Heterostructure Manipulation toward Ameliorating Electrodes for

Subscriber access provided by University of Sunderland

Article

Hetero-structure Manipulation towards Ameliorating Electrodes for Better Lithium Storage Capability Jing Cuan, Fan Zhang, Hongyu Zhang, Jun Long, Shilin Zhang, Gemeng Liang, Qili Gao, Junnan Hao, Linxi Dong, Gaofeng Wang, and Xuebin Yu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04685 • Publication Date (Web): 16 Oct 2018 Downloaded from http://pubs.acs.org on October 19, 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 24 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 Sustainable Chemistry & Engineering

Journal: ACS Sustainable Chemistry & Engineering Manuscript ID: sc-2018-046854

Hetero-structure Manipulation towards Ameliorating Electrodes for Better Lithium Storage Capability Jing Cuan,†, § Fan Zhang,‡ Hongyu Zhang,‡ Jun Long,§ Shilin Zhang,§ Gemeng Liang,§ Qili Gao,‡ Junnan Hao,§ Linxi Dong,† Gaofeng Wang,† Xuebin Yu†, ‡, ‖* †Key Laboratory of RF Circuits and Systems of Ministry of Education, Electronic and Information College

of Hangzhou Dianzi University, Hangzhou 310018, China ‡Department of Materials Science, Fudan University, Shanghai, China §Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, Australia ‖Shanghai Innovation Institute for Materials, Shanghai 200444, China Corresponding Author: *E-mail: [email protected] Full Mailing Address: Handan Road 220, Department of Materials Science, Fudan University, Shanghai, China Keywords: over-potential, hetero-structure manipulation, charge transfer kinetics, hybridity, lithium ion battery

1

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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 24

ABSTRACT As one of the major problems facing lithium ion batteries, sluggish charge transfer often induces undesirable large resistance, over-potential and round trip inefficiency of batteries during recharge. The need to improve charge transport kinetics is motivating research into directions that would rely on high quality hetero-structure designs, since it is reported that the synergistic effects and as-formed inbuilt electric fields of hetero-structures could facilitate charge transport across the hetero-structure, as well as enforce interactions between the active phases. Hetero-manipulation holds great promise for realizing

efficient interconnects between charge transport kinetics and hetero-structure designs. However, most previous studies delineate ensemble measurements of a given static hetero-electrode, which do not permit isolating and dissecting the effects of hetero-structural manipulation on electrochemical performances individually. Here, by choosing conversion type electrodes as example and comparing series samples which were collected in the evolution of hetero-structures, the effects of hetero-structure manipulation towards modifying over-potential and lithium storage capability have been systematically investigated. The results demonstrate that structural features (e.g. robust skeleton, smaller grain sizes, and high quality hybridity) play an important role in engendering faster charge transfer and narrowing overpotential than that at the level of micrometer scales.

2


Page 3 of 24 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


INTRODUCTION As the power system and cornerstones for energy storage techniques, charge carrier plays an important role in the well-operation of electrochemical devices, especially for the popular rechargeable lithium ion batteries (LIBs), which have wide applications in portable devices and electrification of transport. The ever-growing demands for high performance LIBs place requirements for electrode that could combine the high capacity of batteries and fast kinetics of capacitors.1-16 Conversion reaction-based transition metal compounds have been proposed as promising candidates, which can accommodate more than one Li+ in each molecular, with specific gravimetric capacities ~2-3 times larger than for electrodes that react through classical intercalation reactions.15 Upon a charging and discharging cycle, the active phase of transition metal compound will experience a reversible phase transformation between its counterpart metal element. However, despite their superiority in high theoretical capacity, grand challenges still remained. The low solid-state charge transport and sluggish mass/charge transfer kinetics across grain boundaries in most conversion type systems have been proved as the primary causes for giant voltage hysteresis and overpotential between a redox pair. Therefore, the resulted impaired roundtrip efficiency of conversion type systems can hardly approach the level of practical applications, which require further studies to address the associated problems.1, 17-21 Compared with homo-structures, materials made from hetero-structures show great potential to modify the dynamics and chemistry of charge carriers, which have been widely used to build devices that can be utilized for diode, capacitor, transistor, photocatalysis and non-volatile memory, etc.22,

23

For

instance, Kim et al. has verified that after the construction of van der Waals hetero-interfaces between graphene and molybdenum dichalcogenide (MoX2, X = S, Se), nearly 0.5 V negative-shift of intercalation potential and 10-times accumulation of charges have been achieved in comparison with MoX2/MoX2 homo-interfaces.24 Loh et al. fabricated a graphene/black phosphorus hetero-structure, which induced a 3



Page 4 of 24

strong pseudo-magnetic fields (PMFs), leading to the formation of pseudo-Landau levels and valley Hall effect in graphene. Furthermore, as the relative orientation of graphene and black phosphorus changes, the spatial distribution of PMF and the intertwined moiré pattern could be tailored, which prominently influenced the transport properties of the composites.25 Pan et al. fabricated a WSe2/SnS2 composite, which had one order higher hole mobility than pristine WSe2 compound, showing that the charge transport capability of WSe2 has been improved greatly in the hetero-structured composite.26 Based on this, the chemically engineered hetero-structures are promising to reinforce the interactions between the active phases, as well as to tune the charge transport and thermodynamic landscapes of electrodes, which are anticipated to regulate the reversibility and over-potential of redox pairs. Nonetheless, these rational ameliorations of such electrochemical properties place demands on rigorous understanding of accurate hetero-structure manipulation, namely precise hetero-design, which is inaccessible in evaluating a given static hetero-structure. This work reported a dynamic hetero-structure evolution, in which an ensemble of electrodes with sequential hetero-structure-shifting have been compared to scrutinize the effects of hetero-structure manipulation on the electrochemical behaviors of conversion type electrodes. In this work, Mo2C-C⊂xMoO3 (x = 1, 3, 6, 14) hetero-electrodes have been taken as examples, considering the complementary advantages of Mo2C and MoO3 at diffusion barrier, electric conductivity, and lithium storage capacity, etc.2, 27-47 Here, four investigated compositions (x = 1, 3, 6, 14) were selected to check the associated hetero-architecture effects on electrochemical behaviors, mainly in view of their noticeable structural divergence, which could be reckoned as four representative stages during the hetero-morphology shifting. The inspection of physical properties (Rietveld refinement, transmission electron microscopy, field emission scanning electron microscopy, etc.) imply that as a result of varied component proportion and grain sizes, the structural integrity and hybridity (quantity and dispersibility of hetero-interfaces) in each 4


