GrapheneâLi2S Aerogel as Freestanding

Subscriber access provided by Northern Illinois University

Letter 2

Three-Dimensional CNT/Graphene-LiS Aerogel as Freestanding Cathode for High-Performance Li-S Batteries Jiarui He, Yuanfu Chen, Weiqiang Lv, Kechun Wen, Chen Xu, Wanli Zhang, Wu Qin, and Weidong He ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.6b00272 • Publication Date (Web): 22 Sep 2016 Downloaded from http://pubs.acs.org on September 23, 2016

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 free 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 accessible to all readers and 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 Energy Letters 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 18

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 Energy Letters

Three-Dimensional CNT/Graphene-Li2S Aerogel as Freestanding Cathode for High-Performance Li-S Batteries

Jiarui Hea, Yuanfu Chena*, Weiqiang Lvb, Kechun Wenb, Chen Xua, Wanli Zhanga, Wu Qinc and Weidong Hea, b,d*

a

State Key Laboratory of Electronic Thin Films and Integrated Devices. bSchool of Energy Science

and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, PR China. cNational Engineering Laboratory for Biomass Power Generation Equipment, School of Renewable Energy Engineering, North China Electric Power University, Beijing 102206, PR China. d

College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China. E-mail:

[email protected]; [email protected]

1

ACS Paragon Plus Environment

ACS Energy Letters

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

Abstract Three-dimensional (3D) CNT/graphene-Li2S (3DCG-Li2S) cathodes with 81.4 wt% record Li2S loading have been realized through solvothermal reaction and a subsequent liquid-infiltration-evaporation coating method. The highly flexible, conductive 3D mesoporous interconnected network based on two-dimensional (2D) graphene nanosheets and one-dimensional (1D) carbon nanotubes (CNTs) provides highly-efficient channels for electron transfer and ionic diffusion, and leads to a low solubility of polysulfides in electrolytes in charges/discharges. Without polymeric binders or conductive additives , the freestanding 3DCG-Li2S cathode exhibits record electrochemical performances including reversible discharge capacities of 1123.6 mAh g-1 and 914.6 mAh g-1, 0.02% long-term capacity decay per cycle and a high-rate capacity of 514 mAh g-1 at 4 C. The reported 3DCG-Li2S aerogel with ultrahigh Li2S content presents promising application potentials in high-performance Li-S batteries.

2


Page 2 of 18

Page 3 of 18

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 Energy Letters

Lithium-sulfur (Li-S) batteries are regarded as one of the most promising next-generation rechargeable batteries, owing to their high theoretical specific energy capacity.1-6 However, the application of Li-S batteries is still challenged by the poor electrical conductivity, large volume expansion of sulfur, high solubility of the intermediates in the electrolyte leading to active mass loss and shuttle effect,7-11 and the formation of Li dendrite on the anode surface in operation. Compared to sulfur, fully lithiated lithium sulfide (Li2S) is advantageous due to its high theoretical specific capacity (1166 mAh g-1) and the employment of metal-free anodes. In addition, Li2S experiences subtle volumetric expansion during cycling as Li is incorporated into the structure.12-16 However, similar to sulfur cathode, the application of Li2S is also hindered by the high charge barrier in the first charge, the low electronic conductivity (~10-13 S cm-1) and the polysulfide shuttle phenomenon.17-21 To address such issues and improve the electrochemical performances of Li2S, various strategies have been proposed. For instance, the initial charge barrier can be effectively alleviated by decreasing the particle size of Li2S.12,22 Carbonaceous materials such as polypyrrole, microporous carbon, CMK-3, CNT and graphene have been widely used as conductive matrix to enhance the conductivity of Li2S composites.1, 13-14, 17, 19-20, 23-28 Most of those studies have demonstrated that the specific capacity of Li2S is high, however, the content of Li2S in the whole cathode electrode is relatively low ( 80 w%). In our previous report,3 by introducing carbon nanotubes (CNTs) into 3DG to form highly conductive three-dimensional CNTs-graphene (3DCG) matrix, the content of sulfur was effectively increased, since CNTs not only enhanced the overall conductivity, but also formed bimodal mesopore structure, leading to increased active surface of sulfur and polysulfides. 3DCG is also an excellent template for preparing Li2S-based composites with higher Li2S content. In addition, to further increase the content of Li2S in the whole electrode, it is crucial to fabricate free-standing and binder-free Li2S-based composite cathodes, because the conductive additive, polymer binder and metallic current collector are unnecessary for such cathodes. However, so far, it has remained to be a challenge for synthesizing freestanding Li2S composite cathodes with ultrahigh Li2S content while maintaining excellent electrochemical performances. In this work, a well-designed 3D CNT/graphene-Li2S (3DCG-Li2S) hybrid aerogel with ultrahigh Li2S content (81.4 wt%) has been fabricated by facile solvothermal reaction and subsequent liquid infiltration-evaporation coating. The unique mesoporous 3DCG structure with high specific area provides ultrahigh Li2S content and abundant electrochemical 4


