Scientists in Germany and the United States find a way around a common failure of high density lithium metal batteries

Published : June 19, 2021 19:16 IST

Prototype lithium metal batteries with carbon nanomembrane separators. Photo: Courtesy: Sathish Rajendran/Wayne State University

 

The convenience of batteries versus the guilt of adding to electronic waste has played on many a conscience. But good news in the form of some pathbreaking research comes from the Friedrich Schiller University in Jena, Germany.

Scientists at the university in Jena, along with colleagues from Boston University and Wayne State University (WSU), have found a way to at least double the life of lithium batteries that are commonly used in portable electronics and electric vehicles and have a growing market in military and aerospace applications.

A press release from the Friedrich Schiller University clarifies the issues involved. “The energy density of traditional lithium-ion batteries is approaching a saturation point that cannot meet the demands of the future—for example in electric vehicles. Lithium metal batteries can provide double the energy per unit weight when compared to lithium-ion batteries. The biggest challenge, hindering its application, is the formation of lithium dendrites, small, needle-like structures, similar to stalagmites in a dripstone cave, over the lithium metal anode. These dendrites often continue to grow until they pierce the separator membrane, causing the battery to short-circuit and ultimately destroying it.”

Experts have been working on a more sustainable approach to the issue for years and are now one step closer with the development of a two-dimensional membrane that prevents dendrite nucleation. The Encyclopaedia Britannica explains nucleation as “the initial process that occurs in the formation of a crystal from a solution, a liquid, or a vapour, in which a small number of ions, atoms, or molecules become arranged in a pattern characteristic of a crystalline solid, forming a site upon which additional particles are deposited as the crystal grows.” Or, in this case, the growth of crystal dendrites.

The press note throws more light on this fascinating process: “During the charge transfer process, lithium ions move back and forth between the anode and the cathode. Whenever they pick up an electron, they deposit a lithium atom and these atoms accumulate on the anode. A crystalline surface is formed, which grows three-dimensionally where the atoms accumulate, creating the dendrites. The pores of the separator membrane influence the nucleation of dendrites. If ion transport is more homogeneous, dendrite nucleation can be avoided.”

Professor Andrey Turchanin from the University of Jena explains: “That’s why we applied an extremely thin, two-dimensional membrane made of carbon to the separator, with the pores having a diameter of less than one nanometer. These tiny openings are smaller than the critical nucleus size and thus prevent the nucleation that leads to the formation of dendrites. Instead of forming dendritic structures, the lithium is deposited on the anode as a smooth film.” There is no risk of the separator membrane being damaged by this and the functionality of the battery is not affected.

“To test our method, we recharged test batteries fitted with our Hybrid Separator Membrane over and over again,” says Dr Antony George from the University of Jena. “Even after hundreds of charging and discharging cycles, we couldn’t detect any dendritic growth.”

“The key innovation here is stabilising electrode/electrolyte interface with an ultra-thin membrane that does not alter current battery manufacturing process,” says Associate Professor Leela Mohana Reddy Arava from the WSU.

Confident of wide applications for their research, the team has applied for a patent for their method. While battery efficiency will be a huge plus point, the potential of less burden on the environment is even more exciting.

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