The new battery is built from pumpkin-shaped
molecules called cucurbit[6]uril (CB[6]) which are organized in a
honeycomb-like structure.
Credit: Image courtesy of Institute for Basic Science
Lithium ion batteries (LIBs) are a huge
technological advancement from lead acid batteries which have existed
since the late 1850's. Thanks to their low weight, high energy density
and slower loss of charge when not in use, LIBs have become the
preferred choice for consumer electronics. Lithium-ion cells with cobalt
cathodes hold twice the energy of a nickel-based battery and four-times
that of lead acid. Despite being a superior consumer battery, LIBs
still have some drawbacks. Current manufacturing technology is reaching
the theoretical energy density limit for LIBs and overheating leading to
thermal runaway i.e. "venting with flame" is a serious concern.
South Korean researchers at the Center for Self-assembly and
Complexity, Institute for Basic Science (IBS), Department of Chemistry
and Division of Advanced Materials Science at Pohang University, have
created a new LIB made from a porous solid which greatly improves its
performance as well as reducing the risks due to overheating.
Since 2002 there have been over 40 recalls in the US alone due to
fire or explosion risk from LIBs used in consumer electronic devices.
These types of batteries, in all of their different lithium-anode
combinations, continue to be an essential part of modern consumer
electronics despite their poor track record at high temperatures.
The Korean team tried a totally new approach in making the batteries.
According to Dr. Kimoon Kim at IBS, "we have already investigated high
and highly anisotropic [directionally dependent] proton conducting
behaviors in porous CB[6] for fuel cell electrolytes. It is possible for
this lithium ion conduction following porous CB[6] to be safer than
existing solid lithium electrolyte -based organic-molecular
porous-materials utilizing the simple soaking method." Current LIB
technology relies on intercalated lithium which functions well, but due
to ever increasing demands from electronic devices to be lighter and
more powerful, investigation of novel electrolytes is necessary in
order.
The new battery is built from pumpkin-shaped molecules called
cucurbit[6]uril (CB[6]) which are organized in a honeycomb-like
structure. The molecules have an incredibly thin 1D-channel, only
averaging 7.5 Å [a single lithium ion is 0.76 Å, or .76 x 10-10 m] that
runs through them. The physical structure of the porous CB[6] enables
the lithium ions to battery to diffuse more freely than in conventional
LIBs and exist without the separators found in other batteries.
In tests, the porous CB[6] solid electrolytes showed impressive
lithium ion conductivity. To compare this to existing battery
electrolytes, the team used a measurement of the lithium transference
number (tLi+) which was recorded at 0.7-0.8 compared to 0.2-0.5 of
existing electrolytes. They also subjected the batteries to extreme
temperatures of up to 373 K (99.85° C), well above the 80° C typical
upper temperature window for exiting LIBs. In the tests, the batteries
were cycled at temperatures between 298 K and 373 K ( 24.85° C and
99.85° C) for a duration of four days and after each cycle the results
showed no thermal runaway and hardly any change in conductivity.
Various conventional liquid electrolytes can incorporate in a porous
CB[6] framework and converted to safer solid lithium electrolytes.
Additionally, electrolyte usage is not limited to use only in LIBs, but a
lithium air battery potentially feasible. What makes this new technique
most exciting is that it is a new method of preparing a solid lithium
electrolyte which starts as a liquid but no post-synthetic modification
or chemical treatment is needed.
Story Source:
The above post is reprinted from
materials provided by
Institute for Basic Science. The original item was written by Daniel Kopperud.
Note: Materials may be edited for content and length.