M. Venkateswarlu

Rapid microwave assisted hydrothermal synthesis of porous α-Fe2O3 nanostructures as stable and high capacity negative electrode for lithium and sodium ion batteries

Hematite porous α-Fe2O3 nanostructures were prepared within 60 minutes by a rapid microwave assisted hydrothermal process. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies confirm the phase and structural co-ordination of α-Fe2O3, respectively. Scanning electron microscopy (SEM) images reveal the formation of well defined uniform shaped α-Fe2O3 nanospheres. The transmission electron microscopy (TEM) image shows the porous nature of the α-Fe2O3 nanospheres with an interconnected monocrystallites structure. Swagelok type lithium and sodium batteries were fabricated using the developed porous α-Fe2O3 nanostructures as a negative electrode material. As a negative electrode material in Li-ion cells, the porous α-Fe2O3 nanostructures deliver a second cycle discharge capacity of 1000 mA h g−1 at a 0.1 C rate. At a higher current density of 5 C, the porous α-Fe2O3 nanostructures exhibit a specific capacity of 264 mA h g−1. In the case of Na-ion batteries, the porous α-Fe2O3 nanostructures as negative electrode exhibit a reversible capacity of 300 mA h g−1 with excellent cycleability and coulombic efficiency at 0.1 C up to 100 cycles. The observed excellent electrochemical performance is attributed to the porous nature and uniform shape of the α-Fe2O3 nanostructures that are composed of interconnected monocrystallites. Importantly, the architecture of α-Fe2O3 nanostructures, comprising interconnected monocrystallites could be developed within a short time by a rapid microwave synthesis process and it can be applied to develop different morphological nanostructures for better energy storage device applications.

Effect of ZnO filler concentration on the conductivity, structure and morphology of PVdF-HFP nanocomposite solid polymer electrolyte for lithium battery application

The polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP) nanocomposite solid polymer electrolyte films were developed by solution-casting method. PVdF-HFP as a polymer host, lithium perchlorate (LiClO4) as a salt for lithium ion, and ZnO nanoparticles as fillers were used to form the nanocomposite solid polymer electrolyte films. All the prepared samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry, and scanning electron microscopy. The XRD patterns of the pure and nanocomposite solid polymer electrolyte samples indicate the formation of amorphous phase with 17.5xa0wt.% of lithium salt and ZnO fillers up to 3xa0wt.%. The total conductivity and lithium ion transference number were studied at room temperature by using impedance spectroscopy and Wagner’s polarization methods. The highest conductivity at room temperature for solid polymer electrolyte and nanocomposite solid polymer electrolyte are found to be 3.208u2009×u200910−4 and 1.043u2009×u200910−3xa0S/cm, respectively. Similarly, the lithium ion transference number is evaluated for the optimized solid polymer electrolyte and nanocomposite solid polymer electrolyte films with 3xa0wt.% of ZnO fillers. And it is found that ionic transference number could be enhanced from 92 to 95xa0% with the addition of nanosized ZnO fillers to the solid polymer electrolyte.

Enhanced electrochemical performance of carbon-coated LiMPO4 (M = Co and Ni) nanoparticles as cathodes for high-voltage lithium-ion battery

Olivine LiMPO4 (Mxa0=xa0Co and Ni) nanoparticles have been synthesized by the polyvinylpyrrolidone (PVP) assisted polyol method and adopted the resin coating process for carbon coating on the surface of the nanoparticles. The X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies confirmed the phase and structural co-ordination of bare and carbon-coated LiMPO4 (Mxa0=xa0Co and Ni) nanoparticles, respectively. The formation of uniform carbon layer of nanometer-measured thickness over nanoparticles is confirmed by the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS). Wagner’s polarization study explains an improved electronic transport number (te) for carbon-coated LiMPO4 (Mxa0=xa0Co and Ni) cathodes as compared to bare samples. The electrochemical study of the Li-ion cells shows the first cycle discharge capacities of 180 and 97xa0mAh/g at 0.1xa0C for the cathodes LiCoPO4/C and LiNiPO4/C, respectively, which is an improvement of 21.2 and 25.8xa0% as compared to bare samples. The enhancement of electrochemical performance of the cells is attributed to the improved electronic properties of cathode materials due to the presence of carbon on the surface of nanoparticles.

Electrical and dielectric properties of rare earth oxides coated LiCoO2 particles

Pure and rare earth oxides (Sm2O3, La2O3) coated LiCoO2 nanoparticles were prepared by acrylamide-assisted polymeric citrate and resin-coating processes, respectively. The prepared powders were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and impedance spectroscopy. Powder X-ray diffraction patterns confirmed the formation of phase pure LiCoO2 with nanocrystallite size. X-ray fluorescence spectra confirm the presence of Sm2O3 and La2O3 in coated samples. The conductivity, dielectric and electric modulus studies of the samples were carried out at room temperature. Dielectric spectra of the samples show the decrease in dielectric constant with an increase in frequency of the applied field. The modulus studies indicate the non-Debye behavior of the samples, which is due to long-time slow polarization and relaxation of hopping charges.

