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Nanoscale δ′/θ′/δ′ composite precipitate, as another important strengthening phase in the latest generation of Al–Li alloys, exhibits excellent resistance to coarsening. Here, we propose two thickening models for an anomalous δ′/θ′/δ′ that is discovered recently, by analyzing various influencing factors, including the static energy barrier, aging temperature-dependent nucleation conditions, and the elastic distortion suffered during growth. It indicates that the thickness of the δ′/θ′/δ′ composite precipitate seems to depend on the nucleation of the δ′. At elevated aging temperatures, θ′ precipitates can grow and thicken rapidly until the δ′ nucleates on them. This is strikingly different from the dislocation-induced growth mechanism. Subsequently, we propose a vacuum-added methodology to accurately extract the interfacial energy. The results show that this nano-composite precipitate can …