C Composite Microspheres with Three

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Nanoporous TiNb2O7/C composite microspheres with three dimensional conductive network for long-cycle-life and high rate capability anode materials for lithium ion batteries Guozhen Zhu, Qing Li, Yunhao Zhao, and Renchao Che ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b13246 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 8, 2017

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ACS Applied Materials & Interfaces

Nanoporous TiNb2O7/C composite microspheres with three dimensional conductive network for long-cycle-life and high rate capability anode materials for lithium ion batteries Guozhen Zhu, Qing Li, Yunhao Zhao and Renchao Che* Laboratory of Advanced Materials, Department of Materials Science and Collabrative Innovation Center of Chemistry for Energy Materials, Fudan University, Shanghai 200438, P. R. China KEYWORDS: TiNb2O7, three dimensional, conductive network, nanopores, spray drying method, long-cycle-life, high rate capability.

ABSTRACT: Based on the advantages of ideal cycling stability, high discharge voltage (1.65 V) and excellent reversibility, more and more attention has been focused on TiNb2O7 (marked as TNO) as anode material candidate for lithium-ion batteries. However, the poor electronic conductivity and low ionic diffusion rate intrinsically restrict its practical use. Herein, we firstly synthesize the TNO/C composite microspheres with three-dimensionally (marked as 3-D) electro-conductive carbon network and abundant nanoporous structure by a simple spray drying method. The microspheres are constructed by irregularly primary cubic nanoparticle units with

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size of 100-200 nm. The nanopores throughout the microspheres rang from 1 nm to 50 nm. As an anode material, the prepared TNO/C composite microspheres demonstrate a prominent charge/discharge capacity of 323.2/326 mA h g-1 after 300 cycles at 0.25 C (1 C=388 mA g-1) and 259.9/262.5 mA h g-1 after 1000 long cycles at a high current density of 5 C respectively, revealing the ideal reversible capacity and long cycling life. Meanwhile, the TNO/C composite microspheres present ideal rate performance, showing the discharge capacity of 120 mA h g-1 at 30 C after 10 cycles. The super electrochemical performance could be attributed to the 3-D electro-conductive carbon network and nanoporous structure. The nanopores facilitate the permeation of electrolyte into the inter contacting regions of the anode materials. Carbon layers disperse uniformly throughout the 3-D microspheres, effectively improving the electrical conductivity of the electrode. Hence, the prepared TNO/C composite microspheres have great potential to be used as an anode material for lithium-ion batteries.

1. INTRODUCTION To develop lithium ion battery anode materials with high energy density, lightweight and long life span have been becoming an urgent issue for the application fields of hybrid electric vehicles. Graphite, Li4Ti5O12, TiO2, SnO, SiO2, Sn and Si, as the main group of anode electrode materials, have been becoming research hot topics in recent years. However, poor discharge potential,1 low theoretical specific capacity2 and large volume change3 limit their practical application. Figure S1 shows the crystal structure of TNO. An octahedral group is made up of a metal atom (Ti, Nb) and six oxygen atoms. Red spheres represent oxygen atoms, and the green spheres located at the center of octahedron are titanium atoms and niobium atoms, respectively. These octahedral groups are connected through sharing common corners and edges to form a crystallo-


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graphic-shear framework.4 TNO anode materials, monoclinic layered structure with a C 2/m space group, have been attracting more and more attention because of their owning merits, such as high theoretical specific capacity (388 mA h g-1), high discharge voltage (1.65 V) and excellent reversibility.5 The TiNb2O7 with high theoretical specific capacity is possible to act as a new anode materials. Unfortunately, its electrochemical performance has been being strictly subject to its slow ionic diffusion rate and poor electronic conductivity.6 Therefore, a series of sustained efforts are taken to improve the electronic and ionic conductivity. A lot of approaches, including carbon coating,7 nitriding treatment,8 compounding9 and doping,10 have been adopted to solve this problem. Nanoparticles can effectively reduce the length of lithium ions transportation paths to improve its diffusion rate and its electrochemical properties.11-16 Recently, sphere morphology1719

with low interface energy, high volume energy density, perfect fluidity characteristics and

large specific surface area has been attracting lots of attention. It is beneficial to make sufficient contact between active electrode materials and electrolyte. Porous materials are becoming more and more popular, because this structure can bind more easier with electrolyte than isolated bulk nanoparticles do, due to its well infiltration capability with electrolyte. Besides, it can relieve the inevitable volume change during the process of charging and discharging. Nanoporous TNO anode materials exhibit excellent cyclic performance, because the lattice stress strain derived from volume change can be alleviated through its porous structure.20 Porous TNO materials could be prepared by a sacrificial template method, solvothermal method and electro-spinning method. A faveolate-like porous TNO material with a good cycle performance (after 1000 cycles with 84% capacity retention at 5 C) has been reported.21 A mesoporous self-assembly TNO material with 81% capacity retention during 2000 cycles at 10 C was synthesized via block


