Because of the salient impact on the performance of oxygen evolution reaction (OER), the surface dynamics of precatalysts accompanying the surface oxidation and dissolution of catalytic components demands immense research attention. Accordingly, the change in the structural integrity under high current density generally results in inconsistent OER performances. To address this challenge, here, we present the intricate design of precatalysts, strategically followed by reconstruction treatment in the presence of Fe under water oxidation condition, which significantly enhances the OER activity and long-term stability. Notably, the surface tailored heterointerface structures (Fe-doped NiOOH/CoOOH) obtained through the reconstruction of a precatalyst (Ni­(OH)2/Co9S8) with the incorporation of Fe, are abundantly enriched with electrochemically accessible high valence active sites. This results in remarkable OER activity (400 mA cm–2 at 345 mV). Density functional theory (DFT) calculations indicate that Fe-incorporated electrocatalysts give optimal binding energies of OER intermediates and show substantially reduced overpotential compared to Fe-undoped electrocatalysts.

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Lithium rich layered oxide xLi2MnO3∙(1−x)LiMO2 (M = Mn, Co, Ni, etc.) materials are promising cathode materials for next generation lithium ion batteries. However, the understanding of their electrochemical kinetic behaviors is limited. In this work, the phase separation behaviors and electrochemical kinetics of 0.5Li2MnO3∙0.5LiCoO2 materials with various Li2MnO3 domain sizes were studied. Despite having similar morphological, crystal and local atomic structures, materials with various Li2MnO3 domain sizes exhibited different phase separation behavior resulting in disparate lithium ion transport kinetics. For the first few cycles, the 0.5Li2MnO3∙0.5LiCoO2 material with a small Li2MnO3 domain size had higher lithium ion diffusion coefficients due to shorter diffusion path lengths. However, after extended cycles, the 0.5Li2MnO3∙0.5LiCoO2 material with larger Li2MnO3 domain size showed higher lithium ion diffusion coefficients, since the larger Li2MnO3 domain size could retard structural transitions. This leads to fewer structural rearrangements, reduced structural disorders and defects, which allows better lithium ion mobility in the material.

In this study, four different MnO2 polymorphs are synthesized with a controlled morphology of hollow porous structures to systematically investigate the influences of polymorphs in conversion‐based material. As the structure of these materials transforms into nanosized metal and maintains an extremely low‐crystalline phase during cell operation, the effects of polymorphs are overlooked as compared to the case of insertion‐based materials. Thus, differences in the ion storage behaviors among various MnO2 polymorphs are not well identified. Herein, the structural changes, charge storage reaction, and electrochemical performance of the different MnO2 polymorphs are investigated in detail. The experimental results demonstrate that the charge storage reactions, as part of which spinel‐phased MnO2 formation is observed after lithiation and delithiation instead of recovery of the original phases, are similar for all the samples. However, the electrochemical performance varies depending on the initial crystal structure. Among the four polymorphs, the spinel‐type λ‐MnO2 delivers the highest reversible capacity of ≈1270 mAh g−1. The structural similarity between the cycled and pristine states of λ‐MnO2 induces faster kinetics, resulting in the better electrochemical performance. These findings suggest that polymorphs are another important factor to consider when designing high‐performance materials for next‐generation rechargeable batteries.

To further increase the energy density of rechargeable batteries to meet the rapidly growing needs of high-energy consuming devices, various materials are tested as anode materials. Some of these newly developed anode materials exhibit anomalously high capacities that exceed their theoretical values. Advanced analytical techniques have revealed that unconventional reaction mechanisms account for these extra capacities. However, despite the potential to take current battery technology development to the next level, research on the utilization of these reactions is currently limited. Herein, a new strategy is proposed to maximize the reaction of -OH components by using crystal water to increase the extra capacity obtained from the abnormal reactions of LiOH species. In addition to the LiOH phase formed by the conversion reaction of metal hydroxides, the H 2 O inside Ni(OH) 2 crystals contributes to the formation of LiOH, which then reacts with lithium. As a result, water-containing Ni(OH) 2 exhibits greater reversible capacities than bare Ni(OH) 2 and NiO, thereby confirming the beneficial effects of crystal water. This novel concept for the enhancement of electrochemical ion storage capacities through the introduction of crystal water to conversion-based anode materials can expand the design factors for maximizing the available capacities of active materials.