[pyr14][TFSI], [pyr13][FSI], and [EMIM][BF4 - NASA · • Anion exchange secondary to net motion of...

Investigation of structure and transport in Li-doped ionic liquid electrolytes�

Justin B. Haskins,1 William R. Bennett,2 James J. Wu,2 Dionne M. Hernández,2 Oleg Borodin,3 Joshua D. Monk,1

Charles W. Bauschlicher Jr.,4 John W. Lawson5�

1ERC, Inc., NASA Ames Research Center, Moffett Field, CA 94035�2Electrochemistry Branch, NASA Glenn Research Center, Cleveland, OH 44135�3Electrochemistry Branch, U.S. Army Research Laboratory, Adelphi, MD 20783�

4Entry Systems and Technology Division, NASA Ames Research Center, Moffett Field, CA 94035�5Thermal Protection Materials Branch, NASA Ames Research Center, Moffett Field, CA 94035�

��

[pyr14][TFSI], [pyr13][FSI], and [EMIM][BF4]�

https://ntrs.nasa.gov/search.jsp?R=20140017151 2019-12-27T09:19:18+00:00Z

Outline�

��

• Li-doped ionic liquids for electrochemical applications��• Atomistic computational modeling of ionic liquids�

• Influence of Li+ on ionic liquid structure�- Li+/Anion binding and solvation�- Li+ … Li+ network statistics��

• Transport properties of Li-doped ionic liquids��• Kinetics of Li+ transport in ionic liquids�

- Li+/Anion residence times�- contribution of anion exchange to diffusion�

�

��

Ionic liquids for electrochemical applications�

��

•  �� !��"�� #�� $�� %��

�•  �� !�� "��&��

�%�� '��(�� •  �� )��"�� %��

� ! ��%��•  �� *�)��

��(�� *��)�*��$��

•  �� !� ��* �� (�� "��$��

�

��

�+�,�� +��-+�.�*��/0��1��1�2�11�3�

Computational models and molecular dynamics (MD)�

��

•  ��*��4�� *��#�� (��

•  ��(�� !�� & "�� !�� #��5��)�� %�� )� !��%(��2..'67.3�

��

� � � ��•  8��)��( �%�"�)%�!�� & ��•  �%��(��&�� 9�� (��•  :�(�� ;��

F = −∇U

[pyr14][TFSI]�

��

URD = Aij exp(−Bijrij )−Cijrij−6( )

i< j

∑

UES =qiqj4πε0rij

⎛

⎝⎜⎜

⎞

⎠⎟⎟

i< j

∑ −1

2

�μ ⋅�Ei0

i

∑

,+�<��)�� 0��2��13�,+�<��)�� +�� 0�/1�0�1��2��03�,+�<��)�� +�� 0�1��0�11�2��03��

[TFSI]- bis(trifluoromethylsufonyl)imide�

[FSI]- bis(fluorosufonyl)imide�

[BF4]- boron tetrafluoride�

[pyr14]+ N-methyl-N-butylpyrrolidinium+�

[pyr13]+ N-methyl-N-proylpyrrolidinium+�

[EMIM]+ 1-methyl-3-ethylimidazolium+�

��

��

Ionic liquids of interest�

;��

Influence of Li+-doping on anion distributions�

0��

0 4 8 12 16r (Å)

0

1

2

g--(r

)

0 4 8 12 16r (Å)

0 4 8 12 16r (Å)

(g) (h) (i)

[pyr14][TFSI]

0.85[pyr14][TFSI] + 0.15Li[TFSI]

0.67[pyr14][TFSI] + 0.33Li[TFSI]

[pyr13][FSI]

0.85[pyr13][FSI] + 0.15Li[FSI]

0.67[pyr13][FSI] + 0.33Li[FSI]

[EMIM][BF4]

0.85[EMIM][BF4] + 0.15Li[BF4]

0.67[EMIM][BF4] + 0.33Li[BF4]

Small anion separation around Li+�

Li+-Li+ distributions�

/��

0 5 10 15 20r (Å)

