Micron-sized single-crystal cathodes for sodium-ion batteries.

Confining the particle-electrolyte interactions to the particle surface in electrode materials is vital to develop sustainable and safe batteries. Micron-sized single-crystal particles offer such opportunities. Owing to the reduced surface area and grain boundary-free core, particle-electrolyte interactions in micron-sized single-crystal particles will be confined to the particle surface. Here, we reveal the potential of such materials in sodium-ion batteries. We synthesized and investigated the chemical, electrochemical, and thermal properties of single-crystalline P2-type Na0.7Mn0.9Mg0.1O2 as a cathode material for sodium-ion batteries. Single-crystalline Na0.7Mn0.9Mg0.1O2 with a mean particle size of 8.1 µm exhibited high cycling and voltage stability. In addition, the exothermic heat released by the charged single-crystal Na0.7Mn0.9Mg0.1O2 cathodes was four times lower than that of the corresponding polycrystalline Na0.7Mn0.9Mg0.1O2. This significantly enhances the thermal stability of electrode materials and possibly mitigates thermal runaways in batteries. Surprisingly, single crystals of Na0.7Mn0.9Mg0.1O2 were relatively stable in water and ambient atmosphere.

Synthesis of Fast Fluoride-Ion-Conductive Fluorite-Type Ba1- xSb xF2+ x (0.1 ≤ x ≤ 0.4): A Potential Solid Electrolyte for Fluoride-Ion Batteries.

Toward the development of high-performance solid electrolytes for fluoride-ion batteries, fluorite-type nanostructured solid solutions of Ba1- xSb xF2+ x ( x ≤ 0.4) were synthesized by high-energy ball-milling method. Substitution of divalent Ba2+ by trivalent Sb3+ leads to an increase in interstitial fluoride-ion concentration, which enhances the ionic conductivity of the Ba1- xSb xF2+ x (0.1 ≤ x ≤ 0.4) system. Total ionic conductivities of 4.4 × 10-4 and 3.9 × 10-4 S cm-1 were obtained for Ba0.7Sb0.3F2.3 and Ba0.6Sb0.4F2.4 compositions at 160 °C, respectively. In comparison to isostructural Ba0.3La0.7F2.3, the ionic conductivity of Ba0.7Sb0.3F2.3 is significantly higher, which is attributed to the presence of an electron lone pair on Sb3+. Introduction of such lone pairs seems to increase fluoride-ion mobility in solid solutions. In addition, Ba0.7Sb0.3F2.3 was tested as a cathode material against Ce and Zn anode using La0.9Ba0.1F2.9 as the electrolyte. Ba0.3Sb0.7F2.3/La0.9Ba0.1F2.9/Ce cell showed high discharge and charge capacities of 301 and 170 mA h g-1, respectively, in the first cycle at 150 °C.

Facile synthesis of C-FeF2 nanocomposites from CFx: influence of carbon precursor on reversible lithium storage.

Transition metal fluorides are an important class of cathode materials for lithium batteries owing to their high specific energy and safety. However, metal fluorides are electrical insulators, exhibiting slow reaction kinetics with Li. Consequently, metal fluorides can show poor electrochemical performance. Instead, carbon-metal fluoride nanocomposites (CMNFCs) were suggested to enhance electrochemical activity. Chemical synthesis of CMNFCs poses particular challenges due to the poor chemical stability of metal fluorides. Recently, we reported a facile one-step method to synthesize carbon-FeF2 nanocomposites by reacting fluorinated carbon (CFx) with iron pentacarbonyl (Fe(CO)5) at 250 °C. The method resulted in C-FeF2 nanocomposites with improved electrochemical properties. Here, we have synthesized four different C-FeF2 nanocomposites by reacting four different CFx precursors made of petro-coke, carbon black, graphite, and carbon-fibers with Fe(CO)5. Electrochemical performance of all four C-FeF2 nanocomposites was evaluated at 25 °C and 40 °C. It is shown that the nature of CFx has a critical impact on the electrochemical performance of the corresponding C-FeF2 nanocomposites. The C-FeF2 nanocomposites were characterized by using various experimental techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, resistivity measurement, and 57Fe Mössbauer spectroscopy to shed light on the differences in electrochemical behaviour of different C-FeF2 nanocomposites.

