In Situ Reactive Synthesis of Polypyrrole-MnO2 Coaxial Nanotubes as

Subscriber access provided by LUNDS UNIV

Communication

In Situ Reactive Synthesis of Polypyrrole-MnO2 Coaxial Nanotubes as Sulfur Hosts for High-Performance Lithium–Sulfur Battery Jun Zhang, Ye Shi, Yu Ding, Wenkui Zhang, and Guihua Yu Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.6b03849 • Publication Date (Web): 13 Oct 2016 Downloaded from http://pubs.acs.org on October 14, 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.

Nano 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 20

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

Nano Letters

In Situ Reactive Synthesis of Polypyrrole-MnO2 Coaxial Nanotubes as Sulfur Hosts for HighPerformance Lithium–Sulfur Battery Jun Zhang,†‡ Ye Shi,† Yu Ding,† Wenkui Zhang,*‡ Guihua Yu*† † Materials Science and Engineering Program and Department of Mechanical Engineering, The University of Texas at Austin, TX, 78712, USA ‡ College of Materials Science and Engineering, Zhejiang University of Technology, 18 Chaowang Rd, Hangzhou 310014, China

KEYWORDS: Lithium–sulfur batteries, Manganese dioxide, Polypyrrole, Nanotubes, In situ polymerization

ACS Paragon Plus Environment

1

Nano 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

Page 2 of 20

ABSTRACT: Lithium–sulfur batteries are considered as a promising candidate for high energy density storage applications. However, their specific capacity and cyclic stability are hindered by poor conductivity of sulfur and the dissolution of redox intermediates. Here we design polypyrrole-MnO2 coaxial nanotubes to encapsulate sulfur, in which MnO2 restrains the shuttle effect of polysulfides greatly through chemisorption and polypyrrole serves as conductive frameworks. The polypyrrole-MnO2 nanotubes are synthesized through in situ polymerization of pyrrole using MnO2 nanowires as both template and oxidization initiator. A stable Coulombic efficiency of ~98.6% and a decay rate of 0.07% per cycle along with 500 cycles at 1C-rate are achieved for polypyrrole-MnO2 nanotubes encapsulated sulfur with 5 wt% of MnO2. The excellent trapping ability of MnO2 to polysulfides and tubular structure of polypyrrole with good flexibility and conductivity are responsible for the significantly improved cyclic stability and rate capability.


2

Page 3 of 20

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

Nano Letters

High-performance rechargeable batteries are essential for a wide range of applications, such as portable electronic devices, electric vehicles and grid-scale storage of renewable energy.1, 2 Li ion batteries (LIBs) with traditional Li-ion intercalation cathodes are approaching their theoretical energy density limits. It is urgent to develop new energy storage systems with higher energy density and long cyclic stability.3 Rechargeable lithium–sulfur (Li–S) batteries have recently attracted great interest because of their potential advantages including ultrahigh theoretical energy density, low cost, and nontoxicity.4-8 Through the multi-electron electrochemical redox reaction with Li ions 16Li + S8 = 8Li2S, sulfur delivers a theoretical specific capacity up to 1675 mAh g-1, which is 5-10 times of currently used cathodes. Therefore, Li–S battery is a promising candidate for next-generation high density energy storage devices. However, due to the intrinsic insulating nature of elemental sulfur and lithium sulfide/disulfide, Li-S batteries have suffered from low utilization of sulfur and thus low energy density. Over the decades, much effort has been made to solve/alleviate these problems. The most common strategy is using conductive hosts for sulfur, such as carbon materials and conducting polymers. Owing to their high conductivity and high specific surface areas, sulfur can be fully utilized and the intermediate polysulfides (Li2Sx, 3 < x ≤ 8) can be trapped to some extent. Conductive matrixes with high surface area and pore volume were employed to accommodate sulfur, including micro/mesoporous carbon,9-12 activated carbon,13-15 graphene,16-21 hollow carbon fibers,22-24 and porous/hollow carbon spheres,25-27 etc. Meanwhile, conducting polymers such as polyaniline (PANi),28 polypyrrole (PPy)29 and poly(3,4-ethylenedioxythiophne)-poly(styrene sulfonate) (PEDOT:PSS)30 have been also used as the host materials for sulfur through thermal filtration or polymer coating. Cui et al

