PEO-based Solid Polymer Electrolytes Research Articles

Enhancing Sodium Ion Transport in a PEO-Based Solid Polymer Electrolyte System with NaAlO2 Active Fillers

Enhancing Sodium Ion Transport in a PEO-Based Solid Polymer Electrolyte System with NaAlO2 Active Fillers

Revised Atomic Charges for OPLS Force Field Model of Poly(Ethylene Oxide): Benchmarks and Applications in Polymer Electrolyte.

Poly(ethylene oxide) (PEO)-based polymers are common hosts in solid polymer electrolytes (SPEs) for high-power energy devices. Molecular simulations have provided valuable molecular insights into structures and ion transport mechanisms of PEO-based SPEs. The calculation of thermodynamic and kinetic properties rely crucially on the dependability of the molecular force fields describing inter- and intra-molecular interactions with the target system. In this work, we reparametrized atomic partial charges for the widely applied optimized potentials for liquid simulations (OPLS) force field of PEO. The revised OPLS force field, OPLSR, improves the calculations of density, thermal expansion coefficient, and the phase transition of the PEO system. In particular, OPLSR greatly enhances the accuracy of the calculated dielectric constant of PEO, which is critical for simulating polymer electrolytes. The reparameterization method was further applied to SPE system of PEO/LiTFSI with O:Li ratio of 16:1. Based on the reparametrized partial charges, we applied separate charge-scaling factors for PEO and Li salts. The charge-rescaled OPLSR model significantly improves the resulting kinetics of Li+ transport while maintaining the accurate description of coordination structures within PEO-based SPE. The proposed OPLSR force field can benefit the future simulation studies of SPE systems.

Graphene Oxide Enabled Flexible PEO-Based Solid Polymer Electrolyte for All-Solid-State Lithium Metal Battery

Exploring high performance solid electrolytes is essential for the practical application of solid-state lithium–metal batteries. Here, graphene oxide (GO) is employed to improve the electrochemical...

Hydroxyapatite functionalization of solid polymer electrolytes for high-conductivity solid-state lithium-ion batteries

As a key component of next-generation high-safety lithium batteries, solid-state electrolytes (SSE) have attracted extensive attention. Polyethylene oxide (PEO)-based solid polymer electrolytes exhibit outstanding flexibility and excellent electrode-electrolyte interfaces in comparison with that of inorganic solid electrolytes. Unfortunately, the practical applications of PEO-based solid polymer electrolytes are severely limited by the low ionic conductivity arising from the sluggish segment movement of PEO crystal phase. Herein, an SSE design is presented, which leverages the good flexibility of PEO and enhances its ionic conductivity by directly introducing hydroxyapatite (HAP) as filler into solid polymer electrolyte. With negative potential vacancies of surface, HAP filler can facilitate lithium salt dissociation with a minor dissociation energy of −0.76 eV by attracting Li+. A remarkable ionic conductivity of 0.064 mS cm−1 and a Li+ transference number of 0.366 at 30 °C are achieved. In addition, LiFePO4 (LFP)-Li cell with HAP-modified polymer SSE also delivers a capacity of 118 mAh g−1 after 500 cycles at 1 C at 30 °C, which confirms the practical operability of novel SSE and the validity of HAP filler for SSE enhancement.

CNTs/LiV3O8/Y2O3 Composites with Enhanced Electrochemical Performances as Cathode Materials for Rechargeable Solid-State Lithium Metal Batteries.

Solid-state lithium metal battery (SSLMB) is regarded as a safer energy storage system compared to the liquid one. The performance of the SSLMB depends on the cathode performance and the side reactions derived from the interface of the cathode and the electrolyte, which becomes much severe at high temperatures. Herein, we carried out a facile spray-drying route to prepare a CNTs/LiV3O8/Y2O3 (M-LVO-Y) composite. The synthesized cathode material exhibits an outstanding Li+ storage performance with a high reversible capacity of 279.9 mA h g-1 at 0.05 A g-1, excellent power capability (182.5 mA h g-1 at 2 A g-1), and a long cycle lifespan of 500 cycles with a capacity retention of 66.5% at a current density of 1 A g-1. The fabricated rechargeable solid-state Li/M-LVO-Y-2 lithium metal battery (LMB) with a poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE) achieves a high discharge capacity of 302.1 mA h g-1 at 0.05 A g-1 and a stable cycling performance with the highest capacity of 72.1% after 100 cycles at 0.2 A g-1 and 80 °C. The above battery performance demonstrates that SSLMBs with the CNTs/LiV3O8/Y2O3 cathode and the PEO-based SPE film can provide high energy density and are suitable for applying in a high-temperature environment.

