A spongy mesoporous titanium nitride material as sulfur host for high performance lithium-sulfur batteries

Journal Pre-proof A spongy mesoporous titanium nitride material as sulfur host for high performance lithium-sulfur batteries Hairui You, Mingchen Shi, Junwei Hao, Huihua Min, Hui Yang, Xiaomin Liu PII:

S0925-8388(20)30242-5

DOI:

https://doi.org/10.1016/j.jallcom.2020.153879

Reference:

JALCOM 153879

To appear in:

Journal of Alloys and Compounds

Received Date: 23 November 2019 Revised Date:

11 January 2020

Accepted Date: 15 January 2020

Please cite this article as: H. You, M. Shi, J. Hao, H. Min, H. Yang, X. Liu, A spongy mesoporous titanium nitride material as sulfur host for high performance lithium-sulfur batteries, Journal of Alloys and Compounds (2020), doi: https://doi.org/10.1016/j.jallcom.2020.153879. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Thanks for the guidance to sequence the authors. According to the guideline, the correct order of the authors should be as follow, Hairui You, Mingchen Shi, Junwei Hao, Huihua Min, Hui Yang and Xiaomin Liu The roles of all authors have been explained in the revised manuscript. Hairui You: Conceptualization, Data curation, Methodology, Resources and Writing original draft Mingchen Shi: Formal analysis, Investigation and Project administration Junwei Hao: Investigation, Validation Huihua Min: Visualization, Software Xiaomin Liu and Hui Yang: Funding acquisition, Supervision and Writing - review & editing

A spongy mesoporous titanium nitride material as sulfur host for high performance lithium-sulfur batteries Hairui Youa, Mingchen Shia, Junwei Haoa, Huihua Minb, Hui Yanga* and Xiaomin Liua** a

College of Materials Science and Engineering, Nanjing Tech University, Nanjing,

Jiangsu, People’s Republic of China. b

Electron Microscope Lab, Nanjing Forestry University, Nanjing 210037, Jiangsu,

China. *E-mail address: [email protected] **E-mail address: [email protected]

ABSTRACT Lithium/sulfur (Li/S) batteries have attracted great attention due to high theoretical capacity, rich resources and environmental friendliness. However, the shuttle effect and slow redox reactions deteriorate the electrochemical performance and hinder their practical application. Herein, a spongy mesoporous titanium nitride (SMT) material is synthesized via a simple approach and used as an effective sulfur host. Consequently, the S/SMT electrode, with 70 wt% sulfur content, exhibits high initial capacity (1312 mAh g−1 at 0.1 C), excellent rate capability (620 mAh g−1 at 2.0 C) and low capacity decay rate (0.058% and 0.048% per cycle at 1.0 C and 2.0 C, respectively). Moreover, with a high areal sulfur loading of 3.0 mg cm−2, the cathode still achieves an ultrahigh capacity of 665 mAh g−1 at 0.1 C. Key words: Lithium/sulfur, Mesoporous titanium nitride, Spongy structure, Polysulfides

1

1. Introduction The lithium/sulfur (Li/S) battery is the most promising candidate for the next generation energy storage systems due to its high theoretical capacity (1675 mAh g-1), low cost and environmental friendliness [1-3]. However, there are still some issues, such as the extremely low electrical conductivity of element sulfur and its lithiation products (Li2S2/Li2S), the ‘shuttle effect’ caused by the migration of dissolved lithium polysulfides (LiPSs), and the large volume change during cycling, which deteriorate the electrochemical performance of Li/S batteries and hinder their commercial application. Tremendous efforts have been made to overcome those issues in the past several decades, most of them are focused on incorporating sulfur into various hosts with different morphologies and microstructures, such as nonpolar carbon materials and polar metal compounds. Nonpolar carbon materials may not alleviate the ‘shuttle effect’ efficiently since they only present weak physical adsorption to LiPSs[4-8]. In contrast, polar metal compounds can offer strong chemical adsorption to LiPSs[9-11], and moreover, they may accelerate the conversion of soluble LiPSs to solid precipitates[12], therefore suppressing the ‘shuttle effect’ more effectively. Many of them, including transition-metal oxides[13-16], sulfides[17, 18], carbides[19, 20], and nitrides[12, 21, 22], have been investigated as sulfur hosts extensively. Titanium nitride (TiN), with high electrical conductivity (4.0 × 106 S m-1 at room temperature), can be used as the sulfur host to modify the electric conductivity of the cathode encompassing S/Li2S2/Li2S. It has been reported that HCNs@TiN nanoparticles hosting sulfur as cathode show the discharge capacity of 1097.8 mAh g−1 at 0.1C and retain 812.6 mAh g−1 after 200 cycles, corresponding to the capacity decay rate of 0.13% per cycle[23]. The hollow TiN spheres is employed as cathode to host sulfur, which achieves an initial capacity of 923.3 mAh g−1 at 1 C and maintains 623.3 mAh g−1 after 300 cycles (with the decay rate of 0.11% per cycle)[24]. Obviously, mesoporous TiN is an appropriate host candidate which deserves more research to 2

