Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring

Subscriber access provided by UNIV OF DURHAM

Energy, Environmental, and Catalysis Applications

Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring Behavior of Polysulfides for Lithium-Sulfur Batteries Yingze Song, Wen Zhao, Xingyu Zhu, Li Zhang, Qiucheng Li, Feng Ding, Zhongfan Liu, and Jingyu Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b02920 • Publication Date (Web): 24 Apr 2018 Downloaded from http://pubs.acs.org on April 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 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 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.

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 30 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

Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring Behavior of Polysulfides for Lithium-Sulfur Batteries Yingze Songa†, Wen Zhaob†, Xingyu Zhua, Li Zhanga*, Qiucheng Lia, Feng Dingb, Zhongfan Liua and Jingyu Suna* a

Soochow Institute for Energy and Materials InnovationS (SIEMIS), Key Laboratory of

Advanced Carbon Materials and Wearable Energy Technologies of Jiangsu Province, Soochow University, Suzhou, Jiangsu 215006, P. R. China b

Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS),

Ulsan 689-798, Republic of Korea KEYWORDS: lithium-sulfur batteries, vanadium dioxide, graphene, ultrafast anchoring, polysulfides

ABSTRACT: Lithium-sulfur (Li-S) battery has been deemed as one of the most promising energy-storage systems owing to its high energy density, low cost, and environmental benignancy. However, the capacity decay and kinetic sluggishness stemming from polysulfide shuttle effects have by far posed a great challenge on the practical performance. We herein demonstrate the employment of low-cost, wet-chemistry-derived VO2 nanobelts as the effective host additives for the graphene-based sulfur cathode. The VO2 nanobelts displayed an ultrafast

ACS Paragon Plus Environment

1

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 30

anchoring behavior of polysulfides, managing to completely de-color the polysulfide solution in 50 seconds. Such a fast and strong anchoring ability of VO2 was further investigated and verified by experimental and theoretical investigations. Benefited from the synergistic effect exerted by VO2 in terms of chemical confinement and catalytic conversion of polysulfides, the Li-S batteries incorporating VO2 and graphene manifested excellent cycling and rate performances. Notably, the batteries delivered an initial discharge capacity of 1405 mAh g-1 when cycling at 0.2 C, showed an advanced rate performance of ~830 mAh g-1 at 2 C, as well as maintained a stable cycling performance at high current densities of 1 C, 2 C, and 5 C over 200 cycles, paving a practical route towards the cost-effective and environmentally-benign cathode design for highenergy Li-S batteries.

1. Introduction Rechargeable lithium-sulfur (Li-S) batteries have to date captured vast interest as promising energy storage systems due to their exceptional theoretical capacity (1672 mAh g-1), low-cost, high abundance of sulfur, and environmental benignancy.1-5 Despite these favorable advantages, the practical performances of Li-S battery are still handicapped by far by a multitude of obstacles: mainly, the highly insulating nature of sulfur and solid discharge products Li2S, the “shuttle” of soluble polysulfides (Li2Sx, 4 ≤ x ≤ 8) between the anode and cathode, as well as the noticeable volume changes within electrodes during cycling, which would unavoidably give rise to limited sulfur utilization, severe anode degradation, low Coulombic efficiency and rapid capacity fading of batteries.6-8


2

Page 3 of 30 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


In response, to tackle these problems, tremendous efforts have been exerted to design appropriate architectures and host materials for sulfur cathodes. Inspired by the pioneer work from Nazar et al. employing porous carbon CMK-3 to accommodate sulfur,1 fruitful achievements have been attained thus far in using carbonaceous supporting materials with tailored morphology, controlled surface area and enriched surface chemistry.9-13 Carbon hosts enable the improvement of electrical conductivity of sulfur cathodes, the confinement of soluble polysulfides as well as the mitigation of electrode volume changes during lithiation/delithiation processes. Unfortunately, the pure carbon-sulfur hybrid cathodes still fail, to some extent, in addressing the poor cycle and rate performances. This has been speculated to be due to the weak physical interaction between the non-polar carbon and the polar Li2Sx species that results in a less efficient trapping.14,15 Additionally, the introduction of high mass fraction of carbon host materials also results in a lower gravimetric/volumetric energy density. In light of this, a ubiquitously employed strategy deals with the small dosage of polar materials (such as metal oxides, sulfides, nitrides and carbides) into sulfur cathodes or as coating layers targeting chemical anchor of polysulfides.16 Indeed, recent years have seen exciting progress in exploring polar additives as effective polysulfide immobilizers, including Ti4O7,14 TiO2,17,18 MnO2,19-21 MoS2,22 MXene,23 Co3O4,24 BaTiO3,25 Co4N26 etc. Li-S batteries based on these materials are proven to have depressed shuttle effect, enhanced sulfur utilization, and improved cycle stability. More interestingly, several recently-investigated polar hosts (such as Nb2O5,27 Co9S8,28 VS2,29 TiN,30 ReS231) designed for efficient polysulfide entrapment have also been found electrocatalytically active to accelerate the kinetics of polysulfide redox reactions. The conversion of


