Solid Polymer Electrolyte System Research Articles

Enhanced structural, electrical, and electrochemical performance of polyethylene oxides (PEO)‐based polymer electrolytes for solid state K+ ion batteries

AbstractFlexible polymer electrolytes with effective electrochemical characteristics must be developed to meet smart electronic technology demands. The current investigation explores the solid polymer electrolytes (SPEs) prepared by solution‐casting technique, using polyethylene oxides (PEO) doped with KCl salt in different weight percentages. The effect of the dopant on the chemical interactions and structural, optical, thermal, electrical, and electrochemical properties were studied using various strategies. It was found that the incorporation of KCl salt to PEO results in a three order of magnitude enhancement in ionic conductivity of polymer matrix from 10−9 to 10−6 S cm−1. The PEO doped with 20 wt.% KCl salt exhibited the highest ionic conductivity (4.32 × 10−6 S cm−1) and low activation energy (0.25 eV). According to the thermal analysis, the thermal stability of the films improved as the dopant concentration increased. Further, the electrochemical strength improved with increasing dopant concentration, according to cyclic voltammogram experiments. From the results of all the characterizations, PEO loaded with 20 wt.% KCl SPE system is a suitable candidate for use as an electrolyte in energy storage devices such as solid‐state batteries.

To Study the Effect of Nanoparticle TiO2 on Sodium (Na+) – Ion Conducting Solid Polymer Electrolyte System: [80PEO:20NaPF6

AbstractTo study the effect of nanofiller particle TiO2 on sodium (Na+) – ion conducting solid polymer electrolyte (SPE) film: [80PEO:20NaPF6] and nanocomposite polymer electrolyte (NCPE): [80PEO:20NaPF6] + xTiO2, where x = 1–9 wt. (%) have been prepared. SPE film composition: [80PEO:20NaPF6] selects as Ist‐phase host and nano‐sized (<100 nm) filler materials TiO2 as IInd‐phase dispersoid. Both SPE and NCPE films have been prepared by the hot‐press technique. Filler particle‐dependent conductivity study reveals the NCPE system: [80PEO:20NaPF6] + 8TiO2 as the highest conducting composition with σrt − 3.53 × 10−6 S cm−1, which is approximately one order of magnitude higher than the SPE optimum conducting composition (OCC) (σrt) ≈ 7.78 × 10−7 S cm−1. Ion transport properties for both SPE and NCPE system have been evaluated in terms of ionic conductivity (σ) and total ionic (tion)/cationic (t+) transference numbers using combined AC/DC techniques in order to evaluate its usefulness in all‐solid‐state battery applications. Structural/thermal properties have been characterized using X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. A cyclic voltammetry (CV) study has been performed in SPE and NCPE OCC film to evaluate the electrochemical performance for battery application.

Fluorine‐Containing Phase‐Separated Polymer Electrolytes Enabling High‐Energy Solid‐State Lithium Metal Batteries

AbstractSolid‐state lithium (Li) metal batteries (LMBs) have been developed as a promising replacement for conventional Li‐ion batteries due to their potential for higher energy. However, the current solid‐state electrolytes used in LMBs have limitations regarding mechanical and electrochemical properties and interfacial stability. Here, a fluorine (F)‐containing solid polymer electrolyte (SPE) having a bi‐continuous structure of F‐containing elastomers and plastic crystals is reported. The trifluoroethyl acrylate‐based SPE (T‐SPE) exhibits high ionic conductivity over 10−3 S cm−1, superior mechanical elasticity, and robust LiF‐rich interphases at both the Li metal anode and the LiNi0.83Mn0.06Co0.11O2 cathode. Full cells with thin T‐SPEs and low negative/positive capacity ratios below 0.5 at the high‐operating voltage of 4.5 V demonstrate a high specific energy of 538 Wh kganode+cathode+electrolyte−1 and maintain 393 Wh kg−1 at a high specific power of 804 W kganode+cathode+electrolyte−1. The F‐containing phase‐separated SPE system provides a powerful strategy for achieving high‐energy and ‐power solid‐state LMBs.

