Shiro Nishi

Ionic Conductivity of Dual‐Phase Polymer Electrolytes Comprised of NBR/SBR Latex Films Swollen with Lithium Salt Solutions

Dual-phase polymer electrolytes (DPE) with high ionic conductivity and good mechanical strength were prepared by swelling poly(acrylonitrile-co-butadiene) rubber (NBR) and poly(styrene-co-butadiene) rubber (SBR) mixed latex films with lithium salt solutions (e.g., 1M LiClO[sub 4]/[gamma]-butyrolactone). The latex films retain particle morphology in the solid state. The NBR phase (formed from fused NBR latex particles) is polar and is impregnated selectively with polar lithium salt solutions, yielding ion-conductive channels, whereas the SBR phase (formed from fused SBR latex particles) is nonpolar and is not impregnated, providing a mechanically supportive matrix. The ionic conductivity of the DPE increased dramatically with increasing content of lithium salt solution, and higher amounts of solution were imbibed with increasing content of NBR relative to SBR. Several factors which affect the ionic conductivity of this system were examined, and the highest ionic conductivity (>10[sup [minus]3] S/cm) was obtained when either an NBR/SBR 70/30 (w/w) or a 50/50 (w/w) latex film was saturated with 1M LiClO[sub 4]/[gamma]-BL solution or 1M LiClO[sub 4]/[gamma]-BL/DME solution. Ion-conductive behavior changed critically with increasing lithium salt solution uptake. At low levels of lithium salt solution uptake, evidence suggested that ionic conductivity of the absorbed lithium salt solution was strongly influenced by the presence of morexa0» the NBR in the ion-conductive channel, but at higher levels, the effects of the NBR were reduced and free lithium salt solution was present. «xa0less

New concept for polymer electrolyte: Dual-phase polymer electrolyte

Abstract Two types of dual-phase polymer electrolytes (DPE), mixed latex DPE and core-shell latex DPE, were fabricated from styrene-butadiene rubber (SBR) and acrylonitrile-butadiene rubber (NBR) latex mixture, and from polybutadiene (PB)/ poly (vinyl pyrrolidone) (PVP) core-shell latex. Polar phases of films made from these latices were selectively impregnated with lithium salt solution, constituting dual-phase structures. TEM images verified the dual-phase structures. The ionic conductivity vs. NBR conductive-phase content relationship showed a profile characteristic of percolation effect, which also endorsed the dual-phase structure of mixed latex DPE. For both types of DPEs, ionic conductivity on the order of 10 −3 S/cm was obtained. However, the PVP conductive phase of the core-shell latex DPE was partially leached out in the preparation process. The modulus of mixed latex DPE was 6 × 10 6 dyn/ cm 2 at room temperature, even with a lithium salt solution content of 61 wt%, suggesting that the SBR supporting phase is little affected by the lithium salt solution.

Polymer Electrolytes with Multiple Conductive Channels Prepared from NBR/SBR Latex Films Impregnated with Lithium Salt and Plasticizer

Polymer electrolytes, composed of a polar polymer acting as a host matrix for lithium-salt solutions, have high ionic conductivity and have been studied for application in advanced electronic devices such as the rechargeable lithium battery. Polymer electrolytes with high ionic conductivity (> 10{sup {minus}3} S/cm) and good tensile strength were prepared by swelling poly(acrylonitrile-co-butadiene) (NBR)/poly(styrene-co-butadiene) (SBR)/LiClO{sub 4} latex films with {gamma}-butyrolactone ({gamma}-BL) or LiClO{sub 4}/{gamma}-BL plasticizer. Before swelling, the LiClO{sub 4} phase is formed at the particle interface. After politicization, two ion-conductive channels are present: the LiClO{sub 4} phase is present at the interface of the latex particles, and the NBR phase is formed from NBR latex particles. These regions are polar and impregnated selectively with polar {gamma}-BL solvent or LiClO{sub 4}/{gamma}-BL solution, building primary and secondary ion-conductive channels, respectively. The SBR phase (formed from SBR latex particles) is nonpolar and not impregnated, providing a mechanically supportive matrix. High ionic conductivity on the order of 10{sup {minus}3} S/cm is achieved when NBR/SBR(50/50)/LiClO{sub 4} latex film was saturated on 0.2 to 0.4M LiClO{sub 4}/{gamma}-BL solutions. Various microscopic and macroscopic analyses suggest that two types of ion-conductive channels exist in the polymer electrolyte film.

Ac impedance analysis on dual-phase polymer electrolytes prepared from SBR/NBR mixed latices

Dual-phase polymer electrolytes (DPE) are analyzed by ac impedance spectroscopy. DPE is prepared from an NBR/SBR latex mixture in the following process: the latex mixture is dried to produce a polymer matrix film, and the polymer matrix is then impregnated with a lithium salt solution as a plasticizer, which selectively permeates into the NBR phase. When a polymer matrix is impregnated with 1M LiClO4/γ-butyrolactone and its NBR content is small, a distorted complex impedance spectrum, composed of overlapping two semicircles, is observed. The analysis based on an equivalent circuit indicates that isolated fragments of the conductive NBR phase are formulated in addition to the continuous conductive pathways. With increasing content of NBR, the two semicircles get merged. This suggests that the isolated conductive phase comes to be integrated into the continuous ionic pathways. The impregnation process of DPE with a less polar plasticizer was followed by analyzing the complex impedance and modulus spectra. According to this analysis, secondary conductive pathways are formed along the SBR particle boundaries in addition to the NBR conductive phase. Swelling of NBR particles progresses in the secondary conductive pathways, and the NBR particles are finally linked to form continuous ionic pathways between the electrodes.

New Dual‐Phase Polymer Electrolytes Prepared from NBR/SBR Latices

A new type of Li[sup +] ion conducting polymer electrolytes consisting of two phases, one of which is a highly polar region (impregnated with lithium salt solution), forming ion-conductive channels, while the other is a nonpolar region, forming supporting polymer matrices have been prepared from NBR/SBR lattices. TEM measurement and EDX analysis show evidence that dual-phase structure is constructed in the electrolyte. Ionic conductivity of the electrolyte increases with increase of lithium salt solution content. Maximum ionic conductivity of 2.2 [times] 10[sup [minus]3] S/cm is obtained at the lithium salt solution content of 60.5% (w/w). The electrolyte retains rubber-like film with good mechanical strength despite the presence of the solution.