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

Abstract

High-voltage p-type organic cathodes are attracting broad attention for boosting zinc batteries, but are hindered by single-electron reactions and low utilization of redox sites due to 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 in anionic Stokes radius and the increase in charge density (TFSI⁻ → OTF⁻ → SO₄²⁻), SO₄²⁻ exhibits 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 doubly charged SO₄²⁻ anions (99.5% vs. 83.2% of OTF⁻ and 58.1% of TFSI⁻). Consequently, the PHO cathode delivers 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 presents a new paradigm for designing multi-electron organics compatible with optimized anions for better zinc batteries.