Conversion-alloying dual mechanism anode: Nitrogen-doped carbon-coated Bi₂Se₃ wrapped with graphene for superior potassium-ion storage

The construction of an anode material with a conversion-alloying dual mechanism will facilitate the development of potassium-ion batteries (PIBs) with high-energy density. Here a Bi₂Se₃ nanosheets coated with nitrogen-doped carbon and wrapped with reduced graphene oxide (Bi₂Se₃@NC@rGO) is fabricated to boost K-ion storage. The Bi₂Se₃@NC@rGO composite with strong C–O–Bi bonding can provide superior electrode integrity and electrochemical kinetics by combining the synergistic effect of carbon encapsulation and graphene confinement. In situ X-ray diffraction and ex situ transmission electron microscopy analyses demonstrate that K-ion intercalation/deintercalation proceeds via both conversion and alloying/dealloying reactions based on 12-electron transfer per formula unit; the conversion product of K₂Se can efficiently suppress the volume expansion during alloying/dealloying process to improve its stability. Hence, a high reversible capacity of 612.0 mAh·g⁻¹ at 100 mA·g⁻¹; a great rate capability with the capacity of 101.6 mAh·g⁻¹ at 5 A·g⁻¹, and an ultra-long cycling life of over 1000 cycles at 500 mA·g⁻¹ is achieved for the Bi₂Se₃@NC@rGO. The K-ion full cell is also assembled using K₂Ni[Fe(CN)₆] as the cathode, thereby contributing a high-energy density of 162.9 Wh·kg⁻¹ at 10 mA·g⁻¹ and a great cyclability.