New Advanced Stable Electrolytes for High-voltage Electrochemical Energy Storage

Peng Du (Silatronix) Kang Xu (US ARL)

Bryant Polzin (ANL)

DOE Annual Merit Review Meeting June 9th, 2016

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Project ID: ES271

Overview

Timeline• Project start date: 10/01/2015• Project end date: 09/30/2017• Percent complete: 25%

Budget• Total project funding: $ 1,665 K

– DOE share(Silatronix): $897 K– Contractor share: $333 K

• Budget Period 1(FY16): $662 K• Budget Period 2(FY17): $235 K

Barriers • Electrolyte development for

– High voltage stability– Good thermal stability– Stable SEI layer to improve

cycle life

Partners• US Army Research Laboratory• Argonne National Laboratory

2

Objective and Relevance

Project Objective: Develop an electrolyte system stable at high voltage (≥5V) to enable the development of high energy density Li-ion batteries required by the automotive industry.Relevance: This technology, if successful, will have a significant impact on the enablement of high voltage cathode materials in Li-ion battery technology. This in turn will provide a significant pathway for the development of higher energy density electrochemical storage devices, which is critical to expanding the electrification of the US vehicle fleet.Specific Technical Metrics:• Oxidative Stability

• Breakdown voltage > 6 V (vs. Li/Li+)• Parasitic current < 0.02 mA/cm2 ( at 6 V and 50°C )

• High Voltage System Performance • Initial capacity ≥ carbonate control ( e.g. 5V LNMO system) • Initial capacity left >80% (300 cycles at ≥ 55°C)

3

Background: Organosilicon Solvents Can Be Engineered with Targeted Characteristics

• Each group in OS structure adds specific capability for performance.• Dozens of unique structures have been synthesized and characterized for

physical characteristics, stability in electrolyte formulations, and cellperformance benefits.

• OS stabilizes entire electrolyte by protecting LiPF6 from decomposition.– OS3 protects LiPF6 from decomposition through solvation mechanism.– Elimination of reactive decomposition products protects all electrolyte and battery components.– Benefits demonstrated at low OS3 content (< 5%).

General Organosilicon (OS) Structure

4

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Project Milestones

Milestones and Go/No-Go Decision Milestone Verification Process Date Status Baseline characterization: Oxidative breakdown of control electrolytes

Linear scan voltammetry and cyclic voltammetry at Silatronix

Nov. 2015 Complete

Characterize synthesized LCP Verify structure and purity of LCP by ARL

Jan. 2016 Complete

Characterization of 2-3 new HV OS solvents/additives

Purity (>98%) and H2O (<20ppm) by Silatronix

Apr. 2016 In Progress

Go/No-Go Decision: Feasibility of HV performance demonstrated in ref. cells through determination of oxidative breakdown

Lin. scan voltammetry (>6V); Parasitic current 4.5-6.5V at 50°C (<0.02 mAh/cm2 at 6V) at Silatronix

Jun. 2016 In Progress

New HV OS solvents /additives synthesized NMR verification of structures (4-6) by Silatronix

Aug. 2016 In Progress

New HV co-solvents /additives synthesized 4-6 compounds prepared at ARL Sep. 2016 In Progress

Electrochemical evaluation, analysis, and diagnosis of new materials

CV, EIS, leakage current in half-cells Sep. 2016 In Progress

Milestones for Budget Period 1:

7

Technical Progress: Fundamental Mechanistic Studies of New Electrolyte Materials

• Silatronix synthesized four organosilicon solvents (OS3, OS3a, OS3b, OS3c) in the OS3 family that have the potential to show high oxidative stability. – Approach: stability and performance of organosilicon (OS) solvents can be optimized

to address specific application metrics via rational molecular design.

• ARL synthesized 8 new additives with bifunctional groups for protection of both anode and cathode surfaces. Testing has begun with two additives at Silatronix. ARL finished the characterization of lithium cobalt phosphate (LCP) cathode, which significantly improved the performance both in terms of discharge profile and cycling stability.

• Silatronix characterized new HV materials and investigated their fundamental electrochemical behavior.– Approach: LSV, Parasitic current, and other analytical techniques are utilized to

determine the oxidative breakdown voltage and mechanism of breakdown.

