Electrochemical performances of spinel cathode materials have been evaluated in a broad voltage range of 2.0–4.8 V vs. Li/Li+ via in-situ integrating a layered Li2MnO3 phase for high-voltage and high-capacity lithium ion batteries. Effects of sintering temperatures on manipulating hybrid spinel-layered structures have been systematically studied during the decomposition of nonstoichiometric Li0.65Mn0.59Ni0.12Co0.13Oδ material. The spinel component undergoes a phase transition from an initial Li4Mn5O12-type to a LiMn1.5Ni0.5O4-type spinel structure under high temperatures above 700 °C; meanwhile the content of layered Li2MnO3 component is increased. Li2MnO3-stabilized spinel-layered cathodes can deliver the discharge capacity more than 225 mA h/g at 0.1 C and exhibit outstanding capacity retentions above 90% at 0.5 C (1 C = 250 mA/g) in an extended voltage range between 2.0 and 4.8 V. In addition to clarify significant Li2MnO3 impacts on improving cycling stability of spinel cathode materials, it is noticeable that LiMn1.5Ni0.5O4-based spinel materials can effectively suppress the electrochemical activation of the layered Li2MnO3 up to 4.8 V. This work sheds lights on tailoring hybrid structures and maximizing electrochemical performances of Li2MnO3-based spinel-layered cathode materials for superior lithium ion batteries.