Transition-metal-dichalcogenides own a variety of structures as well as electronic properties which can be modulated by structural variations, element substitutions, ion or molecule intercalations, etc. However, there is very limited knowledge on metastable phases of this family, especially the precise regulation of structural changes and accompanied evolution of electronic properties. Here, based on a new developed field-effect transistor with solid ion conductor as the gate dielectric, we report a controllable structural and electronic phase transitions in metastable MoS$_2$ thin flakes driven by electric field. We found that the metastable structure of 1T$^{}$-MoS$_2$ thin flake can be transformed into another metastable structure of 1T$^{}$ -type upon intercalation of lithium regulated by electric field. Moreover, the metastable 1T$^{}$ phase persists during the cycle of intercalation and de-intercalation of lithium controlled by electric field, and the electronic properties can be reversibly manipulated with a remarkable change of resistance by four orders of magnitude from the insulating 1T$^{}$-LiMoS$_2$ to superconducting 1T$^{}$-MoS$_2$. Such reversible and dramatic changes in electronic properties provide intriguing opportunities for development of novel nano-devices with highly tunable characteristics under electric field.
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