25 results on '"Palani Balaya"'
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2. A fire-retarding electrolyte using triethyl phosphate as a solvent for sodium-ion batteries
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Kang Du, Chen Wang, Palani Balaya, Satyanarayana Reddy Gajjela, and Markas Law
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Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Here, we introduce a fire-retarding electrolyte for sodium-ion batteries using fire-retardant triethyl phosphate (TEP) as a solvent. 3% vinylene carbonate (VC) is added to enhance its stability.
- Published
- 2021
3. Developing an O3 type layered oxide cathode and its application in 18650 commercial type Na-ion batteries
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Palani Balaya, Shibo Xi, Satyanarayana Reddy Gajjela, Ashish Rudola, and Abhinav Tripathi
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Materials science ,Extended X-ray absorption fine structure ,Renewable Energy, Sustainability and the Environment ,Analytical chemistry ,02 engineering and technology ,General Chemistry ,Electrolyte ,021001 nanoscience & nanotechnology ,Cathode ,Energy storage ,law.invention ,Anode ,X-ray photoelectron spectroscopy ,Transition metal ,law ,Specific energy ,General Materials Science ,0210 nano-technology - Abstract
A novel, water-stable and high energy density cathode material Na0.9Cu0.12Ni0.10Fe0.30Mn0.43Ti0.05O2 (NCNFMT) is reported here along with a thorough understanding of structural events during battery operation. Systematic substitutions are carried out, which lead to increase in specific energy densities of this family of cathodes from 274.6 W h kgcathode−1 (NCFM – Na0.9Cu0.22Fe0.30Mn0.48O2) to 304.2 W h kgcathode−1 (NCFMT – Na0.9Cu0.22Fe0.30Mn0.43Ti0.05O2) and finally to 350.7 W h kgcathode−1 (NCNFMT – Na0.9Cu0.12Ni0.10Fe0.30Mn0.43Ti0.05O2). Operando X-ray diffraction reveals phase transformations and ex situ EXAFS shows the evolution of local environments around transition metals during charge/discharge. Monoclinic distortions in the NCFM material during O3–P3 phase transformations are suppressed by Ti4+ substitution leading to improvements in the cycling performance of NCFMT. Cu–O octahedral sites exhibit huge Jahn–Teller distortion: Ni2+ substitution in place of Cu2+ not only leads to more ordered Ni–O, but it also helps extract more Na ions from the O3 cathode structure, thus boosting the capacity while also showing good cycling stability due to the highly reversible bond-length and local environmental changes as revealed by EXAFS analyses. X-ray photoelectron spectroscopy shows a titanium-rich surface for NCFMT and NCNFMT which helps improve water-stability. The capacity retention after 200 cycles at 0.2C is 84%, 96% and 90% for NCFM, NCFMT and NCNFMT respectively. The delivered storage capacities of NCFM, NCFMT and NCNFMT are 21 mA h g−1, 47 mA h g−1 and 60 mA h g−1 respectively at 3C. 18650 type Na-ion batteries using the NCNFMT cathode material against a hard carbon anode are also reported to demonstrate potential scalability of the NCNFMT cathode and efficacy of a 1 M NaBF4 tetraglyme electrolyte system for the first time. 18650 cells deliver a specific energy density of 62 W h kgtotal_18650_weight−1 with 90% energy efficiency, thus being suitable for large scale energy storage applications.
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- 2019
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4. Synthesis, characterisation and enhanced electrochemical performance of nanostructured Na2FePO4F for sodium batteries
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Markas Law, Vishwanathan Ramar, and Palani Balaya
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Materials science ,Rietveld refinement ,General Chemical Engineering ,Sodium ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Electrochemistry ,chemistry ,Chemical engineering ,Particle size ,Ball mill ,Faraday efficiency ,BET theory ,Template method pattern - Abstract
Nanostructured pure Na2FePO4F was synthesised by a soft template method, followed by high-energy ball milling (HEBM) process and post-heat treatment. Physical and electrochemical properties of this sample were compared with as-prepared (pristine) sample. FESEM images recorded on the ball milled samples showed that the particles were of spherical morphology, with particle size centred around 100 nm. BET analysis illustrated a correlation between the surface area of the material with the electrochemical performance. Rietveld refinement of XRD patterns of the pristine and the HEBM samples together with the obtained reliability factor values demonstrated lower percentage of antisite disorder in HEBM sample. Compared to the pristine sample, which delivered an initial discharge capacity of only 87 mA h g−1, the HEBM sample showed an impressive storage capacity of 116 mA h g−1 at 0.1 C. Furthermore, at 1 C after 200 cycles, the ball milled sample displayed stable cyclability, retaining almost 80% of its initial discharge capacity, with an average coulombic efficiency of 99.4%. The improved sodium storage performance as compared to the pristine sample is discussed in terms of the reduced antisite disorder and associated sodium ion diffusion.
