Development Of Solid Polymer Electrolytes Research Articles

Developing Single‐Ion Conductive Polymer Electrolytes for High‐Energy‐Density Solid State Batteries

AbstractSingle‐ion conductive polymer electrolytes (SICPEs) with a cationic transference number (tLi+) close to unity exhibit specific advantages in solid‐state batteries (SSBs), including mitigating the ion concentration gradient and derived problems, suppressing the growth of lithium dendrites, and improving the utilization of cathode materials and the rate performance of SSBs. However, the application of SICPEs remains major challenges, i.e., the ionic conductivity is inferior at room temperature. Therefore, the recent accomplishments in improving the ambient ionic conductivity to be compatible SICPEs with a high transference number are discussed in this review. In particular, some strategies of delocalizing charges in polyanions, designing a highly conductive polymer matrix, and utilizing synergistic effects in SICPEs are focused to shed light on the further development of solid polymer electrolytes for SSBs. Finally, multifunctional species of SICPEs are discussed in view of the mechanical contact and/or charge transfer problems at the solid–solid interface in SSBs.

Polymer electrolytes shielded by 2D Li0.46Mn0.77PS3 Li+-conductors for all-solid-state lithium-metal batteries

The development of solid polymer electrolytes (SPEs) is impeded by the severe Li-dendrites growth at the unstable SPE-Li interface. Herein, we demonstrate that the interfacial stability of poly(ethylene oxide) (PEO) electrolytes against Li metal is significantly improved by a shielding strategy, where the nanosheets of a 2D Li+ conductor Li0.46Mn0.77PS3 (LiMPS) serve as nanosized shields to armor PEO against the spears - lithium dendrites. Besides physical inhibition, LiMPS also homogenizes Li+ flux owing to its 2D nature, superior Li+ conductivity (2.1 × 10−4 S cm−1 at 30 ℃) and strong adsorption of Li+. This strategy also enables PEO-LiMPS electrolytes to exhibit superior ionic conductivity of 2.6 × 10−4 S cm−1 at 45 ℃, a nearly tenfold increase compared to bare PEO electrolytes. Furthermore, the electrochemical stability window (ESW) of PEO-LiMPS electrolytes is expanded to 4.8 V (3.8 V for pristine PEO). As a result, symmetric Li/PEO-LiMPS/Li cells deliver short circuit-free cycling over 600 h, and LiNi0.8Co0.1Mn0.1O2/PEO-LiMPS/Li batteries also present a high-capacity retention over 80% after 200 cycles at 0.2 C. In addition, LFP/PEO-LiMPS/Li pouch cell retains 93% of the initial capacity after cycling at 0.2 C for 230 cycles. This 2D Li+-conductive shielding strategy provides a unique protective mechanism for SPEs in solid-state Li metal batteries (SSLMBs).

Lithium-Rich Porous Aromatic Framework-Based Quasi-Solid Polymer Electrolyte for High-Performance Lithium Ion Batteries.

The development of solid polymer electrolytes (SPEs) with high ionic conductivity, wide electrochemical window, and high mechanical strength is the key factor to realize high-energy-density solid lithium ion batteries (SLIBs). Porous aromatic frameworks (PAFs) have the advantages of high porosity, easily functionalized molecular structure, and rigid stable framework, which fully meet the requirements of solid polymer electrolytes with high Li+ capacity, fast Li+ transport, and safety. Herein, a lithium-rich amidoxime (AO)-modified porous aromatic framework (PAF-170-AO) was obtained through the absorption of LiTFSI by amidoxime groups and abundant pores and then compounded with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to prepare a PAF-based quasi-solid polymer electrolyte (PAF-QSPE) with only tiny amounts of plasticizer (∼12 μL). The amidoxime groups of PAF-170-AO restricted the movement of the anions of LiTFSI through hydrogen bonding, which effectively promoted the dissociation and migration number of Li+ (tLi+), reduced the concentration polarization, and inhibited the growth of lithium dendrites. The PAF-QSPE exhibited a high ionic conductivity of 1.75 × 10-4 S cm-1 and tLi+ of 0.55 at room temperature. The activation energy was as low as 0.136 eV. Furthermore, the assembled SLIBs with the PAF-QSPE presented a discharge capacity of 163 mAh g-1 at 0.2 C and a capacity retention rate of 96% after 350 cycles, illustrating a stable cycling performance. This work demonstrated the great application potential of lithium-rich PAFs in QSPEs.

