Electrochemical properties of the NiS powder prepared by co-precipitation method for lithium secondary battery.

We synthesized two nickel sulfide powders by simple method. One is nickel sulfide powder (CNS) by co-precipitation is composed of nano-sized nickel sulfides as NiS and NIS2. The other is nickel sulfide powder (HNS) by heat-treatment of CNS is composed nano-sized NIS. The electrode using CNS has a high first discharge capacity of 600 mA h g(-1) at 0.5 C and the discharge capacity after 20th cycle is 312 mA h g(-1). The electrode using HNS has a high first discharge capacity of 551 mA h g(-1) at 0.5 C and has the discharge capacity of 412 mA h g(-1) after 50th. The discharge rate capability has over 92% at 1 C versus 0.2 C. The nano-sized nickel sulfides are synthesized by simple co-precipitation method has good electrochemical properties such as high first discharge capacity, good cycle life and good rate capability for lithium secondary battery.

Synthesization and characterization of FeS2 by mechanical alloying for Na/FeS2 cell.

In this study, the FeS2 fine compound powders were synthesized by mechanical alloying (MA) for 15 hrs and stearic acid was added as PCA (Process Control Agent) to prevent the excessive cold welding and agglomeration. For the purpose of ulteriorly reducing the particle size to improve the contact areas between the active materials and conducting agents, the wet ball milling process was applied by employing normal hexane (C6H14) as the milling solvent. The mean particle size of FeS2 powders about 1.14 microm were obtained after 24 hrs wet ball milling. The powders were characterized by FE-SEM, XRD, TEM and EDS. To compare the influence of particle size on the properties of charge/discharge, the same electrolyte was employed for both tests by dissolving 1M NaCF3SO3 (sodium trifluoromethanesulfonate) in a liquid of TEGDME (tetraethylene glycol dimethylether). The first discharge capacity of Na/FeS2 cell made by dry ball milled powders was 440 mAh/g with a plateau potential at approximately 1.25 V versus Na/Na+ and 260 mAh/g at the 25th cycle at room temperature. Meanwhile, the initial discharge capacity of Na/FeS2 cell made by wet ball milled powders was 614 mAh/g with the same discharge plateau potential and retained 385 mAh/g at the 25th cycle. And the discharge capacity for wet milled system decreased continuously by repeated charge/discharge cycling in the first 20 cycles and has little change after 60 cycles, which means the good cycling properties, remaining half of its initial discharge capacity of 320 mAh/g even after 100 cycles.

The phase analysis of spark plasma sintered MgB2 after ball milling.

Mg and amorphous B powders below 10 and 3 micro meter were used as raw materials, and mixed by planetary-mill for 9 hours at argon atmosphere. MgB2 bulk was fabricated at the various temperatures by Spark Plasma Sintering. In the sintering process, mixed powders were sintered in graphite mold, at the pressure of 55 Mpa. The fabricated MgB2 samples were evaluated with XRD, EDS, FE-SEM, PPMS. MgB2, MgO and Fe phases were observed from XRD result. In the results, MgO and Fe were impurity which may affect superconducting properties of MgB2 samples, and it's distribution could be confirmed from EDS mapping result. In order to confirm the formation of MgB2 phase, DTA was used as heating rate of 10 degrees C/min at Ar atmosphere from room temperature to 1200 degrees C. In the PPMS result, the Tc (critical temperature) was about 21 K, and the density of spark plasma sintered samples increased to 1.87 g/cm3 by increasing sintering temperature.