Development of a Test Methodology to Design an Overnight Charging Profile to Reduce the SOH Degradation Rate of Li-ion Batteries

Recent focus on fast charging of Li-ion power sources used in wearable and portable consumer electronics products has given rise to the development of charging topologies to charge the battery to a greater extent in the shortest-time period possible. Moreover, research on battery chemistries which are compatible for being charged with a higher current is also on the rise. The tradeoff of charging the battery with a higher current is that the lifespan of the battery reduces drastically as the battery state of health degrades rapidly. To alleviate this, there has been an emergence of a special kind of slow battery charging, wherein the electronic product is charged overnight, when it is not in use, with a low current. This paper proposes a testing methodology of developing an overnight charging protocol for Li-ion battery by following certain salient principles of battery charging and its usage. The charge current is the primary variable which has been investigated in this study. Moreover, SOH of a Liion battery degrades rapidly if it is stored at a higher state of charge (SOC) for a longer period of time. This occurs if a battery is charged overnight using a regular charge profile i.e. a battery is charged completely in an hour and is kept at that condition for four to five hours. To avoid this, the battery charging is interrupted at certain SOCs for a given amount of time so that its storage time at a higher voltage is minimized. Thus, several combinations of interrupt SOCs and times have been experimented with to determine which one results in the least degradation. Finally, after experimentation with these parameters, an overnight charging profile is developed for reduced SOH degradation rate.