Effects of electrolytes and temperature on high-rate discharge behavior of MmNi_5-based hydrogen storage alloys

摘要

A series of experiments have been performed to investigate the effects of electrolyte composition and temperature on the high-rate discharge behaviors of MmNi_5-based AB_5 hydrogen storage alloy electrodes. Two types of AB_5 electrodes have been used using different alloys: Ce-rich alloy V (La_(0.26) Ce_(0.44)Pr_(0.1)Nd_(0.2)Ni_(3.55)Co_(0.72)Mn_(0.43)Al_(0.3)) and La-rich alloy N (La_(0.58)Ce_(0.25)Pr_(0.06) Nd_(0.11)Ni_(3.66)Co_(0.74)Mn_(0.41)Al_(0.18)). Electrolytes EN were obtained by adding a saturated amount of Al_2(SO_4)_3 to the original electrolyte EO (6 M KOH + 1 wt% LiOH). The electrolyte EN has previously been shown to be very effective to stop the self-discharge of the AB_5 electrodes, better charge/discharge cycle life have been observed. The electrochemical properties of the electrodes were measured by two methods: step mode high-rate discharge and continuous mode high-rate discharge. The results indicate that at 298 K and 333 K, high-rate discharge capacity of Ni-MH battery was mostly affected by the chemical composition of the electrolyte, then the type of alloy. Better dischargeabilities in high-rate discharge capacity have been observed in electrolyte EO than in electrolyte EN. The Ce-rich alloy V has a higher high-rate discharge capacity than La-rich alloy N. High-rate discharge capacity decreases in the following order: VEO > NEO > VEN > NEN (VEO denotes the combination of alloy V and electrolyte EO used in the test battery, similarly equivalent representations for NEN, VEO and VEN).