Quasi-solid State Electrolyte Research Articles

Bio and non‐bio materials‐based quasi‐solid state electrolytes in DSSC : A review

Dye-sensitized solar cells (DSSCs) are more attractive than silicon solar cells due to their low dependency on light intensity so that they can perform both indoor and outdoor with low-level lightings. DSSC's global revenue exceeded 16 million USD in 2014 for emerging portable charging, solar bags, and wireless keyboards. However, on-grid DSSC modules are still under R&D for massive commercialization to improve their long-term stability and safety issues due to the liquid electrolyte leakage. Therefore, quasi-solid-state electrolytes (QSE) have been proposed as a novel alternative to overcome the limitations stated above since 2001. Here, we deliver a short outline of the QSE properties, which are linked with the performance of DSSC in terms of different types of QSE structures: gel, hydrogel, and aerogel. Furthermore, these QSE structures are classified under bio and non-bio materials. Finally, the impact, outlook, and future prospects of QSE-DSSC are included as a conclusion in this review.

Development of quasi solid state dye sensitized solar cells

Dye Sensitized Solar Cells (DSSCs) present a significant renewable energy source in terms of control of different parameters governing flexibility, efficiency, lifetime and cost. The liquid electrolytes used inside the cells are generally responsible for the leakage and inefficient encapsulation related issues. These are critical for practical applications of DSSCs. The choice of electrolyte medium used in the cell should take into account the fast regeneration of electrolyte and redox potential of the dye. Organic dyes in general, exhibit better extinction coefficients and variant color ranges. The present work is focused on quasi solid state DSSCs based on an organic dye. For the fabrication of devices, nanocrystalline titanium-di-oxide (TiO2) films were used as the photoanode and well known organic dye Eosin B as the sensitizer. The photovoltaic performance of the cells was measured at different light intensities. The results exhibited the quantum efficiency of organic dye Eosin B which can be used as a potential sensitizer in conjugation with quasi solid state electrolytes. Copyright © 2017 VBRI Press.

Electrospun membrane of PVA and functionalized agarose with polymeric ionic liquid and conductive carbon for efficient dye sensitized solar cell

Environmentally benign biopolymer nanofibrous membrane was fabricated and applied as a quasi-solid state (QSS) electrolyte in dye-sensitized solar cell (DSSC). In this study, electrospun (PVA/PA/PIL/C) nanofibrous membrane was tailored from phthaloyl agarose (PA), poly(3-butyl-1-vinyl imidazolium iodide) (PIL) along with conductive carbon (C) incorporated in poly(vinyl alcohol) (PVA). The morphology, structure and physical properties (electrolyte uptake, porosity) of the membranes were analysed and their photovoltaic and electrochemical effects as electrolyte in DSSC device were studied. The best QSS-DSSC with PVA/PA/PIL/C membrane exhibited good short circuit current density (Jsc = 13.1 mA/cm2), high open circuit voltage (Voc = 0.79 V), comparable power conversion efficiency (η = 6.05%) and greater stability (up to 82% of its initial conversion efficiency after 500 h). This membrane based electrolyte enunciates the great outlook for the advancement of stable and efficient DSSCs.

Hierarchical porous carbon derived from elm bark mucus for efficient energy storage and conversion

The exploration of thermally chargeable supercapacitors has gained intensive interest. However, their practical application is still restricted by complex integration, poor Seebeck coefficient, and unsatisfactory conversion efficiency. Herein, we report a high-performance device with a simplified symmetric configuration based on activated carbon derived from elm bark mucus. Due to high specific surface area, hierarchical porosity, and moderate surface chemistry, such system displays excellent electrochemical properties such as high capacitance, rate capability and thermoelectrical behavior. When coupling with a concentrated electrolyte (26 m KOAc), a 2.0 V symmetric supercapacitor can be fabricated and a maximum energy density of 33.6 Wh kg−1 at power density of 500 W kg−1. A high-power density of 20 kW kg−1 also can be achieved at 21.7 Wh kg−1. Moreover, thermally rechargeable devices with quasi solid-state electrolyte exhibit a high open circuit voltage of ∼24.02 mV and a considerable Seebeck coefficient of about 1.97 mV K−1, indicating satisfying thermoelectrical performances. This work not only demonstrates the applicability of elm bark mucus-derived carbon as advanced materials for energy application, but also provides a new perspective for the development of multifunctional devices.