3


Page 4 of 30

polysulfide back to lithium sulfides is an effective strategy to fundamentally solve the polysulfide shuttle effect.32 For instance, Sun et al. reported the incorporation of VN nanoribbons with porous three-dimensional graphene foams to produce advanced Li-S battery cathode, realizing a high specific capacity of 1471 mAh g-1 at 0.2 C (1 C = 1675 mA g-1) and an excellent rate performance of 953 mAh g-1 at 2 C.33 It was demonstrated therein that VN promoted the polysulfide redox apart from exhibiting strong chemical anchoring of the polysulfides. Similarly, recent investigations by Yuan et al.34 and Zhou et al.29 integrated theoretical calculations and experimental design to systematically elucidate such dual functional roles played by a series of sulfide hosts. Undoubtedly, exploring novel host materials that endow synchronous trapping and catalyzing effect, as well as developing facile yet cost-efficient strategies that lead to optimized cathode configurations would be appealing and imperative to boost the electrochemical performance of Li-S batteries. Vanadium dioxide (B) has long been investigated as a promising electrode material especially in Li-ion batteries because of its high abundance, tailorable morphology, rapid ion diffusion rate and low cost.35,36 Moreover, it has recently been reported that group-V metal oxides such as Nb2O5 and V2O5 could serve as effective host mediators for sulfur cathodes.37 In contrast with other metal oxides such as TiO2, Ti4O7, Co3O4, Cu2O, V2O3, the redox potential of VO2 lies just exactly above the typical redox potential range (>2.4 V) of soluble polysulfides, which endows VO2 high chemical reactivity with polysulfides.36 Motivated by these attractive features, we herein demonstrate an employment of wet-chemistry-derived VO2 (B) nanobelts as novel and effective additives for graphene-based sulfur host in Li-S batteries. The VO2 nanobelts prepared via a facile


4

Page 5 of 30 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


and scalable fashion not only exhibit strong affinity to polysulfides, but also propel the kinetics of polysulfide redox reactions. The ultrafast anchoring behaviour was visualized throughout de-coloring the polysulfide solution in 50 s, and was further verified by experimental and theoretical investigations. The employment of graphene could realize a homogeneous distribution of sulfur and provide a highly conductive platform for the polysulfide conversion.38,39 As such, the Li-S battery incorporating VO2 (~4 wt%) and graphene manifested excellent cycling and rate performances as compared to those of pure graphene-derived counterparts. Notably, the VO2-graphene hybrid cathode delivered a remarkable initial discharge capacity of 1405 mAh g-1 when cycling at 0.2 C, showed an advanced rate performance of ~830 mAh g-1 at 2 C, as well as maintained a stable cycling performance at high current densities of 1 C, 2 C and 5 C over 200 cycles. The present findings offer a novel insight into the desirable design of cost-effective and environmentally-benign cathode materials towards advanced Li-S batteries.

2. Experimental Section Preparation of VO2 (B) nanobelts: VO2 (B) nanobelts was synthesized via a scalable wetchemistry route followed by a freeze-drying process, as shown in Figure 1a. Briefly, 0.6 g NH4VO3 as the vanadium precursor was dissolved in the aqueous mixture (150 mL) of deionized water and ethanol with a volume ratio of 9:1. The pH value of mixture was adjusted to 2 by using HCl (1 mol L-1) and then transferred into a Teflon-lined autoclave. The autoclave was kept under the temperature of 180 oC for 24 h. The VO2 (B) product was finally obtained after rinsing and freeze-drying. In parallel, graphene oxide (GO) flakes were first synthesized from natural graphite via a modified Hummers’ method. where resulting GO flakes were heated at 650 oC for


5


Page 6 of 30

5 h at a tube furnace in an Ar/H2 atmosphere to produce high-quality reduced GO (RGO) product (Figure S1, Supporting Information). Fabrication of nano sulfur-graphene hybrids: As illustrated in Figure 1b, nano sulfurgraphene was prepared with the aid of the sulfur-amine chemistry, according to the previous reported procedure.40 In general, 50 mg of RGO was added into 120 mL solution mixture of deionized water and ethanol with a volume ratio of 10:2 and sonicated for 40 min to obtain the graphene dispersion. Concurrently, 200 mg of sublimed sulfur (99.95% metals basis, Aladdin, China) was dissolved in a 12 ml of ethylenediamine anhydrous (99% AR, Macklin, China) to generate sulfur-amine precursor. The sulfur-amine precursor was dropped in RGO dispersion at a speed of 2 mL min-1, followed by stirring for 30 min. The final product was filtered, rinsed and dried at 50 oC for 12 h in vacuum. Finally, nano sulfur-graphene hybrid could be targetedly obtained (Figure S2). Adsorption tests: Li2S6 solution with a concentration of 7 mmol L-1 (calculated based on sulfur content) was readily fabricated by dissolving within certain amounts of dioxolane/dimethoxyethane mixture. 20 mg of VO2, V2O5, RGO was added into the Li2S6 solution (4 mL), respectively, followed by a gentle shake. The whole testing process was carried out in an Argonfilled glove box. Material characterization: Morphologies of VO2 nanobelts and VO2/G/S cathode were inspected using a Hitachi SU8010 Scanning Electron Microscopy (SEM). Detailed structures and elemental maps of products were observed by a Tecnai G2 F20 S-TWIN Transmission Electron Microscopy (TEM) with the accelerating voltage of 200 kV, which is also capable of imaging in Scanning Transmission Electron Microscope (STEM) mode. X-ray diffraction (XRD) pattern was recorded using a Bruker D8 Advance Diffractometer. Raman spectra of VO2 and graphene,


