Ionic liquid doped PEO-based solid polymer electrolytes for lithium-ion polymer batteries

The influence of adding the room-temperature ionic liquid 1-ethyl-3-methyllimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) to poly(ethylene oxide) (PEO)–lithium difluoro(oxalato)borate (LiDFOB) solid polymer electrolyte and the use of these electrolytes in solid-state Li/LiFePO₄ batteries has been investigated. Different structural, thermal, electrical and electrochemical studies exhibit promising characteristics of these polymer electrolyte membranes, suitable as electrolytes in rechargeable lithium-ion batteries. The crystallinity decreased significantly due to the incorporation of ionic liquid, investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The ion–polymer interaction, particularly the interaction of cations in LiDFOB and ionic liquid with ether oxygen atom of PEO chains, has been evidenced by FT-IR studies. The polymer electrolyte with ～40 wt% of ionic liquid offers a maximum ionic conductivity of ～1.85 × 10^?4 S/cm at 30 °C with improved electrochemical stabilities. The Li/PEO-LiDFOB-40 wt% EMImTFSI/LiFePO₄ coin-typed cell cycled at 0.1 C shows the 1st discharge capacity about 155 mAh g^?1, and remains 134.2 mAh g^?1 on the 50th cycle. The addition of the ionic liquid to PEO₂₀-LiDFOB polymer electrolyte has resulted in a very promising improvement in performance of the lithium polymer batteries.     

Electrochemical testing of industrially produced PEO-based polymer electrolytes

The present report describes the results of the electrochemical tests performed on polyethyleneoxide-based polymer electrolyte thin films industrially manufactured by blown-extrusion. The polymer electrolyte composition was PEO₂₀ LiCF₃SO₃: 16.7% γLiAlO₂. The polymer electrolyte film was tested to evaluate the ionic conductivity as well as the interfacial properties with lithium metal anodes. The work was developed within the advanced lithium polymer electrolyte (ALPE) project, an Italian project devoted to the realization of lithium polymer batteries for electric vehicle applications, in collaboration with Union Carbide.     

新型固态聚合物电解质在锂硫电池中的性能研究

本工作采用（氟磺酰）（三氟甲基磺酰）亚胺锂{Li[(FSO2)(CF3SO2)N],LiFTFSI}和聚氧乙烯（PEO）分别作为导电锂盐和聚合物主链,通过简单的溶液浇铸法制备了新型固态聚合物电解质（SPEs）,并采取示差扫描量热（DSC）、热重（TGA）、线性扫描伏安（LSV）、交流阻抗（EIS）和恒电位直流（DC）极化等方法研究了LiFTFSI/PEO （EO/Li+摩尔比为16）电解质的理化性质和电化学性质。结果表明,LiFTFSI/PEO电解质具有较高的室温离子电导率（σ ≈10−5 S/cm）,较高的氧化电位（4.63 V vs. Li/Li+）,并且耐热温度高达256 ℃。锂硫电池测试结果表明,该类SPEs展现出相对高的首周放电比容量（881 mA•h/g）,有效地抑制了多硫离子的“穿梭效应”,表现出良好的电池循环性能。     

Sodium-ion transfer at the interface between ceramic and organic electrolytes

Sodium-ion transfer through the interface between ceramic and organic electrolytes was studied by AC impedance spectroscopy. Na₃Zr_1.88Y_0.12Si₂PO₁₂ (NASICON) and Na-β″-alumina were used as ceramic electrolytes, and propylene carbonate (PC) and dimethyl sulfoxide (DMSO) containing 0.05 mol dm⁻³ NaCF₃SO₃ were used as organic electrolytes. The semi-circle ascribed to interfacial charge transfer resistance (R_ct) was observed. The activation energies for sodium-ion transfer at the interface between ceramic and organic electrolytes were evaluated by the temperature dependency of R_ct. As a result, the activation energies depended on the ceramic electrolytes but not on the solvents. These results suggest that sodium-ion transfer from ceramic to organic electrolytes should be responsible for the activation energies, which is contrary to the case in a lithium-ion transfer system. Based on these results, the mechanism of interfacial sodium-ion transfer was discussed.     

