Solvation sheath reorganization enables divalent metal batteries with fast interfacial charge transfer kinetics

Abstract

Efficient, rechargeable Mg and Ca batteries Divalent rechargeable metal batteries such as those based on magnesium and calcium are of interest because of the abundance of these elements and their lower tendency to form dendrites, but practical demonstrations are lacking. Hou et al . used methoxyethyl amine chelants in which the ligands attach to the metal atom in more than one place, modulating the solvation structure of the metal ions to enable a facile charge-transfer reaction (see the Perspective by Zuo and Yin). In full battery cells, these components lead to high efficiency and energy density. Theoretical calculations were used to understand the solvation structures. —MSL

Current Status and Challenges of Calcium Metal Batteries

“…Reproduced with permission. [ 4 ] Copyright 2021, American Association for the Advancement of Science. b) 43 Ca NMR spectrum of a Ca(BH 4 ) 2 THF electrolyte in comparison with that after adding LiBH 4 .…”

“…Rechargeable metal battery using metal foil or plate as the anode makes full use of inherent advantages, such as low redox potential, large capacity, high flexibility and ductility, and good electronic conductivity of Li/Na/K/Mg/Ca/Al/Zn (Table 1). [1][2][3][4] Among various metals, calcium exhibits a theoretical redox potential slightly above those of Li and K, and a large capacity of 1337 mAh g À1 and 2072 mAh cm À3 . [5][6][7][8] Ca-ion also offers a charge number doubled that of an alkaline metal ion and favorable polarization much lower than other multivalent metal ions (Mg 2þ , Al 3þ ), which contribute to fast and efficient charge transport.…”

Advancing towards a Practical Magnesium Ion Battery

“…An approach can be to develop new liquid electrolyte based on chelating, like the multidentate methoxyethyl-amines proposed by Hou et al [ 137 ]. These chelants in the solvation sheath of Mg 2+ enable easy desolvation, highly reversible Mg anode as well as fast (de)intercalation of magnesium into high-voltage layered oxide cathodes.…”

“…Thus, the average working of Mg x MnO 2 is ca. 2.5 V, and the capacity is about 270 mAh g −1 [ 137 ]. The chelant-rich solvation sheaths bypass the energetically unfavorable desolvation process, promote interfacial charge transfer kinetics, reduce the overpotential and eliminate the irreversible reactions for both the anode (Mg) and cathode.…”

“…It is foreseeable that in the next years the new (liquid and solid) electrolytes and materials very probably will offer opportunities for developing a practical MIB [ 35 , 115 , 137 , 138 , 139 ]. However, it is worth to note that magnesium is a critical raw material, and China has 87% share of global production.…”