Deciphering the liquid-solid interactions in dealkalization of O3 layered oxides

O3-phase layered oxides are among the mainstream positive electrode active materials for advanced batteries due to a stable topological lattice framework and potential for tunability. However, surface residual alkali due to sensitivity hinders their large-scale application. Water washing, an industrial surface residual alkali removal method in lithium-based positive electrode materials, brings about severe issues in sodium-based materials, such as lattice collapse and extensive active alkali metal ion leaching. Here, we propose an interaction mechanism between host solid-phase positive electrode materials and guest liquid-phase solvents, which elucidates the dependent structural degradation on the molecular configuration of dispersed solvents and the alkali metal-oxygen bond covalency during dealkalization. For H₂O (H₃O⁺), self-propagating molecule intercalation into Na slabs and subsequent protonation induce the leakage of Na ions, leading to lattice destabilization. In contrast, the efficient dealkalizing agent-ethylene glycol-prevents further structural degradation due to the constraint of size effect. Based on the time-dependent deterioration of the extended scope of positive electrode materials, an adaptable analytical framework is established for stability assessment against the liquid phase. Our work provides fundamental theoretical guidance for liquid-phase engineering of O3-phase layered oxides.