Stable Solid Polymer Electrolytes Research Articles

Synthesis of Polyimide-PEO Copolymers: Toward thermally stable solid polymer electrolytes for Lithium-Metal batteries

The rapid pace of technological advancement in field of electric vehicles and need in sustainable energy sources calls for new, high-performance energy storage technologies. Lithium metal batteries (LMBs) based on solid polymer electrolyte represent a promising battery technology to increase energy density of conventional batteries while enhancing safety, eliminating dendrite formation, and providing mechanical flexibility. In this study, we developed novel polyimide-poly(ethylene oxide) (PI-PEO) copolymers and employed them as solid polymer electrolytes for LMBs. Copolymers with 5, 15, and 30 mol% of PEO-containing diamine were synthesized by reacting with aromatic dianhydride and diamine, using a facile and eco-friendly method in a benzoic acid melt. Chemical structures were confirmed using NMR and IR spectroscopy. Glass transition temperatures varied from 24 °C to 195 °C, increasing with a decrease in the PEO/PI moiety ratio. All copolymers demonstrated good thermal stability up to T5% > 345 °C with a two-step degradation and favorable mechanical properties below the glass transition temperature, as observed by DMA measurements. Solid polymer electrolytes with 70 wt% of LiTFSI exhibited an ionic conductivity of 1.4 × 10−4 S cm−1 at 70 °C, with a transference number of 0.7. The polymer electrolyte exhibited non-flammable properties and the potential for utilization in lithium metal batteries, indicating the promising application of these new polymers for high-safety battery systems.

M3+/NaTiO3/PVA–chitosan nanocomposites (M = Ga, Ce, Nd or Er): novel solid polymer electrolytes for supercapacitors

Designing flexible and thermally stable solid polymer-electrolyte (SPE) -based green materials for energy storage devices is an interesting approach from environmental and technological points of view. In this paper, NaTiO3 (ST) nanofibers of diameters in the range of 4.88–9.48 nm were hydrothermally prepared and loaded into the poly(vinyl alcohol)–chitosan (PVA–Ch) bio-blend via solution casting. Additionally, the obtained nanocomposite solution was mixed with Ga3+ and rare Earths (Ce3+, Nd3+, or Er3+) for preparing novel solid polymer electrolyte films. XRD results indicated the semicrystalline nature of all samples, and the degree of crystallinity decreased after loading these additives. FE-SEM and EDS were used to investigate the surface morphology, fracture cross-section and the elemental chemical composition. FTIR analysis confirmed the complexation and complete dissociation of the salts inside the blend. UV–vis spectroscopy showed that the optical band gap of the films was reduced from 4.4 eV to 3.5 eV, and the refractive index is in the range of 2.376–2.648. The thermo-gravimetric analysis (TGA) revealed that the samples are thermally stable until 200 °C, and the maximum decomposition occurs in the temperature range 255–300 °C. In addition, four endothermic peaks were detected in the differential scanning calorimetry thermograms. Dielectric properties were measured in the fRequency range of 100 Hz–8.0 MHz and at temperatures in the range of 30–120 °C. The dielectric constant and ac conductivity were greatly improved due to doping with ST and mixing the salts. The small dielectric loss associated with the improvements in the dielectric constant and ac conductivity suggest the use of the ST/blend and salts/ST/blend films for energy storage devices and related applications.

Ameliorating structural and electrochemical properties of traditional poly-dioxolane electrolytes via integrated design of ultra-stable network for solid-state batteries

Poly(1,3-dioxolane) (PDOL)-based solid electrolytes hold great potential for solid-state lithium metal batteries (SLMBs) due to their high ionic conductivity, good lithium metal compatibility, and facile synthesis through in-situ polymerization. However, traditional PDOL electrolyte suffers from inferior structural stability and low Li-ion transference number (tLi+), which has impeded PDOL from authentic commercialization. Here we design and attain an ultrathin crosslinked polymer electrolyte (viz. PTADOL) to significantly upgrade the functional properties of PDOL. The in-situ formed PTADOL has rational O-Li+ coordination for fast Li+ transport, which enhances both ionic conductivity and tLi+. The unique integrated network structure stabilizes the electrode/electrolyte interface, and achieves additional favorable features, including improved oxidative stability, thermal stability, and flame retardancy. Based on the ultra-stable PTADOL polymer electrolyte, the high-voltage LiNi0.8Mn0.1Co0.1O2||Li solid batteries exhibit excellent operation stability with suppressed polymer degradation. This work provides not only a practical approach to the design of highly stable solid polymer electrolytes for SLMBs, but also the deep understanding of enhancement mechanism.

