A study for the effect of wheat germ oil in the electrolyte on the electrochemical performance of lead acid batteries

Abstract

Abstract A motorcycle lead-acid battery (LAB) was produced and evaluated using different concentration ratios of wheat germ oil (WGO) as 0, 0.5, 1, 1.5, 2, 2.5, and 3% wt./wt. with respect to 3 M H₂SO₄. The crystal structures of the used leady oxide powder, cured plates, and formed positive & negative electrodes were analyzed via X-ray diffraction (XRD). The leady oxide powder contained tetragonal (α-PbO) and orthorhombic (β-PbO) phases, as well as free Pb with a cubic structure. The crystallite size of this lead oxide was 22.4 nm. The XRD pattern for the cured positive plate revealed the following phases: PbSO 4 , mono lead basic sulfate (BS or LBS = PbO.PbSO 4 ), 3PbO.PbSO 4 .H 2 O (3BS), 4PbO.PbSO 4 (4BS), Pb 3 O 4 , and α-PbO. The crystallite size of the cured positive plate was 38.2 nm. The XRD inspection for the cured negative plate revealed the phases of α-PbO, PbSO 4 , BS, 3BS, and 4BS, with a crystallite size of 25.9 nm. The XRD of the investigated crystal structure of the formed positive electrode showed major phases such as β-PbO 4 and α-PbO 2 , along with minor phases such as PbSO 4 , BS, and 3BS. The crystallite size of the formed positive electrode was 23.5 nm. The XRD data for the formed negative electrode indicated that the main phase is Pb, which has a cubic structure, along with minor phases of PbSO 4 and PbO. The average crystallite size is 25.2 nm. The morphology was examined using a field emission scanning electron microscope (FESEM). The FESEM image of lead oxide shows agglomerates formed by flakes of Pb covered in oxide. The average particle size is about 0.5 µm. The FESEM inspection of cured positive plates revealed a dense and fused structure, with an average particle size of 0.12 µm. The FESEM of cured negative plates exhibits a similar dense structure with an average particle size of 0.1 µm. The morphology of the positive active materials in the formed electrode showed that the matrix of lead basic sulfate crystals had transformed into aggregates of PbO₂ particles while retaining the initial substance’s shape. The average particle size was approximately 0.1 µm. The FESEM inspection for the formed negative electrode displayed crystallized zones composed of a network of lead particles. The particle sizes ranged from 1 to 2 µm. The optimum results of electrochemical impedance spectra (EIS) parameters with R ct were 7.6 and 5.72Ω for WGO concentrations of 1% and 1.5% in the 3 M H₂SO₄ electrolyte, versus 82.4 and 150Ω for pure electrolyte and 3% WGO , respectively. Cyclic voltammetry (CV) for both electrodes of positive and negative alloys in 1.5% WGO with 3 M acid shows an intensive huge oxidation peak around -0.4 V that is attributed to the enhancement of the oxidation of Pb to BSs and PbSO 4 . Linear Sweep Voltammetric (LSV) measurements for anodic polarization of Pb alloys were studied. The addition of WGO increases the anodic current density and the occurrence of an anodic peak at ~ 1.38 V. The presence of WGO with different concentrations in the electrolyte compared to the free electrolyte mainly facilitates the oxidation reaction of lead sulfate crystals with a little shift of oxygen evolution potential (OEP) towards less positive values. The lowest OEP value is obtained with 1.5% WGO . On the other hand, the cathodic current density increases with the addition of WGO to more negative potentials. Also, the hydrogen evolution potential (HEP) has moved to a more negative potential. The highest HEP is obtained with 1.5% WGO . Galvanostatic polarization and specific capacity assessments were conducted. The maximum specific discharge capacities results were observed with wheat germ oil ( WGO ) concentrations of 1% and 1.5% in the 3 M H 2 SO 4 electrolyte, leading to a maximum discharge capacity of approximately 127 mAh/g, compared to 100 mAh/g for the battery without WGO . Furthermore, chemical analysis, XRD, FESEM, TEM, HRTEM and SAED characterization were carried out on cycled discharged positive and negative electrodes with some WGO ratios to confirm the role effect of this additive on the performance of LAB.