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International Battery Seminar | Fort Lauderdale, FL | Mar 22, 2017
Feng LinDepartment of Chemistry
Virginia Tech
Controlling the Surface Chemistry of Cathode Materials for Manufacturing High-Energy Rechargeable Batteries
CHARGING UP THE WORLD
2
Lemon Battery
Approximately 6, 000, 000 lemons to give a power of a car batteryApproximately 5, 000, 000, 000 lemons to power a Tesla Model S at its acceleration
Zn anode Cu anode
_ +Separator
𝐸𝐸𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = 𝐸𝐸°[0.337 𝑉𝑉] + 𝑅𝑅𝑅𝑅𝑧𝑧𝑧𝑧
ln 𝑐𝑐𝑜𝑜𝑜𝑜𝑐𝑐𝑟𝑟𝑟𝑟𝑟𝑟
𝐶𝐶𝐶𝐶2+(𝑎𝑎𝑎𝑎) + 2𝑒𝑒− → 𝐶𝐶𝐶𝐶 (𝑠𝑠)
𝑍𝑍𝑍𝑍 (𝑠𝑠) → 𝑍𝑍𝑍𝑍2+(𝑎𝑎𝑎𝑎) + 2𝑒𝑒−
𝐸𝐸𝑐𝑐𝑎𝑎𝑐𝑐𝑐𝑐𝑐𝑐 = 𝐸𝐸°[−0.762 𝑉𝑉] + 𝑅𝑅𝑅𝑅𝑧𝑧𝑧𝑧
ln 𝑐𝑐𝑜𝑜𝑜𝑜𝑐𝑐𝑟𝑟𝑟𝑟𝑟𝑟
𝐸𝐸𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 = 𝐸𝐸𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 − 𝐸𝐸𝑐𝑐𝑎𝑎𝑐𝑐𝑐𝑐𝑐𝑐 ≈ 0.7 𝑉𝑉
iPhone 7 plus11.1 Wh
2015 Mac Air (13 inch)54 Wh
Tesla Modal S 60-100 kWh
Energy storage plantMWh level1 mile lightning flash
300,000 Bacon Cheeseburger Deluxe~ 10 days of lunch to feed VT campus
Get to Know the Scale of Battery Energy
3
Battery Science and Advanced Characterization at Multiple Length Scales
Lin et al Chem Rev (under revision)
Materials Synthesis
Advanced Characterization
Electrode Formulation
Electrochemistry
Our research activity at Virginia Tech 4
Challengeso Poor first-cycle Coulombic
efficiencyo Fast capacity fadingo Inferior rate capabilityo Potentially release oxygen and
induce thermal runaway
High Voltage Failure of NMC Materials
ca. 87% Li deintercalation
Upper cutoff: 4.7 V vs Li+/Li, C rate: C/20
1st cycle20th cycle
Nat. Commun. 5, 3529 (2014)
Upper cutoff: 4.7 V vs Li+/Li, C rate: C/50
After 20 cycles and significant capacity fading, 20% discharge capacity is recovered under extremely slow cycling rate
5
ca. 64% Li deintercalation
Upper cutoff 4.3 V vs Li+/Li
Pristine4.3 V for 20 cycles4.7 V for20 cycles
Less capacity fading at 4.3 V cutoff
Build-up of reduced Mn increased by elevating voltage
Tradeoff In the real world, battery is operated to guarantee that the voltage, temperature, etc do not exceed the safety limit. However, by doing so the energy density is compromised
High Voltage Failure of NMC Materials
6
Common Rocking-Chair Battery Configuration
−eVoc = μLi(C) − μLi(A) = Δμe + ΔμLi+
Open circuit voltage
Chemical potential of cathode as a function of Li content
Chemical potential of anode as a function of Li content
Potential change of charge carriers
7
Schematic Open-Circuit Energy Diagram of a Cell
Anode
Energy
SEI
SEI
LUMO
HOMO
Eg
CathodeμLi(C)
μLi(A)
Voc
Φ(C)
Φ(A)
Oxidant
Electrolyte
Reductant
Cathode work function
Anode work function
SEI: solid-electrolyte interphaseLUMO: lowest unoccupied molecular orbitalHOMO: highest occupied molecular orbital
Electrode-electrolyte interfacial problem is a “1 + 1 > 2” challenge !
Challenges:Electrode materialsElectrolyte
8
T.M.LiO
3a
3b/6c
(R-3m) α-NaFeO2 type
LiNi1-x-yMnxCoyO2 Material: Crystal and Electronic Structures
o Reduced cost?o Enhanced safety?o Higher energy density?
Sci. Rep. 4, 5694, (2014) 9
What happens at the cathode surfaces?
i ii iii
Reaction layer100 nm 50 nm 50 nm
Surface reaction layer (cathode-electrolyte interphase, CEI)
Nat. Commun. 5, 3529 (2014) 10
NMC
Electrolyte exposure
Fully charged
Pristine NMC
What happens at the cathode surfaces?
