Lithium Boosts Flow Battery Energy Storage

Renewable energy generation is inconsistent, creating a mismatch between when power is produced and when it is consumed. Solar panels generate electricity during sunny hours, while wind turbines operate when wind speeds are sufficient. Demand for electricity does not pause during cloudy weather or calm periods. Researchers at Stony Brook University and Purdue University are working to close this gap using redox flow batteries that store excess renewable power for later release.

A recent study led by Professor Nav Nidhi at Stony Brook University explored a cheaper alternative to standard vanadium-based redox flow batteries. The team included PhD candidate Kuldeepsinh Raj and Professor Xiaoliang Wei’s group at Purdue University. Mahla Sarfaraz Khabbaz at Purdue conducted the experimental testing, while Raj handled the computational modeling.

Redox flow batteries store energy in liquid electrolytes held in two separate external tanks. These liquids are pumped through a central cell where electrochemical reactions occur. A membrane separates the two liquids but allows ions to pass between them. Unlike lithium-ion batteries, which use solid electrodes that lock energy capacity and power output together, flow batteries separate these factors. The power output depends on the cell size, while the energy storage capacity depends on the tank size.

Standard ferrocyanide batteries use iron paired with sodium or potassium. These materials have low solubility, which limits the amount of energy they can store. The study tested how replacing sodium or potassium ions with lithium ions would affect the electrolyte. Raj reported that lithium-based ferrocyanide was six to eight times more soluble than its sodium and potassium counterparts under strongly alkaline conditions. This increased solubility allows for higher energy storage in the same volume of liquid.

Molecular dynamics simulations and quantum chemistry calculations explained why lithium performs better. Raj stated that lithium ions interact strongly with both water and ferrocyanide. These interactions form connected structures that remain dissolved even at high concentrations. The research identified the molecular mechanism behind the enhanced solubility and delayed saturation seen in the lithium-based electrolytes.

Higher electrolyte concentrations create a trade-off between energy density and fluid dynamics. As the solution becomes more concentrated, viscosity increases. This makes the liquid harder to pump and may reduce battery efficiency. Nidhi noted that flow batteries offer a distinct advantage for renewable energy systems. Solar farms could store electricity generated during the day for use during high-demand evening hours. The team believes making these batteries more affordable and durable will support a more reliable electricity supply.