As scientists try to boost the lifetime and capacity of lithium-ion batteries, they’ve run into a problem. The materials that would help the batteries store more energy tend to crack and ultimately pulverize during the charging cycle: Lithium ions make the material expand during charging and then contract during discharging. As this happens repeatedly, an inactive layer forms around the material and degrades battery performance. Taking a molecular approach to battery design, a team of chemists has developed a strategy to prevent such breakdown in anode materials.
The team, led by Georgia Tech’s Elsa Reichmanis and Stony Brook University’s Amy C. Marschilok, created single-walled carbon nanotube (SWNT) nets that are anchored to the battery material via poly[3-(potassium-4-butanoate) thiophene], also known as PPBT. PPBT has carboxylate groups that coordinate with the polar surface of the battery material, and its thiophene backbone uses π-bonding to interface with the SWNTs. Electrons can flow through the SWNT-PBBT network. The nanotube net that forms around the battery materials is porous enough for lithium ions to move on and off the material while also preventing dramatic expansion (J. Am. Chem. Soc. 2018, DOI: 10.1021/jacs.8b00693).
The system works with two different types of anode battery materials—magnetite nanoparticles and silicon nanoparticles. This suggests the strategy might be “a generic method to minimize and contain volume changes,” said Reichmanis, who presented the work today in the Polymeric Materials: Science & Engineering (PMSE) division during the American Chemical Society national meeting in New Orleans. “With further optimization, we hope that this can lead to an effective strategy for improving lithium-ion battery performance and the lifetime of the batteries,” she added.
“This is a wonderful demonstration of the usefulness of polymer chemistry in solving practical challenges of next-generation high-energy battery technologies,” remarked Guihua Yu, who studies nanomaterials for energy applications at the University of Texas, Austin.
Paul V. Braun, an expert in polymers and electronic materials at the University of Illinois, Urbana-Champaign, commented that the work provides clear evidence “that to maximize performance, battery electrodes need to be holistically designed to take into account ion and electron conductivity, free volume, and specific chemical interactions.”
For the strategy to be useful in battery technology, Reichmanis said, it will have to move beyond the anode and into a complete battery cell. Also, she said, the components will all need to made uniformly and reliably so that they’re compatible with a commercial process.