Degradation pathways in lithium-ion batteries with ethylene carbonate-free electrolytes

The development of stable electrolyte solutions is critical for improving the lifetime and performance of lithium-ion batteries. Electrolyte instability is a prominent issue with many next-generation electrode materials, such as Ni-rich cathodes, with recent reports identifying ethylene carbonate (EC) as a bad actor at the cathode surface. Herein, electrochemical methods, operando pressure measurements, and post-mortem X-ray and solution NMR studies are combined to investigate electrolyte degradation phenomena in Ni-rich NMC/graphite full cells with EC-containing and EC-free electrolytes. One key finding is that the mechanism for improved performance in EC-free electrolyte arises from improved stability at both electrode-electrolyte interfaces. Suppressed lattice oxygen release and solvent oxidation reactions at the cathode, and hence less formation and cross over of SEI disrupting species, combined with a graphite SEI more resilient towards acid-mediated decomposition, are shown to be important to improve capacity retention. These insights are helpful to understand and mitigate degradation in cells with Ni-rich cathodes.