The state-of-the-art development of fabrication strategies of multi-dimensional titanate and titania nanostructures is reviewed first. This is followed by an overview of their potential applications in environmental, energy, and biomedical sectors.

Lithium-ion batteries using germanium as the anode material are attracting attention because of their high-capacity, higher conductivity, and lithium-ion diffusivity relative to silicon. Despite recent studies on Ge electrode reactions, there is still limited understanding of the reaction mechanisms governing crystalline Ge and the transformations into intermediate amorphous phases that form during the electrochemical charge and discharge process. In this work, we carry out in operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies on Ge anodes during the initial cycles to better understand these processes. These two probes track both crystalline (XRD) and amorphous (XAS) phase transformations with potential, which allows detailed information on the Ge anode to be obtained. We find that crystalline Ge lithiates inhomogeneously, first forming amorphous Li9Ge4 during the beginning stage of lithiation, followed by the conversion of the remaining crystalline Ge to amorphous Ge. The lithiation of amorphous Ge then forms amorphous Li x Ge, which are then further lithiated to form crystalline Li15Ge4. During delithiation, crystalline Li15Ge4 transforms directly into a heterogeneous mix of amorphous Li x Ge, which eventually form amorphous Ge, and interestingly, no amorphous Li9Ge4 are detected. Both our in operando XRD and XAS results present new insights into the reaction mechanism of Ge as anodes in LIBs, and demonstrate the importance of correlating electrochemical results with in operando studies.

Sodium-ion batteries have become a subject of increasing interest and are considered as an alternative to the ubiquitous lithium-ion battery. To compare the effect of two improvement strategies for metal oxide cathodes, specifically Codoping and morphology optimization, four representatives of the prominent material class of layered Na x MO 2 (M = transition metal) have been studied: hexagonal flakes and hollow spheres of P2− Na x MnO 2 and P2−Na x Co 0.1 Mn 0.9 O 2 . The better electrochemical performance of the spheres over the flakes and of the Co-doped over the undoped materials are explained on the basis of structural features revealed by operando synchrotron X-ray diffraction. The higher cycling stability of the material doped with ∼10% Co is attributed to three effects: (i) the suppression of a Jahn−Tellerinduced structural transition from the initial hexagonal to an orthorhombic phase that is observed in Na x MnO 2 ; (ii) suppression of ordering processes of Na + ; and (iii) enhanced Na + kinetics as revealed by galvanostatic intermittent titration technique measurements and in situ electrochemical impedance measurements. Increased capacity and cycling stability of spheres over flakes may be related to smaller changes of the unit cell volume of spheres and thus to reduced structural stress. Co-doped spheres combine the advantages of both strategies and exhibit the best cycling stability.