VOCl as a Cathode for Rechargeable Chloride Ion Batteries.

A novel room temperature rechargeable battery with VOCl cathode, lithium anode, and chloride ion transporting liquid electrolyte is described. The cell is based on the reversible transfer of chloride ions between the two electrodes. The VOCl cathode delivered an initial discharge capacity of 189 mAh g(-1) . A reversible capacity of 113 mAh g(-1) was retained even after 100 cycles when cycled at a high current density of 522 mA g(-1) . Such high cycling stability was achieved in chloride ion batteries for the first time, demonstrating the practicality of the system beyond a proof of concept model. The electrochemical reaction mechanism of the VOCl electrode in the chloride ion cell was investigated in detail by ex situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results confirm reversible deintercalation-intercalation of chloride ions in the VOCl electrode.

Single step transformation of sulphur to Li2S2/Li2S in Li-S batteries.

Lithium-sulphur batteries have generated tremendous research interest due to their high theoretical energy density and potential cost-effectiveness. The commercial realization of Li-S batteries is still hampered by reduced cycle life associated with the formation of electrolyte soluble higher-order polysulphide (Li2Sx, x = 4-8) intermediates, leading to capacity fading, self-discharge, and a multistep voltage profile. Herein, we have realized a practical approach towards a direct transformation of sulphur to Li2S2/Li2S in lithium-sulphur batteries by alteration of the reaction pathway. A coconut shell derived ultramicroporous carbon-sulphur composite cathode has been used as reaction directing template for the sulphur. The lithiation/delithiation and capacity fading mechanism of microporous carbon confined sulphur composite was revealed by analyzing the subsurface using X-ray photoelectron spectroscopy. No higher-order polysulphides were detected in the electrolyte, on the surface, and in the subsurface of the cathode composite. The altered reaction pathway is reflected by a single-step profile in the discharge/charge of a lithium-sulphur cell.

Electrochemical fluorination of perovskite type BaFeO2.5.

Here we report on the first electrochemical fluorination exemplarily performed on perovskite type BaFeO2.5. A cell setup of the type BaFeO2.5 II La0.9Ba0.1F2.9 II MFx (with MFx being MgF2 and CeF3) was used to perform the reaction, charging the cell up to voltages of about 4 V. Formation of a compound of approximate composition BaFeO2.5F∼0.5 was observed, in agreement with diffraction studies of the independently performed chemically fluorinated compound using F2 gas, and also possessing a capacity which is close to the theoretical capacity of the material. This new method gives an alternative towards the use of highly reactive and toxic F2 gas, and provides potential in adjusting the chemical potential for oxidative chemical fluorinations.

Solid electrolytes for fluoride ion batteries: ionic conductivity in polycrystalline tysonite-type fluorides.

Batteries based on a fluoride shuttle (fluoride ion battery, FIB) can theoretically provide high energy densities and can thus be considered as an interesting alternative to Li-ion batteries. Large improvements are still needed regarding their actual performance, in particular for the ionic conductivity of the solid electrolyte. At the current state of the art, two types of fluoride families can be considered for electrolyte applications: alkaline-earth fluorides having a fluorite-type structure and rare-earth fluorides having a tysonite-type structure. As regard to the latter, high ionic conductivities have been reported for doped LaF3 single crystals. However, polycrystalline materials would be easier to implement in a FIB due to practical reasons in the cell manufacturing. Hence, we have analyzed in detail the ionic conductivity of La(1-y)Ba(y)F(3-y) (0 ≤ y ≤ 0.15) solid solutions prepared by ball milling. The combination of DC and AC conductivity analyses provides a better understanding of the conduction mechanism in tysonite-type fluorides with a blocking effect of the grain boundaries. Heat treatment of the electrolyte material was performed and leads to an improvement of the ionic conductivity. This confirms the detrimental effect of grain boundaries and opens new route for the development of solid electrolytes for FIB with high ionic conductivities.

