Creep of selenium near the glass temperature

Creep-type all-solid-state cathode achieving long life

Electrochemical-mechanical coupling poses enormous challenges to the interfacial and structural stability but create new opportunities to design innovative all-solid-state batteries from scratch. Relying on the solid-solid constraint in the space-limited domain structure, we propose to exploit the lithiation-induced stress to drive the active materials creep, thereby improving the structural integrity. For demonstration, we fabricate the creep-type all-solid-state cathode using creepable Se material and an all-in-one rigid ionic/electronic conducting Mo6Se8 framework. As indicated by the in-situ experiment and numerical simulation, this cathode presents unique capabilities in improving interparticle contact and avoiding particle fracture, leading to its superior electrochemical performance, including a superior long-cycle life of more than 3000 cycles at 0.5 C and a high volumetric energy density of 2460 Wh/L at the cathode level. We believe this innovative strategy to utilize mechanics to boost the electrochemical performance could shed light on the future design of all-solid-state batteries for practical applications.

Low-frequency inelastic light scattering in a ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glass

Low-frequency (down to 30 GHz) inelastic light scattering is studied in a multicomponent glass ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) in a wide temperature range. The contributions of the THz vibrational spectrum (boson peak) and of the fast relaxation are extracted and analyzed. It is shown that the fast relaxation spectrum is described by a distribution of relaxation times leading to a power-law ν(α) dependence in the frequency range 30-300 GHz. Temperature dependence of α(T) is well described by the Gilroy-Phillips model, while the integrated intensity of the fast relaxation increases significantly with the temperature. This feature distinguishes the fast relaxation in ZBLAN from the case of most single-component glasses. Thermodynamic and kinetic fragility indexes are significantly different for the ZBLAN glass. The correlations between the boson peak intensity, elastic moduli, and fragility index, found earlier for single-component glasses, are fulfilled for the thermodynamic fragility index of ZBLAN. In contrast, the correlation between the fast relaxation intensity at Tg and the fragility holds better for the kinetic fragility index of ZBLAN. We propose that thermodynamic and kinetic fragilities reflect different aspects of glassy dynamics in the case of glass formers with the complex chemical composition and structure topology: the former correlates with the elastic properties and the boson peak, the latter with the relaxation.