High electrochemical sodium storage performance of ZnSe/CoSe@N-doped porous carbon synthesized by the in-situselenization of ZIF-8/67 polyhedron

Highlights

• ZnSe/CoSe@NPC was synthesized by the in-situ selenization of ZIF-8/67 polyhedron.

• As-prepared ZnSe/CoSe@NPC displays a high capacity 417.6 mAh g⁻¹ for 200 cycles.

• Our hollow ZnSe/CoSe@NPC nanocomposite delivers a capacity of 236.4 mAh g⁻¹ at a high rate of 10 A g⁻¹.

• ZnSe/CoSe@NPC nanocomposite exhibits excellent long cyclic life (303.9 mAh g⁻¹ at 1A g⁻¹ for 900 cycles).

• Kinetic analysis and electrochemical process of ZnSe/CoSe@NPC nanocomposite are studied.

Abstract

Bimetallic selenide (ZnSe / CoSe) was embedded in N-doped carbon rhombic dodecahedron and used as a sodium ion battery (SIB) anode. Metal organic framework (MOF) precursors (ZIF-8 / 67) form hollow structures (denoted as ZnSe/CoSe@NPC)through in situ pyrolysis and selenization processes at specific temperatures. Our selenides have very good electrochemical sodium storage properties. After 200circulation, the capacity of the as-prepared ZnSe/CoSe@NPC nanocomposite electrode was maintained at 417.6 mAh g⁻¹ at 0.1 A g⁻¹. Regarding rate capacity, the capacities of ZnSe/CoSe@NPC nanocomposite electrode are of 460.8, 415.6, 359.9, 346.3, 318.0, 274.1 and 236.4 mAh g⁻¹ at different current densities of 0.1, 0.2, 0.5, 1, 2, 5 and 10 A g⁻¹, respectively. The stability of the ZnSe/CoSe@NPC nanocomposite electrode at high current density is also obtained, and after 900 cycles at a high current density of 1 A g⁻¹, the electrode can maintain a stable reversible capacity of 303.9 mAh g⁻¹. Besides, kinetic analysis of the electrochemical Na⁺ storage behaviour of the ZnSe/CoSe@NPC nanocomposite shows that the external pseudocapacitor results in excellent rate performance and excellent long-cycle stability. This study proposes a new strategy for synthesizing multi-component hollow structures for the manufacture of intended energy storage devices.

Introduction

Rechargeable lithium-ion batteries (LIBs) are the main source of power for portable electronic devices, which is essential for the development and application of renewable and sustainable energy [1], [2], [3]. However, nowadays, due to the heavy use of LIBs, the lack of lithium sources will play an essential role to limit the future development of the LIBs [4]. In this case, sodium metal has attracted attention due to its lower cost and abundant reserves. At present, room temperature sodium ion batteries (SIB) have become very attractive new electrochemical energy storage systems [5], [6]. Yet the radius length of sodium ion is much larger than that of lithium ion, which cause to its difficulty of intercalation into the electrode materials, give rise to the low specific capacity, rate performance and poor cycling stability. Therefore, how to obtain high rate capability and long cycle life by using SIBs still remains a major challenge [7], [8]. Thus, it is an important and urgent task to accelerate the diffusion rate of Na⁺ and cope with the volume expansion accompanying the charge and discharge process.

Incorporating pseudocapacitance charge into the SIBs is a very effective way to overcome obtuse kinetics during sodiation/desodiation process and achieve high rate capability [9], [10]. Reasonable design for electrode materials with high pseudocapacitance has been demonstrated to effectively promote the capacity of these high energy density battery materials [11]. As yet, many compounds with pseudocapacitive charge storage have been successfully applied to SIBs which achieves significant breakthroughs in rate capability. In addition, studies have shown that compounds with unique structures (such as mesoporous structures, ultrathin nanosheets, nanoparticles and nanowires) can provide high pseudocapacitive charge accumulation and ideal rate performance in SIBs [12], [13], [14].Among them, metal organic framework (MOF) is used to build anode materials with various morphologies and structures because of its rich mesoporous structure [15], [16], [17]. The porous carbon of MOF has gained widespread heed as an anode material for SIB owing to its wild surface area, large pore volume, and excellent structural stability, the N doping contained therein can effectively improve the electron transport path and thereby improving the conductivity of the material [18], [19], [20], [21]. Besides, the unique 3D structure can be thought of as a new ideal SIB electrode with excellent electrochemical properties.

Since transition metal selenide has a high theoretical capacity, unique electronic structure, and high electrical conductivity, it is very attractive as an anode material for sodium ion batteries [22], [23], because these properties can provide hope for Na+ storage. Of late, studies have reported some typical metal selenide electrode materials, for instance, SnSe [24], ZnSe [25], CoSe₂ [26], NiSe₂ [27], etc. Liu and his co-workers [28] prepared ZIF-8-derived N-doped ZnSe (N-ZnSe) dodecahedron through a carbonization-selenization process and recombined it with reduced graphene oxide (rGO), the unique structure of the as prepared composites can increase the number of electronically active sites and improve the conductivity of the active materials, which cause a high capacity and cycle stability as LIBs and SIBs anode. Jin et al. [23] synthesis ZnSe/CoSe encapsulated in N-doped carbon polyhedra with carbon nanotubes, and used as LIBs anode materials, it has good cycle performance under low current density, however, its electrochemical performance is not excellent at large current densities (114 mAh g⁻¹ under a current density of 3 A g⁻¹). Hu et al. [29] prepared hybrid nanoboxes with complex shell structures are synthesized by the reaction of cobalt-based zeolite imidazole framework (ZIF-67) nanocube with selenium powder under designated temperature. Due to their unique structure and composition characteristics, these CoSe@carbon nanoboxes exhibit high specific capacity, excellent rate performance, excellent cycle stability, and high initial coulombic efficiency when used as anode materials for lithium-ion batteries. Recently, Hu and co-workers [30] designed the complex bimetallic selenides structure with ZnSe and CoSe₂ nanodots filled into the yolk-shell N-doped carbon nanocages. The electrode exhibited a stable capacity of 308.5 mAh g⁻¹ at a rate of 0.1 A g⁻¹ after 150 cycles in SIBs. It can conclude that the bimetallic selenides display better electrochemical sodium storage performance than single metal selenides. However, the synthesized method was time-consuming, complex and multistep, and when applied in SIBs, the electrochemical performance is not as good as that of LIBs anode. Therefore, it is a challenge to prepare the bimetallic selenides with hollow carbon structure, which can provide better performance.

Here, in this work, we have developed a composite material in which a bimetallic selenide (ZnSe/CoSe) nanoparticles are anchored in a N-doped carbon polyhedron with hollow structure (described as the ZnSe/CoSe@NPC nanocomposite) using a simple room temperature solution method accompanied with the subsequent in situ pyrolysis, and followed by selenization process under specific temperature, meanwhile. CTAB was used to adjust the topography of the material. Binary metal selenide (ZnSe/CoSe) exhibit the hollow structure and the nitrogen-doped carbon matrix. As-prepared ZnSe/CoSe@NPC nanocomposite exhibits a stable specific capacity of 417.6 mAh g⁻¹ at 100 mA g⁻¹ after 200 cycles and outstanding rate performance (236.4 mAh g⁻¹ at 10A g⁻¹). Meanwhile, the long-life cycle performance is also superior (303.9 mAh g⁻¹ after 900 cycles at 1 A g⁻¹).