New technique produces more durable lithium batteries

The big challenge of improving energy storage and increasing battery life, while ensuring safe operation, is becoming more and more critical as we increasingly depend on this. source of energy, from portable devices to electric vehicles. A Columbia Engineering team led by Yuan Yang, an Assistant Professor of Materials Science and Engineering, announced today that it has developed a new method to extend the life of the battery safely by inserting a nano-coating of boron nitride (BN) to stabilize solid electrolytes in lithium metal. Battery. Their findings are described in a new study published by Joule.

While conventional lithium-ion (Li-ion) batteries are commonly used in everyday life, they have a low energy density, which reduces their service life and, due to the presence highly flammable liquid electrolyte, they can cause short circuits and even ignite. . The energy density could be improved by using metallic lithium to replace the graphite anode used in Li-ion batteries: the theoretical capacity of metallic lithium for the amount of charge that it can provide is almost 10 times greater than that of graphite. However, during lithium galvanisation, dendrites often form and, if they enter the membrane separator in the middle of the battery, they can create short circuits, raising concerns about the safety of the battery. drums.

"We decided to focus on solid ceramic electrolytes, which are very promising for improving both safety and energy density, compared to conventional flammable electrolytes in Li-ion batteries," Yang said. "Rechargeable semiconductor lithium batteries are of particular interest to us because they are promising candidates for next-generation energy storage."

Most solid electrolytes are ceramic, and therefore non-flammable, eliminating safety concerns. In addition, solid ceramic electrolytes have a high mechanical strength that can actually prevent the growth of lithium dendrite, making lithium metal a coating option for battery anodes. However, most solid electrolytes are unstable with Li – they can be easily corroded by lithium metal and can not be used in batteries.

"Lithium metal is essential for increasing energy density and so it is essential to be able to use it as an anode for solid electrolytes," says Qian Cheng, lead author of the article and postdoctoral researcher. at the Department of Applied Physics and Applied Mathematics. who works in Yang's group. "To adapt these unstable solid electrolytes to real-world applications, we needed to develop a chemically and mechanically stable interface in order to protect these solid electrolytes against the lithium anode." It is essential that the interface be not only highly insulating Electronically, but also ionically conductive to transport lithium ions, and this interface must be very thin to avoid reducing the energy density of the batteries. "

To meet these challenges, the team worked with colleagues at the Brookhaven National Lab and the City University of New York. They deposited a 5 ~ 10 nm boron nitride (BN) nano-film as a protective layer to isolate the electrical contact between the lithium metal and ionic conductor (the solid electrolyte), as well as the a tiny trace of polymer or liquid electrolyte to infiltrate the electrode / electrolyte interface. They chose the BN as a protective layer because it is chemically and mechanically stable to lithium metal, thus offering a high degree of electronic insulation. They designed the BN layer to have intrinsic defects, through which lithium ions can pass, allowing it to serve as an excellent separator. In addition, BN can be readily prepared by chemical vapor deposition to form large – scale (dm – level), atomic scale (~ nm) and continuous films.

"While earlier studies used polymeric protective layers of up to 200 μm thick, our BN protective film, with a thickness of only 5 to 10 nm, has a record thickness – to the limit of such layers of protection – without reducing the energy density of the batteries ", Cheng said. "This is the ideal material to serve as a barrier to the intrusion of lithium metal on solid electrolyte. Like a bulletproof vest, we have developed a lithium "vest" for unstable solid electrolytes and, with this innovation, has achieved a long life of lithium metal batteries. "

The researchers are now extending their method to a wide range of unstable solid electrolytes and further optimize the interface. They expect to manufacture solid-state batteries with high performance and long life.