染料敏化太阳能电池中准固态聚合物电解质的研究进展

染料敏化太阳能电池（DSSC）制备工艺简单、制造成本低廉且转换效率高,是太阳能电池的重要发展方向,具有广泛的应用前景。目前,基于液态电解质的DSSC的光电转换效率最高已达到13%,但液态电解质封装困难、长期稳定性差等问题阻碍了其实际应用。近些年来,固态和准固态电解质引起了研究学者们的广泛关注。其中准固态聚合物电解质因具有较高的离子电导率、良好的电池界面接触和可加工性能,成为制备高性能DSSC的重要研究方向之一。根据特征、形成机制和电解质的物理状态,可将准固态聚合物电解质分为四大类：准固态热塑性聚合物电解质,准固态热固性聚合物电解质,准固态复合型聚合物电解质和准固态离子型聚合物电解质。本文分析了基于这几类准固态聚合物电解质的DSSC的性能参数,并对其存在的问题和未来的研究方向进行了探讨。     

Preparation and electrochemical characterization of polymer electrolytes based on electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/polyacrylonitrile blend/composite membranes for lithium batteries

Apart from PEO based solid polymer electrolytes, tailor-made gel polymer electrolytes based on blend/composite membranes of poly(vinylidene fluoride-co-hexafluoropropylene) and polyacrylonitrile are prepared by electrospinning using 14 wt% polymer solution in dimethylformamide. The membranes show uniform morphology with an average fiber diameter of 320-490 nm, high porosity and electrolyte uptake. Polymer electrolytes are prepared by soaking the electrospun membranes in 1 M lithium hexafluorophosphate in ethylene carbonate/dimethyl carbonate. Temperature dependent ionic conductivity and their electrochemical performance are studied. The blend/composite polymer electrolytes show good ionic conductivity in the range of 10⁻³ S cm⁻¹ at ambient temperature and good electrochemical performance. All the Polymer electrolytes show an anodic stability >4.6 V with stable interfacial resistance with storage time. The prototype cell shows good charge-discharge properties and stable cycle performance with comparable capacity fade compared to liquid electrolyte under the test conditions.     

Recent advances of electrolytes for sodium-ion batteries

作为一种新型的储能电池体系,钠离子电池具有资源丰富、成本低、比容量较高等优点,近年来引起了全世界范围内的广泛关注。电解质是制备高性能,长循环寿命,安全性良好的钠离子电池的关键材料之一。本文简要介绍有机电解质、水系电解质、离子液体电解质、固体聚合物电解质、无机固态复合电解质和凝胶态聚合物电解质等体系在钠离子电池中的研究进展,讨论这些电解质体系的电导率、电化学窗口、热稳定性等特点。目前应用在钠离子电池中较为成熟的是有机电解质,展现了良好的综合性能,但安全性仍有待改善。而安全性能较好的离子液体电解质、固体电解质及凝胶态电解质还有许多基础科学需要探索,并且需要考虑成本、电导率、机械强度等诸多因素。基于上述评述,展望了钠离子电池电解质的未来发展。     

The effect of nanosized TiO2 addition on poly(methylmethacrylate) based polymer electrolytes

The electrochemical, X-ray diffraction, thermal, rheological and spectroscopic studies have been carried out to examine the effect of nanosized TiO₂ addition in different concentration to polymethylmethacrylate (PMMA) based gel polymer electrolytes (GPE). This work demonstrates that with optimum concentration of TiO₂ loadings in GPE, the ionic conductivity enhances with negligible effect on other electrochemical properties. The obtained ionic conductivity value is >10⁻³ S cm⁻¹. An increase in viscosity by an order of magnitude is obtained which also restricts the flow property of GPE. The addition of TiO₂ retains the amorphicity of the GPE while the T_g increases. Enhanced mechanical stability of these composite polymer electrolytes (CPEs) with solid-like behavior is evident from their appearance. The activation energy has been calculated by fitting the conductivity profile in VTF equation, which decreases on the addition of fillers. FTIR characterization also confirms the interaction of filler with CO of PMMA. The capabilities and properties exhibited by these CPEs will be of immense interest for electrochemists to use them in solid-state devices.     

