Gas Evolution Kinetics in Overlithiated Positive Electrodes and its Impact on Electrode Design

Increasing lithium contents within the lattice of positive electrode materials is projected in pursuit of high-energy-density batteries. However, it intensifies the release of lattice oxygen and subsequent gas evolution during operations. This poses significant challenges for managing internal pressure of batteries, particularly in terms of the management of gas evolution in composite electrodes-an area that remains largely unexplored. Conventional assumptions postulate that the total gas evolution is estimated by multiplying the total particle count by the quantities of gas products from an individual particle. Contrarily, this investigation on overlithiated materials-a system known to release the lattice oxygen-demonstrates that loading densities and inter-particle spacing in electrodes significantly govern gas evolution rates, leading to distinct extents of gas formation despite of an equivalent quantity of released lattice oxygen. Remarkably, this study discoveres that O₂ and CO₂ evolution rates are proportional to ¹O₂ concentration by the factor of second and first-order, respectively. This indicates an exceptionally greater change in the evolution rate of O₂ compared to CO₂ depending on local ¹O₂ concentration. These insights pave new routes for more sophisticated approaches to manage gas evolution within high-energy-density batteries.