NREL-led team overcomes major technical obstacle in Mg-metal batteries by developing artificial solid-electrolyte interphase
Magnesium offers a number of advantages over lithium for rechargeable batteries: it is safer and earth-abundant, and doubles the total charge per ion, delivering larger theoretical volumetric capacity compared with a typical lithium-ion battery. Further, in Mg batteries (MB) the anode is energy-dense Mg metal (~ 3,830 Ah l−1)—surpassing the theoretical volumetric energy density of graphite anodes (~ 700 Ah l−1) and even that of lithium metal (2,062 Ah l–1). (Earlier post.)
However, previous research has found that chemical reactions of the conventional carbonate electrolyte created a barrier on the surface of magnesium that prevented the battery from recharging. The magnesium ions could flow in a reverse direction through a highly corrosive liquid electrolyte, but that barred the possibility of a successful high-voltage magnesium battery.
Now, researchers at the Department of Energy’s National Renewable Energy Laboratory (NREL) and their colleagues have discovered a new approach for developing a rechargeable non-aqueous magnesium-metal battery. In a proof-of-concept paper published in Nature Chemistry, they detail a method to enable the reversible chemistry of magnesium metal in noncorrosive carbonate-based electrolytes and the testing of the concept in a prototype cell. The technology possesses potential advantages over lithium-ion batteries—notably, higher energy density, greater stability, and lower cost.
The researchers developed an artificial solid-electrolyte interphase from polyacrylonitrile and magnesium-ion salt that protected the surface of the magnesium anode. This protected anode demonstrated markedly improved performance.
In lithium-ion batteries the conflict between the cathodic and anodic stabilities of the electrolytes is resolved by forming an anode interphase that shields the electrolyte from being reduced. This strategy cannot be applied to Mg batteries because divalent Mg2+ cannot penetrate such interphases. Here, we engineer an artificial Mg2+-conductive interphase on the Mg anode surface, which successfully decouples the anodic and cathodic requirements for electrolytes and demonstrate highly reversible Mg chemistry in oxidation-resistant electrolytes. The artificial interphase enables the reversible cycling of a Mg/V2O5 full-cell in the water-containing, carbonate-based electrolyte. This approach provides a new avenue not only for Mg but also for other multivalent-cation batteries facing the same problems, taking a step towards their use in energy-storage applications.—Son et al.
|Illustration shows how NREL researchers have addressed the problem with making a rechargeable magnesium battery. (Illustration by John Frenzl / NREL) Click to enlarge.|
The scientists assembled prototype cells to prove the robustness of the artificial interphase and found promising results: the cell with the protected anode enabled reversible Mg chemistry in carbonate electrolyte, which 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. Furthermore, the group has demonstrated the rechargeability of the magnesium-metal battery, which provides an unprecedented avenue for simultaneously addressing the anode/electrolyte incompatibility and the limitations on ions leaving the cathode.
… we have reported a new approach to resolve the dilemma faced in the Mg battery, that is, the conflict between an ethereal organometallic electrolyte and the desired oxidation stability, by engineering an artificial Mg2+-conductive interphase on the surface of a Mg metal electrode, so that reversible Mg plating/stripping chemistry can be enabled in high-voltage electrolytes known to be troublesome for Mg batteries. The elastic and Mg2+-conducting but electronic-insulating polymeric interphase on the surface of Mg metal can effectively prevent the electrochemical reduction of the electrolytes and the water therein, while still allowing Mg2+ to migrate (ionic conductivity 1.19 × 10−6 S cm−1), thus making it possible to use electrolyte components that are oxidation-resistant and non-corrosive.
Superior performances of full cells using the interphase-protected Mg electrodes have demonstrated the feasibility of constructing high-energy Mg-metal batteries with high-voltage oxide cathodes and oxidation-resistant electrolytes; such characteristics have been precluded by the conventional approach of ethereal-based Mg electrolytes.—Son et al.
Other researchers involved with the project were Tao Gao and Chunsheng Wang of the University of Maryland; K. Xerxes Steirer of Colorado School of Mines; and Arthur Cresce and Kang Xu of the US Army Research Laboratory.
Funding for the research came from the Laboratory Directed Research and Development Program at NREL.
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.
Seoung-Bum Son, Tao Gao, Steve P. Harvey, K. Xerxes Steirer, Adam Stokes, Andrew Norman, Chunsheng Wang, Arthur Cresce, Kang Xu & Chunmei Ban (2018) “An artificial interphase enables reversible magnesium chemistry in carbonate electrolytes” Nature Chemistry doi: 10.1038/s41557-018-0019-6