Contributing to the Revolution of Electrolyte Systems via In Situ Polymerization at Different Scales: A Review.

Solid-state batteries have become the most anticipated option for compatibility with high-energy density and safety. In situ polymerization, a novel strategy for the construction of solid-state systems, has extended its application from solid polymer electrolyte systems to other solid-state systems. This review summarizes the application of in situ polymerization strategies in solid-state batteries, which covers the construction of polymer, the formation of the electrolyte system, and the design of the full cell. For the polymer skeleton, multiple components and structures are being chosen. In the construction of solid polymer electrolyte systems, the choice of initiator for in situ polymerization is the focus of this review. New initiators, represented by lithium salts and additives, are the preferred choice because of their ability to play more diverse roles, while the coordination with other components can also improve the electrical properties of the system and introduce functionalities. In the construction of entire solid-state battery systems, the application of in situ polymerization to structure construction, interface construction, and the use of separators with multiplex functions has brought more possibilities for the development of various solid-state systems and even the perpetuation of liquid electrolytes.

Impact of EC-plasticizer on electrical and dielectrical properties of PEO/PVdF/NaNO3 solid polymer electrolyte systems

Impact of EC-plasticizer on electrical and dielectrical properties of PEO/PVdF/NaNO3 solid polymer electrolyte systems

Unleashing the potential of eco-friendly chitosan: Methylcellulose polyblend electrolytes via magnesium acetate doping for solid state batteries

The most popular choice for inexpensive and energy-efficient storage devices has been solid biodegradable polymer electrolyte systems. In this study, chitosan (CS), methylcellulose (MC), and magnesium acetate (Mg(CH3COO)2) salt were mixed to create magnesium ion conducting solid blend polymer electrolyte (SBPE) membranes. The X-ray diffraction (XRD) study exhibited a variation in microstructure due to the addition of Mg(CH3COO)2 salt to the poly-blend matrix, which was also confirmed by Fourier transform infrared (FTIR) spectroscopy. Electrochemical impedance analysis revealed the maximum ionic conductivity of 2.24 × 10−5 S cm−1 for the electrolyte film comprising 30 wt% of Mg(CH3COO)2. The ionic transference number (tion) of about 0.88 was observed for the same salt concentration, indicating the predominance of ions as charge carriers in the SBPE. Electrochemical analyses exhibited maximum electrochemical stability window (ESW) for the highest conducting sample, thus incorporating it as a separator-cum-electrolyte. The oxidation and reduction peaks are observed in the cyclic voltammetry curve of the highest conducting sample. The discharge characteristic profiles of electrochemical cells in the configuration Mg/(CS + MC + Mg(CH3COO)2)/cathode with three different types of cathode materials to explore the synergic effect between electrode and poly-blend electrolyte was studied.

Operando Raman Spectroscopy for Evaluating Concentration Changes in Li- and Na-Based Solid Polymer Electrolytes

The solid polymer electrolytes (SPEs) can apply to all-solid-sate batteries using various cations as the carrier species. Herein, we performed operando Raman spectroscopy to evaluate the concentration changes with ionic transport in the Li- and Na-based SPEs composed of ether-based host polymer and MN(SO2CF3)2 (M = Li, Na; MTFSA), with the aim of extracting differences in behavior under electrochemical operation. In the [Li | Li-based SPE | Cu] cell, the integrated intensities of TFSA anions changed near the working electrode (WE) and counter electrode (CE) sides during cyclic voltammetry measurements, revealing changes in the anion concentration. Then, operando Raman spectroscopy was conducted for the [M | Li- or Na-based SPE | M (M = metallic Li or Na)] symmetric cells during chronoamperometry measurements. The cell using Li-based SPE exhibited increasing and decreasing integrated intensities for TFSA at the WE and CE sides, respectively, before reaching a steady state. In contrast, the integrated intensities of TFSA required a longer time to reach a steady state in the Na-based SPE system, suggesting that the solvation/desolvation of Na+ is more difficult during ionic transport. Overall, operando Raman spectroscopy contributed to elucidating the differences in ionic transport properties between Li- and Na-based SPEs during electrochemical processes.

