Overlooked Solid Electrolyte Interphase Destabilization by Oxygen Gas Crossover in High-Energy Lithium-Ion Batteries

The pursuit of high-energy-density lithium-ion batteries (LIBs) through high-capacity cathodes (e.g., Ni-rich oxides, lithium-rich manganese oxides) is inevitably accompanied by lattice oxygen release and gas evolution, yet the systemic impacts of oxygen crossover in full-cell configurations remain underexplored. This study investigates how oxygen gas permeation across separators triggers capacity degradation in LIBs. By regulating separator permeability and employing differential electrochemical mass spectrometry (DEMS), we quantify oxygen transport pathways and their correlation with interfacial instability. Combined with cryogenic transmission electron microscopy and atomic force microscopy, we reveal that cathode-derived oxygen penetrates separators, attacking the anode to exacerbate heterogeneous solid electrolyte interphase (SEI) growth and mechanical destabilization. Continuous SEI fracture-reconstruction during cycling accelerates active lithium depletion and capacity fading. Employing low-permeability separators can effectively mitigate oxygen crossover and double the cycle life through stabilization of the anode interface. These findings establish oxygen gas crossover as one of the critical yet overlooked degradation vectors, bridging the knowledge gap between cathode oxygen release and anode failure mechanisms.