PEO-based Polymer Electrolytes Research Articles

Halogen-Bonding Nanoarchitectonics in Supramolecular Plasticizers for Breaking the Trade-Off between Ion Transport and Mechanical Strength of Polymer Electrolytes for High-Voltage Li-Metal Batteries.

The low ionic conductivity of poly(ethylene oxide) (PEO)-based polymer electrolytes at room temperature impedes their practical applications. The addition of a plasticizer into polymer electrolytes could significantly promote ion transport while inevitably decreasing their mechanical strength. Herein, we report a supramolecular plasticizer (SMP) to break the trade-off effect between ionic conductivity and mechanical properties in PEO-based polymer electrolytes. Accordingly, the SMP is constructed by tetraethylene glycol dimethyl ether (G4) and SbF3 through halogen bonds. The SMP-plasticized PEO electrolyte (PEO/SMP) presents a simultaneously enhanced ionic conductivity of 2.4 × 10-4 S cm-1 (25 °C) and a high mechanical strength of 8.1 MPa, compared to those of pristine PEO-based electrolytes. Benefiting from the halogen bonds between G4 and SbF3, the Li-O coordination in PEO/SMP is evidently weakened, and thus rapid Li+ transport is achieved. Furthermore, the PEO/SMP electrolyte possesses a wide electrochemical stability window of 4.5 V and, importantly, derives an inorganic-rich SEI with a low interfacial resistance on a lithium metal surface. By using PEO/SMP, the lithium-metal battery with the LiNi0.5Co0.2Mn0.3O2 cathode exhibits a good rate and long-term cycling performance with a capacity retention of 75.3% (500 cycles). This work offers a rational guideline for the design of polymer electrolytes suitable for high-performance lithium-metal batteries.

Effect of CuF2 on Li+ transport in amorphous PEO-based solid polymer electrolytes

The limited Li+ transport capacity of poly(ethylene oxide) (PEO)-based solid polymer electrolytes restricts their practical applications. To enhance the Li+ diffusion coefficient, CuF2 was incorporated. Molecular dynamics simulations were performed on LiTFSI/PEO systems and CuF2/LiTFSI/PEO systems at varying lithium salt concentrations. The findings indicate that the inclusion of CuF2 in LiTFSI/PEO systems with high lithium salt concentration enhances the Li+ diffusion coefficient, whereas it diminishes at low lithium salt concentration. This phenomenon is attributed to the abundant coordination properties of Cu2+.

Synergistic Enhancement of Biaxial Stretching and Multilayer Composites in All-Solid-State Polymer Electrolytes.

As an important component of lithium-ion batteries, all-solid-state electrolytes should possess high ionic conductivity, excellent flexibility, and relatively high mechanical strength. All-solid-state polymer electrolytes (ASSPEs) based on polymers seem to be able to meet these requirements. However, pure ASSPEs have relatively low ionic conductivity, and the addition of inorganic fillers such as lithium salts will reduce their flexibility and mechanical strength. To address the above issues, in this paper, the solvent-free method was used to prepare a poly(vinylidenefluoride-co-hexafluoropropylene)/lithium bis(trifluoromethanesulfonyl) imide/poly(ethylene oxide) all-solid-state polymer electrolyte, which was then subjected to 4 × 4 magnification synchronous bidirectional stretching. Subsequently, it was multilayered with PEO-based composite polymer electrolytes to obtain multilayered composite polymer electrolytes (MCPEs). Bidirectional stretching provides superior in-plane and out-of-plane mechanical properties to MCPEs by inducing molecular chain orientation, which suppresses the growth of lithium dendrites. Concurrently, it facilitates the formation of the β-crystal form of PVDF-HFP, thereby weakening the ion solvation effect and reducing the lithium-ion migration energy barrier. Multilayered compounding improves the interfacial contact between MCPEs and electrodes, thereby reducing the interfacial impedance. Experiments have demonstrated that the MCPEs prepared in this paper exhibit high ionic conductivity at room temperature (1.83 × 10-4 S cm-1), low interfacial resistance (547 Ω cm-2), excellent mechanical properties (26 MPa), and excellent cycling rate performance (a capacity retention rate of 90% after 110 cycles at 0.1 C), which can meet the performance requirements of lithium-ion batteries for ASSPEs.