Polyaspartate Polyurea-Based Solid Polymer Electrolyte with High Ionic Conductivity for the All-Solid-State Lithium-Ion Battery.

The existing in situ preparation methods of solid polymer electrolytes (SPEs) often require the use of a solvent, which would lead to a complicated process and potential safety hazards. Therefore, it is urgent to develop a solvent-free in situ method to produce SPEs with good processability and excellent compatibility. Herein, a series of polyaspartate polyurea-based SPEs (PAEPU-based SPEs) with abundant (PO)x(EO)y(PO)z segments and cross-linked structures were developed by systematically regulating the molar ratios of isophorone diisocyanate (IPDI) and isophorone diisocyanate trimer (tri-IPDI) in the polymer backbone and LiTFSI concentrations via an in situ polymerization method, which gave rise to good interfacial compatibility. Furthermore, the in situ-prepared PAEPU-SPE@D15 based on the IPDI/tri-IPDI molar ratio of 2:1 and 15 wt % LiTFSI exhibits an improved ionic conductivity of 6.80 × 10-5 S/cm at 30 °C and could reach 10-4 orders of magnitude when the temperature was above 40 °C. The Li|LiFePO4 battery based on PAEPU-SPE@D15 had a wide electrochemical stability window of 5.18 V, demonstrating a superior interface compatibility toward LiFePO4 and the lithium metal anode, exhibited a high discharge capacity of 145.7 mAh g-1 at the 100th cycle and a capacity retention of 96.8%, and retained a coulombic efficiency of above 98.0%. These results showed that the PAEPU-SPE@D15 system displayed a stable cycle performance, excellent rate performance, and high safety compared with PEO systems, indicating that the PAEPU-based SPE system may play a crucial role in the future.

Improvement of the Structural and Electrical Properties of the Proton-Conducting PVA-NH4NO3 Solid Polymer Electrolyte System by Incorporating Nanosized Anatase TiO2 Single-Crystal

Improvement of the Structural and Electrical Properties of the Proton-Conducting PVA-NH4NO3 Solid Polymer Electrolyte System by Incorporating Nanosized Anatase TiO2 Single-Crystal

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.

The correlation of Li+ Carrier Towards Immittance Conduction Properties on Alginate-PVA-LiNO3 Complexes-Based Solid Polymer Electrolytes System

The correlation of Li+ Carrier Towards Immittance Conduction Properties on Alginate-PVA-LiNO3 Complexes-Based Solid Polymer Electrolytes System

Conductivity and Dielectric Study of Polylactic Acid- Lithium Perchlorate Solid Polymer Electrolyte Film

The solid polymer electrolyte (SPE) consists of polylactic acid (PLA) with different compositions of lithium perchlorate (LiClO4) were prepared by using the solution casting method. The conductivity and dielectric properties of the SPE system were studied by using an impedance spectroscopy technique with a frequency ranging from 0.1 Hz to 100 MHz. The optimum composition of the LiClO4 in the PLA based electrolyte system is 50 %. The highest ionic conductivity value of the PLA-LiClO4 electrolyte is 2.66 x 10-5 Scm-1. The dielectric permittivity, ɛ′ shows high magnitude in the lower frequency due to electrode polarization (EP) effect and become to decrease at high frequency. The magnitude of ɛ′ increases up to 50 % of LiClO4 in the electrolyte system. The loss tangent was used to measure the relaxation time of the electrolyte system. The shortest relaxation time is PLA- LiClO4 polymer electrolyte system is 7.98 × 10−6 s. The electric modulus, M′ and M′', increases with frequency, indicating that the force of charge carriers increases in depletion and accumulation regions at room temperature.

