Anshuman Dalvi

A comparative study of crystallization kinetics between conventionally melt quenched and mechanochemically synthesized AgI–Ag2O–CrO3 superionic system

Abstract Non-isothermal crystallization kinetics in conventionally melt quenched versus mechanochemically synthesized amorphous AgI–Ag 2 O–CrO 3 superionic solids is discussed. The quenched as well as ball-milled samples exhibit glass ( T g ) and multiple amorphous⇒crystalline ( T c ) transitions. T g as well as T c are found to increase monotonically with heating rate. The activation energy for structural relaxation ( E s ) obtained using Moynihan equation is found to be higher for ball-milled samples that eventually suggests the relatively rigid and highly viscous structure of milled samples. The activation energy associated with nucleation and growth ( E c ) is obtained using Matusita–Sakka equation and its higher value confirms the higher rate of crystallization in ball-milled samples. The values of T c – T g and the enthalpy of phase transformation (ΔH) are also found higher for the ball-milled samples that confirm their comparatively high thermal stability. The electrical conductivity near the crystallization temperatures is studied as a function of time and temperature and these results confirm the presence of amorphous⇒crystalline transition temperatures in the ball-milled as well as in the melt-quenched samples.

Mechanochemically synthesized amorphous superionic systems for solid-state batteries

Solid-state electrochemical cells of the type Ag|a-SIC|I2 are fabricated using mechanochemically synthesized amorphous superionic conductors (a-SICs), AgI–Ag2O–MxOy (MxOy=B2O3, V2O5, CrO3) as electrolytes. The typical value of the conductivity of these systems is in the range 10−2 to 10−3 Ω−1 cm−1 and the transport number of Ag+ ions is near unity. The mechanochemically synthesized powders were directly used as electrolytes. Constant load characteristics for various loads confirm the thermodynamic stability and competency of these materials as electrolytes. The cells are discharged at low (J∼65 μA/cm2) and high (J∼105 μA/cm2) drain currents and nominal cell capacities and energy densities were obtained. Nominal cell capacities for all these cells for low current discharge rates were found within 6–7% of the theoretical capacity of Ag/I2 cell. Whereas, for high discharge rates, ∼3–4% of the theoretical value. A current density of ∼500 μA/cm2 can be drawn safely without any serious polarization.

Transport studies on mechanochemically synthesized amorphous AgI–Ag2 O–CrO3 superionic system

Abstract Mechanochemical synthesis, a relatively new technique in the field of solid state ionics, has been successfully used to obtain highly conducting amorphous materials of composition x AgI(100− x )[0.5Ag 2 O+0.5CrO 3 ] for x =50, 60 and 70. The ionic conductivity of ball-milled amorphous samples is found to be ∼10 −2 Ω −1 cm −1 at room temperature which is ∼3 orders of magnitude higher than that of AgI and comparable with superionic glass of the same compositions. The amorphous samples are thermally stable upto ∼100 °C. On annealing the samples at ∼110 °C there is precipitation of AgI and Ag 2 O nanocrystallites of size ∼10 nm. For all the samples the ionic transport number is found to be near unity. The galvanic cells of the type Ag|a-SIC|I 2 +C, fabricated using mechanically milled materials as electrolyte, are thermodynamically stable. The electrical, structural, electrolytic and thermal properties are very much close to those of AgI–Ag 2 O–CrO 3 and AgI–Ag 2 CrO 4 superionic glasses investigated earlier.

Li2SO4−Li2O−P2O5 ionic glass dispersed with [Bmim] [PF6] ionic liquid: Electrical transport and thermal stability investigations

A fast ionic composite is prepared by dispersion of Ionic liquid [Bmim][PF6] in Li2SO4−Li2O−P2O5 glass matrix by mixing and through grinding. Amorphous/glassy nature of the samples is confirmed by X-Ray diffraction (XRD). Surprisingly, the electrical conductivity of the samples is found to be increasing by ∼ 2 orders of magnitude and exhibits typical Arrhenius behavior with low activation energy. DC polarization and impedance spectroscopy measurements suggest that samples are essentially ionic in nature. The conductivity isotherms were also obtained at different temperatures (T < 100 °C) and found to be appreciably stable at least for ∼ 10 days.

