Lithium-Ion

Surface Oxygen Drives Electrolyte Degradation at Ni-rich Battery Cathodes Gassing observation: the detection of gaseous species evolving from an operating LIB with chip-based electrochemistry mass spectrometry is demonstrated to observe O2 evolution from a NMC811 cathode and electrolyte solvent degradation to CO2 and CO Degradation mechanism: isotopically labelled NMC is investigated to monitor where lattice oxygen is incorporated into electrolyte oxidation products, which identifies a previously unobserved deleterious catalytic CO oxidation mechanism

ONCHIP ELECTROCHEMICAL MS

Observation of isotope-labelled O2 provides concrete evidence that molecular oxygen is released from the NMC811 lattice at potentials greater than 4.3 V

An EC-free electrolyte was tested with 18O-labelled-NMC811 vs. Li. The O2, CO2 and CO evolution rates during this cycling can be seen, showing no CO2 (nor CO, nor O2) during the 4.0 V vs. Li potential hold, unlike with EC

DEGRADATION MECHANISM

The identified catalytic CO oxidation mechanism drives the removal of oxygen from the cathode lattice. Given that CO is reported to evolve from numerous processes in LIBs, the presence of such an active species will have significant deleterious effects on the overall performance of the cathode.

Source: I. Stephens et al, Preprint 2025

Extracted from the PDF; charts and images may read imperfectly.