Ashok Jhunjhunwala

Li-Ion cell manufacturers do provide some information in relation to their cell performance at different but constant charge/discharge rates and at different and constant temperatures, but hardly any of these can be extended to field conditions, where charge/discharge rates and temperature are continuously varying. This paper attempts to take the primary cell testing data gathered in a lab environment and create a first-order model for battery behavior in real-life conditions. At the same time, real-life data for battery packs in 3-wheeler vehicles are obtained on a continuous basis, when driven or when the battery is being charged. The battery packs used are of 1.25 kWh without any forced cooling, and the vehicles are driven in the city of Chennai in India, where in 24 h, the average temperature varies from 25 °C to 48 °C in summers and from 18 °C to 32 °C during winters. The State of Health estimate obtained from the model (and the lab data for cells) is then compared with actual field data; further variances between the two and possible reasons for such variance are discussed. The results show that with some care, the battery behavior in real-life can be reasonably predicted. This is important as two-wheelers and three-wheelers constitute well over 80 % of India's 300 million vehicles, and when converted to electric, these vehicles would not have any kind of cooling.

It is known that the life of a Lithium-ion (Li-ion) battery is affected by charge/discharge rates, temperature, and depth of discharge (DoD). This paper investigates the effect of temperature and DoD on a 18650 Li-Ion cell. An experiment is set up to analyze the impact of temperature and DoD on the performance of Li-Ion cells. The test temperatures of 25°C and 35°C, whereas DoD of 80% and 90%, are considered for the analysis. The paper aims at studying the effects of these parameters on capacity degradation, discharge energy efficiency, and coulombic efficiency over the cell's lifetime.