A minor source of variation in the capacitance values calculated from CV data was whether a manual or computational method was being used to calculate the CV integral. The computational integration calculation is often more accurate than manual analysis, where approximations to rectangles are often used. Additionally, analysis methods for addressing pseudocapacitive behaviour, such as selectively analysing the linear section of the CV profile, can lead to an overestimation of the values. To eliminate those sources of variation, having an established protocol is crucial. The analysis of long-term GCD cycling data was optional. In this analysis, participating groups were asked to report the capacitance retention after 10000 cycles (Figure ). Only 3 out of 14 groups could analyse all 10000 charge-discharge cycles and report capacitance retention values. All of these groups used a computational method to analyse the data. Several groups partially analysed the long-term cycling data, but did not report capacitance retention values. See the Supplementary Information for more details (SI Section 4.5).