Mercury-free Button Alkaline Manganese Batteries

This study was designed to produce mercury-free alkaline Zn/MnO₂ button cells. In this paper, the development of cylinder type alkaline Zn/MnO₂ battery, the way of realizing mercury-free and the method of improving its performance were reviewed in detail. The safety problem, discharge mechanism, battery formula and technique parameters of mercury-free alkaline Zn/MnO₂ button cells were studied and the key materials of the battery, electrolytic manganese dioxide, was modified.It showed that the alkaline Zn/MnO₂ button cells was only suitable for use in low discharge current condition, the utilization rate of the active substance was lower than 80% and the EMD can only release one of its two available redox electrons. The electrochemical polarization of battery was very serious and the utilization rate of active substance was very low if the button cell was short-circuited or used in high discharge current condition. The residue zinc powder released lots of hydrogen gas which would lead to the expansion or even explosion of the cell.According to the above-mentioned facts and the successful mercury-free experience of cylinder type alkaline Zn/MnO₂ battery, we chose a suitable mercury-free corrosion inhibitor and optimized the battery formual to realize the mercury-free of alkaline Zn/MnO₂ button cell. The factors affecting the safety performance of batery such as capacity ratio of anode to cathode, content of electrolyte added in battery, KOH electrolyte concentration, content of ZnO dissolved in KOH electrolyte, content of ZnO added in zinc gel, content of binder added in zinc gel, content of inhibitor added in zinc gel, content of carbon and acetylene carbon black, and content of KMnO₄ added in cathode were studied by experiments and the optimal technology parameters were confirmed. In addition, we adopted mixing method of ball-milling instead of traditonal mechanical agitation, used a new seal zinc gel aging step, used a new particle-making step during the cathode-making process, and improved some procedures affecting the performance of cells. The safety performance of the the LR44 mercury-free alkaline Zn/MnO₂ button cell produced under this improved technique condition satisfied the national standards. The discharge capacity at 1000Ωconstant resistance and 0.9V cutoff voltage was 152mAh. The capacity of 1.3V～1.6V increased by 24.7%, and the utilization rate of zinc powder increased by 13.8%.The research results of optimal anode and cathod indicated that the hydrogen gas evolving out of zinc gel was lower, the inhibitng rate increased by 21% , the conductivity increased by 53% and react activity of the cathode was improved greatly.The EMD was modified by liquid-phase surface treatment method and a kind of EMD/CMD-Bi composite was obtained by coating the chemical manganese dioxide and bismuth oxide on its surface. The discharge capacity of the modified EMD increased by 40.8% than that of un-modified. The rate capability was improved after modifiction, the discharge capacity of 1/3C rate reached up to 97% of that of 1/10C rate.The modified EMD was more suitable for the positive materials of alkaline Zn/MnO₂ button cells.