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Conductive Mesoporous Niobium Nitride Microspheres/NitrogenDoped Graphene Hybrid with Efficient Polysulfide Anchoring and Catalytic Conversion for High-Performance Lithium-Sulfur Batteries Xingxing Li, Biao Gao, Xian Huang, Zhijun Guo, Qingwei Li, Xuming Zhang, Paul K Chu, and Kaifu Huo ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b17376 • Publication Date (Web): 02 Jan 2019 Downloaded from http://pubs.acs.org on January 5, 2019

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ACS Applied Materials & Interfaces

Conductive Mesoporous Niobium Nitride Microspheres/NitrogenDoped Graphene Hybrid with Efficient Polysulfide Anchoring and Catalytic Conversion for High-Performance Lithium-Sulfur Batteries

Xingxing Li,†,# Biao Gao,†, ‡,# Xian Huang,† Zhijun Guo,† Qingwei Li,§, ‡ Xuming Zhang,† Paul K. Chu,‡ and Kaifu Huo*,†,§

†

The State Key Laboratory of Refractories and Metallurgy and Institute of Advanced

Materials and Nanotechnology, Wuhan University of Science and Technology, Wuhan 430081, China §

Wuhan National Laboratory for Optoelectronics (WNLO), School of Optical and

Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China ‡

Department of Physics and Department of Materials Science and Engineering, City

University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong 999077, China

#Xingxing

Li and Biao Gao contributed equally to this work.

KEYWORDS: niobium nitride, polysulfide trapping, chemical absorption, electrocatalytic conversion, lithium-sulfur batteries

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ABSTRACT: Lithium-sulfur (Li-S) batteries are promising next-generation energy storage devices because of the high energy density of 2600 Wh kg-1.

Efficient

immobilization and fast conversion of soluble lithium polysulfide intermediates (LiPSs) are crucial to the electrochemical performance of Li-S batteries.

Herein, we report a

novel strategy to simultaneously achieve large capacity, high rate capability, and long cycle-life by utilizing mesoporous niobium nitride microspheres/N-doped graphene nanosheets (NbN@NG) hybrid as multifunctional host materials for sulfur cathodes. The mesoporous NbN microspheres chemically immobilize LiPSs via Nb-S chemical bonding and catalytically promote conversion of LiPSs into insoluble Li2S resulting in enhanced redox reaction kinetics.

Moreover, the highly conductive NbN and N-doped

graphene nanosheets provide rapid electron transport and consequently, the S/NbN@NG cathode demonstrates a large capacity of 948 mAh g-1 at 1 C (1 C = 1650 mA g-1), high rate capability of 739 mAh g-1 at 5 C, and excellent cycle stability with capacity decay of 0.09% per cycle for over 400 cycles.

The results described here

provide insights into the design of multifunctional host materials for high-performance Li-S batteries.

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INTRODUCTION The rapid development of electronic vehicles, portable electronics, and renewable energy sources has spurred the demand of the high energy density batteries.1,2 Lithium-sulfur (Li-S) batteries are promising next-generation energy storage devices owing to the high energy density (2600 Wh kg-1) and the low-cost and earth abundant sulfur (S) resource.

However, the practical implementation of Li-S batteries has been

impeded by several drawbacks such as dissolution and shuttling of the lithium polysulfide intermediates (LiPSs), low conductivity of S and its discharge products (Li2S2/Li2S) giving rise to low S electrochemical utilization, rapid capacity fading, as well as poor Coulombic efficiency (CE).3-7

Porous carbon materials have been

explored as effective hosts to load active S forming S/carbon composites, which can improve the conductivity of the cathodes and restrain polysulfide shuttling by physical confinement.8-11

However, the effusion and irreversible loss of LiPSs from the

cathodes are unavoidable, especially at large S mass loading because of the limited pore volume and weak interaction of nonpolar carbon towards polar LiPSs (Figure 1a)12,13,14, causing quick capacity decay.

Hence, polar host materials that can chemically

immobilize LiPSs are more promising for Li-S batteries.

Heteroatom-doped carbon

such as pyridinic nitrogen-doped carbon nanoflakes has been demonstrated to improve the sulfur evolution reaction,15, 16 but the doping concentration and number of polar sites are quite limited.17

Recently, metal oxides18-22 such as MnO2, TiO2, V2O3, and SiO2

have been explored as efficient host materials in Li-S batteries to chemically immobilize LiPSs in the sulfur cathodes.

However, the poor conductivity of most

metal oxides cause low S electrochemical utilization and poor rate performance. Moreover, the sluggish redox kinetics cause the aggregation of LiPSs, which passively block the host surface resulting in decreased LiPSs adsorption/trapping. 3


In this


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context, the desirable S host materials in Li-S batteries should not only possess high conductivity to facilitate the electron transfer and polar surface to trap the LiPSs, but also have strong electrocatalytic activity to kinetically promote the LiPSs conversion to solid Li2S2/Li2S.23-26

Recently, transition metal nitrides (TMNs) have been

investigated as electrode materials for supercapacitors and lithium-ion batteries as well as electrocatalysts for water splitting and acetylene hydrochlorination27,28 because of their high conductivity and Pt-like catalytic performance.

Recent reports reveal that

the polar VN and TiN can chemically trap LiPSs in the cathodes and restrain shuttling to produce enhanced Li-S battery performance.6,29,30

However, the electrocatalytic

performance of TMNs with respect to LiPSs conversion in Li-S batteries have not been explored systematically.

Niobium nitride (NbN) is a well-known superconductor31

and polar compound, which is expected as a novel host material for S cathodes but has not been reported so far in Li-S batteries. In this paper, N-doped graphene nanosheets (NG) wrapped mesoporous NbN microspheres (NbN@NG) are described as bifunctional sulfur host materials with strong chemical absorption and electrocatalytic activity towards LiPSs conversion for durable high power Li-S batteries.

The NbN@NG hybrid is prepared by electrostatic

self-assembly of mesoporous niobium oxide (Nb2O5) microspheres and graphene oxide (GO) and subsequent thermal nitridation under ammonia.

The resulting NbN

microspheres consisting of tiny cross-connected nanoparticles (10-20 nm) are encapsulated by the NG nanosheets forming a 3D conductive network.

The favorable

features of the NbN@NG hybrid enabling excellent performance in Li-S batteries are schematically illustrated in Figure 1b.

First of all, the NbN@NG hybrid with a porous

structure and robust mechanical stability allows high mass loading of active sulfur. Secondly, polar NbN chemically traps LiPSs in the cathode and impedes effusion of 4


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LiPSs via Nb-S chemical bonding.

