Effect of zwitterions on electrochemical properties of oligoether-based electrolytes

Solid polymer electrolytes show great potential in electrochemical devices. Poly(ethylene oxide) (PEO) has been studied as a matrix for solid polymer electrolytes because it has relatively high ionic conductivity. In order to investigate the effect of zwitterions on the electrochemical properties of poly(ethylene glycol) dimethyl ether (G5)/lithium bis(fluorosulfonyl) amide (LiFSA) electrolytes, a liquid zwitterion (ImZ2) was added to the G5-based electrolytes. In this study, G5, which is a small oligomer, was used as a model compound for PEO matrices. The thermal properties, ionic conductivity, and electrochemical stability of the electrolytes with ImZ2 were evaluated. The thermal stabilities of all the G5-based electrolytes with ImZ2 were above 150 °C, and the ionic conductivity values were in the range of 0.8–3.0 mS cm−1 at room temperature. When the electrolytes contained less than 5.5 wt% ImZ2, the ionic conductivity values were almost the same as that of the electrolyte without ImZ2. The electrochemical properties were improved with the incorporation of ImZ2. The anodic limit of the electrolyte with 5.5 wt% ImZ2 was 5.3 V vs. Li/Li+, which was over 1 V higher than that of G5/LiFSA

Effect of β-Cyclodextrin on Physicochemical Properties of an Ionic Liquid Electrolyte Composed of N-Methyl-N-Propylpyrrolidinium bis(trifluoromethylsulfonyl)amide

Ionic liquids (ILs) are promising electrolyte materials for developing next-generation rechargeable batteries. In order to improve their properties, several kinds of additives have been investigated. In this study, β-cyclodextrin (β-CD) was chosen as a new additive in IL electrolytes because it can form an inclusion complex with bis(trifluoromethylsulfonyl)amide (TFSA) anions. We prepared the composites by mixing N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)amide/LiTFSA and a given amount of triacetyl-β-cyclodextrin (Acβ-CD). The thermal behaviors and electrochemical properties of the composites were analyzed by several techniques. In addition, pulse field gradient NMR measurements were conducted to determine the self-diffusion coefficients of the component ions. The addition of Acβ-CD to the IL electrolytes results in the decrease in the conductivity value and the increase in the viscosity value. In contrast, the addition of Acβ-CD to the IL electrolytes induced an improvement in the anodic stability because of the formation of an inclusion complex between the Acβ-CD and TFSA anions. CDs are potential candidates as additives in IL electrolytes for electrochemical applications

Water-Processed Organic Solar Cells with Open-Circuit Voltages Exceeding 1.3V

Conjugated polyelectrolytes are commonly employed as interlayers to modify organic solar cell (OSC) electrode work functions but their use as an electron donor in water-processed OSC active layers has barely been investigated. Here, we demonstrate that poly[3-(6’-N,N,N-trimethyl ammonium)-hexylthiophene] bromide (P3HTN) can be employed as an electron donor combined with a water-soluble fullerene (PEG-C60) into eco-friendly active layers deposited from aqueous solutions. Spin-coating a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer prior to the P3HTN:PEG-C60 active layer deposition considerably increases the open-circuit voltage (Voc) of the OSCs to values above 1.3 V. Along with this enhanced Voc, the OSCs fabricated with the PEDOT:PSS interlayers exhibit 10-fold and 5-fold increases in short-circuit current density (Jsc) with respect to those employing bare indium tin oxide (ITO) and molybdenum trioxide coated ITO anodes, respectively. These findings suggest that the enhanced Jsc and Voc in the water-processed OSCs using the PEDOT:PSS interlayer cannot be solely ascribed to a better hole collection but rather to ion exchanges taking place between PEDOT:PSS and P3HTN. We investigate the optoelectronic properties of the newly formed polyelectrolytes using absorption and photoelectron spectroscopy combined with hole transport measurements to elucidate the enhanced photovoltaic parameters obtained in the OSCs prepared with PEDOT:PSS and P3HTN

Oligoether/Zwitterion Diblock Copolymers: Synthesis and Application as Cathode-Coating Material for Li Batteries

