Synthesis of zwitterionic polymer-modified metal-organic frameworks as a quasi-solid-state electrolyte

Abstract

To overcome the challenges associated with the oxidative degradation of electrolytes for high-energy-density lithium metal batteries (LMBs), this work focuses on the reconstruction of a solvation structure to mitigate the strong coordination between lithium and solvents. In this work, a zwitterionic polymer modified metal-organic framework was synthesized via in-situ polymerization to increase the exposure of ionic functional groups and exhibit a high free volume compared to the bulk polymer. Zwitterions exhibit ionic interactions with both lithium ions and solvent molecules within the metal-organic framework. It leads to facilitated lithium ion conduction and a formation of a chemically coordinated environment to solvent molecules similar to that observed in saturated liquid electrolytes. It can effectively reduce the free solvent that is highly reactive with the electrode. Therefore, the synthesized PVIPS@MIL-101 quasi-solid-state electrolyte (QSSE) demonstrated both high ionic conductivity and improved electrochemical stability compared to saturated liquid electrolytes. It exhibits high oxidative stability, making it suitable for applications in lithium metal-NCM-811 batteries and lithium metal-graphite dual-ion batteries (DIBs) that require high-voltage operation. In DIBs, the QSSE operates stably at high voltages without degradation. And the functionalization of the zwitterionic polymer improves the performance at high current rates by facilitating desolvation kinetics on the electrode surface. Overall, this work successfully develops a QSSE with high oxidation stability by controlling the charge of porous particles using the synergistic effect of the MOF and zwitterionic polymer.