How water can both help and hinder lithium-ion batteries

Renewable energy needs a place to be stored. This is often done using lithium-ion batteries (LIBs), which is not the perfect solution. LIBs — which work by moving lithium ions through an electrolyte between the battery electrodes — can be volatile, posing risks like overheating.

Míguez-Roel et al. studied how water added to the electrolyte mixture can help with the energy storage capabilities of LIBs.

It is generally difficult for lithium ions to move around in an electrolyte. The fluid is tightly packed and viscous, forcing ions to slow down and squeeze through.

“Water changes this because it’s small and polar. It inserts itself around the ions — especially the small, highly charged Li+ — and partially screens the electrostatic attraction between them,” said author Hadrián Montes-Campos. “That weakens ion pairing and lets ions move more independently.”

At concentrations of 5%-10% and high operating voltages, the researchers found water can act as a lubricant in the electrolyte to improve lithium transport.

But it can also be harmful if too much is added. Free water molecules — uncoordinated to ions — can decompose, thus creating safety and lifetime problems for the battery.

“Free water isn’t just inert filler,” Montes-Campos said. “Under the battery’s operating voltage, it can split apart electrochemically into hydrogen and oxygen gas, a process that damages the electrode and shortens the electrolyte’s useful lifespan.”

The group hopes their work will offer concrete, quantitative guidelines to battery science, rather than treating water as an all-or-nothing.

“Our work characterizes a competition between two effects of water: the improvement of transport properties and capacitance on one hand, and the risks associated with the electrolysis of free water on the other,” Montes-Campos said.

Source: “Interfacial structure and electrochemical behavior of a ternary ionic liquid-based electrolyte with water and lithium salt: A computational analysis,” by Ángel Míguez-Roel, Martín Otero-Lema, Raúl Lois-Cuns, Miguel A. Boado, Trinidad Méndez Morales, Luis M. Varela, and Hadrián Montes-Campos, Journal of Chemical Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0341138 .