Structural, optical, mechanical, and dielectric properties studies of carboxymethyl cellulose/polyacrylamide/lithium titanate nanocomposites films as an application in energy storage devices

Carboxymethyl cellulose/polyacrylamide (CMC/PAM) blend was used as a matrix material for fabricating nanocomposite samples reinforced with the cubic lithium titanate nanoparticles (Li4Ti5O12 NPs, particle size <55 nm) by the solution casting method. The structural, optical, thermal, mechanical, and dielectric properties of the nanocomposite were investigated. The CMC/PAM structure's increased amorphous areas and the existence of hydrogen and coordination bonds in the nanocomposite samples were both revealed by the XRD and FT-IR spectra. The optical measurements indicated the absorbance significantly improved and the energy band gap decreased as indicated in the UV–Visible spectra. Due to interactions between the polymer and nanoparticles and the fine dispersion of NPs, the inclusion of Li4Ti5O12 NPs improved the thermal stability at high temperatures of CMC/PAM, according to the results of TGA thermograms. The mechanical properties of the CMC/PAM were improved by addition of the nanofiller. The dielectric parameters, such as the dielectric permittivity and modulus spectra, of nanocomposite films were also reported, where these parameters can be advantageously tuned with Li4Ti5O12 content in the CMC/PAM blend that depicts them as attractive biodegradable polymer nano-dielectrics. The relaxation process and predominant effect of interfacial polarization within these hybrid samples are reported. The obtained results depict multifunctionality of these nanocomposite films as optical band gap tuner, development of solid polymer electrolyte, dielectric permittivity controllable nanodielectrics for preparation of high-density energy storing/advanced microelectronic devices.

High-performance quaternary polymer solid-state electrolyte via one-step casting method

Lithium-ion batteries have achieved huge success in the field of energy storage, but they use flammable electrolytes that may cause safety issue. Solid polymer electrolytes have been considered as the final solution to this safety issue, which have received many researchers’ attention. However, solid polymer electrolytes still face several challenges, such as low ionic conductivity. Herein, we report a quaternary solid polymer electrolyte to achieve high ionic conductivity, which was synthesized by one-step casting method. This quaternary electrolyte contains two polymers (poly(vinylidene fluoride-co-hexafluoropropylene) and poly(ethylene oxide) diacrylate), one plasticizer (succinonitrile), and one lithium salt (lithium bis(trifluoromethane)sulfonimide). Long-chain polymer is used as matrix, and short-chain polymer and plasticizer are used to increase ionic conductivity. This quaternary electrolyte achieves a high ionic conductivity of 1.49 × 10−4 S cm−1 at room temperature. When assembled into coin cell with lithium iron phosphate cathode and lithium metal anode, this quaternary electrolyte achieves a capacity of 139 mAh g−1 at 0.2 C after 50 cycles and 106 mAh g−1 at 1 C after 160 cycles. Moreover, this facile one-step casting method provides a new route towards the development of solid polymer electrolytes.

Development of solid polymer electrolytes based on poly (ethylene oxide) complexed with 2-trifluoromethyl-4, 5-dicyanoimidazole lithium salt and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid for Li-ion batteries

Ion conducting solid polymer electrolyte films based on polymer poly (ethylene oxide) (PEO) complexed with 2-trifluoromethyl-4, 5-dicyanoimidazole lithium salt and ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are synthesized using anhydrous acetonitrile as solvent. Prepared electrolyte films are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), complex impedance spectroscopy and cyclic voltammetry techniques. Incorporation of IL into the PEO20-LiTDI polymer electrolyte changes different physicochemical properties of these materials. By characterizations, particularly XRD, DSC and ionic conductivity studies, the synthesized SPEs showed decreased crystallinity, melting points and increased ionic conductivity by the introduction of ionic liquid. The 40 wt% of IL doped polymer electrolyte showed an ionic conductivity of the order of 1.78 × 10−4 S/cm at 60°C with better thermal stability. The optimum conducting composition showed very good electrochemical stability window at ambient temperature. These results suggested that the IL-doped polymer electrolyte would be a potential separator in Li-ion batteries.

