Scientists develop new all-chlorine flow battery

Introduction: A Chinese and American research team has developed an all-chlorine membraneless redox flow battery , which is said to have a round-trip energy efficiency of 91% and an energy density of 125.7Wh/L at 10mA/cm2. The device is based on an aqueous electrolyte made of sodium chloride (NaCl) and uses chlorine (Cl2/Cl-) oxidative coupling as the active material of the positive electrode .

A team of scientists from the University of Maryland and East China University of Science and Technology has fabricated a reversible chlorine redox flow battery for stationary energy storage.

The all-chlorine device has a membrane-less design based on an aqueous electrolyte made of sodium chloride (NaCl) that uses chlorine (Cl2/Cl-) oxidative coupling as the active material for the positive electrode. The researchers said that the theoretical capacity of Cl2/Cl- is 755 mAh/g, which is more than twice that of current vanadium oxide batteries (VO2+/VO2+, 226 mAh/g). In addition, sodium chloride is one of the cheapest commodities due to its abundant sources in seawater and large-scale production.

One of the main costs of vanadium redox flow batteries is the ion-permeable membranes used to minimize so-called crossover. In the battery configuration proposed by the team, chlorine is immiscible with the electrolyte, which means that membranes to prevent crossover are not needed, further reducing costs.

The Cl2/Cl- redox reaction in an aqueous sodium chloride electrolyte was evaluated in a concentric cell coated with porous ruthenium oxide and titanium oxide (RuO2-TiO2) designed to promote the oxidation kinetics of chlorine. Carbon tetrachloride (CCl4) was added through the working electrode and electrolyte, and a graphene composite material called NaTi2(PO4)3 was used as the negative electrode.

The battery showed a round-trip energy efficiency of 91% at 10 mA/cm2, an energy density of 125.7 Wh/L, and a high voltage efficiency, which scientists attributed to fast reaction kinetics and membrane-free configuration. According to scholars, these values ​​represent the best performance of liquid flow battery systems in the past 10 years.