Ligand field regulation of δ-MnO₂ by polyanion modification enables extended potential window in supercapacitors

Extending the potential range of MnO₂ is imperative to improve power density and capacity density for supercapacitors. However, MnO₂ usually suffers from severe Mn dissolution, irreversible phase transition, and poor cycling performance under an extended potential range. Herein, a ligand field regulation strategy is rationally designed to enhance the structural stability of δ-MnO₂ to extend the potential window to 0–1.3 V (vs. Ag/AgCl). As revealed, the generated strong covalent B–O plane triangle or P–O tetrahedron configuration effectively decreases the lattice O activity of δ-MnO₂. The B–O–Mn and P–O–Mn bonding interactions enhance Mn ion crystal field stabilization energy in the MnO₆ octahedra. Therefore, the lattice O loss, Mn dissolution, and irreversible phase transition are well suppressed. The PO₄³⁻ doped δ-MnO₂ electrodes (with a high mass loading of ∼10 mg cm⁻²) can deliver a large specific capacitance (268.3 F g⁻¹ at 0.5 A g⁻¹) and excellent cycling performance (83.5% after 10000 cycles) in the extended potential window of 0–1.3 V (vs. Ag/AgCl). Our ligand field regulation strategy affords opportunities for developing simultaneously high-capacity and high-voltage electrodes for supercapacitors.