Quasi-solid Electrolyte Research Articles

Constructing Highly Conductive and Thermomechanical Stable Quasi‐Solid Electrolytes by Self‐Polymerization of Liquid Electrolytes within Porous Polyimide Nanofiber Films

AbstractSolid electrolytes are being considered as an effective solution to replace liquid ones for building safer batteries, but they suffer either low ionic conductivity or large contact ohmic impedance. Here, a highly conductive and thermomechanically stable quasi‐solid electrolytes (QSE) by self‐polymerization of a commercially available liquid electrolytes (1,3‐dioxolane (DOL), 1,2‐dimethoxyethane (DME), lithium trifluoromethane sulfonimide (LiTFSI) and LiPF6) at room temperature in a porous polyimide nanofiber film are reported. LiPF6 initiates the ring‐opening reaction of DOL and LiTFSI promotes the self‐polymerization to form poly‐DOL (PDOL), while the plasticizer of DME solidifies the PDOL. On the other hand, polyimide has a great affinity with PDOL that facilitates to form stable QSE network. As a result, the QSE film shows a high room‐temperature ionic conductivity of 2.9 × 10−3 S cm−1, a high mechanical strength of 31 MPa, and high heat resistance to 160 °C. The LiFePO4||QSE||Li batteries with a high cathode loading of ≈18.7 mg cm−2 show great cycling performance and stable electrode/electrolyte interfaces at a high current rate of 0.5 C with a capacity retention of 91.8% over 200 cycles at room temperature.

Preparation of poly(ionic liquid) composite quasi-solid electrolyte by incorporating metal − organic framework filler decorated with ionic liquid for lithium batteries

Poly(ionic liquids) (PILs) electrolytes combine the advantages of ionic liquids and polymers and have been widely studied to boost the performance of lithium batteries. However, one main problem that most of PILs electrolytes encounter is the tradeoff between mechanical integrity and high ionic conductivity. Therefore, elevating ionic conductivity is still a problem to be solved urgently. In this work, ether group-functionalized PIL is synthesized and an ionic liquid (IL) decorated metal−organic framework (MOF) filler IL@UIO-66 is prepared. Subsequently, one composite polymer electrolytes (MCPEs) involving IL@UIO-66 and PIL are built via solution-casting approach. The as-prepared optimal MCPE membranes with 10% IL@UIO-66 (MCPE-10%) express higher ionic conductivity as high as 2.06 × 10−4 S cm−1 and larger lithium ion transference number of 0.49 at 30 °C than the electrolytes without filler (CPE). Comparing with CPE, the thermal stability of MCPE-10% is significantly improved to 300 °C by IL@UIO-66 and the electrochemical stability of MCPE-10% with an oxidation potential of 5.10 V vs. Li+/Li is almost unaffected. Besides, the interfacial stability between MCPE-10% and lithium electrode is improved. The assembled LiFePO4/MCPE-10%/Li cells show a promising rate and cycle performance at 25 °C. They show an initial discharge capacity of 123 mAh g−1 at current density of 0.5C, and their discharge capacity retention is up to 95% after 100 cycles with coulombic efficiency higher than 99%.

Durable fast-charging lithium metal batteries designed with cross-linked polymer electrolytes and niobate-coated cathode

A durable lithium metal polymer battery with extended cycle-life is designed by exploiting cross-linked poly(trimethylene carbonate) (PTMC) electrolytes and LiNi0.6Mn0.2Co0.2O2 (NMC622) with well-defined protective coating (0.5 wt% of LiNbO3 on the surface layer, <5 nm thickness). The presented materials demonstrate feasibility of faster cycling at rates of 1C and 2C at temperatures of 40 and 60 °C, exhibiting prominent capacity retention of 91% and 80% SOH (state of health) after 500 cycles. At higher cross-linking densities, the introduced quasi-solid polymer electrolytes afford good cycling performance and sufficient suppression of high surface area lithium depositions as well as improved ability of solvent entrapment, hence reflecting a considerable step forward towards achieving all solid-state polymer-based cells.

