Considerable effort has been devoted to improving the cyclability of silicon (Si) negative electrodes for lithium-ion batteries because it is a promising high specific capacity alternative to graphite. In this work, the electrochemical behaviour of Si in two ionic liquid (IL) electrolytes, triethyl(methyl)phosphonium bis(fluorosulfonyl)imide (P 1222 FSI) and N-propyl-Nmethylpyrrolidinium-FSI (C 3 mpyrFSI) with high and low lithium (Li) salt content is investigated at 50 °C. Results highlight that higher capacity and better cycling stability are achieved over 50 2 cycles with high salt concentration, the first time for a pyrrolidinium-based electrolyte in the area of Si negative electrodes. However, the Si cycling performance was far superior in the P 1222 FSIbased high salt content electrolyte compared to that of the C 3 mpyrFSI. To understand this unexpected result, diffusivity measurements of the IL-based electrolytes were performed using PFG-NMR, while their stability was probed using MAS-NMR and XPS after long-term cycling. A higher apparent transport number for Li ions in highly concentrated ILs, combined with a significantly lower extent of electrolyte degradation explains the superior cycle life of the highly concentrated phosphonium-based system. Si/concentrated P 1222 FSI-LiFSI/lithium nickel cobalt aluminum oxide (NCA) full cells with more than 3 mAh cm-2 nominal capacity deliver a promising cycle life and good rate capability.
The latest advances in the stabilization of Li/Na metal battery and Li-ion battery cycling has highlighted the importance of electrode/electrolyte interface (Solid Electrolyte Interphase -SEI) and its direct link to cycling behaviour. In order to understand the structure and properties of the SEI, we used combined experimental and computational studies to unveil how the ionic liquid (IL) cation nature and salt concentration impact the silicon/IL electrolyte interfacial structure and the formed SEI. The nature of IL cation is found to be important to control the electrolyte reductive decomposition that influences the SEI composition and properties, and the reversibility of the Li-Si alloying process. Also, increasing the Li salt concentration changes the interface structure for a favorable and less resistive SEI. The most promising interface for the Si-based battery was found to be in P 1222 FSI with 3.2 m LiFSI which leads to an optimal SEI after 100 cycles in which LiF and trapped LiFSI are the only distinguishable lithiated and fluorinated products detected. This study shows a clear link between the nano-structure of the IL electrolyte near the electrode surface, the resulting SEI, and the Si negative electrode cycling performance. More importantly, this work will aid rational design of Si-based Li-ion batteries using IL electrolytes in an area that has so far been neglected, reinforcing the benefits of superconcentrated electrolyte systems.
Vinylene carbonate (VC) and polyethylene oxide (PEO) have been investigated as functional agents that mimic the solid electrolyte interphase (SEI) chemistry of silicon (Si). VC and PEO are known to contribute to the stability of Si-based lithium-ion batteries as an electrolyte additive and as a SEI component, respectively. In this work, covalent surface functionalization was achieved via a facile route, which involves ball-milling the Si particles with sacrificial VC and PEO. Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy indicate that the additives are strongly bound to Si. In particular, MAS NMR shows Si−R or Si−O−R groups, which confirm functionalization of the Si after milling in VC or PEO. Particle size analysis by dynamic light scattering reveals that the additives facilitate particle size reduction and that the functionalized particles result in more stable dispersions based on zeta potential measurements. Raman mapping of the electrodes fabricated from the VC and PEO-coated active material with a polyacrylic acid (PAA) binder reveals a more homogenous distribution of Si and the carbon conductive additive compared to the electrodes prepared from the neat Si. Furthermore, the VC-milled Si strikingly exhibited the highest capacity in both half-and full-cell configurations, with more than 200 mAh g −1 measured capacity compared to the neat Si in the half-cell format. This is linked to an improved electrode processing based on the Raman and zeta potential measurements as well as a thinner SEI (with more organic components for the functionalized Si relative to the neat Si) based on XPS analysis of the cycled electrodes. The effect of binder was also investigated by comparing PAA with P84 (polyimide type), where an increased capacity is observed in the latter case.