further improve the electrochemical performance. In this work, a spongy mesoporous titanium nitride (SMT) with large specific surface is designed and synthesized as the host for sulfur. Firstly, with the excellent electrical conductivity, the fabricated SMT host can improve the conductivity of the sulfur cathode. Secondly, the mesoporous structure with large specific surface area can alleviate the shuttle effect not only by physical confinement/chemisorption, but also by offering enough active sites to expedite the reduction of soluble LiPSs to Li2S2/Li2S precipitates. Finally, the large pore volume can accommodate a high sulfur loading and the aroused volume expansion during lithiation. As a result, the S/SMT electrode with 70 wt% sulfur content exhibits a high initial capacity of 1312 mAh g-1, an excellent rate performance and an exceptional cycling performance at 2C with the capacity decay of only 0.048% per cycle within 500 cycles.

2. Experimental 2.1. Synthesis of materials 2.1.1 Synthesis of ZnS template The ZnS template was prepared according to a liquid-phase synthesis method. 1.0 g (or 0.5 g) sodium dodecyl sulfonate (SDS) was dissolved into 50 mL deionized (DI) water at 50 °C. After the obtained solution was cooled down to room temperature, 25mmol Na2S·9H2O was dissolved into it under violent stirring. Then, 50ml 0.5M Zn(CH3COO)2·2H2O solution was added into the above clear solution drop by drop and the white slurry were produced immediately. After 30 min continuous stirring, the formed ZnS nanoparticles were collected by centrifugation, washed for several times with deionized water and followed with freeze-drying. The dispersion degree of ZnS nanoparticles can be controlled by adjusting the concentration of SDS. The samples prepared with different concentrations of SDS are denoted as ZnS-X (X=0.5 or 1.0), where the X value indicates the used quantity (g) of SDS. 3

2.1.2. Synthesis of SMT In order to obtain the spongy mesoporous TiN, the ZnS template was coated by TiO2[25]. The as-prepared ZnS was homogeneously dispersed in ethanol by ultrasonication, followed by the addition of hexadecylamine (HDA) surfactant and ammonia under stirring. Then, 0.4ml titanium isopropoxide (TIP) was added into the dispersion and the mixture was stirred for 10 min. The obtained ZnS/TiO2/HDA was collected by vacuum filtration, washed with ethanol for several times and dried at 60℃ over night. The dried ZnS/TiO2/HDA and melamine were mixed and calcined under N2 gas at 700℃ for 2 h to evaporate the HDA and generate ZnS/TiN. Then hydrochloric acid was used to remove ZnS and the remaining material is spongy mesoporous TiN (marked as SMT). The SMT made from different ZnS-X (X=0.5 and 1.0) is labelled as SMT-0.5 and SMT-1.0, respectively. 2.1.3. Preparation of S/SMT The SMT and the sublimed sulfur powder were mixed at the weight ratio of 3:7. Then the mixture was heated to 155 °C and maintained isothermally for 12 h in a sealed container to fabricate the S/SMT composite. 2.2. Material characterization The X-ray diffraction (XRD) analysis was performed on a DMAX/rB X-ray diffractometer with Cu Kα radiation (Rigaku, Japan). The sulfur loading of S/SMT composites was measured by TGA5500 (TA Instruments, USA). The morphology of samples was characterized by Field-emission scanning electron microscope (FESEM) on JSM-7600F (JEOL, Japan) with the voltage of 30kV and Transmission electron microscope (TEM) on JEM-2010 UHR (JEOL, Japan) with the voltage of 200kV. X-ray

photoelectron

spectroscopy

(XPS)

