Green and Rational Design of 3D Layer-by-Layer MnOx Hierarchically

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Energy, Environmental, and Catalysis Applications

Green and Rational Design of 3-D Layer-By-Layer MnOx Hierarchically Mesoporous Microcuboids from MOF Templates for High-Rate and Long-Life Li-Ion Batteries Xiaoshi Hu, Xiaobing Lou, Chao Li, Qi Yang, Qun Chen, and Bingwen Hu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b00953 • Publication Date (Web): 11 Apr 2018 Downloaded from http://pubs.acs.org on April 11, 2018

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ACS Applied Materials & Interfaces

Green and Rational Design of 3-D Layer-By-Layer MnOx Hierarchically Mesoporous Microcuboids from MOF Templates for High-Rate and Long-Life Li-Ion Batteries Xiaoshi Hu, Xiaobing Lou, Chao Li, Qi Yang*, Qun Chen and Bingwen Hu* State Key Laboratory of Precision Spectroscopy, Shanghai Key Laboratory of Magnetic Resonance, Institute of Functional Materials, School of Physics and Materials Science, East China Normal University, Shanghai 200062, PR China KEYWORDS: eco-friendly, solution-phase reaction, MOF template, MnOx, layer-by-layer, 3-D hierarchical microcuboids, lithium storage

ABSTRACT: Rational design and delicate control on the textural properties of metal oxide materials for diverse structure-dependent applications still remain formidable challenges. Here, we present an eco-friendly and facile approach to smartly fabricate 3-D layer-by-layer manganese oxide (MnOx) hierarchical mesoporous microcuboids from a Mn-MOF-74-based template, using a one-step solution-phase reaction scheme at room temperature. Through the controlled exchange of MOF ligand with OH- in alkaline aqueous solution and in situ oxidation

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of manganese hydroxide intermediate, the Mn-MOF-74 template/precursor were readily converted to Mn3O4 and δ-MnO2 counterpart consisting of primary nanoparticles and nanosheets building blocks, respectively, with well-retained morphology. By XRD, TEM, SEM and HRTEM, N2 adsorption/desorption analysis et. al., their crystal structure, detailed morphology and microstructure features were unambiguously revealed. Specifically, their electrochemical Li ion insertion/extraction properties were well evaluated, and it turns out that these unique 3D microcuboids could achieve a sustained superior lithium storage performance especially at high rates benefited from the well-orchestrated structural characteristics (Mn3O4 microcuboids: 890.7 mA h g-1, 767.4 mA h g-1, 560.1 mA h g-1, and 437.1 mA h g-1 after 400 cycles at 0.2 A g-1, 0.5 A g-1, 1 A g-1 and 2 A g-1, respectively; δ-MnO2 microcuboids: 991.5 mA h g-1, 660.8 mA h g-1, 504.4 mA h g-1, and 362.1 mA h g-1 after 400 cycles at 0.2 A g-1, 0.5 A g-1, 1 A g-1 and 2A g-1, respectively). To our knowledge, this is the most durable high-rate capability, as well as highest reversible capacity ever reported for pure MnOx anodes, and even surpass most of their hybrids. This facile, green and economical strategy renews the traditional MOF-derived synthesis for highly tailorable functional materials and opens up new opportunities for metal oxide electrodes with high performance.

INTRODUCTION Rechargeable lithium-ion batteries (LIBs) now represent one of the most significant and prospective technologies for supporting the development of a sustainable and mobile society.1 It is generally accepted that electrode materials for the next generation rechargeable LIBs should be economical to manufacture, pose minimal environmental hazard, possess superior


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electrochemical properties and well security.1 However, owing to the relatively low Li-storage capacity (372 mAh g-1) and potential safety issues caused by a rather low Li-ion embedding potential (0.2 V vs Li/Li+), the commercial graphite anode could hardly fulfill the requirements of newly emerging large-scale applications, e.g., electric vehicles (EVs), hybrid EVs, and integrated grid systems, where higher energy density and power density are essential. Unlike conventional graphite materials that incorporate Li+ ions through insertion mechanism, electrochemically active transition metal oxides (TMOs), as first proposed by Tarascon et al.2, are endowed with extremely high reversible capacities (2–3 times that of graphite) and better safety, on basis of an unusual conversion-type reaction (MOx + 2xLi+ +2xe- ↔ M + xLi2O). Amidst various TMOs, manganese oxides (MnOx: MnO, MnO2, Mn2O3, and Mn3O4) have aroused much attention for battery electrode because of their high natural abundance, low cost, nonpollution etc.3 In particular, they are even more appealing when considering the lower electrochemical motivation force (emf) of nanometer-sized Mn grains (1.2 V vs Li/Li+) compared to other TMOs (such as cobalt, which has an emf of about 2 V), because the low electromotive force will result in higher output cell voltage and hence higher energy densities in a full cell.3 In spite of these favorable properties, the real-world implementation of MnOx electrodes are greatly retarded by their poor capacity retention and rate capabilities owing to the intrinsically inferior charge/ionic conductivity and repeated volumetric deformation during prolonged cycling, as often observed from TMOs anodes.3 By far, three popular strategies are generally taken to overcome these obstacles. One centers on the scrupulous design of nanostructured MnOx electrodes, such as nanoparticles4, nano-octahedra5, nanosheets6, nanorods7, and nanotubes8. Downsizing materials to nanoscale level can partly relax the lattice stress/strain caused by electrochemical process and provide short solid-state diffusion lengths of electron/Li-


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ion together with ample surface reaction sites relative to their large-size counterparts.9 However, due to high surface energy of MnOx nanomaterials, they inevitably suffer from severe secondary reactions involving electrolyte decomposition and show a strong tendency to self-aggregate during battery operation, which causes a high level of irreversibility (i.e., low columbic efficiency) and performance degradation.9 The second strategy is based on the smart hybridization of MnOx with carbonaceous materials10-35, such as graphene or reduced graphene oxide10-16, carbon quantum dot17, and carbon nanofiber/nanotube18-23. The electrochemical properties of these samples are greatly related with the form and/or structure of the carbon.36-38 Generally, the coupling of carbon-based material with MnOx may simultaneously boost the electrical conductivity, provide stable structural support and maintain a good dispersion of MnOx-based anodes, and overcome the undesirable side reactions between active materials and electrolyte.39 However, the low product yields, multistep and costly operations negated the cost advantage of manganese oxides.39 Recently, building up well-designed three-dimensional (3-D) micro-/nanostructured metal oxide electrodes internally consisting of low-dimensional nanobuilding blocks/nano-domains with desirable mesoporosity has paved a way for development of high-performance electrochemical energy devices.40,

41

As well established, hierarchically

mesoporous micro-/nanostructures are favorable for structure-dependent energy storage and conversion applications because of their common denominator, namely: i) keeping the inherent advantages of the individual nanoentities, while avoiding their disadvantages abovementioned. ii) the prevention of self-aggregation and structural degradation, and iii) convenient electrolyte ingress and accommodation of volume variation.40, 41 However, up to now, research into the reasonable design and accurate synthesis of TMOs functional materials with desirable


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superstructures under mass manufacture, and further application as advanced anode materials for LIBs are still at an early stage. Metal–organic frameworks (MOFs)-templated synthesis is emerging as a universal approach to prepare a wide range of highly functionalized materials (e.g. carbon, metal/carbon, transition metal oxide/sulfide) for broad applications, including catalysis, sensors, gas separation and storage, and energy storage, due to their structural diversities and tunable properties.42 To be mentioned, advanced TMOs electrodes, for example spindle-like mesoporous α‑Fe2O343, high symmetric porous Co3O4 hollow dodecahedra44, multilayer CuO@NiO hollow spheres45, porous core/shell structured ZnO/ZnCo2O4/C hybrids46 and other more complex ones47 can be typically obtained, by selective pyrolysis of related MOFs in a controlled atmosphere and exhibited enhanced electrochemical performance in LIB applications. Manganese-based materials such as MnO/C hybrids48-50, mesoporous MnO/C−N nanostructures51, porous Mn2O3 octahedra,52 minihollow polyhedron Mn2O353, hierarchically porous Mn2O354, Mn2O3 mesoporous nanobars55, Mn2O3 hollow microspheres56, mesoporous Mn3O4/C microspheres57, sponge network-shaped Mn3O4/C58, MnOx-CSs nanocomposites59 and so on have also been prepared via oxidative decomposition of Mn-based MOFs precursors for use as anodes in LIBs in the near term. Notwithstanding these advances, the performance of MnOx materials is still limited by either their power density or their cycle life. On the other hand, this thermally-induced solid-state approach approves to be inefficient, involves the very high energy input and generates volatile and/or toxic species, such as COx and NOx. Furthermore, bulk aggregation and/or undesired structural collapse of the resultant materials easily occurs at elevated temperatures, leading to the loss of their structural frameworks and original shapes, and it seems to be difficult to precisely control and finely tailor the deuterogenic nanostructures,60-62 which tend to show distinct results


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though starting with a similar template and combustion condition. From the perspective of practical applications, there is a strong need to explore other green strategies and concepts to create complex metal oxide hierarchical architecture, utilizing the chemical properties of MOFs with mild moderate operating conditions, good control of the morphology and dimension, and high through-put. Stimulated by the above concerns, in this contribution, we propose and realize a simple, efficient, yet scalable self-sacrifice MOF template-engaged protocol to rationally fabricate 3-D layer-by-layer MnOx hierarchical microcuboids solely by post-basic digest solution treatment of well-designed, single-resource Mn-MOF-74 precursor, during which a controlled ion-exchange reaction between the precursor and OH- and in situ chemical redox of the resulted Mn(OH)2 intermediate took place. The polymorphs of MnOx can be tuned by controlled oxidation with the help of H2O2 in the reaction solution. Significantly, this novel wet templating method substantially save energy and features zero release. Leveraging the peculiar structural properties of these new MnOx materials, we demonstrate their practical applicability toward LIBs.

