Promoting superior K-ion storage of Bi₂S₃ nanorod anode via graphene physicochemical protection and electrolyte stabilization effect

Potassium-ion batteries (PIBs) have been considered as next generation energy storage device due to abundant and inexpensive resources, and exploring suitable anode materials based on conversion-alloying dual mechanism will promote the fast development of high energy density PIBs. In this work, Bi₂S₃ nano-rods wrapped by reduced graphene oxide (Bi₂S₃@rGO) are regarded as anodes for K-ion storage. The physical encapsulation of graphene and chemical bonding of Bi-O can boost the composite to provide outstanding electrochemical kinetics and structure stability. Furthermore, the electrolyte stabilization effect plays an important role in generating a more robust solid electrolyte interface film and maintaining effectiveness of chemical bonding. It is demonstrated by ex situ TEM that Bi₂S₃ electrode undergoes a dual electrochemical mechanism of conversion-alloying relied on 12 K-ion diffusion per formula unit (Bi₂S₃ + 6 K ↔ 2Bi + 3K₂S, 2Bi + 6 K ↔ 2K₃Bi). The above desirable features are integrated into the conductive composite for great cycling stability with high-capacity retention of 148.3 mAh·g⁻¹ after 100 cycles at 50 mA·g⁻¹. This work will guide the way for the construction of dual mechanism anode and the understanding of K-ion storage principle.