Department of Physics
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Item Fabrication and reliability testing of a MEMS piezoelectric acoustic sensor for applications in harsh environments(IOP, 2025-04) Dalvi, AnshumanThe reliability of microelectromechanical system (MEMS) based piezoelectric acoustic sensors is important for a wide range of applications for environmental monitoring, medical diagnostics, and aerospace perspectives. These sensors must have long-term durability and stable performance under a variety of environmental conditions. This article includes a comprehensive framework for assessing the reliability of MEMS piezoelectric acoustic sensors with a focus on mechanical, electrical and thermal stability. The device comprises a zinc oxide layer (ZnO) between two metal electrodes, with a thin silicon dioxide film and micropaths worn on a glass substrate. The sensitivity and resonance frequency for this device were obtained at 203 μV/Pa and 78.9 kHz, respectively. The most critical factors evaluated include layer adhesion, substrate bonding strength of 8.9 MPa, a current bearing capacity of 91 mA, and thermal handling ability up to 600 °C. All of these aspects are important for determining the robustness and consistency of the sensor in performance.Item Role of sulfonamide-based covalent organic frameworks (COFs) in enhancing the electrochemical performance of PEO-based composite polymer electrolytes(ACS, 2025-06) Dalvi, Anshuman; Sarkar, MadhushreeTwo sulfonamide-based covalent organic frameworks (COFs), COP1 and COP2, were successfully incorporated in a poly(ethylene oxide) (PEO)–LiClO4 matrix to generate composite polymer electrolytes (CPEs). The sulfonamide COF, COP1, served as a multipurpose additive for the PEO–LiClO4 matrix by enhancing its ionic conductivity (up to 4.1 × 10–3 S/cm at room temperature and 8.7 × 10–3 S/cm at 50 °C for PEO–5% COP1–LiClO4) with an ionic transport number of 0.998, stable electrochemical window (oxidation resistance up to 1.39 V against stainless steel (SS) electrodes), and thermal and mechanical stability. The presence of strong sulfonamide groups, −SO2NH–, in the COFs enabled the dissociation of lithium ions (Li+ ions) from the lithium salt and also the assembly of the PEO for facile ionic conduction. The COF, COP2, did not result in much improvement in the conductivity of the CPEs, which may be associated with its molecular geometry. The differential scanning calorimetry (DSC) measurements confirmed the absence of any molten state of the electrolyte during the conductivity and electrochemical performance of CPEs. The performance of the supercapacitor cell synthesized using PEO–5% COP1–LiClO4 showed a specific capacitance of ∼186 F g–1 at a current density of ∼0.67 A g–1 and 3 V operating voltage. Further, the supercapacitor cell (PEO–5% COP1–LiClO4) showed a Coulombic efficiency of almost 99% at 1 V. Overall, this study highlights the promising role of sulfonamide COFs as effective additives for polymer-based solid electrolytes and their potential for developing safer and more efficient lithium-metal batteries (LMBs) in the future.Item Solid-state supercapacitors with enhanced performance using AI3+-doped Li+ ion perovskite electrolyte integrated with carbon aerogel electrode(ACS, 2025-08) Dalvi, AnshumanWe report the performance of solid-state ceramic supercapacitors (SSCs) based on a novel composite electrolyte comprising aluminum-doped lithium lanthanum titanate perovskite, Li0.36La0.56Ti0.995Al0.005O3 (Al3+-doped LLTO), and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4). Rietveld refinement of X-ray diffraction data confirms the preservation of the tetragonal perovskite phase after Al3+ substitution, indicating structural stability of the host lattice. