Complex spinel titanate as an advanced anode material for rechargeable lithium-ion batteries

Journal of Alloys and Compounds 611 (2014) 65–73

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Complex spinel titanate as an advanced anode material for rechargeable lithium-ion batteries Wei Chen a, Hanfeng Liang a, Weijian Ren c, Lianyi Shao b, Jie Shu b,⇑, Zhoucheng Wang a,⇑ a

College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, China c College of Materials, Xiamen University, Xiamen 361005, China b

a r t i c l e

i n f o

Article history: Received 3 April 2014 Accepted 17 May 2014 Available online 27 May 2014 Keywords: Lithium-ion batteries Anode material Complex spinel titanate Doping Solid-state reaction

a b s t r a c t In this work, complex spinel titanates Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) have been synthesized by a simple solid state reaction route. Their crystal structures are described and verified by Rietveld refinement. Electrochemical results exhibit that Li2CuTi3O8 has a highest lithium storage capacity of 242 mA h g1 and Li2ZnTi3O8 displays the lowest initial charge capacity of 190 mA h g1 among all the three samples. However, both Li2CuTi3O8 and Li2ZnTi3O8 show poor capacity retention and low reversible capacity after 50 cycles. Li2Zn0.5Cu0.5Ti3O8 shows higher structural and cycling stability than that of Li2ZnTi3O8 and Li2CuTi3O8. As a result, Li2Zn0.5Cu0.5Ti3O8 can deliver a reversible capacity of 162 mA h g1 after 50 cycles with capacity retention of 74%. Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction Due to the lithium-ion rechargeable batteries have some irreplaceable advantages such as high energy density, environmentally-friendly and so on, intense attention from both the academic community and industry has been received in the research of lithium-ion batteries. At present, the lithium-ion batteries are considered as great advancement to solve energy crisis [1,2]. The carbon has been used as an anode material in lithiumion batteries because of its large capacity and low electric potential. As we known, the low charge–discharge plateau of carbon material may lead to the deposition of metallic Li on the electrode at high current densities, causing serious safety problems. So the new inorganic material as lithium-ion batteries anode has been exploited. To the best of our knowledge, Ti-based materials can maintain steady structure during the charge–discharge process [3]. Based on their characteristics, Ti-based materials perform well be in the safety and cycling stability. For instance, Li4Ti5O12 material has been reported that its cycling stability is better than the carbon. However, the practical lithium storage capacity cannot reach to the theoretic capacity of 175 mA h g1 due to its insulator characteristic [4,5]. As ⇑ Corresponding authors. Tel.: +86 574 87600787; fax: +86 574 87609987 (J. Shu). Tel./fax: +86 592 2180738 (Z. Wang). E-mail addresses: [email protected] (J. Shu), [email protected] (Z. Wang). http://dx.doi.org/10.1016/j.jallcom.2014.05.125 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

an efficient method, some divalent metals have been chosen to be doped successfully which makes the material have higher practical capacity and the electronic conductivity also is improved significantly, meanwhile the stable Ti-based frame cannot be broken [6]. Li2MTi3O8 (M = Co, Zn, Mg, etc.) is another kind of Ti-based materials, which show a theoretical capacity of 220 mA h g1 [6,7]. However, few studies about Li2MTi3O8 have been reported in the past two decades [8–12]. In these previous reports, the electrochemical properties of Li2MTi3O8 cannot satisfy the demand of commercial lithium storage materials with high capacity and high power characteristics. Inspired by these studies, Li2ZnTi3O8, Li2CuTi3O8 and Li2Zn0.5Cu0.5Ti3O8 have been synthesized successfully by a simple solidstate reaction in this work. Based on the results of electrochemistry and structure analysis, Li2Zn0.5Cu0.5Ti3O8 exhibited better electrochemistry performance than other two materials.

