Flame Retardant and Stable Li1.5Al0.5Ge1.5(PO4)3-Supported Ionic

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C: Energy Conversion and Storage; Energy and Charge Transport

Flame Retardant and Stable Li1.5Al0.5Ge1.5(PO4)3Supported Ionic Liquid Gel Polymer Electrolytes for High Safety Rechargeable Solid-State Lithium Metal Batteries Qingpeng Guo, Yu Han, Hui Wang, Shizhao Xiong, Weiwei Sun, Chunman Zheng, and Kai Xie J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b02693 • Publication Date (Web): 24 Apr 2018 Downloaded from http://pubs.acs.org on April 24, 2018

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The Journal of Physical Chemistry

Flame Retardant and Stable Li1.5Al0.5Ge1.5(PO4)3-Supported Ionic Liquid Gel Polymer Electrolytes for High Safety Rechargeable Solid-State Lithium Metal Batteries Qingpeng Guo*, Yu Han*, Hui Wang, Shizhao Xiong, Weiwei Sun, Chunman Zheng and Kai Xie College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, Hunan, 410073, China.

ABSTRACT Recently, poor security in conventional liquid electrolytes and high interfacial resistance at the electrode/electrolyte interface are the most challenging barriers for the expanded application of lithium batteries. In this regard, easy processing and flexible composite ionic liquid gel polymer electrolytes (ILGPEs) supporting by Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is fabricated and investigated. The electrolyte is effectively combined with good electrochemical performances and thermal safety. Among these, the effects of different types of fillers such as the inert filler-SiO2 and the active filler-LAGP on the ionic conductivity were studied in detail. LAGP particles can not only effectively reduce the crystallinity of the polymer matrix, but also provide lithium ions and act as the lithium-ion conductor leading to higher ionic conductivity and Li+ ion transference number. Especially, the electrolyte shows good compatibility and no dendrite with Li metal anode, significantly improving cyclic stability of LiFePO4/Li batteries. The results indicate that the ILGPE-10%LAGP is a potential alternative electrolyte for high safety rechargeable solid-state lithium metal batteries.

1. INTRODUCTION Clean and convenient lithium ion batteries (LIBs) have been widely used in most *Corresponding author. Tel.:+86-0731-84573149,fax:+86-0731-84573149. E-mailaddresses: [email protected]( Q, Guo ), [email protected] ( Y, Han ).

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aspects of people’s lives to address the energy shortages, environmental pollution and other issues gradually highlighted.1-5 High security is at the forefront in their many performance requirements except high energy density and good cycle performance for LIBs.6-9 At present, the carbonate-based volatile and flammable liquid electrolytes suffer from drawbacks such as leakage and flammability, causing explosion and other safety risks.10-12 Solid electrolytes are well known as high safety and prompt the development as a hot spot.6,13,14 However, the major challenge to realize practical application of the all-solid-state battery is the poor contact/adhesion at the solid electrolyte-electrode.15-19 The GPEs are generally prepared by swelling the liquid electrolyte in the polymer matrix,20,21 which can take into account both important merits of the above two types of electrolytes. Among GPEs, poly(vinylidenefluoride-co-hexefluoropropylene) (PVDF-HFP) is an ideal candidate polymer matrix because of it has high dielectric constant and plasticity.22-24 Meanwhile, in order to ameliorate the defect of mechanical strength of the gel electrolyte, some approaches such as addition of inorganic solid filler such as SiO2 and TiO2 in polymer matrix have been implemented and shown improved mechanical properties.25 However, the ionic conductivities of the electrolytes are still unsatisfactory. Generally, active ceramic filler is critical for improving the performance of the electrolyte. So far, few studies have specifically compared the effects of active and inert filler on the performance of gel electrolyte and the interaction between the ingredients is still not clear.26 Thus, dispersing the active ceramic filler-LAGP in PVDF-HFP matrix may be a favorable choice for making high


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performance, low cost electrolytes. While allowing the GPEs to be easily incorporated into the solid-state LIBs as much as possible without the need for expensive synthesis costs or complicated manufacturing processes. Herein, LAGP-supported ILGPEs were prepared via solution casting method. The influences of LAGP as active filler on the performance of ILGPE such as ionic conduction, electrochemical stability and thermal stability were investigated. In particularly, the effects of different active and inert fillers on the ionic conductivity of ILGPEs were compared. It is pointed out that the active filler-LAGP has more pronounced effect on improving the total ionic conductivity and Li+ ion transference number of ILGPEs due to the presence of Li+ in their structure. In addition, a stable SEI layer can be constructed on the surface of the Li electrode and the improved interface compatibility can be obtained during cycles. Most importantly, the ILGPEs exhibit incombustibility and good thermal stability. Based on of these, the lithium metal batteries with this electrolyte exhibit good cycling performance and induce high safety. Thus, this kind of electrolyte is expected to become the best choice for the practical application of safety lithium battery, which is considered as the balance of high-energy-density and safety of lithium batteries at present. 2. EXPERIMENTAL SECTION 2.1 The Preparation of Inorganic Ceramics LAGP Powder and ILGPE The inorganic ceramics LAGP powder materials were prepared according to our previous studies.27 Preparation of the ILGPE can be described as follows: PVDF-HFP was completely dissolved in butanone to obtain 6.7 wt% of polymer clear solution



