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reactions), indicating the existence of undiscovered extra charge reservoirs inside the system. [6-9] To shed light on this surprising behavior, Tarascon and co-workers proposed that it is the reversible formation/dissolution of polymeric films around the reduced Co nanoparticles that leads to the unusually large capacity, [10,11] which has been widely accepted. [6,7,12] However, using in situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, Kim et al. demonstrated that the electrolyte decomposition cannot make major contributions to the extra capacity in RuO 2 LIBs. [13] In addition, Maier and co-workers presented an interfacial charge storage mechanism between Li salts and transition-metal nanocrystals. [14-16] Just recently, we demonstrated that the surface capacitance on metal nanoparticles involving spin-polarized electrons is the dominant source of the extra capacity in Fe 3 O 4 LIBs. [17-19] Therefore, the possible contribution of polymeric/gel films to the unusual capacity in CoO deserves to be revisited and clarified in more details, which can foster innovations in modern battery technologies based on this new storage mechanism.

Although aqueous Zn batteries have become a more sustainable alternative to lithium‐ion batteries owing to their intrinsic security, their practical applications are limited by dendrite formation and hydrogen reactions. The first application of a rare earth metal type addition to Zn batteries, cerium chloride (CeCl3), as an effective, low‐cost, and green electrolyte additive that facilitates the formation of a dynamic electrostatic shielding layer around the Zn protuberance to induce uniform Zn deposition is presented. After introducing CeCl3 additives, the electrochemical characterizations, in situ optical microscopy observation, in situ differential electrochemical mass spectrometry, along with density functional theory calculations, and finite element method simulations reveal resisted Zn dendritic growth and enhanced electrolyte stability. As a result, the Zn–Zn cells using the CeCl3 additive exhibit a long cycling stability of 2600 h at 2 mA cm−2, an impressive cumulative areal capacity of 3.6 Ah cm−2 at 40 mA cm−2, and a high Coulombic efficiency of ≈99.7%. The fact that the Zn–LiFePO4 cells with proposed electrolyte retain capacity significantly better than the additive‐free case is even more exciting.

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