Salt, paper, battery!

The technical chefs at M.I.T. have come up with a cheap, fun recipe – with simple ingredients like salt and paper, you can start cooking up electricity:

The salt-and-paper battery is an ideal replacement for the lithium ones used in many low-power portable devices, such as wireless sensors, smart cards, medical implants, and RFID tags. “For these applications, the thinner and smaller the battery, the better,” says Sara Bradford, an energy and power consultant at Frost & Sullivan.

Thin-film batteries have other attractive features. They have a long shelf life, retaining their charge after being stored for many years, and they can be charged and discharged tens of thousands of times, says Raghu Das, CEO of research company IDTechEX and an expert on printed electronics, “enabling wireless sensors that can last for decades with an appropriate energy harvester attached.”

Lithium batteries can deliver 4 volts and have energy densities of 200 to 300 milliwatt-hours per gram. In comparison, a single paper battery cell delivers 1 volt and can store up to 25 milliwatt-hours of energy per gram. When providing maximum current, it loses 6 percent of its storage capacity after 100 recharging cycles. However, Stromme says that her team has already run the battery for 1,000 recharging cycles at lower current. She also points out that these are numbers from an initial laboratory prototype.

The researchers are now working on optimizing the battery.

They think they’ll be able to stack a few sheets of salinated paper together to increase the power at a fraction of the cost of thick metal batteries.