ArticlesDOI: 10.1038/s41560-017-0005-z

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Non-encapsulation approach for high-performance Li–S batteries through controlled nucleation and growthHuilin Pan   1,2, Junzheng Chen   1,2, Ruiguo Cao1,2, Vijay Murugesan1,2, Nav Nidhi Rajput   3, Kee Sung Han   1,4, Kristin Persson3,5, Luis Estevez2, Mark H. Engelhard   4, Ji-Guang Zhang   1,2, Karl T. Mueller1,6, Yi Cui7, Yuyan Shao   1,2* and Jun Liu1,2*

1 Joint Center for Energy Storage Research (JCESR), Pacific Northwest National Laboratory, Richland, WA 99352, USA. 2 Energy and Environmental Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA. 3 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 4 Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA. 5 Department of Materials Science and Engineering, University of California-Berkeley, Berkeley, CA 94720, USA. 6 Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA. 7 Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA. *e-mail: yuyan.shao@pnnl.gov; jun.liu@pnnl.gov

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Non-encapsulation Approach for High Performance Li-S Batteries through

Controlled Nucleation and Growth

Huilin Pana,b, Junzheng Chena,b, Ruiguo Caoa,b, Vijay Murugesana,b, Nav Nidhi Rajputc, Kee

Sung Hana,d, Kristin Perssonc,e, Luis Estevezb, Mark Engelhardd, Ji-Guang Zhanga,b, Karl T.

Muellera,f, Yi, Cuig, Yuyan Shaoa,b*, Jun Liua,b*

a Joint Center for Energy Storage Research (JCESR), Pacific Northwest National Laboratory,

Richland, WA 99352, United States b Energy and Environmental Directorate, Pacific Northwest National Laboratory, Richland, WA

99352, United States c Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States

d Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory,

Richland, WA 99352, United States e Department of Materials Sciences and Engineering, University of California-Berkeley,

Berkeley, CA 94720, United States f Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory,

Richland, WA 99352, United States g Department of Materials Science and Engineering, Stanford University, Stanford, California

94305, United States

Emails: jun.liu@pnnl.gov, yuyan.shao@pnnl.gov

Supplementary Figure 1 |The characterization of low surface area CF. (a) The SEM image

of pristine CFs. (b) The BET surface area calculated from nitrogen adsorption–desorption

isotherms. The CFs used in this work has a much lower surface area (17 m2 g-1) with negligible

pore structure as compared with the commonly used carbon-based matrix for Li-S batteries.

Supplementary Figure 2 | The ex-situ XRD patterns from Non-Encap-S/CF electrodes at

0.1C in the first cycle. The peak intensity of Li2S increases along the nucleation and growth of

Li2S during the discharge process. In the following charge process, the intensity of Li2S

gradually reduces and the XRD peaks of S8 gradually show up.

15 30 45 60

S8

Li2S

Disch-2.1V

Half-Disch

Disch-1.8V

Half-Char

Char-2.39V

Char-2.8V

2Theta / Degree

0.0 0.2 0.4 0.6 0.8 1.00

20

40

60

Volu

me a

bso

rbed

(cc/g

PS

T)

Relative pressure P/Po

Surface area= 17 m2 g

-1

1μm

a b

Supplementary Figure 3 | The SEM image of the cross-section of Non-Encap-S/CF

electrode at discharged state. During discharge, the Li2S is uniformly deposited in the Non-

Encap-S/CF electrode and fills up the CF conducting network very well.

Supplementary Figure 4 | The morphological evolution of sulfur species during charge and

discharge. (a-e) The SEM image of the Non-Encap-S/CF electrode after 30-minutes discharge,

half-discharge, final discharge to 1.8 V, half-charge back and final charge back to 2.8 V in the

first cycle at 0.1C, respectively. (f) The average particle size of sulfur-based species as a function

of time during the discharge and charge process at 0.1C. The scale bar: 3μm. Note that a certain

surface of CF is required to initiate the nucleation process of sulfur species.

