Examining Hysteresis in Li- and Mn-Rich Composite Cathode Materials
Kevin Gallagher, Jason Croy, Dennis Dees, and Mike Thackeray
Chemical Sciences and Engineering Division
Mali Balasubramanian X-Ray Science Division, Advanced Photon Source and the Argonne Voltage Fade Team May 13-17th, 2013 Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting, Washington D.C. Project ID# ES189
This presentation does not contain any proprietary, confidential, or otherwise restricted information
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Overview
Timeline Start: October 2012 Finish: September 2013 Budget Total project funding
– 100% DOE FY2013: $290K
Barriers Development of a safe cost-effective PHEV
battery with a 40 mile all electric range that meets or exceeds all performance goals – Interpreting complex cell
electrochemical phenomena – Identification of cell degradation
mechanisms
Partners (Collaborators) ANL Voltage Fade Team
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Project Objectives - Relevance
Voltage Fade in lithium and manganese rich (LMR-NMC) oxides reduces energy density of lithium-ion cells on calendar–life and cycle–life aging • Mitigating voltage fade will enable the use of these high–energy
NMC composite oxides {xLi2MnO3•(1-x)LiMO2 (M=Ni, Mn, Co)} for PHEV and EV applications
Milestones • Characterization of hysteresis and path dependence in OCV curve
(Dec 2012) complete • Determination of mechanism of hysteresis phenomenon in LMR-
NMC (Sept 2013) on target • Initiate OCV numerical model for LMR-NMC (Sept 2013) on target
2 2.5 3 3.5 4 4.5
dQ/d
V
Voltage (V)
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Approach Multi-institution effort to identify factors that contribute to voltage fade in
lithium– and manganese– rich NMC oxides (LMR-NMC)
Electrochemical Characterization & Modeling
Oxide Synthesis & Surface Modification
Physicochemical Characterization & Atomistic Modeling
Suggest/implement approaches to mitigate voltage fade
TM Metal solutionNH4OH NaOH 8340 8350 8360
Ni4+3.6 Vd
3.9 Vd
4.2 Vd
Nor
mal
ized
Inte
nsity
(a.u
.)
Energy (eV)
3.6 Vc4.2 Vc4.7 Vc
3.1 V
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Major Accomplishments and Technical Progress
Identified that hysteresis in LMR-NMC is actually a 1 V hysteresis in 10-15% of the lithium content
Correlated this hysteresis behavior to the voltage fade phenomenon
Proposed overall mechanism for electrochemical observations: reversible and irreversible transition metal ion (TM) migration
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Hysteresis in battery electrode materials
Exists in many different systems Origin often difficult to discern
– Kinetically driven – Metastable states – Ensemble of particles
Consider Everett’s General Approach – Underlying physics don’t matter – Independent domains, which at least
some can exist in a metastable state
Everett and Whitton Trans. Faraday Soc. 179 (1952)
magnets
Equil. position in absence of magnets
Bimetallic wire opens and closes switch depending on the temperature (T) in room. Hysteresis is observed in measured current between the critical “closed” T and “open “T” due to competition between strain in wire and attraction of magnets
Example:
Cur
rent
, i
Temperature, T
One circuit
Cur
rent
, i
Temperature, T
Distribution of circuits
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Cathode materials examined
HE5050 (Toda) – Li1.2Ni0.15Mn0.55Co0.10O2 or 0.5Li2MnO3•0.5LiNi0.44Mn0.31Co0.25O2 – Synthesis: hydroxide co-precipitation, then calcination with Li2CO3 (?)
