Delicate Control of Multi-shelled Zn-Mn-O Hollow Microspheres as a

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Delicate Control of Multi-shelled Zn-Mn-O Hollow Microspheres as a High-Performance Anode for Lithium-Ion Batteries Jiaying Xu, Hao Zhang, Ruofeng Wang, Peibo Xu, Yinlin Tong, Qingyi Lu, and Feng Gao Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b02632 • Publication Date (Web): 01 Jan 2018 Downloaded from http://pubs.acs.org on January 2, 2018

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Langmuir

Delicate

Control

Microspheres

of

as

a

Multi-shelled

Zn-Mn-O

High-Performance

Hollow

Anode

for

Lithium-Ion Batteries Jiaying Xu,1,3 Hao Zhang,1 Ruofeng Wang,2 Peibo Xu,2 Yinlin Tong,2 Qingyi Lu, 1, * Feng Gao,2, * 1

State Key Laboratory of Coordination Chemistry, Coordination Chemistry Institute,

Collaborative Innovation Center of Advanced Microstructures, Nanjing National Laboratory of Microstructures, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, P. R. China, E-mail: [email protected] 2

Department of Materials Science and Engineering, Collaborative Innovation Center of Advanced

Microstructures, Nanjing University, Nanjing 210093, P. R. China, E-mail: [email protected] 3

School of Chemistry & Chemical Engineering, Yancheng Institute of Technology, Yancheng

224051, Jiangsu, P. R. China

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ACS Paragon Plus Environment

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Abstract Mixed/composite oxides of transition metals with hollow structures, especially multi-shelled hollow architecture, have promising potentials for different applications but their syntheses still remain a big challenge. Herein, a facile coordination polymer precursor method were developed to construct various multi-shelled Zn-Mn-O hollow microspheres including ZnMnO3, ZnMn2O4 and ZnMn2O4/Mn2O3. The composition of the hollow structures can be adjusted by controlling the composition of the coordination polymer precursors, which are easily obtained with Zn2+, Mn2+ and salicylic acid under solvothermal conditions. With a simple programmable heating process, the shell of the hollow structures can be adjusted and double-/triple-shelled ZnMnO3, ZnMn2O4 and ZnMn2O4/Mn2O3 hollow microspheres have been controllably obtained. When the triple-shelled ZnMn2O4 hollow microspheres are used as an anode material for lithium-ion batteries (LIBs), excellent activity and enhanced stability can be achieved. The triple-shelled hollow ZnMn2O4 exhibits a reversible capacity of 537 mAh·g-1 at 400 mA·g-1 and a nearly 100% capacity retention after 150 cycles. This strategy is facile and scalable for the production of high-quality complex hollow nanostructures, with the possibility of extension to the preparation of other mixed metal oxides with complex structures.

Keywords: Mixed/composite metal oxides; Multi-shelled hollow structures; Anode material; LIBs

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Introduction Due to the special structural features of hollow interior, shell permeability, low density and high surface-to-volume ratio, micro/nanoscaled hollow structures have been stimulating tremendous interests in various fields such as catalysis,[1-3] reactors,[4,5] sensors,[6,7] energy storage systems[8-11] and many others.[12] Hollow structures of transition metal oxides (TMOs) with micro-/nanometer-sized features are particularly attractive as photocatalysts,[13] and energy storage devices such as lithium-ion batteries (LIBs),[10,14] electrochemical capacitors[15,16] and fuel cells.[17-19] To optimize the physical/chemical properties of hollow structures for specific applications, researchers have stirred up even more interests in exploring different synthesis approaches which could control the shell structure of hollow architectures. For instance, Dong et al. prepared ZnO hollow microspheres with well-defined structures using carbonaceous microspheres as templates, and found that shell structures result in obvious differences in energy conversion efficiency when applied in the dye-sensitized solar cells.[20] Wang and co-workers reported multi-layered Cu2O hollow nanospheres by using CTAB vesicles as templates [21] and Zhang et [22]

al. fabricated Cu2O multi-level hollow spheres through Ostwald ripening process.

