TiO2 -Based Heterostructures with Different Mechanism: A General Synergistic Effect toward High-Performance Sodium Storage.

The general synergistic effect of TiO2 -based heterostructures has been discovered to improve the sodium storage of anodes, involving conversion, alloying, and insertion mechanism materials. Herein, metal sulfides (MS2 , M = Sn2+ , Co2+ , Mo2+ ), metallic Sb and Sn, as well as, carbon nanotubes (CNTs) are chosen as the model examples from the three kinds. The electrochemical testing demonstrates a better performance of heterostructrues involving TiO2 than the pristine anode components. The introduction of TiO2 into the MS2 and Sb or Sn systems induces a built-in electric field as the charge transfer force at the heterojunctions, greatly reducing the ion transfer resistance and promoting interfacial electron transfer. In the CNT/TiO2 structure, the chemical growth of TiO2 nanoparticles on the outer surface of CNTs makes the interface more compact than the physical blending case, offering better improvement of electrochemistry. The synergy should work via the growth of heterostructures, relying on the interface effects, which always plays the promotion role through the formation of driving force or grain boundaries and/or condense phase interface to facilitate charge transfer at the interface during the storage process. Therefore, the construction of reasonable heterostructures can endow materials with intriguing electrochemical performance based on the synergistic effect.