Dual mediation of MnSe as superior cathodes for Durable Zn-ion energy storage

Layered manganese selenide (MnSe), a member of manganese chalcogenide family, has emerged as a prospective cathode for Zn-ion energy storage. However, the practical application of MnSe cathodes is often hindered by capacity degradation stemming from structural instability and sluggish Zn-ion storage kinetics, ultimately limiting their cycling life. Herein, we propose a dual mediation strategy involving silver selenide (Ag₂Se) hybridization and Fe³⁺ electrolyte additive to enhance energy density and extend rechargeable cycling life of MnSe cathodes. Ag₂Se nanowires within the microenvironment provide additional active sites and expand interlayer spacing, while Fe³⁺ additive increases conductivity and shortens ion transport time. Theoretical calculation proves the dual-mediated mechanism by considerably increasing the Zn affinity and decreasing the Zn diffusion energy barrier in MnSe. Additionally, Fe³⁺ as an electron shuttle in the form of Fe³⁺/Fe²⁺ binds to Ag_xMnSe, stabilizing the structure and restraining oxidation dissolution, thus preventing structural collapse and loss of active sites. Consequently, an assembled Zn-ion capacitor reaches a competitive areal energy of 633.9 μWh cm⁻² and exceptional cycling stability, with a capacitance retention of 94.7 % after 15,000 cycles. This work provides valuable insights into mediation strategies for designing Zn-ion energy storage systems with stable longevity at high areal energy.