A Stable Solid Polymer Electrolyte for Lithium Metal Battery with Electronically Conductive Fillers.

Electronic conduction in solid-polymer electrolytes is generally not desired, which causes leakage of electrons or energy loss, and the electronically conductive domains at electrode-electrolyte interfaces can lead to continuous decomposition of electrolytes and shorting issues. However, it is noticed in this work that in an insulating matrix, the conductive domains at certain aspects could also have positive effects on the electrolyte performance with proper control. This work evaluates the limitation and benefits of electronically conductive domains in a solid-polymer electrolyte system and discusses the approach to improve the electrolyte physicochemical properties with densified local electric field distribution, enhanced bulk dielectric property, and charge transfer. By deliberately introducing the conductive domains in a regular solid-polymer electrolyte, stable cycle life, low overpotential, and promising full cell performance could be achieved.

A Stable Solid Polymer Electrolyte for Lithium Metal Battery with Electronically Conductive Fillers

AbstractElectronic conduction in solid‐polymer electrolytes is generally not desired, which causes leakage of electrons or energy loss, and the electronically conductive domains at electrode‐electrolyte interfaces can lead to continuous decomposition of electrolytes and shorting issues. However, it is noticed in this work that in an insulating matrix, the conductive domains at certain aspects could also have positive effects on the electrolyte performance with proper control. This work evaluates the limitation and benefits of electronically conductive domains in a solid‐polymer electrolyte system and discusses the approach to improve the electrolyte physicochemical properties with densified local electric field distribution, enhanced bulk dielectric property, and charge transfer. By deliberately introducing the conductive domains in a regular solid‐polymer electrolyte, stable cycle life, low overpotential, and promising full cell performance could be achieved.

Properties of the Interphase Formed between Argyrodite-Type Li6PS5Cl and Polymer-Based PEO10:LiTFSI.

All-solid-state lithium metal batteries using thiophosphate solid electrolytes (SE) present a promising alternative to state-of-the-art lithium-ion batteries due to their potentially superior energy and power. However, reactions occurring at the lithium metal | SE interface result in an increasing internal resistance and limited cycle life. A stable solid polymer electrolyte (SPE) may be used as protective interlayer to prevent the SE from direct contact and reaction with lithium metal. This creates a new and rarely studied heteroionic interface between the inorganic SE and the SPE, which we investigate here. The interface resistance between argyrodite-type Li6PS5Cl and a poly(ethylene oxide)/LiTFSI-based SPE is quantified by four-point electrochemical impedance measurements using two wire-shaped reference electrodes (2.4 Ω cm2 at 80 °C). Two distinct processes are observed and attributed to lithium-ion conduction through a formed solid-polymer electrolyte interphase (SPEI) and an ionic charge-transfer (CT) process. The SPEI predominantly consists of polysulfides and lithium fluoride (LiF), as identified by X-ray photoelectron spectroscopy (XPS) analysis. A temperature-enhanced SPEI growth is observed using electrochemical impedance spectroscopy (EIS) and depth profiling combined with time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results highlight the importance of four-point measurements to determine electrolyte-electrolyte interface properties. Overall, the low resistance and low activation energy of the SPEI makes the SPE interlayer an attractive candidate to protect Li6PS5Cl from decomposition at the lithium metal anode.

Synthesis and interface stability of polystyrene-poly(ethylene glycol)-polystyrene triblock copolymer as solid-state electrolyte for lithium-metal batteries

The development of safe and long-term stable solid polymer electrolytes is a major challenge for all solid-state batteries because good interfacial stability toward electrodes is the main concern. In this paper, a triblock copolymer polystyrene-poly(ethylene glycol)-polystyrene (PS-PEG-PS) is synthesized and investigated as solid polymer electrolyte. This polymer electrolyte exhibits a high ionic conductivity of 1.1 × 10−3 S cm −1 at 70 °C, transference number of 0.17, high degree flexibility, good mechanical strength and thermal stability. The interface stability of the solid-polymer electrolyte is investigated in Li metal cell and the comprehensive electrochemical properties are studied in cells with either LiFePO4 or LiNi0.5Co0.3Mn0.2O2 cathode materials. Good rate capability and excellent cyclability of the solid polymer electrolyte is demonstrated, with an electrochemical stability window extending above 4.5 V vs. Li+/Li. Furthermore, constant voltage impedance measurements give evidence of the better interface stability and rate capability of LiNi0.5Co0.3Mn0.2O2//Li battery. Meanwhile, molecular orbital energy levels calculated by density functional theory are consistent with experiments.

