Properties and Characterization of Zinc Anodes for Zinc Batteries

• Main Authors: Fang, Po-Chao, 方柏超
• Other Authors: Lin, Su-Jien
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/64938107749705300549

碩士 === 國立清華大學 === 材料科學工程學系 === 91 === AC impedance together with constant-current discharge measurement, cyclic voltammetry, and microstructural analysis has been used to this study to evaluate the performance of porous zinc anode in a zinc battery (i.e., zinc-air battery) by means of changing the influencing factors of the zinc anode, such as morphology of the zinc powders and the amount of PTFE used. In this manner, one can use this information to design, manufacture, and use the specific designed battery. BET specific surface area is the most important factor in evaluation of the depth of discharge of three kinds of zinc powders (designated by Powders A, B, and C). In this study, it is observed that the BET specific surface areas of zinc anodes made up of Powders A, B, and C are 0.5659, 0.6749, and 0.3182 (m2/g), respectively, for 4% PTFE. Those of zinc anodes made up o Powder A with 10 and 20% PTFE are 0.5342 and 0.3160 (m2/g), respectively. The depth of discharge, ranging from 52 to 87%, increases with increasing specific surface areas studied in this experiment. Randles circuit is used in this experiment to describe the equivalent circuit of the zinc porous anodes. The impedance at 100 kHz is regarded as that of the infinity frequency and it is the resistance of the 8 M KOH electrolyte. This value can be compared to that obtained the constant-current discharge measurement. Thus the latter can be used to measure the inner resistance as a convenient and quick method in this respect. A constant phase element (CPE) of a capacitor effect in the anode can be used to interpret the flattened circle Nyquist plots in this study. The exponent coefficients, α, in the impedance-frequency relation range from 0.75 to 0.90. It is concluded from the obtained α values that the porous zinc anode is less “porous” than the idea porous anode (α= 0.5) and approaches to that of the liquid electrode (α= 1). Microstructural FEG-SEM analysis combined with diluted HCl (1.4 M) etching to the zinc anode shows clearly the porosity state of the anode and the PTFE structure at the optimum heating temperature at 350℃. Analyses also show that large current (0.4 A) discharge has much regularly radiated shape for ZnO than that of small current (0.2 A) discharge. Cyclic voltammetric measurements show only small scanning rate (1 mV/s vs. 2 and 5 mV/s) has the red-ox reaction of Zn in Zn anode. In this study, more detailed AC impedance measurements are made to compare the effects of different zinc powders, amounts of PTFE, discharging states of anode, and static and dynamic discharging on the impedance of the anode. The data show zinc powders are more important than PTFE amounts in an anode. Discharging states are less important in effecting the AC impedance measurements. In summary, the AC impedance is useful in the designing, manufacturing, and application.