Metal organic frameworks enabled rational design of multifunctional PEO-based solid polymer electrolytes

Electrochemical performance, mechanical properties as well as fire safety are crucial factors to evaluate solid polymer electrolytes (SPEs). In this article, we purposely choose metal-organic frameworks (HKUST-1 MOFs) as the multifunctional additive to modify the PEO-based SPEs. The PEO-LiTFSI-10HKUST-1 MOFs electrolyte (PL10HM) has shown enhanced ionic conductivity, which reaches 2.4 × 10−3 S cm−1 at 80 °C. With the HKUST-1 MOFs, the electrochemical stability window and lithium-ion transfer number were largely enhanced as compared to the PEO-LiTFSI electrolyte (PL). The crystal structure, morphology, thermal stability, micro and macro mechanical properties were characterized systematically. The reduction in peak heat release rate (pHRR) of 42% was realized, which means the PL10HM possesses higher fire safety. The as-fabricated Li/PL10HM/LiFePO4 battery exhibited a simultaneous good rate capability up to 1C and highly stable cyclability for over 100 cycles. These results demonstrate the unique characteristics of such a novel electrolyte membrane, potentially enabling the high performance, safe use in the practical solid-state batteries.

Lithium Local Coordination Structure in Polyether-Based Electrolyte with Cyanoethoxy Sidechain: An Experimental and Theoretical Approach

Solid polymer electrolytes (SPEs) have been studied as the alternative for the current liquid electrolytes. Although poly(ethylene oxide) (PEO) with ether structure and poly(acrylonitrile) (PAN) with cyano group have studied for more than decades, these electrolytes have issues such as low ionic conductivity and small transference number of lithium-ion (t Li +). We have reported improved lithium transference number in PEO-based SPE having both ether and cyano groups (PCEO), which showed t Li + of 0.5, compared to that of ca. 0.2–0.3 for PEO counterparts. However, the molecular-level understanding of its ion transport mechanism is still lacking. The main obstacle is the difficulty in experimentally clarify the complex interaction between the ions and the polymer matrix in the PCEO electrolyte.In this study, we combine infrared (IR) spectroscopy with molecular dynamics (MD) simulation to understand the complex interaction within the electrolyte, in order to clarify the Li+ coordination structure as well as its transport mechanism in PCEO electrolytes. We selected lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) as a salt and prepared three PCEO electrolytes with different salt concentrations (a = 10, 3, and 1). High-energy X-ray diffraction patterns and corresponding MD simulated curves were in good agreement, confirming that MD simulation could apply to this system. The local coordination structures around lithium-ion were thus estimated by the distribution function obtained from MD simulation. The simulated average coordination number for PCEO3LiTFSI, with the highest ionic conductivity among the 3 electrolytes, were Li+–CN = 2.2, Li+–O (ether) = 0.5, and Li+–TFSI- = 1.3. The result suggests that the cyano group preferably coordinate with lithium-ion than the other functional group, including ether group. Further supports comes from IR spectroscopy, where the estimated coordination number obtained from the IR peak area of the deconvoluted CN stretching vibration (n = ca. 2250–2280 cm-1) agreed well with the MD result. Based on the experimental and theoretical evidence, we conclude that cyano groups mainly responsible for transporting lithium-ion in PCEO electrolytes. Arrhenius plots of the ionic conductivity showed a curved shape, suggesting that the segmental motion of polymer main-chain transported the ions.In summary, we conclude that the high t Li + for PCEO electrolyte is mainly due to its characteristic lithium coordination structure; lithium-ions are mostly surrounded by cyano groups and transported via the segmental motion of polymer main-chain in PCEO electrolytes. The results emphasize the importance of the coordination structure on the characteristics of the electrolyte, which can provide additional knobs to improve the ionic conductivity as well as lithium transference number, leading further improvements in the performance of polymer electrolytes.