RESULTS AND DISCUSSION Synthesis, morphological, structural characterization Briefly, our strategy for fabricating such unique MnOx superstructure is composed of two steps as illustrated in Figure 1 (see Methods for details). It includes: (1) bottom-up growth of microscale cuboids consisting of orderly stacked Mn-MOF-74 layers under the solvothermal condition, where no extra surfactants are applied, and (2) dispersion of the resultant MOF-74 template/precursor into aqueous alkali solution at room temperature in the absence and presence of H2O2, to afford high-quality hierarchical Mn3O4 and MnO2 products, respectively with well-


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preserved shape and size. Mn-MOF-74 is a member of the well-known MOF-74/CPO-27 series [M2(dobdc), M = Ni2+, Mn2+, Zn2+, Co2+, and dobdc = 2, 5-dihydroxybenzenedicarboxylic acid], that feature a network of one-dimensional honeycomb-shaped channels of ca. 11 Å diameter with open metal sites (Figure 2A, top) and exhibit remarkable textural properties.63 Powder x-ray diffraction (XRD) measurements confirm that our product is identical to a previously determined MOF (CCDC#1494753) (Figure 2A, middle and bottom). The general scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images, shown in Figure 2B-D, announced monodisperse cuboid-like solid particle of dimensions in the range of several µm to several tens of µm. A close observation reveals that these cuboids possessed smooth facets and lamellar stacking characteristic, with the closely packed thin layers (thickness ~ 200 nm) assembled perpendicular to surface (inset in Figure 2(C), and Figure S1). Such well-defined particle morphologies of MOFs with special architecture are important toward the formation of anisotropic inorganic materials. SEM studies (Figure 2E-H) throughout the duration of the crystallization process revealed the gradual growth (horizontal) and aggregation (vertical) of intermediate two-dimensional (2D) layers from the solution with increasing solvothermal time. Thermodynamically, the primary driving force of growing these self-oriented order-aligned aggregates is to minimize the overall surface energy by reducing the large exposed areas of the individual layers.6 In the second step, the MOF templates were suspended in a dilute NaOH solution (0.05 M) in an open-ambient environment (exposed to air) or containing H2O2, followed by collection via filtration and multiple washes with solvents to yield targeted Mn3O4 (PDF#16-0154) and δMnO2 materials (PDF#80-1098) (Figure 3A, B). We surmised that the chemical process to produce MnOx via treatment of Mn-based MOF precursor in oxidative and basic medium could


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be rationalized as follows. After penetrating into the inter-layer open spaces and the small pores (or defects) in the Mn-MOF-74 crystals, OH− could exchange with dobdc4- in Mn-MOF-74 thermodynamically to form Mn(OH)2, similar to postsynthetic exchange64: Mn2(dobdc) (s) + 2OH- (aq.) → Mn(OH)2 (s) + dobdc4- (aq.)

(1)

As Mn(OH)2 is very unstable and can be easily oxidized to oxides by air/dissolved oxygen6, 65 or strong oxidation reagent65 during self-assembly reaction in solution, in situ oxidation of the Mn(OH)2 intermediates may further proceed as described below:: 6Mn(OH)2 (s) + O2 (aq.) → 2Mn3O4 (s) + 6H2O(l)

(2a)6, 65

Mn(OH)2 (s) + H2O2 (aq.) → MnO2 (s) + 2H2O (l)

(2b)65

To exclude the possibility that the Mn-MOFs were oxidized by H2O2 directly without NaOH solution, we performed a control experiment where the Mn-MOF-74 template was added to an aqueous solution of H2O2 while keeping other synthetic conditions unchanged. The final precipitate was examined by XRD (Figure S2). The result revealed that the MOF framework did not react with H2O2, confirming that NaOH was necessary during the preparation of our target product. It should be noted here that, the dobdc4- ligand has been exchanged into the NaOH solution and it will be washed out later on. Therefore, there is no carbon element existent in the final MnO2 or Mn3O4 product. However, the dobdc4- ligand could be possibly reused again to synthesize the Mn2(dobdc), making this method more economic. The broad diffraction peaks with low intensity indicates that the MnOx crystallites are small (Figure 3A, B). IR spectroscopy (Figure S3) and TG traces (Figure S4) suggested that the organic portion of the framework had been completely consumed (see the Supporting Information for details). The information on the surface electronic state and composition of the products were given by XPS analysis (Figure S5, and Figure 3C, D). In the full-survey-scan


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spectrum (0–1200 eV, Figure S5A, B), only manganese and oxygen elements were probed besides the reference C signal. Especially, Na 1s photoelectron peak (～ 1071.1 eV) was also detected on the surface of δ-MnO2 material, as Na+ ions are easily embedded into the interlayer and favourable for the stability of layered MnO2 during the synthesis procedure. The oxidation state of MnOx was determined from the multiplet splitting of the Mn 2p peak. A 2p3/2–2p1/2 doublet centered at 641.7 and 653.5 eV with a spin-energy separation of 11.9 eV in Figure 3C is in agreement with that reported for Mn3O4.13, 23 A 2p3/2–2p1/2 doublet at 642.6 and 654.2 eV with an energy separation of 11.6 eV in Figure 3D is in agreement with previously reported MnO2.10 This identification was further supported by their fitted data8,

13, 23

(Figure 3C, D) and the

exchange splitting for Mn 3s components66 of the two samples (Figure S5C, D) that closely matches the standard values of Mn3O4 (5.50) and MnO2 (4.78), respectively. Figure S5E, F shows the deconvoluted O 1s spectra, where a strong peak located at ～ 529.9 ev correspond to bonds of Mn−O, the peak sitting at ～531.4 eV correspond to defects, under-coordinated lattice oxygen, or species intrinsic to the surface of the TMOs, and the weak shoulder at the high binding energy of 532.8-533.8 ev is generally related to the oxygen in surface adsorbed contaminants and water molecuels.29 All the above-mentioned results corroborate the formation of high-purity MnOx by chemical transformation of the MOF precursor. Creating innovative architectures of TMOs with desired material properties, e.g. microstructural, mechanical and electrical properties, is imperative to the development of a new generation of electrodes with high energy and power density as well as long cycle life.3 Here, two novel manganese oxide superstructures, i. e. 3-D hierarchically ordered microcubes composed of primary zero-dimensional (0-D) Mn3O4 nanoparticles and two-dimensional (2-D) curly MnO2 nanosheets were prepared after chemical eroding the preformed MOFs, as can be seen from the


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SEM observations (Figure 4A-C, Figure 5A-C, and Figure S6). A detailed view presented in Figure 4C, Figure 5C and Figure S6 revealed that typical nanoparticles had diameters of ca. 120 nm and the nanosheets had a thickness of about 70 nm with an average lateral size of ca. 600 nm. These tiny particles, as well as the ultrathin small sheets subunits inter-connect to each other compactly within the limits of the pristine interspaced MOF layers, forming luxuriant pores between neighbors, which can be clearly seen from the TEM images of a randomly selected cuboid particle (Figure 4D and Figure 5D). It should be pointed that the growth of the nanocrystal morphology, namely nanoparticles for Mn3O4 microcubes and nanosheets for δMnO2 microcubes was determined by the intrinsic tetragonal spinel structure of hausmanite lattice (Mn3O4) and layered crystalline structure of birnessite-type δ-phase MnO2, respectively.67 Though different in the basic building blocks, both the two samples substantially inherited the original shape, size, and repeating layer stacking pattern of the Mn-MOF-74 template (Figure 4A-D and Figure 5A-D). From a high-resolution TEM (HRTEM) image (Figure 4E and Figure 5E) and its corresponding selected-area electron diffraction (SAED) pattern (Figure 4F and Figure 5F), the two polymorphs of manganese oxides can be definitely identified as polycrystalline Mn3O4 and δ-MnO2 phase as well, respectively, as previously described by XRD pattern (Figure 3A, B).5, 68 Energy dispersive spectroscopy (EDS) analysis confirms that the samples are composed of Mn and O elements (Figure S7A, B), which is in good accordance with the result of XPS, and these elements are homogeneously distributed throughout a single particle (Figure S7C-F). The EDX also detected Na in δ-MnO2 phase. The high textural porosity of these 3-D hierarchical MnOx microcuboids was further evidenced by N2 isothermal adsorption–desorption measurements (Figure 6). The isotherms show an shape close to type-IV with a hysteresis loop extending over a


