PEO-based Solid Polymer Electrolytes Research Articles

Oxygen Vacancy-Rich Ultrathin Co3O4 Nanosheets as Nanofillers in Solid-Polymer Electrolyte for High-Performance Lithium Metal Batteries

The development of high-performance solid-polymer electrolytes (SPEs) is a key to the practical application of lithium metal batteries (LMBs). The use of two-dimensional (2D) inorganic nanofiller is an efficient way to build poly(ethylene oxide) (PEO)-based SPEs with high ionic conductivity and stability. Herein, a series of 2D oxygen vacancy-rich Co3O4-y−x (x = 1, 2 and 3) with well-defined 2D nanostructures, a high surface area and controllable oxygen vacancy contents (Co3O4-y) was synthesized via a facile self-assembly method and NaBH4 reduction. When the 2D Co3O4-y−x (x = 1, 2 and 3) nanosheets are introduced as nanofillers in PEO-based SPEs, they can interact with the PEO to form a three-dimensional (3D) PEO/Co3O4-y film with uniform Li+ distribution and vertical diffusion channels, as well as strong adsorption of NO3− from LiNO3 electrolyte salt at the defective sites. As a result, the PEO/Co3O4-y−2 film reached a high ionic conductivity of 4.9 × 10−5 S cm−1, high Li+ a transference number of 0.51 and a wide electrochemical window over 4.6 V at 80 °C. The PEO/Co3O4-y−2 film enables the Li||PEO/Co3O4-y−2||LiFePO4 cell to deliver a high reversible capacity of 117.7 mAh g−1 at 2 C and to maintain 126.7 mAh g−1 at 1 C after 250 cycles with an initial capacity retention of 87.9%.

Effects of Molecular Structure of Cross-Linked Solid Polymer Electrolytes on Ionic Conduction Behavior

To improve the safety and energy density of Li batteries, all-solid-state batteries (ASSBs) are desired. Solid polymer electrolytes (SPEs) are expected to be promising candidates, owing to features such as their high flexibility and formability. To achieve high-performance ASSBs, we investigated molecular structure design by fabricating two types of SPEs. First, chemically cross-linked polyethylene oxide/polypropylene oxide (P(EO/PO))-based SPEs were formed with low-molecular-weight PEO as side chains. Second, physically cross-linked SPEs were fabricated with short PEO chains (G2) as soft-units and norbornene (NB) as hard-units with intramolecular phase separation. Evaluation of the physicochemical and electrochemical properties of these SPEs was carried out, and the degree of dissociation of the Li salt was investigated by Raman spectroscopy. The phenomenon of decoupling between the segmental motion of the SPEs and ionic conduction was confirmed by Vogel-Fulcher-Tamman equation analysis. P(NB/G2)-based SPEs also exhibited high thermal stability, which originated from the NB unit, according to TG-DTA and DSC measurements. Furthermore, ionic conductivity increased monotonically with the Li salt concentration, in contrast to conventional PEO-based SPEs. Physically cross-linked SPEs achieved the decoupling of ionic conduction from their segmental motion owing to their differences between the ionic and structural components of the SPEs.

Poly (ethylene oxide) based solid polymer electrolyte improved by multifunctional additives of poly (acrylamide) and LiI

