A Cross-Linking Succinonitrile-Based Composite Polymer Electrolyte

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A Cross-Linking Succinonitrile-Based Composite Polymer Electrolyte with Uniformly Dispersed Vinyl-Functionalized SiO2 Particles for LiIon Batteries Kai Liu,†,‡ Fei Ding,*,‡ Jiaquan Liu,§ Qingqing Zhang,‡ Xingjiang Liu,†,‡ Jinli Zhang,† and Qiang Xu*,† †

School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China National Key Laboratory of Science and Technology on Power Sources, Tianjin Institute of Power Sources, Tianjin 300384, P. R. China § School of Engineering and Applied Science, George Washington University, Washington, D.C. 20052, United States ‡

ABSTRACT: A cross-linking succinonitrile (SN)-based composite polymer electrolyte (referred to as “CLPC−CPE”), in which vinylfunctionalized SiO2 particles connect with trimethylolpropane propoxylate triacrylate (TPPTA) monomers by covalent bonds, was prepared by an ultraviolet irradiation (UV-curing) process successfully. Vinyl-functionalized SiO2 particles may react with TPPTA monomers to form a cross-linking network within the SN-based composite polymer electrolyte under ultraviolet irradiation. Vinyl-functionalized SiO2 particles as the fillers of polymer electrolyte may improve both the thermal stability of CLPC−CPE and interfacial compatibility between CLPC−CPE and electrodes effectively. There is no weight loss for CLPC−CPE until above 230 °C. The ionic conductivity of CLPC−CPE may reach 7.02 × 10−4 S cm−1 at 25 °C. CLPC−CPE has no significant oxidation current until up to 4.6 V (vs Li/Li+). The cell of LiFePO4/CLPC−CPE/Li has presented superior cycle performance and rate capability. The cell of LiFePO4/CLPC−CPE/Li may deliver a high discharge capacity of 154.4 mAh g−1 at a rate of 0.1 C after 100 charge−discharge cycles, which is similar than that of the control cell of LiFePO4/liquid electrolyte/Li. Furthermore, the cell of LiFePO4/CLPC−CPE/Li can display a high discharge capacity of 112.7 mAh g−1 at a rate of 2 C, which is higher than that of the cells assembled with other plastic crystal polymer electrolyte reported before obviously. KEYWORDS: solid-state electrolyte, lithium ion battery, succinonitrile, ultraviolet irradiation, cross-linking recognized widely for its unique characteristic.11,12 Plastic crystal as a mesophase is mainly composed of disklike or quasispherical molecules, which may display rotational and/or orientational disorder while reserving a long-range translational order.13,14 Succinonitrile (SN, NC−CH2−CH2−CN) is a representative example, which may keep the plastic crystalline phase from ca. −40 to 60 °C.15 Because of having a unique structure of trans−gauche isomerism containing molecule rotation along the central C−C bonds of SN, SN-based PCE can reveal a high ionic conductivity of more than 1 × 10−3 S cm−1 at 25 °C. Unfortunately, the SN-based PCE displays poor mechanical strength and low electrochemical performances, which is not suitable for applications. It is well-known that doping ceramic particles such as TiO2, SiO2, Al2O3, and BaTiO3 into the polymer electrolyte of lithium ion batteries may increase their mechanical and electrochemical performances.16−22 In general, incorporation of ceramic particles as the fillers into polymer electrolyte may exhibit the following merits:23−26 (1) increase of the ionic conductivity of

