Long-Life LithiumâSulfur Battery Derived from Nori-Based Nitrogen

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A Long-Life Lithium-Sulfur Battery Derived from Nori Based Nitrogen and Oxygen Dual-doped 3D Hierarchical Biochar Xian Wu, Lishuang Fan, Maoxu Wang, Junhan Cheng, Hexian Wu, Bin Guan, Naiqing Zhang, and Kening Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 10 May 2017 Downloaded from http://pubs.acs.org on May 15, 2017

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ACS Applied Materials & Interfaces

A Long-Life Lithium-Sulfur Battery Derived from Nori Based Nitrogen and Oxygen Dual-doped 3D Hierarchical Biochar Xian Wu, † Lishuang Fan,* ‡ Maoxu Wang, † Junhan Cheng, † Hexian Wu, † Bin Guan, † Naiqing Zhang*‡ , § and Kening Sun ‡ , § † School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin, 150001, China. ‡ State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150001, China. § Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin, 150001, China. KEYWORDS: heteroatom, hierarchical, nori, cycle stability, high rate.

ABSTRACT

Restriction on the low conductivity of sulfur and soluble polysulfides during discharge, lithium sulfur battery is unable for further large scale applications. The current carbon based cathodes suffer from poor cycle stability and high cost. Recently, heteroatom doped carbons have been considered as a settlement to enhance the performance of lithium sulfur batteries. With this strategy, we report the low cost activated nori based N, O-doped 3D hierarchical carbon material (ANC) as a sulfur host. The N, O dual-doped ANC reveals an elevated electrochemical

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performance, which exhibits not only a good rate performance over 5 C, but also a high sulfur content of 81.2 %. Further importantly, the ANC represents an excellent cycling stability, the cathode reserves a capacity of 618 mAh/g at 2 C after 1000 cycles, which shows a 0.022% capacity decay per cycle.

1. INTRODUCTION The current lithium ion batteries (LIB) can not satisfy the requirement of prompt development of portable storage devices and hybrid electric vehicles.1-3 Thus, the disadvantage of LIB should be made up by high energy density batteries. Recently, elemental sulfur has been considered to be a reasonable cathode material by reason of its high specific capacity (1675 mAh/g) and energy density (2500 Wh/kg).4-5 Besides, the feature of cost effective, nature abundance, non-toxic and environment friendly make sulfur possible for further commercial applications. However, lithium sulfur batteries suffer from severe challenges such as large volume expansion from S to Li2S, sulfur and its reduction products (Li2S) are insulator, soluble intermediate products during discharging, which deteriorate the electrochemical performance of the batteries.6-9 To overcome the limitations of sulfur cathodes, composing carbon materials with sulfur has been proven a promising technology. Nazar’s research group firstly use CMK-3 mesocarbon materials as sulfur host to promote the conductivity of the cathode and control polysulfides dissolution into the electrolyte, which shows an discharge capacity as high as 1005 mAh/g during the first cycle.10 After this work, various carbon materials have been utilized as sulfur host subsequently for promoting the cycle stability and rate performance of lithium sulfur batteries. Such as micro and mesoporous carbon,11 carbon nanotube,12 graphene,13-14 hollow


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carbon structure15-16 and hybrid carbon materials.17 Although the enhanced electrochemical performance has been obtained, the expensive synthesis processes impede the further application of such carbon materials in lithium sulfur battery. Porous biomass based carbon has attracted attention on account of economy, environmental benignity and sustainability.18-26 However, biochar-based lithium sulfur battery still encounters an intractable issue resulted from a rapid capacities decrease. It is worth noting that heteroatomdoped carbon materials would provide a polar site to form strong chemical bonds with Li2Sn due to Lewis acid-base interaction, which shows a commendable initial capacity and cycle life.27-29 Despite all that, a complex synthesis process and adding extra sources to dope heteroatoms still restrict the fabrication cost of lithium sulfur battery. Hence, it is urgent to find a carbon material combining the advantages of economic, nontoxic and efficient, and couple with a simple synthetic route as sulfur host to solve the problems of lithium sulfur batteries. In this work, we design and synthesize a novel type of biomass derived carbon via carbonization and subsequent activation to utilize directly natural rich nori as precursor and then obtain activated nori carbon (ANC), without complex synthesis process. It is well known that nori is a kind of nature abundant algae, which provide a high yield by widely artificial breeding. The features of fast growth, short maturity cycle and a large amount of heteroatom functional groups make it promising for practically applications for Li-S batteries. The 3D layered hierarchical structure of the ANC provides an electron transfer network to perform a high discharge capacity even at a high discharge rate. Furthermore, the obtained ANC has abundant nitrogen and oxygen, which provide multiple polar sites to anchor polysulfides, the result demonstrates that a high rate performance of 626 mAh/g is obtained at 5 C. Moreover, even with a high sulfur content (81.2 wt.%), the cathode still reveals a capacity of 657 mAh/g after 100


