Electrochemical Nucleation of Lithium on Copper

Abstract

Batteries are used for energy storage everywhere, from mobile phones and power tools to electric vehicles and in space exploration. Electric vehicles, for exam ple, would gain increased range from batteries with higher energy densities and higher specific energies. By replacing the graphite electrode material in today’s widespread lithium-ion batteries with lithium (Li) metal, the energy density of the cell can be doubled, from 600Wh L−1 to 1200Wh L−1 , and the specific en ergy of the cell can be increased from 250Wh kg−1 to 440Wh kg−1 . However, non-uniform deposition of Li during charging causes problems, including forma tion of ”dead” Li leading to low Coulombic efficiency and a short cycle life, and is a safety risk by potentially creating a short-circuit of the cell. To enable more uniform Li deposition, the first step during deposition − nucleation − needs to be better understood. This work studied the effects of passivation, current, and cell pressure on the nucleation of Li on a copper surface using electrochemical cycling and scanning electron microscopy. More passivation of the copper surface before deposition and a higher deposition current both resulted in a higher overpotential, indicating more instantaneous nucleation. It was also found that uneven pressure leads to uneven deposition of Li, and that more uniform deposition can be achieved by more uniform pressure.