A whole-process safety evaluation framework of lithium-ion batteries integrating multi-dimensional characteristics: Focusing on initial thermal hazards and derived emission hazards

The in-depth exploration of the multi-dimensional disaster-causing mechanisms associated with battery thermal runaway facilitates the whole-process safety evaluation. However, the still insufficient understanding of the thermal failure process and the limited dimensionality of the existing evaluation indexes subsequently lead to ineffective prevention and control and finally result in a high frequency of severe damage and unforeseen casualties. To address this issue, a general framework for evaluating the whole-process safety by integrating thermal and gas perspectives, involving dozens of multi-dimensional characteristic parameters obtained by experimental measurements and theoretical calculations, is proposed. Based on this framework, comparing the initial thermal hazards of lithium iron phosphate and nickel-cobalt-manganese lithium-ion batteries and quantifying the derived hazards of single-phase/multi-phase emissions considering battery venting gases and electrolyte solvent vapors, the significant hidden hazards of emissions dominated by reductive components that can lead to higher derived explosion and combustion risks within the external environment are identified, effectively updating the previous paradigm for evaluating cell-level thermal safety. For single-phase emissions with dominant reductive components, higher risks of low lower explosion limit and high laminar burning velocity are demonstrated; after considering typical solvent vapor types (dimethyl carbonate/ethyl methyl carbonate/diethyl carbonate) and specific mixing ratios, highly reductive multi-phase emissions still exhibit higher risks. The proposed framework reveals the underlying effect of the reductive gas-phase emissions in accelerating and aggravating system-level thermal hazards, providing important guidance and inspiration for the whole-process safety control based on gas-phase atmosphere regulation as well as for the overall safety evaluation of emerging battery material chemistries.