Department of Physics

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A04-0580 - Na3Zr2Si2PO12-Polymer Hybrid Composites for Solid-State Supercapacitor Applications
(IMCS 2020, 2020-05) Dalvi, Anshuman
Various Na+ ions conducting composite polymer electrolytes have been developed in last three decades, but their application is limited due to poor ionic conductivity near room temperature. Recently, we have demonstrated high ionic conductivity of ∼ 10-4 Ω-1cm-1 in NASICON-polymer hybrids and found these systems useful in energy storage applications. A high ionic mobility of ~ 10-1 cm2/V-s was also reported. Present work shows a possible application of these hybrids as electrolyte/separator in all-solid-state supercapacitor. In this work, Na+ NASICON, viz. Na3Zr2Si2PO12 (NZSP) have been prepared by conventional solid state reaction route. Subsequently, their nanoparticles of size ~ 30 nm were obtained via mechanical ball milling. The nanoparticles were mixed with polymer in a ball mill until a homogeneous viscous slurry formation. Further the slurry was dried, hot pressed at ~ 80°C to obtain films of uniform thickness ~ 250µm. This way, composite films with composition (wt%) 10NaI-90(PEO1-xNZSPx), where 0 ≤ x ≤ 0.4, were obtained. Surface morphology, structural and thermal analysis were characterized using FESEM, XRD and DSC. A maximum ionic conductivity of ~ 4 x 10-5 Ω-1cm-1 at room temperature has been achieved for composite with x = 0.4. Impedance spectroscopy was used to understand mechanism of ionic transport. Further, to understand the role of ceramic fillers in enhancing the ionic conductivity, local structure of the composites was studied using x-ray absorption near edge structure spectroscopy (XANES) at Indus II Beamline 01, RRCAT, Indore. These results suggest a significant role of NASICON in providing pathways for Na+ ion transport. The ionic conductivity at room temperature for composite with x = 0.4 were further modified with EMITf and EC+PC as plasticizer. A maximum ionic conductivity of ~ 2 x 10-4 Ω-1cm-1 at room temperature has been achieved with addition of 2 wt% of EMITf in the composite. To elucidate the capacity of these electrolyte as a membrane for all solid-state ionic devices, solid state super capacitors (configuration C|CPE|C) were fabricated. These composites have been found to be competitive candidates for energy storage. A maximum specific capacitance of ~ 26 F-g-1 is obtained for composite with 2 wt% EMITf at room temperature.
Achieving high-performance parameters in NASICON-polymer composite electrolyte-based solid-state supercapacitors by interface modification
(RSC, 2025-02) Dalvi, Anshuman
The present study reveals a strategy to enhance the performance of solid-state supercapacitors based on activated carbon electrodes and a Na3Zr2Si2PO12 (NZSP) dispersed fast ionic solid polymer electrolyte membrane. The electrode–electrolyte interface is optimized using a novel ‘solvent layer’ approach to enhance supercapacitor performance. By adding a small amount of acetonitrile organic solvent (a few μL cm−2) at the electrode–electrolyte interface and utilizing high surface area (1800 m2 g−1) activated carbon, significant improvements in specific capacitance, specific energy, specific power, and cycling stability are achieved. Device performance at various operating voltages and discharge currents reveals interesting results. A specific capacitance of approximately 260 F g−1 and a high specific power of 4780 W kg−1 is achieved at 3 V/5 mA. Moreover, after 10[thin space (1/6-em)]000 galvanostatic charge–discharge cycles (1 V/1 mA), the supercapacitor exhibits ∼99% stable coulombic efficiency along with appreciably high capacitance retention (∼90%). A stack of five such cells can power an 8 V LED circuit for more than 30 minutes. Applying such a solvent layer enables effective use of the surface area of the activated carbon. Results suggest that solvent incorporation enables a local ‘gel-like’ layer formation that couples the electrode with a solid polymer electrolyte and facilitates faster charge movement across the electrode–electrolyte interface.