Amorphous silicon nitride induced high dielectric constant toward long-life solid lithium metal battery

Solid polymer electrolytes are the most promising solid electrolytes due to their mechanical flexibility and manufacturing scalability. However, the low lithium-ion transference number and battery failure with detrimental dendrites growth inhibit its commercial application in solid-state batteries. Here amorphous silicon nitride with high permittivity was introduced to both restrain the anion motion and screen the electric potential under external electric field, by which the lithium-ion transference number was improved and the dendrite growth was inhibited significantly. The symmetric Li//Li cell paired with this solid polymer electrolyte exhibits a high lithium-ion transference number of 0.53, with excellent lithium plating/stripping capability at high current density of 1.0 mA cm −2 over 250 h at room temperature. The practical application of this solid polymer electrolyte is verified by the capacity retention of 86.5% over 500 cycles and 70.5% even after 1000 cycles at room temperature with Li//LiFePO 4 pouch cell at 1C. The fire retardant of this solid polymer electrolyte is demonstrated by an excellent self-extinguish behavior (<1 seconds) in the flame test. Additionally, this solid polymer electrolyte system presents an effective strategy for enhancing anode interfacial stability for other battery systems. Amorphous silicon nitride with high dielectric constant enhances the uniform lithium electrodeposition by screening electric potential at high current density. The reduction product from the in-situ reaction between lithium anode and silicon nitride is beneficial to interfacial chemistry, especially the in-situ formed LiSi 2 N 3 shows a better Li + migration pathway across the inorganic-rich SEI layer.

Relaxation Dynamics and Ion Conduction of Poly(Ethylene Carbonate/Ethylene Oxide) Copolymer-Based Electrolytes

Poly(ethylene carbonate/ethylene oxide) P(EC/EO) copolymer was synthesized from EC monomer as a new matrix component of solid polymer electrolytes (SPEs), and the correlation between polymer dynamics and ionic conductivity in the P(EC/EO)-based SPEs at various lithium salt weight fractions (wLi) was investigated by dielectric spectroscopy, rheology, and molecular dynamics (MD) simulations. With the addition of lithium salt, the molecular motions at various scales (i.e., from local to segmental and global motion scales) were found to change as follows: (i) the local motion of P(EC/EO) was slightly accelerated, and at wLi ≥ 0.22, it was separated into two relaxation modes, one faster and the other slower than that of P(EC/EO), (ii) the segmental motion of P(EC/EO) became significantly slower with the addition of lithium salt, and (iii) the global terminal relaxation became slightly slower with the increase of wLi. Thus, the motion of P(EC/EO) at various scales in SPEs changed with different trends with increasing lithium salt. It was also found that the temperature dependence of the ionic conductivity was described by a Vogel–Fulcher–Tammann-type function, which was correlated with the segmental motion, as is known in other SPE systems. Furthermore, from MD simulations, lithium ions are coordinated with the EC units more likely and with a closer distance than EO units in P(EC/EO), and the coordination number of oxygens around one lithium ion was estimated as 6–7 at the distance of 0.30 nm. These results suggest that the coordination structure of the oxygens around the lithium ion is slightly disrupted due to the presence of EC units compared to the chelating structure of pure PEO electrolytes.

Fast Magnesium Conducting Electrospun Solid Polymer Electrolyte

AbstractMagnesium Ion based Solid State Batteries (MIBs) are subject of intensive studies due to abundance of magnesium, its advantages in volumetric capacity, and the reduced dendrite growth. Here we report on a true solid polymer electrolyte system without liquid additives or plasticizers that reaches conductivities above 10−5 S cm−1 at room temperature and above 10−4 S cm−1 at 50 °C. An electrospun polymer electrolyte membrane fabricated from a polymer electrolyte featuring a composition of PEO : Mg(TFSI)2 36 : 1 [where PEO stands for poly(ethyleneoxide) and Mg(TFSI)2 for magnesium bis(trifluoromethanesulfonyl) imide] was identified as the best performing system. Magnesium transport was substantiated by different methods, and the electrochemical properties including solid electrolyte interface (SEI) formation were investigated. Electrospinning as a preparation method has been identified as a powerful tool to enhance the electrochemical properties beyond conventional polymer membrane fabrication techniques.

