Читать книгу Organic Electronics for Electrochromic Materials and Devices - Hong Meng - Страница 24

GPE also known as plasticized PE was first introduced by Feuillade and Perche in 1975 [13]. GPEs are usually synthesized by incorporating a larger quantity of liquid plasticizer and/or solvents into a polymer matrix to form a stable gel with the polymer host structure, having relatively higher ambient‐temperature ionic conductivity [14]. Generally, GPE consists of an ionically conducting medium polymer such as poly(ethylene oxide) (PEO) and a metal salt (lithium) swollen with a suitable solvent. GPE could exhibit fast ion diffusive nature and cohesive properties comparable to solids [15]. The first one is known for its high conductivity with the H⁺ donors originating from, e.g. sulfuric (H₂SO₄) or phosphoric (H₃PO₄) acid [16]. In the second group mobile Li⁺ species are provided by dissolution of lithium perchlorates (LiClO₄) [17], triflates (LiCF₃SO₃) [18], fluorophosphates (LiPF₆) [19], or fluoroborates (LiBF₄) [20] in protic solvents (propylene, acetonitrile [ACN], ethylene carbonates, etc.). As was reported, binary or ternary solvents, such as EC + PC and DMC + PC + EC, were also employed [21, 22]. These types of electrolytes are characterized by a higher ambient ionic conductivity but poor mechanical properties. Although most PGEs have high ionic conductivity of 10⁻³ S/cm at room temperature, poor mechanical properties and considerable viscosity inevitably result in internal short circuit and cell leakage. UV and heat irradiation are other potential factors for degradation of electrolytes. Plasticizers such as PC, EC, diethyl carbonate (DEC), and dimethyl carbonate (DMC) can be applied in developing the physical characteristics of the overall blend. Plasticizers improve the ionic conductivity by increasing the amorphous phase content, dissociating ion aggregates, increasing ionic mobility within the gel electrolytes, or lowering the glass transition temperature (T_g) of the system [23]. The balance between increasing ionic conductivity and decreasing mechanical strength needs to be maintained while plasticization occurs. Gel electrolytes have been used in many applications but most of recent published papers are about EC applications. In the GPE, the immobilized solvent in the polymer matrix has strong effects on the ionic conductivity. So far, PEO, poly methyl methacrylate (PMMA), poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), and poly acrylonitrile (PAN)‐based gel electrolytes have aroused researchers' interests [24, 25]. Recently, some of gel electrolytes have aroused researchers' interests, such as poly ethylene oxide (PEO), polyethylene glycol (PEG) [26], boronate esters [27], sodium polystyrene sulfonate [28], waterborne polyurethane, [29] polyester and PEO [30], polyvinyl alcohol (PVA), PAN, PMMA, poly(ethyl methacrylate) (PEMA) and poly(2‐ethoxyethyl methacrylate) (PEO EMA), [31] poly vinyl chloride (PVC), poly(vinyl sulfones) (PVS), and PVDF [32].