Electrospun poly(lithium 2‐acrylamido‐2‐methylpropanesulfonic acid) fiber‐based polymer electrolytes for lithium‐ion batteries

Novel single‐ion conducting polymer electrolytes based on electrospun poly(lithium 2‐acrylamido‐2‐methylpropanesulfonic acid) (PAMPSLi) membranes were prepared for lithium‐ion batteries. The preparation started with the synthesis of polymeric lithium salt PAMPSLi by free‐radical polymerization of 2‐acrylamido‐2‐methylpropanesulfonic acid, followed by ion‐exchange of H⁺ with Li⁺. Then, the electrospun PAMPSLi membranes were prepared by electrospinning technology, and the resultant PAMPSLi fiber‐based polymer electrolytes were fabricated by immersing the electrospun membranes into a plasticizer composed of ethylene carbonate and dimethyl carbonate. PAMPSLi exhibited high thermal stability and its decomposition did not occur until 304°C. The specific surface area of the electrospun PAMPSLi membranes was raised from 9.9 m²/g to 19.5 m²/g by varying the solvent composition of polymer solutions. The ionic conductivity of the resultant PAMPSLi fiber‐based polymer electrolytes at 20°C increased from 0.815 × 10^?5 S/cm to 2.12 × 10^?5 S/cm with the increase of the specific surface area. The polymer electrolytes exhibited good dimensional stability and electrochemical stability up to 4.4 V vs. Li⁺/Li. These results show that the PAMPSLi fiber‐based polymer electrolytes are promising materials for lithium‐ion batteries. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Self‐Diffusion Coefficients in Solutions of Lithium Bis(fluorosulfonyl)imide with Dimethyl Carbonate and Ethylene Carbonate

Organic solutions of lithium bis(fluorosulfonyl)imide (LiFSI) are promising electrolytes for Li‐ion batteries. Information on the diffusion coefficients of the species in these solutions is needed for battery design. Therefore, the self‐diffusion coefficients in such solutions were studied experimentally with the pulsed‐field gradient nuclear magnetic resonance technique. The self‐diffusion coefficients of the ions Li⁺ and FSI^? as well as those of the solvents were measured for LiFSI solutions in pure dimethyl carbonate and ethylene carbonate as well as in mixtures of these solvents at 298 K and ambient pressure. Despite the Li⁺ ion being the smallest species in the solution, its self‐diffusion coefficient is the lowest as a result of its strong coordination with the solvent molecules.     

Solid‐state single‐ion conducting comb‐like siloxane copolymer electrolyte with improved conductivity and electrochemical window for lithium batteries

Achievement of high conductivity and electrochemical window at ambient temperature for an all‐solid polymer electrolyte used in lithium ion batteries is a challenge. Here, we report the synthesis and characterization of a novel solid‐state single‐ion electrolytes based on comb‐like siloxane copolymer with pendant lithium 4‐styrenesulfonyl (perfluorobutylsulfonyl) imide and poly(ethylene glycol). The highly delocalized anionic charges of ? SO₂? N^(–)? C₄F₉ have a weak association with lithium ions, resulting in the increase of mobile lithium ions number. The designed polymer electrolytes possess ultra‐low glass transition temperature in the range from ?73 to ?54 °C due to the special flexible polysiloxane. Promising electrochemical properties have been obtained, including a remarkably high conductivity of 3.7 × 10^?5 S/cm and electrochemical window of 5.2 V (vs. Li⁺/Li) at room temperature. A high lithium ion transference number of 0.80, and good compatibility with anode were also observed. These prominent characteristics endow the polymer electrolyte a potential for the application in high safety lithium ion batteries. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45848.     

