Electron Paramagnetic Resonance (EPR) was used to examine lithiated silver vanadium oxide battery materials. EPR can detect unpaired electrons and provide evidence of free radicals. Samples of pure, lithiated, and highly lithiated silver vanadium oxide were tested, and results supported the hypothesis that EPR signals decrease with increased lithium content, corresponding to lower battery capacity. EPR is a technique that can examine battery materials and discharge mechanisms at a microscopic level to help develop higher performance batteries.

1. Electron ParamagneticElectron Paramagnetic
Resonance at Hunter CollegeResonance at Hunter College
Makia Hughes
John F. Kennedy High School
Physics Department, Hunter College of Solid State NMR/EPR Lab
EPR measurements of Lithiated Silver Vanadium Oxide
Dr. John Flowers, Professor of Chemistry at Medgar Evers College of
CUNY

2. Our GoalOur Goal
To use EPR to examine and confirm the
mechanisms of discharge in a Sulfur
Vanadium Oxide (SVO) battery in order to
develop higher quality batteries.

3. What is EPR?What is EPR?
 Electron Paramagnetic Resonance also known as Electron Spin
Resonance is a spectroscopic technique which detect species that have
unpaired electrons.
 A surprisingly large number of materials have unpaired electrons.
(examples: free radicals and many transition metal ions)
 EPR alone yields inconvertible evidence of free radicals and has the
unique power of identifying the paramagnetic species.
Emblem of the
Society of Free
Radical Research

4. EPR InstrumentsEPR Instruments
 The EPR Spectrometer consists of many different components.
– Microwave Bridge: Electromagnetic Radiation Source
– Microwave Cavity: Amplifies weak signals from the sample
– Magnet: Splits the electronic spin energy levels
– Console: Contains signal processing and control electronics and a
units for
acquiring a spectrum
– Computer: Used to analyze data as well as coordinating all the units
for acquiring a spectrum.

5. How does EPR Work?How does EPR Work?
 Like a proton, an electron has a spin, which gives it a magnetic
property known as a magnetic moment.
 When an external magnetic field is supplied, the paramagnetic
electrons can either orient in a direction parallel or antiparallel to the
direction of the magnetic field .
 This creates two distinct energy levels for the unpaired electrons and
measurements are taken as they are driven between the two levels.

6. EPR SpectroscopyEPR Spectroscopy
 EPR spectroscopy is the measurement and interpretation of the energy
differences between the atomic or molecular states.
– These measurements are obtained because the relationship between the
energy differences and the absorption of electro-magnetic radiation.
– To acquire a spectrum, the frequency of the electromagnetic radiation is
changed and the amount of radiation which passes through the sample
with a detector is measured to observe the spectroscopic absorptions

7. EPR ResultsEPR Results
 4 Samples Tested
– 1) Pure SVO- Gives EPR signal due
to the paramagnetism
of SVO; High Q value
– 2) Li0.72Ag2V4O11 Weak or No EPR signal;
Lower Q value
– 3) Li2.13Ag2V4O11 Weak or No EPR signal;
Lower Q value
– 4) Li5.59Ag2V4O11 Definite EPR Signal;
Lower Q value
 Supports our Hypothesis