High ionic conductivity Y doped Li1.3Al0.3Ti1.7(PO4

Journal of Alloys and Compounds 782 (2019) 384e391

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High ionic conductivity Y doped Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte Erqing Zhao a, *, Yudi Guo b, Guangri Xu a, Long Yuan c, Jingcheng Liu a, Xiaobo Li a, Li Yang a, Jingjing Ma a, Yuanchao Li a, Shumin Fan a a

School of Chemistry and Chemical Engineering, Henan Institute of Science and Technology, Xinxiang 453003, China College of Chemistry and Chemical Engineering, Xinxiang University, Xinxiang 453003, China c Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Changchun 130103, China b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 8 October 2018 Received in revised form 11 December 2018 Accepted 13 December 2018 Available online 15 December 2018

Li1.3Al0.3Ti1.7(PO4)3 is regarded as one of the most promising solid electrolytes for all solid state lithium ion batteries (ASSLIBS). However, its grain boundary conductivity is still low, which reduces the total conductivity of electrolyte. In this work, in order to further improve the electrical conductivity of Li1.3Al0.3Ti1.7(PO4)3, a series of Y doped Li1.3Al0.3-xYxTi1.7(PO4)3 (x ¼ 0, 0.025, 0.05, 0.075 and 0.15) solid electrolytes were synthesized using a modified solid state method. Effects of Y doping content on morphology, phase and electrical conductivity of Li1.3Al0.3Ti1.7(PO4)3 electrolyte materials were systematically investigated. All synthetic electrolyte powders show Nasicon-like structure, well-shaped polyhedral morphology as well as good crystallinity. Y dopant content has a great influence on electrochemical properties of electrolytes. The high total conductivity of 7.8 104 S/cm at room temperature and a low activation energy of 0.17 eV is obtained for the electrolyte with the Y doping content of 0.075 due to the increasing of grain boundary conductivity, and its electrical conductivity is about 2 times larger than that of the undoped electrolyte. The excellent electrochemical performance is mainly attributed to high electrolyte density which results from the good sintering property of electrolyte materials as well as the existence of YPO4 phase at grain boundaries. Additionally, this electrolyte has a negligible electronic conductivity. These results suggest that Y doped Li1.3Al0.3Ti1.7(PO4)3 can be used as an alternative solid electrolyte for all solid state lithium ion batteries. © 2018 Elsevier B.V. All rights reserved.

Keywords: Li1.3Al0.3Ti1.7(PO4)3 Solid electrolyte Solid state method Y doping Conductivity

1. Introduction With the rapid development of largeescale applications, such as electrical vehicles and large-scale energy storage devices, they urgently need the power batteries with high power energy density, long cycle life and high safety. The traditional lithium ion batteries can't meet the above requirements due to their safety problems resulting from the leakage or flammability of organic liquid electrolytes. Compared to the liquid lithium ion batteries, all solid state lithium ion batteries have better safety and higher energy density by replacing the liquid electrolytes with solid electrolytes, which can be used as the power batteries for largeescale applications. In an all solid state battery system, it mainly consists of three components: a cathode, an anode and a solid electrolyte. As a key component of all solid state batteries, the electrolyte has an important impact on the battery performances. In the past several

* Corresponding author. E-mail address: [email protected] (E. Zhao). https://doi.org/10.1016/j.jallcom.2018.12.183 0925-8388/© 2018 Elsevier B.V. All rights reserved.

decades, the numerous types of solid lithium ion conductors have been investigated, such as Nasicons [1e4], Lisicons [5,6], perovskites [7,8], garnets [9,10] and sulfide-based systems [11,12]. Among the above evaluated electrolytes, the Nasicon-structure LiTi2(PO4)3 (LTP) material has been regarded as one of the most promising lithium ion electrolytes, whose ionic conductivity can be greatly enhanced by partially replacing Tiþ4 with some trivalent cations of close ionic radii, which is mainly attributed to higher charge carrier concentration, larger lithium ion migration channels and denser structure [13]. In the doped LTP systems, the Li1þxAlxTi2x(PO4)3 electrolytes [14e18] have been studied extensively because of high bulk conductivity, excellent stability against air and water as well as low preparation cost, and the electrolyte with the general formula of Li1.3Al0.3Ti1.7(PO4)3 (LATP) has the high ionic conductivity. Although the LATP electrolyte possesses the high bulk conductivity, its grain boundary conductivity is still low, which needs to be further improved with aim of increasing the total conductivity. Currently, some effective strategies have been adopted to promote the migration of lithium ions at the grain boundaries, which include the advanced sintering techniques [19e21], the addition of