0

2

4

6

8

10

gLi+ -L

i+ (r)

xLi+ = 0.05

xLi+ = 0.20

xLi+ = 0.33

[EMIM][BF4](c)

0 5 10 15 20r (Å)

0

1

2

3

4

gLi+ -

Li+

(r)

xLi+ = 0.05

xLi+ = 0.20

xLi+ = 0.33

[pyr13][FSI]

(b)

0 5 10 15 20r (Å)

0

1

2

3

4

5

gLi+ -

Li+

(r)

xLi+ = 0.05

xLi+ = 0.20

xLi+ = 0.33

[pyr14][TFSI](a)[pyr13][FSI] [EMIM][BF4][pyr14][TFSI]

Li+ …. Li+ clustering at low-r and high doping levels�

10 20 30 40xLi

+ (mole fraction Li-salt)

60

70

80

90

100

Mon

oden

tate

Li+

Lig

ands

(%

)

[TFSI]-

[BF4]-

[FSI]-

Li+/Anion bonding structures�

��

Bidentate (κ2)�Monodentate (κ1)�

•  Li-[TFSI] bonding dependence on Li-doping level�•  More monodentate at high doping levels�

Li+/Anion solvation shells�

1��

[Li][TFSI]�� [Li][BF4]�

��

b)� [Li][FSI]��

300 320 340 360 380 400Temperature (K)

nLi

+

([BF4]-) = 4; (κ

1κ

1κ

1κ

1)

nLi

+

([BF4]-) = 4; (κ

1κ

1κ

1κ

2)

(c)

nLi

+

([FSI]-) = 4; (κ

1κ

1κ

1κ

1)

nLi

+

([FSI]-) = 4; (κ

1κ

1κ

1κ

2)

nLi

+

([FSI]-) = 3; (κ

1κ

1κ

2)

nLi

+

([FSI]-) = 5; (κ

1κ

1κ

1κ

1κ

1)

(b)

300 320 340 360 380 400Temperature (K)

0

25

50

75

100

Coo

rdin

atio

n C

ompl

exes

(%

)

nLi

+

([TFSI]-) = 3; (κ

1κ

1κ

2)

nLi

+

([TFSI]-) = 3; (κ

1κ

2κ

2)

nLi

+

([TFSI]-) = 4; (κ

1κ

1κ

1κ

1)

(a)

300 320 340 360 380 400Temperature (K)

•  4-5 anion neighbors in Li+ solvation shell: [TFSI] (3-4), [BF4] (4), [FSI] (3-5)�

•  [Li(TFSI)2]- and [Li(FSI)3]-2 from expeiment (J.C. Lassegues, et al., J. Phys. Chem. A 113, 305 (2009) and K. Fujii, et al., J. Phys. Chem. C 117, 19314 (2013))�

1-coordinated� 2-coordinated�

3-coordinated�4-coordinated�

Li+ … Li+ networks�

��

10-3

10-2

10-1

100

101

102

Clu

ster

Dis

trib

utio

n (%

)

(b)

[pyr13][FSI]

1 2 3 4 5 6 7NLi

+ (cluster size)1 2 3 4 5 6 7

NLi+ (cluster size)

10-3

10-2

10-1

100

101

102

Clu

ster

Dis

trib

utio

n (%

)

(c)

[EMIM][BF4]

10-3

10-2

10-1

100

101

102

Clu

ster

Dis

trib

utio

n (%

)

xLi+ = 0.33

xLi+ = 0.20

xLi+ = 0.15

xLi+ = 0.10

(a)

[pyr14][TFSI]

1 2 3 4 5 6 7NLi

+ (cluster size)

•  Networks at all levels of Li-doping�

•  5-6 Li-ions in largest networks�

•  Structural impact on anions�

0 10 20 30 40xLi

+ (mol % Li-salt)

30

40

50

60

70

Cis

Isom

er P

roba

bilty

(%

)

[TFSI]-

[FSI]-

solid lines: all anionsdashed lines: anions not bound to Li

+

0.1 0.2 0.3 0.4xLi


50

60

70

80

90

100

Mon

oden

tate

Li+

Lig

ands

(%

)

[pyr13][FSI][EMIM][BF4]