6

Page 7 of 30 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


as well as the in-situ Raman spectra were collected using a HR Evolution Raman Spectroscopy with an excitation wavelength of 532 nm. The X-ray photoelectron spectroscopy (XPS) spectra were collected using an Escalab 250Xi Spectrophotometer. Ultraviolet-visible (UV-Vis) absorption spectra were recorded by using a Lambda 750S UV/Vis/NIR Spectrophotometer. The surface area data of as-obtained materials were collected on a Tristar II 3020 Surface Area Analyzer. Thermogravimetric analysis (TGA) of nano sulfur-RGO was carried out using a TG/DTA7300 Thermogravimetric/Differential Thermal Analyzer. The TGA measurement was carried out in pure N2 atmosphere in the temperature range from 50 °C to 600 °C at the heating rate of 20 °C min-1. Electrochemical characterization: Electrochemical measurements on VO2/G/S and G/S cathodes were operated employing coin-type (LIR 2032) batteries. In detail, VO2/G/S was mixed with super P carbon black and LA132 aqueous binder (Chengdu Indigo Power Sources Co., Ltd) with a weight ratio of 8:1:1 with the aid of a twin-shaft mixer, which enables the effective prevention of material aggregation (Figure 1b). The content of VO2 in the entire cathode materials was kept at ~4 wt% (10 wt% content was also attempted). The as-prepared slurry was cast onto an Al foil (99.99% purity with a thickness of 20 µm). The obtained laminates were punched into circle discs of ca. 1.33 cm2 and dried at 50 °C under vacuum for 12 h prior to use. The batteries were assembled with VO2/G/S cathode, separator (Celgard 2400), lithium anode, and electrolyte in an argon-filled glove box. The electrolyte was 1 M LITFSI in a mixed solution of dimethoxyethane (DME)/1,3dioxolane (DOL) (1:1 in volume) with 5 wt% of LiNO3 as additive (MJS Energy Technology, China). Typical cells were assembled by a sulfur loading of 1.4-2.0 mg cm-2 (70 wt% sulfur content according to the TGA measurement, Figure 1c) and an


7


Page 8 of 30

electrolyte/sulfur ratio of 13:1 (µL mg-1). It is evident from microscopic characterization that all the materials are uniformly dispersed in the cathode (Figure 1d, Figure S3). The thickness of a representative cathode observed from the cross-sectional SEM image (Figure 1d inset) is ~25 µm, corresponding to a sulfur loading at ~1.6 mg cm-2. A Land CT2001A multichannel battery testing system was employed to evaluate the electrochemical performances of batteries including charge-discharge profiles, rate performance and cycling stabilities. The charge-discharge rates were calculated with respect to the theoretical capacity of sulfur (1672 mAh·g-1). The cyclic voltammograms (CV) and the electrochemical impedance spectroscopy (EIS) measurements were performed on an Autolab potentiostat PGSTAT302N (Autolab Instruments, Netherland). The scan rate for CV measurements varied from 0.05 to 0.5 mV s-1. The EIS tests were performed by applying an alternating current in the frequency range from 100 kHz to 0.01 Hz with 5 mV amplitude. For a practical demonstration, the as-assembled Li-S batteries in a tandem connection based on VO2/G/S cathode can power a light-emitting diode (LED) panel (Figure 1e). Theoretical calculation: Density functional theory (DFT) calculations were performed with the Vienna ab initio Simulation Package (VASP).41 The exchange-correlation functional was described by the Perdew-Burke-Ernzerhof version of generalized gradient approximation and the core region by the projector augmented wave method with the cutoff of plane wave set as 400 eV. A 1×1×1 k-point mesh is used. The vacuum layer was larger than 10 Å to avoid interactions of neighboring images. Using the plane-wave-based total energy minimization, all structures were fully relaxed until the force on each atom was less than 0.01 eV Å-1.


8

Page 9 of 30 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


3. Results and Discussion VO2 nanobelts were fabricated by a simple one-step hydrothermal route. The assynthesized VO2 nanobelts are of uniform size and shape distributions, as witnessed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) shown in Figure 2a and b, respectively. The lateral sizes of VO2 nanobelts typically vary from 30 to 80 nm in width and several micrometers in length (Figure 2c). Meanwhile, VO2 nanobelts possess a surface area of 32.5 m2 g-1 based on the Brunauer-Emmett-Teller (BET) results (derived from the N2 adsorption/desorption isotherm in Figure S4). Such nanobelt-shaped VO2 with fluffy features would offer ample sites for accommodating soluble polysulfides and is accordingly beneficial to mitigating the shuttle effects. Moreover, the strong adsorption and activation sites at the interfaces between VO2 and electrolyte might lead to improved polysulfide redox kinetics. Detailed inspections using high-resolution TEM (HRTEM) in combination with selected-area electron diffraction (SAED) disclose that VO2 nanobelts are well crystallized with displayed lattice fringe spacing of ~0.35 nm, in good agreement with the spacing of the (110) plane of VO2 (Figure 2d). The crystal phase of as-obtained VO2 was also analyzed by X-ray diffraction (XRD), where all the reflection patterns can be readily indexed to VO2 (B) (JCPDS No. 31-1438), as depicted in Figure 2e. Further characterization by Raman spectroscopy was carried out to verify the composition of the prepared product. As shown in Figure 2f, the main Raman peaks locating at 138, 276, 403, 691 and 989 cm-1 are associated with the bending vibrations of V-O-V, V=O, and V-O-O bonds, as well as the stretching vibrations of V2-O and V=O bonds, respectively.42 Moreover, the chemical constitution of VO2 was identified by X-ray photoelectron spectroscopy (XPS). The XPS survey spectrum