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- 2015
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5. Hollow Nanospheres and Flowers of CuS from Self-Assembled Cu(II) Coordination Polymer and Hydrogen-Bonded Complexes of N-(2-Hydroxybenzyl)-<scp>l</scp>-serine
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Wei Lee Leong, Mangayarkarasi Nagarathinam, Kuppan Saravanan, Jagadese J. Vittal, and Palani Balaya
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Hydrogen ,Stereochemistry ,Hydrogen bond ,Coordination polymer ,chemistry.chemical_element ,General Chemistry ,Crystal structure ,Condensed Matter Physics ,Copper ,Copper sulfide ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Molecule ,General Materials Science ,Self-assembly - Abstract
Utilization of a novel two-dimensional coordination polymer generated from a trinuclear building block [Cu3(HSser)3(H2O)2]·2H2O (1) as a precursor in the synthesis of copper sulfide serendipitously...
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- 2009
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6. Storage performance of LiFePO4nanoplates
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B. V. R. Chowdari, Kuppan Saravanan, Hao Gong, Jagadese J. Vittal, M. V. Reddy, and Palani Balaya
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Materials science ,Solvothermal synthesis ,Nanoparticle ,Nanotechnology ,General Chemistry ,engineering.material ,Lithium battery ,Amorphous carbon ,Coating ,Chemical engineering ,Materials Chemistry ,engineering ,Thin film ,High-resolution transmission electron microscopy ,Mesoporous material - Abstract
The morphology of electrode materials is addressed as a key factor controlling rapid lithium storage in anisotropic systems such as LiFePO4. In view of this, we have synthesized nanoplates of LiFePO4 with a uniform coating of a 5 nm thick amorphous carbon layer by the solvothermal method and investigated their electrochemical storage behavior. The obtained nanoplates are well characterized by XRPD, SEM, HRTEM and XPS techniques. The thickness along the b-axis is found to be 30–40 nm; such a morphology favors short diffusion lengths for Li+ ions, while the external conductive carbon coating provides connectivity for facile electron diffusion, resulting in high rate performances. Increase in the size of the nanoplates results in poor lithium storage performance. The storage performance of nanoplates is compared with that of mesoporous nanoparticles of LiFePO4 with non-uniform carbon coating. This paper thus describes the advantages of thinner nanoplates for high rate storage performances of battery electrode materials.
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- 2009
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7. Ionic and electronic transport in single crystalline LiFePO4 grown by optical floating zone technique
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Chengtian Lin, Ruhul Amin, Palani Balaya, Joachim Maier, and Dapeng Chen
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Crystal ,Materials science ,Rietveld refinement ,Analytical chemistry ,Ionic conductivity ,Ionic bonding ,General Materials Science ,General Chemistry ,Conductivity ,Condensed Matter Physics ,Thermal diffusivity ,Single crystal ,Ion - Abstract
The present work is devoted to a systematic investigation of ionic and electronic conductivity as well as chemical Li-diffusivity in single crystalline LiFePO 4 as a function of crystallographic orientation over an extended temperature range. Besides chemical analysis of the elemental ratio of the crystal, we also determined the Fe occupancy on the lithium lattice positions by single crystal X-ray diffraction and synchrotron X-ray radiation followed by Rietveld refinement. AC impedance as well as improved DC polarization/depolarization measurements have been carried out using electronically as well as ionically blocking cells. The activation energies obtained for electronic and ionic conductivities are in the range of 0.55–0.59 eV and of 0.62–0.74 eV, respectively, depending on the orientations. The ionic conductivity is much smaller than the electronic conductivity along all three axes and the electronic conductivity, ionic conductivity and chemical diffusivity of Li ion are found to be effectively two-dimensional (i.e., isotropic in the b–c plane).