Page 4 of 18

Page 5 of 18

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 Energy Letters

nanoreactors, and facilitates efficient charge transport as well as electrolyte penetration. Owing to such advantages, as freestanding and binder-free cathode the 3DCG-Li2S aerogel owns an ultrahigh capacity, a high rate capability as well as a low initial charge barrier. This work provides insights into realizing high-capacity cathodes for next-generation flexible Li-S batteries. The reported route to preparing freestanding, binder-free 3DCG-Li2S composite was illustated schematically in Fig. 1a. The 3DCG aerogel was obtained by ultrasonication of the GO/CNTs suspension, solvothermal reduction and assembly, as well as subsequent freeze-drying. Corresponding photographs were shown in Fig. S1 in the Supporting Information. 3DCG-Li2S composite was fabricated by a liquid-infiltration-evaporation coating method, as shown in Fig. 1a. 3DG owns an interconnected 3D conductive porous network, as shown in Fig. 1b. The images in Fig. 1c and Fig. S2a demonstrate that the highly conductive CNTs are homogenously distributed in the 3DCG. Compared to the 3DG, the 3DCG possess substantially more mesopores that provide abundant accessible active sites for hosting Li2S. Such abundant mesopores existing in 3DCG were resulted from the self-assembly process between CNTs and graphene sheets, where the one-dimensional CNTs acted as pillars supporting the two-dimensional graphene nanosheets. In the infiltration-evaporation coating process, the deficient pores cannot host the abundant Li2S nanoparticles, and the surface of 3DG was consequently covered by Li2S agglomeration, as shown in Fig. 1d. Owing to the abundant mesopores in 3DCG, no Li2S agglomeration is observed in the 3DCG-Li2S (Fig. 1e and Fig. S2b). As shown in the TEM images of the 3DCG-Li2S in Fig. 1f, the 3DCG forms a 5


ACS Energy Letters

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

three-dimensional porous conductive architecture with CNTs and graphene sheets cross-linked. The Li2S nanoparticles are uniformly anchored on 3DCG, as shown in the high-magnification TEM images in Fig. 1g. The Li2S nanoparticles are ~8 nm in diameter, the minimum value ever reported for the material,19, 33 and the small size could be attributed to the sufficient cites in 3DCG for Li2S loading as well as periodical infiltration. In addition, such a small size can effectively alleviate the initial charge barrier of 3DCG-Li2S. The inset of Fig. 1g shows the high-resolution TEM image of the Li2S nanoparticles, and the 0.33 nm lattice spacing corresponds to the (111) plane of Li2S.

