Cell Lifetime Degradation Model Development for Li-Ion Coin Cells considering Calendar Aging and Post-Knee Degradation (Invited)

Lithium-ion batteries are the most popular choice for power sources in the modern consumer electronics products, due to their exceptional specific energy, specific capacity, and other features including long cycle life, high columbic efficiency, and low self-discharge rate. To address the modern and ubiquitous concerns of improving product sustainability and counter supply-chain shortages, understanding battery degradation is pivotal for extending battery life, improving battery materials, and informing end user about device battery health to prompt replacement as needed. Battery health degradation as a phenomenon starts even before the battery is put into use in a device, as the battery capacity degrades during storage (calendar aging); and continues even after its cycling life is completed, wherein the battery experiences catastrophic failure as its health degrades rapidly (knee-point failure). Majority of the models available in literature today focus mainly of estimating battery health during its usage phase. However, it is critical to model battery health in the pre-use phase, to understand the battery health status when its put into use, and even after the battery has experienced knee-point failure to inform the user of the need for urgent replacement. This study proposes a cell lifetime degradation model which addresses all the three aforementioned phases of battery life: calendar aging, cycle aging, and post-knee aging. By testing batteries using different case-specific parameters, battery degradation data has been acquired for different aging stages. This data is then used to build individual models for the three stages which have later been combined to form the cell lifetime degradation model. Moreover, the study provides markers to estimate onset of knee-point failure using battery parameters that can be made accessible to the end user.