[pyr14][TFSI]

dashed lines: unclustered Li+

solid lines: all Li+

Influence of Li+ … Li+ networks on structure�

��

•  cis-[TFSI] and cis-[FSI] conformers in Li+ solvation shell�

•  Monodentate binding in [TFSI] networks�

Computational measures of thermodynamics and transport�

��

�� !"�#$�%"� �� "�$�%"� ��&%&"��$!"�

'�� +;� ��0/+1� ��10+1�

()� �+�1/� �+�� +��0�

(�� +�� +�� +��

(�� +��0� �+�01� �+��

*�� ;�� 1� ��/�

+�� +0/� �+�;� ��+�;�

(�� '�,-./0�1��2��(�3� ��(�,��04/ 1��2��5� �� *�,�61��2��7�� +�(mS/cm)�

•  Greater ion mobility with decreasing density and ion size�

•  High accuracy of predicted properties:�-  density within ~1%�-  diffusion within 10-25%�-  conductivity within 10-20%�

Comparison of room-T Li transport�

��

10-2

10-1

100

DLi

+ x 10

10 (

m2 /s

)

0 0.1 0.2 0.3 0.4xLi

+ (mol fraction)

10-2

10-1

�Li+ (

mS

/cm

)

(d)

(g)

0 0.1 0.2 0.3 0.4xLi

+ (mol fraction)

(e)

(h)

0 0.1 0.2 0.3 0.4xLi

+ (mol fraction)

(f)

(i)

(f)

0 0.1 0.2 0.3 0.4xLi

+ (mol fraction)

(i)

luc�

luc�

[pyr14][TFSI][pyr14][TFSI] (exp)

[EMIM][BF4]

[EMIM][BF4] (exp)

[pyr13][FSI][pyr13][FSI] (exp)

[pyr14][TFSI]

•  T = 298 K properties computationally expensive (~200 ns)�

•  Li+ ionic conduction order of magnitude lower in [pyr14][TFSI]�

•  Plateau in ionic conduction at high Li-doping�

2.8 3.2 3.6 4

1000/T (K-1

)

100

101

102

λ (m

S/c

m)

1 M Li[PF6] in 1:1 EC:DMC

0.5 m Li[BF4] in [EMIM][BF4]

0.5 m Li[FSI] in [pyr13][FSI]

0.5 m Li[TFSI] in [pyr14][TFSI]

10 % error bars

Experimental comparison of ionic conductivity to that of Li-ion battery organic electrolytes�

��

Mid-T ion conductivity comparable to conventional electrolytes�

Exchange of anions in the Li solvation shell�

�;��

Li[BF4]�

Li[TFSI]�

Li+/Anion residence times�

�0��

0 0.1 0.2 0.3 0.4xLi


1

10

100

�Li /

- (ns

)

[pyr14][TFSI]

[EMIM][BF4]

[pyr13][FSI]

(a) T = 298 K

300 325 350 375 400T (K)

1

10

100

�Li /

- (ns

)

[pyr14][TFSI]

[EMIM][BF4]

[pyr13][FSI]

(b)

xLi+ = 0.10

•  Longer residence times at higher Li-doping levels�

•  Times follow [TFSI] > [BF4] > [FSI]�

Contribution of anion exchange to diffusion�

�/��

0 5 10 15 20Time (ns)

0

10

20

30

40

MS

DLi (

Å2 )

Total Li DiffusionBAX Li Diffusion

[pyr14][TFSI]; xLi = 0.10; T = 300 K

xLi+ DLi+bax/DLi+ N〈R〉 DLi+

bax/DLi+ N〈R〉 DLi+bax/DLi+ N〈R〉

0.05 0.69 4.4 0.81 3.7 0.89 6.10.10 0.66 4.2 0.85 2.4 1.07 5.80.33 0.59 3.5 0.73 2.0 0.91 3.9

[pyr14][TFSI]� [pyr13][FSI]� [EMIM][BF4]�

•  Anion exchange a secondary factor in Li+ diffusion�

•  Anion exchange more important with larger anions and higher Li-doping�

Conclusions�

��

• Lithium networks present at all levels of doping��• Li/anion binding tends to prefer monodentate at all high levels of doping�

• Transport properties in good agreement with experiment�- density follows [BF4] < [FSI] < [TFSI]�- lithium diffusion follows [BF4] > [FSI] > [TFSI]��

• Anion exchange secondary to net motion of lithium with the solvation shell�

Acknowledgements�

�1��

Miscellaneous slides�

��

Density�

��

300 320 340 360 380 400T (K)

1200

1300

1400

ρ (k

g·m

-3)

(a)

0 0.1 0.2 0.3 0.4xLi

+ (mol fraction Li-salt)

1200

1300

1400

1500

ρ (k

g·m

-3)

(b)

[pyr14][TFSI][pyr13][FSI][EMIM][BF4]

[pyr14][TFSI] (exp)[pyr13][FSI] (exp)[EMIM][BF4] (exp)

��

Viscosity�

��

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

101

102

�xy

(cP

)

xLi+ = 0.10

xLi+ = 0.00

xLi+ = 0.00 (exp)

(c)[pyr13][FSI]

101

102

101

102

�xy

(cP

)

xLi+ = 0.10

xLi+ = 0.10 (exp)

xLi+ = 0.00

xLi+ = 0.00 (exp)

(b)[EMIM][BF4]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

101

102

103

�xy

(cP

)

xLi+ = 0.10

xLi+ = 0.10 (luc)

xLi+ = 0.10 (exp)

xLi+ = 0.00

xLi+ = 0.00 (exp)

[pyr14][TFSI] (a)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

10-2

10-1

100

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

10-2

10-1

100

D x

1010

(m

2 s-1)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

[pyr13]+

[FSI]-

Li+

(e) (f)

0.9[pyr13][FSI] + 0.1Li[FSI][pyr13][FSI]

[pyr14]+ (exp)

[TFSI]- (exp)

Li+ (exp)

10-2

10-1

100

D x

1010

(m

2 s-1)

10-1

100

101

D x

1010

(m

2 s-1)

[pyr14]+

[TFSI]-

Li+

Li+ (luc)

[pyr14]+ (exp)

[TFSI]- (exp)

Li+ (exp)

[EMIM]+

[BF4]-

Li+

[EMIM]+ (exp)

[BF4]- (exp)

Li+ (exp)

(a)

(c)

(b)

(d)

[pyr14][TFSI] 0.9[pyr14][TFS1] + 0.1Li[TFSI]

0.9[EMIM][BF4] + 0.1Li[BF4][EMIM][BF4]

Diffusion�

��

Ionic conductivity�

��

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

0.1

1

10

100

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.15

xLi+ = 0.13 (exp)

(c) [pyr13][FSI]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

0.1

1

10

100

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.10

(c) [pyr13][FSI]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

0.1

1

10

100

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.10

(c) [pyr13][FSI]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

0.1

1

10

100

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.15

xLi+ = 0.13 (exp)

(c) [pyr13][FSI]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

0.1

1

10

100

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.15

xLi+ = 0.13 (exp)

(c) [pyr13][FSI]

1

10

100

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.10

xLi+ = 0.09 (exp)

(b) [EMIM][BF4]

0.1

1

10

100

1

10

100

λ (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.10

xLi+ = 0.09 (exp)

(b) [EMIM][BF4]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

12.6 2.8 3 3.2 3.4

1000/T (K-1

)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

0.1

1

10

� (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.20

xLi+ = 0.18 (exp)

(a) [pyr14][TFSI]

0.1

1

10

λ (m

S/c

m)

xLi+ = 0.0

xLi+ = 0.0 (exp)

xLi+ = 0.20

xLi+ = 0.18 (exp)

(a) [pyr14][TFSI]

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

12.6 2.8 3 3.2 3.4

1000/T (K-1

)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

2.6 2.8 3 3.2 3.4

1000/T (K-1

)

Date post:	06-Sep-2019
Category:	Documents
Upload:	others
View:	4 times
Download:	0 times

[pyr14][TFSI], [pyr13][FSI], and [EMIM][BF4 - NASA · • Anion exchange secondary to net motion of...

Documents