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.