Morphology and ionic conductivity of solid polymer electrolytes based on polyurethanes with various topological structures

Polyurethanes with linear, hyperbranched and comb-crosslinked structures were synthesized and were used to prepare solid polymer electrolytes. The polymer electrolytes were characterized by means of Fourier transform Raman spectroscopy, impedance spectroscopy (IS) and atomic force microscopy (AFM). The results showed that salt concentration significantly influences the morphology and conductivity of the three kinds of polyurethane/LiClO₄ system. When the mole ratios of the ether oxygen atom to lithium ion were controlled to be 12, 4 and 4 respectively for linear, hyperbranched and comb cross-linking polyurethane, the electrolytes typically displayed micro-phase separated morphology and the ionic conductivity also reached maxima respectively at 2.2 × 10^–7 S/cm, 2.8 × 10^–6 S/cm and 2.8 × 10^–5 S/cm at room temperature.     

Novel PEO-based composite solid polymer electrolytes incorporated with active inorganic–organic hybrid polyphosphazene microspheres

Inorganic–organic hybrid poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) microspheres with active hydroxyl groups were incorporated in poly(ethylene oxide) (PEO), using LiClO₄ as a dopant salt, to form a novel composite polymer electrolyte (CPE). The polymer chain flexibility and crystallinity properties are studied by DSC. The effects of active PZS microspheres on the electrochemical properties of the PEO-based electrolytes, such as ionic conductivity, lithium ion transference number, and electrochemical stability window are studied by electrochemical impedance spectroscopy and steady-state current method. Maximum ionic conductivity values of 3.36 × 10⁻⁵ S cm⁻¹ at ambient temperature and 1.35 × 10⁻³ S cm⁻¹ at 80 °C with 10 wt.% content of active PZS microspheres were obtained and the lithium ion transference number was 0.34. The experiment results showed that the inorganic–organic hybrid polyphosphazene microspheres with active hydroxyl groups can enhance the ionic conductivity and increase the lithium ion transference number of PEO-based electrolytes more effectively comparing with traditional ceramic fillers such as SiO₂.     

Performance enhancement induced by electrospinning of polymer electrolytes based on poly(methyl methacrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium)

A series of novel fibrous polymer electrolytes with high ionic conductivity based on electrospun poly(methyl methacrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium) (P(MMA-co-AMPSLi)) membranes were prepared and characterized. P(MMA-co-AMPSLi) was synthesized by free radical copolymerization of MMA and AMPS, followed by ion exchange of the H⁺ with Li⁺. The fibrous polymer electrolytes were fabricated by immersing the electrospun P(MMA-co-AMPSLi) membranes into the liquid electrolyte. Fourier transform infrared spectroscopy and ¹H-nuclear magnetic resonance were used to characterize the structure of the copolymers. Thermogravimetric analysis was applied to investigate the thermal properties of the copolymers. Scanning electromicroscope was employed to observe the morphology of electrospun membranes before and after soaking the liquid electrolyte. AC impedance and linear sweep voltammetry were adopted to measure the electrochemical properties of the fibrous polymer electrolytes. The incorporation of the AMPSLi units effectively improved the electrospinnability of the copolymer, increased the dielectric constants of the electrospun membranes, and enhanced the dimensional stability by maintaining the pore structures even after the membranes absorbing large amounts of liquid electrolytes. As a result, the ionic conductivity of the polymer electrolytes increased with the increase in the molar ratio of AMPSLi units, and the highest ion conductivity was up to 4.12 × 10⁻³ S cm⁻¹ at room temperature. Meanwhile, the polymer electrolytes studied in this work exhibited a sufficient electrochemical stability (up to 5.0 V) that allows the safe operation in lithium-ion batteries.     

