Surface Degradation of Li-Ion Battery Cathodes from First Principles

For the transition from traditional fossil fuels to environmentally friendly renewable energy, lithium-ion batteries based on nickel- and lithium-rich cathodes could potentially provide the required high energy densities as an efficient energy storage system. However, Ni-rich high-energy-density Li-ion battery cathodes are prone to thermal degradation, which leads to safety concerns and hinders commercial adoption. Degradation typically occurs at the particle surface and involves the release of oxygen gas. To identify stable Ni-rich cathode compositions or surface coatings that can prevent undesired phase transformation, an understanding of the fundamental degradation processes on the atomic scale is needed.

Here, we apply first principles atomistic modeling to shed light on surface reactivity, providing information that is complementary to experimental characterization. The mechanism of the self-reductive decomposition of LiNiO₂ is determined using automated density-functional theory calculations. We construct first principles phase diagrams that map out stable surface phases as a function of the state of charge and the temperature. The results obtained from this analysis allow deducing the degradation mechanism and offer guidance for the development of degradation-stable cathode compositions and improved coating materials.