Acid treatment at 0°C of solid solutions yields delithiated well crystalline oxides which do not contain protons. For the nearly stoichiometric nickel‐rich oxides, removal of more than 20% of the lithium leads to a monoclinic distortion of the rhombohedral unit cell. Electron paramagnetic resonance (EPR) of low‐spin Ni3+ ions shows that for up to 0.2 extracted lithium, the generated Ni4+ ions are statistically distributed in the layers while above 0.2 extracted lithium the Ni4+ ions trend to order. During acid delithiation the oxidation of Ni3+ to Ni4+ ions proceeds prior to the oxidation of Co3+ to Co4+ as for a nonaqueous electrolyte. Discharge‐charge cycles of lithium cells using acid‐delithiated oxides as cathode materials show a significant improvement of reversibility compared with the charge‐discharge cycles of the corresponding pristine samples.