Cryogenic engineering of solid polymer electrolytes for room temperature and 4 V-class all-solid-state lithium batteries

Solid polymer electrolytes (SPEs) are promising candidates for all-solid-state lithium batteries (ASSLBs) due to their advantages of good interfacial adhesion and shape flexibility. However, the low ionic conductivity at room temperature (RT) and inferior electrochemical stability at high voltages limit the practical applications of SPEs. In this work, we demonstrate a cryogenic engineering to improve PEO-based SPEs for ASSLBs operated at RT. The rapid in situ cooling process will lead to the uniform formation of PEO crystal nuclei, which can limit the PEO crystal growth in SPEs. The novel crystallization structure could promote the ionic conductivity of SPEs effectively. Such improved cryogenic SPEs display a superior ionic conductivity of 2.17 × 10−5 S cm−1 and a superior electrochemical stability at RT. A discharge capacity of 154.9 mAh g−1 can be achieved at 0.1 C and RT when LiFePO4 (LFP) is used as the cathode. The discharge capacity can remain at ~98%, even after 100 cycles performed at 0.1 C. Notably, cryogenic SPEs can be utilized in 4 V-class ASSLBs. A high discharge capacity of 118 mAh g−1 can be achieved at 0.2 C and RT with the LiNi0.6Co0.2Mn0.2O2 (NCM622) as the cathode and can retain a 94.1% capacity even after 100 cycles. These extraordinary performances of cryogenic SPEs break new ground for the fabrication of ASSLBs operated at RT and high voltages.

Three-Dimensional Porous Alginate Fiber Membrane Reinforced PEO-Based Solid Polymer Electrolyte for Safe and High-Performance Lithium Ion Batteries

The rational design and optimization of solid polymer electrolytes (SPEs) are critical for the application of safety and high efficiency lithium ion batteries (LIBs). Herein, we synthesized a novel poly(ethylene oxide) (PEO)-based SPE (PEO@AF SPE) with a cross-linking network by the introduction of alginate fiber (AF) membranes. Depending on the high-strength supporting AF skeleton and the cross-linking network formed by hydrogen bonds between the PEO matrix and AF skeleton, the obtained PEO@AF SPE exhibits an excellent tensile strength of 3.71 MPa, favorable heat resistance (close to 120 °C), and wide electrochemical stability window (5.2 V vs Li/Li+). Meanwhile, the abundant oxygen-containing groups in alginate macromolecular and the three-dimensional (3D) porous structure of the AF membrane can greatly increase Li+ anchor points and provide more Li+ migration pathways, leading to the enhancement of Li+ conduction and interfacial stability between the SPE and Li anode. Furthermore, the assembled LiFePO4/PEO@AF SPE/Li cells also exhibit satisfactory electrochemical performance. These results reveal that PEO incorporating with AFs can boost the mechanical strength, thermostability, and electrochemical properties of the SPE simultaneously. Furthermore, one will expect that the newly designed PEO@AF SPE with cross-linked networks thus provides the possibility for future applications of safety and high-performance LIBs.

Polycation ionic liquid tailored PEO-based solid polymer electrolytes for high temperature lithium metal batteries

