Nitrogen-Doped Single-Walled Carbon Nanohorns as a Cost-Effective

Subscriber access provided by READING UNIV

Article

Nitrogen doped Single Walled Carbon Nanohorns as cost-effective Carbon-Host towards High Performance Lithium-Sulfur Batteries Umair Gulzar, Tao Li, Xue Bai, Massimo Colombo, Alberto Ansaldo, Sergio Marras, Mirko Prato, Subrahmanyam Goriparti, Claudio Capiglia, and Remo Proietti Zaccaria ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17602 • Publication Date (Web): 23 Jan 2018 Downloaded from http://pubs.acs.org on January 24, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a 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 Applied Materials & Interfaces 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 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Nitrogen doped Single Walled Carbon Nanohorns as cost-effective Carbon-Host towards High Performance Lithium-Sulfur Batteries Umair Gulzar†‡, Tao Li†‡, Xue Bai†§, Massimo Colombo†, Alberto Ansaldo†, Sergio Marras†, Mirko Prato†, Subrahmanyam Goriparti†, Claudio Capiglia#*, Remo Proietti Zaccaria†∥ †

Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy Department of Informatics, Bioengineering, Robotics and Systems Engineering (DIBRIS), University of Genova, via Dodecaneso 35, Genova 16146, Italy § Key Laboratory for Liquid−Solid Structural Evolution & Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China # Multi Energy Innovation Center, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, 466-8555 Japan ∥Cixi Institute of Biomedical Engineering, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Science, 219 Zhongguan West Road, Zhenhai District, Ningbo City, China KEYWORDS Nitrogen doped single wall carbon nanohorns, Lithium sulfur batteries, Sulfur-carbon composites, carbon nanohorns, carbon composites. ‡

ABSTRACT: Nitrogen doped Single-Walled Carbon Nanohorns (N-SWCNHs) are porous carbon material characterized by unique horn-shape structures with high surface area and good conductivity. Moreover, they can be mass produced (tons/year) using a novel proprietary process technology making them an attractive material for various industrial applications. One of the applications is the encapsulation of sulfur, which turns them as promising conductive host materials for lithium-sulfur batteries. Therefore, we explore for the first time the electrochemical performance of industrially produced nitrogen doped SWCNHs as a sulfur encapsulating conductive material. Fabrication of lithium-sulfur cells based on N-SWCNHs with Sulfur composite (N-SWCNHs-S) could achieve a remarkable initial gravimetric capacity of 1650 mAh g-1, namely equal to 98.5% of the theoretical capacity (1675 mAh g-1), with an exceptional sulfur content as high as 80 % in weight. Using cyclic chronopotentiometry and impedance spectroscopy, we also explored the dissolution mechanism of polysulfides inside the electrolyte.

INTRODUCTION Traditional lithium-ion batteries have been successfully serving the demand for energy storage over the last two decades. However, they are approaching their practical performance limits (140-240 Wh Kg-1) hence unable to meet futuristic high-energy demand (̴ 500-600 Wh Kg-1) for electric vehicles and smart grid applications.1,2 In this respect, research in high Ragone (high-energy and power density) battery systems is critical for the development of lighter, smaller and lowercost battery systems.3 Lithium-Sulfur (Li-S) batteries are highly sought-after alternative for future energy applications due to their remarkable theoretical capacity (1675 mAh g-1), energy density (̴ 2600 Wh Kg-1) and low cost4–6. Although lithium air (Li-air) technology, the main competitor of Li-S, provide even higher energy densities (̴ 3505 Wh Kg-1), Li-S cells with a solid-state sulfur cathode are expected to encounter fewer commercialization challenges than Li-air cells, the latter needing gaseous cathodes.7 Furthermore, high abundance of sulfur along with high gravimetric capacity makes Li-S batteries a very attractive solution beyond traditional lithium-ion batteries.

Despite intensive effort on research and development for the commercialization of Li-S batteries by a number of companies8–10, practical applications of these systems are still hindered by two main challenges, namely i) poor electronic and ionic conductivities of sulfur (S8) and lithium sulfide (Li2S)11 ii) dissolution of intermediate lithium polysulfides (Li2Sx, x ≥ 4) in electrolyte solution which cause severe capacity fading (shuttle effect).12,13 Major breakthroughs in solving these problems came from Nazar et al.14 and Mikhaylik et al.15 the former introducing a conductive mesoporous carbon-host for sulfur encapsulation while the latter developed an electrolyte additive (LiNO3) to limit the shuttle effect by supposedly passivation of the lithium electrode. Afterwards, conductive materials such as carbon nanotubes,16–21 graphene22–26 and different kinds of polymers27–30 have been employed as hosts for sulfur encapsulation, while nitrogen doping31–36 and metal oxide37–41 have been used to entrap polysulfides for reducing shuttle effect. Although these carbon-based sulfur composites were supposed to substantially improve the electrochemical performances of Li-S cells, to date high capacity and long cyclability could not be simultaneously achieved while employing high sulfur content (≥ 70 wt%).

1 ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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 10