Thirdly, NbN has strong electrocatalytic activity

in accelerating the LiPSs redox reactions thus enabling enhanced redox kinetics during cycling.

Fourthly, the highly conductive NG and NbN provide a conductive network

facilitating electron transport resulting in high rate capability.

Lastly, the NG

nanosheets coated on the NbN microspheres mitigate loss of LiPSs via physical confinement and N heteroatoms chemical anchoring.

Benefiting from the synergetic

merits of NbN and NG, the sulfur impregnated NbN@NG (S/NbN@NG) cathode has a large capacity of 948 mAh g-1 at 1 C (1 C = 1650 mA g-1), high rate capability of 739 mAh g-1 at 5 C, and long cycle life with a low capacity fading of 0.09% per cycle for over 400 cycles.

Our results reveal a new strategy to design and prepare

multifunctional host materials for Li-S batteries with large capacity, high rate capability, and long cycling life.

RESULTS AND DISCUSSION The preparation procedures of the S/NbN@NG are illustrated in Figure 2a.

The

Nb2O5 microspheres are synthesized hydrothermally with NbCl5 powder, ethyl alcohol, and acetone as precursors followed by calcination at 500 °C in air for 5 hrs.32

The

scanning electron microscopy (SEM) in Figure 2b and transmission electron microscopy (TEM) images in Figure S1a-b and reveal that the diameters of mesoporous microspheres are 800-1000 nm, which comprise cross-connected nanoparticles of 1020 nm.

The X-ray diffraction (XRD) pattern (Figure S1c) can be indexed to the

hexagonal phase Nb2O5 (JCPDS NO. 07-0061) and no impurities are detected.

The

as-obtained Nb2O5 microspheres are dispersed in the poly(diallydimethylamm-onium chloride) (PDDA) solution under vigorous stirring to form positively-charged Nb2O5PDDA by the absorption of PDDA cations.

The Nb2O5-PDDA particles are then

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dispersed into a negative-charged GO solution to form the Nb2O5@GO hybrid by means of the electrostatic interactions between the positively-charged Nb2O5-PDDA and negatively charged GO nanosheets (Figure 2c).

The NbN@NG hybrid is

produced by thermally annealing Nb2O5@GO under NH3 atmosphere at 600 °C for 3 hrs.

The Nb2O5 microspheres are converted into mesoporous NbN while GO is

reduced to NG.

The SEM image (Figure 2d) of the NbN@NG hybrid reveals that the

NbN microspheres are coated with thin NG nanosheets forming a 3D interconnected conductive network. The enlarged TEM image in Figure 3a discloses that the NbN microspheres retain a similar morphology as the precursor of Nb2O5 and NG nanosheets attaching tightly to the surface of the spheres has a thickness of 5-10 nm (Figure S2).

The high-resolution

TEM (HR-TEM) image shown in the inset in Figure 3b reveals lattice fringes of 0.22 nm corresponding to the (200) planes of cubic phase NbN.

Raman scattering discloses

two wide peaks at 1348 and 1580 cm-1 corresponding to the D and G bands of NG (Figure S3a).

X-ray photoelectron spectroscopy (XPS) results reveal the two N 1s

peaks (Figure S3b) of NbN@NG at 396.8 eV and 399.2 eV, which are assigned to Nb-N and Nb-N-O,33 respectively.

The presence of Nb-N-O species is due to incomplete

nitridation and residual oxygen in NbN.27,33 The N 1s peaks at 401.5 eV, 400.3 eV, and 398.2 eV are ascribed to quaternary N, pyrrolic N, and pyridinic N in NG nanosheets, respectively,34 arising from chemical reduction of GO under ammonia. The NG concentration in NbN@NG is calculated to be 25.2 wt% by thermogravimetric (TG) analysis (Figure S4).

The N2 adsorption/desorption profiles of NbN@NG and

Nb2O5 are presented in Figure S5.

NbN@NG has a Brunauer-Emmett-Teller (BET)

surface area of 70.96 m2 g-1, which is larger than that of Nb2O5 (39.83 m2 g-1) and NG

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(16.80 m2 g-1).

The enlarged BET surface area of NbN@NG arises from formation of

more mesopores from Nb2O5 to NbN during nitridation.35 The S impregnated NbN@NG hybrid (S/NbN@NG) is prepared by a meltdiffusion process at 155 oC.

The SEM images (Figure 3c) reveal that the overall

morphology of S/NbN@NG is retained after S incorporation and no visible S particles are observed from the outside surface of NbN@NG.

The scanning TEM (STEM)

image and corresponding energy-dispersive X-ray spectroscopy (EDS) maps of S/NbN@NG are depicted in Figure 3d.

The S elemental distribution is similar to those

of Nb and C, indicating that S is uniformly dispersed into the NbN@NG hybrid.

The

XRD patterns of S/NbN@NG in Figure 3e can be ascribed to the cubic NbN (JCPDS No. 38-1155) and orthorhombic S (JCPDS No. 74-1465).

The surface area and pore

volume of NbN@NG diminish from 70.96 m2 g-1 and 0.22 cm3 g-1 to 7.65 m2 g-1 and 0.014 cm3 g-1 (Figure S5), respectively, confirming that S is impregnated in NbN@NG. The S concentration in S/NbN@NG determined by TG analysis is 62 wt% (Figure 3f). To corroborate the strong chemical interaction between NbN@NG and LiPSs, a visual test is carried out by dispersing 25 mg of NbN@NG or NG in the 10 mM Li2S6 solution.

The Figure 4a shows that the Li2S6 solution containing NbN@NG becomes

lucid and colorless after 24 hrs.

In contrast, the color of the organic Li2S6 solution

containing NG shows no obvious discoloration.

These results indicate the presence

of strong absorption between NbN@NG and Li2S6, which is further evidenced by XPS. The fine XPS Nb 3d spectrum of NbN@NG (Figure 4b) indicates a pair of new peak at 204.1 eV/206.6 eV in addition to Nb5+-O, Nb-N-O, and Nb3+-N bonds33,35,36 after absorbing LiPSs and the fine spectrum of S 2p shows the addition peak at 162.2 eV (Figure S6) corresponding to Nb-S species.37,38

To investigate the catalytic activity of

NbN in polysulfide conversion, symmetrical cells are designed by sandwiching lithium 7



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bis(trifluoromethanesulfonyl) (LiTFSI) electrolyte containing 0.5 M Li2S6 between two identical NbN@NG electrodes (acting as both the working and counter electrodes). The NG electrodes prepared under the same conditions serve as the control and CV is also conducted on the Li2S6-free electrolyte to correct for the capacitive contributions. The open circuit voltage of the symmetrical cells is 0 V and the CV curves of the symmetrical cells in the voltage window between -1.5 and 1.5 V obtained at a scanning rate of 3 mV s-1 are presented in Figure 4c.

