2D Si-Ge layered materials as anodes for alkali-cation (Na+, K+) batteries

Abstract

Recent studies have shown that two-dimensional (2D) materials, such as siloxene and germanane, as electrode in alkali metal ion batteries can lead to excellent performance. The improved electrochemical behavior of these 2D active materials could be due to the limited volume change during charge and discharge, based on an intercalation rather than an alloying mechanism. In addition, if Si is effective in reducing costs due to its low price and abundant resource reserves, its conductivity is low, while Ge can provide higher electronic conductivity than Si, but is more expensive. In this respect, in order to integrate their cheapness and excellent conductivity, we propose a series of layered materials (named siliganes, i.e., Si1-xGex, 0.1 ⩽ x ⩽ 0.9), which consist of 2D Si-Ge composites. Through a simple method, the Ca2+ cations were completely removed from the precursor Ca(Si1-xGex)2, and the lamellar siliganes were obtained. The layered materials were tested in Na- and K- ion batteries. Based on the better electrochemical performance, we identified siligane_Si0.1Ge0.9 as the best candidate. At a current density of 0.05 A g−1, its reversible capacities of the Na ion and K ion cells were 276 mAh g−1 and 132 mAh g−1 after 50 cycles, respectively.