Exploring a novel two-dimensional metallic Y₄C₃ sheet applied as an anode material for sodium-ion batteries

As novel "post lithium-ion batteries" and promising alternatives to lithium-ion batteries (LIBs) suffering from the limited Li resources, sodium-ion batteries (SIBs) are nowadays emerging and show bright prospects in large-scale energy storage applications due to abundant Na resources. However, a lack of suitable anode materials has become a key obstacle for the development of SIBs. Here we explore the potential of the two-dimensional (2D) Y-C space and identify a novel anode material for SIBs, a new Y₄C₃ sheet with P3̄m1 crystal symmetry, by means of first-principles swarm structure calculations. This Y₄C₃P3̄m1 structure has rather good kinetic and thermodynamic stability, possesses intrinsic metallicity, and remains metallic after adsorbing Na atoms, ensuring good electrical conductivity during the SIB cycle. Remarkably, a Y₄C₃ sheet as an anode for SIBs possesses the essential properties of a high specific capacity (∼752 mA h g^-1), a low barrier energy (∼0.1 eV), and suitable open-circuit voltage (0-0.15 V). These characteristics are comparable and even superior to those of another known 2D Y₂C anode material, indicating that the Y₄C₃ sheet can act as an appealing new candidate as an anode material for SIBs and offering new insights into the 2D Y-C space.