Thursday, April 18, 2024

New polymer coating could enhance lithium-ion battery performance

Electrically conductive polymers have found increasing applications in energy conversion and storage devices. In the conventional design of conductive polymers, organic functionalities are introduced via bottom-up synthetic approaches to enhance specific properties by modification of the individual polymers. However, the addition of functional groups leads to conflicting effects, limiting their scaled synthesis and broad applications.

Researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a conductive polymer coating that could enable longer-lasting, more powerful lithium-ion batteries for electric vehicles.

Called HOS-PFM, the 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.

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 degrees Celsius), alkyl end chains on the PFM polymer chain limit the movement of lithium ions. And when heated to about 450 degrees Celsius, the alkyl end-chains melt away, creating vacant “sticky” sites that “grab” onto silicon or aluminum materials at the atomic level.

To demonstrate HOS-PFM’s superior conductive and adhesive properties, the team coated aluminum and silicon electrodes with HOS-PFM and tested their performance in a lithium-ion battery setup. During experiments, the researchers demonstrated that the HOS-PFM coating significantly prevents silicon- and aluminum-based electrodes from degrading during battery cycling. It also delivers high battery capacity over 300 cycles, a performance rate that’s on par with today’s state-of-the-art electrodes.

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.
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.

Gao Liu, Berkeley Lab senior scientist who led the development of the material, said the results are impressive because silicon-based lithium-ion cells typically last for a limited number of charge-discharge cycles and calendar life.

“The advance opens up a new approach to developing EV batteries that are more affordable and easy to manufacture,” said Gao Liu.

The new polymer coating could allow the use of electrodes containing as much as 80% silicon. Such high silicon content increases the energy density of lithium-ion batteries by at least 30%. Also, because silicon is cheaper than graphite, cheaper batteries could significantly increase the availability of entry-level electric vehicles, Liu added.

Researchers next plan to work with companies to scale up HOS-PFM for mass manufacturing.

Journal reference:

  1. Tianyu Zhu, Hadas Sternlicht, Yang Ha, Chen Fang, Dongye Liu, Benjamin H. Savitzky, Xiao Zhao, Yanying Lu, Yanbao Fu, Colin Ophus, Chenhui Zhu, Wanli Yang, Andrew M. Minor & Gao Liu. Formation of hierarchically ordered structures in conductive polymers to enhance the performances of lithium-ion batteries. Nature Energy, 2023; DOI: 10.1038/s41560-022-01176-6