Influence of particle size and fluorination ratio of CF x precursor compounds on the electrochemical performance of C-FeF2 nanocomposites for reversible lithium storage.

Systematical studies of the electrochemical performance of CF x -derived carbon-FeF2 nanocomposites for reversible lithium storage are presented. The conversion cathode materials were synthesized by a simple one-pot synthesis, which enables a reactive intercalation of nanoscale Fe particles in a CF x matrix, and the reaction of these components to an electrically conductive C-FeF2 compound. The pretreatment and the structure of the utilized CF x precursors play a crucial role in the synthesis and influence the electrochemical behavior of the conversion cathode material. The particle size of the CF x precursor particles was varied by ball milling as well as by choosing different C/F ratios. The investigations led to optimized C-FeF2 conversion cathode materials that showed specific capacities of 436 mAh/g at 40 °C after 25 cycles. The composites were characterized by Raman spectroscopy, X-Ray diffraction measurements, electron energy loss spectroscopy and TEM measurements. The electrochemical performances of the materials were tested by galvanostatic measurements.

Improving the energy density and power density of CFx by mechanical milling: a primary lithium battery electrode.

The effect of high energy ball milling on the electrochemical performance of graphite fluoride (CFx) was investigated. A significant improvement was observed in both energy density and power density. The volumetric energy density was increased up to a factor of 3 with ball milled materials compared with pristine materials. The gravimetric energy density was increased up to a factor of 2, depending on the discharge rates. At 6C the ball milled material still delivered 40% of its nominal capacity, whereas the pristine material did not exhibit any capacity any more. We achieved the power density of 9860 W/kg with a gravimetric energy density of 800 Wh/kg for the optimized material.

Remote sensing and GIS techniques for evaluation of groundwater quality in municipal corporation of Hyderabad (Zone-V), India.

Groundwater quality in Hyderabad has special significance and needs great attention of all concerned since it is the major alternate source of domestic, industrial and drinking water supply. The present study monitors the ground water quality, relates it to the land use / land cover and maps such quality using Remote sensing and GIS techniques for a part of Hyderabad metropolis. Thematic maps for the study are prepared by visual interpretation of SOI toposheets and linearly enhanced fused data of IRS-ID PAN and LISS-III imagery on 1:50,000 scale using AutoCAD and ARC/INFO software. Physico-chemical analysis data of the groundwater samples collected at predetermined locations forms the attribute database for the study, based on which, spatial distribution maps of major water quality parameters are prepared using curve fitting method in Arc View GIS software. Water Quality Index (WQI) was then calculated to find the suitability of water for drinking purpose. The overall view of the water quality index of the present study area revealed that most of the study area with >50 standard rating of water quality index exhibited poor, very poor and unfit water quality except in places like Banjara Hills, Erragadda and Tolichowki. Appropriate methods for improving the water quality in affected areas have been suggested.

Assessment and mapping of water pollution indices in zone-III of municipal corporation of hyderabad using remote sensing and geographic information system.

A preliminary survey of area under Zone-III of MCH was undertaken to assess the ground water quality, demonstrate its spatial distribution and correlate with the land use patterns using advance techniques of remote sensing and geographical information system (GIS). Twenty-seven ground water samples were collected and their chemical analysis was done to form the attribute database. Water quality index was calculated from the measured parameters, based on which the study area was classified into five groups with respect to suitability of water for drinking purpose. Thematic maps viz., base map, road network, drainage and land use/land cover were prepared from IRS ID PAN + LISS III merged satellite imagery forming the spatial database. Attribute database was integrated with spatial sampling locations map in Arc/Info and maps showing spatial distribution of water quality parameters were prepared in Arc View. Results indicated that high concentrations of total dissolved solids (TDS), nitrates, fluorides and total hardness were observed in few industrial and densely populated areas indicating deteriorated water quality while the other areas exhibited moderate to good water quality.