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In this paper we implement and test a new approach for the description of the electrochemical data (cyclic voltammetry and chronoamperometry) for phase transforming intercalation electrode materials. This approach assumes the rate-limiting step being associated with the slow nucleation of a new phase in the material particles. As a test model system, we used LiFePO 4 material. It is shown that all the electrochemical data for LiFePO 4 can be self-consistently described assuming a slow nucleation step with only minor influence of ionic diffusion and interfacial charge transfer kinetics on the intercalation rates. The developed formalism allows for a reliable diagnostics of the reaction rate control regime as well as for the extraction of information on the pre-exponential factor and activation energy values. The electrochemical diagnostic criteria for the slow nucleation step are formulated based on the shapes of the cyclic voltammetry peaks, current transients registered under potentiostatic conditions and specific features in the impedance spectra of phase-transforming electrodes.

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Prussian blue analogues (PBAs) are commonly believed to reversibly insert divalent ions, such as calcium and magnesium, rendering them as perspective cathode materials for aqueous magnesium‐ion batteries. In this study, the occurrence of Mg2+ insertion into nanosized PBA materials is shown to be a misconception and conclusive evidence is provided for the unfeasibility of this process for both cation‐rich and cation‐poor nickel, iron, and copper hexacyanoferrates. Based on structural, electrochemical, IR spectroscopy, and quartz crystal microbalance data, the charge compensation of PBA redox can be attributed to protons rather than to divalent ions in aqueous Mg2+ solution. The reversible insertion of protons involves complex lattice water rearrangements, whereas the presence of Mg2+ ion and Mg salt anion stabilizes the proton (de)insertion reaction through local pH effects and anion adsorption at the PBA surface. The obtained results draw attention to the design of proton‐based batteries operating in environmentally benign aqueous solutions with low acidity.