Consumers use long-lasting rechargeable lithium ion batteries in everything from cell phones to the latest portable gadget, and some carmakers want to use them in vehicles. Most lithium ion batteries available today are designed with an oxide of metal such as cobalt, nickel or manganese. Choi and colleagues at the laboratory and at State University of New York at Binghamton wanted to explore both cheaper metals and the more stable phosphate in place of oxide.

The rechargeable batteries work because lithium is selfish and wants its own electron. Positively charged lithium ions normally hang out in metal oxide, which is the stable positive electrode in batteries. Metal oxide generously shares its electrons with the lithium ions.

Charging with electricity pumps electrons into the negative electrode and when the lithium ions see the free-floating negative charges across the battery, they become attracted to life away from the metal-oxide cage. So off the lithium ions go, abandoning the metal oxide and its shared electrons to spend time enjoying their own private ones.

But the affair does not last. Using the battery in an electronic device creates a conduit through which the slippery electrons can flow. Losing their electrons, the lithium ions slink back to the ever-waiting metal oxide. Recharging starts the whole process over.