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wide pressure range

(p/p0 = 0.4–1.0), which indicates that both the samples are mainly

mesoporous with quite few macropores.62 The BarrettJoynerHalenda (BJH) pore size distribution calculated from desorption branches (inset, Figure 6) demonstrates the bimodal pore structure in the mesoporous region (Mn3O4: 2.2 nm and 3.5 nm; δ-MnO2: 3.7 nm and 13.1 nm), which may correspond to the interspaces of MnOx stacked at different locations within the cuboid framework. Furthermore, on the basis of the adsorption–desorption isotherm, the pore volume of MnOx was measured to be 0.28 cm3 g-1 for Mn3O4 and 0.71 cm3 g-1 for δ-MnO2, and the Brunauer EmmettTeller (BET) specific surface area to be 80.5 and 169.5 m2 g−1, respectively, which are higher than that of previously reported MnOx-based electrodes.3 The abundant interconnected pores and open diffusion channels should come from the loss of organic components during the transformation of the MOF, and the gaps between MOF layers. These results are consistent with the previous SEM and TEM observation in Figure 4 and Figure 5. Unambiguously, the excellent porous geometry with the increased surface area of our MnOx electrode is able to maintain structural integrity during repeated insertion/extraction of Li+ ions and can provide a fine electrode/electrolyte contact area and ample active sites for the accumulation of redox ions or charge.69 We also investigated the effect of the concentration of NaOH used in the experiment on the morphology of hierarchical MnOx microcuboids, as shown in Figure 7 and Figure S8. Remarkably, the cuboid morphology of Mn3O4 products collapsed gradually with promoted inward flow of OH- and precipitation of Mn(OH)2 by using higher concentration of NaOH solution (0.25-0.5 M). At a NaOH concentration of 1 M, the structure of Mn3O4 disappeared completely, and particle-like subunits with larger average diameter of 200-350 nm grew remarkably as the final product. These results suggested that the key to keep the structure


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integrity of the MOF precursor was the precise manipulation of the ion exchange reaction by using an alkaline solution with proper concentration. Interestingly, in the case of MnO2 products, the well-defined microcuboids were hardly destroyed with increasing concentration of NaOH (0.5-5 M) until concentrated NaOH solution of 10.0 M was used for the synthesis. This might be ascribed to fast preferable dissolution and re-oxidation/crystallization with the supply of H2O2.70 Therefore, we consider this morphology-conserved solution approach easy, tunable, and costeffective for mass production of MnOx superstructures from MOF precursors.

Performance evaluation as LIB anodes Intrigued by the structural features, we evaluated the mesoporous MnOx microcuboids as anode materials for lithium ion batteries. The general features of the galvanostatic dischargecharge profiles and CV curves of the two samples are in congruence with those of reported manganese oxides that undergo conversion mechanism.3, 71-74 Figure 8A show the discharge/charge curves of Mn3O4 sample aggregated by nanoparticles for the initial two cycles conducted at a current density of 0.2 A g-1 in the potential range from 0.01 V to 3 V vs. Li/Li+. As can be seen, the first discharge-specific capacity (1078.9 mA h g−1) have much higher values than of the charge (625.1 mA h g−1), giving a large capacity loss of 42.1% attributable to the partially irreversible reactions of the electrodes with Li, escape of water, and irreversible degradation of electrolyte accompanied by the growth of a solid electrolyte interface (SEI) layer on the electrode surface.72 This phenomenon has been commonly observed in a number of TMOs anode materials.72 An obvious voltage slope ranging from open voltage (2.94 V) to 0.40 V can be observed in the first discharge curve, consistent with the broad cathodic peak at ca. 1.25 V in the


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cyclic voltammogram (CV) for the first scan shown in Figure 8B, which can be ascribed to the initial lithiation of Mn3O4 to MnO and Li2O (perhaps via formation an intermediate LiMn3O4 phase) in addition to the reductive decomposition of electrolyte solvent.71-73 This peak almost vanished in the next cycle. The long and steady discharging plateau at low potential (ca. 0.28 V) and the succeeding slope to the cut off voltage correspond to the intensive and sharp cathodic peak in the CV close to 0 V, which reflects the conversion of MnO to metallic Mn and Li2O.71-73 Upon recharge, a well-defined voltage plateau at around 1.19 V which is at significantly lower voltage than that of cobalt or iron-based metal oxides, and the succeeding sloping voltage above 2.20 V observed in the first charge curve correspond to the strong anodic peak at ca. 1.21 and the shoulder peak at around 2.49 V (see inset in Figure 8B: enlarged CV curve, which can be seen more clearly in Figure 9D), respectively, in the first anodic CV sweep. The strong anodic peak at ca. 1.21 V should originate from the reverse oxidation of Mn metal to MnO with the concomitant decomposition of Li2O,71-73 and the additional shoulder peak at the higher potential7 may be associated with a further oxidation of MnO back to a higher oxidation state of Mn species (Mn3O4). Correspondingly, a very weak and broad peak occurred at around 1.22 V (inset in Figure 8B, which can be seen more clearly in Figure 9D) in the subsequent reverse CV sweep, reflecting the sloping voltage range from 2.43 V to 0.57 V in the second cycle of the charge/discharge curve should be attributed to the reduction of the higher valence Mn species back to MnO, suggesting a partial reversibility of this redox reaction. However, for the second cycle of CV scan, the main cathodic peak corresponding to MnO reduction migrated to a higher voltage of ca. 0.34 V attributed to initial lithium driven structural rearrangement or textural modifications, which is a common to TMOs-based anodes.3 Similar to the CV results, the corresponding lithiation plateau diverted to a higher potential near 0.51 V during the second


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discharging. However, the anodic peaks or the tendency of the second charge profiles do not change much, implying the high electrochemical reversibility after the first discharge. Following the development of an SEI, the charge-discharge Coulombic efficiency reaches 94.5% in the second cycle. The discharge-charge voltage profile and CV behavior of the MnO2 sample is generally consistent with those of Mn3O4, declaring the lithium storage mechanism are essentially the same for them (mainly through reversible conversion reaction between MnO and metallic Mn), except for the initial discharge, as shown in Figure 8C.71, 72, 74 During the first cathodic process, the electrochemical reduction of MnO2 electrode may proceed in three steps with the consecutive formation of LiMnO2 (sloping voltage plateau at ∼2.64 V; reduction peak at 2.59 V), Li2MnO2 and SEI film (mild slope from 2.39 V to 0.37 V; reduction peak at 1.02 V), and finally metallic Mn and Li2O (long plateau at 0.29 V; intense peak at 0.09 V).71, 72, 74 The initial Coulombic efficiency of MnO2 electrode (48.3%) is thus lower than that observed for Mn3O4 (57.9%), which is reasonably related with its larger irreversible phase transition in the initial cycle.71 Besides, the enhanced specific surface area of mesoporous microcuboids assembled by MnO2 nanosheets may increase the unwanted Li+ consumption from the side reaction and lead to low CE. Figure 8E, F presents the cycling performance at different densities of 0.2, 0.5, 1, and 2 A g−1, respectively. During the cycling test at 0.2 A g−1, the specific capacity of Mn3O4 anode drops slowly for the first 30 cycles to a minimum value of 634.8 mA h g−1, and thereafter, rise gradually and levels off at a high capacity of 890.7 mA h g−1 until 400 cycles with Coulombic efficiency maintained almost 100% (Figure S9). When the electrode is tested at higher current rates of 0.5, 1, and 2 A g−1, the discharge capacity was still retained at 767.4, 560.1 and 437.1 mA h g-1 (much larger than the theoretical capacity of commercial graphite, 372 mA h g-1), respectively, after 400 cycles, which gave a capacity retention of nearly 100% with respect to the


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first charge. In the case of MnO2 anode, the discharge specific capacity also fall off first and then slowly climb up to and stabilize at 991.5 mA h g-1 with a high CE of 99.4% (Figure S9) at 0.2 A g-1 after 400 cycles. At accelerated current rate of 0.5, 1 and 2 A g-1, the reversible capacities could be still kept at 660.8, 504.4, and 362.1 mA h g-1 after 400 cycles. To the best of our knowledge, this is the best performance for pure manganese oxide anodes.3-8,