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- 2008
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8. Enhanced interfacial lithium storage in nanocomposites of transition metals with LiF and Li2O: Comparison of DFT calculations and experimental studies
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Eugene A. Kotomin, Yu F. Zhukovskii, Palani Balaya, and Joachim Maier
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Nanocomposite ,Diffusion barrier ,Inorganic chemistry ,Lithium fluoride ,General Chemistry ,Condensed Matter Physics ,Electronegativity ,chemistry.chemical_compound ,chemistry ,Transition metal ,Ab initio quantum chemistry methods ,Atom ,Physical chemistry ,General Materials Science ,Lithium oxide - Abstract
Me/LiX nanocomposites (Me – transition metal and X = F or O) exhibit extra lithium storage, with pseudo-capacitive behavior and high-rate performance. While LiX surface layers or the interfacial core serves as hosts for extra Li, atoms of contacting transition metal serve as electron sinks, depending on Me electronegativity. To verify the mechanism, we have performed comparative DFT-LCAO calculations on the polar Ti|Li|Li2O(111) and non-polar Cu|Li|LiF(001) interfaces with extra Li atoms inserted inside both 2D interfaces, gradually changing their concentration. Theoretical calculations confirm validity of this interfacial model for explanation of the extra storage capacity at low potentials. The diffusion barrier for extra Li atom along the Me/LiX interface is markedly smaller than the Li penetration barrier into the bulk.
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- 2008
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9. Electrochemical lithiation synthesis of nanoporous materials with superior catalytic and capacitive activity
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Yong-Sheng Hu, Sarmimala Hore, Yu-Guo Guo, Palani Balaya, Joachim Maier, and Wilfried Sigle
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Supercapacitor ,Materials science ,Nanoporous ,Mechanical Engineering ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Carbon nanotube ,Condensed Matter Physics ,Electrocatalyst ,Molecular sieve ,law.invention ,Catalysis ,chemistry ,Transition metal ,Mechanics of Materials ,law ,General Materials Science ,Lithium - Abstract
Nanoporous materials have attracted great technological interest during the past two decades, essentially due to their wide range of applications: they are used as catalysts, molecular sieves, separators and gas sensors as well as for electronic and electrochemical devices. Most syntheses of nanoporous materials reported so far have focused on template-assisted bottom-up processes, including soft templating (chelating agents, surfactants, block copolymers and so on) and hard templating (porous alumina, carbon nanotubes and nanoporous materials) methods. Here, we exploit a mechanism implicitly occurring in lithium batteries at deep discharge to develop it into a room-temperature template-free method of wide applicability in the synthesis of not only transition metals but also metal oxides with large surface area and pronounced nanoporosity associated with unprecedented properties. The power of this top-down method is demonstrated by the synthesis of nanoporous Pt and RuO2, both exhibiting superior performance: the Pt prepared shows outstanding properties when used as an electrocatalyst for methanol oxidation, and the RuO2, when used as a supercapacitor electrode material, exhibits a distinctly better performance than that previously reported for non-hydrated RuO2 (refs 19,20).
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- 2006
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10. Grain size effect on the universality of AC conductivity in SnO2
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S. Ramasamy, Palani Balaya, P. Thangadurai, and A. Chandra Bose
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Materials science ,Mineralogy ,General Chemistry ,Condensed Matter Physics ,Tin oxide ,Power law ,Nanocrystalline material ,Grain size ,Dielectric spectroscopy ,Nanocrystal ,Electrical resistivity and conductivity ,Transmission electron microscopy ,General Materials Science ,Composite material - Abstract
Nanocrystalline tin oxide (SnO2) material with different grain sizes was synthesized by using a chemical precipitation method. This material was characterized by using the X-ray diffraction and transmission electron microscopy. The electrical properties of compressed nanocrystalline SnO2 were studied by using impedance spectroscopy. AC conductivity data for SnO2 material having grain sizes between 9 and 34 nm were analyzed using a power law. The exponent n is found to be 0.5 for bulk (34 nm) and unity for material with grain size below 18 nm. The results show a universal behavior for very low average grain sizes and the non-universal behavior for larger grain sizes even at room temperature.