2. Experimental 2.1. Synthesis of materials Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) samples were synthesized by a facile solidstate method. In a typical synthesis, stoichiometric amounts of nano-size titanium dioxide (TiO2), lithium carbonate (Li2CO3), zinc acetate dihydrate (Zn(CH3COO)22H2O) and/or cupric acetate hydrate (Cu(CH3COO)2H2O) were mechanically ground in an agate jar at a rotate speed of 400 rpm for 12 h. After being dried at 80 °C, the slurries were ball-milled at a speed of 400 rpm for 1 h and calcined at 750 °C for 5 h to get the pure Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5).

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2.2. Characterization X-ray powder diffraction (XRD) patterns were obtained on a Rigaku Ultima IV X-ray diffractometer. The data were collected by a step of 0.02° at the scanning speed 10° min1 over the 2h range of 10–70° for the samples at room temperature. Scanning electron microscopy (SEM) images and energy dispersive spectra (EDS) were recorded on a LEO 1530 microscope. High-resolution transmission electron microscopy (HRTEM) images and corresponding selected area electron diffraction (SAED) patterns were performed with a JEOL JEM-2100 transmission electron microscope at an accelerating voltage of 200 kV. 2.3. Electrochemical measurement The working electrodes were prepared by grinding a mixture of active materials, acetylene black and polyvinylidene fluoride in N-methyl-pyrrolidinone with a weight ratio of 8:1:1 followed by spreading onto a Cu foil. The film was then dried in a vacuum oven at 120 °C for 24 h. The charge/discharge tests were carried out in the potential range of 0–3 V (Li+/Li) at a current density of 100 mA g1. Electrochemical impedance spectroscopy (EIS) patterns were recorded on a CHI660 electrochemical workstation in the frequency range from 0.01 to 100,000 Hz.

3. Results and discussion Fig. 1 shows that the spinels Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) could be synthesized by solid-state reaction. The XRD pattern of Li2ZnTi3O8 could be indexed to a cubic structure with space group P4332 (JCPDS card No. 86-1512). As shown in Fig. 1b, the crystal structure of Li2ZnTi3O8 was described as (Li0.5Zn0.5)tet[(Li0.5)Ti1.5]oct O4 [13,14]. The octahedral structure in which 12d and 4b sites are occupied by 1:3 cation ordering of Li/Ti offers a stable frame

Li2 CuTi3O8

Intensity (a.u.) 10

(c)

Li2 ZnTi3O8

(a)

during lithiation and de-lithiation. In addition, a three-dimensional (3D) network was formed in this structure, where Li and Zn atoms in the tetrahedral structure shared 8a sites forming tunnels. The XRD pattern of Li2CuTi3O8 could be indexed to a cubic structure of space group Fd-3m (JCPDS card No. 49-0448). Similar to Li2ZnTi3O8, the structure of Li2CuTi3O8 is composed of octahedra and tetrahedra (Fig. 1c). And it can be described as (Li0.7Cu0.3)tet [Li0.3Cu0.2Ti1.5]octO4 [11,13]. Only few Cu atoms are located in the octahedral structure. The Li2Zn0.5Cu0.5Ti3O8 may be considered as a spinel composition of Li2ZnTi3O8 and Li2CuTi3O8. And its structure can be described as (Li0.5Zn0.25Cu0.15)tet[Li0.5Cu0.1Ti1.5]octO4 (Fig. 1d). Due to the mount of Cu atom in the octahedral is a little, the structure is close to Li2ZnTi3O8. The assumption can be proved by XRD pattern that the XRD patterns of Li2ZnTi3O8 and Li2Zn0.5Cu0.5Ti3O8 was similar with each other. In the following section, the structure of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) would be further testified by XRD refinement. Fig. 2 shows the Rietveld refinement results of XRD patterns for Li2MTi3O8. According to Rietveld refinement results, the structures of spinels Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) were confirmed that Li2ZnTi3O8 could be described as (Li0.5Zn0.5)tet[(Li0.5)Ti1.5]octO4, Li2CuTi3O8 could be described as (Li0.7Cu0.3)tet[Li0.3Cu0.2Ti1.5]octO4 and Li2Zn0.5Cu0.5Ti3O8 could be described as (Li0.5Zn0.25Cu0.15)tet [Li0.5Cu0.1Ti1.5]octO4. The detailed Rietveld refinement data for Li2ZnTi3O8, Li2CuTi3O8 and Li2Zn0.5Cu0.5Ti3O8 are displayed in the Tables 1–3, respectively. It can be found that the lattice parameters values follow the sequence of Li2ZnTi3O8 (8.3560 Å) < Li2Zn0.5Cu0.5

