Massachusetts Institute of Technology experts are working to "push the envelope" with rock salt science in lithium-ion batteries. Yimeng Huang, first author of a paper on the topic, said in a lab summary that the work produced a new type of cathode, created by a unique union.
"There is typically a trade-off in cathode materials between energy density and cycling stability," Huang said in the report. "[This] material family has high energy density and good cycling stability because it integrates two major types of cathode materials, rock salt and polyanionic olivine, so it has the benefits of both."
In a typical lithium-ion battery, ions move between the anode and cathode, through an electrolyte substance, as the pack charges and discharges. Experts around the world are constantly testing new materials that will improve internal chemistry at less cost and with a more stable supply chain.
The work is important to maintaining full-throttle momentum in the transition to electric vehicles. It's widely reported that the U.S. saw record sales of nearly 1.2 million EVs last year alone. The cleaner rides are helping to reduce the amount of harmful, heat-trapping air pollution spewing from exhausts.
The MIT team, which is led by professor Ju Li, thinks its rock salt cathode can also improve performance for large-scale renewable energy storage. Rock salt cathodes have also been explored for applications in cell phones, per the MIT summary.
"Lithium-ion batteries are a critical part of the clean energy transition. Their continued growth and price decrease depends on the development of inexpensive, high-performance cathode materials made from Earth-abundant materials, as presented in this work," engineering and materials science professor Gerbrand Ceder said in the lab report. He teaches at the University of California, Berkeley.
To that end, the rock salt/polyanionic cathode is manganese-abundant. It's a much more common and far less expensive material than the nickel and cobalt typically used, per the summary.
As for the nuts and bolts of the research, the breakthrough was made possible by addressing oxygen mobility. It's one of the major hurdles for rock salt cathodes. On-the-go oxygen typically causes batteries of this type to degrade during operation.
In answer, the researchers added phosphorus to the mix, which serves as a "glue," holding the oxygen in place, all per the experts.
The result is a win on both the capacity and cycling stability fronts.
The phosphorus "formed so-called polyanions with its neighboring oxygen atoms, into a … rock salt structure that can pin them down," Li said. "That allows us to basically stop the percolating oxygen transport due to strong covalent bonding between phosphorus and oxygen … meaning we can both utilize the oxygen-contributed capacity, but also have good stability as well."
Better battery tech can improve already strong results in the sector. EVs are blowing the doors off range records, traveling hundreds of miles on a single charge. Recharge times are dropping to minutes in some cases.
Importantly, current batteries that use dirtier and expensive metals are still cleaner than gas-burning alternatives. That's true even in states that use mostly fossil fuels to generate the electricity to charge them, according to a government report.
Lucrative tax breaks for new and used EVs can make them valuable buys that can also produce about $1,500 a year in gas and maintenance savings.
For now, the MIT team is studying rock salt cathodes to develop a scalable manufacturing process. The researchers also want to improve performance by fine-tuning the material.
"The future methods, of course, should be industrially scalable," Huang said in the report.
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