Performance Of Solid Polymer Electrolytes Research Articles

Advanced Crosslinked Solid Polymer Electrolytes: Molecular Architecture, Strategies, and Future Perspectives

AbstractSolid‐state batteries (SSBs) have attracted much attention for high‐energy‐density and high‐safety energy storage devices. Solid polymer electrolytes (SPEs) have emerged as a critical component in the advancement of SSBs, owing to the compelling advantages of strong molecular structure‐designability, low cost, easy manufacturing, and no liquid leakage. However, linear SPEs usually have low room‐temperature ionic conductivity due to crystallization, and melting at high temperature. Thus, crosslinked SPEs have been proposed in that the chemical bonding between internal molecule chains can maintain solid state to expand operational temperature, disrupt regularity of segment, and diminish crystalline degree, leading to an enhancement of room‐temperature ionic conductivity. Furthermore, the integration of functional groups within crosslinked SPE network can significantly augment the electrochemical performance of SPEs. Herein, according to the network structure, crosslinked SPEs are categorized into four types: simple network, AB crosslinked polymers (ABCP), semi‐interpenetrating network (semi‐IPN), and interpenetrating network (IPN), then the structure features and advantages and disadvantages of commonly used polymers for these types of crosslinked SPEs are reviewed. In addition, crosslinked SPEs with self‐healing, flame‐retardant, degradable, and recyclability are introduced. Finally, challenges and prospects of crosslinked SPEs are summarized, hoping to provide guidance for the molecular design of SPEs in the future.

Helical peptide structure improves conductivity and stability of solid electrolytes.

Ion transport is essential to energy storage, cellular signalling and desalination. Polymers have been explored for decades as solid-state electrolytes by either adding salt to polar polymers or tethering ions to the backbone to create less flammable and more robust systems. New design paradigms are needed to advance the performance of solid polymer electrolytes beyond conventional systems. Here the role of a helical secondary structure is shown to greatly enhance the conductivity of solvent-free polymer electrolytes using cationic polypeptides with a mobile anion. Longer helices lead to higher conductivity, and random coil peptides show substantially lower conductivity. The macrodipole of the helix increases with peptide length, leading to larger dielectric constants. The hydrogen bonding of the helix also imparts thermal and electrochemical stability, while allowing for facile dissolution back to monomer in acid. Peptide polymer electrolytes present a promising platform for the design of next-generation ion-transporting materials.

In situ synthesis of cross-linking gel polymer electrolyte for lithium metal batteries

The room temperature ionic conductivity of polyethylene oxide (PEO)-based polymer electrolytes is low, the electrochemical window is narrow, and the mechanical strength is relatively poor. In this work, a cross-linking gel-based solid composite polymer electrolyte (CG-SCPE) was synthesized by introducing electrochemically stable carbonate-based functional groups. The synthesized CG-SCPE presents excellent tensile strength (26 MPa) and a wide electrochemical stability window (> 4.5 V vs. Li/Li+). Meanwhile, the in situ polymerization method induced by thermal heating resulted in good compatibility between electrodes/electrolytes. In addition, the assembled LiNi0.5Co0.2Mn0.3O2/CG-SCPE/Li battery exhibited satisfactory electrochemical performance. Therefore, the gel polymer electrolyte CG-SCPE with cross-linking network provides the possibility for future application of safe and high-performance solid-state lithium metal batteries. The results indicate that the introduction of cross-linking framework can simultaneously improve the mechanical strength, thermal stability, and electrochemical performance of solid polymer electrolyte.

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

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

Architecting precise and ultrathin nanolayer interface on 4.5V LiCoO2 cathode to realize poly (ethylene oxide) cycling stability

The poly (ethylene oxide) (PEO) solid polymer electrolytes suffer from narrow electrochemical stability window and cannot match high voltage lithium cobalt oxide (LCO) cathode. Herein, an ultrathin Al2O3 nanolayer was uniformly deposited on the surface of LCO via powder atomic layer deposition (PALD) to realize poly (ethylene oxide) polymer electrolyte cycling stability. The PEO solid polymer electrolyte contains 20 % (w/w) lithium difluoro(oxalate)borate (LiDFOB) and 7.5 % (w/w) lithium titanium aluminum phosphate (LATP) with cellulose nonwoven as a support substrate. The electrolyte exhibitsionic conductivity of 1.2×10−4 S cm−1, an electrochemical stability window of 4.5 V (vs. Li+/Li) and lithium-ion transference number of 0.38. Al2O3@LCO/PEO-LiDFOB20%-LATP7.5%/Li cell at high cut-off 4.5 V delivered better initial discharge specific capacity of 178.5 mAh g−1 and achieved a capacity retention ratio of 81.6 % after 200 cycles under 0.1 C at 50 °C. Further analysis showed that Al2O3 layer served as stable a protective layer to suppress the generation of strong oxidative Co4+ and O– species and separate from the PEO solid polymer electrolyte, inhibiting the side reactions at the cathode-side interface. Therefore, architecting precise and ultrathin protective nanolayer interface on high voltage LCO cathode via PALD is conducive to cycling performance of solid polymer electrolyte.