Figure 1 a) Schematic illustration describing the sulfur encapsulation of N-SWCNHs. The red and orange dots represent the N and S doping, respectively. b) TEM images of N-SWCNHs with dahlia- and bud-like aggregates. Scale bar 50 nm. c) TEM image of NSWCNHs-S composites. Scale bar 100 nm. d) SEM image of N-SWCNHs-S composite electrode. Inset: EDS mapping of sulfur distribution (green represents sulfur, black is carbon). Single-Walled Carbon Nanohorns (SWCNHs) are a kind of carbon material characterized by horn shaped graphitic tubules (2-5 nm diameter and 40-50 nm tube length) which, upon aggregation, form dahlia-like, bud-like and seed-like structures.42,43 Due to their high surface area, good conductivity and unique geometrical structure, SWCNHs have found applications in gas storage,44 catalysis45 and supercapacitors.46 However, few reports mention their application as an anode material for lithium ion batteries47–49 and cathode material for Li-S batteries,50 where the former used SWCNHs as host material for metal oxides (Fe2O3, MnO2 and TiO2) nanoparticles whereas the latter demonstrated its potential for sulfur encapsulation. Our group is extensively investigating the potential of N-SWCNHs as an additive material for high capacity anode (Sn and Ge) and cathode materials. In this work N-SWCNHs were selected and reported for the first time as sulfur encapsulating hosts to be used as cathode material for Li-S batteries. In particular, the choice of nitrogen is motivated by the quest for improved interaction between SWCNHs and the surrounding active material. In this regard, nitrogen as a doping agent is suggested for its high electronegativity, which realizes C-N bonds characterized by permanent electric dipoles located at the surface of the nanohorns. This effect is expected to increase the surface chemical reactivity of N-SWCNHs, hence inducing the link between nitrogen sites and the surrounding active material (sulfur in the present case).51 A simple approach for the synthesis of N-SWCNHs composites with Sulfur (N-SWCNHs-S) via facile melt diffusion method was achieved. N-SWCNHs-S composite with an outstanding sulfur content as high as 80% in weight was obtained and the electrochemical properties were investigated in Li-S batteries by mean of cyclic chronopotentiometry and impedance spectroscopy.

RESULT AND DISCUSSION Figure 1-a illustrates the synthetic scheme of N-SWCNHsS composites, prepared by a facile melt diffusion method. NSWCNHs were produced with novel proprietary industrial process technology and provided by Advanced Technology Partner s.r.l. (ATP), [email protected] Italy. N-SWCNHs (ATP) and sulfur (99.99%, STREM Chemicals) with weight ratios of 1:5 were dissolved in 5 ml of carbon disulfide (CS2) (≥ 99%, anhydrous) and sonicated for 10 min at room temperature. After evaporating CS2, a mixture of dried NSWCNHs and sulfur was placed in a crucible and heated to 155 °C for 24 hours under argon environment. The temperature choice was dictated by the minimum viscosity of sulfur, which facilitates the diffusion of sulfur into N-SWCNHs. To date three different types of SWCNHs aggregates, ‘dahlia-like’, ‘bud-like’, and ‘seed-like’ have been reported.52 In the first type, SWCNHs protrude from the aggregate surface while, in the second and third types, the SWCNHs appear to develop inside the particle itself. The transmission electron microscopic (TEM) analysis of N-SWCNHs depicted in Figure 1b shows dahlia-like (100-150 nm) and bud-like (80100nm) aggregates while Figure 1c shows their aggregation after sulfur encapsulation. Furthermore, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) demonstrate a homogenous distribution of sulfur in the powder sample made from 90% N-SWCNHs-S composite, 5% carbon black and 5% PVDF by weight. (Figure 1d and inset). Due to the graphitic nature of N-SWCNHs, Raman analysis was performed to elucidate the defected nature of these aggregates, as illustrated in figure 2a.


Page 3 of 10 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


Figure 2. a) Raman spectra of N-SWCNHs and sulfur composite. b) XRD patterns of N-SWCNHs, N-SWCNHs-S and pure sulfur taken as reference. Two prominent peaks in the Raman spectrum of SWCNHs are associated to the D and G bands where the former is attributed to disordered sp2 carbon caused by the presence of defects while the latter is related to the vibrational modes of graphitic carbons.53 Due to the topological defects of pentagons and heptagons in SWCNHs, these D and G peaks appears at 1348 and 1590 cm-1, respectively.54 Figure 2a also shows the Raman spectrum of N-SWCNHs-S. Peaks are observed near 1350 cm−1 (D), 1589 cm−1 (G), 2676 cm−1 (2D), 2953 cm−1 (D+G) and 3225 cm−1 (2D'). ID/IG ratio was calculated for both spectra providing values close to unity, result which is explained through the peculiar defects structure associated to NSWCNHs.54 Finally, peaks of sulfur appear in the range of 300-500 cm-1 demonstrating its physical encapsulation inside or on the surface of the carbon material. Interestingly, a hump at 2628 cm−1 was observed in N-SWCNHs-S composites, where the splitting of the 2D peak into 2D1 and 2D2 suggests the stacking of carbon material due to a strong interaction between sulfur and nitrogen groups. X-ray Diffraction (XRD) analysis was then performed to confirm the presence as well as the crystalline structure of sulfur inside N-SWCNHs-S composite. Figure 2b depicts XRD analysis of pure sulfur, pristine N-SWCNHs and their sulfur composites. The pattern of pristine N-SWCNHs shows a broad (002) peak around 2θ = 23°. This wide d002 peak is commonly observed in structures with turbostratic stacking of the graphene sheets.55 An additional peak at 2θ ~ 43°, can be readily assigned to the (10) reflection. Finally, the XRD pattern of NSWCNHs-S composite (red line) shows the presence of characteristic peaks of orthorhombic sulfur (ICSD reference code: 27261) on top of the broad peaks of N-SWCNHs previously described.

Figure 3. a) N2 adsorption/desorption isotherms of NSWCNHs and N-SWCNHs-S measured at standard temperature and pressure (STP). Inset: Pore width of N-SWCNHs, where V is the volume adsorbed in cc and w is the pore width in nm. The data are normalized vs. the weight. (b) TGA analysis of N-SWCNHs-S composites. SWCNHs are known to possess micro (pore size less than 2 nm) and meso-porosity (2-50nm), originating from their peculiar morphology.56 This suggests that SWCNHs might retain high surface area even after nitrogen doping, so that sulfur can infiltrate especially at 155 °C where it shows its lowest viscosity, hence enabling intimate contact between sulfur and the conductive carbon material.57 To verify this aspect N2 physisorption analysis was performed to determine the surface area and the pores size distribution of the as prepared NSWCNHs and N-SWCNHs-S aggregates. Figure 3a shows the N2 adsorption/desorption isotherm obtained for N-SWCNHs and N-SWCNHs-S, the former exhibiting mixed type I and II isotherms, indicating the existence of pore sizes ranging from micropores (pore width: 0.4-1.0 nm, see inset in Figure 3a) to macropores with total surface area of 211 m2 g-1 and total pore volume of 1.097 cm3 g-1. Moreover, for N-SWCNHs, we observed that the micro-pores represent only a minor fraction of the total pore sizes (2.3 %), with an estimated volume of 0.025 cm3 g-1, as summarized in Table 1. On the opposite side, NSWCNHs-S composites showed significantly lower surface area of about 12 m2 g-1 due to the sulfur infiltration. Thermo-gravimetric analysis (TGA) was performed to determine the sulfur content in N-SWCNHs-S composites. Figure 3b illustrates a sharp decrease in weight for temperature increase from 115 °C to 300 °C corresponding to the removal of sulfur. In particular, TGA shows that sulfur accounts for about the 80% of the total weight of N-SWCNHs-S composites.