All-solid-state electric double layer supercapacitors using Li1.3Al0.3Ti1.7(PO4)3 reinforced solid polymer electrolyte
(Elsevier, 2022-05) Dalvi, Anshuman
In this work, we report the fabrication and characterization of all-solid-state supercapacitors based on a conductive filler dispersed solid polymer electrolyte. Fast ionic Li1.3Al0.3Ti1.7(PO4)3 (LATP) reinforced PEO-PEG-LITFSI composite solid polymer electrolyte (CSPE) membranes are prepared by milling assisted route. The electric double-layer capacitor (EDLC) cells, using a hot-roll lamination technique, are fabricated using a CSPE membrane as electrolyte and activated charcoal (surface area ∼ 817m2g−1) on graphite sheet as electrode. The EDLCs display appreciable areal capacitance of ∼ 12 Fcm−2 and ∼40 Fcm−2 at 40 °C and 80 °C, respectively at ∼0.65 mAcm2 and 2 V. These solid-state EDLCs at 40 °C exhibit stability up to ∼16,000 cycles. Further, the electrode-electrolyte (solid-solid) interface remains quite stable after the charge-discharge cycling. The electrical conductivity of the CSPE membranes correlates well with the EDLC performance. The LATP content in the CSPE membranes play important role in enhancing the capacitance. The present investigation suggests that CSPE membranes with conductivity between ∼10−4–10−5 Scm−1 are useful for low-power EDLC applications. The EDLCs cells with LATP dispersed CSPE exhibit better stability during thermal cycling between 40 °C-80 °C.
All-solid-state Na+ ion supercapacitors using Na3Zr2Si2PO12-polymer hybrid films as electrolyte
(Elsevier, 2021-09) Dalvi, Anshuman
We report all-solid-state Na+ ion electrical double layer capacitors (EDLCs) for the first time in this study. These are fabricated using a novel Na+ ion solid polymer electrolyte (SPE) and high surface area (877 m2-g−1) activated carbon electrodes. Using salt (NaI), polyethylene oxide (PEO) and nano particles of Na3Zr2Si2PO12 (NZSP), hybrid electrolyte films with compositions 10NaI-90[PEO1-xNZSPx], where 0 ≤ x ≤ 0.7 are synthesized by a novel milling assisted route. The freestanding flexible film for x = 0.7 exhibits a maximum ionic conductivity of ~ 10−4 Ω−1 cm−1 at room temperature. The 2032 type EDLC with graphite current collector and polymer electrolyte film of composition x = 0.4 exhibits notably high value of specific capacitance (~ 104 F-g−1), and specific energy (~ 44 Wh-Kg−1) with a voltage stability window of ~ 2 volts. The NZSP content in the electrolyte influence the EDLC performance. The EDLCs with graphite sheet as current collector offer superior performance as compared to copper. Galvanostatic charge-discharge studies suggest stability of these supercapacitors at least upto ~ 400 cycles.
All-Solid-State Supercapacitors Based on Na+ Ion Composite Solid Polymer Electrolyte: Tailoring the Interface by Solvent Layer Approach
(SSRN, 2023-12) Dalvi, Anshuman
The present investigation proposes a novel approach to improve the performance of all solid-state supercapacitors (ASSCs). These ASSCs having a composite solid polymer electrolyte membrane (CSPE) and high surface area activated carbon (~ 1800 m2/g) electrodes exhibit improved performance when a novel strategy of ‘solvent layer approach’ at the electrode-electrolyte interface is used. Applying a nominal amount of acetonitrile (~3-5μl/cm2) at the interface leads to higher values of specific capacitance (~260F-g-1 at 2V, 1 mA), coulombic efficiency ~ 99 % and stability at least up to ~ 10000 cycles. It is demonstrated that a stack of five such cells can power an 8V LED circuit for more than 30 minutes. Results suggest that these supercapacitors are predominantly electric-double layer type in nature.