1. INTRODUCTION With rapid progresses of energy industry, Li ion batteries with a high energy density have been widely applied as power sources in many fields, including hybrid electric vehicles, communication equipment, and portable electronics.1 With regard to conventional Li ion batteries, one of the main factors that needs to be considered is the safety due to the flammability and leakage of combustible liquid electrolyte.2 Li ion batteries with the polymer electrolyte have been exploited on account of their advantages, such as longer cycle life, antileakage safety, and simple forming process.3,4 However, the polymer electrolyte including the dry solid polymer and gel polymer still have many problems needed to be solved, which is similar to conventional liquid electrolyte.5,6 The dry solid polymer electrolyte, which contains the lithium salt and polymer substrate, generally offers low ionic conductivity below 1 × 10−6 S cm−1 at 25 °C because poly(ethylene oxide)-based electrolyte has a tendency to form crystalline phases.7,8 The gel polymer electrolyte composed of organic liquid electrolyte and a polymer framework may exhibit high reactivity with lithium electrodes and poor mechanical strength, which limits its practical applications in Li ion batteries.9,10 Recently, the plastic crystal electrolyte (PCE), in which lithium salts are dissolved in the plastic crystals, has been © XXXX American Chemical Society

Received: May 17, 2016 Accepted: August 26, 2016

A

DOI: 10.1021/acsami.6b05882 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

functionalized SiO2 particles were dehydrated at 50 °C in a vacuum for 12 h. 2.2. Preparation of CLPC−CPE. First, LiTFSI was mixed with SN at 60 °C to form the PCE in a glovebox filled with argon gas until a homogeneous solution (1 mol L−1) had been gained. Then, vinylfunctionalized SiO2 particles, TPPTA monomers, and HMPP were put into the solution of PCE at a weight ratio of 1:5:25 (SiO2/TPPTA/ PCE), wherein the content of HMPP was 0.5 wt % versus the weight of TPPTA monomers. Then, the mixture was subjected to continuous agitating for 1 h to obtain a homogeneous dispersion of vinylfunctionalized SiO2 particles. Subsequently, the dispersed suspension was cast onto a polypropylene piece and irradiated by using a UV source (Hg lamp; the peak intensity of irradiation was ∼2000 mW cm−2) for 60 s. Afterward, a layer of translucent gel-like polymer electrolyte film with a thickness of 150 μm could be formed. Finally, the obtained CLPC−CPE film was preserved under an argon atmosphere at 40 °C over 3 d. All above preparing procedures were conducted in a glovebox filled with argon gas, in which the contents of moisture and oxygen were below 0.1 ppm. The UV-curing process is illustrated in Figure 1a, and the molecular structure of CLPC−CPE

composite polymer electrolyte; (2) improvement of the thermal stability of composite polymer electrolyte (or separator); (3) decrease of the interfacial resistance between composite polymer electrolyte (or separator) and electrodes. To further improve the performances of composite polymer electrolyte (or separator), many efforts on the surface modifications for ceramic particles have been conducted. According to the types of modified layers coated on ceramic particles, the modified methods can be divided into three categories: cation adsorption,27,28 macromolecule coating,29,30 and functional groups grafting.31,32 Among these ceramic fillers, SiO2 particles could reduce the interfacial resistance between composite polymer electrolyte (or separator) and electrodes most efficiently.33 Compared to the common filler of Al2O3 particles, SiO2 particles have a better affinity with organic solvents within the composite polymer electrolyte (or separator).34 However, there is no report on SiO2 particles as fillers in the PCE electrolyte until now. Because the combination of inert SiO2 particles with the matrix of polymer electrolyte belongs to mechanical mixing, plastic crystal composite polymer electrolyte dispersed with inert SiO2 particles has not enough mechanical strength to be applied as a self-standing composite polymer electrolyte. To solve this problem, a cross-linking SN-based composite polymer electrolyte dispersed with SiO2 particles coated with vinyl-functional groups (referred to as “CLPC−CPE”) was prepared by an ultraviolet (UV) curing method in this study. CLPC−CPE includes the PCE matrix (acting as lithium ion transport channels) and a cross-linking composite framework composed of trimethylolpropane propoxylate triacrylate (TPPTA) and vinyl-functionalized SiO2 particles (providing a mechanical skeleton). During the UV-curing process, vinylfunctionalized SiO2 particles may react with TPPTA monomers to form a cross-linking composite polymer network within CLPC−CPE. Because the combination of vinyl-functionalized SiO2 particles with TPPTA monomers belongs to a kind of chemical bonding, CLPC−CPE as a solid-state electrolyte can exhibit excellent thermal stability and good interfacial compatibility with electrodes. Meanwhile, the unique structure of CLPC−CPE also ensures its high ionic conductivity at normal temperature. Compared to the batteries assembled with other plastic crystal polymer electrolyte reported before, the cell of LiFePO4/CLPC−CPE/Li may reveal superior cycle performance and rate capability.