Ion conduction path in composite solid electrolytes for lithium metal batteries: from polymer rich to ceramic rich

Solid-state electrolytes (SSEs) can address the safety issue of organic electrolyte in rechargeable lithium batteries. Unfortunately, neither polymer nor ceramic SSEs used alone can meet the demand although great progress has been made in the past few years. Composite solid electrolytes (CSEs) composed of flexible polymers and brittle but more conducting ceramics can take advantage of the individual system for solid-state lithium metal batteries (SSLMBs). CSEs can be largely divided into two categories by the mass fraction of the components: “polymer rich” (PR) and “ceramic rich” (CR) systems with different internal structures and electrochemical properties. This review provides a comprehensive and in-depth understanding of recent advances and limitations of both PR and CR electrolytes, with a special focus on the ion conduction path based on polymer-ceramic interaction mechanisms and structural designs of ceramic fillers/frameworks. In addition, it highlights the PR and CR which bring the leverage between the electrochemical property and the mechanical property. Moreover, it further prospects the possible route for future development of CSEs according to their rational design, which is expected to accelerate the practical application of SSLMBs.     

固态聚合物电解质导电锂盐的研究进展

固态聚合物电解质(solid polymerelectrolytes,SPEs)具有不易泄漏、易加工、抑制锂枝晶生长等优点,能提高固态金属锂电池(solid-state lithiummetalbatteries,SSLMBs)的循环寿命和安全性。导电锂盐作为SPEs的必要组分之一,不仅能够为其离子输运提供锂离子源,而且能够在电极表面发生化学或电化学反应,参与电极/SPE界面膜的构建。因此,导电锂盐的分子结构对于调控SPEs的基础物理和电化学性质及其与电极材料的界面性能有着重要的影响。结合本团队在SPEs导电锂盐领域的相关研究工作,本文主要介绍全氟代和部分氟代磺酰亚胺锂盐作为SPEs导电盐的研究进展,并探讨了SPEs导电锂盐的未来发展方向。     

Gel-type polymer electrolytes with different types of ceramic fillers and lithium salts for lithium-ion polymer batteries

Gel-type polymer electrolytes are prepared using PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ mixed lithium salts and ceramic fillers such as Al₂O₃, BaTiO₃ and TiO₂. The electrochemical properties of these electrolytes, such as electrochemical stability, ionic conductivity and compatibility with electrodes are investigated in addition to the physical properties. The charge–discharge performances of lithium-ion polymer batteries using these get-type polymer electrolytes are investigated. The gel-type polymer electrolytes containing a mixed lithium salt of LiPF₆/LiCF₃SO₃ (10/1, wt.%) exhibit more stable ionic conductivity and lower interfacial resistance than those containing only LiPF₆. In addition, an Al₂O₃ filler improves interfacial stability between the electrode and the polymer electrolyte. Stacking cells (MCMB 1028/LiCoO₂, 8 cm × 13 cm × 7 ea) composed of gel-type polymer electrolytes based on PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ (10/1, wt.%) and Al₂O₃ filler maintain 95% of initial capacity after 100 cycles at a C/2 rate.     

Effect of molecular sieves ZSM-5 on the crystallization behavior of PEO-based composite polymer electrolyte

Polarized optical microscopy (POM) results show that ZSM-5 has great influence on both the nucleation stage and the growth stage of PEO spherulites. Part of ZSM-5 particles can act as the nucleus of PEO spherulites and thus increase the amount of PEO spherulites. On the other hand, ZSM-5 can restrain the recrystallization tendency of PEO chains through Lewis acid–base interaction and hence decrease the growth speed of PEO spherulites. The increasing amount of PEO spherulites, decreasing size of PEO spherulites and the incomplete crystallization are all beneficial for creating more continuous amorphous phases of PEO, which is very important for the transporting of Li⁺ ions. An adequate amount of ZSM-5 can enhance the room temperature ionic conductivity of PEO-LiClO₄ based polymer electrolyte for more than two magnitudes.     

Effect of ultra-thin polymer membrane electrolytes on dye-sensitized solar cells

In-situ ultra-thin porous poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF–HFP) membranes were prepared by a phase inversion method on TiO₂ electrodes coated with Ru N-719 dye. These membranes were then soaked in the organic liquid electrolyte to form the in-situ ultra-thin porous P(VDF–HFP) membrane electrolytes. Dye-sensitized solar cell (DSC) using the membrane electrolyte exhibited an open-circuit voltage (V_oc) of 0.751 V, a short-circuit current (J_sc) of 16.260 mA cm^?2 and a fill factor (FF) of 0.684 under an incident light intensity of 1000 W m^?2 yielding an energy conversion efficiency (η) of 8.35%. The V_oc, FF and η of the solar cell using the membrane electrolyte increased by about 5.8%, 2.2% and 5.7%, respectively, when compared with the corresponding values of a cell using liquid electrolyte. However, the J_sc decreased by about 2.1%.     

