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.
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.