单离子导体聚合物电解质研究进展

聚合物电解质能够避免传统液态电解液漏液的隐患,抑制锂枝晶的生长,提高电池的安全性能。单离子导体是一类锂离子迁移数接近1的聚合物电解质,能有效避免阴离子移动产生浓差极化,降低内部阻抗,从而提高锂电池的容量以及循环性能,成为近年来聚合物电解质的研究热点。本文综述了单离子导体聚合物电解质的研究进展,尤其关注离子电导率和锂离子迁移数较高的体系,并探讨了单离子导体聚合物电解质所面临的挑战以及发展前景。     

Electrochromic devices operating with electrolytes based on boronate ester compounds and various alkali metal salts

Various polymer electrolytes based on boronate esters and different lithium and sodium salts have been evaluated in electrochromic (EC) devices based on WO₃ films. The results showed that the ionic conductivity of the electrolytes was not the most important parameter for the colouration performance of these devices. The use of solid electrolytes containing LiClO₄ resulted in a higher colouration performance than the corresponding liquid electrolytes, even though the latter exhibited a significantly higher conductivity. The results also showed that the transfer process at the interface between the WO₃ layer and the electrolyte played a major role for the colouration process. The presence of Lewis acidic boronate ester groups in the electrolytes significantly improved the performance of the EC devices. The incorporation of boron in the composition of the electrolytes allowed the use of solid electrolytes instead of liquid ones, thus avoiding leakage problems. Furthermore, the highest colouration performance was found in EC devices operating with inexpensive salts. Because of their poor stability, the electrolytes based on LiCl and LiBr were not suitable, while those incorporating LiClO₄ salt exhibited excellent overall characteristics.     

锂离子电池用（聚）离子液体电解质

锂离子电池已广泛应用于便携式电子设备和电动汽车等领域,然而商用锂离子电池中含有大量易燃的碳酸酯类有机溶剂,容易造成安全隐患。离子液体具有蒸汽压低、化学结构设计多样性、热稳定性及电化学稳定性优异等优点,可以用来代替易燃有机溶剂,在电化学储能领域具有广阔的应用前景。聚离子液体是一类聚合物重复单元上含有阴、阳离子的新型聚合物电解质材料,兼具离子液体和聚合物固态电解质不漏液、易于加工的优势。根据离子液体和聚离子液体化学结构的设计合成及其在锂离子电池中的应用形式,综述了近年来离子液体电解质的研究进展,并提出了离子液体电解质未来的应用挑战和发展方向。     

Novel ionic plastic crystal-polymeric ionic liquid all-solid-state electrolytes for lithium ion batteries

离子塑性晶体作为一类新型的固态电解质材料,近年来受到研究人员的极大关注。本文合成了一种新型离子塑性晶体：N,N-二甲基吡咯双氟磺酰亚胺（P₁₁FSI）,并将其与吡咯阳离子离子液体聚合物-聚二甲基二烯丙基铵双氟磺酰亚胺（PILFSI）和锂盐（LiFSI）复合制备了P₁₁FSI-PILFSI-LiFSI全固态电解质。采用差示扫描量热法、热重分析、阻抗测试、线性扫描伏安法及对称锂电池测试等一系列表征技术对全固态电解质的热性能和电化学性能进行了系统研究。所制备的电解质膜具有好的柔韧性和热稳定性,高的离子电导率和电化学稳定性,以及与金属锂良好的界面相容性。将全固态电解质应用于Li/LiFePO₄电池中,在50℃、0.2 C充放电倍率时,电池放电比容量在60次循环后仍可达151.1 mA·h/g,容量保持率为96.8%;且在0.5 C、1.0 C倍率下放电比容量仍然高达138.1 mA·h/g和128.1 mA·h/g,展现出高的放电比容量,好的循环性能和倍率性能,有望应用于全固态锂离子电池中。     

Progress of inorganic solid electrolyte for lithium ion batteries

目前,商品化的锂离子电池电解液主要以碳酸乙烯酯、碳酸二甲酯和碳酸甲乙酯等有机溶剂为溶剂,在电池使用过程中,存在电解液分解、锂枝晶生成和漏液等问题,从而影响电池的稳定性和安全性。无机固态锂电池电解质具有热稳定性高、电化学性能稳定、与高电压正极材料相容性好、安全性高及环境友好等优点,是目前储能领域研究的一个热点。研究和开发具有高离子电导率的无机固态电解质是促进其在电池中应用的关键和难点,本文综述了几类目前研究较多的LiPON型、钙钛矿型、石榴石型、LISICON型电解质,重点关注了其在离子电导率方面的研究及应用进展。     