Characterization and electrochemical cell characteristics of mechanochemically synthesized AgI–Ag2O–MoO3 amorphous superionic system
(Elsevier, 2003-05) Dalvi, Anshuman
Mechanochemically synthesized amorphous and thermally stable xAgI(100−x)[0.5Ag2O+0.5MoO3] system for x=40, 50, 60 and 70 shows high ionic conductivity of ∼10−2–10−3 Ω−1 cm−1 at room temperature. The highest ionic conductivity is achieved for 36 h milled sample containing 50 m/o AgI, which is more than three orders of magnitude higher than that of crystalline AgI at room temperature and comparable with the glassy fast ionic conductor of the same composition prepared by conventional quenching. The samples are thermally stable at least up to ∼70 °C with ionic transport number near unity. These amorphous samples are further characterized by distinct glass transition as well as amorphous⇒crystalline transition temperatures. The FT-IR spectra confirm the presence of MoO42− and Mo2O72− groups in the ball-milled systems. Investigations on galvanic cells of the type Ag|a-SIC|I2+C reveal that these mechanochemically synthesized amorphous samples are stable under battery conditions and the cell performance parameters are comparable with those of earlier investigated Ag/I2 cells prepared using glassy SICs.
Climate justice is central to addressing the climate emergency’s psychological consequences in the Global South: a narrative review
(CUP, 2013-09) Dalvi, Anshuman
We present neutron diffraction results on superionic materials that are good candidates for use as solid-state electrolytes in next generation Li+ ion batteries. Lithium ion conducting glasses of the compositions xLi2SO4-(1-x) [0.5Li2O-0.5(2NH4H2PO2)] ; x=0 and 0.1 were synthesized by conventional melt-quenching. The transparent homogeneous glassy flakes were thus obtained and used for the characterization. The materials are glassy in nature and composed of a complex network of the following sub-units: Li2O, Li2SO4, and 2NH4H2PO2. This disordered structure is integral to its function in that it promotes Li+ ion conduction while suppressing electronic conduction, the necessary qualities of a good Li+ electrolyte. We used neutron diffraction to study the formation of crystallites upon heating of the material above 400°C. The crystallite formation is understood to be detrimental to the Li+ ion mobility and, hence, is identified with a diminished performance in devices that require heating in their fabrication processs. Here, we report the changes in the material, as observed by neutron diffraction, as a function of annealing temperature and temperature history.
Combined electrochemical and dft investigations of znco2o4–wo3@ti3c2tx mxene nanofiber nanocomposite as a cathode for a high-performance flexible asymmetric supercapacitor
(ACS, 2025-08) Ghosh, Sarbani; Dalvi, Anshuman
Interfacial engineering offers an enticing approach to improving the charge-transfer kinetics in supercapacitor electrodes. Herein, a nanocomposite composed of WO3 nanoplates decorated on the surface of ZnCo2O4 (ZCO) nanopetals with the combination of Ti3C2Tx MXene nanofibers (MXNFs) was successfully prepared. This nanocomposite (ZCO–WO3@MXNF) exhibited superior electrochemical performance over its components. Density functional theory (DFT) calculations revealed the improvement of structural stability, charge-transfer efficiency, and electron mobility in the nanocomposite because of the presence of hybridized states throughout the composite and hence the enhancement of its electrochemical properties. The ZCO–WO3@MXNF was used as the positive electrode and MXene-rGOsp as the negative electrode to design the asymmetric supercapacitor (ASC) device. Notably, the fabricated solid-state ASC device offered the energy density of 16 Wh kg–1 at a power density of 204 W kg–1, with the remarkable stability of 93% specific capacitance retention even after ∼5000 charging–discharging cycles. Further, the study of the ZCO–WO3@MXNF//MXene-rGOsp ASC device in a pouch cell assembly was conducted. The pouch cell showed excellent performance, with an energy density of 28 Wh kg–1 and a power density of 578 W kg–1. The fabricated device showed its practical feasibility by lighting up the light-emitting diode (LED) lights. These results suggested its excellent electrochemical activity and its candidacy as a promising electrode material for energy storage devices.
