An artificial interphase allows for successful diffusion of Mg2+ ions during recharge, bypassing a traditional limitation of Mg batteries

By Aalyia Shukat, contributing writer

A group of scientists at the
National Renewable Energy Laboratory (NREL) have discovered a technique that allows Magnesium (Mg) batteries to be recharged. By
generating an artificial metal-electrolyte interphase to protect the anode’s
surface, the team was able to prevent the buildup of a chemical barrier formed during
discharge that blocked recharge efforts. The recently published article, “An Artificial Interphase Enables Reversible
Magnesium Chemistry in Carbonate Electrolytes
,” in the prestigious Nature
Chemistryjournal notes the successful reversible Mg chemistry of assembled
prototype cells.

“This finding will provide a new
avenue for magnesium battery design,” said Seoung-Bum Son, first author and
scientist at NREL. The other co-authors from NREL include Steve Harvey, Adam
Stokes, and Andrew Norman. “The dominant lithium-ion battery technology is
approaching the maximum amount of energy that can be stored per volume, she
said, so “there is an urgent need to explore new battery chemistries.”

Magnesium-based batteries have
several advantages over the prolific lithium-ion (Li-ion) batteries, including
cost-effectiveness (Mg is the fifth most abundant element on earth)
and a higher volumetric capacity (3,832 mAh/cm3 versus 2,061 mAh/cm3
for Li-ion). However, Mg batteries have traditionally had the major
disadvantage of the formation of a surface layer from the metal-to-electrolyte
chemical interaction.

Typically, recharging a battery
forces the ions at the cathode electrode back to the anode to a point at which there is enough electrochemical potential. Li-ion batteries have a permeable
layer, or solid-electrolyte interphase (SEI), between the metal and electrolyte
that allows for ions to pass while preventing the electrolyte from being
reduced.

For Mg batteries, the decomposition
at the interface of the metal generates a blocking passivation layer in Mg
batteries that prevents any reversible electrochemical reaction from occurring. Furthermore,
in the past, a metal-solid interphase was not feasible because the divalent Mg2+
ions typically could not penetrate the layer. And, in scenarios in which the Mg
ions could flow in a reverse direction, it was through a highly corrosive
liquid electrolyte, which prevented the successful implementation of a
high-voltage Mg-battery.

 

Illustration by John Frenzl/NREL.

The novel interphase made from
polyacrylonitrile and magnesium-ion salt demonstrated a highly reversible Mg
chemistry in oxidation-resistant electrolytes. The team at NREL successfully
deployed the artificial interphase in a Mg/V2O5 full cell in the
water-containing, carbonate-based electrolyte to enable reversible cycling.