9


Page 10 of 30

confirms the presence of V and O elements (Figure S5a). The V2p3/2 signal within the high-resolution V2p spectrum deconvolutes into peaks with binding energies centred at 516.3 and 517.6 eV (Figure S5b), which can be attributed to V4+ and V5+ ions, respectively.37 This implies that a discontinuous V2O5 passivation layer was formed on the surface of VO2 nanobelts because of the air-sensitive feature of VO2. To probe the anchoring effect of VO2 with respect to polysulfides, adsorption ability tests of VO2 and graphene (RGO, abbreviated as ‘G’) were performed in parallel for direct visualization. The samples with the same weight of 20 mg were added in sealed vials containing Li2S6 (7 mmol L-1) dissolved in certain amounts of DOL/DME mixture, respectively. As depicted in the Figure 3a inset, the digital photograph exhibits that the Li2S6 solution can be surprisingly de-colored in 50 s by VO2 with the aid of a gentle stirring, suggesting its remarkable polysulfide adsorption capability as compared to other reported materials (Table S1). In comparison, the solution with the addition of pure graphene remains yellow as initial. Furthermore, ultraviolet-visible (UV-Vis) absorption measurements were conducted to investigate the concentration differences of Li2S6 upon adding VO2 and graphene. It can be clearly observed in Figure 3a that the absorption signal of Li2S6 in the visible light range vanishes after the dosage of VO2 in sharp contrast to the scenario of graphene, indicating that polar VO2 nanobelts could suppress the shuttle effect of polysulfides via the enhanced entrapment ability. Moreover, Figure S6 discloses the adsorption capability of V2O5 and VO2 with respect to Li2S6 solution, where a sharp contrast exists between the de-coloring time. Further investigation shows there is no marked difference between the BET surface area values of V2O5 (12.6 m2 g-1) and VO2 (Figure S7). These results indicate that VO2-surface-bound, interspersed V2O5 exerts


10

Page 11 of 30 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


negligible effect on the ultrafast adsorption ability of VO2. In turn, scanning transmission electron microscopy (STEM) imaging and elemental mapping within a representative area was carried out to examine the sulfur distribution on the VO2 nanobelts after Li2S6 adsorption (Figure 3b). Note that the VO2 nanobelts after Li2S6 adsorption was thoroughly washed by using DME solution. The STEM micrograph (Figure 3c) and corresponding elemental maps of vanadium (Figure 3d, e), oxygen (Figure 3f) and sulfur (Figure 3g) manifest that sulfur is homogenously distributed on the nanobelt surface, indicative of tight interaction between the VO2 and polysulfide. In particular, the strong adsorption and trapping behavior of VO2 for polysulfides were verified by in-situ Raman technique. Figure 3h presents the in-situ Raman spectra of the electrolyte obtained at 0.2 C in the first cycle of discharging process with VO2/G composite serving as the sulfur host. Upon discharge, the Raman signals of soluble Li2S8 (~279 cm-1) and Li2S6 (~178 and 397 cm-1) gradually decrease and finally disappear in the course of further discharging.43 This is because of the strong and ultrafast entrapment of polysulfides by VO2, which enables suppressed polysulfide shuttling. In contrast, pure graphene cathode in absence of VO2 additive only displays limited anchoring ability towards polysulfides, where the corresponding in-situ Raman spectra show pronounced polysulfide signals throughout the whole discharging process (Figure S8). First-principles theoretical calculations were performed to substantiate the strong interaction and probe the existing catalytic effects between VO2 and Li2Sx (x = 4, 6, and 8) clusters. Figure 4a shows the optimized structures of Li2S6 cluster adsorbed on Hterminated VO2 (010) surfaces. Considering the preparation procedure and the chemical environment of VO2 in the electrode, H-terminated model is more realistic. Large


11


Page 12 of 30

deformation of Li2Sx clusters can be found in both half-H-terminated and full-Hterminated cases, indicating relatively strong interaction between lithium polysulfide and VO2. Figure 4b discloses the calculated binding energy values. The binding energy could be defined as the energy difference between the Li2Sx-VO2 adsorbed system (E୐୧మ ୗೣି୚୓మ ) and the summation of pure Li2Sx (E୐୧మ ୗೣ ) and pure VO2 (E୚୓మ ), which can be expressed as Eୠ = E୐୧మ ୗೣ + E୚୓మ − E୐୧మ ୗೣ ି୚୓మ . In this respect, larger binding energy value indicates stronger interaction. The binding energy between soluble polysulfide (Li2S4, Li2S6, and Li2S8) and half-H-terminated VO2 was calculated to be 4.86, 4.18, and 5.94 eV, respectively, suggesting enhanced adsorption strength of polysulfides by VO2 as compared with reported polar host materials (Figure S9). The binding energy between these polysulfides species with full-H-terminated VO2 was also considered (1.61, 1.33, and 1.03 eV, respectively, Figure S10). This theoretical evidence is in good agreement with our experimental observation on the ultrafast anchoring behaviour of polysulfides in the presence of VO2 nanobelts. To evaluate the electrochemical performance of the ternary VO2/G/S cathodes, LIR2032 coin cells were assembled. In addition, bare G/S cathode fabricated without the VO2 dosage was also tested under identical conditions, serving as the control to justify the key role played by the VO2. Cyclic voltammetry (CV) profiles for the bare G/S and VO2/G/S cathodes were acquired within a potential window of 1.7-2.8 V at a scan rate of 0.05 mV s-1, as displayed in Figure 5a. It is evident that both electrodes manifest two reduction peaks and one oxidation peak. As such, in the forward-reduction scan, the two representative peaks (i and ii) correspond to the multistep reduction process of sulfur, from solid S8 to the soluble lithium polysulfides (Li2Sx, 4 ≤ x ≤ 8) at the higher potential,


