An electrochemical energy storage system with high energy density, stringent safety, and reliability is highly desirable for next-generation energy storage devices. Here an aqueous rechargeable alkaline Co Ni S // TiO battery system is designed by integrating two reversible electrode processes associated with OH- insertion/ extraction in the cathode part and Li ion insertion/extraction in the anode part, respectively. The prototype Co Ni S // TiO battery is able to deliver high energy/power densities of 83.7 Wh/kg at 609 W/ kg (based on the total mass of active materials) and good cycling stabilities (capacity retention 75.2% after 1000 charge/discharge cycles). A maximum volumetric energy density of 21 Wh/l (based on the whole packaged cell) has been achieved, which is comparable to that of a thin-film battery and better than that of typical commercial supercapacitors, benefiting from the unique battery and hierarchical electrode design. This hybrid system would enrich the existing aqueous rechargeable LIB chemistry and be a promising battery technology for large-scale energy storage.