Combined Modification of Dual-Phase Li4Ti5O12âTiO2 by Lithium

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Surfaces, Interfaces, and Applications

Combined Modification of Dual-Phase Li4Ti5O12-TiO2 by Lithium Zirconates to Optimize Rate Capabilities and Cyclability Jian-Ping Han, Bo Zhang, Li-Ying Wang, Yong-Xin Qi, Huiling Zhu, Gui-Xia Lu, Long-Wei Yin, Hui Li, Ning Lun, and Yu-Jun Bai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b07003 • Publication Date (Web): 02 Jul 2018 Downloaded from http://pubs.acs.org on July 8, 2018

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ACS Applied Materials & Interfaces

Combined Modification of Dual-Phase Li4Ti5O12-TiO2 by Lithium Zirconates to Optimize Rate Capabilities and Cyclability Jian-Ping Han1, Bo Zhang1, Li-Ying Wang1, Yong-Xin Qi1, Hui-Ling Zhu2, Gui-Xia Lu3, Long-Wei Yin1, Hui Li1, Ning Lun1*, Yu-Jun Bai1* 1

Key Laboratory for Liquid-Solid Structural Evolution & Processing of Materials (Ministry of

Education), Shandong University, Jinan 250061, PR China 2

School of Materials Science and Engineering, Shandong University of Science and

Technology, Qingdao, 266590, PR China 3

*

School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, PR China E-mail: [email protected] (Y.-J. Bai), [email protected] (N. Lun).

Keywords: Dual-phase Li4Ti5O12-TiO2; Combined modification; Lithium zirconates; Superficial doping Abstract The low electrical conductivity and ordinary lithium ion transfer capability of Li4Ti5O12 (LTO) restrict its application to some degree. In this work, dual-phase Li4Ti5O12-TiO2 (LTOT) was modified by composite zirconates of Li2ZrO3, Li6Zr2O7 (LZO) to boost the rate capabilities and cyclability. When the homogeneous mixture of LiNO3, Zr(NO3)4•5H2O and LTOT was roasted at 700 ºC for 5h, the obtained composite achieved a superior reversible capacity of 183.2 mAh g-1 to the pure Li4Ti5O12 after cycling at 100 mA g-1 for 100 times due to the existence of a scrap of TiO2. Meanwhile, when the composite was cycled by consecutively doubling the current density between 100 and 1600 mA g-1, the corresponding reversible capacities are 183.2, 179.1, 176.5, 173.3 and 169.3 mAh g-1, signifying the 1

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prominent rate capabilities. Even undergoing 1400 chare/discharge cycles at 500 mA g-1, a reversible capacity of 144.7 mAh g-1 was still attained, denoting the splendid cyclability. From a series of comparative experiments and systematic characterizations, the formation of LZO meliorated both the Li+ migration kinetics and electrical conductivity on account of the concomitant superficial Zr4+ doping, responsible for the comprehensive elevation of electrochemical performance. 1. Introduction Lithium-ion batteries (LIBs) exhibiting high energy density and preeminent service life have been widely extended from portable electronics to high-power vehicles1-2. Li4Ti5O12 (LTO) anode material in LIBs has been largely explored due to its “zero strain” for reversible cyclability, high working potential (1.55 V vs. Li/Li+) for averting electrolyte reduction and abstaining from safety issues3-4. The disadvantages of LTO lie in the low theoretical specific capacity (175 mAh g-1)5, poor electrical conductivity (< 10-13 S cm-1) as well as inferior Li+ diffusion coefficient (10-9 - 10-13 cm2 s-1) 6-7. To boost the electrochemical properties of LTO, several strategies have been proposed in the aspects of changing morphologies (such as nanowires8-9, nanorods10-11 nanospheres12-13 and nanotubes14-15), surface coating16-19, doping with heterogeneous elements20-21 and compositing with other materials22-25. A composite material could achieve performance surpassing the individual components if rationally designed. As reported, dual-phase Li4Ti5O12-TiO2 (LTOT) exhibited performance over the pure LTO due to the increased interfaces for Li-ion storage26-27. However, the inferior electronic and ionic conductivities of anatase TiO2 also affect the rate and cycling performance28-29. Hence, further modification to 2


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ameliorate the electronic and ionic conductivities of LTOT deserves further exploring. Li-ion conductors have been applied in modifying the electrode materials with poor conductivity17,

