One is the loneliest number. It's also the number of materials needed to store and transfer energy -- that is if you are an inventive engineer from the University of Maryland.

Researchers there have developed a working battery made entirely out of a single material. As the scientists explain, most batteries resemble an Oreo cookie. A soft center (the electrolyte) sandwiched by two solid ends (the electrodes).

But in this single-material battery, there is no discernible differentiation between middle and ends. The team at the University of Maryland's Department of Chemical and Biomolecular Engineering was able to create a two-in-one material that integrates the properties and functionality of both the electrodes and electrolyte.

"To my knowledge, there has never been any similar work reported," Dr. Kang Xu, an engineer at Maryland's Army Research Laboratory who was only loosely involved in the study, explained in a press release. "It could lead to revolutionary progress in area of solid state batteries."

A powder-like mixture of sulfur, germanium, phosphorus and lithium form the bulk of the material and serve as the electrolyte highway, across which the charged electrons travel. Engineers added carbon to the material at each end, which moves electrons from one end to the other.

The battery was designed by a team of researcher led by Chunsheng Wang, an engineering professor at Maryland.

To build the battery, the powder is compressed into a steel and plastic cylinder. The advantage of a single-material battery is that the walls that traditionally separate different materials are no longer necessary. These walls resist energy flow, and thus diminish a battery's efficiency.

"Our battery is 600 microns thick, about the size of a dime, whereas conventional solid state batteries are thin films -- forty times thinner," said Fudong Han, the lead author of a new paper on the battery. "This means that more energy can be stored in our battery."

While the battery is powder-based -- safer than ubiquitous leak-prone liquid batteries -- sulfide-based compounds aren't the most environmentally friendly. The researchers plan to incorporate safer chemicals as they perfect their invention.

Han, a grad student under the tutelage of Professor Wang, said: "We are still testing how many times it can change and discharge electricity to see if it is a real candidate for manufacturing."

The battery's development is detailed in the journal Advanced Materials.