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copolymer template.22 A porous TNO/Ti1-XNbXN composite microsphere fabricated through solvothermal method showed 91% capacity retention after 1000 cycles at 5 C and excellent rate performance.23 Porous TNO/Ti1-XNbXN composite nanofibers with a diameter of about 110 nm and pores size ranging from 0 nm to 40 nm via electro-spinning have been studied, exhibiting excellent rate capability at 100 C and good cycle capability of 78% after 500 cycles at 5 C.24 Although the electrochemical performance of TNO anode materials could be enhanced through the aforementioned methods, the synthetic route has disadvantages of complex and expensive. Therefore, it is still on urgent demand to establish a novel synthetic method towards porous TNO materials. Spray drying technique, a simple, large scale production and inexpensive method, has been widely used. A stable and spherical Li4Ti5O12/C granule was synthesized by spray drying method.25 2LiFePO4·Li3V2(PO4)3/C composites spheres has been fabricated via the spray drying method.26 NiO nanospheres synthesized successfully by a facile one-step spray drying method showed good high reversible capacity and long cycling life.27 In this work, we firstly synthesize the TNO/C composite microspheres with 3-D electroconductive carbon network and nanoporous structure by a facile spray drying method. The microspheres are constructed by irregularly cubic nanoparticles with unit size of 100-200 nm. The nanopores stacked from the nanoparticles could accelerate the permeation of electrolyte into the inner surface of electrode materials. Meanwhile, the 3-D electro-conductive carbon network greatly improve the electrical conductivity of the electrode. Owning to these advantages, the electrochemical performance of the prepared TNO/C composite microspheres show great superiority compared with other reported works of TNO. The prepared TNO/C composite microspheres demonstrate a prominent charge/discharge capacity of 323.2/326 mA h g-1 after


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300 cycles at 0.25 C and 259.9/262.5 mA h g-1 after 1000 long cycles at a high current density of 5 C respectively, revealing the ideal reversible capacity and long cycling life. Our findings might shed new light on the fabrication of anode materials with excellent electrochemical performances. 2. EXPERIMENTAL 2.1. Materials. TiO2, Nb2O5, Ethanol and cyclodextrin were all purchased from sinopharm Chemical Reagent Co., Ltd, All the chemical reagents were used without further purification. Deionized water purchased from Milli-Q system (Millipore, Bedford, MA) was used in all experiments. 2.2. Synthesis of TNO. 3.994 g TiO2, 13.29 g Nb2O5 (mole ratio of 1:1) and 200 g zirconium balls were mixed with 173 ml ethanol and milled by a planetary mill at a speed of 350 rpm for 20 hours. The slurry was dried and furthered calcined at 800 oC for 10 h to gain the TNO. 2.3. Synthesis of three dimensional interconnected open nanoporous TNO/C composite microspheres. TiO2 and Nb2O5 were used as titanium source and niobium source respectively to fabricate precursor of three dimensional interconnected open nanoporous TNO/C composite microspheres. (I) carbon source aqueous solution A: cyclodextrin was dissolved in deionized water (mass ratio of 1:10) completely through magnetically stirred for 2 hours. (II) composites B: 3.994 g TiO2, 13.29 g Nb2O5 (mole ratio of 1:1) and 173 ml deionized water were poured into ball milling tank with 200 g zirconium balls. (III) suspension C: subsequently uniform dispersion carbon source aqueous solution A was thoroughly mixed with composites B via planetary ball milling at a rotation speed of 350 rpm for 20 hours continually. (IV) suspension C in the ball milling tank was followed transferred to beaker of 250 ml by filtering process, then suspension C was added into spray drying machine via vacuum pump to obtain precursor powders of three dimensional interconnected open nanoporous TNO/C composite microspheres. Finally, precursor


