Reaction Mechanism and Performance of Innovative 2D Germanane-Silicane Alloys: SixGe1- xH Electrodes in Lithium-Ion Batteries.

The adjustable structures and remarkable physicochemical properties of 2D monoelemental materials, such as silicene and germanene, have attracted significant attention in recent years. They can be transformed into silicane (SiH) and germanane (GeH) through covalent functionalization via hydrogen atom termination. However, synthesizing these materials with a scalable and low-cost fabrication process to achieve high-quality 2D SiH and GeH poses challenges. Herein, groundbreaking 2D SiH and GeH materials with varying compositions, specifically Si0.25Ge0.75H, Si0.50Ge0.50H, and Si0.75Ge0.25H, are prepared through a simple and efficient chemical exfoliation of their Zintl phases. These 2D materials offer significant advantages, including their large surface area, high mechanical flexibility, rapid electron mobility, and defect-rich loose-layered structures. Among these compositions, the Si0.50Ge0.50H electrode demonstrates the highest discharge capacity, reaching up to 1059 mAh g-1 after 60 cycles at a current density of 75 mA g-1. A comprehensive ex-situ electrochemical analysis is conducted to investigate the reaction mechanisms of lithiation/delithiation in Si0.50Ge0.50H. Subsequently, an initial assessment of the c-Li15(SixGe1- x)4 phase after lithiation and the a-Si0.50Ge0.50 phase after delithiation is presented. Hence, this study contributes crucial insights into the (de)lithiation reaction mechanisms within germanane-silicane alloys. Such understanding is pivotal for mastering promising materials that amalgamate the finest properties of silicon and germanium.

Insight into the Catalytic Role of Defect-Enriched Vanadium Sulfide for Regulating the Adsorption-Catalytic Conversion Behavior of Polysulfides in Li-S Batteries.

The performance promotion of Li-S batteries relies primarily on inhibition of the shuttle effect and improvement of the catalytic-conversion reaction kinetics of polysulfides. Herein, we prepare defect-enriched VS2 nanosheets (VS2-x) as catalysts for Li-S batteries and further study the catalytic mechanism of VS2-x via ex situ X-ray diffraction and in situ UV-vis spectroscopy. A multifunctional S cathode was also obtained by assembling VS2-x on a C cloth to achieve high S loading for Li-S batteries. It was found that VS2-x catalysts undergo a lithiation process in the work voltage of Li-S batteries, and the triggered LiyVS2-x intermediates reciprocate VS2-x with a high catalytic activity so as to enhance the performance of Li-S batteries by promoting the dissociation process of S62- to S3•-. Consequently, Li-S batteries with a C/VS2-x/S cathode deliver a high reversible capacity (1471 mAh g-1 at 0.1 C) and good cycling performance (low fading rate of 0.064% per cycle after 400 cycles). Meanwhile, the CC@VS2-x/S cathode with a high S areal loading of 5.6 mg cm-2 can render a satisfactory areal capacity of 4.22 mAh cm-2 at 0.2 C and a cycle stability of over 100 cycles. Therefore, the study on the catalysis of LiyVS2-x intermediates provides a scientific view for revealing the catalysis mechanism of a sulfide-based electrocatalyst and boosting the development of an electrocatalyst for Li-S batteries.

Porous NiCo2S4 Nanoneedle Arrays with Highly Efficient Electrocatalysis Anchored on Carbon Cloths as Self-Supported Hosts for High-Loading Li-S Batteries.

Lithium-sulfur (Li-S) batteries have attracted all-time attention because of their supernormal high energy density and low cost, whereas they are still plagued by the severe polysulfide shuttling and sluggish sulfur redox reaction kinetics. Moreover, poor sulfur electrochemical utilization and rapid capacity degradation are top concerns in the high-loading Li-S batteries, which severely hinder their practical applications. Herein, a completely novel porous nanoneedle array NiCo2S4 electrocatalyst grown on a nitrogen-sulfur-doped carbon cloth (NSCC) (NiCo2S4@NSCC) is constructed as a 3D self-supported sulfur host for high-loading Li-S batteries, in which the highest sulfur loading reaches 4.9 mg cm-2. The as-prepared NiCo2S4@NSCC with a typical sulfur loading of around 2.0 mg cm-2 provides a high discharge capacity of 1223 mA h g-1 at 0.2 C and long-term cycle stability with a low capacity decay of 0.046% per cycle over 500 cycles at 1 C. Additionally, NiCo2S4@NSCC/S with a high sulfur loading of 4.9 mg cm-2 delivers an excellent reversible areal capacity of 4.4 mA h cm-2 g over 50 cycles. Noting that such superior electrochemical performance of NiCo2S4@NSCC/S with high-loading sulfur is mainly attributed to high electronic conductivity and the abundant porous structure of NSCC to transport electrons and ions fastly and accommodate sulfur as well as robust absorbability and the outstanding catalytic effect of NiCo2S4 to accelerate the capture and conversion of the polysulfide intermediate. Predictably, this work can provide a guideline to efficiently and rationally design the structure of metal-based compounds with catalytic functions for various applications.