Glassy Metal–Organic‐Framework‐Based Quasi‐Solid‐State Electrolyte for High‐Performance Lithium‐Metal Batteries

AbstractEnhancing ionic conductivity of quasi‐solid‐state electrolytes (QSSEs) is one of the top priorities, while conventional metal–organic frameworks (MOFs) severely impede ion migration due to their abundant grain boundaries. Herein, ZIF‐4 glass, a subset of MOFs, is reported as QSSEs (LGZ) for lithium‐metal batteries. With lean Li content (0.12 wt%) and solvent amount (19.4 wt%), LGZ can achieve a remarkable ion conductivity of 1.61 × 10−4 S cm−1 at 30 °C, higher than those of crystalline ZIF‐4‐based QSSEs (LCZ, 8.21 × 10−5 S cm−1) and the reported QSSEs containing high Li contents (0.32–5.4 wt%) and huge plasticizer (30–70 wt%). Even at −56.6 °C, LGZ can still deliver a conductivity of 5.96 × 10−6 S cm−1 (vs 4.51 × 10−7 S cm−1 for LCZ). Owing to the grain boundary‐free and isotropic properties of glassy ZIF‐4, the facilitated ion conduction enables a homogeneous ion flux, suppressing Li dendrites. When paired with LiFePO4 cathode, LGZ cell demonstrates a prominent cycling capacity of 101 mAh g−1 for 500 cycles at 1 C with the near‐utility retention, outperforming LCZ (30.7 mAh g−1) and the explored MOF‐/covalent–organic frameworks (COF)‐based QSSEs. Hence, MOF glasses will be a potential platform for practical quasi‐solid‐state batteries in the future.

Development of sodium hybrid quasi-solid electrolytes based on porous NASICON and ionic liquids

Lithium-ion batteries are currently the alternative of choice to overcome the increasing demand of energy. However, besides the scarcity of lithium and limited geolocation, it is believed that such batteries have already reached their maximum maturity. Sodium batteries emerge as an alternative to produce the new, so called, post-lithium batteries. In this study, we explore (i) the effect of sodium content and sintering temperature in solid electrolytes based in NASICON-type compounds and (ii) the use of two methodologies to obtain porous NASICON samples: application of natural substances and organic materials as pore-formers and freeze casting. The main purpose is the attainment of hybrid quasi-solid state electrolytes, with enhanced room temperature conductivity, based on porous ceramic electrolyte layers infiltrated with ionic liquids. Using this approach, porous samples with different microstructure and porous morphology and distribution were achieved, providing an enhancement in conductivity (ranging from 0.45 to 0.96 mS cm−1 at 30 °C) of one order of magnitude for infiltrated samples respect to pore-free samples. According to these results the porous NASICON might be considered as a functional macroporous inorganic separator that can act as a Na+ reservoir.

Nonflammable Ionic Liquid-Based Quasi-Solid-State Electrolytes for Highly Safe Sodium-Ion Batteries

Because of the depletion of fossil fuels and increasing demand for sustainable energy, lthium-ion batteries (LIBs) have been considered one of the promising power sources for electric vehicles and other energy storage systems. However, increasing market demand for LIBs and limited lithium resources have caused a significant rise in cost of lithium sources. Thus, sodium-ion batteries (SIBs) have been considered a promising alternative to LIBs due to the natural abundance and low cost of sodium resources. However, like LIBs, conventional liquid electrolytes containing organic solvents are highly volatile and flammable, which causes safety problems such as fires and explosions. In this respect, ionic liquids (ILs) can be promising solvents for SIB electrolytes because of their attractive properties such as non-flammability, low volatility and exceptional electrochemical stability. Quasi-solid-state electrolytes (QSEs) have also received considerable attention to overcome the safety issues by avoiding leakage of organic solvents. Furthermore, they possess high ionic conductivity and superior flexibility. In this study, we report an IL-based QSEs with high ionic conductivity (1.5 mS cm-1) and non-flammability. The QSEs were prepared by in-situ thermal curing of boron-centered cross-linkers (BCs) in the IL-based electrolyte. Because the BC has anion-trapping boron moieties, it can promote the ionic mobility of Na+ in the QSE. As a result, the sodium cell employing the QSE exhibited stable cycling performance and enhanced safety.

