The current exploration of high-energy-density cathode materials for Li-ion batteries is mainly concentrated on either so-called “Li-rich” or “Ni-rich” oxides. However, both are suffering from formidable practical challenges. Here, we combine these two concepts to obtain “Li-rich Ni-rich” oxides in pursuit of more practical high-energy-density cathodes. As a proof of concept, we synthesized an array of Li1+yNi(3−5y)/3Mo2y/3O2 oxides, whose structures were identified to be the coexistence of LiNiO2-rich and Li4MoO5-rich domains with the aid of XRD, TEM, and NMR techniques. Such an intergrowth structure of 5–20 nm size enables excellent mechanical and structural reversibility for the layered rock-salt LiNiO2-rich domain upon cycling thanks to the robust cubic rock-salt Li4MoO5-rich domain enabling an “epitaxial stabilization” effect. As a result, we achieved high capacities (>220 mA h g−1) with Ni contents as low as 80%; the Li1.09Ni0.85Mo0.06O2 member (y = 0.09) shows much improved cycling performances (91% capacity retention for 100 cycles at C/10) compared with pure LiNiO2. This work validates the feasibility of constructing Li-rich Ni-rich compounds in the form of intergrowing domains and hence unlocks vast possibilities for future cathode design.