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- 2003
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11. Na2Ti6O13: a potential anode for grid-storage sodium-ion batteries
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Hao Gong, S. Devaraj, Kuppan Saravanan, Palani Balaya, and Ashish Rudola
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Battery (electricity) ,Long cycle ,Chemistry ,Sodium ,Metals and Alloys ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Anode ,Chemical engineering ,Materials Chemistry ,Ceramics and Composites ,Thermal stability ,Grid energy storage - Abstract
The ultra-fast (30C or 2 min) rate capability and impressive long cycle life (>5000 cycles) of Na2Ti6O13 are reported. A stable 2.5 V sodium-ion battery full cell is demonstrated. In addition, the sodium storage mechanism and thermal stability of Na2Ti6O13 are discussed.
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- 2013
12. Rapid synthesis and characterization of NH4Ag4I5
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V.Srirama Swaminathan, Palani Balaya, and C.S. Sunandana
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Diffraction ,Phase transition ,Incongruent melting ,Infrared ,Chemistry ,Stereochemistry ,General Chemistry ,Condensed Matter Physics ,law.invention ,Differential scanning calorimetry ,law ,Phase (matter) ,X-ray crystallography ,Physical chemistry ,General Materials Science ,Crystallization - Abstract
Melt quenching of a 1:4 mixture of NH4I and AgI was attempted in order to achieve rapid, large-scale synthesis of NH4Ag4I5 (“145”). The characterization of the as-quenched and annealed samples through DCS, IR and X-ray diffraction reveal (i) the thermodynamic evidence for “145” through endotherms at 235°C (incongruent melting) and −75°C (phase transition); (ii) disordered NH4+ groups and (iii) the need to anneal at temperatures below 147°C to obtain pure “145” phase. Crystallization from KI solution offers another attractive method for synthesis of stable “145”.
- Published
- 1994
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13. Quenched lithium sulphate
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Palani Balaya and C. S. Sunandana
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Quenching ,Relaxation (NMR) ,Analytical chemistry ,General Chemistry ,Activation energy ,Lithium sulfate ,Condensed Matter Physics ,Arrhenius plot ,chemistry.chemical_compound ,Differential scanning calorimetry ,chemistry ,Phase (matter) ,General Materials Science ,Monoclinic crystal system - Abstract
The high-temperature plastic phase (α-phase) of lithium sulphate with FCC structure has been stabilized at ambient by programmed quenching of the melt, aided by a few per cent of lithium carbonate which arrests the cubic to monoclinic phase transformation. The metastable phase thus obtained has been characterized by X-ray diffraction ( a = 6.98(4) A), differential scanning calorimetry (endothermic humps at 351 and 542°C in QL 200 ), a.c. electrical conductivity, infrared and electron spin resonance spectroscopy. DSC experiments provide unequivocal thermodynamic characterization of α-phase. Electrical conductivity of this phase is enhanced by ∼6 orders relative to the insulating monoclinic phase, with an activation energy of 0.4 eV, characteristic of α-Li 2 SO 4 . The micro-crystalline phase obtained by quenching at 300°C shows a two-slope Arrhenius plot (1.13 and 0.05 eV) with a knee separating them. The activation energy for high-temperature conductivity decreases systematically from 1.13 to 0.18eV, upon prolonged isothermal annealing suggestive of molecular relaxation leading to the optimization of Li + conduction paths. The i.r. spectra reflect the quenched-in disorder by way of broadening of peaks characteristic of SO 2− 4 and of the stabilizer CO 2− 3 ions. The ESR spectra of quenched Li 2 SO 4 , upon X-irradiation has given interesting microscopic evidence of a dynamically disordered C0 2− 3 by way of an intense isotropic (g ≈ 2.009) spectrum characteristic of the tumbling CO 3 − radical.