Bifunctional poly(ethylene glycol) based crosslinked network polymers as electrolytes for all‐solid‐state lithium ion batteries

Polymer electrolyte based lithium ion batteries represent a revolution in the battery community due to their intrinsic enhanced safety, and as a result polymer electrolytes have been proposed as a replacement for conventional liquid electrolytes. Herein, the preparation of a family of crosslinked network polymers as electrolytes via the ‘click‐chemistry’ technique involving thiol‐ene or thiol‐epoxy is reported. These network polymer electrolytes comprise bifunctional poly(ethylene glycol) as the lithium ion solvating polymer, pentaerythritol tetrakis (3‐mercaptopropionate) as the crosslinker and lithium bis(trifluoromethane)sulfonimide as the lithium salt. The crosslinked network polymer electrolytes obtained show low T_g, high ionic conductivity and a good lithium ion transference number (ca 0.56). In addition, the membrane demonstrated sterling mechanical robustness and high thermal stability. The advantages of the network polymer electrolytes in this study are their harmonious characteristics as solid electrolytes and the potential adaptability to improve performance by combining with inorganic fillers, ionic liquids or other materials. In addition, the simple formation of the network structures without high temperatures or light irradiation has enabled the practical large‐area fabrication and in situ fabrication on cathode electrodes. As a preliminary study, the prepared crosslinked network polymer materials were used as solid electrolytes in the elaboration of all‐solid‐state lithium metal battery prototypes with moderate charge–discharge profiles at different current densities leaving a good platform for further improvement. © 2018 Society of Chemical Industry     

Effect of surface modified porous inorganic-organic hybrid polyphosphazene nanotubes on the properties of polyethylene oxide based solid polymer electrolytes

2-(2-methyloxyethoxy)ethanol modified poly (cyclotriphosphazene-co-4,4′-sufonyldiphenol) (PZS) nanotubes were synthesized and solid composite polymer electrolytes based on the surface modified polyphosphazene nanotubes added to PEO/LiClO₄ model system were prepared. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) were used to investigate the characteristics of the composite polymer electrolytes (CPE). The ionic conductivity, lithium ion transference number and electrochemical stability window can be enhanced after the addition of surface modified PZS nanotubes. The electrochemical investigation shows that the solid composite polymer electrolytes incorporated with PZS nanotubes have higher ionic conductivity and lithium ion transference number than the filler SiO₂. Maximum ionic conductivity values of 4.95 × 10⁻⁵ S cm⁻¹ at ambient temperature and 1.64 × 10⁻³ S cm⁻¹ at 80 °C with 10 wt % content of surface modified PZS nanotubes were obtained and the lithium ion transference number was 0.41. The good chemical properties of the solid state composite polymer electrolytes suggested that the inorganic-organic hybrid polyphosphazene nanotubes had a promising use as fillers in solid composite polymer electrolytes and the PEO₁₀-LiClO₄-PZS nanotubes solid composite polymer electrolyte can be used as a candidate material for lithium polymer batteries.     

Polymerized ionic liquids with guanidinium cations as host for gel polymer electrolytes in lithium metal batteries

Polymerized ionic liquids (PILs) having guanidinium cations with different counter‐anions, such as PF₆^? and N(CF₃SO₂)₂^? (TFSI^?), were synthesized by copolymerization of a guanidinium ionic liquid monomer with methyl acrylate followed by an anion exchange reaction. Furthermore, incorporating a guanidinium ionic liquid, LiTFSI salt and nano‐size SiO₂, a quaternary gel polymer electrolyte based on one of the PILs as the polymer host was prepared. The quaternary gel polymer electrolyte was chemically stable even at a higher temperature of 80 °C in contact with the lithium anode. In particular, the electrolyte exhibited high lithium ion conductivity, wide electrochemical stability window and good lithium stripping/plating performance. Li/LiFePO₄ batteries with the quaternary gel polymer electrolyte at 80 °C had capacities of 140 and 130 mA h g^?1 respectively at 0.1 and 0.2 C current rates. Copyright © 2011 Society of Chemical Industry     

Compositional Effects on Structure and Transport Properties in a Polyelectrolyte Gel

