Unveiling the Sodium Storage Mechanism of ReTe₂: Insights from First-Principles Calculations

Transition metal dichalcogenides (TMDCs) are increasingly studied for their potential as anode materials in sodium-ion batteries (SIBs) due to their diverse structural phases. Among them, ReTe₂, a low-symmetry distorted 1T-phase with a narrow band gap of 0.2 eV emerges as a particularly promising candidate. This study presents a comprehensive first-principles analysis to elucidate the electrochemical reaction mechanism and sodium (Na) storage properties of ReTe₂. It is uncovered that ReTe₂ undergoes a semiconductor-to-metal transition upon Na intercalation, which is attributed to significant charge transfer. The theoretical investigations suggest a maximum intercalation capacity of x = 1 (Na_xReTe₂), beyond which the structure evolves into a Re monomer and a Na_yTe intermediate phase. As Na intercalation progresses, tellurium (Te) atoms receive an increasing number of electrons from Na, which raises the Fermi level of the system and increases the antibonding contribution in Re–Te bonds. Consequently, the Re–Te bond strength is weakened. The intercalation of Na serves dual roles: bridging the ReTe₂ layers and simultaneously injecting carriers into the lattice, both of which are instrumental in boosting the electrical conductivity. These insights not only confirm ReTe₂ as a viable anode material for SIBs but also provide a detailed understanding of the electrochemical behaviors of low-symmetry 1T-phase TMDCs.