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.

Overlimiting Currents and Sand’s Time Behaviors in Solid Polymer Electrolytes

Dendrite growth in solid polymer electrolytes has been frequently analyzed since it was the critical issue that limited its applications. For the liquid electrolyte systems, the dilute solution theory and the classic Nernst-Planck equation have been proven to be useful tools for analysis of ion transport dynamics and especially the dendrite initiation at Sand’s time. However, characterization of the Sand’s time in solid polymer electrolyte systems is challenging and also seldomly performed. From the experimental perspective, operando observations have been done, but the true local current density was different from the geometrical average current density since there was always heterogeneous current distribution for millimeter-scale electrolytes. From the theoretical perspective, the dendrite initiation time followed the trend predicted by Sand’s equation, but discrepancies were found such as dendrites observed at under-limiting currents or the order-of-magnitude extended Sand’s time compared to theoretical predictions. Here, we use transparent microcapillary cells for solid polymer electrolyte systems to overcome these challenges. These specialized cells allow direct operando optical observations, while the micron-scale cross-sectional area minimizes the discrepancy between true local and averaged geometrical current densities. Comparison between operando image and voltage response during constant current polarization shows that, unlike liquid electrolyte cases, the dendrite initiation for solid polymer electrolytes doesn’t always trigger a voltage spike. We also derived transport parameters from the measured Sand’s time, limiting current density, and conductivity and the cross-validated transport parameters were used to calculate theoretical Sand’s time that can be compared with the experimental values. Using the analytical solution from the Nernst-Planck equation and numerical calculations using Newman’s concentrated solution model and COMSOL Multiphysics, the predicted Sand’s time for the dilute and concentrated solution theory both matched closely with our experimental values. This work demonstrates that while the polarization process and the onset of lithium dendritic growths in solid polymer electrolytes can be still accurately predicted by the dilute solution theory, it may not always result in voltage responses similar to that of the liquid electrolyte cases. It’s also suggested that ensuring the homogenous distribution of lithium flux and avoiding the localized overlimiting current density is the key to realizing the dendrite-free polymer electrolytes.

Facile in-Situ Polymerized Polymer Electrolytes in All Solid-State Lithium-Ion Batteries

With the push towards renewable energy sources and “green” technologies, lithium-ion batteries (LIBs) have proven to be necessary across multiple technological realms, the biggest of which is currently the electric vehicle (EV) and grid storage markets. But the popular choice of liquid organic electrolytes in LIBs suffers from safety concerns, which motivated significant innovations in safer solid-state electrolytes. Among them, solid polymer electrolytes (SPEs) have shown great potential due to their processability, flexibility and tunability of physical properties. The past decade has seen rapid evolution in the development of SPE LIBs, but most of them still stand inadequate. SPEs are typically processed either by using solvents, or by using them in their solid state, to blend with the active electrode materials. While these systems are often subject to additional compression to promote continuous electrolyte-electrode interface, they still suffer from the almost unavoidable formations of voids, and inhomogeneous contact between the active materials and the SPEs. Furthermore, most of these processes require excessive amounts of SPEs, and yet result in a large interfacial resistance.Here we introduce a novel one-step manufacturing strategy for polymer electrolytes in solvent-free SPE LIBs. The process involves in-situ polymerization of a liquid-monomer precursor directly infiltrated into a dry jelly roll or individual electrodes to form SPE cells. Our microscopy and FIB experiments confirmed a near-perfect polymer infiltration in porous cathodes, while electro-chemical tests confirmed excellent characteristics of cathode-electrolyte interfaces. The cycling performance of lithium iron phosphate (LFP) half cells using thus produced and infiltrated SPE showed very good stability and columbic efficiency. In addition to single-ion conductive SPEs, we tested hybrid SPE systems where Li salts were added into the single-ion conductive SPEs to improve rate and capacity utilization.

