An Electrochemically Activated Nanofilm for Sustainable Mg Anode with Fast Charge Transfer Kinetics

Abstract

Highly reversible Mg plating/stripping is key for rechargeable Mg batteries and has typically been successfully demonstrated using transient electrochemical techniques such as cyclic voltammetry measurements. However, little effort has been invested in studying the stability of the electrode/electrolyte interface over an extended time. We report here the development an in situ generated surface film for Mg anodes based on electrodeposited bismuth (E_Bi). This film improves the interfacial stability of Mg in contact with the electrolyte, particularly over an extended time, and possesses fast charge-transfer kinetics (< 30 Ω∙cm2) and low non-time-sensitive interfacial film resistance (ca. 5 Ω∙cm2) for active Mg species.

Ionic Dynamics of the Charge Carrier in Layered Solid Materials for Mg Rechargeable Batteries

“…Identification of this characteristic feature provides guidelines for the rational design of host lattices paired with an ion carrier for an enhanced ion diffusion rate. The computed diffusion barrier of Mg under different external conditions is consistent with previous reports . Hence, we present the workflow as a systematic computational strategy to investigate the diffusion dynamics of ionic complexes in solid-state materials.…”

“… a Original BiOCl lattice. b BiOCl lattice expanded by (MgCl + ) complex insertion. c Fixed-expanded BiOCl lattice from ref . …”

“…Many research efforts have been devoted to the material design of an artificial interphase layer on the anode that mitigates detrimental decomposition reactions and facilitates charge transfer. Several strategies for forming the interphase layer in-situ on the anode surface have demonstrated a protective effect on electrochemical cycling with reduced reaction overpotential. − Direct modification of the Mg anode surface prior to battery assembly with well-designed artificial coating materials has also been shown to enable reversible Mg plating/stripping behavior. − To accelerate materials design for anode artificial coatings, computational research has been focused on the identification of Mg 2+ conductors with desirable electronic and stability properties. Canepa et al systematically evaluated a variety of compounds using first-principles calculations and suggested MgSiN 2 , MgS, MgSe, MgBr 2 , and MgI 2 as promising coating materials.…”

“…Canepa et al have also reported that the cation complex MgCl + is the major electroactive species in most halide-based Mg electrolytes . Several cathodes based on intercalation of Mg 2+ carriers, including Mg­(DME) 3 2+ , Mg­(H 2 O) x 2+ , and MgCl + , have been established to improve the magnesium conduction rate via electrostatic shielding of the Mg 2+ ions. − A recent study of anode interphase modification showed that electrodeposited bismuth effectively functions as a passivation layer that permits diffusion of MgCl + as charge carriers . Fast transportation of ion complexes potentially alleviates the issue of sluggish dissociation and diffusion of bare Mg 2+ ions, which highlights the critical role of MgCl + diffusion in enhancing rate capability.…”

“…The challenges of using AIMD to study solid-state conduction of multivalent ions arise from their high charge density and strong Coulombic interactions with the anion sublattice, which results in sluggish diffusion through solid materials. − Owing to the high computational cost of AIMD simulation and the rare occurrence of multivalent ion hopping, we adopted learning on-the-fly molecular dynamics (LOTF-MD) driven by machine-learned interatomic potentials with automated density functional theory (DFT) retraining to capture the rare transition events of multivalent ions . A layered material, BiOCl, which has been characterized and computed as an effective Mg anode protection layer in our recent study, was selected as a representative host material for this investigation.…”