This study presents a bench‐scale study on the dynamic removal of arsenic from wastewater by an adsorption membrane consisting of a polycaprolactone matrix with iron‐intercalated montmorillonite filler. A 2K factorial design of experiment was employed to study the effect of different adsorption parameters; namely, flow rate, initial influent concentration, and thickness of adsorbent sheets on breakthrough time. Longer breakthrough times were associated with low flow rates, low initial influent concentrations, and thick nanofiber membrane. The bed depth service time (BDST) approach was used to model adsorption kinetics. An empirical equation for predicting service time of the adsorbent membrane was obtained and was used to design the bench‐scale column. The performance of the adsorption column was accurately predicted by the BDST model. This practical, nanocomposite‐based adsorption column offers a promising alternative wastewater treatment for addressing arsenic contamination in water.
Nanocomposite fibers produced via electrospinning have very large surface area by virtue of their nanometer diameter sizes thereby making them very attractive for various applications such as for adsorption of contaminants from wastewater. In this study, a highly adsorbing nanoparticle, iron-modified montmorillonite was used as filler in the nanocomposite. The effects of polymer solution and suspension properties such as polymer concentration, clay loading, and filler type on the electrospinning of the nanocomposite were investigated using a 2k factorial design of experiment. The types of montmorillonite used were zero valent iron-MMT (ZVIMMT) and iron (III)-MMT (FeMMT). It was found from the SEM images that finer fibers were generated from suspensions with lower polymer concentration in the solution specifically at 5 wt% and from suspensions with ZVIMMT particles as filler. However, a common defect in nanofibers called beads was also observed in the fibers produced from 5 wt% polymer concentration. TEM micrographs confirmed that the ZVIMMT fibers have smaller diameter than the FeMMT fibers. In addition, it was recognized that the layered structure of the clay is still intact after the electrospinning process. The XRD pattern of the fibers revealed that the clay particles were intercalated with the polymer molecules based on the calculated d-spacing. Furthermore, elemental analysis on the bead and string regions of the electrospun fibers confirmed the presence of polymer and montmorillonite particles in both regions.
The molecular and ionic assemblies at an electrode/liquid electrolyte interface, i.e., electric double layer (EDL), define battery performance by directing the formation of stable interphases. An unstable interphase can hamper...
Silicon-containing Li-ion batteries have been the focus of many energy storage research efforts because of the promise of high energy density. Depending on the system, silicon generally demonstrates stable performance in half-cells, which is often attributed to the unlimited lithium supply from the lithium (Li) metal counter electrode. Here, the electrochemical performance of silicon with a high voltage NMC622 cathode was investigated in superconcentrated phosphonium-based ionic liquid (IL) electrolytes. As a matter of fact, there is very limited work and understanding of the full cell cycling of silicon in such a new class of electrolytes. The electrochemical behavior of silicon in the various IL electrolytes shows a gradual and steeper capacity decay, compared to what we previously reported in half-cells. This behavior is linked to a different evolution of the silicon morphology upon cycling, and the characterization of cycled electrodes points toward mechanical reasons, complete disconnection of part of the electrode, or internal mechanical stress, due to silicon and Li metal volume variation upon cycling, to explain the progressive capacity fading in full cell configuration. An extremely stable solid electrolyte interphase (SEI) in the full Li-ion cells can be seen from a combination of qualitative and quantitative information from transmission electron microscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and magic angle spinning nuclear magnetic resonance. Our findings provide a new perspective to full cell interpretation regarding capacity fading, which is oftentimes linked almost exclusively to the loss of Li inventory but also more broadly, and provide new insights into the impact of the evolution of silicon morphology on the electrochemical behavior.
The release of arsenic to aqueous environment imposes threats to human health. Montmorillonite supported zero-valent iron (ZVI-MMT) is a material with capability of immobilizing arsenic from aqueous environment. The arsenic adsorption efficiency of ZVI-MMT was obtained. In addition, adsorption kinetics of arsenic contaminated water on the material was determined. Arsenic and iron content was quantified by an inductively coupled plasma mass spectrometer (ICP-MS), interplanar distance of the adsorbent was measured by x-ray diffractometer (XRD), and the morphology of the adsorbent was obtained from a transmission electron microscope (TEM). Isotherm data were analyzed using the Langmuir and Freundlich isotherms. The data fitted well to Langmuir isotherm with derived adsorption capacity of 20.1 mg/g. Kinetics data were analyzed using intra-particle model, Elovich equation, pseudo first-, and pseudo second-order models. Elovich equation and pseudo second-order equation fitted the experimental data with pseudo second-order rate constant of 61.2 x 10-4 g/mg-min.
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