Liquid Electrolyte Solution Research Articles

Boronic ionogel electrolytes to improve lithium transport for Li-ion batteries

Boron containing ionogels were fabricated through chemical crosslinking of boron allyloxide with polyethylene glycol dimethacrylate in an ionic liquid electrolyte solution to obtain mechanically robust gels. Because of the relatively small concentration of crosslinking agent required to fully solidify the ionic liquid electrolyte, good characters of high ionic conductivity, high thermal stability, and good electrochemical stability were observed. A spectroscopic investigation of the boronic ionogels revealed that the lithium mobility was noticeably enhanced compared with ionogels fabricated without the boronic crosslinker, leading to promising Li-ion battery performance at elevated temperatures.

Electroresponsive Dual Functional Display Device Enabling Both Emissive and Reflective Modes by Combining Electrochemiluminescent and Liquid Crystal Materials

A novel electroresponsive multifunctional display device enabling control of both emission and transmittance was successfully fabricated. The device consisted of a liquid crystal-based electrolyte solution containing an electrochemically active luminescent material. Yellow electrochemiluminescence was observed from the device under application of alternating current voltage; modulation of its transmittance was also achieved when direct current voltage was applied to the device.

Electrochemical Preparation of Electro-Active Polymers Having Nitrogen Atom: Chiral Polycarbazole Prepared in Chiral Liquid Crystal by Electrochemical Polymerization

Polycarbazole was electrochemically synthesized in liquid crystal electrolyte solution on ITO glass. The liquid crystal electrolyte solution contains monomer, supporting salt, and matrix liquid crystal. Polarizing optical microscopy observation revealed that the polymer film thus obtained showed fingerprint optical texture derived from the morphology of the liquid crystal electrolyte solution. This result indicates that molecular transcription occurred from molecular level to macroscopic levels. UV-vis optical absorption measurement confirmed that polycarbazole film was successfully obtained by the electrochemical polymerization. Color of the polymer film can be changed from green (as-prepared) to yellow (reduced state) via reduction. Circular dichroism measurement revealed that this polymer film shows optical activity.

Improvement of low-temperature performance by adopting polydimethylsiloxane-g-polyacrylate and lithium-modified silica nanosalt as electrolyte additives in lithium-ion batteries

In this work, poly[dimethylsiloxane-co-(siloxane-g-acrylate)] (PDMS-A) and lithium-modified silica nanosalt (Li202) are used together as low-temperature electrolyte additives in lithium-ion batteries (LIBs), taking advantage of the electrochemical and interfacial stabilities due to their surface functional groups. Using these additives together improves the electrochemical stability and ionic conductivity of liquid electrolyte solution to over 5.5V and 4×10−4Scm−1 at −20°C, respectively. The room-temperature electrochemical performance of a conventional LIB (LiCoO2/graphite) is improved by the addition (e.g., initial discharge capacity of 95.9mAhg−1 obtained after charging at 1.0 C-rate and consequent discharging at 5.0 C-rate). The low-temperature performance is also enhanced, achieving a capacity retention ratio of 63.4% after 50 cycles at −20°C, compared to 38.7% without the additives. It is also notable that the PDMS unit commonly existing in both additives may be the main cause of the synergistic effects on the electrochemical performance due to the compatibility between PDMS-A and Li202.

Electrochemical Preparation of Electro-active Polymers having Nitrogen Atom

New functions of polymer film can be developed by using template. We synthesized polypyrrole (PPy) as a conducting polymer in liquid crystal electrolyte solution. The liquid crystal electrolyte solution for the electrochemical polymerization contains monomer, electrolyte, and matrix liquid crystal. The electrochemical polymerization in liquid crystal was simply performed by using sandwich cell electrochemical polymerization method, which we have originally developed. Application of constant voltage between the two electrodes produces a solid polymer film at anode side through electrochemical oxidation polymerization process. Polarizing optical microscopy observation revealed that the polymer film thus obtained show beautiful optical texture like liquid crystal. The surface texture was derived from molecular structure transcription from the liquid crystal electrolyte solution. The transcription is occurred from molecular level to macroscopic level. Infrared absorption spectroscopy measurements, UV-Vis absorption measurements confirm that the polymer film is exactly pi-conjugated film, although the optical structure is very similar to that of liquid crystal. Furthermore, the polymer film can be tuned its color via electrochemical redox reaction (doping-dedoping). Therefore, the polymer has both liquid crystal order and electro-active property. Lyotropic liquid crystals have good affinity with water, and form crystal like aggregation structure via a self-assembly. Lyotropic liquid crystal shows variety in liquid crystal type, such as columnar phase, smectic phase, nematic phase, and cholesteric phase. In this research, we employed lyotropic liquid crystals for electrolyte solution. Columnar liquid crystals have paid attention as an electrical conduction materials having good carrier mobility. Therefore, the polymer thus prepared can be expected to show structure based unique electrical conduction function through columnar form produced by the transcription from the liquid crystal electrolyte solution in the electrochemical polymerization. Cholesteric liquid crystals show chiral aggregation form. The polymer prepared in cholesteric liquid crystal shows fingerprint texture under the observation of polarizing optical microscope, and optical rotation and circular dichroism. The optical rotation angle can be controlled with electrochemical redox reaction. In this presentation, we report, 1) Preparation of liquid crystal electrolyte solution and characterization 2) Electrochemical polymerization 3) Spectroelectrochemistry. This research can be involved molecularly imprinting (MIP) [3,4]. We discuss the method of electrochemical polymerization, functions, and future prospective of the polymer films prepared in liquid crystals based on electrochemistry.