Poly(ethylene oxide) (PEO)-based polymer electrolytes are promising candidates for solid-state electrolytes in safer, next generation lithium metal batteries. Despite their benefits however, PEO-based electrolyte exhibits highly crystalline ethylene oxide chains that provide poor ionic conductivity and, thus severely limit its practical application. Here, we report the use of hydroxypropyl trimethylammonium bis(trifluoromethane) sulfonimide chitosan salt (HACC-TFSI), which is an amorphous poly(ionic liquid) based biomass chitosan derivative, as a modifier for PEO-based solid polymer electrolytes (SPEs) to address these deficiencies. Hybrid SPEs with HACC-TFSI display enlarged amorphous regions with enhanced ionic conductivity. Interactions between quaternary ammonium cations and TFSI− anions in hybrid SPEs are also found to promote dissociation between Li+ and TFSI−, which further increases ionic mobility. Moreover, the electrochemical stability, mechanical strength, and thermal stability of hybrid SPEs are collectively superior to blank SPEs without HACC-TFSI. LiFePO4/SPEs/Li full-cells assembled using 10wt% HACC-TFSI in PEO (10%HACC-TFSI/SPEs) electrolyte provide a capacity of 161.3 mAh g−1 and operate with excellent cycle performances at 0.2 C and 60 °C. Even when the temperature is increased to 150 °C, LiFePO4/SPEs/Li cells with 10%HACC-TFSI/SPEs still display remarkable cycle performance with 73% capacity retention after 100 cycles at 1 C rate.

Stabilizing and understanding the interface between nickel-rich cathode and PEO-based electrolyte by lithium niobium oxide coating for high-performance all-solid-state batteries

Abstract The pursuit of high energy density and safe lithium ion batteries (LIBs) is a urgent goal for the development of next-generation electric vehicles (EVs). All-solid-state batteries (ASSBs) with the combination of poly(ethylene oxide) (PEO)-based solid polymer electrolyte (SPE) and Ni-rich lithium nickel manganese cobalt oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode are promising candidates for EVs due to their improved energy density and safety. However, the low electrochemical oxidation window of PEO-based SPE and the instability of NMC811 at the charge/discharge process seriously restrict the battery performance. Herein, a high voltage stable solid-state electrolyte layer lithium niobium oxide (LNO) is coated on the NMC811 electrode surface by atomic layer deposition for stabilizing NMC811-PEO solid polymer batteries. Electrochemical tests show that LNO coating can stabilize the NMC811 active materials and mitigate the decomposition of SPE upon the cycling process, rendering a good performance of NMC811-PEO solid polymer battery. Mechanism studies by SEM, STEM, XAS, and XPS disclose that the uncoated NMC811 suffers from chemomechanical degradations along with oxygen release triggering the decomposition of SPE, which results in unstable cathodic electrolyte interphase. With LNO coating, chemomechanical degradations and oxygen release are inhibited and the decomposition of SPE is mitigated. This work renders a stable and high-performance high-energy-density SSB for high voltage application, which paves the way toward next-generation solid-state LIBs.

Exploring porous zeolitic imidazolate frame work-8 (ZIF-8) as an efficient filler for high-performance poly(ethyleneoxide)-based solid polymer electrolytes

The incorporation of inorganic fillers into poly(ethyleneoxide)(PEO)-based solid polymer electrolytes (SPEs) is well known as a low-cost and effective method to improve their mechanical and electrochemical properties. Porous zeolitic imidazolate framework-8 (ZIF-8) is firstly used as the filler for PEO-based SPEs in this work. Due to the introduction of ZIF-8, an ionic conductivity of 2.2 × 10−5 S/cm (30 °C) is achieved for the composite SPE, which is one order of magnitude higher than that of the pure PEO. ZIF-8 also accounts for the broader electrochemical stability window and lithium ion transference number (0.36 at 60 °C) of the composite SPE. Moreover, the improved mechanism of ZIF-8 to the composite SPE is investigated by zeta potential and Fourier transform infrared spectrograph characterizations. The stability at the composite SPE/lithium interface is greatly enhanced. The LiFePO4||Li cells using the composite SPE exhibit high capacity and excellent cycling performance at 60 °C, i.e., 85% capacity retention with 111 mA·h/g capacity retained after 350 cycles at 0.5 C. In comparison, the cells using the pure PEO show fast capacity decay to 74 mA·h/g maintaining only 68 capacity. These results indicate that the PEO-based SPEs with ZIF-8 are of great promise for the application in solid-state lithium metal batteries.

Elimination of "Voltage Noise" of Poly (Ethylene Oxide)-Based Solid Electrolytes in High-Voltage Lithium Batteries: Linear versus Network Polymers.