Enhanced performance of solid polymer electrolytes combining poly(vinylidene fluoride-co-hexafluoropropylene), metal-organic framework and ionic liquid for advanced solid state lithium-ion batteries

The search for sustainable and high-performance materials for lithium-ion batteries is leading to significant advances in solid polymer electrolyte (SPE) technology. However, the current drawbacks of this approach prove the need for further research and development in the field. Herein, novel ternary solid polymer electrolytes have been developed using varying loads of MOF-808 metal-organic framework and [BMIM][SCN] ionic liquid (IL) incorporated in a poly(vinylidene fluoride-co-hexafluoropropylene) matrix. The solid polymer electrolytes were evaluated at morphological, structural, thermal, mechanical and electrochemical levels, and their performance in cycling battery testing was assessed. The results showed a homogeneous structure throughout all the samples and a good dispersion of the distinct components. The polymer polar phase and degree of crystallinity of the samples are increased with increasing IL content, and the thermal and mechanical properties are appropriate for battery application. The ionic conductivity of the samples reaches maximum values of 4.68 × 10−5 S‧cm−1 at room temperature, lithium transference numbers up to 0.65, and high electrochemical stability, making them well-suited for battery applications. The assembled stability after 50 cycles at C/10 with a discharge capacity value of 150 mAh‧g−1 at room temperature was tested/derived. The obtained results show the potential of this system for high performance room temperature solid polymer electrolytes.

Effect of fluorinated polymer matrix type in the performance of solid polymer electrolytes based on ionic liquids for solid-state lithium-ion batteries

Solid polymer electrolytes (SPEs) have been produced using an ionic liquid (IL) (1-Methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide – [PMPyrr][TFSI]) embedded in different fluorinated polymer matrices, including poly(vinylidene-fluoride) – PVDF, poly(vinylidene fluoride-co-hexafluoropropylene) – P(VDF-HFP), poly(vinylidene fluoride-co-trifluoroethylene) – P(VDF-TrFE) and poly(vinylidene fluoride-co-trifluoroethylene-chlorofluoroethylene) – P(VDF-TrFE-CFE), in order to evaluate the effect of the polymer chain polarity, degree of crystallinity and dielectric constant on the electrochemical properties and battery performance. It is shown that the use of the different polymers for SPE development does not have significant influence on the morphology, and thermal properties of the samples. The degree of crystallinity is significantly reduced for the P(VDF-TrFE-CFE) sample. The mechanical characteristics (Young modulus and yield strength and strain) are also associated with the crystallinity degree, being reduced for lower crystallinities. Regarding the electrochemical parameters, the samples present considered high ionic conductivity, with a maximum room temperature value of 6.2 × 10−5 S cm−1 for the P(VDF-HFP) sample. The lithium transference number for all samples show their suitability for application in lithium-ion batteries with an outstanding value of 0.71 for the P(VDF-TrFE-CFE) sample associated with the higher dielectric constant and lower degree of crystallinity of this polymer. Battery cycling tests show a maximum initial discharge capacity of 146 mAh/g for the P(VDF-TrFE) sample at room temperature and C/10 rate. Furthermore, the P(VDF-TrFE-CFE) sample presents an excellent ability to cycle at high discharge rates, achieving 91 mAh/g at 1C rate, an maintaining a high stability after 60 cycles at room temperature, showing excellent potential for application in lithium-ion batteries due to its low crystallinity and high dielectric constant. This work proves the suitability of fluorinated polymer based SPE with embedded ionic liquids for the next generation of solid-state batteries and provides a valuable insight on the role of the polymer dielectric constant and degree of crystallinity on battery performance.

