[PPT] - Novel Electrolytes Enabling High Efficiency Cycling of Rechargeable PowerPoint Presentation

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Novel Electrolytes Enabling High Efficiency Cycling of Rechargeable Li Metal Batteries

The 10th Symposium on Energy Storage beyond Li-Ions IBM Research - Almaden June 27, 2017

Ji-Guang Zhang

Pacific Northwest National Laboratory, Richland, WA

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1. Dendrite Free Li Deposition Using Salt Additives
2. High Rate Li Deposition with High Coulombic Efficiency (CE)
3. Accurate Determination of CE
4. Long Term Cycling of High Voltage Li Metal Batteries
5. Summary

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Outline

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(a) Li metal batteries (b) The typical morphology

f Li dendrite

(Chianelli,1976) (c) Main problems related with dendrite and low Coulombic efficiency.

Challenges on Li Metal Anode

Two main barriers :

1. Dendrite growth; 2. Low Coulombic efficiency

Cathode Anode Li metal LiCoO2 Sulfur Oxygen .

+

Dendrite

Short cycle Life “Dead Li” Short circuit Consuming Li & electrolyte Low energy density Safety hazards High surface Low CE Consequences

Wu Xu, Jiulin Wang, Fei Ding, Xilin Chen, Eduard Nasybulin, Yaohui Zhang and Ji-Guang Zhang, Energy Environ. Sci., 2014, 7 (2), 513 – 537.

High surface area

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1. Dendrite Free Li Deposition Using Salt Additives

Fei Ding, Wu Xu, Gordon L. Graff, Jian Zhang, Maria Sushko, Xilin Chen, Yuyan Shao, Mark H. Engelhard, Zimin Nie, Jie Xiao, Xingjiang Liu, Peter V. Sushko, Jun Liu, and Ji-Guang Zhang, J. Am. Chem. Soc., 2013, 135 (11), pp 4450–4456,

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Li+ Cs+ Rb+ Stand reduction potential (1M)

3.040 V
3.026 V
2.980 V

Effective reduction potential at 0.05M*

3.103 V
3.06 V

Effective reduction potential at 0.01M*

3.144 V
3.098 V

𝑭𝑺𝒇𝒆= 𝑭𝑺𝒇𝒆

∅

− 𝑺𝑼 𝒜𝑮 𝒎𝒐 𝜷𝑺𝒇𝒆 𝜷𝑷𝒚

Nernst Equation:

An cation may have an ERed lower

than those of Li+.

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20 µm

a

20 µm

b

20 µm

c

20 µm

d

20 µm

e

Control electrolyte: 1 M LiPF6 in PC.
CsPF6 concentration in the electrolyte: (a) 0 M, (b) 0.001 M, (c) 0.005 M,

(d) 0.01 M, and (e) 0.05 M.

Cs+ additive can effectively suppress Li dendrite growth.

Effect of CsPF6 Additive on The Morphology of Li Deposition

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1 M LiPF6 in PC 1 M LiPF6 in PC+ 0.05 M CsPF6

Dendrite Free Li Deposition with Salt Additive

Surface Cross section

Dendritic surface
Random growth
Smooth surface
Highly ordered growth

1m 1m Zhang et al, Nano Lett., 2014, 14 (12), pp 6889–6896

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2. High Rate Stable Li Deposition using

High Concentration LiFSI-DME Electrolyte

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Li deposited in 4M LiFSI-DME Electrolyte exhibits a nodule structure with

much smaller surface area as compared to those deposited in carbonate based electrolyte.

J. Qian, W.A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin & J.G. Zhang

Nature Communications, 2015, DOI: 10.1038/ncomms7362.

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Effects of Current Density on the Cycling Stability

The average Coulombic efficiency
f the cycling is >99% (0.2 mA cm-

2), >98% (2.0 and 4.0 mA cm-2) and

>97% (8.0 and 10.0 mA cm-2).

CE is stable up to1000 cycles.

4M LiFSI in DME

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4M LiFSI in DME 4M LiFSI in DME

J. Qian, W.A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin & J.G. Zhang

Nature Communications, 2015, DOI: 10.1038/ncomms7362.

