Application of N-fluoropyridinium salts to battery materials

Abstract

N-Fluoropyridinium triflate (2a) and tetrafluoroborate (2b) and their derivatives with electron-donating and -withdrawing substituents were evaluated for battery materials. Their oxidation potential ranged from −0.37 to +0.37 V vs SCE and electromotive force with Li, Mg, and Zn ranged from 3.6 to 4.4 V/Li, 2.1 to 2.8 V/Mg, and 1.2 to 1.9 V/Zn, depending on the electron-deficiency of the NF site controlled by the substituents. Liquid electrolyte Li battery with N-fluoropyridinium salts as positive active materials provided the satisfactory discharge with high voltage. The addition of a catalytic amount of iodine greatly improved the performance of the batteries. It was also found that dimethyl 2,2-difluoromalonate was a new electrolyte solvent suitable for the batteries at high temperature (60 °C). Quasi-solid Li battery was also evaluated and the good performance suggested that the N-fluoropyridinium salts could act not only as positive active materials but also as electrolytic materials. Furthermore, many N-fluoropyridinium salts with low melting points were prepared, and 3-methyl-N-fluoropyridinium tetrafluoroborate (14b) was selected as a liquid positive active material. The Li battery using liquid 14b worked even at −40 °C. It was thus shown that N-fluoropyridinium salts worked well in a wide range of temperature as solid and liquid positive active materials with high voltage and satisfactory capacity (2b; electromotive force 3.8 V vs Li, theoretical capacity 290 mAh/g). The high performance of N-fluoropyridinium salt batteries was attributed to the novel properties of N-fluoropyridinium salts, which are high electron transfer capability and high ion conductive ability.