12

Page 13 of 30 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


and from high-order lithium polysulfides to insoluble Li2S2/Li2S at the lower potential, respectively. In the backward-oxidation scan, the only existing peak (iii) could be assigned to the conversion of Li2S2/Li2S to intermediate polysulfides and finally into S8.34 The peaks of VO2/G/S cathode are a bit sharper than those of bare G/S cathode, indicative of its higher reaction kinetics. It is also noted that the reduction peak positions (2.31 and 2.08 V) of the VO2/G/S cathode appear at higher peak potentials whilst the oxidation peak position (2.37 V) stays at a lower potential, as compared to those of G/S cathode (cathodic: 2.28 and 2.05 V, anodic: 2.39 V) (Figure S11). Moreover, Figure 5b depicts the plot in terms of the onset potentials of VO2/G/S and G/S cathodes extracted from the CV profiles. The onset potential is defined as the potential at which ~10% or 20% of the current value at the peak potential is reached.44 In this context, the onset potentials of the VO2/G/S cathode in the reduction reactions are higher by ~11 mV with respect to G/S cathode. As for the oxidation process, the onset potential of the VO2/G/S (2.29 V) is ~20 mV lower than that of G/S (2.31 V). Such discernible shifts for peak positions and onset potentials of the VO2/G/S cathode suggest accelerated polysulfide redox processes with the presence of VO2, which was also observed in previously reported sulfur host materials such as Nb2O5,27 ReS2,31 and VN.33 CV at different scan rates from 0.1 to 0.5 mV s-1 were further measured (Figure S12) to explore the electrode reaction kinetics and lithium diffusion properties of both types of sulfur cathodes. As clearly shown in Figure 5c, both of the cathodic peak currents for the measured cathodes display a linear relationship with the square root of scanning rates, from which the classical Randles-Sevcik equation can be applied to describe the lithium diffusion process: Ip = (2.69 × 105)·n1.5·A·D0.5·CLi·υ0.5, where Ip is the peak current, n is


13


Page 14 of 30

the charge transfer number, A is the area of the active electrode, D is the lithium ion diffusion coefficient, CLi is the concentration of lithium ions in the cathode, and υ is the potential sweep rate.29 The slopes of curve in Figure 5c are positively correlated to the lithium ion diffusion rate, since n, A, CLi remain unchanged in the battery systems. As such, VO2/G/S cathodes demonstrate superior diffusion and better reaction kinetics as compared to the bare G/S cathodes, implying that the presence of VO2 could enhance the polysulfide redox kinetics, especially for the sulfur reduction reactions. The electrochemical impedance spectroscopy (EIS) curves of the VO2/G/S and G/S cathodes were collected, as shown in Figure S13. The high-frequency semicircles in the Nyquist plots correspond to the charge transfer resistance (Rct) within the electrodes. The VO2/G/S cathode shows a slightly lower Rct value (36.2 Ω) with respect to the G/S cathode (39.6 Ω). The EIS data suggest that the introduction of semiconducting VO2 has no adverse effect on the charge transfer process, as well as is conducive to the Li+ diffusion capability, which accords well with the CV results. The rate performances of the two cathodes were tested by increasing the discharge/charge current density in a stepwise fashion from 0.2 to 2 C per every 5 cycles. As shown in Figure 5d, when cycled at different rates of 0.2 C, 0.5 C, 1 C, and 2 C, the VO2/G/S cathode was able to deliver discharge capacities of 1450, 1224, 1031, and 831 mAh g-1, respectively, demonstrating high capacity and excellent rate performance. When the current density was switched back to 0.2 C, the VO2/G/S manages to recover by achieving a durable discharge capacity of 1215 mAh g-1, indicating good stability of the cathode at various rates. In contrast, bare G/S cathodes only display inferior discharge capacity and rate capability under the identical conditions. It is also worth-noting from


14

Page 15 of 30 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 5d that the discharge capacity of G/S fades sharply from to 1186 mAh g-1 down to 948 mAh g-1 merely after 5 cycles at a small current density of 0.2 C, possibly owing to the rapid dissolution of polysulfides into the electrolyte without any efficient anchoring agent. Accordingly, the galvanostatic charge/discharge profiles at different rates for both electrodes are plotted, as shown in Figure 5e and f. Impressively, the characteristic dualplateaus can be clearly observed for the VO2/G/S even at a high rate of 2 C (Figure 5e), indicative of its low polarization, smooth mass transport and fast reaction kinetics.20 The galvanostatic charge/discharge behaviours of the VO2/G/S and G/S cathodes at the current density of 0.2 C were further investigated, as displayed in Figure 5g and h, respectively. Two voltage plateaus centring around 2.3 V and 2.1 V can be identified in the discharge curves for VO2/G/S cathode, in good agreement with the multistep reduction process of sulfur reflected by the CV profile in Figure 5a. Figure 5i shows the cycling performances of VO2/G/S cathode and G/S cathode at a current density of 0.2 C. Benefited from the ultrafast polysulfide anchoring capability of VO2, the VO2/G/S cathode manifests an initial discharge capacity of 1405 mAh g-1 and maintains at 990 mAh g-1 after 100 cycles, accounting for 74.5% of initial capacity with an average decay rate of 0.30% per cycle, apparently outperforming the bare G/S cathode with a capacity fading rate as high as 0.59% per cycle (497 mAh g-1 after 100 cycles) under the same conditions. In addition, the Coulombic efficiency of VO2/G/S cathode maintains at more than 99% after 100 cycles at 0.2 C, implying the remarkable cyclic performance. In contrast, the Coulombic efficiency of G/S cathode is apparently inferior as compared with VO2/G/S cathode, showing an inevitable shuttle effect.


15


Page 16 of 30

The long-term cycling performances of VO2/G/S cathode was also tested at high rates of 1 C, 2 C and 5 C for 200 cycles (Figure 5j, Figure S14). At 1 C, the VO2/G/S cathode delivers an initial discharge capacity of 1043 mAh g-1 and retains a discharge capacity of 701 mAh g-1 after 200 cycles. The capacity fading is as low as 0.16% per cycle with a high Coulombic efficiency of over 99.5%. As for bare G/S cathode, cycling at 1 C has witnessed its drastic capacity decay after 200 cycles, although showing a favourable initial capacity of 945 mAh g-1 (Figure S14a). Moreover, at a cycle rate of 2 C, the VO2/G/S cathode delivers an initial discharge capacity of 860 mAh g-1 and high reversible capacity close to 615 mAh g-1 after 200 cycles with a capacity decay of 0.14% per cycle. Even at a high rate of 5 C, the discharge capacity of VO2/G/S cathode maintains at a reasonably acceptable level of 480 mAh g-1 after 250 cycles (Figure S14b), corroborating its outstanding long-term stability. Note that in our Li-S battery system the contribution of VO2 to capacity could be neglected, since VO2 not only displays a low specific capacity of ∼150 mAh g-1 in the potential range (Figure S15a) with a degraded cycling performance (Figure S15b), but also accounts for a low mass ratio in the cathode materials (~4 wt%). A higher mass ratio of VO2 (10 wt%) in the cathode was also attempted, displaying inferior rate and cycling performances to those with 4 wt% content (Figure S16). Furthermore, post-mortem SEM analysis of cathodes was carried out after 200 cycles at 1 C, manifesting good structural stability of VO2/G/S cathode as compared to the bare G/S cathode (Figure S17). These systematic investigations on the electrochemical performances enable us to draw a plausible clarification that the involvement of VO2 could realize advanced Li-S batteries with outstanding specific capacity and cycling stability, where the VO2 plays dual roles: (i) serving as an efficient