Analytical analysis of concentration of charge carriers in polymer electrolytes through different models

The development of solid polymer electrolytes with high ionic conductivity and good chemical and mechanical stability for application in various electrochemical devices has been a critical area of research in the past few decades. For the better performance of the electrochemical devices, the compatibility between the electrodes and electrolytes of the system is the foremost requirement. In addition to this, the ion conductivity of the electrolytes is an important parameter. Understanding the mechanism of changes in ionic conductivity with different concentrations of salt and dispersoid is very crucial. In the present work, we have used three theoretical models, the Rice-Roth model, the Trukhan model and Schutt and Gerdes Model, to understand the reasons behind the variation in conductivity by calculating the concentration and mobility of charge carriers. All the required parameters of the model for the calculation purpose have been taken from Impedance Spectroscopy data. The Trukhan model is a direct method for evaluating the exact value of the diffusion coefficient. The diffusion coefficient of PEO-NaI based electrolyte thin films are calculated from the dielectric tangent loss and further used for analyzing the concentration of charge carrier and ion mobility. Similarly, two more theoretical models, Rice-Roth and Schutt & Gerdes model were used to confirm the value of the number of charge carriers. Further, all the results are compared with each other for the conclusion.

Research progress on solid polymer electrolytes

<p indent="0mm">Since the commercialization of lithium-ion batteries in the 1990s, lithium-ion batteries have been successfully applied in portable electronics, electric vehicles, and grid energy storage. Although current organic liquid electrolytes have high ionic conductivities, they are inherently flammable, volatile, and prone to leakage. Moreover, severe side reactions and dendrite growth on the surface of the lithium anode during the charge-discharge process can cause safety hazards, which greatly impede their applications in lithium metal batteries. Solid electrolytes, including inorganic solid electrolytes and polymer electrolytes, are regarded as effective alternatives to organic liquid electrolytes for the construction of lithium metal batteries with high energy density and safety. Among them, solid polymer electrolytes offer excellent flexibility, processability, and interfacial compatibility over inorganic solid electrolytes, and they are extraordinarily promising for lithium metal batteries with high energy density and safety. Ideal solid polymer electrolytes should have following features: (1) High ionic conductivity (&gt; <sc>10 ^–4 S cm ^–1) </sc> at room temperature; (2) high lithium ion transference number (~1) to reduce the concentration polarization and improve the rate performance of batteries; (3) intimate contact at the electrode/electrolyte interfaces; (4) wide electrochemical window <sc>(&gt;4.5 V</sc> vs. Li/Li ⁺) to match high-voltage cathodes and improve the energy density of batteries; (5) good mechanical stability to resist processing, buffer electrode volume change and inhibit dendrite growth; (6) good thermal stability to withstand environmental changes. Generally, the ionic conductivity of pure solid polymer electrolytes at room temperature is low <sc>(~10 ^–6 S cm ^–1). </sc> Researchers have tried to improve the ionic conductivities by adjusting the lithium salt concentration, such as developing “polymer-in-salt” solid electrolytes. However, increasing the concentration of lithium salt leads to the deterioration of the mechanical strength. Strategies such as developing novel lithium salts, modifying polymer matrix, and incorporating inorganic fillers into solid polymer electrolytes are proposed to promote ionic conductivities of solid polymer electrolytes. In particular, composite polymer electrolytes, fabricated by dispersing a certain amount of inorganic fillers into solid polymer electrolytes, have improved ionic conductivities without sacrificing their mechanical performances. Poor interfacial property between electrodes and electrolytes is also a critical issue for solid polymer electrolytes. On one hand, poor and uneven solid/solid contacts at the electrode/electrolyte interfaces lead to high resistance and sluggish ionic transport kinetics. Furthermore, the volume change of the positive and negative electrodes in the charge/discharge process deteriorates the interfacial contacts, blocks the ion and electron transport through the interfaces, and greatly reduces the electrochemical reaction kinetics. On the other hand, the electrochemical windows of solid polymer electrolytes are usually narrow <sc>(＜4.5 V).</sc> During cycling, redox reactions are prone to occur at the electrode/electrolyte interfaces, causing battery failure. Solid polymer electrolytes have also poor thermal and mechanical stabilities. Therefore, design and synthesis of polymer-based solid electrolytes with excellent comprehensive performances and construction of fast and stable ion transport channels at the electrolyte/electrode interfaces are of great significance for the successful development of solid-state lithium metal batteries. This paper presents a brief review of the research progress in solid polymer electrolytes from two aspects: Improving the ionic conductivities of solid polymer electrolytes and enhancing the interfacial performance at electrolyte/electrode interfaces. First, targeted optimization strategies on ionic conductivities of solid polymer electrolytes, including constructing continuously aligned ionic transport paths and shortening the ionic transport distance, are summarized. Second, interface optimization strategies, including constructing wetting interfaces and synthesizing asymmetric electrolytes, are presented to reduce the interface resistance and improve the interfacial contact. Finally, perspectives on the development of solid polymer electrolytes and high-performance solid-state lithium metal batteries are discussed, and key research directions and advanced test methods are proposed. This review may provide a comprehensive understanding and further guidance for not only the material design of solid polymer electrolytes, but also the structural design of lithium metal batteries with favorable electrochemical and interfacial performances.