analysis

was

carried

out

with

ESCALAB-250XI Scientific spectrometer (Thermofisher, USA). The nitrogen 4

adsorption-desorption isotherms were measured by ASAP 2020M (Micromeritics, USA). 2.3. Electrochemical measurements The S/SMT composite was mixed with acetylene black and poly(vinylidene fluoride) at the weight ratio of 8:1:1 in N-methyl pyrrolidone to form a homogeneous slurry. The slurry was spread onto an Al foil. The cathode was dried at 50 °C for 12 h in a vacuum oven and the loading density of sulfur was about 1.2 mg cm −2. The electrode with high sulfur mass loading of 3.0 mg cm-2 was prepared through the same process. The CR2032 coin cells were assembled with anode (Lithium foil), separator (Celgard 2400 membrane), and cathode (S/SMT electrode) in an argon-filled

glove

box.

The

electrolyte

was

1

mol

L-1

lithium

bis(trifluoromethane-sulfonyl)imide in 1,2-dimethoxyethane and 1,3-dioxolane(v/v = 1:1) with 2.0 wt% of LiNO3. Cycling tests of the batteries were performed within a potential window of 1.7–2.8 V versus Li+/Li. Cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS) data were recorded using Zennium electrochemical workstation. The CV test was carried out in the potential range of 1.7-2.8 V with the scan rate of 0.1 mV s−1. The EIS measurement was performed in the frequency range of 10 mHz to 100 kHz.

3. Results and discussion The synthesis process of SMT is shown in Fig. 1. The HDA molecules are evenly distributed on the surface of ZnS templates, which anchor the TiO2 (hydrolyzed from TIP) via hydrogen bonding, resulting in a layer composed of TiO2 and HDA to wrap the ZnS particles (ZnS/TiO2/HDA). As the reaction proceeds, the ZnS/TiO2/HDA particles agglomerate randomly. The obtained ZnS/TiO2/HDA agglomerates are mixed with melamine and calcined at 700°C to generate the ZnS/TiN with numerous meso-pores. Those pores are produced from the evaporation of HDA (b.p. 177.9℃) 5

[25]. The following removal of ZnS by hydrochloric acid creates lots of cavities, making the final mesoporous TiN with the spongy structure (denoted as spongy mesoporous titanium nitride (SMT)). Finally, the S/SMT composites are fabricated by impregnating the sulfur into the interior of the above SMT at 155 oC. The morphology of the synthesized ZnS-X (1.0 or 0.5) is displayed in Fig. S1. It can be seen clearly that the ZnS-1.0 presents better dispersion than ZnS-0.5 templates, which is consistent with the used quantity of SDS. The crystal structure of the home made ZnS nano-particles matches well with wurtzite-type ZnS (JCPDS no. 65-0309, Fig. 2a). After TiO2 coating and the calcination with melamine, the ZnS in the obtained ZnS/TiN is the mixture of wurtzite-type and blende-type (JCPDS no. 36-1450, Fig. S2).[26] Also it can be observed that there is trace of TiN in the composite (JCPDS no. 65-0565, marked by star in Fig. S2). After removing the ZnS by HCl, the prepared SMT is composed of amorphous carbon (produced by the melamine) and cubic-type TiN (Fig. 2b) only. It can be seen from the TEM image (Fig. 2c) that the TiN crystallite presents well-resolved lattice fringes with interlayer distance of 0.212 nm and 0.244 nm, corresponding to the (200) and (111) crystal plane of cubic TiN. The nitrogen adsorption-desorption isotherms for SMT-1.0, SMT-0.5 and ZnS/TiN samples are obtained and presented in Fig. 2d. All materials exhibit typical type IV adsorption isotherm, which indicates the existence of mesoporous composites [27, 28]. The pore size distribution (inset of Fig. 2d) estimated by the Barrett-Joyner-Halenda (BJH) method suggests the mesoporous TiN with the majority pore size below 10 nm.