Page 4 of 10

Table 1. Pore-structure parameters of N-SWCNHs. Here at, aext, and Vt stand for total surface area, area excluding the contributions from micro-pores and total volume, respectively. Sample

Pore Structure Parameters 2

N-SWCNHs

2

at (m /g)

aext (m /g)

Vt (cm3/g)

Vmicro-porous (cm3/g)

Vmeso-porous (cm3/g)

211

156

1.097

0.025

1.072

Figure 4. a) XPS spectra of N-SWCNHs; b) N-SWCNHs-S composite mixed with carbon black and PVDF; c) and d) High resolution spectra of C1s and N1s peaks; e) High resolution spectrum of S2p peak in the range of 162-174 eV. The surface chemical properties of N-SWCNHs and NSWCNHs-S composite were then studied through X-ray Photoelectron Spectroscopy (XPS). Figure 4a shows the XPS spectrum collected on N-SWCNHs: C 1s, N 1s and O 1s peaks are clearly visible, hence confirming the presence of nitrogen as well as carbon and oxygen within the aggregates. The C 1s peak (Figure 4c) shows the typical shape for graphitic-like compounds58 given by an asymmetric peak centered at 284.4±0.2 eV (corresponding to sp2-hybridized carbon atoms) accompanied by a low intensity shake-up feature at 290.8±0.2 eV, related to π→π* transition. The best fit of the C 1s profile has been obtained by adding other low intensity peaks, ascribable to adventitious carbon species59 (peaks centered at 284.9±0.2 eV, 286.4±0.2 eV, 288.0±0.2 eV and 289.7±0.2 eV, assigned respectively to sp3-hybridized carbon atoms, C-O, C=O and O-C=O species). The peak at 286.4±0.2 eV is also due to C-N species, corresponding to the N-sp2 C bonds originated from the inclusion of N atoms in the carbon network of the nanohorns60. This assignment is supported by the presence

of the N 1s broad peak appearing between 396 and 406 eV (Figure 4d); it could be decomposed into three components centered at 399.0±0.2 eV, 400.8±0.2 eV, and 402.2±0.2 eV, corresponding respectively to pyridinic, pyrrolic, and graphitic nitrogen61 hence confirming the presence of nitrogen doping, together with a fourth component at 404.3±0.2 eV, assigned to oxidized N forms. The atomic percentage of carbon, nitrogen and oxygen were found to be 97.8, 1.1 and 1.1%, respectively (Figure 4a). Similar analysis has been carried out on the electrode material, containing N-SWCNHs-S composite, carbon black, and PVDF. Figure 4b clearly shows the presence of S 2s and S 2p peaks confirming the presence of sulfur in the electrode slurry. High resolution analysis on the S 2p peaks energy region (Figure 4e) revealed that sulfur is present mainly as elemental S (S 2p3/2 component centered at 163.8 eV); low intensity S components are also observed at higher binding energy values (S 2p3/2 component centered at 164.2 eV and at 168.6 eV) and could be assigned to oxidized S species.33


Page 5 of 10 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


Figure 5. Electrochemical characterization. a) Differential Capacity plot (dQ/dE) of N-SWCNHs-S composite. b) Charge/discharge profile of N-SWCNHs-S composite. c) Cycling performance of N-SWCNHs-S composite at 0.1 C. d) Cycling performance of NSWCNHs-S composites at different C-rates.

Electrochemical Characterization In order to explore N-SWCNHs-S composites as cathode material for Li-S batteries, electrochemical properties of NSWCNHs-S composites were tested using cyclic chronopotentiometry (galvanostatic charge/discharge measurements) and impedance spectroscopy. To understand the redox process of sulfur, differential capacity plots of N-SWCNHs-S composites were produced from galvanostatic charge discharge profiles, as shown in Figure 5a. It is quite known that the distribution of polysulfides and their reduction potentials depend on the nature of the electrolyte, the sulfur to electrolyte ratio, current density, sulfur electrode composition and its architecture.62,63 In our case, three prominent reductive peaks were observed in the range of 2.392.29 V (region I), 2.17-2.09 V (region II) and 2.08-1.90 V (region III). The peaks in the regions I to III are usually associated to the reduction of sulfur typical of lithium-sulfur chemistries. In particular, region I corresponds to a relatively fast conversion of elemental sulfur (S8) into lithium polysulfide anions (Li2Sx; where x is typically 4–6) while region III corresponds to the conversion of polysulfides into Li2S2 and then to Li2S.64 Furthermore, we observed additional peaks in the region II which

can be associated to the electrochemical conversion of long chain polysulfides to their shorter counterparts.65 Figure 5b shows charge/discharge profile of N-SWCNHs-S composites represented by three plateaus corresponding to the three regions highlighted in Figure 5a. The achieved initial gravimetric capacity at 0.1 C was 1650 mAh g-1, extremely close to the theoretical capacity (1675 mAh g-1), as shown in Figure 5c. However, a fast capacity decay was recorded during first few cycles with a total capacity loss of about 65 % after 200 cycles. It is interesting and important to notice that the majority of the capacity was lost during the first three cycles (40 %) while only 25 % loss was observed for the remaining 197 cycles with a columbic efficiency in the range of 95-97%. This initial rapid decay can be explained by the dissolution of polysulfide ions from the electrode surface. Once the electrode surface becomes free of polysulfide the capacity stabilizes as the pores of N-SWCNHs are able to avoid further dissolution of polysulfide into the bulk electrolyte due to their confinement properties. This stable behavior can be observed especially in the last 100 cycles where the capacity loss was merely 5 %. Additionally, the capacity associated to lowest plateau (region III) accounts for 65 % of the total capacity, which remains almost constant during cycling, while the remaining 35 % is as-



