The tiny rechargeable battery was formed inside a transmission electron microscope (TEM) at the Center for Integrated Nanotechnologies (CINT), a Department of Energy research facility jointly operated by Sandia and Los Alamos national laboratories.
“This experiment enables us to study the charging and discharging of a battery in real time and at atomic scale resolution, thus enlarging our understanding of the fundamental mechanisms by which batteries work,” said Huang.
It consists of a single tin oxide nanowire anode 100 nm in diameter and 10 micrometers long, a bulk lithium cobalt oxide cathode three mm long, and an ionic liquid electrolyte. The device offers the ability to directly observe change in atomic structure during charging and discharging.
For example, the tin oxide nanowire rod nearly doubles in length during charging – far more than its diameter increases — a fact that could help avoid short circuits that may shorten battery life.
Huang’s group found this flaw by following the progression of the lithium ions as they travel along the nanowire and create what researchers christened the “Medusa front” – an area where high density of mobile dislocations cause the nanowire to bend and wiggle as the front progresses. The web of dislocations is caused by lithium penetration of the crystalline lattice. These observations prove that nanowires can sustain large stress (>10 GPa) induced by lithiation without breaking, indicating that nanowires are very good candidates for battery electrodes.
Although the work was carried out using tin oxide nanowires, the experiments can be extended to other materials systems, either for cathode or anode studies, according to Huang.