Polymer-coated silica dual functional fillers to improve the performance of poly(ethylene oxide)-based solid electrolytes

The application of solid polymer electrolytes (SPEs) is mainly hindered by their low ionic conductivity and the limited mechanical properties. Adding functional small molecules and inorganic fillers are two of the simplest and most effective ways to improve the performance of SPEs. However, most of the time, both methods cannot be implemented concomitantly, and may even inhibit each other. Here, an original dual functional filler, consisting of hollow porous SiO2 nanospheres three-dimensionally wrapped by poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM), is blended with poly(ethylene oxide) (PEO) and LiClO4 to obtain a composite solid electrolyte (CSE). Compared to the reference PEO SPE, the room-temperature ionic conductivity of the synthesized CSE is improved by 4 orders of magnitude reaching 1.3 × 10−4 S cm−1. Moreover, a lithium ion transference number value as high as 0.81 is obtained. The CSE membrane is further assembled with a Li anode and a standard LiFePO4 cathode to obtain an all-solid-state battery showing high capacity (149.3 mAh g−1 at 0.1 C) and long-term stability (0.68‰ loss of capacity per cycle, over 100 cycles). The peculiar structure of the PEO/PTMPM interface is thought to be at the origin of the enhanced LiClO4 dissociation and mobility of lithium ions. Remarkably, the well-known toughening effect of SiO2 fillers is preserved in the CSE.

Promoting ion and heat transfer of solid polymer electrolytes by tuning polymer chain length and salt concentration

ABSTRACT The heat and mass performance of solid polymer electrolytes (SPEs) directly affects their application in solid-state batteries (SSBs). However, high crystallinity and charged clusters hinder the transport of Li+ in SPEs, resulting in low ion diffusivities and thermal conductivities. Therefore, understanding the effects of SPE structure on ion transport and heat conduction is critical for SPE designing. In this work, the ion diffusivities and thermal conductivities of SPEs containing polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt with different PEO chain lengths and salt concentrations are studied and the structural properties are analyzed to determine the mechanisms of ion transport and heat conduction. The results show that the crystallinity and charged clusters decrease in SPEs with short-chain PEO and low salt concentration, thereby improving ion transfer and heat conduction. Moreover, phonon spectra shift to a higher-frequency domain when salt concentration increases, which induces a decrease in thermal conductivity. Decreased salt concentration and chain length increased conductivity by 350% and 176%, respectively, and thermal conductivity by 122% and 140%, respectively. These findings, which indicate that SPEs with short-chain PEO and low salt concentration have better ion and heat transfer, provide valuable insight into the design of PEO-LiTFSI electrolytes.

A Review of Current Trends on Polyvinyl Alcohol (PVA)-Based Solid Polymer Electrolytes

Presently, the rising concerns about the fossil fuel crisis and ecological deterioration have greatly affected the world economy and hence have attracted attention to the utilization of renewable energies. Among the renewable energy being developed, supercapacitors hold great promise in broad applications such as electric vehicles. Presently, the main challenge facing supercapacitors is the amount of energy stored. This, however, does not satisfy the increasing demand for higher energy storage devices, and therefore, intensive research is being undertaken to overcome the challenges of low energy density. The purpose of this review is to report on solid polymer electrolytes (SPEs) based on polyvinyl alcohol (PVA). The review discussed the PVA as a host polymer in SPEs followed by a discussion on the influence of conducting salts. The formation of SPEs as well as the ion transport mechanism in PVA SPEs were discussed. The application and development of PVA-based polymer electrolytes on supercapacitors and other energy storage devices were elucidated. The fundamentals of electrochemical characterization for analyzing the mechanism of supercapacitor applications, such as EIS, LSV and dielectric constant, are highlighted. Similarly, thermodynamic transport models of ions and their mechanism about temperature based on Arrhenius and Vogel-Tammann-Fulcher (VTF) are analyzed. Methods for enhancing the electrochemical performance of PVA-based SPEs were reported. Likely challenges facing the current electrolytes are well discussed. Finally, research directions to overcome the present challenges in producing SPEs are proposed. Therefore, this review is expected to be source material for other researchers concerned with the development of PVA-based SPE material.

A Gel Polymer Electrolyte with 2D Filler‐reinforced for Dendrite Suppression Li‐Ion Batteries

AbstractGel polymer electrolytes (GPEs) incorporate both the high ionic conductivity of organic liquid electrolyte and the high safety performance of all‐solid‐state electrolytes (ASSEs), greatly improving the electrochemical performance of solid polymer electrolytes (SPEs). However, the practical application of GPEs is still limited by inferior interface compatibility, lithium dendrites, etc. Herein, we prepared GPEs based on poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) further co‐blended the two‐dimensional sheet inorganic filler hectorite and poly(methyl methacrylate) (PMMA) to improve the mechanical and electrochemical properties of the GPEs. When the content of PMMA and hectorite is optimal, this GPEs have an ionic conductivity of 1.06×10−3 S cm−1 and outstanding lithium symmetric cells cycle time of more than 3000 h, indicating that the introduction of filler effectively inhibits the growth of lithium dendrites at room temperature. Moreover, the GPEs adopt a relatively simple solution casting method to provide a fresh idea for the synthesis of high‐performance GPEs.

