A novel synergistic strategy for developing high-performance lithium

Subscriber access provided by UNIV OF DURHAM

Letter

A novel synergistic strategy for developing high-performance lithium sulfur batteries of large areal sulfur loading by SEI modified separator Junling Guo, Shupeng Zhao, Gaohong He, and Fengxiang Zhang ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.7b00290 • Publication Date (Web): 20 Feb 2018 Downloaded from http://pubs.acs.org on February 20, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Energy Materials is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Energy Materials

A Novel Synergistic Strategy for Developing High-Performance Lithium Sulfur Batteries of Large Areal Sulfur Loading by SEI Modified Separator Junling Guo, Shupeng Zhao, Gaohong He and Fengxiang Zhang∗ J. L. Guo, S. P. Zhao, Prof. G. H. He and Prof. F. X. Zhang State Key Laboratory of Fine Chemicals and School of Petroleum and Chemical Engineering, Dalian University of Technology, 2 Dagong Road, Liaodongwan New District, Panjin 124221, P. R. China. E-mail: [email protected]

Keywords: Li-S battery; Solid electrolyte interface; CNT array; Large areal sulfur loading; Separator

ACS Paragon Plus Environment

1

ACS Applied Energy Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 25

Abstract As a crucial energy density determining factor, the areal sulfur loading is still low nowadays for practical applications of Li-S batteries. To address this issue, intensive research efforts have been devoted to development of sulfur-hosting materials with ultrahigh specific surface area. However, design and manufacturing process for these materials is complicated. Herein, we report a novel and facile strategy for developing high-performance cathode with high areal sulfur content using conventional sulfur hosts without ultra-high specific area. This strategy features a dense blocking layer of solid electrolyte interface (SEI) on the separator to insure cycle stability of the cathode with a high areal sulfur loading. Meanwhile, a nano-array cathode structure (CNT array on carbon cloth) is adopted to guarantee high sulfur utilization and rate performance. With the synergistic effect of dense blocking layer and CNT array structure, the cathode with 10mg/cm2 sulfur (90.9% in CNT/S composite) shows good rate- and cycle performance. Our strategy may open up a new avenue for the design and construction of superior Li-S batteries with large sulfur loading without complex materials synthesis. Li-S batteries have been regarded as one of the most promising candidates for nextgeneration batteries since their theoretical energy density (~2,600 Wh/kg) is much higher than that of existing lithium-ion batteries (~200 Wh/kg).1,

2

However, there are some

drawbacks impeding their popularization, including low sulfur utilization due to its low electrical conductivity and unsatisfactory cycle performance caused by “redox shuttle reactions” of dissolved lithium polysulfides (PS).3, 4 These issues have been addressed in many previous works; however, the areal sulfur loading, as a crucial factor related to energy-density of the batteries, is still low (< 6 mg/cm2) for practical application.5, 6 Areal


2

Page 3 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


sulfur loading is primarily restricted by the low mass content of sulfur in the cathodes (50%~70%).7-9 This is because, with a low sulfur content, there is no choice but to increase the thickness of the electrode film to obtain a high areal loading.10 However, the thick electrode tends to fracture and delaminate from the current collector, and always exhibits low rate performance, making the sulfur-rich electrode difficult to realize.11, 12 The sulfur content has rarely been successfully improved in previous works, which is likely due to the contradiction between sulfur loading and the surface area of sulfur hosts (carbon or polar materials). High surface area is needed to trap dissolved polysulfide via physical confinement or chemical interactions so that a good cycle stability can be achieved.13-15 High surface area is also needed for immobilizing insoluble Li2S2 or Li2S16,

17

to insure a high sulfur utilization and rate performance; without

adequate surface area, a thick Li2S2 or Li2S layer will deposit on the hosting materials, and impede subsequent reactions of PS and reduce the holistic electrical conductivity of electrode18, 19 . However, if the sulfur content is too high, much surface area will be lost and becomes unavailable for polysulfide trapping and Li2S2 or Li2S immobilization. In the past few years, intensive research efforts have been made to develop sulfur hosts with ultra-high specific surface area.20-22 Through these efforts, the sulfur mass content and areal loading can be increased to 90% and > 6 mg/cm2, respectively.23-24 However, complexity involved in the design and manufacturing process for these materials is not compatible with practical application of the battery.11 Therefore, it is highly desired to design and fabricate a cathode of large areal sulfur loading without involvement of complex sulfur hosts synthesis.


3


Page 4 of 25

Herein, we report a facile and novel synergistic strategy to achieve the above goal. Enlightened by some reported works,25 instead of seeking polysulfide confinement with ultra-high-specific-area sulfur hosts, we explore polysulfide blocking by using a separator modified with a dense solid electrolyte interface (SEI) layer. This SEI modified separator will help confine the dissolved polysulfide between the cathode and the separator, and thus, allow the use of large areal sulfur loading in the cathode. The SEI modified separator differs from literature reported separators decorated with sulfur-hosts such as CNT,26 V2O5,27 graphene28 and so on; these separators, although able to increase the sulfur content in cathode, still work on an adsorption basis, and therefore, the sulfur content (S/hosts in cathode and separator) can hardly support high areal loading of sulfur.26-29 In addition to the use of SEI modified separator, we also adopt a carbon nanotube (CNT) array in the cathode to load insoluble Li2S2 or Li2S and facilitate electron transport, thus insuring high sulfur utilization and rate performance.19, 30 With the synergistic effect of SEI modified separator and CNT cathode structure, our cathode with an areal sulfur loading as high as 10mg/cm2 can give a high rate- and cycle performance. Meanwhile, the mass sulfur content can reach 90.9% in the cathode, and 80.1% when the carbon materials on separator also is counted in. The SEI modification of separator (SC-separator) was achieved simply by charging– discharging a coin cell with the separator that is pre-coated with an active layer of carbon black and PVDF binder (C-separator) at 50 mA/cm2 (~100 mA/g). The compositions of coin cell used for forming SEI is as follows: the carbon layer of C-separator as cathode, the polypropylene membrane of C-separator as separator and Li metal as anode. The electrolyte we used is the normal electrolyte of Li-S battery, which comprised 1 M


