO, H2/N2, H2/CH4, and CO2/CH4 separation (>103, >  103, >  106, and  >  104, respectively) at room temperature. We expect that the findings in this work will expedite theoretical or experimental exploration on gas separation membranes based on transition metal dichalcogenides.