30-32

. The “Li2O-ZrO2” series conductors, such as Li2ZrO3, Li6Zr2O7 and

Li8ZrO6 have good electrochemical properties33-36. Li2ZrO3 with a three-dimension structure beneficial to the Li-ion transfer could enhance the electrochemical performance of LTO37. Nevertheless, the closely packed and stabilized Li2ZrO3 structure influences the mobility of Li-ions38. Li6Zr2O7 with “open” structure reveals higher mobility for Li-ions39-40, but the poor stability of Li6Zr2O7 is disadvantageous for long-term cycling performance of LIBs. If Li2ZrO3 could be appropriately composited with Li6Zr2O7, the composite zirconates might achieve not only the stable structure but also the meliorated Li+ migration by combining their respective advantages. In this work, the dual-phase LTOT was modified by the composite zirconates of Li2ZrO3 and Li6Zr2O7 (LZO) via simply mixing LiNO3 and Zr(NO3)4•5H2O with LTOT and roasting at various temperatures for 5 h (LTOT/LZO). Detailed characterizations and performance tests were conducted to reveal the modification mechanism. 2. Experimental All reagents concerned are chemically pure without further purification. The fabrication of LTOT/LZO includes two steps. (1) 2.6 g LiOH•H2O dissolved in 20 mL pure water was titrated into the solution involving 25.6 g tetrabutyltitanate (TBT) (with a molar ratio of 5:4 for TBT:LiOH•H2O) in 50 mL anhydrous alcohol and magnetically stirred for 30 min. After drying the uniform mixture in an oven at 105 ºC for 12 h, it was roasted at 700 ºC for 5 h in a tube furnace. The dual-phase LTOT was obtained due to the loss of Li2O during roasting37-38. 3



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(2) The mixed solution of 0.0241 g LiNO3 and 0.0375 g Zr(NO3)4•5H2O dissolved in 50 mL pure water was mixed with 1.5 g LTOT under magnetic stirring, when the mixtures dried at 105 ºC for 12 h were roasted at 650 ºC, the ultimate product was named as LTOT/LZO1. Similarly, the products with the same raw materials roasted at 700 and 750 ºC for 5 h were assigned to LTOT/LZO2 and LTOT/LZO3, respectively. The details for material characterizations and electrochemical assessment are supplied in Supporting Information (SI). 3. Results and Discussion 3.1 Structure and Microstructure The X-ray diffraction (XRD) patterns of LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3 are revealed in Figure 1a. Apparently, the four products display similar diffraction peaks to the spinel LTO (JCPDS 49-0207). However, in the enlarged image for the (111) plane (inset in Figure 1a), the peak for LTOT/LZO moves to lower angle with raising the roasting temperature, manifesting the gradually increased lattice constant associating with the replacement of Ti4+ by Zr4+ with the ionic radii of 0.605 and 0.72 Å, respectively

37, 41

.

Also the patterns between 2θ = 22 and 30° were magnified in Figure S1a, the two weak peaks around 25.2 and 27.4° stem from the (101) plane of anatase TiO2 and (110) plane of rutile TiO2 due to the Li2O loss during roasting42-43, and the rutile TiO2 increases with elevating the roasting temperature. In terms of the (111) plane of LTO, the crystallite size is 37.9 nm for LTOT, 29.5 nm for LTOT/LZO1, 30.9 nm for LTOT/LZO2 and 35.2 nm for LTOT/LZO3 (estimated by the Scherrer Equation), demonstrating that further grain growth during the secondary roasting could be impeded to a certain degree by the LZO modification. 4


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Figure 1. (a) XRD patterns and (b) Raman spectra of LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3. To evidence the presence of LZO, uniformly mixed LiNO3 and Zr(NO3)4•5H2O (molar ratio 4 : 1) were separately roasted at 650, 700 and 750 ºC for 5h. From the XRD patterns of the as-roasted products (Figure S1b), both Li2ZrO3 (JCPDS 20-0647) and a small amount of Li6Zr2O7 (JCPDS 34-0312) could be detected, and the Li6Zr2O7 content increases with elevating the roasting temperature. The presence of TiO2 in LTOT and LTOT/LZO products could further be reflected from Raman spectra (Figure1b). Besides the basic peaks around 233, 344, 424, 674 and 743 cm-1 for the pure LTO, the additional peak around 143 cm-1 is attributed to anatase TiO2, and the one around 517 cm-1 to rutile TiO244, suggesting the formation of TiO2 in the products. The gradually intensified TiO2 peaks indicate that the TiO2 content increases with raising the modification temperature, demonstrating from another aspect that the Ti4+ substituted by Zr4+ augments with raising the modification temperature. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) equipped with energy-dispersive X-ray spectroscope (EDS) was employed to determine the distribution of LZO in the products. Taking LTOT/LZO2 as an example, the EDS mappings 5