4

Page 5 of 25

a 2.1 1 1.8 Voltage (V)

1.5 1.2 0.9

3

2

0.6

5

4

6

0.3 0

10k

20k

60

b

40k

c

80

40

40

20

20

20

10 0

0 10

20

80

30 40 Z' (ohm)

50

60

60

20

60

80

0

20

60

80

60

80

40

40

30

40

g

60

Z" (ohm)

40

20

Z' (ohm)

80

f

60

50

40

Z' (ohm)

80

e

70

0 0

Z" (ohm)

0

d

60

60

30

50k

80

Z" (ohm)

Z" (ohm)

40

30k Time (s)

Z" (ohm)

50

Z" (ohm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20

20

10 0

0

0 0

10

20

30 40 50 Z' (ohm)

60

70

80

0

20

40 Z' (ohm)

60

80

0

20

40

Z' (ohm)

h

i

j

k

l

m

Figure 1. (a) Discharge-charge curves of the C-separator. (b-g) Nyquist plots of the Cseparator at different states: (1) before discharge; (2) after one discharge within 0.3–1.0 V; (3-6) after one-four cycles within 0.3–1.0 V. SEM images of the SC-separator at state 1 (h-j) and at state 5(k-m). lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) in a mixture of 1,3-dioxolane (DOL) and dimethoxymethane (DME) (1:1, v/v) and 0.2 M of LiNO3. The corresponding


5


Page 6 of 25

charge–discharge curves were recorded in Figure 1a. Since it is well established that a SEI forms on the surface of a carbon electrode in a Li-ion cell at ~0.8 V versus Li/Li+,3134

and in consideration of the polarization of electrode, we chose 0.3-1.0V as the

charge/discharge potential to form SEI on carbon black. Electrochemical impedance spectroscopy (EIS) was utilized to track the formation of SEI layer.35, 36 The EIS curves corresponding to different charge-discharge states (marked in Figure 1a) are shown in Figure 1b-g. Before discharge (state 1), the battery gave an EIS curve featuring a typical semicircle (Figure 1b). After one discharge at 0.3–1.0 V, the EIS curve (Figure 1c; state 2) is significantly different from that in Figure 1b, but a typical twin-semicircle feature indicating SEI formation is not found.19,

37, 38

With the following cycles, the twin-

semicircle feature became more and more prominent (Figure 1d-e). In the EIS curve of state 5 (Figure 1f), there are two distinct semicircles indicating a stable SEI layer formation after 3 charge/discharge cycles.35-38 Interestingly, the EIS curve following four cycles (Figure 1g) is similar to that resulting from three cycles; this implies that a cycle number of three is enough to establish a stable SEI layer. Consistent with the above EIS findings, SEM observation also indicates successful formation of a surface SEI layer. As shown in the SEM images corresponding to state 1 (Figure 1h-j) and state 5 (Figure 1km), the gaps between carbon particles in state 1 (before discharge) almost disappeared after three cycles (state 5). The SEI layer is further indicated by the TEM images (Figure S1a-d) and energy-dispersive X-ray spectroscopy (EDX) mapping results (Figure S1eg). From the TEM images and EDX mapping, the thickness of the SEI layer was approximately ~10 nm (Figure S1d), and the distribution of F on the carbon surface was uniform (Figure S1f).


6

Page 7 of 25

10k

b

SC-separator

C 1s

C 1s CF2 CH2 PP Carbon black

C-separator

Pure separator

0 295

290 285 Binding Energy (eV)

c

Intensity (a.u.)

C 1s PP Carbon black C-O Li-CO3 ROCO2Li PVDF C-F2 Li-TFSI C-F3 PVDF C-H2

295

290 285 280 Binding Energy (eV)

e

Li-CO3

55 Binding Energy (eV)

4500

50

3000


d

SC-separator

280

Li 1s

C-separator

1500 Pure separator

0 62

275

Li 1s Li-TFSI Li-F Li-ROCO2

60

295

280

Intensity (a.u.)

20k

a

30k

f

60

58 56 54 52 Binding Energy (eV)

SC-separator LiTFSI

Intensity (a.u.)

Intensity (a.u.)

30k

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20k

50

F 1s LiF Li-PVDF

C-separator PVDF

10k

Pure separator

0 695


680

Figure 2. XPS peaks of different separators used in the batteries: (a) C1s for pure-, Cand SC-separators; (b) deconvoluted C1s for C-separator; (c) deconvoluted C1s for SCseparator; (d) Li1s for pure-, C- and SC-separators; (e) deconvoluted Li1s for SCseparator; (f) F1s for pure-, C- and SC-separators.


