[en] The development of low-cost, high-power lithium-ion batteries requires durable anode materials that can store and release lithium quickly. Here a mixed phase of H-Nb${}_2$O${}_5$ and M-Nb${}_2$O${}_5$ (denoted as d-H,M-Nb${}_2$O${}_5$) that demonstrates excellent performance as an anode material for lithium storage is reported. Experimental and computational analyses reveal several salient features of d-H,M-Nb${}_2$O${}_5$. First, the edge-sharing arrangement between the mixed niobium oxygen polyhedral block structures helps alleviate volume expansion during cycling, thereby enhancing stability and reversibility. Second, the mixed-phase structure facilitates a continuous pathway for lithium ion adsorption These characteristics allow for sequential transport of lithium ions, enabling fast charging. As a result, the d-H,M-Nb${}_2$O${}_5$ electrode material exhibits a high capacity of 142 mAh g${}^{-<!--\; ???\; -->1}$ at an ultra-fast charging rate of 100 C, while maintaining 85% of its initial capacity after 5000 cycles. Moreover, its practical feasibility is established by demonstrating full-cell performance at a 5 C discharge/charge rate (13 mA cm${}^{-<!--\; ???\; -->2}$), maintaining 79% of its capacity over 1000 cycles. (© 2023 Wiley‐VCH GmbH)

[en] This work not only summarizes the previous doping research that focused on the optimization of a bulk doping composition but also introduces a new doping strategy, namely, "electrochemical reaction mechanism control doping." The new electrochemical mechanism control technology enables the study of the precise deterioration mechanism of layered cathode materials for Li-ion batteries (LIBs). Accordingly, tremendous efforts have been devoted to the development of various types of layered cathode materials, such as lithium-rich, nickel-rich, and cobalt-rich materials, by using an electrochemical functioning doping method. This progress report also gives a perspective on potential future directions for this field. In this context, detailed methodological approaches are suggested for advanced doping studies, where the consideration of the doping method takes significance as great as designing doping configurations, e.g., chemical composition, doping depth, and doping site control, for the modification of battery material properties. As an instance of the methodological approaches for doping studies, a new "secondary doping" is shown with exemplary experimental results showing that functioning dopants (primary dopants) are homogeneously dispersed on the layered cathode materials by using supporting dopants (secondary dopants). This study will provide insights into the future direction of doping research of LIBs, as well as the history of the development of atomic substitution in layered cathode materials. (© 2020 Wiley-VCH GmbH)

[en] Oxygen vacancies (OV) are native defects in transition metal (TM) oxides and their presence has a critical effect on the physicochemical properties of the oxide. Metal oxides are commonly used in lithium-ion battery (LIB) cathodes and there is still a lack of understanding of the role of OVs in LIB research field. Here, we report on the behavior of OVs in a single-crystal LIB cathode during the non-equilibrium states of charge and discharge. We found that microcrack evolution in a single crystal occurs due to OV condensation in specific crystallographic orientations generated by the continuous migration of OVs and TM ions. Moreover, understanding the effects of the presence and diffusion of OVs in metal oxides enables the elucidation of most of the conventional mechanisms of capacity fading in LIBs and provides new insights for new electrochemical applications. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

[en] Replacing the commercial Pt/C with non-precious metal-based electrocatalysts in the proton exchange membrane fuel cells and metal-air batteries is still challenging. Herein, an electrocatalyst (described as Fe-N-C/Fe_100-x-y-zP_xO_yN_z/NPC, NPC is N, P co-doped carbon) composed of multiple active components, such as NPC, iron-based porous hollow spheres and Fe-N-C, is reported, which exhibits an excellent activity that is comparable to state-of-the-art Pt/C for half-cell and full zinc-air battery in alkaline media. This catalyst exhibits an excellent activity with a half-wave potential of 0.86 V for the ORR in alkaline media, which is 10 mV more positive than to that of Pt/C (0.85 V), and a gravimetric energy density for zinc-air battery is up to 675 Wh Kg_zn⁻¹. The excellent activity is attributed to the synergetic effect of active NPC, iron-based porous hollow spheres (Fe_100-x-y-zP_xO_yN_z) and Fe-N-C in its structure. In addition, phosphoric acid groups are partially remained in the structure for our catalyst that make the catalyst excellent hydrophilicity. This work adds a new member into family of non-precious metal-based ORR electrocatalysts.