Mani Ulaganathan

Research progress in Na-ion capacitors

Research activities on the development of organic Na-ion hybrid electrochemical capacitors (NICs) are described in this review. In particular, more emphasis is given on the development of battery type electrodes (faradaic mechanism), for example, hard carbons, Na2Ti3O7, etc. Also, equal importance is given for the exploration of non-faradaic type counter electrodes derived from bio-mass and polymer precursors. In the recent past, Mxenes have attracted attention as promising candidates for cathodes and anodes for electrochemical energy storage devices. Accordingly, efficient utilization of such Mxenes as positive and negative electrodes in an NIC assembly is given along with their synthetic procedure. Furthermore, the symmetric configuration of other Na-ion based organic supercapacitor is also given in detail.

High energy Li-ion capacitors with conversion type Mn3O4 particulates anchored to few layer graphene as the negative electrode

We report the fabrication of high energy Li-ion capacitors (LICs) using conversion type Mn3O4 octahedrons anchored to few layer graphene (Mn3O4-G) as the negative electrode with activated carbon (AC) as the positive one. First, the Mn3O4-G composite is prepared via a hydrothermal approach using commercially available graphene nanosheets. Li-storage studies of both electrodes (AC and Mn3O4-G) are conducted in single electrode/half-cell configuration with metallic Li to assess the mass balance. Prior to the fabrication of LICs, Mn3O4-G is pre-lithiated in Swagelok fittings with Li and subsequently paired with the desired loading of AC. The AC/Mn3O4-G based LIC delivered a maximum energy density of ∼142 W h kg−1 with excellent cyclability of 9000 cycles with ∼80% retention. This result certainly provides new avenues for the development of high energy LICs using conversion type negative electrodes rather than traditional insertion type anodes.

Role of Different Plasticizers in Li-Ion Conducting Poly(Acrylonitrile)-Poly(Methyl Methacrylate) Hybrid Polymer Electrolyte

In this work, polymer electrolytes composed of PAN/PMMA/LiClO4 with different plasticizers are prepared using solvent casting technique. Ionic conductivity of the electrolytes is evaluated with the help of ac impedance study at various temperatures. Structural and the complexation of the prepared electrolytes are studied by XRD and FTIR analysis, respectively. Thermogravimetric/differential thermal analysis (TG/DTA) is used to find the thermal stability of the polymer electrolytes. PAN/PMMA/EC/LiClO4-based plasticized polymer electrolyte is found to possess optimal properties in terms of conductivity and thermal stability. Porous nature of the polymer gel electrolytes is also confirmed by SEM analysis.

β‐Co(OH)2 Nanosheets: A Superior Pseudocapacitive Electrode for High‐Energy Supercapacitors

In this work, β-Co(OH)2 nanosheets are explored as efficient pseudocapacitive materials for the fabrication of 1.6 V class high-energy supercapacitors in asymmetric fashion. The as-synthesized β-Co(OH)2 nanosheets displayed an excellent electrochemical performance owing to their unique structure, morphology, and reversible reaction kinetics (fast faradic reaction) in both the three-electrode and asymmetric configuration (with activated carbon, AC). For example, in the three-electrode set-up, β-Co(OH)2 exhibits a high specific capacitance of ∼675 F g-1 at a scan rate of 1 mV s-1 . In the asymmetric supercapacitor, the β-Co(OH)2 ∥AC cell delivers a maximum energy density of 37.3 Wh kg-1 at a power density of 800 W kg-1 . Even at harsh conditions (8 kW kg-1 ), an energy density of 15.64 Wh kg-1 is registered for the β-Co(OH)2 ∥AC assembly. Such an impressive performance of β-Co(OH)2 nanosheets in the asymmetric configuration reveals the emergence of pseudocapacitive electrodes towards the fabrication of high-energy electrochemical charge storage systems.

A chemically bonded NaTi2(PO4)3/rGO microsphere composite as a high-rate insertion anode for sodium-ion capacitors

We report on the synthesis of a high rate NaTi2(PO4)3/graphene composite for use as an anode material for high power Na-ion hybrid capacitors with the following characteristics; (1) reduction of the particle size of NaTi2(PO4)3 to the nanometer scale in order to reduce the Na+ ion diffusion length, (2) chemical bonding between NaTi2(PO4)3 nanoparticles and graphene in order to improve electrical conductivity, and (3) interconnected nanoporous structures in order to allow easy access of Na+ ions to NaTi2(PO4)3. For this, the NaTi2(PO4)3/rGO microsphere composite was prepared via a facile spray drying method using a solution mixture of graphene oxide, NaH2PO4·2H2O, Ti(OC2H5)4 and NH4H2(PO4)3, in which all the components of the titanium were present as ionic species in order to facilitate the chemical bonding between NaTi2(PO4)3 and rGO in the composite. The NaTi2(PO4)3/rGO microsphere composite had a Ti–O–C bond between NaTi2(PO4)3 nanoparticles (<80 nm) and rGO and interconnected nanoporous structures. The NaTi2(PO4)3/rGO microsphere composite exhibited a near theoretical specific capacity of 133 mA h g−1 at a 0.1 C-rate and excellent rate capability (70% capacity retention at a 50 C-rate) with very stable cycling performance (only 2% capacity loss after 200 cycles at a high rate of 10C). Furthermore, the energy density and power density of the NHC assembled with a NaTi2(PO4)3/rGO anode and an AC-based cathode are far better than those of other NHCs assembled using other metal oxide-based anodes and AC cathodes.