Solid polymer electrolyte (SPE) as core component of all-solid-state lithium metal battery (ASSLMB) has regained tremendous concerns due to its good flexibility and low cost. However, low ionic conductivity, unstable interphase and unsatisfying cycling stability hinder its practical application in ASSLMB. Herein, we designed a PEO-based SPE (PEO/20PAM/LiI) via adding optimum content of poly (acrylamide) (PAM) and 2 wt% LiI to address above issues. The amide groups (-(C = O)-(NH)) in PAM could effectively facilitate the decomposition of LiTFSI due to the strong coordination of C = O/Li+ and NH/TFSI−, significantly releasing more “Free Li+”. The C = O group also weakens the coordination of Li+/ether oxygen and assists Li+ transfer along the PEO chains, providing an efficient transmission pathway for Li+. Furthermore, LiI could facilitate the uniform Li+deposition at the electrode-electrolyte interface and stimulate the formation of stable interfacial layer, restraining the generation of lithium dendrites. The obtained PEO/20PAM/LiI exhibits high ionic conductivity (2.75 × 10−4 S cm−1, 35 °C), outstanding mechanical strength (0.55 MPa) and wide electrochemical window (∼ 5 V). The assembled Li symmetric battery could endure high critical current density (CCD, 1.8 mA cm−2) and perform Li plating/stripping steadily over 1600 h at 0.1 mA cm−2 at 35 °C. Meanwhile, LiFePO4 (LFP)/Li ASSLMB with this SPE displays preeminent cycling stability over 250 cycles with high capacity retention (97.3%) and high coulombic efficiency (99.9%) at 0.3 C at 35 °C. This rational design strategy shows great potential in simultaneously realizing high ionic conductivity and good interfacial stability for ASSLMB.

Salicylic acid treated Li7La3Zr2O12 achieves dual functions for a PEO-based solid polymer electrolyte in lithium metal batteries

A new approach to treat LLZO particles with salicylic acid (SA) to achieve dual-functionalization. This interfacial modification technique enhances Li+ transport not only at the LLZO/PEO interface, but also throughout the PEO matrix.

Alginate Fiber-Grafted Polyetheramine-Driven High Ion-Conductive and Flame-Retardant Separator and Solid Polymer Electrolyte for Lithium Metal Batteries.

Traditional polymer-based separators and solid polymer electrolytes (SPEs) often suffer from inherent poor flame retardancy and unsatisfied ionic conductivity, which seriously affect the safety and energy storage performance of lithium metal batteries (LMBs). Inspired by the mechanism of Li+ conductivity, an alginate fiber (AF)-grafted polyetheramine (AF-PEA) separator with efficient Li+ transport and excellent flame retardancy is dedicatedly designed, which also can act as the backbone for PEO-based SPEs (PEO@AF-PEA). Based on the intrinsic flame retardancy of the AF, the AF-PEA shows self-extinguishing ability, and its Li+ transport ability (1.8 mS cm-1 at 25 °C) is enhanced by grafting the ion-conductive PEA chain segment. By simulating the transport and distribution of Li+ in the AF-PEA, the PEA with 7-segment chain lengths can uniformly fill the Li+ transport space between the alginate backbone to promote the Li+ adsorption and the utilization of Li+ anchoring points in PEA side chains, increasing the Li+ transport rate and migration capacity. The LiFePO4/Li solid-state battery assembled using PEO@AF-PEA SPEs exhibits high safety and excellent cycling performance (exceeding 100 mAh g-1 after 1500 cycles at 2 C current density and 80 °C with less than 0.016% capacity decay for each cycle).

Failure mechanisms investigation of ultra-thin composite polymer electrolyte-based solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLBs) using solid polymer electrolytes (SPEs) still suffer from the risk of lithium dendrites, and the filling of porous framework can effectively alleviate the short-circuit problem. However, the interfacial failure mechanism of SPE with lithium metal anode and the action of porous framework filler are not fully understood. Herein, thin polyethylene (PE) separator is used as filler of poly(ethylene oxide) (PEO) to prepare ultra-thin composite polymer electrolyte (PE-CPE). Although the PE framework can greatly extend the cycling life of PE-CPE with lithium metal anode, the focused ion beam-scanning electron microscopy (FIB-SEM) results reveal that the uneven deposition and pulverization of lithium at the Li/PEO interface. Nanoparticulate lithium dendrites grow through the SPE resulting in a short-circuit, while the PE framework with small pores restricts the ingress of lithium nanoparticles through physical barrier. This work provides the growth mode of lithium dendrites in PEO-based SPE systems, and simultaneously demonstrates the role of porous framework to block lithium dendrites in SSLBs.

