Operando analysis of the positive active mass of lead batteries by neutron diffraction

 

We have analysed, through neutron diffraction experiments with the volume-gauge technique, the operando performance of lead cells composed of industrial positive and negative electrodes, previously tank formed in the manufacturing plant. The cells, 6.7 cm × 11.5 cm in surface, comprised a 3.4 mm thick positive electrode sandwiched between two 2.3 mm thick negative electrodes. The electrolyte was sulphuric acid diluted in water, both deuterated, and the separators were industrial grade absorptive glass mat (AGM). The experiments, carried out using the VULCAN instrument at the Oak Ridge National Laboratory (TN, USA), showed the evolution of α-PbO₂, β-PbO₂ and PbSO₄ phases in the positive active mass during charge/discharge cycling, comparing the behaviour of fresh and cycled cells. No evidence of PbSO₄ phase in fully charged plates or PbO in any state of charge were found above 1% by weight. Significant inhomogeneity of phase distribution and transition rates inside the positive electrode was observed. The experiments allowed estimation of the energy efficiency by comparing the external energy provided to the cell with the energy stored in the PbSO₄ to PbO₂ transformations.