Fabrication of Li1.4Al0.4Ti1.6(PO4)3 quasi-solid electrolyte with high conductivity and compatibility through AAO template

Employing inorganic ion conductors as solid electrolytes (SEs) is one promising solution to develop advanced all- and quasi-solid-state batteries with high energy and safety advantages. Among numerous Li+ ion conductors, Li1.4Al0.4Ti1.6(PO4)3 (LATP) has attracted extensive attention due to its preponderances of air stability and superior Li+ conductivity. However, the practical application of the LATP electrolyte is still obsessed by serious side reactions at the Li-electrode/electrolyte interface. In this work, one kind of quasi-solid electrolyte (QSE) is designed combining anodic aluminum oxide (AAO), LATP, and liquid electrolyte [LE, LiPF6/ethylene carbonate-dimethyl carbonate (EC-DMC)], wherein well-ordered LATP arrays are constructed in the AAO framework to facilitate ionic transport, and a certain content of the LE is introduced to reduce the interfacial resistances. The characterization results suggest that the ionic conductivity of as-prepared AAO–LATP–QSE (ALQSE) is boosted up to ∼6.50 × 10−3 S cm−1 with a Li+ transference number of 0.66, especially the interval between the LATP compound and the Li-metal electrode can effectively restrain Ti4+→Ti3+ reduction at the Li-anode/electrolyte interface. Thus, the assembled LiFePO4|ALQSE|Li cell exhibits excellent electrochemical stability, delivering an initial discharge capacity of 153.3 mAh g−1 at 0.1C and remaining 152.4 mAh g−1 after 60 cycles with a fairly mild reduction of 0.028% per cycle. This study not only presents a facile strategy to prepare a robust QSE framework employing an AAO template but also promotes the rational interface design between titanium (Ti)-containing solid-state electrolytes and Li-metal anodes.

A flexible and highly conductive quasi-solid single-ion polymer electrolyte for high performance Li-metal batteries

A series of flexible and highly conductive quasi-solid single-ion polymer electrolytes (abbreviated as PU-TFMSI) based on lithium sulfonimide are presented. Owing to the crosslinked structure with three types of segments (hard segment, soft segment and Li rich segment), PU-TFMSI displays a stretchability of 1350% and toughness of 13.6 MJ m−3. These PU-TFMSI single-ion electrolytes deliver high ionic conductivity over 1.3 × 10−4 S cm−1 at ambient temperature, a wide electrochemical stability window (up to 5.0 V vs Li+/Li), a high lithium transfer number (LTN ∼ 0.9), and good compatibility with electrodes. The LiFePO4/PU-TFMSI-2/Li coin cell exhibits stable cycling with an average Coulombic efficiency of 99.58% and superior rate performance. Furthermore, the LiFePO4//Li soft pouch cell with PU-TFMSI-2 single-ion electrolyte maintains functionality under bending. The flexible single-ion polymer electrolytes designed in this study have the potential to be applied in flexible devices and stretchable batteries.

Tailoring the PEO-based ion conductive ionene as potential quasi-solid electrolyte for electrochemical devices

Recently, using ionic liquids (ILs) as ion source for electrochemical devices is enhancing their performance and long-term stability. However, intrinsically, ILs are liquids which are susceptible to leakage in electrochemical devices. This study aimed at substituting liquid electrolyte with safer and more mechanically stable material with exceptional electrochemical characteristics by synthesizing electrolytes in the solid-state derived from poly(ionic liquid)s. Herein, we synthesized a polyelectrolyte based on triazole-containing ionene via copper(I) catalyzed azide-alkyne cycloaddition (CuAAC). To activate cationic moiety, triazole group was quaternized with alkyl groups and subsequently underwent anion metathesis. These unique polyelectrolytes exhibit remarkable ionic conductivity which is at par or if not exceeds the best ionenes in literature. Furthermore, they exhibit good mechanical and thermal stability. Excellent optical transmittances of these ionenes make them a good electrolyte for electrochemical devices. Development of these new electrolytes is promising for the design of no-leak electrochemical devices.