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under constant stirring at 50 °C for 30 min. Then the clear solution was transferred in the glove box. The lithium bis(trifluoromethane)sulfonamide (LiTFSI, 99.9%, Aldrich), fillers of LAGP and 1-ethyl-3-methylimidazolium triluoromethanesufonate (EMITFSI)

with

different

weight

ratio

(the

values

of

mPVDF-HFP:mLiTFSI:mEMITFSI:mLAGP changed from 5:5:7:0.25 to 5:5:7:1) were added into the solution. The resulting mixture was magnetic stirring for 3h and ultrasonically agitated for 20 minutes to break the LAGP aggregates in a sealed container. And then, the solution was poured into a Teflon plate to from the wet membrane and then dried under vacuum for 12 h at 60 ℃. The ILGPEs membrane was cut into circles with diameters of 19 mm and stored in argon atmosphere for further characterizations. 2.2 Characterization of the ILGPE Membrane The morphology of the ILGPEs was observed by SEM with HITACHI S-4800. A small amount of the prepared slurry was dropped onto a carbon film supported on a copper mesh and dried a few minutes, the prepared sample was further observed by TEM (FEI Tecnai 2100). The crystal structure of the membranes was obtained using XRD with Cu Kɑ radiation in the range of 10-60°. The Fourier transform infrared (FT-IR) spectra of the ILGPEs were examined on a Bruke V70 spectrometer in the range of 4000-400 cm-1. The thermogravimetric (TGA) analysis of electrolytes were carried out on a TGA-2950 thermal analysis (Hires, TA instruments) by heating from 50 to 500 ℃ at a heating rate of 10 ℃ min-1 under N2 atmosphere. The flammability test and dimensional stability of the membranes were implemented in air atmosphere. The ionic conductivity of the ILGPEs was evaluated by AC impedance spectroscopic


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method using symmetrical stainless steel electrodes at different temperature range from 0 to 100 ℃. The LSV (from 2.5 V to 6 V) and CV (between -0.5 V and 2.5 V) analyses of ILGPEs were measured using Li/ILGPE/SS at the scanning rate of 0.1 mV s-1. The stability between ILGPEs and Li electrode was evaluated by the symmetric Li/ILGPEs/Li analog battery with current density at 0.1 mA cm-2. The cycled Li electrode washed (with DMC solvent) and dried as the samples for SEM test. Meanwhile, the elemental and chemical group analysis was performed on the recycled lithium metal electrode using X-ray Photoelectron Spectroscopy (XPS, ESCALAB 250). 2.3 Preparation of Electrodes and Cell Assembly The battery performance of the ILGPE with lithium anode and LiFePO4 cathode was evaluated by galvanostatic charging-discharging tests. Particularly, in order to build an effective ion channel in cathode, the composition of the electrolyte was added in the slurry. The cathode was prepared by mixing LiFePO4 powders, carbon black and ILGPE with the weight ratio of 9.9:1:1.96. The loading density of LiFePO4 cathode was controlled to be 2.63 mg cm-2. Cells were assembled in an argon-filled glove box and the testing experiments were conducted in the range of 2.7-3.85 V at room temperature according to the LAND CT2001A. 3. RESULTS AND DISCUSSION 3.1 Synthesis and Physical Characterization of Electrolyte As can be seen from Figure 1, the surface morphology of the GPE keeps transparent and flexible self-sustaining state, indicating that LAGP particles can be



uniformly dispersed in the polymer matrix and can also ameliorate the defect of mechanical strength. Among them, the microstructures of LAGP particles are specifically characterized by SEM images (Figure 2a and 2b). And the average particle size of LAGP is between 850~950 nm. In addition, XRD shows that all the diffraction peak position of LAGP powder are consistent with the lattice structure of LiGe2(PO4)3 (Figure 2g). Figures 2c and 2d show the surface topography of ILGPE-10%LAGP by SEM images. We note that a homogeneous surface with no porous structure instead of some interconnected and gully-like structures exist in the membrane. This may be related to the swelling effect of the ionic liquid (IL) on the polymer matrix and have a positive effect on the conductivity of electrolyte. Furthermore, the composite state between LAGP particles and gel tissue was well characterized by the TEM images (Figure 2e and 2f). The ceramic particle as a crosslinking center was wrapped by the amorphous structure of gel polymer, and more transitional phase which around the grain or between the particles can be obtained to promote the smooth migration of lithium ions between different components. The XRD patterns (Figure 2g) of pure PVDF-HFP show that there have three typical diffraction peaks at about 2θ=20.38, 39.12 and 41.26 °, which meant that the partial crystallization of PVDF units in pour polymer matrix, resulting in a poor ionic conductivity[28]. And the intensity of the semi-crystalline peak of the host polymer decrease with the addition of lithium salt and LAGP filler, however, crystal peaks still exist in the polymer. Furthermore, peaks can be further weakened with the addition of


