Browsing by Author "Naeyaert, PJP"

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    Investigation of K modified P2 Na 0.7 Mn 0.8 Mg 0.2 O 2 as a cathode material for sodium-ion batteries
    (Royal Society of Chemistry, 2018-11-19) Sehrawat, D; Cheong, S; Rawal, A; Glushenkov, AM; Brand, HEA; Cowie, BCC; Gonzalo, E; Rojo, T; Naeyaert, PJP; Ling, CD; Avdeev, M; Sharma, N
    Sodium-ion batteries (NIBs) are emerging as a potentially cheaper alternative to lithium-ion batteries (LIBs) due to the larger abundance of sodium and in some cases the similar intercalation chemistry to LIBs. Here we report the solid state synthesized K-modified P2 Na0.7Mn0.8Mg0.2O2 which adopts hexagonal P63/mmc symmetry. The second charge/discharge capacity for the as-prepared material is 115/111 mA h g−1 between 1.5–4.2 V at a current density of 15 mA g−1, which reduces to 61/60 mA h g−1 after 100 cycles. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDS) analysis shows a heterogeneous distribution of K and solid state 23Na NMR illustrates that the presence of K perturbs the local environment of Na within the P2 Na0.7Mn0.8Mg0.2O2 crystal structure. Larger scale X-ray absorption near-edge structure (XANES) data on the K L-edge also illustrate that K is present on the surface of electrodes in preference to the bulk. In situ synchrotron X-ray diffraction (XRD) data illustrates that the P2 structural motif is preserved, featuring a solid solution reaction for most of charge–discharge except at the charged and discharged states where multiple phases are present. The K-modified sample of P2 Na0.7Mn0.8Mg0.2O2 is compared with the K-free samples in terms of both structural evolution and electrochemical performance. © The Royal Society of Chemistry 2019
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    Manganese metaphosphate Mn(PO3)2 as a high‐performance negative electrode material for lithium‐ion batteries
    (Wiley, 2020-06-15) Xia, Q; Naeyaert, PJP; Avdeev, M; Schmid, S; Liu, H; Johannessen, B; Ling, CD
    We report a novel negative conversion electrode material, manganese (II) metaphosphate Mn(PO3)2. This compound can be synthesized by a facile solid-state method, and after carbon-coating delivers an attractively high reversible capacity of 477 mAh/g at 0.1 C and 385 mAh/g at 1 C. We investigated the reaction mechanism with a combination of ex situ X-ray absorption spectroscopy, in situ X-ray diffraction, and high-resolution transmission electron microscopy. We observed a direct conversion process by monitoring the first discharge in operando, in which Mn(PO3)2 reacts with Li to give fusiform Mn nanograins a few Ångstroms in width, embedded in a matrix of lithium conducting LiPO3 glass. Due to the fine nanostructures of the conversion products, this conversion reaction is completely reversible. © 1999-2021 John Wiley & Sons, Inc.
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    Synthesis, electrochemistry and transition metal-doping of monoclinic Li4Ti5O12 and Na4Ti5O12
    (Elsevier, 2020-10-01) Naeyaert, PJP; Avdeev, M; Ling, CD
    A new candidate Li-ion battery anode material, monoclinic M-Li4Ti5O12, has been prepared for the first time by ion-exchange from monoclinic M-Na4Ti5O12, and found to offer a stable electrochemical performance at rates of C/20 and 2C. The structural and electrochemical effects of transition metal M(III) doping of M-Na4Ti5O12 and Li4Ti5O12 have also been investigated. Doping was found to facilitate the synthesis of the M-Na4Ti5O12 type structure, eliminating the need for strongly reducing conditions; increase the Na-ion content; and improve the stability in atmospheric conditions. Neutron powder diffraction and ex situ X-ray powder diffraction data collected at various points during electrochemical cycling reveal that phase changes in Li4Ti5O12 proceed via a two-phase mechanism, in contrast to M-Na4Ti5O12 which proceeds via a solid-solution mechanism. © 2020 Elsevier B.V.
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    Synthetic, structural, and electrochemical study of Monoclinic Na4Ti5O12 as a sodium-ion battery anode material
    (ACS Publications, 2014-12-04) Avdeev, M; Naeyaert, PJP; Sharma, N; Ben Yahia, H; Ling, CD
    The monoclinic phase of Na4Ti5O12 (M-Na4Ti5O12) has been investigated as a potential sodium-ion battery anode material. In contrast to the previously investigated trigonal phase (T-Na4Ti5O12), M-Na4Ti5O12 has continuous two-dimensional (2D) channels with partially occupied Na sites, providing broader pathways and more space for the intercalation of excess sodium. Electrochemical measurements show that it exhibits a comparable or higher reversible capacity than T-Na4Ti5O12. Neutron powder diffraction reveals the preferred sites and occupancies of the excess sodium. In situ synchrotron X-ray diffraction under electrochemical cycling shows that the crystal lattice undergoes strongly anisotropic volume changes during cycling. © 2014, American Chemical Society.