Sandwich-Structured Quasi-Solid Polymer Electrolyte Enables High-Capacity,Long-Cycling,and Dendrite-Free Lithium Metal Battery at Room Temperature

The insufficient ionic conductivity, limited lithium-ion transference number (t_Li+), and high interfacial impedance severely hinder the practical application of quasi-solid polymer electrolytes (QSPEs). Here, a sandwich-structured polyacrylonitrile (PAN) based QSPE is constructedin which MXene-SiO₂ nanosheets act as a functional filler to facilitate the rapid transfer of lithium-ion in the QSPE, and a polymer and plastic crystalline electrolyte (PPCE) interface modification layer is coated on the surface of the PAN-based QSPE of 3 wt.% MXene-SiO₂ (SS-PPCE/PAN-3%) to reduce interfacial impedance. Consequently, the synthesized SS-PPCE/PAN-3% QSPE delivers a promising ionic conductivity of ≈1.7 mS cm⁻¹ at 30 °C, a satisfactory t_Li+ of 0.51, and a low interfacial impedance. As expected, the assembled Li symmetric battery with SS-PPCE/PAN-3% QSPE can stably cycle more than 1550 h at 0.2 mA cm⁻². The Li||LiFePO₄ quasi-solid-state lithium metal battery (QSSLMB) of this QSPE exhibits a high capacity retention of 81.5% after 300 cycles at 1.0 C and at RT. Even under the high-loading cathode (LiFePO₄ ≈ 10.0 mg cm⁻²) and RT, the QSSLMB achieves a superior area capacity and good cycling performance. Besides, the assembled high voltage Li||NMC811(loading ≈ 7.1 mg cm⁻²) QSSLMB has potential applications in high-energy fields.     

Impedance studies on plasticized PMMA-LiX [X: CF3SO3, N(CF3SO2)2−] polymer electrolytes

Plasticized polymer electrolytes composed of poly(methylmethacrylate) (PMMA) as the host, propylene carbonate (PC) or ethylene carbonate (EC) as a plasticizer and LiX (X: CF₃SO₃⁻ or N(CF₃SO₂)₂⁻) as a salt were prepared by the solution cast technique. Impedance spectroscopy was performed in the temperature range between 303 and 383 K. In this paper, we report the electrical properties of polymer electrolytes with different lithium salts and plasticizers. The polymer electrolytes investigated exhibited high ionic conductivity at room temperature in the range of 10^− 6 to 10^− 4 S cm^− 1. The temperature dependence studies showed that the samples were ionic conductors and seemed to obey the Vogel-Tamman-Fulcher (VTF) rule. FTIR spectroscopy studies confirmed the polymer-salt interaction.     

Impact of ethylene carbonate on ion transport characteristics of PVdF-AgCF3SO3 polymer electrolyte system

The ionic transport in thin film plasticized polymer electrolytes based on polyvinylidene fluoride (PVdF) as the polymer host, silver triflate (AgCF₃SO₃) as salt and ethylene carbonate (EC) as plasticizer prepared by solution casting technique has been reported. Addition of silver triflate has resulted in an increase in the room temperature (298 K) electrical conductivity of the polymer from 10⁻⁶ to 10⁻⁵ S cm⁻¹ whereas incorporation of EC as the plasticizer has further enhanced the conductivity value by an order of magnitude to 10⁻⁴ S cm⁻¹ owing to the possible decrease in crystallinity of the polymer matrix as revealed by the detailed temperature-dependent complex impedance, silver ionic transference number, Fourier transform infrared and X-ray diffraction measurements.     

PAN–PEO solid polymer electrolytes with high ionic conductivity

The transparent and flexible solid polymer electrolytes (SPEs) are fabricated from polyacrylonitrile–polyethylene oxide (PAN–PEO) copolymer. The formation of the copolymer is confirmed by Fourier-transform infrared spectroscopy (FTIR) and Gel permeation chromatography (GPC) measurements. The effects of acrylonitrile (AN) wt% content and M_n(PEO) on ionic conductivity are investigated by alternating current (ac) impedance spectroscopy. By controlling and adjusting the AN wt% content and doping PEO with high molecular weight, the ionic conductivity of SPEs is optimized. The ionic conductivity of PAN–PEO solid polymer electrolytes is found to be high 6.79 × 10⁻⁴ S cm⁻¹ at 25 °C with an [EO]/[Li] ratio of about 10, and are electrochemically stable up to about 4.8 V versus Li/Li⁺. The conductivity and interfacial resistance remain almost constant even at 80 °C.     