40, 41, 75, 76

Even

compared with their related hybrids, the rate capability and cycling stability of our MnOx is still impressive.10-35, 77, 78 Most of the works on manganese oxide-based electrodes only reported its short-term cycle-life durability (≤150 cycles) at a low current density (≤0.2 A g−1; Table S1, Supporting Information). The performance superiority of our MnOx electrodes over other nanostructures can be ascribed to the advantages of their unique 3D architectural structure, which would be scrutinized (see below). Here it is interesting to note that both the Mn3O4 and MnO2 electrode undergo a similar variation trend in terms of discharge capacity: first declined during the initial several tens of cycles and then raised on prolonged cycling. In order to elucidate the evolution of capacity with cycling, some selected voltage profiles are displayed in Figure 9A, B and Figure S10. As shown in Figure S10A, the small quantity of capacity degradation occurred mainly at ca. 0.5 V when discharged and at ca. 1.4 V when charged for Mn3O4 electrode during the initial 30 cycles, and in almost the whole voltage range for MnO2 electrode (Figure S10B). The slight capacity fading and the irreversible capacity in the first few lithiation and delithiation cycles should mainly result from the irreversible insertion reaction, loss of water and slow formation of a complete SEI layer, which is common to virtually all systems based on conversion reactions.72 Beyond the 30th cycle, as shown in Figure 9A, B, for the charging process, the charge capacity increment is gained at both low (below 2 V) and high (over 2 V) potentials. For the discharging


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process, the discharge capacity increment is also gained at both high (over 0.5 V,) and low potentials (below 0.5 V). Accordingly, both the electrode processes corresponding to the high potential range as well as the low voltage range are responsible for the whole capacity increment. Interestingly, the polarization becomes much smaller after cycling as confirmed by the narrower voltage hysteresis, suggesting higher energy efficiency and increased kinetics features of the electrode reaction. Impedance analysis shows clearly the strengthened capacitive-like behavior with cycling.69 As shown in Figure 9C, electrochemical impedance spectra (EIS) of MnOx after 1 and 200 cycles were investigated. All Nyquist curves consist of a high-frequency arc indicative of SEI layer resistance (RSEI), middle-frequency arc representing the charge-transfer resistance (Rct) at the electrode/electrolyte interface, and inclined line at low-frequency region indexed to the Li+ ions diffusion in solid (Zw).69 It can be seen that both Rct and Zw of the two MnOx electrodes are obviously smaller after 200 cycles at 0.2 A g−1 than that after the first cycle (reflected by the decreased diameter of middle-frequency arc and steeper increase of the Z'–Z″ curves at low frequencies, respectively), suggesting the transfer of ions and electrons to the surface of and inside nano-sized active particles become easier after the repeated cycle.69 With reference to previous studies and based on our results, we proposed that the increased mass and charge transport kinetics in the battery may be due to the so-called electrochemical milling (ECM) effects, which modify the morphology of a material and reduce the particle size as well, that are well supported by the SEM micrographs taken from cycled electrode in Figure 10, Figure S11 and Figure S12.29, 79 As we can see, the microcuboid morphology were basically preserved after cycled for hundreds of times (Figure 10A, B, Figure S11 and Figure S12A, B), validating the excellent mechanical stability of the MnOx electrodes. While, from the highmagnification SEM and TEM images of Figure 10C, D and Figure S12C, D, the active MnOx


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material is modified to a more dispersive structure with defects and the initial nanoparticles or nanosheets to smaller particles during prolonged lithium intercalation/deintercalation, which could further shorten electronic and Li+ transport lengths and increase the contact surface area between the electrode and electrolyte, responsible for the consequent decreased cell resistance and lower overpotential of Mn2+ to a higher oxidation state. Therefore, the continuous capacity rise in our case can be ascribed to the activation of the active material via ECM, leading to gradually achieving the complete reaction with cycling. Another possibility, that is, the rising of capacity was attributed to reversible growth of a polymeric gel-like film, could not be completely ruled out. In addition, the stable SEI formed on the electrode material surface (as no obvious impedance increase in RSEI was observed with prolonged cycling from Figure 9C), wellmaintained microcuboid structure and favorable mass and charge transport kinetics after the cycling tests, confirm the sustained excellent cyclability and good rate capability presented in Figure 8.69 By carefully observing the profiles, we can find that the increase in discharge/charge specific capacity with cycling mainly originates from high potential range, which can be revealed by the dramatically increased intensity of the redox peak pair at a higher potential (0.91 V / 2.19 V for Mn3O4, and 0.99 V / 2.13 V for MnO2) in CVs for cycled MnOx electrode after 200 discharge/charge at 0.2 A g−1 (two cycles), as shown in Figure 9D. These results suggest the high reactivity of the redox reaction between MnO and the higher-valence Mn species, and these 3D electrodes in different components (Mn3O4 and MnO2) can reversibly convert to high-oxidation end product respectively in the charge process. Interestingly, these peaks are rarely observed in other bare manganese-based anode materials6, 40, 71, 75, 76 which show MnO as the end product of the charge process, except some MnOx/conductive carbon composite material15, 58 or a pristine MnOx material with a peculiar morphology5, 7. We deduce that the extra electrochemical activity of MnO


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is likely due to the superior kinetics arising from substantial well-developed pores and void space in interlamination/intralamination, large specific surface area, and nanoscale subunits with a much smaller size. This may also explain the high cycling capacity of our MnOx materials, that approximate to the theoretical capacity (937 mA h g-1 for Mn3O4 and 1233 mA h g-1 for MnO2) of a hypothetical fully reversible conversion reaction, and exceed most reported MnOx-based anodes, including their nanocomposites. Further investigations on the details concerning this conclusion are needed in the near future. Based on the above analysis, the MnOx electrodes demonstrate greatly enhanced lithium storage properties with both highly reversible specific capacity and high rate capability, which could be reasonably attributed to its distinct structural and morphological merits. First, its open and highly porous structure with a large specific surface area allows the electrolyte ions to penetrate conveniently, and offer short and flexible transport pathways for the Li+ ions and electron through the electrode/electrolyte interface. At the same time, the special stacked structure of the 3D electrode was supposed to further promote ion movement and reduce charge transfer resistance between the MnOx layers; second, the ultrasmall nanoparticle or ultrathin nanosheet subunits, with a high surface-to-bulk ratio, impart negligible diffusion time in the electrode solid and are also the keys to favorable kinetics and high utilization of the active oxides; third, the typical mesoposity derived from the packing of Mn3O4 nanoparticles or MnO2 nanosheet building blocks along with the separation of the interspaced manganese oxide layers provide additional free space to tolerate the structural strain during repeated Li+ ions insertion/extraction to a large extent. Besides, the unique well-organized 3D structure may also contribute to the overall structural and morphological robustness. Moreover, the hierarchical cuboids particles typically of micro-/submicrometer dimensions might prevent the aggregation of


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the particles as smaller particles with higher surface energies are easier to aggregate together; last but not least, the aging-induced ECM effect of the active MnOx material during cycling accounts for faster reaction kinetics. All of the four factors mentioned above jointly lead to an enhanced cycling ability even at large current rates.

CONCLUSIONS Exploring innovative synthetic paths for accurate preparation of TMOs with well-designed hierarchical micro/nano-morphology and scale-up purposes, starting with MOFs, is of significant importance in both fundamental research and future devices. Here, we put forward a green, sustainable approach toward the large-scale and facile synthesis of 3D layer-by-layer MnOx hierarchically mesoporous microcuboids via precise manipulation of the template-engaged reactions between a unique Mn-MOF-74 template (layer-by-layer micro-sized cuboids) and oxidizing basic etching solution. The novel Mn-MOF-74-based template was prepared by a convenient solvent-thermal method. The reaction between Mn-MOF-74 microcuboids with NaOH/O2 solution leads to the formation of higher-level micrometer-sized assemblies consisting of numerous primary Mn3O4 nanoparticles. While Mn-MOF-74 microcuboids react with the NaOH/H2O2 solution to generate similar assemblies consisting of ultrathin MnO2 nanosheets. When soaking in the solution, the MOF solid goes through an efficient anion-ion exchange process to produce Mn(OH)2 intermediate and subsequent immediate chemical oxidation by air or H2O2. Of particular note, the wet-chemical process only involves the use of ordinary materials and avoids the emissions of toxic gases, thus demonstrating great superiority as compared with the conventional thermal approach. Notably, in electrochemical evaluation, these 3D MnOx electrode display high electroactivities and robustness due to their well-arranged complex


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micro/nano-architectures, endowing a high charge/discharge capacities (ca. 890.7 mA h g-1 for Mn3O4, ca. 991.5 mA h g-1 for MnO2), excellent rate capabilities (up to 2 A g-1), and exemplary cycling performance (up to 400 cycles at 2 A g-1). We strongly believed that our ingenious synthetic concept will afford a fascinating avenue to prepare advanced yet low-cost TMOs functional materials by taking advantage of the unique reactivity of MOFs and intermediate products. METHODS Preparation of Materials. All chemicals and solvents were of analytical grade and used as received without further purification. Direct solvothermal growth of Mn-MOF-74 Template/Precursor. Mn-MOF-74 crystals were successfully synthesized by a modified solvothermal procedure: MnCl2•4H2O (1.098 g, mmol) and 2,5-dihydroxy-1,4-benzenedicarboxylic acid (0.333g, mmol) were dissolved under stirring in a 15:1:1 (v/v/v) mixture of N,N-dimethylformamide (45 mL), ethanol (3 mL), and deionized water (3 mL). The homogeneous solution was then transferred to a 100 mL Teflon-lined stainless steel autoclave, capped tightly and placed in an oven at 135 ℃ for 24 h. After the reaction was completed, a large quantity of bright yellow crystals were collected and washed by N, N-dimethylformamide, water and finally by ethanol, and air-dried for further use. Syntheis of 3-D layer-by-layer MnOx mesoporous microcuboids at room temperature.


