Solid Polymer Electrolyte Based on Polymerized Ionic Liquid for High

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Solid polymer electrolyte based on polymerized ionic liquid for high performance all-solid-state lithium ion batteries Furui Ma, Zeng-Qi Zhang, Wenchao Yan, Xiaodi Ma, Deye Sun, Yongcheng Jin, Xiaochun Chen, and Kuang He ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04076 • Publication Date (Web): 01 Feb 2019 Downloaded from http://pubs.acs.org on February 4, 2019

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ACS Sustainable Chemistry & Engineering

Solid polymer electrolyte based on polymerized ionic liquid for high performance all-solid-state lithium ion batteries Furui Ma†, Zengqi Zhang†, Wenchao Yan†, Xiaodi Ma†, Deye Sun†, Yongcheng Jin†,‡,*, Xiaochun Chen‖,*, Kuang He§,* †

Qingdao Key Laboratory of Functional Membrane Material and Membrane

Technology, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, P. R. China ‡

Center of Materials Science and Optoelectronics Engineering, University of Chinese

Academy of Sciences, Beijing 100049, P. R. China ‖

Beijing University of Chemical Technology, Beijing 100029, P. R. China

§

Institute of metal research, Chinese Academy of Sciences, Shenyang, 110016, P. R.

China Corresponding author: *E-mail: [email protected] Tel: +86 532 80662703 (Y. Jin) [email protected] Tel: +86 10 64441280 (X. Chen) [email protected] Tel: +86 24 83970720 (K. He)

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ABSTRACT Polymerized ionic liquids (PILs) have several advantages over ionic liquids, such as easy handling, good electrochemical performance and chemical compatibility. In this research, a solid state electrolyte composite membrane was successfully fabricated by using an imidazolium-based polymerized ionic liquid as polymer matrix, a kind of porous fiber cloth as rigid frame and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI ) as lithium salt. The ionic conductivity of composite electrolyte with 2.0 mol / kg LiTFSI is 7.78 × 10-5 S cm-1 at 30 °C and reaches 5.92 × 10-4 S cm-1 at 60 °C, which is considered a satisfactory value for potential application in lithium-ion batteries. The specific discharge capacity of the LiFePO4 / Li cell with as-prepared composite electrolyte is 138.4 mA h g-1 and 90% of the discharge capacity is retained after 250 cycles at 60 °C. In order to further improve the conductivity, Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramic electrolyte particles are dispersed in PIL polymer matrix to prepare PIL-LiTFSI-LATP composite electrolyte. LiFePO4 / Li cells using PIL-LiTFSI-LATP (10 wt% LATP) as a solid-state electrolyte exhibit excellent rate performance and high capacity retention (close to 97% after 250 cycles at 60 °C). This work may provide a unique way to prepare new series electrolytes for high-performance solid-state lithium batteries. KEYWORDS: polymerized ionic liquids, synthesis, LATP, composite electrolyte, allsolid-state battery


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INTRODUCTION Solid-state lithium batteries are believed to be better safety, higher energy density and longer cycle life than liquid-electrolyte based Li-ion batteries.1 Among various solid-state electrolytes, solid polymer electrolytes (SPE) present better mechanical properties and flexibility and are considered as most promising electrolyte applied to next-generation all-solid-state Li-ion batteries. The PEO-based solid polymer electrolytes have been widely investigated as a polymer matrix.2-6 However, two major obstacles hindering further applications of PEO-based polymer electrolyte are low ionic conductivity and narrow electrochemical window. 7 To address the above issues, many endeavors have been carried out to reduce its crystallinity, via such as blending,8,9 crosslinking10,11 and adding inorganic filler. 4,12 With the deepening of research, some novel solid polymer electrolytes exhibiting excellent electrochemical performance were constructed, such as poly (propylene carbonate) (PPC),7 thermoplastic polyurethane (TPU),13 hyperbranched multi-arm star polymer,14 providing guideline to improve the lithium ion conductivity for designing high performance solid state electrolyte. However, it is also extremely essential to develop new solid polymer electrolyte with excellent performance to fulfill the requirements of all-solid-state batteries. In the last decade, ionic liquid (IL) has attracted wide attention owning to its high ionic conductivity, wide electrochemical window and chemical stability, and those merits endow ionic liquid with potential application to electrolyte of advanced electrochemical devices, such as supercapacitors, Li-ion batteries and fuel cells.15-19 In addition, moderate contents of ionic liquid were introduced to binary solid polymer



electrolyte, leading increase of the ionic conductivity of native SPE.20,21 Compared with the conductivity of membrane electrolytes without wetted ionic liquids, that of membranes infiltrated ionic liquids is one order of magnitude greater and reaches ~104

