Berkeley Lab conductive polymer coating could enhance performance of EV batteries
08 March 2023
Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a conductive polymer coating—called HOS-PFM—that could enable longer lasting, more powerful lithium-ion batteries for electric vehicles. The advance opens up a new approach to developing EV batteries that are more affordable and easy to manufacture, said Gao Liu, a senior scientist in Berkeley Lab’s Energy Technologies Area who led the development of the material.
A paper on the work is published in the journal Nature Energy.
The HOS-PFM coating conducts both electrons and ions at the same time. This ensures battery stability and high charge/discharge rates while enhancing battery life. The coating also shows promise as a battery adhesive that could extend the lifetime of a lithium-ion battery from an average of 10 years to about 15 years, Liu added.
The HOS-PFM conductive binder is made of a nontoxic polymer that transforms at the atomic level in response to heat. At room temperature (20 ˚C), alkyl end-chains on the PFM polymer chain limit the movement of lithium ions. When heated to about 450 ˚C, the alkyl end-chains melt away, creating vacant “sticky” sites (blue squiggly lines) that “grab” onto silicon or aluminum materials at the atomic level.
PFM’s polymer chains then self-assemble into spaghetti-like strands called hierarchically ordered structures (HOS). The HOS-PFM strands allow lithium ions to hitch a ride with electrons; these lithium ions and electrons move in synchronicity along the aligned conductive polymer chains.
To demonstrate HOS-PFM’s superior conductive and adhesive properties, Liu and his team coated aluminum and silicon electrodes with HOS-PFM, and tested their performance in a lithium-ion battery setup.
During experiments at the Advanced Light Source and the Molecular Foundry, the researchers demonstrated that the HOS-PFM coating significantly prevents silicon- and aluminum-based electrodes from degrading during battery cycling over 300 cycles. The results are impressive, Liu said, because silicon-based lithium-ion cells typically last for a limited number of charge/discharge cycles and calendar life.
Berkeley Lab researchers demonstrated that the HOS-PFM coating significantly prevents aluminum-based electrodes from degrading during battery cycling while delivering high battery capacity over 300 cycles. From left: Scanning electron microscope images of aluminum on a copper bilayer device before battery cycling (Figure A) and after (Figure B). Figure C shows a copper tri-layer device with HOS-PFM coating after battery cycling. (Credit: Gao Liu/Berkeley Lab. Courtesy of Nature Energy.)
The HOS-PFM coating could allow the use of electrodes containing as much as 80% silicon. Such high silicon content could increase the energy density of lithium-ion batteries by at least 30%, Liu said. And because silicon is cheaper than graphite, the standard material for electrodes today, cheaper batteries could significantly increase the availability of entry-level electric vehicles, he added.
The team next plans to work with companies to scale up HOS-PFM for mass manufacturing.
The research was supported by DOE Vehicle Technologies Office. Additional funding was provided by the Toyota Research Institute. The technology is available for licensing.
Resources
Zhu, T., Sternlicht, H., Ha, Y. et al. (2023) “Formation of hierarchically ordered structures in conductive polymers to enhance the performances of lithium-ion batteries.” Nat Energy 8, 129–137 doi: 10.1038/s41560-022-01176-6
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