Microstructure and superelasticity of NiS/TiNi composite electrode

Abstract

Surface Ni sulfides layers were formed on the surface of a Ti-50.0Ni alloy by reacting sulfur and Ni film deposited on the alloy, and then microstructures, transformation behavior, shape memory characteristics, superelasticity and electrochemical properties of a Ti-50.0Ni(at%) alloy with the sulfides were investigated. When Ni film deposited on a Ti-50.0Ni alloy was annealed under the sulfur pressure of 100 kPa at 623 K, sulfides layers consisted of NiS and NiS1.97 were formed. When annealing was made at 648 K annealing with annealing time less than 0.9 ks, sulfides layers consisted of NiS and NiS 1.97 were formed also, while only NiS1.97 was formed when it was made for 1.8 ks. When annealing was made at 673 K annealing with annealing time longer than 0.9 ks, only NiS1.97 was formed. A Ti- 50.0Ni(at%) alloy with surface NiS1.97 layer showed the two-stage B2-R-B19' transformation behavior, the perfect shape memory effect and a partial superelasticity with a superelastic recovery ratio of 78 %. NiS1.97 cathode showed a clear discharge behavior with multi voltage plateaus. Discharge capacity of NiS1.97 cathode decreased abruptly with increasing number of cycles up to 3, above which it decreased gradually.