The specific surface area and the pore volume of the

materials are summarized in Table 1. Obviously, the SMT samples present much greater specific surface area and pore volume than ZnS/TiN, indicating the formation of a large number of cavities during the hydrochloric acid etching process to remove ZnS. In addition, the sample SMT-1.0 has higher specific surface area and pore volume than SMT-0.5, which may be attributed to less aggregation of ZnS-1.0. The ZnS/TiN sample possesses a relatively flat surface (Fig. S3), while the 6

derived sample SMT exhibits a porous structure (Fig. 3a and 3b). It is noteworthy that a few cavities marked by the red circles can be seen in the SMT sample (Fig. 3c and 3d) after etching ZnS, indicating that the ZnS particles are not covered by TiN and prone to be etched. In addition, the SMT-0.5 sample holds larger cavities than SMT-1.0 since the template of SMT-0.5 presents more serious agglomeration. It can be deduced that massive cavities are buried in the main body of the SMT samples, resulting in the sponge structure. Those cavities provide sufficient space not only to store sulfur, but also to accommodate the volume expansion occurred in the lithiation process. In addition, the 3D TiN framework of the SMT samples is favorable for electron conduction and adsorption of the LiPSs, while the interconnected mesopores allow the soakage of electrolyte. Finally, the ‘shuttle effect’ can be alleviated effectively since the acceleration of the electron conduction in the host and the Li+ ion transportation through electrolyte can facilitate the conversion of the adsorbed LiPSs The XPS (Fig. 4) was employed to investigate the chemical states of the elements. The strong Ti 2p signal, at binding energy ranging from 453 to 467eV, can be divided into five peaks, including the Ti–N bond (455.7 and 462.2eV), Ti–N–O bond (456.6 and 463.7eV) and Ti–O bond at 458.0eV. Obviously, an oxide/oxynitride passivation layer forms on the surface of SMT, and such strong chemisorption can effectively suppress LiPSs migration in the electrolyte [29, 30]. The N 1s signal is divided into three peaks at 395.9, 397.9 and 399.8eV, corresponding to N-C, Ti–N and Ti–N–O bond [18, 24, 31]. The two peaks at higher binding energy are consistent with the Ti 2p spectrum and the rest one at lower binding energy can be ascribed to the residues from calcining melamine [21]. The TGA curves in Fig. S4 demonstrate the sulfur loading of both S/SMT-1.0 and S/SMT-0.5 composites are nearly 70 wt%. The electrochemical performances of the S/STM-1.0 and S/STM-0.5 based cells were investigated using cyclic voltammetry. As depicted in Fig. 5a, both CV curves exhibit two reduction peaks and one broad oxidation peak. The reduction peaks around 2.3 V (R1) and 2.0 V (R2) are associated with the reduction of sulfur (S8) to soluble long-chain LiPSs (Li2Sx, 6≤x≤8) and the further conversion to insoluble 7

short-chain lithium sulfide (Li2S2/Li2S) precipitates, respectively, while the oxidation peak around 2.4V (O1) is attributed to the oxidation of Li2S/Li2S2 to long chain lithium polysulfides and finally to elemental sulfur [32]. It can be seen clearly that the S/STM-1.0 based cell presents sharper/more defined peaks, and moreover, smaller potential gap between O1 and R2 than the S/STM-0.5 based cell, suggesting that the S/SMT-1.0 based cell possesses faster reaction kinetics[18]. The reason lies in the phenomena that the S/STM-1.0 composite possesses more surface area for the charge transfer reactions. In addition, the initial five CV cycles of the S/SMT-1.0 based cell are also shown in Fig. 5b. The small difference observed between the 1st and 2nd cycle can be attributed to the form of SEI films (in the cathodic scan) and the redistribution of sulfur species on conductive substrate (in the anodic scan)[31]. Besides, there is no obvious peak shift or current change during the subsequent cycles, indicating the good reversibility of such electrochemical system based on the S/SMT-1.0 composite. The rate capabilities of both samples were measured at different C-rates and shown in Fig. 6a, 6b and Fig. S5. The charge/discharge curves of both S/SMT-1.0 and S/SMT-0.5 based cell maintain the typical plateaus well even under high C-rates (Fig. 6a and Fig. S5), indicating that the SMT sample can provide favorable conduction paths for both electrons and Li-ions to ensure the fast kinetics of charge transfer reactions. As showed in Fig. 6b, the S/SMT-1.0 based cell delivers high discharge capacities of 1217, 917, 803 and 615 mAh g−1 at the C-rate of 0.1, 0.5, 1 and 2C, respectively. The available discharge capacity still reaches 998 mAh g−1 when the C-rate is shifted back to 0.1 C after a series of high rate tests, verifying the structure stability of our SMT sample. In comparison, the S/SMT-0.5 based cell delivers a lower discharge capacity of 1097 mAh g−1 at 0.1 C, which drops quickly to 493 mAh g−1 at 2.0 C. Based on the above data, the values of Q1 (the capacity of the higher discharge plateau), Q2 (the capacity of the lower discharge plateau) and the ratio of Q2/Q1 at various C-rates for both samples are calculated and displayed in Fig. 6c and 6d [33]. It can be seen clearly that the S/SMT-1.0 sample has higher sulfur utilization since it 8

