Deterioration estimation of lithium-ion cells in direct current power supply systems and characteristics of 400-Ah lithium-ion cells

Our evaluation of various characteristics of large-capacity 40 Ah and 80 Ah Lithium-ion (Li-ion) cells developed for industrial use shows that these cells exhibit reduced voltage characteristics and increased internal resistance in degraded conditions. We constructed a DC power supply system for telecommunications equipment using 80 Ah Li-ion batteries incorporating a function to estimate the cell status from the voltage characteristics during an automatic discharge of the battery. The Li-ion batteries in this system are maintained by a floating charge method, and we miniaturized the battery unit. In a field trial test lasting approximately 2 years, this DC power supply system performed well inclusive of the automatic discharge. The specifications and characteristics of prototype 200 Ah and 400 Ah cells, which were assembled to expand the application areas of Li-ion cells, are shown. Because these cells have similar characteristics to those of current 40 Ah and 80 Ah cells, they can be widely used as a substitute for conventional valve-regulated lead-acid (VRLA) cells. (C) 2008 Elsevier B.V. All rights reserved.