Browsing by Author "Li, Ju"

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A Novel Moisture-Insensitive and Low-Corrosivity Ionic Liquid Electrolyte for Rechargeable Aluminum Batteries
(1970-01-01)
Li, Chi
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Patra, Jagabandhu
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Li, Ju
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Rath, Purna Chandra
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Lin, Ming-Hsien
Rechargeable aluminum batteries (RABs) are extensively developed due to their cost-effectiveness, eco-friendliness, and low flammability and the earth abundance of their electrode materials. However, the commonly used RAB ionic liquid (IL) electrolyte is highly moisture-sensitive and corrosive. To address these problems, a 4-ethylpyridine/AlCl3 IL is proposed. The effects of the AlCl3 to 4-ethylpyridine molar ratio on the electrode charge-discharge properties are systematically examined. A maximum graphite capacity of 95 mAh g(-1) is obtained at 25 mA g(-1). After 1000 charge-discharge cycles, approximate to 85% of the initial capacity can be retained. In situ synchrotron X-ray diffraction is employed to examine the electrode reaction mechanism. In addition, low corrosion rates of Al, Cu, Ni, and carbon-fiber paper electrodes are confirmed in the 4-ethylpyridine/AlCl3 IL. When opened to the ambient atmosphere, the measured capacity of the graphite cathode is only slightly lower than that found in a N-2-filled glove box; moreover, the capacity retention upon 100 cycles is as high as 75%. The results clearly indicate the great potential of this electrolyte for practical RAB applications.
A Water-Soluble NaCMC/NaPAA Binder for Exceptional Improvement of Sodium-Ion Batteries with an SnO2-Ordered Mesoporous Carbon Anode
(2018-11-23)
Patra, Jagabandhu
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Rath, Purna Chandra
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Li, Chi
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Kao, Hsien-Ming
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Wang, Fu-Ming
SnO2@CMK-8 composite, a highly promising anode for Na-ion batteries (NIBs), was incorporated with polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and NaCMC/NaPAA mixed binders to optimize the electrode sodiation/desodiation properties. Synergistic effects between NaCMC and NaPAA led to the formation of an effective protective film on the electrode. This coating layer not only increased the charge-discharge Coulombic efficiency, suppressing the accumulation of solid-electrolyte interphases, but also kept the SnO2 nanoparticles in the CMK-8 matrix, preventing the agglomeration and removal of oxide upon cycling. The adhesion strength and stability towards the electrolyte of the binders were evaluated. In addition, the charge-transfer resistance and apparent Na+ diffusion of the SnO2@CMK-8 electrodes with various binders were examined and post-mortem analyses were conducted. With NaCMC/NaPAA binder, exceptional electrode capacities of 850 and 425 mAh g(-1) were obtained at charge-discharge rates of 20 and 2000 mA g(-1), respectively. After 300 cycles, 90 % capacity retention was achieved. The thermal reactivity of the sodiated electrodes was studied by using differential scanning calorimetry. The binder effects on NIB safety, in terms of thermal runaway, are discussed.
Hybrid electrolyte enables safe and practical 5 V LiNi0.5Mn1.5O4 batteries
(2019-07-21)
Rath, Purna Chandra
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Wu, Chia-Jung
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Patra, Jagabandhu
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Li, Ju
;
Lee, Tai-Chou
Bis(trifluoromethylsulfonyl)imide (TFSI)-based ionic liquid (IL) has high thermal and electrochemical stability, but it is not an ideal battery electrolyte due to the poor rate capability of cells that use it, problematic anode compatibility, and high cost. The incorporation of a carbonate solvent could mitigate these problems, but it would also lead to serious Al current collector corrosion at high potential. This long-existing problem is overcome in this study by modulating the LiTFSI concentration and IL/carbonate ratio in the hybrid electrolyte. The Al corrosion and electrolyte decomposition side reactions at 5 V (vs. Li+/Li) can be suppressed in 3 M LiTFSI 25%-IL electrolyte, in which good performance of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode is achieved. Capacities of 140 and 88 mA h g(-1) were measured at 0.1 and 2C, respectively (vs. 25 mA h g(-1) at 2C for a plain LiTFSI/PMP-TFSI IL electrolyte). After 300 charge-discharge cycles, 90% of the initial LNMO capacity was retained. This electrolyte also shows low flammability and great wettability toward a polyethylene separator. Moreover, this electrolyte allows elevated-temperature storage and operation of LNMO cells at 55 degrees C, which is not possible with the conventional carbonate electrolyte. Good compatibility of the electrolyte with a graphite anode is also demonstrated. The proposed electrolyte design concept has great potential for next-generation 5 V Li-ion batteries.
