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EP-4104010-B1 - A FUNCTIONAL AND TRANSPARENT GEL ELECTROLYTE SYSTEM AND FAST SWITCHING ELECTROCHROMIC/ELECTROCHEMICAL DEVICES THEREOF

EP4104010B1EP 4104010 B1EP4104010 B1EP 4104010B1EP-4104010-B1

Inventors

  • DEB, BISWAPRIYA
  • AYYAPPANPILLAI, Ajayaghosh
  • VENUGOPAL, Ranjana
  • PRABHU THULICHAL GANESH PRABHU, Gayathri
  • SHANKAR POOPPANAL, SREEJITH

Dates

Publication Date
20260506
Application Date
20210215

Claims (10)

  1. A transparent gel electrolyte comprising: i. a polymeric gelling agent; ii. a solvent; iii. an additive and; iv. an ionic conductor; wherein the weight composition of solvent, polymeric gelling agent, additive and ionic conductor is in the range 20:2:1:2 to 2000:200:1:20; the solvent is selected from the group consisting of water, a mixture of water and alcohol (R-OH), and water and DMSO; wherein R is independently selected from the group consisting of C 1-12 alkyl, C 1-12 aryl, C 1-12 alkenyl or C 1-12 allyl; the molecular weight of the polymeric gelling agent is in the range of 89,000 - 98,000; the ionic conductor is selected from a salt of lithium or ammonium cations; and the additive is molecular iodine.
  2. The transparent gel electrolyte as claimed in claim 1, wherein the amount of alcohol or DMSO does not exceed 25% of the amount of water.
  3. The transparent gel electrolyte as claimed in claim 1, wherein polymeric gelling agent used is poly-vinyl alcohol (PVA).
  4. The transparent gel electrolyte as claimed in claim 1, wherein the anion of the ionic conductor is selected independently from the group consisting of halides (F - , Cl - , Br - , I - ), sulphonamides [N(CF 3 SO 2 ) 2 ], perchlorates (ClO 4 - ), alkoxides (OR), carboxylates (RCOO - ), hexafluorophosphate (PF 6 - ), and CF 3 (CF 2 ) n SO 3 - (triflates), wherein R is independently selected from the group consisting of C 1-12 alkyl, C 1-12 aryl, C 1-12 alkenyl or C 1-12 allyl.
  5. A process for the synthesis of the transparent gel electrolyte of any one of claims 1-4 comprising the steps of: i. mixing solvent, a polymeric gelling agent, an additive and an ionic conductor at 2000:200:1:20 weight composition followed by heating at temperature in the range of 60 to 90°C for a period in the range of 5 to 24 hrs to obtain a mixture; ii. cooling the mixture as obtained in step (i) followed by drying by freeze thawing (thrice for 1 h each), storing at room temperature in the range of 25 to 30°C.
  6. A sandwich cell device comprising: i. two conducting oxide coated electrode having electrically conductive surfaces; ii. an electrochromic active layer comprising of a redox active material having a predefined color, reversibly changeable upon subjecting to an electric field and; iii. a transparent gel electrolyte as claimed in claim 1 sandwiched between the said substrates separated by an insulating tape as a spacer; wherein (a) the active layer is electrophoretically deposited oxides of first row transition metals with a general formula MO x , where M is tungsten, vanadium or nickel and x > 0, the said active layer having a thickness of 100 nm - 1200 nm; (b) the active layer is spray or dip or spin coated oxides of first row transition metals with a general formula MO x , where M is tungsten, vanadium or nickel and x > 0, the said active layer having a thickness of 500 nm - 1200 nm; or (c) the active layer is spray or dip or spin coated metal-bipyridine, or metal-terpyridine complexes, with a general formula [M(py) n ] m+ mX - or [M(py) n ] m+ mX - and their coordination polymers, where py denotes a coordinating ligand as in bipyridine or terpyridine; wherein M is independently selected from the group consisting of Fe, Os, Ru, Ni, Co, Cu; n and m are integers, each independently selected from 0-3, essentially n, m > 0; X is an anion, independently selected from the group consisting of halides (F - , Cl, Br - , I - ), sulphonamides [N(CF 3 SO 2 ) 2 ], perchlorates (ClO 4 - ), alkoxides (OR), carboxylates (RCOO - ), hexafluorophosphate (PF 6 - ), and CF 3 (CF 2 ) n SO 3 - (triflates); and the said active layer having a thickness of 60 nm - 1000 nm.
  7. The device as claimed in claim 6, wherein the substrate used is selected from the group consisting of doped/undoped glass, TCO (transparent conducting oxide) coated glass, silicon, quartz, metal, metal oxide, polymer, mica, clay, zeolite, membrane, plastic, ceramic, alumina, steel or any conducting substrate, in the form of sheets, beads, columns or plates, with a minimum degree of optical transparency towards UV-vis-NIR spectral lights.
  8. The device as claimed in claim 6, comprising a monolayer of the same or different redox active materials or plurality of layers with the same or different active materials, wherein the said active materials are independently chosen from the oxides of tungsten, vanadium or nickel, or metal-bipyridine, or metal-terpyridine complexes or their coordination polymers sandwiched between the conductive substrates along with the gel electrolyte of claims 1-5.
  9. The device as claimed in claim 6, wherein said device exhibits coloration efficiency in the range of 200-2000 cm 2 /C and a switching speed of 1-3 s.
  10. The device as claimed in claim 6, wherein said device is useful in smart windows, smart mirrors, e-papers, smart displays, helmet visors, smart ophthalmic glasses, optical data storage devices, glare reduction set-ups, heat and light transmission modulators, integrated charge storage devices.