Despite all

these significant advances, most of the recent strategies are only suitable for the synthesis of complex hollow spheres of some specific binary materials, such as ZnO, Cu2O, Co3O4, NiS, TiO2, and MnO2,[20,22,23-26] which greatly limits the opportunities for developing other multi-component metallic functional materials and thus hamper practical applications of these complex materials. Therefore, a new research opportunity for the development of mixed metal oxide hollow structures with multiple shells is highly desirable. However, because of the complicate structure of mixed

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metal oxide with multiple shells, the difficulty of synthesis will also increase. There are few related reports till recently, Lou and co-workers reported the synthesis of a few kinds of multi-shelled mixed metal oxides through a penetration-solidification-annealing strategy, which exhibit good lithium storage properties.[27] In the multi-step synthesis route, carbon spheres were used as template and mixed with metal salt solutions, followed by annealing at high temperature to finally get hollow multi-layered structures. Herein, we proposed a precursor route for facile synthesis of mixed metal oxides with different compositions and shells. The precursors, multi-metal coordination polymer, were obtained by one-step solvothermal route through the coordination

of

metal

salts

and

organic

molecular

ligand.

Compared

with

penetration-solidification-annealing strategy, this coordination polymer precursor route has advantages of brief steps and convenient manipulation. By adjusting the composition of the coordination polymer precursors, various multi-shelled Zn-Mn-O hollow microspheres including ZnMnO3, ZnMn2O4 and ZnMn2O4/Mn2O3 can be systematically obtained. The shell of these hollow structures can be also adjusted by controlling the programmable heating processes. Furthermore, these materials were successfully applied as active anode materials for lithium-ion batteries and showed great performances.

Experimental Materials: All reagents were analytical grade and used as received without further purification. Ethanol was obtained from Shanghai Lingfeng Chemical Reagent Co. Ltd. Zinc acetate (Zn(CH3COO)2·2H2O), manganese acetate (Mn(CH3COO)2·4H2O), salicylic acid (C7H6O3), polyvinylpyrrolidone (PVP) were purchased from Sinopharm Chemical Reagent Co. Distilled

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water was utilized in all experimental procedures. Synthesis of multi-shelled Zn-Mn-O microspheres: The coordination polymer precursors were first synthesized by a simple solvothemal method. Taking Zn/Mn=1:2 as an example, the typical synthesis process is described as follows. 0.325 mmol of zinc acetate dehydrate (Zn(CH3COO)2·2H2O), 0.65 mmol of manganese acetate tetrahydrate (Mn(CH3COO)2·4H2O), 1.3 mmol of salicylic acid and 0.6 g of PVP were dissolved in 30 mL of ethanol at room temperature to form a clear solution. The solution was then transferred to a Teflon-lined stainless steel autoclave and kept at 160 ℃ for 12 h. The precursor was isolated using centrifugation, washed three times with ethanol and dried at 80 ℃ for 12 h. The same procedures were applied to synthesize other coordination polymer precursors with different molar ratios of Zn and Mn, such as 9:1, 1:1, 1:3, 1:4 and 1:9. After the preparation of the coordination polymers, the resultant precursor microspheres were calcined at high temperature to obtain Zn-Mn-O hollow structures. For the synthesis of triple-shelled hollow structures, the precursors were heated to 550 ℃ with the rate of 1 ℃·min-1 and kept for 4 hours in air. For the synthesis of double-shelled hollow structures, the precursors were heated to 550 ℃ with the rate of 5 ℃·min-1 and kept for 4 hours in air. Structural characterizations: The phases of the products were characterized by X-ray powder diffraction (XRD) using a Shimadzu XRD-6000 powder X-ray diffractometer with Cu Kα radiation (λ=1.5418Å). The scanning electron microscopy (SEM) images were collected on a Hitachi S-4800 field-emission microscope operated at 10 KV. Energy-dispersive X-ray spectroscope (EDS) attached to the SEM was used to analyze the composition of the samples.

