Photo‐Assisted Bifunctional Cathodes with Lower Energy Gap and Broadened Light Absorbing Region for Lithium‐Ion Batteries – Extended Conjugation Through Customization

Abstract High‐performance optoelectronic bifunctional cathode materials may simultaneously seize and store solar energy in lithium‐ion batteries to boost their storage capacity. However, such photoactive cathodes with typical intrinsic features are generally limited for UV light applications and offer poor sunlight harvesting which results in lower energy density. Here, the assembly of two oligomers, poly(vat blue 6) (PVB6) and poly(vat blue 6 sulfide) (PVB6S) is reported, through polymerization to extend the conjugated structure of organic optoelectronic small molecules. These oligomers are effectively employed as photo‐assisted bifunctional cathodes for lithium‐ion batteries. The extended conjugated structure narrows the energy gap, promoting exciton dissociation and expanding the light absorption region. PVB6S possesses a narrow energy gap of 1.565 eV, and the discharge‐specific capacity of the battery with PVB6S is enhanced from 203 to 411 mAh g−1 under light illumination, which is approximately twice the original capacity. This demonstrates the extended conjugated structure and charge separation in a cell, which synergistically contributes to the rational design of photo‐assisted bifunctional cathode materials and complementary enhances the performance of lithium‐ion batteries.