A potential curve against capacity during first discharging to -775 mV vs. Sn/SnF2 of the cell BiF3|BaSnF4|Sn is shown in Figure . Based on the changing tendency (slope) of the decreasing potential with capacity and corresponding dQ/dV plot (inset), the first defluorination of BiF3 cathode is primarily composed of three steps for reaching the theoretical capacity of BiF3 (302 mAh g -1 ). In order to reveal the structural evolution of CAM BiF3 as well as the structural stability of the electrolyte, a series of ex-situ X-ray diffraction patterns (Figure ) was recorded on BiF3|BaSnF4|Sn pellets after discharging to specific capacities from 30 mAh g -1 to 444 mAh g -1 . The specific capacities investigated by ex-situ XRD are marked in Figure with colored arrows. The XRD pattern of the as-prepared cathode composite (black curve) serves as a reference, with the initial phases discussed in section 3.1.