Page 5 of 24 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


composite has changed greatly. The evaluated electrochemical properties show that the electrochemical reactions of Mo2C-C⊂x-MoO3 with lithium are more facilitated at a lower value of x, yielding higher lithium storage capacity. Simultaneously, the over-potential and charge transfer resistance have a visible response to the variations of x. Among the four investigated compositions, Mo2C-C⊂x-MoO3 at x = 1, 3 show superior electrochemical performance to other counterparts. The examination of kinetic results revealed that this outperformance may mainly be attributed to the synergistic effects of robust fibrous construction, smaller grain sizes and high quality hybridity in their superior architecture, which could reduce the electron/lithium ion diffusion distance, boost the reaction kinetics, and provide rich interfacial electrochemical active sites at nanoscale. Such improvements signify the significance of hetero-structure manipulation in better ameliorating electrodes for advanced batteries and devices in other fields.

RESULTS AND DISCUSSION

Figure 1. Schematic illustration of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) nanofibers (NFs) prepared via an electrospinning process with a single-needle nozzle. :Mo-PVA nanofiber. :C nanofiber matrix. : Mo2C particle. : MoO3 particle.

Figure 1 delineates the synthesis procedure of the hetero-molybdenum composite series. The pristine Mo-PVA nanofiber (PVA=polyvinyl alcohol) was fabricated through a facile electrospinning method and calcined under Ar atmosphere to form Mo2C-C nanofiber. Subsequently, the collected Mo2C-C nanofiber were grouped into four batches, and were treated under flowing air for 1 h, 3 h, 6 h, and 14 h at the 5



Page 6 of 24

temperature of 300 oC. In this post-calcination treatment process, the phase transition from Mo2C to MoO3 happened,48 accompanying with gradient changes of hetero-structures. (The experimental details were shown in the Experimental Section in Supplementary Information.) The obtained samples were denoted as Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14), in which x represented the post-calcination time in air. Mo2C-C nanofiber also stands for Mo2C-C⊂0-MoO3. The phase purity and crystallographic nature of all the collected samples were examined by powder X-ray diffraction (XRD).

Figure 2. (a) XRD patterns of all the samples, involving Mo2C-C⊂x-MoO3 (x= 0, 1, 3, 6, 14) composites. The PDF card (JCPDS No.72-1683) corresponds to orthorhombic Mo2C (Pbcn(60)), while the other JCPDS card (No. 35-0609) is ascribed to orthorhombic MoO3 (Pbnm(62)). (b) The Rietveld refinement of the X-ray diffraction pattern for Mo2C-C⊂1MoO3. (c) Raman spectra of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) composites. (d-f) High resolution Mo3d, O1s, C1s XPS spectra for Mo2C-C⊂1-MoO3 composite.

Figure 2a demonstrated that two sets of diffraction peaks (at 2θ ≈ 12.8 °, 23.3 °, 25.7 ° and 27.3 °; 34.5 °, 38.1 °, and 39.5 °) were recorded in Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) composites, which could be readily indexed to orthorhombic phases of MoO3 (JCPDS No. 35-0609) and Mo2C (JCPDS No. 721683), respectively. The diffraction intensity of Mo2C component decreases gradually with the increase of x, while that of MoO3 phase increases simultaneously, which are mainly resulted from the continuous 6


Page 7 of 24 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


phase transition from Mo2C to MoO3 at 300 oC under flowing air.48 We note that the diffraction peaks of Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) nanofibers are much weaker and broader in comparison with those of bulk MoO3 and bulk Mo2C (Figure S1a, supporting information), implying that MoO3 and Mo2C particles are nanoconfined within the carbon matrix. The Rietveld refinements of XRD patterns are conducted to determine the mass ratio of two Mo species in Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) samples, which are shown in Figure 2b, Figure S1b-d. All the diffraction peaks of these samples can be indexed to those of orthorhombic MoO3 (space group: Pbnm) and orthorhombic Mo2C (space group: Pbcn). Furthermore, the carbon contents of Mo2C-C⊂x-MoO3 samples were calculated by the joint analysis of Rietveld refinement and thermo-gravimetric analysis (TGA) profiles (Figure S2) under flowing air, and detailed calculation methods have been provided in Supplemental Materials. Table 1 shows the component proportions of the Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) samples. Evidently, it is revealed that carbon content and the mass ratio of Mo2C to MoO3 decline simultaneously as the rise of x, manifesting the gradient evolution of hetero-structures. Note that the feeding ratio of molybdenum salts were identical in Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) composites, on this premise, the relative mole numbers of two individual molybdenum species largely determine the quantity of hybridity. It is easily understood that, if the mole ratio of two molybdenum species is close to the equimolar ratio (1:1), maximum number of hetero-interfaces will be approached, while once deviated from equimolar ratio, the number of heterointerfaces will decline. In this work, the molar ratio of two molybdenum species was proved to be more deviated from equimolar value at larger x (Table 1), which signifies the reduced quantity of corresponding hybridity. To identify the structural differences of the fibrous carbonaceous matrix in Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) samples, their Raman spectra are compared in Figure 2c. All tested samples show two strong and typical bands at 1358 and 1616 cm-1, which represent the disorder-induced D band (sp3 hybridized carbon atom) and in-plane vibrational G band (in-plane vibration of sp2 carbon atoms) of 7



