MoS2 nanosheets with expanded interlayer spacing for enhanced sodium storage

Sodium-ion battery technology is a promising alternative to lithium-ion batteries for low-cost and large-scale energy storage applications. The larger size of the Na-ion relative to the Li-ion imposes kinetic limitations and often results in sluggish Na-ion diffusion. It is a great necessity to explore prominent structural features of materials to overcome the limitations and improve the diffusion. Layered MoS2 has an ideal two-dimensional diffusion pathway because of the weak van der Waals interaction between the layers. However, the limited gallery height of 0.3 nm is insufficient to achieve fast Na-ion diffusion. A facile hydrothermal route at medium-ranged temperatures is reported in this work to obtain interlayer expanded MoS2 nanosheets. The interlayer spacing is greatly expanded to 1 nm and facilitates Na-ion insertion and extraction in the van der Waals gaps. The nanosheet morphology shortens the Na-ion diffusion distance from the lateral side. The interlayer expanded MoS2 nanosheets are used as sodium-ion battery anodes in the voltage window of 0.5-2.8 V, where intercalation reaction contributes to Na storage and the layered structure can be preserved. The nanosheets exhibit a high cycling stability by retaining 92% of the initial charge capacity after 100 cycles and a great rate capability of 43 mA h g(-1) at 2 A g(-1). Kinetics study reveals a significant alleviation of diffusional limitation, verifying the improved Na-ion diffusion and enhanced Na storage. The presented work explores the utilization of the van der Waals gaps to store ions and sheds light on designing two-dimensional materials in other energy systems.