Fast Li+ ion conduction in Li2O–(Al2O3 Ga22O3)–TiO2–P2O5 glass–ceramics

Fast lithium ionic conducting glass-ceramics have been obtained by heat-treatment of glasses in the systems Li₂O–M₂O₃–TiO₂–P₂O₅ (M = Al and Ga). The glass–ceramics were mainly composed of LiTi₂(PO₄)₃ in which Ti⁴⁺ ions were partially replaced by M³⁺ ions. Considerable enhancement of the conductivity with the substitution of M³⁺ ions for Ti⁴⁺ ions was observed. The maximum conductivity obtained at room temperature was 1.3 × 10^–3 S cm^–1 for the aluminium system and 9 × 10^–4 S cm^–1 for the gallium system.     

Study of enhanced dissociation of aliphatic dicarboxylic acids with PVdF addition in polymer gel electrolytes

The ionic conductivity of non-aqueous polymer gel electrolytes containing weak aliphatic dicarboxylic acids has been found to depend upon the dissociation constant of the acid used and conductivity of (1–2) × 10⁻³ S/cm has been obtained at 25^∘C. The addition of polyvinylidenefluoride (PVdF) to the solution electrolytes containing different dicarboxylic acids results in an increase in conductivity, which depends upon the concentration of polymer and acid present in these electrolytes. The enhancement of conductivity with PVdF addition has been explained to be due to the dissociation of undissociated acid present in the electrolytes which results in an increase in free H⁺ ion concentration and has been studied by pH measurements. The variation of viscosity with acid and polymer concentration and temperature has also been studied and viscosity increases exponentially at high PVdF concentrations and plays a dominant role at high PVdF concentrations.     

UV-cured hybrid inorganic-organic polymer electrolyte based on organically modified polysiloxane

Hybrid inorganic-organic polymer electrolyte based on the monomer of organically modified polysiloxane was prepared by UV radiation curing in the presence of liquid electrolyte. The organically modified polysiloxane monomer with acrylate groups at the terminal position was synthesized by hydrolytic condensation of tetramethoxysilane (TMOS) and followed by demethanolation reaction using 2-hydroxyethyl acrylate (2-HEA). The rational formula of the monomer was SiO_1.1436(OH)_0.01606(OCH₃)_1.3394(OCH₂CH₂OCOCH= CH₂)_0.3574 which was determined by proton nuclear magnetic resonance (¹H-NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and silica analysis. The monomer was polyfunctional with a number average molecular weight of 1185 and a weight average molecular weight of 2292 determined by GPC analysis. The electrochemical properties of the hybrid inorganic-organic polymer electrolyte were determined by ac impedance spectroscopy and cyclic voltammetry. Ionic conductivity was greatly enhanced with increasing amounts of liquid electrolyte. When the polymer electrolyte contained 80 wt% liquid electrolytes, the conductivities were around 3.3 × 10^–3 S cm^–1 at 21°C and 8.0 × 10^–4 S cm^–1 even at –23°C. Interface resistance increased initially and reached a steady value after 2 days. Oxidation stability was up to 5.0 V against the lithium reference electrode and electrochemical plating/stripping of lithium on the stainless steel electrode was reversible.     

FTIR investigations on ion–ion interactions in liquid and gel polymeric electrolytes: LiCF3SO3-PC-PMMA

