Thermal safety assessment of commercial cylindrical lithium-ion batteries by means of Accelerating Rate Calorimetry (ARC), comparing different cathode materials

Cylindrical lithium-ion batteries (LIB) of type 21700 have multifaceted usage applications, such as consumer goods, battery electric and hybrid electric vehicles. In consequence, their safety and the conditions provoking a thermal runaway are of particular interest.
Commercial type 21700 cells with different cathode materials in high power as well as in high energy versions were acquired with capacities ranging from 3 Ah to 5 Ah. Preliminary analysis and characterization of the cells was done by means of electrochemical impedance spectroscopy (EIS) and capacity measurement. Moreover, a composition analysis of the cathode and anode by means of inductive coupled plasma optical emission spectroscopy (ICP-OES), confirmed the composition for NMC, NCA and LFP cells.
Thermal runaway behavior was evaluated by two methods, both using Accelerating Rate Calorimetry (ARC). With the Heat-Wait-Seek (HWS) test thermal abuse was studied and exothermal reaction temperature rates were evaluated and compared for different cathode materials and states of charge of 60, 80 and 100%. In addition, nail penetration tests were performed to evaluate the safety during mechanical abuse by puncturing and short-circuiting the cell with a steel nail that is mechanically introduced into the cell, accompanied by temperature and video recording. ... mehr
It was found that thermal runaway behavior differs between cathode materials and between high power and high energy cells. Between NCA and NMC cells the difference for thermal abuse is small and mainly at lower self heating rates, NMC cells have an earlier onset, voltage drop and cooling temperature by about 20 °C than NCA cells. LFP cells have a much different thermal runaway behavior and reach the same temperate rates at temperatures that are more than 40 °C higher than for the NMC and NCA cells This is the case both for thermal and for mechanical abuse.
Thermal runaway depends on the state of charge of the cells, the higher the SOC, the more reactive the cell, reaching critical conditions at lower
temperatures, this was most clearly observed for NCA cells and for both thermal and mechanical abuse.
Further analysis by means of Accelerating Rate Calorimetry (ARC) will consist of adiabatic cycling tests and the usage of a thermal camera during nail penetration experiments in order to study the temperature distribution.