exhibits higher Q1 and Q2 values at all test C-rates than the S/SMT-0.5 sample. The ratio of Q2/Q1 is usually less than 3 (the theoretical value is 3), which is due to the inadequate reaction and the migration of soluble high order LiPSs [34, 35]. Obviously, when being cycled at the same C-rate, S/SMT-1.0 based cell exhibits a higher Q2/Q1 value (1.99-1.47) than the S/SMT-0.5 based cell (1.90 - 1.01). Moreover, the Q2/Q1 value drops more rapidly for the S/SMT-0.5 based cell as the C-rate increases. Both of them prove that the S/SMT-1.0 sample can suppress the shuttle effect efficiently since the higher Q2/Q1 values hint the weaker shuttle effect. Besides rate capability, cycling life performance is also crucial for Li/S battery. As presented in Fig. 6e and f, the S/SMT-1.0 based cell exhibits an initial specific capacity of 764 mA h g−1 at 1C, which decreases to 396 mAh g−1 after 800 cycles, corresponding to a fading rate as low as 0.048% per cycle. Even being cycled at 2C, that cell can still provide up to 620 and 440 mAh g−1 at the 1st and 500th cycle, respectively, with the fading rate of 0.058% per cycle. In comparison, The S/SMT-0.5 based cell shows faster capacity fading rate, up to 0.065% per cycle at 1.0 C (737 and 352 mAh g−1 at the 1st and 800th cycle, respectively) and 0.076% per cycle at 2.0 C (600 and 373 mAh g−1 at the 1st and 500th cycle, respectively). From the perspective of practical application, the S/STM-1.0 based cell with high sulfur loading (3.0 mg cm-2) was also fabricated and its cycling performance was investigated under 0.1C (Fig. S6). This cell delivers an initial capacity up to 665 mAh g-1, which decreases to 406 mAh g-1 after 250 cycles, equivalent to a capacity retention of about 61%. To further explore whether the S/SMT electrodes can enhance the redox kinetics, EIS measurements are carried out and presented in Fig. 7. Both cells are composed of a depressed semicircle and an inclined line, which is associated with the charge transfer resistance (Rct) and the Warburg diffusion process, respectively[18, 36]. The Warburg slope is used (Fig. 7b) to calculate the Li+ diffusion coefficient (DLi+ ) according to the Warburg coefficient (σW) and the following equation[37]: =

(1) 9

where R, T, A, F and C are Gas Constant, temperature, area of the electrode, Faraday Constant and Li+ concentration. The results are summarized in Table 2. It is obvious that the S/SMT-1.0 cathode shows much lower Rct and faster lithium ion diffusion coefficient than S/SMT-0.5, demonstrating that the S/SMT-1.0 based cell is more favorable for obtaining good electrochemical performance. Because of the larger reaction area, the S/SMT-1.0 electrode can provide much more active sites to catalytic the reaction of LiPSs conversion, and finally, achieve excellent cyclic stability and rate capability.

4. conclusion In conclusion, a spongy mesoporous titanium nitride has been fabricated and employed as sulfur host in this context. On one hand, the host alleviates the shuttle effect not only by physical confinement/chemisorption, but also by offering enough active sites to expedite the reduction of soluble LiPSs to Li2S2/Li2S precipitates. On the other hand, the spongy porous structure provides enough space to store sublimed sulfur and effectively suppress the volume expansion. Owing to those advantages, the SMT based cell with sulfur loading up to 70 wt% exhibits a high initial capacity of 1312 mAh g−1 at 0.1 C, an excellent rate capability of 620 mAh g−1 at 2.0 C and long cycle stability with the capacity decay rate of 0.058% and 0.048% per cycle at 1.0 C and 2.0 C, respectively. In addition, even when the areal sulfur loading of the electrode reaches 3.0 mg cm−2, the SMT based cell can deliver the capacity of 665 mAh g-1 at 0.1 C and retain 61% capacity after 250 cycles. This work provides a potential strategy to improve the electrochemical performance of Li/S batteries.