Li2 Zn 0.5 Cu0.5Ti3O8

20

30

40

50

60

70

2-theta (degree)

(b)

(d)

Fig. 1. (a) XRD patterns of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5), (b) schematic representation of the structure of Li2ZnTi3O8 which can be described as (Li0.5Zn0.5)tet[(Li0.5)Ti1.5]octO4, (c) schematic representation of the structure of Li2CuTi3O8 which can be described as (Li0.7Cu0.3)tet[Li0.3Cu0.2Ti1.5]octO4 and (d) schematic representation of the structure of Li2Zn0.5Cu0.5Ti3O8 which can be described as (Li0.5Zn0.25Cu0.15)tet[Li0.5Cu0.1Ti1.5]octO4.

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W. Chen et al. / Journal of Alloys and Compounds 611 (2014) 65–73 Table 1 Rietveld refinement data obtained for Li2ZnTi3O8.

(a)

Li 2 ZnTi 3 O8 (sim)

Site

Li 2 ZnTi 3 O8 (Exp)

Atom

x

Li2ZnTi3O8: a = 8.35596(2) Å; space 4b Li 5/8 8c Li 0.0016(6) 8c Zn 0.0016(6) 8c O 0.392(2) 12d Ti 0.3677(2) 24e O 0.105(2)

Intensity (a.u.)

Difference Observed Reflections

y

z

Occupancy

group: P4332 5/8 0.0016(6) 0.0016(6) 0.392(2) 0.8823(2) 0.128(1)

5/8 0.0016(6) 0.0016(6) 0.392(2) 1/8 0.392(1)

1 0.5 0.5 1 1 1

Table 2 Rietveld refinement data obtained for Li2CuTi3O8.

Y Ax is T itle

Site

Atom

x

y

z

Occupancy

0 0 5/8 5/8 5/8 0.389(1)

0.7 0.3 0.15 0.1 0.75 1

0 -1 0 0 -2 0 0 10

20

30

40

50

60

70

X Axis T itle

10

20

30

40

50

60

70

2-Theta (degree)

Li2CuTi3O8: a = 8.36050(3) Å; space group: Fd-3m 8a Li 0 0 8a Cu 0 0 16d Li 5/8 5/8 16d Cu 5/8 5/8 16d Ti 5/8 5/8 32e O 0.389(1) 0.389(1)

Li 2 Cu Ti 3O8 (Sim)

(b)

Table 3 Rietveld refinement data obtained for Li2Zn0.5Cu0.5Ti3O8.

Li 2 Cu Ti3O8 (Exp) Difference Observed Reflections

Site

Atom

Intensity (a.u.)

Li2Zn0.5Cu0.5Ti3O8: 4b Li 8c Li 8c Cu 8c Zn 8c O 12d Cu 12d Ti 24e O

10

20

30

40

50

60

70

2-theta (degree)

(c)

Li2 Zn 0.5 Cu0.5 Ti3 O8 (Sim) Li 2 Zn 0.5 Cu 0.5 Ti 3O8 (Exp) Difference

Intensity (a.u.)

Observed Reflections

10

20

30

40

50

60

2-Theta (degree) Fig. 2. XRD refinement of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5).

