Abstract:

Suffering from strong electrostatic interactions between divalent Zn²⁺ and host framework, molybdenum disulfide exhibits slow reaction kinetics as cathode for aqueous zinc-ion batteries. The narrow layer spacing of MoS₂ is difficulty in accommodating large size insertion of hydrated Zn²⁺, resulting in a lower discharge specific capacity. Here, NH₄⁺ expanded MoS₂-N was prepared by a simple ammonia-assisted hydrothermal. The result showed that the ammonia promoted hydrolysis of thioacetamide to provide reduced S^2- and generated a large amount of NH₄⁺ as intercalating particles. These particles expanded the layer spacing of pristine MoS₂ from 0.62 nm to 0.92 nm, greatly reducing the Zn²⁺ inserting energy barrier (with its charge transfer resistance of MoS₂-N only 35 Ω), and increased the discharge specific capacity to 149.9 mAh·g⁻¹ at the current density of 0.1 A·g^-1, 2 times that of MoS₂ electrode without NH₄⁺ expansion. Consequently, it exhibited a stable discharge capacity of about 110 mAh·g^-1 at the current density of 1.0 A·g^-1 with nearly 100% Coulombic efficiency after 200 cycles. The approach of ammonia-assisted layer expansion proposed in this study enriches the modification strategy to enhance the electrochemical performance of MoS₂ and provides a new idea for subsequent cathode development.

Key words: MoS₂, ammonia-assisted interlayer-expansion, cathode material, aqueous zinc ion battery, 2D material