Multiphase Ceramic Coatings with High Hardness and Wear Resistance on 5052 Aluminum Alloy by a Microarc Oxidation Method

High-hardness and wear-resistant ceramic coatings were obtained on 5052 aluminum alloy by the microarc oxidation (MAO) process in silicate electrolytes with different nanoadditives (TiO₂, Si₃N₄), and the effects of different nanoadditives on the microstructural and mechanical properties of the ceramic coatings were systematically studied. The microstructure results revealed that the nanoadditives could improve the thickness and compactness of the ceramic coatings. The X-ray diffraction results demonstrated that the nanoadditives were successfully incorporated into the MAO coatings and that some new phases of Si₂N₂O and TiN were formed, enhancing the comprehensive performance of the ceramic coatings. Furthermore, the distributions of elements determined from energy-dispersive X-ray (EDX) spectroscopy and cross-sectional images displayed a good homogeneity to support the excellent mechanical properties of the ceramic coatings. Therefore, the average microhardness, the full indentation force–depth curves, the hardness and elastic modulus, and the <i>H</i>/<i>E</i> and <i>H</i>³/<i>E</i>² ratios of the ceramic coatings with TiO₂ and TiO₂ + Si₃N₄ nanoadditives delivered a very high hardness, implying good antifriction properties. Moreover, the friction coefficients of the ceramic coatings also demonstrated their outstanding wear resistance. Finally, the corrosion resistance and electrochemical impedance spectroscopy results further revealed the compactness of the ceramic coatings, indicating a high hardness and abrasion resistance

Hierarchically Porous Carbon Encapsulating Sulfur as a Superior Cathode Material for High Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are deemed to be a promising energy storage device for next-generation high energy power system. However, insulation of S and dissolution of lithium polysulfides in the electrolyte lead to low utilization of sulfur and poor cycling performance, which seriously hamper the rapid development of Li–S batteries. Herein, we reported that encapsulating sulfur into hierarchically porous carbon (HPC) derived from the soluble starch with a template of needle-like nanosized Mg­(OH)₂. HPC has a relatively high specific surface area of 902.5 m² g^–1 and large total pore volume of 2.60 cm³ g^–1, resulting that a weight percent of sulfur in S/HPC is up to 84 wt %. When evaluated as cathodes for Li–S batteries, the S/HPC composite has a high discharge capacity of 1249 mAh g^–1 in the first cycle and a Coulombic efficiency as high as 94% with stable cycling over prolonged 100 charge/discharge cycles at a high current density of 1675 mA g^–1. The superior electrochemical performance of S/HPC is closely related to its unique structure, exhibiting the graphitic structure with a high developed porosity framework of macropores in combination with mesopores and micropores. Such nanostructure could shorten the transport pathway for both ions and electrons during prolonged cycling

Bifunctional Redox Mediator Supported by an Anionic Surfactant for Long-Cycle Li–O₂ Batteries

Although the soluble redox mediator (RM) has been effectively applied in Li–O₂ batteries, parasitic reactions between the lithium anode and RM⁺ can result in poor cycle performance. Herein, we proposed a nonelectroactive surfactant (sodium dodecyl sulfate, SDS) that could adsorb on the hydrophobic carbon surface and form a stable anionic layer upon charge, which can effectively suppress the diffusion of oxidized RM⁺ and facilitate charge transfer at the electrode–solution interface. To coordinate with SDS, a new RM named 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) was adopted due to its oxidation process following after in situ formation of the anionic layer. Moreover, as a bifunctional mediator, PTIO cannot only get a low charge plateau but also greatly enhance the discharge capacity when applied in Li–O₂ batteries. The electrochemical results demonstrated that the cycling performance, energy efficiency, and discharge capacity were significantly improved owing to the synergistic effect of PTIO and SDS

Rational Design of Void-Involved Si@TiO₂ Nanospheres as High-Performance Anode Material for Lithium-Ion Batteries

A unique core–shell structure of silicon@titania (Si@TiO₂) composite with silicon nanoparticles encapsulated in TiO₂ hollow spheres is synthesized by a simple hydrolysis method combined with magnesiothermic reduction method. It is found that the TiO₂ shell is effective for improving the electrical conductivity and structural stability. More importantly, the well-designed nanostructure with enough empty space would accommodate the volume change of silicon during the cycling. Reversible capacities of 1911.1 and 795 mAh g^–1 can be obtained at 0.05 C and a high current rate of 1 C, respectively. After 100 cycles at 0.1 C, the composite electrode still maintains a high capacity of 804 mAh g^–1. This excellent cycling stability and high-rate capability can be ascribed to the unique core–shell nanostructure and the synergistic effect between Si and TiO₂

Nanospace-Confinement Copolymerization Strategy for Encapsulating Polymeric Sulfur into Porous Carbon for Lithium–Sulfur Batteries

Given their high theoretical energy density, lithium–sulfur (Li–S) batteries have recently attracted ever-increasing research interest. However, the dissolution of polysulfides and uncontrolled deposition of insoluble discharge product significantly hinder the cycling stability. Herein, a nanospace-confinement copolymerization strategy for encapsulating polymeric sulfur into porous carbon matrix is presented. The morphologies and sulfur contents of carbon/polymeric sulfur (C/PS) composites could be readily tailored by controlling the copolymerization time. Confining polymeric sulfur in the porous carbon with abundant interparticle pores facilitates rapid electronic/ionic transport and mitigates dissolution of polysulfides intermediates. More importantly, the organic sulfur units dispersed in the insoluble/insulating Li₂S₂/Li₂S phase could prevent its irreversible deposition. Such nanostructure with tailored chemistry property permits the C/PS electrodes to exhibit enhanced cycling stability and high rate capability. The nanospace-confinement copolymerization strategy features general and facial advantages, which may provide new opportunities for the future development of advanced sulfur cathodes

Prussian Blue Analogue with Fast Kinetics Through Electronic Coupling for Sodium Ion Batteries

Alternative battery systems based on the chemistry of sodium are being considered to offer sustainability and cost-effectiveness. Herein, a simple and new method is demonstrated to enable nickel hexacyanoferrate (NiHCF) Prussian blue analogues (PBA) nanocrystals to be an excellent host for sodium ion storage by functionalization with redox guest molecule. The method is achieved by using NiHCF PBA powders infiltrated with the 7,7,8,8-tetracyanoquinododimethane (TCNQ) solution. Experimental and ab initio calculations results suggest that TCNQ molecule bridging with Fe atoms in NiHCF Prussian blue analogue leads to electronic coupling between TCNQ molecules and NiHCF open-framework, which functions as an electrical highway for electron motion and conductivity enhancement. Combining the merits including high electronic conductivity, open framework structure, nanocrystal, and interconnected mesopores, the NiHCF/TCNQ shows high specific capacity, fast kinetics and good cycling stability, delivering a high specific capacity of 35 mAh g^–1 after 2000 cycles, corresponding a capacity loss of 0.035% decay per cycle