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.