70

x

y

z

a = 8.35792(5) Å; space group: P4332 5/8 5/8 5/8 0.0016(6) 0.0016(6) 0.0016(6) 0.0016(6) 0.0016(6) 0.0016(6) 0.0016(6) 0.0016(6) 0.0016(6) 0.392(2) 0.392(2) 0.392(2) 0.3677(4) 0.8823(4) 1/8 0.3677(4) 0.8823(4) 1/8 0.105(2) 0.128(1) 0.392(1)

Occupancy 1 0.5 0.25 0.25 1 0.05 0.95 1

Ti3O8 (8.3579 Å) < Li2CuTi3O8 (8.3605 Å). Due to the Cu atomic radius (145 pm) was slightly larger than Zn (142 pm), the result of refinement confirms that Li2Zn0.5Cu0.5Ti3O8 phase is formed. Fig. 3 indicates the element composition in Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) as detected by EDS. The content of elements was shown in Table 4. To ideal result, the atomic ratio of M (M = Zn, Cu, Zn0.5Cu0.5):Ti:O should be equal to 1:3:8 in Li2MTi3O8. Due to the effect of SiO2 base, the content of O element would be interfered. As shown in Table 1, EDS results confirm that the atomic ratio of M (M = Zn, Cu, Zn0.5Cu0.5):Ti is close to 1:3. This indicates that the complex spinel titanates Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) have been synthesized. Fig. 4 displays the SEM and TEM images of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5). It is clear that all the products reveal similar morphologies and the particles sizes are found to be several hundreds nanometers. For Li2ZnTi3O8 as shown in Fig. 4c, the lattice fringes were approximately 0.591 and 0.209 nm corresponding to the d110-spacing and d400-spacing, respectively. For Li2CuTi3O8 (Fig. 4g), the lattice fringe corresponding to {400} planes can also be observed. For Li2Zn0.5Cu0.5Ti3O8 (Fig. 4j), the inter-plane distances are scaled to be 0.483 and 0.592 nm matching the inter-plane distances of the {1 1 0} and {1 1 1} planes respectively, which are also consistent with the SAED pattern as shown in Fig. 4l. This also indicates that the complex spinel titanates Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) have been synthesized successfully. The as-obtained spinels Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) were then evaluated as anode materials for lithium-ion batteries. Fig. 5 shows the charge–discharge profiles obtained at a current density

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Fig. 3. EDS of (a) Li2ZnTi3O8, (b) Li2CuTi3O8 and (c) Li2Zn0.5Cu0.5Ti3O8.

W. Chen et al. / Journal of Alloys and Compounds 611 (2014) 65–73 Table 4 EDS results for Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5). Sample

Element

Weight%

Atomic%

Li2ZnTi3O8

OK Ti K Zn K Totals

53.78 30.49 15.73 100.00

79.23 15.07 5.70

Li2CuTi3O8

OK Ti K Cu K Totals

52.30 32.63 15.07 100.00

78.07 16.27 5.66

Li2Zn0.5Cu0.5Ti3O8

OK Ti K Cu K Zn K Totals

42.73 39.38 8.94 8.95 100.00

70.83 21.80 3.73 3.63

69

of 100 mA g1. As revealed in Fig. 5a, Li2ZnTi3O8 exhibits excellent cycling stability with a stable reversible capacity of 190 mA h g1 at a current density of 100 mA g1 after 20 cycles, which may be benefited from its structure (Fig. 5a). During the first 20 cycles, the octahedral structure is relative stable and 3D network made by tetrahedra provides a diffusion space for lithiation and de-lithiation [14]. However, as the reaction goes on, the frame may become unstable due to the large lithium insertion strain, leading to a quick fade in capacity in the following cycles. As a result, a reversible capacity of 140 mA h g1 was retained after 50 cycles. For Li2Zn0.5Cu0.5Ti3O8 (Fig. 5c), the initial capacity is improved by Cu doping (219 mA h g1). After 50 cycles, a reversible capacity of 162 mA h g1 was retained as shown in Fig. 5c. For comparison, although the initial capacity of Li2CuTi3O8 (Fig. 5b) is largely improved to 242 mA h g1, it fades to 90 mA h g1 after 50 cycles with capacity retention of 37.2%. This may be due to the decrease

