Mechanism Study of Carbon Coating Effects on Conversion-Type Anode Materials in Lithium-Ion Batteries: Case Study of ZnMn2O4 and ZnO-MnO Composites

Enhancing lithium storage performance of bimetallic oxides anode by synergistic effects

Spinel bimetallic transition metal oxide anode such as ZnMn₂O₄, has drawn increasing interest due to attractive bimetal interaction and high theoretical capacity. While it suffers from huge volume expansion and poor ionic/electronic conductivity. Nanosizing and carbon modification can alleviate these issues, while the optimal particle size within host is unclear yet. We here propose an in-situ confinement growth strategy to fabricate pomegranate-structured ZnMn₂O₄ nanocomposite with calculated optimal particle size in mesoporous carbon host. Theoretical calculations reveal favorable interatomic interactions between the metal atoms. By the synergistic effects of structural merits and bimetal interaction, the optimal ZnMn₂O₄ composite achieves greatly improved cycling stability (811 mAh g^-1 at 0.2 A g^-1 after 100 cycles), which can maintain its structural integrity upon cycling. X-ray absorption spectroscopy analysis further confirms delithiated Mn species (Mn₂O₃ but little MnO). Briefly, this strategy brings new opportunity to ZnMn₂O₄ anode, which could be adopted to other conversion/alloying-type electrodes.

Comparing the inter-seed effect for some iodine-125 brachytherapy sources through a Monte Carlo simulation approach

BACKGROUND AND OBJECTIVE

One of the principal deficits of TG-43(U1) dosimetry protocol is ignoring the attenuation effect of each seed during the multiseed brachytherapy implants. To take into account this shadowing effect, a parameter known as the inter-seed effect (ISE) has been introduced. Current study aims to evaluate and compare the ISE for some I-125 brachytherapy seeds through a Monte Carlo (MC) simulation approach.

METHODS

Five different models of I-125 seeds including 6711, ProstaSeed, STM 1251, 3500, and IAI-125A were simulated by MCNPX MC Code. Validity of simulated seed models was confirmed through comparing the corresponding dosimetric parameters such as radial dose function and anisotropy function with those reported by relevant literature. Then, the ISE for each seed at different distances was determined in three seeds implant configuration. Additionally, the relevant attenuation factors (AF) were also determined for each brachytherapy source.

RESULTS

The obtained results demonstrated that minimum inter-seed attenuation belongs to the ProstaSeed. In return, the maximum inter-seed attenuation was found for 3500 brachytherapy seed. The mean attenuation factor for 6711, ProstaSeed, STM 1251, 3500, and IAI-125A seed models was equal to 0.764, 0.829, 0.785, 0.594, and 0.772, respectively.

CONCLUSIONS

It can be concluded that the considered I-125 brachytherapy seeds show different inter-seed effects and mean AF values for the same multiseed implant arrangement. This finding can be attributed to discrepancies in internal seed design and configuration.

Impact of the Transition Metal Dopant in Zinc Oxide Lithium-Ion Anodes on the Solid Electrolyte Interphase Formation

Conversion/alloying materials (CAMs) provide substantially higher specific capacities than graphite, the state-of-the-art lithium-ion battery anode material. The ability to host much more lithium per unit weight and volume is, however, accompanied by significant volume changes, which challenges the realization of a stable solid electrolyte interphase (SEI). Herein, the comprehensive characterization of the composition and evolution of the SEI on transition metal (TM) doped zinc oxide as CAM model compound, is reported, with a particular focus on the impact of the TM dopant (Fe or Co). The results unveil that the presence of iron specifically triggers the electrolyte decomposition. However, this detrimental effect can be avoided by stabilizing the interface with the electrolyte by a carbonaceous coating. These findings provide a great leap forward toward the enhanced understanding of such doped materials and (transition) metal oxide active materials in general.

Synergistic Interactions of Different Electroactive Components for Superior Lithium Storage Performance

The fusion of different electroactive components of lithium-ion batteries (LIBs) sometimes brings exceptional electrochemical properties. We herein report the reduced graphene-oxide (rGO)-coated Zn₂SnO_4z@NiO nanofibers (ZSO@NiO@G NFs) formed by the synergistic fusion of three different electroactive components including ZnO, SnO₂, and NiO that exhibit exceptional electrochemical properties as negative electrodes for LIBs. The simple synthetic route comprised of electrospinning and calcination processes enables to form porous one-dimensional (1D) structured ZSO, which is the atomic combination between ZnO and SnO₂, exhibiting effective strain relaxation during battery operation. Furthermore, the catalytic effect of Ni converted from the surface-functional NiO nanolayer on ZSO significantly contributes to improved reversible capacity. Finally, rGO sheets formed on the surface of ZSO@NiO NFs enable to construct electrically conductive path as well as a stable SEI layer, resulting in excellent electrochemical performances. Especially, exceptional cycle lifespan of more than 1600 cycles with a high capacity (1060 mAh g^-1) at a high current density (1000 mA g^-1), which is the best result among mixed transition metal oxide (stannates, molybdates, cobaltates, ferrites, and manganates) negative electrodes for LIBs, is demonstrated.

Effect of Continuous Capacity Rising Performed by FeS/Fe3 C/C Composite Electrodes for Lithium-Ion Batteries

FeS-based composites are sustainable conversion electrode materials for lithium-ion batteries, combining features like low cost, environmental friendliness, and high capacities. However, they suffer from fast capacity decay and low electron conductivity. Herein, novel insights into a surprising phenomenon of this material are provided. A FeS/Fe₃ C/C nanocomposite synthesized by a facile hydrothermal method is compared with pure FeS. When applied as anode materials for lithium-ion batteries, these two types of materials show different capacity evolution upon cycling. Surprisingly, the composite delivers a continuous increase in capacity instead of the expected capacity fading. This unique behavior is triggered by a catalyzing effect of Fe₃ C nanoparticles. The Fe₃ C phase is a beneficial byproduct of the synthesis and was not intentionally obtained. To further understand the effect of interconnected carbon balls on FeS-based electrodes, complementary analytic techniques are used. Ex situ X-ray radiation diffraction and ex situ scanning electron microscopy are employed to track phase fraction and morphology structure. In addition, the electrochemical kinetics and resistance are evaluated by cyclic voltammetry and electrochemical impedance spectroscopy. These results reveal that the interconnected carbon balls have a profound influence on the properties of FeS-based electrodes resulting in an increased electrode conductivity, reduced particle size, and maintenance of the structure integrity.

Influence of phase variation of ZnMn2O4/carbon electrodes on cycling performances of Li-ion batteries

Due to the high specific capacity and low cost, transition metal oxides (TMOs) exhibit huge potential as anode materials for high-performance Li-ion batteries.