Activating layered LiNi0.5Co0.2Mn0.3O2 as a host for Mg intercalation in rechargeable Mg batteries

Abstract

Layered crystal structures are some of the most intensively studied intercalation hosts for guest ion insertion. For Mg insertion, layered transition metal sulfides or selenides have been used for reversible Mg intercalation; however, far less intercalation hosts have been found for layered oxides most likely because of the strong interaction between Mg2+ and the oxide host. Here, we demonstrate that layered LixNi0.5Co0.2Mn0.3O2 (NCM523), which is an important commercial electrode for Li-ion batteries but has been regarded as electrochemically inactive in rechargeable Mg batteries, can function as a reversible host for Mg2+ if water opens up the layers and screens the electrostatic interaction between Mg2+ and the host. Upon the formation of water-intercalated NCM523, the discharge capacity dramatically increases utilizing the multi-redox reaction of Ni2+/Ni3+/Ni4+, which exhibits an average voltage of ∼3.1V (vs. Mg/Mg2+) in rechargeable Mg batteries with an energy density of 589Whkg−1 in the first discharge.