A comparative study of crystallization kinetics between conventionally melt quenched and mechanochemically synthesized AgI–Ag2O–CrO3 superionic system
(Elsevier, 2003-10) Dalvi, Anshuman
Non-isothermal crystallization kinetics in conventionally melt quenched versus mechanochemically synthesized amorphous AgI–Ag2O–CrO3 superionic solids is discussed. The quenched as well as ball-milled samples exhibit glass (Tg) and multiple amorphous⇒crystalline (Tc) transitions. Tg as well as Tc are found to increase monotonically with heating rate. The activation energy for structural relaxation (Es) 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 (Ec) is obtained using Matusita–Sakka equation and its higher value confirms the higher rate of crystallization in ball-milled samples. The values of Tc–Tg 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.
Conductivity and capacitance studies of silica glass composites containing [BMIM]Br and LiCl
(IOP, 2019) Dalvi, Anshuman; Sivasubramanian, S.C.
Ionic liquid (IL) 1-butyl-3methylimidaolium bromide ([BMIM]Br) confined Li+ ion containing silica glass composites have been prepared by hydrolytic sol-gel process. The IL dispersed amorphous systems exhibit improved ionic conductivity. It has been revealed that presence of IL in a low concentration (upto 1 mol %) facilitates Li+ ion motion. Conductivity does not show any appreciable change with increasing IL content in the matrix, particularly when salt content is fixed. However, when the IL content is fixed in the matrix and salt content is gradually increased, the conductivity exhibits a monotonic rise. A maximum ionic conductivity of 4.7 × 10−7 Ω−1 cm−1 with 30 mol % LiCl and only 1 mol% IL has been observed at 523 K. Incorporation of heavy metal ions (Pb2+) in the system further enhances the conductivity marginally. Optimized compositons exhibit high capacitance values of 14.1 Fg−1 at room temperature when sandwiched between high surface area (260 m2 g−1) activated carbon electrodes. These samples exhibit good potential as solid electrolytes in solid state supercapacitor applicatons.
Crystallization and glass transition kinetics in Cu+ ion substituted Cux–Ag1 − xI–Ag2O–V2O5 superionic glasses
(Elsevier, 2011-04) Dalvi, Anshuman
Crystallization kinetics and thermal properties in superionic glasses CuxAg1 − xI–Ag2O–V2O5 for x = 0.1–0.3 have been thoroughly investigated. X-ray diffraction and differential scanning calorimetry measurements confirm the precipitation of at least three compounds during crystallization, viz. AgI, Ag4V2O7 and Ag8I4V2O7. The activation energies for structural relaxation (Es) and crystallization (Ec) obtained using Moynihan and Kissinger formulation exhibit interesting trends with CuI substitution. The Es value decreases with CuI substitution in the system. Further, the Ec values corresponding to precipitation of Ag4V2O7 and Ag8I4V2O7 exhibit increasing trend, whereas, for that of AgI precipitation a decreasing trend with CuI content. The Avrami parameter calculated from Augis–Bennett method and Ozawa equation suggests predominantly surface crystallization in the glassy system. The electrical conductivity–temperature (σ–T) cycles interestingly demonstrate increasing precipitation of AgI with CuI content in the glass matrix.
Crystallization in Li2SO4–Li2O–P2O5 glassy ionic system: An assessment through electrical transport
(Elsevier, 2014-10) Dalvi, Anshuman
The electrical transport during the crystallization of ternary Li2SO4–Li2O–P2O5 glassy ionic system reveals interesting results. Electrical conductivity isotherms recorded at the crystallization temperature are found to be of immense importance, especially, in the understanding of phase transformation. The electrical conductivity falls rapidly during crystallization of LiPO3 compound and saturates at its completion. Such studies on conductivity isotherms further confirm the suppression of crystallization with addition of Li2SO4 in the glass matrix. A systematic variation of the Cole–Cole plots and conductivity spectra during crystallization further suggests a slow and predetermined process of glass–ceramic formation. The mechanism of electrical transport during crystallization is also explained using a crystallite bypass model. It is further revealed that the samples remain purely ionic during and after crystallization.
