batteries - icmab · • in contrast to li, an sei (solid‐electrolyte ... than ni cd and lead...
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A “Gold Rush” for High EnergyA “Gold Rush” for High EnergyA Gold Rush for High Energy A Gold Rush for High Energy Batteries ?Batteries ?
John MuldoonJohn Muldoon Toyota Research Institute of North
A iAmerica
Moving Away From Alloys: Towards Metal AnodesMoving Away From Alloys: Towards Metal Anodes
9
6
7
8
e (p
pb)
3
4
5
Abu
ndan
ce
0
1
2log
Li Na K Be Mg Ca Zn Al
Li Na K Be Mg Ca Zn Al
MWMW (g/mol) 6.94 23.0 39.1 9.01 24.3 40.1 65.4 27.0
Density (g/cm3) 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 SEIReduction at the Anode: the SEIReduction at the Anode: the SEIReduction at the Anode: the SEI
Mg2+ Mg2+
SEI conducts Li+
Li+
Li+
Li+
Passivating layer
Mg Mg2
Mg2+Li+ X
SEI conducts Li
Li/C
Li+ Passivating layer
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 electrolytesReversible 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 Deposition at the Magnesium AnodeMagnesium Anode
Highly dependent ong y pelectrolyte
MagnesiumLithium ag es uSEM resolution: 5000XDeposition rate: 2.0 mAcm−2
SEM resolution: 5000XDeposition 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, 222Matsui, M., J Pow. Sou. 2011, 196, 7048–7055Gregory, T.D.; Hoffman, R.J.;Winterton, R.C. J. Electrochem. Soc. 1990, 137, 775
g
Mg Battery with Mg Organohaloaluminate ElectrolytesMg Battery with Mg Organohaloaluminate Electrolytesg y g g yg y g g y
Cathode: MgxMo3S4Anode: Mg metal
Electrolyte: in situ generated Mg organohaloaluminate 2:1 Bu2Mg : AlClEt2
• First demonstration of rechargeable Mg battery system:• Proven >2000 cycle with <15% capacity fade, 100% DOD, ‐20~80oC • Proposed as a potentially higher energy battery than Ni Cd and lead acid batteries
Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Nature 2000, 407, 724‐727.
• Proposed as a potentially higher energy battery than Ni‐Cd and lead‐acid batteries
Roadblocks Towards a High Energy Magnesium Roadblocks Towards a High Energy Magnesium BatteryBattery
Q
WhLvoldqqVvol 1][/)(/ WhLvoldqqVvol0
][/)(/
1) 2e‐ transfer to the same metal center
Increase voltage Increase capacity
dilithium in Li2NiO2, LiVSe2/Li2VSe2
2) Facile solid state diffusion of magnesium in the cathode) g
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 OrganohaloaluminatesIn Situ Generated Mg Organohaloaluminates
Black: 1:2 Bu2Mg and EtAlCl2Black: 1:2 Bu2Mg and EtAlCl2Red: 1:2 AlCl3 and PhMgCl
THFBu2Mg + 2 EtAlCl2Bu2Mg + 2 EtAlCl2
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 1Crystallization of 1stst Generation ElectrolyteGeneration Electrolyteyy yy
O MgO
Cl Mg
Cl
OO
+
NClSiSiTHF
NSiSi
+ AlCl3 gO
g
Cl O AlCl Cl
Cl24 hrs
NMgCl
3
HMDSMgCl
Kim H S et al Nat Commun 2:427 doi: 10 1038/ncomms1435 (2011)Kim, H.S.et al. Nat. Commun. 2:427 doi: 10.1038/ncomms1435 (2011) .
Electrochemistry of crystalcrystal
In situelectrolyte
HMDSMgCl
Formation of (Mg (μ Cl) 6THF)[(HMDS)AlCl ]HMDSMgCl + AlCl3 → MgCl+ + HMDSAlCl3- Transmetallation (1)
2HMDSMgCl HMDS2Mg + MgCl2 Schlenk equilibrium (2)
Formation of (Mg2(μ-Cl)3·6THF)[(HMDS)AlCl3]
2HMDSMgCl HMDS2Mg + MgCl2 Schlenk equilibrium (2)
MgCl+ + MgCl2 Mg2Cl3+ (3)
3HMDSMgCl + AlCl3 → Mg2Cl3+ + HMDSAlCl3- + HMDS2Mg (4)g 3 g2 3 3 2 g ( )
• Transmetallation is key reaction in the formation of the product• (Mg2(μ-Cl)3·6THF) is the electrochemically active species
The Role of Frontier Orbitals in Electrochemistry of ElectrolytesThe Role of Frontier Orbitals in Electrochemistry of ElectrolytesThe Role of Frontier Orbitals in Electrochemistry of ElectrolytesThe Role of Frontier Orbitals in Electrochemistry of Electrolytes
(eV)
Lowest Unoccupied ( )
Reduction is the addition of electron to LUMO
Oxidation is the loss of electron to HOMO
Energy
Molecular Orbital (LUMO)
Highest Occupied Molecular Orbital (HOMO)
of electron to LUMOorbital
of electron to HOMOorbital
• 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 oxida ve stabilityMore posi ve LUMO energy → higher reduc ve stability
DFT Prediction of Electrochemical PropertiesDFT Prediction of Electrochemical Properties
Table 1 Summary of HOMO and LUMO energy levels for the anion component of the
crystallized electrolytes. 20Electrolyte Anion HOMO (eV) LUMO (eV)
*(HMDS)2AlCl2- --- ---
11015
mA
/cm
2• Based on this logic, our DFT calculations predict the electrolyte order of oxidative
(HMDS)AlCl3- -5.670 0.061
Ph4Al- -5 384 0 182505
J, m
stability to be 4>2>1>3.