Surface reaction layer (cathode-electrolyte interphase, CEI)
O K-edge
F K-edge
Mn L-edge Co L-edge
Ni L-edge
SRL
NMC
10 nm
Energy & Environmental Science 7, 3077 (2014) 11
Challenges in Oxide Cathode Materials: Surface Reactivity and Phase Change
Xu, Fell, Chi & Meng. Energy Environ. Sci. 4, 2223 (2011)
Li[NixLi1/3−2x/3Mn2/3−x/3]O2
5 nm
Lin, Markus, Nordlund, Weng, Asta, Xin & Doeff. Nat. Commun. 5, 3529 (2014)Lin, Nordlund, Markus, Weng, Xin & Doeff. Energy Environ. Sci. 7, 3077 (2014)Lin, Nordlund, Pan, Markus, Weng, Xin & Doeff. J. Mater. Chem. A 2, 19833 (2014)Markus, Lin, Kam, Asta & Doeff. J Phys. Chem. Lett. 5, 3649 (2014)Lin, Markus, Doeff & Xin. Sci. Rep. 4, 5694, (2014)
Li[NixMnyCo1-x-y]O2
Hwang, Chang, Kim, Su, Kim, Lee, Chung & Stach. Chem. Mater. 26, 1084 (2014)
Li[Ni0.5Mn1.5]O4
unpublished result
x in Li1-xTMO2
ΔH
for c
lose
-pac
ked
phas
eΔH = 0
Layered phase
closed packed phase
12
dz2 dx2-y2
Tokura & Nagaosa. Science 288, 462 (2000)
dzx dyz dxy
eg orbitals
t2g orbitals
Crystal field theory d orbitals
13
LiNi1-x-yMnxCoyO2 Material: Energy vs Density of States upon Charging
N (E)
O2- : 2p6
Co3+/4+ : 3d-t2g
Ni3+/4+ : 3d-eg
Ni: 3d-t2g
EF1
Ene
rgy
Ni2+/3+ : 3d-eg
Mn3+/4+ : 3d-eg
Co: 3d-eg
Mn: 3d-t2g
Discharged stateLi1Ni1-x-yMnxCoyO2
N (E)
O2- : 2p6
Ni3+/4+: 3d-eg
Ni: 3d-t2g
Ni2+/3+ : 3d-eg
Mn3+/4+ : 3d-eg
Co: 3d-eg
Mn: 3d-t2g
Co3+/4+ : 3d-t2g
Ene
rgy
EF3
Discharged stateLi0Ni1-x-yMnxCoyO2
During the charging process (cathode under oxidative condition), lithium is deintercalated fromlattice, and charge compensation occurs at transition metal (TM) 3d orbitals, namely, 3d electronoccupancy decreases and Fermi level is lowered. Oxygen participation is expected because of theTM3d-O2p hybridization in TM-O6 octahedral unit.
N (E)
O2- : 2p6
Co3+/4+ : 3d-t2g
Ni3+/4+ : 3d-eg
Ni: 3d-t2g
Ni2+/3+ : 3d-eg
Mn3+/4+ : 3d-eg
Co: 3d-eg
Mn: 3d-t2g
Ene
rgy
EF2
Discharged stateLi0.5Ni1-x-yMnxCoyO2
14
Lin, Nordlund, Weng, Moore, Gillaspie, Dillon, Richards & Engtrakul. ACS Appl. Mater. Interfaces 5, 301 (2013)Ratcliff, Meyer, Steirer, Garcia, Berry, Ginley, Olson, Kahn & Armstrong. Chem. Mater. 23, 4988 (2011)Lin, Nordlund, Weng, Sokaras, Jones, Reed, Gillaspie, Weir, Moore, Dillon, Richards & Engtrakul. ACS Appl. Mater. Interfaces 5, 3643 (2013)Lin, Nordlund, Weng, Zhu, Ban, Richards & Xin. Nat. Commun. 5, 3358 (2014)
Soft X-ray Absorption Spectroscopy (Sensitivity to Surface and Orbital Occupancy)
Synchrotron X-ray
SnO2:F (TCO)
NiOx
Glass
O3
O3
O3
O3
UV Ozone Processing
O3O3
Ni2+ Ni3+o Peak ratio (e.g., L3/L2, a/b)o Properly calibrated absolute peak energy
L3
Ni L3,2 XAS (Ni2p to 3d unoccupied state)
L2
Ni0 [Ar]4s23d8
Ni2+ [Ar]3d8
Ni3+ [Ar]3d7
15
Changes of Ni3d Occupancy during Charging and Discharging
dz2 dx2-y2
Tokura & Nagaosa. Science 288, 462 (2000)
dzx dyz dxy
eg orbitals
t2g orbitals
According to the crystal-field theory, the unpaired eg electrons make the high valency nickelions (e.g., Ni3+/Ni4+) thermodynamically unstable in the octahedral unit (in particular when incontact with electrolytic solution)
Crystal field theory
Li1Ni0.4Mn0.4Co0.2O2
Li0.6Ni0.4Mn0.4Co0.2O2
Li0.2Ni0.4Mn0.4Co0.2O2 (ca. 220 mAh/g)
Li0.7Ni0.4Mn0.4Co0.2O2
Li0.9Ni0.4Mn0.4Co0.2O2
t2g eg