Four distinct peaks at -0.20, -0.70, 0.20,

and 0.70 V are observed from the symmetrical NbN@NG electrodes.

On the contrary,

the NG electrodes only show a pair of drawn-out and smooth redox peak at -1.18 V and 1.18 V.

The current density of the symmetrical NbN@NG electrodes is much larger

than that of the NG electrodes, demonstrating that NbN dynamically accelerates the electrochemical reactions of Li2S2.

Since Li2S6 is the only electrochemically active

species in the initial electrolyte, the peak of -0.7 V in the first cathodic scan from 0 to 1.5 V Li2S6 is ascribed to reduction from Li2S6 to Li2S (or Li2S2) on the working electrode and oxidation from Li2S6 to S8 on the counter electrode.

In the subsequent

anodic scan from -1.5 to +1.5 V, the peak at 0.2 V is attributed to reconstitution of Li2S6 by oxidation of Li2S (or Li2S2) on the working electrode and reduction of S8 forming Li2S6 on the counter electrode.

Thus, the peaks at -0.7 V and 0.2 V are a redox pair

on the working electrode or counter electrode, respectively.39,40

Similarly, the peaks

at 0.7 V and -0.2 V arise from the similar redox reaction in the symmetric cell and these redox reactions on the working and counter electrodes are summarized in Figure S7a. The sharper peaks and smaller peak separation on NbN@NG electrode indicate good electrochemical reversibility and enhanced conversion of Li2S6 compared to NG electrode.23,39,41

The electrochemical impedance spectroscopy (EIS) results

determined from the symmetrical cell composed of the NbN@NG electrodes or NG 8


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electrodes are depicted in Figure 4d.

The two semicircles of the NbN@NG at high

frequencies are correlated with the charge-transfer resistance at the LiPSs/NG and LiPSs/NbN interfaces.23

The symmetrical cell with the NbN@NG electrodes exhibits

a smaller charge transfer resistance than the NG electrodes.

Since the symmetrical

cells are free of metallic Li, the decreased interfacial resistance is attributed to the enhanced interfacial affinity between NbN@NG and LiPSs and rapid charge transport in the redox reactions being agreement with the CV results in Figure 4c.

Figures S7b-

g depict the SEM images of the counter electrodes of the symmetrical cells with NbN@NG or NG before and after first scanning from 0 V to -1.5 V.

The in situ

formed S particles from oxidization of Li2S6 (4Li2S6 ‒ 8e- → 3S8 + 8Li+) are clearly observed from the NbN@NG counter electrode (Figures S7).

On the other hand, S

nanoparticles are hardly observed from the surface of NG electrode, indicating that NbN@NG can enhance conversion of Li2S6 due to the strong electrocatalytic activity of NbN towards Li2S6. The electrochemical performance of S/NbN@NG cathode is evaluated using the CR2016 coin-like cells with a Li foil as the counter anode and DOL/DME (1:1, v/v) with 1 M LiTFSI as the electrolyte.

The S/NbN and S/NG electrodes (Figure S8) with

the same sulfur loading serve as the experimental control.

Figure 5a shows the CV

curves of the S/NbN@NG and S/NG cathodes in the potential range of 1.7-2.8 V (vs. Li+/Li) at a scanning rate of 0.1 mV s-1.

The two cathodic peaks (Peak I and Peak II)

are ascribed to conversion of S to high-order soluble LiPSs (Li2Sn, n = 4~8) and subsequent reduction of Li2Sn to short-order insoluble Li2S2/Li2S.3,19,42,43

The anodic

peaks of Peak III and Peak IV stem from oxidation of Li2S to long-chain LiPSs and S. The S/NbN@NG exhibits higher cathodic peaks potential (I and II), smaller anodic peaks potential (III and IV), and larger peaks currents compared to S/NG electrode, 9



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suggesting NbN substantially mitigates polarization and kinetically accelerates polysulfide redox conversion (S8 ↔ Li2S4 and Li2S4 ↔ Li2S2/Li2S).40,42

Figure 5b and

Figure S9 present the discharging profiles of the S/NbN@NG, S/NG, and S/NbN electrodes at 0.5 C (1 C = 1650 mA g-1) rate, revealing two plateaus typical of the Sbased cathode.17,40,42,44

C1 and C2 are the discharging capacities of two different

stages corresponding to conversion of S to soluble polysulfides (S8→S62-→S42-, 1/4 of the theoretical capacity) and further reduction of long-chain polysulfides to insoluble Li2S (S42-→Li2S2→Li2S, 3/4 of the theoretical capacity).

The capacity ratio of C2 to

C1 (C2/C1) is a good indicator to evaluate the LiPSs conversion kinetics and utilization.45-47

Although the S/NbN@NG, S/NG and S/NbN cathodes exhibit similar

capacity of about 300 mAh g-1 in the first stage (C1), the S/NbN@NG electrode delivers a larger capacity than that of S/NG and S/NbN in the second stage(C2).

The large

C2/C1 of S/NbN@NG (2.27) which is larger than that of S/NG (1.85) and S/NbN (1.95) indicates more LiPSs conversion and higher S utilization, which coincides with the results of the CVs acquired from the symmetrical cells and Li-S cell. The enhanced redox kinetics of NbN@NG can be attributed to the synergetic effects of NbN and NG accelerating charge transfer of Li+/e− and promoting conversion from LiPSs to Li2S2/Li2S.

The EIS and the corresponding equivalent circuit of the S/NbN@NG,

S/NG and S/NbN electrodes are displayed in Figure 5c and Figure S9c.

Rf and Rct are

the electrolyte resistance and charge transfer resistance, respectively, Q1 and W represent the electrical double-layer capacitors on the surface of electrode and Warburg impedance, Q2 is the diffusion impedance of Li+ diffusion process.48,49

A smaller

charge transfer resistance (Rct = 50.9 Ω) on the S/NbN@NG electrode compared to S/NbN (Rct = 150.8 Ω) and the S/NG electrode (215.4 Ω) implies a low energy penalty

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due to the enhanced interfacial affinity and faster redox kinetics on the S/NbN@NG electrode. Figure 5d and Figure S9d show the rate capability of S/NbN@NG, S/NbN and S/NG at various current from 0.2 to 5C.

The S/NbN@NG cathodes have a larger capacity

than the S/NbN and S/NG cathodes at all C-rates.

