Boosting Sodium Storage of Double-Shell Sodium Titanate Microspheres Constructed from 2D Ultrathin Nanosheets via Sulfur Doping

Sodium-ion batteries (SIBs) have drawn remarkable attention due to their low cost and the practically inexhaustible sodium sources. The major obstacle for the practical application of SIBs is the absence of suitable negative electrode materials with long cycling stability and high rate performance. Here, sulfur-doped double-shell sodium titanate (Na₂ Ti₃ O₇ ) microspheres constructed from 2D ultrathin nanosheets are synthesized via a templating route combined with a low-temperature sulfurization process. The resulting double-shell microspheres deliver a high specific capacity (≈222 mAh g^-1 at 1 C), excellent cycling stability (162 mAh g^-1 after 15 000 cycles at 20 C), and superior rate capability (122 mAh g^-1 at 50 C) as anode for SIBs. The improved electrochemical properties originate from synergistic effects between the unique double-shell nanostructures built from 2D nanosheets architecture and sulfur doping. This synergistic effect not only stabilize Na₂ Ti₃ O₇ -based electrode during the cycling, but also improve the sluggish Na insertion/extraction kinetics by narrowing the bandgap of Na₂ Ti₃ O₇ . The synthesis strategy proposed here can be developed into a technical rationale for generating high-performance sodium-storage devices.