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Primary Na/MnO 2 cells are expected to gain importance for replacement of primary Li/MnO 2 cells in future akin to the Na-ion cells as alternative for Li-ion cells. Amorphous MnO 2 is prepared by a drop-wise addition of KMnO 4 solution to MnSO 4 solution, and coin cells of Na/MnO 2 are fabricated in a non-aqueous electrolyte of Na salt. The electrochemical impedance spectroscopy (EIS) data provides a high resistance of Na metal due to the surface passive film. On subjecting the cell for discharge, the surface film causes a delay response of the cell voltage and the closed circuit voltage reaches the normal discharge level following dielectric breakdown of the film. The EIS data measured at different stages of cell discharge are subjected to non-linear least square fitting with the aid of an appropriate equivalent circuit. The impedance parameters are examined to throw light on state-of-charge of Na/MnO 2 primary cells.

Sulfur and metal sulfides have been the materials of choice for the cathodes to achieve high energy density from lithium based batteries. Among several metal sulfides, copper sulfide has been widely investigated as a positive electrode material for Li-ion batteries. In the present study, in situ preparation of copper sulfide by reaction of sulfur coated on copper foil current collector is investigated. Sulfur is blended with either acetylene black as a conducting agent or TiO2 nanotubes as porous and non-conducting additive and electrodes are prepared on Cu foil. Electrodes are also prepared without any additive. Copper reacts with sulfur forming copper sulfide which has been confirmed by X-ray diffraction studies. Formation of sulfides with platelet like morphology has been observed in all the coatings. Specific discharge capacity of 282 mAh g(-1) has been obtained from S-TiO2 electrode based cell as compared to 317 mAh g(-1) from S-C electrode based cell. Discharge capacity of 230 mAh g(-1) has been obtained from the cells with S electrode without any additive. This is attributed to the higher conductivity of copper sulfide than sulfur and also to the formation of conducting copper particles on discharge. On subjecting the cells to 100 discharge-charge cycles, almost stable performance has been observed with S-TiO2 electrode based cell. Furthermore, the discharge capacity of S-TiO2 based cell is greater than S-C based cell and it increases on repeated cycling. (C) 2017 Elsevier B.V. All rights reserved.

Surface of $$\hbox {TiO}_{2}$$ is known to chemically bind the polysulfides in Li–S cell. In the present study, the effect of surface defects or oxygen vacancies in $$\hbox {TiO}_{2}$$ present as a composite with sulfur cathode on the performance of Li–S cell was investigated by using $$\hbox {NaBH}_{4}$$ reduced (black colour) $$\hbox {TiO}_{2}$$ and pristine (white) $$\hbox {TiO}_{2}$$ in cathode. Results show that former is superior in performance.

Achieving high energy density has been the focus of research in rechargeable batteries. Lithiumsulfur system is attractive due to its high theoretical energy density (2500 Wh kg-1). The major problem in Li-S system is associated with the dissolution of lithium polysulfides formed at the cathode during discharge. Shuttling of polysulfides between the cathode and anode during cycling reduces the efficiency of cycling. In the present study, TiO2 nanotubes are prepared from nanoparticles by hydrothermal route. Titania-sulfur composite has been prepared by infiltrating sulfur solution into the TiO2 nanotubes and studied as a cathode material in a non-aqueous electrolyte. Cycling behavior of Li-S cells fabricated using pristine sulfur and TiO2 nanoparticle-sulfur composite is also studied for comparison. Cells with TiO2 nanotubes exhibit better discharge capacity and coulombic efficiency than the cells with TiO2 nanoparticles and pristine sulfur.

Layered composite samples of lithium-rich manganese oxide (Li1.2Mn0.6Ni0.2O2) are prepared by a reverse microemulsion route employing a soft polymer template and studied as a positive electrode material. The product samples possess dual porosity with distribution of pores at 3.5 and 60 nm. Pore volume and surface area decrease on increasing the temperature of preparation. Nevertheless, the electrochemical activity of the composite increases with an increase in temperature. The discharge capacity value of the samples prepared at 800 and 900 °C is about 240 mA h g−1 at a specific current of 25 mA g−1 with a good cycling stability. The composite sample heated at 900 °C possesses a high rate capability with a discharge capacity of 100 mA h g−1 at a specific current of 500 mA g−1. The high rate capability is attributed to porous nature of the composite sample.