Composite Polymer Electrolyte Containing Core-Shell Structured SiO2(Li+) Particles for Suppressing Lithium Dendrite Growth and Improving High Temperature Cycling Stability of LiNi0.5Mn1.5O4

The most widely used electrolyte for lithium-ion batteries is lithium hexafluorophosphate (LiPF6) in a mixture of organic carbonate solvents due to its high conductivity, good electrochemical stability and acceptable cycle performance at low temperatures [1]. However, the use of liquid electrolytes in lithium batteries has many drawbacks, such as high flammability of organic solvents, possibility of leakage and poor thermal stability [2, 3]. Among the potential electrolytes for lithium batteries, polymer electrolyte has received considerable attention due to high ionic conductivity and superior thermal safety with no electrolyte leakage [4]. However, polymer hosts lose their mechanical strength when they are plasticized with liquid electrolyte solution, leading to serious problems in terms of cycle life and safety [5]. In this study, in order to obtain polymer electrolytes with enhanced mechanical strength and good electrochemical properties, core-shell structured SiO2 nanoparticles containing poly(lithium acrylate) in the shell were synthesized. They were used as functional fillers in preparing composite polymer electrolytes for suppressing lithium dendrite growth and preventing HF generation in the electrolyte. The composite polymer electrolytes prepared with SiO2(Li+) particles exhibited high ionic conductivity, good thermal stability and favorable interfacial characteristics. The lithium metal polymer cells composed of lithium metal negative electrode and LiNi0.5Mn1.5O4 positive electrode are assembled and their cycling performances are evaluated. The cells assembled with the composite polymer electrolyte exhibited superior cycling performance both at ambient temperatures and at elevated temperature.

Frontispiece: Is TiO2 (B) the Future of Titanium-Based Battery Materials?

The upper part of the frontispiece shows the operating potential vs. the practical specific charge capacity of different positive and negative Li-ion battery materials. The stability window of todays liquid electrolyte solutions is confined by the formation of the cathode electrolyte interphase (CEI) and the solid electrolyte interphase (SEI). In the lower part of the frontispiece, the overall performance of conventional carbonaceous and titania based materials are compared. In this mini review, Fehse and Ventosa illustrate the promising role of TiO2 (B) as battery material with enhanced safety, cycle stability and rate performance.

Charging a capacitor from an external fluctuating potential using a single conical nanopore.

We explore the electrical rectification of large amplitude fluctuating signals by an asymmetric nanostructure operating in aqueous solution. We show experimentally and theoretically that a load capacitor can be charged to voltages close to 1 V within a few minutes by converting zero time-average potentials of amplitudes in the range 0.5–3 V into average net currents using a single conical nanopore. This process suggests that significant energy conversion and storage from an electrically fluctuating environment is feasible with a nanoscale pore immersed in a liquid electrolyte solution, a system characteristic of bioelectronics interfaces, electrochemical cells, and nanoporous membranes.

Enhanced cycling performance of a high-energy and low-cost lithium–sulfur battery with a sulfur/hardwood charcoal composite cathode material

Lithium–sulfur battery is an attractive candidate for advanced energy storage devices due to its high specific energy of 2600 Wh kg−1 arising from the high theoretical specific capacity (1675 mAh g−1) of the sulfur cathode. However, short cycle life and low cycling efficiency are still the main obstacles preventing the practical development of this promising battery system. In this work, we show that a low-cost Li/S cell employing an activated hardwood charcoal–sulfur (S–AHC) nanocomposite cathode can be operated for more than 300 cycles while still maintaining high specific capacity (600 mAh g−1) and coulombic efficiency of 97 %, achieved by a new formulation of liquid electrolyte containing a fluorinated solvent. Such an improved capacity retention and cycle life, as compared to its conventional counterparts, prove that active mass lost via polysulfide dissolution can be effectively inhibited by utilization of this liquid electrolyte solution. Considering these results, we believe that the Li/S battery consisted of this composite cathode and the liquid electrolyte may be proposed as a promising candidate for low-cost energy storage applications.