Page 8 of 24

carbonaceous materials.49-51 The intensity ratios of D band to G band (ID/IG) for Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) were calculated as 1.4, 1.9, 2.1, 1.9, and 2.0, respectively, implying that amorphous carbon was the primary carbonaceous forms in Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) composites.52 The bonding configurations and chemical states of Mo2C-C⊂1-MoO3 sample were investigated by X-ray photoelectron spectroscopy (XPS). The XPS spectrum in Figure S3 confirms the presence of all expected elements, Mo, O, and C. Three types of Mo valences are identified in the Mo 3d high resolution XPS spectrum (Figure 2d), which correspond to three different oxidation states of Mo. The initial two resolved peaks at lower binding energies of 231.6 eV and 228.5 eV could be ascribed to the typical Mo (II) 3d3/2 and Mo (II) 3d5/2 peaks of Mo2C nanoparticles.53 Another pair of split peaks with mid-range binding energies of 235.1 eV and 232 eV can be assigned to the Mo (V) 3d3/2 and Mo (V) 3d5/2 peaks in MoOx, which may be the partial reduction product of MoO3. The individual peaks located at 236.1 eV and 233 eV can be attributed to the characteristic response of Mo (VI) 3d3/2 and Mo (VI) 3d5/2 peaks in MoO3.54-56 The O 1s XPS spectrum (Figure 2e) can be resolved into three peaks centered at 530.4, 531.9, and 533.3 eV, corresponding to the Mo-O bonds, C-O bonds, and C=O functional groups in Mo2C-C⊂1-MoO3 composite, respectively.54, 57 As observed in the high resolution C 1s XPS spectrum (Figure 2f), three individual peaks of nonoxygenated C-C, C=O, and O=C-O groups are located at 285.4, 286.5, and 290.1 eV, respectively, which are mainly originated from the decomposition of polymer polyvinyl alcohol.54 Table 1. The obtained weight ratio of Mo2C to MoO3 by Rietveld refinement. Sample

Mo2C-C⊂0-MoO3 Mo2C-C⊂1-MoO3 Mo2C-C⊂3-MoO3 Mo2C-C⊂6-MoO3 Mo2C-C⊂14-MoO3

𝒎𝑴𝒐𝟐𝑪

𝒎𝑴𝒐𝑶𝟑

𝒎𝑴𝒐𝟐𝑪 + 𝒎𝑴𝒐𝑶𝟑

𝒎𝑴𝒐𝟐𝑪 + 𝒎𝑴𝒐𝑶𝟑

1 0.48303 0.25908 0.21729 0.2000

0 0.51697 0.74092 0.78271 0.8000

8


𝐶𝑤𝑒𝑖𝑔ℎ𝑡 𝑟𝑎𝑡𝑖𝑜/ % 29.7 28.6 20.2 15.3 13.6

Page 9 of 24 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 3. Left frame (a, d, g, j, m): Zoomed-in schematic illustration of the interior morphology of a singular nanofiber in Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) within the same size of selected area. Grey color represents carbon phase, and pink red color stands for Mo2C phase. Light blue color represents MoO3 phase. Middle frame (b, e, h, k, n): TEM images of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14), respectively. Right frame (c, f, i, l, o): SEM images of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) composites, respectively.

The morphological feature and nanostructure of the as-prepared fibers were characterized by transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FE-SEM). In 9



Page 10 of 24

the panoramic views of TEM images (Figure 3b, e, h, k, n), we can see that Mo2C-C⊂0-MoO3 composite contains many integral and homogeneous fibers with lengths on micrometer scale. Mo2C-C⊂1-MoO3 composite showed a peapod-like fibrous structure, while Mo2C-C⊂3-MoO3 had an obvious carbon coating layer, which tightly encapsulated larger particles of the active phases. Mo2C-C⊂x-MoO3 (x = 0, 1) showed a large number of monodisperse nanoparticles uniformly distributed in the 1D fibrous carbon matrix (Figure 3b, 3e). No isolated nanoparticles of molybdenum species have been observed even after ultrasonic for 30 min to disperse the samples for TEM testing, implying the robust interactions between molybdenum species and fibrous carbon matrix. As post-calcination treatment went to greater depth, aggregated nano-grains appeared in the center of fibrous Mo2C-C⊂x-MoO3 (x = 6, 14) composites, and the particle sizes are found to increase prominently, probably due to heat induced aggregation of crystals.58, 59

As a result, it is easily understood that the dispersibility of hybridity will decline vastly due to the

aggregated and growing grains of molybdenum species. From the high resolution transmission electron microscopy (HRTEM) image of Mo2C-C⊂x-MoO3 (x = 1, 3) composites (Figure S4a, S4b), two types of inter-planar spacings (0.23 nm and 0.32 nm) have been identified, which correspond to the (1 2 1) and (0 2 1) crystal planes of orthorhombic Mo2C and MoO3 phase, manifesting the successful hybridization of molybdenum based species in carbon nanofiber, in contrast, only orthorhombic Mo2C phase has been identified from the HRTEM image of Mo2C-C⊂0-MoO3 (Figure S4c). More morphological details have been characterized by FE-SEM (Figure 3c, f, i, l, o, and Figure S5). The as-electrospun Mo-PVA nanofibers show smooth surfaces up to several micrometers in length with average diameters around 400 nm (Figure S5), which interlace in random orientations, as a result of the electrically driven bending fluctuations associated with the spinning nozzle.60,

61

In Mo2C-C⊂0-MoO3 composite, the fibrous

structures are well preserved with diameters of ~330 nm (Figure 3c). The contracted fibrous diameters are probably caused by the carbonization of organic species (polyvinyl alcohol) and thermal 10


Page 11 of 24 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


decomposition of the starting reactant (NH4)6Mo7O24·4H2O. Similar cases are found in prior reports on V2O5 and SrLi2Ti6O14 nanofibers.60,

62

Upon thermal treatment in air (T = 300 oC) for 1 to 6 h, the

morphology remains intact in the Mo2C-C⊂x-MoO3 (x = 1, 3, 6) composites, while plenty of short rods are observed at x = 14 (Figure 3f, i, l, o). The SEM images illustrate that as the post-calcination time increases, the steady contraction of fibrous diameters and transition of smooth surface to rough occur concurrently. In order to determine the process behind the change in carbon skeletons, isothermalgravimetric analysis of a blank pure PVA-C nanofiber was conducted at 300 oC under air atmosphere. The isothermal TG curve of pure PVA-C nanofiber (Figure S6) verified the occurrence of a continuous weight loss at constant temperature of 300 oC, which could be ascribed to the consumption of carbon by air (T = 300 oC) according to previous studies,48 and rationally interprets the rough surface and reduced diameters of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) nanofibers when x increases.

11



Page 12 of 24

Figure 4. (a) The initial discharge–charge profiles of all the samples for LIBs at the current density of 100 mA·g-1. (b) The corresponding coulombic efficiency of all as-collected electrodes. The first cycle was tested at 100 mA·g-1, while the subsequent cycles were tested at 1000 mA·g-1. (c) The comparisons of galvanostatic discharge profiles for all the electrodes and the corresponding coulombic efficiency of Mo2C-C⊂1-MoO3 at 1000 mA·g-1. (d) Rate performances (discharge capacities) of all the samples, at the current densities of 200, 500, 1000, 2000, and 200 mA·g-1, respectively. (e) The comparison of the second cyclic voltammetry profiles of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) samples within voltage range of 0.05-3 V vs. Li+/Li. (f) The Nyquist plots of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) in the frequency range of 1 kHz–10 mHz after 30 cycling tests at 200 mA·g-1. The inset is the equivalent circuit used to analyze the impedance plots.