sociated to the upper plateaus (regions I and II), which de-

crease

with

Page 6 of 10 increasing

cycle

number

Figure 6. (a-d) Impedance spectra of N-SWCNHs-S composite at different stages of lithiation. a) at OCV (2.6 V). b) at 2.40, 2.35 and 2.30V, c) at 2.20, 2.15 and 2.10V d) at 2.05 and 2.00V. e) Variation in internal resistance (R1) at different voltages during discharge. f) Variation of charge transfer resistance (R2) at different voltage during discharge. After 200 cycles, the gravimetric capacity for N-SWCNHs-S composites was found to be 573 mAh g-1 at 0.1C. In this respect, the columbic efficiency showed an improved response over cycling, approaching 100% after 200 cycles. The performance of the N-SWCNHs-S electrode was also examined at various C-rates as shown in Figure 5d. The discharge capacities of ∼ 1100, 890, 725, 258, 630, 560 and 250 mAh g−1 were recorded at the current rates of 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 1C, respectively.

Impedance Spectroscopy To understand the dissolution of polysulfides ions from the electrode surface, Electrochemical Impedance Spectroscopy (EIS) was performed at various stages of lithiation. The impedance spectra, shown in Figure 6, were obtained at different stage of discharge (from 2.6 V, corresponding to open circuit voltage (OCV), down to 2 V) in the frequency range from 10 KHz to 10 mHz with a stimulus amplitude of 5 mV. The Nyquist plots illustrated in Figure 6a-d show a high frequency

(HF) depressed semicircle and a low frequency (LF) straight line. In particular, the intercept in the HF region is related to internal resistance (R1) of the electrolyte, separator, and current collectors whereas the intercept from the high to middle frequency range is related to the charge transfer processes at the electrode/electrolyte interface (R2). The straight line at LF is instead associated to the diffusion of lithium ions inside the N-SWCNHs-S composite while sulfur is still in its solid elemental form. When the Nyquist plots for the regions I, II and III are compared to the OCV counterpart, a decrease in charge transfer resistance R2 is observed (Figure 6f). Similarly and specifically for the regions I and II, a suppressed straight line in the LF range is also noticed. This rapid lowering of both R2 and the straight line is consequence of the dissolution of polysulfides from the solid cathode into the liquid electrolyte, resulting in high polysulfides mobility and in a cathode surface with beneficial higher porosity/surface area, two characteristics leading to enhanced charge transfer process and increased ionic/electronic conductivity66. Furthermore, in the region I,


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


the dissolution of polysulfide into the electrolyte increases its internal resistance (R1) from 9.61 to 10.51 Ω due to an increased viscosity (Figure 6e). A small semi-circle starts also to appear at 2.15V (region II) and becomes prominent in the region III (Figure 6c) suggesting the formation of Li2S while, due to the consumption of polysulfide from the electrolyte, a slight decrease in electrolyte resistance (R1) is observed until the end of discharge process (Figure 6e). At the end of the discharge process (region III), two depressed semi-circles appear along with the reappearance of the straight line in the LF range, the latter associated to the diffusive behavior of lithium inside solid Li2S. We suggest that the variation in the slope of the straight line could be ascribed to the thickness of Li2S, where a thin layer of Li2S allows for less hindrance as compared to a thick Li2S layer, which is formed at the end of discharge phase. Finally, the semi-circle in the HF range is associated to the conversion of the remained polysulfide on the surface of N-SWCNHs into smaller polysulfide whereas the semi-circle in the middle frequency region (MF) range is related to the formation of Li2S. In order to reproduce the non-ideal behavior of NSWCNHs-S based electrode, therefore to design the plots in Figure 6, we have employed a R//CPE circuit description rather than several R//C circuits in series, as depicted in Figure 7, where the Constant Phase Element (CPE) translates in an empirical manner the non-ideal behavior of the composite electrode67 (porosity of the material, roughness of the surface)

Figure 7. Proposed equivalent circuits of lithium-sulfur cell. R1 represents the resistance of electrolyte and conductors, CPEx are the constant phase elements and R2,3 are associated to the charge transfer resistances. (a) and (b) describe the behavior of electrode before (OCV, region I and II) and after the formation of Li2S phase (region III), respectively. In this regard, CPE1 and CPE2 describe the amplitudes of the semicircles, whereas CPE3 is associated to the Warburg region (straight line) in the LF region. Figure 7a describes the circuit capable of modeling OCV, regions I and II, whereas upon the appearing of an additional semi-circle in the MF region for lower potentials (region III), a different circuit scheme requiring one extra CPE//R has to be considered, as shown in Figure 7b.

CONCLUSION We have explored the physical and electrochemical properties of nitrogen doped single wall carbon nanohorns (NSWCNHs) with the intent of achieving an enhanced sulfur en-

capsulation to realize an efficient cathode material for lithiumsulfur batteries. Our results show that N-SWCNHs-S composites give higher gravimetric capacity with respect to previously reported method 50 where just SWCNHs were employed, providing remarkable capacity values as high as 1650 mAh g-1 at 0.1 C, corresponding to 98.5 % of the theoretical capacity (1675 mAh g-1). A detailed impedance analysis was also performed to understand the behavior of polysulfide formation in our lithium-sulfur cells. From our results we can conclude that N-SWCNHs represent an innovative and cheap solution for sulfur encapsulation. Indeed, owing to their peculiar morphology characterized by high density of micro/mesopores which can assist the mass transport of lithium-ions as well as enhance the active reaction sites density, N-SWCNHs are recognized to provide a fundamental contribute to the improvement of the initial capacity. Finally, these findings suggest that a proper engineering of the micro-porosity and nitrogen doping of N-SWCNHs might be a valid approach to reduce the shuttle effect hence making this active material stable at higher capacities with even higher rate performance.