2. EXPERIMENTAL SECTION Succinonitrile (SN), Li(CF3SO2)2N (LiTFSI), and 2-hydroxy-2methyl-1-phenyl-1-propanone (HMPP, a photoinitiator) were bought from Aldrich Industrial Inc. Trimethylolpropane propoxylate triacrylate (TPPTA, Mw ≈ 644.79) was bought from J&K company. Other organic solvents (battery grade) for the experiments were purchased from Aladdin Co. Ltd. A commercial liquid electrolyte of 1 mol L−1 LiPF6 in a ternary solvent of ethylene carbonate/ethylmethyl carbonate/dimethyl carbonate (EC/EMC/DMC, 1:1:1) was obtained from Dong Guan Shanshan Battery Materials Co. Ltd. 2.1. Preparation of Vinyl-Functionalized SiO2 Particles. SiO2 particles with vinyl-functional groups were prepared by a sol−gel method of triethoxyvinylsilane (TEVS, Aladdin Industrial Inc) in an aqueous system as reported before.35 Typically, a certain amount of TEVS was dropped into the distilled water and stirred for 2 d until the TEVS droplets had drastically disappeared. Then, an appropriate quantity of NH4OH was dropped into TEVS solution, and a reaction of hydrolysis−condensation was performed within the solution for 24 h. After it was centrifuged, the precipitate was washed with ethanol several times. At last, the obtained white powders of vinyl-

Figure 1. Schematic illustration of the CLPC−CPE. The UV-curing process of CLPC−CPE (a). The molecular structure of CLPC−CPE after polymerization (b). after polymerization is shown in Figure 1b. The mass percent of SN in CLPC−CPE is 62.38 wt %. In addition, an organic liquid electrolyte of 1 mol L−1 LiPF6 in a ternary solvent of EC/EMC/DMC (1:1:1) was used as the control electrolyte (with commercial separator) to evaluate the electrochemical performances of CLPC−CPE. 2.3. Characterization of CLPC−CPE. The morphologies of both vinyl-functionalized SiO2 particles and CLPC−CPE samples were investigated by scanning electron microscopy (SEM; Hitachi S-4800). The realization of UV-curing reactions within CLPC−CPE was detected by a Nicolet 6700 Fourier transform infrared (FT-IR) spectrometer. The thermal properties, such as the transition temperature of Tcp (from normal crystal to plastic crystal) and the melting temperature of Tm for the samples of SN, PCE, and CLPC− B


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Figure 2. Photos of CLPC−CPE samples (a, b); SEM image of vinyl-functionalized SiO2 particles (c); SEM image of CLPC−CPE sample (d).

