examining hysteresis in lithium- and manganese-rich composite … · 2014-03-27 · examining...

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

Vehicle Technologies Program

2

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

3

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)

4

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


5

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

6

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

7

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


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

8

Vehicle Technologies Program LLS_Mg

Hysteresis and Path-Dependence in OCV Curve

Scanning curves shift from one boundary to other depends on voltage

9


10

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.


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

11

1.35 1.3 1.25 1.2

(c) (003)

2 θ


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

12

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)


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

13

Ni K


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)

14

-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


Proposed hysteresis model in LMR-NMC electrodes

Majority of intercalation similar to traditional materials 10-15% of the lithium exhibits a ~1 V hysteresis

15


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


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

17


Hysteresis and Voltage Fade Cartoon

18

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?


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

19

Colleagues at Oak Ridge & Pacific Northwest National

Laboratories

Colleagues at Brookhaven &

Lawrence Berkeley National Laboratories


20

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

21



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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

examining hysteresis in lithium- and manganese-rich composite … · 2014-03-27 · examining...

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