1. Understanding the Enhanced Mg2+ Intercalation
Kinetics Originating from Water Co-Intercalation
Anthony Rock, Seattle University, BSME
University of
Maryland
Chemical
Engineering
Department
TE 2015
REU FAIR
Background
Modeling Batteries with
Equivalent Circuits
 Discharge/Charge
 Flow of negatively-charged electrons
balanced by flow of positively charged ions
 Intercalation
 Ions insert themselves into vacancies in the
anode/cathode material
 Space must accommodate for physical
size of ions and strength of charge
Image Source: Nazri and Pistoia, Eds., Lithium Batteries: Science and Technology,
New York: Springer Science+Business Media, LLC, 2003.
Why Magnesium?
 Alternatives:
 Group 1 Elements: Lithium, Sodium, Potassium
 Pros: Low Molar Mass
 Cons: 1-Electron Charge Transfer
 Group 2 Elements: Magnesium & Calcium
 Pros: 2-Electron Charge Transfer
 Cons: Insertion & Kinetics Issues due to strong
charge
Future Work
Acknowledgments
The sincerest thanks must be given to Tao Gao for his
immense contributions of knowledge and time, without
which this work would not be possible.
This work has been supported through the National
Science Foundation grant number EEC 1263063, REU
Site: Summer Engineering Research Experiences in
Transportation Electrification, which is gratefully
acknowledged.
1. Test electrolytes other than propylene carbonate (PC)
2. Find electrolyte compatible with both anode and
cathode
3. Examine impact of water on diffusional impedance
4. Test reversibility of aqueous electrolytic systems
5. Perform rate-limiting step analyses for all electrolytes
6. Maximize cycling with aqueous electrolytes
Results of EIS Tests
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
ZReal
(k)
PC @ 29C
PC-6H2O @ 25C
-ZImag
(k)
2.52 Hz
5.01 Hz
100 kHz
 Diameter of circle is proportional to charge transfer
resistance
 One Order of Magnitude Less when electrolyte
contained water
Image Source: Unpublished work of research paper.
R3
CPE2
CPE1
R1 W1
Element Freedom Value Error Error %
R3 Free(±) 82.8 0.13725 0.16576
CPE2-T Free(±) 1.1772E-6 1.3807E-8 1.1729
CPE2-P Fixed(X) 0.6 N/A N/A
CPE1-T Free(±) 9.4177E-6 6.074E-8 0.64496
CPE1-P Free(±) 0.84492 0.00094496 0.11184
R1 Free(±) 3079 12.469 0.40497
W1-R Free(±) 1.4552E6 1.1004E11 7.5618E6
W1-T Free(±) 256.6 2.1696E7 8.4552E6
W1-P Free(±) 0.8945 0.0040482 0.45257
Mg2+
Electrolytic
Resistance
Pseudo-
Capacitance
Double Layer
Capacitance
Charge
Transfer
Resistance
Diffusion
Element
2e-
(Electrode-Electrolyte
Interface)
O
46%
Si
28%
Al
8%
Fe
6%
Mg
4%
Others
8%
ELEMENTAL ABUNDANCE
IN EARTH'S CRUST
0
500
1000
1500
2000
2500
3000
3500
4000
Li Graphite
(LiC6)
Mg
TheoreticalCapacity
mAh/g mAh/cc
 Left Parallel Circuit
 Mg can either
 Proceed through electrolyte
 Stay on electrode to create capacitor
 Electrode-Electrolyte Interface
 Mg can either
 Stay in electrolyte to create capacitor
 Intercalate into electrode
How to Build a Battery
Attach
Cathode
Wear
Gloves!
Attach
Anode
Fill 10 mL
Beaker with
Electrolyte
Connect to
Load