E. Zhao et al. / Journal of Alloys and Compounds 782 (2019) 384e391

sintering aids with low melting temperature [22,23] and the doping of elements [24e26]. Among them, the elemental doping is a common, effective and convenient way to improve the properties of LATP electrolyte. The host Alþ3 cation in the LATP system is partially substituted by other trivalent cations with larger ionic radii, which not only improves the densification of the electrolyte, but also enlarges the lattice volume. As a well-known doping element, Yttrium has been widely used to dope garnet-type Li7La3Zr2O12 solid electrolytes [27,28], which can stabilize the cubic garnet-like structure at lower sintering temperature, enhance the density of electrolyte and thus contribute to high lithium ion conduction. Similarly, some researchers have attempted to improve the electrical conductivity of LATP using Y element doping. D H Kothari et al. [29] have demonstrated that the Y doping can increase the lattice volume and the density of the LATP electrolyte. However, the overall lithium ion conductivity was not enhanced, which is ascribed to the formation of impurities with low lithium ion conductivity. These impurity phases can be reduced by adjusting the synthetic method for the electrolyte materials. Currently, the solid state method is a common approach to synthesize solid electrolytes due to its simple preparation process and mass production. But it requires high calcination temperature to synthesize the desired targets, leading to high energy consumption and the formation of the harmful purities. In view of this, a modified solid state method was used to prepare a series of Li1.3Al0.3-xYxTi1.7(PO4)3 (x ¼ 0, 0.025, 0.05, 0.075, 0.15) electrolyte in our work, and the effects of Y doping content on the structure and properties of LATP electrolyte was systematically investigated. 2. Experimental The Li1.3Al0.3-xYxTi1.7(PO4)3 (x ¼ 0, 0.025, 0.05, 0.075, 0.15) electrolyte pellets were synthesized via a modified solid state method. The used starting materials were LiNO3 (99.0%, Aladdin Industrial Co., Ltd.), Al(NO3)3$9H2O (99.0%, Aladdin Industrial Co., Ltd.), Y(NO3)3$6H2O (99.0%, Aladdin Industrial Co., Ltd.), NH4H2PO4 (99%, Sinopharm Chemical Reagent Co.,Ltd.) and TiO2 (P25, Degussa), respectively. The typical preparation process can be described as follows: the stoichiometric amounts of LiNO3, Al(NO3)3$9H2O,Y(NO3)3$6H2O and NH4H2PO4 were weighed and dissolved into 10 ml de-ionized water to form the transparent solution. To compensate for possible Liþ volatilization during the heating treatment process, 10 wt% excess of LiNO3 was added during the synthetic process. Glucose (C6H12O6, Sinopharm Chemical Reagent Co., Ltd.) was subsequently added to the above solution under magnetic stirring conditions, and the molar ratio of glucose to total metal cations was fixed at 1.5:1. Then, the stoichiometric content of TiO2 powders were mixed in the solution to form the precursor slurry of Li1.3Al0.3-xYxTi1.7(PO4)3 materials. The obtained slurry was transferred to the ZrO2 jars and ball milled by a planetary mill at 300 rmp for 3 h to homogenize the mixture. To evaporate the solvent, the resultant homogeneous slurry was dried for 12 h by a freeze-drying method. The dried samples was placed in an electric furnace and calcined at 300 C for 2 h to obtain the black carbonated product, which was ground in an agate mortar using a pestle, followed by calcination at 800 C for 4 h at a heating rate of 3 C/min to form the white Li1.3Al0.3-xYxTi1.7(PO4)3 targets. To get the fine electrolyte materials, the as-synthesized powders were further ball milled at 400 rmp for 6 h with the mass ratio of powders and ZrO2 balls of 1:20. After ball milling, the appropriate amount of powders were weighed and pressed into the green electrolyte pellets with the diameter of 15 mm under 10 MPa pressure for 5 min, which were sintered at 850 C for 4 h to form the dense electrolyte samples. To avoid the Liþ evaporation, the green pellets were covered by the Li1.3Al0.3-xYxTi1.7(PO4)3 mother

