Keywords lithium-ion battery ultrasound passive probe internal hazard signals Introduction Lithium-ion batteries (LIBs) are widely used in electric vehicles and large-scale energy storage stations.1,2,3 Real-time monitoring of internal signals in LIBs is crucial and challenging due to the metallic casing and chemical corrosion of the batteries.4,5,6 Current methods for monitoring LIBs rely on external signals, including the surface temperature and exterior pressure.