A review of ultrasonic monitoring: Assessing current approaches to Li-ion battery monitoring and their relevance to thermal runaway

Li-ion batteries (LIBs) are increasingly used in applications from personal electronics to electric vehicles (EVs) and grid scale storage. Research into LIB monitoring, such as state-of-charge (SOC) and state-of-health (SOH), and the effects of abuse on LIBs has received increased attention to allow for better battery performance and safety. To improve LIB safety better detection of thermal runaway (TR) is required for the mitigation of the associated consequences or to prevent it entirely. This paper reviews the growing field of ultrasound (US) sensing of LIBs for state monitoring and thermal runaway detection, with an additional perspective on of advancements made in thermal runaway testing. In this work, US is categorised by: hardware used in research; application for SOC and SOH monitoring. Further, TR is categorised by abuse scenario: overheating; penetration; overcharging; and gas generation. This review summarises the development of US to detect changes within a LIB. However, it is found that further developments are required to (1) isolate and characterise the various abuse/failure mechanisms using US and (2) decouple temperature and charge effects on the US signal. It is shown that decoupling the temperature-charge relationship within the US signal is necessary for accurate SOC and SOH monitoring.