Natural rubber (Hevea Brasiliensis)-based quasi-solid electrolyte as a potential candidate for arresting recombination and improving performance in aqueous dye-sensitized solar cells

We successfully fabricated dye sensitized solar cells (DSSCs) employing a quasi-solid state electrolyte based on pristine insulator natural rubber latex from Hevea brasiliensis and iodide electrolyte. Optimized devices exhibited a maximum power conversion efficiency (PCE) of 1.14% under simulated sunlight with 90 mW/cm2 illumination, 0.46% under 100 mW/cm2 and 7.85% under low intensity illumination of 1000 lx (Daylight LED). This gives a new perspective for the introduction of natural rubber latex abundant in nature as an additive to the water based redox mediator in order to improve the PCE in DSSC. A detailed study on the interfacial charge transfer in fabricated devices revealed that the introduction of rubber helped in arresting the back electron transfer, which was predominant in aqueous electrolyte based dye sensitized solar cell. This opens up opportunities for water-based electrolyte based on natural raw materials to be used in nature inspired DSSC technology.

Shape-Controlled TiO2 Nanomaterials-Based Hybrid Solid-State Electrolytes for Solar Energy Conversion with a Mesoporous Carbon Electrocatalyst.

One-dimensional (1D) titanium dioxide (TiO2) is prepared by hydrothermal method and incorporated as nanofiller into a hybrid polymer matrix of polyethylene glycol (PEG) and employed as a solid-electrolyte in dye-sensitized solar cells (DSSCs). Mesoporous carbon electrocatalyst with a high surface area is obtained by the carbonization of the PVDC-g-POEM double comb copolymer. The 1D TiO2 nanofiller is found to increase the photoelectrochemical performance. As a result, for the mesoporous carbon-based DSSCs, 1D TiO2 hybrid solid-state electrolyte yielded the highest efficiencies, with 6.1% under 1 sun illumination, in comparison with the efficiencies of 3.9% for quasi solid-state electrolyte and 4.8% for commercial TiO2 hybrid solid-state electrolyte, respectively. The excellent photovoltaic performance is attributed to the improved ion diffusion, scattering effect, effective path for redox couple transfer, and sufficient penetration of 1D TiO2 hybrid solid-state electrolyte into the electrode, which results in improved light-harvesting, enhanced electron transport, decreased charge recombination, and decreased resistance at the electrode/electrolyte interface.

An interfacial wetting water based hydrogel electrolyte for high-voltage flexible quasi solid-state supercapacitors

The development of eco-friendly and light-weighted solid-state electrolytes with a wide electrochemical window is critical to apply flexible energy storage devices for powering wearable and implantable electronics. Herein, we report the first demonstration of a quasi solid-state hydrogel electrolyte leveraging the formation of “interfacial wetting water” for facile two-dimensional ion transports instead of typical diffusion in bulk-like water. The hydrogel electrolyte exhibits a wide electrochemical window (2.5 V) in electrical double layer capacitance (EDLC) cell with an extremely effective low salt concentration (6.8 m), 3.1 times lower than the well-known water-in-salt electrolyte (WiSE, 21 m), and a small water retention (24 wt%). Besides, a significant toughness (ultimate tensile strength of 420 kPa and elongation of 6,000%) is achieved. The flexible supercapacitor demonstrates the high specific energy density of 39.1 Wh•kg−1 at 0.5 A•g−1 and 7.6 Wh•kg−1 at power density of 6218 W•kg−1, as well as a subdued self-discharge profile. This interfacial water dominated hydrogel electrolyte provides new directions in designing high-voltage hydrogel electrolyte for safe and sustainable soft energy storage devices.