Ion Conductive Behavior of Oligoether/Zwitterion Diblock Copolymers Containing Magnesium Salt

Rechargeable magnesium (Mg) batteries are envisioned as next generation batteries. The development of solid polymer electrolytes with high ionic conductivity will contribute to realize not only high performance Mg batteries but also reliable and safe devices. In this study, diblock copolymers (PPEGMAm‐b‐SPBn) with oligoether (PEGMA) and zwitterionic (SPB) side‐chains are synthesized in order to develop novel Mg‐ion electrolytes. PPEGMAm‐b‐SPBn copolymers with various unit ratios are synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization. PPEGMAm‐b‐SPBn exhibited two distinct glass transition temperatures. Phase‐separated structures are observed by atomic force microscope (AFM) measurements. PPEGMAm‐b‐SPBn/Mg‐salt composites exhibited a glass transition temperature due to the mixture formation of PEGMA and SPB blocks. When the unit numbers of m and n are 44 and 75, respectively, PPEGMAm‐b‐SPBn/Mg‐salt ([EO]: [Mg] = 6: 1) exhibits the highest ionic conductivity of over 10−4 S cm−1 at 60 °C among 11 composites prepared in this study.

Reducing crystallinity in solid polymer electrolytes for lithium-metal batteries via statistical copolymerization

The discovery that polyethylene oxide promotes ionic conductivity led to the development of solid polymer electrolytes. However, their conductivity is severely reduced by crystallinity. Here, statistical copolymerization is used to design macromolecular architectures where crystallinity is disrupted by a minimal amount of non-ethylene oxide comonomer units. Using the Flory exclusion model, we demonstrate that polymers containing 18 mol% comonomer and 18 wt% LiTFSI are devoid of crystallinity. A 10 mol% comonomer content is sufficient to reach a conductivity of 0.3 × 10−4 S cm−1 at 25 °C. The Li+ transference number is 0.6, indicating that the comonomer units not only limit the crystallinity but also weaken the strength of the Li+ coordination to the polymer. The resulting solid polymer electrolyte is effective in an all-solid LFP|Li-metal battery operating at 25 °C, demonstrating that statistical copolymerization is an efficient tool for polymer electrolyte design.

Study of solid polyurethane electrolytes synthesized from HDI and PEO of different molecular weight

The development of solid polymer electrolyte (SPE) is important for the fabrication of safe and high performance lithium ion battery of the next generation. A series of polyurethanes (PUs) based SPEs synthesized from hexamethylene diisocyanate (HDI) and poly(ethylene glycol)s (PEGs) of varying molecular weight (MW = 300 ~ 1500 corresponding to PU03 ~ PU15) via one-step approach are investigated for the conductivity of lithium ion and other electrochemical properties. These synthetic PUs exhibit semi-crystalline structures when the MW of PEG is higher than 300, and turn into amorphous after the addition of LiClO4. The ionic conductivity decreases with the increasing concentration of LiClO4. The highest lithium ion conductivity was found to be 3.42 × 10−5 S/cm for PU15 with 10 wt% LiClO4 at 50 °C. However, its lithium ion transference number is low by 0.15. All of the PU-based SPEs containing 10 wt% LiClO4 are electrochemically stable up to 4.2 ~ 4.5 V versus Li+/Li, and show very good cycling stability in charge/discharge experiments. In the assembled battery with LiFePO4 as the cathode, PU15 displays higher performances than PU03, indicating good correlation to the molecular weight of PEG.

