Improving Precision and Accuracy in Coulombic Efficiency Measurements of Li-Ion Batteries

In order to develop Li-ion batteries with improved lifetimes, a means of quickly and accurately estimating battery life is required. The use of coulombic efficiency (CE) is an important tool which provides a way to quantify parasitic reactions occurring within cells. As more stable battery chemistries are developed, the rates of parasitic reactions become smaller and differences in CE among cells with different electrolyte additives become increasingly smaller. In order to resolve these differences, charger systems must be developed which can measure CE with increased precision and accuracy. This paper investigates various ways to improve the precision and accuracy of CE measurements. Using the high-precision charger (HPC) at Dalhousie University (built in 2009) as a starting point, a new prototype charger was built with several modifications to the design of the existing HPC. The effect of each of these modifications is investigated in detail to provide a blueprint for the development of next-generation charger systems. This prototype charger shows greatly improved precision and accuracy, with CE results that are approximately four times more precise than those of the existing HPC and over an order of magnitude more precise than high-end commercially available charger systems.