MIT Researchers Turn Used Car Batteries into Solar Cells

Illustration: Christine Daniloff/MIT

Scientists at MIT have concocted what could become the ultimate in green energy: a solar panel made out of hazardous waste. 

In research paper reported in the journal Energy and Environmental Science, researchers describe a method for making perovskite solar cells using the lead from recycled car batteries. The technique can be done in a low-temperature, benign process that’s simpler than today's methods, they say. And after 18 months of testing, the researchers found that their experimental solar cells matched the efficiency of many commercial silicon cells, MIT said yesterday.

Perovskite is a class of materials that has caught the interest of solar photovoltaic researchers because they have made rapid progress in improving the efficiency of solar cells made from materials in the past three years. Compounds in this group promise to be very cheap and relatively simple to manufacture. One company, called Oxford Photovoltaics, is seeking to make commercial solar perovskite cells that can be applied as coatings on windows and other outdoor building surfaces.

One downside is that the material contains a small amount of lead. Extracting lead from ore is a high-temperature, polluting process that creates lead vapor and dust that’s difficult to contain, the MIT researchers note. And if companies begin to produce perovskite solar cells at large volumes, the materials they would be mining and processing could become a serious health or environmental hazard, they say.

(Two labs recently reported perovskite cells using tin instead of lead, but these are much less efficient.)

The other looming problem with lead is that technologies such as lithium ion batteries are advancing to the point that they could soon displace lead acid batteries in cars and trucks. The result, the researchers fear, is a glut of unwanted batteries containing a huge amount of lead waste.

About 90 percent of lead acid batteries in the United States are recycled, but problems remain. In 2011, the New York Times reported that an increasing number of old car batteries are being exported to Mexico from the United States for recycling, but that the work is done with crude methods that expose people to lead poisoning.

The MIT scientists say they have a better idea. In their paper, they spell out a multi-step process they say will give the lead from all those batteries a second life. They've demonstrated the ability to synthesize perovskite solar material using the electrodes straight out of a used lead-acid battery. Lead from the anode is mixed with nitric acid and the lead oxide (made from the lead dioxide cathode) is mixed in acetic acid. Then each compound is mixed with potassium iodide.

The solutions are then purified and deposited on a thin flexible film, which acts as the substrate for the solar cell. (You can watch a step-by-step video demonstration below.) Because it’s a relatively simple process, the researchers are optimistic that it can work at large scale cheaply. And because each of the perovskite cells are just half a micrometer thick, the researchers estimate that a single car battery could produce enough solar panels to provide electric power for 30 households.

MIT professor Angela Belcher and the paper’s lead author, Po-Yen Chen, say they don’t intend to start a company to commercialize their technology. Instead, they wanted to show people who are developing and manufacturing perovskite solar cells that the lead from old batteries performs just as well as mined lead. 

“This paper is about the excitement in the field of these [perovskite] materials and thinking about the environmental implications of extracting lead,” Belcher says. “The beauty is that this new process is pretty interchangeable with the current production method.”

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