Kinetic and thermodynamic synergy of spongiform nanostructure and alien dopants enables promoted sodium-ion transfer for high-performance sodium storage

Abstract

Chlorine-doped spongiform TiO 2 /C composite is synthesized by an NH 4 Cl-assisted annealing strategy with zinc alginate and commercial TiO 2 nanoparticles as precursors, demonstrating superior sodium-ion diffusion kinetics and reaction thermodynamics with well-designed spongiform structure and rational element doping. • A novel NH 4 Cl-assisted annealing strategy is developed to prepare ZATC-Cl. • The spongiform structure of ZATC-Cl results in fast sodium-ion diffusion kinetics. • Cl dopants in ZATC-Cl achieve preferable sodium-ion reaction thermodynamics. • ZATC-Cl delivers remarkable sodium storage performance. 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 TiO 2 /C composite derived from zinc alginate, a NH 4 Cl-assisted annealing strategy is developed to prepare chlorine-doped spongiform TiO 2 /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 TiO 2 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 TiO 2 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.