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Various operational parameters such as charge/discharge rates, relaxation periods, and depth of charge and discharge play an important role in enhancing the cycling life of Li-ion batteries. Providing batteries with a relaxation period after discharging and charging might be essential for removing concentration gradients generated due to passage of current. In the present work, the effect of providing open-circuit time durations after completion of each charge and discharge over the performance of Li-ion cells has been analyzed and quantified. It is shown that relaxing the cell after discharge has significant influence over cell performance, whereas relaxation after charge has a marginal effect. In the former case, a relatively thicker film forms at the solid-electrolyte interface in the negative electrode. Moreover, providing a sufficiently long relaxation to the cell at the end of discharge results in (a) a higher concentration of lithium in the solid matrix of the negative electrode and (b) a lower concentration of lithium in the positive electrode, both leading to a higher cell potential during the discharge phase of the subsequent cycle. Charging the cell following a relaxation period of more than one hour at the end of discharge results in a better utilization of cyclable lithium. Diminishing fossil fuel reserves have made it imperative to develop alternative energy sources to power automotive vehicles. Many researchers have focused their attention toward sources such as biomass, solar, wind, fuel cells and batteries [1][2][3] to accomplish this requirement. By virtue of their lower fuel consumption, silent operation and zero emissions, battery powered vehicles (such as hybrid and electric) offer a substitute to gasoline-fuelled vehicles. 4 In the last decade, Li-ion batteries (LIBs) have been used extensively as power sources for many small and portable electronic devices such as mobiles, camcorders, PDAs, laptops, digital cameras and other communication devices. However, these portable electronic devices require a very low current. For high power applications, such as electric, hybrid-electric and plug-in hybrid-electric vehicles, a higher current is required. This puts limitations on the use of LIBs as power sources in these scenarios since their capacity decreases rapidly at high discharge rates. 5Several studies have focused their attention toward enhancement of battery performance in terms of energy and power density. In this regard, various combinations of electrode/electrolyte materials have been used with different operational and design parameters to minimize the capacity fading of Li-ion cells.5-9 Mesocarbon Microbead (MCMB) has been used commercially as an anode material due to its high reversible capacity, while it has limitation of film formation at solid electrolyte interface (SEI).10,11 Whereas in common cathode materials, manganese oxide is used as it is abundant, cheaper and environmentally friendly in nature. Moreover, use of manganese oxide as cathode material minimizes safety issues a...

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In this study, a mathematical model to investigate the combined effect of SEI film formation and gas evolution over the degradation of Li-ion cells is developed. A Li-ion cell is simulated for three discharge/charge rates until 80% of the rated capacity is irreversibly lost in side reactions. The model shows that the thickness of SEI film and volume of gases evolved is between 0.03-0.22 μm and 1.6-10.6%, respectively. It is shown that, in addition to greater diffusion limitations, capacity degradation at higher cycling rates is faster due to reduction in cyclable lithium caused by its accumulation in the negative electrode.