Solid Polymer Electrolyte Research Articles

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.

Engineering conductive and catalytic triple-phase interfaces for high efficiency polysulfides conversion in Li-S batteries

The well-known shuttle effect of lithium polysulfides (LiPSs) in the ether-based liquid electrolyte and polymer solid electrolytes are the main roadblocks of Li-S batteries to perform high discharge capacity with a long cycling lifespan. Herein, a triple phase interface among carbon/catalysts (vanadium single atoms (VSAs) and metallic cobalt nanoparticles (CoNPs))/electrolyte is proposed for the high-performance Li-S batteries. At the triple-phase interfaces, the LiPSs are chemically immobilized and electrocatalytically transformed into insoluble Li2S at the rate-determining process of liquid–solid conversion. The nucleation and growth of Li2S precipitates were dominated by the interface chemistry and the dispersion of catalysts (3D reconstruction image). In the Li-S batteries with liquid ether-based electrolytes, a discharge capacity of 1343 mAh g−1 was achieved at 0.1 C and the decay of capacity was decelerated with 0.05% per cycle for 500 cycles at 1 C, as well as superb rate capability (808 mAh·g−1 at 5 C). The triple phase interfaces also exhibited high performance in solid state Li-S batteries with solid polymer electrolytes, which the discharge capacity reaches 1289 mAh·g−1 at 0.05 C and 849 mAh·g−1 at 0.5 C.

Enhanced ionic conductivity of PEO-based solid electrolyte through synergistic dissociation effect

Low ionic conductivity is an obstacle to realize the commercial application of PEO-based solid polymer electrolyte due to high crystallinity and poor segment motion of PEO. Herein, a kind of Co-based metal-organic framework (Co-MOF) is synthesized as the filler to inhibit PEO crystallization and produce a synergistic dissociation effect between LiTFSI and PEO so as to improve the ionic conductivity. The Lewis acid-base pairs formed between metal Co2+ and TFSI− facilitates the dissociation of LiTFSI. While the nitro group of the organic framework drags the ether unit of PEO, releases Li+ and improves Li+ hopping. The ionic conductivity of PEO/Co-MOF-5% reaches 1.26×10−4 S cm−1 and a reversible capacity of 111 mAh g−1 is obtained for Li|(PEO/Co-MOF-5%)|LiFePO4 cell after 120 cycles at room temperature.

Non-flammable solvent-free liquid polymer electrolyte for lithium metal batteries

As a replacement for highly flammable and volatile organic liquid electrolyte, solid polymer electrolyte shows attractive practical prospect in high-energy lithium metal batteries. However, unsatisfied interface performance and ionic conductivities are two critical challenges. A common strategy involves introducing organic solvents or plasticizers, but this violates the original intention of security design. Here, an electrolyte concept called liquid polymer electrolyte without any small molecular solvents is proposed for safe and high-performance batteries, based on the design of a room-temperature liquid-state brush-like polymer as the sole solvent of lithium salts. This liquid polymer electrolyte is non-flammable and exhibits high ionic conductivity (1.09 times 10−4 S cm−1 at 25 °C), significant lithium dendrite suppression, and stable long-term cycling over a wide operating temperature range ( ≥ 1000 cycles at 60 °C and 90 °C). Moreover, the pouch cell can resist thermal abuse, vacuum environment, and mechanical abuse. This electrolyte and design strategy are expected to provide enlightening ideas for the development of safe and high-performance polymer electrolytes.

Optical, vibrational, electrical, and electrochemical studies of new plasticized methylcellulose‐based solid polymer electrolytes for supercapacitor application

AbstractIn this work, new plasticized solid polymer electrolytes (SPEs) are developed using MC (methylcellulose) as a polymer host, and sodium iodide (NaI) as a dopant via the solution casting method. Ethyl carbonate (EC) is used as a plasticizing agent to improve the properties of the SPEs. Polarized optical microscopy analysis reveals that the surface morphology of the MC‐NaI‐EC films contained porous amorphous regions owing to the presence of EC. The complex formation between MC, NaI, and EC is confirmed by Fourier‐transform infrared spectra. The addition of EC in the MC‐NaI polymer salt matrix enhances the electrochemical properties of the prepared films. The highest ionic conductivity of 5.06×10−3 S/cm is achieved for the composition: MC+50 wt. % NaI +10 wt. % EC. The linear sweep voltammetry test reveals that the optimal plasticized‐SPE can withstand up to 2.5 V. The ionic transference number analysis reveals that 99% of ions contribute to the total conductivity. The optimized SPE film and graphene oxide‐based electrodes are used to manufacture a solid‐state electrical double‐layer capacitor. The coulomb efficiency of the supercapacitor cell is 100%, and the specific capacitance of the supercapacitor is found to be 18.56 F/g utilizing impedance data at low frequency.