S cm-1 at 20 °C. A lot of attention has also been paid to combine IL with ceramic

particles to reduce interfacial resistance between particles. K. Kwatek formed twophase Li1.3Al0.3Ti1.7(PO4)3-IL composite electrolyte and the conductivity was three orders of magnitude higher compared to the LATP.22 Y. Kim prepared a pelletized hybrid solid electrolyte by blending Li7La3Zr2O12 ceramic powder and an ionic liquid. The ionic conductivity of prepared pellet is 0.4 × 10-3 S cm-1.23 Y. Hu added a small amount of ionic liquids as interfacial wetting agent to enhance the interface contact between electrode and electrolyte.24 However, when IL is used as electrolyte solvents, its fatal drawback is that the component ions of IL also migrate along with the potential gradient.25 In addition, the problem of leakage still remains and the security can not be solved thoroughly in practical applications. In addition to dimensional control and mechanical durability, the polymeric ionic liquids have some novel properties of ILs, making them widely researched.26 Compared with ionic liquids, PILs have advantages of film forming ability, good electrochemical performance and chemical compatibility,27 so they have been considered as a new category of polymer electrolytes and have been widely applied in solar cells,28,29 lithium ion batteries.27,30-32 However, they combined the PIL matrix with ionic liquid to prepared hybrid electrolyte. The hybrid electrolyte with an optimized weight ratio of 50 wt% - 60 wt% IL exhibited excellent performance. Strictly


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speaking, the assembled batteries with this electrolyte can be called semi-solid-state Liion batteries, instead of all-solid-state batteries. Ionic liquid based on aromatic cation imidazolium was perhaps firstly considered for applications to Li-based battery.33 To the best of our knowledge, PIL-based electrolyte without any IL possess a low ionic conductivity and has so far been barely applied to lithium ion batteries. In this work, we prepared polymerized IL by using 1vinyl-3-ethylimidazolium bis(trifluoromethan esulfonyl)imide ([VEIm][TFSI]) as monomer material via one-step process. Subsequently, polymer electrolyte was obtained through incorporating the PIL as the matrix and LiTFSI as lithium salt. In order to improve the mechanical strength,34-36 we herein used polyethylene terephthalate (PET) nonwoven as the rigid frame and PIL-LiTFSI as the ionic transport material. In addition, inorganic electrolyte LATP particles were dispersed in the insulating PIL to form PIL-LiTFSI-LATP composite electrolytes. In order to evaluate the potential use in all-solid-state batteries, all-solid-state batteries were assembled and the charge-discharge properties were studied. EXPERIMENTAL SECTION Preparation of composite electrolyte 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfony)imide ([VEIm][TFSI]) was

provided

by

Lanzhou

Institute

of

Chemical

Physics.

Lithium

bis(trifluoromethanesulfonyl)imide (LiTFSI) and 2, 2’-azobis(isobutyronitrile) (AIBN) and were used as received from Aladdin. Lithium aluminum titanium phosphate (LATP) ceramic powders were obtained via solution method as described in our previous



