Search

To address the bottlenecks of sluggish sodium-ion transfer processes, the electrode materials of sodium-ion battery (SIB) are always designed from the viewpoints of sodium-ion diffusion kinetics or reaction thermodynamics for high-performance sodium storage. Herein, starting with spongiform TiO2/C composite derived from zinc alginate, a NH4Cl-assisted annealing strategy is developed to prepare chlorine-doped spongiform TiO2/C composite (ZATC-Cl). Acting as the anode of SIBs, the obtained ZATC-Cl delivers excellent sodium storage performance with a high reversible capacity of 352.4 mAh g−1 at 50 mA g−1, a superior rate capability of 246.8 mAh g−1 at 2 A g−1 and a considerable high-rate cycling performance of 248.5 mAh g−1 at 2 A g−1 for 1000 cycles. It is believed that the unique spongiform structure and ultra-small sized TiO2 particles in ZATC-Cl can achieve fast sodium-ion insertion/extraction, realizing rapid sodium-ion diffusion kinetics. Moreover, as well evidenced by experiment results and theoretical calculations, the Cl dopants introduced in ZATC-Cl can provide more active sites for robust sodium-ion chemical adsorption, optimizing sodium-ion reaction thermodynamics. This study demonstrates an alternative approach to improve the sodium storage capability of TiO2 anodes by the synergistically engineering the morphological and structural properties and manipulating the surface active sites, from both kinetic and thermodynamic viewpoints of sodium storage processes.

With the properties of high theoretical capacity and excellent structural stability, TiO2 has been widely studied as anode material for sodium-ion batteries (SIBs). In this work, a composite structure of ultra-small TiO2 nanoparticles embedded in carbon nanosheets (TCNS) is obtained by annealing polyvinylpyrrolidone coated Zn-Ti layered double hydroxide under inert atmosphere, with zinc species removed by hydrochloric acid. As sodium-ion battery anode, the resultant TCNS shows a high reversible capacity of 271.2 mAh g−1 at 50 mA g−1 and considerable cycling stability (maintaining 196.7 mAh g−1 after 2000 cycles at 2 A g−1). Ex-situ XRD and TEM investigations clearly illustrate the structure changes of anatase during the sodium storage process. Specifically, ultra-small TiO2 nanoparticles in TCNS show obvious crystal distortion as triggered by the initial insertion of sodium ions, with the reversible sodium storage happening at the (1 0 1) active plane of anatase. As experimentally and theoretically evidenced, the twisted crystal structure is maintained in the subsequent cycles, which can effectively promote the sodium diffusion rate in anatase, resulting in the excellent rate and cycle performances of TCNS anode. This study provides informative guidance to explore high-performance TiO2 anodes for SIBs, with novel insights into the sodium ion insertion/extraction mechanism comprehensively elucidated during reversible sodium storage process.