demonstrate the homogeneous O distribution (Figure 2b), relatively uniform Ti distribution (Figure 2c) and uneven Zr distribution (Figures 2d). Particularly, there are a lot of dispersed zones with high Zr content, corresponding to the nanocrystallites smaller than 20 nm in Figure 2a. Thus, besides the low Zr content resulted from the superficial Zr-doping in the LTOT particles, LZO nanocrystallites are composited with the LTOT particles. For further confirming the existence of tiny crystallites among the LTOT particles, other HAADF-STEM image and the corresponding EDS mappings are exhibited in Figure S2.

Figure 2. (a) HAADF-STEM image of LTOT/LZO2 and the corresponding EDS mappings of O (b), Ti (c) and Zr (d).

6


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Figure 3. TEM and HRTEM of LTOT (a) and (b), LTOT/LZO1(c) and (d), LTOT/LZO2 (e) and (f) and LTOT/LZO3 (g) and (h). 7



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The microstructures of LTOT and LTOT/LZO were acquired by high-resolution transmission electron microscopy (HRTEM) (Figure 3). There are some tiny crystallites dispersed in the LTOT/LZO products (Figures 3a, c, e and g). In the lattice fringe images (Figures 3b, d, f and h), the interplanar distances of 0.484 and 0.252 nm conform to those of the (111) and (311) planes for LTO, and that of 0.352 nm to the (101) plane of anatase TiO2. The planes for Li2ZrO3 were also identified, such as the (320) plane in LTOT/LZO1 (Figure 3d) and LTOT/LZO2 (Figure S3b), the (330) (Figures 3f and h) and (530) planes (Figure S3a) in LTOT/LZO2. Also some phases with low degree of crystallinity were observed around the LTO particles in the LTOT/LZO products, especially in LTOT/LZO3, the phase with light contrast is more distinct, and the detail is displayed in Figure S4. Some weak lattice fringes from Li2ZrO3 could be distinguished between two LTO particles, corresponding to the light contrast LZO around the LTO particles in Figure 3g. But it is hard to recognize the planes resulted from Li6Zr2O7 due to the low content and low degree of crystallinity (Figure S1b). For purpose of understanding the existence of LZO and the structure changes of LTOT/LZO, X-ray photoelectron spectra (XPS) were acquired, and the survey spectra are similar for LTO, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3 except the absence of Zr element in LTOT (Figure 4a). The Ti 2p spectra for LTOT contains two peaks of Ti4+ 2p3/2 at 457.8 eV and Ti4+ 2p

1/2

at 463.5 eV (Figure 4b), the corresponding binding energies are

lower than those for the pure LTO (458.9 and 464.4 eV for Ti4+ 2p3/2 and Ti4+ 2p

1/2,

respectively 8) due to the presence of rutile TiO245. In the LTOT/LZO composites, with elevating the roasting temperature, a gradual shift to lower binding energies for Ti 2p and Zr 3d (Figure 4c) was detected. The shift of Ti 2p associates with the increased content of rutile 8


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TiO2 in the composites because more Ti4+ was substituted by Zr4+ to yield TiO2 with elevating the roasting temperature, while that of Zr 3d is due to the increment of Li6Zr2O7 with lower binding energy46-47, as supported by the XRD results (Figure S1b).

Figure 4. XPS survey spectra (a), core level spectra of Ti 2p (b) and Zr 3d (c) for LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3. 3.2 Electrochemical performance The electrochemical properties of LTOT and LTOT/LZO were measured galvanostatically (Figure 5a). When undergoing 100 cycles at 100 mA g-1, LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3 demonstrate reversible capacities of 164.5, 180.3, 183.2 and 150.4 mAh g-1, respectively. The rate capabilities of the samples were evaluated from 100 to 1600 mA g-1 by consecutively doubling the current density (Figure 5b). The capacities of the 10th cycle at 9



each density are 164.5, 163.3, 141.6, 130.8, 94.6 and 165.3 mAh g-1 for LTOT, 175.6, 171.1, 166.8, 159.3, 120.6 and 172.8 mAh g-1 for LTOT/LZO1, 183.2, 179.1, 176.5, 173.3, 169.3 and 181.2 mAh g-1 for LTOT/LZO2, 152.1, 143.7, 130.8, 105.7, 64.9, and 148.8 mAh g-1 for LTOT/LZO3.