FTIR spectroscopy and ionic conductivity measurements have been employed to study the solvation and conduction mechanism of lithium ions in aprotic liquid electrolytes of LiCF₃SO₃-PC (lithium trifluromethanesulfonate-propylene carbonate) and gel electrolytes containing poly(methylmethacrylate) (PMMA) additionally. Cation solvation occurs via interactions between Li⁺ ions with the ring oxygens as well as the carbonyl oxygen of PC molecules over the entire salt concentration range under investigation (0.025–2 M) for both liquid and gel electrolytes. The ionic conductivity decline for concentrations 0.8 M LiCF₃SO₃-PC is attributed to the formation of ion pairs and/or triplets. Presence of (a) free CF₃SO₃ ^– ions in 0.025 and 0.05 molar LiCF₃SO₃-PC solutions, (b) the LiCF₃SO₃ structure with a monodentate coordinated lithium ion for concentrations 0.5 molar LiCF₃SO₃-PC systems and (c) ion triplets comprising two cations and an anion with a bidentate bridging structure in 2 M LiCF₃SO₃-PC electrolytes, has been established. Ionic conductivity performance concurs with our infrared results. Gel electrolytes containing upto 15 wt% of PMMA have been found to exhibit liquid like behavior but 2 M LiCF₃SO₃-PC systems that incorporate 25 wt% of polymer show a distinct Li⁺–O=C (of PMMA) interaction which is unambiguously determined from the remarkable changes observed for the _sC=O) and _s(SO₃)—the symmetric stretching vibrational modes.     

Self‐Suppression of Lithium Dendrite in All‐Solid‐State Lithium Metal Batteries with Poly(vinylidene difluoride)‐Based Solid Electrolytes

Polymer‐based electrolytes have attracted ever‐increasing attention for all‐solid‐state lithium (Li) metal batteries due to their ionic conductivity, flexibility, and easy assembling into batteries, and are expected to overcome safety issues by replacing flammable liquid electrolytes. However, it is still a critical challenge to effectively block Li dendrite growth and improve the long‐term cycling stability of all‐solid‐state batteries with polymer electrolytes. Here, the interface between novel poly(vinylidene difluoride) (PVDF)‐based solid electrolytes and the Li anode is explored via systematical experiments in combination with first‐principles calculations, and it is found that an in situ formed nanoscale interface layer with a stable and uniform mosaic structure can suppress Li dendrite growth. Unlike the typical short‐circuiting that often occurs in most studied poly(ethylene oxide) systems, this interface layer in the PVDF‐based system causes an open‐circuiting feature at high current density and thus avoids the risk of over‐current. The effective self‐suppression of the Li dendrite observed in the PVDF–LiN(SO₂F)₂ (LiFSI) system enables over 2000 h cycling of repeated Li plating–stripping at 0.1 mA cm^?2 and excellent cycling performance in an all‐solid‐state LiCoO₂||Li cell with almost no capacity fade after 200 cycles at 0.15 mA cm^?2 at 25 °C. These findings will promote the development of safe all‐solid‐state Li metal batteries.     

Interfacial Interaction of Multifunctional GQDs Reinforcing Polymer Electrolytes For All-Solid-State Li Battery

Solid-state polymer electrolytes are highly anticipated for next generation lithium ion batteries with enhanced safety and energy density. However, a major disadvantage of polymer electrolytes is their low ionic conductivity at room temperature. In order to enhance the ionic conductivity, here, graphene quantum dots (GQDs) are employed to improve the poly (ethylene oxide) (PEO) based electrolyte. Owing to the increased amorphous areas of PEO and mobility of Li⁺, GQDs modified composite polymer electrolytes achieved high ionic conductivity and favorable lithium ion transference numbers. Significantly, the abundant hydroxyl groups and amino groups originated from GQDs can serve as Lewis base sites and interact with lithium ions, thus promoting the dissociation of lithium salts and providing more ion pathways. Moreover, lithium dendrite is suppressed, associated with high transference number, enhanced mechanical properties and steady interface stability. It is further observed that all solid-state lithium batteries assembled with GQDs modified composite polymer electrolytes display excellent rate performance and cycling stability.     