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cycles at 0.2 C. It is worth highlighting that the cathode has a high cycle performance, which could maintain a capacity of 618 mAh/g after 1000 cycles at a high rate of 2 C. To the best of our knowledge, nori based carbon provide a significant improvement of electrochemical performance compared with previous biochar materials. 2. EXPERIMENTAL SECTION 2.1. Synthesis of NC and ANC. The nori was purchased from Xizhilang food co., LTD (Hebei province, China) without further treatment. The NC were obtained from a direct carbonized process. The nori were washed by distilled water for several times. After drying, it was carbonized at 800 °C for 120 min with protection by Ar atmosphere. The obtained NC was mixed with KOH with a mass radio of 1:2 in mortar for 30 min, the mixture was annealed at 800 °C for 2 hours with a ramping rate of 2 °C/min under an Ar atmosphere for activation. To remove excess KOH, 1 M HCl solution and DI water were used to wash the resulted black powder. The ANC was collected by filtration and dried under vacuum condition at 80 °C for 12h. 2.2. Synthesis of NC/S and ANC/S. The NC/S compound was obtained from a simple meltdiffusion method. The NC and pure sulfur were mixed with a mass radio of 3:7, and add into a certain amount of CS2 stirred under magnetic stirrers. The collected powder was transferred into a sealed vessel and heat under 155 °C for 12h. The ANC/S was prepared by the same method. To study the electrochemical performance of different sulfur content, the mass radio of ANC and S was adjust to 3:7, 1:4 and 1:9. 2.3. Material Characterization. The morphology and microstructure characterization for NC and ANC was conducted using a SEM (Hitachi, SU8010). The crystal structure were characterized by X-ray diffraction (PANalytical X’Pert PRO, monochromated Cu Kα radiation


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40 mA, 40 kV). The sulfur content in the composite was tested by TG thermogravimetric analyzer system. The specific surface area, pore volume and N2 adsorption/desorption isotherms were measured by using an ASAP 2020 (Micromeritics). XPS analysis was performed at room temperature to analyze the compositions and contents of element. The electronic conductivity was characterized at room temperature with a four-probe conductivity test meter. 2.4. Electrochemical Measurements. The cathodes were prepared by mixing active materials, Ketjen Black and PVDF with a weight ratio of 8:1:1 in NMP to form a uniform slurry, and then directly coated onto a cleaned aluminum foil by a doctor-balding with a sulfur loading of about 1.0 mg/cm2. Then the electrode was dried at 60°C for 12h. The diameter of round disks electrode was 10 mm. The 2025 coin cells were assembled with Li metal disc as anode in a glovebox

filled with Ar. The electrolyte was composed of 1mol/L lithium bis

(trifluoromethanesulfonyl) imide (LiTFSI) in a solvent of 1, 3-dioxolane (DOL) and dimethoxymethane (DME) (1:1 ratio by volume) with 2% LiNO3 addition. CV test was recorded on a CHI 660D electrochemical workstation between 1.5 and 3.0 V. The charge transfer kinetics was investigated by EIS measurements using a PARSTAT 2273 advanced electrochemical system, the frequency range was set between 1 MHz and 100 mHz and the amplitude is 10 mV with an ac signal. A Neware battery test system is used toperform charge/discharge measurements, the voltage window is 1.7–2.8 V for various current rates (1 C is equivalent to 1675 mA/g).30 3. RESULTS AND DISCUSSION The synthesis process for the nori carbon (NC) and activated nori carbon (ANC) is illustrated in Figure 1. The nori is used without further purify and direct carbonized under Ar atmosphere. The protein in nori would provide the element of nitrogen during carbonization