Composite polymer electrolyte incorporating WO3 nanofillers with enhanced performance for dendrite-free solid-state lithium battery

All solid-state lithium batteries (ASS-LBs) with polymer-based solid electrolytes are a prospective contender for the next-generation batteries because of their high energy density, flexibility, and safety. Among all-polymer electrolytes, PEO-based solid polymer electrolytes received huge consideration as they can dissolve various Li salts. However, the development of an ideal PEO-based solid polymer electrolyte is hindered by its insufficient tensile strength and lower ionic conductivity due to its semi-crystalline and soft chain structure. In order to lower the crystallization and improve the performance of PEO-based solid polymer electrolyte, tungsten trioxide (WO3) nanofillers were introduced into PEO matrix. Herein, a PEO20/LiTFSI/x-WO3 (PELI-xW) (x = 0%, 2.5%, 5%, 10%) solid composite polymer electrolyte was prepared by the tape casting method. The solid composite polymer electrolyte containing 5 wt% WO3 nanofillers achieved the highest ionic conductivity of 7.4 × 10-4 S cm-1 at 60 °C. It also confirms a higher Li-ion transference number of 0.42, good electrochemical stability of 4.3V, and higher tensile strength than a PEO/LiTFSI (PELI-0W) fillers-free electrolyte. Meanwhile, the LiFePO4│PELI-xW│Li ASS-LBs demonstrated high performance and cyclability. Based on these findings, it can be considered a feasible strategy for the construction of efficient and flexible PEO-based solid polymer electrolytes for next-generation solid-state batteries.

UV-derived double crosslinked PEO-based solid polymer electrolyte for room temperature

The low ionic conductivity at room temperature and poor dimensional stability at high temperature of polyethylene oxide (PEO)-based solid electrolytes greatly limit the development and utilization of solid polymer electrolytes (SPEs). To reconcile the contradiction between electrochemical performance and mechanical strength of PEO-based SPEs, a cross-linking structure with active –CH2CH2O- soft chains that doped with rigid segments is designed and prepared through a method of green ultraviolet irradiation without solvent. The obtained solid film shows a high ionic conductivity of 0.2 mS·cm−1 and an ionic transference number of 0.51 at room temperature. The activation energy value of 1.92 kJ·mol−1 gives evidence for a favorable migration mechanism of PTP-SPE. A combination of flexibility and strength can be realized by molecular structure design with a tensile elongation of 40%. The reversible overpotential in galvanostatic cycling over 500 h of a Li||Li symmetrical cell indicates that the compact PTP-SPE can inhibit the formation of lithium dendrites. This work provides a new strategy for designing high-performance composite solid electrolytes at room temperature.

Insights Into the Interfacial Degradation of High-Voltage All-Solid-State Lithium Batteries

HighlightsThe cycle performance of poly(ethylene oxide) (PEO)-based all-solid-state lithium batteries with LiCoO2 cathode was greatly improved via coating LiCoO2 with high-voltage stable Li3AlF6.At the upper cutoff voltage of 4.2 V, the poor electrochemical performance is mainly originated from the structure collapse of LiCoO2 at the surface instead of the decomposition of PEO.When the voltage reaches 4.5 V or even higher potentials, the intensive electrochemical decomposition of PEO-based solid polymer electrolyte accelerated interfacial degradation.

