Quantifying capacity losses due to solid-electrolyte interface formation*

Understanding the origins of failure and limited cycle life in lithium-ion batteries (LIBs) requires quantitative linking capacity-fading mechanisms to electrochemical and chemical processes. This is challenging in real systems where capacity is lost during each cycle to both active material loss and solid electrolyte interphase (SEI) evolution. In this talk, I will describe the model system-based approach that we have adopted that combines precision electrochemical measurements of the Coulombic efficiency (CE) and x-ray measurements of the SEI layer and active materials loss. By contrasting these independent quantities, we obtain insight into the SEI growth and evolution. I will discuss how we have used X-ray reflectivity (XRR) to obtain nanoscale insight into solid electrolyte interfaces (SEI) on model anode surfaces that implicate electrochemically formed LiF as playing a major functional role in the SEI. I will also describe how XRR tracks the thickness of a-Si thin films and when this is compared to the CE, we can quantify SEI growth over several cycles. The methodology we are adopting allows to quantitatively track the desirable and undesirable electrochemical processes.