The coating effects of electronically and ionically conductive materials on the surface of LiNi0.5Mn1.5O4 (LNMO) cathodes for Li-ion batteries are examined. In order for the coating layers to promote facile electrochemical reactions, in addition to their protective functions of blocking side reactions between the LNMO surface and the electrolyte, carbon and Li2O–2B2O3 (LBO), which conduct electrons and Li ions, respectively, are chosen as coating materials. The properties of the LBO–carbon composite coating are examined in comparison with those of carbon- or LBO-only coatings. Electrochemical metrics, such as discharge capacity, rate performance, and cyclability, are improved with the addition of the thin-film coatings. The LBO–carbon coating shows the best overall properties, particularly greatly improved capacity retention under elevated-temperature (60 °C) cycling. The multi-conductive feature of LBO–carbon for both electrons and Li ions provides stable electrochemical kinetics under conditions of severe side reactions at elevated temperatures. The proposed simple one-step aqueous process for forming and applying the composite electrode coating may be extended to other materials and the mass production thereof.