Decoupling of Mechanical Strength and Ionic Conductivity in Zwitterionic Elastomer Gel Electrolyte toward Safe Batteries.

Quasi-solid state electrolyte is one of the promising options for next generation batteries due to its superiority on safety and electrochemistry performance. However, the trade-off between the electrolyte swelling ratio and mechanical property of the quasi-solid state electrolyte significantly influences the battery performance. Herein, we design a nonswelling, solvent-adaptive polymer gel composed of oleophobic zwitterion poly(3-(1-vinyl-3-imidazolio)-propanesulfonate) and oleophilic elastomer poly(2-methoxyethyl acrylate) segments to retain high battery performance without sacrificing the mechanical property in lithium batteries. The as-designed gel can not only uptake enough electrolyte for a high ionic conductivity of 1.78 mS cm-1 but also achieve excellent mechanical strength with compression stress at 90% strain (σ0.9) reaching 5.8 MPa after long time soaking for battery safety due to its nonswelling property in ester electrolyte. Moreover, the as-prepared zwitterionic gel is beneficial to electrolyte salt dissociation, which further enhances the ionic conductivity and transference number of batteries. Consequently, the gel electrolyte can cycle for more than 500 h under a high current density of 3 mA cm-2 on dendrite inhibition performance, and when assembled with LiFePO4 as a cathode, the battery demonstrates a reversible specific capacity as high as 70 mAh g-1 under a high current density of 5 C after 300 cycles. The rational designed solvophilic/solvophobic zwitterionic elastomers provide a guidance for engineering quasi-solid state electrolytes of different solvents with broad applications on flexible devices.

Quasi-solid electrolyte developed on hierarchical rambutan-like γ-AlOOH microspheres with high ionic conductivity for lithium ion batteries.

Upgrading liquid electrolytes with all-solid-state electrolytes (ASEs) or quasi-solid-state electrolytes (QSEs) for solid-state batteries (SBs) have emerged not only to address the intrinsic disadvantages of traditional liquid lithium ion batteries, but also to offer more possibilities for the development of new battery chemistries. In this work, a novel rambutan-like yolk-shell-structured porous γ-AlOOH microsphere with a large specific surface area of 262.92 m2 g-1 was firstly obtained by a simple hydrothermal synthesis route, which was then utilized as a robust framework to assemble QSE via encapsulating abundant liquid electrolyte (LE). The obtained γ-AlOOH-QSE exhibits a high ionic conductivity of 4.0 × 10-3 S cm-1, a large lithium ion transference number (tLi+) of 0.76, as well as a wide electrochemical window of 4.72 V vs. Li/Li+. Moreover, the assembled cell of LiFePO4/γ-AlOOH-QSE/Li could maintain a high specific capacity of 144.4 mA h g-1 even after 120 cycles with almost negligible capacity decay, which could be mainly attributed to the excellent interfacial compatibility, prominent performance in suppressing lithium dendrite growth upon cycling (rigid characteristic), as well as the high ionic conductivity of γ-AlOOH-QSE (intrinsic advantage). This work could not only expand the applications of QSE with cost-effective aluminum-based oxides with facile fabrication strategy, but also will shed light on the construction of SEs with more integrated QSEs and ASEs in the field of advanced energy storage.

