“Reversible” Energy Storage For Better, Cheaper, Non-Toxic Batteries
Lithium-ion technology dominates today’s energy storage market, but new alternatives are beginning to bubble up from research laboratories. In the latest development, a team of researchers at Pacific Northwest National Laboratories has unlocked the secret behind a reversible formula that could be used for low cost grid scale energy storage.
Re-Thinking An Energy Storage Formula
The new energy storage breakthrough is based on the familiar zinc-manganese formula. Researchers have been tinkering around with rechargeable zinc-manganese batteries for many years but they have gotten stuck on one problem: getting the manganese to stay on the positive electrode.
After only a few cycles manganese drifts off the electrode and settles into the electrolyte. Once that happens, the battery can hold only a fraction of its intended charge.
That may seem like a lost cause, but the allure of storing energy with relatively cheap, abundant, non-toxic materials is irresistible, so the PNNL team decided to give it another try.
The researchers started from scratch and built their own battery with the aim of finding out exactly why the manganese sloughs off. After subjecting it to chemical and structural analysis, they decided to rethink their entire approach.
The PNNL realized that they had been coming to the problem just like other researchers, with the idea that the zinc-manganese energy storage formula works like lithium-ion.
In a lithium-ion battery, lithium ions are simply passed back and forth between two electrodes. The new study revealed that when a zinc-manganese battery goes through charging cycles, it does something entirely different. The active materials in the battery undergo a reversible chemical reaction and create a new material, zinc hydroxyl sulfate.
A (Really) Rechargeable Non-Toxic Energy Storage Alternative
With that knowledge in hand, the PNNL team developed a strategy for slowing down the rate at which manganese could detach from the electrode:
…they added manganese ions to the electrolyte in a new test battery and put the revised battery through another round of tests. This time around, the test battery was able to reach a storage capacity of 285 milliAmpere-hours per gram of manganese oxide over 5,000 cycles, while retaining 92 percent of its initial storage capacity.
Sweet. Here’s the lowdown from the study, which you can find in the journal Nature Energy under the title “Reversible aqueous zinc/manganese oxide energy storage from conversion reactions:”
Here we demonstrate a highly reversible zinc/manganese oxide system in which optimal mild aqueous ZnSO4-based solution is used as the electrolyte, and nanofibres of a manganese oxide phase, α-MnO2, are used as the cathode. We show that a chemical conversion reaction mechanism between α-MnO2 and H+ is mainly responsible for the good performance of the system.
The team, which includes the University of Washington, also found that the zinc anode was highly stable.
Beyond Li-Ion
Lithium-ion is not going down without a fight, and researchers are still finding new ways to improve the technology.
However, the new PNNL energy storage solution could easily win on cost as well as energy density.