Poly (ethylene oxide) (PEO) has been investigated as an ion-conductive matrix for several decades due to its excellent properties. However, further improvements are needed to enable a PEO-based ion-conductive matrix for practical applications. In order to develop novel solid polymer electrolytes based on zwitterions, we synthesized diblock copolymers (PPEGMA-b-SPBs) with oligoether and zwitterionic side-chains and evaluated their physico-chemical properties. PPEGMA-b-SPBs with various unit ratios were synthesized by RAFT polymerization. PPEGMA-b-SPBs with/without LiTFSA exhibited two distinct glass transition temperatures regardless of the unit ratio of PEGMA and SPB. AFM observations clearly revealed phase-separated structures. The ionic conductivity of PPEGMA-b-SPBs increased even at a high salt concentrations such as [EO]:[Li] = 6:1 and was over 10−5 S cm−1 at 25 °C. This tendency is unusual in a PEO matrix. The oxidation stability of PPEGMA-b-SPBs was about 5.0 V vs. Li/Li+, which is a higher value than that of PEO. The improvement of the electrochemical properties is attributed to the introduction of the SPB block into the block copolymers. PPEGMA-b-SPBs were evaluated as cathode-coating materials for Li batteries. The discharge capacity and coulombic efficiency of the cells employing the cathode (LiNi1/3Mn1/3Co1/3O2 (NMC)) coated with the block copolymers were much higher than those of the cell employing the pristine cathode at the 50th cycle in the cut-off voltage range of 3.0–4.6 V

Synthesis of Optically Active Regioregular Polythiophenes and Their Self-Organization at the Air–Water Interface

Regioregular polythiophenes containing an optically active substituent in the third position of the thiophene ring, <i>head-to-tail</i> poly­(3-[2-((<i>S</i>)-1-methyloctyloxy)­ethyl]­thiophene)­s (<i>HT</i>-P­(<i>S</i>)­MOETs), were synthesized using highly reactive zinc. For comparison, <i>HT</i>-P­(<i>R</i>)­MOET and achiral <i>HT</i>-P­(±)­MOET also were synthesized from <i>R</i>-type monomers and racemic monomers, respectively. The <i>HT</i>-PMOET possessed greater than 95% <i>head-to-tail</i> coupling with a weight-average molecular weight (<i><i>M</i></i>_w) between 1.96 × 10⁴ and 2.94 × 10⁴. The polymers were characterized using ¹H and ¹³C NMR, optical rotatory power measurements, circular dichroism (CD), and UV–vis spectroscopy. X-ray diffraction patterns of the cast films demonstrated that regioregular <i>HT</i>-PMOET possessed a strong tendency to self-assemble into highly ordered, crystalline structures. The <i>HT</i>-P­(<i>S</i>)­MOET and <i>HT</i>-P­(<i>R</i>)­MOET showed strong Cotton effects, while <i>HT</i>-P­(±)­MOET showed very weak Cotton effects. The presence of a circular dichroism effect indicated that the side chain chirality induced optical activity in poly­(thiophene) main chains. The monolayer formation of <i>HT</i>-PMOET spread on the water surface was characterized using a pressure–area (π–<i>A</i>) isotherm. The molecular areas of <i>HT</i>-P­(<i>S</i>)­MOET and <i>HT</i>-P­(<i>R</i>)­MOET molecules on the water surface were 33.5 and 32.9 Ų, respectively, at 10 °C, which were larger than that of <i>HT</i>-P­(±)­MOET (27.9 Ų), suggesting that optically active <i>HT</i>-PMOET expanded because of the chiral repulsion between side chains. Multilayer films of <i>HT</i>-PMOET were prepared by repeating horizontal deposition of the monolayer on the water surface. The multilayer films of optically active <i>HT</i>-PMOET obtained showed stronger Cotton effects than did the cast films. In addition, electrical conductivities of <i>HT</i>-PMOET multilayer films were superior to those of spin-coated films. <i>Head-to-tail</i> poly­(3-[2-((<i>S</i>)-1-methylpropyloxy)­ethyl]­thiophene) (<i>HT-</i>P­(<i>S</i>)­MPET), which contained shorter side chain lengths compared to <i>HT</i>-P­(<i>S</i>)­MOET, also was synthesized. The CD intensities of <i>HT-</i>P­(<i>S</i>)­MPET multilayer films were smaller than those of <i>HT</i>-P­(<i>S</i>)­MOET multilayer films, suggesting that the optically active side-chain length is critically important to the optically active self-assembly