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- 1994
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14. 6Li MAS NMR investigation of electrochemical lithiation of RuO2: evidence for an interfacial storage mechanism
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Joachim Maier, Sevi Murugavel, Palani Balaya, Michel Ménétrier, Emilie Bekaert, Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut Polytechnique de Bordeaux-Université de Bordeaux (UB), Department of Mechanical Engineering [Singapore], National University of Singapore (NUS), Max Planck Institute for Solid State Research, and Max-Planck-Gesellschaft
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Materials science ,General Chemical Engineering ,Storage ,02 engineering and technology ,General Chemistry ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Inorganic compound ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,Nanocrystalline material ,NMR ,Ruthenium ,0104 chemical sciences ,Chemical engineering ,Electrode ,Materials Chemistry ,Mechanism ,0210 nano-technology ,Mechanism (sociology) - Abstract
International audience; Nanocrystalline RuO2 was electrochemically lithiated using a 6Li-enriched negative electrode, and selected samples at various states of lithiation-delithiation were characterized ex situ by 6Li magic-angle spinning nuclear magnetic resonance (6Li MAS NMR). In the first plateau (up to one Li per RuO2), a signal with considerable shift and loss of intensity is observed, showing a strongly paramagnetic character for the LiRuO2 phase. A signal due to solid electrolyte interphase (SEI) appears at 0 ppm on this first plateau, but significantly grows only on the subsequent conversion plateau (from 1 to 4 Li/RuO2). Li2O is detected only at the very end of the latter plateau. On further lithiation (4 to 5.5 Li/RuO2), the magnitude of the Li2O signal remains constant, and a new signal at 4 ppm appears, that we can assign to interfacial Li hypothesized earlier in this system. Upon subsequent delithiation, NMR shows that the interfacial Li first disappears, then Li2O also disappears, and the reconstructed Li-RuO2 phase is clearly different from the one formed during the initial lithiation of RuO2. Besides, the SEI signal slightly changes but does not decrease in magnitude upon delithiation. NMR results are in satisfactory agreement with the characteristic features of the proposed “job-sharing” mechanism.
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- 2009
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15. MnCO3: a novel electrode material for supercapacitors
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S. Devaraj, Haiyan Liu, and Palani Balaya
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Supercapacitor ,Materials science ,Renewable Energy, Sustainability and the Environment ,Rietveld refinement ,Analytical chemistry ,General Chemistry ,Electrolyte ,symbols.namesake ,Impurity ,Phase (matter) ,symbols ,General Materials Science ,Cyclic voltammetry ,Raman spectroscopy ,Faraday efficiency - Abstract
In this manuscript, MnCO3 is introduced as a novel electrode material for supercapacitors. MnCO3 was synthesized by a hydrothermal method using KMnO4 and commercial sugar as precursors. The synthesized product was characterized by powder X-ray diffraction, SEM, TEM and Raman spectroscopic studies. Rietveld refinement of powder X-ray diffraction confirmed the formation of a pure phase of MnCO3. Microscopic studies revealed particles of different shapes with sizes varying from 0.1 to 0.3 μm. Elemental mapping demonstrated a uniform distribution of manganese, carbon, and oxygen and there are no other impurity elements observed. The capacitive storage performance of MnCO3 was evaluated in three different electrolytes, namely, 0.1 M Na2SO4, 0.1 M Mg(ClO4)2 and 6 M KOH by cyclic voltammetry and galvanostatic charge–discharge cycling. A high specific capacitance of 216 F g−1 was obtained at a high loading level of 1.5 mg cm−2 for submicron sized particles of MnCO3 in a 0.1 M Mg(ClO4)2 electrolyte. Good reversibility, high coulombic efficiency, respectable rate performance and long cycle-life are also reported for MnCO3. This study opens up ample avenues to explore a new class of carbonate based materials for supercapacitor applications.
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- 2014
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16. Interconnected nanofibrous titanium dioxide bronze: an emerging lithium ion anode material for high rate performance
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Ivan Yeo, Kuppan Saravanan, Palani Balaya, and Chad W. Mason
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Nanostructure ,General Chemical Engineering ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Autoclave ,Anode ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Phase (matter) ,Titanium dioxide ,Lithium ,Porosity ,Carbon - Abstract
Here we report TiO2, in the bronze phase (TiO2-B), with a porous nanostructure designed for rapid lithium storage and charge transfer. A new synthesis method is described that not only facilitates these improvements, but also removes the requirement for an autoclave, which is usually common in the synthesis of this material. Most notably, peak capacities of 235, 148, and 66 mAh g−1 at 0.2 C, 20 C, and 100 C were attained, respectively. These results were achieved with low conductive carbon contents (5%). In addition, recent atomistic reports on TiO2-B were correlated with these results in order to explain how the morphology reported here was leveraged in order to attain high performance. Diffusion coefficients were also calculated for this novel TiO2-B architecture and found to be in good agreement with a previous study performed using NMR.
