Ionic Conductivity Of Composite Polymer Electrolytes Research Articles

Fiber‐Reinforced Composite Polymer Electrolytes for Solid‐State Lithium Batteries

AbstractSolid‐state composite polymer electrolytes (CPEs) have attracted much attention due to their flexibility and low interfacial impedance. Researchers have been improving their ionic conductivity at room temperature, ionic transference number, and (electro)chemical stability. Here, a fiber‐reinforced CPE is prepared by infusing polyethylene oxide (PEO) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolytes onto polyacrylonitrile (PAN) nanofiber networks. The introduction of both inorganic ceramic filler LLZTO and plasticizer succinonitrile (SN) reduces the crystallinity of PEO, increases the solubility of lithium salts, and further improves ionic transport kinetics. The ionic conductivity of CPE is 2.57 × 10−4 S cm−1 at 30 °C and the lithium‐ion transference number is 0.6. Meanwhile, the high content of LLZTO (60 wt.%) brings a better capability to suppress lithium dendrites, and thus lithium symmetrical cells based on this CPE can be stably cycled for up to 500 h. In addition, the PAN fiber network endows CPE with high mechanical strength and high oxidation resistivity, and accordingly an electrochemical stability window as high as 4.7 V. Both LiFePO4/CPE/Li and LiNi1/3Co1/3Mn1/3O2/CPE/Li cells can be operated at 30 °C for 100 cycles. This work provides a promising strategy for the preparation of thin CPEs for solid‐state lithium metal batteries.

Enhancement of cycling stability of all-solid-state lithium-ion batteries with composite polymer electrolytes incorporating Li6.25La3Zr2Al0.25O12 nanofibers

Li7La3Zr2O12 (LLZO) with cubic phase structure is a kind of lithium-ion-conducting nanoparticles. According to the previous studies, incorporation of c-LLZO can improve electrochemical properties of PEO-based composite polymer electrolytes (CPEs). Therefore, in our study, we synthesized a kind of room-temperature-stable cubic phase LLZAO (Li6.25La3Zr2Al0.25O12) nanofibers, and we aimed to confirm the optimal content of LLZAO nanofibers in PEO-based CPEs. With the incorporating 10 wt% LLZAO nanofibers, ionic conductivity of CPEs are 9.87×10−5 S cm−1 at 30 °C and 8.66×10−4 S cm−1 at 60 °C. The Li/CPE incorporating 10 wt% LLZAO nanofibers/Li symmetric cell exhibits little voltage fluctuation in 1000 cycles under a current density of 0.5 mA cm−2, demonstrating better cycling stability with long cycle life. The LiFePO4/CPE incorporating 10 wt% LLZAO nanofibers/Li cell has a high initial discharge-specific capacity of 155.6 mAh g−1 under 0.1 C rate at 60 °C and remains 94.5% of capacity after 100 cycles. This cell also has great cycling performance under 0.2 C and 0.5 C rate, indicating good rate performance. Our work indicates that incorporation of LLZAO nanofibers enhances electrochemical properties and cycling stability of PEO-based all-solid-state lithium-ion batteries.

Filler effect of ionic liquid attached titanium oxide on conducting property of poly(ethylene oxide)/poly(methyl methacrylate) composite electrolytes.

Composite polymer electrolytes (CPEs) were prepared by containing blend of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) as a host polymer, propylene carbonate as a plasticizer, and LiClO4 as a salt. By an addition of a various content of ionic liquid attached TiO2 (IL-TiO2) to above electrolytes, the effects were studied. As a result, by increasing the IL-TiO2 content, the crystallinity of PEO was decreased and the ionic conductivity was increased. The ionic conductivity of CPEs was dependent on the content of IL-TiO2 and showed the highest value of 1.05 x 10(-4) S/cm at 9 wt.%. However, when IL-TiO2 content exceeds 9 wt.%, the ionic conductivity was decreased due to the slow ionic transport due to immiscibility or aggregation of the IL-TiO2 filler within the polymer film matrix.

