Increasing the energy density of cathode materials for lithium-ion batteries requires raising up the working voltage of cathode materials or/and extracting more lithium ions from their crystal lattice. Therefore, the cathode materials are inevitably exposed to extreme working environment, which may cause the instability of both global crystal structure and/or surface/interfacial structure. Introducing doping elements to electrode is currently the expedient method to improve the performance, however, whether the alien element is doped in the host crystal or not usually lacks of solid experimental proofs, and whether the positive effects is caused by doping is still unknown. The situation becomes even more complex when several elements are doped at the same time. In this report, with a case study focusing on LiCoO₂, evaluation of the interaction between different alien elements including Ti, Mg and Al is conducted with orthogonal experiments. The effects of doping and coating are compared in detail to find out a better way to improve the electrochemical performances of LiCoO₂ at high cut-off voltage of 4.6V vs. Li⁺/Li. The question regarding whether the alien elements are doped in the host crystal or presented as a secondary phase that is aggregated on surface or grain boundaries is also discussed with both first-principle calculations and experimental investigations, such as XRD, X-ray imaging, XPS, thermal analysis by TG and electrochemical tests. By summarizing the results, the major factors affecting the performance of high voltage LiCoO₂ are clearly demonstrated, which we hope it will also be valuable information for the development of other cathode materials for high energy density lithium-ion batteries.