work.37 LiOH.H2O, Al2O3, TiO2, and H3PO4 were dissolved in distilled water under magnetic stirring. Subsequently, a high viscosity paste was formed after removing the excessive water at 180 °C. And then the paste was calcined at 700 °C to form the LATP precursor powders. Finally, the as-synthesized LATP powders with larger particle size were ball-milled by using high energy mechanical ball milling at 450 rpm for 10 h to obtain the fine powders. [PVEIm][TFSI] was prepared via free radical polymerization of [VEIm][TFSI] and AIBN (2 wt%) in trichloromethane at 70 °C under N2 atmosphere for 12 h. After polymerization, the obtained PIL and LiTFSI were dissolved in 1-methyl-2-pyrrolidone (NMP) and stirred for 12 h. Subsequently, LATP particles with different mass ratio (5, 10, 20, 30 and 40 wt %) were added into the PIL / LiTFSI solution respectively. The mixed suspension was poured into PET fiber fabric (~ 200 μm), and then NMP was evaporated under vacuum drying process at 60 °C for 24 h. Characterizations Scanning electron microscopy (SEM, Hitachi S-4800) was employed to determine the microstructure of the samples. FT-IR spectra was used to characterize the chemical bonds of IL monomer and PIL polymer on a Thermo Scientific DXRXI system. Gel permeation chromatography (GPC) was used to characterize the molecular weight of PIL polymer on a Wyatt HELEOS system. Thermogravimetric analysis (TGA) was conducted on a METTLER TOLEDO thermogravimetric analyzer in the range of 30 °C - 700 °C. The thermal shrinkage of membranes was determined by measuring the dimensional change before and after heat treatment at 120 °C for 90 min.


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Electrochemical measurements All electrochemical data were collected by a VMP-300 multi-channel electrochemical workstation (Bio-Logic Science Instruments SAS). The resistance value was tested with a stainless steel (SS) / electrolyte membrane / SS symmetrical cell in the temperature range of 30 °C - 100 °C. And the ionic conductivity was calculated by the classical formula σ = L / RS, where R is total resistance of the composite electrolyte obtained through electrochemical workstation, L, S is the thickness and surface area of electrolyte membrane, respectively. The linear sweep voltammetry (LSV) measurement was conducted at a scan rate of 5 mV s-1 between 2.5 V and 6 V at 60 °C. To evaluate the lithium ion transference numbers, a symmetric Li / electrolyte membrane / Li cell was assembled and tested by potentiostatic polarization. The current of symmetrical battery reached a steady state with a polarization voltage of 10 mV. The lithium ion transference number was calculated according to the classical formula: tLi+ = [Iss × (△V – I0R0)]/[I0 × (△V – IssRss)],38 where tLi+ is the lithium ion transference number, △V is the polarization voltage, R0 and Rss are the impedance before and after polarization, I0 and Iss are the initial current and steady-state current, respectively. The LiFePO4 / electrolyte membrane / Li batteries were assembled in a glovebox filled Ar (MIKROUNA, China), in which the contents of H2O and O2 below 0.1 ppm. The LiFePO4 cathode was composed 80 wt% LiFePO4 as active material, 10 wt% Super-P as conductive agent and 10 wt% PVDF as binder. The obtained LiFePO4 cathode had a loading of 0.35-0.5 mg cm-2. The charge-discharge performance of LiFePO4 / Li cells were carried on a LANDHE instrument (Wuhan LAND electronics



Co., Ltd.). For battery performance test, the potential window of the 2032-type coin cell was arranged from 2.8 V to 4.0 V at various C rates (CC protocol). RESULTS AND DISCUSSION The preparation processes of PIL-based composite electrolyte are described by a schematic illustration as shown in Figure 1. The polymerization reaction and photographs of [VEIm][TFSI] and [PVEIm][TFSI] are shown respectively in Figure S1, transparent liquid is transformed to light yellow powder after polymerization. In order to further confirm the chemical structure of the prepared poly(ILs), the FTIR spectra were measured (Figure S2). Compared with [VEIm][TFSI], the absorption peak at around 1660 cm-1 is assigned to the C=C stretching band disappeared, indicating the successful polymerization of ionic liquid monomers. The C=N and C-N stretching vibration on imidazole ring is located in 1627 cm-1, 1139 cm-1, respectively. The absorption peaks that observed at 1351、1193、1046 cm-1 are assigned to the TFSI anion.28 The absorption peaks that observed at 3151 cm-1 can be assigned to C-H of benzene ring. The stretching vibration of N-H can be observed at 3435 cm-1. 1H solidstate NMR spectrum of polymeric ionic liquids were characterized and shown in Figure S3. 1H NMR (600 MHz, δppm): δ7.82 (s, 1H -N-CH-N-), δ6.76 (s, 1H -N-CH=C-), δ4.96 (s, 1H -C-CHN-C-), δ4.50 (s, 2H, -CH2-), δ1.78 (s, 2H, -CH2-N-), δ0.67 (s, 3H, -CH3). As is shown in Figure S4, the Mw of PIL obtained by GPC is 5.1 × 106. This is much higher than that reported in other literatures.39 The polymer membranes with higher molecular weight may have higher tensile strength.40


