Zinc / Silver Air Battery Failure Mechanisms And Life Extension Methods

Based upon the results of the cycling test, SEM, XIRD and chemical analysis of three stacks of zinc/silver storage for aviation purpose as studying object, the reason responsible for the end of useful life of such battery were analyzed. The objective batteries were belong to different compelling structure with commercial model 1 5XYG45-(3) and 1 5XYG45-.(3)G and were produced by Tai Hong Electric Power Source Group Ld. Cop. The results shown that: I. The major reason responsible for the useful life ending of battery was due to zinc anode, the shape changing, redistribution of active material, progressing of anodic passive and hardness, all these happened on the zinc anode during cycle, made the polarization progressing and the utilization ratio of active materials decrease. 2. The zinc anode shape changing were attribute to the high dissolution of zinc oxide in electrolyte of potassium hydroxide and the change of composition and concentration of electrolyte in anolyte. That is, around the edge of zinc anode the concentration of hydroxide was higher, while the concentration of zinc oxide and zincate were much lower than the center part, so the rate of zinc oxidized dissolution was much larger around the edge than that on center part, while the precipitation rate of zinc oxide and zinc hydroxide were larger in the center part than around the edge, these two respects made the anodic shape changing. 3. Another reason for the losing of capacity was the dissymmetry of the charge efficiency between the anode and the cathode. The large amount of polyvinyl alcohol as paste in such battery, and self-discharge of zinc anode made the charge efficiency of zinc anode to be lower than that of silver cathode, this lead to the accumulation of silver oxide on the cathode at the end of discharge, especially in the latest part of useful life of the battery. The accumulated silver oxide made the positive potential of silver cathode reaching the limited value quickly in the nest charge process, while large amount of zinc oxide on the zinc anode still were not completely changed to metal zinc, so the negative potential of zinc anode which was not fully charged, reached to the limited value quickly during the discharge process. The incomplete usefulness of active material on the two electrodes made the capacity losing of whole battery. 4. The relatively lower charge efficiency of the zinc anode made partial zinc oxide unchanged to metal zinc near the end of charging and the concentration of zincate in electrolyte maintaining at a high level, all these inhibited the zinc dendrite growth during charge, the polyvinyl alcohol used as paste also have the same function. So that the shortage of internal circuit produced by zinc dendrite was impossible. 5. The migration of silver reduced the mass of cathode active material, had little affect upon the capacity near latest period, but the multi-layer diaphragm which had to be used to prevent the silver migration have much affect upon the distribution and convection of electrolyte. 6. Nowadays the useful life of zinc/silver stack is one year, the multi-layer separator diaphragm can meet the requirement, either double layer branched membrane plus double layer reproduced fiber membrane, or single layer branched...