We report an innovative insertion material of LiAl1/4Ni3/4O2 (R (3) over bar m) which is a solid solution of LiNiO2 (R (3) over bar m) and alpha-LiAlO2 (R (3) over bar m). LiAl1/4Ni3/4O2 (interlayer distance: similar to 4.75 Angstrom) shows an overcharge-resistant character due to the formation of an insulator of square(3/4)Li(1/4)-Al1/4Ni3/4O2 having similar to 4.8 Angstrom of interlayer distance. Cycle tests of an Li/LiAl1/4Ni3/4O2 cell between 2.5 and 4.5 V show no noticeable loss in rechargeable capacity (similar to 150 mAh g(-1)). The thermal behavior of Li1-xAl1/4Ni3/4O2 (0 less than or equal to x<< 3/4) is also examined by differential scanning calorimetry and shows that the exothermic reaction of Li1-xAl1/4Ni3/4O2 with electrolyte is remarkably suppressed even for the fully charged state when compared with that of Li1-xNiO2. From these results we discuss on the possibility of designing reliable high-energy, high-volume, lithium-ion batteries.