Buffer layer enhanced stability of sodium-ion storage

Se−Se buffer layers are introduced into tin sequences as SnSe2 single crystal to enhance the cycling stability for long-term sodium-ion storage by blazing a trail of self-defence strategy to structural pulverization especially at high current density. Specifically, under half-cell test, the SnSe2 electrodes could yield a high discharge capacity of 345 mAh g−1 after 300 cycles at 1 A g−1 and a high discharge capacity of 300 mAh g−1 after 2100 cycles at 5 A g−1 with stable coulombic efficiency and no capacity fading. Even with the ultrafast sodium-ion storage at 10 A g−1, the cycling stability still makes a positive response and a high discharge capacity of 221 mAh g−1 is demonstrated after 2700 cycles without capacity fading. The full-cell test for the SnSe2 electrodes also demonstrates the superior cycling stability. The flexible and tough Se-Se buffer layers are favourable to accommodate the sodium-ion intercalation process, and the autogenous Na2Se layers could confine the structural pulverization of further sodiated tin sequences by the slip along the Na2Se-NaxSn interfaces.