Flexible Cellulose-Based Electrodes: Towards Eco-friendly All-paper Batteries

In the present work an easy paper-making technique is used for the manufacture of low cost and low environmental impact all-paper-based Li-ion cells. The cells are composed of two paper-like electrodes, prepared using micrometric-sized graphite (anode) and LiFePO4 (cathode) as active materials and truly natural microfibrillated cellulose as binder, and paper hand-sheets soaked in a standard liquid electrolyte solution as separator between them. The specific capacity obtained is even superior to that of standard PVdF-binded cell assembled with the same electrodes, and remains stable over prolonged cycling, indicating that the cellulose fibres do not affect the cycling stability. In this study, no organic solvents or synthetic polymer binders are used all along the production of the cell components which, in addition, can be easily re-dispersed in water by simple mechanical stirring as well as common paper handsheets.

Flexible and high performing polymer electrolytes obtained by UV-induced polymer–cellulose grafting

A novel UV-induced procedure, in the presence of glycidyl acrylate and proper radical/cationic photoinitiators, is here proposed to promote the in situ grafting of a methacrylic polymer network to the surface of natural cellulose fibers. As a result, composite polymer membranes reinforced by cellulose handsheets are obtained and demonstrate excellent mechanical features. The reactivity of the monomers is studied by FT-IR in real time measurements and the successful grafting is confirmed by surface spectroscopies. The polymer membranes prepared show high elastic modulus and tensile resistance and maintain high flexibility even after activation by swelling into a standard liquid electrolyte solution. The swelling procedure allowed us to obtain high ionic conductivity and remarkable electrochemical behavior when tested in laboratory scale lithium polymer cells. The system shows attractive features such as intrinsic safety, eco-compatibility, and low production cost and industrialization potentials, and is highly suitable for the rapidly expanding field of Li-based flexible batteries.

Improvement of lithium-ion battery performance at low temperature by adopting polydimethylsiloxane-based electrolyte additives

Three kinds of polydimethylsiloxane (PDMS)-based grafted and ungrafted copolymers such as poly[dimethylsiloxane-co-(siloxane-g-acrylate)] (PDMS-A), poly(dimethylsiloxane-co-phenylsiloxane) (PDMS-P), and poly[dimethylsiloxane-co-(siloxane-g-ethylene oxide)] (PDMS-EO) are used as additives to standard liquid electrolyte solutions to enhance the lithium-ion battery performance at low temperatures. Liquid electrolyte solutions with PDMS-based additives are electrochemically stable under 5.0V and have adequate ionic conductivities of 10−4Scm−1 at -20°C. Particularly, liquid electrolytes with PDMS-P and PDMS-EO exhibit higher ionic conductivities of around 5×10−4Scm−1 at -20°C, indicating a specific resisting property against the freezing of the liquid electrolyte components. As a result, the addition of PDMS-based additives to liquid electrolytes improves the capacity retention ratio and rate-capability of lithium-ion batteries at low temperatures.

Preparation and characterization of electrospun nanofiber-coated membrane separators for lithium-ion batteries

Nanofiber-coated membrane separators were prepared by electrospinning polyvinylidene fluoride-co-chlorotrifluoroethylene (PVDF-co-CTFE) nanofibers onto three different microporous membrane substrates. The nanofibers on the membrane substrates showed uniform morphology with average fiber diameters ranging from 129 to 134 nm. Electrolyte uptakes, ionic conductivities, and interfacial resistances were studied by soaking the nanofiber-coated membrane separators with a liquid electrolyte solution of 1 M lithium hexafluorophosphate in ethylene carbonate/dimethylcarbonate/ethylmethyl carbonate (1:1:1 by volume). Compared with uncoated membranes, nanofiber-coated membranes had greater electrolyte uptakes and lower interfacial resistances to the lithium electrode. It was also found that after soaking in the liquid electrolyte solution, nanofiber-coated membranes exhibited higher ionic conductivities than uncoated membranes. In addition, lithium-ion half cells containing nanofiber-coated membranes were evaluated with a LiFePO4 cathode for charge–discharge capacities and cycle performance. The cells containing a nanofiber-coated separator membrane showed high discharge specific capacities and good cycling stability at room temperature. Results demonstrated that coating PVDF-co-CTFE nanofibers onto microporous membrane substrates is a promising approach to obtain new and high-performance separators for rechargeable lithium-ion batteries.

