Structural degradation and side reaction in cathode materials have been regarded as the main issues that compromise the capacity and cycle stability of Ni-rich LiNi0.8Co0.15Al0.05O2. Herein, an inside-out modification method was reported to stabilize internal structure and restrain side reactions of LiNi0.8Co0.15Al0.05O2, composing of doping Mg inside the layer structure and coating Al2O3 outside the cathode materials particles. Through dual protection strategies, an unprecedented capacity retention as high as 99% after 100cycles and 95% after 250cycles (from 178 to 168.9mAhg−1) was achieved at 1.0C, which are much more superior among LiNi0.8Co0.15Al0.05O2 cathodes using previously reported modification methods. X-ray diffraction results indicated that Al and Mg ions were successfully introduced into the bulk materials and exhibited excellent hexagonal structure. This work highlights that the multiple modified method is a promising strategy to enhance the cycling performance of LiNi0.8Co0.15Al0.05O2, and these enhancements can be attributed to the protection from “inside” to “outside” of LiNi0.8Co0.15Al0.05O2 particles, which suppress phase transition and cation mixing inside the materials, and reduce side effects outside the particles, thus allows for rapid electron transport during the electrochemical Li+ insertion/extraction reaction.