Fig. 4. (a) SEM image of Li2ZnTi3O8, (b) TEM image of Li2ZnTi3O8, (c) HRTEM image of Li2ZnTi3O8, (d) SAED image of Li2ZnTi3O8, (e) SEM image of Li2CuTi3O8, (f) TEM image of Li2CuTi3O8, (g) HRTEM image of Li2CuTi3O8, (h) SAED image of Li2CuTi3O8, (i) SEM image of Li2Zn0.5Cu0.5Ti3O8, (j) TEM image of Li2Zn0.5Cu0.5Ti3O8, (k) HRTEM image of Li2Zn0.5Cu0.5Ti3O8 and (l) SAED image of Li2Zn0.5Cu0.5Ti3O8.

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Fig. 4 (continued)

of structural stability resulted from the total replacement of Zn atoms with Cu atoms in the octahedral sites. Besides, the existence of impurity TiO2 may be also responsible for the cycling instability. The different cycling behaviors of the three samples can be intuitively observed in Fig. 5d. As it can be seen, Li2CuTi3O8 has the highest initial capacity while it fades quickly upon cycling. Li2ZnTi3O8 performs excellent cycling stability in first 20 cycles and then capacity fades fast in the subsequent cycles. Compared with these two anodes, the initial capacity of Li2Zn0.5Cu0.5Ti3O8 is relative high and its cycling stability is largely improved. Furthermore, Li2Zn0.5Cu0.5Ti3O8 exhibits the highest efficiency among the three samples as revealed in Fig. 5e.

Differential capacitance measurements were then carried out to characterize the electrochemical performance of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5). As shown in Fig. 6, the reduction process differs between the initial cathodic sweep and subsequent cycles. This can be attributed to local structural changes and polarization of the cell. In the subsequent cycles, the peaks observed essentially remained constant, indicating that lithium-ion intercalation into and deintercalation out of the electrode were reversible. The differential capacitance curves of the three samples are somewhat similar due to their similar spinel structures. For instance, an intense anodic peak at 1.7 V and a weak cathodic peak at 1.5 V were observed which can be assigned to Ti4+/Ti3+ redox couple [16].

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3.0

3.0

(b)

(a) 2.5 1st 2nd 5th 20th 35th 50th

1.5

+

2.0

Potential (V)vs. Li /Li

+

Potential (V)vs. Li /Li

2.5

1.0

1st 2nd 5th 20th 35th 50th

1.5

1.0

0.5

0.5

0.0

2.0

0

100

200

300

0.0

400

0

100

400

500

280

3.0

(d)

260

Discharge capacity ( mAh g -1 )

(c) 2.5

+

300

Capacity (mAhg )

Capacity (mAh g )

Potential (V)vs. Li /Li

200

-1

-1

2.0

1st 2nd 5th 20th 35th 50th

1.5

1.0

0.5

240

Li2 CuTi 3 O8

220

Li2 ZnTi3O8

200

Li2 Zn 0.5 Cu 0.5Ti3O8

180 160 140 120 100 80

0.0

0

100

200

300

0

400

10

20

30

40

50

Cycle number

Capacity (mAh g -1 )

110

(e)

100

Efficiency (%)

90 80

Li2 CuTi3O8 70

Li2 ZnTi3 O8 Li2 Zn 0.5 Cu 0.5Ti3O8

60 50 40

0

10

20

30

40

50

Cycle number Fig. 5. Charge–discharge profiles of (a) Li2ZnTi3O8, (b) Li2CuTi3O8 and (c) Li2Zn0.5Cu0.5Ti3O8, (d) cycle performance and (e) efficiency performance of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) at 100 mA g1.

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6000 5000

(a)

1st 2nd 5th 20th 50th

dQ/dV (mAh g-1 V -1)

4000 3000 2000 1000 0 -1000 -2000 -3000 -4000 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Potential (V) 6000

(b)

dQ/dV (mAh g-1 V -1)

4000

1st 2nd 5th 20th 50th

2000 0 -2000 -4000 -6000

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Potential (V)

dQ/dV ( mAh g-1 V -1)

4000

(c)

1st 2nd 5th 20th 50th

3000 2000 1000 0 -1000 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Potential (V) Fig. 6. Differential capacitance curves of (a) Li2ZnTi3O8, (b) Li2CuTi3O8 and (c) Li2Zn0.5Cu0.5Ti3O8.

