Observation of Water Consumption in Zn–air Secondary Batteries

Abstract

Zn-air battery uses oxygen from the air, and hence, air holes in it are kept open for cell operation. Therefore, loss of water by evaporation through the holes is inevitable. When the water is depleted, the battery ceases to operate. There are two water consumption routes in Zn-air batteries, namely, active path (electrolysis) and passive path (evaporation and corrosion). Water loss by the active path (electrolysis) is much faster than that by the passive path during the early stage of the cycles. The mass change by the active path slows after 10 h. In contrast, the passive path is largely constant, becoming the main mass loss path after 10 h. The active path contributes to two-thirds of the electrolyte consumption in 24 h of cell operation in 4.0 M KOH. Although water is an important component for the cell, water vapor does not influence the cell operation unless the water is nearly depleted. However, high oxygen concentration favors the discharge reaction at the cathode.

Production and Characterization of Bacterial Cellulose Separators for Nickel-Zinc Batteries

“…In Zn-air batteries, the overall electrolyte loss was quantified to be 34.6% after 24 h battery cycling and was assigned to HER, Zn corrosion, and evaporation. The effects of continuous water consumption were, however, not electrochemically detectable until shortly before the cell failure, which coincides here with the sudden capacity decrease during the last two discharge cycles (Figure 6a) [78]. However, soft short circuits due to the buildup of precipitated ZnO within the separator because of zincate supersaturation in the electrolyte (~40 µL) [79], Zn migration to the cathode due to the Zn 2+ -rich electrolyte [11,12], or passivation of the Zn anode [80] could also account for the early cell failure.…”

Improving Cycle Life of Zinc–Air Batteries with Calcium Ion Additive in Electrolyte or Separator

“…Remarkable changes were detected in the concentration of CO 3 2− when adding Ca(OH) 2 , which significantly decreased from 6.182 mol L −1 to 0.800 mol L −1 or 0.547 mol L −1 after cycling with the modified electrolyte or separator, respectively, as shown in Table 3 [ 8 , 11 , 44 ]. Ca 2+ was introduced into the ZAB system to preferentially react with CO 3 2− rather than K + , resulting in the precipitation of granular CaCO 3 prior to K 2 CO 3 [ 51 ], alleviating the blocking effect of micropores on the air electrode surface induced by the carbonation of alkaline electrolyte. Moreover, the modified separator would continuously release Ca 2+ to the electrolyte to consume CO 3 2− during the charge–discharge process, maintaining a relatively low concentration of CO 3 2− in the electrolyte to achieve sustained long-term improvement [ 48 ].…”

Study on failure mechanism on rechargeable alkaline zinc–Air battery during charge/discharge cycles at different depths of discharge

“…The two main carbon sources that cause carbonation of the electrolyte are the continuously oxidized carbon material in the Co 3 O 4 /CB air cathode and the CO 2 that enters the ZAB with the continuous flow of O 2 through the Co 3 O 4 /CB air cathode, respectively (Chang et al, 2021;Zhong et al, 2021;He et al, 2022;Song et al, 2022). Besides, evaporation of water exacerbate carbonation of the electrolyte, increasing the concentration of K 2 CO 3 in the electrolyte (Yang and kim, 2019). Continuous increases of partial K 2 CO 3 concentration led to the increased concentration polarization, more K 2 CO 3 precipitated out of the electrolyte and adhered to the electrodes' surface, hindering the interface reactions between the electrodes and the electrolyte, and affecting the cycle life of ZAB.…”

“…Catalysts suffering from poor durability and even poisoning in air cathodes limits ZAB's performance and roundtrip efficiency (Marcus et al, 2018;Huang et al, 2019;Liu X. R. et al, 2019;Li et al, 2020;Lu et al, 2020;Zhang et al, 2020). In addition, water consumption and carbonation of electrolyte were observed to affect the cycle life of ZAB (Yang and Kim, 2019;Zhong et al, 2021). Therefore, a sufficient survey of the existing literature shows that no consensus on the dominating factors affecting the ZAB's cycle life were reached, which severely limits the improvement of battery cycle life.…”