Research On Surface Modification Of Hydrogen-storage Alloy Negative Electrodes And Performance Of Ni/MH Batteries With Large Capacities

Nickel-metal hydride (Ni-MH) batteries are one of the most promising future vehicular power systems because of advantages such as high specific energy, long cycle life, use of no poisonous heavy metals and great improvement of recharge / discharge performance. Extensive efforts continue to be made to develop Ni-MH batteries to meet the stringent requirements of electric vehicles. There are important values of practicality and theory for the further research of improving the comprehensive performance of Ni/MH batteries.The main contents of this paper includes that the surface modification and surface treatment of hydrogen-storage alloy negative electrode materials of Ni/MH batteries, the design and preparation of a kind of rectangle Ni/MH battery with a larger capacity used for vehicular power, and a new method of the cycle life estimation in terms of the internal pressure characteristic of Ni/MH batteries.The electrochemical techniques of encapsulating the amorphous nickel-nonmetal alloy on the surface of hydrogen-storage alloy electrode or hydrogen-storage alloy powder was used in this paper. The surface component of encapsulated nickel-hydride electrodes was measured by energy dispersive analysis of X-ray (EDX), and the analysis of X-ray diffraction (XRD) confirmed that the prepared nickel-nonmetal alloy, such as Ni-S alloy, on the electrode surface had amorphous structures. The electrochemical measurements showed that the large current discharge performance and the stability of cycle life of treated electrodes were improved, and especially, the self-discharge of treated electrodes received an obvious abatement. The related theoretical analysis was given according to the analytical results of electrochemical impedance spectroscopy (EIS), Cyclic Voltammetry (CV), and X-ray photoelectron spectrum (XPS).The internal pressure variations of different Nickel-metal hydride batteries were studied. A DNY-2 was specially designed to measure indirectly the pressure inside the battery shell without damage to any battery parts. The internal pressure variations were simulated by the Boltzmann function when the batteries were charged with a low current density. The parameters in the simulating function have definite physical meanings, and a special parameter k, which is the variability of internal pressure with the charge state or the charge time of the battery in the region of inflexion of this simulation function can be used to estimate the cycle life of batteries. The result shows that batteries with a smaller k value have a longer cycle life.The rectangle Ni/MH battery with a larger capacity of 100 Ah used for vehicular power was designed and prepared. The effects of materials and structures of positive and negative electrodes, the composition of electrolyte, parts of battery, the initial charge / discharge processes, and the select method of Ni/MH batteries on the battery performances were studied. Besides, the tests of charge or discharge with a large current, the cycle life and safety of prepared battery have been finished, and the simulation and run-in tests of electric vehicles also have been done successfully. The results showed a power density of 75 Wh/Kg, cycle numbers of 1000 at a current of 1/3C for the prepared 100Ah battery with foam nickel negative electrodes and sintered positive electrodes. The electric car with the prepared battery was able to run about 300 km at a speed of 40 km /h.