Structural, electrical and dielectric studies of nanocrystalline LiMnPO4 particles

Olivine-structured LiMnPO4 nanoparticles were prepared by microwave-assisted solvothermal method. The as obtained LiMnPO4 sample was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and impedance spectroscopy techniques. The XRD pattern confirms the formation of LiMnPO4 phase with an orthorhombic structure. The electrical conductivity of the sample at room temperature is found to be 1.2654u2009×u200910−7xa0Sxa0cm−1. Dielectric spectra show an increase in dielectric constant with increase of temperature. The dielectric loss spectra reveal the predomination of DC conduction in the sample. The modulus studies indicate the non-Debye nature of the sample which corresponds to the distribution of elements in the sample. Galvanostatic battery testing showed that LiMnPO4 nanoparticles displayed good cycleability in 30xa0cycles.

Three-dimensional lithium manganese phosphate microflowers for lithium-ion battery applications

The Polyvinylpyrrolidone (PVP)-assisted polyol process was employed for the synthesis of lithium manganese phosphate (LiMnPO4) microflowers as a cathode material for Li-ion battery applications. LiMnPO4 microflowers were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope-energy dispersion spectroscope, and impedance spectroscopy. The microflowers were highly porous with nanosized petals. CR2032 coin cells were fabricated using LiMnPO4 microflowers’ sample and their battery characteristics were tested. The discharge capacity of LiMnPO4 microflowers was found to be 164xa0mAhxa0g−1 at 0.1C. The observed high discharge capacity was attributed to the short diffusion length of Li-ion motion in the nanopetals of the LiMnPO4 microflowers.

Synthesis of hematite α-Fe2O3 nanospheres for lithium ion battery applications

Hematite α-Fe2O3 nanospheres were prepared by a rapid microwave assisted hydrothermal process. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies confirm the phase and structural coordination of α-Fe2O3 respectively. The formation of uniform shape of nanospheres α-Fe2O3 was confirmed from the results scanning electron microscopy (SEM). Galvanostatic battery testing shows that the α-Fe2O3 nanospheres exhibit good electrochemical performance in the voltage range 0.002 - 3u2005V.Hematite α-Fe2O3 nanospheres were prepared by a rapid microwave assisted hydrothermal process. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies confirm the phase and structural coordination of α-Fe2O3 respectively. The formation of uniform shape of nanospheres α-Fe2O3 was confirmed from the results scanning electron microscopy (SEM). Galvanostatic battery testing shows that the α-Fe2O3 nanospheres exhibit good electrochemical performance in the voltage range 0.002 - 3u2005V.

Electrospun nanocomposite fibrous polymer electrolyte for secondary lithium battery applications

Hybrid nanocomposite [poly(vinylidene fluoride -co- hexafluoropropylene) (PVdF-co-HFP)/magnesium aluminate (MgAl2O4)] fibrous polymer membranes were prepared by electrospinning method. The prepared pure and nanocomposite fibrous polymer electrolyte membranes were soaked into the liquid electrolyte 1M LiPF6 in EC: DEC (1:1,v/v). XRD and SEM are used to study the structural and morphological studies of nanocomposite electrospun fibrous polymer membranes. The nanocomposite fibrous polymer electrolyte membrane with 5 wt.% of MgAl2O4 exhibits high ionic conductivity of 2.80 × 10−3 S/cm at room temperature. The charge-discharge capacity of Li/LiCoO2 coin cells composed of the newly prepared nanocomposite [(16 wt.%) PVdF-co-HFP+(5 wt.%) MgAl2O4] fibrous polymer electrolyte membrane was also studied and compared with commercial Celgard separator.

Optical studies of ZnO nanoparticles and 1-D nanofibers

Highly crystalline ZnO nanoparticles and one dimensional (1-D) ZnO nanofibers were prepared respectively by polyol and electrospinning methods. Both the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and UV-vis spectroscopy. The XRD results showed the formation of nanocrystalline phase in both the samples and also the average crystallite size is calculated and it is found to be 65 nm and 26nm for samples prepared by polyol and electrospinning respectively. SEM images showed the spherical size of ZnO sample prepared by polyol and 1-D nanofibers of ZnO samples prepared by electrospinning. Optical properties of different morphology of ZnO nanomaterials were studied by UV-vis spectroscopy. The UV-vis absorption spectra of both the samples showed the different intensity and slight blue shift of absorption peaks in the UV-vis region, which corresponds to change the energy band gap of both the samples.