8

Technical Progress: Preliminary Screening of OS Solvents

Solvents

Neat Solvent Properties Electrolyte Properties (w/1M LiPF6) at 30 °C

Dielectric Flash Pt (°C ) Density (g/cc)Conductivity

(mS/cm) Viscosity (cP)

OS3 16.8 82 0.93 2.8 8.0

OS3a 12.6 72 0.81 1.6 9.4

OS3b 18.2 78 1.09 3.5 7.9

OS3c 19.5 64 1.10 5.0 6.8

EC/EMC (3/7) 22.1 <30 1.10 10 3.1

OS3 Family vs Control: Physical Properties

All OS3 family solvents provide significantly higher flash points than carbonate control, with good conductivity and viscosity in electrolyte blends.

9

Technical Progress: LSV of New OS Electrolyte Materials

LSV of OS3 Family Solvents at Pt Electrode (OCV to 8 V), all with 1M LiPF6 salt. (Test Condition: 30°C)

All OS solvents show higher breakdown voltages than carbonate controls. The investigation of small oxidation peaks before breakdown is in process.

EC/EMC 3/7OS3OS3aOS3bOS3c

30 ⁰C

EC/EMC 3/7OS3OS3aOS3bOS3c

30 ⁰C

10

Technical Progress: LSV of New OS Electrolyte Materials

LSV of OS3 Family Solvents at Pt Electrode (OCV to 8 V), all with 1M LiPF6 salt. (Test Condition: 50°C)

Similar trend have been observed for OS solvents at 50°C, which show better oxidative stability than carbonate control.

EC/EMC 3/7OS3OS3aOS3bOS3c

EC/EMC 3/7OS3OS3aOS3bOS3c

50 ⁰C 50 ⁰C

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Technical Progress: Floating Test of New Electrolyte Materials

Floating Test of Carbonate control and OS3 at Pt Electrode (4.5-6.5 V, 10 min at each voltage. Test Condition: 50°C)

100% OS3 with 1M LiPF6

50 ⁰C

EC/EMC=3/7 with 1M LiPF6

50 ⁰C

6.5V6.0V5.5V5.0V

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Technical Progress: Floating Test of New Electrolyte Materials

Floating Test of Carbonate control and OS3 at Pt Electrode (4.5-6.5 V, 10 min at each voltage. Test Condition: 50°C)

100% OS3 with 1M LiPF6

100% OS3c with 1M LiPF6

50 ⁰C

50 ⁰C

100% OS3b with 1M LiPF6

50 ⁰CParasitic current from OS3 is lower than 0.02 mA/cm2 at 50°C (technical metric), OS3b and OS3c are still much lower than control above 6V.

5.0V

5.5V

6.0V

6.5V

6.5V5.5V6.0V5.0V

6.5V6.0V5.5V5.0V

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UNCLASSIFIED

UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces

LUM

OHO

MO

Strategy for Additive DevelopmentEn

ergy

(eV)

Li, C, or Si Anode (µa)

𝑬𝑬𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 = ~𝟒𝟒.𝟑𝟑𝟑𝟑

LiMO2 Cathode (µc)

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UNCLASSIFIED

UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces

Cathode SEI

Strategy for Additive DevelopmentEn

ergy

(eV)

Li, C, or Si Anode (µa)

𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝒄𝒄𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝒄𝒄𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝒄𝒄𝑬𝑬𝒄𝒄𝒄𝒄𝒄𝒄𝑪𝑪𝑪𝑪𝑪𝑪𝒄𝒄𝑬𝑬𝑪𝑪𝒄𝒄𝑬𝑬

Anode SEI

5V Cathode (µc)

𝑬𝑬𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 > 𝟒𝟒.𝟕𝟕𝟑𝟑

LUMO

HOMO

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UNCLASSIFIED

UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces

Cathode SEI

• Molecular engineering to expand stability window ofbaseline electrolytes with additives (<5 wt%)

• Tune electrode-electrolyte interface chemistry to supporthigh voltage (>5V) electrode couples

– New solvents with intrinsic stability– Self-limiting sacrificial interphase– Redox shuttle