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The hierarchically structured MnOx microcuboids were obtained by the reaction of Mn-MOF74 template with NaOH digest solution at room temperature. Typically, 0.6 g of the presynthesized Mn-MOF-74 precursors was dipped into 200 mL of an aqueous solution of NaOH (0.05 M) under atmospheric conditions or in the presence of 1.06 mL H2O2 (30% wt.% solution in water) under stirring, creating a suspension of MOF. After 10 h’ s reaction, the mixture was filtered, washed with deionized water three times, followed by pure ethanol three times, and finally dried in an oven at 80 ℃ overnight to give brown (Mn3O4) and black (δ-MnO2) powders, respectively. Characterization Techniques. XRD patterns were recorded on a Holland Panalytical PRO PW3040/60 diffractometer with Cu Kα radiation (V = 35 kV, I = 25 mA, λ = 1.5418 Å). FTIR measurements were carried out using a Nicolet-Nexus 670 infrared spectrometer. TG analysis was recorded on an STA 449 F3 Jupiter® simultaneous thermal analyzer from room temperature to 800 °C at a heating rate of 10 °C min−1 in flowing air. SEM images and EDX spectra were achieved on a Hitachi S-4800 system. TEM images, HRTEM observations, and SAED patterns were acquired with an FEI Tecnai F20 instrument. XPS characterization was performed on a Thermo ESCALAB 250XI system with a monochromatic Al (Kα) source (1486.6 eV) by referencing the C 1s peak to 284.6 eV. Nitrogen sorption measurements were performed on a Micromeritics analyzer (ASAP 2020) at 77 K. The specific surface areas and pore size distributions were calculated by Brunauer– Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods, respectively. Electrochemical Measurements.


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The electrochemical performance of the samples was evaluated by assembling CR2032-type coin cell in an Ar-filled glovebox (O2 ≤ 0.1 ppm, H2O ≤ 0.1 ppm). The cells consisted of Cu current collector carrying active material (MnOx) as the working electrode, Li metal as the counter and reference electrode, a Celgard separator, and an electrolyte solution of LiPF6 (1 M) in ethylene carbonate/ethyl methyl carbonate/dimethyl carbonate (1 : 1 : 1 by volume) + 5% fluoroethylene carbonate. To prepare working electrodes, the active material was well dispersed in water with sodium carboxymethyl cellulose binder and Super-P carbon black to produce a 7:2:1 weight ratio slurry of solids. The slurry was coated uniformly on a pure Cu foil by doctor blade. After drying in a vacuum chamber at 100 ℃ for 12 h, the coated Cu foil was cut into 14 mm diameter electrode discs with active substance mass loading of around 1.5 mg. The discharge and charge measurements of the cells were carried out with a multichannel battery tester (LAND CT2001A) between 0.01 and 3.00 V versus Li/Li+ at room temperature. CVs were measured on an electrochemical workstation (Autolab PGSTAT302N) and EIS in the frequency range of 100 kHz to 0.1 Hz at room temperature. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: Supplementary electron microscopy images, XRD pattern, FT-IR spectra, TG analysis, XPS spectra, EDS analysis, Coulombic efficiency, TEM and low-resolution SEM images of cycled electrodes, selected discharge/charge profiles in early capacity-degeneration cycles, and Table S1 (PDF)


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AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]; [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge the support of National Natural Science Foundation of China for Excellent Young Scholars (21522303), National Natural Science Foundation of China (21373086), National Key Basic Research Program of China (2013CB921800), National High Technology Research and Development Program of China (2014AA123401), Basic Research Project of Shanghai Science and Technology Committee (14JC1491000), and the Large Instruments Open Foundation of East China Normal University. JP Amoureux is acknowledged to polish the English. REFERENCES (1) Tarascon, J.M.; Armand, M. Issues and Challenges Facing Rechargeable Lithium Batteries. Nature 2001, 414 (6861), 359-367. (2) Poizot, P.; Laruelle, S.; Grugeon, S.; Dupont, L.; Tarascon, J.M. Nano-Sized Transition-Metaloxides as Negative-Electrode Materials for Lithium-Ion Batteries. Nature 2000, 407 (6803), 496-499. (3) Deng, Y.; Wan, L.; Xie, Y.; Qin, X.; Chen, G. Recent Advances in Mn-based Oxides as Anode Materials for Lithium Ion Batteries. RSC Adv. 2014, 4 (45), 23914-23935. (4) Gao, J.; Lowe, M.A.; Abru A, H.D. Spongelike Nanosized Mn3O4 as a High-Capacity Anode Material for Rechargeable Lithium Batteries. Chem. Mater. 2011, 23 (13), 3223-3227. (5) Huang, S.; Jin, J.; Cai, Y.; Li, Y.; Tan, H.; Wang, H.; Van Tendeloo, G.; Su, B. Engineering Single Crystalline Mn3O4 Nano-Octahedra with Exposed Highly Active {011} Facets for High Performance Lithium Ion Batteries. Nanoscale 2014, 6 (12), 6819. (6) Dubal, D.P.; Holze, R. High Capacity Rechargeable Battery Electrode Based On Mesoporous Stacked Mn3O4


23


Page 24 of 38

Nanosheets. RSC Adv. 2012, 2 (32), 12096–12100. (7) Bai, Z.; Zhang, X.; Zhang, Y.; Guo, C.; Tang, B. Facile Synthesis of Mesoporous Mn3O4 Nanorods as a Promising Anode Material for High Performance Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2 (39), 1675516760. (8) Li, L.; Nan, C.; Lu, J.; Peng, Q.; Li, Y. α-MnO2 Nanotubes: High Surface Area and Enhanced Lithium Battery Properties. Chem. Commun. 2012, 48 (55), 6945. (9) Bruce, P.G.; Scrosati, B.; Tarascon, J. Nanomaterials for Rechargeable Lithium Batteries. Angew. Chem. Int. Ed. 2008, 47 (16), 2930-2946. (10) Li, L.; Raji, A.O.; Tour, J.M. Graphene-Wrapped MnO2-Graphene Nanoribbons as Anode Materials for HighPerformance Lithium Ion Batteries. Adv. Mater. 2013, 25 (43), 6298-6302. (11) Wang, J.; Jin, D.; Zhou, R.; Li, X.; Liu, X.; Shen, C.; Xie, K.; Li, B.; Kang, F.; Wei, B. Highly Flexible Graphene/Mn3O4 Nanocomposite Membrane as Advanced Anodes for Li-Ion Batteries. ACS Nano 2016, 10 (6), 6227-6234. (12) Lavoie, N.; Malenfant, P.R.L.; Courtel, F.M.; Abu-Lebdeh, Y.; Davidson, I.J. High Gravimetric Capacity and Long Cycle Life in Mn3O4/graphene platelet/LiCMC Composite Lithium-Ion Battery Anodes. J. Power Sources 2012, 213, 249-254. (13) Su, L.; Wu, X.; Hei, J.; Wang, L.; Wang, Y. Mesoporous Mn3O4 Nanobeads/Graphene Hybrids: Facile GelLike Film Synthesis, Rational Structure Design, and Excellent Performance for Lithium Storage. Part. Part. Syst. Char. 2015, 32 (7), 721-727. (14) Chae, C.; Kim, K.W.; Yun, Y.J.; Lee, D.; Moon, J.; Choi, Y.; Lee, S.S.; Choi, S.; Jeong, S. PolyethylenimineMediated Electrostatic Assembly of MnO2 Nanorods on Graphene Oxides for Use as Anodes in Lithium-Ion Batteries. ACS Appl. Mater. Inter. 2016, 8 (18), 11499-11506. (15) Li, Y.; Zhang, Q.; Zhu, J.; Wei, X.L.; Shen, P.K. An Extremely Stable MnO2 Anode Incorporated with 3D Porous Graphene-Like Networks for Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2 (9), 3163-3168. (16) Park, S.; Jin, A.; Yu, S.; Ha, J.; Jang, B.; Bong, S.; Woo, S.; Sung, Y.; Piao, Y. In Situ Hydrothermal Synthesis of Mn3O4 Nanoparticles On Nitrogen-doped Graphene as High-Performance Anode Materials for Lithium Ion Batteries. Electrochim. Acta 2014, 120, 452-459. (17) Jing, M.; Wang, J.; Hou, H.; Yang, Y.; Zhang, Y.; Pan, C.; Chen, J.; Zhu, Y.; Ji, X. Carbon Quantum Dot Coated Mn3O4 with Enhanced Performances for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3 (32), 1682416830. (18) Park, S.; Lee, W. Hierarchically Mesoporous Carbon nanofiber/Mn3O4 Coaxial Nanocables as Anodes in Lithium Ion Batteries. J. Power Sources 2015, 281, 301-309. (19) Yang, G.; Li, Y.; Ji, H.; Wang, H.; Gao, P.; Wang, L.; Liu, H.; Pinto, J.; Jiang, X. Influence of Mn Content On the Morphology and Improved Electrochemical Properties of Mn3O4|MnO@Carbon Nanofiber as Anode Material for Lithium Batteries. J. Power Sources 2012, 216, 353-362. (20) Yang, Z.; Lv, J.; Pang, H.; Yan, W.; Qian, K. Facile Synthesis of Coaxial CNTs/MnOx-Carbon Hybrid Nanofibers and their Greatly Enhanced Lithium Storage Performance. Sci. Rep.-UK 2015, 5, 17473.