Figure 5. Performance cycled at 100 mA g-1 (a), varied current densities (b) and 500 mA g-1 (c) for LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3. The cells also underwent cycling at 500 mA g-1 to know about the cyclability. The initial capacities are 152.9, 165.2, 174.5 and 127.3 mAh g-1 for LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3, respectively. The capacity of LTOT/LZO1 decays rapidly with cycling, while those of LTOT/LZO2 and LTOT/LZO3 fade slowly. Especially for LTOT/LZO2, even after 1400 cycles, the retained capacity is 144.7 mAh g-1 (i.e. a capacity fading rate of 0.01 % for each cycle). Despite the good cyclability of LTOT/LZO3, it delivers a markedly inferior 10


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capacity (104.2 mAh g-1) to LTOT/LZO2.

Figure 6. Lithiation/delithiation curves at varied current densities. (a) LTOT, (b) LTOT/LZO1, (c) LTOT/LZO2 and (d) LTOT/LZO3. The lithiation/delithiation curves of the 10th cycle at 100, 200, 400, 800 and 1600 mA g-1 are shown in Figure 6. The long potential platform at about 1.55 V for LTOT/LZO are ascribed to the Ti4+/Ti3+ redox couple in LTO. The reversible capacities together with the difference between the cathodic and anodic plateaus for LTOT/LZO2 changes slightly with elevating the current rate, implying the weak polarization during the electrochemical reactions. However, the polarization is severe in LTOT (in the absence of LZO modification) and LTOT/LZO3 roasted at 750 ºC. Therefore, the LZO modification for LTOT is optimally realized at an appropriate temperature around 700 ºC, i.e. in LTOT/LZO2. 3.3 Electrochemical impedance spectra (EIS) analysis

11



Figure 7. (a) Nyquist plots, (b) the relationship between Zre and ω-1/2 in the low frequency region and (c) equivalent circuit for LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3. The electrochemical kinetics was probed by EIS for the cells cycled 100 times at 100 mA g-1 (Figure 7a). The measured spectra correspond well to the fitted ones in terms of the equivalent circuit in Figure 7c (where Re - electrolyte resistance, Rc - resistance associating with LZO, Rd - resistance with Zr-doped LTO, Rct - charge transfer resistance, CPE - constant phase element, and Zw - Warburg impedance substituted for CPE in accordance with the inclined line

48-49

). The impedance values were listed in Table 1. There is no distinct

difference for Re. The Rc values for all samples roasted under 750 ºC are similar and smaller than that of LTOT/LZO3, because the higher roasting temperature of 750 ºC results in more substitution of Ti4+ by Zr4+ to yield TiO2 and interfaces which enhance electron scattering, giving rise to the increase in Rc value. The Rd values of LTOT/LZO1 and LTOT/LZO3 are slightly higher than that of LTOT/LZO2 on account of the scant (in LTOT/LZO1) and redundant (in LTOT/LZO3) Zr4+ doping. The Rct value of LTOT/LZO2 is much smaller than those of the other samples because of the suitable Zr4+ doping. The higher Rct value for LTOT/LZO1 is attributable to the week interface binding between LZO and LTOT as well as 12


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the insufficient Zr4+ doping at 650 ºC, and for LTOT/LZO3 to the larger grains and more rutile TiO250-51. Therefore, LTOT/LZO2 exhibited the smallest total impedance RT (which equals to the sum of Re, Rc, Rd and Rct) and the superior electrical conductivity. Table 1 Fitted resistance values of LTOT, LTOT/LZO1, LTOT/LZO2, LTOT/LZO3, LTO//LZO2 and LTOT/ Li2ZrO3 Samples

Re (Ω)

Rc (Ω)

Rd (Ω)

Rct (Ω)

RT (Ω)

LTOT LTOT/LZO1 LTOT/LZO2 LTOT/LZO3 LTO//LZO2 LTOT/Li2ZrO3

4.2 8.0 4.7 4.8 3.2 4.3

/ 28.2 23.6 56.6 24.6 24.2

/ 32.5 25.8 37.5 26.2 26.5

145.8 61.3 35.3 83.3 43.7 57.8

150.0 130.0 89.4 182.2 97.7 112.8

In particular, the EIS of LTOT/LZO2 were measured after undergoing 0, 1, 3, 5, 10, 20 and 100 cycles at 100 mA g-1 (Figure S5). The impedance tends to decrease during the initial 100 cycles. The reason for the decrease of resistance is that not all Ti3+ could transform into Ti4+ during electrochemically cycling52, and the coexistence of Ti3+ and Ti4+ favors the electron transfer in LTO53-54. Li+ migration in LTO can be denoted by diffusion coefficient D, as expressed in Eqs. (1) and (2) D = R2T2/2AF4C2σ2

