Ionic Conductivity Of Gel Polymer Electrolyte Research Articles

Unlocking Mechanism of Anion and Cation Interaction on Ion Conduction of Polymer Based Electrolyte in Metal Batteries.

Polymer based electrolyte shows advantages in compatibly improving safety and interface stability of batteries, while its limited ion conductivity and transfer number make it difficult to apply it in batteries with high energy density. Herein, by designing four crosslinking polyesters with different electron withdrawing group (EWG), it is found that strengthening the binding of EWG to anion for weakening the binding of anion to Li+ is critical for high Li+ transfer number (tLi+) and ionic conductivity of electrolyte. As a result, poly(2,2,3,3-tetrafluoropropyl methacrylate) (PTFM) based gel polymer electrolyte (GPE) shows an ionic conductivity of 0.78 mS cm-1 and a tLi+ of 0.85, much higher than those of poly(methyl methacrylate) (PMMA) without EWG. Moreover, PTFM based GPE shows excellent flame retardancy property. Li||PTFM||NCM811 batteries with an ultrahigh capacity of 5.5 mAh cm-2 show stable cycles of 5 times to that of Li||PMMA||NCM811. Moreover, the assembled graphite||PTFM||NCM811 pouch cell shows a capacity retention rate of 92% after 500 cycles. This work clarifies the mechanism of cation||anion interaction on ionic conductivity of GPE, which is important to develop high-performance devices with good safety and flexibility.

Unlocking Mechanism of Anion and Cation Interaction on Ion Conduction of Polymer Based Electrolyte in Metal Batteries

Polymer based electrolyte shows advantages in compatibly improving safety and interface stability of batteries, while its limited ion conductivity and transfer number make it difficult to apply it in batteries with high energy density. Herein, by designing four crosslinking polyesters with different electron withdrawing group (EWG), it is found that strengthening the binding of EWG to anion for weakening the binding of anion to Li+ is critical for high Li+ transfer number (tLi+) and ionic conductivity of electrolyte. As a result, poly(2,2,3,3−tetrafluoropropyl methacrylate) (PTFM) based gel polymer electrolyte (GPE) shows an ionic conductivity of 0.78 mS cm−1 and a tLi+ of 0.85, much higher than those of poly(methyl methacrylate) (PMMA) without EWG. Moreover, PTFM based GPE shows excellent flame retardancy property. Li||PTFM||NCM811 batteries with an ultrahigh capacity of 5.5 mAh cm−2 show stable cycles of 5 times to that of Li||PMMA||NCM811. Moreover, the assembled graphite||PTFM||NCM811 pouch cell shows a capacity retention rate of 92% after 500 cycles. This work clarifies the mechanism of cation||anion interaction on ionic conductivity of GPE, which is important to develop high‐performance devices with good safety and flexibility.

A novel gel polymer electrolyte with multi-functional additive for superior ionic conductivity, stability against Li, and redox activity of lithium-air batteries

Lithium-air batteries have the highest theoretical energy density among the rechargeable batteries. However, Li dendrite growth and the limited decomposition of discharge product, Li2O2, restrict the battery performances. In our recent study, we synthesized and utilized ammonium ionic liquid-functionalized phenothiazine (IL-PTZ) as a new redox mediator with stability against lithium to deal with these issues. Replacing liquid electrolyte to gel polymer electrolyte (GPE) is also one promising approach to enhance electrochemical performance. GPE with functional additive have been studied for improving flexibility, ionic conductivity, and chemical stability. In this study, we introduce IL-PTZ as an additive for the superior mechanical property and ionic conductivity of GPE. The elongation force of the GPE with IL-PTZ (IL-PTZ@GPE) was enhanced two times higher than that of GPE without the additive. The ionic conductivity also increased up to 1.53 × 10−3 and 4.76 × 10−3 S cm−1 at 20 and 80 °C, respectively. Furthermore, IL-PTZ molecules suppressed Li dendrite growth on the Li anode and accelerated oxygen evolution/reduction reactions on the cathode surface. IL-PTZ with only small amount of 0.1 M can act as multi-functional additive, resulting in the synergistic improvements mentioned above. As a result, Li-air cell with IL-PTZ shows superior electrochemical performances with the initial discharge capacity of 4685 mAh g− 1 and 4 times longer cyclability than the cell without additive.

