Be2 C5 Monolayer with Quasiplanar Pentacoordinate Carbon Atoms and Ultrahigh Energy Density as a Dirac Anode for Potassium-Ion Batteries

Abstract

K-ion batteries (KIBs) are of potential importance in the future energy industries. Recent efforts were committed to increasing the energy storage density in KIBs. Here, we search for anode materials with high energy density that are compatible with KIBs, by a combination of the swarm-intelligence structure search method and first-principles calculations. We predict the Be2C5 monolayer to be a kind of material that showcases ultrahigh energy density (∼5455 mWh/g, referenced to the standard hydrogen electrode potential), thanks to an exceptional specific capacity of 2060 mAh/g and low average open-circuit voltage of 0.28 V. This energy density value is much larger than that of most currently known 2D KIB-based anode materials. Furthermore, the Be2C5 anode presents other intriguing behavior, such as (i) the fast diffusion of K ions, as suggested by an ultralow barrier energy of about 0.074 eV; (ii) excellent mechanical strength, with a Young's modulus of about 243 N/m; (iii) robust compatibility with electrolytes; (iv) small-scale volume expansion of 0.68% during the process of potassiation; and (v) a unique "self-doping"effect, which is beneficial for high electronic conductivity.