HKU develops new method to prepare more efficient and safe lithium batteries|Cation|Electrolyte|Anion|Polymer

Covered Automotive In response to climate change and the need for clean energy, there is a growing interest in making safer, higher capacity batteries to enable the continued growth of electric vehicles and grid energy storage systems.

A new generation of lithium-ion batteries developed by a research team at the University of Hong Kong (HKU) is expected to provide a viable solution, according to foreign media reports. The team is headed by Dr Dongming Shen of the Department of Mechanical Engineering. The researchers have identified a range of anionic network solid electrolytes that could form the building blocks of a new battery, making it safer, with higher power density and longer life.

Lithium-ion batteries are currently the most commonly used batteries, benefiting from advanced energy storage technologies. Commercial battery technology uses an electrolyte and a carbon cathode, which has disadvantages such as safety issues, limited lifespan and insufficient power density.

In the electrolyte, the lithium cation and the counter anion move in opposite directions to conduct electricity. Typically, the anions move at least four times faster than the lithium ions, so the lithium cations conduct only 20% of the total ionic current, and too many anions accumulate at the interface between the electrodes and the electrolyte, leading to short circuits and capacity loss within the battery.

The electrolyte's flammability, instability relative to lithium metal, and low ion conductivity have driven research into solid electrolytes. Solid electrolytes are safer and compatible with lithium metal cathodes. Currently, lithium metal cathodes exhibit the highest theoretical specific power capacity.

The team designed a single ion-conducting polymer electrolyte that effectively increases the cation conductivity (by at least a factor of four). This anion network polymer consists of polyethylene glycols with branched chains in different stoichiometric ratios bridging the boron anion, enabling highly selective cation transport by binding and entangling the passing anion in the polymer framework.

The cation conductivity within the polymer, which is controlled by the systematic engineering of chain segment mobility, contributes to the development of comprehensive design rules for new highly conductive solid electrolytes.

This single ion-conducting polymer electrolyte successfully overcomes long-standing problems with solid electrolytes in current batteries, such as low cycling capacity and high overpotential. The new ion-selective electrolyte design rules are expected to accelerate the realisation of rechargeable lithium metal batteries.

Researcher Jing-Yi Gao said, "The single ion-conducting polymer electrolyte is expected to open up a new type of battery chemistry that will bring disruptive changes to the rechargeable battery field and provide high levels of safety, high power density and long life cycles."

Dr Shin added that the use of this ion-selective electrolyte in batteries allows for fast charging. "Allowing electric vehicles to be fully charged in the time it takes to drink a cup of coffee. This advantage will open up a new era of clean energy."