Electrochemical exfoliation of two-dimensional siligene SixGey; material characterization and perspectives for lithium-ion storage

Two-dimensional (2D) silicene-germanene alloy - siligene (SixGey), a novel single-phase material has attracted increased attention due to its two-elemental low-buckled composition and unique physics and chemistry. This new 2D material has the potential to address the challenges caused by low electrical conductivity and the environmental instability of corresponding monolayers. Yet, siligene structure was studied in theory, demonstrating the material’s great electrochemical potential for energy storage applications. The synthesis of free-standing siligene remains challenged and therefore hinders the research and application of this material. Herein we pioneer non-aqueous electrochemical exfoliation of a few-layer siligene from Ca1.0Si1.0Ge1.0 Zintl phase precursor. The procedure was conducted in an oxygen-free environment applying 3.8 V potential. The obtained silicene exhibits a high-quality, high uniformity, and excellent crystallinity; the individual flake is within the micrometer lateral size. The 2D SixGey was further explored as an anode material for lithium-ion storage. Two types of anode have been fabricated and integrated into lithium-ion battery cells, namely 1) siligene_graphene oxide sponge, and 2) siligene_multi-walled carbon nanotubes. The as-fabricated batteries both with/without siligene exhibit similar behaviour, however referring to the increase in the electrochemical characteristics of SiGe-integrated batteries by 10%. The corresponding batteries exhibit 1145.0 mAh·g-1 specific capacity at 0.1 A·g-1. The SiGe-integrated batteries demonstrate a very low polarization confirmed by their good stability after 50 working cycles and a decrease in the solid electrolyte interface level that occurs after the first discharge/charge cycle. We anticipate the growing potential of emerging two-component 2D materials and their great promise for energy storage and beyond.