Solid-state polymer electrolytes for lithium-ion batteries have attracted considerable interest because of their potential for high safety and electrochemical stability, but applications are limited by their low ionic conductivities. However, recently artificial intelligence simulations found that charge-transfer complexes of aromatic polymers could achieve enhanced lithium ionic conduction at room temperature. Meanwhile, certain organic crystals with similar charge-transfer properties were also shown to present high conductivity. In our work, we have fabricated small-molecule organic crystalline electrolytes composed of a charge-transfer complex matrix mixed with different molar ratios of lithium salt. With the intention of carefully studying the charge transport mechanism, the charge transport in this type of mixed ionic-electronic conductor is modeled via an equivalent circuit to deconvolute the ionic and electronic conduction. We find that varying composition and thermal history can impact the relative ionic and electronic contributions to the bulk conductivity simultaneously. Contrary to the conventional solid-state polymer electrolytes with the mechanism of lithium-ion transport in the amorphous polymer region through segmental motion, this type of novel electrolyte, a highly ordered, all-solid-state material, facilitates fast decoupled lithium-ion transport with a wide operating temperature window.

Organic solid-state crystalline complexes as lithium-ion battery electrolytes

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