Browsing by Author "Lee, Tai-Chou"

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Composition Modulation of Ionic Liquid Hybrid Electrolyte for 5 V Lithium-Ion Batteries
(2019-11-13)
Wu, Chia-Jung
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Rath, Puma Chandra
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Patra, Jagabandhu
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Bresser, Dominic
;
Passerini, Stefano
Electrolyte is a key component in high-voltage lithium-ion batteries (LIBs). Bis(trifluoromethanesulfonyl)imide-based ionic liquid (IL)/organic carbonate hybrid electrolytes have been a research focus owing to their excellent balance of safety and ionic conductivity. Nevertheless, corrosion of Al current collectors at high potentials usually happens for this kind of electrolyte. In this study, this long-standing problem is solved via the modulation of the IL/carbonate ratio and LiPF6 concentration in the hybrid electrolyte. The proposed electrolyte suppresses Al dissolution and electrolyte oxidation at 5 V (vs Li+/Li) and thus allows for ideal lithiation/delithiation performance of a high-voltage LiNi0.5Mn1.5O4 (LNMO) cathode even at 55 degrees C. The underlying mechanism is examined in this work. Excellent cycling stability (97% capacity retention) for an LNMO cathode after 300 cycles is achieved. This electrolyte shows good wettability toward a polyethylene separator and low flammability. In addition, satisfactory compatibility with both graphite and Si-based anodes is confirmed. The proposed electrolyte design strategies have great potential for applications in high-voltage LIBs.
Ga-doped lithium lanthanum zirconium oxide electrolyte for solid-state Li batteries
(2020-09-01)
Mishra, Mrinalini
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Hsu, Che-Wei
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Rath, Purna Chandra
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Patra, Jagabandhu
;
Lai, Hong-Zheng
Cubic-phase Li7La3Zr2O12 (LLZO) garnet is a promising solid electrolyte candidate for next-generation Li batteries. As a viable approach, the desired cubic-phase formation of LLZO relies on elemental doping. In this regard, various dopants such as Al and Ga are doped into the LLZO samples, which are synthesized using a solid-state reaction method. The Al-and Ga-doped LLZO can transform to a cubic-phase garnet at 900 degrees C. After 1200 degrees C sintering, a Li2ZrO3 impurity phase is found for the Al-doped LLZO pellet, which still shows many voids and inhomogeneous particles on the surface. The Ga doping seems to be attractive since it can effectively stabilize the cubic phase and desired microstructure within 900-1200 degrees C. Based on the optimized Ga-doped LLZO (LGLZO), various electrolyte architecture designs are developed that include LGLZO pellet electrolytes with and without poly(ethylene oxide) (PEO)-lithium bis(tri-fluoromethylsulfonyl)imide (LiTFSI)-LGLZO coating, and hybrid electrolyte layers of PEO-LiTFSI, PEO-LGLZO, and PEO-LiTFSI-LGLZO composites. Li//LiFePO4 (LFP) cells with various types of electrolytes are assembled, and their charge-discharge properties are investigated. The all-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell exhibits satisfactory charge storage performance, which has revealed potential for practical applications. (c) 2020 Elsevier Ltd. All rights reserved.
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
;
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.
Prior vacuuming for supercritical fluid synthesis of SnO2/graphene nanocomposites with superior electrochemical Li+ storage performance
(2018-12-01)
Xie, Jian-De
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Li, Hui-Ying
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Umesh, Bharath
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Lee, Tai-Chou
;
Chang, Jeng-Kuei
Supercritical CO2 (SCCO2) fluid, exhibiting gas-like diffusivity, extremely low viscosity, and near-zero surface tension, is used to synthesize uniformly dispersed and tightly anchored SO2 nanoparticles (a 3-nm diameter was achieved) on graphene nanosheets (GNSs). Usually, the conventional synthesis processes (in the absence of SCCO2) results in aggregated SnO2 clusters; whereas the technique described in this work eliminates this limitation. This study reveals the significance of two crucial factors (the SCCO2 pressure (i.e., fluid density) and the degassing step (i.e., vacuuming stage) in autoclave before injecting CO2) on the uniform distribution of the synthesized SnO2 nanoparticles on GNSs. Increasing the pressure leads to an increase in SCCO2 density (and viscosity), suppressing the transport of SnO2 precursors throughout the sample. On the other hand, vacuuming the autoclave before injecting CO2 improves the uniformity of SnO2 particle distributions. To assess the electrochemical performance of the synthesized nanoparticles, the specific capacity, rate capability, and cyclic stability were determined for various samples. A capacity of similar to 787 mAh g(-1) at 100 mA g(-1) was achieved for an optimal configuration of the SnO2/GNS electrodes. The capacity retention was 60% when the charge-discharge rate increased to 6000 mA g(-1). (C) 2018 Elsevier Ltd. All rights reserved.
Structural Evolution of a Na/NaFePO4 Sodium-ion Battery during Discharge Determined by in-situ Synchrotron X-ray Diffraction
(2015-06-01)
Huang, E-Wen
;
Wang, Yi-Chen
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Chang, Jeng-Kuei
;
Lee, Tai-Chou
;
Liao, Tzu-Kang
In this study, a newly-developed Na/NaFePO4 cell is studied. We charge the cell up to 2.4V and then apply in-situ synchrotron x-ray diffraction to resolve structural evolution during discharge. An intermediate of NaxFePO(4) diffracts strongest x-ray intensity among all the components of the cell, During discharging, several (hkl) planes of the NaxFePO(4) phase of the cathode are found to expand. The expansion of the cathode-lattice size suggests a Na-insertion mechanism. Upon the lattice expansion, a peak-profile analysis shows a correlation between the increase of the peak-intensity and the decrease of the peak-width evolution. The correlation suggests that there is more well-defined NaxFePO(4) formed during the discharge. Coupled with the Na insertion, the discharge of the Na/NaFePO4 cell shows a convolution of mechano-chemical reaction. Moreover, the time-resolved measurements reveal an asynchronous lattice-strain fluctuations within a stepwise discharge plateau.