31

have systematically investigated the influence of

different conductive polymer coatings in improving hollow sulfur nanospheres cathode


3

Nano 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

Page 4 of 20

performance. Based on good conductivity, flexibility and the physical confinement of sulfur species by high surface area and/or well-designed structures, significantly enhanced capacity has been obtained. However, due to the weak interaction between polar polysulfides and nonpolar carbon/polymers, dissolution of the reaction intermediates in the ether-based electrolyte is inevitable, resulting in low Coulombic efficiency and poor cyclic stability.32 Although lithium anode can be protected by adding LiNO3 in the electrolyte to form a passive layer, long-term stability of Li-S batteries still remains a critical challenge. Recently, metal oxides host materials such as TiO2,33-35 Ti4O7,36, 37 MnO2,38-40 indium tin oxide (ITO),41 La2O3,42 γ-Fe2O3,43 VO2,44 V2O5,44, 45 MoO3,45 Nb2O546 and metal hydroxides including Ni(OH)2

47

and Co(OH)2

48, 49

have

been found to form strong chemical interactions with lithium polysulfides. Through binding between sulfur species and the surface of host materials, the long term cycling stability of Li–S batteries was significantly improved. However, due to their much lower conductivity compared with carbon or conducting polymers, a considerable amount of conductive additives is required to fabricate electrodes, which is not favorable to the overall energy density. In addition, considering the insulating and electrochemically inactive nature of Li2S/Li2S2, controllable and uniform deposition of Li2S/Li2S2 during cycling is beneficial to prevent “dead” active material. Therefore, the combination of polar materials and conducting matrix with rationally designed structures is expected to show advantages over the strategy of simply mixing two components. Recently, nanostructured ternary composites based on sulfur, metal oxide and conductive hosts have been reported to enhance their long term cyclic stability.50,

51

However, the synthetic

strategies remain complicated and ineffective.


4

Page 5 of 20

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

Nano Letters

In this work, we designed PPy-MnO2 coaxial nanotubes to accommodate sulfur. The PPyMnO2 nanotubes were synthesized through a facile in situ polymerization of pyrrole using MnO2 nanowires as both template and oxidization initiator (Scheme 1). The formation of coaxial nanotube structure could be attributed to corrosion-based formation mechanism. And the content of MnO2 in the composite could be controlled by adjusting the ratio of oxidant and pyrrole monomer. Sulfur was then infiltrated into the nanotubes through a well-established meltdiffusion method. In this ternary system, the polar material MnO2 provides strong adsorption to polysulfides while PPy serves as a flexible yet conductive network to tolerate volume change and facilitate electron transport. Therefore, significantly improved cyclic stability, Coulombic efficiency and rate capability are achieved when compared with pure PPy nanotubes encapsulated sulfur. An optimized ratio of MnO2 in the binary composites is found to be 17% (5% in ternary composite of S/PPy-MnO2), which balances the adsorption ability and the conductivity.


5

Nano 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

Page 6 of 20

Scheme 1. Illustration of the synthesis of S/PPy-MnO2 ternary composites and the advantages during charge/discharge process. MnO2 nanowires with an average diameter of ~50 nm were prepared by a hydrothermal process in which they self-assembled to form urchin-like structures (Figure 1a). MnO2 is a strong oxidant and acts as chemical oxidative initiator for pyrrole polymerization. The redox reaction can be expressed by: Cathode: MnOଶ + 4H ା + 2e → Mnଶା + 2Hଶ O

(1.23 V)

(1)

Anode: ݊Cସ Hସ NH → (Cସ Hଶ NH)௡ + 2nH ା + 2e

(0.7 V)

(2)

This reaction enables MnO2 nanowires to act as both the template and the oxidant for polymerization of PPy. As a result, the outer surface of MnO2 nanowires is covered by PPy, leading to a more rapid corrosion inside MnO2 nanowires, and therefore coaxial PPy-MnO2 nanotubes are formed with inner and out diameter about 50 and 90 nm, respectively (Figure 1b). Detailed mechanism can be found in previous literature.52 The elemental mapping results (Figure 1c) confirm that MnO2 is partially etched during the polymerization of PPy. After sulfur infiltration, the PPy-MnO2 nanotubes maintain their morphology (Figure 1d). Elemental mapping shows that sulfur is well-encapsulated inside the nanotubes and signals from N and Mn elements can be detected. Energy-dispersion X-ray Spectrum (EDX) is shown in Figure S1 (Supporting Information). Using the same method, PPy-MnO2 nanotubes with different contents of MnO2 and pure PPy nanotubes were synthesized by adjusting the mole ratio of pyrrole monomer and MnO2 nanowires. Compared with MnO2/C hollow nanofibers prepared via multiple steps including templating coating, thermal treatment and corrosive etching,51 our method is facile and more versatile.