Study of Lithium Ion Battery Manufacturing Process Using Quasi-Solid Electrolyte Sheet

IntroductionIn conventional lithium ion battery (LIB), organic electrolyte exhibiting a high volatility and flammability is applied. Therefore, energy storage system with the LIB possesses a lot of auxiliary components for ensuring its safety, which do not directory contribute to electricity storage and lower its volumetric and gravitic energy density. Hence, the high safety of the LIB is the key to increase the volume energy density and the LIBs using several types of electrolytes such as a gel [1], a solid-state [2] and a quasi-solid-state [3] have been investigated. In particular, 100 Wh-class LIB using quasi-solid-state electrolyte (QSE) as a highly safe electrolyte demonstrated incombustibility in the nail-penetration test [3]. QSE is prepared by pseudo solidifying of solvate ionic liquid which consists of an equimolar mixture of lithium salt and tetraglyme(G4) at oxide particle surfaces. In this research, LIB manufacturing process using QSE that is highly compatible with conventional manufacturing processes was examined.Experiment Solvate ionic liquid, Li(G4)TFSA, was prepared by mixing an equimolar of lithium bis(trifluoromethanesulfonyl)amide, LiTFSA, and G4 [4]. Li(G4)TFSA, silica nano particle, and fluorine-based binder were mixed in a prescribed ratio. QSE sheet was prepared by coating and drying the mixture on the substrate. Li(G4)TFSA has a refractory characteristics. To prepare electrode containing Li(G4)TFSA, the electrode slurry including Li(G4)TFSA was coated and dried on the current collector foil. Li(Ni,Co,Mn)O2 pseudo-ternary oxide and graphite were used as the active material of the positive and negative electrode, respectively. The volatile mixed solution of propylene carbonate (PC) as low viscosity solvent [1] and vinylene carbonate (VC) for suppress the SEI formation was directly coated on the surface of the pressed electrode (coating method). In addition, QSE sheets and the electrode were stacked and heat-sealed by the four sides in order to suppress the volatilization of additive mixed solution (edge sealing structure). NMR analysis of the electrolyte components extracted by immersing in deuterated chloroform solvent after standing under manufacturing environment ( dew point : about -35℃) at various time ( for 0 to 24 hours) was carried out to examine the volatile behavior of PC and VC. Moreover, charge-discharge performance of LIB using QSE was evaluated by a model cell (diameter of electrode was less than 18 mm).Result and discussion In the previous research [5], the same charge-discharge performance as one of the conventional injection method was obtained by the coating method in which a small amount (5ml/cm2) of PC and VC mixed solution was directly coated on the electrode. It indicated that the injection process which had been a bottleneck in the LIB manufacturing process could be omitted. In order to apply the coating method to the mass production process, it is necessary to suppress concentration fluctuations of PC and VC by volatilization. In particular, the vapor pressure of VC is higher than the other electrolyte components. VC is an important component for SEI formation at the negative electrode interface. Concentration fluctuation of VC can be a factor for lowering LIB performance. Therefore, the edge sealing structure as shown in Figure 1 was prepared to seal the additive mixed solution. Figure 2 shows the relation between VC residual ratio and time. In the reference sample without applying the edge sealing structure, VC vapored quickly and the residual ratio decreased to about 60% after 30 minutes. On the other hands, VC residual ratio remained 93% even after 24 hours in the edge sealing structure, which proves the edge sealing can suppress VC volatilization significantly. Figure 3 shows the charge-discharge performance of LIB using QSE with the edge sealing structure. The charge-discharge performance of 24hours after coating the additive mixed solution did not deteriorate compared to the performance of immediately after coating. In this presentation, details of the manufacturing process using the coating method and the edge sealing structure will be discussed.

Robust Strategy of Quasi-Solid-State Electrolytes to Boost the Stability and Compatibility of Mg Ion Batteries.

Magnesium ion batteries (MIBs) have attracted a lot of attention because of the natural abundance of magnesium, high volumetric energy density, and superior safety. Nevertheless, MIBs are still in their infancy because of the significant challenge in developing a suitable electrolyte with low flammability, high ionic conductivity, and compatibility with the Mg anode. Herein, we construct rechargeable quasi-solid-state MIBs based on tailored polymer electrolytes. The quasi-solid state electrolyte of poly(vinylidene fluoride-co-hexafluoropropylene)-nanosized SiO2-Mg(TFSI)2 combines the outstanding dynamic property of a liquid electrolyte and the good stability of a solid-state electrolyte. It exhibits a highly reversible Mg2+ deposition-dissolution capability, high ion conductivity (0.83 mS cm-1), and superior compatibility with the Mg metal and cathode. The quasi-solid-state MIBs with a layered titanic oxide cathode show a high reversible capacity of 129 mA h g-1 at 50 mA g-1 (150 W h kg-1) without any decay after 100 cycles.