Poly(ethylene oxide)-Based Electrolytes for Solid-State Potassium Metal Batteries

Most conventional batteries today employ organic liquid electrolytes (LEs) that are not only flammable, but also serve as a medium for irreversible side reactions at the electrode interfaces, especially when metal is used as electrode. In post-lithium systems, such as potassium batteries, this issue is even more pronounced due to a higher reactivity of the metal as compared to lithium, and typically results in electrochemical instability leading to a rapid capacity fade of the battery.[1] When switching from LEs to solid polymer electrolytes (SPEs) that typically show better electrochemical stability at low (< 0.5 V vs. K+/K) and high (> 4 V vs. K+/K) potentials due to polymers inherent inertness, enhanced cycle life of the battery is expected.[2] Moreover, well-known disadvantage of SPEs in Li-based batteries, i.e., poor ionic conductivity at ambient temperature, could be overcome in systems with larger cation size, e.g. K+ [3,4], potentially removing some of the bottlenecks previously encountered in the case of Li-transport.In this presentation, a series of poly(ethylene oxide) - potassium bis(trifluoromethane sulfonyl)imide (PEO-KTFSI) compositions with different salt concentration was investigated for their potential application as SPEs in potassium metal batteries. To identify the most promising candidate in terms of ion transport and mechanical integrity, the effect of KTFSI concentration on thermal, rheological and electrochemical properties was studied. Several electrolyte compositions were examined in solid-state potassium batteries with a potassium metal negative electrode, and a positive electrode from Prussian blue analogue family. Our results reveal the advantages of solid-state systems with respect to improved capacity retention and Coulombic efficiency as compared to the reference system with carbonate-based LE, as demonstrated in Figure 1, thus paving the way for a new generation of potassium batteries with significantly improved key performance parameters. Figure 1. Comparison of potassium half-cells employing different electrolyte systems: carbonate-based liquid electrolyte (LE) vs. PEO-based solid polymer electrolyte (SPE) (a) capacity retention and (b) corresponding Coulombic efficiencies.[1] H. Wang, D. Zhai, F. Kang, Energy Environ. Sci. 2020, 13, 4583–4608.[2] J. Mindemark, M. J. Lacey, T. Bowden, D. Brandell, Prog. Polym. Sci. 2018, 81, 114–143.[3] M. Perrier, S. Besner, C. Paquette, A. Vallée, S. Lascaud, J. Prud’homme, Electrochim. Acta 1995, 40, 2123–2129.[4] U. Oteo, M. Martinez-Ibañez, I. Aldalur, E. Sanchez-Diez, J. Carrasco, M. Armand, H. Zhang, ChemElectroChem 2019, 6, 1019–1022. Figure 1

Effect of succinonitrile on ion transport in PEO-based lithium-ion battery electrolytes

We report the ion transport mechanisms in succinonitrile (SN) loaded solid polymer electrolytes containing polyethylene oxide (PEO) and dissolved lithium bis(trifluoromethane)sulphonamide (LiTFSI) salt using molecular dynamics simulations. We investigated the effect of temperature and loading of SN on ion transport and relaxation phenomenon in PEO-LiTFSI electrolytes. It is observed that SN increases the ionic diffusivities in PEO-based solid polymer electrolytes and makes them suitable for battery applications. Interestingly, the diffusion coefficient of TFSI ions is an order of magnitude higher than the diffusion coefficient of lithium ions across the range of temperatures and loadings investigated. By analyzing different relaxation timescales and examining the underlying transport mechanisms in SN-loaded systems, we find that the diffusivity of TFSI ions correlates excellently with the Li-TFSI ion-pair relaxation timescales. In contrast, our simulations predict distinct transport mechanisms for Li-ions in SN-loaded PEO-LiTFSI electrolytes. Explicitly, the diffusivity of lithium ions cannot be uniquely determined by the ion-pair relaxation timescales but additionally depends on the polymer segmental dynamics. On the other hand, the SN loading induced diffusion coefficient at a given temperature does not correlate with either the ion-pair relaxation timescales or the polymer segmental relaxation timescales.

Engineering a High-Voltage Durable Cathode/Electrolyte Interface for All-Solid-State Lithium Metal Batteries via In Situ Electropolymerization.