Practical Application of All‐Solid‐State Lithium Batteries Based on High‐Voltage Cathodes: Challenges and Progress

AbstractAll‐solid‐state lithium batteries (ASSLBs) have become a recent research hotspot because of their excellent safety performance. In order to better reflect their superiority, high‐voltage cathodes should be applied to enhance the energy density of solid batteries to compete with commercial liquid batteries. However, the introduction of high‐voltage cathodes suffers from many problems, such as low electrochemical stability, inferior interface chemical stability between cathode and electrolyte, poor mechanical contact, and gas evolution. These drawbacks significantly influence the battery performance, even causing battery failure and hindering the commercialization of solid‐state batteries. This paper first reviews the above failure mechanisms of high‐voltage cathode‐based ASSLBs from different perspectives. Then, recent advances in solid‐state electrolytes for ASSLBs are summarized, mainly including polymer solid electrolytes, sulfide solid electrolytes, and oxide solid electrolytes. In addition, the influence of the cathode materials is also highly critical, and strategies to improve electrochemical performance are put forward, which can be divided into coating protection, synthesis modification, and structure improvement. Finally, guidelines for the future development of solid‐state batteries are also discussed.

Thin Solid Polymer Electrolyte with High-Strength and Thermal-Resistant via Incorporating Nanofibrous Polyimide Framework for Stable Lithium Batteries.

Polyethylene oxide (PEO) based polymer electrolytes show promise in expanding the practical applications of lithium (Li) batteries. However, their applications in Li batteries are usually restricted owing to the lack of mechanical strength, poor oxidative stability, and relatively large thickness. Herein, a nanofibrous polyimide (PI) framework enhanced plasticized-PEO solid electrolyte is prepared to realize good mechanical and electrochemical performances. Following the configuration with the PI matrix, this "polymer in polymer" composite electrolyte with a thickness of 17.5µm exhibits enhanced mechanical strength (13.9MPa) and outstanding thermal stability. Additionally, it preserves the high ionic conductivity (2.25×10-4 Scm-1 , 25°C). The Li||Li symmetrical battery with the modified electrolyte could achieve a steady Li plating/stripping of more than 500h, and the critical current density reaches up to 0.6mAcm-2 at ambient temperature. The LiFePO4 batteries delivery favorable capacity of 132.2mAhg-1 with capacity retentions of 96.4% and 85.9% after 500 and 1000 cycles at 1C, respectively. Acceptable cycling performance also could be achieved in LiNi0.5 Co0. 2 Mn0. 3 O2 solid batteries via an inorganic-rich artificial cathode electrolyte interphase.

High performance of solid electrolyte endowed by SiO2 cross-linking agent towards lithium metal battery

A dual network solid polymer electrolyte is prepared, the cross-linked part is constructed using ring-opening polymerization reaction, in which SiO2 particles connect with polyethylene glycol diglycidyl ether (PEGDE) and polyetheramine (PEA) as cross-linking point. The introduction of SiO2 is conducive to reduce the crystallization of polymer matrix, improve the strength and promote the fast migration of Li ions. The abundant C-O segments in PEGDE and PEA are advantageous to the hopping behavior of Li ions and improve the ionic conductivity of electrolyte. Poly (vinylidenefluoride-hexaflouropropylene) (PVDF-HFP) is selected as linear part due to its robust mechanical behavior and outstanding electrochemical property. The obtained SiO2 functionalized PEGDE and PEA-PVDF-HFP solid polymer electrolyte (referred to as SGPP-ASPE) demonstrates excellent ionic conductivity of 2.4 × 10−4 S cm−1, high lithium-ion transference number of 0.54 and minor interfacial polarization of 0.09 V after 1000 h using Li//Li symmetrical cell. After assembling Li/LiFePO4 cell, a favorable cycling stability with the capacity retention of 93.8% after 100 cycles at 0.2 C is delivered. The reasonable design of advanced polymer electrolytes with dual network opens up a new path for the development of solid high-performance LMBs.

