es157_dudney_2012_p.pdf

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Objectives and relevance
Lithium anodes must be completely isolated from the electrolyte to prevent dendrites, side reactions and to stabilize the structure. Composites of multiple electrolytes may provide the needed combination of properties.
Composite Electrolyte to Stabilize Metallic Lithium Anodes
(Integrated Laboratory Industry Research Program)
Project ID: ES157 Nancy Dudney (PI) Oak Ridge National Laboratory Contributors: Wyatt Tenhaeff, Sergiy Kalnaus, Adrian Sabau, Erik Herbert
Polymer Electrolytes PEO10:LiTFSI Notable Features • High conductivity ( σ25°C = 2x10-6 S cm-1) • Tmelt ≈ 35 °C • Slow crystallization kinetics • Lower conductivity than PEO10:LiTFSI • Faster crystallization kinetics • 100% crystalline • Crystalline phase is conductive • Unity transference number
• Relevance:
– Enables implementation of Li metal anodes for high energy density chemistries (e.g. Li-air, Li-S) – USABC has targeted a 5X improvement in energy density
• Objectives:
– Understand Li+ transport at interface between two dissimilar solid electrolytes, e.g. ceramic/polymer – Develop composites of electrolyte materials with requisite electrochemical and mechanical properties – Fabricate thin membranes to provide good power performance and long cycle life
Ohara
-200
-Z'' (kΩ·cm ) -15.0
PEO16:LiCF3SO3
T=50 °C
100 kHz
)
(kΩ·cm2)
-7.5 1 MHz 0.0 0.0 -250 7.5 15.0 3.16 kHz 100 Hz 1 MHz 125 250 Z' (kΩ ·cm2) 375 500 1 kHz 22.5 30.0
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Milestones
Milestones: 1. A composite electrolyte membrane <1mm thick where the internal interfaces do not significantly impede the Li ion transport. 2. Simulation to estimate the ion conduction of an optimized composite structure. 3. Evaluate composite membrane with a lithium metal electrode for cycling stability and dc transport properties. Target: October 2012 October 2012 October 2012
PEO16:LiCF3SO3 PEO6:LiAsF6
-Sample from P. Bruce at University of St. Andrews (Scotland)
Ceramic and Glass Electrolytes Lithium phosphate oxynitride (Lipon) Li1.3Ti1.7Al0.3(PO4)3 (LTAP) Ohara Nasicon-type (protected composition; • Fabricated as thin film • Chemically compatible with Li • High conductivity • Chemically incompatible with Li • High conductivity • Chemically incompatible with Li • Commercially available
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1000/T (K ) PEO16:LiCF3SO3 PEO10:LiTFSI
2.9
3.1
-1
3.3
3.5
Ohara
Using laminated bilayer samples to characterize interfacial resistances between two dissimilar solid electrolytes
1 MHz 0.1530
T=25 °C
39.8 kHz
-125
631 kHz 10 kHz Z' (Ω ·cm )
2
10 kHz 200
0 0
0 0
1 MHz 10 20 30 Z' (kΩ ·cm2)
251 Hz 40 50
Characteristic time scales of PEO10:LiTFSI and PEO16:LiCF3SO3 are very different enables a useful comparison of the interfacial impedances with Ohara ceramic
Laminated structures provided a well-defined interfacial area which enables quantitative characterization of interfacial impedances
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Approach
1. Develop methodologies to characterize both electrochemical and mechanical properties including impedance spectroscopy and nanoindentation of thin films. Characterize barriers to charge transport in laminated electrolyte structures, e.g. interfacial resistances, poor adhesion. Demonstrate improved properties in composite electrolyte. Simulate the optimal composite design. Fabricate optimized, thin composite membranes with a lithium metal electrode to evaluate cycling stability and DC transport properties
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Conductivities of individual phases vary over several orders of magnitude
1E-3 1E-4 σ (S cm-1) 1E-5 1E-6 1E-7
Individual electrolytes Bilayer composites Dispersed composites Optimized composites
2.
3. 4. 5.
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Approach- Many electrolyte materials have been evaluated.
Managed by UT-Battelle for the Department of Energy
Overview
• Timeline – Start October, 2011 • Technical barriers – Energy density (500-700 Wh/kg) – Cycle life, 3000 to 5000 deep discharge cycles – Safety • Budget – $300k FY12 • Partners – Oak Ridge National Laboratory (lead) – Center for Nanophase Materials Sciences, ORNL – University of Tennessee – SHaRE user facility, ORNL – Companies and collaborators for electrolyte materials
Sample from nGimat
crystal structure is similar to LTAP’s)
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Ionic conductivity is measured by impedance spectroscopy with blocking electrodes
Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting May 2012
“This presentation does not contain any proprietary, confidential, or otherwise restricted information”
2.7 90 80 70 60
T (°C)
50
40
30
20
Melting Temperatures PEO10:LiTFSI = 35 °C PEO16:LiCF3SO3 = 60 °C Controlling reproducibility of polymer electrolytes is a challenge error bars.
-Z'' (kΩ·cm2)
25 °C 50 °C
-25
-0.1
PEO10:LiTFSI
T=50 °C
2
-Z'' (Ω·cm2)
0 0.0
(
(kΩ·cm2)
12.5
-Z'' (kΩ·cm )
-Z'' (kΩ·cm2)
2
1 kHz 1 MHz 1 MHz 0 0
252 kHz
T=25 °C
0.0 0.10 -25