6

Page 7 of 20

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

Nano Letters

Figure 1. (a) SEM image of MnO2 nanowires; (b) TEM image of PPy-MnO2 nanotubes; (c) TEM image of PPy- MnO2 nanotubes and corresponding elemental mapping of O, N and Mn; (d) TEM image of sulfur filled PPy-MnO2 nanotubes; (e) TEM image of a single S/PPy-MnO2 nanotube and corresponding S, N and Mn elemental mapping. X-ray diffraction (XRD) patterns shown in Figure 2a indicate that the as-prepared MnO2 nanowires are of Crytomelane phase. After PPy coating, an additional broaden peak between 2030 degree is found, indicating the coexistence of PPy and MnO2. Owing to the low content of MnO2 (about 5% as determined by thermogravimetric analysis shown in Figure 2b) in the composite after sulfur infiltration, peaks belonging to MnO2 become undetectable. Adsorption


7

Nano Letters

ability was investigated by adding 15 mg of these materials in 2 mL of 0.005 M L2S6 in dioxolane/dimethoxyethane (DME/DOL, 1 : 1 in volume). As shown in Figure 2c, the MnO2 nanowires exhibit excellent trapping ability for polysulfides. The solution becomes completely colorless within several minutes. Addition of PPy-MnO2 nanotubes with 17 wt% of MnO2 results in a very light yellow color in the solution, suggesting their remarkable polysulfide adsorption ability. However, the solution with addition of pure PPy nanotubes remains intense yellow, indicating extremely weak interaction between PPy and polysulfides.

(a)

Intensity /a.u.

S/PPy-MnO2

PPy-MnO2 MnO2 nanowires Sulfur #77-0145 Crytomelane #72-1982

10

20

30

40

2θ /

(b)

50

60

70

o

S/PPy-5% MnO2

100

S/PPy 80

Weight /%

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 8 of 20

~ 70% sulfur

60 40 20 0 100

200

300

400

500

600

o

Temperature / C

(c)


8

Page 9 of 20

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

Nano Letters

Figure 2. (a) XRD patterns of MnO2 nanowires, PPy-MnO2 nanotubes and sulfur filled PPyMnO2 nanotubes; (b) Thermogravimetric analysis of S/PPy and S/PPy-MnO2 composites; (c) Li2S6 Adsorption test (photos were taken after being standing for 30 min). The electrochemical properties of S/PPy-MnO2 and S/PPy were investigated by techniques of cyclic voltammetry and charging/discharging at various current densities. For the first scan, both CV curves (Figure S2) show reduction peaks at lowered potential, which may be attributed to the vulcanization of PPy at 200 °C forming disulfide bonds that require an activation energy during first discharge, which was also observed in S/PANi nanotubes.28 In the following scans, both samples show two reduction peaks at ~2.3 V and 2.05 V and one oxidation peak at 2.5 V. The peaks of S/PPy-MnO2 are much sharper than those of S/PPy, indicating a reduced polarization. Moreover, the CV curves of S/PPy-MnO2 show higher consistency than those of S/PPy in multiple scans, suggesting a higher cyclic stability. Cyclic performance at 0.2C and 1C rates (1C = 1675 mA g−1) is shown in Figure 3a and b. The S/PPy-MnO2 delivers an initial capacity of 1420 mAh g−1 at 0.2C, and retains 985 mAh g−1 after 200 cycles. The contribution of MnO2 and PPy to capacity could be ignored, since their low specific capacity of ~100 mAh g−1 in the potential range (Figure S3) and their low ratio in the composites. At 1C rate, a discharge capacity of 850 mAh g−1 is obtained for the S/PPy-MnO2 composites in first cycle. It maintains 550 mAh g−1 after 500 cylces with a decay rate of ~0.07% per cycle, indicating excellent cyclic stability. In contrast, though showing comparable initial capacity, pure PPy nanotubes encapsulated sulfur samples exhibit drastic capacity decay. In both cases, sulfur is accommodated by conductive tubular PPy nanostructures, which provide efficient electronic transport pathways to sulfur and flexibility for volume expansion. The difference is that the reaction intermediates can be effectively trapped by MnO2 in PPy-MnO2, while for pure PPy


