ZnN and ZnP as novel graphene-like materials with high Li-ion storage capacities

Highlights

• ZnN, ZnP and ZnAs as novel graphene-like two-dimensional (2D) materials are introduced.

• Predicted monolayers are found to be dynamically stable.

• Mechanical, optical and electronic properties of predicted monolayers are studied.

• ZnN and ZnP nanosheets can yield high capacities of 675 and 556 mAh/g for Li-ion storage.

Abstract

In this work, we employed first-principles density functional theory (DFT) calculations to investigate the dynamical and thermal stability of graphene-like ZnX (X = N, P, As) nanosheets. We moreover analyzed the electronic, mechanical and optical properties of these novel two-dimensional (2D) systems. Acquired phonon dispersion relations reveal the absence of imaginary frequencies and thus confirming the dynamical stability of predicted monolayers. According to ab-initio molecular dynamics results however only ZnN and ZnP exhibit the required thermally stability. The elastic modulus of ZnN, ZnP and ZnAs are estimated to be 31, 21 and 17 N/m, respectively, and the corresponding tensile strengths values are 6.0, 4.9 and 4.0 N/m, respectively. Electronic band structure analysis confirms the metallic electronic character for the predicted monolayers. Results for the optical characteristics also indicate a reflectivity of 100% at extremely low energy levels, which is desirable for photonic and optoelectronic applications. According to our results, graphene-like ZnN and ZnP nanosheets can yield high capacities of 675 and 556 mAh/g for Li-ion storage, respectively. Acquired results confirm the stability and acceptable strength of ZnN and ZnP nanosheets and highlight their attractive application prospects in optical and energy storage systems.

Introduction

Two-dimensional (2D) materials are currently considered as the most attractive and vibrant class of materials, in which new members are being continuously introduced, either by theoretical prediction or via experimental realization. The astonishing attraction of this group of nanomaterials stems from their exceptional ability to exhibit diverse and contrasting properties, with unique application prospects for a wide range of advanced devices and technologies. Graphene [[1], [2], [3]], is known as the most prominent member of 2D materials family, with extraordinary mechanical stiffness [4], superior thermal conductivity [5] and surprising optical and electronic features [3,[6], [7], [8]] and thus graphene is referred in the media as the wonder material. Graphene exceptional physics, has already resulted in its utilization in some critical technologies, such as; nanoelectronics, optoelectronics and aerospace industry. Graphene with the hexagonal arrangements of atoms in the unit-cell is also known as the representative member of 2D materials with highly symmetrical and isotropic lattices. This group of symmetrical nanomaterials with hexagonal unit-cells also includes other attractive and well-known compositions, like; hexagonal boron-nitride (h-BN) [9,10], silicene [11,12], germanene [13], indium selenide [14], 2D metal organic frameworks [15] and 2H and 1T phases of transition metal dichalcogenides [16,17]. Nevertheless, 2D materials family shows remarkable diversity, and large number of structures with anisotropic lattices have been experimentally fabricated, such as; borophene [18,19], phosphorene [[20], [21], [22]], antimonene [23] and 1T’ phases of transition metal dichalcogenides [24,25]. Among the various classes of 2D materials, it is conspicuous that the majority of researches have been so-far devoted to fabricate and explore the properties of isotropic lattices with graphene-like structures.

Recent experimental advances with respect to the synthesis of a wide range of graphene-like 2D materials have undoubtedly brightened the prospect for the design and fabrication of other novel symmetrical nanosheets, especially via the chemical vapor deposition technique. Taking this fact into consideration, the basic question is that if other graphene-like binary compositions can stay physically and chemically stable under the usual working conditions or not? In addition, it is highly essential that a general vision concerning the intrinsic properties, such as the electronic, mechanical, optical and thermal properties of these novel 2D systems be provided. To address these challenges, theoretical studies can play unique role to estimate the stability and intrinsic properties as well [[26], [27], [28], [29], [30], [31], [32], [33], [34], [35]]. In this work, we predicted three graphene-like lattices ZnX (X = N, P and As). We then conducted first-principles density functional theory simulations to assess the thermal and dynamical stability, mechanical properties and electronic/optical properties of these novel nanomembranes. Worthy to remind that the application prospects of 2D materials in energy storage/conversion systems, are presently among the most attractive areas of the research on this class of materials. In particular, the efficiency of 2D materials in the design of advanced rechargeable metal-ion batteries has been extensively explored during the last decade. Such a tremendous interest, originates from the large surface to volume ratio, outstanding mechanical flexibility, remarkably high electron mobility and chemical and thermal stabilities of 2D materials. Therefore, in this study we particularly evaluate the suitability of ZnX (X = N, P and As) nanomembranes as anode materials for rechargeable Li-ion batteries.