Flow batteries, capable of storing large quantity of energy, have great potential to increase the flexibility of power systems and improve dynamic response to energy demand. Flow batteries are a rechargeable electrochemical energy system, in which electrolytes contain one or more dissolved electroactive species, and the chemical energy in electrolytes is reversibly converted to electricity. The fuel electrolyte is stored externally in a tank, and delivered to the reactor. Batteries can be recharged by replacing electrolytes, similar to conventional vehicles, or by external electric power that is similar to secondary batteries. Flow battery technology offers advantages in energy storage and conversion, including: 1.) large capacity (determined by the external tank volume); 2.) negligible degradation when left completely discharged for long periods; 3.) charge/recharge through electrolyte replacement or external power source; and 4.) no permanent damage when electrolytes are accidentally mixed. Among the major types of flow batteries, the vanadium redox flow battery is a type of rechargeable flow battery that employs vanadium ions at different oxidation states to store chemical potential energy.

Lithium-based batteries have received a great deal of research attention in recent years owing to their relatively high efficiency and energy density. A major hurdle to their development, however, is the insufficient low energy capability as opposed to fossil fuels. The gasoline’s specific energy is about 13,000 Wh/kg, an order-of-magnitude higher than that of Li-ion batteries. Li-air batteries are an emerging area with a great promise of high specific energy storage. Their theoretical specific energy reaches around 11,680 Wh/kg, comparable to gasoline and higher than methanol. Their unique feature is that the cathode active material--oxygen is obtained from the ambient environment, and the anode uses lithium metal, rather than Li intercalated graphite (LiC6) as that in Li-ion batteries. Air cathodes are a major area of study in non-aqueous Li-air battery. In cathodes, Li compounds such as Li₂O₂ or Li₂CO₃ are produced during discharging. These substances in general have low solubility in major non-aqueous electrolytes, therefore precipitate at the reaction surface. They are also poor electric conductor, causing electrode passivation. As discharging proceeds, the precipitates accumulate inside the pore network, deteriorating voltage drop.

In this talk, I will discuss the ongoing work of modeling development on RFBs and Li-air batteries at UCI. The models are formulated by rigorously accounting for the conservation of mass, momentum, species, charges, and energy, in conjunction with the electrochemical reaction kinetics of vanadium RFBs and Li-air batteries. I will emphasize the similarity and difference in modeling the two types of new battery systems. The models are validated against experimental data.