Effects of electrolytes and temperature on high-rate discharge behavior of MmNi₅-based hydrogen storage alloys

A series of experiments have been performed to investigate the effects of electrolyte composition and temperature on the high-rate discharge behaviors of MmNi₅-based AB₅ hydrogen storage alloy electrodes. Two types of AB₅ electrodes have been used using different alloys: Ce-rich alloy V (La_0.26 Ce_0.44Pr_0.1Nd_0.2Ni_3.55Co_0.72Mn_0.43Al_0.3) and La-rich alloy N (La_0.58Ce_0.25Pr_0.06 Nd_0.11Ni_3.66Co_0.74Mn_0.41Al_0.18). Electrolytes EN were obtained by adding a saturated amount of Al₂(SO₄) 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 AB₅ 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).