Voltage-driven Molecular Switch of Highly Periodically N‒heterocyclic Adlayer Enabled Deep Cycled Zinc Metal Battery

Abstract

The instable Zn/electrolyte interface due to severe corrosion, especially at high utilization of Zn anode, strongly hindered the practical application of aqueous zinc metal battery. Herein, we report a voltage-driven molecular switch through a reversible transition of the nicotinic molecules between zwitterion and anion to enable deep cycled zinc metal battery. In light of in-situ Raman, the switching mechanism of nicotinic molecules in the electrical double layer is unveiled: during plating, nicotinic molecules switches to zwitterion mode (ON state) with periodical pyridine-ring-substrate adlayer while during stripping, shifts to anion mode with periodical carbonyl group-substrate adlayer (OFF state). The transition of NA molecules enables molecular flipping on the substrate due to the electrostatic force and in this way, in both ON and OFF state, the zinc anode is protected by the adlayer to avoid the zinc corrosion on the anode side. Furthermore, the OTF^‒ decomposition is accompanied by the open ring reaction of N‒heterocyclic from nicotinic acid molecules to form highly elastic solid electrolyte interface layer. Benefiting from both the molecular switch function and solid electrolyte interface layer formation, the nicotinic molecules-based electrolyte enables practical zinc metal battery of high energy density (100 Wh/kg_electrode) for over 800 cycles with a cumulative capacity of 2.71 Ah cm⁻² at practical condition of low N/P ratio of 2, and lean electrolyte of 10 μL mAh⁻¹, representing the state-of-the-art performance. These findings highlight the utilization of molecular switch and its interfacial protection of the deep cycled zinc anode, and provide a new tactic for the development of high energy metal battery.