EXPERIMENTAL SECTION Material Characterizations. Thermogravimetric analysis (TGA) was carried out using TGA Q500-TA instrument. Samples were heated from 30 °C to 500 °C at the heating rate of 10 °C/min under nitrogen atmosphere set at the flow rate of 50 ml/min. Transmission electron microscopy images were obtained using a JEOL JEM 1011 (Jeol, Tokyo, Japan) operating at 100 kV acceleration voltage, equipped with a tungsten thermionic electron source and a FEI TECNAI G2 F20 instrument, equipped with a Schottky field emission gun (FEG), operating at 200 kV acceleration voltage. Scanning electron microscopy was carried out with a Nova 600 NanoLab microscope (FEI), equipped with a field emission gun for scanning electron imaging and a focused ion beam of gallium ions for milling. Raman spectroscopy measurements were carried out with Renishaw in Via Micro Raman equipped with a laser source at 633 nm through a 50x objective (LEICA N PLAN EPI 50/ 0.75). XRD patterns were collected on a PANalytical Empyrean X-ray diffractometer equipped with a 1.8 kW CuK ceramic X-ray tube, PIXcel3D 2 x 2 area detector and operating at 45 kV and 40 mA. XPS analysis was performed on a Kratos Axis Ultra DLD spectrometer, using a monochromatic Al Kα source (15 kV, 20 mA). High resolution narrow scans were performed at constant pass energy of 20 eV and steps of 0.1 eV. The photoelectrons were detected at a takeoff angle θ = 0° with respect to the surface normal. The pressure in the analysis chamber was maintained below 7×10-9 Torr for data acquisition. The data were converted to VAMAS format and processed using Casa XPS software, version 2.3.16. The binding energy (BE) scale was internally referenced to the C 1s peak (BE for C−C = 284.8 eV). Specific surface area and porosity measurements were carried out by nitrogen physisorption at 77 K in a Quantachrome equipment, model autosorb iQ. Prior to measurements, samples were degassed for 3 hours at 80 °C under vacuum to eliminate weakly adsorbed species. The specific surface areas were calculated using the multi-point BET (Brunauer–Emmett–Teller) model, considering 11 equally spaced points in the P/P0 range from 0.05 to 0.30. The micropore volume and micropore area were ob-



tained by the t-plot carbon black method. The HorvathKawazoe (HK) method was instead applied to determine the micropore size distribution. Electrochemical Characterization. The electrochemical performance of as-prepared N-SWCNHs-S composite was tested using CR2032 coin cells which consist of lithium chips (15.6 Dia x 0.45t mm; MTI Corporations) as reference and counter electrode, dried glass fibers membrane (Whatman GF/D) as separator and C-S composite, casted on a pre-etched aluminum foil, as working electrode. Slurries casted on aluminum foil (15 mm Dia) were composed of 90% weight C-S composite (containing 80% sulfur, as an active material), 5% super-P carbon and 5% polyvinylidene difluoride (PVDF) mixed with an appropriate amount of N-methyl-2-pyrrolidone. The casted electrodes were dried overnight at 60 °C under vacuum and the mass loadings of active material were found in the range of 1-1.2 mg. 250 µL of electrolyte was used in each coin cell which contain 1 mol L-1 lithium bis(trifluoromethanesulphonyl)imide in 1:1 (v/v) of 1,4dioxane and 1,2-dimethoxyethane with 0.1 mol L-1 of LiNO3 as an additive. After their assembling inside a MBraun glovebox, with H2O and O2 levels below 0.1 ppm, all cells were electrochemically tested using BioLogic BCS-805 multichannel battery unit controlled by BT Lab V1.30. Impedance analyses were performed using the same instrument in the frequency range of 10 kHz to 100 mHz with a voltage amplitude of 5 mV. Impedance spectra were simulated and fitted using BioLogic integrated software Z-SIM and Z-Fit.

AUTHOR INFORMATION

(7)

(8) (9) (10)

(11)

(12)

(13)

(14)

(15) (16)

(17)

(18)

(19)

Corresponding Author * E-mail: [email protected] [email protected]

(20)

ABBREVIATIONS SWCNHs Single wall carbon nanohorns, TEM transmission electron microscopy, XRD X-ray diffraction, TGA Thermogravimetric analysis, XPS X-ray photoelectron spectroscopy, CPE constant phase element, -Im(Z) imaginary impedance, Re(Z) real impedance.

REFERENCES (1)

(2)

(3)

(4)

(5)

(6)

Wild, M.; O’Neill, L.; Zhang, T.; Purkayastha, R.; Minton, G.; Marinescu, M.; Offer, G. J. Lithium Sulfur Batteries, a Mechanistic Review. Energy Environ. Sci. 2015, 8 (12), 3477– 3494. Seh, Z. W.; Sun, Y.; Zhang, Q.; Cui, Y. Designing High-Energy Lithium–sulfur Batteries. Chem. Soc. Rev. 2016, 45 (20), 5605– 5634. Goriparti, S.; Miele, E.; De Angelis, F.; Di Fabrizio, E.; Proietti Zaccaria, R.; Capiglia, C. Review on Recent Progress of Nanostructured Anode Materials for Li-Ion Batteries. J. Power Sources 2014, 257, 421–443. Xin, S.; Chang, Z.; Zhang, X.; Guo, Y.-G. Progress of Rechargeable Lithium Metal Batteries Based on Conversion Reactions. Natl. Sci. Rev. 2016, 4 (1), 54–70. Jin, S.; Xin, S.; Wang, L.; Du, Z.; Cao, L.; Chen, J.; Kong, X.; Gong, M.; Lu, J.; Zhu, Y.; Ji, H.; Ruoff, R. S. Covalently Connected Carbon Nanostructures for Current Collectors in Both the Cathode and Anode of Li–S Batteries. Adv. Mater. 2016, 28 (41), 9094–9102. Yin, Y. X.; Xin, S.; Guo, Y. G.; Wan, L. J. Lithium-Sulfur Batteries: Electrochemistry, Materials, and Prospects. Angew. Chemie - Int. Ed. 2013, 52 (50), 13186–13200.

