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Lithium-ion batteries drive devices from electric cars to
smartphones. And society is demanding more batteries with more capacity from
each battery.
To help meet this demand, Pacific Northwest National
Laboratory’s Environmental Molecular Science Laboratory users and researchers
put their energy behind a clever new idea that, literally, gives batteries a
bit of room to grow. Lithium-ion batteries generate electricity by shuttling
lithium ions through an electrolyte. In a fully charged battery, lithium ions
are stored in a cathode, such as lithium cobalt oxide.
When in use, lithium ions flow from the cathode through an
electrolyte into the anode, most commonly made of carbon. During recharging,
the ions are pushed back to the cathode where they started. Researchers built
upon current technology by making a new type of anode that consists of single
silicon nanoparticles inside carbon shells, much like yolks inside eggs.
In this new design, lithium ions flow from the cathode
through the electrolyte, diffuse through the carbon shells, and enter the
silicon—which can hold ten times as many lithium ions as carbon alone.
By leaving just the right amount of space, the lithiated silicon
nanoparticles swell to fill, but not burst, the carbon shell.
The result?
A lithium-ion battery system that compared to commercial
batteries holds seven times more energy and can be discharged and recharged
five times as many times before it wears out. Critical to its good performance,
the new system forms a stable crust, a solid electrolyte interphase, on the
anode that is a consequence of electrolyte decomposition. Moreover, the team’s
manufacturing process is affordable, efficient, and can be readily scaled up.