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IL, meaning that PVDF-HFP is almost in an amorphous state. The result suggest that adding IL into polymer electrolyte can effectively swell the molecular chain of the polymer, weaken the interaction of the polymer segments and improve the movement of the polymer molecular chain thereby enhances ionic conductivity of the ILGPEs. 3.2 Thermal Stability and Thermal Safety of the ILGPE ILs, usually have very interesting properties such as thermal stability, no measurable vapor pressure and non-flammability.28 Thus, blending polymer matrix with different weight percentages of IL is bound to enhance the thermal stability and safety of electrolyte. The TGA plots (Figure 2h) show that the addition of lithium salts reduces the thermal stability of polymer matrix PVDF-HFP, whereas the thermal stability of the composites is improved with the addition of IL and inorganic ceramics. Eventually, it is more remarkable that ILGPE-10%LAGP showed good thermal stability with a major decomposition at 325 °C. In addition, to further directly verify the safety performance of the electrolyte, flame test was carried out for the different electrolytes. Figure 3a shows that the Celgard membrane is ignited instantly when in contact with the flame of spray gun. In contrast, no flammability is observed for the ILGPE-10%LAGP even under a few seconds of heating experiment. It is confirmed that the flammability of ILGPE is greatly reduced compared to commercial organic electrolytes or commercial Celgard membrane, and the electrolyte can be used to improve the safety of lithium battery in a certain extent. In the meantime, the shrinkage and melting testes at high temperature were implemented to further describe the safety of the electrolyte from another perspective. Figure 3c shows that



Celgard membrane is gradually curled with increasing temperature and begins to melt when the temperature exceeds 150 °C. After that, the membrane almost melted away when the temperature rose to 200 °C. In contrast, ILGPE can always be in flat state, it is noteworthy that there is no obvious crimping or contraction phenomenon of the ILGPEs even the temperature maintained at 200 °C, indicating that ILGPE has significant advantage in terms of heat resistance. Thus, this electrolyte can effectively eliminate security risks of short circuit when the battery is accidentally in high temperature conditions. 3.3 Electrochemical Properties of ILGPE In our previous studies, we have explored the effect of different components on ionic conductivity of the ILGPEs, indicating that there has a relatively high ionic conductivity when the mass ratio of the lithium salt and the IL to the polymer matrix are present at 1:1 and 1.4:1 (Figure 4a), respectively. Here, we further investigated the temperature dependence of the ion conductivity of the composite electrolyte with various active filler-LAGP concentrations ranging from 5% to 20%. As shown in Figure 4b, when increasing the temperature, the conductivity of the ILGPEs also gradually increases in a linear manner, showing thermally activated conduction.29 It is observed that ILGPEs-x%LAGP have a relatively high ionic conductivity with the content of LAGP at 10%, possessing the value of 0.76×10-3 S cm-1 at 25 °C. At the same time, in order to compare the effects of different types of fillers on the ionic conductivity of ILGPEs, we have designed a set of comparative experiments to fully explain the effect of active filler on the electrolyte. The results (Figure 4c) showed


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that ILGPE-20%LAGP demonstrates a higher conductivity with no obvious advantage than ILGPE-20%SiO2, especially when the content of filler is at a relatively low level compared to the other electrolyte component. However, although the same behavior of ionic conductivity tends to decrease when the relative content of the filler increase to 50%, significant differences in ionic conductivity are observed for ILGPE-50%SiO2 and ILGPE-50%LAGP. It can be seen the ILGPE-50%LAGP still shows a considerable level compared to ILGPE-10%LAGP especially at low temperature. By contrast, the ion conductivity of ILGPE-50%SiO2 is greatly attenuated. As a result, active filler could play the important role in the ion transport of the polymer electrolyte. As for the inert filler, the best content value of the nano-SiO2 can effectively reduce the crystallinity of the polymer matrix and promote the transmission of Li+ in polymer. However, when the content exceeds the matching value, the extra fillers become obstacle to hinder the effective migration of Li+ in the membrane (Figure 4d). It is noteworthy that LAGP particles not only effectively reduce the crystallinity of the polymer matrix, but also the filler as the Li+ conductor and the source of Li+ to promote the migration of Li+. It can be pointed out that the transfer route of the lithium ion in the composite electrolyte ILGPE-50%LAGP can be defined as the double-conductive ions between the gel polymer and the interconnected LAGP particles. At the micro level, the lithium ion transport in the ILGPE may closely relate to the interaction between the various components of the electrolyte. FTIR spectroscopy



