Mesoporous Co₃O₄ sheets/3D graphene networks nanohybrids for high-performance sodium-ion battery anode

Highlights

• Co₃O₄ MNSs/3DGNs nanohybrids have been synthesized and investigated as anode materials for sodium ion batteries.

• The nanohybrids exhibit better SIB performance as compare with Co₃O₄ MNSs and Co₃O₄ nanoparticles.

• The improved electrochemical performance is considered due to the mesoporous nature of the products and the addition of 3DGNs.

Abstract

Co₃O₄ mesoporous nanosheets/three-dimensional graphene networks (Co₃O₄ MNSs/3DGNs) nanohybrids have been successfully synthesized and investigated as anode materials for sodium ion batteries (SIBs). Microstructure characterizations have been performed to confirm the 3DGNs and Co₃O₄ MNSs nanostructures. It has been found that the present Co₃O₄ MNSs/3DGNs nanohybrids exhibit better SIB performance with enhanced reversible capacity, good cycle performance and rate capability as compared to Co₃O₄ MNSs and Co₃O₄ nanoparticles. The improved electrochemical performance is considered due to the mesoporous nature of the products, the addition of 3DGNs, 3D assembled hierarchical architecture and decrease in volume expansion during cycling. Thus, SIB is considered as a low cost alternative to LIBs for large-scale electric storage applications.

Introduction

Rechargeable batteries are one of the most important energy storage devices for portable electronics, electric vehicles, and stationary energy storage [1], [2]. Lithium-ion batteries (LIBs) are currently widely used due to their advantages of high energy density, long cycling life, and environmental benignity [3], [4], [5], [6]. However, the limited world's lithium resources could be rapidly depleted due to mass production of huge lithium ion batteries in the near future [7]. Recently, sodium ion batteries (SIBs) have aroused a great deal of interest as a low cost alternative to LIBs for large-scale electric storage applications, because of the high availability of sodium sources, and the similar chemistry of sodium and lithium [8], [9], [10], [11]. Nevertheless, it remains a great challenge to develop suitable electrode materials for SIBs due to the fact that Na ions are larger and heavier than that of Li ions. A variety of sodium host cathodes have been reported to have certain Na-storage capacity and cycleability, but the anodic host materials for sodium ion storage have been less successfully developed [8], [9], [10], [11].

Hard carbon materials are commonly used as anodic materials in the earlier development of SIB due to the modest capacity, but their cycling stability and initial current efficiency are not satisfactory [12], [13]. Some oxide materials, such as Na₂Ti₃O₇ [14] and anatase titania nanorods [7], have been investigated as anodic materials for SIBs, but they all show low capacities (less than 300 mAh g⁻¹), which is far from meeting the demand of high energy storage. Transition metal oxides, which are well known for lithium storage based on conversion reaction mechanism [15], still seldom uninvestigated for analogous sodium storage. For example, Co₃O₄ has been fully studied as one of the promising potential anode materials for LIBs due to its high theoretical capacity (890 mAh g⁻¹). The effects of size, morphology, composition, and crystal plane structure of Co₃O₄ materials on electrochemical performance have been well understood to optimize the lithium storage properties [16], [17], [18], [19], [20], [21]. However, little attention has been paid to study electrochemical behaviors of Co₃O₄ with sodium. Recently, Rahman and coworkers [22] reported sodium reactivity with Co₃O₄ nanoparticles for SIBs, and they found that Co₃O₄ undergoes conversion reaction and exhibits a reversible capacity of 447 mAh g⁻¹ after 50 cycles at a current density of 25 mA g⁻¹. Wen et al. [23] synthesized bowl-like hollow spherical Co₃O₄ structure and studied their sodium-storage behavior. Therefore, nanostructured Co₃O₄ represents a potential candidate anodic host materials for SIBs. However, it is still a challenge to further improve sodium storage properties.

It is widely accepted that the overall performance of SIBs is highly dependent on the inherent properties of the electrode materials [8], [9], [10], [11]. For nanostructured transition metal oxide electrode materials with mesoporous nature, it generally leads to improved energy density, better capacity retention, and superior rate capability, which are due to the large surface area, numerous active sites, short mass and charge diffusion distance, and efficient accommodation of volume changes during charging and discharging process. On the other hand, combining nanostructured transition metal oxide electrode materials with electronically conductive agents, such as carbon nanofibers, carbon nanotubes, and graphene, is considered as one of effective approaches to improve the cycling stability and rate capability [24], [25], [26], [27]. Because the conductive additives can not only act as a “buffer zone” of volume variation induced by cycling process but also a good electron transfer medium [28]. Of various conductive agents, three-dimensional graphene networks (3DGNs) assembled by two-dimensional (2D) graphene nanosheets exhibit continuously interconnected macroporous structures, low mass density, high surface area, strong mechanically strengths and fast mass and electron transport kinetics, which can serve as robust matrix for accommodating electrode materials for improving electrochemical performance of the electrode materials [29], [30], [31], [32], [33].

In this work, we were succeeding in synthesis of anode material for SIBs consisting of Co₃O₄ mesoporous nanosheets/three-dimensional graphene networks (Co₃O₄ MNSs/3DGNs) nanohybrids which exhibit high reversible capacity, excellent rate capability and enhanced cycling performance, making it promising for applications in SIBs.