7


Page 8 of 25

Figure 2 presents the XPS spectra of the following three samples, sample 1 being the pristine polypropylene (PP) separator, sample 2 the C-separator and sample 3 the SCseparator (after SEI modification). The C1s spectrum for sample 1 (Figure 2a) displays only one sharp peak at 285.0 eV, which is attributed to C–H and C–C bonds in PP.39 The deconvoluted C1s peaks for sample 2 (Figure 2b) are attributed to PP (285.0 eV), carbon black (284.5 eV),40 and PVDF binder (C-H at 286.4 eV and C-F at 290.9 eV).41, 42 The spectrum for sample 3 includes C1s peaks (Figure 2c) attributable to Li2CO3 (290.4 eV) and RCO2Li (289.6 eV), the most common ingredients of SEI,19,43-46 and a new peak (293.3 eV) assignable to LiTFSI.40, 47 Sample 3 also exhibits a Li1s peak (Figure 2d), which can be deconvoluted into components (Figure 2e) corresponding to LiTFSI (56.6 eV), ROCO2Li (55.0 eV), Li–CO3 (55.5 eV) and LiF (56.0 eV).19, 40 LiF is also a main ingredient component of SEI; its presence is further confirmed by the F1s peak at 685.0 eV in Figure 2f, where the other F1s peaks can be assigned to LiTFSI (689.0 eV) and LiPVDF (688 eV). Note that the C-F binding energy of PVDF in sample 3 is shifted 0.5 eV relative to that of original PVDF in sample 2; this is probably due to Li coordination with F atom.48 The advantage of SC-separator can be illustrated via comparing the electrochemical performances of the Li-S batteries using a pristine separator, a C-separator and an SCseparator, respectively. The cathodes used in these batteries are carbon cloth electrode with three-dimensional CNT array structure and 10 mg/cm2 sulfur (90.9% in the CNT/S composite). The SEM and TEM images of CNT array are shown in Figure S2. The sulfur content in cathode is 48.3% determined by TGA (Figure S3).


8

Page 9 of 25

2.5

a Voltage (V)

Discharge Charge

0.2 C

2.0 1.5 1.0 0.5 0

b

5000

10000 Time (s)

15000

3.0

Voltage (V)

2.7 2.4

Discharge Charge

2.1 1.8

0.2 C 1.5 0

c

10000 20000 Time (s)

30000

3.0

Voltage (V)

0.2 C 2.5

Discharge Charge

2.0

1.5 0

d

1600

S

1800

e S

Counts (a.u.)

1200

O

1200

600

1600

O

5000

f

10000 Time (s)

15000

20000

O

1200

Counts (a.u.)

2400

Counts (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


800

400

800

400

S 0

5 10 15 Energy (KeV)

20

0


20

0


20

Figure 3. The working scheme, membrane SEM images and first charge-discharge curve at 0.2 C of batteries using pure separator (a), C-separator (b) and SC-separator (c). EDX of Li anodes in the batteries using pure separator (d), C-separator (e) and SC-separator (f).

Figure 3 displays the schematic diagram, corresponding SEM images and first charge-discharge curve at 0.2 C (1C=1675 mA/g) of the batteries assembled with


9


Page 10 of 25

different separators. As shown in Figure 3a, the the pristine separator can not hinder PS that survived CNT adsorption, and therefore, much PS reaches the Li anode, leading to the fatal redox “shuttle” reactions;16, 49 this battery could not be charged normally due to the severe redox shuttle. The battery using C-separator also failed to be charged to 3 V (Figure 3b), meaning the carbon material (including that in cathode and separator) is not enough to adsorb PS because the sulfur content is high (84.0%). On the contrary, the battery with SC-separator could be charge-discharged normally (Figure 3c) due to the existence of SEI layer. Figure S4 displays the charge/discharge curves of these Li-S batteries within 1.8-3 V to distinguish between the plateau of S and that corresponding to LiNO3 decomposition. The reason for the above different PS impeding behaviors of the C-separator and SC-separator can be clearly found in their cross-sectional SEM images. As Figure S5a-c shows, there are conspicuous holes in the C-separator allowing PS migration to Li-anode; such holes almost disappeared in SC-separator due to the presence of SEI (Figure S5d-f), which can obstruct PS more effectively. The advantage of SC-separator can be more clearly demonstrated by a diffusion test where a pure electrolyte solution was separated with a PS solution by the C- or SC-separator between the two compartments of the diffusion cell (Figure S5g-h). It is seen that the electrolyte in the C-separator cell became yellow just after 0.5 h and its color became darker after 1.5 h (Figure S5g); by contrast, no appreciable change in color can be found for the electrolyte in the SC-separator cell even after 1.5 h (Figure S5h), and the electrolyte solution became yellow after 6 h. The above observation suggests that the SC-separator can confine the dissolved polysulfide between cathode and separator more effectively than the C-separator.