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- 2013
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17. Developing a light weight lithium ion battery – an effective material and electrode design for high performance conversion anodes
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Shailendra P. Joshi, Vishwanathan Ramar, Palani Balaya, and S. Hariharan
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Materials science ,General Chemical Engineering ,chemistry.chemical_element ,General Chemistry ,Nitride ,Electrochemistry ,Lithium-ion battery ,Cathode ,Anode ,law.invention ,chemistry ,Chemical engineering ,law ,Electrode ,Lithium ,Graphite - Abstract
The process of lithium storage by conversion reaction is a subject of intense research in the field of lithium ion batteries as it opens up the possibility of storing more than one mole of lithium per formula unit, leading to very high storage capacities. For instance, lithium storage by conversion reaction in hematite (α-Fe2O3) results in high theoretical capacity of 1005 mAh g−1. Despite numerous attempts, the first cycle reversibility and cyclability achieved in this material have been disappointingly low. To overcome these limitations, we report here an effective “active material-electrode design” incorporating the following features: (i) well-connected active material particles; (ii) adequate active material surface area; (iii) strong particle-current collector adhesion and (iv) superior degree of electrode drying. Incorporating these features in α-Fe2O3 electrodes enhances its overall electrochemical performance. For the first time, a high first cycle reversibility of 90% is reported for lithium storage via conversion reaction in α-Fe2O3. The long term cyclability over 800 cycles demonstrated here is one of highest reported values for this material. Even at high current densities of 5.025 A g−1 (12 mins of charge/discharge), this tailored α-Fe2O3 delivers capacities (446 mAh g−1) in excess of graphite (372 mAh g−1). Most importantly, this anode material shows feasible operation in a full cell containing olivine LiMn0.8Fe0.2PO4 cathode. It is believed that this simple design approach could also be extended to other material systems such as phosphides, sulphides, nitrides and fluorides that store lithium via conversion mechanism.
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- 2013
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18. Na2Ti3O7: an intercalation based anode for sodium-ion battery applications
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Chad W. Mason, Ashish Rudola, Palani Balaya, and Kuppan Saravanan
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Materials science ,Renewable Energy, Sustainability and the Environment ,Sodium ,Intercalation (chemistry) ,Analytical chemistry ,Sodium-ion battery ,chemistry.chemical_element ,General Chemistry ,Electrochemistry ,Anode ,X-ray photoelectron spectroscopy ,chemistry ,Electrode ,General Materials Science ,High-resolution transmission electron microscopy - Abstract
We report here the electrochemical properties of Na2Ti3O7, a potential non-carbon based, low-voltage anode material for room temperature sodium ion battery applications. A solid-state route was used to prepare Na2Ti3O7. Further, XRD, SEM, TEM, HRTEM, SAED, XPS and EDX techniques were used to characterize the material. The Na/Na2Ti3O7 cell displayed a charge capacity of 177 mA h g−1 at 0.1 C rate. High rate and long term cyclic performance at different rates showed relatively stable storage capacities. Surprisingly, if the lower cut-off voltage is altered, the appearance of a new charge plateau is seen, with no apparent change in the discharge behaviour. The kinetics of sodium insertion and extraction are discussed utilizing CV and EIS techniques. We also report the sodium chemical diffusion coefficient of the Na2Ti3O7/CB electrode estimated using GITT.
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- 2013
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19. Li2MnSiO4 obtained by microwave assisted solvothermal method: electrochemical and surface studies
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Mirjana Kuezma, Palani Balaya, and S. Devaraj
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Materials science ,Carbonization ,Analytical chemistry ,chemistry.chemical_element ,General Chemistry ,Manganese ,engineering.material ,Electrochemistry ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Coating ,Oxidation state ,Materials Chemistry ,engineering ,Orthosilicate ,Carbon - Abstract
Nanostructured nominally pure Li2MnSiO4 (LMS) is successfully synthesized by a microwave assisted solvothermal method followed by successful coating with conductive carbon using carbonizing agents such as D-(+)-glucono-1,5-lactone (GA) and citric acid (CA). CA is found to be a better carbonizing agent than GA as it shows two times higher capacity than GA. Reversible capacity of 250 mA h g−1 is obtained for carbon coated LMS at C/10 with flat charge/discharge plateau in the narrow potential window 2.0 to 4.5 V vs. Li/Li+. Capacity fades drastically after the first few cycles with a sloppy charge/discharge profile. The possible mechanism for the observed discharge plateau is discussed on the basis of XPS method and electrochemical testing. Ex situ XPS analysis confirms that such a large capacity (exchange of more than one mol of Li per compound reaction) after the first charging of the Li2MnSiO4 material is connected with the complete oxidation of Mn2+ to Mn4+ on the surface. To the best of our knowledge, the Mn4+ oxidation state is confirmed experimentally for the first time in the case of the manganese orthosilicate cathode material that exhibits best theoretical capacity of 330 mA h g−1.