FT-IR and DSC studies of poly(vinylidene chloride-co-acrylonitrile) complexed with LiBF4.

Poly(vinylidene chloride-co-acrylonitrile) (PVdC-co-AN) based solvent free electrolytes were prepared for different compositions of PVdC-co-AN and LiBF4 using solution casting technique. The ionic conductivity, thermal behavior, complexation and structure of polymer electrolytes have been investigated as a function of LiBF4 content at different weight ratios. DSC studies revealed that the glass transition temperature Tg decreases with the increase of salt concentration up to an optimum level. The change in the glass transition temperature (Tg) with respect to the LiBF4 concentration is reflected in the bulk resistance of the electrolytes and the sample containing 6 wt.% of LiBF4 exhibited minimum bulk resistance compared to other samples. FT-IR studies confirm the interaction of polymer and salt which is mainly between Li-cation and nitrogen atom of C≡N group. The crystalline phase of polymer host is completely changed on the addition of Li salt.

Fabrication and electrochemical characterization of Pt–Pd impregnated nanocomposite polymer electrolyte membranes for high concentration DMFCs

Bimetallic Pt–Pd impregnated nanocomposite polymer electrolyte membranes were prepared and the influence of Pd on Pt was evaluated towards a single cell performance. The fabricated membranes were characterised by X-ray Diffraction (XRD) and Field-Emission Scanning Electron Microscopy (FESEM) accompanied with Energy Dispersive X-ray (EDX) spectroscopy for identifying the structural and morphological characteristics, respectively. It was observed that the particle size of the bimetallic particle increased with the increase in Pd content; the bimetallic particles were uniformly deposited in a closely packed structure on the membrane surface. The performance of direct methanol fuel cells (DMFC) with normal membrane electrode assembly (MEA) and Pt–Pd impregnated nanocomposite with various compositions were studied for different methanol concentrations. Pt–Pd nanocomposite MEA with 76.91:23.09 of atomic ratio exhibited an optimal performance with the maximum power density of 52.5 mW cm−2. The result was benchmarked with MEA using commercially available Pt/C catalyst.

Electrochemical analysis on poly(ethyl methacrylate)-based electrolyte membranes

Polymer blend composed of poly(vinyl chloride) and poly(ethyl methacrylate) with lithium perchlorate (LiClO4) and the plasticizer ethylene carbonate (EC) mixture with propylene carbonate, γ-butyrolactone (GBL), dibutyl phthalate and diethyl carbonate have been synthesized using the solution casting technique. Structural changes and thermal stability of the films were resolved using X-ray diffraction analysis and thermogravimetric/differential thermal analysis, respectively. The membrane that contains EC+ GBL exhibits maximum ionic conductivity of the order of 1.208×10−3 S cm−1 at 303 K. The temperature-dependent ionic conductivity of the polymer membranes has been estimated using AC impedance analysis.

Palladium- and gold-nanoparticle-modified porous carbon as a high-power anode for lithium-ion batteries.

Electrode materials: Ultrahigh-power insertion-type anodes are developed by simply decorating Pd nanoparticles on commercially available porous carbon.

S-Doped TiSe2 Nanoplates/Fe3O4 Nanoparticles Heterostructure

2D Sulfur-doped TiSe2 /Fe3 O4 (named as S-TiSe2 /Fe3 O4 ) heterostructures are synthesized successfully based on a facile oil phase process. The Fe3 O4 nanoparticles, with an average size of 8 nm, grow uniformly on the surface of S-doped TiSe2 (named as S-TiSe2 ) nanoplates (300 nm in diameter and 15 nm in thickness). These heterostructures combine the advantages of both S-TiSe2 with good electrical conductivity and Fe3 O4 with high theoretical Li storage capacity. As demonstrated potential applications for energy storage, the S-TiSe2 /Fe3 O4 heterostructures possess high reversible capacities (707.4 mAh g-1 at 0.1 A g-1 during the 100th cycle), excellent cycling stability (432.3 mAh g-1 after 200 cycles at 5 A g-1 ), and good rate capability (e.g., 301.7 mAh g-1 at 20 A g-1 ) in lithium-ion batteries. As for sodium-ion batteries, the S-TiSe2 /Fe3 O4 heterostructures also maintain reversible capacities of 402.3 mAh g-1 at 0.1 A g-1 after 100 cycles, and a high rate capacity of 203.3 mAh g-1 at 4 A g-1 .