Читать книгу Organic Electronics for Electrochromic Materials and Devices - Hong Meng - Страница 33

The field of PE is steadily broadening, as more and more various application are presented. Although lithium‐ion‐based electrolytes have been commercialized, such as applied in pull down window shades on Boeing 787 Dreamliner, smart glass in Ferrari 575 M Superamerica, and Flexity 2 light rail vehicles, some disadvantages such as poor safety, easy leakage, and unstable electrochemical performance limit its further development and wider applications. In this chapter, we have provided fundamental understanding of requirements for EC applications. In the meantime, recent progresses on polymer‐based electrolytes were summarized, including PEO/PVDF/PMMA gel polymer, self‐healing polymer, cross‐linking polymer, ceramic polymer, IL polymer, and gelatin PEs. The use of composite PEs has been identified as a promising method to improve the performance of electrolytes.

Table 2.1 Polymer hosts generally studied with the examples of gel polymer electrolyte complexes and their respective highest ionic conductivities.

Polymer electrolyte	EC materials	Ionic conductivity (S/cm)	Electrochemical stability window (V)	Optical modulation (%)	Stability	References
p(trimethylenecarbonate [TMC])/PEO	Prussian Blue/PEDOT	1.33 × 10−6	−1.5 ∼ 1	8 ∼ 30	Full color switch (>600 s)	[138]
PEO/PVDF	TiO2	6.98 × 10−6	—	90	—	[15]
PEO/LiClO4	PEDOT:PSS	4.2 × 10−4	−3.0 ∼ 3.0	22	No significant change	[139]
P(VDF‐TrFE)/PEO	PEDOT:PSS	6.79 × 10−4	−1.0 ∼ 0.5	60	—	[140]
PEMA/poly (vinylidene fluoride) (PVdF)‐HFP	WO3//CeO2–TiO2	1.46 × 10−6	−1.3 ∼ −0.8	81	—	[141]
PVdF‐HFP/silane‐functionalized ZrO2	PANI:DBSA	1.78 × 10−3	−4.0 ∼ 4.0	70	—	[142]
PVDF‐HFP/POEI‐ISF4	Nanofibers	8.62 × 10−3	0 ∼ 1.2	68.7	95.5% of ΔT	[143]
PVDF‐co‐HFP/[EMI][TFSI]	1,1′‐bis(3‐fluoro‐4‐(trifluoromethyl)phenyl)‐4,4′‐bipyridinium bis(trifluoromethylsulfonyl)imide (TFMFPhV(TFSI)2)	6.7 × 10−3	−0.35 ∼ 0	∼73	∼14% decrease of ΔT after 24 h	[144]
IL/PVDF‐HFP	PEDOT:PSS	1.13 × 10−3	−1.4 ∼ 1.4	∼24	—	[54]
TMPD/HV(BF4)2/SN/PVDF‐HFP	TMPD/HV(BF4)2/succinonitrile	1 × 10−3	0 ∼ 0.9	60.1	74.7% of the original ΔT after 2000 cycles	[145]
[Emim]BF4/PMMA	WO3	2.9 × 10−3(RT)	−3.0 ∼ 1.5	88	—	[146]
Poly(ether ether ketone) membrane	IR‐VEDs	6.8 × 10−3	−1.0 ∼ 1.0	47	Good cycling stability	[147]
PVDF‐HFP:PMMA/LiClO4	—	2.83 × 10−4	—	—	—	[148]
PMMA/SN‐PC	WO3//brain natriuretic peptide (PBNPs)	1.46 × 10−3	−2.5 ∼ 2.0	52.4	44.5% after 2250 cycles	[149]
Poly(ε‐caprolactone) (PCL)/SiO2	PEDOT: PSS	5.2 × 10−3	−4.0 ∼ 1.0	30.6	Good stability (100 cycles)	[150]
Polyvinyl butyral (PVB)‐based GPEFs	WO3//Ni1−xO	4.0 × 10−5	−2.0 ∼ 2.0	65.8	Fading of 4.8% (16 h)	[151]
PAN–DMF–LiTFSI	WO3//CeO2–TiO2	2.54 × 10−4	−2.0 ∼ 1.0	29.1	—	[152]
PADA	LiNiO//WO3	1.33 × 10−2 (RT)	−2.30 ∼ 2.30	61	58.4% after 50 cycles	[153]
PVDF based	P(PVK‐co‐EDOT)	—	−0.9 ∼ 0.5	39.1	—	[154]
2‐APPG /PMDA/ICS	WO3 film	1.01 × 10−3	−3.5 ∼ 2.5	38.2	450 cycles	[155]

Table 2.2 Examples of self‐healingand cross‐linking polymer electrolyte complexes and their respective highest ionic conductivities.

