Engineering Mn Vacancies\nto Enhance Ion Kinetics in\nLayered Manganese Silicate for High-Energy and Durable Intercalation\nPseudocapacitance

Transition metal silicates (TMSs)\nare potential electrodes\nfor\naqueous metal-ion intercalation pseudocapacitors owing to their superior\ntheoretical capacity and high structural stability. However, the narrow\ninterlayer spacing and intrinsic inert basal plane of TMSs lead to\nsluggish ions and charge transfer, causing an undesirable energy storage\nperformance. Herein, rich Mn vacancies are introduced in layered manganous\nsilicates (M<sub>2–<i>x</i></sub>S@FA) to expedite\nK<sup>+</sup> diffusion, while enhancing charge storage capacity and\nprolonging lifespan. In situ characterizations validate the K<sup>+</sup> intercalation pseudocapacitance mechanism with evident crystal\nstructure and valence state variations in M<sub>2–<i>x</i></sub>S@FA. Both theoretical calculations and electrochemical experimental\nevaluations elucidate the imperative role of Mn vacancies in enhancing\nK<sup>+</sup> diffusion kinetics and electron transfer through increased\ninterlayer spacing and activated basal plane. Mn vacancies further\nboost the charge storage capacity by providing additional K<sup>+</sup> storage sites, while simultaneously reinforcing local atomic bonding\nwithin M<sub>2–<i>x</i></sub>S@FA, thereby augmenting\nstructural stability. The assembled aqueous asymmetric solid-state\ncell, featuring a M<sub>2–<i>x</i></sub>S@FA cathode,\ndemonstrates exceptional power and energy densities (144.08 W h kg<sup>–1</sup> at 375.80 W kg<sup>–1</sup>) and ultralong\nlifespan (100% capacity retention after 10,000 cycles). This work\nheralds a paradigm whereby modulating cation vacancies in layered\nTMSs significantly enhances K<sup>+</sup> storage and stability for\nhigh-energy intercalation pseudocapacitance.