High-performance strontium and bismuth bimetallic oxides electrode：combine first-principles calculations with electrochemical tests

Highlights

• DFT combined with electrochemical test is used to study the performance of electrode.

• In 6 M KOH, SrBiO₃ presents the specific capacity of 810.93 F g-1 at 1A g-1.

• The capacitance retention rate of the SrBiO₃ electrode is 80.11 % after 2000 cycles.

Abstract

A series of bimetallic oxides electrode materials were proposed to boost the supercapacitor performance using the density functional theory (DFT) in combination with the electrochemical tests. This work provides a guiding role for exploring energy storage materials with high performance. Based on the plane wave ultra-soft pseudo-potential (PWPP) and general gradient approximate (GGA) in DFT, the electronic and the crystal structures of various strontium bismuth oxides (β-Bi₂O₃, SrBi₂O₄, Sr₂Bi₂O₅ and SrBiO₃) were calculated, and the corresponding energy bands were compared. The simulation results show that SrBiO₃ has a smaller band gap than the other three oxides, due to the significant hybridization of the electronic density of SrBiO₃. The prepared strontium bismuth oxide materials (SrBi₂O₄, Sr₂Bi₂O₅ and SrBiO₃) were characterized using scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD), respectively. In the electrochemical measurement of 6M KOH solution, SrBiO₃ presents the highest specific capacity of 810.93F g⁻¹ (i.e. 126.95 mAh g⁻¹) at a current density of 1A g⁻¹. The capacitance retention rate of SrBiO₃ is 80.11 % after 2000 cycles, which indicates that it has the useful properties of cyclic stability. All the results suggest that SrBiO₃ will be an excellent candidate in electrode materials for the battery-type supercapacitors.

Introduction

With a massive influx of the anomalies of climate change, the accumulation of global warming, the exhaustion of traditional energy sources and much more, people are soberly aware of what energy-related issues and challenges humankind is facing. Therefore, improving energy efficiency and developing clean and renewable energy have become the primary site of scientific interest and industrial concern. Along with that, the electricity storage technologies, such as compressed air, pumped hydroelectric, flywheels, batteries / supercapcitors, and so on, may provide the indirect economic, reliability, and environmental benefits. In this case, the corresponding energy storage materials have developed rapidly in recent years.

The ever-growing demand for high-capacity and high-power electrode materials in many applications, especially for the emerging electric vehicle industry, has prompted many research efforts to develop next-generation high-performance electrode materials [[1], [2], [3], [4]]. Many electrode materials with nanometer materials such as carbon nanotubes, conductive polymers, and metal oxides have been developed. Hereinto, the metal oxides have been popular because of their excellent energy density and electrochemical cycling stability. It has been reported that NiO [5], MoO₃ [6], Co₃O₄ [7], V₂O₅ [8,9], WO₃ [10] and Fe₂O₃ [11] exhibit outstanding electrochemical performance because of their reversible multi-electron redox Faraday reaction. Beyond them, bimetal oxides with a plurality of electrochemically active ions, such as NiMn₂O₄ [12], NiCo₂O₄ [13], MnCo₂O₄ [14], NiMoO₄ [15], and CuCo₂O₄ [16], can give a boost to the electrochemical performance of materials by the synergy between different components, which is a research hotspot recently.

As in typical metal oxides, Bi₂O₃, can be applied to electrode materials, electronic ceramic powder materials, electrolyte materials, photovoltaic materials, high temperature superconducting materials, and catalysts materials, etc. [[17], [18], [19], [20]]. The application prospects of Bi₂O₃ have attracted much attention. Current research has focused on adding different metal ions to Bi₂O₃ [[21], [22], [23]] or combining Bi₂O₃ with carbon materials [24,25] to improve their microscopic properties. Our latest research have preliminarily verified that the strontium bismuth oxide has excellent electrochemical properties, and the proper ratio combination of Bi and Sr generates a large amount of oxygen vacancies for pseudocapacitor charge storage [26]. However, the effects of the strontium on the crystal structure and electronic structure of bismuth oxide have not been studied in depth. Also, to our knowledge, the energy storage mechanisms of strontium bismuth bimetallic oxides are still blank.

In this work, we explored the micro-structures and the related physical and chemical properties of strontium bismuth oxides as an electrode material by combining the first-principles pseudopotential calculation of density functional theory with the electrochemical test analysis, aiming at providing a deep microcosmic material design and comprehensive performance evaluation method.