10

Page 11 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The contribution of SC separator was further confirmed by examining the Li-anode of the batteries containing different separators. As shown in Figure 3d-f, the sulfur content of anode with SC-separator determined by EDX is significantly lower than that of the anodes with pure separator and C-separator. Meanwhile, yellowish area could barely be found on anode of battery with SC-separator, but could be clearly observed on anode of batteries with the pristine- and C-separator. These results suggest that the SC-separator can suppress polysulfide migration efficiently. It should be noted that the cathode with 10 mg/cm2 sulfur could not be charged normally using conventional strategies where the separator is decorated with other hosting materials. As Figure S6 and S7 shown, the carbon sphere- and Li4Ti5O12- coated separator can’t provide enough surface area to adsorb so much dissolved PS. Then, the advantage of nano-array cathode structure is confirmed. Figure 4a shows the Nyquist plot of the CNT powder electrode before loading sulfur, which indicates a slightly higher charge-transfer resistance (~20 Ω) than that of CNT array electrode (~15 Ω, Figure 4c). This is because the CNT array can provide a straight transport pathway (1D direct line) for electrons (inset, Figure 4c) than that of powder structure (inset, Figure 4a).50 However, the charge-transfer resistance (Rct, ~75 Ω) of the powder CNT electrode after loading sulfur (Figure 4b) is much higher than that of the CNT array/sulfur electrode (~28Ω, Figure 4d). This difference can be attributed to different transport pathways for electrons. For the powder electrode, impedance becomes much higher after sulfur loading than that before loading. The S-coated CNT can not transport electrons effectively, and thus the length of the electron transport pathway becomes


11


a

50

b

300 250

40

30

Z" (ohm)

Z" (ohm)

200

20

150 100

10

50

0

0 0

10

c

50

20

30

40

50

0

Z' (ohm)

100

150

200

250

300

80

100

Z' (ohm)

80

Z" (ohm)

Z" (ohm)

50

d

100

40

30

20

60

40

20

10

0

0 0

10

e

3.0

20

30

40

0

50

20

f

Z' (ohm) 3.0

2.4

0.2 C

Voltage (V)

Array electrode

2.1

40

60

Z' (ohm) Charge Discharge

2.7

Voltage (V)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 25

2.5

2.0

1.8

Powder electrode 0.05 C

Powder electrode

1.5

1.5 0

400 800 Capacity (mAh/g)

1200

0

400 800 Capacity (mAh/g)

1200

Figure 4. (a-d) Nyquist plots of different electrodes: (a) CNT powder electrode; (b) CNT/S powder electrode (10 mg/cm2 sulfur loading); (c) CNT array electrode; (d) CNT/S array electrode (10 mg/cm2 sulfur loading). The insets in panels a-d are the schematic illustration of electron transport pathway in corresponding electrode. (e-f) First chargedischarge curves of (e) CNT/S powder- and array- electrode at 0.2 C and (f) CNT/S powder electrode at 0.05C.


12

Page 13 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


significantly longer (inset, Figure 4b) than that before loading sulfur.30 On the contrary, for the array electrode, CNT was grown directly on the surface of carbon cloth so that electron can travel from carbon cloth, along CNT, to sulfur for electrochemical reaction (inset, Figure 4d).19 Therefore, the sulfur-loaded array electrode has slightly higher interfacial impedance than that without sulfur, suggesting that the array structure can significantly offset the electrical conductivity decrease caused by the high sulfur load. The benefit of array structure can be further confirmed by the first charge-discharge curves of these two different electrodes. As Figure 4e shows, the powder electrode has a significantly higher potential polarization than the array, and therefore, sulfur utilization of the powder electrode (650 mAh/g) is much lower than that of the array electrode (1065 mAh/g). The first charge-discharge curve at 0.05 C in Figure 4f well confirms that the powder

cathode can work properly. The advantage of SC-separator can be further

indicated by studying the cycle performance of CNT/S array electrodes with low sulfur loading (3 mg/cm2). As Figure S8 shown, with SC-separator, the cathode can exhibit ~90% capacity retention after 50 cycles at 0.2 C, which is much better than that with pure- or C-separator. Then, the SEM of C-separator and SC-separator is displayed in Figure S9, which indicates that the SEI is stable during charging-discharging within 1.5 ~ 3 V. Due to the synergistic effect of SC-separator and the nano-array cathode structure, our battery exhibits an impressive performance. As shown in Figure 5a, the charge−discharge curves of the battery using the CNT array cathode (with 10mg/cm2 sulfur), SC-separator and Li-anode at 0.1 ~ 2C exhibit low potential polarization and flat plateaus. This suggests that the array cathode can provide fast transport for electrons even


13


with a very large sulfur loading, and therefore, the cathode delivered a good rate performance (Figure 5b): its mass- (and areal-) specific capacity is 1221 mAh/g (12.2 mAh/cm2) at 0.1C, 1096 mAh/g (10.9 mAh/cm2) at 0.2C, 929 mAh/g (9.3 mAh/cm2) at 0.5C, 752 mAh/g (7.5 mAh/cm2) at 1 C and 400 mAh/g (4 mAh/cm2) at 2C, respectively. The cycle performances at 0.5 C is displayed in Figure 5c, which exhibits 88% capacity retention after 100 cycles. The above performance is better than that of the literature reported LSBs with cathode of similar sulfur loading (Table S1).5, 11, 20, 22, 23, 51-53

b 0.1 C

2.4

0.2 C 2.1

0.5 C 1.8

0.1 C 1200

0

400

c 2000

800 1200 Capactiy (mAh/g)

2 C 1600

1200

0.5 C 1C

800

800

2C

Charge Discharge

400

1 C

1.5

0.1 C 0.2 C

2

Capacity (mAh/g)

2.7

Voltage (V)

1600

1600

400

0 50

0 0

10

20

30

Capacity (mAh/cm )

a 3.0

40

Cycle number

Capacity (mAh/g)