translucent, and flexible, which are similar to that of traditional PCE.36 These photos indicate that CLPC−CPE has a good flexibility, which could be applied in flexible Li ion batteries. Figure 2c shows SEM image of the as-prepared SiO2 particles with vinyl-functional groups. As shown in Figure 2c, vinylfunctionalized SiO2 particles exhibit regular spherical shape, and their average diameter is ∼600 nm. Moreover, Figure 2d represents the surface morphology of CLPC−CPE. It can be found that vinyl-functionalized SiO2 particles are dispersed uniformly within CLPC−CPE, suggesting that vinyl-functionalized SiO2 particles have been embedded in the matrix of composite polymer electrolyte. Figure 3 reveals the FT-IR spectra of four samples, which include CLPC−CPE before/after UV-irradiation, TPPTA monomers, and vinyl-functionalized SiO2 particles. From Figure 3a, the FT-IR spectrum of vinyl-functionalized SiO2 particles represents a characteristic broad band around 1100 cm−1, which is related to the asymmetric stretching vibrations of Si−O−Si.37 The appearance of two peaks at 1412 and 1600 cm−1 corresponding to reactive CC double bonds demonstrates that vinyl-functional groups have been introduced on the surface of SiO2 particles successfully.38 Moreover, the FT-IR spectrum of TPPTA is displayed in Figure 3b. Peaks at 1620− 1640 and 1705 cm−1 are the characteristics of acrylic CC double bonds and carbonyl group in TPPTA, respectively.39 Compared to CLPC−CPE before UV curing (Figure 3c), the characteristic peaks relating to CC double bonds on the surface of SiO2 particles and the characteristic peaks associated with acrylic CC double bonds in TPPTA have disappeared or weakened obviously after UV curing (Figure 3d). These results suggest that the cross-linking reaction between vinylfunctional groups on the surface of SiO2 particles and TPPTA monomers was realized after UV-curing.40

CPE, were tested by thermogravimetric differential scanning calorimetry (TG-DSC) analysis from −60 to 80 °C at a heating speed of 5 °C min−1 in hermetically sealed aluminum pans under nitrogen atmosphere. Moreover, the thermal stability of polymer electrolyte was inspected by TG-DSC analysis from 25 to 450 °C at a heating speed of 10 °C min−1 under argon gas atmosphere. The alternating-current (AC) impedance spectra were measured on a symmetrical cell of Li/electrolyte sample/Li during different aging time at 25 °C to evaluate the interfacial compatibility of electrolyte samples, which were performed at a frequency range from 1 × 106 to 1 × 10−1 Hz with an amplitude of 5 mV by a Solartron Instruments model 1400/1470E. The ionic conductivities of electrolyte samples were investigated by AC impedance analysis on a symmetrical cell of stainless steel/CLPC−CPE/stainless steel, which were conducted at a frequency range from 1 × 105 to 1 Hz with an amplitude of 5 mV. These symmetrical cells of stainless steel/CLPC−CPE/stainless steel were kept at every testing temperature (from 30 to 80 °C) for 30 min to achieve thermal equilibrium before measurements. The cyclic voltammetry analysis was implemented on a cell of stainless steel/ electrolyte sample/lithium at a scan rate of 0.2 mV s−1 to explore the electrochemical stability of electrolyte samples. Furthermore, the cointype cell (CR2430) was assembled by LiFePO4-based cathode, lithium anode, and CLPC−CPE electrolyte. The LiFePO4-based cathode was mixed with LiFePO4, Super-P, and poly(vinylidene difluoride) (PVDF) at a ratio of 8:1:1. The galvanostatical charge−discharge tests of coin-type cells were conducted at a voltage range of 2.5−4.2 V on a Land battery testing equipment (CT-2001) at a constant current of 0.1 C (1 C = 170 mA g−1). Rate capabilities of coin-type batteries were measured at a charge current of 0.1 C and a discharge current from 0.1 to 2 C. After cycling tests, these coin-type cells were dissembled to harvest lithium electrodes for characterizations with a scanning electron microscope (FEI Quanta) in a glovebox filled with argon gas.