To check out the effects of hetero-structure evolution towards modifying the lithium storage 12


Page 13 of 24 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


performance of MoO3, the electrochemical performances of hetero-structured samples were compared. Figure 4a shows the initial galvanostatic charge-discharge profiles of all the samples at 100 mA·g-1, which show similar voltage plateau between 1.1-0.4 V. This can be mainly ascribed to the formation of passivated solid electrolyte interphase (SEI) films in the first lithiation process.63, 64 The initial discharge capacities of Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) anodes are 893, 1331, 1158, 1123, and 879 mA·h·g-1, respectively, with corresponding coulombic efficiencies (CEs) of 59.9 %, 73.9 %, 73.7 %, 72.2 %, 65.5 %. Better lithium storage capacity and reversibility were achieved at x = 1, 3, as also reflected by the CE comparisons for the first four cycles (Figure 4b), showing faster CE increase in Mo2C-C⊂x-MoO3 (x = 1, 3). In the long-term cycling (Figure 4c), the discharge capacities of Mo2C-C⊂x-MoO3 (x = 0, 3, 6, 14) are 395, 712, 305 and 154 mA·h·g-1, respectively, while Mo2C-C⊂1-MoO3 anode maintains ~890 mA·h·g-1 over 300 cycles at 1000 mA·g-1. The lithium storage performances of Mo2C-C⊂x-MoO3 at x = 1, 3 appear better among the four investigated hetero-compositions, simultaneously, they were also superior to that of previously reported individual MoO3-C nanofiber (300 mA·h·g-1 at 800mA·g-1, 100th cycle).47 Moreover, the rate performance of Mo2C-C⊂x-MoO3 (x = 1, 3) are also noticeably ameliorated in comparison with those of Mo2C-C⊂x-MoO3 (x = 0, 6, 14) composites. Mo2C-C⊂1-MoO3 affords the discharge capacities of 928, 871, 815, 770 mA·h·g-1 at 200, 500, 1000, 2000 mA·g-1, respectively and retains ~1000 mA·h·g-1 in the subsequent cycles when the current density has been switched back to 200 mA·g-1, manifesting a good rate durability (Figure 4d). For Mo2C-C⊂3-MoO3, the rate performance resembles that of Mo2CC⊂1-MoO3 in the initial 40 cycles, and drops slightly at 200 mA·g-1 in the following cycles. With regard to Mo2C-C⊂6-MoO3, the discharge capacity drastically reduces to 647 mA·h·g-1 at the 110th cycle at 200 13



Page 14 of 24

mA·g-1, although it exceeds those of both the Mo2C-C⊂14-MoO3 and Mo2C-C⊂0-MoO3.65 The long-term cycling and rate performance of Mo2C-C⊂1-MoO3 nanofiber is superior to many reported MoO3-based materials (Table S1), including MoO3@FeOx nanobelts,66 MoO3 nanorods,2 MoO3/SnO2/CNTs,67 MoO3C nanofiber,45 which may originate from its advanced hybridity designs and structural stability with the more dispersive Mo2C-C coating layer to release the undesirable mechanical strain. This trend implies that high quality hetero-structural features at the early stage of reaction (x = 1, 3) may have a more positive role in modifying the reversibility of Li+ insertion/extraction process. It is reported that the hetero-structural characteristics in electrodes could facilitate and accelerate the ion/electron mobility during electrochemical reactions.68-70 To evaluate the effects of hetero-structure manipulation on Li+ transport behaviors, the cyclic voltammetry (CV) profiles of Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) composites were compared. Figure 4e compared the second cycle cyclic voltammetry profiles of Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) composites, in which the typical cathodic/anodic peaks of Mo2Cbased anodes (~1.26/1.36 V) and MoO3-based electrode (0.16/1.23V and 1.61/1.81 V) have been identified.2, 67 We note that, as x decreases, the anodic peaks (~1.23, 1.79 V) shift pronouncedly to cathodic peaks at ~1.55 V (marked by a star), which manifests that the voltage offset of the redox pairs declines significantly as x decreases. Furthermore, as shown in Figure S7, in comparison with Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) composites, bulk MoO3 has shown the largest voltage offset, manifesting that the asprepared Mo2C-C⊂x-MoO3 (x = 0, 1, 3, 6, 14) samples have lower over-potential than bulk MoO3. Among the four investigated hetero-compositions, the narrower over-potential of Mo2C-C⊂x-MoO3 (x = 1, 3) composites implies better mass/charge transfer capability to the other Mo2C-C⊂x-MoO3 (x = 6, 14) samples and bulk MoO3, confirming that the high quality hetero-structural features of robust interleaved conductive skeleton, substantial hetero-surficial sites, and high-quality hybridity have an important role 14


Page 15 of 24 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 modulating the charge transport behaviors, and reduce the voltage offsets between reduction and reverse reaction, at which the redox event is genuinely occurred and ameliorated. The results of electrochemical impedance spectroscopy for Mo2C-C⊂x-MoO3 (x = 1, 3, 6, 14) samples (Figure 4f, Table 2) further verified that at x = 1, 3, the exchange current density together with the charge-transfer/Li+ diffusion conductivity increase prominently, evidencing that the electron/ion transfer kinetics and electrochemical activities of Mo2C-C⊂x-MoO3 (x = 1, 3) are better than that of Mo2C-C⊂x-MoO3 (x = 6, 14).71, 72 Table 2. Impedance parameters for all samples from the fitted equivalent circuits R1(R2CPE1)((R3Ws)CPE2). In the equivalent circuit, R1 represents the electrolyte and contact resistance, R2 and CPE1 represent the resistance of the asformed solid electrolyte interphase, and constant phase element, respectively. R3 and Ws represent charge-transfer resistance and Warburg diffusion impedance, respectively. CPE2 represents the constant phase element. j0 is calculated according to j0 = RT/nFRct, where j0 refers to the exchange current density. R is the gas constant, T is the absolute temperature, n is the number of transferred electrons, and F is the Faraday constant. Sample