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powders were collected to be tested. Precursor powders were performed in a tube furnace using an alumina crucible, heated at 5 oC/min in a flowing argon atmosphere (40 mL/min) until it reached 800 oC, it was then kept at 800 oC for 10 h to gain three dimensional interconnected nanoporous TNO/C composite microspheres (marked as 3D-ITC). 2.4. Material characterization. Phase analysis of products were acquired by Powder X-ray diffraction (XRD) measurements (Bruker D8 Advance) using Cu-Kα radiation at 40 kV and 40 mA, with a step size of 0.02° (2θ) and step time of 2 s between 10 and 60° (2θ). Nitrogen adsorption/desorption isotherms were measured at 77 k after being degassed at 300 oC for at least 3 h (Automated Surface Area and Pore Size Analyzer, ASAP2020). Coated carbon contents were calculated by thermogravimetric measurement (TG-60H) from 20 oC to 900 oC under an air flow of 40 mL/min with a heating rate of 5 oC/min. The analysis of elementary distribution was performed on Energy dispersive X-ray Detector (EDX, Super scan SSX-550). Field-emission scanning electron microscope (FESEM, Hitachi, S-4800) and transmission electron microscope (TEM, JEOL, JEM-2100F) were used to characterize the size and morphology of the prepared materials. Surface composition and element valence state of materials were identified by X-ray photoelectron spectrometer (XPS, Axis Ultra DLD). D band and G band, characteristic peaks of carbon, was tested by Raman spectra (Renishaw in Via Reflex ). 2.5. Measurement of electrochemical performance. The electrochemical performance of the 3D-ITC was tested using CR2016 coin cells, which were assembled in an argon-filled dry glove box. The working electrode was prepared by mixing 80 wt% 3D-ITC, 10 wt% acetylene black and 10 wt% Polyvinylidene fluoride (PVDF) dispersed in 1-methy-2-pyrrolidone (NMP). Then the slurry was uniform cast on the copper foil to prepare the electrode film, which was dried in vacuum drying oven at 80 oC for 6 h to remove the solvent. The electrode film was punched into


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discs with diameters of 12 mm and it was dried in vacuum drying oven at 80 oC for 12 h before assembled in a glove box filled with argon gas. Lithium plate was used as the reference electrode. The electrolyte was 1 M LiFP6 electrolyte solution in 1:1 v/v ethylene carbonate and diethyl carbonate. Cell charge/discharge and cycle tests were performed using a Land Battery measurement system (LAND CT2001A model), operating in galvanostatic mode. Cyclic voltammetry tests were conducted using a CHI604D electrochemical workstation. 3. RESULTS AND DISCUSSION

Figure 1. Schematic illustration of the prepared 3D-ITC Figure 1 illustrates the formation process of the prepared 3D-ITC. (i) The uniformly dispersive liquid suspension containing TiO2, Nb2O5, cyclodextrin and deionized water is inhaled


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into an injector and then sprayed to spherical drops with diameter of about 10 µm. The interspacing room among the particles of the reactants is filled up by water. (ii) Water molecular membrane coated on the surface of microsphere particles evaporates in a short time when microspheres meet hot air at 230 oC. Precursor powders of microspheres with numerous interconnected open nanoporous could be obtained. (iii) The 3D-ITC could be gained by annealing the as-prepared precursor powders at 800 oC for 10 h in pure argon atmosphere.

Figure 2. (a) XRD patterns of TiNb2O7 and 3D-ITC; (b) SEM images of the 3D-ITC; (c) TEM and (d) HRTEM images of 3D-ITC Figure 2 (a) shows the XRD pattern of the prepared two samples, revealing that all the diffraction peaks match well with TNO (JCPDS Card No. 39-1407). The diffraction peaks of


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carbon can not be detected from the XRD pattern of 3D-ITC, which could be ascribed to the low content or amorphous carbon contained in 3D-ITC.28,29 The prepared 3D-ITC exhibit uniform spherical structure with diameter of 2-10 µm, without any obvious aggregation (SEM, Figure 2(b)). The microsphere structure could provide a large tap density, which is beneficial to improve volume energy density.30 Thus, 3D TNO/C composite microspheres show higher tap density compared with other nanostructured TNO materials. Besides, according to the formula of E=CV2/2, the higher discharge capacity is, the higher energy is. Thus, compared to TNO, 3D TNO/C composite microspheres show higher energy, which is helpful to improve volume energy density. Meanwhile, A large amount of nanopores are showed to exist both on the surface and in the inner part of the microspheres (Figures S2(a,b,c)). Figure S2(c) indicates that the primary units of the 3D-ITC are nanoparticles with size of 100-200 nm. The nanoparticles stack together and thus form microspheres during synthesis process, simultaneously contributing to the formation of interconnected porous structure, improving the electrochemical performance of 3DITC.31,32 The prepared TNO contains abundant of closely-connected nanoparticles (Figure S2(d)). Numerous interconnected nanopores are successfully formed in the prepared 3D-ITC (TEM, Figure 2(c)). Which is great benefit for the fast transmit of lithium ions and electrodes to -

