Studies On The Technics For Nickel Metal Hydride Battery

In this thesis, the research and development status of nickel metal hydride batteries have been reviewed. Based on the result mentioned above, the effects of PTFE content ,cut-off voltage and charge time at activation, the different concentration of KOH or LiOH or XaOH in alkaline electrolyte on the key characteristics are studied. The main research results are as follows:The battery after the addition of 0.2% PTFE have overall electrochemical properties. The batteries after the addition of 1% PTFE in negative electrodes have preferably cycle life, voltage plateau decaying, internal resistance decaying with respect to no PTFE. When the hydrogen storage alloy electrodes are treated by hydrophobic method, preliminary discharge capacity and voltage plateau are improved, however, preliminary discharge capacity and voltage plateau decline with the increase of hydrophobic concentration. When the batteries are treated by hydrophobia of 4% PTFE concentration, the cycle life and voltage plateau improves. Internal resistance increase with the increase of PTFE concentration. Charge retention increases with the increase of PTFE concentration after the addition PTFE whether in positive electrodes or in negative electrodes or treated by hydrophobic in the surface of negative electrodes.When reducing the discharge cut-off voltage of the second, the third, the forth step to 850 mV during activation, discharge capacity is improved remarkably, increasing about 24 mAh. But middle point voltage decreases and internal resistance increases about 1 mQ. When every step cut-off voltage decreases to 850 mV, the batteries have over discharged and the leaking proportion increases. When the second, the third step charge time are reduced, the properties of the batteries are improved. When the second step charge time is reduced for 10 minutes and the third step for 5 minutes, discharge capacity increases 3.8 mAh, middle voltage increases 7.2 mV, and internal resistance decreases 0.1 mQ.When KOH concentration is increased, discharge capacity and internal resistance increase, voltage plateau decreases. As KOH concentration reaches 9M or 10M, the batteries have high discharge capacity and low middle point voltage; as concentration reaches 5M or 6M, the batteries have high middle point voltage, but discharge capacity is below 650mAh. Moreover, the batteries can endure long time overcharge with the increase of the KOH concentration. The change of KOH concentration has little effect on the high rate discharge capability. When KOH concentration is 7M, the batteries have better overall electrochemical properties. By contrasting the LiOH or NaOH data to KOH at 7M and 8M, the change of the Li+ orNa+ concentration has little effect on the discharge capacity, internal resistance, voltage plateau and high rate discharge capability.