Synthesis of Aliphatic Poly(ether 1,2-glycerol carbonate)s via Copolymerization of CO2 with Glycidyl Ethers Using a Cobalt Salen Catalyst and Study of a Thermally Stable Solid Polymer Electrolyte.

The synthesis and characterization of linear poly(ether 1,2-glycerol carbonate)s derivatized with pendant butyl, octyl, or stearyl tethers are reported. The polymers are obtained via the ring-opening copolymerization of butyl, octyl, or stearic glycidyl ethers with carbon dioxide using the [rac-SalcyCoIIIDNP] catalyst bearing a quaternary ammonium salt. Synthesized polymers were characterized by 1H and 13C NMR spectroscopy, FT-IR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and rheometry. Polymers with controlled molecular weights in the range of 8970-31 900 g/mol were obtained with low polydispersities between 1.1 and 1.4. Thermal properties of the materials confirm amorphous structures of the polymers with butyl and octyl chains, with glass transition temperatures of -24 and -34 °C, respectively. The stearyl tether polymer exhibited a melting point of 55 °C. Additionally, the potential of poly(butyl ether 1,2-glycerol carbonate) as a thermally stable solid polymer electrolyte was investigated, and it exhibits temperature-dependent conductivity with values comparable to those of optimized PEO-based electrolytes.

A simple P(VdF-HFP)–LiTf system yielding highly ionic conducting and thermally stable solid polymer electrolytes

In the present work, we report a simple solid polymer electrolyte (SPE) system that is solely based on poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)] and lithium trifluoromethanesulfonate (LiTf). The SPEs produced exhibit high ionic conductivity of ~10−4Scm−1 at ambient temperature when 40wt.% of LiTf is incorporated. There is an anomaly when moderate amount of LiTf is added into the polymer. This can be related to formation of neutral ion pairs, and substantiated by calculation of activation energy and scanning electron micrographs. TGA thermograms also show that all the samples tested are thermally stable up to 400°C, even with the incorporation of LiTf. The highest ionic conducting sample achieves highest onset temperature of decomposition.

Synthesis of New Phosphorus-Containing (Co)Polyesters Using Solid-Liquid Phase Transfer Catalysis and Product Characterization

This paper is directed towards the development of safe, and thermally stable solid polymer electrolytes. Linear phosphorus-containing (co)polyesters are described, including their synthesis, thermal analysis, conductivity, and non-flammability. Polycondensation of phenylphosphonic dichloride (PPD) with poly(ethylene glycol) (PEG 12000) with and without bisphenol A (BA) was carried out using solid-liquid phase transfer catalysis. Potassium phosphate is used as base. Yields in the range of 85.0–88.0%, and inherent viscosities in the range of 0.32–0.58 dL/g were obtained. The polymers were characterized by gel permeation chromatography, FT-IR, 1H- and 31P-NMR spectroscopy and thermal analysis. Their flammability was investigated by measuring limiting oxygen index values. The polymers are flame retardants and begin to lose weight in the 190 °C–231 °C range. Solid phosphorus- containing (co)polyesters were complexed with lithium triflate and the resulting ionic conductivity was determined. Conductivities in the range of 10−7–10−8 S cm−1 were obtained.

Ionic conductivity of covalently interconnected polyphosphazene–silicate hybrid networks

Silicate sol–gel precursors of poly[bis(methoxyethoxyethoxy)phosphazene] and their corresponding hybrid networks were synthesized by hydrolysis and condensation reactions. Conversion of the precursor polymers to covalently interconnected hybrid networks with controlled morphologies and physical properties was achieved. Thermal analyses showed no melting transitions for the networks and low glass transition temperatures that ranged from approximately − 38 to − 67 °C. Solid solutions with lithium bis(trifluoromethanesulfonyl)amide in the network showed a maximum ionic conductivity value of 7.69 × 10 − 5 S/cm, making these materials interesting candidates for dimensionally stable solid polymer electrolytes.

Thermally stable solid polymer electrolyte containing borate ester groups for lithium secondary battery

A novel polymer electrolyte having borate ester groups, which are fixed to the backbone chain of the polymer, was prepared. The backbone polymer was synthesized by reaction between polyethylene glycol and boric acid anhydride. The highest conductivity was found for the polymer electrolyte sample prepared by the polyethylene glycol having average molecular weight of 600 (PEG600), the values of the ionic conductivity were 5.8×10 −5 S cm −1 at 30 °C and 2.6×10 −4 S cm −1 at 60 °C, respectively. The solid polymer electrolytes have relatively high thermal stability and electrochemical stability.