Double-Enhanced Core-Shell-Shell Sb2S3/Sb@TiO2@C Nanorod Composites for Lithium- and Sodium-Ion Batteries

For most alloying- and conversion-type anode materials, a huge volume expansion and structure degradation of the electrodes always hinder their applications. In this work, a novel core-shell-shell Sb2S3/Sb@TiO2@C nanorod composite has been designed layer by layer, which includes an inner Sb2S3/Sb heterostructure core protected by an oxygen-deficient TiO2 shell and a conductive carbon shell. It is interesting to observe that, during the carbothermic reduction process, the previous Sb2S3 nanorod cores are partially reduced into a metallic Sb phase and the reduced TiO2 also creates many oxygen vacancies, which can greatly enhance the conductivity of the semiconductor Sb2S3. Thanks to the double effects of the TiO2 middle shell and carbon outer shell, the unique double-shelled structure design creates an enhanced dual protection, which can better accommodate the volume-expansive deformation and preserve the structural integrity of the active Sb2S3/Sb core. Especially, the TiO2 middle layer is self-assembled by numerous nanoparticles acting as a nanopillar backbone, which supports between the nanorod core and outer carbon shell to better buffer the volume changes. As a result, the core-shell-shell Sb2S3/Sb@TiO2@C anode shows lithium and sodium storage performances superior to those of the pristine Sb2S3 and core-shell Sb2S3@TiO2 electrodes. For lithium-ion batteries, the Sb2S3/Sb@TiO2@C nanorod composite achieves an initial discharge/recharge capacity of 1244.9/1005.1 mAh g-1 with an initial Coulombic efficiency of about 80.7%, an enhanced rate capability with a capacity of 593.2 mA h g-1 at 5.0 A g-1, and prolonged cycling life for 500 cycles with a reversible capacity of 495.8 mAh g-1 at 0.5 A g-1. For sodium-ion batteries, the nanorodalso exhibits an improved performance with an initial discharge/recharge capacity of 781.4/574.0 mAh g-1 (initial Coulombic efficiency of about 73.46%) and cycling for 400 cycles with a reversible capacity of 422.6 mAh g-1 at 0.8 A g-1. This research sheds light upon double-shell structure designs with an effective middle shell to enhance the energy storage performance of electrode materials.

Phase-Change Composites Composed of Silicone Rubber and Pa@SiO2@PDA Double-Shelled Microcapsules with Low Leakage Rate and Improved Mechanical Strength

A kind of silicone rubber (SR)/paraffin (Pa)@silicon dioxide (SiO₂)@polydopamine (PDA) phase-change composite was prepared in this work. The double-shelled Pa@SiO₂@PDA phase-change microcapsules were constructed by oxidative self-polymerization of dopamine (DA) in Tris-HCl buffer solution. The effect of the DA content on the properties of Pa@SiO₂@PDA microcapsules and SR/Pa@SiO₂@PDA composites was researched. Due to the protective effect of SiO₂, PDA layer, and SR matrix, the SR/Pa@SiO₂@PDA composites have good leak-proofing performance, and the leakage rate of SR/Pa@SiO₂@PDA-2 is as low as 0.45%. Phase-change enthalpies of the Pa@SiO₂@PDA microcapsules and SR/Pa@SiO₂@PDA composites are reduced slightly with increasing DA content. Meanwhile, the composites displayed improved mechanical strength. The tensile strength of SR/Pa@SiO₂@PDA-2 can be up to 0.560 MPa, which is 1.85 times higher than the tensile strength of pure SR/Pa@SiO₂ because the interface compatibility between Pa@SiO₂ microcapsules and SR is improved through hydrogen bonding between the abundant groups on the PDA surface and the matrix. Moreover, the rough surface of the PDA-modified microcapsules also enhances the interface interaction through physical "interlocking". The new kind of SR/Pa@SiO₂@PDA composite can be used for thermal management.