A graphene oxide and ionic liquid assisted anion-immobilized polymer electrolyte with high ionic conductivity for dendrite-free lithium metal batteries

Development of solid polymer electrolytes (SPEs) with superior performance is crucial for high-energy density lithium metal batteries (LMBs). Herein, a graphene oxide (GO) and ionic liquid (IL) assisted anion-immobilized polymer electrolyte (PGI) is developed, which can effectively prevent the formation of Li dendrite of LMBs. Various characterizations show that the synergetic interactions among the poly (ethylene oxide) (PEO), GO and IL in PGI, greatly reduce the crystallinity of PEO. All of the amorphous PEO, GO, and IL can effectively tether anions and enhance the ionization of lithium salts, which lead to a uniform assignment of charges and lithium ions in the electrolyte, as well as increase the transfer number of lithium ions. The PGI is utilized in all-solid-state batteries with a negligible polarization. The galvanostatic cycling tests (LiFePO4/Li cells using PGI electrolytes) at 60 °C show the initial capacities of 156.2 and 120 mAh g−1 at 0.1C and 0.5C, respectively. Moreover, the electrochemical tests also indicate that the LMBs using PGI electrolytes possess superior cycle stability at room temperature. The study provides a competitive solution for developing high-performance LMBs which can work well at both high temperature and room temperature.

Polyvinylidene fluoride nanofibers with embedded Li6.4La3Zr1.4Ta0.6O12 fillers modified polymer electrolytes for high-capacity and long-life all-solid-state lithium metal batteries

Solid polymer electrolytes replacing traditional liquid electrolytes are considered as an important strategy for developing lithium metal batteries with high safety and energy density. However, poor ionic conductivity and weak mechanical performances have greatly limited the development of solid polymer electrolytes. Here, we dispersed inorganic ceramic particles Li6·4La3Zr1·4Ta0·6O12 (LLZTO) in the polyvinylidene fluoride (PVDF) electrospun nanofibers and then introduced them into polyethylene oxide (PEO) polymers to prepare composite electrolytes. The PVDF nanofibers with embedded LLZTO fillers can simultaneously reduce the crystallinity of the PEO polymer and provide a strong framework support for the composite electrolyte, thereby promoting the transmission of lithium ions and improving the lithium dendrite growth inhibition ability of the composite electrolyte. In addition, the uniform dispersion of garnet-type LLZTO active ceramic filler in the PVDF nanofiber membrane can further optimize the migration path of lithium ions. More importantly, the dehydrofluorination of PVDF due to the introduction of LLZTO can enhance the interaction among PVDF, LLZTO and lithium salts, which promotes dissociation of the lithium salt. The ionic conductivity of the composite electrolyte is as high as 9.30 × 10−4 S cm−1 at 50 °C, and the voltage of Li/Li symmetrical battery would not change significantly during 1200 h at 0.3 mA cm−2. Additionally, the composite electrolytes exhibit good electrochemical stability with the capacity retention rate of 96% under 1 C after 500 cycles. These results provide a strategy for the development of next-generation high-safety all-solid-state lithium metal batteries.

Restricted Ion Transport by Plasticizing Side Chains in Polycarbonate-Based Solid Electrolytes.

Increasing the ionic conductivity has for decades been an overriding goal in the development of solid polymer electrolytes. According to fundamental theories on ion transport mechanisms in polymers, the ionic conductivity is strongly correlated to free volume and segmental mobility of the polymer for the conventional transport processes. Therefore, incorporating plasticizing side chains onto the main chain of the polymer host often appears as a clear-cut strategy to improve the ionic conductivity of the system through lowering of the glass transition temperature (Tg). This intended correlation between Tg and ionic conductivity is, however, not consistently observed in practice. The aim of this study is therefore to elucidate this interplay between segmental mobility and polymer structure in polymer electrolyte systems comprising plasticizing side chains. To this end, we utilize the synthetic versatility of the ion-conductive poly(trimethylene carbonate) (PTMC) platform. Two types of host polymers with side chains added to a PTMC backbone are employed, and the resulting electrolytes are investigated together with the side chain-free analogue both by experiment and with molecular dynamics (MD) simulations. The results show that while added side chains do indeed lead to a lower Tg, the total ionic conductivity is highest in the host matrix without side chains. It was seen in the MD simulations that while side chains promote ionic mobility associated with the polymer chain, the more efficient interchain hopping transport mechanism occurs with a higher probability in the system without side chains. This is connected to a significantly higher solvation site diversity for the Li+ ions in the side-chain-free system, providing better conduction paths. These results strongly indicate that the side chains in fact restrict the mobility of the Li+ ions in the polymer hosts.

