Deep-Discharge Performance of Lead Acid Battery Using Graphite Based Composite As Cathode Current Collector

Abstract

Introduction Lead Acid Batteries (LAB) are used in various fields such as power supplies for automobiles, uninterruptible power supplies and power storage. 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. The LAB can be recharged even both after discharging to zero volt and after discharging to zero volt followed by 2 d 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. For this type of LAB, we investigated long term charge deep-discharge cycle performance, and rechargeability after 0 V discharge followed by open circuit for various long period in this study. Experiment We used two-electrode glass cell for charge-discharge experiments. The cathode active material was prepared by mixing β-PbO2 powder, acetylene black as a conductive additive and PTFE as a binder at the ratio of 80:15:5 in weight. We constructed the cathode by pressing the paste on graphite sheet with 5wt% polypropylene current collector. We used 35 % H2SO4 as electrolyte and lead plate as anode. As the stabilization cycle, we repeated discharge at 9 mA g-1 for 30 min and charge at 180 mA g-1 for 20 min for 20 times, then we conducted charge discharge experiment. Results and discussion Figure1 shows the result of long-term deep discharge durability experiment. One cycle is consisted of 4 times of discharge down to 0V and full-charge, then 48 h rest period. The charge rate was 180 mA g-1 and discharge rate was 9 mA g-1. It is indicated that this LAB could continue the cycle for 5 months. This result means that this type of battery has high durability to deep discharge for many times. The discharge capacity did not degrade during the 5 months period. Cause of the cycle collapse after 5 month was due to falling off of the active material. So, if filling method of active material is improved, it would be possible for this type of battery to maintain the above charge-discharge pattern for longer period. After the stabilization cycle, we discharged the LAB deep to 0V and opened the circuit for 2 d or 4 month, then we restarted charged/discharge cycle. Figure2 shows the charge-discharge characteristics after either open circuit period, 2 d or 4 months. It is indicated that the LAB can restart charge-discharge cycle even after full discharge followed by 4 months open circuit. After 4 month open circuit, the discharge capacity was not degraded and not so different from that for 2 d. It is confirmed that graphite sheet with 5wt% polypropylene current collector made the LAB so durable to over-discharge and long-time open circuit.