Figure 9: (a) Anode, and (b) cathode in fully charged condition
after 130 cycles, (c) anode and (d) cathode in discharged condition
after 130 cycles for cells cycled at -10, 0, 25 and 40°C.
The XRD pattern of anode after 130 cycles in charged condition contained
Pb (cubic) and PbSO4 (anglesite) peaks, like that for
the fresh cells (Figure 9a). Along with Pb and PbSO4,
there were PbO, Pb3O4 peaks for the
cycled cell at different temperatures (Figures 9 a-d). Pb peaks
intensity was higher and sharper in the new cell than the cycled cells,
which confirmed that the PbSO4 was completely converting
into Pb through reduction reaction. However, there was a permanent
deposition of PbSO4 in the cycled cells after 130 cycles
due to surface hardening. The intensity of PbSO4 peaks
was more intense at 40 °C compared to 25 °C and new cell, which could be
attributed to poor reversibility with a higher amount of
PbSO4 at the anode in the charge condition (Figure 9a).
The cathode in charged condition contained PbO2 and
PbSO4 peaks, like that of the fresh cells (Figure 9b).
The cell after 130 cycles also showed Pb, PbO, and
Pb3O4 peaks. The PbO2peaks intensity was higher and sharper in the fresh cell than the cycled
cell after 130 cycles. PbSO4 detected due to permanent
deposits (surface hardening) through charge/discharge cycling, leading
to capacity loss. The PbSO4 peaks was more intense at 40
°C compared to those cycled at 25 °C and fresh cell due to accelerated
kinetics at higher temperature leading to irreversibility. However,
there was not much difference observed in the cells at 0 °C in charged
(Figure 9a) than cell in discharged state (Figure 9c). This could be
because at 0 °C only half of the cell capacity was used, discharge
capacity is 4.1 Ah at 25 °C and 2.15 Ah at 0 °C due to the change in
kinetics at 0 °C temperature. Similarly, at -10 °C the cathode for the
cell after 130 cycles in charged and discharged condition contained
PbO2, Pb3O4 and
PbSO4 peaks (Figure 9b & d). However, at 0 °C, the
anode both in charged and discharged conditions contained Pb (cubic),
PbO and PbSO4 (anglesite) peaks (Figure 9a & c).
The anode in discharged condition for the cell after 130 cycles
contained the Pb (cubic) and PbSO4 (anglesite) peaks, like that of the
fresh cells (Figure 9c). Along with Pb and PbSO4, there
were Pb3O2SO4,
PbSO3, PbO, and Pb3O4peaks in the cell after 130 cycles. The PbO, PbSO4, and
Pb3O4 peaks were identified in Figures
9c & 9d. \soutThe
Pb3O2SO4 peaks were not
detected in XRD, but they do exist in charging condition. The
PbSO4 peaks intensity was higher and sharper in the
fresh cell compared to the cell after 130 cycles, mostly agglomerated
and surface hardened active materials, which confirmed that the Pb was
completely converting into PbSO4 through an oxidation
reaction in the fresh cell.6,17,18,23 Some of the
PbSO4 peaks such as 26.6°, 29.8° and 36° are relatively
higher in the cycled cell compared to the fresh cells. However, the main
peak intensity at 44.4° is more intense in the fresh cell than cycled
cells. This discrepancy observed could be attributed to the
compositional difference on the electrode surface and in the bulk. The
Pb peaks were more intense at 40 °C compared to that at 25 °C and fresh
cell, this is probably due to higher deposition of Pb at anode in the
charged condition.6,23
The cathode in discharged condition contained PbO2 and
PbSO4 peaks for the cycled cells, like that with the
fresh cells (Figure 9d). Moreover, the cell after 130 cycles also showed
Pb3O2SO4,
PbSO3, Pb, PbO, and
Pb3O4 peaks. The PbSO4peaks intensity were higher and sharper in the new cell compared to the
cell after 130 cycles. The PbO2 detected could be due to
the inability of the bulk active material not being able to get reduced
during discharge at elevated temperature, leading to less utilization of
active materials and faster capacity fading/degradation in the cycled
cell. Obviously, the PbO2 peaks was more intense at 40
than compared to 25 °C and the fresh cell due to larger deposition of
PbO2 at the cathode in the charged
condition.13,14 There was not much difference observed
in the Pb peak intensity in charge condition for cathode (Figure 9b) and
cell at discharge condition (Figure 9d) at 0 °C. Similar to anode, this
could be because at 0˚C only half of the cell capacity was used due to
the slower kinetics at this temperature. In summary, the XRD analysis
concludes that the major/minor phases in charged and discharged state
for electrodes are as illustrated in Table 1.
Table 1: Summary of phases present in the electrode from XRD analysis.