9

Nano 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

Page 10 of 20

nanotubes, active material could be still lost through polysulfides dissolution.38 The polysulfides can be absorbed on surface of MnO2, forming active polythionate as anchor and transfer mediator to inhibit dissolution loss. The Coulombic efficiency of S/PPy electrode decreases gradually with cycling, suggesting a growing shuttle effect. Although LiNO3 is added in the electrolyte to form a passive layer on metallic lithium, the reaction between polysulfides and lithium cannot be suppressed after extended cycles. During cycling, the high concentration of polysulfides in the electrolyte results in more and more serious shuttle effect from cathode to anode, leading to considerable self-discharge and thus low Coulombic efficiency. For comparison, the S/MnO2 nanowires composite shows a very high average Coulombic efficiency of 99.7% but fast decay (Figure S4). Although MnO2 nanowires can form strong chemical interactions with polysulfides as demonstrated by the adsorption test (Figure 2c), the as-trapped polysulfides will form the insulating Li2S2/Li2S precipitation covering on the surface of nanowires, which prevents further discharging reaction. Rate tests were conducted by increasing the charge/discharge current density from 0.1C to 4C every 5 cycles, and then recovering back to 0.2C. In comparison to S/PPy, S/PPy-MnO2 composite shows remarkably improved rate capability (Figure 3c). It delivers capacities of 500 mAh g−1 and 350 mAh g−1 at 2C and 4C rates, respectively. After undergoing high rates up to 4C, the capacity of the S/PPy-MnO2 composite can recover to ~1000 mAh g−1 at 0.2 C, demonstrating its excellent rate capability. From the charge/discharge profiles at various rates shown in Figure 3d, the two-plateau characteristic can be clearly identified at 1C, indicative of low polarization. In order to investigate the mechanism for the enhanced electrochemical performance, electrochemical impedance spectra (EIS) measurement was conducted for S/PPyMnO2 and S/PPy samples at initial state and after being charged/discharged for 100 cycles


10

Page 11 of 20

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

Nano Letters

(experimental and fitting results were shown in Figures S5, S6 and Tables S1 and S2). Compared with the S/PPy composite, the S/PPy-MnO2 composite exhibits a lower charge transfer resistance and much lower Warburg coefficient, demonstrating that the ternary composite has better diffusion capability of Li+ and polysulfides anions. After extended cycles, an additional surface resistance Rsl appears in the EIS, which could be assigned to the deposition of insulating Li2S/Li2S2 on the surfaces of cathode and anode.53 Because of the inactive and insulating nature of discharge products Li2S/Li2S2, they cannot be reoxidized completely to sulfur even at fully charged state. With increasing cycle, residual Li2S/Li2S2 accumulate gradually on the surface of cathode. On the other hand, the dissolved polysulfides in the electrolyte diffuse to anode and react with lithium to form Li2S/Li2S2 on anode. It is found that the S/PPy electrode shows much higher Rsl than S/PPy-MnO2, suggesting that a thicker layer of Li2S/Li2S2 is formed on the electrodes’ surfaces during electrochemical cycling. The increase of charge transfer resistance Rct during cycling is induced by the deposition of Li2S/Li2S2 on the surface of active material of cathode. The existence of MnO2 is responsible for the reduced deposition of insulating layer on anode and cathode by trapping polysulfides effectively in the coaxial nanotubes. The Warburg coefficient of both samples decreases significantly compared with their initial states, which could be attributed to the activation of interfaces between the electrode and electrolyte.