Top Inside

10 μm

Disch-30 min Half-Disch End-Disch

Half-char End-Char 0.0

1.5

3.0

4.5

Time / Hour

Av

era

ge

Pa

rtic

le S

ize

/

m

0 5 10 5 10

Discharge Charge

a

e d

c b

f

Supplementary Figure 5 | The XPS of CFs showing a certain O-containing functional

groups on the surface.

Supplementary Figure 6 | The SEM images of Non-Encap-S/CF electrodes discharged to

1.8 V under different C current rates. (a,b) 0.1 C. (c,d) 0.5 C. (e,f) 1 C. The average size of

Li2S decreases when increasing the current densities, but mostly retains the porous structure.

295 290 285 280

C=O

Binding Energy / eV

Inte

ns

ity / a

.u.

C-C

O=C-O

C-O

a

b

c

f

e

d

1 μm

5 μm 5 μm

500 nm

5 μm

1 μm

Supplementary Figure 7 | The operando electrochemical impedance spectra for S/CF | Li

cells during cycling. (a) Non-Encap-S/CF| Li. (b) MD-Encap-S/CF | Li.

Supplementary Figure 8 | The characterizations of active carbon (AC) as host material for

encapsulating sulfur. (a) The BET surface area of AC calculated from nitrogen adsorption–

desorption isotherms. (b,c) The cycling performance and charge and discharge curve of 4.8 M

Li2S8/AC | Li cell at 0.1C. The SEM of AC carbon (d) before cycling and (e,f) after the first

discharge. The high surface area AC shows a high reversible capacity of ~1300 mAh g-1 via

encapsulation of sulfur. Nevertheless, the overpotenial continuously increases during cycling and

0 250 500 750 10000

250

500

750

0 40 80 1200

30

60

-Z''

/

Z' /

a b

0 250 500 750 10000

250

500

750

0 10 20 300

10

1st-Disch

1st-Char

2nd-Disch

2nd-Char

3rd-Disch

3rd-Char

4th-Disch

4th-Char

5th-Disch

5th-Char

20th-Disch

20th-Char

-Z''

/

Z' /

0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800

Vo

lum

e a

bs

orb

ted

(c

c g

-1/

PS

T)

Relative Pessure P/Po

Surface area: 1829 m2 g

-1

0 6 12 18 24 300

400

800

1200

1600

Charge

Discharge

Ca

pa

cit

y /

mA

h g

-1

Cycles0 300 600 900 1200 1500

1.8

2.0

2.2

2.4

2.6

8th

Vo

lta

ge

/ V

Capacity / mAh g-1

2nd

9th10

th

25 μm

e

10 μm

d

10 μm

f

a b c

the capacity suddenly drops to ~600 mAh g-1 due to the disappearance of the second discharge

plateau. The SEM images show the layer-like Li2S coverage on the out surface of AC and the de-

attachment of deposited sulfur species from AC host even after the first discharge.

Supplementary Figure 9 | The electrochemical performance of O2 plasma treated CF

electrode. (a,b) The cycling and charge discharge curves of 4.8 M Li2S8 dissolved DOL:DME

solvent using O2 plasma treated CF free-standing electrodes at 0.1C. Areal capacity: ~3.5 mAh

cm-2. A reversible capacity of >1500 mAh g-1 is reached on the O2 plasma treated CF electrode

after a capacity activation in initial 20 cycles. This is because the poor reaction kinetics from

insulating S/Li2S coverage onto the CF electrodes after O2 plasma treatment.

Supplementary Figure 10 | The SEM images of Li2S morphologies on discharge with O2

plasma treated CF electrodes at 0.1C. This reveals a layer of Li2S coating on carbon fibers,

instead of forming micro-sized flower-like porous particles on bare CF electrode.