Quasi-solid-state lithium-tellurium batteries based on flexible gel polymer electrolytes

A quasi-solid-state Li-Te battery is developed by using a flexible gel polymer electrolyte (GPE), porous carbon/tellurium cathode, and lithium metal anode. The ionic conductivity of GPE is controllable and reaches up to 8.0 × 10−4 S cm−1 at 25 °C. The good interfacial contact with Li metal ensures excellent cycling stability in Li/GPE/Li symmetric cells. Moreover, it is found that, compared to S and Se counterparts, the Li-Te battery exhibits good rate capability due to the high electrical conductivity of Te and excellent interfacial stability among GPE, Li, and Te. This work provides several facile strategies to develop safe and high-performance solid-state Li-Te batteries.

High-performance gel polymer electrolytes derived from PAN-POSS/PVDF composite membranes with ionic liquid for lithium ion batteries

The gel polymer electrolytes (GPEs) with poly(acrylonitrile-polyhedral oligomeric silsesquioxane)/poly(vinylidene fluoride) (PAN-POSS/PVDF) blends as free-standing porous membrane and ionic liquid (IL) as absorption substance were successfully prepared. By tuning the content of PAN-POSS, the porosity and absorptivity of the blended membranes could be regulated. Due to the higher porosity and absorptivity, the ionic conductivity of GPEs with 15 wt% PAN-POSS reaches to 1.91 × 10−3 S cm−1 at 20 oC. Meanwhile, the electrolytes also show excellent mechanical properties, thermal stability, and fire resistance. More importantly, the high electrochemical window of 4.6 V (vs. Li/Li+) has been acquired and the testing cells with Li metal anode and LiFePO4 cathode show a tolerable rate performance. Such prepared GPEs are expected to be applied to lithium batteries with high safety and electrochemical performance.

Properties of Gel Polymer Electrolyte Based Poly(Vinylidine Fluoride-сo-Hexafluoropropylene) (PVdF-HFP), Lithium Perchlorate (LiClO<sub>4</sub>) and 1-Butyl-3-Methylimmidazoliumhexafluorophosphate [PF<sub>6</sub>

This study reported the preparation and characterization of gel polymer electrolyte (GPE) using poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP), lithium perchlorate (LiClO4) and 1-butyl-3-metilimmidazoliumhexafluorophosphate [PF6]. The GPE were prepared by solution casting technique. [Bmim] [PF6] ionic liquid is used as an additive for the purpose of increasing the ionic conductivity of GPE. Morphological analysis showed that the electrolyte gel polymer sample had a smooth and flat surface with the addition of [Bmim] [PF6] and no phase separation effect was observed. This shows the compatibility between PVdF-HFP and [Bmim] [PF6]. ATR-FTIR analysis showed that C-F bond related peaks experienced peak changes in terms of intensity and peak shifting. This proves the interaction of the imidazolium ion with the fluorine atom through the formation of coordinate bonds. Ionic conductivity analysis showed that PVdF-HFP-[Bmim][PF6] samples reached a maximum room temperature ionic conductivity value of 2.44 × 10-4 S cm-1 at 60 wt.% [Bmim] [PF6]. When 20 wt.% of LiClO4 added to the system, the ionic conductivity increased one magnitude order to 2.20 × 10-3 S cm-1.

Gel Electrolytes Incorporated with Graphene-Oxide Quantum Dots for High Performance in Lithium Ion Batteries