Plasticized solid polymer electrolyte based on triblock copolymer poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate) for magnesium ion batteries

Limited global resources of lithium lead to the consideration of magnesium ion batteries as potential energy storage devices. Magnesium ion batteries have potential for high energy density but require new types of electrode and electrolytes for practical applications. Solid polymer electrolytes offer the opportunity for increased safety and broader electrochemical stability relative to traditional electrolytes. Herein, we report the development of solid polymer electrolyte for magnesium ion batteries based on triblock copolymer poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate) (poly(VdCl-co-AN-co-MMA)). The polymer electrolytes are prepared by solution-casting technique using poly(VdCl-co-AN-co-MMA) with various concentrations (10 wt%, 20 wt%, 30 wt%, and 40 wt%) of magnesium chloride (MgCl2) salt. Among the prepared polymer electrolytes, the highest magnesium-ion-conducting polymer electrolyte is 70 wt% poly(VdCl-co-AN-co-MMA):30 wt% MgCl2 polymer–salt composition by electrochemical impedance measurements, and the obtained value of ionic conductivity is found to be in the order of 10−5 S cm−1. Addition of plasticizer succinonitrile in various concentrations (0.1 wt%, 0.2 wt%, 0.3 wt% and 0.4 wt%) with the identified polymer electrolyte of highest conductivity shows increased values of conductivity up to the order of 10−3 S cm−1. Observable changes in crystalline/amorphous nature of the polymer are analyzed using X-ray diffraction pattern. Glass transition temperature of polymer electrolytes has been found using differential scanning calorimetric studies. Transference number measurements have been made to confirm the ionic conductivity. The electrochemical stability for highest conducting plasticized polymer electrolyte is obtained from linear sweep voltammetry as 3.3 V. A primary magnesium ion battery has been constructed with prepared electrolyte of highest conductivity, and its performance and discharge characteristics are also analyzed. The open-circuit voltage of 2.18 V is obtained with the constructed primary magnesium ion battery.

Development of solid polymer electrolytes based on sodium-carboxymethylcellulose (NaCMC)-polysulphide for quantum dot-sensitized solar cells (QDSSCs)

Sodium-carboxymethylcellulose (NaCMC) films have been developed by solution casting technique. The films were soaked into an optimized aqueous polysulphide electrolyte containing 4 M sodium sulphide (Na2S) and 1 M sulphur (S). The optimized aqueous polysulphide electrolyte has the ambient conductivity of (1.46 ± 0.02) × 10-1 S cm-1. The NaCMC films were soaked for different durations of 30, 60, 68 and 75 s. The highest room temperature ionic conductivity (RTIC) of (2.79 ± 0.09) × 10-5 S cm-1 is exhibited by NaCMC film soaked in polysulphide electrolyte for 68 s. The conductivity-temperature relationship of NaCMC-based polysulphide solid polymer electrolytes (SPEs) follows the Arrhenius rule. The highest conducting SPE exhibits the lowest activation energy (EA) value of 0.38 eV. Ionic coefficient of diffusion (D), ionic mobility (μ) and free ions concentration (n) of the SPEs were determined. The newly developed SPEs are used as electrolyte in quantum dot-sensitized solar cells (QDSSCs) application with the configuration FTO/TiO2/CdS/ZnS/SPE/Pt/FTO. Under 1000 W m-2 illumination, QDSSC with CMC-68 SPE exhibits the highest power conversion efficiency (PCE) of 0.90%. The values of short circuit current (JSC) and PCE are closely related to electron lifetime and recombination rate.