High-Potential Cathodes with Nitrogen Active Centres for Quasi-Solid Proton-Ion Batteries.

Although proton-ion batteries have received considerable attention owing to their reliability, safety, toxin-free nature, and low cost, their development remains in the early stages because of lacking proper electrolytes and cathodes for facilitating a high output voltage and stable cycle performance. We present a novel cathode based on active nitrogen centre, which provides a flat discharge plateau at 1 V with a capacity of 115 mAh g-1 and excellent stability. Moreover, a quasi-solid electrolyte was developed to overcome the issue of corrosion, broaden the potential window of the electrolyte, and prevent the active material from dissolving. While using the unique as-developed electrolyte, the newly designed cathode retained 89.67 % of its original capacity after 2000 cycles. Finally, we demonstrated the excellent cycle performance of the as-developed metal-free, flexible, soft-packed battery. Notably, even when a portion of the battery was cut off, it continued to function normally.

A stable quasi-solid electrolyte improves the safe operation of highly efficient lithium-metal pouch cells in harsh environments

Nanoconfined/sub-nanoconfined solvent molecules tend to undergo dramatic changes in their properties and behaviours. In this work, we find that unlike typical bulk liquid electrolytes, electrolytes confined in a sub-nanoscale environment (inside channels of a 6.5 Å metal-organic framework, defined as a quasi-solid electrolyte) exhibits unusual properties and behaviours: higher boiling points, highly aggregated configurations, decent lithium-ion conductivities, extended electrochemical voltage windows (approximately 5.4 volts versus Li/Li+) and nonflammability at high temperatures. We incorporate this interesting electrolyte into lithium-metal batteries (LMBs) and find that LMBs cycled in the quasi-solid electrolyte demonstrate an electrolyte interphase-free (CEI-free) cathode and dendrite-free Li-metal surface. Moreover, high-voltage LiNi0.8Co0.1Mn0.1O2//Li (NCM-811//Li with a high NCM-811 mass loading of 20 mg cm−2) pouch cells assemble with the quasi-solid electrolyte deliver highly stable electrochemical performances even at a high working temperature of 90 °C (171 mAh g−1 after 300 cycles, 89% capacity retention; 164 mAh g−1 after 100 cycles even after being damaged). This strategy for fabricating nonflammable and ultrastable quasi-solid electrolytes is promising for the development of safe and high-energy-density LIBs/LMBs for powering electronic devices under various practical working conditions.

Influence of lithium metal anode coated with a composite quasi-solid electrolyte on stabilizing the interface of all-solid-state battery

Influence of lithium metal anode coated with a composite quasi-solid electrolyte on stabilizing the interface of all-solid-state battery

Nonflammable quasi-solid electrolyte for energy-dense and long-cycling lithium metal batteries with high-voltage Ni-rich layered cathodes

Nonflammable quasi-solid electrolyte is prepared by copolymerizing flexible chains of polymer vinyl acetate and rigid skeletons of triethylene glycol diacrylate with assistance of flame-retardant phosphate solvents. The quasi-solid electrolyte simultaneously features a high conductivity (1.02 mS cm−1), a high Li+ transference number (0.65), a wide electrochemical window (5.2 V vs. Li+/Li) and rigid-flexible coupling characteristics. Moreover, the electrolyte can capture the phosphate solvents with polar molecular interactions to weaken Li+–solvent interactions while promoting Li+–anion interactions, which creates more anion-derived protective layer on both electrodes. Thus, the electrolyte not only suppresses side reactions, irreversible phase transition, stress-corrosion cracking, and the dissolution of transition-metal ions on the cathode side, but also enables highly reversible Li metal stripping/plating, leading to low pulverization on the anode side. Employing the quasi-solid electrolyte, our LiNi0.8Co0.1Mn0.1O2||Li battery increases the upper cut-off voltage from current 4.3 V to 4.5 V (versus Li+/Li), therefore, delivers an ultrahigh specific capacity of > 224.7 mAh g−1, average Coulombic efficiency of > 99.6% and capacity retention of ∼81.2% over 500 cycles.

