CUHK Research: Changing the world

Bridging the gap in battery technologies In the spectrum of battery technologies, on one end is the lithium-ion (Li-ion) battery used in gadgets and electric vehicles, which is lightweight and powerful but also flammable and toxic. On the other end, flow batteries are safe and allow easy expansion of the storage capacity in large-scale applications such as solar and wind farms, but they have a lower energy density. “In the world of batteries, you have something of a very high energy density which is usually flammable and very dangerous. You also have something that is very safe but with a low energy density. We are trying to bridge this gap,” Professor Lu says. She joined CUHK in 2013 after obtaining her PhD degree in material science and engineering at the Massachusetts Institute of Technology. “When I was a student, I worked on more conventional, non-aqueous types of batteries – those that have the safety hazard issues but have the highest energy densities,” she recalls. “But coming to CUHK, I decided that building an absolutely safe battery with a high enough energy density is one of the things I wanted to address the most.” “The grand challenge we are tackling is to make energy storage technology both safe and energy-dense so that it can be widely used to store renewable energy.” Making flow batteries high- powered Safe, low-cost energy storage technologies are critical for large-scale utilisation of renewable energy. Flow batteries, in which electrolyte flows through one or more electrochemical cells in large external tanks, are used in solar farms. But flow batteries on the market are too costly to be widely used because vanadium, the element composing the electrolyte, is limited and expensive. Professor Lu wants to break the bottleneck by using a much cheaper element – sulphur – to replace vanadium. Different polysulfide-based flow battery systems have been developed since the 1980s. But extensive commercialisation has 64