1.0 1500

0.8

0.5 C

1000

0.6 0.4

500 0.2 2

CNT array with 10 mg/cm 0 0

20

40 60 Cycle Number

80

Coulombic efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 25

0.0 100

Figure 5. Electrochemical performances of the battery using CNT/S array electrode, SCseparator and Li-anode. (a) First charge-discharge curves at 0.1, 0.2, 0.5, 1 and 2 C. (b) Rate performance at progressively increased C rates. (c) Cycle performances at 0.5 C. Although there are some works reporting very high sulfur loading (>15 mg/cm2), the batteries can not be charge-discharged properly when the current density is higher than 0.5 C. Since our synergistic strategy can guarantee high sulfur loading and high rate


14

Page 15 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


performance simultaneously, the Li-S battery could drive a mini 30-200 rpm rotationmotor (see Video S1) very easily. In summary, we have developed a novel strategy for constructing high-performance cathodes with large areal loading of sulfur. Differing from the conventional methodology of trapping dissolved polysulfide with ultra-high-specific-area hosting materials, we simply decorated the separator with a dense layer of SEI to confine dissolved polysulfide between the cathode and the separator; this guarantees the cycle stability of the cathode with a large sulfur loading. Meanwhile, we adopted an array structure for the cathode to ensure a good rate performance of the cathode with a large sulfur loading. Attributed to the above synergistic strategy, our battery exhibits an ultrahigh areal specific capacity of 12.2 mAh/cm2 , a high rate performance (1221 mAh/g at 0.1C, 1096 mAh/g at 0.2C, 929 mAh/g at 0.5C, 752 mAh/g at 1 C and 400 mAh/g at 2C, respectively) and good cycle stability (88% capacity retention after 100 cycles at 0.5 C). Our work will open up a new avenue for the facile construction of high-performance sulfur cathodes with large areal loading.

Experimental Methods Materials preparation Carbon black-, carbon sphere- and Li4Ti5O12 coated separators. A homogeneous slurry was prepared by mixing the carbon black or carbon sphere or Li4Ti5O12 with polyvinylidene difluoride binder (8:2 by weight) in the presence of N-methyl-2pyrrolidone. The slurry was then cast on a polypropylene membrane and heated at 60 °C for 12 h under vacuum.


15


Page 16 of 25

CNT array on carbon cloth (CC). A piece of CC (2 cm x 2 cm) was immersed into a precursor solution and kept for 1 h. The precursor solution was prepared by dissolving 0.025 mol Nickel nitrate hexahydrate in a 50 mL mixed solution of alcohol and ethylene glycol (1:1, v/v) under stirring. After dried in ambient air, the treated CC was heated in a tube furnace for 1 h at 800 °C under a flowing N2 atmosphere with an 18 mL mixed solution of ethanol and ethylene glycol (1:5, v/v) placed upstream. Li2S8 electrolyte. The Li2S8 electrolyte (0.2 M) was prepared by dissolving stoichiometric

amounts

of

Li2S

(195

mg),

sulfur

(945

mg),

lithium

bis(trifluoromethanesulfone) imide (LiTFSI, 1 M) and LiNO3 (2wt %) in a mixture (21 mL) of 1,3-dioxolane/1,2-dimethoxy-ethane (DOL/DME) with a volume ratio of 1:1. Materials characterizations Morphology of the as-prepared separators was studied using an FEI NanoSEM-450 Nova scanning electron microscope with a field emission gun (FEG) source. TGA (SDT, Q600) was used to determine the sulfur content under a standard test condition (a heating rate of 10 °C min-1 from room temperature to 500 °C in air). XPS characterization was implemented to confirm existence of SEI using an ESCALAB™ 250Xi ThermoFisher Xray photoelectron spectrometer. Cell assembly and measurements RC2016 coin cells were assembled in an argon-filled glove box using a CNT array electrode as the cathode and Li-metal circular foil (0.59 mm thick) as the anode; different separators were used for the cell assembly, including pristine polypropylene, carbon black-, carbon sphere-, Li4Ti5O12-coated polypropylene and the SC-separator. 50 µL of


16

Page 17 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Li2S8 electrolyte was introduced into the coin cell, corresponding to about 10 mg/cm2 of sulfur mass loading. The electrochemical performance of these batteries was tested by a multi-channel battery tester (Shenzhen Neware Technology Co., Ltd, China) at room temperature. EIS measurements were performed using a CS310 electrochemical workstation with a frequency range from 0.01 Hz to 100 kHz.

Supporting Information Supporting Information is available free of charge via the Internet at http://pubs.acs.org. Fig. S1 displays TEM images of different separator; Fig. S2 shows SEM images of CNT array cathode; TGA curve of CNT/S array on carbon cloth is provided in Fig. S3; Fig. S4 and Fig. S 5 show the SEM and performance of carbon sphere coated separator and Li4Ti5O12 coated separator respectively; Fig. S6 is the cycle performance at 0.2 C of the battery assembled with CNT/S array electrodes (3 mg/cm2 sulfur loading) and different separator; The SEM images of C-separator (a-c) and SCseparator (d-f) after cycled are given in Fig S7; Table S1 is the performance comparison of our battery with literature results. Video S 1 is the video clip for a mini rotation motor (30-200 rpm) driven by a Li-S battery assembled with a 0.25 cm2 cathode of high sulfur loading (10 mg/cm2).

Notes The authors declare no competing financial interest.

Acknowledgments


17


Page 18 of 25

This work was supported by grants from the Fund of State Key Laboratory of Fine Chemicals Panjin (JH2014009), the National Natural Science Foundation of China (No. 21276252 and 21776042) and China MOST (Ministry of Science and Technology) innovation team in key area (No. 2016RA4053).

