The tiny rechargeable lithium-based battery was formed inside a transmission electron microscope (TEM) at the Center for Integrated Nanotechnologies, a Department of Energy research facility by a team led by Jianyu Huang. The center is jointly operated by Sandia and the 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 in a statement.
Lithium-ion batteries' nanowire-based material has the potential to provide major enhancements in power and energy density compared to bulk electrodes. Next-generation plug-in hybrid electric vehicles, laptops, and cell phones should improve with its usage, the labs said.
"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,'' Huang said. "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 new battery consists of a single tin oxide nanowire anode with a diameter of 100 nanometers and a length of 10 micrometers, a bulk lithium cobalt oxide cathode three millimeters long, and an ionice liquid electrolyte. During charging, the tin oxide nanowire rod nearly doubles in length -- far more than its diameter increases -- something the researchers called an unexpected finding. This could help avoid short circuits that may decrease battery life, Huang said, and the elongation is something battery manufacturers should pay attention to in the design process.
The research team found the flaw by following the progression of the lithium ions as they travel along the nanowire. The process created an area where high density of mobile dislocations causes the nanowire to bend and wiggle as the front progresses, which the researchers dubbed the "Medusa front." Lithium penetration of the crystalline lattice causes a "web of dislocations," according to the labs. The team found that nanowires can withstand high levels of stress without breaking, making them good candidates for battery electrodes, Huang said.
"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. "This is the closest view to what's happening during charging of a battery that researchers have achieved so far."
The big mechanical defects that affect the performance and lifetime of high-capacity anodes in lithium-ion batteries are the "lithiation-induced volume expansion, plasticity, and pulverization of electrode materials,'' Huang said. The team's findings have important implications for high-energy battery design and insight into preventing battery failure, he said.
"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," Huang said.
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