Fig. 1 (a) Synthetic procedure of the 3DCG-Li2S composite. SEM images of (b) 3DG, (c)

3DCG, (d) 3DG-Li2S and (e) 3DCG-Li2S composite. (f) Low-magnification TEM images of 3DCG-Li2S, (g) TEM image of Li2S nanoparticles on 3DCG and high-resolution TEM image 6


Page 6 of 18

Page 7 of 18

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 Energy Letters

of Li2S nanocrystals (Inset). Several sharp preaks at 27o, 31o, 45o, 53o, 65o, 72o and 74o in commercial Li2S correspond to the characteristic peaks of Li2S (according to JCPSD No. 26-1188), suggesting the highly crystallinity of commercial Li2S before being encapsulated in 3DCG and 3DG, as presented in Fig. 2a.20 The characteristic peaks of Li2S are also observed in 3DG-Li2S and 3DCG-Li2S, which indicates that the Li2S nanoparticles were introduced in 3DG and 3DCG. Peak broadening in 3DCG-Li2S illustrates that the Li2S nanoparticles were effectively encapsulated in the abundant pores of 3DCG. Fig. 2b shows the energy dispersive X-ray spectroscopy (EDS) of 3DCG-Li2S with 81.4 wt% Li2S content. The correlated elemental mapping of sulfur and carbon are shown in Fig. S3. It can be clearly seen that the Li2S nanoparticles are uniformly distributed in the 3DCG aerogel. Full nitrogen sorption isotherms of the 3DG and 3DCG are shown in Fig. 2. In the relative pressure range of 0.45-1.0 P/P0, a type-IV isotherm with a type-H3 hysteresis loop shown in Fig. 2c, illustrates the mesoporous structure of 3DG and 3DCG. The specific surface area of 3DCG is 370.8 m2 g-1, which is well above that of 3DG (251.6 m2 g-1), as measured with the Brunauer-Emmett-Teller (BET) method. The unique 3D architecture ensures sufficient surface area for Li2S loading. The pore size distribution as derived from the BJH method is illustrated in Fig. 2d. 3DCG possesses abundant bimodal pores of 29.8 nm and 3.7 nm while 3DG only owns monodal mesopores. The difference of the pore size distribution between 3DCG and 3DG shows that the one-dimensional CNTs can effectively tune the structure and density of the mesopores in the 3D architecture. Smaller mesopores in the 3DCG confine the dissolved polysulfides for suppressing the severe capacity fade and the larger pores in the 3DCG allow 7


ACS Energy Letters

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

for efficient charge transport and electrolyte penetration, resulting in high utilization of Li2S.

Fig. 2 (a) XRD patterns of the commercial Li2S, 3DG-Li2S and 3DCG-Li2S composites. (b)

EDS spectrum of 3DCG-Li2S composite suggests the lack of other impurities. (c) N2 sorption isotherm and (d) pore size distribution of 3DG and 3DCG composites. Fig. 3a shows the cyclic voltammetry (CV) curves of 3DCG-Li2S cathodes in the first three cycles. Previous reports reveal that the initial charge barrier exists in Li2S, therefore, the 3DCG-Li2S was scanned to 3.6 V to confirm the presence of the common peaks in the initial cycle. As shown in Fig. 3a, two anodic peaks for 3DCG-Li2S are observed in the initial scanning. The peaks at 2.53 V and 2.62 V are attributed to the conversions of Li2S to Li2S8 and S.22 The value above 3V for 3DCG-Li2S is smaller than that for 3DG-Li2S (in Fig. S4), indicating a significantly reduced initial charge barrier due to less agglomeration of Li2S in 3DCG-Li2S, as compared with 3DG-Li2S. In the cathodic scanning, the peaks at 2.36 V and 8


Page 8 of 18

Page 9 of 18

2.01 V are attributed to the conversions of S to soluble Li2Sn (4≤n≤8) and Li2S2/Li2S.32 After the first sweep, the potential window was then switched from 1.5 V to 3.0 V in the subsequent cycles. The CV curves overlapped after the first cycle, implying the relatively stable cyclic performance of 3DCG-Li2S. Fig. 3b demonstrates the charge/discharge profiles of 3DCG-Li2S for the different cycles at 0.2 C. The voltage plateaus are consistent with the CV results. The potential plateaus change only slightly even after 300 cycles, indicating the high capacity reversibility of 3DCG-Li2S. -2

Areal Capacity (mAh cm ) Potential vs. Li /Li (V)

a 1st 2nd 3th

0.0

-0.4 2.4

+

3.0

3.2 2.8

0

-2

Areal Capacity (mAh cm ) -1 Specific Capacity (mAh g )