References 1.

Armand, M.; Endres, F.; MacFarlane, D. R.; Ohno, H.; Scrosati, B. Ionic-liquid

Materials for the Electrochemical Challenges of the Future. Nat. Mater. 2009, 8, 621-629. 2.

Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Li-O2 and Li-S

Batteries with High Energy Storage. Nat. Mater. 2011, 11, 19-29. 3.

Li, Y.; Yan, K.; Lee, H.-W.; Lu, Z.; Liu, N.; Cui, Y. Growth of Conformal

Graphene Cages on Micrometre-sized Silicon Particles as Stable Battery Anodes. Nature Energy 2016, 1, 15029-10536. 4.

Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F. A Highly

Efficient Polysulfide Mediator for Lithium-sulfur Batteries. Nat. Commun. 2015, 6, 56825689. 5.

Liu, F.; Xiao, Q.; Wu, H. B.; Sun, F.; Liu, X.; Li, F.; Le, Z.; Shen, L.; Wang, G.;

Cai, M.; Lu, Y. Regenerative Polysulfide-Scavenging Layers Enabling Lithium-Sulfur Batteries with High Energy Density and Prolonged Cycling Life. ACS Nano 2017, 11, 2697-2705. 6.

Zhou, G.; Pei, S.; Li, L.; Wang, D. W.; Wang, S.; Huang, K.; Yin, L. C.; Li, F.;

Cheng, H. M. A Graphene-pure-sulfur Sandwich Structure for Ultrafast, Long-life Lithium-sulfur Batteries. Adv. Mater. 2014, 26, 625-631. 7.

Fu, Y.; Su, Y. S.; Manthiram, A. Sulfur-carbon Nanocomposite Cathodes


18

Page 19 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Improved by an Amphiphilic Block Copolymer for High-rate Lithium-sulfur Batteries. ACS Appl. Mater. Interfaces 2012, 4, 6046-6052. 8.

Evers, S.; Nazar, L. F. Graphene-enveloped Sulfur in a One Pot Reaction: a

Cathode with Good Coulombic Efficiency and High Practical Sulfur Content. Chem. Commun. 2012, 48, 1233-1235. 9.

Schuster, J.; He, G.; Mandlmeier, B.; Yim, T.; Lee, K. T.; Bein, T.; Nazar, L. F.

Spherical Ordered Mesoporous Carbon Nanoparticles with High Porosity for LithiumSulfur Batteries. Angew. Chem. Int. Ed. 2012, 51, 3591-3595. 10.

Zhou, G.; Li, L.; Ma, C.; Wang, S.; Shi, Y.; Koratkar, N.; Ren, W.; Li, F.; Cheng,

H.-M. A Graphene Foam Electrode with High Sulfur Loading for Flexible and High Energy Li-S Batteries. Nano Energy 2015, 11, 356-365. 11.

Liu, J.; Galpaya, D. G. D.; Yan, L.; Sun, M.; Lin, Z.; Yan, C.; Liang, C.; Zhang, S.

Exploiting a Robust Biopolymer Network Binder for an Ultrahigh-areal-capacity Li–S Battery. Energy Environ. Sci. 2017, 10, 750-755. 12.

Qie, L.; Zu, C.; Manthiram, A. A High Energy Lithium‐Sulfur Battery with

Ultrahigh‐Loading Lithium Polysulfide Cathode and its Failure Mechanism. Adv. Energy Mater. 2016, 6. DOI: 10.1002/aenm.201502459. 13.

Wang, D.-W.; Zeng, Q.; Zhou, G.; Yin, L.; Li, F.; Cheng, H.-M.; Gentle, I. R.; Lu,

G. Q. M. Carbon-sulfur Composites for Li-S Batteries: Status and Prospects. J. Mater. Chem. A 2013, 1, 9382-9394. 14.

Wu, H. B.; Wei, S.; Zhang, L.; Xu, R.; Hng, H. H.; Lou, X. W. D. Embedding

Sulfur in MOF-Derived Microporous Carbon Polyhedrons for Lithium-Sulfur Batteries. Chem-Eur. J. 2013, 19, 10804-10808.


19


15.

Page 20 of 25

Xu, G.; Ding, B.; Shen, L.; Nie, P.; Han, J.; Zhang, X. Sulfur Embedded in Metal

Organic Framework-derived Hierarchically Porous Carbon Nanoplates for High Performance Lithium-sulfur Battery. J. Mater. Chem. A 2013, 1, 4490-4496. 16.

Zhang, S. S. Liquid Electrolyte Lithium/sulfur Battery: Fundamental Chemistry,

Problems, and Solutions. J. Power Sources 2013, 231, 153-162. 17.

Choi, J.-W.; Kim, J.-K.; Cheruvally, G.; Ahn, J.-H.; Ahn, H.-J.; Kim, K.-W.

Rechargeable Lithium/Sulfur Battery with Suitable Mixed Liquid Electrolytes. Electrochim. Acta 2007, 52, 2075-2082. 18. the

Gao, J.; Lowe, M. A.; Kiya, Y.; Abruña, H. c. D. Effects of Liquid Electrolytes on Charge–discharge

Performance

of

Rechargeable

Lithium/sulfur

Batteries:

Electrochemical and in-situ X-ray Absorption Spectroscopic Studies. J. Phys. Chem. C 2011, 115, 25132-25137. 19.