Quasi-solid-state electrolyte for rechargeable high-temperature molten salt iron-air battery

Molten salts are a unique type of electrolyte enabling high-temperature electrochemical energy storage (EES) with unmatched reversible electrode kinetics and high ion-conductivities, and hence impressive storage capacity and power capability. However, their high tendency to evaporate and flow at high temperatures challenges the design and fabrication of the respective EES devices in terms of manufacturing cost and cycling durability. On the other hand, most of these EES devices require lithium-containing molten salts as the electrolyte to enhance performances, which not only increases the cost but also demands a share of the already limited lithium resources. Here we report a novel quasi-solid-state (QSS) electrolyte, consisting of the molten eutectic mixture of Na2CO3-K2CO3 and nanoparticles of yttrium stabilized zirconia (YSZ) in a mass ratio of 1:1. The QSS electrolyte has relatively lower volatility in comparison with the pristine molten Na2CO3-K2CO3 eutectic, and therefore significantly suppresses the evaporation of molten salts, thanks to a strong interaction at the interface between molten salt and YSZ nanoparticles at high temperatures. The QSS electrolyte was used to construct an iron-air battery that performed excellently in charge-discharge cycling with high columbic and energy efficiencies. We also propose and confirm a redox mechanism at the three-phase interlines in the negative electrode. These findings can help establish a simpler and more efficient approach to designing low-cost and high-performance molten salt metal-air batteries with high stability and safety.

Analysis of Solid-Electrolyte Interphase at the Interface between a Graphite Negative Electrode and a Diluted Solvate Ionic Liquid-Based Quasi-Solid-State Electrolyte

The formation and growth mechanism of a solid-electrolyte interphase (SEI) on a graphite-based negative electrode was investigated to enhance the cycle life of lithium ion batteries with a quasi-solid state electrolyte (QSE). In a QSE, liquid constituents including solvate ionic liquid (SIL), diluting solvent, and additives are quasi-solidified on surface of silica particles, which ensures the safety of a 100 Wh class laminated cell. For the SIL, an equimolar complex composed of tetraethylene glycol dimethyl ether (G4) and lithium bis(trifluoromethanesulfonyl)amide (LiTFSA), was utilized. Propylene carbonate (PC) was used as diluting solvent to enhance the ionic conductivity of the SIL. Vinylene carbonate (VC) additive was introduced to form a robust SEI for inhibiting the reductive decomposition of G4 and PC. Nuclear magnetic resonance and hard X-ray photoelectron spectroscopy revealed that the decompositions of LiTFSA, PC, and G4 contributed to the SEI formation at the initial charge. During charge-discharge cycles, continuous decompositions of G4 and PC were a major reason for the SEI growth. To suppress the decomposition, charging at a low rate was introduced at beginning of the initial charge to enhance the VC decomposition and the robust SEI formation. Consequently, the decomposition of the QSE was inhibited, which enhanced its cycle life.

A study on the microstructural development of gel polymer electrolytes and different imidazolium-based ionic liquids for dye-sensitized solar cells

Quasi-solid state electrolyte (gel-like) based on polymer matrix PVDF-HFP/PEO is considered as a suitable candidate for producing DSSC due to its essential influence on the performance of the device. In this work, PVDF-HFP/PEO membranes were prepared over the whole composition range in presence of either one of the ionic liquids (ILs) including BMII plus LiI, or BMIMBF4 via phase inversion and compared with liquid electrolyte and ILs individually. It was found that the blend ratio affected some of the membrane properties, such as porosity, pore size, pore connectivity, liquid uptake ability, and morphology. SEM analysis and mercury porosimetry were used to study the pore configuration and porosity of the membranes. The effects of two semicrystalline polymers on the morphology and crystallinity of the membrane were examined by DSC and also WAXD. It was found that there is a direct relationship between the crystallinity reduction and improvement of ionic conductivity of the samples. The photovoltaic performances of the fabricated DSSC at the highest ionic conductive optimized membrane revealed an improvement of Voc, Jsc, fill factor, and the solar conversion efficiency of 6.47%. The long-term durability of the quasi solid DSSC was increased compared to a liquid type electrolyte.

