Development of Fluoride-Ion Primary Batteries: The Electrochemical Defluorination of CF x.

The lithium-carbon monofluoride (Li-CF x ) couple has the highest specific energy of any practical battery chemistry. However, the large polarization associated with the CF x electrode (>1.5 V loss) limits it from achieving its full discharge energy, motivating the search for new CF x reaction mechanisms with reduced overpotential. Here, using a liquid fluoride (F)-ion conducting electrolyte at room temperature, we demonstrate for the first time the electrochemical defluorination of CF x cathodes, where metal fluorides form at a metal anode instead of the CF x cathode. F-ion primary cells were developed by pairing CF x cathodes with either lead (Pb) or tin (Sn) metal anodes, which achieved specific capacities of over 700 mAh g-1 and over 400 mAh g-1, respectively. Solid-state 19F and 119Sn{19F} nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman, inductively coupled plasma (ICP), and X-ray fluorescence (XRF) measurements establish that upon discharge, the CF x cathode defluorinates while Pb forms PbF2 and Sn forms both SnF4 and SnF2. Technological development of F-ion metal-CF x cells based on this concept represents a promising avenue for realizing primary batteries with high specific energy.

Holey Graphene/Ferroelectric/Sulfur Composite Cathodes for High-Capacity Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have attracted considerable interest as next-generation high-density energy storage devices. However, their practical applications are limited by rapid capacity fading when cycling cells with high mass loading levels. This could be largely attributed to the inferior electron/ion conduction and the severe shuttling effect of soluble polysulfide species. To address these issues, composites of sulfur/ferroelectric nanoparticles/ho ley graphene (S/FNPs/hG) cathodes were fabricated for high-mass-loading S cathodes. The solvent-free and binder-free procedure is enabled using holey graphene as a unique dry-pressable electrode for Li-S batteries. The unique structure of the holey graphene framework ensures fast electron and ion transport within the electrode and affords enough space to mitigate the electrode's volume expansion. Moreover, ferroelectric polarization due to FNPs within S/hG composites induces an internal electric field, which effectively reduces the undesired shuttling effect. With these advantages, the S/FNPs/hG composite cathodes exhibit sustainable and ultrahigh specific capacity up to 1409 mAh/gs for the S/BTO/hG cathode. A capacity retention value of 90% was obtained for the S/BNTFN/hG battery up to cycle 18. The high mass loading of sulfur ranging from 5.72 to 7.01 mgs/cm2 allows maximum high areal capacity up to ∼10 mAh/cm2 for the S/BTO/hG battery and superior rate capability at 0.2 and 0.5 mA/cm2. These results suggest sustainable and high-yielding Li-S batteries can be obtained for potential commercial applications.

Enhancement of hydrogen gas permeability in electrically aligned MWCNT-PMMA composite membranes.

The multi-walled carbon nanotube (MWCNT) dispersed polymethylmethacrylate (PMMA) composite membranes have been prepared for hydrogen gas permeation application. Composite membranes are characterized by Raman spectroscopy, optical microscopy, X-ray diffraction, electrical measurements and gas permeability measurements. The effect of electric field alignment of MWCNT in PMMA matrix on gas permeation has been studied for hydrogen gas. The permeability measurements indicated that the electrically aligned MWCNT in PMMA has shown almost 2 times higher permeability for hydrogen gas as compare to randomly dispersed MWCNT in PMMA. The enhancement in permeability is explained on the basis of well aligned easy channel provided by MWCNT in electrically aligned sample. The effect of thickness of membrane on the gas permeability also studied and thickness of about 30microm found to be optimum thickness for fast hydrogen gas permeates.

Microstructure change in poly(ethersulfone) films by swift heavy ions.

PES membrane of thickness 25 microm was irradiated by Cl(9+) ions of energy 100 MeV at IUAC, New Delhi. Microstructure changes due to exposure to high-energy ions were investigated by Fourier transform infrared (FTIR) and ultraviolet/visible (UV/vis) absorption spectroscopies, X-ray diffraction technique and by dynamic mechanical analysis (DMA). A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation that could be clearly seen in the absorption spectra. FTIR does not show the remarkable change in the irradiated samples, but there is some change in the surface roughness observed by AFM.