Unique electrochemical behavior of a silver–zinc secondary battery at high rates and low temperatures

This study investigates an unusual charging phenomenon observed in silver–zinc secondary batteries. In the case of general secondary batteries, the specific capacity and coulombic efficiency decrease with increasing battery charging rate because of a concomitant increase in overvoltage. However, this study reveals that, at room temperature and within a specific charging-rate range, the discharge capacity and coulombic efficiency of silver–zinc batteries increase with increasing charging rate. To elucidate this unusual behavior, the charge/discharge characteristics of silver–zinc batteries were systematically analyzed at different charging rates and operating temperatures. In addition, the structural and compositional evolution of the silver cathode with the state of charge of the battery were investigated. The experimental results demonstrated that the phase transformation kinetics of silver oxide to silver peroxide governs the electrochemical performance of silver–zinc batteries and the kinetically unfavorable formation of silver peroxide ironically enables fast-chargeable silver–zinc batteries with high capacity and efficiency. Furthermore, it was confirmed that the suppression of water hydrolysis at low temperatures promotes the silver peroxide formation, resulting in high capacity during low temperature operation. This study provides an effective charge strategy, which could help achieve high-capacity, high-efficiency silver–zinc secondary batteries.