ionic electrolytes for lithium batteries
DESCRIPTION
Una plática que dí hace varios años en una serie de conferencias Alessandro Volta en México DFTRANSCRIPT
Characterization of Transport Propertiesof Lithium Electrolytes
Marcelo VideaDepartment of ChemistryITESM Campus monterret
Ciudad de México, 4 de agosto de 2005
Seminarios Alessandro Volta
• Introduction
• Characteristics of an ideal electrolyte
• Classification of lithium electrolytes
• Transport properties of electrolytes
• Concluding remarks
Energy storage devices:Secondary batteries
Mitsubishi Eclipse
Lithium batteries:Chemical thermodynamics
Li metalAnode
Cathode
Carbon
Battery under discharge:voltamperometric characteristic
Electrochemical stability
the electrolyte has to be stable against the presence of strongly oxidizing and reducing agents, i.e., cathode and anode materials, respectively.
Electrochemical window > 4.5V
Characteristics of an ideal electrolyte
Characteristics of an ideal electrolyte
High ionic conductivity (σ)
limiting value > 10-3 Scm-1
1.5x10-3 Scm-1
l=100 µmA=100 cm2
R=17 mΩ
Transfer number (tLi+≈1)
Characteristics of an ideal electrolyte
Classification of lithium electrolytes
Transport properties of electrolytesConductivity measurements
Impedance spectroscopy analysis
Conductivity:LiAlCl4-LiIm
Ionic conductivity vs. Temperature:Vogel-Fulcher-Tamman equation
Conductivity vs. Fluidity
fluidity
Angell’s Decoupling Index, R*τ
Structural relaxation time
Ionic relaxation time
At the glass transition temperature
C.A. Angell (1983) Solid State Ionics 9/10, 3
Índice de desacoplamiento, R*τ y transición vítrea
Phase Diagram for Ionic systemsDTA, DSC
Results
Binary systems:LiAlCl4-LiIm
Binary Ionic Liquid:LiAlCl4-LiImAlCl3
Composition region Non-crystallizingIonic system
Conductivity measurements:LiAlCl4-LiImAlCl3
Decoupling Index:LiAlCl4-LiImAlCl3
Interpretation of the results in terms of ionic percolation in a two phase system
Self-Diffusivity Measurements for
7Li
Measurement of Lithium self-diffusionPulsed Field Gradient - NMR
Chemagnetics (7 Tesla)
Spin Echo program
Study of LiAlCl4-LiAlI4
Low temperature behaviour
Conclusions
• The use of binary and ternary systems proves to be a useful strategy in the preparation of glass-forming ionic liquids.
• Tg y Rτ are parameters that characterize the mechanical properties of an ionic electrolyte.
• In the system LiAlCl4-LiImAlCl3 both the phenomenon of double glass transition as the sudden increase in the Rτ value serve as evidence to argue for the existence of two immiscible liquid phases.
• The ratios σcalc/ σexp are in a first approximation a measure of the number of transfer. However, in LiAlCl4 y and in the eutectic LiAlCl4-LiAlI4 , tLi+ ≈1.
Acknowledgements
Fondo de investigación DOE (DEF9039ER45541 )Moltech Corp. Dr. C. Austen AngellDr. Eduardo SánchezDr. Xu Kang