Enhanced Diffusion Kinetics of Li Ions in Double-Shell Hollow Carbon Fibers

The rational design and preparation of hierarchical hollow structures have promising potential in electrochemical energy storage systems. In this paper, double-shell hollow carbon fibers (DSHCFs) with tunable thickness and shell spacing are prepared using hollow electrospun polystyrene fibers as the hard template and in situ coated polypyrrole as the carbon source. The as-prepared DSHCFs with an optimized structure exhibit a submicrometer shell spacing and a nanoscaled shell thickness, which guarantees sufficient contact area with the electrolyte and provides abundant electrochemical active sites for Li⁺ storage. Owing to the unique structural advantages, a DSHCF-based anode shows favorable transport kinetics for both Li⁺ ions and electrons during the lithiation/delithiation process, and a high reversible capacity of 348 mAh g^-1 at 5.0 A g^-1 is well maintained even after 500 cycles with no obvious capacity attenuation. Particular emphasis is given to kinetic Li⁺ storage mechanisms in DSHCFs that are discussed in detail, providing a new avenue for developing high-performance carbon materials for the practical application of energy storage devices.

A Chemical-Adsorption Strategy to Enhance the Reaction Kinetics of Lithium-Rich Layered Cathodes via Double-Shell Surface Modification

Sluggish surface reaction kinetics hinders the power density of Li-ion battery. Thus, various surface modification techniques have been applied to enhance the electronic/ionic transfer kinetics. However, it is challenging to obtain a continuous and uniform surface modification layer on the prime particles with structure integration at the interface. Instead of classic physical-adsorption/deposition techniques, we propose a novel chemical-adsorption strategy to synthesize double-shell modified lithium-rich layered cathodes with enhanced mass transfer kinetics. On the basis of experimental measurement and first-principles calculation, MoO2S2 ions are proved to joint the layered phase via chemical bonding. Specifically, the Mo-O or Mo-S bonds can flexibly rotate to bond with the cations in the layered phase, leading to the good compatibility between the thiomolybdate adsorption layer and layered cathode. Followed by annealing treatment, the lithium-excess-spinel inner shell forms under the thiomolybdate adsorption layer and functions as favorable pathways for lithium and electron. Meanwhile, the nanothick MoO3-x(SO4)x outer shell protects the transition metal from dissolution and restrains electrolyte decomposition. The double-shell modified sample delivers an enhanced discharge capacity almost twice as much as that of the unmodified one at 1 A g(-1) after 100 cycles, demonstrating the superiority of the surface modification based on chemical adsorption.

Enhanced Electroresponsive Performance of Double-Shell SiO2/TiO2 Hollow Nanoparticles

The double-shell SiO2/TiO2 hollow nanoparticles (DS HNPs) are successfully fabricated and adopted as dispersing materials for electrorheological (ER) fluids to investigate an influence of shell structure on ER properties. The DS HNPs-based ER fluid exhibits outstanding ER performance which is 4.1-fold higher compared to that of single shell SiO2/TiO2 hollow nanoparticles (SS HNPs)-based ER fluid. The significantly improved ER property of DS HNPs-based ER fluid is ascribed to the enhanced interfacial polarization. In addition, the ER activities of DS HNPs-based ER fluids are examined depending on the particle diameter. The yield stress of DS HNPs-based ER fluids increases up to 302.4 kPa under an electric field of 3 kV mm(-1) by reducing the particle size, which is remarkable performance enough to promise sufficient probability for practical and industrial applications. The enhanced ER performance of the smaller DS HNPs is attributed to the increased surface area of large pores (30-35 nm) within the shells, resulting in a large achievable polarizability determined by dielectric constants. Furthermore, the antisedimentation property is analyzed in order to offer an additional insight into the effect of particle size on the ER fluids.

Different Methods of Increasing the Mechanical Strength of Gold Nanocages

Using the ultrafast coherent modulation of the surface plasmon band intensity with the totally symmetric lattice vibration of gold nanocages, we were able to determine and use their frequencies as a measure of the cage's mechanical stability. The presence of an inner "stiff" transition-metal nanoshell with a higher value of the elastic modulus is found to increase the frequency of the lattice vibration of the outer soft gold nanoshell. This could also explain the observed increase in both the gold lattice vibrational frequency as well as the lattice vibration relaxation time in the Au-Pt and Au-Pd double-shell nanocages. It is also found that when these nanoparticles are assembled into monolayers on quartz substrates by the Langmuir-Blodgett technique, the oscillation frequency of the gold shell with the transition metal having the largest elastic constant suffers the least change in its oscillation frequency as a result of its resistance to distortion as a result of binding to the substrate.