Unlocking the potential of multi-electron p-type polyheterocycle cathode: when it meets small-size and high-charge anion

Abstract

High-voltage p-type organic cathodes are attracting broad attention in boosting zinc batteries, but are trapped by single-electron reaction and low utilization of redox sites due to their high reaction energy barriers with incompatible anions. Here we design polyheterocycle organics (PHOs) via grafting dual-site-active phenothiazine and piperazine motifs to form donor-acceptor-extended structures which show multi-electron p-type redox reactions for superior anion storage. With the decrease of anionic Stokes radius and the increase of charge density (TFSI−→OTF−→SO42−), SO42− delivers the strongest bipedal ion-pairing ability with PHOs during oxidation via an ultralow activation energy (0.20 vs. 0.38 eV of OTF− and 0.45 eV of TFSI−). This facilitates fast and full utilization of phenothiazine/piperazine active motifs by small-sized and two-charged SO42− anions (99.5% vs. 83.2% of OTF− and 58.1% of TFSI−). Consequently, PHOs cathode liberates superior SO42−-storage energy density (317 Wh kg−1) and cycling lifespan (71.4% capacity retention over 100,000 cycles), surpassing OTF− (273 Wh kg−1/67.1%) and TFSI− storage (210 Wh kg−1/60.2%), as well as reported p-type organics. This work gives a new paradigm for designing multi-electron organics compatible with optimized anions for better zinc batteries.