16

Page 17 of 30 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


trapping agent for adsorbing polysulfides; (ii) functioning as an effective electrocatalyst to boost the sulfur redox kinetics.

4. Conclusion In summary, as-prepared VO2 nanobelts with favourable architectures were employed as highly effective host additives for graphene-based sulfur cathodes in Li-S batteries. The remarkable capability of well-dispersed VO2 nanobelts towards ultrafast anchoring polysulfides was verified from both theoretical and experimental investigations, demonstrating that VO2 has enabled strong entrapment of soluble polysulfides as well as marked enhancement of sulfur redox kinetics. The thus-obtained VO2/G/S ternary cathode has achieved outstanding performance with respect to high reversible capacity, good rate capability, long cycling stability and acceptably high sulfur loadings. We anticipate that the present work would open up novel avenues towards the practical applications of highenergy and long-life Li-S battery systems.


17


Page 18 of 30

Figure 1. a, Schematic illustration of key preparation steps of VO2 nanobelts. b, Schematic illustration of fabrication processes of nano sulfur-graphene hybrid, as well as the mixing route. c, TGA curve of the nano sulfur-graphene hybrid. d, SEM image of VO2/G/S cathode before cycling, with the inset showing the cross-section SEM view. e, Digital photograph of a LED panel powered by two Li-S cells connected in series.


18

Page 19 of 30 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, SEM image. b, TEM image. c, Close-up TEM image. d, HRTEM image with the inset showing the corresponding SAED pattern. e, XRD pattern. f, Raman spectrum of assynthesized VO2 nanobelts.


19


Page 20 of 30

Figure 3. a, UV-Vis absorption spectra of a Li2S6 solution prior to and after the addition of RGO and VO2, with the inset showing the Li2S6 adsorption test by using VO2 and RGO. b, TEM image of VO2 after the adsorption of Li2S6. c, Corresponding STEM image. d-g, Elemental maps of vanadium, oxygen and sulfur. h, In-situ Raman spectra based on VO2/RGO hosts collected upon the first discharge at 0.2 C. The mark a-i on the image denotes the spectrum acquisition points at different depths of discharge process.


20

Page 21 of 30 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 4. a, Top and side view of optimized structures of a Li2S4, Li2S6, and Li2S8 cluster adsorbed on the surface of H-terminated VO2 (010) surface, respectively. b, Plot of binding energy values of Li2Sx (x = 4, 6 and 8) clusters on the H-terminated VO2 (010) surfaces.


21


Page 22 of 30

Figure 5. a, CV profiles of VO2/G/S and G/S cathodes in a potential window from 1.7 to 2.8 V. The mark i and ii denotes two reduction peaks, whilst the mark iii denotes the oxidation peak. b, Corresponding onset potentials of VO2/G/S and G/S cathodes in the Li-S battery with respect to the CV peaks in a. The mark i and ii denotes two reduction peaks, whilst the mark iii denotes the oxidation peak. c, Reaction kinetics with respect to the Li+ ion diffusion properties of the cathodes at various voltage scan rates. d, Rate capabilities of VO2/G/S and G/S cathodes. e, f, Galvanostatic charge/discharge profiles of VO2/G/S and G/S cathodes at various rates. g, h,


22

Page 23 of 30 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


Galvanostatic charge/discharge profiles of VO2/G/S and G/S cathodes at 0.2 C. i, Cycling performances of VO2/G/S and G/S cathodes at 0.2 C. j, Long-term cycle performances of VO2/G/S cathodes at 1 C and 2 C.

ASSOCIATED CONTENT Supporting Information. The Supporting Information contains further structural, elemental and electrochemical performance characterizations. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (J. Y. Sun) *E-mail: [email protected] (L. Zhang) Author Contributions †These authors

contributed equally to this work.

Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (51702225, 21473119, 51675275, 51520105003 and 51432002) and Jiangsu Youth Science Foundation (BK20170336). Y.Z.S., X.Y.Z., L.Z., J.Y.S. and Z.F.L. acknowledge


23


Page 24 of 30

the support from Suzhou Key Laboratory for Advanced Carbon Materials and Wearable Energy Technologies, Suzhou, China. Y.Z.S acknowledges the support from the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX172023). J.Y.S. acknowledges the support from the Thousand Youth Talents Plan of China.

