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 Lithium-Ion Lithium-Polymer Battery Charger Using MCP73831 AuthorPanagiotisÂ KalogerisAugust 11, 2013

In the article below i would like to share useful info about Lithium batteries where i found looking all over the internet. Below are the links from the sites i have searched for.They really helped me to understand what's inside a Lithium battery, which methods are used to charge properly a cell, chemical reactions that happening during charging or discharging and also what dangers lies in them. Special thanks to all !!!

A Designer’s Guide To Lithium Battery Charging By Steven Keeping
Info About Lithium-Ion Battery On Wikipedia
A Good Explainatory Article On Li-Po Batteries From www.rchelicopterfun.com
A Brief Article From Adafruit Learning System On Li-Ion, Li-Po Batteries

Lithium Batteries Types...

Lithium-Ion batteries ,also written as Li-Ion or Lib are rechargable batteries where this type of batteries are usually used in most modern electric appliances, such as laptops, tablets, cameras, cell phones, Gps, Mp3 players etc...
This type is widely used because it can provide the higher energy density of any other commercial battery technology. (Such as Nickel-cadmium (Ni-Cd) or Nickel–Metal Hydride (Ni-MH) ).
To be more specific this type of bettery is called Regular/Normal and it is suppose to last for over 500 charges
(with proper charging method), stay safe due to the internal protection battery circuit they have,
and provide a C or two of current.

Lithium-Ion battery used in Nokia Cellphones.

Depending on the shape and chemistry of the lithium cell, you can find them under different nominal voltages. Almost all lithium polymer batteries are 3.7V / 4.2V . This means that the maximum voltage of the cell is 4.2v and that the nominal voltage is 3.7V.
The battery voltage starts at 4.2 (max) and quickly drops to 3.7V for the most of the battery life. As you use the battery the voltage drops lower and lower. When it reaches 3.4V the battery is considered as "dead" and around 3.0V a protection circuit disconnects the battery off the circuit.

Lithium-Polymer batteries ,also written as Li-Po or LiPo are rechargable batteries where are mainly designed for radio controlled cars, planes, quad copters, helos etc...
LiPo batteries are usually composed of several identical secondary cells in parallel to increase the discharge current capability, and are often available in series "packs" to increase the total available voltage.

A Li-Po battery.You can distinguish the power supply cables with the balancer connector.

They can provide a lot of power at once, up to 20C and are designed to never
"cut off" so that the battery will be damaged instead of having the plane fall out
of the sky...
Each cell has same voltage as Lithium-Ion but as we said before, because of
they usually parallel the cells you can find different "nomimal" voltages such as
3.7, 7.4, 11.1, 14.8, 18.5, 22.2, 29.6, 37.0, 44.4 .
This type of battery needs extra caution because it hasn't any protection circuit on the battery. and overcharging it will cause potential explosion!!!!!.
Also a balancer connector (connected on a balancing circuit) ensures that all cells are always within 0.01-0.03 volts per cell so overcharging or discharging one or more cells won’t destroy the battery pack, or worse to explode or catch fire.

The mainly diferences between these two types of batteries are how the manufacturer packs the cells (Shapes)
Li-Po batteries might been seen if soft, cylindrical or any other shape in comparison with Li-Ion batteries where you can usually find them in a hard commonness shell. Anoher amazing feature is the amazing discharge rate that Li-Po can provide, and finally the type of electrolyte that it is used. Li-Ion batteries use a flammable solvent based organic liquid as the electrolyte in comparison to Li-Po batteries where they use a dry electrolyte polymer separator sheet that resembles a thin plastic film.

A Little Bit Of Chemistry...

In the 1970s scientists used titanium sulphide as the positive electrode and pure lithium metal as the negative. Titanium sulphide is an intercalation compound. Such compounds are materials with a layered crystalline structure that allow atoms, ions, or molecules of other materials to migrate and then reside between the layers.
During discharge, lithium ions moved from the negative electrode to the positive. Charging forced them to move back the other way. Unfortunately, after many charging cycles they discovered that the lithium electrode formed dendrites, rough “spikes” of the pure metal that were highly reactive and could cause fire or even explosions!!!.
Innovation came by an alternative lithium-based intercalation compound. After many tests scientists found that
Lithium-cobalt-oxide (LiCoO2) was the perfect option, to replace the pure lithium metal.A material which is stable in the air.

All types of rechargeable batteries, whether lead-acid, nickel-metal hydride (NiMH), nickel-cadmium (NiCd), lithium-ion (Li-ion), or other special types such as nickel-hydrogen (NiH2) or lithium-iron phosphate (LiFePO4) operate on the same rule.....
Each type exploits a reversible electrochemical reaction.Charging is achieved by applying a current that stores energy in the cell to be released later by the reverse reaction.
Lithium-based technology was selected mainly for two reasons:
1)Lithium is the most electropositive metal (I.e. it exhibits a high positive charge), lending itself to batteries with higher voltages than other rechargeable types (around 3.6 V compared to 1.2 to 1.5 V for nickel-based batteries)
2)It is the lightest metal (In fact, only two elements, hydrogen and helium, are lighter) allowing it to store more energy per kilogram than other metals (around 3,900 Ahr/kg compared to 260 Ahr/kg for lead).

Lithium ions are used in modern batteries because they are less reactive than the element’s atoms, making the battery much safer.Today’s Li-ion batteries use two intercalation compounds for the positive and negative electrodes.
LiCoO2 forms the positive electrode, while graphite is used for the negative one.

The three participants in the electrochemical reactions in a Lithium-Ion battery are the anode, cathode and electrolyte.
Applying a current to the battery causes the ions to move from the cobalt-oxide lattice into the graphite one. In the process, positive material is oxidized and the negative material is reduced. The move from one electrode to another increases the ion’s potential energy. When the battery is used to power a device, the ions migrate the other way, releasing the energy stored during the original reaction.

 Inside a Li-Ion battery, lithium atoms move from one intercalation compound to another to charge or discharge. Li-ion charge and discharge reactions.

Proper Charging...

A major benefit with Lithium-Ion batteries is that you can perform recharging cycles without the

Lithium batteries must be treated with caution!!!

Lithium is a highly reactive material that can, burst into flames if it comes into contact with water!!!!! Engineers and scientists have worked hard to develop novel compounds that can leverage the advantages of lithium while producing inexpensive, reliable, and safe batteries.
In addition to that it is very important to charge the Lithium-Ion batteries correctly.... Overcharging a lithium cell will be dangerous since it will explode or catch fire!!!!! Where undercharging a lithium cell will significantly reduces the battery capacity. Undercharging the battery by 1.2% of its optimum full-charge voltage, lowers the capacity by a remarkable 9%. Designers aim to charge the cell to within 1% of its optimum full-charge to get the most out of the battery.

The charging procedure for a single Li-Ion cell is accomplished by 3 steps
1)The preconditioning mode ==>PM (Can be said as trickle charge)
2)The constant current mode ==>CC
3)The constant voltage mode ==>CV

The charging procedure for a set of Li-Ion cells in series is accompished by 4 steps
1)The preconditioning mode ==>PM
2)The constant current mode ==>CC
3)The balancing mode ==>BM (not required once a battery is balanced)
4)The constant voltage mode ==>CV

If you follow these steps and supplying the battery with current rated at 1C of the battery capacity
500mah ---> 500ma (max) 200mah ---> 200ma (max) then you will get the most of the optimum life's battery.