Browsing by Author "Drewett, NE"

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    Biphasic P2/O3-Na2/3Li0.18Mn0.8Fe0.2O2: a structural investigation
    (Royal Society of Chemistry, 2020-12-22) Stansby, JH; Avdeev, M; Brand, HEA; Gonzalo, E; Drewett, NE; Ortiz-Vitoriano, N; Sharma, N; Rojo, T
    The P2/O3 layered oxide system is thought to benefit from a synergistic enhancement, resulting from the presence of both phases, which makes it a promising cathode material for Na-ion battery applications. Here, biphasic P2/O3-Na2/3Li0.18Mn0.8Fe0.2O2 is investigated via a combination of neutron and X-ray scattering techniques. Neutron diffraction data indicates that the O3 alkali metal site is fully occupied by Li. Real time operando X-ray diffraction data shows the structural evolution of the composite electrode – at the charged state there is no evidence of O2, OP4 or Z phases. The results presented herein provide new insight into site preference of Li in biphasic materials and highlights the value of utilizing multiple phases to achieve high performance layered cathode materials for sodium battery applications.© The Royal Society of Chemistry 2021
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    Dopant and current rate dependence on the structural evolution of P2-Na2/3Mn0.8Zn0.1M0.1O2 (M=Cu, Ti): an operando study
    (Wiley, 2021-06-24) Stansby, JH; Sharma, N; Avdeev, M; Brand, HEA; Gonzalo, E; Drewett, NE; Ortiz-Vitoriano, N; Rojo, T
    Variable current rate operando XRD experiments were performed on the P2- Na2/3Mn0.8Zn0.1Cu0.1O2 composition, which displays promising electrochemical properties. The data reveals the reversible formation of a new and previously undetected ordering reflection upon extraction of Na-ions, and that small compositional alterations may dramatically impact structural evolution and electrochemical properties. For P2- Na2/3Mn0.8Zn0.1Cu0.1O2 at all current rates examined (25, 50 and 100 mA.g−1), comparable structural evolution on charge is observed, but the structural evolution on discharge is shown to be significantly influenced by the current applied during the preceding charge step. For both P2- Na2/3Mn0.8Zn0.1Cu0.1O2 and P2- Na2/3Mn0.8Zn0.1Ti0.1O2 comparable structural evolution is observed only at a slower current rate of 25 mA.g−1. Overall, the structural evolution of these layered materials is shown to be dependent on the cycling history, highlighting the significance of applied current rate during cycling, especially during the initial cycle. © 2021 The Authors.
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    P2-Na2/3Mn0.8M0.1M′0.1O2 (M = Zn, Fe and M′ = Cu, Al, Ti): A detailed crystal structure evolution investigation
    (American Chemical Society, 2021-05-24) Stansby, JH; Sharma, N; Avdeev, M; Brand, HEA; Johannessen, B; Gonzalo, E; Drewett, NE; Ortiz-Vitoriano, N; Rojo, T
    Incorporation of various transition metals has been shown to improve the electrochemical performance of Mn-rich Na-ion cathode materials. A greater comprehension of the role of dopant ions, particularly with regard to Mn-rich layered oxides as materials for the positive electrode of Na-ion batteries, is required for their continual development. Here two similar series of Mn-rich P2 cathode materials P2-Na2/3Mn0.8M0.1M′0.1O2 (M = Fe, Zn and M′ = Cu, Al, Ti) are explored, focusing on structural analysis using high-resolution operando synchrotron X-ray diffraction. Notably, under the cycling conditions employed, no P2 to O2 phase transitions toward the charged state were identified for any of the materials investigated. Particularly stable solid solution evolution was observed for P2-Na2/3Mn0.8Zn0.1Cu0.1O2 and P2-Na2/3Mn0.8Zn0.1Al0.1O2 when cycled at 40 mA.g–1 which reflects the electrochemical properties of the materials investigated herein and illustrates that Zn is an excellent choice of dopant for Mn-rich cathode materials. Moreover, the better cyclability of P2-Na2/3Mn0.8Zn0.1Al0.1O2 compared with P2-Na2/3Mn0.8Zn0.1Cu0.1O2 is in keeping with the minimal structural changes observed. This demonstrates that although oxidation state predictions to optimize the initial Mn oxidation state are a good way of initially selecting materials, to truly exploit Mn-rich P2-type materials it is necessary to build up an in-depth understanding of both oxidation states and the associated Jahn–Teller distortion as well as the subtle interplay of synergistic and antagonistic interactions between dopants. Overall, this study illustrates the value of structural investigations to assist in the rational design and validation of novel high-performance materials; the results highlight that the interplay between dopants in addition to the average Mn oxidation state are both crucial considerations when designing high-performance Mn-rich layered oxide materials. © 2021 American Chemical Society