Using a novel automated approach for quickly building and testing thousands of battery cells, Wildcat Discovery Technologies, a startup in San Diego, California, has developed new materials that could boost the storage capacity of lithium-ion batteries for cars and portable electronics by more than 25 percent.
Batteries based on the new materials could extend the range of electric vehicles or allow automakers to keep the same range but use fewer battery cells, thus reducing the cost of the battery pack, an electric car's most expensive part. Work still needs to be done to improve the durability of the new materials, but the results provide validation for Wildcat's high-throughput screening technique that allows researchers to quickly sort through combinations of materials.
High-throughput screening is common in the drug and chemical industries to discover new compounds and catalysts, and the technique has made inroads into battery development. What makes Wildcat's process different is that it makes complete battery cells, not just individual parts of the cells, such as the electrodes. This is important because the performance of any given material in the cell depends on how it interacts with the other parts. "With conventional approaches, you get a lot of false positives and false negatives," says Steven Kaye, Wildcat's chief scientific officer. An electrode material that looks promising on its own may fail in a complete cell as it interacts with electrolytes, additives, and the opposite electrode, he says. And one that looks mediocre could improve markedly when mixed with other materials in a cell.
Wildcat's new material, a variant of lithium cobalt phosphate, is one that would ordinarily have been rejected because it operates at a voltage that quickly destroys the battery's electrolyte, the liquid that conducts lithium ions between the electrodes. But the researchers paired the material with many new electrolyte recipes and eventually discovered one that could survive the high voltage. In all, the company screened 4,000 materials over a period of about four months to find the ones that worked.
The process begins with the automatic mixing of liquid precursor materials, followed by the production of electrode powders with different properties, the formation of electrode films, and the combination of the electrodes, separator, and electrolytes in a coin cell of the sort found in watch batteries. These cells are tested, and the best are improved upon.
The ability to sort through thousands of materials combinations and incorporate them into complete battery cells "is pretty impressive," says Jeff Dahn, a professor of physics at Dalhousie University who uses high-throughput methods to study battery materials. "They've come a long way in a short time," he says.
Wildcat was founded in 2006 and has raised $16.5 million in venture funding. It also has revenue from more than 40 research projects with major manufacturers. Its founders include Peter Schultz, a professor at the Scripps Research Institute and a pioneer of high-throughput combinatorial chemistry.
Battery cells using Wildcat's new materials would store about 60 percent more energy by volume than lithium iron phosphate cells, one type being used by electric vehicle makers. Compared to some higher-energy batteries that could be in next-generation electric vehicles, such as those that use a mix of nickel, manganese, and cobalt, the new materials could yield an energy increase of more than 25 percent by volume, Kaye says.
It's not clear how the materials will affect overall battery cost. The improvement in capacity will lower costs, and the higher voltage of the cells will simplify wiring in battery packs, which will also reduce costs, but the use of cobalt will make them more expensive than lithium iron phosphate. To reduce costs, the company is working on electrode materials that substitute nickel for cobalt.
The new electrolyte formulations that the company has developed could open the possibility of using other relatively high-voltage electrode materials, including a class of materials called fluorophosphates that, when paired with high-performance opposite electrodes, could as much as double battery capacity, Kaye says.
The company is currently producing test batches of its new materials and is hoping to license the technology to materials and battery companies, but the durability of the materials still needs to be improved. After 150 charging cycles, the capacity of the electrode material has decreased by 20 percent. For use in portable electronics, the battery needs to last for a few hundred cycles. For electric cars, the battery must retain 80 percent of its storage capacity for thousands of cycles.
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