Scalable Template-Free Synthesis of Na2Ti3O7/Na2Ti6O13 Nanorods with Composition Tunable for Synergistic Performance in Sodium-Ion Batteries

Solid-state reactions are a simple and scalable synthetic method, but they lack controlled nanostructures at present. Here, we report an energy-efficient solid-state synthesis, via the addition of carbon, to mass-produce uniform, single-crystalline, one-dimensional metal oxide nanorods with tunable composition according to performance demands. The carbon added in the solid-state reaction provides an alternative low-temperature route for the metal oxide formation due to the extra local heat generation and CO2/CO release from carbon oxidation. To demonstrate the methodology, a series of single-crystalline Na2Ti3O7/Na2Ti6O13 nanorods with tunable composition are synthesized and applied in sodium-ion batteries. The local heat generated from carbon allows formation of Na2Ti3O7 at 450 degrees C, a reaction temperature much lower than that of conventional solid-state methods (750-1000 degrees C), and Na2CO3 is regenerated to be recycled in the synthesis. The high theoretical capacity of Na2Ti3O7 and low volume expansion of Na2Ti6O13 upon charge-discharge are synergistically exploited to achieve high electrochemical performance and stability.