<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html lang="en"><head><title>Charging the Lithium Ion Battery</title></head>
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<p align="center"><font color="#003366" size="+2" face="Arial,Helvetica"><br><b><a href="http://www.cadex.com/"><img src="_files/cadex_logo.gif" alt="Cadex Electronics" border="0"></a><br>
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<br><font color="#006699" face="Arial,Helvetica"><b>World Leader in Battery Analyzers and Chargers</b></font></p>
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<tbody><tr><td align="center"><font color="DARKBLUE" size="3"><b>The
following information was reprinted with permission from Cadex
Electronics. For more information on Cadex, please visit their website
at <a href="http://www.cadex.com/">http://www.cadex.com</a></b></font></td></tr></tbody></table>
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<font color="#003366" size="+2" face="Arial,Helvetica"><b>Charging the Lithium Ion Battery</b></font><br>
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</font><p align="justify"><font face="Arial,Helvetica">The Li-ion
charger is a voltage-limiting device similar to that of the SLA
charger. The main differences of the Li-ion charger are higher voltage
per cell (nominal cell voltage of 3.6V vs. 2V on the SLA), tighter
voltage tolerance and the absence of trickle or float charge at full
charge. </font></p><p align="justify"><font face="Arial,Helvetica">Whereas
the SLA has some flexibility in terms of voltage cutoff, the
manufacturers of the Li-ion cells are very strict about the voltage
choice. The voltage threshold of the Li-ion with the <i>graphite electrode</i> is 4.10V whereas the <i>coke electrode</i>
is set to 4.20V with a tolerance on both types of +/- 0.05 volts per
cell. New Li-ion types are in development that will probably require
different voltage limits. Chargers for these batteries will need to be
capable of adapting to the correct charge voltages. </font></p><p align="justify"><font face="Arial,Helvetica">Since
higher voltage thresholds provide higher capacities, it is in the
manufacturer’s best interest to choose the highest voltage threshold
possible without affecting safety. This voltage level, however, is
affected by temperature and the threshold is set low enough on purpose
to tolerate higher temperature charge. Tampering with any Li-ion
charger is not recommended. </font></p><p align="justify"><font face="Arial,Helvetica">On
chargers and battery analyzers that allow adjustment of the voltage
thresholds, the correct setting must be observed when servicing any
Li-ion battery. Most battery manufacturers do not specify which version
Li-ion is used. If the voltage is set incorrectly, a coke version will
yield lower capacity readings and a graphite one will be slightly
overcharged. At a moderate temperature, no damage occurs and the lower
discharge voltage does not harm the graphite version battery. The table
below compares the coke electrode to the graphite electrodes.</font></p>
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<td bgcolor="#cccc99"> </td>
<td bgcolor="#cccc99">Coke</td>
<td bgcolor="#cccc99">Graphite-1</td>
<td bgcolor="#cccc99">Graphite-2</td>
</tr>
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<td bgcolor="#cccc99">Peak charge voltage</td>
<td bgcolor="#ccffcc">4.20V</td>
<td bgcolor="#ccffcc">4.10V</td>
<td bgcolor="#ccffcc">4.20V</td>
</tr>
<tr>
<td bgcolor="#cccc99">End-of-discharge voltage</td>
<td bgcolor="#ccffcc">2.50V</td>
<td bgcolor="#ccffcc">3.00V</td>
<td bgcolor="#ccffcc">2.50V</td>
</tr>
<tr>
<td bgcolor="#cccc99">Recommended Charge Rate</td>
<td bgcolor="#ccffcc">0.2C</td>
<td bgcolor="#ccffcc">0.2C - 0.5C</td>
<td bgcolor="#ccffcc">0.2C - 0.5C</td>
</tr>
<tr>
<td bgcolor="#cccc99">Temperature rise on charge</td>
<td bgcolor="#ccffcc">5°C to 8°C</td>
<td bgcolor="#ccffcc">2°C to 3°C</td>
<td bgcolor="#ccffcc">2°C to 3°C</td>
</tr>
<tr>
<td bgcolor="#cccc99">Typical Manufacturers</td>
<td bgcolor="#ccffcc">Sony, Asahi-Toshiba</td>
<td bgcolor="#ccffcc">Sanyo, Panasonic, Hitachi Maxell, Saft</td>
<td bgcolor="#ccffcc">Asahi-Toshiba, Panasonic, Moli, Sony</td>
</tr>
</tbody></table>
<p><font face="Arial,Helvetica"><i>Performance characteristics of Li-ion cells with coke and graphite electrodes</i><br>
</font></p><p align="justify"><font face="Arial,Helvetica">The charge
time of the Li-ion is about 3 hours and the battery remains cool during
charge. Full charge is attained after the voltage has reached the upper
voltage threshold and the current has dropped and leveled off to a low
plateau. </font></p><p align="justify"><font face="Arial,Helvetica">Increasing
the charge current on a Li-ion charger does not shorten the charge time
by much, especially on the coke type. Although the voltage peak is
reached quicker with high current, the topping charge will take longer.
