Electrochemical lithium and sodium insertion studies in 3D metal oxy-phosphate framework MoWO3(PO4)2 for battery applications

A new type of three-dimensional (3D) oxy-phosphate materials are explored for the application of Li and Na batteries. The molybdenum tungsten oxy phosphate, MoWO₃(PO₄)₂, was synthesized by solid-state method and evaluated for Li/Na insertion/de-insertion electrode material for the first time. The cell at charged state (vs. Li⁺/Li) showed a discharge capacity of 786 mAh g⁻¹ within the voltage window of 0.3 V with amorphization of crystalline MoWO₃(PO₄)₂ as observed from ex-situ powder XRD analysis. The structural integrity was revealed in this material, even with nearly more than 5 Li⁺ ions into the lattice, leading to the discharge capacity of 250 mAh g⁻¹. The reversible charge/discharge behavior with insertion/de-insertion of 2.4 Li⁺ ions in the voltage range of 1.65 − 3.5 V resulted in 110 and 95 mAh g⁻¹ at C/10 and C/5 rates, respectively. On the other hand, poor cycling performance was noticed for Na ion insertion and desertion, with a discharge capacity of 250 mAh/g within the voltage range of 0.3 − 3.5 V (vs. Na⁺/Na).

     

Thermoanalytical investigations on the sol-gel synthesis of YBa2Cu3O72212;δ

The high temperature superconducting compound YBa₂Cu₃O_72212; (Y-123) is synthesised by sol-gel process using various precursors viz., acetate, acetate-citrate, nitrate-citrate and acrylamide. The phase purity of the final product depends on the homogeneity of the gels which intern depends on the bonding of the metal ions in the gels. The samples prepared by acrylamide and nitrate-citrate gel routes yielded phase pure Y-123 compound with better superconducting properties. The mechanism of formation of Y-123 in all these four gel routes is established by characterising the gels and intermediate phases using TG, DTA and XRD techniques. Kinetic analysis is carried out on the mass loss data using the method proposed by Phadni's and Deshpande. Avrami-Erofeev nuclei growth in case of acrylamide, diffusion controlled process in nitrate-citrate and phase boundary reaction mechanisms in case of acetate-citrate gels are found to be responsible for the formation of Y-123 phase.The authors are grateful to Dr. Baldev Raj, Director, Metals and Materials Group, for his constant encouragement and support. We thank Prof. G. V. Subba Rao, Director, Central Electrochemical Research Institute, Karaikudi for his keen interest in this work. Thanks are also due to Dr. Sundaram, CECRI, Karaikudi for his help in thermal analysis experiments.     

Electrochemical Li insertion studies on WNb12O33—A shear ReO3 type structure

Electrochemical lithium insertion studies on WNb₁₂O₃₃ synthesized by solid state reaction (SSR) are carried out in the voltage range 1.0-3.2 V. During first discharge 15.6 Li are inserted with a specific capacity of 221 mAh/g. WNb₁₂O₃₃ is also synthesized by sol-gel (SG) technique with a view to enhance the rate capability and cycling properties. The SSR and SG samples are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and galvanostatic cycling. Electrochemical cycling performance of SG samples is superior to that of the SSR sample at high ‘C’ rates. The sample synthesized by SG method exhibits high specific capacity of 142 mAh/g after 20 cycles at 20C rate.     

Disodium dimolybdate: a potential high-performance anode material for rechargeable sodium ion battery applications

Journal of Solid State Electrochemistry - Na2Mo2O7 was synthesized by solid-state reaction route and explored as possible anode material for sodium ion battery for the first time. The...     

57Fe Mössbauer Studies of Sr2−x Ca x FeReO6 Double Perovskite Compounds

Hyperfine Interactions - We present a 57Fe Mössbauer study of the Sr2?x Ca x FeReO6 double perovskite series, with x=0, 0.1, 0.2, 0.5, 1.0, 1.5 and 2.0. The analysis at 300 and 16 K...     

High Tc superconductors based on Y-Ba-Cu-O system

Preliminary studies on the high T superconductivity encountered in the yttrium or^c rare earth-barium-copper-oxygen system are reported. Zero resistance T_c of 95K has been realized.     

Phase formation and superconductivity in REBaSrCu3−x(PO4)xOy (0 ≤ x ≤ 0.3)

Oxy-anion (PO₄³⁻) substituted phases of the composition REBaSrCu_2.8(PO₄)_0.2O_y have been synthesized. Single phase formation is achieved only for the larger rare earths (La → Ho and Y) and all the phases crystallize in the tetragonal 123 structure. IR studies confirm the presence of a phosphate group in the structure. The total oxygen content (including that associated with the oxy-anion PO₄³⁻) has been found to be in the range 7.01 to 7.10 per formula unit. Except for RE = La, Nd, Yb and Lu, all the phases exhibit superconductivity and the T_c,zero values vary from 18 to 38 K. The T_c,zero increases with decreasing size of RE³⁺. ErBaSrCu₃O₇ is multiphasic and single phase formation is achieved for the first time by phosphate substitution at the copper site. Single phase formation is encountered for x = 0.10 and 0.15 with T_c,zero values of 54 and 37 K respectively.     

New layered hydrogenophosphate, protonic conductor: Mn(H2PO4)2

A new hydrogenophosphate Mn(H 2PO 4) 2 has been synthesized from an aqueous solution. Its ab initio structure resolution shows that the original layered structure of this phase consists of PO 2(OH) 2 tetrahedra and MnO 5OH octahedra, sharing corners to form [MnP 2O 8H 4] infinity layers, whose cohesion is ensured through hydrogen bonds. The excitation and emission spectra of this phase are characteristic of Mn (2+) species. This phosphate is shown to be a good protonic conductor with a conductivity of 10 (-4.4) S/cm at 90 degrees C (363 K).