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(1+x1)(Mn1−y1A′y1)2−x1Oz1 and an olivine compound represented by an empirical formula of Li(1−x2)A″x2MPO4. In another embodiment, an active cathode material comprises a mixture that includes: a lithium nickelate selected from the group consisting of LiCoO2-coated LiNi0.8Co0.15Al0.05O2, and Li(Ni1/3Co1/3Mn1/3)O2; and a manganate spinel represented by an empirical formula of Li(1+x7)Mn2−y7Oz7. 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 cathode via an electrolyte. A system comprises a portable electronic device and a battery pack or lithium-ion battery as described above.