plays a very important role in the investigation of polymer electrolytes structure and the interaction between ingredients.26,30 Figure 4e compares the FTIR spectrum changes of pure PVDF-HFP, PVDF-HFP-LiTFSI, PVDF-HFP-LAGP and ILGPE. After LiTFSI incorporation into the polymer PVDF-HFP matrix, the intensity of the related important vibrational modes and wave numbers exhibited by pure PVDF-HFP are changed. The CH2 stretching vibration mode at 1453 cm-1, the characteristic peaks of α phase at 975, 796, 763 and 615 cm-1, and the swing mode of CF at 510, 475 cm-1 are changed with decreased intensity. Meanwhile, with a smaller increase in the integral area of the two well defined peaks of amorphous phases characteristic absorption peaks at the 875 and 840 cm-1, indicating that lithium salt can weaken the crystallinity of the polymer matrix with not obvious effect. However, the CF2 stretching vibration mode at 1200 cm-1 also undergoes some variations with the decreased intensity and a broader peak deformation, which are associated with the interactions between lithium salt and CF2 groups in the polymer molecular chains. Furthermore, the vibrational modes of the PVDF-HFP-LiTFSI complex have been influenced due to the addition of LAGP filler. The characteristic peaks of the polymer matrix are shifted their wavenumbers and changed their shapes and intensity. The results show that the PVDF-HFP-LiTFSI complex filling with LAGP has a significant reduction in the degree of crystallinity which was consistent with the analysis of Figure 2g. At the same time, the shape of the stretching CF2 modes changed with decreased intensity, which indicated that the Lewis acid-base interaction between LAGP and the fluorine atoms reduced the polarity of CF2 groups and improved the


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migration of lithium ion in electrolyte. It is worth emphasizing that with the occurrence of ionic liquid in the final gel polymer electrolyte, the polymer matrix is almost in the amorphous state, and the C-F stretching mode is disappeared in ILGPE, indicating that IL can also undermine the coordination between the lithium ion and PVDF-HFP, thus making more Li+ easy to migrate in the short-term gel state and reflecting the increased ionic conductivity of the electrolyte. The above results indicate the significantly complex interactions among components in ILGPE. XPS spectra are employed for further investigated. Figure 4f displays the variation of the F 1s spectra for the different electrolyte components. For the pure PVDF-HFP polymer matrix, F 1s spin-orbital splitting photoelectron is located at the binding energy of 687.5 eV.31,32 When lithium salt-LiTFSI was incorporated into the polymer, the C-F binding energy increased to 688.5 eV and a new peak appeared at 687.6 eV next to the peak related to the TFSI-functional group from the lithium salt, which illustrate that there has interaction between the Li+ with the F element of PVDF-HFP. Interestingly, with the appears of LAGP in the mixture of PVDF-HFP-LiTFSI, the binding energy of C-F decreased, which further confirming that LAGP attenuated the strong polar effect of F on lithium ions. Along with the ionic liquid further adding into the above electrolyte, the bonding energy of the C-F bond almost returns to 687.5 eV again, indicating that ionic liquid has a significant effect on reducing the binding of F to Li+ and promoting the dissociation of lithium ions in the electrolyte. 3.4 Interface Compatibility Between ILGPE and Lithium Metal



Generally, the low Li+ ion transference number may leads to a strong space charge near the anode[33]. In addition, the mobile anions also cause undesirable side reactions even the formation of several dendritic Li.34 The transference number of Li+ ion of ILGPE-10%LAGP was estimated by chronoamperometry and presented in Figure 5a. This electrolyte also possesses the tLi+ as high as 0.54, which was higher than ILGPEs without LAGP (PVDF-HFP-LiTFSI-EMITFSI) at 0.46. And this system is usually higher than other electrolyte systems such as PEO-LiTFSI solid electrolyte and carbonate-based liquid electrolytes as shown in Figure 5b.33 Electrochemical stability is an important performance index of electrolyte. Here, CV and LSV are used to characterize the electrochemical stability of ILGPEs. Figure 5c shows the CV curves of Li/ILGPE-10%LAGP/SS cell. During the cathodic scan, the reduction peak occurred with a stable current value for three cycles studied. The higher uniformity and stability of the peaks in ILGPE-10%LAGP indicated that the Li+ can reductive deposition on the electrode, which is less affected by the electrochemical stable of ILGPE-10%LAGP until 0 V. Meanwhile, the polarization current increases sharply when the scanning voltage is greater than 4.8 V, which indicates that the components in electrolyte has occurred decomposition reaction. And the electrochemical stability window of the ILGPE-10%LAGP was found to be 4.8 V. Thus, we believe that such ILGPE-10%LAGP have relatively good electrochemical stability and can be used to match high voltage cathodes for high energy lithium batteries. Compared to the organic electrolyte, gel and solid electrolytes are more