Description

FIELD OF THE INVENTION The present invention relates to a transparent gel electrolyte system useful as a thin film/gel in electrochemical or electrochromic cells and devices. Particularly, the present invention relates to the sandwich cell devices fabricated using these gel electrolytes. The disclosed electrolyte and the device are mechanically and thermally stable, offering sufficiently long periods of stable operation. BACKGROUND AND PRIOR ART OF THE INVENTION Smart material R&D is largely driven by the increasing demand for smart technology applications such as smart switchable windows and related optoelectronic devices. Electrochromic materials are a family of 'smart materials' that can change their optical properties under the application of an electric voltage. The tunable optical properties of electrochromic materials directly reflect in the light and heat transmission properties of the surface, leading to efficient indoor lighting and cooling, aesthetics as well as glare reduction. For instance, the dynamic modulation of heat and light transmission through these smart windows could be directly correlated to the energy consumption in maintaining the indoor temperature and visibility; thus a magnanimous portion of domestic energy consumption could be reduced. Electrolytes, a common component in all electrochemical processes, is a key component in electrochromic devices. The functions of an electrolyte in an electrochromic device includes charge balance or electroneutrality, conductivity and ionic mobility. In an electrolyte, charge transport occurs via the motion of positive and negative ions and its conductivity has a contribution from every ion present. The use an electrolyte in ECDs demands high ionic conductivity, electronic insulation, transparency in the wavelength range, wide electrochemical window of operation and low volatility. Thus, electrolytes are used as the ionic conductor between the two electrodes and separate the cathode and anode thereby avoiding direct electrical contact and permitting mutual ionic exchanges. Several classes of electrolytes have been reported. Typically, aqueous electrolytes, organic liquid electrolytes, ionic liquids, gel electrolytes and solid polymer electrolytes are commonly used in ECDs. Though purely liquid electrolytes provide better ionic conductivity and faster switching, they suffer from low viscosity, leakage and stability and hence gel or solid electrolytes are preferred in ECDs. These are of three major types: (i) polymers mixed with ion conductors in solvent-free states (Eg: PEO/ionic salts), (ii) polymer/gel matrices swollen with aqueous/organic electrolyte solutions (PMMA/PC/ACN/LiClO4) and (iii) ionic species mobile within a polymer matrix (Nafion). PEO or PEO modified polymers are one of the most commonly used class of matrices for solid/gel electrolytes in ECDs (Reference may be made to: (a) Quartarone, E.; et al. Solid State Ionics, 1998, 110, 1-14; (b) Kim, Y. T.; et al. Solid State Ionics, 2002, 149, 29-37; (c) Plancha, M. L.; et al. J. Electroanal. Chem., 1998, 442, 91-7; (d) Serraino, F. F.; et al. J. Eur. Ceram. Soc., 2004, 24, 1385-1387; (e) Guinot, S.; et al. Electrochim. Acta, 1998, 43, 1163-1170; (f) Rhodes, C. P.; et al. Solid State Ionics, 1999, 121, 91-99. Polyether, polyester, nitrogen/sulphur containing polymers, olefin halide polymers, siloxane derived polymers, etc. have been used to dissolve especially Li+ salts without effective crystallization (Reference may be made to: (a) Gong, Y.; et al. Chinese J. Chem. 2007, 25, 1743-1747; (b) Gong, Y.; et al. Chinese J. Polym. Sci., 2008, 26, 91-97; (c) Zhang, S.; et al. J. Functional Mater., 2006, 37, 442-445; (d) Zhang, S.; et al. J. Appl. Polym. Sci., 2007, 106, 4091-4097; (e) Bohnke, O.; et al. J. Electrochem. Soc., 1992, 139, 1862-1865; Agnihotry, S. A.; et al. Electrochim. Acta, 1999, 44, 3121-3126; (f) Yang, D.; et al. Chinese J. Polymer Sci., 2008, 26, 375-380; (g) Erickson, M.; et al. Electrochim. Acta, 2003, 48, 2059-2063; (h) Ramesh, S.; et al. Solid State Ionics, 2002, 148, 483; (i) Magistris, A.; et al. Solid State Ionics, 2002, 152, 347-354; (j) Liang, W. J.; et al.; Polymer, 2004, 45, 1617-1626; (k) Kraft, A.; et al. Solar Energy Mater. Solar Cells, 2006, 90, 469-476; (l) Kobayashi, N.; et al. Electrochim. Acta, 2003, 48, 2323-7). Salts of lithium or ammonium cations have been used as ionic conductors in most of these polymer based electrolytes. The polymer does not contribute to the ionic conductance, however the gel electrolyte, due to the presence of ionic conductors that are freely mobile in the polymer matrix, are generally as conductive as the liquid electrolytes. Several patents have educated the development of electrolytes for use in ECDs. International publication WO 2009130316 (Georen, et al.) presented a three-component gel electrolyte system for laminated electrochromic devices. The described electrolyte consisted of an amide based solvent, an ionisable lithium