A Neutron Powder Diffraction Study of α ‐ and   β ‐ PbO2 in the Positive Electrode Material of Lead‐Acid Batteries

Abstract

A neutron powder diffraction study of α‐normaland β‐PbO2 , both chemically prepared and electrochemically formed in cycled battery plates, was carried out to correlate the electrochemical activity of the lead‐acid battery with the atomic arrangement of the electrode constituents. Our results are consistent with the presence of hydrogen in the structure of β‐PbO2 , but the departure of the occupancy factors from stoichiometric values are not large enough to unambiguously establish whether there are lead or oxygen deficiencies. If the Pb:O ratio corresponds to exact stoichiometry, any hydrogen which is present must be accompanied by a reduction of Pb+4. There is a significant increase in the lattice parameter a of β‐PbO2 in cycled battery electrodes relative to the value found in chemically prepared β‐PbO2 . No change in the c parameter, however, was detected. These dimensional changes are consistent with a configuration for hydrogen similar to that observed in the rutile‐type structure of SnO2 , in which there are OH− ions oriented perpendicular to the c axis. The profile parameters obtained in this analysis show that the crystallites of β‐PbO2 in the positive plate material of a battery cycled three times (Y3) are smaller than those in the chemically prepared compound (∼450Å vs. 800Å), while there are no significant differences between the latter and β‐PbO2 in the positive plate material of a battery cycled 36 times (Y36). The average structure of α‐PbO2 cannot be accurately determined by profile analysis, at the present time. The difficulties encountered in the refinement may be due to extensive defects, nonspherical crystallites of small size, and/or small departures of the structure from orthorhombic symmetry.

Electroanalytical investigations on electrodeposited lead dioxide

“…Other cations may be incorporated in the lattice and influence its stability [13]. However, neutron diffraction studies did not prove evidence for the presence of Pb or O vacancies [14], and the general formula may be also expressed as: (Pb 4+ ) 1 À x/2 (Pb 2+ ) x/2 (O 2À ) 2 À x (OH À ) x or finally (Pb 4+ ) 1 À x/2 (Pb 2+ ) x/2 (O 2À ) 2 One must distinguish the preparation of PbO 2 according to the Planté formation process [15,16], i.e., by cycling a lead electrode in sulphuric acid, and the plating resulting from soluble Pb(II) species present in an electrolyte.…”

Refinement of the structure of orthorhombic PbO (massicot) by Rietveld analysis of neutron powder diffraction data

“…A new refinement of the massicot structure is desirable since recent neutron and X-ray diffraction analyses of the dioxides of lead (Hill, 1982;Jorgensen, Varma, RoteUa, Cook & Yao, 1982;Santoro, D'Antonio & Caulder, 1983;Hill, Jessel & Madsen, 1984) have indicated that small changes in structure and Pb :O stoichiometry may play an important role in determining the electrochemical activity of lead oxides in a battery environment.…”

Rietveld analysis of powder neutron diffraction data displaying anisotropic crystallite size broadening

“…However, it has been reported that (1) can accommodate isotropic broadening by adjustments to U and W (Santoro, D'Antonio & Caulder, 1983), and consequently the above relationship (3) was tested with the assumption that the correction constant, X, would compensate for the increased breadth of a general reflection relative to a hypothetical hkO reflection at the same 20.…”

“…Such broadening results in a departure from a Gaussian shape, and more flexible peak-shape functions have therefore been proposed (Young & Wiles, 1982). With respect to changes in H, although (1) has satisfactorily accommodated broadening effects for some samples (Santoro, D'Antonio & Caulder, 1983), a serious difficulty arises for crystallites with markedly anisotropic dimensions, such as for clay samples (Adams & Hewat, 1981), where crystallite broadening becomes a function of the scattering vector. This effect has been reported even for a ZnO sample (Langford, 1981).…”