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

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

In-situ generated solid-state electrolytes with intimate interface affinity enable conductivity and high performances for lithium-ion batteries

The issues of interfacial compatibility derived from electrolyte/electrodes and unsatisfied ionic conductivity still hinder the practical application of lithium-ion batteries. In the present study, the crosslinked solid polymer electrolytes (SPEs) based on dual epoxy group were prepared through in-situ thermal polymerization method. FSO2NH2 was employed as additive for high reactivity to adapt the kinetic reaction and improve the conductivities of electrolytes. The as-prepared SPEs exhibit a high degree of amorphous structure, lower transmission glass temperature, considerable ionic conductivity (>1.0 mS cm−1) at 25 °C, wider electrochemical stability window, and excellent Li cation transference number. Moreover, the battery performance of the as-prepared PBDE−1 electrolyte-based half-cell means that it delivers a high initial specific capacity (ca. 161.2 mAh g−1), and achieves remarkable Coulombic efficiency of 99.8% after 200 cycles at 0.1 C. X-ray photoelectron spectra further revealed the formation of a solid electrolyte interphase (SEI) layer, which can alleviate Li dendrite growth and facilitate the lifespan stability of Li/graphite anode during cycling. These findings may provide a reference for the development of solid-state lithium batteries.

Enhanced Electrochemical Performance of Hybrid Solid Polymer Electrolytes Encompassing Viologen for All-Solid-State Lithium Polymer Batteries

Enhanced Electrochemical Performance of Hybrid Solid Polymer Electrolytes Encompassing Viologen for All-Solid-State Lithium Polymer Batteries

Single-ion conductors functionalized graphene oxide enabling solid polymer electrolytes with uniform Li-ion transport toward stable and dendrite-free lithium metal batteries

The utilization of poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) has long been deemed promising for the application of state-of-the-art lithium metal metals (LMBs), but still severely impeded by the insufficient Li-ion transporting channels and inhomogeneous Li deposition. Herein, the design of single-ion conductors (PSLi) modified graphene oxide nanosheets (GO-PSLi)-reinforced PEO-based SPEs to address these long-standing issues is proposed. The electronegative sulfonate-rich groups with lithiophilic features on GO-PSLi surface not only effectively enhance the dispersion of nanoparticles within the PEO matrix, but also provide fast Li-ion diffusion pathways. Meanwhile, introducing PSLi chains is also favorable to highly reducing the crystallization of composite SPEs through hydrogen interactions derived from the desired amide functional groups. This, in turn, facilitates segmental relaxation of the PEO backbone, leading to accelerates the Li-ion migration. As a proof of concept, the as-prepared composite SPEs demonstrate a good ionic conductivity of 2.2 × 10−4 S cm−1 and a high lithium transference number of 0.53, significantly outperforming the pure PEO SPEs (1.0 × 10−4 S cm−1 and 0.28, respectively) at 60 °C. In addition, the symmetrical Li||Li cells based on the composite SPEs show excellent reversible lithium plating/stripping performances with dendrite-free uniform lithium deposition over 1100 h under a current of 0.1 mA cm−2 at 60 °C. The Li||LiFePO4 batteries also achieve an impressive capacity of 120.2 mAh g−1 at a high current density of 4C and deliver remarkable cycling abilities with 84.6% retention after 250 cycles under 1C at 60 °C. This study offers a facile and practical strategy to develop advanced composite PEO-based SPEs for safe and dendrite-free solid-state LMBs.

High Ionic Conductivity Motivated by Multiple Ion‐Transport Channels in 2D MOF‐Based Lithium Solid State Battery

AbstractMetal‐organic frameworks (MOFs) have been proposed as novel fillers for constructing polymer solid electrolytes based composite electrolytes. However, MOFs are generally used as passive fillers, in‐depth revealing the binding mode between MOFs and polyethylene oxide (PEO), the critical role of MOFs in facilitating Li+ transport in solid electrolytes is full of challenges. Herein, inspired by density functional theory (DFT) the 2D‐MOF with rich unsaturated metal coordination sites that can bind the O atom in PEO through the metal–oxygen bond, anchor TFSI− to release Li+, resulting in a remarkable Li+ transference number of 0.58, is reported according well with the experimental results and molecular dynamics (MD) simulation. Impressively, after the introduction of the 2D‐MOF, the Li+ can rapidly hop along the benzene ring center within the 2D‐MOF plane, and the interface between the benzene ring and PEO can also serve as a fast Li+ migration pathway, delivering multiple ion‐transport channels, which present a high ion conductivity of 4.6 × 10−5 S cm−1 (25 °C). The lithium symmetric battery is stable for 1300 h at 60 °C, 0.1 mA cm−2. The assembled lithium metal solid state battery maintains high capacity of 162.8 mAh g−1 after 500 cycles at 60 °C and 0.5 C. This multiple ion‐transport channels approach brings new ideas for designing advanced solid electrolytes.

