Identifying degradation mechanisms in lithium-ion batteries with coating defects at the cathode

Understanding the effect of electrode manufacturing defects on lithium-ion battery (LIB) performance is key to reducing the scrap rate and cost during cell manufacturing. In this regard, it is necessary to quantify the impact of various defects that are generated during the electrode coating process. To this end, we have tested large-format 0.5 Ah LiNi0.5Mn0.3Co0.2O2/graphite pouch cells with defects intentionally introduced into the cathode coating. Different types of coating defects were tested including agglomerates, pinholes, and non-uniform coating. Electrodes with larger non-coated surface had greater capacity fade than baseline electrodes, while pinholes and agglomerates did not affect performance adversely. Post cycle analysis of electrodes showed that the anode facing the defective region in the cathode was clearly impacted by the defect. Further characterization using Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction provided evidence for a proposed mechanism for material degradation related to the most detrimental type of coating defect.