A closed-ended MXene armor on hollow Sn4P3 nanospheres for ultrahigh-rate and stable sodium storage

The development of sodium-ion batteries has been seriously discouraged by the major limitation in the rate capability and the cycle life of the anode materials. Sn4P3 is recognized as a potential anode for sodium -ion batteries owing to its ultrahigh specific capacity and low cost, but the great volumetric change and low intrinsic electrical conductivity severely limit the cycling performance. Herein, we propose a closed-ended MXene and Sn4P3 hybrid consisting of active Sn4P3 porous hollow nanospheres (Sn4P3 HS) armored by a conductive MXene shell. Notably, the outer MXene shell protects Sn4P3 from direct exposure to the electrolyte and only allows the inward expansion of Sn4P3 into the hollow space, resulting in the formation of a thin solid-electrolyte interphase layer of high stability. As predicted, the hybrids can deliver an extraordinarily high capacity of 302.1 mAh g-1 even at an ultrahigh rate of 10 A g-1 and cycle at 1 A g-1 for 1500 cycles with a capacity retention of 94.9%. Moreover, the Sn4P3 HS@MXene//Na3V2(PO4)3/C full cell exhibits an outstanding energy density of 287.8 Wh kg-1 and good cyclic ability (390.5 mAh g-1 at 1A g-1 after 500 cycles), exhibiting a great potential in practical application.

Automated summary

A closed-ended hybrid of MXene and Sn4P3, consisting of active Sn4P3 hollow nanospheres armored by a conductive MXene shell, is proposed. The MXene shell protects Sn4P3 from direct exposure to the electrolyte and allows inward expansion, leading to the formation of a stable solid-electrolyte interphase layer. The hybrid system exhibits a high capacity of 302.1 mAh g-1 even at a high rate of 10 A g-1 and can cycle for 1500 cycles with a capacity retention of 94.9%.