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powders before the heating treatment. For comparison, the Li1.3Al0.3-xYxTi1.7(PO4)3 (x ¼ 0, 0.075) electrolyte samples were prepared using the traditional solid state method. LiCO3 (99.0%, Aladdin Industrial Co., Ltd.), Al2O3 (99.0%, Aladdin Industrial Co., Ltd.), Y2O3 (99.0%, Aladdin Industrial Co., Ltd.), TiO2 and NH4H2PO4 were mixed in ethanol by ball milling at 400 rmp for 4 h. The as-obtained slurry was dried at 60 C for 12 h, and subsequently calcined at 800 C for 4 h to form the electrolyte materials. The preparation process of the electrolyte was identical to that of the electrolyte fabricated using the modified solid state method. X-ray diffraction (XRD) patterns of the electrolyte powders and pellets were recorded using a diffractometer (XRD, Bruker-AXS Microdiffractometer D8 Advance, Cu Ka) in the 2q range from 10 to 90 with a step size of 0.02 at room temperature. The XRD data for structural refinements were collected in the 2q range from 5 to 120 with 0.02 steps of 2 s counting time/step. The Rietveld technique using FullProf program was carried out for structural refinements. The infrared experiment was performed on an infrared spectrometer (ATR-FTIR, Nicolet iS50, Thermo Scientific) to examine the structure of as-synthesized powders. The morphologies of electrolyte powders and pellets were observed by a scanning microscope (SEM, Quanta250FEG, FEI). Prior to electrical conductivity measurements, the electrolyte pellets were polished using 1000 mesh SiC papers to increase the adhesion between the electrolyte and the electrode. The thickness of polished electrolyte was about 1 mm. A gold layer was sputtered onto both sides of electrolyte to form ionic blocking electrodes. Electrochemical impedance spectroscopy (EIS) measurements were carried out using an electrochemical station (660E) in the frequency range from 106 Hz to 1 Hz at an amplitude of 5 mV under open circuit condition. The potentiostatic polarization method with a polarizing voltage of 0.2 V was applied to estimate the electronic conductivity of electrolyte pellets.

3. Results and discussions The phases of the synthetic electrolyte powders with different compositions were characterized by XRD. Fig. 1 shows the XRD

Fig. 1. The XRD patterns of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte materials calcined at 800ºCfor 4 h in air.

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patterns of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte materials. As shown in Fig. 1, it can be found that all diffraction peaks of the undoped powders are well matched with typical rhombohedral Nasiconstructure LiTi2(PO4)3 (JCPDS 35-0754), which indicates that Nasicon-structure Li1.3Al0.3Ti1.7(PO4)3 samples have been successfully synthesized. For Y doped Li1.3Al0.3Ti1.7(PO4)3 electrolyte materials, their main diffraction peaks are still assigned to NASICON LiTi2(PO4)3 structure, while other small impurity peaks belongs to YPO4. Moreover, with the increasing of Y dopant content, the peak intensity of YPO4 impurity gradually becomes larger. The formation of YPO4 in the Y doping LATP systems can be due to the fact that Y can't fully enter the LATP lattice because the ionic radii of Y3þ (0.93 Å) is larger than that of Al3þ (0.535 Å) as well as Ti4þ (0.60 Å). The Rietveld refined XRD patterns of Li1.3Al0.3Ti1.7(PO4)3 and Li1.3Al0.225Y0.075Ti1.7(PO4)3 electrolyte materials are shown in Fig. 2. It can be seen that the observed XRD patterns are well consistent with the calculated patterns. The lattice parameters for analyzed samples increase due to the Y doping, which are listed in Table 1, indicating that Y enters the LATP lattice. The structure of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte materials was further analyzed using the infrared experiment. Fig. 3 presents the infrared spectrum of electrolyte materials with different Y doping content. Three identical peaks can be observed in all samples, which are located at about 930, 640 and 575 cm1, respectively, as shown in Fig. 3. The peak at about 930 cm1 corresponds to the vibration of P-O tetrahedron [30], while other peaks at 640 and 575 cm1 are attributable to the vibration of Ti-O octahedron [31]. Therefore, it can be concluded that the results from infrared analysis are consistent with those of XRD. As displayed in Fig. 4 are SEM photographs for morphologies of the Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte materials sintered at 800 C. It can be seen that all electrolyte materials consist of well-shaped

