Stanford PhD students David Mackanic (left) and Zhiao Yu (right) with their battery tester at right. Yu holds a dish of already tested cells that they call "the battery graveyard". Photo: Mark Golden.Hope has been restored for the rechargeable lithium-metal battery. This potential battery powerhouse has been relegated for decades to the laboratory by its short life expectancy and occasional fiery demise, while its rechargeable sibling, the lithium-ion battery, now rakes in more than $30 billion a year.
A team of researchers at Stanford University and SLAC National Accelerator Laboratory has now invented an aluminum-based coating that overcomes some of the lithium-metal battery's defects. They report this coating in a paper in Joule.
In laboratory tests, the coating significantly extended the battery's life. It also dealt with the combustion issue by greatly limiting the growth of tiny needle-like structures – or dendrites – that can pierce the separator between the battery's anode and cathode. In addition to ruining the battery, dendrites can create a short circuit within the battery's flammable liquid electrolyte. Lithium-ion batteries occasionally have the same problem, but dendrites have been a non-starter for lithium-metal rechargeable batteries to date.
"We're addressing the holy grail of lithium-metal batteries," said Zhenan Bao, a professor of chemical engineering at Stanford University, who is senior author of the paper along with Yi Cui, professor of materials science and engineering and of photon science at SLAC. Bao added that dendrites had prevented lithium-metal batteries from being used in what may be the next generation of electric vehicles.
Lithium-metal batteries can hold at least a third more power per pound than lithium-ion batteries, and are significantly lighter because they use lightweight lithium for the anode rather than heavier graphite. If they were more reliable, these batteries could benefit various portable electronic devices, from notebook computers to cell phones, but the real pay dirt, Cui said, would be for cars. The biggest drag on electric vehicles is that their batteries spend about a fourth of their energy carrying themselves around.
"The capacity of conventional lithium-ion batteries has been developed almost as far as it can go," said Stanford PhD student David Mackanic, co-lead author of the paper. "So, it's crucial to develop new kinds of batteries to fulfill the aggressive energy density requirements of modern electronic devices."
The team from Stanford and SLAC tested their coating on the anode of a standard lithium-metal battery, which is where dendrites typically form. Ultimately, they combined their specially coated anodes with other commercially available components to create a fully operational battery. After 160 cycles, their lithium-metal cells still delivered 85% of the power that they did in their first cycle. Regular lithium-metal cells only deliver about 30% of the power after that many cycles, rendering them nearly useless even if they don't explode.
The new coating prevents dendrites from forming by creating a network of molecules that deliver charged lithium ions to the electrode uniformly. It prevents unwanted chemical reactions typical for these batteries and also reduces chemical build-up on the anode, which quickly devastates the battery's ability to deliver power.
"Our new coating design makes lithium metal batteries stable and promising for further development," said the other co-lead author, Stanford PhD student Zhiao Yu.
The group is now refining their coating design to increase capacity retention and testing cells over more cycles. "While use in electric vehicles may be the ultimate goal," said Cui, "commercialization would likely start with consumer electronics to demonstrate the battery's safety first."
This story is adapted from material from Stanford University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.