An electro-thermal approach for improving safety in lithium iron phosphate batteries

Abstract

The growing shift towards clean energy has increased the demand for electric vehicles and energy storage systems powered by lithium-ion batteries (LIBs). Overheating and internal resistive heating can trigger thermal runaway (TR). This study develops an electro-thermal analysis combining impedance spectroscopy and calorimetry to predict safe LIB operating zones and prevent thermal explosion. Frequency-resolved impedance parameters, obtained via equivalent circuit fitting, are converted to Joule heating and combined with calorimetrically measured exothermic heat rates to determine total heat generation across SOC and temperature ranges. A 20 mm LIB coin cell, fabricated from electrodes of a commercial 85Ah cell, with lithium iron phosphate (LFP) cathode and silicon–carbon nanocomposite (SCN) anode was tested. Impedance analysis indicates that charge-transfer resistance dominates over ohmic resistance, and its variation with SOC (0–100 %) follows a non-monotonic trend, which directly influences the Joule heating behavior over frequency range of 0.1 Hz–100 kHz. High capacitance at SOC >75 % improves charge buffering, reducing localized heating and TR risk. Joule heating varies non-monotonically with temperature, revealing two critical temperatures and underscoring the need for careful impedance diagnostics. The proposed safety prediction model quantifies the critical heat removal required to avoid exponential thermal escalation, offering a practical tool for advanced LIB safety management.