Layered Na2Ti3O7/MgNaTi3O7/Mg0.5NaTi3O7 Nanoribbons as High-Performance Anode of Rechargeable Mg-Ion Batteries

We report on layered Na2Ti3O7/MgNaTi3O7/Mg0.5NaTi3O7 nanoribbons for reversible electrochemical Mg storage. First, Mg2+ intercalation with irreversible Na+ deintercalation takes place in the first discharge process (Na2Ti3O7 + Mg2+ + e– → MgNaTi3O7 + Na+). Then, reversible Mg2+ insertion–extraction occurs in subsequent cycling processes (MgNaTi3O7 ↔ Mg0.5NaTi3O7 + 0.5Mg2+ + e–). This reaction with repeatable 0.5 M Mg2+ occupying the sites of Na+ coordinated to seven oxygen atoms offers a theoretical capacity of 88 mA h g–1 (78 mA h g–1 in practical test with Mg2+ electrolyte). Furthermore, the MgNaTi3O7 was used to assemble full Mg-ion batteries (MIBs) with Mg(ClO4)2–diglyme electrolyte and V2O5 cathode. The cell delivers a reversible capacity of 75 mA h g–1 corresponding to an energy density of 53 Wh kg–1. This work displays the potential of layered Na2Ti3O7/MgNaTi3O7/Mg0.5NaTi3O7 as the anode of MIBs.