Lead phosphate prepared from spent lead compounds as a negative additive for lead-acid batteries

Agglomerated nanorods of lead phosphate have been synthesized from the reaction of lead acetate prepared from waste lead paste and Na₂HPO₄, which is used as an additive for the PbSO₄-negative electrode of a lead-acid cell. It has been found that lead phosphate can be all converted to lead sulfate in 36 wt.% sulfuric acid electrolyte and generate phosphoric acid, and the negative active material containing 1 wt.% lead phosphate discharges a capacity of 111 mAh g⁻¹ at 100 mA g⁻¹ till 1.75 V; it still discharges 78 mAh g⁻¹ after 1200 cycles, which is 10.1% higher than the blank PbSO₄ electrode. It is believed that phosphoric acid could remove the non-conductive oxide on the lead alloy grid; thus, a better conductive network could be built. Also, phosphoric acid is adsorbed on PbSO₄ particles, which can improve the reversibility of the electrode and diminish the shedding of PbSO₄.