Issue Date: November 2, 2015
We love our mobile devices but have to put up with a modern-day anxiety: the peculiar discomfort felt when a battery indicator turns red. What if, rather than a desperate search for an outlet for the phone or electric car, we had more powerful, longer-lived batteries?
Surpassing the performance of today’s lithium-ion batteries will require new active materials that react with each other in novel ways. Materials firms are working to develop new electrodes that can deliver more power when the battery is being used. But it’s difficult to control the chemical substances that form when the battery is recharged; those undesirables can cut a battery’s life short—or even cause a fire.
The solution from the scientists and engineers at NOHMs Technologies is new electrolytes and high-voltage cathodes to pack more power into lithium-ion batteries and protect them from degrading.
The job of an electrolyte is to safely move lithium ions between a battery’s anode and cathode. But standard solvent-based electrolytes are too volatile to deliver much more than the 3.7 V offered by today’s cell phone batteries. NOHMs believes it can deliver longer battery life and as much as 5.0 V with ionic liquids—molten salts that are liquid at room temperature. They are nonvolatile, stable at high voltage and temperature, and highly conductive.
“Inherently, they have all the characteristics needed for electrically thermostable batteries,” says Surya Moganty, director of technology at NOHMs. But since the best ionic liquids are quite viscous, NOHMs had to develop a recipe that provides the right electron transport properties.
NOHMs is also working to commercialize a new sulfur-containing cathode for lightweight batteries used in applications such as drones and autonomous robots. The reaction of sulfur with lithium to form Li2S produces large amounts of electrical energy, according to Lynden Archer, a NOHMs founder and chemical engineering professor at Cornell University.
But commercialization of lithium-sulfur batteries has been hindered by unwanted reactions that occur at the cathode when the batteries are recharged. Recharging produces lithium polysulfides, which are very soluble in the electrolyte and can migrate over and ruin the anode.
Fixing this problem required a new cathode design. “That’s what materials scientists usually do. But we brought a different perspective—that of chemical engineers—into the mix,” Archer says. His team includes cofounders Nathan Ball and Shivaun Archer, both chemical engineers.
Lynden Archer and his partners thought a cathode made of a nanocomposite of sulfur and carbon would help prevent sulfur from contacting the electrolyte. However, inserting sulfur into the cathode was a challenge. They turned to Moganty, whose solution was to work with sulfur in the gas phase. As a gas, sulfur can be deposited inside the cathode’s nanostructured carbon pores. Once inside, the sulfur still reacts with lithium, but the resulting polysulfides remain in the pore spaces and don’t degrade the anode, even after many recharge cycles.
With Small Business Innovation Research (SBIR) grants from NASA and NSF, and $1.64 million from the auto-industry-supported U.S. Advanced Battery Consortium, NOHMs is testing its materials in the battery cells of potential customers. Its location at Eastman Business Park is helping speed the process: The Eastman Kodak complex hosts infrastructure for manufacturing the materials and prototyping and testing new batteries.
- Chemical & Engineering News
- ISSN 0009-2347
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