Effect of particle size on phase transitions of positive active materials made from novel leady oxide during soaking process and its influence on lead-acid battery capacity

Novel leady oxides with different particle sizes are prepared via pyrolysis of lead citrate in rotary kiln and subsequent ball-milling. The mechanism of how particle size influences the phase transition route of novel leady oxides during soaking process is investigated. PbO with larger particle size (D50 diameter = 22.4 mu m) is converted to 3PbO center dot PbSO4, and 3PbO center dot PbSO4 is then partially transformed to PbO center dot PbSO4 while PbO center dot PbSO4 are gradually converted to PbSO4. PbO with smaller particle size (D50 diameter = 8.3 mu m) is directly converted to PbSO4, and 3PbO center dot PbSO4 is partially transformed to PbO center dot PbSO4. Phase compositions after the soaking process determine the PbO2 content in positives plates because PbO2 is the oxidation product of PbSO4 in the sequent formation process. Particle size of leady oxides determines the initial capacity of testing cells through affecting the soaking process and a linear correlation between the initial capacity and PbO2 content in positive plates is obtained (R-2 = 0.78). Therefore, leady oxides with larger particle size requires higher sulfuric acid density (1.045 g cm(-3)) to achieve an optimized initial capacity (2.17 Ah), while a lower sulfuric density (1.015 g cm(-3)) is recommended for small particle leady oxides to achieve an optimized capacity of 2.58 Ah.