The copolymerization of lithium 2‐acrylamido‐2‐methyl‐1‐propane sulfonate (LiAMPS) with N,N ′‐dimethylacrylamide has yielded polyelectrolyte systems which can be gelled with an ethylene carbonate/N ′,N ′‐dimethylacetamide solvent mixture and show high ionic conductivities. ⁷Li linewidth and relaxation times as well as ¹H NMR diffusion coefficients have been used to investigate the effect of copolymer composition as well as copolymer concentration in the gel electrolyte with respect to ionic transport and polyelectrolyte structure. It appears that ion association is likely even in the case of low lithium salt concentration; however a rapid exchange exists between the associated and non‐associated lithium species. Beyond 0.2 M of LiAMPS, both the conductivity and solvent diffusion reach a plateau, whilst lithium ion linewidth and spin‐spin relaxation are suggestive, on average, of a less mobile species. The thermal analysis data is also supportive of this association effectively leading to a form of phase separation on the nanoscale, which gives a lower overall activity of lithium ions in the solvent rich regions beyond about 0.2 M of LiAMPS, thereby leading to an increase in the final liquidus temperature of the binary liquid solvent from –9 to +5°C.     

Lewis acid–base property of P(VDF‐co‐HFP) measured by inverse gas chromatography

Poly (vinylidene fluoride‐co‐hexafluoropropylene) P(VDF‐co‐HFP) is an excellent material for polymer electrolytes of lithium ion battery. To enhance the lithium ion transference number, some metal oxides were often embedded into P(VDF‐co‐HFP). The promising mechanism for the increase in lithium ionic conductivity was Lewis acid‐base theory. In this experiment, the Lewis acid–base properties of P(VDF‐co‐HFP) were measured by inverse gas chromatography (IGC). The Lewis acid constant K_a of P(VDF‐co‐HFP) is 0.254, and the base constant K_b is 1.199. Compared with other polymers characterized by IGC, P(VDF‐co‐HFP) is the strongest Lewis basic polymers. Except aluminum ion, lithium ion is the strongest Lewis acidic ion according to their η value of Lewis acids. Therefore, a strong Lewis acid–base interaction will exist between lithium ion and P(VDF‐co‐HFP). This will restrict the transference of lithium ion in P(VDF‐co‐HFP). To enhance the lithium ion transference by blending other metal ions into P(VDF‐co‐HFP), it is suggested that the preferential ions should be Al³⁺, Mg²⁺, Na⁺, and Ca²⁺ because these metal ions have relative large η values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of homogeneously sulfonated poly(ether ether ketone) membranes: Effect of casting solvent

Poly(ether ether ketone) (PEEK) was homogeneously sulfonated to have various degrees of sulfonation from 48 to 83%. The sulfonated PEEK (sPEEK) membranes were prepared by a solvent casting method using a few solvents such as N,N‐dimethyl formamide, N,N‐dimethyl acetamide, and 1‐methyl‐2‐pyrrolidinone. The effect of casting solvent on the membrane morphology and properties was investigated. The sulfonation degree and ion exchange capacity were determined by a back titration method, and the morphology of membrane by SEM. It has been demonstrated that the surface morphology and properties of sPEEK membranes, such as water uptake, methanol permeability, ion conductivity, and mechanical strength, were considerably affected by the type of solvent, where the DMAC‐sPEEK system showed the best performance in the polymer electrolyte membrane application for DMFC. This solvent effect on the membrane morphology and properties was caused by interaction strength (hydrogen bonding) between polymer and solvent. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Single ion conductive characteristics of poly(organoboron halide)-imidazole complex

Summary Poly(organoboron halide)-imidazole complex was prepared by hydroboration polymerization of 1,7-octadiene with monobromoborane-methylsulfide complex and subsequent polymer reaction with 1-methylimidazole and methanol. The ion conductive characteristics of the polymer was evaluated by ac impedance method. The optimized concentration of lithium salt was 100 unitmol% to methoxyboron unit. In the presence of lithium bis(trifluoromethane sulfone) imide (LiTFSI), the polymer complex composed of approximately 50% methoxyboron unit exhibited ionic conductivity of 2.59×1O^-5S/cm at 50°C. The lithium ion transference number for this system was calculated to be 0.47, indicating that anions were significantly trapped by Lewis acidic methoxyboron unit.     

