STABILIZED SPINEL AND POLYANION CATHODESRELEVANCE • To develop high-performance spinel and...
Transcript of STABILIZED SPINEL AND POLYANION CATHODESRELEVANCE • To develop high-performance spinel and...
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STABILIZED SPINEL AND POLYANION CATHODES
ARUMUGAM MANTHIRAMElectrochemical Energy Laboratory (ECEL)Materials Science and Engineering Program
The University of Texas at Austin
May 10, 2011
Project ID #: ES051This presentation does not contain any proprietary, confidential, or otherwise restricted information
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OVERVIEW
Timeline
• Project start date: June 2010• Project end date: May 2012• 75 % complete
Budget
• Total project funding- DOE: $520K
• Funding for FY10- $260K
• Funding for FY11- $260K
Barriers
• Barriers - Cost- Cycle life- Energy and power densities
• Targets- Long cycle life for 4 V and 5 V spinel cathodes
- Low manufacturing cost for polyanion cathodes
- Increased energy and power with spinel and polyanion cathodes
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RELEVANCE
• To develop high-performance spinel and polyanion cathodes for lithium-ion batteries and a fundamental understanding of their structure-composition-performance relationships
- To develop 5 V spinel oxide compositions with controlled morphology and optimum cationic substitutions that can maximize the tap density and electrochemical performance
- To develop a fundamental understanding of the factors that control the electrochemical performance and safety of cation- and anion-substituted stabilized 4 V spinel manganese oxide compositions
- To develop novel low-cost synthesis processes for phosphate and silicate cathodes
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MILESTONES
Month/Year Milestone
September 2010 Polyanion-containing cathodes with controlled nanomorphologies
March 2011 Understanding the self-surface segregation of cations in high-voltage spinel cathodes
September 2011 Development of novel synthesis approaches for high-capacity nanostructured silicate and phosphate cathodes
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APPROACH / STRATEGY
• Develop a firm understanding of the factors controlling the electrochemical performances of cathode materials and utilize the understanding to develop high-performance cathodes for vehicle batteries
- Cationic and anionic substitutions to obtain stabilized 4 V spinel cathodes- Effect of cationic and anionic substitution on thermal stability of 4 V spinel cathodes- Cationic substitutions in 5 V spinels to stabilize the disordered spinel structure- Novel synthesis approaches for polyanion-containing cathodes including nano-olivines that can lower manufacturing cost with improved performance
- Solid-state, high-energy ball milling, and solution-based synthesis approaches- Advanced chemical and structural characterizations- In-depth electrochemical evaluation including impedance analysis- Understanding of the structure-property-performance relationships
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• The influence of cationic substitutions on the bulk and surface structures and electrochemical performances of 5 V spinel cathodes has been identified
