Organic All-Solid-State Lithium Metal Battery Using Polymer/Covalent Organic Framework Electrolyte

Abstract

In this work, we have designed an all-organic and all-solid-state lithium metal battery based on 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as the organic electroactive material and a COF (Covalent Organic Framework)/PEO (PolyEthylene Oxide) composite as solid electrolyte. The use of a solid electrolyte allows fixing the solubility problem of organic electroactive materials in classical liquid electrolytes. This is the first time an all-solid-state organic battery based on TCNQ versus lithium metal is reported, since no liquid additive was included in the formulation of the electrolyte. We obtained a reversible capacity of 88 mAh g⁻¹ at the second discharge, and still 58 mAh g⁻¹ at the tenth discharge. The redox processes were investigated by X-ray Photoelectron Spectroscopy (XPS). We could evidence the involvement of the two lithiation steps of TCNQ (LiTCNQ and Li₂TCNQ) in the reversible capacity. Optimization of the electrode manufacturing and formulation, and replacing the salt (LiI) by alternative ones opens the door to future improvements in the electrochemical performances. This study demonstrates the interest of COF-type organic structures in the formulation of organic solid electrolytes.