Nickel-metal hydride batteries (NiMH) are among the most commonly circulated secondary batteries in Germany, following lithium-ion and lead-acid batteries. The raw materials required for their production are intended to be recycled and reused in the context of the circular economy. To achieve this goal, efficient and safe processing methods are necessary.
In this master’s thesis, written as part of the “Ni2Steel” research project funded by the federal state of Styria, the processes leading to the self-heating of NiMH material during mechanical processing are described. To this end, the reaction kinetics of crushed NiMH material with oxygen, water, and carbon dioxide under isothermal conditions are measured in a differential flow reactor.
Additionally, a characterization of the sample material is conducted, including the examination of its chemical composition, heat capacity and conductivity, permeability, and self-heating capability.
The results show that oxygen does not significantly influence self-heating. However, water is adsorbed, leading to a temperature rise in the material due to the released adsorption enthalpy. CO2 reacts exothermically with the electrolyte of NiMH batteries, releasing heat. Consequently, it is advisable to maintain a dry and CO2-free atmosphere during the shredding and storage of NiMH batteries. These findings can also inform the selection of appropriate extinguishing devices.