Prediction of Solvents and Non-Solvents for Polymers Using Machine Learning Techniques

As renewable energy sources are increasingly gaining traction as an alternative to scarce fossil fuels, exploratory research on energy storage devices which are reliable, cost-effective and have low energy losses has become prolific. This has spearheaded the development of solid polymer electrolytes for safer lithium-ion batteries with comparable properties as conventional liquid electrolyte-based lithium-ion batteries. Synthesizing solid polymer electrolytes involves preparing an electrolyte film from a solution of polymer and Li-ion salts in an appropriate solvent. Identifying appropriate solvents for the polymer solution is usually done by trial-and-error, and therefore, is time-consuming. To mitigate this problem, quantitative measures of solvent-polymer miscibility known as solubility parameters have been developed in the past. In the present study, we first assessed the performance of the Hildebrand and Hansen solubility parameters to predict solvents and non-solvents for a set of benchmark polymers. Based on the results of the assessment, a machine learning model was trained on a dataset of known polymer Hildebrand solubility parameters to predict the solubility parameter of a queried polymer. Matching the predicted value with known solvent solubility parameters was then utilized to identify suitable solvents and non-solvents for the queried polymer. This capability has been implemented at www.polymergenome.org.

Computational Investigation of the Binding Energy and Electrochemical Stability of Poly(ethylene oxide) with Li-Ion Salts

The increasing awareness to maximize the use of energy resources has led to exploration in effective energy storage viz. high energy density batteries which are reliable, cost-effective and have low energy losses. This has spearheaded the development of solid polymer electrolytes for safer lithium-ion batteries with comparable properties to conventional liquid electrolyte-based lithium-ion batteries. Since the polymer functions as the electrolyte as well as the separator, they must possess a number of critical properties to seamlessly function in the battery. The electrochemical stability window (ESW) is a critical consideration which determines the safe operational voltage outside which the electrolyte degrades. Another factor is the Li-binding energy of the ions to the polymer which is a prelude to the Li-ion migration in the electrolyte and provides an estimate of the solubility of the salt in the polymer matrix. An optimal binding energy is desired where it is high enough for the Li-ion to bind to the polymer but not high enough to prevent its migration through the electrolyte. In this work, molecular dynamics (MD) and density functional theory (DFT) calculations are performed to determine the ESW and the binding energy of polyethylene oxide (PEO), an excellent inflammable and stable polymer electrolyte with multiple Li salts namely, LiBr, LiCl, LiI, LiClO4, LiSCN, LiCH3COO, LiNO3, LiBH4, LiCF3SO3 and LiBF4 to ascertain realistic ESW and binding energy values. We establish a relationship between the effects of the salt anion on the ESW and the binding energy. The ESW decreases in the presence of a salt in the polymer host, and we explore the effects of the salt anion size on the ESW. We also determine an optimal binding energy range for PEO with the salts which successfully propagates polymer-salt solvation as well as Li-ion migration. We believe this study should be able to guide the experimental design of stable and safe solid polymer electrolytes in the future.

Enhancement of Mechanical Stability and Ionic Conductivity of Chitosan‐based Solid Polymer Electrolytes Using Silver Nanowires as Fillers

With the emergence of wearable devices and internet of things, it is expected that small flat, and flexible electrochemical devices will be required for these applications. One of the prerequisites for these devices to be applied to such fields is the development of solid polymer electrolytes with high ionic conductivity. Because most solid polymer electrolytes have low ionic conductivity, small organic molecules have been used as plasticizers to increase their ionic conductivity. Since these plasticizers can increase amorphous regions that play the role of ion channels in polymer, their ionic conductivity increases; however, their mechanical stability decreases inversely. Conventionally, to overcome this drawback, inert nanoparticles are added into solid polymer electrolytes as fillers. Herein, we show that 1‐dimensional silver nanowires can increase the mechanical stability of chitosan‐based solid polymer electrolytes as well as their ionic conductivity more than nanospheres can, and discuss a plausible mechanism for such an enhancement.

The role of inorganic nanoparticle on ion conduction of epoxy-based solid polymer electrolytes for lithium-ion batteries

Recently, extensive efforts have focused on the development of solid polymer electrolytes (SPEs) requiring high mechanical performance without sacrificing ion conductivity. To develop such a SPE, we incorporate robust silica mesoporous particles (SMP) into the epoxy-based SPEs, and increasing the SMP content raises the glass transition temperature of the SPEs. This enables to increase the mechanical properties of the SPEs, supported by the microstructural investigation showing a highly compact structure. Ionic conductivities of these SPEs follow Vogel temperature dependence, and increasing the silica nanoparticle content leads to a slight decrease in the conductivity, consistent with the dielectric response investigation.