24

Page 25 of 38 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


(21) Yue, H.; Li, F.; Yang, Z.; Li, X.; Lin, S.; He, D. Facile Preparation of Mn3O4-coated Carbon Nanofibers On Copper Foam as a High-Capacity and Long-Life Anode for Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2 (41), 17352-17358. (22) Luo, S.; Wu, H.; Wu, Y.; Jiang, K.; Wang, J.; Fan, S. Mn3O4 Nanoparticles Anchored On Continuous Carbon Nanotube Network as Superior Anodes for Lithium Ion Batteries. J. Power Sources 2014, 249, 463-469. (23) Qin, J.; Zhang, Q.; Cao, Z.; Li, X.; Hu, C. MnOx/SWCNT Macro-Films as Flexible Binder-Free Anodes for High-Performance Li-ion Batteries. Nano Energy 2013, 2 (5), 733–741. (24) Cao, K.; Liu, H.; Chang, X.; Li, Y.; Wang, Y.; Jiao, L. A Foolproof Method to Fabricate Integrated Electrodes with 3D Conductive Networks: A Case Study of MnOx@C-Cu as Li-Ion Battery Anode. Adv. Mater. Technol. 2017, 2 (3), 1600221. (25) Zhang, Y.; Yue, K.; Zhao, H.; Wu, Y.; Duan, L.; Wang, K.L. Bovine Serum Albumin Assisted Synthesis of Fe3O4@C@Mn3O4 Multilayer Core–Shell Porous Spheres as Anodes for Lithium Ion Battery. Chem. Eng. J. 2016, 291, 238-243. (26) Lai, H.; Li, J.; Chen, Z.; Huang, Z. Carbon Nanohorns as a High-Performance Carrier for MnO2 Anode in Lithium-Ion Batteries. ACS Appl. Mater. Inter. 2012, 5 (4), 2325–2328. (27) Wang, Y.; Han, Z.J.; Yu, S.F.; Song, R.R.; Song, H.H.; Ostrikov, K.K.; Yang, H.Y. Core-Leaf Onion-Like carbon/MnO2 Hybrid Nano-Urchins for Rechargeable Lithium-Ion Batteries. Carbon 2013, 64, 230-236. (28) Zhuang, Y.; Ma, Z.; Deng, Y.; Song, X.; Zuo, X.; Xiao, X.; Nan, J. Sandwich-Like Mn3O4/carbon Nanofragment Composites with a Higher Capacity than Commercial Graphite and Hierarchical Voltage Plateaus for Lithium Ion Batteries. Electrochim. Acta 2017, 245, 448-455. (29) Chu, Y.; Guo, L.; Xi, B.; Feng, Z.; Wu, F.; Lin, Y.; Liu, J.; Sun, D.; Feng, J.; Qian, Y.; Xiong, S. Embedding MnO@Mn3O4 Nanoparticles in an N-Doped-Carbon Framework Derived from Mn-Organic Clusters for Efficient Lithium Storage. Adv. Mater. 2017, 1704244. (30) Huang, S.; Cai, Y.; Jin, J.; Liu, J.; Li, Y.; Yu, Y.; Wang, H.; Chen, L.; Su, B. Hierarchical Mesoporous Urchin-Like Mn3O4/carbon Microspheres with Highly Enhanced Lithium Battery Performance by In-Situ Carbonization of New Lamellar Manganese Alkoxide (Mn-DEG). Nano Energy 2015, 12, 833-844. (31) Liao, J.; Higgins, D.; Lui, G.; Chabot, V.; Xiao, X.; Chen, Z. Multifunctional TiO2–C/MnO2 Core–DoubleShell Nanowire Arrays as High-Performance 3D Electrodes for Lithium Ion Batteries. Nano Lett. 2013, 13 (11), 5467-5473. (32) Lee, R.; Lin, Y.; Weng, Y.; Pan, H.; Lee, J.; Wu, N. Synthesis of High-Performance MnOx/carbon Composite as Lithium-Ion Battery Anode by a Facile Co-Precipitation Method: Effects of Oxygen Stoichiometry and Carbon Morphology. J. Power Sources 2014, 253, 373-380. (33) Jun, Z.; Jia-jia, C.; Cheng-long, Z.; Hang, Q.; Ming-sen, Z.; Quan-feng, D. The Synthesis of a Core–Shell MnO2/3D-ordered Hollow Carbon Sphere Composite and its Superior Electrochemical Capability for Lithium Ion Batteries. J. Mater. Chem. A 2014, 2 (18), 6343-6347. (34) Li, Z.; Liu, N.; Wang, X.; Wang, C.; Qi, Y.; Yin, L. Three-Dimensional Nanohybrids of Mn3O4/ordered Mesoporous Carbons for High Performance Anode Materials for Lithium-Ion Batteries. J. Mater. Chem. 2012, 22


25


Page 26 of 38

(32), 16640. (35) Wang, C.; Yin, L.; Xiang, D.; Qi, Y. Uniform Carbon Layer Coated Mn3O4 Nanorod Anodes with Improved Reversible Capacity and Cyclic Stability for Lithium Ion Batteries. ACS Appl. Mater. Inter. 2012, 4 (3), 1636-1642. (36) Wang, H.; Zhao, X.; Li, X.; Wang, Z.; Liu, C.; Lu, Z.; Zhang, W.; Cao, G. RGO/SnS2/TiO2 Heterostructured Composite with Dual-Confinement for Enhanced Lithium-Ion Storage. J. Mater. Chem. A 2017, 5 (47), 2505625063. (37) Wang, H.; Zhao, X.; Yin, K.; Li, Y.; Chen, L.; Yang, X.; Zhang, W.; Su, B.; Cao, G. Superior Pseudocapacitive Lithium-Ion Storage in Porous Vanadium Oxides@C Heterostructure Composite. ACS Appl. Mater. Inter. 2017, 9 (50), 43665-43673. (38) Li, M.; Wang, W.; Yang, M.; Lv, F.; Cao, L.; Tang, Y.; Sun, R.; Lu, Z. Large-Scale Fabrication of Porous Carbon-Decorated Iron Oxide Microcuboids From Fe-MOF as High-Performance Anode Materials for Lithium-Ion Batteries. RSC Adv. 2015, 5 (10), 7356-7362. (39) Srivastava, M.; Singh, J.; Kuila, T.; Layek, R.K.; Kim, N.H. Recent Advances in Graphene and its MetalOxide Hybrid Nanostructures for Lithium-Ion Batteries. Nanosacle 2015, 7 (11), 4820-4868. (40) Khalid, S.; Cao, C.; Naveed, M.; Younas, W. 3D Hierarchical MnO2 Microspheres: A Prospective Material for High Performance Supercapacitors and Lithium-Ion Batteries. Sustainable Energy & Fuels 2017, 1 (8), 17951804. (41) Gu, X.; Yue, J.; Li, L.; Xue, H.; Yang, J.; Zhao, X. General Synthesis of MnOx (MnO2, Mn2O3, Mn3O4, MnO) Hierarchical Microspheres as Lithium-Ion Battery Anodes. Electrochim. Acta 2015, 184, 250-256. (42) Zhao, Y.; Song, Z.; Li, X.; Sun, Q.; Cheng, N.; Lawes, S.; Sun, X. Metal Organic Frameworks for Energy Storage and Conversion. Energy Storage Mater. 2016, 2, 35-62. (43) Xu, X.; Cao, R.; Jeong, S.; Cho, J. Spindle-Like Mesoporous α-Fe2O3 Anode Material Prepared from MOF Template for High-Rate Lithium Batteries. Nano Lett. 2012, 12 (9), 4988-4991. (44) Wu, R.; Qian, X.; Rui, X.; Liu, H.; Yadian, B.; Zhou, K.; Wei, J.; Yan, Q.; Feng, X.; Long, Y.; Wang, L.; Huang, Y. Zeolitic Imidazolate Framework 67-Derived High Symmetric Porous Co3O4 Hollow Dodecahedra with Highly Enhanced Lithium Storage Capability. Small 2014, 10 (10), 1932-1938. (45) Guo, W.; Sun, W.; Wang, Y. Multilayer CuO@NiO Hollow Spheres: Microwave-Assisted Metal–OrganicFramework Derivation and Highly Reversible Structure-Matched Stepwise Lithium Storage. ACS Nano 2015, 9 (11), 11462-11471. (46) Ge, X.; Li, Z.; Wang, C.; Yin, L. Metal – Organic Frameworks Derived Porous Core/Shell Structured ZnO/ZnCo2O4/C Hybrids as Anodes for High-Performance Lithium-Ion Battery. ACS Appl. Mater. Inter. 2015, 7 (48), 26633-26642. (47) Zhao, Y.; Li, X.; Liu, J.; Wang, C.; Zhao, Y.; Yue, G. MOF-Derived ZnO/Ni3ZnC0.7/C Hybrids Yolk–Shell Microspheres with Excellent Electrochemical Performances for Lithium Ion Batteries. ACS Appl. Mater. Inter. 2016, 8 (10), 6472-6480. (48) Cui, Z.; Liu, Q.; Xu, C.; Zou, R.; Zhang, J.; Zhang, W.; Guan, G.; Hu, J.; Sun, Y. A New Strategy to Effectively Alleviate Volume Expansion and Enhance the Conductivity of Hierarchical MnO@C Nanocomposites


