Three-Dimensional Hierarchical Porous Structures Constructed by Two-Stage MXene-Wrapped Si Nanoparticles for Li-Ion Batteries.

As the demand for batteries increases with the development of electric vehicles, the energy density of lithium-ion batteries (LIBs) should be continuously enhanced. Due to the excellent theoretical specific capacity, silicon (Si) is the most promising anode material for LIBs. Nevertheless, the application of Si-based anodes is constrained by critical problems such as low conductivity and extreme volume change. Herein, we demonstrate an effective strategy for the fabrication of a three-dimensional (3D) hierarchical porous-structured Si-based anode with dual MXene protection (namely, SiNP@MX1/MX2). By electrostatic force induced self-assembly between modified Si with a positive charge and MXene nanosheets with a negative charge on the surface, Si nanoparticles are riveted to the MXene nanosheets (namely, SiNP@MX1), and then embedded into the 3D MXene skeleton (MX2) via a hydrothermal reaction and freeze-drying. Through the tailored and reasonable design, the internal MX1 coating can accommodate the volume expansion and avoid particle aggregation. The external MX2 allows for rapid electron transport and ion transfer while further buffering volume changes. Most importantly, by preventing Si from directly contacting the electrolyte, the double MXene-wrapped protection design benefits from the formation of a stable solid electrolyte interphase (SEI) film. The SiNP@MX1/MX2 anode material has a high capacity of 1422 mA h g at a current density of 0.5 A g after 200 cycles, excellent cycle stability, and good rate performance. At the same time, the method proposed in this study is expected to be applied to the preparation of other alloy anodes/MXene hybrids for storage batteries.