REFERENCES (1) Ji, X.; Lee, K. T.; Nazar, L. F., A Highly Ordered Nanostructured Carbon-Sulphur Cathode for Lithium-Sulphur Batteries. Nat. Mater. 2009, 8, 500-506. (2) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J.-M., Li-O2 and Li-S Batteries with High Energy Storage. Nat. Mater. 2012, 11, 19-29. (3) Manthiram, A.; Fu, Y.; Su, Y.-S., Challenges and Prospects of Lithium-Sulfur Batteries. Acc. Chem. Res. 2013, 46, 1125-1134; (4) Yang, Y.; Zheng, G.; Cui, Y., Nanostructured Sulfur Cathodes. Chem. Soc. Rev. 2013, 42, 3018-3032. (5) Larcher, D.; Tarascon, J. M., Towards Greener and More Sustainable Batteries for Electrical Energy Storage. Nat. Chem. 2015, 7, 19-29. (6) Yin, Y.-X.; Xin, S.; Guo, Y.-G.; Wan, L.-J., Lithium-Sulfur Batteries: Electrochemistry, Materials, and Prospects. Angew. Chem. Int. Ed. 2013, 52, 13186-13200. (7) Manthiram, A.; Fu, Y.; Chung, S.-H.; Zu, C.; Su, Y.-S., Rechargeable Lithium-Sulfur Batteries. Chem. Rev. 2014, 114, 11751-11787. (8) Peng, H.-J.; Huang, J.-Q.; Cheng, X.-B.; Zhang, Q., Review on High-Loading and HighEnergy Lithium-Sulfur Batteries. Adv. Energy Mater. 2017, 1700260. (9) Wang, H.; Zhang, W.; Liu, H.; Guo, Z., A Strategy for Configuration of an Integrated Flexible


24

Page 25 of 30 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


Sulfur Cathode for High-Performance Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2016, 55, 3992-3996. (10) Wang, H.; Zhang, C.; Chen, Z.; Liu, H.; Guo, Z., Large-Scale Synthesis of Ordered Mesoporous Carbon Fiber and Its Application as Cathode Material for Lithium-Sulfur Batteries. Carbon, 2015, 81, 782-787. (11) 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, 798-802. (12) Li, G.; Sun, J.; Hou, W.; Jiang, S.; Huang, Y.; Geng, J., Three-dimensional Porous Carbon Composites Containing High Sulfur Nanoparticle Content for High-Performance Lithium-Sulfur Batteries. Nat. Commun. 2016, 7, 10601. (13) Pei, F.; Lin, L.; Ou, D.; Zheng, Z.; Mo, S.; Fang, X.; Zheng, N., Self-Supporting Sulfur Cathodes Enabled by Two-Dimensional Carbon Yolk-Shell Nano Sheets for High-EnergyDensity Lithium-Sulfur Batteries. Nat. Commun. 2017, 8, 482. (14) Pang, Q.; Kundu, D.; Cuisinier, M.; Nazar, L. F., Surface-Enhanced Redox Chemistry of Polysulphides on A Metallic and Polar Host for Lithium-Sulphur Batteries. Nat. Commun. 2014, 5, 4759. (15) Zhang, Q.; Wang, Y.; Seh, Z. W.; Fu, Z.; Zhang, R.; Cui, Y., Understanding the Anchoring Effect of Two-Dimensional Layered Materials for Lithium-Sulfur Batteries. Nano Lett. 2015, 15, 3780-3786. (16) Liu, X.; Huang, J.-Q.; Zhang, Q.; Mai, L., Nanostructured Metal Oxides and Sulfides for Lithium-Sulfur Batteries. Adv. Mater. 2017, 29, 1601759. (17) Seh, Z. W.; Li, W.; Cha, J. J.; Zheng, G.; Yang, Y.; McDowell, M. T.; Hsu, P.-C.; Cui, Y.,


25


Page 26 of 30

Sulphur-TiO2 Yolk-Shell Nanoarchitecture with Internal Void Space for Long-Cycle LithiumSulphur Batteries. Nat. Commun. 2013, 4, 1331. (18) Wang, X.; Gao, T.; Fan, X.; Han, F.; Wu, Y.; Zhang, Z.; Li, J.; Wang, C., Tailoring Surface Acidity of Metal Oxide for Better Polysulfide Entrapment in Li-S Batteries. Adv. Funct. Mater. 2016, 26, 7164-7169. (19) 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, 1288612890. (20) Zhang, J.; Shi, Y.; Ding, Y.; Zhang, W.; Yu, G., In Situ Reactive Synthesis of PolypyrroleMnO2 Coaxial Nanotubes as Sulfur Hosts for High-Performance Lithium-Sulfur Battery. Nano Lett. 2016, 16, 7276-7281. (21) Rehman, S.; Tang, T.; Ali, Z.; Huang, X.; Hou, Y., Integrated Design of MnO2@Carbon Hollow Nanoboxes to Synergistically Encapsulate Polysulfides for Empowering Lithium Sulfur Batteries. Small 2017, 13, 1700087. (22) Hu, L.; Dai, C.; Lim, J.; Chen, Y.; Lian, X.; Wang, M.; Xiao, P.; Henkelman, G.; Xu, M., A Highly Efficient Double-Hierarchical Sulfur Host for Advanced Lithium-Sulfur Batteries. Chem. Sci. 2018, 9, 666-675. (23) Liang, X.; Garsuch, A.; Nazar, L. F., Sulfur Cathodes Based on Conductive MXene Nanosheets for High-Performance Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2015, 54, 3907-3911. (24) Wang, H.; Zhou, T.; Li, D.; Gao, H.; Du, A.; Liu, H.; Guo, Z., Ultrathin Cobaltosic Oxide Nanosheets as an Effective Sulfur Encapsulation Matrix with Strong Affinity Toward Polysulfides. ACS Appl. Mater. Interfaces, 2017, 9, 4320-4325.