Electrolyte	Ionic conductivity (S/cm)	Electrochemical window (V)	Application	References
B‐PVA/KCl/graphene oxide (GO)	47.5 × 10−3	0 ∼ 1.0	Flexible energy‐storage device	[156]
SiO2–UPy	8.0 × 10−5	0 ∼ 6.0	Lithium‐ion batteries	[157]
P(AA‐VIm‐VSN)	1.26 × 10−4	−1.2 ∼ 0.3	Flexible electrochromic devices	[158]
[P(PO/EM)]/lithium trifluoro(perfluoro‐tert‐butyloxyl)borate (LiTFPFB)	1.55 × 10−4 (70 °C)	3 ∼ 4.2	Lithium metal batteries	[159]
Zn–metal‐organic gel (MOG)	—	0 ∼ 2.1	Flexible supercapacitor	[160]
Poly(ethylene‐co‐acrylic lithium (fluoro sulfonyl)imide) (PEALiFSI)	5.84 × 10−4	2.5 ∼ 4.0	Solid‐state Li‐ion batteries	[161]
Li + ‐PEO	—	−4 ∼ 4	Micro‐supercapacitors	[162]

Although extensive researches have been devoted to the polymer‐based electrolytes, some basic issues still need to be addressed before commercialization. Above all, ionic conductivity is still on lower orders of magnitude than lithium‐based liquid electrolytes. Temperature is one of the most dominant parameters for determining the ionic conductivity. In particular, ionic conductivities in polymer‐based solid electrolytes drop dramatically at lower temperatures. Moreover, the mechanism of interfacial interaction between electrolyte and an EC layer is still unknown.

For now, the GPEs, typically based on PEO/PVDF/PMMA, have also been extensively explored, but they exhibit too low ionic conductivity at room temperature (≈10⁻⁵ S/cm) and poor resistance to oxidation at relatively high voltage. Poor mechanical performance limits the IL electrolyte from increasing the ionic conductivity. Safety issues cannot be neglected. Developing a self‐healing electrolyte that simultaneously exhibits excellent EC properties and good self‐healing behavior at low temperature is still an unmet challenge. The cross‐linked composite PE could effectively encapsulate the electrolyte solution without solvent leakage and exhibit favorable interfacial characteristics. However, low ionic conductivity at room temperature still need to be improved. The difficulty of ceramic PEs is how to construct good dispersion and enhance the interaction between filler and polymer, which restricts the further improvement of ionic conductivity. Gelatin‐based PEs have proved to be one of the alternative binders, but its rheological behavior in the tested conditions inhibited such material to be used at industry level.

To overcome these challenges, several future research directions are suggested as follows.

1 Improving electrolyte's electrochemical stable potential window (ESPW) value. The ESPWs are dependent on the cation and anion of the conducting salt and the solvent. It should be noted that in most cases, an increase in electrolyte ESPWs may result in the deterioration of other properties such as ionic conductivity and viscosity of electrolytes. The improvement of ESPWs could be achieved by exploring new organic solvents and new conducting salt or by optimizing/modifying the commonly used organic electrolytes. However, it is difficult to achieve all the requirements, such as high ESPW, high ionic conductivity, high physicochemical stability, low viscosity, and eco‐friendliness. Some tradeoffs may be reasonable in solving the practical problems.

2 Increasing the working temperature range for ES operation. Some additives like ethylene glycol may be explored to decrease the power temperature limit in aqueous electrolytes. Regarding organic electrolytes, the development of new organic solvent mixtures could possibly obtain electrolytes with a wider operating temperature range.

3 Optimizing the interaction effects between the electrolyte and electrode materials to improve the EC performance. In situ characterization methods such as fourier transform IR (FTIR) and Raman microscopy can be used to characterize the electrolytes in operating condition. The interface between an EC layer and electrolyte can be observed under conventional transmission electron microscopy (TEM) [136, 137].

4 Combining theoretical and experimental investigations to analyze, guide, and design electrolyte. The corresponding ionic mechanism can be simulated and interpreted by material calculations. It is necessary to fundamentally understand the mechanisms of electrolyte ion dynamics by using both theoretical modeling and experimental approaches.

5 Development of standard methods to evaluate the performance of electrolytes. It is necessary and important to develop proper and standardized methods to evaluate the performance of different electrolytes and their associated ECs.

Table 2.3 Comparison of the Li⁺ conductivities of some reported solid polymer electrolytes.