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Long Term Cycling Stability of Li|Li cells Using Electrolyte E1

Current density: 10 mA/cm2.
Stable cycling for more than 6,000 cycles.
No short, no increase in impedance or cell voltage.

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J. Qian, W.A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin & J.G. Zhang

Nature Communications, 2015, DOI: 10.1038/ncomms7362.

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3. Accurate Determination of CE
Different Li CEs were reported even for the same system.
There is an urgent need to identify an general methodology to measure

CE for Li metal anode.

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Factors Affecting Measurement of Li CE

Substrate selection
Substrate treatment approaches
Accuracy of the instrument
Cell design
Measurement protocols

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Method 1: Li|Cu cells – Full stripping for Each Cycle

Average CE = 98.8% for 100 cycles

𝐷𝐹 =

𝑅𝑇 𝑅𝑄

𝐷𝐹𝑏𝑤𝑕 =

𝑅𝑇

𝑅𝑄

𝑜

Average CE: Single Cycle CE:

Current Density = 0.4 mA/cm2 QP = 0.5 mAh/cm2 Electrolyte: 4M LiFSI in DME

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Method 2: Li|Cu cells – Partial Stripping

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𝐷𝐹𝑏𝑤𝑕 = 𝑜𝑅𝑑+𝑅𝑇

𝑜𝑅𝑑+𝑅𝑈

Average CE = 99.2% for 100 cycles

Current Density = 0.4 mA/cm2 QT = 4 mAh/cm2 QC = 0.5 mAh/cm2 Alternative Equation when voltage exceeds upper limit in N cycles :

𝐷𝐹𝑏𝑤𝑕 = 1 − 𝑅𝑈 𝑂𝑅𝑑 + 𝑅𝑈

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Proposed Universal Approach- Method 3: Combination of Conditioning Cycle and Partial Stripping

Conditioning cycle

not included in calculation of CE

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𝐷𝐹𝑏𝑤𝑕 =

𝑜𝑅𝑑+𝑅𝑇 𝑜𝑅𝑑+𝑅𝑈 Current Density = 0.4 mA/cm2 QT = 4 mAh/cm2 QC = 0.5 mAh/cm2

Eliminate the uncertainty related to substrate material

and treatment conditions

Average CE = 99.4% for 100 cycles

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Effect of Li Deposition Rate in Carbonate Electrolytes

CE and cycle life of Li/NCA cell can be improved by slow charge (Li deposition).

Li||NCA cells using 1M LiPF6 EC:EMC (4:6 wt.) electrolyte Li deposition~ charge process Lv & Xiao et al., Adv. Energy Mater. 2015, 5, 1400993

Cross-sectional SEM images of the Li anodes obtained from the cells after 100 cycles at a) 0.2C charge/1C discharge, b) 0.5C charge/discharge, c) 1C charge/discharge, and d) 2C charge/discharge.

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Effect of Li Stripping Rate in Carbonate Electrolytes

Li||NMC cells using 1M LiPF6/EC-DMC (1:2 in volume) electrolytes Li stripping ~ Discharge process

Zheng & Xu et al., Adv. Energy Mater. 2016, 1502151.

CE and cycle life of Li/NMC cell can be improved by fast discharge (Li stripping).
Fast discharging formes a transient highly concentrated Li+ ion solution in the

vicinity of Li surface and reduce the interaction between fresh Li metal and electrolyte.

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High

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Effect of Charge/Discharge Protocol on CE of Li Cycling in Ether Based Electrolyte

a. CE of Cu||Li cells. b. Charge/discharge voltage profiles

f Cu||LiFePO4 cells.

c. Discharge capacity and CE

f

anode-free Cu||LiFePO4 cells.

The CE of Li cycling can be increased to 99.8% with the combination of high

concentration electrolyte (4M LiFSI/DME) and low rate Li deposition/high rate Li stripping protocols.