26

Page 27 of 30 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


(25) Xie, K.; You, Y.; Yuan, K.; Lu, W.; Zhang, K.; Xu, F.; Ye, M.; Ke, S.; Shen, C.; Zeng, X.; Fan, X.; Wei, B., Ferroelectric-Enhanced Polysulfide Trapping for Lithium-Sulfur Battery Improvement. Adv. Mater. 2017, 29, 1604724. (26) Deng, D.-R.; Xue, F.; Jia, Y.-J.; Ye, J.-C.; Bai, C.-D.; Zheng, M.-S.; Dong, Q.-F., Co4N Nanosheet Assembled Mesoporous Sphere as a Matrix for Ultrahigh Sulfur Content LithiumSulfur Batteries. ACS Nano 2017, 11, 6031-6039. (27) Tao, Y.; Wei, Y.; Liu, Y.; Wang, J.; Qiao, W.; Ling, L.; Long, D., Kinetically-Enhanced Polysulfide Redox Reactions by Nb2O5 Nanocrystals for High-Rate Lithium-Sulfur Battery. Energy Environ. Sci. 2016, 9, 3230-3239. (28) Dai, C.; Lim, J.; Wang, M.; Hu, L.; Chen, Y.; Chen, Z.; Chen, H.; Bao, S.; Shen, B.; Li, Y.; Henkelman, G.; Xu, M., Honeycomb-Like Spherical Cathode Host Constructed from Hollow Metallic and Polar Co9S8 Tubules for Advanced Lithium-Sulfur Batteries. Adv. Funct. Mater. 2018, 28, 1704443. (29) Zhou, G.; Tian, H.; Jin, Y.; Tao, X.; Liu, B.; Zhang, R.; Seh, Z. W.; Zhuo, D.; Liu, Y.; Sun, J.; Zhao, J.; Zu, C.; Wu, D. S.; Zhang, Q.; Cui, Y., Catalytic Oxidation of Li2S on The Surface of Metal Sulfides for Li-S Batteries. Proc. Natl. Acad. Sci. USA 2017, 114, 840-845. (30) 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 Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2016, 55, 12990-12995. (31) Gao, J.; Li, L.; Tan, J.; Sun, H.; Li, B.; Idrobo, J. C.; Singh, C. V.; Lu, T.-M.; Koratkar, N., Vertically Oriented Arrays of ReS2 Nanosheets for Electrochemical Energy Storage and Electrocatalysis. Nano Lett. 2016, 16, 3780-3787.


27


Page 28 of 30

(32) 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. 2018, 5, 1700270. (33) 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. (34) 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. (35) Yan, M.; Wang, F.; Han, C.; Ma, X.; Xu, X.; An, Q.; Xu, L.; Niu, C.; Zhao, Y.; Tian, X.; Hu, P.; Wu, H.; Mai, L., Nanowire Templated Semihollow Bicontinuous Graphene Scrolls: Designed Construction, Mechanism, and Enhanced Energy Storage Performance. J. Am. Chem. Soc. 2013, 135, 18176-18182. (36) Chao, D.; Zhu, C.; Xia, X.; Liu, J.; Zhang, X.; Wang, J.; Liang, P.; Lin, J.; Zhang, H.; Shen, Z. X.; Fan, H. J., Graphene Quantum Dots Coated VO2 Arrays for Highly Durable Electrodes for Li and Na Ion Batteries. Nano Lett. 2015, 15, 565-573. (37) Liang, X.; Kwok, C. Y.; Lodi-Marzano, F.; Pang, Q.; Cuisinier, M.; Huang, H.; Hart, C. J.; Houtarde, D.; Kaup, K.; Sommer, H.; Brezesinski, T.; Janek, J.; Nazar, L. F., Tuning Transition Metal Oxide-Sulfur Interactions for Long Life Lithium Sulfur Batteries: The "Goldilocks" Principle. Adv. Energy Mater. 2016, 6, 1501636. (38) Wu, S.; Xu, R.; Lu, M.; Ge, R.; Iocozzia, J.; Han, C.; Jiang, B.; Lin, Z., Graphene^ Containing Nanomaterials for Lithium^Ion Batteries. Adv. Energy Mater. 2015, 5, 1500400.


28

Page 29 of 30 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


(39) Wu, S.; Ge, R.; Lu, M.; Xu, R.; Zhang, Z., Graphene-Based Nano-Materials for LithiumSulfur Battery and Sodium-Ion Battery. Nano Energy, 2015, 15, 379-405. (40) Wang, C.; Chen, H.; Dong, W.; Ge, J.; Lu, W.; Wu, X.; Guo, L.; Chen, L., Sulfur-Amine Chemistry-Based Synthesis of Multi-walled Carbon Nanotube-Sulfur Composites for High Performance Li-S Batteries. Chem. Commun. 2014, 50, 1202-1204. (41) Kresse, G.; Furthmuller, J., Efficiency of Ab-Initio Total Energy Calculations for Metals and Semico Nductors Using a Plane-Wave Basis Set. Comp. Mater. Sci. 1996, 6, 15-50. (42) Wang, H.; Yi, H.; Chen, X.; Wang, X., One-step Strategy to Three-Dimensional Graphene/VO2 Nanobelt Composite Hydrogels for High Performance Supercapacitors. J. Mater. Chem. A 2014, 2, 1165-1173. (43) Chen, J.-J.; Yuan, R.-M.; Feng, J.-M.; Zhang, Q.; Huang, J.-X.; Fu, G.; Zheng, M.-S.; Ren, B.; Dong, Q.-F., Conductive Lewis Base Matrix to Recover the Missing Link of Li2S8 during the Sulfur Redox Cycle in Li-S Battery. Chem. Mater. 2015, 27, 2048-2055. (44) Maillard, F.; Bonnefont, A.; Chatenet, M.; Guetaz, L.; Doisneati-Cottignies, B.; Roussel, H.; Stimming, U., Effect of The Structure of Pt-Ru/C Particles on CO Monolayer Vibrational Properties and Electrooxidation Kinetics. Electrochim. Acta 2007, 53, 811-822.


29


Page 30 of 30


30

Vanadium Dioxide-Graphene Composite with Ultrafast Anchoring

Recommend Documents