Efficient and Stable Magnesium Plating/Stripping in High-Capacity Novel Mg//Ni0.6Co0.4Se2 Batteries Enabled by Interfacial Chemistry Modulation

Rechargeable magnesium batteries (RMBs) are considered as a potential rechargeable for replacing or assisting lithium metal batteries (LMBs). The Mg anode is prone to experiencing a native oxide layer in most electrolytes, resulting in an inferior overpotential and irreversible Mg plating/stripping behavior. Herein, we report for the first time that a novel Mg battery can be assembled using a non-nucleophilic Mg(HMDS)2-based electrolyte with I2 in a relatively large solvent molecule diglyme. An artificial interface phase of MgI2 was constructed in Mg(HMDS)2-AlCl3 electrolyte through the reaction of oxidant I2 and reductant Mg foil. This artificial interface phase is less sensitive to the electrolyte composition. The electrolyte decomposition and the Mg side reaction are effectively inhibited by the MgI2 interphase. In-situ MgI2 interphase significantly lessens the interface impedance and overpotential of the electrochemical Mg deposition/dissolution process. More importantly, the overpotential of the cell using Mg(HMDS)2-2AlCl3- I2/G2 electrolyte is decreased to 0.10 V vs Mg2+/Mg with high Coulombic efficiency of ∼99%, which is superior to the recently reported Mg(HMDS)2-based electrolytes. Besides, the first-principles calculations demonstrate that Mg is uniformly deposited on the MgI2 surface due to reversible Mg plating/stripping, low overpotential, and long-term cycle performance. Note that the as-fabricated novel Ni0.6Co0.4Se2|Mg(HMDS)2-AlCl3- I2/G2|Mg full battery delivers an initial specific capacity of 186 mAh g–1, and retains 120 mAh g–1 with Coulombic efficiency of 100% after 100 cycles. The novel Mg battery verifies the availability of the Mg(HMDS)2-AlCl3- I2/G2 electrolyte through electrolyte additive engineering. The high capacity and stable as-assembled Mg//Ni0.6Co0.4Se2 full cell confirms the compatibility of Mg(HMDS)2 and I2 as well as the utility of modified electrolyte and diselenides cathode materials in RMBs.