Simultaneous High Ionic Conductivity and Lithium-Ion Transference Number in Single-Ion Conductor Network Polymer Enabling Fast-Charging Solid-State Lithium Battery

Developing solid-state electrolyte with sufficient ionic conduction and flexible-intimate interface is vital to advance fast-charging solid-state lithium batteries. Solid polymer electrolyte yields the promise of interfacial compatibility, yet its critical bottleneck is how to simultaneously achieve high ionic conductivity and lithium-ion transference number. Herein, single-ion conducting network polymer electrolyte (SICNP) enabling fast charging is proposed to positively realize fast lithium-ion locomotion with both high ionic conductivity of 1.1 × 10⁻³ S cm⁻¹ and lithium-ion transference number of 0.92 at room temperature. Experimental characterization and theoretical simulations demonstrate that the construction of polymer network structure for single-ion conductor not only facilitates fast hopping of lithium ions for boosting ionic kinetics, but also enables a high dissociation level of the negative charge for lithium-ion transference number close to unity. As a result, the solid-state lithium batteries constructed by coupling SICNP with lithium anodes and various cathodes (e.g., LiFePO₄, sulfur, and LiCoO₂) display impressive high-rate cycling performance (e.g., 95% capacity retention at 5 C for 1000 cycles in LiFePO₄|SICNP|lithium cell) and fast-charging capability (e.g., being charged within 6 min and discharged over than 180 min in LiCoO₂|SICNP|lithium cell). Our study provides a prospective direction for solid-state electrolyte that meets the lithium-ion dynamics for practical fast-charging solid-state lithium batteries.     

DSC and conductivity studies on PVA based proton conducting gel electrolytes

An attempt has been made in the present work to prepare polyvinyl alcohol (PVA) based proton conducting gel electrolytes in ammonium thiocyanate (NH₄SCN) solution and characterize them. DSC studies affirm the formation of gels along with the presence of partial complexes. The cole-cole plots exhibit maximum ionic conductivity (2.58 × 10⁻³ S cm⁻¹) for gel samples containing 6 wt% of PVA. The conductivity of gel electrolytes exhibit liquid like nature at low polymer concentrations while the behaviour is seen to be affected by the formation of PVA-NH₄SCN complexes upon increase in polymer content beyond 5 wt%. Temperature dependence of ionic conductivity exhibits VTF behaviour.     

Achieving Ultra-Stable All-Solid-State Sodium Metal Batteries with Anion-Trapping 3D Fiber Network Enhanced Polymer Electrolyte

All-solid-state sodium metal batteries paired with solid polymer electrolytes (SPEs) are considered a promising candidate for high energy-density, low-cost, and high-safety energy storage systems. However, the low ionic conductivity and inferior interfacial stability with Na metal anode of SPEs severely hinder their practical applications. Herein, an anion-trapping 3D fiber network enhanced polymer electrolyte (ATFPE) is developed by infusing poly(ethylene oxide) matrix into an electrostatic spun fiber framework loading with an orderly arranged metal-organic framework (MOF). The 3D continuous channel provides a fast Na⁺ transport path leading to high ionic conductivity, and simultaneously the rich coordinated unsaturated cation sites exposed on MOF can effectively trap anions, thus regulating Na⁺ concentration distribution for constructing stable electrolyte/Na anode interface. Based on such advantages, the ATFPE exhibits high ionic conductivity and considerable Na⁺ transference number, as well as enhanced interfacial stability. Consequently, Na/Na symmetric cells using this ATFPE possess cyclability over 600 h at 0.1 mA cm⁻² without discernable Na dendrites. Cooperated with Na₃V₂(PO₄)₃ cathode, the all-solid-state sodium metal batteries (ASSMBs) demonstrate significantly improved rate and cycle performances, delivering a high discharge capacity of 117.5 mAh g⁻¹ under 0.1 C and rendering high capacity retention of 78.2% after 1000 cycles even at 1 C.     

Synthesis and characterization of polyethylene oxide based nano composite electrolyte

Polyethylene oxide (PEO) – montmorillonite (MMT) composite electrolytes were synthesised by solution casting technique. The salt used for the study is Lithium perchlorate (LiClO₄). The morphology and percentage of crystallinity data were obtained through X-ray Diffraction and Differential Scanning Caloriemetry. The ionic conductivity of the polymer electrolytes was studied by impedance spectroscopy. The addition of MMT resulted in an increase in conductivity over the temperature range of 25–60^°C. The ionic conductivity of a composite polymer electrolyte containing 1.2 wt% MMT was 1 × 10^?5 S cm^?1 at 25^°C, which is at least one order of magnitude higher than that of the polymer electrolyte (4 × 10^?7S cm^?1). The increase in ionic conductivity is explained on the basis of crystallinity of the polymer electrolyte.     