Solid polymer electrolytes	Type of electrolytes	Anionic center	Ionic conductivity (S/cm) at RT	References
P(MEO‐MALi)	Random copolymer	−CO2−	1.5 × 10−7	[163]
PAE8‐co‐E3SO3Li	Random copolymer	−SO3−	2.0 × 10−7	[164]
Random copolymer	−(C2O4)2B−	1.9 × 10−7	[165]
POE	Random copolymer	‐CF(CF3) SO3−	1 × 10−7	[166]
P(LiSMOEn)s	Random copolymer	−C6H5·SO3−	1.5 × 10−7	[167]
Polyphosphazenes	Random copolymer	‐SO2N−SO2CF3	3.0 × 10−6	[168]
Li[poly(styrenesulfonyl(trifluoromethylsulfonyl)imide) (PSTFSI)‐co‐methoxy poly(ethylene glycol) acrylate (MPEGA)]	Random copolymer	–SO2N−SO2CF3	7.7 × 10−6	[169]
Poly(2‐oxo‐1‐difuluoroethylene sulfonylimide) (LiPI)‐polyether	Blended copolymer	–CO2CF2SO2N−	1 × 10−6	[170]
P(LiSMOEn)	Blended copolymer	–CO2−	1.5 × 10−7	[167]
Poly(5‐oxo‐3‐oxy‐4‐trifluoromethyl‐1,2,4‐pentafluoropentylene sulfonylimide lithium) (LiPPI)	Blended copolymer	−COCF(CF3)O(CF2)2SO2N−	1 × 10−5	[171]
Poly (estercarbonate) (PEC) based	Blended copolymer	–SO2N−SO2CF3	1 × 10−9	[172]
LiTFSI	Blended copolymer	–SO2(CF2)4SO2N−	1 × 10−6	[173]
LiPSFSI/PEO	Blended copolymer	–SO2N−SO2F	1 × 10−8	[174]
poly[(4‐styrenesulfonyl)(trifluoromethyl(S‐trifluoromethylsulfonylimino)sulfonyl)imide] (PSsTFSI−)/PEO	Blended copolymer	–SO2N−SO(NSO2CF3)CF3	1 × 10−8	[174]
PEO based	Block copolymer	–CO2−	1 × 10−7	[175]
poly (ethylene glycol) macromer (PEGM) based	Block copolymer	–SO2N−SO2CF3	2.3 × 10−6	[176]
Polystyrene‐PEO based	Block copolymer	–SO2N−SO2CF3	1.3 × 10−5	[177]
PEO‐PSLiTFSI	Block copolymer	–SO2N−SO2CF3	3.0 × 10−8	[170]
Methacrylic‐PEO	Block copolymer	–SO2N−SO2CF3	3.4 × 10−8	[177]
PEALiFSI	Block copolymer	–CON−SO2CF3	5.84 × 10−4	[178]
PEO‐PLSS	Graft copolymer	–SO3−	7.0 × 10−8	[179]
LiBOPEG600	Homopolymer	–OP−(C2O4)2	1.6 × 10−6	[180]

Table 2.4 Composition and performance of ionic liquid electrolytes.

Year	Electrolyte	Ionic conductivity (S/cm) at RT	References
2005	PVA–KOH	1.0 × 10−2	[181]
2005	PEGDA–PVdF–EC–DMC–ethylmethyl carbonate (EMC)–LiPF6	1.5 × 10−3	[182]
2010	[PPyr11TFSI]28%LiTFSI12%[Pyr14TFSI]60%	1.6 × 10−6	[183]
2010	PEO20LiTFSI1[Pyr1.2O1TFSI]1.5	7.0 × 10−5	[184]
2010	PEO25–LiTf–IL	3.0 × 10−4	[185]
2011	PEO20LiTFSI1[S2.2.2TFSI]1	5.0 × 10−4	[186]
2012	PEO20LiTFSI1[Pip13TFSI]1.27	2.1 × 10−4	[187]
2013	poly(methyl methacrylate–acrylonitrile–vinyl acetate) [P(MMA–AN–VAc)]‐N‐methyl‐N‐butyl pyrrolidinium bis(trifluoromethansulfonyl)imide	1.2 × 10−3	[188]
2013	PEO20LiTFSI2[Pyr14TFSI]6	5.0 × 10−4	[189]
2013	Chitosan–PEO–NH4NO3–EC	2.06 × 10−3	[190]
2014	Poly(ε‐caprolactone)–NH4SCN–EC	3.8 × 10−5	[191]
2014	LiTFSI in P14TFS LiTFSI/P14TFSI/PEO	0.4 × 10−3	[192]
2015	PEO20LiTFSI2[Pyr1.2O1TFSI]4	2.5 × 10−4	[193]
2017	PEO‐1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide	2.2 × 10−4	[194]
2017	PEO‐(EMimFSI)	1.3 × 10−3	[195]
2017	Oligoethylene glycol/N‐butyl imidazole	4.8 × 10−4	[196]
2018	PVDF–HFP(EMITFSI)	0.76 × 10−3	[197]
2018	PVDF–HFP–(SiO2PPTFSI)	0.64 × 10−3	[198]
2019	PIL:[PVEIm][TFSI]	5.92 × 10−4 (60 °C)	[199]
2019	PEO–TBPHP	2.51 × 10−3	[200]
2019	PEO–EMimFSI	3.6 × 10−4	[201]

Finally, struggling to find suitable composite electrolytes with high conductivities during wide range of temperature always deserves more study. Commercial electrolytes require high ionic conductivity at room temperature, safety, and easy processing.