Effect of Guest Solvents on the Ionic Conductivity and Electrochemical Performance of Metal-Organic Framework-Based Magnesium Semi-Solid Electrolytes

Developing suitable electrolytes is crucial for the advancement of rechargeable magnesium batteries. Recently, metal-organic frameworks (MOFs) have shown a great interest in the field of solid electrolytes for metal ion batteries. However, the ionic conductivity as well as the electrolyte stability in the presence of Mg electrodes are shown to be strongly dependent on the guest solvent used to solvate Mg salts in MOFsSEs. Our measurements showed that full evacuation of the MOF structure before semi-solid electrolytes (sSEs) preparation is crucial for achieving relatively low Mg overpotentials regardless of the ionic conductivity values. Moreover, the behavior of the anode/MOFsSEs interfaces (MOF: α-Mg3 [HCOO]6 ; Mg salt : MgCl2 -Mg[TFSI]2 (1 : 1 wt %); guest solvent: acetone, DMF, DEG, DME and tetraglyme) was investigated by EIS, CV and galvanostatic measurements. The current comparative study of the electrochemical deposition processes of magnesium from MOFsSEs revealed that magnesium deposition/dissolution reactions vary depending on the MOF structure, the guest anion species as well as the nature of the guest solvents.

Semi-Solid Supramolecular Ionic Network Electrolytes Formed by Zwitterionic Liquids and Polyoxometalate Nanoclusters for High Proton Conduction

Flexible electrolytes with solid self-supporting properties are highly desired in the fields of energy and electronics. However, traditional flexible electrolytes prepared by doping ionic liquids or salt solutions into a polymer matrix pose a risk of liquid component leakage during device operation. In this work, the development of supramolecular ionic network electrolytes using polyoxometalate nanoclusters as supramolecular crosslinkers to solidify bola-type zwitterionic liquids is reported. The resulting self-supporting electrolytes possess semi-solid features and show a high proton conductivity of 8.2 × 10-4 S cm-1 at low humidity (RH = 30%). Additionally, the electrolytes exhibit a typical plateau region in rheological tests, indicating that their dynamic network structures can contribute mechanical behavior similar to the entangled networks in covalent polymer materials. This work introduces a new paradigm for designing flexible solid electrolytes and expands the concept of reticular chemistry to noncrystalline systems.

Poly(ionic liquid) Electrolytes for a Switchable Silver Mirror

Imidazolium-type small-molecule ionic liquids (ILs) and their corresponding poly(ionic liquid) (PIL) homopolymers were synthesized and applied to reversible electrochemical mirrors (REMs). The effects of alkyl chain length of the carbon chains at the N3 position and cation charge density (mono- and bis-imidazolium) on the electrochromic properties of Ag-based REMs were investigated by analyzing their electrodeposition and spectral properties. Longer alkyl chains and higher charge densities decreased the size and resulted in a more uniform distribution of Ag nanoparticles. Compared with IL-based liquid electrolytes, the PIL-based gel electrolytes formed smaller and denser electrodeposited metallic Ag nanoparticles because of their higher viscosity. These findings were used to guide fabrication of a 50 cm² mirror dynamic window and flexible display. Because of several unique properties of PILs, the PIL-based REM exhibits fast switching speeds, superb cycling durability, small particle sizes, and uniform electrodeposited Ag nanoparticle films. These results make dynamic windows based on PIL electrolytes promising and competitive alternatives to traditional electrochromic windows.