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The thermostability of the [VEIm][TFSI] and [PVEIm][TFSI] were studied by TGA. According to the TGA curves (Figure S5), the [PVEIm][TFSI] shows a thermal stability up to about 340 °C and the weight loss 2% between 30 °C and 340 °C is due to the decomposition of the initiator AIBN. Above this temperature, polymers begin to decompose and most mass is lost before 470 °C. The thermal stability of pure PET, PET-PIL-LiTFSI, PET-PIL-LiTFSI-LATP electrolyte membranes were evaluated by measuring the dimensional changes after exposing them at 120 °C for 90 min, as shown in Figure 2. The shapes and sizes of these membranes have no significant change after heat treatment. The as-prepared composite electrolyte is mechanically flexible, which can be fully bended and winded (Figure S6), making it feasible for fabricating flexible solid-state batteries. Detailed morphology of PET nonwoven and PET-PIL composite electrolyte was shown in Figure 3. PET nonwoven is made of irregularly arranged nanofibers with large-sized pores of 200 µm (Figure 3a). This framework is beneficial to support mechanically polymer electrolyte. Figure 3b and Figure 3b’ are SEM images of the surface and cross-section of PET nonwoven after filling the PIL polymer electrolyte. The surface of the composite electrolyte with continuous structure is smooth and homogenous. The thickness of composite electrolyte obtained from the cross-section SEM image of PET-PIL is about 200 µm. In addition, the consistent and homogeneous structure of PET-PIL composite electrolyte has great significance for preventing possible microshort circuiting.7



The Arrhenius plots were obtained by testing the electrochemical impedance spectroscopy of polymer electrolyte at temperature varies from 30 °C to 100 °C. The temperature-dependent conductivity of PIL-based composite electrolyte is shown in Figure 4. The ionic conductivity is found to increase with the test temperature owing to the Li+ carrier has higher mobility when the temperature increase. Furthermore, the ionic conductivity of PIL-based electrolyte also increases with the LiTFSI ratio increase from 0.3 mol / kg up to 2.0 mol / kg (Figure 4a). The ionic conductivity at 30 °C and 60 °C is 7.78 × 10-5 and 5.92 × 10-4 S cm-1, respectively, which is a satisfactory value for the need of Li-ion batteries application. There are multiple features of a successful electrolyte to determine the practical application performance in high-voltage Li batteries toward high-energy densities, not only ionic conductivity, but also electrochemical window.41 The electrochemical stability window decrease with the increase of lithium salt concentration. The decrease in the decomposition potential relates to the crystallinity of PIL decreases with the increase of lithium salt concentration and the easier reaction of electrolyte with electrodes at higher lithium salt concentration.42 Based on integrative consideration, the optimum concentration of lithium salt is determined as 2.0 mol / kg. Dispersing inorganic fillers in polymer matrix is a promising method to improve ion conductivity, especially, Li+ - conductive inorganic electrolyte fillers.43-46 In order to prepare a promising PIL-LiTFSI-LATP composite electrolyte, LATP was selected to disperse in the PIL matrix. The LATP powder has a mean particle size of around 100 nm as shown in Figure S7. The LATP dispersed in PIL matrix did not impel formation


