Masataka Kubo

Characterization of composite electrolytes based on a hyperbranched polymer

Abstract Composite polymer electrolytes composed of a hyperbranched poly[bis(triethylene glycol)benzoate] with terminal acetyl groups, LiN(CF 3 SO 2 ) 2 as a lithium salt, and an inert ceramic filler such as α-LiAlO 2 or γ-LiAlO 2 were prepared by solvent casting method. Addition of an appropriate amount of the fillers to fully amorphous pristine polymer electrolytes led to an increase in ionic conductivities and lithium ion transference numbers. All composite polymer electrolytes exhibited good compatibility with a lithium metal electrode, and also, addition of fillers improved their mechanical performance. The α-LiAlO 2 filler was effective for improving the electrochemical compatibility with a lithium metal electrode, and the γ-LiAlO 2 filler was effective for enhancing the mechanical properties of the pristine polymer electrolytes.

Thermal, electrical, and mechanical properties of composite polymer electrolytes based on cross-linked poly(ethylene oxide-co-propylene oxide) and ceramic filler

Abstract A fully amorphous cross-linked poly(ethylene oxide-co-propylene oxide) (poly(EO/PO)) polymer electrolyte was prepared by chemical cross-linking reaction of a macro-monomer, poly(ethylene oxide-co-propylene oxide) with trifunctional cross-linkable acryloyl groups at the macro-monomer chain end. The lithium salt LiN(CF3SO2)2 ([Li]/[O]=1/16) and ceramic fillers such as BaTiO3 and γ-LiAlO2 adopted in the polymer electrolyte could maintain the fully amorphous feature of the polymer matrix. The submicron and nano-sized BaTiO3 fillers slightly decreased the thermal decomposition temperature of the polymer matrix, while the nano-sized γ-LiAlO2 filler improved to some extent the thermal stability of the polymer matrix. Both nano-sized BaTiO3 and γ-LiAlO2 fillers increased the ionic conductivity of the cross-linked poly(EO/PO)/LiN(CF3SO2)2 electrolyte and the highest conductivities of 5.67×10−5 S/cm at 30 °C and 5.76×10−4 S/cm at 80 °C, respectively, were obtained for the composite polymer electrolytes with 10 wt.% γ-LiAlO2 filler. However, the submicron BaTiO3 filler, regardless of its content, decreased the ionic conductivity. Addition of ceramic fillers, especially the nano-sized BaTiO3 and γ-LiAlO2, was effective in improving the mechanical strength and elasticity of the fully amorphous composite polymer electrolytes over a wide temperature range.

Effects of alumina whisker in (PEO)8–LiClO4-based composite polymer electrolytes

Abstract This paper reports the morphological, electrical and mechanical characteristics of the PEO-based composite polymer electrolytes with alumina whisker as fillers. The SEM results showed that serious microcracks occurred in the pristine PEO–LiClO 4 polymer electrolytes when they were quenched at room temperature and spherulites were allowed to form in the electrolytes. Addition of alumina whisker effectively prevented the formation of the microcracks. The whiskers were homogeneously dispersed in the polymer electrolyte matrix and exhibited excellent interconnection with PEO–LiClO 4 polymer electrolyte. The addition of whisker additives improved the ionic conductivity of the PEO–LiClO 4 polymer electrolytes to some extent when the content of the whisker was less than 20 wt.%. Moreover, the whisker could remarkably improve the mechanical performance of the PEO–LiClO 4 polymer electrolyte especially at the temperatures higher than its melting point.

Blend-based polymer electrolytes of poly(ethylene oxide) and hyperbranched poly[bis(triethylene glycol)benzoate] with terminal acetyl groups

Abstract Blend-based polymer electrolytes, with favorable mechanical strength, consisting of a linear poly(ethylene oxide) (PEO), a hyperbranched polymer (poly[bis(triethylene glycol)benzoate] with terminal acetyl groups), and LiN(CF3SO2)2 salt, were prepared by the solvent casting technique. Thermal properties, ionic conductivity, electrochemical stability window, lithium ion transference number, and cyclic voltammetric behavior of the blend-based polymer electrolytes were all evaluated and discussed. In comparison with polymer electrolytes based on PEO, the blend-based polymer electrolytes exhibited improved lithium ionic conductivity and lithium/electrolyte interfacial performance. Blend-based polymer electrolyte with a hyperbranched polymer/PEO ratio of 20/80 in wt% and [LiN(CF3SO2)2]0.125 exhibited ionic conductivities as high as 8.1×10−4 S cm−1 at 80°C and 3.8×10−5 S cm−1 at room temperature. The electrochemical stability window was about 4.9 V. It was also demonstrated that crystallinity of the blend-based polymer electrolytes depends significantly on the hyperbranched polymer/PEO weight ratio as well as the lithium salt content.

