Water-containing electrolyte might transform battery production

Researchers working on battery development have typically seen water as the enemy. It had previously been thought that lithium-ion batteries generally needed to be produced under extremely dry conditions in order for them to hold large amounts of charge. 

Now, a research team at the US Department of Energy’s (DOE) Argonne National Laboratory has developed a new battery electrolyte that can hold a thousand times more water than conventional electrolytes, according to Argonne senior battery chemist Zhengcheng ‘John’ Zhang.

“We’ve always thought that water was going to cause major problems for a lithium-ion battery,” he said. “However, it turns out that our formulation can hold dramatically more than previously known, which could help reduce costs in battery fabrication.”

In a battery, ions move between the two electrodes to balance the electrical charge created during charging and discharging, a process that is made possible by electrolytes. However, as lithium-ion batteries are  “dry-cell” batteries, they can only contain trace amounts of moisture, making the battery-production process long and expensive.

By using an electrolyte composed of two kinds of salts – a lithium salt and an ionic liquid – the DOE team was able to create a situation in which vastly more water molecules could be stably absorbed by the electrolyte.

Argonne computational scientist Wei Jiang used the Argonne Leadership Computing Facility’s (ALCF’s) Theta supercomputer to perform simulations of the electrolyte near the electrode surface to get a picture of the behaviour of the water molecules and observe the results of the experiment. 

“The simulations gave us an atomic-scale view into how water affects battery performance, providing insights that were not possible with laboratory experiments alone,” Jiang said.

Even small quantities of water can degrade battery performance. This is because water molecules react with the electrolyte itself, generating corrosive byproducts that eat away at the battery.

However, the new electrolyte could separate and bind up water, sequestering individual water molecules. The Argonne team’s experimental work shows that it can contain as much as a thousandfold more water than electrolytes currently used in electric vehicle and consumer batteries.

The secret lies in the fact that the water molecules do not gather into ‘puddles’ and thereby lose reactivity.

“Even at the electrode surfaces, which are susceptible to water clustering, our atomistic simulations show that the single water molecules are very stable,” Jiang said.

The team identified a quantitative relationship between the electrolyte’s water tolerance and the ‘saltiness’ of the electrolyte’s components. The working hypothesis is that the water molecule is trapped by the different ions at a specific range of concentration ratios in the salty medium, which makes it less reactive.

The research paper – ‘An environmentally benign electrolyte for high-energy lithium metal batteries‘ – has been published in the journal ACS Applied Materials and Interfaces.

Innovation in the battery sector has recently been on the rise, with the UK government providing funding for a EV battery gigaplant in Northumberland and Nissan announcing its plans to have electric vehicles with solid-state batteries on sale in six years time. 

This study provides a potential pathway for battery manufacturers to incorporate water in the battery fabrication process, allowing for lower-cost, more environmentally friendly manufacturing, according to Zhang.