Potassium Ion-Assisted Self-Assembled MXene-K-CNT Composite as High-Quality Sulfur-Loaded Hosts for Lithium-Sulfur Batteries.

We successfully synthesized hybrid MXene-K-CNT composites composed of alkalized two-dimensional (2D) metal carbide and carbon nanotubes (CNTs), which were employed as host materials for lithium-sulfur (Li-S) battery cathodes. The unique three-dimensional (3D) intercalated structure through electrostatic interactions by K+ ions in conjunction with the scaffolding effect provided by CNTs effectively inhibited the self-stacking of MXene nanosheets, resulting in an enhanced specific surface area (SSA) and ion transport capability. Moreover, the addition of CNTs and in situ-grown TiO2 considerably improved the conductivity of the cathode material. K+ ion etching created a more hierarchical porous structure in MXene, which further enhanced the SSA. The 3D framework effectively confined S embedded between nanosheet layers and suppressed volume changes of the cathode composite during charging/discharging processes. This combination of CNTs and alkalized nanosheets functioned as a physical and chemical dual adsorption system for lithium polysulfides (LiPSs). When subjected to a high current at 1.0C, S@MXene-K-0.5CNT with S-loaded of 1.2 mg cm-2 had an initial capacity of 919.6 mAh g-1 and capacity decay rate of merely 0.052% per cycle after 1000 cycles. Moreover, S@MXene-K-0.5CNT maintained good cycling stability even at a high current of up to 5.0C. These impressive results highlight the potential of alkalized 2D MXene nanosheets intercalated with CNTs as highly promising cathode materials for Li-S batteries. The study findings also have prospects for the development of next-generation Li-S batteries with high energy density and prolonged lifespans.

Multi-Role Surface Modification of Single-Crystalline Nickel-Rich Lithium Nickel Cobalt Manganese Oxides Cathodes with WO3 to Improve Performance for Lithium-Ion Batteries.

Compared with the polycrystalline system, the single-crystalline ternary cathode material has better cycle stability because the only primary particles without grain boundaries effectively alleviate the formation of micro/nanocracks and retain better structural integrity. Therefore, it has received extensive research attention. There is no consistent result whether tungsten oxide acts as doping and/or coating from the surface modification of the polycrystalline system. Meanwhile, there is no report on the surface modification of the single-crystalline system by tungsten oxide. In this paper, multirole surface modification of single-crystalline nickel-rich ternary cathode material LiNi0.6Co0.2Mn0.2O2 by WO3 is studied by a simple method of adding WO3 followed by calcination. The results show that with the change in the amount of WO3 added, single-crystalline nickel-rich ternary cathode material can be separately doped, separately coated, and both doped and coated. Either doping or coating effectively enhances the structural stability, reduces the polarization of the material, and improves the lithium-ion diffusion kinetics, thus improving the cycle stability and rate performance of the battery. Interestingly, both doping and coating (for SC-NCM622-0.5%WO3) do not show a more excellent synergistic effect, while the single coating (for SC-NCM622-1.0%WO3) after eliminating the rock-salt phase layer performs the most excellent modification effect.

One-Step Synthesis of Self-Supported Ni3S2/NiS Composite Film on Ni Foam by Electrodeposition for High-Performance Supercapacitors.

Herein, a facile one-step electrodeposition route was presented for preparing Ni3S2/NiS composite film on Ni foam substrate (denoted as NiSx/NF). The NiSx granular film is composed of mangy interconnected ultra-thin NiSx nanoflakes with porous structures. When applied as electrodes for supercapacitors, the ultra-thin nanoflakes can provide more active sites for redox reaction, and the interconnected porous structure has an advantage for electrolyte ions to penetrate into the inner space of active materials quickly. As expected, the obtained NiSx/NF sample exhibited high gravimetric capacitance of 1649.8 F·g-1 and areal capacitance of 2.63 F·cm-2. Furthermore, a gravimetric capacitance of 1120.1 F·g-1 can be maintained at a high current density of 20 mA·cm-2, suggesting a good rate capability. The influence of the different molar ratios of electrodeposition electrolyte (NiNO3 and thiourea) on the morphology and electrochemical properties of NiSx/NF sample was investigated to provide an optimum route for one-step electrodeposition of Ni3S2/NiS composite film. The outstanding performance indicated the Ni3S2/NiS composite film on Ni foam has great potential as an electrode material for supercapacitors.

