Abstract
AbstractGraphite anodes offer low volumetric capacity in lithium‐ion batteries. By contrast, tellurene is expected to alloy with alkali metals with high volumetric capacity (≈2620 mAh cm−3), but to date there is no detailed study on its alloying behavior. In this work, the alloying response of a range of alkali metals (A = Li, Na, or K) with few‐layer Te is investigated. In situ transmission electron microscopy and density functional theory both indicate that Te alloys with alkali metals forming A2Te. However, the crystalline order of alloyed products varies significantly from single‐crystal (for Li2Te) to polycrystalline (for Na2Te and K2Te). Typical alloying materials lose their crystallinity when reacted with Li—the ability of Te to retain its crystallinity is therefore surprising. Simulations reveal that compared to Na or K, the migration of Li is highly “isotropic” in Te, enabling its crystallinity to be preserved. Such isotropic Li transport is made possible by Te's peculiar structure comprising chiral‐chains bound by van der Waals forces. While alloying with Na and K show poor performance, with Li, Te exhibits a stable volumetric capacity of ≈700 mAh cm−3, which is about twice the practical capacity of commercial graphite.
Highlights
Tellurene (Te) is the two-dimensional (2-D) allotrope of bulk tellurium [1,2]
In the case of Na and K, one direction of movement is preferred, which indicates that some Te atoms will encounter an abundance of Na or K atoms, while others in a nonpreferred direction will experience a scarcity of Na or K atoms
We have reported alloying of a range of alkali metals (A = Li, Na or K) with few-layer Tellurene (Te)
Summary
Tellurene (Te) is the two-dimensional (2-D) allotrope of bulk tellurium [1,2]. Bulk tellurium is predicted [3,4] to deliver a high volumetric specific capacity of ~2620 mAh cm-3 when alloyed with Lithium (Li). Few-layered Te flakes can be manufactured using the hydrothermal method with controllable thickness and with a high yield of ~98% [5]. All of these attributes render Te a promising anode material for LIB applications. We present a hypothesis to explain why the isotropic transport of Li within Te enables retention of its single-crystalline nature Such preservation of single-crystal structure could have important practical implications, since it mitigates cell degradation related to secondary grains or particles such as micro-cracks, as has been well documented for single-crystal layered transition-metal oxide cathodes [17]. Our study provides new fundamental insight as to why certain alloying materials are able to preserve their crystallinity when deployed in batteries
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