improve the electrochemical performance. Via the HRTEM image, the (303) crystal plane of TNO with the layer spacing of 0.34 nm can be clearly examined (Figure 2(d)). Besides, the carbon layer with a thickness of about 3 nm wraps uniformly on the surface of the primary TNO nanoparticles. The carbon layers resulted from the carbonation of cyclodextrin play an important role in restricting the growth of primary particles during solid phase reaction, keeping the particle size in the appropriate range and preventing particles from aggregating. Moreover, the carbon layers can provide long-range conductivity and effectively enhance the electronic


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conductivity of the TNO particles, thus contributing to much better electrochemical performances. Carbon element is confirmed to be existed inside 3D-ITC, supported by the characteristic D and G peaks appear at 1328 cm-1 and 1594 cm-1 of Raman data (Figure S3). The peak located at 1002 cm-1 and 889 cm-1 could be attributed to the edge-shared and corner-shared NbO6 octahedra, respectively.33 Both the high peak at 647 cm-1 and low peak at 539 cm-1 could be related to the preferentially occupied edge-shared TiO6 octahedra.34 Figures 3(b, c, d, e) reveal the Ti, Nb, O and C elements distribute uniformly over the entire range. Additionally, Figure S4(e) demonstrates the inside C element distributes even in the internal volume of the microspheres, which effectively enhances the electrical conductivity of the electrode. Thus, the 3-D conductivity network has been successfully confirmed. Carbon content of 3D-ITC is about 5 wt% (Figure 3(f)). Nb 4p, Nb 4s, Nb 3d, Nb 3p, Ti 2p, O 1s, O KLL can be identified to be existed by XPS (Figure S5(a)). Figures S5(b), (c) and (d) show XPS spectrums of Ti 2p, Nb 3d and O 1s, respectively. The two peaks at approximate 459.5 eV and 465.4 eV (Figure S5(b)) are ascribed to Ti 2p 3/2 and Ti 2p 1/2 respectively, indicating that the Ti element of TNO displays tetravalency.35 The peaks located at 207.4 eV and 210.5 eV (Figure S5(c)) correspond to Nb 3d 5/2, showing that the valence state of Nb in TNO is pentavalent, which in accordance with the binding energy of Nb in Nb2O5.33 The peak at 530.7 eV (Figure S5(d)) belongs to O 1s, which originates from oxygen species of TNO.36 The abundant nanoporous structure of 3D-ITC has been confirmed by N2 adsorption/desorption isotherms (Figure S6(a)). The prepared 3D-ITC demonstrate much larger BET surface area (11.2 m2 g-1) than that of the TNO (7.3 m2 g-1), due to the stacked nanoporous structure. Meanwhile, The average pore diameter of 3D-ITC (about 50 nm) is far larger than that of TNO (about 10 nm). A well contact between electrolyte and


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electrode materials can be achieved, due to the larger BET surface area and larger pore diameter, thus improving the electrochemical performance.37-39 Besides, the 3-D interconnected nanoporous network can facilitate the penetration of electrolyte into host materials.40

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Figure 3. EDS elemental mapping images of the outer surface of a single 3D-ITC (a, b, c, d, e); (f) TG curve of 3D-ITC measured from 20 oC to 900 oC under air flow 70 ml/min at heating rate of 5 oC/min. 1 st cycle 2 nd cycle 3 rd cycle 300 th cycle

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1.0 1.5 2.0 Potential (V)

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Figure 4. (a) The first, second, third, 300th charge-discharge curves at 0.25 C of 3D-ITC; (b) Cyclic voltammogram curves in voltage range of 0 V to 3.0 V at a scanning rate of 0.1 mV/s of 3D-ITC; (c) Cycling performance for 300 cycles at 0.25 C of 3D-ITC and TNO; (d) Rate capability under different current rates of 3D-ITC and TNO Figure 4(a) displays the 1st, 2nd, 3rd and 300th charge/discharge curves of the prepared 3DITC at 0.25 C. The detail measured results are showed in Table S1. The initial discharge/charge capacity of 3D-ITC reach 393.3 mA h g-1 and 381 mA h g-1 respectively with the coulombic efficiency of 96.9%. After 300 cycles, the discharge capacity remains at 326 mA h g-1 (82.9% of the initial capacity), which is far exceed that of TNO (Figure S7(a), 157 mA h g-1), illustrating