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of some impurity phases. The crystallinity of LATP has no change after adding into the PIL (Figure S8). However, there is a new peak at 17 。 , which may be contributed to the addition of LATP ceramic particles changed the crystallinity of PIL. EIS measurements of the membranes containing various LATP contents were measured at different temperatures and Arrhenius plots are presented in Figure 4c. In the investigated temperature 30 °C-100 °C, the membrane with a content of 10 wt% LATP achieved the maximum conductivity. According to the equivalent circuit model (Figure S9), the interface resistances (Ri) is 42, 32, 115, 165, 410 Ω for 0% LATP, 10 wt% LATP, 20 wt% LATP, 30 wt% LATP and 40 wt% LATP, respectively. It shows a minimum interface resistance at 10wt% LATP, which is might be due to the different crystal phase content. The apparent activation energy is 1.06, 0.83, 0.66, 0.58, 0.52 eV for the LiTFSI content of 0.3 mol kg-1, 0.5 mol kg-1, 1.0 mol kg-1, 1.5 mol kg-1 and 2.0 mol kg-1, respectively. The apparent activation energy is 0.50, 0.55, 0.56, 0.61 eV for the LATP content of 10 wt%, 20 wt%, 30 wt% and 40 wt%, respectively. The composite electrolyte with 10 wt% LATP has the lowest apparent activation energy (Figure S10). The lower activation demonstrates that the movement of ions in PIL-LiTFSI-LATP electrolyte needs a smaller energy, indicating a lower operating temperature for Li transport processes. The result is consistent with those reports about admixtures of oxides and polymer electrolytes.45,46 The ionic conductivity of PIL-LiTFSI-LATP and PIL-LiTFSI electrolyte is 7.93 × 10-4 S cm-1, 5.92 × 10-4 S cm-1 at 60 °C, respectively. Therefore, the conductivity of PIL-LiTFSI-LATP composite electrolyte is improved 34% compared to that of PIL-LiTFSI. The higher volume fraction of the amorphous phase



can lead to a higher nucleation rate during the solidification process and further result in increase of the ionic conductivity.47 Given these observations,6,12,48 it may generally be stated that the addition of a small amount of ceramic electrolyte has a positive effect on ion conductivity. As is shown in Figure 4d, the oxidation current starts to increase around 4.55 V (vs. Li / Li+). The addition of different amount of LATP makes no difference to the electrochemical stability windows. These results reveal that the composite solid electrolyte can be safely applied to a LiFePO4 / Li cell that is cycled between 2.8-4.0 V. As we know, one of critical factors for cycle performance of lithium battery is the stability of electrode-electrolyte interface. To evaluate electrode-electrolyte interface stability, symmetrical lithium batteries with PIL-LiTFSI and PIL-LiTFSI-LATP were assembled respectively, and examined the impedance transformation following the storage times at 60 °C. As shown in Figure 5a and Figure S11, the interfacial resistance of cell employed PIL-LiTFSI electrolyte increases from 196 Ω to 390 Ω with the increase of storage time, indicating that the interface contact between Li metal electrode and PIL-LiTFSI electrolyte is unstable. However, the average normalized interfacial resistance of the PIL-LiTFSI-LATP is 107 Ω at 60 °C, which is about 64% lower than that of PIL-LiTFSI. Additionally, the interfacial resistance obtained by AC impedance spectroscopy (Figure 5a), which was characterized at equilibrium state gradually, leads to a higher total resistance with a little higher charge transfer resistance than the resistance obtained by the galvanostatic cycling experiment (Figure S12). As is shown in Figure S12, a current density value of 0.5 mA cm-2 was selected to evaluate the


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stability of Li / PIL-LiTFSI-LATP / Li with a long-term cycling at 25 °C (0.5 h charge and discharge). It is observed that the voltage plot delivers a stable voltage plateau, demonstrating highly stable reversibility. The transference number of Li+ (tLi+) is another important parameter to evaluate polymer electrolytes. As shown in Figure 5b, the interfacial resistance of initial state is 133 Ω and change to 161 Ω after polarization. The current value of initial state and steady state is 0.0267 mA, 0.0075 mA, respectively. We could easily calculate the tLi+, about 0.21 for PIL-LiTFSI-LATP composite electrolyte. This value is in good agreement with PEO-LiTFSI system. As is shown in Figure S13, the tLi+ of composite electrolytes with different LATP contents is measured. The tLi+ increases initially and then decreases as the mass fraction of LATP further increases. The regular change is the same as those reported in literatures.41,46 The all-solid-state LiFePO4 / PIL-based electrolytes / Li batteries were assembled and the charge-discharge performance at 0.1 C were examined at 25 °C. As seen from Figure S14a, the polarization between charge and discharge potential plateau is much higher because of the lower conductivity at ambient temperature. The initial specific discharge capacity of the cell with PIL-LiTFSI and PIL-LiTFSI-LATP is 102 mA h g1,

