Figure 4

Change in stoichiometric ratio of phosphorous to nitrogen in the electrodes during cycling.

(a), PVK-based positive electrode. (b), PBPy-based negative electrode. The y-axis value, i.e. P/N ratio was calculated using the relative signal intensity of the phosphorous atoms to the internal reference peaks obtained from the EDX measurement. In this figure, the charged and discharged states of the positive electrode refer to the oxidized (ox.) and reduced (red.) states for PVK, respectively. The negative electrode is the other way around, i.e., the charged and discharged states of the negative electrode correspond to the red. and ox. states for PBPy, respectively. For details, see the experimental part and Supplementary Figures S1 and S2.