Unveiling the Nature of Ultrastable Potassium Storage in Bi 0.48 Sb 1.52 Se 3 Composite.

The conversion and alloying-type anodes for potassium-ion batteries (PIBs) have drawn attention. However, it is still a challenge to relieve the huge volume expansion/electrode pulverization. Herein, we synthesized a composite material comprising Bi 0.48 Sb 1.52 Se 3 nanoparticles uniformly dispersed in carbon nanofibers (Bi 0.48 Sb 1.52 Se 3 @C). Benefiting from the synergistic effects of the high electronic conductivity of Bi 0.48 Sb 1.52 Se 3 and the mechanical confinement of the carbon fiber that buffers the large chemomechanical stress, the Bi 0.48 Sb 1.52 Se 3 @C//K half cells deliver a high reversible capacity (491.4 mAh g -1 , 100 cycles at 100 mA g -1 ) and an extraordinary cyclability (80% capacity retention, 1000 cycles at 1000 mA g -1 ). Furthermore, the Bi 0.48 Sb 1.52 Se 3 @C-based PIB full cells achieve a high energy density of 230 Wh kg -1 . In situ transmission electron microscopy (TEM) reveals an intercalation, conversion, and alloying three-step reaction mechanism and a reversible amorphous transient phase. More impressively, the nanofiber electrode can almost return to its original diameter after the potassiation and depotassiation reaction, indicating a highly reversible volume change process, which is distinct from the other conversion type electrodes. This work reveals the stable potassium storage mechanisms of Bi 0.48 Sb 1.52 Se 3 @C composite material, which provides an effective strategy to enable conversion/alloying-type anodes for high performance PIBs for energy storage applications.