R1 / Ω

R2 / Ω

R3 / Ω

j0 / A·cm-2

Mo2C-C⊂0-MoO3 Mo2C-C⊂1-MoO3 Mo2C-C⊂3-MoO3 Mo2C-C⊂6-MoO3 Mo2C-C⊂14-MoO3

1.591 2.164 2.882 2.138 1.826

90.02 220.6 249.8 226.7 398.8

115.7 267 380.1 713.4 2610

4.44 × 10-5 1.92 × 10-5 1.35 × 10-5 7.19 × 10-6 1.96 × 10-6

Figure 5. TEM images of (a, b) Mo2C-C⊂1-MoO3, (c, d) Mo2C-C⊂3-MoO3, (e) Mo2C-C⊂6-MoO3, (f) Mo2C-C⊂14MoO3 after 30 cycles at 200 mA·g-1. 15



Page 16 of 24

Furthermore, the hetero-structures of Mo2C-C⊂x-MoO3 (x = 1, 3, 6) electrodes have been well maintained after repeated cycle testing, showing intact fibrous structures (Figure 5a-e), while that of Mo2C-C⊂14-MoO3 aggregated severely after cycling tests, implying that Mo2C-C⊂x-MoO3 heteroelectrode at lower value of x is more robust to accommodate repeated volume changes during electrochemical reactions. Based on the above analysis, Mo2C-C⊂x-MoO3 designs at lower x (e.g. x = 1, 3) has more advantageous structural features such as robust conductive skeleton, high quality hybridity, and substantial hetero-surficial sites, which could give rise to high intrinsic electronic conductivity and facilitated lithium ion mobility in Mo2C-C⊂x-MoO3. The structural features are reminiscent of several pioneering work, which have shown that with the introduction of hybridity designs, lopsided charge distribution could be induced in the interior of electrodes. The unbalanced charge distribution could further engender the formation of inbuilt electric field at heterojunctions, and contributes to accelerating the ion diffusion/electron transfer among the active phases.24-26 Based on the above analysis and the as-verified high-rate capability/enhanced electrochemical kinetics of Mo2C-C⊂x-MoO3 at lower x (x = 1, 3), a possible mechanism has been proposed for interpreting the different lithium storage capability of Mo2CC⊂x-MoO3 (Figure 6a). The synergistic effects of high quality hybridity, smaller grain sizes and robust skeletons of Mo2C-C⊂x-MoO3 (x = 1, 3) may induce stronger inbuilt electric fields and interactions around the hetero-interfaces, which will enable the accumulation of charges around the active phases, and guarantee unimpeded charge migration paths inside the hetero-electrodes, as a result, both the charge transfer kinetics and cycling durability could be boosted. The deteriorating architectures (namely, reduced integrity and quality of hybridity) is probably one of the most important reasons for the decreasing lithium storage capability of Mo2C-C⊂x-MoO3 (x = 6, 14) series.

16


Page 17 of 24 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 6. (a) The schematic illustration of lithium diffusion process in Mo2C-C⊂x-MoO3 composites. (b) The estimated trend of hybridity in Mo2C-C⊂x-MoO3.

The above analysis reveals the significance of hetero-structure manipulation in regulating charge transport dynamics and modifying the associated lithium storage performances of electrodes. In this conversion type system, Mo2C-C⊂x-MoO3 compound at smaller x (e.g. x = 1, 3) appears to have more desirable hetero-structures. The associated structural benefits are summarized as: firstly, reduced Li+ diffusion distance and low electric resistance are achieved in such hetero-structures due to the small particle sizes and high electric conductive Mo2C-C hetero-matrix, which leads to accelerated electron/ion transport in the designed hetero-electrodes. In addition, the high quality hybridity of such hetero-structures further guarantee the accumulation of charges and provide substantial electrochemical active sites, leading to prominently improved Li+ insertion/extraction reversibility and reduced over-potential of redox pairs. Furthermore, their robust hetero-structures could render intact charge transport path, good rate durability 17



Page 18 of 24

and long-term cycling performance. This work suggests that, the carefully designed hetero-structures with the aforementioned integrated high quality features could contribute significantly to improving the charge transfer capability and further enhance the properties of devices.

CONCLUSIONS In summary, this work scrutinized the effects of hetero-structure manipulation on the electrochemical behaviors of conversion type electrode. Through the inspection of an ensemble of electrodes with gradient hetero-structure-shifting, it is demonstrated that the quality of hetero-structures has a significant role in regulating the charge transfer behavior, as verified by the results of lithium storage performances and kinetics. The results manifest that, among the four investigated compositions, Mo2C-C⊂x-MoO3 at the early stage of reactions (x = 1, 3) exhibit ameliorated electrochemical performances: small over-potential, high charge-discharge capacity and stable rate performance owing to their superior hetero-structures. Furthermore, Mo2C-C⊂1-MoO3 retained a capacity of ~890 mA·h·g-1 after 300 cycles testing at 1000 mA·g-1, and no capacity fading has been observed after various C-rates cycling. These improvements may mainly be attributed to the synergistic effects of high quality hybridity, small grain sizes and robust fibrous structure in Mo2C-C⊂x-MoO3 (x = 1, 3), which have significantly facilitated the electron and ion transfer among the active phase, as well as enhancing the cycling stability of electrodes. Compositions with such high quality hetero-structural features shed light on better ameliorating electrodes for advanced batteries and devices in other fields and further promoting the round-trip efficiency for batteries employing electrodes via conversion reactions.

ASSOCIATED CONTENT Supporting Information

18


Page 19 of 24 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


Experimental section, Rietveld refinement of X-ray diffraction patterns, TG profiles, X-ray photoelectron spectroscopy, Representative TEM image, SEM image, Table S1.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was partially supported by the National Key Research and Development Program of China (2017YFA0204600), the National Science Fund for Distinguished Young Scholars (51625102), the National Natural Science Foundation of China (51471053), the Key Research and Development Plan Project of Zhejiang Province (No.2018C01036), the Zhejiang Provincial Natural Science Foundation of China under grant LQ15F040006, and the Science and Technology Commission of Shanghai Municipality (17XD1400700). We thank Dr. Kun Rui for her valuable advices for the manuscript, and we also thank Dr. Tania Silver for her critical reading of the manuscript.