Acknowledgements This work was financially supported by the National Natural Science Foundation of China (21573109 and 21206069) and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). 10

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Table 1 Surface area and pore volume of SMT-1.0, SMT-0.5 and ZnS/TiN.

Sample

surface area (m2 g-1)

pore volume (cm3 g-1)

SMT-1.0

285.82

0.44

SMT-0.5

216.06

0.39

ZnS/TiN

70.68

0.14

Table 2 Electrochemical impedance parameters of the S/SMT-1.0 and S/SMT-0.5.

sample

Rs (Ω)

Rct (Ω)

DLi+ (cm2·s-1)

S/SMT-1.0

2.83

71.58

2.49× ×10-10

S/SMT-0.5

2.08

129.10

1.93× ×10-10

Fig. 1. Schematic illustration for the preparation of SMT Fig. 2. (a) XRD patterns of ZnS. (b) XRD patterns of SMT. (c) TEM image of SMT. (d) N2 adsorption-desorption isotherms of the SMT-1.0, SMT-0.5 and ZnS/TiN Fig. 3. (a) and (b) The low-magnification SEM images of SMT. The SEM images of (c) SMT-1.0 and (d) SMT-0.5. Fig. 4. XPS results for SMT-1.0 composite of (a) Ti 2p and (b) N 1s. Fig. 5. (a) CV profiles of S/SMT-1.0 and S/SMT-0.5 at first cycle. (b) The subsequent 5 cycles of the S/SMT-1.0 Fig. 6. (a) Charging/discharging curves of S/SMT-1.0 based cells at various C-rates. (b) Rate performance test of S/SMT-1.0 and S/SMT-0.5 based cells. Q1, Q2 and Q2/Q1 at different C-rates of (c) S/SMT-1.0 and (d) S/SMT-0.5 based cells. Cycling performance and coulombic efficiency (CE) of S/SMT-1.0 and SMT-0.5 based cells at (e) 1.0 C, (f) 2.0 C. Fig. 7. (a) Nyquist plots of cathodes. (b) Correlation between Z’ and ω −1/2 in low frequencies derived from EIS results.

Fig. 1. Schematic illustration for the preparation of SMT

Fig. 2. (a) XRD patterns of ZnS. (b) XRD patterns of SMT. (c) TEM image of SMT. (d) N2 adsorption-desorption isotherms of the SMT-1.0, SMT-0.5 and ZnS/TiN

Fig. 3. (a) and (b) The low-magnification SEM images of SMT. The SEM images of (c) SMT-1.0 and (d) SMT-0.5.

Fig. 4. XPS results for SMT-1.0 composite of (a) Ti 2p and (b) N 1s.

Fig. 5. (a) CV profiles of S/SMT-1.0 and S/SMT-0.5 at first cycle. (b) The subsequent 5 cycles of

the S/SMT-1.0

Fig. 6. (a) Charging/discharging curves of S/SMT-1.0 based cells at various C-rates. (b) Rate performance test of S/SMT-1.0 and S/SMT-0.5 based cells. Q1, Q2 and Q2/Q1 at different C-rates of (c) S/SMT-1.0 and (d) S/SMT-0.5 based cells. Cycling performance and coulombic efficiency (CE) of S/SMT-1.0 and SMT-0.5 based cells at (e) 1.0 C, (f) 2.0 C.

Fig. 7. (a) Nyquist plots of cathodes. (b) Correlation between Z’ and ω −1/2 in low frequencies derived from EIS results.

Highlights A novel spongy mesoporous titanium nitride (SMT) material is designed and used as an effective sulfur host. The spongy structure can be designed by the dispersion degree of ZnS nanoparticles easily which is consistent with the used quantity of SDS. The SMT based cell, with a high sulfur content (70 wt%), exhibits an extraordinary initial capacity (1312 mAh g−1 at 0.1 C), excellent rate capability (620 mAh g−1 at 2.0 C) and low capacity decay rate (0.058% and 0.048% per cycle at 1.0 C and 2.0 C, respectively). Even with a high areal sulfur loading of 3.0 mg cm−2, the cathode still achieves an ultrahigh capacity of 665 mAh g−1 at 0.1 C.

Declaration of Interest Statement No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed.