Two-Dimensional Anode Materials for Non-lithium Metal-Ion Batteries

Abstract

Non-Li metal-ion rechargeable battery systems, e.g., Na-, K-, Mg-, and Ca-ion systems, are at the brink of playing a major role for sustainable energy and grid storage, in part owing to their significant availability as compared to Li-ion rechargeable systems. However, non-Li-based systems pose their own unique set of challenges: the large ionic size of the respective ions especially for Na and K systems, weak kinetics, and low-voltage window of Mg-ion systems, etc., which prevent efficient reversibility. Developing efficient electrode materials with novel morphologies is one of the main ways to harness the potential on the non-Li-ion systems. It is here that two-dimensional (2D) layered materials which have excellent structural, electrochemical, and mechanical properties can be considered to be prime candidates for negative electrode materials in non-Li-based energy storage systems. Therefore, research in the various aspects of 2D materials encompassing their fabrication techniques, tailoring their morphology, and application as anodes in non-Li systems has significantly increased in recent years, with more expected increase in the future. With this perspective in mind, here we provide an exhaustive review of the structure and properties of various 2D materials (graphene, phosphorene, and transition metal dichalcogenides), their performances as anode materials in emerging non-Li-based energy storage systems, and the obstacles that must be overcome at each stage.

TMDs beyond MoS2 for Electrochemical Energy Storage

“…The synthesis techniques of TMDs are generally classified as “top‐down” or “bottom‐up”. As the name suggests, top‐down techniques usually start with the bulk precursor material and then achieve the desired morphology . This is in contrast to the bottom‐up process, in which atomic layers are built up in a “block‐by‐block” or “layer‐by‐layer” fashion.…”

“…Generally, top‐down approaches are relatively cost‐effective and yield a considerable quantity of material, which can be suitably used for electrochemical energy storage applications . Mechanical exfoliation is one of the prevalent techniques that has been used, it has the advantage of providing high‐quality and very pure single layers, but it is not very scalable and it is suitable only for very fundamental studies .…”

“…Organic solvents (e.g., hexane, polyethylene oxide, etc.) are generally used, and sometimes a pre‐intercalating ion such as Li + ( n ‐butyllithium is a common source in such cases) is used to induce and facilitate the exfoliation process . Ambrosi et al.…”

“…On the other hand, the bottom‐up approaches find limited applications for electrochemical energy storage applications, primarily due to the energy intensive nature of the processes themselves and the rather low yields obtained . Chemical vapor deposition (CVD), atomic layer deposition (ALD) are some of the bottom‐up techniques used, in general, to synthesize layered TMDs .…”

“…With a morphology similar to that of graphite, TMD crystals present hexagonally packed transition metal layers alternating between layers of chalcogen atoms, as shown by Figure . The transition metal in the X‐M‐X structure generally crystallize in such a way that the coordination is usually trigonal prismatic or octahedral . Also, TMDs are a family of compounds exhibiting a diversity of structures and crystallographic orientations: from the hexagonal sulfides MoS 2 and WS 2 ( P 6 3 / mmc ) to the orthorhombic tellurides MoTe 2 and WTe 2 (P mn 2 1 ); thereby providing a spectrum of anisotropy in electronic properties, for example, the superconducting NbSe 2 , semiconducting 2H‐MoS 2 , 2H‐WS 2 , and insulating HfS 2.…”