Browsing by Author "Akhtar, Mainul"

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A Lithium-Ion Rechargeable Full Cell Using the Flower-like Na3V2(PO4)(3)@C Cathode and Li4Ti5O12 Anode
(2020-05-18)
Akhtar, Mainul
;
Pradhan, Sunil Kumar
;
Chang, Jeng-Kuei
;
Majumder, Subhasish Basu
;
材料科學與工程學系
In the present work, we have demonstrated that nanopetal-assembled hierarchical carbon-coated Na3V2(PO4)(3) (nNVP@C) microflowers, synthesized via a microwave-assisted hydrothermal route, play an important role for yielding superior electrochemical characteristics of a Li4Ti5O12 (LTO)//nNVP@C full cell. Thus, the full cell yields superior power density with decent discharge capacity after extended cycling and good rate performance. The nanosize petals help Li+ to diffuse faster in NVP particles, and the inner mesoporous morphology of microflowers allows the electrolyte to easily penetrate into the embedded NVP@C nanocrystals. Furthermore, the homogeneous carbon coating provides an elastic buffer to mitigate the strain developed during Na+ extraction and subsequent Li+ insertion and extraction. The LTO//nNVP@C full cell is claimed to be suitable for power applications, where relatively thinner electrodes would be flooded with a sufficient amount of the lithium salt-containing organic electrolyte. To improve the cycleability characteristics, one requires to match carefully the Li+ activity in the organic electrolyte with electrode capacity. This would ensure stoichiometric lithium-ion insertion in the LTO electrode together with predominant lithium-ion insertion in the nNVP@C cathode.
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
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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.