In the present work, Li2-x MnO3-y (LMO) thin films have been deposited by radio frequency (RF) reactive magnetron sputtering using acid-treated Li2MnO3 powder target. Systematic investigations have been carried out to study the effect of RF power on the physicochemical properties of LMO thin films deposited on platinized silicon substrates. X-ray diffraction, electron microscopy, surface chemical analysis and electrochemical studies were carried out for the LMO films after post deposition annealing treatment at 500 A degrees C for 1 h in air ambience. Galvanostatic charge discharge studies carried out using the LMO thin film electrodes, delivered a highest discharge capacity of 139 mu Ah mu m(-1) cm(-2) in the potential window 2.0-3.5 V vs. Li/Li+ at 100 W RF power and lowest discharge capacity of 80 mu Ah mu m(-1) cm(-2) at 75 W RF power. Thereafter, the physicochemical properties of LMO films deposited using optimized RF power 100 W on stainless steel substrates has been studied in the thickness range of 70 to 300 nm as a case study. From the galvanostatic charge discharge experiments, a stable discharge capacity of 68 mu Ah mu m(-1) cm(-2) was achieved in the potential window 2.0-4.2 V vs. Li/Li+ tested up to 30 cycles. As the thickness increased, the specific discharge capacity started reducing with higher magnitude of capacity fading.

In the preset study dye-sensitized solar cells (DSSC) have been fabricated on a flexible titanium metal foil substrate with mesoporous anatase Titania microsphers (TMS) as the electron transport layer for photo anode. These microspheres perform dual function of light scattering and efficient dye absorption. A light to electricity conversion efficiency of 2.93% is achieved with illumination through the counter electrode. Additionally electrochemical impedance spectroscopy (EIS) is used to analyze the electron transport processes occurring at the various interfaces. Copyright © 2013 VBRI press.

LiCoO2 thin films used as cathode layers in thin-film solid-state batteries have been deposited from LiCoO2 powder target using radio frequency (rf) magnetron sputtering in a cost effective approach in terms of material consumption and processing time. Xray diffraction (XRD) studies of the films after post deposition annealing treatment revealed (104) orientation, which is the characteristic of rf sputtered LiCoO2 films. Raman spectroscopy was used to identify the different modes of vibration of atoms in the film. The surface morphology and cross-section of the samples were characterized using field emission scanning electron microscopy (SEM). The chemical analysis of LiCoO2 thin films was examined by X-ray photoelectron spectroscopy (XPS) showed atomic ratio of Li/Co as 0.9 which is close to the ideal value 1. Electrochemical characterization such as charge – discharge and cyclic voltammetry were conducted for LiCoO2 films deposited on platinized silicon substrates in the potential range 3.0 to 4.2 V vs Li/Li + . The maximum discharge capacity of 64 µAh.µm -1 . cm -2 and 52 µAh. µm -1 .cm -2 were achieved when discharged at a current of 5 µA and 50 µA for the first discharge cycle respectively. Moreover the electrochemical investigations of LiCoO2 thin films on flexible copper substrates also investigated and achieved an initial discharge capacity of 83 mAh/g. The possible reasons for degradation in the electrochemical properties have been discussed. The present work indicates suitability of sputtering from powder targets for thin film battery fabrication. Copyright © 2013 VBRI press.

The effects of physical aging on the conductivity of a PEO:LiClO4 (8:1)–Al2O3 (20 wt.%, 24 nm) composite electrolyte were investigated and analyzed. The rate of physical aging was temperature dependent and peaked at 50 °C. Aging causes the structure to densify, leading to a reduction in the size of the coordinating sphere around lithium. The conductivity of the electrolyte also exhibited a memory effect, i.e., at a given temperature the conductivity depended not only upon the temperature but also on prior thermal history. The solvent-less electrolyte displays high conductivity with low temperature coefficient in the 20–100 °C range.

A composite solid polymer electrolyte (CSPE) consisting of polyethyleneoxide (PEO), LiClO4 and Al2O3 of particle size 24 nm was prepared by a melt-cast method. The differential scanning calorimetry (DSC) data suggested that the CSPE is in an amorphous state due to the presence of nanophase alumina. The specific conductivity versus temperature follows Vogel–Tamman–Fulscher (VTF) behavior and the activation energy has been calculated. By analogy with the Marcus theory of solvent reorganization during electron-transfer reactions, the reorganization energy of the polymer chain has been calculated from the energy of activation of ionic conduction. The ac impedance data was analyzed using a non-linear least square (NLLS) fitting program, and the resistance of the passivating film on Li and the charge-transfer resistance of the Li reaction have been evaluated. The charge-transfer resistance has been shown to follow Arrhenius behavior through the standard rate constant for the reaction. Cyclic voltammograms provided evidence of electrochemical activity at the Li/CSPE interface near ambient temperature.