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treatment without additional nitrogen source, and the yield of carbonization process is about 29 %. A common KOH activate method is used to enhance the specific area of NC. The ANC is obtained by mixing NC and KOH in mortar for 30 min, the mixture is heated at 800 °C for 120 min with an Ar atmosphere flow. The yield of activation process is 47 %, which is caused by the reacting with KOH to produce high specific area and abundant mesoporous. To remove excess KOH, 1 M HCl solution and DI water were used to wash the resulted black powder. A simple melt-diffusion method is used to prepare NC/S and ANC/S hybrid. The ANC and sulfur powder are mixed together by a mortar, the mixture is then heated at 155°C for 12h to obtain ANC/S-x (x is the sulfur loading in the compound).

Figure 1. Synthesis scheme of 3D NC/S and ANC/S hybrid.


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Figure 2. N2 adsorption/desorption isotherms with the corresponding pore size distribution for (a) NC and (b) ANC. Inset image show the pore size distribution of NC and ANC.

The N2 sorption isotherm in Figure 2a shows the structural features of the NC. The isotherm of the NC is type IV isotherms with hysteresis. The specific surface area of NC is 54 m2/g and the pore volume is 0.019 cm3/g. The ANC is prepared by heating NC with KOH. The N2 sorption isotherm of ANC in Figure 2b shows a high specific area of 2115 m2/g which is 40 times larger than NC, and large pore volume of 0.711 cm3/g. The high specific area could expose more active sites to anchor polysulfides, and large pore volume is benefits for high sulfur loading.31 . The electrical conductivity of NC, ANC, NC/S and ANC/S measured by a four-probe meter are 0.147, 0.055, 0.067 and 0.053 mS/cm, respectively. The decrease of electrical conductivity after activation is predicted because the abundant open-framework structure of ANC would enlarge the electronic transfer pathway. Compared with NC, the electrical conductivity of NC/S reduce half while the ANC/S compound shows a similar electrical conductivity to ANC, the result is caused by the large pore volume of ANC which is benefit for the uniform distribution of sulfur. The promotion of NC and ANC on the electrical conductivity compared with sulfur is beneficial for specific capacity and rate performance, which is proved in the subsequent discussion.


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The morphology of the NC is characterized by SEM as shown in Figure 3. The NC after carbonization gives a layered 3D hierarchical sorting box like structure as illustrated in Figure 3a. The top view of the NC has a porous layered carbon “cap” and there are many boxes blow the “cap”. We can see from the inset, the thickness of the NC sheet is about 10µm, which gives the NC a large inner volume to storage sulfur and polysulfides. The unique 3D hierarchical structure provides an electron transfer network, which is benefits for high rate performance. Besides, these macropores obviously promote diffusion and infiltration of electrolyte.19 Figure 3b shows the morphology inside the hole, which is a typically porous structure. The inset proves the holes are uniformly distribute on the NC surface, which would trap polysulfides and contain a high sulfur content. The elemental mapping reveals the elements of C, N, and O homogeneous distribution in the NC, as shown in Figure 3c. The morphology of ANC (Figure 3d) has no change after activation. After S impregnation, the S not only distributed within the hole of the ANC/S, but the redundantly S uniformly distributes on the surface of ANC without aggregation (Figure 3e), shows a strong surface adsorption of ANC to sulfur.


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Figure 3. SEM images of (a-b) NC and (c) elemental mapping of C, N, and O. Inset image in (a) shows the profile of NC. SEM images of (d) ANC and (e) ANC/S. (f) Elemental mapping of C and S.

The XPS is obtained to further investigate the surface chemistry of ANC. It is indicated that C, N, O elements are in the ANC, and the doping concentrations of N and O are 3.27% and 13.24% for ANC. Such N and O atoms in carbon matrix can produce abundant active sites to trap polysulfides. The XPS spectrum of C 1s (Figure 4a) proves the presence of C-C, C-N-C, C=C and C=O bonds, which correspond to the peaks at 284.5, 286.0, 288.2, and 292.7 eV, confirming effective doping of N and O into carbon lattice.27 The peaks in N 1s (Figure 4b) reveal the existing of oxidized N, graphitic N, pyrrolic N and pyridnic N at 402.7, 400.0, 398.8 and 398.0 eV,29,