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- 2012
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20. Multi-functional photoanode films using mesoporous TiO2 aggregate structure for efficient dye sensitized solar cells
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Palani Balaya, Chrisopher Yap, and Satyanarayana Reddy Gajjela
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Photocurrent ,Materials science ,business.industry ,Scattering ,Energy conversion efficiency ,Nanotechnology ,General Chemistry ,Light scattering ,Dielectric spectroscopy ,Dye-sensitized solar cell ,Materials Chemistry ,Optoelectronics ,Diffuse reflection ,business ,Mesoporous material - Abstract
We present here the photovoltaic performance of dye sensitized solar cells (DSCs) using sub-micron sized mesoporous TiO2 aggregates which incorporate built-in multi-functional properties such as high dye uptake, efficient light scattering and enhanced charge collection. The DSC prepared with these mesoporous anatase TiO2 aggregates as photoanode with no additional scattering layer exhibits an enhanced conversion efficiency of 9.00% at 1 sun and 10.84% at 0.16 sun illumination. The properties of the photoanode film in DSCs were analyzed by surface area, diffuse reflectance, intensity modulated photocurrent/voltage spectroscopy (IMPS/IMVS) and electrochemical impedance spectroscopy (EIS) measurements in order to gain knowledge of the decisive factors contributing to such high power conversion efficiency. The present study reveals that the mesoporous aggregate offers large internal surface area and high light scattering with its unique structure. Due to the high crystallinity and compact packing of primary nanocrystallites forming the aggregate structure of mesoporous TiO2, the electron diffusion length is substantially long reflecting a lower number of electrons trapped at the grain boundaries. A good compromise of electron transport time and extended life time in mesoporous aggregate films compared to their non-aggregate counterparts leads to efficient charge collection and higher power conversion efficiency.
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- 2012
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21. Hollow α-LiVOPO4 sphere cathodes for high energy Li-ion battery application
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Hwang Sheng Lee, Kuppan Saravanan, Mirjana Kuezma, Jagadese J. Vittal, and Palani Balaya
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Battery (electricity) ,Materials science ,One-Step ,Nanotechnology ,General Chemistry ,Hard spheres ,Triclinic crystal system ,Cathode ,law.invention ,Ion ,Chemical engineering ,law ,Phase (matter) ,Materials Chemistry ,SPHERES - Abstract
Hollow spheres of electroactive α-LiVOPO4 were synthesized via a simple one step solvothermal method. A powder X-ray diffraction study revealed that the obtained product crystallized in the triclinic α-LiVOPO4 phase. The morphology of the product was largely influenced by reaction conditions such as reaction time, temperature, etc., and the product morphology was easily fine tuned from hollow spheres to hard spheres upon changing the reaction time. Without any post-heat treatment or milling with conductive additives, these hollow spheres exhibited comparatively large reversible Li storage of 130 and 61 mA h g−1 at 0.1 and 1.7 C respectively. Excellent capacity retention and long term cycling stability were demonstrated by the hollow spheres of α-LiVOPO4. We believe that α-LiVOPO4 is likely to be a prospective cathode material for high-voltage Li ion batteries application.
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- 2011
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22. Li(MnxFe1−x)PO4/C (x = 0.5, 0.75 and 1) nanoplates for lithium storage application
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Palani Balaya, Vishwanathan Ramar, Jagadese J. Vittal, and Kuppan Saravanan
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Materials science ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,engineering.material ,Electrochemistry ,Copper ,chemistry ,Coating ,Chemical engineering ,Materials Chemistry ,engineering ,Lithium ,High-resolution transmission electron microscopy ,Carbon ,Powder diffraction ,Solid solution - Abstract
A simple solvothermal method was used to synthesize nanoplates of LiMnPO4 (LMP) with a thickness of ∼60 to 80 nm. The LMP nanoplates were well characterized by PXRD, SEM and HRTEM techniques. The reaction conditions for the solvothermal method were found to be crucial to control the morphology of LMP. Carbon, silver, gold and copper have been coated on the surfaces of LMP nanoplates to improve the electronic conductivity. Despite such coating, the electrochemical activity of such metal-decorated LMP nanoplates was found to be minimal due to discontinuous wiring limiting the electronic conduction. Therefore, the Mn2+ in the nanoplates was partially substituted by the Fe2+ ion to obtain the following composition [LiMnxFe1−xPO4 (x = 0.5 and 0.75)]. These solid solutions showed excellent storage performance compared to pure LMP. Especially LiMn0.5Fe0.5PO4/C nanoplates exhibited a reversible capacity of 153, 121, 91 and 31 mA h g−1 at 0.02, 0.1, 5 and 18 C respectively. In addition, LiMn0.5Fe0.5PO4/C also demonstrated a stable long term cycling capacity of 103 mA h g−1 at a 2 C rate up to 1000 cycles.