11

Nano Letters

(a)

(c)

0.1C

1500

S/PPy-MnO2

-1

80 60

1000

S/PPy-MnO2

40

S/PPy

500

20

0.2C 0

50

100

150

Specific capacity/ mAh g

1500

Coulombic efficiency /%


-1

100

0

S/PPy

0.2C

0.2C

1000

0 200

0.5C 1C 2C

500

4C

0

0

10

20 Cycle number

Cycle number

(b)

3.0

S/PPy-MnO2

1000

60

S/PPy 40

500 20

1C 0 0

100

200

300

400

0 500

+

Potential /V vs. Li /Li

80


1500

30

(d)

100

-1


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 20

2.5

2.0

4C

2C

1C

0.5C

0.2C

0.1C

1.5 0

200

Cycle number

400

600

800

1000

1200

1400

-1

Specific Capacity/ mAh g

Figure 3. Electrochemical performance of PPy-MnO2 nanotubes encapsulated sulfur electrode compared with pure PPy nanotubes encapsulated sulfur electrode at (a) 0.2C, (b) 1C, (c) various C-rates and (d) charge-discharge profiles of S/PPy-MnO2 at different rates. The morphology change of the samples after 100 cycles is examined by SEM (Figure S7). It is found that the S/PPy-MnO2 shows a rougher surface after cycling, but still maintains its tubular morphology. Whereas for the S/PPy electrode, much thicker layers resulted from deposition of aggregated Li2S can be observed on the surface, and the tubular structure of PPy is destroyed after 100 cycles. This result is consistent with EIS analysis. To further investigate the effect of MnO2 in the composites, we synthesized S/PPy-MnO2 composites with different amount of MnO2. The composition of PPy-MnO2 coaxial nanotubes was controlled by tuning molar ratio of MnO2 : pyrrole monomer. PPy-MnO2 nanotubes sample with 10, 17 and 28 wt% of MnO2 were prepared. After infiltrated by 70 wt% of sulfur, the


12

Page 13 of 20

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

Nano Letters

weight ratio of MnO2 becomes 3, 5, 8 wt%, respectively, in the S/PPy-MnO2 composites (as determined by thermogravimetric analysis shown in Figure S8). Cyclic stability of these composites at 1C-rate is shown in Figure 4a. Among them, S/PPy-5% MnO2 is found with the best electrochemcial performance including the highest specific cpacity over 700 mAh g−1 and superior cyclic stabiltity. The capacity fluctuation around the 25th and 60th cycle could be attributed to the ambient temperature change. The PPy-MnO2 coaxial nanotubes with 17 wt% MnO2 possess both good conductivity and strong chemisorption to polysulfides, resulting in a synergic advantage. It is also found that the S/PPy-8% MnO2 composite shows comparable initial specific capacity with S/PPy-3% MnO2 but better cyclic stability, which could be attributed to stronger chemisorption in the S/PPy-8% MnO2. In addition, we test the S/PPy-5% MnO2 electrodes with a higher sulfur mass loading of 2 mg cm–2. As shown in Figure 4b, a specific capacity of about 800 mAh g–1 is achieved at 0.5C-rate for higher mass loading. Furthermore, the electrodes show very high Coulombic efficiency and good cyclic stability within 100 cycles. A comparison of rate capability and areal capacity with literature that used metal oxides as the host matrix for sulfur is shown in Figure S9. The PPy-MnO2 nanotubes encapsulated sulfur shows comparable capacity with those below 1C-rate,38-40,

54

but inferior

capacity at higher C-rate that is attributed to its limited ionic conductivity. Nevertheless, the S/PPy-MnO2 composites exhibit very stable cyclic performance at 0.5C with a high areal capacity of 1.6 mAh cm–2, showing potential for the practical application of high-energy and long-life Li–S batteries.


13

Nano Letters

100 1000 80

800

60

600 400

S/PPy-3% MnO2

200

S/PPy-5% MnO2

20

S/PPy-8% MnO2

1C

0 0

20

40

60

80

0 100

Cycle number

(b) -1

40


1200

1200

100

1000 80 800 60 600 40

400

20

200 -2

2 mg cm

0.5C

0 0

20

40

60

80

0 100

Coulombic efficiency / %


-1

(a)