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Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images were taken on a JEOL JEM-2100 microscope operated an acceleration voltage of 200 KV. Fourier transform infrared (FT-IR) spectra were measured on a Bruker TENSOR 27 IR spectrometer. Thermogravimetric analysis (Pyris Diamond TG/ DTA, Perkin-Elmer) of the powders were performed in air. The flow rate of air was set at 120 mL⋅min−1 and the temperature was increased from room temperature to 600 °C at a rate of 5 °C/min. Electrochemical Measurements: The electrodes for electrochemical property studies were prepared with 70 wt% of ZnMn2O4, 20wt% of acetylene black (Super-P), and 10 wt% Polyvinylidene Fluoride (PVDF) binder in N-methyl-2-pyrrolidone (NMP). This mixture was then pasted on a clean copper foil and dried in vacuum at 80 ℃ for 12 h. After that, the coated foil was roll-pressed and cut into a disc. Electrochemical measurements were carried out on CR2032 (3V) coin-type cells, which were fabricated using lithium foils as the counter electrode and the reference electrode, Celgard 2400 as the separator, and a solution of 1 M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 v/v) as the electrolyte. The assembly of the cell was carried out in an Ar-filled glove-box (Vigor, SG1200/750, oxygen and water concentration below 5 ppm). The cell was discharged and charged from 0.01 to 3.0 V at different rates on LAND CT-2001A instrument (Wuhan, China). Cyclic voltammograms (CV) were performed on a CHI-660D electrochemical workstation (Shanghai Chenhua, China) over the potential range of 0.01-3.0 V at a scan rate of 0.2 mV S-1.

Results and discussion The synthesis of Zn-Mn-O multi-shelled hollow spheres involves two steps, formation of the

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coordination polymer precursor and subsequent thermal conversion to Zn-Mn-O under controlled conditions. The coordination polymer precursors were obtained with Zn2+, Mn2+ and salicylic acid under solvothermal conditions. Different Zn-Mn molar ratios were used and SEM images of the resulted products are shown in Figure 1a, 1b and Figure S1. As observed in Figure 1a, the obtained precursor with Zn/Mn ratio of 1:2 are composed of dispersive microspheres and although there are some small microspheres, most of the microspheres are with a diameter in the range of 500-600 nm. Figure 1b displays an SEM image with a relative larger magnification, confirming that the obtained microspheres have smooth surfaces. The inset in Figure 1b shows the corresponding TEM image of a single microsphere, which demonstrates that the precursor microsphere is solid and does not have hollow interior. The relative uniform spherical morphology can be obtained with a large range of Zn/Mn ratio. Figure S1 exhibits SEM images of the products prepared with different Zn/Mn molar ratios under the same solvothermal conditions. It can be observed that with the molar ratio of Zn2+ to Mn2+ decreasing from 9:1, 1:1 to 1:2, 1:3, 1:4, and 1:9, almost all the obtained coordination polymers are composed of dispersive microspheres with uniform sizes except some small nanoparticles form when the Zn/Mn ratio is 1:9. The structures of coordination precursors were further studied using FT-IR analysis. Figure 1c displays the infrared spectra of the coordination precursor with Zn/Mn ratio of 1:2 and the ligand, salicylic acid. FT-IR spectra of the precursors with other ratios are shown in Figure S2a. The characteristic vibrational frequencies for coordination precursor and ligand are basically similar. However, compared with salicylic acid, O-H stretching vibration absorption peaks of Zn-Mn precursor becomes wider and shifts to higher wave number. The shift of O-H stretching vibration frequencies of IR reveals that the coordination

