The researchers, led by Yet-Ming Chiang, a professor of materials science at MIT, and a founder of both A123 Systems and 24M, tested various materials for the electrodes, including lithium cobalt oxide, which is commonly used in laptop batteries. They demonstrated that the device can charge and discharge at the rates needed in electric vehicles, Chiang says.
The paper also describes how the researchers address one of the biggest challenges of the design: pulling the electric charge out of the sludge. In an ordinary lithium ion cell, the electrons make their way by jumping through the connected conductive particles in the solid electrode until they reach a current collector. In the new battery, the electrons won’t flow through the electrolyte. So Chiang and colleagues mixed nanoscale carbon particles into the sludge; the particles spontaneously form interconnected networks in the fluid to provide pathways for the electrons to escape.
Challenges remain before the battery can be commercialized. The electrical conductivity is still about 100 times less than it should be in a practical system, Chiang says. He’s also working on increasing the concentration of active materials in the sludge.
Jeff Dahn, a professor of physics and chemistry at Dalhousie University, notes that to achieve the power levels needed to propel a car, the electrochemical cell would still need to be large: the separator material would have to cover an area of about three meters by four meters. It could be cut into manageable pieces and stacked up, but this could make the system complicated, and even with this approach the cell could be bulky, he says.
“We’re making good progress on the technology,” says 24M CEO Throop Wilder. “The acceptance of the paper is strong validation of the fundamental principles that drive our development.” 24M consists of about 20 employees, and has raised roughly $16 million.
“It’s a very clever device,” says Dahn. “I don’t know if it will ever be more than an idea in a paper, but Chiang has surprised people before.”