As climate change presents a significant challenge and clean energy demand increases, there is a growing need to address concerns regarding the production of batteries that offer elevated levels of safety and capacity. This is essential in supporting the ongoing expansion of electric vehicles and grid energy storage systems.
Dr Dong-Myeong Shin and his team from the Department of Mechanical Engineering at the University of Hong Kong (HKU) have developed a new generation of lithium-ion batteries that could provide a viable solution. These batteries incorporate a series of anionic network solid electrolytes, which enhance safety, increase power density, and extend the battery’s lifespan.
The results of this research have been documented in an article titled “Engineered networking in a family of solvent-free single-ion conducting borate network polymer electrolytes for Li-metal battery applications” and published in the Chemical Engineering Journal.
Lithium-ion batteries are widely used due to their advanced energy storage capabilities. However, the current commercial battery technology primarily employs liquid electrolytes and carbonaceous anodes, which pose safety concerns, have a limited lifespan and lack sufficient power density.
Liquid electrolytes function by allowing lithium cations and counter anions to move in opposite directions to create an electric current. Typically, anions move at a faster pace than lithium cations, resulting in the transfer of only a small fraction (20%) of the overall ionic current through the lithium cations. This creates an excess of anions at the electrode-electrolyte interface, which can lead to internal short circuits and reduce the battery’s capacity over time.
Liquid electrolytes are highly flammable, unstable in the presence of lithium metal, and possess low ion selectivity for conduction. As a result, researchers are focusing on developing solid electrolytes that can offer better safety levels and are compatible with lithium metal anodes. Lithium metal anodes currently have the highest theoretical specific power capacity.
The team has developed single-ion conducting polymer electrolytes that exhibit a significant increase (at least 4-fold) in cationic transport. The team’s anionic network polymers consist of borate anions linked together by branched ethylene glycol linkers with varying stoichiometric ratios, with the anions incorporated into the polymer framework to enable highly selective cation transport. The team was able to control cation conductivity by systematically manipulating segmental mobility, paving the way for a new class of highly conductive solid electrolytes with comprehensive design rules.
With the single-ion conducting polymer electrolytes addressing persistent issues associated with current solid electrolytes in battery cells, including low cyclability and high overpotential, a new design rule for ion-selective electrolytes is poised to accelerate the development of rechargeable Li-metal batteries.
The first author of the paper and a PhD student of Dr Shin, Jingyi Gao, expressed optimism that the single-ion conducting polymer electrolytes would pave the way for new battery chemistries that will transform the field of rechargeable batteries. Gao believes that the new technology will offer exceptional safety, high power density, and long cycle life.
Dr Shin also notes that ion-selective electrolytes in batteries can facilitate fast charging due to their low overpotential. He believes that this technology could enable electric vehicles to be fully charged in the time it takes to drink a cup of coffee, unlocking a new era of clean energy.
