Optimization of the Lead-Acid Battery Discharge Capacity using Alternative Electrolytes From Natural Plant Extracts

Abstract

Lead-acid batteries present an innovative strategy to aid the integration and adoption of renewable energy sources. The build-up of inert lead compounds on the negative electrode is the main obstacle to a longer life span for these batteries. The main objective of this study was to optimize the discharge capacity of the flooded lead-acid battery using electrolyte additive from natural plant extracts. The specific objectives were to; develop electrolyte additive from natural plant extracts; evaluate the electrochemical potential of the electrolyte solutions; evaluate and compare the battery discharge capacity of electrolyte with plant derived additive versus conventional electrolyte; and determine optimum additive amount. Extracts from Calyces of Hibiscus Sabdariffa and leaves of Bidens Pilosa were obtained by a decoction procedure using distilled water. The aqueous plant extracts were mixed with conventional dilute battery sulfuric acid in concentrations of 15.86% (w/v), 10% (w/v), 44% (w/v) and 30% (w/v) while one electrolyte solution was maintained with 100 percent dilute battery sulfuric acid. Evaluation of the electrochemical potential of the electrolyte solutions was done using a floating hydrometer to measure the specific gravity of the electrolyte solutions and results varied between a maxima of 1170 kg/m³ to 1220 kg/m³ and the minima varied between 1140 kg/m³ and 1160 kg/m³ within which the highest electrochemical activity was achieved. The evaluation of the discharge capacity was done by comparing discharge cycles, coulombic efficiency, and energy efficiency. The highest recorded discharge duration was 4.63 hours in the 15.86% (w/v) Roselle additive-electrolyte solution, 0.13 hours longer than the conventional electrolyte. The highest coulombic efficiency in 44.14% (w/v) Hibiscus Sabdariffa additive electrolyte solution was 97.3% and 94.6% in 15.86% (w/v) Bidens Pilosa electrolyte compared to 87.3% in conventional electrolyte. In terms of energy efficiency, the highest value in 44.14% (w/v) Hibiscus Sabdariffa additive electrolyte solution was 83.8% and 81.3% for 15.86% (w/v) Bidens Pilosa electrolyte compared to 74.9% in conventional electrolyte. Optimal additive parameters, 44.14%(w/v) Bidens Pilosa, 15.86% (w/v) Bidens Pilosa, 15.86% (w/v) Hibiscus Sabdariffa, were determined by a numerical optimization procedure using the experimental data. The results from this study show that bio-active compounds present in Hibiscus Sabdariffa and Bidens Pilosa aqueous extracts can be used as electrolyte additive to influence the discharge capacity of the lead-acid battery without altering the chemical composition of the battery active materials. In conclusion, the phytochemicals present in the extracts from Bidens Pilosa and Hibiscus Sabdariffa can be used to enhance the discharge capacity of lead-acid battery. It is recommended that plant extracts should be incorporated in lead-acid battery technology as alternative electrolytes to improve the battery discharge capacity whilst minimizing usage of chemical based conventional electrolytes.