Dendritic Magnesium Formation in Conventional Electrolytes: Local Adsorption of Amine Solvents at Inner Helmholtz Plane Matters

Key Words:METAL BATTERIES; LITHIUM

Abstract:Simple salts electrolyte is imperative for developing commercially feasible rechargeable magnesium (Mg) metal batteries. However, Mg electro-plating/stripping reversibility in these electrolytes is far from satisfactory, which is mainly caused by interfacial passivation and dendrite growth of Mg-metal anode. Therefore, it is of great urgent to develop a molecule-level mechanistic understanding on electrode-electrolyte interfacial reactions. In this work, the transformation pathways of solvents at the inner Helmholtz plane are revealed to play a key role in reversibility deterioration and cell failure of Mg-metal anodes. A benzylamine co-solvent is introduced into simple salts electrolyte, which is closely to gas evolution, MgH2 formation and possible electrochemical active species formation on surface of Mg-metal anodes. The uneven adsorption of active species leads to a multiplicative effect on local current density, which causes dendrite growth. Interestingly, benzylamine solvents are demonstrated to do not directly participate in the first Mg2 solvation sheath structures, instead they exhibit specific adsorption at the inner Helmholtz plane attributed to significant steric hindrance. As a result, visual bottle-type asymmetric cells display a fair cycle life of above 500 cycles, while coin-type assembly exhibits serious soft short circuit and recovery behavior during cycling.

Volume:35

Issue:11

Translation or Not:no