The world’s smallest battery — its anode a single nanowire one seven-thousandth the thickness of a human hair — has been created.
The tiny, rechargeable, lithium-based battery was formed inside a transmission electron microscope at the Center for Integrated Nanotechnologies (CINT), a Department of Energy research facility jointly operated by Sandia and Los Alamos national laboratories.
"The methodology that we developed should stimulate extensive real-time studies of the microscopic processes in batteries and lead to a more complete understanding of the mechanisms governing battery performance and reliability," said Sandia researcher Jiyanyu Huang.
Nanowire-based lithium ion batteries could provide big improvements in power and energy density, meaning the research should help improve plug-in hybrid electric vehicles, laptops and cellphones.
Huang's battery consists of a single tin oxide nanowire anode 100 nanometers in diameter and 10 micrometers long, a bulk lithium cobalt oxide cathode three millimeters long and an ionic liquid electrolyte. It allows researchers to observe changes in atomic structure during charging and discharging of the individual 'trees'.
An unexpected find was that the tin oxide nanowire rod nearly doubles in length during charging — not in width, as was previously thought — a fact that could help avoid short circuits that shorten battery life.
Huang’s group found this flaw by following the lithium ions as they travel along the nanowire and create what the researchers christened the 'Medusa front' — an area where the 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," said Huang.
“Our observations — which initially surprised us — tell battery researchers how these dislocations are generated, how they evolve during charging, and offer guidance in how to mitigate them."
The electronic noise level generated from the measurement system was too high to read electrical currents, but Sandia co-author John Sullivan estimates that the battery achieved a current of one picoampere during charging and discharging. The nanowire was charged to a potential of about 3.5 volts, Huang said.