Lithium secondary cells using LiX (X=ClO4, BF4) as electrolyte and poly(2,5-pyrrolylene) and poly(2,5-thienylene) as materials for positive electrodes

Abstract

Repeated charge-discharge cycles of lithium secondary cells using poly(2,5-pyrrolylene) and poly(2,5-thienylene) on carbon fibre plates as the materials for positive electrodes have been tested. When the Li|LiBF4|poly(2,5-pyrrolylene) secondary cell is charged and discharged at 0.1 mA cm−2, it gives 91% current efficiency and 70% energy efficiency with an average discharging voltage of 2.75 V at the 9th charge-discharge cycle. This secondary cell has a theoretical energy density of 135 kW kg−1 based on the energy stored and the weights of poly(2,5-pyrrolylene) and the active materials. The Li|LiClO4|poly(2,5-thienylene) secondary cells show somewhat lower current efficiency and energy efficiency at the 9th charge-discharge cycle. The lithium cells using the polymers are rechargeable more than 50 times, but after about 50 cycles considerable lowering of the current efficiency and energy efficiency of the cells is observed, presumably due to degradation of the polymer.