Guo, J.; Du, X.; Zhang, X.; Zhang, F.; Liu, J. Facile Formation of a Solid

Electrolyte Interface as a Smart Blocking Layer for High‐Stability Sulfur Cathode. Adv. Mater. 2017. 29, DOI: 10.1002/adma.201700273. 20.

Cheng, X.-B.; Huang, J.-Q.; Zhang, Q.; Peng, H.-J.; Zhao, M.-Q.; Wei, F. Aligned

Carbon Nanotube/Sulfur Composite Cathodes with High Sulfur Content for Lithiumsulfur Batteries. Nano Energy 2014, 4, 65-72. 21.

Papandrea, B.; Xu, X.; Xu, Y.; Chen, C.-Y.; Lin, Z.; Wang, G.; Luo, Y.; Liu, M.;

Huang, Y.; Mai, L.; Duan, X. Three-dimensional Graphene Framework with Ultra-high sulfur Content for a Robust Lithium-sulfur Battery. Nano Res. 2016, 9, 240-248. 22.

Li, G.; Sun, J.; Hou, W.; Jiang, S.; Huang, Y.; Geng, J. Three-dimensional Porous

Carbon Composites Containing High Sulfur Nanoparticle Content for High-Performance


20

Page 21 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Lithium-sulfur Batteries. Nat. Commun. 2016, 7, 10601-10610. 23.

Chang, C. H.; Chung, S. H.; Manthiram, A. Effective Stabilization of a High-

Loading Sulfur Cathode and a Lithium-Metal Anode in Li-S Batteries Utilizing SWCNTModulated Separators. Small 2016, 12, 174-179. 24.

Kim, H. M.; Sun, H.-H.; Belharouak, I.; Manthiram, A.; Sun, Y.-K. An Alternative

Approach to Enhance the Performance of High Sulfur-Loading Electrodes for Li–S Batteries. ACS Energy Lett. 2016, 1, 136-141. 25.

Yu, X. W.; Bi, Z. H.; Zhao, F.; Manthiram, A. Polysulfde-Shuttle Control in

Lithium-Sulfur Batteries with a Chemically/Electrochemically Compatible NaSICONType Solid Electrolyte. Adv. Energy Mater. 2016, 6, DOI: 10.1002/aenm.201601392. 26.

Su, Y.-S.; Manthiram, A. A New Approach to Improve Cycle Performance of

Rechargeable Lithium-sulfur Batteries by Inserting a Free-standing MWCNT Interlayer. Chem. Commun. 2012, 48, 8817-8819. 27.

Li, W.; Hicks-Garner, J.; Wang, J.; Liu, J.; Gross, A. F.; Sherman, E.; Graetz, J.;

Vajo, J. J.; Liu, P. V2O5 Polysulfide Anion Barrier for Long-lived Li-S Batteries. Chem. Mater. 2014, 26, 3403-3410. 28.

Huang, J.-Q.; Zhuang, T.-Z.; Zhang, Q.; Peng, H.-J.; Chen, C.-M.; Wei, F.

Permselective Graphene Oxide Membrane for Highly Stable and Anti-self-discharge Lithium-sulfur Batteries. ACS Nano 2015, 9, 3002-3011. 29.

Yao, H.; Yan, K.; Li, W.; Zheng, G.; Kong, D.; Seh, Z. W.; Narasimhan, V. K.;

Liang, Z.; Cui, Y. Improved Lithium-sulfur Batteries with a Conductive Coating on the Separator to Prevent the Accumulation of Inactive S-related Species at the CathodeSeparator Interface. Energy Environ. Sci. 2014, 7, 3381-3390.


21


30.

Page 22 of 25

Guo, J.; Zhang, X.; Du, X.; Zhang, F. A Mn3O4 Nano-wall Array Based Binder-

free Cathode for High Performance Lithium-sulfur Batteries. J. Mater. Chem. A 2017, 5, 6447-6454. 31. Andersson, A. M.; Henningson, A.; Siegbahn, H.; Jansson, U.; Edstrom, K. Electrochemically lithiated graphite characterised by photoelectron spectroscopy. J. Power Sources, 2003, 119, 522–527 32. Edstrom, K.; Herstedt, M.; Abraham, D. P. A new look at the solid electrolyte interphase on graphite anodes in Li-ion batteries. J. Power Sources, 2006, 153, 380–384. 33. Bryngelsson, H.; Stjerndahl, M.; Gustafsson, T.; Edstrom, K. How dynamic is the SEI? J. Power Sources, 2007, 174, 970–975. 34. Verm, P.; Maire, P.; Novák, P. A review of the features and analyses of the solid electrolyte interphase in Li-ion batteries. Electrochim. Acta, 2010, 55, 6332–6341. 35.

Zhang, S. S.; Xu, K.; Jow, T. R. EIS Study on the Formation of Solid Electrolyte

Interface in Li-ion Battery. Electrochim. Acta 2006, 51, 1636-1640. 36.

Ratnakumar, B.; Smart, M.; Surampudi, S. Effects of SEI on the Kinetics of

Lithium Intercalation. J. Power Sources 2001, 97, 137-139. 37.

Steinhauer, M.; Risse, S.; Wagner, N.; Friedrich, K. A. Investigation of the Solid

Electrolyte Interphase Formation at Graphite Anodes in Lithium-Ion Batteries with Electrochemical Impedance Spectroscopy. Electrochim. Acta 2017, 228, 652-658. 38.

