Ionic electrolytes for Lithium Batteries

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