Poly(ethylene oxide) (PEO)-based polymer electrolytes have been widely studied as a result of their flexibility, excellent interface contact, and high compatibility with a lithium metal anode. Owing to the poor oxidation resistance of ethers, however, the PEO-based electrolytes are only compatible with low-voltage cathodes, which limits their energy density. Here, a high-voltage stable solid-state interface layer based on polyfluoroalkyl acrylate was constructed via in situ solvent-free bulk electropolymerization between the LiNi0.8Mn0.1Co0.1O2 (NCM811) cathode and the PEO-based solid polymer electrolyte. The electrochemical oxidation window of the as-synthesized electrolyte was therefore expanded from 4.3 V for the PEO-based matrix electrolyte to 5.1 V, and the ionic conductivity was improved to 1.02 × 10-4 S cm-1 at ambient temperature and 4.72 × 10-4 S cm-1 at 60 °C as a result of the improved Li+ migration. This fabrication process for the interface buffer layer by an in situ electrochemical process provides an innovative and universal interface engineering strategy for high-performance and high-energy-density solid-state batteries, which has not been explicitly discussed before, paving the way toward the large-scale production of the next generation of solid-state lithium batteries.

Effects of lithium salts on PEO-based solid polymer electrolytes and their all-solid-state lithium-ion batteries

Effects of lithium salts on PEO-based solid polymer electrolytes and their all-solid-state lithium-ion batteries

Fluoride-Rich Solid Electrolyte Membrane in Solid-State Li–S Batteries: Improvement of Lithium Cycle Stability and Shuttle Effects

Although employing solid polymer electrolytes (SPEs) in solid-state Li–S batteries (SSLSBs) is a promising approach to obtain both high energy density and safety, the actual cycle property is still rather unsatisfactory. In this work, by combining experiments and calculations, we revealed that a coupling effect between lithium polysulfides (LiPSs) and polyethylene oxide (PEO)-based SPEs was the cause of interfacial instability of the poor cyclelife of lithium anode in SSLSBs. In light of this, a fluorine-rich polymer perfluoropolyether alcohol (PFA) was introduced as an interfacial layer between the SPE and lithium anode. PFA decouples from LiPSs because of the shielding effect of F in PFA on the electron cloud of O and the spatial effect. As a result, the PFA interlayer plays a role in preventing corrosion of the lithium metal from LiPSs and the electrochemical decomposition of PEO-based SPEs. The PEO-based SSLSBs with PFA showed a discharge capacity of 627.4 mA h gS–1 after 100 cycles at 0.05 mA cm–2 and 60 °C. This work emphasized the significance of SPE decoupling from LiPSs in SSLSBs and provided a feasible guidance for the design of high-performance SSLSBs.

Phosphazene Loaded Halloysite Nanotubes as Bifunctional Nanohybrid Fillers for Peo-Based Solid Polymer Electrolytes

Phosphazene Loaded Halloysite Nanotubes as Bifunctional Nanohybrid Fillers for Peo-Based Solid Polymer Electrolytes

Enabling high-performance all-solid-state hybrid-ion batteries with a PEO-based electrolyte.

All-solid-state hybrid-ion batteries exhibiting a synergistic Na+/Li+ de/intercalation mechanism were designed and assembled, by using modified PEO-based solid polymer electrolyte, Na2V2(PO4)2O2F cathode, and Li metal anode. The batteries exhibited a high average working voltage of 3.88 V, and an energy density of 432.37 W h kg-1, providing a new avenue for the development of high-safety and low-cost secondary batteries.