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for Lithium Ion Batteries. J. Mater. Chem. A 2017, 5 (41), 21699-21708. (49) Zheng, F.; Xia, G.; Yang, Y.; Chen, Q. MOF-derived Ultrafine MnO Nanocrystals Embedded in a Porous Carbon Matrix as High-Performance Anodes for Lithium-Ion Batteries. Nanoscale 2015, 7 (21), 9637 - 9645. (50) Sun, D.; Tang, Y.; Ye, D.; Yan, J.; Zhou, H. Tuning the Morphologies of MnO/C Hybrids by Space Constraint Assembly of Mn-MOFs for High Performance Li Ion Batteries. ACS Appl. Mater. Inter. 2017, 9 (6), 5254–5262. (51) Niu, J.L.; Hao, G.X.; Lin, J.; He, X.B.; Sathishkumar, P. Mesoporous MnO/C-N Nanostructures Derived from a Metal-Organic Framework as High-Performance Anode for Lithium-Ion Battery. Inorg. Chem. 2017, 56 (16), 9966–9972. (52) Zhang, B.; Hao, S.; Xiao, D.; Wu, J.; Huang, Y. Templated Formation of Porous Mn2O3 Octahedra From MnMIL-100 for Lithium-Ion Battery Anode Materials. Materials & Design 2016, 98, 319-323. (53) Cao, K.; Jiao, L.; Xu, H.; Liu, H.; Kang, H.; Zhao, Y.; Liu, Y.; Wang, Y.; Yuan, H. Reconstruction of MiniHollow Polyhedron Mn2O3 Derived from MOFs as a High-Performance Lithium Anode Material. Advanced Science 2016, 3 (3), 1500185. (54) Bai, Z.; Zhang, Y.; Zhang, Y.; Guo, C.; Tang, B. MOFs-derived Porous Mn2O3 as High-Performance Anode Material for Li-ion Battery. J. Mater. Chem. A 2015, 3 (10), 5266-5269. (55) Maiti, S.; Pramanik, A.; Mahanty, S. Electrochemical Energy Storage in Mn2O3 Porous Nanobars Derived From Morphology-Conserved Transformation of Benzenetricarboxylate-Bridged Metal – Organic Framework. Crystengcomm 2016, 18 (3), 450-461. (56) Zheng, F.; Xu, S.; Yin, Z.; Zhang, Y.; Lu, L. Facile Synthesis of MOF-derived Mn2O3 Hollow Microspheres as Anode Materials for Lithium-Ion Batteries. RSC Adv. 2016, 6 (96), 93532-93538. (57) Peng, H.J.; Hao, G.X.; Chu, Z.H.; Lin, J.; Lin, X.M. Mesoporous Mn3O4/C Microspheres Fabricated From MOF Template as Advanced Lithium-Ion Battery Anode. Cryst. Growth Des. 2017, 17 (11), 5881–5886. (58) Sambandam, B.; Soundharrajan, V.; Song, J.; Kim, S.; Jo, J.; Duong, P.T.; Kim, S.; Mathew, V.; Kim, J. A Sponge Network-Shaped Mn3O4/C Anode Derived From a Simple, One-Pot Metal Organic FrameworkCombustion Technique for Improved Lithium Ion Storage. INORGANIC CHEMISTRY FRONTIERS 2016, 3 (12), 1609-1615. (59) Chen, S.; Cai, D.; Yang, X.; Chen, Q.; Zhan, H.; Qu, B.; Wang, T. Metal-Organic Frameworks Derived Nanocomposites of Mixed-Valent MnOx Nanoparticles In-Situ Grown on Ultrathin Carbon Sheets for HighPerformance Supercapacitors and Lithium-Ion Batteries. Electrochim. Acta 2017, 256, 63-72. (60) Chen, T.; Hu, Y.; Cheng, B.; Chen, R.; Lv, H.; Ma, L.; Zhu, G.; Wang, Y.; Yan, C.; Tie, Z.; Jin, Z.; Liu, J. Multi-Yolk-Shell Copper Oxide@Carbon Octahedra as High-Stability Anodes for Lithium-Ion Batteries. Nano Energy 2016, 20, 305-314. (61) Wu, R.; Qian, X.; Yu, F.; Liu, H.; Zhou, K. MOF-templated Formation of Porous CuO Hollow Octahedra for Lithium-Ion Battery Anode Materials. J. Mater. Chem. A 2013, 1 (37), 11126-11129. (62) Kim, A.; Kim, M.K.; Cho, K.; Woo, J.; Lee, Y.; Han, S.; Byun, D.; Choi, W.; Lee, J.K. One-Step Catalytic Synthesis of CuO/Cu2O in a Graphitized Porous C Matrix Derived from the Cu-Based Metal–Organic Framework for Li- and Na-Ion Batteries. ACS Appl. Mater. Inter. 2016, 8 (30), 19514-19523.


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Page 28 of 38

(63) Liao, Y.; Li, C.; Lou, X.; Wang, P.; Yang, Q.; Shen, M.; Hu, B. Highly Reversible Lithium Storage in Cobalt 2,5-Dioxido-1,4-Benzenedicarboxylate Metal-Organic Frameworks Boosted by Pseudocapacitance. J. Colloid Interf. Sci. 2017, 506, 365-372. (64) Kim, M.; Cahill, J.F.; Su, Y.; Prather, K.A.; Cohen, S.M. Postsynthetic Ligand Exchange as a Route to Functionalization of ‘Inert’ Metal–Organic Frameworks. Chem. Sci. 2012, 3 (1), 126-130. (65) Moon, J.; Awano, M.; Takagi, H.; Fujishiro, Y. Synthesis of Nanocrystalline Manganese Oxide Powders: Influence of Hydrogen Peroxide On Particle Characteristics. J. Mater. Res. 1999, 14 (12), 4594-4601. (66) Kim, N.D.; Yun, H.J.; Kyu Song, I.; Yi, J. Preparation and Characterization of Nanostructured Mn Oxide by an Ethanol-Based Precipitation Method for Pseudocapacitor Applications. Scripta Mater. 2011, 65 (5), 448-451. (67) Huang, M.; Zhang, Y.; Li, F.; Zhang, L.; Ruoff, R.S.; Wen, Z.; Liu, Q. Self-Assembly of Mesoporous Nanotubes Assembled from Interwoven Ultrathin Birnessite-Type MnO2 Nanosheets for Asymmetric Supercapacitors. Sci. Rep.-UK 2015, 4 (1). (68) Li, J.; Zou, M.; Zhao, Y.; Lin, Y.; Lai, H.; Guan, L.; Huang, Z. Coaxial MWNTs@MnO2 Confined in Conducting PPy for Kinetically Efficient and Long-Term Lithium Ion Storage. Electrochim. Acta 2013, 111, 165171. (69) Hu, X.; Li, C.; Lou, X.; Yang, Q.; Hu, B. Hierarchical CuO Octahedra Inherited From Copper Metal-Organic Frameworks: High-Rate and High-Capacity Lithium-Ion Storage Materials Stimulated by Pseudocapacitance. J. Mater. Chem. A 2017, 5 (25), 12828-12837. (70) Lou, X.W.; Deng, D.; Lee, J.Y.; Feng, J.; Archer, L.A. Self-Supported Formation of Needlelike Co3O4 Nanotubes and their Application as Lithium-Ion Battery Electrodes. Adv. Mater. 2008, 20 (2), 258-262. (71) Fang, X.; Lu, X.; Guo, X.; Mao, Y.; Hu, Y.S. Electrode Reactions of Manganese Oxides for Secondary Lithium Batteries. Electrochem. Commun. 2010, 12 (11), 1520-1523. (72) Yue, J.; Gu, X.; Chen, L.; Wang, N.; Jiang, X.; Xu, H.; Yang, J.; Qian, Y. General Synthesis of Hollow MnO2, Mn3O4 and MnO Nanospheres as Superior Anode Materials for Lithium Ion Batteries. J. Mater. Chem. A 2014, 2 (41), 17421-17426. (73) Ma, F.; Yuan, A.; Xu, J. Nanoparticulate Mn3O4/VGCF Composite Conversion-Anode Material with Extraordinarily High Capacity and Excellent Rate Capability for Lithium Ion Batteries. ACS Appl. Mater. Inter. 2014, 6 (20), 18129-18138. (74) Guo, X.; Han, J.; Zhang, L.; Liu, P.; Hirata, A. A Nanoporous Metal Recuperated MnO2 Anode for Lithium Ion Batteries. Nanoscale 2015, 7 (37), 15111-15116. (75) Li, T.; Guo, C.; Sun, B.; Li, T.; Li, Y.; Hou, L.; Wei, Y. Well-Shaped Mn3O4 Tetragonal Bipyramids with Good Performance for Lithium Ion Batteries. J. Mater. Chem. A 2015, 3 (14), 7248-7254. (76) Bai, Z.; Fan, N.; Ju, Z.; Guo, C.; Qian, Y. Facile Synthesis of Mesoporous Mn3O4 Nanotubes and their Excellent Performance for Lithium-Ion Batteries. J. Mater. Chem. A 2013, 1 (36), 10985-10990. (77) Kong, D.; Luo, J.; Wang, Y.; Ren, W.; Yu, T.; Luo, Y.; Yang, Y.; Cheng, C. Three-Dimensional Co3O4@MnO2 Hierarchical Nanoneedle Arrays: Morphology Control and Electrochemical Energy Storage. Adv. Funct. Mater. 2014, 24 (24), 3815-3826.