Even at a large current density of 5

C, the S/NbN@NG cathodes still deliver a high discharging capacity of 739 mAh g-1 which is superior to that of other reported S-based cathodes so far.41,50-57

Moreover,

when the current switches back to 1 C after 30 cycles, the specific capacity of S/NbN@NG returns to that of the initially low rate, indicating high electrochemical reversibility.

Compared to S/Nb2O5@rGO, S/NbN@NG has the larger capacities at

all the measured current density (Figure S10) due to the high conductivity and electrochemical activity of NbN.

The long-term cycling performance of the

S/NbN@NG and S/NG cathodes at 1 C rate are shown in Figure 5e. The first 2 cycles at the 0.2 C are measured for gradual activation.

The S/NbN@NG electrode shows

an initial capacity of 1311 mAh g-1 at 0.2 C with initial CE of 90.4% and large capacities of 948 mAh g-1 at the 10th cycle and 814 mAh g-1 at the 100th cycle at 1 C with CE close to 100%.

After 400 cycles, the S/NbN@NG cathodes still show a high capacity of

598 mAh g-1 with a capacity decay rate of 0.09% per cycle from the 10th to 400th cycle suggesting good cycle stability.

In contrast, the S/NbN and S/NG cathodes have lower

specific capacities of 695 and 664 mAh g-1 at the 100th cycle, respectively, and exhibit faster capacity decay (0.17 and 0.30% per cycle, respectively) (Figure S9).

When the

sulfur loading is increased to 73.4%, the S/NbN@NG cathode also delivers a good rate capability of 710 and 480 mAh g-1 at 1 and 5 C rates, respectively, and a high capacity of 616 mAh g-1 with a capacity retention of 82% after 150 cycles at 1 C (Figure S11). To show the advantages of NbN@NG hybrid performance, we compared the 11



electrochemical performances of previously reported S cathodes with the current work, which are listed in Table S1.

Even at higher sulfur loading of 5.5 mg cm-2, the

S/NbN@NG cathode shows a high discharge capacity of 745 mAh g-1 (corresponding to the areal specific capacities of 4.1 mAh cm-2) (Figure S12). These results confirm that S/NbN@NG delivers outstanding electrochemical performance because of the strong chemical interaction and electrochemical catalytic capability of the mesoporous polar NbN towards LiPSs as well as the high conductivity of NbN@NG. The structural stability of the NbN@NG host during cycling favors cycling stability. After 400 cycles at 1 C, we disassemble the coin cell (S/NbN@NG as cathode) at the fully-charged state of 2.8 V and then wash the electrode with DOL/DME electrolyte thoroughly.

The SEM image reveals that the structure and morphology of NbN@NG

are retained after 400 cycles and micro-size NbN spheres can be clearly observed without structure breakage (Figure S13a).

The EDS mapping images shown in

Figures S13b-d indicate that sulfur is uniformly distributed along the NbN@NG without aggregation of S particles, suggesting that the S species are confined in the NbN@NG host during cycling.

The superior electrochemical performance of

NbN@NG can be ascribed to the synergetic effects rendered by the conductive polar NbN microspheres and NG nanosheets.

As schematically illustrated in Figure 5f,

NbN microsphere effectively captures LiPSs species on the surface and the LiPSs can be converted swiftly into short-chain Li2S or Li2S2 due to the strong electrochemical catalytic capability of the mesoporous polar NbN.

On the other hand, the N-doped

graphene nanosheets provide fast electron transfer paths and further impede outdiffusion of LiPSs by heteroatoms N and physical impediment.

CONCLUSION 12


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In summary, we design and synthesize 3D conductive NbN@NG composites as promising multifunctional host materials in Li-S batteries by simple self-assembly of mesoporous Nb2O5 microspheres and GO based on electrostatic interactions and subsequent thermal nitridation.

The NbN chemically anchors polysulfide via Nb-S

bonding and catalytically accelerates conversion of soluble polysulfides into insoluble Li2S.

Benefiting from the N-doped graphene nanosheets having high conductivity and

physical trapping effects, the NbN@NG cathode delivers high-rate performance (capacity of 739 mAh g-1 at 5 C) and excellent cycling stability (capacity fading of 0.09% per cycle).

The strategy described in this paper based on strong chemical anchoring

and fast conversion ability of NbN@NG provide a novel route to design and utilize transitional metal nitrides in high-performance Li-S batteries.

EXPERIMENTAL SECTION Preparation of Nb2O5 microspheres. A facile solvothermal method was employed to synthesize the Nb2O5 microspheres, as our previous report.32

In a typical

experiment, the 250 mg of NbCl5 powders (99 %, Sigma-Aldrich) were dissolved in the solution containing 20 ml of ethyl alcohol (C2H6O, AR, Sigma-Aldrich) and 5 mL of acetone (C3H6O, AR, Sigma-Aldrich).

The solution was then transferred to a 60 mL

Teflon-lined autoclave and heated to 210 °C for 24 hrs.

After cooling to room

temperature, the white product was collected and further washed several times using ethanol and deionized water (DW), and then dried at 80 °C for 12 hrs.

Finally, the

Nb2O5 microspheres were obtained by annealing the collected white product precursor under air at 500 °C for 5 hrs. Preparation of NbN@NG. 200 mg of the Nb2O5 microspheres were dispersed in 50 mL of DW and then 1 mL of the poly (diallyldimethylammonium chloride) (PDDA) 13



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solution was added to produce the positively-charged Nb2O5 microspheres/PDDA. The extra PDDA was removed by centrifugation/washing/re-dispersion multiple times. Graphene oxide (GO) was prepared by the modified Hummers method.58

The as-

obtained positively-charged Nb2O5 microspheres were added dropwise to the diluted GO solution (10 mg mL-1) under magnetic stirring.

After stirring for 5 min, the

suspension with the Nb2O5 microspheres embedded by graphene oxide (Nb2O5@GO) was quickly frozen with liquid nitrogen and vacuum freeze-dried.

Finally, the

composite comprising NbN microspheres encapsulated with nitrogen doped reduced graphene oxide (NbN@NG) was obtained via annealing Nb2O5@GO under NH3 at 600 °C for 3 hrs.

The conductivity of electrode material was conducted via four-tip

method and the conductivity of NbN@NG was about 5.05×103 Ω-1 m-1.

For

comparison, we also prepared the NG by the same treatment method without Nb2O5 and prepared the Nb2O5@rGO by self-assembling Nb2O5@GO followed by annealing under Ar. Preparation of S/NbN@NG. The sulfur impregnated NbN@NG (S/NbN@NG) was obtained by melt-diffusion method.