(1)

Zre= Re + Rc + Rd + Rct + σω-1/2

(2)

where T - testing temperature, A - surface area of electrode (1.54 cm2), F - Faraday constant, C - molar concentration of Li+ (4.37×10-3 mol cm-3)55, and σ - Warburg impedance coefficient associating with the line slope in Figure 7b. The D values calculated are 1.3×10-13、8.1×10-13、3.4×10-12 和 3.0×10-13 cm2 s-1 for LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3, respectively. The D values of LTOT/LZO are 13



higher than that of LTOT due to the presence of LZO and Zr4+ doping. However, the values of LTOT/LZO1 and LTOT/LZO3 are relatively lower than LTOT/LZO2, because the binding interface between LTOT and LZO was poor in LTOT/LZO1 due to the lower roasting temperature of 650 °C, while in LTOT/LZO3, the higher roasting temperature of 750 °C results in the larger grain size for Li-ions to transfer through. Moreover, the relative content of Li6Zr2O7 and Li2ZrO3 might be another reason for the lower D values of LTOT/LZO1 and LTOT/LZO3, as will be revealed in the comparative experiments. 3.4 Comparative Experiments

Figure 8. Performance cycled at 100 mA g-1 (a), varied current densities (b) and 500 mA g-1 (c) for LTOT/LZO2-A, LTOT/LZO2 and LTOT/LZO2-B. The effect of LZO content on the properties of LTOT/LZO was investiged by roasting another two samples with different LZO/LTOT mass ratios at 700 ºC for 5 h, i.e. 0.0142 g 14


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LiNO3, 0.0221 g Zr(NO3)4•5H2O and 1.5 g LTOT in LTOT/LZO2-A, 0.0482 g LiNO3, 0.075 g Zr(NO3)4•5H2O and 1.5 g LTOT in LTOT/LZO2-B. As demonstrated in Figure 8, either the cycling performance at 100 (Figure 8a) and 500 mA g-1 (Figure 8c) or the rate capacities (Figure 8b) for LTOT/LZO2-A and LTOT/LZO2-B is inferior to that for LTOT/LZO2 due to the improper mass ratio between LZO and LTOT, as discussed in our previous work 37. The effect of TiO2, LZO on the performance was probed by comparing the performance of LTO, LTOT, LTO modified by LZO (LTO/LZO2), LTOT modified by LZO (LTO/LZO2) and LTOT modified by Li2ZrO3 (LTOT/Li2ZrO3) at 700 ºC for 5 h. The mass ratios for LZO/LTO and Li2ZrO3/LTOT are the same as that for LZO/LTOT in LTOT/LZO2. Apparently, LTOT reveals higher reversible capacity that LTO due to the increased interfaces for Li-ion storage. Similarly, LTOT/LZO2 exhibits enhanced reversible capacity compared to LTO/LZO2. Therefore, the coexistence of dual phases LTO-TiO2 is beneficial for the electrochemical properties. When LTO was modified by LZO (LTO/LZO2), the reversible capacity especially at rates higher than 500 mA g-1 (Figures 9b and c) improved due to the simultaneously ameliorated ionic and electronic conductivities (Figures 7 and 11). When LTOT was modified by LZO under the same conditions (LTOT/LZO2), the performance further enhanced with respect to that of LTO/LZO2. Although the diffraction peaks of TiO2 also present in the XRD pattern of LTO/LZO2 due to the replacement of Ti4+ by Zr4+, much weaker than those of LTOT/LZO2 (Figure 10b), Meanwhile, the RT value is 97.7 Ω for LTO/LZO2, slightly larger than that for LTOT/LZO2 (89.4 Ω), and the D value of LTO/LZO2 is 3.5×10-13 cm2 s-1, greatly inferior to that of LTOT/LZO2 (3.4×10-12 cm2 s-1), signifying that the absence of anatase TiO2 leads to 15



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bad performance. Thus the LZO-modified dual-phase LTO-TiO2 exhibits the better performance than the LZO-modified individual LTO.