Synthesis and electrochemical properties of nano-composite IrO2/TiO2 anode catalyst for SPE electrolysis cell

A composite catalyst of nano-grade IrO2/TiO2 powder is synthesized by Adams’ fusion method for reducing overvoltage of solid polymer electrolyte (SPE) cell and cost-down of noble metal catalyst, simultaneously. The IrO2/TiO2 catalysts, which has a porous composite nanostructure, are prepared according to molar ratio of Ir and Ti element with a specific surface area of 34.1–55.3 m2 g−1. It is found that crystal structure of TiO2 is more dominated by the rutile phase than by Anatase. For a SPE system, total catalyst loading of anode which made of TiO2 and IrO2 is prepared as low as 0.77 mg cm−2 or less, in which the loading amount of the IrO2 only is set to 0.6 mg cm−2 or less. The anode catalyst layer of about 10 ㎛ thickness is coated on the membrane (Nafion 212) for the membrane electrode assembly (MEA) by the decal method. The strong adhesion between the catalyst electrode the membrane is observed by Scanning electron microscopy (SEM). Linear sweep voltammetry (LSV) results shows that the nano-composite IrO2/TiO2 catalysts has better oxygen evolution reaction (OER) than that of the synthesis IrO2 only. Finally, the IrO2/TiO2 catalysts is applied as anode electrode for SPE cells and it is observed that in spite of the lower loading amount of the IrO2 less than 0.5 mg cm−2, working voltage of 1.68 V is observed at a current density of 1 A cm−2 and operating temperature of 80 °C.

Characterization of the structure and chemistry of the solid-electrolyte interface by cryo-EM leads to high-performance solid-state Li-metal batteries.

Solid-state lithium-metal (Li0) batteries are gaining traction for electric vehicle applications because they replace flammable liquid electrolytes with a safer, solid-form electrolyte that also offers higher energy density and better resistance against Li dendrite formation. Solid polymer electrolytes (SPEs) are highly promising candidates because of their tuneable mechanical properties and easy manufacturability; however, their electrochemical instability against lithium-metal (Li0), mediocre conductivity and poorly understood Li0/SPE interphases have prevented extensive application in real batteries. In particular, the origin of the low Coulombic efficiency (CE) associated with SPEs remains elusive, as the debate continues as to whether it originates from unfavoured interfacial reactions or lithium dendritic growth and dead lithium formation. In this work, we use state-of-the-art cryo-EM imaging and spectroscopic techniques to characterize the structure and chemistry of the interface between Li0 and a polyacrylate-based SPE. Contradicting the conventional knowledge, we find that no protective interphase forms, owing to the sustained reactions between deposited Li dendrites and polyacrylic backbones and succinonitrile plasticizer. Due to the reaction-induced volume change, large amounts of cracks form inside the Li dendrites with a stress-corrosion-cracking behaviour, indicating that Li0 cannot be passivated in this SPE system. On the basis of this observation, we then introduce additive engineering, leveraging from knowledge of liquid electrolytes, and demonstrate that the Li0 surface can be effectively protected against corrosion using fluoroethylene carbonate, leading to densely packed Li0 domes with conformal and stable solid-electrolyte interphase films. Owing to the high room-temperature ionic conductivity of 1.01 mS cm-1, the high transference number of 0.57 and the stabilized lithium-electrolyte interface, this improved SPE delivers an excellent lithium plating/stripping CE of 99% and 1,800 hours of stable cycling in Li||Li symmetric cells (0.2 mA cm-2, 1 mAh cm-2). This improved cathodic stability, along with the high anodic stability, enables a record high cycle life of >2,000 cycles for Li||LiFePO4 and >400 cycles for Li||LiCoO2 full cells.