Ferrocene as a Novel Additive to Enhance the Lithium-Ion Storage Capability of SnO2/Graphene Composite.

Improving the reversibility of conversion reaction is a promising way to enhance the lithium-ion storage capability of SnO2-based anodes. Herein, we report ferrocene as a novel additive to improve the Li-ion storage performance of the SnO2/graphene (SnO2/G) composite. Through a simple mixing method, ferrocene can be uniformly dispersed into the SnO2/G electrode. It is found that the ferrocene additive can effectively suppress the agglomeration of Sn/SnO2 and retain the nanoscale Sn/Li2O interface. Furthermore, metallic Fe is formed from ferrocene in the discharge process and acts as a catalyst to promote the reversible conversion between Sn/Li2O and SnO2. As a result, the SnO2/G electrode with the addition of 10 wt % ferrocene (10%Fc-SnO2/G) exhibits a superior Li-ion storage performance. It displays a reversible capacity of up to 1084.5 mAh g-1 at 0.1 A g-1 after 150 cycles with a good rate capability (752 mAh g-1 at 1 A g-1). In addition, the 10%Fc-SnO2/G electrode can retain a capacity of 787.2 mAh g-1 at 0.5 A g-1 after 220 cycles. This work demonstrates the promising additive of ferrocene in enhancing the reversible capacity of SnO2-based anodes for lithium-ion batteries.

Characterization of partially reduced graphene oxide as room temperature sensor for H2.

Reduced graphene oxide (RGO) was synthesized under H(2)/Ar treatment from 100 °C to 900 °C. RGO-300 shows excellent sensitivity to H(2) and a dual sensing mode was observed. The balance between the chemical adsorption capacity and electronic conductivity, and the dominance of either electrons or holes are the key factors.

Identification of the nitrogen species on N-doped graphene layers and Pt/NG composite catalyst for direct methanol fuel cell.

Heat treatment of graphene oxide (GO) with ammonia flow at various temperatures resulted in different distribution of nitrogen species. Synchrotron based X-ray absorption near-edge structure (XANES) spectroscopy provides unambiguous evidence for the presence of three nitrogen species. The Pt/NG-800 composite exhibits outstanding electrocatalytic activity for methanol oxidation.

An XANES study on the modification of single-walled carbon nanotubes by nitric acid.

X-ray absorption near-edge structure (XANES) spectroscopy has been applied to identify the modification process of single-walled carbon nanotubes (SWCNTs) treated by nitric acid. The carboxyl groups created by the nitric acid treatment have been found to be formed on both the carbonaceous fragments and the side walls of SWCNTs. The carbonaceous fragments could be removed by a following washing treatment with sodium hydroxide. XANES spectra indicate that carbonaceous fragments are the result of the synthesis process and/or of the nitric acid treatment. Tube walls of SWCNTs are weakly oxidized by the nitric acid treatment although, after removing carbonaceous fragments, a direct oxidation process of SWCNTs is observed. Experimental data address the removal of carbonaceous fragments on SWCNTs as an efficient method for side-wall modification of a SWCNT.

First principles study on the diffusion of alkali-metal ions on the armchair single-wall nanotubes.

In this paper we have performed density-functional study on the adsorption and diffusion of various alkali-metal ions on the surface of pristine and defective armchair single-wall carbon nanotubes. In the pristine SWNT system, the position above the hexagon is believed to be the most stable site for adsorption, while the adsorption is enhanced in the defective SWNT. In pristine SWNT all the ions prefer to diffuse along the axial direction, with low barriers less than 0.25 eV. In defective SWNT, the axial diffusion is also energetically most preferable, and the barriers increase only slightly and have little influence on the diffusion as compared to pristine SWNT.