Rechargeable liquid fuels set out to power electric vehicles

9 October 2019

Novel rechargeable “e-fuel” technology, developed by a Hong Kong-based Croucher Senior Research Fellow and capable of recharging electric vehicles in minutes, could pave the way for a much greater role for renewables in energy generation in the future.

Renewable energy carries the potential to be a highly effective tool in combating climate change. Yet the intermittent nature of key sources such as solar and wind present major challenges for energy scientists and engineers. For example, the sun doesn’t shine every day nor the wind blow with the same strength yet consistent levels of energy generation need to be available for grids and other uses.

Capturing such forms of energy so that they can be deployed whenever and wherever needed requires new energy storage technologies that are scalable, efficient, site-dependent, durable and safe.

This is the quest being undertaken by Professor Tianshou Zhao (Croucher Senior Research Fellowship 2008) of Hong Kong University of Science and Technology (HKUST), who is leading an interdisciplinary research team involving electrochemists and thermofluidic scientists to develop such technology.

“We have successfully developed a stable lithium-sulfur battery that promises to be energy-dense and capable of storing energy at low cost, and can be applied to both electric vehicles and grids transmitting a high fraction of solar and wind energy,” Zhao explained.

In addition, the team’s work has led to a further significant development. “The biggest excitement for us is that we can transform the lithium-sulfur battery to a flow system, or e-fuel, as we call it,” Zhao said.

The novel liquid fuel can be recharged with electricity from solar photovoltaics (PVs) and wind turbines and deployed on demand. Similar to fossil fuels, the electricity generated by e-fuel power packs can be integrated into the grid as well as power off-grid communities.

While recharging a current battery for an electric vehicle lasts hours, recharging a vehicle with e-fuel takes a matter of minutes. What’s more, as e-fuel is rechargeable, it doesn’t disappear as fossil fuels do after consumption. At the recharging station, the energy-depleted e-fuel is removed from the fuel tank, which is then refilled with fully charged e-fuel.

The e-fuel system adopts the chemistry of a lithium-sulfur battery in order to leverage the high capacity of lithium metal and low cost of the sulfur cathode.

However, challenges still remain for the team to overcome. First, dendrites forming on the lithium surface may shorten the battery life. Second, the discharged sulfur can dissolve and diffuse, damaging the lithium anode.

Assistant Professor Chen Qing, who is working on the project with Zhao, explained the team’s new methodology to form a porous lithium anode with surface protection to solve this difficulty. While such protection had previously involved impractical, strenuous fabrication procedures, the Zhao team has made thermodynamics work on their behalf. “With two spontaneous reactions, we formed a porous lithium anode on a carbon skeleton, and coated it with a protective, composite layer,” he said.

This simple yet effective approach led to one of the best performance records yet achieved for a high-loading lithium-sulfur battery.

While the research is still on-going, selected results have been published in Nature Communications.

Professor Tianshou Zhao is the Cheong Ying Chan Professor of Engineering and Environment, Director of HKUST Energy Institute, Chair Professor of Mechanical and Aerospace Engineering, and Senior Fellow of the HKUST Jockey Club Institute for Advanced Study. Zhao combines his expertise in research and technological innovation with a commitment to creating clean energy production and storage devices for a sustainable future. He has made seminal contributions in the areas of fuel cells, advanced batteries, multi-scale multiphase heat and mass transport with electrochemical reactions, and computational modelling. He received his Croucher Senior Research Fellowship in 2008.

To view Tianshou Zhao’s Croucher profile, please click here.