Transport Properties of Ion‐Exchange Membranes During Pervaporation of Water‐Alcohol Mixtures

Abstract

Pervaporation properties of PESS ion‐exchange membranes in contact with water‐aliphatic alcohol mixtures were obtained. PESS ion‐exchange membranes were prepared by chemical modification of the interpenetrating polymer network system polyethylene‐poly(styrene‐co‐divinylbenzene). PESS membranes were loaded with different alkali metal ions as counterions. The obtained data showed that properties of PESS membranes depended strongly on the kind of counterions, degree of crosslinking, and difference in the polarities between water and organic component of the binary mixture. Results obtained for PESS membranes were compared with data obtained for Nafion 117 ion‐exchange membrane.     

Novel polymeric systems for lithium ion batteries gel electrolytes: II. Hybrid cross-linked poly(fluorosilicone-ethyleneoxide)

Cross-linked, self-supporting, membranes for lithium ion battery gel electrolytes were obtained by cross-linking a mixture of polyfluorosilicone (PFSi) and polysilicone containing ethylene oxide (EO) units [P(Si-EO)]. The membranes were also reinforced with nanosized silica. The two polymer precursors were synthesized with functional groups capable to form inter-molecular cross-linking, thus obtaining three-dimensional, polymer matrices. The precursors were dissolved in a common solvent and cross-linked to obtain free-standing PFSi/P(Si-EO):SiO₂ composite films. The latter were undergone to swelling processes in (non-aqueous, aprotic, lithium salt containing) electrolytic solutions to obtain gel-type polymer electrolytes. The properties of the swelled PFSi/P(Si-EO):SiO₂ samples were evaluated as a function of the electrolytic solutions and the dipping time. The PFSi/P(Si-EO):SiO₂ membranes exhibited large swelling properties, high ionic conductivity and good electrochemical stability.     

Pervaporation separation of water–ethanol mixtures using metal‐ion‐exchanged poly(vinyl alcohol) (PVA)/sulfosuccinic acid (SSA) membranes

Poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) membranes in the hydrogen form were converted to monovalent metal ion forms Li⁺, Na⁺, and K⁺. The effect of exchange with metal ions was investigated by measuring the swelling of water–ethanol (10/90) mixtures at 30 °C and by the pervaporative dehydration performance test for aqueous ethanol solutions with various ethanol concentrations at 30, 40, and 50 °C. In addition, electron spectroscopy for chemical analysis (ESCA) analysis was carried out to study the quantity of metal ions in membranes. From the ESCA analysis, the lithium ion quantity in the resulting membranes is greater than that of any other metal ions in question because of the easy diffusion of a smaller metal ion into the membrane matrix. The swelling ratio was in the following order: PVA/SSA‐Li⁺ > PVA/SSA‐Na⁺ > PVA/SSA‐K⁺ membranes. For pervaporation, the PVA/SSA‐Na⁺ membrane showed the lowest flux and highest separation factor for all aqueous ethanol solutions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1867–1873, 2002     

Comparative studies on the effects of casting solvent on physico‐chemical and gas transport properties of dense polysulfone membrane used for CO2/CH4 separation

The effects of casting solvents on the physico–chemical and transport properties of polysulfone membranes were investigated. Comparative analysis of the properties of membranes prepared from a new solvent (diethylene glycol dimethyether, DEG) and other commonly used solvents (1‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, dimethyl sulfoxide and N,N‐dimethylformamide) were performed using gas permeation, X‐ray diffraction, scanning electron microscopy, thermogravimetric, and Fourier transform infrared spectroscopy analyses. The degree of polymer–solvent interaction was evaluated using the solvent molar volume, and Hansen and Flory–Huggins parameters. Membrane prepared from DEG displayed a relatively higher permeability of 29.08 barrer and CO₂/CH₄ selectivity of 23.12 compared to membranes prepared from other solvents. This improved performance was attributed to the better interaction between the DEG solvent and polysulfone than other solvents that were considered. DEG has the highest molar volume of 142.280 cm³/mol and the lowest Flory–Huggins parameter of 0.129. Thus a thorough evaluation of polymer–solvent interaction is very crucial in preparing membranes with optimum performance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42205.     

