Browsing by Author "Majumder, S. B."

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High Power Na3V2(PO4)(3)@C/AC Bi-material Cathodes for Hybrid Battery-Capacitor Energy Storage Devices
(2020-01-08)
Akhtar, Mainul
;
Chang, Jeng-Kuei
;
Majumder, S. B.
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have reported the synthesis and electrochemical characteristics of carbon-coated sodium vanadium phosphate/activated carbon (NVP@C/AC) bi-material electrodes. We have reported that bi-material type NVP@C/AC cathodes offer superior rate performance as compared to either NVP@C or AC electrodes. Through a detailed impedance spectroscopy analyses, we demonstrated that the synergic effect observed in the bi-material electrodes correlates well with the lowering of their charge transfer resistances (R-CT) and the increase of Li(+)diffusion coefficient (DLi+) with the increase of activated carbon content from 0 to 0.60 weight fraction. Through a detailed cyclic voltammogram analyses we have delineated the faradaic and capacitive contribution towards the overall capacities of the bi-material electrodes at various rate conditions. For both these bi-materials, irrespective of the AC content and rate, capacitive contribution dominates the overall capacity. NVP@C/AC40 yields discharge capacities of 67 and 40 mAh g(-1)with capacity retention of more than 93% and 67% after 500 cycles measured at 50 and 1000 mA g(-1), respectively. These bi-materials are demonstrated to be excellent material candidates for high power density lithium titanium oxide (LTO)//NVP@C/AC hybrid battery-capacitor (bat-cap) energy storage devices.
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.