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8/7/2019 Electrochemical Investigation Chem 157.1
http://slidepdf.com/reader/full/electrochemical-investigation-chem-1571 1/18
Journal of Applied Electrochemistry
Electrochemical Investigation of Li-Al Anodes inoligo(ethylene glycol) dimethyl ether, LiPF6
Y.N. Zhou, et. al.
Tan, Elaine D.
January 20, 2011
Chem 157.1 – Physical Chemistry II Lab
Professor Geoffrey C. Li
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Objectives
General Objectives:To investigate on OEGDME500, 1 M LiPF6 as anew electrolyte for metal deposition andbattery applications
Specific Objectives:To usea.) conductivity,b.) electrochemical stability and,
c.) Li deposition and dissolution at Al as thethree main criteria for the investigation.
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Batteries
• One or more electrochemical cells
• Chemical energy electrical energy
• Has a number of voltaic cells
• 1 voltaic cell has 2 half-cells
• Half-cell 1: anode (+ to -) & electrolyte
• Half-cell 2: cathode (- to +) & electrolyte
Thus, to make batteries work, you need electrolytes –substances that contain free ions to make a substanceelectrically conductive.
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Solvent: OEGDME
• High boiling point
• High electrochemical stability• OEGDME250: commercially available;
but immiscible with LiPF6
OEGDME500
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Experimental
1. Electrolyte preparation
2. Conductivity measurements
3. Electrochemical experiments4. In situ XRD measurements
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Experimental 1. Electrolyte Preparation:
LiPF6 added to OEGDME500,
shaken from time to time untildissolved. (3-4 days)
*Kept for 3 weeks.
2. Conductivity Measurements
*conductivity: the measure of anelectrolyte to conduct electricity
*unit: Siemens/meter or S/m
*determined using resistance of solutionbetween two electrodes
- Electrodes used: Pt electrodes
- Standard used: 0.01 M KCl (aq.)
- Cell constant was determined
Determining conductivity:
Theoretical Approach:
Experimental Approach:
Relationship of Resistance &Conductivity:
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Experimental3. Electrochemical Experiments
(Cyclic Voltammetry)*In cyclic voltammetry, electrode potential is ramped linearly
versus time; called the experiment’s scan rate (V/s).
*Potential: Applied bet. R and W.
*Current: Measured bet. W and C.
*Plot: Current (i) vs. Potential (E)
Electrode Thickness (mm) Type
Al 0.25 Working
Li 0.25 Counter
Cu n/a Reference3a. Small Electrodes
(Three – Electrode System)
3b. Large Electrodes
(Three – Electrode System)
Electrode Surface (cm2) Type
Al 0.05 Working
Pt 0.05 Counter
Ag/AgCl 0.005 Reference
4. XRD Measurements
*XRD: used to determinecrystallographic structure
*In this experiment, used to determinethe formation of an Li-Al alloy.
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Concept Review: Electrodes
Three – Electrode System
a. Working Electrode
- makes contact with the analyte
- is where desired potential is applied to, to facilitate transfer of charge
b. Counter Electrode
- allows potential of working electrode to be measured against aknown reference electrode without compromising the stability of that electrode
c. Reference Electrode
- has a known reduction potential
- does not pass any current
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Results:
A. Conductivity of the Electrolyte
0
0.5
1
1.5
2
2.5
3
3.5
4
25 45 65 85
Plot of Conductivity vs.Temperature
C
ondu
ctivity(S
x10
-
3
/cm)
Temperature (0C)Criticism:
Literature values of attractive conductivity ranges were not provided.
Significance:
-The temperature-dependent conductivity shown is attractive, ascompared toconventionalelectrolytes.
-Allows operatingtemperature above 1000C.
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ResultsB. Electrochemical Stability of the
Electrolyte (Using Cyclic Voltammetry)Scan Rate: 0.5 mV/s
Window of Electrochemical Stability: 5.3 V
Potential Region: -3.3 V to 2.5V
*Forward Scan: Producescurrent peak, increasesthen fields off
*Reverse Scan: Produces
current that will re-oxidizeelectrolyte
Cyclic Voltammogram of Small Al Electrode in
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ResultsB. Electrochemical Stability of the
Electrolyte (Using Cyclic Voltammetry)Significance:Large window of electrochemical stability stable electrolyte.
Minor anodic current was shown stable electrolyte.
Criticism:Literature values for the window of electrochemical stabilities of commonly-used electrolytes were not provided.
Text says that potential region is from -3.3 V to 2.5 V, graph shows that potential region is from -3.3 V to 2.0 V.
Window is 5.3 V, meaning to say that there is probably a typographical error in the text.
Window was described only for small electrodes; was not described for large electrodes because window for
large electrodes is relatively small.
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ResultsC. Lithium Deposition and Dissolution at Al Electrodes
C-1. Cyclic Voltammogram for the Small Electrode
During the back scan, the current crossed zero.
Inference:
The Al electrode (working) is acting like a Li electrode (counter). Thus,not all of the Li deposited was alloyed.
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ResultsC. Lithium Deposition and Dissolution at Al Electrodes
C-2. Cyclic Voltammogram for the Large Electrode
Two cycles were conducted.
The current did not cross zero at all.
Shows that at 0.2 mV/s, the all the Li deposited was alloyed.
Scan Rate: 0.2mV/s
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ResultsC. Lithium Deposition and Dissolution at Al
ElectrodesCriticisms:• Inconsistencies:
Number of Cycles
Scan Rate
(mV/s)
Window
(V)
Small 1 0.5 5.3
Large 2 0.2 Omitted, notmentioned.
From thegraph: 2.75
Criteria
Sizeo
fAlEle
ctrode
These inconsistencies in the experiment areunjustifiable.
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Results:
D. XRD Measurements
Graph shown Is similar to that formed by AlLialloy.
Inference:
Alloy formed is AlLi.
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Results
E. Potentiostatic Measurements
Time: 35 hours
Mol of Li: 0.93 x 10-4
Mol of Al: 2.5 x 10
-4
Stoichiometry: Al3Li
Result of potentiometric measurements does not agree withthat of XRD measurements.
Potentiostatic measurements were not described in theExperimental section of the article.
Stoichiometry of the alloy formed cannot be inferred.
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Conclusion
Although the OEGDME500, LiPF 6has
electrolytic properties such as highboiling point, attractive conductivity
and high stability, further researchmust be conducted due to the
inconsistencies and omissions found
in this research article.