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.

Environmental Impact Assessment of Solid Polymer Electrolytes for Solid‐State Lithium Batteries

Solid‐state batteries play a pivotal role in the next‐generation batteries as they satisfy the stringent safety requirements for stationary or electric vehicle applications. Notable efforts are devoted to the competitive design of solid polymer electrolytes (SPEs) acting as both the electrolyte and the separator. Although particular efforts to attain acceptable ionic conductivities and wide electrochemical stability widows are carried out, the environmental sustainability is largely neglected. To address this gap, here the cradle‐to‐gate environmental impacts of the most representative SPEs using life cycle assessment (LCA) are quantified. Raw material extraction and electrolyte fabrication are considered. Global warming potential values of 0.37–10.64 kg CO2 equiv. gelectrolyte −1 are achieved, where PEO/LiTFSI presents the lower environmental burdens. A minor role of the polymer fraction on the total impacts is observed, with a maximum CO2 footprint share of 0.61%. Following ecodesign approaches, a sensitivity analysis is performed to simulate industrial‐scale fabrication processes and explore environmentally friendlier scenarios. The electrochemical performance of SPEs is further analyzed into Li/LiFePO4 solid lithium metal battery cell configuration. Overall, these results are aimed to guide the ecologically sustainable design of SPEs and facilitate the implementation of next‐generation sustainable batteries.

An acrylate-based quasi-solid polymer electrolyte incorporating a novel dinitrile poly(ethylene glycol) plasticizer for lithium-ion batteries

The performance of solid polymer electrolytes is characterized by lower ionic conductivity than conventional liquid electrolytes but provides advantages in terms of operational safety. A quasi-solid polymer electrolyte (QSPE) based on a new plasticizer 4,7,10,13-tetraoxahexadecane-1,16-dinitrile (bCN-PEG4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) incorporated into a polyacrylates matrix was successfully prepared via UV-induced copolymerization. The matrix consists of units of trimethylolpropane ethoxylate triacrylate (ETPTA), poly(ethylene glycol) diacrylate (PEGDA), and the monoacrylate poly(ethylene glycol) methyl ether acrylate (mPEGa). The QSPE containing 55 wt% bCN-PEG4 exhibits highly uniform morphology, thermal stability > 200 °C, ionic conductivity of 1.8 × 10−4 S cm−1 at 30 °C, and 1.3 × 10−3 S cm−1 at 80 °C, coupled with very high electrochemical stability (> 5 V vs. Li/Li+) and a low glass transition temperature (− 55.7 °C). A cycling experiment in a Li/QPSE/Li cell setup demonstrated the compatibility toward lithium metal additionally. The bCN-PEG4 offers an overall satisfying performance as a plasticizer in a poly(ethylene oxide)-based solid polymer electrolyte. The new QSPE is an alternative to dinitrile-based (e.g., succinonitrile) or glycol ether-based (e.g., tetraglyme) plasticizers with application potential in high-voltage lithium-ion batteries.Graphical abstract

Impact of charge carrier transport properties on conductivity-temperature dependence of gellan gum-LiCF3SO3 biopolymer electrolyte

Charge carrier density, mobility and diffusivity are three important transport properties in determining the ionic conductivity as well as the performance of solid polymer electrolyte. In this work, biopolymer electrolytes samples were prepared using the solution casting method by complexing gellan gum with different concentrations of lithium trifluoromethanesulfonate (3–15 wt.%). The values of charge carrier concentration, mobility, and diffusivity for electrolyte samples were estimated by fitting the Nyquist plot with an equation developed based on electrical impedance spectroscopy. At room temperature, the optimum electrolyte conductivity is 1.29×10−8 Scm−1 at 6 wt.% salt concentration. This result was supported by the highest percentage of free ions, 31.45%, observed in the FTIR method. As the temperature increases, the ionic conductivity increases to the optimum value before dropping. The highest conductivity of each sample was obtained at different temperatures (80°C–90°C) using the impedance method, whereas the percentage area of free ions was highest at 80°C for all samples with FTIR analysis. Overall, the ionic conductivity of this system has been dominated by the carrier charge density. Results suggest that, under these experimental conditions, electrical impedance spectroscopy is suitable for evaluating the charge transport properties at low temperatures.

Improved Performance of Solid Polymer Electrolyte for Lithium-Metal Batteries via Hot Press Rolling.