REFERENCES [1] Rui K.; Wen Z. Y.; Lu Y.; Jin J.; Shen C. One-step solvothermal synthesis of nanostructured manganese fluoride as an anode for rechargeable lithium-ion batteries and insights into the conversion mechanism, Adv. Energy Mater. 2015, 5, 1401716. [2] Ding J.; Abbas S. A.; Hanmandlu C.; Lin L.; Lai C. S.; Wang P. C.; Li L. J.; Chu C. W.; Chang C. C. Facile synthesis of carbon/MoO3 nanocomposites as stable battery anodes, J. Power Sources 2017, 348, 270-280. [3] Zhou T.; Zheng Y.; Gao H.; Min S.; Li S.; Liu H.; Guo Z. Surface engineering and design strategy for surfaceamorphized TiO2@Graphene hybrids for high power Li-Ion battery electrodes, Adv. Sci. 2015, 2, 1500027. [4] Zheng Y.; Zhou T.; Zhao X.; Pang W.; Gao H.; Li S.; Zhou Z.; Liu H.; Guo Z. Atomic interface engineering and electric-field effect in ultrathin Bi2MoO6 nanosheets for superior lithium ion storage, Adv. Mater. 2017, 29, 1700396. 19



Page 20 of 24

[5] Li D.; Wang H.; Zhou T.; Zhang W.; Liu H.; Guo Z. Unique structural design and strategies for germanium-based anode materials toward enhanced lithium storage, Adv. Energy Mater. 2017, 7, 1700488. [6] Goodenough J. B.; Kim Y. Challenges for rechargeable Li batteries, Chem. Mater. 2009, 22, 587-603. [7] Ellis B. L.; Lee K. T.; Nazar L. F. Positive electrode materials for Li-ion and Li-batteries, Chem. Mater. 2010, 22, 691-714. [8] Bruce P. G.; Scrosati B.; Tarascon J. M. Nanomaterials for rechargeable lithium batteries, Angew. Chem. Int. Ed. 2008, 47, 2930-2946. [9] Dresselhaus M.; Thomas I. Alternative energy technologies, Nature 2001, 414, 332-337. [10] Shen L.; Uchaker E.; Zhang X.; Cao G. Hydrogenated Li4Ti5O12 nanowire arrays for high rate lithium ion batteries, Adv. Mater. 2012, 24, 6502-6506. [11] Zhou X.; Wan L.; Guo Y. Facile synthesis of MoS2@ CMK-3 nanocomposite as an improved anode material for lithium-ion batteries, Nanoscale 2012, 4, 5868-5871. [12] Reddy M.; Subba R. G.; Chowdari B. Metal oxides and oxysalts as anode materials for Li ion batteries, Chem. Rev. 2013, 113, 5364-5457. [13] Hao J.; Zhang J.; Xia G.; Liu Y.; Zheng Y.; Zhang W.; Tang Y.; Pang W.; Guo Z. Heterostructure manipulation via in-situ localized phase transformation for high-rate and highly durable lithium ion storage, ACS Nano, DOI: 10.1021/acsnano.8b06020. [14] Liu Y.; Tai Z.; Zhou T.; Sencadas V.; Zhang J.; Zhang L.; Konstantinov K.; Guo Z.; Liu H. An all‐integrated anode via interlinked chemical bonding between double‐shelled–yolk‐structured silicon and binder for lithium‐ion batteries, Adv. Mater. 2017, 29, 1703028. [15] Kalluri S.; Yoon M.; Jo M.; Liu H.; Dou S.; Cho J.; Guo Z. Feasibility of cathode surface coating technology for high‐energy lithium‐ion and beyond‐lithium‐ion batteries, Adv. Mater. 2017, 29, 1605807. [16] Cao K.; Jiao L.; Liu H.; Liu Y.; Wang Y.; Guo Z.; H. Yuan, 3D hierarchical porous α‐Fe2O3 nanosheets for high‐performance lithium‐ion batteries, Adv. Energy Mater. 2015, 5, 1401421. [17] Yu S. H.; Lee S. H.; Lee D. J.; Sung Y. E.; Hyeon T. Conversion reaction-based oxide nanomaterials for lithium ion battery anodes, Small 2016, 12, 2146-2172. [18] Cao K.; Jin T.; Yang L.; Jiao L. Recent progress in conversion reaction metal oxide anodes for Li-ion batteries, Mater. Chem. Front. 2017, 1, 2213-2242. [19] Malini R.; Uma U.; Sheela T.; Ganesan M.; Renganathan N. G. Conversion reactions: a new pathway to realise energy in lithium-ion battery—review, Ionics 2008, 15, 301-307. [20] Cao Y.; Yang Y.; Ren Z.; Jian N.; Gao M.; Wu Y.; Zhu M.; Pan F.; Liu Y.; Pan H. A new strategy to effectively suppress the initial capacity fading of iron oxides by reacting with LiBH4, Adv. Funct. Mater. 2017, 27, 1700342. [21] Yang Z.; Qian K.; Lv J.; Yan W.; Liu J.; Ai J.; Zhang Y.; Guo T.; Zhou X.; Xu S.; Guo Z. Encapsulation of Fe3O4 nanoparticles into N, S co-doped graphene sheets with greatly enhanced electrochemical performance, Sci. Rep. 2016, 6, 27957. [22] Wu Y. Multifunctional devices from asymmetry, Nat. Electronics 2018, 1, 331-332. [23] Wang J.; Liu J.; Yang H.; Chao D.; Yan J.; Savilov S. V.; Lin J.; Shen Z. X. MoS2 nanosheets decorated Ni3S2@ MoS2 coaxial nanofibers: constructing an ideal heterostructure for enhanced Na-ion storage, Nano Energy 2016, 20, 110. [24] Bediako D. K.; Rezaee M.; Yoo H.; Larson D. T.; Zhao S. Y. F.; Taniguchi T.; Watanabe K.; Brower-Thomas T. L.; Kaxiras E.; Kim P. Heterointerface effects in the electrointercalation of van der Waals heterostructures, Nature 2018, 20


