Sandwich-Structured Sn₄P₃@MXene Hybrid Anodes with High Initial Coulombic Efficiency for High-Rate Lithium-Ion Batteries

Abstract

The high theoretical capacity makes metal phosphides appropriate anode candidates for Li-ion batteries, but their applications are restricted due to the limited structural instability caused by the huge volume change, as in other high-capacity materials. Here, we design an integrated electrode consisting of Sn₄P₃ nanoparticles sandwiched between transition-metal carbide (MXene) nanosheets. Tetramethylammonium hydroxide (TMAOH) plays an essential role in the formation of such sandwich structures by producing negatively charged MXene sheets with expanded layer spacings. The strong C-O-P oxygen bridge bond enables tight anchoring of Sn₄P₃ nanoparticles on the surface of MXene layers. The obtained Sn₄P₃-based nanocomposites exhibit high reversible capacity with an initial Coulombic efficiency of 82% and outstanding rate performance (1519 mAh cm^-3 at a current density of 5 A g^-1). The conductive and flexible MXene layers on both sides of Sn₄P₃ nanoparticles provide the desired electric conductivity and elastomeric space to accommodate the large volume change of Sn₄P₃ during lithiation. Therefore, the Sn₄P₃@MXene hybrid exhibits an enhanced cyclic performance of 820 mAh g^-1 after 300 cycles at a current density of 1 A g^-1.