3. RESULTS AND DISCUSSION Figure 2a,b display the photos of CLPC−CPE film. The CLPC−CPE film presents some characteristics of smooth, C


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the curve of PCE, it can be found that mixing of LiTFSI with SN (i.e., 1 mol L−1 PCE) may cause a large reduction of Tm from 59 to 23 °C but a little change of Tcp. The obvious decreasing of Tm reveals that the quantity of structural defect (i.e., trans-isomers) of SN has increased. Furthermore, both Tcp and Tm of CLPC−CPE are similar to that of the PCE, indicating that the thermal characteristics of PCE have not been destroyed after introduction of a three-dimensional skeleton composed of UV-cured TPPTA/vinyl-functionalized SiO2 particles.41 Figure 4b exhibits the TG thermograms of CLPC−CPE. As shown in Figure 4b, CLPC−CPE is negligibly volatile until at a temperature of 230 °C except for a slight loss due to volatilization of trace water, suggesting that vinylfunctionalized SiO2 particles may improve the thermostability of CLPC−CPE effectively. On behalf of having a high melting point, vinyl-functionalized SiO2 particles may act as a thermostable framework to resist dimensional variations of CLPC−CPE at high temperature.42 For comparison, the thermostabilities of some plastic crystal composite polymer electrolyte are listed in Table 1. Figure 4c displays the ionic Table 1. Thermostabilities of Different Plastic Crystal Electrolyte

Figure 3. FT-IR spectra of four samples. Vinyl-functionalized SiO2 particles (a); TPPTA monomers (b); CLPC−CPE before UV curing (c); CLPC−CPE after UV curing (d).

samples before polymerization ETPTA/PCE/Al2O3 PET immersed in ETPTA/PCE TPPTA/PVDF-HFP/PCE/Al2O3 TPPTA/vinyl-functionalized SiO2/PCE

The plastic crystal behavior of CLPC−CPE was surveyed by detecting Tcp and Tm of CLPC−CPE. Figure 4a shows the results of TG-DSC analysis for the samples of SN, PCE, and CLPC−CPE. In the curves of SN, two endothermic peaks at −32.5 and 59 °C correspond to Tcp and Tm, respectively. From

thermal stability ≤130 ≤150 ≤200 ≤230

°C °C °C °C

Figure 4. DSC curves of CLPC−CPE at the temperature range of −60−80 °C (a). The TG curve of CLPC−CPE under argon-filled atmosphere at a heating rate of 10 °C min−1 (b). Temperature-dependent ionic conductivity of CLPC−CPE (c). Cyclic voltammograms of CLPC−CPE at a scan rate of 0.2 mV s−1 (d). D


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Figure 5. AC impedance spectra of symmetrical cells (Li/electrolyte/Li) with different electrolyte after different storage time. With the electrolyte of CLPC−CPE (a). With the liquid electrolyte (commercial separator) (b).

Figure 6. Initial charge−discharge profiles of LiFePO4/Li cells assembled with the CLPC−CPE and liquid electrolyte at a current density of 0.1 C, respectively (a). Discharge capacities of LiFePO4/Li cells assembled with the CLPC−CPE and liquid electrolyte during cycling at a current density of 0.1 C (b). Rate capabilities of LiFePO4/Li cells assembled with the CLPC−CPE and liquid electrolyte at different current densities (c).

reduction and oxidation peaks are observed at a potential range of −0.5−0.5 V (vs Li/Li+), corresponding to the reversible plating and stripping of metallic lithium. Furthermore, the oxidative degradation of CLPC−CPE takes place at ∼4.6 V (vs Li/Li+), demonstrating that the electrochemical stability of CLPC−CPE is suitable for application in rechargeable Li ion batteries.49 Figure 5a depicts the AC impedance spectra of the symmetrical cell of Li/CLPC−CPE/Li after different storage days. From Figure 5a, the diameter of capacitive arcs in AC impedance spectra, which is a representation of interfacial resistance of the electrolyte with electrodes,50 increases with rising of storage time and tends to a stable value gradually. The spectrum of symmetrical cell of Li/CLPC−CPE/Li after storage of 16 d coincides with that of the symmetrical cell of Li/CLPC−CPE/Li after storage of 17 d, demonstrating that the compatibility of CLPC−CPE with lithium electrodes is very

