Performance degradation and failure characterization of Li-ion batteries in hearing aids: Insights from field data

Lithium-ion batteries (LIBs) are widely used due to their high energy density, power density, and low selfdischarge rates, powering applications from portable electronics to electric vehicles. However, despite technological advances, LIBs face challenges in reliability and performance, particularly if used in devices exposed to climatical stress. Devices like hearing aids (HAs), which benefit from miniaturization and LIB technology, are vulnerable to electronic corrosion due to their exposure to harsh conditions, which could influence LIBs charging and discharge characteristics if power management circuits malfunction. This has led to critical reliability issues on electronic devices and LIBs used in hearing aids. This research investigates LIB failure modes in field failed batteries used in hearing aids through electrochemical techniques and imaging methods. Cyclic testing was utilized to replicate failures by stressing new batteries to study the effects of electronic corrosion. The results showed that a high discharge current and deep depth of discharge, due to exposure conditions, can accelerate the battery degradation, leading to increased capacity and power fade. The field-failed batteries showed reduced discharge capacity and reduced electrochemical performance due to the increased internal resistance (fx. microcrack formation on electrodes, loss of lithium inventory) and an increased barrier to electron transfer (fx. SEI layer growth) and slower electron transfer reactions. The findings highlight the risk of electronic corrosion on components in power management circuits, which can compromise the reliability of LIBs in hearing aids.