WASHINGTON (Reuters) - Researchers who have trained a tiny virus to do their bidding said on Thursday they made it build a more efficient and powerful lithium battery.

They changed two genes in the virus, called M13, and got it to do two things: build a shell made out of a compound called iron phosphate, and then attach to a carbon nanotube to make a powerful and tiny electrode.

Such an electrode could conceivably make more powerful memory devices such as MP3 players or cellular telephones, and are far more environmentally friendly than current battery technologies, said Angela Belcher, a Massachusetts Institute of Technology materials scientist who led the research.

"It has some of the same capacity and energy power performance as the best commercially available state-of-the-art batteries," Belcher said in a telephone interview.

"We could run an iPod on it for about three times as long as current iPod batteries. If we really scale it, it would be used in a car," she added. Such scaling is not even close, Belcher cautioned.

The technology is inherently green because it involves a live virus. "We are having organisms make the materials for us," Belcher said. "We are confined to temperatures and solvents -- water -- that organisms can live in. It's a clean technology. We can't do anything that kills our organisms."

Reporting in the journal Science, Belcher's team said their genetically engineered viruses were designed to grow shells of amorphous iron phosphate.

The material is generally not a good conductor, but makes a useful battery material when patterned at the nanoscale -- a microscopic molecular scale.

Lithium batteries are powerful and light, but they do not release their electrons very quickly. The virus-made material did, however. This translates into more battery power.

"My students hate it when I say we sit back and let them (the viruses) do the work. We put a lot of work in too," Belcher said.

"But once you have the right genetic sequence and have the right proteins then you just put them in solution with water and ions and they template the battery in the same way an abalone templates a shell. They build little shells around themselves."

The team is already working on a second-generation battery using materials with higher voltage and electrical capacity, such as manganese phosphate and nickel phosphate, said Belcher. This new technology could go into commercial production, she said.

(Editing by Eric Beech)

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