Li2MnO3_Ni (Argonne) – Li1.2Ni0.4Mn0.4O2 or 0.5Li2MnO3•0.5LiNi0.5Mn0.5O2 – Synthesis: Li2MnO3 treated with NiNO3 in Nitric Acid, then calcination
LLS_Mg (Argonne) – Li 1.25Mn0.65Ni0.33Mg0.02O2.28 or 0.94{0.3Li2MnO3•0.7LiMO2}•0.06Li0.5M’O2 – Synthesis: oxalate co-precipitation, then calcination with Li2CO3
Cell configurations – Lithium half cells – 1.2 M LiPF6 in EC/EMC (3:7 wt), no additives in 2032 coin cell – All cycling data at least in duplicate at room temperature
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Use slow cycling or GITT study to determine open-circuit voltage as function of lithium concentration
Large stable hysteresis observed in LMR-NMC cathodes after activation of Li2MnO3 domains in xLi2MnO3(1-x)LiMO2
Hysteresis loop does not close even after seven day hold at 3.7 V
Measurement of Open-Circuit Voltage Function
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Vehicle Technologies Program LLS_Mg
Hysteresis and Path-Dependence in OCV Curve
Scanning curves shift from one boundary to other depends on voltage
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Other LMR-NMC materials exhibit 1 V hysteresis
3.0 3.5 4.0 4.5
dQ/d
V
Open Circuit Voltage (V)
2.0 - 4.7 V 2.0 - 4.2 V 3.6 - 4.7 V
Li2MnO3_Ni
Increasing Li2MnO3 content and adding Cobalt both add complexity to the open-circuit voltage vs SOC function.
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HE5050
Post-activated dQ/dV suggests lithium removed above 4.3 V but does not fill these sites until 3.3 V on discharge
Not an impedance issue as still exists at 85 °C (and 7 day hold data) Capacity associated with hysteresis around 10-15% of total lithium content Could vacant sites be blocked by migrating TMs?
In situ and Ex situ (APS) Synchrotron X-ray Diffraction
• Behavior appears similar to LiNi0.5Mn0.5O2
• No strong evidence observed for ~1 V electrochemical hysteresis
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1.35 1.3 1.25 1.2
(c) (003)
2 θ
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0 10 20 30 40 50 60 70 80 90 1002.84
2.85
2.86
2.87
2.88
2.89
SOC (100% = 200 mAh/g)
a (Å
)
charge discharge
0 10 20 30 40 50 60 70 80 90 100
14.42
14.44
14.46
14.48
14.50
14.52
SOC (100% = 200 mAh/g)
c (Å
)
charge discharge
0 10 20 30 40 50 60 70 80 90 100100.5
101.0
101.5
102.0
102.5
103.0
103.5
104.0
104.5
Vo
lum
e (Å
3 )
SOC (100% = 200 mAh/g)
charge discharge
X-ray Absorption Spectroscopy: HE5050
Examine oxidation and coordination at different states of lithiation – HE5050 for 7th cycle 2-4.7 V vs Li at 22 °C
Ex-situ measurements completed at Advanced Photon Source
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2 3 4 5
2
0
2
1
2
dQ/d
V
Cell voltage (V)
3
4
5 6 7
8
(b)
nominal voltage relaxed voltage for endpoints
0 50 100 150 200 2502.0
2.5
3.0
3.5
4.0
4.5
5.0
76
5
4
3
2
1,8
Capacity (mAh/g)
(a)
Cel
l vol
tage
(V)
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Spectroscopic Verification of Hysteresis
Samples charged and discharged to 4.2 V have similar XAS Samples charged and discharged to same SOC are different
– 65 mAh/g Li remaining = 75% SOC = 4.2 V charge or ~3.9 V discharge – Nickel XANES clearly shows lower oxidation state for 3.9 V on discharge
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Ni K
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Ni K
Summary of observations from characterization
1 V hysteresis for 10-15% of lithium content No obvious structural changes from XRD XAS shows hysteresis in Nickel oxidation state
– Nickel more reduced during discharge than charge at 75% SOC
Remaining questions (only a few listed here) – Where is the additional capacity originating? (Mn(V) etc) – Spectroscopic detection of reversible TM migration (Neutrons)
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-3
-2
-1
0
1
2
3
2.75 3.25 3.75 4.25 4.75
dQ/d
V, m
Ah/c
m2
V
Open circuit voltage, V
2 - 4.62 - 4.22 - 4.02 - 3.8
8340 8350 8360
Ni4+3.6 Vd
3.9 Vd
4.2 Vd
Nor
mal
ized
Inte
nsity
(a.u
.)
