Exposing elusive cationic magnesium–chloro aggregates in aluminate complexes through donor control

Abstract

The cationic magnesium moiety of magnesium organohaloaluminate complexes, relevant to rechargeable Mg battery electrolytes, typically takes the thermodynamically favourable dinuclear [Mg2Cl3](+) form in the solid-state. We now report that judicious choice of Lewis donor allows the deliberate synthesis and isolation of the hitherto only postulated mononuclear [MgCl](+) and trinuclear [Mg3Cl5](+) modifications, forming a comparable series with a common aluminate anion [(Dipp)(Me3Si)NAlCl3](-). By pre-forming the Al-N bond prior to introduction of the Mg source, a consistently reproducible protocol is reported. Usage of the green solvent 2-methyltetrahydrofuran in place of THF in the context of Mg/Al battery electrolyte type complexes is also promoted.

Fast kinetics of magnesium monochloride cations in interlayer-expanded titanium disulfide for magnesium rechargeable batteries

“…1a ). First, as MgCl + is the major electroactive species in typical halide-based Mg electrolytes 32 – 39 , the Mg−Cl bond needs to be broken to free up the intercalating Mg 2+ species, which process requires a high activation energy ( E a ) of at least 3 eV 37 . Second, most Mg-ion cathodes studied so far suffer from sluggish Mg 2+ diffusion because of the extremely high-energy barrier for Mg 2+ migration in host materials 3 , 40 .…”

Exploiting cation aggregation in new magnesium amidohaloaluminate electrolytes for magnesium batteries

“…Electrolyte complexes possessing the mononuclear (MCE), dinuclear (DCE) and trinuclear (TCE) magnesium chloride cation aggregations in conjunction with the common aluminate anion [(Dipp)(SiMe 3 )NAlCl 3 ] − 23 were synthesised according to the methodology previously developed in our group. 15 The main prerequisite for a candidate electrolyte in a secondary metal-anode battery is the ability to reversibly plate and strip metal ions at the metal anode surface. To evaluate this plating and striping behaviour of the three magnesium amidohaloaluminate complexes presented here, polarisation tests of symmetrical cells with Mg-metal electrodes were performed (Fig.…”

“…The anion [R x AlCl 4−x ] − may be easily modified using different R groups, and by introducing halide, alkyl, aryl, amido or alkoxide ligands to the aluminium metal centre. [10][11][12][13][14][15][16] These studies revealed evidence that the nature of the Al-R bond is key to a number of properties, such as the solubility, nucleophilicity and oxidative stability. 17 In almost all of these case studies, the cation adopts the thermodynamically-favoured dinuclear magnesium cation [Mg 2 Cl 3 •6THF] + .…”

“…1). 15 These cationic species include mononuclear [MgCl] + and trinuclear [Mg 3 (μ 3 -Cl) 2 (μ 2 -Cl) 3 ] + aggregates, whose existence in the electrolyte solution were previously postulated as playing an important role in Mg deposition when using a formally [Mg 2 Cl 3 ] + based electrolyte. [18][19][20] With these three cation aggregation states to hand (accompanied by a common aluminate counteranion), the potential to investigate the effect of cation aggregation on electrolyte performance is now available.…”

A comprehensive review of lithium salts and beyond for rechargeable batteries: Progress and perspectives

“…The electroactive species in halide-based electrolytes is MgCl + or Mg 2 Cl 3 + [241][242][243][244][245][246][247][248]. The organohalo-aluminate electrolytes obtained by reaction between a Grignard reagent and AlCl 3 [241], was a subject of a review publication [249].…”