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- 2011
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23. Lithium storage in a metal organic framework with diamondoid topology – a case study on metal formates
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Palani Balaya, Jagadese J. Vittal, Mangayarkarasi Nagarathinam, and Kuppan Saravanan
- Subjects
Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,Electrochemistry ,Diamondoid ,Metal ,chemistry.chemical_compound ,chemistry ,Transition metal ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Formate ,Metal-organic framework ,Lithium ,Fourier transform infrared spectroscopy - Abstract
In this manuscript, a systematic investigation on the electrochemical performance of as-synthesized metal organic framework (MOF) Zn3(HCOO)6 with diamondoid structure for the Li storage using conversion reaction at low potential is described. Nearly an invariable capacity of 560 mAh g−1 (9.6 moles of Li) was obtained up to 60 cycles at 60 mA g−1 within the voltage range 0.005–3.0 V. The regeneration of the MOF during the cycling and the improved cyclability are evidenced from the electrochemical results along with ex situ PXRD, FTIR and TEM studies. The electrochemical cycling suggests that metal formate frameworks react reversibly with Li through conversion reaction. The matrix involved during the cycling was lithium formate rather than the typical Li2O and this is well supported by the ex situ FTIR results. The thermodynamic feasibility to transform the lithium formate to transition metal formate is more highly favored than from Li2O and this is further confirmed by reacting lithium formate with respective transition metal nitrates. The reversible formation or regeneration of FOR1 MOF plays a vital role in attaining the superior Li storage performance. Ultimately, the observation of improved storage performance and good cycling stability of Co3(HCOO)6 and Zn1.5Co1.5(HCOO)6, and the overall simple and eco-friendly synthesis method demonstrates that robust, thermally stable MOFs are a prospective class of electrode materials for Li ion batteries (LIBs).
- Published
- 2010
- Full Text
- View/download PDF
24. ESR of Ag2+ in 60AgI-30Ag2O-10B2O3 glass
- Author
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Palani Balaya and C.S. Sunandana
- Subjects
Nuclear magnetic resonance ,Chemistry ,Physical chemistry ,General Materials Science ,General Chemistry ,Condensed Matter Physics ,Spectral line - Abstract
An ESR study on 60AgI-30Ag2O-10B2O3 (300–473 K) is reported. The spectra showed two Ag2+ centres at RT. The origin of these centres is discussed in light of the model structure of Minami et al. and our DSC results.
- Published
- 1990
- Full Text
- View/download PDF
25. Calorimetric and electrical studies on quenched Li2So4.H2O
- Author
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Palani Balaya and C.S. Sunandana
- Subjects
Quenching ,Phase transition ,Chemistry ,Analytical chemistry ,Thermodynamics ,General Chemistry ,Activation energy ,Condensed Matter Physics ,Thermal conduction ,Differential scanning calorimetry ,Electrical resistivity and conductivity ,Phase (matter) ,Materials Chemistry ,Ionic conductivity - Abstract
DSC, a.c. electrical conductivity and IR spectra of quenched Li2So4 are employed to investigate the nature of the f.c.c. superionic (high temperature) phase stabilized at ambient temperatures by quenching. DSC results suggest a two-state phase transition in the range 520–570°C with the enthalpies of the two stages depending sensitively on quenching temperature, pointing to the existence of two structurally distinct SO2-4 groups, one of which is possibly involved in superionic conduction. Electrical conductivity is enhanced by many orders of magnitude with lower activation energy compared to the purely low temperature phase. IR spectra contain features that provide additional evidence for co-operative rotations of distinct SO2-4 group (characteristic of plastic phase) as a feasible mechanism for enhanced Li+ ion conduction.
- Published
- 1989
- Full Text
- View/download PDF
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