Electrolytes for electrochromic devices

Electrolytes typically used in ECDs, as in any other electrochemical cell, belong to four main classes aqueous electrolytes, organic liquid electrolytes, ionic liquids and solid polymer electrolytes. The adoption of so-called ionic liquids, such as ethyl ammonium nitrate ([EtNH3][N03]), l-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) or hexafluorophos-phate ([BMIMjfPFg]), can result in improved lifetime and response speed for electrochromics and actuators, and are best proposed being mixed with polymer or gel matrices.  

Most of the solid polymer electrolytes used can be classified as follows (1) polymer or gel matrixes swollen with liquid electrolyte solutions (e.g. ethylene carbonate (EC)/PAN/sodium perchlorate (NaC104)) (2) singleion systems in which only one ionic species is mobile within a polymer matrix (e.g. perfiuorosulphonate ionomer Nafion ) (3) solvent-free ion-coupled systems consisting of ion-solvating polymers mixed with salts, so that cations and ions become mobile within the polymer network, e.g. PEO mixed with salts. 

The polymer matrix is the main component and the framework for polymer electrolytes. The matrix plays the role of excipient and sustains the shape as a layer of film or membrane for the polymer electrolytes. 

1 Structure types of ionic passageway in a polymer matrix 

A proper polymer matrix must possess following properties  

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Electrolytes for Electrochromic Devices Liquids are generally used as electrolytes in electrochemical research, but they are not well suited for practical devices (such as electrochromic displays, fuel cells, etc.) because of problems with evaporation and leakage. For this reason, solid electrolytes with single-ion conductivity are commonly used (e.g., Nafion membranes with proton conductivity. In contrast to fuel cells in electrochromic devices, current densities are much lower, so for the latter application, a high conductivity value is not a necessary requirement for the electrolyte. 

Nguyen, C.A., Argun, A.A., Hammond, P.T., Lu, X., Lee, P.S., 2011. Layer-by-layer assembled solid polymer electrolyte for electrochromic devices. Chem. Mater. 23,2142-2149. 

Vondrak, J., M. Sedlafikova, J. Reiter, and T. Hodal. 1999. Rolymer gel electrolytes for electrochromic devices. Electrochim Acta 44 3067-3073. 

Thakur VK, Ding G, Ma J, Lee PS, Lu X. Hybrid materials and polymer electrolytes for electrochromic device applications. Adv Mater 2012 24 4071-4096. 

Abstract The chapter begins by discussing the characters and composition of polymer electrolytes for electrochromic devices. It then describes the four types of the polymer electrolytes dry solid polymer electrolyte, gel polymer electrolyte, porous gel polymer electrolyte and composite solid polymer electrolyte, their preparation procedures and properties especially ion conductivity of the samples. Finally, new types of polymer electrolytes including proton-conducting, alkaline, single ionic polymer electrolytes and electrolytes with ionic liquids are also introduced. 

Polymer electrolytes for electrochromic devices 491 Table 12.1 Different composition of geis... 

GONG, Y., FU, X., ZHANG, s., JIANG, Q., Preparation of star network peg-based gel polymer electrolytes for electrochromic devices, Chinese J. Polym. ScL, 2008, 26(1), 91-7. 

STEVENS, J.R., RADUCHA, D., WIECZOREK, w., JEFFREY, K.R.., Nonaqueous polymet electrolytes for electrochromic devices, l.M. Khan, J.S. Harrison (Eds.), Field Responsive Polymers, ACS Symposium Series, Oxford Univ. Press, Washington, 1999. 

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