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promising to match the lithium metallic electrode. Therefore, we further investigated the interfacial stability between ILGPE and Li electrode. Figure 5d shows the interface impedance variation of Li/ILGPE-10%LAGP/Li cells with time evolution under open circuit. It can be seen that, the bulk resistance (Rb) remained almost constant and the interface charge transfer resistance (Ri) changed in the first 8 days and could keep constant eventually. This suggests that part of the chemical reaction has occurred between ILGPE and Li electrode forming a layer of SEI film. And the interface reaction is suppressed when a stable SEI film exists on the surface of Li electrode, showing the value of Ri increased firstly and reduced to a steady state (Figure 5e). In addition, the lithium plating and stripping experiment through lithium symmetric batteries was used to study the interfacial stability and deposition, dissolution reversibility of lithium ion between electrolyte and the lithium metal interface. Figure S1a shows the time-dependent voltage profile of the cell obtained with ILGPE-10%LAGP and cycled at current density of 0.1 mA cm-2. A gradual increase in voltage during the first hours cycles is due to the formation of the passive film on lithium anode. After that, the symmetric cell presented a stable voltage until the end of the experiment 500 h. This result indicates that the ILGPE-10%LAGP has good compatibility with the Li metal electrode during cycles, and most importantly, the passive film on the surface of the Li metal electrode can be stably present. In order to further verify whether the ILGPE-10%LAGP sufficiently effective to suppress the growth of Li dendrite and identify the effective constituent of the interfacial



membrane, the surface of cycled lithium electrode was monitored by SEM and XPS. As seen in Figure 5f, there have no lithium dendrites on the surface of cycled lithium metal, and the uneven particles on the surface are more possibly some of electrolyte residues. Thus we can deduce that ILGPE-10%LAGP has good interface compatibility with Li metal electrode. Figure S1b presents the XPS spectra of different elements of the lithium electrode after cycles. As shown the peak around 399.1 eV of N 1s spectra and 170.6 eV of S 2p spectra are assigned to the imide groups in the IL-EMITFSI or the lithium salt-LiTFSI.35 In addition, the peak around 402.2 eV is attributed to the C-N* in the EMI+. Thus, the SEI components on the lithium electrode surface are main modified by the IL which agree with the related research.33 Meanwhile, from the spectra of F 1s, the decomposition product of LiF is founded on the surface of cycled Li metal. The ILGPE also promotes the generation of LiF during cycling, which has been confirmed to be advantageous for the formation a stable interfacial layer.36,37 Thus we can deduce that the passivation interphase is effective for preventing the Li dendrite growth and can be stable during cycling. 3.5 Performance of the LiFePO4/ILGPE/Li Battery A battery composed of LiFePO4 (cathode), Lithium metal (anode), and ILGPE-10% is illustrated in Figure 6a. The cycling performance of the battery is depicted in Figure 6b. The discharge capacity of the cell for first cycle is found to be 138.1 mAh g-1 at a current rate of 0.05 C and the coulomb efficiency is only 89.7%. However, it quickly improves in the second cycle. The discharging capacity is stable and its value is about 131 mAh g-1 up to 50 cycles. No significant loss in discharge capacity may also be


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due to the development of an improved SEI layer, which improves the interface stability between the electrode/electrolyte and the reversibility of lithium ion intercalation/de-intercalation also greatly improved. The first charge and discharge platforms of battery are about 3.48 V and 3.37 V respectively. The both voltage platforms show a smaller polarization from the first cycle to 25th and the 50th (Figure 6c). This result is also well matches with the changes of impedance spectra of the cell as shown in Figure S2. The reduced cell impedance may be attributed to the stable interfacial film resulting in a better contact between electrode and electrolyte during cycles. Figure 6d presents the discharge capacity of the battery at different current rates. The discharge capacity is found to decrease as the current rate increase from 0.05 C to 2 C, especially at higher current rates of 2C. This unsatisfactory rate performance is mainly because intrinsic lower ionic conductivity of the GPEs and the local concentration of electric current increase resulting in increased polarization and electrolysis of TFSI-.38 4. CONCLUSIONS In summary, a freestanding IL-based polymer electrolytes film of ILGPE with active fillers of LAGP is developed as the electrolyte for Li/LiFePO4 cell. The ILGPE exhibits decent ionic conductivity (0.76×10-3 S cm-1) for 10% LAGP loading at 25 °C and a wide electrochemical window about 4.8 V vs Li+/Li. Compared to the inert filler, LAGP particles not only can effectively reduce the crystallinity of the polymer matrix, but also the filler itself can provide lithium ions and act as the lithium-ion conductor leading to a high ionic conductivity and Li+ ion transference number. Further,



ILGPE-10%LAGP is found to have good thermal stability and no flammability, which means that it can be used in batteries with higher safety properties. Especially, the good electrochemical stability and compatibility with lithium electrode endows the lithium metal batteries a better discharge capacity and cycling performance. Thus, these results demonstrated that ILGPE-x%LAGP as the promising and alternative electrolyte for high safety and considerable performance of solid-state lithium metal batteries. ASSOCIATED CONTENT Supporting Information Voltage profile of the lithium plating/striping cycling with a current density of 0.1 mA cm-2; XPS patterns of the cycled lithium anode; impedance spectra of the cell with a structure of LiFePO4/ILGPE-10%LAGP/Li changes before and after cycles. These informations are available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *Tel.:+86-0731-84573149, fax:+86-0731-84573149. E-mail: [email protected]( Q, Guo ), [email protected] ( Y, Han ).