6.4

800

3.2

400

1.6

0

0.0 300

200

600

1200

120

4.8

100

300

-1

1200

0

900

1.6

Specific capacity (mAhg )

-1

3DGC-Li2S 3DG-Li2S

4.8

2.0

3.6

80

c

1600

3.6

2.4

Potential vs. Li /Li (V) Coulombic Efficiency (%)

2.4 1st 2nd 100th 200th 300th

-2

1.8

1.2

b

1600

d

1200

0.1C 0.2C

6.4

3DGC-Li2S 3DG-Li2S 0.5C

0.1C 4.8 1C 2C

800

3.2

4C

400 0

1.6 0

Areal Capacity (mAh cm )

0.4

3.6

+

-1

Current (mA mg )

0.0 0

Specific Capacity (mAh g )

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 Energy Letters

10

20

30

40

50

60

70

0.0

Cycle Number

Cycle Number

Fig. 3 (a) CVs of the 3DCG-Li2S cathode at 0.1 mV s-1 in a potential window from 1.5 V to 3.6 V vs Li+/Li for the initial cycle and 1.5 V to 3 V vs Li+/Li for the 2nd and 3th cycles. (b) Discharge/charge voltage profiles of 3DCG-Li2S composite for the 1st, 50th, 100th, 200th and 300th cycles at 0.2 C. (c) Cyclic performances of 3DG-Li2S and 3DCG-Li2S cathodes at 0.2 C for 300 cycles. (d) Rate performances of 3DG-Li2S and 3DCG-Li2S cathodes at various 9


ACS Energy Letters

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

C-rates. Of crucial importance to Li-S battery applications is the cyclic performance. The 3DG-Li2S delivers a low initial discharge capacity of 672 mAh g-1 (2.69 mAh cm-2), as presented in Fig. 3c. Then it rapidly decreases to 365.5 mAh g-1 (1.46 mAh cm-2) after 100 cycles and decreases to 287.9 mAh g-1 (1.15 mAh cm-2) after 300 cycles. For the 3DCG-Li2S, a high initial specific capacity of 1052.1 mAh g-1 (4.21 mAh cm-2) is obtained. Even after 300 cycles, a capacity of 958.3 mAh g-1 (3.83 mAh cm-2) is obtained, corresponding to a high capacity retention of 94.5% and a low capacity fading rate of 0.02% per cycle with nearly 100% Columbic efficiency. Such pronounced performances are attributed to the inhibition of the shuttle effect that is regarded as the biggest shortcoming of the Li-S battery. In Fig. 4, the post-mortem SEM of the lithium plate paired with 3DCG-Li2S after 300 cycles shows slight corrosion and a relatively smooth surface, which confirms the good confinement of polysulfides. The EDS spectrum in Fig. 4 also illustrates the sufficient protection from shuttle effect. The better cyclic performance, as compared to that of 3DG-Li2S, correlates with the abundant bimodal mesopores in 3DCG which provide sufficient confinements for polysulfides in charges/discharges.

10


Page 10 of 18

Page 11 of 18

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 Energy Letters

Fig. 4 SEM images of the lithium plate paired with (a) 3DG-Li2S and (b) 3DCG-Li2S after 300 cycles. Corresponding EDS spectra of the lithium plate paired with (c) 3DG-Li2S and (d) 3DCG-Li2S after 300 cycles. The high-rate capability of the 3DCG-Li2S cathode at various rates is shown in Fig. 3d. The 3DCG-Li2S exhibits excellent rate performances with a high capacity of 1123.6 mAh g-1 (4.49 mAh cm-2, 96.4% of its theoretical capacity), 847.4 mAh g-1 (3.39 mAh cm-2) and 514 mAh g-1 (2.06 mAh cm-2) at 0.1 C, 1 C and 4 C, respectively. The correlated voltage profiles are provided in Fig. S5. When the rate is reduced back to 0.1C, the discharge capacity can be well recovered (1108.3 mAh g-1), showing a high rate capability of the 3DCG-Li2S cathode. The excellent rate capability indicates that the degradation of of 3DCG-Li2S has been mitigated efficiently, as confirmed by the post-mortem SEM images in Fig. 5. In strong contrast, the 11


