Rechargeable battery discovery promises cheaper renewable energy storage

April 20, 2016 // By PAUL BUCKLEY
A team of researchers based at the US Department of Energy’s Pacific Northwest National Laboratory (Richland, WA) have discovered a rechargeable zinc-manganese battery that is as inexpensive as conventional car batteries but provides a much higher energy density.

The PNNL researchers identified the energy storage potential after realizing the new battery works in a different way than they had assumed. The journal Nature Energy has published a paper that describes the battery.

“The idea of a rechargeable zinc-manganese battery isn’t new; researchers have been studying them as an inexpensive, safe alternative to lithium-ion batteries since the late 1990s,” explained PNNL Laboratory Fellow Jun Liu, the paper’s corresponding author. “But these batteries usually stop working after just a few charges. Our research suggests these failures could have occurred because we failed to control chemical equilibrium in rechargeable zinc-manganese energy storage systems.”

After years of focusing on rechargeable lithium-ion batteries, researchers are used to thinking about the back-and-forth shuttle of lithium ions. Lithium-ion batteries store and release energy through a process called intercalation, which involves lithium ions entering and exiting microscopic spaces in between the atoms of a battery’s two electrodes.

The concept is so engrained in energy storage research that when PNNL scientists, collaborating with the University of Washington, started considering a low-cost, safe alternative to lithium-ion batteries - a rechargeable zinc-manganese oxide battery - they assumed zinc would similarly move in and out of that battery’s electrodes.

After testing, the team was surprised to realize their device was undergoing a different process. Instead of simply moving the zinc ions around, their zinc-manganese oxide battery was undergoing a reversible chemical reaction that converted its active materials into entirely new ones.

Liu and his colleagues started investigating rechargeable zinc-manganese batteries because they are attractive on paper. They can be as inexpensive as the lead-acid batteries because they use abundant, inexpensive materials (zinc and manganese). And the battery’s energy density can exceed lead-acid batteries. The PNNL scientists hoped they could produce a better-performing battery by digging deeper into the inner workings of the zinc-manganese oxide battery.