• Based on the assumption that
Ph4Al -5.384 0.182
Ph3AlCl- -5.678 0.047
Ph2AlCl2- -6.045 0.058 2
-51 1.5 2 2.5 3 3.5 4 4.5
E , V vs Mgthe HOMO energy level gap between the (HMDS)AlCl3‐ and (HMDS)2AlCl2‐ anions is similar to h b PhAlCl
PhAlCl3- -6.402 -0.062
Cl4Al- -6.742 -1.384
Fig. 5 Linear scan voltammograms depicting typical voltage stability of (Mg2(μ-
Cl)3·6THF)(HMDSnAlCl4-n) (n=1,2) (blue), (Mg2(μ-Cl)3·6THF)(PhnAlCl4-n) (n = 1 – 4)
the energy gap between PhAlCl3‐and Ph2AlCl2‐ anions.
3 Ph4B- -4.819 -0.536
(turquoise), (Mg2(μ-Cl)3·6THF)(BPh4) (red) and (Mg2(μ-Cl)3·6THF)[B(C6F5)3Ph] (green)
on a Pt working electrode with a surface area of 0.02 cm2. Scan rate for all scans is 25
4 (C6F5)3BPh- -5.559 -0.422
*The structural flexibility of (HMDS)2AlCl2- makes its geometry difficult to optimize.
mV s-1; magnesium reference and counter electrodes are used at a temperature of 21 �°C.
Problem Charging in a 2025 Coin CellProblem Charging in a 2025 Coin Cell
• why cannot charge above 2 2V?• why cannot charge above 2.2V?
• voltage stability of gen1 on Pt working electrode (w. e.) is 3.2V
Voltage Stabilities of Voltage Stabilities of Gen 1 Gen 1 on Various Working Electrodes on Various Working Electrodes
20
15
2
NiSS Pt CAu
A B5
10
J, m
A/c
m
-5
0
SEM of stainless steel before (A) and after (B)
51.5 2 2.5 3 3.5 4 4.5
E vs Mg, V( ) ( )
exposure to 1st generation electrolyte for 1 week
• Crystallized magnesium organohaloaluminates are corrosive in nature
Voltage Stabilities for Voltage Stabilities for Gen 2 Gen 2 ElectrolyteElectrolyte
2030
m2
Pt working electrode
3PhMgCl + BPh3 → [Mg2Cl3+][BPh4‐] + Ph2Mg
100
1020
J, m
A/c
g
-101.25 1.75 2.25 2.75 3.25 3.75
E , V vs Mg
J
15SS ki l d
, g
05
10
mA
/cm
2 SS working electrode
-50
1.25 1.75 2.25 2.75 3.25 3.75
J,
E , V vs Mg
C i t f 400 V i lt t bilit
No pitting observed
• Causes an improvement of 400 mV in voltage stability
Muldoon, et al, Energy and Environ. Sci., 2012. 5, 5941
• Anion has dramatic effect on corrosion
Voltage Stabilities for Voltage Stabilities for Gen 3 Gen 3 ElectrolyteElectrolyte
352 Pt working electrode
3PhMgCl + B(C6F5)3 → [Mg2Cl3+][B(C6F5)Ph3‐]+ Mg(C6F5)2
51525
J, m
A/c
m2 Pt working electrode
-51 2 3 4 5
E , V vs Mg
J
352 SS ki l d
5152535
, mA
/cm
2 SS working electrode
Hysteresis-5
0 1 2 3 4 5E , V vs Mg
J
y
• 1.0V improvement in voltage stability on Pt w.e. : 3.7V
Corrosion observed• Corrosion on SS limits potential window to 2.2V
Muldoon, et al, Energy and Environ. Sci., 2012. 5, 5941
Chlorine Free Magnesium OrganoboratesBPh +B M (BPh B ) M
Mixture and FilterBPh3 +Bu2Mg (BPh3Bu)2Mg Soluble in THF <0.1M
Gen 4
THFBPh3 +Ph2Mg (BPh4)2MgTHF
Electrolyte Solvent Solubility
[Mg2Cl3+][BPh4‐] (gen 2) THF >0.4M
(BPh3Bu)2Mg (gen 4) THF <0.1M
(BPh4)2Mg (gen 5) THF <0.01M
(BPh4)2Mg (gen 5) Acetone >0.5MGen 5
16Chlorine free magnesium organoborates lack adequate solubility in low dielectricSolvents compatible with Mg such as THF
Electrolyte Preparation by Ion Switching y p y g
gen3On SS316
gen2gen1
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
Bl 1C bBlue: 1C – membrane Black: 1C – non‐membraneRed: 5C – membrane 0.1C ‐membrane
Improved lifetime and C – rates on encapsulation with a selective membrane