A novel approach for the atomic scale characterization of Li-ion battery components probed by positron annihilation lifetime spectroscopy

Recent research has focused on solid polymer electrolytes (SPEs) as the best liquid electrolyte replacements. Poly(ethylene oxide) (PEO) is the most frequent one because of its fast segmental movements in the free volume which controls lithium-ion transport between electrodes. Therefore, PEO-based copolymer electrolytes that can be tailored for mechanical strength and ionic conductivity are often studied. The most popular material is PEO chains containing PMMA because PEO transports ions, and PMMA has good mechanical properties. Further investigations on PEO-based solid polymer electrolytes (SPEs) have shown that chain designs with more nonlinear branches prevent crystallinity and maintain fast segmental dynamics. For this purpose, we worked on PEO-grafted-PMMA copolymers in which the free volume probed by positron annihilation lifetime spectroscopy considerably affects the structure-ionic conductivity relationship. Finally, we investigated the free volume theory of ionic condcutivity using Yahsi-Ulutas-Tav (YUT) theory.

Integrating Polymer Electrolytes-Based Thick Composite Cathodes in All-Polymer Solid-State Lithium Metal Batteries

High energy density solid-state batteries require high areal loading composite cathodes (>4 mAh/cm2). However, increasing the cathode loading or thickness can introduce additional challenges apart from the expected rate capability limitations, which are much less pronounced in low loading or thin composite cathodes. These include greater volume changes during cycling at the cell level, which can introduce stresses at the various interfaces. While there are many successful reports showing long-term stable cycling of high loading composite cathode in all-inorganic solid-state cells, these cells are typically cycled under high pressures (>10 MPa), which may be impractical to commercialize. Such high pressures can alleviate the interfacial contact loss issues generated due to volume changes during cycling. Polymer electrolytes are non-rigid and can potentially accommodate strains to maintain contact at the interfaces during cycling, given sufficient adhesion. In this work, we will show some of the design strategies that were implemented to alleviate the contact loss issue at the polymer electrolyte separator/composite cathode interface in order to achieve stable cycling with thick polymer electrolyte-based composite cathodes in coil-cell configuration. Nickel-rich NMC (LiNixMnyCozO2) cathodes (NMC811 or 622) were used as the active materials. Since polymer electrolytes are known to be unstable with high voltage cathodes such as NMCs, the contribution of oxidative instability to the overall capacity decay will also be discussed by comparing two polymer electrolytes with different oxidative stability (a PEO-based dual-ion polymer electrolyte, and a single-ion polymer electrolyte). This research was sponsored by the U.S. Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office’s Advanced Battery Materials Research Program (Simon Thompson, Program Manager). A part of this research was sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. The SEM in this work was performed and supported at the Center for Nanophase Materials Sciences in Oak Ridge National Lab, a DOE Office of Science user facility.

Stabilization of P2 layered oxide electrodes in sodium-ion batteries through sodium evaporation

Sodium-ion batteries are well positioned to become, in the near future, the energy storage system for stationary applications and light electromobility. However, two main drawbacks feed their underperformance, namely the irreversible sodium consumption during solid electrolyte interphase formation and the low sodiation degree of one of the most promising cathode materials: the P2-type layered oxides. Here, we show a scalable and low-cost sodiation process based on sodium thermal evaporation. This method tackles the poor sodiation degree of P2-type sodium layered oxides, thus overcoming the first irreversible capacity as demonstrated by manufacturing and testing all solid-state Na doped-Na~1Mn0.8Fe0.1Ti0.1O2 ǀǀ PEO-based polymer electrolyte ǀǀ Na full cells. The proposed sodium physical vapor deposition method opens the door for an easily scalable and low-cost strategy to incorporate any metal deficiency in the battery materials, further pushing the battery development.