The NbN@NG was mixed with a certain amount

sublimed sulfur powers and then heated to 155 °C for 12 hrs in a sealed vacuum glass tube.

We also prepared the S/NG by the same melt-diffusion method.

Polysulfide adsorption test.

The Li2S6 catholyte with concentration of 10 mmol

L-1 was selected for polysulfide adsorption test, which was obtained by dissolving sublimed sulfur powers and lithium sulfide (5:1, ratio by molar) in a certain amount of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (v/v = 1:1) under intense magnetic stirring for 12h at 50 °C. The NbN@NG and NG with the same mass of 25 mg were separately added into 3 mL of the Li2S6 catholyte. After shaking 1 min and resting 24 hrs, the digital photographs were collected to record the discoloration of the 14


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above samples and the precipitated products (NbN@NG-Li2S6 and NG-Li2S6) were studied by X-ray photoelectron spectroscopy (XPS, ESCALB MK-II). Materials Characterization. The sample morphology and element distribution were examined by field-emission scanning electron microscope (SEM, FEI Nova 450 Nano) and high-resolution transmission electron microscope (TEM, FEI Titan G2 60-300) equipped with energy-dispersive X-ray spectroscopy (EDS, Oxford). The X-ray powder diffractometer (XRD, Philips X’ Pert Pro) with Cu Kα radiation was conducted to identify the crystalline structure of samples.

XPS (ESCALB MK-II) and Raman

scattering (HR RamLab) were used to analyse the chemical bonding states.

The

Nitrogen adsorption/desorption isotherm curves were acquired via Micromeritics ASAP 2020 instrument at -196 °C (77 K).

The specific surface area and average pore

distribution was obtained by the Brunauer-Emmett-Teller (BET) equation.

Thermal

analysis (Naichi Corporation STA449) was performed in different atmospheres at 10 °C min-1. Electrochemical Assessment. The working cathode was prepared with S/NbN@NG or S/NG (80 wt%) as the active materials, acetylene black (10 wt%) as the conductive additive, and polyvinylidene fluoride (PVDF) (10 wt%) as the binder. N-methyl pyrrolidinone (NMP) solution was added into the mixed power to form slurry, which was uniformly coated on the Al foil current collectors and vacuum-dried at 80 °C for 12 hrs as the electrodes. The coin-like 2016 type cells were assembled in an Ar-filled glovebox with the above electrodes (diameter of 12 mm, areal sulfur loading of 2.4-5.5 mg cm-2) as the cathode and lithium foil as the anode.

The electrolyte was 1 M lithium

bis(trifluoromethanesulfonyl) (LiTFSI) and 0.1 M LiNO3 in DOL/DME (1:1, v/v) and Celgard 2400 film acted as the separator. The electrolyte/sulfur ratio was about 15.0 μL mg-1 for cathodes.

The CHI760e electrochemical workstation was used to test the 15



Page 16 of 31

cyclic voltammogram (CV) at 0.1 mV s-1 and electrochemical impedance spectroscopy (EIS) in the frequency range between 0.1 Hz and 100 kHz at open circuit voltage of fresh cells. Galvanostatic discharging-charging tests were carried out on the electrochemical test system (Land CT2001A) under different current densities (based on the mass of sulfur) in the potential range of 1.7-2.8 V.

All of electrochemical

assessments were performed at room temperature (about 25 °C/298 K) Symmetrical Cell Assembly and electrochemical evaluation. The symmetrical cells are designed by sandwiching LiTFSI electrolyte containing 0.5 M Li2S6 between two identical NbN@NG or NG electrodes (acting as both the working and counter electrodes).

The active materials (NbN@NG and NG) and PVDF binder (4:1, ratio

by weight) were mixed in NMP, then the slurry was uniformly coated on Al foil.

The

electrode foil was punched to disks with a diameter of 13.0 mm and areal sulfur loading of 1-1.5 mg cm-2.

The coin cells were assembled with two same disks as the cathode

and anode, Celgard 2400 separator, and 40 μL catholyte containing 0.5 M LiTFSI and 0.5 M Li2S6 in DME/DOL (v/v = 1/1).

The CV data were obtained from the

symmetric cell at a scanning rate of 3 mV s-1 within the potential window between -1.5 V and 1.5 V.

The counter electrode after scanning to -1.5 V was disassembled from

the cell and rinsed with DOL thrice to remove the lithium salt on the surface.

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Figure 1. Schematic diagram of the LiPSs adsorption and conversion processes on (a) Carbon materials and (b) Conductive NbN/carbon materials.

17



Figure 2. (a) Schematic illustration of the fabrication processes of NbN@NG; SEM images of (b) Nb2O5, (c) Nb2O5@GO, and (d) NbN@NG.

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Figure 3. Structural characterization of NbN@NG and S/NbN@NG: (a) TEM image of NbN@NG; (b) HR-TEM image of NbN. (c) SEM image of S/NbN@NG; (d) TEM image of S/NbN@NG and corresponding EDS elemental maps of Nb, C and S; (e) XRD patterns of NbN@NG and S/NbN@NG; (f) TG curves of S/NbN@NG in the Ar atmosphere.

19



Figure 4. (a) Digital pictures showing the LiPSs adsorption performance after addition of NbN@NG and NG; (b) High-resolution Nb 3d XPS spectra of NbN@NG before and after LiPSs adsorption; CV curves (c) at a scanning rate of 3 mV s-1 and electrochemical impedance spectra (d) acquired from the symmetrical cells with NbN@NG and NG electrodes in the electrolytes with and without 0.5 M Li2S6.

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Figure 5. Electrochemical performance of S/NbN@NG and S/NG. (a) CV curves of Li-S battery based on the S/NbN@NG and S/NG cathode at the scanning rate of 0.1 mV s-1; (b) Typical voltage profile of S/NbN@NG and S/NG at 0.5 C and C1 and C2 represent the discharge capacities in stages 1 and 2, respectively (inset: Corresponding discharge capacity in stages 1 and 2 for S/NbN@NG and S/NG); (c) Electrochemical impedance spectra of S/NbN@NG and S/NG at the open circuit voltage; (d) Rate performance at different C-rates; (e) Long-term cycling ability of S/NbN@NG and S/NG (1 C = 1675 mA g-1 based on the mass of S;. (f) Schematic illustration of the immobilization and conversion of LiPSs on the NbN@NG host in the Li-S battery.

