No abstract

The effect of Cr-doping on the structural, physical and electrochemical properties of Li 2 MnO 3 and LiNi 0.5 Mn 0.5 O 2 is reported. The formation of the solid solution and local distortion of the structure with the increase in Cr doping (0.7Li 2 MnO 3 -0.3LiNi 0.5 Mn 0.5 O 2 ) was confirmed respectively, by X-Ray diffraction and Raman spectroscopy. Morphological investigations and elemental mapping showed the formation of primary particles in the range 0.5-1.0 μm and homogeneity, respectively. Electrochemical measurements on the materials were carried out in different voltage ranges and temperatures. Structural transformation of the material from layered to spinel symmetry has been observed with cycling in case of the samples with low Li 2 MnO 3 content (0.3Li 2 MnO 3 -0.7LiNi 0.5 Mn 0.5 O 2 ). Cr acted as a catalyst to enhance the activation of the material with high Li 2 MnO 3 content.

Available onlineKeywords: Activation energy dc conductivity ac impedance and diffusion coefficient A B S T R A C T Cathode materials in nano size improve the performance of batteries due to the increased reaction rate and short diffusion lengths. Lithium Iron Phosphate (LiFePO4) is a promising cathode material for Li-ion batteries. However, it has its own limitations such as low conductivity and low diffusion coefficient which lead to high impedance due to which its application is restricted in batteries. In the present work, increase of conductivity with decreasing particle size of LiFePO4/C is studied. Also, the dependence of conductivity and activation energy for hopping of small polaron in LiFePO4/C on variation of particle size is investigated. The micro sized cathode material is ball milled for different durations to reduce the particle size to nano level. The material is characterized for its structure and particle size. The resistivities/ dc conductivities of the pellets are measured using four probe technique at different temperatures, up to 150°C. The activation energies corresponding to different particle sizes are calculated using Arrhenius equation. CR2032 cells are fabricated and electrochemical characteristics, namely, ac impedance and diffusion coefficients, are studied.

0.5Li 2 MnO 3 -0.5LiMn 0.5 Ni 0.5 O 2 composite cathode material with and without ZnO treatment has been synthesized using carbonate based co-precipitation method for rechargeable lithium ion battery. The X-ray diffraction study confirms that the material has layered LiNi 0.5 Mn 0.5 O 2 structure along with the formation of the superlattice ordering of Li 2 MnO 3 ; without any major change in the crystal structure with ZnO treatment. Raman spectroscopy has revealed two different types of ionic arrangements corresponding to space groups of C2/m and R3m for Li 2 MnO 3 and LiNi 0.5 Mn 0.5 O 2 respectively. Morphological studies revealed primary particles are of ∼1 micron size and have sharp, elongated edges. The particles are present as spherical agglomerates (∼10 micron). Elemental mapping and X-ray photoelectron spectroscopy confirmed the presence of Zn in the ZnO treated samples. Charge/discharge capacity of the composite cathode materials (with and without ZnO coating) increases with number of cycles due to more and more activation of the Li 2 MnO 3 . However, ZnO treated 0.5Li 2 MnO 3 -0.5LiMn 0.5 Ni 0.5 O 2 composite material showed higher charge/discharge capacites attaining saturation in less number of cycles. Lower resistance to charge transfer in the case of ZnO treated sample is responsible for its better performance.

Aluminized high explosives are known to give better underwater performance. All explosive formulations for underwater targets are filled into warheads and shells by casting method. TNT, a high explosive is used as casting medium due to its lower melting point. Plastic bonded explosives are fast replacing TNT-based high explosive formulations for the reasons that they are more insensitive and low vulnerable explosives with better shelf life. Few aluminized plastic bonded explosive formulations based on RDX, aluminum, and HTPB have been processed, varying the aluminum content from 0 to 35% and evaluated underwater. The present paper discusses the experimental methodology adopted to evaluate the above formulations for their ballistic parameters, viz., peak over pressure and impulse. Explosion bulge tests have been conducted with each explosive formulation and extent of bulge in test plates is presented and compared with a standard underwater explosive, viz., HBX-3.