Heterostructured TiO₂ Spheres with Tunable Interiors and Shells toward Improved Packing Density and Pseudocapacitive Sodium Storage

Abstract

abundance, as well as almost unlimited sodium resources on earth, sodium-ion batteries (SIBs or NIBs) are continuously attracting increasing attentions in both of the academic and industrial fields as competitive alternatives for the possible replacement of LIBs. [2][3][4] Similar with the performance limit issues in LIB systems, the key challenges for the application and commercialization of NIBs are regarded as the appropriate electrode material selection and design. [5][6][7] Among the various candidates for NIB anodes, titanium dioxide (TiO 2 ) is a promising choice on account of its several superiorities such as structural stability based on intercalation mechanism, safety insurance due to the high working voltage, environmental friendly, and low cost. [8][9][10][11][12][13] However, the relatively low specific capacity and inferior rate capability of TiO 2 -based anode materials make them still have the necessity of promotion and optimization. To relieve these natural drawbacks, hollow, hierarchical, and porous architectures are proved to be effective for meliorating the sluggish Na + diffusion kinetics, increasing the Insertion-type anode materials with beneficial micro-and nanostructures are proved to be promising for high-performance electrochemical metal ion storage. In this work, heterostructured TiO 2 shperes with tunable interiors and shells are controllably fabricated through newly proposed programs, resulting in enhanced pseudocapacitive response as well as favorable Na + storage kinetics and performances. In addition, reasonably designed nanosheets in the extrinsic shells are also able to reduce the excess space generated by hierarchical structure, thus improving the packing density of TiO 2 shperes. Lastly, detailed density functional theory calculations with regard to sodium intercalation and diffusion in TiO 2 crystal units are also employed, further proving the significance of the surface-controlled pseudocapacitive Na + storage mechanism. The structure design strategies and experimental results demonstrated in this work are meaningful for electrode material preparation with high rate performance and volume energy density.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

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