World's tiniest battery out

 Its anode a single nanowire one seven-thousandth the thickness of a human hair, the tiny rechargeable, lithium-based 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.

More stringent investigations of their operating properties should improve new generations of plug-in hybrid electric vehicles, laptops and cell phones. “What motivated our work is that lithium ion batteries (LIB) have very important applications, but the low energy and power densities of current LIBs cannot meet the demand,” said Huang.

“To improve performance, we wanted to understand LIBs from the bottom up, and we thought in-situ TEM could bring new insights to the problem.”

The tiny battery created by Huang and co-workers consists of a single tin oxide nanowire anode 100 nanometre in diameter and 10 micrometre long, a bulk lithium cobalt oxide cathode three millimeters long, and an ionic liquid electrolyte.

An unexpected find of the researchers was that the tin oxide nanowire rod nearly doubles in length during charging—far more than its diameter increases.

“Manufacturers should take account of this elongation in their battery design,” Huang said.

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. “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,” Huang said.

Lithiation-induced volume expansion, plasticity and pulverisation of electrode materials are the major mechanical defects that plague the performance and lifetime of high-capacity anodes in lithium-ion batteries, Huang said.

“So our observations of structural kinetics and amorphisation (the change from normal crystalline structure) have important implications for high-energy battery design and in mitigating battery failure.”

“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,” he said.

“Our experiments also lay a foundation for in-situ studies of electrochemical reactions, and will have broad impact in energy storage, corrosion, electrodeposition and general chemical synthesis research field.”

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