John Muldoon

A “Gold Rush” for High Energy
Batteries
John Muldoon
Toyota Research Institute of North
America

Moving Away From Alloys: Towards Metal Anodes
9
8
Abundance
(ppb)
log
7
6
5
4
3
2
1
0
Li Na K Be Mg Ca Zn Al
Li Na K Be Mg Ca Zn Al
MW
(g/mol)
Density
(g/cm 3 )
6.94 23.0 39.1 9.01 24.3 40.1 65.4 27.0
0.53 0.97 0.86 1.85 1.74 1.55 7.14 2.7
A magnesium anode is very attractive due to high capacities, reductive potential
and abundance in the earth crust

Reduction at the Anode: the SEI
Li +
Li +
Mg 2+ Mg 2+
Mg 2+
Li + Li SEI conducts Li
+
Passivating layer
+
X
Li/C
Mg
• In contrast to Li, an SEI (solid‐electrolyte interface) on Mg precludes the
use of many electrolytes.
• Reversible Mg deposition can be observed in Grignard‐based electrolytes,
first shown by Overcash and Mathers in 1933.
Overcash, D. M.; Mathers, F. C. Trans. Electrochem. Soc. 1933, 64, 305.
Gregory, T. D.; Hoffman, R. J.; Winterton, R. C. J. Electrochem. Soc. 1990, 137, 775‐780.
Lu, Z.; Schechter, A.; Moshkovich, M.; Aurbach, D. J. Electroanal. Chem. 1999, 466, 203‐217.

Deposition at the Magnesium Anode
Highly dependent on
electrolyte
Lithium
SEM resolution: 5000X
Deposition rate: 2.0 mAcm −2
Magnesium
SEM resolution: 5000X
Deposition rate: 2.0 mAcm −2
Mg is less
reductive than Li =>
• Mg does not form SEI in ether solvents
• Mg does not form dendrites
Dey, A.N.; Sullivan, B.P. J. Electrochem. Soc. 1970, 117, 222
Matsui, M., J Pow. Sou. 2011, 196, 7048–7055
Gregory, T.D.; Hoffman, R.J.;Winterton, R.C. J. Electrochem. Soc. 1990, 137, 775

Mg Battery with Mg Organohaloaluminate Electrolytes
Anode: Mg metal
Cathode: Mg x Mo 3 S 4
Electrolyte: in situ generated Mg organohaloaluminate 2:1 Bu 2 Mg : AlClEt 2
• First demonstration of rechargeable Mg battery system:
•Proven >2000 cycle with

Roadblocks Towards a High Energy Magnesium Battery
Q
/
vol
V
(
q
)
dq
/
vol
[
WhL
0
1 ]
Increase voltage
Increase capacity
1) 2e ‐ transfer to the same metal center
dilithium in Li 2 NiO 2 , LiVSe 2 /Li 2 VSe 2
2) Facile solid state diffusion of magnesium in the cathode
3) High voltage, non‐corrosive electrolyte
Whittingham, S., Chem. Rev., 2004, 104, 4271‐4301.
Dahn, J.R, U. von Sacken, Michal, C.A, Sol. State. Ion., 1990, 44, 87‐97.

In Situ Generated Mg Organohaloaluminates
Black: 1:2 Bu 2 Mg and EtAlCl 2
Red: 1:2 AlCl 3 and PhMgCl
Bu 2 Mg + 2 EtAlCl 2
THF
Crystallization product was electrochemically inactive when re-dissolved in THF.
Aurbach, D et al, Nature, 2000, 407, 724‐727.
Aurbach, D et al, Chem. Record 2003, 3, 61‐73.
Aurbach, D et al, Adv. Mater., 2007, 19, 4260‐4267.

Crystallization of 1 st Generation Electrolyte
+
Si
THF
O
N
Si + AlCl 3
OMg
24 hrs
MgCl
O
Cl
Cl
Cl
O
Mg
O
O
Si Si
N Cl
Al
Cl Cl
HMDSMgCl
Kim, H.S.et HSetal. Nat. Commun. 2:427 doi: 10.1038/ncomms14351038/ncomms1435 (2011) .

Electrochemistry of crystal
crystal
In situ
electrolyte
HMDSMgCl
Formation of (Mg 2 (μ-Cl) 3·6THF)[(HMDS)AlCl 3 ]
HMDSMgCl + AlCl 3
→ MgCl + + HMDSAlCl 3
-
Transmetallation (1)
2HMDSMgCl HMDS 2 Mg + MgCl 2 Schlenk equilibrium (2)
MgCl + + MgCl 2
Mg 2
Cl 3
+
(3)
3HMDSMgCl + AlCl 3
→ Mg 2
Cl 3+ + HMDSAlCl 3- + HMDS 2
Mg (4)
• Transmetallation is key reaction in the formation of the product
• (Mg 2 (μ-Cl) 3·6THF) is the electrochemically active species

The Role of Frontier Orbitals in Electrochemistry of Electrolytes
Oxidation is the loss
of electron to HOMO
orbital
(eV)
Energy
Lowest Unoccupied
Molecular Orbital (LUMO)
Highest Occupied
Molecular Orbital (HOMO)
Reduction is the addition
of electron to LUMO
orbital
• Reductive stability may be predicted by calculating LUMO energy value
•Oxidative stability may be predicted by calculating HOMO energy value
More negative HOMO energy → higher oxidave stability
More posive LUMO energy → higher reducve stability