Crystallization studies on AgI–Ag2O–MoO3 superionic system synthesized by melt quenching and mechanical milling
(Elsevier, 2005-05) Dalvi, Anshuman
Crystallization in the melt-quenched (MQ) and mechanically milled (MM) superionic systems has been thoroughly investigated using differential scanning calorimetry, X-ray diffraction and electrical conductivity measurements. It is observed that the two systems obey different crystallization processes. The conventionally melt-quenched samples exhibit only one crystallization peak near 112 °C, whereas, the mechanochemically synthesized samples show two well-separated crystallization peaks at Tcl∼75–97 °C and Tc2∼132±2 °C. The higher value of electrical conductivity in the mechanochemically synthesized samples (∼10−2 Ω−1 cm−1 at 300 K) than the melt-quenched samples is attributed to the higher value of disorder (entropy) in the former.
Dispersion of Li2SO4-LiPO3 glass in LiTi2(PO4)3 matrix: Assessment of enhanced electrical transport
(Elsevier, 2019-04) Dalvi, Anshuman
A novel mechanical milling assisted synthesis route has been used to prepare new generation Li+ ion glass-ceramic composites using (i) glassy system 60[Li2SO4]-40[LiPO3] (60LSLP) and (ii) Li+ NASICON, i.e., LiTi2(PO4)3 known as LTP. Effect of compositional alterations, sintering conditions and cooling process on electrical transport has been investigated. Preparation conditions along with compositional alterations have yielded in reporting the best conducting composition. The ionic glass content was varied in (60LSLP)y-(LTP)100-y matrix for y = 5–20 wt %. It has been observed that various parameters viz. milling time, composition, annealing temperature, time and cooling conditions have a significant impact on ionic transport. The highest in-grain (∼2 × 10−4 Ω−1 cm−1) and grain boundary (∼1 × 10−5 Ω−1 cm−1) Li+ ion conductivity values at 100 °C have been obtained for y = 20 wt%. These have been found to be significantly higher than that of the pristine LTP prepared with similar preparation conditions. Electrical response (Z″-ω) and dielectric relaxation (tan δ - ω) investigations suggest that mobile Li+ ions from glassy phase significantly contribute to conductivity. The elemental distribution investigations using Energy Dispersive X-ray Spectroscopy (EDS) mapping on fractured surface suggests homogeneous distribution of LTP and glassy phase in the composite. Cyclic Voltammetry (CV) results reveal no degradation in the electrochemical stability in 20 cycles, and that these composites are potential candidates for Li+ ion all-solid-state battery applications.
Effect of conditional glass former variation on electrical transport in Li2O–P2O5 glassy and glass-ceramic ionic system
(Elsevier, 2014-10) Dalvi, Anshuman
Giving emphasis to electrical transport in the thermally unstable region, a conditional glass former based system 50Li2O–(50-x)P2O5–xMoO3 is investigated. Though glass forming region is narrow, the electrical conductivity exhibits significant rise up to x ≤ 15 mol%. Scanning electron microscopy investigations suggest existence of tiny crystallites well separated by glass tissues for higher MoO3 content samples. It is therefore revealed that addition of MoO3 improves the thermal stability. Electronic conductivity in this system is found to be fairly low and suggests phonon assisted polaron hopping. Electrical conductivity is found to be comparable to glass and glass-ceramic samples.