New crosslinking agent as a Lewis acid for solid polymer electrolytes

Poly(ethylene glycol) borate acrylate (PEGBA) was synthesized as a new crosslinking agent for solid polymer electrolyte (SPE) based on non-woven matrix. It has not only three crosslinkable acrylate groups for higher crosslinking density, but also Lewis acid center acting as an anion receptor. The ionic conductivity of SPE containing 15 wt.% PEGBA reached 5.5 × 10⁻⁴ S cm⁻¹, because the content of non-volatile plasticizer, poly(ethylene glycol) dimethyl ether (PEGDME), could be increased to 85 wt.% without leakage. In addition, its transference number and electrochemical stability were also enhanced to 0.37 and 5.2 V, respectively, due to the presence of Lewis acid center in PEGBA.     

Effects of surface lithiated TiO2 nanorods on room-temperature properties of polymer solid electrolytes

Polymer solid electrolyte with high ionic conductivity at room-temperature is most likely to be widely used in solid-state lithium batteries. In this work, the novel surface lithiated TiO₂ nanorods were firstly used as ionic conductor in polymer solid electrolyte. The surface lithiated TiO₂ nanorods-filled polypropylene carbonate polymer composite solid electrolyte (CSE) has an uniform composite structure with a thickness of about 60 μm. The ionic conductivity at room-temperature is 1.21 × 10⁻⁴ S cm⁻¹ and the electrochemical stability window is up to 4.6 V (vs Li⁺/Li). The assembled NCM622/CSE/Li solid-state battery shows a stable cycle performance with a retention capacity of 120 mAh g⁻¹ after 200 cycles at the current density of 0.3 C and a high coulomb efficiency of 99%. Compared with TiO₂ particles, this novel surface lithiated TiO₂ nanorods can provide more continuous ion transport channels and more Lewis acid-base reactive sites, provide a novel way to enhance the lithium ion transport in polymer solid electrolyte.     

Effect of salts on the fumed silica-based composite polymer electrolytes

Polymer electrolytes, which are ubiquitous and indispensable in all electrochemical devices, have been investigated and a study to explore their performance characteristics on salt type and salt concentration and different binary solvents has been performed. LiBETI salt exhibits less variation with change in molar concentration and is expected to form less ion pair formation. It has been realized that though the addition of inert ceramic fillers, i.e. fumed silica, enhances the mechanical integrity but decreases conductivity marginally in the LiIm, LiBETI and LiBF₄ based salt. This decrease in conductivity is due to their more interaction with the PMMA as established by FTIR. Moreover these electrolytes were found to be exhibited high conductivity (>mS/cm) to warrant their practical applications. The glass transition temperature increases with the addition of fillers pointing towards the lower mobility of Li⁺ ions and these electrolytes also exhibit high-thermal stability.     

Synthesis of supramolecular solid polymer electrolytes via self-assembly of diborylated ionic liquid

Novel supramolecular type solid polymer electrolytes were prepared by self-assembly of diborylated ionic liquid in the presence of bifunctional ligands. The polymers obtained were well soluble in methanol, and their structures were supported by ¹H and ¹¹B NMR spectra. The ionic conductivity of the polymers was evaluated by ac-impedance method after the samples were dried thoroughly. The ionic conductivity observed was 8.8 × 10⁻⁶ to 5.4 × 10⁻⁶ S cm⁻¹ at 51 °C in the presence of equimolar amount of LiTFSA to ionic liquid unit. The temperature dependence of ionic conductivity was successfully fitted to VFT (Vogel-Fulcher-Tamman) plots, indicating that ionic conduction is taking place according to typical ion transport model in viscous matrix.     

