Lithium-ion secondary battery

In one embodiment, an active cathode material comprises a mixture that includes: at least one of a lithium cobaltate and a lithium nickelate; and at least one of a manganate spinel represented by an empirical formula of Li(MnA')Oand an olivine compound represented by an empirical formula of LyA"MPO. In another embodiment, an active cathode material comprises a mixture that includes: a lithium nickelate selected from the group consisting of LiCoO-coated LiNiCoAlO, and Li(NiCoMn)O; and a manganate spinel represented by an empirical formula of LiMnO. A lithium-ion battery and a battery pack each independently employ a cathode that includes an active cathode material as described above. A method of forming a lithium-ion battery includes the steps of forming an active cathode material as described above; forming a cathode electrode with the active cathode material; and forming an anode electrode in electrical contact with the cathodeviaan electrolyte. A system comprises a portable electronic device and a battery pack or lithium-ion battery as described above.