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  • Novel Cathode Materials for...
    Hwang, Jang-Yeon; Myung, Seung-Taek; Yoon, Chong Seung; Kim, Sung-Soo; Aurbach, Doron; Sun, Yang-Kook

    Advanced functional materials, November 22, 2016, Letnik: 26, Številka: 44
    Journal Article

    The development of high‐energy and high‐power density sodium‐ion batteries is a great challenge for modern electrochemistry. The main hurdle to wide acceptance of sodium‐ion batteries lies in identifying and developing suitable new electrode materials. This study presents a composition‐graded cathode with average composition NaNi0.61Co0.12Mn0.27O2, which exhibits excellent performance and stability. In addition to the concentration gradients of the transition metal ions, the cathode is composed of spoke‐like nanorods assembled into a spherical superstructure. Individual nanorod particles also possess strong crystallographic texture with respect to the center of the spherical particle. Such morphology allows the spoke‐like nanorods to assemble into a compact structure that minimizes its porosity and maximizes its mechanical strength while facilitating Na+‐ion transport into the particle interior. Microcompression tests have explicitly verified the mechanical robustness of the composition‐graded cathode and single particle electrochemical measurements have demonstrated the electrochemical stability during Na+‐ion insertion and extraction at high rates. These structural and morphological features contribute to the delivery of high discharge capacities of 160 mAh (g oxide)−1 at 15 mA g−1 (0.1 C rate) and 130 mAh g−1 at 1500 mA g−1 (10 C rate). The work is a pronounced step forward in the development of new Na ion insertion cathodes with a concentration gradient. The tailored microstructural design of spoke‐like nanorods assemblies and their unique chemical composition contribute to high capacity, excellent rate capability, and low temperature performance due to their superior mechanical strength during Na+ ion insertion and extraction even at high rates. Furthermore, this unique particle morphology guarantees high thermal stability in the desodiated state of electrodes materials.