Ultrasonic inspection of lithium-ion batteries to determine state of charge, state of health, and battery safety

Accurately estimating state of charge (SOC), state of health (SOH), and other metrics of battery safety remains a challenge for lithium ion batteries outside the laboratory, where one may use techniques such as X-ray diffraction, electrochemical impedance spectroscopy, or neutron imaging. Existing in situ methods to estimate SOC and SOH employ voltage monitoring or Coulomb-counting. Unfortunately, these methods remain inaccurate because they assume a battery capacity or voltage per discharge, while capacity and voltage are known to vary with C-rate and cycle age. The present work explores the viability of interpreting SOC, SOH, and safety metrics by monitoring and interpreting ultrasonic signals propagating through a battery as it is cycled between charged and discharged states in various environmental conditions. Of specific interest are cases where a battery enters dangerous operating conditions which lead to the formation of gases within the battery as well as increases in internal temperature, pressur...