Enhanced electron cloud through π-π interaction in charge-transfer complexes for all-solid-state lithium batteries

Organic cathodes have the advantages of abundant resources, high theoretical specific capacity, and mild synthesis conditions, but suffer from low density, poor electronic conductivity, and high solubility in liquid electrolytes. Herein, we develop a charge-transfer complex by combining 2,5-dihydroxyterephthalic acid (Li4C8H2O6) and tetracyanoquinodimethane (TCNQ) at room temperature in 1,3-Dioxolane (DOL) solvent, for application in all-solid-state battery to overcome the above problems. Li4C8H2O6 /TCNQ act as the electron donor/acceptor and combine to form an enhanced electron cloud through π-π interaction to facilitate electron transport. The electron conductivity of charge transfer complex Li4C8H2O6-TCNQ is enhanced to 7×10-5 S/cm, which is three orders of magnitude higher than the two pristine materials and much higher than most conventional organic cathodes. The Li4C8H2O6-TCNQ electrode exhibits a discharge specific capacity of 172 mAh/g at 0.5 C, which is approximately 2.5 times higher than that of Li4C8H2O6 and higher than its capacity in a liquid cell, and is stable for 100 cycles at 2 C. This result demonstrates that enhancing electron cloud through π-π interaction in charge transfer complexes is an effective way to realize the practical application of organic cathodes in sulfide all-solid-state batteries.