Page 21 of 24 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


558, 425-429. [25] Liu Y.; Rodrigues J. N. B.; Luo Y. Z.; Li L.; Carvalho A.; Yang M.; Laksono E.; Lu J.; Bao Y.; Xu H.; et al. Tailoring sample-wide pseudo-magnetic fields on a graphene–black phosphorus heterostructure, Nat. Nanotechnol. 2018, 13, 828834. [26] Yang T.; Zheng B.; Wang Z.; Xu T.; Pan C.; Zou J.; Zhang X.; Qi Z.; Liu H.; Feng Y.; et al. Van der Waals epitaxial growth and optoelectronics of large-scale WSe2/SnS2 vertical bilayer p-n junctions, Nat. Commun. 2017, 8, 1906. [27] Yan D.; Luo X.; Zhang H.; Zhu G.; Chen L.; Chen G.; Xu H.; Yu A. Single-crystalline α-MoO3 microbelts derived from a bio-templating method for superior lithium storage application, J. Alloys Compd. 2016, 688, 481-486. [28] Santos-Beltrán M.; Paraguay-Delgado F.; Santos-Beltrán A.; Fuentes L. Getting nanometric MoO3 through chemical synthesis and high energy milling, J. Alloys Compd. 2015, 648, 445-455. [29] Zhou L.; Yang L.; Yuan P.; Zou J.; Wu Y.; Yu C. α-MoO3 nanobelts: a high performance cathode material for lithium ion batteries, J. Phys. Chem. C 2010, 114, 21868-21872. [30] Meduri P.; Clark E.; Kim J. H.; Dayalan E.; Sumanasekera G. U. MoO3-x nanowire arrays as stable and high-capacity anodes for lithium ion batteries, Nano Lett. 2012, 12, 1784-1788. [31] Cai L.; Rao P. M.; Zheng X. Morphology-controlled flame synthesis of single, branched, and flower-like α-MoO3 nanobelt arrays, Nano Lett. 2011, 11, 872-877. [32] Zhang D.; Zhou Y.; Cuan J.; Gan N. A lanthanide functionalized MOF hybrid for ratiometric luminescent detection of an anthrax biomarker, CrystEngComm 2018, 20, 1264-1270. [33] Chen J.; Cheah Y. L.; Madhavi S.; Lou X. Fast synthesis of α-MoO3 nanorods with controlled aspect ratios and their enhanced lithium storage capabilities, J. Phys. Chem. C 2010, 114, 8675-8678. [34] Ibrahem M. A.; Wu F. Y.; Mengistie D. A.; Chang C. S.; Li L. J.; Chu C. W. Direct conversion of multilayer molybdenum trioxide to nanorods as multifunctional electrodes in lithium-ion batteries, Nanoscale 2014, 6, 5484-5490. [35] Zhou J.; Lin N.; Wang L.; Zhang K.; Zhu Y.; Qian Y. Synthesis of hexagonal MoO3 nanorods and a study of their electrochemical performance as anode materials for lithium-ion batteries, J. Mater. Chem. A 2015, 3, 7463-7468. [36] Mariotti D.; Lindström H.; Bose A. C.; Ostrikov K. K. Monoclinic β-MoO3 nanosheets produced by atmospheric microplasma: application to lithium-ion batteries, Nanotechnology 2008, 19, 495302. [37] Dewangan K.; Sinha N. N.; Sharma P. K.; Pandey A. C.; Munichandraiah N.; Gajbhiye N. Synthesis and characterization of single-crystalline α-MoO3 nanofibers for enhanced Li-ion intercalation applications, CrystEngComm 2011, 13, 927-933. [38] Chen X.; Huang Y.; Zhang K. α-MoO3 nanorods coated with SnS2 nano sheets core-shell composite as highperformance anode materials of lithium ion batteries, Electrochim. Acta 2016, 222, 956-964. [39] Hassan M. F.; Guo Z.; Chen Z.; Liu H. Carbon-coated MoO3 nanobelts as anode materials for lithium-ion batteries, J. Power Sources 2010, 195, 2372-2376. [40] Li H.; Liang M.; Sun W.; Wang Y. Bimetal-organic framework: one-step homogenous formation and its derived mesoporous ternary metal oxide nanorod for high-capacity, high-rate, and long-cycle-life lithium storage, Adv. Funct. Mater. 2016, 26, 1098-1103. [41] Pang W.; Kalluri S.; Peterson V. K.; Dou S.; Guo Z. Electrochemistry and structure of the cobalt-free Li1+xMO2 (M = Li, Ni, Mn, Fe) composite cathode, Phys. Chem. Chem. Phys. 2014, 16, 25377-25385. [42] Jiang J.; Li Y.; Liu J.; Huang X.; Yuan C.; Lou X. Recent advances in metal oxide-based electrode architecture design for electrochemical energy storage, Adv. Mater. 2012, 24, 5166-5180. [43] Liu L.; Guo H.; Liu J.; Qian F.; Zhang C.; Li T.; Chen W.; Yang X.; Guo Y. Self-assembled hierarchical yolk-shell 21