Solid-state batteries (SSBs) are gaining attention as they promise to provide better safety and a higher energy density than conventional liquid electrolyte batteries. Solid polymer electrolytes (SPEs) are promising candidates due to their flexibility providing better interfacial contact between electrodes and the electrolyte. However, SPEs exhibit very low ionic conductivity at ambient temperatures, which prevents their practical use in batteries. Herein, a simple and effective technique of hot press rolling is demonstrated to improve ionic conductivity and, hence, the performance of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)-based solid polymer electrolyte. Applying hot press rolling to the electrolyte membrane induced structural changes in the grain boundaries, which resulted in a reduction in the crystallinity of the material and, hence, an increase in the amorphous phase of the material, which eased the movement of the lithium ions within the material. This technique also improved the surface of the membrane, making it homogeneous and smoother, which resulted in better interfacial contact between the electrodes and electrolyte. Electrochemical tests were carried out on electrolyte membranes treated with and without hot press rolling to evaluate the effect of the treatment. The hot pressed electrolyte membrane showed significant improvements in its ionic conductivity and transference number. The cycling performance of the LFP/Li batteries using a hot press rolled electrolyte was also evaluated, which gave a specific discharge capacity of 134 mAh/g at 0.1 C. These results demonstrate that hot press rolling can have a significant effect on the electrochemical performance of solid polymer electrolytes.

Macromolecular Design of Lithium Conductive Polymer as Electrolyte for Solid-State Lithium Batteries.

In the development of solid-state lithium batteries, solid polymer electrolyte (SPE) has drawn extensive concerns for its thermal and chemical stability, low density, and good processability. Especially SPE efficiently suppresses the formation of lithium dendrite and promotes battery safety. However, most of SPE is derived from the matrix with simple functional group, which suffers from low ionic conductivity, reduced mechanical properties after conductivity modification, bad electrochemical stability, and low lithium-ion transference number. Appling macromolecular design with multiple functional groups to polymer matrix is accepted as a strategy to solve the problems of SPE fundamentally. In this review, macromolecular design based on lithium conducting groups is summarized including copolymerization, network construction, and grafting. Meanwhile, the construction of single-ion conductor polymer is also focused herein. Moreover, synergistic effects between the designed matrix, lithium salt, and fillers are reviewed with the objective to further improve the performance of SPE. At last, future studies on macromolecular design are proposed in the development of SPE for solid-state batteries with high energy density and durability.

The Impact of Absorbed Solvent on the Performance of Solid Polymer Electrolytes for Use in Solid-State Lithium Batteries.

SummaryThe effects of solvent absorption on the electrochemical and mechanical properties of polymer electrolytes for use in solid-state batteries have been measured by researchers since the 1980s. These studies have shown that small amounts of absorbed solvent may increase ion mobility and decrease crystallinity in these materials. Even though many polymers and lithium salts are hygroscopic, the solvent content of these materials is rarely reported. As ppm-level solvent content may have important consequences for the lithium conductivity and crystallinity of these electrolytes, more widespread reporting is recommended. Here we illustrate that ppm-level solvent content can significantly increase ion mobility, and therefore the reported performance, in solid polymer electrolytes. Additionally, the impact of absorbed solvents on other battery components has not been widely investigated in all-solid-state battery systems. Therefore, comparisons will be made with systems that use liquid electrolytes to better understand the consequences of absorbed solvents on electrode performance.

Al4B2O9 nanorods-modified solid polymer electrolytes with decent integrated performance

With the proliferation of energy storage and power applications, electric vehicles particularly, solid-state batteries are considered as one of the most promising strategies to address the ever-increasing safety concern and high energy demand of power devices. Here, we demonstrate the Al4B2O9 nanorods-modified poly(ethylene oxide) (PEO)-based solid polymer electrolyte (ASPE) with high ionic conductivity, wide electrochemical window, decent mechanical property and nonflammable performance. Specifically, because of the longer-range ordered Li+ transfer channels conducted by the interaction between Al4B2O9 nanorods and PEO, the optimal ASPE (ASPE-1) shows excellent ionic conductivity of 4.35×10−1 and 3.1×10−1 S cm−1 at 30 and 60°C, respectively. It also has good electrochemical stability at 60°C with a decomposition voltage of 5.1 V. Besides, the assembled LiFePO4//Li cells show good cycling performance, delivering 155 mA h g−1 after 300 cycles at 1 C under 60°C, and present excellent low temperature adaptability, retaining over 125 mA h g−1 after 90 cycles at 0.2 C under 30°C. These results verify that the addition of Al4B2O9 nanorods can effectively promote the integrated performance of solid polymer electrolyte.

Carbonyl-coordinating polymers for high-voltage solid-state lithium batteries: Solid polymer electrolytes

ABSTRACT