Mh-ni Battery Performance

Ni/MH battery has been highly evaluated in the field of chemical power source all over the world due to no Cd pollution, high energy density, better resistance to overcharge and overdischarge and replacement of Cd/Ni battery. The cycle life of nickel hydroxide positive electrode and metal hydride negative electrode was studied. The chemical composition and particle size distribution for hydrogen storage alloy before and after cycling were determinated. The characteristics of AA-type Ni-MH battery before and after cycling, such as capacities at different discharge rates, internal resistance, charge and discharge reserve capacity, internal pressure were compared. The results show that the degradation of discharge performance at early cycling period is closely related to the characteristic of the separator between the electrodes. Discharge capacity at 1 C rate for the improved AA type Ni-MH battery degrades into only 15% after 500 cycles. The effect of filling density of MH electrode, formation process, battery structure and negative electrode additive on internal pressure for Sc-type Ni-MH battery was systematically investigated. The internal pressure at the time of 40mm for Sc-type Ni-MH battery during charging at 2C(5A) current could be decreased from 1 .8MPa to 0.67MPa due to some improvements. High capacity AA-type Ni-MH battery was manufactured by reducing the amount of inactive materials, decreasing the thickness of separator, elevating the channel position. Capacity at 0.2C rate for the battery is larger than 1 600mAh, and capacity at 1C, 3C rate is larger than l500mAh. Mm-based hydrogen storage alloy was treated with EDTA. The best treatment condition is: EDTA with pH 7 at the temperature of 800C for 8 hours. The result of XPS shows that the surface of treated alloy has lower oxygen content. Treated MH electrode has lower polarization than untreated one during charging and discharging at IC rate. Sealed prismatic Ni-MH battery with the capacity about 4OAh was designed and prepared. Its discharge performance at different rates at 20 0C and -18 0C self-discharge rate and cycle behavior were evaluated. Its specific energy by volume and weight are 232.8Wh!L and 66.2 Wb/kg respectively, and the rate of self-discharge is about 15%. Low-temperature characteristics for several sizes of Ni-MH battery were examined. And the effect of mixed electrolyte and the ratio of negative capacity and positive capacity were discussed. Decreasing the thickness of MH electrode or increasing discharge reserve capacity may considerably improve the low-temperature characteristics of Ni-MH battery. At -340C the discharge capacity percentage for D-type Ni-MH battery at 0.4C current increases from 72.2% to 80.8%, and discharge voltage is enhanced about 4OmV after improvement.