Study On The Characterization Method For Ni-MH Batteries Performance

Nowadays, MH-Ni batteries have been served as important resource for various equipments, such as electric vehicle,portable computers and mobile telephones. Cycle life is one of the most important parameters of MH-Ni battery and is also considered as one of significant standards of evaluating battery performance. It is so difficult to accurately test battery's cycle life if we do not destroy the battery that there is practical significance for researching a method of forecasting the battery's cycle life.In this experiment, the variation of inner pressure of Ni-MH battery concerning different electrolyte quantity and different ratio of anode/cathode materials in batteries is measured by inner pressure testing apparatus, when batteries are being charged at different current densities. By measuring the change of inner pressure in battery on the condition of charging up and placement, the variation of inner pressure of battery along with charging time is mathematically disposed and function relationship between them is confirmed. The physical meanings of eigenvalues of the function are analyzed. At last, a new method of evaluating battery performance has been established from the relation of eigenvalues and cycle life.Our experiment display that it is unsuitable and unilateral of evaluating battery performance (especially cycle life) simply by utilizing the value of inner pressure of battery. The trend of inner pressure of the whole process of charging must be analyzed. The inner pressure curve which tested by charging batteries at small current density, can be simulated by Boltzmann function and the physics meaning of mathematical model has been explained. It is found that the eigenvalue k has certain relationship with cycle life of MH-Ni battery: the larger the value of k, the faster the inner pressure increases and the shorter the cycle life. At end of the experiment, the model is used to simulate inner pressure curves of batteries of which cycle life has ended. After simulating, it is showed that the value of k is larger than that of new batteries. Therefore, this experiment can displayed that Boltzmann function can figure variation of inner pressure of Ni-MH battery when batteries are being charged at small current densities, and this function is to some extend feasible to forecast cycle life of MH-Ni battery.