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the ideal reversibility of 3D-ITC. The initial 5 cyclic voltammogram curves of the prepared 3DITC at the scanning rate of 0.1 mV/s are as shown in Figure 4(b). The sharp oxidation/reduction peaks at 1.7 V/1.5 V correspond to the transformation between Nb5+ and Nb4+. The narrow oxidation peak at 1.16 V could be attributed to the transformation between Nb4+ and Nb3+. The broad oxidation/reduction peaks at 2.0 V/1.75 V could be attributed to the variation of Ti4+/Ti3+. The peak value are consistent with charge/discharge platform (Figure 4(a)). The curves remain almost coincident, indicating the excellent cycling stability of the electrode. Figure 4(c) exhibits the cycling performance of the prepared 3D-ITC and TNO at 0.25 C for 300 cycles, 3D-ITC show more excellent cycling stability and higher coulombic efficiency (approximating 100%) comparing with TNO. The rate capability of the prepared 3D-ITC and TNO are shown in Figure 4(d), demonstrating the discharge capacity of 350 mA h g-1, 320 mA h g-1, 300 mA h g-1, 280 mA h g-1, 260 mA h g-1, 230 mA h g-1, 120 mA h g-1 and 345 mA h g-1 at 0.25 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, 30 C and 0.25 C, respectively, which is far higher than that of TNO (260 mA h g-1, 215 mA h g-1, 175 mA h g-1, 130 mA h g-1, 110 mA h g-1, 80 mA h g-1, 35 mA h g-1 and 220 mA h g-1 at 0.25 C, 0.5 C, 1 C, 2 C, 5 C, 10 C, 30 C and 0.25 C). Even cycling at a current density as high as 30 C, the capacity still maintains at an ideal value of 120 mA h g-1, revealing the outstanding performance of the 3D-ITC in the process of fast and repeated discharge/charge. The excellent rate performance can be attributed to the porosity, which could not only alleviate the changing of volume, but also shorten the transport path of lithium ions and electrons during the process of charge/discharge. To further reveal the excellent Li-storage performance of 3D-ITC, the long-term cycling test is conducted at the higher current density of 5 C as shown in Figure S7(b). The charge/discharge capacity remain 259.9 mA h g-1 and 262.5 mA h g-1 after 1000 cycles, respectively, corresponding to the coulombic efficiency of 99%. The charge/discharge


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capacity of TNO hold only 100.1 mA h g-1 and 100.3 mA h g-1 at 5 C after 1000 cycles respectively, which fells far behind that of the prepared 3D-ITC. Which indicates that the structure of TNO/C composite microspheres maintains stable. The discharge specific capacity of 3D-ITC exceeds significantly other TNO materials reported previously at 5 C for 500-1000 cycles (Table S2).41-46 Charge-discharge curves of 3D-ITC and TNO at different current rates are presented in Figure S7(c,d), it is obviously that a short pseudo-plateau appears at 1.7 V at 0.25 C, which coincides with CV curves (Figure 4(b)). The discharge and charge plateau voltages shift toward lower potentials and higher voltages with the current rate increase, which can be attributed to the increased electrode polarization. The change of voltage for 3D-ITC is significantly littler than that of TNO, showing the electrode polarization of TNO is more serious than 3D-ITC. The carbon layers uniformly distributed on the whole microsphers plays a key role in decreasing the electrode polarization to improve the electrochemical performance. Besides, the discharge capacity of 3D-ITC is far exceed that of TNO at different current rate. The electrochemical impedance spectra (EIS) measurements are performed to explain the more excellent electrochemical performance of 3D-ITC electrode than that of TNO electrode (Figure S8). The diameter of semicircle for 3D-ITC electrode is significantly much smaller than that of TNO electrode, showing that the charge-transfer resistance of 3D-ITC is lower than that of TNO. Which is ascribed to the porous structure and carbon uniformly distributed on the surface and inner part of 3D-ITC. A 3D network structure with well conductivity is formed because of existing of carbon layers, which improves the conductivity of 3D-ITC. To further clarify the superior cycle properties of the prepared 3D-ITC, SEM images acquired from the samples after 1000 cycles at 5 C reveal that the microspheric and nanoporous structure are generally