Notes The authors declare no competing ﬁnancial interest. ACKNOWLEDGMENTS This work was financially supported by the Research Project of National University of Defense Technology. REFERENCES (1) Yu, R.; Bao, J. J.; Chen, T. T.; Zou, B. K.; Wen, Z. Y.; Guo, X. X.; Chen, C. H. Solid Polymer Electrolyte Based on Thermoplastic Polyurethane and Its Application in All-Solid-State Lithium Ion Batteries. Solid State Ionics 2017, 309, 15-21. (2) Saha, T.; Choudhury, S.; Naskar, K.; Stamm, M.; Heinrich, G.; Das, A. A Highly Stretchable


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Gel-Polymer Electrolyte for Lithium-Sulfur Batteries. Polymer 2017, 112, 447-456. (3) Gupta, H.; Shalu; Balo, L.; Singh, V. K.; Singh, S. K.; Tripathi, A. K.; Verma, Y. L.; Singh, R. K. Effect of Temperature on Electrochemical Performance of Ionic Liquid Based Polymer Electrolyte with Li/LiFePO4 Electrodes. Solid State Ionics 2017, 309, 192-199. (4) Cao, J.; He, R.; Kyu, T., Fire Retardant. Superionic Solid State Polymer Electrolyte Membranes for Lithium Ion Batteries. Current Opinion in Chemical Engineering 2017, 15, 68-75. (5) Hu, P.; Duan, Y.; Hu, D.; Qin, B. S.; Zhang, J.; Wang, Q.; Liu, Z.; Cui, G.; Chen, L. A Rigid-Flexible Coupling High Ionic Conductivity Polymer Electrolyte for an Enhanced Performance of LiMn2O4/Graphite Battery at Elevated Temperature. Acs Applied Materials & Interfaces 2015, 7, 4720. (6) Puthirath, A. B.; Patra, S.; Pal, S.; Manoj, M.; Balan, A. P.; Jayalekshmi, S.; Narayanan, T. N. Transparent Flexible Lithium Ion Conducting Solid Polymer Electrolyte. Journal of Materials Chemistry A 2017, 5, 11152-11162. (7) Kim, J. K. Hybrid Gel Polymer Electrolyte for High-Safety Lithium-Sulfur Batteries. Materials Letters 2017, 187, 40-43. (8) Kumar, D.; Suleman, M.; Hashmi, S. A. Studies on Poly(Vinylidene Fluoride-CoHexafluoropropylene) Based Gel Electrolyte Nanocomposite for Sodium-Sulfur Batteries. Solid State Ionics 2011, 202, 45-53. (9) Le, H. T.; Ngo, D. T.; Kalubarme, R. S.; Cao, G.; Park, C. N.; Park, C. J. Composite Gel Polymer Electrolyte Based on Poly(Vinylidene Fluoride-Hexafluoropropylene) (PVDF-HFP) with Modified Aluminum-Doped Lithium Lanthanum Titanate (A-LLTO) for High-Performance Lithium Rechargeable Batteries. Acs Applied Materials & Interfaces 2016, 8, 20710.



(10) Naderi, R.; Gurung, A.; Zhou, Z.; Varnekar, G.; Chen, K.; Zai, J.; Qian, X.; Qiao, Q. Activation of Passive Nanofillers in Composite Polymer Electrolyte for Higher Performance Lithium-Ion Batteries. Advanced Sustainable Systems 2017, 1700043. (11) Pandey, G. P.; Hashmi, S. A. Ionic Liquid 1-Ethyl-3-Methylimidazolium Tetracyanoborate-Based Gel Polymer Electrolyte for Electrochemical Capacitors. Journal of Materials Chemistry A 2013, 1, 3372-3378. (12) Pandey, G. P.; Klankowski, S. A.; Li, Y.; Sun, X. S.; Wu, J. Z.; Rojeski, R. A.; Li, J. Effective Infiltration of Gel Polymer Electrolyte into Silicon-Coated Vertically Aligned Carbon Nanofibers as Anodes for Solid-State Lithium-Ion Batteries. Acs Applied Materials & Interfaces 2015, 7, 20909. (13) Zhang, M. Y.; Li, M. X.; Chang, Z.; Wang, Y. F.; Gao, J.; Zhu, Y. S.; Wu, Y. P.; Huang, W. A Sandwich PVDF/HEC/PVDF Gel Polymer Electrolyte for Lithium Ion Battery. Electrochimica Acta 2017. (14) Simonetti, E.; Carewska, M.; Maresca, G.; Francesco, M. D.; Appetecchi, G. B. Highly Conductive, Ionic Liquid-Based Polymer Electrolytes. Journal of the Electrochemical Society 2017, 164, A6213-A6219. (15) Chai, J.; Liu, Z.; Zhang, J.; Sun, J.; Tian, Z.; Ji, Y.; Tang, K.; Zhou, X.; Cui, G. A Superior Polymer Electrolyte with Rigid Cyclic Carbonate Backbone for Rechargeable Lithium Ion Batteries. Acs Applied Materials & Interfaces 2017, 9. (16) Wang, Y.; Li, B.; Ji, J.; Eyler, A.; Zhong, W. H. A Gum-Like Electrolyte: Safety of a Solid, Performance of a Liquid. Advanced Energy Materials 2013, 3, 1557-1562. (17) Tan, G.; Wu, F.; Zhan, C.; Wang, J.; Mu, D.; Lu, J.; Amine, K. Solid-State Li-Ion Batteries