- cationic substitutions stabilize the disordered spinel structure, facilitate segregation of certain cations to the surface, and thereby improve significantly the electrochemical performances (cycle life and rate capability)
• Precursors with unique morphologies have been synthesized by novel synthesis approaches to maximize the tap density and performance of 5 V spinels
• The factors that influence the cycle life and safety of 4 V spinels have been identified; oxyfluorides offer better safety than the oxide counterparts
• Substitution of small amounts of Fe significantly improves the electrochemical performances of both LiMnPO4 and LiCoPO4 due to surface segregation
• The substitution of VO for Fe in LiFe1-x(VO)xPO4 has been found to create vacancies in the Fe sites; the LiFe1-x(VO)xPO4 phases formed by the microwave-assisted process are metastable and disproportionate at high temperatures
TECHNICAL ACCOMPLISHMENTS AND PROGRESS
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INFLUENCE OF CATIONIC SUBSTITUTIONS IN 5 V SPINEL
0 10 20 30 40 50 60 70 80 90 100
40
60
80
100
120
140
Ca
paci
ty (m
Ah/g
)
Cycle number
LiMn1.5Ni0.5O4
LiMn1.5Ni0.42Cr0.08O4
LiMn1.5Ni0.42Fe0.08O4
LiMn1.5Ni0.42Ga0.08O4
25 oC
0 10 20 30 40 50 60 70 80 90 10020
40
60
80
100
LiMn1.5Ni0.5O4
LiMn1.5Ni0.42Cr0.08O4
LiMn1.5Ni0.42Fe0.08O4
LiMn1.5Ni0.42Ga0.08O4
Coul
ombi
c ef
ficie
ncy
(%)
Cycle number
25 oC
0 2 4 6 8 100
20
40
60
80
100
LiMn1.5Ni0.5O4
LiMn1.5Ni0.42Cr0.08O4
LiMn1.5Ni0.42Fe0.08O4
LiMn1.5Ni0.42Ga0.08O4
Norm
aliz
ed d
isch
arge
cap
acity
(%)
C rate
0 10 20 30 40 50 60 70 80 90 100
40
60
80
100
120
140 55 oC
Capa
city
(mAh
/g)
Cycle number
LiMn1.5Ni0.5O4
LiMn1.5Ni0.42Fe0.08O4
LiMn1.5Ni0.42Ga0.08O4
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• Fe segregates to the surface during the synthesis and cooling process, which is consistent with our earlier XPS data
• Self-surface segregation is an attractive strategy to develop a robust electrode-electrolyte interface with the high-voltage cathodes
SELF-SURFACE SEGREGATION IN 5 V SPINELS
0 10 20 30 40 500
100
200
1000
10000
54Fe+
Ni+
Mn+
LiMn1.5Ni0.5O4
Inte
nsity
(cou
nts)
Sputtering time (s)0 10 20 30 40 50
0
100
200
1000
10000
LiMn1.5Ni0.42Fe0.08O4
Inte
nsity
(cou
nts)
Sputtering time (s)
Mn+
Ni+
54Fe+
Time-of-flight – secondary ion mass spectroscopy (TOF-SIMS)
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MORPHOLOGY CONTROL OF 5 V SPINEL CATHODES
• Morphology could be controlled with different precipitating agents and additives such as AOT, CTAB, or (NH4)2SO4
oxalate, AOT, polyhedral
carbonate, CTABcubic
carbonate, (NH4)2SO4spherical
•Microcubic precursor is preheated at 450 °C, followed by mixing with LiOH and firing at 900 °C for 12 h•Precursor morphology is retained in the final spinel sample•High tap density: 2.0 g/cm3
LiMn1.5Ni0.5O4 spinel
5 μm 10μm
10μm
200 μm 10 μm
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5 V SPINEL WITH MICRO-CUBIC MORPHOLOGY
•The 5 V spinel was obtained from the single-phase micro-cubic carbonate precursor•The 5 V spinel exhibits excellent cyclability without any capacity fade compared to a commercial 5 V spinel sample
0 5 10 15 20 25 30 3520
40
60
80
100
120
140
Disch
arge C
apac
ity (m
Ah/g)
Cycle Numbers
LiMn1.5Ni0.5O4: MicrocubicLiMn1.5Ni0.5O4: Commerical
0 20 40 60 80 100 120 140
3.5
4.0
4.5
5.0
Volta
ge (V
)
Capacity (mAh/g)
First Charge First Discharge
10 20 30 40 50 60 70 80
carbonate precursor
heated at 450 oC
Inte
nsity
(a.u
.)
