Decoupling the Failure Mechanism of Li-Rich Layered Oxide Cathode During High-Temperature Storage in Pouch-Type Full-Cell: A Practical Concern on Anionic Redox Reaction

In addressing the global climate crisis, the energy storage performance of Li-ion batteries (LIBs) under extreme conditions, particularly for high-energy-density Li-rich layered oxide (LRLO) cathode, is of the essence. Despite numerous researches into the mechanisms and optimization of LRLO cathodes under ideal moderate environment, there is a dearth of case studies on their practical/harsh working environments (e.g., pouch-type full-cell, high-temperature storage), which is a critical aspect for the safety and commercial application. In this study, using pouch-type full-cells as prototype investigation target, the study finds the cell assembled with LRLO cathode present severer voltage decay than typical NCM layered cathode after high-temperature storage. Further decoupling elucidates the primary failure mechanism is the over-activation of lattice oxidized oxygen (aggravate by high-temperature storage) and subsequent escape of oxidized oxygen species (Oⁿ⁻), which disrupts transition metal (TM) coordination and exacerbates electrolyte decomposition, leading to severe TM dissolution, interfacial film reconstruction, and harmful shuttle effects. These chain behaviors upon high-temperature storage significantly influence the stability of both electrodes, causing substantial voltage decay and lithium loss, which accelerates full-cell failure. Although the anionic redox reaction can bring additional energy, but the escape of metastable Oⁿ⁻ species would introduce new concerns in practical cell working conditions.