32

and all these four N species can create the chemisorption sites for

polysulfides, which is indicated by recent researches.27 The crystal texture of the materials are verified by XRD. As illustrated in Figure 4c, the X-ray diffraction pattern of elemental sulfur can be indexed as orthorhombic structure. The ANC sample shows a typical feature of amorphous carbon with a low intensity and the high peak broadening. As expected, the ANC/S70 composite produces a similar pattern to sulfur but the peaks for S are weak, confirming embedded sulfur in the porous loses its orthorhombic structure. In comparison, ANC/S-90 shows a strong peak of sulfur due to outward sulfur restricted on the pore volume of ANC. TGA is used to evaluate the S content in ANC/S compound as presented in Figure 4d. The sulfur in the compounds begins to decrease at 200 °C and the loss of weight is completed at 450 °C. In proportion, 64.5, 68.0, 75.1, and 81.2 wt.% of sulfur for the NC/S, ANC/S-70, ANC/S-80 and ANC/S-90 compounds are determined respectively, the results are consistent with the contents of


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sulfur used in the compounds, the small amounts of sulfur loss are caused by the heat-treat procedure during compounds preparation.

Figure 4. XPS analysis of ANC: (a) C 1s and (b) N 1s. (c) XRD pattern of sulfur, ANC, ANC/S-70 and ANC/S-90 composites. (d) The TGA traces of ANC/S-70, ANC/S-80 and ANC/S-90 composites.

2.2. Electrochemical Performance of NC/S and ANC/S Composites Based Cathodes The electrochemical mechanism is investigated by cyclic voltammetry within a potential window of 1.5–3.0 V of the as-prepared lithium-sulfur batteries. The CV curves of NC/S electrode are revealed in Figure 5a. The 2.23 V at high potential can be agreed with the reduction of sulfur to Sn2- (n≥4) ions. Continued discharging into the lower voltage plateau


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results in Li2S2/Li2S. In the subsequent scanning back, the broad anodic peak at 2.46 V corresponded to the oxidation of short-chain polysulfide ions to long-chain, and these have been observed in a few sulfur-conductive matrix materials,12-13 indicating significant improved reversibility, high conductivity, and low polarization. After the first cycle, the CV curve shows a distinct positive shift in the cathodic peak and a negative shift in the anodic peak, indicating a decrease in cell polarization.33 Figure 5b illustrates the CV curves of the ANC/S-70 cathode, the ANC/S-70 shows higher reduction potentials and a lower oxidation potential, indicating a lower polarization. The sharp peak and repeatability current of ANC/S-70 also represent the better electrical conductivity and reversible during discharging and charging.

Figure 5. CV curve of (a) NC/S and (b) ANC/S-70. (c) The rate capability tests for NC/S and ANC/S-70 cathode. (d) Typical charge–discharge voltage profiles of ANC/S-70 cathode at 0.2 C. Cycle life of NC/S and ANC/S-70 cathode at a rate of (e) 0.2 C and (f) 1 C (after the first five activation processes at 0.1 C).

Furthermore, a good rate performance of NC/S and ANC/S-70 at a series of C rates is presented in Figure 5c. The ANC/S-70 delivers an initial specific discharge capacity of 1203,


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982, 899, 817, 731 and 626 mAh/g at 0.1, 0.2, 0.5, 1, 2 and 5 C. Moreover, the battery regains a specific capacity of 935 mAh/g as the current is restored to 0.1C, indicating a high rate performance. Moreover, the NC/S cathode shows a capacity of 1158, 916, 753, 663, 583 and 363 mAh/g at 0.1, 0.2, 0.5, 1, 2 and 5 C, which has a similar capacity at 0.1C compared with ANC/S70 cathode, but has a much serious capacity decrease especially at high rate. The reason is that the high specific area could explore more active sites and large pore volume would provide a more uniformly sulfur distribution, and the 3D layered hierarchical structure promotes electron transfer efficiency, thus ANC shows a good electron transmission and achieves a commendable rate performance. It's worth noting that the reported biomass based cathodes hardly perform such a high discharge rate. Figure 5d shows typical charge/discharge curves of ANC/S-70 at a rate of 0.2 C. The curves consist of two well-defined discharge plateaus at 2.32 V and 2.09 V, and one charge plateau at 2.36 V, in agreement with the CV curves in subsequent cycles. Compared with NC/S, the slope of ANC/S-70`s discharging curves below 2.1 V is in agreement with microporous and mesoporous materials. Figure 5e reveals the cycle stability of NC/S and ANC/S-70. Compared with NC/S cathode, ANC/S-70 shows a higher initial capacity of 1170 mAh/g, and a high discharge capacity of 826 mAh/g is still maintained after 100 cycles, while NC/S suffers from a relatively rapid decrease in the capacity, showing poor reversible capacity from 1068 to 719 mAh/g after 100 cycles. Figure 5f reveals the stability for long cycles at the rate of 1C. It is known that activation at a low rate would avail for high rate cycle stability.34 Hence, the batteries are activated at 0.1 C for 5 cycles before testing at 1C. The NC/S shows a capacity of 787 mAh/g and maintains 528 mAh/g after 500 cycles, 0.066% decay of capacity per cycle. However, the ANC/S-70 cathode reveals an excellent performance even at a high rate. The ANC/S-70 after activation shows an initial discharge capacity of 945 31mAh/g and maintain a