2θ (Degree)
LiMn1.5Ni0.5O4
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5µm
10µm
5µm
5µm
20µm
5µm
EFFECTS OF REACTION TIME AND CATIONIC SUBSTITUTIONS
Mn0.75Ni0.25CO3 LiMn1.5Ni0.5O4
3 hour reaction time
6 hour reaction time
12 hour reaction time
Mn0.75Ni0.25-zFezCO312 hours, pH 7.9 +/- 0.05
Mn0.75Ni0.25CO3
Mn0.75Ni0.225Fe0.025CO3
Mn0.75Ni0.2Fe0.05CO3
•Morphology changes with reaction time; 12 h gives spherical morphology•Fe(OH)2 formed due to hydrolysis
with Fe substitution, which becomes FeOOH at 120 oC
5µm
10µm
10µm
20 30 40 50Cu Kα 2θ(degree)
Inte
nsity
(arb
itrar
y un
it)
FeO(OH)Mn0.75Ni0.2Fe0.05CO3
LixNi1-xOLiMn1.5Ni0.5O4
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0.0 0.1 0.2 0.30
5
10
15
20
Capa
city
fade
in 5
0 cy
cles
(%)
x in Li1.1Mn1.8Al0.1O4-xFx
3.65 3.60 3.55 3.50Mn valence
0.0 0.1 0.2 0.3 0.40
5
10
15
20
Capa
city
fade
in 5
0 cy
cles
(%)
x in Li1.1Mn1.8Fe0.1O4-xFx
3.65 3.60 3.55 3.50 3.45Mn valence
0.0 0.1 0.2 0.30
5
10
15
20
Capa
city
fade
in 5
0 cy
cles
(%)
x in Li1.1Mn1.8Cr0.1O4-xFx
3.65 3.60 3.55 3.50Mn valence
•Capacity fade increases drastically above a fluorine content of 0.2 or below a Mn valence of ~ 3.55+
•This is due to an increasing amount of Mn3+
and the consequent Mn dissolution and dynamic Jahn-Teller distortion
•The initial Mn valence should be maintained above ~ 3.6+ to realize acceptable performance
CYCLABILITY OF CATION-SUBSTITUTED 4 V OXYFLUORIDE SPINELS
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• The capacity fade in 4 V oxyfluoride spinels- increases with decreasing Mn valence
below ~ 3.6+- decreases with increasing electronegativity
of the substituted cations M from Ti to Ni- decreases with decreasing M-O bond
dissociation energy
3.5 3.6 3.7 3.8 3.9 4.0 4.10
5
10
15
20
Li1.1Mn1.8Al0.1O4-xFx
Li1.1Mn1.8Cr0.1O4-xFx
Li1.1Mn1.8Fe0.1O4-xFx
Li1.1Mn1.8Ni0.1O4-xFx
Li1.1Mn1.8Ti0.1O4-xFx
LiMn2-x-yLixCoyO4-zFz
Capa
city
fade
in 5
0 cy
cles
(%)
Mn valence
0
4
8
12
1.5
1.6
1.7
1.8
1.9
Ti Al Cr Fe Co Ni300
400
500
600
700
Ave
rage
ca
paci
ty fa
de (%
)
Elec
tron
egat
ivity
Bon
d di
ssoc
iatio
n en
ergy
(kJ/
mol
)
UNDERSTANDING THE CAPACITY FADE IN 4 V OXYFLUORIDE SPINELS
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THERMAL STABILITY OF 4 V SPINEL CATHODESDSC Plots of Ni-substituted cathodes in the
charged state, wetted with electrolyte
• Samples with lower lithium content in the charged state show better thermal stability
• Metal-oxygen bond strength affects the thermal stability significantly
• Similar results were obtained for Al- and Li-doped samples
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OLIVINE SOLID SOLUTIONS
LiMn1-yFeyPO4
• Substitution of Fe for Mn or Co improves the electrochemical activity
LiCo1-yFeyPO4
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MICROWAVE-SOLVOTHERMAL (MW-ST) SYNTHESIS OF LiFe1-x(VO)xPO4
Compound V (Å3) Li/P V/P Fe/P
LiFePO4 289.85 1.00 ----- 0.99
LiFe0.95(VO)0.05PO4 287.82 0.99 0.05 0.96
LiFe0.90(VO)0.10PO4 287.29 0.97 0.10 0.86
LiFe0.85(VO)0.15PO4 286.40 1.02 0.16 0.77
LiFe0.75(VO)0.25PO4 285.21 0.99 0.24 0.70
• Substitution of a larger (VO)2+ for a smaller Fe2+ should increase the unit cell volume, but exactly the opposite is found due to the formation of Fe vacancies as indicated by a lower Fe/P ratio in the sample in the ICP analysis and Fe3O4 impurity that could be removed with a magnetic bar
• Fe vacancies are formed to accommodate the larger (VO)2+ ions