Conductivity gradient modulator induced highly reversible Li anodes in carbonate electrolytes for high-voltage lithium-metal batteries

Lithium metal has been considered as the ultimate anode for rechargeable batteries due to its lowest redox potential and ultra-high theoretical capacity. Nevertheless, uneven Li deposition, uncontrolled dendrite growth, and fragile solid electrolyte interphase (SEI) seriously impede the widespread application of lithium-metal batteries (LMBs), especially those cycled in carbonate electrolytes. Herein, a flexible LiNO3-modified conductivity gradient host (LNOCGH), which comprises a dielectric top layer with excess decorated LiNO3 particles and carbon nanofiber layers with upward attenuation of electrical conductivity, is demonstrated to manipulate Li deposition behavior in carbonate electrolytes. The top layer can steadily release LiNO3 to form a robust nitride-rich SEI while the conductivity gradient structure endows Li deposited in a dendrite-free manner by shifting the preferential deposition spots from the anode/separator interface to the anode bottom, which is confirmed through experiments and simulations. Benefiting from the elaborate and comhensive design, the stability of LNOCGH electrodes was significantly improved. The full cell with limited LNOCGH@Li anodes and high mass-loading LiNi0.8Co0.1Mn0.1O2 cathodes (N/P ratio of 2.3) can work stably for over 60 cycles with 72.9% capacity retention. As a proof-of-concept, flexible quasi-solid electrolyte can also be assembled with the as-obtained anode enables flexible LMB with excellent electrochemcial performance.

Quasi-solid electrolytes with tailored lithium solvation for fast-charging lithium metal batteries

Using quasi-solid electrolytes (QSEs) can make lithium metal batteries (LMBs) considerably safer. However, formulating QSEs with rate capabilities rivaling those of liquid electrolytes is extremely difficult. Herein, we develop a QSE characterized by safety, high conductivity above 2 × 10 −3 S cm −1 , and high lithium-ion transference number ( t Li + ) above 0.8. Computations and experiments reveal that these characteristics are achieved by adjusting the Li + solvation through a weak interaction with the polymer skeleton and strong coordination with NO 3 − . The further inclusion of fluoroethylene carbonate leads to the formation of a Li 3 N- and LiF-rich solid electrolyte interphase on the lithium metal. Consequently, QSE-based LMBs are capable of fast charging and high-power density, as well as stable and long cycling. By adjusting Li + solvation and lithium metal stability, this work rationally develops QSEs for fast-charging LMBs. • Quasi-solid electrolyte prepared with high-donor-number solvent and LiNO 3 • In-depth investigations on lithium solvation and ion transport by atomic simulations • Fast-charging lithium metal battery based on the QSE • Safe, flexible, and non-flammable pouch-type lithium metal battery Zhou et al. design a quasi-solid electrolyte with tailored lithium solvation and diffusion for fast-charging lithium metal batteries. The impact of the high-donor number solvent and LiNO 3 on solvation and charge-transfer mechanisms is studied experimentally and computationally.

Novel Dispersion of 1D Nanofiber Fillers for Fast Ion-Conducting Nanocomposite Polymer Blend Quasi-Solid Electrolytes for Dye-Sensitized Solar Cells.

