Synthesis and Characterization of Network Single Ion Conductors Based on Comb-Branched Polyepoxide Ethers and Lithium Bis(allylmalonato)borate

Abstract

Network single ion conductors (NSICs) based on comb-branch polyepoxide ethers and lithium bis(allylmalonato) borate have been synthesized and thoroughly characterized by means of ionic conductivity measurements, electrochemical impedance, and cycling in symmetrical Li/Li half cells, Li/V 6 O 13 full cells in which a NSIC was used as both binder and electrolyte in the cathode electrode and as the electrolyte separator membrane, and by dynamic mechanical analysis (DMA). The substitution of the trimethylene oxide (TMO) unit into the side chains in place of ethylene oxide (EO) units increased the polymer-ion mobility (lower glass transition temperature). However, the ionic conductivity was nearly one and half orders of magnitude lower than the corresponding pure EO-based single ion conductor at the same salt concentration, which may be ascribed to the lower dielectric constant of the TMO side chains that result in a lower concentration of free conducting lithium cations. For a highly cross-linked system (EO/Li ) 20), only 47 wt % plasticizing solvent (ethylene carbonate (EC)/ethyl methyl carbonate (EMC), 1/1 by wt) could be taken up, and the ionic conductivity was only increased by 1 order of magnitude over the dry polyelectrolyte, while for a less densely cross-linked system (EO/Li ) 80), up to 75 wt % plasticizer could be taken up and the ionic conductivity was increased by nearly 2 orders of magnitude. A Li/Li symmetric cell that was cycled at 85 °C at a current density of 25µA cm -2 showed no concentration polarization or diffusional relaxation, which was consistent with a lithium ion transference number of 1. However, both the bulk and interfacial impedance increased after 20 cycles, which was apparently due to continued cross-linking reactions within the membrane and on the surface of the lithium electrodes. A Li/V 6 O 13 full cell constructed using a single ion conductor gel (propylene carbonate (PC)/EMC, 1/1 in wt) was cycled at 25 °C at a current density of 25µA cm -2 and showed an initial capacity of 268 mAh g -1 of V 6 O 13 , which stabilized at around 200 mAh g -1 after the first 20 cycles. During the DMA measurements on the NSICs, it was found that besides the main glass transition (R transition) there was a distinct secondary glass transition (β transition) for NSICs having five EO units in the side chains, while this (the secondary transition) was not clearly visible in the network single ion conductors (NSICs) with shorter side chains (two, three, and four EO units). The main glass transition (R transition) was attributed to the whole network structure of the single ion conductors and secondary glass transition (β transition) appeared to be due to the complexation of lithium by the side-chain chains. Both the main glass transition and the secondary transition were found to shift to higher temperature with increasing salt concentration.

Gel Polymer Electrolytes for Electrochemical Energy Storage

“…These GPEs suffer from concentration polarization caused by the salt concentration change across the membrane and within the electrodes during the cycles of discharge, because there is no electrode reaction for the anions. [62] The generation of salt concentration gradients leads to poor performances including high internal impedances, voltage losses, and undesirable reactions in the electrolyte state such as phase transition or salt precipitation. In addition, the LTN of dual-ion conducting GPEs is generally lower than 0.5 because the motion of Li + is strongly related to the segmental motion of the polymer host.…”

Compliant glass–polymer hybrid single ion-conducting electrolytes for lithium batteries

“…Concentration polarization is absent in single-ion conductors, wherein the anions are immobilized (2). Nonflammable, single ionconducting solid electrolytes have the potential to dramatically improve safety and performance of lithium batteries (3)(4)(5)(6).…”

Photoactive Branched and Linear Surface Architectures for Functional and Patterned Immobilization of Proteins and Cells onto Surfaces: A Comparative Study

“…The mixture was heated to 80 8C during 18 h. DMF was distilled off (at 5 10 À2 mbar) and the residue was taken up in ethyl acetate (125 mL), washed with 1 n HCl (2 50 mL) and saturated NaHCO 3 solution (2 30 mL), and dried over anhydrous sodium sulphate. (8): [33] Compound 3 (7.5 g, 32 mmol), tetrabutylammonium hydrogen sulphate (11.6 g, 34 mmol) and 50 % aqueous sodium hydroxide solution (13 mL) were mixed and cooled in an ice bath to 0-4 8C. (+ /À)-Epichlorhydrin was slowly added under vigorous stirring.…”