Ethylene carbonate plasticized polymer electrolyte for chloride ion batteries with enhanced reversible capacity

Chloride ion batteries (CIB) are attracting more and more attention in recent years because of abundant chloride sources, high energy density, and high safety. The electrode dissolution into the liquid electrolyte remains a great challenge in CIBs. Exploring solid polymer electrolyte provides a feasible solution to address this issue. Herein, a novel gel polymer electrolyte composed of poly(ethylene oxide) (PEO) as a host polymer, tributylmethylammonium chloride (TBMACl) as a salt, and ethylene carbonate (EC) as a plasticizer was prepared by a solution casing method. The addition of plasticizer can not only decrease the PEO crystallinity but also increase salt dissociation. As a result, the ionic conductivity of the plasticized PEO-TBMACl-EC polymer electrolyte reached 5.27 × 10−5 S cm−1 at room temperature, which is much higher than 3.45 × 10−7 S cm−1 of the unplasticized PEO-TBMACl polymer electrolyte. When assembled into CIBs with the FeOCl/Li electrode couple, higher reversible capacities were achieved with the plasticized PEO-TBMACl-EC polymer electrolyte compared to unplasticized PEO-TBMACl polymer electrolyte.

In situ generated of hybrid interface in poly(1,3-dioxolane) quasi solid electrolyte and extended sulfone cosolvent for lithium-metal batteries

The practical application of lithium metal batteries with high energy density are difficult to apply due to the problem of uncontrolled lithium dendrite growth with commercial liquid electrolytes. Herein, we designed a poly 1,3-dioxolane (PDOL) based quasi solid polymer electrolyte with in-situ polymerization. A small amount of lithium difluoro(oxalato)borate (LiDFOB) provides cationic initiation center for the polymerization of dioxolane (DOL). Sulfolane (SL) were further introduced into the system as a cosolvent and the ionic conductivity was increased to 3.22 × 10-4 S cm-1followed with a high Li+ transfer number of 0.73 at room temperature. Trace amount of SbF3 was introduced to form a robustness inorganic-rich hybrid interface that reduces the decomposition of electrolyte components and retards the formation of lithium dendrites during cycling. The superior rate performance and stable 5C long cycle performance are obtained in LiFePO4||Li full cell owing to the interaction between Li+, SL and PDOL. This work expands the choice of components in quasi solid electrolytes to manufacture qualified LMBs with enhanced performance.

Inorganic Composites Improving Conductivities of Solid Polymer Electrolytes for Lithium Batteries: A Review

AbstractFor high‐energy‐density lithium batteries, the research and development of solid‐state electrolytes is crucial. Inorganic‐organic composite electrolytes with high mechanical strength and ionic conductivity of inorganic ceramic electrolytes, as well as high interfacial compatibility of polymer electrolytes, have become a current research hotspot. Based on a brief discussion of lithium dendrite growth and Li+ ion transport mechanisms, this article provides a comprehensive review of the nanostructure design and performance of inorganic‐organic composite electrolytes in recent years, and focuses on the mechanism of homogeneous monolayer composite electrolytes and heterogeneous multilayer composite electrolytes to enhance the performance of electrolytes. In addition, the future prospect of inorganic‐organic composite electrolytes is discussed, providing practical guidance for researchers in this field.

Fluorination of (Mg,Cu,Al,Fe)-based LDHs template for conversion materials usable in all-solid state lithium metal batteries

Iron and copper fluorides are of interest as conversion cathode materials in lithium batteries but they suffer from high hysteresis and low cyclability, respectively. To overcome these limitations and take advantage of the electrochemical properties of each of the fluorides, fluoride mixtures that combine the two redox centers Fe3+ and Cu2+ are synthesized using Layered Double Hydroxides (LDH) as a 2D multi-metallic template. Hydrotalcite-type phases substituted with Cu2+ and Fe3+ ions are prepared by coprecipitation then fluorinated with fluorine gas in static mode at temperatures chosen according to their thermal evolution monitored by mass spectrometry. After each fluorination treatment, the materials are characterized by X-ray diffraction and most LDH materials are found stable up to 200 °C, treatment above leads to the formation of fluorides of each of the cations. The initial dispersion of the cations in the LDH sheets nevertheless allows, after fluorination, a composite of fluorides making them totally accessible to the phenomenon of electrochemical conversion shown here in a metallic lithium battery assembly with a Solid Polymer Electrolyte (SPE). In such All-Solid-State Battery (ASSB) configuration often limiting in terms of columbic efficiency, 76% the first discharge capacity is recovered in charge for an optimized composition (up to 560 mAh.g−1). This good reversibility positions these LDH templates very well for future investigations in the field of electrochemical storage.