Effect of mixed glass formers on the crystallization kinetics in AgI–Ag2O–V2O5–MoO3 glassy superionic system
(Springer, 2011-01) Dalvi, Anshuman
The crystallization and glass transition kinetics using differential scanning calorimetry (DSC) in 50AgI–33.33Ag2O–16.67[(V2O5)1−x –(MoO3) x ] superionic glassy system is discussed. Thermal stability of glass, studied using various criteria, does not vary significantly with glass former variation. However, the activation energies for structural relaxation (E s) at glass transition temperature and crystallization (E c) obtained using Moynihan and Kissinger, Matusita-Sakka formulations found to exhibit interesting trends with MoO3 substitution in the glass matrix. It is noticed that the electrical conductivity (σ)–temperature (T) cycles obtained at a typical heating rate of 1 °C/min do exhibit significant thermal events. The conductivity after first heating cycle at room temperature is found to be increasing with MoO3 content and maximum for x = 0.3 (~10−3 Ω−1 cm−1 at 30 °C) which is comparable to that of the host 50AgI–33.33Ag2O–16.67V2O5 glassy system. The parameters obtained from σ–T plots and DSC scans do complement each other in a particular range of composition.
Electrical And Electrochemical Characterization Of ‐ Composite Polymer Electrolytes
(AIP, 2011-07) Dalvi, Anshuman
The flat, thin, and flexible ion conducting polymer films were prepared by solution casting technique from PEO complexed with 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 at for sample with 15 weight percent of in PEO matrix. 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 Characterization of PVA-MgSO4 and PVA-Li2SO4 Polymer Salt Composite Electrolytes
(Elsevier, 2019) Dalvi, Anshuman
Polymer composite films of two types have been prepared by dissolving (i) MgSO4 and (ii) Li2SO4 in polyvinyl alcohol (PVA) matrix. Electrical conductivity exhibits enhancement with salt addition. Preliminary studies suggest that salt ions contribute to electrical transport. In case of PVA:[MgSO4], upto 10 wt % of salt could be dissolved in the polymer matrix. Whereas, in case of PVA:[Li2SO4] free standing composite films can be formed at least with ∼ 20 wt % of salt. Composite films have been found to be partially crystalline in nature and may be useful for Li+/Mg+ ion battery applications
Electrical conductivity and thermal studies on [EMIM]BF4, Li+ and Cu2+ confined silica gel composites
(AIP, 2020-11) Dalvi, Anshuman; Sivasubramanian, S.C.
Ionic liquid ([EMIM]BF4), Li+ and Cu2+ confined silica gel of composition 33.3LiNO3-xCuCl2-1IL-(65.7- x)SiO2 have been prepared via sol gel route. Structural, thermal and electrical conductivity investigations have been carried out on these composites which reveal interesting results. X-ray diffraction patterns of the samples confirm their amorphous nature. TGA shows continuous water elimination from the as prepared composite. EPR spectrum shows existence of Cu2+ ions in the solid matrix at room temperature. Electrical conductivity of the composites increases with increase in the amount of CuCl2 in the composite as well as due to the increase in temperature. As these composites exhibit good ion conducting properties, they seem to have good potential as solid electrolytes in Li+ ion battery applications.
Electrical transport and crystallization in Cu+ ion substituted AgI–Ag2O–V2O5 glassy superionic system
(Elsevier, 2010-01) Dalvi, Anshuman
A new glassy solid electrolyte system CuxAg1 − xI–Ag2O–V2O5 has been synthesized. The structural, thermal and electrical properties of the samples have been investigated. The glassy nature of the samples is confirmed by X-Ray diffraction and Differential Scanning Calorimetry studies. The electrical conductivity of these samples increases with CuI content and approaches a maximum value of ∼ 10−2 Ω− 1 cm− 1 for x = 0.35 at room temperature. Ionic mobility measurements suggest that enhancement in the conductivity with Cu+ ion substitution may be attributed to increase in the mobility of Ag+ ions. The electrical conductivity versus temperature cycles carried out at well-controlled heating rate above Tg and Tc reveal interesting thermal properties. For lower CuI content samples conductivity exhibits anomalous rise above Tg and subsequent fall at Tc. It is also found that CuI addition into AgI–Ag2O–V2O5 matrix reduces the extent of crystallization.