MXene/Si@SiO_x@C layer-by-layer superstructure with autoadjustable function for superior stable lithium storage

Despite its very high capacity (4200 mAh g^-1), the widespread application of the silicon anode is still hampered by severe volume changes (up to 300%) during cycling, which results in electrical contact loss and thus dramatic capacity fading with poor cycle life. To address this challenge, 3D advanced Mxene/Si-based superstructures including MXene matrix, silicon, SiO_x layer, and nitrogen-doped carbon (MXene/Si@SiO_x@C) in a layer-by-layer manner were rationally designed and fabricated for boosting lithium-ion batteries (LIBs). The MXene/Si@SiO_x@C anode takes the advantages of high Li⁺ ion capacity offered by Si, mechanical stability by the synergistic effect of SiO_x, MXene, and N-doped carbon coating, and excellent structural stability by forming a strong Ti-N bond among the layers. Such an interesting superstructure boosts the lithium storage performance (390 mAh g^-1 with 99.9% Coulombic efficiency and 76.4% capacity retention after 1000 cycles at 10 C) and effectively suppresses electrode swelling only to 12% with no noticeable fracture or pulverization after long-term cycling. Furthermore, a soft package full LIB with MXene/Si@SiO_x@C anode and Li[Ni_0.6Co_0.2Mn_0.2]O₂ (NCM622) cathode was demonstrated, which delivers a stable capacity of 171 mAh g^-1 at 0.2 C, a promising energy density of 485 Wh kg^-1 based on positive active material, as well as good cycling stability for 200 cycles even after bending. The present MXene/Si@SiO_x@C becomes among the best Si-based anode materials for LIBs.