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.

We report a (Ni)­MnO2 layered birnessite material with a framwork doping of Ni ions as the cathode for much enhanced aqueous Na-ion storage. Characterized by neutron total scattering and pair distribution function (PDF) analysis, in situ XRD, in situ X-ray PDF, XANES, and XPS, the synergistic interaction between disordered [NiO6] and ordered [MnO6] octahedra contribute to the enhanced specific capacity and cycle life (63 mAh g–1 at 0.2 A g–1 after 2000 full-cell cycles). Electro-kinetic analysis and structural characterizations show that stable local structure is maintained by [MO6] octahedra during charge–discharge processes, while disordered [NiO6] octahedra significantly improve pseudocapacitive redox charge storage. This finding may pave a new way for designing a new type of low-cost and high performance layered electrode materials.

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Supercapacitors are a class of energy storage devices that store energy by either ionic adsorption via an electrochemical double layer capacitive process or fast surface redox reaction via a pseudocapacitive process. Supercapacitors display fast charging and discharging performance and excellent chemical stability, which fill the gap between high energy density batteries and high-power-density electrostatic capacitors. In this book chapter, the authors have presented the current studies on improving the capacitive storage capacity of various electrode materials for supercapacitors, mainly focusing on the metal oxide electrode materials. In particular, the approaches that mathematically simulate the behavior of interaction between electrode materials and charge carriers subject to potentiodynamic conditions (e.g., cyclic voltammetry) have been described. These include a general relationship between current and voltage to describe overall electrokinetics during the charge transfer process and a more comprehensive numerical modeling that studies ionic transport and electrokinetics within a spherical solid particle. The two aforementioned types of mathematical analyses can provide fundamental understanding of the parameters governing the electrode reaction and mass transfer in the electrode material, and thus shed light on how to improve the storage capacity of supercapacitors.

We reported that the incorporation of conductive polymer into V2O5 materials resulted in an increased interlayer distance of 2.2 nm, favoring K-ion storage in an aqueous electrolyte. In situ X-ray...

This study aims to systematically illustrate the mechanism of supercritical fluid extraction (SFE) and modification on the coal liquefaction residue (CLR) and to identify the evolution and characteristics of the mesophase produced from the carbonization of SFE extracts. Results show that the extraction performance of SFE and the properties of the mesophase precursor were strongly dependent upon the selection of operating conditions and solvents. The SFE process using acetone and isopropanol presented excellent extraction performance, owning to the effect of solvent polarity on the degradation or supercritical reaction, achieving their respective CLR extraction yields of 45.85 and 30.12 wt %, while an extraction yield of 53.78 wt % was attained when using benzene, benefiting from its strong affinity to condensed aromatic hydrocarbons. More practically, quinoline-insoluble (QI) fraction decreased from 48.84 to 1.13 wt % after SFE processing, which significantly upgraded the quality of the mesophase precursor. To an extent, supercritical acetone exhibited strong reaction activity during extraction because its extract contained a higher amount of the hexane-soluble (HS) fraction, which could optimize the molecular weight distribution of the mesophase precursor. The well-developed bulk mesophase in the carbonized SFE extracts was remarkably improved in comparison to raw CLR. Presumably, the SFE extract was favorable to forming 100% mesophase, where dominated flow textures were observed.

Iron hydroxides are desirable alkaline battery electrodes for low cost and environmental beneficence. However, hydrogen evolution on charging and Fe3O4 formation on discharging cause low storage capacity and poor cycling life. We report that green rust (GR) (Fe2+ 4Fe3+ 2 (HO–)12SO4), formed via sulfate insertion, promotes Fe­(OH)2/FeOOH conversion and shows a discharge capacity of ∼211 mAh g–1 in half-cells and Coulombic efficiency of 93% after 300 cycles in full-cells. Theoretical calculations show that Fe­(OH)2/FeOOH conversion is facilitated by intercalated sulfate anions. Classical molecular dynamics simulations reveal that electrolyte alkalinity strongly impacts the energetics of sulfate solvation, and low alkalinity ensures fast transport of sulfate ions. Anion-insertion-assisted Fe­(OH)2/FeOOH conversion, also achieved with Cl– ion, paves a pathway toward efficient utilization of Fe-based electrodes for sustainable applications.

Rechargeable alkaline iron batteries that constitute environmentally benign electrolytes and earth-abundant industrial materials are desirable green solutions for large-scale energy storage. As one of the most abundant metal elements in the earth’s crust, iron (Fe) can satisfy nearly all criteria for low-cost and safe battery electrodes. However, challenges in achieving reversible Fe redox impede their extensive implementation in modern energy supply systems. This study revealed that Cl-anion insertion into Fe­(OH)2 layered double hydroxide (LDH) formed a green rust intermediate phase with the formula [Fe2 2+Fe1 3+(HO–)6]+[Cl]−, which assisted a high Fe­(OH)2/FeOOH conversion reaction (64.7%) and improved cycling stability. This new iron redox chemistry was validated by operando X-ray diffraction, electrochemical testing, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS) analysis, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy (STEM-EDS) mapping, and molecular dynamics (MD) simulations. Our study provides new insight into designing LDH materials for high-capacity alkaline iron batteries.