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Researchers at the University of Hong Kong have discovered a series of solid anion lattice electrolytes that may offer at least a four-fold improvement in cation transport for lithium-metal battery applications.
Although lithium metal batteries could offer greater safety, better energy density, and lighter weight than lithium-ion technology - thanks to the replacement of the heavier graphite with lithium metal as the anode - this battery chemistry does not work well with conventional electrolytes.
Therefore, research efforts have been directed towards solid electrolytes that can offer better performance and are compatible with the lithium metal anode, which currently has the highest theoretical specific power capacity.
Now, researchers at the University of Hong Kong (HKU) have designed solvent-free, single-ion polymer electrolytes that have provided a significant improvement in ion transport for lithium-metal battery applications.
In liquid electrolytes, lithium cations and anions move in opposite directions to conduct electricity. Normally, anions move at least four times faster than lithium cations, so lithium cation transfer contributes only a small fraction (20%) of the overall ionic current. Meanwhile, an excess of anions accumulates at the interface between the electrode and the electrolyte, causing internal short circuits and loss of battery capacity.
New single-ion conducting polymer electrolytes designed by the HKU researchers overcome these limitations and increase cation transport by at least four times.
Anionic network polymers are made up of borate anions linked by ethylene glycol branch bonds of different stoichiometric ratios, where the anions are bound to the polymer backbone, allowing highly selective cation transport.
The researchers controlled the cationic conductivity within the polymer by systematically engineering segmental mobility. This helped them draw up the design rules of thumb for a new class of highly conductive solid electrolytes, successfully overcoming persistent problems with todays solid electrolytes, such as low cyclability and high overpotential.
“We believe that single-ion conducting polymer electrolytes would open up the possibility of new battery chemistries that would revolutionize the field of rechargeable batteries, offering a high level of safety, high power density, and long cycle life,” says Jingyi. Gao, first author of the research paper.
According to HKUs Dong-Myeong Shin, ion-selective electrolytes can also speed up charging due to their low overpotential. “It can allow electric vehicles to be fully charged in just the time it takes to have a cup of coffee. This remarkable advantage will open a new era in the world of clean energy”, he adds. |