conductivities of CLPC−CPE based on temperature. From Figure 4c, the ionic conductivity of CLPC−CPE rises with increase of temperature. Moreover, the ionic conductivity of CLPC−CPE at 25 °C was also measured, which is ∼7.02 × 10−4 S cm−1. This high conductivity of CLPC−CPE at room temperature can be ascribed to the establishment of threedimensional network within CLPC−CPE, which may provide abundant lithium ion channels.43 There are two diffusion ways for lithium ion conduction in CLPC−CPE under the action of electric field. On the one hand, lithium ion passes through the PCE in accordance with the paddle-wheel mechanism, and the translational motion of lithium ion correlates with anionic reorientation. 44,45 On the other hand, the motion of −CH2CH2O− segments of TPPTA may drive the diffusion of lithium ion by transient binding with the side chains of polymer.46−48 Figure 4d reveals the cyclic voltammogram of CLPC−CPE. From Figure 4d, it can be found that distinct E


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Figure 7. SEM images of lithium electrodes before/after 100 charge−discharge cycles. Before charge−discharge cycling (a). After 100 charge− discharge cycles (b).

well and a layer of stable passivation film (SEI) has been formed on lithium electrodes.51 Furthermore, AC impedance spectra of the control cell of Li/liquid electrolyte/Li after different storage days are described in Figure 5b. From Figure 5b, the diameter of capacitive arcs in AC impedance spectra increases with improvement of the storage time constantly. These results indicate that the interfacial compatibility between CLPC−CPE and lithium electrodes is superior to that of liquid electrolyte with lithium electrodes.52 Because the high surface area of vinyl-functionalized SiO2 particles is in favor of capturing residual impurities and preventing the side reactions of organic solvents with lithium electrodes, the growth rate of passivation layer between CLPC−CPE and lithium electrodes could be suppressed effectively.53 Figure 6a reveals the initial discharge capacities of two kinds of cells of LiFePO4/CLPC−CPE/Li and LiFePO4/liquid electrolyte/Li at a constant rate of 0.1C, respectively. As shown in Figure 6a, the cell of LiFePO4/liquid electrolyte/Li provides a discharge capacity of 161.2 mAh g−1 and a Coulombic efficiency of 96.1%. However, the cell of LiFePO4/CLPC−CPE/Li delivers a discharge capacity of 164.8 mAh g−1 and a Coulombic efficiency of 98.3%. These results manifest that the initial discharge performances of two kinds of cells assembled with different electrolyte are similar at low current densities. This is ascribed to the good compatibility of CLPC−CPE with electrodes as well as the excellent conductivity of CLPC−CPE.54 Figure 6b displays the cycle performances of two kinds of cells of LiFePO4/CLPC−CPE/Li and LiFePO4/liquid electrolyte/Li at a constant charge− discharge current of 0.1 C, respectively. From Figure 6b, the cell of LiFePO4/liquid electrolyte/Li reveals a discharge capacity of 157.4 mAh g−1 and a capacity retention ratio of 97.8% after 100 charge−discharge cycles. However, the cell of LiFePO4/CLPC−CPE/Li exhibits a discharge capacity of 154.4 mAh g−1 and a capacity retention ratio of 93.7% after 100 charge−discharge cycles. These results demonstrate that the cycle performance of the cell of LiFePO4/CLPC−CPE/Li is close to that of the cell of LiFePO4/liquid electrolyte/Li. This is because vinyl-functionalized SiO2 particles as the fillers have a better affinity with organic solvents and may improve interfacial compatibility of the electrolyte with electrodes.55 Figure 6c exhibits the rate capabilities of two kinds of cells of LiFePO4/ CLPC−CPE/Li and LiFePO4/liquid electrolyte/Li at a current range from 0.1 to 2.0 C, respectively. From Figure 6c, the discharge capacities for both the cells of LiFePO4/CLPC− CPE/Li and LiFePO4/liquid electrolyte/Li reduce with improvement of discharge current gradually. The discharge capacities of the cell of LiFePO4/CLPC−CPE/Li and the cell

