Thickness Effect of Composite Cathode of Active Material and Graphite Current Collector on Performance of Lead Acid Battery

Abstract

Introduction Lead Acid Batteries (LAB) are used in various fields, due to its low cost, high safety and excellent recyclability. Conventionally, LAB cannot be recharged after over-discharged and its performance is greatly declined. We have found that the above deterioration is caused by the formation of α-PbO2 on the surface of cathode active material β-PbO2 due to the reduction by local cell reaction between β-PbO2 and lead current collector. We also have revealed that the formation of α-PbO2 can be prevented by using gold instead of lead as current collector. In this case, the LAB can be recharged even after either discharging to 0 V or discharging to 0 V followed by 48 h open circuit [1,2]. In the case of carbon, electrode potential does not come out, so we thought that carbon has a role of stopping local cell reaction. We revealed that the LAB using graphite sheet with 5wt% polypropylene as current collector has high resistance to over-discharge [3,4]. This LAB can charge-discharge without performance degradation even after full discharge followed by 48 h rest period.We fabricated composite cathode composed of β-PbO2 as active material and expanded graphite adding 5wt% polypropylene as current collector, in order to have higher performance and ease of fabrication. It was found that the LAB using composite cathode can also be recharged even after full discharge followed by 48 h rest period. High resistance to over-discharge was indicated. Also the discharge characteristics of the LAB using the composite cathode improved, when the content of β-PbO2 was increased. The composite cathode made the LAB not only very durable in over discharge but also highly practical for use [5]. In this study, we fabricated the composite cathode of various thickness and investigated the effect of thickness on the LAB performance. Experiment We made the composite cathode with various thickness composed of expanded graphite, polypropylene 0.05 times the weight to expanded graphite and β-PbO2 1.0 times the weight to expanded graphite by a pressure molding. We used 35 % H2SO4 as electrolyte and lead plate as anode. The composite cathode was processed to 40 mm × 14 mm and the area immersed in sulfuric acid was 10 mm × 14 mm. We conducted charge-discharge experiments by using the LAB constructed as above mentioned. As the stabilization cycle, we repeated discharge at 0.25 mA for 30 min and charge at 2 mA for 20 min for 20 times, then we conducted charge discharge experiment. Results and discussion After the stabilization cycle, we discharged the LAB deep to 0 V and opened the circuit for 48 h, then we resumed charge-discharge cycle. Figure1(a) shows the charge-discharge characteristics of conventional type LAB using lead plate cathode current collector. Conventional type LAB could not resume charge-discharge cycle after full discharge followed by48 h open circuit. Figure1(b) shows the case of the LAB using composite cathode with 1.0 mm thickness. It was indicated that the LAB could resume charge-discharge cycle even after full discharge followed by 48 h open circuit.Figure2 shows detailed discharge curves for the LAB using of the composite cathode with 0.5 mm thickness or 1.0 mm thickness. The charge rate and the discharge rate was 2.0 mA and 0.1 mA, respectively. The composite cathode with 1.0 mm thickness has better characteristics in longer discharge time and higher discharge potential than that with 0.5 mm thickness. Flat discharge potential around at 1.7 V was clearly observed for the LAB using the composite cathode with 1.0 mm thickness. This means the excellence in practical performance. It was indicated that the thickness of the composite cathode is one of key factor to make the LAB highly practical for use. Reference [1] T. Iwai, D. Kitajima, S. Takai, T. Yabutsuka and T. Yao, J. Electrochem. Soc. Vol 163, Issue 14, A3087-A3090 (2016)[2] T. Iwai, M. Murakami, S. Takai, T. Yabutsuka and T. Yao, Journal of Alloys and Compounds, Vol 780, 85-89 (2019)[3] T. Yao, H. Okano, T. Iwai, S. Takai, T. Yabutsuka, T. Hosokawa, N. Misaki, K. Kurihara “Positive Electrode for Lead Storage Battery and Lead Storage Battery Using Same” PCT/JP2018/005947[4] Y. Nakamura, T. Ohkubo, H. Okano, T. Inoue, T. Hosokawa, A. Takeda, T. Iwai, T. Yabutsuka, S. takai and T. Yao, 235th ECS Meeting. Soc. Z01-2143 (2019)[5] K. Sugimoto, F. Ohira, Y. Hano, H. Okano, T. Iwai, T. Yabutsuka, S. Takai, T. Hosokawa, Y. Akamatsu, S. Yoshikawa, M. Miki, M. Kuninaka and T. Yao,239th ECS meeting. Soc. Z01-1989 (2021) Figure 1