Safety of Li-Ion Cells and Batteries at Various States-of-Charge

Abstract

With the increase in demand for li-ion batteries in the wide variety of applications they are used in today, billions of cells and thousands of batteries are manufactured every month. The challenge arises when every single cell and battery should be tested before they are shipped out to assure that the cells are manufactured with a high quality and the batteries were assembled and tested to high standards and that they were not subjected to any off-nominal conditions during the manufacturing or testing process. This challenge has led to concerns in several sectors such as the shipping and transportation industry. This led the ICAO to set temporary bans on the shipment of Li-based cells and batteries as cargo in passenger and cargo aircraft, with a restriction of the state of charge of a li-ion cell or battery to not exceed 30%. The safety of li-ion cells and batteries at various states of charge have not been studied comprehensively in the past and hence the goal of this study was to determine if the result of an off-nominal condition would vary with varying SOC. Cells of different form factors (18650, 26650, and pouch), cathode chemistries (NCA, NMC, and LFP), capacities (2.5-10Ah), and quality (based on nominal price and inexpensive) were studied under this program. Battery designs were also studied. To characterize the behavior under off-nominal conditions, cells and batteries were subjected to two types of tests: heating method using a heating tape, and low impedance external short. In addition to that, the stability of charge retention was studied at the various SOCs. The results of this comprehensive study will be presented.