ASSOCIATED CONTENT Supporting Information TEM image and XRD pattern of Nb2O5; Raman and XPS spectra of NbN@NG hybrid 21



and NG; TG curves of NbN@NG; Nitrogen adsorption/desorption isotherms and pore size distributions of NbN@NG, S/NbN@NG, Nb2O5 and NG; XPS spectra of NbN@NG and NG after LiPSs adsorption; SEM images of NbN@NG and NG before/after scanning to -1.5 V; SEM, XRD and TG of S/NG; The electrochemical properties of S/NbN@NG, S/NbN, S/NG and Nb2O5@rGO; TG curves and electrochemical properties of S/[email protected]%; Areal capacity of S/NbN@NG cathode with sulfur loading of 5.5 mg cm-2; SEM image and the corresponding elemental maps of S/NbN@NG after 400 cycles.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Author Contributions #Xingxing

Li and Biao Gao contributed equally to this work.

Notes All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by National Natural Science Foundation of China (Nos. 51572100, 21875080, 61434001 and 51504171,), Major Project of Technology Innovation of Hubei Province (2018AAA011), Wuhan Yellow Crane Talents Program, HUST Key Interdisciplinary Team Project (2016JCTD101), Hong Kong Research Grants Council (RGC) General Research Funds (GRF) No. CityU 11205617.

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REFERENCES (1) Son, Y.; Lee, J.S.; Son, Y.; Jang, J. H.; Cho, J. Recent Advances in Lithium Sulfide Cathode Materials and Their Use in Lithium Sulfur Batteries. Adv. Energy Mater. 2015, 5, 1500110. (2) Salem, H. A.; Babu, G.; Rao, C. V.; Arava, L. M. R. Electrocatalytic Polysulfide Traps for Controlling Redox Shuttle Process of Li-S Batteries. J. Am. Chem. Soc. 2015, 137, 11542-11546. (3) Fang, R.; Zhao, S.; Sun, Z.; Wang, D. W.; Cheng, H. M.; Li, F. More Reliable Lithium-Sulfur Batteries: Status, Solutions and Prospects. Adv. Mater. 2017, 29, 1606823. (4) Tan, G.; Xu, R.; Xing, Z.; Yuan, Y.; Lu, J.; Wen, J.; Liu, C.; Ma, L.; Zhan, C.; Liu, Q.; Wu, T.; Jian, Z.; Shahbazian-Yassar, R.; Ren, Y.; Miller, D. J.; Curtiss, L. A.; Ji, X.; Amine, K. Burning Lithium in CS2 for High-performing Compact Li2S-graphene Nanocapsules for Li-S Batteries. Nat. Energy 2017, 2, 17090. (5) Bao, W.; Su, D.; Zhang, W.; Guo, X.; Wang, G. 3D Metal Carbide@Mesoporous Carbon Hybrid Architecture as a New Polysulfide Reservoir for Lithium-Sulfur Batteries. Adv. Funct. Mater. 2016, 26, 8746-8756. (6) Sun, Z.; Zhang, J.; Yin, L.; Hu, G.; Fang, R.; Cheng, H. M.; Li, F. Conductive Porous Vanadium Nitride/Graphene Composite as Chemical Anchor of Polysulfides for Lithium-Sulfur Batteries. Nat. Commun. 2017, 8, 14627. (7) Li, Y.; Wang, L.; Gao, B.; Li, X.; Cai, Q.; Li Q.; Peng, X.; Huo, K.; Chu, P. K.

Hierarchical Porous Carbon Materials Derived from Self-Template Bamboo Leaves for Lithium-Sulfur Batteries. Electrochim. Acta 2017, 229, 352-360. (8) Chen, M.; Jiang, S.; Huang, C.; Wang, X.; Cai, S.; Xiang, K.; Zhang, Y.; Xue, J. Honeycomb-Like Nitrogen and Sulfur Dual-doped Hierarchical Porous Biomass 23



Page 24 of 31

Carbon for High-Energy-Density Lithium-Sulfur Batteries. ChemSusChem 2017, 10, 1803-1812. (9) 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, 4044-4049. (10) Wang, H.; Zhang, C.; Chen, Z.; Liu, H. K.; Guo, Z. Large-scale Synthesis of Ordered Mesoporous Carbon Fiber and Its Application as Cathode Material for Lithium-Sulfur Batteries. Carbon 2015, 8, 782-787. (11) Zang, J.; An, T.; Dong, Y.; Fang, X.; Zheng, M.; Dong, Q.; Zheng, N. Hollowin-Hollow Carbon Spheres with Hollow Foam-Like Cores for Lithium-Sulfur Batteries. Nano Res. 2015, 8, 2663-2675. (12) Pei, F.; An, T.; Zang, J.; Zhao, X.; Fang, X.; Zheng, M.; Dong, Q.; Zheng, N. From Hollow Carbon Spheres to N-Doped Hollow Porous Carbon Bowls: Rational Design of Hollow Carbon Host for Li-S Batteries. Adv. Energy Mater. 2016, 6, 1502539. (13) Song, J.; Yu, Z.; Gordin, M. L.; Wang, D. Advanced Sulfur Cathode Enabled by Highly Crumpled Nitrogen-Doped Graphene Sheets for High-Energy-Density Lithium-Sulfur Batteries. Nano Lett. 2106, 16, 864-870. (14) Zhu, X.; Zhao, W.; Song, Y.; Li, Q.; Ding, F.; Sun, J.; Zhang, Li.; Liu, Z. In Situ Assembly

of

2D

Conductive

Vanadium

Disulfide

with

Graphene

as

a

High‐Sulfur‐Loading Host for Lithium-Sulfur Batteries. Adv. Energy Mater. 2018, 8, 1800201. (15) Yuan, H.; Zhang, W.; Wang, J. G.; Zhou, G.; Zhuang, Z.; Luo, J.; Huang, H.; Gan, Y.; Liang, C.; Xia, Y.; Zhang, J.; Tao, X. Facilitation of Sulfur Evolution Reaction by Pyridinic Nitrogen Doped Carbon Nanoflakes for Highly-Stable Lithium-Sulfur Batteries. Energy Storage Mater. 2018, 10, 1-9. 24