Ionic conductivity and thermal property of solid hybrid polymer electrolyte composed of oligo(ethylene oxide) unit and butyrolactone unit

Various hybrid polymers composed of oligo(ethylene oxide) unit and butyrolactone unit, such as polymer blend, block copolymer and random copolymer, were synthesized by radical polymerization of poly(ethylene oxide) methyl ether methacrylate (PEOMA) and/or α-methylene-γ-butyrolactone (MBL), and the ionic conductivities and thermal properties of the solid polymer electrolytes using those hybrid polymers and LiN(SO₂CF₃)₂ were investigated. The solid polymer electrolyte using homopolymer of PEOMA (poly(PEOMA)) showed higher ionic conductivity and larger temperature dependence of ionic conductivity than those of the solid polymer electrolyte using homopolymer of MBL (poly(MBL)). The ionic conductivities of the solid hybrid polymer electrolytes were improved at especially low temperature region compared with each homopolymer electrolyte. This result indicates that the decline in the ionic conductivity at low temperature, which is characteristic of PEOMA unit, has been effectively reduced by combining with MBL unit. The poly(PEOMA) and the block or random copolymer electrolytes showed the higher thermal stability than the poly(MBL) and the polymer blend electrolytes.     

Investigation of PEO-imidazole ionic liquid oligomer electrolytes for dye-sensitized solar cells

Ionic liquid oligomers prepared by incorporating imidazolium ionic liquid with PEO oligomers were investigated as electrolytes for dye-sensitized solar cells (DSSCs). The influences of PEO molecular weight and imidazolium group of the ionic liquid oligomers on the ionic conductivity, apparent diffusion coefficient of the redox species in the electrolytes and the performance of solar cells were examined. The structural effects of the ionic liquid oligomers on the kinetic behaviors of dye regeneration and triiodide reduction reactions taken place at nanocrystalline TiO₂ electrode and Pt counter-electrode, respectively, were further studied by cyclic-voltammetry and electrochemical impedance spectroscopy measurements. The increase of the PEO molecular weight of the ionic liquid oligomers results in the faster dye regeneration rate and lower charge transfer resistance of triiodide reduction leading to the improvement of cell performance effectively.     

Nanocomposite electrolytes with fumed silica in poly(methyl methacrylate): thermal,rheological and conductivity studies

Composite polymer electrolytes (CPEs), were prepared by adding hydrophilic fumed silica in different proportions upto 5 wt.% to gel polymeric electrolyte (GPE) comprising liquid electrolyte (1 M LiClO₄ in propylene carbonate) immobilized with 15 wt.% poly(methyl methacrylate) (PMMA). The effect of fumed silica content in the CPEs on the ionic conductivity and viscosity over a wide temperature range was investigated. The resultant CPEs showed room temperature conductivity (σ₂₅) as high as 3.8 mS cm⁻¹ along with viscosity value of 3700 P for 2 wt.% SiO₂ addition. Fumed silica addition both to the liquid electrolyte and to the GPE exhibits similar conductivity behaviour and this suggests a passive role of PMMA. The shear thinning behaviour, pointing towards easy processablity, high thermal stability and low volatility, makes these CPEs potential candidates as solid-like electrolytes for electrochemical devices.     

Quasi solid state polymer electrolyte with binary iodide salts for photo-electrochemical solar cells

Quasi-solid-state polymer electrolytes can be used in dye sensitized solar cells (DSSCs) in order to overcome various problems associated with liquid electrolytes. Prior to fabricating commercially viable solar cells, the efficiency of quasi solid state DSSCs needs to be improved. Using electrolytes with a binary iodide mixture is a novel technique used to obtain such efficiency enhancement. In this work we report both conductivity and solar cell performance enhancements due to incorporation of a mixture containing LiI and tetrahexylammonium iodide in a quasi-solid-state electrolyte. The conductivity of the electrolyte increases with added amounts of LiI and thus the highest conductivity, 3.15 × 10⁻³ S cm⁻¹ at 25 °C, is obtained for the electrolyte 100 wt% LiI. The predominantly ionic behavior of the electrolytes was established from dc polarization measurements. The iodide ion conductivity, measured using iodine pellet electrodes decreased somewhat with increasing amount of LiI even though the overall conductivity increased. However, the highest efficiency was obtained for the DSSC containing a polymer electrolyte with Hex₄N⁺I^¯:LiI = 1:2 mass ratio. This cell had the largest short circuit current density of about 13 mA cm⁻² and more than 4% overall energy conversion efficiency. The results thus show that electrolytes with Hex₄N⁺I^¯/LiI mixed iodide system show better DSSC performance than single iodide systems.     