ACS Energy Letters

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

3DG-Li2S displays disadvantageous rate performances, as shown in Fig. 3d. The specific capacity of 842.7 mAh g-1 (3.37 mAh cm-2) for 3DG-Li2S at 0.1C quickly drops to 155.3 mAh g-1 (0.62 mAh cm-2) as the rate increases to 1C. It is noted that the 3DCG-Li2S with a high Li2S content still displays a high rate capability even at 4C, which is significantly higher compared with previous Li2S hybrids, as shown in Table S1.13, 17, 19-20, 23-27 The excellent rate capability of 3DCG-Li2S is correlated with the unique architecture of 3DCG, the interconnected mesopores of which provide efficient paths for fast ion diffusion and electron transfer.

Fig. 5 SEM images of (a) 3DG-Li2S and (b) 3DCG-Li2S composites after cycling. The Nyquist plots of 3DCG-Li2S and 3DG-Li2S after 300 cycles are shown in Fig. 6. Both cells exhibit a depressed semi-circle in the high frequency region, corresponding to the charge transfer resistance (Rct) of the Li2S cathode and an inclined line at low frequency, correlated with the Warburg diffusion process (Zw). The intersections of the semi-circle at the real axis at the high frequency region (denoted as Rs) are attributed to the internal resistance. The cell with 3DCG-Li2S exhibits a Rct of 57.81 Ω and a Rs of 0.95 Ω, which are well below those of the cell with 3DG-Li2S (72.47 Ω and 3.13 Ω, respectively). Such EIS data are again suggestive of the efficient electron transfer and ion conduction due to the interconnected pores 12


Page 12 of 18

Page 13 of 18

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 Energy Letters

in 3DCG-Li2S.

Fig. 6 EIS spectra of the 3DG-Li2S and 3DCG-Li2S composite. The inset is the fitting relevant equivalent circuit models.

The structural advantages of the 3DCG-Li2S are confirmed by the theoretical calculation, as shown in Fig. 7. To realize efficient calculation, the structure of one piece of graphene sheet and one carbon nanotube with one Li2S molecule placed in-between is established to represent the microstructure of 3DCG-Li2S. Compared with normal Li2S-graphene interaction in Fig. 7a, molecular Li2S exhibits substantially larger interaction with graphene and CNT in the hierarchical 3DCG-Li2S, which is demonstrated by the shorter separation between Li2S and CNT or graphene/CNT, as shown in Figs. 7b-7c. The larger overlap of electron density between Li2S and CNT/graphene compared with Li2S/graphene indicates that the charge transport of Li2S can be dramatically enhanced. As seen in the optimized structure in Fig. 7c, the interacting graphene sheet and CNT construct a closely-packed microstructure, as consistent with the TEM images in Fig. 1. The structure not only ensures a high energy

13


ACS Energy Letters

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

capacity of the 3DCG-Li2S cathode, but also mitigates the dissolution of Li2S in the electrolyte, a major cause of capacity decay for a Li-S battery.

Fig. 7 Predicted optimized configurations (left column) and electron density maps (right column) between (a) graphene sheet and Li2S, (b) a CNT and Li2S, and (c) a Li2S molecule intercalated into graphene/CNT composite structure.