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy further corroborate the successful incorporation of Al3+ without forming secondary phases. The addition of ∼6 wt % EMIM BF4 into Al-LLTO matrix significantly enhances the room-temperature ionic conductivity to ∼10–3 Ω–1 cm–1, nearly 3 orders of magnitude greater than that of pristine LLTO, resulting into improved long-range electrical transport. Further, novel SSCs have been fabricated by sandwiching the composite electrolyte between high surface area freeze-dried carbon aerogel (FD-CA) coated copper electrodes and assembled using a low-cost hot-roll lamination approach. The devices at 35 °C exhibited a high specific capacitance of ∼370 F g–1 at 1 mA/2 V, excellent cycling stability with ∼87% capacitance retention over 15,000 cycles at 2 V and 2 mA (1 A g–1), and stable Coulombic efficiency of ∼99%. These symmetric SSCs demonstrate ideal electric double-layer capacitive behavior for operating potential ≤ 2 V. These results highlight the potential of Al3-doped LLTO/EMIM BF4 composite electrolytes in combination with FD-CA-based electrodes for the development of safe, efficient, stable and scalable solid-state supercapacitors.Item 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, AnshumanInterfacial 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.Item Temperature-tolerant solid-state supercapacitors using Li+-garnet-ionic liquid composite electrolyte(Springer, 2025-10) Sivasubramanian, S.C.; Dalvi, AnshumanThis investigation uses garnet-structured Li+ conductors added with a nominal amount of ionic liquid (IL) as an electrolyte to develop solid-state supercapacitors (SSCs) that operate across a wide temperature range from 0 to 100 ℃. A composite of LALZO (Li6.75Al0.25La3Zr2O12) with ~ 6 wt% of IL-EMIM BF4, having high conductivity ≥ 10−4 Ω−1 cm−1, is used as an electrolyte by compressing it between high surface area activated carbon (~ 1500 m2-g−1) electrodes and assembled in 2032 type cell geometry. A typical SSC at 35 °C exhibits a specific capacitance value of ~ 562 F-g−1 at 2 V/1 mA (0.57 A-g−1). Such SSCs exhibit stable performance at least up to ~ 4000 galvanostatic charge-discharge (GCD) cycles with a maintained coulombic efficiency of ~ 99%. These SSCs are found to be essentially electric double-layer type for operating voltages of ≤ 1.5 V. However, for 1.5 < V ≤ 2.5 V, pseudo-capacitive effects become significant in charge storage. A stack of four SSCs can effectively power two white LEDs (6 V) in series for about 30 min during direct discharge. The SSCs demonstrate stable GCD and CV cycles at 0 °C and 100 °C, with high performance parameters. The findings indicate that the LALZO-ionic liquid composites can be effectively utilized in high-performance, thermally stable supercapacitors.Item High-performance, high energy density symmetric supercapacitors based on δ-MnO2 nanoflower electrodes incorporated with an ion-conducting polymer(RSC, 2024-11) Dalvi, AnshumanThe present work investigates liquid-based and liquid-free supercapacitors assembled using δ-MnO2-nanoflower-based electrodes. An optimized electrode composition was prepared using acetylene black (AB), a polymer (PEO), a salt (LiClO4), and δ-MnO2 and used for device fabrication. The composite electrode was tested against a liquid electrolyte and a ‘liquid-free’ composite solid polymer electrolyte (CSPE) membrane. In a three electrode geometry, with 1 M solution of LiClO4 as an electrolyte, the specific capacitance of the electrode was found to be ∼385 F g−1, with a specific energy of ∼23 W h kg−1 and specific power of ∼341 W kg−1 (at 1 mA, 1 V). Dunn's method confirmed that the charge storage process was predominantly pseudocapacitive. When the device was assembled in a two-electrode Swagelok cell, a stable specific capacitance of ∼216 F g−1 was observed with a specific energy of 30 W h kg−1 and a specific power of 417 W kg−1. The supercapacitors exhibited stable performance up to ∼7000 cycles with ∼90% capacitance retention and ∼97% coulombic efficiency. A combination of these cells could light two white light-emitting diodes (LEDs, 3 V) for at least ∼10 minutes. Further, all-solid-state supercapacitors (ASSCs) were fabricated using a Li+ ion (CSPE) membrane. The ASSCs exhibited a specific capacitance of ∼496 F g−1 after ∼500 cycles, with a specific energy and power of ∼19 W h kg−1 and ∼367 W kg−1, respectively. The investigation reveals that the electrodes are versatile and show compatibility with liquid and solid electrolytes. The polymer in the electrode matrix plays an important role in enhancing