ABSTRACT
Silicon (Si) has a large theoretical capacity of 4200 mAhg-1 and has great potential as a high-performance anode material for Li ion batteries (LIBs). Meanwhile, nanostructures can exploit the potential of Si and, accordingly, many zero-dimensional (0D) and one-dimensional (1D) Si nanostructures have been studied. Herein, we report on two-dimensional (2D) Si nanostructures, Si nanosheets (SiNSs), as anodes for LIBs. These 2D Si nanostructures, with a thickness as low 5 nm and widths of several micrometers, show reversible crystalline-amorphous phase transformations with the lithi-/delithiation by the dimensionality of morphology and large surface area. The reversible crystalline-amorphous phase transformation provides a structural stability of Li+ insertions and makes SiNSs promising candidates for reliable high-performance LIBs anode materials.
ABSTRACT
In this work, we report the electrochemical properties of 0.5Li2MnO3·0.25LiNi0.5Co0.2Mn0.3O2·0.25LiNi0.5Mn1.5O4 and 0.333Li2MnO3·0.333LiNi0.5Co0.2Mn0.3O2·0.333LiNi0.5Mn1.5O4 layered-layered-spinel (L*LS) cathode materials prepared by a high-energy ball-milling process. Our L*LS cathode materials can deliver a large and stable capacity of â¼200 mAhâ¯g(-1) at high voltages up to 4.9 V, and do not show the anomalous capacity increase upon cycling observed in previously reported three-component cathode materials synthesized with different routes. Furthermore, we have performed synchrotron-based in situ X-ray diffraction measurements and found that there are no significant structural distortions during charge/discharge runs. Lastly, we carry out (opt-type) van der Waals-corrected density functional theory (DFT) calculations to explain the enhanced cycle characteristics and reduced phase transformations in our ball-milled L*LS cathode materials. Our simple synthesis method brings a new perspective on the use of the high-power L*LS cathodes in practical devices.
ABSTRACT
The intercalation mechanism of zinc ions into 2 × 2 tunnels of an α-MnO2 cathode for rechargeable zinc batteries was revealed. It involves a series of single and two-phase reaction steps and produces buserite, a layered compound with an interlayer spacing of 11 Å as a discharge product.
ABSTRACT
Carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, have attracted significant attention as good candidates for next-generation heat-spreading materials because of their high thermal conductivity, mechanical flexibility, etc. Regarding the thermal spreading performance of carbon-based nanofilms, remarkable test results have been reported mainly from the industrial side, but their validity and the physical mechanism underlying the heat transfer enhancement are still under debate. In this study, we assess the thermal spreading performance of a multi-walled CNT film on a copper foil using a non-contact characterization method in a simple and methodical manner, and discuss the possibility of carbon nanofilms as heat spreaders based on the experimental and numerical results. This study provides useful information on heat transfer enhancement by carbon nanofilms and could contribute to the development of high-performance carbon-based heat-spreading coatings.
ABSTRACT
Core/shell-like nanostructured xLi2MnO3·(1-x)LiMO2 (M = Ni, Co, Mn) composite cathode materials are successfully synthesized through a simple solid-state reaction using a mechanochemical ball-milling process. The LiMO2 core is designed to have a high-content of Ni, which increases the specific capacity. The detrimental surface effects arising from the high Ni-content are countered by the Li2MnO3 shell, which stabilizes the nanoparticles. The electrochemical performances and thermal stabilities of the synthesized nanocomposites are compared with those of bare LiMO2. In particular, the results of time-resolved X-ray diffraction (TR-XRD) analyses of xLi2MnO3·(1-x)LiMO2 nanocomposites as well as their differential scanning calorimetry (DSC) profiles demonstrate that the Li2MnO3 shell is effective in stabilizing the LiMO2 core at high temperatures, making the nanocomposites highly suitable from a safety viewpoint.
