Silicate covalent organic frameworks and porous organic polymers for energy applications

Abstract

With merit to the ultra-high theoretical capacity of the metallic Li anode, lithium metal batteries (LMBs) hold great promise as next-generation batteries to replace Li-ion batteries and spearhead decarbonization efforts. However, safety concerns arise from the uncontrollable dendrite growth and leakage of liquid electrolyte, which can be mitigated by replacement via a solid-state electrolyte (SSE), or by creating an artificial solid-electrolyte interphase (SEI). Herein, we demonstrate the ionic covalent organic frameworks, (iCOFs) or ionic porous organic polymers, (iPOPs) can be designed for either strategy, using anionic silicate as a motif for construction of the polymer frameworks. In the first project, the ionic covalent organic framework AQ-SiCOF-Li was coated on metallic Li chip to form an artificial SEI layer. AQ-SiCOF- Li, featuring both redox active anthraquinone linkers and anionic hexacoordinate silicate nodes was coated on a metallic Li anode as a bifunctional SEI, exhibits an ion conduction of 9.1 mS cm^–1 with transference number ?_??+ of 0.92. Full cells with AQ-SiCOF-Li coated anodes exhibited an enhanced specific capacity of 200 mAh g^–1 at 0.2 C. Taken together, AQ-SiCOF-Li demonstrates its versatile high performance as both electrode and conductive interphase. In the second project, the porous polymer ionic SiPOP-Li, integrating both silicate nodes and lithium sulphonate linkers was successfully mechanochemically synthesized, and demonstrated Li⁺ conductivity of 5.9 × 10^-5 S cm^–1 without plasticizers or solvents, competitive with all-solid-state iCOF electrolytes. By bypassing the normal solvothermal route, SiPOP-Li also demonstrates the potential to be rapidly synthesized while minimizing the use of solvents, enhancing its fabrication viability. All in all, the strategies explored herein show huge potential for designed fast ion conductors with diverse ionic or redox active moieties to enable Li metal batteries in the near future.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Yoonseob KIM (Supervisor)