NREL scientists say they have pioneered a method which enables the reversible chemistry of Mg metal in the noncorrosive carbonate-based electrolytes and have tested the concept in a prototype cell.
NREL believes the technology possesses potential advantages over lithium-ion batteries – notably, higher energy density, greater stability and lower cost and the team said that their approach enables them to investigate material degradation and failure mechanisms at the micro- to nano-scale.
Chunmei Ban of NREL explained that dominant lithium-ion battery technology is approaching the maximum amount of energy that can be stored per volume and, therefore, there was an urgent need to explore new battery chemistries capable of providing more energy at a lower cost.
The team hopes that this discovery will provide a new avenue for Mg battery design.
An electrochemical reaction powers a battery as ions flow through a liquid (electrolyte) from the negative electrode (cathode) to the positive electrode (anode). For batteries using lithium, the electrolyte is a salt solution containing lithium ions. The scientists said that the chemical reaction must be reversible, so that the battery can be recharged.
Mg batteries theoretically contain almost twice as much energy per volume as lithium-ion batteries. However, chemical reactions of the conventional carbonate electrolyte create a barrier on the surface of Mg that in previous research has prevented the battery from recharging. The mg ions could flow in a reverse direction through a highly corrosive liquid electrolyte, the team say, but that barred the possibility of a successful high-voltage Mg battery.
To overcome this, the researchers developed an artificial solid-electrolyte interphase from polyacrylonitrile and Mg-ion salt that protected the surface of the Mg anode. This, the team explains, protected anode demonstrated markedly improved performance
The scientists said that they assembled prototype cells to prove the robustness of the artificial interphase, finding ‘promising’ results: the cell with the protected anode enabled reversible Mg chemistry in carbonate electrolyte, which the team claim, has never been demonstrated before.
The cell with this protected Mg anode also delivered more energy than the prototype without the protection, and continued to do so during repeated cycles, the team adds. Furthermore, the group say it has demonstrated the ‘rechargeability’ of the Mg-metal battery. According to NREL, this provides an ‘unprecedented’ avenue for simultaneously addressing the anode/electrolyte incompatibility and the limitations on ions leaving the cathode.
In addition to being more readily available than lithium, NREL explains that Mg has other potential advantages over more established battery technology. Firstly, Mg releases two electrons to lithium's one, giving it the potential to deliver nearly twice as much energy as lithium. Secondly, unlike lithium-ion batteries, Mg-metal batteries do not experience the growth of dendrites, which are crystals that can cause short circuits and consequently, dangerous overheating and even fire.
