Phenazine-based cathodes enabled by reducing LUMO energy level for high mass loading and low temperature zinc-organic batteries

Abstract

Organic small molecule electrode materials are regarded as highly promising cathode materials for aqueous zinc ion batteries (AZIBs) due to their tunable structure, environmental friendliness, and sustainable generation. However, rapid capacity degradation and sluggish kinetics hinder their practical application, particularly at high mass loadings and low temperatures. Here, we design and synthesize two conjugated small molecules with different numbers of carbonyl groups (namely nitrogen heterocyclic dione (PZPQ), nitrogen heterocyclic tetraketone (PZDPQ). In addition, the introduction of electron-withdrawing carbonyl groups lowers the energy level of the lowest unoccupied molecular orbital (LUMO) of phenazine and extends the π-conjugated system, which enhances the voltage, capacity and redox kinetic of PZDPQ. Thus, the PZDPQ cathodes for AZIBs exhibit high capacity of 340 mAh g⁻¹ at 0.2 A g⁻¹, a high capacity retention of 97.8% after 8000 cycles, and outstanding rate performance (200 mAh g⁻¹ at 10 A g⁻¹), even function efficiently at high mass loading of 49 mg cm⁻² and low temperature at -40 °C. Further mechanistic researches by in-situ quartz crystal microbalance demonstrate that the fully conjugated molecular configuration enables reversible Zn²⁺/H₃O⁺ synergistic storage.