Table 1 Rietveld fitting results of Li1.3Al0.3Ti1.7(PO4)3 and Li1.3Al0.275Y0.025Ti1.7(PO4)3 electrolyte materials. formula

Li1.3Al0.3Ti1.7(PO4)3

Li1.3Al0.275Y0.025Ti1.7(PO4)3

space group a (Å) b (Å) c (Å) a ¼ b(deg) g(deg) V (Å3) Rp Rwp

R-3c 8.4984(1) 8.4984(1) 20.8403(7) 90 120 1303.50(3) 0.0863 0.1281 23.50

R-3c 8.5009(2) 8.5009(2) 20.8464(8) 90 120 1304.63(7) 0.0747 0.1224 21.19

c2

Fig. 3. The infrared spectrum for Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte materials calcined at 800ºCfor 4 h in air.

Fig. 2. The Rietveld refined XRD patterns of Li1.3Al0.3Ti1.7(PO4)3 and Li1.3Al0.275Y0.025Ti1.7(PO4)3 electrolyte materials.

cubic particles with the sizes in the range of several hundred nanometers and several microns. In addition, the particles show smooth surfaces, indicating that the electrolyte materials have high crystallinity. In order to obtain the dense electrolytes, the as-pressed green electrolyte pellets were sintered at 850 C for 4 h. The structure of the sintered samples was also identified by XRD. As shown in Fig. 5, all diffraction peaks of the undoped sample are well matched with the standard pattern of LiTi2(PO4)3 NASICON structure. And the main diffraction peaks in the XRD patterns of the Y doping electrolytes still belong to LiTi2(PO4)3 Nasicon structure, except for small peaks attributed to the YPO4 impurity as secondary phase. The XRD analysis of the electrolyte pellets is similar to that of electrolyte powders, indicating that the Li1.3Al0.3-xYxTi1.7(PO4)3 materials possess excellent structural stability, which also demonstrates that Nasicon-structure Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes have been successfully prepared. The microstructures of the as-obtained electrolytes were observed using SEM. Fig. 6 presents the cross-sectional SEM micrographs of the Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes sintered at 850 C. From Fig. 6, it can be found that the sintered electrolyte samples are composed of numerous irregular cubic particles with the sizes ranging from several micrometers to tens of micrometers. Moreover, the cubic particles tightly contact with each other, which contributes to high dense structure of electrolytes, as shown in Fig. 6. The high dense structure can be originated from good sintering properties of electrolyte materials as well as the secondary


387

Fig. 4. SEM micrographs of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte materials calcined at 800ºCfor 4 h in air: (a) x ¼ 0; (b) x ¼ 0.025; (c) x ¼ 0.05; (d) x ¼ 0.075; (e) x ¼ 015.

Fig. 5. The XRD patterns of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes sintered at 850 C for 4 h in air.

phase of YPO4. These SEM observations illustrate that the Li1.3Al0.3have been well sintered. It is expected that the Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes can give high lithium ion conductivity. Subsequently, effects of Y doping content on the performances of electrolytes were investigated using EIS technique. Fig. 7 displays the impedance profiles of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes measured at the temperatures ranging from 25 C to 90 C, where the optimal Y doping content was determined. In Fig. 7, the impedance responses of all samples are similar, which consist of a semicircle at high frequency region and a sloping straight line at low frequency region. The high frequency semicircle corresponds to the grain boundary resistance (Rbg), while a tail at low frequencies represents the ion blocking effect of Au electrode. The low- and high-frequency intercepts of the semicircle at the real impedance axis are assigned to the bulk resistance (Rb) and total resistance (Rt) [5,32], respectively. As the testing temperature increases, the impedance for each electrolyte sample decreases. This phenomenon can be explained by the fact that the lithium ion migration rate