In summary, a facile method has been presented to synthesize three-dimensional carbon nanotube/graphene-Li2S (3DCG-Li2S) aerogel with ultrahigh Li2S content. The well-designed flexible, highly conductive matrix and the unique 3D bimodal-mesoporous architecture of 3DCG-Li2S give rise to the pronounced electrochemical performances of 3DCG-Li2S. As the 14


Page 14 of 18

Page 15 of 18

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 Energy Letters

3DCG-Li2S is employed as free-standing and binder-free cathode without any polymer binders or conductive additives, the reversible discharge capacity is as large as 1123.6 mAh g-1, and the capacity decay is as low as 0.02% per cycle. Moreover, the high-rate capacity up to 4 C is as large as 514 mAh g-1. The 3DCG-Li2S aerogel with high Li2S content is promising as freestanding cathodes for high-performance lithium-sulfur batteries. ASSOCIATED CONTENT

Supporting Information Available: Experimental details for the preparation of 3DCG-Li2S; electrochemical and materials characterization; Electrochemical properties of Li2S-C composites in Table S1; Characterization of materials by digital camera, SEM and EDS; Further electrochemical characteristics of electrode materials.

Acknowledgements The research was supported by the National Natural Science Foundation of China (Grant Nos. 51372033, 21403031, 51202022, and 61378028), the Fundamental Research Funds for the Central Universities (Grant Nos. ZYGX2013Z001, ZYGX2014J088 and ZYGX2015Z003), National High Technology Research and Development Program of China (Grant No. 2015AA034202), the 111 Project (Grant No. B13042), the Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 20120185120011), the Science & Technology Support Funds of Sichuan Province (Grant No. 2016GZ0151). Sichuan Youth Science and Technology Innovation Research Team Funding (Grant No. 2011JTD0006), and the Sino-German Cooperation PPP Program of China (Grant No. 201400260068).

15


ACS Energy Letters

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

REFERENCES 1. Ji, X.; Lee, K. T.; Nazar, L. F. A Highly Ordered Nanostructured Carbon–Sulphur Cathode for Lithium–Sulphur Batteries. Nat. Mater. 2009, 8, 500-506. 2. Manthiram, A.; Fu, Y.; Chung, S.; Zu, C.; Su, Y. Rechargeable Lithium–Sulfur Batteries. Chem. Rev. 2014, 114, 11751-11787. 3. He, J.; Chen, Y.; Li, P.; Fu, F.; Wang, Z.; Zhang, W. Three-Dimensional CNT/Graphene–Sulfur Hybrid Sponges with High Sulfur Loading as Superior-Capacity Cathodes for Lithium–Sulfur Batteries. J. Mater. Chem. A 2015, 3, 18605-18610. 