Electrochemical properties of PEO/PMMA blend-based polymer electrolytes using imidazolium salt-supported silica as a filler

In this study, the composite polymer electrolytes (CPEs) were prepared by solution casting technique. The CPEs consisted of PEO/PMMA blend as a host matrix doped with LiClO4. Propylene carbonate (PC) was used as plasticizer and a small amount of imidazolium salt-supported amorphous silica (IS-AS) as a filler was prepared by the sol–gel method. At room temperature, the highest conductivity was obtained for the composition having PEO–PMMA–LiClO4–PC–4wt. % IS-AS with a value of 1.15 × 10−4 S/cm. In particular, the CPE using the IS-AS filler showed a higher conductivity than any other sample (fumed silica, amorphous silica). Studies of differential scanning calorimetry and scanning electron microscopy indicated that the ionic conductivity increase was due to an expansion in the amorphous phase which enhances the flexibility of polymeric chains and the homogeneous structure of CPEs. It was found that the ionic conductivity and interfacial resistance stability of CPEs was significantly improved by the addition of IS-AS. In other words, the resistance stability and maximum ambient ionic conductivity of CPEs containing IS-AS filler were better than CPEs containing any other filler.

Polyindole–CuO composite polymer electrolyte containing LiClO4 for lithium ion polymer batteries

This study presents the preparation of a composite polymer electrolyte (CPE), polyindole-based CuO dispersed CPE containing lithium perchlorate by sol–gel method. Morphology and the structural studies were conducted by scanning electron microscopy and X-ray diffraction. The ionic conductivity of CPE was measured for different concentration of the monomer by impedance spectroscopy. CPE containing CuO/indole (2:1 w/w ratio) (CPE3) exhibited enhanced conductivity of 1.9498 × 10−5 S/cm at RT. This CPE showed a linear relationship between the ionic conductivity and the reciprocal of the temperature, indicative of the system decoupled from the segmental motion of the polymer.

Morphology and Electrical Characteristics of (PEO)<sub>10</sub>LiClO<sub>4</sub> Electrolyte with Nanosized CeO<sub>2</sub>

In the present work, using nanosized rare earth oxide CeO2 as filler and acetonitrile as organic solvent, a novel solid-state composite polymer electrolyte (CPE) films (PEO)10LiClO4-x wt.%CeO2 (x=0,2,6,9,12,15) was prepared by solution-casting technique. The effect of CeO2 filler concentration on morphology and electrical characteristics of CPE films has been investigated and analyzed. The AC impedance measurements show that the ionic conductivity of CPE can be efficiently enhanced by adding appropriate CeO2. The highest room temperature (25OC) ionic conductivity of 1.71×10-5S•cm-1 is achieved with the CeO2 content of 9 wt.%. With the CeO2 content continues to increase, CPE ionic conductivity begin to decline. This is because appropriate CeO2 can disorder the chain structure and effectively inhibit the crystallization of PEO, which expands the amorphous region required for the lithium-ion transport.

Electrochemical Behaviour of the Composite Polymer Electrolyte P(VDF-HFP)-PMMA/CaCO<sub>3</sub>(SiO<sub>2</sub>)

Electrochemical behavior of the composite polymer electrolyte (CPE) prepared from polyvinylidene fluoride-co-hexafluoropropylene (P (VDF-HFP)), poly (methyl methacrylate) (PMMA), and nanosized CaCO3 (SiO2) particles was investigated by confocal laser scanning microscopy, X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Results show that CPEs have many micropores, and that the addition of PMMA can increase the absorption potential of the liquid electrolyte and therefore improve ionic conductivity. The best performance of CPE was found at a P (VDF-HFP) /PMMA mass ratio of 1:1. The composite polymer electrolyte that was produced by adding nanosized CaCO3 and SiO2 to a P (VDF-HFP)-PMMA base keeps the amorphous structure of the original polymer base. The ionic conductivity of CPE can reach 3.42 mS•cm^(-1) and the electrochemical window can be up to 4.8 V at room temperature. A test on Li/CPE/GMS cells showed that the composite polymer electrolyte was compatible with graphite anodes. The battery made from Li/CPE (CaCO3) /LiCoO2 was shown to have a superior rate discharging performance to Li/CPE (SiO2) /LiCoO2.