Heterogeneously doped polyethylene glycol as nano-composite soft matter electrolyte

We have applied the concept of heterogeneous doping [1] to prepare and examine composite electrolytes, consisting of silica particles, low molecular weight polyethylene glycol solvents and lithium perchlorate salt. These “soggy sand” electrolytes combine high ionic conductivities (on the order of mS cm⁻¹) and high Li transference numbers (typically 60–80%) with improved mechanical properties. They were characterized using differential scanning calorimetry, dc-polarization and ac-impedance spectroscopy, zeta potential measurements and viscosimetry. Oxide, size and concentration as well as solvent molecular weight were varied to better understand the influence of ceramic oxide fillers on the ion conduction in these systems. As regarding the filler content, we observe that both conductivity and transference number of Li⁺ start increasing already at low volume fractions of oxide particles, reach a maximum and subsequently decrease to low values. The percolating network is – after initial partial coarsening – found to be stable within the time periods of the measurements.     

ForceSpinning of polyacrylonitrile for mass production of lithium‐ion battery separators

We present results on the Forcespinning^® (FS) of Polyacrylonitrile (PAN) for mass production of polymer nanofiber membranes as separators for Lithium‐ion batteries (LIBs). Our results presented here show that uniform, highly fibrous mats from PAN produced using Forcespinning^®, exhibit improved electrochemical properties such as electrolyte uptake, low interfacial resistance, high oxidation limit, high ionic conductivity, and good cycling performance when used in lithium ion batteries compared to commercial PP separator materials. This article introduces ForceSpinning^®, a cost effective technique capable of mass producing high quality fibrous mats, which is completely different technology than the commonly used in‐house centrifugal method. This Forcespinning^® technology is thus the beginning of the nano/micro fiber revolution in large scale production for battery separator application. This is the first time to report results on the cycle performance of LIB‐based polymer nanofiber separators made by Forcespinning^® technology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42847.     

Hybrid Cation Exchange Membranes with Lithium Ion‐Sieves for Highly Enhanced Li+ Permeation and Permselectivity

Cation exchange membranes (CEMs) hold promise for efficient and environment‐friendly lithium extraction from salt‐lake brine. However, development and practical application of CEMs are significantly hindered by the low Li⁺ permeation and permselectivity. Herein, novel hybrid CEMs are developed by dispersing lithium ion‐sieves (LMO) into sulfonated poly(ether ether ketone) matrix. Two kinds of LMOs are synthesized including acidified LMO (HMO) and its sulfonation compound (HMO‐S). The physicochemical property and separation performance of hybrid membranes are systematically investigated. The uniformly dispersed HMO and HMO‐S enhance the thermal, mechanical stability, and swelling resistance of hybrid membranes. Furthermore, these fillers obviously reduce the area resistance from 8.0 to less than 6.0 Ω cm^?2. Importantly, the unique Li⁺ transfer channels in HMO/HMO‐S efficiently elevate the Li⁺ permeation by up to 66%. While the “ion‐sieve effect” of the channels weakens the migration of Mg²⁺ and K⁺, thus notably rising Li⁺/Mg²⁺ and Li⁺/K⁺ permselectivities by ≈5 times, which is difficult to realize with conventional fillers. Comparing with HMO, HMO‐S shows higher improvement for permselectivity because of the reduced area resistance of the resultant hybrid membrane. This study paves a way to design and development of selective Li⁺ exchange membranes for transport and separation applications.     

