Na2Ti3O7 nanowires with TiO2 and N-doped carbon dual-shells as binder-free electrodes for efficient sodium storage

Abstract

Insufficient electronic/ionic conductivities and structural deformations upon sodiation/desodiation of layered Na2Ti3O7 severely hinder its full application in sodium-ion batteries. Na2Ti3O7 nanowires with TiO2 and N-doped carbon dual-shells are synthesized by hydrothermal synthesis to construct conductive interpenetration network anode for efficient sodium storage. The Na2Ti3O7-based interpenetrating network is sequentially subjected to controllable H+-Na+ ion exchange, dopamine/pyrrole modification, and thermal treatment to form the Na2Ti3O7@TiO2@N-doped carbon nanowires. Because of the rigid TiO2 shell to protect the Na2Ti3O7 core, the nitrogen-doped carbon shell with high specific surface area to enhance the conductivity, and the interpenetrating network to provide direct and fast diffusion pathways, the resultant NTO@TiO2@N-doped carbon electrode exhibits excellent electrochemical performances. Even at a high current density of 80 C (1 C = 177 mA g−1), the reversible capacity of the electrode is up to 78.3 mA h g−1, 6.6 times that of bare Na2Ti3O7 electrode. Further kinetic analyses of the CV curves at various scan rates reveal that the pseudocapacitive process contributes as high as 88.4% of the total capacity at the high scan rate of 10 mV s−1.