Piezoelectric MoS2 with expanded interlayers: a flexible anode for a “zero” interfacial quasi-solid-state ammonium-ion asymmetric supercapacitor

Abstract

Ammonium ion (NH₄⁺) supercapacitors are gaining significant interest because they are less expensive, safer, and more environmentally friendly compared with metal ion supercapacitors. However, the development of ideal electrode materials for high-efficiency NH₄⁺ storage that have fast diffusion kinetics is still falling short of expectations. Herein, we propose 1T/2H phase MoS₂ nanosheets with expanded interlayers grown on carbon cloth (Exp-MoS₂/CC) as a promising flexible anode for NH₄⁺ asymmetric supercapacitors. In terms of its huge space for NH₄⁺ storage, Exp-MoS₂/CC delivers a specific capacitance reaching up to 2003.8 mF cm⁻² at 1 mA cm⁻² and exhibits 90.3% capacitance retention after 5000 cycles. Experimental results and theoretical calculations reveal the unique piezoelectric effect of Exp-MoS₂/CC, which functions as an extra accelerator to significantly promote NH₄⁺ transfer and leads to a faster NH₄⁺ diffusion rate relative to that of contrastive T-MoS₂/CC and MoS₂/CC. Moreover, a flexible quasi-solid-state supercapacitor with a “zero” interface was successfully assembled by integrating with an Exp-MoS₂/CC anode and MnO₂/CC cathode, achieving a specific capacitance of 497.6 mF cm⁻² and an energy density of 223.7 mW h cm⁻². Overall, this work holds significant promise for designing new-fashioned NH₄⁺ insertion electrodes with a unique nanostructure configuration and remarkable electrochemical performance.