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interaction may take place during the formation of the coordination polymer. After high-temperature annealing process, the as-obtained yellow-colored precursor was decomposed to black powders. The decomposition behaviors of the Zn-Mn precursor were investigated by TGA in an air atmosphere from 30 °C to 600 °C. As shown in Figure 1d, there are two weight losses with the temperature increasing. The first one with about 9.88% weight loss occurs at 50 °C ~ 160 °C, which can be attributed to the loss of adsorbed water. The second one is calculated to be 69.8 wt% from 320 to 540 °C due to the structure decomposition. Based on the TGA data, the obtained Zn-Mn coordination polymer precursors were calcined at 550 °C in air with different ramping rates to obtain Zn-Mn-O oxides or composites. Figure 2a shows XRD patterns of the resultant products by calcining Zn-Mn precursor (1:2) with the ramping rate of 1 °C/min and 5 °C/min, respectively. The diffraction peaks of the both samples at 29.4, 31.3, 33.1, and 36.5 correspond to the (112), (200), (103), and (211) planes of hetaerolite ZnMn2O4 phase (JCPDS card no. 18-1484). No other diffraction peaks can be observed, suggesting that the carbon source from salicylic acid has been completely removed and the Zn-Mn precursors have been completely converted to ZnMn2O4 through the calcination treatment in air. IR spectrum of ZnMn2O4 in Figure 1c displays no characteristic adsorption from 650 to 4000 cm-1, further demonstrating no carbon existence after the calcination process. SEM image in Figure 2b displays the homogenous microsphere structure of the product obtained with ramping rate of 1 °C/min, confirming that the obtained ZnMn2O4 keeps the precursor’s morphology with a rather narrow size distribution of about 500-600 nm. But unlike the solid interior feature of the precursor, TEM images displayed in Figure 2c and d indicate that these microspheres are exclusively characteristic of triple-shelled hollow structures with sphere-in-sphere morphology. HRTEM image (the inset in panel Figure 2d) gives clear lattice fringes with spacing of about 0.24 nm, corresponding to (211) planes of tetragonal ZnMn2O4. Elemental mappings by scanning electron microscopy were further carried out to investigate the formation of mixed metal oxides. As shown in Figure 2e~h, the elements Zn, Mn and O are distributed homogeneously over the triple-shelled hollow microspheres and the individual shells are enriched with Zn, Mn and O, which further demonstrate the successful formation of mixed metal oxide ZnMn2O4, consistent with the XRD result. The 8


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formation of the multi-shelled hollow structures of ZnMn2O4 would be related to inward contraction resulting from the weight loss and adhesion action of the outer shell. At the beginning of calcination, a ZnMn2O4 shell would form quickly on the surface of the precursor spheres. Then, the oxidative degradation of the organic species in the precursor sphere would lead to inward shrinkage of the ZnMn-salicylic acid precursor. As the calcination goes on, the inner ZnMn-salicylic acid will further contract inward and detach from the preformed outer shell, resulting in the formation of the multi-shells. By this mechanism, the heating rate would play important roles on the formation of the different shells. Slower heating rate would give more time for inner core to detach from the outer shell, resulting in the formation of more shell, which can be confirmed by the product prepared by calcining the precursor with a higher speed of 5 °C min-1. As TEM images in Figure 2i and j show, by decreasing the ramping rate to 1 °C min-1, the obtained ZnMn2O4 microspheres are with double-shelled hollow structure. The simple multi-metal-complex precursor method can not only bring us ZnMn2O4 hollow spheres with different shell structures, but also provide us a general route for other Zn-Mn-O structures. Figure 3a shows SEM image of ZnMn precursor (1:1), confirming that the morphology of the precursor (1:1) are topological solid sphere, similar to that of the ZnMn precursor (1:2). Also similar to the previous calcination of the ZnMn precursor (1:2), when the ZnMn precursor (1:1) was calcined at 550 °C, it can be transferred to multi-shelled hollow microspheres. XRD patterns of the resultants are shown in Figure 3b, in which the identified diffraction peaks are all well indexed to the cubic ZnMnO3 phase (JCPDS card no.19-1461). When the ZnMn precursor (1:1) was heated to 550 °C at the speed of 1 °C·min-1, the ZnMnO3 product has the unique structure of triple shells as TEM image in Figure 3c shows. In HRTEM image (inset Figure 3c), the 0.25 nm crystal spacing is well consistent with the crystal spacing of (311) planes of cubic ZnMnO3. On the other hand, when the heating rate was 5 °C·min-1, the hollow ZnMnO3 is double-shelled (Figure 3d). Here again, the scanning SEM image and EDS mappings of ZnMnO3 hollow spheres show in Figure 3e-h that the elements Zn, Mn and O are homogeneously distributed inside the triple-shelled hollow microspheres and the individual shells are enriched with Zn, Mn and O.

