Diaphragm fiber bragg grating sensors for in situ monitoring of internal gas pressure in lithium-Ion batteries during cycling and overcharge to thermal runaway

Malfunctions within battery management systems (BMS) may result in lithium-ion batteries (LiBs) experiencing overcharging, potentially initiating thermal runaway, and causing serious safety hazards. Therefore, early recognition of thermal runaway under overcharging conditions remains essential. The present study introduces a diaphragm-type fiber Bragg grating pressure sensor (DFBGS-P) to continuously monitor internal gas pressure inside LiBs. The sensor is installed through laser welding into a high-capacity 280 Ah prismatic battery, providing a wide measurement range between −0.1 and 4 MPa with a pressure sensitivity of −0.3788 nm/MPa and an expanded uncertainty of 0.01 MPa (k = 2), and aligning with typical battery manufacturing protocols. The embedded sensor demonstrates excellent electrochemical compatibility in lithium-ion batteries, the capacity decreases by 0.33 %, with the coulombic efficiency maintained above 99.8 % over 50 cycles. The sensor exhibits electrochemical stability over 50 cycles, reflecting the progressive mechanical changes within the battery. Experimental results verify the sensor’s effectiveness in tracking pressure fluctuations of approximately ±0.15 MPa induced by electrode expansion and contraction during standard charge-discharge cycling. During the overcharge stage, a critical threshold pressure of 1.34 MPa and a pressure change rate 0.39 MPa/s can serve as an early warning signal for thermal runaway, preceding external temperature indications. This technology presents a novel approach for improving safety diagnostics in lithium batteries and reducing the risk of operational failure.