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stable cycling performance after 500 cycles, just 0.055% decay of capacity per cycle. These phenomenons are in line with the rate performance.

Figure 6. (a) Typical charge–discharge voltage profiles and (b) cycle stability of different sulfur content ANC/S cathodes at a rate of 0.2 C. (c) Cycling performance and Coulombic efficiency of ANC/S-70 cathode at 2 C (after the first ten activation processes at 0.1 C).

High sulfur loading is a key issue for commercial application of Li-S battery. To prove ANC/S could perform a good electrochemistry performance even at a high sulfur loading, we prepare a series of different sulfur loading cathodes and test their electrochemistry performance (Figure 6). As illustrated in Figure 6a, the charge/discharge voltage profiles indicate that the three S content cathodes have a similar initial capacities and high coulombic efficiency, but the ANC/S-90 shows a serious polarization due to its high S content. Figure 6b shows the cycle


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stability of different sulfur content ANC/S cathodes, although there is a strong capacity lose after the first discharge of high S content cathode because the thick S layer can hardly anchor on the surface of ANC altogether, the ANC/S-90 cathode still keeps 657 mAh/g after 100 cycles at 0.2 C. Cycling stability is a key issue which hinder the development of lithium sulfur battery, cycling performance and coulombic efficiency of ANC/S-70 cathode at 2 C are showed in Figure 6c. After activation of 10 cycles at 0.1 C, the ANC/S-70 delivers a capacity of 800 mAh/g at 2 C, and retains a capacity of 618 mAh/g after 1000 cycles, which shows a capacity decay rate of 0.022% per cycle. This excellent cycle stability could be primarily ascribed to the following two factors. Firstly, a substantial number of active sites can effectively anchor the polysulfides, and these sites are provided by the N and O heteroatoms on the surface of ANC. The other factor is that the large specific area provides a fast electron transfer pathways, which display a high specific capacity even at a high rate. The electrochemical performance of ANC/S70 is best compared with the previous biomass based carbon materials for lithium sulfur batteries (Table 1), which displays a high rate performance and a high sulfur content. In particular, the cycle stability of our composite cathode is more stable than most of other biochar-sulfur composite cathodes. Table 1. Electrochemical performance of Li–S cells basing on different porous biochar carbon Biochar type

Rate

Pig bone carbon Pomelo peels carbon Glucose Olive stone carbon litchi shells carbon Bamboo carbon Banana peel

— 0.2 C 2C ~0.06 C 0.5 C 0.1 C 1C 0.2 C 2C

Nori carbon

Initial Capacity (mAh/g) 1,265 1,280 923 930 1520 1,295 735 1170 800

Cycled capacity (mAh/g) 643 (50th) 750 (100th) 564 (90th) 670 (50th) 499 (200th) 756 (50th) 570 (500th) 826 (100th) 618 (1000th)