SummaryFrequently, poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) reveal a failure with high-voltage electrodes, e.g. LiNi0.6Mn0.2Co0.2O2 in lithium metal batteries, which can be monitored as an arbitrary appearance of a “voltage noise” during charge and can be attributed to Li dendrite-induced cell micro short circuits. This failure behavior disappears when incorporating linear PEO-based SPE in a semi-interpenetrating network (s-IPN) and even enables an adequate charge/discharge cycling performance at 40°C. An impact of any electrolyte oxidation reactions on the performance difference can be excluded, as both SPEs reveal similar (high) bulk oxidation onset potentials of ≈4.6 V versus Li|Li+. Instead, improved mechanical properties of the SPE, as revealed by compression tests, are assumed to be determining, as they mechanically better withstand Li dendrite penetration and better maintain the distance of the two electrodes, both rendering cell shorts less likely.

Nanocomposite solid polymer electrolytes based on semi-interpenetrating hybrid polymer networks for high performance lithium metal batteries

This research reports the synthesis of nanocomposite solid polymer electrolytes (ncSPEs) for solid state lithium metal batteries. These materials are composed of a controlled hybrid organic-inorganic network of glycidyl POSS® and Jeffamine® ED2003, in which linear high molecular weight poly (ethylene oxide) (PEO) chains are entangled to improve both mechanical and electrochemical properties of the ncSPE. Synthesis and preparation of self-standing membranes are achieved with a facile one-pot catalyst-free method with considerably reduced amount of organic solvent, which is a plus toward a future scale-up. We found that the component ratio plays a crucial role in ncSPEs’ performance as a simple variation (i.e. cross-linking degree) is sufficient to completely change the electrochemical behavior of the solid state cell. For instance, increasing POSS® amount guarantees better resistance to lithium dendrites penetration, better electro-oxidation stability, and significantly extends cycle life in Li/ncSPE/LiFePO4 solid state cells. Furthermore, besides improving cell performance at higher C-rate of Li/LiFePO4 cells, this PEO-based ncSPE gives better response than reference PEO-LiTFSI electrolyte in high voltage Li/LiNi0.6Mn0.2Co0.2O2 cells with up to 10 cycles at 60 °C with discharge capacity retention above 80%. Despite the poor performance, to the best of our knowledge, this electrolyte is one of the few examples of PEO-based solid polymer electrolytes being capable of cycling with high voltage cathodes.

Determining the limiting factor of the electrochemical stability window for PEO-based solid polymer electrolytes: main chain or terminal –OH group?

Terminal –OH group in PEO-based solid polymer electrolytes is the limiting factor of the electrochemical stability window, replacing it with more stable groups can accelerate the development of high-voltage solid-state batteries.

The effects of the size and content of BaTiO3 nanoparticles on solid polymer electrolytes for all-solid-state lithium-ion batteries

For all-solid-state lithium-ion batteries, several disadvantages such as low ionic conductivity and poor interfacial stability have been concerned. According to previous studies, BaTiO3 nanoparticles can improve the electrochemical properties of PEO-based solid polymer electrolytes (SPEs). This study elucidates the effects of different sizes and contents of BaTiO3 fillers on SPEs. The BaTiO3 nanoparticles with average size of 5 nm, 100 nm, and 500 nm and content from 4 to 20 wt% were incorporated into SPEs by solution casting method. For the SPE with 8 wt% 5 nm BaTiO3, it possesses the highest ionic conductivity of 2.2 × 10−5 S cm−1 at 25 °C and 1.9 × 10−3 S cm−1 at 80 °C. In the LiFePO4/SPE with 8 wt% 5 nm BaTiO3/Li cell, it indicates a high initial discharge specific capacity of 140.7 mAh g−1 at 0.1 °C rate and the specific capacity remains 97.8% after 50 cycles at 80 °C.

