Browsing by Author "Liu, G"

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    Driving forces for the phase transition of CuQ2-TCNQ molecular crystals
    (Royal Society of Chemistry, 2016-05-23) Yu, DH; Kearley, GJ; Liu, G; Mole, RA; McIntyre, GJ; Tao, X
    The driving forces for the phase transition and relative stability of the two forms of CuQ2-TCNQ molecular crystals have been studied using inelastic neutron scattering (INS), density functional theory (DFT), and Hirshfeld surface analysis. DFT molecular dynamics (MD) simulations show that form-II has a lower enthalpy, but with increasing temperature form-I becomes thermodynamically stable due to the greater entropy. INS and MD simulations both show that the entropy of the hydrogen-bond network that holds molecules together within layers is higher in form-I. The interlayer π–π interactions are also weaker in form-I, leading to an overall “loosening” of the structure. The phase transition is kinetically hindered by the requirement to re-optimize the orientation of the layers. The strong H-bond interactions keep the in-plane atomic arrangement stable, while the weak interlayer π–π interactions provide the coupling between layers during the phase-transition. This subtle interplay of the two interactions maintains the integrity of the crystal upon phase transition even with dramatic physical dimension changes. © The Royal Society of Chemistry 2016
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    High ionic conductivity and dendrite-resistant NASICON solid electrolyte for all-solid-state sodium batteries
    (Elsevier, 2021-06-01) Shen, L; Yang, J; Liu, G; Avdeev, M; Yao, X
    The low ionic conductivity and poor dendrites suppression capability of Na3Zr2Si2PO12 solid electrolyte limit the practical application of all-solid-state sodium batteries. Herein, the optimized Na3.4Mg0.1Zr1.9Si2.2P0.8O12 electrolyte is obtained by simultaneously substituting the Zr4+ with Mg2+ and P5+ with Si4+ through solid-state reaction. The Na3.4Mg0.1Zr1.9Si2.2P0.8O12 electrolyte has superior room temperature ionic conductivity of 3.6 × 10−3 S cm−1, which is 17 times higher than that of pristine Na3Zr2Si2PO12. No short circuit of the Na/Na3.4Mg0.1Zr1.9Si2.2P0.8O12/Na symmetric battery is observed up to 2.0 mA cm−2, and the symmetric battery displays stable sodium plating/stripping cycles for over 2000 h at 0.1 mA cm−2 and 300 h at 1.0 mA cm−2. The resultant Na3.4Mg0.1Zr1.9Si2.2P0.8O12 electrolyte is further employed in two all-solid-state sodium batteries. The Na3V2(PO4)3/Na3.4Mg0.1Zr1.9Si2.2P0.8O12/Na all-solid-state sodium battery maintains a discharge capacity of 93.3 mAh g−1 at 0.1C after 50 cycles, and the FeS2/Na3.4Mg0.1Zr1.9Si2.2P0.8O12/Na all-solid-state sodium battery delivers a discharge capacity of 173.1 mAh g−1 at 0.1C after 20 cycles, which are significantly enhanced compared with those based on pristine Na3Zr2Si2PO12. This strategy provides an efficient method to prepare optimized NASICON solid electrolytes with high ionic conductivity and excellent dendrites suppression capability and promotes the practical application of all-solid-state sodium batteries. © 2021 Elsevier Ltd.