decay per cycle

Sulfur content

0.98% 0.41% 0.05% 0.56% 0.34% 0.83% 0.04% 0.29% 0.02%

— 60 66 80 50 50 65 68 68

Ref. 18 19 20 21 22 23 24 This work

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The EIS is used to investigate the charge transfer kinetics of NC/S and ANC/S cathodes before cycling and after charging for cycles. The EIS spectra of fresh cathodes are illustrated in Figure 7a, a semi-circle at medium to high frequency is represents the charge-transfer resistance between the electrolyte and sulfur electrode. The oblique line in the low frequency region, which represents the Warburg impedance, is associated with semi-infinite diffusion of lithium polysulfide in the electrolyte. After cycling, all of the EIS spectra in Figure 7b transform into two semicircles in the high frequency domain. The emerging semicircle is associated with the SEI film formed on the surface of the electrode. The intercept at real axis Z’ is owed to the resistance of the electrolyte. It is obviously observed that the ANC/S cathode has a smaller charge transfer impedance than NC/S due to the uniformly distribution of sulfur. After charging for five cycles, the charge transfer impedance turns smaller for both ANC/S and NC/S. The decrease of the charge transfer impedance is owed to the rearrangement of S in the compound and possessing a more electrochemically beneficial position, resulting in a shorter pathway and better cover between the sulfur and carbon matrix.

Figure 7. Nyquist plots for NC/S and ANC/S-70 (a) fresh and (b) after 5th charge.


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To further understand the effect of surface affinity for improving the performance of the ANC/S composites, the surface morphology of the ANC/S composites after 100th cycles are observed by SEM. As shown in Figure 8, the ANC/S-70 in the fresh cathode has a sulfur layer on the surface confined to the pore volume. After 100th discharge, the surface turn to rough due to the volume expand after discharge, the morphology of the surface becomes porous caused by volume shrink but still closely combines with ANC after charge. This phenomenon indicates that the ANC can effectively restrain shuttle effect, even on the surface of ANC, lithium polysulfides can be strongly anchored on the ANC surface by chemical bonding effect. Figure 8d exhibits separators after 100 cycles at 0.2 C. The bare S cathode was prepared by mixing sublimed sulfur, Ketjen Black and PVDF with a weight ratio of 7:2:1 without any sulfur host. The separator in the S cathode turned yellow after 100 cycles, it is worth to compare that the separator in NC/S cathode has a little discolor while the separator in the ANC/S cathode shows a similar color to the fresh separator, which declares little sulfur have been dissolve and deposit outside of the electrode during cycling and the shuttle effect have been effectively restrained by ANC.


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Figure 8. SEM images of ANC/S-70 electrode (a) fresh, (b) after 100th discharge (c) after 100th charge. (d) The digital picture of separators in different batteries after 100 cycles at 0.2 C.

4. CONCLUSIONS In summary, the ANC is synthesized for the first time as the host material for sulfur cathode via a facile, simple approach. The ANC/S compound exhibits a cost-effective but high performance cathode. These raised electrochemical performance include high initial capacity, good rate performance, high sulfur content and excellent cycle stability. The ANC/S-70 could maintain a high reversible capacity of 618 mAh/g at a rate as high as 2 C after 1000 cycles. The highly enhanced performance of ANC/S is owed to several factors: (1) the unique 3D layered hierarchical structure largely increases electron transfer efficiency of carbon material, which


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yields a high rate property; (2) the high specific area and large pore volume, which could carry a high sulfur content and uniformly distribution of sulfur; (3) exceptional ability for the adsorption of polysulfides owing to the existing of N and O heteroatom, this adsorption still takes place on the ANC surface, which achieves a superb cycle stability. Consequently, the ANC with these numerous advantages opens a new pathway for development of lithium sulfur batteries with large scale commercial applications.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected](N. Z.) Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (no. 21646012), the State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (no. 2016DX08) and China Postdoctoral Science Foundation (no. 2016M600253).) ABBREVIATIONS NC, nori carbon; ANC, activated nori carbon; REFERENCES 1. Armand, M.; Tarascon, J.-M., Building Better Batteries. Nature 2008, 451, 652-657. 2. Goodenough, J. B.; Kim, Y., Challenges for Rechargeable Li Batteries. Chem. Mater. 2009, 22, 587-603. 3. Jiang, H.; Ren, D.; Wang, H.; Hu, Y.; Guo, S.; Yuan, H.; Hu, P.; Zhang, L.; Li, C., 2D Monolayer MoS2–Carbon Interoverlapped Superstructure: Engineering Ideal Atomic Interface for Lithium Ion Storage. Adv. Mater. 2015, 27, 3687-3695.


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