• Manage oxidative stability of electrolyte withoutcompromising other critical properties

– Salt solubility– Ionic conductivity– Temperature stability– Safety

Strategy for Additive DevelopmentEn

ergy

(eV)

Li, C, or Si Anode (µa)

Anode SEI

5V Cathode (µc)

𝑬𝑬𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 > 𝟒𝟒.𝟕𝟕𝟑𝟑

Fluorinated Solvents, Additives

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UNCLASSIFIED

UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces

HOMO-LUMO as QC Guide

-12

-10

-8

-6

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-2

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2TSMPi MTFA PHC TMSHFiP LCC DM Ester MHC HFiP

Ene

rgy

(eV

)

Additive HOMO LUMO Values (by gap size)

5.89

2 eV

7.41

8 eV

7.59

4 eV

7.67

6 eV

8.17

8 eV

8.25

1 eV

8.46

5 eV

8.78

3 eV

***Reduction and oxidation potentials cannot predict consequent interphase chemistry

Holistic Design Approach: Key functional groups effective in forming cathode and anode SEI are synthetically integrated in each additive chemistry

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UNCLASSIFIED

UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces

Subst’d LiCoPO4 Characterization

X-Ray Diffraction confirmsPhospho-olivine structure

SEM : ½ micron particle sizeBET surface area: 4.4 m2 g-1

Stable discharge capacity in baseline electrolyte1.2M LiPF6 in 3:7 EC:EMC + 2 wt.% additive

Stable discharge voltage in baseline electrolyte1.2M LiPF6 in 3:7 EC:EMC + 2 wt.% additive

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Technical Progress: Development for Specific HV Systems

• ANL provided 5V LNMO cathode and graphite anode for laboratory testing at Silatronix and ARL.

• Silatronix utilized cathode half cells to determine the fundamental behavior of the new materials with the 5V LNMO system.

EC/EMC:3/7 with 1M LiPF6

4.9V 5.0V 5.1V 5.2V

C/20

C/2

Method: Cathode half cells (LNMO/Li) are cycled at C/20 for 2 cycles (3.5-4.9 V) and C/2 for another 10 cycles (3.5-4.9 V), then charged at C/20 again to 4.9V, hold for 10h at each voltage until 5.2V.

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Technical Progress: Initial Evaluation of OS Formulations (without additives) in Li/LNMO Half Cell

Cycled at C/20 for 2 cycles (3.5-4.9 V) and C/2 for another 10 cycles (3.5-4.9 V).

EC/EMC:30/70OS3/EC/EMC:20/20/60OS3/EC/EMC:60/20/20OS3/EC/EMC:20/30/50OS3/EC/EMC:5/30/65

Different OS3 formulations (OS3 ≤ 20%) show similar performance compared to carbonate control; 60% OS3 shows better stability at 5.2 V and requires appropriate additives to improve cycling performance.

4.9V 5.0V5.1V 5.2V

Li/LNMO Half Cell

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Technical Progress: Cycling of OS Formulations(with Additives) in Li/LNMO Half Cell

Cycled at C/20 for 2 cycles (3.5-4.9 V) and C/2 for another 10 cycles (3.5-4.9 V).

C/20 C/2

EC/EMC:3/7, 0.1M LiBOB&0.1M LiDFOBOS3/EC/EMC:2/2/6, 0.1M LiBOB&0.1M LiDFOBOS3/EC/EMC:6/2/2, 0.1M LiBOB&0.1M LiDFOB

C/20 C/2

EC/EMC:3/7, 2% FECOS3/EC/EMC:2/2/6, 2% FECOS3/EC/EMC:6/2/2, 2% FEC

C/20 C/2

EC/EMC:3/7, 2% FEC, 0.1M LiBOB&0.1M LiDFOBOS3/EC/EMC:2/2/6, 2% FEC, 0.1M LiBOB& 0.1M LiDFOBOS3/EC/EMC:6/2/2, 2% FEC, 0.1M LiBOB& 0.1M LiDFOB

All additive packages show performance improvement with 60% OS3 formulations, however, FEC is not as good as borate additives.