0 20 40 600

400

800

1200

1600

Charge

Discharge

Cap

acit

y / m

Ah

g-1

Cycles

0 400 800 1200 16001.5

2.0

2.5

3.0

Vo

ltag

e/ V

Capacity / mAh g-1

1st 10

th 20th

a b

5 μm 10 μm

a b

Supplementary Figure 11 | The initial discharge potential profiles of 1 M Li2S8 dissolved in

TMS, DOL:DME and DMSO solvents at CF free-standing electrodes respectively. The

counter electrodes are Li metals. The discharge rate is 0.1C. 0.5 M LiTFSI is used as supporting

salt in TMS, DOL: DME. 2 M LiTFSI is used for DMSO solvent. Note that side reaction with

DMSO might occur on the cathode and contribute additional capacity.1 Further study is needed

to stabilize cathode and anode in DMSO system for long-term cycling.

Supplementary Figure 12 | The cycling performance of S/CF electrodes with 1 M Li2S8 in

TMS and DMSO solvents. 0.5 M LiTFSI, 2 wt% LiNO3 and 2 M LiTFSI, 2 wt% LiNO3 were

used as supporting salt and additive in TMS and DMSO solvents respectively. The layer-like

precipitation of sulfur species in TMS causes low sulfur utilization and capacity fading due to the

passivation in following cycles. Small sulfur particles formed in DMSO produce high initial

sulfur utilization but poor cycling due to the instability of Li metal and possible accumulation of

small particles on the cathode in DMSO solvent.

Supplementary Figure 13 | SEM images of Li metal surface with different solvents. (a)

TMS; (b) DOL:DME; (c) DMSO in the charge states of the fifth cycle (0.1C). Electrolyte: 1 M

Li2S8, 0.5 M LiTFSI, 2 wt% LiNO3 in TMS and DOL:DME; 1 M Li2S8, 2 M LiTFSI, 2 wt%

LiNO3 in DMSO. Scale bar: 100 μm. Ether-based DOL:DME exhibits the most smooth Li

surface after cycling (Supplementary Fig. 13b), which also accounts for the excellent cyclic

stability as shown in Fig. 3b-3c in the main text. Some large aggregates are shown on the Li

metal surface in TMS solvent, but the most part of Li surface still retains smooth (Supplementary

Fig. 13a). DMSO solvent system shows the least stability with Li among the three solvents.

Fortunately, the corrosion of Li metal is greatly alleviated in the 2 M LiTFSI DMSO electrolyte

showing large area of flat lithium surface (Supplementary Fig. 13c), which enables the Li-S cell

charge/discharge so that we can study the initial nucleation process of S/Li2S on the cathode side.

Supplementary Table 1 | The comparison of CF based sulfur electrodes with different

morphologies.

Sulfur

electrode

Sulfur mass

loading

(mg cm-2)

Electrode

thickness

(μm)

Electrode

density

(g cm-3)

Areal

capacity

(mAh cm-2)

Gravimetric

energy density

(Wh kg-1)

Volumetric

energy density

(Wh L-1)

MD-Encap-S/CF 2.48 125 0.36 1.485 725 260

Non-Encap- S/CF 2.32 36 1.26 3.79 1835 2317

Note: The obtained results in above table are collected from the experimental data of the cells in Fig. 2a

and 2d at discharge state. (The diameters of MD-Encap-S/CF and Non-Encap-S/CF electrodes are 9/16”

and 5/8’’. The sulfur utilization of 35% and 100% are used for the calculation of MD-Encap-S/CF and

Non-Encap-S/CF electrodes. The sulfur mass ratios in the cathdoes are 60% and 65.7% respectively.) The

net thickness of sulfur electrodes are measured using a millimeter at discharged states. The electrode

gravimetric and volumetric energy densities are calculated based on overall cathode only at discharge

state (including reacted lithium, conducting carbon and binder). The average operating voltage of Li-S

cell is chosen as 2.2 V. The bulk densities of sulfur, CF, super P and PVDF binder those are used for the

above calculation are 1.92, 1.5, 1.5 and 1.78 g cm-3 respectively.

a b c

Supplementary references:

1. Pan H, et al. On the Way Toward Understanding Solution Chemistry of Lithium Polysulfides for

High Energy Li–S Redox Flow Batteries. Advanced Energy Materials 5, 1500113 (2015).