Electrospun nanocomposite polymer blend poly(vinylidene difluoride-co-hexafluoropropylene) (PVDF-HFP)/poly(methyl methacrylate) (PMMA) membranes with a novel dispersion of x wt % of one-dimensional (1D) TiO2 nanofiber fillers (x = 0.0–0.8 in steps of 0.2) were developed using the electrospinning technique. The developed nanocomposite polymer membranes were activated using various redox agents such as LiI, NaI, KI, and tetrabutyl ammonium iodide (TBAI). Introduction of the 1D TiO2 nanofiber fillers improves the amorphous nature of the blended polymer membrane, as confirmed through X-ray diffraction (XRD) and Fourier transform infrared (FTIR), and yielded an electrolyte uptake of over 480% for a 6 wt % TiO2 nanofiber filler-dispersed sample. PVDF-HFP/PMMA–1D 6 wt % TiO2 nanofiber fillers with the LiI-based redox electrolyte provided a high conductivity of 2.80 × 10–2 S cm–1 and a power conversion efficiency (PCE) of 8.08% to their fabricated dye-sensitized solar cells (DSSCs). The observed better ionic conductivity and efficiency of the fabricated DSSCs could be due to the faster movement of the smaller-ionic-radius (Li) ions entrapped inside the amorphous polymer. This enhanced mobility of ions in the quasi-solid electrolyte leads to faster regeneration of the depleting electrons in the photoanode, resulting in improved efficiency. Further, the achieved high conductivity was analyzed in terms of the dynamics and relaxation mechanisms involved by the ionic charge carriers with complex impedance spectroscopy using a random barrier model and Havriliak–Negami formulation. It was observed that the high-conducting PVDF-HFP/PMMA–1D 6 wt % TiO2 nanofiber fillers with LiI-based redox electrolyte show better ac conductivity parameters such as a σ of 5.82 × 10–2 S cm–1, ωe (12685 rad s–1), τe (0.909 × 10–4 s), and n (0.578). Also, dielectric studies revealed that the high-conducting sample has a higher dielectric constant and subsequently high loss. The J–V characteristics were studied using the equivalent circuit of a single-diode model, and the parameters influencing the photovoltaic performance were determined by Symbiotic Organisms Search (SOS) algorithm. The results suggest that the high-efficient sample possesses a minimum series resistance of 1.33 Ω and a maximum shunt resistance of 997 Ω. Hence, the highest-conducting electrospun-blended polymeric nanocomposite (PVDF-HFP–PMMA–6 wt % TiO2 nanofiber fillers) with LiI-based redox agent and tert-butyl pyridine (TBP) additive as the polymer quasi-solid electrolyte nanofibrous membrane can be a better electrolyte for high-performance dye-sensitized solar cell applications.

Suppression of Co2 Induced Lithium Anode Corrosion by Fluorinated Functional Group in Quasi-Solid Polymer Electrolyte Enabling Long-Cycle and High-Safety Li-Co2 Batteries

Suppression of Co2 Induced Lithium Anode Corrosion by Fluorinated Functional Group in Quasi-Solid Polymer Electrolyte Enabling Long-Cycle and High-Safety Li-Co2 Batteries

Mesoporous silicas tethered with anions as quasi-solid electrolytes for lithium-metal batteries.

Mesoporous silicas tethered with anions were developed as quasi-solid electrolytes for Li-metal batteries. The high grafted density of trifluoromethylsulfonyl (-NTf-) groups and their uniformly distributed negative charge endow MCM41-NLiTf with a room temperature single Li-ion conductivity of up to 2.4 × 10-4 S cm-1, which enables stable cycling of LFP‖Li batteries.

Ultra-Long-Life and Ultrathin Quasi-Solid Electrolytes Fabricated by Solvent-Free Technology for Safe Lithium Metal Batteries

Ultra-Long-Life and Ultrathin Quasi-Solid Electrolytes Fabricated by Solvent-Free Technology for Safe Lithium Metal Batteries

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.

