Performance of Lead Acid Battery Using Graphite Composite Current Collector

Abstract

Introduction Conventionally, Lead Acid Battery (LAB) cannot be recharged after over-discharge and its performance is greatly degraded. We have revealed 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 revealed that the formation of α-PbO2 can be prevented by using gold instead of lead as cathode current collector and that this operation made the LAB rechargeable even after over-discharge [1,2]. We have also revealed that the LAB using graphite sheet as a current collector can charge-discharge even the circuit is opened for 48 h after over-discharge to 0V [3]. Especially in the improvement of tensile strength and discharge potential, it is concluded that 5wt% polypropylene addition to raw graphite sheet is most suitable for use as a cathode current collector in our previous study [4]. In this study, for practical use of this type of LAB, we investigated its characteristics, in particular the relationship between discharge energy and charge voltage. Experiment We used two-electrode glass cell for charge-discharge experiments. The cathode slurry was prepared by mixing β-PbO2 powder as active material, acetylene black as conductive additive and polyvinylidene fluoride as binder at the ratio of 8:1:1 in weight with solvent of N-methyl-pyrrolidone. We used graphite composite sheet with 5wt% polypropylene mixed for cathode current collector. We constructed the cathode by applying the cathode slurry to the current collector. We used 35% H2SO4 as electrolyte and lead plate as anode. As the stabilization cycle, we repeated discharge at 45μA cm2 -1 for 30 min and charge at 0.9 mA cm2 -1 for 20 min for 20 times, then we conducted charge discharge experiment. We determined charge-discharge rate using the coating area of cathode active material. Results and discussion Figure 1 shows the typical charge/discharge curve between 0 V and 2 V of the LAB using graphite sheet with 5wt% polypropylene as cathode current collector at about 1C discharge. It was confirmed that this LAB could be discharged to 0V and that showed flat discharge potential around between 2V and 0.7V. We charged this LAB to various potential and discharged to 0V. We calculated the discharge energy by the integral of the obtained discharge curve from each charge potential to 0.7V. Figure 2 shows discharge energy ratio at 2.0V, 1.8V, 1.6V and 1.4V charge voltage to discharge energy at 2.0V charge voltage. Discharge energy increased with charge voltage. It was found that this LAB using graphite composite sheet with 5wt% polypropylene mixed for cathode current collector could recover more than 50% of discharge energy obtained at 2.0V charge by charging to 1.8V. References [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. Hano, H. Okano, T. Inoue, T. Hosokawa, A. Takeda, T. Iwai, T. Yabutsuka, S. Takai and T. Yao, 238th Electrothem. Soc. Z01-3448 (2020) Figure 1