Structural water and disordered structure promote aqueous sodium-ion energy storage in sodium-birnessite

Abstract

Birnessite is a low-cost and environmentally friendly layered material for aqueous electrochemical energy storage; however, its storage capacity is poor due to its narrow potential window in aqueous electrolyte and low redox activity. Herein we report a sodium rich disordered birnessite (Na0.27MnO2) for aqueous sodium-ion electrochemical storage with a much-enhanced capacity and cycling life (83 mAh g−1 after 5000 cycles in full-cell). Neutron total scattering and in situ X-ray diffraction measurements show that both structural water and the Na-rich disordered structure contribute to the improved electrochemical performance of current cathode material. Particularly, the co-deintercalation of the hydrated water and sodium-ion during the high potential charging process results in the shrinkage of interlayer distance and thus stabilizes the layered structure. Our results provide a genuine insight into how structural disordering and structural water improve sodium-ion storage in a layered electrode and open up an exciting direction for improving aqueous batteries.

XRD/Raman spectroscopy studies of the mechanism of (de)intercalation of Na+ from/into highly crystalline birnessite

“…Several mechanisms for Na + -(de)intercalation into birnessite were already postulated. Most of them have in common, that they focus mainly on the variations of the d 001 -spacing which were explained by the (de)intercalation of Na-ions 5,17,28 or hydrated Na-ions 5 . In this regard, the current response in potential regions, where no variations in d 001 -spacing or changes in the Raman spectra were observed, were assigned to surface processes.…”

“…Layered metal oxides are attractive cathode materials for sodium- [1][2][3][4][5] and potassium-ion [6][7][8] batteries and pseudocapacitors. One promising material belonging to this material class are birnessitetype manganese oxides which exhibits a theoretical capacity of 243mAhg -1 .…”

Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate

“…This partial solvation shell is known as frustrated water and has shown enhancements in electron transfer within catalyst materials. [20,99] While the structure/order of water in layered materials can be assessed through neutron diffraction/scattering studies, [100,101] distinct types of water (free vs bound water) can also be identified through thermogravimetric analysis (TGA) of the as-prepared zirconium phosphate catalyst powders. [57] In TGA measurements, the removal of weakly coordinated water (free water) is associated with the first dehydration event and is usually observed below 90-120 °C.…”

Interlayer Chemistry of Layered Electrode Materials in Energy Storage Devices

“…[ 56 ] The co‐intercalation of water molecules and cations can significantly impact the performance of the resultant materials, as evidenced by Shan et al. [ 57 ] As shown in Figure 6g, the authors synthesized Na‐inserted birnessite (Na 0.27 MnO 2 ) using a solution‐phase method. Upon co‐intercalation of Na cations and water molecules, the sodium storage capability improved substantially.…”