Effect of spark plasma sintering temperature on electrochemical properties of La_0.82Mg_0.18Ni_3.50Co_0.15 alloy

Abstract

Electrochemical properties of La_0.82Mg_0.18Ni_3.50Co_0.15 alloys synthesized by spark plasma sintering (SPS) were investigated based on the electrochemical measurements, physical parameters and microstructure observation. The sintering behavior of La_0.82Mg_0.18Ni_3.50Co_0.15 alloys at the temperatures of 900, 950 and 1000 °C is characterized by four stages, i. e., initial slight shrinkage, expansion, abrupt shrinkage and slight expansion. The maximum shrinkage displacement increases with increasing sintering temperature. All of the alloys consist of (La,Mg)₂ (Ni,Co)₇ phase; additionally, temperatures of 900 and 950 °C are beneficial to the formation of (La, Mg) (Ni, Co)₃ phase, whereas the LaNi₅ phase is easy to form in the alloy synthesized by SPS at 1000 °C. The electrochemical measurements indicate an evident change of the electrochemical performance of the alloys associated with increasing the sintering temperature. The discharge capacity of the alloys first increases and then decreases as sintering temperature rises, whereas their cycle stability clearly grows all the time. Furthermore, the charging-discharging potential difference and discharging efficiency both demonstrate that the electrochemical properties of the alloy electrodes first augment and then decline with increasing sintering temperature.