Thermal Runaway of a Commercial 18650 Li-Ion Battery with a NCA Cathode - Impact of SOC and Overcharge

Li-ion batteries excel in energy density and cycle life. Unfortunately those benefits come with a price: When Li-ion batteries are mistreated with high over-temperature or strong overcharge, they can transit into a so-called thermal runaway(TR). During the TR, exothermic reactions increase the temperature. In turn, the increased temperature accelerates those reactions and the system destabilizes. At the end of the TR, battery temperatures higher than 900°C can be reached and high amounts of burnable and harmful gases are released.

We examined the TR characteristics of a commercially available 18650 cell made by a well known manufacturer. This cell is based on Li_x(Ni_0.80Co_0.15Al_0.05)O₂cathode and has energy density of 254Wh/kg. Destructive temperature-ramp experiments with discharged, partially charged as well as fully charged and over-charged cells were done. Additionally, we dismantled one cell to make a mass split and to identify the compositions of the cell components.

In the presentation correlations between SOC and the TR parameters (onset temperature, max. temperature, amount of produced vent-gas, vent-gas composition) will be shown. An attempt will be made to rationalise the amount and composition of the vent-gas with a simplified chemical reaction system.

We hope that the results of this work can aid the industry to enhance the safety of battery driven devices and to find appropriate mitigation measures for some of the battery abuse scenarios.