Measuring the ionic conductivity of solid polymer electrolyte powders

Ex-situ characterization of solid polymer electrolytes plays an important role in their development as materials for energy applications, with ionic conductivity being a crucial parameter to quantify. Conventional measurements of ionic conductivity often require the formation of a free-standing polymer film which in many instances is difficult to fabricate, thus there may be a need to quantify their ionic conductivity in powder form. In this work, we present a practical and reproducible method for measuring the ionic conductivity of solid polymer electrolytes (SPEs) in their powder form. By using a modified configuration of a through-plane cell, demonstrated with both a proton conducting- and an anion conducting-solid polymer electrolyte powder (SPEP), we are able to obtain ionic conductivity values under variable conditions in order to explore the influence of external parameters on the ionic conductivity of powders. Two types of SPEs in insoluble powder form were employed in this work: (1) a proton-exchange material (SPEP-H+) based on a hyperbranched, sulfo-phenylated poly(phenylene) SPEP (HB-sPPT-H+), with measured ionic conductivity of ⁓ 210 mS cm−1 at 80 °C and 95 % of relative humidity (RH); (2) an anion-exchange conducting polymer in its chloride form (SPEP-Cl-), consisting of a radiation-grafted ultra-high density polyethylene insoluble SPEP containing covalently-bonded benzyltrimethylammonium (BTMA) head-groups, with measured ionic conductivity of ⁓ 53 mS cm−1 at 80 °C and 95 % RH.

Development of composite solid polymer electrolyte for solid-state lithium battery: Incorporating LLZTO in PVDF-HFP/LiTFSI

Solid-state batteries (SSBs) are regarded as favorable future technology as they promise to deliver high energy density and improved safety. However, despite extensive research efforts, the development of SSBs still fall short of expectations mainly because of suitable solid electrolyte which can provide high ionic conductivity as well as good flexibility to enhance interface contact between electrolyte and electrodes. In this work, we have prepared free-standing, flexible composite solid polymer electrolyte (CSPE) membranes by incorporating LLZTO ceramic particles in PVDF-HFP/LiTFSI based solid polymer electrolyte (SPE). Addition of 20 wt% LLZTO has shown to improve the electrochemical properties of the solid electrolyte such as ionic conductivity (8.2 × 10−4 S cm−1 at 60 °C), transference number, electrochemical stability and long-term interface stability with the lithium-metal also showed significant improvement. Furthermore, solid-state LiFePO4/SPE/Li and LiFePO4/CSPE/Li batteries were fabricated, and charge/discharge cycling was performed, where battery with SPE and CSPE exhibited discharge capacity of 119 mA h g−1 and 131 mA h g−1 respectively at 0.1C rate, 60 °C.

A Sustainable Gel Polymer Electrolyte for Solid-State Electrochemical Devices.

Nowadays, solid polymer electrolytes have attracted increasing attention for their wide electrochemical stability window, low cost, excellent processability, flexibility and low interfacial impedance. Specifically, gel polymer electrolytes (GPEs) are attractive substitutes for liquid ones due to their high ionic conductivity (10-3-10-2 S cm-1) at room temperature and solid-like dimensional stability with excellent flexibility. These characteristics make GPEs promising materials for electrochemical device applications, i.e., high-energy-density rechargeable batteries, supercapacitors, electrochromic displays, sensors, and actuators. The aim of this study is to demonstrate the viability of a sustainable GPE, prepared without using organic solvents or ionic liquids and with a simplified preparation route, that can substitute aqueous electrolytes in electrochemical devices operating at low voltages (up to 2 V). A polyvinyl alcohol (PVA)-based GPE has been cast from an aqueous solution and characterized with physicochemical and electrochemical methods. Its electrochemical stability has been assessed with capacitive electrodes in a supercapacitor configuration, and its good ionic conductivity and stability in the atmosphere in terms of water loss have been demonstrated. The feasibility of GPE in an electrochemical sensor configuration with a mediator embedded in an insulating polymer matrix (ferrocene/polyvinylidene difluoride system) has also been reported.