High Capacity Utilization of Li Metal Anodes by Application of Celgard Separator-Reinforced Ternary Polymer Electrolyte

PEO-based solid polymer electrolytes typically show limited capability for the suppression of Li metal dendrites, which is mainly attributed to their low mechanical strength. To tackle this issue, we improved the mechanical strength of a ternary solid polymer electrolyte (TSPE: PEO-LiTFSI-Pyr14TFSI) by integrating Celgard 2500 separator as a high modulus domain. The Celgard-reinforced TSPE (CgTSPE) presents a significantly higher elastic modulus (223 MPa) than TSPE (0.2 MPa) at 60°C, which in result leads to more lithium anode utilization. Specifically, the Columbic efficiency of Li electrodeposition/dissolution during cycling in Li|CgTSPE|Cu cells (≈90%) is distinctly higher than in Li|TSPE|Cu (≈30%). Furthermore, the cycling of Li||Li symmetric cells with CgTSPE displays an improved cycling stability, due to the presence of Celgard, in which high surface area lithium (HSAL), e.g., dendrite formation is suppressed. Operando electrochemical dilatometry (ECD) analysis as well as post mortem surface analysis with SEM reveal the formation of “dead lithium” and cavities under an areal capacity utilization of 5 mAh/cm2. It is also suggested by the cycling behavior of the Li||Li cell with high areal capacity utilization that lithium surface treatment is required to completely eliminate the formation of “dead lithium” and of cavities.

Effects of Halloysite Nanotubes on Ionic Conductivity, Morphology, Crystallinity and Mechanical Properties of PEO-based Solid Polymer Electrolyte

Abstract Solid polymer electrolytes (SPEs) were prepared by solution casting and followed by hot pressing process. The halloysite nanotubes (HNTs) were added to polyethylene oxide (PEO)- trifluoromethanesulfonate (LiCF3SO3) composites and its effects on ionic conductivity, morphology and crystallinity of SPEs were investigated. The ionic conductivity was determined by impedance spectroscopy, the ionic conductivity of SPEs was found to increase with the increasing of HNTs. The results revealed that 15 wt% of HNTs provided the highest ionic conductivity of 3.46 x 10-5 S.cm-1 at room temperature (RT.), which higher than that of the PEO–LiCF3SO3 electrolyte (1.74 x 10-5 S.cm-1). At above 15 wt% of HNTs, the ionic conductivity decreased because of the HNTs aggregation as shown on the SEM image. The crystallinity of SPEs was characterized by X-ray diffractometer (XRD). The glass transition and melting temperatures and the degree of crystallinity were investigated by differential scanning calorimetry (DSC).The interaction between PEO-LiCF3SO3 and HNTs was observed by Fourier transform infrared spectrometer (FT-IR).

Development of the PEO Based Solid Polymer Electrolytes for All-Solid State Lithium Ion Batteries.

Solid polymer electrolytes (SPEs) have attracted considerable attention due to the rapid development of the need for more safety and powerful lithium ion batteries. The prime requirements of solid polymer electrolytes are high ion conductivity, low glass transition temperature, excellent solubility to the conductive lithium salt, and good interface stability against Li anode, which makes PEO and its derivatives potential candidate polymer matrixes. This review mainly encompasses on the synthetic development of PEO-based SPEs (PSPEs), and the potential application of the resulting PSPEs for high performance, all-solid-state lithium ion batteries.

Effects of the shapes of BaTiO3 nanofillers on PEO-based electrolytes for all-solid-state lithium-ion batteries

BaTiO3 nanofillers can improve the electrochemical properties of PEO-based solid polymer electrolytes (SPEs). Therefore, we aimed to elucidate the effects of different shapes of BaTiO3 nanofillers on PEO-based SPEs. Five weight percent of BaTiO3 nanowires, nanocubes, and nanospheres were added into SPEs and membranes were prepared by solution casting method. Different BaTiO3 nanofillers have different effects on the ionic conductivity and the electrochemical stable window of SPEs. For the SPE with BaTiO3 nanospheres, it possesses the highest ionic conductivity of 1.8 × 10−5 S cm−1 at 25 °C and 1.6 × 10−3 S cm−1 at 80 °C. The LiFePO4/SPE with BaTiO3 nanospheres/Li exhibits the highest initial discharge-specific capacity of 135.6 mAh g−1 at 0.1 C rate and the discharge-specific capacity remains 97.5% after 50 cycles at 80 °C. This work demonstrates that BaTiO3 nanospheres are ideal nanofillers for SPEs, due to the highest specific surface area.