110 mA h g-1at 0.1 C, respectively. After 50 cycles, the capacity retention of the cell

is 88%, 95%, respectively (Figure S14b). It is noted that the cell with PIL-LiTFSILATP displays superior cycle durability. The conventional lithium batteries used flammable organic electrolytes, which limited the operating temperature below to 60 °C.43 The operating temperature can be extended by using solid state electrolyte. The discharge performance of LiFePO4 / PIL-



LiTFSI / Li battery operating at 30 °C to 80 °C at the rate of 0.5 C is shown in Figure 6a and Figure 6b. The capacity is 52 mA h g-1 at 30 °C and increases with increasing measure temperature and reaches about 152 mA h g-1 at 80 °C. The charge-discharge profile and discharge capacity of LiFePO4 / PIL-LiTFSI / Li obtained at various rates at 60 °C are shown in Figure 6c and Figure 6d. Obviously, the discharge capacity of the cell with PIL-LiTFSI is 156.4, 150.6, 146.5, 138.4, 123.7, and 79.4 mA h g-1 at current density of 0.1, 0.2, 0.5, 1, 2 and 5 C, respectively. Figure 7a and Figure 7b show the first charge/discharge curves of the LiFePO4 / PIL-LiTFSI-LATP / Li battery at a rate of 0.5 C at different temperatures. The capacities LiFePO4 / Li cells can reach from 65.8 to 153 mA h g-1 with temperature varies from 30 °C to 80 °C, demonstrating a wide operation temperature range. The typical charge-discharge curves of LiFePO4 / Li cell were also examined at different current densities at 60 °C. The impedance profile of LiFePO4 / PIL-LiTFSI-LATP / Li battery is shown in Figure S15. The large semicircle corresponds to the charge transfer reaction is only 115 Ω, which indicates the contact between electrolyte and electrodes is much more sufficient. As displayed in Figure 7c and Figure 7d, LiFePO4 / Li cell using PIL-LiTFSI-LATP exhibits excellent rate performance. It can deliver capacities of 163.2, 160.2, 152.5, 141.3, 129.5 and 94.3 mA h g-1 at varied rates of 0.1, 0.2, 0.5, 1, 2 and 5 C, respectively, which are much better than those with PIL-LiTFSI. The capacity is able to recover to the initial value at 0.1 C after the rate measurement, which further demonstrating the good stability of the PIL-LiTFSI-LATP composite electrolyte.


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The cycle stability is studied by operating the all-solid-state batteries at 60 °C at the rate of 1 C. As shown in Figure 8, the initial capacity of the LiFePO4 / PIL-LiTFSI / Li battery is 138.4 mA h g-1 and 90% of the discharge capacity is retained after 250 cycles. The cell using PIL-LiTFSI-LATP display about 3.6% capacity loss after 250 cycles (from 141.3 mA h g-1 to 136.2 mA h g-1), indicating that PIL-LiTFSI-LATP can afford superior cycle durability at the elevated temperature. The improved cycling stability and rate capability of LiFePO4 / Li batteries using PIL-LiTFSI-LATP electrolyte can be ascribed to the introduction of LATP can improve the interfacial stability and compatibility against electrodes. CONCLUSIONS The polymerized IL was successfully prepared by using 1-vinyl-3ethylimidazolium bis(trifluoromethanesulfony)imide as monomer material. We use polyethylene terephthalate (PET) nonwoven as the backbone to improve the mechanical strength and PIL-LITFSI as the ionic transport material. The ionic conductivity of PILLiTFSI with 2.0 mol / kg LiTFSI is 7.78 × 10-5 S cm-1 at 30 °C and reaches 5.92 × 104

