Most of us own a device that uses Lithium Ion (Li-Ion) and Lithium Ion Polymer (Li-Pol) batteries.  These devices include Pocket PC's, PDA's, Mobile Phones and Laptop Computers.

The purpose of this Tech Note is to give the user a better understanding of this new energy source and how to get the most out of the battery.

A little bit of History, Courtesy of an article faxed through by Premier Batteries...

Lithium batteries actually started out with G.N. Lewis back in 1912 but never became commercially available until after 1970.  Rechargeable Lithium batteries were made in the 1980's, but failed due to safety reasons.  What follows is a quote from the article in mention:

After much research on rechargeable lithium ion batteries during the 1980's, it was found that cycling causes changes on the lithium cathode.  These transformations, which are a part of normal wear and tear, reduce the thermal stability, causing potential thermal runaway conditions.  When this occurs, the cell temperature quickly approaches the melting point of lithium, resulting in a violent reaction called 'venting with flame'.  A large quantity of rechargeable lithium batteries sent to Japan had to be recalled in 1991 after a battery in a mobile phone released flaming gasses and inflicted burns to a person's face.

Since this research uncovered inherent dangers in the design of a lithium metal electrode battery, focus has shifted to using non metal electrodes and lithium ions.  These batteries have less energy density than the full metal electrode variety, but are inherently a lot safer, and have found their way to being one of the most popular battery chemistries of modern times.

So what is a Lithium Ion battery and how does it work?

These batteries comprise an Anode, a Cathode and an electrolytic substance (non aqueous solution containing salt ions) seperating the two electrodes.  A porus graphite electrode is used as the cathode (-ve battery terminal) and a porus metal oxide electrode is used for the anode (+ve battery terminal).  The anode can be Lithium Cobalt Oxide (LiCoO2) for example.  So where does the Lithium come in?  The Lithium metal (Li) is intercalated (inserted) into the porus graphite cathode and is stored there.  When the battery is placed onto a load, the Lithium atoms gives up an electron to the graphite cathode.  When these atoms have given up their electron, the electrons travel from the Cathode, through the load and back to the anode.  The Lithium ions have become more posatively charged (Li+) and move across the electrolyte solution to the metal oxide anode (+ve). There the Li+ ion takes an electron and intercalates with the anode material.  This completes the chemical reaction during discharge.

The above reaction is highly reversable leading to a very good rechargeable battery.

Now that the batteries have been explained, what are their characteristics?  Below is a good excerpt from an artical entitled "Taking the Mystery out of Battery Charging" from the July 2004 Issue of "What's New In Electronics"

Lithium Ion cells (as opposed to battery packs) are so sensitive to charge and discharge conditions they require special electronics built into the battery as protection.
Lithium Ion cells do not tolerate overcharge hence charging must be terminated when the battery reaches full charge.
Lithium Ion cells do not tolerate over-discharge and cells must not be discharged below 2.5 V/cell or permanent damage may occur.
Lithium Ion cells are charged at 4.1 or 4.2 V/cell with a maximum current of C/2.

Batteries should be charged after use as self discharge can discharge the cells below 2.5 V and cause permanent damage.  Lithium Ion batteries do not suffer memory effect and like Sealed Lead Acid (SLA) batteries give longer life from shallow discharges.


From this we see that Li-Ion batteries don't suffer from the same memory effect as do NiCd batteries and they have a much higher energy density.  They do suffer from over charge (not Li-Ion battery packs), over-discharge, and self-discharge.

Li-ion batteries typically discharge at the rate of 10% per month, if not recharged.

Along with some Internet research, I also contacted an Engineer from Premier Batteries in Sydney, and found out a few interesting points...

Li-Ion batteries have a working life of approximately 3 years.  This starts from the day of manufacture.  When buying a replacement Li-Ion battery, do not purchase second hand, and if buying new, find out the date of manufacture.  Unfortunately this information is not printed on the battery.  It would be no good buying a new battery that has been sitting on the stock shelf for 12 months!

With reference to more material from Premier Batteries, the Ah rating of a cobalt based lithium battery can easily be increased by adding in a bit more nickel.  This has the effect of reducing the stability, by allowing the build up of lithium metal and potential for 'venting with flame'.  Cheaper batteries on the market manufactured by newer companies will be produced in this manner.  More established companies will design their batteries with safety in mind.

Lithium Ion batteries should be stored below 15 deg. C.  Battery temperatures of greater than 40 deg C actually lead to reduced capacity.  Keep in mind that the electrolytic substance is highly flammable and can lead to 'venting with flame' if the cell is punctured or crushed etc...

What does all this information mean to everyday users of this technology?

If you own and use a Li-Ion based device, keep it constantly topped up at 100% charged.  When not using your device, leave it connected to it's charger (to prevent self discharge).  The electronics on board the Li-Ion based device will ensure over charging never occcurs, however over-discharge and consequent damage can't be guarranteed.  When you are finished using your device, place it back on charge.  Don't let it discharge down to 30% or less on a daily basis, or your battery capacity will be severely affected.  Just remember, shallow battery use equates to the best battery life possible.  When replacing your battery, ensure you are buying one from the latest batch, and not one that has been gathering dust on the stock shelves!

I hope this clears up some confusion relating to Li-Ion and Li-Pol batteries.