A comparative study of gel polymer electrolytes based on PVDF-HFP and liquid electrolytes, containing imidazolinium ionic liquids of different carbon chain lengths in DSSCs

The photoelectrochemical characteristics of titanium dioxide (TiO₂)-based dye-sensitized solar cells (DSSCs) containing gel polymer electrolyte (GPE) and organic liquid electrolyte (OLE) were studied in detail. GPE was prepared by adding poly(vinyidene fluoride-co-hexafluoro propylene) (PVDF-HFP) to imidazolinium ionic liquids (IILs) of the type, 1-methyl-3-alkyl imidazolinium iodides (alkyl is C_nH_2n+1, where n=3–10) in methoxy propionitrile (MPN) and the OLE contained the above molten salt in MPN. The IILs were synthesized in the laboratory and characterized by ¹H nuclear magnetic resonance spectroscopy (NMR). The conductivities (σ) of both GPE and OLE decrease with increase in chain length (n) of the alkyl group of IILs; however, the effect is more drastic in the former case. The performance of the DSSCs containing OLE increases with the increase in alkyl chain length of IIL from C3 to C7, whereas, there is a linear decrease in the efficiency of the DSSCs incorporated with GPE containing IIL of alkyl chain length from C3 to C10. The change in short circuit current density (J_SC) determines the cell efficiency as the V_OC of the DSSCs remains almost the same with increase of alkyl chain length of IILs for both the electrolytes. The change in J_SC values and the consistency of the V_OC of the DSSCs for both the electrolytes may be explained on the basis of increase in viscosity of IILs from C3 to C10 and the dominating role of the 4-tertiary butyl pyridine (TBP), respectively, on the phenomenon of charge recombination.     

Polymer electrolytes containing guanidinium-based polymeric ionic liquids for rechargeable lithium batteries

The electrochemical properties of solvent-free, quaternary polymer electrolytes based on a novel polymeric ionic liquid (PIL) as polymer host and incorporating 1g13TFSI ionic liquid, LiTFSI salt and nano-scale silica are reported. The PIL-LiTFSI-1g13TFSI-SiO₂ electrolyte membranes are found to be chemically stable even at 80 °C in contact with lithium anode and thermally stable up to 320 °C. Particularly, the quaternary polymer electrolytes exhibit high lithium ion conductivity at high temperature, wide electrochemical stability window, time-stable interfacial resistance values and good lithium stripping/plating performance. Batteries assembled with the quaternary polymer electrolyte at 80 °C are capable to deliver 140 mAh g⁻¹ at 0.1C rates with very good capacity retention.     

A binary ionic liquid system composed of N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide and lithium bis(trifluoromethanesulfonyl)imide: A new promising electrolyte for lithium batteries

Room temperature ionic liquids are nowadays the most appealing research target in the field of liquid electrolytes for lithium batteries, due to their high thermal stability, ionic conductivity and wide electrochemical windows. The cation structure of such solvents strictly influences their physical and chemical properties, in particular the viscosity and conductivity.In this paper we report on the preparation and characterization of a complete series of solutions between lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and the promising N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide (PY_1,2O1) ionic liquid. A wide molality range has been explored in order to identify the optimal compositions in terms of conductivity and electrochemical stability. Our thermal results show that the solutions are amorphous independently on the LiTFSI content. Up to salt concentration of 0.4 mol kg⁻¹ the solutions have a very low viscosity (η ∼ 36 cP), a high ionic conductivity, even at temperatures below 0 °C, and a good electrochemical stability. Cations transport numbers ranging between 0.05 and 0.39 have been determined as a function of LiTFSI content. The combination of these properties makes the PY_1,2O1-based solutions potentially attractive liquid electrolytes for lithium batteries.     

