Thermodynamic Analysis Enables Quantitative Evaluation of Lattice Oxygen Stability in Li-Ion Battery Cathodes

Oxygen release from Li-ion battery cathodes is a longstanding and serious problem that deteriorates electrochemical performance and triggers thermal runaway. Yet little is understood about the mechanism of the oxygen release process. Herein, we succeed, for the first time, to discuss lattice oxygen stability of LiNixCoyMnzO2 cathodes from experimentally evaluated oxygen release behavior and the partial molar enthalpy of oxygen which reflects the binding energy of oxygen. Combining thermodynamic analysis and X-ray absorption spectroscopy, we revealed that energy for oxygen release by Ni3+ reduction (∼0.5-1.5 eV) is much smaller than that by Co3+ reduction (∼1.8-2.7 eV). Obtained results in this work are well consistent with some reported theoretical calculations and supplement their discussion. The approach demonstrated in this work enables quantitative evaluation of lattice oxygen stability of oxide-based battery materials from the thermodynamics perspective and can provide valuable guidance for advanced high-energy-density and robust batteries.