Charge-Transfer Complexes for Solid-State Li⁺ Conduction

Abstract

Contradictory to the conventional understanding of solid-state ionics, we find that some organic crystals are highly ion conducting (>10 −4 S/cm at room temperature). Through the microparticles of charge-transfer (CT) complexes, dissociated lithium ions move readily. Fast conduction is observed for a wide variety of compounds that form CT complexes, irrespective of the functional groups. Automatic relationship analysis via machine learning indicates the importance of polarization of the CT complexes for the ionic conduction. The decoupling system, where ion transport is not dominated by the segmental motion of media molecules, paves the way for achieving superionic properties in organic monomeric and polymeric conductors.

Automated design of Li+-conducting polymer by quantum-inspired annealing

“…Although the mechanism is unknown, the polarisation in the polymer may have contributed to the dissociation and migration of ions. [10,26] The conductivity was higher than a conventional PEO electrolyte around room temperature (Figure 6e). The PEO electrolyte exhibited higher conductivity at higher temperatures than the new electrolyte.…”

“…Our original database, containing experimental records of solid-polymer and liquid lithium-ionconducting electrolytes, [10,26] was used for machine learning (>1000 cases at room temperature, Figure 6a). Most electrolytes consist of multiple components, including lithium salts, solvents, and other components.…”

“…[28] However, our prior machine learning and experimental study indicated that their polarised structures could induce ion dissociation and even superionic properties. [10,26] We focused on the de novo automated design of charge-transfer complex electrolytes in the present study.…”

“…A self-standing polymer electrolyte film was prepared by combining lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the donor polymer, and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a strong acceptor. [26,28] Commercially available TCNQ was selected instead of the proposed chemicals for synthetic ease. The new electrolyte exhibited promising ionic conductivity at room temperature during the impedance measurements (Figure 6d).…”

“…Our original lithium-ion-conducting molecular electrolytes database [10,26] was used to construct potential 𝐸 reg and 𝐸 RBM (Figure 6). The database contained more than 1000 records of monomeric and polymeric lithium-ion-conducting electrolytes around room temperature.…”