Pseudocapacitive sodium storage in a new brand foveolate TiO2@MoSe2 nanocomposite for high-performance Na-ion hybrid capacitors

Abstract

Preparation of a material with excellent rate performance and high capacity contribution is significant for sodium-ion hybrid capacitors (SIHCs). TiO₂ has been extensively studied due to its outstanding chemical stability, but the low specific capacity greatly hinders its practical application. Herein, TiO₂ with a foveolate-shape is prepared via a precisely controlled Ostwald maturation procedure. Benefiting from the unique structure, foveolate TiO₂ possesses satisfactory electrochemical performance. When used as the anode for SIHCs, a high reversible specific capacity of 290 mA h g⁻¹ is obtained with an ultrahigh initial coulombic efficiency of 96% at 100 mA g⁻¹. Even if the current density increases to 1000 mA g⁻¹, the specific discharge capacity can still be maintained at 158 mA h g⁻¹ after 1500 cycles. To further improve its capacity, the TiO₂@MoSe₂ composite electrode is synthesized by using foveolate TiO₂ as the skeleton for the successful growth of MoSe₂ nanosheets. A higher reversible specific capacity of 551 mA h g⁻¹ is achieved at 100 mA g⁻¹. Moreover, a reversible specific capacity of 164 mA h g⁻¹ is maintained after 500 cycles at 5000 mA g⁻¹. The foveolate TiO₂ preparation method developed in this work provides new ideas for the development of both substrate materials and active materials in the field of energy storage.