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Technical Progress: Initial Evaluation of ARL Additives with OS Solvent

4.9V 5.0V 5.1V 5.2V4.9V 5.0V 5.1V 5.2V

Cycled at C/20 for 2 cycles (3.5-4.9 V) and C/2 for another 10 cycles(3.5-4.9 V).

EC/EMC:30/70, 1% MHC) OS3/EC/EMC:20/20/60, 1% MHCEC/EMC:30/70, 1% TMSHFiPOS3/EC/EMC:20/20/60, 1% TMSHFiP

No clear difference for ARL additives with 20% OS3.

MHC vs. TMSHFiP Control vs. TMSHFiP

23

Summary of Technical Progress

Task 1: Fundamental Mechanistic Studies of New Electrolyte Materials• Four organosilicon solvents (OS3, OS3a, OS3b, OS3c) in the OS3 family have

been successful synthesized and characterized. OS3 and its analog OS solvents showed great oxidative stability based on LSV and floating test results at Pt electrode both at 30°C and 50°C.

• ARL synthesized eight new additives with bifunctional groups for protection of both anode and cathode surfaces.

• Lithium cobalt phosphate (LCP) cathode has been characterized and shows significantly improved performance, both in terms of discharge profile and cycling stability.

Task 2: Development for Specific HV Systems• Electrolytes containing 20% OS3 solvent showed higher parasitic current above

4.9V than carbonate control in LNMO/Li cell, which may relate to interaction between OS3 and Li metal anode.

• 60% OS3 containing electrolyte displayed a lower parasitic current than carbonate control at higher voltages (>5V). Electrolyte optimization with different additive packages can enhance cycling performance.

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Proposed Future Work

• Silatronix and ARL will continue design and synthesis of new materials for HV applications.

– New OS solvents/additives will be identified from fundamental understanding of HV electrolyte decay mechanisms

– Modeling of additives with OS-based electrolyte components will seek to form a robust SEI on the surfaces of HV cathode and graphitic anode.

– HV solvents and additives will be evaluated with analytical and electrochemical methods

• Silatronix and ARL will continue to optimize the electrolyte formulations for HV system

– Properties and safety of initial electrolyte formulations will be characterized– Electrolyte formulations will be developed with select new materials for the 5V LNMO

full cell system for both performance and safety evaluation. – 30°C and 55°C cycling tests will begin; floating tests will be extended to full cell; post

cell analyses will be conducted

• Top performing HV electrolyte formulations will be tested in 5V LNMO pouch cells (13 layers, 200-300 mAh) at ANL.

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Acknowledgements

Contract Support:

Collaborators:

Questions?

• U.S. Army Research Laboratory (Kang Xu, Project team member)

• Argonne National Laboratory (Bryant Polzin, Project team member)

• US Department of Energy Office of Energy Efficiency and Renewable Energy (DOE EERE)

• FY 2015 Vehicle Technologies Office Incubator Program• Award #: DE-EE0007232

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Technical Back-Up Slides

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Technical Progress: Floating Test at 30°C

Floating Test of Carbonate control and OS3 at Pt Electrode (4.5-6.5 V, 10 min at each voltage. Test Condition: 30°C)

Carbonate control displays much higher parasitic current values than OS3 at higher voltages .

EC/EMC=3/7 with 1M LiPF6 100% OS3 with 1M LiPF6

30 ⁰C 30 ⁰C

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Floating Test of OS3 Family at Pt Electrode (4.5-6.5 V, 10 min at each voltage. (Test Condition: 30°C)

Parasitic currents from different OS solvents are all lower than 0.02 mA/cm2 at 6 V.

100% OS3 with 1M LiPF6

100% OS3b with 1M LiPF6

100% OS3c with 1M LiPF6

30 ⁰C

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6.5V6.0V5.5V5.0V

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6.5V6.0V5.5V5.0V

Technical Progress: Floating Test at 30°C

29

UNCLASSIFIED

UNCLASSIFIED The Nation’s Premier Laboratory for Land Forces

Additive Candidates

Dimethyl Ester

Methyl Trifluoro-acetate

LCC

HFiP

TMSHFiP

MHC PHC

TMSPi

Holistic Design Approach: Key functional groups effective in forming cathode and anode SEI are synthetically integrated in each additive chemistry

30