This study incorporates graphene oxide quantum dots (GOQDs) in to a gel polymer electrolyte (GPE) designed for lithium ion batteries (LIBs). The GPE comprises poly(acrylonitrile-co-vinyl acetate) copolymer (PVA) blending poly(methyl methacrylate) (PMMA) as a host swelled by a liquid electrolyte (LE) of 1-M LiPF6 in a carbonate solvent. The major concerns for GPE-based LIBs is the capacity retention and cycle life under high-rate operation. Among numerous functional polymer segments used for GPEs,1 poly(acrylonitrile) (PAN) exhibits excellent thermal stability, ion-solvating ability, material processibility, and electrochemical stability,2 whereas poly(vinyl acetate) (PVAc) strongly absorbs solvent molecules to facilitate polymer swelling and ion transport. The segmental motion of PVA can be further promoted by blending PMMA; therefore, the polymer framework developed in this study represents an ideal host for GPEs. Previous studies have used inorganic oxide nanoparticles, such as SiO2, TiO2, Al2O3, ZrO2, as fillers to improve both the mechanical strength and ionic conductivity of GPEs.3 GOQDs,which contain numerous oxygen functional groups on the surface, have strong affinity to polymer chains for uniform dispersion in GPEs. The present study finds that the incorporated GOQDs substantially increase the mobility of lithium ions in the developed GPE by accelerating lithium-ion hopping along the polymer chains. A resulting Li/GPE/LiFePO4 battery delivers a high discharge capacity of 70 mAh g-1 at 17 C-rate, which is much higher than that of a Li/LE/LiFePO4 battery (35 mAh g-1). References P. Hu, Y. Duan, D. Hu, B. Qin, J. Zhang, Q. Wang, Z. Liu, G. Cui, L. Chen, ACS Appl. Mater. Interfaces 2015, 7, 4720-4727.S.H. Wang, P.L Kuo, C.T Hsieh, H. Teng, ACS Appl. Mater. Interfaces 2014, 6, 19360−19370M. Osińska, T. Jesionowski, K. S-S. Tefańska, M. Walkowiak, Cent. Eur. J. Chem. 2010,8(6),1311-1317 Acknowledgments: This research was supported by the Ministry of Science and Technology, Taiwan (104-2221-E-006-231-MY3, 104-2221-E-006-234-MY3, 105-3113-E-006-005, and 104-3113-E-006-011-CC2), and by the Ministry of Education, Taiwan, The Aim for the Top University Project to the National Cheng Kung University.

Interfacial compatibility of gel polymer electrolyte and electrode on performance of Li-ion battery

Interfacial compatibility of composite polymer electrolyte and electrode is the key factor to affect the performance of polymer Li-ion batteries. In this work, liquid electrolyte, pristine PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) gel polymer electrolyte (GPE) and nano-TiO2-poly(methyl methacrylate) (PMMA) hybrid doped PVDF-HFP composite polymer electrolyte (CPE) are used to investigate the interfacial compatibility between electrolyte and electrode on performance of LiCoO2/Li cells. The electrochemical performances of cells are studied by charge/discharge tests and electrochemical impedance. The interfacial compatibility coefficient (λ) that related to the interface of electrolyte and electrode is evaluated in terms of the fitting (i=e, sf, b and ct) with equivalent circuit and diffusion resistance (Rdiff). The results confirm that the C-rare performance of cells with GPE is more significantly associated with the interfacial compatibility than the ionic conductivity of GPE.

Synthesis and properties of gel polymer electrolyte membranes based on novel comb-like methyl methacrylate copolymers

Based on the principle of molecular design, three comb-like methyl methacrylate copolymer matrixes for gel polymer electrolyte (GPE) were designed and synthesized by reacting methyl methacrylate-maleic anhydride copolymer (P(MMA-MAh)) with poly(ethylene glycol) monomethyl ether (PEGME) of different molecular weight (350, 600, and 750) respectively. The structures of comb-like polymers were characterized by Fourier transform infrared (FTIR) and 1H-nuclear magnetic resonance ( 1H NMR), and their thermal properties were investigated with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The membranes of P(MMA-MAh) copolymer and comb-like copolymer based polymer electrolytes, plasticized with propylene carbonate (PC) and LiClO 4 as salt, have been prepared by solution casting technique respectively. And AC impedance was used to characterize the ion conductivity of GPE systems. Compared with P(MMA-MAh) copolymer, introducing the flexible ether chain segments can reduce the resistance of ion transport in polymer matrix and improve the mobility of electroactive ions in the GPE systems. With the increase in side chain length of copolymers, ionic conductivity of GPEs is improved dramatically. The highest conductivity observed in MMA/MAh-g-PEGME600 GPE system (matrix content: 45 wt%) is 1.22 × 10 −3 S/cm at 60 °C. And temperature dependence of GPE membranes could be described by Vogel–Tamman–Fulcher (VTF) behavior. TGA curves showed that these gel polymer electrolyte membranes possessed favorable thermal stability for lithium ion battery use.