Ionic conductivity of the hyperbranched polymer-lithium metal salt systems

Abstract Terminal-acetylated hyperbranched poly(ethylene glycol) derivatives containing diethylene and triethylene glycols and 3,5-dioxybenzoate branching units were prepared and the ionic conductivities of these polymers complexed with lithium metal salts such as LiCF3SO3 and Li(CF3SO2)2N as polymer electrolytes were investigated. It was found that the hyperbranched polymer with a triethylene glycol chain and with Li(CF3SO2)2N shows higher conductivity and also the number of charge carriers increases with Li(CF3SO2)2N salt concentration.

Effect of branching in base polymer on ionic conductivity in hyperbranched polymer electrolytes

Abstract Novel hyperbranched polymer, poly[bis(diethylene glycol)benzoate] capped with a 3,5-bis[(3′,6′,9′-trioxodecyl)oxy]benzoyl group (poly-Bz1a), was prepared, and its polymer electrolyte with LiN(CF3SO2)2, poly-Bz1a/LiN(CF3SO2)2 electrolyte, was all evaluated in thermal properties, ionic conductivity, and electrochemical stability window. The poly-Bz1a/LiN(CF3SO2)2 electrolyte exhibited higher ionic conductivity compared with a polymer electrolyte based on poly[bis(diethylene glycol)benzoate] capped with an acetyl group (poly-Ac1a), and the ionic conductivity of poly-Bz1a/LiN(CF3SO2)2 electrolyte was to be 7×10−4 S cm−1 at 80 °C and 1×10−6 S cm−1 at 30 °C, respectively. The existence of a 3,5-bis[(3′,6′,9′-trioxodecyl)oxy]benzoyl group as a branching unit present at ends in the base polymer improved significantly ionic conductivity of the hyperbranched polymer electrolytes. The polymer electrolyte exhibited the electrochemical stability window of 4.2 V at 70 °C and was stable until 300 °C.

Synthesis and polymerization of 4-vinyl [2.2]paracyclophane

Summary4-Vinyl [2.2]paracyclophane (1) was successfully prepared as white crystals in 45 % yield via three step reactions. Monomer 1 was homopolymerizable with 2,2′-azobis(isobutyronitrile) (AIBN), boron trifluoride etherate, and butyllithium. Monomer 1 was copolymerizable with methyl acrylate and p-chlorostyrene in the presence of AIBN in benzene at 60 °C. It was found that monomer 1 was less conjugative and more electron-donating than styrene.

Synthesis of a well‐defined cyclic polystyrene via α‐carboxyl, ω‐amino heterodifunctional polystyrene

Living anionic polymerization of styrene was carried out in benzene at room temperature using 1-(3-lithiopropyl)-4-methyl-2,6,7-trioxabicyclo[2.2.2]octane and 2,2,5,5-tetramethyl-1-(3-bromopropyl)-1-aza-2,5-disilacyclopentane as an initiator and terminator, respectively, to obtain α-2,2-bis(hydroxymethyl)propoxycarbonyl, ω-amino heterodifunctional polystyrene. It was hydrolyzed to α-carboxyl, ω-amino heterodifunctional polystyrene which gave a well-defined cyclic polystyrene by the intramolecular cyclization under high dilution conditions.

Synthesis and polymerization of 7-alkoxycarbonyl-7,8,8-tricyanoquinodimethanes and 7,7-bis(alkoxycarbonyl)-8,8-dicyanoquinodimethanes

Abstract Attempts were made to prepare novel 7-alkoxycarbonyl-7,8,8-tricyanoquinodimethanes (ethoxy(5a), isopropoxy(5b), and tert-butoxy(6c)), 7,7-bis(alkoxycarbonyl)-8,8-dicyanoquinodimethanes (ethoxy(6a), isopropoxy(6b), and tert-butoxy(6c)), and 1-(2,2-dimethyl-1,3-dioxane-4,6-dione-5-ylidene)-4-(dicyanomethylene)-2,5-cyclohexadiene(6d). 5c and 6d were obtained as yellow and orange needles, respectively, but 5a, 5b and 6a-c could not be isolated as crystals. Homopolymerizations of 5c and 6d and their copolymerizations with styrene were studied.

Polymerization of meta‐naphthoquinone methide: 3,4‐benzo‐6‐methylenebicyclo [3.1.0] hex‐3‐ene‐2‐one

Polymerization behavior of meta-naphthoquinone methide, 3,4-benzo-6-methylenebicyclo[3.1.0]hex-3-ene-2-one (1), was studied. Radical initiator 2,2′-azobis(isobutyronitrile) (AIBN) induced polymerization of 1, but ionic initiators potassium tert-butoxide, butyllithium, and boron trifluoride etherate did not. Polymerization of 1 proceeded via ring-opening and aromatization to give a polymer with head-to-tail monomer unit placement. Compound 1 copolymerized with methyl methacrylate (MMA) in the presence of AIBN to obtain the monomer reactivity ratios r1 (1) = 0.28 ± 0.07 and r2(MMA) = 0.39 ± 0.02 at 60°C and Q and e values of Q = 1.04 and e = −1.03, indicating that 1 is a conjugative and electron-donating monomer. Ring-opening and aromatization of 1 also took place in the copolymerization.