DFT Prediction of Electrochemical Properties
Table 1 Summary of HOMO and LUMO energy levels for the anion component of the
crystallized electrolytes. 20
Electrolyte Anion HOMO (eV) LUMO (eV)
1
2
J , mA/cm 2
*(HMDS) 2 AlCl 2
-
(HMDS)AlCl 3
-
15
10
5
0
-5
--- ---
-5.670 0.061
Ph - 4 Al -5384 -5.384 0182 0.182
Ph 3 AlCl - -5.678 0.047
Ph 2 AlCl 2
-
1 1.5 2 2.5 3 3.5 4 4.5
E , V vs Mg
-6.045 0.058
•Based on this logic, our DFT
calculations predict the
electrolyte order of oxidative
stability to be 4>2>1>3.
•Based on the assumption that
the HOMO energy level gap
between the (HMDS)AlCl 3‐ and
(HMDS) 2 AlCl 2‐ anions is similar to
the energy gap between PhAlCl ‐
3
and Ph 2 AlCl 2‐ anions.
-
Fig. 5 Linear PhAlCl scan 3 voltammograms -6.402 depicting typical -0.062 voltage stability of (Mg 2 (μ-
Cl 4 Al - -6.742 -1.384
Cl) 3·6THF)(HMDS n AlCl 4-n ) (n=1,2) (blue), (Mg 2 (μ-Cl) 3·6THF)(Ph n AlCl 4-n ) (n = 1 – 4)
(turquoise), (Mg 2 (μ-Cl) 3·6THF)(BPh 4 ) (red) and (Mg 2 (μ-Cl) 3·6THF)[B(C 6 F 5 ) 3 Ph] (green)
3 Ph 4 B - -4.819 -0.536
on a Pt working electrode with a surface area of 0.02 cm 2 . Scan rate for all scans is 25
mV s -1 ; magnesium reference and counter electrodes are used at a temperature of 21 °C.
4 (C 6 F 5 ) 3 BPh - -5.559 -0.422
*The structural flexibility of (HMDS) 2 AlCl 2 - makes its geometry difficult to optimize.

Problem Charging in a 2025 Coin Cell
• why cannot charge above 22V 2.2V
•voltage stability of gen1 on Pt working electrode (w. e.) is 3.2V

Voltage Stabilities of Gen 1 on Various Working Electrodes
20
15
SS Ni Pt C Au
A B
2
J , mA/cm
10
5
0
-5
1.5 2 2.5 3 3.5 4 4.5
E vs Mg, V
SEM of stainless steel before (A) and after (B)
exposure to 1 st generation electrolyte for 1 week
• Crystallized magnesium organohaloaluminates are corrosive in nature

Voltage Stabilities for Gen 2 Electrolyte
m 2
mA/c20
J ,
mA/cm 2
J ,
30
20
10
0
-10
Pt working electrode
1.25 1.75 2.25 2.75 3.25 3.75
15
E , V vs Mg
SS working electrode
10
5
0
-5
1.25 1.75 2.25 2.75 3.25 3.75
E , V vs Mg
3PhMgCl + BPh 3 → [Mg 2 Cl 3+ ][BPh4 ‐ ] + Ph 2 Mg
No pitting observed
• Causes an improvement of 400 mV in voltage stability
•Anion has dramatic effect on corrosion
Muldoon, et al, Energy and Environ. Sci., 2012. 5, 5941

Voltage Stabilities for Gen 3 Electrolyte
235
25
15
5
-5
J , mA/cm 2
235
25
, mA/cm 2
J
15
5
-5
Pt working electrode
1 2 3 4 5
E , V vs Mg
SS working electrode
Hysteresis
0 1 2 3 4 5
E , V vs Mg
3PhMgCl + B(C 6 F 5 ) 3 → [Mg 2 Cl 3+ ][B(C 6 F 5 )Ph 3‐ ]+ Mg(C 6 F 5 ) 2
•1.0V improvement in voltage stability on Pt w.e. : 3.7V
• Corrosion on SS limits potential window to 2.2V
Corrosion observed
Muldoon, et al, Energy and Environ. Sci., 2012. 5, 5941

Chlorine Free Magnesium Organoborates
Mixture and Filter
BPh 3 +Bu 2 Mg (BPh 3 Bu) 2 Mg Soluble in THF 0.4M
(BPh 3 Bu)2Mg (gen 4) THF

Electrolyte Preparation by Ion Switching
gen3
On SS316
gen1
gen2
genX
genX
• Solubility of genX is >0.5M in glyme
• Chlorides Are the Culprit of Corrosion
• Its reductive stability must be improved
Muldoon et al, Energy Environ. Sci., 2013, 6, 482–487

Membrane Encapsulated Sulfur Cathodes
membrane
0.1C ‐ membrane
Blue: 1C – membrane
Black: 1C –non‐membrane
Red: 5C – membrane
Improved lifetime and C – rates on encapsulation with a
selective membrane

Conclusions
Anion structure as well as
combination between cation
and anion strongly gyaffected
the oxidation stability and
corrosion of the electrolyte.
There is a need for
developing high dielectric
solvents with a higher
reductive stability such that
they are compatible with Mg