Structural evolution from layered Na2Ti3O7 to Na2Ti6O13 nanowires enabling a highly reversible anode for Mg-ion batteries
The development of suitable host materials for reversible storage of divalent ions such as Mg2+ is still a big challenge and its progress to date has been slow compared to monovalent Li+ or Na+. Herein, we present the study of layered sodium trititanate (Na2Ti3O7) and sodium hexatitanate (Na2Ti6O13) nanowires as anode materials for rechargeable Mg-ion batteries. It’s firstly found that the structural evolution of the phase transition from layered Na2Ti3O7 to Na2Ti6O13 with more condensate three-dimensional microporous structure enables remarkably enhanced Mg-ion storage performance. Na2Ti6O13 electrode can achieve large initial discharge and charge capacity of 165.8 and 147.7 mAh g-1 at 10 mA g-1 with a record high initial Coulombic efficiency up to 89.1%. The ex-situ XRD, Raman measurements and EDX mapping were used to investigate the electrochemical reaction mechanism. It’s suggested that irreversible structure change and the formation of insoluble NaCl with high yield and large particles when Na+ is replaced by inserted Mg2+ for Na2Ti3O7 electrode could be ascribed to the rapid decline in capacity. By contrast, Na2Ti6O13 electrode exhibits good structure stability during Mg-ion insertion/extraction process, leading to good rate performance and cycling stability.