Layered Na₂Ti₃O₇/MgNaTi₃O₇/Mg_0.5NaTi₃O₇ Nanoribbons as High-Performance Anode of Rechargeable Mg-Ion Batteries

We report on layered Na 2 Ti 3 O 7 /MgNaTi 3 O 7 /Mg 0.5 NaTi 3 O 7 nanoribbons for reversible electrochemical Mg storage. First, Mg 2+ intercalation with irreversible Na + deintercalation takes place in the first discharge process (Na 2 Ti 3 O 7 + Mg 2+ + e – → MgNaTi 3 O 7 + Na + ). Then, reversible Mg 2+ insertion–extraction occurs in subsequent cycling processes (MgNaTi 3 O 7 ↔ Mg 0.5 NaTi 3 O 7 + 0.5Mg 2+ + e – ). This reaction with repeatable 0.5 M Mg 2+ 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 Mg 2+ electrolyte). Furthermore, the MgNaTi 3 O 7 was used to assemble full Mg-ion batteries (MIBs) with Mg(ClO 4 ) 2 –diglyme electrolyte and V 2 O 5 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 Na 2 Ti 3 O 7 /MgNaTi 3 O 7 /Mg 0.5 NaTi 3 O 7 as the anode of MIBs.