High valence dopants in nickel-rich battery materials: Where do they go and what do they do?

Selecting and optimizing a cathode active material (CAM) is a crucial step in the layout of a battery when it comes to mass production. Therefore, a fundamental understanding of the impact of each element on the overall chemical compound is needed.

Here, we focus on the establishment of a descriptor model to predict the impact of a dopant introduced into the CAM and the influence on electrochemical properties. We targeted the mechanisms and processes on an atomic scale since computing on this scale provides a better understanding of binding properties and changes in the crystal lattice.

Thereby, we aim to predict changes of the gassing behavior by introducing tantalum as dopant into the here used model system NMC811. Gassing is a driving aging factor in Nickel-rich materials and is mainly impacted by the stability of their structure which can be successfully suppressed by doping. Due to its electronic structure, e.g. its high oxygen binding energy, tantalum is a suitable candidate to gain these insights.

We propose that the oxygen binding energy of a dopant to be correlated with the electrochemical performance since it has a direct impact on structural and electronic properties of the compound. Beneficially, this approach achieves high precision in the calculation of thermodynamic properties without adding excessive complexity. In complementary experimental tests, we could determine an impact on structure and voltage of the doped CAM. Thereby, we could observe a linear behavior in c-parameter in dependence of the tantalum content. Furthermore, tantalum content influences the overall cell potential as the tantalum is octahedral coordinated within the former Ni-sites. In DFT simulations we could confirm the coordination of tantalum by comparing formation energies with experimental data.