Engineering Mn Vacancies to Enhance Ion Kinetics in Layered Manganese Silicate for High-Energy and Durable Intercalation Pseudocapacitance

Transition metal silicates (TMSs) are potential electrodes for aqueous metal-ion intercalation pseudocapacitors owing to their superior theoretical capacity and high structural stability. However, the narrow interlayer spacing and intrinsic inert basal plane of TMSs lead to sluggish ions and charge transfer, causing an undesirable energy storage performance. Herein, rich Mn vacancies are introduced in layered manganous silicates (M_2-xS@FA) to expedite K⁺ diffusion, while enhancing charge storage capacity and prolonging lifespan. In situ characterizations validate the K⁺ intercalation pseudocapacitance mechanism with evident crystal structure and valence state variations in M_2-xS@FA. Both theoretical calculations and electrochemical experimental evaluations elucidate the imperative role of Mn vacancies in enhancing K⁺ diffusion kinetics and electron transfer through increased interlayer spacing and activated basal plane. Mn vacancies further boost the charge storage capacity by providing additional K⁺ storage sites, while simultaneously reinforcing local atomic bonding within M_2-xS@FA, thereby augmenting structural stability. The assembled aqueous asymmetric solid-state cell, featuring a M_2-xS@FA cathode, demonstrates exceptional power and energy densities (144.08 W h kg^-1 at 375.80 W kg^-1) and ultralong lifespan (100% capacity retention after 10,000 cycles). This work heralds a paradigm whereby modulating cation vacancies in layered TMSs significantly enhances K⁺ storage and stability for high-energy intercalation pseudocapacitance.