Rational design of a tubular, interlayer expanded MoS2–N/O doped carbon composite for excellent potassium-ion storage

Abstract

Potassium ion batteries (KIBs) are the emerging and promising energy storage system for large-scale electrochemical energy storage. However, the development of KIBs is greatly hindered by their low capacity, poor rate performance and cycling stability resulting from the large-sized potassium ion (K⁺). Herein, a tubular, interlayer expanded MoS₂–N/O doped carbon composite (E-MoS₂/NOC TC) is rationally designed and fabricated for accelerating K⁺ diffusion rate and enhancing structure stability. It is demonstrated that the expanded interlayer spacing (0.92 nm) of ultrathin MoS₂/C nanosheets facilitates the insertion/extraction of K⁺, resulting in the acceleration of K⁺ diffusion rate. Moreover, the N/O carbon skeleton can not only buffer the volume expansion and improve the electronic conductivity, but also effectively inhibit the side reactions and the dissolution of active components. Meanwhile, the tubular structure can further maintain the structural stability by mitigating large mechanical strain after the intercalation of large-sized K⁺. Therefore, thanks to the unique structure, E-MoS₂/NOC TC delivers a high capacity of 220 mA h g⁻¹ after 300 cycles at a current density of 250 mA g⁻¹, and it still remains at 176 mA h g⁻¹ (0.09% decay per cycle) over a long period of 500 cycles even at 1000 mA g⁻¹. Density functional theory (DFT) calculations further confirm that both the combination of MoS₂ with the carbon interface, and the expansion of interlayer spacing can reduce the diffusion energy barriers of K⁺ in the interlayer of the electrode material. All this provides a facile pathway for the structural design of two dimensional transition metal dichalcogenides for potassium ion based energy storage.