Flame-retardant reinforced halloysite nanotubes as multi-functional fillers for PEO-based polymer electrolytes

High ionic conductivity, fire safety, and broad electrochemical windows are crucial considerations for the next generation of solid polymer electrolytes (SPEs) employed in solid-state lithium-ion batteries. Based on these factors, we design a novel nanohybrid filler by loading a phosphazene-based flame retardant into halloysite nanotubes (HNT@FPPN). A 36 % reduction in the peak heat release rate (pHRR) confirms the enhanced fire safety of poly(ethylene oxide) (PEO)-based PEO-5HNT@FPPN SPE. Besides, the PEO-5HNT@FPPN electrolyte exhibits an enhanced ionic conductivity of 1.82 × 10-4 S cm−1 at 45 °C. The improved ionic conductivity is attributed to the plasticization effect of nanohybrids, which reduces the crystallinity and aids the motion of PEO chains. After 100 cycles, the as-fabricated Li/PEO-5HNT@FPPN/LiFePO4 cell shows stable cycling at 0.1C with a specific discharge capacity of 145 mAh/g. These findings demonstrate the unique properties of modified PEO SPEs, which may open new pathways for designing safer electrolytes.

Novel PEO-based Solid Polymer Electrolyte with High Elasticity and High Ionic Conductivity for Room Temperature Lithium Metal Batteries

The development and application of polyethylene oxide (PEO) based solid polymer electrolyte (SPE) is severely constrained by its low ionic conductivity and poor tensile resistance. To improve the electrochemical performance of SPE without losing its mechanical properties, a benzene sulfonate-based additive is adopted into crosslinking system composed of -CH2-CH2-O- segments to obtain a membrane with a high ionic conductivity of 1.47 × 10−4 S cm−1 and an ionic transference number of 0.70 at room temperature. The activation energy value of 0.128 eV gives evidence for a favorable migration mechanism of PTH-SPE. Anti-dendrite growth and contact optimization can be realized by molecular structure design with a tensile elongation of 490%. The reversible overpotential of Li||Li symmetric cell within 1000 h demonstrates that the compact PTH-SPE can inhibit the growth of lithium dendrite. This work provides a new strategy for designing high-performance solid electrolytes for room temperature via a green solvent-free method.

Stabilization of the Interface between a PEO-Based Lithium Solid Polymer Electrolyte and a 4-Volt Class Cathode, LiCoO2, by the Addition of LiPF6 as a Lithium Salt

Stabilization of the Interface between a PEO-Based Lithium Solid Polymer Electrolyte and a 4-Volt Class Cathode, LiCoO2, by the Addition of LiPF6 as a Lithium Salt

Flexible High Lithium-Ion Conducting PEO-Based Solid Polymer Electrolyte with Liquid Plasticizers for High Performance Solid-State Lithium Batteries.

Lithium-ion secondary batteries (LIB) with high energy density have attracted much attention for electric vehicle (EV) applications. However, LIBs have a safety problem because these batteries contain a flammable organic electrolyte. As such, all-solid secondary batteries that are not flammable have been extensively reported recently. In this study, we have focused on polymer electrolytes, which is flexible and is expected to address the safety problem. However, the conventional polymer electrolytes have low electrial conductivity at room temperature. Various attempts have been made to solve this problem, such as the addition of inorganic fillers and ionic liquids; however, these composite polymer electrolytes have not yet reached a practical level of lithium-ion conductivity. In this study, high electrical conductivity and lithium dendrite formation-free PEO based composite electrolytes are developed with both a filler of Li6,4La3Zr1.4Ta0.6O12 and liquid plasticizers of tetraethylene glycol dimethyl ether and 1,2 dimethoxyethane. The proposed flexible polymer electrolyte shows a high electrical conduciviy of 6.01×10-4 S cm-1 at 25 °C.

Effect of hBN on Response Times of PEO-Based Electrochromic Devices

In this study, all solid state electrochromic devices (ECDs) without plasticizer such as propylene carbonate were fabricated by sol-gel spin coating method. WO3 nanoparticles and PEO based polymer electrolyte solutions with hBN and without hBN nanoparticles were prepared. These solutions were sol-gel spin- and dip-coated on ITO-glass, respectively. For determining the effect of hBN nanoparticles, four configuration of ECDs were fabricated. The fast bleaching and coloring times of fabricated ECDs were obtained with hBN nanoparticles in WO3 and PEO based polymer electrolyte thin films as 1.15 seconds. Glass/ITO/hBN-WO3/hBN-PEO-based-polymer electrolyte/ITO/Glass electrochromic device is turned on and off 60 times. After 60 cycle, the device coloring time changed to 2-3 seconds, bleaching times changed to 30 seconds.