Page 22 of 24

structured NiO@C from metal-organic frameworks with outstanding performance for lithium storage, Chem. Commun. 2014, 50, 9485-9488. [44] Lu P.; Lei M.; Liu J. Graphene nanosheets encapsulated α-MoO3 nanoribbons with ultrahigh lithium ion storage properties, CrystEngComm 2014, 16, 6745-6755. [45] Li X.; Xu J.; Mei L.; Zhang Z.; Cui C.; Liu H.; Ma J.; Dou S. Electrospinning of crystalline MoO3@C nanofibers for high-rate lithium storage, J. Mater. Chem. A 2015, 3, 3257-3260. [46] Ko Y. N.; Park S. B.; Jung K. Y.; Kang Y. C. One-pot facile synthesis of ant-cave-structured metal oxide–carbon microballs by continuous process for use as anode materials in Li-ion batteries, Nano Lett. 2013, 13, 5462-5466. [47] Wang G.; Ni J.; Wang H.; Gao L. High-performance CNT-wired MoO3 nanobelts for Li-storage application, J. Mater. Chem. A 2013, 1, 4112-4118. [48] Luo Y.; Wang Z.; Fu Y.; Jin C.; Wei Q.; Yang R. In situ preparation of hollow Mo2C–C hybrid microspheres as bifunctional electrocatalysts for oxygen reduction and evolution reactions, J. Mater. Chem. A 2016, 4, 12583-12590. [49] Kalaiselvi N.; Manthiram A. Solution combustion synthesis of high-rate performance carbon-coated lithium iron phosphate from inexpensive iron (III) raw material, J. Power Sources 2010, 195, 2894-2899. [50] Zhu Y.; Wang S.; Zhong Y.; Cai R.; Li L.; Shao Z. Facile synthesis of a MoO2-Mo2C-C composite and its application as favorable anode material for lithium-ion batteries, J. Power Sources 2016, 307, 552-560. [51] Cheng Y.; Huang L.; Xiao X.; Yao B.; Yuan L.; Li T.; Hu Z.; Wang B.; Wan J.; Zhou J. Flexible and cross-linked N-doped carbon nanofiber network for high performance freestanding supercapacitor electrode, Nano Energy 2015, 15, 66-74. [52] Li H.; Su Y.; Sun W.; Wang Y. Carbon nanotubes rooted in porous ternary metal sulfide@N/S-doped carbon dodecahedron: bimetal-organic-frameworks derivation and electrochemical application for high-capacity and long-life lithium-ion batteries, Adv. Funct. Mater. 2016, 26, 8345-8353. [53] Chi J.; Yan K.; Gao W.; Dong B.; Shang X.; Liu Y.; Li X.; Chai Y. M.; Liu C. C. Solvothermal access to rich nitrogen-doped molybdenum carbide nanowires as efficient electrocatalyst for hydrogen evolution reaction, J. Alloys Compd. 2017, 714, 26-34. [54] Ruiz F.; Benzo Z.; Garaboto A.; León V.; Ruette F.; Albornoz A.; Brito J. L. An X-ray photoelectron spectroscopy study of the atomization of Mo from pyrolytic graphite platforms in electrothermal atomic absorption spectroscopy, Spectrochim. Acta, Part B 2017, 133, 1-8. [55] Sun Y.; Wang J.; Zhao B.; Cai R.; Ran R.; Shao Z. Binder-free α-MoO3 nanobelt electrode for lithium-ion batteries utilizing van der Waals forces for film formation and connection with current collector, J. Mater. Chem. A 2013, 1, 47364746. [56] Wu Z.; Lei W.; Wang J.; Liu R.; Xia K.; Xuan C.; Wang D. Various structured molybdenum-based nanomaterials as advanced anode materials for lithium ion batteries, ACS Appl. Mater. Interfaces 2017, 9, 12366-12372. [57] Gao Q.; Zhao X.; Xiao Y.; Zhao D.; Cao M. A mild route to mesoporous Mo2C-C hybrid nanospheres for high performance lithium-ion batteries, Nanoscale 2014, 6, 6151-6157. [58] Kharieky A. A.; Saraee K. R. E.; Strek W. The size effect on luminescence properties of praseodymium doped LuAG prepared by Pechini method, J. Lumin. 2017, 190, 443-450. [59] Lee J.; Kwak S. Y. Tubular superstructures composed of α-Fe2O3 nanoparticles from pyrolysis of metal–organic frameworks in a confined space: effect on morphology, particle size, and magnetic properties, Cryst. Growth Des. 2017, 17, 4496-4500. [60] Li H.; Shen L.; Ding B.; Pang G.; Dou H.; Zhang X. Ultralong SrLi2Ti6O14 nanowires composed of single-crystalline 22


Page 23 of 24 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


nanoparticles: promising candidates for high-power lithium ions batteries, Nano Energy 2015, 13, 18-27. [61] Arico A. S.; Bruce P.; Scrosati B.; Tarascon J. M.; Schalkwijk W. V. Nanostructured materials for advanced energy conversion and storage devices, Nat. Mater. 2005, 4, 366-377. [62] Viswanathamurthi P. Vanadium pentoxide nanofibers by electrospinning, Scr. Mater. 2003, 49, 577-581. [63] Wang P.; Cheng Z.; Lv G.; Qu L.; Zhao Y. Coupling interconnected MoO3/WO3 nanosheets with a graphene framework as a highly efficient anode for lithium-ion batteries, Nanoscale 2017, 10, 396-402. [64] Ihsan M.; Wang H.; Majid S. R.; Yang J.; Kennedy S. J.; Guo Z.; Liu H. MoO2/Mo2C/C spheres as anode materials for lithium ion batteries, Carbon 2016, 96, 1200-1207. [65] Tian W.; Hu H.; Wang Y.; Li P.; Liu J.; Liu J.; Wang X.; Xu X.; Li Z.; Zhao Q. Metal–organic frameworks mediated synthesis of one-dimensional molybdenum-based/carbon composites for enhanced lithium storage, ACS Nano 2018, 12, 1990-2000. [66] Yao Y.; Xu N.; Guan D.; Li J.; Zhuang Z.; Zhou L.; Shi C.; Liu X.; Mai L. Facet-selective deposition of FeOx on alpha-MoO3 nanobelts for lithium storage, ACS Appl. Mater. Interfaces 2017, 9, 39425-39431. [67] Cao D.; Gu H.; Xie C.; Li B.; Wang H.; Niu C. Binding SnO2 nanoparticles onto carbon nanotubes with assistance of amorphous MoO3 towards enhanced lithium storage performance, J. Colloid Interface Sci. 2017, 504, 230-237. [68] Zheng Y.; Zhou T.; Zhang C.; Mao J.; Liu H.; Guo Z. Boosted charge transfer in SnS/SnO2 heterostructures: toward high rate capability for sodium-ion batteries, Angew. Chem. 2016, 125, 3469-3474. [69] Chang X.; Wang T.; Zhang P.; Zhang J.; Li A.; Gong J. L. Enhanced surface reaction kinetics and charge separation of p–n heterojunction Co3O4/BiVO4 photoanodes, J. Am. Chem. Soc. 2015, 137, 8356-8359. [70] Wang J.; Zhou Y.; Shao Z. Porous TiO2 (B)/anatase microspheres with hierarchical nano and microstructures for high-performance lithium-ion batteries, Electrochim. Acta 2013, 97, 386-392. [71] Kim A. Y.; Kim J. S.; Hudaya C.; Xiao D.; Byun D.; Gu L.; Wei X.; Yao Y.; Yu R.; Lee. J. K. An elastic carbon layer on echeveria-inspired SnO2 anode for long-cycle and high-rate lithium ion batteries, Carbon 2015, 94, 539-547. [72] Zhou G.; Wang D.; Li L.; Li N.; Li F.; Cheng H. Nanosize SnO2 confined in the porous shells of carbon cages for kinetically efficient and long-term lithium storage, Nanoscale 2013, 5, 1576-1582.

23



Page 24 of 24

TOC/Abstract Graphic

Synopsis Hetero-manipulation helps to ameliorate the reversibility of electrochemical reactions for sustainable energy storage, in particular for lithium ion batteries.

24


Heterostructure Manipulation toward Ameliorating Electrodes for

Recommend Documents