(Invited) Surface Modification of Wide Band-Gaped Anode of Dye-Sensitized Solar Cells by Ionic Liquid Molecules

Dye-sensitized solar cells have attracted worldwide attention due to its unique properties such as cost effective, temperature insensitive, and with high quantum efficiency under low illuminations. Among all studies, the topic of replacement of commonly used liquid electrolyte solution to reduce solution leakage becomes one of the emerging research focuses. The replacement of solvent of electrolyte solution by ionic liquid is one of the approaches. The reduced leakage by these approaches is expected to realize yet at the expense of reduced solar cell efficiency, due to lowered charge transfer rates in the electrolyte solutions. However, we found that the partial replacement of commonly used electrolyte solution by imidazolium salt solution enhances the solar cell efficiency instead.In this study, we report that the surface treatment of the wide band-gaped anode of titanium oxide by ionic liquid molecules accounts for at least part of the solar cell efficiency enhancement. We found that the imidazole-derived molecules act as barrier for electron-hole premature recombination between photoelectrons transported on the conduction band of anode and the holes in the electrolyte on the anode/electrolyte interface. The significant efficiency enhancement is not necessarily due to increased dye adsorption on anodes, because we can manage a reduced dye adsorption condition while the solar cell still provides enhanced efficiency.The ligand of imidazolium salts plays a very crucial role on the effectiveness of imidazole-derived molecules on the enhancement of solar cell efficiency. The presence of sulfite ligand secures the molecule adhesion on titanium oxide through the sulfite ligand itself.We would like to present the parameters of treatment of such sequence of imidazole and dye adsorption, the use of solvent, dip duration time, and solution concentration. From the interrogation of the experiment results, we can confirm the exact role of imidazole-derived molecules on the enhancement of the solar cell efficiency.

Enhanced high-temperature cycling of Li2O–2B2O3-coated spinel-structured LiNi0.5Mn1.5O4 cathode material for application to lithium-ion batteries

A Li2O–2B2O3–glass-coated LiNi0.5Mn1.5O4 (LNMO) cathode active material (GC-LNMO) was synthesized to enhance the thermal stability of LNMO-based electrodes for lithium-ion batteries. The morphologies of the surface-coating layers were analyzed using transmission electron microscopy. The glass coating prevented the surface of the LNMO-based electrode from being directly exposed to the liquid electrolyte solution, preventing Mn at the electrode surface from dissolving into the electrolyte and thus preventing the cell impedance from increasing through the undesirable formation of a cathode–electrolyte-interphase layer and the development of facile charge transfer kinetics during cycling. The electrochemical performance measurements demonstrated that the GC-LNMO-based electrode exhibited remarkably enhanced electrochemical reversibly and stability at elevated temperature (60°C).

Thermal Properties and Ionic Conductivities of Confined LiBF4Dimethyl Carbonate Solutions

Solutions of lithium tetrafluoroborate dissolved in dimethyl carbonate (DMC) are confined within MCM-41, a mesoporous silica matrix. Thermal measurements indicate that the melting points of pure DMC and the DMC solutions are significantly reduced when confined within the pores of MCM-41 compared to unconfined samples; this is an observation that is consistent with the Gibbs–Thomson equation. The melting point onsets of confined solutions are slightly lower than that of pure DMC, suggesting the dissolved salts impact the phase-transition temperature of DMC when confined within mesoporous silica. Rotational dynamics of the confined solutions are explored by doping DMC with small quantities of Tempone, an electron paramagnetic resonance (EPR)-active spin probe. Tempone rotational correlation times are an order of magnitude slower for confined liquids compared to unconfined solutions. Temperature-dependent conductivity measurements of the composite materials suggest that the liquid electrolyte solution is distributed among the MCM-41 pores and the intergrain voids between individual MCM-41 particles. Ionic conductivities of confined electrolyte solutions remain above 0.01 mS·cm–1 for temperatures greater than −50 °C. However, the ionic conductivity of the unconfined solutions (i.e., solution occupying the spaces between the MCM-41 particles) rapidly decreases over subzero temperatures. Limitations associated with directly implementing these materials as low-temperature ion conductors are discussed.