Reinforced flexible solid-state electrolyte membrane by polyurethane polymer of intrinsic microporosity for high-energy-density lithium metal battery

Poly (ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) are restricted in commercial applications due to the low ionic conductivity at ambient temperature and fragile mechanical properties. Polyurethanes (PUs) are unique materials coupled with superior rigidity and flexibility. Herein, we designed a novel polyurethane polymer of intrinsic microporosity (PPU), which was incorporated with PEO-based polymer electrolyte to prepare composite polymer electrolyte (CPE). The physicochemical and electrochemical properties of CPE membranes were explored. The high ionic conductivity (1.82 × 10−3 S cm−1 at 50 °C) and superior interfacial stability with the lithium anode was obtained. Furthermore, the rate performances and the cycling properties of CPE in LiFePO4 (LFP) batteries were extensively studied. The CPE-15% PPU film showed the excellent electrochemical stability of 84.3% capacity retention after 890 cycles at 0.5 C and 82.4% capacity retention after 500 cycles at 1.0 C at 50 °C. Especially, the CPE matched with high-voltage LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode delivered long-term stable cycling performances. The novel polymer electrolyte acquired could open up a new horizon to achieve high stable lithium metal batteries.

Correlation between Ionic Conductivity and Mechanical Properties of Solid-like PEO-based Polymer Electrolyte.

Poly(ethylene glycol) methyl ether methacrylate polymer networks (PEO-based networks), with or without anionic bis(trifluoromethanesulfonyl)imide (TFSI)-grafted groups, are promising electrolytes for Li-metal all solid-state batteries. Nevertheless, there is a need to enhance our current understanding of the physicochemical characteristics of these polymer networks to meet the mechanical and ionic conductivity property requirements for Li battery electrolyte materials. To address this challenge, our goal is to investigate the impact of the cross-linking density of the PEO-based network and the ethylene oxide/lithium ratio on mechanical properties (such as glass transition temperature and storage modulus) and ionic conductivity. We have synthesized a series of cross-linked PEO-based polymers (si-SPE for single ion solid polymer electrolyte) via solvent-free radical copolymerization. These polymers are synthesized by using commercially available lithium 3-[(trifluoromethane)sulfonamidosulfonyl]propyl methacrylate (LiMTFSI), poly(ethylene glycol)methyl ether methacrylate (PEGM), and [poly(ethylene glycol) dimethacrylate] (PEGDM). In addition, we have synthesized a series of cross-linked PEO-based polymers (SPE for solid polymer electrolyte) using LiTFSI as the ionic species. Most of the resulting polymer films are amorphous, self-standing, flexible, homogeneous, and thermally stable. Interestingly, our research has revealed a correlation between ionic conductivity and mechanical properties in both the SPE and si-SPE series. Ionic conductivity increases as glass transition temperature, α relaxation temperature, and storage modulus decrease, suggesting that Li+ transport is influenced by polymer chain flexibility and Li+/EO interaction.

Influence of Carbon Black on Conductivity and Structure of Polyethylene Oxide Based Polymer Electrolyte Film

AbstractThe potential applications of carbon black are expected to grow as science and technology improve offering up new possibilities for innovation throughout disciplines included in the field of energy storage. The present work shows the influence of carbon black to improve the ionic conductivity of the polymer electrolyte. The synthesis of polyethylene oxide: ammonium iodide based polymer electrolyte incorporated with carbon black varying from 0.01 to 0.06 wt% with respect to PEO: NH4I system by solution casting method. Different characterizations like polarized optical microscopy (POM), impedance spectroscopy, and ionic transference number (tion) are studied in detail. The maximum ionic conductivity is achieved at 0.05 wt% carbon black shows 1.20 × 10−5 S cm−1 at ambient temperature. In accordance with POM data, the amorphous region has increased whereas the crystalline region has shrunk which further indicated the increase in ionic conductivity. The value of (tion) is calculated to be 0.97 which shows the system is ionic in nature. PEO based polymer electrolyte doped carbon black can be used for the fabrication of energy storage devices.

