T. H. Nam, G. B. Cho, K. W. Kim, H. J. Ahn, Gyeongsang National University, Jinju, South Korea
Ti-Ni base sulfide electrode was prepared, and then its structure, mechanical properties and discharge performance were investigated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractions, differential scanning calorimetry(DSC), thermal cycling tests under constant load and tensile tests. The sulfide electrode was fabricated by isothermally annealing an equiatomic Ti-Ni alloy at 873 K for 7.2 ks – 72 ks under the sulfur pressure from 5 kPa to 320 kPa. Two-layered surface sulfide was formed, consisting of an outer Nickle sulfides(NiS and NiS1.97) and an inner Titanium sulfide(Ti8.2S11). Thickness of the sulfide layers increased from 5 µ to 35 µ with increasing sulfur pressure from 5 kPa to 80 kPa. By sulfurizing the Ti-Ni alloy, DSC peaks of the alloy were broaden and martensitic transformation start temperature(Ms) increased from 281 K to 289 K, which were ascribed to an inhomogenity in composition caused by surface sulfide layers and a compressive stress imposed by surface sulfide layers. A sulfurized equiatomic Ti-Ni alloy showed good shape memory characteristics and partial superelasticity. The surface sulfide layers were not detached after tensile deformation of 3%, although some cracks were observed in them. The discharge curve of the Ti and Ni sulfides cathode formed on the Ti-Ni current collector at the first cycle shows a plateau voltage of 1.6 V and the discharge capacity is known to be about 530 mAh/g-NiS1.97.
Summary: This paper shows an application of Ti-Ni alloys for electrodes of secondary battery. By sulfurizing Ti-Ni alloys, an integrated electrode consisted of metal sulfides such as Ti sulfides and Ni sulfides and Ti-Ni alloys was obtained. Ti and Ni sulfides acted as active materials and Ti-Ni alloys acted as current collectors. The integrated electrode showed superelasticity and clear charge-discharge behavior