Manipulation of Nitrogen-Heteroatom Configuration for Enhanced Charge-Storage Performance and Reliability of Nanoporous Carbon Electrodes
(2020-07-22)
Sutarsis
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Patra, Jagabandhu
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Su, Ching-Yuan
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Li, Ju
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Bresser, Dominic
In this study, various nitrogen-containing functional groups, namely, pyridine (N-6), pyrrole (N-5), oxidized N (N-O), and quaternary N (N-Q), are created on activated carbon (AC) surface via melamine, ammonia, and nitric oxide doping methods. N-5 and N-6 groups markedly alter the specific surface area and pore size of AC. N-O is found to affect electrolyte wettability, and the N-Q content is closely associated with AC electronic conductivity. The nitrogen-containing groups do not contribute to pseudocapacitance in propylene carbonate and acetonitrile electrolytes. However, the nitric-oxide-treated carbon (AC-NO) exhibits the best highrate charge-discharge performance among the investigated materials. The N-Q-enriched and N-5/N-6-depleted AC-NO most effectively suppresses the leakage current and gas evolution of supercapacitors. Online gas chromatography is used to analyze the gaseous species produced from AC electrodes. With an appropriate surface functionality on carbon, the cell voltage can be increased to similar to 3 V, increasing the energy and power densities. The aging behavior of the carbon electrodes with and without nitrogen modification after being floated at 2.5 V and 70 degrees C for 3 days is investigated. An effective strategy for enhancing supercapacitor performance and reliability is proposed.
Microwave growth and tunable photoluminescence of nitrogen-doped graphene and carbon nitride quantum dots
(2019-05-14)
Gu, Siyong
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Hsieh, Chien-Te
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Gandomi, Yasser Ashraf
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Chang, Jeng-Kuei
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Li, Ju
Tunable photoluminescent nitrogen-doped graphene and graphitic carbon nitride (g-C3N4) quantum dots are synthesized via a facile solid-phase microwave-assisted (SPMA) technique utilizing the pyrolysis of citric acid and urea precursors. The atomic ratio, surface functionalization, and atomic structure of as-prepared quantum dots strongly depend on the ratio of citric acid to urea. The quantum dots have a homogeneous particle size and tend to form a circle and/or ellipse shape to minimize the edge free energy. The atomic ratio of surface nitrogen to carbon (N/C) in the quantum dots can reach as high as 1.74, among the highest values reported in the literature. The SPMA technique is capable of producing high-quality quantum dots with photoluminescence (PL) emission at various wavelengths on a pilot scale. The atomic structures of the N-doped graphene and g-C3N4 quantum dots are explored using molecular dynamics simulations. Increasing the urea concentration increases the tendency of in-plane N (i.e., quaternary N) substitution over that of other amino functionalizations, such as pyrrolic and pyridinic N. The PL emission can be precisely tuned via a one-step SPMA method by adjusting the precursor composition. A high quantum yield of 38.7% is achieved with N-doped graphene quantum dots, indicating the substantial influence of the N- and O-rich edge groups on the enhancement of PL efficiency. A bandgap structure is proposed to describe the interstate (*-) transition of quantum dots. This work introduces a novel approach for engineering the chemical composition and atomic structure of graphene and g-C3N4 quantum dots, facilitating their research and applications in optical, electronic, and biomedical devices.