Browsing by Author "Luo, Xu-Feng"

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Physicochemical and electrochemical properties of the (fluorosulfonyl) (trifluoromethylsulfonyl)amide ionic liquid for Na secondary batteries
(2020-09-15)
Yang, Huan
;
Luo, Xu-Feng
;
Matsumoto, Kazuhiko
;
Chang, Jeng-Kuei
;
Hagiwara, Rika
In this study, thermal, physical, and electrochemical properties of the ionic liquid electrolyte system, Na[FTA]-[C(3)C(1)pyrr][FTA], (FTA(-) = (fluorosulfonyl) (trifluoromethylsulfonyl)amide and C(3)C(1)pyrr(+) = N-methyl-N-pro-pylpyrrolidinium) have been investigated for Na secondary batteries. The asymmetric FTA. structure provides a wide liquid-phase temperature range, especially at low x(Na[FTA]) (x(Na[FTA]) = molar fraction of Na[FTA]) and low temperature range. Glass transition at 170-209 K is the only observed thermal behavior in the x(Na [FTA]) of 0.0-0.4. Temperature dependence of viscosity and ionic conductivity obeys the Vogel-Tammann-Fulcher equation, and the correlation between molar conductivity and viscosity follows the fractional Walden rule. The anodic potential limits are above 5 V vs. Na+/Na at 298 and 363 K. The noticeable effects of x(Na [FTA]) are observed in the electrochemical performance of Na metal and hard carbon electrodes. In both cases, a moderate concentration, x(Na[FTA]) of 0.2-0.3, enables favorable charge-discharge behavior. At 363 K, the discharge capacities of the hard carbon electrode at x(Na[FTA]) of 0.3 are 260 and 236 mAh g(-1) at the current densities of 20 and 200 mA g(-1), respectively. The optimum cycling performance occurs at x(Na[FTA]) = 0.3, providing satisfactory capacity retention and high average Coulombic efficiency.
Tuning of Na+ Concentration in an Ionic Liquid Electrolyte to Optimize Solid-Electrolyte Interphase at Microplasma-Synthesized Graphene Anode for Na-Ion Batteries
(2019-10-07)
Luo, Xu-Feng
;
Chiang, Wei-Hung
;
Su, Ching-Yuan
;
Wu, Tzi-Yi
;
Majumder, S. B.
Two-dimensional (2D) materials are promising anodes for Na-ion batteries owing to their unique architectures and tunable physiochemical properties. However, their high surface area requires sophisticated electrolyte/electrode interface control to improve the charge-discharge efficiency and reversibility. This study uses microplasma-synthesized graphene nanosheets (MPGNSs) as a model 2D material. The effects of NaFSI concentration in an N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid (IL) electrolyte are systematically investigated. It is found that the chemical composition of the solid-electrolyte interphase depends on the electrolyte formulation, leading to distinct Coulombic efficiency, discharge capacity, rate capability, and cyclability of the MPGNS electrodes. The thermal reactivity of the sodiated MPGNSs (in terms of exothermic onset temperature and total heat released) upon heating is studied using differential scanning calorimetry. The IL electrolyte with a proper Na+ fraction is superior to a conventional organic carbonate electrolyte for practical NIB applications.