2D Metallic Abnormal Li2Cl Crystals with Unique Electronic Characteristics Applied in Capacitor and Humidity Sensor

Abstract

Abstract Understanding the configuration and properties of the simplest lithium‐ion crystal, the Li‐Cl crystal, is essential for developing Li‐based electrochemical energy storage and conversion devices. Under ambient conditions, LiCl in a 1:1 stoichiometry is the only known stable form of the Li‐Cl crystal, and the corresponding crystals are insulating. Here, using cryo‐electron microscopy (cryo‐EM) and X‐ray photoelectron spectroscopy (XPS), this work reports a novel abnormal 2D Li2Cl crystal in ultra‐thin reduced graphene oxide (rGO) membranes by simply soaking the rGO membrane in unsaturated LiCl solution under ambient conditions and showed its high‐resolution image. Unexpectedly, such Li2Cl crystal presents metallic properties rather than insulating properties. Using vacuum filtration of the unsaturated LiCl solution through rGO membranes, this work prepares the rGO membranes with high content Li2Cl, displaying a high areal capacitance of 220 mF cm−2. Remarkably, the Li2Cl‐rGO membranes also exhibit heterostructure property and piezoelectricity. For the excess Li and unique electrical characteristics, these Li2Cl‐rGO membranes can be used as a humidity sensor. These findings point to possibilities for creating new Li‐based materials and fabricating novel high‐performance electronic devices, transistors, and sensors.

Keywords

• areal capacitance
• cryo‐electron microscopy
• heterostructure
• Li 2Cl‐rGO membranes
• piezoelectricity