Charging operation with high energy efficiency for electric vehicle valve-regulated lead-acid battery system

A new, high-energy-efficiency charging operation with as little amount of overcharge as possible is proposed to improve the energy efficiency and the cycle life for an EV valve-regulated lead-acid battery. Under this operation, the EV battery system is charged with 105% of amount of the preceding discharge five out of six times and once with 115% in order that it is fully charged. The cycle lives were estimated using a valve-regulated lead-acid battery system of 12 modules connected in series, by SFUDS79 pattern discharging and measurement of the amount of discharge every 50 cycles. Three-step constant current charging with 115% of amount of the preceding discharge required more than 5 h with the final charging step of more than 210 min, with coulomb efficiency of only 87% and energy efficiency of 74%. On the other hand, under the high-energy-efficiency charging operation, three-step charging with 105% shortens the final charging time to 132 min. It was completed in less than 4 h with coulomb and energy efficiency of 95% and 84%, respectively. This operation increased the energy efficiency from 74% to 83% on average in six chargings, and extended the cycle life by about 30% to more than 400 cycles. Decreasing the amount of charge by as much as possible suppressed the corrosion of the grids in the positive plate and the heat evolution in batteries due to shortening of the final charging step. Although the high-energy-efficiency charging operation led to the accumulation of inactive PbSO4 at the upper part of the negative plate, possibly due to the decreasing amount of overcharge, this operation could prolong the cycle life. Full charging once every six times is though to be effective in suppressing degradation caused by the accumulation of inactive PbSO4 in the negative plate due to the shortage of charge. (C) 2000 Elsevier Science S.A. All rights reserved.