Morphology,crystallinity, and electrochemical properties of in situ formed poly(ethylene oxide)/TiO2 nanocomposite polymer electrolytes

A method to produce nanocomposite polymer electrolytes consisting of poly(ethylene oxide) (PEO) as the polymer matrix, lithium tetrafluoroborate (LiBF₄) as the lithium salt, and TiO₂ as the inert ceramic filler is described. The ceramic filler, TiO₂, was synthesized in situ by a sol–gel process. The morphology and crystallinity of the nanocomposite polymer electrolytes were examined by scanning electron microscopy and differential scanning calorimetry, respectively. The electrochemical properties of interest to battery applications, such as ionic conductivity, Li⁺ transference number, and stability window were investigated. The room‐temperature ionic conductivity of these polymer electrolytes was an order of magnitude higher than that of the TiO₂ free sample. A high Li⁺ transference number of 0.51 was recorded, and the nanocomposite electrolyte was found to be electrochemically stable up to 4.5 V versus Li⁺/Li. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2815–2822, 2003     

Preparation and properties of a novel green solid polymer electrolyte for all-solid-state lithium battery

Solid polymer electrolyte (SPE)-based lithium batteries have easy processing and safety for energy vehicles and storage. However, the preparation process of SPEs mostly used a lot of organic solvents, which will threaten human living space and body health. Herein, a novel green solid polymer electrolyte (ionic liquid type waterborne polyurethane, IWPUS) without no organic solvents was prepared from hybrids of ionic liquid-based waterborne polyurethane (IWPU) and LiClO₄. The structure and properties of IWPUS were investigated by IR, SEM, XRD, TGA, ion conductivity test. The results showed that Li⁺ of LiClO₄ could coordinate with  CO and  C O C in the polyurethane matrix. LiClO₄ had been well dispersed in IWPU. The conductivity of IWPUS increased with the increase of LiClO₄ content. The higher conductivity of IWPUS with 20% LiClO₄ at 80°C was 1.8 × 10⁻⁴ s•cm⁻¹. IWPUS based on ionic liquid-based waterborne polyurethane would be promised to become an environmentally friendly candidate for all solid-state lithium ion batteries.     

Novel electrospun polymer electrolytes incorporated with Keggin‐type hetero polyoxometalate fillers as solvent‐free electrolytes for lithium ion batteries

In this study, solvent‐free nanofibrous electrolytes were fabricated through an electrospinning method. Polyethylene oxide (PEO), lithium perchlorate and ethylene carbonate were used as polymer matrix, salt and plasticizer respectively in the electrolyte structures. Keggin‐type hetero polyoxometalate (Cu‐POM@Ru‐rGO, Ni‐POM@Ru‐rGO and Co‐POM@Ru‐rGO (POM, polyoxometalate; rGO, reduced graphene oxide)) nanoparticles were synthesized and inserted into the PEO‐based nanofibrous electrolytes. TEM and SEM analyses were carried out for further evaluation of the synthesized filler structures and the electrospun nanofibre morphologies. The fractions of free ions and crystalline phases of the as‐spun electrolytes were estimated by obtaining Fourier transform infrared and XRD spectra, respectively. The results showed a significant improvement in the ionic conductivity of the nanofibrous electrolytes by increasing filler concentrations. The highest ionic conductivity of 0.28 mS cm^?1 was obtained by the introduction of 0.49 wt% Co‐POM@Ru‐rGO into the electrospun electrolyte at ambient temperature. Compared with solution‐cast polymeric electrolytes, the electrospun electrolytes present superior ionic conductivity. Moreover, the cycle stability of the as‐spun electrolytes was clearly improved by the addition of fillers. Furthermore, the mechanical strength was enhanced with the insertion of 0.07 wt% fillers to the electrospun electrolytes. The results implied that the prepared nanofibres are good candidates as solvent‐free electrolytes for lithium ion batteries. © 2020 Society of Chemical Industry