Local Cell Reaction Study for Lead Acid Battery

Introduction

 Lead acid battery has been widely used for more than 100 years and still now, it is very important for vehicles. Recently, lead acid battery has been intensively studied for the energy storage because of its low cost and high power. However, despite of its long history of study, some chemical reactions in a cell has not been clarified yet. The cathode material is PbO₂ which has two types of crystal structures, α- PbO₂ and β- PbO₂. It is reported that PbO₂ exists as β- PbO₂ in an acidic region and as α- PbO₂ in an alkaline region^[1]. However, α- PbO₂ also coexists with β- PbO₂ in the cathode of lead acid battery and this reason is not revealed well till now. α- PbO₂ shows the better cycle performance than β- PbO₂ and β- PbO₂ shows the larger discharge capacity than α- PbO₂^[2]. Therefore, it is important to control the ratio of these two phases for the practical use of lead acid battery.

In the open circuit, local cell reaction between electrode material and current collector (CC) will occur^[3]. Till now, the effect of local cell reaction has not been studied enough. In this study, we focused on the local cell reaction between the cathode material (PbO₂) and various CCs for lead acid battery. The effect on the formation of α- PbO₂ was investigated.

Experiment

β- PbO₂ (A Johnson Matthey Company) was mechanically crushed in the mortar for 1d. The cathode was fabricated by mixing powder of the crushed PbO₂ as the active material, acetylene black as a conducting additive and PTFE as a binder at the ratio of 80:15:5 by weight. Lead plate was used as counter electrode. The electrolyte was a 30wt% sulfuric acid. Two kinds of CC, platinum mesh and lead plate were used for the cathode to compare the local cell reaction between cathode material and CC. At first, we discharged for 30min at 9mA/g and charged for 20 min at 180mA/g for 20 cycles to make the cell reaction stable. Then, we discharged the cell deeply to the cutoff voltage of 0V at 9mA/g and opened the circuit. After the rest for 1d, X-ray diffraction of the surface of cathode was measured using RINT-TTR (Rigaku co., CuKα, 200mA, 30kV) for each CC.

Results and Discussion

 Fig.1 shows XRD patterns after the rest time. Upper pattern (a) shows the result when using lead plate as CC, and lower pattern (b) shows the result when using platinum mesh as CC. The peak of α- PbO₂ was observed for pattern (a). However, the peak of α- PbO₂ was not observed for pattern (b). In the open circuit, local cell will be formed between electrode material and CC. When using platinum mesh as CC, PbO₂ works as an anode and CC works as a cathode. On the contrary, when using lead plate as CC, PbO₂ works as a cathode and CC works as an anode. It is suggested that this local cell reaction will affect on the formation of α- PbO₂.

References

[1] Battery Handbook, third edition, (2001) 170

[2] E. Kadlecova et al. , PIERS ONLINE, VOL.2, No.6, (2006) 648-652

[3] T. Yao, T. Iwai and H. Tagashira, PCT/JP2013/ 74165 (2013)