Nano-sponge ionic liquid-polymer composite electrolytes for solid-state lithium power sources

Solid polymer gel electrolytes composed of 75 wt.% of the ionic liquid, 1-n-butyl-2,3-dimethylimidazolium bis-trifluoromethanesulfonylimide with 1.0 M lithium bis-trifluoromethanesulfonylimide and 25 wt.% poly(vinylidenedifluoro-hexafluoropropene) are characterized as the electrolyte/separator in solid-state lithium batteries. The ionic conductivity of these gels ranges from 1.5 to 2.0 mS cm⁻¹, which is several orders of magnitude more conductive than any of the more commonly used solid polymers, and comparable to the best solid gel electrolytes currently used in industry. TGA indicates that these polymer gel electrolytes are thermally stable to over 280 °C, and do not begin to thermally decompose until over 300 °C; exhibiting a significant advancement in the safety of lithium batteries. Atomic force microscopy images of these solid thin films indicate that these polymer gel electrolytes have the structure of nano-sponges, with a sub-micron pore size. For these thin film batteries, 150 charge-discharge cycles are run for Li_xCoO₂ where x is cycled between 0.95 down to 0.55. Minimal internal resistance effects are observed over the charging cycles, indicating the high ionic conductivity of the ionic liquid solid polymer gel electrolyte. The overall cell efficiency is approximately 98%, and no significant loss in battery efficiency is observed over the 150 cycles.     

Functionalized imidazolium ionic liquids as electrolyte components of lithium batteries

Some basic properties and compatibility toward lithium electrode for electrolytes based on substituted imidazolium ionic liquid have been investigated. The ionic liquids having imidazolium cation substituted by methylcarboxyl or cyano group suffers from low conductivity. However, reversible lithium deposition–dissolution process was observed in electrolytes based on these electrolytes. In particular, lithium salt solution in cyanomethyl-substituted imidazolium ionic liquid provided similar cycle efficiency to conventional organic solvent electrolyte at constant-current condition. The mixed ionic liquid electrolyte containing the cyanomethyl-substituted ionic liquid also provided good cycle performance despite of containing large amount of 1-ethyl-3-methyl imidazolium (EMI)-based ionic liquid. Such mixed electrolyte system serves both the stability of lithium electrode process and valid conductivity for practical use.     

Ionic conductivity and electrochemical properties of cross-linked solid polymer electrolyte using star-shaped siloxane acrylate

A star-shaped siloxane acrylate with a different number of repeating units of oligo(ethylene oxide) (EO) was synthesized as a cross-linker of solid polymer electrolytes. The cross-linked solid polymer electrolytes blended with the ionic conducting plasticizers, such as low molecular weight poly(ethylene oxide)dimethyl ether (PEGDME) were prepared by the in situ thermal curing of the star-shaped siloxane acrylate. Different morphologies of the cross-linked polymer electrolytes were observed according to the number of repeating units of EO (n) in the cross-linker. A micro-phase separated solid polymer electrolyte was obtained when the n of cross-linker was 1. When the n of cross-linker was larger than 1, homogeneously blended solid polymer electrolytes were prepared. The ionic conductivity was measured to be 6.3 to 7.8 × 10⁻⁴ S cm⁻¹ with 80 wt.% PEGDME at 30 °C. The ionic conductivity of the micro-phase separated solid polymer electrolyte was slightly higher than that of the homogeneously blended solid polymer electrolyte. The electrochemical stability window of the resulting solid polymer electrolyte could be extended to up to 4.8 V versus Li/Li⁺ reference electrode.     

Review of recent progress in solid-state dye-sensitized solar cells

The dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs) provide a promising alternative concept to conventional p–n junction photovoltaic devices. However, liquid-state DSSCs possess the problem of low stability since a volatile liquid electrolyte is utilized. An effective approach to solve such a problem is by replacing the volatile liquid electrolyte with solid-state or quasi solid-state hole conductor, such as p-type semiconductors, ionic liquid electrolyte and polymer electrolyte. In this paper, the recent progress on the selection and utilization of these hole conductors are mainly discussed. Research on mechanisms of solid-state DSSCs was also summarized here including the hole transfer process at dye/hole conductor interface, ionic transportation inside hole conductor media and the factors which depress the efficiency of solid-state cells. With a thorough analysis of the problems of solid-state DSSCs, several ways towards higher efficiency and lower cost are suggested.