Fig. 3

Fitted magnetic susceptibilities of the cell during the discharge/charge. For simplicity, the cell is assumed to have a uniform volume susceptibility in a. Error bars are smaller than the size of the points. Knowing the cell construction, one can, however, also determine the average susceptibility of the cathode material in b. Details of the calculations are shown in Supplementary Table 1, Supplementary Table 2, and the Methods section. The susceptibility values are given in ppm indicating a factor of 10–6