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    Inside Back Cover: t-Na2(VO)P2O7: A 3.8 V pyrophosphate insertion material for sodium-ion batteries
    (Wiley, 2014-06-23) Barpanda, P; Liu, G; Avdeev, M; Yamada, A
    Pyrophosphate oxyanionic framework compounds offer a great platform to investigate new battery materials. In our continuing effort to explore pyrophosphate cathodes for sodium-ion batteries, we report, for the first time, the synthesis and use of tetragonal Na2(VO)P2O7 as a potential sodium-ion insertion material. This material can be easily prepared by using a conventional solid-state route at a relatively low temperature of 400 °C. Stabilizing as a tetragonal structure with an open framework, the material offers pathways for Na+ diffusion. The as-synthesized material, with no further cathode optimization, yields a reversible capacity (Q) approaching 80 mAh g−1 (QTheoretical=93.4 mAh g−1) involving a one electron V5+/V4+ redox potential located at 3.8 V (vs. Na/Na+). Furthermore, the material exhibits decent rate kinetics and reversibility. Combining green synthesis and moderate electrochemical properties, t-Na2(VO)P2O7 is reported as a new addition to the growing family of pyrophosphate cathodes for sodium-ion batteries.© 2014, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Na2FeP2O7: a safe cathode for rechargeable sodium-ion batteries
    (American Chemical Society, 2013-09-10) Barpanda, P; Liu, G; Ling, CD; Tamaru, M; Avdeev, M; Chung, SC; Yamada, Y; Yamada, A
    Vying for newer sodium-ion chemistry for rechargeable batteries, Na2FeP2O7 pyrophosphate has been recently unveiled as a 3 V high-rate cathode. In addition to its low cost and promising electrochemical performance, here we demonstrate Na2FeP2O7 as a safe cathode with high thermal stability. Chemical/electrochemical desodiation of this insertion compound has led to the discovery of a new polymorph of NaFeP2O7. High-temperature analyses of the desodiated state NaFeP2O7 show an irreversible phase transition from triclinic (P (1) over bar) to the ground state monoclinic (P2(1)/c) polymorph above 560 degrees C. It demonstrates high thermal stability, with no thermal decomposition and/or oxygen evolution until 600 degrees C, the upper limit of the present investigation. This high operational stability is rooted in the stable pyrophosphate (P2O7)(4-) anion, which offers better safety than other phosphate-based cathodes. It establishes Na2FeP2O7 as a safe cathode candidate for large-scale economic sodium-ion battery applications. © 2013, American Chemical Society.
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    t-Na2(VO)P2O7: A 3.8 V Pyrophosphate insertion material for sodium-ion batteries (ChemElectroChem 9/2014)
    (Wiley, 2014-09-04) Barpanda, P; Liu, G; Avdeev, M; Yamada, A
    The picture shows a bond valence sum map of a fresnoite Na2(VO)P2O7 cathode that acts as a novel 3.8 V insertion host material for sodium-ion batteries. This work is presented on p. 1488 by P. Barpanda, A. Yamada et al. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Ultrastable all-solid-state sodium rechargeable batteries
    (American Chemical Society, 2020-08-11) Yang, J; Liu, G; Avdeev, M; Wan, H; Han, F; Shen, L; Zou, Z; Shi, S; Hu, YS; Wang, CS; Yao, X
    The insufficient ionic conductivity of oxide-based solid electrolytes and the large interfacial resistance between the cathode material and the solid electrolyte severely limit the performance of room-temperature all-solid-state sodium rechargeable batteries. A NASICON solid electrolyte Na3.4Zr1.9Zn0.1Si2.2P0.8O12, with superior room-temperature conductivity of 5.27 × 10–3 S cm–1, is achieved by simultaneous substitution of Zr4+ by aliovalent Zn2+ and P5+ by Si4+ in Na3Zr2Si2PO12. The bulk conductivity and grain boundary conductivity of Na3.4Zr1.9Zn0.1Si2.2P0.8O12 are nearly 20 times and almost 50 times greater than those of pristine Na3Zr2Si2PO12, respectively. The FeS2||polydopamine-Na3.4Zr1.9Zn0.1Si2.2P0.8O12||Na all-solid-state sodium batteries, with a polydopamine modification thin layer between the solid electrolyte and the cathode, maintain a high reversible capacity of 236.5 mAh g–1 at a 0.1 C rate for 100 cycles and a capacity of 133.1 mAh g–1 at 0.5 C for 300 cycles, demonstrating high performance for all-solid-state sodium batteries. © 2020 American Chemical Society