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

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.