Co increases low-temperature capacities, and cycle life of superlattice alloy.

Co deteriorates high-temperature voltage stand and high-temperature performance.

Alloy with 4.7 at% Co shows good balance among main battery requirements.

Failure of Co-free superlattice alloy was due to the pulverization of the cathode.

Pulverization, oxidation and shortage are failure modes for Co-containing alloys.