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maintained. The stable structure guarantees the excellent long-term cycling stability of the prepared 3D-ITC (Figure S9). The mechanism of the correlation between electrochemical performance and structure design is shown in Figure 5. The excellent cycle stability of 3D-ITC can be ascribed to the structure advantage. Firstly, 3D interconnect channels can provide an unhindered pathway for the fast transportation of electron. Secondly, the carbon layers with excellent conductivity uniformly coated on the surface of nanoparticles with dimensional of 100 nm-200 nm, accelerating the diffusion speed of lithium ions. Thirdly, the porous structure can effective relieve the unexpected stress arising from the process of repeated charging/discharging of lithium ions. Thus, the cycling performance of 3D-ITC was improved.

carbonization

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3D-ITC

Single TNO@C

Figure 5. The mechanism of the correlation between electrochemical performances and structure 4. CONCLUSIONS In summary, we firstly proposed a spray drying method to prepare three dimensional open nanoporous 3D-ITC materials. The 3D-ITC have unique structural features for the ultra-excellent


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electrochemical performance, because (i) the porous structure favored a shorter diffusion length for lithium ions and electrodes; (ii) the exterior electronic conductive carbon coating facilitated the electronic transport. As a result, the 3D-ITC demonstrated higher rate capability and longer cycle life comparing with TNO. The prepared 3D-ITC demonstrated a prominent charge/discharge capacity of 323.2/326 mA h g-1 after 300 cycles at 0.25 C and 259.9/262.5 mA h g-1 after 1000 long cycles at a high current density of 5 C respectively, revealing the ideal reversible capacity and ultra-long cycling life. Meanwhile, the 3D-ITC present ideal rate performance, showing the discharge capacity of 120 mA h g-1 at 30 C after 10 cycles. Therefore, 3D-ITC can be a promising anode candidate for the development of high-rate, long-life and highsafety LIBS.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publication website at DOI: XXXXX. Crystal structure of TiNb2O7; SEM images of 3D-ITC and TiNb2O7; Raman images of 3DITC and TiNb2O7; EDS elemental mapping images of 3D-ITC; XPS spectra of 3D-ITC; N2 adsorption/desorption isotherms and the pore size distribution of 3D-ITC and TiNb2O7; Electrochemical properties of 3D-ITC and TiNb2O7 (PDF)

AUTHOR INFORMATION Corresponding Authors Tel: +86 021 51630213; Fax: +86 021 51630210; E-mail: [email protected] Notes


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The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported by the Ministry of Science and Technology of China (973 Project 2013CB932901), the National Natural Science Foundation of China (51672050, 51172047), NSFC-NASF: U1330118, Science and Technology Commission of Shanghai Municipality (2016YFE0105700). ABBREVIATIONS 3-D, Three-dimensionally; TNO, TiNb2O7; 3D-ITC, Three dimensional interconnected nanoporous TNO/C composite microspheres. REFERENCES (1) Han, J. T.; Huang, Y. H.; Goodenough, J. B. New Anode Framework for Rechargeable Lithium Batteries. Chem. Mater. 2011, 23, 2027-2029. (2) Han, J. T.; Goodenough, J. B. 3-V Full Cell Performance of Anode Framework TiNb2O7/Spinel LiNi0.5Mn1.5O4. Chem. Mater. 2011, 23, 3404-3407. (3) Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22, 587-603. (4) Song, H.; Kim, Y. T. A Mo-doped TiNb2O7 Anode for Lithium-ion Batteries with High Rate Capability due to Charge Redistribution. Chem. Commun. 2015, 51, 9849-9852. (5) Lin, C. S.; Yu, S.; Wu, S.; Lin, Z. Z.; Zhu, J. Li.; Lu, L. Ru0.01Ti0.99Nb2O7 as an Intercalationtype Anode Material with a Large Capacity and High Rate Performance for Lithium-ion Batteries. J. Mater. Chem. A. 2015, 3, 8627–8635.


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Synergistically

Enhanced

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Hierarchical

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500

-1

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Specific capacity (mAh g )


400 0.25C 0.5C 300

0.25C 1C 2C

200

3D-ITC

5C

10C

TNO

30C

100 0

0

10

20

30 40 50 60 Cycle number

TOC


24

70

80

C Composite Microspheres with Three

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