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(78) Wang, N.; Yue, J.; Chen, L.; Qian, Y.; Yang, J. Hydrogenated TiO2 Branches Coated Mn3O4 Nanorods as an Advanced Anode Material for Lithium Ion Batteries. ACS Appl. Mater. Inter. 2015, 7 (19), 10348-10355. (79) Hassan, M.F.; Guo, Z.; Chen, Z.; Liu, H. Α-Fe2O3 as an Anode Material with Capacity Rise and High Rate Capability for Lithium-Ion Batteries. Mater. Res. Bull. 2011, 46 (6), 858-864.

Figure 1. Schematic illustrating the fabrication processes of the 3-D layer-by-layer MnOx hierarchically mesoporous microcuboids.

Figure 2. (A) PXRD patterns of Mn-MOF-74. The top plot in (A) represents a portion of the Xray crystal structure of Mn-MOF-74 viewed along the c axis. (B, C) FE-SEM images, and (D) TEM images of the obtained microcuboid-like Mn-MOF-74 template. SEM images of Mn-MOF74 precursors hydrothermally synthesized at 135 ºC for 2 h (E, F); 6h (G); and 12h (H). (inset in


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(C) is magnified SEM image from the arrow-marked area of the surface; (F) is magnified image of the framed area in (E)) (A)

(C) Mn 2p

20

40

2p3/2 2p1/2

Intensity (a.u.)

(220)

(105) (312) (303) (321) (224) (314)

(004)

(101)

(112) (200)

(103)

Intensity (a.u.)

(211)

Mn-MOF-74 precursors after NaOH treatment Standard Mn3O4 PDF#16-0154

60

80

+2 +4

660

655

2 theta (deg.)

650

645

640

635

Binding energy (eV)

(B)

(D) Mn 2p

2p3/2

Intensity (a.u.)

(-112)

(-111)

(002)

(001)

Precursors after NaOH/H2O2 treatment Standard δ-MnO2 PDF#80-1098

Intensity (a.u.)

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

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2p1/2 +4

+3 +2

10

20

30

40

50

60

70

80

660

655

650

645

640

635

Binding energy (eV)

2 theta (deg.)

Figure 3. PXRD pattern of (A) Mn3O4 and (B) δ-MnO2 materials. High-resolution XPS spectra on Mn 2p of (C) Mn3O4 and (D) MnO2 materials.


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Figure 4. (A-C) SEM images at various magnifications, (D) TEM images, (E) HR-TEM images and (F) SAED pattern of the Mn3O4 materials by Mn-MOF-74 templating at room temperature.

Figure 5. (A-C) SEM images at various magnifications, (D) TEM images, (E) HR-TEM images and (F) SAED pattern of the δ-MnO2 materials by Mn-MOF-74 templating at room temperature.


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200 0.016 -1

0.012

3

-1

160

dV / dD (cm nm g )

3

-1

Adsorption volume (cm g )

(A)

120

80

0.008

0.004

0.000 20

40

60

80

100

Relative pressure (P/P0)

40 Adsorption Desorption

0 0.0

0.2

0.4

0.6

0.8

1.0


(B)

500 0.028 -1

g ) 0.021

-1

400

3

dV / dD (cm nm

3

-1

Adsorption volume (cm g )

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

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300 200

0.014

0.007

0.000 20

40

60

80

100

Pore size (nm)

100 Adsorption Desorption

0 0.0

0.2

0.4

0.6

0.8

1.0


Figure 6. N2 adsorption–desorption isotherms and the associated BJH pore-size distribution curve (inset) of the hierarchical porous MnOx microcuboids: (A) Mn3O4, (B) δ-MnO2.


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Figure 7. SEM images of the final products of Mn3O4 (A-C) and δ-MnO2 (D-F) obtained by chemical corrosion in NaOH solution with different concentration: (A) 0.25 M, (B) 0.5 M, (C) 1.0 M, (D) 0.5 M, (E) 5 M and (F) 10 M. (magnified images of the corresponding framed area in (A-F) are presented in Figure S8 (A-F), respectively.)


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(A)

3.5 1st 2nd

3.0 +

voltage (V vs. Li/Li )

+

Voltage (V vs. Li/Li )

(C)

1st 2nd

2.5 2.0 1.5 1.0 0.5 0.0

2.5 2.0 1.5 1.0 0.5 0.0

0

200

400

600

800

1000

1200

0

200

-1

(B)

600

800

1000

1200

Specific capacity (mA h g )

(D) 1

400

-1


1st 2nd

1st 2nd

0.5

0.1 Current (mA)

-1

-2

-3

0.0 -0.1

0.5

1.0

0.30

-0.5

-1.0

-0.2 0.5

0.0

0.0

Current (mA)

Current (mA)

0

Current (mA)

1.0 1.5 2.0 2.5 + Voltage (V vs. Li/Li )

1.5

2.0

2.5

0.15 0.00

-0.15 0.5

3.0

1.0

1.5

2.0

2.5 +

3.0


-1.5 3.0

0.0

0.5

1.0

+

1.5

2.0

2.5

3.0

+



-1


(E) 1000 800 -1

0.2 A g

600 -1

1 Ag

-1

0.5 A g

400

-1

2Ag

200 0 0

50

100

150

(F)

200

250

300

350

400

300

350

400

Cycle number 1400

-1


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

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1200 1000 800 -1

600

0.2 A g

-1

-1

0.5 A g

400

1Ag

-1

2Ag

200 0 0

50

100

150

200

250

Cycle number

Figure 8., (A, C) galvanostatic charge–discharge curves at the constant current density of 200 mA g-1, (B, D) CV curves at a scan speed of 0.2 mV s-1, and (E, F) long-term cycling


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performance at various current rates of hierarchically mesoporous Mn3O4 (A, B and E) and δMnO2 (C, D and F) microcuboids. (insets: enlarged view of the square area shown in (B, D)


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+

2.5 2.0

33th-160th

1.5 1.0 0.5

9 110 0 13 0

70

50

2.0

32th-170th 1.5 1.0 0.5 0.0

0

200

400

600

800

1000

-1


(C)

0

0

25 50 Z' (Ohm)

75

100

Mn3O4-1st Mn3O4-200th

500

MnO2-1st MnO2-200th

0 0

500

1000

1500

Current (mA)

-Z'' (Ohm)

0

1000

800

1000

Mn3O4 MnO2

0.2

10

600

Specific capacity (mA h g ) 0.4

30

400

-1

40

20

200

(D)

50

1500

0 17

2.5

0.0

2000

32

3.0


+


3.0

70 90 11 0 13 0 16 0

(B) 33 50

(A)

-Z'' (Ohm)

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 36 of 38

0.0 -0.2 -0.4 -0.6 -0.8 0.0

0.5

1.0

1.5

2.0

2.5

3.0

+

Z' (Ohm)


Figure 9. (A, B) Selected discharge/charge curves in the capacity-rise cycles at 0.2 A g−1 of Mn3O4 (A) and MnO2 (B) anode. (C) Electrochemical impedance spectra after the 1st and 200th cycles at 0.2 A g-1 of the Mn3O4 and MnO2 anodes. (inset: the close-up view of EIS at high frequency region.) (D) CVs of Mn3O4 and MnO2 electrode after 200 discharge/charge cycles at 0.2 A g−1.


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Figure 10. Low-magnification (A, C) and High-magnification (B, D) SEM images of Mn3O4 (A, B) and δ-MnO2 (C, D) electrode at charged state after 200 cycles at 0.2 A g−1.


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Page 38 of 38

Graphical Abstract

Green and rational design of 3-D layer-by-layer MnOx hierarchically mesoporous microcuboids from MOF templates by a solution-based approach at room temperature for high-rate and longlife Li-Ion batteries.


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Green and Rational Design of 3D Layer-by-Layer MnOx Hierarchically

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