of LiFePO4/liquid electrolyte/Li are similar at the rates of 0.1, 0.2, and 0.5 C, respectively. Although the discharge capacities are lower than that of the cell of LiFePO4/liquid electrolyte/Li at the rates of 1 and 2 C, the cell of LiFePO4/CLPC−CPE/Li has still released 143.9 mAh g−1 at a rate of 1 C and 112.7 mAh g−1 at a rate of 2 C. Figure 7 shows SEM photos of lithium electrodes before/ after 100 charge−discharge cycles. From Figure 7a, lithium electrodes present a flat surface with many stripes. From Figure 7b, there is no growth of lithium dendrite except for some residues of noncuring SiO2 particles on the surface of lithium electrodes after 100 charge−discharge cycles. These results also suggest that the interface of CLPC−CPE with lithium electrodes is well-compatible during the cycling procedure of cells, which is similar to above analytical results of AC impedance spectra. Compared to the performances of cells assembled with other plastic crystal polymer electrolyte reported before,56 the cell of LiFePO4/CLPC−CPE/Li exhibits not only a larger discharge capacity but also a higher rate capability, which can be ascribed to the following aspects. On the one hand, vinyl-functionalized SiO2 particles may react with TPPTA to form a cross-linked network structure within SN-based composite polymer electrolyte after UV curing, in which SN can be surrounded by a complex framework composed of UV-cured TPPTA and inorganic particles. The three-dimensional framework within CLPC−CPE can decrease the reaction activity of SN with lithium electrodes effectively and may lead to an improvement of cycle performance of the cell of LiFePO4/CLPC−CPE/Li.57 On the other hand, adding vinyl-functionalized SiO2 particles as the fillers into SN-based composite polymer electrolyte can decrease interfacial resistance of the electrolyte with electrodes more efficiently.58 Therefore, the total internal resistance of the cell of LiFePO4/CLPC−CPE/Li has been lowered during the charge−discharge cycling.59

4. CONCLUSION A novel cross-linking SN-based composite polymer electrolyte (CLPC−CPE) with uniformly dispersed vinyl-functionalized SiO2 particles has been synthesized by a UV-curing method successfully. Addition of vinyl-functionalized SiO2 particles as the fillers into CLPC−CPE may improve its thermal stability and interfacial compatibilty with electrodes effectively. There is no weight loss for CLPC−CPE until above 230 °C.The ionic conductivity of CLPC−CPE can reach 7.02 × 10−4 S cm−1 at 25 °C, and CLPC−CPE has no significant oxidation current until up to 4.6 V (vs Li/Li+). Moreover, the cell of LiFePO4/ CLPC−CPE/Li reveals excellent cycle stability and rate F


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capability. The cell of LiFePO4/CLPC−CPE/Li can deliver a discharge capacity of 154.4 mAh g−1 at a rate of 0.1 C after 100 charge−discharge cycles, which is similar to that of the cell of LiFePO4/liquid electrolyte/Li. Furthermore, the cell of LiFePO4/CLPC−CPE/Li may exhibit a discharge capacity of 112.7 mAh g−1 at a rate of 2 C, indicating that the cell of LiFePO4/ CLPC−CPE/Li has a superior rate capability. Consequently, CLPC−CPE as a promising polymer electrolyte should be used in next-generation Li ion batteries.

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AUTHOR INFORMATION

Corresponding Authors

*Phone: +86-022-23959712. Fax: +86-022-23383783. E-mail: [email protected]. (F.D.) *Phone: +86-022-27890322. Fax: +86-022-27401684. E-mail: [email protected]. (Q.X.) Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Foundation of National Key Laboratory of Science and Technology on Power Sources (No. 9140C16020212-DZ2801), P. R. China.

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