CeO₂ regulated vacancies and coordination environment of δ-MnO₂ cathode for durable flexible zinc-ion batteries

Aqueous Zn||MnO₂ batteries have emerged as highly promising for flexible energy storage systems due to their intrinsic safety and environmental benignity. However, their application remains hindered by the limited density of electrochemically active sites, poor structural stability, and ambiguous charge-storage mechanisms of MnO₂ cathodes. Herein, a CeO₂ nanoparticle-modified layered δ-MnO₂ microcrystalline cathode (CeO₂@δ-MnO₂) is rationally designed, and the underlying energy-storage mechanisms of the Zn||CeO₂@δ-MnO₂ battery are systematically investigated. The short-range ordered microcrystalline structure of δ-MnO₂ effectively tailors the coordination environment of Mn centers, inducing abundant oxygen vacancies (V_o) that facilitate synergistic H⁺/Zn²⁺ co-insertion, thereby substantially enhancing charge-storage capability. Meanwhile, the incorporation of CeO₂ nanoparticles not only reinforces the structural integrity of the layered δ-MnO₂ framework but also triggers pronounced Jahn-Teller distortion, which further promotes V_o formation and accelerates electrochemical kinetics. Benefiting from these synergistic effects, the Zn||CeO₂@δ-MnO₂ battery delivers a high reversible capacity of 372.6 mA h g⁻¹ at 0.5 A g⁻¹ and retains 92.14% of its initial capacity after 2000 cycles, markedly outperforming pristine δ-MnO₂. Furthermore, a flexible quasi-solid-state zinc-ion battery with a sandwich configuration exhibits excellent mechanical flexibility and safety, maintaining a high capacity of 240 mA h g⁻¹ after 300 bending cycles. This work provides an effective defect- and distortion-engineering strategy for the rational design of high-performance flexible MnO₂-based cathodes.