Page 18 of 25

Page 19 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Using Fast, Stable, Glassy Nanocomposite Electrolytes for Good Safety and Long Cycle-Life. Nano Letters 2016, 16, 1960. (18) Tao, X.; Liu, Y.; Liu, W.; Zhou, G.; Zhao, J.; Lin, D.; Zu, C.; Sheng, O.; Zhang, W.; Lee, H. W. Solid-State Lithium-Sulfur Batteries Operated at 37 °C with Composites of Nanostructured Li7La3Zr2O12/Carbon Foam and Polymer. Nano Letters 2017, 17, 2967. (19) Tong, Y.; Xu, Y.; Chen, D.; Xie, Y.; Chen, L.; Que, M.; Hou, Y. Deformable and Flexible Electrospun Nanofiber-Supported Cross-Linked Gel Polymer Electrolyte Membranes for High Safety Lithium-Ion Batteries. Rsc Advances 2017, 7, 22728-22734. (20) Pandey, G. P.; Hashmi, S. A. Experimental Investigations of an Ionic-Liquid-Based, Magnesium Ion Conducting, Polymer Gel Electrolyte. Journal of Power Sources 2009, 187, 627-634. (21) Wang, S.; Shi, Q. X.; Ye, Y. S.; Wang, Y.; Peng, H. Y.; Xue, Z. G.; Xie, X. L.; Mai, Y. W. Polymeric Ionic Liquid-Functionalized Mesoporous Silica Nanoplates: A New High-Performance Composite Polymer Electrolyte for Lithium Batteries. Electrochimica Acta 2017. (22) Bai, J.; Lu, H.; Cao, Y.; Li, X.; Wang, J. A Novel Ionic Liquid Polymer Electrolyte for Quasi-Solid State Lithium Air Batteries. Rsc Advances 2017, 7, 30603-30609. (23) Tong, Y.; Xu, Y.; Chen, D.; Xie, Y.; Chen, L.; Que, M.; Hou, Y. Deformable and Flexible Electrospun Nanofiber-Supported Cross-Linked Gel Polymer Electrolyte Membranes for High Safety Lithium-Ion Batteries. Rsc Advances 2017, 7, 22728-22734. (24) Zhang, Q.; Ding, F.; Sun, W.; Sang, L. Preparation of LAGP/P(VDF-HFP) Polymer Electrolytes for Li-Ion Batteries. Rsc Advances 2015, 5, 65395-65401. (25) Prabakaran, P.; Manimuthu, R. P.; Gurusamy, S.; Sebasthiyan, E. Plasticized Polymer



Electrolyte Membranes Based on PEO/PVDF-HFP for Use as an Effective Electrolyte in Lithium-Ion Batteries. Polym. Sci. 2017, 35, 407-421. (26) Zhang, X.; Liu, T.; Zhang, S.; Huang, X.; Xu, B.; Lin, Y.; Xu, B.; Li, L.; Nan, C. W.; Shen, Y. Synergistic Coupling between Li6.75La3Zr1.75Ta0.25O12 and Poly(Vinylidene Fluoride) Induces High Ionic Conductivity, Mechanical Strength and Thermal Stability of Solid Composite Electrolytes. Journal of the American Chemical Society 2017, 139, 13779. (27) Guo, Q.; Han, Y.; Wang, H.; Xiong, S.; Li, Y.; Liu, S.; Xie, K. A New Class of LAGP-Based Solid Polymer Composite Electrolyte for Efficient and Safe Solid-State Lithium Batteries. Acs Applied Materials & Interfaces 2017. (28) Karuppasamy, K.; Prasanna, K.; Kim, D.; Kang, Y. H.; Rhee, H. W. Headway in Rhodanide Anion Based Ternary Gel Polymer Electrolytes (TILGPEs) for Applications in Rechargeable Lithium Ion Batteries: An Efficient Route to Achieve High Electrochemical and Cycling Performances. Rsc Advances 2017, 7. (29) Sasi, R.; Chandrasekhar, B.; Kalaiselvi, N.; Devaki, S. J. Green Solid Ionic Liquid Crystalline Electrolyte Membranes with Anisotropic Channels for Efficient Li-Ion Batteries. Advanced Sustainable Systems 2017, 1, 1600031. (30) Polu, A. R.; Rhee, H. W., Effect of TiO2 Nanoparticles on Structural, Thermal, Mechanical and Ionic Conductivity Studies of PEO12-LiTDI Solid Polymer Electrolyte. Journal of Industrial & Engineering Chemistry 2016, 37, 347-353. (31) Chiang, C. Y.; Reddy, M. J.; Chu, P. P. Nano-Tube TiO2 Composite PVDF/LiPF6 Solid Membranes. Solid State Ionics 2004, 175, 631-635. (32) Tran, Q. C.; Bui, V. T.; Dao, V. D.; Lee, J. K.; Choi, H. S. Ionic Liquid-Based Polymer


