UCLA paves the way for better lithium

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Invented by John B. Goodenough in the 1980s, lithium-ion batteries are an indispensable part of our lives. They make up for effective electrical energy storage systems and are used in electronics, toys, handheld power tools, small and large appliances, wireless headphones, electric vehicles, etc.

But they come with their risks and challenges. If charged too quickly, these batteries can explode or cause fires. They can provide extremely high currents and can discharge rapidly when short-circuited.

In fact, over 100 bikes have exploded in New York City due to the lithium-ion batteries that power those bikes. It resulted in 13 deaths this year alone.

Lithium-ion batteries descend from another technology - the lithium-metal battery, which has a greater potential of exploding, given they have about double the energy capacity.

A lithium-ion battery stores positively charged lithium atoms in a cage-like structure of carbon that coats an electrode. Whereas a lithium-metal battery instead coats the electrode with metallic lithium, which packs 10 times more lithium into the same space. This gives the latter a higher-performing battery.

And now, a study by a research team at the University of California Los Angeles (UCLA) claims that it’s found a way to stop lithium-metal batteries from exploding. This could lead to safer lithium-metal batteries with the potential to outperform lithium-ion batteries.

If the charge and discharge currents and the batteries' temperature are controlled, they are safe. But metallic lithium can corrode immediately when the metal is laid down on a surface, such as an electrode, because it reacts quickly with chemicals. But the team at UCLA developed a technique that prevents this corrosion.

The team prevented the corrosion and found that instead of the ‘chunky’ or ‘column-like’ shapes the lithium metal structure would usually take, they saw a singular polyhedron, which the team describes as a “rhombic dodecahedron, a 12-sided figure similar to the dice used in role-playing games like Dungeons and Dragons,” in the press release.

In the absence of corrosion, the team said that the singular polyhedron is the true shape of lithium. The discovery can have significant implications for high-performance energy technology.

“Scientists and engineers have produced over two decades’ worth of research into synthesizing metals including gold, platinum, and silver into shapes such as nanocubes, nanospheres, and nanorods,” said Yuzhang Li, co-author of the study. “Now that we know the shape of lithium, the question is, Can we tune it so that it forms cubes, which can be packed in densely to increase both the safety and performance of batteries?”

The study was published in the peer-reviewed journal Nature.

Study abstract:

Electrodeposition of lithium (Li) metal is critical for high-energy batteries. However, the simultaneous formation of a surface corrosion film termed the solid electrolyte interphase (SEI) complicates the deposition process, which underpins our poor understanding of Li metal electrodeposition. Here we decouple these two intertwined processes by outpacing SEI formation at ultrafast deposition current densities while also avoiding mass transport limitations. By using cryogenic electron microscopy, we discover the intrinsic deposition morphology of metallic Li to be that of a rhombic dodecahedron, which is surprisingly independent of electrolyte chemistry or current collector substrate. In a coin cell architecture, these rhombic dodecahedra exhibit near point-contact connectivity with the current collector, which can accelerate inactive Li formation. We propose a pulse-current protocol that overcomes this failure mode by leveraging Li rhombic dodecahedra as nucleation seeds, enabling the subsequent growth of dense Li that improves battery performance compared with a baseline. While Li deposition and SEI formation have always been tightly linked in past studies, our experimental approach enables new opportunities to fundamentally understand these processes decoupled from each other and bring about new insights to engineer better batteries.