Anode-free Cu||LiFePO4 cell can retain 54% capacity after 100 cycles.

a

b

c

Cu||LiFePO4

Electrolyte: 4M LiFSI-DME

Qian et al, Adv. Funct. Mater. 2016,DOI:10.1002/adfm.201602353

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4. Long Term Cycling of High Voltage

Li Metal Batteries

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100 200 300 400 500 50 100 150 200 Dual-salt (LiTFSI + LiBOB) E-control (1M LiPF6) Specific capacity (mAh g

1)

Cycle number 0.175 mA cm

2

1.75 mA cm

2

0.0 0.5 1.0 1.5 2.0 Areal capacity (mAh cm

2)

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50 100 150 200 2.5 3.0 3.5 4.0 4.5

E-control (1M LiPF6) Voltage (V vs. Li/Li

+)

Specific capacity (mAh g

1)

1

st

5

th

25

th

50

th

100

th

150

th

200

th

250

th

300

th

350

th

400

th

450

th

500

th

100

th cycle

50 100 150 200 2.5 3.0 3.5 4.0 4.5

450

th cycle

Dual-salt (LiTFSI + LiBOB) Specific capacity (mAh g

1)

1

st

5

th

25

th

50

th

100

th

150

th

200

th

250

th

300

th

350

th

400

th

450

th

500

th

50 100 150 200 2.5 3.0 3.5 4.0 4.5

500

th cycle

Dual-salt + 0.05 M LiPF6 Specific capacity (mAh g

1)

1

st

5

th

25

th

50

th

100

th

150

th

200

th

250

th

300

th

350

th

400

th

450

th

500

th

100 200 300 400 500 50 100 150 200 Dual-salt + 0.05 M LiPF6 Dual-salt (LiTFSI + LiBOB) E-control (1M LiPF6) Specific capacity (mAh g

1)

Cycle number 0.175 mA cm

2

1.75 mA cm

2

0.0 0.5 1.0 1.5 2.0 Areal capacity (mAh cm

2)
LiTFSI-LiBOB dual salt electrolyte with LiPF6 additive shows better stability

with Li metal. Electrochemical behaviour of Li||NMC cells

Zheng, M. H. Engelhard, D. Mei, S. Jiao, B. J. Polzin, J.-G. Zhang, and W. Xu, Nature Energy, 2017, 2, 17012.

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Effects of testing temperature and charge current density

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LiPF6 additive (optimum 0.05M) improves the cycling performances at

high temperature and low charge current.

100 200 300 400 0.0 0.5 1.0 1.5 2.0 1.75 mA cm-2

Dual-salt + 0.05 M LiPF6 Dual-salt (LiTFSI + LiBOB) E-control (1M LiPF6)

Areal capacity (mAh cm

2)

Cycle number

60 oC 200 400 600 800 0.0 0.5 1.0 1.5 2.0 2.5 3.0 30 oC Electrolyte: Dual-salt + 0.05 M LiPF6 , discharge: 1.75 mA cm-2 Charge: 0.58 mA cm-2

Efficiency Capacity Areal capacity (mAh cm

2)

Cycle number

200 400 600 800 20 40 60 80 100 120

Coulombic efficiency (%)

Zheng, M. H. Engelhard, D. Mei, S. Jiao, B. J. Polzin, J.-G. Zhang, and W. Xu, Nature Energy, 2017, 2, 17012.

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5. Summary
Most reliable method for CE measurement is by combining a conditioning

cycle and partial plating/stripping of Li metal using Li/Cu cells.

The combination of high concentration electrolyte (4M LiFSI/DME) and low

rate Li deposition/high rate Li stripping protocols can further increase the CE of Li cycling to 99.8%.

LiPF6 additive (0.05M) in LiTFSI-LiBOB dual salt electrolyte can largely

enhance long-term cycling stability (> 800 cycles) of high voltage Li metal batteries.

A new electrolyte enables high efficiency cyling of both Li metal anode (up

to 99.5%) and stable cycling of Li/NMC cells (>95% capacity retention after 300 cycles and 85% capacity retention after 600 cycles).

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Acknowledgments

PNNL: Wu Xu, Shuru Chen, Jianming Zheng, Fei Ding, Jiangfeng Qian, Yaohui Zhang, Brian D. Adams, Wesley Henderson, Ruiguo Cao, Shuhong Jiao, Jie Xiao, M. H. Engelhard, M. E. Bowden, D.H. Mei, J. Liu ARL: Oleg Borodin, Kang Xu Financial Support

DOE/OS/BES/The Joint Center for Energy Storage Research

(JCESR)

DOE/EERE/OVT/Advanced Battery Materials Research Program

(BMR) and Battery 500 Program

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