Metal cation and crystal lattice water molecule stabilized highly mesoporous manganese oxide network for excellent durable electrode in sodium-ion storage

• Binder-free hydrated K + ions pre-intercalated layered MnO 2 for sodium-ion storage. • HKMO exhibits an outstanding electrochemical property in a broad potential of 3 V. • DFT calculations showed that the interlayer distance increased by intercalating K + ions into the MnO 2 matrix. • SIS device displays an excellent specific energy with outstanding cyclability. Potassium birnessite is a remarkable material with a wider inter-planar spacing, which enables to accommodate more electrolytic ions to improve overall electrochemical performances. In this work, controlled synthesis of K 0.46 Mn 2 O4(H 2 O) 1.4 (HKMO) nanosheets were interconnected mesoporous networks uniformly grown on carbon cloth (CC) via a one-step hydrothermal process. Specifically, the HKMO sample synthesized at 100 °C for 12 h (100@HKMO-12 h) exhibited a mesoporous morphology with a large specific surface area. The binder-free 100@HKMO-12 h electrode exhibits a maximum specific capacitance of 255F g −1 (323F cm −3 ) in 1 M NaClO 4 /acetonitrile electrolyte over a broad potential range of 3 V. DFT studies demonstrated the interlayer distance increased by the insertion of K + ions into the MnO 2 matrix. Bader charge analysis showed a 12.09 |e| charge difference for K-birnessite in the inter-layer region compared to the normal birnessite, supported the increase of inter-layer region in the MnO 2 matrix. Significantly, the increased interlayer the distance, promoted rapid intercalation/deintercalation of Na + ions and allowed the reversible faradic pseudocapacitance reaction to occur at a wider potential window. Moreover, the symmetric full-cell fabricated utilizing the 100@HKMO-12 h electrodes have a wide voltage of 2 V and the device delivered a maximum specific energy of 43 Wh kg −1 (28 Wh cm −3 ) at a minimum specific power of 556 W Kg −1 (349 W cm −3 ). Besides, the device showed an excellent capacitance retention of ∼94 % even after 10,000 continuous charge–discharge cycles at a current of 5 A/g, indicating it is a potential candidate for next-generation sodium energy storage devices.