Page 25 of 31 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


(16) Li, Q.; Song, Y.; Xu, R.; Zhang, Li.; Gao, J.; Xia, Z.; Tian, Z.; Wei, N.; Rümmeli, M. H.; Zou, X.; Sun, J.; Liu, Z. Biotemplating Growth of Nepenthes-like N-Doped Graphene as a Bifunctional Polysulfide Scavenger for Li-S Batteries. ACS Nano 2018, 12, 10240-10250. (17) Peng, H. J.; Zhang, G.; Chen, X.; Zhang, Z. W.; Xu, W. T.; Huang, J. Q.; Zhang, Q. Enhanced Electrochemical Kinetics on Conductive Polar Mediators for LithiumSulfur Batteries. Angew. Chem. Int. Ed. 2016, 55, 12990-12995. (18) Rehman, S.; Guo, S.; Hou, Y. Rational Design of Si/SiO2@Hierarchical Porous Carbon Spheres as Efficient Polysulfide Reservoirs for High-Performance Li-S Battery. Adv. Mater. 2016, 28, 3167-3172. (19) Li, Y.; Cai, Q.; Wang, L.; Li, Q.; Peng, X.; Gao, B.; Huo, K.; Chu, P. K. Mesoporous TiO2 Nanocrystals/Graphene as an Efficient Sulfur Host Material for High-Performance Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2016, 8, 23784-23792. (20) Li, Z.; Zhang, J.; Lou, X. W. Hollow Carbon Nanofibers Filled with MnO2 Nanosheets as Efficient Sulfur Hosts for Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2015, 54, 12886-12890. (21) Tao, X.; Wang, J.; Ying, Z.; Cai, Q.; Zheng, G.; Gan, Y.; Huang, H.; Xia, Y.; Liang, C.; Zhang, W.; Cui, Y. Strong Sulfur Binding with Conducting Magnéli-Phase TinO2n-1 Nanomaterials for Improving Lithium-Sulfur Batteries Nano Lett. 2014, 14, 5288-5294. (22) Song, Y.; Zhao, W.; Wei, N.; Zhang, L.; Ding, F.; Liu, Z.; Sun, J. In-situ PECVD-Enabled Graphene-V2O3 Hybrid Host for Lithium–Sulfur Batteries. Nano Energy 2018, 53, 432-439. (23) Fang, R.; Zhao, S.; Sun, Z.; Wang, D. W.; Amald, R.; Wang, S.; Cheng, H. M.; 25



Li, F. Polysulfide Immobilization and Conversion on a Conductive Polar MoC@MoOx Material for Lithium-Sulfur Batteries. Energy Storage Mater. 2018, 10, 56-61. (24) Liu, D.; Zhang, C.; Zhou, G.; Lv, W.; Ling, G.; Zhi, L.; Yang, Q. H. Catalytic Effects in Lithium-Sulfur Batteries: Promoted Sulfur Transformation and Reduced Shuttle Effect. Adv. Sci. 2108, 5, 1700270. (25) Li, Y. J.; Fan, J. M.; Zheng, M. S.; Dong, Q. F. A Novel Synergistic Composite with Multi-Functional Effects for High-Performance Li-S Batteries. Energy Environ. Sci. 2016, 9, 1998-2004. (26) Yuan, H.; Chen, X.; Zhou, G.; Zhang, W.; Luo, J.; Huang, H.; Gan, Y.; Liang, C.; Xia, Y.; Zhang, J.; Wang, J.; Tao, X. Efficient Activation of Li2S by Transition Metal Phosphides Nanoparticles for Highly Stable Lithium-Sulfur Batteries. ACS Energy Lett. 2017, 2, 1711-1719. (27) Han, Y.; Yue, X.; Jin, Y.; Huang, X.; Shen, P. K. Hydrogen Evolution Reaction in Acidic Media on Single-Crystalline Titanium Nitride Nanowires as an Efficient Nonnoble Metal Electrocatalyst. J. Mater. Chem. A 2016, 4, 3673-3677. (28) Shao, M.; Chang, Q.; Dodelet, J. P.; Chenitz, R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem. Rev. 2016, 116, 3594-3657. (29) Cui, Z.; Zu, C.; Zhou, W.; Manthiram, A.; Goodenough, J. B. Mesoporous Titanium Nitride-Enabled Highly Stable Lithium-Sulfur Batteries. Adv. Mater. 2016, 28, 6926-6931. (30) Song, Y.; Zhao, Wen.; Kong, L.; Zhang, L.; Zhu, X.; Shao, Y.; Ding, F.; Zhang, Q.; Sun, J.; Liu, Z. Synchronous Immobilization and Conversion of Polysulfides on a VO2-VN Binary Host Targeting High Sulfur Load Li-S Batteries. Energy Environ. Sci. 2018, 11, 2620-2630. (31) W. Robbins, S.; Beaucage, P. A.; Sai, H.; Tan, K. W.; Werner, J. G.; Sethna, J. 26


Page 26 of 31

Page 27 of 31 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


P.; DiSalvo, F. J.; Gruner, S. M.; Dover, R. B. V.; Wiesner, U. Block Copolymer SelfAssembly-Directed Synthesis of Mesoporous Gyroidal Superconductors. Sci. Adv. 2016, 2, e1501119. (32) Ma, G.; Li, K.; Li, Y.; Gao, B.; Ding, T.; Zhong, Q.; Su, J.; Gong, L.; Chen, J.; Yuan, L.; Hu, B.; Zhou, J.; Huo, K. A High-Performance Hybrid Supercapacitor Based on Graphene-Wrapped Mesoporous T-Nb2O5 Nanospheres Anode and Mesoporous Carbon-Coated Graphene Cathode. ChemElectroChem 2016, 3, 1360-1368. (33) Cui, H.; Zhu, G.; Liu, X.; Liu, F.; Xie, Y.; Yang, C.; Lin, T.; Gu, H.; Huang, F. Niobium Nitride Nb4N5 as a New High-Performance Electrode Material for Supercapacitors. Adv. Sci. 2015, 2, 1500126. (34) Han, K.; Shen, J.; Hao, S.; Ye, H.; Wolverton, C.; Kung, M. C.; Kung, H. H. Free Standing Nitrogen-doped Graphene Paper as Electrodes for High-Performance Lithium/Dissolved Polysulfide Batteries. ChemSusChem 2014, 7, 2545-2553. (35) Gao, B.; Xiao, X.; Su, J.; Zhang, X.; Peng, X.; Fu, J.; Chu, P. K. Synthesis of Mesoporous Niobium Nitride Nanobelt Arrays and Their Capacitive Properties. Appl. Surf. Sci. 2016, 383, 57-63. (36) Tao, Y.; Wei, Y.; Liu, Y.; Wang, J.; Qiao, W.; Ling, L.; Long, D. KineticallyEnhanced Polysulfide Redox Reactions by Nb2O5 Nanocrystals for High-Rate LithiumSulfur Battery. Energy Environ. Sci. 2016, 9, 3230-3239. (37) Dash, J. K.; Chen, L.; Dinolfo, P. H.; Lu, T. M.; Wang, G. C. A Method Toward Fabricating Semiconducting 3R-NbS2 Ultrathin Films. J. Phys. Chem. C 2015, 119, 19763-19771. (38) Ou, X.; Xiong, X.; Zheng, F.; Yang, C.; Lin, Z.; Hu, R.; Jin, C.; Chen, Y.; Liu, M. In Situ X-ray Diffraction Characterization of NbS2 Nanosheets as the Anode Material for Sodium Ion Batteries. J. Power Sources 2016, 325, 410-416. 27