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

Page 14 of 20

Cycle number

Figure 4. (a) Cyclic performance of PPy-MnO2 coaxial nanotubes encapsulated sulfur composites with different content of MnO2; (b) Cylcic performance of PPy-5% MnO2 coaxial nanotubes encapsulated sulfur electrode with mass loading of 2 mg cm-2 at 0.5C rate. In summary, we have designed PPy- MnO2 coaxial nanotubes with adjustable content of MnO2 to encapsulate sulfur as a high-performance cathode for Li–S batteries. Compared with pure PPy encapsulated sulfur, the S/PPy-MnO2 composites show much enhanced electrochemical performance, including Coulombic efficiency, cyclic stability, and rate capability. The synergic effect of the strong interaction between MnO2 and polysulfides, and highly conductive and flexible polymer with tubular-structure is responsible for the improved


14

Page 15 of 20

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

Nano Letters

properties. With optimized ratio of MnO2, the composites exhibit the ability to prevent polysulfides from dissolution, leading to high Coulombic efficiency and excellent cyclic stability. EIS analysis and morphology characterization demonstrated that the controlled deposition of insulating Li2S/Li2S2 in S/PPy-MnO2 composites is also a key factor for cyclic stability. This facile and controllable method to fabricate MnO2-conductive polymer nanotubes represents a useful strategy for design and synthesis of scalable, high-performance Li–S batteries.

ASSOCIATED CONTENT Supporting Information. Detailed experimental procedures, supplementary characterization methods including EDS, SEM, TGA, and other electrochemical measurement. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors * (G.Y.) E-mail: [email protected] * (W.Z.) E-mail: [email protected] Notes The authors declare no financial competing interest. ACKNOWLEDGMENT


15

Nano 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

Page 16 of 20

G.Y. acknowledges the funding suppot from National Science Foundation award (NSF-CMMI1537894). J.Z. and W.Z. are grateful to the financial support from Zhejiang Natural Science Foundation of China (LY15B030003) and National Natrual Science Foundation of China (51572240).


