Study on the failure mechanism and thermal safety of nickel-cobalt-manganese ternary lithium-ion cells after float-charging at different voltages
Ternary lithium-ion cells,recognized for their superior electrochemical properties,are extensively utilized in the energy storage sector.This research uses commercial 18650 lithium nickel-cobalt-manganese(NCM)/graphite cells as experimental samples to explore the effects of float-charging at 4.2,4.4,and 4.6 V.We conducted a series of analyses including capacity tests,incremental capacity analysis,and impedance tests,complemented by X-ray diffractometry(XRD),X-ray photoelectron spectroscopy(XPS),and scanning electron microscopy(SEM)of electrode materials from disassembled cells.The influence of float-charging on thermal safety of NCM cells was studied through the accelerating rate calorimeter(ARC)test.Our findings indicate that higher float-charging voltages accelerate cell aging,with an average capacity loss rate of 1.166%/day at 4.6 V.Float-charging at elevated voltages intensifies the interface reactions between the electrolyte and electrode,resulting in a thicker solid electrolyte interface(SEI)film and a substantial increase in impedance.Furthermore,it induces corrosion of the positive collector,leading to aluminum precipitation and deposition at the negative electrode,which further accelerates the capacity attenuation.The onset temperature of self-heating(Tonset)of the cells is reduced after float-charging,indicating a decrease in thermal safety.Through float charging process analysis,failure material characterization,and thermal runaway experiments,this study provides theoretical insights and technical guidance on the impacts of float-charging on the electronic and thermal safety performance of lithium-ion cells.
lithium ion cellfloat-chargingthermal runawayfailure mechanismthermal safety
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