Organic dye sensitized TiO2–Nb2O5 electron collecting bilayer photoanode for efficient power conversion in solar cells

Abstract This article describes the advantage of the organic dye sensitized TiO2–Nb2O5 electron collecting bilayer photoanode for efficient power conversion in solar cell devices. The bilayer photoanodes were prepared using Nb2O5 coated TiO2 nanoparticles/nanosticks composite film. The solar cell devices were fabricated using organic dye DIAC sensitized photoanodes with different types of electrolytes and cobalt sulphide counter electrode. The power conversion efficiency of 6.64% was achieved in the solar cell device fabricated with the bilayer photoanode and quasi-solid state electrolyte. This solar cell device exhibited high power conversion efficiency as compared to bare photoanode solar cell devices. The enhanced power conversion efficiency of the cell ascribes the bilayer photoanode improved the electron transport and reduced the recombination of charge carriers at photoanode/dye/electrolyte interface.

Development of new solid-state electrolytes based on a hexamethylguanidinium plastic crystal and lithium salts

There is an urgent need to improve the safety of lithium batteries, mainly due to the flammable and volatile organic solvent-based electrolytes currently used. Organic ionic plastic crystals (OIPCs) are showing promise as safe alternative solid-state electrolytes. The new OIPC hexamethylguanidinium bis(fluorosulfonyl)imide ([HMG][FSI]) displays excellent properties, such as high conductivity and a wide electrochemical stability window, making it a promising material as a starting point for the development of new solid state electrolytes. In this work, mixtures of [HMG][FSI] with lithium salts of bis(trifluoromethanesulfonyl)imide ([TFSI]) or bis(fluorosulfonyl)imide ([FSI]) were prepared and the effects of lithium salt addition and the influence of anion on the electrolyte properties were investigated. Simultaneously, the effect of the salt concentration was studied by the addition of increasing amounts of lithium salt in [HMG][FSI] (10, 50 and 90 mol% of LiFSI and LiTFSI). The thermal properties, ionic conductivities, self-diffusion properties, electrochemical stabilities and lithium transport properties were evaluated for all electrolytes and the neat OIPC. Overall, all of the prepared quasi-solid state electrolytes showed good transport properties and supported reversible deposition and stripping of lithium, thus highlighting an important new avenue for the development of OIPCs as solid-state electrolytes for lithium batteries.

Functional Covalent Triazine Frameworks‐Based Quasi‐Solid‐State Electrolyte Used to Enhance Lithium Metal Battery Safety

AbstractThe development and use of lithium metal batteries (LMBs) has been hampered by uneven Li deposition and dendrite formation during repeated cycling. Here, a new class of quasi‐solid‐state electrolytes (QSSE) consisting of ionic liquid functional covalent triazine‐based frameworks (IL‐fCTF) and a Li salt‐ionic liquid (LIL), formed by simple mechanical mixing, is shown to overcome these problems. The IL‐fCTF based QSSE exhibits high strength stability, due to its robust CTF skeleton that suppresses unwanted Li dendrite formation. Moreover, LIL absorbed in the ordered porous structures of the CTF skeleton forms three‐dimensional (3D) continues ion transport channels, beneficial for Li‐ion conduction and ensuring even Li deposition. The QSSE used in LMBs shows a high room‐temperature ionic conductivity (1.33 mS cm−1 at 30 °C), due to its excellent electrolyte uptake, ultra‐high Li‐ion transfer number (0.648), improved electrochemical/cycling stability and good rate capacity. The easily fabricated QSSE‐based battery's excellent performance makes it a promising candidate for practical application in LMBs.