Energy (eV)
3.6 Vc4.2 Vc4.7 Vc
3.1 V
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Proposed hysteresis model in LMR-NMC electrodes
Majority of intercalation similar to traditional materials 10-15% of the lithium exhibits a ~1 V hysteresis
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Is hysteresis related to voltage fade?
Examine by cycling HE5050 in different voltage windows – One activation cycle, then one average voltage measurement – 20 cycles in truncated window, all have 4.7 V upper potential – Measure average voltage in full voltage window – 30°C, 10 mA/g 1st cycle, 20 mA/g for all others
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0 50 100 150 200 250 300 350
Cell
Volta
ge, V
Capacity, mAh/g16
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Cycling accelerates fade compared to calendar hold
Cycling up to 4.7 V with varying lower cutoff voltage
Maximum voltage fade occurs with lower cutoff around 3.0-3.3 V
– Does that mean calendar time is everything? (see bottom right)
Slight improvement when cycled to less than 3.0 V, current hypothesis unproven
Calendar induced voltage fade does not
match cycling Lower cut-off voltage of 3.0 to 3.3 V is
worst case
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Hysteresis and Voltage Fade Cartoon
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Structural rearrangement of layered lithium metal oxides – Transition metal moves in/through tetrahedral site in Li layer – Formation of Li+---TMz+ dumbbells1,2 (and possibly Li+---Li+)
– Exact voltage fade state still uncertain – redox near 3.1 V so not pure LiMn2O4 spinel but rather a different cubic environment with Li in octahedral sites
Oxidation reaction around 4.2 V – Lithium from tetrahedral sites – Vacancy ordering – Li+---TMz+ dumbbell formation?
Reduction reaction around 3.3V – Lithium into octahedral sites – Li+---TMz+ annihilation?
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1. Reed, Ceder, Van der Ven, Electrochem Solid St. Lett. 2001, 4, A78-A81 2. Armstrong et al. Chem. Mater. 2004 16, 3106-3118
Collaborations
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Colleagues at Oak Ridge & Pacific Northwest National
Laboratories
Colleagues at Brookhaven &
Lawrence Berkeley National Laboratories
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Future Work
• Determination hysteresis – voltage fade mechanism in LMR-NMC positive electrode materials • Collaborate across the entire Voltage Fade inside/outside Argonne • Vary Ni to Mn ratio • Use solid state NMR • Neutron analysis for tetrahedral site occupation
• Initiate OCV numerical model for LMR-NMC • Capture OCV behavior in a volume averaged numerical model • Model should account for both hysteresis and voltage fade
Hysteresis and Voltage Fade Summary
1 V hysteresis in ~10-15% of the lithium content – Dumbbell formation > 4.0 V on charge – Dumbbell annihilation ~ 3.3 V on discharge
Cycling accelerates voltage fade faster than calendar testing Maximum voltage fade occurs at the lower potential cut-off correlated
to hysteresis Hypothesis: TM migration involves
– Fast reversible TM migration between original & metastable state – Slow irreversible TM migration from metastable to faded state
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Acknowledgements & Collaborators
Support for this work from DOE-EERE, Office of Vehicle Technologies is gratefully acknowledged – David Howell & Peter Faguy
Collaborators: Argonne National Laboratory
– Zhonghai Chen, Yang Ren, Anthony Burrell, Baris Key – Daniel Abraham, Y. Li, M. Bettge – Wenquan Lu, Sun-Ho Kang, Donghan Kim, Andrew Jansen, Chris
Johnson, Javier Bareno, Jack Vaughey