Protection of non-aq. lithium cells against over-discharge - by the use of conductive organic polymers which can be reversibly charged and discharged and alter their conductivity

摘要

Electrochemical sec. batteries using non-aq. electrolyte, based on Li, have a positive electrode contg. a reducible inorganic material. The batteries have between the active material of the anode and its current connection, a contact medium made of a polymeric material. The polymer can reversibly gain and lose ionic dopant and so be charged and discharged which results in a variation of conductivity. The polymer can be used to form a matrix in which the active material is embedded or be mixed with the active material in powder form, pref. giving a ratio of polymer to active mass of 1-30 wt.%, esp. 5-15 wt.%. The polymer can also be used in the form of a film, pref. 0.1-100 micron, esp. 2-20 micron thick, between the current connection, which is pref. metallic, and the active mass or as the current conductor. USE/ADVANTAGE - The construction prevents discharge below 2V because of the increase of the resistivity of the polymer material. The cell can still be discharged to below 2 V, but this has no effect on the active mass, which is shielded by the polymer. The method is used in Li-cells to give a higher resistance against over-discharging esp. in low drain cells. In an example, a button cell with Li metal cathode and MnOx active mass, mixed with soot, at the anode was made with conventional construction (1) and another cell was made using an addition of powdery polypyrrole to the MnOx. The electrolyte used was 1M LiClO4 in propylenecarbonate. The fig. shows the effect of several discharges, including over-discharges on the cell capacity.