Preparation and Properties of Poly (vinylidene fluoride)/poly(dimethylsiloxane) graft (poly(propylene oxide)-block-poly(ethylene oxide)) blend porous separators and corresponding electrolytes

This work aims exploring the high performance porous separators that can be activated into gel electrolyte membranes for lithium ion batteries. A comb-like copolymer poly (dimethylsiloxane) graft poly (propylene oxide)-block-poly (ethylene oxide) (PDMS-g-(PPO-PEO)) was synthesized and blended with poly (vinylidene fluoride) (PVDF) to fabricate porous separators via a typical phase inversion process, and then the separators absorbed liquid electrolyte solution and formed into polymer electrolyte membranes. By measuring the composition, morphology and ion conductivity etc, the influence of PDMS-g-(PPO-PEO) on structure and properties of blend separators were discussed. Compared with pure PVDF separator with comparable porous structure, the adoption of PDMS-g-(PPO-PEO) decreased the crystallinity and increased the liquid electrolyte uptake and stability effectively. It was also found that the electrode/electrolyte interfacial resistance could be reduced greatly. The resulting electrolyte membrane using separator with PVDF/PDMS-g-(PPO-PEO) mass ratio in 8/2 exhibited highest ionic conductivity in 4.5×10−3 S/cm at room temperature, while the electrochemical stability was up to 4.7V (vs. Li/Li+). Coin cells assembled with such separators also exhibited stable cycle performance and improved rate capabilities, especially when discharge rate higher than 0.5C.

A novel electrospun PVDF/PMMA gel polymer electrolyte with in situ TiO2 for Li-ion batteries

Gel polymer electrolyte films with and without in situ TiO2 were prepared by electrospinning 16 wt.% poly(vinylidene fluoride)/poly(methyl methacrylate)-polymer solution at room temperature. Then the gel polymer electrolyte was obtained by immobilizing 1 M LiClO4–ethylene carbonate/propylene carbonate liquid electrolyte solutions in the membranes. The electrospun poly(vinylidene fluoride)/poly(methyl methacrylate) gel polymer electrolyte with 3% in situ TiO2 shows the highest ionic conductivity of 3.9 × 10− 3 S cm− 1 with electrochemical stability up to 5.1 V versus Li+/Li at room temperature. The properties of the gel polymer electrolyte prepared with in situ TiO2 were observed to be comparatively better than the one without in situ TiO2. With the superior performances, the gel polymer electrolyte prepared with in situ TiO2 is very suitable for application in Li-ion batteries.

Two Dimensional Li Diffusion in Ion-Conductive Lithium Lanthanum Titanates

Developing energy storage systems is an indispensable and keyfactor in realizing a sustainable society. Although a pumped storage hydroelectric power station converts gravitational to kinetic energy via the movement of water and constitutes a reliable secondary battery system, such a system is a huge facility covering a vast area. By substituting the less dense substance Li for water and replacing the stronger chemical interaction of Li for the weaker gravitational force, a Li-ion battery attains high energy density. 1,2 Currently, most Li-ion batteries use a combustible liquid electrolyte solution, which requires them to be securely and heavily sealed in small packages. The use of a liquid electrolyte in batteries not only creates safety issues but also leads to degradation due to repetitive cycling. An irreversible reaction with Li is reported to happen at the anode surface, known as the solid electrolyte interface (SEI) region. 3 Preventing the loss of active Li at the SEI and eliminating the combustible liquid from the battery, will open the door to the development of large size, high-capacity batteries. For thisreason, researchers have devoted their attentions to incorporating a solid electrolyte into Li-ion battery systems. We have focused our efforts on studying the fundamental mechanism of Li diffusion in a particular solid electrolyte system, the lithium lanthanum titanates (LLTO), which show a high conductivity of 10 −3 Sc m −1 . 4,5

Electrospun nanofiber‐coated separator membranes for lithium‐ion rechargeable batteries

AbstractNanofiber‐coated composite membranes were prepared by electrospinning polyvinylidene fluoride‐co‐chlorotrifluoroethylene (PVDF‐co‐CTFE) and PVDF‐co‐CTFE/polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐co‐HFP) onto six different Celgard® microporous battery separator membranes. Application of a PVDF‐based copolymer nanofiber coating onto the surface of the battery separator membrane provides a method for improving the electrolyte absorption of the separator and the separator‐electrode adhesion. Peel tests showed that both PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber coatings have comparable adhesion to the membrane substrates. Electrolyte uptake capacity was investigated by soaking the nanofiber‐coated membranes in a liquid electrolyte solution. PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber‐coated membranes exhibited higher electrolyte uptake capacities than uncoated membranes. It was also found that PVDF‐co‐CTFE nanofiber‐coated membranes have higher electrolyte uptakes than PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber‐coated membranes due to the smaller diameters of PVDF‐co‐CTFE nanofibers and higher polarity of PVDF‐co‐CTFE. The separator–electrode adhesion properties were also investigated. Results showed PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber coatings improved the adhesion of all six membrane substrates to the electrode. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013