The effect of [EMIm]BF4/Li+ Ionic liquid on PEO-based solid polymer electrolyte membranes characteristics as lithium-ion batteries separator

Lithium-ion batteries have liquid electrolytes, which are corrosive and volatile, that would cause leakage and explosion during the rechargeable process at high temperatures. To overcome these problems, it is necessary to change the liquid electrolyte into a solid one, namely a solid polymer electrolyte. This work has prepared the solidpolymer electrolyte membranes by casting various 1-ethyl-3-tetrafluoroborate, [EMIm]BF4/Li+ ionic liquid, and PEO. In this study, [EMIm]BF4/Li+ , a Li+ ion-attached ionic liquid, has been synthesized using a simple metathesis reaction between 1-ethyl-3- methylimidazolium-bromide, [EMIm]Br, and lithium tetrafluoroborate, LiBF4 salt. [EMIm]Br has been synthesized from 1- methylimidazole and bromoethane precursors using Microwave Assisted Organic Synthesis (MAOS) method. The functional groups and structures of [EMIm]Br and [EMIm]BF4/Li+ have been confirmed by Fourier Transform Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectra analysis. The analysis of ionic conductivities, crystallinities, mechanical properties, surface morphologies, and thermal stabilities have been confirmed by using Electrochemical Impedance Spectroscopy (EIS), X-ray Diffraction (XRD), and tensile tester, Scanning Electron Microscopy (SEM), and Thermogravimetry Analysis (TGA), respectively. The highest ionic conductivity is 1.83 x 10-3 S.cm-1 at room temperature for polymer electrolyte membrane with 16% weight of the [EMIm]BF4/Li+ ionic liquid and also exhibits good mechanical flexibility and thermal stability

Enhancing Li ion transfer efficacy in PEO-based solid polymer electrolytes to promote cycling stability of Li-metal batteries

Li+ transfer efficacy enhancement of PEO-based electrolyte, determined via constructing fast Li+ transfer channel and weakened interaction between Li+ and PEO, leading to significant improvement of electrochemical performance of Li-metal batteries.

Organic ionic plastic crystal enhanced interface compatibility of PEO-based solid polymer electrolytes for lithium-metal batteries

Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) are appealing solid electrolytes for lithium-metal batteries (LMBs) due to their high safety, low cost and flexibility. However, PEO'snarrow electro-chemical potential window and poor interfacial compatibility with the electrode restrict PEO-based SPE development. Herein, we used a solution-casting method to prepare PEO-based SPE membranes reinforced with an organic ionic plastic crystal—N,N-diethylpyrrolidinium bis(fluorosulfonyl)amide (C2epyrFSI). The as-prepared SPE exhibits high ionic conductivity of 3.02 × 10−4 S cm−1 at 50 °C, an extremely wide electro-chemical window (5.1 V) and flexible mechanical properties. Using SPE, the Li symmetric cells can cycle for 2000 h at a current density of 0.1 mA cm−2 without short circuiting at 50 °C. Furthermore, the Li|SPE|LiFePO4 all-solid-state LMBs have a high initial discharge specific capacity of 157.3 mAh g−1 at 0.2C and a capacity retention rate of 96% after 120 cycles. This study shows that the PEO-C2epyrFSI SPE is a promising electrolyte for all-solid-state LMBs.

Improved mechanical and electrochemical properties of PVDF/PEO/LiClO4 based solid polymer electrolyte by using TiO2 and MgO nanoparticles

The poly (vinylidene fluoride) PVDF and poly (ethylene oxide) PEO-based solid polymer electrolytes are gaining popularity due to their good electrochemical and mechanical characteristics. In the present work the polymer electrolyte is prepared by taking 80% PVDF, 20% PEO, and 20% LiClO4 through rigorous mixing. Further, the properties of PVDF/PEO/LiClO4 based electrolyte are improved by adding TiO2 and MgO nanoparticles in different proportions. The results show that the addition of TiO2 and MgO nanoparticles has a significant effect on the electrochemical characteristics and mechanical properties of the electrolyte. The maximum current onset potential of 4.97 V is observed with a 4% concentration of TiO2 nanoparticles. Also, the mechanical properties such as ultimate stress and failure stress are increased with the addition of nanoparticles. The ionic conductivity of the electrolyte first increases with an increase in the concentration of nanoparticles but it starts decreasing after 2% concentration.