xYxTi1.7(PO4)3electrolytes

in the electrolyte becomes larger with the increasing of temperature. From Fig. 7, it can be observed that the Y doping content has a great influence on the electrochemical properties of Li1.3Al0.3xYxTi1.7(PO4)3 electrolytes. To obtain the conductivities of the electrolytes with different compositions at room temperature, the impedance spectrum were fitted using an equivalent circuit model consisting of Rg(CPE1Rgb)CPE2 (where Rb, Rbg and CPE represent a bulk resistor, a grain boundary resistor and a constant phase element, respectively.). The electrical conductivity of electrolytes can be calculated from the following equation: st ¼ l/RtS, where st, l, Rt and S represent total electrical conductivity, thickness, total resistance and effective area of the electrolyte, respectively. Table 2 shows the impedance fitting results of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes. As the Y doping content varies from 0 to 0.075, the total electrical conductivity of electrolyte increases. The electrolyte with the Y doping content of 0.075 displays the greatest total electrical conductivity of 0.78 ms/cm at room temperature, which is about 2.5 times as high as that of undoped electrolyte and even comparable to those of Nasicon-type lithium ion solid electrolytes reported in Refs. [23,33e39]. Table 3 presents the values of total electrical conductivity for LATP-based solid electrolytes at ambient temperature. For comparison, the Li1.3Al0.3Ti1.7(PO4)3 and Li1.3Al0.225Y0.075Ti1.7(PO4)3 electrolyte materials were synthesized using the traditional solid state method. As shown in Fig. S1 in the supplementary material are the XRD patterns of electrolyte materials. From Fig. S1, it can be observed that some impurity phases, such as Li4P2O7 and YPO4, exist in the electrolyte materials. Then, the impedance spectra of the electrolytes were also obtained, as displayed in Fig. S2 in the supplementary material. The electrical conductivities for Li1.3Al0.3YTi1.7(PO4)3 and Li1.3Al0.225Y0.075Ti1.7(PO4)3 electrolytes can be calculated as 1.93 ms/cm and 1.22 ms/cm, respectively, which are lower than those of the electrolytes prepared using the modified solid state method. The excellent electrochemical performance of Y doped Li1.3Al0.3Ti1.7(PO4)3 electrolyte prepared by the modified solid state method is mainly ascribed to high density of electrolytes which is favorable for lithium ion conduction. As shown in Table 2, the density of electrolyte is closely related to Y doping content. The undoped electrolyte has a density of 2.65 g/cm3, while the densities of the electrolytes with Y doping content of 0.025, 0.05, 0.075 and 0.15 are 2.79, 2.80, 2.76 and 2.69 g/cm3, respectively, which are due to the YPO4 secondary phases. The YPO4 phases in the Y doped LATP samples tend to segregate at the grain boundaries, which can bind the grains together, and thus leads to the increasing of the

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Fig. 6. The impedance profiles for Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes measured at different temperatures under open circuit condition.

electrolyte density [29]. When x further increases up to 0.15, the corresponding electrical conductivity decreases. As a non lithium ion conductor, the excess YPO4 phases accumulate at the grain boundaries and block lithium ion conduction [40]. Fig. 8 shows the temperature dependence of total electrical conductivity. As shown in Fig. 8, the plots of logsT against 1/T are found to be well linear, suggesting that the relationship between total conductivity and temperature is well fitted to the Arrhenius's equation sT ¼ Aexp(Ea/kT), where Ea is the activation energy, A is the pre-exponential factor, k is the Boltzmann's constant and T is the absolute temperature. The activation energies can be calculated from the line slopes of Arrhenius's plots, whose values are 0.3, 0.26, 0.24, 0.17, and 0.19 eV for the undoped electrolyte and Y dopant electrolytes with x ¼ 0, 0.025, 0.05, 0.075 and 0.15, respectively. The electrolyte sample with Y doping content of 0.075 has a low activation energy of 0.17 eV. As a solid electrolyte adopted in an all-solid-state lithium ion

battery, it also requires a negligible electronic conductivity except for high ionic conductivity. Herein, the electronic conductivities of the electrolytes with different compositions were measured via a potential static polarization method using Au/Li1.3Al0.3-xYxTi1.7(PO4)3/Au structure cell. Fig. 9 shows the polarization period dependence of the current under a polarization voltage of 0.2 V. From Fig. 9, it can be observed that the current gradually decreases with the increasing of polarization period and finally achieves the steady state. The electronic conductivities of electrolytes can be estimated from the steady-state current. The electronic conductivities for the electrolytes with Y doping content of 0, 0.025, 0.05, 0.075 and 0.15 are 5.37 109, 7.20 109, 1.58 108, 1.02 108 and 3.46 109 S/cm, respectively. Based on the above results, it can be concluded that the contribution of electronic conductivity to total conductivity is negligible.