the figure below<i> </i>shows the charge stages of a Li-ion charger. Observe the similarities with the SLA charger.
</font></p><p>
<font face="Arial,Helvetica"><img src="_files/figure7.gif" alt="Charge Stages of a Li-ion battery" border="1" width="511" height="299"></font></p><p>
<font face="Arial,Helvetica"><i>Charge Stages of a Li-ion Battery</i></font></p><p>
</p><p align="justify"><font face="Arial,Helvetica">A more basic charge
method terminates the charge as soon as the voltage level is reached.
This charger is quicker and simpler than the two-stage charger but can
only charge the battery to a 70% capacity level. </font></p><p align="justify"><font face="Arial,Helvetica">No trickle
charge can be applied because the Li-ion is unable to absorb any
overcharge. Trickle charge could cause plating of the metallic lithium,
a condition that would make the cell unstable. Instead, a brief topping
charge should be applied from time to time to compensate for the small
amount of self-discharge the battery and its protective circuit
consume. </font></p><p align="justify"><font face="Arial,Helvetica">Commercial
Li-ion batteries contain several built-in protection devices.
Typically, a fuse opens if the charge voltage of any cell reaches 4.30V
or the cell temperature approaches 100°C (212°F). A pressure switch in
each cell stops the charge current if a certain pressure threshold is
exceeded; and internal voltage control circuits cut off the battery at
low and high voltage points. </font></p><p align="justify"><font face="Arial,Helvetica">Most
manufactures do not sell the Li-ion cells by themselves but make them
available in a battery pack, complete with protection circuit. This
precautionary procedure is understandable when considering the danger
of explosion and fire if the battery is charged and discharged beyond
its safe limits. </font></p><p align="justify"><font face="Arial,Helvetica">A
potential problem can occur if commercial battery packs reserved for
NiCd and NiMH chemistries are fitted with the Li-ion cells. Such
battery packs may end up on the wrong charger and cause danger if the
pack is not properly protected against charging on a wrong charger.
Manufacturers are asked to make the charge terminals of the Li-ion
types incompatible with their nickel-based cousins. </font></p><p align="justify"><font face="Arial,Helvetica">Non-rechargeable
lithium batteries have found a strong market niche in applications such
as still cameras, watches and small electronic devices. Because of
their long shelf life and high energy density, the Lithium batteries
are also used for military applications and emergency response teams. </font></p><p align="justify"><font face="Arial,Helvetica"><i><b>Warning:</b>
Never try to charge a non-rechargeable lithium battery! Attempting to
charge these batteries can cause explosion and fire which spreads toxic
material that can inflict injury and damage equipment.</i>
</font></p><p align="justify"><font face="Arial,Helvetica"><i><b>Important:</b>
In case of rupture, leaking electrolyte or any other cause of skin or
eye exposure to the electrolyte, immediately flush with water. If eye
exposure, flush with water for 15 minutes and consult physician.</i>
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