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Another rational design for Zn-Mn-O hollow microspheres demonstrated in this study is the transformation of the obtained ZnMn-salicylic acid precursors with the Zn-Mn molar ratio 1:3 through heat treatment. After heating the ZnMn precursor (1:3) at 550 °C, the products are composite materials of ZnMn2O4 (JCPDS card no.18-1484) and Mn2O3 (JCPDS card no. 06-0540), which can be confirmed by XRD patterns shown in Figure 4a. EDS analysis in Figure 4b shows that the main elements of the composite are oxygen, manganese, and zinc and the approximate atomic ratio of Zn: Mn is about 1:3. However, different calcination programs do not have a change of morphology like the previous results. Figure 4c and 4d show the TEM images of ZnMn2O4/Mn2O3 composites with calcination speed of 1 °C·min-1 and 5 °C·min-1, respectively. The TEM images show that the ZnMn2O4/Mn2O3 hybrids are both double-shelled hollow structures. Figure 4e presents HRTEM image of ZnMnO3/Mn2O3 hybrids. The lattice fringes with d-spacing of 0.25 nm and 0.49 nm can be assigned to (211) planes of tetragonal ZnMn2O4 and (111) planes of tetragonal Mn2O3, respectively, which further confirm the co-existence of ZnMn2O4 and Mn2O3. SEM images and EDS mapping of the resulting hybrids show that the elements Zn, Mn and O are homogeneously distributed inside the double-shelled hollow microspheres (Figure 4f-i). Using the electrochemical half-cell device of Li-ion batteries, the Li-storage performances of the annealed multi-shelled hollow Zn-Mn-O spheres were studied as anode material for LIBs. Figure 5a shows the typical cyclic voltammograms (CVs) of the triple-shelled hollow ZnMn2O4 electrode for the 1st, 2nd and 3th cycles in a voltage range of 0.01-3.0 V vs. Li/Li+ at a scan rate of 0.2 mV·s-1. From the CV curves, two cathodic current peaks at 0.23 V and 1.25 V appear in the first cycle, which is in agreement with previous reports.[28-30] The peaks can be attributed to the initial reduction of metal ions (Mn2+ and Zn2+) to Mn0 and Zn0 embedded in Li2O matrix and the formation of amorphous Li2O and solid electrolyte interface (SEI). The anodic current peak can be

related to the oxidation of metallic Mn to manganese oxide, together with the decomposition of the Li2O. Thus the mechanism of the reaction between lithium and the triple-shelled hollow ZnMn2O4 could be summarized as the following electrochemical process:[31-33]