Page 20 of 25

Page 21 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electrolytes Via Surfactant-Assisted Polymerization at the Plasma-Liquid Interface. Acs Applied Materials & Interfaces 2016, 8, 16125. (33) Zhao, C. Z.; Zhang, X. Q.; Cheng, X. B.; Zhang, R.; Xu, R.; Chen, P. Y.; Peng, H. J.; Huang, J. Q.; Zhang, Q. An Anion-Immobilized Composite Electrolyte for Dendrite-Free Lithium Metal Anodes. Proceedings of the National Academy of Sciences of the United States of America 2017, 114, 11069. (34) Cui, Y.; Chai, J.; Du, H.; Duan, Y.; Xie, G.; Liu, Z.; Cui, G. Facile and Reliable in-Situ Polymerization of Poly(Ethyl Cyanoacrylate) Based Polymer Electrolytes Towards Flexible Lithium Batteries. Acs Applied Materials & Interfaces 2017, 9, 8737. (35) Li, N. W.; Yin, Y. X.; Li, J. Y.; Zhang, C. H.; Guo, Y. G. Passivation of Lithium Metal Anode Via Hybrid Ionic Liquid Electrolyte toward Stable Li Plating/Stripping. Advanced science (Weinheim, Baden-Wurttemberg, Germany) 2016, 4, 1600400. (36) Tran, Q. C.; Bui, V. T.; Dao, V. D.; Lee, J. K.; Choi, H. S. Ionic Liquid-Based Polymer Electrolytes Via Surfactant-Assisted Polymerization at the Plasma-Liquid Interface. Acs Applied Materials & Interfaces 2016, 8, 16125. (37) Miao, R.; Yang, J.; Xu, Z.; Wang, J.; Nuli, Y.; Sun, L. A New Ether-Based Electrolyte for Dendrite-Free Lithium-Metal Based Rechargeable Batteries. Scientific Reports 2016, 6, 21771. (38) Lin, Y.; Li, J.; Lai, Y.; Yuan, C.; Cheng, Y.; Liu, J. A Wider Temperature Range Polymer Electrolyte for All-Solid-State Lithium Ion Batteries. Rsc Advances 2013, 3, 10722-10730.



Figure 1. The schematic diagram of preparation process about ILGPE and the photograph of the membrane.

Figure 2. (a) and (b) SEM images of LAGP particles. (c) and (d) Surface SEM images of prepared ILGPE-10%LAGP. (e) and (f) TEM image of dispersed ILGPE-10%LAGP sample. (g) The XRD patterns of LAGP, polymer matrix PVDF-HFP and polymer electrolytes with different ingredients. (h) TGA curves of electrolytes with different ingredients.


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Figure 3. (a) and (b) Flammability tests of commercial Celgard membrane and ILGPE-10%LAGP, respectively. c) Continuous heating experiment of different electrolytes.

Figure 4. a) The different components of electrolyte dependence of ionic conductivities at 25 °C. b) Arrhenius plots of ILGPEs with various LAGP concentrations. c) Arrhenius plots of ILGPEs with different fillers. d) The possible mechanism illustration of Li+ movement in ILGPE with different fillers. e) FTIR spectrum changes with different components of electrolyte. f) XPS patterns of the electrolyte with different components. The code names of (1)-(5) were introduced to denote the electrolytes of PVDF-HFP, PVDF-HFP-LiTFSI, PVDF-HFP-10%LAGP, PVDF-HFP-LiTFSI-10%LAGP, ILGPE-10%LAGP (PVDF-HFP-LiTFSI-10%LAGP-EMITFSI).



Figure 5. a) Chronoamperometry profiles in Li/ILGPE-10%LAGP/Li with a step potential of 10 mV. b) tLi+ of 1#-1M LiPF6-EC/DEC, 2#-PEO-LiTFSI solid electrolyte, 3#-PVDF-HFP-LiTFSI-EMITFSI and 4#-ILGPE-10%LAGP. c) CV and LSV curves of ILGPE-10%LAGP at 25 °C. d) Time evolution of the impedance response of Li/ILGPE-10%LAGP/Li cell. e) Time evolution of the interfacial resistances (Ri) of the cell for diﬀerent storage time. f) SEM images of Li metal anode in Li/ILGPE-10%LAGP/Li cell after cycles with different scale bar.

Figure 6. (a) The Schematic diagram of the LiFePO4/ILGPE-10%LAGP/Li solid-state battery. (b) Cycling performance of the LiFePO4/ILGPE-10%LAGP/Li. (c) The charge and discharge profiles corresponding to LiFePO4/Li battery with ILGPE-10%LAGP. (d) Rate capability behavior at varied rates.


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Flame Retardant and Stable Li1.5Al0.5Ge1.5(PO4)3-Supported Ionic

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