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Table 2 Fitted results for impedance spectra, total conductivities and densities of Li1.3Al0.3xYxTi1.7(PO4)3 solid electrolytes. Chemical formula

Rb ( U)

Rbg (U)

Rt ( U)

Conductivity (ms/cm)

Density (g/cm3)

Li1.3Al0.3Ti1.7(PO4)3 Li1.3Al0.29Y0.01Ti1.7(PO4)3 Li1.3Al0.25Y0.05Ti1.7(PO4)3 Li1.3Al0.225Y0.075Ti1.7(PO4)3 Li1.3Al0.15Y0.15Ti1.7(PO4)3

20.66 28.27 31.47 39.32 53.60

208.70 124.30 77.42 55.54 110.27

229.36 152.57 108.89 94.86 163.87

0.31 0.46 0.66 0.78 0.44

2.65 2.79 2.80 2.76 2.69

Table 3 Comparison of the total conductivities for LATP electrolytes, measured at room temperature. Composition

Total electrical conductivity (ms/cm)

Reference

LiBO2 added Li1.3Al0.3Ti1.7(PO4)3 W doped Li1.3Al0.3Ti1.7(PO4)3 Li1.4Al0.4Ti1.6(PO4)3 Li1.3Al0.3Ti1.7(PO4)3 Li1.3Al0.3Ti1.7(PO4)3 Li1.4Al0.4Ti1.6(PO4)3 Li1.4Al03Fe0.1Ti1.6(PO4)3 Li1.4Al0.3Cr0.1Ti1.6(PO4)3

0.35 0.549 0.366 0.48 0.315 0.533 1.01 1.06

[23] [33] [34] [35] [36] [37] [38] [39]

Fig. 8. The Arrhenius plots for electrical conductivities of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes.

4. Conclusions

Fig. 7. The cross-sectional SEM images of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolyte pellets sintered at 850 ºCfor 4 h in air: (a) x ¼ 0; (b) x ¼ 0.025; (c) x ¼ 0.05; (d) x ¼ 0.075; (e) x ¼ 015.

In summary, Nasicon-structured Y doped Li1.3Al0.3Ti1.7(PO4)3 electrolyte materials with good crystallinity as well as well-shaped polyhedral morphology were successfully synthesized. Electrochemical properties of Li1.3Al0.3Ti1.7(PO4)3 electrolyte can be enhanced via the Y doping approach. The electrolyte with the Y doping content of 0.075 offers a highest electrical conductivity of 7.8 104 S/cm at room temperature among all electrolyte samples, which is far higher than that of the pristine Li1.3Al0.3Ti1.7(PO4)3 electrolyte. The excellent electrochemical performance is mainly attributed to the reduction of grain boundary resistance which results from high electrolyte density. The YPO4 phases in the doped electrolyte can segregate into the grain boundaries and promote effective densification of electrolyte. Additionally, the Y doping has no obvious effect on the electronic conductivity of electrolyte. All Y doped electrolyte samples show a negligible electronic

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Fig. 9. The polarization current vs. time curves of Li1.3Al0.3-xYxTi1.7(PO4)3 electrolytes at a polarization voltage of 0.2 V.

conductivity. These properties indicates that the Y doped Li1.3Al0.3Ti1.7(PO4)3 material is promising as solid electrolyte of ASSLIBS.

Acknowledgments This work is funded by National Natural Science Foundation of China (51502318), Science & Technology Basic Research Program of Nantong (MS12015123), National Natural Science Foundation of China (41606096), and Scientific Research Program for High-level Talents of Henan Institute of Science and Technology (2016034).

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2018.12.183.

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