16

Page 17 of 20

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

Nano Letters

REFERENCES (1) Dunn, B.; Kamath, H.; Tarascon, J. M. Science 2011, 334, 928-935. (2) Goodenough, J. B. Acc. Chem. Res. 2013, 46, 1053-1061. (3) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M. Nat. Mater. 2012, 11, 19-29. (4) Seh, Z. W.; Sun, Y.; Zhang, Q.; Cui, Y. Chem. Soc. Rev. 2016, DOI: 10.1039/c5cs00410a. (5) Yin, Y. X.; Xin, S.; Guo, Y. G.; Wan, L. J. Angew. Chem. Int. Ed. 2013, 52, 1318613200. (6) Manthiram, A.; Chung, S. H.; Zu, C. X. Adv. Mater. 2015, 27, 1980-2006. (7) Manthiram, A.; Fu, Y. Z.; Su, Y. S. Acc. Chem. Res. 2013, 46, 1125-1134. (8) Bai, S.; Liu, X.; Zhu, K.; Wu, S.; Zhou, H. Nat. Energy 2016, 1, 16094. (9) Ji, X. L.; Lee, K. T.; Nazar, L. F. Nat. Mater. 2009, 8, 500-506. (10) Schuster, J.; He, G.; Mandlmeier, B.; Yim, T.; Lee, K. T.; Bein, T.; Nazar, L. F. Angew. Chem. Int. Ed. 2012, 51, 3591-3595. (11) Li, Z.; Yuan, L. X.; Yi, Z. Q.; Sun, Y. M.; Liu, Y.; Jiang, Y.; Shen, Y.; Xin, Y.; Zhang, Z. L.; Huang, Y. H. Adv. Energy Mater. 2014, 4, 1301473. (12) Li, Y. J.; Fan, J. M.; Zheng, M. S.; Dong, Q. F. Energy Environ. Sci. 2016, 9, 1998-2004. (13) Zhang, J.; Xiang, J. Y.; Dong, Z. M.; Liu, Y.; Wu, Y. S.; Xu, C. M.; Du, G. H. Electrochim. Acta 2014, 116, 146-151. (14) Zhang, S. T.; Zheng, M. B.; Lin, Z. X.; Li, N. W.; Liu, Y. J.; Zhao, B.; Pang, H.; Cao, J. M.; He, P.; Shi, Y. J. Mater. Chem. A 2014, 2, 15889-15896. (15) Lee, J. T.; Zhao, Y. Y.; Kim, H.; Cho, W. I.; Yushin, G. J. Power Sources 2014, 248, 752-761. (16) Yang, X.; Zhang, L.; Zhang, F.; Huang, Y.; Chen, Y. S. ACS Nano 2014, 8, 5208-5215. (17) Wang, Z. Y.; Dong, Y. F.; Li, H. J.; Zhao, Z. B.; Wu, H. B.; Hao, C.; Liu, S. H.; Qiu, J. S.; Lou, X. W. Nat. Commun. 2014, 5, 5002. (18) Zhang, J.; Dong, Z. M.; Wang, X. L.; Zhao, X. Y.; Tu, J. P.; Su, Q. M.; Du, G. H. J. Power Sources 2014, 270, 1-8. (19) Peng, L.; Zhu, Y.; Chen, D.; Ruoff, R.S.; Yu, G. Adv. Energy Mater. 2016, 6, DOI: 10.1002/aenm.201600025. (20) Shi, Y.; Peng, L.; Ding, Y.; Zhao, Y.; Yu, G. Chem. Soc. Rev. 2015, 44, 6684. (21) Wang, H. L.; Yang, Y.; Liang, Y. Y.; Robinson, J. T.; Li, Y. G.; Jackson, A.; Cui, Y.; Dai, H. J. Nano Lett. 2011, 11, 2644-2647. (22) Zheng, G. Y.; Yang, Y.; Cha, J. J.; Hong, S. S.; Cui, Y. Nano Lett. 2011, 11, 4462-4467. (23) Zheng, G. Y.; Zhang, Q. F.; Cha, J. J.; Yang, Y.; Li, W. Y.; Seh, Z. W.; Cui, Y. Nano Lett. 2013, 13, 1265-1270. (24) Guo, J. C.; Xu, Y. H.; Wang, C. S. Nano Lett. 2011, 11, 4288-4294. (25) Zhang, C. F.; Wu, H. B.; Yuan, C. Z.; Guo, Z. P.; Lou, X. W. Angew. Chem. Int. Ed. 2012, 51, 9592-9595. (26) Zhou, G. M.; Zhao, Y. B.; Manthiram, A. Adv. Energy Mater. 2015, 5, 1402263. (27) He, G.; Evers, S.; Liang, X.; Cuisinier, M.; Garsuch, A.; Nazar, L. F. ACS Nano 2013, 7, 10920-10930. (28) Xiao, L. F.; Cao, Y. L.; Xiao, J.; Schwenzer, B.; Engelhard, M. H.; Saraf, L. V.; Nie, Z. M.; Exarhos, G. J.; Liu, J. Adv. Mater. 2012, 24, 1176-1181.


