ABSTRACT
[Formula: see text] is a promising material for developing high-capacity anodes for lithium-ion batteries (LIBs). However, microstructural changes of [Formula: see text] anodes at the particle and electrode level upon prolonged cycling remains unclear. In this work, the causes leading to capacity fade on [Formula: see text] anodes were investigated and simple strategies to attenuate anode degradation were explored. Nanostructured [Formula: see text] from diatomaceous earth was integrated into anodes containing different quantities of conductive carbon in the form of either a conductive additive or a nanometric coating layer. Galvanostatic cycling was conducted for 200 cycles and distinctive trends on capacity fade were identified. A thorough analysis of the anodes at selected cycle numbers was performed using a toolset of characterization techniques, including electrochemical impedance spectroscopy, FIB-SEM cross-sectional analysis and TEM inspections. Significant fragmentation of [Formula: see text] particles surface and formation of filigree structures upon cycling are reported for the first time. Morphological changes are accompanied by an increase in impedance and a loss of electroactive surface area. Carbon-coating is found to restrict particle fracture and to increase capacity retention to 66%, compared to 47% for uncoated samples after 200 cycles. Results provide valuable insights to improve cycling stability of [Formula: see text] anodes for next-generation LIBs.
ABSTRACT
Here we report on the first structural and optical high-pressure investigation of MASnBr3 (MA = [CH3NH3]+) and CsSnBr3 halide perovskites. A massive red shift of 0.4 eV for MASnBr3 and 0.2 eV for CsSnBr3 is observed within 1.3 to 1.5 GPa from absorption spectroscopy, followed by a huge blue shift of 0.3 and 0.5 eV, respectively. Synchrotron powder diffraction allowed us to correlate the upturn in the optical properties trend (onset of blue shift) with structural phase transitions from cubic to orthorhombic in MASnBr3 and from tetragonal to monoclinic for CsSnBr3. Density functional theory calculations indicate a different underlying mechanism affecting the band gap evolution with pressure, a key role of metal-halide bond lengths for CsSnBr3 and cation orientation for MASnBr3, thus showing the impact of a different A-cation on the pressure response. Finally, the investigated phases, differently from the analogous Pb-based counterparts, are robust against amorphization showing defined diffraction up to the maximum pressure used in the experiments.
ABSTRACT
Lithium oxosilicate was synthesized via the solid-state method using Li2O and SiO2 as starting reactants. In situ synchrotron powder X-ray diffraction (SPRXD) coupled with Rietveld refinement allowed describing the synthesis as a two-step process where Li2O and SiO2 react to form Li4SiO4 and, at higher temperatures, lithium orthosilicate reacts with the remaining Li2O to form Li8SiO6. Time-resolved measurements allowed determining the temperatures at which each phase transformation occurs as well as the time required to complete the synthesis. The CO2 capture properties of Li8SiO6 in the temperature range from room temperature to 770 °C were studied in detail by time-resolved in situ SPXRD. The crystallographic phases present during Li8SiO6 carbonation were identified and quantified via Rietveld analysis. Results showed that, within the temperature range from 200 to 690 °C, Li8SiO6 carbonation produces Li4SiO4 and Li2CO3, while, at temperatures from 690 to 750 °C, a secondary reaction occurs, where previously formed Li4SiO4 reacts with CO2, producing Li2SiO3 and Li2CO3. These findings allowed proposing a mechanism of reaction for Li8SiO6 carbonation in the temperature range that is of interest for high temperature solid-state sorbents.
