Electrochemistry and Battery Research

Introduction

• Electrochemistry: Study of chemical reactions involving electron transfer
• Importance: Used in battery materials research

Basics of Electrochemistry

Key Reactions

• Oxidation: Loss of electrons (e.g., Metal 2+ -> Metal 3+)
• Reduction: Gain of electrons (e.g., Metal 2+ -> Metal 1+)
• Redox Reactions: Combination of oxidation and reduction reactions

Example Reactions

• Oxidation of Iron: Fe + O2 -> FeO
• Reduction of Oxygen: O2 + 4e- -> 2O2-
• Conditions affecting reactions: Oxygen content, temperature, presence of water, acidity

Non-Redox Reaction Example

• Precipitation Reaction: No electron transfer
• Example: Iron compounds in the presence of a base (e.g., ammonium hydroxide) form spinel oxides

Measuring Electrochemical Reactions

Standard Reduction Potential

• Lists species based on their reduction potential
• Higher reduction potential species are lower on the list (e.g., Lithium has low reduction potential)
• Standard Hydrogen Electrode (SHE): Reference point for measuring potentials

Practical Measurement

• Use inert electrodes (e.g., platinum) and standard electrodes (e.g., SHE)
• Open Circuit Voltage: Ideally, no current should flow during measurement

Gibbs Free Energy and Cell Potential

• Positive cell potential means thermodynamic driving force for the reaction
• G (Gibbs Free Energy) related to E (cell potential)

Setup Examples

• Single solution setup: Hard to measure, reactions happen at electrode interface
• Two-cell setup: Measure potential using reference electrodes separated by a salt bridge

Three-Electrode Cell

• Working Electrode: Where desired reaction happens
• Reference Electrode: Measures potential against working electrode
• Counter Electrode: Balances the reaction by giving or taking electrons

Diagrams in Electrochemistry

Pourbaix Diagram

• Shows stable species at given pH and reduction potential

Ellingham Diagram

• Used for metallurgy to determine reducing agents for metal oxides

Basics of Batteries

Essential Parts

• Cathode, Anode, Electrolyte: Main components
• Separator: Prevents the anode and cathode from touching
• Non-aqueous Systems: Use organic solvents

Key Definitions

• Capacity: Number of electrons transferred (measured in Coulombs, Amp-hours)
• Energy: Product of capacity and voltage
• Power: Energy transferred over time

Charge Storage Mechanisms

Intercalation

• Insertion/removal of ions without significant structure change (e.g., graphite)

Conversion

• Breakdown of initial material to form a significantly different structure (e.g., SnO2 to Sn)

Alloying

• Formation of alloy with lithium (e.g., Silicon)
• Issues: Significant volume change leading to mechanical deformation

Battery Testing

Setup for Research

• Mixing active material, carbon, and binder to form the electrode
• Electrode assembly in an argon glovebox

Common Tests

Cyclic Voltammetry

• Controls voltage, measures current
• Determines at what voltage different redox reactions occur

Galvanostatic Cycling

• Controls current, measures voltage
• Shows capacity and voltage profile over cycles

Rate Stability Testing

• Measures capacity and performance at different current rates

Practical Considerations

• Inert electrodes, maintaining charge neutrality, electrolyte selection

Conclusion

• Overview of electrochemistry and its role in battery research
• Various tests and practical aspects of studying battery materials