device performance.Item High energy density solid state symmetric supercapacitors using ionic liquid dispersed Li+ ion-perovskites(RSC, 2025-01) Dalvi, AnshumanThe study reports solid-state ceramic supercapacitors (SSCs) assembled using a novel composite electrolyte based on Li+ ion conducting perovskite-type LLTO (Li0.34La0.51TiO3) and an ionic liquid (EMIM BF4). Small amounts of various ionic liquids (ILs) were added to LLTO to enhance the ionic conductivity and improve electrode compatibility. The optimal composition with approximately ∼6 wt% EMIM BF4 in LLTO exhibited a high ionic conductivity of around ∼10−3 Ω−1 cm−1 at room temperature, nearly three orders of magnitude higher than that of the pristine LLTO. Optimized electrolyte composition was therefore used for fabrication by compressing between high surface area activated carbon-coated copper electrodes and assembled in an affordable lamination cell geometry. The SSCs demonstrated stable cycling performance for at least 10[thin space (1/6-em)]000 cycles at 2 V operating voltage and 1.13 A g−1 (2 mA) discharge current, with a remarkably high coulombic efficiency of ∼99%. A typical laminated cell at 35 °C exhibited a specific capacitance of around 510 F g−1 at 0.57 A g−1 (1 mA), and 2 V. Supercapacitors operating below 2 V showed a pure electric double-layer type nature. A stack of 4 cells in series can power two white LEDs (6 V) for ∼40 minutes.Item Achieving high-performance parameters in NASICON-polymer composite electrolyte-based solid-state supercapacitors by interface modification(RSC, 2025-02) Dalvi, AnshumanThe 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.Item High-performance flexible solid-state asymmetric supercapacitor with NiCo2S4 as a cathode and a MXene-reduced graphene oxide sponge as an anode(RSC, 2024) Dalvi, AnshumanTi3C2 MXenes have revealed immense potential in energy storage systems. Herein, we report the development of a flexible solid-state asymmetric supercapacitor (ASC) device by assembling spherical NiCo2S4 as a cathode, a MXene-reduced graphene oxide sponge (rGOsp) nanocomposite as an anode, and polyvinyl alcohol (PVA) hydrogel comprising a mixture of 3 M KOH and 0.1 M K4[Fe(CN)6] as an electrolyte cum separating membrane. This device (NiCo2S4//MXene-rGOsp) provides a specific capacitance (CS) of 98 F g−1 (at 4.5 A g−1), coulombic efficiency of ∼99% at 15 A g−1, and CS of ∼95% after 4000 cycles. Moreover, it provides an energy density of 35.75 W h kg−1 at a power density of 3693 W kg−1. This device establishes its mechanical flexibility by exhibiting almost similar performances at various deformed structures. The performance of this flexible NiCo2S4//MXene-rGOsp ASC device is superior to many reported MXene-based supercapacitors. This device is also capable of illuminating a series of LED lights. In conclusion, the results clearly prove the potential of this device in high-performance energy storage applications.Item Ionic liquid composites with garnet-type Li6. 75Al0. 25La3Zr2O12: Stability, electrical transport, and potential for energy storage applications(Elsevier, 2024-04) Dalvi, Anshuman; Sivasubramanian, S.C.Garnet composites with ionic liquid dispersion have been prepared for electrolytic applications. Various ionic liquids (ILs) in small amounts were added to garnet type Li6.75Al0.25La3Zr2O12 (LALZO) to improve its ionic conductivity and electrode-electrolyte interfacial compatibility. The optimal composition having ∼6 wt% EMIM BF4 in LALZO showed a high ionic conductivity of 6 × 10-4 Ω-1cm-1 at room temperature, which is almost two orders of magnitude higher than the pristine garnet pellet. Such a high conductivity is attributed to the alteration of the ionic liquid-garnet interface by a weak non-uniform chemisorption. The thermal stability of the composites was confirmed by high-temperature X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamic electrical transport measurements, which suggested their stability at least up to 200 °C. The electrochemical performance of the composite was evaluated by assembling 2032-type LFP//LALZO-IL//Li cell, which displayed promising candidature for energy storage applications.