Takeshi Yabe

Polymer electrolyte plasticized with PEG-borate ester having high ionic conductivity and thermal stability

Abstract We have focused on the PEG-borate ester as a new type of plasticizer for solid polymer electrolyte composed of poly(ethyleneglycol) methacrylate (PEGMA) and lithium bis-trifluoromethanesulfonimide (LiTFSI). The PEG-borate ester shows good thermal stability and high flash point. Ionic conductivity of the polymer electrolyte increases with increasing amount of the PEG-borate ester and exhibits values greater than 10−4 S cm−1 at 30 °C and 10−3 S cm−1 at 60 °C. Furthermore, PEG-borate ester has three EO chains whose lengths are variable, and various ionic conductivities are expected to depend on EO chain length. As a result, polymer electrolyte containing the PEG-borate ester whose EO chain length is n=3 shows highest ionic conductivity. Furthermore, polymer electrolytes containing PEG-borate esters show excellent thermal and electrochemical stability. The electrolytes are thermally stable up to 300 °C and electrochemically up to 4.5 V vs. Li+/Li.

Influence of Lewis acidic borate ester groups on lithium ionic conduction in polymer electrolytes

Polymer electrolytes having borate ester groups, which are part of the polymer matrix, have been prepared. The transference number of the lithium ions increases with increasing concentration of the borate ester groups, and therefore it is considered that the borate ester groups, having Lewis acidity, interact with Lewis basic anions. Furthermore, the transference numbers of lithium ions in the polymer electrolytes containing LiCF3SO3 or LiClO4 were found to be higher than that in the electrolyte with LiN(CF3SO2)2. Ab initio calculations were performed to estimate the interactions between the borate ester groups and the anions. The calculated results indicate that the borate ester group prefers to interact with a ‘hard’ basic anion, CF3SO3− or ClO4−. This is in good agreement with the obtained experimental results.

Influence of PEG-Borate Ester as a Lewis Acid on Ionic Conductivity of Polymer Electrolyte Containing Mg-Salt

We produced a novel Mg 2+ conducting polymer electrolyte and added a poly(ethylene glycol) (PEG)-borate ester as a new type plasticizer having a Lewis acidity and investigated the influence of the Lewis acidity of the PEG-borateester to a solid polymer electrolyte containing Mg(ClO 4 ) 2 salt. Adding the PEG-borate ester into the electrolyte shows the increase in the ionic conductivity of the polymer electrolyte. By measuring the glass transition temperature ( T g ) of the polymer electrolytes using differential scanning calorimetry, it became clear that the mobility of the carrier ion increases with increasing the amount of the PEG-borate ester. By investigating the temperature dependence of the ionic conductivity using William-Landel-Ferry type equation and measuring Raman spectra of the polymer electrolytes, it was found that the concentration of the carrier ion increases with increasing the amount of the PEG-borate ester in the polymer electrolyte. Furthermore, by estimating the transference number of the Mg 2+ cation and performing the ab initio calculation for the PEG-borate ester, it is suggested that the PEG-borate ester may enhance the degree of dissociation of the Mg salt in the polymer electrolyte to increase the ratio of the free ion, especially Mg 2+ , by interacting with and trapping the ClO 4 - anion of the salt as a Lewis acid.

Thermally stable solid polymer electrolyte containing borate ester groups for lithium secondary battery

Abstract A novel polymer electrolyte having borate ester groups, which are fixed to the backbone chain of the polymer, was prepared. The backbone polymer was synthesized by reaction between polyethylene glycol and boric acid anhydride. The highest conductivity was found for the polymer electrolyte sample prepared by the polyethylene glycol having average molecular weight of 600 (PEG600), the values of the ionic conductivity were 5.8×10 −5 S cm −1 at 30 °C and 2.6×10 −4 S cm −1 at 60 °C, respectively. The solid polymer electrolytes have relatively high thermal stability and electrochemical stability.

Investigation of the Effect of Lewis Acid on Ionic Conductivity of Polymer Electrolyte Containing Mg Salt

In order to investigate the influence of Lewis acidity on the ionic conductivity of poly(ethylene glycol) (PEG) poly(ethylene oxide) (PEO)-type polymer electrolyte, we designed a new solid polymer electrolyte based on Mg(ClO 4 ) 2 salt complexs of PEO chains cross-linked by a boric acid (BO 3 ) group as a Lewis acid. To change the concentration of the Lewis acid point in the polymer electrolyte, the length of the PEO repeating unit was controlled. The ionic conductivity of the polymer electrolyte increased with increasing the length of the PEO chain and with decreasing the concentration of the cross-linking point by the boric acid group. By measuring the glass transition temperature (T g ) of the polymer electrolytes using differential scanning calorimetry, it was found that the T g increases with decreasing the concentration of the cross-linking point. By investigating the temperature dependence of the ionic conductivity using William-Landel-Ferry-type equation and measuring Raman spectra of the polymer electrolytes, it became clear that the concentration of the carrier ion in the polymer electrolyte increased with increasing the concentration of the Lewis acid point by the boric acid group. Furthermore, the transference number of the Mg 2+ cation (tMg 2+ ) increased with increasing the concentration of the boric acid group. By the ab initio calculation for the PEG-berate ester as a model molecule to investigate on the Lewis acidity of boric acid group, it was supported that the boric acid group may act as a Lewis acid to enhance the solubility of the salt in the polymer electrolyte by interacting with and trapping the CIO 4 anion of the salt.

Influence of PEG-borate ester on thermal property and ionic conductivity of the polymer electrolyte

We have focused on the poly(ethylene glycol) (PEG)-borate ester as a new type plasticizer for solid polymer electrolyte for lithium ion secondary battery. Adding the PEG-borate ester into the electrolyte shows the increase in the ionic conductivity of the polymer electrolyte. By measuring the glass-transition temperature of the polymer electrolytes with DSC, it is found that the increase in ionic conductivity of the polymer electrolyte is due to the increase in ionic mobility. By investigating the temperature dependence of the ionic conductivity of the polymer electrolytes using William-Landel-Ferry type equation, we considered that the PEG-borate ester does not have any influence for dissociation of Li-salt.