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Exploration of Electrolytes for Zn Anode Rechargeable Batteries: Room Temperature Ionic Liquids as Major or Supporting Components Open Access

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Other title
Subject/Keyword
Battery Electrolytes
Room Temperature Ionic Liquids
Zn Anode Rechargeable Batteries
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Xu, Min
Supervisor and department
Ivey, Douglas (Chemical and Materials Engineering)
Examining committee member and department
Luo, Jingli (Chemical and Materials Engineering)
Mar, Arthur (Chemistry)
Liu, Qi (Chemical and Materials Engineering)
Chung, Hyun-Joong (Chemical and Materials Engineering)
Ivey, Douglas (Chemical and Materials Engineering)
Sharp, David (Chemical and Materials Engineering)
Chen, Zhongwei (ext reader, Chemical Engineering, University of Waterloo)
Department
Department of Chemical and Materials Engineering
Specialization
Materials Engineering
Date accepted
2014-08-27T14:14:01Z
Graduation date
2014-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
For Zn anode rechargeable batteries, there are a number of shortcomings associated with using traditional KOH aqueous electrolytes. These include drying-out of the electrolyte due to water evaporation and dendrite formation at the Zn electrode during recharging, which severely impair battery performance (e.g., cycle life and capacity) and limit their application. In particular, to solve the problem of dendrite formation that could cause short-circuit issues, many attempts have been made to modify the Zn electrode and the electrolyte, as well as to choose a desirable and robust separator. However, no breakthrough has been achieved on the basis of conventional KOH aqueous electrolytes. It is, therefore, critical to either modify conventional KOH aqueous electrolytes or explore alternative electrolytes to eliminate these bottlenecks to the development of a feasible Zn anode rechargeable battery system. Room temperature ionic liquids (RTILs) in recent years have been increasingly recognized as potential electrolytes or electrolyte components for rechargeable batteries. Applying non-volatile RTILs as electrolytes provides potential benefits of achieving a longer service life, as drying out due to water evaporation is no longer a problem. Furthermore, RTILs demonstrate the capacity to modify metal deposit morphology, which may contribute greatly to preventing Zn dendrite formation and improving battery cycle life. On the other hand, compared with alkaline electrolytes, a simple electrolyte system composed of an RTIL as the sole component faces the challenge of enhancing its low conductivity (one to two orders of magnitude lower than aqueous electrolytes) before it can be practically applied in a battery. With the purpose of developing electrolyte systems that can harness the benefits from both RTILs (Zn morphology control) and aqueous electrolytes (rapid Zn redox kinetics), two groups of electrolytes are investigated in this study. One is based on RTILs, composed of pyrrolidinium or imidazolium cations and bis(trifluoromethanesulfonyl)imide or dicyanamide anions, with the incorporation of diluents (water and/or dimethyl sulfoxide (DMSO)). Another one adopts RTILs as additives to modify conventional KOH aqueous electrolytes. A larger portion of this work was focused on the former group. By applying cyclic voltammetry (CV), potentiodynamic polarization and chronoamperometry (CA), the kinetics, reversibility and cyclability of Zn redox behavior is explored in the studied electrolytes. The morphology of Zn deposits is observed and analyzed using scanning electron microscopy (SEM). With respect to RTIL-based electrolytes, conductivity measurements, together with Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and gas-phase density functional theory (DFT) are performed to investigate water interaction with RTIL ions and to shed light on the mechanisms for improved Zn redox behavior with water addition. For RTIL-based electrolytes, to balance the pros (improved electrolyte conductivity and Zn redox kinetic performance) and cons (reduced electrochemical stability of RTILs) of adding diluent(s) is of great importance in the development of workable electrolyte systems. Among six kinds of studied RTILs, i.e., 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (BMP-TFSI), 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPrP-TFSI), 1-methyl-1-pentylpyrrolidinium bis(trifluoromethanesulfonyl)imide (MPP-TFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMI-TFSI), 1-butyl-1-methylpyrrolidinium dicyanamide (BMP-DCA) and 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA), an electrolyte system composed of EMI-DCA with the addition of both water and DMSO at a mole ratio of EMI-DCA:H2O:DMSO = 1:1.1:2.3 exhibits the best performance in terms of electrolyte conductivity, electrochemical properties for Zn redox reactions and Zn deposit morphology. For conventional alkaline aqueous electrolytes, adding an appropriate RTIL as the electrolyte additive can effectively eliminate Zn dendrite formation during electrodeposition. It is worth noting that hydrophilic RTILs are better relative to hydrophobic RTILs when it comes to obtaining desirable Zn morphologies and preventing dendritic Zn formation. An electrolyte composed of 9.0 M KOH + 5.0 wt% ZnO with a hydrophilic RTIL, i.e., 0.5 wt% EMI-DCA, appears to be a promising electrolyte system. These results give insights into developing novel alkaline aqueous electrolytes, which are deliberately modified with hydrophilic RTILs, for Zn anode rechargeable batteries.
Language
English
DOI
doi:10.7939/R39882W1D
Rights
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
Citation for previous publication
M. Xu, D.G. Ivey, Z. Xie, W. Qu, Electrochemical behavior of Zn/Zn(II) couples in aprotic ionic liquids based on pyrrolidinium and imidazolium cations and bis(trifluoromethanesulfonyl)imide and dicyanamide anions, Electrochimica Acta 89 (2013) 756-762.M. Xu, D.G. Ivey, W. Qu, Z. Xie, Y. H. Bing, Cyclic voltammetry of Zn/Zn(II) couple in dicyanamide anion and bis(trifluoromethanesulfonyl)imide anion based ionic liquids, ECS Transactions, 50 (25) 13-22 (2013).M. Xu, D.G. Ivey, Z. Xie, W. Qu, E. Dy, The state of water in 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide and its effect on Zn/Zn(II) redox behavior, Electrochimica Acta, 97 (2013) 289-295.M. Xu, D.G. Ivey, W. Qu, Z. Xie, E. Dy, X. Z. Yuan, Zn/Zn(II) redox kinetics and Zn deposit morphology in water added ionic liquids with bis(trifluoromethanesulfonyl)imide anions, Journal of The Electrochemical Society, 161 (1) A128-A136 (2014).M. Xu, D.G. Ivey, W. Qu, Z. Xie, X. Z. Yuan, The effect of water addition on Zn/Zn(II) redox reactions in room temperature ionic liquids with bis(trifluoromethanesulfonyl)imide anions, ECS Transactions, 53 (36) 41-50 (2013).M. Xu, D.G. Ivey, W. Qu, Z. Xie, Improved Zn/Zn(II) redox kinetics, reversibility and cyclability in 1-ethyl-3-methylimmidazolium dicyanamide with water and dimethyl sulfoxide added, Journal of Power Sources, 252 (2014) 327-332.M. Xu, D.G. Ivey, W. Qu, Z. Xie, E. Dy, Exploration of electrolytes for Zn-anode rechargeable batteries: room temperature ionic liquids as major or supporting components, in: Ionic liquids: synthesis, characterization and applications, A. Brooks (Eds.), Nova Science Publishers, Inc., 2014, pp. 99-123.

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