Electrochemical Investigation Chem 157.1

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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.