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

Page 8 of 10

Bruce, P. G.; Freunberger, S. a.; Hardwick, L. J.; Tarascon, J.M. Li–O2 and Li–S Batteries with High Energy Storage. Nat. Mater. 2011, 11 (2), 172–172. GS Yuasa Lithium Power http://www.gsyuasa-lp.com/ (accessed Feb 3, 2017). OXIS Energy: Next generation Battery Technology https://oxisenergy.com/ (accessed Feb 3, 2017). Licerion: Revolutionizing energy and battery life http://www.sionpower.com/technology-licerion.php (accessed Feb 3, 2017). Fan, F. Y.; Carter, W. C.; Chiang, Y.-M. Mechanism and Kinetics of Li2S Precipitation in Lithium–Sulfur Batteries. Adv. Mater. 2015, 27, 5203–5209. Mikhaylik, Y. V.; Akridge, J. R. Polysulfide Shuttle Study in the Li/S Battery System. J. Electrochem. Soc. 2004, 151 (11), A1969–A1976. Wang, J.; He, Y.-S.; Yang, J. Sulfur-Based Composite Cathode Materials for High-Energy Rechargeable Lithium Batteries. Adv. Mater. 2015, 27 (3), 569–575. Ji, X.; Lee, K. T.; Nazar, L. F. A Highly Ordered Nanostructured Carbon-Sulphur Cathode for Lithium-Sulphur Batteries. Nat. Mater. 2009, 8 (6), 500–506. Mikhaylik, Y. V. Electrolytes for Lithium Sulfur Cells. US7354680 B2, 2008. Yuan, L.; Yuan, H.; Qiu, X.; Chen, L.; Zhu, W. Improvement of Cycle Property of Sulfur-Coated Multi-Walled Carbon Nanotubes Composite Cathode for Lithium/sulfur Batteries. J. Power Sources 2009, 189 (2), 1141–1146. Guo, J.; Xu, Y.; Wang, C. Sulfur-Impregnated Disordered Carbon Nanotubes Cathode for Lithium-Sulfur Batteries. Nano lett. 2011, 11 (10), 4288–4294. Seh, Z. W.; Zhang, Q.; Li, W.; Zheng, G.; Yao, H.; Cui, Y. Stable Cycling of Lithium Sulfide Cathodes through Strong Affinity with a Bifunctional Binder. Chem. Sci. 2013, 4 (9), 3673–3677. Sun, L.; Li, M.; Jiang, Y.; Kong, W.; Jiang, K.; Wang, J.; Fan, S. Sulfur Nanocrystals Confined in Carbon Nanotube Network as a Binder-Free Electrode for High-Performance Lithium Sulfur Batteries. Nano Lett. 2014, 14 (7), 4044–4049. Dörfler, S.; Hagen, M.; Althues, H.; Tübke, J.; Kaskel, S.; Hoffmann, M. J. High Capacity Vertical Aligned Carbon Nanotube/sulfur Composite Cathodes for Lithium–sulfur Batteries. Chem. Commun. 2012, 48 (34), 4097–4099. Zheng, G.; Yang, Y.; Cha, J. J.; Hong, S. S.; Cui, Y. Hollow Carbon Nanofiber-Encapsulated Sulfur Cathodes for High Specific Capacity Rechargeable Lithium Batteries. Nano Lett. 2011, 11 (10), 4462–4467. Wang, J.-Z.; Lu, L.; Choucair, M.; Stride, J. a.; Xu, X.; Liu, H.K. Sulfur-Graphene Composite for Rechargeable Lithium Batteries. J. Power Sources 2011, 196 (16), 7030–7034. Zhang, K.; Wang, L.; Hu, Z.; Cheng, F.; Chen, J. Ultrasmall Li2S Nanoparticles Anchored in Graphene Nanosheets for HighEnergy Lithium-Ion Batteries. Sci. Rep. 2014, 4, 6467. Wang, H.; Yang, Y.; Liang, Y.; Robinson, J. T.; Li, Y.; Jackson, A.; Cui, Y.; Dai, H. Graphene-Wrapped Sulfur Particles as a Rechargeable Lithium-Sulfur Battery Cathode Material with High Capacity and Cycling Stability. Nano lett. 2011, 11 (7), 2644–2647. Chen, H.; Wang, C.; Dong, W.; Lu, W.; Du, Z.; Chen, L. Monodispersed Sulfur Nanoparticles for Lithium-Sulfur Batteries with Theoretical Performance. Nano Lett. 2015, 15 (1), 798–802. Zhao, M.-Q.; Zhang, Q.; Huang, J.-Q.; Tian, G.-L.; Nie, J.-Q.; Peng, H.-J.; Wei, F. Unstacked Double-Layer Templated Graphene for High-Rate Lithium-Sulphur Batteries. Nat. Commun. 2014, 5, 3410. Wu, F.; Chen, J.; Chen, R.; Wu, S.; Li, L.; Chen, S.; Zhao, T. Sulfur/Polythiophene with a Core/Shell Structure: Synthesis and Electrochemical Properties of the Cathode for Rechargeable Lithium Batteries. J. Phys. Chem. C 2011, 115 (13), 6057–6063. Wang, J.; Chen, J.; Konstantinov, K.; Zhao, L.; Ng, S. H.; Wang, G. X.; Guo, Z. P.; Liu, H. K. Sulphur-Polypyrrole Composite Positive Electrode Materials for Rechargeable


Page 9 of 10 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

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36)

(37)

(38)

(39)

(40)

(41)

(42)

(43) (44)

(45)

(46)