High energy density carbon supercapacitor with ionic liquid-based gel polymer electrolyte: Role of redox-additive potassium iodide

Carbon supercapacitors with quasi-solid and flexible gel polymer electrolytes (GPEs) are of current interest due to their potential applicability as commercial power sources. In the recent development, improvement in specific energy of such devices is the main focus of research. Enhancement in interfacial redox-activity by adding appropriate redox-agent in electrolyte is found an excellent method to improve specific energy. In this report, a free-standing, non-aqueous, redox-active GPE is presented comprising an ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide added with additive KI, entrapped in poly(vinylidene fluoride-co-hexafluoropropylene) for its application in quasi-solid-state-supercapacitors. The optimum composition of GPE shows flexible nature, excellent mechanical and thermal stabilities with high ionic conductivity (3.9 × 10−3 S cm-1 at room temperature) and wide electrochemical stability (∼5.05 V versus Ag). Carbon supercapacitor is fabricated with redox-active GPE and symmetrical electrodes of porous activated carbon (AC) derived from waste-biomass pollen-cone. The incorporation of KI in GPE instils fast redox-activity at the AC-electrode/GPE interfaces, hence, found responsible for substantial improvement in capacitance (from ∼115 to ∼250 F g−1) and energy (from ∼31 to ∼65 Wh kg−1) at maximum power of 34–36 kW kg−1. The supercapacitor with redox-active GPE demonstrates reasonable self-discharge behavior and cycling performance with only ∼11% initial fading. The capacitor offers retention rate of ∼70% in specific capacitance and energy after ∼10,000 charge-discharge cycles.

Li+ Dynamics of Liquid Electrolytes Nanoconfined in Metal-Organic Frameworks.

Metal–organic frameworks (MOFs) are excellent platforms to design hybrid electrolytes for Li batteries with liquid-like transport and stability against lithium dendrites. We report on Li+ dynamics in quasi-solid electrolytes consisting in Mg-MOF-74 soaked with LiClO4–propylene carbonate (PC) and LiClO4–ethylene carbonate (EC)/dimethyl carbonate (DMC) solutions by combining studies of ion conductivity, nuclear magnetic resonance (NMR) characterization, and spin relaxometry. We investigate nanoconfinement of liquid inside MOFs to characterize the adsorption/solvation mechanism at the basis of Li+ migration in these materials. NMR supports that the liquid is nanoconfined in framework micropores, strongly interacting with their walls and that the nature of the solvent affects Li+ migration in MOFs. Contrary to the “free’’ liquid electrolytes, faster ion dynamics and higher Li+ mobility take place in LiClO4–PC electrolytes when nanoconfined in MOFs demonstrating superionic conductor behavior (conductivity σrt > 0.1 mS cm–1, transport number tLi+ > 0.7). Such properties, including a more stable Li electrodeposition, make MOF-hybrid electrolytes promising for high-power and safer lithium-ion batteries.

Research and Development of Thermally Durable Electrolyte for Lithium Ion Battery

For ensuring safety of lithium ion batteries (LIBs), we have extensively investigated the quasi-solid electrolyte where lithium ion conducive liquid is quasi-solidified at silica surfaces as thermally durable electrolyte, and applied it to high capacity and high energy density LIB. For the liquid phase, a solvate ionic liquid, which is an equimolar complex of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and tetraethylene glycol dimethyl ether (G4), Li(G4)TFSA, was used. For enhancing discharge capability at a higher rate, Li(G4)TFSA was diluted by low viscos solvent such as propylene carbonate (PC). The developed electrolyte possessed a favorable volatilization temperature higher than 373 K. A 100-Wh-class laminated LIB with energy density of 363 Wh L−1 was fabricated by employing the electrolyte to graphite-LiNixCoyMnzO2 chemistry, and it generated neither fire nor smoke in a nail-penetration test. The result suggest that the developed LIB has high safety compared to a LIB comprised of a conventional organic liquid electrolyte. In addition, to enhance the cycle life of the LIB, the formation and growth mechanism of a solid-electrolyte interphase on a graphite-based negative electrode was investigated. 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, and that continuous decompositions of G4 and PC were a major reason for the SEI growth during charge-discharge cycles. Based on these analysis, we have substituted a highly concentrated sulfolane based liquid which exhibits a high Li ion conductivity with less amount of the low viscos solvent, for the G4 based liquid. The modification effectively improved the electrochemical durability of the electrolyte, leading to a higher capacity retention after charge-discharge cycle test.