Researchers have applied mechanical engineering solutions in helping to understand – and utilise – dendrites, the needle-like growths that can be detrimental to the performance of lithium-metal batteries.
Lithium-metal batteries hold promise as a high-density energy storage technology but uncontrolled lithium dendrite growth on the anode can induce unwanted reactions that reduce energy density or can cause shorting of the electrodes.
New research from Arizona State University that involves a 3-dimensional layer of Polydimethysiloxane (PDMS), or silicone, as the substrate of lithium metal anode has been found to mitigate dendrite formation and stands to extend battery life and diminish safety risks. A paper describing the work – Stress-driven lithium dendrite growth mechanism and dendrite mitigation by electroplating on soft substrates – was published in Nature Energy.
According to Hanqing Jiang, a professor in Arizona State University’s School for Engineering of Matter, Transport and Energy and a lead researcher on the paper, the findings have relevance for lithium-ion and lithium-air batteries, as well as implications for other metal-anode-based batteries.
“Almost all metals used as battery anodes tend to develop dendrites,” said Jiang. “For example, these findings have implications for zinc, sodium and aluminium batteries as well.”
Rather than approaching the problem from a materials or electrochemical perspective, Jiang and the team are said to have looked for solutions as mechanical engineers. “We already know that tiny tin needles or whiskers can protrude out of tin surfaces under stress, so by analogy we looked at the possibility of stress as a factor in lithium dendrite growth.
The first round of research involved adding a layer of PDMS to the bottom of battery anodes. “There were remarkable reductions in dendrite growth,” said Jiang. The researchers discovered that this is directly related to the fact that stress accumulated inside the lithium metal is relieved by the deformation of the PDMS substrate in the form of ‘wrinkles’.
“This is the first time convincing evidence shows that residual stress plays a key role in the initiation of lithium dendrites,” said Jiang.
In addition to obtaining a fundamental understanding of the lithium dendrite growth mechanism, Jiang’s group devised a way of utilising the phenomenon to extend the life of lithium-metal batteries while maintaining their high energy density.
The solution is to give the PDMS substrate a three-dimensional form with a large surface area.
“Envision sugar cubes that contain a lot of small internal pores,” said Jiang. “Inside these cubes, the PDMS forms a continuous network as the substrate, covered by a thin copper layer to conduct electrons. Finally, lithium fills the pores. The PDMS, which serves as a porous, sponge-like layer, relieves the stress and effectively inhibits dendrite growth.”
“The finding has broad implications for making lithium-metal batteries a safe, high-density, long-term energy storage solution,” said Prof Ming Tang, a research team member at Rice University. “Potential applications range from personal electronic devices to powering electric cars for exceptionally longer periods to being the back-up electric supply for solar power grids.”
