Exposed high-energy facets in ultradispersed sub-10\u2009nm SnO2 nanocrystals anchored on graphene for pseudocapacitive sodium storage and high-performance quasi-solid-state sodium-ion capacitors

Panpan Zhang,Wei Huang,Jinhui Wang,Faxing Wang,Yang Li,Yuping Wu,Zaichun Liu,Ying Huang,Hongyan Li,Yusong Zhu,Xinne Zhao,Gang Wei,Zhiqiang Su,Lijun Fu

doi:10.1038/s41427-018-0049-y

Abstract

The development of sodium (Na) ion capacitors marks the beginning of a new era in the field of electrochemical capacitors with high-energy densities and low costs. However, most reported negative electrode materials for Na+ storage are based on slow diffusion-controlled intercalation/conversion/alloying processes, which are not favorable for application in electrochemical capacitors. Currently, it remains a significant challenge to develop suitable negative electrode materials that exhibit pseudocapacitive Na+ storage for Na ion capacitors. Herein, surface-controlled redox reaction-based pseudocapacitance is demonstrated in ultradispersed sub-10 nm SnO2 nanocrystals anchored on graphene, and this material is further utilized as a fascinating negative electrode material in a quasi-solid-state Na ion capacitor. The SnO2 nanocrystals possess a small size of <10 nm with exposed highly reactive {221} facets and exhibit pseudocapacitive Na+ storage behavior. This work will enrich the methods for developing electrode materials with surface-dominated redox reactions (or pseudocapacitive Na+ storage).

Highlights

Increasing interest in portable electronic devices, electric vehicles, and smart grids is creating significant demand for low-cost, environmentally friendly energy storage devices[1,2,3,4]
The SnO2/graphene nanocomposite was synthesized through a one-step hydrothermal reaction of fewlayered Graphene oxide (GO) (2–3 layers, 2–10 μm, Supplementary Fig. S2) and SnCl2·2H2O in an aqueous solution at 200 ° C
Due to the strong electrostatic interactions between Sn2+ and GO, SnO2 nanocrystals are uniformly anchored on the surface of the graphene nanosheets

Summary

Introduction

Increasing interest in portable electronic devices, electric vehicles, and smart grids is creating significant demand for low-cost, environmentally friendly energy storage devices[1,2,3,4]. The electrochemical capacitor ( called supercapacitor) is one of the most promising energy storage devices, as it has a fast power delivery and long cycle life, it still suffers from a moderate energy density compared with those of rechargeable batteries[5,6,7]. To improve the energy densities of electrochemical capacitors, lithium (Li) ion capacitors have been constructed from a capacitortype electrode (such as activated carbon, carbon nanotubes (CNTs), and graphene) and a battery-type electrode (such as Li4Ti5O12, TiO2, Fe3O4, and Li3VO4) in a Li salt-containing electrolyte since 20012– 16. The technologies of Na ion capacitors based on liquid electrolytes have made significant advances in the past several years[24,25,26,27,28,29,30]. Solid electrolytes would be a perfect choice to solve this crucial problem[31,32,33]

Methods

Results

Conclusion