The Role of Gas Evolution in Particle Surface Cracking in Nickel-Rich Lithium-Ion Cathode Materials

Abstract

Nickel-rich layered oxide cathode materials (LiNixTM(1-x)O2 where x > 0.8) are of great interest because they offer increased capacity compared to current commercial materials while maintaining compatibility with supply chain and production processes already in place. However, recent studies have shown that these materials in their current form are unsuitable for commercial applications due to the accelerated degradation caused by replacing more stable transition metals with the relatively unstable nickel. While various strategies have already been proposed to mitigate this issue, the fundamental degradation mechanism still needs to be better understood to inform the design of the next generation of nickel-rich cathode materials. In this work, differential electrochemical mass spectrometry (DEMS) is combined with titration mass spectrometry (TiMS) to measure gases evolved in a lithium half-cell during cycling as well as surface species which evolve gas upon addition of strong acid to an extracted cathode. Along with qualitative observations of particle cracking by scanning electron microscopy (SEM), these results reveal correlations between particle cracking, electrolyte reactivity, and carbonate oxidation and deposition on the changing cathode surface in nickel-rich cathode materials.