Heins, T. P.; Harms, N.; Schramm, L. S.; Schröder, U. Development of a new

Electrochemical Impedance Spectroscopy Approach for Monitoring the Solid Electrolyte Interphase Formation. Energy Technol. 2016, 4, 1509-1513. 39.

Morent, R.; De Geyter, N.; Leys, C.; Gengembre, L.; Payen, E. Comparison


22

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Between XPS- and FTIR-analysis of Plasma-treated Polypropylene Film Surfaces. Surf. Interface Anal. 2008, 40, 597-600. 40.

Ensling, D.; Stjerndahl, M.; Nytén, A.; Gustafsson, T.; Thomas, J. O. A

Comparative XPS Surface Study of Li2FeSiO4/C Cycled with LiTFSI- and LiPF6-based Electrolytes. J. Mater. Chem. 2009, 19, 82-88. 41.

Kim, E.-S.; Kim, Y. J.; Yu, Q.; Deng, B. Preparation and Characterization of

Polyamide Thin-film Composite (TFC) Membranes on Plasma-modified Polyvinylidene Fluoride (PVDF). J. Membr. Sci. 2009, 344, 71-81. 42.

Zhu, L. P.; Yu, J. Z.; Xu, Y. Y.; Xi, Z. Y.; Zhu, B. K. Surface Modification of

PVDF Porous Membranes via Poly(DOPA) Coating and Heparin Immobilization. Colloids Surf. B Biointerfaces 2009, 69, 152-155. 43. Barghamadi, M.; Best, A. S.; Bhatt, A. I.; Hollenkamp, A. F.; Mahon, P. J.; Musameh,M.; Rüther, T. Effect of LiNO3 additive and pyrrolidinium ionic liquid on the solid electrolyte interphase in the lithiumesulfur battery. J. Power Sources, 2015, 295, 212-220. 44. Zheng, J.; Gu, M.; Chen, H.; Meduri, P.; Engelhard, M.; Zhang, J.; Liu, J.; Xiao, J. Ionic liquid-enhanced solid state electrolyte interface (SEI) for lithium–sulfur batteries. J. Mater. Chem. A, 2013, 1, 8464-8470. 45. Diao, Y.; Xie. K.; Xiong, S.; Hong, X. Insights into Li-S Battery Cathode Capacity Fading Mechanisms:Irreversible Oxidation of Active Mass during Cycling. J. Electrochiem. Soc., 2012, 159, A1816-A1821. 46. Xiong, S.; Xie, K.; Diao, Y.; Hong, X. Characterization of the solid electrolyte interphase on lithium anode for preventing the shuttle mechanism in lithiumesulfur


23


Page 24 of 25

batteries. J. Power Sources, 2014, 246, 840-845. 47.

Leroy, S.; Martinez, H.; Dedryvère, R.; Lemordant, D.; Gonbeau, D. Influence of

the Lithium Salt Nature Over the Surface Film Formation on a Graphite Electrode in Liion Batteries: An XPS Study. Appl. Surf. Sci. 2007, 253, 4895-4905. 48.

Chiang, C.-Y.; Shen, Y. J.; Reddy, M. J.; Chu, P. P. Complexation of

Poly(vinylidene fluoride):LiPF6 Solid Polymer Electrolyte with Enhanced Ion Conduction in ‘Wet’ Form. J. Power Sources 2003, 123, 222-229. 49.

Zhang, S. S.; Read, J. A. A New Direction for the Performance Improvement of

Rechargeable Lithium/Sulfur Batteries. J. Power Sources 2012, 200, 77-82. 50.

Guo, J.; Cai, Y.; Zhang, S.; Chen, S.; Zhang, F. Core–Shell Structured o-

LiMnO2@ Li2CO3 Nanosheet Array Cathode for High-Performance, Wide-TemperatureTolerance Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2016, 8, 16116-16124. 51.

Peng, H.-J.; Xu, W.-T.; Zhu, L.; Wang, D.-W.; Huang, J.-Q.; Cheng, X.-B.; Yuan,

Z.; Wei, F.; Zhang, Q. 3D Carbonaceous Current Collectors: The Origin of Enhanced Cycling Stability for High-Sulfur-Loading Lithium-Sulfur Batteries. Adv. Funct. Mater. 2016, 26, 6351-6358. 52.

Patel, M. D.; Cha, E.; Kang, C.; Gwalani, B.; Choi, W. High Performance

Rechargeable Li-S Batteries Using Binder-free Large Sulfur-loaded Three-dimensional Carbon Nanotubes. Carbon 2017, 118, 120-126. 53.

Qie, L.; Manthiram, A. A Facile Layer-by-layer Approach for High-areal-capacity

Sulfur Cathodes. Adv. Mater. 2015, 27, 1694-1700.


24

Page 25 of 25

Graphical Abstract

SEI layer 20

2000

15

10 5

Capacity (mAh/g)

2

Capacity (mAh/cm )

1.0 1500

0.8

0.5 C

1000

0.4 500 2

CNT array with 10 mg/cm 0

0.6

0 0

20

40 60 Cycle Number

80

0.2

Coulombic efficiency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.0 100

The synergistic effect of solid electrolyte interface (SEI) modified separator and CNT array structure produces good rate- and cycle performance for a cathode with 10mg/cm2 sulfur (90.9% in composite).


25

A novel synergistic strategy for developing high-performance lithium

Recommend Documents