Discussion on the influence of DES content in CA-based polymer electrolytes

The degree of crystallinity in the matrix formed by cellulose acetate (CA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were reduced by embedding with deep eutectic solvent (DES) which is a type of ionic mixture synthesized from choline chloride and urea in a specific ratio. The fabrications of thin films were done by solution casting technique. The sample with composition of CA:LiTFSI:DES (28 wt%:12 wt%:60 wt%) appears as the highest conducting sample with the calculated value of 2.61 × 10⁻³ S cm⁻¹ at ambient temperature. This high conducting sample possesses low relative viscosity so as to have high ion fluidity of 0.19. SEM micrographs were used to study the structural alternation that took place in the presence of DES at different ratio in the polymer electrolytes matrix. The dielectric loss tangent plot reveals the low relaxation time for high conducting sample which has immense movements of lithium conducting ion (Li⁺). The enhancement in the ionic conductivity of the DES plasticized samples with temperature obeys Arrhenius rule.     

AC impedance and dielectric spectroscopic studies of Mg<Superscript>2 + </Superscript> ion conducting PVA–PEG blended polymer electrolytes

Polyvinyl alcohol (PVA)–polyethylene glycol (PEG) based solid polymer blend electrolytes with magnesium nitrate have been prepared by the solution cast technique. Impedance spectroscopic technique has been used, to characterize these polymer electrolytes. Complex impedance analysis was used to calculate bulk resistance of the polymer electrolytes. The a.c.-impedance data reveal that the ionic conductivity of PVA–PEG–Mg(NO₃)₂ system is changed with the concentration of magnesium nitrate, maximum conductivity of 9·63 × 10^− 5 S/cm at room temperature was observed for the system of PVA–PEG–Mg(NO₃)₂ (35–35–30). However, ionic conductivity of the above system increased with the increase of temperature, and the highest conductivity of 1·71 × 10^− 3 S/cm was observed at 100°C. The effect of ionic conductivity of polymer blend electrolytes was measured by varying the temperature ranging from 303 to 373 K. The variation of imaginary and real parts of dielectric constant with frequency was studied.     

Thiol-Branched Solid Polymer Electrolyte Featuring High Strength,Toughness, and Lithium Ionic Conductivity for Lithium-Metal Batteries

Lithium-metal batteries (LMBs) with high energy densities are highly desirable for energy storage, but generally suffer from dendrite growth and side reactions in liquid electrolytes; thus the need for solid electrolytes with high mechanical strength, ionic conductivity, and compatible interface arises. Herein, a thiol-branched solid polymer electrolyte (SPE) is introduced featuring high Li⁺ conductivity (2.26 × 10⁻⁴ S cm⁻¹ at room temperature) and good mechanical strength (9.4 MPa)/toughness (≈500%), thus unblocking the tradeoff between ionic conductivity and mechanical robustness in polymer electrolytes. The SPE (denoted as M-S-PEGDA) is fabricated by covalently cross-linking metal–organic frameworks (MOFs), tetrakis (3-mercaptopropionic acid) pentaerythritol (PETMP), and poly(ethylene glycol) diacrylate (PEGDA) via multiple C S C bonds. The SPE also exhibits a high electrochemical window (>5.4 V), low interfacial impedance (<550 Ω), and impressive Li⁺ transference number (t_Li+ = 0.44). As a result, Li||Li symmetrical cells with the thiol-branched SPE displayed a high stability in a >1300 h cycling test. Moreover, a Li|M-S-PEGDA|LiFePO₄ full cell demonstrates discharge capacity of 143.7 mAh g⁻¹ and maintains 85.6% after 500 cycles at 0.5 C, displaying one of the most outstanding performances for SPEs to date.