S cm-1 at 60 °C, which is a satisfactory value for its future application in all-solid-state

batteries. The specific discharge capacity of the LiFePO4 / Li cell with PIL-LiTFSI is 138.4 mA h g-1 and 90% of the discharge capacity is retained after 250 cycles. Inorganic electrolyte LATP particles are dispersed in PIL to form PIL-LiTFSI-LATP composite electrolytes to improve the conductivity. LiFePO4 / Li cell using PIL-LiTFSI-LATP exhibited excellent rate performance. The cell can deliver a capacity of 141.3 mA h g-1 at 1 C and be operated for more than 250 cycles with the capacity retention of 96.4%,



indicating that PIL-LiTFSI-LATP can afford superior cycle durability at the elevated temperature. Supporting Information General synthetic procedure for the preparation of [PVEIm][TFSI]; FT-IR spectra of IL monomer and PIL; 1H solid-state NMR spectrum and molecular weight of PIL; TGA curves of IL monomer and after polymerization; photographs of PET-PIL-based electrolyte at bended and winded states; SEM of LATP particles; XRD patterns of composite electrolytes containing different contents of LATP; the activation energy of composite electrolytes with different contents of LiTFSI or LATP; time evolution of interfacial resistance of Li / electrolyte membrane / Li after various storage times at 60 °C; the long-term cycling stability of the Li / Li symmetric cell at a current density of 0.5 mA cm-2; the tLi+ of composite electrolytes with different LATP contents; the first cycle charge-discharge profile and capacity retention of initial 50 cycles of PIL-based composite electrolytes obtained at 25 °C of 0.1 C; impedance profile of LiFePO4 / PILLiTFSI-LATP / Li battery at 60 °C. ACKNOWLEDGEMENTS This work was supported by the “100 Talents” program of Chinese Academy of Sciences and the Development Program of China: National Key R&D Program of China. REFERENCES (1) Sun, C. W.; Liu, J.; Gong, Y. D.; Wilkinson, D. P.; Zhang, J. J., Recent advances in all-solid-state rechargeable lithium batteries. Nano Energy, 2017, 33, 363-383. DOI: 10.1016/j.nanoen.2017.01.028.


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Figure captions Figure 1. Schematic illustration of the preparation of PIL-based composite electrolyte. Figure 2. The thermal shrinkage test of (a) PET, (b) PET-PIL-LiTFSI, (c) PET-PILLiTFSI-LATP before (a, b, c) and after (a’, b’, c’) heating to 120 °C for 90 min. Figure 3. Typical SEM images of (a) the surface and (a’) cross-section of PET nonwoven, (b) the surface and (b’) cross-section of PET-PIL composite electrolyte. Figure 4. (a) Arrhenius plots and (b) Linear sweep voltammetry (LSV) curve of PILLiTFSI electrolyte. (c) Arrhenius plots and (d) LSV curve of PIL-LiTFSI-LATP electrolyte. Figure 5. (a) Impedance spectra for cells of Li / PIL-LiTFSI / Li and Li / PIL-LiTFSILATP / Li at 60 °C. (b) Current-time curve following a DC polarization of 10 mV of the PIL-LiTFSI-LATP composite electrolyte. Inset are impedance profiles before and after polarization. Figure 6. (a) Charge-discharge profiles and (b) discharge capacity of LFP / PIL-LiTFSI / Li obtained at various temperatures at 0.5 C. (c) Charge-discharge profiles and (d) discharge capacity of LFP / PIL-LiTFSI / Li obtained at various rates at 60 °C. Figure 7. (a) Charge-discharge profiles and (b) discharge capacity of LFP / PIL-LiTFSILATP / Li obtained at various temperatures at 0.5 C. (c) Charge-discharge profiles and (d) discharge capacity of LFP / PIL-LiTFSI-LATP / Li obtained at rates at 60 °C. Figure 8. Cycle performance of cells with PIL-based electrolyte at 60 °C and at 1C.



Figure 1


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Figure 2



Figure 3


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Figure 4



Figure 5


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Figure 6



Figure 7


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Figure 8



ABSTRACT GRAPHIC

A novel composite electrolyte prepared by combining polymerized ionic liquid with inorganic electrolyte for fabricating all-solid-state battery with exhibit excellent performance.


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Solid Polymer Electrolyte Based on Polymerized Ionic Liquid for High

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