The origins of critical deformations in cylindrical silicon based Li-ion batteries

Abstract

A manifold of degradation mechanisms causes premature capacity fade of Li-ion batteries. To understand their origin, we need a detailed diagnosis of battery (mal-)function over time. Here we employ correlative neutron and X-ray imaging to observe microstructural changes over time inside high energy density cylindrical cells and focus on unraveling the causes of localized defects where the silicon-graphite anode becomes damaged. We discover that these defects are due to local silicon enrichments occurring during electrode wet process manufacturing. We identify a threshold defect size beyond which internal cell structure and functioning is compromised, indicating the need for rigorous electrode-slurry quality control to avoid agglomerations above 50 microns. Our study elucidates defect genesis and their criticality, providing opportunities to better predict and mitigate unwanted aging and failure modes.