W. Chen et al. / Journal of Alloys and Compounds 611 (2014) 65–73

and Li2CuTi3O8 (111.3 X), indicating that Li2Zn0.5Cu0.5Ti3O8 exhibits lower charge transfer resistance for lithium ion transportation. Therefore, the electrochemical performance of Li2Zn0.5Cu0.5Ti3O8 is better than Li2ZnTi3O8 and Li2CuTi3O8.

500

4. Conclusions 300

,,

(Ohm)

400

-Z

73

200

Li2 Zn0.5Cu0.5Ti3O8 Li2 ZnTi3O8

100

Li2CuTi3O8 0

0

100

200

300

, Z (Ohm)

400

500

Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5) were synthesized by a simple solid state reaction route. The difference of structure between the synthesized Li2ZnTi3O8 and Li2CuTi3O8 was testified by XRD refinement. Due to the difference in structure, Li2ZnTi3O8, Li2CuTi3O8 and Li2Zn0.5Cu0.5Ti3O8 display different electrochemical behaviors. A large capacity of 162 mA h g1 can be kept for Li2Zn0.5Cu0.5Ti3O8 after 50 cycles at a current density of 100 mA g1. In contrast, Li2ZnTi3O8 and Li2CuTi3O8 can merely deliver the reversible capacities of 140 and 90 mA h g1 after 50 cycles. Therefore, this work can provide a support to improve the electrochemical performance of spinel Li2MTi3O8 by element doping.

Fig. 7. The impedance spectra of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5).

Acknowledgements Table 5 The simulated data from EIS spectra using an equivalent circuit. Sample

Rs (X)

Rct (X)

CPE (lF)

W (X)

Li2Zn0.5Cu0.5Ti3O8 Li2ZnTi3O8 Li2CuTi3O8

7.525 6.269 7.840

96.33 117.6 111.3

8.252E5 4.447E5 6.709E5

0.0045 0.0071 0.0045

While some slight differences caused by their different structure (e.g. atom location) can be still observed. For example, a reduction peak near 0.5 V can be observed for Li2ZnTi3O8 and the intensity of the peaks weakens in the following cycles (Fig. 6a). According to previous reports, this peak may be attributed to the multiple restoration of Ti4+ [15,16]. After cycles, all the peaks shift obviously, indicating the polarization of Li2ZnTi3O8 occurs. Different from Li2ZnTi3O8, the peak near 0.5 V could not be observed for Li2CuTi3O8 (Fig. 6b). In addition, although the intensities of anodic and cathodic peaks weaken quickly after the first cycle, the peaks do not show any significant shift. In the case of Li2Zn0.5Cu0.5Ti3O8, the polarization decreases and the structural stability is enhanced due to the Cu doping. These results are in agreement with the results obtained from galvanostatic charge–discharge experiments. To further understand the effects of metal (Zn or Cu) ions doping on the electrochemical behavior of Li2MTi3O8 (M = Zn, Cu, Zn0.5Cu0.5), the electrochemical impedance spectra were measured. As shown in Fig. 7, a semicircle in high frequency region followed by a line in low frequency region can be observed for all three samples. The diameters of semicircles are measured to calculate the charge transfer resistances, which are related to electrochemical reactions between the electrode and the electrolyte. The equivalent circuit is shown in the inset of Fig. 7. And the Rs, CPE1, Rct, and Zw are electrolyte resistance, constant phase element, charge transfer resistance and Warburg impedance, respectively [9]. As shown in Table 5, the calculated result reveals that the value Rct of Li2Zn0.5Cu0.5Ti3O8 (96.33 X) is smaller than that of Li2ZnTi3O8 (117.6 X)

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