Nail Penetration of Small Pouch Cells under Water: Investigation of Hydrofluoric Acid Formation in Dependence of the State of Charge

Abstract

Accidental damage to electric vehicle batteries can poses an unknown safety risk and, as such, they are placed in a container filled with water. The present study investigates the extent to which a battery stored under water may still react in the case of an event. The focus of this study was to find out if hydrofluoric acid (HF) is formed after nail penetration of small lithium-ion battery cells under water. Three different states of charge (SoC) were examined: 0%, 50%, and 100%, to determine how strongly HF formation depends on this parameter. The test was repeated three times at each SoC level. The highest formation of HF was found at a SoC of 100%. Despite the use of the same cells, the same and mostly automatically procedure, a high variation of fluoride concentration was observed for 100% SoC. The cells with a SoC levels at 0% and 50% showed quite low fluoride concentrations. Overall, it was concluded that the low reactivity of the cells was caused by the surrounding water.