4. Yu, M.; Ma, J.; Song, H.; Wang, A.; Tian, F.; Wang, Y.; Qiu, H.; Wang, R. Atomic Layer Deposited TiO2 On a Nitrogen-Doped Graphene/Sulfur Electrode for High Performance Lithium–Sulfur Batteries. Energy Environ. Sci. 2016, 9, 1495-1503. 5. He, J.; Chen, Y.; Li, P.; Fu, F.; Wang, Z.; Zhang, W. Self-Assembled CoS2 Nanoparticles Wrapped by CoS2-Quantum-Dots-Anchored Graphene Nanosheets as Superior-Capability Anode for Lithium-Ion Batteries. Electrochim. Acta 2015, 182, 424-429. 6. He, J.; Chen, Y.; Lv, W.; Wen, K.; Li, P.; Wang, Z.; Zhang, W.; Qin, W.; He, W. Three-Dimensional Hierarchical Graphene-CNT@Se: A Highly Efficient Freestanding Cathode for Li–Se Batteries. ACS Energy Lett. 2016, 1, 16-20. 7. Li, Z.; Li, C.; Ge, X.; Ma, J.; Zhang, Z.; Li, Q.; Wang, C.; Yin, L. Reduced Graphene Oxide Wrapped MOFs-Derived Cobalt-Doped Porous Carbon Polyhedrons as Sulfur Immobilizers as Cathodes for High Performance Lithium Sulfur Batteries. Nano Energy 2016, 23, 15-26. 8. Zhang, K.; Xu, Y.; Lu, Y.; Zhu, Y.; Qian, Y.; Wang, D.; Zhou, J.; Lin, N.; Qian, Y. A Graphene Oxide-Wrapped Bipyramidal Sulfur@Polyaniline Core – Shell Structure as a Cathode for Li–S Batteries with Enhanced Electrochemical Performance. J. Mater. Chem. A 2016, 4, 6404-6410. 9. Ma, J.; Fang, Z.; Yan, Y.; Yang, Z.; Gu, L.; Hu, Y.; Li, H.; Wang, Z.; Huang, X. Novel Large-Scale Synthesis of a C/S Nanocomposite with Mixed Conducting Networks through a Spray Drying Approach for Li-S Batteries. Adv. Energy Mater. 2015, 5, 201500046. 10. He, J.; Chen, Y.; Li, P.; Fu, F.; Liu, J.; Wang, Z. Facile Fabrication of RGO Wrapped LiMn2O4 Nanorods as a Cathode with Enhanced Specific Capacity. RSC Adv. 2015, 5, 80063-80068. 11. He, J.; Chen, Y.; Li, P.; Wang, Z.; Qi, F.; Liu, J. Synthesis and Electrochemical Properties of Graphene-Modified LiCo1/3Ni1/3Mn1/3O2 Cathodes for Lithium Ion Batteries. RSC Adv. 2013, 4, 2568-2572. 12. Fan, F. Y.; Carter, W. C.; Chiang, Y. Mechanism and Kinetics of Li2S Precipitation in Lithium-Sulfur Batteries. Adv. Mater. 2015, 27, 5203-5209. 13. Seh, Z. W.; Wang, H.; Liu, N.; Zheng, G.; Li, W.; Yao, H.; Cui, Y. High-Capacity Li2S-Graphene Oxide Composite Cathodes with Stable Cycling Performance. Chem. Sci. 2014, 5, 1396. 14. Wu, F.; Lee, J. T.; Magasinski, A.; Kim, H.; Yushin, G. Solution-Based Processing of Graphene-Li2S Composite Cathodes for Lithium-Ion and Lithium-Sulfur Batteries. Part. Part. Syst. Char. 2014, 31, 639-644. 15. He, J.; Chen, Y.; Lv, W.; Wen, K.; Li, P.; Qi, F.; Wang, Z.; Zhang, W.; Li, Y.; Qin, W.; 16


