Traditional temperature and pressure sensors only respond in the middle and late period of thermal runaway. Battery internal failure undergoes SEI decomposition (80\120°C), electrolyte decomposition (120\150°C), pressure rise (150~200°C) and cathode collapse (>200°C). Only EIS can capture subtle impedance changes in the earliest SEI stage, realizing ultra-early warning.

EIS working principle: Apply controllable AC excitation to the battery pack → synchronously collect voltage and current response → calculate impedance amplitude and phase → scan multiple frequencies to form impedance spectrum → correlate with SOC, SOH, temperature and aging state.

This design selects active balancing circuit multiplexing excitation scheme, no additional excitation power stage required. The design supports 0.04Hz~2kHz accurate scanning, with single cell magnitude deviation <2% and phase deviation <1°, having excellent repeatability and SOC/temperature distinguish-ability. The design can be used for thermal early warning, high-precision state estimation and battery batch screening.