Title
Electronic effects of substituents on redox shuttles for overcharge protection of li-ion batteries
Advisor(s)
Kuzhikalail M. Abraham, Sanjeev Mukerjee
Contributor(s)
Max Diem, David E. Budil
Date of Award
4-2012
Date Accepted
4-2012
Degree Grantor
Northeastern University
Degree Level
M.S.
Degree Name
Master of Science
Department or Academic Unit
College of Science. Department of Chemistry and Chemical Biology.
Keywords
Ferrocene, Lithium Batteries, Overcharge Protection, Redox Shuttles
Disciplines
Chemistry | Materials Chemistry
Abstract
The redox behavior and kinetic parameters of five ferrocene derivatives were investigated in an electrolyte comprised of 1M LiPF6 in 50:50 volume percent EC:EMC (ethylene carbonate: ethyl methyl carbonate), a typical electrolyte used in lithium-ion batteries. Using cyclic voltammetry (CV) and rotating disc electrode voltammetry (RDE) techniques, the effect of electron donating and withdrawing substituents on each derivative was evaluated from the view point of the Hammett substituent constant. The reaction rate constants and exchange current densities were determined as a function of the Hammett constants. A useful comparison between two Hammett approaches, which was based on CV and RDE results, were established versus oxidation potential for each derivative. We found that electrochemical rate constants of the ferrocene derivatives can be related to the Hammett equation which gives an accurate approximation for predicting the oxidation potential of redox shuttles when changes are desired in their electron donating and electron withdrawing properties by means of functional group substitution. Our results show that the exchange current density and reaction rate for oxidation decrease as the electron withdrawing property of the substituent increases. It is also shown that electron donating and electron withdrawing properties of a substituent affect the exchange current density and electrochemical oxidation reaction rate obeying a trend opposite to that of the Hammett substituent constants (σ). The correlations found here are expected to improve the ability to systematically design chemical overcharge protection reagents through judicious substitution of functional groups on redox shuttles.
The first chapter provides an introduction to lithium ion (Li-ion) battery basics and its importance as an alternative renewable energy source to meet the global energy demand. After a brief, general, perspective on lithium battery principles, the first Chapter continues with a discussion of safety issues of Li-ion batteries. Finally, it ends with a discussion of the fundamental mechanism of overcharge protection of Li-ion batteries, along with theoretical aspects of chemical redox shuttles which are developed to overcome the overcharge-related safety concerns of these batteries.
Presented in the second chapter are experimental procedures employed in this work, followed by a detailed discussion of the results obtained from cyclic voltammetry and rotating disc electrode studies of redox shuttle reagents.
The final, third chapter, concludes with ramifications of this research and mentions a brief discussion of future research directions.
Document Type
Master's Thesis
Rights Holder
Mehmet Nurullah Ates
Permanent URL
Recommended Citation
Ates, Mehmet Nurullah, "Electronic effects of substituents on redox shuttles for overcharge protection of li-ion batteries" (2012). Chemistry Master's Theses. Paper 25. http://hdl.handle.net/2047/d20002720
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