Unconventional PEO-PPC quasi-solid state blend polymer electrolyte for high efficiency solid-state Li-metal batteries

Polymer electrolytes represent a safer alternative over traditional liquid electrolytes, enabling the use of higher energy density active materials as electrodes for batteries. Among the wide variety of different polymeric matrix that are currently been proposed, polyethylene oxide (PEO) is considered one of the most promising. In this work, a PEO-based quasi-solid polymer electrolyte (QSPE) was produced by easily scalable solution casting technique, optimized with addition of plasticizers and blended with polypropylene carbonate (PPC). The resulting polymer electrolyte was ultimately supported to glass fiber separator. Improvement of ionic conductivity, transfer number and electrochemical stability window of the different formulations was confirmed through electrochemical impedance spectroscopy and linear sweep voltammetry. Plating and stripping tests in symmetric LiLi cells and charge–discharge tests in half-cell configuration (Li vs LFP) were performed to evaluate the cyclability and stability of the QSPEs. The PEO-PPC polymer electrolyte showed improved efficiency and stability during charge–discharge cycles, at room temperature, suggesting the positive effect of the presence of carbonate groups in the polymer matrix. The promising results demonstrate that the as-prepared QSPE could represent a feasible and viable alternative to conventional liquid electrolytes and could accelerate the adoption of high energy density storage systems, like Li-metal batteries.

Double gyroid-structured electrolyte based on an azobenzene-containing monomer and its polymer.

The self-assembled structure has a significant impact on the performance of ion conductors. We prepared a new type of electrolyte with self-assembled structures from an azobenzene-based liquid crystalline (LC) monomer and its corresponding polymer. By doping different amounts of monomers and lithium salt LiTFSI, the self-assembled nanostructure of the electrolyte was changed from lamellae to double gyroid. The ionic conductivity of the azobenzene-based electrolytes with the double gyroid structure was 1.64 × 10-4 S cm-1, higher than most PEO-based polymer electrolytes. The azobenzene-based system provides a new strategy to design solid electrolytes with self-assembled structures that may be potentially used in solid-state lithium-ion batteries.

Different-grain-sized boehmite nanoparticles for stable all-solid-state lithium metal batteries.

PEO is one of the common composite polymer electrolyte vehicles; however, the presence of crystalline phase at room temperature, high interface impedance, and low oxidation resistance (<4.0 V) limit its application in stable all-solid-state lithium metal batteries. Herein, we designed a PEO-based solid polymer electrolyte (SPE) by adding boehmite nanoparticles to address the above-mentioned issues. Different-grain-sized boehmite nanoparticles were synthesized by adjusting the hydrothermal temperature. Moreover, the impacts of these distinct grain-sized boehmite nanoparticles used to fabricate boehmite/PEO polymer electrolytes (BPEs) on the performance of all-solid-state lithium metal batteries were investigated. It was found that with the increase in boehmite's grain size, BPEs show better performance. The best BPE exhibited an improved Li+ transference number (0.59), high ionic conductivity (1.25 × 10-4 S m-1), and wide electrochemical window (∼4.5 V) at 60 °C. The assembled lithium symmetric battery can stably undergo 500 hours of lithium plating/stripping at 0.1 mA cm-2. At the same time, the LiFePO4/BPE/Li battery exhibits excellent cycling stability after 100 cycles at 0.5C. This reasonable design strategy with a superior capacity retention rate (86%) demonstrates great potential in achieving high ionic conductivity and good interface stability for all-solid-state lithium metal batteries simultaneously.

Janus nanofibers with multiple Li+ transport channels and outstanding thermal stability for all-solid-state composite polymer electrolytes

Herein, PEO-based composite polymer electrolytes enhanced by Janus nanofibers with multiple Li+ transport channels and outstanding thermal stability were prepared, which exhibit ultra-long cycle stability in all-solid-state lithium metal batteries.

The deconstruction of a polymeric solvation cage: a critical promotion strategy for PEO-based all-solid polymer electrolytes

PEO could be regarded as a macromolecular version of G4, Li+-transport is hindered by its multi-scale polymer structure. A strategy loosening the chain entanglement and tight (EO)n–Li+ interaction is established to improve the Li+-transport of PEO.

Pentafluorobenzene boronic acid with strong Lewis acidity for the modification of PEO-based polymer electrolytes

PFBBA modifies PEO-based electrolytes by endowing B atoms with stronger Lewis acidity and forming a LiF/Li–B–O rich SEI film.