Surface film formation dominates the electrochemical response of alkaline earth metals, materials well suited as anodes for high energy density battery chemistries. Conventional electrolytes are generally observed to undergo reductive decomposition on both Mg and Ca producing films that block the transport of the metal cation preventing the high efficiency electrodeposition and electrodissolution required for a reasonable cycle life rechargeable battery. The Mg cation can be introduced into several different complex forming electrolytes in which deposition/dissolution can be driven at greater than 99% Columbic efficiency. Examples of such electrolytes include the ether-based Lewis acid – base organic and inorganic chloroaluminates and the organoborate solutions. This general scheme of creating a ligand and solvent co-coordinated complex has been driven to the point where cathode stability (oxidative stability) has displaced metal anode stability as an electrolyte development focus. The goal within the research community is now to incorporate higher voltage cathode materials to supplant the limited choices that currently exist. Conventional electrolytes still hold promise for use with Mg provided the background science is conducted to determine why a film acts to block Mg cation transport in the first place. In this paper, we demonstrate that filmed Mg interfaces are ubiquitous being present even in well-behaved chloroaluminate electrolytes. It is also demonstrated that chloride plays a unique role in stabilizing the Mg surface in ether solvents. We exploit this knowledge of surface films to explore candidate electrolytes where surface films facilitate ion transport and stabilize the Mg electrodeposit structure with cycling. Several supporting electrolyte salt and solvent compositions are presented where an interfacial film plays a critical role. We describe the identity, structure, and properties of these films and their impact on morphological evolution at electrodeposition and electrodissolution rates relevant for practical transportation applications.<br/>This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000.

Mg anode interfacial films: Enabling rechargeable Mg batteries

249th National Meeting (2015)

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