(39) Lin, H.; Yang, L.; Jiang, X.; Li, G.; Zhang, T.; Yao, Q.; Zheng, G. W.; Lee, J. Y. Electrocatalysis of Polysulfide Conversion by Sulfur-Deficient MoS2 Nanoflakes for Lithium-Sulfur Batteries. Energy Environ. Sci. 2017, 10, 1476-1486. (40) Yuan, Z.; Peng, H. J.; Hou, T. Z.; Huang, J. Q.; Chen, C. M.; Wang, D. W.; Cheng, X. B.; Wei, F.; Zhang, Q. Powering Lithium-Sulfur Battery Performance by Propelling Polysulfide Redox at Sulfiphilic Hosts. Nano Lett. 2016, 16, 519-527. (41) Kong, L.; Chen, X.; Li, B. Q.; Peng, H. J.; Huang, J. Q.; Xie, J.; Zhang, Q. A Bifunctional Perovskite Promoter for Polysulfide Regulation Toward Stable LithiumSulfur Batteries. Adv. Mater. 2018, 30, 1705219. (42) Cheng, Z.; Xiao, Z.; Pan, H.; Wang, S.; Wang, R. Elastic Sandwich-Type rGOVS2/S Composites with High Tap Density: Structural and Chemical Cooperativity Enabling Lithium-Sulfur Batteries with High Energy Density. Adv. Energy Mater. 2018, 8, 1702337. (43) Jin, B.; Kim, J. U.; Gu, H. B. Electrochemical Properties of Lithium-Sulfur Batteries. J. Power Sources 2003, 117, 148-152. (44) He, J.; Chen, Y.; Manthiram, A. MOF-derived Cobalt Sulfide Grown on 3D Graphene Foam as an Efficient Sulfur Host for Long-Life Lithium-Sulfur Batteries. iScience 2018, 4, 36-43. (45) Zhou, J.; Li, R.; Fan, X.; Chen, Y.; Han, R.; Li, W.; Zheng, J.; Wang, B.; Li, X. Rational Design of a Metal-Organic Framework Host for Sulfur Storage in Fast, LongCycle Li-S Batteries. Energy Environ. Sci. 2014, 7, 2715-2724. (46) Su, D.; Cortie, M.; Fan, H.; Wang, G. Prussian Blue Nanocubes with an Open Framework Structure Coated with PEDOT as High-Capacity Cathodes for LithiumSulfur Batteries. Adv. Mater. 2017, 29, 1700587. (47) Su, Y. S.; Fu, Y.; Cochell, T.; Manthiram, A. A Strategic Approach to 28


Page 28 of 31

Page 29 of 31 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


Recharging Lithium-Sulphur Batteries for Long Cycle Life. Nat. Commun. 2013, 4, 2985. (48) Deng, Z.; Zhang, Z.; Lai, Y.; Liu, J.; Li, J.; Liu, Y. Electrochemical Impedance Spectroscopy Study of a Lithium/Sulfur Battery: Modeling and Analysis of Capacity Fading. J. Electrochem. Soc. 2013, 160, A553-A558, (49) Peng, X.; Wang, L.; Zhang, X.; Gao, B.; Fu, J.; Xiao, S.; Huo, K.; Chu, P. K. J. Power Sources 2015, 288, 214-220 (50) Cai, J.; Wu, C.; Zhu, Y.; Zhang, K.; Shen, P. K. Sulfur Impregnated N, P CoDoped Hierarchical Porous Carbon as Cathode for High Performance Li-S Batteries. J. Power Sources 2017, 341, 165-174. (51) Zhou, G.; Zhao, Y.; Manthiram, A. Dual-Confined Flexible Sulfur Cathodes Encapsulated in Nitrogen-Doped Double-Shelled Hollow Carbon Spheres and Wrapped with Graphene for Li-S Batteries. Adv. Energy Mater. 2015, 5, 1402263. (52) Zhang, Z.; Li, Q.; Jiang, S.; Zhang, K.; Lai, Y.; Li, J. Sulfur Encapsulated in a TiO2-Anchored Hollow Carbon Nanofiber Hybrid Nanostructure for Lithium-Sulfur Batteries. Chem. Eur. J. 2015, 21, 1343-1349. (53) Hao, Z.; Yuan, L.; Chen, C.; Xiang, J.; Li, Y.; Huang, Z.; Hu, P.; Huang, Y. TiN as a Simple and Efficient Polysulfide Immobilizer for Lithium-Sulfur Batteries. J. Mater. Chem. A 2016, 4, 17711-17717. (54) Liu, Z.; Zheng, X.; Luo, S. L.; Xu, S. Q.; Yuan, N. Y.; Ding, J. N. High Performance Li-S Battery Based on Amorphous NiS2 as the Host Material for the S Cathode. J. Mater. Chem. A 2016, 4, 13395-13399. (55) Mi, Y.; Liu, W.; Li, X.; Zhuang, J.; Zhou, H.; Wang, H. High-Performance LiS Battery Cathode with Catalyst-Like Carbon Nanotube-MoP Promoting Polysulfide Redox. Nano Res. 2017, 10, 3698-3705. 29



(56) Li, X.; Ding, K.; Gao, B.; Li, Q.; Li, Y.; Fu, J.; Zhang, X.; Chu, P. K.; Huo, K. Freestanding Carbon Encapsulated Mesoporous Vanadium Nitride Nanowires Enable Highly Stable Sulfur Cathodes for Lithium-Sulfur Batteries. Nano Energy 2017, 40, 655-662. (57) Li, Z.; Zhang, J.; Guan, B.; Wang, D.; Liu, L. M.; Lou, X. W. A Sulfur Host Based on Titanium Monoxide@Carbon Hollow Spheres for Advanced Lithium-Sulfur Batteries. Nat. Commun. 2016, 7, 13065. (58) Song, H.; Fu, J.; Ding, K.; Huang, C.; Wu, K.; Zhang, X.; Gao, B.; Huo, K.; Peng, X.; Chu, P. K. Flexible Nb2O5 Nanowires/Graphene Film Electrode for HighPerformance Hybrid Li-ion Supercapacitors. J. Power Sources 2016, 328, 599-606.

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Table of Contents

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Nitrogen

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