Page 16 of 18

Page 17 of 18

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 Energy Letters

He, W. Highly-Flexible 3D Li2S/Graphene Cathode for High-Performance Lithium Sulfur Batteries. J. Power Sources 2016, 327, 474-480. 16. He, J.; Chen, Y.; Lv, W.; Wen, K.; Wang, Z.; Zhang, W.; Li, Y.; Qin, W.; He, W. Three-Dimensional Hierarchical Reduced Graphene Oxide/Tellurium Nanowires: A High-Performance Freestanding Cathode for Li – Te Batteries. ACS Nano 2016 (10.1021/acsnano.6b04622). 17. Wu, F.; Kim, H.; Magasinski, A.; Lee, J. T.; Lin, H.; Yushin, G. Harnessing Steric Separation of Freshly Nucleated Li2S Nanoparticles for Bottom-Up Assembly of High-Performance Cathodes for Lithium-Sulfur and Lithium-Ion Batteries. Adv. Energy Mater. 2014, 4, 201400196. 18. Yang, Y.; Zheng, G.; Misra, S.; Nelson, J.; Toney, M. F.; Cui, Y. High-Capacity Micrometer-Sized Li2S Particles as Cathode Materials for Advanced Rechargeable Lithium-Ion Batteries. J. Am. Chem. Soc. 2012, 134, 15387-15394. 19. Wu, F.; Lee, J. T.; Fan, F.; Nitta, N.; Kim, H.; Zhu, T.; Yushin, G. A Hierarchical Particle--Shell Architecture for Long-Term Cycle Stability of Li2S Cathodes. Adv. Mater. 2015, 37, 201502289. 20. Wu, F.; Magasinski, A.; Yushin, G. Nanoporous Li2S and MWCNT-Linked Li2S Powder Cathodes for Lithium-Sulfur and Lithium-Ion Battery Chemistries. J. Mater. Chem. A 2014, 2, 6064-6070. 21. He, J.; Li, P.; Lv, W.; Wen, K.; Chen, Y.; Zhang, W.; Li, Y.; Qin, W.; He, W. Three-Dimensional Hierarchically Structured Aerogels Constructed with Layered MoS2/Graphene Nanosheets as Free-Standing Anodes for High-Performance Lithium Ion Batteries. Electrochim. Acta 2016, 215, 12-18. 22. Wang, C.; Wang, X.; Yang, Y.; Kushima, A.; Chen, J.; Huang, Y.; Li, J. Slurryless Li2S/Reduced Graphene Oxide Cathode Paper for High-Performance Lithium Sulfur Battery. Nano Lett. 2015, 15, 1796-1802. 23. Seh, Z. W.; Wang, H.; Hsu, P.; Zhang, Q.; Li, W.; Zheng, G.; Yao, H.; Cui, Y. Facile Synthesis of Li2S-Polypyrrole Composite Structures for High-Performance Li2S Cathodes. Energ. Environ. Sci. 2014, 7, 672. 24. Nan, C.; Lin, Z.; Liao, H.; Song, M.; Li, Y.; Cairns, E. J. Durable Carbon-Coated Li2S Core–Shell Spheres for High Performance Lithium/Sulfur Cells. J. Am. Chem. Soc. 2014, 136, 4659-4663. 25. Liang, S.; Liang, C.; Xia, Y.; Xu, H.; Huang, H.; Tao, X.; Gan, Y.; Zhang, W. Facile Synthesis of Porous Li2S@C Composites as Cathode Materials for Lithium-Sulfur Batteries. J. Power Sources 2016, 306, 200-207. 26. Zhang, K.; Wang, L.; Hu, Z.; Cheng, F.; Chen, J. Ultrasmall Li2S Nanoparticles Anchored in Graphene Nanosheets for High-Energy Lithium-Ion Batteries. Sci. Rep.-UK 2014, 4, 6467. 27. Wu, F.; Lee, J. T.; Zhao, E.; Zhang, B.; Yushin, G. Graphene-Li2S-Carbon Nanocomposite for Lithium-Sulfur Batteries. ACS Nano 2016, 10, 1333-1340. 28. Wu, F.; Lee, J. T.; Nitta, N.; Kim, H.; Borodin, O.; Yushin, G. Lithium Iodide as a Promising Electrolyte Additive for Lithium-Sulfur Batteries: Mechanisms of Performance Enhancement. Adv. Mater. 2015, 27, 101-108. 29. Wang, X.; Chen, Y.; Qi, F.; Zheng, B.; He, J.; Li, Q.; Li, P.; Zhang, W.; Li, Y. 17


ACS Energy Letters

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

Interwoven WSe2/CNTs Hybrid Network: A Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution. Electrochem. Commun. 2016, 72, 74-78. 30. Lin, J.; He, J.; Chen, Y.; Li, Q.; Yu, B.; Xu, C.; Zhang, W. Pomegranate-Like Silicon/Nitrogen-Doped Graphene Microspheres as Superior-Capacity Anode for Lithium-Ion Batteries. Electrochim. Acta 2016, 215, 667-673. 31. Wang, X.; Chen, Y.; Zheng, B.; Qi, F.; He, J.; Li, Q.; Li, P.; Zhang, W. Graphene-Like WSe2 Nanosheets for Efficient and Stable Hydrogen Evolution. J. Alloy. Compd 2017, 691, 698-704. 32. Zhou, G.; Paek, E.; Hwang, G. S.; Manthiram, A. High-Performance Lithium-Sulfur Batteries with a Self-Supported, 3D Li2S-Doped Graphene Aerogel Cathodes. Adv. Energy Mater. 2015, 201501355. 33. Hwa, Y.; Zhao, J.; Cairns, E. J. Lithium Sulfide (Li2S)/Graphene Oxide Nanospheres with Conformal Carbon Coating as a High-Rate, Long-Life Cathode for Li/S Cells. Nano Lett. 2015, 15, 3479-3486.

18


Page 18 of 18

GrapheneâLi2S Aerogel as Freestanding

Recommend Documents

GrapheneâLi2S Aerogel as Freestanding