Meaning
Highly reactive electronic state of molecular oxygen occurs when the spin of the outer electrons is flipped during electrochemical charging. Liberation of singlet oxygen from the cathode lattice is a major driver of electrolyte degradation in high nickel batteries. This species is far more aggressive than the standard triplet oxygen found in the atmosphere.
It attacks the organic carbonate solvents, leading to the formation of gaseous byproducts and resistive surface films.
Reaction Mechanism
Energy transfer from the delithiated cathode surface provides the stimulus for the formation of this excited state. Because singlet oxygen is short lived and highly localized, it reacts almost immediately with the nearest solvent molecules. This process consumes the electrolyte and reduces the ionic conductivity of the cell over time.
Stabilization Method
Dopants and surface coatings are used to increase the bonding energy of the oxygen within the crystal structure. By suppressing the release of singlet oxygen, these modifications prevent the initiation of parasitic chemical chains. Research into quenchers that can deactivate this species within the liquid phase is ongoing.
Thermal Consequence
Heat is released during the chemical attack on the electrolyte, which can contribute to the self heating of the cell. If the production of singlet oxygen is not controlled, it can lower the threshold for thermal runaway. Managing this reactive species is critical for the development of next generation batteries with higher energy densities.
