16
During low rate discharge (5-10 microamps/cm
2
), the lithium ions that allow the cell to operate
can migrate through the passivation layer. As the rate of discharge increases (0.1-1.0
milliamp/cm
2
), so does the porosity of the passivation layer, allowing greater ion flow and higher
power output. This change in the structure of the passivation layer is illustrated in the diagram
below.
Under normal conditions, the thin passivation layer does not degrade cell performance. When the
layer grows too thick, however, discharge performance may be affected. The growth of the
passivation layer is influenced greatly by storage conditions. Long storage periods and/or high
storage temperatures will cause the passivation layer to grow thicker. A passivated cell may
exhibit voltage delay, which is the time lag that occurs between the application of a load on the
cell and the voltage response. As the passivation layer thickens, the voltage delay becomes more
severe. Eventually though, the voltage of a passivated cell will rise to a level equivalent to the
load voltage of an unpassivated cell.
Adjusting storage conditions to reduce the likelihood of passivation is the best way to reduce
voltage delay. However, there are several effective methods for dealing with excessive
passivation when storage conditions cannot be controlled. The layer can be kept from growing
too thick by maintaining a light load on the cell during storage. Alternatively, a higher load, placed
on the cell at regular intervals during storage, or just prior to the anticipated start-up of the cell,
can be used to disrupt the passivation layer and restore normal performance. Both of these
methods will have an impact on the useable capacity of the cell. In particular, a low rate discharge
tends to increase the normal self-discharge reaction of the cell and reduce the available capacity.
.
Electrochem utilizes additives in many of its cell chemistries (including CSC, PMX and MWD
cells) to minimize passivation formation and enhance restart performance. Under most
operating conditions, depassivation of an Electrochem cell is unnecessary. However, under
some more severe conditions (such as high temperature storage) it may be beneficial to
depassivate a cell. For the most effective depassivation, Electrochem generally recommends
discharging a cell near the specified maximum continuous discharge rate. The table below shows
the maximum discharge current and recommended depassivation load for several of the most
widely used Electrochem cell models. Note that the load given in the table will yield close to the
rated maximum continuous current for an individual cell. The load should be adjusted
accordingly for multi-cell battery packs. A depassivation load should be applied until the cell
voltage recovers to a normal level (> 3.0 volts). The recovery duration will depend on the severity
of the passivation. Any questions regarding the performance of Electrochem cells should be
directed to an Electrochem Sales or Customer Service representative, or to an authorized
Electrochem dealer.
Cell Type Part Number Maximum Rated
Discharge (mA)
Depassivation Load
(Single Cell) (ohm)
BCX AA 3B0064 100 30
BCX C 3B0070 500 6
BCX D 3B0075 1000 3
BCX DD 3B0076 3000 1
CSC AA 3B0024 150 20
CSC C 3B0030 1000 3
CSC D 3B0035 2000 2
CSC DD 3B0036 4000 1
PMX AA 3B1065 150 20
PMX C 3B3700 500 6
PMX CC 3B3000 500 6
PMX DD 3B2800 2000 2
VHT C 3B4800 250 10
MWD CC 3B3200 1000 3
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Kommentare zu diesen Handbüchern