Battery Chemistry

Since the year 1800 when the first voltaic battery was invented portable battery power has been a fascination by many. In 1991 Sony commercialized the first lithium-ion battery and in 1999 lithium-polymer came out commercially with PDAs.

But what are the differences of the two chemistries and in terms of your PDA battery which one is better? In a nutshell the two chemistry types are similar but one benefit that lithium-polymer offers is that enables slim geometry that allows it to fit in small places like a PDA.

Let's look inside the battery technology a bit more!

Lithium-ion Battery:

    * The lightest of all metals
    * The greatest electrochemical potential
    * The largest energy density for weight.
    * The load characteristics are reasonably good in terms of discharge.
    * The high cell voltage of 3.6 volts allows battery pack designs with only one cell versus three.
    * It is is a low maintenance battery.
    * No memory and no scheduled cycling is required to prolong the battery's life.
    * Lithium-ion cells cause little harm when disposed.
    * It is fragile and requires a protection circuit to maintain safe operation.
    * Cell temperature is monitored to prevent temperature extremes.
    * Ccapacity deterioration is noticeable after one year (whether the battery is in use or not).

Lithium Polymer Battery:

    * The lithium-polymer differentiates itself from the conventional battery in the type of electrolyte used (a plastic-like film that does not conduct electricity but allows ion exchange – electrically charged atoms or groups of atoms).
    * The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.
    * The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry.
    * Cell thickness measures as little as one millimeter (0.039 inches).
    * Can be formed and shaped in any way imagined.
    * Commercial lithium-polymer batteries are hybrid cells that contain gelled electrolyte to enhane conductivity.
    * Gelled electrolyte added to the lithium-ion-polymer replaces the porous separator. The gelled electrolyte is simply added to enhance ion conductivity.
    * Capacity is slightly less than that of the standard lithium-ion battery.
    * Lithium-ion-polymer finds its market niche in wafer-thin geometries, such as PDA batteries.
    * Improved safety – more resistant to overcharge; less chance for electrolyte leakage.

Until next time – Dan Hagopian,
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