Mechanism of Improvement of Electrochemical Properties of Lead Acid Batteries By Antimony Addition Using Advanced Analysis
Authors: Hayakawa Yoshiki , Ban Ikumi , Hojo Eiji , Ando Kazunari , Sawai Ken , Watanabe Toshiki , Matsunaga Toshiyuki , Uchimoto Yoshiharu 
Published: December 2024

Lead-acid batteries are used in a wide variety of fields, such as automobiles and industrial applications, and the quality and reliability required of these batteries are critical.

Recently, there has been an increase in the demand for lead-acid batteries for idling-stop vehicles and auxiliary equipment for electric and hybrid vehicles to reduce CO2 emissions, and battery development to meet market needs has been progressing 1,2). It is expected that lead-acid batteries will continue to play a role as one of the important rechargeable batteries. In addition, in order to reduce the environmental burden, it is an important issue to reduce the amount of lead used in the lead-acid battery industry as a whole, and there is a need to supply high-quality, high-performance lead-acid batteries with the minimum amount of lead required. Therefore, it is necessary to develop lead-acid batteries that satisfy the requirements even in harsh conditions where deeper charging and discharging is frequently performed than conventional lead-acid batteries.

When the charge/discharge is repeated, a degradation mode called softening proceeds in the positive electrode active material. Repeated charging and discharging cause the lead dioxide particles, which are the positive electrode active material, to crystallize, as well as coarsening and smoothing of the particles, leading to a decrease in the bonding strength between the lead dioxide particles. The decrease in bonding strength breaks the bonds between particles, causing them to shed from the current collector, resulting in a decrease in battery performance. This state of active material in which the bonding strength between particles decreases is called softening, and is known as one of the major degradation modes in the positive electrode. It is known that softening of the active material can be suppressed by the presence of Sb in the active material3), and Sb2O3 is currently used as a positive electrode additive. On the other hand, Sb added to the positive electrode has a negative effect on the electrolyte, since some of the Sb is transferred to the anode during the battery usage process, causing a decrease in hydrogen overvoltage, which in turn increases the electrolyte depletion. Therefore, it is important to construct the positive electrode with as little Sb2O3 addition as possible. However, it is not clear what structure is responsible for the softening and its suppression mechanism by Sb. If this can be elucidated, it is expected to contribute to the development of additives that inhibit softening and reduce the amount of cathode active material.

The purpose of this study is to clarify the mechanism of softening, which is one of the degradation modes in the positive electrode of lead-acid batteries. In this report, in order to clarify the state change of Sb in cathode active materials during charging and discharging, X-ray diffraction measurement and X-ray absorption fine structure (XAFS, SPring-8) measurement of Sb-Kedge using synchrotron radiation were used in combination. X-ray diffraction measurements using synchrotron radiation suggest that antimony is substituted for lead in PbO2 in the charged state. X-ray absorption near edge structure (XANES) shows that Sb in the active material exists in the pentavalent state in both the charged and discharged states. To further clarify the local structural changes of Sb during charging and discharging in detail, Extended X-ray absorption fine structure (EXAFS) measurements were performed at low temperatures of 10 K in the charged and discharged states. EXAFS measurements at low temperatures make it possible to obtain information on the second and third neighborhoods of Sb that is not clear from measurements at room temperature. In the charged state, a second neighboring peak due to Sb-Pb bonding around Sb was clearly observed, consistent with the synchrotron X-ray diffraction results that Sb is substitutionally solid-soluble in the Pb sites of PbO2. On the other hand, the second neighboring peak of Sb disappears in the discharged state, suggesting that Sb, which was substituted solid-solution at the Pb site of PbO2, is dissolved once by the discharge and moves to the active material surface, increasing the bond strength between PbO2 particles.

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Figure 1