A yolk-shell Fe3O4@void@carbon nanochain as shuttle effect suppressive and volume-change accommodating sulfur host for long-life lithium-sulfur batteries

Electrode Materials of Cobaltous Fluoride for Supercapacitor and Electrocatalysis Applications

Herein, CoF₂ was synthesized by a solvothermal method. The characterization results of the phase and morphology of the sample show that it was successfully synthesized and its morphology is composed of micron particles with uneven size and shape. The electrochemical test results of SCs in different electrolytes show that CoF₂ has electrochemical activity only in alkaline electrolytes. Notably, the electrochemical behavior of CoF₂ in LiOH solution is different from that in other alkaline solutions in that charge-discharge curve has a quasi-isosceles triangle shape and the CV curve has no obvious redox peak. That is, it has pseudocapacitance behavior in LiOH. Furthermore, CoF₂ as catalyst for HER requires an overpotential of only 168 mV to obtain current density of 10 mA cm^-2 and a Tafel slope of 116 mV dec^-1 in 1 M KOH solution. This research provides a novel way to explore excellent performance electrode materials for SC and HER.

Lychee-like TiO2@Fe2O3 Core-Shell Nanostructures with Improved Lithium Storage Properties as Anode Materials for Lithium-Ion Batteries

In this study, lychee-like TiO2@Fe2O3 microspheres with a core-shell structure have been prepared by coating Fe2O3 on the surface of TiO2 mesoporous microspheres using the homogeneous precipitation method. The structural and micromorphological characterization of TiO2@Fe2O3 microspheres has been carried out using XRD, FE-SEM, and Raman, and the results show that hematite Fe2O3 particles (7.05% of the total mass) are uniformly coated on the surface of anatase TiO2 microspheres, and the specific surface area of this material is 14.72 m2 g-1. The electrochemical performance test results show that after 200 cycles at 0.2 C current density, the specific capacity of TiO2@Fe2O3 anode material increases by 219.3% compared with anatase TiO2, reaching 591.5 mAh g-1; after 500 cycles at 2 C current density, the discharge specific capacity of TiO2@Fe2O3 reaches 273.1 mAh g-1, and its discharge specific capacity, cycle stability, and multiplicity performance are superior to those of commercial graphite. In comparison with anatase TiO2 and hematite Fe2O3, TiO2@Fe2O3 has higher conductivity and lithium-ion diffusion rate, thereby enhancing its rate performance. The electron density of states (DOS) of TiO2@Fe2O3 shows its metallic nature by DFT calculations, revealing the essential reason for the high electronic conductivity of TiO2@Fe2O3. This study presents a novel strategy for identifying suitable anode materials for commercial lithium-ion batteries.

Multi-function hollow nanorod as an efficient sulfur host accelerates sulfur redox reactions for high-performance Li-S batteries

The "shuttle effect" of lithium polysulfides (LiPSs) leads to loss of active materials and the deterioration of cycle stability, which seriously restricts the practical progress of lithium-sulfur (Li-S) batteries. The diffusion of soluble discharge intermediate is the root cause of the above problems. Herein, we synthesized a porous organic framework material (HUT-8) based on triazine network, the polar groups above the hollow structure can not only adsorb LiPSs through electron donating effect, but also anchored cobalt (II) ions provide a large number of binding sites for the in-situ growth of CoS2. This ensured maximized exposure of catalytic centre and improve their interactions with sulfur redox species under the confinement of mesopores, which can catalytically accelerate capture/diffusion of LiPSs and precipitation/decomposition of Li2S. Based on the synergistic effect of the composite materials, the CoS2-HUT-8/S cathode maintained a capacity of 583 mAh g-1 after 500 cycles at 1 C, and a minimum capacity fading rate of 0.046% per cycle. A freestanding CoS2-HUT-8/S cathode with sulfur loading of 5.2 mg cm-2 delivered a high areal capacity of 4.01 mAh cm-2 under a lean electrolyte, which would provide great potential for the practical progress of Li-S batteries.

Rational construction of a CNTs@VO2 nanosheets modified separator for enhancing the performance of lithium-sulfur batteries

Although lithium-sulfur (Li-S) batteries possess great potential to become the next generation of energy storage technology due to their fivefold higher energy density than commercial lithium-ion batteries, their practical application is still hindered by their poor cycling stability, especially resulting from the disturbing shuttle effect of soluble intermediates. In this study, vanadium dioxide (VO₂) nanosheets were successfully grown onto CNTs to form CNTs@VO₂ through hydrothermal and calcining processes. The hollow structure of the high conductive CNTs offers internal space and mesopores to accommodate the electrolyte combined with the polar metal oxide VO₂ nanosheets providing the chemical anchoring. The hollow binary core-shell host acting as the nanoreactor that serves as the modifier of the separator results in the intensive physical and chemical dual adsorption of lithium polysulfide species (LiPSs), promoting the conversion of long-chain LiPSs to alleviate the shuttle effect significantly and boosting the performance. In addition, the CNTs enhance the electronic conductivity and the electrolyte infiltration of the separator. Notably, the modified separator demonstrates a high initial discharge capacity of 1397 mA h g^-1 at 0.2C and retains a stable cycling ability with a reversible capacity of 965 mA h g^-1 over 200 cycles at 1C. Even for the high sulfur loading of 7.4 mg cm^-2, it can deliver a high areal capacity of 5.4 mA h cm^-2 at 0.5C.