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ZnMn2O4 + 9Li+ + 9e-

ZnLi + 2Mn + 4Li2O

ZnLi + 2Mn + 3Li2O

ZnO + 2MnO + 7Li+ + 7e-

In the subsequent cycles, the cathodic peak initially at 0.23 V shifts to a higher potential (0.49 V), which could be related to the electrochemical milling effect in the first cycle with the formation of metal particles dispersed into Li2O matrix. Furthermore, the CV profiles of the 2nd and 3rd cycles almost overlap, suggesting the reversibility of electrochemical processes and the good structural durability of the fabricated triple-shelled ZnMn2O4 anode during the following Li+ insertion/extraction processes. The 1st, 2nd and 3rd charge/discharge plots at a current of 400 mA g−1 of triple-shelled hollow ZnMn2O4 microspheres are displayed in Figure 5b. From the initial cycle, the discharge and charge capacities of the ZnMn2O4 anode are 1028 mAh g−1 and 537 mAh g−1, respectively. The second and third discharge/charge capacities declined slightly and the capacity loss of the electrode resulted from the formation of a SEI film and the incomplete reaction of metallic Zn and Mn to their initial oxides. The discharge and charge capacities of the second and the third cycle are around 571 mAh g−1 and 516 mAh g−1, respectively and the two curves are nearly overlapping. The almost overlapping discharge/charge curves prove that the multi-shelled hollow structure of the ZnMn2O4 has good electrochemical stability. Furthermore, the cycle duration and rate performance of the fabricated triple-shelled ZnMn2O4, triple-shelled ZnMnO3 and double-shelled ZnMn2O4 anodes were studied and shown in Figure 5c and d. As observed from Figure 5c, there are an obvious capacity loss at the first several cycles. This phenomenon of capacity loses during the initial cycles can be attribute to the formation of a stable SEI layer and the establishment of a compact electric contact with the current collector.[34] And after continuous 150 charge-discharge cycles at 400 mA g-1, triple-shelled ZnMn2O4 retains approximately 537 mAh g-1 discharge capacity, corresponding to 87% of the second cycle discharge capacity, which demonstrates an excellent cyclability of the hollow ZnMn2O4. The excellent cyclabiblity can be attributed to the stable triple-shelled hollow structure of ZnMn2O4. As shown in Figure S3, after the cycling test, the ZnMn2O4 sample keeps the original triple-shelled hollow structure although the shells become more coarse and appear many holes due to the lithium intercalating in and out of the ZnMn2O4

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shells. Meanwhile, the electrode also shows a high Coulombic efficiency of about 96%. Notably, the multi-shelled ZnMn2O4 electrode in this work exhibits competitive cycling stability compared to other existing material based ZnMn2O4 and carbon composite cathodes. Zhong and co-workers reported that the MnO@ZnMn2O4/N-C hybrids exhibit an reversible capacity of 803 mAh g−1 at 50 mA g−1 after 100 cycles.[35] In Dong’s report, the ZnMn2O4/N-doped graphene (ZMO/NG) hybrids deliver a reversible capacity up to 747 mA h g−1 after 200 cycles at a current density of 500 mA g−1.[36] These materials are composed of carbon composites, although they maintain good cycling performance. Furthermore, as shown in Figure 5c, after 150 charge-discharge cycles at 400 mA g-1, the discharge capacity of the triple-shelled ZnMn2O4 (537 mAh g-1) is much larger than those of the triple-shelled ZnMnO3 anodes (about 290 mA h g-1) and the double-shelled ZnMn2O4 (about 483 mAh g-1). Figure 5d presents the rate capability of the triple-shelled ZnMn2O4, the double-shelled ZnMn2O4 and the triple-shelled ZnMnO3 at increasing current densities from 100 to 1000 mA·g-1. With the current density increasing from 100 to 200, 400, and 1000 mA g-1, the discharge specific capacity of the triple-shelled ZnMn2O4 material is 641, 571, 509 and 405 mAh·g-1, respectively. Indeed, at a current density of 1000 mA g-1, the specific capacity of the multi-shelled ZnMn2O4 microspheres anodes also stays around 405 mAh g-1. When the current density is returned to 100 mA g-1, a specific capacity of 687 mAh g−1 is obtained. After a series of high-rate charge–discharge cycling process, the inside of the hollow ZnMn2O4 has almost complete penetration of the electrolyte, the capacity increases when the current density is reduced to 100 mA/g. The great increase of capacity illustrates the excellence of the multi-shelled hollow structure. In comparison, the triple-shelled ZnMnO3 and the double-shelled ZnMn2O4 electrodes deliver lower reversible capacities at all the current densities. These results demonstrate that the triple-shelled ZnMn2O4 outperforms the other two Zn-Mn-O materials as the electrode material of LIBs. The high lithium-storage capacity, remarkable cycling capability and excellent rate performance are probably ascribed to the special multi-shelled hollow structure, which provides a fast and efficient transport of Li ions.[37] In addition, the porous shell structure allows the electrolyte to easily penetrate into the exterior shells to reach and utilize the inner more-shells for increased capacity.[15] The above results indicate that the multi-shelled ZnMn2O4 nanospheres

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are a promising anode candidate for the LIBs.