17

Nano 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

Page 18 of 20

(29) Dong, Z. M.; Zhang, J.; Zhao, X. Y.; Tu, J. P.; Su, Q. M.; Du, G. H. RSC Adv. 2013, 3, 24914-24917. (30) Yang, Y.; Yu, G. H.; Cha, J. J.; Wu, H.; Vosgueritchian, M.; Yao, Y.; Bao, Z. A.; Cui, Y. ACS Nano 2011, 5, 9187-9193. (31) Li, W.; Zhang, Q.; Zheng, G.; Seh, Z. W.; Yao, H.; Cui, Y. Nano Lett. 2013, 13, 55345540. (32) Barghamadi, M.; Best, A. S.; Bhatt, A. I.; Hollenkamp, A. F.; Musameh, M.; Rees, R. J.; Ruether, T. Energy Environ. Sci. 2014, 7, 3902-3920. (33) Seh, Z. W.; Li, W. Y.; Cha, J. J.; Zheng, G. Y.; Yang, Y.; McDowell, M. T.; Hsu, P. C.; Cui, Y. Nat. Commun. 2013, 4, 1331. (34) Hwang, J. Y.; Kim, H. M.; Lee, S. K.; Lee, J. H.; Abouimrane, A.; Khaleel, M. A.; Belharouak, I.; Manthiram, A.; Sun, Y. K. Adv. Energy Mater. 2016, 6, 1501480. (35) Yu, M.; Ma, J.; Song, H.; Wang, A.; Tian, F.; Wang, Y.; Qiu, H.; Wang, R. Energy Environ. Sci. 2016, 9, 1495-1503. (36) Tao, X. Y.; Wang, J. G.; Ying, Z. G.; Cai, Q. X.; Zheng, G. Y.; Gan, Y. P.; Huang, H.; Xia, Y.; Liang, C.; Zhang, W. K.; Cui, Y. Nano Lett. 2014, 14, 5288-5294. (37) Pang, Q.; Kundu, D.; Cuisinier, M.; Nazar, L. F. Nat. Commun. 2014, 5, 4759. (38) Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F. Nat. Commun. 2015, 6, 5682. (39) Wang, X.; Li, G.; Li, J.; Zhang, Y.; Wook, A.; Yu, A.; Chen, Z. Energy Environ. Sci. 2016, 9, 2533-2538. (40) Liang, X.; Nazar, L. F. ACS Nano 2016, 10, 4192-4198. (41) Yao, H. B.; Zheng, G. Y.; Hsu, P. C.; Kong, D. S.; Cha, J. J.; Li, W. Y.; Seh, Z. W.; McDowell, M. T.; Yan, K.; Liang, Z.; Narasimhan, V. K.; Cui, Y. Nat. Commun. 2014, 5, 3943. (42) Sun, F. G.; Wang, J. T.; Long, D. H.; Qiao, W. M.; Ling, L. C.; Lv, C. X.; Cai, R. J. Mater. Chem. A 2013, 1, 13283-13289. (43) Li, W.; Liang, Z.; Lu, Z.; Tao, X.; Liu, K.; Yao, H.; Cui, Y. Nano Lett. 2015, 15, 73947399. (44) Liang, X.; Kwok, C. Y.; Lodi-Marzano, F.; Pang, Q.; Cuisinier, M.; Huang, H.; Hart, C. J.; Houtarde, D.; Kaup, K.; Sommer, H.; Brezesinski, T.; Janek, J.; Nazar, L. F. Adv. Energy Mater. 2016, 6, 1501636. (45) Zhang, Q.; Wang, Y.; Seh, Z. W.; Fu, Z.; Zhang, R.; Cui, Y. Nano Lett. 2015, 15, 37803786. (46) Tao, Y.; Wei, Y.; Liu, Y.; Wang, J.; Qiao, W.; Ling, L.; Long, D. Energy Environ. Sci. 2016, DOI: 10.1039/c6ee01662f. (47) Jiang, J.; Zhu, J.; Ai, W.; Wang, X.; Wang, Y.; Zou, C.; Huang, W.; Yu, T. Nat. Commun. 2015, 6, 8622. (48) Niu, X. Q.; Wang, X. L.; Wang, D. H.; Li, Y.; Zhang, Y. J.; Zhang, Y. D.; Yang, T.; Yu, T.; Tu, J. P. J. Mater. Chem. A 2015, 3, 17106-17112. (49) Zhang, J. T.; Hu, H.; Li, Z.; Lou, X. W. Angew. Chem. Int. Ed. 2016, 55, 3982-3986. (50) Yan, M.; Zhang, Y.; Li, Y.; Huo, Y.; Yu, Y.; Wang, C.; Jin, J.; Chen, L.; Hasan, T.; Wang, B.; Su, B.-L. J. Mater. Chem. A 2016, 4, 9403-9412. (51) Li, Z.; Zhang, J. T.; Lou, X. W. Angew. Chem. Int. Ed. 2015, 54, 12886-12890. (52) Pan, L. J.; Pu, L.; Shi, Y.; Song, S. Y.; Xu, Z.; Zhang, R.; Zheng, Y. D. Adv. Mater. 2007, 19, 461-464.


18

Page 19 of 20

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

Nano Letters

(53) Deng, Z.; Zhang, Z.; Lai, Y.; Liu, J.; Li, J.; Liu, Y. J. Electrochem. Soc. 2013, 160, A553-A558. (54) Li, Y.; Ye, D.; Liu, W.; Shi, B.; Guo, R.; Zhao, H.; Pei, H.; Xu, J.; Xie, J. Y. ACS Appl. Mater. Interfaces 2016, DOI: 10.1021/acsami.6b04270.


19

Nano 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

Page 20 of 20

Table of Contents Graphic


20

In Situ Reactive Synthesis of Polypyrrole-MnO2 Coaxial Nanotubes as

Recommend Documents