ACS Applied Materials & Interfaces Lithium Batteries. Electrochim. Acta 2006, 51 (22), 4634–4638. Xiao, L.; Cao, Y.; Xiao, J.; Schwenzer, B.; Engelhard, M. H.; Saraf, L. V.; Nie, Z.; Exarhos, G. J.; Liu, J. A Soft Approach to Encapsulate Sulfur: Polyaniline Nanotubes for Lithium-Sulfur Batteries with Long Cycle Life. Adv. Mater. 2012, 24 (9), 1176– 1181. Zhou, W.; Yu, Y.; Chen, H.; Disalvo, F. J.; Abruña, H. D. YolkShell Structure of Polyaniline-Coated Sulfur for Lithium-Sulfur Batteries. J. Am. Chem. Soc. 2013, 135 (44), 16736–16743. Cao, Y.; Li, X.; Aksay, I. a; Lemmon, J.; Nie, Z.; Yang, Z.; Liu, J. Sandwich-Type Functionalized Graphene Sheet-Sulfur Nanocomposite for Rechargeable Lithium Batteries. Phys. Chem. Chem. Phys. 2011, 13 (17), 7660–7665. Ji, L.; Rao, M.; Zheng, H.; Zhang, L.; Li, O. Y.; Duan, W. Graphene Oxide as a Sulfur Immobilizer in High Performance Lithium/Surfur Cells. J. Am. Chem. Soc. 2011, 133, 18522– 18525. Zhang, L.; Ji, L.; Glans, P.-A.; Zhang, Y.; Zhu, J.; Guo, J. Electronic Structure and Chemical Bonding of a Graphene Oxide-Sulfur Nanocomposite for Use in Superior Performance Lithium-Sulfur Cells. Phys. Chem. Chem. Phys. 2012, 14 (39), 13670–13675. Wang, Z.; Niu, X.; Xiao, J.; Wang, C.; Liu, J.; Gao, F. First Principles Prediction of Nitrogen-Doped Carbon Nanotubes as a High-Performance Cathode for Li-S Batteries. Rsc Adv. 2013, 3 (37), 16775–16780. Chung, S. H.; Han, P.; Manthiram, A. A Polysulfide-Trapping Interface for Electrochemically Stable Sulfur Cathode Development. ACS Appl. Mater. Interfaces 2016, 8 (7), 4709– 4717. Zheng, G.; Zhang, Q.; Cha, J. J.; Yang, Y.; Li, W.; Seh, Z. W.; Cui, Y. Amphiphilic Surface Modification of Hollow Carbon Nanofibers for Improved Cycle Life of Lithium Sulfur Batteries. Nano Lett. 2013, 13 (3), 1265–1270. Ding, N.; Zhou, L.; Zhou, C.; Geng, D.; Yang, J.; Chien, S. W.; Liu, Z.; Ng, M.-F.; Yu, A.; Hor, T. S. A.; Sullivan, M. B.; Zong, Y. Building Better Lithium-Sulfur Batteries: From LiNO3 to Solid Oxide Catalyst. Sci. Rep. 2016, 6 (August), 33154. Pang, Q.; Nazar, L. F. Long-Life and High-Areal-Capacity Li–S Batteries Enabled by a Light-Weight Polar Host with Intrinsic Polysulfide Adsorption. ACS Nano 2016, 10 (4), 4111–4118. Wei Seh, Z.; Li, W.; Cha, J. J.; Zheng, G.; Yang, Y.; McDowell, M. T.; Hsu, P.-C.; Cui, Y. Sulphur-TiO2 Yolk-Shell Nanoarchitecture with Internal Void Space for Long-Cycle Lithium-Sulphur Batteries. Nat. Commun. 2013, 4, 1331. Pang, Q.; Kundu, D.; Cuisinier, M.; Nazar, L. F. SurfaceEnhanced Redox Chemistry of Polysulphides on a Metallic and Polar Host for Lithium-Sulphur Batteries. Nat Commun 2014, 5 (May), 4759. Tao, X.; Wang, J.; Liu, C.; Wang, H.; Yao, H.; Zheng, G.; Seh, Z. W.; Cai, Q.; Li, W.; Zhou, G.; Zu, C.; Cui, Y. Balancing Surface Adsorption and Diffusion of Lithium-Polysulfides on Nonconductive Oxides for Lithium-Sulfur Battery Design. Nat. Commun. 2016, 7, 11203–11211. Iijima, S.; Yudasaka, M.; Yamada, R.; Bandow, S.; Suenaga, K.; Kokai, F.; Takahashi, K. Nano-Aggregates of Single-Walled Graphitic Carbon Nano-Horns. Chem. Phys. Lett. 1999, 309 (3– 4), 165–170. Iijima, S.; Ichihashi, T. Single-Shell Carbon Nanotubes of 1-Nm Diameter. Nature 1993, 363 (6430), 603–605. Liu, Y.; Brown, C. M.; Neumann, D. A.; Geohegan, D. B.; Puretzky, A. A.; Rouleau, C. M.; Hu, H.; Styers-Barnett, D.; Krasnov, P. O.; Yakobson, B. I. Metal-Assisted Hydrogen Storage on Pt-Decorated Single-Walled Carbon Nanohorns. Carbon N. Y. 2012, 50 (13), 4953–4964. Adelene Nisha, J.; Yudasaka, M.; Bandow, S.; Kokai, F.; Takahashi, K.; Iijima, S. Adsorption and Catalytic Properties of Single-Wall Carbon Nanohorns. Chem. Phys. Lett. 2000, 328 (4–6), 381–386. Izadi-Najafabadi, A.; Yamada, T.; Futaba, D. N.; Yudasaka, M.; Takagi, H.; Hatori, H.; Iijima, S.; Hata, K. High-Power Supercapacitor Electrodes from Single-Walled Carbon Nanohorn/Nanotube Composite. ACS Nano 2011, 5 (2), 811–

(47)

(48)

(49)

(50)

(51)

(52)

(53)

(54)

(55)

(56)

(57)

(58)

(59)

(60)

(61)

(62)

(63)

(64)

(65)