• Formation of Fe vacancies and the corresponding oxidation of Fe2+ to Fe3+
decrease the unit cell volume
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THERMAL STABILITY OF LiFe1-x(VO)xPO4
• The MW-ST LiFe1-x(VO)xPO4 samples are metastable and cannot not be made by conventional high-temperature methods- With increasing heating temperature in 5 %
H2 – 95 % Ar, the vanadium activity changes from that of (VO)2+/3+ in LiVOPO4 to that of V3+/4+/5+ in Li3V2(PO4)3
- LiFe0.85(VO)0.15PO4 synthesized by conventional heating shows only V3+/4+/5+
activity without any (VO)2+/3+ activity, indicating the instability of LiFe0.85(VO)0.15PO4
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COLLABORATION AND COORDINATION WITH OTHER INSTITUTIONS
• National Renewable Energy Laboratory – Dr. Anne Dillon- ALD coating of Al2O3 on 5 V spinel cathodes
• University of Rhode Island – Professor Brett Lucht - Investigation of SEI layer formation with stabilized 5 V spinel cathodes
• Pacific Northwest National Laboratory – Dr. Jiguang (Jason) Zhang- Discussion and coordination of results on 5 V spinel cathodes
• Lawrence Berkeley National Laboratory – Dr. Jordi Cabana Jiménez- Discussion and coordination of results on 5 V spinel cathodes
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PROPOSED FUTURE WORK
• Continue to identify the factors that influence the electrochemical performances of the 5 V spinel cathodes, e.g., role of ordered vs. disordered spinel structure, segregation of cations to the surface, synthesis temperature, and morphology
• Extend the morphological-control synthesis approach pursued for LiMn1.5Ni0.5O4
spinel to other cation-substituted LiMn1.5Ni0.5-yMyO4 (M = Cr, Fe, and Ga)
• Recognizing that the substitution of a small amount of Fe improves the performances of LiMnPO4 and LiCoPO4, explore whether surface segregation of Fe plays a role in improving the performance of LiM1-xFexPO4 (M = Mn and Co)
• Following our earlier work, explore the microwave-assisted solvothermal synthesis approaches to obtain Li2Fe1-xMxSiO4 (M = Mn, Co, and Ni) silicate that have the potential to reversibly insert/extract two lithium per transition metal ion
• Explore the microwave-assisted solvothermal synthesis approach to obtain nanostructured NASICON-related Li3V2(PO4)3 and Li9V3(P2O7)3(PO4)2 cathodes that has the potential to extract more than one lithium per transition metal ion
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5 V Spinel LiMn1.5Ni0.5O4
• Cationic substitutions stabilize the disordered spinel structure, eliminate the Ni1-xLixO impurity, and improve significantly the electrochemical performance
• Certain cations like Fe3+ segregate to the surface during the synthesis process of LiMn1.5Ni0.5-xFexO4 and provide a robust interface with the electrolyte
• Controlled synthesis with unique morphologies offer high tap density
4 V Spinel LiMn2-yMyO4-zFz
• The Mn valence has to be above ~ 3.6 + to offer acceptable cycle life
• Electronegativity of M and M-O bond energies play a role in the capacity fade
• The oxyfluoride spinels offer better safety than the oxide counterparts
Polyanion cathodes
• Substitution of Fe improves the performances of LiMnPO4 and LiCoPO4
• The substitution of VO for Fe in LiFe1-x(VO)xPO4 is accompanied by the formation Fe vacancies and oxidation of Fe2+ to Fe3+
• The LiFe1-x(VO)xPO4 phases are metastable and decompose at high temps.
SUMMARY