Ti³⁺ Induced Brown TiO₂ Nanotubes for High Performance Sodium-Ion Hybrid Capacitors

Abstract

Sodium-ion hybrid capacitors are attracting great attention and are emerging as promising energy storage devices, with their remarkable footsteps in energy and power densities. However, the development of efficient electrode materials that result in a minimum trade-off between their energy and power densities, and that allow long-term cycling stability, still remains a challenge for realizing their full potential as an alternate energy storage system for commercial applications. Herein, for the first time, we study the sodium-ion intercalation pseudocapacitance behavior of brown TiO2 nanotubes for their application as an efficient anode material for Na-ion hybrid capacitors. We synthesized semicrystalline and crystalline anatase brown TiO2 nanotubes, aggregated in a flowerlike morphology, through a hydrothermal route, and performed detailed electrochemical studies. The kinetic studies reveal that semicrystalline brown TiO2 exhibits a Na-ion intercalation pseudocapacitive behavior with 57% of capacitive storage at 1.0 mV s–1, whereas crystalline brown TiO2 is more faradaic in nature. Further, hybrid Na-ion capacitors are fabricated with brown TiO2 materials as an anode and activated carbon as a cathode, and the fabricated device showed an excellent electrochemical performance with a high energy density of ∼68 Wh kg–1 and a high power density of ∼12.5 kW kg–1 and with a good cycling stability up to 10 000 cycles with ∼80% capacitive retention. The obtained results represent a promising approach toward developing efficient electrodes for hybrid Na-ion capacitors.

Recent Progress in Understanding Ion Storage in Self‐Organized Anodic TiO2 Nanotubes

“…Different approaches of nanostructuring TiO 2 have been employed to render it suitable for SIB application, similar to previous approaches for LIBs. Graphene‐supported TiO 2 nanospheres, graphene‐coupled TiO 2 sandwich‐like hybrids, flower‐like brown TiO 2 NTs, anatase nanoparticles, and self‐organized TiO 2 NTs have been investigated toward efficient Na‐ion storage capability. Xiong et al described the first amorphous TiO 2 anode for SIBs, and their electrodes demonstrated a reversible capacity of 150 mAh g −1 in a potential range between 2.5 and 0.9 V vs Na/Na + at 0.05 A g −1 (C/3) .…”

Sodium‐ion capacitors: Materials, Mechanism, and Challenges

“…Shaijumon and co‐workers prepared semicrystalline and crystalline anatase brown TiO 2 nanotubes (BTNT) with flower‐like structure by using hydrothermal route, as shown in Figure a . As an efficient pseudocapacitive Na + intercalation material, the as‐prepared brown TiO 2 exhibited good electrochemical performance.…”

“…b) Rate capability of SICs at different scan rates and current densities, respectively. Reproduced with permission . Copyright 2018, American Chemical Society.…”

Recent progress and future prospects of sodium-ion capacitors

“…Besides carbon materials, many transition metal oxides such as V 2 O 5 , MnO 2 , Fe 3 O 4 , MoO 2 , Nb 2 O 5 and TiO 2 . [45,56] with constructed nanostructures have been explored as pseudocapacitive anode materials, in which the disctinctive microstructures with sizable tunnels can reduce the diffusion pathways of the ions. As reported, the layer-structured V 2 O 5 with large lattice distance of 9.5 Å ((001) plane) has miscellaneous oxidation states, demonstrating obvious pseudocapacitive behavior.…”