New generation Li+ NASICON glass-ceramics for solid state Li+ ion battery applications

Lithiumion conducting NASICON glass-ceramics have been prepared by a novel planetary ball milling assisted synthesis route. Structural, thermal and electrical investigations have been carried out on the novel composites composed of LiTi(PO4)3 (LTP) and 50[Li2SO4]-50[Li2O-P2O5] ionic glass reveal interesting results. Composites were prepared keeping the concentration of the ionic glass fixed at 20 wt%. X-ray diffraction and diffe rential thermal analysis confirm the glass-ceramic formation. Moreover, the structure of LTP remains intact during the glass -ceramic formation. Electrical conductivity of the glass-ceramic composite is found to be higher than that of the pristine glass (50LSLP) and LTP. The bulk and grain boundary conductivities of LTP exhibit improvement in composite. Owing to high ionic conductivity and thermal stability, novel glass -ceramic seems to be a promising candidate for all solid-state battery applications.Lithiumion conducting NASICON glass-ceramics have been prepared by a novel planetary ball milling assisted synthesis route. Structural, thermal and electrical investigations have been carried out on the novel composites composed of LiTi(PO4)3 (LTP) and 50[Li2SO4]-50[Li2O-P2O5] ionic glass reveal interesting results. Composites were prepared keeping the concentration of the ionic glass fixed at 20 wt%. X-ray diffraction and diffe rential thermal analysis confirm the glass-ceramic formation. Moreover, the structure of LTP remains intact during the glass -ceramic formation. Electrical conductivity of the glass-ceramic composite is found to be higher than that of the pristine glass (50LSLP) and LTP. The bulk and grain boundary conductivities of LTP exhibit improvement in composite. Owing to high ionic conductivity and thermal stability, novel glass -ceramic seems to be a promising candidate for all solid-state battery applications.

Enhanced electrical transport in ionic liquid dispersed TMAI-PEO solid polymer electrolyte

A polymer composite is prepared by dispersing ionic liquid [Bmim][BF4] in Polyethylene oxide-tetra methyl ammonium iodide composite and subsequent microwave treatment. X-ray diffraction patterns confirm the composite nature. To explore possibility of proton conductivity in these films, electrical transport is studied by impedance spectroscopy and DC polarization. It is revealed that addition of ionic liquid in host TMAI-PEO solid polymer electrolyte enhances the conductivity by ∼ 2 orders of magnitude. Polarization measurements suggest that composites are essentially ion conducting in nature. The maximum ionic conductivity is found to be ∼2 × 10−5 for 10 wt % ionic liquid.

Structural relaxation at glass transition temperature in Li2O−B2O3 glassy ionic system

Structural relaxation using glass transition kinetics in Li2O−B2O3 glassy system is reported. Amorphous and glassy nature of the samples is confirmed by X-Ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). The activation energy for structural relaxation at Tg, obtained from glass transition kinetics using Moynihan equation, exhibits interesting trend with Li2O content. It is observed that due to such structural relaxation at the glass transition temperature the ionic conductivity exhibits an anomalous rise, deviating from Arrhenius behavior.

Electrical transport and structural investigations in Cu2O substituted AgI-Ag2O-V2O5 glass-ceramic nanocomposites

Glass-ceramic nanocomposites in Cu2O substituted AgI-(Ag2O)1-x-(Cu2O)x-V2O5 superionic system are prepared by annealing the melt-quenched glasses above the crystallization temperatures. Structural and electrical properties have been investigated. Scanning electron microscopy suggests the existence of fine particles of size 20-200 nm dispersed in the annealed glass matrix. Samples are essentially ionic and stable under conductivity-temperature cycles upto ∼ 160 °C. It is found that the conductivity in the nanocomposites increases with Cu2O substitution and highest conductivity is found to be ∼ 2 × 10−3 Ω−1cm−1 for x = 0.3 at room temperature. Differential scanning calorimetry scans confirm the existence of silver iodide crystallites in all the glass-ceramic compositions.

Electrical And Electrochemical Characterization Of PEO‐Ag2SO4 Composite Polymer Electrolytes

The flat, thin, and flexible ion conducting polymer films were prepared by solution casting technique from PEO complexed with Ag2SO4. Structural, electrical and electrochemical properties have been studied. The samples are found to be essentially ionic in nature. The highest conductivity is found to be 7×10−4 Ω−1 cm−1 at 20 °C for sample with 15 weight percent of Ag2SO4 in PEO matrix. Ag/I2 cells are fabricated using polymer films as electrolytes do confirm the ionic nature. The films are found to be stable under the battery conditions.

Electrical transport in superionic thin films prepared by pulsed laser deposition

Superionic thin films are obtained using PLD technique from Ag+ ion oxysalt glassy target. The structural and electrical properties of the films have been investigated. Partially amorphous nature of the films has been confirmed by X‐ray diffraction measurements. The electrical conductivity of the sample has been measured at well controlled heating rate of 1 °C/min. Conductivity temperature cycles suggest that deposited films are essentially ionic in nature.