819. Xu, W.; Wang, Z.; Guo, Z.; Liu, Y.; Zhou, N.; Niu, B.; Shi, Z.; Zhang, H. Nanoporous Anatase TiO2/single-Wall Carbon Nanohorns Composite as Superior Anode for Lithium Ion Batteries. J. Power Sources 2013, 232, 193–198. Zhao, Y.; Li, J.; Ding, Y.; Guan, L. A Nanocomposite of SnO2 and Single-Walled Carbon Nanohorns as a Long Life and High Capacity Anode Material for Lithium Ion Batteries. RSC Adv. 2011, 1 (5), 852–856. Lai, H.; Li, J.; Chen, Z.; Huang, Z. Carbon Nanohorns as a High-Performance Carrier for MnO2 Anode in Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2012, 4 (5), 2325–2328. Wu, W.; Zhao, Y.; Wu, C.; Guan, L. Single-Walled Carbon Nanohorns with Unique Horn-Shaped Structures as a Scaffold for Lithium–sulfur Batteries. RSC Adv. 2014, 4 (54), 28636– 28639. Wu, F.; Li, J.; Tian, Y.; Su, Y.; Wang, J.; Yang, W.; Li, N.; Chen, S.; Bao, L. 3D Coral-like Nitrogen-Sulfur Co-Doped Carbon-Sulfur Composite for High Performance Lithium-Sulfur Batteries. Sci. Rep. 2015, 5 (August), 13340. Kasuya, D.; Yudasaka, M.; Takahashi, K.; Kokai, F.; Iijima, S. Selective Production of Single-Wall Carbon Nanohorn Aggregates and Their Formation Mechanism. J. Phys. Chem. B 2002, 106 (19), 4947–4951. Yang, C. M.; Noguchi, H.; Murata, K.; Yudasaka, M.; Hashimoto, A.; Iijima, S.; Kaneko, K. Highly Ultramicroporous Single-Walled Carbon Nanohorn Assemblies. Adv. Mater. 2005, 17 (7), 866–870. Fujimori, T.; Urita, K.; Aoki, Y.; Kanoh, H.; Ohba, T.; Yudasaka, M.; Iijima, S.; Kaneko, K.; Agency, T. Fine Nanostructure Analysis of Single-Wall Carbon Nanohorns by Surface Enhanced Raman Scattering. Sci. Technol. 1900, No. c, 5–6. Bandow, S.; Kokai, F.; Takahashi, K.; Yudasaka, M.; Qin, L. C.; Iijima, S. Interlayer Spacing Anomaly of Single-Wall Carbon Nanohorn Aggregate. Chem. Phys. Lett. 2000, 321 (May), 514–519. Yang, C.-M.; Noguchi, H.; Murata, K.; Yudasaka, M.; Hashimoto, A.; Iijima, S.; Kaneko, K. Highly Ultramicroporous Single-Walled Carbon Nanohorn Assemblies. Adv. Mater. 2005, 17 (7), 866–870. Xi, K.; Cao, S.; Peng, X.; Ducati, C.; Vasant Kumar, R.; Cheetham, A. K. Carbon with Hierarchical Pores from Carbonized Metal–organic Frameworks for Lithium Sulphur Batteries. Chem. Commun. 2013, 49 (22), 2192–2194. Dai, H.; Gao, X.; Liu, E.; Yang, Y.; Hou, W.; Kang, L.; Fan, J.; Hu, X. Synthesis and Characterization of Graphitic Carbon Nitride Sub-Microspheres Using Microwave Method under Mild Condition. Diam. Relat. Mater. 2013, 38, 109–117. Miller, D. J.; Biesinger, M. C.; McIntyre, N. S. Interactions of CO2 and CO at Fractional Atmosphere Pressures with Iron and Iron Oxide Surfaces: One Possible Mechanism for Surface Contamination? Surf. Interface Anal. 2002, 33 (4), 299–305. Wei, D.; Liu, Y.; Wang, Y.; Zhang, H.; Huang, L.; Yu, G. Synthesis of N-Doped Graphene by Chemical Vapor Deposition and Its Electrical Properties. Nano Lett. 2009, 9 (5), 1752–1758. Zhang, C.; Fu, L.; Liu, N.; Liu, M.; Wang, Y.; Liu, Z. Synthesis of Nitrogen-Doped Graphene Using Embedded Carbon and Nitrogen Sources. Adv. Mater. 2011, 23 (8), 1020–1024. Wujcik, K. H.; Wang, D. R.; Raghunathan, A.; Drake, M.; Pascal, T. A.; Prendergast, D.; Balsara, N. P. Lithium Polysulfide Radical Anions in Ether-Based Solvents. J. Phys. Chem. C 2016, 120 (33), 18403–18410. Cuisinier, M.; Hart, C.; Balasubramanian, M.; Garsuch, A.; Nazar, L. F. Radical or Not Radical: Revisiting Lithium-Sulfur Electrochemistry in Nonaqueous Electrolytes. Adv. Energy Mater. 2015, 5 (16), 1–6. Yamin, H.; Gorenshtein, A.; Penciner, J.; Sternberg, Y.; Peled, E. Lithium Sulfur Battery: Oxidation/Reduction Mechanisms of Polysulfides in THF Solutions. J. Electrochem. Soc. 1988, 135 (5), 1045–1048. Mikhaylik, Y. V.; Akridge, J. R. Low Temperature Performance of Li/S Batteries. J. Electrochem. Soc. 2003, 150 (3), A306–



(66)

A311. Cañas, N. a.; Hirose, K.; Pascucci, B.; Wagner, N.; Friedrich, K. A.; Hiesgen, R. Investigations of Lithium–sulfur Batteries Using Electrochemical Impedance Spectroscopy. Electrochim. Acta 2013, 97, 42–51.

(67)

Page 10 of 10

Barchasz, C.; Leprêtre, J. C.; Alloin, F.; Patoux, S. New Insights into the Limiting Parameters of the Li/S Rechargeable Cell. J. Power Sources 2012, 199, 322–330.

.

Table of Content


Nitrogen-Doped Single-Walled Carbon Nanohorns as a Cost-Effective

Recommend Documents