To make accurate measurements, field mills must be calibrated in a known DC electric field space charge in which the quantities can be control1ed. A simulation model of the generation apparatus of the electric field with a space charge has been built. Based on the combination of the electric field and the transfer of a dilute substances model, the influence of openings in the metal screen was calculated. Simulation results showed that the opening size of the high-voltage electrode has a great influence on the distribution of the electric field and ion density at the calibration zone. Next, a generation apparatus was designed and developed and ion mobility was researched. The experimental results showed that ion mobility decreased with an increase in electric field strength. However, ion mobility tends to be saturated when the electric field reaches a certain critical value. Two fitting formulas of ion mobility of positive and negative charge are proposed that can be used to predicate ion mobility in a high electric field.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Summary
Thermal runaway is the most dangerous failure faced by lithium‐ion batteries (LIBs). In this paper, ethylene (C2H4), methane (CH4), and carbon monoxide (CO) were selected as the characteristic gases, the cantilever‐enhanced photoacoustic spectrometer was adopted as the gas detector, and a thermal runaway early warning system for LIBs was built based on characteristic gas sensing technology. After a series of repeated experimental calibrations and tests, the effectiveness of the thermal runaway warning system for lithium nickel cobalt manganese oxide (NCM) LIBs was verified. The experimental results show that the average warning times of the thermal runaway warning system were 7.3 and 11.5 min, respectively, for NCM LIBs with a state of charge of 50% and 100%. The warning times of the established system can meet both the requirements of the Chinese national standard GB 38031‐2020 and the United Nations global technical regulation ECE/TRANS/180/Add.20. Thus, the thermal runaway early warning system proposed in this paper can gain more time for the fire management of the NCM LIB system and the safe evacuation of personnel.
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