Figure 9. Performance cycled at 100 mA g-1 (a), varied current densities (b) and 500 mA g-1 (c) for LTO, LTOT, LTO/LZO2, LTOT/LZO2 and LTOT/ Li2ZrO3. Also from Figure 9, when the dual-phase LTO-TiO2 was merely modified by Li2ZrO3 (LTOT/Li2ZrO3), the performance is markedly lower than that of the LTOT modified by the Li2ZrO3 and Li6Zr2O7 composites, demonstrating the better modification effect of composite zirconates than individual Li2ZrO3. Compared to the XRD patterns for LTOT/LZO2 and LTO/LZO2, the right shift of the (111) plane for LTOT/Li2ZrO3 is due to insufficient Zr4+ doping (The structure of Li2ZrO3 is more stable than that of LZO

4-6

), thus LTOT/Li2ZrO3

exhibits poor electronic conductivity (RT = 112.8 Ω) and ionic conductivity (D = 3.9×10-15 16


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cm2 s-1) in the presence of only Li2ZrO3 rather than the coexistence of Li2ZrO3 and Li6Zr2O7.

Figure 10. (a) XRD patterns and (b) the enlarged XRD patterns in the range of 2θ = 22-30° for LTO/LZO2, LTOT/LZO2 and LTOT/Li2ZrO3.

Figure 11. (a) Nyquist plots and (b) the relationship between Zre and ω-1/2 in the low frequency regions of LTO/LZO2, LTOT/LZO2 and LTOT/Li2ZrO3. Comprehensively considering the above analysis, the presence of anatase TiO2 could slightly improve the reversible capacity of LTO (LTOT), and the modification by LZO could boost the cycling and rate performance of LTOT (LTOT/LZO2) on account of the simultaneously meliorated Li+ diffusion kinetics and electrical conductivity. So the presence of Li2ZrO3 and Li6Zr2O7 composite is dominantly responsible for the elevated properties of LTOT. From the contrast experiments, the excellent cycling and rate properties of LTOT/LZO2 are 17



mainly elucidated as follows. First, at the suitable roasting temperature of 700 ºC, appropriate anatase TiO2 could bring about additional capacity for LTO due to the increased interfaces for Li-ion storage26-27. Second, the coexistence of Li2ZrO3 and Li6Zr2O7 is preferential for Li-ion migration, resulting in the significantly improved ionic conductivity for LTOT. Third, the proper superficial Zr4+ doping in LTOT contributes to boosting the electrical conductivity. Thus, the dual-phase Li4Ti5O12-TiO2 modified by the composite zirconates of Li2ZrO3 and Li6Zr2O7 at 700 ºC achieves the optimal electrochemical performance. 4. Conclusions In conclusion, the dual-phase Li4Ti5O12-TiO2 modified by the composite zirconates of Li2ZrO3 and Li6Zr2O7 was prepared by roasting the mixture of LiNO3, Zr(NO3)4•5H2O and Li4Ti5O12-TiO2 at temperatures of 650-750 ºC for 5 h. The LTOT/LZO roasted at 700 ºC reveals the optimized cycling performance and rate capabilities on account of the markedly meliorated ionic conductivity induced by the combined effect of Li2ZrO3 and Li6Zr2O7 together with the enhanced electrical conductivity caused by the superficial Zr4+ doping. Consequently, the LTOT/LZO with boosted performance is promising for potential application in fabricating advanced LIBs. Associated content Supporting Information Material characterization; Electrochemical assessment; XRD patterns of LTOT, LTOT/LZO1, LTOT/LZO2 and LTOT/LZO3, as well as LZO-650, LZO-700 and LZO-750; TEM images for LZO with low degree of crystallinity in LTOT/LZO3; HAADF-STEM image of LTOT/LZO2 and the corresponding EDS mappings; HRTEM images of LZO 18


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crystallites among the LTO particles in LTOT/LZO2; Nyquist plots of LTOT/LZO2 measured after 0, 1, 3, 5 10, 20 and 100 cycles at 100 mA g-1. The supporting Information is available free of charge via the Internet at http://pubs.acs.org. Acknowledgements This work was supported by Natural Science Foundation of Shandong Province, P. R. China (ZR2016EMM18 and ZR2016EMB13), Key research and development program of Shandong Province, P. R. China (2015GGX102005 and 2016GGX102031), Shandong Province Higher Educational Science and Technology Program (J17KA015), Qingdao Postdoctoral Research Project (2016198), and the High Talent Scheme of Qingdao University of Technology.

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Combined Modification of Dual-Phase Li4Ti5O12âTiO2 by Lithium

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