Energy Environ. Sci. 7, 3077 (2014)
Ni L-edge
16
2 nm
Li+ pathway
R[100]
(00-3)(01-2)
(011)
R3m_
F[110]
(1-11)(1-1-1)
(002)
Fm3m_
Surface Phase Transition after Cycling
Nat. Commun. 5, 3529 (2014)Phys. Chem. Chem. Phys. 17, 21778 (2015)
“Rock-salt”“Layered”
1 cycle
17
“Layered”
Ni2+, Mn4+, Co3+
“Rock-salt”
Ni2+, Mn2+, Co2+
Stable R-3m“Layered”
Stable Fm-3m“Rock-salt”
Thermodynamic DFT Calculation: Undesired Phase Transition
2Lix(Ni1/3Mn1/3Co1/3)O2 2(Ni1/3Mn1/3Co1/3)O + O2 + 2xLi+ + 2e−
“Layered” “Rock-salt”
ca. 188 mAh/g
Nat. Commun. 5, 3529 (2014)J Phys. Chem. Lett. 5, 3649 (2014) 18
Nat. Commun. 5, 3529 (2014)Nat. Commun. 5, 3358 (2014)
Surface Phase Transition Grows as Cycle Number Increases
I = I0 exp (-Ax)
Mn2+ rich
Mn4+ rich
Soft XAS (surface sensitive, ~10 nm)
o Pristine electrode showed exclusively Mn4+ (“layered”)o Mn2+ dominated surface layer (“rock-salt”) continued to
grow as cycle number increasedo Mn2+ can be dissolved in electrolyte, migrate to anode and
interrupt SEI
Cyc
le n
umbe
r
19
2 nm
Lin, Markus, Asta & Doeff et al. unpublished result
Surface Oxygen Activity: Chemical Side Reaction
Surface oxygen is more reactive
Energy Environ. Sci. 7, 3077 (2014)Nat. Commun. 5, 3529 (2014)
The higher state of charge, the higher possibility of side reactions, due to the activation of oxygen 2p orbitals
20
J Phys. Chem. Lett. 5, 3649 (2014)Nat. Commun. 5, 3529 (2014)
Stable R3m“layered”
Stable Fm3m“Rock-salt”
Pristine NMC
“Substituted” NMC
LiNixMnyCo1-x-y-zTizO2
_
_
Partial Aliovalent Substitution to Expand Thermodynamic Window
21
Li
OCoMn
Mn
Polaron state
J Phys. Chem. Lett. 5, 3649 (2014)Nat. Commun. 5, 3529 (2014)
Partial Aliovalent Substitution to Improve Electronic Conductivity
22
Electrolyte Development for Li/Mn rich NMC Materials
Tris(2,2,2-trifluoroethyl) borate (TTFEB)
Ma, Y et al. Chem. Mater. 29, 2141–2149 (2017)
Li1.16Ni0.2Co0.1Mn0.54O2
23
XPS Surface Analysis of Electrolyte Decomposition Layer
24
Less surface electrolyte decomposition layer on the cathode with the TTFEB additive
Ma, Y et al. Chem. Mater. 29, 2141–2149 (2017)
XAS Surface Analysis of Transition Metal Reduction Layer
25
Less surface TM reduction layer on the cathode with the TTFEB additiveSurface of cathode becomes more stable with the TTFEB additive
Ma, Y et al. Chem. Mater. 29, 2141–2149 (2017)
XAS Surface Analysis of Al2O3 Surface Protection for LNMO Spinel
Xin, F et al. Adv. Funct. Mater. 27, 1602873 (2017) 26
More stable surface with Al2O3 surface protection
Conclusion
Pristine
Build up
Roc
k-Sa
lt Fo
rmat
ion
Anode
SEI
SEI
LUMO
HOMO
Eg
CathodeμLi(C)
μLi(A)
Voc
Φ(C)
Φ(A)
Oxidant
Electrolyte
Reductant
• Electrochemical interface and interphase in batteries• Cathode surface chemistry and failure mechanism• Methods of stabilizing surfaces: (1) Surface engineering
(2) aliovalent substitution(3) optimization of electrolyte 27
Acknowledgement
Dr. T.-C. Weng, Dr. D. Nordlund, Dr. D. Sokaras, Dr. Y. Liu, Dr. H. Xin
Office of Vehicle Technologies
Dr. Marca Doeff
28
Xin FangYulin MaChongwu ZhouIsaac MarkusMark Asta
Thank You
Feng LinDepartments of Chemistry and MSEVirginia Tech900 West Campus DriveBlacksburg, VA 24061Office: Hahn Hall North 306-XYZPhone: (540) 231-4067E-mail: [email protected]