The development of electrodes for ambient temperature sodium-ion batteries requires the study of new materials and the understanding of how crystal structure influences properties. In this study, we investigate where sodium locates in two Prussian blue analogues, Fe[Fe(CN)6]1-x·yH2O and FeCo(CN)6. The evolution of the sodium site occupancies, lattice and volume is shown during charge-discharge using in situ synchrotron X-ray powder diffraction data. Sodium insertion is found to occur in these electrodes during cell construction and therefore Fe[Fe(CN)6]1-x·yH2O and FeCo(CN)6 can be used as positive electrodes. NazFeFe(CN)6 electrodes feature higher reversible capacities relative to NazFeCo(CN)6 electrodes which can be associated with a combination of structural factors, for example, a major sodium-containing phase, ∼Na0.5FeFe(CN)6 with sodium locating either at the x = y = z = 0.25 or x = y = 0.25 and z = 0.227(11) sites and an electrochemically inactive sodium-free Fe[Fe(CN)6]1-x·yH2O phase. This study demonstrates that key questions about electrode performance and attributes in sodium-ion batteries can be addressed using time-resolved in situ synchrotron X-ray diffraction studies.

. Structural evolution of electrodes in the NCR and CGR cathode-containing commercial lithium-ion batteries cycled between 3.0 and 4.5 V: an operando neutron powder-diffraction study. Journal of Materials Research, 30 (3), 373-380. Structural evolution of electrodes in the NCR and CGR cathodecontaining commercial lithium-ion batteries cycled between 3.0 and 4.5 V: an operando neutron powder-diffraction study AbstractThe dissimilar lattice-evolution of the isostructural layered Li(Ni,Co,Al)O 2 (NCR) and Li(Ni,Co,Mn)O 2 (CGR) cathodes in commercial lithium-ion batteries during overcharging/discharging was examined using operando neutron powder-diffraction. The stacking axis (c parameter) of both cathodes expands on initial lithiation and contracts on further lithiation. Although both the initial increase and later decrease are smaller for the CGR cathode, the overall change between battery charged and discharged states of the c parameter is larger for the CGR (1.29%) than for the NCR cathode (0.33%). We find these differences are correlated to the transition metal to oxygen bond (as measured through the oxygen positional-parameter) which is specific to the different cathode chemistries. Finally, we note the formation of and suggest a model for a LiC x intermediate between graphite and LiC 12 in the anode of both batteries. The dissimilar lattice-evolution of the iso-structural layered Li(Ni,Co,Al)O 2 (NCR) and Li(Ni , Co , Mn , )O 2 (CGR) cathodes in commercial lithium-ion batteries during overcharging/discharging was examined using operando neutron powder-diffraction. The stacking axis (c parameter) of both cathodes expands on initial lithiation and contracts on further lithiation. Although both the initial increase and later decrease are smaller for the CGR cathode, the overall change between battery charged and discharged states of the c parameter is larger for the CGR (1.29%) than for the NCR cathode (0.33%). We find these differences are correlated to the transition metal to oxygen bond (as measured through the oxygen positional-parameter) which is specific to the different cathode chemistries. Finally, we note the formation and suggest a model for a LiC x intermediate between graphite and LiC 12 in the anode of both batteries.

The evolution of the 003 reflection of the layered Li(Ni,Co,Mn)O 2 (CGR) and Li(Ni,Co,Al)O 2 (NCR) cathodes in commercial 18650 lithium-ion batteries during charge/discharge were determined using in situ neutron powder diffraction. The 003 reflection is chosen as it is the stacking axis of the layered structure and shows the largest change during charge/discharge. The comparison between these two cathodes shows that the NCR cathode exhibits an unusual contraction near the charged state and during the potentiostatic step, where the potentiostatic step is recommended by the manufacturer. This feature is not shown to the same degree by the CGR cathode. The behavior is likely related to the compositions of these cathodes, the amount of Li/Ni site mixing and the presence of Al or Mn.

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