Sequential Rietveld refinement of the unit cell parameters and metal positions from operando galvanostatic electrochemical (de)lithiation was performed in GSAS-II. The initial structure model was taken from the structure refined with neutron diffraction data at 20 K. Rietveld refinement of the first in situ diffraction pattern prior to application of an applied current allowed the unit cell parameters, background, Nb coordinates, and instrument parameters (zero offset, U, V, and W) to vary. For the sequential refinement, unit cell parameters, background coefficients, strain, and Nb coordinates were allowed to vary. 2D diffraction images (integrated to 1D patterns) were recorded every 173 seconds by summing 20 subframes of 0.5 seconds each. The 10 s time resolution corresponds to a x of 0.0053 in LixNaNb7O18 during each diffraction image collection.