Conclusions In summary, we demonstrate controllable syntheses of multi-shelled Zn-Mn-O hollow microspheres. By using salicylic acid as coordination ligand, via a simple solvothermal synthesis and a simple programmable heating process, we have prepared Zn-Mn-O hollow microspheres with well-defined structures, in which the number of shells and the Zn/Mn molar ratios can be delicately controlled. Furthermore, ZnMn2O4 hollow microspheres with triple shells show high-performances when used as anode material in the lithium-ion batteries. Combining the high specific capacity, remarkable cycling stability, and excellent rate performance, the electrochemical performances of the three-shelled ZnMn2O4 nanospheres electrode can make them become a promising anode candidate for the LIBs. This work may open up new opportunities for fabricating high efficiency lithium-ion batteries anode materials based on structural design and manipulation of multi-component metal oxide functional materials with multi-shelled hollow structures.

Supporting Information: SEM images; IR spectra; and TEM images (Supporting Figures S1-S3). This material is available free of charge via the Internet at http://pubs.acs.org.

Acknowledgment: This work is supported by the National Basic Research Program of China (Grant No. 2013CB922102), the National Natural Science Foundation of China (Grant No. 21471076) and a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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Figure Captions Figure 1 (a, b) SEM images; (c) IR spectra and (d) TG curve under air with a ramp of 5 ℃ min-1 of the coordination polymer precursor with Zn/Mn ratio of 1:2. The inset in panel (b) is the corresponding TEM image. Figure 2 (a) XRD pattern; (b) SEM image; (c, d) TEM images and (e-h) SEM image and EDS mappings of ZnMn2O4 microspheres obtained by thermal conversion of Zn-Mn precursor (1:2) with a ramping rate of 1 ℃ min-1; (i, j) TEM images of double shelled ZnMn2O4 microsphres obtained from the precursor with a ramping rate of 5 ℃ min-1. The inset in panel (d) is the corresponding HRTEM image. Figure 3 (a) SEM image of the coordination polymer precursor with Zn/Mn ratio of 1:1; (b) XRD pattern; (c) TEM image (triple-shelled); (d) TEM image (double-shelled) and (e-h) SEM image and EDS mappings of ZnMnO3 microspheres obtained by thermal conversion of Zn-Mn precursor with Zn/Mn ratio of 1:1. The inset in panel (c) is the corresponding HRTEM image. Figure 4 (a) XRD pattern; (b) EDS spectrum; (c, d) TEM images; (e) HRTEM image; (f-i) SEM image and EDS mappings of the resulting Zn-Mn-O micorspheres obtained by thermal conversion of Zn-Mn precursor with Zn/Mn ratio of 1:3. Figure 5 (a) CVs of the initial three cycles of the triple-shelled ZnMn2O4 nanospheres; (b) Discharge-charge profiles of the triple-shelled ZnMn2O4 nanospheres at a current density of 400 mA g-1 in the voltage range of 0.01-3.0 V; (c) Cycling performance at a current density of 400 mA g-1; (d) Rate cyclability at different discharge current densities.

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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a

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triple-shelled ZnMn2O4 double-shelled ZnMn2O4 triple-shelled ZnMnO3

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For Table of Contents Only A facile coordination polymer precursor method was developed to construct various multi-shelled Zn-Mn-O hollow microspheres including ZnMnO3, ZnMn2O4 and ZnMn2O4/Mn2O3. The composition of the hollow structures can be adjusted by controlling the composition of the coordination polymer precursors and the shell of the hollow structures can be adjusted by different programmable heating processes. When the triple-shelled ZnMn2O4 hollow microspheres were used as anode material for LIB, excellent activity and enhanced stability can be achieved.

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Delicate Control of Multi-shelled Zn-Mn-O Hollow Microspheres as a

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