Novel Electrolytes Enabling High Efficiency …. Dendrite Free Li Deposition Using Salt Additives...
Transcript of Novel Electrolytes Enabling High Efficiency …. Dendrite Free Li Deposition Using Salt Additives...
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
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
3
(a) Li metal
batteries
(b) The typical morphology
of 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 metalLiCoO2
Sulfur
Oxygen
.
+ -
Dendrite
Short cycle Life
“Dead Li”
Short circuit
Consuming Li& electrolyte
Low energy density
Safety hazards
High surface
Low CE
Co
nseq
uen
ces
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
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, 4
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
𝑬𝑹𝒆𝒅= 𝑬𝑹𝒆𝒅∅ −
𝑹𝑻
𝒛𝑭𝒍𝒏𝜶𝑹𝒆𝒅𝜶𝑶𝒙
Nernst Equation:
An cation may have an ERed lower
than those of Li+.
5
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
6
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
1m
1m
Zhang et al, Nano Lett., 2014, 14 (12), pp 6889–6896
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/ncomms7362.7
Effects of Current Density on the Cycling Stability
The average Coulombic efficiency
of 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.
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
𝐶𝐸 =𝑄𝑆
𝑄𝑃
𝐶𝐸𝑎𝑣𝑔 = 𝑄𝑆𝑄𝑃
𝑛Average CE:
Single Cycle CE:
Current Density = 0.4 mA/cm2
QP = 0.5 mAh/cm2
Electrolyte: 4M LiFSI in DME
Method 2: Li|Cu cells – Partial Stripping
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𝐶𝐸𝑎𝑣𝑔 =𝑛𝑄𝑐+𝑄𝑆
𝑛𝑄𝑐+𝑄𝑇
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 :
𝐶𝐸𝑎𝑣𝑔 = 1 −𝑄𝑇
𝑁𝑄𝑐 + 𝑄𝑇
Proposed Universal Approach-
Method 3: Combination of Conditioning Cycle and Partial Stripping
Conditioning cycle
not included in
calculation of CE
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𝐶𝐸𝑎𝑣𝑔 =𝑛𝑄𝑐+𝑄𝑆
𝑛𝑄𝑐+𝑄𝑇
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.
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
of Cu||LiFePO4 cells.
c. Discharge capacity and CE of
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
4. Long Term Cycling of High Voltage Li Metal Batteries
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0 100 200 300 400 500
0
50
100
150
200
Dual-salt (LiTFSI + LiBOB)
E-control (1M LiPF6)
Sp
ecific
ca
pa
city (
mA
h g
-1)
Cycle number
0.175 mA cm-2
1.75 mA cm-2
0.0
0.5
1.0
1.5
2.0
Are
al ca
pa
city (
mA
h c
m-2)
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0 50 100 150 2002.5
3.0
3.5
4.0
4.5E-control (1M LiPF6)
Vo
lta
ge
(V
vs.
Li/L
i+)
Specific capacity (mAh g-1)
1st
5th
25th
50th
100th
150th
200th
250th
300th
350th
400th
450th
500th100
th cycle
0 50 100 150 2002.5
3.0
3.5
4.0
4.5
450th cycle
Dual-salt (LiTFSI + LiBOB)
Specific capacity (mAh g-1)
1st
5th
25th
50th
100th
150th
200th
250th
300th
350th
400th
450th
500th
0 50 100 150 2002.5
3.0
3.5
4.0
4.5
500th cycle
Dual-salt + 0.05 M LiPF6
Specific capacity (mAh g-1)
1st
5th
25th
50th
100th
150th
200th
250th
300th
350th
400th
450th
500th
0 100 200 300 400 500
0
50
100
150
200
Dual-salt + 0.05 M LiPF6
Dual-salt (LiTFSI + LiBOB)
E-control (1M LiPF6)
Sp
ecific
ca
pa
city (
mA
h g
-1)
Cycle number
0.175 mA cm-2
1.75 mA cm-2
0.0
0.5
1.0
1.5
2.0
Are
al ca
pa
city (
mA
h c
m-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.
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.
0 100 200 300 400
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)
Are
al c
ap
aci
ty (
mA
h c
m-2)
Cycle number
60 oC
0 200 400 600 8000.0
0.5
1.0
1.5
2.0
2.5
3.030
oC
Electrolyte: Dual-salt + 0.05 M LiPF6
, discharge: 1.75 mA cm-2
Charge: 0.58 mA cm-2
Efficiency
Capacity
Are
al c
ap
aci
ty (
mA
h c
m-2)
Cycle number
0 200 400 600 800
0
20
40
60
80
100
120
Cou
lom
bic
effic
ien
cy (
%)
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