Lithium-air battery is anticipated as the battery with highest energy density among all existing rechargeable battery systems known now. Literature reports suggest that the theoretical energy density of Li-air battery is close to that of gasoline. Thus, if successfully developed, rechargeable Li-air battery will be a suitable substitute for gasoline for electric vehicles. The research and development work is at initial stages worldwide at present. Electrochemistry of oxygen in non-aqueous electrolytes is one of the crucial factors. Development of a suitable catalyst for reversible oxygen electrode for long cycle-life is important. The research and development work available in the literature and also in the investigator's laboratory is based on small experimental cells. Furthermore, the cells function as primary (non-rechargeable) cells, and attempts to recharge do not produce significant results. Hardly a few cycles are reported. In the present studies, cells are assembled with electrodes of area of about 10 sq cm and evaluated for electrochemical discharge. For achieving rechargeability, several attempts are made with different catalysts, carbons, electrolytes, etc., but a few cycles are achieved in some of the cells.

Several solid electrolytes derived from poly(ethylene oxide) doped with lithium tetrafluoroborate and a high conductivity lithium borosulfate glass were formulated and investigated for their electrochemical performance. The electrochemical characterization included a.c. impedance measurements, the temperature dependence of conductivity, scanning electron microscopy (SEM), cyclic voltammetry (CV), and the charge/discharge cycling of symmetric cells. the ionic conductivities of these electrolytes at ambient temperature were around 10 −7 S cm −1 . Although no significant improvement in conductivity was observed, the cyclic voltammetry, impedance spectroscopy, and cycling data on Li/polymer/Li and Li/polymer/ Ni cells reveal that the electrode reactions are facilitated by the glass incorporation.

Studies were undertaken to examine the effect of substrate materials on impedance behaviour of lithium dipthalocyanine (Li2Pc). Several symmetrical cells were assembled using stainless steel (SS), gold foil, gold sputtered SS, copper, nickel and lithium electrodes. It was found that the Nyquist impedance spectrum obtained with SS electrodes consisted of two semicircles with total resistance of 1700 kOhm. But the cell with gold electrodes produced a single semicircle with resistance of 450 kOhm. Similarly, different values of impedance were obtained by varying the substrate materials. It was concluded that Li2Pc exhibits chemical reactivity with metallic substrates used in the study.

Dilithium phthalocyanine (Li2Pc) possesses mixed electronic-ionic conductivity due to overlap of pi-pi orbitals (electronic) and mobility of Li+ ion (ionic) in a channel formed due to stacking of the macromolecules. Electrochemical impedance measurements provide separation of electronic and ionic conductivities. The temperature dependence studies are employed for calculation of activation energies. The electronic conductivity shows a marked increase on applying DC bias voltage across a symmetrical cell of Li2Pc with blocking electrodes, whereas the ionic conductivity is marginally influenced.

The electrooxidation of ascorbic acid $(H_2A)$, which does not occur on a bare Ni electrode, has been shown to take place on a polyaniline (PANI)-coated Ni electrode in aqueous electrolytes of a wide pH range. The characteristic voltammetric peak of PANI in $0.1 M H_2SO_4$ at 0.2 V vs SCE corresponding to the transformation of leucoemeraldine to emeraldine gradually diminishes with an increase in concentration of $H_2A$ as a result of adsorption. This peak disappears before the appearance of another peak corresponding to the oxidation of $H_2A$ at a concentration of 1 mM. The irreversible oxidation current of $H_2A$ exhibits a linear dependence on the concentration. The effect of adsorption of $H_2A$ on PANI has been shown to increase the voltammetric peak current. A study on the variation of the PANI thickness and its influence on the voltammetric oxidation of $H_2A$ has led to an optimum thickness of $1.6 \mu m$. The oxidation currents on the porous PANI/Ni electrode have been found to be several times higher at lower potentials in comparison with the data of a Pt electrode. The reaction has also been studied by ac impedance spectroscopy. In alkaline electrolytes, the Nyquist impedance plot is characterized by two semicircles instead of a single semicircle in acidic electrolytes. Thus, Ni, which is a non-platinum metal, has been found to be useful, by surface modification with PANI, for electrooxidation of $H_2A$. The data are reproducible in the electrolytes of a wide pH range, thus suggesting a good stability, reusability and a long life for the PANI/Ni electrodes.

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