Lithium batteries composed of aluminate polymer complexes as single-ion conductive solid electrolytes

Single-ionic conductors, which display lithium ion migration exclusively (without anion migration), have been realized as the polymeric solid electrolytes with lithium orthoaluminate repeating units carrying oligo(oxyethylene) main chain and two side chains of endomethoxy{oligo(oxyethylene)}. The ionic conductivity of the aluminate polymer complexes is about 10⁻⁶–10⁻⁷ S/cm at room temperature. Thin film lithium secondary batteries were fabricated into 5.5 cm×4.5 cm×0.02–0.03 cm (thick) cells from lithium foil (anode), aluminate polymer complex (electrolyte) and TiS₂ (cathode). These batteries show minimal decay of output voltage upon constant current discharging and their capacity of first cycle was about 146 mA h/g of active cathode material. By contrast typical bi-ionic conductor of (aluminate polymer complex+5% LiClO₄) hybrid system showed, on the contrary, rapid decay of output voltage, due to polarization.     

溶剂热法合成三维花瓣状石榴石型固态电解质及其在固态聚合物电解质中的应用

石榴石型固态电解质由于具有离子电导率高、对金属锂稳定、成本低等一系列优点而被认为是最具应用前景的固态电解质材料体系之一,针对石榴石型电解质及其复合电解质的研究快速发展,然而,石榴石型电解质的合成方法研究较少,特别是具有特征微观形态的石榴石型电解质的研究鲜有报道.本工作首次报道了溶剂热法合成三维花瓣状石榴石型固态电解质(...     

Optimized lithium-doped ceramic electrolytes and their use in fabrication of an electrolyte-supported solid oxide fuel cell

Lithium-gadolinium-doped ceria electrolytes (2–5 mol% of lithium) are prepared by fast and reliable one-pot sol gel combustion synthesis and sintered at low temperature. The aim is to improve the microstructure, electrochemical and power generation of electrolyte-supported intermediate temperature solid oxide fuel cells. Time-of-flight coupled secondary ions mass spectroscopy and transmission electron microscopy reveal the uniform distribution of lithium and the structural modification and surface change induced by the doping. Lithium addition reduces the sintering temperature to 950 °C, and the electrochemical properties compared to the pure gadolinium doped ceria are highly superior. A maximum of 3.59·10⁻²–1.41·10⁻¹ S·cm⁻¹ for total conductivity are achieved for 3 mol.% of lithium addition at intermediate operative temperature range. An electrolyte-supported solid oxide fuel cell is then fabricated and tested in different gas conditions and operative temperatures. The maximum power density is 359 mW·cm⁻² at 668 mA·cm⁻² (750 °C). The results demonstrate the reliability, the short time-to-product and the feasibility of both synthesis cycle and electrolyte production for industrial application to develop a cost-effective and marketable fuel cell technology.     

High ionic conductivity in CeO2 SOFC solid electrolytes; effect of Dy doping on their electrical properties

Ionic conductors composed of lanthanide-doped ceria with general formula Dy_yCe_1-yO_2-δ (y = 0.05, 0.1 and 0.15) were synthesized by mechanochemistry (mechanical milling), and their electrical properties analyzed to be used as solid electrolytes in low-temperature SOFC. Starting oxide reagents were milled at different times in a planetary mill and the evolution of their structures and phases with milling time and temperature (up to 1500 °C) was followed by XRD. Just milled powders were also uniaxially pressed and sintered at different temperatures (1200, 1350 and 1500 °C), and analyzed by FE-SEM, to explore their morphologies as a function of temperature and Dy content. The electrical properties of these materials and undoped commercial CeO₂ were analyzed by impedance spectroscopy at different temperatures (200–650 °C) and frequencies (100 Hz - 1 MHz). Results showed that mechanochemistry is a suitable method to obtain the Dy_yCe_1-yO_2-δ systems after 20 h of milling, since XRD patterns of these milled powders reveal the formation of fluorite-type cubic solid solutions for all studied compositions. Increasing of temperature generates a higher crystallinity in these materials while the absence of phase transitions in them is corroborated at 1200 °C. Analysis of electrical properties of samples sintered a 1200 °C corroborates the viability of these systems to be used as solid electrolytes in the SOFC technology, being that high dc conductivities (σ_dc) were obtained for all doped samples, especially for the composition Dy_0.1Ce_0·9O_2-δ, which showed a σ_dc = 1 × 10^−1.91 S cm⁻¹ at 650 °C. This value represents an increase of almost three orders of magnitude for this composition with respect to the undoped CeO₂ sample (y = 0, σ_dc = 1 × 10 ^−4.83 Scm⁻¹).